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(

I

r

MANUAL

OF

Practical Anatomy

BY

The Late D. J. GUNNINGHAM

M.D. (EDIN. ET DUBL.). D.SC.. LL. D. (ST. AND. ET GLAS.), D.e.L. (0X0N.), F.R.S., LJiTE PROPESSOR 0F ANATOMY IN THE UNIYERSITY OF EDINBURGH

FIFTH EDITION

EDITED BY ARTHUR ROBINSON

PROPESSOR OF ANATOMY IN THE UNIYERSITY OF EDINBURGH

y

VOLUME SEGOND THORAX; HEAD AND NECK

WITH 236 ILLUSTRATIONS

NEW YORK WILLIAM WOOD AND GOMPANY

MDCCCCXII

PREFACE TO FIFTH EDITION

E main object of this preface is to thank those who have kindly assisted me in the produetion of the booL At the le time, it may be pointed out that the reasons for the )ption of the Basle nomenelature were fully stated in vol. i., 1 that the alterations whieh have been made in the plans disseetion in vol. ii. are not less numerous than those made vol. i. The alterations inelude ehanges in the method of seeting the face, the posterior triangle, and the deeper ts of the neek. Two plans of disseetion to display the ddle ear and its surroundings are deseribed. They ean be ried out on opposite sides of the head, and the steps of i seeond method are those followed by the surgeon operat- ; for the relief of mastoid and middle ear disease. The seetion of the thorax has been very largely re-arranged h the object of giving the disseetor an opportunity of dying the relative positions of the organs in the medi- inum whilst they are praetieally undisturbed. The various plans of disseetion deseribed were deeided )n, ter many trials, as those best adapted to give the dent a elear idea of the relative positions of important letures ; and I am greatly indebted to my iirst and seeond istants, Dr. E. B. Jamieson and Mr. T. B. Johnston, and Professor R. B. Thomson of Cape Town, for the trouble y have taken and the help they have given in devising, difying, and testing new plans of work. I am indebted also to Dr. Jamieson for disseetions of the in and heart ; to Mr. Johnston for the disseetions of the otid gland; to Mr. W. W. Carlowfo^"* '^'«seetion of the diastinum ; and .to Messrs. M. B" "^. Rogers,

V

vi PREFACE TO FIFTH EDITION

and F. M. Halley for other disseetions upon whieh they have expended time and skill, and whieh have been used in the preparation of the new illustrations.

I wish also to thank Professor Arthur Thomson for per- mission to use the illustrations of his beautiful disseetions of the eye ; Professor A. M. Paterson for permission to use two diagrams illustrating the eonneetions of some of the eranial nerves ; and Dr. Logan Turner for the loan of the speeimens from whieh the illustrations of the disseetion of the mastoid region and middle ear were made.

All the new illustrations are from drawings made by Mr. J. T. Murray. They are eharaeteristie of his excellent work, and I am indebted to him for the eare and skill he has ex- pended on their produetion.

The new indiees and the glossary are the work of Mr. J. Keogh Murphy, F.R.C.S. I beHeve they will prove to be of great service ; and I desire to thank him not only for the time and trouble he has spent upon them, but also for many useful suggestions whieh he has made during the progress of the work.

ARTHUR ROBINSON.

Edinburgh, July 1912.

eONTENTS

Introdcctory, Thoragig Wall,

THORAGie CaVITY,

Thoracic Joints,

THORAX-

lO

1:2

HEAD AND XECK. Face and Prontal Region of Head.

SlDE OF THE NeCK,

POSTERIOR TRIANGLE,

THE ScALP AND THE SUPERFICIAL STRCCn;RE5 OF THE

Temporal Region, .... The DissEenoN of the Back, . Remoyal of the Brain, .... The Anterior Part of the Negk, Temporal and Ineratemporal Regions, Submaxillary Region, .... Orie Ganglion and Tensor Palati, . The Great Yessels and Neryes of the Neck, The Lateral Part of the Middle Cranial Possa. Dissegtion of the Orbit, Preyertebral Region, . The Joints of the Neck, Mouth and Pharynx, . Garotid Ganal, . Neryus Makillaris, Nasal Gayities, .

"7

142

161 200

222

265

279

292

294 325

■^ ■* -^

330 356 364

385 386

389

VIII

eONTENTS

Spheno - Palatine Ganglion and Internal Makillary

ARTERYj .......

The Larynx, .......

The Tongue, . . . . . ■ .

PAGE

402 406

429

ENGEPHALON— THE BRAIN.

Membranes and Blood Vessels of the Brain, Base of Brain, ..... The Gerebrum, ..... The Mesengephalon, .... Basal Ganglia of the Gerebral Hemispheres, The Parts of the Brain whigh lie in the Posterior Granial Fossa, ......

439

452

459 506 512

520

THE AUDITORY APPARATUS.

EXTERNAL MeATUS, ....

Membrana Tympani,

Tympanig Gayity or Middle Ear,

AUDITORY OsSIGLES, ....

AUDITORY TUBE, .....

Intrapetrous Part of the Facial Nerve and the AeusTie

Nerve, . . ...

Yestibulum, .....

Ganales Semicirculares Ossei, The Cochlea, .....

547 549

550

555 559

562

566 567 567

BULBUS OeULI.
General Strugture of the Eyeball, . . -571
The Sglera, .....			572
The Gornea, ....			573
TuNiCA Vasculosa OeuLi,			574
The Retina, ....			579
The Vitreous Body,			581
Lens Grystallina,			■ 583
Ghambers of the Eyeball,			. 584

DEX,

585

A GLOSSARY

OF THE

INTERNATIONAL (B.N.A.) ANATOMIGAL TERMINOLOGY

GENERAL TERMS. Terms indigating Situation and Direction.

Longitudinalis

Verticalis

Anterior

Posterior

Yentral

Dorsal Granial

Gaudal Superior

Inferior Proximalis

Distalis Sagittalis

Frontalis

Longitudinal

Yertieal

Anterior 'i Posterior / Yentral

Dorsal Granial

Gaudal Superior'

Inferior . Proximal

Distal Sagittal

Prontal

}

Referring to the long axis of the lxxly.

{Referring to the position of the long axis of the body in the ereet posture. r Referring to the front and baek of the ^^ body or the limbs.

{Referring to the anterior and posterior aspeets, respectively, of the body, and to the flexor and extensor aspeets of the limbs, respectively. rRe^erring to position nearer the head J or the tail end of the long axis. 1 Used only in reference to parts of l the head, neek, or body. Used in reference to the head, neek, and body. Equivalent to eranial and eaudal respectively. rUsed only in reference to the limbs. -! Proximal nearer the attaehed end. l Distal nearer the free end. 'Used in reference to planes parallel with the sagittal suture of the skull, i.e, vertical antero-posterior planes.

{Used in reference to planes parallel with the eoronal suture of the skull, ue. transverse vertical planes.

IV

GLOSSARY

Horizontalis

Medianus Medialis

Lateralis

Intermedius

Superiieialis

Profundus

Externus

Internus Ulnaris

Radialis Tibial

Fibular

Horizontal

Median Medial ^

Lateral ,

Intermediate

Superficial 1 Deep /

External

Internal Ulnar \

Radial/ Tibial \

Fibularj

{Used in reference to planes at right angles to vertical planes. /Referring to the median vertical l antero-posterior plane of the body. /'Referring to struetures relatively nearer to or further away from the median plane. Referring to struetures situated be- tween more medial and more lateral struetures.

{Referring to struetures nearer to and further away from the surface. {Referring, with few exceptions, to the walls of cavities and hoUow organs. Noi to be used as synonymous with medial and lateral. {Used in reference to the medial and lateral borders of the forearm, respectively. rUsed in reference to the medial and J lateral borders of the leg, re- [ spectively.

THE BONES.

B.N.A. Terminology. YertebrsB

Fovea eostalis superior

Fovea eostalis inferior

Fovea eostalis transversalis Radix areus vertebrae

Atlas

l?ovea dentis

Epistroplieas Dens

Stemum

Gorpus sterni Proeessus xiphoideus Ineisura jugularis Planum sternale

Ossa Granii.

Os frontale

Spina frontaIis Proeessus zygomaticus Facies eerebralis Facies frontalis

Old Terminology. YertebraB

Ineomplete facet for head of rib,

upper Ineomplete facet for head of rib,

lower Facet for tuberele of the rib Pediele

Atlas

Facet for odontoid proeess

Axis

Odontoid proeess

Sternum

Gladiolus Ensiform proeess Supra-sternal noteh Anterior surface

Bones of Skull.

Prontal

Nasal spine

External angular proeess Internal surface Erontal surface

GLOSSARY

XI

B.N.A. Terminology.

Os parietale

Lineae temporales Suleus transversus Suleus sagittalis

Os oeeipitale

Ganalis hypoglossi Foramen oeeipitale magnum Ganalis eondyloideus Suleus transversus Suleus sagittalis Clivus

Linea nuehse suprema Linea nuehae superior Linea nuehae inferior

Os sphenoidale

erista infratempora1is

Suleus ehiasmatis

Grista sphenoidalis

Spina angularis

Lamina medialis proeessus ptery-

goidei Lamina lateralis proeessus ptery-

goidei Ganalis pterygoideus [Vidii] Fossa hypophyseos Suleus earotieus Gonehae sphenoidales Hamulus pterygoideus Ganalis pharyngeus Tubereulum sellae Fissura orbitalis superior

Os temporale

Ganalis facialis [Fallopii] Hiatus eanalis facialis Vagina proeessus styloidei Ineisura mastoidea Impressio trigemini Eminentia areuata

Suleus sigmoideus Fissura petrotympaniea Fossa mandibularis Semieanalis tubse auditivae

Os ethmoidale

Labyrinthus ethmoidalis Lamina papyraeea Proeessus uneinatus

Old Tkrmi.sdlogy.

Parietal

Temporal ridges Groove for lateral sinus Groove for sup. long. sinus

Oeeipital

Anterior eondyloid foramen Foramen magnum Posterior eondyloid foramen Groove for lateral sinus Groove for sup. long. sinus Median part of up{>er surface ()f

basi oeeipital Highest curved line Superior curved line Inferior cur\'ed line

Sphenoid

Pterygoid ridge Optie groove Ethmoidal erest Spinous proeess Internal pterygoid plate

External pterygoid plate

Vidian eanal Pituitary fossa Cavemous groove Sphenoidal turbinal bones Hamular proeess Pterygo-palatine eanal 01ivary eminenee Sphenoidal fissure

Temporal Bone

Aqueduct of P'alloi^ius

Hiatus P'allopii

Vaginal proeess of tympanie bone

Digastrie fossa

Impression for Gasserian ganglion

Eminenee for sup. semieireular

eanal Eossa sigmoidea Glaserian fissure Glenoid cavity Eustaehian tube

Ethmoid

Lateral mass Os planum Unciform proeess

X]l

GLOSSARY

B.N.A. Terminology.

Os laerimale

Hamulus laerimalis Grista laerimalis posterior

Os nasale

Suleus ethmoidalis

Maxilla

Facies anterior Facies infra-temporalis Sinus maxillaris Proeessus frontalis Proeessus zygomaticus Ganales alveolares Ganalis naso-laerimalis Os incisivum Foramen incisivum

Os palatiham

Pars perpendieularis Grista eonehalis Grista ethmoidalis Pars horizontalis

Os z7gomaticam

Proeessus temporalis Proeessus fronto-sphenoidalis Foramen zygomatico-orbitale Foramen zygomatico-faciale

Mandibala

Spina mentalis Linea obliqua Linea mylohyoidea Ineisura mandibulse Foramen mandibulare Ganalis mandibulae Protuberantia mentalis

Old Terminology.

Laelirymal Bone

Hamular proeess Laehrymal erest

Nasal Bone

Groove for nasal nerve

Saperior Ma^illary Bone

Facial or external surface Zygomatic surface Antrum of Highmore Nasal proeess Malar proeess Posterior dental eanals Laerimal groove Premaxilla Anterior palatine foramen

Palate Bone

Vertical plate Inferior turbinate erest Superior turbinate erest Horizontal plate

Malar Bone

Zygomatic proeess Frontal proeess Tempora-malar eanal Malar foramen

Inferior Masillary Bone

Genial tuberele or spine External oblique line Intemal oblique line Sigmoid noteh Inferior dental foramen Inferior dental eanal Mental proeess

The SkuU as a Whole.

Ossa suturarum

Foveol3e granulares (Paeehioni)

Fossa pterygo-palatina

Ganalis pterygo-palatinus

Foramen laeerum

Ghoanae

Fissura orbitalis superior

Fissura orbitalis inferior

Wormian bones Paeehionian depressions Spheno-maxillary fossa Posterior palatine eanal Foramen laeerum medium Posterior nares Sphenoidal fissure Spheno-maxillary fissure

GLOSSARY

XIII

B.N.A. Tesmin'ology.

Claviciila

Taberositas eoiaeoidea Taberositas eostalis

Seapola

Ineisura seapularis Angulus lateralis Angulus medialis

Hiunenu

Suleus intertubereularis Grista tubereuli majoris Grista tubereuli minoris Facies anterior medialis Facies anterior lateralis Mai^o medialb Margo lateralis Suleus nervi radialis Gapitulum

Epieondylus medialis Epieondylus lateralis

Ulna

Ineisura semilunaris Ineisura radialis Grista interossea Facies dorsalis Facies Yolaris Facies medialis Margo dorsalis Margo Yolaris

Badius

Tuberositas radii Ineisura ulnaris Grista interossea Facies dorsalis Facies volaris Facies lateralis Margo dorsalis Margo Yolaris

Garpns

Os navicalare

Os Innatam

Os trignetmm

Os mnltangnlnm majns

Os mnltangnlnm minns

Os eapitatnm

Os hamatnm

Old Tlkminouigy. Clavicle

Impressioo for eonoid ligament Impression for rhomboid ligament

Seapnla

Supra-seapular noteh Anterior or lateral angle Superior angle

Hnmenu

Bieipital grooYe

Extemal lip

Intemal lip Internal surface £xtemal surface Intemal border - £xtemal border Museulo-spiral groove Gapitellum Intemal eondyle £xtcmal eondyle

Ulna

Greater sigmoid cavity Lesser sigmoid cavity £xternal or interosseous border Posterior surface Anterior surface Internal surface Posterior border Anterior border

Radins

Bieipital tuberosity

Sigmoid cavity

Internal or interosseous border

Posterior surface

Anterior surface

External surface

Posterior border

Anterior border

Garpns Seaphoid Semilnnar Cnneiform Trapezinm Trapezoid Os magnnm nnciform

XIV

GLOSSARY

Lower Extremity.

B.N.A. Terminology.

OS C0X8B

Linea glutsea anterior Linea glutaea posterior Linea terminalis Spina isehiadiea Ineisura isehiadiea major Ineisura isehiadiea minor Tubereulum pubieum Ramus inferior oss. pubis Ramus superior oss. pubis Ramus superior ossis isehii Ramus inferior oss. isehii Peeten ossis pubis Facies symphyseos

Pelvis

Pelvis major

Pelvis minor

Apertura pelvis minoris superior

Apertura pelvis minoris inferior

Femur

Fossa troehanteriea Linea intertroehanteriea Grista intertroehanteriea Gondylus medialis Gondylus lateralis Epieondylus medialis Epieondylus lateralis

Tibia

Gondylus medialis Gondylus lateralis Eminentia intereondyloidea Tuberositas tibige Malleolus medialis

Fibala

MalleoKis lateralis

Old Terminology.

Innominate Bone

Middle curved line Superior curved line Margin of inlet of true pelvis Spine of the isehium Great saero-seiatie noteh Lesser saero-seiatie noteh Spine of pubis Deseending ramus of pubis Aseending ramus of pubis Body of isehium Ramus of isehium Pubie part of ilio-peetineal line Symphysis pubis

Pelvis

False pelvis True pelvis Pelvic inlet Pelvic outlet

Femar

Digital fossa

Spiral line •

Post. intertroehanterie line

Inner eondyle

Outer eondyle

Inner tuberosity

Outer tuberosity

Tibia

Internal tuberosity External tuberosity Spine Tuberele Internal malleolus

Fibala

External malleolus

Bones of the Foot.

Talas Galeaneas

Tuber ealeanei

Proeessus medialistuberis ealeanei Proeessus lateralis tuberis ealeanei .Os caneifonne primam Os caneiforme seeandam Os caneiforme tertiam

Astragalas Os ealeis

Tuberosity of Inner Outer

Inner caneiform Middle caneiform Onter caneiform

GLOSSARY

XV

THE LIGAMENTS. LigamentB of the Spine.

RN.A. Terminology. Old Tf.rminoi.(k;y.

Lig. longitndinale anterios

Lig. longitndinale posterius

Lig. flava

Membrana teetoria

Artieulatio atlanto-epistrophiea

Lig. alaria

Lig. apieis dentis

Anterior eommon ligament Posterior eommon ligament Ligamenta subflava Posterior occipito-axial ligament Joint between the atlas and the axis Odontoid or eheek ligaments Suspensory ligament

The Bibs.

Lig. eapituli eostae radiatum Lig. stemo-eostale interartieulare Lig. stemo-eostalia radiata Lig. costoxiphoidea

Anterior costo-vertebral or stellate

ligament Interartieular ehondro-stemal liga-

ment Anterior and posterior ehondro-

stemal ligament Chondro-xiphoid ligaments

Lig. temporo-mandibulare Lig. spheno-mandibulare Lig. stylo-mandibulare

The Jaw.

External lateral ligament of the jiiw Internal lateral ligament of the jaw Stylo-maxillary ligament

Upper £xtremity.

Lig. costo-claviculare

Labrum glenoidale

Artieulatio radio-ulnaris proximalis

Lig. eollaterale ulnare

Lig. eollaterale radiale

Lig. annulare radii

ehorda obliqua

Artieulatio radio-ulnaris distalis

Diseus artieularis

Reeessus sacciformis

Lig. radio-earpeum volare

Lig. radio-earpeum dorsale

Lig. eollaterale earpi ulnare

VOL. II — b

Rhomboid ligament

Glenoid ligament

Superior radio-ulnar joint

Intemal lateral ligament of elbow-

joint External lateral ligament Orbieular ligament Oblique ligament of ulna Inferior radio-ulnar joint Triangular fibro-cartilage Membrana sacciformis Anterior ligament of the radio-

earpal joint Posterior ligament of the

earpal joint Internal lateral ligament of

wrist joint

radio-

the

XVI

GLOSSARY

B.N.A. Terminology. Lig. eollaterale earpi radiale

Artieulationes interearpse Lig. aeeessoria voIaria

Lig. eapitulorum (oss.

palium) transversa Lig. eollateralia

metaear-

Old Terminology.

External lateral ligament of the

wrist joint Garpal joints Palmar ligaments of the metaearpo-

phalangeal joints Transverse metaearpal ligament

Lateral phalangeal ligaments

The Lower Extremity.

Lig. areuatum

Lig. saero-tuberosum

Proeessus falciformis Lig. saero-spinosum Labrum glenoi<3ale Zona orbieularis Ligamentum iIiofemorale Lig. isehio-eapsulare Lig. pubo-eapsulare Lig. popliteum obIiquum Lig. eollaterale Abulare Lig. eollaterale tibiale Lig. popliteum areuatum Meniseus lateralis Meniseus medialis Pliea synovialis patellaris Pliese alares

Artieulatio tibio-fibularis Lig. eapituli fibulae

Syndesmosis tibio-fibularis

Lig. deltoideum

Lig. talo-fibulare anterius

Lig. talo-fibulare posterius

Lig. calcaneo-fibulare

Lig. talo-ealeaneum laterale

Lig. talo-ealeaneum mediale

Lig. calcaneo-navicuIare plantare

Lig. talo-naviculare

Pars calcaneo-navicularis "1 lig.

-bifur- Pars ealeaneo-euboidea I eatum

Subpubie ligament

Great saero-seiatie ligament

Falciform proeess Small saero-seiatie ligament Gotyloid ligament Zonular band Y-shaped ligament Isehio-eapsular band Pubo-femoral ligament Ligament of Winslow Long external lateral ligament Internal lateral ligament Areuate popliteal ligament External semilunar eartilage Internal semilunar eartilage Lig. mueosum Ligamenta alaria Superior tibio-fibular artieulation Anterior and posterior superior

tibio-fibular ligaments Inferior tibio-fibular artieulation Internal lateral ligament of ankle Anterior fasciculus of external

lateral ligament Posterior fasciculus of external

lateral ligament Middle fasciculus of external lateral

ligament External ealeaneo-astragaloid liga-

ment Internal ealeaneo-astragaloid liga-

ment Inferior calcaneo-navicuIar ligament Astragalo-seaphoid ligament Superior ealeaneo-seaphoid liga-

ment Internal ealeaneo-euboid ligament

GLOSSARY

XVII

THE MUSGLES. Masdes of the Baek.

Snperfici&l.

B.N.A. Terminology. Levator seapulse

OLD Tf.KMINOU)GT.

Levator anguli scapulx

Serratus anterior

Masdes of the dhest,

Serratus magnus

Mnseles of Upper Ertremity.

Bieeps braehii

Laeertus fibrosus Braehialis Trieeps braehii

Caput mediale

Caput laterale Pronator teres

Gaput ulnare Braehio-radialis Supinator

Extensor earpi radialis longus Extensor earpi radialis brevis Extensor indieis proprius Extensor digiti quinti proprius Abduetor pollieis longus Abduetor pollieis brevis Extensor pollieis brevis Extensor pollieis longus Lig. earpi transversum Lig. earpi dorsale

Bieeps

Bieipital fascia Braehialis antieus Trieeps

Inner head

Outer head Pronator radii teres

Goronoid head Supinator longus Supinator brevis Extensor earpi radialis longior Extensor earpi radialis brevior Extensor indieis Extensor minimi digiti Extensor ossis metaearpi pollieis Abduetor pollieis Extensor primi internodii pollieis Extensor seeundi internodii pollieis Anterior annular ligament Posterior annular ligament

Museles of Lower Eztremity.

Tensor fasciae latae

Ganalis adduetorius (Hunteri)

Trigonum femoraIe (fossa Searpae

major) Ganalis femoralis Annulus femoralis M. quadriceps femoris —

Reetus femoris

Vastus lateralis

Vastus intermedius

Vastus medialis

M. artieularis genu Tibialis anterior

Tensor fasciaj femoris Hunter's eanal Searpa's triangle

Grural eanal Grural ring Quadriceps —

Reetus femoris

Vastus externus

Grureus

Vastus internus

Suberureus Tibialis antieus

XVIII

GLOSSARY

B.N.A. Terminology.

Tendo ealeaneus Tibialis posterior Quadratus plantae Lig. transversum eruris Lig. erueiatum eruris Lig. laeiniatum Retinaeulum museulorum

nseorum superius Retinaeulum museulorum

naeorum inferius

pero-

pero-

Old Terminology.

Tendo Aehillis

Tibialis postieus

Aeeessorius

Upper anterior annular ligament

Lower anterior annular ligament

Internal annular ligament

External annular ligament

Axial Museles. Museles of tlie Baek.

Serratus posterior superior Serratus posterior inierior	Serratus postieus superior Serratus postieus inferior
Splenius cervicis	Splenius eolli
Saero-spinalis Ilio-eostalis—	Ereetor spinse Ilio-eostalis —
Lumborum	Saero-lumbalis
Dorsi	Aeeessorius
Cervicis	Cervicalis aseendens
Longissimus — Dorsi	Longissimus — Dorsi
Cervicis	Transversalis cervicis
Capitis Spinalis — Dorsi	Traehelo-mastoid Spinalis— Dorsi
Cervicis	Colli
Capitis Semispinalis — Dorsi	Capitis Semispinalis — Dorsi
Cervicis	Colli
Capitis Multifidus	Complexus Multifidus spinpe

Museles of Head and Neek.

Epieranius Galea aponeurotiea Proeerus

Pars transversa (nasalis) Pars alaris (nasalis) Aurieularis anterior Aurieularis posterior Aurieularis superior Orbieularis oeuli Pars laerimalis

Occipito-frontalis Epieranial aponeurosis Pyramidalis nasi Oompressor naris Dilatores naris Attrahens aurem Retrahens aurem AttoUens aurem Orbieularis palpebrarum Tensor tarsi

GLOSSARY

XIX

B.N.A. Terminology.

Triangularis

Quadratus labii superioris —

Gaput zygomaticum

Gaput infraorbitale

Gaput angulare Zygomaticus Ganinus

Quadratus labii inferioris Mentalis Platysma Stemo-thyreoid Thyreo-hyoid

Old Tekminology. I>epressor anguli oris

Zygomaticus minor

Levator labii su()erioris

Levator labii su()crioris alxt)uc nasi

Zygomaticus major

Levator anguli oris

Depressor labii inferioris

Levator menti

Plat}'sma myoides

Stemo-thyroid

Thyrohyoid

Moseles and Fascia of the Orbit.

Fascia bulbi Gapsule of Tenon

Septum orbitale Palpebral ligaments

Reetus lateralis Reetus medialis

Reetus externus Reetus internus

Museles of the Tongue.

Genio-glossus Genio-hyo-glossus

Longitudinalis superior Superior lingualis

Longitudinalis inferior Inferior lingualis

Transversus linguse Transverse fibres

Verticalis linguoe Yertieal fibres

Pharyngo-palatinus M. uyulse

Levator veli palatini Tensor veli palatini Glosso-palatinus

Museles of the PhaiTni.

Palato-pharyngeus Azygos uvul?e Levator palati Tensor palati Palato-glossus

Deep Lateral Museles of Neek.

Sealenus anterior Sealenus antieus

Sealenus posterior Sealenus postieus

Longus eapitis Reetus eapitis antieus major

Reetus eapitis anterior Reetus eapitis antieus minor

Museles of Thorax.

Transversus thoraeis Diaphragma pars lumbalis

Crus mediale

Crus intermedium

Crus laterale Areus lumbo

(Halleri) Areus lumbo

(Halleri)

eostalis medialis

Triangularis sterni Diaphragm, lumbar part —

Crura and origins from areuate ligaments

Ligamentum areuatum internum

eostalis lateralis Ligamentum areuatum externum

XX

GLOSSARY

Museles of the Abdomen.

B.N.A. Terminology.

Ligamentum inguinale (Pouparti) Ligamentum laeunare (Gimbernati) Eibrae intererurales Ligamentum inguinale reflexum

(Gollesi) Annulus inguinalis subeutaneus

Crus superius

Crus inferius Falx aponeurotiea inguinalis M. transversus abdominis Linea semieireularis (Douglasi) Annulus inguinalis abdominalis

Old Terminology.

Poupart's ligament Gimbernat's ligament Intereolumnar fibres Triangular fascia

External abdominal ring

Internal pillar

External pillar Conjoined tendon Transversalis musele Fold of Douglas Internal abdominal ring

Perineuin and Pelvis.

Transversus perinei superficialis M. sphineter urethrae membranaeeae Diaphragma urogenitale

Fascia diaphragmatis urogenitalis

superior Fascia diaphragmatis urogenitalis

inferior Areus tendineus fasciae pelvis Ligamenta puboprostatiea

Fascia diapbragmatis pelvis superior Fascia diaphragmatis pelvis inferior

Transversus perinei

Gompressor urethrge

Deep transverse musele and sphine-

ter urethrse Deep layer of triangular ligament

Superficial layer of the triangular

Ugament White line of pelvis Anterior and lateral true ligaments

of bladder Visceral layer of pelvic fascia Anal fascia

THE NERYOUS SYSTEM.

Spinal Gord.

Fasciculus anterior proprius (FIech-

sig) Fasciculus lateralis proprius Nueleus dorsalis Pars thoraealis Suleus intermedius posterior Golumnse anteriores, ete. Fasciculus eerebro-spinalis anterior Fasciculus eerebro-spinalis lateralis

(pyramidalis) P'aseieulus eerebello-spinalis Fasciculus antero - lateralis super-

ficialis

Anterior ground or basis bundle

Lateral ground bundle eiarke's eolumn Dorsal part of spinal eord Paramedian furrow Anterior grey eolumn Direet pyramidal traet Grossed pyramidal traet

Direet eerebellar traet Gowers' traet

GLOSSARY

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XXII

GLOSSARY

Brain.

B.N.A. Terminology.

Rliombeneeplialon

Eminentia medialis

Ala einerea

Ala aeustiea

Nueleus nervi abdueentis

Nuelei n. aeustiei

Fasciculus longitudinalis medialis

Gorpus trapezoideum

Ineisura eerebelli anterior

Ineisura eerebelli posterior

Suleus horizontalis eerebelli

Lobulus eentralis

Folium vermis

Tuber vermis

Lobulus quadrangularis

Braehium conjunctivum eerebelli

Lobulus semilunaris superior

Lobulus semilunaris inferior

Gerebram

Peduneulus eerebri GoUieulus superior Gollieulus inferior Aqueductus eerebri

Foramen interventriculare

Hypothalamus

Suleus hypothalamieus

Massa intermedia

Fasciculus thalamo-mammillaris

Pars opereularis

Thalamus

Pallium

Gyri transitivi

Fissura eerebri lateralis

Gyrus temporalis superior

Gyrus temporalis medius

Gyrus temporalis inferior

Suleus eentralis (Rolandi)

Suleus temporalis superior

Suleus temporalis medius

Suleus eireularis

Suleus temporalis inferior

Gyrus fusiformis

Suleus interparietalis

Suleus eorporis eallosi

Suleus einguli

Fissura hippoeampi

Gvrus einguli

Old Terminology.

Eminentia teres

Trigonum vagi

Trigonum aeustieum

Nueleus of 6th nerve

Auditory nueleus

Posterior longitudinal bundle

Gorpus trapezoides

Semilunar noteh (of eerebellum)

Marsupial noteh

Great horizontal fissure

Lobus eentralis

Folium eaeuminis

Tuber valvul3e

Quadrate lobule

Superior eerebellar pedunele

Postero-superior lobule

Postero-inferior lobule

Grus eerebri

Anterior eorpus quadrigeminum Posterior eorpus quadrigeminum Iter e tertio ad quartum ventri-

eulum, or aqued. of Sylvius Eoramen of Monro Subthalmie region Suleus of Monro Middle eommissure Bundle of Vicq d'Azyr Pars basilaris Optie thalamus Cortex eerebri Anneetant gyri PMssure of Sylvius First temporal gyrus Seeond temporal gyrus Third temporal gyrus Eissure of Rolando Parallel suleus Seeond temporal suleus Limiting suleus of Reil Oeeipito-temporal suleus Oeeipito-temporal convolution Intraparietal suleus Gallosal suleus Galloso-marginal fissure Dentate fissure Gallosal convolution

GLOSSARY

XXIII

B.N.A. Terminology.

Stria temiinalis

Trigonum eollaterale

Hippoeampus

Digitationes hippoeampi

Fascia dentata hippoeampi

edumna fomicis

Septum pellueidum

Inferior eornu

Gommissura hippoeampi

Nueleus Ientiformis

Pars frontalis eapsulae intemie

Pars oeeipitalis eapsulae intemae

Radiatio oeeipito-thalamiea

Radiatio eorporis eallosi

Pars frontaIis

Pars oeeipitalis

Old Termingldgy.

Taenia semieireularis

Trigonum ventriculi

Hippoeampus major

Pes hippoeampi

Gyms dentatus

Anterior pillar of fornix

Septum lueidum

Deseending horn of lateral ventricle

Lyra

Lentieular nueleus

Anterior limb (of internal eapsule)

Posteriorlimb(ofinternaIcapsule)

Optie radiation

Radiation of eorpus eallusum

Forceps minor

Forceps major

Membranes of Brain.

Gisterna eerebello-medullaris eisterna interpeduneularis Granulationes araehnoideales Tela ehorioidea ventriculi tertii Tela ehorioidea ventriculi quarti

eisterna magna Gisterna 1)asalis Paeehionian bodies Velum interpositum Tela ehoroidea inferior

Gerebral Nerves.

N. oeulomotorius N. troehlearis N. trigeminus

Ganglion semilunare (Gasseri)

N. naso-eiliaris

N. maxillaris

N. meningeus (medius)

N. zygomaticus

Rami alveolares superiores pos- teriores

Rami alveolares superiores medii

Rami aWeolares superiores an- teriores

Ganglion spheno-palatinum

N. palatinus medius

N. mandibularis

Nervus spinosus

N. alveolaris inferior N. abdueens N. facialis N. intermedius N. aeustieus

Third nerve

Fourth nerve

Fifth nerve

Gasserian ganglion Nasal nerve

Superior maxillary nerve Reeurrent meningeal nerve Temporo-malar nerve Posterior superior dental

Middle superior dental Anterior superior dental

Meekel's ganglion External palatine nerve Inferior maxillary nerve Reeurrent nerve Inferior dental

Sixth nerve

Seventh nerve

Pars intermedia of Wrisberg

Eighth or auditory nerve

XXIV

GLOSSARY

B.N.A. Terminology.

Ganglion superius N. reeurrens Ganglion jugulare Ganglion nodosum Plexus oesophageus anterior 1 Plexus oesophageus posterior J Nervus aeeessorius Ramus internus

Ramus externus

Old Terminology.

Jugular ganglion of 9th nerve Reeurrent laryngeal nerve Ganglion of root "^ ^ Ganglion of trunk j ^^ ^

Plexus gulse

Spinal aeeessory

Aeeessory portion of spinal

aeeessory nerve Spinal portion

Spinal Nerves.

Rami posteriores

Rami anteriores

N. eutaneus eoUi

Nn. supraclaviculares anteriores

Nn. supraclaviculares medii

Nn. supraclaviculares posteriores

N. dorsalis seapulse

Nn. intereosto-braehiales

N. thoraealis longus

N. thoraeo-dorsalis

N. eutaneus braehii medialis

N. eutaneus braehii lateralis

Fasciculus lateralis Fasciculus medialis N. eutaneus antibraehii lateralis

N. eutaneus antibraehii medialis

Ramus volaris

Ramus ulnaris N. eutaneus antibraehii dorsalis

N. axillaris

N. interosseus volaris

Ramus palmaris N. mediani

Nn. digitales volares proprii

Ramus dorsalis manus

Ramus eutaneus palmaris

N. radialis

N. eutaneus braehii posterior

N. eutaneus antibraehii dorsalis

Posterior primary divisions Anterior primary divisions Superficial cervical nerve Suprasternal nerves Supraclavicular nerves Supra-aeromial nerves Nerve to the rhomboids Intereosto-humeral nerve Nerve of Bell Long subseapular nerve Lesser internal eutaneous nerve Gutaneous braneh of circumflex

nerve Outer eord (of plexus) Inner eord Gutaneous braneh of museulo-euta-

neous nerve Internal eutaneous nerve Anterior braneh Posterior braneh External eutaneous braneh of mus-

eulo-spiral Circumflex nerve Anterior interosseous Palmar eutaneous braneh of the

median nerve GoUateral palmar digital branehes

of median nerve Dorsal eutaneous braneh of ulnar

nerve Palmar eutaneous braneh of ulnar

nerve Museulo-spiral nerve

Internal eutaneous braneh of

museulo-spiral nerve External eutaneous branehes of museulo-spiral nerve

GLOSSARY

XXV

B.N.A. Tekminology.

Ramus superHeialis N. interosseus dorsalis

Nn. digitales dorsales

N. ilio-hypogastrieus

Ramus eutaneus lateralis

Ramus eutaneus anterior

N. genito-femoralis

N. lumbo-inguinalis

N. spermatieus extemus

N. eutaneus femoris lateralis N. femoralis N. saphenus

Ramus infrapatellaris

N. isehiadieus

N. peronseus eommunis

Ramus anaslomotieus pero- nseus

N. peronseus superHeialis

N. peromeus profundus N. tibialis

N. eutaneus surse medialis N. suralis

N. plantaris medialis N. plantaris lateralis N. pudendus

Old Terminology.

Radial nerve

Posterior interosseous nerve Dorsal digital nerves IIio-hyp<^astric nerve

Iliae braneh of ilio-hypogastrie

ncrvc Hypogastrie braneh of ilio- hypogastrie nerve Genito-erural nervc

Grural braneh of genito-erural

nerve Genital braneh of genito-erural nerve External eutaneous nerve Anterior erural nerve Long saphenous nerve

Patellar braneh of long saph- enous nerve Great seiatie nerve External popliteal nerve

Nervus eommunieans tibularis

Museulo-eutaneous nerve

Anterior tibial nerve Internal popliteal nerve

Nervus eommunieans tibialis Short saphenous nerve Internal plantar External plantar Pudie nerve

THE HEART AND BLOOD-VESSELS.

Heart.

Atrium

Aurieula eordis Ineisura eordis Trabeeulse earneae Tubereulum intervenosum Suleus longitudinalis anterior Suleus eoronarius Limbus foss3e ovalis Valvula venae cavge Valvula sinus eoronarii

Auriele

Aurieular appendix

Noteh at apex of heart

Golumnae earneae

Intervenous tuberele of Lower

Anterior interventricular groove

Auriculo-ventricular groove

Annulus ovalis

Eustaehian valve

Valve of Thebesius

XXVI

GLOSSARY

Arteries.

B.N.A. Terminology.

Sinus aortse

A. profiinda linguse

A. maxillaris externa

A. alveolaris inferior

Ramus meningeus aeeessorius

A. bueeinatoria

A. alveolaris superior posterior

Aa. alveolares superiores anteriores

Ramus earotieo-tympanieus

A. ehorioidea

A. auditiva interna

Rami ad pontem

A. perieardiaeo-phreniea Rami intereostales Truneus thyreo-cervicalis A. transversa seapulae A. intereostalis suprema A. transversa eolli A. thoraealis suprema A. thoraeo-aeromialis A. thoraealis lateralis A. circumflexa seapulae A. profunda braehii A. eollateralis radialis

A. eollateralis ulnaris superior A. eollateralis ulnaris inferior Ramus earpeus volaris Ramus earpeus dorsalis Aa. metaearpege dorsales A. volaris indieis radialis Areus volaris superficialis Areus volaris profundus A. interossea dorsalis A. interossea reeurrens

A. interossea volaris

Ramus earpeus dorsalis

Ramus earpeus volaris

Aa. digitales volares eommunes

Aa. digitales volares propriae

Arteriae intestinales

A. suprarenalis media A. hypogastriea A. umbiliealis A. pudenda interna A. epigastrioa inferior

Old Terminology. Sinuses of Valsalva Ranine artery Facial artery Inferior dental artery Small meningeal artery Bueeal artery Posterior dental artery Anterior superior dental arteries Tympanie braneh of int. earotid Anterior ehoroidal artery Auditory artery Transverse arteries (branehes of

Basilar artery) Arteria eomes nervi phreniei Anterior intereostal arteries Thyroid axis Supraseapular artery Superior intereostal Transversalis eolli Superior thoraeie artery Aeromio-thoraeie artery Long thoraeie artery Dorsalis seapulge Superior profunda Anterior braneh of superior pro-

funda Inferior profunda Anastomotiea magna Anterior radial earpal Posterior radial earpal Dorsal interosseous arteries Radialis indieis Superficial palmar areh Deep palmar areh Posterior interosseous artery Posterior interosseous reeurrent

artery Anterior interosseous artery Posterior ulnar earpal Anterior ulnar earpal Palmar digital arteries GoUateral digital arteries Intestinal branehes of sup. mesen-

terie Middle eapsular artery Internal iliae artery Obliterated hypogastrie Internal pudie artery Deep epigastrie artery

GLOSSARY

XXVII

B.N.A. Terminology.

A. spermatiea externa Aa. pudendae estemse

A. circuinflexa femoris medialis

A. circumflexa femoris lateralis

A. genu suprema

A. genu superior lateralis

A. genu supenor medialis

A. genu media

A. genu inferior lateralis

A. genu inferior medialis

A. malleolaris anterior lateralis

A. malleolaris anterior medialis

A, peronsea

Ramus perforans

A. malleolaris posterior lateralis A. malleolaris posterior medialis Rami ealeanei laterales Rami ealeanei mediales A. plantaris medialis A. plantaris lateralis Aa. metatarsese plantares Aa. digitales plantares

Old Terminology.

Cremasteric artery

Superficial and deep extemal pudie arteries

Intemal circumflex artery

External drcumflex artery

Anastomotiea magna

Superior extemal artieular artery

Superior intemal artieular artery

Azygos artieular artery

Inferior external artieular artery

Inferior intemal artieular artery

Extemal malleolar artery

Intemal malleolar artery

Peroneal artery

Anterior peroneal artery Posterior peroneal artery

Intemal malleolar artery

Extemal ealeanean artery

Intemal ealeanean artery

Intemal plantar artery

External plantar artery

Digital branehes

Gollateral digital branehes

Yeins.

V. eordis magna

V. obliqua atrii sinistri

Lig. venae cavge sinistrae

Vv. eordis minimae

Sinus transversus

Confluens sinuum

Plexus basilaris

Sinus sagittalis superior

Sinus sagittalis inferior

Spheno-parietal sinus

V. eerebri internae

V. eerebri magna

V. terminalis

V. basalis

V. transversa seapulae

V. thoraeo-aeromialis

Vv. transversae eolli

V. thoraealis lateralis

V. azygos

V. hemiazygos

V. hemiazygos aeeessoria

V. hypogastriea

V. epigastriea inferior

V. saphena magna

V. saphena parva

Great eardiae vein Oblique vein of Marshall Vestigial fold of Marshall Veins of Thebesius Lateral sinus Toreular Herophili Basilar sinus

Superior longitudinal sinus Inferior longitudinal sinus Sinus alae parv8e Veins of Galen Vena magna Galeni Vein of the eorpus striatum Basilar vein Supraseapular vein Aeromio-thoraeie vein Transversalis eolli veins Long thoraeie vein Vena azygos major Vena azygos minor inferior Vena azygos minor superior Internal iliae vein Deep epigastrie vein Internal saphenous vein External saphenous vein

XXVIII

GLOSSARY

Lymphaties.

B.N.A. Terminology. Old Terminology.

Gisterna ehyli Reeeptaeulum ehyli

THE YISGERA.

Digestive Apparatus.

Areus glosso-palatinus

Areus pharyngo-palatinus

GI. lingualis anterior

Duetus submaxillaris

Gl. parotis aeeessoria

Duetus parotideus (Stenonis)

Dentes praemolares

Dens serotinus

Papillge yallatae

Reeessus pharyngeus

Tela submueosa

Plieae eireulares

Gl. intestinales

Valvula eoli

Golumnae reetales

Plieae transversales reeti

Valvula spiralis

Noduli lymphatiei aggregati

(Peyeri) Intestinum jejunum Intestinum ileum Noduli lymphatiei lienales

(Malpighii)

Anterior pillar of fauces Posterior pillar of fauces Gland of Nuhn Wharton's duet Soeia parotidis Stenson's duet Bieuspid teeth Wisdom tooth Circumvallate papillae Lateral reeess of pharynx Pharyngeal aponeurosis Valvul£e conniventes Grypts of Lieberkuhn Ileo-oeeal valve Golumns of Morgagni Valves of Houston Valves of Heister Peyer's patehes

Jejunum

Ileum

Malpighian eorpuseles

Bespiratory

Laryiix

Prominentia laryngea

Ineisura thyreoidea superior

M. ary-epiglottieus

M. Yoealis

M. thyreo-epiglottieus

Appendix ventriculi laryngis

Pliea Yoealis

Pliea ventricularis

Ligamentum ventriculare

Ligamentum vocale

Glottis

Rima vestibuli

Gartilago thyreoidea

Apparatus.

Adam's apple

Superior thyroid noteh

Aryteno-epiglottidean musele

Internal thyro-arytenoid musele

Thyro-epiglottidean musele

Laryngeal sae

True vocal eord

False vocal eord

Superior thyro-arytenoid ligament

Inferior thyro-arytenoid ligament

Glottis vera

Glottis spuria

Thyroid eartilage

GLOSSARY

XXIX

B.N.A. Terminology.

Membrana hyo-thyreoidea Gartilago eomieulata (Santorini) Tubereulum epiglottieum Pars intermembranaeea (rimae

glottidis) Pars intereartilaginea (rimse

glottidis) Gonus elastieus (membranae

elastieae larynges) Glandula thyreoidea Glomus earotieum

Nose

Goneha nasalis suprema (Santorini) Goneha nasalis superior Goneha nasalis media Goneha nasalis inferior

Old Termin<>l<k;y Thyro-hyoid membrane Gartilage of Santorini Gushion of epiglottis Glottis Yoealis

Glottis respiratoria

Grieo-thyroid membrane

Thyroid gland Interearotid gland or body

Highest turbinate bone Superior turbinate bone Middle turbinate bone Inferior turbinate bone

Urogenital Apparatns.

Gorpuseula renis

Paradidymis

Appendix testis

Duetus deferens

Gl. urethrales

Glandula bulbo-urethralis (Gowperi)

FoIlicuIi oophori vesicuIosi

Gumulus oophorus

Tuba uterina

Epoophoron

Appendiees vesiculosi

Duetus epoophori longitudinalis

Orificium internum uteri

Orificium externum

Proeessus vaginalis

Glandula magna vestibuli

Malpighian eorpuseles

Organ of Giraldes

Hydatid of Morgagni (male)

Vas deferens

Glands of Littr^

Cowper*s gland

GraaHan foIIicIes

Diseus proligerus

FalIopian tube

Parovarium

Hydatids of Morgagni (female)

Gartner's duet

Intemal os (of uterus)

External os

Ganal of Nuek

Bartholin's gland

Peritoneuin.

Bursa omentalis Eoramen epiploieum Lig. phrenieo-eolieum Excavatio reeto-uterina (cavum

Douglasi) Lig. gastro-lienale

Lesser peritoneal sae Eoramen of Winslow Costo-colic ligament Poueh of Douglas

Gastro-splenie omentum

SENSE ORGANS. Tlie Eye.

Selera Selerotie eoat

Lamina elastiea anterior (Bowmani) Bowman's membrane

XXX

GLOSSARY

B.N.A. Terminology.

Lamina elastiea posterior (Des-

eemeti) Spatia anguli iridis Angulus iridis Zonula eiliaris Septum orbitale Fascia bulbi

Gommissura palpebrarum lateralis Gommissura palpebrarum medialis Tarsus superior Tarsus inferior Lig. palpebrale mediale Raphe palpebralis lateralis Tarsal glaiads

Old Terminology. Descemet*s membrane

Spaees of Fontana Irido-eomeal junction Zonule of Zinn Palpebral ligament Gapsule of Tenon External eanthus Internal eanthus Superior tarsal plate Inferior tarsal plate Internal tarsal ligament Extemal tarsal ligament Meibomian glands

The Ear.

Ganalis semieireularis lateralis Duetus reuniens Duetus eoehlearis Reeessus spherieus Reeessus elliptieus Paries jugularis Paries labyrinthiea

Eenestra vestibuli

Eenestra eoehleae Paries mastoidea

Antrum tympanieum Paries earotiea Proeessus lateralis Proeessus anterior

External semieireular eanal Ganalis reuniens Membranous eoehlea Fovea hemispheriea Fovea hemi-elliptiea Floor of tympanum Inner wall

Eenestra ovalis

Eenestra rotunda Posterior wall

Mastoid antrum Anterior wall

Proeessus brevis (of malleus) Proeessus graeilis

MANUAL

OF

PRACTICAL ANATOMY.

THORAK.

nPHE disseetion of the thorax is eommeneed on the thirteenth -^ day^ after the subject has been plaeed in the disseeting- room. By that time the upper limbs have been detaehed from the trunk.

In form, the thorax resembles a truneated eone. Anteriorly and posteriorly it is Aattened ; laterally it is full and rounded. During Hfe the movements of the thoraeie walls produee alterations in the eapaeity of the ehest cavity, and play an essential part in the function of respiration ; these movements the student should study upon himself and his friends.

The thoraeie cavity is bounded anteriorly by the sternum and eostal eartilages ; it is bounded posteriorly by the twelve thoraeie vertebrae and the intervening fibro-cartilages, together with the portions of the ribs whieh extend laterally from the vertebral eolumn as far as the angles ; the lateral boundaries are formed by the bodies of the ribs, from their angles posteriorly to their anterior extremities anteriorly. These parts eonstitute the framework of the thorax, and ean be studied on the skeleton as well as upon the part before the disseetion is eommeneed.

The anterior wall of the thorax is shorter than the posterior wall and, during expiration, the upper margin of the sternum

^ Saturdays and Sundays are not eounted.

a THORAX

lies opposite the iibro-eartilage between the seeond and third thoraeie vertebra, whilst the lower end of the body of the sternum eorresponds in level with the middle of the body of the ninth thoraeie vertebra. The bodies of the thoraeie vertebrse project anteriorly into the cavity of the thorax, and greatly diminish its antero-posterior diameter in ihe median plane ; but the baekward sweep of the posterior portions of the ribs produees a deep hollow on either side of the yertebral eolumn, for the reeeption of the most massive part of the lung.

The superior aperture, in/e/ of the ihorax, is a narrow opening whieh is bounded by the first thoraeie yertebra, the

ieal Domes of ihe Pleural Saes, and parts in rt

iirst pair of eostal arehes, and the manubrium sterni. The plane of this opening is very oblique ; it slopes from the tirst thoraeie vertebra anteriorly and downwards. Through the inlet of the thorax the apiees of the lungs project upwards into the root of the neek, and, between them, the follow- ing struetures pass through it : — the windpipe, the gullet, the vagi, the phrenie nerves, the left reeurrent nerve, the ganglion- ated sympathetie trunks, the thoraeie duet, and the great arteries and veins whieh earry blood to and from the head and neek and the upper limbs.

The base or inferior end of the thoras is very wide, and is sometimes ealled the outlei. Anteriorly it is bounded by the xiphoid proeess, and posteriorly by the twelfth thoraeie vertebra. Between these points the lower margin of the thorax presents a curved outline. Starting from the sternum, it passes downwards, laterally, and posteriorly, as far as Ihe tip of the eleventh eostal eartilage ; thenee it proeeeds up-

THORAGie WALL 3

wards, posteriorly, and medially to the vertebral eolumn. In the iirst part of its extent it is formed by the eartilages of ihe seventh, eighth, ninth, tenth and eleventh ribs, and in the seeond part by the lower border of the twelfth rib.

The lower margin of the thorax gives attaehment to the diaphragm, a highly vaulted or dome-shaped museulo-tendinous partition, whieh intervenes between the cavity of the thorax above and that of the abdomen below. It forms a convex floor for the thorax, and a concave roof for the abdomen. By its upward projection it greatly diminishes the general vertical depth of the thoraeie cavity.

But the diaphragm does not form an unbroken partition. It presents three large openings, by means of whieh struetures pass to and from the thorax, viz. — (i) for the aorta, thoraeie duet, and vena azygos; (2) for the oesophagus and vagi nerves ; (3) for the inferior vena cava. Besides these there are other smaller apertures whieh will be mentioned later.

THORAGie WALL.

Tkoo days at least should be devoted to the disseetion of the thoraeie wall.

In addition to the osseous and eartilaginous framework, the walls of the ehest are built up partly by museles, and partly by membranes, and in eonneetion with these there are numerous nerves and blood-vessels.

/ External intereostals. ^ I J Internal intereostals.

' Transversi thoraeis.

tSubeostals. Anterior intereostal membranes. Membranes, . . - Posterior intereostal membranes.

Pleural membrane (parietal part).

{Intereostal nerves. Aortie intereostal arteries. buperior intereostal arteries. Internal mammary arteries.

Disseetion, — Portions of eertain of the museles of the upper limb and of the abdominal wall are still attaehed to the thoraeie wall on eaeh side. Antero-posteriorly the disseetor will meet with the peetoralis major, the peetoreUis minor, and the serratus anterior, whilst towards the lower margin oi\ the ehest he will reeognise the reetus abdominis anterior^^. and the obtiquus extemus and latissimus dorsi upon its lateral aspeet. '. rouDded tendon of the subclavius may also be seen taking origin fro' the first eostal areh. These remnants must be removed so as to li bare the eostal arehes and the intereostal museles. In detaehing

11 — \a

4 THORAX

serratus anterior and external oblique be careful not to injure the lateral eutaneotis nerues whieh make their appearanee in the intervals between their digitations. The anterior etUaneous nerues and perforating branehes of the internal mammary artery must also be preserved ; they pieree the origin of the peetoralis major in the intervals between the eostal eartilages, elose to the margin of the sternum.

Intereostal Museles and Membranes. — These museles and membranes oeeupy the eleven intereostal spaees on eaeh side. In eaeh spaee there are two strata of museular fibres — a superficial and a deep. The superficial layer of museular fibres is ealled the extemal intereostal musele, and the deep layer the intenial intereostal musele,

The extemal intereostal musdes are already exposed, and very little eleaning is neeessary to bring out their eonneetions. Note that entering into their eonstitution there is a large admixture of tendinous fibres, and that these, as well as the museular fibres, are direeted obliquely downwards and anteriorly from the lower border of the rib above to the upper border of the rib below. They do not extend farther anteriorly, in the various spaees, than the region of union of the bony with the eartilaginous parts of the eostal arehes. In many eases, espeeially in the upper spaees, they do not reaeh so far. When the museular fibres stop, the tendinous fibres are prolonged onwards to the sternum in the form of a membrane, whieh is ealled the anterior intereostal mem- brane, The external intereostal museles of the two lower spaees are exceptions to this rule. They extend anteriorly to the extremities of the spaees. Posteriorly the museles ex- tend as far as the tubereles of the ribs, but this is a point whieh ean be satisfactorily demonstrated only after the thorax has been opened.

Disseetion. — To bring the intemal intereostal musdes into view it is neeessary to reflect the external intereostal museles, and also the anterior intereostal membranes. Divide them along the lower border of eaeh spaee, and throw them upwards. In effecting this disseetion, eare must be taken of the intereostal vessels, whieh lie between the two museular strata, and of the lateral branehes of the intereostal nerves.

The internal intereostal museles, thus laid bare, will be seen to be similar in their eonstitution to the external museles. The fibres, however, run in the opposite direetion — viz., from above, obliquely downwards and posteriorly. Superiorly, eaeh is attaehed to the inner surface of the upper rib, immediately above the eostal groove ; inferiorly, it is attaehed upon the

THORAGie WALL 5

inner surface of the lower rib, elose to the upper margin. The intemal intereostal museles are prolonged anteriorly to the sternum. Posteriorly they extend to the angles of the ribs. The posterior intereostal membranes extend from the spine to posterior borders of the intemal intereostals where they beeome eontinuous with the fascial layer hetween the external and intemal intereostal museles. They will be seen when the thorax is opened.

If the internal oblique musele of the abdomen has not been removed, the disseetor should note that the anterior Hbres of the lowest two internal intereostal museles beeome eontinuous with the tibres of that musele.

Sternum / / / i

M. transversus thoraeis / / ;

* « I Intemal mammary artery ' /

Anterior intereostal membrane /

Anterior eutaneous nerve ■

Pleura/ Lateral eutaneous nerve

Anterior root. Posterior root •

Internal iiiter- eostal musele

Trunk of thoraeie nerve /')\ /\ ^"^mHSSM^T Anterior braneh of thoraeie

Posterior braneh ()'' /^ ^ I nerve (intereostal)

' / External intereostal musele

Anterior costo-transverse ligament ' . . , ,

Postenor mtereostal membrane

FiG. 2. — Diagram of one of the Upper Intereostal Nerves.

Intereostal Nenres. — The intereostal nerves are altogether out of sight in the present stage of the disseetion. They are hidden by the lower borders of the ribs whieh bound the intereostal spaees superiorly. By gently pulling upon their lateral eutaneous branehes they ean be drawn downwards, and they are then seen to He between the two museular strata as far anteriorly as a point midway between the vertebral eolumn and sternum. There they sink into the substanee of the in- ternal intereostal museles, amidst the fibres of whieh they may be traeed to the anterior extremities of the bony parts of the ribs, where they reaeh the deep surface of inter

6 THORAX

intereostal museles and are earried medially, iirst anterior to the pleura, and then anterior to the transversus thoraeis musele. Lastly, they eross anterior to the internal mammary artery and turn anteriorly, at the side of the sternum, as the anterior eutaneous nerues of the peetoral region. Eaeh nerve, before it reaehes the surface, pierees — (a) the internal inter- eostal musele ; (b) the anterior intereostal membrane ; (c) the origin of the peetoralis major ; and (d) the deep fascia

(Fig. 2).

This deseription holds good for the upper five inter- eostal nerves only. The lower six nerves leave the anterior ends of the intereostal spaees and run into the abdominal wall. As they leave the thoraeie wall the upper four of the six pass posterior to the upturned eostal eartilages, and all six pass between the interdigitating slips of the diaphragm and the transversus abdominis museles.

The intereostal nerves are the anterior branehes of the upper eleven thoraeie nerves. As they traverse the thoraeie wall they give off — {a) the lateral eutaneous branehes, (S) twigs to the intereostal, subeostal, and transversus thoraeis museles. The terminal extremities of the upper five beeome the anterior eutaneous nerves of the thorax. (For the abdominal distribution of the lower six see Vol. I., p. 394.)

The lateral eutaneous branehes arise midway between the vertebral eolumn and the sternum. They pieree the external intereostal museles, and pass between the digitations of the serratus anterior.

The first intereostal nerve does not give a lateral braneh, and it does not beeome eutaneous anteriorly. The lateral eutaneous braneh of the seeond intereostal nerve is the so- ealled intereosto-braehial nerve.

It is not neeessary to make a disseetion of the intereostal nerves in more than two or three of the spaees.

Intereostal Yessels. — The intereostal arteries should be disseeted in spaees in whieh the nerves have not been traeed, and in whieh, therefore, the internal intereostal museles are still entire. It is only in a well-injected subject that a satisfactory view of these vessels ean be obtained. In eaeh intereostal spaee one artery is found passing dorso-ven- trally \ and in eaeh of the upper nine intereostal spaees, two anterior infcrcostal arteries run ventro-dorsally.

THORAGie WALL 7

In the upper two spaees the vessels whieh nin dorso- yentrally are derived from the superiar intenostal division of the costo-cervical braneh of the subclavian artery ; in the lower nine spaees they spring direetly from the aorta, and are ealled the aortie intereostal arieries,

The anterior intereostal arteries of the upper six spaees proeeed direetly from the internal mammary, whilst those of seventh, eighth, and ninth spaees arise from the museulo- phrenie artery.

The intereostal vessels are distributed for the most part between the two museular strata. From the angles of the ribs onwards to a point midway between the vertebral eolumn and stemum, the aortie intereostal arteries lie under shelter of the lower margins of the ribs whieh bound the spaees superiorly, and at a higher level than the eorresponding nerves. Then eaeh divides into two branehes, whieh pass ventrally in relation to the upper and lower margins of the intereostal spaee. They give ofif small branehes whieh aeeompany the lateral eutaneous nerves. The lower two aortie intereostal arteries are earried onwards into the abdominal wall. The branehes of the superior intereostal artery are disposed in a manner similar to the aortie intereostal vessels.

The anterior intereostal arteries are two in number for eaeh spaee, except the last two. At their origins they lie under cover of the internal intereostal museles, and they run later- ally in relation to the upper and lower margins of the ribs bounding the spaees. After a short eourse they pieree the internal intereostal museles, and end by anastomosing with the aortie and superior intereostal arteries.

Dissedion, — ^The disseetor should next proeeed to remove the intereostal museles. This disseetion must be done with great eare, for immediately subjacent to the intemal intereostals and the ribs is the delieate pleural membrane whieh lines the inner surface of the ehest wall. The membrane must not be injured or detaehed from the deep surfaces of the ribs during this stage of the disseetion. As the internal intereostal museles are removed, the anterior perforating branehes of the internal mammary and museulo- phrenie arteries, and the anterior eutaneous nerves must be preserved.

When the museles are removed the internal mammary artery with its two accompan)ning veins will be seen behind the eostal eartilages, about half an ineh from the side of the sternum. Glean these arteries in the iritervals between the eartilages and note the small lymph glands whieh lie beside them. Eaeh internal mammary artery ends by dividing into superior epigastrie and museulo-phrenie terminal branehes in the intenral between the sixth and seventh rib eartilages. Most likely this spaee will be so narrow that a view of the bifurcation eannot be obtained. If this is the ease, pare away the edges of the eartilages over the artery, or,

TT 1 h

THORAX

ore the medial part of the sixth eartilage eompletely. The musele posleiioT to Ihe intema] mammaty artery is the transversus thoraeis (O.T. triangulaiis stemi). Endeayout to define its slips in the inleivals betweeu the eostal carli1:^es.

Tiie disseetor should note. as an importanl praetieal point, that towards the lower margin of the thorax ihe pleural sae is nol prolonged downwards to Ihe lowest limit of the reeess between the diaphragni and the eostal aiehes. Indeed, in Ihe axillary tine, it will be Coani3 to fal1 eonsideiably

FiG 3 — Diss

short of this ConEequently the disseetoi will eome down direetly iipon the diaphragm, when the mtetnal mtereostai museles are remoied from this portion of the ehest wall The fibres of the diaphragm eorrespond somewhal in their direetion with those of the mtemal intereostat museles, and it ts no uneommon oeeurrenee for the sludent lo remove them and thus expose the pentoneum undei the impiession ihat hc has simply laid bare the pleuta. When the disseetion is propeily executed a strong fascia will be seen It passes ftom the sutfice of Ihe diaphiagm to Ihe surface of the eostal pteuia and holds the lattei in position. Preserve this mem- brane for furthet esamination.

THORAGie WALL 9

Arteria MammaTia Intema. — This vessel arises, in the root of the neek, from the first part of the subclavian. It enters the thorax by passing downwards, posterior to the sternal end of the clavicle and the eartilage of the first rib, and it deseends to the interval between the sixth and seventh eostal eartilages, where it ends by dividing into the superior epigastrie and the museulO'phrenie branehes.

Plaeed anterior to the intemal mammary artery are the upper six eostal eartilages, with the intervening intemal inter- eostal museles and anterior intereostal membranes. The inter- eostal nerves eross anterior to it before they turn forwards to gain the surface. Posterior to the upper part of the artery is the pleura ; and the transversus thoraeis intervenes between the lower part of the artery and the pleural sae.

In addition to its two terminal branehes, a large number of small eollateral twigs proeeed from the internal mammary —

I. The anterior intereostal,

2. The perforating,

3. The perieardio-phrenie,

4. Mediastinal and thymie, ' 5. Superior epigastrie,

6. Museulo-phrenie, .

\ to the thoraeie parietes.

> to parts in the interior of the thorax.

> the terminal branehes.

The anterior intereostal arteries are supplied to the upper six intereostal intervals, and have been disseeted already (p. 6). Two are given to eaeh spaee: frequently these arise by a eommon trunk.

The perforating arteries aeeompany the anterior eutaneous nerves, and reaeh the surface by piereing the internal inter- eostal museles, the anterior intereostal membranes, and the peetoralis major musele. One, or perhaps two, are given ofif in eaeh intereostal spaee. In the female those of the seeond, third, and fourth spaees attain a speeial importanee, inasmueh as they eonstitute the prineipal arteries of supply to the mammary gland.

The superior epigastrie artery passes between the sternal and eostal origins of the diaphragm and enters the sheath of the reetus musele of the abdominal wall.

The museulo-phrenie artery turns laterally and downwards, along the eostal origin of the diaphragm and behind the rib- eartilages. Opposite the eighth eostal eartilage it pierees the diaphragm and terminates on its abdominal surface. It gives off the anterior intereostal arteries to the seventh, eighth, and ninth intereostal spaees (p. 7).

lo THORAX

Museulus Transyersus Thoraeis (O.T. Triangularis Sibemi). — This is a thin museular layer plaeed on the deep surface of the sternum and eostal eartilages. It is eontinuous below with the transversus abdominis, and arises from the posterior surface of the xiphoid proeess, the lower part of the body of the sternum, and from the medial ends of the fifth, sixth, and seventh eostal eartilages. Its fibres radiate in an upward and lateral direetion, in the form of five slips, whieh are inserted into the deep surfaces and lower borders of the seeond, third, fourth, fifth, and sixth eostal eartilages, elose to their junction with the ribs (Fig. 3).

In many eases the musele is feebly developed, and does not show sueh wide eonneetions. Upon its anterior aspeet are plaeed the internal mammary artery and some of the intereostal nerves.

It is only a partial view of the musele whieh is obtained in the present disseetion, but it is not advisable to remove the eostal eartilages to expose it further, as this would materially interfere with the subsequent display of other more important struetures in their proper relations.

THORAGie CAVITY.

Before the disseetion of the interior of the thorax is eom- meneed it is neeessary that the disseetors should have some general knowledge of the cavity and its eontents. The shape and the boundaries have been studied already (p. i), and it must now be understood that the cavity is divided into two lateral parts by a median septum ealled the mediastinum, whieh extends from the sternum anteriorly to the vertebral eolumn posteriorly, and from the upper aperture of the thorax above to the diaphragm below.

The mediastinum is formed by the heart, enveloped in a fibro-serous sae ealled the perieardium ; the great vessels passing to and from the heart, i,e, the pulmonary artery and veins, the aorta, and the vena cava superior ; the eesophagus ; the traehea and the eommeneements of the bronehi; the thoraeie duet ; the azygos, hemiazygos and aeeessory hemi- azygos veins ; the vagi and phrenie nerves ; numerous lymph glands ; and the areolar tissue in whieh these struetures are embedded and by whieh they are bound together. For eon- venience of deseription the mediastinum is divided into a superior and an inferior portion^ by an imaginary plane whieh passes from the lower border of the manubrium sterni nteriorly, to the lower border of the fourth thoraeie vertebra

THORAGie CAV1TY ii

posteriorly ; and the inrerior mediastinum is .subdivided Inlo anterior, middle, and posterior portions. Tho anUrior mediasHnum is the part anterior to the perieardium, the posterior mediastinum the part posterior to the perieardium, whilst the perieardium and the heart wilh the great vessels and the phrenie nerves with their aeeompanying vessels form the middie mediasHnum. It is eustomary, howevcr, to speak o^ the mediastinum as if tt weie a spaee, and to say that the various viscera, vessels, ete, lie in the mediastina (Fig. 19, p. 44). - The lateral portions of the Ihoraeie cavity are known as

eostal pan of parklal plnira Cu>ial pan i)f parietal pkura

■Diagrammalie represenialion of a eross seetion ihrough

the pleural spaees; eaeh eontains the eorresponding lung surrounded by an invaginated serous membrane ealled the pleural sae. There are therefore two pleural saes, and eaeh is so disposed that it not only lines the ehamber in whieh the lung lies, but is also reAeeted over the surface of the lung, so as to give it an external covering whieh is intimately eonneeted with the pulmonary substanee. ConsequentIy, the wall of eaeh pleural sae is separable into two portions, an invesling or yiseeral part whieh covers the surface of the lung, and a lining or parietal part whieh elolhes the inner surfaces of the boundary of eaeh lateral part of the thoraeie cavity. It must be elearly understood, however, that the two terms are merely applied to indieate different portions of a eontinuous membrane.

12 THORAX

Eaeh lung lies free in the pleural spaee except along its medial surface, where it is attaehed to the heart by the pulmonary vessels, to the eorresponding bronehial tube, and by a fold of pleura to the side of the perieardium.

The disseetion whieh has already been made shows the pleura lining the deep surfaces of the eostal arehes and the internal intereostal museles. This part is ealled the eostal pleura^ and it is part of the parietal pleura^ but before it ean be more fully investigated and before the remaining parts of the pleurae and the lungs ean be examined, further disseetion is neeessary.

Disseetion, — The pleural membrane previously exposed by the removal of the eontents of the intereostal spaees must now be carefully separated from the inner surfaces of the ribs by the gentle pressure of the iingers. The separation should be earried anteriorly to the junction of the ribs with their eartilages and posteriorly as far as possible. When this has been done the ribs, from the seeond to the sixth inclusive, must be divided, with bone forceps, at their junctions with their eartilages, and at the same time any fibres of the transversus thoraeis whieh may be attaehed to them must be eut. The first and the seventh and those below the seventh must not be inter/ered with, Afterwards the ribs must be divided as far dorsally as possible and the separated portions removed. After the separ- ated parts of the ribs are detaehed, remove any sharp spieules of bone from the eut ends of the remaining portions.

The outer surface of the eostal part of the parietal pleura will be exposed in the area from whieh the ribs have been removed, and the disseetor should notiee that it has the appearanee of a fibrous membrane with a rough surface, the roughness being due to fragments of the connective tissue (endothoraeie fascia) whieh eonneet it with the adjacent parts.

After he has examined the outer surface of the pleura, the disseetor should divide it by a vertical ineision about midway between the anterior and posterior borders of the area exposed. At eaeh end of the vertical ineision a transverse ineision must be made. One of the two flaps so formed must be thrown anteriorly, and the other posteriorly. The pleural sae is now opened and the lateral surface of the lung, covered with the visceral portion of the pleura, is exposed.

The cavity of the sae and its relations to the mediastinal septum, the diaphragm, and the root of the neek ean be explored with the fingers ; and the borders, surfaces, and the root of the lung ean be examined.

The Pleural Saes are two in number, a right and a left. They are serous saes, and are therefore elosed. After opening into the interior, the disseetor should notiee the difference between the rough outer surface of the wall of the sae and its smooth and glistening inner surface, and in order that he may thoroughly understand the relationship of the wall of the sae to the lung, the mediastinum and the wall of the thoraeie cavity, he should follow the wall of the sae, with his fingers, at three different levels — (i) at the level of the

THORAGie CAVITY 13

manubrium sterni; (2) at the level of the third intereostal spaee ; and (3) at the level of the fifth eostal eartilage. He must traee the wall of the sae in the vertical plane also.

Commencing at the level of the third intereostal spaee, he should plaee his fingers on the surface of the lung and follow it anteriorly and medially until, behind the sternum, he reaehes the sharp anterior border, whieh should be pulled laterally ; then, turning from the lung to the parietal pleura, he should plaee his fingers on the inner surface of the anterior flap and ibllow it medially. He will find, at a eertain point posterior to the sternum, and to the left of the median plane, that his fingers eease to pass towards the opposite side but are earried posteriorly, along the lateral boundary of the medi- astinum, until they eome to the big blood vessels and the air tube of the lung whieh collectively form its root. Along the front of the vessels his Aingers will now pass laterally, following the reflection of the pleura on the front of the vessels, to the medial surface of the lung, and then anteriorly to its anterior border. Round the anterior border they will arrive at the lateral surface of the lung ; along this they will pass to the posterior border and thenee anteriorly along the posterior part of the medial surface to the posterior surface of the root, where they will feel, distinetly, the hard outline of the bronehus. Following the posterior surface of the root medially, they will reaeh the posterior part of the lateral boundary of the mediastinum, along whieh they will pass posteriorly to the vertebral eolumn, and thenee laterally along the posterior parts of the ribs, and finally anteriorly along the inner surface of the posterior flap to its anterior margin.

If the disseetor has followed the above instruetions he eannot fail to have reeognised that the pleural sae is in- vaginated by the lung, whieh in its growth laterally from the mediastinal septum has invaginated and expanded a part of the medial wall of the sae. The disseetor should now examine a transverse seetion of a hardened thorax, or if that is not available, the diagram on p. 11. The study of either will convince him that the lung earrying the in- vaginated part of the wall of the pleural sae on its surface has expanded until it has praetieally obliterated thecavity of the sae, and he will find that the invaginated pleura on the surface of the lung, whieh is ealled the visceral pleura^ everywhere in elose apposition with the non-invaginatec

14 THORAX

portion whieh is termed the parietal pleura ; all that inter- venes between the two portions being a thin stratum of fluid, sufficient to lubrieate the surfaces and prevent friction during the movements of the lung and the ehest wall.

After he has grasped the facts noted above the disseetor should follow the inner surfac^of the pleura in the transverse plane at tho level of the mth^eostal eartila^e, that is, below the level of the root of the lung. At that level he will find that the parietal pleura covering the lateral surface of the mediastinal septum is eonneeted with the visceral pleura on the medial surface of the lung by a thin fold, the pulmonary ligament (O.T. ligamentum }atum pulmonis). This eonsists of an anterior and a posterior layer, whieh eorrespond, respectively, with the layers on the front and the baek of the root of the lung, but are in eontaet with eaeh other at the level of the fifth rib, on aeeount of the absenee of the great blood vessels and air tube of the lung. The pulmonary li^^ament extends laterally from the mediastinum to the medial surface of the lung, and from the root of the lung above, to within a short distanee from the diaphragm below. Its medial, lateral, and upper borders are attaehed respectively to the mediastinal septum, the lung, and the lower border of the lung root, and are eontinuous with the pleura covering eaeh, but its lower border is free. When he has satisfied himself regarding the nature and the attaehments of the pulmonary ligament, the disseetor should traee the pleura in the hori- zoiital plane at the level Qf thp rnamihri]|m gtPYni, that is, above the level of the root of the li^ng. Th^yg h^ will find that the medial wall of the sae is not reAeeted on to the lung, but that it passes posteriorly along the lateral surface of the mediastinal septum from the sternum anteriorly to the vertebral eolumn posteriorly, and thenee laterally and anteriorly to the sternum in an unbroken eirele. In the same way he will be able to traee the visceral pleura in a similar but smaller unbroken eirele around the upper partof the lung.

Having traeed the pleura in three horizontal planes the disseetor must next traee it in the vertical plane, first around the lung, and then around the wall of the thorax. Gommeneing with the lung, the fingers should be passeH along the anterior border to the apex, thenee, down the thiek posterior border, to the base, and anteriorly, aeross the concave base, to the anterior border. By doing this he will again demonstrate to himself

THORAGie CAVITY

15

the fact that the lung is ensheathed in visceral pleura. N'ext, plaelDg his hngera on the inner surface of the parietal pleura behind the eostal eartilages, he should eany them upwards towards the head, and he will find that they pass upwards into the root of the neek for a distanee of from one to two inehes above the level of the anteriot part of the first rib, but, on aeeount of the obUque position of the rib, only to the level of its neek posteriorly. The apex of the sae, therefore, lies in

the root of the neek, and by carefully palpating ils inner surface,the disseetor will be able to distinguish the subclavian artery whieh passes aeross its anterior surface below the highest point, and, possibly, he may be able to loeate the interna! mammary and costo-cervical arteries (O.T. superior inter- eostal). The hrst deseends from the subclavian trunk anterior eo the apex of the sae, and the seeond passes first upwards to the apex and then posteriorly above it. Afler disseetor bas examined the position and relations

1 6 THOR AX

apex of the sae he should follow its posterior wall downwards, just lateral to the line of the vertebral eolumn, and, if he is dealing with a subject in good eondition, he will iind that he ean pass his fingers downwards to the lower border of the twelfth rib, where they will be earried anteriorly on to the diaphragm and over its surface to the anterior wall of the thorax. If the disseetor earries out the examination of the pleural sae in a thorough manner, and if he has appreeiated the significance of the arrangements found at different levels, he will have repeatedly convinced himself that the lung, earrying the blood vessels and air tube with it, has invaginated a portion of the lower part of the medial wall of the pleural sae, and has then expanded anteriorly, posteriorly, upwards and, to a eertain extent, downwards beyond the margins of the aperture of invagination, whose position is indieated by the root of the lung and the line of attaehment of the pulmonary ligament. The portion of the wall of the pleura whieh is invaginated by the lung is represented by (i) the visceral pleura, (2) the layers covering the root of the lung, and (3) the pulmonary ligament. .

Before eaeh lung is removed the disseetors should note that its anterior margin does not extend so far anteriorly, and the inferior margin does not extend so far downwards, as the eorresponding part of the pleura. The portions of the pleura unoeeupied by the lung are ealled the pleural sinuses. The sinus along the anterior margin of the pleura is the eosto-mediastinal sinus^ and that along the lower margin, the phrenieo-eostal sinus, The walls of the sinuses are separated by a eapillary spaee filled with pleural fluid, and the margins of the lungs enter into the sinuses and reeede from them during inspiration and expiration, respectively.

•

In the event of the lungs not having been hardened in situ by formalin injection the disseetors may, with the eonsent of the disseetors of the head and neek, introduee the nozzle of the bellows into the cervical part of the traehea and inflate the lungs with air. A truer eoneeption of these organs will thus be obtained, and a demonstration will be affbrded of their high elastieity, and of their oonneetion with the wind-pipe.

After the disseetor has eompleted the general examination of the walls of the pleural sae, he should pull the anterior margin of the lung laterally to expose its medial surface, the front of the root and the front of the pulmonary ligament ; then he should divide the root and the pulmonary ligament, from above downwards, elose to the medial surface of the

THORAGie CAVITY 17

lung. The lung, thus set free, is to be removed from the thorax, wrapped in a eloth damped with preservative solution,

and plaeed aside for future study.

When the lung has been removed the margins of the pleural sae must be examined, and their positions relative to the ehest wall noted. This eannot be done to the best advantage until both lungs have been removed. When this has been done the dis- seetor should introduee one hand into eaeh pleura, and plaeing an index finger in eaeh apex, he should note that the apex issituated about one_inch above the jujiction of the lateraL.two-thirds with the medial third of the elayiele, a fact whieh he ean demonstrate with the aid of his partner on the opposite side, who should hold two maeerated clavicles in their. proper posi- ""EToiis. The apiees of opposite sides, there- fore, are some distanee apart, and are separ- aled from eaeh other i by the struetures oeeu- pying the median part of the neek; i'.e. the air tube, ihe gullet, and the great arteries passing upwards to the head. As the anterior margins of the pleurEe are traeed down- wards from the apiees they will be found to converge, passing behind the sterno-clavicular joints and eoming into apposition at the lower border or the manubrium sterni, immediateiy to the left of the median plane. Traeed further downwards the anterior margins remain in apposition, the right frequently over- lapping the left and both inelining sli|htly to the left, to the Ievel of the fourth eostal eartilages. From the fourth eartilage VOL. 11—2

6.— Diagram lo show the relation of ihe asa aad Ihe pleural saes to Ihe nnterior e depieled in

d ibe pleural s;

i8 THORAX

the anterior margin of the right sae eontinues to deseend, still with a slight indination to the left, till it reaehes the xiphoid proeess, where it beeomes eontinuous with the inferior margin. This turns laterally, passing behind the xiphoid proeess and the eartilage of the seventh rib ; it then erosses the junction

and heart	The	iitline of ihe heart		ted inred by a dotied
and ihe a		argins of Ihe pleura	saesa	e represented by blue

of the bone and eartilage of the eighth rib and reaehes the level of the tenth rib in the mid-axillary hne; turning posteriorly, it erosses ihe eleventh and twelfth ribs, and just below the middle of the latter it beeomes eontinuous with the posterior margin, whieh aseends along the line of the angle of the ribs to the apex. On the left side, at the level of the fourth eostal eartilages, the anterior margin of the ]eft pleura turns away from the median plane, for a variable distanee,

THORAGie CAVITY 19

passing behind the fifth eosul eanilage ai the margln of the sternum, or even an ineh more laterally ; il then deseends to the lower border of the sixih eaitilage, where it beeomes

■;. a.— t^I Pleuial 5ac, of a subject b opened imo by the removal of Ihe c ba^ been renioYed so as to display the along whieh ihe pleura is retleeted froni th wall is uhibited.

liaphra

eontinuous with the lower maipn of the pleura, whieh p; laterally and posteriorly along ihe lower border of the sl eartilage, aeross the medial end of the sixih spaee, and aer the seventb eartilage to the junciion of the eartilage a 11—2«

20 THORAX

bone of the eighth rib. The remainder of its eourse and the positioti of its posterior margin are the same as on the right side.

¥ia, 9. — The Righl Pleural Sae, in a subject hardeneil by forin.'>Jin iiyeetioii, opened inio by the removal of the eostal parl of Ihe parietal pleura. The riEhi lung also has been remoYed 10 display Ihe righi niediaslinal pleura. Note Ihe line of diaphragmatie reHeetion of the pleura.

The student should mark out the margins of the pleural saes on the living body, using himself and his friends for the purpose, until he ean indieate them eorreetly, judging from the eontour of the body alone and without feeling for the skeletal points.

THORAGie CAVITY »i

After the disseetor has made himself thoroughly conversani

piG. lo, — The Right Pleural Chaniber opened up by ihe Temoval of its lf wall. Tbe lung has been laken away so as lo expose (he media^ wall oT Ihe pleiu^ ebamber, 5everal of the siruetures in tbe me [inal septum are seen shinitig tbrough the tnediastinal pleura.

2 2 THORAX

with the limits of the pleural saes, he should examine the eut seetion of the root of the lung, and should endeavour to reeognise, through the mediastinal part of the parietal pleura, the positions of the main eonstituent parts of the mediastinum. As these vary on the opposite sides, eaeh side must be eon- sidered separately, and eaeh disseetor must make himself well acquainted with the eonditions on both sides.

On the rightside^ in the posterior part of thefaceof the seetion of the lung root, at least two parts of the bronehial tube will be seen ; an upper, whieh is the so-ealled eparterial bronehus, and a lower, the main stem of the right bronehus. Anterior to and between the two bronehi is the pulmonary artery, and more anteriorly, and at a slightly lower level, the upper pul- monary vein. The lower pulmonary vein lies in the lowest part of the root, below and slightly posterior to the main bronehus. If the speeimen is well injected, branehes of the right bronehial artery may be distinguished on the posterior faces of the air tubes ; and anterior to and between the great blood vessels, and between them and the bronehi, are a number of bronehial glands, whieh are easily distinguished by the blaek pigment deposited within them.

In the posterior part of the root of the lung, on the left side, the disseetors will see the eut seetion of the left bronehus, . and, in many eases, a seetion of its first ventral braneh also. The left pulmonary artery is above the bronehus, and its anterior wall is on a slightly anterior plane. The upper left pulmonary vein is anterior to the bronehus, and the lower left pulmonary vein is below the bronehus. In a well in- jected speeimen the two left bronehial arteries may be seen on the posterior wall of the bronehus, and a number of bronehial glands will be found between and around the large blood vessels and the bronehus.

Turning next to the mediastinal pleura on the right side, the disseetors will note, anterior to and below the root of the lung, a large bulging, due to the heart and perieardium, whieh lie in the middle mediastinal area. Gontinuous with the upper and lower ends of the posterior part of this bulging they will see two longitudinal elevations. The upper, from the level of the third eostal eartilage to the lower margin of the lirst rib, is due to the superior vena cava and above that level, to the right innominate vein. The lower elevation is very short, and is eaused by the upper part of the inferior

THORAGie CAVITY 23

vena cava. A seeondary ridge, formed by the phrenie nerve and the aeeompanying blood vessels, deseends along the elevation eaused by the superior vena cava, erosses anterior to the root of the lung, nins down along the posterior part of the bulging due to the heart, and the anterior border of the inferior caval elevation. Arehing over the root of the lung is a curved ridge, due to the upper part of the vena azygos, as it passes anteriorly to join the superior cava. Above the vena azygos and posterior to the superior cava, the right lateral surface of the traehea, or main air tube, may be seen or felt in the superior mediastinal region, and, deseending obliquely aeross it, from above downwards and posteriorly, the right vagus nerve ean be palpated or seen. Posterior to the root of the lung and to the bulging due to the heart, the oesophagus may be reeognised in the posterior mediastinal area, either by toueh or sight, or both. Somewhat posterior to the oesophagus the margin of the aseending portion of the vena azygos may be noted, and still further posteriorly are the bodies of the vertebrae and the posterior parts of the ribs. Grossing the bodies of the vertebrae trans- versely the right intereostal vessels may be visible or they may be felt, and, deseending along the line of the heads of the ribs, the ganglionated trunk of the sympathetie ean be reeognised by toueh, if not by sight.

The disseetors should examine next the mediastinum and the posterior wall of the thorax on the left side (see Figs. 8, II, and 13).

By inspeetion and palpation they will easily reeognise the positions of the larger and more important struetures. Below and anterior to the root of the lung the mediastinal pleura is bulged mueh more laterally on the left than on the right side by the heart covered by the perieardium. Arehing posteriorly and to the left, over the root of the lung, in the superior mediastinal area, is the areh of the aorta, and from its posterior end the deseending aorta runs downwards, in the posterior mediastinal area, first posterior to the root of the lung, and then posterior to the heart but separated, in part, from the latter by the oesophagus, whieh diverges towards the left side in the lower part of the thorax. Above the areh of the aorta the left eommon earotid and subclavian arteries and the oesophagus ean be distinguished in the above orde antero - posteriorly. A long slender seeondary ridge, p

bone of Ihe eighth rib. The remainder of its eourse and the position of its posterior margin are the same as on the right side.

FiO. y. — The Right Pleural Sae, in a subject hardened by formalin iiijeclion, opened inio by Ihe remoyal of Ihe eoslal part of Ihe parielal pleura. The righi Lung also bas been removed lo display Ihe right mediastinal pleura. Nole Ihe line of diaphraEmalie reHeelion of the pleura.

The student should mark out the margins of the pleural saes on the living body, using himself and his friends for the purpose, until he ean indieate them eorreetly, judging from the eontour of the body alone and without feeling for the skeletal points.

THORAGie CAVITV ii

After the disseetor has made himseir thoroughly conveTsant

fiG. lo.— The Right Pleural Chamber opened up by (he removal of its laleral wall. Tbe lung has been laken away so as to expose ihe media5liDal wall of tbe pleund ehamber. Sevenil of ihe sirueiures in Lhe medias- linal septum are seen shining Ihrough the mediaslinal pleura. 11—26

20 THORAX

bone of the eighth rib. The remainder of its eourse and the position of its posterior margin are the same as on the right side.

(hyparlerialpail)

Kl<i. 9. — The kight Pleural Sae. in a subjecl hardened by fotmaUn injeclion, opened into by the remova1 of the eoslal part of the parietal pleura. The rig^t lung also has been removed to display Ihe right medlaslinal pleura. Note the line of diaphragmalie reHedion of Ihe pleura.

The student should mark out the margins of the pleural saes on the living body, using himself and his friends for the purpose, until he ean indieate them eorreetly, judging from the eontour of the body alone and without feeling for the slteletal points.

THORACIC CAVITY After the disseetor has made himself thoroughly

pie. lo. — The Righl Pleural Ghambet opened up by Ihe removaI of its laleral wall. The lung ha^ been laken away so aE to e>:pc>se Ihe niediastlaal wall of Ihe pleural ehaniber. Several of the slruelures In the medias- tiual seplum are seen sbiniug Ihrougli Ihe mediaslinal pleura.

bone of the eighlh rib. The remainder of its eourse and the posilion of its posterior margin are ihe same as on the right side.

KiO. 9.— The Righl Pleural Sae, in a sabjecl hardened by formalin iiyeetion, opened inlo bylhe removal of Ihe eostal part of the parietal pleura, The ri£ht lung also has been remoyed lo display Ihe right mediaslinal pleura. Nole the line of diaphragniatie reHeetion of the pleura,

The student should mark out the margins of the pleural saes on the living body, using himself and his friends for the purpose, until he ean indieate them eorreetly, judging from the eontour of the body alone and without feeling for the skeletal points.

THORAGie CAVITY ii

After the disseetor has made hiinself ihoroughly convcrsant

fIG. lO. — TbeRighlPleuraiehamberopenedupliy ll wall. The lung has betn (aken away so as to i wall of Ibe pleural etianiber. Several ot Ihe stn liiial 9q>tuin aie seen shining ihrough the mediost

n— 2&

30 THORAX

at the level of the seeond eostal eartilage (see Fig. 12). As it turns anteriorly the vein lies immediately to the right side of the oesophagus, traehea and vagus nerve.

The tributaries of the vena azygos are : (i) The right superior intereostal vein whieh drains blood from the greater part of the seeond and third intereostal spaees. (2) The eight lower intereostal veins and the subeostal vein of the right side. (3) The vena hemiazygos, and frequently (4) the vena hemiazygos aeeessoria. Both the latter enter it from the left. In many eases the aeeessory azygos vein joins the hemiazygos vein. (5) Two or more bronehial veins from the right lung. (6) Some veins from the oesophagus. (7) Some minute perieardial veins.

The vena azygos eommenees in the abdomen where it anastomoses either with one of the upper lumbar veins or direetly with the inferior vena cava. Thus it forms a more or less direet anastomosis between the two venge cavae.

The intereostal veins and the aeeompanying arteries and nerves, on both sides, and the hemiazygos and aeeessory azygos veins will be studied at a later period of the disseetion (see p. 108).

Contents of the Mediastiniun and the Struetures of the Posterior Part of the Left Half of the Thorax seen irom the Ijeft Side. — After the removal of the four pleural flaps deseribed on p. 25 the following struetures are visible on the left side of the thorax (see Fig. 13). Below and anterior to the root of the lung is the perieardium, covering the left ventricle, the left atrium, the eonus arteriosus of the right ventricle and the pulmonary artery. Above the root of the lung is the areh of the aorta. The areh of the aorta terminates posteriorly in the deseending aorta, whieh passes downwards posterior to the root of the lung and the perieardium, but it is separated from the lower part of the posterior wall of the perieardium by the oesophagus, whieh, at this level, is passing towards the left side. On the left and anterior aspeet of the aortie areh, from behind forwards, lie the left vagus nerve, the superior cervical eardiae braneh of the left sympathetie trunk, the inferior cervical eardiae braneh of the left vagus, and the left phrenie nerve with its aeeompanying vessels. Grossing the areh obliquely, from behind forwards and upwards, is the left superior intereostal vein, whieh passes lateral to the vagus and medial to the phrenie nerve. Above

THORAGie CAVITY 31

the areh or the aorta are the lower parts of the Ieft eommon

earotid and left subclavian arteries, and posterior to the latter lies the oesophagus, with the thoraeie duet running along its Ieft lateral border.

32 THORAX

Posterior to the deseending aorta are the left aortie inter-

eostal arteries, the aeeompanying veins, and the splanehnie

nerves ; and still more posteriorly and laterally lie the

sympathetie trunk of the left side and the left intereostal

,spaces and their eontents.

Dissedlon. — After the struetures exposed by the removal of the left pleura have been loeated, the disseetors should direet their attention to the sympathetie trunk and its branehes and eommunieations. The arrange- ment of these is exactly similar to that already deseribed on the right side (see p. 26). When the disseetors have confirmed this statement they should turn to the left subclavian artery, whieh is the most posterior of the three great branehes whieh spring from the areh of the aorta. Glean this vessel without disturbing the vagus nerve, whieh deseends along its anterior border. Afterwards elean the part of the aortie areh whieh lies posterior to the vagus nerve, and the deseending aorta. Whilst eleaning the areh avoid injuring the left superior intereostal vein, and, as the deseending aorta is being eleaned, endeavour to preserve any of the aortie branehes of the sympathetie whieh may have been found previously during the examination of the sympathetie trunk.

As the aorta is eleaned the left border of the lower part of the oesophagus will be brought more elearly into view, but the disseetor must not attempt to elean the oesophagus at this stage.

After the deseending portion of the aorta is eleaned, the left aortie intereostal arteries should be examined. They are nine in number ; they emerge from the posterior aspeet of the aorta, and they all pass medial to the sympathetie trunk as they approaeh the intereostal spaees. The upper arteries aseend very obliquely to gain their proper spaees. Aeeompanying the arteries are the eorresponding veins. The lower veins pass, posterior to the aorta, to their terminations in the hemiazygos and aeeessory hemiazygos veins, and will be more fully studied at a later stage ; but the veins from the seeond and third spaees unite into a trunk ealled the left superior intereostal vein.

The Left Superior Intereostal Vein. — This vein is formed by the intereostal veins from the seeond and third intereostal spaees of the left side, and it not uneommonly receives a eommunieation from the first and fourth spaees. It deseends along the medial border of the first left aortie intereostal artery to the posterior end of the aortie areh, there it turns anteriorly, along the left side of the aortie areh, and, passing at the same time obliquely upwards, it erosses lateral to the left vagus and medial to the left phrenie nerve. At a later period of the disseetion it will be traeed to its termination in the left innominate vein.

Disseetion. — After the left superior intereostal vein has been seeured and studied, the disseetors should elean the region posterior to the left subclavian artery, and expose thoroughly the left border of the oesophagus, as that tube lies in the superior mediastinum, and the upper part of the thoraeie portion of the thoraeie duet, whieh runs along the border of the oesophagus.

THORAGie CAVITY 33

After this stage of the disseetion is eompleted, the disseetors should exainine the triangular interval between the left phrenie and left vagus neryes in the upper part of the thorax. Com- meneing aboye, they should follow the vagus nerve down- wards ; just before it reaehes the lower border of the aortie areh, it gives off a very distinet braneh whieh turns round the lower border of the areh. This is the important reeurreni nerue whieh supplies the majority of the intrinsie museles of the larynx of the same side. Immediately anterior and medial to the point where the reeurrent nerve turns beneath the areh, a very distinet fibrous eord must be defined. It eonneets the areh with the upper border of the Ieft pulmonary artery elose to its origin. This is the ligamentum arteriosum^ and it is the remains of the duetus arteriosus, through whieh blood passed from the pulmonary artery to the aorta during foetal life. When this has been seeured the areolar tissue between the phrenie and vagus nerves must be carefully removed. In this tissue two small nerves will be found whieh run downwards, parallel with the vagus, aeross the areh of the aorta. The one next the vagus is the superior cervical eardiae braneh of the left sympathetie, and the one next the phrenie is the inferior cervical eardiae braneh of the left vagus. When these nerves are followed downwards they will be found to end in the superficial eardiae plexus, whieh lies in the areolar tissue below the aortie areh and to the right of the ligamentum arteriosum.

Disseetion, — After the perieardium has been eleaned, ineisions should be made through it on eaeh side, and the flaps formed should be turned aside so that the disseetors may make themselves familiar with the relation- ships of the heart to the mediastinal portions of the pleural saes. Two longitudinal ineisions must be made on eaeh side, one anterior and one posterior to the longitudinal strip of pleura Ieft on the lateral surface of the phrenie nerve (see Figs. 12 and 13). On the right side the ineisions should eommenee at the level of the upper pulmonary vein. On the left side the anterior ineision should begin at the lower border of the aortie areh and the posterior at the level of the left pulmonary arlery (see Fig. 13). On both sides the longitudinal ineisions must deseend to the lower border of the perieardium. On both sides ineisions should be earried anteriorly from the upper and lower ends of the anterior longitudinal ineision to the line aloDg whieh the mediastinal pleura was left attaehed to the anterior surface of the perieardium (see Figs. 12 and 13). From the upper end of the posterior longitudinal ineision on the right side a eut shoukl be made downwards and posteriorly along the anterior aspeet of the root of the lung to the upper end of the inferior vena cava (see P ig. 12).

From the upper end of the posterior longitudinal ineision on the left side an oblique eut must be made downwards and posteriorly, along the line of

VOL. II — 3

34 THORAX

the anterior surface of the root of the left lung. When the ineisions have been made, the anterior flaps ean be turned anteriorly and the posterior flaps downwards. None of the flaps must be removed, for it will be neeessary to replaee them in position at a later stage of the disseetion.

When the flaps marked out by these ineisions are turned aside the disseetors will find that, on the right side, they have exposed the greater part of the right atrium (see Fig. 12). They should note that the area of the atrium whieh is exposed is separated into two parts by a vertical suleus, the suleus terminalis^ whieh runs from the anterior face of the eardiae end of the superior vena cava to the anterior aspeet of the terminal part of the inferior vena cava. This suleus divides the atrium into a posterior part, the sinus venosus, and an anterior part, the atrium proper, whose upper and anterior part is prolonged medially to the anterior surface of the heart. On the left side the greater part of the heart exposed by the reflection of the perieardial flaps is the left ventricle, but in the upper part of the area the auriele (O.T. aurieular appendage) of the left atrium is seen. Anterior to it lie the stem of the pulmonary artery and the upper part of the anterior portion of the right ventricle. A line of fat, in whieh lie the interventricular braneh of the left eoronary artery and the aeeompany- ing vein, indieates the position of the septum between the left and right ventricles (Fig. 13).

After the disseetion is eompleted and the disseetors have carefully noted the relative positions of the various struetures whieh have been exposed, they should proeeed to study the phrenie nerves, whieh have been retained in position by the strips of pleura on their lateral surfaces (see Figs. 12 and 13).

Nervi Phreniei. — Eaeh phrenie nerve arises in the neek from the cervical plexus, receiving fibres from the third, fourth, and fifth cervical nerves. It deseends on the sealenus anterior musele and, at the root of the neek, passes anterior to the subclavian artery and posterior to the eorresponding vein, but on the left side, as it leaves the Sealenus anterior, it lies anterior to the subclavian artery and posterior to the eommeneement of the innominate vein. As it enters the upper aperture of the thorax it erosses the internal mammary artery, passing from its lateral to its medial side, then it deseends along the lateral border of the mediastinum, anterior to the root of the lung, to the diaphragm where it breaks up into branehes. The majority of the branehes pass between the museular fibres of the diaphragm and, after eommunieating with the abdominal sympathetie nerve fibres whieh form the diaphragmatie plexus, they are distributed to the musele from its lower surface. The re- lations of the phrenie nerves in the thorax are different on the two sides, and the left phrenie nerve, as a whole, is on a plane somewhat anterior to the right.

The right phrenie nerue deseends along the lateral borders of the right innominate vein and the superior vena cava to the point where the latter enters the perieardium, then along

THORAGie CAVITY 35

the side of the perieardium, whieh separates it from the yenous sinus of the right atrium (see Fig. 12).

The Left Phrenie Nerue. — In the upper part of the thorax the left phrenie nerve runs downwards between the left eommon earotid and the left subclavian arteries and, whilst lying between them, it erosses anterior to the left vagus and posterior to the left innominate vein. In the lower part of the superior mediastinum it passes lateral to the areh of the aorta and the left superior intereostal vein, then, deseending into the middle mediastinum, it lies at first anterior to the root of the left lung, and afterwards it runs downwards along the side of the perieardium, whieh separates it from the anterior part of the left atrium and from the lateral part of the left ventricle of the heart.

The left phrenie nerve is longer than its fellow of ihe right side, partly on aeeount of the lower position of the diaphragni, and partly on aeeount of the greater projection of the heart on the left side.

Branehes of the Phrenie Nenres. — The main distribution of the phrenie nerves is to the diaphragm, but some minute sensory twigs are given off by eaeh nerve to the perieardium and to the pleura. The student should note the great import- anee of the phrenie nerves. They are the nerves of supply to the diaphragm, whieh is the chief musele of respiration.

Pulmones. — Before proeeeding to the further disseetion of the eonstituent parts of the mediastinum, the disseetors should study the lungs whieh they previously removed. The lungs are two soft, comparatively light, spongy organs plaeed one on either side of the mediastinum. The weight of the right lung, when it is filled with an average amount of blood, is 22 oz. and that of the left 20 oz. When the thorax is opened the lungs eollapse to about one-third of their original bulk (unless they have been hardened in situ\ and it is difficult for the student to realise their proper size and shape until they are distended to their original dimensions with the aid of the bellows (see p. 16).

When healthy and sound, the lungs lie free within the cavity of the ehest, and are attaehed only by their roots and by their pulmonary ligaments. It is rare, however, that a healthy lung is seen in the disseeting-room, for adhesions be- tween the visceral and parietal portions of the pleura, due to pleurisy, are generally present. Eaeh lung is aeeurately adapted to the spaee in whieh it lies, and, when hardened

II— 3 a

36 THORAX

in sifu, it bears on its surface impressions and elevations whieh are an exact eounterpart of the inequalities of the struetures with whieh its surfaces are in eontaet at the moment of fixation.

In the natural eondition eaeh lung resembles half a eone, and il presents for examination an apex, a ^ase, a casfa/ surface, a medial sur/aee. An anterior and a posierior border separate the medial from the lateral surface ; and an inferior or basal border separates the base from the medial and lateral

LungB of a Child, hardened in injeclion,

surfaces. The apex rises into the root of the neek for one and a half inehes above the level of the anterior parl of the Arst rib, and it is erossed by the subclavian artery, whieh makes a groove upon the anterior border, a short distanee below the summit, although the artery is separated from the lung by the membranous cervical diaphragm (Sibson's fascia), and by the pleura.

The base of eaeh lung has a semilunar outline and is adapted to the upper surface of the diaphragm. Consequent]y it is deeply hollowed out, and, as the right eupola of the

THORAnr rAyiTY

I diaphragm aseends higher than ihe lert. ihe basal concavity 1 I of ibe right lung is deeper than that of ihe !eft hing. The I Ilateral and posterior parts of tbe basa! margin of ihe lung J l.are thin and aharp and estend downwards into the phre I eostal sinus of the pleura, whieh intervenes between the I l.diaphragm and the wall of the lhorax. This margin reaehes a 1 I mueh iower position posteriorly and laterally ihan anleriorly, f I but in all siluations it falls eonsiderably short of the bultom of I >inus. The mediastinal part of the basal margin, whieh T I Jies along the lower border of the peHeardium, is niore 1 irounded.

The diaphragm separates ihe base of the right lung from 1

I

the upper surface of the right lobe ol ihe iiver, and the base Df the left lung from the left lobe of the iiver, ihe stomaeh, the spleen, and, in some eases, from the left extremity of the transyerse eolon.

The eostal sutface of tbe lung is very extensive and convex. ;It lies in relation witb the eostal pleura, whieb separates it, from tbe ribs and intereostal museles, the transversus thoraei»^ and the sternum, and it bears the impressions of the eostal' arehes.

Themedial surraee is separable into an antenoTOTnie/iias/im portioH and a posterior or vertebral portion. The yerlebral portion lies against the sides of tbe bodies of the vertebrK. The mediastina! part is applied against the mediaslinal partition and presents markings whieh are the exact eounter- parts of the ine^ualities of Ihe eorresponding laleral surfar- li— 3

lal

er-^li

38 THORAK

of the mediastinum. Thus, it is deeply hollowed out in adaptation to the perieardium upon whieh it fits. The perieardial concavity oeeupies the greater part of the mediastinal surface, and, owing to ihe greater projection of the heart to the left side, it is mueh more extensive in the left lung than in the right lung.

'Medial of a Left Lung hardened it

At the upper and posterior part of the perieardial area is the hilus of the lung. This is a wedge-shaped depressed area through whieh the bronehus and the pulmonary artery enter and the pulmonary veins and lymphaties leave the lung. It is surrounded by the pleura whieh is ref!ected from its mai^in on to the root of the lung, and the layer of reAeeted pleura round the hilus is eontinuous, below, with the pulmonary ligament. The portion of the perieardial area anterlor to the upper part of the hilus of the left lung eorresponds with the

THORAGie CAVITY

39

position of the eonus arteriosus and the stem of ihe pulmonary artery, and the same portion of the i>ericardial area on the right side eorresponds with the position of ihe lower part of the superior vena cava postetiorly and with the aseending aorta anteriorly (Fig, 1 7). Below and poslerior to the lower

F:g. 17. — The Medial Surfaeeof a Righl Lung hardened

and posterior part of the perieardial area on the rigtit lung is a seeondary depression due to the upper part of the inferior vena cava. Posterior to the perieardial area and the hilus there is a narrow strip of the mediastinal surfacc of the lung whieh is in relation with the lateral wall of the posterior mediastinum. On the right lung this portion of the surface presents a longitudinal depression whieh eorresponds with the right border of the oesophagus, and more posteriorly at the upper part there may be a groove eaused by the vena

40 THORAX

azygos. The left lung in the eorresponding situation is marked by a deep longitudinal groove whieh is produeed by the eontaet of the lung with the deseending thoraeie aorta ; and, elose to the base, a small triangular area, anterior to the aortie groove, lies in relation with the left border of the lowest part of the thoraeie portion of the oesophagus.

The portion of the mediastinal surface whieh lies above the hilus and perieardial hollow is applied to the lateral aspeet of the superior mediastinum and the markings upon it are different on the two sides. On the left side a broad deep groove, eaused by the aortie areh, curves over the hilus and beeomes eontinuous posteriorly with the aortie groove on the posterior mediastinal area. From this arehed groove a sharply eut suleus, eaused by the left subclavian artery, aseends on the medial side of the apex and, turning laterally above, it erosses the anterior border of the apex a short distanee below the summit. Immediately anterior to the subclavian suleus the medial surface of the apex is oeeasion- ally marked by a shallow suleus eaused by the lateral margin of the left innominate vein, and more inferiorly its anterior margin is depressed by the first rib. That portion of the surface whieh lies posterior to the subclavian suleus is separated by areolar tissue from the eesophagus.

On the right lung also a curved -suleus arehes over the hilus. It is eaused by the vena azygos, as it passes anteriorly to join the superior vena cava. This groove is mueh narrower and less distinet than the suleus on the left lung due to the aortie areh. From the anterior end of the suleus for the azygos vein a broad shallow suleus passes upwards to the lower and anterior part of the apex. This is produeed by the superior vena cava and the innominate vein, and in some eases it is prolonged to the upper part of the apex by a slight longitudinal depression due to the pressure of the internal jugular vein. Arehing laterally, aeross the upper part of the anterior aspeet of the apex, there is a shallow groove produeed by the right subclavian artery. Posterior to the suleus for the innominate vein, the medial surface. of the apex lies in relation with the right side of the traehea, and still further posteriorly it is either in relation with the right lateral border of the superior mediastinal part of the eesophagus, or it is separated from it by a mass of areolar tissue.

The anterior and posterior borders of the lung are in

THORAGie CAVITY 41

marked eontrast with eaeh other. The anterior is eompara- tively short and thin and it extends medially into the eosto- mediastinal sinus of the pleura, whieh lies posterior to the sternum and the eostal eartilages. It eommenees at the apex, curves downwards, anteriorly and medially, posterior to the sterno-clavicular artieulation, to the lower border of the manubrium sterni, and then it deseends vertically to the base. Immediately below the highest point of the apex it is grooved by the subclavian artery on eaeh side, and on the left side it presents a eardiae noteh at the leverof the fifth eostal eartilage. The posterior border is rounded and indistinet. It deseends from the apex to the base, along the line of the artieulations of the heads of the ribs with ^ie bodies of the vertebrge, and it is mueh longer than the anterior border.

Lobes of the Lniigs. — The left lung is divided into two lobes by a long, deep obligue fissure whieh penetrates its substanee to within a short distanee of the hilus. This fissure begins above at the posterior border, about two and a half inehes below the apex, at the level of the vertebral end of the third rib, whieh eorresponds with the medial end of the spine of the seapula. It is eontinued on the lateral surface, in a somewhat spiral direetion, downwards and anteriorly till it euts the inferior margin opposite the lateral part of the eostal eartilage. The upper lobe of the lung lies above and anterior to this cleft It is eonieal in form, with an oblique base. The apex and the whole of the anterior border belong to it. The lower lobe^ somewhat quadrangular, is more bulky than the upper, and lies below and posterior to the Assure ; it eomprises the entire base and the greater part of the thiek posterior border.

In the right lung there are two fissures subdividing it into three lobes. The obligue fissure is very similar in its position and relations to the fissure in the left lung, but it is more yertieal in direetion. It separates the lower lobe from the upper and middle lobes. The seeond cleft, the horizontal fissure^ begins at the anterior border of the lung at the level of the fourth eostal eartilage and extends horizontally till it joins the oblique fissure. The middle or intermediate lobe, thus eut off, is wedge-shaped in outline. It lies between the oblique and horizontal fissures.

i:dfrerences between the two Lungs. — The disseetors should partieularly note the following differences between the two

4»

THORAX

lungs : — (i) The right lung is slightly larger than the left, in the proportion of ii to lo. (2) The right lung is shorter and wider than the left lung. This di^Terenee is due to the great bulle of the right lobe of the Iiver, whieh eleyates the right eupola of the diaphragm to a higher Ievel than the Ieft eupola, and also to the heart and perieardium, whleh project more to the !eft than the right, and thus diminish the width of the left lung. (3) The anterior sharp margin of the right lung is more or less straight; the eorresponding margin of the left lung presents, in its lower part, a marked angular' deficiency [ineisura eariiaed) for the

/"'■'•■"

reeeption of the heart and the perieardium. (4) The right lung is subdiyided into three lobes, and the lcfi lung into two. Ba>diz Pulmonis. — The root of the lung is formed by a number of struetures whieh enter the lung at the hilus or siit on its mediastinal suriaee, The struetures whieh form the root are held together by an inrestment of pleura, and they eonstitute a pediele whieh attaehes the lung to the eontents of the mediastinum. The pleura has already been remoyed from around them, and now a more detailed examination of the eonstituent parts of the root and of its relations must be made. The portion of the root still

THORAGie CAVITY 43

attaehed to the mediastinum should be used for this purpose.

Disseetion, — Commence with the vagus nerve and follow it downwards from a point just above the vena azygos on the right side, and from the areh of the aorta on the left, looking carefully for small branehes whieh spring from its anterior border and pass to the anterior surface of the root, where they eommunieate with the twigs from the sympathetie ganglia, and from the deep eardiae plexus, to form the anierior ptdmonary pUxus^ from whieh branehes are distributed to the walls of the air tube and the blood vessels. On the left side a few twigs may be found passing from the super- ficial eardiae plexus to the anterior pulmonary plexus. After ihe branehes of the vagus to the anterior pulmonary plexus have been identified, the trunk of the vagus, on eaeh side, must be followed down to the posterior surface of the root of the lung, where it breaks up into branehes whieh unite with twigs from the eorresponding sympathetie trunk to form the posterior pulmonary plexus (see p. 28). The posterior pulmonary plexuses of opposite sides are eonneeted together by strong branehes, whieh pass both anterior and posterior to the oesophagus, and eaeh gives branehes to the walls of the bronehial lube and the blood vessels of the root of its own side. These various branehes must be found and identified. After the posterior pulmonary plexuses are satisfactorily displayed the bronehial blood vessels should be found and deaned.

Arterise Bronehiales. — As a rule, two bronehial arteries are distributed to the left lung and one to the right lung. The two left bronehial arteries spring from the deseending aorta. The right bronehial artery is a braneh either of the Arst right aortie intereostal artery or of the upper left bronehial artery. The bronehial arteries and their branehes run along the posterior surfaces of the bronehi and their branehes, and are the proper nutrient yessels of the lungs. Part of the blood whieh they convey to the lungs is returned by the pul- monary veins to the left atrium of the heart, but the remainder is returned by bronehial veins, whieh open on the right side into the vena azygos, and on the left side into the vena hemiazygos aeeessoria, or into the left superior intereostal vein.

Dissedion. — After the bronehial vessels have been traeed, the disseetor should separate the great vessels and the air tube from eaeh other. Whilst attempting this, he will find that his work is greatly impeded by the hardened and pigmented bronehial glands. The relative positions of the eonstituent parts of the roots of the lung have been noted already (p. 22).

The Belations of the Boots of the Limgs. — Anterior to the root of eaeh lung are the phrenie nerve, with its aeeompanying vessels, and the anterior pulmonary plexus ; behind it, the posterior pulmonary plexus, and below it, the ligamentum pulmonis. In addition, in front of the root of the right lui

44

THORAX

is the superior vena cava, aiid above and behind it, tlie vena azygos. Whitst above the root of the left lung is the aortie areh, and behind it, the deseending aorta (Figs. la and 13). Bronehi. — There are two primary bronehial tubes, one for eaeh lung. They spring froni Ihe lermination of the traehea, and eaeh passes downwards and laterally, in the root of the eorresponding lung, to the hilus, througb wbieh it enters the lung. After passing through the hilus it deseends, in the substanee of the lung, to ihe base, lying nearer the posterior than the anterior border. In the root of the lung the brouehus is erossed anteriorly by the pulmonary artery,

whieh afterwards deseends on the postero-lateral aspeet of the intra-pulmonary part of the bronehial tube.

The relations of the bronebi are eonsidered later (p. 96).

The MediaBtmum and its Contents. — It has been pointed out already that the raediastinum is the interval whieh extends froni the sternum to the vertebral eolumn between the two pleural saes ; that it is oeeupied by some of the most important yiseera, vessels and nerves in the body, i.e. the heart endosed in the perieardium ; the aorta and its great branehes ; the great vessels whieh earry the blood to and from the beart ; the eesophagus and traehea ; the vagi and phrenie nerves; and ihe thoraeie duei. It was

THORAGie CAVITY

45

noted furlher that the nriediastinuiii is separated, for deserip- tive purposes, into two main parts, the superior and the inferior mediastinum, by an imaginary plane whieh passes from the lower border of the tnanubrium anteriorly to the

in of the Anlerior P«tl eostal eartilages were replaeed in posit made. The rigtil sealenus ai Ihe level of the upper border of Ihe !

away from il

lower border of the fourth thoraeie vertebra posteriorly ; it has been noted also that the inferior mediastinum is separable into three parts: (i) the anterior mediastinum, anterior to the perieardium, (a) the posterior mediastinum, posterior to the perieardium, and (3) the middle mediasttnum oeeupied by the perieaidium, the heart, the great vessets immediately adjacent

46 THORAX

to the heart, and the phrenie nerves with their aeeompanying yessels. These seetions of the mediastinum and their eon- tents must now be examined in detail.

Disseetion. — The remains of the anterior part of the mediastinal pleura must be divided longitudinally immediately posterior to the sternum, from the lower end of the thorax to the apiees of the pleural saes. The sternal extremities of the first ribs must be then eut through, elose to the manu- brium sterni, and, at the same time, the sternal heads of the stemo-mastoid museles must be separated from the manubrium, if that has not already been done by the disseetor of the head and neek. After the sterno- mastoid museles and the first ribs are divided, the sterno-hyoid and stemo- thyreoid museles must be eut through transversely, as elose to the upper margin of the manubrium as possible. Next, the body of the sternum must be separated from the xiphoid proeess and the tips of the seventh eostal eartilages. The sternum with the attaehed eostal eartilages may then be removed and plaeed aside, but it must be carefully preserved for future use.

When the sternum is removed the mediastinum is exposed from the front. As seen from the front, the superior mediastinum, whieh lies posterior to the manubrium, is a relatively wide triangular area, with its apex below. The anterior mediastinum, on the other hand, is merely a narrow cleft between the adjacent anterior margins of the pleural saes, except opposite the anterior end of the left fifth eostal eartilage where the left pleural sae deviates slightly to the left and the anterior mediastinum beeomes slightly wider (Fig. 20).

The anterior parts of both the superior and the anterior mediastina are oeeupied by areolar tissue in whieh, as far down as the third or fourth eostal eartilages, remains of the thymus gland niay be found.

Thymus. — The thymus gland is a bilobed organ, developed from the third yiseeral clefts. It is well developed in the foetus and in the ehild until the end of the seeond year. Then it frequently undergoes atrophy, but it may persist even until old age.

Disseetion. — All the remains of the mediastinal pleura and the thymus gland should now be taken away, and the anterior surface of the perieardium and the eontents of the superior mediastinum should be thoroughly eleaned. When this has been done the right and left innominate veins and their tributaries will be exposed. The innominate veins should be traeed to their union with the superior vena cava. To the left of the superior vena cava and below the left innominate vein lie the upper part of the aseending portion of the aorta, and the anterior part of the aortie areh. When these eontents of the upper part of the mediastinum have been thoroughly eleaned, the various struetures found in the mediastinum must be studied in detail.

Venae Anonymse. — The innominate vein of eaeh side is formed posterior to the sternal end of the eorresponding clavicle by the union of the internal jugular and subclavian veins of the same side, and it ends, at the lower border of the right first eostal eartilage, by uniting with its fellow of the opposite side to form the superior vena cava.

The right innominate vein is short and its eourse is

THORAGie CAVITY

47

almost vertical, It is aeeompanied on its medial side by the innominate artery, on its lateral side by the righl phrente nerve, and posterioriy by the right vagus nerve. Antero-laterally it is in relation with the anterior margin of the right pleura. The kft innominate vein is mueh longer than the right

\e nvemge adult.

It passes obliquely to the right and downwards, posterior to the upper half of the manubrium sterni ; it lies posterior to the re- inains of the ihymus glandandthe lower ends of the sterno-hyoid and thyreotd museles, and anterior to the three great branehes of the aortie areh and the left phrenie and vagus nerves.

Tributaries. — These are (i) the internal jugular vein, (2) the subclavian vein, (3) the yertebral vein, (4) the internal mammary vein, and frequently (5) the inferior thyreoid vein

48

THORAX

of the same side. In addition, the right innominate vem receives the right lymph duet, or lymph vessels from the head and neek, the upper extremity and the right half of the thoras of the same side ; and the left innominate vein receives (a) the lefi superior intereostal vein, (i) some peri- eardiae and thymie veins, and (i^) the thoraeie duet.

Disue/iiin.—AtleT the innominate veins and their tributaries have been studied the left vein may be pushed aside, or, ir neeessaiy, it may be eut

n order to display the thtee great branehes of the areh

^rsi'!

Arteria Anonyma, — The innominate artery is the largest of the three great branehes of the aortie areh. It eom- menees, from the upper border of the areh, posterior to the eentre of the manubrium, passes upwards and to the right, and terminates, posterior to the upper border of the right sterno- clavicular artieulation, by dividing into the right eommon earotid and ihe right subclavian arteries. Anterior to it are the manubrium sterni, with ihe attaehments of the sterno- hyoid and thyreoid museles, the right sterno-elayieular jo!nt, the remains or the thymus gland, and the left innominate vein.

THORAGie CAVITY 49

Posterior to its lower part is the traehea, but as the artery passes upwards and to the right it gains the side of the traehea and has the upper part of the lung and pleura posterior to it. To its left, at its eommeneement, is the left eommon earotid artery, and at a higher level the traehea. On its right side is the right innominate vein, whieh separates it from the right phrenie nerve and the pleura. As a rule it gives off its terminal branehes only, but oeeasionally a small artery, ealled the thyreoidea ima^ springs from it

The Thyreoidea Ima.— This artery is frequently absent. When it is present il springs from the innominate artery, or from the areh of the aorta, and runs upwards, anterior to the traehea, to the thyreoid gland.

Arteria Oarotis Gominanis Sinistra. — The left eommon earotid artery springs from the areh of the aorta immediately to the left of, and slightly posterior to, the innominate artery. It passes upwards, through the superior mediastinum and posterior to the left sterno-clavicular joint, into the neek. Its anterior relations in the thorax are similar to those of the innominate artery. Posterior to it^ from below upwards, are the traehea, the left reeurrent nerve, the oesophagus and the thoraeie duet, and, on a plane somewhat more to the left, the left phrenie and vagus nerves, and the subclavian artery. To its right lie iirst the innominate artery, and then the traehea \ and to its left is the left pleura. It gives off no branehes in the thorax.

Arteria Subclavia Sinistra. — The left subclavian artery springs from the posterior part of the aortie areh, posterior to the left eommon earotid. It passes vertically upwards, through the superior mediastinum and posterior to the sternal end of the clavicle, into the root of the neek. Anterior to it are the left phrenie and vagus nerves, whieh separate it from the left eommon earotid artery. Posterior^ and to its left side, it is in relation with the left mediastinal pleura and the lung. To its right side are the traehea and the left reeurrent nerve, and, at a higher level, the eesophagus and the thoraeie duet. It gives off no branehes in the thoraeie part of its eourse.

Disseetion, — The lateral walls of the perieardium have already been exposed and opened (see p. 33) ; the flaps then made should be replaeed and fixed in position. When this has been done, the outline of the sae will be fully displayed, and the disseetors ean then study its relations to adjacent organs.

YOL. II — 4

So THORAX

The Perieardium. — This is a Abro-serous sae whieh oeeupies the middle mediastinum. It surrounds the heart and the roots of the great vessels whieh enter and leave the heart.

TTie Fibrous Perieardium, — The fibrous or outer part of the perieardium is eonieal in form. Its base rests upon the diaphragm, prineipally on the eentral tendon but also upon the museular portion, partieularly upon the left side. Near the median plane it is blended with the eentral tendon, and ean be separated from it only by the aid of the edge of the sealpel; more laterally the areolar tissue whieh eonneets the perieardium and the diaphragm is easily broken down by the handle of the knife. The diaphragm separates the perieardium mainly from the upper surface of the liver, but also, towards the left and anteriorly, from the fundus of the stomaeh. The apex of the fibrous sae blends with the outer eoats of the aorta, the pulmonary arteries and the superior vena cava. The anterior su?face lies behind the body of the sternum and the eartilages of the ribs from the seeond to the sixth inclusive, but it is separated from them by the lungs and pleurae, except (i) in the median plane of the anterior medi- astinum, where eondensations of the areolar tissue of the medi- astinum, ealled the superior and inferior sterno-perieardiae ligaments^ eonneet the anterior surface of the fibrous sae to the upper and lower ends of the body of the sternum respectively, and (2) in the region of the sternal extremity of the left fifth eostal dartilage, where the left pleura retreats somewhat towards the left side, and the perieardium eomes into direet relation with the sternum and the left transversus thoraeis musele. This portion of the perieardium is the so-ealled bare area. It is usually of small extent, and frequently it does not extend beyond the margin of the sternum, but it is of importanee beeause through it the surgeon attempts to tap the perieardium when the sae is distended with fluid.

The lateral walls of the perieardium are in relation with the mediastinal pleura, the phrenie nerve and the perieardiaeo- phrenie vessels intervening (O.T. eomes nervi phreniei). The posterior surface lies anterior to the deseending aorta and the oesophagus medially, whilst laterally it is supported posteriorly by the lungs and pleurae. At the junction of the upper parts of the lateral and posterior surfaces, on eaeh side, two pulmonary veins enter the perieardium and receive sheaths from its fibrous wall.

THORAGie CAVITY

S'

Dissediim. — When the relationa and prolongations of ihe tibrous peri- eaidium have been studied, the two anterioi fUps already made in the liteial walls oF the sae (see p. 33) shouhl be eonneeted ((^ethei and eon- vetted into one large aDterioi flap. This ean be done by a liansverse eut, passing aeioss the median plane jus( above (he diaphragm. The large

(riangulai tlap thus forn

Sould be (hrown upwards towards ihe apcx of

7(fe Serous Perieardium. — The serous perieardium is a elosed and invaginated sae whieh iines the inner sutface of the fibrous sae and envelops the heart and the roots of the great vessels passing to and froin the heart.

The uninyaginated portion of the wall of the serous sae,

5»

THORAX

whieh lines the inner surface of the Abrous saCj is ealled the parietal layer, and the invaginated portion, whieh enveiops the heart, is the visceral portion. The inner surface of the sae is lined by a iiat endothelium, and, during health, is smooth and

-The Perieardiiim ani having been opened by ihe

if the Hearl. The thorade injeclion, Ttie perieardium lerior wall, the gteat yessels

glistening. The parietal and visceral layers are separated, during health, merely by a thin layer of serous fluid, whieh prevents friction between the two suriaees as they move over eaeh other during the eontraetions and expansions Df the beart.

THORAGie CAVITY 53

The Stemo-eostal 8iirilftce of the Heart. — B€fore the disseetors disturb the heart, whieh- has been exposed by the reflection of the anterior wall of the perieardium, they should note carefully not only the parts of the heart whieh are visible, but also their relations to the anterior wall of the thorax. The latter they ean easily do by replaeing the sternum and eostal eartilages in position from time to time.

They will find that the stemo-eostal surface is divided into an upper, right, or atrial portion and a lower, left, or ventricular portion by an oblique suleus, the eoronary su/eus (O.T. auriculo-ventricular\ whieh is quite distinet below and on the right, but is masked above and to the left by the roots of the pulmonary artery and the aorta. The position of this suleus ean be indieated on the surface by a line extending obliguely downwards and to the right, from the sternal end of the third left to the sternal end of the sixth right eostal eartilage. Below and to the left of the suleus is the ventricular part of the sterno-eostal surface, termi- nating on the left and below in the apex of the heart, whieh lies posterior to the fifth left intereostal spaee, three and a half inehes from the median plane. The ventricular area of the sterno-eostal surface is divided by the anterior longitudinal suleus (O.T. anterior interventricular suleus) into a right two-thirds, formed by the right ventricle, and a left third, formed by the left ventricle. The anterior longitudinal suleus terminates on the lower border of the sterno-eostal surface, to the right of the apex, in a slight noteh, the ineisura eordis. The apex, therefore, is formed entirely by the left ventricle. The lower margin of the stemo-eostal surface lies on the diaphragm. It is formed chiefly by the lower border of the right ventricle, and only to a small extent by the apieal part of the left ventricle.

The upper and right portion of the sterno-eostal surface is formed by the atria, whieh are to a large extent eoneealed by the pulmonary artery and the aseending part of the aorta. Above and to the right is the right atrium, eontinuous above with the superior vena cava and below with the inferior vena cava, whilst its aurieular portion (O.T. aurieular appendage) curves upwards and to the left, along the line of the eorona suleus, to the root of the pulmonary artery.

Grossing the front of the right atrium, immediately b the lower end of the superior vena cava, is a suleus, the s

54

THORAX

terminalis. If the heart is pulled a little over to the left this suleus ean be traeed downwards, along ihe lateral aspeet of the right atriuni) to the anterior aspeet of the upper end of the inferior vena cava. It indieates the separation belween

KiBhlee	inunaa e.iiotid «rlery	L.ftcominoii(ar<
;<>rriEh[im	«mal iuEular vfln ,	BndoeitdiT
' Rigb. su		, U(. i<A«V
Righ,.ulxL	ivLiii>tin ;	L-:fli

FiG. 25. — Disseeti

ihe venous sinus of the atrium, into whieh the great veins open, and the cavity of the atrium proper.

The whole of the right border of the heart is formed by the right atrium. Its positton ean be indieated on the surface by a line, convex to the right, whieh eommenees at the level if the ihird right eostal eartilage, half an ineh from the

THORAGie CAVITY 55

sternum, and terminates opposite the sixth right eartilage at the same distanee from the right margin of the sternum. At the ugp^er and left eorner pf the atrial area is the apex of the left auriele (O.T. aurieular appendage), and between the two auncles~are the roots of the pulmonary artery and the aorta, the former anterior to the latter. The rounded portion of the upper part of the right ventricle, immediately below the pulmonary artery, is the eonus arteriosus,

If a finger is introdueed into the cleft between the aorta anteriorly and the superior vena cava posteriorly, it ean be passed aeross, froni the right to the left side of the perieardial cavity, through a passage, ealled the iransverse sinus of the perieardium (Figs. 24 and 27). This sinus lies anterior to the superior vena cava and the atria, and posterior to the aseending aorta and the stem of the pulmonary artery. The upper border of a finger plaeed in the sinus will indieate the position of the upper border of the heart. This border is formed to a slight extent by the upper border of the right atrium, but mainly by the upper border of the Jeft atrium. Its position ean be in- dieated, on the anterior surface of the body, by a line eom- meneing half an ineh from the side of the sternum at the lower border of the seeond left eostal eartilage, and ending at the same distanee from the sternum on the upper border of the third right eartilage. Whilst a finger is kept in the transverse sinus a pointer should be introdueed into the right pulmonary artery through its eut end in the root of the right lung. The disseetor will note, as the pointer traverses the right pulmonary artery, that it passes first posterior to the superior vena cava and then along the upper border of the transverse sinus, that is along the upper border of the heart where that border is formed by the left atrium ; therefore the position of the right pulmonary artery may be indieated, on the anterior surface of the body, by the right two-thirds of the line whieh marks the position of the upper border of the heart.

The left border of the anterior surface of the heart is formed, to a slight extent, by the left atrium, but mainly by the left ventricle. It is convex to the left and its position is marked, on the surface of the body, by a line whieh eom- menees above at the lower border of the left seeond eostal eartilage, half an ineh from the sternum, and terminates b at the apieal point in the fifth left intereostal spaee.

Before proeeeding further the disseetor should s»

56 THORAX

the information he has gained regarding the relationship of the apex of the heart and the borders of the sterno-eostal surface of the heart to the anterior wall of the thoraK, The upper border is formed by the atria, and as the heart lies in situ it is eoneealed to a great extent by the aorta and the

a C1avic1> LA. Leftal LV, Ltflw

Puloionary ot Righlalrium. lUehl venliic

pulmonary artery, Its position is marked on ihe surface by a line extending frora the lower border of the seeond left to the upper border of the third right eostal eartilage, eommeneing and terniinating about lialf an ineh from the border of ihe slernum. The righl bordtr is foriiied entirely by the right atrium, and its position is indieated on the sur-

THORAGie CAVITY 57

face by a line, convex to the right, eommeneing above at the lower border of the right seeond eostal eartilage, half an ineh from the side of the sternum, and terminating below at the sixth right eartilage half an ineh from its junction with the sternum. More than two-thirds of the lower border are formed by the right ventricle, and the remainder by the apieal portion of the left ventricle, and the two parts may be separated by a distinet noteh, the indsura eordis. This border is slightly concave downwards, in eorrespondenee with the upward convexity of the diaphragm on whieh it rests, and it has a slight inelination downwards and to the left. It is marked, on the surface of the body, by a line extending from the sixth right eostal eartilage, near the sternum, to the apieal point, whieh lies in the left fifth intereostal spaee from 3^ to 3I inehes from the median plane. The left border, whieh is formed mainly by the left ventricle and only to a slight extent by the left atrium, extends from the apex to a point on the lower border of the left seeond eostal eartilage half an ineh from the margin of the sternum.

The eoronary suleus, whieh indieates the plane of union

of the atria and ventricles and, therefore, the plane of the

atrio-ventricular and aortie and pulmonary orifices of the

heart, ean be indieated, on the surface, by a line extending

from the sternal end of the third left eostal eartilage to the

sternal end of the sixth right eartilage. Posterior to the left

extremity of this line, at the level of the upper part of the

third left eostal eartilage, is the orifice of the pulmonary artery.

The aortie orifice is a little lower and slightly to the right,

posterior to the sternum at the level of the lower border of the

third left eartilage. Immediately below the aortie orifice,

posterior to the left margin of the sternum, at the level of the

upper part of the fourth left eartilage, lies the mitral orifice ;

and the trieuspid orifice is situated posterior to the middle of

the sternum, opposite the fourth intereostal spaees. The

positions of the great orifices eannot be confirmed at this

stage of the disseetion, and they will be noted again at a

later period when the heart is opened.

After the sterno-eostal aspeet of the heart, the boundaries of the transverse sinus, and the general position of the heart have been studied, the disseetors should turn the apex of *' heart upwards and to the right, and examine the in< and posterior surfaces whilst the heart is still in situ.

56 THORAX

the mformation he has gained regarding the relationship of the apen of the heatt and the borders of the sterno-eostal surface of the heart to the anterior wall of the thoraK. The upper bordtr Is formed by the atria, and as the heart lies in situ it is eoneealed to a great extent by the aorta and the

pulmonary artery. Its position is marked on the surface by a line extending from the lower border of the seeond lert to the upper border of the third right eostal eartilage, eommeneing and terminating about half an ineh from the border of the sternum. The righi border is foriiied entirely by the right atrium, and its position is indieated on the sur-

THORAGie CAVITY 57

face by a line, convex to the right, eommeneing above at the lower border of the right seeond eostal eartilage, half an ineh from the side of the stemum, and terminating below at the sixth right eartilage half an ineh from its junction with the sternum. More than two-thirds of the lower border are formed by the right ventricle, and the remainder by the apieal portion of the left ventricle, and the two parts may be separated by a distinet noteh, the indsura eordis, This border is slightly concave downwards, in eorrespondenee with the upward convexity of the diaphragm on whieh it rests, and it has a slight inelination downwards and to the left. It is marked, on the surface of the body, by a line extending from the sixth right eostal eartilage, near the sternum, to the apieal point, whieh lies in the left fifth intereostal spaee from 3^ to 3j inehes from the median plane. The left border, whieh is formed mainly by the left ventricle and only to a slight extent by the left atrium, extends from the apex to a point on the lower border of the left seeond eostal eartilage half an ineh from the margin of the sternum.

The eoronary suleus, whieh indieates the plane of union of the atria and ventricles and, therefore, the plane of the atrio-ventricular and aortie and pulmonary orifices of the heart, ean be indieated, on the surface, by a line extending from the sternal end of the third left eostal eartilage to the sternal end of the sixth right eartilage. Posterior to the left extremity of this line, at the level of the upper part of the third left eostal eartilage, is the orifice of the pulmonary artery. The aortie orifice is a little lower and slightly to the right, posterior to the sternum at the level of the lower border of the third left eartilage. Immediately below the aortie orifice, posterior to the Ieft margin of the sternum, at the Ievel of the upper part of the fourth left eartilage, lies the mitral orifice ; and the trieuspid orifice is situated posterior to the middle of the sternum, opposite the fourth intereostal spaees. The positions of the great orifices eannot be confirmed at this stage of the disseetion, and they will be noted again at a later period when the heart is opened.

After the sterno-eostal aspeet of the heart, the boundaries of the transverse sinus, and the general position of the heart have been studied, the disseetors should turn the apex o^ heart upwards and to the right, and examine the and posterior surfaces whilst the heart is still in sit

6o THORAX

examination of the yense cavae will show that the lower ineh of the superior vena cava lies within the fibrous perieardium and that it is ensheathed, except along its postero-medial border, by a covering of the serous layer, whilst the inferior vena cava ean seareely be said to have any intra-perieardial eourse, for it joins the lower and posterior part of the right atrium immediately after piereing the fibrous layer, but the margin of the orifice by whieh it enters is surrounded by the serous layer except along a narrow Hne posteriorly. The left pulmonary veins are covered by the serous layer on their superior, anterior, and inferior aspeets, but not posteriorly; and the right pulmonary veins, whieh enter the left auriele as soon as they have piereed the fibrous perieardium, are in rela- tion with the serous layer merely along the medial and lateral borders of the orifices in the fibrous layer through whieh they enter.

Disseetion. — After the examination of the reflections of the serous layer of the perieardium is eompleted, the disseetors should study the vessels and nerves whieh supply the walls of the heart. They are the eoronary arteries and the eardiae veins and nerves, and they lie in the eoronary and longitudinal sulei of the heart, whieh have been noted already. To display them the visceral perieardium superficial to them must be eut and turned aside, the fat whieh lies in the sulei around the vessels must be removed, then the main vessels ean be traeed to their origins and terminations, and an endeavour should be made to preserve the fine nerves whieh aeeompany the vessels.

ArteiisB Coronaxise. — The eoronary arteries are the nutrient vessels of the heart. They spring from dilatations of the eom- meneement of the aorta whieh are ealled the sinus aortee (Valsalva). There are three sinuses of the aorta, an anterior and two posterior, and only two eoronary arteries, a right and a left ; the right artery springs from the anterior sinus, and the left from the left posterior sinus.

The right eoronary artery passes anteriorly from the anterior aortie sinus, between the pulmonary artery and the right auriele ; turns downwards and to the right, in the eoronary suleus, to the lower part of the right margin of the heart, round whieh it curves. Then it proeeeds to the left, in the posterior part of the eoronary suleus, till it reaehes the posterior end of the inferior (posterior) longitudinal suleus, where it divides into a small transverse and a large interventricular braneh. The transverse braneh eontinues to the left till it anastomoses with the circumflex braneh of the left eoronary artery. The interuentrieular (deseending) braneh runs anteriorly in the

THORACIC CAVITY 6i

inrerior longitudinal suleus on the diaphragmatie surface of the heart, and it anastomoses with the intcrvcntriculaT or deseending braneh of the left eoronary artery at the eardiae noteh on the lower margin of the heart. In addition to iis terminal branehes, the right eoronary artery supplies branehes to the roots of the pulnionary artery and ihe aorla, and to

of riahl eortpnary ortery

FiG. 28.— The Base of the Ventricular Pan of ihe Htarl from whieh the Airia have been remoi«d. The detaehed atria are depieted in Fig. 31. The speeimen was hardered i'b sila.

the walls of the right atriuni and the right ventricle, the larger and more nuinerous branehes being given to ihe ventricle. One of the latter, the marginai braneh^ passes along-the lower margin of the heart towards the apex of the ventricle (see Fig. 29).

The , ltft eoronary artery, as it springs from the left posterior aortie sinus (Fig. 28), lies posterior to the pulmonary artery. For a short distanee it nins to the !eft, then it tums anteriorly, between ihe pulmonary artery and the Ieft auriele,

62 THORAX

aiid diyides into a deseending or interyentrieular, and a circumflex braneh. The inUrventricular branek passes down the sterno-eostal surface of the heart, in the anterior longitudinal suleus (Fig. 29), and turning tound the lower border, in the eardiae noteh, it anastomoses with the inteTventricular braneh

ELghl_

of the right eoronary artery. The circumfiex braneh nins to .theleft, in the eoronary suleus, turns round the left border of the heart (Fig. 28) and anastomoses, on the posterior surface, wilh the transverse terminal braneh of the light eoronary. Prom the stem of the artery twigs are given to the roots of tho pulmonary artery and the aorta, and its terminal branehes 3u[)ply the walls of both ventricles and the_ walls of the left atrium.

Yeiue Goidis. — The eardiae veins are : (i) the eoronary;-

THORAeie CAvrry

<>>

ver

(i) the great eardtae vein ; (3) the inferior (posterior) ventrkular vein ; (4) the iniddle eardiae vein ; (5) the obli(]ue (6) the small eardiae vein; {7) the anterior eardiae and (3) the venfe minimse eoniis. The eoromry sinus lies at the base of the heart, in tlie isterior part of the eoronaiy suleus, between the left atrium 'and the left ventride, It ean be displayed when the apex of the heart is turned upwards and lo ihe righl. Its righl eKtremity opens into ihe right atrium, immediately below and to the left of the oriliee of tlie inferior vena cava, At its lefl

ihe Surtaee of the

extremily it reeeiyes the great eardiae vein. The greal eardiae vein aseends along the anterior longitudinal suleus (Fig. 29), where it lies in relation with the interventricular braneh of the left eoronary artery. Al the upper end of the interventricu]ar suleus it turns round the left border of the heart, with the circuinflex braneh of the left eoronary artery, and it ends in the left extremity of the eoronary sinus. The inftrior (posterior) ventriatlar vein or yeins, from the diaphragmatie surface of the left ventricle, and the middle (ardiae vein, whieh mns posteriorly in Ihe inferior longitudinal suleus, end in the T border of the eoronary sinus. The oblique vein deseends

l^^runs poste l^^^bwer bord

64

THORAX

on the posterior wall of the left atriuni and ends in the upper border of the sinus; and the small eardiae vtin (O.T. right eoronary) runs along the lower margin of the heart with the marginal braneh of the right eoronary artery, curves rourtd the right border of the heart, in the eoronary suleus, ends in the right extreniity of the eoronary sinus. The anterior eardiae

iHeeliun Df seruus perkardiun

FiG. 31.— The Amei

s depieled in Fig. 28. The speeini

veins are small vessels whteh aseend along the anterior surface of the right ventricle and terminate direetly in the lower aod

anterior part of the right atrium. The ventt eordis minima are small veins whioh pass from the substanee of the heart, and more partieularly from the walls of the right atrium and ventricle, and open, by small oriliees, into the cavity of the right atrium. Tlie orifice through whieh the great eardiae vein opens into the eoronary sinus is usually provided with a valve ; the orifice of the small eardiae vein may be provided

J

Oardia-: N

T - .

*■ •;

» '_

_ -j' _i • >«

* ~ ■ ^ ■

r.r. r_'c:

XI •^.... ........

•^ -r • ^

l r '■■"'• -s ~ r»x ••--*-

.'. ■ ...■--. ^ * " i_r V * " • • • . ; . • .

'"•- ,_,..- ••.•r»*;v.*'"

a.,:.... .- ■ .-^ V-' ^ Tav *-. >:-- " V- * •

lir.: :-r:r "■ r.5 .■..-i-;"' . ■^- i •

■wr. So.

Atrium Dextrum ( O.T Bight Aunele . <.;...:: atrium bv means of the fo.^.wKig .n.:>: .... I.: :.: a: the apex of the aune.e (0. 1. aur!..-^..ir u: :.-::: ■,

thesuleus terminalis and thruugh the Iatera;_w.:.. = ! :

to ihe posterior

border of the lower up.d nf ti.e cavv then downwards, posterior to ihe sUi.:i> tcr::.:s... . •

■ .' : « r-rivi • and finallv anteriorlw aemsr, thv '. a •

mferior vena ca\a . "*,.,- . •' .

0' the .suleus terminahs and above the anterior a^pt. : : : lower end of the inferior vena cava, to the o..r..:iary s,: r Throw the Aap thus formed anteriorly, and elean the ::!ivr:.>r of the cavity ^vith a sponge.

. , Aap is turned anteriorly a vertical museular ! i::Klle will be noted on its inner surface. This is the eristn hrniituilis^ whieh eorresponds in position with the suleus tL-rnii^^a'.is un the outer surface. It marks the boundary betweLU ihe

« ^ • «oi-t the atrium, and the posteriur part, whieh anterior part, lh*- > ^ r i ,

is k own as the venous smus beeause the great vein.s ol You n — 6

66

THORAK

the body and heart open into it. These two parts of the cavity differ, however, not only in position and their relations to the great yeins, but also in the eharaelers of their walls. The whole of the interior of the atrium presents a polished glossy appearanee, due to the endoeardial lining; but whilst the wall of the venous sinus is smooth, the rest of the wall of the atrium is rendered rugose by a large number of museular ridges

whieh eommenee at the erista terminalis and run anteriorly to the right margin of the atrium. These bundles, on aeeount of their somewhat parallel arrangement, are ealled the museuli pietinali.

The veins whieh open into the right atrium are the (i) superior vena cava, (2) inferior vena cava, (3) eoronary sinus, (4) anterior eardiae veins, and (5) venK eordis minimte. The aperture by whieh the blood leaves it is the trieuspid orihee.

The orijice of the superior vena (ava is in the upper and posterior part of the atrium, at the Ievel of the tliird right eostal

THORAGie CAVITY

67

eartilage. It is entirely devoid of any valvular arrangenienl, Immediateiy below it on the posterior wall of the atrium, in a well-lixed heart, will be found a rounded prominenee, t?u intervenous tubtrek (Lower), whieh tends to throw the

FiG. 33.— Sagittalst

stream of blood entering the atrium by Ihe superior vena cava downwards and anteriorly into the atrio-ventricuIar orifice. The orifice of the inferior vma cava is in the lower and posteriorpartoftheatrium, at the level ofthesixth right eostal eartilage and the lower border of the eighth thoraeie vertebra. Running along its anterior margin, and intervening between it and the atrio-ventricular opening, is the remnant of a valve, the valve qf the vena cava (Eustaehian). It terminates, to the left, in the lower end of a museular ridge, limbus fosne ova!is

(O.T. annulus malis), whieh lies on the inter-atrial septum and forms the anterior and upper boundary of a shallow fossa, the fossa twalis. At the upper end of this fossa there

was, during fcetal life, a forainen, the/e^

<ivak, through whieh the two atria eommunieatedwith eaeh other, The object of the valve of the vena cava, whieh in fcetal life was mueh more perfect, was to di- reetthe oxygenated inferior caval blood through the fora- men ovale into the left atrium, whenee it was passed into the !eft ventricle, and was then dis- tributed, by the aorta, throughout the whole system.

During fcetal life it would have been use- less to pas5 the blood through the lungs.

»hichw<

FiG. 34.

df:void of air. At the een by ihe same time, had the waii, or inat wall op- ox)^enated blood been of ihe Yentrieles. This is passed through the e speeimen ihal is depieled right atrium mto the in pig. 31. tight ventricle, it would

have faileti to reaeh the heod and the upper extremities, for, leaving the right ventricle liy Ihe pulmonary artery, it would have enlered the aorta through the duetus arteriosus beyond the origin of the left subclavian atlery and, thereibre, beyond ihe innominate and leri eommon earolid a.rteries.

In many eases a small part of the foramen ovale persists in the adult If it is present it will be found on the left of the upper euryed end of the Umbus ovalis.

The opening of the eoronary sinus Hes to the left of the lower end of the hmbus ovalis and direetly posterior to the trieuspid oriliee. On its right margin lies a valvu]ar fold, the va!ve of

THORAGie CAVITV 69

the eoronary stnus (O.T, Thebesian)^ whieh tums ihe Mootl, Aowing from lert to right in the sinus, anteriorly Inlo tht' atrio- ventricular orifice. The venK minimae eordis and ihe anierior eardiae veins open direetly into ihe alriuni hj- small orillees seattered irregularly over the walls.

The Irieuspid orifice is in the lower and anterior lOTi of the atrium. Il opens anteriorly inlo the lower and i>osicriur [lart iif the cavity or the right ventricle, and is sufficieni1y large to admit the tips of three Angei^ It is boundL-d by a fil>rous ring to whieh the eusps of the righl atrio-vcntricular valve are attaehed. These eusps will bc esamined when ihu righl ventricle is opened.

■ough Ihe L'pper 1

Tlie Septnm Atriornin ajid the Fobu Oralis. — The inier-

atrial septum is a fibro-muscular partition whieh intervenes between the right and ieft atria. In the fcetus it is piereed by an obliquely direeted foramen, the foramen ovale, already reterred to ; and in the adult it is marked on the lower and posterior part of its right side by a shatlow depression, the/ossn ovalis, whieh is bounded anteriorly and above by a museular ridge, the limbus ovalis, whilst below and posteriorly it fades away into the orifice of the inferior vena cava.

The floor of the fossa ovaIis is very thin ; it marks the situation of the lower part of the foramen ovale of the fcetus, and is formed by a portion of the inter-atrial wall whieh, during fcetal life, aeted as a flap valve and prevented regurgi- tation of blood from the lefl to the right atrium.

The Vena OaTO Saperlor. — The superior vena cava returns to the right atrium the blood from the bead and neek, the

70 THORAX

upper extremities, the wall of the thorax, and the upper parts of the walls of the abdomen. It eommenees, by the union of the right and left innominate veins, at the level of the lower border of the sternal end of the right first eostal eartilage ; and it terminates, in the upper and posterior part of the right atrium, at the level of the right third eostal eartilage, about half an ineh from the right border of the sternum. It lies partly in the superior and partly in the middle mediastinum, and its lower half is within the fibrous perieardium and is partly ensheathed by the serous perieardium.

Tributaries. — The tributaries of the superior vena cava are the two innominate veins, by whose junction it is formed, and the vena azygos, whieh enters it immediately before it pierees the fibrous perieardium, at the level of the seeond right eostal eartilage.

Relations. — The superior vena cava lies to the right of, and somewhat posterior to, the aseending aorta. Posterior to its upper part are the right pleura and lung on the right, and the right vagus and the vena azygos on the left, and, at a lower level, the right bronehus, the right pulmonary artery, and the upper right pulmonary vein. Anteriorly and on the left it is overlapped by the aseending aorta, and on the right by the right pleura and lung. On its left side above is the lower end of the innominate artery, and below is the aseending aorta ; and on the right side is the right pleura, with the right phrenie nerve and the aeeompanying vessels intervening.

The Thoraeie Part of the Iiiferior Vena Cava. — Only a small portion, about three-quarters of an ineh, of the inferior vena cava is found in the thorax. It aseends from the diaphragm along the mediastinal surface of the right pleura and lung, pierees the perieardium anterior to the lower border of the right ligamentum pulmonis, and immediately ends in the lower and posterior angle of the right atrium.

Relations. — Anterior to it is the diaphragm ; posterior to it the vena azygos, the splanehnie nerves and the thoraeie duet ; and to its right the phrenie nerve with its aeeompanying vessels and the right pleura and lung (see Fig. 12).

Yentrieulus Dexter. — The cavity of the right ventricle should be opened by three ineisions. The first should be made transversely aeross the upper end of the eonus arteriosus, immediately below the eommeneement of the pulmonary artery. It should begin a little to the right of the upper

THORAGie CAVITY

71

end of the anterior longitudiiul suleus and terminate a little to the left or the eoronary suleus. The seeond must eommenee at the right end of the first and pass obliqucly downwards and to the right, along the left margin of the eoronary suleus, to the lower border of ihe heart, The third eommenees at the lefl end of the first, follows the line of the aiiterior tnter-ventricular suleus, lying a little to its right side.

FiG. 36.

ofthe Right Vtn

and also terminates at the lower margin of the heart. After the triangular flap thus formed is turned downwards and lo the right, the cavity of the ventricle should be eleaned with the aid of sponge and forceps. If the moderator hand of musele fibres, whieh eonneets the anterior wall of the ventricle with the inter-ventricular septum, interferes with the neeessary displaeement of the flap, it must be divided.

The cavity of tbe right ventricle has a triangular outline. The atrio-ventricuiar orifice opens into the lower and posterior angle, the pulmonary artery springs from the upper and

la THORAX

anterior angle, and between the two orifices is a strong and rounded museular ridge, /Af supra-ventricular ridge. This projects into the cavity eonyerting it into a U-shaped tube whieh eommenees posterior to and below the supra-ventricular ridge, runs anteriorly and to the left, towards the apex, and turns upwards and anteriorly, along the anterior part of the inter-ventricular septum and anterior to the supra-ventricular rid^e, to the oriliee of the pulmonary artery.

On transverse seetion the cavity of the right ven tnele is semilunar in outline in consequence of ihe thiek I ' '^^^^^^ X.ik inter ventricular septum,

i^^^^H^ B^ ^^hii.h forms the left and '^^■■pp' ^Kk. postenur wall bulging mto ■^ "^^^ ^ml. \\ the e-i^ity (Fig 37) Its

walls are mueh thieker than the walls of the right FiG 37 -Transierse seeiion thtoueh ^trium but much thinner

Ihe Yentrieular Pan of the Hearl than the walls of the left seen froni ahove. ( Prom Lusehka, ) ventricle (Fig. 41). The

I. C»viiyofright™nrkk. reason for these differences

». Cavity of leik «nirieie. is obvious : the auride has

4! 'i^ick"w^rfwiveinrid= merely to force the blood

5. ThiDnerwaiiofrithtvemricie. through the wide atrio-

6. inisTior lungiiudinni (inisr.ven- ventricular orifice into the

v.in and inferior braneh of righi '"'g"^ ventricle, and the nght eotonary attery. ventricle has only to send

j, Anler™ longiiudlnal (inWr-ven- (l,g blood thrOUgh the lungS

vein (uid anwtior btaneh "^or M '^ the left atrium ; but the

eoioraiy antry. left ventricle has to (oree

the blood through thewhole

of the body, the head and neek, aod the limbs ; and the

niuseular strenglh of the walls of the cavities of the heart is

proportiona! to the work they have to do.

The portion of the right ventricle whieh aseends to the orifice of ihe pulmonary artery is the eonus arteriosus. Its walls are smooth and devoid of projecting museular bundles, but the inner surface of the walls of the remaining part of the ventricle is rendered extremely irregular by the projeclion of a laee-work of Aeshy ridges ealled irabeeula eamea. Some of the trabeeulK are merely ridges raised in relief upon the

THORAGie CAVITY 73

surface; others are attaehed to the wall at eaeh extremity, but are free in the rest of their extent. The cavity of the ventricle is invaded, however, not only by the trabeeulse earneae, but also by a number of eonieal museular projections, the museuli papillares, These are attaehed by their bases to the wall of the ventricle, whilst their apiees are eonneeted, by a number of tendinous strands, to the margins and the ventricular surfaces of the eusps of the atrio-ventricular valve. As a rule there is one large anterior papillary musele attaehed to the anterior wall, a large inferior papillar)* musele attaehed to the inferior wall, and a number of smaller papillary museles attaehed to the septal wall. Oeeasionally the anterior and inferior museles are represented by a number of smaller projections. It must be noted that the ehordae tendineae from eaeh papillary musele, or group of papillary museles, gain insertion into the margins and ventricular surfaces of two adjacent eusps of the valve. The result of this arrange- ment is, as the papillary museles eontraet simultaneously with the eontraetion of the general wall of the ventricle, that ihe ehordae tendineae hold the margins of the eusps together and prevent them being driven baekwards into the atrium.

One of the trabeeulae earneae, whieh is usually strong and well marked, passes aeross the cavity from the septum to the base of the anterior papillary musele. This is the moderator band, It tends to prevent over-distension of the cavity of the ventricle, by fixing the more yielding anterior wall of the ventricle to the more solid septum.

There is one opening of entranee into the right ventricle, the atrio-ventricular, and one opening of exit, the pulmonary orifice. Eaeh is guarded by a valve.

The right atrio-ventricular orifice lies at the lower and posterior part of the right ventricle, its eentre being behind the middle of the sternum at the Ievel of the fourth intereostal spaee. It is about one ineh in diameter, and is surrounded by a fibrous ring. It admits the tips of three hngers, and it is guarded by a valve possessing three eusps, an anterior, a medial, and an inferior. The anterior eusp intervenes between the atrio-ventricular orifice and the eonus arteriosus. The medial eusp lies in relation with the septal wall ; and the inferior eusp with the inferior wall of the ventricle.

The bases of the eusps are attaehed to the fibrous ring

74

THORAX

rouiid the margin of the orifice. Their apiees, margins, and ventricular surfaces are attaehed to the ehord» tendineje. Their aurieular suriaees, over whieh blood flows as it enters the ventricle, are smooth, and their yentrieular surfaces are more or less roughened by the attaehment of the ehordae tendineae, but the roughening is less marked on the ventricular surface of the anterior eusp over whieh the blood flows as it passes through the eonus arteriosus to the pulmonary oriiiee.

Rue □f mediaTeusp <ff LrieuAiHd

Tht Alrio-vailricular Bundle. — The atrio-ventr[eulat bundle is 3. stnaU bundle of peeuliai musele tibres, of pale eolour, whieh forms tlie only direet museular eonneetion between the walls of tlie atria and Ihe ventricles (see p. 92). To expose this bundle, the antetior part of the medial eusp of the trieuspid vilve must be detaehed from the Sbrous atrio-ventricular ring. When Ihis has been done, the pars membranaeea, or upper tibrous parl of Ihe inter-ventricu1ar septum will be esposed, and ihe atrio-ventricular bundle will be foun<i ninning alone ils posterior and lower border to the upper end of the museular part 0' the septum, where it divides into right and Ieft bcajiches. The right hraneh tuns along the rigbt side of the septum lo the moderalor ^nd, along whieh it passes lo the anterior papillary mltsele. The left braneh passes belween Ihe pars membranaeea

THORAGie CAVITY 75

and the upper end of the museular part of the septum, and then deseends along the left side of the septum. Hoth branehes send oAT numerous rami- fications whieh are distributed to the various parts of the walls of the

ventricles.

The pulmonary orifice lies at the upper, anterior, and left part of the ventricle, at the apex of the eonus arteriosus. Its eentre is behind the third left eostal eartilage immediately to the left of the left border of the stemum, and its margin is surrounded by a thin fibrous ring to whieh the bases of the three semilunar eusps of the pulmonary valve are attaehed

Disseetton. — Note that immediately above its eommeneement the waJl of the pulmonary artery shows three distinet bulgings ; these are the pulmonary sinuses (Valsalva) of whieh two are anterior, and the third is situated posteriorly. Make a transverse ineision aeross the wall of the pulmonary artery immediately above the dilatations, and fr(>m eaeh end of the transverse ineision make a vertical ineision upwards towards the areh of the aorta ; raise the flap so formed and examine the eusps of the valve from above.

Tke Pultnonary Valve, — Eaeh eusp of the valve is of semi- lunar form. Its upper or arterial surface is concave, its lower or ventricular surface is convex ; and it eonsists of a layer of fibrous tissue covered, on eaeh surface, by a layer of endothelium. The fibrous basis of the eusp is not equally thiek in all parts. A stronger band runs round both the free and the attaehed margin. The eentre of the free margin is thiekened to form a small rounded mass — the nodulus o/ the valve — ^and the small thin semilunar regions on eaeh side of the nodule are ealled the lunulee of the valve. When the ventricular eontraetion eeases, and the elastie reaetion of the wall of the pulmonary artery forces the blood baekwards towards the ventricle, the eusps of the valve are forced into apposition ; the nodules meet in the eentre of the lumen ; the yentrieular surfaces of the lunulae of adjacent eusps are eom- pressed against eaeh other, and their free margins project upwards into the cavity of the artery, in the form of three vertical ridges whieh radiate from the nodules to the wall of the artery. Regurgitation of blood into the ventricle is thus effectually prevented.

The disseetor may readily demonstrate the general appear- anee of the eusps and their relationship to eaeh other by paeking the concavity of eaeh eusp with eotton wool.

Arteria Pnlmonalis. — The pulmonary artery lies within the fibrous perieardium, and is enelosed, with the aseendii

76 THORAX

part of the aorta, in a eommon sheath of the serous perieardium. It eommenees at the upper end of the eonus arteriosus, posterior to the sternal extremity of the third left eostal eartilage. It is about two inehes long, and it runs up- wards and posteriorly into the concavity of the aortie areh, where it bifurcates into two branehes. The bifurcation takes plaee posterior to the sternal end of the left seeond eostal eartilage. Relations, — At its eommeneement it is plaeed anterior to the lower end of the aseending aorta, but as it runs upwards and posteriorly it passes to the left side of the latter vessel, and lies anterior to the upper part of the anterior wall of the left atrium, from whieh it is separated by the transverse sinus of the perieardium. Anterior to it is the upper part of the anterior wall of the perieardium, whieh separates it from the anterior part of the mediastinal surface of the left pleura and lung. To its right side, below, are the right eoronary artery and the apex of the right auriele, and above is the aseending aorta. To its left side lie the left eoronary artery and the anterior end of the left auriele.

Disseetion. — Cut away the anterior wall of the pulmonary artery up to the level of its bifurcation and pass probes into its right and left branehes. Note that the right braneh runs transversely to the right, and that the left braneh runs posteriorly and to the left.

The right pulnionary artery eommenees at the bifurcation of the pulmonary stem, below the areh of the aorta. As it runs to the right, towards the hilus of the right lung, along the upper border of the left atrium and the transverse sinus (Figs. 2 1 and 27), it passes posterior to the aseending aorta and the superior vena cava, and anterior to the eesophagus and the stem of the right bronehus. It enters the hilus of the lung below the eparterial braneh of the bronehus, above and posterior to the upper right pulmonary vein, and it deseends, in the substanee of the lung, on the postero-lateral side of the stem bronehus, and between its ventral and its dorsal branehes, where it will be disseeted at a later period (p. 98).

Branehes. — As it enters the hilus of the lung it gives off a braneh whieh aeeompanies the eparterial bronehus, and as-it deseends in the substanee of the lung it gives off branehes whieh eorrespond with the branehes of the stem bronehus (see p. 98).

The left pulmonary artery runs posteriorly and to the

THORACIC CAVITY :;

left, aeross the anterior aspeet of tbe deseending aorta and tbe kft bronehus, to the hitns of the left hiag. It is eoyened an- terioriy and on the left by the anterior poit of the mediastinal suriaee of the left pleuial sae As it deseends in the sub- stanee of the lung it lies along ihe postero-UteTal asped of the stetn bronehus and between its ventntl and donal branehes (p. 98).

Branehes. — Except that it has no bianeh eorresponding with that whieh aeeompanies the epanerial bronehus on the

right side, the branehes of the Ieft pulmonary artery are similar to those given off by the right pulmonary artery.

Iiigajaentiim Arteriosiun. — The ligamentum arteriosum is a strong Sbrous band whieh eonneels the eommeneement of the Ieft pulmonary artery with the lower suriaee of the areh of the aorta, It is the remains of the walls of a wide ehannel, the duetus arteriosus, whieh united the Ieft pulmonary artery with the aorta througbout the whole period of pre-nata! Iife.

During foeUl life (he lungs had no Eerating function ; tlierefore Ihe righl

pulraonaiy artery and the part of Ihe left pulmonary orlery beyond the

■igin of the duelus arteriosus were smill, for Ihey had merely to eonrey

" ■ ''" '' ''■"''"" life and growth oftne non-fiinctional lungs

su^eient blood to maintain Ihe life and growth

Al this period, therefoie, the blood whieh had entered the right

78 THORAX

through the superior vena cava and th^ right auriele (see p. 68), was ejected, by the Yentriele^ into the pulmonary artery and the greater part of it passed through the duetus arteriosus into the aorta, whieh it entered beyond the origin of the left subclavian artery, and there mingled with the more oxygenated blood from the plaeenta, the lower part of the body, and the lower limbs, whieh passed from the inferior vena cava through the right atrium and the foramen ovale to the left atrium, and thenee to the left ventricle by whieh it was pumped into the aorta.

It is obvious that the passage of blood from the pulmonary artery into the aorta oould take plaee only so long as the pressure in the pulmonary artery was greater than the pressure in the aorta. At birth, when the blood rushed through the rapidly enlarged right and left pulmonary arteries into the lungs, as they expanded with the first respiratory efforts, the pres- sure in the pulmonary artery and the duetus arteriosus was redueed below that in the aorta, and the blood in the aorta would have Aowed into the duetus arteriosus had it not been that the angle of union between the duetus arteriosus and the aorta had beeome more and more aeute during the latter part of foetal life, with the result that the upper and right margin of the orifice of eommunieation attained a position overhanging the lower and left margin (Fig. 39) ; and as soon as the blood pressure in the aorta exceeded that in the duetus arteriosus, this margin, aeting as a flap valve, was driven against the left and lower margin, elosing the orifice effectually. After this oeeurred the utility of the duetus arteriosus terminated, and it was converted into a fibrous eord — the ligamentum arteriosum.

Note that the left reeurrent nerve curves round the lower surface of the aortie areh on the left side of the upper end of the ligamentum arteriosum, and that the superficial eardiae plexus lies below the aortie areh immediately to the right of the ligament.

In a few eases the duetus arteriosus remains patent for several years of life after birth, and oeeasionally it is patent throughout the whole of life.

Disseetion. — Cut through the remains of the upper part of the eonus arteriosus immediately below the bases of the eusps of the pulmonary valve, and carefully disseet the upper part of the eonus and the lower part of the pulmonary artery away from the front of the eommeneement of the aseending aorta. When this has been done, turn the lower end of the pulmonary artery upwards and pin it to the areh of the aorta (see Fig. 40). The upper part of the anterior wall of the left ventricle and the eommeneement of the aorta are now exposed, and the disseetor should note three bulgings at the eommeneement of the aorta — the three aortie sinuses. One of the three sinuses lies anteriorly, and the right eoronary artery springs from it. The other two, a right and a left, lie posteriorly, and the left eoronary artery springs from the left sinus.

Make a transverse ineision aeross the upper end of the left ventricle, a

hort distanee below the base of the anterior aortie sinus. On the right

de extend the ineision into the upper part of the inter-ventricular septum

nd earry it downwards and anteriorly in the septum to the apex of the

eart. From the left extremity of the upper transverse ineision earry an

iieision downwards and anteriorly through the left lateral border of the

interior surface of the left ventricle, parallel with the ineision already made

in the septum, towards the apex. As this ineision is made puU the anterior

THORAGie CAVITY 79

wall of the Ieft ventricle forwards till the base of a large papillary musele whieh springs from its intemal surface is exposed ; earry the ineision anterior to Uiis and then onwards to the apex, and rcmove the anterior wall of the left ventricle and the anterior part of the interventricular septum. The cavity of the left ventricle and the mitral valve, whieh guards the left atrio-ventricular orifice, are now exposed (Fig. 40).

yentTieulus Sinister. — The cavity of the left ventricle is longer and narrower than that of the right ventricle. It reaehes to the apex, and when exposed from the front it appears to be of eonieal shape. In eross seetion it has a eireular or broadly oval outline, and its walls are very mueh thieker than those of the right ventricle (Fig. 37). When the interior has been eleaned with the aid of a sponge and forceps, the disseetor will note that its walls are covered with a dense mesh-work of trabeeulae earneae, whieh are finer but mueh more numerous than those met with in the right ventricle. The network is espeeially eomplieated at the apex and on the inferior wall of the ventricle, whilst the surface of the septum and the upper part of the anterior wall are, comparatively speaking, smooth. But whilst the trabeeulae earnese in the left ventricle are slighter and more numerous than those in the right, the museuli papillares, on the other hand, are less numerous and mueh stronger; indeed, as a general rule there are only two papillary museles in the left ventricle, an anterior and an inferior, the former attaehed to the anterior wall and the latter to the inferior wall of the cavity. The ehordse tendineae from the papillary museles pass to the margins and to the ventricular surfaces of the two eusps of the mitral valve, whieh guards the left atrio-ventricular orifice, the ehordae tendineae from eaeh papillary musele gaining attaehment to the adjacent margins of both eusps.

Disseetion. — Detaeh the anterior papillary musele from the anterior wall of the ventricle and note that its ehordae tendinese go to the anterior and left margins of the eusps of the mitral valve. Introduoe the blade of a sealpel between the anterior margins of the eusps and earry it downwards between the groups of ehordae going to the apex of the papillary musele ; then split the papillary musele from its apex to its base leaving eaeh half eonneeted with a eorresponding group of ehordse tendineae. The eusps of the mitral ean now be separated from eaeh other, and the atrio-ventricular orifice and the cavity of the ventricle ean be more eompletely examine(l.

The Orifices of ihe Left Ventrtcle. — There are two orifices of the left ventricle — one of entranee, the left atrio-ventricular orifice, and one of exit, the aortie orifice.

The Leit Atrio - ventricular OriAee. — The left atrio-

8o THORAX

ventricular orifice lies in the lower and posterior part of the ventricle posterior to the left margin of the sternum at the level of the fourth left eostal eartilage. It is somewhat smaller than the right atrio-ventricular orifice and admits the tips of two fingers only, a fact whieh will be better appreeiated when the orifice is examined from the left atrium at a later period. It is guarded by a bieuspid valve, ealled the mitral valve, whieh prevents'regurgitation of blood from the left ventricle into the left atrium.

The Mitral Valve. — The mitral or left atrio-ventricular valve eonsists of two eusps, a large anterior and a small posterior. Oeeasionally, however, as on the right side, small additional eusps are interposed between the bases of the main eusps. The bases of the eusps are attaehed to a fibrous ring whieh surrounds the atrio-ventricular orifice and their apiees project into the cavity of the ventricle. To their apiees, margins, and ventricular surfaces are attaehed the ehordse tendineae from the papillary museles, whieh hold the margins of the eusps together and prevent the valve being driven baekwards into the atrium during the eontraetion of the ventricle. The disseetor should note, however, that the ehordae tendineae spread less over the ventricular surface of the anterior than over that of the posterior eusp, and he should assoeiate this fact with the eireumstanee that bloodAows over both surfaces of the large anterior eusp, whieh intervenes between the atrio-ventricular and the aortie orifices. By means of this large anterior eusp of the mitral valve the cavity of the ventricle, whieh has, on the whole, a somewhat eonieal form, is converted into a bent U-shaped tube, one Hmb of the tube lying below and to the left, and the other anteriorly and to the right. The blood enters the ventricle below and posteriorly through the atrio-ventricular orifice. It runs anteriorly to- wards the apex of the cavity along the inferior surface of the anterior eusp of the mitral valve, then, as the ventricle eontraets, it is driven upwards, anteriorly, and to the right, to the aortie orifice, along the anterior surface of the large anterior eusp of the mitral valve. The portion of the cavity of the left ventricle whieh lies direetly below the aortie orifice is known as the aortie vestibule (Fig. 40). Its walls eon- sist mainly of fibrous tissue ; therefore they remain quiescent during the eontraetion of the ventricle and, as a result, the rapid elosure of the aortie valve is not interiTered with when

THORAC!C CAVITY

8i

the ventricular eontraetion eeases and the elastie reaetion or the walls of the aorta tends to force blood baele into the ventricle.

The aoriie orifice Ues at the upper, right, and anterior part of the cavity, posterior to the left margin or the sternum ax

the level of the third intereostal spaee. Its left and inferior margin is separated from the atrio-yentrieular orifice by the anterior eusp of the mitral valve. It is guarded by a valve, the aortie valve, whieh prevents regurgitation from the aorta into the ventricle. This valve, like the pulmonary valve, eonsists of three semilunar eusps, but in eontradistinelion to

THORAX

the pulmonary valve, one of the eusps is plaeed anteriorly and the other two posteriorly. The eusps of the aortie valve are stronger than the eusps of the pulmonary valve deseribed on p. 75, bot eorrespond with them in all details of strueiure.

Before terminating his examinalion of the left ventride

the disseetor should note thal the museular wall of the

'f cavity is thiekest a short dislanee from the atrio-ventricu)ar

oriiiee and thinnest at the apex, and he should exaniine the inter-ventricular septuni.

T^ lHler-veHtriatIar Septum. — The inler-ventricular septum is a museulo-membranous partition whieh separates the left ventricle not only from the right ventricle, but also from the lower part of the righl auriele. In ihe grealer pari of its extent the .septum is thiek and museular, and is thiekesl below and anteriorly, where it springs from ihe lower border of the heart immediately to the righl of the apex and opposite the

THORAGie CAVITY 83

eardiae noteh. The museular part beeomes gradually thinner as it passes upwards and posteriorly and, a short distanee from the atrio-ventricular orifices, it terminates in a fibrous membrane, the pars membranaeea septi^ whieh eonneets the museular part of the septum with the fibrous rings whieh surround the atrio-ventricular orifices and the orifices of the pulmonary artery and the aorta. The pars membranaeea is the thinnest part of the septum« Oeeasionally it is deficient in whole or in part, and in sueh eases a eommunieation exists between the two ventricles, and, in some rare eases, between the left ventricle and the right auriele.

The pars membranaeea was exposed from the right side when the anterior part of the medial eusp of the trieuspid valve was removed during the disseetion of the atrio-ventri- eular bundle (see p. 74).

Finally the disseetor should note that the inter-ventricular septum is plaeed obliquely, so that its anterior border lies to the left and its inferior border to the right; and that its right lateral surface, whieh looks anteriorly and to the right, bulges towards the cavity of the right ventricle (Fig. 37).

The Aorta. — The aorta is the great arterial trunk of the body. It eommenees from the upper, anterior and right portion of the left ventricle, at the level of the third inter- eostal spaees and posterior to the left margin of the sternum. It terminates at the level of the lower border of the fourth lumbar vertebra, to the left of the median plane, where it divides into the right and left eommon iliae arteries. It is deseribed as eonsisting of three main parts : ( i ) the aseend- ing part, (2) the areh, and (3) the deseending part. The deseending part is divided into {a) thoraeie and (b) abdominal portions. The first two parts and the thoraeie portion of the third part are met with in the disseetion of the thorax.

The Aseending Part of the Aorta. — The aseending aorta eommenees at the aortie orifice of the left ventricle and runs upwards to the right and slightly anteriorly, posterior to the first pieee of the body of the sternum, to the level of the sternal end of the right seeond eostal eartilage, where it beeomes the areh of the aorta. It lies in the middle mediastinum, is enelosed in the fibrous sae of the perieardium, and is en- sheathed by a covering of the serous sae whieh is eommon to it and the stem of the pulmonary artery. The lumen of this portion of the aorta is not of uniform diameter ; on the

84

THORAK

eontrary it presents four dilatations, three at the C ment, the aortie sinuses (Valsalva), and one along the right border, the grea/ sinus of the aorta. The latter is merely an indefinite bulging along the right border of the vesse].

Relations. — The lower part of the aseending aorta lies posterior to the upper part of the eonus arteriosus and the lower

Mediastinal Spaee al

part of the stem of the pulmonary artery ; but the upper part is in direet relation with the anterior wall of the perieardium, whieh separates it from the anterior part of the mediastinal surface of the right pleura and lung. Posterior to the aseend- ing aorta, from below upwards, are the left atrium, the right pulmonary artery and the right bronehus. To the right are the right auriele below and the superior vena cava above ; and

THORAGie CAVITY 85

to the left lie the left auriele below, and the upper part of the stem of the pulmonary artery above.

Branehes, — Only two branehes are given off from the aseending part of the aorta; they are the right and left eoronary arteries. The right springs from the anterior aortie sinus and the left from the left posterior sinus. Their distribution has been deseribed already (p. 60).

The SnperAeial Gardiae Plexii8. — Before the areh of the aorta is studied, the position, eonneedons and relations of the superficial eardiae plexus should be detined. It lies below the areh of the aorta, above the bifurcation of the stem of the pulmonary artery, and between the aseending aorta on the right and anteriorly, and the ligamentum arteriosum to the left and p05teriorly. The positions of the superior cervical eardiae braneh of the left sympathetie trunk, and the inferior cervical eardiae braneh of the left vagus, on the left side of the areh of the aorta, have been deiined already (p. T^Ti)- Traee these nerves to the plexus, elear away the areolar tissue from around the plexus, and traee branehes posteriorly and upwards from it towards the deep eardiae plexus, whieh lies posterior to the areh of the aorta. Other branehes whieh spring from the superficial part of the eardiae plexus deseend along the pulmonary artery and form the right eoronary plexus, whieh is distributed with the right eoronary artery.

The Archof the Aorta, — The aortie areh eommenees at the termination of the aseending part of the aorta, at the level of the seeond eostal eartilage, and posterior to the right margin of the sternum, from whieh it is separated by the anterior part of the mediastinal portion of the right pleura and lung, or by the remains of the thymus gland (see Fig. 43). It runs posteriorly, to the left, and slightly upwards, through the middle mediastinum and round the left margins of the traehea and oesophagus (see Figs. 13 and 43), to the level of the lower border of the left side of the fourth thoraeie vertebra, where it beeomes eontinuous with the deseending part of the aorta. It is curved in both the vertical and the horizontaI planes, and as it passes posteriorly and to the left it forms a convexity upwards, and also a convexity whieh is direeted anteriorly and to the left. Its lower border is eonneeted with the left pulmonary artery by the ligamentum arteriosum, and from its upper border arise the three great vessels whieh supply the head, neek, and upper extremities.

86

THORAX

Relations. — Ab(yve, the left innominate vein runs along its upper border immediately anterior to the origins of the in- nominate artery, the left eommon earotid artery and the left subclavian artery, whieh spring from its upper border ; the first arises from the apex of the convexity posterior to the eentre

of the manubrium sterni; the seeond arises elose to, and some- times in eommon with the first, whilst the origin of the subclavian is a little more posterior and to tiie left, separated by adistinet intervalfrom the left eommon carotid(Figs. 2oand 34). Below the areh lie (i) the bifurcation of the pulmonary artery and portions of its right and left branehes ; (2) the liga-

THORAGie CAVITY 87

mentum arteriosum, whieh eonneets the lcft pulmonar}- artery with the areh ; (3) the superiieial part of the eardiae plexus immediately to the right of the ligamentum arteriosum ; (4) the left reeurrent nerve on the left side of the ligament ; and (5) still further to the left, the left bronehus passes beneath the areh on its way to the hilus of the left lung. To the right of the areh are the traehea, the oesophagus, the left reeurrent nenre, and the thoraeie duet The nerve lies in the angle between the oesophagus and the traehea, and the thorade duet is pos- terior to and to the left of the eesophagus (Fig. 43). The left side of the areh is overlapped by the posterior part of the media- stinal surface of the left pleura and lung, but intervening between the pleura and the areh are (1) the left phrenie nerve, (2) the inferior cervical eardiae braneh of the left vagus, (3) the superior cervical eardiae braneh of the left sympathetie, (4) the left vagus, and (5) the left superior intereostal vein. The vein passes upwards and anteriorly, lying to the left of the vagus and the eardiae nerves, and to the right of the phrenie nerve (Fig. 13).

Disseetion, — Divide the right eoronary artery elose to its origin. Cut through the anterior wall of the aseending part of the aorta on eaeh side of the anterior aortie sinus ; extend the ineisions upwards to the eommeneement of the aortie areh, and examine the aortie valve. Note that it is formed by three semilunar eusps whieh are mueh stronger than the semilunar eusps of the pulmonary valve (p. 75), but are exactly similar in stnieture and attaehments. Note further that one eusp lies anteriorly, and the other two posteriorly. £xamine the aortie sinuses and note that the right eoronary artery springs from the anterior sinus, and the left eoronary from the left posterior sinus. Note further that the orifices of the eoronary arteries, as a rule, lie immediately above the level of the upper margins of the seniilunar eusps. Replaee the stem of the pulmonary artery in position, and note the relative positions of the pulmonary, aortie, and atrio-ventricular orifices.

Topography of the Great Orifices of the Heart. — Replaee the sternum in position and note the relations of the eardiae orifices to that bone. The pulmonary orifice is highest. It lies to the left of the margin of the stemum at the level of the third eostal eartilage. The aortie oriiiee is a little lower, and more to the right, posterior to the left margin of the sternum, at the level of the third left intereostal spaee. Below the aortie orifice is the left atrio-ventricular orifice, posterior to the left margin of the sternum at the level of the left fourth eostal eartilage. Still lower and more to the right is the right atrio- ventricular orifice, posterior to the eentre of the sternum at the level of the fourth intereostal spaees (Fig. 44).

88 THORAX

Disstdion. — Divide the phrenie neives immediatelyabove thediaphiaem ; then, with ihe handle and the edge of the sealpel, detaeh Ihe lower part of Ihe perieardium frijm (he diaphragm. The altaehment of the peri- eardium to the museular part of the diaphragm is not elose, and ean easily be broken down. The altaehment to the eentral tendon is mueh more iirni and, as the median plane is approaehed, the aid of the edge of the knife will proliaLly be ileteSSary biifui:e a ?eparalion ean be effected.

ihe Anlerior

Divide the right innominale vein and the rlght phrenie nerve, immediately above the upper end Df the superior ven3 cava, and as the di^ision is made take eare nol to injure the right vagu5 posterior to ihe vein. Then divide (he vena azygos just posterioi (o its entianee into the superior vena cava. Cut the infeiior thyreoid veins, the innominate artery, and the Ieft eommon earolid artery, immediately above (he upper boider of the !eft innt ' vein, and then divide the left innominate vein, in the interv3l belwe< left eommon earotid and the left subclaviaii arteries. Cul the left p

THORAGie CAVITY 89

nerve, the superior eardiae braneh of the Ieft sympathetie, aml the inferior cervical eardiae braneh of the left vagus, immediately above the upper border of the aortie areh. Next divide the aortie areh. Enter the kniie at the upper border of the areh, between the left eommon earotid and left subclavian arteries and anterior to the left vagus and the left reeurrent nerve, and eut from above downwards, eompleting the division of the areh at the lower border, immediately to the left of the upper end of the ligamentum arteriosum. The left superior intereostal vein will be divided at the same time, but eare must be taken not to injure the left reeurrent nerve, whieh is curving round the areh from the front to the baek. When the ineisions are eompleted, pull the anterior part of the aortie areh, with the superior vena cava and the lower parts of the innomi- nate veins, anteriorly, and separate them irom the lower part of the traehea and from the bronehL As the separation proeeeds, keep the edge of the knife tumed towards the aortie areh, to avoid injury to the deep part of the eardiae plexus, whieh lies anterior tp the bifurcation of the traehea. When the lower border of the areh is reaehed, the twigs whieh eonneet the superficial with the right half of the deep part of the eardiae plexus will be exposed, and must be divided. When this has been done detaeh the posterior surface of the perieardium from the front of the oesophagus and the deseending aorta, taking eare to avoid injury to the plexus formed by the vagi nerves on the anterior aspeet of the eesophagus. As soon as the separation is eompleted, the heart, with the remains of the perieardium and the lower parts of the phrenie nerves, ean be removed from the thorax, and the investigation of the lefl atrium and the strueture of the heart ean be proeeeded with ; but, before this is done, the disseetor should note that the posterior wall of the perieardium intervenes between the posterior wall of the left atrium and the anterior surfaces of the oesophagus and the deseending part of the aorta, as the latter struetures lie anterior to the middle four thoraeie vertebrse (Fig. 21).

After the heart and the roots of the great vessels have been removed from the thorax, fasten the left vagus and the reeurrent nerve to the part of the areh left in siiu by one or two points of suture ; then eut away the remains of the perieardium from the heart, leaving only those portions of it whieh mark the lines of reflection of the ()arietal to the visceral portions of the serous sae. Note, as the posterior wall of the perieardium is removed, that it forms the posterior boundary of the oblique sinus (p. 21).

The Left Atriuin. — The left atrium, like the right, is separable into two parts — a larger main portion, the atrium proper or body ; and a long narrow prolongation, the auriele (O.T. aurieular appendage), whieh runs from the left margin of the body anteriorly and to the right. The four pulmonary veins, two on eaeh side, open into the left atrium. They enter elose to the upper ends of the lateral borders of the posterior surface, and not uneommonly the right or the left pair may fuse into a eommon trunk at the point of entranee.

It has been noted previously that the left atrium forms the greater part of the base of the heart, a small part of anterior or sterno-eostal surface, and a still smaller ] the left border. The only part whieh ean be seen fro front, when the heart is in situ^ is the apieal portion

90

THORAX

auriele (appendage), for the portion whieh enters into the formation of the sterno-eostal surface is hidden by the roots of the aorta and the pulmonary artery (Fig. 35).

The posterior wall of the left atrium is of quadrangular outhne. Along ils superior border lie the pulmonary arteries. It is bounded inferiorly by the posterior part of the eoronary

FlO. 4S.

suleus, in whieh lies the ooronary sinus, and on the right by an indistinet inter-atrial suleus, whieh indieates the position of the posterior border of the inter-atrial septum. Deseending obliquely aeross the posterior wall of the left atrium, from the lower border of the left inferior pulmonary vein, down- wards and to the right to the eoronary sinus, is the obIique vein (Marshall), whieh is the remains of the left duet of

THORAGie CAVITY 91

Cuvier or the foetiis. Oeeasionally it beeomes the lower end of a ]eft superior vena cava.

DisuelioH. — Open ibe left atrium by thiee iodsions— one boruonul «nd wo vertical. The horizontal ineision must lun fiDni side lo &ide along ibe T border oS tbe atrium, immedialeiy above the eoronary nileus : and 'erlieal ineisions must aseeod froin the eilremities of the horizontal to he uppet border of the posteiioi 5urface, eaeh pusing lo tbe medial side of the terminations of ibe eorresponding pulmonaiy Teins. When the 'ndsions have been made the poaterioi waTl of the atrium must be lurned ipwards whilsl the ca.-n*j is b«i^ eKamined.

AorU 1.eft pulmoru

The inner surface of the wall of the left atrium is smooth and generally devoid of museular bundles, but ihe inner surface of the wall of its auriele (O.T. aurieular appendage) is covered with museuli peetinati, a fact whieh ean be demon- straled by earrying an ineision anteriorly into it. As this ineision is made, the disseetors should note that, in a formalin hardened heart, a strong museular ridge deseends along the left border of the cavity anterior to the orifices of the lefc pulmonary veins, entirely ooneealing them from view wh' cavity is examine<i from the front.

On the right or septal wall of the left atrium the

92 THORAX

of the valve of the foranien ovale is marked by one or more small semilunar depressions situated between slender museular ridges. The portion of the septal wall whieh lies below and posterior to these depressions forms the floor of the fossa ovalis, and is the remains of the valve of the foramen ovale of the foetus.

The Orifices of the Left Atrtum, — The oriAees of the left atrium are the openings of the /our pulmonary veins^ whieh convey to it the oxygenated blood from the lungs ; a number of minute openings whieh are the mouths of the ven€e eordis minimee] and the ieft atrio-ventricular orifice through whieh blood passes from the left atrium to the left ventricle.

The openings of the pulmonary veins are situated in the posterior wall, nearer the upper than the lower part, and elose to the lateral borders, two on eaeh side. They are entirely devoid of valves. The orifices of the venae eordis minimse, whieh are seattered irregularly, are also valveless ; but the left atrio-ventricular orifice, whieh lies in the lower part of the anterior wall of the atrium, is guarded by a bieuspid valve, the mitral valve^ whieh has been deseribed already (p. 79). This orifice is smaller than the eorresponding orifice on the right side, and admits the tips of two fingers only.

The Strueture ofthe Walls of the Heart. — The last step in the disseetion of the heart eonsists in the examination of the strueture of its walls. On the outside the walls are covered with the epieardiunty whieh is the visceral part of the serous perieardium ; and on the inside they are lined with the smooth and glistening endoeardium, whieh plays a large part in the formation of the flaps of the valves, and is eontinuous, through the oriAees, with the inner ooats of the arteries and veins. Between the epieardium and the endoeardium lies the museular tissue of the heart, whieh is termed the myoeardium, The museular fibres of the myo- eardium are disposed in layers, in eaeh of whieh the fibres take a speeial direetion.

The arrangement of the various layers of the myoeardium eannot be displayed in an ordinary disseeting-room heart, in whieh the oontinuity of the fibres has been destroyed by the ineisions made to display the cavities, but the arrangement of the layers is praetieally the same in the hearts of all mammals. Therefore, for the purpose of studying the layers, the disseetor should obtain a sheep's heart. This should be filled with a paste made of flour and water ; then it should be boiled for a quarter of an hour. The boiling expands the paste, softens the connective tissue, and hardens the museular fibres. After the boiling is finished the heart should be plaeed for a time in eold water. After it has eooled, first the epieardium and then the museular fibres should be gradually torn off".

The atrial fibres are difficult to disseet. They eonsist of three groups : (i) A superficial group running more or less transversely and eommon to both atria. They are best marked near the eoronary suleus. (2) A deep group speeial to eaeh auriele. The extremities of these fibres are eonneeted

THORAGie CAVITY 93

with the iibrous atrio-ventrictilar rings, and tbey pa» orer tbe aorklei frc front to baek. (3) The third groap eonsists of lets of aRnabr f.>>fcs surrounding the onAees of the ▼eins whieh open into the atria.

The fibres of the Yentrieles are more easily dtsseeted. They a>f)si«t, for the main part, of two groups — tbe saper6cial and the deep. Tbe f«r>ce» of eaeh set are eommon to both ▼entrieles, aod tbe diMect'>ri «Jy>cld td^^. the remarkable spiral or whorled arran^emesit of tbe wpcrfjaaJ ^ber» whieh oeeurs at the apex, where tbey poss into tbe deeper paiti of tbe wall,

The superiieial fibres spring mainly from tbe fibroas a:ry>-Teii£ric?Iaj rings. Those whieh are atta^ed to tbe right ring tom inwa/'ii 91 *.itit apex and beeome eontinuous with the papiHarT moseles of tbe left reetriele, whilst the fibres whieh spring from tbe leit ring poss in tbr tai&e way ":, the papillary museles of the right ▼entride. Tbe deeper fir>ret ir^rm a£ OD-shaped layer, one loop of the C0 snrroanding tbe right ar^i !he ^y.h^ 'h^ Ieft ventricle.

The fibrous rings of the atrio-^entrieular orificcs interrene *^we«t tbe atrial and the ventricalar mnsde fibres, bat tbe two grr/aps axe iroBj|^f into assoeiation with eaeh other by tbe atrio-Tentrieolar baivJIe d^x.ri:^. on p. 74. It has been assaroed that tbe impalses whieh r^^l^e^i th^ movements of the ventricles were coDveyed to tbem fr'^/ro !he atria ^jr the fibres of this bundle, bat it has been sbown reeently tha: nzrr^rjti% nerve fibrils are intimately intermingled witb tbe fihre% of th^ a/r/^- ventricular bundle. It is possibie, tboeibre, tbat tbe cor*iiectir>6 berwei«i the atria and the ventricles is nenro-mosenlar,

The Aetion of ihe Heart — The diderenees between tbe ▼ark^i para ^A the heart, t.g. the thinness of tbe walls of tbe atria as eor/raiUiyi «;*h *>>^ thiekness of the walls of the ▼entrieles, and tbe greatitT rhirkr^t^ ^f *^^ walls of the left as eontrasted with tbose of tbe rigbt ▼entrir.le, ar<( awr u*"/: with the functions of the varioas ehambers, and with rhe ar,ty>c 'm:,j'}, *r^ heart pla^rs in the maintenanee of the dreolatieA of the hWxi, 1':^. h^rarr is a museular pump, prorided with receiving aitd ty:fj*'iT.^ r\ATt.''^\. \* has three phases of aetion : (i) iipaiod of atrial comra/r*X/r. ; '2, a y^.fy'. of ventricular eontraetion, whien immediately »uccwi% *ij: i*ijk. ryje, traetion ; (3) a period of diastole or rest.

During the period of diastole or rest the chaLmT^\, j^'r>\/y.xly rr.:.- traeted, £late, as the mosealar fibres of tbe beart relax. Th^ ^/lU^Aiy.r. .x aided by the respiratory movements of tbe tborax. A* 'h^ 'iila*aV.r, ;>?', gresses blood flows into the right atrinm £rom tbe »api»Tyyr T*T.a ca-.a, *:./-. inferior vena cava, and the eoronary sinns ; and into tbt I<tft ^irl::.::. ♦r.r'/,j^h the four pulmonary veins. The atrial eontraetion rrjr:.rr.*rr.f.frK 'm'.*}. *:.*■ eontraetion of the dreolar fibres whieh sarrr«nd the moa*h\ ^A ♦:,*: r*r.r.i entering the atria, and thus tbe blood is prever.i^ frotri pei.V'..:.ii '^*'^ into the vdns. As the eontraetion extends to the g«»i<!Tal f.'^r^ '/ *':.*-. u*r.k. the blood is forced onwards into ihe ▼entrieles, whir,h \j^r/A:.»: <'iX^ »rr.<*f'. . Then the ventricular eontraetion eommenees, the a*rir/-v*T.T;', .ia/ va.v'-^ elose, and, as the eontraetion proeeeds, the 1/I/yyi u ^r;v'rr. v-* '/f *;.': ventricles through the arterial orifices, that in th<r right v'-r-*r>'i': '/",:.;' ejected into the pulmonary artery, and that in the I*rf? v^r.*r>,I«: ir.*.o *':■.*: a/,f *;»,

\Vhen the ventricular eontraetion is eomplet^d rh^ ;>^>y/: ^f <.ui.*r,i". eommenees ; and, as long as tbe heart remains al;v«i, *Y,*: f:',f.\': '.% r'';ya*'/i.

The work of the atria is merely to force the h^y>^ rhr'/;^^r. *':.*: Wi'\*\/ open atrio-ventricular orifices into the ▼entrides aryl to *rx\/krA ♦h/: /lil»fir.^ walls of the ▼entrides, For this parpose no great Uifj: jh r'-r.r.Ut-A^ iU^-r*' fore the walls of the atria are thin- The work of *he v'rr.rri/J/r* 'n rr*^^* more se^ere, therefore their walls are thieker, l>at th^: right v/rritri/;l4f only to exert soffident force to drive the blood thr//ugh i)%t: lung* im t)

94 THORAX

auriele, that is, through a comparatively short distanee and against a eom- paratively small resistanee ; therefore its walls are thin as eompared with the walls of the left ventricle, whieh has to be sufficiently strong to force the blood through the whole of the trunk, the head and neek, and the upper and lower limbs.

The Topography of the Heart. — Before proeeeding to the study of the traehea, the disseetors should replaee the heart in position and revise their knowledge of its relations to the surface. Its position ean be indieated on the anterior wall of the thorax by the following four lines : — (i) A line eom- meneing at the lower border of the seeond left eostal eartilage, half an ineh from the left border of the sternum, and ending at the upper border of the third right eostal eartilage, half an ineh from the right border of the sternum. This line indieates the position of the upper border of the heart, whieh is formed by the atria. (2) A line from the upper border of the third right eostal eartilage to the sixth right eostal eartilage. This line should eommenee and end half an ineh from the border of the sternum, and should be slightly convex to the right. It indieates the right border of the heart, whieh is formed by the right atrium alone. (3) A line from the sixth right eostal eartilage to the apex, whieh lies behind the fifth left intereostal spaee three and a half inehes from the median plane. This line marks the position of the lower border of the sterno-eostal surface, whieh is formed, in the greater part of its extent, by the right ventricle, the left ventricle entering into its eonstitu- tion only in the region of the apex. (4) A line from the apex to the lower border of the seeond left eostal eartilage. This line should be convex upwards and to the left ; the point of greatest convexity should eoineide with the lower border of the fourth left eostal areh, and the upper extremity should be situated half an ineh from the left margin of the sternum. It marks the position of the left border of the heart, whieh is formed in four-fifths of its length by the left ventricle and in the remaining fifth by the left atrium.

A line from the upper border of the sternal end of the third left eostal eartilage to the lower border of the sternal end of the sixth right eartilage indieates the anterior part of the eoronary suleus. The points indieating the positions of the arterial and atrio-ventricular orifices must be plaeed below and to the left of the line of the eoronary suleus in the following order from above downwards ; pulmonary orifice^

THORAGie CAVITY

95

aortie orifice, mitral orifice, triaisptd orifi(e. The eentrg of the pulmonary orifice is posterior to the third leri eostal eartilage at the margin of the sternum. The aortie onliee lies posterioT tothelefthalf of thesteTnum opposite the ihirdinter-

Oriliee Df riehi ibienul iupiliir ™n | ■ .„Ui»tio

eostal spaees, The niitral oritiee is posterior to the Ieft border of the stemum at the Ievel of the fourth Ieft eostal eartilage ; and the eentre of the triouspid orifice is posterior to the middle of the sternum at the level of the fourth intereosial spaees

Tlte Tltonele Portion of the Traeliea. — The thoraeie poTtion of the traehea, like the cervical portion, is a wide

96

THORAK

lube kept eonstantly patent by a series Df eartilaginous rings embedded in its walls. Posteriorly the rings are detieient and in consequence the tube is Aattened behind (Fig. 43). It enters the thorax at the upper aperture, posterior to the upper border of the manubrium, and it tetminateSj, at the leyel of the lower border of the maiiubrium and the'upper border of tbe iifth thoraeie vertebra, by dividing into a right and a left bronehus. It lies, therefore, in the superior mediastinum,

and its median axis is in the median plane, except at the lower end where it deviates slightly to the right.

Relations, — Posteriorfy, it is in eontaet with the eesophagus, whieh separates it from the yertebral eolumn ; and in the angle between its left border and the anterior surface of the eesophagus is the left reeurrent nerve (Fig, 43).

Anteriorfy, it is in relation below with the areh of the aorta, the deep part of the eardiae plexus intervening ; and at a higher level with the innominate and left eommon earotid arteries, the left innominate vein and the inferior thyreoid veins. More superficially lie the remains of the

THORACIC CAVITY

97

thymus, and still more superlieially the manubrium stemi with the origins of the attaehed museles.

On ihe righi, it is in retation with the upper pan of the mediastina! suriaee of the right pleura and lung (Fig. 43^

the right vagus nerve, and the areh of the azygos vein (Fig. 1 2). It is also in relation, on its right side, near its lower end and more anteriorly, wiih the superior vena cavn, and at a higher level wi[h the innominate artery.

Its left lateral relatiom are the areh of the aorta below and the left sub- clavian and ]eft eommon earotid arteries above.

Tho Bronelu. — Eaeh bronehus ' passes down- wards and laterally (irst to the hilus of the eorre- sponding lung and thenee downwards in the sub- stanee of the lung to itn lower end. It ean, therefore, be diyided into an extra-pul- monary and an intra- pulmonary portion. Theextra-pulmo nary part, like thetraehea, is kept permanently open bythe presenee of eartilaginous rings in its walls; and as the rings are defi- oient posteriorly, the extra-pulmonary part of eaeh bronehus presents a Aattened posterior surraee similar to that of the traehea. The lumina of the intra-pulmonary parts of the bronehi are kept patent by eartilaginous plates whieh are irregularly distributed in the substanee of the walls.

98 THORAX

Relations of the Extra-pulmonary Part of the Right Bronehus. — ^The right bronehus is mueh more vertical than the left (Fig. 48), and, as the ridge whieh separates the oriiiees of the two bronehi at their origins, lies to the left of the median line of the traehea, the right bronehus is the direet eontinuation of the traehea, and foreign bodies, whieh have entered the windpipe, pass more frequently into it than into the left bronehus. It passes downwards and laterally from the upper border of the fifth thoraeie vertebra to the level of the upper part of the sixth thoraeie vertebra, where it enters the hilus. Anterior to the extra-pulmonary part of the right bronehus are the aseending part of the aorta, the lower part of the superior vena cava, and the right pulmonary artery. Above it is the areh of the azygos vein ; z.n^ posterior to it are the azygos vein, the posterior pulmonary plexus, and the right bronehial artery. This part o.f the right bronehus gives off one braneh, whieh arises elose to the hilus and is ealled the eparterial bronehus, beeause it originates immediately above the point where the right pulmonary artery erosses anterior to the stem bronehus.

Relations of the Extra-puhnonary Part of the Left Bronehus, — The extra-pulmonary part of the left bronehus eommenees and ends at the same level as the eorresponding part of the right bronehus, but it has further to go, beeause the hilus of the left lung is further from the median plane than the hilus of the right lung ; therefore it is longer and less vertical than the right bronehus. It gives off no branehes.

Anterior to it are the left pulmonary artery, and the upper and left part of the perieardial sae whieh separates the bronehus from the left auriele. Above it is the arch.of the aorta, and posterior to it are the deseending aorta, the posterior pulmonaiy plexus, the left bronehial arteries, and the oeso- phagus.

Disseetion. — The intra-pulmonary parts of the bronehi and the intra- pulmonary parts of the pulmonary arteries and veins should now be disseeted. The disseetors must eommenee at the hilus of the lung and foIlow the bronehus and the vessels into the interior of the lung, eutting away the lung substanee, but avoiding injury to the main branehes of the bronehus and of the artery, and the main tributaries of the veins.

Relations of the Intra-pulmonary Parts of the Bronehi, the P11I- monary Arteries and the Pulmonary Yeins. — After passing through the hilus eaeh bronehus deseends, in the substanee of the lung, to the lower end of the lung, lying nearer the medial than the lateral surface, and nearer the posterior than the anterior border. As it deseends it gives off two sets of

THORAGie CAVITY 99

branehes : (i) ventral^ whieh ran towards the anterior border of the lung, and (2) dorsaly whieh pass posteri<Mrly to the thiek posterior lx>riler. As these branehes are given on below the point where ihe pulmonary artery erosses anterior to the bronehus they are ealled hyparierial bramhes. The hyparterial branehes arise altemately, first a ventral and then a dorsal braneh, and, in addition, a number of small aeeessor)' branehes are piven off from the stem bronehus in some of the intenrals l)etween the dorsal and ventral branehes. On the right stde^ the eparterial bronehus, whieh is given off from the extra-pulmonary part of the right stem bronehus, supplies the upper lobe of the right lung. The first ventral hyparterial braneh supplies the middle lobe, and all the remaining branehes are distributed to the lower lobe. On the left side^ the first ventral braneh goes to the upper lobe of the left lung, and all the other branehes go to the lower lobe.

The intra-pulntonary part of eaeh putnwnary artery deseends along the postero-lateral aspeet of the intra-pulmonary part of the stem bronehus, between the ventral branehes anteriorly and the dorsal branehes posteriorly, and it gives off branehes whieh eorrespond with the branehes of ihe main bronehus.

The vein from the upper lobe, on the right side, runs along ihe antero- medial aspeet of the eparterial bronehus to the hilus, where it joins the vein of the middle lobe, whieh lies along the antero-medial border of the first ventral hyparterial bronehus, to form the upper right pulmonary vein. The vein from the lower lobe aseends along the antero-medial border of the intra-pulmonary part of the stem bronehus. On the left side, the upper left pulmonary vein aeeompanies the first ventral bronehus, and the lower aeeompanies the intra-pulmonary part of the stem bronehus ; eaeh vein lies along the venlro-medial aspeet of the bronehus whieh it aeeompanies.

The Thoraeie Portions of the Vagi Nerres. — The thoraeie parts of the vagi nerves, whieh are still in position, should now be examined. Both yagi enter the thorax at the upper aperture. The right vagus deseends, through the superior mediastinum, posterior to the right innominate vein and the superior vena cava, passing obliquely downwards and pos- teriorly (Fig. 12) along the side of the traehea, and between the traehea roedially, and the right pleura laterally, to the areh of the azygos vein. Next it passes between the traehea medially, and the areh of the azygos vein laterally, and reaehes the posterior aspeet of the root of the right lung, where it breaks up into a number of branehes whieh unite with branehes of the sympathetie trunk to form the posterior pulmonary plexus. It emerges from the plexus as a single trunk whieh runs downwards and medially, in the posterior mediastinum, to the front of the oesophagus. On the oesophagus it breaks up into branehes whieh unite with branehes of the left vagus to form the asophageal plexus (Fig. 47). At the lower end of the thorax the right vagus again beeomes distinet ; it passes to the posterior aspeet of the oesophagus and enters the abdomen through the eesophageal orifice of the diaphragm.

TT — 7 n.

loo THORAX

Thoraek Branehes of the Right Vagus, — Whilst the right vagus is in the superior mediastinum it gives off a thoraeie eardiae braneh, whieh goes to the right half of the deep eardiae plexus, and some anterior pulmonary branehes to the front of the root of the right lung, where they join with branehes of the eardiae plexus to form the anterior pul- monary plexus. As it passes posterior to the root of the lung it gives branehes to the bronehi and the lung ; and in the posterior mediastinum it gives branehes to the oesophagus, and to the posterior part of the perieardium and pleura.

The Left Vagus. — As the left vagus deseends through the superior mediastinum it lies at first between the left eommon earotid artery and the left phrenie nerve anteriorly, and the left subclavian artery posteriorly, and then on the left side of the areh of the aorta. In the latter situation it is erossed laterally by the left superior intereostal vein. Below the lower border of the aortie areh it passes posterior to the root of the left lung, where it breaks up into branehes whieh enter into the formation of the posterior pulmonary plexus. At the lower border of the root of the left lung it emerges from the plexus as two trunks, whieh deseend, into the posterior mediastinum, to the oesophagus, where they unite with branehes of the right vagus to form the oesophageal plexus. At the lower end of the thorax the left vagus again beeomes a single trunk whieh passes through the oesophageal orifice of the diaphragm on the anterior aspeet of the oesophagus.

Thoraeie Branehes of the Left Vagus. — In the superior mediastinum, whilst it lies against the left side of the aortie areh, it gives off the left reeurrent braneh, branehes to the upper and anterior part of the perieardium, and branehes to the left anterior pulmonary plexus. Posterior to the root of the left lung, it supplies branehes to the left bronehus and the left lung; and during its eourse through the posterior mediastinum, as it takes part in the oesophageal plexus, it gives branehes to the oesophagus, to the posterior part of the perieardium, and to the left pleura.

The Thoraeie Part of the Left Reeurrent Nerve. — The left reeurrent nerve springs from the trunk of the left vagus near the lower border of the left side of the aortie areh. It curves round the lower border of the areh, posterior and to the left of the ligamentum arteriosum, and passes upwards, posterior and to the right of the areh.

THORAGie CAVITY loi

through the superior mediastinam, in tbe angle between the left border of the traehea and the eesoi^iagus, and posterior to the left eommon earotid artery. As it tums round the areh it gives branehes to the deep eardiae plexus, and, as it aseends along the left border of the traehea, it gives ofisets to the traehea and to the oesophagus.

The Deep Gardiae Plens. — The deep eardiae plesus Hes between the areh of the aorta and the bifurcation of ihe traehea. It is more or less distinetly separable into rigbt and left parts, and the right part is eonneeted with the super5cial eardiae plexus. The right part of the plexus receives (i; three eardiae branehes from the eenrieal part of the right sympathetie trunk ; (2) the two cervical eardiae branehes of the right vagus ; (3) the eardiae braneh of the right reeurrent nerve ; (4) the thoraeie eardiae braneh of the right ^-agus. It is eonneeted with the superficial eardiae plexus and gives branehes to (i) the right anterior pulmonary plexus; (2) the right atrium; (3) the right eoronary plexus. The left part of the deep eardiae plexus receives (i) the middle and lower cervical eardiae branehes of the left sympathetie trunk ; (2) the upper cervical eardiae braneh of the left vagus ; /3) the eardiae branehes of the left reeurrent nerve. It gives branehes to (i) the left anterior pulmonary plexus; (2) the left atrium ; (3) the left eoronary plexus.

Disseetion. — Cutthrough the right and lelt bronehi, elose to their origins from the traehea ; then divide the traehea at the upper aperture of the thorax and remove its thoraeie portion, but avoid injury to the vagi and the left reeurrent nerves. The extra-pulmonary parts of the l^ronehi will be retained in position by the bronehial arteries and ihe Lranehes of the pulmonary plexuses ; and the thoraeie part of the ^irsophagus will be fully exposed.

The Thoraeie Part of the (Esophagiis. — The thoraeie part of the oesophagus enters the thorax at the upper aperture, passes downwards, through the superior and posterior mediastina, and leaves, at the level of the tenth thoraeie vertebra, by passing through the eesophageal orifice of the diaphragm into the epigastrie region of the abdomen. As it enters the superior mediastinum it Hes somewhat to the left of the median plane, but as it deseends it passes medially, gains the median plane at the level of the fifth thoraeie vertebra, and eontinues downwards in that plane to the level of the seventh thoraeie vertebra. There it passes forwards

I02 THORAX

and to the left, aeross the anterior aspeet of the deseending aorta and posterior to the perieardium (Figs. 12 and 21).

Posterior Relations. — In the superior mediastinum it is an- terior to the left longus eolli musele and the vertebral eolumn. In the upper part of the posterior mediastinum it is separated from the vertebral eolumn by (i) the posterior part of the oeso- phageal plexus, (2) the upper six right aortie intereostal arteries, (3) the thoraeie duet, (4) the vena azygos, (5) the vena hemi- azygos and the accessoryhemiazygos vein; and in the lower part by (6) the oesophageal plexus and (7) the deseending aorta.

Anterior Relations. — Anterior to it, in the superior media- stinum, lie the traehea, the left reeurrent nerve, the upper part of the left eommon earotid artery, the left subclavian artery, the areh of the aorta, and the struetures whieh lie anterior to those already mentioned. As it passes from the superior to the posterior mediastinum its anterior relations are iirst the eommeneement of the left bronehus and then the right pulmonary artery.^ In the posterior mediastinum^ the eesophageal plexus is on its anterior surface, intervening between it and the posterior wall of the perieardium, whieh separates both the plexus and the oesophagus from the posterior wall of the left atrium ; and at a lower level the oesophagus lies posterior to the diaphragm (Fig. 21).

Right Laieral Relations. — In the superior mediastinum^ it is in relation with the right pleura and lung and with the areh of the vena azygos (Figs. 12 and 22), and in the posterior mediastinum with the oesophageal plexus and right pleura and lung, until it passes anteriorly and to the left, anterior to the deseending aorta.

Left Lateral Relations. — In the superior mediastinum, it is in relation on the left side with the thoraeie duet, the left subclavian artery, the left pleura and lung, and the termination of the areh of the aorta. From the fifth to the seventh thoraeie vertebra its left lateral relations are the oesophageal plexus and the deseending aorta ; and at its lower end^ as it lies anterior to the deseending aorta, it eomes again into relation with the left pleura and lung.

The disseetor should note (i) that, after death, the~ oesophagus is somewhat eompressed antero-posteriorly by the struetures between whieh it lies. It probably has a similar form during life when empty and flaccid, but beeomes

^ Verify this statement by replaeing the heart in situ.

THORAGie CAVITV

103

tnoie eireular when solids or Suids ue passing along it ; and (2) that it is somewhat eonstrieted at the level of the Iefi bronehus.

An ineh or more of the upper part of the posterior mediastinal poition of tbe tube should be renioved and di»- seeted under water in a eork-lioed tray. It will bc found to possess from without inwards the following eoais : (■) an extemal fibrous sheath; (a) a museular eoat ; (3) a sub- mueous eoat ; and (4) a mueous intemal lining. The submueous eoat forms a loose eonneetion between the museular and mueous eoats ; consequent]y, when the museular

eoat is eontraeted the mueous lining is thrawn into longi- tudinal folds. The museular eoat eonsists of an extemal layer of longitudinal fibres and an intemal layer of eireular fibres.

Aorta DeBeendens. — The deseending aorta eommenees at the termination of the aortie areh, at the lower border of the left side of the fourth thoraeie yertebra. Il passes down- wards, through the posterior mediastinum, and it leaves ihe thorax by[iassingthrough theaortieaperture of the diaphragm, opposite the lower border of the twelfth thoraeie vertebra. Its length is about seven inehes, In the upper part of its extent it lies to the left of the vertebral eotumn ; but in the lower part it lies anterior to the eolumn, in the median plane.

Braruhes. — Branehes spring from both the anlerior and ihe posterior aspeets of the deseending aorta. Those from the anterior aspeet are the two left bronehial arteries, four II— 7 e

104 THORAX

eesophageal branehes, and some small and iiregular media- stinal and perieardial branehes. The posterior branehes are nine pairs of aortie intereostal arteries and one pair of sub- eostal arteries.

Relations. — Anteriorto the thoraeie part of the deseending aorta, from above downwards, are the root of the ]eft lung ; the upper part of the posterior wall of the perioardium, separating the aorta from the left atrium ; the eesophagus, separating the aorta from the lower part of the posterior wall of the perieardium ; and the erura of the diaphragm, whieh separate the lower portion of the thoraeie aorta from the

omental bursa of the peritoneum and from the posterior surface of the eaudate lobe (O.T. Spigelian) of the Iiver, Posteriorly are the vertebral eolumn, its own intereostal and subeostal branehes, the hemiazygos and aeeessory hemiazygos veins ; and it is overlapped posteriorly in the upper part of its extent by the left pleura and lung. Along tts rigkt side, in its whole length, are the thoraeie duet and the vena azygos, and anterior to them, from the fiflh to the lower part of the seyenth thoraeie vertebra, lies the eesophagus. At a lower leyel a mass of areolar tissue separates the aorta from the right pleura and lung. On its le/t side it is in relation with the left pleura and lung.

Disseetiott. — Turn ihe remains of ihe lower parl of the ossophagus down- wards lowards the diaphragm. Clean the ihoraeie duel, the right aortie intereostal arteries. and the hemiazygos and aeeessory hemiazycos veins, whieh lie postetior to the oesophagus. Then traee the thoraeie duet in the

THORAGie CA\nTY

FiG. 52- — The Thoraeie Duet and ils Tributaries.

io6 THORAX

whole of the thoraeie portion of its eourse, and arrange with the disse(;tor of the head and neek to display the cervical portion of its eourse.

The Thoraeie Duet. — The thoraeie duet is a vessel of small ealibre but of great importanee, for it conveys, to the left innominate vein, the whole of the lymph from the lower extremities, the abdomen (except that from part of the upper surface of the liver), the left side of the thorax, ineluding the left lung and pleura and the left side of the heart, the left upper extremity, and the left side of the head and neek. It is the upward prolongation of a dilated sae, the eisterna ehyli, whieh lies between the right erus of the diaphragm and the bodies of the first and seeond lumbar vertebrae. It enters the thorax through the aortie orifice of the diaphragm, lying between the aorta on the left and the vena azygos on the right. It eontinues upwards through the posterior mediastinum, lying between the deseending aorta and the vena azygos, anterior to the right aortie intereostal arteries and the hemiazygos and aeeessory hemiazygos veins, and posterior to the right pleura below and the oesophagus above. At the level of the fifth thoraeie vertebra it erosses to the left of the vertebral eolumn, and then aseends, through the superior mediastinum, along the left border of the oesophagus, in eontaet, on the left, with the left pleural sae, and separated posteriorly from the left longus eolli musele by the mass of areolar tissue. Anterior to the thoraei'e duet, in the superior mediastinum, are the termination of the aortie areh, the left subclavian, and the left eommon earotid arteries, in that order from below upwards. At the upper end of the thorax the thoraeie duet enters the root of the neek, and, at the level of the seventh cervical vertebra, it turns laterally, posterior to the left eommon earotid artery, the left vagus nerve, and the left internal jugular vein, and anterior to the vertebral artery and veins, the thyreo-cervical trunk or inferior thyreoid artery, and the phrenie nerve. Then, turning downwards, anteriorly and medially, on the anterior aspeet of the sealenus anterior, it erosses anterior to the transversa eolli and transversa seapulse arteries, and terminates in the upper end of the innominate vein, in the angle of junction of its internal jugular and sub- clavian tributaries. Immediately before its termination it receives the left eommon jugular and subclavian lymphatie trunks, unless they end separately in one or other of the three large veins. When the thoraeie duet is distended it

THORAGie CAVITY

107

bas 3 beaded or nodulated appearanee on aeeount or ihe numerous valves whieh lie in its interior. The terminal valve is usually situated a short distanee from the point of entianee ot the duet into the lert innominate vein.

The lUght Irmphatie Dnet. — From the point where the thorade duet tums from the front to the left of the Tertebral eolumn a small lymphatie yessel, whieh frequently eommunieates with the thoraeie duet, may be traeed upwar along the ftom of the eolumn to the root of the neen,

io8 THORAX

where it ends in the eommeneement of the right innominate vein. This is the right lymphatie duet. Immediately before its termination it may be joined by the right eommon jugular and right subclavian lymphatie trunks, but, as a rule, the two latter vessels open separately into the sub- clavian, the internal jugular, or the innominate veins (Parsons). The right lymphatie duet conveys lymph from the upper part of the right lobe of the liver, the right side of the thorax, ineluding the right pleura and lung and the right half of the heart, and, if it is joined by the jugular and subclavian trunks, the lymph from the right upper extremity and the right side of the head and neek also.

L^rmphoglandiilsB Thoraeales. — During the disseetion of the thorax the disseetor will have noted eertain groups of lymph glands. These are of eonsiderable importanee, for their enlargement in disease is not infrequently the eause of serious thoraeie irouble ; but whilst some, sueh as the bronehial glands, are quite obvious, others are frequently so small that they eseape notiee. The following are the chief groups : — ( i ) Two ehains of minute glands wliieh are plaeed in relation to the anterior thoraeie wall and follow the eourse of the internal mammary vessels. They are termed stemal lymph glands, and are joined by lymphatie vessels from the anterior thoraeie wall, the mammary glands, the anterior part of the diaphragm, and the upper part of the anterior wall of the abdomen. (2) Two ehains of glands on the posterior thoraeie wall — one on either side of the vertebral eolumn in relation to the vertebral extremities of the ribs. These are very minute ; afferents to them aeeompany the intereostal vessels ; therefore they are ealled the intereostal lymph glandSi and they receive the lymphaties of the posterior thoraeie wall. (3) Anterior mediastinal lymph glands, two or three in number, whieh receive lymphaties from the diaphragm and upper surface of the liver. They oeeupy the lower open part of the anterior mediastinum. (4) Posterior mediastinal lymph glands, whieh follow the eourse of the thoraeie aorta, and are joined by lymphaties from the diaphragm, perieardium, and oesophagus. (5) Superior media- stinal lymph glands, an important group, eight to ten in number, and plaeed in relation to the aortie areh and the biiureation of the traehea. The lymphaties of the heart, perieardium, and thymus enter these. (6) Bronehial lymph glands, eontinuous above with the preeeding, and massed chiefly in the interval between the two bronehi. They are also prolonged into the roots of the lungs. The lymphatie vessels of the lungs pour their eontents into them. In the adult, they are generally dark in eolour, and sometimes quite blaek.

Dissedion. — Cut through the deseending aorta immediately above the diaphragm. Detaeh its upper end from the left vagus and the left reeurrent nerve whieh were previously fastened to it, then draw it forwards and divide the intereostal and subeostal arteries, whieh arise from its posterior surface, elose to their origins and remove it.

ArterisB Intereostales. — There are eleven pairs of inter- eostal arteries. The upper two pairs are derived indireetly

THORAGie CAVITV 109

from the subclavian arteries; the remaining nine pairs are branehes of the thoraeie part of the deseending aorta.

The Aortde Intereostal Arieries. — The nine pairs uf aortie intereostal arteries spring from the posterior suHaee of the deseending aorta, either separately or by a series (»f eomnion trunks, one for eaeh pair. The right arteries are longer than the left beeause the aorta lies to the left of the median plane : and, sinee the deseending aorta eommenees only at the lcvel of the lower border of the fourth thoraeie vertebra, the four or five highest pairs have to aseend to gain the level of the spaees to whieh they are distributed.

The right aortie intereostal arteries run aeross the anterior aspeets of the bodies of the vertebra2, lying posterior to the thoraeie duet and the vena azygos; then they turn posteriorly, between the sides of the bodies of the vertebrai and the parietal pleura ; and, finally, immediately before they enter the inter- eostal spaees, they pass between the sides of the bodies of the vertebrse medially and the sympathetie trunk laterally. The shorter left aortie intereostal arteries run posteriorly, first between the left pleura and the bodies of the vertebrae, and then between the sympathetie trunk and the vertebral bodies. As eaeh artery enters the spaee to whieh it belongs it gives oiT a dorsal braneh^ whieh passes posteriorly, between the vertebral eolumn medially and the anterior costo-transvcrse ligament laterally ; it gives off a spinal twig, whieh enters the verte- bral eanal through the eorresponding intervertebral foramen ; then it divides into a medial and a lateral braneh whieh aeeompany the medial and lateral divisions of the posterior braneh of the eorresponding thoraeie nerve. After giving off the dorsal braneh, the trunk of the artery runs laterally, along the upper border of the spaee to whieh it belongs, at first anterior to the posterior intereostal membrane, and then between the internal and external intereostal museles. Its further eourse has been deseribed already (p. 6). As it passes along the upper border of the intereostal spaee, in the shelter of the subeostal groove of the rib, it is situated between the intereostal vein above and the anterior braneh of the thoraeie nerve below.

The Subeostal Arteries. — The subeostal arteries are the last pair of branehes whieh spring froni the posterior aspeet of the thoraeie part of the deseending aorta. They enter the abdomen, by passing beneath the lateral lumbo-eostal

iio THORAX

arehes, and they run, in eompany with the last thoraeie nerves, along the lower borders of the last pair of ribs.

ArterisB Intereostales Supremse. — The superior intereostal arteries, whieh supply the upper two intereostal spaees on eaeh side, are derived from the costo-cervical branehes of the subclavian arteries (Fig. 5). Eaeh superior intereostal artery eommenees at the level of the upper border of the neek of the first rib. It deseends anterior to the neek of the rib, posterior to the parietal pleura and between the first thoraeie ganglion of the sympathetie trunk medially and the first thoraeie nerve; whieh is passing upwards to the braehial plexus, laterally (Fig. 5). At the lower border of the neek of the first rib it gives off the posterior inter- eostal artery to the first intereostal spaee; then it erosses anterior to the neek of the seeond rib, and, turning later- ally, it beeomes the posterior intereostal artery of the seeond spaee.

Nervi Intereostales. — The intereostal nerves are the anterior branehes of the thoraeie nerves. They pass laterally in eompany with the arteries. The twigs whieh eonneet them with the sympathetie ganglia have been noted already (p. 26). Eaeh nerve lies at a lower level than the eorre- sponding artery, and is at first plaeed between the posterior intereostal membrane and the pleura, and then between the two museular strata. The further eourse of the nerves is deseribed on p. 5.

The first thoraeie nerve runs upwards, anterior to the neek of the first rib, to join the braehial plexus. It gives a small braneh to the first intereostal spaee, but this nerve, although it is disposed after the manner of an intereostal nerve, does not furnish, as a rule, a lateral eutaneous or an anterior braneh. The seeond intereostal nerue^ as a rule, sends a braneh upwards, anterior to the neek of the seeond rib, to join that portion of the first thoraeie nerve whieh enters the braehial plexus. This eommunieating twig is usually minute and in- significant, but sometimes it is a large nerve; when this is the ease, the intereosto-braehial nerve (O.T. intereosto- humeral), or lateral eutaneous braneh of the seeond intereostal nerve, is very small or altogether absent.

YensB Intereostales. — The intereostal veins differ in their arrangement upon the two sides of the body. On the right side they terminate in three different ways : —

THORAGie CAVn Y 1 1 1

1. The intereostal vein of the first or highest s|>ace joins ihe right

innominate vein (sometimes the vertebral retM).

2. The intereostal veins of the seeond and third spaees (and sometimes

that of the fourth spaee) unite into a eommon trunk, termed the rig'A/ superior intereosial vein^ whieh joins the upjK.'r part of the vena azygos. '

3. The intereostal veins of the lower eight spaees join the vetta azy^s.

On the ie/i stde of the hoAy four modes of termination may be reeognised : —

1. The intereostal vein of the first spaee joins the left innominate vein

(sometimes the vertebral vein).

2. The intereostal veins of the seeond and third spaees (and sometimes

that of the fourth spaee) converge and by their union form a single trunk, termed the left superior intereostal vein^ whieh erosses the areh of the aorta and joins the left innominate vein independently of the first intereostal vein. The union with the left innominale vein may be absent, and then ihe trunk formed by ihe veins of the seeond and third spaees joins the aeeessory hemiazygos vein.

3. The intereostal veins of the fourth, fifth, sixth, seventh, and eighth

spaees terminate in the aeeessory hemiazygos vein (O.T. vena azygos minor superior), whieh erosses posterior to the aorta and joins ihe hemiazygos vein, or it ends direetly in ihe vena azygos.

4. The intereostal veins of the ninth, tenth, and eleventh spaees join the

hemiazygps vein (O.T. vena azygos minor inferior).

Vena Azyg08 (O.T. Vena Azygos Major). — This has already been studied, but -should now be revised (p. 29), and then the disseetor should examine the hemiazygos and aeeessory hemiazygos veins.

Vena Hemiazygos Aeeessoria. — The aeeessory hemiazygos vein is formed, on the left side of the body, by the union of the intereostal veins of the fourth, fifth, sixth, seventh, and eighth spaees. It eommunieates above with the left superior inter- eostal vein, whieh earries the blood from the seeond and third intereostal spaees to the left innominate vein ; and it receives the left bronehial veins. At the level of the seventh thoraeie vertebra it erosses to the right, posterior to the aorta and thoraeie duet, and ends by joining either the hemiazygos vein or the vena azygos. In addition to the intereostal veins it receives the left bronehial veins.

Vena Hemiazygos (O.T. Vena Azygos Minor Inferior). — This vein takes origin within the abdomen as the left aseending iumbar vein. It enters the thorax by piereing the' left erus of the diaphragm, and is eontinued upwards, upon the vertebral eolumn, as far as the eighth or seventh thoraeie yertebra. At this point it turns to the right, and,

iio THORAX

arehes, and they run, in eompany with the last thoraeie nerves, along the lower borders of the last pair of ribs.

Arteriae Intereostales Supremse. — The superior intereostal arteries, whieh supply the upper two intereostal spaees on eaeh side, are derived from the costo-cervical branehes of the subclavian arteries (Fig. 5). Eaeh superior intereostal artery eommenees at the level of the upper border of the neek of the first rib. It deseends anterior to the neek of the rib, posterior to the parietal pleura and between the first thoraeie ganglion of the sympathetie trunk medially and the first thoraeie nerve; whieh is passing upwards to the braehial plexus, laterally (Fig. 5). At the lower border of the neek of the first rib it gives off the posterior inter- eostal artery to the first intereostal spaee; then it erosses anterior to the neek of the seeond rib, and, turning later- ally, it beeomes the posterior intereostal artery of the seeond spaee.

Nervi Intereostales. — The intereostal nerves are the anterior branehes of the thoraeie nerves. They pass laterally in eompany with the arteries. The twigs whieh eonneet them with the sympathetie ganglia have been noted already (p. 26). Eaeh nerve lies at a lower level than the eorre- sponding artery, and is at first plaeed between the posterior intereostal membrane and the pleura, and then between the two museular strata. The further eourse of the nerves is deseribed on p. 5.

The first thoraeie nerue runs upwards, anterior to the neek of the first rib, to join the braehial plexus. It gives a small braneh to the first intereostal spaee, but this nerve, although it is disposed after the manner of an intereostal nerve, does not furnish, as a rule, a lateral eutaneous or an anterior braneh. The seeond intereostal nerue, as a rule, sends a braneh upwards, anterior to the neek of the seeond rib, to join that portion of the first thoraeie nerve whieh enters the braehial plexus. This eommunieating twig is usually minute and in- significant, but sometimes it is a large nerve ; when this is the ease, the intereosto-braehial nerve (O.T. intereosto- humeral), or lateral eutaneous braneh of the seeond intereostal nerve, is very small or altogether absent.

Venae Intereostales. — The intereostal veins differ in their arrangement upon the two sides of the body. On the right side they terminate in three different ways : —

THORAGie CAVn Y 1 1 1

1. The intereostal vein of the first or highest si^aee joins the ri^ht

innominaie vein (sometimes the vertebral vein),

2. The intereostal veins of the seeond and third spaees (and sometimes

that of thefourth spaee) unite into a eommon trunk, termed the ri^A/ superior intereostal ^ein^ whieh joins the upiw i>art (>f the vena azygos, '

3. The intereostal veins of the lower eight spaees juin the x'etta azy^s,

On the Uft side of the bodyy^r modes of termination may be reeognised : —

1. The intereostal vein of the first spaee joins the left innominate vein

(sometimes the vertebral vein).

2. The intereostal veins of the seeond and third si)aces (and sometimes

that of the fourth spaee) converge and by their union form a single trunk, termed the /e/t superior intereostal rein^ whieh erosses the areh of the aorta and joins the left innominate vein independently of the first intereostal vein. The union with the left innominate vein may be absent, and then the trunk formed by ihe veins of the seeond and third spaees joins the aeeessory hemiazygos vein.

3. The intereostal veins of the fourth, fifth, sixth, seventh, and eighth

spaees terminate in the aeeessory hemiazygos vein (O.T. vena azyg<)s minor superior), whieh erosses posterior to ihe aorla and joins ihe hemiazygos vein, or it ends direetly in thevena azygos.

4. The intereostal veins of the ninth, tenth, and eleventh spaees join the

hemiazygos vein (O.T. vena azygos minor inferior).

Vena Azyg08 (O.T. Vena Azygos Major). — This has already been studied, but -should now be revised (p. 29), and then the disseetor should examine the hemiazygos and aeeessory hemiazygos veins.

Vena Hemia^ygos Aeeessoria. — The aeeessory hemiazygos vein is formed, on the left side of the body, by the union of the intereostal veins of the fourth, fifth, sixth, seventh, and eighth spaees. It eommunieates above with the left superior inter- eostal vein, whieh earries the blood from the seeond and third intereostal spaees to the left innominate vein ; and it receives the left bronehial veins. At the level of the seventh thoraeie vertebra it erosses to the right, posterior to the aorta and thoraeie duet, and ends by joining either the hemiazygos vein or the vena azygos. In addition to the intereostal veins it receives the left bronehial veins.

Vena Hemiazygos (O.T. Vena Azygos Minor Inferior). — This vein takes origin within the abdomen as the left aseending lumbar vein, It enters the thorax by piereing the' left erus of the diaphragm, and is eontinued upwards, upon the yertebral eolumn, as far as the eighth or seventh thoraeie yertebra. At this point it turns to the right, and,

iio THORAX

arehes, and they run, in eompany with the last thoraeie nerves, along the lower borders of the last pair of ribs.

Arteriae Intereostales Supremse. — The superior intereostal arteries, whieh supply the upper two intereostal spaees on eaeh side, are derived from the costo-cervical branehes of the subclavian arteries (Fig. 5). Eaeh superior intereostal artery eommenees at the level of the upper border of the neek of the first rib. It deseends anterior to the neek of the rib, posterior to the parietal pleura and between the first thoraeie ganglion of the sympathetie trunk medially and the first thoraeie nerve ; whieh is passing upwards to the braehial plexus, laterally (Fig. 5). At the lower border of the neek of the first rib it gives off the posterior inter- eostal artery to the first intereostal spaee; then it erosses anterior to the neek of the seeond rib, and, turning later- ally, it beeomes the posterior intereostal artery of the seeond spaee.

Nervi Intereostales. — The intereostal nerves are the anterior branehes of the thoraeie nerves. They pass laterally in eompany with the arteries. The twigs whieh eonneet them with the sympathetie ganglia have been noted already (p. 26). Eaeh nerve lies at a lower level than the eorre- sponding artery, and is at first plaeed between the posterior intereostal membrane and the pleura, and then between the two museular strata. The further eourse of the nerves is deseribed on p. 5.

The first thoraeie nerue runs upwards, anterior to the neek of the first rib, to join the braehial plexus. It gives a small braneh to the first intereostal spaee, but this nerve, although it is disposed after the manner of an intereostal nerve, does not furnish, as a rule, a lateral eutaneous or an anterior braneh. The seeond intereostal nerve, as a rule, sends a braneh upwards, anterior to the neek of the seeond rib, to join that portion of the first thoraeie nerve whieh enters the braehial plexus. This eommunieating twig is usually minute and in- significant, but sometimes it is a large nerve ; when this is the ease, the intereosto-braehial nerve (O.T. intereosto- humeral), or lateral eutaneous braneh of the seeond intereostal nerve, is very small or altogether absent.

Venae Intereostales. — The intereostal veins differ in their arrangement upon the two sides of the body. On the right side they terminate in three different ways : —

THORAGie CAVn Y 1 1 1

1. The intereostal vein of the tirst or highest s{Kice joins the ri^ht

innominaie vein (sometimes the V€rteoral fein).

2. The intereostal veins of the seeond and third s|>accs (and sometimes

that of thefourth spaee) miite into a eommon trunk, termed the rig'At superior intereostal yein^ whieh joins the upi^er {^rt (>f the vena azygos. '

3. The intereostal veins of the lower eight s{)aces join the rena aty^s.

On the left stde of the \xAyfimr modes of terniination may be reeognised : —

1. The intereostal vein of the first spaee joins the left innominate vein

(sometimes the vertebral vein).

2. The intereostal veins of the seeond and third s{)aces (and sometimes

that of the fourth spaee) converge and by their union form a single trunk, termed the le/t superior intereostal rein^ whieh erosses the areh of the aorta and joins the left innominaie i*ein inde{)endently of the first intereostal vein. The union with the lt'ft innominale vein may be absent, and then the trunk formed by the veins of the seeond and third si^aees joins the aeeessory heniiazygos vein.

3. The intereostal veins of the fourth, fifth, sixth, seventh, and eighth

spaees terminate in the aeeessory hemiazygos vein ((J.T. vena a/ygos minor superior), whieh erosses }x>sterior to the aorta and joins the hemiazygos vein, or it ends direetly in thevena azygos.

4. The intereostal veins of the ninth, tenth, and eleventh sp>aces join the

hemiazygps vein (O.T. %>ena azygos ininor inferior).

Vena Azyg08 (O.T. Vena Azygos Major). — This has already been studied, but should now be revised (p. 29), and then the disseetor should examine the hemiazygos and aeeessory hemiazygos veins.

Vena Hemiazygos Aeeessoria. — The aeeessory hemiazygos vein is formed, on the left side of the body, by the union of the intereostal veins of the fourth, fifth, sixth, seventh, and eighth spaees. It eommunieates above with the left superior inter- eostal vein, whieh earries the blood from the seeond and third intereostal spaees to the left innominate vein ; and it reccives the left bronehial veins. At the level of the seventh thoraeie vertebra it erosses to the right, posterior to the aorta and thoraeie duet, and ends by joining either the hemiazygos vein or the vena azygos. In addition to the intereostal veins it receives the left bronehial veins.

Vena Hemiazygos (O.T. Vena Azygos Minor Inferior). — This vein takes origin within the abdomen as the left aseending lumbar vein. It enters the thorax by piereing the' left erus of the diaphragm, and is eontinued upwards, upon the yertebral eolumn, as far as the eighth or seventh thoraeie yertebra. At this point it turns to the right, and,

1 1 2 THORAX

erossing posterior to the aorta and the thoraeie duet, it joins the vena azygos. Before it terminates it may receive the aeeessory hemiazygos vein.

The thoraeie tributaries of this vein are the intereostal veins of the lower three spaees of the left side and the left subeostal vein. In the abdomen it receives the upper two left lumbar veins.

The Anterior Intereostal Yeins. — The blood is drained from the anterior part of the thoraeie wall by veins whieh aeeompany the intereostal branehes of the internal mammary arteries. They terminate in the internal mammary veins.

The veins of the thoraeie parietes are extremely variable, and the deseription given above must be looked upon as representing merely their more usual arrangement.

THORAGie JOINTS.

The disseetor should now eomplete the disseetion of the thorax by an examination of the various thoraeie joints.

Disseetion. — When the portion of the sternum with the eartilages of the ribs, whieh was laid aside, is studied, the following joints will be noted : inter-sternal, eosto-sternal, and inter-ehondral. Very little disseetion is neeessary. After the ligaments have been defined, the 4issector should remove a thin sliee from the anterior aspeet of eaeh artieulation, in order that the interior of the joint may be displayed.

Synehondrosis Stemalis. — The joint between the manu- brium and the body of the sternum is a synehondrosis. The opposing surfaces of bone are covered with a layer of hyaline eartilage, and are united by intermediate fibro-cartilage. The joint is supported by some anterior and posterior longitudinal iibres whieh are developed in eonneetion with the strong and thiek periosteum. The posterior ligament is the stronger of the two. The joint between the body of the sternum and the xiphoid proeess is also a synehondrosis till middle life, at whieh period the two parts beeome ossiAed together.

Stemo-eliondral Artieulations. — Seven ribs artieulate with eaeh side of the sternum by means of their eartilages.

The artieulations of the first and the sixth are peeuliar, inasmueh as they artieulate with single pieees of the sternum, viz. with the manubrium and the lowest pieee of the body, respectively ; whereas eaeh of the eartilages of the other true ribs artieulates with two segments of the sternum. The eartilage of the first rib is implanted upon the side of the manubrium

THORAGie JOINTS 113

without any s)movial membrane, or other material, intervening. The seeond eostal eartilage is usually separated from the sternum by two synovial cavities, between whieh an interartieular ligament is dcveloped. In the ease of the other joints it is more eommon to hnd a single synovial cavity and no interartieular ligament. There is, however, eonsiderable variety in these artieulations, and a synoviaI membrane is very frequently wanting altogether in the sterno-ehondral joint of the seventh eostal eartilage.

With the exception of the first, whieh is a s^mehondrosis, the sterno-ehondral joints belong to the diarthrodial variety. They are provided with anterior and posterior ligaments, and also, in those eases where the joint presents a double synovial oayity, with an interartieular ligament.

Anterior and posterior stemo-eostal radiate ligaments, These are strong, fiattened bands of fibres whieh radiate from the extremities of the rib-eartilages and blend with the periosteum on the anterior and posterior surfaces of the sternum. The interartieular ligaments are feeble bands whieh pass from the tips of the rib-eartilages to the stemum, and divide the artieu- lations in whieh they exist into an upper and a lower eom- partment, eaeh of whieh is lined with a synovial stratum.

Iiiter-eliondral Artienlations. — Interehondral joints are formed between the adjacent margins of the ribs from the sixth to the tenth. The joint cavities are surrounded by ordinary eapsular ligaments, eaeh of whieh is lined internally with a synovial stratum ; they are, therefore, diarthrodial joints.

Costo-vertebral Artienlations. — The costo-vertebral joints are separable into two groups, eapitular and costo-transverse.

The eapitular artieulations are the joints between the heads of the ribs and the bodies of the vertebrae and the interverte- bral fibro-cartilages ; they are diarthrodial joints. With the exceptions of the first and the last three ribs, the head of every rib artieulates with the bodies of two adjacent vertebrae and the intervening intervertebral fibro-cartilage, and it is eonneeted with them by an artieular eapsule and an inter- artieular ligament. The interartieular ligament eonneets the intervertebral fibro-cartilage with the ridge whieh separates . the two facets on the head of the rib. It is united, anteriorly and posteriorly, with the eapsule, and separates the joint cavity into an upper and a lower eompartment. The anterior part of the eapsule is speeialised into three radiating bands whie form the radiate ligament, The upper and lower bands

VOL. II — 8

114 THORAX

to the eorresponding verlebr!e, whilst the intermedi.ite band is attaehed to the intervertebral Hbro-eartilage. The eapilular joints of the first, and the tenth, eleventh, and twelfth ribs are eaeh formed between the head of the rib and the eorrespond- ing vertebra. The interartieular ligament is absent; therefore eaeh joint possesses only one cavity. The anterior parts of the eapsules of these joints are not, as a rule, speeialised into radiate bands.

Tlie Oosto-tianaTerse Artteulations are the joints fornied

between the neeks and the tubereles of the ribs and the trans- verse proeesses of the vertebrEe.

The tuberele of eaeh rib, with the exception of the eleyenth and tweUth, artieulates with the tip of the ttansyerse proeess of the vertebra of the same number, by a eireular artieular facet whieh is surrounded by an artieular eapsule lined with a stratum synoviale. The joint is, therefore, a diar- throdial joint and the upper and posterior part of the eapsule is greaily thiekened, and is ealled the ligament of tke tubereh (O.T. posterior eosto-transmrse liganieni). In addltion to the eapsule and its posterior thiekening there are three aeeessory

THORAGie JOINTS 1 1 5

costo-transverse bands, the anterior and posterior eosto-trans- yerse ligaments and the ligament of the neek of the rib. The anterior eosto - transyerse ligament aseends from the anterior margin of the upper border of the neek of the rib to the lower border of the transverse proeess above. The posterior costO'transverse ligament passes upwards from the posterior part of the upper border of the neek of the rib to the junction of the lamina and the transverse proeess of the vertebra above ; and the ligament 0/ the neek of the rib (O.T. middle costo-transverse iigament) eonneets the posterior aspeet of the neek of the rib with the anterior aspeet of the transverse proeess of the vertebra of the same number.

In the ease of the eleventh rib the costo-transverse liga- ments are rudimentary or absent, and in the ease of the twelfth rib they are usually entirely absent.

Intenrertebral Artiealations. — The bodies of the vertcbrae are held together by a series of synehondrodial joints, sup- ported anteriorly by an anterior longitudinal ligament, and posteriorly by a posterior longitudinal ligament. The vertebral arehes, by means of the artieular proeesses, form a series of diarthrodial joints surrounded by eapsular ligaments, eaeh eapsule being lined with a synovial stratum. Gertain ligaments pass between different portions of the vertebral arehes and their proeesses, viz., the ligamenta flava between adjacent laminse, the inter-transverse, the inter-spinous, and the supra-spinous ligaments.

The laminse and the spinous proeesses of the vertebrae have been removed by the disseetor of the head and neek in opening up the vertebral eanal to display the spinal meduUa. Consequently, the ligamenta flava, the inter-spinous and supra-spinous ligaments, eannot be seen at present.

The anterior longiiudinal ligament (O.T. anterior eommon ligament) is situated anterior to the bodies of the vertebrae, and extends from the atlas vertebra above to the iirst pieee of the saerum below. It eonsists of stout glistening fibrous bands, whieh are firmly attaehed to the margins of the verte- bral bodies and to the intervertebral fibro-cartilages. The most superficial fibres are the longest, and extend from a given vertebra to the fourth or fifth below it. The deeper fibres have a shorter eourse, and pass between the borders of two, three, or four adjacent vertebrae. The disseetor eannot fail to notiee that the origin of the longus eolli musele is inseparably eonneeted with this ligament.

II — 8«

ir6 THORAX

The posterior lon^tudinal ligament (O.T. posterior eommoti ligammt) is plaeed on the posterior aspeets of the vertebral bodies, and therefore within the vertebral eanal. It is Hrmly eonneeted to the margins of the vertebral bodies and to the intervertebral fibro-cartilages, but is separated from the eentral parts of the bodies by some loose connective tissue and by a plexus of veins, It is eonstrieted where it covers this venous plexus, but widens out opposite the fibro-canilages. It there- fore presents a sealloped or dentieulated appearanee. The interuertebral fibro- ' eartilages are a series of dises of white fibro-car- tilage, thieker anteriorly than posteriorly, whieh are interposed between the bodiesofadjacentvertebrse. The peripheral part of eaeh dise, annulus fibroms, is tough and Sbrous ; the eentral portion, nudeus pulposus, is soft and pulpy. The dises inetease the elastieity of the spine, and tend to restore it to its natural curvature after it has been deflected by museular aetion.

e intervettebral :artilages eonstitute the main bond of union between the bodies of the vertebr£e, but, except in old people, they are not direetly attaehed to the bone. A thin layer of en- erusting hyaline eartilage eoats the opposing vertebral surfaces.

Fio. ss- — Posterior Longitiidinal Liga- mem of liie Yeitebral Goliimn. The yertebral arehes have been remored froni Ihe veriebrEe,

The intertransmrse Kganunts are feeble bands whieh pass between the tips of the transverse proeesses. In the lower part of the thoraeie region they are intimately blended with the intertransverse museles i in the middle and upper parts of the thoraeie region they entirely replaee the museles.

FACE AND PRONTAL REGION 0F HEAD 117

HEAD AND NECK.

The disseetors of the Head and Neek begin work as soon as the subject is brought into the room. During the first three days, whilst the body is in the lithotomy posture, they disseet the face, the anterior part of the eyelids, the superficial part of the nose, and the anterior part of the sealp. During the following five days, when the body is lying on its baek, they disseet the posterior triangle, and eomplete the disseetion of the sealp.

It is only by disseeting the face at this period, whilst the parts are in good eondition, that the disseetor ean gain any satisfactory idea of its eomponent parts ; and it is essential that the eontents of the posterior triangle, whieh is sueh an important surgieal region, should be displayed before the disseetor of the arm has disturbed its posterior boundary.

The first day should be devoted to the examination of the anierior part of the frontal region of the head and the face, the study of the surface anatomy of the oeular appendages, the reflection of the skin, and the elean- ing of the superficial museles of the face and anterior part of the sealp. On the seeond day the disseetors should display the superficial surface of the parotid gland ; they should also find and elean the superficial vessels and nerves, and traee them to their terminations. On the third day the superficial museles must be reflected, and the deeper vessels and nerves must be exposed and eleaned, and the auriele should be examined and disseeted. On the fourth day, when the body has been plaeed upon its baek, the disseetors should eommenee the disseetion of the posterior triangle of the neek, and should eomplete that part of the disseetion in three days. On the seventh day they should eomplete the examination of the sealp. The eighth day should be devoted to a final study of the braehial plexus in assoeiation with the disseetors of the upper extremity.

FACE AND FRONTAL REGION 0F HEAD.

The disseetors should eommenee the study of the face and frontal region by an examination of the bony prominenees and ridges in the area to be disseeted.

In the eentre of the facial area is the prominent outer portion of the nose, eonsisting of a lower mobile part formed mainly by skin and eartilage, and an upper rigid portior formed by the nasal bones and the frontal proeesses

ii8 HEAD AND NECK

the maxill9e. On either side of the nose are the soekets for the eyeballs, eaeh of whieh is bounded above by the supra-orbital margin of the frontal bone and below by the orbital margins of the maxilla and the zygomatic bone (O.T. malar). The supra- and infra-orbital margins meet laterally in the region of the eheek bone (zygomatic). From the posterior part of the zygomatic bone, the zygomatic areh, formed partly by the zygomatic and partly by the temporal bone, extends posteriorly to the ear. Above the zygomatic areh is the region of the temporal fossa, whieh is bounded superiorly by the temporal line. The line terminates anteriorly in the lateral part of the supra-orbital margin. Above the medial part of the supra-orbital margin the supereiliary areh ean be felt, and at a higher level, above the lateral part of the supra-orbital margin, lies the frontal tuber. The region above the nose and between the medial ends of the supereiliary arehes is the glabella,

Below the zygomatic areh lies the ramus of the mandible covered by the masseter musele; and extending anteriorly from the lower end of the ramus is the body of the mandible. A line dropped vertically through the junction of the medial third with the lateral two-thirds of the supra-orbital margin, will eut through the supra-orbital noteh of the frontal bone, the infra-orbital foramen of the maxilla, and the mental foramen of the mandible, all three of whieh may be felt if firm pressure is made in the proper situations. The first, whieh lies in the supra-orbital margin, transmits the supra-orbital vessels and nerve. The seeond is plaeed about half an ineh below the infra-orbital margin. It transmits the infra-orbital vessels and nerve. The third lies midway between the seeond premolar tooth of the mandible and the lower border of the mandible ; it transmits the mental branehes of the inferior alveolar vessels and nerve.

After the bony points of the region have been studied, the surface anatomy of the oeular appendages should be examined. Under this head are ineluded (i) the eyebrows; (2) the eyelids; (3) the conjunctiva.

The eyebrows are two curved tegumentary projections plaeed over the supra-orbital areh of the frontal bone ; they intervene between the forehead above and the oeular regions below. The short stiff hairs whieh spring from the eyebrows have a lateral inelination.

FACE AND FRONTAL REGION 0F HEAl) 119

The eyelids (palpebne) are the semilunar eurtains ;>rovidcd for the proteetion of eaeh eyebalL The upper lid is the longer and mueh the more movable of the Iwo. \\'hen the eye is open, the margins of the two lids are slightly concavc and the interval between them, rima palptbranim, is elliptieal in outline, When the eye is elosed, and ihe margins of the lids are in apposition, the rima palpebrarum is redueed to a

Fia. 56. — Eyelid slighlly everled 10 shoH Ihe Coiijunciiva (enlarged).

nearly horizontal line. Owing to the greater length and mobility of the upper hd, the rima, in this eondition, is piaeed below the Ievel of the eomea or elear part of the eyeball.

At the extremities of the rima palpebrarum the eyelids meet and form the palfebral eommissures, and immediately lateral to the medial eommissure the rima expands into a small triangular spaee ealled the laeiis laerimalis. If the disseetor now esamines the free margins of the iids he will note that to the lateral side of the laeus laerimalis they

I20 HEAD AND NECK

are flat, and that in eaeh ease the eyelashes project from the anterior border, whilst the tarsal glands open along the posterior border, a distinet interval intervening between the eilia and the mouths of the glands. On the other hand, the small portion of the margin of eaeh eyelid whieh bounds the laeus laerimalis is more horizontal in direetion, somewhat rounded, and destitute both of eyelashes and of tarsal glands. At the very point where the eyelashes in eaeh eyelid eease, and the palpebral margin beeomes rounded, a minute emi- nenee with a eentral perforation will be seen. The eminenee is the papilla laerimalis^ whilst the perforation, ealled the punetum laerimak^ is the mouth of the laerimal duet^ whieh conveys away the tears. Endeavour to pass a bristle into eaeh of the orifices. The upper duet at first aseends, whilst the lower one deseends, and then both run horizontally to the laerimal sae.

The conjunctiva is the membrane whieh lines the deep surfaces of the lids, and is reflected from them on to the anterior aspeet of the eyeball. At the margins of the lids it is eontinuous with the skin, whilst, through the puneta laeri- malia and the laerimal duets, it beeomes eontinuous with the lining membrane of the laerimal sae. The line of re- flection of the conjunctiva from the lids on to the eyeball is termed the fornix conjunctivce. Owing to the greater depth of the upper lid, the conjunctival reeess between the upper lid and the eyeball is of greater extent than that of the lower lid. The conjunctiva is loosely eonneeted with the eyelids on the one hand, and with the selera of the eyeball on the other. Over the eornea the membrane beeomes thinned down to a mere epithelial covering, whieh is elosely adherent.

In eonneetion with the conjunctiva, the pliea semiiunaris and the earuneula laerimalis must be examined. The earuneula is the reddish fleshy-looking elevation whieh oeeupies the eentre of the laeus laerimalis. From its surface a few minute hairs project. The pliea semilunaris is of interest beeause in the human eye it is the rudimentary representative of the membrana nietitans, or third eyelid, found in many animals. It is a small vertical fold of conjunctiva, whieh is plaeed immediately to the lateral side of the earuneula, and it slightly overlaps the eyeball at this point.

Dissedion, — Distend the eyelids slightly by plaeing a little tow or eotton wool steeped in preservative solution in the conjunctival sae ; then stiteh

FACE AND PRONTAL REGION OF HEAD 121

the margins of the lids together. Distend the eheeks and Iifis slightly by plaeing tow or eotton wool steeped in preservative solution in the vesti)iule of the mouth — that is, between the eheeks and lips extemally an<l the teeth and gums intemally ; then stiteh the red margins of the lips together.

Reileet the skin by means of three indsions, a median longitudinal and two transverse. Gommenee the median ineision midway belween the root of the nose and the exiemal oeeipital protuberanee, eanry it anteriorly to the forehead and then downwards aiong the median line of the forehea(l, the nose and the lips, to the tip of the ehin. Gommenee the upper horizontal ineision at the level of the rima palpebrarum ; carr>' it laterally from the longitudinal ineision to the medial eommissure, then round the margins ot the rima tothe lateral eommissure, and, Anally, posteriorly to the ear. The lower horizontal ineision should run from the angle of the mouth to the posterior border of the ramus of the mandible. Keflect the upper and middle Aaps and leave them attaehed posteriorly. KeHeet the lower Hap downwards to the lower border of the mandible. Note, whilst reflecting the skin, that many of the superHeial Abres of the facial museles are implanted into its deep surface. It is these fibres whieh tend to displaee the margins of wounds of the face, and neeessitate the applieation of numerous and firmly tied sutures in order to seeure quick and aeeurate union. Whilst reAeeting the skin the disseetor must be careful to keep his knife playing against its deep surface ; otherwise he is eertain to injure Ihe sphineter musele of the eyelids, and the superficial extrinsic museles of the ear whieh lie in the temporal r^on.

After the skin is reSeeted the superficial museles must be eleaned. That whieh will first attraet attention is the orbieu- laris oeuli around the orbit Above the orbieularis oeuli is the frontalis belly of the epieranial musele. To the medial side of the orbieularis oeuli he the museles of the nose, and below it the museles of the upper lip pass downwards to the orbieularis oris. Passing anteriorly and upwards, over the posterior part of the lower border of the mandible, are the upper and posterior fibres of the platysma, and more medially are the museles of the lower lip.

Gommenee with the Orbieularis Oeuli (O.T. Orbieularis Palpebranun). — Pull the eyelids laterally and note a prominent eord-like band whieh extends from the frontal proeess of the maxilla to the medial eommissure, where it beeomes eontinuous with both eyelids ; this is the medial palpebral ligament (O.T. intemal tarsal ligament). A somewhat similar band, the lateral palpebral raphe (O.T. external tarsal ligament), extends from the lateral eommissure to the zygomatic bone. After the medial palpebral ligament has been reeognised, elean first the thieker orbital part of the orbieularis oeuli, whieh covers the superficial bony boundaries of the orbit, and then the thinner palpebral portion^ whieh lies in the eyelids. The palpebral part is not only thin but also pale, and its fibrf

122 HEAD AND NECK

eaeh eyelid, sweep in gentle curves from the medial palpebral ligament to the lateral palpebral raphe, gaining attaehment to both. They form a eontinuous layer of uniform thiekness in eaeh eyelid, except near the free margins, where, elose to the bases of the eyelashes, there is a more pronouneed fasciculus termed the dliary bundie.

The orbital portion of the musele passes upwards to the forehead, laterally to the temporal region and downwards into the eheek. Its fibres are relatively dark and eoarse. They all take origin medially from the medial part of the palpebral ligament, the medial angular proeess of the frontal bone, and the frontal proeess of the maxilla, and they sweep laterally round the margin of the orbit in the form of a series of eon- eentrie loops. The pars laerimalis of the orbieularis* oeuli (O.T. tensor tarsi) will be deseribed when the eyelids are disseeted (p. 140).

Museulus Epieranius (O. T. Oeeipito - Prontalis). — The epieranius is a quadricipital musele possessing two oeeipital heads, the oeeipitales museles, and two frontal heads, the frontales museles ; they are all inserted into an intermediate aponeurosis, the galea aponeurotiea (O.T. epieranial aponeur- osis\ whieh extends from the frontal to the oeeipital region (p. 158). The lower part of eaeh frontal head blends with the orbieularis oeuli, and from its medial border a small museular bundle, known as the museulus proeerus (O.T. pyramidalis nast), deseends to the dorsum of the nose. At present only the frontalis and the proeerus are to be displayed.

The Frontalis beeomes apparent immediately above the upper border of the orbieularis oeuli. As it is eleaned eare should be taken to avoid injury to the branehes of the supra- orbital nerve whieh pieree it. It has little or no attaehment to bone. Below, its fibres either blend with the fibres of the orbieularis oeuli or they are attaehed to the skin of the eye- brows. Above, they terminate in the galea aponeurotiea in the region of the eoronal suture. The lateral border is attaehed to the temporal ridge by aponeurotie fibres, and the medial border blends with its fellow of the opposite side for a short distanee above the root of the nose. Above the union the medial fibres of opposite sides diverge, and below it they pass downwards over the nasal bones as the proeeral museles.

Museulus Proeerus (O.T. Psrramidalis Nasi). — The proeeral museles are often absent ; when present, eaeh springs from

FACE AND PRONTAL REGION OF HEAD 123

the lower and medial part of the eorresponding Trontalis. It deseends over the nasal bone and ends on the dorsum of the nose, where some of its fibres blend with the trans- verse part of the nasalis and others are inserted into the skin.

Along the lower and medial border of the orbieularis oeuli will be found the museles of the nose and the upper lip.

The proper museles of the nose are the museulus nasalis and the museulus depressor septi, but the proeerus may also be looked upon as partly a nasal musele, and the angular head of the quadratus labii superioris has a nasal attaehment.

MtLseulus Nasalis. — The museulus nasalis eonsists of two parts, the pars tranwersa (O.T. eomprtssor naris\ and the pars alaris (O.T. dilator narii), The pars transversa springs from the root of the frontal proeess of the maxilla, passes aeross the eartilaginous part of the nose, above the ala, and ends in an aponeurosis whieh eonneets it with its fellow of the opposite side. The pars alaris springs from the maxilla, at the side of the lower part of the anterior nasal aperture, and it terminates in the posterior part of the ala and the mobile part of the septum of the nose. The nasalis is partly eoneealed by the medial fibres of the quadratus labii superioris.

MtLseulus Depressor Septi Nasi. — This small musele is frequently difficult to display. It springs from the superficial fibres of the upper part of the orbieularis oris, and is inserted into the anterior part of the septum of the nose. It depresses the septum and reduees the antero-posterior diameter of the anterior nasal aperture.

After the museles of the nose have been examined elean the superficial museles of the mouth and eheek.

Tlie Museles of the Mouth and Gheeks. — The museles of this group form two layers, a superficial and a deep. Those of the superficial group are the orbieularis oris, quadratus labii superioris, zygomaticus, triangularis, risorius, quadratus labii inferioris ; those of the deeper group are the bueeinator, eaninus, incisivi and mentalis. All, with the exception of the orbieularis oris, are bilateral. The members of the superficial group must be examined first ; the deeper museles will be displayed after the superficial vessels and nerves have been disseeted.

Orbieularis Oris. — The orbieularis oris is the sphineter musele of the oral aperture. It lies in the substanee of the lips, and eonsists of a deeper layer of fibres whieh are arrange^'

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HEAD AND NECK

in eoneentrie ellipsoidal rings, and a series of superficial fibres into wliieh all tlie otlier museles of the lips and eheeks eon- vet^e. The detaiis of its formalion eannot be understood until the attaehments of the Other museles have been studied.

FiG. 57. — The Facial Museles.

MnseulnB Qiiadratns Labii SuperioriB.— The qiiadratus labii superioris possesses three heads — a zygomatic, an infra- orbita!, and an angular. As the musde is eleaned the disseetor should seeure the upper part of the anterior facial vein, whieh erosses ils superficial surface.

FACE AND FRONTAL REGION OF HEAI) 125

The zygomatic head (O.T. sygomatieus minor) springs from the anterior part of the facia] surface of the zygomatic bone, under cover of the lower lateral part of the orbieularis oeuli. It runs downwards and anteriorly, and is inserted into the lateral part of the upper portion of the orbieularis oris and into the adjacent part of the skin of the upper lip.

The Infra-orbital Head (O.T. Levator Labii Suptrioris Proprius). — This head springs from the whole length of the infra-orbital border, under cover of the orbieularis oeuli. It is inserted into the upper lateral part of the orbieularis oris and the skin of the upper lip.

The angular head (O.T. levator iabii superioris alirque nasi) springs from the frontal proeess of the maxilla. It broadens as it deseends, and it is inserted into the ala of the nose and into the upper part of the orbieularis oris.

MuseultLS Z7goiiiaticii8. — The zygomaticus (O.T. zygo- matieus major) is a comparatively long, slender museular band whieh springs from the facial suHaee of the zygomatic bone, under cover of the lower lateral fibres of the orbieularis oeuli and to the lateral side of the zygomatic head of the quadratus labii superioris. Its fibres pass downwards and medially to the angle of the mouth, where some blend with the orbieularis oris and others are inserted into the skin.

The Bisorius. — This musele, when well developed, eonsists partly of some of the uppermost fibres of the platysma musele of the neek, whieh bend anteriorly to the angle of the mouth, and partly of additional fibres whieh spring from the fascia over the masseter musele and the parotid gland. Both groups of fibres blend with the fibres of the orbieularis oris at the angle of the mouth.

Museulus Triangularis. — The triangularis (O.T. depressor anguli oris) springs from the oblique line on the lateral surface of the body of the mandible. Its fibres converge as they pass anteriorly and upwards, and, at the angle of the mouth, they blend with the orbieularis oris, in whieh some of them curve past the angle and terminate in the substanee of the upper lip (Figs. 57, 58).

Museulus Quadratus Labii Inferioris (O.T. Depressor Labii Inferioris). — ^This musele springs from the lower part of the superficial surface of the mandible, between the mental tuberele and the mental foramen, its posterior border h^^^^r- overlapped by the triangularis. The fibres pass ^

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HEAD AND NECK

and medially, some to blend with the orbieularis oris and others to gairi attaehment to the slein of the lower lip.

PlatyBma. — Only the upper part of the broad, flat, quadrangular subeutaneous musele of the neek is at present visible. The posteriot fibrcs aseend over the lower border of the ramus and the posterior part of the lower border of the body of the maiidible, and they have already been seen taking part in the formation of the risorius. The anterior fibres gain direet insertion into the anterior part of the lower

border of the body of the mandible. The latter attaeh- ment is the only bony attaehment whieh the musele possesses, all its other attaehments being either to fascia or to skin.

DisseetiBn. let

the masseter ; then tuin ihe risorius and ihe detaehed part of the platysma lowaids Ihe angle Qf the mouth. Whilst doing this be cateful to avoid inJHring the bianehes of the vessels and neives of the fiice.

As soon as the platysma and the risorias are reAeeted Seareh below the level of the ear for bianehes of the great aurieular nerve whieh aseend over the lower part of ihe parotid gland. Some of them pieree the parotid and terminate in ils sulistanee, others end in Ihe akin of the masseterie legion.

Fin<l the anlerior faciat vein and the exteinat niaxillary artery at Ihe

FACE AND PRONTAL REGION OF HEAD 127

lower and anterior angle of the masseter as ihey eross ihe lower Iwirder <)f the mandible. Clean them at this }X)int, but do nut traee them townnls their terminations at present.

At the posterior border of the mandible note the fascia »>vcr the su|Xfr- ficial surface of the parotid gland. It aseemls from the fascia of the neek, and is attaehed above to the zygomatic areh. Note also that at the anterior lx)rder of the parotid this fascia blends with the fascia on the sui>erticial surface of the masseter musele. Cut through the fascia covcrmg the parotid gland immediately anterior to the ear, extending ihe ineision from the zygoma above to the angle of the mandil)Ie l)eIow ; then raise the fascia from the gland, disseeting carefully anteriorly, upwards, and down- wards. As the extremities and the anterior border of the gland are approaehed, look carefully for nerves and vessels whieh einerge ^roin beneath them, and also for the duet of the gland, whieh ap{x^ars from under cover of the anterior border alK)ut a rtnger's breadth l)elow the zygoma. The duet has thiek walls, is of eonsiderable size, and is easily re- eognised. It runs anteriorly aeross the masseter and turns rt^und the anterior border of the musele, bending at right angles to its original eourse. It pierees, in turn, the fascia covering the bueeinator musele, the bueeinator musele itself and the mueous membrane of the mouth ; and it opens into the vestibule of the mouth, on a small papilla opposite the sec»)nd molar tooth of the maxilla. Above the duet and below the /ygomatie areh find (i) the aeeessory parotid, a small detaehed part of the parotid whieh lies a short distanee anterior to the anterior border of the main mass of the gland ; (2) the transverse facial vessels ; and (3) the zygoniatic branehes of the facial nerve. Below the duet find the bueeal and the mandibular branehes of the facial nerve. At the upi^er end of the parotid seek for the superficial temporal vessels. Posterior to them lies the aurieulo- temporal braneh of the third division of the trigeminal nerve, and an- terior to them, the temporal branehes of the facial nerve. Kroni, or froni beneath,'the lower extremity of the gland emerge (l) the cervical braneh ()f the facial nerve, (2) the posterior facial vein ((3.T. anterior division of ihe temporo-maxillary vein), and (3) the external jugular vein.

The Terminal Branelies of the Facial Nerve. — The dis- seetor should note that there are five terminal branehes, or groups of branehes, of the facial nerve : (i) temporal ; (2) zygomatic ; (3) bueeal; (4) mandibular; (5) cervical. They all emerge from under cover of the parotid gland, the temporal branehes at its upper end, the cervical at its lower end, and the remaining three groups of branehes at its anterior border. The temporal branehes will be followed when the temporal region and the sealp are being disseeted, and the cervical braneh when the anterior triangle of the neek is displayed; but the remaining three groups of branehes should now be followed to their terminations.

The upper filaments of the zygomatic braneh or branehes run anteriorly, aeross the zygomatic bone, and terminate, in both the upper and the lower eyelid, in the fibres of the orbi- eularis oeuli. If the branehes are carefully traeed, one of them will be found to eommunieate with the zygomatico-

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HEAD AND NECK

facial braneh of tbe seeond or maxillary diyision of the fifth ■ nerve. This small nerve pierees the ^ygomatie bone a short distanee below ihe lateral border of the orbit.

The lower Slaments are larger. They run anteriorly along the lower border of the zygomatic areh, under cover of the museulus zygomaticus and the infra-orbital part o^ the

FiG. 59. — Nerve3 of Ihe Tae

3. ZyK™

quadratus labii superioris, and deep to the latter they eoni- raunieate with the infra-orbital braneh of the maxillary diyision 0f the fifth nerve, forming wilh it the infra-orbitat plexus.

The bueeal braneh or branehes run towards the angle of the mouth. At the anterior border of the masseter they eom- munieate, around the anterior facial vein, with the bueeinator braneh (O.T, ^long bneeal) of the third division of the fifth, and they supply the bueeinator and the orbieularis oris.

FACE AND PRONTAL REGION 0F HEAI) 129

and the quadratus labii superioris immediately 1>elow their origins. and turn them downwards towards the upper lip. When this has l^een done, elear away the fatty tissue whieh lies on the deep asi^eet of the (|uadratus labii superioris and seeure the infra-orbital vessels and nerve, as they emerge from the infra-orbital foramen. The infra-orbital plexus lies deep to the quadratus labii superioris, and on the superHeial as}XK:t (>f the museulus eaninus. From the plexus three groups of branehes are distril)uted : ( i ) palpebral, whieh pass upwards to the lower eyelid ; (2) nasal, whieh run medially to the nose ; and (3) labial, whieh deseend to the upper lip. Kither by means of these branehes, or more direetly, the lower zygomatic twigs of the facial nerve are distributed to the museulus zygomaticus, the museles of the lower eyelid, museles of the nose, and tlie museles of the upper lip.

The mandibular braneh or branehes run anteriorly along the mandible to be distributed to the museles of the lower lip. As they pass anteriorly they lie deep to the triangularis, and they eommunieate, under cover of it, with the mental braneh of the inferior alveolar (O.T. dental) nerve. To display this eommunieation the triangularis must be reflected, and the mental vessels and nerves must be found as they emerge from the mental foramen.

Arteria Maxillaris £xtema (O.T. Facial). — The ex- ternal maxillary artery is a tortuous vessel whieh enters the face at the lower and anterior angle of the masseter, after turning round the lower border of the mandible and piereing the deep fascia of the neek. From that point it runs anteriorly and upwards to the angle of the mouth and then, assuming a more vertical direetion, it is prolonged upwards, as the angular artery, to the medial eommissure of the eyelids, in the substanee of the angular head of the quadratus labii superioris. Immediately after its entranee into the face it is comparatively superficial, being covered by skin, super- ficial fascia, and platysma, and it is easily eompressed against the bone. More anteriorly it lies between the zygomaticus superficially and the bueeinator deeply, then between the quadratus labii superioris and the eaninus, and, as already stated, its terminal part is usually embedded in the substanee of the quadratus labii superioris.

Brandies, — The branehes of the external maxillary artery form two groups, a posterior and an anterior. The branehes of the posterior group pass posteriorly and are of small size. They are distributed to the masseterie, bueeal, and malar regions where they anastomose with the transverse facial, the bueeinator, and the infra-orbital arteries.

The branehes of the anterior group run anterior'

VOL. II — 9

130

HEAD AND NECK

ccivc speeial naineii : ihey are Ihe inferior labial, the superior bbiAl, ihe laieral iiawl, and the angular eontinuation.

Tlie inknW l.iN.i! (O.'l'. in/mor anwmry) arises below the loYd of ilii' angle of ihe moulh and passes towards the

mediai

libno, uiulor eiiwr of the triangularis, the quadratU5

inreri.iris, and ihe orbicul;iris iiris. Iii the substanee of

) il lies immedialely adjacent lo ihe mueous membrane,

:iuast(inioses in tlu; mediaii plane with its feIlow of the

opposiie side.

riie superior lahial arises about the level of Ihe angle

the li; and ii

FACE AND FRONTAL REGION 0F HEAl) 131

of the mouth and runs medially in the upi^er lip, between the orbieularis oris and the mueous membrane. Before it anastomoses with its fellow of the opposite side, it gives off a braneh, the septal artery of the nose^ whieh passes upwards and ramifies on the lower and anterior part of the nasal septum, where it anastomoses with the septal braneh of the spheno- palatine artery.

The Angular Artery, — ^This is the eontinuation of the external maxillary beyond the point of origin of the lateral nasal braneh. It runs upwards in the substanee of the angular head of the quadratus labii superioris, and it terminates at the medial eommissure of the eye by anastomos- ing with the nasal braneh of the ophthalmie. The lateral nasal braneh springs from the external maxillary at the point where it beeomes the angular. It ramifies on the side of the nose and anastomoses in the median plane with its fellow of the opposite side.

In addition to the branehes already noted, a very definite braneh is usually given off from the anterior aspeet of the external maxillary artery immediately after it erosses the lower border of the mandible. This braneh (O.T. inferior labial) runs towards the median plane under covor of the triangularis and the depressor labii inferioris, and it anasto- moses not only with the inferior labial (O.T. inferior eoronary) above, and its fellow of the opposite side in the median plane, but also with the mental braneh of the inferior aIveolar artery.

Yena Facialis Anterior (O.T. Facial). — The anterior facial vein is a less tortuous vessel than the external maxillary artery to whieh it eorresponds, and it lies posterior, and on a slightly more superficial plane. It eonimenees as the angular vein^ whieh is formed at the medial eommissure of the eyelids, by the union of the frontal and supra-orbital veins, whieh deseend from the forehead. It passes down- wards and posteriorly, in a comparatively straight line, to the anterior inferior angle of the masseter, whieh it erosses immediately behind the external maxillary artery ; then it pierees the deep fascia of the neek, and enters the sub- maxillary triangle. In the upper part of the face it lies on the quadratus labii superioris ; then it is situated between the zygomaticus and the risorius superficially and the bueeinator deeply ; and as it erosses the anterior angle of the masseter it is covered with the skin, superficial fascia, and the platysma.

II — 9a

132 HEAD AND NECK

Tributaries, — In addition to the frontal and supra-orbital veins, it receives external nasal, palpebral, superior labial, inferior labial, masseterie and superficial parotid tributaries. As it erosses the bueeinator musele it is joined by the deep facial vein, whieh eonneets it with the pterygoid plexus of veins in the infra-temporal region.

Disseetion. — After the branehes of the facial nerve, the external maxillary artery and the anterior facial vein have been studied, the disseetion of the deeper museles and the deeper vessels and nerves must be proeeeded with ; but the supra-orbital and supra-troehlear nerves, the supra-orbital vessels, and the eorrugator supereilii musele may be left till the sealp is disseeted (p. 156).

Museulus Ganinus (O.T. Levator Anguli Oris). — The

eaninus is eoneealed by the lower part of the orbieularis oeuli, the quadratus labii superioris, and the zygomaticus, and it is erossed superficially, near the angle of the mouth, by the external maxillary artery. When the struetures superficial to it are turned aside, the musele will be found springing from the eanine fossa below the infra-orbital foramen. It passes downwards to the angle of the mouth, where it blends with the orbieularis oris, some of its fibres passing into the lower lip (Fig. 57). It is an elevator of the angle of the mouth.

The Bueeinator. — This musele oeeupies the interval between the upper and the lower jaws and forms a most important part of the substanee of the eheek. Above, it springs from the alveolar border of the maxilla, in the region of the molar teeth. Below, it arises from the alveolar border of the mandible, also in the region of the molar teeth, and, posteriorly, it is attaehed to the pterygo- mandibular raphe, whieh forms a bond of union between the bueeinator and the superior eonstrietor of the pharynx. This attaehment will be seen to better advantage when the wall of the pharynx is stiidied (p. 373). Anteriorly, its fibres converge towards the angle of the mouth, where they blend with the orbieularis oris, of whieh they form a large part. The manner in whieh the fibres enter the orbieularis must be carefully noted. The upper and lower fibres pass direetly to the eorresponding lips ; the middle fibres, on the other hand, deeussate at the angle of the niouth, so that the lower fibres of the series enter the upper lip, whilst the higher fasciculi reaeh the lower lip (Fig. 61).

The Molar Glands. — The bueeinator is covered posteriorly

cia whieh must bc turcfullj renoTed. As tbb b bda^ ae Ihe disseaoi will iiDd. boih luperiiai] aoA deep m ; fascia, a number of bduH gUndt, the tmiar ssSet^ , nds. The duets or these gLuid» pietee tbe baeenutor aod I ^en into the restitnite t>r tbe momb. Oik oc t«o htteml \ wiph glands aiso are sometime* (utiod rtstii^ on tbe s

" J suriaee of the baeeinalor. ' DiistOiMi.—A!^ dK dineeikn ef llir liiiiiailiii ud ttm ■ b eompletnl, lenHHe ihe *tilcbes &tia tke Bft t c«cn ibe ^» m

'lie mueoui memlmni: ftom Ibe iict}> «otHei*. ia unleT ta e _, .

Miseuiar slios irliicliailai.-h ilw<>*tiiinilwki«talu ik >I>«uiU> RurKNM«flhB pper aiui tlir Imrrr )iin, iihI Iu tlit{<iy Ibe niTMal» niaelr. A» tlir lip re eveittd thr iltSKnrlor Umli) Bn|e lli*t ■ biU nl ■nieoin mrmbatK. ihe pVH»/u'/f /j*iV, [aiits frtpni cic!i lip lo llir gBm i.f thr c. ^tr-pnniliog 'ytir in

le mediaD plaae ; and as thi nall laiiai salivary giandi

They are leadily fell in tbe liiine wib}ecl by {iresine ihe tip ol II angue againsl thf iniier surraees <jf the li[is. UnBenli IneisiTi Labii SnperioiiB et IntnrioriB. — These | ; fou[ small museular bundles, two upper and two lower, Sthieh attaeh ihe deepur pait of ihe orbieularis oris to the ~alveolar margins of the jaws in ihe regions of the upi^er and lower lateral ineisor teeth.

Unaenlns Mentalis.— When the incisive musdes of the i —lower jaw are detaehed from ihe bone and ihe lower lip j £ Turther eyerted, a distinet museular bundle will be Tound c leb side, springing f[om the ouler surface of the soeket of the I line tooth, under cover of the quadratus labii inferioris. J 'he two bundtes eoni'erge and blend logether, between tbe i le^al borders oT the museuli quadrali labii iiiferiuris, to I a Btngle bundle whieh is inserled into [he skiii of the J II is an elevator of the skin of the ehin ■9i

134

HEAD AND NECK

Nervus Bueeinatorius (O.T. Long Bueeal). — This nerve is a braneh of the third division of the trigeminal nerve. It passes anteriorly into the eheek from under cover of the ramus of the mandible. It is a sensory nerve, and it supplies branehes to the skin on the outer surface and the mueous membrane on the inner surface of the bueeinator musele. In order to display it at the present stage it may be neeessary to make an antero-posterior ineision through the middle of the anterior border of the masseter.

Eyelids. — The following strata will be exposed in eaeh eyelid as the disseetion is earried from the surface towards the conjunctiva.

Upper Lid.	LOWER LlD.
1. Integument. 2. Palpebral part of the orbieularis oeuli. 3. The tarsus, the palpebral fascia, and the expanded ten- don of the levator palpebrae superioris. 4. Conjunctiva.	1. Integument. 2. Palpebral part of the orbieularis oeuli. 3. The tarsus and the palpebral fascia. 4. Conjunctiva.

In addition to these struetures, two ligamentous bands, named the medial palpebral ligament (O.T. internal tarsal ligament) and the lateral palpebral raphe (O.T. external tarsal ligament), will be notieed. They attaeh the tarsi to the medial and lateral margins of the orbit.

Integument and Orbieularis Oeuli. — These strata have been examined already, and the skin has been reiieeted.

Disseetion. — Separate the palpebral part of the orbieularis oeuli from the remainder by a eireular ineision ; turn the palpebral part towards the rima palpebrarum, and take eare, whilst raising the musele fibres, to preserve the palpebral vessels and nerves, and at the same time to avoid injury to the palpebral fascia. As the disseetion is eompleted the origin of the musele from the medial palpebral ligament (p. 121) will be displayed.

Tarsi. — The removal of the palpebral part of the orbieularis oeuli brings into view the palpebral fascia and the tarsi. These lie in the same morphologieal plane, and they eonstitute the ground-work of the eyelids.

The tarsi are two thin plates of eondensed librous tissue, plaeed one in eaeh eyelid so as to oeeupy an area immediately

FACE AND ERONTAL REGION 0F HEAD 135

adjoining its free maigin. They differ very materially from eaeh other. The superior tarsal plate is mueh the larger of the two, and presents the figure of a half oval. Its deep surface is intimately eonneeted with the subjacent conjunctiva, whilst its superficial surface is elothed by the orbieularis musele, and is in relation to the roots of the eyelashes. Its superior border is thin, convex, and eontinuous with a tendinous expansion of the levator palpebrse superioris. The inferior border of the tarsal plate is thiekened and straight, and the integument adheres firmly to it.

The inferior tarsal plate is a narrow strip whieh is similarly plaeed in the lower lid.

Glandol» Tarsales (O.T. Meibomian rollieles). — At this stage the student should examine the tarsal glands, whieh he will display by everting the eyelids. They are plaeed on the deep surfaces of the tarsi. To the naked eye they appear as elosely plaeed, parallel, yellow granular-looking streaks, whieh run at right angles to the free margins of the lids. They are more numerous and of greater length in the upper lid, and, being lodged in furrows on the deep surface of the tarsal plates, they are distinetly yisible upon both aspeets of these, even while the conjunctiva is in position. Their duets open upon the free margin of eaeh lid posterior to the eyelashes.

The Palpebral Fascia. — The palpebral fascia is a sheet of fibrous membrane whieh oeeupies the interval between the tarsi and the margins of the orbit, forming, with the tarsi, a septum between the orbit and the exterior. Its peripheral border is attaehed to the orbital margin, except at the medial angle of the orbit, where it oeeupies a more posterior plane, and is attaehed to the erista laerimalis, posterior to the medial palpebral ligament and the laerimal sae. Its eentral border in the lower lid is eonneeted with the lower border of the lower tarsus. In the upper lid it blends with the expanded tendon of the levator palpebrae superioris, and is attaehed with it to the anterior surface of the upper tarsus. It is piereed by the supra-orbital, supra-troehlear, and laerimal branehes of the first division of the trigeminal nerve, and by the terminal branehes of the ophthalmie artery.

Raphe Palpebralis Lateralis, — The lateral palpebral raphe (O.T. extemal tarsal ligament) is merely a thiekening of the palpebral fascia, between the lateral eommissure and thf II— 9 c

136 HEAD AND NECK

medial border of the fronto-sphenoidal proeess of the zygomatic bone (0-T. nialar), to whieh it eonneets both the tarsi.

Ligamentum PalpebraU Mediale (O.T. Internal Tarsal Ligameni). — The medial palpebral ligament is a strong fibrous band whieh eonneets the medial ends of both tarsi to the frontal proeess of the maxilla. It lies between the skin anteriorly, and the laerimal sae posteriorly. Byits upper and lower borders it gives attaehment to fibres of the orbieularis

oeuli, and by the laieral part of its posterior surface, to the pars laetimalis of the orbieularis oeuli (0-T. tensor tarsi).

Iievator Palpebne Superioris. — Only the anterior expanded tendon of this musele ean be seen at the present stage of the disseetion, and that, as a rule, in only a partially satisfactory manner. The musele arises within the orbital eayity, ex[ends forwards to the upper eyelid, and ends in an expanded tendon whieh splits into three lamellEe; a superior lamella, whieh blends with the upper part of the palpebral fascia and is attaehed with it to the anterior surraee of the upper tarsus ; an intermediate lamella, whieh is eonneeted with the upper

FACE AND PRONTAL REGION 0F HKAD

137

border of tbe upper tarsus; and an inrerior lamelb, whieh gains insertion into the upper fomix of the conjunctiv3. It raises the upper eyelid by pulling on the upi)ei larsus, and at the same time elevates the upper fornix of the conjuncIiva.

Yessels uid Herries of the Eyelids. — At the niedial eoni- missure two arteries, Mnt palpehral branehes of ihe ophthalmie, pieree the palpebral fascia and run laterally, one in the upper and one in the ]ower lid. At the lateral margin or the orbit, one or more branehes of the laerimal dIvision of the ophthalmie pieree the palpebral fascia and anastomose with

the palpebral arteries. An arterial areh, arats Uwseus, is thus formed elose to the margin of eaeh eyelid, between the orbieularis musele and the tarsus.

The veins nin medially towards the root of the nose and open into the frontal and angular veins.

The neryes are more numerous and eome from a number of different sourees. The motor Tilaments for the various parts of the orbieularis oeuH are derived from the temporal, and zygomatic branehes of the facial nerve. They enter from the lateral margins. The sensory twigs for the upper hd eome from the laerimal, supra-orbital, supra-troehlear, and infra-trochlear branehes of the first or ophthalmie division of the trigeminal nerve ; and the lower lid is suppHed by t'

138 HEAD AND NECK

infra-orbital braneh of the seeond or maxillary division of the fifth nerve. The laerimal nerve will be found piereing the palpebral fascia near the lateral part of the upper border of the orbit ; the supra-orbital lies in the supra-orbital noteh at the junction of the lateral two-thirds with the medial third of the upper border ; and the supra- and infra-trochlear pieree the palpebral fascia at the medial end of the upper border. The branehes of the infra-orbital nerve pass to the lower lid in the palpebral branehes of the infra-orbital plexus (p. 128).

Apparatus Laeriinalis. — The following struetures are in- eluded under this head : (i) the laerimal gland and its duets ; (2) the conjunctival sae ; (3) the puneta laerimalia ; (4) the laerimal duets ; (5) the laerimal sae; (6) the naso-laerimal duet ; (7) the laerimal part of the orbieularis oeuli.

Glandula Laeninalis. — This lies in the upper and lateral part of the orbital cavity under cover of the zygomatic proeess (O.T. external angular) of the frontal bone. It ean be exposed by eutting through the palpebral fascia at the upper and lateral angle of the orbit, and it will be found that the anterior part of the gland projects slightly beyond the orbital margin and rests upon the conjunctiva as the latter is reflected from the lateral part of the upper lid on to the eyeball. If the anterior border of the gland is raised and the point of the knife earried carefully up and down in the fascia under it, several exceedingly fine duets will be found passing from the gland into the lateral part of the upper fornix of the conjunctiva. The duets vary in number, and the seeretion whieh they convey, whieh eonstitutes the tears, is earried, by the in- voluntary movements of the upper eyelid, over the exposed surface of the eyeball and is direeted towards the medial eommissure ; there it passes through the puneta laerimalia into the laerimal duets, and is earried by them to the laerimal sae, whenee it passes by the naso-laerimal duet into the inferior meatus of the nose. Under ordinary eireumstanees, the amount of laerimal seeretion is merely suAieient for lubriea- tion, and praetieally the whole of it is evaporated from the surface of the eyeball ; consequently, when the laerimal duets and the laerimal sae are extirpated, a proeeeding whieh is neeessary under eertain eireumstanees, the patient suATers little or no inconvenience from the overflow of tears, so long as the seeretion is not excessive. If the amount of seeretion is greater than ean be removed by evaporation, the excess,

FACE AND PRONTAL REr.lON 0F HKAD

under ordinaiy eireumstanees, pxsscs thri>iif;h ihe pniuta the duets and thenee through ihe lacrtiii:il sa<- :ind ii laerimal duet to the nose ; and ir the seeruiion beennK.- abundlnt that it eannot be reniovcd liy i.v;iiiur;Ui(ni drainage, p.irt fiows through the rima as tuars.

7'he Conjuncliml Sae. — 'l'he conjunctival sae is the potential spaee between the eyelids and the eyebail. It opens exlernally through the rima and eommunieates with the laerimal sae through the puneta and the laerimal duets.

The Puneta Laerimalia. — It has been noted already that the punetum laerimale of eaeh lid lies at the lateral ma of tiie laeus laerimalis (p. iso). Smal! probes should n»

140 HEAD AND NECK

passed through the puneta into the laerimal duets and along the duets into the laerimal sae (Fig. 64).

Saeeus Laerimalis. — The laerimal sae is the blind upper end of a eanal whieh extends from the orbit to the inferior meatus of the nose. It is lodged in the fossa laerimalis in the anterior part of the medial wall of the orbit. It lies posterior to the medial palpebral ligament, from whieh it receives a iibrous expansion, and it is covered on its lateral aspeet, and on the lateral part of its posterior aspeet, by the pars laerimalis of the orbieularis oeuli. The laerimal duets open into its antero-lateral aspeet, under cover of the medial palpebral ligament ; and it is eontinuous below with the naso- laerimal duet. The anterior wall of the sae should be ineised and a probe passed down the naso-laerimal duet into the nose. Note that as the probe passes along the duet it inelines downwards, laterally. and slightly posteriorly.

Pars Laerimalis Orbieularis Oeuli (O.T. Tensor Tarsi). — This small speeial portion of the orbieularis oeuli springs from the posterior aspeet of the lateral part of the medial palpebral ligament and passes posteriorly and medially, round the lateral part of the laerimal sae, to the erista laerimalis of the laerimal bone, to whieh it is attaehed. When it eontraets it Gompresses the laerimal sae, and so tends to facilitate the flow of the laerimal seeretion into the nose.

Duetus Naso-Laerimalis. — This duet will be seen at a later period of the disseetion. It is a bony eanal, lined with mueo-periosteum, whieh runs, in the lateral wall of the nose, from the laerimal sae to the upper and anterior part of the inferior meatus. It is about half an ineh long. At the medial side of its lower end is a fold of mueous membrane, the pliea laerimalis, whieh serves as a flap valve (Fig. 64).

The disseetion of the face should be eompleted by an examination of the nasal eartilages and the external nasal braneh of the ophthalmie division of the trigeminal nerve. The nerve will be found emerging between the lower border of the nasal bone and the lateral eartilage. After its emergenee it deseends to the tip of the nose supplying Alaments to the skin.

I

Dissedion. — The eartilaginous part of the nose should now be exainined by stripping off the nasalis musele and Ihe remains of the integument.

Nasal Gartilages. — In addition to the septal eartilagei

FACE AND FR.ONTAL REGION OF HKAl) m

whieh will be more appropriately studied in ihe disseetion of the nasal cavities, two eartilaginous plates will l>c found upon eaeh side. These are : —

The l<^al earHiage is a triangular plate whieh, by ils posterior margin, is attaehed to the lower border of the nasal bone and the upper part of the sharp margin of the nasal noteh of the maxilla. In the median plano this earlilage

FiG. 65.— C;\rlilagc5 of

beeomes eontinuous with its fellow of ihe opposile sidt', and also with the subjacent anterior border of the seiUal eartilage of the nose. Below, there is a slight intcrval between ihe two lateral eartilages, in whieh is seen the margin of the nasal septal earttlage. The inferior bordor of the lateral eartilage is eonneeted with the lateral part of the alar eartilage by some dense fibrous tissue.

The alar eartilagt is bent upon itself and folded round the orifice of the nostril anteriorly and laterally. Posteriorly it is deficient. The iateral part is ovaI, and does not reaeh down to the margin of the nostril, nor postoriorly as far as the nasal noteh of the maxilla. The interyal between it and the bone is filled in by fibrous tissue in whieh one or two small islands of eartilage (eartilagines minores vel sesa- moideie) appear. Anteriorly, the bent part of eartilage eona into eontaet with its neighbour and forms the point 0*"

142 HEAD AND NECK

nose. Medially^ the medial part of the eartilage is in the form of a narrow strip whieh lies upon the lower part of the septal eartilage, and projects slightly below it so as to support the margin of the nostril upon this side. Its extremity is turned slightly laterally.

SIDE 0F THE NECK.

On the fourth day after the body is brought into the room it is plaeed upon its baek, and the disseetors of the head and neek should examine the side of the neek and eommenee the disseetion of the posterior triangle.

The side of the neek is bounded below by the clavicle, above by the lower border of the mandible, the mastoid portion of the temporal bone, and the superior nuehal line of the oeeipital bone. Anteriorly it extends to the median plane, and posteriorly to the anterior border of the trapezius musele. It is divided into anterior and posterior parts, the anterior and posierior triangles^ by the sterno-mastoid musele. If the head is pulled over towards the opposite side, the sterno- mastoid musele will be seen deseending from the mastoid portion of the temporal bone and the superior nuehal line of the oeeipital bone, to the upper border of the sternal third of the clavicle and the anterior surface of the manubrium sterni.

In the lower part of the posterior region, posterior to the sterno ■ mastoid and above the convex middle third of the clavicle, there is a depression ealled the fossa supraclavicularis major, to distinguish it from the fossa supraclavicularis minor whieh lies above the sternal end of the clavicle between the sternal and clavicular heads of the sterno-mastoid. The braehial plexus, the third part of the subclavian artery, and the supra-clavicular lymph glands lie in the region of the fossa supra-clavicularis major, and the fossa supra-clavicularis minor indieates the position of the internal jugular vein near its lower end.

POSTERIOR TRIANGLE.

Dissedion, — To expose the boundaries and eontents of the posterior triangle make the following three ineisions through the skin. (i) From the baek of the auriele along the upper border of the mastoid part of the

POSTERIOR TRIANGLE 143

temporal bone and the superior nuehal line to the external oeeipital pro- tuberanee. (2) From the stemal to the aeromial end (>f the clnviclc. following the line of that bone. (3) Join the anterior extrcmities of i and 2 by a vertical indsion passing along the baek of the external aeustie meatus and then down the middle of the stemo-mastoid musele. Retleet the flap, thus marked out, from before baekwards, and note that the skin is thieker over the upper and posterior part of the triangle than ()ver the lower and anterior part.

When the skin is reiieeted the superficial fascia and the lower |xirt ()f the platysma musele will be exposed.

The 5uperficial fascia in the region of the posterior triangle is comparatively thin, and embedded in its lower and anterior part is the lower and posterior part of the platysma.

The Platysma. — The platysma is a thin sheet of musele whieh eommenees in the superficial fascia of the infra-clavi- eular region, whenee it aseends aeross the clavicle and through the superficial fascia of the side of the neek, to the face where its upper border has been examined already (p. 126). It covers the lower and anterior part of the posterior triangle, and the upper and posterior part of the anterior triangle ; and it is supplied by the cervical braneh of the facial nerve, whieh emerges from the lower end of the parotid gland.

Disseetion. — Make an ineision through the lower part of the platysma along the line of the clavicle, and tum the part above the ineision upwards and anteriorly. Whilst making the ineision and whilst reflecting the musele, be careful not to injure the supraclavicular eutaneous nerves and the external jugular vein, whieh lie direetly subjacent to it.

After the platysma is reflected, elean the external jugular vein, whieh emerges from the lower end of the parotid and passes downwards, in- elining posteriorly, to the lower and anterior angle of the posterior tri- angle, where it pierees the deep fascia. Whilst eleaning the vein, avoid injury to the nervus eutaneus eolli, whieh sometimes erosses superAeial to the vein about the middle of its length. Seeure and elean the posterior aurieular vein, whieh deseends behind the auriele and joins the external jugular a little below the level of the angle of the mandible. Next, Hnd and elean the superHeial branehes of the cervical plexus as they pieree the deep fascia. They are (l) deseending branehes, the anterior, middle, and posterior supra-clavicular nerves. (2) A transverse braneh, the nervus eutaneus eolli (O.T. transverse cervical). (3) Aseending branehes, the great aurieular and the small oeeipital.

The anterior and middle supra-clavicular nerues will be found piereing the deep fascia immediately above the clavicle, the anterior at the posterior border of the sterno-mastoid and the middle above the convexity of the clavicle. They deseend into the peetoral region as far as the lower border of the seeond rib and their lower portions will be displayed by the disseetor of the arm. T\\!t posterior supra-clavicidar 7ierves pieree the deep fascia at a somewhat higher level. They deseend aeross the lower and anterior part of the trapezius to the aeromial region, and to the skin of the arm over the upper part of the deltoid, where they will be exposed by the disseetor of the arm.

HEAD AND NECK

The Deep Fascia. — The deep fascia fonns the superiieial boundary or roof of the posterior triangle. It Is attaehed below to the upper border of the middle third of the clavicle ;

FiG. 66. — The siiperlieial

above, to the superior nuehal Hne of the oeeipital bone; anteriorly it is eontinuous with the fascia of the sterno-mastoid and posteriorly with the fascia of the trapezius. It is piereed by (i) the supra-clavicular branehes of the cervical plexus, (2) the esternal jugular vein, (3) small eutaneous branehes of the

POSTERIOR TRIANGLE 145

transverse cervical, transyerse seapular (O.T. supraseapular), and oeeipital arteries, and, oeeasionally, by the oeeipital artery itself. It is not a very strong layer, and it is frequently dif)icult to display it as a eontinuous sheet. Over the upper part of the triangle it forms a single layer, but below, it splits into two lamellse, a superiieial and a deep. The superficial layer whieh is already displayed, is attaehed to the upper border of the clavicle from the sterno-mastoid anteriorly to the trapezius posteriorly. It is piereed by the external jugular vein and the supraclavicular nerves.

Disseetion, — Traee the supraclavicular nerves upwards through the deep fascia to the posterior border of the sterno-mastoid ; then, puUing theni aside, eut through the superBeial layer of the deep fascia immediately above the clavicle and along the posterior border of the sterno-mastoid, and turn it upwards. Introduee the handle of the sealpel behind the claviclc and note that it ean be passed downwards as far as the posterior border of the lower surface of the bone. Its further progress is barred by the attaehment of the seeond layer of the deep fascia to this border, where it blends with the posterior lamella of the eosto-eoraeoid membrane. Pass the handle of the knife forwards behind the stemo-mastoid and note that, without using any great force, it ean be pushed medially until it erosses the median plane ; therefore, the spaee between the two layers of deep fascia in the lower part of the posterior triangle is eontinuous anteriorly with the spaee whieh lies above and posterior to the manubrium sterni, between the first and the seeond layers of the deep fascia of the anterior part of the neek. Laterally, this spaee extends as far as the eoraeoid proeess, and upwards to a short distanee above the posterior belly of the omo-hyoid musele. Clear away the areolar tissue whieh lies between the two layers of the deep fascia, and expose a further part of the external jugular vein, and the terminal parts of the transverse cervical and the transverse seapular (supraseapular) veins, as they join the posterior border of the external jugular. Pull the lower part of the external jugular vein posteriorly and expose the termination of the anterior jugular vein in its anterior border. Disseet carefully behind the clavicle and find the transverse seapular (supraseapular) artery. Traee the seeond layer of the deep fascia upwards and note that it is eontinuous with the fascia whieh surrounds the posterior belly of the omo-hyoid musele ; indeed it is the tension of this portion of the deep fascia whieh holds the posterior belly of the musele down in its position.

Remove the remaining parts of the deep fascia, first from the upper, and then from the lower part of the triangle, and expose the floor and the remaining eontents of the triangle.

Gommenee above, in the region of the junction of the upper third and the lower two-thirds of the posterior border of the sterno-mastoid, and seeure the great aurieular, the small oeeipital, the aeeessory nerve, and the nervus eutaneus eolli. The great aurieular is most easily found. It turns round the posterior border of the sterno-mastoid, in the region indieated, and runs upwards and anteriorly, parallel with and slightly above and posterior to the external jugular vein. The small oeeipital will be found hooking round the lower border of the aeeessory nerve a little above the great aurieular ; and the nervus eutaneus eolli lies a little below the great aurieular.

Follow the small oeeipital and the great aurieular nerves to their

VOL. II — 10

146 HEAD AND NECK

terminations, but the nervus eutaneus eolli must be traeed only to the point where it erosses either superficial or deep to the external jugular vein. It eventually divides into upper and lower terminal branehes, whieh will be seen when the anterior triangle is disseeted.

Nervu8 Oeeipitalis Minor. — The small oeeipital is a sensory braneh of the seeond cervical nerve. It emerges from under cover of the sterno-mastoid, and aseends for a short distanee along its posterior border, then it passes to the superficial surface of the musele, pierees the deep fascia, and divides into oeeipital, mastoid, and aurieular branehes. The oeei- pital and mastoid branehes supply the skin in the regions indieated by their names. The aurieular is distributed to the skin of the upper third of the eranial surface of the auriele.

Nennis Anrieularis Magnus. — This eonsists of eutaneous filaments derived from the seeond and third cervical nenres. After turning round the posterior border of the sterno-mastoid it runs upwards and anteriorly, towards the angle of the mandible, in the deep fascia on the superficial surface of the sterno-mastoid, and breaks up into three sets of terminal branehes, mastoid, aurieular, and facial. The mastoid branehes go to the skin of the mastoid region. The aurieular bramkes supply the skin of the lower two-thirds of the eranial surface and the lower third of the lateral surface of the auriele. The facial branehes, whieh have already been seen, ramify in the posterior part of the face, in the parotid and masseterie regions. Some of the filaments enter the substanee of the parotid.

Disseetion. — The aeeessory nerve, previously found at the junction of the upper third with the lower two-thirds of the posterior border of the sterno-mastoid, must now be traeed downwards and posteriorly, through the trian^^le, to the point where it disappears under cover of the trapezius, at the junction of the upper two-thirds with the lower third of the anterior border of that musele. As the nerve is eleaned, attempt to seeure twigs from the third and fourth cervical nerves whieh eommunieate with it in the posterior triangle.

Turn next to the posterior belly of the omo-hyoid musele, whieh erosses the lower part of the triangle. Note that it divides the triangle into a large upper or oeeipital portion, and a small lower or subclavian portion. Cut through the fascia on the surface of the musele, parallel with the musele fibres, and turn it upwards and downwards ; then turn the upper border of the musele laterally and find the herve from the ansa hypoglossi, whieh emerges from under cover of the sterno-mastoid and enters the deep surface of the omo-hyoid to supply it.

Take away the remains of the superficial layer of deep fascia, and the areolar tissue beneath it from the upper part of the triangle. Whilst removing the latter note a number of lymph glands whieh lie embedded in it along the posterior border of the sterno-mastoid, superficial to the stems and branehes of the cervical nerves. At the apex of the triangle look for the oeeipital artery, whieh either emerges between the adjacent

POSTERIOR TRIANGLE 147

borders of the trapedus and the sterno-mastoid, or pierees the trapezius a little further posteriorly.

Between the aeeessory nerve above and the posterior belly of the omo* hyoid below find (i) the upper part of the braenial plexus ; (2) its braneh to the subclavius ; (3) its supraseapular braneh ; (4) its dorsalis seapuUe braneh ; (5) its long thoraeie braneh ; (6) branehes from the third and fourth cervical nerves to the levator seapulse ; (7) branehes from the third and fourth cervical nerves to the trapezius, and others whieh eommunieate with the aeeessory nerve in the posterior triangle ; and (8) the upper and posterior part of the transverse eenrieal artery. Find the transverse cervical artery as it appears from under cover of the upper border of the omo-hyoid. It nins upwards and posteriorly. Next seeure the nerve to the sulx:lavius, whieh lies under cover of the deep fascia above the omo-hyoid and a short distanee behind the stemo-mastoid. Traee it upwards to its origin from the trunk formed by the union of the fifth and sixth cervical nerves. Clean the latter nerves and the upper part of the seventh cervical nerve, whieh lies immediately below them. Then find the suprascaj)ular nerve, whieh springs firom the lateral border of the trunk formed by the fifth and sixth nerves. It lies immediately above the anterior part of the posterior l)elly of the omo-hyoid, and disappears under cover of the posterior part. Tum the trunk formed by the fifth and sixth cervical nerves anteriorly and find, posterior to it, the upper roots of the long thoraeie nerve, whieh spring firom the fifth and sixth nerves, and are emerging through the fibres of the sealenus medius musele. The nervus dorsalis seapula: (O.T. nerve to the rhomboids) lies at a slightly higher level than the supraseapular nerve. It springs from the fifth cervical nerve, runs downwards and posteriorly, and disappears, through the floor of the triangle, between the adjacent borders of the levator seapulae above and the sealenus medius below. Above the dorsal seapular nerve are the branehes firom the third and fourth cervical nerves to the trapezius and the eommunieations to the aeeessory nerve.

When the struetures mentioned above have been found and eleaned, proeeed to the disseetion of the subclavian portion of the triangle. Find the transverse seapular artery (O.T. supraseapular), whieh lies behind the clavicle, and therefore, strietly speaking, outside the limits of the triangle. Then remove the seeond layer of deep cervical fascia whieh binds the posterior belly of the omo-hyoid to the posterior border of the clavicle, and find behind it (i) a further part of the external jugular vein ; (2) a further part of the transverse cervical artery ; (3) the lower part of the nerve to the subclavius ; (4) the upper portion of the third part of the subclavian artery ;

(5) the lowest root and the lower parts of the trunks of the braehial plexus ;

(6) a part of the long thoraeie nerve ; (7) supraclavicular lymph glands. First elean the lower end of the external jugular vein and follow it

behind the clavicle to its termination in the subclavian vein. Note the valves near its lower end. Next elean the transverse cervical artery and the nerve to the subclavius. Follow the nerve to the subclavius aeross the front of the third part of the subclavian artery ; and afterwards elean the lower part of the subclavian artery and the adjacent part of the braehial plexus, whieh lies behind and above the artery. Note that the artery and the plexus are covered by a layer of deep cervical fascia, the baekward prolongation of the prevertebral layer of fascia, whieh passes on to them from the lateral border of the sealenus anterior, and is prolonged along them to beeome eontinuous with the sheath of the axillary artery.

As the areolar tissue is eleared from the subclavian portion of the triangle a number of supraclavicular lymph glands may be noted. They receive lymph from the axillary glands, and they transmit it to the large lymph vessels at the root of the neek. II— lOa

t^S

HEAD AND NECK

Ader the eontents of Ibe lower part of the Iriangle are thoroughly eleaned, remove the lemains of the fascia covering the niuseles whieh fono the HooT of the Iriangle. Note Ihal this fa5cia is eontinuous anteriorly, round the tips of the IransTerse proeesses of the cervica1 vertebr:e with the prevertebral fascia. Posteiiotly it blends with the sheaths of the deeper

museles it the liaek of the neek ; above it is attaehed to the superior nuehal line ; and below, as already stated, it is protonged inio the aidlla along the axi11ary vesae1s and nerves.

BoimdarieB and Contenta of tlie Posterior Triangle. — The

disseetioii of the triangle should be eompleted in two days. On the third day the disseetor should revise his knowledge of the boundaries and the re!ative positions of the eontents.

POSTERIOR TRIANGLE 149

The triangle is bounded anUriarfy by the posterior border of the stemo-mastoid ; posteriorly by the anterior border of the trapezius; below by the upper border of the niiddle third of the clavicle ; and abave by the superior nuehal line of the oeeipital bone^ or by the meeting of the upper ends of the sterno- mastoid and the trapezius. The roof is formed by the deep cervical fascia, whieh is covered by superiieial fascia and skin, and in its lower and anterior part by the platysma, whieh is embedded in the superficial fascia. It is piereed by (i) the extemal jugular vein at the lower and anterior angle ; (2) the supraclavicular nerves, a short distanee above the clavicle ; (3) small eutaneous branehes of the transverse seapular, trans- verse eendeal, and oeeipital arteries ; (4) lymphatie vesscls passing from the superficial struetures to the glands in the triangle. It is frequently stated that the small oeeipital, the great aurieular, and the cervical eutaneous nerves also pieree the roof. As a general mle they turn round the posterior border of the stemo-mastoid under cover of the fascia, and pieree the fascia as it lies on the musele.

The floor is formed by the splenius eapitis, the levator seapulae, the sealenus medius, and the sealenus posterior musdes, with the addition, oeeasionally, of a small part of the semispinalis eapitis (O.T. complexus) above, and the upper serration of the serratus anterior below ; the latter appears in the area of the triangle only when the clavicle is very fully depressed. The museles of the floor are covered with a layer of fascia whieh is the baekward eontinuation of the prevertebral fascia of the anterior cervical region.

The eontents of the posterior triangle are : —

1. Fatty areolar tissue.

2. The posterior belly of the omo-hyoid musele.

3. Lymph T Post sterno-mastoid.

Glands, \ Supraclavicular.

{Third part of subclavian. TransYerse cervical and its terminal branehes. Oeeipital (sometimes). f External jugular. I Transverse cervical. 5. Yeins,'* \ Transverse seapular (O.T. supraseapular). ^Termination of anterior jugular.

^ The transverse seapular artery (O.T. supraseapular) lies posteribr to the clavicle and is not, strietly speaking, in the triangle.

^ The subclavian vein is posterior to the clavicle 3Jid there^ore is not eontained within the triangle.

11-10 6

^50

HEAD AND NECK

6. Nenres, ^

Branehes of cervical plexus.

' Aeeessory. Small oeeipital. Great aurieular. Nervus eutaneus eoUi. To levator seapulae. ,, trapezius. ,, sealenus medius. , , , , posterior. Supraclavicular. To posterior belly of omo-hyoid from ansa hypoglossi. Trunks of braehial plexus. The nervus dorsalis seapulae. ^

long thoraeie. [^ Branehes of the braehial

supraseapular. j plexus.

})

)>

»)

nerve to the subclavius.

Some of the eontents of the triangle whieh are now displayed require further eonsideration.

The Posterior Belly of the Omo-hyoid Musele. — The posterior belly of the omo-hyoid musele springs from the upper border of the seapula and upper transverse seapular ligament. It enters the posterior triangle, at its lower and posterior angle, and runs upwards and anteriorly, at a yariable distanee from the clavicle, to the posterior border of the sterno-mastoid. Either immediately behind or under cover of the posterior border of the sterno-mastoid it joins the intermediate tendon whieh eonneets it with the anterior belly. Its nerve has already been seen entering its deep surface (p. 146) it divides the posterior triangle into a lower or subclavian portion and an upper or oeeipital portion.

The Aeeessory Nenre (O.T. Spinal Aeeessory). — The portion of the aeeessory nerve whieh appears in the posterior triangle eonsists of iibres whieh arise from the cervical part of the spinal medulla and with them are ineorporated some tilaments derived from the seeond cervical nerve. Before appearing in their present situation the spinal iibres entered the eranium through the foramen magnum and left it by pass- ing through the jugular foramen ; then they passed downwards and posteriorly, through the deeper Abres of sterno-mastoid, where theyreceived theeommunieation from the seeond cervical nerve. As already pointed out, the nerve usually enters the posterior triangle at the level of the union of the upper third with the lower two-thirds of the posterior border of the sterno- mastoid. It runs downwards and posteriorly through the triangle, along the line of the levator seapulae, and disappears

POSTERIOR TRIANGLE 1 5 1

under the trapezius at the junction of the upper two-thirds with the lower third of its anterior border. As it enters the triangle the smaU oeeipital nerve turns round its lower border, and, as it erosses the triangle, it is joincd hy twigs from the third and fourth cervical nerves.

The Branehes of the GerTieal Plenis. — Ihe disseetor should note that whilst many of the branehes of the cervical plexus lie within the area of the posterior triangle, the plexus itself is under cover of the upper part of the sterno- mastoid, where it will be exposed and studied when the sterno - mastoid is reAeeted. The branehes whieh appear in the triangle are the superficial branehes — the small oeeipital, the great aurieular, the nervus eutaneus eolli, and the supra- clavicular nerves; and the deep posterior branehes^ that is, the nerves to the sealenus medius and posterior, the nerve to the levator seapulae, the branehes to the trapezius and the eommunieation to the aeeessory nerve.

The Third Part of the Sabclavian Artery. — Only a portion of this part of the subclavian artery is in the triangle ; the lower and lateral part is behind the clavicle. The part in the triangle is situated deeply in the anterior inferior angle and below the omo-hyoid musele. It is covered 7vith the skin, superficial fascia, the platysma, deep fascia, the external jugular vein, the ends of the transverse seapular, and trans- verse cervical veins, and the nerve to the subclavius musele. Behind it is the lowest trunk of the braehial plexus, whieh separates it from the insertion of the sealenus niedius. Below^ it rests upon the first rib, against whieh it ean be eompressed, and, more medially, on the cervical pleura.

The Braehial Plexus and its Supraclavicular Branehes. — Only the upper portion of the braehial plexus lies in the region of the posterior triangle, i,e. the roots, the trunks, and some of the branehes ; the remainder lies either posterior to the clavicle or in the axilla. The cervical portion lies in the lower and anterior part of the posterior triangle partly in the oeeipital and partly in the supraclavicular areas. The detailed study of the plexus should be left till the fifth day after the body has been plaeed upon its baek, when the disseetor of the head and neek will assist the disseetor of the upper extremity to disartieulate the clavicle and to lay bare the whole of the plexus (p. 1 60).

The fourth day after the body ^'^" ^^en plaeed upon its

iSa HEAD AND NECK

baek should be deyoted to the study of the temporal region and the anterior part of the sealp.

THE SGALP AND THE SUPERFTCIAL STRUGTURES 0F THE TEMPORAL REGION.

Under the term " sealp " are ineluded the soft struetures whieh cover the vault of the eranium above the temporal ridges and anterior to the superior nuehal line. Its eon- stituent parts are arranged in iive layers : (i) skin; (2) super- ficia] fascia ; (3) the epieranius, eonsisting of four museular

FiG. 68. — Seetion through the Sealp and Cranial WaU.

bellies, ihe two oeeipitales and the two frontales museles, and the aponeurosis ealled the galea aponeurotiea, whieh eonneets them together ; (4) a layer of ioose areolar tissue ; (5) tbe periosteum, whieh is here ealled the perieranium. In the teTiiporal region the wall of the eranium is mueh more thiekly covered than m the sealp area, and it is possible to distinguish eight layers of sofl tissues between the surface and the bone: (1) skin; (2) superficial fascia ; {3) extrinsic museles of the ear ; {4) the thin lateral extensions of the galeaaponeurotiea; (5) a thin layer of fascia deseending from the temporal ridge to the auriele ; (6) the strong temporal fascia ; (7)the temporal musele; (8) periosteum.

TAe Sealp. — The sealp and the superficial temporal r^ion are riehly supplied with biood vessels and nerves, whieh all

AURIGLE 153

enter froin tbe peripbery, passing into the superReial Taseia afteT piereing tbe deep laseia of adjaccnt regions. As a consequence of this arrangetnent lai^e flaps of ihe sealp may be torn froin the eentre towards the margin, but, to long as they remain attaehed at the periphery, their sourees of vitality are not seriously interiered with, and if ihey are eleaned and replaeed healing oeeurs rapidly and satisfac[orily.

Oineeliim. — The skin ha$ alteady been retnovnl Troin ihe Rnlerior porls of the sealp and the teroporal region, A meilian longiludiiul in- eision must now oe made Ibtough Ihe skin of the posleriot pan of (he sealp as far as the exterQHl oeeipital proluberanee, and ihe Hap on eilher side of Ihe ineision must be turned downwaids and posteriorly to ihe superior uuehal line. When Ihis has been done Ihe dtsseetor should ex- amine the auriele of the external ear, and fami1iarise himselC wilh ils yaeious pans before he eommenees the disseelion of iU

FiG. 69.-Th(

Anriele or Pinna. — The auriele eonsists of a thin plate of yellow Abro-eartilage, covered with integument. It is fixed in position by eertain ligaments, and possesses two sets of feeble museles — viz., one group termed the cxirinsic musdei, passing to the eartilage from the aponeurosis of the epieranius and the mastoid proeess, and a seeond group in eonneetion with the eartilage alone, and therefore ealled the tntrinsie musdes.

The eotuha is the wide and deep fossa whieh leads into tbe external meatus ; the antihdix is the curved prominenee whieh bounds this posteriorly ; the helix is the folded or in- curved margin of the auriele ; and the lobule is its soft dependent part. The eoneha is partially subdivided into an upper and a lower part by the eommeneement of the helix, whieh curves upwards and forwards on its floor to beeome eontinuous with the anterior border of the auriele. This portion of the helix is ealled the erus heltm. A small pro-

154 HEAD AND NECK

minenee anterior to the meatus, and projecting posteriorly so as to overshadow it, is termed the tragus, whilst a similar eminenee posterior to and below the meatus receives the name of the antitragus. The noteh between these two prominenees is termed the indsura intertragiea. But it will be noted that the upper end of the antihelix bifurcates, and in this way two fossae are marked off from eaeh other; one — the fossa of the helix, or seaphoid fossa — is plaeed between the helix and the antihelix, and the other — thefossa of the antihelix, or triangular fossa — is situated between the two diverging erura of the antihelix.

Ligaments,

Anterior. Superior. Posterior.

r Aurieularis anterior.

Extrinsic museles,-! Aurieularis superior.

^Aurieularis posterior.

TMuseulus helieis major. ^

I Museulus helieis minor. I Upon the lateral face of the

T , . • 1 ! Museulus traedeus. { eaitilaee.

Intrmsie museles, ^, a/t i j?* • I

' ' Museulus antitragieus. )

Museulus transversus. \Upon the eranial face of

.Museulus obliquus. / the eartilage.

Dissedion. — When the disseetor has noted the various parts of the auriele he should endeavour to display its extrinsic museles ; they are the aurie ulares anterior [O.T. attrahens), superior{O.T. attollens)^ ?Lnd posterior (O.T. retrahens). The two former spring from a lateral prolongation of the galea aponeurotiea into the temporal region. The anterior is inserted into the front of the heHx, and the superior into the eranial surface of the auriele. To display them pull the auriele downwards and posteriorly, and carefully remove the superficial fascia and, at the same time, avoid injury to the aurieulo-temporal nerve, the temporal branehes of the facial nerve, and the branehes of the superficial temporal artery whieh are aseending through the superheial fascia of the temporal region to the sealp. The aurieularis posterior arises from the outer surface of the mastoid part of the temporal bone and passes anteriorly to its insertion into the eranial aspeet of the eoneha. To display it puU the auriele anteriorly and remove the fascia from the surface of the musele, at the same time seeure the posterior aurieular artery and nerve as these aseend posterior to the e^ternal meatus. As this is being done one or more mastoid lymph glands may be seen, and eare must be taken to avoid injuring the braneh of the posterior aurieular nerve to the oeeipitalis musele, whieh passes posteriorly along the lower border of the aurieularis posterior or on its deep surface.

The aurieulares museles are supplied by the facial nerve ; the anterior and the anterior part of the superior by its temporal branehes, and the posterior and the posterior part of the superior by the posterior aurieular braneh. After the aurieulares museles have been defined remove the skin from the entire extent of the auriele to display the eartilage, the ligaments, and the intrinsie museles.^ Great eare is required to make a successful disseetion.

1 In niost eases it will be advisable to defer this part of the disseetion till the body is turned on its baek for the seeond tirae (p. 200).

AURIGLE 155

The anrieiilar earillag^ extends throughout the entire auriele, with the exception of the lobule and the portion between the tra^^us and tlie hclix. These portions are eomposed merely of integument, fatty tissue, and eondensed connective tissue. The shape of the eartilage corres{M)nils with that of the auriele itself. It shows the same elevations and depressions, and by its elastieity it serves to maintain the form of the auriele. But it also enters into the formation of the eartilaginous or lateral iK>rtion of the extemal aeustie meatus. By its medial margin this part ot the eartilage is firmly fixed by Abrous tissue to the rough outer e<lge of the auditory proeess of the temporal bone, but it does not form a eomplete tulK*. It is deiident above and anteriorly, and here the tube of the meatus is eompleted by tough fibrous membrane, whieh stretehes l^tween the tragus and the eommeneement of the helix.

In a sueeessiul disseetion of the eartilage of the auriele, two other |K)ints will attraet the attention of the student. The tirst is a deep slit, whieh passes upwards so as to separate the lower |xirt of the eartilage of the helix, termed the proeessus helieis eaudaius^ from the eartilage ()f the anti- tragus ; the seeond is a sharp spur of eartilage whieh projects anteriorly from the helix, at the level of the upper margin of the zygoma. This is termed the spina helieis,

The LigamentB of the Anriole. — The ligaments are three bands of fascia. The anterior passes from the spine of the lielix to the root of the ^goma. Thesuperior and p)osterior are both attaehed to the eartilage in the region of the eoneha ; the former blends above with the temp<jral fascia, and the latter is attaehed to the mastoid portion of the teniporal bone.

The Intrinsie MuBeleB of the Auriele. — The two museles of the helix, the tragieus and the antitragieus, are plaeed upon the lateral face of the eartilage. The transversus and the obliquus lie ujx)n the eranial surface of the auriele.

The museu/us antitragieus is the best-marked member of the lateral group. It lies upon the lateral surface of the antitragus, and its llbres pass obliquely upwards and posteriorly. Some fasciculi ean be traeed to the proeessus helieis eaudatus.

The museulus tragieus is a minute bundle of short vertical fibres situated upon the lateral surface of the tragus. When well developed a slender fasciculus may sometimes be observed to pass upwards from it to the anterior part of the helix, where it is inserted into the spine of the helix.

The museulus helieis major is a well-marked band, whieh springs from the spina helieis, and extends upwards upon the anterior part of the helix, to be inserted into the skin whieh covers it.

The museulus helieis minor is a minute bundle of Aeshy fibres whieh is plaeed upon the erus helieis as it erosses the bottom of the eoneha.

The museulus transversus auriculcB is found upon the eranial aspeet of the auriele. It is generally the most strongly developed musele of the series, and its fibres bridge aeross the hollow whieh, on this aspeet of the auriele, eorresponds to the antihelix.

The museulus obliqtms au7-iculce is eomposed of some vertical fasciculi bridging aeross the depression whieh eorresponds to the eminenee of the lower limb of the antihelix.

After the aurieular museles and the auriele have l)ecn disseeted, traee the temporal branehes of the facial nerve, the branehes of the super- ficial temporal vessels, and the aurieulo-temporal nerve upwards, from the point where they emerge from under cover of the upper end of the parotid through the superficial fasciaof the temporal region to their termina- tions in the superficial fascia of the seal»^ * ' ^ half an ineh behind the zygomatic proeess of the frontal bone angular proeess) find

156 HEAD AND NECK

the zygomatico-temporal braneh of the maxillary nerve. Next pull the auriele anteriorly and traee the posterior aurieular nerve to its termination in the oeeipitalis musele, and in the intrinsie and extrinsic museles of the auriele, and the posterior aurieular artery to its anastomoses with the oeeipital and superficial temporal arteries. After this part of the disseetion is eompleted, turn to the anterior part of the sealp and find the medial and lateral branehes of the supra-orbital nerve. The medial braneh pierees the fibres of the frontalis and the lateral braneh pierees the galea aponeurotiea a little further posteriorly. Traee both branehes baekwards through the superficial fascia as far as possible ; they extend to the level of the lambdoid suture. Then seeure the supra-troehlear nerve, whieh pierees the frontalis above the medial margin of the orbit, and traee it upwards to its termination. With the branehes of the supra-orbital nerve are branehes of the supra-orbital artery, and the supra-troehlear nerve is aeeompanied by the frontal braneh of the ophthalmie artery.

When the nerves and vessels in the anterior region have been eleaned, the head should be turned well over to the opposite side, and the branehes of the oeeipital artery and the great oeeipital nerve should be sought for in the posterior region ; they radiate upwards and anteriorly from the upper extremity of the trapezius. After they have been seeured, the oeeipitalis musele must be eleaned. It springs from the lateral part of the superior nuehal line, and after a short eourse upwards and anteriorly it terminates in the galea aponeurotiea. The remains of the superficial fascia should now be removed from the surface of the galea aponeurotiea (O.T. epieranial aponeurosis), and then the disseetor should make a survey of the vessels and nerves whieh are met with in the sealp and the superficial fascia of the temporal region.

Nenres and Yessels of the Sealp and the Saperficial Temporal Begion. — Branehes of ten nerves are found, on eaeh side, in the superiieial fascia of the region whieh lies above the supra-orbital margin, the zygomatic areh and the superior nuehal line. Of these, five He mainly anterior to the auriele and five posterior to it ; and of eaeh group four are sensory and one is motor. The four sensory nerves anterior to the auriele are all branehes of the trigeminal nerve. They are the supra-troehlear and supra-orbital branehes of the first or ophthabnie division ; the zygomatico-temporal braneh of the maxiUary or seeond division ; and the aurieulo-temporal braneh of the mandibular or third division. The motor nerve is the temporal braneh of the facial nerve.

The four sensory nerves, distributed mainly to the sealp area behind the auriele, are the great aurieular and the small oeeipital branehes of the cervical plexus ; the great oeeipital^ whieh is the medial division of the posterior braneh of the seeond cervical nerve ; and the smailest oeeipital, not yet seen, but whieh will be displayed when the body is tumed on its face. It lies medial to the great oeeipital, and is the medial division of the posterior braneh of the third cervical nerve.

NERYES AND YESSELS 0F SCALP 157

Tbe motor nerve distributed posterior to the auride is the posterior aurieular braruh of the Taeial nerve.

The arteries distributed to the sealp are five in number on eaeh side; they anastomose freely, and are derivcd, either indireetly or direetly, from the internal and external earotid arteries. Three are distributed mainly anterior to, and two posterior to the region of the auriele. The three anterior to the auriele are the /rontal and supra-orbital branehes of the ophthalmie braneh of the intemal earotid, whieh aeeompany the supra-troehlear and supra-orbital nerves, and the sup€rficial temporal braneh of the external earotid. This braneh dividcs into two main branehes, an anterior, whieh aeeompanies the temporal branehes of the facial nerve, and is usually a very tortuous vessel, and a posterior braneh, whieh aeeompanies the aurieulo-temporal nerve, as it aseends anterior to the auriele towards the vertex of the eranium. The two arteries posterior to the auriele are both branehes of the external earotid. They are the posterior aurieular^ whieh aeeompanies the posterior aurieular braneh of the facial nerve to the mastoid region and the posterior part of the parietal region, and the oeeipital^ whieh is distributed to the oeeipital area and posterior part of the parietal area.

The terminations of the veins w^hieh drain the blood from the sealp are as follows. The /rontal and supra-orbital veins unite, at the medial border of the orbit, to form the angidar vein^ whieh is the eommeneement of the anterior facial vein abeady disseeted (p. 131). The blood it conveys passes eventually to the internal jugular vein. The superficial temporalvein aeeompanies the eorresponding artery. It unites, immediately above the posterior root of the zygoma, with the middle temporal vein, whieh pierees the temporal fascia at that point. The trunk formed by the union of the superAeial and middle temporal veins is the posterior /aeial vein, whieh deseends through the parotid gland, emerges from under cover of its lower end and terminates immediately below the angle of the mandible by joining with the anterior facial vein to form the eommon facial vein. Whilst in the gland, it gives off the eommeneement of the external jugular vein. The posterior aurieular vein deseends posterior to the external meatus and terminates in the external jugular vein. The oedpital vein aeeompanies the f 'ery into the sub-

oeeipital region, and ends in t' yenous plexus.

158 HEAD AND NECK

In addition to the arteries and veins there are numerous lymph vessels in the sealp, but they eannot be displayed by ordinary disseeting methods. Nevertheless, it is important that the student should remember their usual terminations. The lymph vessels of the anterior area end in small lymph glands whieh are embedded in the superAeial surface of the parotid gland. Those of the posterior area terminate either in lymph glands whieh lie superficial to the mastoid part of the temporal bone, or in oeeipital lymph glands, whieh lie in the neighbburhood of the superior nuehal line.

Disseetion. — After the vessels and nerves of the sealp have been traeed, the disseetor should eut through the fibres of the orbieularis oeuli and the frontalis over the medial part of the supra-orbital eminenee and display the eorrugator supereilii musele. It springs from the medial end of the supra-orbital ridge of the frontal bone and passes anteriorly and laterally, through the fibres of the orbieularis oeuli, to its insertion into the skin of the eyebrow. It is supplied by the temporal braneh of the facial nerve.

Galea Aponeurotiea (O.T. Epieranial Aponeurosis). — The galea aponeurotiea is fully exposed as soon as the superficial fascia of the sealp is eompletely remoyed. It is a strong layer of aponeurosis eonneeted anteriorly with the frontal bellies of the epieranius, posteriorly with the oeeipital bellies, and between the oeeipital bellies, with the external oeeipital protuberanee and the medial parts of the superior nuehal lines, or with the supreme nuehal lines wheh they are present. Laterally it beeomes thinner, deseends over the upper part of the temporal fascia, and gives origin to the anterior and superior aurieulares museles. It is so elosely eonneeted with the superjacent skin, by the dense superficial fascia, that the two eannot be separated, except with the aid of the eutting edge of the sealpel ; but above the supra-orbital ridges, the temporal ridges, and the superior nuehal lines it is only loosely eonneeted to the perieranium by the layer of loose areolar tissue ; therefore the three elosely eonneeted superficial layers, the skin, superficial fascia, and the galea aponeurotiea, ean easily be torn from the perieranium, a eireumstanee taken advantage of by the Indians who sealped 'their defeated foes. The looseness of the areolar tissue beneath the galea aponeurotiea permits the latter to be drawn forwards and baekwards by the alternate eontraetions of the oeeipitalis and frontalis museles, and, as it moves, it earries with it the skin and superficial fascia with whieh it is so elosely blended.

SGALP 1 59

Disseetum, — The ditseetor, aftcr stud^ng the auaehments <if ihe galea aponeurotiea, and after be has made himself thoroughly ronYersant with the nenre and vasciilar sapply of the sealp, an<l has appreeiatetl the fact that every part of its area is suppli^ by more than one ncrvc aml that the blood vessels anastomose Yery treely together, should ncxt C(>nvincc hini*»clf of the greater looseness of the areolar layer l)eneath the galea in the metlial area and its greater denseness and eloser attaehment to the varii>us {larts of the superjacent epieranius, and the subjacent perieranium at the mar);in> of the sealp area. He may do this by introdueing the hamlle (>f a sealiirl through a median ineision in the galea, aml {lassing it anteriorly aml posteriorly and from side to side.

The Layer of Loose Areolar Tissue. — This is the f()urth layer of the sealp. It is but slightly vascular and is ()f I(K)sc texture, but is not §qually loose ovcr the whole area of iho sealp; on the eontrary in the regions of the temporal and supra-orbital ridges it beeomes mueh denser, and, at thesame time, mueh more elosely eonneeted with the galea aponeurotiea and the frontalis museles, whilst posteriorly it disappears where the oeeipitalis museles and the galea beeonie attaehed to the superior nuehal lines. It is on aeeount of these peeuliarities that eATusions of blood or inAammatory exudations in the areolar layer easily raise the greater part of the sealp from the bone, but sueh eiTusions do not readily pass from beneath the sealp into either the facial, temporal, or oeeipital regions.

On the fifth day after the body has been plaeed upon its baek, the eighth after it was brought into the room, the disseetor of the head and neek must assist the disseetor of the upper extremity to display the whole extent of the braehial plexus and the origins of the branehes whieh spring froni it ; and he should take the opportunity to revise his ow^n know- ledge of the plexus. Detaeh the clavicular head of the sterno-mastoid from the clavicle, and displaee the stemal head towards the median plane. When this has been done the anterior and upper parts of the sterno-clavicular joint eapsule will be fully exposed, for the peetoralis major, whieh covered the lower part of the anterior surface, has already been reSeeted by the disseetor of the upper extremity.

Disseetion, — The sterno-cLavicular joint is deseribed on p. 28 of Vol. I. After the disseetors have noted that the fibres of the eapsule run medially and downwards from the clavicle to the sternum, the anterior, superior, and posterior portions must be divided elose to the sternum, eare being taken to avoid injury to the anterior jugular vein, whieh passes laterally elose to the upper and baek part of the joint. When the division is eompleted, elevate the sternal end of the clavicle by depressing the

i6o HEAD AND NECK

aeromial end, introduee the knife into the cavity of the joint, elose to the sternum, and earry it laterally below the clavicle, to detaeh the lower part of the interartieular eartilage from the sternum and the eartilage of the first rib, and to divide the lower part of the eapsule and the costo-clavicular ligament, whieh lies immediately lateral to it. If the subclavius musele has not already been detaehed, it also must be divided, and then the clavicle ean be displaeed laterally, and the whole extent of the plexus will be exposed.

The Braehial Plexus. — The braehial plexus is fully deseribed on p. 28, Vol. I., and only a brief resume of the main facts regarding it is given here. The plexus is formed by the last four cervical nerves and the larger part of the first thoraeie nerve ; it also receives a eommunieation from the fourth cervical nerve and not uneommonly a small twig from the seeond thoraeie nerve. These various nerves eonstitute the roots of the plexus. The roots of the plexus emerge from between the sealenus medius and the sealenus anterior, and unite to form three trunks^ upper, middle, and lower, whieh lie superficial to the sealenus medius, the lowest of the three being wedged in between that musele posteriorly and the third part of the subclavian artery anteriorly. The upper trunk is formed by the fifth and sixth nerves and the eommunieation from the fourth. The seventh nerve alone forms the mtddle trunk ; and the lowest trunk is formed by the eighth cervical and first thoraeie nerves and the eommunieation from the seeond thoraeie. Almost immediately after their formation the trunks divide into anterior and posterior divisions, and the divisions reunite to form three eords, lateral, medial, and posterior. The lateral eord is formed by the anterior divisions of the upper and middle trunks, the medial eord by the anterior divisi6n of the lowest trunk, and all three posterior divisions unite to form the posterior eord. The eords deseend behind the clavicle and subclavius musele, through the cervico-axillary eanal, to the level of the eoraeoid proeess of the seapula where the plexus terminates and eaeh eord divides into two terminal branehes. The terminal branehes of the lateral eord are the lateral head of the median nerve and the museulo-eutaneous nerve. Those of the medial eord are the medial head of the median and the ulnar nerve, and the posterior eord divides into the axillary (O.T. circumflex) nerve and the radial (O.T. museulo-spiral). In addition to the terminal branehes, eollateral branehes are given off from the roots, the trunks and the eords ; and the roots are eonneeted with the middle and lower ganglia of the cervical part of the sympathetie trunk by grey rami eommunieantes. The branehes given off from the roots are twigs of supply to the longus eolli, the sealenus anterior, the sealenus medius, and the sealenus posterior, the roots of origin of the long thoraeie nerve, whieh supplies the serratus anterior (O.T. magnus) and the dorsal seapular nerve (O.T. nerve to the rhomboids). The roots of the long thoraeie nerve spring from the fifth, sixth, and seventh nerves ; the upper two pieree the sealenus medius and the lowest passes anterior to that musele. The three unite, behind the trunks of the plexus, to form the stem of the nerve, whieh deseends behind the eords of the plexus into the axilla. The dorsalis seapulse nerve arises from the lateral border of the fifth nerve ; it disappears under cover of the levator seapulse and supplies the two rhomboid museles, and, sometimes, the levator seapulae.

The branehes from the trunks of the plexus are the supraseapular nerve and the nerve to the subclavius. They both spring from the upper trunk. The eoUateral branehes of the three eords of the plexus, are ( i ) from the outer eord : the lateral anterior thoraeie nerve ; (2) from the posterior eord : the upper and lower subseapular nerves and the thoraeo-dorsal nerve (O.T. long subseapular) ; and (3) from the medial eord : the medial anterior thoraeie, the medial eutaneous nerve of the arm (O.T. lesser internal

iDISSECTION 0F THK BACK i6i

medial eataneoiis nenre of the foreann (O.T. iotenud fA€ Braehiat Ptexus.—Tht plexu8 liet in the lower and posterior triangle of the neek, partly abo^e and partly Dellv of the omo-hyoid ; postenor to the elaTide ; and tfe tke clavicle it is eoTered by the skin, the saperficial fsma, branehes of the supraelaTieular nerTes, the Tirst , the extemal jugular vein, and the terminal parts of the and transverse (supra) seapular veins ; the seeond eal fascia, the transverse eenrieal artery, the posterior 'oid, the nerve to the subclavius, and tne third part of sry. Bekind the clavicU it is erossed superBdall^ b^ iilar artery (O.T. supraseapular). Belew the elanele it skin and superficial fasda, the platysma, the middle ires, the deep fascia, the peetoralis major, the |XK:toralis : vdn, the branehes of the thoraeo-aeromial artery, the ibrane, and the axillary artery and vein. tions in the neek are the sealenus medius and the long ( the eueilla the serratus anterior, the fat in the interval is anterior and the subseapularis, and linaUy the sub- dal plexus has been examined, the clavicle must l)c \ and the skin flap, reflected from the posterior triangle, ad fixed in position by a few sutures. i day after the body is brought into the room, ixth day after it has been .plaeed on its baek, . be tumed upon its face, with the thorax and the pelvis »rted by bloeks. The body will remain upon its face for ays, and during that period the disseetors of the head eek must eomplete the disseetion of the posterior part 5 sealp ; disseet the museles, vessels and nerves of the and the suboeeipital region ; and remove and examine )inal meduUa.

THE DISSEGTION 0F THE BAGK.

seetion. — Make a median longitudinal ineision from the external il protuberanee to the seventh cervical spine, and a seeond laterally le seventh cervical spine to the aeromion, and throw the flap laterally. this has been done the posterior triangle will be exposed from behind, ; disseetor should take the opportunity of noting the positions of the :s and the eonstituent parts of the floor from this aspeet. Afterwards 5t look for the superficial nerves in the superficial fascia over the part of the trapezius. If the great oeeipital nerve was not found the disseetion of the sealp seeure it at onee, as it pierees the deep :overing the upper end of the trapezius, about midway between the il oeeipital protuberanee and the posterior border of the mastoid . of the temporal bone ; traee it upwards through the dense superficial )f the sealp and elean the branehes of the oeeipital artery whieh are ited in the same region. The smallest oeeipital nerve will be found L. II — 11

i62 HEAD AND NECK

in the superficial fascia between the great oeeipital and the median plane. It is the medial division of the posterior braneh of the third cervical nerve, and it supplies the skin of the medial and lower part of the posterior portion of the sealp and the adjacent part of the skin of the baek of the neek. Traee it upwards to its termination and downwards to the point where ii pierees the deep fascia covering the trapezius. At a still lower level look for the medial divisions of the posterior branehes of the other cervical nerves. They are variable in number and position, but those whieh are present will be found piereing the deep fascia over the trapezius, at a short distanee from the median plane, and running downwards and laterally towards the posterior triangle.

After the eutaneous nerves have been found remove the remains of the superficial fascia and the deep fascia from the surface of the trapezius.

The Terminal Part of the Great Oeeipital Nerve. — The great oeeipital nerve is the large medial division of the posterior braneh of the seeond cervical nerve. It enters the posterior part of the sealp, after piereing the upper part of the trapezius and the deep fascia of the baek of the neek, and ramifies in the superficial fascia of the sealp over the oeeipital bone and the posterior part of the parietal bone, aeeompanying the branehes of the oeeipital artery, and eommunieating with the great aurieular and small oeeipital nerves.

Arteria Oeeipitalis. — After emerging from between the trapezius and the sterno-mastoid, at the apex of the posterior triangle, or piereing the upper part of the trapezius, the terminal part of the oeeipital artery passes through the deep fascia of the baek of the neek and enters the superficial fascia of the posterior part of the sealp. It anastomoses with its fellow of the opposite side, and with the posterior aurieular and the superficial temporal arteries. As a rule, it breaks up into two main branehes, a lateral and a medial. The medial braneh gives ofF eutaneous twigs and a meningeal braneh, whieh passes through the parietal foramen and anastomoses with a braneh of the middle meningeal artery. Through the same foramen, passes an emissary vein whieh eonneets the oeeipital veins with the superior sagittal (longitudinal) sinus.

Mnseulus TrapeziiLS. — The trapezius and latissimus dorsi eonstitute the first layer of the museles of the baek. Only that part of the trapezius whieh lies above the level of the seventh cervical spine belongs to the disseetor of the head and neek ; the lower part and the latissimus must be eleaned by the disseetor of the arm, but the disseetor of the head should take the opportunity to revise his knowledge of the whole origin and insertion of the musele. It arises from the medial third of the superior nuehal line of the oeeipital bone,

THE DISSECTION 0F THE BACK

163

the extenial oeeipital protuberanee, the whole length uf the ligamentum nuehie, the seventh cervical sptne, the tij>R of all the thorade spines and the eorresponding supraspinous ligaments.

Id Ihe r^on of the seventh eerriesl spne Iheorigin is miitt; aponeuiiitie than elsewheie, and the line tendinous libtes of the miis<:li.-<i a( ihi; twu ^;iile<> fom an ovoid apmiearotie area some two inebes in lenpih.

Fic. 70, — SuperBeial disseetion of the Baek of the Neek,

The upper fibres of the musele deseend in obIique curves and are inserted into the lateral tliird of the posterior border and the adjacent part of the superior surface of the c!avicle ; the interraediate fibres run horizontal!y, towards tlie shoulder, and are inserted into the medial border of the aerotnion and the upper lip of the posterior border of the spine of the seapula. The lower fibres aseenH ""'' terminate in a small

i64 HEAD AND NECK

triangular tendon whieh plays over the smooth triangle at the root of the seapular spine and is inserted partly into the lower and partly into the upper lip of the spine. The mi^sele is supplied by the aeeessory and the third and fourth cervical nerves. It draws the seapula medially and braees theshoulder baekwards, raises the tip of the shoulder, or depresses the seapula and turns the glenoid fossa upwards aeeording to whether the intermediate, the upper, or the lower iibres are mainly in aetion.

Disseetim. — On the seeond day after the subject has been plaeed on its face, the trapezius may be reAeeted. This must be done in conjunction with the disseetor of the arm. First separate the musele from the oeeipital bone, and then divide it about half an ineh from the spines of the yertebrse. The musele ean now be raised and thrown laterally towards its insertion. On its deep surface the aeeessory nerve, the twigs of supply from the third and fourth cervical nerves and the superficial cervical artery will be notieed. It is the duty of the disseetor of the upper limb to disseet these, but the disseetor of the head and neek should traee the superficial cervical artery to its origin from the transversa eolli.

The attaehments of the levator seapulae also must be defined. Two twigs from the third and fourth cervical nerves, whieh lie on its surface and finally enter its substanee, have already been seeured. Further, passing downwards under cover of this musele, the dorsal seapular nerve (O.T. nerve to the rhomboids) and the deseending braneh (O.T. posterior seapular) of the transversa eolli artery will be found. Almost invariably the dorsal seapular nerve gives one or two twigs to the levator seapulse.

The levator seapulae, the rhomboids, the posterior serrati and the splenius are elassed as museles of the seeond layer. The rhomboids and the lower part of the levator belong to the disseetor of the arm ; the remaining museles are the property of the disseetor of the head and neek.

Mnseulus Levator Seapulse. — This musele arises by four slips from the posterior parts of the transverse proeesses of the upper four cervical vertebrae. These unite to form an elongated musele whieh extends downwards and posteriorly to be inserted into that portion of the vertebral border of the seapula whieh is plaeed above the root of the spine. Its nerve-supply eomes from the third and fourth cervical nerves, and also from the dorsal seapular nerve.

The origin of the posterior belly of the omo-hyoid musele may now be examined. It is attaehed to the upper transverse ligament of the seapula and the adjacent part of the superior border of the bone. The transverse seapular artery (O.T. supraseapular) will be notieed passing over the upper trans- verse ligament whilst the supraseapular nerve traverses the noteh below it.

The seeond days work is now eompleted, and on the same day the

THE DISSECTION OF THE BACK

>6S

biek, :

i liiiuh hi* ihare or the disseetion of ihe II lirgin Ihe ion o( the deeper stiueluiei on the dorsal U|i«:t <>r ihi^ itunk. Three days are allowed Hit Ihis disseetion, and lhfNC miy lie ilis]X)sed of in the follomDg mannee : — Oit (hejlnt day, all ihe iiiu&c1l'S, fa<icin.', neTYes, and blood vessels of the b&ek, wilh the cxci.'|>lii>n (>f Ihiise in eonneetion witli the sub - oeeipilal tiiangle, should l>c sluiliiil : on ihe stamd day, the sub-oeeipilal tiiangle musl be examined ; an<) un the thiid day the medulla splnalis (O.T. s^mdaI eord) musl be displayeil.

Unseali Senati Posteriores. — These are two thin sheets of Seshy iibres, whieh are plaeed upon the posterior aspeet

FiG. 71. — Diaigram 10 she

of the thoraeie wall. The serratus posterior superior is mueh the smaller of the two ; it arises by a thin aponeurotie tendon from the lower part of the ligamentum nuchje ; from the spinous proeess of the seventh cervical.vertebra ; and from the spinous proeesses of the upper two or three thoraeie vertebr£e. It passes obIiquely downwards and laterally, and is inserted into the outer suriaees of the seeond, third, fourth, and fifth ribs, a short distanee anterior to theit angles.

The serratus posterior inferior will be brought into view by raising and throwing medially that portion of the latissimus dorsi whieh the disseetor of the upper limb has left altaehed to the lumbo-dorsal fascia. It takes origin from the spinous proeesses of the last two thoraeie and upper two lumbar

i66 HEAD AND NECK

vertebrae, and the supiaspinous ligaments between them. The disseetor will note, however, that this is not an indepen- dent and distinet attaehment, but that it is effected through the medium of the lumbo-dorsal fascia, with whieh the aponeurotie tendon of the musele blends. The musele passes upwards and laterally and is inserted into the outer surfaces of the lower four ribs.

Fascia Lumbo-dorsalis. — On the third day after the body is plaeed upon its face the disseetor of the head and neek should assoeiate himself with the disseetor of the abdomen in the examination of the lumbo-dorsal fascia. It is an aponeurotie layer, thin in the thoraeie portion of its extent, but thiek and strong in the lumbar and saeral regions ; and in all these regions it binds down the museles of the baek to the sides of the spinous proeesses and to the transverse proeesses of the vertebrae.

The Dorsal Part of the Lumbo-dorsal Fascia (O.T. Yertebrat. Aponeurosis). — This part of the lumbo-dorsal fascia is a thin transparent lamina whieh extends from the tips of the spines and the supraspinous ligaments to the angles of the ribs. At the upper end of the thoraeie region it dips beneath the serratus posterior superior into the neek, and at the lower end it blends with the aponeurosis of origin of the serratus posterior inferior, and through that beeomes eontinuous with the posterior layer of the lumbar portion.

Disseetion. — To display the lumbar part of the lumbo-dorsal fascia elear away the remains of the origin of the latissimus dorsi, whieh springs irom its posterior surface, and then reflect the serratus posterior inferior by eutting through it at right angles to its fibres and turning it medially and laterally towards its origin and insertion. As the lateral part is tumed aside seeure its nerves of supply, whieh are derived from the lower inter- eostal nerves, and enter its deep surface. Next remove the remains of the origin of the serratus posterior inferior, and then the posterior layer of the lumbar part of the lumbo-dorsal fascia will be eompletely exposed.

The Lumbar Part of the Lumbo-dorsal Paseia, — This portion of the lumbo-dorsal fascia is separable into three lamellae, a posterior, a middle, and an anterior. All three fuse together laterally, where they beeome eonneeted with the internal oblique and the transversus abdominis museles. Tht posterior layer^ whieh is the strongest of the three, is a dense tendinous aponeurosis. It is eontinuous above with the thoraeie part. Below^ it is attaehed to the posterior part of the lateral lip of the iliae erest, and to the dorsum of the saerum and the coccyx.

THE DISSEGTION OF THE HACK 167

MedieUly^ it is attaehed to the tips of the spines of the lumbar yertebrae and the saerum ; and lattrally it blends ^ith the posterior surface of the middle lamella (Fig. 71). The aponeurosis of origin of the latissimus dorsi and the serratus posterior inferior arise from its posterior surface.

Disseetion. — Make a longitudinal ineision through the {)ostcrior layer of the lumbar part of the lumbo-dorsal fascia, midway tM.'twccn its medial and its lateral borders. At eaeh end of the longitudinal ineision make a transverse ineision extending from the spine medially to the lateral border of the rounded mass of spmal museles lying under cover ()f the fascia. Tum the medial part of the divided fascia towards the median plane, and verify its attaehment to the vertebral spines and the supraspinous ligaments. Pull the lateral part aside, and at the lateral border ot the mass of posterior spinal museles it will be found to blend with a deeper layer, the middle lamella. Push the mass of posterior spinal museles towards the median plane, and follow the middle lamella of the fascia to its attaehment.

The middk lamella is attaehed medially to the tips of the transverse proeesses of the lumbar vertebrae ; below to the iliae erest, and above to the last rib. Laterally it blends with the posterior and anterior lamellai, and immediately lateral to its line of union with the posterior lamella the internal oblique arises from its posterior surface. To expose it thoroughly the mass of posterior spinal museles must be pushed medially.

Disseetion. — After the middle lamella has been examined divide it longitudinally, elose to its attaehment to the tips of the transverse proeesses, and transversely along the line of the iliae erest, and turn it laterally. A eonsiderable part of the posterior surface of the quadratus lumborum musele will then be exposed. Displaee the lateral border of the quadratus lumborum towards the median plane, and the anterior lamella of the lumbar part of the lumbo-dorsal fascia will be brought into view.

•

The anterior lamella of the lumbar part of the lumbo- dorsal fascia is attaehed medially to the anterior surfaces of the roots of the transverse proeesses of the lumbar vertebrae ; laterally it blends with the fused middle and posterior lamellae to form the eommon aponeurosis of origin of the transversus abdominis musele, and it is by means of the three lamellae of the lumbar fascia that the latter musele arises from the tips of the spines, and the tips and the roots of the transverse proeesses of the lumbar vertebrse. The upper border of the anterior lamella beeomes thiekened, and extends anterior to the quadratus lumborum from the last rib to the trans- verse proeess of the first lumbar vertebra as the areus lumbo-eostalis lateralis (O.T. external areuate ligament); the

11—11 6

i68 HEAD AND NECK

lower border blends with the ilio-lumbar ligament. The disseetor should verify these various attaehments by passing his fingers over the posterior surface of the lamella from its lateral to its mediai border, and from its upper to its lower end.

Disseetion. — After satisfying himself regarding the lamellae of the lumbar part of the lumbo-dorsal fascia and their relations to the posterior spinal museles, to the quadratus lumborum, and to the internal oblique and the transversus abdominis museles, the disseetor should make a longitudinal ineision through the anterior lamella, and the peri-renal fascia anterior to it ; and, introdueing his finger through the opening into the extra-peritoneal fatty tissue, he should serape away the latter until he exposes the kidney, below the level of the last rib, and the adjacent part of the eolon, whieh lies along the lower and lateral part of the kidney. After this has been done he should reflect the serratus posterior superior and seeure its nerves of supply whieh spring from the upper intereostal nerves and enter its deep surface ; then he should remove the thoraeie part of the lumbo-dorsal fascia and eommenee the study of the posterior spinal museles, beginning with the splenius.

Mnseulus Splenius. — The splenius has a eontinuous origin from the lower half of the ligamentum nuehae, and from the spines of the seventh cervical and upper six thoraeie vertebrae. Its fibres pass obliquely upwards and laterally, forming a thiek flat musele, whieh soon divides into a cervical and a eranial portion, termed respectively the splenius cervicis and the splenius eapitis.

The splenius eeruids turns anteriorly and is inserted by tendinous slips into the tubereles of the transverse proeesses of the upper two or three cervical vertebrse, medial to the levator seapulae.

The splenius eapitis passes under cover of the upper part of the sterno-mastoid musele, and gains insertion into the lower part of the mastoid portion of the temporal bone and into the lateral portion of the superior nuehal line of the oeeipital bone. To see this insertion, the sterno-mastoid musele may be divided along the superior nuehal line, but it must not be detaehed from the temporal bone.

Disseetion. — The deeper spinal museles must now be disseeted. B^n by reflecting the splenius musele. Detaeh it from its origin and throw it laterally and upwards towards its insertion. Whilst doing this, preserve the eutaneous branehes of the cervical nerves whieh pieree it.

When the splenius eapitis is fully reflected, a small triangular spaee will be notieed elose to the superior nuehal line of the oeeipital bone. Anteriorly, it is bounded by the longissimus eapitis (O.T. traehelo-mastoid) ; posteriorly, by the lateral border of the semispinalis eapitis (O.T. eom- plexus) ; and above, by the superior nuehal line of the oeeipital bone. The floor of this little spaee is formed by the superior oblique musde of

THE DISSECTION 0F THE BACK 169

the head, and it is travened by the oedpital artery, whieh in thii part of its eourse gives off its deseending braneh (O.T. arteria prineeps eenrids), and its meningeal braneh.

The Third Layer of MnidM.— Under this head are ineluded a series of museular strands whieh streteh with a greater or less degree of eontinuity along the entire length of the dorsal aspeet of the vertebral eolumn. In the lumbar region they eonstitute a bulky Aeshy mass whieh niay l>c eonsidered the main starting-point. This mass is the miiaoiiliiB ■ftcro-tpiiudii whieh has the following origins : — (i) from the spines of all the lumbar Yertebne ;

(2) from the supraspinous ligaments whieh bind the lumbar spines togelher ;

(3) firom the dorsum of the saerum and from the posterior saeroiliae liga- ment ; (4) from the posterior fifth of the iliae erest ; (5) from the deep surface of the posterior layer of the lumbo-dorsal fascia. In great part the superficial suriaee of this museular mass is covered l)y and is adherent to the posterior layer of the lum1x>>dorsal fascia.

Superiorly the saero-lumbalis divides into three eolumns. The lateral eolumn first separates from the general mass, and to it the name (>f ilio- eostalis b given ; the middle eolumn is termed the longissimuSy and the medial eolumn, whieh beeomes quite distinet only as the upper part of the dorsal region is approaehed, is ealled the spinalis. The semispinalis musele is also ineluded in the third layer.

The Ilio-eoatalis is a eolumn of museular bundles whieh extends from the lumbar to the cervical region. It is separable into three segments known, from below upwards, as the ilio-eostalis lumborum, the ilio-eostalis dorsi, and the ilio-eostalis cervicis.

Ilio-eostalis Lumborum. — This musele and the longissinius dorsi beeome distinet at the Ievel of the last rib, and the interval l)etween them is marked by the exits of the lateral divisions of the posterior branehes of lower thoraeie nerves,

The musele ends above in a series of six or se^ren slender tendons, whieh are inserted into the angles or the eorresponding parts of the lower six or seven ribs.

The Ilio-eostalis Dorsi (O.T. Museitlus Aeeessorius) arises by six or seven slender tendons from the angles of the lower ribs, on the medial sides of the tendons of insertion of the ilio-eostalis lumborum, and it is inserted by a series of similar tendons into the angles of the upper six ribs and to the transverse proeess of the seventh cervical vertebra.

The Ilio-eostalis Cervicis (O.T. Cervicalis Aseendens). — This highest segmeht of the ilio-eostalis arises, on the medial side of the ilio-eostalis dorsi, by four slips whieh spring from the third, fourth, fifth, and sixth ribs ; it is inserted into the transverse proeesses of the fourth, fifth, and sixth cervical vertebrge.

To display the ilio-eostalis properly, the disseetor should first evert the lowest segment, and then in turn the middle and upper segments, but whilst doing this he must take eare to preserve the lateral divisions of the posterior branehes of the spinal nerves.

The Longplssimus is the middle and largest of the three musele eolumns. It extends upwards, through the thoraeie and cervical regions, to the head, and it also is separable into three segments : longissimus dorsi, longissimus cervicis, and longissimus eapitis. The interval between the longissimus and the spinalis is frequently diflficult to define, but if the fascia is carefully eleaned from the lateral to the medial border of the longissimus in the upper thoraeie region, the separation will beeome apparent, and after it has been found the attaehments of the longissimus must be defined.

Longissimus Dorsi. — The dorsal part of the longissimus possesses two rows of slips of insertion : a medial row of tendinous slips whieh are

lyo HEAD AND NECK

attaehed to the tips of the transverse proeesses of the thoraeie and the aeeessory proeesses of the lumbar yertebrse, and a lateral row of museular slips whieh are inserted into the lower ten ribs, on the lateral sides of their tubereles, and to the transverse proeesses of the lumbar vertebrse, and to the posterior surface of the middle lamella of the lumbar fascia.

Longissimus Cervicis{O.T. Transversalis Cervicis). — This portion of the longissimus springs from the transverse proeesses of the upper four thoraeie vertebroe, and is inserted into the posterior tubereles of the transverse proeesses of the cervical vertebr3e from the seeond to the sixth inclusive.

Longissimus Capitis (O.T. Traekelo-mastoid). — The longissimus oapitis lies in the neek under cover of the splenius. It arises in oommon with the longissimus cervicis from the transverse proeesses of three or four of the upper thoraeie ^ertebrse, and, in addition, from the artieular proeesses of a like number of the lower cervical vertebr3e. The narrow Aeshy band whieh results is inserted into the posterior part of the mastoid portion of the temporal bone, under cover of the splenius eapitis and sterno-mastoid museles.

The Spinalis. — This is the most medial, shortest, and weakest of the three eolumns, and the most difficult to define. Below, it is intimately blended with the longissimus dorsi, but it may be regarded as taking origin by four tendons from the spines of the upper two lumbar and lower two thoraeie vertebr£e. These end in a small museular belly, whieh is inserted by a series of slips into a very variable number of the upper thoraeie spines. It is elosely eonneeted with the subjacent semispinalis dorsi.

Spinalis Cervicis. — This upward prolongation of the spinalis is not always easy to define. It springs from the si^ines of the lower four cervical ^ertebrte and is inserted into the spines of the seeond, third, and fourth cervical vertebrae.

Disseetion. — The oeeipital artery has already been seen erossing the apex of the posterior triangle (p. 149), and its terminal branehes have been disseeted as they ramify in the sealp (p. 157). The seeond part of the vessel, whieh extends from under shelter of the mastoid proeess, along the superior nuehal line of the oeeipital bone, to the point where it pierees the trapezius to beeome superficial, ean now be exposed fully. To efFect this, the longissimus eapitis (O.T. traehelo-mastoid) must be divided a short distanee below its insertion, and, along with the splenius eapitis, thrown upwards as far as possible.

Arteria Oeeipitalis. — The seeond part of the oeeipital artery is now displayed. In the region of the mastoid proeess it is very deeply plaeed ; indeed, no less than five struetures lie superficial to it. These are (enumerating them in order from the vessel to the surface) — (i) the origin of the posterior belly of the digastrie musele ; (2) the mastoid proeess; (3) the longissimus cervicis ; (4) the splenius eapitis ; and (5) the sterno-mastoid.i As the artery runs posteriorly, it very soon emerges from under cover of the first three of these struetures, and a little farther on it leaves the shelter of the splenius, and is then covered by the sterno-mastoid alone. Issuing from under cover of the posterior border of that musele,

^ It is not uneommon to find the artery at this point of its eourse between the splenius and the longissimus eapitis.

THE DISSECTION OF THE BACK 171

the artery erosses the apex of the posterior triangle, and disappears under the trapesius, whieh it finally ()ierces near the extemal oeeipital protuberanee, to reaeh the sealp. Two museles eonstitute its deep relations — y\z^ the insertions of the superior oblique and the semispinalis eapitis (O.T. complexus).

The following brafuhes may be traeed from this portion of the ooeipital artery : (i) deseending (O.T. arteria p)rince|>s eeryids) ; (2) meningeal ; (3) museular.

The ramus deseendens (O.T. arteria prirueps eerrids) is a twig of some size, whieh passes medially to the lateral border of the semispinalis eapitis (O.T. complexus) ; there it divides into a superficial and a deep braneh. The fonner ramities on the surface of the semispinalis eapitis, whilst the latter sinks under that musde, where it will be followed to its anastomosis with the deep eendeal artery at a later stage in the disseetion.

The small meningeal hraneh enters the posterior eranial fossa through the mastoid foramen, and supplies the dura mater and eranial wall in this region.

The museular twigs go to the neighbouring museles.

The ffeins eorresponding to the oeeipital artery are two, or perhaps three, in number. They drain the blood from the oeeipital portion of the sealp, and open into the sub-oeeipital plexus, whieh is drained by the vertebral and deep cervical yeins. The most lateral of the oeeipital veins frequently eommunieates with the transverse sinus (O.T. lateral) through the mastoid foramen.

Disseetion, — The semispinalis eapitis, whieh has been exposed by the reflection of the splenius and the turning aside of the longissimus cervicis and longissimus eapitis, must now be eleaned, and whilst this is being done and its attaehments are being defined, eare must be taken of the medial divisions of the posterior branehes of the seeond, third, fourth, and fifth cervical nerves. The first of these — or, in other words, the great oeeipital — from its great size, runs little risk of injury, but the others are liable to be overlooked. They all emerge from the substanee of the musele elose to the median plane.

Semispinalis Capitis (O.T. Complexus). — The semispinalis eapitis is the uppermost part of a museular eolumn eonsisting of three segments, whieh are spoken of collectively as the semispinalis, and individually as the semi- spinalis dorsi, the semispinalis cervicis, and the semispinalis eapitis. It belongs to the third layer of museles, of whieh the greater number have been disseeted already. The two lower segments will be disseeted subse- quently, but it is convenient to examine the semispinalis eapitis at onee. It is a thiek Aeshy mass whieh springs by tendinous slips from the transverse proeesses of the upper six thoraeie vertebrae and the artieular proeesses of the fourth, fifth, and sixth cervical vertebr3e. Its massive upper extremity

172

HEAD AND NECK

U inserted into a somewhat oval area on the oeeipital bone, between the superior and inrerioi nuehal lines elose to the eKtemal oeeiintal erest. It is sepaiated tioin its fellow musele of Ihe oppo^le side by the ligamentum nuehii; ; and its most medial part, whieh is to a eettain extent distinet from the genetal mass, is divided into two bellies by an inlermediale tendon and is freqiiently spoken of as Ihe bhieuter eemieis. Oeeasionally the remainder of the musele is also interseeted by a tendinous septum.

eate, not only on aeeount of the nerves whieh have been seen to peribrate the musele to reaeh the surface, but also on aeeount of the stnietures whieh it covers. In its upper part it lies over the sub-occipilal triangle and the museles bounding it, whitst below it eoyers the semispinuia ceivicis. A thiek dense fascia isplaeed over these subjacent parls, and iil this lie eerlain of the cervical nerves and the anastomosis between the deseending braneh of the oeeipital artery and the arteiia profunda eemdE. The disseelor must speeially look fDr a smal! Iwig fiom the posterior braneh of the sub-oeeipital nerve whieh enleis the deep suiface of the uppei part of Ihe semispinalt^ eapitis, and foi a larger bianeh to the same musele rroni the greal oeeipital netve.

LigamAiitum Hnelue (Fig. 72). — This is a strong fibious partition plaeed in the median plane between the museles on

THE DISSECTION 0F THE BACK 1 73

eaeh side of the baek of the neeL It represents a |K)wcrful elastie strueture in guadrupeds, whieh helps to sustain the weight of tbe dependent head. In man, however, there is nut niu(*h elastie tissue developed in eonneetion with it, and it ap|>cars to be a eontinuation upwards of the supraspinous liganient from the spine of the seventh cervical vertebra to tlie cxtcrnal oeeipital protuberanee. In shape it is soniewhat triangular. By its base it is attaehed to the external oeeipital erest ; by its anterior border it is fixed by a series of sli|)s to the posterior tuberele of the atlas, and to the bifid spines of the cervical vertebrae, in the intervals between their tubereles. Its apex is attaehed to the spine of the seventh cervical vcrtebra, whilst its posterior border is, in a measure, frec, and givcs origin to the traj>e2ius, rhomboid, serratus i>osterior superior, and splenius museles.

Arberia ProAmda GenrieiB. — The deep eeruieal artery springs from the costo-cervical braneh of the subclavian, and reaehes the dorsum by passing posteriorly between the transvcrse proeess of the last cervical vertebra and the neek of the first rib. At the present stage of the disseetion it is seen aseend- ing upon the semispinalis cervicis musele and anastomosing with the deseending braneh of the oeeipital. Both vesscls anastomose with twigs from the vertebral artery.

The arteria profunda cervicis is aeeompanied by a large vein — the vena profunda eeruieis, This vessel begins in the sub-oeeipital plexus, and it ends in the yertebral vein elose to its termination. It reaehes this point by turning forwards under the transverse proeess of the last cervical vertebra.

Posterior Branelies of the Spinal Nenres. — The nerves of the baek must now be examined. They are the posterior branehes of the spinal nerves. With four exceptions (viz., the first cervical, fourth and fifth saeral, and the eoeeygeal neryes), eaeh posterior division will be found to divide into a lateral and a medial division,

Examine these nerves successively in the cervical, dorsal, and lumbar regions. It is well, however, to defer the disseetion of the saeral and eoeeygeal nerves until the multifidus musele has been studied.

Cervical Begion. — In this region the posterior branehes of the spinal nerves are eight in number. The posterior braneh of the sub-oedpital or first nerue fails to divide into a medial and a lateral division. It lies deeply in the sub-

174 HEAD AND NECK

oeeipital triangle, and will be examined when this spaee is disseeted.

The posterior braneh of the seeond eeruieal nerue is very large. It appears between the vertebral arehes of the atlas and epistropheus vertebr3e. The posterior branehes of the sueeeeding six eeruieal nerues arise from the eorresponding spinal nerve-trunks in the intervertebral foramina. They turn dorsally on the medial sides of the posterior intertransverse museles, and appear in the intervals between the transverse proeesses.

The lateral divisions are of small size, and are entirely devoted to the supply of adjacent museles.

The medial divisions are not all distributed alike, nor indeed do they present the same relations. Those from the seeond^ third^ /ourth^ and fifth nerues run medially towards the spinous proeesses, superficial to the semispinalis cervicis musele, and under cover of the semispinalis eapitis. When elose to the median plane they turn posteriorly, pieree the semispinalis eapitis, splenius, and trapezius museles, and beeome superficial. In their eourse to the surface they give numerous twigs to the neighbouring museles.

The medial division of the seeond nerve is remarkable for its large size. It receives the speeial name of great oedpitaL It will be notieed turning round the lower border of the inferior oblique musele, to whieh it supplies some twigs. In passing to the surface it pierees the semispinalis eapitis (O.T. complexus) and trapezius. To the former it gives several twigs. The distribution of this nerve on the oeeiput has been notieed already (p. 156).

The medial division of the third nerve also sends an oiTset to the oeeipital portion of the sealp (p. 156).

The medial divisions of the lower three posterior branehes of the cervical nerves resemble the preeeding, in so far that they take a eourse medially towards the spinous proeesses. They difFer from them, however, in running deep to the semi- spinalis cervicis, and in being, as a rule, entirely expended in the supply of museles.

Dorsal Begion. — The posterior branehes of the thoraeie nerves make their appearanee in the intervals between the transverse proeesses. The lateral divisions proeeed laterally, under cover of the longissimus musele, and appear in the interval between the longissimus dorsi on the one hand and

THE DISSECTION OF THE BA(K 17^

the ilio-eostalis on the other. The ufper stx or snrm ui these nerves are exhausted in the supply of the mtdille ami Ijtcral eolumns of the saerospinalts ; the lawtr^rt or stx, hiiwi:vrr. are eonsiderably larger, and eontain both onotdr and scn9«ir\' fibres. After giving up their motor fibres to the niuv Icv they beeome superlieial, by piereing the serratus (Kisterinr in ferior and the latissimus dorsi, in a line mith the angles (if the ribs. The eutaneous distribution of these mnt-s hxs already been examined by the disseetor of the up|H.*r linih.

The tnedial divisions also are distributed diHerently in ihe upper and lower portions of the dorsal region. The lowtr five or six are very small, and end in the multifidus musele. The upper six or seven pass medially l)etwcen the multifidus and semispinalis, and after supplying the museles between whieh they are situated, they beeome suj)erficial. In passing towards the surface they pieree the splenius, rhom- boids, and trapezius museles, and thus gain the su{)erficia] fascia, where they have been disseeted already.

Ltimhar B^on. — The medial dirisions of the [)osterior branehes of the five lumbar nerves are small, and, like the eorresponding twigs in the lower dorsal region, they havc a purely museular distribution. * They end in the multifidus.

The iateral divisions sink into the substanee of the saero- spinalis, and are eoneemed in the supply of that musele, and also of the lumbar intertransverse museles. The upper three of these nerves are of large size, and beeome eutanoous by piereing the superficial lamella of the lumbo-dorsal fascia. They have already been traeed by the disseetor of the lower limb to the skin of the gluteal region. The lowest lateral division eommunieates with the eorresponding braneh of the first saeral nerve.

Blood Vessels of the Baek. — In the eeruieal region the disseetor has already notieed the arteria profunda cervicis, and the deseending braneh of the seeond part of the oeeipitai artery. Deep in the sub-oeeipital region he will subsequent]y meet with a small portion of the vertebral artery. In addition to these, however, minute twigs may be discovered, in a well- injected subject, passing posteriorly from the vertebral artery in the intervals between the transverse proeesses, and also in the sub-oeeipital spaee. These supply the museles, and anastomose with the other arteries in this region.

In the dorsalregion \ht posterior branehes oi the aortie inter-

176 HEAD AND NECK

eostal arteries make their appearanee between the transverse proeesses. Eaeh of these vessels reaehes this point by .* passing dorsally in the interval between the body of a vertebra ^ and the anterior costo-transverse ligament. It is assoeiated with the eorresponding posterior braneh of a spinal nerve^ and is distributed with it to the museles and integument of the baek.

In the lumbar reglon similar branehes are derived from the lumbar arteries. They are distributed in the same manner.

In both dorsal and lumbar regions these vessels, before reaehing the baek, furnish small spinal branehes whieh enter ! the vertebral eanal through the intervertebral foramina. ■■[ These will be traeed at a later period. \

The veins aeeompanying the dorsal branehes of the lumbar and intereostal arteries pour their blood into the lumbar and intereostal veins. They are of large size, being joined by tributaries from the posterior vertebral venous plexus, and also by others from within the vertebral eanal.

Disseetion. — The remains of the third layer of spinal museles must now be disseeted. They are the semispinalis dorsi and semispinalis cervicis.

The semispinalis cervicis is already exposed ; but to display the semispinalis dorsi it is neeessary to remove the spinalis dorsi musele.

The semispinalis dorsi is eomposed of a series of museular slips, with long tendons at either end, whieh arise from the transverse proeesses of the sixth to the tenth thoraeie vertebr£e. It is inserted into the spines of the upper four thoraeie and lower two cervical vertebr9e. The semispinaUs cervicis lies under cover of the semispinalis eapitis. It springs from the transverse proeesses of the upper five thoraeie ^ertebrse, and is inserted into the spines of the seeond to the fifth cervical vertebrae. The slips eomposing the semispinalis museles streteh over five or more ^ertebrse.

Disseetion. — The fourth layer of museles must now be examined. It ineludes the multifidus, the rotatores, the interspinales, theintertransversales, and the reeti and oblique museles of the sub-oeeipital region. The latter have already been exposed by the reflection of the semispinalis eapitis (complexus). To display the other members of the group the semispinalis dorsi and cervicis must be detaehed from the spines and drawn aside, and the saerospinalis must be separated from the lumbar and saeral spines and turned laterally, if this has not already been done in traeing the nerves.

Museulus MultiAdus. — In the lumbar and saeral regions the multi- fidus will be seen to eonstitute a thiek Aeshy mass, whieh elings elosely to the vertebral spines. In this situation it has a very extensive origin — viz., (i) from the deep surface of the aponeurotie origin of the saerospinalis ;

(2) from the posterior surface of the saerum as low as the fourth aperture ;

(3) from the posterior saero-iliae ligament ; (4) from the posterior superior spine of the ilium ; and (5) from the mammillary proeesses of the lumbar vertebr8e. In the thoraeie region it takes origin from the transverse proeesses of the vertebr3e, and in the cervical region from the artieular proeesses of at least four of the lower cervical vertebr8e. The bundles whieh eompose the

THE DISSECTION OF THE H.\(K 177

maldfidus pass over two, three, or four vertc)tr.r. an*! .irt* inMitt-il ti:(<i iU*- wholelength of the various siiinous nroct>M-s iif thr iiii>v.il>Ii \i-iti>^r r .10 high up as the epistropheus <f ).T. axis).

Muenli Sotatorei. — These are a series uf mii.iII iiiu<h-1< h %«)ui Ii iiu\ l>r exposed by raising the multiAdus. In the (lor^.il rt-f;i>>ii 1-31 )i iiiu<» li* Hpriii^'» from the root of a transverse proci>ss, and is in'4-rt(-<l iiit>t tlu- I.1111111.1 ur ihe vertebra immediately a)K>ve, elose to ihi* ri>«»i i»f !)i»' H|in"U-» iriKi-*x. Somewhat similar museles have lieen desrrilK-il in thir t (-rvi( .il .iii<i luinlMi r^ons, and also a series of lonoer and mt>rr ^uiie-rtiei.il olips \«hi« h «-..ihm 1 1 altemate vertebne with eaeh otner.

MoBeiili IntenpiiialM aad IntartraiiiTtnarii. 'rin- n:/^^ /^in .-<

museles ean hardly be said to exist in the dor'^1 n-i^ion. i-xi-r|it in it<. ui ;« i

and lower piarts, where the}' are present ina ruiliiiu*nt.iry « ••ii'hii>>M. l:i

the neek they are arranged in pairs, oeeupyini; eaeh inirrN|.in..iiN iii:.i\ I,

with the exception of that between the opistropluus :in<i ,111.1-«. In ili«-

lumbar region also they are well marked and in |>;ur< : Ihti- ihey ait-

attaehed to the whole length of the spinous procc>sc>. rht- ////<-/■// i/;/..-v; e

mtisdes are strongly develoi)ed in the luint>ar rcj;i«»n. an! iK."t u]y tlu- mtire

length of the intertransverse inlervals. AddititMial ri»un'!iii t'.i««ii<'uli niay

be observed passing between ihe access«iry prtK\s««iN. TIu-ni- an- ttTnu<i

Wit interaeeessorii. In the dorsal ref^on inttTtransvtT«»o nuiM l. s ]mmii1\

developed — are found only in the lower three or ft)ur >]ia(\N. In iIk- •,r:u-,i:

region they are present in pairs and will Ik: c\aniiiuti -^ulisi-<juintly.

Leyatores eostamm. — These eonstituie a suries ()f twtUe fan-shaped museles, whieh are classifiecl as niiisrks()f ihe ihoraN, but they are exposed when the longi.ssimus aiid ilio eostalis are removed, and therefore should bc cxanHnod now. 'i'lu y pass from the transverse proeesses to the ril)s. The firsi musele of the series springs from the tip of the transversc proeess of the last cervical vertcbra, and, exi)anding as it proeeeds downwards and laterally, it is inserted int(; the outer border of the iirst rib, immediately beyond the tuberele. Eaeh of the sueeeeding museles takes origin from the tip of a thoraeie transverse proeess, and is inserted into the outer surface of the rib immediately below, along a line extending from the tuberele to the angle.

Posterior Branehes of the Saeral Nerves. — These are very small. The upper four will be found emerging from the posterior saeral foramina ; the fifth appears at the lower end of the saeral eanal.

To expose the upper three the multifidus covering the upper three saeral apertures must be carefully removed. Eaeh of these three nerves will be found to divide in the usual manner into a medial and lateral division.

The medial dwtswns are very fine, and end in the multifidus.

The lateral dwisions are somewhat larger, and join

voL. II — 12

178 HEAD AND NECK

together so as to form a looped plexus upon the dorsum of the saerum. This eommunieates above with the lateral division of the last lumbar nerve and below with the posterior braneh of the fourth saeral nerve. Branehes proeeed from the loops to the surface of the saero-tuberous ligament (O.T. great saero- seiatie). Einally they beeome superficial by piereing the glutaeus maximus musele, and they supply a limited area of skin over the glutaeal region. They have already been examined by the disseetor of the lower limb.

The lowest two posterior branehes of the saeral nerves do not separate into medial and lateral divisions. They are very small, and, after eommunieating with eaeh other, and also with the eoeeygeal nerue^ they distribute filaments to the parts on the posterior aspeet of the lower portion of the saerum and on the dorsal aspeet of the coccyx.

Twigs from the lateral saeral artery aeeompany the saeral nerves and anastomose with twigs from the glutseal arteries,

Posterior Braneh of the Goeeygeal Nerve. — ^This is a slender twig whieh emerges from the inferior opening of the saeral eanal, and, after being joined by a filament from the last saeral nerve, is distributed on the dorsum of the coccyx.

Posterior Vertebral Venous PlexiLS. — A plexus of veins is situated upon the superficial aspeet of the vertebral arehes subjacent to the multifidus musele. This plexus eolleets blood from the integument and museles of the baek, and in the thoraeie and lumbar regions pours it into the posterior tributaries of the intereostal and lumbar veins. In the neek it is espeeially well marked, and its blood is emptied into the vertebral veins. Not many of these venous ehannels will be seen in an ordinary disseetion. They are, however, a souree of serious trouble during operations upon the vertebrae.

Disseetion. — The fourth day after the body is plaeed upon its fece must be devoted to the disseetion of the sub-oeeipital triangle, and the fifth day to the display of the meduUa spinalis (O.T. spinal eord), its membranes, nerve-roots, and blood yessels.

If the disseetor is pushed for time, it is better that he should proeeed at onee to expose the spinal medulla, and defer the disseetion of the sub- oeeipital region until the head and neek have been removed from the body.

Sub-Occipital Spaee. — The sub-oeeipital spaee is a small triangular area, exposed by the reflection of the semi- spinalis eapitis (O.T. complexus) and the splenius musele. It is bounded by three museles — (i) the reetus eapitis

THE DISSEGTION OF THE BUK .79

posteiior ma}or fonns its uppei and medial IwundaTy ; (1) the obliquus iDferior limits it below ; and (3) ihe oblitiiius niperior bounds it above and lo Ihe lateral side. /A ^oer eonsists of tvo Btmettires — viz. Ihe posterior areh of Ibe atlas and the thin posterior atlanto-oeeipiial membrane.

It eontains a portion of the vertebral artery and the posterior braneh of the sub-oeeipital or first cervical nerve.

Z>/!/«/i(>H.— Before eleaning the museles bounding Ihe Iriangle, the

poslerior braneh of the sub-oeeipitaL nerve muBl be seeuted. Tlus ean

best be done by Iraeing inlo the spaee Ihe minule twig whieh it has been

seen to give lo the deep suriaee of the semispinalis eapitis, or, if this has

II— 12«

i8o HEAD AND NECK

not been retained, by endeavouring to fmd the twig whieh it gives to the reetus eapitis posterior major. The tissue in whieh the nerve lies is very dense, and the disseetion is in consequence somewhat difficult.

Eeetus Gapitis Posterior Major. — This musele springs by a pointed origin from the spine of the epistropheus (O.T. axis), and, expanding as it passes upwards and laterally, it is inserted into the oeeipital bone along the lateral portion of the inferior nuehal line and the surface immediately below.

Eeetus Oapitis Posterior Minor. — This is a small fan- shaped musele, plaeed to the medial side of, and overlapped by, the preeeding musele. It takes origin from the tuberele on the posterior areh of the atlas, and is inserted into the medial part of the inferior nuehal line of the oeeipital bone and the surface between this and the foramen magnum.

Obliquus Oapitis Iiiferior.— This musele extends from the extremity of the spine of the epistropheus to the posteridr border of the transverse proeess of the atlas. The great oeeipital nerve will be seen hooking round its lower border.

Obliquus Oapitis Superior. — This musele springs from the transverse proeess of the atlas, and is inserted into the oeeipital bone in the interval between the nuehal lines, below and to the lateral side of the semispinalis eapitis.

Posterior Braneh of the Sub-Oeeipital Nerve. — The posterior braneh of the sub-oeeipital nerve does not divide into medial and lateral divisions. It enters the sub-oeeipital triangle by passing dorsally, between the posterior areh of the atlas and the vertebral artery, and at onee breaks up into branehes whieh go to supply five museles — viz. the two posterior reeti, the two oblique museles, and the semispinalis eapitis. In addition to these museular twigs it gives a eom- munieating, and sometimes a eutaneous filament.

The eommunieating braneh generally proeeeds from the nerve to the obliquus eapitis inferior, and joins the great oeeipital nerve. The eutaneous braneh, when present, aeeom- panies the oeeipital artery to the integument over the oeeiput.

Arteria Vertebralis. — Only the third portion of this vessel lies in the sub-oeeipital triangle. Emerging from the foramen in the transverse proeess of the atlas, it runs posteriorly and medially in the groove upon the posterior areh of the same bone. In this eourse it lies immediately posterior to the lateral mass of the atlas and above the sub-oeeipital nerve. It leaves the spaee by passing anterior to the thiekened lateral ex-

THE DISSECTION OF THE BACK 181

tension of the posterior atlanto-oeeipital membrane, whieh nins from the posterior areh of the atlas to the i^osterior lip of its artieular proeess and is ealled the obIi()ue ligamont of the atlas ; then it pierees the dura mater and entors the vertebral eanaL

Small branehes proeeed from the vertebral arter>- in this situation to supply the parts in its immediate neighbourhood, and to anastomose with the deseending braneh of ihe oeeipital artery and the arteria profunda cervicis.

DiBseetioii to op«ii the Yerielnral Ganal.— The first step eonsists in thoroughly eleaning the laminae and spinous proeesses u{K>n iHith sides. The multitidus must be eompletely removed froni the tU^rsuni of the saerum. At the same time the posterior branehes of ihe ncrves niust be retained, so that their eontinuity with the various spinal nerve-trunks may be afterwards established. The posterior wall of the vertehral eanal should now be remoyed in om pieee by sawing through the laniin;ir on either side, and diyiding the ligamenta flava, froni the third cervical yertebra down to the lower opening of the eanal on the baek of the saerum.

In making this disseetion the student must attend to the following points : — (i) the eut should be direeted through the laminiv elose to the medial sides of the artioular proeesses ; (2) the saw must be used in an obli(jiie plane, so that the eut through the laminx slants slightly medialwards ; (3) in eutting through the cervical laminae the head and neek should hang oyer the end of the table, and be flexed as mueh as }X)ssil)le, whilst the saw is worked from below upwards ; (4) in the ease of the lumbar region, where, indeed, most difficulty will be met, a high bloek must be plaeed under the abdomen of the subject, whilst the bloeks supporting the ehest and pelvis are removed. It will probably be neeessary at this }X)int to have reeourse to the hammer and ehisel.

The laminse and spinous proeesses whieh are thus removed are eonneeted with eaeh other by the ligamenta flava and the suprasi^inous and inter- spinous ligaments. They should be laid aside for the present. A de- seription of these ligaments will be found on p. 358. When the speeimen is firesh, however, the disseetor should test the high elastieity or the ligamenta flava by stretehing the sp>ecimen.

Between the dura mater and the walls of the eanal, the disseetor will notiee a quantity of loose areolar tissue and soft fat. The latter is espeeially plentiful in the saeral region, where it somewhat resembles the marrow in the meduUary cavity of a long bone. Great numbers of large veins and minute arteries ramify in this areolo-fatty material.

Arterise Spinales. — In a well-injected subject a minute spinal artery will be seen entering the yertebral eanal through eaeh intervertebral foramen. These arteries are derived from different sourees in the different regions of the spine. In the eeryieal region they eome from the yertebral artery, and in the thoraeie region from the posterior branehes of the inter- eostal arteries ; in the lumbar region from the dorsal branehes of the lumbar arteries. They supply the spinal medulla and its

11—12 6

i82 HEAD AND NECK

meninges, the bones, the periosteum, and the ligaments ; and their arrangement is very mueh the same in eaeh of the three regions.

Eaeh spinal artery may be looked upon as giving off three main twigs: of these, one, termed the pre-laminar braneh^ a very small twig, ramifies upon the deep surface of the vertebral arehes and ligamenta flava ; another, the neural braneh^ ean be followed to the dura mater, whieh it pierees immediately above the point of exit of the eorresponding spinal nerve; whilst the third, \ht post-eentral branehy is earried medially, anterior to the dura mater, towards the posterior surface of the vertebral bodies, and divides into an aseending and a deseending twig. These anastomosewith the eorrespond- ing twigs above and below, and in this manner a eontinuous series of minute arterial areades is formed, from whieh branehes pass medially to form a series of eross anastomoses with the eorresponding vessels of the opposite side.

In the eeruieal re^on small branehes from the aseending cervical artery also find their way into the vertebral eanal ; whilst in the saeral portion of the eanal the disseetor will find branehes from the lateral saeral arteries.

Intemal Yertebral Venoiis Plexus. — This plexus extends along the whole length of the vertebral eanal, and eonsists essentially of four subsidiary longitudinal plexuses, two anterior and two posterior, whieh anastomose freely with eaeh other.

The posterior plexuses are united by many eross branehes, whieh run along the deep aspeet of the vertebral arehes and ligamenta flava. Above, they eommunieate with the oeeipital sinus, whilst all the way down they are eonneeted with the posterior vertebral venous plexus by wide ehannels whieh pieree the ligamenta flava. Laterally they send branehes through the intervertebral foramina to join the posterior branehes of the intereostal and lumbar veins.

The anterior pleoeuses eannot be disseeted whilst the medulla spinalis (O.T. spinal eord) and its membranes are in situ^ but it is convenient to deseribe them at this stage. Ihdeed, the disseetion is one of eonsiderable difficulty, even under the most advantageous eireumstanees. They form two main longitudinal venous ehannels plaeed one upon either side of the posterior longitudinal ligament of the vertebral bodies, and they are joined by transverse branehes whieh eross the median

THE DISSECTION 0F THE BACK 183

plaue anterior to that ligament opposite eaeh vertcbral body. Eaeh trarisverse vem receives large tributaries from the in- terior of the vertebra. Superiorly, eaeh of the niain longitudinal ehannels eommunieates with the oeeipital sinus or the basilar plexus within the eranium ; and eaeh of the posterior ehannels gives off a braneh whieh emerges above the posterior areh of the atlas to join the eommeneement of the vertebral vein. Opposite the various intervertebral fibro-cartilages the anterior plexus sends off branehes whieh run towards the inter- vertebral foramina, where they join with eorresponding branehes of the posterior plexus, to form the intervertebral veins whieh aeeompany the eorresponding spinal nerves.

Memnges of the Medulla Spinalis (Fig. 74). — The medulla spinalis, like the brain, with whieh it is eontinuous, is enveloped bythree membranes termed memnges, The most external investment is a strong fibrous membrane ealled the dura fnater\ the seeond, in order from without inwards, is a non- vascular tunie termed the arachnoid\ whilst the third and most internal is the pia mater, These membranes are direetly eontinuous with the eorresponding investments of the brain.

Disseetion. — Theouter surface of the dura mater must now be eleaned. This is effected by removing the loose areolar tissue, soft fat, and posterior intraspinal veins from the yertebral eanal. It is neeessary, also, to define earelully the numerous lateral prolongations whieh the membrane gives to the spinal nerves.

Dura Mater Spinalis (Fig. 74). — In the vertebral eanal the dura mater eonstitutes an exceedingly dense and tough fibrous tube, whieh extends from the foramen magnum above, to the level of the seeond or third pieee of the saerum below. It is separated from the walls of the vertebral eanal and its lining periosteum by an interval, whieh is filled by loose fat and areolar tissue, and the internal vertebral venous plexus. Even before the membranous tube is laid open, the disseetor ean readily satisfy himself that it forms a very loose sheath around the spinal medulla and the nerve-roots whieh form the eauda equina ; in other words, it is very eapaeious in eomparison with the volume of its eontents. Its ealibre, moreover, is by no means uniform ; in the cervical and lumbar regions it is eonsiderably wider than in the thoraeie region, whilst in the saeral eanal it rapidly eontraets and>finally ends by blending with the filum terminale, a fibrous thread whieh is prolonged II— 12c

i84 HEAD AND NECK

downwards through the saeral eanal from the extremity of the medulla spinalis (O.T. spinal eord),

The eylindrieal tube of spinal dura mater does not lie free within the vertebral eana!, although its attaehments are of sueh a nature that they do not in any way interfere wilh the free movement of the yertebral eolunin. Above, the dura mater is firmly attaehed to the seeond and third cervical

vertebr£e, and around the margin of the foramen magnum ; below, the tilum terminale, on whieh it terminates, ean be traeed as far as the dorsal aspeet of the coccyx, where it is lost by blending with the periosteum. On either side the spinal nerve-roots, as they pieree the dura mater, earry with them into the intervertebral foramina tubular sheaths of the membrane, whieh are attaehed to the margins of the foramina, whilst, anteriorly, loose librous prolongations — more numerous above and below than in the dorsal region — eonneet the tube of dura mater to the posterior longitudinal ligament of the

THE DISSEGTION 0F THE BA(:K 185

vertebral eolumn. No eonneetion of any kind cxists lM.*twccn the dura mater and the vertebral arehes or ligamenta flava.

Disseetion. — The tube of dura mater may now l»c u|ii'nct! with the seissors. The ineision should 1)e earrieil through the nunilirane in the median plane. Care, however, must 1)C taken not to injurc the delieate araehnoid, whieh is subjacent.

Caviim SaMunde. — The subdural cave (O.T. spaee) is the eapillary interval between the dura niater and the araehnoid (Fig. 74). The deep surface of the dura, whieh is lurned towards this spaee, is smooth, moist, and polished. The disseetor will notiee, upon either side, the series of apertures of exit for the roots of the spinal nerves. These are ranged in pairs opposite eaeh intervertebral foramen. The subdural spaee is prolonged laterally, for a short distanee, upon eaeh of the nerve-roots, and has a free eommunieation with the lymph paths present in the nerves.

Viewed from the inside of the tube of dura niater, eaeh of the two nerve-roots belonging to a spinal nerve is seen to earry wiih it a s])ecial and distinet sheath. When examined, however, on the outside of the tube of dura mater, they appear tobe envehiped in one sheath, beeause the two sheaths are elosely held together on the outside hy intervening connective tissue, whioh ean be removed with a little careful elisseetion. When this is done, the two tubular sheaths will be seen to remain distinet as far as the ganglion on the posterior root of the nerve. At that point they blend with eaeh other.

Araehnoidea Spinalis (Fig. 74). — The araehnoid resembles the dura mater in forming a loose, wide inyestment for the spinal medulla. Unlike the dura, however, it is remark- able for its great delieaey and transpareney. The sae whieh it forms is most eapaeious, and ean be demonstrated most easily towards its lower part, where it envelops the extremity of the spinal medulla and the eoUeetion of long nerve-roots whieh eonstitute the eauda equi?ia. Make an ineision into it, and insert the handle of the sealpel, or, better still, inflate the sae with air by means of a blowpipe. Above, the araehnoid beeomes eontinuous, at the level of the foramen magnum, with the araehnoid membrane of the brain, whilst, laterally, it is prolonged upon the various nerve-roots, thus eontributing to eaeh a tubular sheath. It terminates blindly below at the level of the seeond or third saeral vertebra.

Cavum Subaraehnoideale (Fig. 74). — This term is applied to the wide spaee between the araehnoid and pia mater. It is oeeupied by a variable amount of eerebro-spinal fluid, and

i86 HEAD AND NECK

is direetly eontinuous with the eranial sub-araehnoid spaee. Three ineomplete septa partially subdivide the spinal sub- araehnoid spaee into eompartments. One of these septa is a median partition ealled the septutn subaraehnotdeale^ whieh eon- neets the pia mater covering the posterior aspeet of the spinal medulla with the araehnoid. In the upper part of the cervical region the subaraehnoid septum is represented merely by a number of strands passing between the two membranes ; in the lower part of the cervical region and in the thoraeie region it is almost eomplete. The two other septa are formed by the liga- menta dentieulata. These spread outwards from eaeh side of the medulla spinalis, and will be studied with the pia mater.

Disseetion. — Take away the araehnoid mater from a portion of the spinal meduUa, and proeeed to the study of the pia mater.

Pia Mater Spinalis. — This is a firm vascular membrane, elosely adherent to tl^e surface of the medulla spinalis (O.T. spinal eord). It is thieker and denser than the pia mater of the brain, largely owing to the addition of an outer layer of fibres whieh run chiefly in a longitudinal direetion. The pia mater sends a fold into the antero-median fissure of the medulla spinalis, and the septum whieh oeeupies the posterior median fissure of the medulla spinalis is firmly attaehed to its deep surface. Anteriorly, in the median plane, the pia mater is thiekened to form a longitudinal glistening band, whieh receives the name of the linea splendens, Of eourse, this ean be seen only after the medulla spinalis (O.T. spinal eord) has been removed from the vertebral eanal. The blood vessels of the medulla spinalis lie between the two layers of the pia mater before they enter the substanee of the spinal medulla, and the various spinal nerves receive from it elosely fitting sheaths whieh blend with their connective-tissue sheaths.

Ligamentum Dentieulatum (Figs. 74 and 75). — ^This is a remarkable band, whieh stretehes laterally from either side of the meduUa spinalis, and eonneets it with the dura mater. Its pial or medial attaehment extends in a eontinuous line, between the anterior and posterior nerve-roots, from the level of foramen magnum above to the level of the body of the first lumbar vertebra below. Its lateral margin is widely serrated or dentieulated. From twenty to twenty-two dentieulations may be reeognised, and the highest is attaehed to the margin of the foramen magnum. They oeeur in the intervals between the

THE DISSECTION OF THE BACK

1S7

spinal nerves, aod, pushing the aiaehnoid bcfore them, they are attaehed by their pointed extremttics to ihe inner surraee of the dura mater.

The ligamenta dentieulau maintain Ihe meduUa 5[iina]is (O.T. spinaleord) in the middleof the tubeotdura materand partially subdivide the sub-araehnoid spaee into an anterior and a posterior eompartment In the anterior c(im[»artment the anterior nerve-roots pass latetally ; the posterior eomparl- ment eontains the posterior nerve-roots, and is imperfectly subdivided into two lateral subdivisions by the septum postieum.

Medulla Spmalis (O.T. Spinal Gord). — The spinal meduUa itself may now be studied in sifu. It is aeylindrieal strueture, slightly Aattened an- terior-ly and pos- teriorly,whichextends from the foramen magnum, where it is conti!iuous with the meduUa oblongata of the brain, to t lower border of the body of the first or the upper border of the body of the seeond lumbar vertebra. Its lower end rapidly tapers to a point, and is termed the iemus medullaris. From the extremity of this, a slender fila- ment, termed the filum krminak, is prolonged downwards to the dorsal surface of the coccyx.

In the female the average length of the meduUa spinalis is 43 cm. ; in the male it is 45 cm.

Throughout the greater part of the thoraeie region of the spine the meduUa spmalis presents a uniform girth, but in the cervical and lower thor-ieie regions it shows marked swellings, termed respectively the inlumesuntia cervicalis and intumeseentia lumbalis. From these enlargements proeeed the nerves whieh supply the upper and lower limbs The eeniieal swelling is the more evident of the two It begins at the upper end of the meduUa spinalis (O.T. spmal eord) and attains its greatest

FiG. 75.— Lalenilviewof Ihe Medulla Spinali Dura Maier, and Liganieolum Denlieulatur (Hirschfeldand Lenill^)

iS8

HEAD AND NECK

breadth (13 to 14 mni.) opposite the fifth or sixth cervical vertebra. Below, it subsides opposite the seeond . thoraeie yertebra. The lumbar swelling begins at the level of the tenth thoraeie yertebra, and attains its maximum transverse diameter (11 to 13 mm.) opposite the last thoraeie vertebra. Below, it rapidly tapers into the eonus medullaris.

Filnm Teminale. — This delieate thread-like hlament lies amidst the numerous long nerve-roots whieh oeeupy the lower [lart of the vertebral eanal, but it ean readily be de- teeted from these (i) by its silvery glistening ap- pearanee, and (z) by its eontinuity with the ex- tremity of the eonus meduUaris.

Although the eentral

eanal of he medulla

nd spnals sp olonged

^ down n s nteno

fo nea ly half ts

leng h and neryous

^ ^ elemen s ean be

a m raeed n s sub-

s an e fo a 1 ke

d stan e he filum

e m n le s ch efly

eomposed of p a

ma e The Inea

^^gh h P "//«:/ n and the

lowe ends of he

u a a m y also be ons de ed o be eon nued

the level of he seeond o h d a al veneb a

ape ed end of he ube of du a ma er and

and finally ea h ng he lowe

s by blend ng t '

he

it pierees

receives an n e n en f 1

end of the sa al eanal

periosteum on he do sal surfa e of he coccyx o the last

pieoe of the saerum

THE DISSECTION 0F THE BACK 189

In length it measures about six inehes. The part within the tube of dura is termed the fiium terminaU intemum^ the portion outside is \h^filum terminale extemum.

Spmal Nerve8. — Thirty-one spinal nerves take origin from eaeh side of the medulla spinalis (O.T. spinal eord). These are classified into five groups, aeeording to the yertebrae with whieh they are assoeiated. The thoraeie, lumbar, and saeral neryes eorrespond in number with the yertebrae in eaeh of those regions — thus, there are twelve thoraeie, five lumbar, and five saeral nerves, eaeh of whieh issues from the vertebral eanal below the vertebra with whieh it numerieally eorresponds. In the cervical region, however, there are eight nerves, the first of whieh eomes out between the oeeiput and the atlas, and is therefore distinguished by the speeial name of the si^b- oedpital neroe, There is only one eoeeygeal nerve on eaeh side.

Spinal Nerve-Boots (Figs. 75 and 77). — Eaeh spinal nerve springs from the side of the spinal medulla by tivo roots — an anterior 2in6. 2iposterior. Except in the ease of the sub-oeeipital nerve (where the posterior root is sometimes absent), the posterior nerve-root is the larger of the two. In addition, the posterior root is distinguished by possessing an oval ganglion, termed the spinal ganglion. There is, also, a wide physiologieal difference between the two roots — the posterior root is eomposed of afferent fibres, the anterior root eonsists of efferent fibres. Immediately beyond the ganglion the two roots unite to forni the spinal nerue-tnmk, whieh eontains a mixture of both efferent and afferent nerve-fibres.

The mode of attaehment of the two nerve-roots to the side of the medulla spinalis is somewhat different in the two eases. In eaeh instanee they are attaehed by several separate fila radieularia^ whieh spread out from eaeh other as they approaeh their attaehments. In the ease of the posterior root the fila enter the spinal medulla consecutiveIy along a eontinuous straight line and at the bottom of a slight furrow. The fila of the anterior root, on the other hand, are not so regularly plaeed. They emerge from the medulla spinalis over an area of some breadth. The portion of the medulla spinalis whieh stands in eonneetion with a pair of nerves receives the name of a " neural segment."

It will be noted that the size of the nerve-roots differs greatly. The lower lumbar and upper saeral nerve-roots are mueh

igo HEAD AND NECK

the larger, whilst the lower saeral and the eoeeygeal roots are the smaller. In the cervical region the roots inerease in size from above downwards, but more rapidly in the lower members of the group ; in the thoraeie region the roots of the iirst nerve are large, but those whieh sueeeed it are small and of uniform size.

In relaliye length, and in the direetion whieh they follow in the vertebral eanal, the nerve-roots also show great differences, This is due to the medulla spinalis being so mueh shorter than the eanal in whieh it lies. In the upper part of the cervical region the nerve-roots are short, and proeeed laterally in a more or less horizontat direetion. Below the upper cervical

region the nerve-roots beeome more oblique, and the lower the origin of the nerve the longer is its eourse in the eanal. The arrangement of the lower thoraeie, the lumbar, saeral, and eoeeygeal nerve-roots is partieularly eharaeteristie. They are exceedingly long, and deseend vertically from the lower portion of the meduUa spinalis, forming a bundle whieh is ealled the eauda equina.

Mode of Ezit of Spinal Neires ftom Vertebral OanaL — The lower six cervical nerves, the thoraeie nerves, and the lumbar nerves make their exit through the intervertebral foramina ; whilst eaeh of the two branehes of the upper four saeral nerves finds its way out by a saeral foramen. The upper two cervical neryes, the fifth saeral nerve, and the eoeeygeal nerve, however, fo]low a diAerent eourse, The sub-oeeipital emerges by passing over the posterior areh of

THE DISSEeriON 0F THE BACK

191

the atlas, and the seeond cervical nerve by passing over the yertebral areh of the epistropheus {O.T. axis). The fifth saeral aud the eoeeygeal nerve leave ihe saeral eanal through its lower aperture (Fig. 78).

1] Cana1

This ean be easily done by snipping away ihe artieular proeesses with the bone-forceps. The posilion of Ihe ganElion on the poslerior toot, the eonneetions of the sheath of dura mater, the union of the two loots to form the spinal nerve-trunk, and the dirision of ihe lattet into the anterior and posleriot btanehes ean thus be studied. An attempt should also be made at the same time to discovet the minute ranius meningeas. This is a tine twig whieh is formed by the union of a small fi1ament ftain thespinal nerve-trunk with a minule braneh ftom the sympathetie trunk.

192 HEAD AND NECK

It takes a reeurrent eourse through the intervertebral foramen to end in the bones and periosteum of the vertebral eanal.

Ganglia Spinalia. — These ganglia are oval swellings de- veloped upon the posterior nerve-roots, just before they unite with the anterior roots to form the spinal nerve-trunks. They are found upon the posterior roots of all the nerves, except, oeeasionally, upon those of the sub-oeeipital and the eoeeygeal nerves.

The spinal ganglia are formed upon the posterior nerve- roots as they lie in the intervertebral foramina, except in the eases of the lirst two cervical and the saeral and eoeeygeal nerves. The ganglia of the Arst two cervical nerves lie upon the posterior areh of the first and the vertebral areh of the seeond cervical ^ertebrae respectively ; the ganglia of the saeral nerves are plaeed within the saeral eanal, but out- side the tube of dura mater. The ganglion on the posterior root of the eoeeygeal nerve is inside the tube of dura mater.

Spinal Nerve-Trunks. — These are formed by the union of the anterior and posterior nerve-roots immediately beyond the spinal ganglia. This union takes plaee in the ease of the eoeeygeal and saeral nerves in the saeral eanal; in the lumbar, thoraeie, and lower six cervical nerves, in the inter- vertebral foramina; and in the ease of the first two cervical nerves, on the arehes of the atlas and epistropheus.

The nerve-trunk is exceedingly short; indeed, it divides almost immediately into its anterior and posterior branehes,, In the ease of the saeral and eoeeygeal nerves, this subdivision takes plaee in the saeral eanal, and the spinal nerve-trunks of these nerves are distinetly longer than in the ease of the nerves whieh oeeupy a higher level.

The distribution of the posterior branehes has already been examined (p. 173).

Disseetion, — At this stage the disseetor may adopt one of two methods in the further treatment of the medulla spinalis and the nerves whieh spring from it. If the medulla spinalis is fresh and in sueh a eondition that it may be successfully hardened, it is best to transfer it at onee to the preservative iluid. If, on the other hand, it is soft and not fit for proper preservation, it should be removed with all its membranes and nerve-roots, and plaeed in a eork- lined tray filled with water. There is no method by whieh the araehnoid, the pia mater, the ligamenta dentieulata, and the nerve-roots ean be so well studied as this.

In removing the medulla spinalis, the spinal nerves should be divided as they lie in the intervertebral foramina, and in sueh a manner that as long a pieee as possible of eaeh nerve remains attaehed to the dura

THE DISSEGTION 0F THE BACK 193

mater and the spinal medulla. Wherever it is possible the ganglia should be taken with the nerves. The same rule applies to the saeral nerves also. The medulla spinalis and its membranes should then be eut aeross at the highest limit of the vertebral disseetion. By pulling upon the dura mater the whole spedmen may now be lifted from the vertebral eanal and trans- ferred to the water-bath. The dura mater should then be slit down the median plane, and the edges of the ineision must be tumed aside. By fixing the dura mater with pins to the eork at the bottom of the tray, the iurther disseetion ean be eondueted with great advantage.

Aiteries of the Mednlla Spinalis (O.T. Spinal Oord). — It

is only when the arterial injection is partieularly good that the spinal arteries ean be made out satisfactorily.

A large number of small arteries are supplied to the meduUa spinalis. These are the anterior and posterior spinal arteries whieh spring from the vertebral in the eranium, and a series of lateral spinal arteries whieh reaeh the side of the medulla spinalis and are derived from di^Terent sourees in eaeh region. In the neek they eome from the vertebral, aseending cervical, and deep cervical arteries; and in the thorade and lumbar regions from the posterior branehes of the intereostal and lumbar arteries. By the anastomoses of these arterial twigs, five longitudinal trunks are formed upon the surface of the medulla spinalis. One of these lies in the median plane anteriorly, and may be termed the antero- median artery. The other four are plaeed in relation to the sulei along whieh the posterior nerve-roots enter the medulla spinalis. One runs downwards anterior to the line of entranee of these roots, and the other posterior to it on eaeh side of the meduUa spinalis. These slender arterial trunks may there- fore be termed the postero-lateral longitudinal vessels,

The antero-median vessel is formed above by the union of the two anterior spinal branehes of the vertebral arteries. One of these is larger than the other, and takes a mueh greater share in the formation of the median trunk. Below the level of the fifth pair of cervical nerves the eontinuity of the median vessel depends upon the reinforcements whieh it obtains from the lateral spinal vessels. The number of lateral spinal arteries whieh join the median vessel is very variable. The majority of these arteries end on the nerve-roots ; only five to ten reaeh the median vessel. The antero-median artery runs downwards, under cover of the linea splendens of the pia mater. Its ealibre is uniform throughout, and where the medulla spinalis ends it proeeeds onwards for some distanee upon the filum terminale.

Th^ postero-lateral arteries on eaeh side of the medulla spinalis are formed in the upper part of the cervical region by the bifurcation of the eorre- sponding posterior spinal braneh of the vertebral artery. Lower down their eontinuity is maintained by twigs whieh reaeh them on the posterior roots of the spinal nerves from the lateral spinal arteries. It may be

VOL. II — 13

194

HEAD AND NECK

regarded as a rule, that where a lateral spinal artery gives a braneh to one of the postero-lateral arterial trunks, it does not furnish another to the antero-median arterial trunk. In this way diflferent lateral spinal arteries are in eonneetion with the longitudinal trunks on the anterior and posterior aspeets of the medulla spinalis. The postero-lateral vessels end at the lower extremity of the meduUa spinalis.

From the five main arterial ehannels whieh thus extend along the spinal medulla numerous anastomosing twigs ramify in the pia mater.

Yeins of the Medulla Spinalis. — These veins are small and numerous, and their disposition eannot be said to eorrespond with that of the arteries. They are very tortuous, and form a plexus with elongated meshes. Six more or less perfect longitudinal venous trunks may be notieed on the surface of the medulla spinalis in eonneetion with this plexus ; two of these are median, and are plaeed respectively on the anterior and posterior aspeets. The anterior trunk runs upwards under cover of the antero-median spinal artery. The other four are lateral, and are situated two on either side, in relation, respectively, to the anterior and posterior nerve-roots.

Upon eaeh side, the veins of the medulla spinalis effect eommunieations with the veins in the vertebral eanal by means of small twigs whieh run laterally on the nerve-roots.

How to distinguish the anterior from the posterior surface of

the medulla spinalis.

Anterior Surface.

1. Linea splendens.

2. Single anterior spinal artery in

median plane.

3. Anterior nerve - roots smaller

than posterior, and springing by fila whieh emerge from the medulla spinalis, not in a eontinuous straight line, but irregularly over an area of some width.

POSTERIOR SURFACE.

1. The postero - lateral arteries in

relation to the posterior ncrve- roots.

2. Fila of origin of posterior

nerve-roots entering themeduUa spinalis along a straight and eontinuous line, and at the bottom of a distinet suleus.

3. Posterior nerve-roots larger than

the anterior, and provided with ganglia.

Preseruation of the Mediilla Spinalis. — If the medulla spinalis is in a fit state for preservation, it should be immersed for a few weeks in methylated spirit, to whieh a small amount (4 per eent) of formalin has been added. When sufficiently firm, the disseetor should endeavour to learn something of its internal strueture by making transverse seetions aeross it at different levels, and inspeeting the eut surface elosely with the naked eye, or with the aid of a magnifying glass.

Intemal Strueture of the Medulla Spinalis. — A good deal ean be learned by a naked-eye inspeetion of eross seetions of

THE DISSECTION 0F THE BACK 195

tbe tnedulla spinalis iaa.de in diSerent r^ions and at different levels.

In sueh seetions the arUero-median fissure ond the postero- median stptum and suleus, whieh pariially divide it along the whole of its length into right and left halves, beeome obvious.

The antero-median fissure is mueh shorter than the posterO' median septum. IC dips dorsally to a eommissure of white matter, anterior while eommissure, whieh eonneels the two halyes of the medulla spinalis ; and il eontains a Told of pia mater and branehes of the anlerior spinal vessels. The postero-median suleus is a shallow furrow whieh runs along

the posterior surface of the medulla spinalis in the median plane, and the postero-median septum extends from the bottom of the suleus to a transverse grey eommissure ealled the posterior eommissure.

The two halves of ihe medulla spinaUs, thus marked oiT from eaeh other, are to all intents and purposes symmetrieal, and they are joined by a more or less broad band or eom- missure whieh intervenes between the anterior fissure and the posterior septum.

An inspeetion of the surface of eaeh lateral half of the medulla spinalis brings into view a groove or furrow at some little distanee from the postero-median suleus ; it is ealled the poslero-lateral sulms. Along the bottom of this groove

196 HEAD AND NECK

the fila of the posterior nerve-roots enter the medulla spinalis (O.T. spinal eord) in aeeurate linear order. There is no eorresponding furrow on the anterior part of eaeh lateral half of the meduUa spinalis in eonneetion with the emergenee of the fila of the anterior nerve-roots ; and it should be noted that these fila emerge over a broad area, whieh eorresponds in its width to the thiekness of the subjacent anterior eolumn of grey matter.

The medulla spinalis is eomposed of an inside eore of grey matter whieh is surrounded on all sides by an external eoating of white matter.

Grey Matter of the Medulla Spinalis. — The grey matter in the interior of the medulla spinalis has the form of a Auted eolumn. When seen in transverse seetion, it presents the shape of the letter H. In eaeh lateral half of the medulla spinalis there is a eomma-shaped mass of grey matter, the concavity of whieh is direeted laterally. The ereseents of opposite sides are eonneeted aeross the median plane by a transverse band, whieh is ealled the grey eommissure, The postero-median septum passes from the surface of the medulla spinalis to the grey eommissure. The bottom of the antero- median fissure is separated from it by an intervening strip of white matter whieh is termed the anterior white eommissure, In the grey eommissure may be seen the eentral eanal of the spinal medulla. It is just visible to the naked eye as a minute speek. This eanal tunnels the entire length of the spinal medulla, and opens above (after having traversed the lower half of the medulla oblongata) into the fourth ventricle of the brain. The portion of the grey eommissure whieh lies posterior to the eentral eanal is ealled ih^ posterior eommissure^ the portion anterior to it receives the name of anterior grey eommissure,

In eaeh ereseentie mass of grey matter eertain well-defined parts may be reeognised. The projecting portions whieh extend posterior and anterior to the eonneeting transverse grey eommissure are termed the posterior and the anterior grey eolumns, They ean be distinguished from eaeh other at a glanee.

The anterior grey eolumn is short, thiek, and very blunt at its extremity. Eurther, its extremity is separated from the surface by a tolerably thiek eoating of white matter, through whieh the fila of the anterior nerve-roots pass on their way to the

THE DISSECTION 0F THE BACK 197

surface. The thiekened end of the anterior eolumn is termed the eaput eolumna anteriorts^ and the eonstrieted part elose to the grey eommissure is ealled the ceroix eolumna anterioHs. The posterior grey eolumn in most loealities is elongated and narrow. Further, it is drawn out to a fine point, whieh almost reaehes the bottom of the postero-lateral suleus. This pointed extremity receives the name of the apex eolumme posterioris] the slightly swollen part whieh sueeeeds it is the eaput eolumnae posterioris ; whilst the slightly eonstrieted part adjoining the grey eommissure goes under the name of the cervix eolumnee posterioris,

Covering the tip of the posterior eolumn there is a substanee whieh differs in its eomposition from the general mass of grey matter, and presents a translueent appearanee. It is termed the substantia gelatinosa {Rolandt).

The grey matter is not present in equal quantity through- out the entire length of the meduUa spinalis. Therefore it is neeessary that it should be eonsidered in different regions, and it must be understood, when the terms cervical, lumbar, saeral, ete., are applied to different portions of the spinal medulla, that these terms apply to the regions to whieh the nerves of the same name are attaehed.

Wherever there is an inerease in the size of the nerves attaehed to a partieular part of the medulla spinalis, there a eorresponding inerease of the grey matter may be notieed. It follows from this that the distriets in whieh the grey matter bulks most largely are the lumbar and cervical swellings. The great nerves whieh go to form the limb plexuses enter and pass out from those portions of the medulla spinalis. In the intermediate thoraeie region there is a reduetion in the quantity of grey matter, in eorrespondenee with the smaller size of the thoraeie nerves.

The shape of the ereseentie masses of grey matter is not the same in all regions. In the thoraeie region both eolumns are narrow, although the distinetion between the anterior grey eolumn and the more attenuated posterior grey eolumn is still sufficiently manifest. In the cervical region the eontrast between the grey eolumns is most marked ; the anterior grey eolumn is very thiek in eomparison with the posterior grey eolumn. In the lumbar region, on the other hand, the difference in the thiekness of the two grey eolumns is not nearly so apparent, owing to a broadening out of the 11—13 h

HEAD AND NECK

Fk;. 8o.— TranEverse seelions Ihiough Ihe Medulli Spinalis in different regions. A. Cervical Region B. Mid-lhoraeie Region; C. Lower Thoraeii Region ; D. Lumbat Region,

posterior grey eolumn. A see- tion taken rrom the eentre o£ eaeh region ean very readily be reeog- nised by the featuies men- tioned.

In the thoTaeie region of th e spinal medulla, more espeeially in the upper part, there is another ehar- aeter whieh is very distinctive. A pointed an d promi- nent triangular projection juts out from the lateral aspeet of the eres- eentie mass of grey matter nearly opposite the grey eommissure. This is ealled the laieral grey eolunm (Eig. 80, B and C). It disappears in the cervical and lumbar swelhngs, but again heeomes evident both in the upper cervical and in the lower saeral regions, Below the

thoraeie region the postero-med- ian septum dimin- ishes and the antero-median iissure inereases in depth, until,

THE DISSEGTION 0F THE BACK 199

m the saerat region they are almost equal in depth and the eentral eanal oi.cupies the eentre of the medulla spmalis

White Matter of the Mednlla Spliudu — The white matter rorms a thiek eoat ng on the outside of the Huttd eolumn of grey matter It is marked oS mto three funicuh The postertor funiciilus is wedge shaped in transverse seet on and hes between the postero median st.ptun and the postenor grey eolumn The laieral /unieuius oeeupies Ihe concavity of the grey ereseent Postenorly it ts bounded by ihe posterior gre} eolumn and the postero lateral suleus v^hilst anteriorly tt e\tends as far as the most laieral fila of the anterior nerve roots The antmor /unieulus ineludes the white matter

FiO. 81, — Tran5verse seelioii through Ihe upper cervical part of Ihe MeduUa Spinalis of a (ull-time l'uitus, irealed by the Pal-Weigerl proeess.

betweeti the antero-median Assure and the anterior eolumn of grey matter, and also the white matter whieh separates the thiek extremity of the anterior grey eolumn from the surface of the spinal medulla and is traversed by the emerging fi]a of Ihe anterior nerve-roots.

In the cervical region a faint longitudinal groove nins downwards on the surface of the posterior funiculus of ihe medulla spinalis. This indieates the position of a septum whieh passes into the funiculus from the deep surface of the pia mater and divides it ineompletely into two unequal strands. The groove is termed the intermediale posterior suleus. The strand on its medial side is the /aseimlus gradlis (Goll's), whilst the lateral and larger strand receives the name of the /aseieulus euneatus (Burdaeh's).

II— 13c

200 HEAD AND NECK

The white matter of the medulla spinalis inereases steadily in quantity from below upwards.

The fasciculi graeilis and euneatus, whieh form the posterior funiculus of the medulla spinaiis, are eomposed of iibres whieh enter the spinal medulla as the fila of the posterior nerve-roots. In the lower portion of the medulla spinalis the two fasciculi are not marked off from eaeh other.

In the lateral and anterior funiculi of the adult spinal medulla it is not possible with the naked eye to distinguish the different strands of fibres of whieh they eonsist, but the student should remember that sueh strands or traets are present. The three l)est-defined traets in the antero-lateral part of the spinal medulla are, (i)the fasciculus eerebello-spinalis (O.T. direet eerebellar traet) ; (2) the fasciculus eerebro-spinalis lateralis (O.T. erossed pyramidal traet) ; (3) the fasciculus eerebro-spinalis anterior (O.T. direet pyramidal traet).

The fasciculus eerebello-spinalis aseends to the eerebellum, but, traoed in the opposite direetion, it is found to disappear in the lower thoraeio region of the medulla spinalis. The /aseieulus eerebro-spinalis lateralis oeeupies a larger distriet of the medulla spinalis. It is plaeed in the lateral iunieulus anterior to the posterior eolumn of grey matter and immediately medial to the fasciculus eerebello-spinalis. As the fasciculuscerebello-spinalis disappears in the lower part of the medulla spinalis the fasciculus eerebro-spinalis lateralis eomes to the surface, and it ean be traeed as low as the fourth saeral nerve. T\it fasciculus eerebro-spinalis anlerior {orms the narrow strip of the anterior funiculus, whieh lies immediately adjacent to the antero-median fissure. It reaehes down to about the middle of the thoraeie r^on of the meduUa spinalis and then disappears.

After the body has been five days on its face it will be replaeed upon its baek with the thorax and pelvis supported by bloeks, and the disseetors of the head and neek should at onee proeeed to elean the temporal fascia, and afterwards to remove the brain and study the interior of the eranium.

Disseetion. — Take away the anterior and superior aurieular museles and remove the thin layer of fascia subjacent to them whieh deseends from the lower border of the galea aponeurotiea to the zygomatic areh. When this has been done the strong temporal fascia will be exposed. Note that it is attaehed above to the temporal ridge and below to the upper border of the zygomatic areh. The details of its eonneetions will be studied at a later period.

REMOYAL 0F THE BRAIN.

After the superficial attaehments of the temporal fascia have been noted the disseetors of the head and neek should proeeed to remove the brain.

Disseetion. — The head being supported upon a bloek, extend the median ineision, already made in the galea aponeurotiea, to the nasion anteriorly and

REMOVAL 0F THE BRAIN loi

to the extenial ocd[MtaI protuberanee posteriorly, and eul through the loose areoiar tissue and the perieranium in the same line down to Ihe bone. With the handle of the sealpel, or with a ehisel, detaeh the perieianium from Ae bone on eaeh side and turn it posteriorly and downwards to the temporal ridges, leaving the bone perreetly bare. Nolelhatalthough ihe perieranium is loosely altaehed over Ihe surface of the various bones of the vault, it is finnly attaehed along the lines of ihe erania! sutures by proeesses thal dip in belween the bones and separate theit edges. Delaeh the galea aponeutotiea and the lemporal fascia from the lemporal lidge on eaeh side withthe edge of theknife; then eairyingtheedgeot the knifeanleriorly and posteriorly between ihe temporal musele and the bone delaeh the upper partof themusclefrom theskull. When this has been done, eaeh halfof the seah' ean be tuined down over the ear.

The disseetors should next obtain a saw, a ehisel, and a mallet, and

proeeed to remove the eaUaria. The line along whieh the saw ia to be used may be marked out on the skull by eneirding it wilh a pieee of string, and then marking the eranium with a peneil along the line of the strbg. Anterioily, the eut should be made fully three-quatters of an ineh above the marginsoftheorbits ; postetiotly, it should be earried tound at lhelevel of a point midway between the lambda' and the extemal oeeipital proluberanee. The saw shouid be used to divi(ie the outer table of the skull only. When the diploe is teaehed, the sawdust will beeonie red and moist, and the saw shouid then be abandoned, The hammerand ehisel ate now btought into

iequisition, and by shoit shaip readily be split along the line in i divided. When this has been <Io cio5s-bar of the ehisel into the lissu Dnia Mater Eneephali.— distinet membranes, whieh ;

ilh these the 'hieh the outer table of the eranium is le, insinuale the hook at the end of the e in fionl, and wteneh off the skull-eap.

-The brain is elothed by three re termed the meninges. These

ieapex

inital bone, or Ihe point

202 HEAD AND NECK

are from without inwards — (i) the dura mater; (2) the araehnoid ; and (3) the pia mater.

When the skull-eap is detaehed, the outer surface of the dura mater, as it covers the upper surface of the eerebral hemispheres, is exposed It is rough, and dotted over with bleeding points. If a portion is plaeed in water, its roughness beeomes still more manifest, and is seen to be due to a multi- tude of fine fibrous and vascular proeesses by whieh it is eonneeted with the deep surface of the bones. These have neeessarily been torn asunder in the removal of the skuU- eap. The bleeding points are most numerous along the median line, or, in other words, along the line of the superior sagittal sinus (O.T. longitudinal) ; and if the handle of the knife is run from before baekwards, so as to make pressure along this line, a eonsiderable quantity of blood will ooze out. This shows that a number of small veins from the eranial bones have been ruptured. The degree of adhesion between the dura mater and the inner surface of the eranial bones varies in different subjects and in different loealities. In all eases it is strongly adherent along the lines of the sutures, like the perieranium externally; and, further, it is mueh more firmly attaehed to the base than to the vault of the eranium. In the ehild — indeed, as long as the bones of the eranium are grow- ing — it is more adherent than in the adult ; and it is more firmly bound to the bone again in old age.

The disseetors should now elean the outer surface of the dura mater with a sponge. They will then reeognise the middle meningeal artery upon eaeh side, aseending in the substanee of the membrane, and sending off its branehes in a widely arboreseent manner. It stands out in bold relief from the membrane. If the skull-eap is examined, its inner surface will be observed to be deeply grooved by the branehes of the artery and the veins whieh aeeompany and lie external to them (Wood Jones). The meningeal arteries are not intended for the supply of the membrane alone, as the name might lead one to imagine. They are also the nutrient vessels of the inner table and diploe of the eranial bones.

Granulationes Araehnoideales (O.T. Paeehionian Bodies). — These granulations are almost invariably present, and, as a rule, are best marked in old subjects. They are small granular bodies, ranged in elusters on either side of the superior sagittal (O.T. longitudinal) sinus, into whieh many of them

REMOYAL 0F THE BRAIN

»03

protnide (Fig. 83), As a general rule, they are most evident towards the postenor part of the par etal reg on At first s ght they appear to be protrus ons from the dura mater but this is not the ease They spnng from the araehnoid and the sub. araebnoid t ssue, and are enlai^ements of ihe normal v Ih of the membrane (F g 84)

Two Layerg of the Dnr» Mater — Hav ng noted these prel m nary deta Is from an exam na on of he outer surface of the dura n ater the student s n a pos t on to understand that th s membrane does not belong ent relj lo the broin. It performs a double functon (i) t aets as an intemal penosteum to the bones forming the eran al cavity and (a)

FlG. B3.— Median seetion IhrouE'i t the Superior Sagillai Blood Si s«n prolruding into the sinus.

(E.I:

rontal Bone and eorresponding part of The araehuoideal granulationa are :d.)

it gives support to the dilTerent parts of the brain. Gonse- quently, it eonsists of two strata, whieh, in most loealities, are firmly adherent, but they ean usually be easily demonstrated in the disseeting-room, These strata may very appropriately be termed the endoeranial and the supporttng layers. Along eertain lines these two layers sepatate from eaeh other. In some eases they separate so as to form blood ehannels, termed sinus dura matris, for the conveyance of venous blood; in other eases they separate in order that the inner supporting layer may form strong folds or partitions, whieh pass in between eertain parts of the brain ; and by these partitions the eranial cavity is divided tnto eompartments eommunieating freely with one another, and eaeh holding a defioite sub- division of the brain (Fig. 87).

Disstetiim. — These points mlist now be ¥erified. Begin I"

204

head fbrwards. Support the dura miter m an ant guperior saeiltal slnus, aod along

HEAD AND NECK

this position, and make

; two ineisions Ihiough iireeiion— one on eaeh side of the ; whole iength. From the mid- it of eaeli of these ineisions another eut must be made Ihrough eaeh lateral portion of the dura mater downwards to the eut mai^in of (he skull immediately above Ihe eat (rig. 85). The dura maler covering the upper aapeet of the brain is thus divided inlo a eentral strip eontaining the superior sagittal sinus, and four triangular flaps. The llaps should now be tuined downwaids Dvet the eut matgin of the skull, and in this position Ihey preserve the brain, during its removal, fiom laeeration by the sharp bony edge.

CaTiim Subdnrale. — The subdural spaee is the term applied

to the interval between the dura mater and the araehnoid — Figs. 83 and 84. It eontains a very small quantity of serous fluid, whieh moistens the opposed surfaces of the membranes. A striking eontrast between the two suriaees of the dura mater ivill be noted. The external surface is rough and Aoeeulent ; the internal surface is smooth and glistening.

Veiue Oetebri. — The eerebral veins whieh return the blood from the surface of the eerebral hemispheres will be seen shining through the araehnoid. They are lodged for the most part in the sulei between the gyri, and run upwards to the median plane. When they reaeh the superior sagittal sinus they turn anteriorly, and lie against the wall of the sinus, for some distanee, before they open into it.

REMOVAL 0F THE BRAIN

ao5

Sinns Sagittalis Snperioi (O.T. Superior Longitndisal). — Open into this venous ehannel by ninning the knife through its upper wall froni behind forwatds (Pigs. 85 and 86). It begins anteriorly at the erista galli of the ethmoid bone, where it not iiifrequently eommunieates with the veins in the nasal cavity through the foramen cjecum. It extends

posteriorly, grooying the eranial vault in the median plane, to the internal oeeipital protuberanee, on the right aspeet of whieh it beeomes eontinuous with the right transvetse sinus (O.T. lateral). Its lumen, whieh is triangular in eross-seetion, is very small anteriorly, but expands greatly posteriorly. On either side of the sinus, and opening into it, are a number of clefts between the two layers of the dura raater ; thi

2o6

HEAD AND NECK

the lateral laeuna. The inferior angle of the ehannel is erossed by a number of minute bands, named elwrda WilUsii; and araehnoideal granulations bulge into it. The mouths of the superior eerebral veins open into the sinuSj or into the lateral laeunse, pouring their blood into the sinus in a diree- tion eontrary to that in whieh the blood flows within tbe

VII. FacU1 Titrv

ehannel — that is, the terminal portions of the veins are direeted anteriorly, whilst the blood in the sinus flows posteriorly.

Th« Belation o[ the ArBelmDideal GiauulationB to the Snpeilor SoKittal Sinus and tha Lateral Laenn». — When the granulations push themselves inlo the sinus or the lateial laeuna: they push before (hetn a thin eontinuous covering of the floot Df the spaee, and when they project still further and eneroaeh upon the bones of Ihe skuU they a.re coveied also liy B thin expansion of the roof of the spaee.

Falx Gerebri (Figs. 86, 87). — This is a siekle-shaped redupli- eation of the inner layer of the dura mater, whieh deseends in the median plane, between the two eerebral hemispheres.

REMOYAL 0F THE BRAIN 207

In order to expose it, the eerebral veins must be divided as they open into the superior sagittal sinus, and ihe hemisphere gently pulled lateraily. Anteriorly, the falx eerebri is narrow, and attaehed to the erista galli of the ethmoid bone. Ii inereases in breadth as it passes baeltHards, and posteriorly it is attaehed in the median plane to the upper surface of ihe tentorium eerebelli. The anterior part of the falx is frequently cribriform, and is sometimes perforated by aperlures to sueh an extent that it almost resembles laee-work. Along

FlC. 87. — Fronial seetion Ihrougli ihe Craniiil Civity in a plane whieh passes through the posterioi' part of Ihe foranien magnum. The poslerior parl of Ihe eranial cavity, from whieh the brain has been removed, is depieted.

eaeh border its two layers separate to enelose a blood-sinus. Along its upper convex margin runs the superior sagittal sinus ; along its concave free border eourses the mueh smaller in/erior sagittal sinus ; whilst along its attaehment to the tentorium is enelosed the straight sinus. Its inferior concave margin overhangs the eorpus eallosum, with whieh, however, it is not in eontaet, eseept to a very slight extent, posterlorly.

KBmoTal ot the Brain,— The disseetors should now proeeed lo remove the brain. IIaving divided Ihe attaehment of the falx eerebri lo Ihe erista galli, puU it posleriorly. Next, removing the bloek upon whieh the head rests, and siipporting. the oeeiput and poslerior lobes of the bruti with the left hand, let the head drop well downwards. In all probaWlit' the frontal lobes will fall away by thelr own weight from the anter^'

2o8 HEAD AND NECK

of the base of the eranium, and perhaps earry with them the olfactory bulbs. Should they remain in position, however, gently raise them with the fingers, and at the same time separate the olfactory bulbs from the cribriform plate of the ethmoid with the handle of the knife. As the olfactory bulbs are raised the minute olfactory nerues whieh spring from them and perforate the cribriform plate of the ethmoid bone are torn aeross. The large round and white optie nerues (seeond pair of eerebral nerves) now eome into view, as they leave the eranial cavity through the optie foramina. When these are divided, the intemal earotid arteries will be exposed, and more posteriorly, in the median plane, the infundibulum will be seen ; it is a hollow eonieal proeess whieh extends from the tuber einereum at the base of the brain to the hypophysis (O.T. pituitary body), whieh lies in the fossa hypophyseos (O.T. pituitary fossa). Divide the earotid arteries and the infundibulum. Posterior to the infundibulum is the upper border of the dorsum sellae, terminating on eaeh side in the rounded posterior elinoid proeess. Passing anteriorly on eaeh side of the dorsum sellse is the eorresponding third eerebral nerve, whieh must not be touehed at present. A little more laterally, and on a slightly lower plane, is the medial or free border of the tentorium eerebelli, a fold of the inner layer of the dura mater whieh lies above the eerebellum and forms the roof of the posterior fossa of the eranium.

Carefully displaee the temporal pole of the brain from under cover of the posterior border of the small wing of the sphenoid, whieh lies to the lateral side of the optie nerve and the eut end of the internal earotid artery ; then raise the temporal lobe from the floor of the middle fossa, and from the upper surface of the tentorium eerebelli. Pass the knife posterior to the dorsum sellae, immediately above the level of the third eerebral nerve, and eut through the midbrain, as it aseends from the posterior fossa, from its lateral surface inwards to the median plane. Repeat the operation in the same way on the opposite side, and remove the eerebrum and upper part of the midbrain from the eranium.^

Plaee the removed eerebrum in the vault of the eranium and lay it aside. Then note the relative positions of the parts exposed. Anteriorly lies the floor of the anterior fossa of the eranium ; behind it, on a more depressed plane, the middle fossa, and still more posteriorly the sloping tentorium eerebelli.

In the median plane anteriorly is the projecting erista galli, partially dividing the anterior fossa into lateral halves. On either side of the erista galli is the depression from whieh the olfactory bulb was dislodged, and still more laterally are the portions of the floor of the anterior fossa whieh form the roofs of the orbits ; they bulge upwards as well-marked convexities. Eaeh lateral part of the floor of the anterior fossa terminates posteriorly in a sharp margin, formed by the posterior border of the small wing of the sphenoid. This margin overhangs the anterior part of the middle fossa. It is covered with a thiekening of dura mater in whieh runs the spheno- parietal blood sinus, and it terminates medially in a projecting proeess, the anterior dinoid proeess. On the medial side of eaeh anterior elinoid proeess lie the eorresponding optie nerve and internal earotid artery, and springing from the upper surface of the artery is its ophthalmie braneh, whieh runs anteriorly under cover of the optie nerve. Posterior to the divided ends of the internal earotid arteries, and in the median plane, is the infundibulum deseending into the hypophyseal fossa, and more posteriorly, on either side, are the projecting posterior elinoid proeesses. The area between the four elinoid proeesses is covered by a fold of the inner layer

* For alternative method see p. 217.

REMOYAL 0F THE BRAIN

109

(J tbe dara niatet, lenned the dia^hragma sMr. In ils epntte is nn apeitaie Ibioogh whteh the ioiiindibuluni pusses lo join Ihe hypophysis (O.T. pitoilaiy bod;) ; and it binds down Ihe h) ;»ph]-sis in ihe Tossa. In ils antoioe and posterior margins, respeclively, are loilged the sinus inter- -- lior and Ihe anus inlereayetnosus posterior (O.T. eiieuliu

FlG. 88.— Interior of the Cranium afler the rcmova1 of the eerebtum. The iransYerse, stratght, and superior petrosal sinuses have been openedn and ihe dura maler has been removed from Ihe tloor of the middle tossa,

In the dura mater, on eaeh side of the hypophyseal (pituitary) fossa, lies the eorresponding cavernous sinus, whieh will be disseeted later, and slill more kierally are the de- pressed lateral portions of the middle eranial fossa, lined with dura mater, in whieh the trunk and sonn<" "*■ the branehes of

VOL, n — 14

2IO HEAD AND NECK

the middle meningeal artery are visible. Posterior to the middle fossaliesthe tentorium eerebelli coveringthecerebellum. The peripheral margin of the tentorium is attaehed, on eaeh side, to the posterior elinoid proeess, the upper margin of the petrous part of the temporal bone, the posterior inferior angle of the parietal bone, and to the transverse ridge on the inner surface of the oeeipital bone. The eentral or free margin erosses the attaehed margin behind the posterior elinoid proeess on eaeh side, and is attaehed anteriorly to the apex of the anterior elinoid proeess. It bounds an oval opening, the door of the tent, through whieh pass the midbrain sur- rounded by the araehnoid and the pia mater, and the posterior eerebral arteries. Piereing the midbrain nearer its posterior than its anterior border is the aqu8eductus eerebri (O.T. aqueduct of Sylvius). Posterior to the aqueduct is the lamina quadrigemina of the midbrain and anterior to it the pedun- euli (O.T. erura) eerebri. Eaeh pedunele eonsists of an anterior part, the basis peduneuli (O.T. crusta\ and a posterior part, the tegmentum^ the two being separated by a lamina of dark eoloured tissue, the subsiantia nigra, The bases pedun- euli are entirely free from eaeh other, but the tegmental portions are united together anterior to the aqueduct.

Running anteriorly and laterally from the medial side of eaeh pedunele to the angle between the anterior ends of the free and the attaehed borders of the tentorium, is the third eerebral nerve. Glose to the midbrain the ner\'e passes between the posterior eerebral artery above and the superior eerebellar artery below; and between the free and attaehed borders of the tentorium it pierees the dura mater, in the middle fossa, and enters the wall of the cavernous sinus. Between the posterior ends of the third nerves lies the upper end of the basilar artery, dividing into the two posterior eerebral branehes; and the disseetors should note that the arteries lie in an enlargement of the subaraehnoid spaee whieh is known as the dsterna interpeduneularis. In the median plane posterior to the midbrain is the divided vena eerebri magna (O.T. great vein of Galen). It passes posteriorly and upwards, and pierees the apex of the tentorium to enter the straight sinus, whieh lies in the angle of union between the falx eerebri and the tentorium eerebelli.

Curving posteriorly around the midbrain and ending posteriorly in the great eerebral vein on eaeh side is the vena

REMOYAL OF THE BRAIN 211

basalis^ and immediately above it, running anteriorly, is the slender fourth eerebral nerve. If the free border of the tentorium is turned laterally, at the point where it is erossing the attaehed border, the fourth nerve will be seen perforating the inner layer of the dura mater to enter the wall of the cavernous sinus.

When the disseetors have verified the facts noted above, they should examine the lower free border of the falx eerebri, in whieh they will find the small inferior sagittal sinus, whieh terminates posteriorly, at the apex of the tentorium, in the straight sinus. The straight sinus must now be opened by earrying the knife posteriorly through the falx eerebri along its line of union with the tentorium. Then the falx eerebri must be eut away from the oeeipital bone, and as this is done the posterior part of the superior sagittal sinus will be opened up. After the falx has been removed the right and Ieft transverse and the right and left superior petrosal sinuses must be opened by ineisions earried along the attaehed border of the tentorium (Fig. 88). The disseetors will probably find that the superior sagittal sinus turns to the right and beeomes eontinuous with the right transverse sinus, whilst the posterior end of the straight sinus turns to the left and joins the left transverse sinus. In a eertain number of eases this arrange- ment is reversed, and not uneommonly, as in the speeimen shown in Fig. 88, there is a eommunieation between the right and left transverse sinuses aeross ihe front of the internal oeeipital protuberanee. Oeeasionally the superior sagittal, the two transverse sinuses, the straight sinus, and the oeei- pital sinus unite anterior to the internal oeeipital protuber- anee in a eommon dilatation, the confluens sinuum (O.T. toreular Herophili). The transverse sinus, on eaeh side, runs from the internal oeeipital protuberanee to the lateral end of the superior border of the petrous part of the temporal bone, where it dips downwards into the posterior fossa, and at the same point it is joined by the superior petrosal sinus, whieh runs postero-laterally along the superior border of the petrous part of the temporal bone from the cavernous sinus to the transverse sinus, eonneeting the two together.

Disseetion. — With the point of the sealpel open the spheno-parietal sinus, whieh runs along the posterior border of the small wing of the sphenoid, and traee it medially to the cavernous sinus, but do not open the latter. Then remove the dura mater ii^^^ ^^^» ^"«^eral part of the middle fossa on one side to expose the semilur 'an) ganglion of the

II — 14 a

212 HEAD AND NECK

fifth nerve, the middle meningeal artery and its two terminal branehes, the aeeessory meningeal artery, if it is present, and the great superficial petrosal nerve. Gommenee immediately to the lateral side of the anterior part of the free border of the tentorium, where a eut through the inner layer of the dura will open into a spaee (O.T. Meekel's cave) between the two layers of the dura, in whieh lies the semilunar ganglion. From the postero-medial border of the ganglion \ht posierior braneh or sensory root passes baekwards into the posterior lossa to enter the pons ; and from its anterior-lateral border the ophthalmie braneh passes upwards and anteriorly in the lateral wall of the cavernous sinus, the maxillary braruh runs anteriorly to the foramen rotundum, and the mandibular braneh passes downwards into the foramen ovale. By theside of the mandibular nerve the aeeessory meningealartery may befound entering the eranium ; and a little further posteriorlythe middle men- ingeal artery will be seen passing into the middle fossa through the foramen spinosum. After entering the eranium the middle meningeal artery runs anteriorly and laterally, aeross the floor of the middle fossa, towards the lateral wall and divides into an anterior and a posterior braneh ; the former aseends on the anterior part of the lateral wall to the anterior inferior angle of the parietal bone, and the latter runs posteriorly and laterally, and then aseends on the inner surface of the squamous part of the temporal bone. The g}'eai superjicial petrosal nerue appears on the anterior surface of the petrous part of the temporal bone through the hiaius nerui /aeialis^ whieh lies to the medial side of the eminentia areuaia. It runs anteriorly and medially and disappears beneath the semilunar ganglion.

After the struetures mentioned above have been found and eleaned, the disseetors must remove the tentorium eere- belli. Cut through the free border immediately posterior to the point where it erosses the attaehed border; the fourth nerve also will be divided by this ineision. Repeat the ineision on the opposite side, and then eut through the membrane elose to its attaehed border, but to the medial sides of the superior petrosal and transverse sinuses ; next divide the ven8e basales at their points of junction with the vena eerebri magna (O.T. vein of Galen); then raise the anterior part of the tentorium and, passing the knife beneath it, separate it from the falx eerebelli, whieh is attaehed to its lower surface in the median plane. The tentorium may now be Hfted out and the araehnoid covering the upper surface of the eerebellum will be exposed.

After the upper surface of the eerebellum has been eleaned, eut through the third eerebral nerves, and then press baek- wards the peduneuH eerebri and the pons (Yarolii), whieh lies immediately below them, to expose the fifth and the sixth nerves. Cut the fifth nerves as they eross the upper borders of the petrous parts of the temporal bones, and then divide the small sixth nerves, whieh lie more medially and at a shghtly deeper level. Press the pons and eerebellum still

REMOYAL 0F THE BRAIN 213

further baele and divide the seventh and eighth nerves as they enter the internal aeustie meatus. Below the eighth neives lie the ninth, tenth, and eleventh nerves. These also

must be eut ; and the roots of the twelfth nerves, whieh lie deeper and more medially, must be identified and divided. The pons ean then be displaeed still furthe' ' -ly and

the front of the meduUa oblongata wil' into

11—14 h

ai4

HEAD AND NECK

view. Pass the knife downwards, anterior to the meduUa oblongata, into the vertebral eanal, and, eutting firmly baek- wards and laterally, on eaeh side, divide the medulla spinalis and the vertebral arteries. Withdraw the knife, pass two fingers downwards anterior to the medulla oblongata and lift it and the pons and the eerebellum out of the posterior fossa. Plaee these iower parts of the brain, whieh collectively eonstitute the hind brain, with the bemispheres previously

1 ihrougb Ihe Head a little lo ibe tight or ihe Median hows Ihe posterior erania.1 lossa and the upper part or tbe lal afier the removaI o( Ihe brain ajid the medulla spinalis.

removed, and tben examine the eut ends of the eerebral nerves and the blood sinuses whieh lie in the region of the posterior fossa.

In the upper end of the vertebral eanal iies the upper extremity of the severed meduila spinalis, attaehed on either side to the margin of the foramen magnum by the uppermost dentation of the ligamentum dentieulatum. Anterior to the ligamentum dentieulatum, on eaeh side, is the verlebral artery, and still more anteriorly, on a slightly deeper plane, the fi!a of ibe anterior root of the first cervical

REMOYAL 0F THE BRAIN 215

nerve may be distinguished. At a higher level on eaeh side the two rootlets of the hypoglossal nerve pieree the dura, as they pass into the hypoglossal eanal (O.T. anterior eondyloid foramen). The spinal root of the aeeessory nerve passes through the foramen magnum into the eranium, posterior to the ligamentum dentieulatum, and, turning laterally over the margin of the foramen magnum, it joins the eerebral fibres of the aeeessory and the tenth nerve, with whieh it passes through an aperture in the dura opposite the jugular foramen. Immediately above the eleventh and tenth nerves the smaller trunk of the ninth nerve pierees the dura. Above the ninth nerve the eighth nerve and the motor and sensory roots of the seventh nerve pass into the internal aeustie meatus, aeeompanied by the small auditory braneh of the basilar artery and the auditory vein. The two roots of the seventh nerve lie in a groove on the upper and anterior aspeet of the eighth, the small sensory root (O.T. pars intermedia) being situated between the motor root and the eighth nerve. The small motor and the large sensory root of the fifth nerve pass through an opening in the dura whieh lies above and medial to the internal aeustie meatus ; and the sixth nerve pierees the dura mater below and to the medial side of the opening for the fifth nerve, opposite the side of the base of the dorsum sellae. The small fourth nerve pierees the under surface of the free border of the tentorium at the point where it is erossing the attaehed border.

After the disseetors have familiarised themselves with the positions of the eerebral nerves as they pieree the dura mater, they should examine the falx eerebelli and eomplete the display of the eranial blood sinuses.

The Falx Oerebelli is a small sagittal fold of the inner layer of the dura mater whieh projects anteriorly, between the lateral lobes of the eerebellum, from the internal oeeipital erest (Figs. 87, 89).

Sinus Transversus (O.T. Lateral). — The horizontal part of the transverse sinus has already been traeed from the internal oeeipital protuberanee to the superior border of the petrous part of the temporal bone, where it turns downwards to the jugular foramen. At first the deseending portion runs downwards, on the inner surface of the mastoid part of the temporal bone, and then anteriorly and again downwards aeross the upper and anterior surfaces of the juc

II — 14 c

2i6 HEAD AND NECK

of the oeeipital bone. On aeeount of the sinuosity of its eourse this part is ealled the sigmoid portion of the transverse sinus, Open this part of the sinus and find the mouth of the mastoid emissary vein in its posterior border about half-way down.

The disseetors should now obtain the basal part of a maeerated skuU and should note the relation of the transverse sinus to the outer surface. They will find that the position of the sinus ean be indieated on the external surface, by a line whieh eommenees at the external oeeipital protuberanee, passes forwards, with a slight upward convexity, along the superior nuehal line to the upper part of the mastoid part of the temporal bone and then deseends to the level of the lower margin of the external meatus.

Sinus Oeeipitalis. — The oeeipital sinus is not uneommonly absent. When it is present it eommenees in the right or left transverse sinus or the eonAuens sinuum, and deseends for a short distanee in the posterior border of the falx eerebelli. It terminates below in two lateral branehes, whieh leave the falx eerebelli and run along the borders of the foramen magnum between the layers of the dura mater, to terminate anteriorly in the lower ends of the transverse sinuses.

Sinus Petrosus Inferior. — The inferior petrosal sinus lies along the posterior angle of the petrous part of the temporal bone extending from a point lateral to the opening for the sixth nerve to the medial side of the opening in the dura for the ninth nerve of the same side. Lay the sinus open. It opens anteriorly into the cavernous sinus, from whieh it receives blood, and it passes posteriorly through the jugular foramen to join the upper end of the internal jugular vein.

Plexus Basilaris, — The two inferior petrosal sinuses are eonneeted together aeross the upper surface of the basilar part of the oeeipital bone by a plexus of small venous ehannels, to whieh the term basilar plexus is applied. Unless these ehannels happen to be distended with blood the disseetors will probably be unable to display this plexus.

The disseetors should note that the dura mater is mueh more firmly attaehed to the bones of the base than it was to the bones of the vertex, a fact whieh should have attraeted their attention as they removed the membrane from the floor of the middle fossa. They should note also that it gives sheaths to the nerves whieh pieree it, and that at the margins

REMOYAL 0F THE BRAIN 217

of the yarious foramina its outer layer beeomes eontinuous with the periosteum on the outer surface of the eranium, whilst at the margin of the foramen magnum the inner layer beeomes eontinuous with the single layer of dura mater whieh surrounds the medulla spinalis ; and that at the same level the araehnoid and pia mater of the brain beeome eontinuous with the araehnoid and pia mater of the spinal meduUa (O.T. spinal eord). Before terminating the survey of the interior of the eranium the disseetors should revise their knowledge of the blood vessels, and their relations to the dura mater ; and they should remove the hypophysis (O.T. pituitary body) and in- vestigate its naked-eye strueture.

Siniis Darse Matris. — Four blood sinuses lie iti the median plane\ (i) the superior sagittal sinus in the upper or attaehed border of the falx eerebri ; (2) the inferior sagittal sinus in the free part of the lower border of the falx eerebri ; (3) the straight sinus along the line of attaehment of the falx eerebri with the tentorium eerebelli; (4) the oeeipital sinus in the upper part of the attaehed border of the falx eerebelli.

Two sinuses lie in a Mgher horizontal plane : these are the spheno-parietal sinuses, whieh run along the posterior borders of the small wings of the sphenoid bone.

Six sinuses lie in a lower horizontal plane\ (i) the two cavernous sinuses at the sides of the body of the sphenoid ; (2) the two superior petrosal sinuses along the upper angles of the petrous parts of the temporal bones, in the anterior parts of the attaehed border of the tentorium eerebelli ; (3) the horizontal parts of the transverse sinuses in the posterior parts of the attaehed border of the tentorium. The terminal parts of the transverse sinuses deseend along the anterior parts of the lateral walls of the posterior fossa.

Two sinuses run obliquely dowmuards, posteriorly^ and later- ally : these are the two inferior petrosal sinuses.

Three sinuses run transversely eonneeting paired sinuses of opposite sides : (i) the anterior intercavernous sinus in the anterior border of the diaphragma sellae ; (2) the posterior intercavernous sinus in the posterior border of the diaphragma sellae; and (3) the basilar plexus whieh eonneets together the inferior petrosal sinuses aeross the upper surface of the basilar part of the oeeipital bone.

Alternatiye Method of Remoying the Brain. — Ifit j«-^^ ^* desirable to remove the brain entire by the more rapid but le*'

2i8 HEAD AND NECK

method usually adopted in the post-mortem room, then the following steps should be taken after the falx eerebri has been detaehed from the erista galli and the dura mater lining the vault of the eranium has been thrown aside (see p. 204).

Remove the bloek upon whieh the head has been resting, and, support- ing the oeeiput and the posterior part of the brain with the left hand, let the head drop well downwards and in all probability the weight of the frontal lobes will draw them away from the floor of the anterior fossa of the skuU, and possibly the olfactory lobes may be earried with them. If the olfactory bulbs remain in position on the cribriform plates of the ethmoid at the sides of the erista galli, gently raise them with the handle of the sealpel and press them baekwards on to the under surfaces of the frontal lobes. As the olfactory bulbs are raised the ol/adory nerue fila- ments whieh pass from their lower surfaces through the cribriform plates are torn. As the frontal lobes are pressed baekwards the large round and white optie nerues eome into view as they are leaving the eranial cavity through the optie foramina. When these are divided the intemal earotid arteries will be exposed, and more posteriorly in the median plane lies the in/undibulum^ a hoUow eonieal proeess whieh eonneets the hypophysis eerebri (O.T. pituitary body) with the tuber einereum at the base of the brain, and more laterally are the oeulo-motor nerues. Sever eaeh of these struetures in turn. On the lateral side of eaeh third nerve lies the medial or free border of the tentorium eerebelli passing anteriorly to be attaehed to the anterior elinoid proeess. Turn this margin aside with the point of the knife, and the minute troehlear nerve (fourth eerebral nerve) will be brought into view. It lies under shelter of the free border of the tentorium, and should be divided at this stage. The head must in the next plaee be turned forcibly round, so that the face is direeted over the left shoulder. Raise the posterior part of the right eerebral hemisphere with the fingers, and note that it rests upon the tentorium eerebelli — a broad horizontal proeess of dura mater whieh intervenes between it and the eerebellum. Divide the tentorium along its attaehed border, and take eare whilst doing this not to injure the subjacent eerebellum. Now turn the head so as to bring its left side uppermost, and treat the tentorium on that side in the same manner. The two parts of the trigeminal nerue (fifth eerebral nerve) per- forating the dura mater near the apex of the petrous portion of the temporal bone ; the abdueent nerue (sixth eerebral nerve) piereing the dura raater behind the dorsum sellae of the sphenoid bone ; the facial nerue and the aeustie nerue disappearing into the internal aeustie meatus ; the glosso- pharyngeal, the vagus, and the aeeessory nerues leaving the skull through the jugular foramen ; and the two slips of the hypoglossal nerue piereing tne dura mater over the hypoglossal eanal (O.T. anterior eondyloid foramen), will eaeh in turn eome into view upon either side, and must be divided in sueeession. In the ease of the three nerves passing out of the eranium through the jugular foramen, the disseetor should endeavour to leave the aeeessory of the right side intaet within the eranium, by dividing its roots of origin from the meduUa oblongata, whilst on the other side he should remove it with the brain. This nerve is readily reeognised beeause it aseends from the vertebral eanal into the eranial cavity through the foramen magnum. Now thrust the knife into the vertebral eanal, and divide the medulla spinalis and the vertebral arteries, as they turn anteriorly upon the upper part of the meduUa spinalis (O.T. spinal eord) ; then sever the aeeessory nerve of the left side, and the roots of the first pair of spinal nerves. When this has been done let the head fall well downwards, gently dislodge the medulla oblongata and eerebellum, and the whole brain ean be removed. The vena eerebri magna (Galen), as it passes from the

REMOYAL 0F THE BRAIN 219

interior of the brain to enter the straight sinus, is ruptured by this proeeeding.

Meniiigeal Yeins. — In addition to the named blood sinuses, venous ehannels aeeompany the meningeal arteries and more partieularly the trunks and branehes of the middle meningeal artery. These vessels are of wider ealibre than the eorresponding arteries, and lie external to them in the grooves on the inner surfaces of the eranial bones. When the arteries are distended they eompress the middle parts of the veins and drive the blood into their anterior and posterior margins. When this oeeurs eaeh artery appears to be aeeompanied by two veins, a eireumstanee whieh is probably responsible for the statement that some of the meningeal arteries have venae eomites.

Emissaria. — Emissary veins are blood ehannels whieh eonneet the sinuses of the dura mater with the veins whieh lie outside the eranium. They are : (i) Emissary veins eon- neeted with the superior sagittal sinus — {a) from the anterior extremity of the sinuses an emissary vein passes through the foramen eaeeum. This vein divides below and either beeomes eontinuous with the veins of the nasal foss8e, or its branehes pass through foramina in the nasal bones and join the angular veins; {b) two parietal emissary veins, whieh pass through the parietal foramina and eonneet the superior sagittal sinus with the oeeipital veins. (2) Emissary yeins eonneeted with the transverse sinuses — {a) two mastoid emissary veins, one on eaeh side, pass through the mastoid foramina and eonneet the sigmoid parts of the transverse sinuses with the posterior aurieular veins ; {b) two post- eondyloid veins, one on eaeh side, pass through the eondyloid eanals and eonneet the lower ends of the transverse sinuses with the plexuses of veins in the suboeeipital triangles. (3) Emissary veins eonneeted with the cavernous sinuses— («) a vein whieh traverses the foramen ovale, or the foramen Yesalii, and eonneets the cavernous sinus with the plexus of veins around the external pterygoid musele ; {b) a plexus of veins whieh passes through the temporal bone with the internal earotid artery and eonneets the cavernous sinus with the pharyngeal venous plexus; {c) in a sense the ophthalmie vein may be eonsidered an emissary vein, for although under ordinary eireumstanees it is a tributary of the sinus, blood ean flow through it in the opposite direetiori from the sinus into the orbit, and then along the tributaries whieh eonneet t^ ophthalmie vein with the angular vein, and along the c r whieh eonneet the ophthalmie vein through the 1 orbital fissure with the veins in the infratemporal regioi

220 HEAD AND NECK

The Arteries of the Oranial Cavity. — (i) The vertebral arteries ; {2) the internal earotid arteries ; (3) the meningeai arteries,

Arteria Yertebrales. — The vertebral arteries pieree the spinal dura mater below the foramen magnum, through whieh they enter the eranium. As eaeh artery passes through the foramen it lies anterior to the highest dentation of the liga- mentum dentieulatum, and it passes between the hypoglossal and first cervical nerves. It was divided when the hind brain was removed, and its eut extremity lies near its point of entranee into the eranial cavity.

Arteria Oarotides Intemse. — Eaeh internal earotid artery enters the eranium at the laeerate foramen between the apex of the petrous part of the temporal bone and the body of the sphenoid, where it pierees the outer layer of the dura mater. Then it runs anteriorly in the cavernous sinus to the medial side of the anterior elinoid proeess, where it turns upwards, pierees the inner layer of the dura mater and the araehnoid, and gives off its ophthalmie braneh, whieh runs anteriorly below the optie nerve to the orbit. The artery was eut immediately behind its ophthalmie braneh during the early stages of the removal of the brain.

Meningeal Arteries. — These are the nutrient arteries of the dura mater, and of the inner table and diploe of the eranial bones. They are derived from a great number of diSerent sourees, but the only one of any size is the middle meningeal braneh of the internal maxillary artery. The others are small twigs, and, except in a well - injected subject, will not be easily made out. They are: (i) anterior meningeal from the anterior ethmoidal artery ; (2) the aeeessory meningeal from the internal maxillary artery; (3) some small branehes from the aseending pharyngeal, oeeipital, and vertebral arteries.

Eaeh middle meningeal artery is a braneh of the eorre- sponding internal maxillary artery. It enters the eranium through the foramen spinosum of the sphenoid, and divides upon the inner surface of the great wing of that bone into two large terminal branehes. Of these, the anterior braneh aseends upon the great wing of the sphenoid, and the anterior inferior angle of the parietal bone, grooving both deeply, whilst the posterior braneh turns posteriorly upon the squamous portion of the temporal bone. The branehes whieh proeeed from these trunks spread out widely and,

REMOYAL 0F THE BRAIN

221

with the aeeompanying venous ehannels, oeeupy the arbor- eseent grooves on the inner surface of the eranial vault.

The vein whieh aeeompanies the middle meningeal artery passes through the foramen spinosum and ends in the plexus around the external pterygoid musele.

Eaeh anterior meningeal artery proeeeds from the anterior ethmoidal artery as it aeeompanies the anterior ethmoidal nerve aeross the cribriform plate of the ethmoid bone. It supplies a limited area of dura mater and bone in the anterior fossa of the eranium.

The aeeessory meningeal arteries (O.T. small meningeat) are somewhat ineonstant; they arise either direetly from the

FiG. 91. — I, Hypophysis ; 2, in median seetion ; 3, in horizontal seetion. (Sehwalbe. )

cu Anterior lobe. b. Posterior lobe. em. Gorpus mamillare.

i. Tuber einereum. ch. Optie ehiasma in seetion.

ro. Optie reeess of the third ventricle. o. Optie nerve. a'. Infundibulum with projection from

anterior lobe upwards anterior

to it.

internal maxillary or from the middle meningeal. Eaeh enters the eranium through the eorresponding foramen ovale, but it should not be looked for at the present stage, as it is best examined along with the semilunar (O.T. Gasserian) ganglion and the three divisions of the trigeminal nerve.

The meningeal branehes from the aseending pharyngeal arteries are the terminal twigs of those vessels. They enter the eranium through the laeerate and jugular foramina, and through the hypoglossal eanal (O.T. anterior eondyloid foramen). The braneh whieh passes through the jugular foramen is the largest.

The meningeal branehes of the oeeipital and 'uertebral arteries are small, and are distributed in the posterior eranial fossa. The former enter through the jugular, mastoid, and parietal foramina, the latter through the foramen magnum.

222 HEAD AND NECK

The meningeal veins may be regarded as being arranged in two sets : one set eonsists of small ehannels whieh pour their blood into the blood sinuses; the other set is eomposed of veins whieh aeeompany the meningeal arteries and earry their blood to venous trunks on the exterior of the eranium.

Hypophysis Oerebri (O.T. Pituitary Body) (Fig. 91). — The over-hanging margin of the diaphragma sellae should be eut away and the hypophysis carefully dislodged from the fossa hypophyseos (O.T. pituitary fossa) of the sphenoid bone. It is an oval strueture, slightly Aattened from above down- wards, and with its long axis direeted transversely. It eonsists of a large anterior lobe, and a smaller posterior lobe. The anterior lobe is hollowed out posteriorly so as to form a concavity for the lodgment of the posterior lobe. If a sagittal seetion is made through the body, the line of separation between the two lobes is seen very distinetly. The infundi- bulum, whieh eonneets the hypophysis with the tuber einereum of the brain, is attaehed to the posterior lobe only (Fig. 91, i). Thus, even in the adult, there is a elue to the different modes of development of the two lobes. The posterior lobe is derived from the brain, whilst the anterior lobe is an off-shoot from the primitive bueeal cavity.

When the inspeetion of the interior of the eranium is eompleted the disseetors must fill the eranial cavity with tow steeped in preservative solu- tion ; replaee the skull-eap in position and retain it by bringing the sealp flaps over it, and stitehing them aeeurately together. The brain must be put in a jar in a 5 per eent solution of formaIin and plaeed aside till the disseetion of the remaining parts of the head and neek is finished.

THE ANTERIOR PART 0F THE NEGK.

After the skull-eap has been replaeed and the sealp has been stitehed over it let the head hang down over the end of the table, pull the ehin as far from the sternum as possible and fix it in position with hooks. Then examine the region of the front of the neek. It is a large triangular area, bounded laterally by the anterior borders of the sterno-mastoid museles, above by the lower border of the mandible, and below by the middle part of the upper border of the manubrium sterni ; and it is divided by the median plane into two smaller subsidiary triangles, the anterior triangles of the neek^ eaeh of whieh is bounded above by the mandible, posteriorly by the stemo-

THE ANTERIOR PART 0F THE NECK 223

mastoid, and anteriorly by the median plane. Pass the iridex finger from the ehin to the sternum along the median line and loeate in sequence the body of the hyoid bone, the angular anterior border of the thyreoid eartilage, the rounded areh of the erieoid eartilage and the rings of the traehea. The latter are partly masked by the isthmus of the thyreoid gland. Plaee the thumb and the forefinger on the body of the hyoid bone and earry them posteriorly, one on eaeh side, along its great eornua. Note that the posterior ends of the eornua lie immediately in front of the anterior borders of the sterno- mastoid museles. Above the body of the hyoid bone lies the submental triangle roofed in by the mylo-hyoid museles, whieh form the diaphragm of the mouth ; and above eaeh great eornu is the eorresponding submaxiUary region, Between the body of the hyoid bone and the upper margin of the thyreoid eartilage is the thyreo-hyoid spaee, bounded posteriorly by the middle part of the thyreo-hyoid membrane, whieh lies anterior to the upper part of the pharynx and the middle of the epiglottis (Fig. 159). Traee the upper border of the thyreoid eartilage posteriorly and note that it terminates on eaeh side in a pointed projection, the superior eornu, whieh lies immediately in front of the anterior border of the sterno- mastoid. Between the lower margin of the thyreoid eartilage and the upper border of the erieoid eartilage lies the erieo- thyreoid ligament, forming part of the anterior wall of the lower portion of the larynx.

The disseetors should make themselves thoroughly familiar with the landmarks mentioned above, both on their own neeks and on the neeks of their friends, and they should note that whilst in the dead subject there may be some difficulty in palpating the isthmus of the thyreoid gland, as it erosses anterior to the seeond, third, and fourth rings of the traehea, they will have no difficulty in loeating the small soft eushion- like mass in the living subject.

Disseetion.—The skin was eut along the lower border of the mandible at the eommeneement of the disseetion of the face ; now, make a median ineision through it ftom the ehin to the sternum and turn the triangular flap, thus marked out, posteriorly and laterally, to a short distanee beyond the anterior margin of the sterno-mastoid. When this is done the super- ficial fascia covering the anterior triangle on eaeh side will be eKpos'^H • i*f is thiekest and most laden with fat in the submental region. Ir part of it lie the fibres of the platysma, running upwards ar towards the mandible. The anlerior fibres of the musele to the anterior part of the lower border of the mandible, ana .

THE ANTERIOR PART OF THE NECK 225

of the dee > a about half-way between the sternum and tlie thyteoi oart e. The altaehments of the seeond layer of deep fascia of the lower part of the neek may be summarised as Tollows. Il is attaehed below to the posterlor surface of the manubrium sterni and to the posterior border of the clavicle, to whieh it binds the posterior belly of the omo-hyoid (p. 145). Above, it fuses with ihe more superficial layer, along an oblique line whieh aseends fTom the level of the eoraeoid proeess to the level of the upper end of the traehea. Above that level it forms, with the superficial layer, a eommon lamella, whieh aseends on the infra-hyoid museles to gain attaehment to the body and great eomu of the hyoid bone. The spaee between the two layers eontains, in the region of the anterior triangle, ihe lower parts of the anterior iugular veins, the anastomosis between them, and the areolar tissue in whieh they are embedded. In the posterior triangle its eontents are the lower end of the extema! iugular vein, the terminations of the transverse cervical and transverse seapular veins, the transverse seapular artery, and areolar tissue. Note that the anterior iugular vein on eaeh side lies superficial to the deep fascia in ihe upper part of the neek ; then it pierees the first layer of deep fascia and lies between the two layers, where it anastomoses with its fellow of the opposite side ; finally it tums laterally deep to the stemo-mastoid, and terminates in the external jugular vein at the anterior boundary of the sub- clavian part of the posterior triangle.

J}iss£ciion. — Make two ineisions througU the deep faseia cif the upper patt or the anterior triangle, one along the lower bonler of the mandible ftom the angle to half an ineh from the ehin, and a seeond at right angles to the (irst, Trom its middle to the great eornu of Ihe hyoid bone. Whilst making the horizontal ineision avoid injuiiiig Ihe eieteinal maxillaiy arteiy (O.T. Taeial) and the anterior facial vein, whieh pieree the deep faseia at the le¥el or the anteriot bordet of the massetet. Keflect the two triangular ilaps of iasaa. matked out by the ineisions and expose the lowet surface of the submaj:illary gland, the submaxillaty lymph glands, Ihe anterior and posterioi bellies of the digastrie musele, the lower part of the stylo-hyoid musele, and a fuithei pait of the anterior facial vein.

The maiority of the submaxillary lymph glands lie the lower border of the mandible on the superfidal the submaxillary gland. The anterior facial vein ci 1

posterior part of the submaxillary gland su i

external maxillary artery dips deeply betv of the mandible and the submaxillary j VOL. II — 16

2 26 HEAD AND NECK

and lower part of the submaxillary gland usually overlaps the stylo-hyoid and the posterior belly of the digastrie museles, and not infrequently it overlaps the great eornu of the hyoid bone also. Its anterior border may overlap the anterior belly of the digastrie. Raise the lower border of the gland and expose another layer of deep fascia covering the museles whieh lie deep to it. Plaee the handle of the knife on this fascia and push it gently upwards. Note that it passes upwards to the level of the mylo-hyoid line on the inner surface of the mandible, to whieh the mylo-hyoid musele is attaehed. The fascial sheath in whieh the submaxillary gland is enelosed eonsists, therefore, of a superlieial layer of deep fascia whieh extends from the great eornu of the hyoid bone to the lower border of the mandible, and a deeper layer whieh passes from the great eornu of the hyoid to the mylo-hyoid line of the mandible. The two layers blend in front of the anterior belly of the digastrie, and posteriorly they unite, behind the posterior belly of the digastrie, with the connective tissue in whieh the earotid vessels are embedded.

Disseetion, — Remove the deep fascia in the region of the anterior triangle and expose the divisions and the eontents of the triangle.

The Divisions of the Anterior Triangle. — After the deep fascia is removed, the disseetor will reeognise that eaeh anterior triangle may be divided into three subsidiary areas whieh are ealled the digastrie, the earotid, and the museular triangles, by means of the two bellies of the digastrie musele and the anterior belly of the omo-hyoid musele.

The digastrie triangle is bounded by the two bellies of the digastrie musele and the lower border of the mandible.

The boundaries of the earotid triangle are, above and in front, the posterior belly of the digastrie ; below and in front, the anterior belly of the omo-hyoid ; and, behind, the anterior border of the sterno-mastoid.

The museular triangle is bounded, above and behind, by the anterior belly of the omo-hyoid; below and behind, by the anterior border of the sterno-mastoid ; and in front, by the middle line of the neek.

An additional triangle eommon to the two sides lies between the hyoid bone below, the two anterior bellies of the digastries laterally, and the mandible above. This is ealled the submenidl triangle.

The Middle Line of the Neek. — Before eommeneing the

THE ANTERIOR PART OF THE NECK

27

disseetion of the eontents of the subsidiary parts of the anterior triangle the disseetors of both sides should, together, study the struetures whieh lie in the middle line of the neele and immediately to either side of it ; for this region is of the highest importanee to the surgeon. The area is diyided by the hyoid bone into supra-hyoid and infra-hyoid portions,

In the supra-hyoid part lie struetures whieh are eoneerned in the eonstruetion of the floor of the mouth. The disseetor

will have notieed already that the fatty superficial fascia ts more fully deyeloped here than elsewhere in the neek, and that the anterior margins of Ihe two platysma museles meet and deeussate iii the median plane, for about half an ineh or so, below the ehin. The anterior belHes of the two digastrie museles are attaehed to tbe mandible, one on either side of the symphysis. From this they deseend towards the hyoid boiie, and diverge slightly from eaeh otber so as to leave a narrow triangular spaee, the submental triangU, be- tween them (Fig. 93). The floor of this spaee is formed by : portions of the two mylo-hyoid museles, whilst

2 26 HEAD AND NECK

and lower part of the submaxillary gland usually overlaps the stylo-hyoid and the posterior belly of the digastrie museles, and not infrequently it overlaps the great eornu of the hyoid bone also. Its anterior border may overlap the anterior belly of the digastrie. Raise the lower border of the gland and expose another layer of deep fascia covering the museles whieh lie deep to it. Plaee the handle of the knife on this fascia and push it gently upwards. Note that it passes upwards to the level of the mylo-hyoid line on the inner surface of the mandible, to whieh the mylo-hyoid musele is attaehed. The fascial sheath in whieh the submaxillary gland is enelosed eonsists, therefore, of a superlieial layer of deep fascia whieh extends from the great eornu of the hyoid bone to the lower border of the mandible, and a deeper layer whieh passes from the great eornu of the hyoid to the mylo-hyoid line of the mandible. The two layers blend in front of the anterior belly of the digastrie, and posteriorly they unite, behind the posterior belly of the digastrie, with the connective tissue in whieh the earotid vessels are embedded.

Disseetion, — Remove the deep fascia in the region of the anterior triangle and expose the divisions and the eontents of the triangle.

The Divisions of the Anterior Triangle. — After the deep fascia is removed, the disseetor will reeognise that eaeh anterior triangle may be divided into three subsidiary areas whieh are ealled the digastrie, the earotid, and the museular triangles, by means of the two bellies of the digastrie musele and the anterior belly of the omo-hyoid musele.

The digastrie triangle is bounded by the two bellies of the digastrie musele and the lower border of the mandible.

The boundaries of the earotid triangle are, above and in front, the posterior belly of the digastrie ; below and in front, the anterior belly of the omo-hyoid ; and, behind, the anterior border of the sterno-mastoid.

The museular triangle is bounded, above and behind, by the anterior belly of the omo-hyoid; below and behind, by the anterior border of the sterno-mastoid ; and in front, by the middle line of the neek.

An additional triangle eommon to the two sides lies between the hyoid bone below, the two anterior bellies of the digastries laterally, and the mandible above. This is ealled the submental triangle,

The Middle Line of the Neek. — Before eommeneing the

THE ANTERIOR PART 0F THE NECK 23J

disseetion of the eontenls of the subsidiary parts of the anterior triangle the disseetors of both sides should, together, study the struetures whieh lie in the middle line of the neek and immediately to either side of it ; for this region is of the highest importanee to the sui^eon. The area is divided by the hyoid bone into supra-hyoid and infra-hyoid portions.

In the supra-hyoid part Ue struetures whieh are eoneemed in the eonstruetion of the floor of the mouth. The disseetor

FlG, 92.— Diagram 10 show the Boundaries of the Triangles of the Neek.

will have notieed already that Ihe fatty superlieial fascia is more fully developed here than elsewhere in the neek, and tbat the anterior margins of Ihe two platysma musdes meet and deeussate in tbe median plane, for about half an ineh or so, below tbe ehin. The anterior bellies of the two digastrie museles are attaehed to tbe mandible, one on either side of ihe symphysis, From this they deseend towards tbe hyoid boiie, and diverge shghtly from eaeh other so as to Ieave a narrow triangular spaee, the submentai triangk, be- tween them (Fig. 93). The floor of this spaee is formed by the anterior portions of the two mylo-hyoid iri> '"s. wbilst II— 15a

2 26 HEAD AND NECK

and lower part of the submaxillary gland usually overlaps the stylo-hyoid and the posterior belly of the digastrie museles, and not infrequently it overlaps the great eornu of the hyoid bone also. Its anterior border may overlap the anterior belly of the digastrie. Raise the lower border of the gland and expose another layer of deep fascia covering the museles whieh lie deep to it. Plaee the handle of the knife on this fascia and push it gently upwards. Note that it passes upwards to the level of the mylo-hyoid line on the inner surface of the mandible, to whieh the mylo-hyoid musele is attaehed. The fascial sheath in whieh the submaxillary gland is enelosed eonsists, therefore, of a superficial layer of deep fascia whieh extends from the great eornu of the hyoid bone to the lower border of the mandible, and a deeper layer whieh passes from the great eornu of the hyoid to the mylo-hyoid line of the mandible. The two layers blend in front of the anterior belly of the digastrie, and posteriorly they unite, behind the posterior belly of the digastrie, with the connective tissue in whieh the earotid vessels are erabedded.

Disseetion. — Remove the deep fascia in the region of the anterior triangle and expose the divisions and the eontents of the triangle.

The Divisions of the Anterior Triangle. — After the deep fascia is removed, the disseetor will reeognise that eaeh anterior triangle may be divided into three subsidiary areas whieh are ealled the digastrie, the earotid, and the museular triangles, by means of the two bellies of the digastrie musele and the anterior belly of the omo-hyoid musele.

The digastrie triangle is bounded by the two bellies of the digastrie musele and the lower border of the raandible.

The boundaries of the earotid triangk are, above and in front, the posterior belly of the digastrie ; below and in front, the anterior belly of the omo-hyoid ; and, behind, the anterior border of the sterno-mastoid.

The museular triangle is bounded, above and behind, by the anterior belly of the omo-hyoid; below and behind, by the anterior border of the sterno-mastoid ; and in front, by the middle line of the neek.

An additional triangle eommon to the two sides lies between the hyoid bone below, the two anterior bellies of the digastries laterally, and the mandible above. This is ealled the submental triangle,

The Middle Line of the Neek. — Before eommeneing the

THE ANTERIOR PART 0F THE NEGK

237

disseetion of the eontents of the subsidiary parts of the anterior triangle the disseetors of both sides should, together, study the struetures whieh lie in the middle line of the neek and immediately to either side of it ; for this region is of the highest importanee to the surgeon. The area is diyided by the hyoid bone into supra-hyoid and infra-hyoid portions.

In the supra-hyoid part tie stnietures whieh are eoneerned in the eonstruetion of the floor of the mouth. The disseetor

FlG. 92, — DiagTam to show Ihe Boundaries of the Triangles of (fae Neek.

will have notieed already that the fatty superficial fascia is more fully developed here than elsewhere in ihe neek, and that the anterior margins of the two platysma museles meet and deeussate iri the median plane, for about half an ineh or so, below the ehin. The anterior bellies of the two digastrie museles are attaehed to the mandible, one on either side of the symphysis, From this they deseend towards the hyoid bone, and diverge slightly from eaeh other so as to leave a narrow triangular spaee, the submenlal triangk, be- tween them {Fig. 93). The floor of this spaee is formed by the anterior portions of the two mylo-hyoid museles, whilst

2 26 HEAD AND NECK

and lower part of the submaxillary gland usually overlaps the stylo-hyoid and the posterior belly of the digastrie museles, and not infrequently it overlaps the great eornu of the hyoid bone also. Its anterior border may overlap the anterior belly of the digastrie. Raise the lower border of the gland and expose another layer of deep fascia covering the museles whieh lie deep to it. Plaee the handle of the knife on this fascia and push it gently upwards. Note that it passes upwards to the level of the mylo-hyoid line on the inner surface of the mandible, to whieh the mylo-hyoid musele is attaehed. The fascial sheath in whieh the submaxillary gland is enelosed eonsists, therefore, of a superiieial layer of deep fascia whieh extends from the great eornu of the hyoid bone to the lower border of the mandible, and a deeper layer whieh passes from the great eornu of the hyoid to the mylo-hyoid line of the mandible. The two layers blend in front of the anterior belly of the digastrie, and posteriorly they unite, behind the posterior belly of the digastrie, with the connective tissue in whieh the earotid vessels are embedded.

Disseetion, — Remove the deep fascia in the region of the anterior triangle and expose the divisions and the eontents of the triangle.

The Divisions of the Anterior Triangle. — After the deep fascia is removed, the disseetor will reeognise that eaeh anterior triangle may be divided into three subsidiary areas whieh are ealled the digastrie, the earotid, and the museular triangles, by means of the two bellies of the digastrie musele and the anterior belly of the omo-hyoid musele.

The digastrie triangle is bounded by the two bellies of the digastrie musele and the lower border of the raandible.

The boundaries of the earotid triangle are, above and in front, the posterior belly of the digastrie ; below and in front, the anterior belly of the omo-hyoid ; and, behind, the anterior border of the sterno-mastoid.

The museular triangle is bounded, above and behind, by the anterior belly of the omo-hyoid; below and behind, by the anterior border of the sterno-mastoid ; and in front, by the middle line of the neek.

An additional triangle eommon to the two sides lies between the hyoid bone below, the two anterior bellies of the digastries laterally, and the mandible above. This is ealled the submental triangle.

The Middle Line of the Neek. — Before eommeneing the

THE ANTERIOR PART 0F THE NECK 227

disseetion of the eontents of the subsidiary parts of the anterior triangle the disseetors of both sides should, K^ether, study the struetures whieh lie in the mlddle line of the neek and immediately to either side of it ; for this region is of the highest importanee to the surgeon. The area is divided by the hyoid bone into supra-hyoid and infra-hyoid portions.

In the supra-hyoid part lie struelures whieh are eoneemed in the eonstruetion of the floor of the mouth. The disseetor

of the Triangles of ihe Neek.

will have notieed already that the fatty superlieial fascia is more fully developed here than elsewhere in the neek, and that the anterior margins of the two platysma miiseles meet and deeussate iii the median plane, for about half an ineh or so, below the ehin. The anterior bellies of the two digastrie museles are attaehed to the mandible, one on either side of the symphysis. From this they deseend towards the hyoid boue, and diverge slightly from eaeh other so as to leave a narrow triangular spaee, the submtnlal triangle, be- tween them (Fig. 93). The floor of this spaee is formed by the anterior portions of the two mylo-hyoid museles, whilst

228

HEAD AND NECK

biseeting the floor of the triangle, in the median plane, is the fibrous raphe into whieh these museles are inserted. Not infrequentiy the medial margins of the digastrie museles send deeussating fibres aeross the interval. Within the subraental triangle are the submental glands, whieh receive lyroph from

FlG, 93. — Disseetion of the Kront of the Neek. The Righl Sterno-masloid

the median part of the lower lip and ehin and the anterior part of the tongue.

In ihe median area of the infra-hyoid part there is a narrow interrauseular interval, bounded on eaeh side, above, by the medial margins of the sterno-hyoid museles, and to a smaller extent, below, by the medial margins of the sterno- thyreoid museles (Fig. 93); raore lateraily lie the anterior bellies

THE ANTERIOR PART 0F THE NECK 229

of the omo-hyoid museles. In this median intermuseular interval the following struetures will be found : (i) the median part of the thyreo-hyoid membrane ; (2) the anterior border of the thyreoid eartilage with the projecting prominentia laryngea (O.T. pomum adami) at its upper end ; (3) the areh of the erieoid eartilage ; (4) the erieo-thyreoid ligament with the anastomosis between the erieo-thyreoid arteries, and the anterior ends of the erieo-thyreoid museles; (5) the first ring of the traehea with the anastomosis between the medial terminal branehes of the superior thyreoid arteries ; (6) the isthmus of the thyreoid gland ; (7) the inferior thyreoid veins, and (8) the lower cervical rings of the traehea. Oeeasionally the third or middle lobe of the thyreoid gland and the levator glandulae thyreoidea,*or one or other of them, is found extending upwards from the isthmus of the thyreoid gland. When it is present the middle lobe either terminates above in a pointed extremity or beeomes eontinuous with a fibrous eord, the remains of the thyreo-glossal duet, whieh disappears posterior to the hyoid bone. The levator extends from the isthmus or from the third lobe, and is attaehed above to the lower border of the hyoid bone.

Disseetion. — To display these struetures fully the fascia whieh covers and binds together the infra-hyoid museles of opposite sides must be removed. When this has been done the anterior part of the thyreoid eartilage will be exposed, and, above it, in the thyreo-hyoid interval, lies some loose areolar tissue. If an ineision, direeted upwards and posteriorly, is made into this tissue, behind the lower border of the hyoid bone, the infra-hyoid bursa will be opened, and when this and the areolar tissue are removed, the thyreo-hyoid membrane will be exposed. Note that the membrane extends from the upper border of the thyreoid eartilage posterior to the body of the hyoid bone to its upper border. When the areolar tissue in the lower part of the intermuseular interval is removed the inferior thyreoid veins will be displayed ; they disappear, below, behind the sternum where they join tbe innominate veins. Oeeasionally also a small unpaired artery, the thyreoidea ima^ will be found aseending, in the median plane, to the isthmus of the thyreoid gland. Behind the inferior thyreoid veins lies another layer of deep cervical fascia, the pretraeheal layer. It covers the front of the traehea,' envelops the isthmus of the thyreoid gland, and is attaehed above to the lower border of the thyreoid eartilage. The part whieh extends from the isthmus of the thyreoid gland to the tbyreoid eartilage aets as a suspensory ligament of the isthmus. The disseetors will find that, so long as the attaehments of this part of the pretraeheal fascia are not interfered with, they eannot displaee the isthmus of the thyreoid gland downwards. On the other hand, if they eut through the attaehment of the fascia to the thyreoid eartilage, introduee the handle of the knife through the ineision, and press downwards, they will be able to displaee the isthmus of the thyreoid gland to a lower level and expose the upper rings of the traehea. At the root of the neek the pretraeheal fascia deseends into the thorax, 11—15 6

2 30 HEAD AND NECK

along the anterior surface of the traehea, and it blends below with the fibrous perieardium.

Remove the pretraeheal fascia from the region of the intermuseular interval, first above and then below the isthmus of the thyreoid gland. As the fascia is disseeted away the following struetures will be displayed. Immediately below the thyreoid eartilage is the erieo-thyreoid ligament, overlapped on eaeh side by the anterior part of the erieo-thyreoid musele. Grossing anterior to the ligament, transversely, is the anastomosis between the erieo-thyreoid branehes of the superior thyreoid arteries. It lies nearer the lower than the upper border of the ligament. Below the erieo-thyreoid ligament is the convex anterior part of the erieoid eartilage ; then follows the erieo-traeheal ligament, uniting the erieoid eartilage to the first ring of the traehea. The isthmus of the thyreoid gland lies at a lower level opposite the seeond, third, and fourth rings of the traehea. Along its upper border is the anastomosis between the medial terminal branehes of the superior thyreoid arteries, and below it are the lower cervical traeheal rings.

The superficial layers of the deep fascia must now be removed from the whole area of eaeh anterior triangle, and for this purpose and for the satisfactory disseetion of the eontents of the triangles, it is neeessary that the head be turned well over to the opposite side ; therefore the disseetors must arrange to work alternately.

Commence with the digastrie triangle. Its boundaries are the lower border of the mandible and the two bellies of the digastrie musele.

Its eontents are: (i) the lower part of the submaxillary gland; (2) the submaxillary lymph glands; (3) part of the external maxillary artery ; (4) part of the anterior facial vein ; (5) the mylo-hyoid nerve; (6) the mylo-hyoid artery; (7) a small part of the hypoglossal nerve ; (8) a small part of the lingual vein.

Disseetion. — Remove the deep fascia whieh was previously turned aside (p. 225) and elean the submaxillary lymph glands. Most of these glands lie immediately below the mandible in the angle between it and the sub- maxillary gland, but some may be found on the superficial surface of the gland. Turn the gland upwards and fix it with hooks ; then seeure the mylo-hyoid nerve and artery as they enter the posterior border of the anterior belly of the digastrie about the middle of its length. Define the band of fascia whieh surrounds the intermediate tendon of the digastrie and binds it to the great eornu of the hyoid bone. Note that the tendon is em- braeed by the cleft lower end of the stylo-hyoid musele. Glean the posterior belly of the digastrie and the stylo-hyoid musele whieh deseends along its anterior border. Note that the posterior belly of the digastrie and the stylo-hyoid disappear, postero-superiorly, under cover of the angle of the mandible. Clean the anterior belly of the digastrie, and then examine the floor or medial boundary of the triangle. Immediately behind the anterior belly of the digastrie it is formed by the posterior fibres of the mylo-hyoid musele ; and more posteriorly and on a deeper plane it is formed by the hyoglossus.

eiean the portion of the mylo-hyoid whieh is exposed and, at its posterior border, immediately above the great eornu of the hyoid bone,

THE ANTERIOR PART 0F THE NECK 231

seeure the hypoglossal nerve and the lingual vein, the vein lying l^elow the nerve. Displaee the lingual vein and the hypoglossal nerve upwards ; eut through the fibres of the hyoglossus, immediately alx)ve and parallel with the great eornu, and display the Ungual arter}', whieh in this }x>silion lies immediately above rhe great eornu, parallel with the lingual vein but separated from it by the hyoglossus musele.

All the struetures whieh have been mentioned above will be met with in the disseetion of other regions, when a full aeeount of them will lje given.

Turn next to the earotid triangle, so ealled beeause it eontains parts of the eommon, internal, and external earotid arteries. It is bounded posteriorly by the anterior border of the sterno-mastoid ; above and anteriorly by the posterior belly of the digastrie ; and below and anteriorly by the anterior belly of the omo-hyoid.

Disseetion. — Traee the anterior facial vein from the digastrie triangle aeross the superficial surface of the posterior belly of the digastrie to its posterior border, where it unites with the posterior facial vein, whieh is deseending from under cover of the lower end of the parotid gland. The trunk formed by the union of the anterior and posterior facial veins is the eommon facial vein. Traee the eommon facial vein downwards and posteriorly to its union with the intemal jugular vein, at or under cover of the anterior border of the sterno-mastoid. Remove the deep fascia and the areolar tissue, and the lymph glands whieh he in the angle belween the posterior belly of the digastrie and the anterior border of the stemo- mastoid, below the lower end of the parotid gland ; seeure the lingual vein, whieh passes baekwards from the tip of the great eornu of the hyoid bone to join the intemal jugular vein ; and the hypoglossal nerve as it erosses anteriorly at a higher level, superficial to the internal and extemal earotid arteries. As the nerve turns anteriorly aeross the large arteries it is itself erossed, superficially, by the sterno-mastoid braneh of the oeeipital artery, and it gives oflf its deseending braneh. Traee the deseending braneh downwards, in the fascia whieh lies superficial to the lower part of the internal and the upper part of the eommon earotid arteries, to the point where it disappears under cover of the anterior belly of the omo-hyoid, avoiding injury to the lingual, eommon facial, and superior thyreoid veins ; ^ and seeure the eommunieating braneh, from the seeond and third cervical nerves, whieh joins its posterior aspeet The latter nerve may eross either superficial or deep to the intemal jugular vein. Return to the hypoglossal nerve at the point where it gives oflf its deseending braneh, and traee it anteriorly to the upper aspeet of the posterior end of the great eornu of the hyoid bone, wnere it gives ofF the braneh of supply to the thyreo-hyoid musele. Traee the braneh into that musele below the level of the great eornu, then follow the trunk of the hypoglossal anteriorly to the digastrie triangle. Note that as it runs anteriorly it passes deep to the posterior belly of the digastrie and the stylo-hyoid musele, and superficial to the hyoglossus, whieh aseends to the tongue from

^ The lingual vein may join the eommon facial vein, in whieh ease the latter usually enters the internal jugular opposite the interval between the hyoid bone and the th^rreoid eartilage, as in the speeimen depieted in Fig. 93. The superior th^rreoid vein joins the interaal jugular or the eommon facial vein opposite the th3n*eo-hyoid interval.

II — 15 c

232 HEAD AND NECK

the upper border of the great eornu. Remove the fascial sheath from the superficial surfaces of the lower parts of the internal and external earotid arteries, and from the upper part of the eommon earotid artery. Note that the latter divides into the two former at the level of the upper border of the thyreoid eartilage, and that the external earotid is at first medial and anterior to the internal earotid.

Five branehes may spring from the external earotid in the earotid triangle, three from its anterior surface : the superior thyreoid, the lingual and the external maxillary ; one from its medial surface, the aseending phar)nigeal ; and one from its posterior surface, the oeeipital ; but not un- eommonly the oeeipital and the external maxillary arise beyond the limits of the earotid triangle under cover of the posterior belly of the digastrie. The superior thyreoid springs from the front of the lower part of the ex- ternal earotid below the level of the great eornu of the hyoid and runs downwards to the lower angle of the earotid triangle, where it disappears under cover of the anterior belly of the omo-hyoid. The lingual arises immediately above the level of the tip of the great eornu. It runs an- teriorly above the level of the eornu, forming a loop, convex upwards, whieh lies deep to the hypoglossal nerve ; and it disappears under cover of the posterior border of the hyoglossus musele. The aseending pharyngeal braneh, whieh springs from the medial surface of the lower end of the ex- terpal earotid, aseends on a deeper plane, between the external and in- ternal earotids and the wall of the pharynx, and will be followed at a later stage of the disseetion. The external maxillary and the oeeipital arise immediately below the posterior belly of the digastrie and almost at onee disappear under cover of the musele ; not uneommonly they arise under cover of its lower border. Before proeeeding to elean the branehes of the external earotid seeure the internal and external laryngeal branehes of the superior laryngeal braneh of the vagus nerve. The internal braneh will be found in the posterior part of the thyreo-hyoid interval below the great eornu of the hyoid b.one and behind the posterior border of the thyreo-hyoid musele, beneath whieh it disappears. It is aeeompanied by the laryngeal braneh of the superior thyreoid artery. The external braneh is more difficult to find ; but, if the superior thyreoid artery and the upper part of the eommon earotid are displaeed posteriorly, the nerve will be Ibund, lying deep to them, in the fascia whieh covers the anterior part of the inferior eonstrietor musele. Remove the fascia from the surface of the in- ternal jugular vein, whieh overlaps the posterior borders of the eommon and internal earotid arteries. Disseet in the interval between the vein and the arteries and seeure the vagus nerve, whieh Hes deeply. Remove the remains of the fascia from the earotid arteries and the internal jugular vein, but avoid injury to the hypoglossal nerve and its branehes ; and note the presenee of the upper deep cervical lymph glands whieh lie on the superficial surfaces of the great arteries and the internal jugular vein. The glands are sometimes very large, and the disseetors should remember that they receive lymph from the face, the mouth and tongue, the posterior part of the nose and the upper part of the pharynx. After the large vessels are eleaned, remove the fascia from the branehes of the external earotid artery and the twigs they give off, so far as they lie in the region of the earotid triangle. Gommenee with the superior thyreoid. Immediately after its origin it gives off a small infra-hyoid braneh, then a laryngeal braneh whieh aeeompanies the internal laryngeal braneh of the superior laryngeal nerve ; and, just before it disappears under cover of the anterior belly of the omo-hyoid, a sterno-mastoid braneh arises from its posterior border and runs downwards and posteriorly, along the upper border of the omo-hyoid, aeross the super- ficial aspeet of the eommon earotid artery and the internal jugular vein.

■ THE ANTERIOR PART 0F THE XECK 233

Next, dean the luigual artety and note its smil] $apn-hyi-t-! tinnkrh. Tbe extemal maiillary artery giresoS no branehes in the eW'-ti'i iriaogle. l-ul » stemo-niastoid braneh of the oeeinUil arteiy «ill usually \< liian-i [ouing downwards and posteriorly, Euperheial to Ihe loop or ibe hrpngkiHal ncrve. Push ihe lower border of the parotid gtand upwards. and immwliately under cover [>f it, at Ihe level of the aikgle of Ihe mandiUe, seeure (he aeeeHoor

of the sealenus anlerior m

ts it emerges trom under covei of the posterior belly or (he digastrie O'inastoid rioin the oeeipital

The floor or medial boundary of the earotid triangle is forraed by the upper part of the thyreo-hyoid musele, the

234

HEAD AND NECK

posterior part of the hyoglossus and the middle eonstrietors of the pharynx. The two latter mi be displayed at present, but the thyreo-hyoid is e: the great eornu of the hyoid bone, and part of th< ean be seen in the angle between the great eomu and the lower part of the posterior belly of the dij

The MuseiiLar Triaiigle. — When the deep covers the museular triangle is removed port three museles are brought into view. Posten the anterior belly of the omo-hyoid, more antei the same plane is the sterno-hyoid, and below anj the latter, but on a deeper plane, is a small part thyreoid.

The museles mentioned may be eonsidered floor or medial boundary of the triangle, and ii taken the struetures they cover, whieh lie mor^ under cover of the floor. These struetures exposed.

Disseetion. — Divide the anterior belly of the omo-h] anterior border of the sterno-mastoid and tum it upwards | into the hyoid bone. As this is done its twig of supply froi glossi will be eut. Divide the stemo-hyoid as low down it upwards to its insertion into the body of the hyoid bone of supply from the loop whieh is ealled the etnsa hypeglos by the union of the deseending braneh of the hypogk eommunieating braneh from the cervical plexus. Seeure sterno-thyreoid from the ansa h)rpoglossi ; then remove the : the lower part of the thyreo-hyoid musele, the greater thyreoid and the anterior part of the thyreoid eartilage. sterno-thyreoid is inserted into an oblique line on the oiit< lamina of the thyreoid eartilage and that the thyreo^hyoid a same line and is inserted into the great eomu of tne hy^ erieo-thyreoid braneh of the superior thyreoid artery may " downwards and anteriorly along the upper end of th< aeeompanied by the external laryngeal nerve ; or the n€ may lie deep to the upper end of the musele.

Divide the sterno-thyreoid as low down as possible and to its insertion ; remove the fascia under cover of it and ej lobe of the thyreoid gland, and below it a small part of traehea.

The disseetor should note that whilst the stemo-mastoi< turbed the posterior part of the lateral lobe of the thyreoi< lower extremity are not exposed, but if the sterno-mast< posteriorly the whole of the lateral surface of the lobe is br< The disseetor should note also that until the stemo-mast< posteriorly only a small portion of the upper end of the eomi the lower parts of the internal and external earotid artei indeed, the eommon earotid may be entirely eoneealed. of the anterior border of the internal jugular vein projects

THE ANTERIOR PART 0F THE NEGK 235

sterno-mastoid in the upper and posterior angle of the earotid triangle ; and it also is not uneommonly hidden when the sterno-mastoid is well developed. During life, however, when the musele is soft and pliable the struetures eoneealed by it are readily exposed, for the musele is easily displaeed posteriorly after the fascia has been divided along its anterior border. In the disseeting-room it is not possible to obtain a proper view of the eourse and relations of the eommon earotid artery and the internal jugular vein, or to appreeiate the relations of the tirst part of the subclavian artery and the relations of the sealenus anterior musele, until the sterno-mastoid has been reflected. Divide the external jugular vein immediately below the point where it is joined by the posterior aurieular tributary and turn it downwards. Divide the great aurieular nerve at the level of the angle of the mandible and turn it posteriorly ; and turn posteriorly the neryus eutaneus eolli, whose two terminal branehes have been eut already. The clavicular head of the sterno-mastoid was eut when the clavicle was removed ; now divide the sternal head, turn the musele upwards towards its insertion. As the musele is turned upwards, sterno-mastoid branehes of the transverse seapular, superior thyreoid, and oeeipital arteries will be exposed ; and if they interfere with the reflection of the musele they must be divided. Slightly above the level of the sterno-mastoid braneh of the oeeipital artery the aeeessory nerve will be found passing through the deeper fibres of the musele, and eare must be taken to avoid injury to it ; but it may be disseeted out of the musele and left in position on the lateral surface of the internal jugular vein.

Deep Cervical Fascia. — When the sterno-mastoid has been reflected a deep fascial plane of the neek is exposed in whieh lie many lymph glands. Before earrying the disseetion further the disseetor should reeonsider the arrangement of the deep cervical fascia. He has already seen that it forms a eomplete sheath enelosing the museles of the neek and the struetures whieh lie between and under cover of them. The general arrangement of the fascia is studied best on transverse seetions of the neek made at the level of the isthmus of the thyreoid gland and a short distanee above the sternum. At the former level it is possible to reeognise (i) a superficial layer; (2) a pretraeheal layer ; (3) a prevertebral layer; and (4) a fascial sheath whieh eneloses the eommon earotid arteries, the internal jugular vein and the vagus nerve, as they lie in the angular interval between the sterno-mastoid laterally, the thyreoid gland, the traehea, eesophagus medially, and the prevertebral museles posteriorly. ThQfirst or superficial layer, as it is traeed posteriorly, splits to enelose the sterno-mastoid musele. Beyond the sterno - mastoid it passes posteriorly to the anterior border of the trapezius musele, forming the roof of the posterior triangle, then splits again to enelose the trapezius, along the surfaces of whieh it is prolonged till it blends with the suprasDinons ligaments and the ligamentum

236

HEAD AND NECK

nuehse. The lamella whieh covers the deep suriaee of the stetno-mastoid is blended with the lateral surface of the earotid sheath. The pretraeheal layer, whieh has been disseeted already in the median plane, ensheaths the thyreoid gland and ble ds po tero-late ally wth the medial suriaee of the ca ot d heatb The prevertebral layer covers the anterior su faces of he preverteb al museles and passing laterally, blends V tb the poster or aspeet of tbe ca otid sheath ; then,

turn ng round the tips

,^^^^*g^pp U of the transverse pro-

— ~ . I ^ eesses of the vertebrse, t I asses posteriorly, co er ng the museles wh ch form the floor of the posterior triangle ; and t beeomes eontinu- ous ith the sheaths of the deep museles of the posteriorpartoftheneck. Laterally and pos- te orly, the superficial la>e of the deep fascia pa ses upwards over the sterno-mastoid and the trapezius to be attaehed to the superior nuehal 1 nes and the mastoid port ons of ihe temporal bones In the anterior cerv eal reg on t s attaehed to the bod) and the great eomua of the hyoid bone, and then, as t is prolonged further upwards, it sptits anteriorly to endose the submaKillary gland, and posteriorly to enelose the parotid. It bas been noted already that the lamella whieh passes superficial to the subma^illary gland is attaehed to the lower border of the mandibte, and tbat whieh passes deep to the gland is eonneeted above to the mylo-hyoid line on the inner surface of the mandible. The layer whieh passes superficial to the parotid gains attaehment to the zygoma and is prolonged forwards to blend with the fascLa covering the masseter. The lamella whieh passes deep to the parotid covers its postero-medial and antero-medial surfaces ; the posterior part is attaehed above to the lower

THE ANTERIOR PART 0F THE NECK

237

border of the tympanie plate and the anterior part to the posterior border of the petro-tympanie fissure (O.T. Glaserian). It also gains an intemediate attaehment to ihe styloid proeess and to the posterior border of the angle of the mandible. This partieular portion is relalively thiek ; it lies in relation with the lower part of the antero-medial surface of the parotid and is known as the stylo-mandibular ligament.

When the supirficial layer is traeed downwards it is found to split, between the erieoid eartilage and the sternum, irito two lamellae. The more superficial of the two lies superficial to the sterno-mastoid and is at- Yitsi layn ordeip fa5cui

taehed below to the upper border of the sternum and the upper border of the clavicle. In the anterior region the deeper lamella deseends upon the anterior surfaces of the intra-hyoid museles and is at- taehed below to the posterior surface of the manubnum ; laterally it passes deep to the stemo - mastoid and is fused with the lateral border of the earolid sheath. In the posterior triangle the deeper lamella ensheaths the posterior belly of the omo-hyoid and binds it down to the posterior border of the elayiele. The spaee ■ between the two lamellas has been ealled the supra-sternal spaee. Its boundaries and eontents have been fully deseribed already {p. 224).

The upper atlaehment of the pretraeheal layer is to the erieoid eartilage and to the laminEe of the thyreoid eattilage below the insertion of the sterno-thyreoid musele. At its lower end it blends with the fibrous perieardium in the middle mediastinum.

The pr^ertebral layer ean be followed upwards to the base of the skull, where it is attaehed, in the anterior cervical region, to the posterior and medial raargins of the jugular foramen and to the basilat part of the oeeipital bone, anterior

;. 96. — Diagram of deep cerv leve1 of ibe ibyteoid gland.

338 HEAD AND NECK

to the insertions of the prevertebral museles and posterior to the superior eonstrietor of the pharynx. Below, it blends with the fascia on the anterior aspeet of the vertebral eolumn in the posterior mediastina! region.

The Garotid Staeath. — The term earotid sheath is applied to the fascia whieh surrounds and embeds the earotid arteries, the internal iugular vein, and the vagus nerve. Part of it has been removed already, and the disseetor will have noted that it is in no sense a membrane, but merely the fibro-areolar tissue whieh fills the interval between the transverse proeesses of the yertebrae posteriorly, the traehea, Iaryrx, pharynx, eesophagus, and the lateral lobe of the thyreoid gland medially, and the sterno-mastoid laterally ; that it is eontinuous with the fascial planes in its immediate neighbourhood, and that

FiG. 97.

through it run the earotid arteries, the internal jugular vein, and the vagus nerve, eaeh in its own speeial eompartment.

Disseetisn. — Remove the areolar lissue and the glands whieh lie under cover of the stemo-mastoid ; stiteh ti^ether Ihe two parls of the divided anlerior belly of the omo-hyoid musele and ltx the musele to the eommon earotid arte^ and the internal jugular vein with one or two stitehes ; Ihen proeeed lo display the struetuies whieh lieunder cover of thesterno-masloid. A glanee at the followii^ list will convince the disseetor that (hey are extremely numerous.

Struetures heneath the Stenio-Uastoid

MuseleB. — The upper part of the splenius eapitis ; the upper and posterior part of the posterior beliy of the digastrie; the origins of the levator seapulEe, the sealenus medius, the longus eapitis {O.T. reetus eapltis anlieus major), the reetus eapitis lateralis and the sealenus anterior ; the intermediate

THE ANTERIOR PART 0F THE NECK 239

tendon of the omo-hyoid, and the lower and posterior part of the stemo-hyoid and sterno-thyreoid.

Arteries. — The upper part of the eommon earotid (the lower part is still eoneealed by the lower parts of the omo- hyoid and the lower parts of the stemo-hyoid and sterno- thyreoid museles) ; the transverse seapular and its sterno- mastoid braneh ; the transverse cervical ; the stemo-mastoid braneh of the superior thyreoid ; the oeeipital and its stemo- mastoid branehes.

Vems. — The greater part of the internal jugular vein ; a part of the lower transverse portion of the anterior jugular vein ; and, oeeasionally, the lower end of the extemal jugular vein when that vessel dips anteriorly to its termination.

Nerves. — The cervical plexus and its branehes, ineluding the phrenie nerve ; part of the aeeessory nerve.

If the lower parts of the divided stemo-hyoid and sterno- thyreoid museles are displaeed downwards, the lower part of the eommon earotid and the eommeneement of ihe first part of the subclavian artery will be exposed. Grossing the front of the latter are the lower portion of the cervical part of the vagus and a strand of sympathetie iibres ealled the ansa subclavia ; on the left side, the subclavian artery and the ansa are eon- eealed by tlie eommeneement of the innominate vein. At the same time the middle thyreoid vein will be exposed, and the posterior border of the lateral lobe of the thyreoid gland also.

Disseetion. — Commence by eleaning the anterior branehes of the eenrieal nenres from the seeond to the eighth, as they emerge between the museles attaehed to the tubereles of the transverse proeesses of the cervical yertebrse. The first nerve, whieh tums downwards anterior to the trans- yerse proeess of the atlas, will be exposcd later. As the upper nerves are eleaned the disseetors will find that the seeond is eonneeted to the third, and the third to the fourth, by looped strands, convex posteriorly, whieh eonstitute the two lower loops of the cervical plexus. The seeond nerve is eonneeted with the first also by a loop, convex anteriorly, whieh passes upwards anterior to the transverse proeess of the atlas and posterior to the upper part of the internal jugular vein. It ean be exposed if the vein is pulled anteriorly ; and the disseetor must at the same time seeure the twigs of eonneotion whieh pass from the medial side of the loop to the hypoglossal nerve and to the superior cervical ganglion of the sympathetie trunk, whieh lies behind the upper part of the intemal earotid artery.

After he has defined the loops of the plexus he should traee the remains of the small oeeipital, the great aurieular, the transverse eutaneous nerve of the neek and the supraclavicular branehes, whieh he displayed in the posterior triangle, to their origins from the roots of t|ie plexus. The eommunieating branehes whieh pass anteriorly to the deseendens h^rpe^lossi from the seeond, and s^* — ** — " also from the third cervical nerve, must be

240

HEAD AND NECK

followed ; they may eross either superficial or deep to the internal jugular vein. Then the phrenie nerve, whieh springs from the fourth cervical nerve, and receives additional twigs from the third and fifth nerves, must be followed downwards and anteriorly till it disappears under cover of the lower part of the internal jugular vein. It lies upon the surface of the sealehus anterior and passes deep to the omo-hyoid musele and the trans- verse cervical and transverse seapular arteries. Running parallel with, and anterior to it, is the aseending cervical braneh of the inferior thyreoid artery.

Small occipitalj R H

Great aurieular

Hypoglossal

Nervus eutaneus eolli

Braneh to levator seapulae

Braneh to levator seapulae

Deseending trunk

To genio-hyoid

Thyreo-hyoid nerve Deseendens h^rpoglossi

Ansa hypoglossi

eatin^ to fifth cervical

Phrenie

FiG. 98. — Diagram of the Cervical Plexus and the Ansa

Hypoglossi.

I, II, III, IV.— Anterior branohes of the upper four cervical nerves.

R. Branehes to reeti and longus eapitis. S. M. Branehes to the sterno-mastoid. C.C. Rami eommunieantes cervicales.

C.H. Communicating braneh to hypo- glossal.

This diagram shows that the deseendens hypoglossi, the braneh to the thyreo-hyoid, and in all probability the branehes to the genio-hyoid, are eomposed of fibres given to the hypoglossal by the eommunieating twigs it receives from the first cervical nerve.

Plexiis Cervicalis. — This is a looped plexus formed by the first four cervical nerves. It lies in the upper part of the side of the neek under cover of the sterno-mastoid. The upper loop of the plexus, whieh eonneets the first and seeond nerves together, is direeted forwards and lies between the internal jugular vein anteriorly, and the transverse proeess of the atlas posteriorly. The seeond and third loops, whieh

THE ANTERIOR PART 0F THE NECK 241

unite the seeond and third and the third and fourth nerves are direeted posteriorly ; and they lie on the superficial surface of the upper p'art of the sealenus medius musele. The first loop is eonneeted with the upper ganglion of the sympathetie trunk and with the hypoglossal nerve ; and the roots of the seeond, third and fourth nerves also are eonneeted, by grey rami, with the upper cervical sympathetie ganglion.

The branehes of the plexus are divisible into two main groups, the superficial and the deep. The deep branehes are separable into two groups : the anterior, whieh run forwards and the posterior, whieh run baekwards ; and the superficial branehes are classified as aseending, transverse and deseending.

The anterior group of deep branehes ineludes : (i) the ramus eommunieans cervicalis, and (2) the phrenie nerve.

The posterior group of deep branehes is formed by : (i) The eommunieating branehes to the aeeessory nerve. (2) Branehes of supply to (a) the sterno-mastoid from the seeond nerve; (p) the levator seapulse from the third and fourth ; (c) the trapezius from the third and fourth ; (d) the sealenus medius from the seeond, third, and fourth. (3) Less im- portant museular branehes from the first loop to {a) the reetus eapitis lateralis; (^) the reetus eapitis anterior (O.T. reetus eapitis antieus minor); {c) the longus eapitis (O.T. reetus eapitis antieus major). (4) Museular branehes from the third and fourth nerves to the longus eolli.

The aseending group of superficial branehes is formed by the small oeeipital and great aurieular nerves. The transverse braneh is the nervus eutaneus eolli, and the deseending branehes are the supraclavicular nerves. All the superficial nerves have already been traeed in the earlier stages of the disseetion (pp. 145, 146), but the phrenie nerve requires careful eonsideration.

Nennis Phrenieus. — The importanee of the phrenie nerve depends upon the fact that it is the nerve of supply to the chief musele of respiration, the diaphragm. The majority of its fibres spring from the fourth cervical nerve, but it receives twigs from the third and, not uneommonly, from the fifth nerve also. It deseends from the neek through the superior and posterior mediastinal regions of the thorax, and, after piereing the diaphragm, it is distributed on its lower surface. Only the cervical portion of the nerve belongs to the dis- seetor of the neek ; the remainder is displayed by the disseetor

VOL. II — 16

242 HEAD AND NECK

of the thorax (p. 341). In the neek the nerve runs down- wards and anteriorly, on the superiieial surface of the sealenus anterior, whieh forms its deep relation. In this part of its eourse it is covered by skin, superficial fascia and platysma, deep fasciaandsterno-mastoid; and, deep to the sterno-mastoid, it is oyerlapped by the internal jugular vein, and it is erossed by the omo-hyoid, the anterior jugular vein, and the transverse cervical and transverse seapular arteries on both sides ; on the left side by the thoraeie duet, and on the right side by the right lymph duet. At the root of the neek it passes from the medial border of the anterior sealene to the anterior surface of the first part of the subclavian artery ; and it is covered anteriorly by the clavicle on both sides, by the subclavian vein on the right side, and by the eommeneement of the in- nominate vein on the left side, and it erosses either anterior or posterior to the internal mammary artery. It gives off no branehes in the neek, but it sometimes receives a eommuniea- tion from the nerve to the subclavius.

After the disseetor has eompleted the examination of the formation, tbe relations, and the branehes of the cervical plexus, he should replaee the divided ihfra-hyoid museles in position and study their attaehments and relations.

The Infra-hyoid Museles are a series of flat, band-like museles whieh lie upon the traehea, thyreoid gland, and larynx. They are disposed in two strata — viz., the omo-hyoid and the sterno-hyoid eonstituting a superficial layer; and the sterno-thyreoid and thyreo-hyoid a deep layer.

Museulus Omohyoideus. — This is a two-bellied musele. The posterior belly springs from the upper border of the seapula and the upper transverse seapular ligament. It erosses the posterior triangle of the neek, dividing it into oeeipital and subclavian portions, and terminates under cover of the sterno-mastoid musele in an intermediate tendon ; and it is superficial to the phrenie nerve and the sealenus anterior. The tendon is held in position by a strong proeess of cervical fascia whieh is firmly attaehed below to the sternum and the first eostal eartilage. The anterior belly emerges from under cover of the anterior border of the sterno-mastoid, and takes an almost vertical eourse through the anterior triangle. It is inserted into the lower border of the body of the hyoid bone, at the lateral side of the sterno-hyoid. In the anterior triangle of the neek it forms the boundary between the

THE ANTERIOR PART OF THE NEGK 343

earotid and the museular subdivisions, and it lies supertieial to the internal jugular vein, the eommon earotid artery, the deseendens hypoglossi, the superior thyreoid artery, the ex- ternal laryngeal nerve, the attaehments of the sterno-thyreoid and Ihyreo-hyoid museles to the lamina of the thyreoid

eartilage; and immediately below its insertion it covers part of the thyreo-hyoid membrane, Both bellies are supplied by branehes from the ansa hypoglossi.

Museulus Stemokyoidtus. — This arises from the posterior aspeet of the medial end of the clavicle, the posterior sterno-clavicuIar ligament, and the posterior surface of the manubrium. It is inserted into the lower border of the body

244 HEAD AND NECK

of the hyoid bone, between the median plane and the insertion of the omo-hyoid. A short distanee above the sternum an oblique tendinous interseetion frequently divides it into two portions. The lower part of the musele is covered by the sterno-mastoid, and it is erossed by the anterior jugular vein. Its prineipal deep relations are the lower part of the eommon earotid artery and the sterno-thyreoid musele, whieh separates it from the lateral lobe of the thyreoid gland. It is supplied by branehes from the ansa hypoglossu

Museulus Stemothyreoideus, — This musele lies under cover of the preeeding and is both broader and shorter. It springs from the posterior aspeet of the manubrium sterni and from the eartilage of the first rib. Diverging slightly from its fellow as it aseends, it is inserted into the oblique line on the lateral face of the lamina of the thyreoid eartilage. An ineomplete tendinous interseetion may sometimes be notieed interrupting its museular fibres. The nerve supply is derived from the ansa hypoglossi, In the neek it is covered in the greater part of its extent by the sterno-hyoid ; but the posterior part of its insertion is covered by the anterior belly of the omo-hyoid ; and the lower and anterior part is covered by skin and fascia only. The nerve supply is derived from the ansa hypoglossi.

Museulus Thyreohyoideus. — This musele lies on the same plane as the sterno-thyreoid, and may be regarded as its upward eontinuation. It takes origin from the oblique line on the outer surface of the lamina of the thyreoid eartilage, and is inserted into the lower border of the great eornu of the hyoid bone under cover of the omo-hyoid musele. It eoneeals part of the lamina of the thyreoid eartilage and the lateral part of the thyreo-hyoid membrane, and the aperture in the membrane through whieh the laryngeal braneh of the superior thyreoid artery and the internal laryngeal nerve enter the pharynx. It is supplied by a twig from the hypoglossal nerue.

Disseetion. — The disseetors of the head and neek should now proeeed to study the relations of the eommon earotid and subclavian arteries, the cervical part of the thoraeie duet, and the dome of the pleura, before these are disturbed by the disseetors of the thorax. Whilst this is being done, the omo-hyoid must be retained in position, but the upper and lower portions of the other infra-hyoid museles may be turned upwards and downwards respectively.

Remove the remains of the fascial sheath from around the oommon

THE ANTERIOR PART 0F THE NECK 245

earotid artery and the adjacent part of the internal jugular vein. Separate the vein from the artery and elean the portion of the vagus nerve whieh lies between them on a posterior plane. Note that on the right side the nerve erosses the anterior surface of the subclavian artery, and there gives off its reeurrent braneh ; and that on the left side it lies medial to the sub- clavian artery on an anterior plane.

After the lower parts of the vagi have been eleaned, look for the terminal part of the thoraeie duet on the left side and for the right lymphatie duet on the right side. In seeking for the thoraeie duet pull the lower end of the left internal jugular vein aside and displaee the eommon earotid artery anteriorly ; then look for the duet as it turns laterally from the border of the oesophagus a little below the level of the erieoid eartilage ; traee it posterior to the internal jugular vein to its termination in the eommenee- ment of the innominate vein. On the right side look for the right lymphatie duet entering the innominate vein in the angle of union of the internal jugular and subclavian veins. Next look for the cervical portion of the sympathetie trunk, whieh deseends posterior to the eommon earotid. Glean the nerve trunk carefully and elean also the inferior thyreoid artery, whieh erosses anterior or posterior to it, at the level of the erieoid eartilage. Dis- plaee the eommon earotid laterally, and in the angle between the borders of the traehea and the oesophagus find the reeurrent braneh of the vagus ; traee it upwards to the point where it disappears under cover of the lateral lobe of the thyreoid gland, and downwards to the subclavian artery.

Arteria Oarotis Ooiniimnis.— The eommon earotid arises diATerently on the two sides. On the right side it springs from the termination of the innominate artery, behind the sterno-clavicular joint, and on the left side from the aortie areh in the superior mediastinum. The left artery aseends to the baek of the left sterno-clavicular artieulation. From the sterno-clavicular joint eaeh eommon earotid artery runs upwards, posteriorly, and slightly laterally to the upper border of the thyreoid eartilage, whieh lies opposite the dise between the third and fourth cervical ^ertebrse ; and there it ends by dividing into its two terminal branehes — the internal and the external earotid arteries.

Superficial Relations, — Above the level of the anterior belly of the omo-hyoid the eommon earotid artery is covered by the skin, the superiieial fascia and the platysma, the deep fascia and the anterior margin of the sterno-mastoid. It is erossed immediately above the omo-hyoid by the sterno- mastoid braneh of the superior thyreoid artery and, at a higher level, by the superior thyreoid vein ; and it is overlapped by the anterior margin of the internal jugular vein. In the lower part of its extent it lies more deeply : its superiieial relations are the skin and superiieial fascia, the deep fascia and the sterno-mastoid ; the anterior jugular vein, erossing transversely, deep to the sterno-mastoid and above the upper

246

HEAD AND NECK

border of the clavicle ; the omo-hyoid, the sterno-hyoid, and the sterno - thyreoid museles. Deep £o the museles, the branehes of the ansa hypoglossi deseend in front of its sheath; and the middle thyreoid vein erosses it to ioin the internal jugular vein.

Postenor to it lie the transverse proeesses of the cervical vertebr£e and the origins of the longus eolH, longus eapitts (O.T. reetus eapilis antieus major), and the sealenus anterior. The inferior thyreoid artery erosses posterior to it at the level of the erieoid eartilage ; and the vertebral artery lies between it and the transverse proeess of the seventh cervical vertebra. On the right side, the reeurrent braneh of the vagus erosses

posterior to it, iramediately above its origin ; and on the Ieft side the thoraeie duet turns laterally behind it, between it and the vertebral artery.

To its medial side, below, lie the traehea and eesophagus, with the reeurrent nerve in the angle between their adjacent borders ; and to the medial side of its upper part are the larynx and pharynx. The lateral lobe of the thyreoid gland lies either medial to the artery, separating it from the eesophagua, pharynx, traehea, and larynx, or it forms a direet anterior relation (Figs. 97, loi). Between its upper extremity and the inferior eonstrietor musele of the pharynx lies the earotid body. As a rule, the terminal divisions are the only branehes of the eommon earotid, but oeeasionally the superior thyreoid or ihe aseending pharyngeal artery arises

THE ANTERIOR PART 0F THE NECK 347

{rom it, instead of from the extema.l earotid. Thls is more espeeially the ease when the division of the eomnion earotid takes plaee at a higher levei than usual.

earotid Body. — This is a liltU oval, reddish-brown body, plaeed upon Ihe deep aspeel of the eommon eaiotid aiteiy at the point where it birureales. To eitpose it, thererore, the vessel must he twisled lound ia siieh a manner thal its posteiior surraee eomes to look roiwBids. It is elosely eonneeted with (he sympathelie tiUments wbieh twine around the eatotLd vessels ; and in strueture it is similar in its natute lo ihe minule eoeeygeal body, whieh rests upon the antetiot aspeel or ihe coccyx. It ii ineluded, thererore, in the group or duetless glands. Entenng it ale numeious minule arterial (wigs, whieh take oiigin rrom ihe teimination of the eommon eaiotid and the eommeneemenl of ihe exletnal earolid. The runetion of this remarkable liltle body is quite unknown. MoM likely it

Arteria SnbelaTiA. — The relations of the third part of the subclavian artery were exainined during the disseetion of the posterior triangle (p. 1 5 1 ). Those of the first and seeond parts must now be studied. On the right side a small portion of the iirst part is already exposed between the lower ends of the internal iugular vein and the eommon earotid artery ; the remainder ean be seen if the intemal jugular vein is drawn aside. On the Ieft side the first part of the artery is eoneealed by the eommeneement of the innominate vein, whieh must be pushed aside. On both sides the seeond part of the artery lies posterior to the sealeniis anterior, whieh must be left in position.

The subclavian artery is the first portion of the great arterial trunk whieh earries blood for the supply of the upper

248 HEAD AND NECK

extreiTiity. It arises ditTerently on the two sides of the body. On the right side it takes origin behind the sterno-clavicular artieulation from the bifurcation of the innominate artery.

FiG. loa,— DeepDis5ectionof theKooiofthe Neek on the Left Side lo show Ihe Dome of the Pleura and the relations of the Terminnl Pnrt of the Thoraeie Duet. The slerno-niasloid and tlie depressors of the hyoid and larynji have been remoyed,

On the Uft side it arises from the aortie areh in the superior mediastinum. In both eases it takes an arehed eourse laterally aeross the root of the neek, posterior to the sealenus anterior and on the anterior surface of the cervical dome of -.

THE ANTERIOR PART 0F THE NECK

'49

pleura, a short distanee below its summit \.t the outer border of the first nb it beeomes the axilkrj artery.

For descriptive purposes the artery is divided into three parts. The _^rst part extends from the ongin of the vessel

to the medial margin of the sealenus anterior; the seemd portion lies posterior to that musele ; and the tkird part extends from the lateral border of the sealenus anterior to the outer border of the first rib.

First /'ar/.—Omng to the dilTerenee of origin, the relations of the first portion of the subclavian artery are not the same

250 HEAD AND NECK

on the two sides of the body. The first part of the right subclavian extends obliquely upwards and laterally, and at its termination at the medial margin of the sealenus anterior it has reaehed a point above the level of the clavicle. It is plaeed very deeply. Anteriorly, it is covered by the skin, superficial fascia, platysma, deep fascia, and three museular strata — viz., the clavicular origin of the sterno-mastoid, the sterno-hyoid, and the sterno-thyreoid. Three veins and some nerves are plaeed anterior to it. At the medial margin of the sealenus anterior it is erossed by the internal jugular and vertebral veins, whilst the anterior jugular vein, as it passes laterally under cover of the sterno-mastoid, is separated from it by the sterno-hyoid and sterno-thyreoid museles. The nerves whieh eross anterior to it are the vagus, a loop from the sympathetie (ansa subclavia), and in some eases eardiae branehes of the vagus and sympathetie as they run to the thorax. At the lower margin of the artery the vagus nerve gives off its reeurrent braneh.

The cervical dome of the pleura is both below and posterior to the artery, and the reeurrent braneh of the vagus nerve hooks round below and aseends posterior to it.^

On the left side^ the first part of the subclavian aseends almost vertically from its origin from the aortie areh, and, reaehing the root of the neek, it curves laterally aeross the dome of the pleura to the medial margin of the sealenus anterior. The relations of the cervical part are somewhat different from those on the right side. The same fascial and museular layers, and the same nerves and veins, are anterior to it. Owing to its different direetion, however, the neryes and veins are plaeed more or less parallel to it. Three additional relations are established — viz., the phrenie nerve and the left innominate vein lie anterior to it ; and the thoraeie duet first passes upwards in relation to its medial or right side, and then arehes over it to reaeh the angle of junction between the subclavian and internal jugular veins.

The reeurrent nerve on the left side hooks round the areh of the aorta, and lies to the medial side of the subclavian artery.

Seeond Part. — The seeond portion of the subclavian artery

^ If the liing has been removed by the disseetor of the thorax the lower and posterior relations should be verified by examination from the thoraeie side.

THE ANTERIOR PART 0F THE NEGK 251

forms the highest part or summit of the areh, and rises from half an ineh to an ineh above the level of the clavicle.

In this part of its eourse the vessel is not so deeply plaeed. Anteriorly it is covered by — (i) skin ; (2) superiieial fascia and platysma ; (3) deep fascia ; (4) clavicular head of the sterno-mastoid ; (5) sealenus anterior. The phrenie nerve on the right side is also an anterior relation, but it is separated from the artery by the medial margin of the sealenus anterior. Posteriorly and inferiorly^ the vessel is in relation with the pleura, Sibson's fascia intervening. The subclavian vein lies at a lower level than the artery and on an anterior plane, and is separated from it by the sealenus anterior.

The third part of the subclavian artery is deseribed on p. 151.

Branehes of the Subclavian Artery. — Four branehes spring from the subclavian trunk (Fig. 103). Three take origin, as a general rule, from the iirst part of the artery elose to the sealenus anterior, and one from the seeond part. They are —

Yertebral, 2. Thyreo-cervical

Inferior thyreoid Transverse cervical Transverse seapular.

From the J , first part. \

V3. Internal mammary. From the i ^ . . f Superior intereostal.

seeondpart. [ Costo-cervical. [Deep cervical.

In a great number of eases a braneh of eonsiderable size will be observed springing from the third part of the subclavian artery. This, in all probability, is the deseending braneh of the transverse cervical, arising direetly from the subclavian. It is so eommon an oeeurrenoe that the disseetor must always be prepared to meet it.

Arteria Yertebralis. — This is the first braneh whieh is given off by the subclavian. It springs from the upper and posterior aspeet of the trunk about a quarter of an ineh from the m.edial margin of the sealenus anterior on the right side, and from the point where the vessel reaehes the root of the neek on the left side. Only a small portion of it is seen in the present disseetion. It proeeeds upwards in the interval between the longus eolli and the sealenus anterior museles, posterior to the eommon earotid, and disappears into the foramen transversarium of the transverse proeess of the sixth cervical vertebra. It is plaeed very deeply, and is covered

252 HEAD AND NECK

anteriorly by its eompanion vein and the eommon earotid artery. Numerous large sympathetie twigs aeeompany it.

The yertebral artery on the left side is posterior to the internal jugular vein and the eommon earotid artery, and it is erossed by the thoraeie duet.

The vertebral vein issues from the aperture in the transverse proeess of the sixth cervical vertebra. It passes downwards, antero-lateral to its eompanion artery, and posterior to the internal jugular vein, to open into the posterior aspeet of the eommeneement of the eorresponding innominate vein. Near its termination it erosses the subclavian artery. It receives the deep eeruieal and the anterior vertebral veins,

Tnineus Thyreocervicalis (O.T. Thyroid Axis). — This is a short wide trunk, whieh arises from the anterior aspeet of the subclavian artery, elose to the medial margin of the sealenus anterior, and under cover of the internal jugular vein. It lies between the phrenie and vagus nerves, and almost immediately breaks up into its three terminal branehes — viz., the inferior thyreoid, the transverse seapular, and the transverse cervical.

Arteria Thyreoidea Inferior. — This vessel takes a sinuous eourse to reaeh the thyreoid gland. At first, it aseends for a short distanee along the medial border of the sealenus anterior, and under cover of the internal jugular vein ; then, at the level of the erieoid eartilage, it turns suddenly medial- wards and passes posterior to the sympathetie, the vagus, and the eommon earotid artery, to the posterior border of the thyreoid gland, where it gives off branehes to the larynx and then deseends along the posterior border of the gland, dis- tributing branehes to its substanee and to the traehea and the oesophagus.

The following branehes will be notieed arising from the inferior thyreoid artery : —

1. Aseending cervical.

2. Inferior laryngeal.

3. Traeheal.

4. Pharyngeal.

5. GEsophageal.

6. Glandular.

7. Museular.

Arteria Cervicalis Aseendens. — This small but eonstant vessel runs upwards in the interval between the sealenus anterior and longus eapitis, and gives branehes to the museles in front of the vertebral eolumn. It also gives o^ spinal branehes^ whieh enter the vertebral eanal upon the spinal nerves, and

THE ANTERIOR PART 0F THE NECK 253

anastomose with branehes from the vertebral artery. The ultimate distribution of the spinal branehes has been notieed already (p. 193).

Arteria Laryngea Inferior, — This small vessel aeeompanies the inferior laryngeal nerve to the larynx. The traeheal^ eesopha- geal, and pharyngeal branehes supply the traehea, the gullet, and the pharynx. They are of small size, and anastomose with the bronehial and oesophageal branehes of the thoraeie aorta. The glandular branehes are usually two in number. One aseends upon the posterior aspeet of the lateral lobe of the thyreoid gland, whilst the other is given to its base or lower end. They inoseulate with the eorresponding vessels of the opposite side, and also with the branehes of the superior thyreoid artery. The museular branehes are a series of irregular twigs given to the various museles in the neighbourhood.

Vena Thyreoidea Inferior — The inferior thyreoid vein does nbt run in eompany with the artery of the same name. It is a comparatively large vessel whieh eomes from the lateral lobe and the isthmus of the thyreoid gland, and deseends upon the traehea under cover of the sterno-thyreoid musele. The veins of both sides enter the thorax, and frequently unite to form a short eommon stem, whieh opens into the left in- nominate trunk. In other eases, however, the right vein will be observed to open separately into the angle of union between the two innominate veins. Both veins, as they proeeed downwards, receive tributaries from the larynx, traehea and oesophagus.

The anterior vertebral vein aeeompanies the aseending cervical artery, and opens into the vertebral vein as it issues from the foramen transversarium of the sixth cervical vertebra.

The Transyerse Seapular and Transverse Gervical Arteries. — Both of these arteries have already been examined in the greater part of their eourses (p. 147). After taking origin from the thyreo-cervical trunk, they both pass laterally aeross the sealenus anterior musele and the phrenie nerve under cover of the clavicular head of the sterno-mastoid. The transverse seapular erosses the anterior sealene musele elose to its insertion, immediately above the subclavian vein ; the transverse cervical is plaeed at a slightly higher level.

The transverse seapular and transverse eeruieal veins have already been seen joining the external jugular vein.

2 54 HEAD AND NECK

Arteria Mammaria Intema. — The internal mammary artery springs from the lower and anterior aspeet of the subclavian, direetly below the thyreo-cervical trunk. It passes downwards upon the anterior surface of the pleura, posterior to the medial end of the clavicle and the medial end of the subclavian vein, to reaeh the thorax. As it lies posterior to the subclavian vein the phrenie nerve passes from the lateral to the medial side, either anterior or posterior to it. In the neek the in- ternal mammary artery is not aeeompanied by a vein.

Truneus Costocervicalis. — This braneh takes origin from the posterior aspeet of the seeond portion of the subclavian artery, elose to the medial border of the sealenus anterior. On the left side, however, it proeeeds, as a rule, from the first part of the parent trunk. To bring it into view the subclavian artery must be dislodged from its position. It is a short trunk whieh passes upwards and posteriorly over the apex of the pleura to the neek of the first rib, where it divides into the deep cervical artery and the superior intereostal artery.

If the lung is removed from the thorax the disseetor should take the opportunity of examining this artery from the thoraeie aspeet.

Arteria Cervicalis Profunda. — This braneh passes dorsally and disappears from view between the transverse proeess of the seventh cervical vertebra and the neek of the first rib. It has been already notieed in the disseetion of the baek of the neek (p. 173).

The deep eeruieal vein is a large vessel. It joins the vertebral vein.

Arteria Intereostalis Suprema. — The superior intereostal artery turns downwards anterior to the neek of the first rib, between the first thoraeie nerve and the first thoraeie ganglion of the sympathetie. It gives a posterior intereostal braneh to the first spaee and ends as the posterior intereostal artery of the seeond spaee (Fig. 5).

Vena Subclavia. — The subclavian vein is the eontinuation of the axillary vein into the root of the neek. It begins at the outer border of the first . rib, and arehes medially on the anterior surface of the lower end of the sealenus anterior. At the medial margin of this musele, and posterior to the sternal end of the clavicle, it joins with the intemal jugular to form the innominate vein. In eonneetion with

THE ANTERIOR PART 0F THE NECK 255

the subclavian vein note: (i) that the areh whieh it forms is not so pronouneed as the areh of the eorresponding artery; (2) that throughout its whole eourse it lies at a lower level, and upon a plane anterior to the artery; and (3) that it is separated from the artery by the sealenus anterior and the phrenie nerve. In the whole of it§ eourse the vein lies posterior to the clavicle.

The sheath of the subclavian vein is attaehed to the posterior surface of the eosto-eoraeoid membrane. This is a relation of some praetieal import- anee ; for, on aeeount of it, a forward movement of the clavicle drags upon the vein, and in eases where the vessel is wounded there is always a danger of air being sueked into the vein by sueh a movement.

. The tributary of the subclavian vein is the external jugular vein, whieh joins it at the lateral margin of the sealenus anterior.

Duetus Thoraeieus et Duetus Lsrmphatieus Dexter. — The thoraeie duet is the vessel by means of whieh the ehyle and the lymph, derived from by far the greater part of the body, are poured into the venous system on the left side (p. 106). Its terminal or cervical portion is displayed in the disseetion of the neek. It is a small, thin-walled vessel, frequently mistaken for a vein, whieh enters the root of the neek at the left margin of the oesophagus. It is there that it should be sought. At the level of the seventh cervical vertebra it arehes laterally and anteriorly, and then downwards, above the apex of the pleura, and it enters the innominate vein in the angle of the union of the internal jugular vein with the subclavian. As the thoraeie duet eourses laterally it lies at a higher level than the subclavian artery, and passes posterior to the eommon earotid artery, the vagus nerve and the internal jugular vein, and anterior to the vertebral artery and vein and the thyreo-cervical artery or its inferior thyreoid braneh ; and as it runs downwards to its termination it is separated from the sealenus anterior by the transverse cervical and transverse seapular arteries and the phrenie nerve. Eurther, as it approaehes the point at whieh it ends, it erosses the first part of the subclavian artery.

A valve eomposed of two segments guards its entranee into the innominate vein.

Duetus Lymphatieus £>exter. — The right lymph duet is the eorresponding vessel on the right side, but it is a eom- paratively insignificant ehannel whieh conveys lymph from a

256 HEAD AND NECK

mueh more restrieted area. It eommenees in the posterior mediastinum, where it not uneommonly eommunieates with the thoraeie duet : and it aseends to the root of the neek

FlG. 104-— DeepDisseetionof IheRoot of1he Neek oti the Lefl Side lo show the Dome i>f ihe Pleura and the relations of the Terminal Parl of the Thoraeie Duet. The sterno-mastoid and the depressors of the hyoid and larynx have been removed.

the right side, where it terminates in the eommeneement of the innominate vein by opening into it in the angle of union of the subclavian and internal jugular veins. As in the ease of the thoraeie duet, its orifice is guatded by a double valve, Lymph passes to it from the intereostal giands wbieh lie in

THE ANTERIOR PART 0F THE NECK 257

the upper interspaees of the right side, and from the thoraeie yiseeral glands of the right side. About half an ineh from its tennination it is sometimes joined by the right subclavian and jogular lymph trunks, whieh convey lymph from the right upper extremity and the right side of the head and neek, respectively. Under these eireumstanees it eonstitutes the main lymph drain for the following distriets : ( i ) right upper hmb ; (2) right side of the head and neek ; (3) upper part of right thoraeie waD; (4) right side of diaphragm and upper surface of liver; (5) thoraeie viscera on right side of median plane, viz. right side of heart and peri- eardium and the right lung and pleura. But not uneommonly the right jugular and subclavian lymph trunks open separately into the internal jugular, the subclavian, or the innominate vein.

Oendeal Plenra. — The pleural sae of eaeh side, with the

apex of the eorresponding lung, projects upwards into the

root of the neek, and the disseetor should now examine the

height to whieh it rises, and the eonneetions whieh it estab-

lishes (see Figs. i and 5). Its height with reference to the

first pair of eostal arehes varies in diiTerent subjects. In

some eases it extends upwards for two inehes above the

stemal end of the first rib ; in others for not raore than one

ineh. These diATerenees depend on the degree of obliquity

of the thoraeie inlet. Posteriorly, in the majority of eases,

the apex of the pleura eorresponds in level with the neek

of the first rib. It forms a dome-like roof for eaeh side of

the thoraeie cavity, and is strengthened by a fascial expansion

(frequently termed Sibson' s fascia\ whieh covers it eompletely,

and is attaehed on tbe one hand to the transverse proeess

of the seventh cervical vertebra and on the other to the inner

margin of the first rib.

Note that it is in relation with : (i) the sealenus anterior ; (2) the sealenus medius; (3) the subclavian artery; (4) the yertebral artery ; (5) the costo-cervical trunk; (6) the superior intereostal artery; (7) the internal mammary artery; (8) the innominate vein ; (9) the vertebral vein ; (10) the subclavian vein; (11) the vagus nerve; (12) the phrenie nerve; (13) the reeurrent nerve on the right side; (14) the first thoraeie nerve; (15) the first thoraeie ganglion of the sympathetie ; (16) the ansa subclavia (Yieusenii).

The sealenus anterior covers the antero-lateral part of the

V0L. 11—17

35»

HEAD AND NECK

dome, separating h from the subclavian vein, whieh ends at the medial border of the musele. Immediately above the vein the subelayian artery erosses the dome below its apex. The internal mammary artery deseends from the subclavian, passes posterior to the subclavian vein, and is erossed, as it hes behind the vein, by the phrenie nerve, whieh .passes in some easesanterior to, and in others posterior to the artery.

Iltary, and Sublingual Gland

The costo-cervical arlery aseends from the subclavian and erosses the apex of the dome ; its superior intereostal braneh deseends, posterior to the apex, between the Arst intereostal nerve on the lateral side, and the first ihoraeie sympathelie ganglion on the medial aide. The vagus nerve deseends anterior to the medial part of the subclavian artery, and, on the right side, its reeurrent braneh turns round the lower border of ihe artery; the ansa subclavia lies to the lateral side of the reeurrent nerve.

PASDTED GLiSrr'

u>d liie bnn ^kt. i^ He: ii

elanu aittiT, ^e&irt jBi«j!rJu^ u Ite n

GlsndnlA Puotu. — Hie parodd gland is «edged into a raore or less triangular inlerval, the parolid s/tut, whieh is bounded anteriorly by the posterior borders of the masseter, the ramus of the roandible, and the intemal ptetygoid, and postero-medially by the anterior border of the stemo-mastoid, the mastoid proeess, the posterior belly of the digastrie, the styloid proeess, and the stylo-hyoid musele. The spaee extends upwards to the estemal ac ic meatus, and it >s prolonged downwards into t 'riangle, into whieh

26o HEAD AND NECK

the lower extremity of the gland deseends for a short distanee beyond the angle of the mandible. The gland, however, is more extensive than the spaee and passes for a yarying distanee forwatds beyond its anterior border over ihe superheial surface of the masseter.

In aeeordanee with the position whieh it oeeupies the gland tnay be deseribed as possessing three surfaces, two extretnities, and four borders. The surfaces are superficial or laleral, postero-medial, and antero-medial ; the extremities, upper and lower ; the borders, anterior, posterior, medial, and

FiG. 107.— Pari

superior. The medial border separates the antero-medial from the postero-medial surface. The anterior and posterior borders separate the lateral surface from ihe antero-medial and postero-medial surfaces, respectively. The upper border interyenes between the upper siirface and the other three surfaces.

The superficial surface is triangular in outline (Fig. 1 05). It is covered by skin, superficial fascia, platysma and risorius, and deep fascia. Embedded in it are a few superficial parotid lymph glands, whieh receive lymph from the anlerior part of the sealp, the face above the !evel of the mouth, and froni the lateral surface of the auriele. Posteriorly, it is in relalion with the mastoid proeess and the anterior border of

PAROTTD GLAXP rti

the stemo-mastoid mosekL Aberrt. :t z'jD'.rjtSr ±»t T«:si*r-i:ir part of the lower border of tbe zy^'j:iii. LZii u^ ^i'Ter sirii;::^ of the extemal meatus^

From beneath the pait zzi eeeiiae: "wtit. ii.'t r"r'-»iiii. tnntnr-t ihe aurieulo-temporal nerre. ibe t£z:i»:rLl iirLnLrji:f :c mt facial nerve, and the super^eiil lempiril ^^t:ry. in. iirsr vr3 i: the sealp ; and the posterior far:?.' Tt^i. CJ5L.t«p»f:ir* iriiDir in.'^tr of it. Its lower eitremitT, wbiei is we^irei 'iteriet:*::! li**: ^rieiir of the mandible and the anterior bieDrr :c lii*: s:*r:i:-ii;2siinc- is usually in eontaet with ocke ti ir.e '^^^K^ 6t?t-: Krratil glands, whilst the posterior fajcial Ttdr. irit -'r-^ -^^r-.*^^' 'x the extemal jugu]ar Tein, and the oerTS-:aZ 'iirij:i±. :c nerve emerge from it : the forn:er ys^^kr^ orjwz: posteriorly, and the two latter dowewsLrdr irjC ir.i*ri:r}T-

From beneath the ^Lnttnor bOTOer, TLi"^ rt?s:i tC'CJc: dbe masseter, the duet of the gland /Seernierii^ ±rf: trsssrsrse facial artery, and the zygoma2k:. b!XX2LL ^riid ^g^ierr/iugr branehes of the laeial nerre pass rorwards : irid tie tstaspen* facia] vein disappears under eorer ^A ii,

The due^ of t?ie parotid j^md 4Ste:i5er.'i t, '^Js 2g.9SEriasr from under cover of tbe anteiior border oc tryt gui^wi nra anteriorly aeross the masseter. at tiiC krrcC 'A sl lisae criwx from the lobule of the anriele to a j»c3t sbtoLreid aaaewT between the red margin of the rs^^ '^ 2sc ia>t ala of the nose. At the anterior border of tlt: ixj2JMfx: :t rsr» inwards, at right angles to its fonner eoer^ aa: ii» yjK^je:^ the sueking pad of fat, the hueeinaior iasda, di«t 'T>3cjcarjat<w' musele and the mueous membrane rX tbe Tt$tix«it *:/ ti*t mouth, it opens into the restibale, on the a;« <rj a yst^l^ opposite the seeond molar tooth of tbe maxi]b,

Immediately anterior to the 3nxenoT \^/rdtT ^A t3>t ?5aw3, below the zygoma and above the daet, lies a saaaH «r^OMsS^S portion of the gland substanee ealled the aeeesu^ par^^^ 3t% duet opens into the main duet.

£>£ssectum.—The gland mnst bc remored ytau:ssja^ « •-ii^: trru!r.i^*a whieh pass through it are diweeted oot. The fuiaJ BitTre asri iU 'mw^ are the most superficial struetiires io the satAta&ee 'A ihn \at'f:A ? ti-er^^^ they must be disseeted first. Traee the termaal lnajcha yjifjtTjr^n ^^-'^ the gland until they j<Mn the main dirisioos, v1dca axe ibt u^r -^ Um;^^'^ facial and the lower or eermeo'^aeiai. The tem|wrai ajyi tr^x:^x, 'x^r^ spring from the temporo-£u3al dirisioo, theUioeal, a&a£*f:':^iifer, i'^ o^i-^i from the cervico-fecial divisioii. FoIlaw the ^amifXA yM^*x,j ^'ff^ the posterior isieial vein-to their mnoD with the tnmk 'A t^ r>tnr% »?/xi pierees the postero-medial sm^Mre of tbe g^and ; then tra<:^ tbs: tr«.ii ^:i'm

11—17 6

262 HEAD AND NECK

the root of the styloid proeess to the stylo-mastoid foramen and seeure the braneh whieh springs from it to supply the posterior belly of the digastrie and the stylo-hyoid museles, and the posterior aurieular braneh. As the trunk of the nerve is being eleaned the posterior aurieular braneh of the external earotid artery will probably be exposed, passing upwards and posteriorly along the upper border of the posterior belly of the digastrie to the baek of the external meatus, and erossing either superAeial or deep to the nerve. Next, remove the deeper parts of the gland and expose^the posterior facial vein, deseending towards the angle of the mandible. It receives the trans- verse facial and the internal maxillary veins, and it gives off the eommenee- ment of the external jugular vein ; and then it passes out of the lower end of the gland and unites with the anterior facial vein to form the eommon facial vein. Deep to the veins will be found the upper end of the external earotid artery dividing into its superficial temporal and internal maxillary branehes ; and the transverse facial and middle temporal offsets of the superficial temporal will also be displayed.

When the remains of the deeper part of the gland have been removed, the styloid proeess with the origin of the stylo-hyoid musele, and the posterior belly of the digastrie will be exposed ; and the internal jugular vein and the internal and external earotid arteries will be seen disappearing under cover of the digastrie. If the oeeipital artery lies at its lower level, it also will be noted as it runs upwards and posteriorly, along the lower border of the digastrie, erossing superficial to the two large vessels, and to the aeeessory nerve, whieh emerges from under cover of the digastrie and passes downwards and posteriorly aeross the internal jugular vein.

The disseetor should now obtain a gland whieh has been removed uninjured from the parotid spaee, or a east of a gland, and proeeed to study the relations of the upper end and the postero-medial and antero-medial surfaces.

The upper extremity presents a deep concavity whieh is usually separable into a larger lateral part whieh lies in eontaet with the eartilaginous part of the external meatus, and a smaller medial part whieh touehes the bony wall of the meatus (Fig. 109). The anterior boundary of the upper end forms a sharp ridge, whieh lies in the narrow interval between the eapsule of the temporo-mandibular artieulation and the front of the external meatus.

Tht postero-medial sufface is marked by a series of depres- sions whieh eorrespond with the struetures in the postero- medial boundary of the parotid spaee. Above is a shallow depression eorresponding with the anterior border of the mastoid proeess, and below the latter a groove eaused by the anterior border of the sterno-mastoid. More medially is a shallow depression due to the posterior belly of the digastrie and the stylo-hyoid, and, still more medially and at a higher level, a suleus whieh eorresponds with the position of the styloid proeess. Below the level of the digastrie groove the postero-medial surface covers portions of the internal jugular

PAHOTID GLAXD ri;

vein and the intemal a«i ensmil ci-:oz irisns. Tri eoiiimeneement of the eiterru; ."^^^ii-r ^r. :rt ;«:!s;iri:r facial vein, aod the eerrieal b*5i>cr. :?' :!■; ir^ t-tn-i -.irtrrt from this part of the sDTface. Iic=:*cii:=.'; i.ZK-- zzk :,-si=r^z groove, elose to the medu] t'itee. lii-t o.:t^=i:- xir:c.i; =Ci=» the gland ; and direetly U:era! :c :r* =7«- =■! :t tr-t ir:':'^ for the styloid proeess the facil :*rre ^a^^^s =:: :i>t e^rii substanee. The disseetor shocJc :xr^ iLii :bt j<'jKE-:-2:*fi surface of the gland is sepaiated ^-e ii ;; t« ^ura :c '^ut internal jugular vein and the interr-a^ eario: ir^sry. i-e T-jn

PDslen>Hiwi]u} bcnlrrvf ^po'a^^

the last four eerebral nerves by the posteiioT beily ol ti^ digastrie, the styloid proeess and the mnseks aiatiitd t& n.

The medial border of tbe gland lies in tke an^ hetwttn the postero-medial and the anterim bonntlaiies of tbe ;a;rx3d spaee, where the styloid proeess, the stylo.|iyoid mm'^ a.-jd the posterior belly of the digastrie disppear tmder eorer ol the posterior border of the intemal pterygoid mnsde: and from it a proeess, ike pterygind khe, nsitally proieets zi'jmj^, for a short distanee, between the intemal pttrygoid arai tbe inner surface of the lamus of the mandible Tlirough the base of this proeess tbe exienial earotid passes fr'ym the postero-medial to tbe antero-medial mi&ee of the gland.

Tke AnUro-meMal Snr/aee.- — Tbe medial pait <A the

264 HEAD AND NECK

antero-medial surface is direeted anteriorly and Hes in relation with the lower part of the posterior border of the internal pterygoid, the stylo-mandibular ligament, and tbe posterior border of tbe ramus of the mandible. The more lateral part is direeted medially and rests against the lateral surface of the masseter. This surface is piereed (i) by the external earotid artery, {2) ihe posterior facial and the internal maxil!ary veins, {3) all the terminal branehes of the facial nerve except the cervical, and (4) by tbe duet of the gland.

As the disseetor examines the parotid spaee he will note that as the external earotid disappears under cover of ihe

FiG. 109.— ParotidGland, amero-medial aspeet.

posterior belly of the digastrie it is plaeed so far anteriorly that it is also under cover of tbe posterior border of the mandible ; and it does not emerge from under cover of the mandible until it reaehes the level of the neek of the bone, wbere it appears on the antero - medial surface of the gland and divides into its two terminal branehes. Purther, he will now readily reeognise tbe impossibility of studying the upper end of the cervical part of the internal earotid, the upper part of the internal jugular vein, and the last four eerebral nerves, until he is in a position to reflect the posterior belly of the digastrie and the styloid proeess ; and as both of them are, to a eertain extent, under cover of the

TEMPORAL AND INPRATEMPORAL REGIONS 265

mandible it is obvious that the mandible must be removed. This will be done during the disseetion of the temporal and infratemporal regions, whieh must now be proeeeded with.

TEMPORAL AND INPRATEMPORAL REGIONS.

Fa£cia Temporalis. — The temporal fascia is a strong glistening membrane whieh is stretehed over the temponU fossa, binding down the temporal musele. Its upper margin is attaehed to the upper of the two curved lines whieh eonstitute the temporal ridge on the lateral aspeet of the skull, and anteriorly to the temporal line of the fronta] bone. As it approaehes the zygomatic areh, it splits into two laminae, whieh are separated from eaeh other by a narrow interval filled with fat. The two laminae are attaehed one to the upper border of the zygomatic areh and the posterior border of the zygomatic bone, and the other to the medial surfaces of these two portions of bone. They ean readily be demonstrated by dividing the superficial layer elose to its attaehment, and throwing it upwards ; by the handle of the knife the attaehment of the deep layer ean then be made out In the upper part of its extent, the temporal fascia b eom- paratively thin and the fibres of the subjacent musele may be seen shining through it ; below, it is thieker, and owing to the fat whieh is interposed between its laminae, it is perfectly opaque. It is piereed immediately above the posterior part of the zygomatic areh by the middle temporal braneh of the superficial temporal artery and by the middle temporal vein (p. 157).

Museulus Masseter. — The masseter is a massive quadrate musele whieh covers the ramus of the mandible. Its fibres are arranged in two sets — a superficial and a deep. The superficial part of the musele arises A-om the anterior two- thirds of the lower border of the zygomatic areh, and its fasciculi are direeted downwards and posteriorly. The deep part springs from the whole length of the medial aspeet of the zygomatic areh, and also from the posterior third of its lower border. Its fibres proeeed downwards and anteriorly. Only a small pieee of the upper and posterior part of this portion appears on the surface. The masseter is inserted into the lateral surface of the ramus of the mandible, over an area

266

HEAD AND NECK

whieh extends downwards to the angle, and upwards inelude the lateral aspeet of the eoronoid proeess.

Disseetim. — To display the temporal musele, and at the expose the nerve and artery of supply to the masseter, make the foI disseetion. Divide the deep part of the temporal fascia along the border of the zygomatic areh and remove it. The middle temporal and the ^Ygomatirn-^^rpp^yal "^gy^i whieh pieree it, must be dis ^ from it ana preserved. The zygomatic areh, with the attaehed i must next be thrown down by dividing the bony areh anterior and to the origin of the musele. First make use of the saw, and then the division by means of the bone forceps. The posterior eut sh< made immediately anterior to the mandibular (O.T, glenoid) the head of the lower jaw ; the anterior eut must extend obliquely the zygomatic bone, from the extreme anterior end of the upper mi the areh, downwards and anteriorly to the point where the lower meets the zygomatic proeess of the maxilla. When the division pleted, and the nerve and artery to the masseter are divided, the areh and the attaehed masseter may be readily thrown downwards the angle of the mandible. The Aeshy origin of the deep the masseter from the medial surface of the zygomatic areh ean seen. The disseetion is frequently eomplieated by a number of fibi the temporal musele joining this part of the masseter. In turi masseter down, its nerve and artery of supply must first be cl< they pass laterally through the ineisura mandibulse (O.T. sigmend posterior to the tendon of the temporal musele. Leave the attaehed to the angle of the jaw and elean the temporal musele.

Museulus Temporalis. — The temporal musele is fan- It arises from the whole extent of the temporal fossa, lower of the two lines whieh eonstitute the temporal ri< the infratemporal erest on the great wing of the sphi It receives additional fibres also from the deep si the temporal fascia. From this broad origin the converge towards the eoronoid proeess of the man< The anterior fibres deseend vertically, the posterior fil iirst pursue a nearly horizontal eourse, whilst the intemu fasciculi proeeed with varying degrees of obliquity. approaehes its insertion, a tendon is devel8ped u] superficial aspeet, and this is inserted into the summil anterior edge of the eoronoid proeess. The deep part musele remains Aeshy, and gains insertion to the surface of the same bony prominenee by an attaehment reaehes as low down as the point where the anterior m\ the ramus merges into the body of the mandible. The tion eannot be fully examined at present ; it will be dealtj later.

Disseetion. — Detaeh the eoronoid proeess from the mandible, it upwards with the attaehed temporal musele. A very oblique

TEMPORAL JkXI> I

nnelei eora di ibe ^b9- pMe •■ Ac SH^

tetnpotst ioBsa. 11»

anrGme to Iblkrar the give brondUB to ihe M □f the tempanl beae. tiaeed to tiw \riaL a

d SOTfaoeirf thg j|;fifl8

iif the temponl

The iDRatimpanl n^ opened ap by leidantng* )« lontal euu Dnssi be iB»ik ^mt An^^ I Dthei imnudmelT alM*e ik leHd «f tte rorsDien. Tolnd tlielc:Mla<tk> thruu between Ibe

a]veolai

Parts diqliTel br tt* akom DiMetta.— When tbe &i

ajid areobr tissae are nniKrml, tbe pleiygtMl attielei wID eome iDto riew. The t^irrmU ptrrygaid exlcnd* tutrieontall; to the oeek «r the maDdilile. Tbe imttrmd ptrryg/id, «nbrae- ing the antenor pait of th^: eUtanal plerygtitd intuiele betwern its two heads of oi^n, proeeetb doirnwards and ptMleriarly ■ upon the deep sur&ee uf ibe nuous uf tbe mandible. It I bears ver7 mud) ihe sain« relatko [£> the mnlial atpeirt »f the ramus tbat the masaeter preseuls to its lotetal lurbei^ The greal btood iressel of the spac« — Ibe inttrmU maxi!lary trttry — proeeedi anteriorly tipoa (frequc»t]y under cover <rf> ihe estemal pter):goid mnsele. Thc ttertts tif ihe rt^giiin obo will be found in elose tebtionsbip to llie >ufnc tnusdr. Thm, emei^ng froia between itt Upper border and thi: i:ninLil wiill, at the levei of die tnfratt;tnpofaJ iwsi, are ihe masi/ttrie and the two dtt/ tempora/ ruroa ; appeaiio]; fn>ai iindtr t?oTer of its iower ttorder are llte in/erior ahMtiar and the Sngnai Herves; whilsi the auriewi^ee>i^ft>ral nnrr ts nilaied lo iu medial sutfacc posierkrly and Uii: bttidnater iurtx anienori^. i

368

HEAD AND NECK

The fonner appears posterior lo the temporo-mandibular joint, and the bueeinator nerve either pierees it or emerges from between its two heads of origiii. The spheno-mandibulM- ligament also will be seen. It is the thin strip of membraiie whieh lies medial to the inferior alveolar nerve.

MnseulaB Pterygoidens EAeniiis. — The extemal pterygoid

arises ir the infratemporal fossa by two heads, an upper and a lower. The upper head springs from the infratemporal ridge and surface of the great wing of the sphenoid; the lower head takes origin from the lateral surface of the laieral pterygoid lamina (O.T. external pterygoid plate). The musele diminishes in width as it passes posteriorly, and it is inserted into the fovea pterygoldea on the anterior surface of the neek of the mandible, and also into the anterior margin of the diseus artieularis of the temporo-mandibular artieulation.

TEMPORAL ANi' :n57l-.ti::: ! }_^

Mnsenlns PteiTSOide^ IrT«Erc£ — T'* . -.. - : also is bieip::^: i: i'.s -r '.:-::- -v • . :. origin of ihe "..-^t: r.'r.i ' :: . • "- superficiai and sn:i:!tr : --• . ' :■ - ■.".:. - . . - ^ from the io'A-er ar.d y^-t^ .' -.^. *■. . ■

maxilla, and :i:s-^ :.':zi ir.t .----:--: : ■• . " ...

proeess 'O.T. :u':.-er::::; .: :-t ::..::- ■• ■-. ■ - - - . ..^ hidden bv tl':e e.x:trr-2^ ::-:^.z: i Lr.:-r: • ■-:--: . fossa from ihe r:.t:i.\2L :">r:i:-: :■:■-. ..-.-. : -. - . . .:.:. -

and from ihe surt'aee :■: :r.r :_■*:":_•-. :* -'r ■ -. : -

bone whieh apr-ear? 'r.n'.'^rir. :i- :v " :~ : : ..— ■.■ The two heads c: ihe rr.-^5.:.i -.-:.:z i- :■ -. v:- ■/..-:.- - anterior part of ihe tir.tT"^ y.-—z'. - :." : ■ : ■ * :- ■ •••: downwards wiih a ;■:?:-:: -!::■:': - -.: - :.* : :.. " insertion into ihe ar.r^e :: :.":■= ::\:.-^. -.. l* i .• .• -. v ■- and posterior par: :f \:.t :: t i-i Lne." :•' ■.:•: -:.r: l: t: high as the manGib--:i: f:ri:::t.'-

Arteria MaTillaris Intena. — T-.-i -r; .- .. .:«-. i:-:r \ the two lerminal brar.er.ts :f :it ti't^.i. ji.-:':i1 i.^--.— takes origin in:mecia:t:y p':--':tr. : - :: -_:-: •.-.-; ::#-

mandible andproeeeds c.r,:tr.:r;; :: '-i-: l-:--^!:' :;l.- ' ::i- infratemporal fo55a- where :: disipi'tri--: '":'r -■^-•v '■ «-^r -; between the two heads of irigi.-: :c i^t tir.tr-.;*. y.^j . ii musele and enterins :r.t '•-•^r'-'i=iA'^ "-* '.':-:-i- l ;. divided into three ps-ns f:r •::r.-.t--.:::.'::t :' v.:»:':rr.r. T':»^ first part runs horizonia::v '>::Trtf.': *.::■: "..r:!. :-" ::i- r^i.-i:;: n- and the spheno-mar-dii'.::^^ ii'Lnt.-.: Z: r:: i.r.r^ ::,-. lower border of ihe pos^en^r ;.;i.-: :f v_t ti^t-T.i. :-.t^-::'i: musele, and usually erosses :Le :.i:*ri:r s--.t;:.i/ -.itnt :.:::rr ficially. The sec(md part tr:tz.Zi :•:.:-. i^-i; ::'Vi.--.: i.-i: anteriorly upon the Ia:enil s'^kr^t 'A '^xi •::-.-:^*.i. ^r.rry.u', musele, under cover of ir.t \zj^rL'.z. "A "L-^t '.rr: :•:'-*. :: -t .1-. The third part dips hti'Kttri ^r.t :t^ bts.ii :>•' -.^rt *r:.-tr-;i. pterygoid into the pierygo-p&Ji:;r-e f-.Aii-

This is the most htrrutr.i ATrs.r.^rfZj^r- 'js. r. .■: -r.r uneommon to find the seeone par: :f ::-jt ir:tr;. -r.-i :: • deeper plane, viz. between t:^.t i.':*jtrr-a: ir-i t-r--rr-:i.. :r.*r;;:«.: museles. In that ease the ves5<t: r- ?*■*;■ i -^r^ii .i.:— i. ■ between the heads of tbe exterr-il ^etri^'-'^i .:- ^y.r- * -.: appears on its surface before er.itrir-s: V..* ^»:*r;T>Vii ■'"''•- fossa.

The branehts of the intemal maxi:'-^'~* antr irt :iS.-j-. 'r--:

270

HEAD AND NECK

aeeording to the portion of the vessel from whieh they spring. Only one braneh of the third part, viz. the posterior superior alveolar artery^ ean be studied in this disseetion. Those arising from the first and seeond parts are : —

From the First Part. 1. Arteria aurieularis profunda. 2. Arteria tympaniea. 3. Arteria meningea media. 4. Ramus meningeus aeeessorius. 5. Arteria alveolaris inferior.	From the Segond Part.
1. Arteria masseteriea. 2. Rami pterygoidei. 3. Arterise temporales profundae. 4. Arteria bueeinatoria.

The Deep Aurieular Artery, — This small vessel pierees the anterior wall of the external aeustie meatus to supply the skin whieh lines it, and also the superficial part of the tympanie membrane.

The Meningeal and Tympanie Branehes proeeed upwards under cover of the external pterygoid musele, and, therefore, eannot be fully studied until that musele is reflected.

The In/erior Aheolar Artery arises opposite the middle meningeal, and runs downwards, upon the spheno-martdibular ligament, to enter the mandibular foramen. It is generally aeeompanied by two ven8e eomites, and it is plaeed posterior to the inferior alveolar nerve. Just before entering the foramen, the inferior alveolar artery gives off the slender mylo'h^oid' braneh, whieh is earried downwards and anteriorly, with the eorresponding nerve, upon the deep aspeet of the mandible, to the digastrie triangle of the neek.

The branehes from the seeond part are given off for the supply of the neighbouring museles. The Masseterie passes horizontally, posterior to the temporal musele, with the nerve of the same name, and has been seen entering the masseter musele. The Ptery^oid Branehes^ are irregular twigs to the pterygoid museles. The Deep Tempgral JSranches are two in number — anterior and posterior\ they pass upwards in the temporal fossa, between the bony wall of the eranium and the temporal musele. They supply twigs to the temporal musele, and they anastomose with the middle temporal artery. The Bueeinator Braneh aeeompanies the bueeinator nerve, and

-| II ■! I ■■ I I II I •• '' '

is distributed to the bueeinator musele and the mueous

TEMPORAL AND INPRATEMPORAL REGIONS 271

membrane of the eheek. It anastomoses with the external maxillary (O.T. facial) artery.

The PosUrior Su1>erior Alyeolar Braneh, from the third part of the internal maxillary artery, deseends upon the posteriolr aspeet of the maxilla, and sends branehes through the alveolay . eanals of the maxilla for the supply of the upper molar and praemolar teeth (Fig. iio). Some small twigs go to the gum and others supply the lining membrane of the maxillary * sinus.

Pterygoid and Intemal Maxillaxy Yeins. — The veins in this region are very numerous, but they eannot be studied satisfactorily in an ordinary disseetion. They eonstitute a dense plexus, termed the ptery^oid pleoeus^ around the external pterygoid musele. Tributaries eorresponding to the branehes of the internal maxillary artery open into this network, whilst the blood is led away from its posterior part by a short wide trunk, ealled the internal maxillary^vein. This vessel aeeompariies the first part of the internal maxillary artery into the parotid gland, and joins the posterior facial vein behind the neek of the mandible.

The pterygoid venous plexus is eonneeted with the cavernous sinus by an emissary vein. It eommunieates with the inferior ophthalmie vein, through the inferior orbital fissure, and with the anterior facial vein by an anastomosing ehannel ealled the deep facial vein whieh deseends aeross the external

surface of the bueeinator musele.

Artic\ilatio Mandibularis. — Before the external pterygoid musele is thrown anteriorly, the temporo-mandibular joint must be examined. It is a diarthrodial joint of the ginglymus type, and its cavity is separated into an upper and a lower part by a diseus artieularis. In eonneetion with it there are the following ligaments : —

LlGAMENTS PROPER.

ACCESS0RY LlGAMENTS.

[. Cfl.psnle. I. Spheno-mandibular.

5. Temporo-mandibiilar. | 2. h)iylo-mandibular.

I. Cai^

nporo-mandil

Diseus Artigularis.

The eapsule eneloses the joint cavity. Above, il is attaehed • posteriorly, laterally, and mf ' ** margin of the man-

212 HEAD AND NECK

dibular fossa, and anteriorly to the anterior margin of the artieular luberde. Below, it is attaehed to the neek of the mandible ; and between its uppsr and lower attaehments it is eonneeted with the margins of the diseus artieularis.

The Umporo-mandibular Itgament {O.T, txtemal laterat) is a strong triangular band whieh is attaehed above to the lateral surface of ihe posterior part of the zygoma aryd to the tubeteie at the root of the zygoma. Its fibres run down- wards.and posteriorly to the neek of the mandible.

The spheno-mandibular ligament {O.T. internal lateral) is a long membranous band whieh extends from the spine of the sphenoid to the lingula and to the sharp medial margin of the

Styloid pr..a

\ ""'"'"■^' FiG. III. — Seetion Ihrough Temporo-mandibular Jomt,

mandibular foramen. It is not in direet relationship with the joint. Above, it lies medial to the external pterygoid musele and the aurieulo-temporal nerve; lower down, the intemal maxillary yessels intervene between it and the neek of the mandible ; whilst, still lower, the inferior alveoIar vessels and nerve are interposed between it and the ramus of the mandible.

The stylo-maniibular ligament has been notieed already. It is a fibrous band, derived from that portion of the deep cervical fascia whieh forms a part of the eapsule of the parotid gland. It is attaehed above to the styloid proeess, and below to the angle and posterior border of the ramus of the mandible, between the internal pterygoid and masseter museles.

An examination of these ligaments will show that veiy

TEMPORAL AND INPRATEMPORAL REGIONS 273

«* — ^^'•»

little is added to the strength of the joint by their presenee. The seeurity of the joint depends not so mueh upon its liga- ments as upon the strong museles of mastieation, whieh keep the head of the mandible in its plaee.

The diseus artieularis is an oval plate of fibro-cartilage, with its long axis direeted transversely. It is interposed between the eondyle of the mandible below and the mandibul^r fossa (O.T. glenoid) and the artieular tuberele (O.T. eminentia artieularis) above, and it divides the joint cavity into upper and lower parts, eaeh of whieh is provided with a separate synovial lining. To expose the eartilage, the temporo-man- dibular ligament must be removed. The dise will then be seen to be adapted to the two bony surfaces between whieh it lies. Above, it is concavo - convex in eorre- spondenee with the tuber- eulum artieulare and the mandibular fossa of the tem- poral bone; whilst below, it is concave, and fits upon the upper aspeet of the eon- dyle of the mandible. In the eentre it is thin, and in

SOme eases it is perforated. p^. 112.— Diagram of th^ different ItS circumference is thiek, positions oeeupied by the head of the more espeeially pOSteriorly. niandible and the diseus artieularis xx 1 u i_ \. j 1 ^\\ as the mouth is opened and elosed.

It should be noted also that

the external pterygoid musele is partly inserted into its

anterior border.

The synovial stratum whieh lines the eapsule enelosing the upper cavity of the joint is of greater extent and looser than that of the lower eompartment. This is in assoeiation with the larger size of the artieular surface of the temporal bone as eontrasted with the eondylar surface.

Moyements. — The movements whieh the mandible ean perform at the temporo-mandibular joint are the following : — (i) depression ; (2) elevation ; (3) protraetion ; (4) retraetion ; (5) lateral or ehewing move- ments. When the mandible is depressed the diseus artieularis and the eondyle move anteriorly on the mandibular fossa, and the eondyle finally takes up a position on the tubereulum artieulare. This forward gliding of the dise and eondyle in the upper eompartment of the joint is aeeom- panied by another movement ''^wer eompartment of the joint,

VOL. II — 18

2 74 HEAD AND NECK

whieh eonsists in a rotation of the eondyle of the mandible on the lower surface of the artieular dise. Elevation of the mandible or elosure of the mouth is brought about by a reverse series of ehanges in both eompartments of the joint. Whilst these movements are going on, the mandible rotates around a transverse axis whieh traverses the bone in the neighlwurhood of the mandibular foramen. This is the point, there- fore, of least movement, and consequently in opening and shutting the mouth the inferior alveolar vessels and nerves are not unduly stretehed. In protraetion and retraetion the movement is chiefly eonBned to the upper eompartment of the joint, and the eondyle of the mandible with the artieular dise glides anteriorly and posteriorly upon the temporal artieular surface. In the lateral movements of the jaw the mandible is earried alternately from side to side, as in the proeess of ehewing.

The museles on eaeh side whieh are chiefly engaged in produeing these movements are the following : — (i) depressors — the platysma, the mylo- hyoid, and the anterior belly of the digastrie ; (2) elevaiors — the masseter, internal pterygoid, temporal ; (3) protraetors — the external pterygoid, and to some extent the internal pterygoid and the superlieial fibres of the masseter ; (4) retraetor — the posterior fibres of the temporal and the deep iihres of masseter ; (5) lateral fnovement is produeed by the museles of opposite sides aeting alternately.

BeAeetion of Ezternal Pterygoid. — The eondyle of the mandible must now bc disartieulated and thrown anteriorly with the attaehed external pterygoid musele. It is well to detaeh the diseus artieularis with the head of the bone, in order that it may be more thoroughly examined. Care niust be taken not to injure the aurieulo-temporal nerve, whieh lies in elose proximity to the medial asp'^t ol Tli^^Sint. When the dis- artieulation is eomplete, the musele may be displaeed anteriorly by gently pushing the eondyle under the internal maxillary artery.

The rcflection of the external pterygoid musele brings into view, after a little disseetion, the mandibular division of the trigeminal nerve, emerging from the foramen ovale, and breaking up into its branehes of distribution. The slender diorda tympani will be found proeeeding down- wards and anteriorly to join the lingual nerve ; and the middle meningeal, tyuipauie^ and aeeessory meningeal arteries may be traeed to the points where they leave the infratemporal region.

ArteriaB Meningea Media et Tympaniea and Bamus Menin-

geus Aeeessorius. — The middle ineningeal artery has already heen seen arising froni the first part of the internal maxillary artery. It proeeeds upwards, medial to the external ptery- goid musele and lateral to the tensor palati, and disappears from view through the foramen spinosum, by whieh it enters the eranial cavity (p. 212). It is usually embraeed by the two roots of the aurieulo-temporal nerve.

The aeeessory meningeal artery and the tympanie artery generally arise Trom the mieklle meningeal. The aeeessory meningeal inelines anteriorly and upwards, and enlers the eranial cavity by passing through the foramen ovale ; the tympanie runs upwards and posteriorly, and reaehes the lympanum by passing through the petro-tympanie fissure (O.T. Glaserian). In the tympanie cavity it anastomoses with the styloid-mastoid braneh of the posterior aurieular artery.

TEMPORAL AND INPRATEMPORAL REGIONS 275

Hemis MtuidibiilariB. — The mandibular braneh of the trigeminal nerve arises within the eranium from the semilunar (O.T. Gasserian) ganghon, and enters the infratemporal region through the foramen ovale. It is eomposed of sensory fibres, but it is aeeompanied through the foramen by the small ntotor root of the ttigeminal nerve ; and by the union of the sensory and motor parts, immediately after they gain the exterior of the eranium, a mixed nerve-trunk

TiG. 113.— Diagram of Mandibular Nerve. By Prof. A. M. Paterson.

resuits. This nerve-trunk lies medial to the external pterygoid musele and lateral to the tensor palati, and after a very short eourse (not exceeding 5 mm.) it ends by dividing into two parts, named the anterior and posterior dmsions of the mandibular nerve (Fig. 113).

The trunk of the mandibuiar nerve gives off two branehes before it divides, va., (1) nersus spinosus (O.T. reeurrent nerae), 3"d (z) the nerve to the internal ptpryi-piH nm'mplp

The neruus spinosus is a very slender twig whieh enters

2 76 HEAD AND NECK

the eranium by aeeompanying the middle meningeal artery through the foramen spinosum. It supplies the dura mater.

The neroe to the internal pterygoid will be found passing under cover of the posterior border of the internal pterygoid musele at its upper end. In elose relation to the root of this nerve is the otie ganglion,

From the two terminal diyisions of the mandibular trunk the chief branehes of distribution arise. The anterior diyision is mueh the smaller of the two, and is eomposed almost entirely of motor iibres derived from the motor root of the trigeminal nerve. The only sensory iibres whieh it eontains are those whieh form the bueeinator nerve, It gives off the following branehes : —

i;__Mass£teiic.

2. Two deep temporal.

3. External pterygoid. 4.nBuccinator.

The large posterior division is chiefly sensory. It eontains only a very few fibres from the motor root, and these are prolonged into its inferior alveolar braneh, and afterwards eome off in the form of the mylo-hyoid nerye, The branehes of the posterior division arel ( i ) aurieulo-temporal ; (2) inferior alveolar ; (3) lingual.

Neruus Masseterieus, — The masseterie nerve runs hori- zontally above the external pterygoid musele, and, passing through the ineisura mandibulse (O.T. sigmoid noteh) posterior to the temporal musele, it enters the posterior and upper part of the deep surface of the masseter. Before reaehing the masseter it gives one or two twigs to the temporo-mandibular joint.

Nerui Temporales Profundi, — There are usually two deep temporal nerves, anterior and posterior, The posterior nerve is the smaller of the two ; it frequently arises by a eommon root with the masseterie. Both deep temporal nerves pass laterally above the external pterygoid, and then turn upward on the medial wall of the temporal fossa. They supply the temporal musele.

Neruus Buednatorius. — The bueeinator nerve (O.T. long bueeal) is the largest of the branehes arising from the anterior division of the mandibular nerve. It proeeeds laterally between the two heads of the external pterygoid musele, and then runs downwards and anteriorly under cover of the temporal musele, and under cover of the anterior

TEMPORAL AND INFRATEMPORAL REGIONS 277

border of the masseter also, to reaeh the outer surface of the bueeinator musele. There it unites with branehes of the facial nerve to form the bueeal plexus^ from whieh branehes are distributed to the mueous membrane and skin of the eheek.

The bueeinator nerve is a sensory nerve, and all the sensory fibres in the anterior diyision of the mandibular nerve enter into its eomposition. A few motor fibres, however, are also prolonged into it; these eome off from it in two branehes, viz., (i) in the nerye to the extemal pterygoid. whieh, as a rule, arises in eommon with the bueeinator nerve ; and(2) in a third twig of supplv to th^ tpmpnral mnsHe. This temporall)ranch springs from the bueeinator nerve, after it has reaehed the lateral surface of the external pterygoid, and proeeeds upwards to supply the anterior part of the temporal musele (Fig. iio). In some eases the bueeinator nerve pierees the temporal musele instead of passing under cover of it.

Nervus Aurieulo - Temporalis. — The aurieulo - temporal nerve springs by two roots from the posterior division of the mandibular nerve, under cover of the external pterygoid. The two roots are eomposed of sensory fibres and eaeh receives a eommunieation from the otie ganglion, by means of whieh it is brought indireetly into assoeiation with the glosso- pharyngeal nerve. The roots embraee the middle meningeal artery, and unite posterior to it to form a stem whieh runs posteriorly between the neek of the mandible and the spheno-mandibular ligament. At the interval between the ear and mandible it turns upwards, in relation to the deep surface of the parotid gland, erosses the zygoma in eompany with the superficial temporal artery, and enters the sealp, where it breaks up into terminal branehes.

Its branehes are : (i) one or two strong branehes of eommunieation t^ thf r^"npr^r/yfani<ii nprv^; (2) a few slender filaments whieh enter the posterior aspeet of the temporo- mandibular joint ; (^ some twigs to the parotid gland ; (4' terminal filaments to the skin over the temporal regiori ant summit of the head ; (5) aurieular branehes.

The aurieular branenes are usually two to the skin lining the interior of the external meatus, and iwo to the integument over the upper and anterior part of the auriele. The former gain the interior of the meatus by passing between the osseous and eartilaginous portions of the eanal.

Nennis Alveolaris Iiiferior. — The inferior alveolar nerve

II— 18t

2 78 HEAD AND NECK

(O.T. inferior dental) is the largest braneh of the mandibular nerve. Emerging from under cover of the external pterygoid, at the lower border of the musele, it passes downwards upon the spheno-mandibular ligament and enters the mandibular foramen. The inferior alveolar artery runs downwards posterior to it, whilst the lingual nerve is anterior to it and upon a somewhat deeper plane. The inferior alveolar is a sensory nerve, but a few iibres from the motor root are prolonged downwards within its sheath as far as the mandibular foramen. At this point they eome oflf as the slender mylo-hyoid nerve.

The mylo-hyoid nerue, aeeompanied by the artery of the same name, pierees the spheno-mandibular ligament and proeeeds downwards and anteriorly in a groove upon the inner surface of the mandible to the digastrie triangle. A narrow prolongation of the spheno - mandibular ligament bridges over the groove and holds the nerve and vessel in position. In the digastrie triangle the mylo-hyoid nerve has been disseeted already (p. 230). It breaks up into numerous branehes for the supply of two museles, viz., (i) the mylo- hyoid, and (2) the anterior belly of the digastrie.

Nennis Lmgualis. — The lingual nerve is entirely sensory. In the iirst part of its eourse, like the other branehes of the mandibular nerve, it lies medial to the external pterygoid musele. As it deseends it appears at the lower border of the musele. Then it proeeeds downwards and anteriorly, between the internal pterygoid musele and the mandible, and enters the submaxillary region, where it will afterwards be traeed to the tongue. It lies anterior to and on a slightly deeper plane than the inferior alveolar nerve. It gives off no branehes in the infratemporal region, but, whilst still under cover of the external pterygoid, it is joined at an aeute angle by the ehorda tympani braneh of the facial nerve. Not infrequently, also, a eommunieating twig passes between it and the inferior alveolar nerve.

Ghorda Tympani. — This is a slender nerve whieh arises from the facial in the eanalis nervi facialis (O.T. aqueduct of Fallopius). It gains the infratemporal region by traversing the tympanie cavity and appearing through the medial part of the petro-tympanie Assure (O.T. Glaserian), whenee it runs downwards and anteriorly, medial to the spheno-mandibular ligament. It is joined by a slender filament from the otie

SUBMAXILLARY REGION 279

ganglion, and it unites with the lingual nerve a short distanee below the upper end of the latter.

Disseetion. — The student should now endeavour, by means of a Hey's saw, a ehisel, and the bone forceps, to remove the outer table of the mandible, and thus open up the mandibular eanal.

Straetures within the Mandibular GanaL — The mandibular eanal is traversed by the inferior aheolar vessels and nerue^ whieh give oflf twigs to the roots of the molar and praemolar teeth. Both the artery and the nerve terminate by dividing into a mental and ineisor braneh.

The mental artery and nerue appear on the face through the mental foramen, and have been examined already ; the ineisor artery and nerve pass anteriorly to the symphysis and send up twigs to the eanine and ineisor teeth. The vessel anastomoses in the bone with the eorresponding artery of the opposite side.

SUBMAXILLARY REGION.

The superficial area of the submaxillary region has been disseeted already, under the name of the anterior part of the digastrie triangle (p. 230). It is now neeessary to earry the disseetion to a deeper plane, in order to expose a number of parts in eonneetion with the tongue and floor of the mouth. The struetures thus displayed are : —

1. Submaxillary gland and its duet.

2. Sublingual gland.

3. Side of the tongue, and the mueous membrane of the mouth.

Mylo-hyoid. Digastrie. Stylo-hyoid. Hyoglossus. Stylo-glossus. Genio-hyoid. Genio-glossus.

{Mylo-hyoid. Hypoglossal. Lingual. Glosso-pharyngeal.

6. Submaxillary ganglion.

7. Lingual artery and veins.

8. Part of the external maxillary artery.

9. Stylo-hyoid ligament.

4. Museles. H

Disseetion. — To prepare the part for disseetion, it is neeessary to throw baek the head to its full extent, and turn it slightly to the opposite side. II— 18c

28o HEAD AND NECK

If the stufi&ng in the mouth has not been previously removed, it should be taken out now. When this has been done, divide the external maxillary artery and the anterior facial vein at the point where they eross the lower border of the mandible. Next detaeh the anterior belly of the digastrie from its attaehment to the anterior part of the medial aspeet of the lower border of the mandible ; and then, with the saw, eut through the mandible lateral to the median plane.^ It is essential that thedivision of the anterior part of the mandible should be slightly lateral to the median plane on eaeh side, in order that the median part of the bone, with the attaehments of the genioid museles, may be left intaet.

After the division of the bone has been eompleted the lower border of the lateral part of the mandible must be everted, turned slightly upwards, and fixed in position with hooks. When this has been done the boundaries and eontents of the submaxillary region ean be examined.

Part of the region has already been seen as the digastrie portion of the anterior triangle of the neek, but it will now be obvious that the region oeeupied by the submaxillary gland is mueh more extensive than the digastrie triangle ; for, although both are bounded anteriorly and posteriorly by the anterior and posterior bellies of the digastrie musele, the upper boundary of the digastrie triangle is the lower border of the mandible, whilst the submaxillary region extends upwards to the level of the mylo- hyoid ridge on the inner surface of the mandible.

After the mandible has been turned upwards the disseetor should proeeed, in the first plaee, to examine the relations of the digastrie and stylo-hyoid museles, then the mylo-hyoid musele, and afterw£yrds he must study the submaxillary and sublingual glands and the deeper struetures whieh are found in the medial boundary of the submaxillary region.

Museuliis Digastrieus. — This musele limits the sub- maxillary region inferiorly and separates it from the earotid and submental triangles.

The anterior belly of the digastrie springs from the inner surface of the lower border of the mandible elose to the symphysis ; and the posterior belly arises from the mastoid noteh of the temporal bone on the medial side of the mastoid proeess. The two bellies converge upon the upper border of the hyoid bone, where they are united by an intermediate tendon, whieh is attaehed to the hyoid bone at the junction of the body with the great eornu, by a strong loop of fibrous tissue developed from the deep cervical fascia. Posterior to the loop, through whieh it plays, the intermediate tendon passes through the cleft lower end of the stylo-hyoid musele.

Relations, — The anterior belly is covered by the skin, superficial fascia and the platysma, and the deep fascia. It is overlapped by the anterior border of the submaxillary gland, and its deep surface is in eontaet with the mylo-hyoid musele. Its anterior border is the posterior boundary of the submental

^ If the part is soft and pliable there may be no neeessity to make this diyision of the bone.

SUBMAXILLARY REGION 281

triangle, and its posterior border is the anterior boundary of the digastrie triangle.

The relations of the posterior belly are more numerous and important. Posteriorly, it is covered by the mastoid proeess and the attaehments of the sterno-mastoid and splenius eapitis museles. Between the mastoid proeess and the angle of the mandible it forms part of the postero-medial boundary of the parotid spaee and is covered by the parotid gland ; next it is covered by the angle of the mandible and the insertion of the internal pterygoid musele. As it lies in the anterior triangle it is covered by the skin, the superficial fascia and platysma, and the deep fascia; it is erossed by the anterior facial vein, and is overlapped by the posterior part of the submaxillary gland.

It is superficial to the internal jugular vein, the internal and the extemal earotid arteries, the external maxillary artery, the middle eonstrietor of the pharynx, and the lower and posterior part of the hyoglossus musele. The aeeessory nerve passes posteriorly and downwards between it and the internal jugular vein, and the oeeipital artery passes upwards and posteriorly under cover of its lower border, superficial to the aeeessory nerve. The hypoglossal nerve deseends vertically on its deep 8urface in the angle between the internal jugular vein and the internal earotid artery, and the glosso-pharyngeal nerve passes anteriorly and downwards between it and the internal earotid. The posterior aurieular artery runs upwards and posteriorly along the posterior part of its upper border under cover of the postero-medial surface of the parotid, and the stylo-hyoid musele deseends along the same border.

The posterior belly is supplied by the facial nerue^ and the anterior belly by the mylo-hyoid braneh of the inferior alveolar nerve.

Museulus Stylohyoideus. — The stylo-hyoid musele is a small museular bundle whieh springs from the posterior border and lateral surface of the middle third of the styloid proeess and deseends along the upper border of the posterior belly of the digastrie. It divides below into two slips whieh embraee the intermediate tendon of the digastrie and are then inserted into the hyoid bone, at the junction of the great eornu with the body. Its main relations are praetieally the same as those of the posterior belly of the digastrie, but it is

2 82 HEAD AND NECK

not under cover of the mastoid proeess, the sterno-mastoid, and the splenius museles. It is supplied by \ht /aeial nerue,

Dissedion, — Turn the anterior part of the submaxillary gland posteriorly, and elean the posterior part of the mylo-hyoid musele, whieh lies deep to it. Note that a proeess, the deep part of the gland, springs from the medial surface of the superficial part and passes anteriorly, deep to the mylo-hyoid. Disseet the external maxillary artery out of the deep suleus in the posterior part of the gland, without injuring its submental braneh whieh runs anteriorly along the lower border of the mandible ; then displaee the posterior part of the gland anteriorly and expose the hypoglossal nerve immediately above the great eornu of the hyoid bone, and, at a higher level, the lingual nerve. Both nerves lie on the lateral surface of the hyoglossus musele. Hanging from the lower border of the lingual nerve is the small submaxillary ganglion, from whieh several branehes pass to the gland. Note again the deep part of the gland, springing from the medial surface of the superficial part, and also the duet of the gland emerging from the superficial part of the gland and passing anteriorly, with the deep part, between the mylo-hyoid musele laterally and the hyo-glossus medially. Then study the position and relations of the superficial portion of the gland. The relations of the deep part will be seen after the mylo- hyoid is reflected.

Glandula Submaxillaris. — The submaxillary salivary gland eonsists of a superficial larger portion and a deep smaller portion. The superficial portion is lodged in a spaee whieh is bounded anteriorly by the anterior belly of the digastrie ; posteriorly by the posterior belly of the digastrie, the stylo-hyoid, and the stylo-mandibular ligament ; below by the deep fascia of the neek ; and laterally by the inner surface of the body of the mandible and the lower part of the medial surface of the internal pterygoid musele. The fascial relations of the gland have been deseribed already (p. 226). The disseetor should note now that, in aeeordanee with the eontour of the spaee in whieh it lies, he ean reeognise that the superficial part of the gland possesses an anterior and a posterior extremity, and three more or less well-defined surfaces, inferior, lateral, and medial. The posterior extremity abuts against the stylo-mandibular ligament, whieh sepa^^tes it from the parotid, and it overlaps the stylo-hyoid and posterior belly of the digastrie. It is cleft by a groove in whieh lies the external maxillary artery. The anterior extremity rests on the anterior belly of the digastrie.

The inferior surface is covered by the layer of deep cervical fascia whieh extends upwards from the great eornu of the hyoid bone to the lower border of the mandible ; it is erossed posteriorly, under cover of the deep fascia, by tbe

SUBMAXILI.ARY REGION

283

anterior facial vein. Along its upper border lie the majority of the subniaxillary lymph glands ; the external ima^illary artery turns round between it and the lower border of the mandible at the anterior border of the masseter ; and the sub- mental braneh of the external maxillary artery runs anteriorly in the angle between it and the bone,

The lateral surface is in relalion posteriorly with the lower

part of the medial surface of the internal pterygoid, and anteriorly with the inner surface of the body of the mandible below the mylo-hyoid ridge. The external maxillary artery, after it emerges from the groove in the posterior end of the gland, and beforo it turns round the lower border of the mandible, riins anteriorly and downwards between this surface and the internal pterygoid ; and the ,my]o-hyoid artery and nerve lie between it and the body of the mandible before they pass, more ant' ' "^ the medial surface of the gland.

284 HEAD AND NECK

The medial surface is in relation with the mylo-hyoid and hyoglossus, the lingual nerve and the subniaxillary ganglion, and the hypoglossal nerve. It overlaps the stylo-hyoid musele, both bellies of the digastrie, and the great eornu of the hyoid bone ; and the deep part of the gland and the duet both spring froni this surface before they pass anteriorly between the mylo-hyoid and the hyoglossus museles.

The nerve supply of the gland is derived from the lingual nerve, the submaxillary ganglion, the sympathetie plexus on the external maxillary artery ; and its vascular supply eonsists of small submaxillary branehes from the external maxillary artery.

The relations of the deep part of the gland and the duet will be investigated after the mylo-hyoid has been reflected.

Disseetion. — Displaee the superficial part of the gland and the submental braneh of the external maxillary artery posteriorly ; eut the mylo-hyoid vessels and nerve, and turn the anterior belly of the digastrie downwards ; then elean the mylo-hyoid musele and examine its attaehments.

Museulus Mylohyoideus. — This is a thin sheet of museular fibres, whieh arises from the mylo-hyoid ridge upon the inner surface of the body of the mandible, by an origin whieh extends from . the last molar tooth to the symphysis. Its fibres are direeted downwards, medially, and anteriorly, and present two different modes of insertion. The posterior fibres are inserted into the body of the hyoid bone; these, however, form a comparatively small part of the musele. The greater number of the fibres are inserted into a median raphe, whieh extends between the symphysis of the lower jaw and the body of the hyoid bone. The two mylo-hyoid museles, therefore, streteh aeross from one side of the body of the mandible to the other, in front of the hyoid bone, and eonstitute a floor for the anterior part of the mouth. This floor is frequently termed the diaphragma oris, The mylo-hyoid musele is supplied by the mylo-hyoid braneh of the in/erior alveolar nerue.

Disseetion. — Cut the mylo-hyoid musele a little below its origin from the mylo-hyoid ridge and turn it downwards and anteriorly. Whilst doing this be careful not to injure the mueous membrane of the mouth whieh lies in eontaet with it above.

Parts exposed by the ReAeetion of the Mylo-hyoid (Fig. 115). — The side of the tongue is now brought into view, with a number of struetures in eonneetion with it. First

SUBMAX1LLARY REGION 285

note the mueous rnembrane stretehing from the tongue lo the gum of the lower jaw ; then identify the various museles. The hyoglossus, a portion of whieh was previously visible behind the mylo-hyoid, is fully exposed. It is a quadranguiar sheet of Aeshy iibres whieh extends from the hyoid bone to the side of the tongue. Mark its position, beeause all the struetures in this region have a more or less intimate relation- ship to it Thus, posterior and also superiieial to its upper part, the stylthglossus musde will be reeognised, whilst anterior

.,_ Slylo-EloKus

to it are the gento glossus and the genio-kyoid. The genio- hyoid musele oeeupies the antero-inferior part of the region, whilst the anterior part of the genio^lossus is seen in the interval between it and the hjoglossus. Upon the surface of the hyoglossus, the lingual and hypoglossal nerves, the eon- neeting loop between them, the deep portion of the sub- maxillarygland with the submasillary duet, and the submaxillary ganglion are to be disseeted. The lingual nerve oeeupies the highest leve!, and passes anteriorly upon the musele near its insertion into the tongue. The kypogiossal nerve, with its vena eomitans, err p to the hyoid bone, whilst the

286 HEAD AND NECK

deep part of Ihe submaxillary gland and the submaxtUary duet (Wharton's) oeeupy an intermediate plaee Although the mbmaxiltary gangltm is very minuie, its relations are so preeise that it is very easily found By seizing the hngual nerve and disseeting carefully in the interval between it and the deep part of the submaxillary gland, the ganghon will be exposed, and tts roots and branehes of distnbution tnade out Upon the genio glossus, antenor to the

laterior nasal eoneha (O T iof«ior turbm»!)

Eitemil DuxILUry artety Sup«£dal parl or ibmakiUaiy Bland

submuillaiy gk Hypogle- -'

hyoglossus, the disseetor will note the sublingual gland with its artery of supply. If the stylo-hyoid and the posterior belly of the digastrie are displaeed posteriorly, eertain struetures wiil be seen passing under cover of the posterior margin of the hyoglossus musde. These are:— ^i) the glosso-pharyngeal nerve immediately below the stylo-glossus musele; (2) the stylo-hyoid ligament a little lower down ; and (3) the lingual artery elose to the hyoid bone,

Museulus HyogloSBua.— This isa quadrate, flat musele whieh arises from the whole lengih of the greater eomu, and also from

SUBMAXILLARY REGION 287

the body of the hyoid bone, Its (ibres pass upwards to the posterior part of the side of the tongue, mediaj to the stylo- gloBSUS. The hyoglossus is supplied by ihe hypoglossal

Muaeulns Stylo-glossus. — The stylo-glossus musele is an elongated Aeshy sHp whieh takes origin from the anterior aspeet of the styloid proeess near its tip, and, lo a slight extent, from the upper part of the stylo-hyoid ligament also. Passirig down-

wards and anteriorly its fibres may be traeed upon the side of the tongue as far as the tip. Some of them deeussate with the fasciculi of the hyoglossus «lusele. The nerve of supply to the stylo-glossus eomes from the hypoglossal.

MuseuluB Geniohyoideus. — The genio-hyoid musele is plaeed elose to the median plane, in eontaet with its fellow of the opposite side, It is a short musele whieh arises from the spina mentalis upon the posterior surface of the symphysis of the m; ' extends downwards and posteriorly to

gain insi anterior aspeet of the body of the

hyoid bq 'ossal rterve supplies the genio-hyoid.

2 88 HEAD AND NECK

The Deep Part of the Submaodllary Gland. — It has been noted already that the small deep part of the submaxillary gland springs from the medial surface of the superficial part at the posterior border of the mylo-hyoid musele. It will now be obvious that it passes anteriorly and upwards, between the mylo-hyoid laterally and the hyo-glossus and genio-glossus medially, until it eomes into eontaet with the sublingual gland. It is aeeompanied by the lingual nerve and the submaxillary duet, both of whieh lie on its medial surface.

Duetus Subinaxillaris. — The duet of the submaxillary gland (O.T. Wharton's duet) emierges from the medial surface of the main part of the gland, and proeeeds, with the deep part of the gland, anteriorly and upwards upon the hyo- glossus musele. At first it lies between the lingual nerve above and the hypoglossal nerve below. Reaehing the surface of the genio-glossus musele, it is erossed laterally, and then below and medially, by the lingual nerve. Then it passes to the medial side of the sublingual gland, and gains the floor of the mouth, where it opens by a small orifice plaeed on the summit of a papilla whieh lies elose to the side of the frenulum linguae.

The wall of the duet is mueh thinner than that of the parotid duet. If a small opening be made in it, the disseetor will experience little difficulty in passing a fine probe or bristle along it into the mouth.

Glandula Sublingualis. — ^The sublingual gland lies in the floor of the mouth, and is the smallest of the larger salivary glands. It is almond shaped, about one ineh and a half long ; and its relations are very dehnite. Its prominent upper border ean be seen within the mouth, beneath the anterior part of the tongue, where it is covered by a fold of mueous membrane termed the pliea sublingualis (Fig. 146). Medially it rests upon the genio-glossus musele, whilst laterally it is lodged in a fossa on the inner aspeet of the mandible, immediately lateral to the symphysis and above the mylo- hyoid ridge. Below^ it is supported by the mylo - hyoid musele. Its anterior extremity reaehes the median plane, above the anterior border of the genio - glossus, and is in eontaet with its fellow of the opposite side. The duet of the submaxillary gland and the lingual nerve are prolonged anteriorly medial to the sublingual gland.

Numerous small duets (the number varying from eight

SUBMAXILTJVRY REGION 289

to twenty) proeeed from the sublingual gland. These, as a rule, open into the mouth on the summit of the pliea sub- lingualis (Birmingham).

Nervus Tiingnalls. — In the disseetion of the infratemporal region, the lingual nerve was seen passing downwards between the ramus of the mandible and the internal pterygoid musele. As it deseends it inelines anteriorly, and, after passing over the attaehment of the superior eonstrietor musele of the pharynx to the posterior end of the mylo-hyoid ridge, it lies below and posterior to the last molar tooth between the mueous membrane of the mouth and the body of the mandible. At this point it is in danger of being hurt by the elumsy extraction of one of the lower molars, and here also it may be divided by the surgeon, from the inside of the mouth. In its further eourse the nerve keeps elose to the side of the tongue, erossing the styloglossus and the upper part of the hyoglossus, and, beyond that, the submaxillary duet. Its terminal branehes are plaeed immediately under the mueous membrane of the mouth, and it ean be traeed as far as the tip of the tongue.

The branehes whieh proeeed from the lingual nerve in the submaxillary region are of two kinds — (i) twigs of eom- munieation ; (2) branehes of distribution.

{I. Two or more to the submaxillary ganglion. 2. One or two whieh deseend along the anterior border of the hyoglossus musele to unite with the hypoglossal nerve.

T, 1 r I. Slender filaments to the mueous membrane of the

Branehes I ^^^^^ ^^^ ^^^

T\' ^ ^u *• I 2. A few twigs to the sublingual gland. Distribution. I^t> i-?*u* •&&

\, 3. Branehes to the tongue.

The lingual branehes pieree the substanee of the tongue, and then ineline upwards to supply the mueous membrane with the papillae over the anterior two-thirds of this organ.

Ganglion Submaiillare. — This is a minute ganglion whieh lies upon the upper part of the hyoglossus musele in the interval between the lingual nerve and the deep part of the sub- maxillary gland. In size, it is not larger than the head of a large pin; and, when freed from the connective tissue surround- ing both it and its branehes, it will be seen to be suspended from the lingual nerve by two short branehes, whieh enter its upper border, and are separated by a distinet interval. Of these, the posterior eonneeting twig is frequently in the form of two

VOL. II — 19

I I

HEAD AND NECK

< or three Rlaments, whieh convey to the ganglion its sensory and seeretory roots, whilst the anterior eonneeting braneh miist be looked upon as a twig given by the ganglion to the lingual Derye.

In eommon with the other ganglia developed in eonneeiion with the branehes of the trigeminal nerye, this ganghon has three roots — viz. (i) a sensory root from the lingual nerve ; (3) , a seerelory root from the ehorda tympani ; and {3) a sympathetie rool from the plexus around the external maxillary artery.

From its lower border seyetal minute twigs proeeed, and these are distributed — (1) to the submaxil]ary gland and duet; {2) to ihe sublingual gland froru the braneh whieh it gives to the Hngual nerve ; and (3) to the mueous mem- brane of the mouth.

Norrus HypoglosBUs. — This nerve has been traeed in the disseetion of the anlerior triangle to the point where it disappears under cover of the mylo-hyoid musde (p. 231). It is now seen passing anteriorly upon the hyoglossus musele, ahove the hyoid bone and below the level of the deep part of ihe submax!llary gland. At the anterior border of the hyoglossus it gains the surface of the genio-glossus musele, into the substanee of whieh it sinks; and (inally it breaks up into branehea whieh supply the museular sub- stanee of the tongue. Upon the hyoglossus musele it is aeeompanied by a vena eomitans.

The branehes whieh spring from the hypoglossal nerve in this region are very numerous, and are entirely distributed to museles. It supplies — (i) ibestylo-glossus; (2) thehyoglossus; (3) the genio-glossus ; (4) the genio-hyoid ; and (5) the intriiisie museles of the tongue,

In addition, it eommunieates freely with the lingual nerye. The more apparent of these eonneetions take plaee in the form of one or more loops in relation to the anterior border of the hyoglossus. Other eommunieations with the same nerve are effected in the substanee of the tongue.

BaAeetion of tJie Hyaslo'HnE. — The hyoglossus should now bc earerully delaehed from Ihe hyoid bone, and Ihrown upwnrds towards tbe tongue. In doing thls there is no need to divide the slnielures whieh lie upon its surraee. By the reAeetion of this musele Ihe follQw- ing stnietures will be (iilly displayed— (i) the profunda linguie artery and the veiiis whieh aeeumpany it ; (2) the dorsales lingu^ arteries and L vrans; (3) the posterior poit of the genio^lossuE ; (4) the origin ai the middle eonstrieloi of Ihe phaiynx ; and (5) the attaehment of the slylo- hyoid ligAment,

SUBMAXILLARY REGION 291

Museulus Gtenioglossns. — This is a flat triangular musele, the medial surface of whieh is in eontaet with its fellow of the opposite side in the median plane. It arises by a short pointed tendon from the upper mental spine on the posterior aspeet of the symphysis of the mandible, and from this its Aeshy fasciculi spread out in a fan-shaped manner. By far the greater part of the musele is inserted into the tongue by an insertion whieh extends throughout the whole length of the organ from the tip to the base; below the tongue, a few iibres reaeh the side of the pharynx. The genio-glossus is supplied by twigs from the hypoglossal nerue,

Axteria Lingualis. — As the lingual artery is now fully exposed, it ean be conveniently studied at this stage. It springs from the anterior aspeet of the external earotid, and is separable into two parts — viz. (1) a part extending from its origin to the posterior border of the hyoglossus musele ; (2) a part lying in relation to the upper border of the hyoid bone and extending to the anterior border of the hyoglossus, where it divides into two terminal branehes, the sublingual and the deep artery of the tongue.

The first part has been fully examined in a previous disseetion. It lies in the earotid triangle of the neek, and is therefore comparatively superficial. It is erossed by the hypoglossal ner\'e, and lies, medially, against the middle eonstrietor. The seeond part proeeeds anteriorly along the upper border of the great eornu of the hyoid bone, and is covered by the hyoglossus musele, whieh intervenes between it and the hypoglossal nerve. The nerve, how- ever, is plaeed at a slightly higher level. The deep or medial relations of the artery in this stage of its eourse are the middle eonstrietor of the pharynx and the genio- glossus.

The branehes of the lingual artery are : —

1. Suprahyoid from the^r^/ part (p. 233).

2. Dorsalis linguae from the seeond part.

3. Sublingual.

4. Profunda.

Rami Dorsales Linguee. — The dorsalis ^linguse is generally represented by two or more well-marked branehes, whieh pass upwards, under cover of the hyoglossus musele, to end in twigs to the mueous membrane covering the pharyngelal# part of the dorsum of the tongue. Some twigs are supplied

II— 19a

292 HEAD AND NECK

also to the museular substanee of the organ, and a few may be traeed baekwards into the tonsil.

Arteria SubUngualis, — This springs from the termination of the seeond part and emerges from under cover of the anterior border of the hyoglossus, and then aseends upon the genio-glossus to reaeh the sublingual gland, whieh it supplies. It gives branehes to the surrounding museles also ; and it anastomoses with its fellow of the opposite side and with the submental braneh of the external maxillary artery.

Arteria Profunda Linguee, — The deep artery of the tongue aseends almost yertieally upon the genio-glossus, overlapped by the anterior border of the hyoglossus ; when it reaehes the under surface of the tongue, it runs towards the tip and ends in terminal branehes. It ean easily be exposed by dividing the mueous membrane along its eourse, when it will be seen to lie elose to the attaehment of the frenulum of the tongue, and to be eontinued forwards in the interyal between the genio - glossus and the inferior longitudinal musde. Its eourse is tortuous to allow of the protrusion or elongation of the organ, and it gives off numerous branehes.

Lingnal Veins. — The lingual artery is aeeompanied by two small venae eomites whieh lie with it under cover of the hyoglossus ; but the main vein of the tongue erosses the lateral surface of the hyoglossus, and another smaller vein, the vena eomitans hypoglossi^ aeeompanies the hypoglossal nerve. The ven8e eomites of the artery and the vena eomitans hypoglossi unite with the main vein to form the lingual vein, whieh opens into the eommon facial vein or into the internai jugular vein.

Stylo-hyoid Ligament. — This is the last strueture to be examined in this disseetion. It is a iibrous eord whieh springs from the tip of the styloid proeess and passes antero-inferiorly to be attaehed, under cover of the hyo- glossus musele, to the lesser eornu of the hyoid bone. It is not uneommon to find it partially ossiiied; in other eases it may assume a ruddy hue and eontain museular iibres.

OTie GANGLION AND TENSOR PALATI.

During the disseetion of the submaxillary region the disseetor has noted a nerve ganglion, the submaxillary gangiion^ eonneeted with the lingual braneh of the mandibular nerve,

OTie GANGLION AND TENSOR PALATI 293

and when he was examining the infratemporal region refer- enee was made to the otie ganglion, whieh is assoeiated with the tnink of the mandibular nerve and the braneh whieh it supplies to the internal pterygoid musele. This ganglion and its eonneetions should now be displayed, and afterwards the tensor palati musele should be eleaned and followed from its origin to the hamulus of the medial pterygoid lamina.

Disseetion. — Cut the lingual and inferior alveolar nerves immediately below their origins ; evert the upf)er part of the mandibular nerve and examine the otie'ganglion ; then divide the intemal pterygoid, along the posterior border of the lateral pterygoid lamina, depress the lower part of the musele and elean the tensor palati, whieh forms the medial relation of the middle meningeal artery, the otie ganglion and the mandibular nerve, separating them from the lateral surface of the auditory tube (Eustaehian).

Gkmglion Otieuin. — This is a minute oval body about 4 mm. in length. It lies immediately below the foramen oyale, between the mandibular nerye laterally, the tensor veli palatini medially, and the middle meningeal artery posteriorly ; and it is intimately assoeiated with the origin of the nerve to the internal pterygoid.

The otie ganglion is usually deseribed as receiving motor, sensory, and sympathetie roots. The motor root is supplied by the nerve to the intemal pterygoid musele ; the sympathetie root eomes from the plexus around the middle meningeal artery. In addition to these, the small superficial petrosal nerue enters the posterior border of the ganglion, and conveys to it sensory fibres.

The following are the branehes whieh proeeed from the otie ganglion : —

(A twig whieh passes downwards and anteriorly to the tensor veli palatini. (Tensor palati.) A twig whieh proeeeds upwards and posteriorly to supply the tensor tympani. {One or more fine filaments to one or both of the roots of the aurieulo-temporal nerve. A minute eommunieating filament to the ehorda tympani.

Museulus Tensor Veli Palatini.— This flat and band-like musele is elosely applied to the deep surface of the internal pterygoid musele. It arises from the seaphoid fossa at the rbot of the medial pterygoid lamina, from the posterior border of the lower surface of the great wing of the sphenoid, from the spine of the sphenoid, and from the lateral aspeet of the auditory tube (O.T. Eustaehian). It deseends to the lower end of the medial pterygoid lamina and ends in a tendon whieh turns horizontally under the hamulus into the soft palate, where its attaehments will be seen later. 11—19 h

294 HEAD AND NECK

THE GREAT YESSELS AND NERYES

0F THE NECK.

As soon as the disseetion of the infratemporal and the submaxillary regions is eompleted the disseetor should tum to the study of the external earotid artery and its relations.

Arteria Gaxotis Eztema. — The external earotid is one of the two terminal branehes of the comm6n earotid. It eommenees therefore at the level of the upper border of the thyreoid eartilage, opposite the dise between the third and fourth cervical ^ertebrae; and, after running upwards and posteriorly to the level of the neek of the mandible, it terminates, between that portion of bone and the upper part of the antero-medial surface of the parotid gland, by dividing into two terminal branehes, the superAeial temporal and the internal maxillary. At its eommeneement it lies anterior and medial to the internal earotid ; and it is ealled external not on aeeount of its relation to the internal earotid, but beeause it is distributed mainly to the parts on the exterior of the skull. It is at first comparatively superficial in the upper part of the earotid triangle ; next it passes under cover of the lower part of the postero-medial surface of the parotid and the posterior belly of the digastrie and the stylo-hyoid musoles. At the upper border of the stylo-hyoid it enters a groove in the medial border of the parotid, through whieh it passes to the upper part of the antero-medial surface of the gland, posterior to the neek of the mandible, where it terminates.

Relations. — As it lies in the earotid triangle it is covered by the skin, superficial fascia and platysma, branehes of the nervus eutaneus eoUi and the cervical braneh of the facial nerve, and the deep fascia. Beneath the deep fascia it is erossed superficially by the eommon facial and lingual veins and the hypoglossal nerve ; and, at the upper end of the triangle, it is eoneealed by the lower end of the parotid gland and it is erossed from behind forwards by the posterior facial vein. After it leaves the earotid triangle it is overlapped by the angle of the mandible, and is erossed by the posterior belly of the digastrie and the stylo-hyoid. At its termina- tion it is eoneealed by the upper part of the parotid and is erossed by branehes of the facial nerve.

GREAT VESSEI^ AND NERVES 0F NECK 295

To tts medial side lies tlie wall of the pharynx, rrom whieh tt is separated, in the region of ihe earotid triangle, by the external and internal laryngeal branehes of the superior

laryngeal nerve. The medial relations at a higher level will be seen to greater advantage at a later stage when the styloid proeess is detaehed and displaeed. They are the pharyngeal braneh of the yiigii^, the stylo-pharyngeus, the glosso-pharyngeal

296 HEAD AND NECK

nerve, and the styloid proeess or the stylo-hyoid ligament. These struetures lie to its medial side after they have passed obliquely between it and the internal earotid, whieh has gradually attained a plane posterior and medial to that in whieh the external earotid lies.

In the whole of its extent the extemal earotid is aeeom- panied by numerous sympathetie nerve libres, derived from the upper cervical sympathetie ganglion ; they eonstitute the external earotid plexus^ whieh distributes offsets along all the branehes of the artery.

Bratiehes, — The branehes of the external earotid artery are the superior thyreoid, the lingual, and the external maxillary from its anterior aspeet; the oeeipital and the posterior aurieular from its posterior aspeet ; the aseending pharyngeal from its medial side ; and the superficial temporal and the internal maxillary are its terminal branehes.

Arteria Thsrreoidea Superior. — This vessel arises within the earotid triangle, from the anterior aspeet of the extemal earotid elose to its origin. It runs downwards and anteriorly, under cover of the omo-hyoid, sterno-hyoid, and sterno-thyreoid museles, to the apex of the lateral lobe of the thyreoid gland, where it ends by breaking up into three terminal branehes.

The following branehes proeeed from it : —

1. Hyoid.

2. Superior laryngeal.

3. Sterno-mastoid.

4. Grieo-thyreoid.

5. Glandular.

Rarnus Hyoideus. — This is a minute twig, whieh springs from the superior thyreoid in the earotid triangle. It runs along the lower border of the hyoid bone, under cover of the thyreo-hyoid musele, and anastomoses with its fellow of the opposite side, and with the hyoid braneh of the lingual artery.

Arteria Laryngea Superior — This is a larger vessel. It springs from the superior thyreoid in the earotid triangle, and, assoeiating itself with the internal laryngeal nerve, it enters the pharynx after piereing the thyreo-hyoid mem- brane.

Arteria Sternodeidomastoidea. — The sterno-mastoid braneh is a small vessel whieh runs downwards and posteriorly, aeross the earotid sheath along the upper border of the anterior belly of the omo-hyoid musele, to reaeh the deep surface of the sterno-mastoid musele, into whieh it sinks. It gives,

GREAT YESSELS AND NERVES OF NECK 297

in addition, minute twigs to the depressor museles of the larynx.

Ramus Cncothyreoideu5. — The erieo-thyreoid artery runs medially upon the erieo-thyreoid ligament, and anastomoses with its fellow of the opposite side. It has already been notieed in the disseetion of the middle line of the neek (p. 229).

Rami Glandulares. — The glandular rami are the three terminal branehes. They spring from the main trunk at the apex of the lateral lobe of the thyreoid gland. The largest is distributed on the medial surface of the lateral lobe; the smallest ramifies on its lateral suriaee; whilst the third runs downwards upon the anterior border of the lateralj lobe, and then along the upper border of the isthmus towards its fellow of the opposite side. The anastomosis between the thyreoid arteries of the two sides is by no means free.

Ven(B Thyreoideee Superiores. — The superior thyreoid veins emerge from the gland and form a trunk whieh receives tributaries eorresponding in a great measure with the branehes of the artery. It erosses the upper part of the eommon earotid and joins the internal jugular vein.

Arteria Lingualis. — The lingual artery springs from the external earotid at the level of the great 'eornu of the hyoid bone in the earotid triangle. It runs along the upper border of the great eornu. As its name indieates it is the artery of supply to the tongue. It has already been disseeted in the earotid triangle and the submaxillary region, and the details of its eourse and relations are given on

PP- '^ZZ^ 291.

Arteria Maxillaris Extema (O.T. Facial Artery). — The ex- ternal maxillary artery ean be studied, at the present stage of the disseetion, from its origin up to the point where it mounts upon the mandible to reaeh the face. This is termed the cervical part oi the artery. It springs from the anterior aspeet of the external earotid, immediately above the lingual, in the upper part of the earotid triangle, and passes vertically upwards, on the lateral surface of the middle eonstrietor musele of the pharynx, to the angle of the mandible, where it disappears under cover of the posterior belly of the digastrie and the stylo-hyoid musele. At this point the «uperior eonstrietor is medial to it and separates it from the

2gS HEA.D AND NECK

lateral surface of tlie tonsil. At the upper border of the stylo-hyoid it enters a deep groove in the posterior end of the submaxillary gland. Emerging from this it turns down- wards and anteriorly between ihe laleral surface of the gland

iperneiol CEapDnJ

and the intotnal pterygoid musele, and turning round the lower border of the mandible at the anterior border of the masseter it enters the face. For details of its facial eourse see p. 129. l'our named brnnehes spring froni the e.vtcrnol niaxillary artery in the ccrvical part of its eourse :■ — ■

GREAT YESSELS AND NERYES 0F NECK 299

Arkria Palatina Asemdms. — The aseending palatine

braneh is given off for the supply of the soft palate, but

il distributes branehes to the tonsil and auditory (O.T.

Eustaehtan) tube also. It aseends between the stylo-

«	*	'su	yLanw
Hy«;	bone
Ihftr	)rhi-o		=r.

pharyngeus and stylo-glossus museles, and wiU be seen when the styloid proeess is reiieeted.

Ramus Tonsi//aris.~The tonsillar braneh runs upwards between the internal pterygoid and stylo-glossus museles, then turns medially, pierees the superior eonstrietor, and enters the lonsil.

The glandu/ar branehes are given to the submaxillary gland as the external maxillary artery passes through it.

300 HEAD AND NECK

Arteria Submentalis, — This is a braneh of some size. It arises elose to the base of the mandible, and nins towards the ehin upon the mylo-hyoid musele. Near the symphysis it ehanges its direetion, and is earried upwards over the border of the mandible, to end in branehes for the museles and integument of the ehin and lower lip. In the submaxillary region it gives numerous twigs to the surrounding museles and glands, and anastomoses with the sublingual artery by branehes whieh pieree the mylo-hyoid musele. It anasto- moses, in the face, with the inferior labial braneh of the external maxillary and the mental braneh of the inferior alyeolar.

Vena Facialis Anterior. — The eeroieal porHon of the anterior facial has already been seen (p. 231) passing posteriorly and downwards, superiieial to the submaxillary gland. After receiving tributaries eorresponding to the branehes of the similar part of the external maxillary artery, it joins the posterior facial vein. The short trunk thus formed is termed ih^ eommon /aeial vein, and it pours its blood into the intemal jugular at the level of the hyoid bone.

Arteria Oeeipitalis. — The oeeipital artery springs from the posterior aspeet of the external earotid at the same level as the external maxillary. It takes the lower border of the posterior belly of the digastrie musele as its guide, and runs upwards and posteriorly, under cover of the sterno-mastoid musele, and generally under cover of the lower border of the posterior belly of the digastrie, to reaeh the interval between the mastoid portion of the base of the skuU and the transverse proeess of the atlas. Thenee onwards it has been studied in the disseetion of the sealp and the baek of the neok (pp. 162, 170). The first part of the vessel erosses the internal earotid artery, the vagus nerve, the aeeessory nerve, and the internal jugular vein, whilst the hypoglossal nerve hooks round it.

The only branehes whieh spring from this portion of the oeeipital are : (i) museular twigs; and (2) a meningeal braneh.

The museular twigs are given to the neighbouring musoles, and one of them, larger than the others and very eonstant, is termed the sterno-mastoid braneh, runs parallel with the aeeessory nerve, and sinks with it into the substanee of the sterno-mastoid musele.

GREAT YESSELS AND NERVES 0F NEGK 301

A tneningeal braneh assoeiates itself with the internal jugular vein, and ean be followed upwards upon it to the jugular foramen, through whieh it passes into the eranium.

Arteria Aurieiilaris Posterior. — The posterior aurieular artery will be found above the level of the posterior belly of the digastrie, and, like the oeeipital, it takes origin from the posterior aspeet of the external earotid artery, In the first part of its eourse it is plaeed deeply, and runs upwards and posteriorly between the styloid proeess of the temporal bone and the postero-medial surface of the parotid gland to reaeh the interval between the mastoid proeess and the baek of the auriele. Then it joins the posterior aurieular nerve. Its further eourse has been studied in the disseetion of the sealp (p. 157).

This portion of the posterior aurieular artery gives off (i) museular twigs ; (2) a few branehes to the parotid gland ; and (3) the stylo-mastoid artery.

Arteria Stylomastoidea. — This is a slender vessel whieh enters the stylo-mastoid foramen. In the interior of the tem- poral bone it has an extensive distribution. It supplies twigs to the mastoid eells and to the tympanie cavity and is earried onwards in the eanalis facialis (O.T. Eallopian) to anastomose with the petrosal braneh of the middle meningeal.

Arteria Maxillaris Intema. — The eommeneement of the internal maxillary artery, from the termination of the external earotid, between the neek of the mandible and the antero- medial surface of the parotid gland, has been seen already, and the artery has been traeed through the infratemporal region to the pterygo-palatine fossa, where its terminal branehes will be disseeted at a later period.

Arteria Temporalis Superficialis. — Like the internal maxillary, this artery eommenees between the neek of the mandible and the antero-medial surface of the parotid gland. It passes upwards and, as it emerges from under cover of the upper end of the parotid, it erosses the posterior end of the zygomatic areh and enters the superficial fascia of the sealp, in whieh it aseends on the superficial surface of the temporal fascia, and anterior to the auriele it breaks up into two branehes, /rontal and parietal. These anastomose with eaeh other and with their fellows of the opposite side. The frontal anastomoses with the supra-orbital and

302 HEAD AND NECK

frontal branehes of the ophtlialmie also, and the parietal with Ihe posterior aurieular and the oeeipital arteries. Whilst it is still undet cover of the parotid it gives branehes to the

eiior ihyreoU Brtety Thyreo-hyoid muKle

gland ; anterior aurieuiar branekes i.0 t\\.^ i\ir\c\& ; the transverse facial, whieh passes along the lower border of the zygoraatic areh aeross the masseter. As ihe superficial temporal erosses the zygoma it gives off a zygomatico-orbital bramh, whieh runs to the lateral border of the orbit, and a niiddle temporal

GREAT YESSELS AND NERYES 0F NECK 303

branehy whieh peHbrates the temporal fascia and anastomoses in the temporal fossa with the deep temporal branehes of the internal maxillary. The eourse of this braneh and also the distribution of the terminal branehes have been followed in earlier stages of the disseetion (pp. 266, 267).

Disseetion, — Divide the posterior belly of the digastrie immediately below its origin, and tum it downwards and anteriorly towards the hyoid bone ; then examine the stylo-pharyngeus musele. It may be neeessary to eut the oedpital and posterior aurieular arteries in order to gain free aeeess to the deeper parts, but this should not be done unless it is neeessary. Care must be taken whilst eleaning the stylo-pharyngeus to avoid injuring the glosso-pharyngeal nerve, whieh turns round its posterior border and erosses its superiieial surface.

MtLsenliis Stylopharyngeus. — This is the longest of the three slender museles whieh spring from the styloid proeess. It arises from its deep or medial surface elose to its root, and extends downwards and anteriorly to gain the side of the pharynx, where it disappears under cover of the upper border of the middle eonstrietor musele. Whilst under cover of the middle eonstrietor its fibres blend with those of the palato- pharyngeus, and, with these, are inserted into the posterior border of the eorresponding lamina of the thyreoid eartilage. Some of the fibres, however, are lost in the wall of the pharynx. If the disseetor removes the fascia at the posterior part of the thyreo-hyoid spaee he will expose the lower fibres of the middle and the upper fibres of the inferior eonstrietor, and in the interval between them, on a deeper plane, the lateral surface of the lower part of the stylo-pharyngeus.

Disseetion. — Snip through the base of the styloid proeess with the bone forceps, and throw it and the attaehed museles downwards and anteriorly. The upper parts of the internal earotid artery and the internal jugular vein are now exposed, and the aseending pharyngeal artery ean be followed to the base of the skull.

Arteria Pharyngea Aseendens. — To expose this vessel the disseetor must push the external earotid anteriorly and elean the interval between it and the internal earotid. The aseending pharyngeal springs from the medial surface of the external earotid elose to its lower end and is its smallest braneh. It aseends along the lateral border of the pharynx, lying between the stylo-pharyngeus laterally and the eon- strietors of the pharynx medially, first in a plane between the external and internal earotid arteries, and then to the medial side of the internal earotid. As it passes upwards it gives

304 HEAD AND NECK

pharyngeal branehes to the wall of the pharynx and prevertebral branehes to the prevertebral museles. At the base of the skull it gives off meningeal branehes, whieh enter the eranial cavity through the hypoglossal canaV the jugular foramen, and the foramen laeerum; and palatine branehes, whieh pieree the pharyngeal aponeurosis above the upper border of the superior eonstrietor and deseend, along the levator palati, to the soft palate. Offsets from these branehes are given to the auditory tube (O.T. Eustaehian) and to the tonsil.

Disseetion. — After the aseending pharyngeal artery has been examined, the iniernetl earotid artery^ the glosso-pharyngeal^ ^agus, aeeessory, and hypogLossal nerues, and the superior cervical ganglion, with their various eonneetions and branehes, must be disseeted. A dense and tough fascia envelops these struetures, and a great amount of patienee is required to traee the branehes of the nerves through it. One nerve — the pharyngeal braneh of the vagus — whieh proeeeds downwards and anteriorly upon the superficial or lateral aspeet of the internal earotid, is espeoially liable to injury, and must thereibre be borne in mind from the very outset of the disseetion. The intemal laryngeal and the extemal laryngeal nerves have been previously displayed in the anterior triangle of the neek. These, if traoed upwards, will lead to the superior laryngeal braneh of the vagus, whieh lies in relation with the deep aspeet of the internal oarotid artery. Near the base of the skull all the nerve-trunks will be found making their appearanee, elose together, in the interval between the intemal jugular vein and the internal earotid artery ; whilst posterior to the vein the reetus lateralis musele and the Jirst loop of the eeruieal plexus will be seen.

Arteria Oarotis Intema. — The internal earotid artery is one of the two terminal branehes .of the eommon earotid, and it eommenees at the level of the upper border of the thyreoid eartilage. From this point it proeeeds upwards in the neek, in a vertical direetion, until it reaehes the base of the skull; there it disappears from view by entering the earotid eanal of the petrous portion of the temporal bone, through whieh it reaehes the interior of the eranium. The internal earotid artery ean therefore be very appropri- ately divided into three parts — viz. (i) a cervical ; (2) a petrous ; and (3) an intraeranial. The cervical part alone eomes under the notiee of the student in the present disseetion.

In the first part of its extent the internal earotid artery lies in the earotid triangle, and is therefore comparatively superficial. It is covered by the integument, platysma, and fascia, and is overlapped by the sterno-mastoid musele and

GREAT YESSELS AND NERYES 0F NECK 305

the anterior border of the internal jugular vein ; it is erossed by the hypoglossal nerve and the sterno-mastoid braneh of the oedpital artery, the lingual and eominon facial veins ; and the

deseendens hypoglossi deseends on its superiieial suri'aee. As it proeeeds upwards, it eomes to lie under cover of the lower end of the parotid gland, and then at a bigher level under cover of the posteriot belly of the Hitrastrie, the stylo-hyoid, VOL. II — 20

3o6 HEAD AND NECK

the stylo-pharyngeus, and the styloid proeess, whieh separate it from the postero-medial surface of the parotid gland. It wlll be noted also that three neroes and two arteries eross the vessel superficia]ly, viz. : —

The hypoglossal, as already noted, erosses it in the eaiotid triangle ; the other nerves eross it under cover of the posterior

belly of the digastrie. The oeeipital arlery erosses it at the level of the lower border of the posterior belly of the digastrie, and the posterior aurieular at the level of its upper border.

The relationship of the external earotid artery to the internal earotid is a varying one. At first the external earotid hes antero-medial to it ; but soon, owing to its in- elination posteriorly, it eomes to he direetly superficial to the internal earotid. The fo]lowing struetures intervene between the two vessels i — ■

1. Slyloid proeess. I 4. l'haiyngeal 1jranche$ of vagus

2. .Stylo-pharyngeus musele. ani) syuipnthetie.

3. Glosso-pharyngeal nfrve. | 5. A |)orlion of Ihe parolid gland.

Posterior to the internal earoiid is the longus eapitis (O.T. reetus eapitis aniieus major) and the sympathetie trunle; postero-laterally are the glosso-pharyngeal, the vagus, the aeeessory and the hypoglossal netve ; and still more laterally

GREAT YESSELS AND NERVES 0F NECK 307

and posteriorly is the internal jugular vein. On its tnedial asped the intemal earotid is related to the pharynx, the aseending pharyngeal artery and the levator veli palatini.

Before leaving this vessel, note that near the base of the skull four nerves appear in the interval between it and the internal jugular vein ; these are the glosso-pharyngeal, the vagus, the aeeessory, and the hypoglossal.

Vena lugularis Intema. — The internal jugular vein is the largest venous ehannel of the neek. It enters the neek through the postero-lateral eompartment of the jugular foramen, where it is direetly eontinuous with the transverse sinus of the eranial cavity. From the jugular foramen it proeeeds downwards, until it reaehes the posterior aspeet of the medial end of the clavicle, where it joins the subclavian vein to form the innominate vein. Its eommeneement in the jugular foramen shows a slight dilatation, termed the bulb^ the lumen of whieh remains at all times patent owing to the eonneetion of its walls to the margins of the foramen. The skull eap should be removed and a probe should be passed from the trans- verse sinus into the internal jugular vein, to demonstrate the eontinuity of the two ehannels.

Reiations. — At its eommeneement the internal jugular vein lies postero-lateral to the upper end of the cervical part of the internal earotid artery, from whieh it is partially separated by the last four eerebral nerves. As it deseends it assumes a more direetly lateral relationship, first to the internal and then to the eommon earotid, overlapping eaeh vessel to a slight extent anteriorly ; and it is enelosed with them and the vagus nerve in a eommon sheath of deep cervical fascia, the nerve lying in its own eompartment of the sheath between the arteries medially and the vein laterally, and in a posterior plane.

The superficial or lateral relations of the vein in the upper part of its extent are the styloid proeess, with the stylo- pharyngeus and stylo-hyoid museles, and the posterior belly of the digastrie, whieh separate it from the upper part of the postero-medial surface of the parotid gland. In this part of its extent it is erossed superficially, along the upper border of the posterior belly of the digastrie, by the posterior aurieular artery, and at the lower border of the digastrie by the aeeessory nerve, passing downwards and posteriorly, and by the oeeipital artery passing upwards and posteriorly

11—20 a

M

3o8

HEAD AND NECK

superficial to the nerve. At a slightly lower Ievel it js eon- eealed by the lower part of the postero-medial surface of the parotid, and il is erossed by the sterno-mastoid braneh of the oeeipital artery. After it emerges frotn under cover of the parotid, it lies under cover of the anterior border of the sterno-mastoid, eseept in the region of the upper part of the earotid triangle, where it may project anteriorly, beyond the anterior border of the musele, for a short distanee. It is separated from the sterno-mastoid by numerous deep cervical lytnph glands ; and under cover of the rausele it is erossed superlieially, at the level of the upper part of the thyreoid

eartilage, by the eommunieans cervicalis from the cervical plesus, and, at the level of the erieoid eartilage, by the intermediate tendon of the oino-hyoid, the sterno-mastoid braneh of the superior thyreoid artery and the nerve to the posterior belly of the omo-hyoid. Below the omo-hyoid it is covered by the posterior border of the sterno-hyoid, and is erossed by the anterior jugular vein ; and at its termination it lies posterior to the sternal end of the clavicle.

Posteriorly, it is in relation with the reetus eapitis lateralis ; the reetus eapilis anterior (O.T. andeus minor) ; and the loop between the iirsl and seeond cervical nerves. At a lower level its posterior relations are the Iransyerse proeesses of the cervical vertebrffi and the museles attaehed to their anterior tubereles, viz., the longus eapitis (O.T. reetus eapitis antieus

GREAT YESSELS AND NERVES 0F NEGK 309

major) and the sealenus anterior. Between its posterior surface and the sealenus anterior are the aseending cervical artery, the phrenie nerve, and, erossing superiieial to the latter, the transyerse cervical and the transyerse seapular arteries. On the left side the terminal part of the thoraeie duet also erosses the phrenie nerve posterior to the internal jugular vein. At the medial border of the sealenus anterior the thyreo- cervical artery is posterior to it, and at a lower level, the first part of the subclavian artery and the dome of the pleura.

The right vein is usually the larger of the two; and as they approaeh the root of the neek both veins ineline slightly to the right, with the result that, on the right side, the lower part of the vein is separated from the eommon earotid artery by a small triangular interval bounded below by the subclavian artery, whilst on the left side the vein overlaps the anterior aspeet of the eommon earotid artery.

Tributaries, — Immediately below its eommeneement the internal jugular vein is joined by the inferior petrosal sinus, and then, successively, by offsets from the pharyngeal plexus, by the lingual vein, the eommon facial vein, the superior and middle thyreoid veins. In some eases it is joined near its upper end by a vena eomes whieh runs with the oeeipital artery; and, oeeasionally, near its lower end, it receives the lymph trunks whieh usually open into the eommeneement of the innominate vein.

Disseetion. — Slit open the lower part of the vein and examine the valve whieh lies elose to its extremity. It eonsists of two or three semilunar flaps whieh prevent regurgitation of blood from the innominate vein into the internal jugular.

Nervi Glosso-pharsrngeus, Yagus, Aeeessorius. — After the removal of the brain these nerves were seen leaving the eranial cavity through the middle eompartment of the jugular foramen in the interval between the eommeneement of the internal jugular vein postero-laterally and the inferior petrosal sinus antero-medially (p. 215, and Fig. 125, p. 31 o). The disseetor should again examine the interior of the eranial cavity and refresh his memory as to the manner in whieh they enter the foramen. The glosso-pharyngeal oeeupies the most anterior position, and it is eut off from the others by a separate tube-like sheath of dura mater. The aeeessory is plaeed posterior to tlie vagus^ and both are ineluded within the same sheath of dura mater. They therefore

11—20 1

31«

HEAD AND NECK

traverse the foramen in elose eontaet with eaeh other. Reaehing the exterior of the skull, the three beeome assoeiated with the hypoglossal nerve; and the four nerves lie for a short distanee in the interval between the internal jugular vein and the interiial earotid artery, but soon they ehoose different routes. The lueessory inelines posteriorly, superlieial or deep to the intemal jugular vein ; the glosso- pharyngeal runs anteriorly, supertieial to the intemal earotid.

■etion through Ihe H&id a II stiows Ihe posterior eranial fos£a and the upper part ot the vertebral eanal afier the removal of the brain and the medulla spinalis,

and under cover of the posterior belly of the digastrie ; at a lower level the hypoglossal turns anteriorly aeross the external and internal earotld arteries ; and the vagus proeeeds vertically downwards, lirst between the internal jagular vein and the internal earolid, and then between the vein and the eommon earotid (Fig. loo).

In &a ordinary disseetion it i<i imposslble 1o follow out many ai the minule twigs whieh lake origin ftom these nerves in the region of the basis eratiii. To do so it is neeessary lo possess a perfeclly fresh part whieh has been speeially prepared by having ihe soft parts toughened with spirit and Ihe bone softened by immersion in a wealt solution of aeid.

GREAT YESSELS AND NERYES 0F NEGK 311

Even then the disseetion is a difficult one, although it should eertainly be undertaken by the advanced student, in the event of his being able to obtain a part for the purpose.

In the following deseription of these nerves the aeeount of the branehes whieh ean in all eases be traeed is printed in ordinary type^ whilst that of those requiring speeial disseetion is printed in small type,

Nennis Glosso-phaiTiigeus. — The glosso-pharyngeal nerve inelines downwards and anteriorly and erosses the internal earotid artery superiieially. At iirst it lies medial to the styloid proeess and the stylo - pharyngeus musele, then it hooks round the lower border of the musele and eunres anteriorly upon its superlieial surface to gain the base of the tongue. In the disseetion of the submaxillary region, its terminal part was seen disappearing under cover of the hyoglossus musele, where it ends in lingual branehes,

In the present disseetion the following branehes should be made out : —

1. Communicating braneh from

the facial.

2. Nerve to the stylo-pharyngeus.

3. Pharyngeal.

4. Tonsillitie.

5. Lingual.

The eommunieating braneh from the facial springs from the nerve to the posterior belly of the digastrie, and, as a rule, emerges from midst the (ibres of that musele to join the glosso-pharyngeal elose to the lower part of the jugular foramen.

The stylo-pharyngeal nerue is a small twig whieh enters the musele of the same name. The greater part of its fibres, however, are eontinued through the musele to the mueous membrane of the pharynx.

Tht pharyngeal branehes eonsist — (i) of one or two small twigs whieh perforate the superior eonstrietor to reaeh the mueous membrane of the pharynx ; and (2) a larger nerve whieh eomes off higher up and passes with the pharyngeal braneh of the vagus to the pharyngeal plexus. It frequently divides into two or more branehes.

The tonsillitie branehes proeeed from the glosso-pharyngeal near the base of the tongue. They form a plexus over the tonsil, termed the eireulus tonsiilaris, and give twigs to the mueous membrane of the isthmus faucium and the soft palate.

The terminal or lingual branehes will be followed in the disseetion of the tongue.

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313

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Tbere are still olher points in eonneetion with the glosso-pl nerve wbieh Tei|uiie tnenllon. A( the lowei part of the jugula[ two small gai^lia ore fornied upon its trunk, and froin the lower eertain mlnute branehes are given off. The upper BMglior "" " gaitglion supeHm ; the luwer one Is teimed the gtmgheit feriv.

The superior gangiioH \% a. small ganglionie swdlin^, wl only a portion of the tibres of the nerve trunk. It 'k plaeed i upper part of the bony gioove in whieh the nerve lies os il proeeeds ti the jugular foramen. No branehes arise from it.

The petrmis ganglien is a larger swelling, whieh invoIves the e nerve-trunk, and lies at the opening of the jugulai forlinen, betnee vagus oerve and the inferior petrosal sinus (whieh in and the anteiior Irarder of the foramen). Its length is or three lines. Thiee hianehes of eommunieation entei oi pioeeed fiai These eonneet It with — (i) the supeiior eerrieal sympathEtie ganglion the auiieular bianeh of the vagus ; and (3) the jugulai gangLoo ol

In addilion to these twigs the lympanie ntme tak^ origin troia petious ganglion.

T;nipuiie Nmw.— The ullimate destinalion of this r^aided as the olie ganglion, but it takes a veiy dreuito' thal strueture an<l it gives olTliranehes on the way, It enters s small ^oran on the lidge whieh sepaiates the jugular fossa fiom the earotid foraiJ on the lower surface of Ihe petious Irane, and it is eondueted by a eanal to the tympanie cavity. It erosses the innei wall of this chantfl giooving the piomontoiy. Having gained the anterior part of W tympanum, it enteis the bone a seeond time, and runs in a mimite eal whieh tunnels the petrous bone below the upper end or the ehanneS

whieh is lodged the tensoi tympani musele. In this pail of i'-

tympanie neive is ioined by a braneh fiom the ganglian genieuli facial neive, and, anei the junciion is eileeted, it is teimed the s/'ial Jicial ptlrosal iierue.

The eanal in whieh the nnall !uperjkial petrosal Berve is lodged c into the eranial cavity upon the anleiior surface of the petious 1: immediately lateial to the hiatus eanalis faciatis (O.T. Pallopii). Thr this the neive emerges, and soon Ieaves the interior of the eranium 1 passing downwards in the inleryal between the gieat wing of the sphenoB and tlie petious nart oi the lemporal bone, 01 Ihtough Ihe esnalieul^ innuininatus, oi thiou^h Ihi' forameo ovaIe. Outside the aku joimng the olie ganglion.

In Ihe tympanie cavity Ihe lynipanie nenie giveE biandies of tiipM — (I) to Ihe mueous membiane of the tymponum j {2) to the litud memlHane of the mastuid eells ; and (3) to the mueous membtane nt lh| audiloiy tube (Kustaehian). It is eonneeled with the sympathetie plw

n the mternal enrotid arteiy by the sttperii

bramhe

ind inferi

:e ihe siibslanee of Ihe petrous parl ot the ti

NsiTUA Vagus. — The vagus passes through the niid< eonipartment of the jugu]ar foramen in eompany with the I aeeessory — both being induded within the same shealh of \ dura mater. In the neek it pursues a vurtica! eourse, lying, at lirst, between the internal jugular vein and the internal earotid arlery, and afterwards between the same '

^msS!^

■ ^

CLES

artery. It arises I

proeesses of the tl

K, and, tapering si

the sealene tubi

and also into

n ihe two subela

rib,

facg is eoneeakd by

• the clavicle, king its medial boi ihe intemal juf o-hyoid ; ihe phi illy ; and the trans^ rteries passing pos! ierve. Belween it

above, with the tip ind below, with f the subclavian arl t/era! boriir touehes he medial border is ry, its inferior thyn

raore powe ngs from the poste ; proeesses (with iiid it is inserted i the upper surfact he rib and the gro

iterior triangle of

lation with the brae

Hibelayian artery.

pulie ; aod the dc

ineh ot the transv

musele. The k

Itioo with the ape

()f ihe li)ng thoi

|:k.

; sealenus posterit

; sealenus me

Iprings by two or l

HEAD AND NECK

of the eranium. Stroi^ bran'

between it and the first and the superior eendoal gan r'urther, the bypoglossal ncrve to it by fibrous attaehment, erehange of nerve filaments takes d it Distribntion of tlie Oeirieal ] branehes whieh spring from the neek are the foliowing: (i) aryngeal; {3) reeurrent; (4) cardia3 hairngenB. — The pharyngeal branl pper part of the ganglion nodosumB and anteriorly, superheial to tiie interB ;nd in the pharyngtal plextii, It two branehes, of whieh the upper ii Laryneeus Snpeiior. — This, a niueh largH . the middle of the ganglion nodosum. s and anteriorly, but differs rrom the passing deep to the intemal eari tion it ends by dividing into the tn/emaim rnal laryngeal nerves ; both of these '. ly seen in the disseetion of the anteriorl

it divide5, Ihe supetior laryngeat eATtets eos fine twigs with the superiot cervical ganglion of the s> ) receives one ot two rilaments from the phaiyiigeal pleJ

intemal laryngeal nerve runs to the interyal t »id bone and the thyreoid eartilage ; therJ iring under cover of the posterior border 1 hyoid musele, it pierees the membrane of thl uid enters the pharynx, and then deseends W

exkmal laryngeal nenie is a very slender braneh.l downwards and anteriorly to reaeh the erieo-tl in whieh it ends.

ng braneh from the superior cervical gangB

na BeeniTe&s. — The reeurrent nerve arisea 1 the two sides. On the right sidt, after spri

HEAD AND NECK

:ion, and one or more mirute

1 eonneetion with it. Its termina! twigs are

;]es and mueous membrane of the pharynx,

(the ramits lingualis vagi) eoniieets the pl_ ■poglossal nerve. HypoglossaB. — The hyp<^lossal nerve makes 1 the eranium through the eanalis hypoglJ ;rior eondyloid foramen). It pierees the dura ti jaraCe parts, whieh unite into one s my eanal, As it issues from the eanai it lies dee 3 the internal iugular vein and the internal ca immediately afterwards it inelines laterally, . half spiral turn around the ganglion nodosuni of t; t appears between the two vessels, and deseends betwel o the lower border of the posterior belly of the d j, where it passes into the earotid triangle. Its cl<4 etion with the ganglion nodosum of ihe yagus 1 noted already (p. 314). In the earotid triangle it hQo| 1 the lower end of the oeeipital artery, telo^ oid braneh, and, turning anteriorly, it ereiisses the oeeipita nternal and external earotid arteries and the loop of t" ual artery superlieially. Then it passes on ihe med :s of the posterior belly of the digastrie and the slylo-hyoi^ l enters the digastrie triangle, where it disappears medial be mylo-hyoid, and at the anterior border of the hyoglossuM nters the base of the tongue.

iramheso/eommunkaliiHi.—'Sei.iKhe baaeoT fhe skul! Ihehype^los ■oughl inlo eonneetioo wilh— (l) Ihe superior cervi(.-a1 ganglion ; (a) tl . is ; and (3) the firEt eenrieal nerve ; as it lurns loHnd the ociijMtBL ry it receives {4) the ramus Uiigualis vagi from Ihe pharyngeal pleitusa on the surface oi the hyoglossus it eommunieate'i witli (5) the linr"'"™ -e (|). 290).

Branekes of Dislribution. — (i) The meningeal braneh a he upper part of the eanalis hypoglossi, and, regaining E ;rior of the eranium, it is distributed to the dura 1 und the foramen magnum. (2) Yasmlar twigs are sajtd t supplied to the deep aspeet of the intemal jugular x The deseetidens kypoglosst, whieh conveys fibres of I t cervical ncrve to the infra-hyoid museles. (4) Tti«fr 'Ae thyreo-hyoid, whieh also eonsists of first cervical E es. (5) The terminal branehes, whieh ^'inuly the | lid and ail the intrinsie and extrinsic m ept the palato-glosstis.

3i8 HEAD AND NECK

Nerms Caroticus Internus, — This braneh has been noted passing from the upper end of the ganglion into the earotid eanal. Its distribution will be eonsidered later.

Nervi Garotiei Extemi, — Two to six iilaments, ealled external earotid branehes, run to the external earotid artery, and form a loose interlaeement around it and its branehes. From this extemal earotid plexus b, braneh is given to the earotid body, and prolongations are eontinued on all the branehes of the artery. The part eontinued upon the extemal maxillary artery supplies the sympathetie root to the sub- maxillary ganglion, whilst the subdivision upon the middle meningeal artery furnishes the eorresponding root to the otie ganglion, as well as the external superficial petrosal nerve whieh runs to the ganglion genieuli of the facial nerve.

Rami Laryngo-pharyngei, — The laryngo-pharyngeal branehes pass between the two earotid arteries to join the phar^oigeal plexus, and some join the superior laryngeal nerve.

Neruus Gardiaeus Superior, — This is a long slender braneh whieh springs by several roots from the ganglion, and then proeeeds downwards, posterior to the earotid artery. At different stages of its eourse it is joined by other branehes of the sympathetie, by a braneh from the vagus, and also by Alaments from the external laryngeal and reeurrent nerves. The right superior eardiae nerue is eontinued into the thorax by passing posterior or anterior to the subclavian artery, and it ends in the deep eardiae plexus. The lefi superior eardiae neroe follows the left eommon earotid artery in the thorax, and, erossing the left side of the areh of the aorta, ends in the superficial eardiae plexus.

Ganglion Cervicale Medium. — This ganglion is the smallest of the three ganglia of the neek. It is plaeed opposite the sixth cervical vertebra in elose proximity to the inferior thyreoid artery, upon whieh it not infrequently rests. Its branehes are: {^i) grey rami eommunieantes^ ^ibieh pass between the eontiguous margins of the sealenus anterior and longus eolli museles and eonneet it with the fifth and sixth cervical nerues ; (2) thyreoid branehes, whieh run to the thyreoid gland, along the inferior thyreoid artery, and form eonneetions with the external laryngeal and reeurrent nerves ; (3) the middle eardiae nerve.

On both sides the middle eardiae nerue enters the thorax and is lost in the deep eardiae plexus. On the right side

THYREOII) (;LANI) ^ir;

it passes posterior or anterior to tho sul>claviari ariery ; (m the /e// side it is eontinued downwards !)etwccn tlie r «iiiiinon earotid and subclavian arteries.

Gkmglion Gervicale Iiiferiiis. — The infcri(}r(;crvir.i] ^'an^Mion is lodged in the interval between the transvcrsc \i\uiK^^. of th»; seyenth cervical vertebra and the neek of the Tirst rib. In thi^ position it lies posterior to the vcrtcbral ariery. It ii by u*, means uneommon to find it more or less i:u\\.\i\*:\*-\\ fi] ■*■'], over the neek of the first rib, with the fii:»t thora' i'. '^\\u'^\v,u. The eonneetion between it and the middle fcrvi';i] \l;a\.'^\.'.u \. generally in the form of two or more >lcr:d'-r u*:x\k 'sr«! . *,{ whieh one passes anterior to the sulx:lavian ,kn*:\'y 'W.*-. latter loops round the subclavian nrlery nr.d i-! N.r:;*/! th'- ansa subclavia (Yieussenii).

The branehes of the infcrior ccrvira! i:ari''i:^r: .ir';

1. (}rey rami eommunieantes to ihe :»cV'.Ti'ri a:.': • -,;:.":. ' ■ : : .-

2. Kami vasculares.

3. Inferior eardiae nerve.

The rami vasctilares are fmc brai 1 '. h •: -. -a ;. ; ^ : , \',:\\. :i ;,]''., around the subclavian artery and its fyr'j.'y ;.■ .. '].'...•: around the vertebral artery are rerriari-ia'.!'; :'or i;,»:;r .;';;' ../• .

The neruus eardiaeus in/erior on b-^^ \\i -.y:-: . • ; r , r ♦: r . ' : . * : ':-';/ eardiae plexus.

After the vcssels and ner\es of •.,-,•: :.-:'.'/. :.-i.;*: -,':*■:. .*.#:.*': ihe disseetors should exani:,''jj *.:.■: *.:,}. -.'.;': ;;..;,';,

Glandula Thyreoidea. — Th-: tr.yr':'.;c ;.:;:.': i. o :..'/:.., vascular solid body, whieh elas;.-. \:.': ;.;.; *:r \/^r. 'A ?;,#; traehea-and extends upv.ard-. for ':;^r/i'; «'ii'/a. '.'.'; ■.]/,:. *::it\. side of the larynx. It vari'js greatiy :n ■.iz'; ;.'. (i'Ai».:'::/. m dividuals ; and in femaIo-s and (,r.:yirf:u it ;•, aiv.a)'; r';iat;v':i) larger than in adult nr-ale?;. I*. ^/jr.\'. .*.. 'A \:.T*:t: '*•«;;! ;/.ark':d subdinsions, viz., two latei-a! io'^e-h '//.:. f:*\ a^r/.h th'; u.t.rA^itt plane by the isthmus. Ea'.r. lattral loU ':\ •■,orr.';v.;ja*. ^.oni^al in form ; its base lies at '.he i';v-:i ^A \:.*: fifth or iu*: f>jxtli traeheal ring, whibt its a:y:.x T'sW'i ii'ti/^lr/.i tfiC bide ^^ the thyreoid eartilage. Its lupir/idal or lateral mr/au is fuU ai rounded. and is elothed r^y the \trf:\rdJAi*:'d\. biy4:r t fascia, from whieh it derive.s a hTA^sairt ; and it is c sterno-th)Teoid, stemo-hyoid, and orr. r>-hyoid mu the anterior border of the sterno-mastoid (f ij Its deep cr medial sur/aet is adapted to the 9

HEAn AND NF.CK

lies, viz., to ihe side of the traehea, the erieoid eartilage, and the thyreoid eartilage. Its postertor bttrder is in telation ' with the lateral margins of the eesophagus and the lateral

^^K margin or the pharj-nx, and in many eases it overlaps the ^^V eommon earotid artery. Its anterior border is eonneeted with

V* My

ispondiiig border of the opposite lateral lobe by the isthmus. Above the isthmus it is in relation with the anterior termiaal braneh of the superior thyreoid artery, and below the isthmus with the eommeneement of the inferior thyreoid vein. The isthmui of the thyreoid glaiid has already been seen in the disseetion of the middle line of the neek. It is a 'i band of varying width whieb lies anterior to the seeond, third,

TRAGHEA AND CESOPHAGUS 321

and fourth rings of the traehea, and, therefore, nearer the lower than the upper ends of the two lateral lobes.

An additional lobe, the pyramidal or middle lobe^ is frequently present. It is an elongated slender proeess whieh springs from the isthmus, on one or other side of the median plane (more usually on the left side), and extends upwards towards the hyoid bone. To this it may be eonneeted by fibrous tissue, or by a narrow slip of museular fibres ealled the levator glandulee thyreoideee, In some eases this little musele has an attaehment to the thyreoid gland independ- ently of the pyramidal proeess. The thyreoid gland is firmly eonneeted to the parts upon whieh it lies, and therefore follows the larynx in all its movements.

The disseetor should note the great vascularity of the thyreoid gland. Four large arteries, and oeeasionally a fifth smaller vessel, convey blood to its substanee. The two superior thyreoid branehes of the external earotid arteries divide at the apex of eaeh lateral lobe into three branehes for its supply ; the two inferior thyreoid branehes^ from the thyreo-cervical trunks of the subclavian arteries, distribute their terminal branehes to the basal portion and deep surface of eaeh lateral lobe. The oeeasional artery is the thyreoidea ima^ a braneh of the innominate or, more rarely, of the eommon earotid or the aortie areh. It aseends upon the anterior aspeet of the traehea to reaeh the isthmus of the thyreoid gland. These thyreoid arteries anastomose with eaeh other.

The veins whieh drain the blood away from the thyreoid gland are still more numerous. They arise in part by tributaries whieh spring from a venous network on the anterior face of the strueture, but chiefly by branehes whieh emerge from its substanee. They are three in number on eaeh side — viz. the superior thyreoid, the middle thyreoid, and the inferior thyreoid. The superior and middle t hyr,eo i d veins eross the eommon earotid artery and join the internal jugular ; the inferior thy^-eeid vein deseends on the traehea. At the root of the neek it usually joins its fellow of the opposite side to form a eommon stem whieh opens into the left innominale.

Traehea and (Esophagus. — The windpipe and the gullet in the cervical portion of their eourse may now be studied. Both begin at the level of the erieoid eartilage, anterior to the sixth cervical vertebra. From this point they extcnd downwards, anterior to the vertebral eolumn, to the thoraeie cavity.

The traehea, or windpipe^ is a wide tube whieh is kept eonstantly patent by the eartilaginous rings embedded in its walls. These rings do not form eomplete eireles ; posteriorly they are deficient, and, in consequence, the posterior surface of the traehea is Aattened. Above, it is eontinuous with the larynx, and, throughout its eourse in the neek, it is plaeed in the median plane of the body. The anterior relations of the

voL. II — 21

HEAD AND NECK

tiaetiea have already been rully diseussed in eonneetioii with the deseription of the parts oeeupying the middle line of the 1 neek {]). aig). Posteriorly, it rests upon the guUet. Upor «V(fer«flfe is tlieeommon earotid artery; whilst elosely applied ' to it in its upper part is the lateral lobe of the thyreoid gland. The reeurrent nerve aseends, on eaeb side, in the i angle between the traehea and eesophagus.

IThe eesophagus or gulkt is a narrow tube, with thiek , museular walls, whieh extends frora the pharynx to the stomaeh. In the cervica! part of its eourse it lies between the \ traehea and the longus eolli rausdes, and as il deseends

' Vsgu

r

it inelines, shghtly to the left, so that t eomes n ore elosely -I into relation with the lat ra! obe of the h) eo d gland and I the earotid sheath upon the left s de tban w th the same J struetures on the oppos te s de

The disseetor n ay erm a e h s d sseet on of the neek byl an examination of the sealene n useles and the reetus eap tts'l lateralis.

Museuli Sealeoi. — These museles eonstitute the Aeshy mass I whieh is seen extending from tbe transvcrse proeesses of the I cervical vertebr3e to the upper two eostal arebes. They are I three in number, and are named, from tbeir relative positions, f anterior, ttttdius, aad postrrior.

Afusculus Sealettus Anlerior. — ^Tbis is a well-defined musclej whieh is separaled from ihe sealenus medius by the rool

SGALENE MUSGLES 323

the braehial plexus and the subclavian artery. It arises froin the anterior tubereles of the transverse proeesses of the third, fourth, fifth, and sixth cervical vertebrae, and, tapering some- what as it deseends, it is inserted into the sealene tuberele on the inner margin of the first rib, and also into the superior surface of the same bone between the two subclavian grooves.

The upper part of its anterior surface is eoneealed by the sterno-mastoid and the lower part by the clavicle. The eommon earotid artery deseends along its medial border. Between it and the sterno-mastoid lie the internal jugular vein ; the intermediate tendon of the omo-hyoid ; the phrenie nerve, passing downwards and medially; and the transverse cervical and transverse seapular arteries passing postero- laterally, superficial to the phrenie nerve. Between it and the clavicle lies the subclavian vein.

Its posterior surface is in relation, above, with the tips of the lower cervical transverse proeesses, and below, with the apex of the pleura, the seeond part of the subclavian artery, and its costo-cervical braneh. The lateral border touehes the roots of the braehial plexus, and the tnedial border is in relation with the thyreo-cervical artery, its inferior thyreoid braneh, and with the vertebral artery.

Museulus Sealenus Medius, — This is a more powerful musele than the preeeding. It springs from the posterior tubereles of all the cervical transverse proeesses (with the exception, in some eases, of the first), and it is inserted into a rough oval impression whieh marks the upper surface of the first rib between the tuberele of the rib and the groove for the subclavian artery.

It forms part of the floor of the posterior triangle of the neek. Its superficial surface is in relation with the braehial plexus and the third part of the subclavian artery. Its posterior border touehes the levator seapulse ; and the dorsal seapular nerve and the deseending braneh of the transverse cervical artery pass between it and that musele. The lower part of its anterior border is in relation with the apex of the pleura, and the upper two roots of the long thoraeie nerve pieree the substanee of the musele.

Museulus Sealenus Posterior. — The sealenus posterior is generally inseparable, at its origin, from the sealenus medius. It is the smallest of the three, and springs by two or three

II— 21«

3i8 HEAD AND NECK

Nerms Caroticus Iniernus, — This braneh has been noted passing from the upper end of the ganglion into the earotid eanal. Its distribution will be eonsidered later.

Nervi Carotici Extemi. — Two to six filaments, ealled external earotid branehes, run to the external earotid artery, and form a loose interlaeement around it and its branehes. From this extemal earotid plexus a braneh is given to the earotid body, and prolongations are eontinued on all the branehes of the artery. The part eontinued upon the external maxillary artery supplies the sympathetie root to the sub- maxillary ganglion, whilst the subdivision upon the middle meningeal artery furnishes the eorresponding root to the otie ganglion, as well as the external superficial petrosal nerue whieh runs to the ganglion genieuli of the facial nerve.

Rami Laryngo-pharyngeL — The laryngo-pharyngeal branehes pass between the two earotid arteries to join the pharyngeal plexus, and some join the superior laryngeal nerve.

Nerous Cardiacus Superior — This is a long slender braneh whieh springs by several roots from the ganglion, and then proeeeds downwards, posterior to the earotid artery. At different stages of its eourse it is joined by other branehes of the sympathetie, by a braneh from the vagus, and also by filaments from the external laryngeal and reeurrent nerves. The right superior eardiae nerue is eontinued into the thorax by passing posterior or anterior to the subclavian artery, and it ends in the deep eardiae plexus. The lefi superior eardiae neroe follows the left eommon earotid artery in the thorax, and, erossing the left side of the areh of the aorta, ends in the superficial eardiae plexus.

Ganglion Cervicale Medium. — This ganglion is the smallest of the three ganglia of the neek. It is plaeed opposite the sixth cervical vertebra in elose proximity to the inferior thyreoid artery, upon whieh it not infrequently rests. Its branehes are: {i) grey rami eommunieantes, whieh pass between the eontiguous margins of the sealenus anterior and longus eolli museles and eonneet it with the fifth and sixth eeruieal nerues \ (2) thyreoid branehes^ whieh run to the thyreoid gland, along the inferior thyreoid artery, and form eonneetions with the external laryngeal and reeurrent nerves ; (3) the middle eardiae nerve.

On both sides the middle eardiae nerue enters the thorax and is lost in the deep eardiae plexus. On the right side

312 HEAD AND NECK

There are still other points in eonneetion with the glosso-pharyngeal nerve whieh require mention. At the lower part of the jugular foramen two small ganglia are formed upon its trunk, and from the lower of these eertain minute branehes are given off. The upper ganglion is ealled the ganglion superius ; the lower one is termed the ganglion petrosum,

The superior gangiion is a small ganglionie swelling, whieh involves only a portion of the fibres of the nerve trunk. It is plaeed in the upper part of the bony groove in whieh the nerve lies as it proeeeds through the jugular foramen. No branehes arise from it.

The petrous ganglion is a larger swelling, whieh involves the entire nerve-trunk, and lies at the opening of the jugular foramen, between the vagus nerve and the inferior petrosal sinus (whieh intervenes between it and the anterior border of the foramen). Its length is not more than two or three lines. Three branehes of eommunieation enter or proeeed from it. These eonneet it with — (i) the superior cervical sympathetie ganglion ; (2) the aurieular braneh of the vagus ; and (3) the jugular ganglion of the vagus.

In addition to these twigs the tympanie nerue takes origin from the petrous ganglion.

Tympanie Nerye. — The ultimate destination of this nerve may be regarded as the otie ganglion, but it takes a very eireuitous route to gain that strueture and it gives off branehes on the way. It enters a small foramen on the ridge whieh separates the jugular fossa from the earotid foramen on the lower surface of the petrous bone, and it is eondueted by a narrow eanal to the tympanie cavity. It erosses the inner wall of this ehamber, grooving the promontory. Having gained the anterior part of the tympanum, it enters the bone a seeond time, and runs in a minute eanal, whieh tunnels the petrous bone below the upper end of the ehannel in whieh is lodged the tensor tympani musele. In this part of its eourse the tympanie nerve is joined by a braneh from the ganglion genieuli of the facial nerve, and, after the junction is effected, it is termed the small super- ficial petrosal nerue.

The eanal in whieh the small superficial petrosal nerue is lodged opens into the eranial cavity upon the anterior surface of the petrous bone, immediately lateral to the hiatus eanalis facialis (O.T. Fallopii). Through this the nerve emerges, and soon leaves the interior of the eranium by passing downwards in the interval between the great wing of the sphenoid and the petrous part of the temporal bone, or through the eanalieulus innominatus, or through the foramen ovale. Outside the skull it ends by joining the otie ganglion.

In the tympanie cavity the tympanie nerve gives branehes of supply — (i) to the mueous membrane of the tympanum ; (2) to the lining membrane of the mastoid eells ; and (3) to the mueous membrane of the auditory tube (Eustaehian). It is eonneeted with the sympathetie plexus on the internal earotid artery by the superior and inferior earotieo-tympanie branehes whieh pieree the substanee of the petrous part of the temporal bone.

Nennis Vagus. — The vagus passes through the middle eompartment of the jugular foramen in eompany with the aeeessory — both being ineluded within the same sheath of dura mater. In the neek it pursues a vertical eourse, lying, at first, between the internal jugular vein and the internal earotid artery, and afterwards between the same

GREAT YESSELS AND NERYES 0F NECK 313

vein and the eommon earotid artery, enelosed within the sheath whieh envelops the vessels, but on a plane posterior to them. Its posterior relations, therefore, are similar to those of the internal and eommon earotid arteries. At the root of the neek it enters the thorax, and has different relations on the two sides. On the right side it erosses the first part of the subclavian artery ; on the left side^ after erossing anterior to the thoraeie duet, it proeeeds downwards between the eommon earotid and left subclavian arteries, posterior to the left innominate vein. For its thoraeie relations see p. 99.

The vagus, like the glosso-pharyngeal, has two ganglia in eonneetion with its upper part. These are the ganglion jugulare and the ganglion nodosum,

Ganglion Jugulaxe (O.T. Ganglion of Root).— This is situated within the jugular foramen. It is a rounded swelling whieh is eonneeted by eom- munieating twigs with several of the nerves in the neighbourhood, and it gives off two branehes of distribution.

Branehes of Communication. — (i) With the facial nerve ; (2) withthe petrous ganglion of the glosso-pharyngeal ; (3) with the aeeessory ; (4) with the superior ganglion of the sympathetie.

Branehes of Distribution. — (i) Meningeal ; (2) Aurieular nerve.

The meningeal braneh is a minute twig whieh runs upwards through the jugular foramen, and, dividing into two branehes, is distributed to the dura mater in the posterior eranial fossa.

The aurieular nerue (O.T. Arnold's nerve) obtains a filament of eom- munieation from the petrous ganglion of the glosso-pharyngeal, and passes posteriorly upon the lateral surface of the bulb of the internal jugular vein to enter a minute aperture on the posterior part of the lateral wall of the jugular fossa. A narrow eanal then eonduets it through the substanee of the temporal bone, and, on its way, it erosses the eanalis facialis a short distanee above the stylo-mastoid foramen. It is thus brought into elose relation with the facial nerve and is eonneeted with it by an aseending and a deseending braneh of eommunieation. Finally, it appears on the surface of the skull, in the interval between the mastoid proeess and the external aeustie meatus, where it eommunieates with the posterior aurieular braneh of the facial. It supplies the skin on the posterior aspeet of the outer surface of the walls of the meatus, the skin covering the lower half of the inner surface of the wall of the meatus, and the lower half of the tympanie membrane.

Ganglion Nodosum. — After emerging from the jugular foramen, the vagus nerve is joined by the eerebral portion of the aeeessory nerve^ and swells out into the ganglion nodosum (O.T. ganglion of trunk).

The ganglion nodosum is an elongated reddish-eoloured swelling of about three-quarters of an ineh in length, whieh is developed upon the stem of the vagus half an ineh

322 HEAD AND NECK

traehea have already beeti fully diseussed in eonneetion with the deseriplion of the parts oeeupying the middle line of the neek (p. 229). Posteriorly, it rests upon the gullet Upon eiiher side is the eommon earotid artery ; whilst elosely applied to it in its upper part is the lateral lobe of the thyreoid gland. The reeurrent iierve aseends, on eaeh side, in the angle between the traehea and eesophagus.

The «sophagus or gullet is a narrow tube, with thiek museular walls, whieh extends Trom the pharynx to the stomaeh. In the cervical part of its eourse it lies between the traehea and the longus eoUi museles, and as it deseends

it inelines slightly to the left, so that it eomes more dosely into relation wiih the lateral lobe of the thyreoid gland and the earotid sheath upon the left side than with the same struetures on the opposite side.

The disseetor may terminate his disseetion of the neek by an examination of the sealene museles, and the reetus eapitis lateralis.

Museuli Sealeni,— -These museles eonstitute the Aeshy mass whieh is seen extending from the transverse proeesses of the eeryieal vertebrK to the upper two eostal arehes. They are three in number, and are named, from their relaliye positions, anterior, medius, 2.nA posierior.

Miiseulus Sealenus Anterior. — This is a well-delined musele whieh is separated from the sealenus medius by the roots of

SGALENE MUSGLES 3« 3

the braehial plexus and the subclavian artery. It arises frotn the anterior tubereles of the transverse proeesses of the third, fourth, fifth, and sixth eenrieal yertebrse, and, tapering some- what as it deseends, it is inserted into the sealene tuberele on the inner margin of the first rib, and also into the superior surface of the same bone between the two subclavian grooyes.

The upper part of its anterior surface is eoneealed by the sterno-mastoid and the lower part by the clavicle. The eommon earotid artery deseends along its medial border. Between it and the stemo-mastoid lie the intemal jugular vein ; the intermediate tendon of the omo-hyoid ; the phrenie nerve, passing downwards and medially; and the transverse cervical and transverse seapular arteries passing postero- laterally, superficial to the phrenie nerve. Between it and the clavicle lies the subclavian vein.

Its posterior surface is in relation, above, with the tips of the lower cervical transverse proeesses, and below, with the apex of the pleura, the seeond part of the subclavian artery, and its costo-cervical braneh. The lateral border touehes the roots of the braehial plexus, and the medial border is in relation with the thyreo-cervical artery, its inferior thyreoid braneh, and with the vertebral artery.

Museulus Sealenus Medius, — This is a more powerful musele than the preeeding. It springs from the posterior tubereles of all the cervical transverse proeesses (with the exception, in some eases, of the first), and it is inserted into a rough oval impression whieh marks the upper surface of the first rib between the tuberele of the rib and the groove for the subclavian artery.

It forms part of the floor of the posterior triangle of the neek. Its superficial surface is in relation with the braehial plexus and the third part of the subclavian artery. Its posterior border touehes the levator seapulse ; and the dorsal seapular nerve and the deseending braneh of the transverse cervical artery pass between it and that musele. The lower part of its anterior border is in relation with the apex of the pleura, and the upper two roots of the long thoraeie nerve pieree the substanee of the musele.

Museulus Sealenus Posterior, — The sealenus posterior is generally inseparable, at its origin, from the sealenus medius. It is the smallest of the three, and springs by two or three

11—21 a

3»4

HEAD AND NECK

slips from the transverse proeesses of a eorresponding number of the lower cervical vertebr£e in eommon with the sealenus medtus. It is inserted into the upper border of the seeond rib, immediately anterior to the insertion of the levator eostse.

The sealene museles are supplied by twigs from the anierior branehes of tht cervical nerves, partiatlarly the lower

Dhseelion.—Tbs liltle muEele termed (he reelus eapilis lateralis should now be eieaned, and its attadiments detined. It lies in the inlerral between the transverse proeess of the alks and Iheiueular proeess of the oeeipital bone, posterior lo Ihe eommeneement of the inlernal jugular veiD. Tbe anterior braneh of the (irsl eenrieal nerve wiU t>e seeo emerging from under cover of its medial mai^in.

LATERAL PART OF MIDDLE GRANIAL EOSSA 325

Beetns Oapitis Lateralis. — ^The reetus lateralis arises from . the anterior part of the upper surface of the extremity of the transverse proeess of the atlas, and is inserted into the under surface of the jugular proeess of the oeeipital bone. It is supplied by a twig from the anterior braneh of the first cervical nerve.

BemoTal of the Head and Neek from the Tnmk.— By the time that the disseetors of the head and neek have arrived at this stage of their work, the disseetors of the thorax have in all probability finished their disseetion. If this is the ease, the head and neek may be removed from the tnink by eutting through the vertebral eolumn at the level of the intervertebral fibro- eartilage between the third and fourth thoraeie vertebrae. By this pro- eeeding the upper three thoraeie ^erte'brse, with the attaehed portions of the first, seeond, and third pairs of ribs, are removed with the neek. The sealene museles and the longus eoUi are therefore preserved intaet.

THE LATERAL PART 0F THE MIDDLE

GRANIAL FOSSA.

The struetures eontained within the middle eranial fossa may now be examined. In earrying out this disseetioii, the head should be supported on a bloek so that the floor of the eranial cavity looks upwards. The following are the struetures whieh must be displayed : —

1. Cavernous venous sinus.

2. Internal earotid artery.

3. Middle meningeal artery.

4. Aeeessory meningeal artery.

5. The two roots of the Trigeminal nerve, with the Semilunar

ganglion and the three main divisions of the trigeminal nerve.

6. Oeulo-motor nerve (3rd eerebral). . .

7. Troehlear nerve (^th eerebral).

8. Abdueent nerve (6th eerebral).

9. Internal earotid plexus of the sympathetie.

10. Greater superficial petrosal nerve.

11. Smaller superficial petrosal nerve.

Disseetion. — ^The dura mater has already been removed from one half of the middle eranial fossa, and on that side it is only neeessary to differentiate the stnietures whieh lie in the cavemous sinus ; on the other side the dura mater must be stripped from the medial part of the lateral portion of the middle eranial fossa. Enter the knife at the anterior elinoid proeess, and earry it posteriorly to the apex of the petrous bone. This ineision must go no deeper than is neeessary to divide the dura mater, and must be made immediately to the lateral side of the openings in the membrane through whieh the oeulo-motor, the troehlear, and tngeminal nenres pass.* It is

6 HEAD AND NECK

f important to preserve these apertures inlaet, so ttia.t the prenumal 5 of the nerve9 may be held in position duiing the disseetion. The n thiDUgh the daea. matei may now be earried postero-Iaterally along

the upper border of the petrous bone ii

the li

if ihe supeiioi petrosal

sr with great

eare, for it is intimately eonneeted with the netve» whieh lie subiaeent to it. Tbus, where il forms the latera! watl of the cava^oiis sinus, it is elosely applied to the oeulo-motor and tioehlear nerves, and tirmly attaehed to tbe ophthalmie division of Ihe tiigeminal nerve, whilst over the petrous bone it is united to the surface of tbe semilunai gajiglion. The edge of tbe knire, theTefole, musl be kept elose to the membrane, and > small portion of the membrane may be left upon ihe neryes. This ean be removed afterwa.rds as Ihe neryes are delined.

Sinns CavenioBtt8. — The cavernous sinus has been opened

by the above disseetion. It is a short, wlde venous ehannel, whieh extends along the side of the body of the sphenoid bone, from the lower and medial end or the superior orbital Sssure (O.T, sphenoidal lissure} to the apex of the petrous pbrtion of the temporal bone. Anteriorly, blood is eondueted into it by the ophthalmie veins and the spheno-parietal sinus ; whilst posteriorly the blood is drained away by the superior and inferior petrosal sinuses. But it has still other eonneetions. Thus, it receives blood from the lower part of the lateral surface of the brain by the superficial middle eerebral vein and some small inferior eerebral veins. It is united with the eorresponding sinus of the opposite side by means of the anterior and posierior intercavernous sinuses (p. 2 1 7). Lastly, one or more emissary veins Ieave its lower aspeet ; one passes out of the eranium by the foramen ovale, or it may be

SGALENE MUSGLES 323

the braehial plexus and the subclavian artery. It arises froin the anterior tubereles of the transverse proeesses of the third, fourth, fifch, and sixth cervical yertebrie, and, tapering some- what as it deseends, it is inserted into the sealene tuberde on the inner margin of the first rib, and also into the superior surtaee of the same bone between the two subclavian grooves.

The upper part of its anterior sur/aee is eoneealed by the stemo-mastoid and the lower part by the elayiele. The eommon earotid artery deseends along its medial border. Between it and the stemo-raastoid lie the internal jugu!ar vein ; the intermediate tendon of the omo-hyoid ; the phrenie nerve, passing downwards and medially; and the transverse cervical and transverse seapular arteries passing postero- laterally, superficial to the phrenie nerve. Between it and the clavicle lies the subclavian vein.

Its posterior sur/aee is in relation, above, with the tips of the lower cervical transverse proeesses, and below, with the apen of the pleura, the seeond part of the subckvian artery, and its costo-cervical braneh. The lateral border touehes the roots of the braehial plexus, and the medial border is in relation with the thyreo-cervical artery, its inferior thyreoid braneh, and with the vertebral artery.

Museulus Sealenus Medii/s.—Tius is a inore power^nl musele than the preeedlng. It springs from the posterior tubereles of all the cervical transyerse proeesses (with the exception, in some eases, of the first), and it is inserted into a rough oval impression whieh marks the upper surface of the first rib between the tuberele of the rib and the groove for the subclavian artery.

It forms part of the floor of the posterior triangle of the neek. Its superficial surface is in relation with the braehial plexus and the third part of the subclavian artery. Its posterior border touehes the !evator seapulas ; and the dorsal seapular nerve and the deseending braneh of the transverse cervical artery pass between it and that musele. The lower part of its anterior border is in relation with the apex of the pleura, and the upper two roots of the !ong thoraeie nerve pieree the substanee of the musele.

Musmlus Sealenus Posterior. — The sealenus posterior is generally inseparable, at its origin, from the sealenus medius. It is the smallest of the three, and springs bytwo or Ihree

328 HEAU AND NECK

Nerva8 Trigemiiius. — The two roots of this nerve have already been seen piereing the dura mater at the apex of the petrous portion of the temporal bone under the anterior margin of the tentorium. Now that the dura mater has been raised from the lateral part of ihe middle eranial fossa, the further relations of these nerve-roots within the eranium may be studied, It will be noiieed that the loosely eonneeted

■ned lalerally.

and parallel funiculi of the portio major, or sensory root, at onee begin to divide and join with eaeh other so as to form a dense plexiform arrangement, whilst, at the same time, the nerve-root inereases somewhat in breadth. The interlaee- ment, thus brought about, oeeupies the smooth depression whieh marks the anterior aspeet of the apex of the petrous portion of the temporal bone, and it sinks into the semilunar ganglion (O.T. Gasserian).

LATERAL PART 0F MIDDLE GRANIAL POSSA 329

The Ganglion Semilunare (O.T. Gasserian) is somewhat ereseentie in form. It lies upon the sutural junction between the apex of the petrous bone and the great wing of the sphenoid bone, where it is enelosed within a reeess or spaee, ealled the cavum Meekelii^ formed by a separation of the two layers of the dura mater. The concavity of the ganglion is direeted postero-medially, and it is upon this aspeet that it receives the interlaeing libres of the sensory root of the trigeminal nerve ; the convexity of the ganglion is direeted antero-laterally and from it emerge the three main divisions of the trigeminal nerve. These are — (i) the lirst, or ophthalmie division ; (2) the seeond, or maxillary division ; and (3) the third, or mandibular division. The medial border of the ganglion is eonneeted with the internal earotid sympathetie plexus by filaments of eommunieation.

The/or/io minor or motor root of the fifth nerve should now be followed. Before the nerve pierees the dura mater the motor root lies along the medial side of the large sensory root, but it soon ehanges its position and eomes to lie beneath the sensory part. To display this relationship, draw the eut ends of the two roots through the aperture in the dura mater whieh leads into the cavum Meekelii, and, gently dislodging the semilunar ganglion from its plaee, turn it antero-laterally so as to expose its deep surface. The small and firm motor root ean readily be reeognised lying in a groove upon the deep surface of the ganglion ; and if it* is displaeed from this, it will be seen to have no eonneetion with the ganglion, but to be eontinued onwards towards the foramen ovale. It ultimately joins the mandibular division of the trigeminal nerve. This junction may take plaee within the eranium, in the foramen ovale, or immediately outside the skull.

The three prineipal divisions of the trigeminal nerve may next be examined. Begin with the mandibular division, whieh is the largest. This proeeeds direetly downwards, and almost immediately leaves the eranial cavity through the foramen ovale.

-• Whilst isolating this large nerve-tnink and defining the bony aperture through whieh it makes its exit, look eareiiilly for the aeeessory meningeal artery, whieh enters the eranium through the same foramen. If the injection has been forced into this vessel it ean easily be deteeted. An emissary vein whieh eonneets the cavemous sinus with the pterygoid venous plexus also passes through the foramen oyale.

330 HEAD AND NECK

The maxillary division is eomposed entirely of sensory Abres. It runs anteriorly in relation to the lower and lateral part of the cavernous sinus, and, after a short eourse within the eranium, makes its exit through the foramen rotundum. Near its origin it gives off a fine meningeal braneh to the dura mater of the middle fossa of the eranium.

The ophthalmie division is the smallest of the three branehes of the trigeminal nerve, and, like the maxillary, it is eoni- posed entirely of sensory fibres. It passes anteriorly in the lateral wall of the cavernous sinus, and ends, elose to the superior orbital fissure, by dividing into three terminal branehes. As it traverses the sinus it is aeeompanied by the oeulo- motor and troehlear nerves, both of whieh oeeupy a higher level. Like the other two divisions of the trigeminal nerve, the ophthalmie nerve gives off a meningeal braneh, This small twig passes into the tentorium eerebelli.

The terminal branehes of the ophthalmie division of the trigeminal nerve are the naso-eiliary, the laerimal, and the frontal. The naso-eiliary^ as a rule, takes origin first ; the laerimal is given off soon after; and then the stem of the nerve is eontinued onwards as the /rontal. These three nerves enter the orbit through the superior orbital fissure.

Neryus Oeulomotorius (Third), Nervus Troehlearis (Foiirtli), and Nennis Abdueens (Sixth). — It has been noted already that the oeulo-motor nerve pierees the dura mater within the small triangular area, in the middle eranial fossa, whieh lies immediately anterior to the erossing of the attaehed and free margins of the tentorium (p. 210). It has been noted also that the troehlear (fourth) nerve pierees the dura mater in the posterior fossa under the free margin of the tentorium. Both now proeeed anteriorly in the lateral wall of the cavern- ous sinus. The oeulo-motor nerve oeeupies the highest level, then eomes the troehlear nerve, and immediately below that the ophthalmie division of the trigeminal nerve. They therefore present a numerieal order from above down- wards. The abdueent nerue^ whieh pierees the dura mater in the posterior fossa, at the lower and lateral part of the dorsum sellas, curves round the lateral side of the internal earotid artery, and then passes anteriorly more direetly within the cavernous sinus than the others (Fig. 130).

The oeulo-motor, troehlear, and abdueent nerves during their eourse in the cavernous sinus receive eommuniea-

LATERAL PART OF MIDDLE GRANIAL FOSSA 331

tions from the earotid plexus and froni the ophihalmie nerve, and they al] enter the orbit by passmg through the supenor orbital fissure Before domg so, the oeulo motor nerve dmdes into an upper and a lower division As they pass through the supenor orbital fissure the vanous

nerves undergo a ehange in their relative positions. This, howeyer, will be studied in the disseetion of the orbit.

Arteria Garotis Interna. — The intraeranial portion of the intemal earotid artery may now be examined. It Hes upon the bteral aspeet of the body of the sphenoid, and, for the greater part of its eourse, it traverses the cavernous sinus. It emerges from the earotid eanal into the foramen laeenim at the apex of the petrous bone ; then it passes through the upper part of the foramen laeerum, pierees the outer layer

332 HEAD AND NECK

of dura mater, and enters the middle eranial fossa at the root of the posterior elinoid proeess ; there it bends at right angles, and passes anteriorly to the lower root of the small wing of the sphenoid, where it turns abruptly upwards and pierees the inner layer of the dura mater, immediately posterior to the entranee of the optie nerve into the optie foramen, and on the medial side of the anterior elinoid proeess. It was severed at this point during the removal of the brain ; but it will be afterwards seen to end on the basal aspeet of the brain, at the eommeneement of the Assura lateralis (O.T. Sylvian fissure), by dividing into the anterior and middle eerebral arteries. Throughout its whole eourse it is surrounded by sympathetie Alaments, and soon after its entranee into the eranium the abdueent nerve erosses its lateral side.

The intraeranial portion of the internal earotid artery giyes off the following branehes : —

These are minute twigs whieh arise in the cavernous sinus.

1. Branehes to the hypophysis,

2. Branehes to the semilunar ganglion,

3. Branehes to the dura mater,

4. Ophthalmie, ^

5. Posterior eommunieating, I These will be studied at a later

6. Anterior eerebral, \ terminal j stage.

7. Middle eerebral, / branehes. J

8. Ghoroidal.

Plexiis Oarotieus Intemus. — The sympathetie filaments whieh form this plexus ean be satisfactorily disseeted only in a subject whieh has not been injected ; and even then, the disseetion is an exceedingly difl5cult one. The intemal earoHd plexus is plaeed in the cavernous sinus and is chiefly massed upon the lower and medial aspeet of the internal earotid artery, at the point where it makes its bend upwards. It supplies filaments to the hypophysis, to the third and fourth nerves, and to the ophthalmie division of the trigeminal nerve, and gives the sympathetie root to the eiliary ganglion (O.T. lentieular ganglion).

Nervus Petrosus Superficialis Major. — ^This small nerve, along with a small arterial twig from the middle meningeal artery, ean readily be exposed in the groove on the anterior face of the petrous bone whieh leads from the hiatus eanalis facialis to the foramen laeerum. It is plaeed under the semilunar ganglion, whieh must therefore be turned antero-laterally. In the eanalis facialis it joins the ganglion genieuli of the facial nerve. When traeed in the opposite direetion, it will

DISSEenON OF THE ORBIT 333

be foiiiid to mtor the foiamen laeennn, where it joins the nenms fetrosus pra/undus firoin the earodd plexus. The tnink formed by the union of these two fi1aments is the nerms eanalis ^aygoidei {pjT, Vidian neroey,

NenmB Petoosus SuperAeialiB Idior appeais upon the anterior face of the petrous bone, throogh an apertnre whieh is plaeed immediately lateral to the hiatns eanalis ^aieialis. It leaves the eramal cavity by passing down¥Fards between the great wing of the sphenoid and the petrous part of the temporal bone, or through the eanalieulus innominatus or through the foramen ovale, to reaeh the otie ganglion. This minute nerve, as has been mentioned already (p. 312), is formed by the union of the tympanie braneh of the glosso-pharyngeal with a braneh from the ganglion genieuU of the &cial.

Ertomal Saperficial Petrosal Nerre. — It is convenient at this stage to take note of a fourth petrosal nerve — the extemal supcrficial petrosaL It takes origin from the sympathetie plexus whieh aeeompanies the middle meningeal artery, and, entering the petrous bone, is eondueted to the ganglion genieuU of the facial nenre.

Middle and Aeeessory Menmgeal Arteries. — The entranee of the middle meningeal artery through the foramen spinosum should now be examined. It gives minute twigs to the semilunar ganglion, and one — the petrosal artery — whieh aeeompanies the great superficial petrosal nerve into the hiatus eanalis facialis. The further eourse of the middle meningeal artery has been deseribed already (pp. 220). The neryus spinosus of the mandibular nerve also enters the eranium through the foramen spinosum (p. 275).

The aeeessory meningeal artery enters the eranium through the forameh ovale, and is distributed chiefly to the semilunar ganglion.

DISSEGTIGN 0F THE ORBIT.

Within the orbital cavity the following struetures are grouped around the eyeball and the optie nerve : —

'Reetus superior. Reetus inferior. Reetus lateralis. Museles, . ,\ Reetus medialis. Obliquus superior. ObUquus inferior. . Levator palpebrae superioris. I Ophthalmie artery and its branehes. Yessels, . . ^. Ophthalmie veins (superior and inferior) witb their tribo- \ taries.

334 HEAD AND NECK

Nerves,

''Oeulo-motor (^rd eerebral). Troehlear (^th eerebral). Abdueent (6th eerebral). Prontal,

j . j I from ophthalmie division of the trigeminal

XT -i-' 1 or fifth eerebral nerve. Naso-eihary, j

Zygomatic braneh of the maxillary division of the tri-

geminal nerve.

Giliary ganglion.

Laerimal gland.

Fascia Bulbi.

Dtsseetion. — The roof of the orbit must be removed with the aid of the saw, the ehisel, and the bone forceps. Begin by removing the thiek eranial wall above the orbital opening, leaving only a thin portion eorre- sponding to the superior orbital areh. Whilst this is being done, eare should be taken to preserve the soft parts of the forehead and the upper eyelid. It is of great advantage to retain, throughout the whole examination of the orbital cavity, the bony ring whieh eonstitutes its opening on the face. The thin roof of the orbit may next be removed with the ehisel and bone forceps. The lesser wing of the sphenoid, where it forms the upper boundary of the superior orbital fissure, should be taken away by the bone forceps, but the disseetor should carefully preserve intaet the ring of bone around the optie foramen. The superior orbital fissure is now fully opened up, and the various nerves, as they enter the orbit from the cavernous sinus, may be followed out. Lastly, the anterior elinoid proeess may be taken away with advantage.

Periosteum. — If the disseetion has been successfully earried out, the periosteum elothing the under surface of the orbital roof will be exposed uninjured. The periosteum of the orbit forms a funnel-shaped sheath, whieh eneloses all the eontents of the cavity except.the zygomatic nerve, and is but loosely attaehed to its bony walls. Posteriorly it is direetly eontinuous, through the superior orbital fissure, with the dura mater. Expanding with the cavity, it beeomes eon- tinuous anteriorly, around the orbital opening, with the periosteum whieh elothes the exterior of the skull. Here also it presents important eonneetions with the palpebral fascia.

BeAeetion of the Periosteum and the subse^uent DiBseetion. — The

periosteum should be divided along the middle line of the orbit, and then transversely elose to the orbital opening. It ean now be thrown medially and laterally. When this is done, the laerimal gland will be exposed in the antero-lateral part of the cavity. Further, the large frontal nerve, lying upon the upper surface of the levator palpebroe superioris, will be seen in the middle line of the orbit ; as it approaehes the anterior part of the cavity it is joined by the supra-orbital artery. The other superficial struetures are usually more or less obseured by the soft pliable fat, whieh every- where fills up the interstiees between the different orbital eontents. On carefully separating this, along the medial wall of the orbit, the superior oblique musele will be more fully displayed, and lying upon and entering

DISSEGTION OF THE ORBIT

335

the posterior part of this musele the small Itoehleai or fourth eeiebtal nerve will be discovered. The disseetor often fails to find this nerve, beeause as a geneial nile he looks for il too lat fotwatd5. Lastly, the Inerimal ncrve aod attery will be found, running along the lateta! wall of the orbit, above the level of the uppei margin of the lateral reetus musele.

These struetures must be thoioughly eleaned and isolaled by the removal of ihe .fal from around them. As the superior ohUque musele is followed anteriorly it will be found to end in a slender tendon, whieb passes through a ring-like pulley attaehed to the medial angular proeess of

;. 133— The Ophtha

delined, and the tendon of tbe musele followe<l lalerally from it to its inseition inlo Ihe eyeball. Nole that the levator paipebia; superioiis lies upon tbe upper suiface of the supeiiot reetus, and, if it is laised, a nerve twig will be notieed emerging ftom the substanee of Ihe reetus superiot for the supply of ibe levator palpebrs musele. This is a braneb of ehe supeiioi division of the third netve. .

The disseetion of the above parts wiU be facilitated by grasping the anterior part of the eyeball wilh Ihe foiceps and drawing it forwards. It may be retained in this position by running a line needle and thiead through the oeulat conjunctiva and stitehing it to the nose. In doing ibis, however, take eate that the needle does nol penetrale Ihe eomea, beeause this might lender the subsequenl inilation of tJie eyeball impos^ble.

336 HEAD AND NECK

Nennis Prontalis. — The frontal nerve is the eontinuation of the stem of the ophthalmie division of the trigeminal nerve, after it has given off its laerimal and naso-eiliary branehes. It enters the orbit through the superior orbital fissure, above the museles, and runs anteriorly upon the upper surface of the levator palpebrse superioris, immediately sub- jacent to the periosteal lining of the orbital cavity. It ends at a variable distanee from the orbital opening by dividing into the supra-orbital and supra-troehlear branehes.

The supra-iroehlear nerve is the medial and smaller of the two terminal branehes of the frontal. It runs towards ihe troehlea of the superior oblique musele, above whieh it pierees the palpebral fascia, leaves the orbit, and turns round the orbital areh to reaeh the forehead. Its further eourse has been deseribed already (p. 156). In the orbit it gives off one small twig elose to the pulley of the superior musele. This passes downwards to join the infra-trochlear braneh of the naso-eiliary nerve.

The supra-orbital nerue is eontinued onwards, in the line of the parent stem, and, passing through the supra-orbital noteh or foramen, it turns upwards on the forehead (p. 156). In the disseetion of the sealp this nerve has been seen to divide into a lateral and a medial division. Some- times the separation takes plaee within the orbit, and in that ease the larger lateral part oeeupies the supra-orbital noteh.

Neryus Laerimalis. — This is the smallest of the terminal branehes of the opKlhalmie division of the fifth. It enters the orbit through the superior orbital fissure, above the level of the museles, and runs anteriorly, along the lateral wall of the cavity, above the upper margin of the lateral reetus musele. At the anterior part of the orbit it eontinues its eourse, under cover of the laerimal gland, until it reaehes the lateral part of the upper eyelid, in whieh it ends (p. 137). Within the orbital cavity it gives numerous twigs to the deep surface of the laerimal gland, and sends downwards a filament whieh eonneets it with the zygomatic braneh of the maxillary nerve.

Nervus Troehlearis. — The small fourth nerve is destined entirely for the supply of the superior obligue musele. Having entered the orbit through the superior orbital fissure, above the museles, it passes antero-niedially, under the periosteum, and

DISSEGTION 0F THE ORBIT 337

finally sinks into the upper or orbital surface of the superior oblique musele not far from its origin.

GlandulaLaerimalis. — Thelaerimalglandis asmall, flattened and distinetly lobular strueture of oval form, whieh is plaeed transversely in the antero-lateral part of the orbit. It eon- sists of two parts or groups of lobules — a superior and an inferior — imperfectly separated from eaeh other. The glandula laerimalis superior^ whieh eonstitutes the main mass of the gland, lies in the orbital cavity. Its lateral convex surface is lodged in a hollow upon the medial aspeet of the zygomatic proeess of the frontal bone, and it is bound to the lateral part of the orbital areh by short fibrous bands whieh proeeed from the periosteum. The deep or medial surface is slightly concave, and rests upon the levator palpebrse superioris and lateral reetus, whieh intervene between it and the eyeball. The glandula laerimalis inferior lies below and anterior to the superior part, from whieh it is partially separated by the ex- panded tendon of the levator palpebrae superioris. It projects into the base of the upper eyelid, and rests upon the eon- junctiva whieh lines the under aspeet of the lid. This portion of the gland has been already examined in the disseetion of the eyelids (p. 138). Even in the undisseeted subject it ean be seen through the conjunctiva when the upper eyelid is fully everted.

The laerimal gland seeretes the tears, and its duets (three to five from the superior part and three to nine from the iii!enoi^part) open upon the under snrfarfi nf thp upper evelid in The neighhnnrhond nf tl^ fornix (Fig. 64).

Museulus Leyator Palpebrse Superioria. — This_muscle rests upon the upper surface of the rer.tns snpprinr. Posteriorly, it is narrow and pointed, but it expands as it passes above the eyeball to reaeh ihe upper eyelid. ItJiises from the under surface of the rQof of the orbit immediately anterior to-the optie fQramen. and in the anterior part of the orbital cavity it widens out int^ a hm^r] Tpemhrannnt; t^ypansion, the Con- neetions of whieh have been deseribed already (p. 136). The lateral and medial margins of this expansion are fixed to the rim of the orbital opening, in elose proximity to the liga- mentum palpebrale mediale and the raphe palpebralis lateralis. By these attaehments excessive aetion of the musele upon the upper eyelid is in a measure eheeked.

• Dissedion. — Divide f ^ throw the ends anteriorly and

V0L. II — 22

338

HEAD AND NECK

posteriorly. The levator palpebrae superioris also may be eut midway between its origin and insertion. On raising the posterior portion a minute nerve twig will be seen entering its deep or oeular surface. This eomes from the superior division of the third or oeulo-motor nerve.

The eyeball should now be indated. This may be done from the front or from behind. If the latter method is seleeted, gently separate the fat under cover of the superior reetus musele, and push the eiliary vessels and nerves away from the optie nerve. Next make a small ineision through the sheath of the nerve. Pass a ligature round the nerve anterior to the opening, and then pass a blowpipe, provided with a stylet, through the ineision and along the nerve into the interior of the eyeball. When the globe of the eye is fully inAated, the ligature may be tightened as the blow- pipe is withdrawn. A very mueh better plan, however, is to inflate the

eyeball from the front. For this purpose make an oblique valvular aperture in the selero-eorneal junc- tion, with the point of a sharp narrow-bladed knife. Through this the blow-pipe may be intro- duoed, and on its withdrawal after the inAation of the eyeball the valvular eharaeter of the opening is sufficient to prevent the eseape of the air.

Posterior to the eyeball the dis- seetor will notiee a quantity of loose bursallike tissue. Thi? is the fascia bulbi (O.T. eapsule of Tenon). Seize the upper part of this with the forceps, and remove a small portion with a pair of seissors. An aperture is thus made into the fascia, and the handle of the knife ean be intro- dueed into the spaee between it and the eyeball. In favourable eases the extent of the fascia ean be gauged, and perhaps even the pro- longations or sheaths whieh it gives to the tendons of the oeular museles may be made out. The deseription of the fascia bulbi is given on p. 347.

Museulus Reetus Superior.— The reetus superior, whieh lies under cover of the levator palpebrse superioris, is now fully exposed. It arises from the upper marp;in of the optie foramen, passes anteriorly above the <^p^^^ nprvp, and ends. upoiTthe upper asp^r^ nf thp pyphall in a thin, delieate tendon. whieh expands somewhat to be inserted into the selera about three or four lines posterior to the selero-enrneal jnnrtinn, It is supplied by a braneh from the suj>erior diyision of the oeulo-motor nerue.

Museulus ObliaUUS Superior. — This mnsrl^ arisps frnm the rOOf^' 0f the Orbit immediately nntprinr_ ^(^ fhp npppr anH

medial part of the nptir fnrampn. It passes ^anteriorl^^-along

FiG. 134. — Diagram of the Superior Oblique Musele. (From Hermann Meyer. )

a. Troehlea and synovial sheath.

DISSEGTION 0F THE ORBIT 339

the medial wall of the cavity above the medial reetus. At

the anterior part ot the orbit it enas in a siender tendon, whieh enters the troehlea and at onee ehanges its direetion. prnrppHing pngtprn-latprally^ upon the upper surface of the eyeball, under cover of the superior reetus. Beyond the lateral edge of the superior reetus the tendon expands some- what, and is inserted into the selera midway between the entranee of the optie nerve and the eomea.

The troehlea ox pulley through whieh the tendon passes is a small fibro-cartilaginous ring, whieh is attaehed by hbrous tissue to the troehlear fossa — a depression in the frontal bone elose to the medial angular proeess. The puUey is lined with a synovial sheath whieh facilitates the movement of the tendon, and from its lateral margin it gives a hbrous invest- ment to the tendon.

Disseetion. — Divide the superior reetus midway between its origin and its insertion, and reAeet the eut ends. On raising the posterior part of the musele the superior division of the oeulo-motor nerve is brought into view, as it sinks into the deep or oeular surface of the musele.. It sends a twig to the levator palpebrse superioris. The removal of some fat will bring the optie nerve more fully into view. At the posterior part of the orbit three struetures will be seen erossing the optie nerve — viz., (i) the naso-eiliary nerve ; (2) the ophthalmie artery ; and (3) the superior ophthalmie vein. These should be carefully eleaned and their branehes followed out. From the naso-eiliary nerve one or two delieate thread- like branehes — the long eiliary nerues — will be found passing along the optie nerve to reaeh the eyeball. The shoTi eiliary nerves, mueh more numerous, aeeompany the long eiliary branehes, and ean readily be dis- engaged from the fat whieh surrounds the optie nerve. A strong member of this group should be seleeted and followed posteriorly ; it will lead the disseetor to the eiliary ganglion. This is a minute body whieh is situated upon the lateral side of the optie nerve in the posterior part of the orbit. With a little patienee and eare the roots whieh the naso-eiliary nerve and inferior division of the oeulo-motor nerve give to this gangUon ean be isolated, and perhaps even the sympathetie root from the internal earotid plexus will be found.

Nervus Optieus. — The optie nerve enters the orbit through the optie foramen. It earries with it a strong loose sheath of dura mater, and also more delieate investments from the araehnoid and pia mater. The ophthalmie artery, whieh aeeompanies it, lies on its infero-lateral aspeet. Within the orbit the nerve ihelines antero - laterally, and at the same time somewhat downwards, to the baek of the eyeball, where it pierees the selera a short distanee to the medial side of its eentre. The disseetor has noted already that the ophthalmie artery and vein and the naso-eiliary nerve eross

340 HEAD AND XECK

above ihe op::c r.er^e, ar.d thar it is elosely aeeompanied by ihe de'.:oji:e c:::.in- nerves and vessels. The optie nerve is sl:4:h:';v lo::£:er :hap. :he disMnee whieh it has to nin from the opiio ioran:en :o :he i^'.obe o! the eve. so that the movements ot the eyelur. may ::o: be :r.:erfered with. Within the eye- ball ihe optio nen-e spreads ou: in the retina.

Nerms Naso-ciliaxi& — The naso-eiliar}- nerve (O.T. nasal) arlses irom the oph:hai:r.:c di^'ision of the trigeniinal in the anterior j>an of :he cavernous sinus. Ii passes through the superior orb::al nssure a:id er.iers ihe orbital eayity, between the two heads of :he la:eral rec:'.:s musele and between the two divisions of :ho ihird ::erve. It then indines antero- mediar.y, and, croi^i:'ii: the op:ic nerve obliqueIy, it runs be:wee:i the ir.edial rec:us and superior oblique museles to the medial waU of :he orbi^ whero it di^ides into two ter- minal branehes — \i-\, :he i::fra-:roch!ear and the anterior e:h:iioidal nerves. In .iddi:ion :o :hese ii gives off in the orbi: :he fo'lowi::g bra::ches: ^i^ long root to the eiliary ga:iglion : ^^^ long ci'.iar\- ::er\os : ^3^ posterior ethmoidal nerve.

A\:,:;".v /..■•;^c-: u,:\c-:: C:\':\:r:s. — This is a very slender tV.amen: whieh s'ori::^* fro:r. :he n.iso-ci:iarN- as it enters the orbit bo:ween :he hoads of :he '..r.eral reetus. It runs along iho lateral side of :he op::c nor\e, and enters the upper and pos:orior par: of ihe oiliary g.\;:glion.

.\Vr:/ Ci':\:r^s .'.."•:,<t'. — The two long eiliary branehes spri:ig fro:ii ihe naso-ciliar\- as i: erosses the optie nenre. They pass an:oriorly. upon :he mov:ia'. side of the optie nerve. :o roaoh ihe globe of :he eye where they pieree the selora. One of the lo:^.g ei'iary ::or\es very eonstantly u:i::os wi:h one of :he shor: ci'.'..iry ::'..; :::en:s.

^A Vr: ;. y £: ': ":.•;-". :.';> / ' s:: • ;'. • '■ p.- ssos : h rough the posterior e:h:v.oidal foramen :o tho o:h:::oid.'.l oo'ls and the sphenoidal air si::us.

.Wr: ■;. .% A' v-.j.'/\v ^■.V.; rs. — Tho in: ra- ; roohloar bnineh runs

aloiig :he medi.il wall of :ho orbi: bo'.ow iho superior oblique

muso'e. Afior passi:ig u::dor :ho :roch!oa of that musele it

emorgos from iho orbi: and appoars upo:i the face, where it

^as boen dissoc:od alroady ^p. i^S^. Noar the pulley it

eei ves a co m m ;: :i i oa t i n e i w i e * ro :u t h. 0 s u 'ora • t r^H'hlear nerve.

AVr:v/j: Z''V".\vJ.:.';> .:/»;.vr;.'r — This is the lar^r of the

' terminal branohes of the naso-oiliarv ner\*e. Il lea^'es

DISSEGTION 0F THE ORBIT 341

the orbit by the anterior ethmoidal eanal, and is eondueted to the interior of the eranium, in whieh it appears at the lateral margin of the cribriform plate of the ethmoid. The eanal in whieh it luns ean readily be opened up with the bone- forceps to expose the nerve. Upon the cribriform plate it turns anteriorly, under the dura mater, and almost immedi- ately disappears, through a sHt-like aperture at the side of the erista galH, into the nasal cavity. There it gives intemal nasal branehes to the mueous membrane, and is eontinued downwards upon the posterior aspeet of the nasal bone. EinaHy, it emerges upon the face, as the external nasal nerue^ by passing between the lower margin of the nasal bone and the lateral eartilage of the nose. Its terminal iilaments have been deseribed already (p. 140).

Ganglion Oiliare (Fig. 138). — The eiHary gangHon is a smaH quadrangular body, not mueh larger than the head of a large pin. It is plaeed in the posterior part of the orbit, between the optie nerve and the lateral reetus musele, and very eommonly on the lateral side of the ophthalmie artery. At its posterior border it receives it5 three roots ; whilst from its anterior border the short eiHary nerves are given off.

The sensory root eomes from the naso-eiHary, and is eaHed the long root. The short or motor root is a short, stout trunk ; it eomes from the braneh of the oeulo-motor nerve whieh goes to the inferior obHque musele. The sympathetie root eomes from the internal earotid plexus, it joins the ganglion, elose to the entranee of the long root from the naso-eiliary nerve. In some eases it joins the long root before it reaehes the ganglion.

Nervi Ciliares Breves. — The short eiliary nerves are from four to six in number. They eome off in two groups, superior and inferior. The lower nerves are generally more numerous than the upper. As these fine nerves pass along the optie nerve they divide and thus inerease in number ; at the baek of the eyeball from twelve to eighteen may be eounted. Finally they pieree the selera by a series of apertures whieh are plaeed around the entranee of the optie nerve.

Arteria Ophthalmiea. — The ophthalmie artery is a braneh of the internal earotid. It aeeompanies the optie nerve into the orbit through the optie foramen. At first it lies below the optie nerve, but soon winds round its lateral side, and, erossing above it, passes anteriorly along the medial

II— 22a

340 HEAD AND NECK

above the optie nerve, and that it is elosely aeeompanied by the delieate eiliary nerves and vessels. The optie nerve is slightly longer than the distanee whieh it has to run from the optie foramen to the globe of the eye, so that the movements of the eyeball may not be interfered with. Within the eye- ball the optie nerve spreads out in the retina.

NeiYUS Naso-eiliaris. — The naso-eiliary nerve (O.T. nasal) arises from the ophthalmie division of the trigeminal in the anterior part of the cavernous sinus. It passes through the superior orbital fissure and enters the orbital cavity, between the two heads of the lateral reetus musele and between the two divisions of the third nerve. It then inelines antero- medially, and, erossing the optie nerve obliquely, it runs between the medial reetus and superior oblique museles to the medial wall of the orbit, where it divides into two ter- minal branehes — viz., the infra-trochlear and the anterior ethmoidal nerves. In addition to these it gives ofF in the orbit the following branehes: (i) long root to the eiliary ganglion ; (2) long eiliary nerves ; (3) posterior ethmoidal nerve.

Radix Longa Ganglii Ciiiaris, — This is a very slender filament whieh springs from the naso-eiliary as it enters the orbit between the heads of the lateral reetus. It runs along the lateral side of the optie nerve, and enters the upper and posterior part of the eiliary ganglion.

Nerui CiUares Longi. — The two long eiliary branehes spring from the naso-eiliary as it erosses the optie nerve. They pass anteriorly, upon the medial side of the optie nerve, to reaeh the globe of the eye where they pieree the selera. One of the long eiliary nerves very eonstantly unites with one of the short eiliary filaments.

Neruus Ethmoidalis Posterior passes through the posterior ethmoidal foramen to the ethmoidal eells and the sphenoidal air sinus.

Neruus Infratrochlearis. — The infra-trochlear braneh runs along the medial wall of the orbit below the superior oblique musele. After passing under the troehlea of that musele it emerges from the orbit and appears upon the face, where it has been disseeted already (p. 128). Near the puUey it receives a eommunieating twig from the supra-troehlear nerve. Neruus Ethmoidalis Anterior. — This is the larger of the two terminal branehes of the naso-eiliary nerve. It leaves

DISSEGTION 0F THE ORBIT 341

the orbit by the anterior ethmoidal eanal, and is eondueted to the interior of the eranium, in whieh it appears at the lateral margin of the cribriform plate of the ethmoid. The eanal in whieh it runs ean readily be opened up with the bone- forceps to expose the nerve. Upon the cribriform plate it tums anteriorly, under the dura mater, and almost immedi- ately disappears, through a slit-like aperture at the side of the erista galli, into the nasal cavity. There it gives intemal nasal branehes to the mueous membrane, and is eontinued downwards upon the posterior aspeet of the nasal bone. Finally, it emerges upon the face, as the external nasal neroe^ by passing between the lower margin of the nasal bone and the lateral eartilage of the nose. Its terminal Alaments have been deseribed already (p. 140).

Ganglion Giliare (Fig. 138). — The eiliary ganglion is a small quadrangular body, not mueh larger than the head of a large pin. It is plaeed in the posterior part of the orbit, between the optie nerve and the lateral reetus musele, and very eommonly on the lateral side of the ophthalmie artery. At its posterior border it receives its three roots ; whilst from its anterior border the short eiliary nerves are given off.

The sensory root eomes from the naso-eiliary, and is ealled the long root, The short or motor root is a short, stout trunk ; it eomes from the braneh of the oeulo-motor nerve whieh goes to the inferior oblique musele. The sympathetie root eomes from the internal earotid plexus, it joins the ganglion, elose to the entranee of the long root from the naso-eiliary nerve. In some eases it joins the long root before it reaehes the ganglion.

Nerui Ciliares Breves. — The short eiliary nerves are from four to six in number. They eome off in two groups, superior and inferior. The lower nerves are generally more numerous than the upper. As these fine nerves pass along the optie nerve they divide and thus inerease in number ; at the baek of the eyeball from twelve to eighteen may be eounted. Finally they pieree the selera by a series of apertures whieh are plaeed around the entranee of the optie nerve.

Arteria Ophthalmiea. — The ophthalmie artery is a braneh of the internal earotid. It aeeompanies the optie nerve into the orbit through the optie foramen. At first it lies below the optie nerve, but soon winds round its lateral side, and, erossing above it, passes anteriorly along the medial

11—22 a

34» HEAD AND NECK

wall of the orbit, below the superior obHque musele. At the medial side of the oebit it ends hy dividing into two terminal branehes — viz., the frontal and the dorsal nasal (Fig. 136).

The branehes of the ophthalmte artery are very numerous, and they ean seldom be 5atisfaclorily displayed, unless a speeial injection has been made. They are : —

1. Laerimal. 1	4. Giliary.	1 7. Palpebral.
2. Museular. 1	5. Supta-orbital.	8. Dorsal nasal.
3. Arleria eenlralis letin^. |	6. Ethmoidal.	1 9. Piontal.

Arteria Laerimalis. — The laerimal braneh aeeompanies the laerimal nerve, and supplies the gland ot that name and

the conjunctiva. In eaeh eyelid an arlerial areh, the areiis tarseus, is formed by the anastomoses of the two lateral palpebra! branehes of the laerimal with the two medial palpebral branehes of the ophthalmie.

Jiami Museulares eome off at variab!e points, not only from the main artery, but also from eerEain of its branehes. They supply the museles eontained in the orbital cavity.

The Arteria Centralis Retinee is a minute but important artery. It pierees the infero-medial surface of the optie nerye, about half an ineh posterior to the eyeball, and passes, in its substanee, to the interior of the globe of the eye.

Arteria Ciliares are very numerous. Two groups are

DISSEGTION 0F THE ORBIT

343

reeognised — y\z., a posterior and an anterior. The posierior eiliary arieries run with the eiliary nerves. They arise as two trunks whieh spring from the ophthalmie whilst it lies below the optie netve. These divide into several slender branehes, whieh pieree the selera around the entranee of the optie nerve. Two members of this group of vessels enter the eyeball on eithet side of the optie nerye, soraewhat

apart frora the others. They are termed arteria diiares posteriores longie (Fig. 135). The arterim eiltares anleriores eome off, in the anterior part of the orbit, from the laerimal and museular branehes. They vary in number from six to eight, and run to the anterior part of the eyeball, where they form an arterial eirele under the conjunctiva. Pinally, they pieree the selera inimediately posterior to the eornea.

Arteria Supraorbilalis. — This aeeompanies the supra-orbital nerve to the forehead, where it was disseeted at a previous stage(p. 157).

344 HEAD AND NECK

■ Arteri(B Ethmoidales, — There are two ethmoidal branehes, an anterior and a posterior ; they pass through the anterior and posterior ethmoidal foramina on the medial wall of the orbit. The arteria ethmoidalis posterior supplies the mueous lining of the posterior ethmoidal eells, and sends twigs to the upper part of the nose. The arteria ethmoidalis anterior is a larger braneh. It runs in eompany with the anterior ethmoidal nerve, and gives off minute twigs at eaeh stage of its eourse. Thus in the anterior ethmoidal foramen it gives branehes to the mueous lining of the anterior ethmoidal eells and the frontal sinus ; during its short sojourn in the eranial cavity it gives off a small arteria meningea a?iterior] in the nasal cavity it gives twigs to the mueous membrane. Its terminal braneh appears on the face and supplies the side of the nose.

Arteria Dorsalis Nasi, — The dorsal artery of the nose is distributed at the root of the nose, and anastomoses with the angular braneh of the external maxillary artery.

Arteria Brontalis. — This aeeompanies the supra-troehlear nerve to the forehead, where it has been disseeted already

(P- 157).

Vense Oplitlialimese. — As a general rule there are two

ophthalmie veins, superior and inferior. The superior

ophthalmie vein is the larger of the two and it aeeompanies

the artery. It takes origin at the root of the nose, where

it eommunieates with the angular vein. The inferior

ophthalmie vein lies below the level of the optie nerve, and

it is brought into eommunieation with the pterygoid venous

plexus by an offset whieh passes through the inferior orbital

fissure. The two ophthalmie veins receive numerous tribu-

taries during their eourse through the orbit ; finally they

pass between the two heads of the lateral reetus musele, and

through the superior orbital fissure to open into the cavernous

sinus, either separately or by a eommon trunk.

Museuli Reeti Oeuli. — The four straight museles of the

eyeball diverge from the apex of the orbit. They form the

sides of a four-sided or pyramidal spaee in whieh are en-

elosed the optie nerve and the greater part of the globe of

the eye. The reetus superior^ whieh has been refiected, has

been studied already. The reetus medialis springs from the

medial side of the optie foramen, and the reetus inferior takes

origin from a fibrous band whieh bounds the medial end of the

DISSEGTION 0F THE ORBIT 345

superior orbital fissure. The reetus lateralis is distinguished from the others by arising from a iibrous areh, the extremities ■ of whieh are termed its two heads of origin. The lower htad arises iti eommon with the reetus inferior from the body of the sphenoid, where tbis bounds the media! end of the superior orbital fissure ; the upptr head is attaehed above the superior orbital tissure upon the lateral side of the optie foramen, where its origin beeomes eontinuous with the superior reetus. Through the arebway whieh intervenes between the two beads of the lateral reetus pass the two

divisions of the oeulo-motot nerve, the nasoeiliaiy nerve, the abdueene nerve, and fbe ophtbalmie veins (Fig. 137).

A belter view of these attaehments may be obtained by dWiding Ihe optie ni;rve dose to the optie fotamen and turning the eyeball anteriorly.

Tbe manner in wbieb the reeti museles ate inserted into tbe eyeball should next be studied. Eaeh ends in a deheate meinbranous tendon, wbieh is inserted into tbe selera, about a quarter of an ineb posterior to tbe selero-eorneal junction.

NerTus Ooulomotoriua. — Tbe two divisions of tbis nerve enter the orbit through the saperior orbital fissure, between tbe two heads of the lateral reetus. Tbe superior dwision bas

346 HEAD AND NECK

been traeed to the reetus superior and the levator palpebrae superioris. The inferior division is larger. It almost im- mediately divides into three branehes for the supply of the reetus medialis, the reetus inferior, and the obliquus inferior. The nerves to the two reeti enter the oeular surfaces of the museles ; the nerve to the inferior oblique is prolonged anteriorly, in the interval between the reetus inferior and reetus lateralis, and enters the posterior border of the inferior oblique musele. Soon after its origin this braneh giyes the shori motor root to the eiliary ganglion.

Neryus Abdueens. — The sixth nerve will be found elosely applied to the oeular surface of the lateral reetus. It enters the orbit through the narrow interval between the heads of lateral reetus musele and it supplies this musele only.

Arrangement of the Nerves in the Superior Orbital Pissure. — When the orbit is disseeted, and the various nerves met with in the disseetion of the cavernous sinus are traeed into the cavity, the disseetor will note that the arrangement of the nerves in the superior orbital fissure is somewhat different from that in the sinus.

The laerimal, frontal, and troehlear nerves enter the orbit above the museles on very mueh the same plane (Fig. 137). The other nerves enter between the heads of the lateral reetus. Of these the superior division of the oeulo-motor nerve is the highest, next eomes the naso-eiliary nerve, then the inferior division of the oeulo-motor nerve, and the abdueent nerve oeeupies the lowest level.

Disseetion. — The inferior oblique musele is plaeed very diflferently from the other museles of the orbit. It is situated below the eyeball, running below its inferior surface to gain its lateral surface. It must be disseeted from the front. It is neeessary, therefore, to restore the eyeball to its natural plaee. Next, evert the lower eyelid and remove the conjunctiva from its deep surface as it is reflected on to the globe of the eye. A little disseetion in the floor of the anterior part of the orbit and the removal of some fat will reveal the inferior oblique musele.

Museulus OblioLuus Inferior. — This musele arises from a small depression on the orbital surface of the maxilla, immediately lateral to the opening of the naso-laerimal duet. It passes laterally, below the inferior reetus musele, and, inelining slightly posteriorly, ends in a thin membranous tendon, whieh gains insertion into the lateral aspeet of the selera of the eyeball under cover of the reetus lateralis. The insertion is not far from that of the superior oblique, but

DISSEGTION OF THE ORBIT

347

is plaeed more posteriorly. It is supplied by the in/erior division of the third nerw.

Taseia Bnlbi (O.T. Gapsole of Teson). — The eonneetions of the iibrous sheath of the eyeball are somewhat eom- plieated, and they eannot be satisfactorily displayed, in every detail, in an ordinary disseetion. The fascia may be studied

Lcvalor [olpebtrEiiupPrioii'i--

from a threefold point of view — (i) in its eonneetion with the eyeball; (z) in its eonneetions with the museles inserted into the globe of the eye ; and (3) in its eonneetions with the walls of the orbit.

The relation whieh the fascia bulbi beats to the eyeball is very simple. The menibrane is spread over the posterior five-sixths of the globe — the eornea alone being free from it. Anteriorly, it lies in relation with the oeular conjunctiva, with whieh it is ir nneeted, and it ends by bleoding

348 HEAD AND NECK

with the conjunctiva elose to the margin of the eornea. Posteriorly^ it fuses with the sheath of the optie nerve where the nerve pierees the selera. The internal surface of the membrane (i.e, the surface towards the globe of the eye) is smooth, and is eonneeted to the eyeball by some soft yielding and humid areolar tissue, the interval between them eon- stituting, in fact, an extensive lymph spaee ealled the spatium inter/asdale. Its external surface is in eontaet posteriorly with the orbital fat, to whieh it is loosely adherent ; and it is iirmly attaehed to the oeular conjunctiva more anteriorly. It obviously, therefore, forms a membranous soeket in whieh the eyeball ean glide with the greatest freedom.

The tendons of the various oeular museles are inserted into the eyeball within this fascia, and they gain its interior by piereing the membrane opposite the equator of the globe (Fig. 139). The lips of the openings through whieh the four reeti museles pass are prolonged posteriorly upon the museles, in the form of sheaths, very mueh in the same manner that the infundibuliform fascia is prolonged upon the spermatie eord from the abdominal inguinal ring. These sheaths gradually beeome more and more attenuated, until at last they blend with the perimysium of the museular bellies. In the ease of the superior oblique musele the eorresponding prolongation is related only to its reflected portion ; when it reaehes the pulley it ends, by beeoming attaehed to its margins. The sheath of the inferior oblique may be traeed upon the musele as far as the floor of the orbit. The medial or oeular edge of eaeh of the four apertures through whieh the reeti museles pass is strengthened by a slip of fibrous tissue (Loekwood), and as the fascia bulbi is firmly bound to the bony wall of the orbit at various points these slips aet as pulleys, and proteet the globe of the eye from pressure during eontraetion of the museles. The aperture for the superior oblique is not furnished with sueh a slip, and it is doubtful if the opening for the inferior oblique musele possesses one.

Disseetion. — An admirable view of the relations whieh the fascia bulbi presents to the eyeball and the tendons of the oeular museles ean be obtained by the following disseetion : — Divide the lateral eommissure of the eyelid to the margin of the orbital opening. PuU the eyelids widely apart, so as to expose as mueh as possible of the anterior face of the eyeball. Next divide the conjunctiva by a eireular ineision just beyond the eornea. At this point the fascia bulbi is so intimately eonneeted with the conjunctiva that it is divided at the same time. Now raise eare-

DISSECTION 0F THE ORBIT

The openings in the fascia bulbi foT the tendons of the oeular museles and the thiekened matgins of these apertures ate well seen. Note also the sheaths whieh are given to the ^nuseles.

Check and Snspansory Lig&ments.-— The eonneetions of the Taseia bulbi to the walls of the orbital cavity are somewhat eomplieated. The susptnsory ligament (Loekwood) plays an important part in this respeet. It stretehes aeross the anterior part of the orbit, after the fashion of a hammoek, and gives support to the eyeball, Its two e^tremities are

FiG. 139.— Dlsseelion of Ihe Paseia Bulbi from Ihe fronl.

narrow, and are attaehed respectively to the zygomatic and laerimal bones. Below the eyehall it widens out and blends with the fascia bulbi. The lateral and medial eheek ligamenls also eonstitute bonds of union between the fascia bulbi and the orbital wall. They are sttong bands whieh pass from the sheaths around the lateral and medial reeti museles to obtain attaehinent to the zygomatic and laerimal bones respeetiyely, where they are brought into assoeiation with tbe entremities of the suspensory ligament. The function of the eheek ligaments is to Hmit the eontraetion of the media] and lateral reeti museles, and thus prevent excessive rotation of the eyeball in a lateral or medial direetion. There is a similar but iess direet provision by means of whieh the aetion of the auperior and inferior reeti musdes is limited.

350 HEAD AND NECK

The aetion of the former musele is eheeked through an intimate eonneetion with the levator palpebrae superioris in the anterior part of the orbit ; the aetion of the inferior reetus is eheeked through a eonneetion with the suspensory ligament.

Disseetion. — In order that the zygomatic braneh of the maxillary division of the trigeminal nerve may be displayed in its eourse through the orbit, the orbital eontents must be removed. The nerve will then be found in the midst of a little soft fat in the angle between the floor and lateral wall of the orbit.

Nervus Zygomaticus (O.T. Temporo-MaIax). — This small nerve arises, in the infra-temporal fossa, 'from the maxillary diyision of the trigeminal nerve. It enters the orbit by passing through the inferior orbital iissure and almost immediately diyides into two terminal branehes — the zygomatico-temporal and the zygomatico-facial.

Ramus Zygomaticotemporalis. — This braneh runs antero- superiorly upon the lateral wall of the orbit, under cover of the periosteum, and, after receiving a eommunieating twig from the laerimal nerve, it enters the zygomatico - orbital eanal of the zygomatic bone. This eonduets it to the anterior part of the temporal region, where it has been examined already (pp. 155 and 156).

Ramus Zygomaticofacialis. — The zygomatico-facial braneh also enters a zygomatico-orbital eanal, and is linally eon- dueted to the face by the zygomatico - facial eanal whieh traverses the zygomatic bone (p. 127).

PREYERTEBRAL REGION.

The following are the struetures to be displayed in this disseetion : —

Prevertebral museles. Intertransverse museles. Cervical nerves. Yertebral artery.

Yertebral vein.

Yertebral and cranio-vertebral artieulations.

Disseetion. — To separate the anterior part of the head with the pharynx from the posterior part and the vertebral eolumn a somewhat eomplieated disseetion is neeessary. Plaee the head upside down, so that the eut margin of the skuU rests upon the table ; divide the eommon earotid artery, me internal jugular vein, the vagus nerve, and the sympathetie tnink, on eaeh side, at the level of the neek of the first rib ; puU the traohea and oesophagus, together with the great blood vessels and nerves, away from the anterior surface of the vertebral eolumn. The separation must

PREYERTEBRAL REGION 351

be effected right up to the base of the skull. At this point great eaution must be observed, otherwise the pharyngeal wall or the insertions of the prevertebral museles will be damaged. The base of the skull having been reaehed, the point of the knife should be earried aeross the basilar portion of the oeeipital bone, between the pharynx and the prevertebral museles, to divide the thiek investing periosteum.

The basilar portion of the oeeipital bone must now be divided by means of a ehisel. Still retaining the part upside down, plaee the skull so that its floor rests upon the end of a wooden bloek. Then apply the edge of the ehisel to the under surface of the basilar portion of the oeeipital bone, adjust it aeeurately in the interval between the pharyngeal wall and the prevertebral museles, and with a wooden mallet drive it through the base of the skull, inelining it, at the same time, slightly posteriorly.

The next step in the disseetion eonsists in making two saw-euts through the eranial wall. The head having been plaeed upon its side, the saw must be applied to the lateral aspeet of the skull, half an ineh posterior to the mastoid proeess, and be earried obliquely antero-medially to reaeh a point immediately posterior to the jugular foramen. A similar saw-eut must be made upon the opposite side of the head.

To eomplete the disseetion the disseetor must again have reeourse to the ehisel. Plaeing the preparation so that the floor of the eranium looks upwards, divide the base of the skull, on eaeh side, in the interval between the petrous portion of the temporal bone and the basilar portion of the oeeipital bone. Anteriorly, this eut should reaeh the lateral extremity of the ineision already made through the basilar portion ; whilst posteriorly, it should be earried to the medial side of the jugular foramen to reaeh the medial end of the saw-eut. When this has been done upon both sides of the basilar portion, the anterior part of the skull earrying the phar)mx and the great blood-vessels and nerves ean be separated from the pwsterior part of the skull and cervical portion of the vertebral eolumn. The only large nerve whieh will be divided is the hypoglossal, but, as it is eut elose to the basis eranii, and above its eonneetion with the ganglion nodosum of the vagus, it retains its position.

The pharynx and anterior portion of the skull should now be covered with a pieee of eloth soaked in preservative solution, and the whole enveloped in an oil-eloth wrapper. It ean then be laid aside until the disseetion of the prevertebral region and the ligaments of the cervical vertebr3e and the oeeiput have been eompleted.

Returning to the posterior part of the skull and the cervical portion of the vertebral eolumn, the disseetor should proeeed to define the attaehments of the museles whieh lie anterior to the transyerse proeesses and the bodies of the yertebrae. These are three in number on eaeh side, viz. : —

1. The longus eolli.

2. The longus eapitis (O.T. reetus eapitis antieus major).

3. The reetus eapitis anterior (O.T. antieus minor).

Museulus Longus CoIIi. — This is the most powerfuI of the prevertebral museles, and it lies nearest to the median plane. Its eonneetions are some- what intrieate, but when it has been thoroughly eleaned it will be seen to eonsist of three portions — viz., upper and lower oblique parts, and an intermediate vertical part.

The lower oblupie division arises from the lateral aspeet of the bodies of

aHA~ .OT? N^eS

ihrw! tpri'liri'iu» slips froin the anteriot tubereles of the Iransrerse pioeesses <>f the thir'I, foutth, an'l fifth ceTvical Teriebr.t ; ii iat<eTi somewliat as it pr'ieeR'lt iipH'arr]) anii inedially to obtoin a poinled anA tendinous insetlion Hil'i Ibe Biitnri'ir lulitrele of Ihe atlas. The :,rn\ii/ (ari of the musele is niueh Ibe bree^t 'if Ihe ihiee divisions. It lies along the medial side of the iiUi'jiin i^irti'iTis, aiirl is iDtimately eonneeied witb tuih of them. It arisei in C(>mni'in with tln: inferioi obIique part by two oi ibree slips fioin the niilntnT thu iMitliet 'if the upper two or three thoraei): yertebrK ; above

PREYERTEBRAL KKr,UA

» \ «

this it derives additional slipK of orijjin froin ihe U».lu> ..| ili. ;. «. ., cervical reriebr^E- : lastly, its lateral l»>n]t.'r is iiiiiluii • «I \^\ n|;j.x ■,. transrerse proeeises (.•£ ihe l'iwer lhri.-c i»r l-.ur «ii\n,>l \.i;.i. \ stretehes vcr::cally ::- w:iri>. arj'l i- inN.;it..i ii]>i>ii ih> iii.«liil .|.i, . • .-. upper obli'j-j- yi.n ■.■f iLt :: us !•.■ "••y thn.- t. n.hi.Mi, |.|.., .^.. .. «Ii. ■.

obtain a:i2:h2-irr.: :: ih-. ■•.•Jj-_-- ■ :' :•,-. v.-..-rri, •!..i-!. .ui.l i tii , , n i. ,|

vertebr;<:.

LoD^nB Gapiids '.T. £eeciiiCa.pLUi Asti(nullajor I !.• I -ni: i .i| ihh is aa tl:i^h.iiri n.Uriiiit v:.ill L.rii'!:.- :•; ir^r ■— . •. •- !.;• fi .rn !).. .niii m>>i tiriierrles :■:' uit --'Lii---- trri.-. :r )•.•_-.-*-.- *''•,: " ■.- . '•?".. J.f'li. ;ii.-l ntli

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£&rSLJ *^-*T*''--" *^T=.*"^i| " in.'<nr.kw^t§ KsiSi?

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354 HEAD AND NECK

the infeTior obliqne, and the superior oblique. The anterior tubereles and the eostal porlions of the transverse proeesses of the Ihird, fourth, fifih, and sixth cervical vertebrie should then be snipped oS with the bone forceps.

Arteria VertebraJia. — ^This is an artery of great importanee, for te^ether with its fellow of the opposite side and the basilar artery, whieh is formed by their union, it supplies the hind- brain, the mid brain, and the postenor parts of the eerebral hemispheres, and it helps to supply the spinal medulla. It

of the Vertebra]

eommenees at the root of the neek, as a braneh of the first part of the subclavian artery, and it runs upwards, through the transyeree proeesses of the cervical vertebrfe, to the base of the skuU. It enters the skuU through the foramen magnum and unites in the posterior fossa of the eranium, at the lower border of the pons, with its fellow of the opposite side to form the basilar artery. On aeeount of its varying relations it is divided into four parls. Tbe iirst part, whieh extends from the subclavian artery to the transverse proeess of the sixth cervical yertebra, has been seen already (p. 251). It lies between the longus eolli medially, the sealenus anterior

PREYERTEBRAL REGION 355

laterally, the transverse proeess of the seventh cervical vertebra and the inferior eendeal ganglion of the sympathetie posteriorly, and the vertebral vein and the eommon earotid artery anteriorly.

The seeond part, now exposed, eommenees where the artery enters the transverse proeess of the sixth cervical vertebra. It passes vertically upwards, through the series of foramina transversaria, till it reaehes the foramen in the transverse proeess of the epistropheus. In that it runs laterally as well as upwards to gain the foramen in the more laterally plaeed transverse proeess of the atlas ; and, as it emerges upon the upper aspeet of the atlas, the third part eommenees and curves round the lateral and posterior aspeets of the upper artieular proeess of that bone, in a groove upon the upper surface of the posterior areh. As soon as it has passed under cover of the lateral margin of the posterior atlanto-oeeipital membrane it beeomes the fourth part. The fourth part turns upwards, pierees the dura mater and passes into the skull through the foramen magnum, anterior to the uppermost digitation of the ligamentum denti- eulatum; then, turning antero-medially, between the h)^po- glossal nerve above and the first cervical nerve below, it passes to the anterior surface of the medulla oblongata, and, as already stated, joins its fellow of the opposite side at the lower border of the pons.

Relations, — The relations of the first part have already been sufficiently eonsidered. The seeond part lies in and between the transverse proeesses of the cervical vertebrae, medial to the intertransverse museles, lateral to the bodies of the vertebrge, and anterior to the anterior branehes of the cervical nerves as they pass laterally. It is surrounded not only by the sympathetie nerve plexus derived from the inferior cervical ganglion, whieh aeeompanies all parts of the artery, but also by a venous plexus whieh terminates below in the vertebral vein or veins. The third part of the artery lies on the posterior areh of the atlas in the anterior boundary of the sub-oeeipital triangle. As it turns posteriorly from the foramen in the transverse proeess of the atlas the anterior braneh of the first cervical nerve lies to its medial side, between it and the lateral mass of that bone ; and, as it tums medially, posterior to the upper artieular facet, the trunk of the first cervical nerve lies below it on the posterior areh, and

11—23 a

356 HEAD AND NECK

the posterior braneh enters the triangle from beneath its lower border. For the relations of the fourth part see above and p. 443.

Branehes. — No braneh of importanee is given off from the first part. The seeond part gives off lateral spinal (p. 193) and museular branehes. The branehes from the third part are museular twigs, and branehes to anastomose with twigs from the oeeipital and the deep cervical arteries. The fourth part gives off a meningeal braneh before it perforates the dura mater and, afterwards, a series of branehes to the eentral nervous system (see pp. 443, 444).

Vena Yertebralis. — Only the first part of the vertebral artery is aeeompanied by a definite vertebral vein. There are no aeeompanying veins with the fourth part of the artery, but a plexus is formed round the eommeneement of the third part, by the union of tributaries from the venous plexus in the vertebral eanal and from the plexus of veins in the sub-oeeipital triangle. This plexus aeeompanies the seeond part of the artery through the transverse proeesses of the cervical ^ertebrae ; it anastomoses with the venous plexuses in the vertebral eanal ; and it terminates below in one or two vertebral veins ; these aeeompany the first part of the artery and end in the posterior aspeet of the eommeneement of the innominate vein.

Disseetion. — The museles must now be eompletely removed, in order that the vertebral and cranio-vertebral joints, and the ligaments in eon-" neetion with the cervical portion of the vertebral eolumn may be examined.

The Joints of the Negk.

The epistropheus, atlas, and oeeipital bone present a series of artieulations in whieh the uniting apparatus is very different from that of the ^ertebrae below.

Artieulations of the Lower Five Cervical Vertebr8B. — The lower five cervical vertebrae are united together very mueh upon the same plan as the vertebrae in other regions of the vertebral eolumn. Both the bodies and the vertebral arehes are eonneeted by distinet artieulations and speeial ligaments.

Three separate joints may be said to exist between the opposed surfaces of the bodies of two adjacent cervical vertebrae — viz., a eentral synehondrosis and two small lateral diarthrodial joints.

JOINTS OF THE NECK 357

The synehandrosis oeeupies by far the greatest part of the interval between the vertebra} bodies, and it presents the usual eharaeters of sueh an artieulation. The opposed bony surfaces are eoated with a thin layer of hyaline or enerusting eartilage, and are brought into direet union by an interposed dise of fibro-cartilage. The intervertebral fibrD-cartiiages are distinetly deeper anteriorly than posteriorly, and upon this eireumstanee the cervical cuivature of the eolumn in great measure depends,

The two diarthrodial joinis are plaeed one on eaeh side where the dise of fibro-cartilage is absent. They are of stnall extent, and are confined entirely to the interva]s between the projecting lateral lips . of the upper surface of the body

and the bevelled-off lateral margins of the lower surface of the yertebral body immediately above. The bony surfaces are eoated with enerusting eartilage, and are separated by a synovial cavity proteeted by a feeble eapsular ligament

The ligaments whieh bind the bodies of the lower five cervical vertebr£e together are the direet eontinuation upwards of the anterior and the posterior longitudinal ligaments of the vertebrje. When the medulla spinalis was removed, the lamina of the vertebrse, below the epistropheus, were taken away so that very little disseetion will be required to make out the eonneetions of both of these hgaments. The anterior longitudinal ligament is a strong band plaeed on the anterior faces of the vertebral bodies, It is mpre firmly fixed to the intemning intervertebral fibro-cartilages than to the bones. The posterior longitudinal ligament, whieh lies on

358 HEAD AND NECK

the posterior aspeets of the vertebral bodies, eonstitutes the anterior boundary of the vertebral eanal. In the cervical region it eompletely covers the bodies and does not present the dentieulated appearanee whieh is so eharaeteristie lower down. It is attaehed ehieiiy to the fibro-cartilages and the adjacent margins of the bones.

The vertebral arehes of the lower five cervical vertebrae are bound together by (a) the artieulations between the artieular proeesses; (S) ligamenta flava; (c) interspinous ligaments; and {d) intertransverse ligaments ; (e) ligamentum nuehse.

The yoints between the opposing artieular proeesses are of the diarthrodial variety. The surfaces of bone are eoated with eartilage; there is a joint cavity surrounded by a distinet eapsular ligament lined with a stratum synoviale. This ligament is more laxly arranged in the neek than in the lower regions of the vertebral eolumn.

The Ugamenta fiava may be examined on the laminse whieh were removed for the display of the spinal meduUa, and whieh the disseetor was direeted to retain. They fill up the gaps between the laminse of the yertebrae, and ean be best seen when the anterior aspeet of the speeimen is viewed.

Ligamenta Flava, — These ligaments are eomposed of yellow elastie tissue. Eaeh is attaehed superiorly to the anterior surface and inferior margin of the lamina of the vertebra above, whilst inferiorly it is fixed to the posterior surface and superior margin of the lamina of the vertebra next below. In this way they form with the laminae a smooth, even, posterior wall for the vertebral eanal. Eaeh ligament extends from the posterior part of the artieular proeesses to the median plane, where its free thiekened median border is in eontaet with its fellow of the opposite side. The median slit between them, in the spaee between eaeh pair of vertebral arehes, is filled with some lax connective tissue, whieh allows the egress from the vertebral eanal of some small veins. The width of the ligaments in the different regions of the vertebral eolumn depends upon the size of the vertebral eanal. Therefore they are widest in the neek and in the lumbar part of the eolumn. The ligamenta flava, by virtue of their great strength and elastieity, are powerful agents in maintaining the curvatures of the vertebral eolumn ; they also give valuable aid to the museles in restoring the

JOINTS 0F THE NECK

3S9

vertebral eolumn to its original position afteT it has been bent in a ventral direetion.

The interspinous Hgamnis are most strongly developed in the lumbar region, where they fill up the intervals between the adjacent margins of eontiguous spinous proeesses. In the thoraeie region, and more so in the neek, they are very weak,

The supraspin&us ligaments are thiekened bands whieh eonneet the summits of the spinous proeesses. In the neek they are replaeed by the ligamentum nuehs (p. 172).

FlG, 143. — The Ligamenta Flava ia the Lumbar RegiOD of the SpiM,

The intertrans7}<rse Ugaments are feebly marked in the cervical region and extend chiefly between the anterior bars of the transverse proeesses.

Artienlations of ttie Epistropheiu, Atlas, and Oedpital Bone. — The artieulations whieh exist between these three bones all belong to the diarthrodial eiass, Between the atlas and epistropheus (O.T. axis) ihere are three sueh joints — viz., a pair between the opposed artieular proeesses, and a third between the anterior face of the dens and the posterior face of the anterior areh of the atlas, Between the atlaa and oeeipital bone there is a pair of joints — viz., between the oeeipital eondyles and the elliptieal cavities upon the upper aspeets of the lateral masses of the atlas.

36o HEAD AND NECK

The ligaments eonneeting these three bones together may be divided into three main groups, as follows : —

Ligaments eonneeting atlas with epistropheus, . . .

Ligaments eonneeting oeei- pital bone with atlas, . ,

Ligaments eonneeting oeei- pital bone with epistro- pheus,

' Anterior longitudinal. Ligamenta flava. Gapsular. Transverse portion of erueiate ligament

with inferior erus. Aeeessory ligaments of the atlanto-epis- tropheal joints. ' Anterior longitudinal ligament. Anterior oeeipito-atlantal membrane. Posterior oeeipito-atlantal membrane. Transverse part of erueiate ligament with superior erus. ^ Gapsular.

^' Membrana teetoria. Superior and inferior erura of the erudate

ligament. Alar. Apieal.

Anterior Longitudinal Ligament (Fig. 144). — This is a eontinuation upwards of the eommon anterior longitudinal ligament. Below, it is attaehed to the anterior aspeet of the body of the epistropheus, whilst above, it is fixed to the anterior areh of the atlas. It is thiek and strong in the middle, but thins ofif towards the sides.

Ligamenta Flava. — These iill the interval between the laminae of the epistropheus and the posterior areh of the atlas, to the eontiguous margins of whieh they are attaehed. They are broader and more membranous than the ligamenta fiava at lower levels.

Oapsulse Artieulares. — These are somewhat lax, and are attaehed to the margins of the artieular proeesses.

Membrana Atlanto-Oeeipitalis Anterior (Fig. 144). — This membrane extends from the upper border of the anterior areh of the atlas to the under surface of the basilar portion of the oeeipital bone, anterior to the foramen magnum. On eaeh side of the median plane it is thin and membranous, and stretehes laterally so as to abut against the atlanto-oeeipital eapsular ligament. In the median plane it is strengthened by the upper part of the anterior longitudinal ligament.

Membrana Atlanto-Oeeipitalis Posterior. — This is a thin and weak membrane whieh oeeupies the gap between the posterior areh of the atlas and the posterior border of the foramen magnum, to both of whieh it is attaehed. It is very finnly

JOINTS 0F THE NECK

361

eonneeted with the dura mater, and oti eaeh side it reaehes tbe atlanto-oeeipital eapsular ligament. Eaeh of its kteral borders fontis an areh over the groove, posterior to the upper aitieular facet of the atlas, tn whieh the vertebra] artery and the lirst cervica1 nerve are lodged. It is not uneommon to find these &brous arehes ossiSed.

AtUmto-Oeeipital eapsnlar Ligamenta. — These eonneet the oedpital eondyles with the lateral masses of the atlas.

iUe of eanihe

ween xht body of Ihe e[

They eompletely suiround the joints, and are eonneeted anteriorly with the anterior atlanto-oeeipital membrane, and posterioriy with the posterior atlanto-oeeipital membrane.

The oeeipital bone, therefore, around the foramen magnum is attaehed by speeial ligaments to eaeh of the four portions of the atlas — viz., to the anterior areh, to the two lateral masses, and to the posterior areh.

362 HEAD AND NECK

is neeessary therefore to remove, with the bone forceps, the laminse of the epistropheus and the posterior areh of the atlas. The squamous part of the oeeipital bone also must be taken away by sawing it through, on eaeh side, imraediately posterior to the jugular proeess and the eondyle, earrying the saw eut into the foramen magnum. The upper part of the tube of dura mater, whieh still remains in the vertebral eanal, must next be carefully detaehed. A broad membranous band stretehing upwards over the posterior aspeet of the body and dens of the epistropheus is displayed. This is the membrana teetoria.

The Membrana Teetoria (O.T. Posterior Occipito-axial Ligament). — This is a broad ligamentous sheet whieh is attaehed below to the posterior aspeet of the body of the epistropheus, where it is eontinuous with the posterior longitudinal ligament of the vertebrae. It extends upwards, covering the dens and the anterior margin of the foramen magnum, and is attaehed above to the superior grooved surface of the basilar portion of the oeeipital bone.

Dissedion. — Detaeh this membrane from the epistropheus and throw it upwards upon the basilar portion of the oeeipital bone. By this pro- eeeding the aeeessory ligaments of the atlanto-epistropheal joints and the erueiate ligament are brought into view, and very little further disseetion is required to define them.

Aeeessory Atlanto-epistropheal Ligaments (Fig. 145). — These are two strong bands whieh take origin from the posterior aspeet of the body of the epistropheus elose to the base of the dens. Eaeh band passes upwards and laterally, and is attaehed to the medial and posterior part of the lateral mass of the atlas. To a eertain extent they assist the alar ligaments in limiting the rotary movements of the atlas upon the epistropheus.

Ligamentum Orueiatum (Fig. 145). — The erueiate ligament is eomposed of a transverse and a vertical part. The liga- mentum transversu?n atlantis is by far the most important eon- stituent of this apparatus. It is a strong band whieh stretehes from the tuberele on the medial aspeet of the lateral mass of the atlas on one side to the eorresponding tuberele on the opposite side. With the anterior areh of the atlas it forms a ring whieh eneloses the dens — the pivot around whieh the atlas bearing the head turns. It is separated from the posterior aspeet of the dens by a loose synovial membrane whieh extends anteriorly on eaeh side until it almost reaehes the synovial membrane in eonneetion with the median joint between the dens and the anterior areh of the atlas. Indeed,

JOINTS 0F THE NECK 363

in Eotne eases a eommunieation exists between the two synorial cavities.

The vertical part of the enieiate ligament eonsists of an upper and a lower limb, whieh are termed the enira. Both are attaehed to the dorsal surface of the transverse ligament. The erus superius is the longer and Aatter of the two, and extends upwaids on the posterior aspeet of the dens to be attaehed to the upper aspeet of the basilar part of the oeeipital bone immediately beyond the anterior margin of

the foramen magnum. The erus it^erius, mueh shorter, extends downwards, and is fixed to the posterior aspeet of

the body of the epistropheus.

Disstdim. — Detaeh the superioi eras froiii the oedpital boDe, ind (hrow it downwards. The apieal ligament is Ihus displayed, and a bettei view of the alar ligamenis is obtained.

Ligamentum Apieis Dentis.— The apieal ligament of the dens eonsists of two parts — an anterior and a posterior. The posterior part is a rounded eord-like ligament whieh is attaehed below to the summit of the dens, and above to the anterior margin of the foramen magnum. This ligaraene, inasmueh

364 HEAD AND NECK

as it is developed around the eontinuation of the ehorda dorsalis from the dens to the basis eranii, is a strueture of eonsiderable morphologieal interest. The anterior part of the apieal ligament is a flat and weak band whieh is attaehed above to the anterior margin of the foramen magnum at the same point as the posterior portion. Below, the two portions are separated by an interval filled with eellular tissue, and the anterior part is attaehed to the dens immediately above its artieular facet for the anterior areh of the atlas.

Ligamenta Alaria (Fig. 145). — These are very powerful bands whieh spring, one from eaeh side of the summit of the dens. They pass laterally and slightly upwards to be attaehed to the medial aspeet of the eondyloid eminenees of the oeeipital bone. They limit rotation of the head, and in this they are aided by the aeeessory atlanto-epistropheal ligaments.

Moyements. — Nodding movements of the head are permitted at the atlanto-oeeipital artieulations. Rotatory movements of the head and atlas around the dens, whieh aets as a pivot, take plaee at the atlanto- epistropheal joints. Excessive rotation is eheeked by the alar ligaments.

MOUTH AND PHARYNX.

The disseetors must now return to the anterior part of the skuU, whieh had been laid aside while the disseetion of the prevertebral region was being earried on. The mouth and pharynx should engage their attention in the first instanee.

Mouth. — The mouth is the expanded upper part of the alimentary eanal whieh is plaeed in the lower part of the face, below the nasal ehambers. Its cavity is eontrolled by museles whieh are under the inAuenee of the will, and it is separable into two parts : a smaller external part, termed the vestibule, whieh is bounded externally by the lips and eheeks, and internally by the teeth and gums; and a large part, the moutk proper^ whieh is plaeed within the teeth.

The mueous lining of the mouth should be thoroughly eleansed, and the two subdivisions of the cavity examined through the oralfissure,

Yestibulum Oris. — The vestibule of the mouth, whieh passes round the teeth and gums, is a mere fissure-like spaee, except when the eheeks are inAated with air. It is into this part of the mouth that the parotid duets open (p. 261).

MOUTH 365

Above and below^ it is bounded by the reflection of the mueous membrane from the lips and eheeks on to the alveolar margins of the maxilla and mandible. Anteriorly^ it opens upon the face by means of the oral fi§sure ; whilst posieriorly^ it eommunieates, on eaeh side, with the cavity 6f the mouth proper through the interval between the last molar tooth and the anterior border of the ramus of the mandible. The existence of this eommunieation is of import- anee in eases of spasmodie elosure of the jaws when all the teeth are in plaee, beeause through it Auids may be introdueed into the posterior part of the mouth proper.

In paralysis of the facial museles the lips and eheeks fall away from the dental arehes and food is apt to lodge in the vestibule.

Oayum Oris Proprium. — The mouth proper is bounded anteriorly and laterally by the gums and teeth, whilst posteriorly it eommunieates by means of the i^hinus_fqudufn with the pharynx. The floor is formed by the tongue and the mueous membrane whieh eonneets it with the inner aspeet of the mandible ; the root is vaulted, and is formedby the hard an(i the soft palates. Into this pairt of the bueeal cavity the duets of the submaxillary glands and the duets of the sub- lingual glands open (p. 288). When the mouth is elosed the dorsum of the tongue is usually applied more or less elosely to the palate and the cavity is almost eompletely obliterated.

The various parts whieh bound the oral cavity may now be examined in turn.

Labia Oris. — The strueture of the lips has in a great measure been examined already in the disseetion of the face (P' ^'^'h)' Eaeh lip is eomposed of four layers : (i) Cuta- neous; (2) museular; (3) glandular; and (4) mueous. The skin and mueous membrane beeome eontinuous with eaeh other at the free margin of the lip. From the inner aspeet of the upper lip the mueous membrane is reflected to the alveolar margin of the maxilla and from the inner aspeet of the lower lip to the mandible. In eaeh ease it is raised in the median plane in the form of a free fold termed the /renulum, The museular layer eonstitutes the chief bulk of the lips. It is formed by the orbieularis oris and the various museles whieh converge upon the oral Assure. Numerous laUal glands lie in the submueous tissue whieh intervenes between

366 HEAD AND NECK

the mueous membrane and the museular Abres. The duets of these glands pieree the mueous membrane and open into the vestibule. In eaeh hp there is an arterial areh formed by the eorresponding labial arteries (p. 130).

The lymph vessels of both lips join the submaxillary lymph glands, but some of the lymph yessels of the upper lip pass to the supertietal parotid glands.

Buees. — Six layei5„enter into the eonstruetion of the eheeksLa.lL of_wliich_haYe-]i£

FiG, 1+6, — The Sublingual Regioii in Ihe Inlerior of the Moulh.

of the faee_- (i) Skin ; (2) a fatty layer traversed by some of the facial museles and the external m3xi!lary artery; (3) the bueeo-pharyngeal aponeurosis; (4) the bueeinator musele; (5) numerous bueea! glands, similar in eharaeter to the labial glands, lie in the submueous tissue between the mueous mem- brane and the bueeinator musele ; (6) the mueous membrane. Four or five mueous glands of larger size, termed the tnolar glands, oeeupy a more superficial position. They Iie either external or internal to the bueeo-pharyngeal aponeurosis, elose to the point where this is piereed by the parotid duet, and their duets open into the vestibule of the mouth. The buuo-pharyngeal aponeurosis is a dense fascia whieh covers the bueeinator musele. Above and below, it is attaehed to

MOUTH

367

the alveolar portions of the maxilU and mandible, whilst posteriorly it is eontinued over the pharyn». The museles whieh traverse the fatty layer are chiefly the zygomaticus, the risorius, and the posterior fibres of the platysma. The parotid duet pierees the inner three layers of the eheek, and opens into the vestibule of the mouth opposite the seeond molar tooth of the maxilia.

aingiTie et Dentes. — The mueous membrane of the gums is smooth, vascular, and firmly bound down to the subjacent

FlG. 147.- — Isihmus of the Fauces as seen through Ihe widdy opened Monlh. The tonsils in the subject rrom whieh ihis drawing wiu made were somewbat enlarged.

periosteum of the alveolar portions of the jaws by a stratum of dense connective tissue. It is eontinuous on the one hand with the mueous membrane of the lips and eheeks, and on the other with the mueous membrane of the mouth proper. The gums elosely embraee the neeks of the teeth.

In the adult the teeth in eaeh jaw number sisteen. From the median line posteriorly, on eaeh side, they are the two ineisors, the eanine, the two prasmolars, the three molars.

Hoor of the Uonth. — Tbe mueous membrane ts reflected from the inner aspeet of the mandible to the side of the tongue, but in the anterior part of the mouth the tongue lies

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--■T— -^- ^- - - -;■"■ -V^ :." :::e fu.:-:zg^vr:i:!3. 3mzct :f "ue 3£^a:i2. — 7i r i*ir-i i::«i ±:e ser: ralates fonii ::= :::-._:: ..t ::'.^:.it :-ic -ii.:*^ r:i:c :c rre moath (Fig. : . . . 7? ; :•: : "^ r":3: :z.-: —-«iile :£ iie ri:scericr eee maigin ::' :ir :•: "■: z^j^iz. lz i r.ie^-::; -Tee :z.e iersm c£ the toi^e, :-~.r *r. j -*--_ :«, fce.i 7.; :-* . ?^iz — g il.rng the median .-.iz'"r! :■: :_: iTT .■Li.-i i_-'i ir-r 5.:i^ ruiiies is a raphe ■V _-..:_-. -.tri' ..:»:::: iz:ir.:r-- :-:j«::r::z ±.e ir:cL5ive ^oramen,

Ir. ±i^ i::::r. ;: y^:: ::" ::.i i^-ri r»ilj.:e lie nueeas membrane, :r. ej.:.i ?.ie :f :ir riyir. :? ii::-5-=. in:o three or foiir :7.ir.?v:r5c 11: i ::~i^i:::r? :: r.i^rs : =::re posteriorly it is ::.T.rj.ri::.e. ^r::::!. 7;. :irr:illv r^r^idsg the postero- '.j.:rril i::^".f*? ::' :ir :ili:f :ie i:55o::jr s^i'.l be able to feel :ir iir:i-: :f :i: r:ri:il ::rryg::i ljz:in:e.

Isihniis Fa::ci:iixL — rr.:? r.ii::e is ziven :o the eommuni- c:i:::r. ■r-:-:vTrtr :ir ri:i:i yr:yer ir.d r:e pharyiut (Fig. 147). To cb:i:r. 1 g::i v:r-v :: i: :r.e rieurh must be well opened and :he ::r.i:-ie iryressed The isihn^us taudum and the parrs whlih i :i::i :: ear. be exarii::ed best in the Iiving subject«F> 147'. I: :s bvur.ded above by the soft palate, below by :he d:rsiri of the rongue, a:id on eaeh side by two curved tolds of mueous merr.brane, remied respectively the areus glossopalatinus (O.T. anrerlor pillars of the fauces) and the areus phar)-ngopalatinus (O.T. posterior pillars of the fauces).

The areus palatini spring from the base of the uvula, and areh laterally and then downwards. The areus glossopalatinus inelines anteriorly as it deseends ; it ends upon the side of tln: posterior part of the tongue, and it eneloses the glosso-

PHARYNX 369

palatinus musele. The areus pharyngopalatinus^ more strongly niarked, inelmes posteriorly, and is lost upon the side of the pharynx ; it eneloses the pharyngo-palatinus musele.

In the triangular interval whieh is formed by the divergence of these two folds lies the tonsiL

Strietly speaking, the term isthmus /atieium should be confined to the interval between the two glosso-palatine arehes, as the tonsil and the pharyngo-palatine arehes belong to the lateral wall of the pharynx.

Pliax3rnz. — The pharynx is a wide museulo-aponeurotie eanal, about 5 inehes long, whieh extends from the base of the eranium to the level of the body of the sixth cervical vertebra. There, at the lower border of the erieoid eartilage, it beeomes eontinuous with the eesophagus. Plaeed posterior to the nasal cavities, the mouth and the larynx, it serves as the passage whieh eonduets air to and from the larynx, as well as the food from the-mouth to the eesophagus.

Under ordinary eonditions it is expanded from side to side and eompressed antero-posteriorly, so that it possesses anterior and posterior walls and two lateral borders. Above the level of the orifice of the larynx there is always sufficient spaee for the passage of air to the lungs, but below the orifice of the larynx the anterior and posterior walls are in eontaet, except when separated by the passage of food.

It is widest above, at the base of the eranium, posterior to the orifices of the auditory tubes (O.T. Eustaehian). Thenee it narrows to the level of the hyoid bone. It widens again at the level of the upper part of the larynx and then rapidly narrows to its termination.

To obtain a proper idea of the eonneetions of the pharynx, the disseetor should distend its walls moderately by stuffing it with tow. This may be introdueed either from above, through the mouth, or from below, through the oesophagus.

The pharynx will now present a somewhat ovoid form. Posteriorly^ its wall is eomplete, and, when in position, it lies anterior to the upper six cervical vertebrae, the prevertebral museles, and the prevertebral fascia. To these it is bound by some lax connectiv^ tissue whieh offers no impediment to the movements of the eanal during the proeess of degluti- tion. Laterallyy the pharynx is related to the great vessels and nerves of the neek, as well as to the styloid proeess and the museles whieh take origin from it. Upon this aspeet of

VOL. II — 24

370 HEAD AND NECK

the pharynx also is plaeed the pharyngeal plexus ot nerves, whieh supplies its walls with motor and sensory twigs. An- teriorly^ the pharyngeal wall is interrupted by the openings of the nasal cavities, mouth, and larynx; and it is from the struetures whieh lie in proximity to these apertures that it derives its prineipal attaehments. Thus from above down- wards it is attaehed on eaeh side — (a) to the medial pterygoid lamina; (b) to the pterygo-mandibular raphe; (^)to the side of the tongue ; (d) to the inner aspeet of the mandible ; (e) to the hyoid bone ; (/) to the thyreoid eartilage ; (^) to the erieoid eartilage. Above^ it is attaehed to the basis eraniL These various attaehments will be studied more fully when the eonstituent parts of its walls are disseeted.

It should be noted that an altogether false idea of the natural fonn of the pharynx is obtained when it is examined in its present stuffed eondition, and removed from the vertebral eolumn. When seen in transverse seetions of the frozen body it will be noted that, with the exception of its upper or nasal part, whieh remains patent under all eonditions, the anterior wall is more or less nearly approximated to the posterior wall, and below the opening of the lar^m^ it presents the appearanee of a simple transverse slit.

Pharsmgeal Wall. — The wall of the pharynx eonsists of four well-marked strata. These are from without inwards: (i) bueeo-pharyngeal fascia; (2) pharyngeal museles ; (3) pharyngeal aponeurosis; (4) mueous membrane. The museular layer, whieh is eomposed of the three eonstrietor museles, with the stylo-pharyngeus and pharyngo-palatinus on eaeh side, must now be disseeted.

For this purpose plaee the preparation so that the ehin rests upon a bloek and the pharynx hangs downwards with its posterior surface towards the disseetor. The eonstrietor museles should now be carefully eleaned, in the direetion of the museular fibres, by removing the bueeo- pharyngeal fascia, whieh covers them.

Bueeo-pharyngeal Fascia. — This is a eoating of fibrous tissue whieh ensheaths both the bueeinator and the pharyn- geal museles.

Yenae Pharynge». — Upon the posterior wall and lateral borders of the pharynx the disseetor should notiee numerous veins joined together in a plexiform manner. These eon- stitute the pharyngeal venous plexus^ whieh eolleets blood from the pharynx, soft palate, and prevertebral region. It eommunieates with the pterygoid plexus and the cavernous sinus. Two or more ehannels lead the blood from it to the

PHARYNK

371

intemal jugular vein. This venous plexus, together with the phar^mgeal plexus of neTves, will iequire to be remoyed in order to display the museles properly,

OonstrietoT Unseles. — The eonstrietor museles are three curved sheets of museukr iibres whieh are so arranged that they overlap eaeh other from below upwards ; thus, the

t. Middie eonstrietor.

g. Thyteo-byoid.

^. Hyoglouus.

i- Stylo-hyind.

/. Mylo-hyoid. tn. Crico.tbyreoid.

j*. Stylo-hymd Ligameni

1. Si

laryngeal ne

14S.-

inferior eonstrietor overlaps the lower part of the middle eonstrietor, whilst the middle eonstrietor, in tum, overIaps the 'lower part of the superior eonstriotor, The three museles are inserted, in the median plane, into the median raphe whieh deseends from the basilar portion of the oeeipital bone along the posterior aspeet of the pharynx.

MusmIus Constrictor Pharyngts Inferior (Fig. 148, f). —

372 HEAD AND NECK

The inferior eonstrietor musele is relatively short anteriorly at its origin, and relatively long posteriorly, where it blends with the fellow of the opposite side in the median raphe of the posterior wall of the pharynx. It arises from the posterior part of the side of the erieoid eartilage, and from the inferior eornu, the oblique line, and the upper border of the thyreoid eartilage. The musele curves posteriorly and medially around the pharyngeal wall to meet its fellow of the opposite side in the median raphe. The lower fibres take a horizontal direetion, but the remainder aseend, with inereas- ing degrees of obliquity, until the highest fibres reaeh the raphe at a point a short distanee below the basis eranii. The lower margin of the inferior eonstrietor overlaps the eommeneement of the oesophagus, and the inferior laryngeal nerve and the laryngeal braneh of the inferior thyreoid artery pass upwards, under cover of it, to reaeh the larynx.

Museulus Constrictor Pharyngis Medius, — This is a fan- shaped musele (Fig. 148, e\ It arises from the great and small eornua of the hyoid bone and from the lower part of the stylo-hyoid ligament. From this origin its fibres pass round the pharyngeal wall, to be inserted with the eorre- sponding fibres of the opposite side into the median raphe. As they pass postero-medially, the lowest fibres deseend, the highest aseend, and the intermediate fibres run horizontally. The lower portion of this musele is overlapped by the inferior eonstrietor, and in the interval whieh separates the margins of the museles anteriorly, opposite the thyreo-hyoid interval, the internal laryngeal nerve and the laryngeal braneh of the superior thyreoid artery will be seen piereing the thyreo-hyoid membrane to gain the interior of the pharynx.

Dissedion. — The superior eonstrietor possesses a somewhat eomplieated origin, and to bring this fully into view it will be neeessary to eut through the internal pterygoid musele about its middle, if this has not already been done (p. 293), and turn the upper and lower portions aside.

Museulus Gonstrietor Pharyngis Superior (Fig. 148, d\ — The superior eonstrietor has a weak but eontinuous line of origin from the following parts : {a) the lower third of the posterior border of the medial pterygoid lamina and its * hamulus ; (b) the pterygo-mandibular raphe, whieh is eommon to it and the bueeinator musele; {e) the posterior end of the mylo-hyoid ridge on the inner aspeet of the mandible ; (i) the mueous membrane of the mouth and side of the tongue.

PHARYNX 373

From tliis somewhat extensive origin, the fibres curve postero- medially to reaeh the median raphe, whilst, as a rule, some of the highest gain a distinet insertion into the pharyngeal tuberele on the under surface of the basi-oeeipital bone.

The lower part of the superior eonstrietor is overlapped by the middle eonstrietor, and the stylo-pharyngeus passes into the interval between the two as it deseends to its insertion (Fig. 148, «). The upper border of the musele, whieh is free and ereseentie, falls short of the basis eranii.

Baphe Pterygo-mandibularis (Fig. 148, q). — This is a strong, narrow, tendinous band, whieh extends from the hamulus of the medial pterygoid lamina to the posterior part of the mylo-hyoid ridge of the mandible. It aets as a tendinous bond of union between the bueeinator and superior eonstrietor museles, and its eonneetions ean be appreeiated best by introdueing the finger into the mouth and pressing laterally along the eourse of the raphe.

Sinus of MorgagiiL — This name is applied to the semi- lunar spaee whieh intervenes between the upper ereseentie margin of the superior eonstrietor and the basis eranii. The deficiency in the museular wall of the pharynx in this region is eompensated for by the inereased strength of the pharyngeal aponeurosis, whieh, in this situation, is ealled the pharyngo-basilar fascia. In eontaet with the outer surface of the aponeurosis are two museles belonging to the soft palate — viz. the ievator veli palatini and the tensor veli palaiini (Fig. 1 48, c and S). The levator, whieh is rounded and Aeshy, lies posterior to the tensor, whieh is flat and more tendinous. The tensor ean readily be reeognised from its position in relation to the deep surface of the internal pterygoid musele and from its tendon turning medially under the hamulus of the medial pterygoid lamina. In the upper part of the spaee, elose to the basis eranii and between the origin of the two museles, will be seen the auditory tube (O.T. EustaeMan tube).

Phaiyngeal Aponeurosis. — The upper part of the pharyn- geal aponeurosis, the pharyngo-basilar /asda^ is strong, and it maintains the integrity of the wall of the pharynx where the museular fibres are absent. As it is traeed downwards it gradually beeomes weaker, until it is ultimately lost as a disjtinct layer. It lies between the musdes and mueous mem- brane and eomes to the surface only where the museles are absent It is the prineipal means by whieh the pharynx is

II— 24a

374 HEAD AND NECK

attaehed to the base of the skull, and it is united also to the auditory tubes and the bony margins of the ehoana.

extreniity of Ihis eul, the knife should be C! biisis eranii. The stuffing should be remo' the phatyns eleansed.

Interior of tlio Pharysi. — The mueous membrane is now exposed, and it should be noted that it is eontinuous,

PHARYNX 375

through the various apertures whieh open into the pharynx, with the mueous membrane of the nasal cavities^ the auditory tubes and tympanie cavities, the tnouth proper^ the larynx, and the oesophagus,

Raeemose glands^ whieh lie immediately subjacent to the mueous membrane and seerete mueus, are present in great numbers. There are also numerous lymph /ollieles^ and in eertain loealities these are aggregated together into large masses (the tonsils and the pharyngeal tonsil). These will be studied with the regions of the pharynx in whieh they are plaeed.

The soft palate projects into the pharynx, posterior to the isthmus faucium, and divides the cavity of the pharynx into an upper and a lower part. The upper part^ ealled the naso - pharynx^ eommunieates with the nasal cavities and the tympanie cavities by four apertures, viz. the two ehoanae (O.T. posterior nares) and the two auditory tubes (O.T. Eustaehian tubes).

The lower portion of the pharynx may be regarded as eonsisting of an oral part^ whieh lies posterior to the mouth and tongue, and a laryngeal part^ plaeed posterior to the larynx. Below the soft palate there are three openings into the pharynx, viz. the opening of ihe mouth or isthmus /aueiumy the opening of the larynx, and the opening of the oesophagus,

Pars Nasalis. — The naso-pharynx is situated immediately posterior to the nasal cavities and below the body of the sphenoid and the basilar part of the oeeipital bone. It is the widest part of the pharynx. Its walls, except the soft palate, are not eapable of movement, and, consequently, its cavity always remains patent, and presents under all eonditions very mueh the same form.

In its anterior boundary are the ehoanae, through whieh it opens into the nasal cavities. The ehoanee are two oblong orifices whieh slope from the base of the eranium downwards and anteriorly to the posterior border of the hard palate. Eaeh is an ineh long and half an ineh wide, and it is separated from its fellow by the posterior part of the septum nasi, whieh in this region is formed by the vomer. By looking through the ehoanae a partial view of the lower two meatuses of the nose and of the posterior ends of the middle and inferior eonehae may be obtained. 11—24 h

376 HEAD AND NECK

On the lateral wall of the naso-pharynx, on eaeh side, is seen the orifice of the auditory tube, and posterior to it the pharyngeal reeess. The ostium pharyngeum of the auditory tube lies immediately posterior to the lower part of the eorresponding ehoana, at a level whieh eorresponds elosely with the posterior end of the inferior eoneha. It is bounded above and posteriorly by a prominent and rounded margin termed the torus tubarius^ whieh is altogether deficient below and anteriorly. A fold of mueous membrane, termed the salpingo-pharyngeal fold^ deseends upon the lateral wall of the pharynx from the posterior lip of the orifice of the auditory tube. As this is traeed downwards it gradually disappears.

The disseetor should pass a Eustaehian eatheter through the nose into the auditory tube. Hold the eatheter with the point downwards. Pass it posteriorly through the right nasal cavity, along the septum of the nose, to the posterior wall of the pharynx. Pull it towards the palate till the bent end of the eatheter eatehes against the baek of the hard palate. Turn the point through a quarter of a eirele to the right side of the head and it will enter the right auditory tube. If it is desired to eatheterise the left auditory tube pass the eatheter through the left nasal cavity, and in the final stage tum the point to the left side.

In the natural eondition of parts there is a deep reeess on the lateral wall of the naso-pharynx immediately posterior to the prominent posterior lip of the orifice of the auditory tube. This is termed the lateral reeess of the pharynx.

The roof and posterior wall of the naso-pharynx are not marked off from eaeh other. They form together a eontinuous curved surface. The upper portion of this surface looks downwards and may be regarded as the roof ; the lower portion, whieh looks anteriorly, eonstitutes the posterior wall. The roof is formed by the basilar part of the oeeipital bone, and also by a small part of the under surface of the basi-sphenoid, covered with a dense periosteum and a thiek eoating of mueous membrane. The posterior wall is supported posteriorly by the anterior areh of the atlas and the anterior surface of the epistropheus. In that part of the roof whieh lies between the two lateral reeesses of the naso-pharynx there is a marked eolleetion of lymphoid tissue, the pharyngeal tonsil, Over its surface the mueous membrane is thiekened and wrinkled, and in its lower part a small median pit, termed the pharyngeal bursa, may usually be found ; it is just large enough to admit the point of a fine probe.

The fioor of the naso-pharynx is formed by the curved,

PHARVNX

377

sloping upper surface of the soft palate. Between the posterior border of the soft palate and the posterior wall of the pharynx there is an interval, termed the pharyngeal hihmus, through whieh the naso-pharynx eonnmunieates with the oral pharynx.

Il is imporlant to nole that the posterior wall and rixtf or the naso- pharynx ean be explored by the tinger introdueed through the mouth and the pharyngeal isthmus.

When the naso-pharynx is illuminated. by lighl reAeeled froin a mirror

introdueed thtough the mouth, a view of the four oritiees whieh open into this patt of the pharynn may be obtained. Owing to the mitror being plaeed obliquely, and lielow the level of the bard palate, only the posterior parts of the infeiior eoneha; are risible through the ehoanEe, and the inferior meatuses of the nose are aitogether out of sight. The mitidle and superior meatuses of the nose and the middle and superior eonehEe, however, ean be btought into view and their eondition aseertained. The lateral walls of the naso-pharynx and the oriiiees of the auditory tubes ean also be fu11y inspeeted.

Pars Oralis. — The oral pharynx hes posterior to the mouth and tongue. The pharyngeal part of the tongue, whieh looks

378 HEAD AND NECK

more or less direetly posteriorly, forms its anterior wall in its lower part. Above this is the isthmus of the fauces, or the opening into the mouth, limited on either side by the glosso-palatine areh. These arehes may be regarded, there- fore, as the lateral boundary lines between the mouth and the pharynx. On the lateralwall of the oral pharynx the pharyngo- palatine areh forms a prominent fold whieh is gradually lost as it is traeed downwards. Within this fold is the pharyngo- palatine musele. This is an important relation, beeause the posterior palatine arehes form the lateral boundaries of the pharyngeal isthmus, and by the eontraetion of the pharyngo-palatine museles the two posterior arehes ean be approximated until the opening of the isthmus is obliterated ; the passage of food and Auids from the oral pharynx into the naso-pharynx is thus prevented.

The areus glosso-palatinus and the areus pharyngo-palatinus form, on eaeh lateral wall of the oral pharynx, the anterior and posterior limits of a triangular interval in whieh is lodged the tonsil. The upper part of this area, above the level of the tonsil, presents a small depression termed the supra'tonsillar fossa,

In the ehild, and not uneommonly in the adult, a triangular fold of mueous membrane, the pliea triangularis^ extends posteriorly from the lower part of the glosso-palatine areh and the base of the tongue aeross the surface of the tonsil. The upper border of the fold may be free or it may beeome attaehed to a greater or less extent to the surface of the tonsil.

Pars Larsmgea. — The laryngeal portion of the pharyngeal cavity diminishes rapidly in width to the level at whieh it be- eomes eontinuous with the oesophagus. In its anterior wall, from above downwards, may be seen : (i) the epiglottis; (2) the superior aperture of the larynx with the reeessus piriformis on either side ; and (3) the posterior surfaces of the arytaenoid and erieoid eartilages, covered with museles and mueous membrane.

Aditus Laryngis. — The superior aperture of the larynxy situated below the pharyngeal part of the tongue, is a large, obliquely plaeed opening whieh slopes rapidly from above downwards and posteriorly. It is somewhat triangular in outline, and the basal part of the opening, plaeed above and anteriorly, is formed by the free border of the epiglottis.

PHARVNX 379

Posteriorly, the opening rapidly narrows, and tinally ends in the interval between the two arytsenoid earlilages. The sides of the aperture are formed by two sharp and prominent folds of mueous membrane, termed the ary-epiglottie fo/ds, whieh eonneet the lateral margins of the epiglottis wiih the aryt£enoid eartilages. Two small nodules of eartilage, in the posterior part of eaeh ary-epiglottie fold, give rise to two rounded eminenees, of whieh the anterior is the cuneiform tuberde, and the posterior the eornieulate tuberde.

On either side of the lower part of the laryngeal open- ing there is a small three-sided or pyramidal depression, ealled the reeeisus piriformis. On the lateral side it is

bounded by the posterior part of the lamina of the thyreoid eartilage and the thyreo-hyoid membrane ; on the medial side _ by the aryttenoid eartilage and the ary-epiglottie fold ; whilst its posterior wall is formed by the posterior wall of the pharynx, when ihis is in plaee. The reeessus piriformis presents a wide entranee, whieh iooks upwards ; but it rapidly narrows towards the bottom (Figs. isoand 151); and it is important to the surgeon beeause in this little poeket foreign bodies intro- dueed into the pharynx are liable to be eaught.

Below the opening of the Iarynx, the anterior and posterior walls of the pharynx are always elosely applied to eaeh other, except during the passage of food.

;/ opening is plaeed opposite the lower border

38o HEAD AND NECK

of the erieoid eartilage. This is the narrowest part of the pharynx.

Velum Palatinum. — The soft palate is a movable eurtain, whieh projects downwards and posteriorly into the pharynx. During deglutition it is raised, and helps to shut off the nasal part of the pharynx from the portion below. Anteriorly^ it is attaehed to the posterior margin of the hard palate ; on eaeh side it is eonneeted with the lateral wall of the pharynx ; whilst posteriorly it presents a free border. From the eentre of this free margin the eonieal proeess, termed the umla^ projects ; whilst the sharp concave part of the border, on either side of the uvula, beeomes eontinuous with the pharyngo- palatine areh, whieh deseends on the side wall of the pharynx. The upper surface of the soft palate is convex and eontinuous with the floor of the nasal cavities; the inferior surface is concave and forms part of the vaulted roof of the mouth. From the posterior part of this surface on eaeh side a glosso- palatine areh curves downwards ; and along its median plane may be seen a slightly marked median ridge or raphe.

The soft palate is eomposed of a fold of mueous membrane, between the two layers of whieh are interposed museular, aponeurotie, and glandular struetures, together with blood vessels and nerves.

(The two levatores veli palatini. The two tensores veli palatini. The two glosso-palatini. The two pharyngo-palatini. The museulus uvul8e. Palatal aponeurosis. Palatal glands.

{Aseending palatine from external maxillary. Palatine braneh from aseending pharyngeal. Twigs from the deseending palatine braneh of the internal maxillary. Middle palatine, . . . ^

• I

T^, J Posterior palatine, . . I from the spheno - palatine

JNerves, . \ T^ranehes ^— ->.o,„«™i X ^.«„i;^«

plexus,

Branehes from pharyngeal \ ganglion.

The raeemose mueous glands in the soft palate form a very thiek layer, immediately subjacent to the mueous membrane whieh elothes its inferior surface. Glose to the posterior border of the hard palate the soft palate eontains very few museular fibres; there it is eomposed chiefly of the two layers of mueous membrane enelosing the glands, and the palatal aponeurosis.

PHARYNX 381

Disseetion. — The disseetion of the soft palate is difficult, and it is only in a fresh part that the preeise relations of the different museular layers ean be made out. Begin by rendering it tense by means of a hook, and then remove carefully the mueous membrane from its upper and lower surfaces, and also from the glosso- and pharyngo-palatine arehes. The latter proeeeding will expose the glosso - palatine and the pharyngo- palatine museles on eaeh side.

Museulus Glosso-palatinus. — The glosso-palatinus is a delieate museular slip, whieh arises from the side of the posterior part of the tongue and curves upwards and medially to reaeh the under surface of the soft palate, above the glandular layer. There its iibres spread out and beeome eontinuous with the eorresponding fasciculi of the opposite side. It forms the lowest museular stratum of the soft palate.

Museulus PhaoTngo-palatinus. — The pharyngo-palatinus forms two museular strata in the soft palate whieh enelose, between them, the museulus uyulae and the levatores palati museles. The upper layer is very weak and confined to the posterior part of the velum. It eonstitutes the most super- ficial museular stratum on the upper aspeet of the soft palate, and beeomes eontinuous with the eorresponding portion of the musele of the opposite side. The deeper layer takes origin from the posterior margin of the palate bone and from the palatal aponeurosis, and some of its fibres mingle with those of the eorresponding musele of the opposite side. Lateral to the soft palate the two strata eome together, and are joined by one or two delieate museular slips whieh spring from the lower border of the eartilage of the auditory tube. These slips are sometimes deseribed as the salpingo-pharyngeus museie, The pharyngo-palatinus, thus formed, arehes downwards and posteriorly in the posterior areh of the fauces, and spreads out into a thin sheet of fibres in the wall of the pharynx. Blending to some extent with the stylo-pharyngeus, it is inserted into the posterior border of the thyreoid eartilage. Some of its fibres, however, ineline posteriorly and are inserted into the pharyngeal aponeurosis.

Museulus UvulsB. — This delieate musele is plaeed on the upper aspeet of the soft palate, and, posteriorly, it is covered by the superficial fibres of the pharyngo-palatinus. These must be removed to expose it fully. It eonsists of two minute slips whieh, as a rule, arise from the posterior nasal spine of the hard palate, and lie one on either side of the

382 HEAD AND NECK

median plane. As they pass posteriorly into the uvula they unite into a single rounded museular bundle.

Disseetion, — The levator palati musele has been seen already on the outer aspeet of the pharynx in the sinus of Morgagni. To display it from the inside it is neeessary to remove the wall of the pharynx between the auditory tube above and the upper border of the superior eonstrietor below, and then follow its fibres into the soft palate. In a well-injected subject the disseetor will observe the aseending palatine artery in rela- tion to this musele.

Museulus Levator Veli Palatini. — The levator palati is a rounded Aeshy musele whieh arises from the lower and medial border of the eartilage of the auditory tube, and from the rough surface on the under aspeet of the apex of the petrous part of the temporal bone. It passes downwards and an- teriorly, erosses the upper border of the superior eonstrietor, pierees the pharyngeal aponeurosis, passes below the orifice of the auditory tube and enters the soft palate. There its fibres spread out below the uvular musele and above the anterior or deep portion of the pharyngo-palatinus. Anteriorly, some of the fibres are inserted into the palatal aponeurosis; but more posteriorly, the majority of the fibres beeome eontinu- ous with the eorresponding fasciculi of the opposite side.

Museulus Tensor Veli Palatini. — The origin of the tensor veli palatini and the relations of its museular belly were noted on p. 293. The musele deseends from the base of the skuU along the lateral surface of the medial pterygoid lamina, and ends in a tendon whieh turns horizontalIy towards the median plane, below the hamulus, where a bursa mueosa facilitates the play of the tendon on the bone. In the soft palate the tendon ex- pands below the lower layer of the pharyngo-palatinus, and some of its fibres blend with the palatal aponeurosis whilst others gain attaehment to the horizontal part of the palate bone.

Palatal Aponeurosis. — The palatal aponeurosis extends posteriorly from the posterior margin of the hard palate to give strength and support to the soft palate. At first it is strongly marked, but it weakens rapidly as it passes posteriorly. The small portion of the soft palate whieh it supports eontains few museular fibres, and remains always more or less horizontal in position. The mueh more extensive posterior museular part of the soft palate eonstitutes the movable sloping portion. The tensor palati operates upon the anterior aponeurotie portion of the soft palate.

PHARYNX 383

Yessels and Nerve8 of the 8oft Palate. — The aseending palatine braneh of the extemal maxillary artery is, as a rule, the prineipal art^ry of supply to the soft palate. It has already been traeed on the wall of the pharynx (p. 299), where it lies in the sinus of Morgagni, in relation to the levator palati musele, whieh it aeeompanies into the soft palate. Th^palatine braneh of the aseending pharyngeal artery may also be traeed into the soft palate. In eases where the preeeding artery is small, this twig will be found enlarged so as to take its plaee (p. 304). The deseending palatine braneh of the internal maxillary artery also sends small twigs to the soft palate and tonsil.

Two nerues enter the soft palatie from the spheno-palatine ganglion — viz. the posterior palatine and the middle palatine nerue. It would appear, however, that they do not supply the museles, but are distributed to the mueous membrane. The levator palati, the museulus uvul3e, the glosso- palatinus, and the pharyngo-palatinus are supplied by twigs from the pharyngeal branehes of the vagus, whieh convey to them fibres whieh are originally derived from the eerebral part of theaeeessory nerve {v. p. 315) (W. Aldren Tumer). The tensor palati is probably supplied by the braneh whieh it receives from the otie ganglion, whieh conveys to it fibres originally derived from the motor part of uie trigeminal nerve.

Tonsillae Palatinse. — The mlatine tonsils are two prominent masses of lymphoid tissue, plaeed one on* eaeh lateral wall of the pharynx, in the triangular interyal between the two palatine aret^es and immediately above the pharyngeal'part of 4h£_J;pngue. The pharyngeal or internal surface of the tonsil is eoyered with mueous membrane and presents a number of oriiiees whieh lead into erypts or reeesses in its substanee. The deep or external surtaee is embedded in the pharyngeal wall and is supported by the superior eonstrietpr musele of the pharynx (see p. 2q8). It is covered by a^layer of fibrous tissue whieh forms an ineomplete eapsule for the organ. It is important to note that between the tonsil and the superior eonstrietor there is some lax connective tissue, so that the organ ean be pulled forwards by the volsellum with- out dragging the wall of the pharynx with it

The tonsils have a rieh blood-supply, They derive arterial twigs from the tonsillar and aseending palatine branehes of the external maidllary. the deseending palatine braneh of the internal maxillary, the aseending phaiyngeal, and the dorsalis linguae.

Tuba Auditiva (O.T. Enstaehiaii Tube). — ^This is the

384 HEAD AND NECK

■

eanal whieh conveys air from the pharynx to the tympanie cavity. It is divided into two portions, aeeording to the parts whieh enter into the eonstruetion of its wall. Thus, in the lateral part of its eourse, as it nears the tympanie cavity, its wall is bony, and it runs in the interval between the tympanie and petrous portions of the temporal bone. The medial part eonsists mainly of eartilage. It is plaeed on the base of the skull, and is lodged in the gutter or groove between the petrous part of the temporal bone and the great wing of the sphenoid. This is the subdivision of the tube whieh eomes under the notiee of the disseetor at the present stage, and he should first note its direetion and then study its relations and the eonstruetion of its wall.

The direetion of the eanal ean be readily aseertained by passing a probe into it through its pharyngeal orifice. It runs postero-laterally with a slight inelination upwards and passes first above and then to the lateral side of the levator palati, and along the medial side of the upper part of the tensor palati. It lies, therefore, in a eonsiderable part of its extent between the two museles.

Before removing the mueous membrane from the pharyngeal part of the tube the disseetor should note that at the lower margin of the orifice there is a prominent rounded eminenee, the levator eushion^ due to the subjacent levator veli palatini. The removal of the mueous membrane will reveal the fact that the wall of the tube is formed, in great part, by a triangular plate of eartilage, whieh is folded upon itself so as to proteet the tube on its upper and medial aspeets. The eartilage is deficient below and laterally, its plaee being taken by dense fibrous tissue, whieh eonneets the margins of the eartilage and eompletes the wall of the eanal. The projecting free base of the eartilage gives rise to the torus tubarius already examined on the lateral wall of the naso- pharynx (p. 376). A museular slip, whieh deseends from the lateral margin of the eartilage, in relation to the outer un- proteeted side of the tube, has been termed the dilatator tubee (Rudinger). It joins the tensor palati. The interior of the tube is lined with mueous membrane eontinuous with that of the pharynx and the tympanie cavity ; and its ealibre varies eonsiderably in different parts of its eourse. It is narrowest at a point termed the isthmus^ situated at the junction of the osseous and eartilaginous parts. As the tube is traeed

CAROTID CAXAL -5?

thenee to the phaiyni it gradually inerease? ir. c::2:':'re:. mi attains its greatest widlh at its opening in:o the liasr-TeunTL]

GAROTID GANAU

The earotid eanal, whieh traverses the interieir of tbe petrous part of the temporal bone, oontains tbe internal earotid artery, the intemal earotid eondnuation of the oerrkaLl sympathetie and a plexus of veins,

Disseetion, — The earotid eanal may be opened np br retoaraa^ its inferior wall with the bone forcep6. In doing this, it is x>oii Deeessair to interfere with the auditory tube, whieh lies in dose proadmiir. The dis- seetion must be made on one side only.

Arteria Garotis Intema. — The intemal earotid artei>- in this part of its eourse is about three-quarters of an ineh long. At first it aseends yertieally ; then, bending suddenly, it nins horizontal]y antero-medially. It emerges from the eanal at the apex of the petrous bone and enters the foramen laeeram, where it turns upwards, pierees the extemal layer of the duia mater^ and enters the middle fossa of the skulL From this point onwards the internal earotid artery has been examined already (p. 331). Whilst within the earotid eanal it lies below and anterior to the eoehlea and the tympanie cavity. The great superficial petrosal nerve and the semilunar ganglion are plaeed above it, but are separated from it by a thin plate of bone, whieh is, however, sometimes absent

Nenrus Garotieus Intemus. — The disseetor has already noted this large braneh proeeeding from the upper end of the superior cervical ganglion and entering the earotid eanal with the internal earotid artery. It divides almost im- mediately into two parts, whieh are plaeed on either side of the artery. Eaeh of these soon divides into a number of branehes whieh eommunieate together around the internal earotid artery forming the intemal earotid piexus. The further disseetion of these branehes is a matter of some difficulty, and ean be satisfactorily eflfected only under speeially favourable eireumstanees.

At the posterior end of the cavemous sinus a ganglion is sometimes found in the plexus, and where the sixth nerve erosses the internal earotid artery the plexus is very dense. This part is known as the eauemous plexus. At the anterior end of the cavemoas sinus the earotid plexus

YOL. 11 — ^25

386 HEAD AND NECK

breaks up into branehes whieh aeeompany the anterior and middle eerebral arteries.

The internal earotid plexus eommunieates with the tympanie plexus by means of superior and inferiorcarotico-tympanic branehes given off in the earotid eanal, and with the spheno-palatine ganglion by the great deep petrosal braneh, whieh unites with the great superBeial petrosal of the facial nerve to form the nerve of the pterygoid eanal (O.T. Vidian). It gives branehes also to the semilunar ganglion, the third, fourth, sixth and the ophthalmie braneh of the fifth nerve, and a braneh whieh aeeompanies the naso-eiliary nerve into the orbit and joins the eiliary ganglion.

NERYUS MAXILLARIS.

As the maxillary nerve passes anteriorly, from the semilunar ganglion to the face, it traverses the foramen rotundum, the upper part of the pterygo-palatine fossa, the pterygo-maxillary fissure, the inferior orbital fissure and the infra-orbital eanal. The disseetor should therefore proeeed to expose the nerve in these loealities.

Disseetion. — Remove the temporal musele and the upper head of the external pterygoid musele, and, plaeing the saw upon the eut margin of the skull at a point immediately above the external meatus, earry it obliquely downwards and anteriorly through the squamous part of the temporid bone and the great wing of the sphenoid, towards the medial end of the superior orbital fissure. This saw-eut should enter the superior orbital fissure immediately to the lateral side of the foramen rotundum. A seeond saw-eut should then be made from the eut margin of the eranial wall, immediately above the anterior margin of the great wing of the sphenoid bone, downwards into the superior orbital fissure to meet the first saw-eut. The wedge-shaped pieee of bone ineluded between these euts ean now be removed. Additional spaee may be obtained, and the pterygo- palatine fossa may be more fully opened up, by removing what remains of the great wing of the sphenoid upon the lateral side of the foramen rotundum, but the circumference of this aperture must be carefully preserved. Proeeed, in the next plaee, to open up the infra-orbital eanal. In its posterior part its upper wall is usually so thin that it ean easily be removed by a pair of disseeting forceps, but anteriorly it sinks deeply under the lower part of the rim of the orbital opening, and here the ehisel must be employed. The maxillary nerve ean now be defined and its branehes displayed. The infra - orbital artery and vein, whieh aeeompany the nerve in the infra-orbital eanal, will be exposed at the same time.

Nennis Maxillaris. — The maxillary nerve springs from the semilunar ganglion within the eranial cavity (p. 330). It is eomposed entirely of sensory fibres, and passes anteriorly, outside the dura mater and in relation to the lower part of the cavernous sinus, to the foramen rotundum through whieh it enters the pterygo-palatine fossa. It erosses the upper part of this fossa, curves laterally through the pterygo-maxillary

NERVUS MAKILLARIS

387

fissure into the infra-teinpora! fossa, and, near the middle of the inferior orbital fissure, enters the infra-orbital eanal, where it receives the name of infra-orbital. The infra- orbitat eanal traverses the floor of the orbit, whieh, it should be remembered, forms the roof of the masillary sinus also, Finally, the nerve emerges upon the face through the infra-orbital foramen, and breaks up, under cover of the quadratus labii superioris, into numerous branehes whieh form a dense plexus with twigs from the facial nerre. Its

F[G. 152. — Diagiam i>f (he Maxillary Nerve.

termina] fitamen[s are distributed to the lower eyelid, the nose, and the upper lip. The eourse of the maxillary nerve may be separated into five stages, in eaeh of whieh branehes are given ofF. These are : —

c (already deseribed). superior alTeolat. . In the inlia-OTbital TMiddle supeiioi B]veolar. eanal, . . . \ Anlerior superior alveolaj'. CPalpebraI,\ 5. In the laee, . . \ Nasal, l- alteady deseribed. |.Ubial, )

3SS HEAD AND NECK

The z\^t>'nti/:\- m^rre, whieh has already been disseeted in ihe orbii, ean now be traeed to its origin from the maxillary ner>-e in the int'ra-temporal fossa. The spheno- palatiiu hranekis are two stout twigs whieh arise from the under aspeet of the maxillary ner>-e, and proeeed vertically downwards, in the pter\-go-palatine ^ossa, to the spheno-palatine ganglion. of whieh ihey eonsiirute the s^nsery roots,

Xerri A!:eo'ans Su/rn'i^rts. — These are usually three in number, and are distinguished as posterior, m^ddle, and anterior. The middle superior alveolar ner\-e is sometimes absent as a separate trunk, in whieh ease it arises in eommon with the anterior superior alveolar braneh.

The p^sUrier su/^W a/z't\\\ir naree takes origin in the infra-temporal fossa, and almost immediately diN-ides into two branehes, whieh proeeed downwards upon the posterior aspeet of the body of the maxilla. They eontribute a few fine filaments to the mueous membrane of the eheek and to the gum, and then disapp>ear into the minute posterior dental foramina to supply the three molar teeth and the lining membrane of the maxillar\' sinus.

The middU superior aJzY.'/ar mrre supplies the two premolar teeth. It arises from the infra-orbital nerve, and ean be easily deteeted (when present) by gently raising the parent trunk from the floor of the infra-orbital eanaL It deseends in a minute eanal whieh traverses the lateral wall of the maxillan* sinus.

The anterior su/<rrior a/reo/ar «irrcv, mueh the laigest of the three alveolar branehes, springs from the infra-orbital as it approaehes the anterior j\irt of the eanal. It ean be brought into view by raising the j>arent trunk from the floor of the eanal, and it will then be seen to enter a speeial bony tunnel whieh traverses the maxilla in the anterior wall of the maxillary sinus. The disseetor should endeavour to open up this eanal with ihe ehisel. After supplying a braneh to the mueous membrane of the lowor and anterior part of the nasal cavity, the anterior superior aheolar nerve diyides into branehes for the ineisor and the eanine teeth.

WTiile traversing the ma\illa. ihe ihree superior aIveolar branehes eommunieate wiih eaeh oihor. ami form iwo nerve-loops (Fig. 152). Numerous twigs proeeed from these, and ioin in a tine plexus. It is from this plexus that the terminal tilamonts to the toeih and gum take origin.

Arteria Infi:a-orbitali3. — The infm-orbital artery is a

NASAL CAVITIES 389

braneh of the intemal maxillary. It arises in the pterygo- palatine fossa and aeeompanies the infra-orbital nerve. In the face its terminal twigs anastomose with branehes of the external maxillary, transverse facial, and bueeinator arteries ; in the infra-orbital eanal it gives some fine branehes to the eontents of the orbital cavity, and also the anterior superior alveolar artery whieh aeeompanies the nerve of that name, and supplies the ineisor and eanine teeth, and the lining membrane of the maxillary sinus.

The in/ra-orbttal vein joins the pterygoid plexus.

NASAL CAVITIES.

Disseetion, — The portion of the mandible whieh still remains, te^ether with the tongue and larynx, must now be removed from the upper part of the skuU. From the angle of the mouth on eaeh side earry the knife posteriorly, through the bueeinator and the mueous membrane of the eheek, the pterygo-mandibular raphe, and the lateral wall of the pharynx. The internal pterygoid musele has been divided already, but it will be neeessary to eut the intemal earotid artery, the smaller vessels whieh are still un- divided and the nerves whieh still eonneet the pharynx with the skull. The larynx and tongue must be laid aside for iuture disseetion.

The anterior part of the skull should next be divided into two lateral parts by sawing through it in the sagitta]* direetion elose to one side of the nasal septum. As a general rule the nasal septum is not vertical, but deviates more or less to one or other side of the median plane. This deviation is more frequently direeted to the right than to the left side. Endeavour to determine the direetion whieh it takes in the skuU under observation, by passing a probe into the nasal cavity through the ehoanae. The seetion through the skuU should be made elose to the concave side of the septum. Begin anteriorly by introdueing a knife into the nostril of that side, and earry it upwards through the eartilaginous part of the nose to the nasal bone. Then plaee the speeimen so that the face rests upon the table, and divide the sort palate in the median plane. The seetion may now be eompleted by sawing through the hard palate and bony roof of the nasal cavity to the side of the median plane. The disseetor should make every effort to preserve the septum of the nose intaet. As a general rule the upper eoneha is partially injured. This is not a very serious matter, as the lateral aspeet of the nasal cavity ean be studied upon the opposite side when the septum of the nose has been removed.

Septum Nasi. — The nasal jeptum 4^^^^^^ the cavity of the nose into two t\'^tccv» eh^mhers — ^the "gl^t ^"^ ^^^^ naeai eayities. It is not plaeed aeeurately in the median plane, but" almost invariably shows a bulging or deviation to one or other side (more frequently to the right side). Im- mediately above the orifice of the nostril or anterior aperture of the nasal cavity, the septum shows a slight depression,

39° whieh

HEAD AND NECK

eorresponds to the vestibule of the nose, and forms the raedial wall of this subdivision ot the nasal cavity. The vestibular part of the partition is elothed with skin, eontinuous with the external integument ; from this a number of sti£f hairs, termed vibriua, project. Over the rest of its extent the septum nasi is covered with mueous membrane, whieh is elosely adherent to the subjacent peri- osteum forming with it a mueo-periosteum; and it is

separable into two distriets, viz., a lower or respiraiory area, and a mueh smaller upper or olfactory area, eomprising noi more than the upper third of the septum, in whieh branehes of the olfactory nerve spread out. The respiratory mueous membrane is very ihiek and spongy. It is highly vascular and eontains numerous mueous glands. The minute oriRees of the gland duets ean be deteeted by the naked eye. Over the olfactory distriet of the septum the mueous membrane is softer and more delieate, and not so Ihiek. In the fresh state it presents a yellowtsh eolour, and the glands are smaller.

NASAL CAVITIES 391

In favourable eases a minute orifice may be deteeted in the mueous membrane, on the lower and anterior part of the nasal septum, immediately posterior to the vestibular area. It is plaeed above the anterior end of a well-marked elongated projection whieh passes obliquely posteriorly and upwards, and eorresponds to the thiekened lower margin of the septal eartilage. This aperture varies in diameter from ^ mm. to ij mm. (Sehwalbe). It leads into a narrow eanal, whieh passes posteriorly for a short distanee, and then ends blindly. It is of interest beeause it represents in the human subject the rudiment of the vomero-nasal organ (O.T. ormn of Tacohpn\. a tubular strueture whieh is highly developed in some of tne lower animals.

Constnufbion of the Nasal Septum. — Strip the mueo- periosteum from the exposed surface of the septum nasi and the parts forming the septum will be rendered visible. The bulk of the partition is eomposed of the perpendieular lamina of the ethmoid and the vomer posteriorly, and of the septal eartilage anteriorly. Small portions of other bones take a minor part in its eonstruetion. Thus, ^bo^^ apd posteriorly there are the erest and rostnim of the sphengid ; above and anteriorly is the nasal spine of the frontal bone : whilst below there is the erest of bone formed hy the apposition of tlie palatSTproeesses of the palate and maxillary bones of opposite sides.

Gartilago Septi Nasi. — The septal eartilage fills up the wide angular gap whieh intervenes between the perpendieular lamina of the ethmoid and the vomer, and it projects anteriorly towards the point of the nose. It is a broad irregularly quadrilateral plate. Its upper and posterior border is in ap- position with the anterior border of the perpendieular lamina of the ethmoid ; its lower and posterior border^ mueh thiekened, is received into the groove in the anterior border of the vomer and the nasal erest of the maxillse. The angle between these two borders is prolonged posteriorly, for a varying distanee, in the form of a tongue-shaped eartilaginous proeess, whieh oeeupies the interval between the two plates of the vomer. The upper and anterior border of the septal eartilage is in eontaet above with the suture between the two nasal bones ; below this it is related to the two lateral eartilages of the nose, whilst still lower down it is seen in the interval between the two larger alar eartilages.

Its eonneetion with the lateral eartilage on eaeh side is a very intimate one ; indeed, below the nasal bones, the three eartilages are direetly eontinuous, but lower down they are separated by a fissure whieh runs upwards for some distanee on eaeh side. The lower and anterior border is very short ; it is free, and extends posteriorly to the anterior nasal spine.

392 HEAD AND NECK

The anterior angle of the septal eartilage is blunt and rounded, and does not reaeh to the point of the nose, whieh is fonned by the alar eartilages.

The deyiation of the septum nasi from the median plane will now (in all probability) be seen to be due to a bulgiiTg to one side of the yogier and perpendieular lamina ot tiie ethmoid along their line of unionl It is not deveIoped until after the seventh year.

Disseetion. — The septal eartilage and thin bony part of the septum must now be removed pieeemeal. This must be done very carefully, as it is neeessary to preserve intaet the mueo-periosteum whieh elothes the opposite side of the septum. It is in this mueo-periosteum that the nerves and blood vessels must be examined.

Yessels and Nenres of the Septum Nasi. — The following is a list of the nerves : —

Nervesof Smell, . OIfactory.

[ I. Naso-palatine.

Nerves of Gommon

2. Medial nasal braneh of the anterior eth- moidal nerve.

sensation, . . | 3. Nasal branehes from spheno-palatine

I ganglion and from the nerve of the

l, pterygoid eanal (O.T. Vidian).

The Medial Group of Olfactory Nerues, — These nerves are distributed in the mueo-periosteum of the upper part of the nasal septum and are barely distinguishable, except in a fresh part ; further, they are so soft that it is hardly possible to isolate them. They enter the nasal cavity through the medial series of apertures in the cribriform plate of the ethmoid, and pro- eeed downwards in grooves on the surface of the perpen- dieular lamina of the same bone.

Neruus Naso-palatinus, — The naso-palatine nerve is a long slender twig whieh ean easily be deteeted upon the deep surface of the mueo-periosteum of the septum. It springs from spheno-palatine ganglion, and enters the nasal cavity through the spheno-palatine foramen. In the first part of its eourse it runs medially upon the inferior surface of the body of the sphenoid. Having gained the nasal septum, it ehanges its direetion and passes downwards and anteriorly, in a shallow groove on the surface of the vomer under cover of the mugo- periosteum. Finally it enters the foramen of Searpa, and, where the two foramina of Searpa open into the eommon incisive foramen, the neryes of opposite sides unit^ in a plexus from whieh branehes are given to the mueous membrane covering the anterior part of the \y^xc{ palatp, The naso- palatine nerve is aeeompanied bv the posterior nasal septal artery; and, as it hes on the surface of the vomer^ it supplies Rpmp sir?\)l twigg to the mueo-periosteum of the septum nasi.

NASAL CAVITIES 393

A few nasai brgnehts froin the spheno-palatine ^an^lion^ and also from the nerye of the pterygoid eanal^ reaeh the mueo- periosteum over the superior and posterior part of the septum. They are very minute, and it is questionable if the disseetor will be able to discover any traee of them in an ordinar}- part.

The medial nasal branehes of the anterior ethmoidal nerye will be found deseending over the anterior part of the nasal septum. They may be traeed as far as the vestibule.

The arteries whieh convey blood to the septum nasi are : (i) the posterior nasal septal, whieh aeeompanies the naso- palatine nerve ; (2) a braneh of the anterior ethmoidal aeeom- panying the medial branehes of the anterior ethmoidal nerve ; (3) some minute twigs to the upper part of the septum from the posterior ethmoidal artery ; (4) the septal braneh of the superior labial artery, whieh is distributed upon the eolumna nasi.

Disseetion, — The mueo-periosteum of the septum may now be divided, by the seissors, along the roof of the nasal cavity. Before doing this, disengage from its surface the naso-palatine nerve and the medial branehes of the anterior ethmoidal nerve, in order that they may be aiterwards traeed to their origins. When the layer of mueo-periosteum, thus detaehed from the roof of the nose, is thrown down the nasal cavity is expo6ed.

Cava Na.si. — The nasal cavities are two ehambers plaeed one on eaeh side of the septum nasL They are narrow, but the vertical depth and antero-posterior length of eaeh cavity is very eonsiderable. The width inereases somewhat from above downwards; thus, in the upper part, the superior eoneha is separated from the septum by an interval of only 2 mm., whilst lower down a spaee of 4 or 5 mm. intervenes between the inferior eoneha and the septum. £ach nasal cavity presents a medial wall formed by the septum, a lateral wall, a roof, a floor, and an anterior and a posterior aperture.

The anterior apertures of the nasal cavities, or nostrils, are two oval orifices whieh open upon the face and look down- wards. The posterior apertures^ or ciestf^i open into the naso- pharynx and look posteriorly and downwards.

The narrow roo/ of the nasal cavity eonsists of an inter- mediate horizontal portion formed by the cribriform plate of th£_ethmoid bone, and of an anterior and a posterior sloping part. The anterior part is formed by the narrow grooyed nasal surface of the irontal spine of the ^rontal bone^ the nasal bone, and the angle between the lateral eartilage and

394 HEAD AND NECK

the septal eartilage. The posUrior pari of the roofJs_COffi- posed (>f the aniprifir and iinder siirfaces of the bodv of the SEhenoid, and also of the ala of the yornei, tIie_S2henoidaJ proeess of the palale bone, and the. vaginal proeess of the medial pterygoid lamina, all of whieh are apphed to the under suitaee of the sphenoidal body.

The^^r of the nasal cavity is of eonsiderable width. It is formed by the palatal proeesses of the maxilla and the palate ljones, and is concave from side to side. Purther, it presents a. gentle antprn-pnstprior slnpp, being slightly higher anteriorly tlpn posteriorly. On the anterior part of the iioor, and elose n(; the septum nasi, the disseetor may see a minute funtiel- shaped depression of the tniiro-perinstpum into Ihe ineisiye tbramen. This is of interest ftom a developmental poTnt ol view ; for it is a vestige of the extensive eommunieation whieh

NASAL CAVITIES 395

existed injlie_enibryo between the ea^UkS-OLllie-^iose and the mouth.

Lateral Wall of the Nasal Gayity. — The lateral wall of the nasal cavity is rendered uneven and eomplieated by the projection of the threeeonehae (O.T. turbinal bones).

The part whieh the different bones take in the formation of ihe lateral wall of the cavity of the nose must in the first plaee be studied in a sagittal seetion through the maeerated skull, and the disseetor should eonstantly refer to sueh a preparation during the disseetion. Anteriorly, il is formed by the lateral earlilage, the alar eartilage, the nasal bone» andthe

is lormea Dy tne laterai eariiiage, tne aiareartugge, tne nasai Done» anu tne frontal^rocess of the maxijjg. MorejStl5orly the laerimal» the *;thninid- and the mfenor concha,'with a small portion of the bo^y of the msueilla,

enter into its eonstruetion ; whilst still more posteriorly are the perpen- dieular part of the palate bone and the medial pterygoid lamina 01 the sphenoid. Plaeed in relation to the lateral aspeet of this wall are the ethmoidal air-eells, whieh intervene between the upper part of the nasal cavity and the orbit, whilst, at a lower level, the great air sinus of the maxilla, the maxillary sinus, is situated immediately to the lateral side of the nasal cavity (Fig. 154).

Tuming now to the disseetion, the disseetor will see that the lateral wall is separable into three areas or' distriets. These are — (i) the vestibule; (2) the atrium meatus medii ; (3) the repion of the eonehas and theinteryening meatuses.

Yestibulum Nasi-^^he vestibular part (Fig. 155, 6, 6') of the lateral wall is a depression of a somewhat oval form plaeed immediately above the aperture of the nostril. It is partially divided into anjipper and lower portion by a short ridge, whichj)rojects anteriorly from its posterior boundarv : and it is HnthpH throughout with integument enntini^^^ns with the_skin. From this anumber of stout, stiff hairs^ termed yibrissa^ project (Fig. 155, 5). The vibrissae whieh spring from the anterior part of the region ineline posteriorly, whilst those wEiehare implapted into tbe posterior part are direeted anteriiirly ; in this manner a sieve-likearrangement is proyided at the_aiiterior aperture of the n^e. The vestibular part of the lateral wall is plaeed opposite the eorresponding area on the septum nasi, and the two together eonstitute an ampullated entranee to the nasal cavity. The eapaeity and shape of this seetion of the cavity is inAueneed to a eertain extent by the eontraetion of the nasal museles.

Atr^Tim Meatns Medii — ^This part of the lateral wall of the nasal cavity (Fig. 155, s) is plaeed above, and slightly posterior to the vestibular distriet, and it receives its name from the fact that it lies immediately anterior to the middle meatus.

39« -

HEAD AND NECK

It is slightly hoUowed out and concave, and at its upper pait, near the nasal bone, a feeble eleyation termed the agger nasi may be notieed ; this begins elose to the anterior part of the attaehed margin of the middle eoneha, and runs obliquely

FiG. 155.— Laleral Wall of ihe Left Nasal Cavity. (From Sehwalbe.)
,. PronlalairsLnus.	11. Keeessus sphcni>4Ihn]oidiilis.
0. Fr«borderorihcnssslbonc.
4. Sphenadal air >JTiiis.
S. Vibrisaa.
	16. Pliea naso-phaiyngea.
7. Elerad™ inl«v«,mg belwesn fhe	ij. Moalus naso-phaiyogms.
yeslibular disiriei aiid ihe atrium.	18. Oriiiee of auditory lube.
	19. Posteriot lip oF audilory lulie.
	ao. LaleralrteessoTpharynK.
0. eoneha suprenm. ^	a, i, c. Fr« border of ibe niiddle lonehs

down.ffiardajjii?nteriorly. It represents an additional eoneba whieh is present in some mammals. A slight depression above the agRer nasi. whieh leads posteriorly to the nlfart(irv distriet of the lateral wall of the nasal cavi ty, is the sukus olfactorius.^^ ^

Coiiclfe (O.T. turtinal bones). — Posterior to theyestibule

'*'«)U!a..

NASAL CAVITIES 397

and the atrium are the eonehae with the intervening meatuses. The superior egneha (Fig. 155, 12), whieh projects from the labyrinth of the ethmoid bone, is very short, and is plaeed on the upper and posterior part of tht^ lateral wall of the cavity. Its free border begins a short distanee below the centre^of the cribriform plate, and passes obliguely down- wards^ and posteriorly to a point immediately below the body of the sghenoid, where it ends. The middle eoneha (Fig. 155, 14) also is a part of the ethmoid. Its free border begins a short distanee below the anterior end of the eribri- forna42laJ:e, and at first takes a vertical eourse downwards ; then, bending suddenly^ it passes posteriorly. and it ends midway between the body of the sphenoid and the posterior border of the hard palate. The inferior eoneha (Fig. 155, 15) is an independent bone ; it extends posteriorly upon the lateral wall ^f the nasal cavity, midway between the middle eoneha and the tloor of the npse. Its lower free margin is some- what convex downwards.

Meatus Nasi. — The superior meatus (Fig. 155, 13) is a short narrow fissure between the superior and middle eonehae. The posterior ethmoidal eells open into its upper and anterior partbyone, or, m some eases, by several apertures.

To bring these orifices into view, the superior eoneha should be turned aside by introdueing the blade of a pair of forceps under its entire length, and forcing it upwards. Care should be taken not to injure the mueous membrane more than is neeessary.

The middle meatus is a mueh more roomy passage whieh extends posteriorly fram the atrium, between the middle and inferior eonehae.

The middle eoneha should be forcibly tilted upwards and posteriorly,

The upper and anterior part of the middle meatus leads into a funnel-shaped passage whieh runs upwards into the eorre- sponding frontal sinus. This passage, the intundibulum^ eon- stitu1;es th^rhannel of eommunieation bet^een— the-iroiltal sinus, and the nasal cavi ty .

Upon the Jateral wall of the middle meatus a deep curved groove or gutter, whieh eommenees at thp infnnHihnhim and runs frgm_ abo:ye downwards and post^norly. will be_seen. In this grooye, whieh is termed the hiSS^ semilunaris (Fig. 156), are the openings of the anterior ethmoidal eells and

39» HEAD AND NECK

the ojaxillary. sinus. The upper boundary of the hiatus semilunaris is prominent and bulging. It is termed the bulla eihnwidalis. On or above the bulla is the aperture of the niiddle "ethmoidal eells (Fig. 156). The sUt-like opening of the maxillary sinus lies in the posterior part of the hiatus semilunaris.

Tbe disseetoi should now open up the niaxillary sinus by remoTing its laleral wall. This may be done by sawing upwards Ihrough the toot of the lygoiUBlie proeess of the maxilla.

means of whieh this great air s

munieates with the middle meatus lies in the medial wall of the cavity mueh nearer the roof than the iioor — a position highly unfavourable for the eseape of Auids whieh may eolleet in it. Sometimes, however, a seeond orifice, eireular / in outline, will be found. This is situated lower down ; when it is present it opens into the middle meatus, immediately above the middle point of the attaehed margin of the inferior eoneha.

The diaseetor should note Ihat, on aeeount of the relationship of the intundibulum to Ibe hiatus seiniluna.ris and of the lallei lo the opening of the mixillaiy sinus, there is a tendeney, in some eases, for the » ' ' of the frontal sinuses lo flow into the masillary sinus.

NASAL CAVITIES 399

The inferiQr_jumius is the horizoniaL_passage whieh lies between the inferior eoneha and the floor and lateral wall of the nasal cavity. It is plaeed-pDsterior to the yestibule, and the fre£__hQrder of the iiiferior_concha turns downwards and limits it anteriorly (Fig. 156). On this aeeount, and beeause its floor slopes downwards and posteriorly, the in- ferior meatus is more aeeessible to the eurrent of expired air than to the eurrent of inspired air. In the anterior part of this meatus will be found the opening of the naso-laerimal duet whieh conveys the tears to the nasal cavity (Fig. 156).

To bring the aperture of the naso-laerimal eanal into view, remove a small portion of the anterior part of the inferior eoneha with the seissors.

The orifice of the naso-laerimal duet varies in form, aeeording to the manner in whieh the mueous membrane is arranged around it. Sometimes it is wide, patent, and eireular ; at other times the mueous membrane is prolonged over the opening, redueing its size and aeting as a flap valve to the orifice. In some eases, indeed, the orifice may be so minute that it is difficult to find. Its eontinuity with the laerimal sae should in all eases be established by passing a probe from above downwards through the naso-laerimal eanal (Fig. 64).

Kfourth meatus is generally present on the lateral wall of the nasal cavity. This is due to the partial subdivision of the superior eoneha into an upper and lower part by a short groove whieh proeeeds anteriorly from the anterior aspeet of the body of the sphenoid. This additional meatus is termed the reeessus si)heno-ethmoidalis^ and in its posterior part is the aperture ot the sphenoidal air sinus (Fig. 156). This orifice may be eireular or slit-like, aeeording to the manner in whieh the mueous membrane is disposed around it.^ The upper portion of the superior eoneha whieh is plaeed above this additional meatus is ealled the eoneha suprema (Fig. 155, 10).

To the narrow cleft-like portion of the nasal cavity whieh extends from the roof to the floor between the septum medially and the eonehae laterally the term meatus eommunis is applied; and the part of the cavity whieh lies posterior

^ When the reeessus spheno-ethmoidalis is absent, the sphenoidal air siniis opens into the intenral between the roof of the nasal cavity and the superior eoneha.

4oc HEAD AND NECK

to ihe einehal repon, i::id herween ii and the ehoans, is tbe nasc-fi*in^^^' y-^'v> *F^. 155. -.-l

11 neo-periosteum of the lAtoil Wall of tlie GaTnm NasL — Ii has been noted tha: iher^iibele :s lined with integument The remainder of the Latera] wall ^s well 35 the roof and floor of the naal tossa. is T.ned with muiyr^ Tn^mhran^* wKlrh j«^ so eloselY blended with the yiiSpripnt ppn'rwai^nnn that the two ^are inseparable and form a nmeo-periosteum. This is eonnnuous throuj:h the naso-!acr:n:al duet with the oeular

conju|xcti\-a, through the ^]}ri.-^^I^^~J!p^!I!lI!^ ^^^ ^^^ dp1itratf* lining membrane oi :he air>ctel]s whieh open into the nas^ cavity, and through^ ih^ ^hnany ir^T}^ the phar)-pgf>al rnnnnTta membrane. On the lateral wall. as on the septum, the mueo-periosteum is^ mapped out into an upp^r nlfa^t»ry aP<3l a lower resp:ratorv ponion. This subdivision eannot be appreeiated by the naked eye. for the one distriet passes into the other wi:hout any sharp line of demareatioiu The olftutory rigion eomprises merely the upper eoneha; the respiratory n^.en ineludes the middle and inferior eonehse, the middle meatus, the lower meatus. and the atrium. In the lower pait of the lateral wall the mueo-periosteum is thiek and spongy. This is partieularly notieeable over the lower borders and posterior extremities of the middle and inferior eonehae, where the membrane presents an irregular surface and forms soft bulging eushions. This eondiiion is largely due to the presenee of a rieh venous ple^us, the vessels of whieh nin for the most part in an antero-posterior direetion. In the ease of the lower eoneha, the veins are so numerous that the mueo-periosteum assumes the eharaeter of cavemous tissue, andJg^ometimes spoken of as the *'yectile body." When turgiawith blood it swells out and obliterates the inter\'al between the eoneha and the septum. The mueo- periosteum oi the floor, meatuses, and the atrium, is smoother than, and not so thiek as, that over the eonehse. Ever)'where numerous mueous glands are embedded in it, and the minute punctiform orifices of the duets are yisible to the naked eye. In the olfactor}' region the lining membrane of the nose, in the fresh state, is of a yellowish eolpur, and it is softer andmore delicatg..ihati_in_ths^resjniratory part

The great yaseularity of the mueous membrane Qf the pose is doubtless (or^the purpose of moistening and raising the temperature of the inspired^dr.

NASAL CAVmES 401

Nerve8 and Ves8el8 on tlie Lateral Wall of the Hasal

Cavity : —

Nerves of Smell, . 01factory nenres. »±jAM

fi, Lateral nasal branehes of anterior ethmoidalA / ^^^ 2. Nasal braneh oF anterior supenpr alveolar.C^' ^^** Nerves of Gommon 3. Posterior superior nasal branehes from spheno-^ Sensation, . / palatme ganglion and from the nerve ot the

pterygoia eanal. ,4. Two postenor inferior nasal branehes frqm the antenor palatine nerve.

The olfactory neroes are from twelve to twenty fine filaments whieh spring from the lower surface^n(i' llie eAtiemity Of the olfactofy„bulb, and, passing through the apertures in the eribri- form plate of the ethmoid Jnto the nasal cavity, they separate into a lateral and a medial grmip. To eaeh nerve an inyest- mentTrom the eerebral membranes is given. The niedMot sei>tal neryes were deseribed on p. ,^q 2 . The lateral nerues deseend in the mueo-periosteum on the lateral wall of the nasal cavitY. At first lodged in shallow grooves or minntp bogy eai^als, they SOOn diyide into bunehes of hranrheg^whir^isprpari out over the upper eoneha and the region immediately below. The disseetion of these neryes is exceedingly difficult, butjn a well-preserved part ^hpy r^n gpn^rally be partially displayed.

The posterior superior nasal nerves^ whieh eome from the spheno-palatine ganglion and from the nerve of the pterygoid eanal, are minute filaments, but the disseetor should nevertheless endeavour to traee them to their distribution upon the lateral- wall. Theyenter the nose through the spheno-palatine foramen, whieh is situated at ttie posterior end of the superior meatus.

The best plan to adopt for their display is to traee the largest of the group, the naso-palatine nerve, whieh has already been exposed on the nasal septum, laterally aeross the roof of the nasal cavity. This will lead the disseetor to the foramen, and by carefully disseeting the mueo-periosteum in its neighbourhood the other nenres of the group may be deteoted as they enter the nasal cavity.

They are distributed to the mueo-periosteum over the upper and middle eonehse, and the posterior part of the Aeptum.

The inferior nasal nerues are two in number; they both arise from the anterior palatine nerve.

V

Make a vertical ineision, through the mueo-periosteum over tbe posterior part of the medial pterygoid lamina, and carefully raise the membrane from the posterior part of the lateral wall of the nasal cavity.

ii

The upper of the two inferior nasal nerves will be found emerging through a small aperture in the perpendieular part YOL. II — 26

402 HEAD AND NECK

of the palate bone, at a point between the posterior extremities of the middle and inferior eonehge. It divides into an aseend- ing and deseending braneh. Both nin anterioriy ; the former on the middle eoneha, the latter on the inferior eoneha. The lawer of the two inferior nasal nerves appears through a foramen in the perpendieular part of the palate bone, immediately posterior to the inferior eoneha, upon whieh it is distributed.

The anterior ethmoidal nerue (O.T. nasat) should be ex- posed as it deseends in the groove upon the deep surface of the nasal bone (p. 393). It gives medial branehes to the septum, and lateral branehes to the mueo-periosteum over the anterior part of the lateral wall, and to the anterior parts of the middle and inferior eonehae.

The main artery of supply to the nasal mueo-periosteum is the spheno-palatine^ a braneh of the internal maxillary. It gains entranee to the nasal cavity through the spheno-palatine foramen, in eompany with the posterior superior nasal neryes. The septal braneh of this vessel aeeompanies the naso-palatine nerve, whilst others are distributed upon the lateral wall of the cavity. Several twigs are given also by the deseending palatine braneh of the internal maxillary and the two ethmoidal arteries^ but these are small and will be seen only in eases where the injection of the subject has been unusually successful.

SPHENO-PALATINE GANGLION AND INTERNAL

MAXILLARY ARTERY.

The spheno-palatine ganglion is situated in the pterygo- palatine fossa on the lateral side of the spheno-palatine fora- men ; and at this stage it ean be exposed best by disseeting from the medial or nasal side.

Disseetion. — The mueo-periosteum has already been removed irom the posterior part of the lateral wall of the nasal cavity, and the inferior nasal branehes of the anterior palatine nerve have been found piereing the perpendieular part of the palate bone. The disseetor eannot fail to notiee the eourse taken by the trunk from whieh these filaments arise. The lamina of bone whieh forms the medial wall of the pter^'go-palatine eanal is so thin that the nerve ean bc distinetly seen through it. By carefully opening up this eanal with a ehisel, and following the anterior palatine nerve upwards, the disseetor will be led to the ganglion in the pterygo-palatine fossa. The naso-palatine nerve should at the same time be traeed to its origin. The ganglion is so hemmed in by the bony walls of the fossa that it is very difficult to display it thoroughly ; but by removing the orbital proeess of the

SPHENO-PALATINE GANGLION 405

palate bone, and a portion of the body of the sphenoid, with the bone forceps, it may be more or less satisfactorily exposed. In the same restrieted spaee will be found the terminal portion of the internal maxillary artery, from whieh numerous branehes are given off.

Ganglion Spheno-palatinum. — This is a small, triangular Aattened body, whieh is lodged in the pterygo-palatine fossa. It is embedded in soft fat, and is surrounded by the ter- minal branehes of the internal maxillary artery. Two stout spheno - palatine branehes deseend from the maxillary nerve and join it from above, but only eertain of their fibres are involved in the ganglion ; the remainder are eontinued direetly into the nasal and palatine nerves whieh proeeed from the ganglion. The spheno-palatine branehes may be regarded as eonstituting the sensory roots of the ganglion.

From the splieno-palatine ganglion branehes are given oflf whieh radiate in four direetions — viz., medially to the nose ; downwards to the palate ; posteriorly to establish eonneetions with the facial nerve and earotid plexus, as well as to supply the mueous membrane of the pharynx ; and anteriorly to the orbit.

Medial branehes, . Posterior superior nasal nerves.

'Anterior palatine. Middle palatine. Posterior palatine. Nerve of pterygoid eanal. Some lateral posterior superior nasal branehes. Anterior branehes, . Orbital.

Deseending branehes, Posterior branehes, .

From the internal maxillary artery twigs are given oflf whieh aeeompany these nerves.

Posterior Superior Nasal Nerues, — There are two groups of the posterior superior nasal nerves, a medial and a lateraL The medial branehes pass through the spheno - palatine foramen and aeross the roof of the nasal cavity to the posterior part of the septum. The largest of them, the naso-palatine nerve, runs downwards and anteriorly in a groove on the surface of the vomer (p. 392). Some of the branehes of the lateral posterior group also pass through the spheno-palatine foramen and are distributed to the superior meatus, to the superior and middle eonehae, and to the posterior ethmoidal air eells. Other branehes of the lateral group pass posteriorly, some in the mueo-periosteum of the upper and posterior part of the nasal cavity, and one in the pharyngeal eanal (O.T.

II— 26«

404 HEAD AND NECK

pterygo-palatine or pharyngeal nerve). They are distributed to the mueo-periosteum of the posterior part of the roof of the nasal cavity, to the adjacent parts of the wall of the pharynx, to the sphenoidal air sinus, and to the pharyngeal part of the auditory tube.

The deseending branehes are the palatine nerves, and with them are ineorporated the posterior inferior nasal nerves. The palatine nerves are three in number, anterior (O.T. great or posterior palatine), middle, and posterior. As a rule these spring by a eommon trunk from the lower aspeet of the ganglion. The trunk deseends in the pterygo-palatine eanal, whieh has been opened up already, but to expose the nerves a dense iibrous investment must also be removed. The nerve-trunk will then be seen breaking up into its eon- stituent parts.

Disseetion, — Traee, in the first instanee, the two smaller nerves — viz., the middle and posterior palatine branehes. These leave the main eanal and enter the small palatine eanals, whieh eonduet them through the pyramidal proeess of the palate bone. Before opening these up it is well to seeure the nerves as they emerge from the lower openings of the eanals. This ean very readily be done, by disseeting posterior to the hamulus of the medial pterygoid lamina and gently separating the soft parts from the under aspeet of the pyramid of the palate bone. As the disseetion is being made from the inside, the middle palatitte nerve will be first en- eountered, and it will be seen to pass posteriorly into the soft palate, under cover of the tendinous expansion of the tensor veli palatini.^ This must be divided, in order that the nerve may be followed to its distribu- tion. The posterior palatine nerue will be found issuing from its eanal a short distanee to the lateral side of the preeeding nerve. It is distributed to the soft palate in the neighbourhood of the tonsil. It is smaller than the middle palatine nerve, and is sometimes absent. The large anterior palatine nerue should now be followed onwards to the hard palate. To do this the lower part of the palatine eanal must be opened up by removing a small portion of the posterior and lateral part of the horizontal plate of the palate bone.

The a?iterior palatine nerue is the largest braneh of the spheno-palatine ganglion. It deseends through the pterygo- palatine eanal, aeeompanied by the great palatine braneh of the internal maxillary artery ; it enters the palate through the great palatine foramen and runs anteriorly, in a groove on the lower aspeet of the hard palate, towards the incisive foramen. It supplies the gum, the mueous membrane, and the glands of the vault of the mouth ; and, in the neighbourhood of the incisive foramen, it eommunieates with the naso-palatine

^ The present is a good opportunity to observe the eomigated or wrinkled appearanee of the tendon of the tensor palati, as it passes under the hamulus.

SPHENO-PALATINE GANGLION 405

nerve. As it passes down the pterygo-palatine eanal the posterior inferior nasal branehes, whieh were enelosed in its sheath, leave it and enter the nasal cavity (p. 401).

In traeing the anterior palatine nerve in the palate, the disseetor should note the numerous glands whieh are plaeed under the mueous membrane of the vault of the mouth, and the manner in whieh these indent the bone.^

Disseetion. — Gonsiderable difficulty will be experienced in exposing the nerves in the pharyngeal and pterygoid eanals^ whieh are very inaeeessible.

To open up the pharyngeal eanal the sphenoidal proeess of the palate bone must be eautiously removed with the bone forceps, and then the disseetor should proeeed to open up the pterygoid eanal (O.T. Vidian), whieh traverses the root of the pterygoid proeess. As the bone is very hard and brittle at this point, the disseetion must be effected very carefully.

The neroe of the pharyngeal eanal belongs to the posterior superior nasal group (p. 403).

Neruus Canalis Pterygoidei (O.T. Vidian), — The nerve of the pterygoid eanal is formed by a junction between the great superficial petrosal braneh of the laeial and the great deep petrosal braneh of the earotid plexus. It traverses the pterygoid eanal, and joins the posterior aspeet of the spheno- palatine ganglion, of whieh it may be eonsidered to repre- sent both the motor and sympathetie root, In the eanal it is invested by a strong iibrous envelope, and when this is removed it may sometimes be notieed to break up into a fine plexus whieh surrounds the aeeompanying artery. It has already been seen to give some fine filaments to the mueo-periosteum of the nose.

The Rami Orbitales, — The orbital branehes of the ganglion are exceedingly minute ; they pass anteriorly through the inferior orbital fissure to supply the periosteum of the orbit.

Termination of Intemal Maxillary Artery. — The intemal maxillary artery breaks up into its terminal branehes in the- pterygo-palatine fossa. They are —

1. Posterior superior alveolar (p. 271).

2. The infra-orbital (p. 388).

3. The deseending palatine.

4. The spheno-palatine.

The Deseending Palatine Artery, — The deseending palatine

^ An equally good method of traeing the anterior palatine nerve is to remove the palatal proeesses of the palate and maxilla with the bone forceps, and then to display the nerve and artery on the upper surfaces of the mueous membrane and glands.

4o6 HEAD AND NECK

artery is a terminal braneh of the internal maxillary artery. As it deseends in the pterygo-palatine fossa it gives ofr, usually, the artery of the pterygoid eanal, and as it enters the pterygo- palatine eanal several small palatine arteries spring from it ; then it beeomes the great palatine artery, The great palatine artery deseends through the great palatine fQtamen into the hard palate; there it runs anteriorly to reaeh the incisive foramen, through whieh it passes into the nasal cavity to anastomose with the posterior artery of the septum, whieh is an offset of the spheno-palatine artery.

The stnall palatine arteries^ whieh spring from the deseend- ing palatine, immediately before it beeomes the great palatine artery, in the upper part of the pterygo-palatine eanal ; they deseend through the small palatine eanals, and are distributed to the soft palate, the palatine arehes, anti to the tonsil.

The Spheno-palatine Artery. — The spheno-palatine artery enters the nasal cavity through the spheno-palatine foramen. It gives off (i) a braneh to the sphenoidal air sinus, (2) a braneh whieh passes posteriorly to the upper part of the pharynx through the pharyngeal eanal (O.T. pterygo-palatine artery) to be distributed to the roof of the posterior part of the nasal cavity and to the roof of the pharynx ; this braneh anastomoses with the aseending pharyngeal artery. Then the spheno-palatine artery divides into lateral and septal posterior nasal branehes. The lateral branehes are distributed to the lateral wall of the nasal cavity, where they anastomose with the branehes of the posterior and anterior ethmoidal arteries, and with the lateral nasal braneh of the external maxillary. They supply not only the mueo-periosteum of the lateral wall of the nasal cavity, but also the mueo-periosteum of the air sinuses whieh open into the cavity. The posterior septal braneh of the spheno-palatine artery aeeompanies the posterior nasal septal nerve along the surface of the vomer ; it anastomoses with the great palatine artery, and with the septal braneh of the superior labial artery.

THE LARYNX.

The lateral portions of the mandible, whieh are still attaehed by mueous membrane to the sides of the tongue, should be removed, and the disseetion of the larynx eom- meneed.

THE LARYNX 407

Gtoneral Constraction and Position. — ^The larynx eon- stitutes the upper expanded portion of the air-passage whieh is speeially modiiied for the produetion of the voice. Its walls are eomposed of eartilages, museles, ligaments, and an in- ternal lining of mueous membrane. Before proeeeding with the disseetioh 'Skhe student should study the form and eon- neetions of the nine laryngeal eartilages in a permanent speei- men (v, p. 422).

The jarvnx_is plaeed -in the upper and anterior part of th^ neek, where it forms a marked projection. It lies below the hyoid bone and tongue, and is direetly eontinuous with the traehea inferiorly. Anteriorly it is covered by the integument and fasciae, and, on either side of the median plane, by two thin strata of museles — viz., the sterno-hyoid and omo-hyoid ; the sterno-thyreoid and the thyreo-hyoid. As a general rule a narrow proeess of the thyreoid gland, termed the pyramidal lobe^ is also eontinued upwards on its anterior surface. On eaeh side the lateral lobe of the thyreoid gland is prolonged upwards upon it ; and it is related to the great vessels of the neek. Posteriorly it is in relation to the pharynx, whieh separates it from the prevertebral museles. If the tip of the epiglottis is taken as its upper limit, the larynx in the adult may be regarded as being plaeed anterior to that portion of the vertebral eolumn whieh extends from the lower >rder of the second-to the lower bnr<j[pr ^r thp sixth r.pryjy^1 vejtebrg.s; but its position alters somewhat with the movements of the head and also during deglutition.

Interior of the Larsmi. — The cavity of the larynx is smaller than might be expected from an inspeetion of its exterior. On looking into its interior from above it will be seen to be subdivided into thr^^ pnrrinns by two eleyated folds of mueous membrane whieh extend antero-postenoHy^ and project inwarSs fr6m eaeh side of the cavity. ^The upper folds are termed the plie^R m^irieulares (O.T. false vocalcords) ; the lower pair receive the name of the p/iea vocales (O.T. true vocal eords), The latter are the chief agents in the produetion of the voice, and the larynx is so eonstrueted that ehanges in their relative position and in their degree of tension are brought about by the aetion of the museles and the reeoil of the elastie ligaments.

Yestibulum Laryngis. — ^The vestibule is the upper sub- division of the laryngeal cavity (Fig, 150); it extends from the

4oS

HEAD AND NECK

Thyreoid -earUlsgr

superior aperture (aditus laryngis) of the larynn down to the plic£e ventriculares. In its lower part it exhibits a marked lateral eompression. Its width, therefare, diminishes froni above downwards, whilst owing to ihe obliquity of the aditus the anterior wall is longer than the posterior. Anteriorly it is bounded by the posterior surface of the epiglottis and the thyreo-epiglottie ligament, both covered with mueous mem- brane. This wall deseends obIiquely from above down- wards and anteri- orly, and beeomes narrower as it approaehes the anteriorends of the plicEe ventriculares. Eaeh lateral wall of the vestibule is formed by the medial surface of the ary-epiglottie fold. For the most part it is smooth and slightly eon- cave, but in its posterior part the mueous membrane bulges medially in the form of two elongated vertical elevations plaeed one posterior to the other. The r elevation is formed by the cuneiform eartilage and a mass of glands assoeiated with it, enelosed within, the ary-epiglotiie fold; the posterior elevation is due to the anterior margin of the aryt.tnoid eartilage and the eor- nieulate eartilage. A shallow groove deseends between these rounded elevations and terminates beiow by running into ihe interval between the ventricular and the vocal folds. The posterior wallo{\.\^& vestibule is narrow, and eorresponds totbe interval between the upper parts of the two arytsenoid eartilages.

Fra 157.-

0 show ihe eompattii

ough ihe Larynx

THE LARYNX 409

The aditus laryngis has already been examined in the disseetion of the pharynx (p. 378). The parts whieh bound it should again be carefully studied.

The epiglottis projects upwards posterior to the root of the tongue. Its lingual or anterior surface is free in the upper part of its extent only, and is attaehed to the pharytigeal part of the tongue by a prominent median fold of mueous membrane, termed the glosso-epiglottie fold, Two lateral folds are also present; they eonneet its margins with the lateral walls of the pharynx at the side of the tongue and are ealled the pharyngo-epiglottie/olds, Between the two layers pf mueous membrane whieh eonstitute eaeh of these three folds, there is a small amount of elastie tissue. The depression on eaeh side between the tongue and the epiglottis whieh is bounded by the glosso-epiglottie and the pharyngo-epiglottie folds is termed the vallecula (Fig. 150). The posterior free surface of the epiglottis forms the greater part of the anterior boundary of the vestibule of the larynx. The upper part of this surface is convex, owing to the manner in whieh the upper margin is curved towards the tongue ; below this convexity there is a slight concavity, and still lower a marked bulging over the upper part of the thyreo-epiglottie ligament. This last projection is ealled the tuberde of the epiglottis\ it forms a eonspieuous object in laryngoseopie examinations of the larynx.

The ary-epiglottie folds of mueous membrane enelose between their two layers some connective tissue, the ary- epiglottie museles, and, posteriorly, the cuneiform and the eornieulate eartilages, whieh surmount the arytaenoid eartilages. As already mentioned, these small nodules of eartilage raise the posterior part of the ary-epiglottie fold in the form of two rounded eminenees or tubereles whieh are easily seen when the larynx is examined by the laryngoseope.

The Middle Subdivision of the Larsoigeal Cavity (Fig. 157) is the smallest of the three. Above it is bounded by the ventricular folds, below by the vocal folds ; it eommunieates with the vestibule above and the inferior eompartment of the larynx below.

Plieee Ventriculares {O.T.false vocal eords). — The ventricular folds are two prominent mueous folds whieh extend antero- posteriorly on the lateral walls of the laryngeal cavity. They are soft and somewhat flaccid, and their free borders are

410 HEAD AND NECK

slightly arehed, with the concavities looking downwards. Within eachfold are eontained — ( i ) a ligamentum ventriculare ; (2) numerous glands whieh are chiefly aggregated in its middle part ; and {3) a few musele hbres. The interval between the ventricular folds is termed the riTna vestibuU\ it is eonsider- ably wider than that between the vocal folds. It foUows, therefore, that the four folds are distinctively visible when the cavity of the laryns is examined from above, but when examined from belaw, the vocal folds alone ean be seen.

Plieee Vocahs (O.T. Thte vocal eords). — The vocal foIds are plaeed below the ventricular folds, and extend from the angte between the laminie of the thyreoid eartilage, anteriorly, to the

vocal proeesses of the arytsenoid eartilages posteriorly. E^eh Yoeal fold is sharp and prominent, and its mueous membrane is thin and is hrmly bound down to the subjacent vocal ligament. In eolour it is pale, almost pearly white, whiist posteriorly the point of the vocaI proeess of the arytsenoid eartilage, whieh stands out in relief, presents a yellowish tinge. In frontaI seetion eaeh vocal fold is somewhat prismatie in form, and the free border looks upwards and medially (Fig. 157).

The vocal foIds are the agents by nieans of whieh the voice is produeed. The ventricular foIds are of little importanee in this respeet ; indeed, they ean in great part be destroyed without any appreeiable difference in the voice resulting.

The rima glottidis is the elongated lissure by means of whieh the middle eomparlment of Ihe Iarynx eommunieates with the iower subdivision. It is plaeed somewhat below

THE LARYNX 411

the middle of the laryngeal cavity, of whieh it eonstitutes the narrowest part. Anteriorly it eorresponds to the interval between the vocal folds ; posteriorly it eorresponds lo the interval between the bases and vocal proeesses of the ary- tienoid eartilages (Fig. 160). It is eomposed, therefore, of two very distinet parts — (i) a narrow anteriior portion, be- tween the vocal folds, involving less than two-thirds of its length, and ealled

Hyo-tpteloa

the pa.

membranaeea ; (2) a

broader, shorter por-

tion, between the

arytsnoid eartilages,

termed the pars in-

tereartilaginea. The

form of the rima

glottidis undergoes

frequent aiterations

in the living person.

During ordinary

quiet respiration it is

laneeolate in outline,

and the intermem-

branous part has

the form of an elon-

gated triangle with

the base direeted

posteriorly. When

the giottis is widely

opened the broadest

part of the hssure

lies between the ex-

tremities of the vocal

proeesses of the arytsenoid eartilages, and there eaeh side

of the rima presents a marked angle. The two vocal folds,

on the other hand, may be approximated so elosely to eaeh

other, as in singing a high note, that the intermembranous

parl is redueed to a linear ehink, The length of the entire

fissure diiTers eonsiderably in the two sexes. In the male

its average length is 23 mm. ; in the female, 17 mm.

The laterai wail of the !arynx, in the interyal between the ventricular and the vocal foids, shows a poeleet-like depression

□f epiglotlit

byaryt.-PDDid enniillEe

.ttilage

412 HEAD AND NECK

or reeess, termed the ventriculus laryngis (O.T. laryngeal sinus). The disseetor shouid endeavour to gauge the extent of this, by means of a probe bent at the extremity. The reeess passes upwards, undermining the ventricular fold, and its mouth or orifice is narrower than its cavity. Under cover of the anterior part of the ventricular fold a slit-like aperture will be deteeted. This leads into the appendix ventricuK (O.T. laryngeai saeeuie), a small diverticulum, whieh aseends between the ventricular fold and the lamina of

the thyreoid eartilage. This sae is of variable extent, but as a rule it ends biindly at ihe level of the upper border of the ihyreoid eartilage.

The Lowost Sn1>divisioa of the Laryngeal Cavity (Fig. 1 57) leads direetly downwards into the traehea. Above, it is narrow and laterally eompressed, but it graduaOy widens out until in its lowest part it is eireular. It is bounded by the sloping inner surface of the eonus elastieus, and by the irmer

THE LARYNX 413

aspeet of the erieoid eartilage. It is through the anterior wall of this eompartment that the opening is made in the operation of laryngotomy.

Mueous Membrane of the Laryiue. — This is eontinuous above with that lining the pharynx, and below with the mueous lining of the traehea. Over the laryngeal or posterior surface of the epiglottis it is elosely adherent, but elsewhere, above the level of the vocal folds, it is loosely attaehed by submueous tissue. As it passes over the vocal folds it is very thin and tightly bound down, and in inAammatory eonditions of the larynx, attended by oedema, this attaehment usually prevents the iniiltration of the submueous tissue from extend- ing downwards below the rima glottidis.

The mueous membrane of the larynx has a plentiful supply of raeemose glands whieh seerete mueus. Over the surface of the vocal folds these are eompletely absent.

Disseetion. — Plaee the larynx upon a bloek so that its anterior surface looks upwards, and fix it in that position with pins. The branehes whieh the external laryngeal nerve gives to the erieo-thyreoid musele should in the first plaee be followed out ; and, carefully preserving the superior and inferior laryngeal vessels and the internal and inferior laryngeal nerves, the dis- seetor should in the next plaee proeeed to remove the thyreoid gland, and the omo-hyoid, sterno - hyoid, sterno-thyreoid, and thyreo-hyoid museles. The fibres of origin of the inferior eonstrietor musele also should be eleared away from the thyreoid and erieoid eartilages. The broad thyreo- hyoid membrane, the erieo - thyreoid ligament, and the erieo-thyreoid museles are now exposed, and their attaehments may be defined.

Membrana Hyo-thyreoidea. — This is a broad membranous sheet, whieh oeeupies the interval between the hyoid bone and the thyreoid eartilage. It is not equally strong throughout, but shows a eentral thiek portion, the median thyreo-hyoid Ugament^ largely eomposed of elastie fibres, and eord-like right and left margins, the lateral thyreo-hyoid ligaments, whilst in the intervals between the eentral part and the lateral margins it is thin and weak. The median ligament is attaehed above to the posterior aspeet of the upper margin of the body of the hyoid bone ; below, it is fixed to the sides of the deep median noteh whieh interrupts the superior border of the thyreoid eartilage. The upper part of its anterior surface is, therefore, plaeed posterior to the posterior hollowed-out surface of the body of the hyoid bone ; a mueous bursa is interposed between them, and in eertain movements of the head and larynx the upper border of the thyreoid eartilage is allowed to slip upwards posterior to the hyoid bone. On eaeh side of

414

HEAD AND NECK

the strong eentral part the thyreo-hyoid membrane is attaehed below to the upper margin of the lamina of the thyreoid eartilage, and above to the deep aspeet of the great eornu of the hyoid bone. It is piereed by the internal laryngeal nerve and superior laryngeal vessels. The lateral thyreo-hyoid ligament, whieh forms the posterior border of the membrane, on eaeh side, is rounded and eord-lilee, and is eomposed chiefly of elastie fibres. It extends from the tip of the great eornu of the hyoid bone to the extremity of superior eomu of the thyreoid eartilage. In this ligament there is usually developed a small oval eartilaginous or bony nodule, whieh is termed the eariilago tritieea. MuseuluB Grieo- tliTTeoideus. — The erieo- thyreoid musele is plaeed on the side of the erieoid eartilage, and bridges over the lateral portion of the erieo - thyreoid interval. Taking origin from the lower border and outer surface of the areh of the erieoid eartilage, its fibres spread out in an upward and posterior direetion, and are inserted into the inner aspeet of the lower margin of the thyreoid lamina, and also into the anterior border of its inferior eornu. As a general ruie, it is divided into two parts. The anterior or obUque pari is eomposed of those iibres whieh are attaehed to the lamina of the thyreoid eartilage; the posterior or straight part is formed of those fibres whieh are inserted into the inferior eornu of the thyreoid earlilage. It is elosely assoeiated with the inferiOr eonstrietor musele. The erieo-thyreoid musele is supplied by the extemal laryngeal braneh of the superior iaryngeal nerve.

eonuB Elastieus. — Extending upwards, from the upper border of the anterior and lateral parts of the erieoid eartilage to the thyreoid and arytasnoid eartilages, is a strong elastie membrane, the eonus elastieus, whieh is separable into a

— The Crico-thyr

THE LARYNX 415

median and two lateral parts. The median part is the erko- thyreoid ligament whieh extends from the upper border of the anterior part of the erieoid areh to the lower border of the thyreoid eartilage. Eaeh lateral part (O.T. lateral part of erieo-thyreoid membrane) runs upwards and medially and terminates in a free thiekened border, the ligamentum loeale^ whieh lies in the substanee of the pliea vocalis and is attaehed posteriorly to the vocal proeess of arytaenoid, and anteriorly to the angle of union of the two laminae of the thyreoid eartilage. The inner surface of the eonus elastieus is covered with the mueous membrane of the lowest seetion of the cavity of the larynx, and the outer surface is in relation with the lateral erieo-arytaenoid and the vocalis museles.

Dissedion. — The position of the laiyme mnst now be rerersed- Fix it upon the bloek in sueh a manner that its posterior aspeet is direeted upwards. The oesophagus should then be siit open bj a median iDeisioo through its posterior wall. Next remove the maeoos membraDe vliicfa covers the posterior aspeet of the erieoid and arytaeiK»d eartilages. In doing this, bear in mind that the inferior laryi^eal artery and the infenor laryngeal nerre pass upwards, between the thyreotd and erieoid eaitilages, and must be presenred.

Upon the posterior aspeet of the broad lamina of the erieoid eaitilage the disseetor will now note the two posterior erieo-arytaEnoid mtueles, aod the attaehment of the tendinous band throagh wlueh tbe longitiidinal fifarcs of the oesophagus are fixed to the erieoid eartilage. Tbe haod takes or%in from the prominent median ridge on the posterior aspeet of tbe eriooHl eartilage. On the posterior surface of the ar^rtaenoid eartilages, and bridg- ing aeross the interval between them, are the transverse and oldiqise ports of the ar^rtsenoid musele. Espeeial eare mnst be taken in deanii]^ tlns musele in order that the eonneetions of the saperficial deenssatii^ fibres may be aseertained fully.

The lateral layer of the right ary-epglottie fold of moooas membraDe should now be eautiously removed. This will ex]x>se the aiy-epigiottie musele, the cuneiform eartilage, and the eomiealate eaitilage 6f that side. This is perhaps the most difficalt part of the disseetion, beeanse the disseetor has to establish the eontinuity of the sparse fibres, wlueh oom- pose the pale ary-epiglottie musele, with the deenssaring fibres of tbe aryt^enoid musele.

Museulus erieo-Arytaenoideiis Posteiior. — The posterior erieo-arytaenoid musele is somewhat fan-shaped (Fig. 162). It springs by a broad origin from the depression whieh marks the posterior surface of the erieoid eartilage, on eaeh side of the median ridge, and its fibres conveige to be inserted into the posterior surface of the museular prouss or projecting lateral angle of the base of the arytaenoid eartilage.

In pursuing this npward and lateral eoarse, tbe fibres run with different degrees of obbqaity. The appennost fibres are short and nearly borizoDial ;

HEAD AND NECK

MuseuluB ArTttanoidens. — The aiytsenoid tnusele eonsists of two portions — a superficial part, tenned the arylxnoideus t?bliquus, and a deeper layer, ealled the aryteBnoideus transversus.

The arytanoideus obliquus is eomposed of two bundles of museular (ibres, eaeh of whieh springs from the posterior aspeet of the museular proeess of the eorresponding ar}tsenoid

Ary-tpigloHie B)ld ThyreD-hyniil Dwmbrane.

PiG. 162. — Museles of the Poslerior Aspeet of Oie Lat7nx.

eanilage (Fig. 162). From these points the two Aeshy slips proeeed upwards aiid medially, and eross eaeh other in the median plane like the limbs of the letter X. Reaehing the summit of the arytienoid eartilage of the opposite side, some of the fibres are inserted into it, but the greater proportion are prolonged, round the base of the eomieulate eartilage, into the ary-epiglottie foId. There they receive the name of the aty-epighttieus musde, and as they approaeh the epiglottis they are joined by the fibres of the thyreo- epiglottieus musele. The oblique arytsenoid museles may be eonsidered as eonstituting a ■ ' -"hineter musde

THE LARYNX 417

for the superior aperture of the larynx, £ach bundle

starting from the base of one of the aryteenoid eartilages is prolonged into the ary-epiglottie fold of the opposite side, and along this to the margin of the epiglottis.

The arytanoideus iransversus is an unpaired musele. It is eomposed of transverse tibres whieh bridge aeioss the interval between the two arytienoid earlilages, and are attaehed to the posterior aspeet of the lateral border of eaeh arytsenoid eartilage. Many of the libres tum round the arytaenoid

FlG. 163. — Laleral view of ihe Museles of ihe ILarynK. The filH™ passing poatero-Euperiorly froni the upper border of the museulus vocaIis are the Hbres of the Ihyreo-epiglollieus. Ihey blend above wilh the ary-

eartilage and beeome eontinuous, on eaeh side, with the fibres of the thyreo-arytEenoid musele.

Disseelien. — The further disseetioti of the laiyngeal museles should be eontined to the right side of the latyrui. The lelt side should be teserved for the study of the net^es and vessels. Plaee the Iarynx on its lell side, and, having fixed it in this position, Temove the right eneo-thyieoid musele. The light lateral pait of the thyreo-hyoid membrane should next be divided, and the light inlerior eotnu of the thyieoid eaitilage disartieulated from ils facet on the side of the erieoid earliUge. An indsion should now be made through the right lamina of the tbyieoid eartilage, a shoit distanee to the VOL. II — 27

41 8 HEAD AND NECK

right side of the median plane, and the detaehed pieee must be earelully removed. Three museles are now exposed, and must be eleaned. They are named from below upwards : —

1. The lateral erieo-arytoenoid.

2. The th)nreo-aryt0enoid.

3. The th)nreo-epiglotticus.

Museulus eheoarytsenoideus Lateralis. — The lateral erieo arytoenoid musele is triangular in form,-and smaller than the posterior erieo-arytaenoid (Fig. 163). It springs from the upper border of the lateral part of the erieoid eartilage, ex- tending to the facet on the lamina whieh supports the base of the arytaenoid eartilage ; a few of its fibres take origin from the eonus elastieus also. From this attaehment its fibres run posteriorly and upwards, and converge to be inserted into the anterior surface of the proeessus museularis of the arytaenoid eartilage. The superficial or lateral surface of this musele is covered by the lamina of the thyreoid eartilage and the upper part of the erieo-thyreoid musele ; its deep surface is appHed to the eonus elastieus.

Museulus Yoealis. — The museulus vocalis is a sheet of museular fibres whieh springs, anteriorly, from the angle of union of the two laminae of the thyreoid eartilage. It runs posteriorly, along the ligamentum vocale and the upper part of the eonus elastieus, and is inserted into the lateral surface of the body and the anterior surface of the museular proeess of the arytaenoid eartilage. Its lower fibres blend with the upper margin of the lateral erieo-arytaenoid musele and the medial fibres, whieh run along and to a eertain extent are attaehed to the ligamentum vocale,^ form a bundle, triangular in frontal seetion, to whieh the term internal thyro-arytaenoid musele was formerly applied. The vocalis musele protraets the arytaenoid eartilage, and adduets and relaxes the vocal ligaments.

Museulus Thyreoepiglottieus. — The thyreo - epiglottie rnusele springs from the thyreoid eartilage, immediately above the museulus vocalis, with the upper border of whieh it is more or less blended. Its fibres run posteriorly and upwards, into the ary-epiglottie fold, where they blend with the ary-epiglot- tieus, and they are inserted into the lateral border of the lower half of the epiglottis.

^ The fibres whieh are attaehed to the ligamentum vocale are ealled collectively the ary-vocalis musele.

THE LARVNX

419

Mnseiiliis ThrreoarytonoidenB (O.T. TliyTo-uTteiioideiu

EitemuB). — This musele also springs froin the angle of union of the two laminEe of the thyreoid eartilage, in elose assoeia- tion with the vocalis. Its fibres pass posteriorly, and are inserted into the lateral surface of the arytanoid eartilage. It protraets the arytainoid eartilage, and adduets and relaxes the vocal fold.

FiG. 164. — Promal seelion of Laryni showing Museles.

DineslioH. — The la.leta.1 erieo-arytsenoid mnsele should now be csiefutly reinove<l, and a.t the same time the disseetor shouid endeaYoui to disengage Ihe libTes or the thyreo-arylsnoideus fiom the deeper museulus vocaliB, in order that the relation of the Ia.ttei to the vocb1 liguaent ma; be stndied. Fina.lly remoye the museulus vocalis. This will display the outer surraee of the eonus elastieus, the vi>ch1 ligament, and the wall ol the laiyn- geal ventric1e. By careful]y disseeting between the two layers of mueous membrane whieh form the ventticular fold, the weak ventricular ligament, whieh gives it support, may be discovered, as well as a number of raeemose glands whieh Ue in telation lo it.

Lisamentum Vocale. — This ligament is the thiekened free border of the lateral part of the eonus elastieus, and it eonstitutes the support of the vocal fold. It is attaehed, anteriorly, elose to its fellow of the opposite side, to the middle of the angular depression between the two laminie of

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THE LARYNX 421

Disseetion. — Remove the remains of the ary-epiglottie fold, the ventricular and the vocal folds, and the lateral part of the eonus elastieus on the right side of the larynx, but be eareiul not to injure the arytaenoid eartilage or the eornieulate eartilage. Should the cuneiform eartilage be present in the ary-epiglottie fold it should be detaehed and preserved. By this disseetion a eloser view of the side wall of the laryngeal cavity ean be ob- tained. The undisseeted vocal fold of the left side should be examined again, the laryngeal ventricle and appendix explored, and their preeise eonneetions and extent determined. When the disseetor has satistied himself upon these points he ean proeeed to display the vessels and nerves of the larynx. The superior laryngeal artery and the internal laryngeal nerve reaeh the pharynx by piereing the lateral thin part of the thyreo-hyoid membra'ne, and they deseend along the lateral wall of the reeessus piriformis to the larynx. By applying traetion to the nerve, and at the same time dividing the mueous membrane upon the medial surface of the thyreo- hyoid membrane, they ean easily be discovered. In following the branehes into whieh they divide, the mueous membrane must be gradually removed from the wall of the larynx. The inferior laryngeal artery and nerve enter from below and proeeed upwards, under cover of the lamina of the thyreoid eartilage. They ean be satisfactorily displayed only by the removal of this pieee of eartilage, but the disseetor is not reeommended to adopt this method unless another larynx is available for the examination of the eartilages and joints. By drawing the thyreoid eartilage laterally the more important branehes ean be studied.

Bamus Intemus of the Nervus Lax3riigeus Superior. —

In the disseetion of the neek the internal laryngeal nerve was seen springing from the superior laryngeal braneh of the vagus. It is a sensory nerve, and its branehes are distributed chiefly to the mueous membrane of the larynx. After piere- ing the lateral part of the thyreo-hyoid membrane, it divides into three branehes. The uppermost of these sends Alaments to the ary-epiglottie fold, to the mueous membrane whieh covers the epiglottis, and to the three folds anterior to it. The twigs whieh go to the epiglottis ramify on its posterior surface, but many of them pieree the eartilage to reaeh the mueous membrane on its anterior surface. The intermediate braneh of the internal laryngeal nerve breaks up into iilaments, whieh are given to the mueous membrane lining the side wall of the larynx. The lowesi braneh deseends and gives filaments to the mueous membrane whieh covers the lateral and posterior aspeets of the arytaenoid and erieoid eartilages. A fairly large twig, whieh proeeeds from this braneh, runs down- wards upon the posterior aspeet of the erieoid eartilage to join the laryngeal braneh of the reeurrent nerve.

Nervus Beeurrens. — The reeurrent nerve has previously been seen arising from the vagus, and it has been traeed, in the neek, up to the point where it disappears under cover of

11—27«

42 2 HEAD AND NECK

the lower border of the inferior eonstrietor musele and beeomes the i?iferior laryngeal nerue^ whieh aseends upon the lateral aspeet of the erieoid eartilage, immediately posterior to the erieo-thyreoid joint. There it is joined by the eommunieating twig from the intemal laryngeal nerve, and almost immediately afterwards it divides into two branehes. The largeroi the two proeeeds upwards, under cover of the lamina of the thyreoid eartilage, and breaks up into filaments whieh supply the lateral erieo-arytaenoid, the thyreo-arytsenoid, the vocalis and the thyreo-epiglottie museles; the smaller ox posterior braneh inelines upwards and posteriorly, upon the posterior aspeet of the erieoid eartilage, and under cover of the posterior erieo- arytaenoid musele. It suppUes twigs to that musele, and is then eontinued onwards to end in the arytaenoid museles.

The inferior laryngeal nerve is, therefore, themotor nerve of the larynx. It supplies all the museles with the exception of the erieo-thyreoid, whieh obtains its nerve-supply from the external laryngeal. The inferior laryngeal nerve, however, eontains a few sensory fibres also. These it gives to the mueous membrane of the larynx below the rima glottidis.

Laiyngeal Arteries. — The superior laryngeal artery^ a braneh of the superior thyreoid, aeeompanies the internal laryngeal nerve ; the inferior laryngeal artery^ whieh springs from the inferior thyreoid, aeeompanies the inferior laryngeal nerve. These two vessels ramify in the laryngeal wall and supply the mueous membrane, glands, and museles.

Laryngeal Oartilages and Joints. — The eartilages whieh eonstitute the skeleton of the larynx and give support to its wall are the following : —

n--A^ I 4- Ar^'lrenoid, \

3'. Gar'tilage of the \ ^^^g^^* 5- Corniculate, paired.

^ epiglottis, J 6- Cuneiform, J

They are eonneeted by eertain ligaments.

Dissedion. — The mueous membrane and museles must be carefuily removed from the eartilages, and the ligaments must be defined. Great eaution must be exercised in eleaning the arytoenoid eartilages and the eornieulate eartilages, in order that the latter may not be injured.

Oartilago Epiglottiea. — The epiglottie eartilage is a thin, leaf-like lamina of yellowfibro-cartilage whieh is plaeed posterior to the tongue and the body of the hyoid bone, anterior to the upper aperture of the larynx. When divested of the

THE LARYNX 423

mueous membrane whieh covers it posteriorly and also, to some extent, anteriorly^ the epiglottie eartilage has the form of an obovate leaf and is indented by pits and piereed by numerous perforations. In the pits glands are lodged, and through the foramina vessels and, in some eases, nerves pass. The broad end of the eartilage is direeted upwards and is free; its margins are to a large extent enelosed within the ary-epiglottie folds. The anterior surface is free only in its upper part. This part is covered with mueous membrane and looks towards the base of the tongue. The posterior surface is covered throughout its whole extent with the mueous membrane of the larynx. The pointed lower end of the eartilage, the petiolus^ is eonneeted by a stout fibrous band, termed the thyreo-epiglottie ligament, to the angle between the laminae of the thyreoid eartilage.

Epiglottie Ligaments. — The epiglottis is bound by ligaments to the base of the tongue, to the side wall of the pharynx, to the hyoid bone, and to the thyreoid eartilage. The glosso-epiglottie fold and the two pharyngo-epiglottie folds have been studied already. In eaeh there is a small quantity of elastie tissue. The hyo-epiglottie ligament is a short, broad elastie band whieh eonneets the anterior face of the epiglottis to the upper border of the body of the hyoid bone. The thyreo-epiglottie ligament is strong, elastie, and thiek. It proeeeds downwards, from the lower pointed extremity of the epiglottis, and is attaehed to the angular depression between the two laminae of the thyreoid eartilage, below the median noteh.

The triangular interval whieh is Ieft between the lower part of the eartilage of the epiglottis and the median part of the thyreo-hyoid membrane eontains a pad of soft fat, and is imperfectly elosed above by the hyo-epiglottie ligament.

Oartilago Thyreoidea. — This is the largest of the laryngeal eartilages. It is eomposed of two broad and somewhat quadri- lateral plates, termed the laminee^ whieh meet anteriorly at an angle, and beeome fused along the median plane. Posteriorly, the laminae diverge from eaeh other and enelose a wide angular spaee. The anterior borders of the laminae are fused only in their lower parts. Above they are separated by a deep, narrow V-shaped noteh ealled the ineisura thyreoidea superior. In the adult male the angle formed by the meeting of the anterior borders of the two laminae, espeeially in the upper part, is very projecting ; and, with the margins of the

434

HEAD AND NECK

Buperior thyreoid noteh, whieh lies above, it eonstitutes a marked

subeutaneous prominenee in the neek, whidi receives the name of the laryngeal prorninenee {O.T. pomum Adamt^ The posUrior border of eaeh lamina is thiek and rounded, and is prolonged beyond the superior and inferior borders of the lamina in the form of two slender eylindrieal proeesses, termed the eomua. The superior eomu, longer than the

HyoU

Liganieiits of l.aTyiii.

infcrior eornu, givcs attaehment to the lateral thyreo-hyoid ligament. The shorter, stronger inferior eornu curves sl^htly medially. On the medial aspeet of its lip there is a facet whieh artieulates with the side of the erieoid eartilage. The, superior border of the lamina is for the most part slightly convex, and anteriorly it dips down lo beeome eontinuous with the mai^in of the superior thyreoid noteh. The in/erior border is to all intents and purposes horizontaIj but it is divided by a projection, termed the in/erior tuberde, into

THE LARVNX

425

a short posterior part and a longer anterior part. The outer sur/aee of the lantina is relatively flat. Immediately below the posterior part of the upper border, and anterior to ihe root of the superior eornu, there is a distinet prominenee ealled the superior iuberele. From this an ohlique ridge deseends towards the inferior tuberde on the lower border of the lamina. This ridge gives attaehment to the sterno-thyreoid, thyreo-hyoid and the inferior eonstrietor museles, and divides the outer surface of the

r and a pos- terior part. To the latter, whieh is mueh the smaller of the two, is attaehed the inferior eonstrietor musele of the pharyns, The inner surface of the lamina is smooth and slight- ly concave. To the angular depression hetween the two lamin^ are attaehed the thyreo-epiglottie iigament, the ven- trieular andthevocal ligaments.

erieo-thyreoid Joiiits. — The artieu- lation, on eaeh side, between the tip of the inferior eornu of the thyreoid ear- tilage and the side of the erieoid eartilage, belongs to the diarthrodial variety. The opposed surfaces are surrounded by a eapsular ligaraent whieh is lined with a synoyial stratum. The raovements whieh take plaee at these joints are of a twofoId eharaeter — viz., (i) gliding; (z) rotatory. In the first ease the erieoid facets glide upon the thyreoid surfaces in different direetions. The rotatory movement is one in whieh the erieoid eartilage rotates around a transverse aitis whieh

436 HEAD ANt) NECK

passes thtOTigh the eentre of the two joints. Eaeh eapsular ligament is strengthened by stout bands on the posterior aspeet of the j'oinL

eartUago Cricoidea. — This is shaped like a signet ring.

aspeLt of Cart liges and Ligamenls of Laryny.

The broad postenor part, iie lamtna, is somewhat quadrilateral in form. Its superior border presents a Taintly marked median noteh, and on eaeh side of this there is an oval convex facet whieh artieulates with the base of the arytEenoid eartilage. The posterior suriaee of the laniina is divided, by an eleyated median ridge, into two slightly hollowed-out areas whieh give attaehment to the posterior erieo-arytaenoid museles. The median ridge itself gives origin to a tendinous

THE LARYNX 427

band whieh proeeeds upwards from the longitudinal fibres of the oesophagus. The anterior part of the erieoid eartilage is the areh, The lower border of this is horizontal, and is eonneeted to the first traeheal ring by membrane, the erieo- traeheal ligament The areh is narrow anteriorly, and is attaehed to the lower border of the thyreoid eartilage by the erieo-thyreoid ligament. Posteriorly, the upper border rapidly aseends. Upon the posterior part of the lateral surface of the erieoid eartilage there is a eireular, slightly elevated, convex facet, whieh looks laterally and upwards,- for artieulation with the inferior eornu of the thyreoid eartilage. Internally the erieoid eartilage is lined with mueous membrane, and its lumen is eireular below, but elliptieal above.

The narrow band-like part of the anterior areh of the erieoid eartilage lies below the lower border of the thyreoid eartilage, whilst the lamina is received into the interval between the posterior portions of the laminae of the thyreoid eartilage.

Oartila^ines Comiculatse. — Before proeeeding to the study of the arytsenoid eartilages the disseetor should examine the eornieulate eartilages and the manner in whieh they are held in position. They are two minute pyramidal nodules of yellow elastie eartilage whieh are plaeed on the summits of the, arytsenoid eartilages, and are direeted posteriorly and medially. Eaeh eornieulate eartilage is enelosed within the eorresponding ary-epiglottie fold of mueous membrane, and is joined to the apex of the arytaenoid eartilage by a synehondrodial joint.

Oartilagines ArsrtaBnoideae. — In dealing with the arytaenoid eartilages it is well to remove one in order that its external form may be studied; the other should be retained in position, for the purpose of examining the erieo-ar^rtaenoid joint and the movements whieh ean be performed at that artieulation.

The aryteenoid eartilages are pyramidal in form, and sur- mount the upper border of the lamina of the erieoid- eartilage. The apex of eaeh is direeted upwards, and is curved postero-medially. It supports the eornieulate eartilage. Of the three surfaces, one looks medially, towards the eorre- sponding surface of the opposite eartilage, from whieh it is separated by a narrow interval; another looks posteriorly; whilst the third is direeted antero-laterally. The medial

428 HEAD AND NECK

surface is narrow, vertical, and even, and is elothed with mueous membrane. The posterior stirface is concave; it lodges and gives attaehment to the arytaenoideus transversus musele. The antero-lateral surface is the most extensive of the three, and is uneven for museular and ligamentous attaeh- ments. Upon this aspeet of the arytsenoid eartilage the museulus vocalis and the thyreo-arytaenoid museles are in- serted. The surfaces of the arytaenoid eartilage are separated by three borders, viz., an anterior, a posterior, and a lateral. The lateral border is the longest, and, at the base of the' eartilage, it is prolonged postero-laterally in the form of a stout prominent angle or proeess, termed the proeessus museu- laris, It gives attaehment anteriorly to the erieo-arytsenoideus lateralis musele; and posteriorly to the erieo-arytsenoideus posterior. The anterior border of the arytaenoid.eartilage is prolonged into the projecting anterior angle of the base. This is ealled the proeessus vocalis, It is sharp and pointed, and gives attaehment to the vocal ligament (O.T. true yoeal eord). The base of the arytaenoid eartilage presents an elongated concave facet, on its under aspeet, for artieulation with the upper border of the lamina of the erieoid eartilage.

Crico-arytsenoid Joiiits. — These artieulations are of the diarthrodial variety. There is a distinet joint cavity sur- rounded by a eapsular ligament, whieh is lined with a S)movial stratum. The erieoid artieular surface is convex, that of the arytaenoid concave ; both are elongated in form, but they are plaeed in relation to eaeh other so that the long axis of the one interseets or erosses that of the other, and in no position of the joint do the two surfaces aeeurately eoineide. The movements allowed at this joint, as the disseetor ean readily determine, are of a twoibld kind — (i) giiding, by whieh the arytaenoid is earried medially or laterally, or, in other words, a movement by whieh the arytaenoid advances towards or retreats from its fellow ; (2) rotatory^ by whieh the arytaenoid eartilage revolves round a vertical aMS. By this movement the vocal proeess is swung laterally or medially, so as to open or elose the rima glottidis.

The disseetor should note that the eapsule of this joint is strengthened posteriorly by a strong band whieh plays a most important part in the meehanism of the artieulation. It restriets movement of the arytaenoid eartilage.

eartilagines Cuneifonnes. — These are two little rod-shaped

THE TONGUE 429

nodules of yellow elastie eartilage, whieh are plaeed one in eaeh ary-epiglottie fold near its posterior end. They are not always present.

Aetion of the Laryngeal Museles. — The disseetor should now eonsider the manner in whieh the museles of the larynx operate upon the vocal ligaments in the produetion of the voice. Tension Qf the vocal eords is p^o- dueed by the eontraetion of the e^r.o-t^yr^gi^ ^^^.^u^ tKo oblique parts of the niuseles puU the upper border of the erieoid earlilage upwards, whilst the straight portions, through their insertions into the inferior eornua, draw the erieoid eartilage posteriorly, thereby inereasing the distanee between the angle of the thyreoid eartilage and the vocal proeesses of the arytrenoid eartilages. When the erieo-thyreoid museles eease to eontraet, the relaxation of the eords is brought about by the elastieity of the ligaments. The vocalis. and the thyreo-arytoenoideus must be regarded as antagonistie to the erieo-thyreoid museles. When they eontraet they approximate the angle of the thyreoid eartilage to the arytsenoid eartilages, and still further relax the eords, and when they eease to aet, the elastie ligaments of the larynx again bring about a state of equilibrium.

The width ofthe rit?ia glottidis is regulated by the arytoenoideus musele, whieh draws together the arytaenoid eartilages. The lateral and posterior erieo-arytaenoid museles also modify the width of the rima glottidis. When they aet together they assist the arytaenoid musele in elosing the glottis, but when they aet independently they are antagonistie museles. Thus the crico-arytcBnoidei posteriores^ by drawing the museular proeesses of the arytsenoid eartilages postero-laterally, swing the proeessus vocales and the vocal folds laterally, and thus open the rima. The erieo-arytanoidei laierales aet in exactly the opposite manner. By drawing the museular proeesses in an opposite direetion they elose the rima.

But the museles of the larynx have another function to perform besides that of vocalisation. It was formerly thought that the superior aperture of the larynx was elosed, during deglutition, by the folding baek of the epiglottis ; that in fact the epiglottis, during the passage of the bolus of food, was applied like a lid over the entranee to the vestibule of the larynx. The investigations of Prof. Anderson Stuart have slinwn ^hi^f; t)^f^ «;ypf;i;inr aperture of the larynx is elosed during swallowingLUY^the elose apposition and the for war3" pr^^ (IT^ two *afy tienoid cartjlages, wnien are

Toreeoagainst t£eXubercle"^'fflee|5iglotHs. The muscleTchiefly eoneemed in this movement are the~t"liy7eo-arytsenoid museles and the transverse aryteenoid musele. These museles form a true sphineter vestibuli. The ary-epiglottieus musele also assists in the elosure.

THE TONGUE.

The tongue is a museular organ plaeed on the floor of the mouth. It has important duties to perform in eonneetion with the functions of mastieation, deglutition, and artieulation,- Moreover, the mueous membrane whieh covers it is speeially modified, in eertain loealities, in eonneetion with the peripheral terminations of the nerves of taste. The root of the tongue is attaehed to the hyoid bone ; the pointed anterior extremity

430 HEAD AND NECK

is free ; the upper border of the base forms the lower boundary of the isthmus faucium.

Mueous Membrane. — The lingual mueous membrane is a part of the general mueous lining of the bueeal cavity. The dorsum of the tongue^ when the mouth is elosed and the organ is at rest, is strongly arehed antero-posteriorly, and, for the most part, is moulded into the vaulted roof of the mouth. The tongue eonsists of two developmentally distinet parts, termed oral and pharyngeal. These are marked off from eaeh other, even in the adult, by a V-shaped groove ealled the sukus terminalis, The apex of this suleus points posteriorly, and eoineides with a median blind pit whieh receives the name of the /oramen eeeeum, From this the two limbs of the suleus diverge antero-laterally, and they reaeh the margins of the tongue at the attaehments of the glosso-palatine arehes.

The oral part of the tongue, by its upper or dorsal surface, stands in relation to the hard palate, and to some extent to the anterior part of the soft palate also. The pharyngeal part of the tongue looks posteriorly, and forms the anterior wall of the oral portion of the pharynx. In its upper part it is related to the soft palate, whilst below it is intimately related to the epiglottis. On the lateral wall of the pharynx, immediately above this portion of the tongue, is the tonsil.

The mueous menfbrane whieh envelops the tongue presents very different appearanees in different loealities. That portion whieh is spread over the pharyngeal part of the tongue, and is prolonged upwards over the surface of the tonsil, is smooth and somewhat glossy and presents no visible papillae. It is from this distriet that the glosso- epiglottie fold takes origin, and every here and there the surface is studded with low projections, whieh are produeed by lymph follicles plaeed subjacent to the mueous membrane. Eaeh of these small elevated areas, as a rule, presents in the eentre a minute pit, visible to the naked eye.

Anterior to the foramen eaeeum and suleus terminalis the mueous membrane whieh covers the dorsum, sides, and tip of the oral part of the tongue is beset with papillae of different kinds. As these are individually visible to the naked eye the mueous membrane presents a very eharaeteristie appearanee. Purther, a median groove or suleus extends

THE TONGUE 431

posteriorly from the tip of the tongue to Ihe foramen eseeom, and divi<ies the atiterior two-thirds of the dorsum into two halves.

On the under suriaee of the tongue the mueous mem- brane is smooth and comparatively thin. In the median plane it forms Ihe/renulum lingua^ whieh has been studied at an earlier stage. On eithet side of the median line the deep lingual vein may be notieed, in the liying subject, ex- tending anteriorly towards the tip. To the lateral side of this,

Tipo^n«^.

and, therefore, somewhat nearer the border of the tongue, is a delieate and feebly marked foId of mueous membrane, from the free border of whieh a row of fringe-like proeesses or fimbrije project. It is termed xhe pliea Jimbriala ; as it extends anteriorly, towards the tip of the tongue, it inelines towards the median plane. On the side of the tongue, immediately ■ anterior to the lingual attaehment of the glosso-palatine arehes, five short vertical fissures in the mueous membrane, separated by interyening folds, may be notieed. These are ikiit papilla /oliatm. They are the representatives of Ieaf-Iike foIds of the mueous membrane, whieh are mueh more highly developed in eertain of the lower animals (hare and rabbit).

432 HEAD AND NECK

and whieh are speeially eoneemed in receiving the impressions of taste.

Papill» Linguales. — These are of four kinds, and differ in size, shape, and in the position they oeeupy on the surface of the tongue. They are termed the vallate, the fungiform, the eonieal, and the filiform.

Papillee VaUat(B, — The yallate papillae (O.T. circumvallate), seven to twelve in number, are the largest, and are plaeed immediately anterior to the suleus terminalis, in two rows whieh diverge from eaeh other in an antero-lateral direetion, like the two limbs of the letter V. The foramen eaeeum lies immediately posterior to the median vallate papilla, whieh forms the apex of the V. In form, a vallate papilla is broad and somewhat eylindrieal, slightly narrower at its attaehed than at its free extremity, arid it is sunk in a pit. It is thus surrounded by a deep treneh, the outer wall of whieh, termed the vallum, is slightly raised beyond the general surface of the mueous membrane, and forms an annular eleva- tion whieh eneireles the free extremity or summit of the papilla.

Papillee Fungiformes. — The fungiform papillae are mueh smaller, but are present in mueh greater numbers. They are found chiefly on the tip and sides of the tongue, but they are seattered at irregular intervals over the dorsum also. Eaeh papilla presents a large, full, rounded, knob-like extremity, while it is greatly eonstrieted at the point where it springs from the mueous surface. In the living tongue the fungiform papillae are distinguished by their bright red eolour.

Papillee Conicce, — The eonieal papillae are present in very large numbers. They are smaller than the fungiform variety, and although they are quite visible to the naked eye they ean be more conveniently studied by the aid of an ordinary poeket lens. They are minute eonieal projections whieh taper towards their free extremities, and they oeeupy the dorsum and sides of the tongue anterior to the suleus terminalis. They are arranged in parallel rows whieh are plaeed elose together, and in the posterior part of the dorsum these diverge from the median suleus in an antero-lateral direetion. Towards the tip of the tongue the rows of eonieal papillae beeome more or less transverse in direetion, and on the sides of the tongue they are arranged perpendieularly.

Papillee Filiformes. — The filiform papillae are similar in

THE TONGUE

433

general eharaeters to the eonieal papillte, but the epithelial eap at the apex of the eone is broken up into thread-like proeesses.

Hnselea of the Tongne. — The tongue is eomposed almost entirely of museular hbres, with some adipose tissue inter- miKed. It is divided into two lateral halves by a median septum, and the musdes in eonneetion with eaeh of these

PoMeriDr Mly

FiC 170 — Museles of

eonsist of an mtnnsie and an extnnsic group Th follows :—

GeniO'glossus.

Hyo-e[os5U5.

ehondro-glossus. l Stylo-glossus. - Palato-glossus.

Superior longitudinal,

Interior longitudinal.

Vertical.

Transverse.

Intrinsie Museles,

\i

The extrinsic musdes take origin from parts outside the tongue, and thus are eapable not only of giving rise to ehanges in the form of the organ, but also of produeing ehanges in its position. The intrinsie museles, whieh are plaeed entirely within the substanee of the tongue, are, for the most part, eapable of giving rise to alterations in its form only.

voi,. 11—28

434 HEAD AND NECK

Wilb the exception of Ihe ehondeo-glossus, the extiinsic moseles haye been studied already, hut the disseetor should take this opportuDity of examining more lulty theii insertions, and ihe manner in whieb ibeir tibres ire related to one another and lo Ihose of the intrinsie museles. For this putpose caiefu11y teileet the mueous membiane from the light half of the tongue, and follow the museles into that side of the organ. At the same time the lingual nerve and the piofunda linguse aitery should be preserved. On Ihe undet suiface of the tongue, near the tip, the removal of the mueotis membiane will expose a group of glands, ag^regated togelber so as to form a small oval mass on eaeh side of ihe median plane. This is known as the apieal^andat \iu: ^and o/ NiiAn.

The st}!oglossus will be seen running along the side of the tongue to the tip where the museles of opposite sides beeome to a eertain extent eontinuous The hyo-glossus extends upwards to the side of the tongue, and its fibres pass,

.^ i

e posteiior part

for the tnost part, under eoyer of those of the stylo-glossus to reaeh the dorsum, over the posterior part of whieh they spread out, beneath the mueous membrane. The genio-glossus sends its fibres vertically upwards into the tongue on eaeh side of the median septum, and its insertion stretehes from the tip to the base. The fibres of the palato-glossus beeome eon- tinuous with those whieh form the stratum transyersum.

The ekoiidro-glessus is not always pieaenl. Il is sepaiated fiom the deep suiface of the hyo-glossus hy the lingual vessels, and by the pbaiyn- geal slip of the genio-glossus. It is a alender museular band whieh lakes oiigin fiom the medial aspeet of the loot of Ihe smaller eornu, and the adjoining pait tiS ihe hody of ibe hyoid hone. Its tihres aseend, to entei the tongue and linally spiead oul on tbe dorsum under cover of the superior longitudinal musele.

Musailus Longituiiina/is Superior. — This is a eontinuous layer of longitudinal Abres whieh covers the entire dorsum linguK, from the root to the tip, immediately beneath the mueous membrane. Towards the base of the tongue it is

THE TONGUE 435

thinner than in front, and there it is overlapped by the trans- verse fibres of the hyo-glossus, and is intermixed with the fibres of the ehondro-glossus.

Museuli LongitudiKales In/eriores. — The inferior longi- tudinal museles are two rounded Aeshy bundles plaeed upon the inferior aspeet of the tongue, one on eaeh side. Pos- teriorly, eaeh inferior longitudinal musele lies tn the interval between the hyo-glossus and the genio -glossus, and is attaehed to the hyoid hone; anteriorly, it is prolonged to the apex of the tongue hetween the medial border of the stylo-glossus and the genio^lossus ; with the former it is more or less blended.

Museulus Transversus Lingua. — The fibres of this musele

Inrer DT odgiluduui]

lie under the superior longitudinal hbres, and eonstitute a thiek layer whieh extends laterally from the lateral face of the septum linguje, to the side of the tongue. The fibres of the genio^lossus aseend through this transverse stratum and break it up into numerous lamellse (Fig, 172). It is joined by the fibres of the palato-glossus (Henle) {Fig. 171).

Museulus Yertiealis Zingu(e.—The vertical fibres extend in a curved direetion from the dorsum to the under aspeet of the tongue, and deeussate with the fibres of the transverse musde.

Nerres and YesBelB of the Toiijn& — The nerve5 of the tongue are — (i) the glosso-pharyngeal ; (2) the lingual; (3) the hypoglossal ; and (4) a few twigs from the internal laryngeal. These should be traeed on the left side of the tongue, where the mueous membrane is still in position.

Tihe g/osso-piaryngea! nerveh&s been traeed up to the point

436 HEAD AND NECK

where it disappears under cover of the byo-glossus e There it divides into two branehes. The smaller of these extends anteriorly, upon ihe side of ihe tongue, and may be traeed as far as a point midway between ihe root and the tip. The larger braneh tums upnards, and is distributed to the mueous membrane «hieh invests the posterior third of the dorsum linguae. It gives twigs to the rallate papillse, and some line tilaments may be followed to the anterior surface of the epiglotlis. The glosso-phaiyngeal nene is a nerre of taste and of eommon sensibility.

The tingual and hypogloaal nerves are deseribed on pages 289 and 316, and their terminal branehes should aow be traeed as far as is possible.

Hyoid lone Genio'hyoid PiG. 173. — TransYerse Beeiion ihrough Ihe Tongue. (Prom Aely.)

The intemal laryngeal nerse gives a few delieate filaments to the glosso epiglotiie and pharyngo-epiglottie folds and the mueous membrane of the root of the tongue.

The arteria pro/unda lingua should be followed to the tip or the tongue, where it Ibrms a small loop of anastomosis with its feIlow of the opposite side.

Septniii Lingna.— The septum of the tongue ean be seen best by making a transverse seetion through the organ. This will display, in a measure, the transverse and vertical museular fibres also. The septum is a median tibrous partitionl It is strongest posteriorly, where it is attaehed to the hyoid bone. It does rot reaeh the dorsum of the tongue, being separated from it by the superior longitudinal musele.

GENERAL APPEARANGE 0F BRAIN 437

ENGEPHALON— THE BRAIN.

Diredions. — If the brain was divided into two parts, when it was removed, they should be fixed together with large pins passed through the eerebellum into the eerebral hemispheres ; the brain should then be plaeed on a disseeting-room platter, with its superior surface uppermost. It is neeessary to keep it moist, during the whole disseetion, by means of a eloth dipped in water. Unless this is done the membranes are apt to beeome dry, and then they are exceedingly difficult to remove.

General Appearanee of the Brain. — When viewed from above, the brain presents an ovoid Agure, with the broad end direeted posteriorly. Its greatest transverse diameter is in the neighbourhood of the part whieh lies between the two parietal tubers of the eranium. The only portions whieh are visible when the brain is in this position are the two convoluted hemispheres of the eerebrum. These are separated from eaeh other by a deep median cleft, ealled the longitudinal fissure^ whieh extends from the anterior to the posterior end of the brain.

The position of the brain should now be reversed. Turn it so that it rests on its superior surface.

The inferior aspeet of the brain is usually termed the "base." It presents an uneven and irregular surface, whieh is more or less aeeurately adapted to the inequalities on the floor of the eranium. On this surface the main subdivisions of the organ may be reeognised. Thus, posteriorly is seen the short eylindrieal portion, ealled the medulla oblongata^ through whieh, at the foramen magnum, the brain beeomes eontinuous with the spinal meduUa. The meduUa oblongata rests on the under surface of the eerebellum, being received into the vallecula or hollow whieh intervenes between the two eere- bellar hemispheres. The eerebellum is a mass of eonsiderable size whieh lies under the posterior parts of the eerebral hemispheres. It ean be easily reeognised on aeeount of the elosely set, curved and parallel fissures whieh traverse its surface. Above the medulla oblongata, and in direet eonnee- tion with it, is a prominent white elevation ealled the pons, The basilar artery extends upwards in a median groove on its surface. Immediately anterior to the pons there is a deep hollow or reeess. This is bounded posteriorly by the

II— 28«

43» THE BRAIN

pons, on either side by the proieeting temporal lobes of the eerebrum, and anieriorly by the orbital portions of the frontal lobes of the eerebrum. At the present stage of the

examination of the brain, the bottom of this hollow is hidden from view by the araehnoid, whieh stretehes over it like a veii ; but the hypophysis will be seen within its iimits if it has been removed wiih the brain. Passing laterally from either side of the anterior part of this reeess will be seen Ihe deep

MEMBRANES AND BLOOD YESSELS 439

Assura lateralis (O.T. Sylvian fissure), whieh intervenes between the pointed and projecting extreniity of the temporal lobe and the frontal lobe of the eerebrum ; whilst in the median plane, anteriorly, the longitudinal fissure will be seen between the frontal portions of the eerebral hemispheres. On either side of the longitudinal fissure, and separated from it by a narrow gyrus, the olfactory traet and bulb may be reeognised.

MEMBRANES AND BLOOD YESSELS 0F

THE BRAIN.

Araelmoidea Eneephali. — The araehnoid forms the inter- mediate covering of the brain. It is plaeed between the dura mater and the pia mater, and is direetly eontinuous with the araehnoid of the spinal medulla. It is an exceedingly thin and delieate membrane, whieh ean be seen best on the base of the brain, as in that loeality it is not so elosely applied to the pia mater as elsewhere. Unlike the pia mater it does not (except in the ease of the longitudinal and the lateral fissures) dip into the sulei or fissures on the surface of the eerebrum and eerebellum. It bridges over the inequalities on the surface of the brain and it is spread out in the form of a very distinet sheet over the medulla oblongata, the pons, and the hollow on the base of the brain whieh lies anterior to the pons. The eut ends of several of the eerebral nerves will be seen passing through this sheet ; whilst, anteriorly, immedi- ately to the lateral side of the optie nerve, the internal earotid artery will be notieed piereing it.

Gavum Subaraelmoideale. — The interval between the araeh- noid and the pia mater receives the name of the subaraehnoid spaee. It eontains the subaraehnoid Auid, and is broken up by a meshwork of fine filaments and trabeeulae, whieh eonneets the two bounding membranes (viz., the araehnoid and the pia mater) in the most intimate manner, and form a delieate sponge-like interlaeement between them. Where the araeh- noid passes over the summit of a eerebrd gyrus, and is eon- sequently elosely applied to the subjacent pia mater, the meshwork is so elose and the trabeeulae so short that the two membranes eannot be separated from eaeh other. To the disseetor they appear to form a single lamina. In the intervals between the rounded margins of adjacent gyri distinet

44°

THE BRAIN

angular spaees exist between the araehnoid and the pia mater. In these the subaraehnoid tissue ean be studied, and it will be seen that these intervals on the surface of the eerebrum serve as eommunieating ehannels for the free passage of the subaraehnoid fluid from one patt of the brain to another. The larger branehes of the arteries and veins of the brain traverse the subaraehnoid spaee ; their walls are direetly eonneeted with the subaraehnoid trabeeulse and are bathed by the subaraehnoid iluid.

eutenua Subaraehiioidaales. — In eertain situations the araehnoid is separated from the pia mater by interval5 of

eonsiderable depth and extent. These expansions of the subaraehnoid spaee are termed oisternas subaraehnoideales. In them the subaraehnoid tissue is relatively redueed. There is no longer a elose meshwork ; the trabeeulae oonneeting the two bounding membranes lake the form of long tilamentous interseeting threads whieh traverse the spaees. A beautiful demonstration of these may be obtained by dividing in the median plane, with the seissors, the sheet of araehnoid whieh is spread over the medulla oblongata and pons, and tuming the two pieees gently aside.

Gertain t>( the eistern^ [equire speeial mention. The la[^est and most eonspieuous is ealled the (isUrna (ertbetlo-mtdullai-is (O.T. magna). Il is a ilireel upwitd eontinuation of the posteriot pait of the subaraehnoid spaee

MEMBRANES AND BLOOD YESSELS

441

ofthespinal meninges into the posterior partof theeranium. It is formcd by the araehnoid membiane bridging ovei the wide interval belween the postetioi pait of Ihe undei £uiface af the eeiebellum and the medulla oblongata.

The eistema poittis is the name given to another of these leeesses. It is the eontinuation upwards, on Ihe noor of the eranium, of the snterior part of Ihe subaraehnoid spaee of Ihe spinal meninges. In ihe r^on of ihe medulls oblongata it is eontinuoiis on eithei ^de with the eeiebello-medul- hiry eistem, 50 that this subdivi^on of ihe biain is eompletely sunounded bya wide subaiaehnoid spaee. Wilhin theeisteina pontis aie the veTtebia1 and basilar aiteiies

An o o he pon he a a hno d memb ane osse be ween Ihe pro-

I dd e pordon of the ibranei of tbe brain

jecling temporai lobes, and covers in the deep hollow in this legion of tbe base of the biain. This spaee is eailed the eistema ittitrpedmuularit, and within it aie plaeed the laige arteries whieh take pait in the fonna-

thiasmatis, whieh lies ante eeiebral arteries.

AII the subaiaehnoid c one anothei, and also with the nariow intervals 01 bium. The subaiaehnoid spaee does n the subduial spaee. In eeitain toeatities, however, il the ventticiilar system of the brain. Three sueh apertures are deseribed in. eonneetion with the fourth ventiicle, whilst anothei slit, on eaeh side, is said (o lead fiDm Ihe eisleina interpeduneulaiis into the lower end of the eoiie- sponding infctior horn of the lateral ventricle,

Extending laterally from the eistema interpeduneularis, on eaeh side, is the eislerna fossie lateralis eeiebri, wbieh exlcnds along the stem of the lateial tissure into the lateial fbssa, aiound the middle eerebial aiteiy. Anterioily (be eisteina ehiasmatis is eontinuous wilh a piolongation whidi

the freeEt manner with the surface of tbe eeie- any way wlth

442 THE BRAIN

extends into the longitudinal- iissure with the anterior eerebral arteries. A dilatation of the subaraehnoid spaee over the dorsum of the mid-brain round the great eerebral vein (O.T. vena magna Galeni) is eailed the eisterna veme magme eerebri,

Granulationes Araelmoideales (O.T. Paeehionian Bodies).

— The eonneetion of the araehnoideal granulations with the araehnoid has been referred to already (p. 202).

Pia Mater Eneephali. — The pia mater forms the immediate investment of the brain. It is finer and more delieate than the eorresponding membrane of the spinal medulla, and it follows elosely all the inequalities on the surface of the brain. Thus, in the ease of the eerebrum, it lines both sides of every suleus and forms a fold within it. On the eerebellum the relation is not so intimate ; it is only the larger fissures of the eerebellum whieh eontain folds of pia mater.

It has been noted that the larger blood vessels of the brain run in the subaraehnoid spaee ; the finer twigs enter the pia mater and ramify in it before passing into the substanee of the brain. As they enter they earry with them sheaths derived from the pia mater. Consequently, if the disseetor raises a portion of this membrane from the surface of the eerebrum, a number of fine proeesses will be seen to be with- drawn from the eerebral substanee. These are the blood- vessels, and they give the deep surface of the membrane a rough and Aoeeulent appearanee.

The pia mater is not confined to the exterior of the brain. A fold is earried into its interior. This will be exposed in the disseetion of the brain, and will be deseribed under the name of the tela ehorioidea (O.T. velum interpositum) of the third ventricle.

Disseetion. — The blood vessels of the brain should now be followed out as far as it is possible to do so without laeeration of the brain substanee. Begin by stripping the araehnoid from the base of the brain. This will bring into view the main trunks. As the vessels of the brain are deseribed, many parts whieh have not yet eome under the notiee of the disseetor must be mentioned.

Arteries whieh supply Blood to the Brain. — Four main

arterial trunks earry blood into the eranium for the supply of the brain — viz., the two internal earotid arteries and the two vertebral arteries. The vertebral arteries enter through the foramen magnum, whilst the internal earotid arteries gain admittanee through the laeerate foramina after traversing the earotid eanals. These vessels have been divided in the

MEMBRANES AND BLOOD YESSELS 443

removal of the brain. The eut ends of the internal earotids will be seen, on the base of the brain, immediately to the lateral sides of the optie nerves ; the yertebral arteries lie on the sides of the meduUa oblongata. A very remarkable and eomplete anastomosis takes plaee at the base of the brain by the inoseulation of branehes whieh spring from the internal earotid and vertebral arterial systems. This is termed the dreulus arteriosus (Willis), and the branehes whieh take part in its formation lie in the eisterna inter- peduneularis and the eisterna ehiasmatis.

Two systems of branehes, both going to the eerebrum but differing greatly in their mode of distribution, proeeed from the vessels forming the arterial eirele. One system eonsists of very numerous slender twigs, whieh, as a rule, eome off in groups in eertain loealities, and at onee pieree the substanee of the eerebrum so as to gain its interior. These are the eentral or basal branehes, The other system is eomposed of branehes whieh ramify over the surface of the eerebrum, and is termed the system of eortieal branehes. The eentral parts of the brain, ineluding the basal ganglia, receive their blood- supply from the basal system, and the vessels whieh eon- stitute this group do not anastomose with eaeh other. The eortieal vessels supply the eerebral cortex and the finer branehes, whieh ramiiy in the pia mater, anastomose with one another ; therefore, the neighbouring vascular distriets of the eerebral cortex are not sharply eut oif from eaeh other.

Arteria Vertebralis. — The vertebral artery enters the sub- araehnoid spaee in the upper part of the vertebral eanal by piereing the dura mater and the araehnoid. Gaining the interior of the eranium, through the foramen magnum, it is eontinued upwards on the side of the medulla oblongata. Soon it inelines to the anterior aspeet of the medulla oblongata, and, meeting its fellow of the opposite side in the median plane, it unites with it, at the lower border of the pons, to form the basilar artery.

During this part of its eourse the vertebral artery gives off the following branehes : —

1. Posterior spinal.

2. Posterior inferior eerebellar.

3. Anterior spinal.

4. Bulbar.

Arieria Spinalis Posterior, — This is the first braneh that is given off after the vertebral artery pierees the dura mater.

444

THE BRAIN

It passes downwards on the spinal medulla along the line of the posterior nerve-roots (p. 193)-

Arteria CertbelH In/erior Posterior. — The posterior inferior eerebellar artery is the largest braneh of the vertebral artery, It takes origin immediately above the posterior spinal artery,

FlG. 177. — Floor of the eranium afler the removal of the btf Tenlorium Gerebelli. The blood vessels forming the Gireulu! have been left in plaee. \^ 'A,UC> *"

and pursues a tortuous eourse posterioriy, on the side of the upper part of the medulla oblongata, among the Ala of the hypoglossal nerye, and then among the iila of the yagus. pinally, turning round the resttform body, it gains the yalleeula of the eerebellum, where it ends by dividing into two terminal branehes. Of these, one turns j)osteriorly, in the vallecula, between the inferior vermis and the lateral hemisphere of the eerebellum, whilst the other ramifies on the posterior

MEMBRANES AND BLOOD YESSELS 445

part of the inferior surface of the eorresponding eerebellar hemisphere.

Arteria Spinalis Anterior. — The anterior spinal artery arises near the lower border of the pons, and it is rare to find the vessels of the two sides of equal size. They converge on the anterior surface of the medulla oblongata and unite, forming the eommeneement of the median vessel whieh extends downwards on the ventral face of the spinal medulla.

The bulbar arteries are minute vessels whieh enter the substanee of the medulla oblongata ; they spring both from the vertebral artery itself and also from its branehes.

Arteria Basilaxis. — The basilar artery, whieh is formed by the union of the two vertebral arteries, is a short trunk. It extends, in the median plane, from the lower to the upper border of the pons. At the latter point it ends by dividing into the two posterior eerebral arteries. The basilar artery lies in the middle part of the eisterna pontis and oeeupies the median groove on the ventral or anterior surface of the pons. Anteriorly it is supported by the basilar portion of the oeeipital bone and the dorsum sellae of the sphenoid.

The branehes whieh spring from the basilar artery proeeed laterally for the most part from either side of the vessel. They are : —

1. Pontine.

2. Internal auditory.

3. Anterior inferior eerebellar.

Rami ad Pontem. — The pontine branehes are numerous slender twigs whieh run laterally on the surface of the pons and enter its substanee.

Arteria Auditiva Intema. — The intemal auditory artery will be seen amongst the pontine branehes. It aeeompanies the aeustie nerve into the internal aeustie meatus, and is distributed to the internal ear.

Arteria Cerebeili Inferior Anterior. — This artery inelines postero-laterally to reaeh the anterior part of the inferior surface of the eerebellum.

Arteria Gerebelli Superior, — The superior eerebellar artery is a large vessel whieh springs from the basilar elose to its termination. It winds laterally and posteriorly, along the upper border of the pons, to reaeh the upper surface of the eerebellum, upon whieh it spreads out in a number of large branehes.

4. Superior eerebellar.

5. Posterior eerebral.

446 THE BRAIN

Arteria Cerebri PoBterior. — Iminediately beyond the origin

of the two superior eerebellar arteries the basilar tmnk bifurcates into the two posterior eerebral arteries. These diverge from eaeh other, and, curving laterally and posteriorly, eneirele the meseneephalon. Then ihey nin posteriorly towards the under sufface of the splenium of the eorpus eallosum. In this eourse eaeh posterior eerebral artery lies deeply in the interyal between the eorresponding peduneulus eerebri and the hippoeampal gyrus, and, tinally, passing on to the tentorial surface of the eerebral hemisphere it disappears

FlG. 178. — Medial and Tentorial Surfaces of Ihe lefi Cerebral Hemispliere. Tlie dislriel siipplieii by Ihe anterior eerebtal anery is linted psrpU ; hy the middle eerebral artery, itut ; and Uy the posterior eerebral nrtery, red. (Senii-diagraninintie.}

from yiew, by sinking into the anterior extremity of the eal- earine fissure. In this fissure the artery ends by diyiding into two terminal branehes, viz., the ealearine and the parieto- oeeipital (Figs. 178 and 180).

The oeulo-motor nerve passes anteriorly in the interval between the posterior eerebral and the superior eerebellar arteries, elose to the plaee where they arise from the basilar ; and the small troehlear nerye winds round the peduneulus eerebri below the posterior eerebral artery.

The following liranehes spring from the posterior eerebral artery ;—

{Postero-tnedian. 1 [ Tetnporal.

rostero-laleral. Corlical < CHlcatine.

Posterior ehoiioidal. ] I, l'arieto-oeeiiMtaL

MEMBRANES AND BLOOD YESSELS 447

The postero-median eentral arteries arise elose to the origin of the parent trunk. They proeeed upwards, in the interval between the peduneuli eerebri, and, piereing the substantia perforata posterior (O.T. posterior perforated spaee), they supply the thalami and the medial parts of the peduneuli eerebri.

The postero-lateral eentral arteries are a group of small slender twigs whieh arise on the lateral surface of the peduneulus eerebri, and go to the eorpora quadrigemina and the thalamus.

The posterior ehorioidal artery^ somewhat larger, goes to the tela ehorioidea of the third ventricle and the ehorioid plexus of the lateral ventricle (Figs. 178 and 179).

The temporal branehes, two or three in number, turn laterally, over the hippoeampal gyrus, and ramily on the under surface of the temporal lobe of the eerebrum (Figs. 178 and 180).

The ealearine braneh follows the ealearine fissure to the oeeipital pole of the eerebral hemisphere, round whieh it turns to reaeh the lateral surface of the oeeipital lobe. It is the chief artery of supply to the euneus and the lingual gyrus, and is therefore speeially eoneerned in the nutrition of the visual eentres of the eerebral cortex (Fig. 178).

The parieto-oeeipital artery is the smaller of the two terminal branehes of the posterior eerebral. It runs upwards in the parieto-oeeipital fissure, and reaehing the upper margin of the eerebrum it turns round it to reaeh the lateral surface of the oeeipital lobe. It supplies branehes to the euneus and prseeuneus (Figs. 178, 180).

Arteria Oarotis Intema. — The eut extremity of this great vessel lies on the lateral side of the optie ehiasma, in the angle between the optie nerve and the optie traet. At the substantia perforata anterior, elose to the eommeneement of the lateral iissure, it ends by dividing into the anterior and middle eerebral arteries (Fig. 1 79). The middle eerebral artery is the larger of the two terminal branehes, and, as it enters the lateral (O.T. Sylvian) iissure, it appears to be the eontinuation of the parent trunk. The anterior eerebral artery^ on the other hand, proeeeds medially from the internal earotid at almost a right angle. This explains how it is that emboli pass more frequently into the middle eerebral than into the anterior eerebral artery. From the internal earotid artery, after it has emerged from the cavernous sinus (p. 331), the following branehes arise : —

1. Ophthalmie (already studied,

P- 341)-

2. Posterior eommunieating.

3. ehorioidal.

4. Middle eerebral.

5. Anterior eerebral.

Arteria Communicans Posterior. — This, as a rule, is a slender braneh whieh passes posteriorly to join the posterior eerebral between its postero-median and postero-lateral groups of basal twigs (Fig. 181).

Arteria Ghorioidea, — The ehorioidal artery enters the

448

THE BRAIN

inferior eornu of the lateral yentriele, and passes into the ehorioid plexus in that cavity (Fig. 179).

Arteiia Oerebri Anterior. — The anterior eerebral runs first horizontally, above the optie ehiasma, towards the median plane (Figs. 178, 179). Then, bending sharply upon itself, it tuma upwards in the anterior part of the longiludinal (issure, anterior

FiG. 179. — Iiiferior Surface of Ihe Cerebral Hemisphere. The dislriets sup- pliod by the three eetebral arleries are linted differeQlly ; poslerior lerebt^ Mtery, reii; middle eerebial arlery, i/ue ; aoleritir eerebral artery, /iir]«Jlr.

Co the laniina terminalis, and along the rostrum to the genu of the eorpus eallosum, round whieh it bends ; then it passes posteriorly along the medial face of the hemisphere, on the upper surface of the eorpus eallosum, to the parieto-oeeipital Assure (Ftg. 1 78). As it lies anterior to the lamina terminalis it is eonneeted with the opposite anterior eerebral artery by the ankrior eonimunieating artery, and as it passes along the longitudinal fissure, between the hemispheres, it lies elose to its fellow of the opposite side.

MEMBRANES AND BLOOO YESSELS 449

Numerous branehes proeeed from the anletioT eerebial artery : — Basal or eentral { Antero-median.

l Medkl orbital. Cortical J ■^"""O' medial fronlal.

I Intermediate medial froiital.

l. Posterior medial frontaL

The anlero-mediaii arteries pieree the base of the brain anterior lo the optie ehiasma. They supply the rostrum of the eotpus eallusum, the lamina teiminalis, and the septum pellueidum.

The medial erbital branehes are two or Ihree in numlier. They turn round the matgln of the longitudinal lissure to reaeh ihe medial pait of the

=■1

i dislrielssupplied (Semi-diagram-

orbital sutfaceoflhefrontal lobe. Theysuppiylhegytustcelus,theolfacloiy traet and bulb, and the medial orbital gyrus (Figs. 17S and 179)-

The anlerisr medial /ronlal artery tamifies upon (he anterior part of the inedial surbee of Ihe fronlal lobe, and its terminal Iwigs turn lound the uppet mai^in of the eerebtal bemispbeie, aad supply the upper part or (he lateral surSee of the frontal lobe (Fig. 178)-

The intermediate inedial /rontal ariery ramifiei oa Ihe medial surfice of tbe frontal lobe postetiot to the preeeding braneh. Its (erminal pait ■ ■ ■■ - -' mof (he

passes ovet the paraeetittal lobule, and leaehes Ihe adjac

I porlKm 01

Arteria Oerebri Media. — At 6rst the middle eerebral artery passes laterally and then upwards in the lateral fissure. It

VOU II— -28

■^- ■/'- \-' ■':•'',/' ."-• /-«- •-j, j— •^■5^15. -r *--f» ■ —^^^-'rT Tt=^":rP- i^^w*

Tr>» ',rtrj--rj« »rJi'i: ^^rir^g fr:ci iie z:3i'il'; isrs-rml ir-irT 3xaj be 'r,T4rj'.r.*--..

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Fr'-t:*.5.I - Inrtri^r lii-inl ^irTrr:!' * Aseesin^ 5r::ci2l_

T*n:pcraL

'I h': ar ^rr:*--! '.,5 tr.t arUin'lTiir-il -aiil /»"-"»/ are Trar n \h*rt'^. *!:**-, v:->.*i.''.*.l.i r^rtora.*^ an*-er:or *-•£ =^??^7 ^ Iei:ii5jcm rrneleiis, •r.': iT^.^.rr^l ar.'i '.h* eiternal eap.'^^I-^. rhe ca-ii:i ^.^rl'eTii. ind a portiaD of *c.^, *hal;irr.j-..

17»*: /ronial a.'.i pKiri'tial hranehe: t^im r^en-i :he iipeer Iip of the f/'/%*.*Tior rirnit of th^ \z.\tT2X rjszzt zzA aseend oc :be Lneril sartKe of the h':rr,:*ph-rr*;. Th»: /r'yntal hrart'^'m: are : ■!■ laieril :-r^i:^ to tbe laeenl ;Ar: of •h'i ^rhi''jal 'Ts-rraee of '.r,t (Trtr.isl I:be : 2 in^irirr ljxeral fnmeal *o 'h': i.'.f':r:'^r a.'.'-i rr.M'ile it'-^r.'.^l gyri ; -3. a:cir^inz f^^7n:zl^ «-hieh nns ijp*Aar'i'- ir» T*-A'a.\v»r: to the ar.terior eer.u^ gy^^-

Tfi': a:rendini^ parieiil hrineh eitends :n an upwnrd and posterior «'Jir':/'/iori ir; rf:Iati^r* to :he p^^steer.tral g^TU.^. ar:i 13 :errnin.il twigs snpply ^h': j.^r':aV:r ;.ar: ^/the c^.r.-:x of :he 5-jper::r par:e:al iobele.

'I he pririetotemporal hraneh ii a very large anery whieh issaes fiK>iii rh': \/>\*-.x'v>x :>ar: of :he ^r^terior hraneh of :he Ia:eral nssure : it sends hrar.'-h':'-. ■.i:jW^x'1- to the infer:or parietal lobwle. an-i others vhich indme '!o'Anwari-, ov':r the :/>s:-rr:or par of the :en:poraI I?l-e. Its twigs, as ;t rjl';, '■iO not ':r.':roach u;/jn the Ia:eral 5urface 01 ihe oeeipital lobe.

Th': temporal hran^he:, two or three in riUinb"er. issue troai the posterior rrifr.j . of th'; la*':ral fis=ure, and, tuming downwaris and posteriorly, over if '. low:r lip '/.-?. the 5u;y:rior temp^oral g>TU>., they ramit}- apon the I;i*':ral '-.:irf;i''y; of the terri[Xjral lo:^.

eireulus Arteriostis CO.T. Girele of Willis). — This re-

rnarkable anastomosis is plaeed beneath the base of the brain in th^; deep hollow anterior to the pons. It takes the fonn of a heptagonal or hexagonal figure, and the vessels whieh eorripos/; it lie in the eisterna interpeduneularis and the eistema ^:hiasrriatis. .\nteriorlv it is elosed bv the anterior eommuni- (:nut\pr artery whieh links together the two anterior eerebral artf ries. ()n either side is the posterior eommunieating ;jrtery eonneeting the internal earotid (from whieh the anterior

MEMBRANES AND BLOOD YESSELS 451

eerebral springs) with the posterior eerebraL The arterial ring is eompleted posteriorly by the bifurcatibn of the basilar artery into the two posterior eerebral vessels (Fig. 181). As a rule the eireulus arteriosus is not symmetrieal. One posterior eommunieating artery is almost invariably larger than its fellow of the opposite side. .

Dissedion. — The brain being plaeed with its base uppermost, the disseetor should proeeed to remove the blood vessels and membranes from

nterior eerebral artery

Anterior eommunieating earotid Middle eerebral

Antero-lateral basal arteries Posterior eommunieating

Postero-median basal arteries Posterior eerebral artery

Superior eerebellar artery

FiG. 181. — Diagram of the Gireulus Arteriosus.

its surface. This must be done with the forceps and a pair of seissors. It is a disseetion whieh requires very delieate manipulation, beoause the eerebral nerves, at their points of attaehment to the brain, are so intimately eonneeted with the pia mater that any undue traetion applied to the membranes will tear the nerves away. Indeed, in the ease of the medulla oblongata, the disseetor is advised to. leave the pia mater in position until the nerve roots have been studied. The relation of the pia mater to the fourth ventricle also renders this desirable.

In removing the araehnoid and pia mater from the lateral surface of the eerebrum, it is well to raise it first from the margins of the hemisphere, and then to work towards the lateral fissure (Sylvian). By this method, the membranes and vessels within this great fissure and in relation to the insula ean be withdrawn without damage to the brain substanceC Of eourse, at the present stage, the membranes eannot be removed from every part of the brain ; but as the disseetion proeeeds, opportunities for eompleting the proeess will arise.

11—29 a

452 THE BRAIN

BASE 0F BRAIN.

Fossa Interpeduneularis. — ^When the membranes are re- moved from the base of the brain, the peduneuli eerebri (O.T. crura\ two large rope-like strands, will be seen issuing from the upper aspeet of the pons. Plaeed elose together as they emerge from the pons, they diverge as they proeeed upwards and anteriorly, and, fmally, eaeh pedunele disappears into the eorresponding half of the eerebrum. Turning round the lateral aspeet of eaeh pedunele, where it passes into the eerebrum, will be seen a Aattened band, ealled the optte traet. These bands converge as they pass anteriorly, and are Anally joined together by a short transverse eommissural portion, termed the optie ehiasma. This ehiasma is plaeed below the posterior end of that portion of the longitudinal fissure whieh intervenes between the inferior surfaces of the frontal lobes of the eerebrum. The optie nerues run antero-laterally from the ehiasma.

The eerebral peduneles, the optie traets, and the optie ehiasma enelose a deep rhomboidal or lozenge-shaped interyal on the base of the brain, whieh is termed the interpeduneular /ossa. Within the limits of this area the following parts may be seen. The substantia perforata posterior bounded an- teriorly by the eorpora mamillaria] anterior to the eorpora mamillaria is the tuber einereum, and attaehed to it is the infundibulum of the hypophysis. These struetures take part in the formation of the floor of the third ventricle of the brain.

The oculo-7?iotor nerues issue from the brain within the interpeduneular fossa. Eaeh nerve emerges from the medial side of the eorresponding peduneulus eerebri.

Substantia Perforata Posterior (O.T. Posterior perforated spaee). — At its posterior angle, immediately anterior to the pons, the interpeduneular fossa is very deep, and is roofed by a layer of grey matter in whieh are numerous small apertures. This is the substantia perforata posterior. From the apertures whieh are dotted over its surface the postero- median basal branehes of the posterior eerebral artery have been withdrawn.

Oorpora Mamillaria. — These are two small, white, pea- shaped eminenees plaeed, side by side, anterior to the sub- stantia perforata posterior. At a later stage of the disseetion

BASE 0F BRAIN

453

their eonneetions with the eolumns of the fornix will be displayed.

Tnber emereiun. — This is a slightly raised field of grey matter whieh oeeupies the interval between the eorpora

mamillaria posteriorly, the optie ehiasma anteriorly, and the optie traets laterally. Springing froiii the anterior part of the tuber einereum, immediately posterior to the optie ehiasma, is the inrundibulum or stalk of the hypophysis. In the

RASE 0F BRAIN

ral prominenee ealled the olive. A distinet suleus or grooye, ^ieh passes downwards anterior to this body, separates it elongated strand, termed ihe pyraniid of the medulla fc]ongata. From the bottom of this suleus and its prolonga- n downwards issue a series of nerve fila whieh belong to two t nerves. Those whieh issue from the lower part of 3ve, below the level of the olive, belotig to the anlerior vot of the firit eemkal nerve ; those whieh emerge from the

Optic.hL-iir,,n_ _

^^br^

Mesi-'iieeplialo» of a full-l!

e Fo:lus.

upper part of the groove, in the interval between the olive and the pyramid, form the hypoglossal ntrve.

OIoaso-phaiynKeal,'Va^,aiidAcceasoiyNeiveB. — Posterior to the olive, in the postero-laleral suleus of the meduUa oblongata, is atiolher eontinuous Tow of nerve fila. These fxtend downwards, beyond the level of the olive, and are :ittached to ihe whole lenglh of the medulla oblongata in linear ordor. They lielong lo three nerves, but it is im- •ipossible at present (seeing that the nerve-trunks whieh

454 THE BRAIN

removal of the brain its eonneetion with that body was severcd.

Snbstantiae Perforat» Anteriores. — These are small iriangular distriets of grey matter, one on eaeh side. Eaeh is bounded posteriorly by the uneinate extremity of the hippo- eampal gyrus; anteriorly by the diverging striae of the olfactor)- traet : and medially by the optie traet. I^terally it passes into the roof of the lateral iissure, and is perforated by the antero-lateral basal arteries. The grey matter in this area is eontinuous above with the grey matter of the lentiform nueleus (O.T. lentieular).

TiamiTia Terminalis. — If the anterior border of the optie ehiasma is displaeed posteriorly a thin lamina will be notieed. It passes upwards from the ehiasma into the longitudinal fissure, to beeome eonneeted with the rostrum of the eorpus eallosum. This is the latnina terminalis, It eloses the third ventricle anteriorly, and is eontinuous on either side with the grey matter of the substantia perforata anterior.

Superficial Origins of the Oerebral Nerves. — Twelve eerebral nenes are enumerated arising from the brain on either side of the median plane. They are the olfactory or first ; the optie or seeond ; the oeulo-motor or third ; the troeh- lear or fourth ; the trigeminal or fifth ; the— abdueent or sixth ; the facial or seventh ; the aeustie or eighmT^e glosso-pharyngeal or ninth; the vagus or tenth ; the aeeessory or eloventh ; and the hypoglossal or twelfth.

Eaeh of these nerves is said to have a " superficial " and a " deep " origin. By the term " superficial origin " is meant the region where its fibres enter or leave the brain surface ; the term ** deep origin " indieates the eonneetions whieh are established by the fibres of the different nerves with nuelei or elusters of nerve-cells within the substanee of the brain. These nuelei are of two kinds : ( i ) those in eonneetion with whieh the afiferent or entering nerve fibres end ; and (2) those from whieh the efierent or emerging ner\'e fibres arise. It is the superficial attaehments only whieh eome under notiee of the disseetor at the present time.

No fewer than eight of the eerebral ncr\*es have a superficial attaehment to the ventral part of the hind brain whieh is formed by the meduUa oblongata and the pons.

Hypoglossal Nerve. — Upon the lateral aspeet of the medulla oblongata, in its upper half, is a very eonspieuous

BASE 0F BRAIN

455

oval prominenee ealled the olive. A distinet suleus or groove, whieh passes downwards anterior to this body, separates it from an elongated strand, termed ihe pyramid of the medulla oblongata. From the bottom of this suleus and its prolonga- tion downwards issne a series of nerve fi]a whieh belong to two different nerves. Those whieh issue from the lower part of the groove, below the level of Ihe olive, belong to the anlerior root of the first cervical nerve ; those whieh emerge from the

upper part of the groove, in the interval between the olive and the pyramid, form the hypoglossal nerse.

GlosBO-phairngeal, YaguB, and AeeessoryHorres.— Posterior

to the olive, in the postero-lateral suleus of the medulla oblongata, is another eontinuous row of nerve Pila. These estend downwards, beyond the Ievel of the olive, and are attaehed to the whole length of the medulla oblongata in linear order. They belong lo three nerves, but it is im- possible at present (seeing ihat the nerve-trunks whieh they

45^

THE BRAIN

build up are divided) to determine preeisely the number of fila whieh belong to eaeh. From below upwards the nerves whieh they (orra are the aeeessory, the vagus, and the glosso- pharyngeal. The fila of the vagus and the glosso-pharyngeal are mueh more elosely erowded together than those of the aeeessory,

The roots of the aeeessory, whieh spring from the medulla oblongata, eonstitute only one part of the nerve. The spinal

part springs from the spinal medulla, as low down as the sixth cervical nerve, by a series of roots whieh issue from the lateral funiculus, posterior to the attaehment of the ligamentum dentieulatum.

Aenatie and Fiu:ial Nerres. — These issue elose together at the lower border of the pons, and imraediately above the restiform body. The aatsHe nerve is the larger of the two, and it lies on the lateral side of the facial. Its two roots, termed the eoehlear and the vestibular, embraee the restiform body.

BASE 0F BRAIN

457

The facial neme issues from the poiis elose to its lower border, and just to the medial side of the aeustie nerve, by two roots, a large motor root, and a small sensory root (O.T. pars intermedia), The two roots unite in the internal

Abdueant Nerve. — This is a small nerve whieh emei^e's from the groove between the iower border of the pons and the lateral part of the pyramid.

Trigemuial Nerve, — This is the largest of all ihe eere^ nerves. It appears at the side of the pons, nearei^ts'^per

c.	eerebelluni. MKemephale	i.phen^
;	Itraehium poniis. . RBlirLirn, liody.
"'	in whieh thi (From Sehi	«albe.)	part5of

than its lower border and in a line with the facial and aeustie neryes. It eonsists of two roots — a large sensory root, portio major, eomposed of a great number of lila loosely held together, and a smali, more eompaet motor root, portio minor, whieb emerges antero-medial to the point at whieh the sensory root enters the pons.

Troehlear Nerve. — The superficial origin of the troehlear or fourth nerve eannot be seen at presenL It emerges from the anterior medullary velum, on the dorsal aspeet of the brain-stem. It is a delieate little nerve whieh has a long intraeranial eourse. It winds round the lateral side of the peduneulus eerebri, between the eerebrum and eerebellum.

458 THE BRAIN

Oeulo - motor Nerve. — This may be seen within the interpeduneular fossa. It issues by several fila from the suleus oeulomotorius on the medial face of the eerebral pedunele.

Optie Nerve. — This is a large round nerve whieh passes antero-laterally from the optie ehiasma.

01factory Nerves. — These arise from the olfactory bulb and enter the nasal cavity through the foramina in the cribriform plate of the ethmoid bone,

Gteneral Oonneetions of the Several Parts of the Brain. — Before proeeeding to the more partieular study of the different parts of the brain the student should acquire a general eoneeption of the manner in whieh these are eonneeted with eaeh other. In the posterior eranial fossa, below the ten- torium, are plaeed the medulla oblongata, the pons, and the eerebellum, whieh eonstitute collectively the Rhomben- eephalon or hind-brain. They surround a cavity whieh is ealled the fourth ventricle of the brain, and all stand in intimate eonneetion with one another. The upper end of the medulla oblongata terminates chiefly in the pons, but two large strands on its posterior or dorsal aspeet, termed the restiform bodies, pass posteriorly into the eerebellum (Fig. 185, d). The transverse fibres of the pons are gathered together on either side in the form of a large rope-like strand, the braehium pontis. This disappears into the eorresponding hemisphere of the eerebellum (Fig. 185, c\

The great mass of the brain is termed the eerebrum. This oeeupies the anterior and middle eranial fossse, and extends posteriorly into the oeeipital region above the tentorium eerebelli. The greater part of the eerebrum is formed by the eerebral hemispheres, whieh are separated from eaeh other, in the median plane, by the longitudinal fissure. At the bottom of this fissure may be seen the corfus eallosuin^ a broad eommissural band whieh eonneets the two eerebral hemispheres with eaeh other. Eaeh hemisphere is hollow — the cavity in its interior being termed the lateral ventricle of the brain. Between and below the eerebral hemispheres, and almost eompletely eoneealed by them, is the thalameneephalon, The prineipal parts forming this portion of the brain are the two thalami, between whieh is the third ve?itricle of the brain — a deep, narrow cavity oeeupying the median plane. The third ventricle eommunieates with the

THE GEREBRUM 459

lateral ventricles through the foramen interuentrieulare (O.T. /oramen qf Monro),

The eerebrum is eonneeted with the parts in the posterior eranial cavity (pons, eerebellum, and medulla oblongata) by a narrow stalk ealled the mid-brain^ or meseneephalon. The mid-brain is built up of a ventral portion, the peduneuli eerebri, passing between the pons and the eerebrum (Fig. 185, a\ and a dorsal portion, the lamina quadrigemina. It is tunnelled by a narrow passage — the aquceductus eerebri (O.T. agueduet of Sylvius) — ^whieh eonneets the fourth and the third ventricles.

THE GEREBRUM.

Gerebral Hemispheres. — Eaeh eerebral hemisphere presents a lateral, a medial, and an inferior surface, whieh are separated from one another by more or less distinetly marked borders. The lateral surfa£e is convex, and is adapted to the concavity of the eranial vault. The medial surface is flat and perpen- dieular, and is more or less eompletely separated from the eorresponding surface of the opposite hemisphere by the falx eerebri, whieh oeeupies the longitudinal fissure. The inferior surface is irregular, and is adapted to the anterior and middle eranial foss3e, and also to the upper surface of the tentorium eerebelli. Traversing this surface, in a transverse direetion, nearer the anterior than the posterior end of the hemisphere, is the stem of the lateral fissure (O.T. Sylvian) (Fig. 182). This deep cleft divides the inferior surface into an anterior or orbital area^ whieh rests upon the orbital plate of the frontal bone and is, consequently, concave from side to side, and a more extensive posterior or tentorial area^ whieh lies on the floor of the lateral part of the middle eranial fossa and the upper surface of the tentorium eerebelli. The tentorial portion of the inferior surface is arehed antero-posteriorly, and looks medially as well as downwards.

The borders whieh separate the surfaces from eaeh other are the supero-medial, the supereiliary, the infero- lateral, the medial oeeipital, and the medial orbital. The supero-77iedial border, convex antero-posteriorly, intervenes between the medial and lateral surfaces. The superdliary border is highly arehed, it separates the orbital surface

46o THE BRAIN

from the lateral surface. The infero-lateral'harder marks off the tentorial part of the inferior surface from the lateral surface. The medial oeeipital border is not very distinet, except in eases where the brain has been hardened in situ, It extends from the posterior extremity of the hemisphere to the posterior end of the eorpus eallosum, and intervenes between the medial surface and the tentorial part of the inferior surface. The medial orbital margin extends from the frontal pole to the lamina terminalis and separates the orbital from the medial surface.

The most projecting part of the anterior end of the eerebral hemisphere is ealled the frontal pole^ whilst the most projecting part of the posterior end is termed the oeeipital pole, On the under surface of the hemisphere, the prominent rounded portion of eerebral substanee whieh ex- tends anteriorly below the lateral iissure receives the name of the temporal pole. In a well-hardened brain a broad groove is usually present on the medial aspeet of the oeeipital pole of the right hemisphere. This eorresponds to the termination superior sagittal venous sinus.

Longitudinal Fissure. — This great median cleft is oeeupied by the fold of dura mater termed the falx eerebri. Anteriorly and posteriorly, it eompletely separates the eerebral hemi- spheres from eaeh other, but the intermediate part is Aoored by the eorpus eallosum — the eommissural band whieh passes between the hemispheres and eonneets them together. The upper surface of the eorpus eallosum ean be displayed by gently drawing asunder the two sides of the longitudinal fissure.

Dissedion. — If two brains are available, the disseetor is adyised, at this stage, to separate the eerebrum from the eerebellum, pons and medulla oblongata in one of them, by eutting transversely through the mid brain if this has not been done already. The eerebrum may then be split in the median plane by plaeing a long knife in the longitudinal iissure and divid- ing, with one sweep, the various parts whieh eonneet the two sides to eaeh other. By this proeeeding, the three surfaces of eaeh eerebral hemisphere are exposed, and the gyri and sulei ean be studied fully and satis£Eu:torily. If only one brain is at the disposal of the student, he should not, at this stage, . separate the eerebral hemispheres from eaeh other, but should endeavour to follow out the gyri and sulei with the various parts of the brain in position. No doubt he studies the hemisphere in this way at a dis- advantage, but as the disseetion proeeeds, opportunities will oeeur whieh will enable him to examine those distriets of the surface whieh he ean see only imperfectly at present.

Gerebral Gyri and Sulei. — The surfaces of the eerebral

THE GEREBRUM 461

hemispheres are rendered highly irregular by the presenee of gyri, separated from one another by intervening furrows, termed sulei and fissures. The surface pattern whieh is pre- sented by these gyri and sulei is, in its general features, the same in all human brains; but when the eomparison is pushed into more detail many di^Terenees beeome manifest, not only in the brains of different individuals but also in the two eerebral hemispheres of one individuaL

Of the furrows two yarieties must be reeognised, viz., eomplete and ineomplete. The eomplete fissures are few in number and they eonsist of inwardly direeted folds whieh involve the whole thiekness of the eerebral wall. They eon- sequently show in the interior of the eerebral cavity or lateral ventricle in the form of elevations on its walls. In this eategory are ineluded (i) the hippoeampal fissure ; (2) the anterior portion of the ealearine fissure ; and (3) a portion of the eollateral fissure. The ineomplete fissures and the suki are merely furrows of varying depth whieh do not produee any effect on the surface of the ventricular walls.

O-eneral Strueture of the Gerebral Hemispheres. — Eaeh eerebral hemisphere is eomposed of an outside eoating of grey matter, spread in a eontinuous and uninterrupted layer over its surface, and an internal eore of white matter. The grey eoating is termed the eerebral cortex^ whilst the white internal part is ealled the medullary eentre, Eaeh gyrus shows a eorresponding strueture. It has an extemal covering of grey matter supported upon a eore of white medullary matter. But, in addition to the grey matter on the outside, there are eertain large deposits of grey matter em- bedded in the substanee of eaeh hemisphere in its basal part, These eonstitute the basal nuelei, and although to a eertain extent they are isolated from the grey matter on the surface, nevertheless, at eertain points, they are direetly eontinuous

with it.

By means of the gyri and sulei the grey matter on the surface of the hemisphere is inereased, and its elose assoeiation with the vascular pia-mater is maintained without any unneeessary inerease of the bulk of the organ. The vascular pia-mater dips into every fissure and suleus, and opportunity is therefore afforded for the eortieal vessels to break up into twigs of exceeding fineness before they enter the substanee of the hemisphere. The distribution

46j

THE BRAIN

of the blood to the grey cortex is in this way rendered uniform.

Oerebral Lobes and Inteiloliar FiBBtireB. — Cenain of the fissures whieh traverse tbe surface of the eerebnini are arbitrarily ehosen for the purpose of subdividing the surface into distriets, termed lobes. These fissures, whieh receive the name of interhhar, are the following — (i) the lateral fissure (O.T. Sylvian); (j) the eentral (O.T. fissure of Rolando); (3) the parieto-oeeipitai ; (4) the eollateral; and (5) the eireular suleus (O.T. limiting suleus of Reil).

— Gyri and Sulei on Ihe Latenil Surface of Ihe Gerebral Hemisphere.

The lobes whieh are mapped out by these fissures are — (i) the frontal; (2) the parietal ; {3) the oeeipital ; (4) the temporal ; (5) the insula. To these may be added a sixth lobe, in no way related to the interlobar Rssures, viz., the olfactory lobe.

Lateral Pissnre (O.T. Sylvian). — This is the most eon- spieuous lissure on the surface of the eerebrum. It is eomposed of a short main stem, from the lateral extremity of whieb three branehes tadiale. The stem is plaeed on the inferior surface of the eerebrum (Fig. i8z). It begins at tbe substantia perforata anterior. Thenee it passes laterally, forming a deep cleft between the temporai pole and the orbital surface of the frontaI lobe. Appearing on the lateral

«;t -■

(3' :■■-■- ■■

T.-.-: /

1 r»-* -■ - ^- - - -

u:.''v:.:^

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464 THE BRAIN

the insula to meet the temporal opereulum. Its margin forms the upper lip of the posterior braneh of the latend iissure.

The /rontal opereulum (Fig. 186) is the small triangular pieee of eerebral cortex between the anterior aseending and horizontal branehes of the lateral lissure. It is sometimes termed the/ar^ triangularis,

The orbital opereulum (Fig. 186) is for the most part on the under surface of the hemisphere. It lies below the anterior horizontal limb of the lateral lissure, and passes posteriorly from the orbital aspeet of the frontal lobe over the anterior part of the insula.

Suleus Oentralis (O.T. Fissure of Bolando). — The eentral suleus takes an oblique eourse aeross the lateral surface of the eerebral hemisphere (Fig. 186). Its upper end in many eases euts the supero-medial border of the hemisphere a short distanee posterior to the mid-point between the frontal and oeeipital poles, whilst its lower end terminates above the middle of the posterior braneh of the lateral iissure. When its superior extremity turns round the supero-medial border of the hemisphere it is eontinued posteriorly, for a short distanee, on the medial surface (Fig. 187). Although in its general direetion the suleus eentralis is oblique, it is far from being straight. Nearer to its upper than to its lower end it is bent posteriorly so as to form a bay, within whieh is aeeommodated a portion of the eerebral cortex whieh represents the motor area of the opposite upper limb. The upper and lower limits of this bay are termed the upper and lo%ver genua of the fissure.

Pissura Parieto - oeeipitalis. — The greater part of this fissure is situated on the medial surface of the eerebral hemi- sphere (Fig. 187); only a very small part appears on the lateral face (Fig. 186).

The lateral part of tJie parieto-oeeipital fissure (O.T. extemal parieto-oeeipiiat) euts the supero-medial border of the hemi- sphere, in a transverse direetion, from one and a half to two inehes anterior to the oeeipital pole. It is usually not more than half an ineh in length, and it is brought to an abrupt termination by an arehing convolution whieh winds round its extremity, and receives the convenient name of areus parieto- oedpitalis (Fig. 186).

The medial part of the parieto-oeeipital fissure (Fig. 187)

CL

r-'x

i downwards, in a :w.' :■* •^\-.; \'f. / %'', . .*. • .. - - ■• ••.•.- - •»re of the hemisrKt*-.';'. ^.> >. ,v..'.v.v.. . .. •■ - -.'. ,•■.%■.- . . V **1:, at its lower onr.. ^' ■'> i>'r ,-;;\;;-. .■/.- .■.v.. .v

^■.;sura Oollateralis i^y.s: *. S-^ V''.r .\..;. v ■.;.■..---. ■•. ■= •. ■nely marked fis$uro o.'; ',:\c ',c\\uk\.V, \\--..\ »v; •.:•.. .•.•..; •.•.,-.x *^''C of the eerobni'i ho',v.:>;^l*.<'iv" 1; ^.e •,■.♦.■: •.♦., ■.» \*\w Iial pole, and ONtoiu'.s ;;?*.;or.iMl\ (im>:;\\;-. \\\x- -., i\>jsm »1 Posteriorly il lios ^oIonn a\u\ \\\\i\\\i-\ i«« U». . »l. \tiiw.

I .-1111 >l ai«li »..'

/ * . \ I ...l.i . ...|».U

^ 1 ■ A •

• *^ »

• •i |P.

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, ry*-*-v:. •*- — ^ -1j/

^i^ eallosuiu Keptuiii peUueiduni

Anterior com[i]is.tui*.:

li \»-nv

.^ tllllll>il< > ir>/{. •

^ i''icj. 187. — The J'jvri 1»'' \mIi«. ••»» ^to .■'.\,':i..". .n.< * v,»i. -...■.».

"* "^, whilst anterioriv it .k ;»»::.'i*.''.v.'.«/. v.*.'v. :•..*. •.•.•.\«-r^ i.u-.yi. 7 by the hippoeamn'ii v"'.x«: i-'-.n:'. 1: :-..* •.•.^/.\..v iv..\ "lodial convolution >fi tu» i^nuM'u. ;.•••.' -.«* ".-..^ t '.-.;>. «*,*..• f the hemispher»' 'j'*q. -<' .

ior tO the eollat'^riil Il^imIi ^ :h'.illi\it* .ul.».u, .w \t

ic anterior end of ^*-' ••iiii)/vi->..i i\)'j* iwt', ni,\.^ •*.»*». the temporal \)'''^*<^. i*"*^! ^»'* iiu»iu!c.»* \» w\/\)'.'Ji'.» '\ of the hippocf*rrTrj.^J j\T*i* .' ««t t- 'w» .',•;. -,^1 '//> or eeto-rhinal fi^^urt ^Y\%. ro8^, ^eus Oinguli (O.T. -^* ] > -' 'i. ^•.

;.'.is is a stroi ^ m» t -atlterior' jiftr*. >r

. n — 30

.Ji

466

THE BRAIN

the medial surface of the hemisphere. It eommenees on the lower portion of the anterior part of the medial surface, curves Tirst upwards and then posteriorly. Finally, tuming upwards, it euts the supero-medial border of the hemisphere a short distanee behind the upper end of the suleus eentralis, and terminates on the lateral surface of the parietal lobe. It separates the anterior portion of the medial surface into a marginal and a eentral area. The eentral part is the gyrus dnguli (O.T. eallosal gyrus^ The marginal part is separ- ated into two portions by a braneh of the suleus einguli, whieh projects upwards above the middle of the eorpus eallosum. The anterior part is the m.edial area of the superior frontal gyrus ; the posterior part is \}\t paraeentral lobule,

Bonndaries of the Prontal Lobe. — The frontal is the largest of the eerebral lobes. On the lateral surface of the hemisphere it is bounded posteriorly by the eentral suleus, and below by the posterior braneh of the lateral fissure. On the medial surface it is limited by the suleus einguli ; whilst on the inferior surface of the hemisphere the stem of the lateral fissure forms its posterior boundar}'.

Lateral SuriiEU» of the Prontal Lobe. — On the lateral surface of the frontal lobe the following sulei and g^rri may be reeognised : —

Sulei

''Suleus preeeeniralis in- ferior.

Suleus prieeeniralis su- perior.

Suleus parametlialis.

Suleus frontalis superior.

Suleus frontalis medius.

Suleus frontalis inferior.

Suleus diagonalis. ^Suleus fronto-marginalis.

Gyri

' Gynis eentralis anterior. Gj'rus front- f Pars superior. alis superior\Pars interior. Ciyrus front- rPars superior. alis medius \Pars inierior. rPars basilaris. Gyrus front- 1 Pars triangu-

alis inferior

■1

laris. Pars orbitalis.

Sukus Pnreentralis Inferior (Fig. i86). — The inferior prae- eentral suleus eonsists of a vertical and a horizontal part, and, when present in a well-marked forni, it presents a figure like the letter T or F. The vertical portion lies anterior to the lower part of the eentral suleus (O.T. fissure of Rolando), and the horizontal portion extends antero-superiorly into the middle frontal g}TUS.

Suleus Praeentralis Superior (Fig. i86). — This is a short vertical suleus whieh lies ant^"^»' to the upper part of the

THE GEREBRUM 467

eentral suleus. It is almost invariably eonneeted with the posterior end of the superior Trontal suleus.

Gyrus Centralis Anterior. — ^The anterior eentral gyrus is a long eontinuous g)mis whieh is limited anteriorly by the two praeeentral sulei, and posteriorly by the eentral suleus. It extends obliquely aeross the hemisphere, from the supero- medial margin above to the posterior braneh of the lateral fissure below (Fig. 186).

Suleus Prontalis Superior (Fig. 1 86). — The superior frontal suleus extends anteriorly from the suleus praeeentralis superior.

Gyrus Prontalis Superior (Figs. 186, 187). — The superior frontal gyrus lies above the superior frontal suleus and passes round the supero-medial border on to the medial surface of the hemisphere. It terminates anteriorly in the frontal pole.

Suleus Prontalis lnferior (Fig. 186). — This lies at a lower level than the superior suleus of the same name. The posterior end of the inferior frontal suleus is plaeed in the angle between the vertical and horizontal parts of the inferior praeeentral suleus, and is not infrequently eonAuent with one or other of these. It passes anteriorly towards the supereiliary margin of the hemisphere, and ends a short distanee from it in a terminal bifurcation.

Gyrus Frontalis Medius (Fig. 186). — The middle frontal gyrus is the broad convolution whieh lies between the superior and inferior frontal sulei.

Gyrus Prontalis Inferior (Fig. 186). — The inferior frontal gyrus is that portion of the lateral surface of the frontal lobe whieh is plaeed anterior to the inferior praeeentral suleus and below the inferior frontal suleus.

The suleus paramedialis is the term applied to a series of short irregular furrows arranged longitudinally, elose to the supero-medial border of the hemisphere. These rudimentary sulei partially subdivide the superior frontal gyrus into an upper and lower division, and are of interest in so far that they are best marked in high types of brain.

The middle frontal sukus (Fig. 186) lies horizontally in the anterior part of the middle frontal gyrus, and divides it into an upper and a lower part (Fig. 186). As it approaehes the supereiliary margin of the hemi- sphere it bifurcates, and its terminal branehes spread out widely from eaeh other, and together eonstitute a transverse furrow ealled the suleus /ronto- marginalis.

Owing to the subdivision of the superior and middle frontal gyri in the manner indieated, the g)rri in the anterior part of the lateral surface of the frontal lobe are arranged in five horizontal tiers.

468

THE BRAIN

Gyrus Prontalis Inferior. — The inferior frontal gyrus possesses a speeial interest and importanee, on aeeoiint of the supposed loealisation within it, on the left side, of the

Longitudinal iissure

01factOTy suleus

01factor>- bulb.

Orbital suleus,

01factor>' traet- Teroporal pole-

Ineisura teniporalis

Inferior

.frontal

gynis

Inferior . temporal suleus

Collateral /issure

Galoarine fissure

Longitudinal fissure

FiG. 188. — Gyri and Sulei on the Tentorial and Orbital Siirfaces of the

Gerebral Hemispheres.

speeeh-eentre. It eonsists of an upper non-opereuiar and a iower opereular portio7i. The latter is eut up into three parts by the two anterior branehes of the lateral lissure. These

THE GEREBRUM 469

are termed the pars basilaris, the pars triangularis, and the pars orbitalis.

The pars basilaris (Fig. 186) is that part whieh lies be- tween the vertical limb of the inferior praeeentral suleus and the anterior aseending ramus of the lateral fissure. It forms the anterior portion of the fronto-parietal opereulum, and it is traversed in an oblique direetion by a shallow furrow, termed the suleus diagonalts,

The pars triangularis (Fig. 186) is simply another name for the frontal opereulum. It is triangular in form, and lies between the anterior aseending and anterior horizontal rami of the lateral fissure.

The pars orbitalis (Fig. 186) is plaeed below the anterior horizontal ramus of the lateral fissure.

Medial Surface of the Frontal Lobe. — On this aspeet of the frontal lobe is the elongated, more or less eontinuous, medial part of the superior frontal gyrus (O.T. marginal gyrus). It lies between the supero-medial border of the hemisphere and the suleus einguli (Fig. 187).

In the anterior part of this gyrus one or two curved sulei are usually present. These are termed the sulei rostrales.

The posterior end of the medial surface of the superior frontal gyrus is more or less eompletely eut oflf from the anterior part. It forms part of the paraeentral lobule^ and lies anterior to the upper end of the eentral suleus (Fig. 187).

Orbital Siirface of the Frontal Lobe. — On this aspeet of the frontal lobe there are two sulei — viz. the olfactory and the orbital.

Suleus Olfactorius. — The olfactory suleus (Fig. 188) is a straight furrow whieh runs parallel to the medial orbital border of the hemisphere. It is oeeupied by the olfactory traet and bulb, and it euts oflf a narrow strip of the orbital surface elose to the medial border whieh receives the name oi gyrus reetus (Fig. 188).

The orbital suleus is a eompound furrow whieh assumes many different forms. Most frequently it takes the shape of the letter H, of whieh the three eomponent parts are a lateral limb, a medial limb, and a transverse limb.

The lateral limb curves round the orbital part of the inferior frontal gyrus, and limits it medially. The medial limb marks off a convolution between itself an'd the olfactory

472 THE BRAIN

parieto-oeeipitalis, it bifurcates into two widely spread-out branehes. These form a short transverse fissure in the oeeipital lobe, termed the suleus oedpitalis transversus (Eeker) (Fig. i86).

The upturned ends of the posterior braneh of the lateral fissure, of the superior temporal suleus and of the middle temporal suleus (Fig. i86) extend for a short distanee, one posterior to the other, into the inferior parietal lobule.

Gyri on the Lateral Surface of the Parietal Lobe. — The interparietal suleus maps out three distriets or areas on the lateral surface of the parietal lobe. These are the posterior eentral gyrus and the superior and inferior parietal lobules.

The gyrus eentralis posterior (Fig. i86) is a long gyrus whieh extends obliquely aeross the hemisphere from the supero- medial border above to the posterior braneh of the lateral fissure below. Anteriorly, it is bounded by the eentral suleus, and posteriorly, by the superior and inferior posteentral sulei.

The superior parietal lobule is the area of eerebral cortex whieh lies between the ramus horizontalis below and the supero-medial border of the hemisphere above. It is bounded anteriorly by the superior posteentral suleus ; and posteriorly, it is Gonneeted with the oeeipital lobe by the areus parieto- oeeipitalis. It is eontinuous around the supero-medial border of the hemisphere with the prseeuneus.

The inferior parietal lobule lies below the ramus horizon- talis and the ramus oeeipitalis, and posterior to the inferior posteentral suleus. It is more or less direetly eontinuous with the oeeipital lobe posteriorly and with the temporal lobe below. It presents three arehing gyri, viz. the supra- marginal anteriorly, the post-parietal posteriorly, and the angular between them.

The supra-77iarginal gyrus (Fig. i86) is folded round the upturned end of the posterior braneh of the lateral fissure and is eontinuous with the superior temporal gyrus. The angular gyrus (Fig. i86) arehes over the upturned end of the superior temporal suleus, and is eontinuous with the middle temporal gyrus. The post-parietal gyrus (Fig. i86) winds round the upturned end of the middle temporal suleus, and runs into the inferior temporal gyrus.

Boundaries of the Oeeipital Lobe. — The oeeipital lobe forms the posterior pyramidal part of the eerebral hemi-

THE GEREBRUM 473

sphere, and it eneloses the posterior horn of the lateral ventricle. On the surface it is very imperfectly mapped off from the parietal and temporal lobes, whieh lie anterior to it. It presents three surfaces and an apex or oeeipital pole. On the medial aspeet of the hemisphere it is separated from the parietal lobe (i.e. the praeeuneus) by the parieto-oeeipital Assure. On the tentorial part of the inferior surface it is not separated either from the temporal lobe or from the gyrus hippoeampi, whieh lie anterior to it. It is neeessary, there- fore, on this aspeet, to employ an arbitrary line of demareation, whieh extends from the prae-oeeipital noteh, on the infero- lateral border of the hemisphere, to the isthmus of the gyrus fornicatus, whieh lies below the posterior end of the eorpus eallosum. On the lateral surface the parieto-oeeipital iissure, and an arbitrary line from that hssure to the pr^-occipital noteh, may be regarded as separating the oeeipital from the parietal and temporal lobes.

Medial Aspeet of the Oeeipital Lobe. — On the medial surface are (i) the ealearine hssure; (2) the euneus; and (3) P^^*^ of ^^ gyrus lingualis.

The ealearine fissure eommenees below the isthmus of the gyrus fornicatus and takes a curved eourse towards the oeeipital poie where it bifurcates into short branehes. At a point somewhat nearer its anterior than its posterior extremity it is joined by the parieto-oeeipital fissure and the two fissures together form a >-- shaped figure.

When ealearine and parieto-oeeipital iissures are iiilly opened up, so as to expose the bottom in eaeh ease, two well-marked deep or submerged gyri will be displayed (Fig. 189). One of these, the gyrus eunei^ marks off the parieto-oeeipital fissure from the ealearine fissure ; the other in- terrupts the ealearine hssure immediately posterior to its junction with the parieto-oeeipital. It is ealled the anterior euneo-lingual deep gyrusy and it divides the ealearine fissure into an anterior and a posterior part. The anterior part of the calcarinefis5ure eorresponds very nearly to the stem of the >--shaped hssural arrangement. It is very deep and, being a eomplete fissure, it gives rise to an elevation, ealled the ealear avis, on the medial wall of the posterior horn of the laterai ventricle. The posterior part of the eakarine fissure is mueh shallower.

The euneus (Fig. 187) is the wedge-shaped or triangular distriet on the medial aspeet of the oeeipital lobe between the parieto-oeeipital and ealearine fissures.

The gyrus lingualis (Figs. 187, 188) is a well-marked gyrus situated between the ealearine fissure above and the pos-

472 THE BRAIN

parieto-oeeipitalis, it bifurcates into two widely spread-out branehes. These form a short transverse iissure in the oeeipital lobe, termed the sukus oeeipitalis transversus (Eeker) (Fig. i86).

The upturned ends of the posterior braneh of the lateral iissure, of the superior temporal suleus and of the middle temporal suleus (Fig. i86) extend for a short distanee, one posterior to the other, into the inferior parietal lobule.

Gyri on the Lateral Surface of the Parietal Lobe. — The interparietal suleus maps out three distriets or areas on the lateral surface of the parietal lobe. These are the posterior eentral gyrus and the superior and inferior parietal lobules.

The gyrus eentralis posterior (Fig. i86) is a long gyrus whieh extends obHquely aeross the hemisphere from the supero- medial border above to the posterior braneh of the lateral fissure below. Anteriorly, it is bounded by the eentral suleus, and posteriorly, by the superior and inferior posteentral sulei.

The superior parietal lobule is the area of eerebral cortex whieh lies between the ramus horizontalis below and the supero-medial border of the hemisphere above. It is bounded anteriorly by the superior posteentral suleus ; and posteriorly, it is eonneeted with the oeeipital lobe by the areus parieto- oeeipitalis. It is eontinuous around the supero-medial border of the hemisphere with the prseeuneus.

The inferior parietal lobule lies below the ramus horizon- talis and the ramus oeeipitalis, and posterior to the inferior posteentral suleus. It is more or less direetly eontinuous with the oeeipital lobe posteriorly and with the temporal lobe below. It presents three arehing gyri, viz. the supra- marginal anteriorly, the post-parietal posteriorly, and the angular between them.

The supra-marginal gyrus (Fig. i86) is folded round the upturned end of the posterior braneh of the lateral fissure and is eontinuous with the superior temporal gyrus. The angular gyrus (Fig. i86) arehes over the upturned end of the superior temporal suleus, and is eontinuous with the middle temporal gyrus. The post-parietal gyrus (Fig. i86) winds round the upturned end of the middle temporal suleus, and runs into the inferior temporal gyrus.

Boundaries of the Oeeipital Lobe. — The oeeipital lobe forms the posterior pyramidal part of the eerebral hemi-

THE GEREBRUM 473

sphere, and it eneloses the posterior horn of the lateral ventricle. On the suriaee it is very imperfectly mapped off from the parietal and temporal lobes, whieh lie anterior to it. It presents three surfaces and an apex or oeeipital pole. On the medial aspeet of the hemisphere it is separated from the parietal lobe (i.e, the praeeuneus) by the parieto-oeeipital Assure. On the tentorial part of the inferior suriaee it is not separated either from the temporal lobe or from the gyrus hippoeampi, whieh lie anterior to it. It is neeessary, there- fore, on this aspeet, to employ an arbitrary line of demareation, whieh extends from the prge-oeeipital noteh, on the infero- lateral border of the hemisphere, to the isthmus of the gyrus fornicatus, whieh lies below the posterior end of the eorpus eallosum. On the lateral surface the parieto-oeeipital iissure, and an arbitrary line from that iissure to the pr^-occipital noteh, may be regarded as separating the oeeipital from the parietal and temporal lobes.

Medial Aspeet of the Oeeipital Lobe. — On the medial surface are (i) the ealearine fissure; (2) the euneus; and (3) part of the gyrus lingualis.

The eakarine fissure eommenees below the isthmus of the gyrus fornicatus and takes a curved eourse towards the oeeipital poie where it bifurcates into short branehes. At a point somewhat nearer its anterior than its posterior extremity it is joined by the parieto-oeeipital fissure and the two fissures together form a >-- shaped figure.

When ealearine and parieto-oeeipital fissures are iiilly opened up, so as to expose the bottom in eaeh ease, two well-marked deep or submerged gyri will be displayed (Fig. 189). One of these, the gyrus eunei^ marks off the parieto-oeeipital iissure from the ealearine Assure ; the other in- terrupts the ealearine fissure immediately posterior to its junction with the parieto-oeeipital. It is ealled the anterior euneo-lingiuU deep gyrus, and it divides the ealearine fissure into an anterior and a posterior part. The anterior part of the calcarinejissure eorresponds very nearly to the stem of the >--shaped fissural arrangement. It is very deep and, being a eomplete fissure, it gives rise to an elevation, ealled the ealear avis, on the medial wall of the posterior horn of the lateral ventricle. The posterior part of the ealearine Jissure is mueh shallower.

The euneus (Fig. 187) is the wedge-shaped or triangular distriet on the medial aspeet of the oeeipital lobe between the parieto-oeeipital and ealearine fissures.

The gyrus lingualis (Figs. 187, 188) is a well-marked gyrus situated between the ealearine fissure above and the pos-

474 THE BRAIN

terior part of the eollateral fissure below. the oeeipital pole and narrows, as it passes anteriorly, to its union with the hippoeampal gyrus. It lies partly on the medial surraee and partly on the tentorial surface of the oeeipital lobe.

Tentorial Siiiface of the Oeeipital Lobe. — On this aspeet lie part of the gyrus lingualis and the posterior part of the fusiforin gyrus. They are separated by the posterior part of the eollateral fissure. The gyrus fusiformis takes part, anteriorly, in the formation of the temporal lobe, and it is separated from the inferior temporal gyrus by ihe inferior temporal suleus.

FiG. iBg. — Poslerior part of medial siixface of Ihe Left Hemisphere. The ealearine anil ihe pajielo.occipital hssures are widely opened up lo show

tbe deep gyri wilhin Ihe

Lateral SiiTface of the Oeeipital Lobe. — There are two well- marked su!ci on this surface of the oeeipital !obe — ^viz. the suleus oeeipitalis transversus and the suleus oeeipitalis lateralis or suleus lunatus or EUiot Smith.

The su/ajs oatpitalis transversus (Fig. i86) extends trans- yersely aeross the upper pan of the lobe posterior to the areus parietu-oeeipitalis. It has already been deseribed as the terminal bifurcation of the ramus oeeipitalis of the inter- parietal suleus.

The suleus oeeipitalis lateralis (Fig. i86) is a short horizontal furrow whieh divides Ihe lateral surface of the lobe into an upper and a lower area of very nearly equal extent. These areas are eonneeted by means of superiieial anneetant gyri with the parietal and temporal lobes.

THE GEREBRUM 475

Boundaries of the Temporal Lobe. — ^The temporal lobe lies posterior to the stem of the lateral fissure and below its posterior braneh. It presents an upper, a lateral, and a tentorial surface, with a free apex or pole whieh projects anteriorly. Above, it is bounded by the posterior braneb of the lateral fissure together with the artificial Hne drawn posteriorly from that fissure. On the tentorial surface it is separated from the hippoeampal gyrus by the eollateral fissure ; whilst posteriorly, it is marked off from the oeeipital lobe by the arbitrary Hnes deseribed on p. 470. The apex or temporal pole projects anteriorly on the under surface of the brain. It should be notieed that the recurved extremity of the hippoeampal gyrus, whieh Hes to the medial side of the hemisphere, does not reaeh the temporal pole, but is separated from it by the ineisura temporalis or eetorhinal fissure.

Upper or Opereular Surikee of tlie Temporal Lobe. — ^This is the surface of the temporal opereulum whieh is opposed to the insula and the fronto-parietal opereulum. The lateral fissure must therefore be widely opened up to expose it. For the most part the surface is smooth, but towards its posterior part there are a few shallow furrows, ealled the sulei of Hesehl^ whilst anteriorly, also on the deep aspeet of the temporal pole, two or three furrows are evident.

Lateral Siirface of tlie Temporal Lobe. — On this aspeet of the lobe there are two horizontal sulei, ealled the superior and middle temporal sulei.

The superior temporal sukus (Fig. 186) is a long, eontinuous and deep cleft whieh begins near the temporal pole and proeeeds posteriorly, below the posterior braneh of the lateral Tissure. Its posterior end turns upwards, into the parietal lobe, and is surrounded by the angular gyrus.

The middle temporal suleus is plaeed midway between the superior temporal suleus and the infero-lateral border of the hemisphere. It is very rare to find it in the form of a eon- tinuous cleft. Usually it is broken up into several isolated pieees, plaeed one posterior to the other. Its posterior part turns upwards into the parietal lobe (Fig. 186), where it is surrounded by the post-parietal gyrus, and lies elose to the artificial line of demareation between the oeeipital and parietal lobes.

By these two temporal sulei the lateral surface of the

476

THE BRAIN

temporal lobe is mapped out into three tiers of horizontal gyri, whieh are termed the superior, in/erior, and middk temporal gyri {Pig. i86).

Tentorial Snitaee of the Temporal Lobe. — On this surraee there is one fissure, termed ihe inferior temporal suleus.

The inferior tem/ioreii sukus (Fig. i88) lies below and lateral

1, and 3- Thtee shon gyri on the fl

panofthein.suls. snd s. Two long gi'ri ,in parieta] p

F. Orbiul opereulum (rot Ihe i

Ti. Superior lemporal gyms. T9. Middle temporal Eynis. x.y. GyfiofHtKhl.

to the eollateral fissure, and elose to the infero-!ateral border of the hemisphere. It runs in an antero-posterior direetion and is not always confined to the temporal lobe, but may extend posteriorly towards the oeeipital pole. It is usually broken up into two or more separate pieees.

The fusiform gyrus (Fig. i88) is sltuated between the eoliateral fissure and the inferior temporai suleus. It extends from the oeeipital pole to the temporal pole.

The narrow strip of 5urface below and lateral to the

THE GEREBRUM 4::

inferior temporal suleus is eondnuous, round ihe irJer»iii< margin of the hemisphere, with the inferior :emj:<?ral bT^^ on the lateral surface of the eerebrum, and is reekooed as a part of it.

The three temporal gyri and the fusiform gynis nin into oot another at the temporal pole.

Insiila (O.T. Maiid of Reil). — ^The insula is a triar^gUiar lield of eerebral cortex whieh lies on a deeper plase thaa the general surface of the hemisi^ere, and is hidden fTozc view by the four opereula whieh overlap it Ip. 463^ It 2$ bounded by a distinet limiting suleus, sy/iiis dreularis (Reili. whieh has been deseribed abeady ; and its dependent apieai part or pole, whieh looks downwards, is in eiose relatioo to the stem of the lateral fissure, and to the substantia pedbrata anterior on the base of the brain.

The insula is divided into sereral diverging gyri by a series of radiating suleL Of the latter, one, whieh pte- sents the same direetion and lies in the same plane as the eentral suleus, receives the name of the sukus eaitralis insukt, It divides the insula into an anterior /rottial pait and a posterior parietal portion.

01factory Lobe. — The olfactory lobe is small and rDdi- mentary in the human brain. It eomprises (i; the oliaetory bulb and traet with the three striae, and (2) the trigonain olfactorium.

The olfactory traet is a narrow white prismade band, wiueii expands anteriorly into a swollen bulbous extremity termed the olfactory bulb. Both the traet and the bulb lie in the olfactory suleus on the orbital surface of the frontal lobe^ whilst the inferior surface of the bulh, when the brain is in position, rests on the cribriform plate of the ethmoid bone and receives the numerous olfactory nenres whieh reaeh it through the foramina in that part of the eranial floor.

Posteriorly, the olfactory traet divides into two or three diverging striae. The medial stria (O.T. mesial rootj eurres abruptly medialwards, and may be followed into the extreinity of the gyrus einguli and the subeallosal gyrus. The laieral stria (O.T. lateral root) runs postero - laterally over the lateral part of the substantia peribrata anterior, and gradtially disappears from view. In animals, in whieh the oUadory apparatus is better developed than in man, it may bc traeed into the uneinate cxtremity of the

\%\%:%:i^\\\\i'-

47« THE BRAIN

gynis. The intermediate stria, whieh is not always present, runs posteriorly aeross the trigonum olfactorium.

The gyrus sub-eallosus is a narrow eortieal strip, of some morphole^eal importanee, whieh lies on the medial surface of the hemisphere immediately below the genu of Ihe eorpus eallosum.

The trigonum olfactorium is the little triangular field of grey matter whieh oeeupies the interval between the medial and lateral striae of the olfactory traet at the point where they begin to diverge.

Osnms Fomicattis. — ^This gyrus, sometimes ealled the limbie lobe, is seen on the medial and tentorial surfaces of the hemisphere. It is a ring-like convolution, the extremities of whieh approaeh eaeh other elosely at the substantia perforata anterior.

The upper and anterior part of the gyrus fornicatus lies in intimate relation to the extremities and upper surface of the eorpus eallosum, and it is ealled the gyrus eingulu The lower portion of the gyrus fornicatus is termed the hippoeampal gyrus, and forms the medial part of the tentorial portion of the lower surface of the hemisphere. The eontinuity between the hippoeampal g^niis and the gyrus einguli is established, below the posterior end of the eorpus eallosum, by a narrow portion of the gyrus fornicatus ealled the isthmus, From this point the hippoeampal gyrus extends anteriorly towards the temporal pole. Finally, at the side of the peduneulus eerebri, the hippoeampal gyrus is folded on itself, and ends in a recurved hook-like extremity, termed the uneus, The uneus does not reaeh the temporal pole.

The gyrus dnguli (O.T. eallosal convolution) begins below the anterior end of the eorpus eallosum at the substantia peribrata anterior, and, winding round the genu of the eallosum, it is eontinued posteriorly on its upper surface to the thiekened posterior extremity or splenium. Finally, curving round this, it beeomes greatly narrowed through the ealearine fissure eutting into it. This narrow part is termed the isthmus, and eonstitutes the link of eonneetion between the gyrus einguli and the hippoeampal gyrus.

The gyrus einguli is separated from the superior frontal gyrus and the paraeentral lobule by the suleus einguli; from the prseeuneus by the subparietal suleus ; and from the lingual gyrus by the ealearine fissure. It is separated from the eorpus eallosum by the eallosal suleus.

THE GEREBRUM 479

The hippoeampal gyrus is bounded below and laterally by the anterior part of the eollateral iissure, and anteriorly by the ineisura temporalis, whieh separates its booked extreniily, or uneus, from the temporal pole. Supero-medially it is limited by the hippoeampal fissure; whilst posteriorly it is divided into two parts by the anterior extremity of the ealearine fissure. Of these, the upper is the isthmus, whieh eonneets it with the gyrus einguli, whilst the lower portion is eontinuous with the gyrus lingualis.

If the hippoeampal tissure, whieh lies above the hippoeampal gyrus, is opened up, in a soft brain, the /aseia deniata and the fimbria lying side by side will be brought into view. In a hardened brain the examiraition of this region should be deferred (p. 492).

The Corpus Gallosum.

A disseetion should now be made with the view of exposing the upper surface of the eorpus eallosum, whieh is the eom- missural band eonneeting the eerebral hemispheres at the bottom of the longitudinal tissure.

Disseetion. — With a long knife sliee off the top of the right hemispbere at the Ievel of the suleus einguli. The white medullary eentre of the eerebral hemisphere, enelosed on all hands by the grey cortex, is brought into view, and the appearanee receives the name of eentrum 5emi-avaU, From the eentral white mass medullary prolongations proeeed into all the gyri.

A transverse ineision may next be made through the middle of the gyrus einguli ; then the anterior and posterior parts of the gyrus einguli should be torn away from the hemisphere in a lateral direetion. If this is done successfully the manner in whieh the fibres of the eorpus eallosum enter the hemisphere will be seen. In eases where the student is disseeting the brain for the seeond time the knife should not be used at all in earrying out this disseetion. The top of the hemisphere down to the level of the suleus einguli should, in the first instanee, be tom off, and then the gyrus einguli may be treated in the same way. By this expedient the fibres of the eorpus eallosum may be traeed into the g^rri.

eingulmn. — If the deep surface of the gyrus einguli, whieh has been torn away, is examined, a large bundle of longitudinally direeted fibres will be notieed embedded in its substanee. This is the eingulum. It ean be easily dislodged ; a very slight degree of traetion is all that is required to lift it out of its bed. It begins anteriorly at the substantia perforata anterior, curves round the convexity of the eorpus eallosum, and then deseends, round its posterior end, and terminates in the hippoeampal gyrus. The eingulum is a

long assoeiation bundle eomposed of several systems of fibres whieh run only for short distanees within it. It is elosely assoeiated with the gyrus fornicatus.

Dissation. — The gyri and sulei on the medial surface of the left hemi- sphere may now be studied, and Iheo ihe disseetion, whieh has been earried out with the view of exposing [he eorpus eallosum, may be repeated

on ihe left side. In doing this, however, take eare not to injure the medial surface of ihe left hemisphere poslerior to the parieto - oeeipital iissure, indeed, an effort should be made lo preserve that Hssure intaet, SO that it and the euneus may be studied afterwards, on this ^de, in eonneetion wllh theeyri and sulei on the under surface of the hemisphere.

'nie upper surface of the eorpus eallosum is nowr exposed, ind it will be seen that it unites into one mass the medullary eentres of the two hemispheies. The eontinuous white lield, eonsisting of the eorpus eallosum and the medullary eentre of eaeh hemispheie, ieceives the name of

Gorpus eallosum. — This is the great transrerse eommissure

THE GEREBRUM 481

of the eerebrum, It is plaeed nearer the atiterior ihan the posterior end of the brain, and it unites the medial surfaces of the two eerebral hemispheres throughout very nearly a half of their antero-posterior length.

Its upper surface is convex antero-posteriorly and concave ftom side to side, and it forms the bottom of the longitudinal tissure. On eaeh side of the fissure it is covered by the gyrus einguli (O.T. eallosal gyrus). Only in its posterior part

is it touehed by the falx eerebri ; anteriorly, that fold of dura mater falls eonsiderably short of it. The upper surface of the eorpus eallosum is eoated by an exceedingly thin layer of grey matter eontinuous, at the bottom of the eallosal sukus, with the grey cortex of the hemisphere. In this are embedded, on either side of the median plane, two deUeate longitudinal bands of fibres ealled the striae longitudinales medialis and iateralis. The stria hngitudinalu medialis is the more strongly marked of the two, and it is separated from voi.. 11 — 31

482 THE BRAIN

its felIow of the opposite side by a faint median ' furrow. The slria loni^tudtnahs laterahs is plaeed more laterally. So thin is the gre> eoating of the eorpus eallosum thal the transverse direetion of the bundles of eallosal fibres ean be easily seen through it

The strin: wilh the tbin layer of grey matter assoeiated wilh them represent a g)riis ealled the^trui supi aiallosus

The two extremiltes of the eorpus eallosum (Fig. 193) are

■iid of Ihe Gorpus Callosum and the Subeallosal Gyri 3w when ihe froiital lobes of the hemispheres are d rrom eaeh other. (Krom Cruveilhier. )

greatly thiekened, wliilst the intermediate part, the truneus (O.T. body) is eonsiderably thinner. The massivc posterior end, whieh is full and rounded, iies over the meseneephalon, and extends posteriorly as far as the highest point of the eere- bellum. It is ealled the spknium. The anterior end, whieh is not quite so massive, is folded, downwards and posteriorly, upon itself, and is ealled the genu. The recurved lower portion of the eorpus eallosum rapidly thins as it passea posteriorly, and is termed the rostrum. The fine terminal edge of the rostrum, the lamina rostralis, is eonneeted with the lamina terminalis (Fig. 192).

Both the lateral and the medial longitudinal strise, whieh lie upon the upper surface of the eorpus eallosum, tum

THE GEREBRUM 483

downwards, round the splenium, and end in the fasciola einerea, The fasciola einerea, whieh is situated immediately beneath the splenium, is a narrow strip of grey matter, eontinuous posteriorly with the medial and lateral striae of the same side and anteriorly with the fascia dentata hippoeampi. Anteriorly, the strige pass round the genu, and then along the under surface of the rostrum until they terminate in the eorresponding gyrus subeallosus, The gyrus subeallosus is a ridge whieh deseends from the rostrum of the eorpus eallosum and passes to the surface of the substantia perforata anterior. There the fibres of the striae eontained in the gyrus emerge from its substanee, and pass postero- laterally along the posterior limit of the substantia perforata anterior towards the anterior extremity of the temporal lobe.

Pibres of the Oorpus eallOBUin. — The transverse fibres of the eorpus eallosum, as they enter the white medullary eentre of the eerebral hemisphere, radiate from eaeh other towards various parts of the eerebral cortex. This radiation is ealled the radiatio eorporis eallosi, The more anterior of the Abres whieh eompose the genu of the eorpus eallosum sweep anteriorly in a series of curves towards the frontal pole of the hemisphere. They form the /oreeps minor. A large part of the splenium, forming a solid bundle termed the forceps major, bends suddenly and abruptly posteriorly into the oeeipital lobe. Fibres from the trunk of the eorpus eallosum and also from the splenium curve round the lateral ventricle and form a very definite stratum ealled the tapetum, This is a thin. layer in the medullary eentre of the hemisphere whieh forms the roof and lateral wall of the posterior horn and the lateral wall of the posterior part of the inferior horn of the lateral ventricle.

Ventriculus Lateralis.

The lateral ventricle, in the interior of the eerebral hemi- sphere, should now be opened up on eaeh side. The eorpus eallosum, whieh forms the roof of the eentral part (O.T. body) and anterior horn of this cavity, must, therefore, be partially removed.

Disseetion. — Make a longitudinal ineision, through the eorpus eallosum, about a quarter of an iheh from the median plane on eaeh side. The eentral portion of the eorpus eallosum whieh lies between these ineisions is to be kept in position. The lateral portions must be tumed laterally and detaehed eompletely. As this is being done, it will beeome evident that the lower part of the splenium whieh is prolonged into the forceps major is in reality a portion folded anteriorly in elose apposition with the under surface of the posterior end of the eorpus eallosum. Be careful to leave the forceps major in its plaee.

The eentral part and the anterior hom of the ventricle are now exposed ; but the cavity of the ventricle runs posteriorly into the oeeipital lobe in

11—31 a

484 THE BRAIN

the Eirm r)f a posterii>r horn, and dowTiwariis and anleriorly into the temporal Idln- fls the iata'uit horr. The ]>05terior hotn ean, at preaent, be opened 011 Ihe right nide oaly. Carry thu kn!fe iwsleriorh' through the medullary «utHitanei; whieb fomi9 iU rcK)f, and remove a sufficienl amount of tliis to

giyu a eoniiikte view of the interior of Ihis part of ihe cavily. Greater diHieully will bi: esperieneeil in ii|>eninf; u]! the inretior horn. Plaee the point of the knife in Ihe uppei ])arl of tlie horn, where il joins ihe eentral parl of ihe vcnlricle, and eairy ihe blado in an antcto-infetior direetion,

THE GEREBRUM 485

through the lateral part of the temporal lobe, towards ihe tempoial pole, roUowing the eourse of Ihe Cavi(y. This eorresponds very nearly wilh Ihe eourse of Ihe superior temporal suleus. The laleral wall of the inferior hom is thus inetsed, and a suffident amount of :he lateral part of the temporal lobe must he remoYed to giye a view of the cavity. In doing Ihis, the temporal opereulum will be taken away, bul the sui^aee of the insuta siiould be pieserved from injury.

Lateral Tentriele. — The disseetor will now perceive that eaeh eerebral hemisphere is hollow, The cavity in the ititerior is ealled the lateral yentriele. It is lined with a thin dark-

95.— Casl of ihe Ventricles of Ihe Brain (from Rewius).

eoloured layer of epithelium, whieh is termed the ependyma. In eertain plaees its walls are in apposition with eaeh other, but in other ioeahties spaees of varying eapaeity, and eontwning eerebro-spinal fluid, are left between the bounding walls. The lateral ventricle eommunieates with the third ventricle of the brain by means of a smal! foramen, whieh is termed the interuentrkular /oramen (O.T. /oramen of Monro). This aperture, whieh is just large eiiough to admit a crow-quill, lies at the anterior end of the thalamus, and posterior to the eolumn of the forniK (O.T, anterior pillar).

The shape of the lateral ventride is very irr^;ular, and ean be best understood by the study of a plaster east of its interior (Fig. igg). It is eomposed of a eentral part (O.T. body) and three horns, viz., an anterior, a posterior,

THE BRAIN

and an inferior horn. The anterior hom is that part of the cavity whieh ]ics anterior to the interYentrieular foramen.

Gotnua of the

The eentral part is the portion of the ventricle whieh extends from tlie intcrvenlricular foramcn to the splenium of the eorpus eallosum. At that point the posterior and inferiot

THE GEREBRUM

487

horns diverge from the posterior end of the eentral part The posterior hom curves posterioriy and medially into the oeeipital lobe. It is very variable in its length and eapaeity. The inferior korn passes with a bold sweep round the posterior end of the thalamus, and then tunnels, in an antero- inferior direetion, through the temporal lobe towards the temporal pole.

Goniu AntBriuA Yentrieuli Lateralia. — The anterior horn forms the anterior part of the cavity, and extends antero- laterally and downwards in the frontal lobe. When seei frontal seetion it presents a iriangular outline — the tloor sloping upwards and laterally to meet the roof at an aeute angle (Fig. 197). It is bounded anteriorly by the posterior surface of the genu of the eorpus eallosum, whilst the roof is formed by the anterior parl of the trunk of the eorpus eallosum. The medial wall, whieh ia yertieal, is formed by.

488 THE BRAIN

the septum pellueidum — a thin median partition between the lateral ventricles of opposite sides. The sloping floor presents a marked elevation or bulging, viz., the smootb rounded and enlarged anterior extremity of the pear-shaped eaudate nudms.

Para eentralis Tentrienli Lateralis. — The eentral part of the ventricle is roofed likewise by the eorpus eallosum. On the tntdial side it is bounded by the posterior part of rtie septum pellueidum, and more posteriorly by the attaebment of the fornix to the under surface of the eorpus eallosum.

198,-

On the lateral side it is elosed, as in the ease of the anterior horn, by the meeting of the roof and the floor of the cavity,

On the floor a number of importanE objects raay be reeognised. Latero-medially, and, at the same time, to some extent antero-posteriorly, these are— (i) the eaudate nueleus;

(2) a groove extending obiiquely, postero-laterally, between the eaudate nueleus aiid the thalamus, in whieh are plaeed the terminal vein (O.T. vein of eorpus striatum) and a wbite band ealled the stria terminalis (O.T. tienia semieireularis) ;

(3) a portion of the upper surface of the thalamus; (4) the ehorioid plexus; (5) the thin sharp lateral edge of Uie fornix.

THE GEREBRUM 489

The eaudate nueleus as it passes posteriorly, on the lateral part of the floor of the eentral part of the lateral veiitricle, narrows very rapidly.

The terminal vein Ls seen through the ependyma in the groove between the eaudate nueleus and the thalamus. It joins the internal eerebral vein (O.T. vein of Galen) at the interventricular foramen, In the same groove is plaeed the stria terminalis — a natrow band of white raatter, whieh bends downwards and disappears from view in the region of the

interventricular foramen. Its fibres ultimately reaeh the substantia perforata anterior, in whieh they end.

The portion of the upper surface of the thalamus, whieh appears in the fioor of the lateral ventricle is, in great part, covered by the ehorioid plexus of the lateral ventricle. The plexus is a rieh vascular fringe whieh appears from imder cover of the sharp lateral edge of the fomix, It is eon- tinuous anteriorly, through the interventricular foramen, with the eorresponding ehorioid plemis of the opposite side; whilst posteriorly, it is earried into the inferior hom of the ventricle. Although the ehorioid plexus has all the appearanee of lying free within the ventriclc it is invested by an epithelial layer

490 THE BRAIN

of ependyma, whieh excludes it from the cavity and is eonneeted on the one hand to the sharp margin of the fornix, and on the other to the upper surface of the thalamus.

Comu Posterius Yentrieuli Lateralis. — The posterior horn is a diverticulum whieh runs, from the posterior end of the eentral part of the ventricle, into the oeeipital lobe. It tapers to a point and deseribes a gentle curve, the convexity of whieh is direeted laterally. The roof and lateral wall of this portion of the ventricular cavity is formed by the tapetum of the eorpus eallosum.

Upon the niedial wall two elongated curved elevations may be seen. The upper of these, termed the bulb of the eornu, is produeed by the fibres of the forceps major as they curve posteriorly, from the lower part of the splenium of the eorpus eallosum, into the oeeipital lobe. The lower elevation is known as the eakar avis, It varies greatly in size, in different brains, and is eaused by an infolding of the ventricular wall whieh eorresponds with the anterior part of the ealearine fissure.

Disseetion. — The disseetor should now insinuate his fingers undemeath the fronto-parietal opereulum of the insula and tear this portion of the cortex away in an upward direetion. The frontal opereulum (pars triangularis) and the orbital opereulum should be dealt with in the same manner. The greater part of the temporal opereulum has already been removed in opening up the inferior horn of the ventricle ; therefore the insula is now fully exposed to view, and its relation to the parts in the interior of the ventricle ean be seen.

eomu Inferius Yentrieuli Lateralis (O.T. Deseending Comu). — The inferior horn must be regarded as the direet eontinuation of the main ventricular cavity into the temporal lobe. The posterior horn is merely a diverticulum from -the main cavity. At first direeted postero-laterally, the inferior horn suddenly sinks downwards, posterior to the thalamus, into the temporal lobe, in whieh it takes a curved eourse, antero- medially, to a point about an ineh posterior to the extremity of the temporal pole. In the angle between the diverging inferior and posterior horns the cavity of the ventricle exhibits a triangular expansion of varying eapaeity. This is ealled the trigonum eollaterale,

The lateral wall of the inferior horn is formed, for the most part, by the tapetum of the eorpus eallosum. At the extremity of the horn the roof presents a slight bulging into the ventricular cavity. This is the amygdaloid tuberde^ and it is

THE GEREBRUM

49«

produeed by a superjacent eolleetion of grey matter, termed the amygdaloid nudeus. The stria terminalis and the greatly attenuated and e>;panded tail of the eaudate nudeus are both prolonged into the inferior horn, and are earried anteriorly in its roof to the amygdaloid nueleus.

On the floor of the inferior hom the disseetor will note the following parts : (i) the hippoeampus; (2) the ehorioid plexus; (3) the fimbria; and (4) the eminentia eollateralis.

Hippoeampns (O.T. HippoeampoB Major). — This is over- lapped by the ehorioid p!exus, whieh must be tumed aside.

of Inretior Comu ol

It is a prominent elevation on the floor of the inferior hom of the lateral ventricle, and is strongly curved in conformjty with the eourse taken by the hom in whieh it lies. It pre- sents, therefore, a medial concave mai^in and a lateral convex margin. Narrow posteriorly, it enlarges as it is traeed anteriorly, and it ends, below the amygdaloid tuberele, in a thiekened extremity, the pes hippoeampi. The surface of the pes hippoeampi is marked by some faint grooves whieh inter- vene between a number of ridges ealled the hippoeampal digitations. The hippoeampus is the intemal eIevation whieh eorresponds to the hippoeampal tissure on the esterior of the wall of the ventricle.

rimbria (Hippoeampi). — The fimbria is a narrow but Tety

492 THE BRAIN

distinet band of white matter whieh is attaehed by its lateral margin along the concave medial border of the hippoeampus. The white matter eomposing it is eontinuous with the thiit white layer {alveus) whieh is spread over the surface of the hippoeampus, and it presents two Tree surfaces and a sharp free medial border. The timbria has been noted already in eonneetion with the hippoeampal hssure and the fascia dentata (p. 479), and the relations whieh it presents to the erus of the fornix and the uneus are pointed out on p. 494.

ehorioid rissure of the Cerebnim.— When the pia mater in the region of ihe hippoeampal iissure is removed from the surface of the brain, the ehorioid plexus in the interior of the inferior horn of the lateral ventricle is usually withdrawn with it, and a fissure appears between the fimbria and the roof of the ventricular horn. This is termed the ehorioid fissure o/ the eerebrum ; it is the lower part of the greai lransverse fissure. By the withdrawal of the ehorioid plexus it is converted into an artificial gap, whieh leads direetly from the exterior of the brain into the interior of the inferior horn of the lateral ventricle.

THE GEREBRUM

493

Pleziis ehoiioidenB. — The ehorioid plexus is a system of convoluted blood-Yessels enelosed within a fold of pia mater whieh is prolonged, into the inferior hom of the

lodyoriUE«]vH.lricli ehoriMdpl™

. — Fronta1 BcclioQ through the Cerebnim, Mid-brain, and Pons m Ibe le or the genieulate bodiea, It shows the relation of the deatate and ehorioid Rssures to the inferior horn of the lateral yentriele.

lateral ventricle, through the diorioid fissure of the eerebrura. It lies on the suriaee of the hippoeampus and, at the posterior extremity of the thalamus, it beeomes eontinu- ous with the ehorioid plexus in the eentral part of the

494 THE BRAIN

lateral ventricle (Fig. 200). But it must not be supposed that the ehorioid plexus lies free in the ventricular cavity. It is elothed in the most intimate manner by an epithelial epen- dymal layer, whieh represents the medial wall of the inferior horn pushed into the cavity by the ehorioid plexus. The ventricle, therefore, opens on the surface through the ehorioid iissure only a^ter this thin epithelial layer is torn away by the withdrawal of the ehorioid plexus.

Emmentia Oollateralis. — This eminenee may present two distinet forms, whieh may be distinguished from eaeh other as the eminentia eollateralis posterior and the eminentia eol- lateralis anterior.

The posterior eoUateral eminenee is a smooth elevation in the floor of the trigonum eollaterale, in the interval between the ealear avis and the hippoeampus as they diverge from eaeh other. The anterior eollateral eminenee is not always present. It forms an elongated elevation on the floor of the inferior horn of the lateral ventricle, on the lateral side of the hippoeampus. Both eminenees eorrespond to the eol- lateral fissure on the tentorial aspeet of the eerebral hemisphere.

Disseetion. — The remains of the right temporal lobe and of the right oeeipital lobe should now be detaehed from the eerebrum by eutting through the forceps major of the splenium of the eorpus eallosum and through the fmibria where it passes into the erus of the fomix. The knife should then be earried anteriorly from the anterior extremity of the inferior horn, above the level of the uneus, through the temporal pole. The temporal lobe, with the hippoeampal gyrus along its medial side, ean then be separated from the remainder of the brain, along the line of the ehorioid fissure of the eerebrum. In the detaehed part of the eerebrum (Fig. 201) a good view is obtained of the floor of the inferior hom and of the parts in relation to it. Further, by replaeing it in position, the ehorioid Tissure ean be better understood, and by tuming the brain upside down a view is obtained of the roof of the inferior horn and the straetures in relation to it. In this way the tail of the eaudate nueleus and the stria terminalis ean bc traeed into the amygdaloid nueleus.

The eut edge of the eentral part of the eorpus eallosum, whieh is still in position, should now be still further pared away, so as to bring the sub- jacent septum pellueidum and the fornix more fully into view.

Fimbria (Figs. 200, 201). — This is simply a eontinuation of the erus (O.T. posterior pillar) of the fornix. It is a eon- spieuous band of white matter, whieh presents a prominent free border. Anteriorly, it runs into the recurved extremity of the uneus, whilst, if it is traeed posteriorly, it will be seen to curve upwards, posterior to the thalamus, and beeome

THE GEREBRUM 495

eontinuous with the erus of the fornix below the posterior part of the eorpus eallosum (p. 491).

Fascia Dentata Hippoeampi. — The fascia dentata is the free edge of grey matter whieh is plaeed between the iimbria and the deep part of the upper surface of the hippo- eampal gyrus. The groove between it and the Anibria is termed the fiinbrio-dentate suleus. Its margin is notehed, and its surface is seored with numerous elosely-plaeed transverse grooves. It begins posteriorly, in the region of the splenium of the eorpus eallosum, and it runs anteriorly into the cleft of the uneus, from whieh it emerges again in the form of a delieate band, ealled the frenulum of Giaeomini, . whieh erosses the recurved part of the uneus in a transverse direetion.

Hippoeampal rissure. — This is a eomplete iissure, and the elevation on the ventricular wall, whieh eorresponds to it, is ealled the hippoeampus (Fig. 217). It begins posterior to the splenium of the eorpus eallosum, where it is eontinuous with a shallow part of the eallosal suleus, and it passes anteriorly, between the fascia dentata and the hippoeampal gyrus. Its anterior end is embraeed by the uneus.

Septum Pellugidum — FoRNix — Tela Chorioidea

Ventriculi Tertil

Septum Pellueidum. — This is a thin vertical partition whieh intervenes between the anterior eornua and the anterior parts of the eentral portions of the two lateral ventricles (Fig. 198). It is triangular in shape, and is prolonged posteriorly in the narrow interval between the trunk of the eorpus eallosum and the fornix, to eaeh of whieh it is attaehed. Anteriorly, it oeeupies the gap posterior to the genu of the eorpus eallosum ; whilst below, in the narrow interval between the rostrum of the eorpus eallosum and the fornix, it is prolonged downwards to the base of the brain-(Fig. 207).

The septum pellueidum is eomposed of two thin laminae whieh lie one on eaeh side of the median plane. The median cleft between the layers is termed the eamtn septi pellueidi {O.T,fifth ventricle) (Figs. 194 and 196).

Disseetion. — The narrow middle strip of the eorpus eallosum, posterior to the genu, should now be removed. Cut it transversely aeross, and, gently raising it, separate the upper edge of the septum pellueidum from its lower

496

THE BRAIN

5tufice. PosteiioT lo the septum pellueidum the under sorbee of the median ]>art o( the eoipus eallosuiD will be found to lie upon and to be eonneeied with the appei siirface of the ^ornis. Sever ihis eonneetioii also. Tbe left half of^the forceps major should be preserred, so Ihat its eonneelion wilh the oeeipital lobe may be more fully made out later. By snipping iilTthe upper edge or Ihe septura pellueidum with the seissors, the two laminae, with the interposed cle!t, will be expo5ed.

OaTTiin Septi Pellueidi (O.T. Fiftli Teiitriele). — Thisis the name whieh is apphed to the median cleft between the two laminse of the septum pellueidum. It varies greatly in extent, in dilTerent brains, and it eontains a little Auid. It is eompletely

relalions of the Fornix.

isolated, having no eommunieation either with the ventric]es or with the exterior.

Fomix. — The fomix is an arehed strueture, eomposed of longitudinal and transverse fibres. It eonsists of a eentral part or body, whieh ends in two eolumns anteriorly and two erura posteriorly.

Gorpus Pormds. — The body of the fornix is triangular in shape. Anteriorly, where it is eontinuous with the eolumns, it is narrow ; posteriorly it broadens out, beeomes Aattened, and is prolonged into the erura. The upper surface of the body of the fornix is in eontaet with the under surface of the eorpus eallosum, and is adherent to it in the median plane

THE GEREBRUM 497

posteriorly. More anteriorly it is attaehed to the posterior part of the lower edge of the septum pellueidum. Beyond these attaehments the upper surface of the body of the fornix forms a part of the floor of the lateral ventricle, on eaeh side, and is elothed with ependyma. It presents a sharp lateral edge, from under whieh the ehorioid plexus projects into the cavity of the lateral ventricle. The lower surface of the body of the fornix rests upon the tela ehorioidea of the third ventricle (O.T. velum interpositum), a fold of pia mater whieh separates it from the third ventricle and the two thalami.

ColumncB Fornicis (O.T. anterior pillars). — The two eolumns of the fornix are two rounded strands whieh emerge from the anterior end of the body of the fomix, and then, diverging slightly, pass downwards anterior to the interventricular foramen. Their lower ends sink into the grey matter on the lateral walls of the third ventricle, and end at the base of the brain in the eorpora mamillaria.

Eaeh eorpus mamillare has the appearanee of being a twisted loop of the eorresponding eolumn of the fomix, in whieh the fibres turn upon themselves, and are then eontinued upwards and posteriorly into the anterior tuberele of the thalamus. This appearanee, however, is deeep- tive. In the interior of the eorpus mamillare there is a nueleus of grey matter. In this the fibres of the eolumn end ; while the other fibres, whieh seem to be eontinuous with the fornix fibres, take origin within the nueleus. The strand, thus formed, is ealled the fasciculus thalamo- mamillaris (O.T. bundle of Vicq d'Azyr) (Fig. 203).

The eonneetions whieh have just been deseribed eannot be made out at present, but at a later period the disseetor will experience little difficulty in traeing the eolumn of the fornix to the eorpus mamillare, and in dis- playing the eonneetion of this with the fasciculus thalamo-mamillaris.

Orura Fomicis (O.T. posterior pillars). — The erura of the fornix are Aattened bands whieh diverge widely from the body of the fornix. At first they are adherent to the under sur- face of the eorpus eallosum, but soon they sweep downwards, round the posterior ends of the thalami, and enter the inferior horns of the lateral ventricles. There eaeh erus eomes into relation with the eorresponding hippoeampus, and a portion of its nbres beeome spread out on the surface of that prominenee, forming the alveus, whilst the remainder eonstitute the fimbria, whieh has been deseribed already (p. 494, Fig. 203).

The transverse fibres of the fornix eross the lower surface of the body and the anterior part of the interval between the diverging erura. In the latter plaee they may be adherent to the lower surface of the eorpus eallosum. On eaeh side

VOL. II — 32

Soo THE BRAIN

Disseelion. — Eaeh vcna terminalis should now be dlnded u it unite* wilh the internal eerebral vein. The apex of the tela ehorioidea should Chcn be seiied with the forceps and pulled posterioTl;, till the whole stTuelure i& reversed. The enliie upper surtaee of tlie thalamus on eoeh side is thus expo$cd, aud, between the thalami, is seen tlie third vcntriclc. The epithelial roof of this ventricle, whieh is invaginated into the cavily liy the ch<irioid plexuscs of the thiid vent[icle on the under surfacc of the tela, is torn away with the tela. The basal part of the tela is intimatdy eonneeteil wilh the pineal 1)ody, whieh lies on the mesen- eephalon liehind ihe Ihird venlricle. Care lherefore must be taken to extricale (his body ftom the pia maler ; otherwise it is sure to be puUed

The Thalami and the Third Ventricle.

Thalamus — The thalamus is a large mass of grey matter whieh lies obl ^uely aeross the path of the peduneulus eerebri as it aseends into the hemisphere The smaller antertor end

T a Frt en nelo S ue on eorpus e^loaiiin

of the thalamus lies elose to the raedian plane, and is separ- ated from the eorresponding part of the opposite side only by a very narrow intetyal. Tlie enlarged posterior ends of the two thalami are plaeed more wideiy apart ; and in the iiiterval between them, the eorpora quadrigemina are situated. In their anterior two-thirds, the two thalami lie elose together, but are separated by a deep median cleft, the third ventricle

THE GEREBRUM 501

of the brain. Eaeh Ihalamus presents an anterior and a posterior extremity, and foHr surfaces. The inferior and lateral surfaces are in apposition and, indeed, direetly eon- neeted with adjacent parts. The supurior and medial surfaces are free.

The lateral siir/aee of the thalaraus is applied to a mass

of white matter, termed the intertial eapsuk, whieh is eomposed largely of fihres fTOm the basis peduiieu/i. The in/erior or venlral sur/aee of the thalamus rests chiefly upon the su6' thalamie region, whieh is the prolongation upwards of the tegmental part of the peduneulus eetebri. The relation, therefore, whieh the thalamus presents to the upward eontinua- tion of the peduneulus eerebri is yery intimate.

The superior sur/aee of the thalaraus is free. On the Jateral side it is bounded by the groore whieh inter-

--.2 THE BRAIN

m

v-jr.os V;r.v;h;:i r.-.r; :r.ulamus and the eaudate nueleus and o'.r.^ai.-.s ■r.r; v-:;Vi :r:rnr.iria;is a:id the stria terminalis. On "-.•'; r.-.r:^-::.:; sidit:. rr.e .superior surtaee of the thalamus is v::.''ir.-«rrjr:. in ::.=» ar.rerior halr. from rhe medial surface bv a ^'..ir:, ''/\jri. -.r pr-.n'.ir.ent ledge, of the ependyma of the rr.ir'^l '.-^r.trioie. Tr.is i.s r.a'.ied the t^znia thalami. and the rA]ifi ^r.irh i: r'-,rrri.s i.s arj-,entuated by the fact that subjacent ro it ti-.-^rr; '.ie-s a lor;^:tiidinaI strand of dbres ealled the stria m^'iuo'ari:. .\ short di.stanoe anterior to the pineal body the t.'f;r.ia iios -.pori :he upper border Gf a raised white band, the

'[ :.ft .-..^v;r. .'.X .;v;:-ii ;,«■.';* iriorly intw two pan.s, one of whieh beeomes ■ ■■-r.';.'. . V'. - ■*■:''. 't.^. ;ir.':a! V.riy. whiist :he other passes aeroas to ihe ', ^.'/-/si • ■■ r. a .•■• r. ; ! .1 . * r. r '-': gh *: he •za-:enular :om m is2uri. whieh lies anterior 'o "r.e -ir.r.n; -.:a'.<.

f>'; : A Kf', n : h e h a he n u 1 a nr. edial 1 y a nd the up per quadrigeminal \}f>f\j ;;Ostr;rior;y. iies a smali triangular depressed area, the

'\fr: suporior .surface of the thalamus is slightly convex, and i.s of a ihiti.sh eolour owing to the presenee of a thin supf;rf;^iai ^oating of ner\-e fibres ^stratum zonale). It is d ;■/:''!•• d in'.o t'A'o areas by a faint obIique groove whieh \)fy^)u\ r.-ihr the an:erior extremity of the thalamus, and ex- t^;nds obii'; jrj]v. iaterailv and posteriorU*. This suleus eorre- ■-.ponrh. to the frr;r; lateral edge of the fomix. The two areas th'is rf.ripp'';d out an:- \tTy differently related to the ventricles of th^: brain. The lateral area ineludes the anterior extremity (){ \}.\i\ th;ilamn.s, and form5 a part of the floor of the lateral \i\u\n<\(',\ ir is oovered with ependyma, and overlapped by th^- r;horioid fJexus. The medial area intervenes between tli': latoral anrl third ventricles of the brain, and takes no p;j.rt iri the formation of the walls of either. It is covered •A'ith t.h^: tf;]a ohorioidea, above whieh is the fomix. It inrhid'::-; the posterior extremity of the thalamus.

'l'he anterior extremity of the thalamus, ealled the anterior tuhe.rr.le., is rounded and prominent. It projects into the l;irr:r;j.I vf;ntrir:le, lie.s postero-lateral to the free portion of the r()\\\u\\\ ()f thf; fornix, and bounds the in:erventricular foramen po .l.^iriorly.

'l'h'r posterior extremity of the thalamus is very prominent, ;inH [)roj(;cts posteriorly over the meseneephalon (Fig. 206). Thi.s projerting part is ealled the pulrinar. But the posterior

THE GEREBRUM 503

end of the thalamus shows another prominenee. This is situated below and to the lateral side of the pulvinar. It is oval in form, and reeeiyes the name bf the eorpus genieulatum laterale,

The medial surfaces of the two thalami are plaeed very elose together, and are covered not only with the lining ependyma of the third ventricle, but also with a moderately thiek layer of grey matter eontinuous with the grey matter whieh surrounds the aqu9eductus eerebri (Sylvius). A band of grey matter, termed the massa intermedia, erosses the third ventricle and joins the two thalami together.

eorpus Pineale. — This is a small body of a darkish eolour, and about the size of a eherry-stone, whieh is plaeed between the posterior extremities of the two thalami on the dorsal aspeet of the meseneephalon (Fig. 206). It oeeupies the depression between the two superior quadrigeminal bodies, and is shaped like a fir-cone. Its base, whieh is direeted anteriorly, is attaehed by means of a hoUow stalk or pedunele. This stalk is separated into a dorsal and a ventral part by a eontinuation into it of a pointed reeess of the cavity of the third ventricle, The dorsal part of the stalk beeomes eon- tinuous on eaeh thalamus with the taenia thalami ; the ventral part is folded round a narrow but eonspieuous eord-like band of white fibres {posterior eommissure) whieh erosses the median plane immediately below the base of the pineal body.

eoiumissura Anterior Oerebri. — In the anterior part of the cleft between the two thalami, and immediately anterior to the eolumns of the fornix, a round bundle of white fibres will be seen erossing the median plane. This is the anterior eommissure, It is very mueh larger than the posterior eommissure, and will be afterwards followed towards the temporal lobe, in whieh the greater part of it ends.

Yentrieulus Tertius. — This name is given to the deep narrow cleft between the two thalami. It is deeper anteriorly than posteriorly, and extends from the pineal body posteriorly to the anterior eommissure and lamina terminalis anteriorly. Its Jioor is formed by the parts already studied within the interpeduneular fossa on the base of the brain, viz., the tuber einereum, the eorpora mamillaria, and the grey matter of the substantia perforata posterior, and also, more posteriorly, by the tegmenta of the eerebral peduneles. Anteriorly, it is bounded by the lamina terminalis and the anterior eommissure ; whilst

5 «4

THE BRAIN

its lateral walli are Tormed by the medial surfaces of the two thalami. A little anterior to the middle of the ventricle the cavity is erossed by the massa intermedia, whieh eonneets the thalami with eaeh other, and anterior to this the eolumn of the forrix is seen deseending in the lateral wall. At Srst the eolumn is distinet and prominent, but as it approaehes the eorresponding eorpus mamillare it gradually beeomes

more 'and more sunk in the grey matter on the side of the ventric!e.

The roo/oi the third yentriele is formed by a thin epithelial layer whieh stretehes aeross the median plane, from the one t;enia thalami to the other, and is eontinuous with the remainder of the epithelial lining of the cavity. It is applied to the under surface of the tela ehorioidea, whieh overhes the ventriclo, and is invaginated into the cavity by the ehorioid plexuscs whieh hang down from the uiider surface of that fold of pia niater. In the removai of the tela eborioidea the thin epithelial roof was torn away.

The third ventricle eommunieates freely wilh the lateral

THE GEREBRUM 505

ventricles, and also with the fourth ventricle. The aguee- duetus eerebri (Sylvius\ a narrow ehannel whieh tunnels the meseneephalon, brings it into eommunieation with the fourth ventricle. The opening of this eanal will be seen at the posterior part of the floor of the ventricle, immediately below the posterior eommissure. The interuentrieular /oramen^ whieh puts it into eommunieation with the two lateral ventricles, is a Y-shaped aperturewhieh liesat the anterior part of theventricle, and its two diverging limbs pass laterally and slightly upwards, between the most prominent parts of the eolumns of the fornix and the anterior tubereles of the thalami. They are usually large enough to admit a crow-quill, and through them the epithelial lining of the three ventricles beeomes eontinuous.

PORAMEN INTERYENTRieULARE

ANTR.COM: -^d^r	\
— \mA88A INTERMEOIA
OPTie OHiASMA^^^l,™,^	NyREOeSSUS eOsUPRAPINEALlS
C^^^ \ J^^ ^^	S. ^REOeSSUS PINEALIS
i/lNFUNDIBULUM	>^ P08TR. OOM. AQU>EDUCTUS
^gg^^^	GEREBRI
mH^Bhypophysis

FiG. 208. — Diagrammatie outline of the Third Ventricle as viewed from the side.

From eaeh lateral part of the interventricular foramen a distinet groove passes posteriorly, on the lateral wall of the ventricle, to the mouth of the aquaeductus eerebri. It is termed the suleus hypothalamieus,

The outline of the third ventricle is seen to be very irregular when it is viewed from the side in a median seetion through the brain (Fig. 207), or as it is exhibited in a plaster east of the ventricular system of the brain. It presents several diverticula or reeesses. Thus, in the anterior part of the floor there is a deep funnel-shaped reeess, reeessus in/undibuli^ leading down, through the tuber einereum, into the infundibulum of the hypophysis. Another reeess, reeessus optieus^ lies above the optie ehiasma. Posteriorly, two additional reeesses are present. One, the reeessus pinealisy passes posteriorly, above the posterior eommissure and the entranee of the aquae- duetus eerebri, for a short distanee into the stalk of the pineal body. The seeond is plaeed above this, and is earried posteriorly for a greater distanee. Its walls are epithelial, and therefore it eannot be seen in an ordinary disseetion. It is termed the reeessus suprapinealis,

Disseetion. — The further study of the eerebral hemispheres should be postponed until after the examination of the mid-brain or meseneephalon. The membranes should be removed from the upper surface of the eere- bellum, and the prominent anterior part of that organ may then l)e

5o6 THE BRAIN

pulled posteriorly to expose, as far as possible, the eorpora quadrigemina, i.e. the four rounded eminenees on the dorsal aspeet of the meseneephalon. In doing this, eare should be taken to seeure and preserve the slender troehlear nerve whieh issues from a lamina, ealled the anterior medullary velum, immediately below the inferior pair of quadrigeminal bodies, and winds round the lateral side of the peduneulus eerebri.

THE MESENGEPHALON.

The meseneephalon is the stalk whieh oeeupies the aperture of the tentorium eerebelli, and eonneets the eerebral hemi- spheres with the parts in the posterior eranial fossa.^ It is about three-quarters of an ineh long, and it eonsists of a dorsal part, the latnina guadrigemina, and a mueh larger ventral part, whieh is formed by the two large peduneuU eerebri In the undisseeted brain the lamina quadrigemina is eom- pletely hidden from view by the splenium of the eorpus eallosum, whieh projects posteriorly over it, and also by the superimposed eerebral hemispheres. The peduneuli eerebri, however, ean be seen, to sorpe extent, at the base of the brain, where they bound the posterior part of the inter- peduneular fossa. The meseneephalon is tunnelled from below upwards by a narrow passage ealled the aqu3eductus eerebri (Sylvius). This ehannel lies mueh nearer the dorsal than the ventral surface.

Lamina Qiiadrigemma. — The dorsal surface of the lamina quadrigemina is raised into four eminenees or eollieuU^ two superior and two inferior, whieh are ealled the eorpora guadri- gemina. Eaeh eollieulus is eomposed, for the most part, of grey matter, although eaeh has a superficial eoating of white fibres. The superior pair are larger and broader than the in/erior pair^ but they are not so well defined nor yet so prominent.

A longitudinal and a transverse groove separate the quadri- geminal bodies from eaeh other. The longitudinal groom oeeupies the median plane, and extends upwards as far as the posterior eommissure. From its lower end a short but well- defined narrow band of white fibres, the /renulum veU^ passes to the anterior medullary velum, a lamina plaeed immediately below the inferior pair of quadrigeminal prominenees. The

^ If the nieseneephalon was divided, when the brain was removed, the dirided parts niust be fixed together with pins while the superiieial charax:ters are being studied.

THE MESENGEPHALON 507

upper part of the longitudinal groove is oeeupied by the pineal body. The tranwerse groove curves round posterior to eaeh of the superior pair of ^uadiigeminal bodies and separates them froni ihe inferior pair.

Braehia of the OoipoTa Onadrigemuia. — The eorpora quadrigemina are noE marked off from the side of the mesen- eephalon, for eaeh body has in eonneetion with it, on that aspeet, a prominent white strand, whieh is prolonged upwards and anteriorly under the projecting pulyinar. The strands are ealled the braehia of the eorpora quadrigemina, and they are separated from eaeh other by a eontinuation, on the side of the meseneephalon, of the transverse groove whieh inter- venes between the two pairs of bodies.

eorpiis OenienUtum Mediale. — Glosely eonneeted with the braehium of the inferior quadrigeminate body will be seen the eorpus genieulatum mediale.

It is a little oval eminenee, very pul^n" ^o^p.^.^^ .^.-i-^

sharply defined, whieh lies on , . - > i-i'«>t.

theside of the upper part of the I .' -' , ■-"tMiiun

meseneephalon under sheher < the pu!vinar of the thalamus.

Coimections of the Broehiii and the Origin of the Optie Traot. — It will now be seen that the braehia are intimately eon- neeted with the optie traet. The in/erior braehium proeeed- ing upwards from the lower quadrigeminal body advances towards the eorpus genieulatum mediale, and disappears from view under cover of that prominenee. Upon the opposite side of the same genieulate body, the medial rool of origin of the optie traet arises, and the appearanee is sueh that the disseetor might very naturally eonelude that the inferior braehium and the root of the optie traet are eontinuous. That, however, is not the ease. The superior bruehium is earried upwards and anteriorly between the overhanging pulvinar and the eorpus genieulatum mediale. It partly enters the eorpus genieulatum laterale, but a portion of it is direetly eontinuous with the lateral root of Ihe optie traet.

5o8 THE BRAIN

tatend reet U panly ednlinaous uilh tbe soperim' braehiuin, and parlly H'ilh ihe eoipus genieulatum laleraJe and Ihe palviilaT. The supeiioe quadrigeTninal body, the eoipus genieulatuin lalerale, and the pulTinai cr,nslilule ihe lmvir t-iiuat italns.

Pedtmenli Geiebri (O.T. enm eOTobri). — The peduneuli eerebri eonslitute the chief bulk of the meseneephalon. When viewed from be!ow, they appear as two lai^e rope- like strands, whieh emerge, elose together, from the upper aspeet of ihe pons, and diverge as they proeeed upwards to enter ihe eerebral hemisphere. At the point where eaeh

pedunele disappears into the eorresponding hemisphere, it is embraeed, on its lateral side, by the optie traet and the gyrus hippoeampi.

The peduneulus eerebri of eaeh side eonsists of two parts, v\z., a dorsal iegmentum, whieh is prolonged upwards to the region below the thalamus ; and a ventral iasis (O.T. entsla), whieh is earried upwards into the internal eapsule on the lateral side of tbe thalamus. When the base of the briun is examined it is tbe basis peduneuli wbieh is seen. It is wbite in eolour and streaked in the longitudinal direetion. On the exterior of the meseneephalon, the separation between ibe two parts of the peduneulus eerebri {i.e. the tegmentum and the basis peduneuli) is indieated by a niedial and a lateral groove or suleus, The medial suleus is the deeper

THE MESENGEPHALON 509

and more distinet. It looks into the interpeduneular fossa, and from it emerge the fila of the oeulo-motor nerve. It consequently receives the name of the suleus oeulomotorius, The lateral suleus is termed the suleus lateralis,

Cut Surface of the Meseneephalon. — Mueh nearer the dorsal than the yentral surface of the meseneephalon the transversely divided aguaduetus eerebri may be seen. This narrow passage leads from the fourth ventricle below to the third ventricle above. It is surrounded by a thiek layer of grey matter, ealled the eentral grey matter of the agueduet. In a fresh brain this is always very eonspieuous, and in its midst are situated the nuelei of the oeulo- motor and troehlear nerves, and the upper motor nueleus of the trigeminal nerve, although of eourse these eannot, except in very favourable eireumstanees, be deteeted by the naked eye. Below, the grey matter of the aqueduct is eontinuous. with the grey matter spread out on the anterior wall of the fourth ventricle ; whilst above, it is eon- tinuous with the grey matter on the floor and sides of the third ventricle.

The division between the tegmentum and the basis peduneuli, on eaeh side, is rendered very evident by a eon- spieuous lamina of dark pigmented matter whieh intervenes between them. This is termed the substantia nigra,

Substantia Nigra. — As seen in transverse seetion, the sub- stantia nigra presents a somewhat ereseentie outline. It is a thiek band interposed between the basal and tegmental parts of the peduneuli eerebri, and it eonsists of a mass of grey matter in the midst of whieh are large numbers of pig- mented nerve eells. It begins below, at the upper border of the pons, and it extends upwards into the subthalamie region. Its margins eome to the surface at the oeulo-motor and lateral sulei, and its medial part is traversed by the emerging fibres of the oeulo-motor nerve. The surface turned towards the tegmentum is concave and uniform ; the opposite surface is convex, and is rendered highly irregular by the presenee of numerous slender prolongations of its substanee into the basis peduneuli.

Basis Peduneuli (O.T. erusta). — The basis peduneuli is somewhat ereseentie when seen in seetion, and stands quite apart from its fellow of the opposite side. It is eomposed of a eompaet mass of longitudinally direeted nerve fibres whieh

5IO THE BRAIN

are earried upwiirds into the intenial eapsule. The inter- niediate third or more of eaeh basis peduneuli is eomposed of the \mpor\ZT\l (erebro-spinal /asdeulus {O.T. fyramidal trad) as it deseends from the motor area of the eerebral coTtex, but this is quite indistinguishable from the portions of the erusta whieh lie on either side of it

qiiadngcmLiuL body

Vlti. aii. — TranEvcrsc seelion ilirough the Meseneephalon al the 1evel of Ihe mfcr[or qua(lrigcniinal body : the right side only is reprodueed. The ilrawing is taken fn}m a Weigert-Pal speeinien, and therefore the grey in.itter is pale and the strands of white matter are datk. Tbe dark eolotir of the substanlia nigra is nol eyident owing to the Ihinness of the seelion.

Tegmeiitiun. — Unlike the basis pedtaneuli, the tegmentum

is undWided, a faint hne in the median plane, termed the median rapke, alone indieating its bilateral eharaeter. To- wards the dorstim of the meseneephalon it is fused with the bases of the eorpora quadrigemina, and its lateral suiTaees only are free.

The tegmentum is eomposed of an admixture of giey and white matter, eonstiluting what is termed a fei-matie rtlindaris. The while matter is conii>oacil of iibres ninning both tiansvcise]y and longitudinally. Ceitain

THE MESENGEPHALON 511

of the longitudinal fibres are grouped t<^ether and form well-marked traets, whieh, in aseetion through the meseneephalon of a fresh brain, (an be deteeted by the naked eye. These traels are ; (l) the medial longi- tudinal bundles ; (j} the braehia. conjuncliva ; (3) the lemniseus.

The medial longitudiiud bundle (Figs. 211 and 212) is a small eompaet fasciculus whieh is plaeed upon the lateral aspeet of the lower portion of the eentral grey raattei of the aqueduct.

The bra'.hia c0nfunftiva (O.T. stiperior (irebdlar pedundes) are two

G. 212.— Seetion through upper parl of Meseneephalon al level of supei quadrieemmal liody. The drawing is taken frora a Weigert-Pal speeim The dark eolour of the Bubstaulia nigra is nol evidcnt owing (o

large stiands whieh are eontinued upwards from the eerebellum inlo the meseneephalon. 6y pulling away the raorgin a{ the eerebetlum, where it overlaps the lower quadiigeminal bodies, these biaehia W)!l be seen on the suriaee as they converge in an upward direetion. Stretehing aeross the interval between them, and bringing them into eontinuity with eaeh othei, is 3. thin lamina ealled the anterior medullary ve]um. When the braehia conjunctiva leaeh the bases of Ihe inferiot quadrigeminal bodies, they sink inlo Ihe substanee of the meseneephalon, and, in a traiisverse seetion through the lower part of ihis poitiou of the brain, they may bc seen as two white strands, semilunar in outline and plaeed one on either side of the grey matter of the aqueduct. As they aseend, they gradually assume a deeper (i'.e. a mote ventral) position in Ihe tegmental part of the mesen-

512 THE BRAIN

eephalon, and they deeussate with eaeh other aeross the median plane anJ proeeed upwanls to the red nuelei.

•The term Umniseus {iy.'Y, JUUt) is given to two traets presenting very di^Terent eonneetions. The medial Umniseus (Figs. 21 1 and 212) is a sensory traet passing upwards to the thalamus. The UUeral Umniseus t>elongs to the auditory apparatus, and is a part of a ehain throiigh whieh the eoehlear nuelei estabhsh eonneetion with the inferior quadrigeminal t)o<ly and the medial genieulate body. The lateral lemniseus ean be readily detectc<l as it emerges from the upper part of the lateral suleus of the mid-brain, and passes, postero - superiorly, to the lower border of the inferior (luadrigeminate body and inferior braehium. It has the form of a raised triangular band whieh eneireles the lateral surface of the upper end ()f the braehium conjunctivum (Fig. 221).

Within the upper part of the tegmentum there is a eolleetion of nuelear matter whieh is termed the nudeus ruber^ from its ruddy appearanee when seen in seetion. It is rod-like in form, and extends upwards into the tegmental region below the thalamus. In transverse seetion it presents a eireular outline, and it is elosely assoeiated with the upward prolongation of the fi])res of the braehia conjunctiva eerebelli. The braehium conjunc- tiyum eerebelli is an efferent traet from the nueleus dentatus of the lateral hemisphere of the eerebellum, and its tibres end in the red nueleus and the pulvinar of the thalamus of the opposite side. The t^^entum of the i>edunculus eerebri may be eonsidered to eonsist of two parts : vi«., a l<nver piti^ whieh is subjacent to the inferior quadrigeminal bodies, and is largely oeeupied by the deeussation of the braehia conjunctiva eerebelli ; and an upper part^ subjacent to the superior quadrigeminal b<xlies, whieh is traversed by the emerging bundles of the third nerve, and eontains the nueleus ruber.

BASAL GANGLIA 0F THE GEREBRAL

HEMISPHERES.

The basal ganglia of the eerebral hemispheres must now be examined. They are the eaudate and lentiform nuelei, whieh together forpi the eorpus striatum ; the elaustnim ; and the amygdaloid nueleus. With these it is neeessary to study also the eomposition of the thalamus and the extemal and internal eapsules.

Disseetion. — The right and left portions of what remains of the eerebrum should be separated from eaeh other by a median ineision. On the left portion the sulei and gyri on the lower surface of the hemisphere may be examined, if this has not been done already on another speeimen.

A series of seetions should, in the next plaee, be made through both the riglit and left portions of the eerebrum, with the view of displaying the basal ganglia. On the right side remove a sueeession of thin sliees by earrying a long knife in a horizontal direetion through the parts whieh form and lie below the floor of the eentral part of the lateral ventricle. It is not advisable to proeeed farther down than the level of the anterior eommissure.

On the Ieft side of the brain a series of vertical-transverse or frontal seetions should be made through the remaining portion of the eerebrum.

BASAL GANGLIA SU

B^n by eutting off the portion anlerioi to the head of the eaudate nueleus, and then proeeed posleriorly untii the posterior part of the thalamus is reaehed. One of the seetions should be planned lo pass thiough

Nuelens Gaadatus. — This nueleus has already been partly examined in eonneetion with the lateral ventricle, into the

cavity of whieh it bulges. It is a piriform highly arehed mass of grey matter, whieh presents a thiek swollen head or anterior extremity, and a long attenuated tail. The head projects into the anterior horn of the lateral venlricle, whilst its narrower part is prolonged laterally and posteriorly on the iioor of the eentral part of the yentriele, where it is separated from the thalamus by the stria terminalis. Finally, its tail turns downwards and then anteriorly into the inferior hom

YOL. II — 33

514 THE BRAIN

of the lateral ven£ricle, on the roof of whieh it is prolonged until it finally joins the amygdaloid nueleus. The eaudate nueleus, therefore, presents a free ventricular surface covered with ependyma, and a deep suriaee embedded in the sub- stanee of the hemisphere, and for the most part related to the internal eapsule.

Owing to its arehed fomi, it follows that in horizontal seetions, below a partieular level, it is eut at two points, and both the head and the tail must be looked for in the field of

)ii ihrough Ihe Proinal l^^bes of the Cerebrum, The srior p.Trt of the eerebrum is depieled so thBI 1G anterior homs of the L-Lteral ventricles from

seetion (Ftg. 213). In frontal seetions posterior to the amyg- daloid nueleus it is also divided at two plaees.

Nneleus Leiitifonni3. — 'l'his mass of grey matter lies on the lateral side of ihe eaudate nueleus and the thalamus, and is, for the most part, eompletely embedded within the medullary substanee of the eerebral hemisphere. It does not oeeupy so large an area as the nueleus eaudatus. Indeed, it presents a very elose eorrespondenee in point of estent with the insula on the surface.

When seen in horizontal seetion (Fig. 213) it presents a shape similar to that of a biconvex lens. Its medial suTface

BASAL GANGLIA 515

bulges more than the lateral suriaee, and its point of highest convexity is plaeed opposite the stria terminalis or the interval between the eaudate nueleus and the anterior end of the thalamus.

When seen in frontal seetion, the appearanee presented by the ]entifonn nueleus differs very mueh in the different planes of seetion. Pigure 215 represents a seetion through

Corpu£ ealloAum Lc1ngiludi11.1l lissure

ir pari of Ihe lenliibrm nueleus. Seen fr

r portion. Here it is semilunar or ereseentie in outline. Further, it is intimately eonneeted with the head of the eaudate nueleus by bands of grey matter whieh pass between the two nuelei and break up the anterior part of the internal eapsule. It is due to the ribbed or barred appeae- anee whieh Is presented by sueh a seetioD as this that the term eorpus striatum is given to the two nudeL

When the seetion is made in a more posterior plane, the divided lentifonn nueleus assumes an altt^ether different shape, and is seen to be eompletely cut off fn)m the eaudate

5i8 THE BRAIN

it thiekens eonsiderably, and at the base of the brain it eomes to the surface, at the substantla perforata anterior, and beeomes eontinuous with the grey matter of the eerebral cortex. Its extent eorresponds very nearly with the area oeeupied by the insula, and its lateral surface shows ridges and depressions eorresponding to the insular gyri and sulei.

Oapsola Intetna.— This term is applied to the broad band of white matter whieh intervenes between the lentiform nueleus laterally, and the thalamus, stria terminalis, and eaudate nueleus on the medial side. Anteriorly it is mueh

■nal eapsule

d Pyramidal Fib»es.

broken up, by the eonneeting bands of grey matter whieh . pass between the bead of the eaudate nueleus and the anterior part of the putamen of the lentiform nudeus (Fig. 215), but more posieriorly it forms a solid white mass of nerve fibres. When seen in horizontal seetion, the intemal eapsule is bent upon itself opposite the interval between the eaudate nueleus and the thalamus (Fig. 216). This bend, whieb points medially, is ealled the genu. About one-third of the internal eapsule lies anterior to the genu, and this part is ealled the anlerior limb; the remaining two-thirds, whieh lie posterior to the genu, eonstitute l)\& posterior limb.

OonneetionA of the Intemal Capaiile. — 1'he internal eapsule is direetly eontinuous below with the basis of the eerebral

BASAL GANGLIA 519

pedunele. The disseetor ean easily satisfy himself in the speeimens before him of this eontinuity ; it is apparent in the more posterior of the frontal seetions whieh he has made through the left portion of the eerebnim.

It has been mentioned already that the fibres whieh oeeupy the middle third or more of the basis of the eerebral pedunele belong to the motor eerebro-spinal fasciculus. In the internal eapsule these fibres oeeupy the anterior two-thirds of the posterior limb, being thus plaeed immediately posterior to the genu. The fibres whieh eonstitute the medial third of the basis peduneuli eome from the anterior limb of the internal eapsule ; whilst the fibres whieh form the lateral third of the basis peduneuli are situated in the posterior limb.

When the fibres of the internal eapsule are traeed upwards, they are found to spread out in a radiating manner so as to reaeh the various gyri of the eerebral hemispheres. This arrangement is termed the eorona radiata. As the fibres of the eorona radiata are liberated from the internal eapsule, and spread out to reaeh their destinations, they are interseeted by fibres of the eorpus eallosum, whieh also radiate in every direetion to gain the cortex of the eerebrum, and they are inter- seeted also by bundles of assoeiation fibres.

Nuelei of the Thalamus. — When a horizontal seetion is made through the thalamus in a fresh brain, or in one whieh has been preserved by means of formalin or a ehromie salt, the grey matter eomposing it is seen to be broken up into a lateral, a medial, and an anterior nueleus by thin white medullary laminae.

Oapsula Extema. — This term is applied to the thin stratum of white matter whieh intervenes between the lentiform nueleus and the elaustrum (Figs. 213 and 216).

Disseetion. — The fasciculus thalamo-mamillaris and the anterior eom- missure should now be foIIowed, as far as this is possible, in what remains of the right half of the eerebrum. The disseetion is not difiicult.

By the removaI of the remains of the lentiform nueleus the anterior eom- missure will be exposed in its eourse towards the temporal lobe. In the first instanee, it passes transversely, then postero-laterally below the putamen. Next it bends suddenly in a posterior direetion above the inferior horn of the lateral ventricle to reaeh the meduUary eentre of the temporal lobe. If the disseetion be successfully aeeomplished, the anterior eommissure will be seen to present a twisted or rope-like appearanee.

The fasciculus thalamo-mamillaris may be traeed (rom the eorpus mamillare upwards into the anterior nueleus of the optie thalamus by seraping away the grey matter on the side of the third ventricle. The eontinuity between the eolumn of the fornix and the eorpus mamillare should at the same time be established. Within the eorpus mamillare there is a nueleus of grey matter.

The disseetors have now examined all those portions of the brain whioh

lie in the anterior and middle eranial foss3e, and eertain terms, not hitherto

mentioned in eonneetion with the various struetures whieh have been

studied, now require eonsideration. It has been noted already that the

II— 33^/

S20 THE BRAIN

part of the brain whieh eonneets the lower segment in the posterior fossa with the upper segment in the middle and anterior fossa is ealled the meseneephaloiL The parts above the meseneephalon form collectively the proseneephalon, and the meseneephalon and proseneephalon together eonstitute the eerebnim.

The proseneephalon itself is separable into two main parts, the teleu- eephalon (end brain), and the dieneephalon. The teleneephalon ineludes the eerebral hemispheres with their grey nuelei, the olfactory bulbs and traets and the assoeiated parts, and the pars optiea hypo- thalami; under the latter term are ineluded the tuber einereum, the infundibulum, the hypophysis, the optie traets, the optie ehiasma, and the lamina terminalis.

The dieneephalon ineludes two elosely assoeiated segments, the pars mamillaris hypothalami and the thalameneephalon,

The pars mamillaris hypothalami is formed by the mamillary bodies and those portions of the walls of the third ventricle whieh lie below the suleus hypothalamieus. The thalameneephalon is separated into the thalamus (O.T. optie thalamus)^ the metathalamus, formed by the two genieulate bodies, and the epithalamust whieh eonsists of the pineal body, the habenula, the habenular eommissure, and the trigonum habenulae.

THE PARTS 0F THE BRAIN WHIGH LIE IN THE POSTERIOR GRANIAL FOSSA.

The parts whieh lie below the tentorium eerebelli in the posterior eranial fossa are the medulla oblongata, the ponSy and the eerebellum. These are grouped around the /ourth ventricle of the brain — a cavity whieh eommunieates with the eentral eanal of the meduUa spinalis below and with the aquceductus eerebri above ; and they eonstitute the rhomben- eephalon or hind brain.

Medulla Oblongata. — This is the eontinuation of the spinal medulla into the brain. It is not more than one ineh in length, and may be reekoned as beginning at the level of the foramen magnum. Thenee it proeeeds upwards, in a very nearly vertical direetion, and ends at the lower border of the pons. At first its girth is similar to that of the spinal medulla, but it rapidly expands as it approaehes the pons, and consequently it presents a more or less eonieal appearanee. Its anterior surface lies in the groove on the basilar portion of the oeeipital bone, whilst its posterior aspeet is sunk into the vallecula of the eerebellum.

The medulla oblongata is a bilateral strueture, and this is evident even on an inspeetion of its exterior. The antero- median and postero-median sulei on the surface of the spinal

MEDULLA OBLONGATA 521

medulla are prolonged upwards on the anterior and posterior Euriaees of the medulla oblongata.

The antero-median groom, as it passes from the spinal medulla on to the meduUa oblongata, is interrupted, at the leve] of the foramen magnum, by several strands of fibres whieh eross the median plane from one side to the other. This intererossing is teraied the deeussation of the pyramids. Above this level the furrow is earried upwards to the lower

border of the pons, There it expands slightly, and ends in a blind pit, termed tiie/orat»en eaeum.

The postero-median fissure is eaTried up for only half the length of the meduUa oblongata. Then the eentral eanal of the medulla spinalis beeomes the fourth ventricle of the bratn, and as it expands dorsally it pushes aside the lateral lips of the posterior median suleus till the epithelium of its posterior wall appears on the surface, in the triangular interval between the diverging posteiior eolumns of the medulla oblongata,

522 THE BRAIN

where it forms the posterior wall or roof of the lower part of the fourth ventricle.

The surface of eaeh lateral half of the meduUa oblongata should now be studied. It is well, however, to defer the examination of the meduUary part of the floor of the fourtb ventricle till a later period. The disseetor has already notieed two linear rows of nerve fila issuing from and entering the medulla oblongata on eaeh side. The anterior row eonsists of the roots of the hypoglossal and the uppermost part of the anterior root of the iirst cervical nerve. They eontinue up- wards on the meduUa oblongata in the line of the anterior nerve roots of the spinal medulla, and they emerge along the bottom of a more or less distinet groove. T\\t. posterior row is formed of the nerve fila of the aeeessory, vagus, and glosso-pharyngeal nerves, and they lie in series with' the posterior roots of the spinal nerves.

By these two rows of nerve fila, eaeh side of the medulla oblongata is divided into three distriets, viz., an anterior, a lateral, and a posterior, similar to the surface areas of the three funiculi on the side of the meduUa spinalis. At first sight, indeed, they appear to be direet eontinuations upwards of those portions of the spinal medulla ; it is easily demonstrated, however, that that is not the ease, and that the fibres in the three funiculi of the medulla spinalis undergo a rearrangement as they are traeed into the medulla oblongata.

Anterior Area of the Medulla Oblongata — Pyramis. — The distriet between the antero-median furrow and the row of hypoglossal nerve fila issuing from the meduUa receives the name of the pyramid. An inspeetion of the surface is almost sufficient to show that this is formed by a eompaet mass of longitudinally direeted fibres. It expands somewhat, and assumes a more prominent appearanee as it passes upwards, and, finally, reaehing the lower border of the pons, it beeomes slightly eonstrieted and disappears from view by plunging into that strueture. The pyramids are the great motor strands of the medulla oblongata.

Although the pyramid, at first sight, appears to be the eontinuation upwards of the anterior funiculus of the spinal medulla, it eontains within itself only a very small proportion of fil)rcs whieh oeeupy that funiculus. This will be at onee manifcst if the deeussation of ihe pyrainids is examined. For this purpose introduee the baek of the knife-blade into the

MEDULLA OBLONGATA

523

antero-tnedian furrow below the deeussation, and on one side push in a lateral direetion the anterior funiculus of the medulla spinalis. The pyramid will then be seen to divide into two portions, vlz., a small strand termed the fasciculus eerebro- spinalis anttrior (O.T. direet pyramidal trac(), whieh proeeeds downwards into the anterior funtculus of the spinal medulla

elose to the antero - median furrow, and a mueh larger strand ealled the /aseieulus eerebrospinalis lateraiis (O.T. erossed pyramidal traet), whieh, at this level, is broken up into three or more eoarse bundles whieh sink posteriorly and, at the same time, eross the median plane to take up a position in the opposite lateral funiculus of the spinal meduUa, elose to the posterior eolumn of grey matter. It is the inter- orossing of the eorresponding bundles of the fasciculi eerebro-

5^4 THE BRAIN

spinales laterales of opposite sides whieh produees this ehai

aeteristie deeussation.

But if the laseieulus eerebrospinalis anteiioi of the anteiior funiculiia of the £|una1 meduUa is alone represenled in the eorresponding distriet of the raedullaobloneata, it maybeasked: What beeomes of Ihe krger lateral part of theantetiorTunieulusorthe spinal medulla in tbe medulla oblongala ? It is ihrust aside by Ihe deeussating bundles of the fasciculus eeiebrospinalia laierniis, and thus eomes lo oeeupy a deep positlon in the medulla oblongata.

Lateial Area of the Mednll» Oblongata. — ^This is the distriet on the surface cf the medulla oblongata whieh is ineluded between the two rows of nerve fila, viz., the hypo- glossal fita anteriorly, and the fila of the accessor>', vagus, and glosso-pharyngeal posteriorly. It presents a very different appearanee in its upper and lower parts. In its lower portion it appears to the eye as a eontinuation upwards of the lateral fumculus of the spinal medulla ; in its upper part is seen the striking oval prominenee named the olive.

The lower part of this distriet, however, is very far from

MEDULLA OBLONGATA 515

being an exact eounterpart of the lateral funiculus of the spinal medulla. It has been noted already that the large fasciculus eerebrospinalis lateralis, whieh in the spinal medulla lies in the lateral funiculus, is not present in that distriet of the medulla oblongata ; above the deeussation of the pyramids it forms the chief part of the pyramid of the opposite side. Another small strand of fibres, the /aseieulns etrebellospinalis (O.T, direet eerebellar trtsei), prolonged upwards in the lateral

^iuadrkgeoimii] body

or ihe Medulla Oblotigata. Poiu, and Mesoi- : K(etU5. The grealer pait ti Ibe nxrf of Ibe

rouilh venlrLcle is lemoyed.

funiculus or the spinal medulla, gradually leaves this poTtion of the medulla oblongata. This traet of Gbres Hes on the surface, and it is often yisible to the naked eye as a white streak inelining obliquely into the posterior dUtriet rf tbe medulla oblongata to join its uppet parl, i.e., the re*tifonii body. The great majority of the remairider of the fitirct whieb are prolonged upwards from the lateral funiculitt of the spinal medulla disappear from the surface at the lower border of the olive, by dipping into the substanee <»f the meduila oblongata under cover of that projection. A nairow band, however, is earried upwards to the [Kins, in the inteml

526 THE BRAIN

between the posterior border of the olive and the fila of the vagus and glosso-pharyngeal nenres.

The olive is a smooth oval projection, whieh oeeupies the upper part of the lateral area of the meduUa oblongata. Its long axis, whieh is vertical, is about half an ineh long, and its upper end is separated from the lower border of the pons by an interval or groove.

Posterior Area of the Mednlla OUongata. — In its lower half this region is formed by the euneate and graeile funiculi ; and in its upper half it is formed, medially, by the ependymal roof of the fourth ventricle and, laterally, by the diverging funiculi.^ It is separated from the lateral area on eaeh side by the row of fila belonging to the aeeessory, vagus, and glosso-pharyngeal nerves.

The lower part of the posterior area eorresponds more or less elosely with the posterior funiculi of the spinal medulla. It will be remembered that in the cervical part of the spinal meduUa the posterior areas on eaeh side is divided by a distinet septum of pia mater into a postero-median strand and a postero-lateral strand. These are prolonged upwards into the medulla oblongata, and in the lower part of the posterior area they stand out distinetly, and are separated from eaeh other by a eontinuation upwards from the medulla spinalis of the postero-intermediate suleus. In the medulla oblongata these strands receive different names. The medial one is ealled the /unieulus graeilis, whilst the lateral one is designated the /unieulus euneatus. Eaeh of these strands, when it reaehes the lower part of the fourth ventricle, ends in a slightly expanded prominenee. The swollen extremity of the funiculus graeilis is ealled the clava ; it is thrust aside from its fellow of the opposite side by the opening up of the eentral eanal to form the fourth ventricle. The thiekened end of the euneate funiculus receives the name of the tubenulum einereum, but it is in the young brain only that it is well marked.

In seetions through this region of the meduUa oblongata, it is seen that the prominenees produeed by the two strands and their enlarged extremities are in a great measure due to the

' Tlie disseetor should note that the lower part of the cavity of the hind- l)riii», i.e. the fourth ventricle, is not behind but in the upper part of the ineehilla, whieh it separates into dorsal and ventral parts ; the dorsal part forms a portion ()f the roof of the ventricle, whilst the ventral pait forms a portion of lh<' lloor.

MEDULLA OBLONGATA 527

presenee of two elongated nuelei, whieh lie subjacent to them and gradually inerease as they are traeed upwards. These are termed the graeile and the eumeate tnulei, and it ean easily be shown that as the grey matter inereases in quantity the fibres of the two eorresponding strands diminish in number. Indeed, it is doubtful if any of their fibres are prolonged upwards beyond the level of the nuelei.

But a third longitudinal elevation also is apparent in the lower part of the posterior area of the medulla oblongata. This is plaeed on the lateral side of the fimiculus euneatus — between it and the posterior row of nerve fila — and it has no eounter- part in the posterior funiculus of the spinal meduUa. It is ealled the /unieulus of Rolando^ beeause it is produeed by the substantia gelatinosa Rolandi approaehing the surface. Extremely narrow below, the funiculus of Rolando widens somewhat as it is traeed upwards, and it, finally, ends in an expanded extremity ealled the tuberde of Rolando. The thin layer of fibres whieh appear on the surface of the tuberele and funiculus of Rolando and cover the substantia gelatinosa Rolandi in this position belong to the traetus spinalis (O.T. spinal root) of the trigeminal nerve.

The restiform body forms the upper part of the posterior area on eaeh side. It lies between the lower part of the floor of the fourth ventricle and the fila of the vagus and glosso-pharyngeal nerves, and is thrust laterally by the en- largement of the fourth ventricle. It is a large rope-like strand, whieh inelines upwards and laterally, and then finally takes a turn posteriorly, and enters the eerebellum, of whieh it eonstitutes the inferior pedunele, The restiform body, there- fore, is to be regarded as the main eonneetion between the eerebellum, above, and the medulla oblongata and medulla spinalis below. At the same time, it must be understood that it is not formed of fibres whieh are prolonged into it from the funiculus graeilis and funiculus euneatus of its own side. It is true that a surface inspeetion of the medulla oblongata might lead very naturally to this supposi- tion, beeause there is no sharp line marking it ofF from the tubereles of these strands.

The fibres whieh build up the restiform bodies eome from several differ- ent sourees. It will be sufficient to indieate the more important of these — ( I ) from the lateral funiculus of the spinal medulla through the fasciculus eerebellospinalis ; (2) from the eerebellum as the cerebello-clivary fbres

f2>, THE E1L\IX

*

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>/*':: v.r<ii«r.'' ^: t;.^ '/:v^ 2. r. -=:_'' er ^.t eirTed beisdles oT tibres^ UrTte,*/: tr.': txUrnal ar:uaU fJri:, slit be ooiieedL They vary jfr':s*iv i.'i r.u.T.'ir:!' ar.'i :n eisdnetness. and aie some- tirn'r^ \'> nf;rr»ero*i- a.^ :o ccver t'r.e olrre alniost endrely. Ari 'A\'^jiT\ivi*i ';xarr.:r.a::or. wil: s'r.ew :hat they eome to the virinfJ: in th'; an:ero-rr.ecLar. nssure between the pyiamids^ ifi rh': ;?roove ly:t-A';en :he p}Tin::d and the oliTe, and some- tirri':-; al-.o thr^K^r, the su'r/stanee of the prramidsu Biit at wh;it,'rv':r f//in'. t;.ey reaeh the 5i:rfice, the majority have one /|':^tination, vi/„, the re5:iform body — a eonsiderable part of whi^h th«:y forrn. They are derived from the etmeate and yx:%<'\\*: nu^Iei of the opjj05ite side.

/hr.rrtion. Th': y/rsLTT.'A of or** side shouW now bc carefnlly raised. \Vh'f» '\i.\'/\\f;-*\ U'mu\ irs r/Td i*. .should be ger.tly pnilled npwaids towaids \)it' ytU'.. Iri rhis way its er.tranee into the pons is brooght yeiy t\fnf\'/ irito '/]<:%'. I'iirth'rr, nuiTierous areuate fibres will be seen riMiniMi^ ;irit':riorly u^^^^ri th': m'rdial aspeet of the opposite pyramid to r<-»' h tii<; '.wii'A',*:, and th': vcntral edge of the medial lemnisens will be

«■/J/'/i''d ;ilv;.

Ponn. The i>ons is the marked prominenee on the base of th^: hr;iin whieh is interposed between the meduUa ob- ion^^'ita i\x\i\ \\\i: peduneuli eerebri, and lies anterior to the r<rnThf!llurn. It is convex from side to side, as well as antero- p';iitrriorly, anrl the tran.sverse streaks on its surface show th;it, siip(:rrH:i;illy, it is eomposed of transyerse bundles of n<Tvi: lil)n:s. r)n either side these transverse fibres eoUeet thrnis(:lv(:s togother to form a large eompaet strand whieh sink:i |)ostcro l.'ilerally into the eorresponding hemisphere of thr r;crr:h(:lhim. This strand is termed the braehium ptmtis (O.T. tniddle eerebellar pedunele).

TIh: v(:ntnil surfacc of the pons is in relation to the basilar portion of the oeeipital bone and the dorsum sellae of the ;,phrn()i(l hone. It |)rcsents a median groove whieh gradually widens ;js it is traeed upwards (Fig. 219). The groove |(»(lj'r:i ilu' hiisihir artery, but is not cause(i by that vessel; it is (liK' to the prominenee produeed, on either side, by the pass:jg(: downwards through the pons of the bundles of lihres whieh form the pyramids of the meduUa oblongata.

GEREBELLUM 529

Where the pons beeomes the braehium pontis the large trigeminal nerve will be seen entering its ventral surface, nearer its upper than its lower border.

With the exception of the restiform bodies, the whole of the medulla oblongata enters the lower aspeet of the pons, and its eonstituent parts are earried upwards within it. The peduneuli eerebri emerge from its upper aspeet. The dorsal surface of the pons eannot be studied at present. It is turned towards the eerebellum, whieh hides it from view, and it forins the upper part of the anterior boundary or floor of the fourth ventricle.

Cerebelliiin. — The eerebellum is distinguished by the numerous parallel and more or less curved sulei whieh traverse its surface and give it a foliated appearanee. As in the ease of the eerebral hemispheres, the grey matter is spread over the entire surface, whilst the white matter forms a eentral eore in the interior.

The eerebellum eonsists of a median portion, the vermts^ and two lateral kemispheres, The distinetion between these main subdivisions of the organ is not very evident on its superior surface. Anteriorly and posteriorly there is a marked deficiency or noteh in the median plane (Fig. 223). The posterior noteh is smaller and narrower than the anterior noteh. It is bounded laterally by the posterior parts of the eerebellar hemispheres, and anteriorly by the vermis, and it is oeeupied by the falx eerebelli. The anterior noteh is mueh wider and, when viewed from above, it is seen to be oeeupied by the inferior pair of quadrigeminal bodies and the braehia conjunctiva eerebelli. Its sides are formed by the lateral hemispheres, and the posterior end is bounded by the vermis.

On the superior surface of the eerebellum there is little distinetion to be noted between the vermis and the upper surface of eaeh lateral hemisphere. The upper surface of the vermis forms a median elevation, from whieh the surface slopes gradually downwards, on eaeh side, to the margin of the hemisphere. On the upper surface of the vermis four regions are reeognise.d. Anteriorly, at the posterior end of the anterior noteh, lies the eentral lobe^ and prolonged up- wards from it on the dorsal surface of the anterior meduUary velum, between the braehia conjunctiva, are a few folia whieh eonstitute the lingula, Posterior to the eentral lobe is the montieulus^ separable into two parts — an anterior elevated end,

VOL. II — 34

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\\ V'.': :.'.■:':■..'. '.:' :■.-: -.-:rr.-.:.=. where ic form5 the posterior '.',.-,':,:/ '/' : :. •: j .', : --: :.'.': r. o :cr. on the superior 2sgccX of ':.•: ''::':^r:!. ..-.'.. V. 's-,r.\..- raiied. and a: rhe same time the rr.'-.'r.^- ;i:.;il'..'. :": :, .!!-:C ar.^er-^rly, t^o stninds lying upoD ^r.': '\'»r:\. '\.\r/,\ r,f ::.,; prr.s will be seen. These aie ':.': hra hia ':onjun',H'.t e^.rdt^li (O.T. supirior pedumdes). 'I ;.'■;/ « ::.f:r;.^': ^.'o.r, ::.-: u'hire rr;a::er of tbe eerebelluiii, i ux\-i*'.'j*\ .']■, r.:.-:y \,:'/.-.i:(\ upwards, and. finally, they dis- :i;,:,' -ir .'.':-:: rr.-': \r'SKr/ti ciiadri£en:inal bodies. The thin l;nfii[i:i •//:.>.,'. ., .\:f:\(\\i:<\ aoros.s i^etween them is the anterior medu/hiry ^^ium. Jt :-: r.ontin'^ous below with the white eore t\ *\i'- vf ::::.:., &:.'! !: r.elps :o form the roof of the upper ]r.iT\ fA :};■: f'/.rr:. V';ntncle. From its dorsal surface, dose '.', M.': ;rif-r!^r '':-j'].driL'r;rriiria: bodv. the small troehlear nerres

t

f u,' T'/*-.

(',trv.i\tt of tli'; sui'';i which traverse the surface of the ' ' r'-l/ ■lliirn, fl':':p^-r rmd longer than the others, map out d I , » r I ^ ! ■ . ■.'/ 1 j i ^ 1 1 ;iTf: 1 0 r rr. rjd lobe 5. Th e most eonspieuous of ,il! ili'-','- f.\<-U.\ is i\if: j^''re'7/ }ioriz'''ntai sulais.

Orrsat Horizontal Suleus of the Cerebellnm. — The great li'.n/.'intril '.nlr.u.'s brgin.s antL-riorly, and passes round the ' II' \\\\\W\t'\\f'A'. f)i the r.erehellum. rutting deeply into its lateral ;iii'l j;o'.t<fior ni.'irp.Mn'.. .\ntcriorly. its lips diverge from eaeh

' ■. . im . I /!'.!.<■ l'.'- •■: »;•.!.■.■! i.-i' r" :'f c:' !:'.■• :" ■.:■■:]: v-i'trio!o and its co\-ering 1,1 |,ii iii.it. r mII 1h- t'ir;. :: .v-:y. :.n.l t:-.o '.OA«r p.v: of the tloor or anterior l.'.iiii'l II ■,■ i,i ih'- l'/;iftli ^.■iilrie!'^ \vi!I lio i-.i.-p'.ayoil.

GEREBELLUM

53'

other so as to enibraee the lai^e braehia pontis {O.T. middle peduneles), where they pass into the interior of the eere- bellum, The great horizontal suleus divides the eerebellum into an upper and a lower part, whieh may be studied separately.

IiObBB on tha Upper Snrtaee of tli« eaiebellum.— It has l)een noled already that ihe upper surface of the verTnis superiot is sulKlivided. The divisions eommeneing from Ihe anlerior end are ;— (i) 'he lingula ; (z) the eenlral lobule ; (3) the eulmen montieuli ; [4I ihe dec1ive montieuli ; (5) ihe folium vermis, With the exception of the lingula, eaeh of these is tx

on eilher sido wilh a eorresponding distriet on the upper sut&ee of the hemi- sphere, and forms wilh these distriets a eerebeltar lohe. Thus, the eenual lohule h prolonged tateTally on eaeh side in an expansion ealled the ala ; the eulmen eonstitutes a median eonneeting pieee between the two atiitrior eresieiitie lobules ai the hemL'ipheres ; the declive stands in the same relation tii the posterior ertseentie Mults ; and the folium vermis is the eonneeting haml lietween ihe superior semilunar lotules of the hemispheres.

LingalB. — The lingula ean \x seen only when the posterior boundary of the antericff noteh is pushed posteriorly. It eotaists of four or five smalt fii1ia, eontinuous with tlie grey niatter of the vermis, prolonged anteriorly on the surface ur the anterior medullary velum, in the interval tietween Ihe hraehia conjuncliva.

Lobna eentraUa wlth ita Al». — The eentral tohule lies at the posterior

::,; THE BRAIN

■■■.■. r:::-i'.-'i :• ■■.:!!. uni: i^ Ittrgely luddeo by the eolinen. Il is »

-■ -. .e'. :r.:.~> H;:i'.h it ;>; 1 -n^ed lalerallj f<ii a Ehort distaiiee romld

■■■•"..■::■ :■.}. ;:. -.he f ■im '.■( \v.' ex;iansi[>iis. termed tbe ala.

Lobui eolliiiBit. -The ru.'Ken tKimiimli eeinstitntet I}]C snmmit oc

d laterall; oa

r<; run

vl.ii:li il i. t,.:]iiira''''l l.y a. ilistiiiel tissure, an<! il ftinns th« 5lo|»iig part or \i-,i-\,\ i,f tli': iiiiinlieulus '>f Ihe verinis. On eaeh side il is eontinuotu lilli \\v /■ir.lrriiir rreseeiiti' lobuli o( the lateral hemisphere, and the three

'l'lir iw" i^rr^-iiilii: liiliuluii 'in Iho u]i]icr Biirfari; <if the hemiBphere are ■ ■■.|ii.-Mlly 'l.-«:rilii:'l Hn,n:lli.r nj ihu .piadrale lahii/e.

l.nliua SemilntiaTis Superior (O.T. lobus eaeuminii),— The />^ibih '.■)/«/, r.iiiiis l)ii: iii..ht [Kisluri'ir imrt of Ihe svif>eri(ir porlion of the ''■niii,, :iii.l ii li.inn'l.s liie jjr«il lioriHintal Bssure, superiorly, at the iiisiiii.ir ii.iii'li. [1 Ik a siiiRle foliuni, the surface of whieh niay be iii..'illi .11 l.i^vt willi ru'limenlary seeondnry f(>liit, nnd il is the eonnee" iiiL l.ilw.i'ii tlit iwo stiperior seiiiHuiiar lebiile! of Ihe hemisphen

GEREBELLUM 533

Ihe three parts eonstituting the lobus stpiilimaris supiriar. As the folium Yermis is traeed laterally inlo the semilunar lobule of Ihe hemisphere, it is round to expand greatly. The result of this is thal Ihe lobug semilunaris superior on eaeh ^e forms an extensive foliated distriet bounding ihe posterior part of the great horizonlaI suleus superiorly.

LobeB ou the imd«r Bnrfacs of the eereballtLm.— The eonneeiion between the several porlions of the inferior part of ihe yeimis, and Ihe eorresponding dialriets on the under surface of ihe two hemispheres is not nearly so distinet as in the ease of the superior part of the vermis and ihe lobules on the upper surface of tbe heniispheres.

Proeeeding poslero-anteriotly the following subdiTisions of the inferior

on Ihe braehium ponti 2 he * nt al Ubule, whieh Hes immediately

whieh traverses its surface ; (3) the tomil, a lounded lobule, Ihe vallecula on the medial side of the biventTaI lobule ; (4) the in/erisr semiluaar laiule, plaeed posterior to the biventral lobule, and bounding the great horiiontal suleus inferiorly.

These lobules of Ihe bemispheres, with the eorresponding portions of the inferiot part of the vermis, eonstitute the lobes on the under aspeet of the eerebellum.

Lobua NoduU.—The lobus noduli eomprises the nodule and Ihe Aoeeulus of either side with an exceedingly delieate eonneeting lamina of white matter, termed the posleriBr meduUary velum.

The velum eannol be properly seen at present, but it will be exposed at a later stage of the disseetion.

Lobus UtuI». — The uvula is a triangulai eleyation plaeed between the two tonsils. It is eonneeted aeross the suleus valleculs with eaeh lonsil by a low-lying ridge of grey matter whieh is seored by a few shallow furrows, and in consequence termed \he /urreraied band. The two tonsils and the uvula form the lobus itvuht.

To see the furrowed band it will be neeessary to remove Ihe tonsil on one side, wben ihe poslerior medullary velum also wiU be exposed.

534 THE BRAIN

Loboi "PynmidiM. — The pyramid is eonneeted with the biventral lobule on eaeh side by a faint ridge whieh erosses the suleus ▼alleeula:. The terni /of>iis pyramidis is giyen to the three lobules whieh are thus assoeiateii with eaeh other.

Lobns Tuberis. - -The tuberrermis^ whieh forms the most posterior part <>f the verniis, is com{)ose(l of several folia, whieh run direetly into the inferior semihmar loljule on eaeh side. The three parts of the lobus ttiberis are thus linked to^^ether. The inferior semilunar lobule is traversed by two, or ii may lje three, curved fissures. The most anterior of these euts off a narrow, curved strip of eerebellar surface ealled the lobtdus greuilis,

Disseetion.- A median seetion should now be made through the vermis of the cere1>ellum and the two medullary vela into the cavity of the foarth Yentriele. When the two ])arts of the eerebellum are drawn slightly asunder, a view of the fourth vcntricle is obtained ; further, the eonneetions of the two medullary vela and the arrangement of the peduneles of the ccrolH;Ilum ean be more elearly understood.

Arbor Yit» GerebellL — The eut surface of the eerebellum presents a very eharaeteristie appearanee. The grey matter on the surface stands out distinetly from the white matter in the interior. Further, the eomplete manner in whieh the surface is eut up by the sulei into seeondary and tertiary folia is seen. The eentral mass of white matter in the vermis is termed the eorpus medullare, From this, prolongations pass into the various lobules, and these give off branehes to supply eaeli folium with a eentral white stem or eore. The term arbor vitce is applied to the appearanee whieh consequently results when a seetion is made through the eerebellum.

Cerebellar Pedtmeles. — The eerebellar peduneles are the struetures whieh eonneet the eerebellum with the medulla oblongata, the pons and the mid-brain. They are three in nuniher on eaeh side — viz., the middle, the superior, and the inrerior. They are all direetly eonneeted with the white niedullary eentre of the eerebellum, and are eomposed ot Tibres whieh emerge from or enter the wliite eentral sub- slanee o^ the organ.

The middle pedunde is the braehium pontis, and is mueh ihe largest of the three. It is formed by the transverse fibrcs of the pons, and it enters the eerebellar hemisphere on tlie hiteral side of the other two. The lips of the anterior part o{ the great horizontal suleus are separated widely from eaeli other to give it admission.

Tlie inferior pedunde is simply the restiform body of the nieihilla oblongata. Leaving the dorsum of the meduUa oblongata it turns sharply posteriorly and enters the eerebellum between the other two peduneles.

MEDULLARY VELA 535

The superior peduneles are the braehia conjunctiva of the eerebellum. They are eomposed of fibres whieh eome, for the most part, from the nueleus dentatus of the eerebellar hemisphere. As they issue from the eerebellum, the pedunele lies elose to the medial sides of the eorresponding middle peduneles. They then proeeed upwards towards the inferior pair of quadrigeminal bodies. At first they form the lateral boundaries of the upper part of the fourth ventricle, but they converge, as they aseend on the dorsal aspeet of the pons, so that ultimately they overhang the fourth ventricle and enter into the formation of its roof. They disappear under cover of the quadrigeminal bodies, and their eourse in the meseneephalon has been deseribed already (p. 511).

Medullaxy Yela.. — The medullary vela are elosely assoeiated with the peduneles. They eonsist of two thin laminse of white matter whieh are projected out from the white eentral eore of the eerebellum. The anterior medullary velum stretehes aeross the interval between the two braehia conjunctiva (superior peduneles), with the medial margins of whieh it is direetly eontinuous. It is triangular in form', and is eon- tinuous below with the white matter of the eerebellum. Spread out on its dorsal surface is the tongue-shaped prolonga- tion of grey matter from the cortex of the eerebellum whieh is termed the lingula^ and issuing from its substanee, elose to the inferior quadrigeminal bodies, are the two troehlear nerves.

Hh^posterior medullary velum is somewhat more eomplieated in its eonneetions. It presents the same relatioh to the nodule that the anterior velum presents to the lingula. It is a wide thin lamina of white matter — so thin that it is translueent — whieh is prolonged out from the white eentre of the eerebellum above the nodule. From the nodule it stretehes laterally to the Aoeeulus, thereby bringing these two small portions of the eerebellum into assoeiation with eaeh other. Where it issues from the white matter of the eerebellum it might almost be said to be in eontaet with the anterior meduUary velum, but as the two laminae are traeed anteriorly they diverge from eaeh other : the anterior velum is earried upwards between the braehia conjunctiva of the eere- bellum, whilst the posterior meduUary velum turns downwards, round the nodule, and ends in a slightly thiekened free ereseentie edge. The cavity of the fourth ventricle is earried

536 THE BRAIN

posteriorly between the two vela, whieh fonn a tent-like roof for it.

Isthmns BhombeneeplialL — If the disseetors examine the rhombeneephalon from the side they will reeognise that there is a region below the lamina quadrigemina and above the eerebellum whieh is bounded dorsally by the anterior medullary velum, laterally by the braehia conjunctiva, and ventrally by the upper part of the pons ; it is to this region that the term isthmus rhombeneephali is applied. It eontains the upper part of the fourth ventricle.

Yentriouliis Qiiartas. — This cavity is somewhat rhomboidal in form. Below, it tapers to a point and beeomes eontinuous with the eentral eanal of the lower part of the medulla oblongata; above, it narrows in a similar manner and is eontinued into the aquaeductus eerebri of the mid-brain. The anterior wall is termed the Aoor^ and is formed by the dorsal surface of the ventral part of the upper portion of the medulla oblongata and by the dorsal surface of the pons. The posterior wall is ealled the roof, On either side a narrow pointed prolongation of the ventricular cavity is earried laterally, from its widest part, round the upper part of the eorresponding restiform body. This is termed the laterai reeess (J^\g. 222, p. 525). It is seen to the greatest advantage when the eerebellum is divided in the median plane and the halves are turned aside.

The lateral boundary of the fourth ventricle, on eaeh side, is formed, from below upwards, by the clava, the upper part of the funiculus euneatus, the restiform body or inferior pedunele of the eerebellum, the braehium pontis or middle pedunele of the eerebellum, and the braehium conjunctivum or superior pedunele of eerebellum.

Dissedion. — On one side eut through the braehium conjunctivum, the braehium pontis and the restiform body, and so separate one lateral half of the eerebellum, whieh must be laid aside for the present but must be preserved for future use.

When the disseetion is eompleted the disseetors will be able to reeognise that the anterior part of the cavity of the fourth ventricle is rhomboidal in form. It eonstitutes the so- ealled rhomboidal /ossa, whieh is surrounded by the lateral boundaries of the ventricle and elosed anteriorly by the pons and the posterior surface of the ventral part of the upper portion of the medulla oblongata. Only the iower part of the

FOURTH VENTRICLE 537

rhomboidal fossa lies in the medulla oblongata : tbe inter- mediate part is in the meteneephalon, that is, it lies anterior to the eerebellum and posterior to the lower part of the |>ons ; and the upper part is in the isthmus rhombeneephah.

The lower part of the rhoniboideU /ossa is triangular in out- line, and its inferior angle is eontinuous with the eentral eanal of the lower part of the medulla oblongata. The anterior boundary or floor of this part of the fossa is marked by a number of converging sulei, and is ealled the ealamus seriptorius, Along the lateral margins of the lower part of the fossa will be seen the remains of the torn epitheHal roof of the lower part of the fourth ventricle. These torn margins are the teeniee of the fourth ventricle. The intermediate part of the rhomboidal fossa is separable into a lower wider part, whieh is prolonged laterally, on eaeh side, below and posterior to the restiform body, as the lateral reeess of the fourth ventricle, The upper seetion of the intermediate part of the fossa is bounded laterally by the braehia pontis and is mueh narrower than the lower part. The upper part of the rhomboidal fossa lies posterior to the pons and between the braehia conjunctiva. At its upper end it beeomes eontinuous with the aquaeductus eerebri of the mid-brain.

Tht fioor^ or anterior boundary^ of the fossa rhomboidalis is the floor, or anterior boundary, of the fourth ventricle. In the upper part of its extent it is formed by the posterior surface of the pons, and in the lower part by the posterior surface of the ventral part of the upper portion of the medulla oblongata. It is divided into lateral portions by a median suleus whieh is deeper below, in the region of the ealamus seriptorius, and shallower above. On eaeh side of the median suleus is the eminentia medialis. In the upper part of the fossa the eminentia medialis oeeupies praetieally the whole of eaeh lateral half of the floor; in the upper part of the intermediate portion of the fossa a nodular eminenee, the eollieulus facialis^ appears on its surface; below the eollieulus it narrows rapidly, and it terminates, below, in a pointed tri- angular proeess ealled the trigonum hypoglossi, The medial eminenee is bounded laterally by a suleus, the suleus limitans, In the upper r^on, along the lateral border of the suleus limitans, is a narrow bluish tinted area ealled the locu% eeeruleus ; the eolour of this area is due to a subjacent eiA- leetion of pigmented eells idiieh eonstitute the tubstantia

538 THE BRAIN

/errughiea, Opposite the eollieulus facialis the suleus limitans expands into a shallow fossa, the superior fovea, The lower end of the suleus Hmitans terminates, in the upper part of the inferior seetion of the rhomboidal fossa, in a deflnite depression, the tn/erior fovea. To the lateral side of the superior and inferior foveae and the intermediate part of the suleus limitans is the area aeustiea^ whieh is prolonged lateraUy into the lateral reeess where, in rare eases, a projection, the tubereulum aeustieurn^ appears on its surface. Below the inferior fovea, between the trigonum hypoglossi medially and the area aeustiea laterally, lies a depressed, grey-eoloured, triangular area ealled the aia einerea^ whieh is separated from the lower part of the floor, the area postrema^ by a raised bundle, the funicuius separans, Immediately above the in- feriorfoveaa number of ridges, the meduilary striee (O.T. stria acusticce\ eross the floor of the fossa. Laterally they eross the restiform body, at the lateral border of the fossa, and beeome eontinuous with the eoehlear root of the aeustie nerve ; and medially they disappear into the median suleus.

The roof of the fourih ventricle is formed, in the upper area, by the medial parts of the braehia conjunctiva and the inter- vening anterior meduUary velum. Deseending upon the latter, from above, is the frenulum veli ; and issuing from it, in the same region, are the rootlets of the troehlear nerves. The lower part of the upper portion of the roof is covered by the lingula of the eerebellum. The roof of the inter- mediate seetion of the ventricle is the white matter of the vermis of the eerebellum, and the roof of the lower part is epithelial ependyma and the obex.

The tela ehorioidea of the fourth ventricie is the layer of pia mater whieh covers and strengthens the epithelial roof of the lower part of the cavity. Between it and the epithe- lium at the lower end of the roof, is a thin layer of grey matter, ealled the obex, Above, at the posterior medullary velum, the tela beeomes eontinuous with the pia mater on the lower surface of the vermis of the eerebellum. Laterally the tela is prolonged, on eaeh side, posterior to the restiform body, over the lateral reeess, and it forms the stronger part of the wall of that expansion. Between the medial part of the tela ehorioidea of the fourth ventricle and the pia mater on the lower surface of the vermis of the eerebellum lies the eisterna eerebello-medullaris (O.T. eisterna magna).

NUGLEUS DENTATUS 539

Apertures in the Tela Chorioidea of the Fourth Ventricle, — In the early stages of development the tela ehorioidea and ependyma form an unbroken layer, but at a later period they are perforated by three apertures. One of the apertures, the apertura medialis ventriculi guarti (O. T. /oramen of Magendie\ Ues immediately above the obex, at the lower angle of the ventricle, and through it the cavity of the fourth ventricle eommunieates with the eerebello-medullary portion of the subaraehnoid spaee. The other two apertures lie at the apiees of the lateral reeesses, immediately posterior to the fila of the glossopharyngeal nerves.

ehorioid Plexuses of the Fourth Ventricle. — The ehorioid plexuses are vascular invaginations of the ependyma beneath the tela ehorioidea. In the lower part of the ventricle they form two parallel bands, one on eaeh side of the median plane, and their lower ends project through the medial aper- ture. At the upper part of the tela ehorioidea they eom- munieate together, and then eaeh passes laterally into the eorresponding lateral reeess and their lateral extremities project through the lateral apertures.

Dissedion. — The disseetor should now introduee his fingers into the great horizontal suleus of that half of the eerebellum whieh is still eonneeted with the medulla oblongata and the pons, and tear the upper part of this side of the organ away from the lower part. By this proeeeding the manner in whieh the peduneles enter the white medullary eentre, and also to some extent the general distribution of their fibres, will be seen.

When these have been demonstrated this half of the eerebellum should also be separated by eutting through the peduneles at the points where they enter the eentral white matter. A horizontal seetion may then be made through the other half of the organ, rather nearer its upper surface than its lower surface. This will reveal the nueleus dentatus.

Nueleus Dentatus of the Cerebelluin. — This is a eolleetion of grey matter, embedded in the white medullary eentre of ihe lateral hemisphere of the eerebellum. It presents an appearanee very similar to a nueleus whieh lies in the olive of the medulla oblongata. It is a thin lamina of grey matter, whieh appears on seetion as a wavy line folded upon itself, so as to form a erumpled grey eapsule with a mouth open towards the median plane. The greater number of the fibrcs whieh build up the braehium conjunctivum issue from its mouth.

There are other smaller isolated nuelei of grey matter in ihe white medullary eentre of the eerebellum, but these eannot, as a rule, be

THE BRAIN len obtuned in the dUseeting-room. The; lie

DiistdioH. — A series ot tcflnsveise seelions should now be made Ibrough ihe pons and Ihe medulla oblongata, in oTdei that soniet3]ii]g of

theii inlernBl sliueture may lie leained.

As a matler of bet little ai the stnieture of the medulla oblongata ean he leamt from speeimens oblained in the disseetine-toom ; but in seelioni giropeely prepared and stained a numbsT of impoetant poinls ean he

gbnetura of Uw HednllK OUonKata. — When tiansveise seetions are

made Ihrough the meduUa oblungata at diAerent levels, a faint line, ealled llie median raphe and oeeiipying ihe median plane, is seen lo divide it Graeile nnekus

into two exiicily similar lateral porlions. Tbe raphe is tmmed by the elose inteTseetion of tibies running in ditferent direetions.

Eaeh h!tlf of the medulla oblongata is eomposed of (a) strands of white matter ; (*) grey matler, wbieh is present bolh in ihe fotm of diteel eon- tinuations into Ihe medulla oblongata of portions of tbe grey matter of the spinal medulla, and in the Torm of isolated elumps, whieh are nol represented in the spinal medulla ; and (e) Ihe fotmatio retieularis, a substinee whieh is eomposed of grey matter eoarsely broken up by Rhres whieb lraveTse it in ditTerent diteetions. The white matter, as in the E[unal medulla., is disposed for tbe most part on tbe surface and the grey matter in the interior. but in the open part of the medulla oblongata the grey malter eomes to the sutface on its dotsal aspeet, and forms the obex (p. 538).

When the grey matler of the spinal medulla is traeed up into the medulla oblongata, many sttiking ehanges in its attangement beeome apparent. Owing to the inerease in siie of the large wedge-shaped graeile and euneate funiculi, the postetior eolumns of grey matter beeome pressed kterally, so that they soon assume a position at tight angles to tbe median plane, and lie very nearly in the same transverse line. At Ihe same time, Ihe euneate

STRUGTURE OF MEDULLA OBLONGATA 541

eraeile nueleat eolumrs of grey matter iiliieh gtow out frrim the \asa\ of Ihe poslerioi eoluina and underlie [he stiands or ihe saiiie: nanie,

— Tran;verEe seelioii ihrough ihi. loner parl of the Medutk Obiongala of a full Iime FieIus above the Deeussalion of ihe Pymmids. treiled b) the Weigert Pal melhod The grey maller is nhile, and Ihe medullaled strands of nerve fibres are blaek

— Transver5e seet on Ihrough lower end of Ihe Medulla Oblongila or l me Fcelus trealed by Ihe We gert Pal melhod The Erey ni.itler Tcfore bleaehed white ; whilsl the medullaled traels are blaek.

5.1J THK BRAIN

lu'ek 'ir llii: ]iiiNlLTicir eolumn, so aE to reaeh Ihe raphe. The eaput riiluinii.1' IK in Ihii «ray eul oH Itom th« basal poiliDn. The ba&al portion n-maiiu in rlim n-latiiin la the eentral eanal, whilst Ihe eaput and suWnlilia ^i-laliniiui I Kiilaoiioi k ptaeed elose to the £urface, enlai|^ as it ii IrniTil il|iwanls, flni) reirmi Ihe [irpininenee on ihe surface whieh has been ■Irsi'rilH^I alrrady os Ihe Tunieulus and luberde or Kolanilo. The Rbres whii'li luive ihni litiiken up ihe neek of Ihe posterior eolumn, and wMeh riiiiir rniiii llir ntneale anil {^r.teile nuelei, are lermed the itUimal artuaU lihrtt. 'nii-y reai'h Ihe inphe un the (leep or doisal aspeet o^ the pyramids, aml, iii lh(! nirilian plnne, they Torm a. very eomplete deeussalion wtth Ihe iii(Teii|iiinilin|' lilirra ur the op|K>sile side. This deeussation is tenned Ibe u btl u f i tt ttt h n y d saium A soon hey s] h med b g h nt mal uat

'..'-.-> Iiiiu upunrils .ttiil fiiiiii a li>n{;ituilin.il ti.iet etlled the leainiieta. It is pl.ii-nl i-lOM- ti> Ihi- ra]ihc aniliin the dorsal aspeet of the eoriesponding

riii' .iiili'iiiii i'iihiiiin of i;ri'y niattei shares .1 like Tate in the medulls iil'li'ii[;.il.i. t>ul :il :i li"Hcr U'vi.'l. nl llie han<is of the fasciculus eerebio- ■■l'iii.ili'. I.il.-Kili-^ vl >.T, i-rossiil ji)-ramiilal Iradl. This great bundle, in l..i'.'.iii;; 1111111 tlu' (.yi.iiiiiil intii tlie latt'ral fiiiiiculus of the opposile side of ilii' '.|'in.il iiii^liill.i, ir.nptse» the anterior eolumn, eompletely hieaks up il-- iiili'ini.^U.ili' i'.in iiiiil seiiaratm iln head Troni its basal |)oilion. The liiiHii'i hi>ii.iv ,.r 1I10 .U'l.ii:ru'd hMd nee.1 not be tmeel, liut il is well iii iii.i.' iti.li ilii' ki.<il |Mtl iif tho anterior eulunin of Riey matter remaina 111 ].i.siii..ii 1.11 itu- vi'iiir;il iiiul Inleinl asiwl iif tlio rentinl eanal.

\( .1 tii];hi-i li'ii'l ihi' i'iiilml ennnl, suitimnded liy Ihe basal porlions of ilii- m.. 11. hniinsi.t [;«•!■ niiiltet. urailually inelines lowards ihedorsalaspeet, iiiilil ii n'.iihi-s iho sutriii.'e. ITie grey matler whieh suirounds it is now >l<i>'.iil i.iii i>n llii' tliiiiT or Ihe fouTth YeDlriele, and in sueh a manner that

STRUGTURE 0F MEDULLA OBLOX(;ATA 543

thepoition whieh earrespomls to tbe bual port of the ui:cri'--rcof3iDDof tbe spinal medulla is ^tuated elose to the niRtisn plane. whil>< ihe ^ait «hieb represents the base of Ibe posterior eolumn oeeupaa a more Liieri] pisitiun. Therefote the nueleus of origin of ibe hypo|^ossal nene i* f4ace<l io Ibe median part of (he flooi, whilsi ibe □neleiu of teTminalton of ihe vigus and elosso-pharyngeal neires lies in Ibe lateral pait of the floor.

Tne most eonspieuous of ihe isolated elumps of grey matler in iSe' medulla are the olivary nudeus and tbe two aeeessory oliyaiy nueleL Tbe oUvary nu^leus lies subjacent to the olivaiy eminenee, and is a very eon- spieuous ob)ecl in transrerse seetioiu thioi^h ihis i^on. In sueh seelions,

Jevel of the r

towarda tbe median plane. Il is in leality a lamina Brranged in a pnne- like mannei with its open mouth direeted towaids ihe raphe.

The aeeessory olivary nuelii are Iwo band-like laminie of grey mattei, whieh are plaeed one on the dorsal and one on the medial aspeets of (he main nueleus.

l'osteiior to, ot deepet tban, Ihe olivc and pyramid is the /grmalio i-etiattaris of Ihe medulla oblongala. It is divided into a lateial and a medial lield by the lila of ihe hypoglossal netve as they traver5« the sub- slanceof the medulla oblongala to reaeh Ihe surface. In Ibelateral pottion, whieh lies postetiot lo Ihe olive, there is a eonsideiable (|uantity of gtey mattet, eontinuous with that of (he spinal meduUa ; it is tbetefote ealled (he /ormatio grisea. In Ibe medial part, however, whieh lies posterior (o the pyramid, the gtey matter is extremely seanty, and the retieulai matter heie is termed \\\i/ormaiio alba.

544

THE BRAIN

e fibic5 whieh traverse the foTmado retieulaiis nin both in tbe

! and in the longitudinal direetion. The transvenefibra are the

inUmat areuale Jibres. The longiludinal Jiirts are deriTed Kom difierent $ouTCf 5 in the Iwo lieids. In the lateral part of Ihe formation tbey represeot the tihres ol^ the laleral funiculus (afler the removaI of the ceiebello-s[niial aiHl the lateral eerebiospinal laseieuli), whieh are eontinued up undereorei of the olive. In Ihe medial parl, or formatio alba, two lonritudinal strands take oiigin, yli., the lemniseus and the median longitudinal ^asdeulul. Bolh lie elose to the raphe The lemmseus is plaeed immediatel; posterioi lo the pyramid, and is fonned by Ihe mlernai areuate fibres after thdr deeussation. The niaiian longili^inal /aseieulus takes fotm in the upper part or the medulla o1 longata, immediately sub]acent to the grey mattei

of Ihe floor of the fouilh ventric1e, It is formed by longiludinal tibres of the foTmatio alba. whieh eome from the fascicu1uE anterioi proprius of the spinal medulla.

Intetnal StroetuTe of the Poua. — When transverse seetions are made througb the pons, it is seen to eonsist of two we1l-definfd paits, viz., a

itral and a dorsal. Broadly speaking, the vealral part, pars basatis.

rebii.

The basal fart of Ibe pons is ihe lai^er of the two subdiyiaons. It is eomposed of a large number of transverse bundles of fibres, througb tbe midst of whieh eoarse longitudinal bundles of iibiea proeeed down- wards from Ihe bases of the peduneuli eeiebri to form, in the meduHa oblongata, the two pyiamids. Seattered amongst these tiansveise snd longitudinal bundles of Tibres, and filling up Ihe inteistiees between them.

INTERNAL STRUGTURE 0F PONS 545

there is a large amount of grey matter whieh forms the nudei pontis. Of the transverse fibres two distinet sets may be reee^ised, viz., the superficial transverse fibres, through the midst of whieh the bundles of eerebro-spinal fibres are prolonged, and a deeper set termed the eorptts trape^oidum. The superficial transverse fibres traverse the entire thiekness of the venlral part of the pons, and on eaeh side, pass into the eorresponding braehium pontis. The trapezial fibres lie posterior to the eerebro-spinal bundles in the boundary area between the dorsal and ventral parts of the pons, but eneroaehing eon- siderably into the ground of the former. They are seen only in the lower part of the pons, and they pass into the lateral lemniseus. They take origin in the terminal nueleus of the eoehlear division of the aeustie nerve.

The dorsal or tegmental part of the pons is, for the most part, formed of a prolongation upwards of the formatio retieularis of the medulla. Superiorly it is earried into the t^^ental parts of the j^unculi eerebri. It is divided into two lateral parts by a median raphe, whieh is eontinuous below with the raphe of the medulla oblongata and above with the raphe of the tegmental part of the meseneephalon, whilst over its dorsal surtaee is spread a thiek layer of grey matter whieh belongs to the upper part of the floor of the fourth ventricle. In transverse seetions through the pons a dark spot in the lateral part of the floor indieates the position of a small mass of pigmented eells ealled the substantia /erruginea. It underlies the loeus eoeruleus.

Four strands of longitudinal fibres are seen on eaeh side in transverse seetions through the dorsal part of the pons. These are (i) the medial lemniseus, (2) the lateral lemniseus, (3) the medial longitudinal bundle, and (4) the braehium conjunctivum.

The medial lemniseus assumes in the pons a ribbon-shaped form. It is plaeed between the ventral part of the pons and the fonnatio retieularis of the dorsal part.

The lateral lemniseus^ largely eomposed of fibres derived direetly or in- direetly from the eorpus trapezoidum, is seen in the upper part of the pons. It sweeps round the lateral side of the braehium conjunctivum to gain the surface.

The medial longitudinal buneUe is mueh more distinet than it is lower down in the medulla oblongata. It has separated itself more eompletely from the longitudinal fibres of the formatio retieularis, and it is now seen, elose to the median plane, immediately subjacent to the grey matter of the floor of the fourth ventricle.

The braehium conjunctivum, in transverse seetions, presents a semi- lunar outline. It oeeupies a lateral position in the dorsal part of the pons, and gradually sinks deeply into its substanee, although it does not beeome eompletely submerged until it reaehes the meseneephalom

The superior olive is a small isolated elump of grey matter whieh is embedded in the dorsal part of the pons in the path of the eorpus trapezoidum.

VOL. II — 36

546 THE AUDITORY APPARATUS

THE AUDITORY APPARATUS.

Thk organ of hearing adniits of a very natural subdivision into ihree parts, viz., the exteirnal, the middle, and the internal ear. The external ear eonsists of the auriele and ihe external aeustie meatus. The auriele eolleets the waves of sound, and is, comparatively speaking, of subsidiary im- portanee in man, although it is highly developed and of eonsiderable service in some of the lower animals. The external aeustie meatus is a passage leading inwards fr6m tlie boTtom ot the eoneha to the membrana tympani, whieh separates the cxternal trom the middle ear. The middle ear is a narrow ehamber termed the tympanie eayity, It igjijtfir- posed between the external aeustie passage and the intemal ear 'oriabynntn, and the main part of its laterai wall is formed by the membrana tympani. ^etehmg aeross the cavity of the^ tympanum, from its lateral to its medial wall, there is a ehain of three small bones^ ealled the auditory ossieles. ,The internal ear or labyrinth is a most essential part of the organ. It eonsists of a^omplieated system of eayities situated in the densest part of the petrbus portion of the temporal bone. These cavities eontain fiuid ealled perilymph, and also a membranbus eouiiterpart ot the bony ehambers, ealled the membranous labyrintni Within the latter there is fluid termed endolymph.

Disseetion. — The disseetion of the ear should be eondueted differently on opposite sides.

On one side remove the lateral pterygoid lamina and the remains of the extcrnal and internal pterygoid museles, if that has not been done already. Then elear away the tensor palati musele and expose the lateral suHaee of the auditory tube. Disseet on the postero-medial aspeet of the tube and cxpose the levator palati musele from the lateral side. Follow the musele downwards and medially, below the lower orifice of the tul)e, into the- soft palate. Then detaeh the «audii.ory tube from the posterior border of the medial pterygoid lamina ; eut the levator palati, at the point where it enters the soft palate, and separate the eartilaginous part of the auditory tube from any parts of the wall of the pharynx whieh may still be eonneeted with it. When this has been done turn to the temporal bone ; plaee the saw at right angles to the extcrnal surfacc of the squamous part and saw through the bone, along the line of the petro-tympanie fissure, to the posterior border of the spine of the sphenoid. Turn next to the medial surface and saw through the body of the sphenoid at the level of the anterior boundary of the foramen laeerum ; then, with the aid of the ehisel and bone forceps, detaeh the posterior border of the great wing of the sphenoid from

EXTERNAL MEATUS

547

the anterior angle of the pelrous part 0^ Ibe temporal bone. When the eiisseetion is properly done the gteater parl of the temporal bone is removed froiii the remamder of the skiilT, wilh the eartilaginous part or Ihe auditory tube nttaehed to the anterior angle of its petrous portion, «nd a small part of the body of the sphenoid bone attaehed to its npex. The anterior walt of the mandibular fossa was separated by the tirst saw eut, and the posteiior wall is exposed, with the eaitilaginous part of the auditoiy tube attaehed to its mediiil end nnd Ihe eartilnginous pari of the enternil aeustie meatus lo its lateral boider. The disseetor should now eut away the tragus of the

wall o( ihe eaitilaginons pait or Ihe external meatus. Neit piiss a probe into ihe bony part of the nieatus to gauge its lengtb, and, whilst Ihe probe is kept in position as a guide, eut away the anterior wall of Ihe bony part or the meatua, taking eaie not to injure the tympanie membrane whien eloses the medial end of ihe meatus. Whe h d'ss ' ' ompteted Ihe boundaries of the meatiis and thi: outer sur c membrone

should be ei

nined.

Meatoa AeuBtieus Eitemus. — Th

mns anteriorly and medially froiu media) boundary, and, during its co with the convexity upwards. Its to 1 the bottom of the eoneha to the tymp

tie meatus

nfice to its

. a light curve

m ured from

b e, is about

548 THE AUDITORY APPARATUS

24 mm., orwhieh S mm. eorresponds with the eartilaginous, and i6 mm., with the bony part of the eanal ; but, as ihe membrana tympani is plaeed obHquely, the anterior wall and the floor are longer than the posterior wall and the roof, respectively, Moreover, the diameter of the eanal is not uniform. It is narrowest al ihe isthmus, whieh lies about 5 mm. frora the lympanie merabrane ; and its yertieal diameter is greatest at the lateral end, whilst its anierO'posterior diameter is greatest at its medial end. These facts must be borne in mind during the removal of foreign bodies whieh. have made their way into the eanal. ' As the tube passes from

the surface medially it deseribes a gentle sigmoid curve, but its genetal direetion is towards the median plane with a slight indination anteriorly. The skin lining the eartilaginous portion is abundantly furnished with eeruminous glands and is provided also wilh laterally direeted hairs, whieh tend to prevent the enlranee of dust. The eutaneous lining of the osseous part, whieh is thin and tightly adherent to the subjacent periosteum, is destilute of hairs, and glands are for the most part absent. The eutaneous hning of the meatus Is eontinued in the form of an exceeding!y delieate layer over the outer surface of the membrana tympani.

MEMBRANA TYMPANI 549

When the direetion, the length, and the diameters of the external meatus have been noted, the disseetors should examine the lateral surface of the tympanie membrane.

Membraua Tympani. — The slope of the tympanie mem- brane has already been referred to. It slopes very obliquely" downwards, anteriorly and medially, and it is deeply concave externally. The deepest point of the concavity is the umbo^ whieh eorresponds with the lower end of a bar of bone, the handle of the malleus^ whieh is embedded in the membrane and ean be seen through the thin layer of tissue covering it. The handle of the malleus extends upwards, and slightly posteriorly, from the umbo towards the roof of the meatus; and a short distanee from the upper margin of the membrane it beeomes eontinuous with a small laterally direeted proeess, the lateral proeess of the malleus^ whieh bulges the membrane towards the meatus. Above the lateral proeess of the malleus is a portion of the membrane whieh is less tense than the remainder. This is the membrana flacctda (ShrapnelPs membrane). It is bounded anteriorly and posteriorly by relatively thiekened folds, the anterior and posterior tympano-malleolar folds, The whole of the peripheral margin of the membrane, except that whieh eorresponds with the membrana Aaeeida, is lodged in a ring-like suleus of bone, the annulus tympanieus^ whieh is formed by the tympanie element of the temporal bone.

Dissedion. — After the examination of the exteraal meatus is eompleted the disseetor must seeure the tensor tympani musele, whieh springsirom the anterior aspeet of the petrous part of the temporal bone, elose to the apex and above the level of the eartilaginous part of the auditory tube. Haying seeured it, he must traee it laterally, above the auditory tube, to the point where it passes into the bony eanal through whieh it enters the tympanum. Then he must eut away the antero-lateral wall of the eartilaginous part of the auditory tube, from the pharyngeal orifice to the lipper extremi^,~aiid pass a probe through the bony part of the tube into the tympanum. He should next turn to the anterior surface of the petrous part of the temporal bone and, with ehisel and bone forceps, carefully remove the tegmen tympani and expose the tympanie cavity from aboye. The disseetion must be earried anteriorly into the auditory lube and posteriorly into the tympanie antrum. As the disseetion is earried anteriorly a narrbw margin of bone nmst be left along the anterior border of the tympanie membrane, and eare must be taken to avoid injury to the tendon of tne tensor lympani, whieh emerges from the extremity of its bony eanal, near the medial wall of the tympanum, and erosses the cavity to be inserted into the malleus. The ehorda tympani nerve, whieh passes anteriorly, elose to the tympanie niembrane and above the tendon of the tensor tympani, must also be preserved if possible.

550 THE AUDITORY APPARATUS

Tsrmpanie Cavity or Middle Ear. — The tympanie cavity is a small ehamber, filled with air, whieh is plaeed between the bottom of the meatus extemus and the internal ear or labyrinth. Posteriorly it eommunieates, by a relatively large orifice, with the tympanie antrum and mastoid air-eells; whilst anteriorly the auditory tube opens into it and puts it into eonneetion with the cavity of the pharynx. It eon- tains the ehain of auditory ossieles whieh erosses from its lateral to its medial wall, and it is lined with delieate mueous membrane.

The vertical depth and the antero-posterior length of the tympanie cavity are eaeh about half an ineh (12.5 mm.).

Its width, from side to side, is about a sixth of an ineh (4.5 mm.); and, as both its lateral and medial walls bulge into the cavity, its width in the eentre is still further redueed. The tympanie cavity eonsists of (i) an upper part, whieh extends up- wards beyond the level of the mem- brana tympani, and to whieh the FiG. 234.— Sehematie verticai term reeessus epitytnpanieus is ap-

whieh lies immediately to the mner

I. External meatus. • j r ^t_ i_ ^ •

2. Tympanie cavity (the upper ^ide of the membrana tympani. " 2 " is in the reeessus epi- The tympanic cavity presents for tympanieus). examination a root and a floor,

3. Promontory on medial wall. • t r n • • *■ '

4. Membrana tympani. Wlth f0Ur Walls, V1Z., aotenor, £OS-

terior, lateral, and rnedial.

The roof is eomposed of a thm plate of bone termed the tegmen tympani, This separates it from the middle fossa of the eranium. In ehronie inAammatory eonditions of the middle ear, an extension of the inAammatory proeess to the meninges of the brain is always to be feared.

^);\<^floor or jugular wall is narrow, and is also formed by a thin osseous lamina, whieh is interposed between the tympanum and the jugular fossa. It separates the tympanum from the bulb of the internal jugular vein, and an exten- sion of an inAammatory eondition of the middle ear, through the bone to the vein, may lead to thrombosis.

The posterior or mastoid wall presents, in its upper part, the opening or aditus w^^'"*^ ^^ads from the reeessus epi-

TVMPANIC CAVITY 551

tynipanieus into the t)'rapanic antram, and below tliis, dose to the medial wall, is a small hollow eonieal projection teraied tke pyramid. This is peribraled, on its summit, and the aperture leads into a eana! whieh curves posteriorly and then downwards until it opens into the lower part of the last stage of the eanalis facialis. Ttie curved eanal of the pyraraid lodges the stapedius musele, the deUeate tendon of whieh enters the tympanie cavity through the aperture on the stimmit or the pyramid. Lateral to the pyramid is the aper-

FliJ. =35- — Lert Membrana Tympani and Reeesaus Epiiympanioi

rrom wilhin, The neek and head of the mnlleus haye heen remOTed tB^ eIiow the membrana Hau^ida. (Howden.)

ture on the posterior wall ealled the aptrtura tympanka canaf-. lieuli cftordie through whieh the ehorda lympani nerve entera the tympanum,

The anterior wall\s narrow, heeause the medial and lateral. walls converge anteriorly. The upper part of ihis wall ia oeeupied by the opening of the tensor tympani eanal; intermediate part by the tympanie orifice of the auditory tube j and the lowest part is a lamina of bone whieh separatea the tympanie cavity from the earotid eanal. The tympanie end of the septum between the auditory tube and the tensor tyinpani eanal, the proeesius eoehhari/ormis, serves as a pulley

55»

THE AUDITORY APPARATOS

round whieh the tendon or the musele turns abniptly, in a lateral direetion, touards the malleus

The mtdial wall, Mhieh intervenes between the tympanum

and the lab>nnth, presents eertam important pomts for study. The greater part of this wall bulges laterally, into the cavity, in the form of a \ery evident e!evation termed ihG promoniory. Above the postenor part of the promontory there is an oval foramen, the /inestra vestihih Its long axis is direeted antero-postenorly, and it opens into the vestibular part of

the labyrinth in the maeerated bone, but is elosed in' the reeent state by the footpiece of the stapes, the most medial or the auditory ossieles. The pyramid, on the posteiiM^-wall, is imniediately posterior lo the fenestra vestibuU. Above the fenestra vestibuli, in the angle formed by the meeting of the roof and niedial wall of the tympanum, and there- fore in the reeessus epitympanieus, is an antero-p^enot ridge. This is produeed by the eanalis facialis bulging into the tympanum. The wall of the eanal is very thin, and allows the white eolour of the facial nerve, whieh is eontained within the eanal, to be readily see- ■ the postenor

end of the promontory is the J an aperture

<;gchlea, but^

whieh' is stretehed

MEMBRANA TYMPANI 533

"""""""'(1 ^n?! Iriii- into thr rnyity nf thr

,te, it is_cIosed_by_aji _ id reeeiyes the naipe_of the

tSram ofthe tym^annm.

The lateral wall of the tympanie cavity is formed by the membrana tympani and thesquamous part of thetemporal bone.

Membrana TympaiiL — The membrana tympani is an elliptieal dise of membrane whieh \% stTetehed aenras the medial end of the meatus aeustieus extemus, and it forms the greater part of the lateral wall of the tympanum. It is plaeed very ob]iquely ; its lower and its anterior borders both inelining

^l^

(^,,-^-'^

G. 237. — Left Tympani

in whieh ihe tympoDk □r qiiiidmn1s. jHow

"■)

the eKleroal n The dolled lines indieale the nrnnntr I ,ubdlvided Hebienirily inlo tour aica$, J

Its raode of attaehment deBerves some attention. i medial end of the meatus a ring-like ridge of bone, distincl.iy grooved, fonns, as it were, a frame in whieh the membrane is set. But this ridge is deficient above, where the extremities of the bony ridge are separated by a deep n.oteh (the noleh of Rivinus). This noteh is oeeupied by a portion of the memlirarie whieli is not so dense in its texture (aeeing that the fibrous layer is absent), and not so tightly stretehed as the remainder ; eonseguently it reeeiyes the narae of the mimbrana flamda (Shjapnell's membrane). Xhe edge of that part of the membrane whieh is fixed in the eireular hony groove, sukus iympankus, is thiekened, and at ihe noteh of Rivinus it is earried down, anterior and posterior to Ihe

J

554

THE AUDITORY APPARATUS

membrana Aaeeida, in the fomi of two bands, ealled respee- tively the anterior 2m^ posterior tympatto-malleolar /oids.

The meinSrana tympani is eomposed of three'Tayers — viz., an eKternal eutieular layer, an intennediate Abrous lamina, and an internal mueous layer. The handle of the malleus is intimately eonneeted with the iibrous layer, and is covered medially by the mueous layer. It diaws the membrane towards the tympanie cavity, and is the eause of the concavity on the outer suriaee. The deepest point of thts concavity

eorresponds with the Aattened extremity of the handle of the malleus, and is termed the um^.

In examiniTig the ]iving ear. with a speeulum, the £urface o{ the mem- brane appears hiehly polisheil, and a eone of liEht exlends downwards and foiwards f[om the lip af the handle of the maUeus, A pair of stiite (Prussak's slrlEe), whieh eortespond lo the anterior and posterior tympano- malleolar foIds, extend from the proeessus lateralis of the malleua to the maigins of Ihe noleh of Kivinus, and thus map oul the menibrana tlaedda. The long erus of the ineus ean be fiuntly seen through the membrana tympani, parallel wilh and poslerior to the handle of the malleus.

Antruni Tsrmpaiiieum. — The I' 'im is a reeess

or air-ehamber, in the petrous pai . bone, with a

AUDITORY OSSIGLES

555

diameter of about one-third of an ineh. It is plaeed posterior to the tympanum, and eommunieates by a relatively large opening, ihe aditus, with the upper part of that cavity. It lies at a depth of about ha]f an ineh from the surface of the skull in the adult, but in the ehild it is plaeed mueh more superficially. It is hned with mueous membrane, whieh is eontinuous with the lining membrane of the tympanum. The mastoid portion of the temporal bone also is oeeupied by air- spaees, the air-telh, whieh niay extend downwards tnto the mas- toid proeess. They are eontinu- ous with one another and with the tympanie antruni, and are lined by a eontinuation of the same mueous membrane.

Tympanie Maeoiis Membnuie. — The tympanum is lined throughout with a thin mueous membrane whieh is eontinuous with the mueous membiane of the pharynx. As already men- tioned, it forms the innormost layer of the membrana tyrapani, and it is prolonged posteriorly into the tympanie antrum and mastoid air-eells, It covers the ossieles also, and it inyests Ihe tendons of the stapedius and i t^tilw 'Sr Th* 'tmToura 'rf Sb. tensor tympani museles. ino.» wkh 'j?= f"^^'')' '^ "*

Ossieula Aoditas. — The audi- tory ossieles are the malleus, the ineus, and the stapes.

The malleus presents a head, a neek, a manubrium, and two proeesses termed the proeessus lateralis and the pro- eessus anterior. The head is large and rounded. It is direeted upwards, nnd lies above the teyel of the raem- brana lyropani, in the reeessus epitympanieus, elose to the roof of the tympanum. On its posterior aspeet ihere is a noteh-like artieular surface, for artieulation with the body of the ineus. The matmbriitm is attaehed to the fibrous layer of the membrana tympani. The proeessus lateralis (O.T. l'revis) is a stunted projection whieh springs from ihe root of the manubrium. It is direeted laterally, and abuts against ihe

556

THE AUDITORY APPARATUS

membrana tympani immediately below the membrana Aaeeida. The proeessus anterior (O.T. graeilis) is a slender spieule of bone whieh passes anteriorly into the petro-tympanie fissure. It almost invariably breaks in detaehing the malleus from the

Head

Neek

Facet for ineus

Facet for Head

ineus I Proeessus anterior

Proeessus lateralis

Manubrium Manubrium

A B

FiG. 240. — The Left Malleus. (Howden.)

A. Posterior aspeet. B. Medial aspeet.

adult skull, but it ean be easily preserved in the skull of an infant.

The ineus is shaped somewhat like a praemolar tooth in

Artieular surface for head of malleus

Crus breve

Body

Crus

longum

Proeessus lentieularis

FiG. 241. — The Lcft Ineus. (Howden.) A. Anterier aspeet. B. Medial aspeet.

whieh the roots are very divergent. It presents a body and a long and a short erus. The body ' ' \ with an

artieular surface, whieh looks anterie lates with

the head of the malleus. The s/wrt C7 f>steriorly,

AUDITORY OSSIGLES 557

and its extremity is attaehed, by ligaments, to the posterior wall of the tympanum, near the opening into the tympanie antrum. The long erus proeeeds downwards and medially, in a direetion nearly parallel to that of the manubrium of the malleus, but more medial, and on a plane posterior to that proeess. On its inferior extremity, whieh is bent medially, there is a small knob of bone ealled the proeessus lentieularis, This artieulates with the head of the stapes.

The malleus and ineus move together on an axis whieh is formed by the proeessus anterior of the malleus and the erus breve of the ineus. The artieular surfaces of the two bones are provided with peeuliar eateh- teeth whieh interloek when the bones are performing their ordinary movements. When, however, force is applied to the inner surface of the membrana tympani, as, for instanee, when the tympanum is inAated through the auditory tube, the ineudo - malleolar joint gapes and the malleus moves by itself. Traetion upon the attaehments of the stapes, through the ineus, is €3" — Head

thus avoided. y^ Neek

^rus anterior

The stapes is shaped Uke a stirrup, j^^h-Crus postenor and presents a head or lateral extremity /* ■ ^~5^Foot-piate separated by a slightly eonstrieted neek from two erura whieh join a medial plate, the basis stapedis. The head\% ^^^' ""1«;^^!?. f ^^' excavated by an artieular eup for the proeessus lentieularis of the ineus. The erura are grooved longitudinally on their concave sides (suleus stapedis). The posterior erus is more sharply curved than the anterior erus. The base fits into the fenestra vestibuli and eorresponds in its outline with that aperture. Its lower border is straight, whilst its upper border is curved.

Ligaments of the Auditory Ossieles. — In addition to the delieate eapsular ligaments, whieh surround the joints between the auditory ossieles, there are eertain bands whieh eonneot the bones to the walls of the tympanum and serve to restrain their movements.

In eonneetion with the malleus there are (i) an anterior ligament whieh passes from its anterior part, at the root of the proeessus anterior, to the anterior wall of the tympanum in the neighbourhood of the petro-tympanie fissure ; (2) a lateral ligament whieh extends from its lateral proeess to the margin of the noteh of Rivinus ; and (3) a superior ligament whieh eonneets Uie head with the roof of the tympanum.

The ligament of the ineus binds the extremity of its short erus to the posterior wall of the tympanum, whilst the annuiar ligament of the stapes eonneets the margin of its base to the circumference of the fenestra vestibuli.

558

THE AUUITORY APPARATUS

Tympame Mnseles. — These are two in number, viz., the stapedius and the tensor tympani.

'ITio st<ifcdius oeeupies the interior of the pyramid and tlie eanal whieh curves downwards Trom it. The delieate tendon of the stapedius enters the tympanuni, through the aperture on the summit of the pyramid, and is inserted into the posterior aspeet of the neek of ihe stapes. It is supplied by a braneh from ihe/aa'a/ rren-e.

Tlie /e»sar tynipani arises froKi the upper part of the eartilage of the auditory tube and from the eontiguous parts of the great wing of the sphenoid and the petrous part or tho temporal bone. From its origin it passes postero- latorally, upon the proeessus cochleariformis and above the ossooiis part of the auditory tube. In the tympanie cavity tlie tendon turns at right angles, round the extremity of the proeessus cochleariformis, and passes |f 'owards the

lateral wall of the tympanum, to its ir he upper

AUDITORY TUBE

part of the medial surface of the manubrium of the malleus. The tensor tympani receives its nerve of supply from the <^£

eiioTda Tympani Nerre. — The ehorda tympani, whieh traverses the tympanie eayity in elose relation to the upper part of the membrana tympani, is deseribed on p. 546.

Tympaoue Flexiis. — This has been deseribed previously onp. 312.

Taha Auditiva (O.T. Eustaehian). — The auditory tube is the passage whieh plaees the tympanie cavity in eommuniea* tion with the pharynx. Through it air reaehes the tympanie

cavity and antrum and the mastoid eells. It eonsists of an osseous aiid a eartilaginous porlion. The osseous porHon is about half an ineh in length. It is widesl at its entranee into the tympanum, and narrowest at its other end. eanilagimus portion is about an ineh in length, and has already deseribed on p. 383.

Disseelion : Seeend Methad. — On the oppoale side the bony part of the extemal meatus, Ihe tympanie Bntrum, and the tyinpanie cavity shouid lii; approaehed from the poatero-laternl aspeel. The disseelion of the bone should be earried oul after themanuer ado]rted by the surgenn when opemt- iiig for the eure of extensix'e mastoid and miiidle ear disease, but. lo facililate the disseetion, and to gain betler aeeess to the bone, Ihe auriele may be reniovcd by eutting Ihrough the eattilnginous part of ihe enlernBl

beeqfl

Aftcr the auriele haa

u eut away elenr all Ihe 5oft parts. !nclading_

56o THE AUDITORY APPARATUS

the periosleum, tiom the outer surraee of the mastoid part of the temporal lieine, and iclentify (i) the supra-ineatal triangle and the supra-meatal spine, whieh lie nt the junction of Ihe superiot with the poslenor border iif Ihe l>ony part of the cxternal meatus, and (2) the temporal line whieh passes, posteiiorly anil upwards, a.1)ove the snpra-meatal triangle.. The objects of the iirsl slage or the disseetion are (l) the removal of the iiutei eumpnet layer ; (2) the opening up of the eRneellons tissue of the iiiastuiil part of the tcm]Kiral bone, and the eiposure of the mastoid aii- eells aiid the cavily of the tympanie antrum, whilst, at the same time, injury to Ihe ]x)sterior wall of the bony part of the extemal mealus and to Ihe sigmoid part of the tiansverse sinus, whieh lies in a groove on the inner aspeet of ihe posterior part of the mastoid portion of Ihe temporal bone, is ayoideiL The tym^ianie antrum lies at the level of the supra- mental triangle, Ihal is above and postetior to the external meatus, and

FiG 345.— Disseclionof IheTympanieAntiumand Ihe petro-mastoid pait ot the tempoial lione fioni the oulei side. The anow is passing through the aditUB fconi llie tympanie anlrum into the lympanLe eayily.

aboul half an ineh from Ihe supeiiieial surface of the temporal bone. The disseetion should be eommeneed above, below the tempoial Une and should be earried, anteiiorly and medially, into the bone, parallel with the posterior wall of ihe external meatus, unlil the tympanie antrum is opened into. Afler the tympanie antrum has been identiBed, the eaneellous tissue of the anlerior part of the mastoid area must be eradunlly removcd till the niore medially situated and more eompaet bone is exposed. When this slage of the disseetion 15 eompleted, the disseetor should note the following points :— (1) In the anterior boundary of the eitposed area is the eompaet poslerior wall of the bony part of the external nieatus. (z) I'osterioriy is a broad projecting ndge indi- eatine the position of Ihe groovc whieh lodges the sigmoid parE of the transverse sinus. (3) At the upper and doeper part of the area are the medial vrall of the tympanie antrum and the aililus leading inlo Ihe lym- uanie cavitv. (4) The inteimediale area is o- the remains of

the mastoid air-cclls, whieh may extend d Ve tip of the

mastddproeess. They are eontinuous aboye thetymp-nw

TYMPANUM 561

nntriim. (5) On Ihe niedial wall of the aditus and the anterior part of the iiiedial wall ur tho tympanie antrum is a horizonta1 ridge whien indieates Ihe posilion of the latetal semieireular eaoal of the lah^rinlh, and, beiow il, on the niedial wall of the mouth of the aditus, 13 a vertical ridge indieating the position of the eanalis Tadalis, whieh lodgea the imporlant

The nexl stnge of the disseetion eonsisls in the removal of the posterior wall of the eiiternal raeatus, and the exposure of Ihe outer surface of the tympanie membrane (p. 549). Afler the lympanie membmne has been cxamined, a seeker should be passed through tlie aditus into the tympanie caviiy, aod its handle should be allowed to rest on the lower pait o( the esposed aita ; then, whilst Ihe setker lemains inpc«ition, the TeTnaindtT of ihe posterior wall and the upper boundaty of the eiternal meatus, &om Ihe levei of the seeker to the level Qf the roof of the lympaiiie antruni, ean

be eut ttwny wilhoul fear of injury lo any imporlant struetnre. Tili' disseelion should be eompleted by the removal of Ihe tympanie membBUUL. and ossieies, and when this has been done a very eomplete view wiil be J obtained of the mediat walls of the tympanie caviiy, the aditus, and tlie lympanie antrum. Anteriorly, on the meilial wall ot the lynipanie cavity, is the promonlory, whieh marks the posilion of the iirst lum of tte eoehlea. Above and posleriot to the promontoiy is the fenestta vestibHli, The reneslta eoehlete lies at the lowet and posterior pait of the proroontoiy, in ihe anteiior part of a teeess ealled the fossula feneslric eoehleas. Above the fenestia vestibu1i is a ridge eaused by the poslerior horiionlnl part of Ihe eanalis facialis ; this beeomes eontinuous, on Ihe medial wall of Ihe | aditus, witb the Teilieal lidge whieh hidiealea Ihe posilion of Ihe ver1ical'| IKitt of the eonal. Above the kttei is ihe horiiontal ridge due to tbe I latetal aemieiteular eanal. The disseeior should opuii the eanatis /aeiAll* I lo liipose the facial m:rve; then he should opm Ihi! Inleral semidieulat il eaimi, and nfterwnriJs rcmovc the l>onc «bovc «nd puaterior la it ta j exfi>:>sc the walls or tbe superior and posterior vertical semidieulai eanalg J (l'igs. 245, 346). ^"

VOL. 11—38

562 THE AUDITORY APPARATUS

INTRAPETROUS PART 0F THE FACIAL NERVE AND THE AGUSTie NERVE.

The facial and aeustie nerves have already been traeed into the internal aeustie meatus (p. 215). The disseetor should now open up this meatus and follow the facial nerve in its eourse through the petrous portion of the temporal bone. The eanal whieh it oeeupies is termed the eanalis /aeiaiis (O.T. agueduet of Fallopius\ It begins at the bottom of the internal aeustie meatus, and opens on the exterior of the skull at the stylo-mastoid foramen. Between it^ eom- meneement and termination it pursues a eomplieated eourse, and this, eombined with the density of the bone, renders the disseetion very difficult.

Disseetion. — On the side on whieh the middle ear has been opened from the lateral aspeet and the eanalis facialis has already been partially opened up, the disseetor should eoniplete the disseetion of the intrapetrous part of the facial nerve and should examine the aeustie nerve.

Separate the temporal bone from the other eranial bones whieh still adhere to it, and fix it in the natural position (in a'vice if possible). Remove the squamous portion by a horizontal saw eut at the level of the upper surface of the petrous portion. Make a seeond horizontal saw eut, im- mediately above the roof of the internal aeustie meatus, and earry it laterally into the tympanum, in whieh it should emerge immediately above the already opened eanalis facialis where the latter lies above the fenestra vestibuli. Then, with the bone forceps or ehisel, remove the remains of the roof of the internal meatus and follow the facial nerve along the eanalis facialis to the hiatus eanalis facialis, and so expose the ganglion genieuli. Seeure the branehes whieh arise from the ganglion and then follow the nerve posteriorly above the fenestra vestibuli. The greater part of the vertical portion of the eanal has already been opened from the lateral aspeet ; the remainder ean now be displayed by means of two saw euts — (i) a frontal seetion (vertical transverse) earried medially from the lateral surface of the bone to the posterior border of the stylo-mastoid foramen ; (2) a sagittal eut (vertical antero-posterior) earried from the posterior surface of the bone to meet eut (i). The portion of bone between the two euts must then be removed, and the disseetion must be eompleted with bone forceps. Three branehes are given off in this part of the eanal.

Intrapetrous Portion of the Facial Nerve. — As the facial nervc traverses the petrous bone, it may be divided into four stages, whieh differ from one another in the relations they present and in the direetion whieh they take. They are : —

1. A part within the internal aeustie \\\

2. A very short part whieh extends of the internal

aeustie meatus to the ganglion \

INTRAPETROUS PART OF FACIAL NERVE 563

3. A part whieh oeeupies tliat portion of the eanalis facia1is whieh runs

along the medial wall of the tympanie eayily.

4. A part whieh exlends vertica!ly downwards to the stylo-mastoid

fotamen.

First Stage. — In the internal aeustie meatus, the facial nerve runs almost direetly laterally in eompany wilh the aeustie nerve. In this stage of its eourse it lies io relation to the upper and anterior part of the aeustie nerve, and ■ t ot nd n > ots j 'n At the bottom of the u i I f 1

Fjg	247.
1. N	'7:;^		»a 1»,
		Ki^
	"'rn'		jS
		„.,.	ga«nc (

J

an Bt M

h=llr).

slylo-liyoir

Seeond Slage. — The seeond part of the facial nerve is yst^ shoTt. It runs laterally, with a stight inelination anterioil^l between the vestibule and eoehlea, and very soon ends tBk the swelling lermed the ganglim geniaili.

Third Stage. — At the ganglion genieuli, the facial nerv6i bends suddeiily and proeeeds posteriorly and slightly'

564 THE AUDITORY APPARATUS

downwards in that portion of the eanal whieh runs along the upper part of the medial wall of the tympanie cavity, immediately above the fenestra vestibuH (O.T. ovalis).

The Tirst three portions of the facial nerve are nearly horizontal, and pursue a somewhat V-shaped eourse. The apex of the V is direeted anteriorly, and eorresponds to the ganglion genieuli.

'Yhe/ourth stage is vertical, and arehes downwards, posterior to the pyramid, to gain the stylo-mastoid foramen.

The branehes whieh spring from or join the facial nerve during its passage through the temporal bone are : —

1. The greater superficial petrosal nerve, "1

2. Communicating twig to the smaller superficial I from ganglion

petrosal, \ genieuli.

3. External superficial petrosal nerve, J

4. Nerve to stapedius.

5. Ghorda tympani.

6. Gommunieating twigs to the aurieular braneh of vagus.

The great snperficial petrosal nerue has been examined already (p. 212). Its origin from the ganglion genieuli of the facial ean now be seen.

The eommunieating braneh to the small superiieial petrosal arises from the ganglion genieuli, and unites with the iibres of the tympanie nerve whieh issue from the tympanie plexus. The external petrosal nerue is not always present. It joins the sympathetie plexus whieh aeeompanies the middle meningeal artery.

The nerue to the stapedius niusde arises from the facial as it arehes downwards posterior to the pyramid. It enters the base of the pyramid and thus reaehes the stapedius musele.

The eommunieating twigs to the aurieular braneh of the vagus arise a short distanee above the stylo-mastoid foramen. ehorda Tympani. — The ehorda tympani represents to a large extent the sensory hbres set free from the trunk of the facial nerve. It is the largest braneh given off by the facial during its passage through the eanalis facialis. It takes origin a short distanee above the stylo-mastoid foramen, and arehing upwards and anteriorly, in a narrow eanal in the petrous portion of the temporal bone (the eanalieulus ehordae tyni])ani), it appears in the tympanum by passing through llu* tympanie aperture of the eanalien^"" '^h.ordae below the l)jisc ()f the pyramid, and elose to "^r margin of

ACUSTIC NERVE 565

membrana tympani, The bony tunnel whieh it oeeupies ean easily be opened up in a decalcified bone, but is somewhat difiiculi to expose io the hard bone. After entering the tympanum the ehorda tympani runs anteriorly upon the upper part of the membrana tympani under cover of the mtieous layer. It erosses the handle of the malleus on the medial aspeet near its tooL Pinally, reaehing the anterior end of the tympanie cavity it erosses the anterior proeess (O.T. graeilis) of the malleus, passes above the tetwor tympani, and traverses the medial end of the petro-tympanie Hssure, whieh eonduets it to the exterior of the skull. From this point to its junction wlth the lingual nerve the ehorda tympani has already been traeed {p. 278).

Aenstie Nerve. — In ihe internal aeustie meatus the aeustie nerve lies at a lower leve! thiin the ^aeial, and at the bottom of the passage it splits into two parts, termed the eoehlear and vesti!iular divmons, These trunks again sub- divide and supply the diHerent parts of the labyrinth of the ear through the foramina of the lamina eribrosa.

After the cxamination of the intrapetrous parl of the facial ne[ve and the aeustie nerve is oompleted the diaseetor should display ihe labyrinth of the inteinal ear by means of two saw euts — (1) an anlero-posterioi veTtica1 eut eariied from the upper siirface of the bone downwuds to the iloor of ihe tympanuni along the juncUon of its medial and posterior boundaiies ; (z) a huiizantat eut. Thiseut shonld be eommeneed at the apex of the petrous iiart of the temporal bone and should be earried laterally till it join3 ihe vetlical eut posleriorly, and enters the tynipanie eavily anleriotly at the levei of the mid-height of the promontoiy. When the upper part of the petrous poition of the temporal bone, sepaia.ted by the two euts, is removed, Ihe vestibulsr and eoehlear parts ai the labyrinlh and poitions Df the seaiieireular eanals will be displayed. Thtt disseelor shoukl demonstrate the positions aud euires of the semidieulur' . eanals and ihe eanalis facia]is by passing biistles thiough them,

Auria Iiitema~ — The intemal ear or labyrinth eonsists of an intrieate system of cavities in the petrous part of the teraporal bone, the osseous liibyrinlh, and a series of hollow memhranous struetures, eonneeted with the filaments of the aeustie nerve, whieh lie in the osseous labyrinth and eonstitute the mem- 1 branous laiiyrinik.

The osseous labyrinth is eomposed of an intermediate ehamber termed ihe vestibiile, posterior to whieh are plaeed the three semieireular eanals, whilst anteriorly is the eoehlea, AII these cavities eommunieate with one another. The eorre- sponding membranous parts do not eompletely oeeupy the

566 THE AUDITORY APPARATUS

uss<;i)us etinmbers, and the intervening spaee is tilled with a lluid lernied the perUymph. The membranous iaAyrmlA also euntains a lluid whieh receives ihe name of endolymph.

■yertibtiliun.— "1116 vestibule is a small ovoid bony ehamber, [iwsstsMng an antero-posterior diameter of about one-sixth uf an ineh. It is situated between the medial wall of the tynipanum and the bottom of the intemal aeustie meatus.

Into the posterior part of the vestibule the three semi- eireular eanals open by five round apertura; wbilst in its luwer and anterior part is the opening of the seala vestibuli of the eoehlea.

On tlit; lateral wall is the fenestra ytstibuli, whieh is dosed, in the reeent state, by the delieate periosteal lining of the ehamber and the base of the stapes, When these parts are removed, the yestibule eommunieates direetly with the tym- panum. On the anterior part of the medial wall of the yestibule there is a eireular depression, termed the reeessus sphieri^us, whieh is bounded posteriorly by a vertical ridge, ealled the erista vestibuli The bottom of the reeessus sphEerieus is pcrforatcd by some minute holes whieh give adraission to filanient.s from the aeustie nerve. On the roofoi the vestibule is another depression, named the reeessus elliptieus. It is plaeed [lostorior to the erista vestibuli.

A small aperture plaeed on the posterior part of the inL'dial wall also deserves mention. It is the mouth of the aquuduclus vestibuli — a small eanal w' ' posteiiorly to

LABVRINTH 567

the posterior surface orthe petrous part of the temporal bone, where it opens under the dura mater.

OanaleB Semieireulares Ossel. — These are three bony eanals or tubes plaeed posterior to the vestibule. They are bent upon themselyes, so that eaeh forms eonsiderably more than half a eirele, and they oeeupy planes at right angles to eaeh other lilie three faces of a eube. They are termed superior, posterior, and iateral, and ihey open into the posterior part of the vestibute by five round orifices, the number of openings being thus redueed through tlie adjoining extremities of the superior and posterior eanals beeoming fused together so as to present a eommon eanal, the erus eomnium, with a single

F[G. 249, — Left Bony Lahyrinlh viewed from lateral side. (Howden.)

orifice. One extremily of eaeh eanal where it joins the vestibule beeonies expanded into what is termed its ampuUa. There are thus ihree amirallated ends.

The superior semieireular mnal forms the highest part of the labyrinth, and gives rise to a smooth eIevation on ihe anterior surface of the petrous part of the temporal bone,. immediately anterior to its superior angle. It is vertical, and plaeed almost transversely to the long asis of the petrous part of the temporal bone. The posterior semieireular eanal, whieb is the longest of tbe three lubes, is also yertiea!, ar lies in a plane parallel to the posterior Burface of the petroi part of the temporal bone. The laleral semidreuiar eanal the shortestof the tubes, and it lies in a horizontal plane.

eoehlea. — The eoehlea is a lapering tube whieh is eoiled

\

568 THE AUDITORY APPARATUS

spirally for two turns and a half around a eentral pillar, termed the modiolus. The appearanee produeed is somewhat similar to that of a spiral shell. The eoehlea lies anterior to the vestibule, with its base direeted towards the bottom of the internal aeustie meatus; whilst its apex is direeted antero- laterally, and lies in elose relation with the eanal for the tensor tympani musele.

The eoehlear tube rapidly diminishes in diameter as it is traeed towards the apex of the eoehlea, and its elosed extremity is termed the eupola. The iirst turn whieh it takes around the modiolus produees the bulging on the medial wall of the tympanum, whieh has been deseribed under the name of the promontory.

The modiolus is thiek at the base, but rapidly tapers towards the apex. Its base abuts against the bottom of the internal aeustie meatus. It forms the inner wall of the eoehlear tube, and winding spirally round it, like the thread of a serew, is a thin lamina of bone, termed the lamina spiralis^ whieh partially subdivides the tube into two passages.

Numerous minute eanals traverse the modiolus, and one more eon- spieuous than the others, the longituditial eanal of tke modiolus, extends along its eentre. The spiral lamina also is tunnelled by small eanals in eommunieation with those in the modiolus, whilst one, the spiral eanal of the modiolus^ winds spirally around the eentral pillar in the attaehed margin of the spiral lamina. All these ehannels convey filaments from the eoehlear division of the aeustie nerve to the membranous eoehlea, whilst the spiral eanal lodges the gangiion spirale eoehlea, whieh is the peripheral ganglion of the eoehlear part of the aeustie nerve.

The membranous eoehlear tube or duetus eoehlearis is plaeed between the free margin of the spiral lamina and the opposite side of the wall of the eoehlear tube, and eompletes the subdiyision of the bony eoehlea into two eompartments, whieh are termed the seala tympani and the seala yestibulL The seala iympani is the larger of the two. It begins at the fenestra eoehleai, where the seeondary membrane of the tympanum shuts it off from the tympanie cavity. At the apex of the eoehlea it eommunieates with the seala yestibuli by means of an aperture, termed the helieoirema, At the base of the eoehlea the seala vesiibuli eommunieates with the lower and anterior part of the vestibule. The perilymph lhcrefore, in the semieireular eanals and vestibule, is direetly eontinuous with that in the seala vestibuli and seala tympani.

LABYRINTH 569

It ean Dow be underslood how vibiatians of the [yiembrana tympaDi are eammunieated to ttie perilymph within tlie osseous labyiinth. The ehain of audilory 03sicles [brough the base of the stapes affect5 the perilymph in ihe veslibuLe. The vibrations of Ihe perilymph passing along Ihe seala veslibuli into the seala tympani in turn affect the seeondaiy membrane of the tympanum whieh is streti^ed aeloss the fenestta eoehlese. With cvery inward movement of the membrana tympani and Qf the base of the stapes, there is an oulward movemeDt of Ihe membrane of the fenestra eoehleie, and -Tria versa. Tbe vibTatioD$ of Ibe perilymph affect the endolymph in the membtanous labyrinth, and thus e: " ' ' lionsoftheaf

Hembmnoua Labyriuth. — In the Yestibule there are two mem- branous saes, termed Lhe alriele and ihe saeenle. The utriele oeeupies the reeessus elliptieus on Ihe wall of Ihe vestil)ule, and lies above and posterior to the saeeuie. Into it open the miniir'anaui stmiiireular

The saeeule is smaller, and oeeupies the reeessus spha;ricus on the anterior part of the media! wall of the veslibule. Il eommunieates by means of a short narrow tube, termed the eanalis reuniens, with the duetus eoehlearis or membranous eoehlear tube.

The saeeule and Ihe ulriele are only indiredly hroughl into eommnniea- tion with eaeh other ; a slender tube tetmed the dutlus iHdelympkalleu! oeeupies the aquieduclus vestibuli, and divides into two branehes whieb

BULBUS OeULI

BULBUS OeULL

'i lit: \/u\huri 'y*uli or eyeball is not j>erfect}y s])herical ; it Ta2j \f* >.aid to U: rom;K»sed of the segments of two spiheres. 'i\^t' uttUnur or eorneal segment. forming only abont ODe-STTth i/i i\it' t ti\it*: «r)^balL possesses a Bhorter radius than thepos- h iM/f or V l»rral v ^^rnerit. The anterior dear eomeal part o^ flii « y« l/al) f'/nn^, therefore, a dome-like bulging or prominepee «//1 ili'- Ir'ynl of the glol>e of the eye. The terms anterier A\\t\ ptnterior poU are resi>ectively apphed to the eentral points i/l iIm' ;irii<-n'/r and j><^?>terior segments Qf the eyebalL Tbe MM;ij.Mfi:i ry lirw: whid) joins these poles receives the nanie mI iIm' stiyjffui axiif wlnlst another line dravn in a OOTonal ilii< « ii«/n arourKl i\n: glo^>e (A the eye midiray between the iwo |M/lih t^o ;is U) ciivide the eyebaU into two hemispheies iti \t itni'ti \\it* et/uator. Irnaginary meridional Hnes also are iliuwn l/« iwr<*n ilie two poles so as to eut the eqiiatorial line .ii \\\i\\\ an^lr^.

IU\M,iion II I thf Eyrlmll. A }ialisCactory disseetion of tbe globe of Ibe « yi i.ih l»«- iii.ulr only wlii-n \\itt eyeball is fresli, or aiter it has been li.inli ii< «I (•ii >.« v« i.il «la):t iti u io % f»olution of formoL In the disseeting-

K' 11 I:) •ilieii iiii|K>:)i>il>l«' t«/ o!/tain suitable spedmens; bnt it is alwa^rs

1 .1.-) i.i |iiMi iiir iy« liall:^ «if i|j<r pijf, shcep, or ox, and these snit the poipose .«.liiiii.il.ly li i^i a«lvi-»:iM»*, howcver, that the disseetor shonld oomplete lii^ ^iiii.ly ..I ilii «ii^aii liy tli'! ('xamination of a fresh humaneyeball obtained li>.iii ilii /■.'•■/ nioitein r<*«*iii. Iii |>oint of size, and also in other partieiilars, ilii i p l..ill ..( ili«' |/i}.; iin*r<* (losely resembles the human eyeball, but it in |.. ili.i|.:^ I.«liii tliut tlie slu<lcnl should lx^n with the eyeball of the '.«, .5. . iii{' tli.ii iii ii ilit- (li^iv«lion ean be more easily earried out.

\\ li. II ilii «liMriiriiii ha;^ |»rovi<le<l himsclf with six eyeballs obtained from

• .11 II, lii rslii.iilil leiinwr' (roiii tlu.'ni the conjunctiva, fascia bulbi, oeular i.iii.tIis, ,iinl l.ii, wliii h aillu-rr lo thetn. Pinehing up, with the forceps, ilii I .iiijiiiii iiv.t .tiiil tli«* laseia lnilhi elose to the eomeal margin, he should .iiii|. ilii..iii.;^li ihihi- luyiis with tht! seissors and divide them round the \\li..li «.h'« <il iht' K.Mita. Ile e.'in ihen easily strip all the soft parts li.iiii ili« hiiil.ui- iil iln- hi hra, working steadily posteriorly towards the iiiii.iii. i: ..1 ihr upiir ii«Tvc'. A liulc posterior to the equator of the . ^. l-.ill ih. vi ii.i Vi.iiir<»'.;f will he notieed issuing from the selera at wide ii.h iv.ih ln.iii «•.»t h iillur, aii«l on apj)roaching the posterior aspeet of the

• Vi l'.ill ih.- iK.r^ii lii.i « iliaiy artt-rii's and the eiliary nerves will be seen |.i< I. iii}; ilii- .hi 1(1. i iiii.uiiil tlu' tMilr:incc t)f the optie nerve.

iSiN.ii- l.«jMiiiiiii^^ ihr aetuiil (lisseetit)n of the eyeball, it is important ih.tt ihi- htuiliMit shiiuhl tihlain a general eoneeption of the parts whieh 1 iiiii|...)«' ii. 'l'hi'i ( an he (Iiiiu* by seetions through three hartlened speei- iiirii;> III ihiee «lilliMcnt |>lanfs. C)nc speeimen may be divided at the ii|u.ti<ii iiiiii an antt-ritir aiul \\ posterior portion. Another may be divided

EYEBALL 571

in >□ antero-posterioi direetion into a medial and a lateral hair. A tliird sliould be divided hoiizODtally aod a. poetion of ihe vitre»us iKHly shonld bc removed (Fi§. 251 )■ When Ihe seelions are made, thty should lie plaeed under watei in a eork-lined Iray, and pieseived Tor refeience as the study of the eyeball is proeeeded wilh.

G«neraJ Stmetnre of tlie Eyeb&lL — The eyeball eonsists of three eoneentrieally arranged eoats enelosing a cavity in whieh three refracting media are plaeed.

The tunies are : (i) an external tibrous envelope eom- posed of a posterior opaque part, ealled the le/era, and an

ofEyeball.

anterior elear transparent portion ealled the eomea ; (2) an intermediate vascular envelope known as the a&ea/ /mW, in whieh three subdiyisions are reeognised, viz., a posterior part ealled the ehorioid, an anterior portion termed the iris, whieh lies posterior to the eornea, and an intermediate eiliary body ; (3) ihe nen'ous internal tunie or retina, in whieh the fibres of the optie nerve spread out.

The refracting media are : (1) posterior to the oornea a watery Auid, ealled the a<jueous humour, eontained in a spaee partially subdivided by the iris into the two ehambers of tke eye; {2) the erystallim iens posterior to the posterior

572 BULBUS OeULI

ehamber; and (3) the vitreous body^ oeeupying the posterior part of the interior of the eyebalL

Disseetion. — The superficial surface of the selera and the eomea should now be examined ; but to eomplete the study of the extemal tunie a Turther disseetion is required. Seleeting an eyeball for this purpose, an ineision should be made, with a sharp knife, through the selera at the equator. This must be done carefully, and the moment that the sub- jacent blaek ehorioid eoat appears the knife should be taid aside. The eut edge of the selera should now be sei^ed with the forceps, and the indsion earried eompletely round ihe eyeball, with the seissors, along the line of the equator. The outer fibrous lunie is thus divided into an anterior and a ix)sterior portion. These must now be raised from the subjacent parts. As the anterior portion is turned anteriorly, some resistanee will be met elose to the margin of the eornea from the attaehment of the eiliary musele to the deep surface of the selera. This ean easily be broken through with the blunt point of the elosed forceps ; as soon as this is done the aqueous humour eseapes. In the ease of the posterior part of the selera, its eomplete separation ean be effected by dividing the fibres of the optie nerve elose to the point where they appear through the selera.

When the above disseetion is successfully earried out, the outer fibrous tunie is isolated in two portions, whilst a eontinuous view of the inter- mediate vascular eoat is obtained. The eyeball, denuded of its extemal tunie, should now be plaeed in a shallow vessel filled with water.

Selera. — The sclera_is what is eommonly known as the white of the eye. It is a dense, resistant tunie, opague- white in eolour, whieh enyelops the posterior five-sixths of the globe^ the eye. It is thiekest posteriorly, and beeomes thinner as it is traeed anteriorly. Near the eornea, however, it again beeomes thieker, owing to the aeeession of fibres whieh it rcceives from the tendons of the oeular museles. Kxccpt at the optie entranee and elose to the margin_Qf the eomea, where it adheres to the surface of the subjacent eiliary musele, the deep surface of the selera is very loosely attaehed to the ehorioid eoat. Some pigmented Aoeeulent c()nnective^tissue, the larnina fusc^ passes between the two eoats and trayerses _what is in reality an extensive lymph spacCj^ termed the periehorioidal spaee,

'l'he point at whieh the optie nerve pierees the selera (loes not eorrespond with the posterior pole of the eyeball. The optie entranee^ as it is termed, is_situated about 3 mm. to thi' inalial ornasal side of the posterior pole and i mm. helow it. There the outer iibrous sheath of the optie nciv(\ whi(^h is derived from the dura mater, blends with Ihr selt'ia, and the bundles of nerve fibres pass through a •411 irs or sniall apertures. This perforated portion Qf the tsi li'ia is t-allod the iamina eribrosa.

eORNEA 573

The selera is piereed also by numerous blood-vesseU and nerves. The long and shoit posleiior eiliaiy aitettes with the eiliaiy nenes peribrate the selera aiound the optie entianee ; foui oi five venx vorticoss issue from the interior of Ihe eyeball by piereing (he seleia a short ilistanee posterior to the equatoi, at wide irtervals froni eaeh otber ; whilst the anteriot eiliaty arteries pietee it neai ihe eotneal maigin.

Anteriorly the selera is not only eontiguous to, but is direetly and strueturally eontinuous with, the eornea, This is termed the eorneO'Sekral juncHon, and the faint groove on the surface, whieh eorresponds with it, receives the name of the ssUral sul(us. At this junction the seleral tissue slightly overlaps the eomeal tissue, and the line of union, when

seen in seetion, is obhque eiosetothisa. mmute eanal in the jubstance of the selera termed ihe stnus yenosus selera (O.T. eanal of Sehlemm) eneireles the margm of the eomea. Oomea. — The eomea forms the antenor sixth of the outer tunie of the eye. It is transparent and glass-like, and it ■ forms the window through whieh the rays of hght gain admittanee into the eyeball The curvature of the eornea is more aeeentuated than that of the selera, and thus it eonsti- tutes the segment of a smaller sphere When Yiewed from the posterior aspeet t appears c reular but when looked at from the front it is seen to be slightly wider m the transverse direetion. This is due to the fact that the selera overlaps it to a greater extent above and below than it does at ihe sides. T hejiosterior concave surface of the eornea fonns the anterior

5 74 BUI.BUS OeULI

boundan- of the anterior ehamber of the eyebalL and is separated by the agueous humour from the anterior surface ot" the iris.

The anterior cQnvex surface of the eornea js elothed with the conjunctiva, redueed to a transparent_epithelial laypr On its posterior aspeet there^ is an elastie glassy stratum, termed the postenor elastie lamina, When the eomea is relaxed this membrane beeomes wrinkled, and it ean be tom away in shreds from the proper eomeal tissue.

Ligamentnm Peetinatnin Iridis. — At the margin of the eornea the posterior elastie lamina is fibrillar, and some of its fibres are eontinued into the iris, forming the li^amentum p^etinatiim iridis, whilst others are prolonged posteriorly into the ehorioid and the selera. The ligamentum peetinatum iridis bridges aeross the angle between the eornea and the iris, and the bundles of fibres into whieh the pgsterior elastie lamina breaks up in this region eonstitute an annular mesh- work or sponge-like series of minute spaees termed the spatia anguli iridis (O.T. spaees of Fontand), These eommunieate \^nth the anterior ehamber of the eyeball, and are filled with aqueous humour.

Tnniea Yasenlosa OenlL — The intermediate or yaseular tunie, frequently spoken of as the uveal traet, is exposed, in its entire extent, in the eyeball from whieh the selera and the eornea have been removed. It is separable into three parts — (i) a posterior portion, the ehorioidea; (2) an intermediate parr, the eorpus eiliare ; and (3) an anterior segment, the iris.

Ghorioidea. — The ehorioid is the largest part of the vas- eular tunie. It lines the posterior segment of the eyeball, between the selera externally and the retina internally. It is thiekest posteriorly, where it is piereed by the optie nerve, and beeomes thinner anteriorly, as it approaehes its union with the eiliary body. Its superficial surface is eonneeted with the deep surface of the selera by some lax connective tissue, and also by blood-vessels and nerves whieh pass from ihe one into the other. The H^pp snrfarp <^^ thp nHorioid is nioulded upon the retina ang eonneeted with a layer of (leeplYpigmented eells whieh usually adheres to the ehorioid wlieii that tunie is removed, althouKb in ^eality it is a port;ion oT ihe retina.

\w llu' ryes of many mammals, but not in man, the posterior part of the

eiLIARY BODY 575

ehorioid, when viewed from the fronl, presents an e;itensive briEhtly-eoloured area, whieh exhibits a melallte lustre. This appearanee is due to the presenee of an additional layer^ in ihe ehiarioid iermed the laptlum. In ihe horse, elepbant, ~^d~oi(7^i(? t3UVtUiii-4s-i:Qiiiposed of libres Itapelum iibroEum) ; in carnivorajJt^isjonnedjJlxells (tapetum eellulosum), In the ox, it is a brilllant greeii eolour with a golden lustre ; In the dog, it is whlle with a bluisli bordei ; In the horse, it is blue wilh a silyeiy lustie.

The chief bulk of the ehorioid eoat is eomposed of blood- vessels. TTiese are arranged in two well-marked layers, viz.," a deep, elosely-meshed eapillaiy layer eaUed the lamina. ehorio- £aplllaris, and a raore superfi.cial venous layer eomposed of

the va a 11 rh o The ho po 0 rj eries_gass

an eno y be ween e a ula aje

The eyeball in whieh the outei surface of Lhe eborioid is BKposed should be imraetaed in watei and the pigment washed oat of il by meaiiB of * eaniel-hair brush. The vasa vottia)Ba will Ihen anpear as white euiTed lines converging towards four ot five points, from whieh Ihe vei^_yQr!isDse lakeorigin |Fig. 253).

Oorpua Giluire. — The ci!iary_body is separable into an antero-exteriial parl, the orbieulus eil.iaris, and a postero- internal pari, the enrona eiliaris.

The ^i^mT__ eiliiiris eonsists of the eiliary niusele, the ganglionated eihary iierve pltyius, and plexuses of arteries and veins assoeiated with the iris and eiliary body. It is

57«

BULBUS OeULI

eontinuous witli the irls iniemally, the selera anteriorly, and ihi,- eorona eiliaris and the ehorioid posteriorly.

eiliory Muaele.— This is eomposed of invoIuntary museular tissue, but the arrangement of its fibres ean be seen only when thin seetions of the eyeball are examined under the mieroseope. It is then obvious that the fibres are disposed in two groups, viz., a radiating and a eireular.

The radiatin^ ^bres arise from the deep aspeet of the selera dose to _the margtn of the eomea. From this they radiate posteriorly, in a tneridional direetion, and gain insertion into the ehorioid eoat in the region of th^ nilianr

proee!

of two or three bundles

md Zoau1a Ciliaris.

plaeed upon the deep aspeet of the radiating portion of the musele. They form a museular ring around the outer eireum- ference of the iris.

Disseeiion.—Ta obtain a view of tlie eiliary proeesses, a frontal seetion should lie iiiadt- ihtough an eyeball a shorl distanee anteriot to the eauator. The portion of Ihe yLtteous hody whieh oeeupies the posterior semnent of the eyeball should be caiefully remoyed. When this is done, the deep asi«ct of Ihe eotona eiliaris will be seen. Il is covered wilh eiliary proeesses whieh radiate poaleriorly ftom the dtcumference of the etystalline lens. Ly washing out the pigment from Ihis nart of the va5cular tunie, the annngement of the proeesses will be displayed moie fu1Iy.

A seeond disseetion may bc mnie in anolher eyeball with the object of expiKinE liie eiliaty proeesses ftoni Iho fiont. In Ihis ease iemove the eotnea with Ihe seissots liy eutling tound the eotneo-seleral junction. The itis is now btought eonspieuously into view, and may, with advantage, be studied ai this stage. Heve[a! euts in the meridional direelioo, and at

eiLIARY BODY

separated from the eiHary musele, and pinned

lined tiay fiUed wilh water. The iast step in the disseetion eonsists in the

removal of the iris.

The eorona eiliaris lies nn il»' pi-tBtprinr aspeet Qf the orbieulus eiliaris and is eontinuous anteriorly with the iris and pnHteriorly wtth the ehorioid. It eonsists of a number of larger folds, iha proeeisits eiliares, 70 to 72 in number, whieh mingled with a number of smaller folds, the pliem

eiliares. The eiliary proeesses extend ^rTH tlif ■'"'-''""ttr m;irgin (if thp rhnrioid to the anterior maTRin of the eorona nilinris, where thpy pr,(\ in hiilhr>n<; PArti-pmitipg The_buibous ends oeeupy the spaee between the peripheral m.i.rf;in nf the iris and the margin pf the anterior surlaee of the erystalline lens, and they form tne peripheral botandary of the posterior r.hnmhpr r.f ths pypliall. The pliea eiliares are mueh less prominent than the eiliary proeess, and both the proeesses and the folds are in relation posteriorly with the hyaloid membrane, whieh .separates them from the viCreous body, and with the peripheral part of the zonula eiliaris to whidi they are attaehed. voL. n — .37

is le

\

" I

I

J

-« BULBUS OeULI

Iris. 'Jhc in?> lies anierior to the erystalline leQ& and it i^ ^':\jjj'jiU:ti Irorii tlie eornea by the anterior ehamber filled wi!!i^a^juc'jus h'jnjour. By its drcumference it is eontinuous

wi'li tlj«; riliury body, and il is rnnnerteH hy the ligaTn^ntriTn

ii<.-^ tmat'Tiii Iridis^with ihe margin of the eomea.

'ihr iris i?> <.ir<:ular in form, and has a eentral perforation ti;rnn.d tlie /////7. Its anterior surface is faintly striated in a radial direetion. It is eoloured diflferently in diSerent iM<Jividuals. Iis jjosterior surface is deeply pigmented. 'J'1j«; puj>il presents a ver)' nearly dreular outline,^ and <Iiinij^; lile ii eonslantly varies in its dimensions so as to < ini\rn\ tln; anuipy^t (A light •whieh is admitted intn ^lie iiit<;rifir <jf the eyeliall. These ehanges in the size Qf the li'ipil are produeed by the two groups of in voluntarv musenlar \]\)u:s wlii<.h are uresent in the substanee of the iris, One jir<>iij> is (:oirij><jsed of museular fibres arrang^ed en'riiTgrly arou]i<r tlie |jujji7 in the form of a sphincter\ the seeond ^r<>ni|r o^iisists of filjres whieh have a radial direetion, and I>ass froni the sphineter towards the drciimfprenre of the iris, so as to <:<jnstitute a dilatator musele. By some an:il(>iiiists ttirsr radial fihrf^'; are eonsidered to be elastu_ aii<i n<jl museular.

Oiliary NerveB. — The eiliary nerves arise from the dliary J4;iiij4li<)n and the naso-dliary nerve. They pieree the selera mouini tlie oj)ti(: entranee, and extend anteriorly, between \\\v ^( itni and ihe ehorioid, in the periehorioidal lymph spaee. 'rii<y will be seen, in the speeimen in whieh the selera has l)(tn IuiirmI aside in separate fiaps, in the form of delieate wiiiie rilanienls (Fig. 253). In the posterior part of the (■ythall ilu,y oeeui^y grooves on the deep surface of the selera, ;iii(l ean l)c suparated from it only with difficulty. Reaehing ilh* ('iliary /.one the eiliary nerves break into branehes, whieh j«)iii in a j)lexiform nianner and send twigs to the eiliary iuusele, ilu: iris, and the eornea.

eiliary Arteries. — There are three groups of eiliary arltiit's : (i) the short posterior eiliary arteries; (2) the long |)«)',it*ri()r ('iliary arteries; and (3) the anterior eiliary arteries.

'l'lu- short posterior eiliary arteries^ branehes of the (»|)liih;ilmi(*, pieree the selera around the optie entranee,

' li iM.iv l»i- as weli to nuMition here that the pupil in the ox and the •ahti'l» is j4n*aiiy flt)ngat«'(l in the transverse direetion. In the pig, how- r\vx, n is ai>pu)xiniatt*ly eireular.

RETINA

S79

and are distributed in the ehorioid eoat between the vasa vorticosa and the membrana ehorio-eapillaris.

The iong posUrior eiliary arleries, also branehes of the ophthalmie, are only two in number, They perTorate the selera on either side of the optie nerve (Fig, 252), a short distanee beyond the short dliary arteries, and then pass anteriorly between the selera and the ehorioid. When they gain the eiliary zone eaeh artery divides into an aseending and a deseending braneh, and these, with the anterior eiliary arteries, form an arterial ring termed the dreulus iridis major. Branehes are given off froni this eirele to the eiliary musele, the eiliary proeesses, and the iris.

The anterior dliary arieriu are very small twigs, whieh arise from the branehes of supply to the reeti museles, They pieree the selera elose to the margin of the eoraea, take part in the fomiation of the eireulus iridis major, and - send twigs to the eiliary proeesses.

Yeiue VorticoBSB. — From eaeh venous vortex in the ehorioid a large vein arises, whieh makes its exit from the eyeball by piereing ihe seiera, obliqueIy, a short dislanee posterior to the equator. They are four or tive in numher.

DhseitU>n. — The vilreoiis hody and retina, in tlie posteriar part of the eyeball whieh was eut inlo two for Ihe purpoEe o^ eipming the dliary I proeesses from the posteriot aspeel, should now be dialodged. By raising ^ the ehoriuid eoat irom the deep suiiHee of tlie selera, under a flow of water f[om the (ap, the vena; vorticosK entering the deep sutface Qf the . seleta will be brought inlo view. Wheo these are dirided, and the separa- tion of the two eoats is eairied posteriorly towards the optie entranee, the posterior short eiliaty arleries, as they emerge from the selera and entet the postetior patt of the ehotioid, will be seen.

In the eyeball from whieh the selern and eornea have been reinoved, the iiis, eiliary proeesses, and the ehorioid should be earerully stripped Dff pieeemeal under watet. Tiils will expo5e the tetina.

Betina. — The retina is eomposed of two strata— viz., a thin pigmenlary iayer, whieh adheres to the deep surface of the ehorioid eoat, and has been removed with it, and ; delieate nervous layer, whieh is moulded on the surface of the vitreous body, but presents no attaehment to it except at the optie entranee. The retina extends anteriorly, beyond the equator of the eyeball, and, a short distanee from the eiliaiy zone, it appears to end in a well-defined wavy or

5 5= BULBUS OeULI

fe^::»:r.ec bi^reer tenr.ed :he era sirrata. TYns appearanee, "r.:"»-ever. :s >:~:ewr.2: cecepdve- The nenre elements, it ii :r-e, e^nie :: ir. er.d along this line, but a lamina in ::r.::r. j.::y ^::h :he re:::Li is :n reality prolonged antero- .T.rl!j. '.".;.- i> lir 25 the nurgin or" the pupiL The part in relj.:::r. :: the c:I:iry proeesses is exceedingly thin, and ear. r.o: 're ce:ec:ed by the naked eye. It is tenned the Tars .i.'isn's rf::K^. The ponion on the deep surface of the :r:s :s e^Ilee :he s:rj^'r /:.prtff!^' in'J:s.

Durlr.^ l::e :he ry/:rj J^r'/^r is transparent, but after death i: so-ori assumes a eu'*. gre\ish tint and beeomes opaque. Pos:erlor'y :: :> ::ec down at the optie entranee. WTien v:ewed r'rorr. :he :Lr.:er:or .ispeet this appears as a eonspieuous eireular d:>c ternied :he /ii/:VJa nerri o/tia, upon whieh is a depressio:^. the ^.u-.:r-.:.':l' Js2/i/»\c. From this spot the op::c r.er\e r.bres rad:a:e out so as to form the deep or anterior '.ayer cf :he retina. The optie dise, in eorrespond- enee \v::h :he e:::!Ttr.ce ot the optie nerve, lies to the medial or r..\5al s:de of the antero-posterior asis of the eyeball. Exactly in the cen:re of the human retina, and therefore in the axis of the globe of the eye, there is a small yellowish spot rermed the ma^'itla Jutea.^ It is somewhat ovaI in ourline, and a depression in its eentre is ealled the /airea ■.'z'n/rti.Vs.

Setinal Aiteries and Yeins. — In a fresh eyeball the arteria eer.tr.i.'is r:tin<c will be seen entering the retina at the optie dise. It inimediately di^ndes into a superior and an inferior braneh, and eaeh of these breaks up into a large lateral or temporal division, and a smaller medial or nasal division. These ramify in the retina as far as the ora serrata : but the resultant branehes do not anastomose with eaeh other. nor with any of the other arteries in the eyeball.

The retinal veins converge upon the optie dise, and disappear into the substanee of the optie ner\-e in the form of two small tiunks whieh soon unite.

The reiinal vessels. the optie dise, and ihe maeula ean all be examined in the living e\ e by nieans of the ophthalmoseope. The red reflex obtained from the funiius of the eyeball is produeed by the blood in the lamina ehorio-eapillaris.

1 There is no maeula lutea in the eyeb^* or sheep.

YITREOUS BODY 581

Dissictieii.—Fcit tbe study oEthe vitreous body and the erystalline lens, whieh (ogethei may he termed Ihe " cye-lteme1," it is better to lake an eyeball whieh is not perfectly fresh (Anderson Stuart). The eyeball seleeled for this puipose should be allowed to stand untouehed from one to ihree days, aeeording to the season. The eoats of the eye should then be dtvided round the equator, and on genlly separating the eut edges, and turningthe eoals anteriorly and posterioily, the "eye-kernel" witl slipout. It should be allowed to drop into a vessel filled with elean water. The examination of the parts ibrming the "eye-kemel" will be greatly facilitated by plaeing it ea masse in sitoog piero-earmine solulion far a tew minuteK. When temoved from the staining fiuid, it should be well washed in watet. In this way the hyaloid membrane endosing the vitreous body, the eapsule of the lens, and the lonula eiliaris, are slained red, and their eoiuieelions beeome very apparent (Anderson Stuart).

VitreoTis Body. — This is a soft, yielding, transparent, jelly-like body, whieh oeeupies the posterior fQur-fiftlis of the interior of the eyebalL The retina is spread over its surraee as far forwards as the ora serrata, but is in no way attaehed to it, except at the optie dise. Anterior to the ora serrata, the eiliary proeesses are applied to the vHtreous body and indent its surface. More anteriorly, the yitreous body pre- sents a deep concavity, the /ossa hyaloidea, for the reeeption of the posterior convex surface of the erystalline lens.

The substanee of the yitreous body is enelosed within a delieate transparent membrane, whieh eompletely enveIops it, and reeeiyes the name of the hyaloid membrane. Extend- ing anteriorly through tho midst of the vitreous mass, from the region of the optie dise to the erystalline lens, is a minute eanal, lined with a tube-Uke prolongalion of the hyaloid membrane, and eontaining a watery fluid. This is termed the hyaloid eanal; it represents the palh taken by a braneh of the arteria eentralis retinie, whieh, in the fcetus, estends to and supplies the eapsule of the lens, but afterwards disappears.

The hyaloid eanal, as a rule, eannot he seen in an ordioary disseetion of tbe eyeball j but if ihe " eye-kernel" be shalien up in tbe piero-eanniiie solution as reeommended by Anderson Stuatt, it may somelimes be rendered evi<Ient through the staining fiuid entering it. It is represented diagram- matieally in Fig. 151.

Zonala Oiliaris (O.T. Zatiiila of Ziim). Between the eorona eiliaris enternally and the margin of the lens intemally lies a Abrous membrane ealled the zonula eiliaris. Its external margin is attaehed to the posterior surfaces of tbe eiliary proeesses and the hyaloid merabrane, and its internal margin is eonneeted with the lens. As it approaehes the margin of the eryslalline lens, it splits into two parts, viz., an

SRi BULBUS OeULl

<;xccedingly delieate deep lamina, whieh lines the fo5sa hyaluidea, and a more superficial stronger part, whieh beeomes attaehed to the eapsule of the erystalhne lens.

The zonula eiliaris lies subjacent to the eiliary proeesses, and is radially plaited or wrinkled in eorrespondenee with these. Thus the clevations or wrinkles of the zonuIa extend into the intertals between the eiliary proeesses, whilst the eiliary proeesses in their turn lie in the depressions between the wrinkles of the zonula. When the eye is fresh, these opposing parts are elosely adherent

The zonula eiliaris is strengthened by radially direeted elastie Abres, and after the deheaie membrane whieh lines

l''i<;. 256.— Uingrammatie represeouiion of ihe Giliaiy Regiou,

the Tossa hyaloidea is given off from its deep surface, it extcnds inwards as a distinet layer, and is attaehed to the anterior surface of the eapsule of the lens a short distanee beyond the margin of that body. In this manner the suspensory Hgament of the lens is formed. But tbis is not ihe only attaehment of the suspensory ligament. Some seattered fibres are altaehed to the circumference or equator of the lens (cquatorial fibres), whilst others are fi]ted to its posterior suri'aee elose to its mai^n {post-eqiiP*' -■""■

In this way the erystalline lens is firmly in llio fossa hyaloldea, Purther, the degr suspensory ligament is inAueneed by the

reiiee ui cqua[or are fixed to its

LENS 583

the eiliary musele, whieh by their eontraetion pull upon the eiliary proeesses, and produee relaxation of the zonula eiliaris.

Spatla Zonularia (O.T. eanal of Petit). — In reality the spatia zonularia eonstitute a more or less eontinuous eireular lymph spaee, whieh surrounds the circumference of the lens. It lies between the anterior and posterior layers of the suspensory ligament and is filled with a watery fluid.

By introdueing the point of a fine blow-pipe into the spatia zonularis through the suspensory ligament, it ean be partially, or, perhaps, eom- pletely, inAated with air. It then presents a saeeulated appearanee.

Disseetion, — The erystalline lens may be removed by snipping through the suspensory ligament with seissors.

Lens Orystallina. — The erystalline lens is a biconvex, solid, and transparent strueture whieh lies between the iris and the vitreous body. It is enelosed within a glassy, elastie eapsule, to whieh the different parts of the zonula eiliaris are firmly eemented, and it presents for study an anterior surfacei a posterior surface, and a circumference or equator.

The anterior surface is not so highly curved as the posterior surface. Its eentral part, whieh eorresponds with the pupillary aperture of the iris, looks into the anterior ehamber of the eye. Around this part the margin of the pupillary orifice of the iris is in eontaet with the lens, whilst nearer the equator the anterior surface of the lens is separated from the iris by the fluid in the posterior ehamber of the eyeball. Th^ posterior surface of the lens presents a higher degree of curvature than the anterior surface, and is received into the fossa hyaloidea of the vitreous body. The eguator or circumference is rounded. It forms one of the boundaries of the spatia zonularia, and the manner in whieh the zonula eiliaris is attaehed to the eapsule in this vicinity has been deseribed already.

Faint radiating lines may be seen on both surfaces of the lens. These give a elue to the strueture of the lens. They indieate the planes along whieh the extremities of the lens- fibres eome into apposition with eaeh other.

The eapsule of the lens is a resistant glassy membrane, whieh is eonsiderably thieker anteriorly than posteriorly.

The anterior wall of the eapsule may now be divided with a sharp knife. A little pressure will eause the body of the lens to eseape through the opening. The stained eapsule ean be very advantageously studied whilst Aoating in water.

5S4 BULBUS OeULI

I:' :hr len* :->iy :« eompressed beiween the finger and thumb, it will L^ r..:c"i :h2t :he :u:er rortii^n ot eertieal part is soft, whilst the eentral jv3r: cr nu.'.iu: :> iisUErtly nmier. ^Mien the lens is hardened in aleohol :: ean eisily ':«e :r;.ved :ha: i: is eomposed of numerous eoneentrieally

Ghainbeis of the EyebalL — The anterior ehaniber of the eyeba'I is ihe spaee between the eomea anteriorly, and the iris and eeniral part of the lens posteriorly. At the irido- eorneal angle it is bounded by the ligamentum peetinatum iridis. and there the aqueous humour whieh tills this ehamber tinds aeeess to the spaiia anguli iridis.

The posUrior ehambtr is a eireular spaee or interval whieh is bounded anteriorly by the posterior surface of the iris, and posteriorly by the circumferentiai part of the anterior face of the lens. Extemally, this spaee is elosed by the thiek anterior projecting ends of the eiliary proeesses. It also is filled with aqueous humour.

INDEX.

Aeeessory parotid, 126, 127, 261 Aditus laryngis, 378, 408, 409 Agger nasi, 396 Alae of thyreoid eartilage, 414, 415,

421, 423 Alveus, 497 Ampullse of semieireular eanals,

567 Amygdaloid nueleus, 491, 494, 512,

Annular ligament of Stapes, 557 Ansa hypoglossi, 146, 234, 243, 244, 246 subclavia, Yieussenii, 239, 250, 257, 258, 319 Antihelix, 153 Antitragus, 154 Aorta, 10, 83

areh, 23, 30, 32, 44, 78, 85, 89, 96, 98, 100, 102, 103, 106, 247 position of, 85 aseending, 39, 55, 83, 98

position of, 83 deseending thoraeie, 31, 44, 50, 58, n, 89, 98, 102, 104, 106, 109, III Aortie groove on left lung, 40 eusp, 87

great sinus of, 84 oriAee, 74, 83

sinus of (Valsalva), 78, 80, 84, 87 valve, 87 Apertura medialis ventriculi quarti,

53? tympaniea eanieuli ehordse, 551,

564 Apex eolumni anterioris, 197 Apieal gland, 434 Apiees of the aurieles, 55, 65, 76,

84, 89, 98

585

Aponeurosis, 366

bueeo-pharyngeal, 366

of palate, 382

pharyngeal, 373

vertebral, 235, 236, 237 Appendix ventriculi, 412, 421 Aqu3eductus eerebri, 503, 505, 506,

509, 5" vestibuli, 566

Aqueous humour, 571, 584

Araehnoidea eneephali, 438, 439

spinalis, 185 Araehnoideal granulations, 202,

206, 442 Areh lateral lumbo-eostal, 109, 167

glosso-palatine, 430, 431 Areus glosso-palatinus, 368, 378, 380, 381, 382, 430, 431

parieto-oeeipitalis, 464, 471, 472,

474 phar)mgo-palatinus, 368, 369,

378, 380, 381, 382 tarseus, 137, 342 Area aeustiea, 525 Artery or Arteries, aWeolar, an- terior superior, 386, 389 alveolar inferior, 270, 272, 278,

279 aWeolar posterior superior, 270,

271 angular, 128, 131

of external maxillary, 344 anonyma. See Innominate anterior eerebral, 450, 447, 448 branehes of — anterior medial frontal, 449 antero-median, 449 intermediate medial frontal, 449 medial orbital, 449 posterior medial irontal, 449

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lateral nss^i. 131

lingual, 231. 232, 21^, 2S6, 291,

292, 296, 297 ]uinbar, 176 mammar}', 9

intemal, 7, 9, 15, 34, 251, 254,

357.25«

T L 232

ur, 245

INDEX

587

Artery or Arteries —

maxillary, internal, 242, 262, 267,

269, 272, 274, 294, 296, 301, 402, 403, 405, 406

mediastinal, 104

of the medulla spinalis, 193 meningeal, anterior, 220, 221, 344

aeeessory, 212, 220, 221, 270,

274, 333 of aseending pharyngeal, 220,

221, 304 of internal maxillary, 220, 221 middle, 202, 210, 212, 220,

270, 274, 277, 293, 333 of oeeipital, 220, 221, 301 of yertebral, 220, 221, 356

mental, 279, 30» museulo-phrenie, 7, 9 mylo-hyoid, 270, 278, 283 nasal branehes of anterior eth- moidal, 393 of posterior ethmoidal, 393, 406 posterior (of spheno-palatine),

406 posterior of the septum, 392 nutrient of skull and diploe, 202 oeeipital, 145, 149, 156, 157, 162, 169, 170, 232, 239, 262, 296,

300, 302, 303, 306 deseendingbraneh, 169, 171, 172 meningeal braneh, 169, 171 sterno-mastoid braneh, 316

oesophageal, 103, 104, 253, 307 ophthalmie, 220, 339, 341 palatine, aseending, 383

of aseending pharyngeal, 304,

383

deseending, 383, 405, 406

of dorsalis linguae, 383

of laerimal, 342

of ophthalmie, 342

small, 406 palpebral, 137, 342 parieto - oeeipital (of posterior

eerebral), 447 perforating, of internal mammary,

.4, 9 perieardial, 104

perieardiaeo-phrenie, 50

petrosal of middle meningeal,

301, 333 pharyngeal, 253

aseending, 232, 246, 296, 303,

307, 406

branehes, 304

eanal, artery of, 485

Artery or Arteries —

pontine, 445

posterior aurieular, 302

eerebral, 457

eommunieating, 480

oeeipital, 303

of septum, 406 prevertebral branchesof aseending

pharyngeal, 304 profunda cervicis, 172, 173, 175

linguse, 290, 291 pterygoid, 270

eanal, artery of, 405 pulmonary, 10, 22, 30, 34, 38, 44, 55» 70, 75» 78, 84, 85, 90, 99

right, 76, 84, S6, 98, loi

left, 76, 86, 99

foetal eondition of, 77

relations of extra-pulmonary part, 99

orifice of, 83

relations of, 76

topography of, 76 ranine, 434 retinal, 581 septal of the nose, 131 short posterior eiliary, 574 spheno-palatine, 402, 405, 406 spinal, 109, 176, 181, 182, 193, 252

neural branehes of, 182

pre-laminar branehes of, 182

post-eentral branehes of, 182

anterior, 445

posterior, 443 sterno-mastoid, of oeeipital, 231, 233» 235, 239, 300, 308

of superior thyreoid, 232, 235, 239, 245, 296, 308

of transyerse seapular, 235, 239 stylo-mastoid, 147, 151, 161, 274,

307 subelayian, 23, 25, 31, 32, 34, 35,

235» 239, 246, 247, 254, 257,

258, 309» 315» 323 branehes of, 251

left, 86, 88, 89, 100, 102, 106,

250, 255 right, 250 subeostal, 104, 109 sublingual, 291, 292, 300 submental, 282, 283, 284, 292,

300 superior epigastrie, 7, 9 intereostal, 7, 109, iio

588

INDEX

Artery or ArteriM—

superior labial, 130, 393

septal braneh of, 393 supra-hyoid of lingual, 232, 291 supra-orhital, 156, 157 tcm[x>ral of posterior eerebral, 447 deep, 267, 270, 303 middle, 262, 265, 266, 267,

270, 302 supertieia], 127, 157, 261, 262, 277, 294, 296, 301 thoraeo-aeromial, 161 thyreo-cervical, 106, 251, 252,

253.. 254» 309» 323 aseending cervical braneh of,

240

inferior, 106, 235, 245, 246,

251, 252, 255, 315, 321, 323 superior, 229, 230, 232, 234,

243, 246, 253, 296, 308, 321 thyreoidea ima, 49, 229, 320, 321 t(msillar, 299 traeheal, 253 transversa eolli, 106, 145, 147,

149, 161, 164, 239,242, 251,

252, 253, 255, 323 transverse facial, 127

seapular, 106, 145, 147, 149, 161, 164, 225, 242, 251, 252,

253, 255, 309, 323 tympanie, 270, 274 vertcl)ral, 106, 175, 179, 180,

214, 220, 246, 251, 252, 253,

255. 257, 323» 353» 354, 355,

442, 443 /ygomatieo-orbital, 302 Artioulations. See Joints Ary-cpij;h)ttic folds, 329, 408, 409,

415, 418, 420, 421, 427 Aryt;cnoi(l eartilages, 379, 420 Atria of heart, 34, 65, 68. See

lleart Atri()-vcntricular apertures, 69, 71,

73. 79, «3, 92 bundle, 74, 83, 93

librous rings, 93 Atrium medii nasi, 395 Audilory api^aratus, 546 Auditory tube, 293, 299, 312, 375, 37^^, l"^^, 3«2, 383, 384, 559

bony position, 559

eartilage of, 384

earlilaginous portion, 539

lcvator eushion of, 384

ossieles, movcments of, 557

l)arls of, 384

I Aaditory tnbe —

phar^mgeal orifice of, 384 I Auriele, 153, 546

eartilage of, 270

1 Baek, 161

I blood-vessels, 170, 175 nerves, 162, 173, 177 Rasal ganglia, 512 Basilar sinus, 183, 216 Basis peduneuli, 508, 509, 510 Biventral lobule, 533 Braehia conjunctiva, 511, 545

eerebelli, 529, 530 Braehial pleius, 151 Braehium pontis eerebri, 458, 531

conjunctiva eerebelli, 512 Brain. Aho voL i. p. 28 basal ganglia, 437, 512 base, 437 blood-vessels, 442 eerebellum, 437 eerebral hemispheres, 459 eerebrum, 459 eorpus eallosum, 479 fomix, 496

fourth ventricle, 458, 520 general appearanee, 437 general connexion of several

parts, 458 general stnieture, 461 lateral ventricles, 458 lobule paraeentral, 466 lobe frontal, 466-470

lateral surface of, 466 medial surface of, 469 orbital surface of, 469 limbie, 477-479 oeeipital, 472-474 lateral surface of, 474 medial surface of, 474 tentorial surface of, 474 olfactory, 477-478 parietal, 470-472

lateral surface of, 471 medial surface of, 470 temporal, 475-477 lateral surface of, 475 opereular surface of, 475 tentorial surface of, 476 medulla oblongata, 437 meninges, 439 meseneephalon, 506 origin of nerves, 454 parts in posterior eranial fossa, 452

INDEX

5S9

Brain —

peduneles of, 506, 508

pons Yarolii, 437

posterior hom of ▼entnde, 473

preservatioD of, 437

removal from eTaniam, 211, 217

septum pellueidiim, 495

thalami, 500

third ventricle, 503

velum interpoatum, 498 Bronehi, 10, 22, 38, 44, 70, 77, 97

eparterial, 22, 76, 98

hyparterial, 10, 38, 44, 70

left, 87, 98, 103

relations of intrapulmoiiaiy part,

98 right, 84, 98, loi

Bueeal aponeurosis, 366

glands, 366

plexus, 277 Bueeo-pharyngeal iasda, 366, 370 Bulb,

of eomu, 490

of jugular vein, 307, 350

olfactory, 208 Bulla ethmoidalis of nose, 398 Bundle, atrio-ventricalar, 74 Bursa, pharyngeal, 376

Galamus seriptorius, 537

Galear avis, 473, 490

Galearine fissure, 446, 465, 473.

478, 490 eanal earotid, 385

eentral, of spinal medulla, 181

of modiolus, 568 facial, 552, 561, 562, 563, 564,

565 for tensor tympani, 551

hyaloid, 581

laerimal, 138, 140

membranous, 569

pharyngeal, 405

pterygoid, 405

semieireular, 561, 565 lateral, 567 posterior, 567 superior, 567

spiral, of modiolus, 568 Ganalis reuniens, 569 Ganalis facialis, 552, 561-565 Ganthi, 120

Gapitular artieulations, 112 eapBule, extemal, 450, 512, 519

interaal, 450, 512, 514, 518

oflens, 583

W

%.

*ep. ^ «5. «9^ 96, 99.

I

100

«""Pnr6dal. 13> 43. 65. 7S, S$,

^3 CaiDtidbod|f, 247

eaiial.185

gluid,a94

Fkni>3iS

diauh,235

tiiaiigle, 2j6, 232, 233

eantHa^i^ aiytaenoid, 379, 408, 410,

411, 414. 415, 416, 417. 41«.

419. 4»^ 421* 427 eornieiilate, 40>f 415* 4i6, 421«

427 oieoid, 250, 414, 415. 426

aaiaSam^ 408, 415, 4», 4JS

ofqK;lattii»423

]atenlof noae, 141

alar<»fiioae, 141

iiunororifiaiiidof noM^ 141

orpiima, 155

ffwii'wid <■ r

tritieaea, 414

tliTieaid, 229^ 230, 414, 41$, 421,

423 Gaitilagine» eoraieiiiatar, 422, 427

Ganinenla laeriaalis, 120

P.afufat4> imrltW f dAA» jttL aSiL JOf.

518

Gawnoas plem, 2S5, 5|s« 33S, 3|K

nmiSy 209^ 210 CaTityoftlionx, i, fo Ca;vnin MirkHH, 212, 329

oris,3l^^

snhaiaehiioideale, 185,439 sabdtnale» iS^ 204 Gentnl eanal otinnal MednOay 196 of medHlla, 521 of modiolnt, 568 peyniattero^aeinednet, 505 Gentnl lobe;, 462

loiiale,53i Cetttiie, lomsr Yisiial, 508 Gentnnn owale, 480 Gerebdlar prdnndet, 534

snpeiior, 535 GenlidkMdiwiy tnet, 5:9 -^iiiial tnety 525

OMPikillmi, 437. 5^

590

INDEX

eerebeUam—

arlx)r vitce, 534 braehia conjunctiva, 535 eorpus meilullare, 534 tissures, 529, 531 hemispheres, 529 lingula of, 538

lobes, 529, 531, 532, 533, 534 lobules, 531, 533

eentral, 529, 531

linguli, 538 lobus noduli, 533

Pyramidis, 534

tuberis, 534

uvula;, 533 montieulus, 529 notehes, 529 I>etluncles, superior, 532

braehia pontis, 529

inferior, 527 surfacc of, infcrior, 530

superior, 535 vallecula, 530 vcrmis, 529 Gerebral cortcx, 461 hemispheres, 461

basal ganglia, 512

borders, 459, 460

eorona radiata, 519

cortex, 461

fissures, 462-479

general strueture, 458

grey matter, 461

gyri, 461, 462, 479

internal eapsule, 518

island of Reil, 477

lobes, 462, 466, 470, 472, 475,

477 medullary eentre, 461

orbital area, 459

poles, 465

sulei, 461

tentorial area, 459

ventricles, 483,492, 49^, S<^3'S^ eerebrum, 459, 520

anterior eommissure, 503, 519 borders of, 459 eorpus eallosum, 446, 497 fornix, 488, 496, 499 frontal pole of, 460 hemispheres, 459 inferior surface, 459 lateral surface, 459

ventricles, 483-492 longitudinal fissure, 439, 449 massa intermedia, 504

Cerebram —

medial surface, 459 oeeipital pole of, 460 orbital area, 459 peduneuli, 210, 212 posterior eommissure, 503, 505 septum pellueidum, 449, 488 temporal pole of, 460 tentorial area, 459 thalamus, 447-450 third ventricle, 503-506 transverse fissure, 499 tela ehorioidea, 442 Geruminous glands, 548 Geryieal fascia, 235 ganglion, inferior, 319 middle, 318 superior, 317, 318 pleura, 248, 250, 257 plexus, 151, 239, 240 eommunieating branehes of, 241 museular branebes, 241 sympathetie, 245, 247, 252 Cervix eolumnse,

anterioris, 197 posterioris, 197 Ghambers of eyeball, 571, 584 Gheeks, 366 ehest. See Thorax Ghiasma, optie, 441 Ghoanse, 374, 375, 377, 389 Ghondroglossus, 434 ehorda tympani, 564 ehordoe tendinese, 73, 74, 79, 80

Willisii, 206 Ghorioid, 571, 574 eoat, 574

lamina eorporis eapillaris, 575 plexuses, 497 vasa vofticosa, 575 Ghorioidal fissure, 492, 493, 494 Ghyle, 105

Giliary body, 571, 574 eireular fibres of, 576 folds, 577 ganglion, 338 musele, 576 orbieularis eiliaris, 576 proeesses, 577 radiating fibres, 576 zone, 579, 583 eingulum, 479 Gireular sinus, 209, 217

suleus, 462, 463 eireulus arteriosus, 441, 443, 450 iridis major, 579

INDEX

59J

Gireulus iridis minor, 579

tonsillaris, 311 eistema eerebello-medullaris, 440,

538 ehiasmatis, 441, 443, 450 ehyli, 105 interpeduneularis, 210, 441, 443,

450 pontis, 441

subaraehnoidales, 440

ven3e magnte eerebri, 442 eiaustrum, 512, 516, 517 Clava, 526 Clivus, 532 Cochlea, 565, 567

eanal of, medial longitudinal, 568

eupola, 568

duet of the, 569

ganglion spirale, 568

lamina spiralis, 568

membranous eoehlear tube, 568

modiolus of, 568

eanal, medial spiral of, 568

seala vestibuli, 566 Collateral fissure, 461, 462, 465 Colliculus facialis, 537 Colliculi (of lamina quadrigemina),

506 Column of Burdaeh, 199

of GoU, 199 Columns of grey matter of eord, 197

lateral grey, 198 Commissures, anterior, of brain,503,

519 posterior, 503, 505

Commissures of eord, 195, 196

palpebral, 119 Conchae of ear, 153

of nose, 376, m, 389, 395, 396,

397, 399, 400, 401, 402, 403 Conical papilloe, 432

Conjunctiva, 120, 139

fornix conjunctivDe, 120

pliea semilunaris, 120

earuneula laerimalis, 120 Conus arteriosus, 30, 39, 54, 70, 72, 74, 78, 84

elastieus, 414, 415, 418, 419, 421

medullaris, 187, 188 Convolution. See Gyrus Cord, gangliated, of sympathetie, 2, 23, 25, 108, 109

spinal. See Spinal medulla

vocal, 579, 581 Cords of braehial plexus, 151

Comca, 572, 573. 574- ?:? Comco-scleral jur.:::- r. 573 Comu Ammonis. 401, .102. 4''<'5- i'-7 Goraua of lateral vcr.tr. :1t^. i'7. 490, 491. 49^

of thyreoid eartilagt. x^ Gorona eiliari». 577

radiata, 519, 57^. 596

radiator, 519 Goronary plexu*. O5. S3

sinus, 89

suleus, 68

valve, 81 Gorpora mamillaria. 452, 453. .±07.

503, 5p4 quadrigemma, 2ic. 447, 300. yJj.

507,511,512. 529

superior, 503, ^'.d, 307

braehia of, 507

genieulatum. 512

Oorpas eallomin. 446. 45S. 473.

478, 479, 480, 4<»i, i>*- ^y-*.

495» 496. 497, 49S, 499 eentral {lart, 494

Abres, 4^8 1, 483

genu, 448, 478, 482, 4&3, 4^7.

495 lamina rostralis. of, 482

rostrum, 448, 449, 482. 483

radiation, 483

truneus of, 482, 487

splenium, 446, 478, 482, 483.

486, 494, 495. 499

Corpu3 genieulatum eitemal, 503

intemal, 507

laterale, 507, 508

mediale, 506, 507

Gorpus mamillare, 519

striatum, 512, 515

trapezoidum, 545

Gosto-mediastinal «sinus, 12, 16, 25

-traiisverse jointt, 113

ligameots of the tu:>er<:I««, 113

-▼ertebral artieulati^iiu, j 12

Cranial fossa, middle, 325, 333

Greseentie lobule, 531, 532

Grieoid eartilage, 230, 414, 415, 426

Grieo-thyreoid meml>raoe, 297, 415

Grista ▼estibali, 566

Onira of emeial iigament, 3^3

Cnira of stapes, 557

Crus helieis, 153

Cnis laterale of malleet, 555

of ineits, 555

erystalUoe lens, 571, 37*, 5*1, $>?

enlmen montienli, ^y^, 531

592

INDEX

Guneate funiculus, 540, 541

nuolous, 541

lul>ercle, 379 Cuneiform eartilage, 408, 415, 421

tuberele, 379 Guneus, 447. 473 Gupola niodioli, 568

Deeostation of the lemniseus, 542

motor, 542

of pyramids, 542

sensory, 542 l)eclive Montieuli, 531 Dentate fascia, 479, 483, 492,

495 hssure, 479, 495

nuoleus ()f cerel>elluni, 539

Diaphragm, 3, 35, 50, 70, 88, 99,

100, 102, 103, 105, 241

eentral temlon of, 88

enira of 104, 105, iii

membranous cervical, 36

l)iaphraj^ina oris, 284

sella', 209

Diaphra^niatie line of pleural reflec-

tion, 14, 17, 18, 19

pleura, 16

Dij;astric triani;le, 226

Dilatator pupilUe, 578

1 )ionre[iliaK)n, 520

Dise, intervcrtel)ral, 357

optie, 580, 581

Diseus artieularis of jaw-joint, 268,

271, 272, 273, 274

DiBBeotions — Thoraz —

thoraeie wall, 3, 4, 7

thoraeie cavity, 12, 25, 29, 32,

33» 43. 46, 4^"^ perieardium and heart, 49, 51,

60, 65, 76, 78, 79, 87, 88,

89, 91 deep of the thorax, 98, lOi,

104, 109 thoraeie joints, 112 Head and Neek —

face, 117, 120, 126, 128, 132,

133. 134, 140 posterior triangle of neek, 142,

143, 145, 146 sealp, 153, 154, 158, 159 sterno-clavicular joint, 159 baek, 161, 162, 164, 166, 167,

168, 171, 172, 176, 178, 179,

181, 185, 191, 192, 200 removal of the brain, 200, 203,

207, 211, 217, 222

Disseetions — Head and Neek —

anterior part of neek, 223, 225,

229, 230, 231, 234, 238, 239,

244, 261, 262, 303, 304, 309,

310, 317, 324, 325 temporal and infratemporal

regions, 266, 274, 279, 293 submaxillary region, 279, 282,

284 great yessels and nerves of

neek, 303, 304, 309, 324 lateral part of middle eranial

fossa, 325, 329 orbit, 334, 335, 339, 346, 348,

350 prevertebral region, 350, 353,

356 jomts of neek, 358, 361, 362, 363 maxillary nerve, 386 pharynx, 369, 370, 372, 374,

376, 381, 382 nasal cavities, 389, 393, 397,

398, 399 spheno-palatine ganglion, 402,

405 larynx, 413, 415, 417, 419, 421,

422 brain, 457, 460, 479, 480, 483,

484, 485, 490, 494, 495, 496,

498, 500, 505, 512, 519, 528,

536, 539. 540 auditory apparatus, 546, 549,

559 intrapetrous portion of facial

nerve, 562, 565

eyeball, 570, 572, 575, 576,

579, 581, 583 Duet, lymphatie, right, 48, 242,

245» 255 naso-laerimal, 120, 140, 346, 399 of Cuvier (foetal), 91 parotid, 126 sublingual, 289 sub-maxillary, 288 thoraeie, 2, 18, 31, 32, 48, 49, 70, Sy, 102, 104, 106, 108, III, 242, 245, 255 Duetus arteriosus, 33, 77, 78 eoehlearis, 569 endolymphatieus, 569 Dura mater eneephali, 201 layers of, 202, 203 partitions, 203 sinuses, 162, 202, 205, 207, 211,

217 spinalis, 183

INDEX

593

Ear, 547

annulus tympanieus, 549

eoneha of, 546, 547

external, 546

internal or labyrinth, 546, 565

mastoid ear eells, 550

meatus - external aeustie, 546,

547, 548, 549» 550, 559, 560, 561

membrana tympani, 547, 548,

549, 553, 554, 555, 5^1 middle ear, 546, 550

tragus of, 547

tympanie cavity, 546, 550

tympanie antrum, 550, 551, «;54,

555, 559, 560, 561 tympanie membrane, umbo of,

549

Eeto-rhinal fissure, 465, 475

Elastie lamina of eornea, 574 Eminenee, olivary, 524, 525, 526 Eminentia eollateralis, anterior, 494

posterior, 494 Endoeardium, 92 Endolymph, 546, 566 Eparterial bronehus, 22, 76, 98 Ependyma, 485, 526 Epieardium, 92 Epieranial aponeurosis, 122, 123,

154, 156, 158 Epiglottis, 379, 408, 409, 423

aetion of, 429

eartilage, 422

frenum, 409

petiolus of, 423

tuberele of, 409 Ethmoidal eells, 395 Eustaehian orifice, 293, 299, 312,

375, 376, 381, 382, 383, 384

tube, 293 Excav'atio papillge, 580 Eyeball, 570

bulbus oeuli, 570

ehambers, 571, 584 anterior, 585 posterior, 585

equator, 570, 572

general strueture of, 571

meridional lines, 570

poles, 570

refracting media, 571

sagittal axis, 570

tunies, 571 Eyebrows, 118 " Eye-kernel," 581 Eyelids, 119, 134

VOL, II — 38

Eyelids, conjunctiva, 119 glands, 132 ligaments, 121 tarsi, 134 vessels and nerves, 137

Face, 117

arteries, 128

museles, 120

nerves, 126

surface anatomy, 117 Falciform lobe, 465, 481 Falx eerebelli, 212, 215, 529 Easeia, axillary, 147

bueeinator, 261

bueeo-pharyngeal, 366, 370

bulbi, 347-350

earotid sheath, 235, 236, 238

eerebri, 206, 459

cervical, 145, 224, 225, 235

deep cervical, 235

deep of posterior triangle, 144

dentate, 479, 483, 492, 495

intra-thoraeie, 12

lumbo-dorsal, 166, 167

palpebral, 135

parotid, 126

peri-renal, 168

pharyngo-basilar, 373

pretraeheal, 229, 230, 235, 236,

237 prevertebral, 235, 236, 237

of Sibson, 36

submaxillary, 226

superficial cervical, 235

temporal, 265, 266

Fasciculus eerebro - spinalis, 510,

519, 527 eerebello-spinalis, 200

anterior, 200

lateralis, 200, 542

Fasciculus euneatus, 199, 200

graeilis, 199, 200

thalamo-mamillaris, 447

Easeiola einerea, 483

Fauces, isthmus of, 365, 368

pillars, 368

Eenestra eoehleae, 552, 561, 568

vestibuli, 552, 557, 561, 562, 564,

566

Eibrae areuatae, 528

Filum terminale, 183, 187, 188

Eimbria, 479, 491, 492, 494

FiBBure or FiBSures, ealearine, 446,

461, 465, 473, 478, 490

eentral, 462, 464

594

INDEX

FiB8ure or risBiires —

of eerebellum, 529, 531 of eerebrum, 462, 479 ehorioid, 492, 493, 494 eollatoral, 461, 462, 465, 474, 475,

476. 479» 499

(lontate, 479

eeto-rhinal, 465, 475

great horizontal, 530

lont^^itudinal, 439, 449, 460 transvcrse of brain, 492

hipi>ocampal, 461, 465, 495

lateral of hrain, 451, 459, 462, 463, 466, 476 anterior aseending limb, 463 anterior horizontal limb, 463 j>oslerior ramus, 463

longitudinal of brain, 437, 439,

449. 460 of lung, 41 ofmedulla, 195 oral, 365 palpebral, 119

liarieto-oeeipital, 448, 462, 464 lateral, 464, 470, 473, 480 medial, 464 ()f spinal medulla, 195 transverse of brain, 499 F(CtaI eireulation, 68, 69, *]*] Fold, ary-epiglottie, 379, 408, 409, 415, 418, 420, 421, 427 glosso-epiglottie, 409, 423, 430 pharyngo-epiglottie, 409, 423 salpingo-pharyngeal, 376 tympano-malleolar, 549 anterior, 549, 554 posterior, 549, 554 ventricular. See Plieie vestigial, 91 vocal. See Pliere Kolium vermis, 530 Kontana, spaees of, 574 Forainen eoeeum of medulla oblon- gata, 521 ca3cum of tongue, 430 interventriculare, 459, 486, 489,

502, 505 of Magendie, 539 ovale, 68, 78, 92 Koramina vcnae minimae eordis,

92 Forceps major, 483, 490, 494, 496 minor, 483 Formatio alba, 543 grisea, 543

Formatio retieularis, 510, 543, 545 Foniix, 488, 492, 495, 496, 499

body, 496, 497, 49i8, 499

eolumns of, 485, 497

of conjunctiva, 119

orura of, 496, 497, 498

transverse fibres of, 497 Fo8sa of antibelix, 154

eranial, middle, 325, 333

ofhelix, 154

hyaloidea, 581, 582, 583

interpeduneularis, 452, 503

nasal, 393

ovalis, 68, 69, 92

pterygo-palatine, 386, 388

reeessus, 379

rhomboidalis, 536, 537

seaphoid of ear, 154

supraclavicularis, major^ 142 minor, 142

supra-stemal, 178

supra-tonsillar, 378

triangular of ear, 154 Fourth yentriele, 536

ala einerea, 538

area aeustiea, 538

area postrema, 538

eollieulus facialis, 538

eminentia medialis, 537

floor, 536

fovea superior, 538

funiculus separans, 538

lateral reeesses, 536

medullary strise, 538

plexus ehorioid, 539

roofof, 536, 538

substantia ferruginea, 538

tubereulum aeustieum, 538 Fovea eentralis retinae, 580

inferior, 538 reeessus elliptieus, 566 reeessus spheerieus, 566

superior, 538 Frenulum of Giaeomini, 495

oflips, 133, 365

veli, 506 Krenum of epiglottis, 409

linguse, 288, 292, 368 Frontal lobe, 449, 462

opereulum, 463

pole, 465

region of head, 117

sinus, 396, 397 Pronto-parietal opereulum, 463, 475 Fungiform papillae, 432 FuniculuB anterior, 199, 200

izj, 'S^,

rnitionliu —

graeilis, 540, 541

lateral, 199, 200

posterior, 199, 200

Kurrowed band, 533

Galea aponeuroliea, 1

.56, 158 OuiKliat«d eord of sympaihelie, 2,

23, 26, 10S, 109 Ganglion, basal, 512 eervical, inferior, 355 middle, 318

Superius of glosso-phaiyngeal, 312 eiliary, 332, 339, 341, 386. 578 long rool of, 340 short roots of, 34

commumcitionsof, 313

iirst thoraeie sympalhetie, 1 10,254

genieuli of facial, 312, 332, 333,

562, 563, 564 jugulare of vBgus, 312, 313 nasal branehes of, 393 nodosum of vagus, 313, 314, 315.

3'6, 317 orbital branehes of, 405 otie, 276, 277, 279. 293, 383. 559 pelrosum of glosso-pharyngeal,

312. 313, 317 semilunar, 2lt, ZI2, 275, 326,

328, 329, 332, 333, 385, 386 spheno-palatme, 386, 388, 392,

393. 402, 403, 404, 405 spinal, 189 spirile, 568 splanehnie, 28

submaiillaiy, 282, 284, 2S5, 318 infeiior cervical sympathetie, 317,

3'9 middle cervical sympathetie, 318,

319 superior cervical sympathetie,

312, 314, 317, 385 superius, ofglos50-pharyngeal, 312 ofvagu5, 313,315 Gemeulate bodies, 507 Genu of eorpus eallosum, 44S, 47S

of internal eapsule, 51S Giaeomini, frenulum of, 495 Gialiella, mS Gland, bueeal, 366 earolid, 305, 306 labial, 365 laeiimal, 13S, 334, 336, 337

Gland, laeiimal inferior, 337

supen

■,337

,366

mueous o{ Eoft palate, 3S0 subHngual, 368 duets of, 36S submasillary, 225, 226, 368 Ihyreoid, 407 lateral lobe, 407 pyramidal lobe, 407 Globus pallidus, 516 Glo55o-epiglottic Tolds, 409, 423, 430 G-lottis, Irue, 410

pais interearlilaginea, 411

voc3li5, 407, 410 Goll, eolumn of, 199 Graeile fiiDiculus, 540, 541

lohule, 534

nudeus, 541 Graiinlationea AraebDoideales, 302,

Grey

196

OrooYe, aortie on left tung, 40 eoionary, 53, 57, 71,89,91 interveDtriculBr, 53, 63, 71 Gullel, 2, JO, 17, 23, 26, 29, 30, 31, 32.39,40,49,50.58.85.87. 09, 96, 99, 100, !01, 103, 106

Gums, 367

Gyrns or Gyri, 461, 462, 479 angular, 472, 475 eallosal. 479

eential interior, 450, 467 inferiDr. 467, 468 middle, 467 superior, 467 ;inguli. 466, 471, 478. 479, 481

■, 47S

, 447- 473 euneo-lingual, anterior deep, 473 dentalus, 479. 4S3. 491, 495 Ibmieatus, 473, 478, 480 of (rontal iobe, 450 frontal, 450 inferioi, 469 middle, 4JK superior. 466, 469 fusifbnnis, 474, 476 hippoeampal, 446, 447, 465, 474. 47S, 478. 479. 494- 495. 508 opereula. 469 ^^^^

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l-:^r'ier, ltf:, 55

chor5:t lendine.-e, 73, 74, 79, 80 eonus aneri-:)5u>, 30, 39, 54, 70, 72. 74. 7S, S4

e.ronar}' ?inus. 6S

5Uj.u>, 53. 57. 71, S9, 91

valve of, 69 erista lerminalis. 65, 66 cn'Jocardium, 92 epieardium. 92 ex:ernal form, 53 foramen ovale. bS foramina venL\: minimee eordis,

64, 69, 92 fo5sa ovalis, 6S, 69 general relations, 50 £;reat sinus of aorta, 84 ineisura eordis, 53, 57 infc-rior lungitudinal surface, 58 inieratrial suleus, 89 limbus fos.<n: ovalis, 67, 69 mitral valve, So, 92 moderator band, 71, 74 museuli papillares, 73, 79, 80

peetinati, 66, 91 myneardium, 92 ne'rves, 33, 43, 65, 7S, 85, 87, 89,

96. 99, 100 orifices. top^graphy of great, 87 pars membranaeea septi, 74, 83

pulmonary oriflce, 71, 72

cu3psofvalve, 75

lunuke uf Ihe valve, 75

nodules of the valve, 75

sinus, 75

lopography of, 75, 87

vaW, 75, 78 semilunar va[ves, 73. 7«, 81 septum atriorum, 69

venlriculoTum, 71, 73, 78, S2 sinus venosus, 34, S4, 66 sulcusanteriorinler-venlriculs[,7l

letminalis, 34, 54, 63 supra-ventricular ridge, 72 surfiices, 53, 56, 5S

diaphragmatie, 5S

sternoeoslal, 53, 56 lopt^aphy, 57, 75, 94 liabeeulee earneie, 72, 70 trieuspid valve, 66, 73, 83

eusps of, 73 tuberele, intervenous (Lower), 67 valve of the eotoniry sinus, 69 viilve of the vena cava (Eus-

taehian), 67 Tentriele, I«ft, 79

cavity, 79

fibres of the ventricles, 93 TBntriele. right, 70, 74

cavity, 72

eonus arteriosus, 72

ventricles, 34, 53. 55, 70, 74. 79

vessels. 63, 64, 76, 78, 85, 87

wall, 92 Helieotrema, 568 Helix, 158

erus, 153

fossa, 154

pioeessuE eaudatus, 155

spine, 155 HemiBpbsre, eerebellar, 529

eerebral. S^e Gerelial henii-

Hesehl, sulei of, 475

Hiatus semilunaris of nose, 397. i^

HippoeiimpuE, 491, 492, 493, 497

<iiEilations, 491

minor, 494

pes, 49:

t^nia, 442, 447 Horner, niusele of, 121 Hyaloi<l eanal, 581

membrane, 581 llyparterial hronehi, 10, 38,44, ;o

Incisive bundle, Uj, 133

pad, 133 IneiBUTa eardiaea, 53

inleitiagiea, 154

ternporalis, 465, 475

thyreoidea, 423 Ineus, 556, 557

body, 556

erus, long, 536 shoit, 557

ptoeessus anlieularis, 557 Inferiur eorpus quitdrigemiimm, 530 Infia-oibital plexu5, 12S, 129, 389 Infiindibulum of brain, 2o8, ai8, 453

of hypophysis, 505

ofnose, 397

lUBUla, 450, 475, 476, 477, 490, 57S

opeieula of, 477 Interartieular meniseus, 113 Interattiai suleus, 8g

Iiiler-ebondial ariieulations, 113 Intereostal membianes, 4, 108, 109 Intemal aeusite nieatus, 566 etipBUle, 501, 515, S16, 51S anteriot limb, 518 coune<:tionsof, 518,519 genu, 518 posteriot limb, 518 eai. 546, 565 Interpeduneulat fosss, 452 Intervertebral libro-eiililages, 112 [nlumeseentia cervicalis, IB7 lumbalis, 1S7 I'is. 571.574.576.577,578, 579 tsland of Reil, 477 iBthmus of auditoiy mealus, 548 of nuditory lube, 3S4 of fauces, 368, 369, 37S of Eynis einguli, 478. 479

rotnieatiis, 478 of limble lobe, 47S of phaiyiiii, 376, 377 o! thyreoid gland, 229, 320 of rhombeneephalon, 536

jBCobson's nerve, 312, 563 JoiiitB, atlanto-epistropheal, 363

Ettlanto-oeeipital. 361

eapitular, 113

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c-r::'»:lar, 112

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intecvertebral, Il6 libro-eaitilage, ii6 annulus iibrosus, il6 nudeus pulposus, Il6

of malleus, a " " ' —

ofiii

*. 557

lateral, 557 " -■. 557

mediii palpebral, I3I, 134, 136,

140. 337 of neek of rib, 114 oblique of allas, 181 oeeipito-atlantal, 362, 363 of pmna, 153 pterygo-mandibular, 463 pulmonary, 14, 16, 35, 43, 70 posterioi costo-transvetse, 115 postetiot longitudinal, ll^, 182,

357

ofstapes, 557

o-tuberous, 178 spheno - mandibular, 268. 269,

270, 271, 272, 277, 278 sterno-ebondral, 113 steino-cIavicular, 243 stemo-eostal tadiate, 113 sterno-perieardiae, 50 stylo-hyoid, 286, 287,290, 292,296 stylo-mandibulat, 237, 263, 271,

supraspinaus, l65, 173, 181. 359 suspensory, of aiiis, 363

of lens, 583

oforbit, 349

of Loekwodd, 349

□f eyelids, palpebral, 12[ tempoio-mandibulat, 271, 272,

273 thyteo-epiglottie, 40S, 420, 423 thyteo-hyoid, median, 413

lateral, 413, 414

of the neek of the rib, 115 transverse, ofatlas, 362

of tbe tubeteles, 114 upper transverse of seapula, 164,

pulmonis, 14, 16, 35, 43

nueha;, 172

peetinatum tridis, 574, 584

Ligamentum ventriculare, 410,

Ligamenla fiava, iSl, 358, 360

Ligula, 53 1

Limbie lobe, 478

Limbus fossie ovBlia, 67

Lines splendens, 1S6, [SS

Lines of pleural retleetion, 14, 17,

iS, 19 Lingual glands, 283, 434 Lingula, 529, 535 Lips, 365, 366 LItbt, eaudate lobe of, 104 Loba or LobeH, of eerebelluni under surface, 533 eential, oreerebeUum, 531 of eerebruai, 462 alie of, 532 eerebeilai, 531 eetebial, 462

montieuli, 532

eulmi

'. 532

ofcU¥US, 532

of eulmen, 532 fiontal, 449, 462 ii,..l.r, ,6» limbie, 478 Lobus tuberis, 534 eulminis eetebelli, 532

i. 53Z

folium

'. 53^

graeilis, 534

semilunaris supeiioi, 532 Iiobe or Lobes, o^ lung, 41

ofnodulus, 533

oeelpital, 450, 462

olfactory, 462

parietal, 450, 462

of pytamid, 534

pytamidaJ, of thyteold gland, 321

subslantia peribtata anlerior, 462

semilunai superior, 532

lemporal, 450, 462

of tuber, 534

of uvula, 534 Lobale or I^ibiileB, blventid, 533

eenttal, of eerebellum, 531

ereseentie, anteiioi, 531, 532 posterioi, 331, 532

ofeai, 153

giaeile, 534

pataeeDttal, 449

parietal, 450 '^ ,

6oo

INDEX

Lobule or LobnleB —

)i.iri(.t.il indrior. 471. 472

>uiKri »r, 471, 472 j iiHii-ii.ir siijii;ri'ir. 531

«iu.uli.iu-. 532 I."iU's i--itu]l-us. 537, 545 Knn^ituilin.il l)un<i]c, medinl, 51 1

>.i^iii.il, infcriitr. 217 su|K*ri«)r. 207 LuniU>-iU>rs.il fascia, 166, 167, 16S Lung. 17, 35

auriie grm»vi.*. 40

ajir\, 17. 30

a/yj;'»> ijriMivo. 40

l»asi-, 3(>. 37

lH)r»iers, 30

l>ronchi, 22

tlitlerenees l>ctwocn right and lcft,

ti>sNuri->. 41

hiUiN, 3S, 4»!. 44

iiu'i^ura «\nili.u*a, 42

iiiiioniinatt.' i;ri) >vi-. 40

li^ainenluin ]iulni>>nis, 33

lttl)L*s, 41

l>cilic]<.". 14, 42, 43

root, 42, 43

.sulK*lavian j;roovo. 36, 40

surfaci'S, 30, 37

sulei, 40. 42

Lunuhe, 75

Lymph duet, right, 4S, 107

Lymph glands, apieal of l<>ngiie,

434 . hronriiial, 22, 43, lOeS

hui'i-al, 133

ccrvii:al, 14O

upj)cr (U'ci), 232, 201, 308 inlereostal, loS, 256 niasloid, 154, 15S niediaslinal, 10, S9

antcri()r, 7, loS

j)()Stcrior, loS

sui^erior, loS c)ccij)ilal, 158 I)aroli(l, 15S, 260, 366 spaee, periehorioidal, 578 sternal, 107, loS sul)maxillary, 225, 230, 2S3, 366 subniental, 228 suj)raclavicular, 147 of thorax, 10, loS, 257 thor.acic visceral, 257 l.ynij)li yessels of lips, 366 vcsscls, inilmonary, 38

I

Lymph tninks, Icft eommon jiigular, 106 left subclavian, 106 right jugular, I08, 257 right subclavian, 108, 257

Lyra, 498

Maeula lutea, 580 Magendie, foramen of, 539 Malleus, 552, 554, 555, 556, 557, 565

handle of, 549, 565

head, 555

lateral proeess of, 549

proeessus lateralis, 554, 555

anterior, 555, 556, 565 Mammillary bodies, 452, 453, 497,

503, 504 Manubrium, 549, 554, 555, 557

Marshall, oblique vein of, 90

vestigial fold of, 90

Mastoid antrum, 565

air eells, 555, 559, 560

MeatUB, extemal, aeustie, 259

intemal aeustie, 562, 563, 565, 568

nasi, 397

inferior, 399

middle, 397

superior, 297

naso-pharyngeal, 400

MediaBtinal lymph glands, 10, 89

pleura, 14, 23, 25, 33, 46, 49, 50^

70, 76, 77, 84, 85, 87

spaee, 14

Mediastinum, 10, 44

anterior, ii, 45, 46

inferior, 10, 45

middle, ii, 45

posterior, i, ii, 26, 30, 45

superior, 10, 45, 46

Medulla oblongatB,, 520

antero-median groove of, 521.

anterior area of, 522

eentral eanal, 521

elosed part, 520

deeussation of pyramids, 520,

522

external areuate fibres, 438,

528

floor of fourth ventricle, 526-

528

formatio retieularis, 510, 543,

545 toramen ca;cum, 521

fossa rhomboidalis, 536, 537

funiculus euneatus, 525, 526

graeilis, 526

Hednlla oblongata —

Tunieulus lateralis, 525 of Rolando, 526

erey matter, 540 intermd slrueture, 540 lateial area of, 524 lemniseus et traetus eerebello- spinalis, 512, 535, 545

olivary eminenee, 525, 526, 528 open patt, 536-539 origin of neives, 522 posleiini aiea of, 526

median tissure of, 521 pyramidal tiaet, 522 pyiatnids, 532, 528 laphe, 540, 542 restiform body, 525 sttuctuieof, 540,541, 542, 543 tubeiele of Rolando, 527, 5ji white mattei, 540 Hedulla apiiuilis, l36, 1S7, 194 differences in suriaees, igt

inteinal stiueluie, 194 grey matter of, 196 white mattei of, 199 Medullaiy eentre, 461 extetnal, 576 inteinal, 576 laniinee, 516 ve]a, 535 Meibomiaii follides. See Tarsa!

glands Hembtana ehoiio-eapillaris, 579 Aaeeida. 556 tympani, 556 Hembtaue, eiieo-thyreoid, 297, 41 S anteiior, 360, 361 eosto-eoiaeoid, 161 tlaedda, 553, SS4 hyaloid, 58 1 inteieostal, anterior, 4 poslerior, S, 29, 109, Uo

of Shiap'neU, 556

posterior atlanto - oeeipital, 179, iSi. 355. 360. 361

leetoria, 362

Ihyreo-hyoid, 229, 243, «96, 413 417

tympanie, 270 HenlDseB of biain, 201, 414

of spinal meduUa, 183 Meseneephalon, 459, 506, S20 Middleeai, 546, 550

Mittal valve, 80, 92 Moderator baiid, 71, 74 Modiolus, S6S Molni salivaiy glands, 133 Montieulus uf eerrbellum, 529 Morgagni, sious of, 372, - "

Mot

1. 542

ioof, 36K tongue, 431 vestibule, 304, 366 Mueo-peiiosteum of nose, 400 olfactory r^ion, 400 respiralory legion, 400

UaEele ot Uuseles — angular head uf quadrate musele,

124 antitiagieus, ISS ary-epiglutlicu5, 415, 416, 429 aiytienoideus, 429 obliqiius, 415, 416 ttanEversus, 415, 416, 417, 420, 429

penoi, 154

■ 27, 131, 261, 370, 277, 37^. 373 eamnus, 123, 128 ehondro-glossus, 435 eiliary, 57=. 57S, 5^3

ofeyelid, 376 eonstrietor, niiddte of phaiynK, 234, 281, 290, 291, 297, 303, i , 315. 37>,372. 373 inferioi of pharyoK, 234, 346, 303.314.315. 371. 372.413. superior of pharynK, 132, 289,

297. 299. 304, 3". 371.373, '

. 373. 382. 383 I

cnco-aiyla:noideus lalemHa, 415, '

418, 419, 422, 429

posterior, 415, ^rB, 42?, 429

erieo-thyreoid, 330, 314, 413, 414, j

417. 429 depressoi septi nasi, 123 digastrie, 230, 238, 2S9. ^*. 264, 274, 278, 2S0, 2S1, 282, 286, 294. 297. 300, S^i. 305. 306, 307. 3'6 ddatatoi pupaUe, 578 tubee, 384

of«

IS4

^0 2

INDEX

Musele or Mnielet -

•#f «-ar, i:.'T::,'.].- . 155

• |#i' rai.i it, 122

<il !)•■, laN-ral r- " .-. 355. 34O-

Ul. iM- >45^ 34<i 'l""'^. )35. 337- 3>^- 339-

'>:ili-iiiii

^:ij»«ri'>r ij{ eyt, 35

ii7. 33^. 34^^ 342, 34^J.

i4H iii'di.il rtrtus, ^O, 344, 346

oliliijmi.» iiif«-ri'^r of eye, 341. i4S. W>. 34«

ii| l.li <-, 1 2()

liMlil.tii ., I 22

i;< iiKi (•J<...u^, 2X5, 2S6, 2S7, 288,

J«^i. -•(>i, 292, 454. 435 j;i iii.i li)..i.|, 2K5, 287, 29^^ l'l.i-. ... ji.il.iliiius, 3S1, 3S3 i'lul • u . iii.i\iiiius, 17S li< li< I . iii.(|<)t , I 5^

IIIIIIOI, I<^<^

liN..i;l...-ui-., 2\i), 2^1, 2^4, 2S1, '-•.S.', jS.|, ,!Ss, 2SO, 2S7, 2S8, -•S.;. .•(><•, 291, 292, 310, 311, i>". 4vl. 435

llli. i ii-.l.tll-., !(.() I i'l \ h I-., I (ti)

ili.iM. i(..). lys

luinl •> i| UUi . l(ii) iii. 1 .1 N u .. l ' \, l \\ iiili I li\..i.l. -• Hi. -•.|.*, J.\\, 2.J4

iiiii i..i l.ii.il lii-.ul ol (jua(lratc iiiu .. I.-. 1 -•.!

inl. I ii . I- . .. M II. l '/■/

inl I I . i. .1 .1 1. I , |i II)

I n I . I ■ 1 . 11 1 1 1 . . , 1/(1, 1 / ■/

inl. I 1 1 in .\ , I ..ili-., 1/(1, 177» 353»

» '1 ■» . .| I I \\ in. '\ I in>nl-., .' \\ .'I I II \ lu'.il in.>\ i-mi"Ht-., .J2() I t. I iin.ili'., I .' I I il I , .iinir. «I>.|M, ;, 1(1,* li \ ii . >i i'.tliil I, ;. 1 1

f\ III, lul \ lli\ i..i.li-.\-, .'.'»), 321

|> ll|.. I«l »• •.U|«i"l i.u u., l \S, I 3^>,

... ... ..^1 ,»•» ••V .^i^

» \ I . t \Si \ v'> \ \, • ,\.>'^« .\.>*'.

\|«'

■.. .ii'ul» . l J«). l Si», l(>.*, 23S,

•|». .i-'3 \.li j.,i|,tluu, 3»>-/. 373, 3S2, •s ' 'S I

li\.il..ii'. \ ii'.l.ii um, 1 /7 liu};u,tK-., .'«)»». 2^)2 l»>nj;issiuius, !()()

i'a|>itis. loS, 170, 3i)(>. ]^l

loogisssmus^ eenrids. 170

dorsL 169, 174 l'^agitadiiia] of t(X^e, inferior,

292.435 ^upeiie.r, 434, 435, 436

obliqinu eapstis snperior, 168,

171, 179, 180

enernns abtiominis, 3

eapilis iiifeiior, 174, 179,

180

of orbil, 546

intemiis abdominis, 167

oedpitalis, 156

superior, of neek, 180

of orbit, 338

longus eapitis, 246, 308, 351

eoUi, 102, 106, 241, 246, 251,

322, 351, 354 masseter, 126, 127, 259, 261, 265, 266, 270, 274, 276, 277, 283, 298, 302 mentalis, 123, 133

levatores eostarum, 177 of mouth, 123, 132 multifidus, 176, 177 mylo-hyoid, 230, 270, 274, 278, 280, 282, 284, 285, 288, 290, 300, 316 nasalis, 123

pars transversa, 123 pars alaris, 123 naso-eiliary, 336 ofnose, 122 ol)lique superior of head, 354

inferior of head, 354 oblieiuus aurieulae, 155 omo-hyoid, 146, 150, 161, 164, 234, 238, 242, 244, 246, 290,

413 orhieularis oris, 121, 122, 123,

132, 136 oeuli, 121, 134

orbital part, 121 palpebral portion, 121, 134 lurs laerimalis, 122, 136 I^alato-^lossus, 434, 435 I)harynjro-palatinus, 303, 369, 378,

38 1, 382, 383 IH'otorales, 3 l)latysma, 120, 126, 127, 143, 161,

260, 274 l)rcvcrtebral, 351 ptcryj;oitl, external, 267,268,269, 270, 271,273,274,275, 276, 277, 278, 546

■tuele or Hiuelei —

pterygoid, intemal, 259, 263, 267, 269, 274, 275, 276, 278, 281, 282, zi83, 289, 293, 298, 299, 373. 546 ptoeenis, 122, 123 quadrHtus latni iiiferionS, 12J. 125 lumboium, 167

labii supeiiotis, 123, 124, 129, 387 angular head, 12$, 12S Lntia-otbital.head, 125, 12S zygomatic head, 125 reetus abdominis, 3 eapitis mteiioi, 238, 34], 308,

35' eapitis lateralis, 238, 141, 30S,

353 infeiioi, 344 1aterali9, 304 lateralis of neek, 345 medialis, 344 postetioi major, 179, iSo posterinr minor, 180 superior, 324, 325 ihomboideus majot, 164

minoi, 164 risoiius, 123, 125. "6. 2^ lotatotes spin^, 176, 177 saeio-spinalis, [69 satpingo-phaiyngeus, 3S1 sealenus anterioi, 34. 106, 235, 238, 242, 246, 247, 248. 249, 251, 252,255,257,259,309. 322. 323. 354 medios, 149, 161,238, 241,257,

323 postetiot, 149. 323 semispinalis eapitis, i.^, 16S, 170, 171, 172, 174, 178 ceivids, 171, 172, 174. 176 dotsi, 171, 176 serralus antetioi, 3, 149. 161 posteiioi, infeiiar, 164, 165,

166, 167 postetior, supeiiot, 164, 165, 168 sphinetet pupillie, 578 spinalis, 169, 170 ceivicis. 170

tapedius, 551, 554, 555, 558 tetno-hyoid, 46, 47, 48, 239, 242, 243. 246, 250. 296. 3'6.4J4

HuMl» «r Klsdl»—

245, 25°. 25I1 259, 261, 281, 296, 300, 304, 31S, 323 sterno-ma.&tDidstiiictures,l)eneaIh

sterno-thyreoid, 46, 47, 4S, 239,

243. 244, 246, 250, 434 slylo-glossus, 285, 2S6, 287, 289,

290j 299, 413, 434, 435 slylo-hyoid, 230, 259, a6a, 263,

280, 2S1, 282, 284, 2S6, 297,

29S, 305. 3°7. 4"3 stylo-pharyngeus, 294, 295, 299,

303. 373. 381 subeostiLlis, 29, 306

subseapularis, 16 .upia-troehleat, 336

5Upta-i

1.336

temporal, 265, 266, 267, 269, 270, '

274, 27b, 277 tensoi veU palatini. 274, 275, 293 ■ tarsi, 121,373,382, 383,384,404 I lympani, 293, 312, 549 lhyteo-arytafnoidens, 417, 419, ,

422, 429 thyreo-epiglottieus, 418, 422 thyreo-hyoid, 231, 234, 243, 244,

296, 3M, 413 ]

tragieus, 1"-

19 abdon 155

Ihora

,167

!, 5°

trapeiius, 162, 241, 315 iriangularis, 123, 125, 128, «g of tympanie cavity, 558 u«ulfc, 3S1, 383 vertical, ortongue, 435 vocales, 415, 41S, 419, 422, 429

lygon

i, J23. 1

t, 129

Museular triangle of neek, 222, *a6, . 232. 233. 359 I

Myoeaidium, 92 [

NarBB, poEterior, 374, 375, 377. 389 ■ t!a.tal eaitilages, 140 eayities, 393

antetior apertures of, 393 pirt, 393

eonehiE, 395

Hoor, 394

lateml wall, 395

postetior apeituies of, 393. 394

toof of, 393 -^^^m

6o4

INDEX

Nasal foB8a, 393 atrium, 395 c«mch:i;, 396, 397 infori«)r meatus, 399 infun(lil)ulum, 397 lateral wall, 395 middle meatus, 397 olfactory part, 400 reeessus spheno - ethmoidalis,

399 respiratory part, 400

suiKirior meatus, 397

vestibule, 395

Nasal septum. 391

eartilage of, 391 eonstruetion of, 391 olfactor\' area of, 390 respiratory area of, 390 vessels and nerves of, 392 Nasal yestibulum, 395 Naso-laerimal duet, 140 Naso-pharynx, 375 Neek, 141

anterior triangle, 226 deep disseetion, 294 digastrie triangle, 226 earotid triangle, 226 fasci%, 224

infra-hyoid region, 227 joints, 356 mid-line, 226 museular triangle, 226 oeeipital triangle, 168 posterior triangle, 142 side of, 142

submaxillary triangle, 226 submenlal triangle, 226, 227 supraclavicular region, 224 suprahyoid region, 227 surface anatomy, 224 Nerve or Nerves, abdueent, 212, 215,218,327, 330,345, 346,

386, 457 aeeessory, 145, 146, 150, 162, 213, 218, 232, 235, 239, 262, 281, 300, 304, 307, 309, 310,

3f2, 313^ 315» 455, 456 aeromial, 182, 228 aeustieus, 213, 215, 218, 456, 562, 563, 565 eoehlear division, 565 vestibular (livision, 565 anterior eutaneous, 4, 1 10 anterior tboraeie, 160 alveolar inferior, 267, 268, 276, 277, 278, 279, 293

I

Nerye or Neryes — alveolar superior, 388

anterior, 388

middle, 388

posterior, 388 aortie, 100

aurieular of aurieulo - temporal, 277

great, 126, 143, 145, 146, 151, 156, 235, 239, 241

of great oeeipital, 156

posterior, 154, 156, 157

of small oeeipital, 239, 241

ofvagus, 312, 313 aurieulo-temporal, 127, 156, 261, 267, 274, 276, 277, 293

branehes of, 277 axillary, 160 to azygos uvulae, 383 braehial, 109, 147, 157, 160,

323 bueeinator, 128, 134, 267, 268,

276, 277

of facial, 126, 128

of sympathetie, 314 eardiae, 30, 33, 65, 87, 89, 250

inferior, 319

middle, 318

of vagus, 30, 33, 87, 89, 99, 100, 250, 314, 315

superior, 317, 318 earotie external, 317, 318

internal, 317, 318, 385 earotieo-tympanie, 312, 386 eerebral superficial origins, 454 cervical, 353 cervical, first, 353, 522

anterior branehes, 324, 325

loop between first two, 353

posterior divisions, 162, 173,

174 ehorda tympani, 549, 551, 552,

565 eiliary, 141, 149, 161, 578

long» 339» 340 short, 341

clavicular, 274, 278, 290, 293

eoeeygeal, 178

eoehlear, 565

eommunieans hypoglossi, 308, 316

eommunieating of 9th to 7th,

eommunieation of hypoglossal,

316 eords of braehial plexus, 160 eranial, 123, 456

Harre or NarreB-^

CTaiiia.l, super^al origin of, 454,

45S. 456. 457. 458. 459 eutaneous eolK, 143, 145, 151,

124, 235, 339, 241 deseendens hypt^lossi, 239, 243,

305 deseending of cervical plexus,

143 to digaslrie, 267, 26S, 276, 277,

278, 279, 293 dorsal, posteiior divisions of, 174

seapular, 147, 160, 164, 323 ethmoidal, 344 anterior. 340, 402

medial nasal, 393

■; 340

long thorade, 323 of &ce, 126

facial, 213, 215, 218, 263, 2S1,

a82, 313. 338. 456. 457- 557.

558, 561,562, 563. 564

bueeal branehes, 127, 12S, z6i

cervical brauehes, 127,1261, 294

division, 184, 19S, 262 cervico-facial division, 26: eommunieating branehee of,

facial, eommunieating with iiuri-

eulo-lemporal, 277

of gteat aurieular, 126, 146,241

intrapeUous part, 562, 563, 564

mdibutar branehes, 127, 12S,

museular to ^tylohyoid and

digastiie, 262, 281 posterior aurieular, 262, 301 seiisory root, 215 super(icial origin, 4 58 lempord branehes, 127, 128,

137, 156, 261 temporo-facial divis!on, 261 lygomatie bnnehes, :27. 128,

137,261 frontal, 330. 334, 336, 346 glosso-pharyngeai, 213, 215. 218,

277, 281,286,304,306, 307,

309, 310, 311, 435, 436,

455 ganglion, bUpeilus of, 3II hngual branehes, 311 pettous ganglion, 312 supeiBeial origin, 458, 522 tynipanie braneh, 312, 563 of beart, 33, 43, 65, 78, 85, 87, 89, 96-99, 100

EX 605

Kwn or NerrM—

hypoglossal, 213, 215, 218, 220, 231, 232, 233, 244, 281, 282, 284, 285, 287, 288, 290, 291, 292, 294, 300, 304, 305, 306, 307. 309. 310, 314, 3'fi, 3'7, 35', 355-435,436,455.52* superficial origin, 457, 522 ineisor, 279 infia-DiandibuIar, 164 infia-orbital, 128, 120, 13S, 3S7 nasal branehes, 12S oibilal branehes, 12S palpeliial btanche5, 12S pleius, 12S infia-trocblear, 137, 138, 340 intereostal, 28, iio

intereosta-braehial, 110

of JacobEon, 312, 563

labial, 129

laerimal, 137, 138, 330, 33S, 336.

346 latyngeal, cxtemiil, 232, 234, 243, 295, 3"4 infciior, 315,372, 413, 421, 422 intemal, 232, 295. 304, 314, 372. 413. 421, 422, 435, 436 larytieal, leeurrenl, 2, 33, 49, 7B, 87, 89, 96, 100, loS, 245, 946, aso, a57, 258,314,315,421 superioi, 232, 295, 304, 314, 318 mlernal braneh of, 421 laryngo-pliaiyngeal, 317, 318 laleial eulaneous, 4, 6, ito

nasal Df inlem^ ethmoidal, 481 to levator palati, 380

scapul[c, 151 lingual, 267, 274, 276, 278, 279, 2S2, 2S4, 285, 2S6, 288, 2S9, 290, 292, 293, 434, 435, 436, 565 bianehes Df, 2S9 of nintb, 314 of vagus, 316 Iting thotaeie, 160 lumbar, 150, 166

posterioi (livbions af, 171; malar, 261, 263, 265, 347 mandibular, 212, 274, 375 -27S, 393 raasseterie, 267, 276 masloid. 110, 136 niaKillaty, 212, 403 niedial eulnneous, of — ■'" offorearm, 161

6o6

INDEX

Nenre or NenreB —

meningeal braneh of trigeminal,

327, 330» 385 of vagus, 313

of hypt^lossal, 316

mental, 128, 129, 279

mylo-hyoid, 230, 276, 278, 281,

284

museulo-eutaneous, of arm, 160

nasal of anterior superior alveolar,

401

cxternal, 341

internal, 341

of infra-orl)ital, 129

posterior inferior, 405

superior, 401, 402, 403

naso-eiliary, 140, 330, 339, 340,

341» 345» 346, 386 palatine, 392, 401, 402, 403 oeeipital, great, 156, 161, 162, 174 small, 143, 145, 146, 151, 156,

239, 241 smallest, 156, 161 oeulo-motor, 210, 212, 218, 326, 327, 330, 331, 332, 335» 338, 345. 346, 347, 386, 446, 458 nueleus of, 509 oesophageal, 99, 109 , 'olfactory, 208, 218, 392, 401, 458^ TCrt)mb-hyoid, 146, 150 ophthalmie, 212, 386 optie, 208, 218, 339, 341, 458,

572 superficial origin, 458 to palate, 380, 383 palatine, anterior, 402, 403, 404,

405 great, 380

middle, 383, 404

posterior, 383, 404

small, 380 palpebral, 129, 138 parotid, 277 perieardiae, 34, 99 petrosal, external superficial, 318, 333, 386, 564

great deep, 333, 386, 405, 564

great superficial, 212, 332, 385,

405 small superficial, 333

pharyngeal, 311

of pharyngeal eanal, 405

of glosso-pharyngeal, 295, 315

of sympathetie, 315

of vagus, 295, 304, 306, 314,

315, 383

Nerye or Neryes —

phrenie, 2, 10, 23, 25, 30, 33, 34,

43» 49, 50» 70, 87, 88, 89, 239, 240, 241, 250, 251, 253» 254» 255, 257, 258, 309,

323 pneumogastrie. See Nerve, Vagus long thoraeie, 147 pterygoid, 293, 333 of pterygoid eanal, 386, 393, 405 pulmonary, 43, 99, 100, 10 1 radial, 160 roots of aeeessory, 522, 526

glosso-pharyngeal, 522, 526 vagus, 522, 526 saeral, 177

posterior branehes of, 177 to sealenus medius, 151

posterior, 151 ofscalp, 156

spheno-palatine, 388, 403 spinal, 5, 189, 192

anterior primary divisions, 109, 192

elassiheation, 189

exits from vertebral eanal, 190

ganglia, 185, 189, 192

origin from eord, 189

posterior primarydivisions, 173, 174, 178, 192

roots, 185, 189 spinal aeeessory. See Aeeessory

aeeessory part, 215

spinal part, 215 spinosus, 275, 333

to external pterygoid, 277

to internal pterygoid, 275, 276 splanehnie, 26, 28, 32, 70

great, 28

lowest, 28 to stapedius, 564 sternal, 145 stylo-hyoid, 230, 285 to stylo-pharyngeus, 311 to subclavius, 147, 161 sub-oeeipital, 172, 173, 179, 180,

190 subseapular, 160

supraclavicular,of braehial plexus, 145, 149, 161

of cervical plexus, 143, 151, 161, 239, 241 supra-orbital, 121, 137, 138, 156 supra-seapular, 147 supra-troehlear, 137, 138, 156, 340, 344

INDEX

607

Nerye or Neryes —

s^nnpathetie. See Sympathetie

temporal, of aurieulo - temporal, 277 of bueeinator, 277 deep, 267, 276 of facial, 137, 156, 261 of orbital, 334, 350, 388

to tensor palati, 293 tympani, 293

thoraeie first, 109, 254, 257

thyreoid, 318

thyreo-hyoid, 316

tonsillitie, 311

to trapezius, 151

trigeminal, 212, 218, 329, 330,

457, 529 mandibular division, 329

maxillary division, 329, 330

motor root, 215, 329

ophthalmie division of, 326,

327, 329, 330, 336 roots of, 328

semilunar ganglion, 211, 212

sensory root, 212, 215, 328

traetus spinalis of, 527

for temporo-mandibular joint, 277

thoraeo-dorsal, 160

troehlear, 211, 212, 215, 218, 326,

327, 330, 332, 335» 336, 346, 386, 446, 457, 506, 530 roots of, 538 superficial origin, 457 tympanie, 312 ulnar, 160

vagus, 2, 10, 23, 25, 30, 32, 33, 35» 49» 89, 100, 106, 108, 213, 215, 218, 232, 239, 245, 252, 257, 258, 300, 304, 307, 309, 310, 312, 313, 315, 435, 456 ganglion jugulare, 313

nodosum, 313 left, 30, 99 right, 23, 99 superficial origin, 455 thoraeie branehes of, 99 vascular of hypoglossal, 316 vestibular division of aeustie, 565 zygomatic, 334, 350, 388 zygomatico-temporal, 156, 266,

267, 350 -facial, 350 Nietitating membrane, 120 Nodule of eerebellum, 533 Nose, eartilages of, 140, 391

Nose—

eonehse of, 401

fossse. See Nasal foss3e

septum, 390, 401, 402

vestibule, 390 Nostril, 390 Noteh, preoeeipital, 470, 473

of Rivinus, 553, 554 Nneleas, amygdaloid, 491, 494,

512, 514 auditory, 538 eaudate, 488, 489, 491, 494, 502,

512, 513, 514, 515, 518, 538 eoehlear, 512 euneatus, 527 dentatus of eerebellum, 450, 454,

512, 514, 515, 517, 518, 539 glosso-pharyngeal, 538 graeilis, 527, 541 hypoglossal, 537 of lens, 5S4

lentiform, 514, 515, 517, 518 oeulo-motor, 509 olivary, 543

aeeessory, 541 of optie thalamus, 519 pontis, 545 pulposus, 115 ruber, 512 trigeminal, 509 troohlear, 509 vagus, 538 Niihn, gland of, 434

Obex, 538

Obliqae BinuB of perieardium, 58,

59,89 Obliterated duetus arteriosus, 33,

77,78 Oeeipital lobe, 450, 462

pole, 465

sinus, 183, 216, 217

triangle, 163 GEsophageal plexus, 99-102 (Esophagiu, 2, 10, 17, 23, 26, 29,

30, 31, 32, 39» 40, 49, 50, 58, 85, 87, 89, 96, 99, 100, loi, 104, 106 01factox7 bulb, 322, 439, 469, 477 lobe, 418 striae, 477, 478 traet, 439, 469, 477 trigone, 478 Oliyary eminenee, 524, 525, 526

nneleus, 543 01ive, 524, 525, 526

6o8

INDEX

01ive, superior, 545 Omental bursa, 104 Opereula insulir, 463

frontal, 464, 490

fronto-parietal, 463, 475, 490

orbital, 464, 490

temix)ral, 463, 475, 490 Optie ehiasma, 452, 505

dise, 580, 581

entranee, 572, 578, 579

thalamus, 417, 450, 487

traet, 452, 507, 508 Optie nnelenB —

lateral root, 507, 508 medial root,5o7, 508 Ora serrata, 580, 581 Oral fissure, 365 Orbit, 333 Orbital opereulum, 464, 490

periosteum, 334 Ossieles, auditory, 546, 550, 554,

555, 556 Ostium pharyngeum, 376

Otie ganglion, 276, 277, 279, 293, 383

Palate, hard, 373

soft, 375, 380, 382 Palatal aponeurosis, 382 Palpebrte, 119, 134 Palpebral eommissures, 1 19

conjunctiva, 119

fascia, 135

fissure, 119

lateral palpebral raphe, 121

medial palpebral ligament, 121 Papilla? foIiata3, 432

ineisiye, 368

laerimalis, 120 PapilliTe vallalne, 432

eonieal, 432

filiform, 432

foliataf, 431

fungiform, 432 Papilla nervi optiei, 580 Paraeentral lobule, 449 Paramedian suleus of spinal meduUa,

195 Parietal lobe, 450

lobule, 450 Parieto-oeeipital fissure, 462 Parotid, aeeessory, 261

duet, 127, 261

fascia, 126

gland, 126, 127, 233, 259, 281

lymph glands, 257

Parotid, pterygoid lobe of, 263 spaee, 259, 262, 281 surfaces of, 260, 262

Pars basilaris of inferior frontal gynis, 469

Pars eiliaris retinse, 580

mamillaris hypothalami, 520 membranaeea septi, 74, 83 orbitalis of inferior frontal gynis,

triangularis of inferior frontal gyrus, 464 Pedunele of brain, 446, 447 Pedoneles of eerebrum, 210, 212,

452, 500» 501

basis peduneuli, 210

tegmentum, 210, 503, 508, 509, 510, 512 Perieardium, 10, 25, 26, 30, 33, 38, 50, 98, 104

bare area of, 50

fibrous, 50, 70, 75, 83

oblique sinus, 58, 59, 89

parietal, 52, 89

serous, 51, 59, 70, 75

transverse sinus, 54» 59» 76

vestigial foId, 92

visceral, 52, 89 Perilymph, 546, 566

vibrations of, 569 Pes anserinus hippoeampi, 491, 492,

493» 497 Petrosal sinus, inferio¥, 312

superior, 326

Petrous ganglion, 312, 313, 317

Pharyngeal aponeurosis, 370

bursa, 373, 376

plexus, 309, 311, 314

tonsil, 376 Pharynx, 369

bueeo-pharyngeal fascia, 370

eonstrietor museles, 370, 371

glands, 375

interior of, 374

isthmus, 384

laryngeal part, 378

lateral reeesses, 376

lymphoid foIlicles, 376

museles, 371

naso-pharynx, 375

ersophageal opening, 379

openings, 370, 375, 376

oral part, 377

reeess of, 376

relations of, 369

roof, 376

U

INDEX

609

Pharyiue —

tonsil, 376

yeins, 370

walls, 370 Phrenieo-eostal sinus, 16 Pia mater eneephali, 442

spinalis, 186 Pillars of fauces, 368 Pineal body, 500, 503, 505 Pinna, 153

extrinsic museles of, 1 53

intrinsie museles of, 153 Piriform reeess, 379 Pleura, 7, 11, 12, ^^

apexof, 15, 257

base of, 16

cervical, 15, 248, 250, 257

eostal, 12, 25

diaphragmatie, 16

dome of, 309

lines of reflection, 14, 17, 18, 19

mediastinal, 14, 23, 25, 33, 46,

49, 50» 70, 76, 77, 84, 85, 87

parietal, 12, 14

pulmonary ligament, 14

relations, 76

visceral, 11, 14, 104, 105 Pleural cavities, 12

sae, 12 Plexiifl,basilar, venou5, 183,216,217

braehial, 109, 147, 151, 160, 323. See also vol. i. p. 28

bueeal, 277

eardiae, deep, 65, 85. 89, 96, 100,

loi, 315 superficial, 33, 43, 65, 78, 85,

87, 315 earotid, 247, 296, 341, 386

external, 31 8

internal inervou5,i. 3S5

cavemous, 331, 332, 385, 386

eer^-ieal, 151. 239, 240

communicatinj^ branehes, 241 deepix;steriorbra.nches, 151,241 museular branehes, 241 superheial branehes, 143, 151, 241

ehorioid, 488, 489, 492, 493, 494, 499, 502

eoronary .f h'.art, l':ft, 65, lOI right,'65. 85. loi

diaph ra:;r:-. a t i c , 34

h>T>o-l';^^al, 316

infra- .r..:tal. 12S, 129, 387 bran:.- = of, 129

iDterr.i: '.rrtebral (vcnou.s), 182

VOL. 11—^9

Plezii8 —

intraspinal (venous), 182 oesophageal, 99, 100, 102, 104 phar>Tigeal, 309, 311, 314, 315

nervous, 370 position of, 16 posterior saeral, 178 posterior vertebral (venous), 176,

178

pter}'goid (venous), 132, 271, 370,

389 pulmonary, anterior, 43, 99, lOO,

lOI

posterior, 43, 98, 100, 10 1 renal, 28

spinal (venous), 182 suboeeipital {venous;, 157, 173 submaxillary s\-mpathetic, 284 tympanie, 386 vertebral (venous), 355, 356 s)Tnpathetic, 355 Pliea sublingualis, 2S8, 289 Bmbriata, 368

of tongue, 431 laerimalis, 140 semilunaris, 119. 120 triangularis, 378 Plieae ventriculares, 407, 408, 409, 411, 419, 421 vocales, 407, 409, 410. 41 1, 419, 421 Poles of eerebrum, 465 of eyeball, 570 oeeipital, 465, 473, 474, 476 temporal, 465, 475, 479, 485,

487, 494 Pon» Yarolii, 212, 437, 528 braehium pontis, 528 bundle, medial longitudinal oi^

545 eorpus trapezoidum, 545

fibres, superficial transYerse of^

545 longitudinal of, 545

trapezial of, 545

floor of fourth ventricle, 536

internal stnieture, 544

lemniseus, 542, 545

nuelei, 545

pyramidal traet, 544

raphe, 540, 544

retieular formation, 543

8ul>stantia femiginea, 545

tegmental part, 545

tranwerse Bbres, 545

Posterior longitudinal bandle, 544

6io

INDEX

I'rteuneus, 449, 470, 472, 473^ 477,

478 rr.wKreipital nnteh, 473, 490 rretraeheal fa^cia, 229, 230, 23$ rrcvcrtcl»ral fascia, 235. 236, 237 ProeeBB, anterior (if inalleus, 556 eiliary, 577, 579, 581, 582, 5S3,

(•ix:hlcariformis, 551, 55S iK-lieis eaudatus, 155 lentieularis nf ineus, 557 niuseular, of arylicn(ji(l, 42S vocalis, of aryta.'noi(l, 42S

rrtunonti^ry of lyniiianum, 552, 50S

Triiseneephalon, 520

l'russak, striie of, 554

Pterygoid lohe of parolid gland, 263 I)lcxus, vcnous, 132, 271, 370,

■587

I*tcrygo-inaxillar)- region, 152, 263 l'ulley of sui^erior obli^iue, 335, 339 Puh'inar (if ihalanius, 507 runela laerinialia, 120, 139

l'ui'il,57S sphineter and dilatalor museles

of, 578

I'utamen of thalanms, 516

Pyramid of eerebellum, 533

dccussati(jn of, 533, 534

of medulla, 523

of tympanum, 551, 552, 558, 564

l'yramidal lobe of ihyreoid, 321

traet, 544

cr(^sscd, 544

direet, 544

Quadrate lobule of eerebelluni, 532 Quadrigcminal bodies, 506, 507 braehia of, 506, 507

Radiate ligament, 113 Radiatio eorporis eallosi, 483 Rami eommunieantes, grey, 28

white, 26 Baphe, lateral palpebral, 121, 134,

135, 337 of meduUa, 540, 542

of palate, 382

of pharynx, 373

pterygo-mandibular, 132, 373,

389

of tongue, 436

Reeesses, lateral, of fourth vcntricle,

536 of pharynx, 376

• Reeessus epitympanieus, 550, 552,

555 elliptieus, 566

infundihuli, 505

pinealis, 505

piriformis, 379

spheno-ethmoidalis, 399

sphivricus, 566

suprapinealis, 505

triangularis, 505 Red nueleus, 512 Reil, island of, 477 j Restiform body, 527, 528, 529 Relina, 571, 579, 580 Rhombeneephalon, 458, 520 Rima glottidis, 410

Yestibulse, 410

palpebrarum, 119 Riyinus, duets of, : noteh of, 553, 554 ■ Rolando, eentral Tissure of, 462, 464

funiculus of, 199, 200

substantia gelatinosa of, 542 Root-ganglia, 189, 191 Root of lung, 22 I Roots of oIfactory traet, 482 ' of spinal nervcs, 189, 191 Rostrum of eorpus eallosum, 458

Saeeule, 569 8ac laerimal, 136 Salivary glands, molar, 133

labial, 133 Salpingo-pharyngeal foId, 376 Seala media, 569

tympani, 568, 569

vestibuli, 568, 569 Sealene tuberele, 313 Sealp, 132

bIood-vessels, 157

epieranial-aponeurosis, 158

fascia, 158, 159

loose areolar tissue, layer of, 159

nerves, 156

strata, 152, 159

temporal region of, 152

surgieal anatomy, 153, 159 Selera, 571, 572, 573, 574, 579» 57» Seleral eoat, 572

suleus, 573 Semieireular eanals, lateral, 561, 567 Semilunar valves, 75, 78, 81 Sensory deeussation, 542 Septal eartilage of nose, 391 Septum atriorum, 69

nasal, 389

497 posterius of araehnoid, iS6 ventricuIorum, 71, 72, 78, 82 She!(th, ea^otid, 235 Sibson's iiiseia, 36, 251, 257 8inaa, aortie, 60, So basilar, 1S3, 216 bulb of, 307

cavernous, 209, zio, 217, 271 325.326,327.329.330.331 332. 334, .346 eonHuens sinuum, 217 eoronary, 89

eosto-mediastinal, 16, 370 (rontal, 396, 397 inferio[ sagittal, 207, 211, 217

petrosal, 309 intereayernous, 3^6

pOEterior, 209, 217 masillary, 395, 398 obligue, of perieardiuu

89 oeeipital, 183, 216, 217 of Mo^g^i, 373, 382, 383 petrosal, inferio

3»«

supenor, 211, 217, 326 petro-squamous, 217 pharyngeal venous, 327 pbrenieo-eostal, 16, 37 pterygoid venous, 327 pulmonary (Valsalva), 60, 75 sigmuid part, 560 sigmoid portion of, 216 s^enoidal, 397, 399 spheno-parietal, 211, 217, 326 slraight, 207, 210, 211, 217

I. 59.

7. 312

499 lerior sagitla

, 162, ^

7 , 20S, 2

217. 307. 560 of perieardium, 54, 59, 76 Spaee interpeduneular, 452 mediastinal, 10 parotid, 259 l>erichorioidal, 572 subaraehnoid, 439 subdural, 204

Spatiuin interfasciale (of eye), 348

Spheno-ethmoidal reeess, 399 sinus, 397, 399

Spheno-palatine gangUon, 386, 388, 392

Sphmeter pupillEt, 578

Spina helieis, 158

Spinal meduUa, 28.

anterior surraee, 194 arteries, 193 eaput of eolumns, 197 centra.I eanal, 10 cervical enlargement, 187 eolumns, 196, 197, 199 eommissures, 196 eonus medullaris, 1S8 direet eerebeilor traet, 200 fftscii;ulis eerebro-spinalis later-

lissures, rgs prey matter, 196 internol strueture, 194 lumbai' enlargement, ]SS meninges, 183 origin of neryes, 189 posterior suTface, 187 „sio™, 198

substantia gelalinosa, 197 sulei, 195 sutlaees, i87

1, 194

199

nerve-trunks, 1S9, 192

venou5 plesuses. See Piexus. Sptrol eanal of modiolus, 568 Splanehnie ganglion, 2S Splenium 01 eorpus ealloium, 446 Stapes, SSl, 557, 566

base, 557

erura, SS7

head, SS7

neek. SS7 Stenisen, duet of, 261 Stemal line of pleural retleetion, iS^. ■9

lymph glands, 107 Stemo-ehondial artieulalions, Sterno-eostat radiate ligament, tl^

imerartieular ligaments, tii Slraigbl sinus, 54, 59, 76

6t2

INDEX

Stratinn ]ii{^nicnti iridis, 580 Stria lon^itiulinalis nK'dinlis, 481, 482, 500

lateralis, 482, ^83

nK'diillaris, 502

terminalis, 4SS, 489, 491, 502,

51.?. 5M, 578 oIfactory, 477, 478

Strix nietliillares, 538

lon^itiulinales, 482

of Prussak, 554

Su]>arachnoi<l cistern.x*, 439

spaee, 439

SulK*Iavian j;nM>ve, 40

trianp;Ie, 249

SulKlural spaee, 204

Sublinj;ual pland, 280, 286, 288,

2S9, 290, 292

Submaxillary duet, 282, 285, 286,

2SS, 2S9

jranj;li()n, 2S2, 2S4, 285, 318

gland, 225, 2S0, 2S1, 2S2, 283,

2S4, 2S5, 286, 2SS, 289,

290

nerve supply, 284, 29S

re^^ion, 279

trian^de, 279, 2S0

Subniental trianj;le, 223, 226, 227

Sul)<K'cii)ilaI spaee, 17S

Sul)stantia ferruginea, 545

l^elatinosa, Rolandi, 197, 527

nij;ra, 210, 510

perforata anterior, 447, 450, 454,

47«. 479» 483. 517. 518 l^osterior, 447, 452, 503

Subthalamie rej;ion, 501

Suckinj^ patl of fat, 133, 266

Suleus or Sulei, of brain, 461

eallosal, 47S

eentralis insul;v, 464, 466, 467, 469, 470, 471, 472, 477

einiTuli, 465, 466, 469, 479

eireular, 477

roronary, 68

diaj;onal, 469

find)rio (lontate, 495

frontal, infi'rior, 467 niiddle, 467 su]H'rit)r, 467

fronto niarginal, 467

(if llesrhl, 475

of spinal niedulla, 195

interniediate ix)Stcrior of spinal nR'ilulla, 199

^reat hori/ontal, 530, 531

hyiH)-thalamic, 505

Sulens or Snlei — intraparietal, 471, 472 horizontaI ramus of, 471 oeeipital ramus of, 471, 474 lateralis meseneephali, 5o(3 limitans (of 4th ventricle), 537,

538 lunatus, 474

of lungs, 41

oeeipitalis transversus, 472, 474

lateralis, 474

olfactorius, 396, 469

olfactory, 477

orbital, 469

lateral, 469

medial, 469

transverse, 470

paramedial, of eerebrum, 467

post-eentral, inferior, 471, 472

superior, 471, 472

postero-lateral of eord, 195

preeentral, 467

inferior, 466, 469

superior, 466

rostrales, 469

seleral, 573

sub-parietal, 471, 478

temporal opereulum, 485

inferior, 476, 477

middle, 472, 475

superior, 472, 475, 485

terminalis of heart, 34

of tongue, 430

tympanieus, 553

valleculoe, 530

venosus seleroe, 573

Surface anatomy of neek, 223

Suprasternal fossa, spaee, 224

Supratonsillar fossa, 378

superior, 317, 318

inferior, 319

middle, 318

Sympathetie, cervical, 245, 247, 252

abdominal, 34

branehes of, 27, 28, 32, 254

dorsal braneh, 108

first thoraeie ganglion, iio, 257,

258

gangliated eord, 2, 23, 25, 27

thoraeie, 2, 23, 26, 109, iio,

254

Synehondrosis sternalis, 112

Tsenia of 4tli ventricle, 537 Tapetum, 483, 490, 574 of ehoiroid, 575

Tarsal glands, rw	Thyreoid, eaililage. 229, 234, 244
Tars{, 134	423
mferior, 135	isthniiis, 229, 320, 321
Euperior, 135	ineisura, 423
Tegmentum, 210, 503, 508, 509, 510,	laiyngeal prominenee, 424
512	lateral lalie, 407
Tegmen tympani, 550	paiamedla! !obe, 407
Tela ehorioidea, 442, 447, 497, ^98,
499. 500, 502, 504, S3S that whieh is in, 539	pytamidal lobe of, 321
Tongue, 429
Teleneephalon, 520	d m 430
Tomporaa taBoia, 265, 266
lobe, 462	fel nd 283, 434
noteh, 470, 473	I II hesof, 319
opereulum, 463	n u membrane, 430
pole, 465	U5cl 2S5, 433, 434
region, 152, 265	t\es 89, 435
Tensor tympani, 565	Ipar 430
palati, 547	pai Ilte, 432
Tentonum eetebelh, 208, 212, 218,	ph yng al pntt, 430
459	1 n of, 319
Thalameneephalon, 458, 520	phim 436
.Thaliuno-m(LnullaTj rBgion, 5^9	1 21, 435
anterior tuhetele, 502	ToHBil 299. 369- 3S3
laletal area, 502	bell t, 533
massa inlermedia, 503, 504	pb yngeal, 378
medial atea, 502	5>-l f, 383
5urface, 503	T p gt phy of heart, 94
postetiot extreniily, 502
puWinar, 502	T batius, 376
ThalamuB. 447, 450, 487, 488, 4S9,	T h ul-e cattieiC, 72, 79
497.499. 512. 513. S'4. S'S,	T a hen 10, 17, 13. 49, 85, Sf4
520	89, 95. 99. lot, 321
epi-thalamus, 520	Ttagus, 15S

a-thalan

i, 520^

Third venlricle of brain, 49S, 499, Soo. 502, 503, S04, 505 tienia thalami, 500, 501, 502, 503, 504, 505, 508 Thoraeie duet, 2, 10, 31, 32, 48, 246, 250, 313 ganglia, 312, 314, 317 ThoraK. I cavily, 1, 10

lymph glands, 107 outlel, 2

Thymus gland, 46, 47, 48, 85 Thyreo-hyoid membtane, 229, 243,

296, 413, 417 Thyreoid gland, 229, 234, 244,

246, 252, 253, 297, 3'0. 320,

321, 322, 407

: of petieardium, 54, 5%

eaiotid, 226, 232, 233, 259

eontenls of, 231 digttslrie, 226

museulai, of neek, 226, 234

oeeipitai, 168

posteHoi, of neek, 148 eontents Df, 149

subclavian, 349

submaxillary, 233

submeatnl, 223, 226, 227

suhoeeipital, 168, 172

supradaYieulEir, 149

supramealal, 560 Triangulai fo55a, 154 Ttieuspid valve, 69

<1

M

i\nEx

Trigonum j ll.i'.tr. -'.-.■. 4*>o :;.i' '.■:..:! * . y?2

I'r :'..'.:. \ :"--.::-.r: r o'. !: :.:e. ;;o T :.::.'?;, ': -r-.'.I .i >;•■.-.■:. i6l

. -■•■%'^«>ai ^ ■ ■ . ■ ■ * ■• ^ hM . « % 1 %

T:.::."^- :" " :.:;:.:.:! : :v\::-i. 151 Tdbe. auditoiT. 20;. 504. 540. 547.

54';'' 55^' 5^^- 55'?

wMr::..!^:::. -- *. .^.r:. 559

r.:' vr j;:-.-jrf:::r.. 455. 503. yO^,

...■■.• - « *

.•■9-v... ■ ^*^

.1 . . ■ . " » « .. > ^ ^ 1

\ -. : ..."«. ^ !_"» Tuberele. .:::'.>.: :.\L>::, 490. 403

■ ■ i

«^.■.jr. r ^. . ■ ..^^iA^^ 1 «.^. ^^3 * .•■■'*■■*-•■■ '••■t'\

V ■■■.^ -..-■.«« y . ^'

.■»■ ■• .^»«« **l^

« *« -..rv-'** ■■ *; f ■■*

■ .i.^A*^^. *■ m • .

" l * ' ' M «

. '' •'■\T •■ * •-••■'■I.»r» J "» I _1"»C

.■■lK« ■ ^h»i... »*^^V tt bA ^b* • *T^ '

^ • ^'■■•^-« * T *

l..l^ *•■! •■■■•!. V>' A.»ft 1*« ■«*• ^ v*T

Tympanum. 312, 537, 5 58. 559

.1 :::"»:■• ■ ■ ' , ^ ^ ^ . > o i

\:\'j \\.\\ \\.\\\ o\, 361 ar.:fri'»r w.ill. 331 an:r;::n, 337 oaviiy. 305

eayi:)-, |r"nionior\- .>f. 361 tloor, 550 jui;ular wall. 530 latoral wall. 333 inasioi'! wall. 350 nK-'lial wall, 552 nienihrane- ()f. 553 niueuu.-^ menihrane, 555 nuiseh.'.s 558 <)s.^iclcs, 555 ])nst<.'ri»)r wall. 550 prdmontnry <)f, 552, 56S j)yr.uni.l of, 551, 552, 55S.

5'>4

i.inr. 330

S'i'»n«l;iry menibrane of, 553

1' ;;min lympnni, 550 l'mli. I 'il ivm|iani(; mem])rane, 554 IH. 11« "1 Inppneamiial gyni.s, 478,

Uiriele. 569 Uveal iraei, 571 Uvula. 36S, 380

of eerebellum, 533

palate, 3S0

Vallate papilLie, 432 Valk'cula eerebelli, 520, 530

Iar\'nx, 409 Val>alva, sinuses of, 60 Valve, aortie, 87

lueuspid, 80, 92

eoronan-, 68

mitral, So, 92

pulmonar)', 75, 78

of eoronar)' sinus, 89

of the vena cava (Eustaehian),

67 semilunar, 75, 78, 81

irieuspid, 69

Ven.v vorticosa.\ 573

alveolar inferior, 267, 270

an:erior, 262, 2S0, 281

Vein or Veiii8, angular, 131, 137,

157. 344 anonyma. Szc Innominate aseemling lumbar, m auai:ory, 215

aurieular. posterior, 143, 157 a/ygo.^. 10, 23, 26, 29, 40, 44, 70, SS, 98, 99, 102, 104, 106, 109, III

hemiaz}'gos, 10, 30, 102, 104, 106. III aeeessory- hemiazygos, 10, 30,

102, 104, 106, III basalis. 211. 212 brain, internal of, 499 bronehial, 30, 11 1 eardiae, 60, 63 eephalie, 161 eerebral, 204, 206

inferior, 326

internal. 4S9

supertieial middle, 326 cervical deep, 254 eoronary sinus, 63 eomitans ner\^i hypoglossi, 290, 292

of oeeipital artery, 309 of the medulla spinalis, 194

parietal emissar>'. 219

posterior aurieular, 235 emissary, 162, 172, 216, 219, 326

anterior ' "••» facial, ^ (92

Yein or TeiiiB—

362, 263, 271, 294

transYerse, 262 frontal, 132, 137, 157 greal eentral, 499 hemia.z)^OE, 10, loi

aeeessory.

inferior iabial, 132 inTraorbilal, 242, 245, 247, 250, 252.253,254,255. 256,257,

. , 26, 32, 34, 35, 46, 47, 48, 49, 50, 85, 88, 89, 96, 99. 106. III, 239, 313 intereostal, 30, 32, iio

superior, 30, 32, 35, 4S

intereostal-righl supeiior, 111

intra^pinal, 17S

jugular, anlerior, 224, 225, 239, 242, 245, 250, 30S eNtemal, 127, 145, 147, 149, 161, 225, 235, 239, 255, 261, 262, 263 internal, 40, 47, lo*), 234, 335, 239, 242, 243, 245, 246, 247, 250, 252, 255, 256, 257, 259, 262, 264, 281, 300, 303, 305, 307,309,310.312, 313.315. 316, 323

hneual, 231, 292, 294, 305, 309

lumbar, 176

magna eerebii, 210, 212, 21S,

"■7,

inteinal, i

mediastinal, 46 meningeal, 219, 222, 300 minimae eordis, 69 nasal, 205

obIique of Marshall, 90 oeeipital, 157, 162, 172 eesophageal, 30 ophthalmie, 219, 271, 326,

. KS

inrenot, 344

supenor, 339, 344 palpebial, 132 perieardial, 30, 48

EX 61S

Voin 01 Telna— pharyngeal, 370 post-eondyloid, 319 piofunda cervici3, 173 ptBr)^oid, 132, 271 pulmonary, 10, 22, 33, 38, 50, 58, 6d, 70, 89, 92 relalions of intia-pulmonary parts, 99 ranine, 231, 292, 294, 305 retinal, 580 spinnl. 194

eardlae veins, anterior, 64 greal eardiae vein, 63 middle, 63 small, 64 Taeial vein, posterior, 126 oblique vcin, 63

1,30

snperior inlereosta], 30, 32, 35,

87, «9, '«>. I" temporal soperdeial, 15? venae minims, eordis, 64, gx yentrieular vein, inferior, 63 sabclavian, 40, 47, 106, 108, 250, 254, 256, 2S7i 358, 259, 323 supertieial parotid, 132 superior labial, 132 supra-orbital, 132, 157 tempoial middle, 265 tennioalis, 4SS, 499, 500, 502 of thoraeie wall, 1 10 thyreoid, infetior, 47, 88, 96, 229, 253. 320. 321 middle, 239, 247, 309, 311 superior, 231, 245, 297, 309,

321 thymie, 48

seapular, [61, 225,

anterioi medoUaiy, 506, 511«

S35 posterior roedullary, 533, 535 Vela medullary, 535 Velum palatinum, 3S0 museles of, 3S0 medullaiy, tnreri(.i, 535 anterioi, 506, 530 superior, 506, 530 Vena cava inferior, 23, 26, 33, jf,

39, 54. S^. ^5, ^7, 70 -.^^

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Bla, nmygiUlold, 490^ ilin »( ilulMnuD, 503 ieiilato, 379 rironn, 379 ■venotta, 67 i>lanib, 5:1;; lyteoid aulilii||;c, 424, rtie 313 ^"nl»i S.1.1 ino-malleolai foIiU,

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al wall, 553

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