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LECTURES

TRANSLATED FROM THE FRENCH OF

I E R, ^ GLC'/'L- •

CUV

Mcnibv of tbe National Inatitute, Prafcaaor In the Coilocc of France, and In the
Central dciiool of the Pantheon, &c.

a

By WILLIAM ROSS;

UNDER THE IKIFBCTION OR

JAMES MACARTNEY,

Lecturer on Comparative Anatomy and Physiology In St. Bartholomew’s Hospital, &cV

VOL. II,

/

O.V THE ORGANS OF SENSATION.

X LONDON,

PRINTED, AT THE ORIENTAL PRESS, BY WILSON AND CO.
FOR T.N. LONGMAN AND O. REES, PATERNOSTER-ROW,

1802.

j

' ~ •• *<v *.

* •

t

TABLE

Of

4

CONTENTS.

VOL. II.

LECTURE VIII.

Pai*

Of the Head considered as the Principal Recep-
tacle OF the Organs of Sense, 1

Article I. Of the Cranium, of its Form and its Fropor-

tions, nuith refpeS to the Face, S

A. la Man, and other Mammiferosis Animals, 6

B. In Birds, IS

C. In Reptiles and Fijbes, 1 <•

Art. II. Of the Bones <whicb compofe the Cranium, ....

A. In Man, ibid.

B. In other Mammiferous Animals, 20

1 . Number of the Bones of the Cranium in Mammalia, 2 1

2. Connexions of the Bones of the Cranium in Mam-
malia, 23

S. Forms of the Bones of the Cranium in Mammalia, 25

C. In Birds, 28

As D. /*

vi

CONTENTS.

Pgae

Ti. Jn ReptiUsy 3 0

E. In Fijhes, 33

Art. III. Of the Eminences and Depref/ions of the Internal

Surface of the Cranium, S4

A. In Man, ibid.

B. In other Mammiferous Animals, 36

C. In Birds, 42

D. In Reptiles, 43

E. In Pijhes, 44

Art. IV. Of the Foramina of the Ba/e of the Cranium, ibid.

A. In Man, ibid.

B. In other Mammiferous Animals and Birds, 4g

1. Optic Foramina, ibid,

2. Spheno-orbitar FiJJ'ure, .51

S. Foramen Rotundum, 52

4. Foramen Onjale, 5.3

5. Foramen Lacerum Anterius, 54

6. Canalis Carotideus, 55

7. Foramen Lacerum Pofterius, ibid.

8. Meatus Auditorius Internus, ^ 56

C. In Reptiles, 5 7

Art. V. Of the Bones nxihich compofe the Face, 5g

A. In Man, tbid.

B. In other Mammiferous Animals, 64

C. .In Birds, 71

D. In Reptiles, 74

-E.InFtJhes, 77

Art. VI. Of the Fojf^ of the Face, 80

A. In Man, fhtd.

B. In other Animals, 82

J . Na/al Fojfoe, ibid.

2. Or bitar hofj'*, 8.5

.3. Temporal FoJJ'a, 88

Art. VII. Of the Holes of the Face, ibid.

. CONTENTS. TU

! . S/heno-MaxUlary Fiffurty 9O

2. Internal Orbitar Foramina, 9^

3. Foramen I ncif or mm, 92

4. Sub-orbitar Foramen, 9^

5. Spbeno.Palatlne Canal, 0^

•

LECTURE IX.

Of the Brain of Animals with Vertebra.

Art. I. Of the Organization of the Nervous Syftem in

general, 97

Art. II. Of the Nervous Syfiem conjidered in AHian, ... lOg
Art. III. General Comparifon of the different Nervous

Syftems, 126

Art. IV. Defcription of the Human Brain, 130

A. The Brain of Man •vie'wed on its fupertcr Surface,, ibid,

B. The Brain of Man njteaxed laterally, IS I

C. The Brain of Man vie'wed inferiorly, 132

D. Development of the Brain, 1S6

E. SeSions of the Brain, 142

1. Vertical SeSions, 143

2. Horizontal Sections, 145

F. Of the Origin of the Nerves, , 143

1. The OlfaSory Nerve, ibid,

9, The Optic Nerve, ibid.

3. The Oculo-Mufcular Nerve, i4g

4. The Pathetic Nerve, ibid,

5. The Trt.facial Nerve, 150

6. The Abduilor Nerve, 151

7. The Auditory Nerve, or Portia Mollis of the Se-
venth Pair,

f . The Facial Nerve, or Portio Dura of the Seventh

Ii2

9. The Gloffo-pharyngeus, Par V agum, and Nervus
Spinalis or Acceffonus, commonly called the Nerves
of the Eighth Pair,

A -i 10, The

TIU

CONTENTS.

Pagt

153

xbid.

10. ’The Great Hypoglojfal Ner^>es^ ,

Art. V. Of the Jirain of Mammalia^

J. Proportion, (f the PAafs of the Eratn to the rejl of the

B.ody, ibid.

' Pfetportion of the Brain to the Cerebellum and Me.

dulla oblongata, 157

5. General Form, -iCO

4. Clrcum'voluttons, ' 1 6 1

5. Deojelopment of the internal Parts of the Brain in

Mammalia, / l63

0. Of the Bafe of the Brain, and the Origin of the

Ner-ves, 1 G4

Art. VI. Of the Brain of Birds, lG5

Art. VII. Of the Brain of Reptiles, iGS

Art. VIII. Of the Brain of Fijhes, 171

. 1 . The Tubercles of the Olfailory Kernses, 173

2. The Eminences nuithin the Uemifpheres, 1?4

3. The Ceiebellum, 175

4. The Tubercles ftuated behind the Cerebellum, ibid,

5. Origin of the Nerves, 170

Art. IX. Recapitulation of the Charaders peculiar to the

Brain in the Four Clajfes of Vertebral Animals, 177

Art. X. Of the Membranes of the Brain, 180

Art. XI. Of the Vejfels of the Brain, 180

Art. XII. Of the Medulla Spinalis, IQS

1. Vejfels of the Medulla Spinalis, 194

f . Membranes of the Medulla Spinalis, 19®

LECTURE X.

Distributionof thr PrikcipalNervfsinAnimals

with Vertebra. _ *57

Art. I. Of the Olfadorj Nerve, or the Firft Pair of the

Brain, *5**

A, In Man, and other Mammiferous Animals, ibid.

B. In

CONTENTS.

ix

B. In Birds 200

C. In Reptiles,

D. In Fijhes,

Akt. II. Of the Optic Nerve, or the Second Pair of the

Brain, *01

Akt. III. Of the Ner<ves of the ’Third, Fourth, and Sixth

Pairs, 2 OS

1. Of the Oculo-Mufcular Nerote, or the Third Pair,, ibid,

S. Of the Pathetic Nerve, or the Fourth Pair, 204

3. Of the jdbdu^tor Nerve, or the Sixth Pair, 205

Art. IV. Of the Trifacial Nerves, or the Fifth Pair,, ibid.

I. Of the Nervus Ophthalmicus, or Firjl Branch of the
Fijth Pair in Man and other Mammijerous ulnimals, 205

A. In Man, ibid.

13. li other Mamfiferous Animals, 202

II. Of the Nervus Maxillaris Superior, or Second

Branch of the Fifth Pair in Man and other Mam-
miferous Animals, 210

A. In Man, ibid.

B. In other Mammiferous Animals, 213

III. Of the Nervus Maxillaris Inferior, or Third

Branch of the Fifth Pair in Man and other Mam-
miferous Animals, 215

A. In Man, ibid.

B. In other Mammiferous Animals, 218

IV. Of the Nerve of the Fifth Pair in Birds, 21 9

V. Of the Nerve of the Fifth Pair in Reptiles, 221 .

VI. Of the Nerve of the Fifth Pair in Fifhes, 223 >

Art. V. Of the Facial Nerve, or Sjmpatheticus Minor <

of Winjlovs, ?27

A. In Man, ibid.

B. In other Mammiferous Animals, 230

C. In Birds and Reptiles, 2S2

D. In Fijhes, ibid.

Art. VI. Of the Auditory Nerve, or Poftio Mollis of the

Seventh P^ir, 233

' Art. VII.

X

CONTENTS.

jPaft

•Art. VII, Of the P neumo.gafinc Ner-vtf or Par Vagunty
•vulgarly called the Eighth Pair, 235

A. In Man, ibid.

B. In other Mammiferous Animals,/- 238

C. In Birds and Reptiles, ibid.

D. In Fijhes, .* 23C)

Art. VIII. Of the GloJfo-pharjngeal Nerue, 242

Art. IX. Of the Great Hypogloffal hlernje, or Tnuelfth

245

Art. X. Of the Sub-Occipital and Cervical Nerves, ... 247

A. In Man, ibid.

B. In other Mammiferous Animals, 251

C. In Birds, ibid.

D. In Reptiles, 25 2

E. In Fifjes, ibid.

Art. XI. Of the Diaphragmatic Nerve, 253

Art. XII. Of the Qorfal and Lumbar Nerves, 25 5

A. In Man, ibid.

B. In ether Mammiferous Animals, and in Birds, .... 257

C. In Reptiles, 258

D. In Fijhes, ibid.

Art. XIII. Of the P-elvic and Caudal Nerves, ibid.

Art. XlV. Of the Brachial Plexus, and the Nervet of

the Ihoracic Member, 262

A. In Man, ibid.

1 . Of the Median Nerve, 2t)3

2. Of the Vhtar Nerve, . . . .' 205

y. Of the Radial Nerve, ‘ 2fi(i

4. OJ the Axillary Nerve, 267

5. Of the Thoraeic and Scapular herves, ibid.

6. Of the External Cutaneous, or Mufculo-Cuta.

netus herve, 2^)8

7. Of the Internal Cutaneous Nerve, 26f)

B. In other Mammiferous Animals, tbtd.

C. In Birds *7«

D. In Reptiles, . ., *78

^ I£. In

C0NTENT5-

ai

Fagt

E. In Fijhes,

Art. XV\ Of the Nerves of the Abdominal Member^ . . 280

A. In Man, . jbid,

1. Of the Subpttbic, or Obturator Nerve, 281

2. Of the Anterior Femoral, or Crural Nerve, .... tbid.

S. Of the Ifchiatie, or Sciatic Nerve, 282

4. Of the fibial Nerve, or Popllteus Internus, .... 283

5. Of the Peroneal Nerve, or Popllteus Externus, . . 284

B. In other Mammiferous Animals, 285

C. In Birds, 28(>

D. In Reptiles, 28 8

E. In Fi/ies, 289

Art. XVI. Of the Great Sympathetic, alfo called tbeGreat

Intercoftal or fri-f planch nic Nerve, SQO

A. In Man, ibid.

B. In other Mammifcrous Animals, CQi

C. In Birds, 2yg

D. In Reptiles, 301

E. In Fijkes, 302

LECTURE XI.

Description of the Nervous System op Animals

WHICH HAVE NO VeRTEBRjC, 3O4

A R T . I . B rain and Nerves of the Cephalopodous Mollufca, ibid.
Art. II. Brain and Nerves of the Gajieropodous Mallufca, 308

A. In the Snail ( Helix Pomatla,J 308

B. In the Slug (Llmax Rufus,) 3^^

C. In the Aplyfta, 3,y

D. In the Cho-borealis, 3jj

E. In the Doris, y I 2

F. In the Scyllea, ’.

G. -In the Sea Ear ( Halyotis Tuberculata,) 313

II. In the Bnhmus of Ponds (Helix St agnails Li.n.) and in

fhe Planorhis Cornea (Helix Cornea Lin.; 315

Art. III.

^ CONTENTS.

Pag*

Art. 111. £rat» and Nerves of the Acephalous Mollu/cOf Sit

A. In the AnodontiteSf or Frejh.nuater Mufclesy in Cockles^

in the Venus, the Maiira, and the My a, 51 6

B. In the Afctdia, 3 1 g

C. In the Tritons of Linnaus nnhich inhabit the Anatife.

tons and Balanite Shells- (Lepas Lin.) ibid.

Art. IV. Bram and Nerves of the Crujlacea, 381

A. Brain of the common Cray. Fijh, ( AJiacus Fluviatilis,

Fab.) . . 322

B. In the Common Crab (Cancer M*enas, Lin.) 323

C. In the Onifcus Afellusy 324

D. In Monoculiy 325

Art. V. Brain and Nerves of the Larvee of InfeSls,. . . ibid,

A. Coleoptera, ibid.

1. Larva of the Scarabceus Nafcornis, ibid.

2. Larva of the Stag Beetle ( Lucanus Cervus,) .... 527

3. Larvae of the Cerambyx, Hydrophilus, Carabus,

and Staphylinus, S?9

4. Larva of the Water Beetle ( Dytifcus Marginalis,) 3SO

B. Orthoptera and Hemiptera, .' 332

C. Hymenoptera, .' ibid.

D. Neuroptera, SS3

E. Lepidoptera, 334

F. Diptera, S89

Art. VI. Brain and Nerves of Perfeil Infells, 342

A. Coleoptera, ibid,

1. In the Stag Beetle (Lucanus Cervus,J tbid,

2. In the Scarabceus Nafcornis, 344

3. In the Water Beetles ( Dytifcus J, and the Ground ''

Beetles (Carabus,) 345

4. In the Great Diver ( Hydrephilus Pictus Lin,). . . 347

B. Orthoptera, 349

In the Cockroach ( Blatta Americana,) tbid.

In the Great Green Gra/s/oopper (Gryllns Virtd\Jfi.

mus Lin.) 350

In the Mole Cricket ( Acheta Grylh.talpaJ 353

C: He.

CONTENTS-

• • •

xm

Pj^t

C. IIem\ptera,

In the aval Heater SeorpioK fNefia Ctaerea Lin.) . , thiJ,

D. Lepldoptera,

In the Ztg-Zitg Math ( rhalana Di/ptr Lin.) .... tktd.

L. NeutofJera,

F. Hjmenoptera,

G. Dtptera,

H. Guathaptera,

Art. VII. Brain and Nervei of fl arms, SGl

I. In the Aphrodtta AculeatOf ibid.

i. In the Leeches, 3 6.3

3. In the Earth H arm, 364

4. In the Gordius Argtllaceus, 365

&. In the Herets and Tertbella, tbsd.

6. In the Sea fl'orm, f Luntbrtcus Marinus Lin.) S66

7* In the A/carls Lumbruoldes of Man and the Horfe,. Ibid,

Art. V’III. Of Animals, in nuhicb no diftinft her-vcus

Syfiem has yet been difcyvertd, 568

1. In the Sea Stars ( Ajiertas,) 36g

C. In the Holothurla, ibid.

5. In the Stpunculus, 370

4. In the Sea Urchins f Echinus Marinus,) ibid,'

5. In the ASinia and the Medufa, 571

6. 1st the Polyps ’luitb Arms (Hydra,) ibid,

LECTURE XII.

Of the Organ ®f Sight, or of the Ete, 373

Art. I. General Idea of Vifian, ibid.

Art. II. Of the h umber, Mobility, relatvve Magnitude,
Pojition and DirePtion of the Eyes in different Animals, 379
Art. III. Of the entire Figure of the Globe of the Eye;
of the Form and Proportion of its Chambers ; and of the

Denfty of its tranfparent Parts, 384

A. Form, ibid.

B, Proper,

CONTKNTf,

B. Proportions 3gy

C. Denftty, gg9

D. Conjijience^ Sgl

Art. IV. Of the Ftrjl Coat of the Pyoy or the ScleroUcay 3Q4
Art. V. Of the tranf parent Cornea, and of the Con-

. junainia, Sgg

Art. VI. Of the Second Coat of the Eye, or the Choroides
and its Appendages, 403

A. In Man, ibid,

B. In other Animals, ' 406

1. Of the Ciliary Procejfes, 407

2. Of the Membrana Ruyfchiana, 40Q

3. Of theTapetum, 410

4. Of the Choroid Gland of Fifhes, 411

Art. VII. Of the Iris and Pupil, and of their Motions,, 4 14

A. StruSure of the Iris, ibid,

B. Fibres of the Uajea, 4l6

I C. Motions of the Iris, 417

D. Figure of the Pupil, '. 418

E. Membrana Pupillaris, 420

Art. VIII. Of the Entry of the Optic Nerve into the Eye,

and of the Origin, Nature, and Limits of the Retma, . . ibid.
A. Of the Entry of the Optic Nerve, ibid.

1. In Mam'miferous Animals, 421

2. In Birds, 422

S. In Reptiles and Fifhes, 42»

4. In the Sepia, 427

* B. Of the Retina, ibid.

Art. IX. Of the Nature of the Transparent Parts of the
Eye, of their proper Membranes, iAc 42c)

A. Of the Pitreous Humour, tbtsP.

B. Of the Cryjlalline, 430

C. Of the Aqueous Humour, 432

Art. X. Of the Sufpenfton ef the Globe of the Eye, and of

Its Mufcles, 433

Art, XI. Of the Eye. lids and their Motiont, 437

A. In

CONTENTS.

XT

A. In Man,

i B. In other Mammtftroux Animnlsy 43“*

C. In

D. In Refti/esy

E. In

F. In Mollufcay

Art. XII. Of the Glands that furround the Eye, 4-15

A. In Man,

B. In other Mammiferous Animals, 447

C. In Birds, ‘i4()

D. In Reptiles, 460

Art. XIII. Of the Eye of Infeils and Crufacea, 431

LECTURE XIII.

Of the Organ of Hearing, or, Of the Ear, 455

Art. I. Of Sound, and Hearing In general, Ibid.

Art. II. Of the different Firms of the Membrane nuhicb
contains the Auditory Pulp, or of the Membranous Laby-
rinth, 462

A. In Crcy-fijb, 468

B. In the Sepitr, . v tbtd.

C. In Fljbes that.ha’ve free Branchla, 4C4

D. In Fljbes that ha^je fixed Branchue, 470

E. In Reptiles, 471

F. In Birds, 474

G. In Mammalia, 475

Art. III. Of the Manner In nxhtch the Membranous La-
byrinth is contained in the Bones, or of the OJfeous La-
hyrlnth, . 47*

A. In Fljbes that hanse free Branchlte, 479

B. In the Chondropterygil, 481

C. In Reptiles, *482

D. In Birds and Mammalia, ibid.

Art, IV. Of the Can. ’ities fituated betnjjcen the Labyrinth

6 and

CONTENTS.

Xvi

' Page

and .the external Element y or, Of the Ca'vity of the
Tympanum, and tts Appendages, 4 88

A. In Reptiles, 4 89

B. .In Birds, . . 491

C. In Mammalia, 4g4

1. External Form of the C amity of the Tympanum

m Mammalia, 495

2. Internal Dimifton of the Camity of the Tympa-
num, and Maftoid Cells, 4 97

S. Form and Proportions of the Feneftra Omalis, and

Fenefra Rotunda, 499

4. Enjiachian Tube, 501

D. Particular Defcription of the Barrel or Comity of

the Tympanum, in Cetacea, 502

Art. V. Of the Membrane of the Tympanum, and its Of-
feous Frame, 504

1. Subjlance of the Memhrana Tympani, ibid,

2. Surface and Diredlion of the Membrana Tympani,. 505

S. Frame of the Membrane of the Tympanum, 507

Art. VI. Of the OJJicula mohich ejiablijh a Communication
hetmoeen the Membrana Tympani and the Fencjira Oma-
lis, and of their Mnfclcs, 5 10

I. Of the Bones, ibid.

A. In Mam miff rous Animals, ibid,

1 . I he Malleus, ... 511

2. The Incus, 514

3. The OJJiculum Lenticulare, 515

4. The Stapes, 5lG

B. In Birds, tbia,

C. In Reptiles, 5 1 7

II. Of the 519

Art. VII. Of the Meatus Auditorius Externns, of the

Concha, and of the Mufcles of the External Ear, 523

I. The external OJfeous Meatxs, 524

II. The external Cartilaginous Meat ns, and the Con-
cha, 530

a. Sixe,

CONTENTS.

xva

Pagt

S'tZty 527

b. Direfiion, 528

C. Figure, ibtd,

d. Eminences, 52C)

e. Compafition, 530

HI. The Mufcles, 53 1

A. In Man, ibid,

B. In Quadrupeds, ibid,

;i. Mufcles •which proceed from the Head to the

Scutum, 534

b. Mufcles rwhich prifteed from the Head to the

Concha, or to its Tube, 535

C. Mufcles •which unite the Scutum to the Concha,

or to the Tube of the Ear, 538

a. The Superfcial, ibid.

/8. The Deep Seated, 539

d. Mufcles auhich extend from one Part of the

Concha of the Ear to another, ibid.

Art. VIII. Of the Difribution of the Ner<ves •within the
Far, 540

LECTURE XIV.

(Jr THE Sense of Tovch, and its Organs, 547

Art. I. Of the Senfations produced bj T ouch or Feeling, ibid.
Art. II. Of the Skin and its Organization, 552

1. The Cuticle,

2. The Rete Mucofum, 5gj

3. Corpus Papillare, or the Villous Surface of the Skin, 566

4. The Lutis, ■ ... 50‘y

Art. III. Of the Mufcles of the Skiu, cr the Panniculus

Carnofus, .^2

Art. IV, Of the Glands of the Skin, and the Subcutaneous
Fat,

1. The Glands,

VoL. II.

b

. . 584
. . ibid.
2. The

coirrENTs.

Pagt

T’he Adtpofe Suljlauce, 589

Art. V. Of the Fingers and Toes, and of their Strufiure

relative to the Senfe of Touch, 59 1

Art. VI. Of the Appendices nxshich fupply the Place of the

Fingers in exerciftng the Senfe of Touch, 60l

Art. VII. Of the Infenfeble Parts luhtch cover the Or.
gans of Touch, and proteS them agatnfl too Jlrong^Im.

prejjions, .* ' 607

]. Of Hairs, 6O8

2. Of Feathers, . . ! 6 1 5

3. Of Horns, 623

4. Of Nails, 626

5. Of Scales, 630

6. Of the Infenfible Parts in the Animals veithout

Vertebres, 635

LECTURE XV.

Of the Organs of Smell and Taste, 637

SECTION I.

I

Of the Organs of Smell, 638

Art. I. Of the Senfe, and its Organs in general, ibid.

Art. II. Of the Form and Magnitude of the Nafal Cavity, 643
Art. III. Of the Sinufes vohich increafe the Extent of the
Nafal Cavity, .’ C44

A. In Man, C45

B. In other Mammiferous Animals, ibid.

1. The Frontal Sinufes, ibid.

2. The Maxillary Sinufes, 648

8. The Sphenoidal Sinufes, C49

Art. IV. Of the Projefiing Laminof vuhich increafe the

Internal Surfaces of the Nafal Cavity, 650

A. In Man, .'

CONTENTS.

3UX
P»p

B. In other Mammlferous Animals, . . . . 632

1. Of the OJfa Turbtnata Infertara, ibid,

‘2. Of the Offa Turblnata^Superiora, and of the

Ethmoidal Cells, 656

C. In Birds, 657

D. In Reptiles, 6*8

E. In Fljbes 659

Art. V, Of the Pituitary Membrane, 6CO

Art. VI. Of the Nerves 'which are dijiributed to the In-
ternal Parts of the Nofe, 662

I. The Olfadory Nerve, 66S

A. In Mammiferous Animals, ibid,

1. The Cribriform Lamella, ibid.

2. The Olfadory Nerve, 065

B. In Bird,, 666

C. In Reptiles, 667

D. In Pijbes, ibid.

II. The Nerve of the Fifth Pair, ibid.

Art. VII. Of the Cartilages 'which cover the Aperture of

the Nojirils, and their Mufcles, 66g

A. In Man, ibid,

I. The Cartilages, ibid,

II. The Mufcles, 67O

B. In other Mammiferous Animals, ibid,

C. In Birds, 630

D. In Reptiles, ibid,

E. In Fijhes, 681

Art. VIII. Of the Nares and the Spiracles of Cetacea, . 682
Art . IX. Of the Organs of Smell in Animals that have no

Vertebra:, 68 7

SECTION II.

Of THt Organs OP Taste, ggg

Art, I. Of the Senfation ofTaJle, ibid.

Art.

XX

CONTBNT'sr

Pagt

Art. II. Of the Subjiance of the Tongue, of its Form, and

of its Mobility, 69 1

Art. III. Of the Teguments of the Tongue, 6q7

A. In Man, ibid.

B. In other Mammiferous Animals, 699

C. - In Birds, 703

D. In Reptiles, 707

E. In Fijhes, . . 70S

Art. IV. Of the Dijiribution of the Nerves in the

Tongue, ibid,

i

ERRATA.

fACt— UN*

For

ai— >12 Cherioptera
— 29 mucleus
23 orachnoidra
36c — 5 Gnothoptcra
'^93 — j Cherioptera •

614 3 Spinois ant-eater (cchudna)

696—17 Stomaxp ^

Read

Cheiroptera

nucleus

arachnuidea

Gnathaptera

Cheiroptera

.Spinous aiit-catcr (echidna)
Stomoxys

LECTURES

ON

COMPARATIVE .\JSI ATOMY.

LECTURE EIGHTH.

%

Of the Head, confidered as the principal Receptacle
of the Organs of Senfe.

Iv treating of the organs of motion, -we con-
lidcred the Head, as far as its figure, its motions,
and the mufcles which aCl upon it, were con-
cerned. Were we to ftop there, our knowledge
of this portion of the body would be very im-
perfect. The hiftory of its bones forms the
principal part of Comparative Ofteology, be-
caufe they are the moft variable and complicated
of all the fkeleton ; and a knowledge of them
is befides of great importance, on account of the
number of effential parts which they either fuf-
tain or envelope. The brain — the principal
nerves — the organs of feeing, hearing, fmelling,
and tafting — thofe of maflication and degluti-
tion— and a part of thofe of refpiration, and
VoL. II. B voice.

2 Lect. VIII. Osteology of the Head.

voice, are cither enclofed within the Head,
attached to fome one of its bones, or pafs
through its holes and canals. Having concluded
our treatife on the Organs of Motion, it is pro-
per that we fliould now delcribc the Head, which
■vvill complete our Syftem of Ofteology, and
commen-'e an account of the Organs of Senfe.
We {hall thus fix with precifion the limits of

each branch of our fubjetfl.

/

Article I.

f

Of the Cranium — of its Form, and its Propor-
tions with refped: to the Face,

The Head allows of two principal divifions, iff,
the cranium, which forms an olfeous cafe to en-
clofe the brain; 2d. the face, which is made up
of a colledfion of different bones, containing
very complicated Cavities, in which are lodged
the organs of fight, fmell and taftc. The or-
gans of hearing are fituated in the lateral parietes
of the cranium.

The tw’o organs which occupy the greatefi
portion of the face are thofe of fmell and tafi(;.
In proportion as the organs of thefe two fenfes
are developed, the magnitude of the face, and its
proportion, with rcfpcdf to the cranium, is in-
creafed. On the contrary, as the brain is cniar*

N

- Art. I. Form OF THE CRANiUiVr. 3

"cd, the cranium which contains it augments in
capacity, and becomes more confiderable when
Compared with the face.

An extenfive cranium and a fniall face, there-
fore, indicate a large brain, with little devclopc-
ment of the organs of taflc and fmell ; while a
fmall cranium, and a large face, point out the
oppofite proportions — a brain ot a fmall volume,
with very perfect organs of tafle and fmell-
ing.

C»

The nature of each animal depends in a great
mcafure on the relative energy of each of its
fundions, and it may be faid to be influenced
and governed by thofe fenfations which are the
moft powerful. We obferve daily illuftrations
of this truth among ourfelves, though the dif-
ferences which exift in that refpedl, between one
man and another, are much lefs than thofe
which may be remarked between other animals.
We fhall fee hereafter that the brain, the com-
mon centre of all the nerves, is alfo the point in
which all perceptions terminate, and the inftru-
ment'by which the mind combines thofe per-
ceptions, compares them, and makes deduc-
tions ; in a w^ord, refleds'tuid thinks.

We (hail alfo find that animals participate
more in this laft faculty, or at leaft appear to
enjoy it more perfectly, in proportion as the
mafs of the medullary fubftance, which forms
their brain, furpafles that which conflitutes the
.remainder of their nervous fyftem ; that is to

B 3 fay.

4 Lect. VIII. O STEOLOGY OF THE H EAD,

fay, in proportion as the central organ of the
fenfes exceeds their external organs.

The relative proportion of the cranium and
the face, which indicates immediately that of the
brain, with refpeefi; to two of the principal exter-
nal fenfes, is likewife a mark of more or Icfs per-
feiflion in the internal ficulties. But another con-
fideration adds to its importance as an index of
this kind, which is, that the turn fenfes we have
mentioned are thofc which aifl with the greateft
force on animals; thofe which govern them moft
powerfully in confequence of the energy which
tw'oof the frongef; deli res, hunger and love, com-
municate by the means of their perceptions. The
aeftions to which thefe defires determine animals,
are thofe into which they enter wdth the moft
blind fury, and the greateft bcftiality, if we may
be allowed to exprefs ourfelves thus, when man
is not the fubjed of confideration.

It is not aftonifhing, therefore, that the form
of the Head, and the proportions of the two parts
which compofc it, are indications of the facul-
ties of animals, of their iiiftindl, of their docility,
and, in a word, of all their fcnfitive being. This
circumftance renders the ftudy of thefe propor-
tions highly important to the Naturalifl.

Wc ftiall foon find that man is the animal
which has the largcft cranium, and the final left
face; and that, according as this proportion is
departed from in other animals, they become
more ftupid or more ferocious.

Among

5

Art. I. Form of the Cranium.

Among the diHercnt means that have been
employed to oxprefs convenienily the propor-
tions of thefe pai ts, one of the moll (imple, but
which is not always fufheient, is the fcicuil Iptf
of Camper, and the angle which it lorms with
the bafe of the cranium. I'he lacial line is lup-
pofed to pafs along the edge of the luperior
dentes inciforeSj and the moll prorrdnent point
of the forehead. The hafilar line of the cranium
is that which bifc»fls longitudinally a plane pair-
ing through the external meatus auditorii, and
the inferior edge of the anterior aperture of the
noflrils. It is evident, that in proportion as the
cranium is enlarged, the forehead mud projecl
more forward, and the facial line form a larger
angle with the balilar. On the contrary, in pro-
portion as the cranium diminii'hes in lize, that
line will incline farther back. We lliall lliew
by a table, of the dill'ercnt fizes of the facial
angle, that it is wider in man than in any other
animal, and that it becomes always more acute
in the mammalia, as they are removed from
man, and in birds, reptiles and filhes. The
vulgar are even accullomed to attribute llupidity
to animals which have very long fnouts, as
cranes and woodcocks; but when fomecircum-
llances tend to elevate the facial line, without
augmenting the capacity of the cranium, as we
lind takes place in the elephant and the owl, in
confequcnce of the extraordinary thicknefs of
the diploe of the os frontis, we fancy we fee in

B 3 animals

\

6 Lect. VIII. Osteology of the Head.

animals of that defcription a peculiar air of in-,
tclligence^ and are induced to afcribe to them
qualities which they do not really poflefs. We
know that the owl has been conlidered as the
emblem of wifdom, and that the elephant. has
in India a name which indicates that he pof-
felles reafon.

The ancients appear to have been very fen-
iible of thefe relations. They not only perceived
that an elevated facial line was the indication of
a noble nature, and one of the characlcriftics of
beauty ; but they even ftepped beyond nature,
and made this line incline fomewhat more for-
ward than it does in man, in ; figures to which
they were defirous of giving a more than hur
man air, as the flatues of their gods, and
thofe of their heroes, 'or men whom they wiflied
ihould appear to partake of divinity. It feems
they were defirous of placing .man between be-
ings of this fort, or a more perfedl order, and
brutes ; and that they wiflied to indicate, by the
oppofite inclination of the forehead, that their
heroes were still more removed than common
men from the forms or the nature of the inferior
animals.

A. In Man and other Mammiferous yhiinials.

The facial angle being determined in the man-
ner I have pointed out, which is that of Camper,
we find that in ^turopean heads this angle is

ufuall^

7

Art. I. Form or the Cranium.

uTually 8o°, in Mongols 75°, and in Negroes 70®,
wich the variations ot forne degrees in rcfpcdl to
age and individuals. For example, the face in
children is lliort, bccaufe their pofterior teeth
are wanting. This makes their facial line more
perpendicular, and is one of the caufes which
renders their countenance always agreeable, and
in confcquence of which they become almoft al-
ways lefs beautiful as they increafe in age. The
ancients, when they wilhed to imprefsan auguft
character on their figures of men, have increafed
the facial angle to 90“, and they have even ex-
tended it to lOOo in their figures of gods. This
links the eyes more, and renders the branches of
the lower jaw fliortcr than in nature.

In the oiirang oHtangy the facial angle is 65“.
In the fapajous, and the gunwns, it is about 60'*.
In the tnagols, and the macaques^ about 45°. Lall-
ly, in the w/a/ruW/^, which are the moft mifehiev-
ous and ferocious of all the apes, it is only 30”.
In the fpecics which have the ear much elevated,
and the guttural cavity very deep, as the Bata-
vian pongo, and the alouatte, the fmallnefsof this
angle does not indicate a proportional elongation
of the fnout. To demonftrate this accurately,
the balilar line of the cranium Ihould be drawn
parallel to the bafe of the noftrils.

Even with this regulation, however, the facial
angle is not important, with rcfpccl to the brain,
except in the human fpecies, and among the
Quadrumana, becaufe they have only very fmall

4 frontal

S Lect. Vlll. Osteology of the Head.

frontal finufes, which do not elevate the facial
line in a fcnfible degree, and becaufe the nofe
falls under that line.

But there are fome quadrupeds, as the Sarco-
phaga, the hogSy fome Ruminantia, and particu^
larly the elephant y in which the frontal finufes
fwell the cranium to fuch a degree, that they
elevate the facial line much beyond what the
proportion of the brain would require. In
others, as the morjey and the greater part of the
Rodentia, the nofe occupies fo large a fpace that
the cranium is inclined backward, and none of
its parietes are entirely free anteriorly. In this
conformation it is impoflible to tell what ought
to be the diredlion of the facial line. Laflly,
the Cetacea have the cranium elevated in the
form of a pyramid, and fituated above a face
which is very much prolonged, but flattened
horizontally. Tlic inclination of the facial line
would be greater than it ought to be with re-
fpeefl: to the real capacity of their face.

The following, how'ever, is a table of the ex-
tent of the facial angle, in a certain number of
animals, formed by drawing a line parallel to the
bafe of the noflrils, and another pafling along
the anterior edge of the alveoli, and touching
the convexity of the cranium, whether the point
of confaft be concealed by the face, or life
above it.‘

European Infant _ _ - - 90*.

European Adult « - - - 85®.

Aged

Art. T. Form of the Cranium.

9

Aged European _ - - -

Adult Negro - - - -

Young Ourang-outang - - -

Sapajou _ _ - - -

Talapoiii Monkey » _ -

Young Mandrill ----

Coati ------

Pole-cat - - - - -

Pug-dog - _ - - -

MadilFdog, the tangent taken at the

75«.

70".

670.

63“.

57'**

42°.

28®.

3i“*

35°*

external furface ot the cranium 41*.

at the internal furfacc - 30®.

Hyaena, at the external lurfacc - 40®.

at the internal - - - 23?.

Leopard, at the internal furface - 28®.

(A tangent cannot be drawn to the external
furface, on account of the convexity of the nofe.)
flare ------ 30®.

Marmorte - - - - - 25®.

Porcupine ----- 23®.

The three laft are meafured by the internal fur-
face of the cranium, becaufe a tangent cannot be

brought to the external.

Pangolin ----- 39*.

BabiroulTa ----- 29°.

Ram 30°.

Horfe ----- 23®.

Dolphin ----- 25°.

We may, however, difeover more important
^■elations, in confidering the cranium and the

face.

to Lect. VIII. Osteology of the Head.

face, under the vertical and longitudinal fedion
of the Head. With refpcd to their relative pro-
portions, the cranium, in this fedion, occupies
an area fometimes greater, fometimes lei's, and
Sometimes nearly equal to that of the face.

, in the European^ the area of the fedion of the
cranium is almofl; four times greatpr than that of
the face, the lower jaw not included.

In iheNegro^ the cranium remaining the fame,
the area of the fedion of the face is increafed
about one-fifth. In the Calmuc^ it increafes only
one-tenth.

The proportion is lefs in the ourang outang,
the fapajouSy the area of the face is almoll
one-half of the cranium. It is nearly equal in
the mandrills^ and in moft of the Ca/nivora,
except in the varieties of fiiort-nofed dogs, as
the pugy which have the face fomewhat fmaller
in proportion to the cranium. The Rodentia,
the Pachydermata, the Ruminancia, and the Soli-
peda, have all the area of the fedion of the face
larger than that of the cranium. In the Roden-
tia, thchare^ and the marmotte, have it one-third
larger. It is more than double in the porcupine.
It is nearly double in the Ruminantia; a little
more than double in bogs^ nearly triple in the
hippopotamusy and almofi quadruple in the borfe.

The niorfe and the clepbant have a large face,
in confcquencc of the height ot the alveoli; but
it cannot, in them, be coiilidercd as augmenting
the extent of the organs of fenfe.

The'

Art. I. Form of the Cranium. ii

The Cetacea have the cranium very globular,
and the face very flat, in confcquence of which
the area of the latter is proportionally di-
miniflied ; bcfides, the face is not occupied by
the nofe throughout its whole extent, and ought
not to be confldered heie under this relation.
The area of the face in the dolphin is perhaps
about one-third larger than that of the c ranium.

With rcfpcvfl to figure ; were the curve
of the human cianium continued inferiorly
from the foramen magnum to the root of the
nofe, the feclion would form an oval which
would be a little narrowed anteriorly, and of
which the greatell axis would be nearly parallel
to the floor of the nollrils, or at lealt inclined
very little backward, and its proportion to the
fmall axis would be as 5 : 4. But in the fpace
I have pointed out, and which forms the limits
of the cranium and the face, there is, inftead of
this curve, an irregular line forming a falient
angle within the oval. The fection of the face
IS a triangle, with its greatefl: fide towards the
cranium, and the fmallell directed outward.
The angle, which the latter forms with the
third fide, or the palate, is precifely the facial
angle.

In monkics^ the great axis is fomewhat elon-
gated with refpecT; to the lelfer ; the line which
feparates the cranium and the face becomes more
flraight, and the anterior and inferior fide of the
triangle of the face is fo much elongated, that

the

1 2 Lect. VIII. Osteology of the Head.

the fide which touches the cranium is the fmall-
efi: of the three in the macaques and the man-
drills. It is found the leafi: alfo in other qua-
drupeds. In the Sarcophaga and the Roden-
tia, the anterior part of the oval of the cranium
is the narrowefi. In the Ruminantia, and the
horfe^ the pofterior is the mofi: narrow. We per-
ceive a ftrong angle within the cavity of the
cranium of thofe that have an ofieous feparation
between the cerebrum and the cerebellum.

The great axis of the oval inclines forward
in the Sarcophaga, wfith refpedt to the bafe of
the noftrils, but backward in all the herbivorous
fpecies. Its form and direction in the morje arc
the fame in the Sarcophaga.

The feeflion of'the cranium of the dolphin is
almofi; triangular, the fides are convex, and the
angles rounded. One fide is anterior ; another, •
■which is pofierior, is perforated by the foramen
rnagnum. The third, which forms the bafe- of
the cranium, and which correfponds with the
line that unites the cranium to the face, in
other animals, is, however, fituated completely
behind the face, and is even parallel to the arch
of the palate.

We may alfo examine the tranfverfe vertical
fedlion of the cranium, that is to fay, a fedtion
made by a plane perpendicular to its great axis.

This forms in man a very conliderable portion
of a circle, wanting only a fegmeiit fomewhat lefs
than a third of the circumference towards the

inferior

Art. I. Form OF THE Cranium.

13

inferior part. The cranium of the Negro is flatter
on the lides than that of the European, becaufe hia
temporal foflle are greater and deeper. This
diminillies his face upwards, but enlarges it in-
feriorly on account of the prominence of the
cheeks.

In the Sarcophaga this fetflion produces a femi-
ellipfis rounded towards the upper part, and hav-
ing the bafe nearly equal to its height.

In theZ>5^, it is an oval which is longefl: verti-
cally, and the Tides of which are made irregular
by large angles towards the pars petrofa direiil-
cd interiorly.

In ihchorfe, the oval is more broad than high,
and the inferior half has nearly the fame cur-
vature as the fuperior.

Thefe remarks are the more interefling, as in
all mammalia the brain is molded in the cavity
of the cranium, which it fills exadllv; To that
the defeription of the ofTeous part affords us a
knowledge of at leaft the external form of that
medullary mafs.

B. In Birds.

The longitudinal and vertical feiflion of the
cranium in birds generally reprefents an oval,
with its narrowefl: part anteriorly, the fide cor-
refponding to the face lefs convex than that
which is fuperior and pofterior, and the great
axis directed upward and forward. The otc/r

are

14 Lect. VIII. Osteology oe the Head.

are the only birds in which this feeT;ion is oval,
and Contradled nearly equally above and below,
with the great axis almoft. vertical.

The face of birds being chiefly formed by
their bill, their phyliognomy depends upon the
thicknefs and length of that part; but as the
nofe occupies a very fmall portion of it, and as
the tongue is frequently fo fmall as to take up
very little room in the mouth, the proportion
which the cranium bears to the face does not
afford the fame induftions in birds as in qua-
drupeds.

C. In Reptiles and Fijlies,

As the brain of reptiles and fifhes occupies
only a fmall part of the cavity of their cranium^
no important confequcnccs can be deduced from
its fl’.ape and fize. In the tortoife this cavity is
large, narrow from right to left, elevated an-
teriorly, and depreffed pofleriorly. Its lateral
parietes are almofl: vertical, and its bafe is pa-
rallel to the palate. The external form of the
head, and its apparent magnitude, areoccafioned
by the acceffory bones, between which and the
cranium there is a large fpacc occupied by muf-
clcs and glands.

The fmall fize of the cavity of the cranium,
with refpedt to the external bulk of the hcaJ, is
Hill more extraordinary in the crocodile. In an
individual four metres long, that cavity will

hardly

Art. I. Form OF THE Cranium, 15

hardly adndt the thumb, and the area of the
fcL^ion of the cranium is not one-twentieth part
of that of the whole head. The figure of the
fedlion is oblong, rather larger anteriorly, and
defeending poficriorly. There is a confidcrable
deprefiion for the pituitary gland. Its breadth
is equal to its height; and the lateral parts of
the head, as in the tortoife, cover only the tem-
poral fofllc.

The cranium of frogi falamanders is al-
mofi: prifmatic.

That of fifiics is generally very fmall in pro-
portion to the relf of the head, but it varies
greatly with refpecl to its form, and cannot be
compared e'itherwiih the brain or the furround-
ing parts. Its (hape, however, approaches moft
frequently to an oval.

’ Article II.

Of the Bones u-hich compofc the Cranium.

A. In Man.

THEofleous cafe which forms the cranium, is
divided into a certain number of bones, which
are joined by immoveable articulations, called
futures. Thefe difappear more or lefs with age,
becaufe the reciprocal indentations by which

3 the

i6 Lect. VIII. Osteology ot the Head*

the edges of the contiguous bones arc united, arc
fooner or later offified together. As there exifis,
however, always fome traces of the feparations of
the bones, and as their fituation or difpofition is
varied in different animals, a knowledge of them
becomes highly ufeful to the Anatomill, who
wifhes to difcover the part and the kind of cra-
nium to which fragments of foflile heads fliould
be referred. We lhall examine thefe futures, or
lines of reparation between each of the bones of
the cranium, in the different kinds of animals,
beginning with Man.

The human cranium is compofcd of eight
bones ; they are all fupported on one of their
number, which is fituated at the bafe of the
cranium, to the arch of which it may be faid to
fervc as the key. It has been compared to the
figure of a bat, and is called os sphenoidesy or os
cuneiforme, becaufe it anfwers the purpofe of a
wedge, with refpccfl to the bones between which
it is cnclofcd.

We fnall here confider its fliape abflradledly
from its eminences and holes. It is bounded
before by a curved line, the concavity of which
is anterior, and which is continued obliquely on
the bottom of each orbit of the eye, the external
fide and bottom of which are occupied by the
fphenoid bone This line is called the fpbenoidal
future. At the temporal angle of the orbit, it
is direded backward in the temporal foffa, until
it comes in contad: with the os temporum. It

feparates

Art. II. Bones of the Cranium.

17

feparates the fphenoU from the frontal bone
throughout almoll its whole length; the two
extremities ot the os fphenoides only touch the
parietal bones. It is bounded on each fide by
another curved line, which makes an acute angle
with the firll, and which feparates the fphenoid
from the temporal bone ; this is called ihc fpheno-
temporal, or temporal future. The concavity of
the bone is external ; as it approaches the mid-
dle it defeends and is carried backwards, fo
that the poflerior border of the bone is much Icfs
extcnhve than the anterior; the poflerior border
is divided into three lines, which are nearly
llraight ; a middle one, which is paiallel to the
middle of its anterior margin; and two lateral
lines, direded obliqu ly b...kwa:d, each uniting
with the external margin of the fame fide by an
acute angle. The middle part of the poflerior
margin feparates the os fphenoides from the os
occipitis. This, which is called the bafilar y«-
/«rc, exifls, only in youth. The two hones are
afterwards united, and form only one; its lateral
parts feparate it from the pars petrofa of the os
temporum. The longitudinal axis of the os
fphenoides is nearly one half the length of its
pofierior margin, and fomewhar more than a
fourth of the anterior.

/ All the bones of the cranium are feparated by
lines which proceed from difierent points of the
os fphenoides. front al or coronal future ex-

tends from a point very near the lateral fuperioc
VoL. II. C angle

i8 Lect. VIII. Os TEOLOGY OF THE HrAD.

angle of this bone, to the correfponding point on
the other fide, crofling the arch of the cranium
almoft at the top. This future is the poflerior
boundary of the bone which forms the forehead,
and the fuperior arch of the orbits. The name
given to this bone is the os frontis. In children
it is divided by a longitudinal future, which
fometimes remains even at a very advanced agCr
This feparation is marked in fome fkulls by a
pretty confpicuous depreflion, and in others by a
ridge more or lefs elevated. It is called the
medial or proper frontal future. The os frontis
is nearly of a femi-circular form. It is trun-
cated inferiorly, and bends backward to form
the arch of the orbits. Its vertical heighth is
nearly two-thirds of its breadth.

At the external and fuperior angle of the
fphenoid bone, another future commences,
which is continued along the edge of the os tem-
porum ; the curve it forms is nearly circular.
It is called the fquamotis future^ becaufe the edges
of the bones which form it have the appearance
of fcales ; the fuperior and internal edge of the
os temporum, covering the external and inferior
cdo-e of the os parietalc. After deferibing about
one-third of a- circle, the edge of the temporal
bone turns up, forms with the futurcan obtufc and
inward angle, and isdireded poflcriorly until it

reaches the os occipitis.

A line proceeds from each fide of the point

where the bafilar joins the pctro-fphenoidal fu-
ture.

Art. II. Bones of the Cranium.

^9

ture, and feparatcs the pars petrofa from the os
occipitis ; rhcfe two lines bend outward until
they arrive oppofite the middle ot each occipital
condyle, where they are fuddenly carried back-
ward, and rc-afeend a little to finilh the out-
line of the temporal bone. All this pofterior
part of the edge of the bone is called the maf-
toid future.

The thin, and almoft: circular portions of the
ofl'a temporum, form a part ot the lateral pa-
rietes of the cranium. The podcrior edge of
the temporal bone is rounded as it advances to
join the occipital. Its inferior edge produces
that thick and hard prominence, called os pe-
trofum, fituated between the bafilar procefs and
the poderior lateral edge of the os fphenoides.and
thus forming a part of the bafe of the cranium.
This pars petrofa is feparated from the red of
the bone in the human foetus: it extends from
the back part obliquely inward and forward.

The lambdotdal or occipito-parieial future, which
concludes the figure of the os occipitis, begins
at the middle of the maftoid future, and afeends
fomewhat poderiorly, fo as to form an angle with
the correfponding future. It unites the occipital
with the parietal bones, which complete the fu-
perior arch of the cranium. The portion of the
occipital bone included between the foramen
magnum and the os fphenoides, is cii^led the
bafilar or cuneiforjn procefs. It is almod fquare
in man, narrowed a little anteriorly, and very

C 2 fhort.

I

20 Lect. VIIT. Osteology of the Head.

Hiort. In youth it is feparated from tlie reft of
the bone by two futures which interfect the an-
terior portion of the condyles. The remainder
of the bohe, which forms what is properly called
the occiput, is of an oval form, very concave
internally, and pointed fuperiorly. Its pofttion
is.fuch, that when the human body is ereeft, the
cuneiform procefs afeends fomewhat forward,
and its other part is direded backw-ard.

The ofia parietalia are feparated from each
other by a longitudin 1 linCi called the parietal
or Jagittal future. The fhape of thefe bones is
quadrangular, the edge by which they touch'
each other is the longeft. Their temporal
margin is the ftiorteft and the moft concave.
Their convexity is nearly uniform.

The os frontis has a vacant fpace'between the
two orbits, which is occupied by the cribriform
lamella of the os ethmoides. The form of this
fpace is that of a long fquare. It is bounded
poftcriorly by the os fphenoides. The line of
reparation is called i\\Q- ethmoidal futurCn

r>. In other Mammiferous Animals.

The principal differences obfcrvable in the
•cranium of mammiferous animals, confill in the
number of the bones which conftitute it ; in the
connections of thefe bones; and, laftly, in the
particular form which each of them affumes.
We lhall proceed to confidcr the craniums of

21

Art. II. Bones of the Cranium.

%

the different families of mammalia under thefc
three general points of view.

J. Number of ihc Bones of the Cranium in
Alummulia.

All the Quadrumana have eight bones in the
cranium, but the os fphenoides is frequ ntly di-
vided into two parts; one of which form.s the
orbitar wings, and the anterior clinoid procefl'es;
and the other the temporal wings, the pollerior
clinoid proceffes, and the bafilar fofla. The
two offa parietalia unite together at a very early
period in the Cherioptera, fo as to form only one
bone ; the fame thing takes place in almoll all
the other Sarcophaga, which alfo generally have
the os froiuis divided into 'two parts by a medial
future. The cavity of the tympanum is fe—
parated from the rell of the temporal bone, by a
future, which feldom offifies in the caty dogy and
civet genera.

This cavity is alfo feparated in the Ro-
dentia, and the os frontis remains divided into
two parts, dheir parietal bone is fometimes
fingle, as in the the cavyi, the porcupine,
the marmot tCy the rats, and fqutrrels ; and fome-
times double, as in the mice, the dormice, and
the rabbit.

The os frontis and the offa parietalia of the
elephant are, at a very early period, united by ofli-

C 3 fication

32 Lect. VIII. Osteology of the Head.

%

fication with all the other bones of the cra-
nium ; fo that the whole forms a brain-cafe,, in
which no traces of the futures appear.

In the hog, the tapir, and the hippopotamus, the
two parietal ia form only one piece. Their os
frontis is doubie : the rhinoceros has the frontal
and parietal bones double, but the reparation
of the lad foon olTifics. The os fphenoides of
the animals of this and the two fucceeding fa-
milies, remains for a long time divided into two
parts. The one forms the orbitar wing, 'or the
little wings of Ingraflias ; the other produces the
large wings, or temporal proceflcs, which are
here much the fmalled. This difpodtion is ex-
actly the oppofite oT that obferved in man.

In the Ruminantia and Solipeda the os frontis
remains for a confiderable time divided by a
medial future. In thefe animals the place of
the tw'o parictalia is fupplied by afinglepiece
which forms the top of the cranium. The
cavity of the tympanum is always diflindt.

The fcals have tw o parietal ia, and the os fron-
tis divided into two parrs j this alfo takes place ,
in the morfe. The lamamin has only one pa-
rietal bone, and the cavity of the tympanum is
fepa rated from the body of the temporal bone.

In the Cetacea the parictalia arc very foon
united with the occipital and temporal bones,
in fuch a manner that thefe five bones form only
one. The bone of the car is always feparatc,
and is connected with the cranium only by foft

parts.

Art. II. Bones OF THE Cranium. 23

parts. The fphenoides remains long diftinfl,
and is even divided into feveral pieces.

12. Connections of the Bones of the Cranium in

Mammalia.

Of all the Quadrumana, the oran^-outang has
the cranium moft fimilar to that of man in its
form. It differs however in the connection ot
the bones. The temporal w ing of the os fphe-
noides ise.xtremely narrow, and docs not extend
to the parietal bone. It touches the os frontis
with its fuperior extremity only, fo that the
temporal partly articulates with the frontal bone.
The temporal future is indented, and the edges
of the bone are not fquamous. In the jocko^ this
portion of the temporal wing neither touches
the os frontis nor the olfa parietalia; but the os
temporum articulates immediately with the os
malae, by its fquamous part.

In the mandrilsy the macaques, the magots, and
the guenons, the connexion is the fame as in the
orang-outang.

In the fapajous, the os frontis does not come
in contadl w’ith the temporal w ing of the fphe-
noid bone, and the parietal articulates with the
cheek-bone. In the alouates the connection is
the fame as in man.

The conneeflions of the bones of the cranium
with each other are the fame in all the Sarco-
phaga as in man.

C4

In

24 Lect. Vlll. Osteology op the Head.

In all the Rodentia, the os fphenoides only
articulates with the os frontis, and oflTa tem-
porum, without touching the offa parietalia.
Its extent in the orbi-tar and temporal folTa is
very limited."

In the armadillos, the pangolins, and the Jlolhi,
we difcover the fame conne<5tions as in the
Rodentia; but in the ant-eaters, the olTa parie-
talia are carried under the cranium, and unite in
a very extenfive manner with the os fphenoides,
at the pofterior part of the temporal and orbiiar
foffa.

In the elephant, the bones of the cranium
are, at a very early period, united by oHification,
and form only one piece. The bone of the
car is always diftinifl and feparate from the os
temporurn.

In the hog, the tapir, the rhinoceros, and the
hippopotamus, the os fphenoides does not unite
with the parietal bones, and its large wings
occupy only a very fmall fpace in the orbicar
and temporal folfa. Only a fmall part of the
orbitar procelfes appear externally, though they
are extended much farther than the large wings.
The bone of the car, which is very dihindl, is,
however, ofiihcd at its bafe to the circumference
of the meatus auditorius,

The os fphenoides of the Ruminantia articu-
lates, as in man, with all the other bones of the
cranium, but its orbitar wing, which is very ex-
tenfive, is concealed in a great mcafvire withii>

the

f

Art. II. Bones OF THE Cranium. 25

tlic cerebral cavity, and covered by the orbitar
lamella of the os frontis.

In the Cetacea in general, the futures which
exill after an early age are all ot the fquamous
kind.

3. Forms of the Bones of' the Cranium in the

Mdinmalia.

The fliape of the os frontis is more irregular
in the orang-outang than in man. The arch of
the orbits is Ids deprdfed. In l\\Q fapajous^ the
frontal boqe has ti>e form of a triangle, and ter-
minates in a point towards the crown of the
head. In the other monkirSy this bone is nearly
oval, and the orbitar arches almoll Braight.
Thefe ar:hes form, in all monkies, as well as in
man, th.e anterior margin of the os frontis, be-
caufe the root of the nofe is very narrow. In
the tnakis it begins to aflume a broad fhape, and
the eyes become oblique. This gives a rhom-
boidal form to their os frontis.

The os frontis of the Sarcophaga, and in gene-
ral of all the fucceeding mammalia down to the
Cetacea, exhibits the irregular furfaceefaprifm or
cylinder, in which three principal furfaces (hould
be confidered; one fuperior, which is connected
with the nofe anteriorly, and with the reft of the
cranium pofteriorly ; and two lateral, which de-
feend each into the orbitar and temporal folTa
of the fame fide.

The

*6 Lect. VHI, OsTEOLOG Y OF THE Head.

The form of the fuperior furface is principally
determined by the pofition of the orbits. In
dogSy cats, bears, ternate-bats, %<ueafels, oppoffums,
i^c. thefc orbits correfpond with the anterior
part of its lateral margins, and give to the whole
bone a rhomboidal figure. In the Rodentia, the
orbits form notches in the middle part of the
lateral edges of the os frontis, and give to it a
form more or lefs redtangular.

It is the fame in the jiying-lemur.

The hedge-hogs, the moles, the Jhrews, the ant-
eaters, the feats, the morjes, and the rhinocerofes
have no orbitar arches properly fd called. The
frontal bone is fimply contracted, and becomes
almofl cylindrical between the orbits. It is en-
larged pofieriorly.

In the hippopotamus, the Ruminantia, and the
Solipeda, the frontal bone is enlarged, and forms
a vault over each orbit.

Laftly, in the Cetacea, the os frontis is narrow
from the front backward. It rcfembles a fillet
extended acrofs the cranium; but as, according
to the laws which govern the firudlure of the
head in mammiferous animals, this bone (hould
form the upper part of the orbits ; it defeends
for that purpofe below the maxillary bones,
fo that the order of the pofition of the bones
in ihefe animals is entirely reverfed to preferve
that of their connections.

The ofTa parietalia of the orang-outang,
difl'er only from thofe of man in having their

y temporal

Art. II. Bones OF THE Cranium. 27

temporal edges almoft flraight ;*thofe of the
monkies are narrower, and their angles become
more oblique in proportion as the cranium is
flat. They return almoft to a rectangular form
in the Sarcophaga and the Edentata. We have
already fliown that they are united into a Angle
piece in a conAderable number of the Rodentia.
That piece is almoft nearly fquare ; but it is
fometimes flat, fometimes rounded, and fome-
times furmounted with a creft.

The Ruminantia have alfo a parietal bone in
a Angle piece. In the flags, the greater part of
the antelopes, the Jbeep, and the goats, it is broad,
and a narrow flip extends on each Adc of the
temporal foffa. It is Atuated before the occipital
arch. In the camel it is narrow, and has a longi-
tudinal creft. In the ox, and in the antilope-
hiibalis, it is Atuated behind the occipital creft,
and refembles a ribbon furrounding the pof-
terior parr of the head tranfverfely.

In the Solipeda, the parietal bone, which is
Angle, is almoft. fquare, and Atuated before the
occipital creft.

We have already explained the forms of the
os occipitis in the flrft volume, when deferibing
the motions of the head on the fpine.

We ftiall at prefent only notice the fquamous
part of the os temporum, referving our account
of the pars petrofa until we treat of the ear. In
the orang-outang and moft apes, the fquamous
portion of the os temporum is of a trapezoid

figure.

t

28 Lect.VIII. Osteology of the Head.

figure; the fuperior fide is the longed, and
its height varies ' according as the cranium
is more or Icfs elevated. It is fliortefi; in the
Japajous.

The 'fquamous portion in the Sarcophaga is
fimilar to that of the apes.

In the Rodentia it is very narrow pofteriorly.

In thefhort-nofed Edentata, in the Ruminantia,
and the Pachydermata, it is rounded a little.

It is necefTary to remark, that the maftoid
procefs forms a part'of this bone only in 7nan
and jnonkieSy and that in all the other mammalia
it belongs to the os occipitis.

We fiiail deferibe the zygomatic procefs of
the os temporum when we treat of the face, and
particularly of madication.

The os ethmoides (hall be deferibed when we
treat of the fenfe of fmclling.

The os fphenoides has been fufficiently ex-
plained, and we fliall have no occafion to return
to it. Its precedes will be deferibed in our ac-
count of the bones of the face.

C. In Birdv.

«

The bones which compofe the cranium of
birds, arc united at an early period, and the
futures cannot be perceived cxcqit in very
young fubje^ffcs.

Thefe bones correfpond in their number and
pofition to ihofe of ttic mammalia. There are

two

Art. II. Bones or theCranium. 29

two frontal bones which are prolonged .anterior-
ly to form the roof of the orbits. When birds
have a horn, or a crell, it is alio attached to the
os frontis.

There arc two fmall olTa parietalia behind the
frontal bones.

The olTa temporum occupy the fides of the
cranium and the auricular region.

I'he os fphenoidcs cannot be didinguiflicd
from the occipital bone, ‘even in fubjc(fts that
have the futures very confpicuous.

It Ihoiild be further remarked, that this fpheno-
occipital bone unites with the offa temporum
fooner than the other bones unite with each
other. ' -

In new-hatched birds, however, we obferve a
future which extends tranfverfely in a ftraight
line from the one ear to the other, and which
feparates the fphenoid from the occipital bone;
the latter is then nearly of an annular form,
and is fubdivided into four portions; one fupe-
rior, two lateral, and one inferior, which is very
fmall.

The os fphenoides forms the greater part of
the bafe of the cranium. It is almoft triangu-
lar, and has anteriorly a fmall eminence, which
articulates with the palatine arches, which we
fliall deferibe when we treat of the face. It
wants the pterygoid procelfes, and does not come
in contadt with the pofterior aperture of the
nollrils.

The

30 Lect. VIII. Osteology of the Head.

The temporal bone has no zygomatic procefs,
but there is a fmall apophyfis which contributes

to the formation of the pofterior margin of the
orbit.

The os frontis having covered a part of the
cranium, is prolonged forward into a lamina
more or lefs broad, which forms the fuperior
part of the orbits, and the lateral edges of which
are ufually notched by thefe folTae. The two or-
bits are feparated from each other by only a ver-
tical lamina, which alfo belongs to the os frontis,
and which is attached to the plate that forms
their roof.

The olfeous eminences which we obferve on
the heads of the caffowary^ the horn-bill^ the
pintado^ and fome curasows, &cc. are enlargements
of this fupra-orbitar portion. Their interior is
filled with diploe of a very loofe texture.

D. In reptiles.

The bone of the bafeof the fkull in the croco-
dile has the form of a very irregular truncated
pyramid. The point of this pyramid is down-
ward, and its bafe contains the cavity of
the cranium. This pyramid has three furfaces,
one pofterior, which forms the occiput, and two
lateral. The occipital furface is almoft tri-
angular; one of its angles is inferior, the other
two arc fuperior, and greatly prolonged back-
wards and to the fide, in order to form the

•7 enormous

Art. II. Bones OF THE Cranium. 31

enormous articular procefles, which receive the
lower jaw. Xheir pofition is alniofl horizontal.
The foramen magnum is fitiiated in the middle
of this furface, and under it the fingle condyle for
articulating the head with the vertebral column.

Three futures depart from the foramen mag-
num, which divide the occiput into particular
bonea. The fuperior part of the cranium is
formed by a fingle parietal bone. Anterior to
it, there is an os frontis, alfo fingle, which forms
the roof of the orbits.

The ofl'a temporum are fituated on each fide
of the parietal bone, and are partly fupported by
that articular procefs for the lower jaw already
mentioned.

A fmall arch^on each fide, different from the
zygoma, leaves between it and the parietal bone
a large round hole, which perforates the tem-
poral foffa. The arch is partly formed by a
procefs of the os temporum, and partly by a par-
ticular bone articulated to the juneftion of the
parietal and frontal. This particular bone oc-
cupies the place of the poil-orbitar procefs of
the os frontis in the mammalia ; for it defeends
behind the orbit to join the cheek-bone, and
with it finilhes the frame of the orbit.

A cranium limilar to this of the crocodile, is
found in the other lizards, notwithftanding the
great differences in the form, proportion, and
the dirediion of the parts. In the camelion,
therefore, the foramina by which the temporal

foffa;

32 Lect. Vlir. Osteology of the Head.

fofTas communicate with the cranium, arc fd
large, and the bony edges which form them fo
thin, that the latter reprefent three flender bran-
ches rifing to fupport the kind of helmet which
diftinguifhes this animal. The articular proceffes
are not direcfted backw'ard, but downward.

The laft peculiarity is alfo obferved in the
other lizards, but they have not the crefts of the ^
camelion, and the upper part of their cranium
is broad like the crocodiles. >

' Tn fro^s and falamanders the cranium is nearly
of a cylindrical form, flat fuperiorly, and en-
larged pofteriorly ; the frontal bones have the
fhape of an elongated rediangle, and occupy the
interval of the orbits. The Surinam toad has the
cranium much flatter than the other genera.

The eminences intended to aflifl: in the ar-
ticulation of the jaw arc turned diredly towards
the fidcs.

The ftrudure of the cranium of tortoifes bears
more refemblance to that of crocodiles than of
frogs. The frontal bones form only therocf of
the orbits, and the cranium docs not. pafs be-
tween thefe cavities. They are very fliort, and
the parietalia are three times longer. The lat-
ter arc not confined to covering the craniuin.
I'hey extend on each fide, and form an arch
over the temporal fofla. . In ihe fca tortoifes this
arch is completed by two peculiar bones which
extend from the os parictalc to the zygoma, and
the anterior of which bounds the orbit behind.

The

Art. II. Bones or THE Cranium. 33

The articular procefTes arc direcfled downward^
as in the camelion. Above theic and the mea-
tus auditorius, we tind coniiderablemaftoid pro-
cefles which arc pointed fuperiorly in !and tor-
tmfeSy but are rounded and marked by a longi-
tudinal furrow in theyi’ti tcrtcifes.

Serpents have two frontal bones almoU fquare,
and a fingle parietal bone. Tlicir cranium ad-
vances forward between the orbits, as in frogs.
The occipital bone has a procef> dircclei back-
ward, and connected with a particular moveable
bone, analogous to the fquare bones of birds, to
which the lower jaw, and the arches which form
the upper, are articulated.

E. In Fijhes.

The bones of the cranium of fifhes are foon
olTified together, and as the futures which unite
them are fquamous, it is not eafy to difeoverany
traces of their reparation. The cranium of
fillies forms in general a very final 1 portion of
the head. Its figure varies confiderably ; but as
it is covered with fkin only, its forms appear
externally; thefe have therefore been well de-
feribed by Naturalills, and we have no occafion
to give any account of them here*

VoL. It,

t)

ARTIa

34 Lect. VIII, Osteology of the Head.

Article III.

Of the Eminmces and Deprejjions of the Internal
Surface of the Cranium.

A. In Man.

The fuperior part of the cranium is almoft
quite fmooth internally ; it is only (lightly
marked by the vefTels of the dura mater, and the
circumvolutions of the brain. The mod remark-
able of the imprelTions thus produced, is that
which extends along the whole of the middle of
this vault, and which correfponds to the longi-
tudinal (inus. The bafe or floor of the cranium,
however, is more unequal, and we obferve in it
fome very confpicuous cavities and eminences.
It may be divided into three regions or large
foflae. '

The pojierior foffa is named cerebellons, be-
caufe it is chiefly occupied by the cerebellum.
It is the deepeft of the three, and has alfo bcerB
called the inferior occipital fofla. Its lowed part
is perforated by the foramen magnum of the os
occipitis. A flight excavation afeends obliquely
forward from this foramen, and terminates an-
teriorly by an elevated ridge, having on each
Tide a final 1 hook, denominated poferior clinoid
procefs. This ridge forms the anterior boundary
9/ the fofla. U is an apophyfls of the os fphe-

n»ides ;

A. III. Internal Surface op theCranium. 35

hoides; but the broad canal fituated behind it is
chiefly formed by the cuneiform procefs of the
occipital bone, and is called the lajilar foffa.

Another projecfting ridge extends from each
iide of the clinoid procefs, and is directed ob-
liquely backward. This ridge belongs to the
petrous portion of the temporal bone, and com-
pletes the anterior limits ot the large cerebcllous
folTa. This fotl'i is inclofed pofleriorly by an
elevated line proceeding like the branches of a
crofs from the tuberofity in the middle of the
os occipitis. Another elevated line, which pro-
ceeds likewife front this tuberofity, defeends to
the edge of the foramen magnum, and divides
the ccrebellous foffa into two parts, throughout
the whole of its length. In this foffa there alfo
appear fomc impreffions of vcffcls, of which we
ihall f{>eak hereafter.

The level of the anterior fojfa is more elevated
than that of the other two. It is fituated above
the orbits and the nofe. It is united anteriorly,
without any confpicuous reparation, to the fu-
penor vault of the cranium. Pofleriorly it is
feparared from the middlefoffa; by a fharp ridge ,
which is concave on the back part, and formed
by the orbitarwing of the os fphenoides. Thefe
two ridges extend towards the middle line, and
backward. They are terminated nearly oppofite
to the poflerior clinoid proceffes, but fomewhat
more outward, each by a hook called anterior
clinoid procefs •, the interval between theie two

D 2 hooks

36 Lect. VIII. Osteology of the Head.

I

hooks confifls of another ridge, but lefs fliarp,
which completes the boundary of this folTa pof-
teriorly. The middle of the foflk is more de-
prelTed ; it is formed by the cribriform lamella of
the os ethmoides, which bears on its middle a
lharp edged ridge in the form of a ploughfhare,
called the c rift a gallic or ethmoidal creft. Its la-
teral parts are convex and fcabrous.

The middle foftce of the cranium 'occupy the
fpace between the anterior and pofterior; their
limits have therefore been already defcribed.
Their level is intermediate between that of the
other two. As the anterior and pofterior folTae are
more extenlive towards the middle than at their
lides, they approach each other at that part.
The interval, which feparates them, and which is
lituated between the four clinoid procefTes, is
more elevated than the middle folfae, and is de-
nominated fella iurcicdy or fella f-phenoidalis.

13. In other Mammiferous Animals.

The three large folTae of the cranium exifl: in
the inferior mammalia; but they are Icfs deep,
and the eminehccs which feparatc them are ef-
faced in proportion as the animal is removed
from man. Kven in x\\t jocko, wc begin to ob-
ferve, that the cerebcllous foffa is nearly on a le-
vel with the middle foffa; that the fella turcica
1% Icfs marked, and that the ridge of the fmall

wings

A. III. Internal Surface of the Cranium. 37

wings is lefs eminent. The cribriform lamella
of the os ethmoides is more depreffed, and ha^
no creft.

The mandrils^ the magots, and different fpecies
of gue7ionSt differ from the jocko, only in having
their pofterior foffa narrower, and not fo deep ;
while their os petrofum extends diretffly back-
ward, and the occipital furface of their cranium
is more elevated. The frontal foffa has two lateral
convexities, which are more globular, particu-
larly in the guenons.

In the JapajouSy the orbitar wings of the os
fphenoides have no ridge. Inftead of the an-
terior foffa, there is only a convexity : the inter-
mediate folfas are as deep as the pofterior. 1 he
fella turcica is nearly on a level with them, and
the cribriform lamella is fituated in a narrow
depreffion.

In the alouateSy the pofterior and the inter-
mediate foffiE, and the fella turcica, form only
one plane, from which the two offa petrofa, and
the four clinoid proceflTes, arife. Inffead of the
anterior folfa, there is an oblique furface, the
middle of which is depreffed, and leads to a
very fmall cribriform lamella.

The fame level exifts in the different parts of
the bafe of the cranium in all the Sarcophaga,
in which the anterior foffa is feldom diftinguiffi-
cd from the intermediate foffae, but forms merely
a Ihort and broad canal, terminated anteriorly by a
very large cribriform lamella. It muff: be obferved,

D 3 however.

•38 LecT. VIII. OSTEOLOG V OF THE Head.

however, that, in the hcar^ the middle foffae arc
Tcpaiatcd from the anterior fofTa by a ridge at-
tached to the fide of the cranium, and belonging
partly to the os frontis, and partly to the os pa-
fietale. In the Jcal^ on the contrary, there is no
anterior fofTa, properly fo called, as the front of
the cranium rifes perpendicularly like a wall,
and has the cribriform lamella in its fuperior
.part. The fuperior fofTa is more confpicuous
in the morfe. With refped: to all thefc animals,
it will be cafily conceived, that, in proportion as
the cerebellous fofTa is flattened, and the foramen .
jnagniim is diredted backward and upward, the
bafilar fofTa mufl: be elongated. At the fame time
the poflerior boundary of the cerebellous fofTa will
afeend, and terminate by forming a gp*dle, di-
viding the cranium vertically, and fituated be-
fore the cerebellum. In the greater part of the
Sarcophaga, the cerebellous fbfTa is formed by a
broad and thin proje^fling lamina, which con-
tinues over the ofTa petrofa, and Teems to
form a particular cavity for the cerebellum.
The Sarcophaga have no fella turcica, properly
To called, and their clinoid procefTcs arc very
fmall.

The bafe of the cranium is very level in the
Rodciitla. There is no diftindion between the
anterior and the middle TofTac. The ridge of the
purs petrofa is obtufe. Only a few fpecies, as the
hares and the agoutis, have the clinoid pro-
fflTes. The place which corrcTpond; with the
A ^tuation

A.ni. Internal Surface of tiir Cranium. 39

fituation of the fella turcica is even depreffed in
the cavy.

There is alfo very little difference as to level
in the folhe of the cranium of the Edentata.
Their cribriform lan’tella is fituatcd in a deprcl-
liori diftinguifhed by a vertical ridge. 'I he limit
between the middle and pioflerior foiliC is not
very apparent in the ll >tbs^ the armadillos y and
the aui-eateys \ but in the pangolin it is a large
vertical feptum, perforated by an oval hole in
the middle.

The three folTac are very dirtintfl: in the clephanl.
I'hc middle is the moll deprcllcd ; they arc fe-
parated by blunt elevations : the cribriform la-
mella occupies almoll the whole ot the bottom
of the anterior folia, hecaufe the nofc of this
animal is lituated under the cranium, as in Man,
and not before it, as in the Sarcophaga, the Ro-
dentia, 6cc. The fella turcica is not very much
elevated. The clinoid procefTes are Ihort, par-
ticularly the poflerior.

The anterior and the middle foiTse are nor
dillinguiflied from each other in the rhinoceros.
The pollcri'or fofl'a is deeper than the others, and
'is fepurated from the middle foffge by an acute
elevated ridge, which is fituated before them, but
is not attached to the pars petrofa. The part
which correfponds to the fella turcica is confider-
- ably more deprelTed than the middle folTa, in-
llead of being elevated, as in man. The part an-
Iwcrmg CO the poflerior clinoid procefles is not

E) 4 attached.

40 LtCT. VIII. Osteology of the Head.

attached, as in other animals, to the bafe of
the cranium, but extends like a bridge from
the one middle folia to the other ; while the
fella turcica, which, as we have obferved, is low-
er than thefc foITae, communicates under this
bridge with the cuneiform procefs of the os
occipitis.

The three foffae, and the fella turcica, are on
the fame level in the hippopotamusy and cannot
be diftinguilhed from each other, except by a
projeding lamina, which correfponds to the
pofterior clinoid procelTes. The offa petrofa,
the figure of which is very irregular, projed:
into the cranium, but they form no regular par-
titions. It is the fame with refped to the tapir ;
but, in the hog, the pofterior folTa is lower than
the others, and is diflinguiflied from them, as in
tht rhinoceros, by an elevation fituated before the
offa petrofa. The pofterior clinoid procefles
are attached to the bottom of the cranium ; the
anterior proceftes do not exift, and the part
-which correfponds to the fella turcica is deprefled
and very broad. The anterior fofta is dif-
tinguift’/cd from the middle, merely by a little'
more elevation, and a flight convexity. All
thefe Pachydermata have the cribriform lamella
of the os cthmoidcs very broad, much depref-
fed, and divided into two parts by a very thick
creft.

In the Riiminantia the middle foftic arc fcarcc-
)y perceptible from the anterior. The fella turr

cic;^

A. III. Internal Surface of the Cranium. 41

cica is very broad, and confiderably lower than the
middle folTae, between which it is fituated. It
continues on the fame level with the pofterior
foflsE, without any diflin(flive mark, except a
fmall lamella, which correfponds to the pofterior
clinoid procefTes. The fella turcica of y7u^jand
camels is lefs depreffed than that of the other
genera. The cribriform lamellae of the os cth-
moides are broad, but they are more deprelTed,
and feparated by a broader creft in the camel
•than in the other genera. In the chevrotins, the
anterior foffa is proportionally fomewhat more
elevated than the middle foflTae.

In the Solipeda the fella turcica is Icfs depreffed
than in the greater part of the Ruminantia. On
each os petrofum there is an elevated ridge, which
extends to the fuperior vault of the cranium, as
in the Sarcophaga.

In the Cetacea the cerebellous foffa is dif-
tinguifhed from the middle foffae by a lateral
partition, but the whole bafe of the cranium is
nearly level, and there is neither ethmoidal fof-
fa, nor cribriform lamella. The middle foffae
are much feparated from each other, and a little
more elevated than the cerebellous. There are
no clinoid proceffes ; the line of divifion be-'
tween the middle and pofterior foffae is not form-
ed by the os petrofum ; that ridge is fuuated
j?efore it.

C. In

. 42 Lect, VIII, Osteology of the Head.

C. In Birds.

The cranium of birds is divided into two
principal foflae, one of which is lituatcd above
and fomewhat before the other. The firft con-
, rains the cerebrum, properly fo called, and con-
letjuently correfponds to the anterior and part
of the middle foffze of the human Ikull. The
iecond contains the thalami nervorum optico-
rum, the cerebellum and the medulla oblongata,
and correfponds to a part of the middle foflae
and the cerebellous foffa of man. The line
• which feparates thefe two foffas is fliarp and
horizontal on the (ides, but, pofteriorly, it
afeends and forms an arch above the cerebel-
lum. The fuperior fofia is feparated into two
parts, by a flight convex eminence, produced by
the roof of the orbit; but the inferior foffa pre-
sents feveral remarkable cavities.

In the firff place, there is, on each fide, under
the ridge which feparates it from the firfffofla,
a round cavity which contains the correfpond-
ing thalamus. Between thefe two optic cavi-
ties there is another which correfponds to the
feila turcica, and in which we obferve a particu-
lar excavation for the pituitary gland. Thefe
three little foffac form together a kind of arch,
the convexity of which is directed forward. In
the concavity of this arch, and before the fora-
men

A. III. IlsTERNAJ. SURFACEOE THeCraKIUM. 43

men magnum, there is a fourth folTa, which cor-
refponds to the bafilar folTa in man, and, like it,
fupports the medulla oblongata.

The inferior folki-of the cranium of birds,
being comidcrably narrower than the fuperior,
the body of its lateral parictes is occupied by
the cavities of the internal ear.

The differences which cxill in birds, w'ith re-
fped: to the internal foffx of their cranium, arc
very inconliderable, and confifl: merely in a
greater or Icfs degree of depth, in general,
we obferve, that their inequality is lefs in the
fwimming and wading birds; and that, on the
contrary, the parrot kind, and birds of prey,
have thefe inequalities largcft.

D. In Reptiles.

The general form of the cavity of the cranium
of reptiles is oblong, and almofl: of an equal
breadth, being merely a little contracfled be-
tween the ears. The tortoife has a kinckof fella
turcica, the four clinoid procefles of which are
diredled forward. The fphenoidal folfa is fome-
what depreffed in the ferpents^ but it has no cli-
noid proceffes. It is a femi-lunar deprelTion^
the plane of which is fituated obliquely frorn
before' backward.

The bafilar foffa is lower than the other folTg?
in th^ crocodile^ and in fome iortoifes.

44 Lect. VIII. Osteology OF THE Head.

I

' E. In Fijhes.

We have alfo very little to Hate with refpedl
to the infide of the cranium of fifhes. As the
cavity of their cranium is not completely filled
by the brain, its form does not correfpond with
the eminences of that vifcus, and the different
depreflions we obferve within the cranium are
not feparated by fharp ridges. The bafe is al-
moft always plain, with the exception of a dc-
prcflion found in fome fpecies, and which cor-
refponds by the place it occupies to the bafilar
fofTa, but which is deftined to contain the whole
of the brain.

The cranium of ofTeous fiflies is enlarged be-
tween the cars inffead of being contracted, be-
caufe thcfe organs are contained in the fame
cavity as the brain. The contrary difpofition
prevails in the Chondropterygii.

Article IV.

Of the Foramina of the Bafe of the Cranium.

A. In Man.

T..» bafe of the cranium is perforated by a
great number of holes, which afford paffages for

nerves

Art. IV. Foramina OF THE Cranium. 4$

nerves and vefiels. Some communicate with
the face, others open into the parts fituated pof-
teriorly. The moft confiderablc of the latter
is the foramen magnum occipitaUy through which
the medulla oblongata, and the vefTels that ac-
company it, pafs. It is fituated at the bottom
of the cerebellous folTa, immediately below and
behind the bafilar folTa. Its fhape is oval, its
greateft diameter is between the tore and back
part. Under the anterior of each of its lateral
edges, we find one of the prominences by which
the head is articulated with the vertebral column,
and which are called the occipital condyles. The
body of each of thefe condyles is perforated by a
fmall canal, which is diredled from within out-
ward, and a little forward and upward, and through
whichthe nerves of the ninth pair are tranfmitted.
This is thetzv’/m‘orro«i(r/o;iforamen, which atFords
a pafiageto the nervus hypoglofus major. A little
more outward and backward, we obferve another
fmall hole, which is fometimes wanting ; it is
direifled backward and downward, and ferves
for the pafiage of a fmall vein. This is called
the pojlerior condyloid foramen.

A little farther forw'ard and outw'ard, there is
a large hole formed by the pofterior edge of the
os petrofum and the os occipitis. It is called
the foramen lacerum pojicrius. It is fituated ex-
aifily below' an imprefiion formed behind the os
petrofum by the great lateral finus. A groove,
made by the inferior petrous finus, alfo joins

this

46 Lect. VIII. Osteology op the Head.

this hole, and it is indeed by it that all the
blood of the brain dtfeends into the jugular
Tein. This hole, at the fame time, affords a pafT-
age for the par vagum^ the gloffo-pharyngetus j and
the nervus accefforius of the eighth pair. The
part which tranfmits the gloffo-pharyngsus
is frequently feparated by a fmall offeous
lamina.

At the pofterior furface of the os petrofum, a
little above the foramen lacerum, we find a coni-
cal depreflion direfted outward. It penetrates
into the interior of the os petrofum, where it
terminates in tw'o holes, the inferior of which
tranfmits the auditory nerve into the labyrinth
of the ear. The other is the orifice of a canal
which contains the facial nerve in its paffage
through the os petrofum, and which is termi-
nated between the mafioid and fiyioid procefles
by a fmall hole called foramen jlyh-mafioideunu
The depreflion we have deferibed is denominate
meatus audit orius internus.

The cerebellous foffa alfo exhibits on each
fide fmall holes for the paffage of the blood^-
veffcls. One is fituated in its temporal part
behind the mafioid procefs j its courfe is very
oblique. It correfponds internally with the
cavity of the lateral finus.

Another called aqu^eduilus CoruNvrr, is fitu-
ated towards the crefi of the os pctrf'fum, above
and without the meatus auditorius internus. Ic
admits foQie fmall branches of veins.

In

Art. IV. ForamIna of the Cranium. 47

In the middle foffcC, we remark the following
holes ;

forameu lacerum fituated between

the point of the os petrofum and the poflerior
angle of the fella turcica. Its edges are formed
by the temporal, the fphenoid,and the occipital
bones. It is clofed in the frelh date by a carti-
laginous fubrtance. There is another hole at its
external Tide, through which the carotid artery
enters the cranium, and w hich is only the open-
ing of a twidcd canal, the oriiice of w hich is in
the inferior furface of the os petrofum, im-
mediately before the foramen lacerum poderius.
This is called the canuHs carottJeus. It tranf-
mits, bcfides the artery, the great fympathetic
nerve.

In the inferior furface of the os petrofum,
and before the oriheq of the carotid c.anal, \vc
obferve the opening of another canal, which
communicates with the cavity of the tympanum,
and which forms a part of the Eufiaebian tube, or
guttural conduit of the car.

In the fphenoid bone, a little before the os
petrofum, and without the anterior foramen,
there is a large hole, called foramen ovale^ and
which is really of an oval ihape. It gives palT-
age to the third branch of the fifth pair of nerves,
called maxillaris inferior,

A little behind, and without the foramen ovale,
there is another hole called foramen fpinale,
through which an artery palfes.

Internally,

4S LeCT. vm. OsTEOLOdY OF THE HeaD'.

Internally, with rcfpedl to the foramen ovalc^
and very near the poflerior angle of the fella
turcica, there is another fmall hole which tranf-
mits a vein.

Still more forward, but not quite fo near the
fella, we find the foramen rotundum^ which is
directed forward, and tranfmits the fecond
branch of the fifth pair of nerves, called maxiU
laris fuperior •, it is fmallerthan the oval foramen.

Under the fharp ridge which feparates the
anterior fofia from the middle foflas, there is a
long flit which proceeds from the anterior angle
of the fella turcica, andextends obliquely outward
and forward. It communicates with the bottom
of the orbit, and tranfmits to it the firfi: branch
of the fifth pairofnervesjor ophthalmicus o^ JVillis,
and the whole of t\\Q thirds fourth y and fixth pairs
of nerves of the brain, as well as the internal
orhitar artery : this is called the fuperior orhitar
fijfurey or fpbeno-orbitar fijfure.

The optic foramina open into the cranium a
little above the anterior edge of the fella turcica,
and on the infide of the anterior clinoid pro-
celfes they are diredlcd obliquely outward into
the orbit, to which they convey the optic nerve
and the centra! artery of the retina.

Thcnumcrous holes of the cribriform lamella,
of which there arc about 40, occupy the bottom
of the anterior fofia, and afibrd a pafiage for the
olfatlory nerves to the nofe.

Before the crifia galli, and at its union with

the

Art. IV. FoRAMfs'A of the Cranium. 49

the os frontis, we obferve a fmall hole which
tranfroits a vein to the nofe; It is called foramen
ciecum, or foramen fronto-etbmoidale.

Ih In othei* Mdmmiferous Jn'nnah, and in tlifdx.

In examining fucccfTivelv the variations which
exih in the mammalia and birds, with rcfpetfl to
the principal foramina of the cranium; we
lhall begin with thofe fitiiatcd anteriorly, and
lhall omit the foramen magnum, which we have
alteady deferibed in the 3d Le<flure, when we
treated of the articulation of the head ; and the
foramina of the cribriform lamella, which w ill
be noticed under the article Smelling.

1. Optic Foramina.

a. Thofe foramina are not fo far feparate in
nwnkiesy as in man.

In the Sarcophaga, thefe holes and their in-
tervals arc fometimes covered by an ofleous
lamella, directed from before, backward like a
roof.

In fome of the Rodent ia, as the agouti^ they
are feparated by only a thin vertical lamina,
which is altogether wanting in the hare. They
are however very much feparated in the greater
number of the-genera.

In i\\c four- toed ant-eater the optic foramina
are very large, and united at their origin fo as

Vot, IL# E ' to

50 Lect. VIII. Osteology of the Head.

to form a fmall fofTa on the orbitar portion of
the os fphenoides. In the armadillo^ and more
particularly in the pangolin^ they are very fmall.
'I hey exhibit no peculiarity in the Jloth.

The optic holes of the elephant arife from a
common canal formed upon the body of the os
Iphenoides, at the origin of which we obferve
a hole which penetrates that bone. The direc-
tion of thefe holes is oblique ; they form a very
obtufe angle anteriorly.

T. hey are diftintfl in the rhinoceros, and extend
almoft direcUy forward, cind form a canal in the
body of the bone, of nearly one decimetre in
length.

In the hippopotamus thefe holes are very much
removed from one another, and they are more
oval than round.

Their direction and their refpeclive diftance
vary in the Ruminantia. In the chezrotin, there
is only a fingle optical hole divided by the vomer'

b. The optic foramina of birds, arc fituated
before the fmall folfa which is placed between
their two optic foITzc. They are feparated only
by the fame vertical lamina which divides their
orbits.

§

The part of this lamina which correfponds to
them being fometimes notched, as in the cock,
&c. they there appear to form only one hole»
when viewed on the infide of the cianiurn.

s

»

2. Sphrno-

Art. IV. Foramina OF THE Cranium. 5^

2. Sphaw-orhitar F'lJJhre.

a. The fpheno-orbitar filTare of monkies is
very fhorr, and is even reduced to a fimple oval
foramen, except in the orang ou/ang, in which it
rcfembles that of man.

In the Sarcophaga it is always oval, and has
the form of a canal.

In the Rodentia there is only one hole in-
ternally, which fupplies the place of both tbe
fpheno-orbitar filTure, and the foramen rotun-
dum.

In the Izvo-toed ant-eater the fpheno-orbitar
fifTure, which is very diflincl from the optic
hole in the infidc of the cranium, is confounded
with that hole in the orbitar and temporal fofla.
It is rounded, and before it penetrates the cra-
nium, is indicated by a long furrow or canal in its
bafe : the fame ftriuflurc prevails in the other
ant-eaters and armadillos, as well as in ihtjloths ;
except that in the latter, the fifTure, infiead of
being rounded within the cranium, has there a
triangular form.

In the cranium of the elephant this fifTure is a
large hole rounded internally ; it proceeds di-
reftly downward into the tempero-orbitar fofia,
but before it, we obferve another hole which is
directed horizontally into the body of the bone.
Thefe two holes, as w-ell as that of the optic
nerve, are covered on the outfide by an ofleous

E 2 lamina.

52 Lect. VIII. Osteology o^“ the Head.

lamina, which extends from the fuperior orbitar
angle to the mod pofl'erior part of the os max-
illare fuperius ; fo that we obferve no hole in the
orbit, but merely this, large olTeous margin.

In the rhinoceros the fpheno-orbitar fiflure
takes the place of the foramen rotundum ; it
forms a round canal, the internal opening of
which is fituated in the fphenoidal fofla, which
is very deep. Its external opening is covered
by an ofTeous ridge at the bottom of the tem-
poral folfa. 1

. In 'the hippopotamus this filTure is a fimple
round hole, of a large diameter.

In the Ruminantia it is alfo a hole, rounded
inferiorly, but truncated and angular fuperiorly.

In the Solipeda it is intcrfedted throughout
its whole length, by an elevated ofTeous line,
which divides it into two diflindt holes.

b. There is no fphcno-orbirtir fifTure in birds,
but its place is fupplied by four difHiufl holes ;
one is fituated above the optic hole, for the nerve
of the fourth pair; two behind, very near each
other, for that of the third pair ; and the oph-
thalmic branch, of the fifth pair. Lafliy, one
under the bafe of the cranium anteriorly, which
correfponds on the infide to the balilar folTa, and
which ferves for a pafTage to the nerve of the
fixth pair.

3. Foramen J\oiumhim.

a. The foramen rotundum of the monkey is

marked.

) I

Art. IV. Foramina of the Cranh/m. 53

marked, for a confiderable length, before it
leaves the cranium, by a furrow on the internal
furfacc of the os fphenoides, near the fella tur-
cica.

In the Sarcophaga it is rather oval than round,
and very large.

In the Rodentia it is frequently confounded
with the fpheno-orbirar filFure, as in the porcu^
pine, the envy, and the marmot.

In the Edentata the round hole is always dif-
tlnift, and forms a canal of dill’ercnt lengths,
according to the genus, within the bone.

In the elephant the round foramen is con-
founded with the fpheno-orbitar filTurc. The
fame difpolition prevails in the rhinoceros and
the hippopotamus ; in the Ruminantia and the
Solipeda.

b. There is only one hole in birds which oc-
cupies the place of the round and oval foramina
of man ; it exifts in the line which feparates the
optic from the bafilar folTa,

4. Forameti Ovale.

In monktes this bole does not perforate the os
fphenoides only, but is included between that
bone and the os petrofum.

In the Sarcophaga it exiHs entirely in the os
fphenoides. In feveral genera, as hears, cats,
and the avet, the external edge of this hole is'

E 3 prote^^-d

54 Lect. VIII., Osteology of the Head.

protected by an ofleous lamina, which extends
along it to the Tpheno-orbitar fifTurc.

In the Jealy the bear, the badger ^ and the ronJ~
Jety this hole is wanting, or rather it unites with
the foramen rotundum.

Amongfi the Rodentia, the marmot y the agontiy
and the/^«/rr^/, have a diftindb oval foramen;
but in the cavjy and the porcupincy it is con-
founded with the anterior foramen lacerum.

In the ten-banded armadilloy and iht four-toed
ant-eatery the oval hole does not exiR, or i§
confounded either with the foramina lacera,
which are united, or with the foramen rotun-
dum, which is very large, and of an oblong form.

The foramen ovale is very diflindt in the Jloth.

In the elephant, it is confounded with the an-
terior foramen lacerum, which is very large. It
is the fame with refpedt to the hippopotamus.

In the Ruminanti'a, animals which have no
anterior foramen lacerum, the ovale foramen is
very large.

It docs not cxifl in the Solipcda.

5. Foramen Lacerum Jntcrius.

a. This hole is wanting in monkies, and the
Sarcophaga. In feveral of the Rodentia, as the
cavyy the porcupine, and the marmot, it is very
large : we obferyc it alfo in the agouti and the
hare, but it is not found in i\\c fqnirrel.

In the pangolin and x.\\eJloths, this hole is very

fmall.

Art. IV. Foramina of the Cranium. 55

fnull. Ie is confounded with the pofterior fo-
ramen lacerum in the armadillo.

It is very large^ in proportion to the others,
in the elephant y and very diftindt from the caro-
tid canal.

In the bippepotamus it is confounded with the
pofterior foramen laccrum.

It does not exift in the Ruminantia.

In the Solipeda it is confounded with the pof-
terior foramen.

b. Birds have no anterior foramen lacerum.

«

6. Canalts Carotideus.

This canal is fimilar in monkies, and in man ;
but it is much ftiortcr, and lefs tortuous, in the
Sarcophaga .

It does not exift in the Rodentia-, and the ar-
tery palTes immediately through the anterior fo-
ramen lacerum. ,

■ In the elephant, it perforates the body of the
os petrofum, and terminates at the internal ex-
tremity of its anterior angle.

In the hippopotamus it is confounded with the
foramina lacera.

The fame thing takes place in birds.

7. Toramm Lacerum Pqfierius.

a. This foramen exhibits no peculiarity either
in monkies or the Sarcophaga. It is fmall in

E 4 moll

^6 Lect. VIII. Osteology of the Head.

molt of the Rodentia; it forms a very round
hole in the pangolin, and the Jloth’, but the ante-
rior condyloid foramen is very remarkable in thefe
animals, as it is exceedingly large, and fituated
before the condyle.

In x.\\^ elephant , thepoftcrior foramen lacerum
is oval, and very great. This animal has no
anterior condyloid foramen.

In the rhinoceros, the anterior and pofterior
foramina lacera are confounded in one large fif-
fure, which furrounds the os petrofum. The
anterior condyloid hole is very diRincI, and very
large : there are even fometimes two foramina
on the fame fide, which unite and form one.

With refpeft to the Ruminantia, the poderior
foramen lacerum, in the jlag, is a very narrow
fiffurc pofteriorly, and round anteriorly; in the
camel it is contradl-ed before, and circular pof-
teriorly,

b. This foramen, in birds, is a fmall round
hole, fituated under and within the external aper-,
^ure of the car;

8. Meatus Auditorius Intenius.

a In the monkies 2lbo\’c, and without ^hc meafns
puditorius internus, there is another larger de-
prcHion, which receives a projedion of the ce-
rebellum ; the bottom of this deprelTion is not
perforated. It is wanting in the orang-outang
find jocko.

Art. IV. Foramina of the Cranium. 57

This depreflion is even deeper in the Sarco-
phaga than in monkies.

The meatus auditorius internus of tlic elephant ^
is covered by a large oireous ridge of the os pe-
trofum, at the point of which it is lituatcd.

In the rhinoceros, it is fmall, oval, and fituatcd
in the middle of the petrofe bone. Its greatell
diameter extends from before backward.

In the hippopotamus, the meatus Is lituated in
the middle of the os f'Ctrofum. Its diameter is
very large, and its edges form a kind of oireous
canopy.

It prefents no remarkable peculiarly in the
Ruminantia. It is lituated in the centre of the
Gs petrofum. Its place is the fame in the So-
lipeda.

b. The meatus auditorius internus of birds,
is in general pretty coniidcrable,

C. In Reptiles and Fijhes.

\

. \

The interior part of the cranium is frequently
not clofed by ofiification in reptiles and fifhes,
and the olfatHiory nerves pafs through a large
vacant fpace, which is not fub-divided into par-
ticular holes. This at leaft is the cafe with the
camelion, the iguana, iortoifes, the pike, the anar-
chichas, &c. In others, the olfactory hole is
contradted, but is Hill fimple, as in the crocodile.

It

58 Lect. Vlir. Osteology of the Head.

It is double in Frn^s falamanders. The rays
and ihtjharhs have alfo two holes, which are con-
liderably removed from each ocher.

The optic Iioles are bkewife fometimes united
into one, as in the crocodile : thofe of the iortoife
are much removed from each other, andaredif-
' tingUiflied from the great hole in the front of
the cranium, by only a fmall boney partition.
The ftru(5lurc of the cranium in the pike is fimi-
lar. In the the rays, the anarrbichas, s.nd
it fliould feem, in the greater number of ftfhes,
the optic holes arc at a great diftance from each
other, and perforate the fides of the cranium,
Thefe animals have no fpheno-orbitar fiffure,
and the fmall nerves tranfmitted to the eyes,
pafs each through a particular foramen.

There is, in general, only one hole on each
lide for the three branches of the fifth pair of
nerves, which, therefore, fupplies the place of
the foramen rotundum, foramen ovale, and in
part of the fpheno-orbitar fiffure. This hole,
however, is divided into three in the carp.

The meatus auditorius internus cxifls only in
the Reptiles, and the Chondropterygii order of
fifhes. The other fiflies, having the cavity of
the ear united with that of the cranium, want
this hole.

I'idics have ajaigc foramen for the eight pair
of nerves, which is very confidcrable ; and a
fmall hole befide the foramen magnum, for the

ninth

59

Art. V. Bones of the Face.

ninth pair. It mufl be remarked, that the veins
do not pafs through this hole, as in the Mam-
malia and birds.

Article V.

Of the Bones which compofc the Face.

A. In Man.

E have already obferved, that the face is that
portion of the head which is fituated under the
anterior part of the cranium : its form is chiefly
determined by the bones of the upper jaw, or
ojfa maxiUaria fuperiora ; we (hall commence our
defeription with them.

W'hen the maxillary bones are united, the
common bafe reprefents a parabola ; it is arched
inferiorly, to fdrm the palate, and its circum-
ference contains the alveoli of the teeth. A fu-
ture, which extends from its anterior part back-
ward, divides it into two femi-parabolse. The
body of the bones has the fame curvature, as it
arifes from this bafe ; but it foon enlarges to-
wards the Tides, and becomes flattened anteriorly.

Its fuperior part, a proportion of \Vhich ferves
for the lower furface of the orbit, is plain, aU
moil triangular, and inclined forward and out-
ward. The internal edges of the fuperior fur- ^

faces

I

6o Lect. VIII. Osteology of the Head.

faces of thefc two bones, do not come in contacfl:
Jike thofe of their bafe : on the contrary, they
are very much removed from each other by the
nafal foITa, which penetrates the face horizon-
tally from before, backward, between the two
olTa maxillaria, and to which the arch of the
palate ferves as a bafe. The external angle of
the fuperior furface of each jaw-bone is inclined
Hill more outward than the other parts ; this
gives to the lateral enlargement of thefe bones
a Iharp figure : to this external prominence,
which is called the malar procefs, is articulated
the cheek bone {os mal^e, or os jugale), one of
the bones by which the face is joined to the
cranium.

From the internal and anterior angle of this
orbitar furface of the os maxillare, as well as
from the anterior edge of the body of the bone,
there arifes another apophyfis, called the af-
, cending gr nafal procefs, which forms the in-
ternal margin of the orbit, and articulates with
a correfponding procefs of the os frontis. Be-
tween the nafal procelfes of the two olfa maxil-
laria, we find the two bones of the nofe {ojfa
qiiadralay or o[fa nafi), which form a kind of roof
above the entrance of the nafal folfae ; this is
one of the points by which the face is attached
to the cranium.

The os ctbmoidcs is fituatcd between the orbi-
tar procelfes of the maxillary bones. VVe have
already obferved, in treating of the cranium,

that

Art. V. Bones of the Face. 6i

that the cribriform lamella of this bone fills up
the vacant fpacc of the os frontis, between the
two arches of the orbits : there defeends trom
each Tide of the cribriform lamella, a thin plain
lamina, which joins the internal edge ot the
fuperior furfacc of the maxillary bone, and thus
forms the internal parietes of the orbit. Ihis
lamina was formerly called os planum : between
it and the nafal procefs of the os maxillarc,
there remains a fmall fpace, which is occupied
by a thin bone, called os unguis, or lacrymale.

From what has been obferved, rcTpecling the
os ethmoidcs, it will appear, that it may be faid
10 form the ceiling of the nafal fofTa ; this ceil-
ing is very irregular ; we fliall deferibe its dif-
ferent laminae and linufes when we come to the
article Smelling: at prefent we Hull juft men-
tion, that there is a vertical lamina extended
longitudinally over its middle part, and which,
being continued with the ^corner, by means of a
cartilage, divides the cavity of the nares into
two- portions nearly equal.

This cavity of the nares is extended pofte-
riorly beyond the ofla maxillaria ; its pofterior
limits are partly formed by the os fphenoides,
and partly by the c/j palaii.

The os fphenoides contributes to terminate
the cavity of the nares pofteriorly, by the means
of tw'o procefles, w'hich defeend almoft verti-
cally from each fide of its body, between the
foramen rotundum, and foramen ovale; thefe

are

Lect. \ III. Osteology of the Head.

are called the pte)ypidy or wing-like procefTes ;
they are divided poficriorly by a fofTa, into two
lamina, called the internal and external wings,
into which fomc mufcles are infcrtcd.

Between the anterior edge of this procefs, and
the poftcrior edge of the os maxillare fuperius
of the fame fide, we find the os palali, which is a
fmali bone, compofed of two laminae, or prin-
cipal parts; one is inferior and horizontal, and
is continued with the arch of the palate, of
which it forms the pofierior border; the other
afeends againfi: the internal parietes of the nafal
fbffa, pafies over the os maxillare, and is arti-
culated with the fphenoidal and ethmoidal bones
in the bottom of the orbit.

We have thus traced the middle jundlion of,
the face with the cranium, by the os frontis, os
ethmoides, and os fphenoides. It remains for
us to flicw how its lateral conncdlion takes place,
for which it is only necclTary to deferibe the os
nialae. <

This bone, as we have already obferved, is
attached to the malar procefs of the os maxil-*
lare ; its external furface exhibits four edges :
1. That by which it joins the before mentioned
procefs, and which forms an oblique future in
the front of the face, under the eye : 2. That by
which it afiifis, with the os frontis, and os max-
illarc, in completing the anterior frame of the
orbit ; it is joined in this part to the os frontis,
by an afeending procefs, which correfponds to

&

ft

\

Art. V. Bones of the Face. 6>

t

the external orbitar procefs of that bone : be-
hind this procefs there is a lamina, which ex-
tends a little inward and backward. It unites
with the orbitar procefs of the os fphcnoides,
and in concert with it completes the external pa-
rietes of the orbit : Laflly, The other two edges of
the malar bone are feparated by a procefs called
i\\t zypmatic^ which is connected w ith one pro-
duced from the os temporum, and with it forms
a figure like the handle of a vefi'cl, on each
fide of the head, which is named zygoma, or
> the zygomatic or juga! arcb.

f The zygomatic procefs of the os temporum

arifes a little above and before the meatus audi-
^ toriiis externus, by a double elevated ridge, and

■ forms nearly two thirds of the jugal arch; un-

^ der its bafe is lituated the glenoid cavity, which
\ ferves for the articulation of the lower jaw. We

"s fliall fhortly notice this laft part, to complete

our accoant of the bones which compofe the
face ; it w’ill, however, be deferibed more in
^ detail when we treat of Maftication.

^ The curvature of the maxilla inferior is near-

ill ly the fame as that of the alveolar edge of the

^ I ofTa maxillaria fuperiora. In white men its fur-

' j face is continued with that of the upper jaw,

• but in negroes thefe two'furfaces form ante-

riorly an angle of 70° : its lateral parts are more
V prolonged pofteriorly, and rife towards the zy-
'j • gomatic arch. This afeending branch is nearly
fquare ; its fuperior edge is deeply notched ; the
8 ^ condyle.

64 Lect. VIII. Osteology of tiie Head*

condyle, which ferves for its articulation, i^
fituated at the j:>ofterior angle. The anterior
angle, which is called the coronoid procefs, is flat
and pointed ; it affords an attachment to the
mulck’s, which afilft in maflication.

I

B. In other Miimmiferous Animals.

The fliape and fizc of the face depend chiefly
on the form and extent of the bones of the up-
per and lower jaw.

f^adrupeds have two bones in the jaws, in
addition to thofe of man ; they are called ojfa
inter -maxillaria^ offa ineijoria^ or oJfa labiatia^ and
are. fituated at the extremity of the mouth, be-
tween the offa maxillaria: they contain the den-
tes incifores. This difference, however, be-
tween quadrupeds and man, is not in reality of
very great importance ; for the future which fe-
parates thefe bones from the maxillary, cxifis
alfo in the human foetus, and is obliterated at a
very early period, in fome quadrupeds. The
fkeleton of the jorko of the mufeum, though
young, exhibits no trace of this future, but it
is very diftincfl in that of the oran^-outang.

The face of monkies ^ in other refpeds, does
not differ from that of man, as to the manner
in which it joins the cranium, nor as to the
bones of which it is comj)ofcd. The principal
difference as to form, is produced by the great
7 elongation

Art. V, Bones of the Face. 6<;

elongation of their o(Ta palati, and oft.i maxil-
laria, in proportion to their height ; and by the
anterior part of thofe bones being inclined
more or Ids forward, inftcad dt being aliiiolt
vertical, as in man.

This prolongation of the face varies confidcr-
ably in the dillerent fpecies : it may be deter-
mined by' the angle, which its anterior plane
forms with its bafe, or the palate ; this angle is
more acute in proportion as the face is elon-
gated .

Thefc animals have frequently only one nafal
bone, which is very narrow’. The fap.i^us,
however, laaveahvays two: the interval between
the orbits is more contraded than in man, and
pofteriorly it is reduced to a limplc partition.
.It is thus in the guenons, and in the fapajous.
But the onvigs, the magots, and the alouates, have
this interval fufficiently broad to allow' tllfc na-
fal folTiE to afeend into it^

The face of the Sarcophagi is diftinguifhed
from that of the Quadrumana; ill. In having
the afeending procelfes of the ofla maxillaria
much broader, which removes the orbits to-
wards the Tides ; adly, Becaufe the orbitar furface
does not form the -inferior, but the anterior pa-
rietes of the orbit ; 3dly, Becaufe the os malae
neither articulates with the os frontis nor os
fphenoides, and only contributes to form the*
zygomatic arch, and the inferior edge of the
orbit ; 4thly, Becaufe the orbit is not inclofed
'VoL. If. either

*4

66 Lect. VIII. Osteology of the Head.

either poflcriorly or inferiorly, and communi-
cates freely with the temporal fofla ; 5thly, Bc-
caufe the ofla palati are much elongated, and
form a conliderable portion of the internal pa-
rietes of the orbit, to which the os ethmoides
contributes nothing.

The fnout alfo differs with refpedl to the de-
gree of its elongation ; the anterior opening of
the nofe is truncated more or lefs obliquely at
i- the extremity.

The os lachrymale advances a little upon the
cheek in fome fpecies, as the flying lemur.

The feparation of the orbits is ftill larger in
the Rodentia than in the ^arcophaga ; their
inter-maxillary bones, which are immenfe, in-
confequence of the magnitude of their incifive
teeth, throw the offa maxillaria very far back :
the latter form a great part of the internal pa-
rietes of the orbit, in which the palate bones
occupy only a fmall fpace. The anterior pari-
ctes are formed by a procefs of the os maxillare,
which aflifis in compofing the zygomatic arch,
fo that the cheek-bone is fufpended in the mid-
dle of that arch between the maxillary and
temporal procefTes ; it neither joins the os fron-
tis nor the os fphenoides. The elongation of
the bones of the nofe is fuch, that the aperture
is always fitiiatcd at the extremity of the fnout.

The face of the elephant has the grcatell rc-
fcmblancc to that of the Rodentia ; the magni-
tude of the intcr-maxillary bones, the polition

of

Art, V. Bones of the Face. 67

of the ofl'a maxillaria, and ofla malarum, and
the connccflions of the latter are limilar. 1 he
height of the alveoli ot the tufks elevates, how-
ever, the fituation of the nofe, and fliortens its
bones. This circumflance completely changes
the phyfiognomy of the head.

The face of the JJolbs is very fliort fupcriorly,
in proportion to the cranium : the olTa maxilla-
ria extend to the internal furtace of the orbits :
the os malas is attached to the os maxillare only ;
it does not join the zygomatic procefs of the os
temporum, and there is a vacant interval be-
tween thefe two bones : the ofla malarum have
a long defeending procefs. Though thefe ani-
mals want theinciflve teeth, they have two very
fmall offa inter-maxillaria, which form the in-
ferior margin of the aperture of the noflirils.

In the long-nofed Edentata the face has a
conical form; the maxillary bones do not ex-
tend to the orbit; the os lachrymale, being very
large, feparates them from it ; and the os palati,
which is very long, forms alone the lower part
of the internal parietes of that fofla. The ptery-
goid procefles are fupplied by two laminae,
which are continued with the olTa palati, and
which, joining each other inferiorly, prolong
the canal of the nares to the foramen magnum.
The zygomatic arch is not entirely oflified iit
the ant-eaters and pangolins y but it is completed
in the ory^eropiiSy or cape ant-eatery and in the
armadillos. The fituation of the os malte of

F i thefe

6s Lect. VIII. Osteology OF THE Head.

thcfe animals is iilmoft the fame as in the Ro-
dentia.

The form and difpofition of the bones of the
fice in hogs, are nearly the fame as In the Sarco-
phaga, except that the oila lachrymalia advance
farther upon the cheek. In the tapir, the os
maxillare is direded backward under the orbit,
to which it furnifnes a kind of horizontal floor.
1 he bones of the nofe do not form an arch,
which, with the ofla niaxillaria, w'ould inclofe
the nafai cavity, but only furnifh to it a kind of
projeding roof, which fupports the fupericr
part of the probofeis.

The os maxillare of the rhinoceros paffes undet
the orbit, as in the tapir ; the ofla nafi do not
form a continued canal with the m.axillary bones,
but a kind of fufpended arch, which is very
thick, and which fupports the horn: when there
are two horns, the poflerior one is fupported by
the os frontis. The inter-maxillary bone is
very fmall.

The difpofiiion of the offa nafi is the fame in
the hippopotamus as in the liog ; the intcr-max-
illary bones arc very large; the jaw-bones do
jiot form the lower part of the orbits ; their an-
terior portion, which contains the tufks, is di-
reded confulerably outward. This circumflance
produces that great breadth of the muzzle ob-
ferved in the hippopotamus. The os mala.* has
a pofl-orbitar [)rocefs, which neaily joins that
of the os frojuis ; but it docs not unite to the

08

Art. V. Bones of the Face.

69

os fphenoidtA?, and the orbit is not feparated
from the temporal fofla pollcriorly, though its
frame is almoll complete.

The daman [byrax), which fliould be claffcd
with the Pachydermata, and not with the Ro-
dentia, to which order it has hitherto been re-
ferred, refemblcs the hog in the difpofition of
the bones of the face, it is only proportionally
fliorter, and the maxillary bone pafTes under the
orbit, fo as to form its inferior parietes, as in
the tapir.

The face of the Ruminantia has much refem-
blance to that of the hog ; the inter-maxillary
bones are prolonged farther forward, and arc
not fiirniftied with teeth, except in the camel ; '
the olfa maxillaria form a fmall part of the floor
of th« orbit. The os lachrymale is extended con-
fiderably forward on the cheek, where it is per-
forated in different ways, and moft remarkably
in the deer. The poft-orbitar procefs of the os
malce unites by a future to a like procefs of the
os frontis, and thus completes the frame of the
orbit; but as it does not touch the os fphenoides,
there remains a large communication pofteriorly,
between the orbit and the temporal foffa.

The face of the Solipeda differs little from
that of the Ruminantia, except that it is not
joined to the os frontis by an afeending procefs
of the os mala^ ; on the contrary, a procefs de-
feends from the os frontis, and joins the body
of the os utalce, behind the orbit.

f3

/

The

yo Lect. VIII. Osteology OF the Hkad.

The orbits are always widely feparatc from
each other in the Ruminantia and Solipeda.

The magnitude of the alveoli of the dentes
canini greatly enlarge the os maxillare of the
morfcy and give a fwollen appearance to the an-
terior part of the muzzle, but the connection of
the bones is nearly the fame as in the Sarco-
phaga.

In the lamantiny the ofTa maxillaria are not
much elevated ,• they form a bafe to the orbit,
and afterwards extend to a confiderable diftance
behind it. That fofia being much advanced, a
procefs of the os frontis, which is extended for-
ward and outward, forms the roof of the orbit,
and contributes to inclofe the anterior aperture
of the nafal folTa, which is very large, and has
its plane direciled upward. The inter-maxillary
bones arc very extenfive, although the incifive
teeth are wanting.

In the Cetacea, the maxillary and inter-maxil-
lary bones arc prolonged into a kind of flattened
beak, which they divide into four parallel
bands, the ofla inter-maxillaria forming the two
middle, and the maxillaria the two external
bands. The latter only contain the teeth in
thofc genera which are furniflicd with them.
The nafal folia is perforated vertically in the
anterior part of the cranium ; the inter-maxil-
lary bones afeend to it, and incfofc it anteriorly
and on the fides. The ofla maxillaria alfo af-
cend fo as to cover all the part of the os frontis,

which

71

Art. V. Bones of the Face.

which forms the arch of the orbit, but they do
not enter into that cavity. The oiTa nafi are
two fmall tubercles implanted in the os fron-
tis above the aperture of the nares. The
os maljE has a ftyloid form, and is fufpended by
cartilages below the orbit. The frame of this
folfa is completed pofteriorly by a procefs of
the os frontis, which defcends to join the zy-
gomatic procefs of the os tcmporum, but the
orbitar and temporal foffae communicate with
each other below that procefs.

C. In Birds.

We have already Ihewn that the os frontis of
birds is prolonged 'above the orbits in a plate
more or lefs thick, more or lefs narrow, and
more or lefs notched, under which is fituated
vertically the feptum, w-hich feparates thefe two
foifse, and which adheres by its fuperior edge '
to the os frontis, and by its poflerior to the os
fphenoides. The inferior and anterior edges of
this feptum are free from adhefion, but they ar-
ticulate with the bone of the bill, as we ihall
hereafter explain.

The os lachrymale, or os unguis, is articulated
to the external and anterior angle of the os fron-
tis. It has two principal procefles : one ex-
tends from above downward, and forms the an-
terior margin of the orbit ; the other is di-

F 4 reded

72 Lect. VIII. Osteology op the Head.

recftcd from before backward, and forms the fu-.
perciliary ridge. The lafl procefs is mofl: re-
markable in the diurnal birds of prey, inwhicK
it is prolonged by an epiphyfis, jn the form of
a plate, and produces a confiderable projeclion
above the eye.

In the ojiricb there is a feries of fmall bones,
which continues this arch to the fuperior edge
of the orbit, leaving a vacancy between it and
the 06 frontis. This procefs is very Ihort, or is
‘even altogether wanting in \.\\o.owls^ x.\\t parrots^
the grallge, and the web-footed birds.

The defeending procefs of the os lachrymale
is moft confiderable in the parrots-, it extends
backward to form the inferior margin of the
orbit, which is complete in this genus only.

Next to the parrots the ducks have this pro-
cefs the longeft, and the frame of their orbit is
almoft complete. ,

7'he remainder of the face of birds is formed
by the bone of the upper mandible, which, in
thcm,-reprcfents the ofia maxillaria, inter-max-
illaria, riafi and palati of the mammalia ; wc
even fometimes obferve futures correfponding
to thofc which feparatc thefe bones in mammi-
ferous animals.

The form of the bone of the mandible is
commonly that of the bill itfclf, to which it
ferves as the mould or nniclcus. It reprefenrs
more or Icfs accurately the half of a cone or
pyramid; tho convex furfacc of which is out-

Art. V. Bon'es op the Face.

I

73

ward and upward, and the plain or concave fur-
fiiceof which I'lipplies the place of the palate. We
ihall not here deferibe the forms and curvatures
of different bills. That is one of the objecfls of
natural hiftory ; and belidcs we fliall have occafion
to return to it when we treat ot maOication.

The bafe. of the convex furfacc of the mandi-
bula is united to the anterior extremity of the
os frontis, fometimes by a moveable articula-
tion; and fometimes their parts arc foldered to-
gether, but always in fuch a manner as may ad-
mit fome degree of motion, as the offcous lami-
na at this place is more or lefs claflic.

The bafe of the palatine furface of the bill is
divided into four branches, which extend back-
ward as they diverge, and which are fometimes ar-
ticulated, and fometimes intimately united with
the bone of the mandible. The two external
branches correfpond to the zygomatic arches ;
they arc generally thin, and articulate poflerior-
ly to a fmall bone peculiar to birds, called os
quadrat ttm, which moves upon the temporal
bone before the ear. The two intermediate
arches correfpond to the pterygoid proceffes of
mammiferous animals They are almoft paral-
lel, are lituated under the feptum of the orbits,
and are not above half the length of the zvo-o-
niatic arches ; but there is a fmall flender bone
at their pofterior extremity, which alfo joins
with the os quadratum. We fltall deferibe in
,^3etail all thefe pafts, £ind the variations they

undergo.

\

74 Lect. VIII. Osteology OF THE Head.

undergo, when we come to the article of Maftica-
tion, as it is on them the mobility of the fupe-
rior mandible of birds depends. The inferior
mandible is articulated to the os quadratum.

D. In Reptiles.

In the crocodile the face refembles one half of
a cone irregularly flattened on its convex fur-
face. It is chiefly formed by two ofTa maxil-
laria, and two offa nafi, which are fltuated almofl;
parallel to each other, and two offa inter-maxil-
laria, which form the end of the muzzle, and
furround the aperture of the nofe like a ring.

The bones analogous to the lachrymalia are
four in number, two on each fide. The os malae,
which is very large, after forming the inferior,
and affording a fmall procefs to the pofterior
edge of the orbit, extends diredlly backward to
join the great mafloid protuberance: thus the
temporal fofla has no communication outward-
ly, except by a hole which is fmaller than the
orbit, and the greater part of which is covered
by thefe bones, as by an arch.

The nafal fofla: are continued in a long and
narrow tube under the foramen magnum. They
jicrforate the ofla palati, and a particular bone
which is analogous to the jitcrygoid procefles of
the 03 fphcnoidcs. This bone is fituated almoll
prccifely under the cranium, and is enlarged on

each

Art. V. Bones of the Face.

75

each fide until it forms a kind of fquare and al-
molt horizontal v/ing. An olTcous branch unites
it laterally to the os maxillare and os mala;, in
fuch a manner that a large hole is left on each
fide of the arch of the palate.

' In the camclioH the face is concave fuperiorly,
and bordered by a ferrated ridge throughout the
whole of Its circumference. We obferve two
holes which communicate with the orbits, and
two other oval foramina, which correfpond to
the incifive holes in the palatine furface. The
bones which compofe the face are nearly the fame

as thofe of the crocodile. The other lizards ex-

%

hibit ftill lefs difference.

The frog and the f^lamander have the nafal and
inter-maxillary bones very fhort, and broader
than long, vhich renders their face round an-
teriorly. The os maxillare is very narrow, and
is fcarcely contracled in forming the zygoma-
tic arch. The orbits are large, but have no in-
ferior furface, and therefor? communicate with
the palatine loffa. The ofHi palati form thp
anterior edge of the orbitar folia inferiorly.
They refemble portions of a circle. They are
furnifhed wirh pointed teeth on their circum-
ference. The canal of the nares is very iTiort in
the Jalamandcr. There is only a fimple hole in
the

The face of the Surinam toad is very fiat, bu-t
the bones are the fame as in the frog. The or-
bitar

76 Lect. VIII. Osteology of the Head.

bitar fofTx are oval, and no aperture fimilar to the
canal of the narcs can be dirtinguifhed.

The face ferpenis is rounded nearly in the
fame manner as that of the lizards. Between
the os frontis and os parietale, there is a parti-
cular bone which terminates the frame of the
orbit pofteriorly. Thefe animals have no os
malae. We can, however, cafily diftinguifh two
offa nafi, two ofTa maxillaria fuperiora, two ofla
intcr-maxillaria, and fome bones analogous to
the palatine arches of birds, which are furnillied
with teeth, and which are articulated to the
bone which fupplies the place of the os quadra-
turn, with refpect to the lower jaw. Two par-
ticular bones unites thefe arches to the maxil-
laria fuperiora.

In thofe that have teeth or poifonous hooks,
as the viper, the rattlefnake, &c. there are be-
fides two fmall peculiar bones, articulated and
moveable, which fupport thofe teeth. They arc
fituated upon the inter-maxillary bones and the
anterior extremity of the olTeous branch which
joins the fuperior maxillary bone to the arch of
the palate.

The face of the tortoife is circular before, and
rounded on every fide. It is compofed of nearly
the fame bones as that of the crocodile. The
inter-maxillary bones arc, at a very early period,
confolidated with thofe of the upper jaw. The
bones analogous to the os malx arc three in

nunibcr \

Art* V. Bones OF THE Face.

77

nuinber ; one articulates with the os icmnorum
and with the two others ; it is lituated poBcrioriy,
and forms the zygomatic arch. The other two
portions are received on its anterior extremity;
one extends upwards, and unites with theorbitar
angle of the os Irontis ; the other is dircifled
downward, and articulates with the poflerior and
external procefs of the os maxi Hare luperius.

The olfa palati are broad, and form the poBe-
rior arch of the nafal loHhe.

The bones of the face of tortoifes commonly
cover each other at their edges, which are re-
lined into thin laminae. It is therefore very
difhcult to diflinguilh the futures.

In the yi-a tortoifes the temporal fofTae, which
are very deep, are covered by an olfcous lamina,
which forms a very Iblid arch above them.

E. In Fishes.

Fiflics, like birds, have commonly a feptum or
vertical lamina between theorbits, which proceeds
from the bafe of the cranium. This lamina is
very remarkable in the auarrbicbas, which has it
entirely olTeous. In the greater number of other
fiflies it is membraneous, and fupported infe-
riorly by an olfeous canaliculatcd Balk, which
is directed towards the end of the mouth, where
it is enlarged, and to which it is ofiified. This

bone

7? Lect. VIII. Osteology oi‘ the Head.

bone refcmbles the vomer. It is greatly elon-
gated in the whiting, the turbot, &c.

The oHa palati, which are fmall, receive the
anterior extremity of the vomer. They are fur-
nifhed with teeth in a great number of fifhes.
The form and difpofition of thefe teeth vary
confiderably, as will appear when we treat of
Maftication.

Two bones, and even fometimes four, proceed
from the anterior and fuperior parts of the cra-
nium to the anterior extremity of the vomer.
They reprefent the offa nafi. They cover the
olfactory nerves; a fmall interval is left between
them in the filurus galeatus.

As in birds, there is on each fide of the cra-
nium a large moveable bone, to w'hich the lower
jaw and the arches of the palate are attached,
but in-fifiies it alfo fupports the operculum of
the branchiae. It is not fquare as in birds ; it
is elongated, flattened, and bent lengthways, fo
as to prefent its concave edge anteriorly, and its
convex edge pofteriorly towards the branchiae.
This bone is exceeding large in the pleurouc&es.
It has fome acceflary laminae in the perch, the
pike, and a number of other fiflics.

The arches of the palate appear to form part
of the ofla maxillaria fuperiora. They arc arti-
culated to the bones which fupport the lower
jaw ; they arc frequently flattened, and projed
from the lateral parts of the mouth, as in the

dory.

Art. V. Bones of the Face.

79

^ory, the zvhitingy the herring, &c. : they arc
cylindrical towards the middle, fiat pofteriorly,
furnifiied with teeth in the front, and lituated
in the centre of the mouth, in the Jca-zoolf, or
aiiarrbichas .

I'he zygomatic arches are fituated obliquely ;
they defeend from before backward, between the
extremity of the fnouu, behind the inter-max-
illary bones, and the middle or pofterior portion
of the lower jaw ; their pofierior extremity fre-
quently does not extend to the bone analogous
to the os quadraturn of birds : when this is the
cafe, it remains free in the fiefit, as in the her-
ring, the pike, the fcrch, the jea-dragon, and
fome pleurone^es, as the plaice and the /ole.
Thefe zygomatic arches never extend to the
teeth.

Two bones, commonly furnilhed with teeth,
are fituated before the anterior extremities of
the arches ; they may be regarded as inter-max-
illary bones ; they form the anterior part of the
fnout; they are very large and folid in the anarr-
hichas ; narrow, and much elongated pofie-
riorly, in the the perch, and the fea-dra-

gon ; fnort, triangular, and flat in the pike, and
the chcetodons I that on the fide, which does
not contain the eyes, is confiderably more de-
veloped in the pleiiroyiecJes.

Befides the anterior and pofierior orbitar pro-
cefies which form the anterior part of the cra-
nium, there is a bone, or rather a feries of fmall
^ bones,

8o Lect*V1II, Osteology or the Heao*

bones, fituated under the orbit, which con>-
pletcs the frame of that cavity ; thcfe bones ap-
pear analogous to the os lachrymale : they are
wanting in the falfe orbit which vve obferve on
one fide of the head of x\\t pleuroneHes^

The face of the Chondropterygii, though fi-
milar in its compofition to that of other fiflies,
differs from them with refpedh to its conneeflion,
as it i articulated with the cranium only, by
the means of the bone analogous to the os
quadratum of birds.

Article VI.

Oj' ihe YojJle of the Face.

A. In Man.

A FRONT view of the face exhibits three prin-
cipal foffae ; the nofe and the two orbits.

'fhe anterior aperture of the nofe is oval, and
notched in the middle by a fmall fpine ; it is
bounded by four bones, the two fuperior maxiU
lary, and the two nafal. The interior of this
foU'a will be deferibed more in detail when wc
come to the article Smelling.

The orbits aretwo folTtc, th.c margin of w hich
is irregularly rounded, and almoll rhomboidal ;
they .arc contrasflcd into the form of R funnel ;
n the

Art. VI. Foss-^e of the Face. 8t

the edges of their aperture are nearly in the fame
plane. Three bones contribute to the torma-
tion of thefe edges, the os frontis, the os inaxil-
lare, and the os iiialae. Seven bones form their
parietes, viz. the frontal, ethmoid, lachrymal,
palatine, maxillary, malar, and Iphenoid :
their internal, external, and inferior parietes
are almoft plain ; the fuperior is concav'c, the
internal or nafal parietes of the two orbits are
parallel to each other,- the internal llde forms,,
with the external, an angle of about 45®; and
the axes of the two orbits form an angle of fi-
milar magnitude.

On viewing the face laterally, there appears
a large dcprcflion, fituated behind the orbit. It
is called the temporal fo(Ta ; a confiderable por-
tion of it is imprclTed on the cranium. The
zygomatic arch extends like a bridge over this
fofla, which becomes deeper as it defeends be-
fore— it is molt hollowed at the pofterior furface
of the fuperior maxillary bone, and the adjacent
portion of the os fphenoides. The part which
is oppofite to the zygoma is called the zygo-
matic fofla ; fome mufcles are lodged in it.
When the face is viewed infcriorly, this foITa is
alfo feen.

In this laft view of the face, we alfo perceive
the palatine folTa, or arch of the palate, en-
circled on the front, and on the fides, by the
teeth : — the poflerior extremity of the nafal
fo^^a^, and at their fide the pterygoid fitu-

VoL. II. G ated

S2 Lect. VIII. Osteology or the Head.

ated between the two proccfTes of that name>
which belong to the os fphenoides. — Laftly, all
the fpace included between the foramen mag-
num, and the pofterior margin of the palate,
■which is called the guttural faffa.

B. In other Animals.

We fliall proceed to confidcr each folTa of
the face feparately, in all the clafTes of animals,

1. Kaful To fj'ce.

a. Tire anterior aperture of the nafal fofTa in
ihejockoy is, as in man, broadefl: inferiorly.

In the orang-outangy fapajousy alonateSy
and fome guenoyiSy it is oval, and is broadefl: in
its middle part. In other guenons, as the Cbi^
neje monkey, &c. in the Barbary ape, and the
mandrils, it is broadefl: towards the upper part.
In all thefe animals this aperture is flattened
down upon the face, and furrounded by four
bones only, viz. the olTa nafi, and the ofla in-
ter-maxillaria.

In the Sarcophaga, this aperture approaches
nearer to the end of the fnout; its form is nearly
round, but broadefl towards the upper part ; it
is inclined more backward in the feal, than in
the other genera.

In the Rodentia, it cuts the end of tha muz-
zle

Art. VI. Foss.^ of thU Face. S.?

v.te vertically ; its form is that of a heart, with
the broaded fide uppermoft.

This form is nearly liinilar in the Edentata. In
the Jlotbs, however, the aperture of the nollrils
is furrounded by fix bones, viz. the intcr-niax-
illary, maxillary, and the nafal. In the ant-
ealers, this foffa is extended towards theloranicn
magnum.

The nafal fofto; of the elrphant open at nearly
an equal dirtance between the lummit ot the
head, and the edge of the alveoli their breadth
confidctably exceeds their height, and their form
icfeinbles that of two ovals joined together.

In the F'achydernuta the oITa nafi of the bo-^
form a pointed projeclion over the aperture ol
the nafal fofTae. Betw'een their point, and the
oorrefponding part of the ofTa inter-maxiliana,
there are two fmall peculiar bones, which ferve
to drengthen the fnout, called the bones of the
fnOHt. In the rhinoceros, and particularly in the
iapir, the aperture of the nares is conlidcrably
longer; the olla nafi advance upon it beyond its
anterior extremity in the rhinoceros, but only
one third of its length in the tapir: in both ic
is furrounded by fix bones. In the hippopota-
mus the aperture of the nofe is very broad, and
fituated vertically at the end of the muzzle.

In the Ruminantia this aperture is very large,
and inclined backward. The ofla nafi form only
a diort (errated projection in the ox, the deer,
the camel, and the mujk. The projection is

G 2 pointed

?4 Lect. VIII. Osteology of the Head.

/

pointed in the antelopes, the Jhcep, and the
goats.

In the morfe this projecftion is long and
pointed.

The morje has a fmall round aperture in the
middle of the end of his thick fnout; the dugon
and the Imnantin have a large oval aperture di-
redled upward ; their ofiTa nafi are very fmall.

In the Cetacea the aperture of the nares is
direcTted upward, or even backward ; it is more
broad than long, and furrounded by fix bones;
the ofla nafi are fmall tubercles.

b. The nafal folTas of birds do not form a
canal pafiing from before backward, but merely
a cavity which occupies the thickell part of the
bafe of the bill, and which opens upward by two
nares, and downward by a filTurc, leaving be-
tween them the two palatine arches : it is not
feparated from the orbit poficriorly by an
olTcous lamina, but by a membrane.

The external aperture of the nares is formed
in the bafe of the convex furface of the bill.
Its figure and magnitude, which vary confidcr-
ably, fiiall be deferibed when we treat of the
Organ of Smell.

c. The nafal foITa of tortoifes forms a large fpace
occupying the thick part of the nofe before the
eyes ; it is very fiiort from before backward ; it
opens outwardly by a large hole almoft fquarc,
the plane of which is a little inclined, and po-
fieriorly by two round holes, which correfpond

n nearly

✓

Art. VI. FosSi^: of the F.-vce. 85

nearly to the middle of the palate ; its anterior
aperture is furrounded by iix bones.

In the crocodile the nafal folFi is a long nar-
row cansl, which extends from the end of the
fnout to below the occiput ; its anterior aper-
ture is direded upward ; it is furrounded by the
two ofTa inter-maxillaria only.

The nares in other lizards open nearly in the
fame manner as thofe in birds, that is to fay,
outwardly upon the nofe, and inwardly on the
middle of the palate. In frogs they are still
I fliorter.

d. The nafal foffae of rays and (harks ^ are fim-
'}■ pie cavities formed in the bone, and do not
communicate with the mouth ; it is the fame in
l feveral ofleous fi flies, fuch as i\\c gurnards \ but
■ j' in mod: of the other fiflies thefe folTae are in part
h-* otTeous, and completed by membranes.

^ •> 2. Orbitar l of/cc.

a. All the monkey tribe have their orbits di-
reeled forward, as in man, and the angle formed
>!, by their axes is even fmaller chan in the human
cranium. The form of thefe cavities, and the
V bones which furround them, exhibit no dif-
; ^ fercnce, but the fliape of their margins vary.

! In the jocko they are fimilar to thofe in man.

orang-outang and ihtfapajons have them oX
i an oval form, always higher than broad. In the

' ^nenpns, ;he fuperior arch is lefe cuvvated than

G 3 the.

86 Lect. VIII. Osteology o? the Head,

the reft of the margin, which produces a con-
spicuous angle on the lide of the nofcj the
breadth of their foITae exceeds their heighth :
this difference is ftill greater in the Barbary ape.

The angle formed by the axes of the orbits,
enlarges in the other animals, as we have already
remarked. The margins of the orbirar fofiiE are
nearly round in the Sarcophaga, the Rodentia,
the Edentata, and the Pachydermataj but pofte-
riorly thert is always an arch which is not in-
clofed by the bones ; there is alfo no partition
between the orbit and the temporal fofla. In
treating of the face, we have already pointed
out the differences which prevail in the number
and kind of the bones that contribute to form
this foffa.

The Ruminantia and the Solipcda have a
round orbit, the margin of which is complete,
but it is notfeparated from the temporal foffa.

The roof of the orbit of the Cetacea is femi-
circular ; their two axes are in the fame right
line : they have no inferior parictes.

b. The orhitar foffae of birds are fimilar to rhe
impreffions which might be produced by two
fingers pinching the cranium in a foft Bate ;
they have no oifeous parictes inferiorly : the la-
mina which feparates the orbits is only par-
tially offified, and the portion which continues
membranous is even very large in fume birds ;

' ^ut there is nothing uniform in this refpecT:.
g, The orbitar foffx of reptiles are never fc-

parated

Art. VI. Foss.i of the Face, 87

parated from the temporal folFe, except by an
olTeous branch, which even is not complete in
the lizards zn\\ the tortoifes, and which does not
exlft at all in frogs, fafamanders, and ferpents.

The plane of the edges of the orbit is lateral
in tortoifes , ferpents, and the camelton: it is di-
rected more or lefs upward in the crocodiles, fa-
lamandcrs, and frogs.

It varies from a circular to a triangular form.

The inferior parietes is never complete ; it
is fometimes entirely wanting; at other times it
is perforated by a large hole. The fame obfer-
vation applies to the feptum between the or-
bits.

d. The orbitar foffa of filhes varies confidcr-
ably with refpeCt to its (hape, its dire(5tion, and
the compolition of the bones that form its edges.
It is lateral in the orreatcr number, but is direCled
upward in fome, as in the fiar-ga%er, and fe-
veral others. The pleuroneFJes have only one
perfect orbitar fofla. We can, w ith difficulty,
difeover the fecond in their fkeleton ; becaufe it
is placed on the fame lide with the other, and
is exceedingly fmall and deformed.

The inferior margin of the orbitar fofla is
formed, in fome fifhes, by a continued piece
analogous to the os malse ; and in the others', by
a feries of fmall bones, fufpended by ligaments
articulated to each other. There arc frequently
live of thefe bones.

There is never any ofleous feparation between

G 4 / the

88 Lect. VIII. Os TEOLOGY OF THE HeaD.

the orbits and the temporal and palatine
foITae.

S. Temporal Fojfce.

a. The extent of the temporal foITa depends
on the magnitude of the fpace depreffed on the
fide of the cranium, and of the external con-
vexity of the zygomatic arch ; this fofla is en-
tirely occupied by the temporal mufcle which
raifes the lower jaw. It appears, however, more
proper to refer our account of this fofla to the
article on Mafiication.

. To the fame article we fliall alfo refer the con-
fideration of the palatine pterygoid, and gut^
tural foITs.

Article VII.

Of the Holes of the Face.

A. In Man.

HE orbitar i'ofla communicates with the intc-
•rior of the cranium, by the optic foravtai, and
by tlTe fpheuo^orbitar fiffurc, of which we have al-
ready treated ; it communicates with the deep
portion of the temporal fofla, by the fpheno-
maxillary fiffurc, extending between the orbitar
procefs of the os fphenoides, and the orbit
' ■ ‘ fur face

Art. VII. Holes of the Face.

89

fiirface of the os maxillarc, which arc not united,
part of the fifth pair of nerves pafl'cs through
this fiffure, as it proceeds from the orbit into
the temporal fofTa. The communication of the
orbitar with the nafal foifa takes place, lirff,
by one or tw'o final 1 holes, fituated fome times
in the os frontis, and fometimes in the future,
by which it joins the os planum ; thefe are call-
ed the anterior internal orhUar foramina ; they
afford a pallage to the nafal nerve, which pro-
ceeds from the ophthalmic branch of the fifth
pair. Secondly, it communicates with the nofe
by the lachrymal canal, w hich paffes along the
inner margin of this folia, and is lituated partly
in the afeending procefs of the os rnaxillare,
and partly in the os lachrymale; it defeends al-
inoll verticallv into the nofe.

The fpheno-maxillary filfurc is prolonged a
little as it defeends into the temporal fofFie. In
its deeped part is found ihx fpbeno-pafaHne hole,
■which is formed by a groove in that part of the
palate bone which joins with the body of the
os fphenoides ; it extends partly into the nofe,
and aflifts in forming the orifice of a finall con-
duit, which defeends between the os palati and
the pterygoid procefs, and which opens towards
the poderior angle of the arch of the palate, by
a hole called foramen gujlatorium, or poferior
guftatory hole ; it adords a pafTage to n fmall ra-
i\iification of the fifth pair of nerves, in its
CQurfe towards the uiperior maxillary branch.

There

90 Lect. VIII. Osteology OF THE Head.

There is a]fo in the middle future of the arch
of the palate, and immediately behind the den-
tes inciiores, a Angle hole, Q-dX\t^ foramen inci-
forium. , Some branches of the fuperior maxil-
lary nerve pafs through this hole.

Laftly, we obferve in the front of the face,
and under the orbit, another hole, called the
Jiih'-orbitar foramen. It ferves as the outlet of a
fmall canal, which palfes under the floor of the
orbit, and gives exit to the lafl branches of the
iiiperior maxillary nerve. We alfo remark a
much fmaller hole above the orbit, which is
fometimes merely a notch; it is called the fuper-^
ciliary foramen^ and tranfmits the frontal branch
of the ophthalmic nerve.

I

B. In other Jnimals.

We fhall conflder the principal holes of the
face as they appear in the different claffes of
animals.

The lachrymal canal we fhall omit till we
have occaflon to treat of the Eye.

1. Spheno-maxillary Fiffure.

The fphcno-maxillary fiffurc of the monkey
kind is much fliortcr than that of man ; it is
reduced to a Ample hole in ^omc fapajous. It is
entirely clofcd in the alouale; it is partly fup-

Art. VII. Holes of the Face. 91

plied by a hole in the cranium, fituated beliind
the orbit, at the deepeft part of. the zygomatic
folFa, and probably alfo by a pretty large round
hole fituated in the os rnalae.

The animals that have no partition between
the orbit and the temporal folia, have alfo no
fpheno-temporal filFure; the latter, therefore,
does not exill in any of the mannmalia, except
the Quadrumana, nor in any of the other clalTea.

£. Internal Orbitar Foramina.

The anterior and podcrior internal orbitar
foramina, are very fmall in the tnonkieS', the lat-
ter is even often wanting ; when it exifts, it
palTcs through the os frontis.

In the Sarcophaga, the anterior foramen is
very large, and fituated at the inferior part of
the orbit in the os maxilUre: the po|Ierior fo-
ramen terminates in the cranium by an aperture,
fituated behind and above the cribriform la-
mella.

In the Rodentia, the anterior foramen refem-
blcs that of the Sarcophaga ; the pofterior is
frnaller, and fituated entirely behind the cribri*
form lamella.

In the Edentata, the anterior internal orbitar
foramen is fituated altogether in the lower part
of the orbit, and perforates the os palati ; the
pofierior foram.cn, on the contrary, is fituated

above,

I

92 Lect. VIII. Osteology of the Head.

above, and fomcvvhac before the orbit, in the
body of the os frontis.

In the elephant the two internal orbitar fora-
mina are formed in the os frontis ; the anterior
iomewhat before the orbitar fiffure, and the pof-
terior under the olFeous ridge which covers that
hlfure ; the a[>erture of the latter, in the cra-
nium, is licuated behind, and a little above the
cribrii'orm lamella.

It is nearly the fame with refpedl to the other
Pachydermata,

In the Kuminantia and Solipeda, the anterior
Internal orbitar hole is very large, and perforated
below and before the orbit, between the os pa-
lati and the os fphenoidcs : the pofterior is alfo
confiderable; it is diredled towards the fide, and
behind the cribriform lamella.

It is very difficult to trace thefe holes in the
Cetacea, becaufe they arc covered with offcous.
laminae, and are very fmall.

The internal orbitar foramina do not exifi:' in
the other clafles of animals.

, 5. Foramen Inciforiim.

a. In all the mammalia, the foramen incifo-
rium belongs to the inter-maxillary bones; it is
fmall and finglc in the jocko and the orang oiitangi
but it is fomewhat enlarged in the other mon-
kies, and in the Sarcophaga it is double.

In the Rodentia the hares have it very large,

even

✓

Art. VII. Holes of the Face. 93

even exceeding the folid part of the palate ; it
is fmaller in the other genera; it occupies nearly
the middle fpace between the incifor and the
malar teeth.

The Edentata, which have very fmall inter-
maxillary bones, have alfo the foramen incifo-
rium fmall, and lituated near the end of the
muzzle.

It is fingle and elongated in the tapir and
the rhinoceros. In the elephant its place is fup-
plied by a long narrow canal.

In the Ruminantia it is exceedingly large;
it is oval, double, and lituated quite at the end
of the fnout.

It is nearly (imilar, but Icfs in borfes2i.x\A bogs.
In the horl'e there is a fingle round hole, fituated
before the two incifive holes.

It is almofi: obliterated in the morfe \ fmall,
and much removed from the edge of the alveoli
in the dugon ; fingle, oval, large, and fituated
clofe at the end of the fnout in the lamantin.

The Cetacea have no foramen inciforium.

b. In fome birds, as the heron ^ the fiamingOy
the eagle ^ &c. the incifive foramina are fmall
and numerous ; there is only one of a middle
fizc, and fituated towards thebafe of the bill, in
the ducky the curaJfoWy the cormoranty the Jpoon^
billy &c. The cajfoivary has a fmall foramen
fituated towards the point of the bill. Th&ozvls
> and the have it pretty ' large. It is of, a
very great fize in the ojlrich.

c. The

Legt. Vllli Osteology of The Head^

c. The foramen inciforium of the crocodile
confidcrable ; as is likewife that of the frog and
the filamander. I he torloife has two very fmall
ioramina. We have not been able to difeover
them in the other lizards.

There can be no foramen inciforium in
fiflies, as no part of their face can, with pro-
priety, be called the nafal cavity.

4. Suh-orbitai- Foramen.

t

The fub-orbitar foramen is finglc only in the
jocko. There' are two fmall foramina in the
orang-outangs and the fapajotis \ three in the
greater number of guenons and magots\ four or
live in the macaques and mandrils i the lemurs
have but one.

There is alfo only one in the Sarcophaga ; it is
pretty large, and Ihould rather be named the
ante ox pr<s-orbiiar foramen: it is fituated far-
ther forw’ard in dogs than in the other genera.

In’ the Rodentia it is (imple, and exceedingly
large. In the cavys, the agoutis, the porcupines,
the rats, and particularly xnihcjerboai, it almoft
equals the orbit in fizc. It is formed in the
malar proceCs of the maxillary bone.

In the other genera of Rodentia, as the hares,
beavers, fquirrcls, and marmots, it is fmall, and
lituated upon, or even before the firlt 'dentes
inolarcs.

It is iimplc and fmall in ihe jloths, but in the

long-

Art. VII. Holes or the Face. 95

long-nofcd Edentata, it forms a canal in the
bafe of the malar procefs of the os maxillare.

In the drphant it is of a confiderable fi7.c,
and opens on the lower part of the malar pro-
cefs.

In the other Pachydermata it is nearly the
fame as in the dog.

It is the fame in the Ruminantia and Soli-
peda.

The Jeals^ the morje^ and the lamantina^ have
it fituated in the bafe of the malar procefs.

There are three or four of thefe foramina in
the Cetacea, fituated in a longitudinal line ; one
of them is even perforated in the inter-maxillary
bone; thofe that are fuperior have a retrograde
diredion. The pofition of the os maxillare in
ihefe animals places the foramina above the or-
bit, inrtead of below it.

There are no fub-orbitar foramina in birds, or
in the other clafles, as the mammalia alone have
lips.

5. Spheno-palatinc Canal.

The fpheno-palatine canal of apes does not
differ from that of man.

But in all animals, in which the temporal fof-
fa is not feparated from the orbitar, we eafily
diftinguifli a fuperior aperture fituated in the
lower and fore part of the temporal foffa. It
receives two canals, one of which extends to.

the

/

{

96 Lect. Vin. Osteology of the Head*

/

the nofe, and the otlier to the palate ; the latter
is fomctimcs very fliort, and has often two or
three openings into the palate. /It is almoft ho-*,
rizontal in the Cetacea.

There is none in birds. We find it, however,
in reptiles ; not indeed in the form of a canal,
but as a limple hole in the palatine bone.

/

LECTURE

[ 97 -]

LECTURE NINTH.

or THE BRAIN OF ANIMALS WITH VERTEDR.i:.

Article I.

Of the Organization of the Nervous Syfcm in

General.

The nerves, with the central mafs from which
they all arife, that is to fay the fpinal marrow
and brain, form the common organ of fenfation
and volition.

The fenfations we experience from the acflion
of external bodies on our own, are more perfeiT
in proportion as the nerves terminating at the
part which receives the impreffion, arife more
immediately from the medulla fpinalis, and
through it from the brain.

If thefe nerves, however, are tied or cut, all
the parts of the body to which they are diflri-
buted become infenfible, whatever be the diftance
from the brain at which the feclion or ligature
is made.

In the fame manner, if we tie or divide the
fpinal marrow’ itfelf in the neck, the whole body

VoL. II. H becomes

98 L. IX. Brain of Animals with Vertebr^^:.

becomes paralytic and infenfiblc, though the
vifeera may for a time continue their motions,
becaufe they receive a great part of their nerves
immediately from the brain. Finally, a general
compreffion of the brain inflantly deftroys every
kind of fenfation.

Thefe obfervations have produced the opinion
that there exifls a Jenforium cemmune^ or centre
of fenfation, to which the impreflions of all the
nerves arc tranfmitted ; and this commoji organ
is fuppofed to be the brain,

There arc, however, feveral animals in which
this union of the branches of the nerves, with
their common trunk, is not neceflary to fenfa-
tion. fTiny, for exaniple, Completely remove
brain of a torto|fe or a frog, and thefe ani-
mals w'ill ftill feem to Ihew by their niotions
that they polTcfs fenfation and volition.

There are aifo infedls and worms, which, when
cut into two or feveral pieces, form immedi-
ately two or feveraf individuals, having each a
fyflem of fenfation and volition. It is only in
the animals which are the mod perfed, and
which a])proach neardt to man, that the con-
nection of the different parts of the nervous
fyllem, and particularly the prefence of its cen-
tral parts, is abfolutcly ncccffary to the cxifcncc
of its functions.

The ncccflity of this connexion increafes in
proportion to the magnitude of the common
trunk, compared with its. randfications. The

more

A. I. OrGANI'/aTIOV ^//ij^-NcRVOUsSYSTEM. 99

more equally the niedullarv mafs is diflributcd,
the lefs eirential is the exigence of eentfal parts :
animals which have this rcnfitivc fiibftance
dill'iifcd over the whole body, as is the cafe
in polyps, mav be divided and fubdivided to
any degree of tninutenefs, yet each fragment
w ill be endowed with a particular felf-exijleitcr,
and become a fe|xirate and perfert individual of
its'kindt

From thefeobfervations, it mav bcconjetfliircd,
that the parts of the nervous fvflcm arc homo-
geneous, and fufceptiblc of a certain number of
limilar fun^flions, in the fame manner as the
fragments broken from a large magnet, become
each a iinallcr magnet, having its poles and
morion ; and that in the higher orders of ani-
mals the connexion of parts is rendered necef-
fary only by accefibry circumflances, and the
complication of the functions they have to per-
form, which is alfo the reafon that each part
anfwers a particular ufe.

With refpect to the faff fa^ff, it indeed ap-
pears that the appropriation of certain nerves
to the acquirement of determined fenfations,
and of others to the performance of particular
functions, is the eRcvft of the nature of the ex-
ternal organs, in which the former terminate,'
and the number of blood vefTcIs which the lat-
ter receive at their divifions and unions : in a
word. It is rather to be aferibed to any acceflbry

2 circum-

I

lOo L.IX. Brain of Animals with Vertebra.

circumftance, than to the peculiar nature of the
nerves themfelves.

We {hall render the truth of this obfervation
more apparent, by proceeding to confider the
general dijlrihution oi the nervous fyftem, and the
nature of its fubflance.

With refped to the diftrihution, we hnd that,
in all animals which have diftinifl nerves, thefe
nerves arife from one common mafs, which moft
frequently is of a cord-like figure, and called the
fpinal marrow-, the anterior extremity of this me-
dullary rope is always more or lefs enlarged,
and exhibits feveral tubercles or eminences,
which, in animals that have vertebrje, arc fitua-
ted in the head, and have obtained the common
name of byain.

There are animals, as fome Molufca, in which
we difeover only a limple medullary mafs with-
out any cord-like prolongation.

The nerves arife by pairs from the common
trunk, or from the mafs which fupplies its
place, and ramify like the branches of a tree
as they proceed to the parts they are deftined to
ani/nate.

Some of thefe nerves have a fimplc origin ;
but the greater part arife or proceed from the
trunk in feveral filaments, which afterwards
unite and form one common fafciculus.

The principal branches of the nerves do not
always continue to fubdivide : on the contrary,

it

A. I. Organization (p/'/Zj^’NervousSv STEM. lOi

it frequently happens that fevcral branches, \\ he-
ther belonging to the fame or different nerves,
unite and feparate again in various manners to
form plexus, from w hich new trunks of nerves
arife.

Neither do the ramifications always diminifli
in thicknefs, in proportion as they divide. Wc
very often meet with a branch which is thicker
than that from which it proceeds.

It is even obvious, that the nerves muff in-
creafe in magnitude as they advance towards the
extremities; for the fkin, which is fenfible in
every part, and which confequently is every
where furniflied with nerves, has fevcral hundred
times more fuperficial extent than all the roots
of the nerves taken together.

Communications are cffabliflied between a
great rtumber of very different nerves, by cords
which extend from the one to the other . w^here
thefe communications take place, there is al-
moft always an enlargement or fmall mafs of
medullary matter, which feems to be only a
very compadl plexus, and which is called a gan-
glion.

I'ilaments, proceeding from feveral nerves,
very often unite into one ganglion, from w'hich
other filaments arife, and are tranfmitted to
different parts.

Sometimes alfo a fingle nerve fwells into a
ganglion, and is afterwards contradled.

From this fummary defeription, it appears

H 3 that

102 L. IX. Bratnof Animalsw'ith Vertebr.t.

that the comparifon of t+ic nervous fyftcm to
the trunk of a tree and its branches is nor per-
fecflly accurate; it Ihoi.dd rather be conlidcrcd as
a kind of complicated net-work, in which the
greater part of the threads communicate with
each other, and in which there appear, at differ^
ent places, malTcs or enlargements, more or lefs
confpicuoiis, which may be confidcred as centers
of communication.

The middle part of this net- work always pre-
ferves the greatefl: fize, the mod: immediate con-
nexion, and the mod: powerful induence with
refpeA to all the other parts.

But the degrees of this influence vary as much
as thofe of its proportional magnitude.

In the animals of the higher cladcs, the dze of
the medulla fpinalis vadly exceeds that of the
nerves which proceed from it, and the brain
alfo greatly furpaflTes in dze thefpinal marrow^.

Thefe tw’o circumdances are more remarkable
in man than in any other animal. His brain is
the larged of all, in proportion to the red of the
nervous fydem. In the other warm-blooded
animals, the volume of the brain diminidies in
proportion as the fpinal marrow becomes larger.
In the nioUifca there is only a brain, from which
the nerves proceed like radii, and form fcat-
tcred ganglia almod as large as the brain itfcif.
In infeds, the brain is not larger than each of
the numerous ganglia of the fpinal marrow, and
the nerves arife from |x)th in the fame planner ;

A. I.ORGANIZATION/^/i^i’NERVOUsSvSTEM. lOJ

thus, in proportion as we defcend in the fcalc of
animals, we find the medullary fubftance lefs
concentred in a particular region of the fyficm,
and more equally difiributed to all the parts.

The 'texture of the nervous fyflcrn may be
confidered in the brain, in the medulla oblon-
gata, in the medulla fpifwlis, in the nerves, and
in the ganglia.

The brain of animals that have red blood and
vertebrae, confills of a mafs varying in folidity
and fitfnnefs, ealily divided or comprefled, and
nightly vifcous. We obrei*^^ in it two princi-
pal fubftances, the cortica} the medullary j and
two others Icfs e.^tcnfive, which are called the
Joft and the black fubflanccs. The brain of cold-
blooded animals is fofccr than that of the warm
blooded. Some fillies have the brain almofl fluid.

The cortical fubflance is reddifh, and femi-
tranfparent ; it appears homogeneous to the eye.
Injeclions, however, penetrate its fubftance to a
certain extent, and fhew that it is chiefly com-
pofed of blood-veftels. Its pofttiony with re-
fpeebto the medullary fubftance, varies in the
different parts of the brain ; but in the circum-
ference of the hemifpheres, and of the cerebel-
lum, it is external. Hence it has received its
name. The limits of thefe two fubftances are
very diftindl. They do not change by degrees
into each other. The cortical fubftance poftefles
no fenfibility. Its quantity, wkb refpecfl to
the reft of the brain, decrcafes in the cold-

H 4 blooded

104 L. IX. Brain OF Ani'mals with VERTEBRi«.

blooded animals. It is proportionally greater
in man than in other animals.

The mcdiiUary fubftance is white, opaque, and
firmer than the cortical. It appears to the eye
compofed of very fine fibres, the direftions of
which are various. Few velTels are obferved in
it, and inje^Uons do not pervade its intimate
ftrucSture. This fubftance forms the greater
part of the interior of the brain; and the medulla
oblongata, and medulla fpinalis, are its pro-
longations. Their texture is altogether fimilar
to that of the medullary part of the brain. We
obfcrve in them the fame fibrous appearance,
mixed internally with a fmall quantity of cine-
ritious fubflance.

The foft fubftance is greyifh, femi-tranfparent,
and almoft fluid. In fome parts it covers the
furface of the brain. The black, or blackijh fub-
ftance, colours the medullary part of the brain
in two places.

The medullary and cortical fubftances of
white-blooded animals prefent no diftcrence as
to colour, and it is even with fomc difficulty
that we difcover any in their confiffence. The
Cruftacea and the infedls only have a kind of
fpinal marrow. It is compofed of a double
medullary cord, united at different fpaces by
ganglia. Perhaps it ftiould rather be regarded
as a kind of great fympathctic nerve.

The texture of the nerves ought to be confi-
dcred in' their courfe, at their cerebral extre-

A.I.ORGANIZATIONO//i7^NERVOUsSYSTEM. IO5

mity or origin, and at their termination in the
different parts of the body.

The nerves are not merely enveloped by mem-
branes, which appear to be continuations of
thofe that furround the brain. The membrane
to which fomc modern anatomifts have given
the name of neurilernay ( nerve-tunic) ^ penetrates
alfo into the interior, and forms fepta, which
divide the medullary filaments from each other.
The medullary fubftance may bediffolved by alca-
line lixivia, and there will remain only the tubes
formed by the neurilema. The latter may alfo
be difi’olvcd by acids; we then obferve that the
medullary filaments, which ftill remain, anafio-
mofe together in various ways. The nerves re-
ceive a confidcrable quantity of blood, which is
tranfmitted to their fubftance by the veflels of
the neurilema, in the fame manner as the blood
is conveyed to the brain by the vcffels of the
pia mater.

The term origin of the nerves is applied to that
part of them w hich is neareft the brain or me-
dulla fpinalis, before it has entered the fheath
furnifhed by the dura mater.

Some nerves appear to derive the medullary-
fibres, of which they are compofed, from the
furface of certain parts of the brain. Such in
particular are the olfatflory and optic nerves in
all red-blooded animals, and the auditory nerve
in mammalia and birds. Others feom to come
from the internal fubftance of the brain, into

which

io6 L.IX. Brainof Animals WITH VERTEBRi^:.

t

which their roots may be traced like thofe of a'
tree into the earth. This is moft remarkable in
the third pair of nerves in the mammalia ;T>ut
the greater part of the nerves arife by filaments,
which are connected to the medulla oblongata,
or medulla fpinalis, and which unite to form
nervous trunks. This, at leaft, is the difpofi-
tion which prevails in all animals that have red
blood, with refped to the nerves that fuccced
the auditory, that is to fay, reckoning from the
par vagum.

It is probable that all the nerves penetrate
more deeply into the fubftance of the brain and
medulla than it is pofiible for us to trace them.
It is even fuppofed that they crofs each other,
fo that thofe which proceed to the left fide of
the body arife in the fight fide of the brain j and
that thofe tranfmitted to the right of the body
coijie from the left of the brain. It is certain
that wounds received on one fide of the brain
have frequeently produced a para*Iyfis on the
oppofirc fide of the body. We can alfo clearly
perceive the deenffarion of the optic nerves of
fiflies, and We conclude that the fame thing
takes place in other animals, as one of the nerves
frequently diminifhes in fize above and below
the place where they are confounded in crofs-
ing.

The fibres that compofe the medulla fpinalis ‘
feem alfo to crofs each other in the groove by
which it is divided.

7

In

A. 1. Org AN iz ATioN Nervous System . 107

I n animals that have vt h ite blood, the nerves pro-
cecd from the brain or the other ganglia; but they
never arife immediately from the fpinal marrow.
Their fibres, however, cannot be difiinguiflted
either in thefc ganglia or the tubercles.

li'iiQ terminal ion of tbe nerves is difierent, accord-
ing to the parts to which they are tranfmiticd.
Thofe which are difiributed internally, are ac-
companied by the neurilema to their moll im-
perceptible extremities. The optic nerve, is
terminated by a nervous expanfion which fpreads
over the interior of the eye. The acoullic ter-
minates by filaments which fwim in a gelati-
nous fluid. The nerves that belong to the organ
of tafic are dilated in the nervous papillfcof the
tongue; thofe of feeling terminate in the pa-
pilla: of the fkin, ^c.

The ganglia of red-blooded animals do not
appear to differ trom nervous ptexiiSy except that
the filaments which conipofe them are more
compad, and more intimately united. Evea
the limple ganglia, that is to fay, thofe that are
formed by a fingle nerve, are refolved, by ma-
ceration, into feveral filaments, which anafto^
mofe together.

'It is the fame with refpecl to the Molufea ;
but in the Crullacea, the Infecfts, and the Worms,
the ganglia are merely homogeneous enlarge-
ments of the medullary cord to which they be-
long.

J'rom what has been faid, it is obvious, that

>ve

loS L. IX. Brain OF Animals WITH Vertebr it.

Ave hav'e but a very limited knowledge of the
real texture of this medullary fubftance which
forms the efiential part of the nervous fyftem.
Is it merely an accumulation of excretory vef-
fels ? Is it a kind of gland or parenchyma ? Or
is it limply a homogeneous. mafs ? Each of thefe
opinions has its partizans and its adverfaries.

The chemical nature of this medullary fub-
flance is alfo imperfecflly known to us. It is
certain, however, that it differs effentially from
all other animal matter. It is foluble in cauflic
alkali, and partly in oil : it is not fat : and yields
no oil by expreflion. It dilutes, but does not
diffolve in water; alcohol extracts from it, when
warm, a fubftance, which in cooling precipitates
into needles or fmall lamince. This matter may
be compreffed or extended between the fingers.
It foftens a little at the heat of boiling water,,
becomes black at a greater heat, and burns with-
out fufing, emitting the fame odour, and leav-
ing the fame carbon as other animal fubftances.
The medullary part of the nerves prefents the
fame chemical refults as the medullary part of
the brain.

Article

Art. II. Action of the Nervous System. 109

Article II.

t

Of the Kervous S^iem conjidered in ^dBion.

T„ E nervous fyftem is fufceptiblc of two kinds,
of adtion; one wliich is confined to our fcnlitive
faculty ; and another which affecls our vital and
vegetative fundtions only. Voluntary motions
and fenfations belong to the firfl: of thcfe ac-
tions ; the influence of the nerves on digeftion,
circulation, and fecretion, to the fecond. The
fympathies and phyfical changes which arc the
confequencc of certain ideas, or of certain pal-
lions, feem to participate in the cffecl; of both.

Senfatioris may be divided into external, in-
ternal, and Jpontaneous. The firfl are produced
by the impreflions of external bodies on our
fenfes. The fecond by changes which take
place in the flatc of the internal parts of the
body, to which the nerves are diflributed. The
third refemble both the former as to effeefl ; but
they are caufed by a change in the nerves, or in
the brain itfelf, without any external excite-
ment. The fenfations we experience in dreams
are limilar to thofe produced in us by external
bodies : they originate, however, from motions
produced in the brain by internal caufes, and
may be excited or allayed by certain medi-
cines.

Men

lio L.IX. Brainof Animalswith Vertebra.

Men M'ho have loft their eyes frequently dream
that they lee ; thofe who have had their limbs
amputated, imagine fometimes, even when awake,
that they experience pains in the abfent mem-
bers .

Ihefe'-kind of fenfations tend to throw a
light on the nature of others. They confirm
what feclions and ligatures of nerves had already
Ihewn ; that fenfation does not refidc in the ex-
ternal organs, but merely in the centre of the
nervous fyltem, and that the external organs
ferve only to receive the adion of external bo-
dies, and to convey it to the nerves, by which
it is propagated to a greater dilfance.

' They alfo farther demonftrate, that this pro-
pagation is not produced by any matter or
concuflion, vvhich external bodies could alone
communicate, but by a change in the date of
the nervous fubftance, which may arife from
internal caufes.

This change may alfo he produced by exter-
ternal caufes altogether different from thofe
W'hich ufually occafion it. A blow on the eye;
the Conrad of two different metals, one piece
being placed under the upper lip, and another
under the t-onguc, make us perceive a fiaJh in
the fame manner as if light had really fhuck
the eye: this can only take place in confcqucncc
of a change in the optic nerve fimilar to that
\vhich light itfclf produces.

Other phccnomcna afford fomc farther no-
tions

Art. II. Action or the Nervous System, i i i

tions refpecfling the nature of this change. It
feems, for example, that the fenfitive faculty is
confumed or exhaullcd, not only in a body fa-
tigued by too lively or too long continued fen-
lations, but alfo in each particular organ. Feeble
Jenfations are fcarcely perceptible when they
I'ucceed thofe that arc much Itronger ; a fenfa-
tion becomes weaker by duration, though the
external bodies which caufe it remain the lame:
for example, if at twilight we look Iledfalily
towards a point of the fky, in which fomeobfeure
body appears upon the a'zurc ground, and after-
wards turn the eye to another part of the Iky,
we iball flill continue to fee the figure of the
obfeure body; but that figure vill then appear
more luminous than the rcll of the (ky. The
caufe of this is, that the part of the retina, on
which the fhade fell, receives (frongcr impref-
lion from the light than the part of the fame
membrane which was exp'ofed to its rays before,
w hile the former part experienced a kind of re-
pole. For the contrary reafon, after the eye has
been fixed on a very luminous body, it fees for
a time an obfeure fpot of the fame fhap>e as that
body.

The other fenfes afford fimilar examples, but
they arc not fo evident; becaufe in this we have
the advantage of comparing two parts of the fame
organ, which have been both aefed upon, and
one of which has experienced the action for a
longer time than the other.

This

112 L. IX. Brain OF Animals WITH Vertebr.*^

This experiment (hews that the nerves arc
>Jiot merely palTive agents with refpedl to our
fcTifations ; and that they are not fimply the con-
dudors of a matter furnifhed by external bodies,
nor even the refervoirs of a matter in which
thefe bodies may excite vibrations, but that the
fubftance which produces fenfation is liable to
be confumed, or to lofe its adivity, by exertion.

There are phaenomena which fhew that the
general fufeeptibility of the nerves, for receiv-
ing fenfations, may vary in confequence of
caufes external to the nerves themfelves, and
^ which can only operate by altering their fub-
ftance. Certain medicines weaken or revive
that fufeeptibility — inflammation frequently en-
creafes it to an exceffive degree. Does this take
place in confequence of an increafed fecretion
,of the nervous'matter ? the mod: remarkable
change that occurs in the fufeeptibility of nerves,
is deep. It is not unnatural to fuppofe that
this change maybe occafioned by the temporary
'lofs of the fubftance which is clTentially fenfi-
tive. But how does it happen that deep depends,

' in a certain degree, on the will ? Why do we
awake fuddenly, or from caufes which do not
appear calculated toredore that fubflance? Why
does cold' produce deep? From thefe obferva-
tions may it not rather be fuppofed that this
date is the cfTedt of a change in the chemical
nature of tlie nervous fiibdancc ?

But whether the fubllance contained in the

nerves

Art. II. Action of the Nervous System, i ij

nerves is exhaufleJ by fenfations, or whether it
merely undergoes an alteration in its chemical
conipofition, and becomes, as it were, natura-
lized, it inufl remain in the nerve throughout
the whole of its coui fe, and leave it only at one
of its extremities. It docs not, however, rc-
femble the blood in the veilels, cither as to the
manner in which it is retained, or in w'hich it
moves in the nerve. There is no evidence of
the nerves being tubular. No phrenomenon in-
dicates that any matter efcapes from them w hen
they are divided. Befides, what vcirds could
have parictes fulacicntly compavfl to retain fo
lubtile a fluid as that of the nerves nuifl: be.
It ks fur more probable that it is I’ctained in the
nerves, in the fame manner as the elcdric mat-
ter is in eleclric bodies, by communication and
infulation; and that the nervous fyftem is its
only condudor, while all the other parts of the
animal body arc, with refpecl: to it, cohibent
lubftanGCs.

In whatever manner the received aclion is
tranfmitted, it is neceffary, at leaf! in all the
higher orders of animals, that it Ihould be pro-
pagated to the brain. But what part of the
brain is particularly defined to receive its im-
prelbon ? Confiderable portions of that vifeus
have been loft by wounds, without producing
any diminution in the fenfitive faculty, WTen
wounds have penetrated farther, they have caufed
pains and convulficns which have too much
VoL. II, I altered

114L. IX. Brain OF Animals with Vert ebRj^.

altered the refult of the experiment. Thefe
means, therefore, are not capable of refolving
the queftion. It has been endeavoured to form
fome conjectures founded on the flrucd:ure of
the parts. It has been generally imagined that
the common fenforium muft be found in fome
central part, with which all the nerves might
be fuppofed to communicate ; fome havechofen
for this part the pineal gland, others the cor-
pus callofum; but the latter exifls only in the
mammalia and the pineal gland, only in red-
blooded animals ; the latter even is not very ap-
parent in all fifhes. The cerebellum is the only
part of the brain which conflantly cxids in all
animals that have a vifible nervous fyftem; and
on this account it might have fome claim to the
pofTclFion of this common fenforium : but it
has been fuggefted by M. Soemmering, that a
folid part is not fufficiently moveable, nor al-
terable, with fudicient promptitude, to admit
the iinprcflions of the nerves with that rapidity
which really takes place. Having befidcs ob-
ferved, that all the nerves appear to arife me-
diately, or immediately, from the parictes of
the ventricles, and that thefe ventricles always
contain a certain quantity of water ; he has fup-
pofed that it is precifcly this Iluid which an-
swers all the conditions of the j)ioblcm, and
that it ought to be regarded as the common cen-
tre of fcn.'ation.

To trace the nervo s n.otijn to its centre, and

to

Art. II. Actig.-^ of the Nervous System. 115

tocflabliih, with certainty, what M’e have hi-
therto advanced only as conjeeflures, more or
lefs probable, is a tafle which the anatomill has
yet to perform.

How does it happen that an idea or linage, of
which we are confeious, is formed within us, at
the moment this change takes place in the ner-
vous fyllem ? How are thofe ideas accumulated
in our memory ? I3y w hat means is otir imagi-
nation able to re-produce them, and our judg-
ment to combine them, draw conclulions, and
form abllracdions from them ? Thefe, and other
eftedls of habit and attention, the mctaphylician
may cftablilh hillorically, but the phyfiologilt
cannot explain.

Phyfiology, however, flicws us that there is
a certain order of corporeal motions w'hich cor-
refpond exac'tly to thofe fenfations and combi-
nations of ideas : ftudy, too long continued,
produces a fenfation of fatigue in the brain.
Certain dates of difeafe change the natural order
of ideas ; fiipj^refs, or conifantly prefent them
of a certain kind ; perplex and diforder the ima-
gination : age renders our ideas lefs vigorous ;
wine and opium produces confiderable changes
in them. Other aliments, or other medicines,
produce lefs important alterations ; but each
operates according to its fpecies, and according
to the difpofition. of the fubjecT:. Befides, the
imagination and the will produce phyfical eftecis
on the body, which feem to be a repercuflion of

i 2, the

1 i6L. IX. Brain of Animals with Vertebr.^.

the influence which the phyfical changes of the.
body has on them.

Thefe efiecflis of the will and the imagination
conffitute two other clalTes of animal adions,
originating in the nervous fyftem. That v/hich
includes voluntary motion was confidered, in
the firfl: volume of this work, in treating of the
mufcular fibre : it was there fhewn that the
nerves are the organs by which the will excites
the contraction of mufcles, and that it is pro-
bable this contradion takes place in confequence
of a chemical change which the nerve produces
in the fibre. But is the matter that caufes this
change the fame as that which excites fenfation,
and is it tranfmitted by the fame portion of
nerve ? How does it happen that, in certain
difeafes, wepreferve the free ufe of our members,
while they are totally deprived of fenfibility?
Is this the confequence of an alteration which
affeds only the external organ of feeling, and
not the nerve? In the night-mare, why is our
Ifrong dclire to efcape from the imaginary ob-
jeds that opprefs us inedcdual, and w hy is the
w ill incapable of producing the final lefl: motion
in the body ? When a nerve, which has been di-
vided, is afterwards united, why is motion only
re-eflablifhed, and not feniation ?

Some have fupj^ofed that the envelopes of
the nerves form the condudor of their moving
power, and their medullary part that of their
ienfibility. To the rcafons which they have ad-
vanced

Art. II. Action of the Nervous System, i 17

vanccd in fiipport of this opinion, wc may add,
that the envelopes communicate >vith the ven-
tricles by the plexus choroides, which are con-
tinuations of the pia-mater. It mull be confcTs-
ed, however, that this idea can as yet be regarded
only as an hypothelis.

There are eifeebs which belong to the imagi-
nation, as voluntary motion belongs to the will ;
they are confined almoll entirely to a fudden
augmentation of certain fecretions, or the ac-
cumulation of blood in certain paxts. Ik-fore
wc attenijit to explain thefc clfecls, it is nccef-
fary to enquire how far the nervous fyflem par-
ticipates in the purely vegetative fuikbions of
our body.

The part it {>erforms in that refpedb is very de-
cided. We know that the influence of the nerves
on the vital organs, and of the latter on the
nerves, is reciprocal. (Tief, or an exceflive
application of the mind, alters digeftion, and
diminilhes the fecretion of the gadric and fe-
minal fluids. On the ocher hand, an over-loaded
domach blunts fenlihilit?, and induces deep. If
this kind of excefs be too frequently repeated,
dupor fei/.es the mental faculties. Too great a
wade of the fpermatic fluid dedroys memory,
extinguidies imagination, and produces extreme
irritability and fearfulnefs. Remedies, calcu-
lated to redore the powers of the mind, give
alfo new energy and vigour to the vital organs.
The difeafes which mod enfeeble the powers of

I 3 percepti.-jn

iiSL.IX.Brain of Animals with Vertebr-«.

perception and undcrftanding, alfo reduce the
body to an inert ftate, which is fpeedily follow-
ed by difTolution. Mental excitation is ufually
accompanied by heat, irritation, and an increafed
energy in all the vital motions,

Upon an attentive examination of this fuh-
jedt, it will appear that the part the nerves per-
form, in all thefe fundlions, may be reduced to
their influence on the irritability of the arteries:
by preferving this irritability the' nerves pro-
mote circulation to the extremities of the vef-
fels, and keep up all the fecretions. When the
excitement of the nerves heightens the irritabi-
lity, the fecretions are augmented.

All the phyfical changes that take place in
the body, in confequcnce of the images that oc-
cupy the mind, belong to the fame clafs of
adfion. In general the mind polTefles no influ-
ence over the organs of circulation, and the
w'ill cannot flop their motion : but when lively
images heighten the excitement of the whole,
or a part of the nervous fyftem, the mental
influence extends to thofe mufcular fibres which
produce circulation : thus the hope of a much
defired event caufes the heart to palpitate.
Voluptuous ideas make the blood flow into
the cells of the corpora cavernofa of the penis,
and produce eredtion ; anger or fliame impclls it
to the Ikin of the face, whence it is driven back
again by the rc-adlion of the vefl'cls ; this is the
reafon why thefe paflions produce alternate

blufliin|j

Art, II. ActionoftheNervol’sStstf.m. 119

blufhingand palcnefs. Sudden terror inftantly
augments the fecrction of the Huids of the in-
tellines, and caufcs a diarrhoea. The fight ol a
good meal occafions a great fecrction of faliva
in a hungry man ; even mentioning viduals is
fufficient, according to the common phrale, to
make bis moiilhnatcy\ in the fame manner fpeaking
of difgufiing fubfiances, ferves to ficken the
Itomach of men of delicate feelings. Exceflivc
forrow or joy increafes the fecrction of the tears
fo confiderabiy, that they cannot flow through
the lachrymal points, but fall upon the cheek.

In other cafes the adion of the imagination
does not extend beyond the nervous fyrtem ; it
is confined to the produdion of fenfations in
certain parts of the body» independently of any
external impreffion. Fear and uncertain hope
always excite a fingular fenfation in the prae-
cordial region. This fenfation, which doubt-
iefs takes place in the nervous plexus of that
region, is ufually the precurfor of that alvine
excretion which is excited by the nerves pro-
ceeding from thefe plexus ; in the fame manner
a?, by a contrary movement, the accumulation
of blood in the corpora cavernofa of the penis
precedes that vivid fenfation which has reached
Its height at the moment of the expulfion of
the femen. Efforts made to recoiled certain
painful feelings which we have experienced,
Ibmctimes bring back thofe fenfations them-
fclves.

I4

The

1 20 L. IX. Brain OF Animals WITH Vertebra.

The fufeepribility of the nervous fyflem to
be thus governed by the imagination, may be
more varied than the capacity it poirefiTes for
receiving external impreflions. The age, fex,
and health of the individual ; the manner in
which^a perfon has been educated, either with
refpe^t to his body or moral principles ; the
empire which reafon holds over his imagination,
and the temporary ftate of his mind, all produce
in this refpeCl aftonifliing differences ; which
may be compared to thofe that difeafe, fleep,
medicines, &:c. may occafion in the fufeeptibi-
lity of the nerves for external impreflions.

There appear befides, in the nervous fyftem,
certain phaenomena w'hich depend on the union
of different nerves, whether that communica-
tion be produced by cords palling from one to
the other, or through the medium of the brain.
Thefe phaenomena are called fympaihirs : they
conliff of involuntary motions, or rather of fen-
fations, experienced in places different from
thofe that are aflecfted. Thefe fenfations do not
feem -to depend upon the influence of the will,
or the imagination, and frequently eyifl: while
we are ignorant of the place rc*ally affeded, or
the motion that has occurred.

The fncezing which fuccceds to irritations
of the noflrils, affords an example of the fym-
pathy produced by the union of nerves : the
nerves of the noflrils, which come from the
ophthalmic branch of the fifth pair, arc conned-

Art. II. Action of the Nervous Svstem. 121

cd by the fympatheticus major, with the nerves
of the diaphragm, and by this means the ex-
citement is communicated. The fneezing
which takes place upon looking at a bright
light, is to be aferibed to the union of the cili-
ary nerves with the fifth pair : the irritation is
communicated to the nol'e, and thence to the
diaphragm.

Another example of the lame kind coniills in
the great changes which the eyes prefent in dif-
ferent internal difeafes of the body. Thefc
changes, fo important to the phyfician, are al-
moll all produced by the union of the fympa-
thcticiis major with the fifth pair, and by that
pair with the ciliary nerves.

Sympathetic aefions occur dill more fre-
quently, when different parts of the body re-
ceive branches of the fame nerve, which may
communicate irritation.

Thus tears are excited by a drong finell. This
is occafioned by the ophthalmic nerve fending
at the fame time branches to the nodrils and the
lachrymal gland.

The vomiting produced by pudaing a finger
into the throat, is owing to the didribution of
the eight pair of nerves, which go both to the
pharynx and the domach.

This eight pair, or nervus vagus, and the
great intercoftal or trifplanchnicus, are the
nerves which produce the greated number of
this kind of phenomena, bccaufe they are didri-

buted

122 L. IX. Brain ofAnimalswithVertkbr.^:.

buted to a great number of parts, and form
unions M'ith a great many other nerves ; they
have therefore been named Jympatheliciis major ^
and fympathelicus mediiis.

To conclude this brief account of the adlion
of the ne.rvous fyflem, we Ihould alfo notice
the influence which the nervous fyflem of two
different individuals may exercife upon each
other. The abufe which has been made of this
influence by impoflors, and the exaggeration
with which it has been deferibed, have brought
the fubjeefl: into fuch contempt, that philofophers
can fcarcely think themfelves permitted to
mention it.

It muft be confelfed, tlnit it is extremely diffi-
cult, in the experiments which have this adion
for their objeefl-, to diflinguifh the elfei3: of the
imagination of the perfon fubjc(fl;ed to the ex-
periment, from the phyfical effe<fl produced by
the operation ; and the problem is frequently
very complicated. The effects, however, ob-
tained on perfons who were infenfiblc before
the procefs commenced, thofe that appear in
others after the operation itfelf has rendered
them infenfible, and thofe exhibited by dif-
ferent animals, place it beyond all doubt, that
the proximity of two animated bodies, in cer-
tain fituations, and with certain motions, pro-
duces a real effect, independent of any partici-
pation of the imagination of one of them. It
alfo appears fuffidemly evident, that thefe ef-
fects

Art. II. Action OF THE Nervous System. 123

feifis take place in confequence of a certain com-
munication being eflabliflicd between their ner-
vous fyftems.

Finally, it were to be wilhecl that we were
able to compare the action of the nervous fyllcm,
in the different orders of animals, in the fame
manner as we fliall compare its ffrutflure and
diftribution : but this examination prefents in-
furmountable difficulties ; becaufe we have no
means of difeovering the manner in which ani-
mals are affeeffed, except by very equivocal
marks.

In all animals that have nerves, voluntary
motions, and direcT: fenfations, take place by
the fame means as in man. I'hc differences in
their motions depend partly on the intrinfic mo-
bility of their fibres, and partly on the difpo-
fition of their mufcles, and the parts to which
they are attached. Thcfe differences have been
explained in the firft part of this work.

The differences in their fenfations depend on
the number of their fenfes, and the perfeclion
of the organs belonging to each fenfe. The
animals that approach neareft to man have their
fenfes equal in number to his. In certain fpe-
cies fome of thefe fenfes are even more perfecT:
in the ftrudture of their organs, and fufceptible
of more lively and delicate impreffions than
ours : on the contrary, in proportion as animals
are removed from us, the number of their fenfes
and the perfection of certain organs are dimi-

niffied ;

• •

124 L. IX. Bratk ofAnimals with Vfrtebrak.

nifhed ; but perhaps feme animals at the fame
time pofTefs fenfes of which we can form no
idea. We (liall particularly confider thefe fub-
jcL^s in this fecond part of our work.

We know not Avhethcr there are differences in
the inrrinfic fenfibility of the nervous fyftem of
different animals ; that is to fay, whether an
equal imprefiion, applied to an organ equally
perfedf, would affeifl every animal with the fame
force. This it is evident we fhall never be able
‘to learn.

The animals next in order to man have, like
him, fpontaneous fenfations. Images are ex-
cited in them at times when they receive no
immediate impreffion from external objefts.
Dogs and parrots dream; but we are not certain
whether the very inferior fpecies of animals ex-
perience fimilar fenfations.

The pafiions produce effedls in animals which
rcfcmblc thofc they produce in us. Love is
manifcflcd in the fame manner in all clalfes :
terror occafions a difeharge of excrements m
quadrupeds and birds : fear makes them trem-
ble, and even renders infedts immoveable; but
the other animals afford fewer examples of thefe
kind of phaenomena than man, bccaufe they are
not maflcrs of their imagination, cannot diredt
it towards certain objcdls and create for them-
felves fadlitious paffions. Wc are even ignorant
whether their imaginations can, like ours, be
wrought up to fuch a pitch as to make them

experience

Art. II. A CTION OF THE Nervous System. 125

experience emotions of anger, dclire, or fear
from fimple ideas or fimple recollections ; and
whether the real prefence of the obje<fts which
caufe thefe paflions, is not always necelPary to
excite them in the inferior animals : ve know,
however, that thofe which approach nearclt to
us, the mammalia and the birds, have their lor^
rows. Theafflidion they feel oiT the abfence or
lofs of a companion, friend or benefador, is ma-
nifefted by evident ligns, in the fame ntanner
as they teftify their attachment without any
temporary inducement.

The fame animals exhibit frequent proofs of
a very perfed memory ; fome even appe;ir to
pofl'efsa certain degree of judgment.

But does any thing limilar exift in the inferior
clafTcs, and particularly in the lowed? of this
we fhall probably remain always ignorant.

With fo much refemblance in the drudure of
the nervous fyftem, in its mode of adion, and in
the number and ftrudure of the principal ex-
ternal organs, why is there fo vaft a difference,
as to the total .refult, between man and the moft
perfed animal ?

Is this owdng to a more accurate proportion,
in the relative perfedion of the external organs,
fo that one does not too much furpafs another t
or has the internal organs, in which are per-
formed all the intermediate operations between
the fenfation received and the movement exe-
cuted, that is to fay, the organ of perception,

memory

126 L. IX. Brain of Animals with Vert ebr.?:.

memory and judgment, greater differences
than have yetobferved? or finally, is the
fubflance by which thefe proceffes are efie<fted
of a different nature.^ Thefe, however, are not
anatomical queffions.

The fympathies or effeeffs refulting from the
connections of nerves with each other, and the
influence of the nerves on the vegetable or ve-
getative functions, are fubject to the fame laws
in naan and the other animals.

Article III.

Cc.icral Campari fen of the different Nercous

Spjlems.

On comparing together all the nervous fyffems,
■we find only one common part, which is a iin-
izle tubercle, ficuated at the anterior extremity
of the fyffem, and always producing two lateral
and tranfverfe fafciculi or crura, which unite it
to the reft of the fyffem.

This part appears always to correfpond to
that named cerebellum in man. The cerebellum
of animals that have red blood and vertebrae, is
always preceded by fevcral pairs of tubercles,
forming ufually a larger mafs than the ccrcbd-
liim itfdf, and united to the rell of the fyffem

by

A. III. Comparison of Nervous System. 127

by two longitudinal fafciculi or crura, which are
interwoven in crofling with thofe of the cere-
bellum. This union takes place in fuch a
manner that both are confounded in the com-
mon mafs which forms the root of the medulla
oblongata, and medulla fpinalis, and leave no
fpace between them. Thefe tubercles make
what we call the cerebrum. They prefent con-
fiderable differences in the various clalfes of
animals, which we fliall explain in fubfequent
articles.

In the white-blooded animals, or thofe that
have no vertebra;, there are alfo tubercle* fitu-
ated before the part correfponding to the ce-
rebellum ; but thefe tubercles are a great deal
fmaller, much removed from each other, and
conneded with the cerebellum only by feparate
nervous filaments. The crura of the cerebellum
leave a large interval between them, which re-
ceives the oefophagus as in a collar.

I'he long produdion of the brain, called the
medulla oblongata, and medulla fpinalis, in ver-
tebral animals, is fituated on the back, above
the inteflinal canal, and is inclofed in the canal
of the vertebrae. The two fafciculi which form
it are intimately united, and no trace of their
feparation remains, except a longitudinal fur-
row before and behind. But in the animals that
have no vertebrse, when this produdion exiffs, it
is formed below the oefophagus by the union of
the two crura of the cerebellum. Thefe two

fafei-

128 L.IX. Brain of Animals with Vertebr.^.

fafciciili commonly remain diftlruTc througliout
the greater part of their length, and are only
united at dili'erent fpaces by knots from which
the nerves proceed. This produClion, however,
irequently does not exid. In fome animals
with white blood, which have no elongation of
the medullary fubftance, as in the Molufca, the
nervous trunks, which are derived from the
crura of the cerebellum, enlarge and form gan-
glia, or two or three nerves unite with each
other to produce a common ganglion; and in
general it is only from their ganglia that the
nerves, which are didributed throughout the
body, rake their origin.

In thofe white-blooded animals that have a
knotted and double medullary production, that
is to fay, the infeds, the crudacea, and certain
worms, the nerves all arife from the knots or
ganglia of the medulla, or from fome of the an-
terior ganglia of the cerebellum.

In the red-blooded animals the nerves of the
fpine arife frorn the medulla fpinalis in two
bundles of medullary filaments, which unite
after the pofterior bundle has formed a ganglion.
They afterwards feparate into two trunks, the
anterior of which communicates with the great
fynjj>athetic nerve by one or tw"0 filaments, and
a ganglian is always formed at the place where
they unite.

The nerves of the brain do not arife precifely
in the fame manner, the dllicrcnt tubercles
n which

A. III. Comparison OF NtRvous System. 129

which form it, however, feem to fervc as gan-
glia. This at leall is evident in the corpora
firiata, with refpecT: to the oltadory nerves; and
in thethalami nervorum opticorum, with refped
to the optic nerves. Thcnerveof the fifth pair has
a particular tubercle, which is very confpicuous
in fiflies. The corpora olivaria may be confidcred
as the ganglia of the eighth pair. There are no
tubercles apparently belonging to the third and
fourth, though the tejles may perhaps be afllgn-
ed to the latter.

The fympatheticus major, which isconflantly
found in all red-blooded animals, exifts in none
of thofe with white blood; unlefs wc fliould re-
gard, as that nerve, the tw o nervous cords w'hich
unite all the ganglia, and which wc have called
medulla fpinalis in the cruftacea, infeds, and
worms.

Were this opinion adopted, a medulla fpina-
lis would no longer be attributed to thefe ani-
mals, and the abfence of that produdion w’ould
then be the common charader of all the white-
blooded clafies.

K

VoL.II.

Arti-

130 L. IX. Brain ofAnij^ials\vithVertebr>e.

I

Article IV.

Dcfcription of the Human Brain.

A. The Brain of JMan 'cicxvecl on its fuperior

Saif ace.

w„ EN we remove the upper part of the cra-
nium and the dura-mater, there appears an oval
fubftance, the length of which is to its breadth
nearly as 4: 3. . This oval contradts a little an-
teriorly. Its convexity is pretty uniform, and
nearly half as high as broad.

A deep filTure, which receives the falx, divides
this oval longitudinally into two nearly equal
parts, called hemifphercs.

In this view' we do not fee the cerebellum,
becaufe that part is entirely covered by the
brain.

The furrows of this furface are very numerous
and deep. The depth of fome is equal to 0.021
metre. They convolute in various dircdlions.
The parts of thefe intervals, which arc vifible
externally, arc about o.oi metre broad, more or
lefs ; thefe convolutions have the appearance of
a number of fmall inteflines.

Reckoning ihofe which touch the fiffiirc that
divides the two hemifphercs, we fiiul eighteen
.or twenty. Reckoning tranfverfely, we find ten

or

Art. IV. The Hlman Braix. 131

or twelve: but thefe numbers depend upon that
part in which they are counted.

The fuiTacc by which each hemifpherc is op-
pofed to the other is plane; \\c find turrows in it
as well as in the convex, rurface. Its height is
0.04. The falx, which is not fo high, docs not
feparate thefe furfaces entirely; and the hemi-
fphercs unite below the falx by vcfiels and cel-
lular fubllance.

On feparating the hemifphcres, we obferve,
at the bottom of the fiHlire, w hich divides them,
a kind of bridge of medullary fubllance, which
extends from the one to the other, and difap-
pears under them. It docs not cover the whole >
length of the fiirure, but leaves anteriorly a
fpacc equal to one-third of its length ; and
polleriorly another fpace which is double the
former: the bridge then is only half the length
of the hemifphcres. We obferve that it folds
under itfelf at both extremities.

B. The Brain of ]\[an xiexced laterally.

In this view' the fuperior margin of the brain
prefents a curved line, w hich refembles one half
of an elliplis ; but its inferior margin is very
irregular. It firft exhibits a concave line,
which extends downward from the pofterior ex-
tremity to the middle of the total length, which
is alfo the loweft point. The cerebellum, which

K 2 is

JJ2 L. IX. Brain ofAnimalsvvith Vkrtebr.®.

is entirely covered by the cerebrum, is fituated
under this concave line.

The area of the cerebellum, viewed thus in
profile, is fcarcely equal to one-eighth of that
of the cerebrum ; the part of the brain fituated
above the cerebellum, is called the pofierior lobe
of the cerebrum ; the part projeefting down-
ward, which is terminated by the before-men-
tioned concave line, is called the middle lobe ;
this line bends fdrwai'dj and after being conti-
nued in a convex form, terminates in a deep
fulcus, which is diredled backward on the late-
ral furface of the brain, and completes the divi-
fion of the middle lobe from the anterior. The
anterior lobe, fituated before the fulcus, occu-
pies nearly one-fourth of the whole length of
the cerebrum ; but inferiorly, and towards the
middle line, it is prolonged backward to the in-
ternal fide of the middle lobe, at the deprefllon
which contains the pituitary gland.

The furrows on this lateral furface of the
brain are as numerous, and as irregular, as thofe
on its fuperior part.

C. The Brain of Man viciced infa'iorhj.

The lower furface of the human brain c.xhi-
bits four eminences, which correfpond to the
foffa; of the bafis cuviii: one of thefc eminences
is fituated pofieriorly, and comprehends the in-
ferior

133

Art. IV. The Human Brain.

ferior furface of the cerebellum, the medulla
oblongata, and the-pons Varolii; the two lateral
and intermediate eminences form the middle
lobes of the cerebrum: the two that are fit'.iateJ
farthcH: forward, are called the anterior lobes.

Between thefe four eminences there is a deep
depreflion, which contains the infundibulujTi,
the tubercul.i mammillaria, and the origin of
the optic nerves, and above which, in this in-
verted pofition, we obferve the pituitary gland.

The poftcrior eminence is an irregular oval,
the tranfverfe diameter of which is, to the lon-
gitudinal, nearly as 4:3: this oval is deeply
notched polleriorly, in confequcnce ot the di-
vifion of the cerebellum ; anteriorly, on the
contrary, the pons Varolii forms a rounded pro-
jedlion, correfponding to the depreflion in the
middle of the bafe of the cranium.

The exterior outline of the tivo lohea of tbd
cerebellumy is round; their furface is nv-d. rately
convex, nearly equal, and has two remarkable
eminences, viz. one a little without, and behind
the place where the pons Varolii lofes itfelf in
the fubftance of the brain ; and another, which
is larger and oval at the anterior part of the
line by which the two lobes of the cerebellum
join. Their whole furface is marked with flight,
and nearly parallel furrows, about a line diflant
from each other; their direction is almoft paral-
lel to the edge of the lobes, except towards the
anterior, which they cut obliquely.

K3

The

1 34 L. IX. Brain" of Animals with Vertebr/®.

proce/fus afumlaris, or pons Varolii, reprc-
fcnts a kind of crefccnt ; its anterior edge is
convex, and almoft femi-circular ; its poftcrior
edge is concave.

Its furface exhibits a medullary fubflance, the
fibres of which are parallel to each other, and
to both edges ; they approximate outwardly, to
form the two horns of this kind of crefeent, and
are loft in the cerebellum, under, or rather upon
the little round eminence. This annular pro-
tuberance correfponds to the bafilar fofta of the
os occipitis : its greateft breadth is double its
length.

The medulla oblongata appears immediately be-
hind the pons Varolii, by which it feems to be
bound, as with a collar ; its bafe is broadeft,
and it contrads, by degrees, fo as to reprefent
a kind of bulb : we obferve a longitudinal fur-
row on its middle, and another on each of its
fides; within each lateral furrow there is a flight
oval eminence, which both together are called
corpora olivaria: between each corpus olivarium,
and the middle furrow, there are fome longitu-
dinal fibres, called corpora pyramidalia ; there is
a fmall triangular depreflion between the bafes
of thefe pyramidal eminences, and the poflerior
■edge -of the pons Varolii. Another depreflion
is alfo obferved betw'cen the corpora olivaria,
which feparates them from the fame edge. The
fibres of the portion of the medulla oblongata
which is fitualed without each corpus oliva-

riuin.

Art. IV. The Human Brain. i3S

rium, are dircdlcd obliquely outward and for-
ward.

The two lateral eminences, or middle lobes of
the cerebrum y are- nearly of a triangular (liape ;
they are marked by irregular furrows, like all
the other parts of the furface of the cerebrum ;
they are feparated frr5m the anterior lobes by a
groove, called the fiffure of Sylvius, whjch re-
ceives the pofterior edge of the fmall wings of
the fphenokl bone.

All the parts before thefe two eminences be-
long: to the anterior lobes of the brain ; thefe
are lefs convex, and Icfs elevated ; they likewife
exhibit irregular furrows, and in this inverted
portion the olfatflory nerves are fituated upon
them, parallel to the middle line which fepa-
rates them.

To didinguifli the parts fituated between thefe
four eminences, the cerebellum, and the pons
Varolii, muft be prelTed backward, and the mid-
dle lobes towards the fides : we then perceive
the crura of the cerebrum, which are two cy-
lindrical medullary bodies, and appear to the
eye to be the continuation of the medulla ob-
longata, after its pafiage under the pons Varolii:
they touch each other by their internal edges';
after proceeding forward, and a little outward,
they fink each on its refpedlive fide, under the
mafs of the cerebrum, between its anterior and
middle lobes : at this place, each of the crura
is croflTed by one of the optic nerves, which

K 4 arife

i

136 L. IX. Brain OF Animals WITH VERTEBRi?:.

arife from the fame depreOion, and are directed
forward, and obliquely inward, to unite in the
middle line. Between the crura of the cere-
brum, and the optic nerves, there is a fpace at
the pollcrior part, of which we obferve two
round white eminences, called tubercula mam-
'miliaria. The remainder of this fpace is occu-
pied by a cone, formed of an afli-coloured fub-
flance, and called infundibulum ; this cone is pro-
longed into a flender flalk, that adheres to the
union of the optic nerves, and terminates in the
pituitary gland, which, in this inverted pofition,
.is uppermoft, and covers it.

j ' I I

. D. Developement of the Brain.

■ *v *• -

To obtain a right knowledge* of the internal
paKs of the brain, it is ncc^eil^ry to divide the
crufa.cereBri immedia,te#flieforG the cerebellum,
and the pons Vardlii : we''’then find that the
cerebrum is connefled to the reft -of the brain,
^by only a crefeent, about 0,03 broad, which
makes prccifely the fedion of the crura, and
which occupies nearly the middle of the inferior
furfacebf the cerebrum, thus feparated.

The continuation of its fuperior margin is in-
terrupted by the fedion of the aqiicdnbl of Syl-
•vius, of which wc fliall fpcak hereafter. On
fcparating'a little the crura of the cerebrum, wc
obf?rvc a kind of fmall medullary bridge over

this

Art. IV. The Human Brain.

*37

this aquaeducl: : on the fuperior furface of this
bridge there are four eminences, which have
been named tuherculci quadrigemina.

The two fuperior a-nd anterior eminences,
called nates, are of an oval form, and rather
larger than the others ; the inferior and pofte-
rior, called teftes, arc round, but they are pro-
longed obliquely to the external lides of the
nates.

Where this prolongation meets the root of the
optic nerve, which, as we have already obferved,
crolles the crus, as it afeends obliquely back-
ward, we obferve another eminence, which may
be regarded as forming a third pair ol tubercles*.
Between the telles pofteriorly, there is a fmall
triangular fraenum, which is of a greyifli co-
lour, and fomewhat hard.

A little before the optic nerve reaches the la-
teral eminence of the tejlis, it is enlarged and
divided by a furrow into two parts ; the moft ex-
ternal of which forms a fmall oval tubercle, and
afterwards feems to expand over the pofterior
part of the large eminence, called the thalamus
nervi optici.

The fuperior furface of the two optic thalami,
which is lituated under the cerebrum, reprefents
a triangular fpace, having a notch polteriorly,
which contains the tubercula quadrigemina; the
hdes of this fpace are round, and the middle is

' depreffed

* Vicq-d’azir, pi. XVI, No. i4.

13!? L.IX. Brain OF Animals WITH Vertebr.'E.

dcprclTed longitudinally : on feparating the tha-
lami, we obfcrve that they are intercepted by a
cavity, called the third ventricle', this cavity is
alfo divided : there is extended, from one of its
furfaces to the other, a prodiidtion of a pulpy
and almoft fluid fubftance, which is named the
/oft commijjure of the optic thalami.

This ventricle communicates by the aquae- .
du6tus Sylvii, which palfes under the tubercula
quadrigemina, with another which is under the
cerebellum, and is called t\\Q fourth ventricle.

The anterior part of the third ventricle pene-
trates-between the tubercula mammillaria, and
the union of the optic nerves, to form a kind of
funnel of a pulpy fubflance, which we have al-
ready noticed, under the name of infundibulum.

Each fuperior edge pf the third ventricle
is marked by a white line, which is prolonged
backward, tb form the peduncle of the pineal
gland, which is a fmall oval afli-coloured body,
fufpended above the tubercula quadrigemina.
The fame white line extends forward towards the
lower part, and then bends fuddcnly back, to
join a thick medullary cord, which forms one
part of the anterior pillar of the fornix.

A little more forward we obfcrve a tranfverfe
medullary cord, wjiich pafles from one fide of
the cerebrum to the other, and which is called
its anterior commijfure.

There is andthcr commiflurc nearly fimilar,
over the entrance of the aqua^dudus Sylvii, ami

under

Art. VI. The Human Brain.

139

under the peduncle of the pinc.1I gland ; it is
named the pofterior commiffnre. The entrance of
the aqua^du^fl is denominated the anus.

Between the anterior commifl'ure, and the
union of the optic nerves, there is a (pace which
is inclofcd only by the pia-inater, and a very-
thin ftratiim of that pulpy fubflance which
lines the infule of the third ventricle; lids is
namCvl the vulva.

On the outfide, and before the optic thalami,
\vc find two eminences, which ;ireallo concealed
umicr the cerebrum ; thefe arc called corpora
flriata, on 'account of their internal texture,
which wc fliall deferibe in another place.

The corpora ftriata are broad anteriorly, where
they approach the middle line of the brain ;
they are contracted pofteriorly, and removed
from each other to make room for the optic
thalami ; they end in a fort of tail, which fol-
lows exacflly the outline of the thalamus, and
the root of the optic nerve, and are terminated
inferiorly by a fmall obtufe enlargement ; thus
each corpus ftriaium refembles a horfe-fhoe,
with one of the branches conliderably longer
than the other. In the natural polition of the
brain, this horfe-fhoe is fituated on its narrow-
ed: fide, fo that the large branch is uppermoff,
and a little more forward and inward than the
other.

In the furrow, which feparates the corpus
ftriatum from the optic thalamus of the fame
' ' fide.

140 L. IX. B.iain of Animals with Vertebrae.

fide, there is a band of medullary fubftance,
which takes the fame courfe as the furrow, and
IS named Unea femi-lunaris.

All the part of the cerebrum that is vifiblc
externally, is a kind ot appendix of the corpora
frriata, but an appendix which greatly furpafles
them in fize in man. The mafs of each hemi-
fphere is joined to the whole external margin of
the corpora ftriata. After proceeding down-
ward and outward, it turns upw^ard and inward,
to reft on that of the oppofite fide and join the
corpus callofum. The portion of this mafs
which joins the infleded cauda of the corpus
flriatum, forms what is called the middle lobe.

The pofierior part of the hemifphcres, and the
corpus callofum itfclf, bend downward, and the
inflefled part penetrates under the former, co-
vering the tubercula quadrigemina and the
optic thalami. In this manner, but ahvays con-
tracting, it arrives above the anterior commif-
fure of tlic cerebrum, where it is terminated by
two medullary cords, which penetrate into the
fubftance of each thalamus. This fold has ob-
tained the name of the fornix with three pillars \
pofieriorly it is united immediately to the in-
ferior furfaceof the corpus callofum ; anteriorly
this union is formed by two medullary lamina:,
which form a very thin partition, called/c/>/«;/;
lucidum. The margins of the fornix extend
backward, feparating at the fame time from
each other fo as to form a triangle, and defeend

into

Art. IV. The Human Brain.

141

into the interior of the middle lobe, prcfcrving
nearly the fame curvature as the caudae of the
corpora flriata. Behind each of thcfe margins
there is a fuelling of the breadth of a finger,
which hill keeps the fame curvature, and is.
called cornu amrnonis, or pcs hippocampi : under
the fame edge there is a grc) ilh Terpentine band
which appears fringed, and is named corpus jim-
brialntn.

The inferior furface of the fornix is marked
by one or two longitudinal flrite on its middle
and anterior part. Poncriorly ,we obferve feme
tranfverfc fibres, which are the continuation of
thofe of the corpus callofum. The different
folds of which the hemifpheres are compofed,
do not join each other by their internal furfaces;
they are intercepted by a large cavity in each
hemifphcre: thefe two cavities are i\\q anterior
ventricles of the cerebrum. With rcTpecl to their
form, they may be compared to an Italic capi-
tal f Tituated thus The vault of their fupc-
rior branch is formed by the corpus callofum,
and its floor by the corpus ftriatum : the de-
feending branch contains the cauda of the cor-
pus ftriatura anteriorly, and the cornu ammonis
pofteriorly. The angle formed by the union of
thefe two branches penetrates backwards into
the portion of the hemifphere which is fituated
above the cerebellum, where it forms a blind
cavity which bends inwardly; it has received
the name of the digital cavity : on its internal

furface

I42 L.IX. Brain OF Animals with Vertebras,

furtace there is a fmall eminence, called the
ergot or fpur.

The two ventricles arc feparated anteriorly
by the Jepiiim luctdum only, and they would
open into each other under the fornix, were it
not for a produdlion of the pia-mater, which we
lhall deferibe hereafter under the name of plexus
choroides, and which leaves them no commu-
nication except a fmall hole near the anterior
pillar. By the fame pafTagd they communicate
. with the third ventricle, and by that with the
fourth ; thus thofe four cavities may be faid to
form only one.

There is a fifth cavity between the two layers
of the feptum lucidum, but it has no external
communication. This is l\\c fifth ventricle.

The cerebellum is conneefted to the reft of the
brain by two medullary trunks, one on the right
and the other on the left, which feem to take
root in its internal fubftance, in order to pro-
duce a crucial intermixture of their fibres with
thofe of the medulla oblongata. The fibres of
the inferior plane of each of thefe trunks, are
continued to form the pons Varolii, and to unite
together on the middle line : th'ofe of the fupe-
rior plane form a more flcnder fafciculus, which
is direded towards the teftes, and which is join-^
, ed to the fafciculus of the oppofite fide, by a
very thin medullary lamina, called vahiiJa ce-
rebri. The poflerior edge of this valve is
united to the mafs of the cerebellum.

8 The

N

M3

Art. IV. The Human Brain.

The cerebellum is not in conta6l with the fu-
perior furface of the medulla oblongata, but is
placed over it like a bridge. The interlHcc be-
tween them is called t\\t four tb ventricle.

This cavity communicates with the third by
the aqutedudlus Sylvii. In the bottom ot this
, ventricle we obferve an angular imprefiion,
called calamus fcript or ius.

The cerebellum itfelf is divided into three
parts ; the two lateral, which arc moft conli-
derable, are called its lobes. The middle,
which is the fmallefl:, and concealed in the filTure
that feparates the two ocher parts, is named the
vermiform procej's.

E. Sections of the Brain.

There are different methods of difieifling the
brain, in order to fhew its ftrudturc. Some
fedions are vertical, others horizontal and ob-
lique.

1. Vertical SeRions.

The 100(1: important of the vertical fedions
is' that which divides the brain into two equal
parts, leaving the two hemifpheres, as well as
the corpora ftriata and optic thalami untouch-
ed ; and bifeding the corpus callofum, the
fornix, the three commiffures, the glandula pi-

nealis.

144 L.IX. Brain of Animals with VeIiteer.?:*

nealis, the tubercula quadrigemina, the pons
Varolii, and the medulla oblongata.

This fedlion fliows, ifl, that the corpus cal-
lofum, has a curvature nearly parallel to that of
the vault of the cranium, and that it folds un-
der itfelf both anteriorly and pofteriorly. 2dly,
That the fornix is a continuation of its pofterior
fold. 3dly, That the feptum lucidum is a trian-
gular I'pace, included between the corpus callo-
fum and the anterior fold of the fornix. 4thly,
That the anterior commifTure, the union of the
optic nerves, and the mammillary tubercle, form
a triangle which is almofl: equilateral. This
fedlion al fo affords a diftindl view of the great
fpace in the middle of the brain, which com-
mences anteriorly at the infundibulum, then
forms the third ventricle, the aqusedudlus Syl-
vii, and the fourth ventricle. The fedlion of the
latter is triangular ; that of the aquaedudl is
long and narrow ; that of the third ventricle is
nearly femi-circular, and its parr which dc-
fccnds towards the infundibulum, is almofl
fquarc. The divifion of the medulla oblongata
and pons Varolii, exhibits crucial fibres more or
lefs remarkable. Wc fomcrimes obferve a fafci-
culus arifing near the fourth ventricle, which,
after bending, gives origin to the third pair of
nerves.

A fedlion of the cerebellum difplays fome
medullary lineaments, reprefenting a tree with
five principal brunches, which arc fub-divided

twice

Art. IV. The Human Brain. 14^

twice in fLiccefTion into fmallcr ramifications.
This is called arbor vit<e. AH the parallel fec-
tions made more towards the lides exhibit the
fame figure.

On penetrating the interior of this vertical
fediion, towards the external lide, we dilcover
fevcral particulars worthy of notice: i. That
the peduncle of the anterior pillar of the fornix
palfes into the fubfiance of the optic thalamus,
to terminate in the tuberculum mamniillare. 2d,
That another medullary fafciculus departs from
this tubercle, and alfo traverfes the fubfiance
of the optic thalamus to near its fuperior fur-
face. 3d, That the fibres of the crura cerebri are
continued acrofs the optic thalamus to the cor-
pus firiatum, and acrofs the pons Varolii to the
medulla oblongata. 4th, That a fmall greyilb
line winds in a ferpentine manner round the
corpus olivarium internally. As this line is
feen in whatever direction that eminence is cut,
it is obvious that it muft: contain a body of a
very irregular furface, and covered with a thin
layer of a grcyilti fubfiance, the fections of
W'hich exhibit thele linear appearances.

£. Horizontal StBions.

The horizontal feefiions may commence with
the fuperior or inferior furface.

When we cut the two hem'ifphercs fuperiorly
at the level of the corpus callofum, we difeover

VoL, II. L the

146 L. IX. Braino F Animals WITH Vertebra.

the greateft medullary fpace that can be demon-
flrated in the brain. The grey fubftance ap-
pears on the edges only, all the reft is white, and
is named the centrum ovale of Vieiijfens.

If we difTcdl farther downward, the two an-
terior ventricles foon appear. From this view
we obferve that their anterior cornua arc ap-
proximated, while the poflerior are removed
from each other.

I'he corpus callofum being completely re-
moved, the fornix is rendered vifible, and we
can difeern very diftindly its triangular form.
After this we expofe the fifth ventricle, by fe-
parating the two lamina that form the feptum
lucidum. Then cutting the anterior pillar of
the fornix, and throwing the fornix itfclf back-
ward, we lay entirely open the fuperior furface
of the optic thalami, the aperture of the third
ventricle, the three commifTures, and the tuber-
cula quadrigemina. The eye may even pene-
trate into the infundibulum.

On making deeper fedlions, we obferve that
the interior of the corpora firiata is filled with
white ftriae, which feem to arife from the optic
thalami, and through them from tho crura of
the cerebrum. From the white firias being fe-
parated by others of a cincritious colour, thefe
eminences have obtained the name of corpora
jlriata.

Penetrating flill farther, wc obferve that the
anterior commifTurc of the cerebrum extends on

each

Art. IV. The Human Brain,

147

each fide into the fubftance of the optic thalami,
in a white line fornewhat refembling a bow.
The pofterior commiirure is loft almoft as fooii
as it enters the fubftance ot the optic thalami.

The tubercula quadrigemina, divided hori-
zontally, prefent an almoft uniform greyifli fub-
ftance.

The horizontal feiftions of the cerebellum ex-
hibit fome white lines pafting from right to left,
and which arc precifely thofe that form the
arbor vitae in the vertical fckftions.

The horizontal feebions of the medulla ob-
longata, and pons Varolii difplay the fame di-
reeftion in the fibres as we have already deferib-
ed. Thofe of the crura of the cerebrum have a
dark brown fpot internally.

On making horizontal fecUons in the inferior
furface, we difeover feveral remarkable circum-
ftances ; i . The pofterior fold of the corpus cal-
lofum, which forms inferiorly a large roil behind
what is properly called the fornix. 2. The two cor-
pora fimbriata, each of which proceeds from one
of the extremities of this roll, and extends to
the pofterior pillars of the fornix, the curvature
,of which they exadly follow. 3. The fecHon
of the crura of the cerebrum, in which we obferye
the black fpot, which in this view appears femi-
circular. 4. In this manner we fliew the infe-
rior furface of the fornix and lyra in the natural
fituation. Laftly, on removing the fornix, we
difeover the inferior furface of the corpus cal-

L 2 lofum.

T48 L. IX. Brainof Animals WITH Vertebra.

lofum, that is to fay, the roof of the lateral or
anterior ventricles, to the middle part of which
the leptum lucidum adheres by the two lamirue
of which it is compofed.

F. Of the Origin of the Nerves.

1. The Olfactory Nerve.

The olfadtory nerve lies under the anterior
lobes of the cerebrum, in a furrow near and pa-
rallel to the middle line.

The anterior extremity, which is fituated
upon the cribriform lamella of the os ethmoides,
confifts of a grey fubftance. The remainder of
the length of the nerve is white, and of a trian-
gular prifmatic fhape. Its bafe is enlarged and
divided into three roots, didinguidied by an
fqual number of white filaments, which termi-
nate in the grey fubflance of the brain. That
which is internal is diredled outward, until it
reaches the fUfura Sylvii, where it is loft. The
external afeends upon the internal furface of the
bemifphcre as far as the corpus callofum. The
middle one is much ftiortcr than the other two,
and is even fometimes wanting.

2. The Optic Nerve.

The optic nerve evidently arifos by the fibres,
which wcobferve at the fuperior part of the optic

7 thalami.

Art. IV. The Human Brain. 149

thalami. It defcends outwardly, and furrounds,
in the form of a ribbon, the crura of the cere-
brum, from which it is feparated on its internal
edge, but united to them by its external. It
approaches to the middle line before the infun-
dibulum, where it is intimately united with its
correfpondent nerve, in fuch a manner that
neither the eve nor the knife can difeover whe-
ther they crofs each other, or are only limply
joined. After this union, they feparate again
to go out of the cranium by the optic foramina.
The portion which is anterior to their union is
cylindrical,

3. The Oculo-miifcular Nerve.

This nerve arifes near the middle of the crus
of the cerebrum, a little before the pons Varolii^^
but its origin may be traced into the body of the
crus. It is a medullary filament, which, in
afeending, bends backw'ard under the floor of
the fourth ventricle. It has been ^rroneoufly
fuppofed that this filament proceeded to the tu-
berculum mammillare. This nerve is direcfled
a little towards the fide, in order that it may
pafs out of the cranium by the fpheno-orbitar
fiflure, after it has traverfed the dura mater,

4. The Pathetic Nerve.

Some filaments behind the telles, at the fide
of the little frtenum, form the origin of this

L 3 nerve.

T50 L. IX. Brain of Ani mals with Vertebra.

nerve. Farther back, on the valvula cerebri,
we obferve feveral white fibres, fome of which
extend to the pons Varolii, and the others di-
verge, more or lefs, from that direeflion. Thefe
fibres fometimes appear to contribute to the for-
mation of the nerve.

This nerve pafies between the middle lobe of
the cerebrum, and the adjacent part of the pons
Varolii, and the crus. After a pretty long curve,
it goes out of the cranium by the fpheno-orbitar
filTure, behind the pofterior clinoid procefles.

5. The Tri-Jacial Nerve.

Each nerve of the fifth pair arifes from that
part of the crus cerebelli which contributes to
form the pons Varolii, very near where the crus
palTes out of the cerebellum. M. Soemmering
afTerts that it may fometimes be traced into the
fubftance of that crus, until it is lofi: under the
floor of the fourth ventricle. It is very foft at
its origin, but it foon becomes very hard, and
is divided into a number of filaments, arranged
in the form of a flat ribbon. This' ribbon is
compofed of three fafciculi, on which account
the nerve has received the name of trigemiuous or
tri-facial. Thcfc fafciculi thcmfclvcs have each
a particular name, viz, nervus ophthalmicus,
maxillaris fuperior, and maxillaris inferior.

6. The

I

Art. IV. The Human Brain. 151

* ■ 6. The Abductor \ervc.

The fixth pair of nerves commence on the
pofterior edge of the pons Varolii, by fome fila-
ments which come from the fulcus that fepa-
rates that pons from the corpora pyrami-
dalia. 'Some of the filaments appear to rife from
the pons iifelf. They proceed diredtly under the
pons Varolii, a'dvancing towards the fpine of the
os petrofum, where they penetrate the cavernous
' finus, whence they are tranfmitted to the orbit
in the manner we fliall hereafter explain.

7. The Auditory Nerve, or Portio mollis of the
Seventh Pair.

The acouftic or auditory nerve appears to
commence by feveral white fibres, which we
obferve on the inferior furface of the fourth ven-
tricle, and which vary in number from two to
five. Thefe filaments approximate and defeend
to the fides of the bafe of the medulla oblon-
gata, and there form the origin of this nerve,
which feparates from the mafs a little more out-
wardly than the preceding. It is conveyed into
the internal ear, where we fhall follow its diftri-
bution in the article on the fenfe of hearing.

L4

8. The

152 L.IX. BraINOF AnIMALSWITH VzRTtBR/E,

8. The Facial Nei're, or Portio dura of the
Seventh Fair.

This nerve derives its origin from the fulcus,
•^hich feparates the pons Varolii from the me-
dulla oblongata, a little more outward than the
corpora olivaria. It arifes by a flat portion, and
by another which appears fomewhat more fi-
brous, but which is intimately united with the
former. It enters the canal of the dura mater,
which is common to it, and the portio mollis,
with which it palfes into the meatus auditorius
internus.

£). The GloJJo-pharyngeus, parvagiim, and nervus

fpinalis or acceforius, commonly called the

Nerves of the Eighth Pair.

The glolTo-pharyngeus, and the vagum, arife
from the fulcus, which forms the external boun-
dary of the corpus olivarium. The gloffo-pha-
ryngeus is fuuated farthell: forward, and is com-
pofed of three, four, or five filaments. The va-
gum is formed by a far more Confiderablc num-
ber, which occupy all the reft of the fulcus.

The fpinal nerve is formed by fevcral fila-
ments which arife on the fides of the medulla
fpinalis, as far down as the roots of the fourth,
fifth, and fomctinics the fevenih cervical nerves.
It approaches the vagum, and palTcs with it and
the gloffo-pharynpeus through the foramen la-
cerum pofterjus.

ro. The

Art. IV. The Human Brain.

153

10. The Great Hypoglojjal Nerves.

Thefe form the twelfth pair, though they arc
generally demoiirtratcd as the ninth. Each
nerve arifes from the medulla oblongata, a little
below and between the corpora olivaria and py-
ramidalia, by a great number of fmall filaments
w'hich make a kind of circle. Thefe filaments
prefently unite into two or three fafciculi, which
pafs through the os occipitis by the anterior
condyloid foramen.

Article V.

Of the Brain of Mammalia.

The brain of the other mammiferous artimals
contains precifely the fame parts as that of man,
and thofe parts arc difpofed in a fimilar order :
it varies, ho\vever, in the proportion it bears to
the reft -of the body, 'to the cerebellum, and to
the medulla oblongata; in its general form; in
its circumvolutions ; in its internal develop-
ment; and laftly, in the difterences w'hich its
bafe and the origin of the nerves exhibit.

1. Proportion of the 3fafs of the Brain to ike
rejl of the Body.

It is very difficult, if not impoffible, to efta-
•^lilh this proportion in a comparative manner,

bccaufe

154 L. IX. Brain OF Animals with Vertebrje.

becaufe the weight of the brain remains the
fame, while that of the body varies confiderably
according as the animal in whom the compari-
fon is made, is fat or lean. Thus the proportion
of the weight of the brain to that of the reft of
the body, has been ftated by one author to be
in the cat as i to 56, and by another as i to 82 ;
in the dog as i to 305, and as i to 47, &c.

The following is, however, a table of thefe
proportions, collecfted from different authors,
and from my own obfervations. It will appear
that, all t;hings confidered, the fmaller animals
have the brain proportionally the largeft ; that
man is furpafled in this refpccft only by a fmall
number of animals, all of which are lean and
meagre, as mice, fmall birds, &c. ; that among
the mammalia, the Rodentia have in general the
largeft brain, and the Pachydermata the fmalleft ;
and that cold blooded animals have it infinitely
fmaller than the warm blooded.

Man - - - - - - TT TT tV tV

according as he is young or old.

ORANGS.

Long-armed ape, or gibbon - - - - aV

SAPAJOUS.

Orange monkey (simla sciurea) - " ” vt

Capucin monkey (simia capucina) - - - tt

Striated monkey (simia jacchus) - - • -iV

Four-fmgered monkey (simia paniscus) - -

GUENONS.

Art. V, Brain of Mammalia

155

GUENONS.

Malbrouck (simia faunus) young
The green and red monkeys
Varied monkey (simia mona)

White eye-lid monkey (simia icthiops)

MAGOTS AND MACAC^JES.

Hair-lipped monkey, or macaque
Barbary ape, or magot _ - -

Papion, or great baboon

MAKIS.

Ring7tailed maucauco, (lemur catta) young
Vari (lemur macaco) - - -

CHEIROPTERA.

Great bat (vespertilio nodlula)

' PLANTIGRADA.

Mole - _ _ - _

Bear - - _ _ _

Hedge-hog , -

I

■XT

I

TX

I

XT

I

XT

t

IT

TT

Dog

Fox

Wolf

Cat

Panther

Martin

Ferret

CARNIVORA.

I I I , I X

TT To” TT TTT

1 X

S ^ ^ 4

RODENTIA.

156 L.IX. Brain of Ani malswit^i Vertebr^^

RODENTIA.

Beaver - ' _

(

Hare

X

Rabbit - _ _ _ _

t

TTH-

X

Ondatra, or Musk beaver

T^6-

rrr

X

Rat

ttt

I

blouse - - _ _ _

X

I

Field mouse _ _ _ _

zr

1

TT'

PACHYDERMATA,

Elephant - - _ > _

mm

T t> J

C Wild boar _ _ >

1

Hogs Domestic hog

J

TTT

TTT

X

TTT

Siamese hog -

-

-

I

TTT

RUMINANTIA.

Stag

Roe, young
Sheep
Ox
Calf

t

I

77

I I

TTT •nrr

“ T5T3T
YI7

Horse

Ass

SOLIPEDA.

7^7

I

TjT

Dolphin

Porpoise

CETACE/.

Ilf I

tt ry yy tht

_ _ I ♦

ITT

2.

* 'I'o prevent the needliry of returning to this fubjeft in the
articles that treat of the brain of the other clafles, we (liall fub-

joi^

Art. V. Brain of Mammalia. 157

2. Propoi'tion of the Brain to the Cerebellum
and Medulla oblongata.

The proportion of the weight of the brain to
the cerebellum and medulla oblongata, may be

obtained

join a table of its proportion to the reft of the body in fome
birds and reptiles. It is taken partly from Haller, and partly
from our own obfervations.

BIKOS.

f^agle

Falcon . - _ - _

Sparrow - - - . _

Canary-bird « _ - .

Silkin - - - _ .

Chaffinch . _ _ ^

RcJbreaft - - - .

Blackbird - .

Cock - _ . . ,

Duck - - - - _

Goofe - , _ _ .

REPTILES.

Land tortolfc .

Sea tortoife . _ . _

Collar fnake -

Frog

FISHES.

White fhark (fqualus carcharias)
Great dog-fifti (fqualus canicula)
Tunny (fcomber thynnus)

Pike - - . .

Carp _ - . _

Silurus glanis

I

TOT

I

TT

I

IT

1

47

1

IT

I

TT

A

Zf

I

rr-

I

■rrT

Tr®

I

3 C 8 8
7TS

I

ttt

I

I

TT++®

TToT

TZV

r-grr

158 L. IX. Brain of Animals with Vertebr^^

obtained with precifion, becaufe no variation in
the health, corpulence, &c. of individuals, has
any apparent influence on thefe parts.

This proportion is more confiderable in man,
than in almofl; all the other mammalia, as will
appear from the following table. The Roden-
tia have the cerebellum largefl, in proportion
to the brain. ,

In man, the cerebellum is to the brain.

as _ _

Orange-monkey
Capucin-monkey
Magot - _ _

Barbary ape, or Baboon
Varied monkey
Dog - - _

Cat 1 . _

Mole _ _ _

Beaver _ » _

Rat _ _ _

Moufe - _ _

Hare _ _ _

Wild-boar
Ox - - -

Sheep _ _ _

Horfe _ , _

I : 9
I : 14
I : 6
1 : 7
I = 7

I : 8
I : 8
I : 6

4i

I : 3
J • 3i

J : 2
I : 6

I- 7
i: 9

5

7

The proportion of the brain to the medulla
oblongata, is eflimated by the meafure of their
diameters. M. Sermmering and M. Ebel have

6 flicwn.

Art. V. Brain of Mamm^alia. 159

fhevvn, that this proportion is more in favour
of the brain in man, than in all the other ani-
mals, and that it is an excellent criterion of the
degree of intelligence an animal enjoys; becaufe
it is the beft index of the pre-eminence which
the organ of refledlion preferves over thofe of
the external fenfes. There are, however, fome
exceptions to this rule ; and that which the dol-
phin affords, is very remarkable.

We fubjoin a table of the proportions be-
tween the breadth of the medulla oblongata,
meafured at its bafe, and the greateff breadth of
the brain in fome animals.

In man, the breadth of the medulla oblon-

gata, behind the pons Varolii,

is to that of

the brain as - -

1 = 7

Short-tailed Macaque

- I : 5

Chinefe-monkey

I : 4

Dog - - . »

6:11

or - - _ _

3 '• 8

Cat - _

8 : 22

Rabbit _ _ _

3: 8

or-

I • 3

Hog - - . .

5 : 7

Ram \ _

5 = 7

Stag - _ , .

2 • 5

Roe - - _ _

I : 2

Ox ... .

5 * 13

Calf - _ . ■ ,

2: 5
Horfe

i6o L. IX. Brain of Animals with Vertebra.

Horfe - - - ’-8:21

Dolphin - - » I : 13*

3. General Form.

The difrercnces in the general form of the
brain, depend principally on a greater or lefs
magnitude, and dcvcloptnent of the two pro-
dinflions of the corpora flriata, called the he-
mifphercs ; thefe parts are thicker in every di-
re(5lion, in man, than in any other animal, and
hence the peculiar rotundity of /his brain.

The brain begins to appear flatter in the mon-
key ^nd ; their hemifpheres are lengthened
backward, like thofe of man, to form the pof-
terior lobes which lie on the cerebellum. In all
the other quadrupeds, however, commencing
with the.Sarcophaga, the hemifpheres arc not
only fmall, and confequently the filTure which
feparates them of little depth and the upper
furface of the brain flat; but the middle lobes
are much Icfs convex infcriorly, and the pofle-
rior do not exifl: at all. The cerebellum appears
unctfvered behind the cerebrum.

With

* Wc (hall here add 3 ftatement of the proportioii,of the fame

parts in fome birds.
Falcon -

13 :

C/vvl - - "

-

-

U :

Duck . - -

-

-

10 : J?7

1 urkey

-

-

le : 3S

Sparrow ...

-

-

7 : 18

i6i

Art. V. Brain of Mammalia.'

With refped to the external (hape, the brain
of monkies very much refembles that of man,
in confequence of its oval form ; but in the Sar-
cophaga it is proportionally narrower anteriorly,
and approaches more to the triangular fhape.
This is particularly apparent in the dog and the
oppojfum.

Some Rodentia, as the bares and the rabbits^
have alfo this form; but others, as the beaver
and the porcupine^ have the cerebrum almoft cir-
cular.

In the other herbivorous kinds, the brain is
generally of an oval form, broader behind than
before.

The cerebrum of the dolphin is of a very ex-
traordinarv Ibape ; it is very large, and covers
the cerebellum fuperiorly: it is rounded on
every lide, and almoft twice as broad as long.

The cerebellum of man having its middle
lobe concealed under, the other two, feems at
firft fight to have no more than two lobes, the
general outline of which is nearly round.

In the other animals, even in monkies, this
middle lobe is proportionally larger, and is
vifible externally. It is equal to the other lobes
in the Rodentia : we find it proportionally fmaller
in the dolphin than in monkies.

4. Circiim'colutions.

The circumvolutions of the brain are deep^‘

VoL. II. , M

m

i62 L. IX. Brain ofAnimalswith Vertebra.

in man than in any other animal, and very few
have them fo numerous.

They are much fewer in the monkey kind, par-
ticularly in the fapajous ; the pofterior lobe has
fcarce any, except in jocko and the gibbon, in
which that lobe is feparated from the reft ante-
riorly, by a very'diftineft tranfverfe fiflure.

In the Sarcophaga, the furrows of the brain
are pretty numerous, and exhibit a certain or-
der, which is preferved throughout the greater
number of fpecies ; we obferve, pofteriorly,
two on each fide, parallel to the middle line,
and a Ihort one anteriorly, which crolTes it.

The Rodentia have, in general, no fenfible
circumvolutions ; their hemifpheres are almoft
entirely fmooth, or exhibit only very flight fur-
rows ; but we find a number of convolutions in
the hoofed animals, and particularly in the Ru-
minantia and the horfe.

The dolphin has numerous and deep circum-
volutions.

All the other mammalia: have, like man, the
furfacc of the cerebellum marked by tranfverfe
furrows, parallel and adjoining to each other;
but they differ amongft themfelves with refpcift
to the other furrows, which divide the cerebel-
lum into lobules, and which feem to form cir-
cumvolutions limilar to thofe of the cerebrum.

'I'hey are fomewhat numerous in the Sarco-
phaga, the Ruminantia, and the Solipeda: wc
obferve fewer in the other orders.

5. Develop-

Art. V. Brain of Mammalia. 163

5. Devclopmcyit of the internal Parts of the
Brain in Mammalia.

The tubercula quadrigemina are proportion-
ally larger in the animals that are removed from
man, and are very confiderable in the herbivo-
rous kinds, whether Rodentia, Ruminantia, or
Solipeda ; all thefe herbivorous animals have
the nates round, and much larger than the tejles ;
this renders it probable that thefe tubercles
were fo named by the ancients, in confequcncc
of their being firft obferved in animals of that
order.

In the monkies, their refpecbive proportion is
nearly the fame as in man ; but in the Sarco-
phaga, the tejles are generally larger than the
nates.

In the dolphin, they are at leaf): triple the fizc
of the nates.

The tubercles which we have pointed out as
forming a third pair in man, become, in the
f»/o-and the dog, as large as thofe of the other
pairs ; but they are very little, or not at all, ap-
parent in the Ruminantia.

The optic thalami, the third and fourth ven-
tricle, and the pineal gland, prefent no remark-
able peculiarities.

The corpora llriata do not differ, except a
little more or lefs in breadth. The fame ob-
fervation applies to the corpus callofum and
the fornix. The cornua ammonis are in general

M a proper-

164 L. IX. Brain of Animals with Vertebra.

proportionally larger in the quadrupeds; there is
‘no fwoln appearance on their furface, as in man.

The anterior ventricles have no digital cavity
except in man and the monkies : that part cx-
ifts in no other mammiferous animal ; its pre-
fence depends on that of the pofterior lobes.

6. Of the Bafe of the Bra'm, and the Origin
of the Nerves.

The bafe of the brain prefents much fewer
inequalities in quadrupeds than in man ; the
infundibulum is not fo deep; the middle lobes,
and the pons Varolii, are lefs 'prominent ; the
corpora pyramidal ia are extended farther back-
ward. With refped: to the nerves, we obferve
no remarkable differences, except in the olfac-
tory.

In the monkies only, the olfacflory nerve is, as
in man, diftin(ft at its bafe from the mafs of
the brain, and forming a medullary filament.
In the other animals we perceive only fomc whit-
ilh marks, and, inflead of the nerve, a large afli-
colourcd eminence, which fills the ethmoidal
foffa, and contains a cavity which communi-
cates with the anterior ventricle ; this eminence
was called, by the ancients, caruncula mammil-
laris.

The dolphin has no olfacflory nerves, nor any
thing that fupplies their place. It is the fame
in fcveral other Cetacea.

It

Art. V. Brain or Mammalia. i6

It refuks from thefe obfervations, that the
peculiar charadler of the brain of man, and the
monkey, confifts in the exigence of the poke-
rior lobe, and the digital cavity : that of the
brain of the Sarcophaga, in the fmallnefs of the
nateSy in proportion to the tejies ; that of the
brain of the Rodentia, in the largenefs of the
natesy and in the abfence or little depth of the
circumvolutions ; that of the brain of hoofed
animals, in the great fize of the nateSy and the
numerous and deep convolutions ; that of the
brain of Cetacea, in its great height and breadth,
and in the total abfence of the olfaAory nerves.
Thus it appears, that all the herbivorous animals
have the nates larger than the tejieSy and that it is ..
quite the contrary in the carnivorous. Only
man, and the quadrumana, have nerves, which,
in propriety of language, can be called olfac-
tory. In the true quadrupeds, they are replaced
by the carunculse mammillares ; and they arc
entirely wanting in the Cetacea.

Article VT.

I

Of the Brain of Birds.

The brain of birds is diftinguilhed at the firk
view, by being formed of fix malTes or tuber-
cles, all vifible externally, viz. two hemi-

M 3 fpheres.

i66,L. IX. Brain of Animals with VERTEBRi^:.

fpheres, two optic thalami, a cerebellum, and a
medulla oblongata.

The two hemifpheres reprefent the figure of a
rounded heart, the point of which is directed
forward : the optic thalami are two round tu-
bercles, placed under the hemifpheres, but are
not enveloped by them : the cerebellum is only
a fingle lobe, comprefied laterally ; the medulla
oblongata has neither corpora pyramidalia nor
olivaria, nor pons Varolii ; it reprefents a large
fmooth furface between the two optic thalami :
the crura of the cerebellum pafs into it imme-
diately, without forming any proje6tion.

There are no circumvolutions on the hemi-
fpheres, nor on the optic thalami; but the cere-
bellum has'fome tranfverfe lines parallel, and
clofe together, as in the mammalia.

Birds want the corpus callofum, fornix, and
feptum lucid um. On feparating the two he-
mifpheres, we obferve that they are diTlindl:
throughout the whole of their height, and that
they do not unite to each other except pofte-
riorly towards the anterior commiflure of the
cerebrum. The furface, by which they join,
prefents fomc white radiated lines, which are
derived from this commiffure ; that furface is
formed by a thin partition, which ferves as the
internal parietes to the anterior ventricles. This
partition is, as ufual, a fold of the appendix of
the corpus firiatum, which appendix is very
fmall in birds, in which the corpus firiatum

forms

Art. VI. Brain or Birds. 167

forms in itfelf almoft the whole of_the hemi-
fphere. It takes the figure of a kidney, but has
no Cauda. The anterior ventricles alfo are not
infledled downward, as in the mammalia, and
confequently there is no cornu ammonis. Be-
hind their internal partition there is a fiffure,
by which they communicate together, and with
the third ventricle, if the plexus choroides pre-
fent no obftacle.

The anterior commifTure is prolonged on each
fide into the fubfiance of the hemifpheres, as in
man and in quadrupeds.

'I'he third ventricle is fituated between the
optic thalami ; the white lines w’hich bound it
fuperiorly are prolonged, as ufual, to form the
peduncle of the pineal gland. There is an
anterior and pofterior commiflure which are
white. ‘

The bottom of the third ventricle communi-
cates with the infundibulum. Its pofterior part
communicates likewifewith the fourth ventricle,
but the arch placed over the aquaedu(5l of Sylvius
does not fuftain the tubercula quadrigemina.
It is a fimple thin lamina, which is merely the
valvula cerebri extended farther forward.

The fourth ventricle refembles that of mam-
malia, and has alfo the longitudinal imprefiion,
called calamus fcripcorius.

The optic thalami contain each a ventricle
which communicates with the others by the
aqusedu(fi:us Sylvii.

M 4

There

i68 L. IX. Brain ofAnimals with Vertebra.

\

There' are no mammillary tubercles or emi-
nences. The corpora ftriata do not exhibit al-
ternate white and grey ftrise internally. The
arbor vitae is lefs corpplex than in the mam-
malia.

Between the corpora ftriata, and tho optic
thalami, there are four round eminences which
are better diftinguifhed in the ojlrich than in
other birds. The firft are fituated before
the anterior commifture, even in the anterior
ventricles. The others are behind that com-
mifture, and projecfl into the third ventricle^
nearly at the place where the foft commilTure is
lituated in the mammalia, There is nothing
analogous to thefe tubercles in the human
brain, but we find fimilar ones in that of fillies.

The olfadtory nerves arife from the point of
the hemifpheres, and do not come from their
bafe as in the mammalia ; they appear to be a
mere continuation of thefe bodies.

The'other nerves of the brain do not difler ii^
their origin.

Article VII.

/

Of the Brain of Reptiles.

All the parts of the brain of reptiles arc
fmooth, and without circumvolutions. The

optic

169

Art. VII. Brain of Reptiles.

optic thalami are fituated behind the hemi-
fpheres, but are not covered by them. They
contain each, as in birds, a cavity which com-
municates with the third ventricle. At the ex-'
tremities of this ventricle, wc obferve the an-
terior and pofterior commiirure, but there is no
foft commiflhre, nor tubcrcula quadrigemina.

In the tortoife the hcmifpheres form an oval.
Their anterior part is feparated from the poftc-
rior by a fulcus, and reprcTcnts a kind of bulb,
which ferves as a root to the olfaiflory nerves.
The lize of this bulb is about equal to one-third
of the hemifpherc. The interior of the hemi-
fphere is, as ufual, excavated by a ventricle, and
contains a fubftance analogous to the corpus
ftriatum, and which pretty much refemblcs in
its form that of birds.

The optic thalami arc not larger than the
bulbs of the olfactory nerves. Their form is
nearly round. They extend downward and for-
ward, under the hemifphcres, to produce the
optic nerve. The valve of the cerebrum is fi-
tuated between them and the cerebellum. No
tubercle is either placed above it or before it,
and it gives origin, as ufual, to the fourth pair
of nerves.

Before the optic thalami, and under the po-
fierior part of the hcmifpheres, there is a tuber-
cle which correfponds to that we have remark-
ed in birds.

The cerebellum is nearly hcmifphcrical. The

fourth

\

170 L. IX. Brain OF Animals WITH Vertebra.

fourth ventricle penetrates a confiderable way
into its fubftance.

In the frog the hemifphercs are longer and
narrower. The optic thalami are larger in pro-
portion to the hemiTpheres. Their ventricle is
very diftin<5l. It is the contrary in falamanders,
which have the optic thalami very fmall> and
the hemifpheres almoft cylindrical.

The cerebellum of thefe two kinds of reptiles
is fiat, triangular, and lies pofteriorly on the
medulla oblongata.

in the ferpents the two hemifpheres form to-
gether a mafs which is broader than long. The
optic thalami are almoft round, and one half
lefs than the hemifpheres behind which they
are fituated. The olfa(ftory nerve has no appa-
rent bulb. The cerebellum is exceedingly
fmall, flat, and in the form of a portion of a
circle.

in all thefe animals the inferior furface of the
brain is nearly fmooth. The optic thalami
make no projeeftion downward, and the pons
Varolii docs not exift.

The olfadtory nerves arife, as in birds, from
the anterior extremity of the hemifpheres. 'I'he
optic nerves feem to derive their origin from a
common eminence, fituated under the middle of
the hemirpheres. The other nerves exhibit no
particularities as to'thcir origin.

Arti-

Art. VIII. Brain of Fishes.

171

Article VIII.

Of the Brain of Fijhes,

The different lobes and tubercles which com-
pofe the brain of fifhes, are fituated behind each
other, in fiich a manner that the whole, inflcad
of appearing as one common mafs, more or lefs,
approaching an oval form, refcmbles a kind of
double chaplet. This comparifon is more pro-
perly applied to the brains of fi(h, than to thofe
which we have_ juft noticed, on account of the
greater number of thofe tubercles or lobes.

The cerebellum is always lingle. It is pro-
portionally larger than in w'arm-blooded ani-
mals. It even frequently furpaftes the hemi-
fpheres in ftze.

The two hemifpheres always exift. They are
generally of an oval form, without any apparent
circumvolution, and each contains a ventricle,
the floor of which prefents an elevation analo-
gous to the corpus ftriatum.

The optic thal-ami are conftantly lituated, as
in birds, below the hemifpheres. They arefmaller
than the latter, but each of them alfo contains a
ventricle.

On the two fides of the origin of the medulla
oblongata, behind the cerebellum, there are al-
moft always fome tubercles, which appear to

form

172 I,. IX. Brain of Animals with Vertebr-®.

form the origin of feveral pairs of nerves, and
which are often as large as the hemifphcres.
There is fometimes a lingle tubercle between
them, which feems to form a fecond cerebel-
lum.

The olfadlory nerves, at their origin, form
fwellings or knots, the number of which varies,
and which are frequently fo large that fome
authors hav^ miflaken them for the real brain.

Finally, in feveral fiflies there are under the
common arch of the hemifpheres, fomefimes
two, fometimes four tubercles, which vary in
their figure and proportions, but which would
prefent a ftriking analogy to the tubercula qua-
drigemina, were they not like thofe that refem-
ble them in birds, fituated before and above the
optic thalami.

The brain of fiflies is always very fmall in
proportion to their body. It never completely
fills the cavity of the cranium. The furface of
the hemifpheres is always fmooth. The cere-
bellum and its lateral tubercles occafionally ap-
pear rugous.

The brain may vary in the different kinds of
fiflies. iff. In the number and form of the tu-
' lierclcs of the olfadlory nerve. 2. In the num-
ber and form of the eminences contained within
the hemifpheres. 3. In the form of the cere-
bellum. 4. In the tubercles which are fituated
behind the cerebellum. Wc proceed to examine
it under thefe different points of view.

j . The

Art. VIII. Brain of Fishes.

*73

1. The Tubercles of the OlfaRory Nerves,

In the rays and the /harks the tubercles are
united into one mafs of various lengths, but
which is more than double the fizc of the he-
mifpheres. It contains no cavity, and its infide
is entirely formed of a homogeneous medullary
fubftance. The olfacflory nerve, properly fo
called, arifes from each of the lateral parts of
this mafs, which fcveral authors have deferibed
as the cerebrum, and others as its anterior lobes.

Thefe tubercles are long and narrow in the
Jhirgeon: they are limplc, oval, and fmaller than
the hemifphercs in the lump fijb and the moon jif?
(Telrodon mola Lin.) The genus gaJus, that is to
fay, foif, ivhitings, 8cc. have them fimple and
round. In the cod they are even almoft as large
as the hemifphcres. The wraj/es., and all the
genus ryprinus, that is to fay, carps^ barbels^
tenchciy &c. have them alfo fimple and round,
but dilHnguHhed by a flight furrow, which gives
them the form of a kidney. In the pleurone^es^
the herrtngSy the pikes^ the perches, and in all the
falmon genus, which includes the trouts and the
/melts, 6rc. there are two pair of tubercles, the
anterior of which is fmaller than the other, but
they do not equal the hemifphcres in magnitude.
Finally, in the eel genus there are three pair of
tubercles, which diminifh in magnitude, begin-
ing with the lafi-. Their brain therefore pre-
fents altogether ten eminences before the cere-
5 bellum.

174 L. IX. Brain OF Animals WITH VERTEBRi^:.

bellu/n, eight of which are fuperior, viz. the lix
tubercles, and the two hemifpheres; and two
inferior, which are the optic thalami.

2. The Eminences within the Hemifpheres.

a. The corpora firiata are not apparent in the
raps and Jharks, and the interior of their ventri-
cle prefents no eminences. In moft of the other
fifhes the corpora flriata reprefent two feg-
ments of a circle, the concavity of which is
turned inward. From the convex fide fome
very fine medullary ftrias proceed, which are
prolonged tranfverfely on the internal parictes
of the ventricle. Thefe corpora flriata vary in-
breadth according to the fpecies. They form
two elevated oval bodies in the whiting. Their
anterior extremity approaches nearer to the
middle line than the pofterior. The anterior
commifTure of the brain is fituatcd a little below
them. Between them we obferve a fifTurc,
which leads into the third ventricle. The fu-
perior portion of each hemifpherc is nor, as in
the other red. blooded animals, an appendix of
the corpora flriata, which bends infcriorly to
form a vault.

b. The tubercles, fin^ilar to the quadrigemina,
do not exifl in the rays and the Jharks. There
is only a lingle pair in the crls^ the haddocks^
and the herrings, which jiroduccs a femi-oval
eminence before the cerebellum, between the

pofterior

I

Art. VIII. Brain of Fishes. 175

poflerior extremities of the corpora ftriata. The
pikes, the trouts, and /a/wow, and the perches, have
two pairs, which form four round fmall tu-
bercles, the pofterior of which are rather the
largcft.

In the carp genus there arc alfo four emi-
nences, but they arc very unequal. 1 he pollc-
rior are fmall and round, the anterior are ex-
tremely long, cylindrical, and bent outward and
backward, following the curvature of the late-
ral ventricles, all the cavities of which they oc-
cupy. Their poflerior furfacc is marked by a
longitudinal furrow.

3. The Cerebellum.

The cerebellum of fifhes doe.s not merely cover
the fourth ventricle; that cavity rifes into its fub-
ftance ; it is fometimes rounded, and fomeiimes
approaches more or lefs to a conical form. In
the rays and the Jharks it is irregularly furrowed.
It is fmooth in almoft all the ocher lifli. Inter-
nally, we obferve no vefliges of the arbor vitae,
except fomc indiftind; whitifh linfes. Where hs
form is conical, as in the cod and the carp, its
point is infleded a little backward, which gives
it the form of a Phrygian cap.

»

4. The Tubercles Jituated behind the Cerebellum.

Thefe tubercles are peculiar to fi flies, unlefs

.we

I'jS L.IX. Brainof Animals WITH Vertebra.

we regard them as fupplying the place of the
corpora olivaria.

In the ray they are large, irregularly furrowed,
and evidently give origin to the greater part of
the fifth pair of nerves.

The carp has them as large as the hemi-
fpheres, and in the form of kidneys. Betw'een
them there is a large round tubercle, which
may be called a fecond cerebellum, but which is
immediately conne(fled with the dorfal part of
the medulla oblongata, and which enclofes no
ventricle.

In the zvhiting and the cod the tubercles are
oval, and fituated altogether above the medulla.
It is nearly the fame in the common eels and
conger eels.

Thcfe parts are little apparent in the pikes ^
troiitSy falmoHy and perches.

h. Origin oj the Net'ves.

In fiflics the olfadlory nerves are merely con-
tinuations of the tubercles fituated before the
hemifpheres. They frequently take a long
courfe before they arrive at the noflrils. The
optic nerves arife under the cerebrum where the
thahimi are' fituated. Thcfe nerves arc very
large, and are compofed cither of diflimfl fila-
ments, or of a fingle Hat hand which is foinc-
times folded longitudinally on itfelf. They
crofs w ithoLit being confounded, and we plainly

fee

/

Art. IX. Characters OF Braixs. 177

fee that the nerve of the left fide proceeds to
the right eye, and that of the right fide to th«
left.

The fifth pair of nerves arife fo near the audi-
tory that they feem but one. The fafeial nerve,
on the contrary, is very diftindl from the audi-
tory. The nerve of the eighth pair is very
thick; the others prefent no peculiarity.

Article IX.

Recapitulation of the CharaRers peculiar io
the Brain in the Four Clajfcs of Vertebral
Animals.

From the examination we have jufl concluded,
it refults,

I. That the characfler which diftinguifhes the
brain of mammalia from that of the other red-
blooded animals, confifts,

a. In the exifience of the corpus callofum,
the fornix, the cornua ammonis, and the pons
Varolii.

b. In the tubercula quadrigemina being
placed upon the aqusedudlus Sylvii.

c. In the abfence of ventricles in the optic
thalami, and in the pofition of thefe thalami
within the hemifpheres.

VoL. II. N

d. In

\’J% L;IX. BRAINOFANIMALSWITilVERTEBRi®;.

d. In the alternate white and grey lines within
the corpora flriata.

2. The charadler peculiar to the brain of birds
corififts,

a. In the thin and radiated feptum, which
fhuts each anterior ventricle on the internal fide.

3. The characfler of the brain of reptiles dc^
pends,

a. On the pofition of the thalami behind the
hemifpheres.

4. The character belonging to the brain of
fifhes confifts,

a. In the tubercles of the olfadlory nerves, and
^e tubercles fituated behind the cerebellum.

5. The three lafl: clafTes have, in common, the
following charadters, by which they are diftin-
guifhed from the firfl :

a. Neither corpus callofum, nor fornix, nor
their dependencies.

b. Some tubercles, more or lefs numerous,
fituated between the corpora ftriata, and the op-
tic thalami.

c. The thalami containing ventricles, and
being diftindt from the hemifpheres.

d. The abfence of any tubercle betw^cen the
thalami and the cerebellum, as well as the ab-
fence of the pons Varolii.

6. Fiflics have certain charadlcrs in common
with birds, which are not to be found in the
other clalTes : thefe arc.

a, Tht?

Art. iX. Characters of Brains. 175

a. The portion of the optic thalami Under
the bafe of the brain.

b. The number of the tubercles placed before
thefe thalami, which are commonly four.

7. Fifhes and reptiles have for a common
character diftinguifhing them from the two
firft clafles, the abfence of the arbor vita: in
the cerebellurii.

8. All red-blooded animals have the follow-
ing charadters in common :

a. The principal divifion into hcmifpheres,
optic thalami, and cerebellum.

b. The anterior ventricles double, the third
and fourth Angle, the^ aquaedudlus Sylvii, the
infundibulum, and a-communication between all
thefe cavities.

c. The corpora ftriata and their appendices
in the form of a vault, called hcmifpheres.

d. The anterior and pofterior commilTurcs;
and the valve of the cerebrum.

e. The bodies named pineal and pituitary
glands;

f. The union of the great Angle tubercle or
cerebellum, by two tranverfe crura, with the reft
of the brain, which gives origin to the two lon-
gitudinal crura of the medulla oblongata.

9. It alfo appears that there exift certain re-
lations between the faculties of animals and the
proportions of their common parts.

Thus the intelligence they poftefs, appears
more perfed: in proportion to the volume of the

N 2 appendix

1 8o L. IX, Brain of Animals with V^ERTEBRii:.

appendix of the corpus ftriatum, which forms
the vault of the hemifpheres.

Man has that part greater, more extended,
and more refledted than the other animals.

In proportion as we defccnd from man, we
obferve that it becomes fmaller and fmoother on
the furface, and that the parts of the brain arc
lefs^complicated with each other, but feem to
be unfolded and fpread out longitudinally. •

It even appears that certain parts affume, in
all claffes, forms which have a relation to parti-
cular qualities of animals: for example, the
anterior tubercula quadrigemina of carps, which
are the moft feeble and leaft carnivorous of
fifhes, arc proportionally larger than in the
other genera, in the fame manner as they are in
the herbivorous quadrupeds. By following thefe
inquiries, we may hope to obtain fome know-
ledge of the particular ufes of each of the parts
of the brain.

Article X.

Of the Membranes of the Brain.

In all the rcd-bloodcd animals, the brain, as
well as the other parts of the nervous fyflcm, is
covered by three membranes.

That which is next to it, is named the pia-

mater ;

Art. X. Membranes OK THE Brais. iSi

mater \ the external is called the dura-mater ;
and that which is intermediate, has been deno-
minated arachnoides.

a. The dura-mater is a thick opaque mem-
brane, which lines all the oireous cavity of the
cranium, and the vertebral canal.

The greater part of the fibres of the external
lurface are longitudinal, and moil of ihofe of
the internal furface are tranlverle ; but a con-
iiderable number of others run in various di-
re ions.

Within the cranium the dura-mater is inti-
mately united to the bones, and fupplies the
place of the periollcum. Its external furface is
cellular and flocculent: its internal is fmooth
and glofly. In the vertebral canal it is more
loofe, and is not intimately united to the bones;
but its organization is the fame. This mem-
brane is regarded by anatomifts as formed of
two laminae, though it is extremely difficult to
feparate them. Blood veflels are diftributed
between thefe lamina, and the internal appears to
be detached from the external, to form feveral
refleeftions.

Seven of thefe refledlions have been deferibed
in man.

1. The falx of the cerebrumy which extends
from the crifta galli of the ethmoid bone, to the
internal fpine of the os occipitis. Its inferior
edge is unattached. It is narrow anteriorly,
broad pofteriorly, and is fituated between the

N 3 two

i82 L. IX. Brain OF Animals WITH Vertebrae.

two hemifpheres, which it feparates from each
other,

2. The tentorium cerebelli, which feparltes the.
two pofterior lobes of the cerebrum from the
cerebellum. It arifes from the dura-mater> be-
fore the two branches of the occipital crofs, and
extends towards the pofterior clinoid proceffes,
leaving a vacancy for the paflage of the medul-
lary prolongations of the cerebrum.

3. Th^falx of the cerebellum^ which correfponds
to the inferior line of the occipital crofs, and is
extended fome way between the lobes of the ce-
rebellum.

4. The two folds which pafs from the ante-
rior to the pofterior clinoid procefles, and in
that manner circumferibe the pituitary fofla.

5. Finally, the two reflecftions which feparatc
the anterior from the middle lobes of the cere-
brum, and furround the orbitar procefles of the
os fphenoidcs, called the little wings of In-
grafllaB.

In the other mammalia, the falx of the cere-
brum diminifties greatly both in length and
breadth.

The tentorium ccrcbclli; on the contrary, is
very conftderable : it is even fupported by an
ofleous lamina in thofe that run fwift, as we
have pointed out in the Oftcology of the Head,
Art. 3, This fold feems deftined to prevent the
fridion of the two parts of their brain, in the
fame manner as tbc falx of the cerebrum pre-
vents

Art. X. Membranes of the Brain. 183

vents the one hemifphere from prefTing on the
other, when the head repofes on one fide.

The falx of the cerebellum difappears entirely
in all animals in which the vermiform procefs
projects more than the lateral lobes, as is the
cafe in all the real quadrupeds.

We find the falx of the cerebrum in birds.
In the turkey it has the form of the fegment ot a
circle: it extends from the middle fpace be-
tween the openings for the olfacflory nerves, to
the tentorium of the cerebellum. The falx of
the cerebellum is wanting. The tentorium,
which is not extenfive, is fuftained by an oflTe-
ous lamina, and there are befides two particular
folds on each fide which feparate the hemi-
fpheres from the optic thalami.

None of thefe folds are found in the animals
that have cold red blood. The dura-mater of
reptiles and fifhes adheres in every part to the
internal furface of the cranium : it is even fepa-
rated from the brain by a mucous or oily fluid
of more or lefs confiftence.

b. The membrana orachnoidea is thus named
from its texture, which is- extremely delicate and
tranfparent, and which has therefore been com-
pared to that of a fpider's web: it envelopes the
pia-mater, but does not penetrate with it into the
furrows of the brain ; it is ftretched over thefe
deprellions in the manner of a bridge, except at
fome places where the internal lamina of the
dura-mater is prolonged : it makes a large fun-

N 4 nel.

184 L.IX. Brain OF Animals with Vertebra.

nel, which receives the medulla fpinalis. In
man this fac appears to commence immediately
below the origin of the optic nerve.

The cold-biooded animals in which, as we
have already obferved, the brain does not fill
the cavity of the cranium, have the arachnoides
replaced by a lax cellular fubftance, which oc-
cupies all the fpace included between the dur^
and pia-mater j it is commonly moiftened by a
gelatinous fluid, as in the cartilaginous fifhes,
and fometimes coloured with blood. In the
carp and the falrnon this humour appears like an
oily froth.

c. The pia-mater is the membrane which im-
mediately envelopes the fubftance of the brain ;
it defcends into all the furrows that appear on
its furface, and which form its circumvolu-
tions. It would appear to confift altogether of
blood- vefTels, but the arteries and veins only
pafs through it. We obferve that it is much
more folid, and has a greater number of veflels
at thofe places where it covers the cincritious
parts of the brain, than where it envelopes the
medullary fubftance and the nerves : it accom-
panies and invefts the fpinal marrow j it pene-
trates into the fcvcral ventricles, but is not at-
tached to their parietes ; it floats in their cavi,.
ty where it fupports the vcifels. Thefc produc-
tions are called pUxus choroides.

The proceffes of the pia-mater, which arc re-
fle(ftcd between the convolutions, arc attached

6 to

Art. X. Membranes OF THE Braix. 185

to the brain by a fine cellular firutflure, which
appears to be formed by blood-veflels of an ex-
treme tenuity.

In mammiferous animals the greatefi: pro-
longation of the pia-mater is found in the part
of the anterior ventricles corresponding to the
lower edge of the fornix, and the fuperiorof the
optic thalami. It is a vafcular web, folded on
itfelf^ and forming a kind of cord. W'hcn ex-
tended, its figure is nearly triangular: the vef-
fels which penetrate it arc very clofely inter-
laced on the edges of this web, and thofe parts
have more particularly received the name of
plexus choroides. There is a plexus fimilar to
the middle of the inferior furface of this web,
placed exadlly upon the aperture of the third
ventricle.

In birds there arc two narrow bands which
pafs into the ventricles, and occupy the whole
of their length.

There is alfo an analogous ftrueflure in fifhes ;
but the plexus adheres to the parietes of the
ventricles, and does not float within them.

We find two other productions of the pia-
mater, in the fourth ventricle, lituated under the
cerebellum, one on each fide. They appear to
be unattached.

They are wanting in birds.

Articli

I S6 L.IX. Brain of Animals with VERTEBRii:.

Article XI,

Of the VcJJ’ds of the Brain.

In man, fix principal arteries enter the cranium,
three on each fide : one is diflributcd to the
dura-mater, and is called arteria fpheno-fpinalis ;
the other two, which extend to the brain, are
named arteria carotis interna^ and arteria verle-
bralis.

The fpinal artery is a branch of the internal
maxillary, and palTes into the cranium, through
the fmall foramen of the pofterior procefs of
the os fphenoides. Upon reaching the interior
of the cranium, it afeends tow'ards the internal
furface of the parietal bone j it there fpreads
upon the body of the dura-mater, by a great
number of ramifications, which anaftomofe to-
gether in a manner which may be compared to
the nervures of a fig leaf.

This arrangement is the fame in all the mam-
malia.

The internal carotid artery comes forth from
the ofleous conduit of the temporal bone, and
proceeds for fome time involved by the dura-
mater, and bathed in the vcinous blood con-
tained in the cavernous finus : it afterwards
pafles into the cranium behind the anterior cli-
noid procefics ; it is then named arteria cerchra-
lis \ it diflributcs fcveral fmall ramifications to

the

Art. XI. Vessels OF THE Brain. 187

the adjacent parts, and always fends off a large
branch pofleriorly, which is united with the
trunk of the vertebral arteries, and is named
arteria commnnicans.

Two fmall branches, which extend to the
plexus choroides, ufually arife from the cere-
bral artery when it has furniflicd the commnnicans.
The trunk is afterwards bifurcated ; and one of
the branches goes forward above the corpus cal-.
lofum, whence it is named arteria callofa. Like
all the other branches, it gives off a number of
ramifications to the neighbouring parts : the
other branch is fomewhat larger than the form-
er ; it is direifted outward to the furface of the
hemifpheres, into the pia-mater, and fiffure of
Sylvius, where it is divided and fub-divided
without end, in order to be conveyed by ex-
tremely minute veffels, even into the fubfiance
of the brain.

The vertebral art cries y after fuffering nume-
rous inflexions in the canal formed by the holes
t^rith which the five intermediate vertebrae of the
neck are perforated, pafs into the cranium
through the foramen magnum ; they then go
forward into the bafilar foffa of the os occipitis,
where they unite into one common trunk, call-
ed arteria bafilaris ; but they previoufly detach
two branches to each fide of the pons Varolii,
which ramify upon the inferior furface of the
cerebellum : one of thefe ramifications is deno-
Spinalis pojleriory becaufe it penetrate^

the

1^8 L. IX. Br AIN OF A N I M A LS WI Til VeRTEBR.j^,

,the fourth ventricle, and accompanies the me-
dulla fpinalis pofteriorly, as far as the lumbar
vcrtebra3. The fame vertebral arteries furnifh
x\iQ.Jpinales anteriorcs ; thefe unite towards the
great hypogloflal nerves, into a fiiigle trunk,
■which runs down the vertebral canal on the
fore part of the fpinal marrow, to the os fa-
crum, fending oft a number of fmall branches,
which anaftomofe with other arteries.

, The bafilar trunk is again bifurcated to pro-
duce the arterta Jtiperiores cerebelliy fttuated be-
tween the cerebrum and cerebellum, and alfo
the art eri<e comynunic antes y which, as we have al-
ready ftiewn, are united wdeh the carotids.

There are no large trunks formed by the veins
of the brain ; they open into conduits of a par-
ticular nature, called finujes ; thefe are formed
by duplicatures of the dura-mater, attached
to the bones by ftrong cellular fubftance, and
provided internally with a compa6l tex-ture and
ligamentous fraena. The veins are inferred into
them in a manner contrary to the courfe of the
blood. The objcdl of this oi-ganization appears
to be, to prevent the reflux of the venous blood,
which might affedt the brain.

All the finufcs difgorge the blood they con-
tain, either diredUy or mediately, into a dilated
part called the foflTa of the jugular veins : this
fofla is fituated above the poftcrior foramen la-
ccrum, by which the vein pafles out of the cra-
nium.

The

Art. XI. Vessels of the Brain. 189

The finufes of the human brain are, the pojle-
rior lon^itiidinaU ^vhich extends along the con-
vex edge of the falx; the inferior longituMnaU
fituated on its concave edge; the fraigbt^ which
proceeds from the pollerior extremity of the
preceding, and opens into one or other of the
lateral fimijes : the lateral are diftinguilhed into
the right and the left ; the one commonly re-
ceives in itfclf alone the blood from the lupe-
rior longitudinal finus ; the other ufually re-
ceives that which is contained in the right linus:
each on its rcfpeiflivc fide follows the fulcus,
traced between ihc cerebrum and cerebellum,
to the bafe of the os petrofum, along the poUc-
rior edge of which they defeend into the ju-
gular folia.

The circular fiKus of the fella turcica furrounds
the pituitary gland ; it empties itfelf into the
two great refervoirs, fituated on the fides of the
fella, called the cavernous finufes, in which the
carotid artery, and feveral pairs of nerves, are
contained. A venous conduit, which extends
from the cavernous fnus to the jugular fofla, is
named the inferior petrous finus. Laftly, we dif-
tinguifli, under the name of the fuperior petrous
finus, another fmall conduit, which accompa-
nies the projecting angle of the os petrofum,
and which opens into the right finus.

The blood-veflels within the cranium of other
mammiferous animals, do not differ from thofe
of man, except in their pofition. In the eighth

Lecture

igb L.IX. Brain of Animals with Vertebrae;

Lecture we have pointed out the cavities of the
interior of the cranium, and the furrows traced
upon it, as thefe furrows are impreffions made
by veflels; they indicate to a certain degree the
direxflions of thofc veflels : thus, by the defcrip-
tion of the carotid canal, and the fpinous and
Vertebral foramina, we are made acquainted with
the points from which the arteries proceed;
Thofe of the brain are difpofed nearly as in
man : but they alTume other curvatures, which
are determined by the form of the lobes.

There is, however, a particular arrangement
of the velTels around the carotid artery, jufl: at
the part where that vefTel paflTes into the cra-
nium: this is what the ancient anatomifts called
reie viirahile^ or 'ivonderful plexus. It was fonn-
erly fuppofed that this difpofition of vefTcls ex-
ifted in man; but it is now well known to pre-
vail only in a certain number of animals. The
Tollowing is its mofl; ufual diflribution : the
rete mirabilc is the produce of arterial ramifi-
cations, W'hich proceed from the carotid artery,
and which furround the pituitary gland: all
thefe minute branches, in which the artery feems
to be as it were diflTolved, arc rc-united anew
into one trunk. This at leafl appears to be the
cafe in the greater number of the Sarcophaga.
'I'hc elephant and the beaver do not prefent this
arrangement of velfcls.

'I'he arterial and various vclTels of birds arc
analogous to thofe of mammalia; but we have

not

Art. XI. Vessels OF THE Brain. 191

not yet examined them accurately. We pro-
pofe, however, to dirccT: our enquiries to that
fubjedt, both in them and in reptiles.

In fiflies, particularly in the cartilaginous
kind, as rays, Jharks, &c. the arterial vclTels of
the brain proceed from two recurrent trunks, of
the firll pair of branchial veins: thefc two ar-
teries afeend forward towards the cranium,
which they penetrate inferiorly, near the point
of its union with the vertebral column. Hav-
ing reached the cavity of the cranium, they di-
vide each into three branches, one of which
defeends into the vertebral canal, to be united
to its correfpondent of the other fide, and to a
Imall middle trunk, of which we lliall fpeak
hereafter. The union of thofc three branches
forms a large artery, which accompanies the
fpinal marrow inferiorly, and may be named the
fphial artery. A number of ramifications fe-
parate from it, which follow the courfe of the
nerves. The fecond branch of the vertebral
artery extends obliquely forward, under the
medulla fpinalis ; it there meets the middle
trunk, and the correfponding branch of the
other fide. The third branch of the vertebral
artery is more anterior ; having arrived at the
root of the medulla fpinalis, it fends off two
branches, which extend to a vafcular ring, pro-
duced by the middle velfel, which runs acrofs
it, fo as to form a kind of capital Greek phi
accompanied with two fcmi-circles affixed to it

in

192 L.IX. Brain of Animalswith Vertebra.

in oppofitc directions, thus 3^>c. The branch
ftill continues to advance until it reaches the
nerves of the eighth pair ; it there detaches two
new trunks, which being rejoined, form the
commencement of the middle veflel, which we
have fcveral times mentioned, and which ter-
minates by producing the fpinal artery, follow-
ing in this manner the inferior line of the
brain : the anterior branch continuing its direc-
tion forward, furnifhes a number of fmall arte-
ries to the cerebrum ; it pafTes under the origin
of the nerve of the fifth pair, and finally arrives
under the olfaClory tubercle, where it expands,
like the foot of a goofe, and furrounds it on
every fide.

Such are all the principal branches in the
brain of fiflies : the venous veflels are alfo very
numerous, and are diftributed into the greafy
or mucous liquor which covers the brain ; they
are not, however, fufticiently known to us to
enable us to deferibe them.

Article XIL

\

^ Of the Medulla Spimlis.

The elongation of the brain, which comes out
of the cranium by the foramen magnum, has

been

Art. XII. Medulla Spinalis. 193

been named Mednlhi Spinalis : it appears to be
formed, as we have already lliewn, by the union
of the two medullary productions of the cere-
brum and cerebellum.

The fpinal marrow appears externally to be
entirely conjpofed of a white fubftance, but af-
fumes a greyilh tinge internally. Covered with
its membranes, it has more conliftence than the
brain, but it liquifies alrnoft as foon as the en-
velope is removed. The form of this medul-
lary prolongation, is that of a cylinder, fome-
what comprelTed ; it feems to be compofed of
two cords, divided by two furrows, one on the
fide of the body of the vertebrte, and the other
on that of its fpinous procefs : on feparating a
little the edges of thefc furrows, we obferve
fibres which feem to crofs each other, and unite
the two fafciculi of the medulla; its thicknefs
varies in different parts of the canal through
V which it paffes. In general, the diameter of
the fpinal canal is greatefl: in the inferior part of
the neck. In this place the medulla fpinalis is
alfo largeft : it again experiences a kind of en-
largement towards the lafi: dorfal vertebras. In
the lumbar Region it contradls, and becomes co-
nical, and finally terminates in a filament,
which belongs to its envelope, and which is
placed at the extremity of the vertebral canal.
The ftrucfiure is nearly fimilar in all the red-
blooded animals.

The medulla fpinalis gives origin to as many
Voi. II, O pairs

N

19+ L.IX. Brain of Animalswith VERTEBRit.

pairs ot nerves as there are holes between the
vertebrae; thefe nerves receive names from the
region of the fpine whence they proceed.

The cervical ncr-ves are feven in number in
inofl ot the Mammalia ; the three-toed floth
and the Cetacea excepted. In birds this num-
ber is much greater. It is ufually fmaller in
the reptiles, and frequently there are none 'in
filhes.

The nerves of the other regions likewife vary
exceedingly ; but we adduce no more examples
here, becaufe they would be only repetitions of ‘
what we have flared in Ledl. III. Art. i.

The origin of all the vertebral nerves is nearly
fimilar; they appear to be produced by two
roots, one of which arifes before and the other
behind the medulla. Thefe two roots are fepa-
rated from each other by a membranous pro-
duction, which we fliall notice when we treat of
the membranes of the medulla fpinalis. The
nervous roots ifTue from the vertebral canal by
two diftind: holes which perforate the dura-ma-
ter before the intervertebral foramina. They .
afterwards unite and form a ganglion that pro-
duces vertebral nerves, which we fliall de-
fer! be in the next Ledlurc.

1. VejU’els of the Medulla Spinalis.

The arteries of the medulla fpinalis are nu-
merous : two arc furnifhed by the vertcbralcs;
one poflerior and the other anterior, which arc

diftin-

Art. XII. Medulla Spinalis. 195

difl’inguifhed under the name of fpinales : they
are diftributed in the pia-mater, and feveral mi-
nute ramifications penetrate into the fubfiancc
of the medulla itfelf. The others proceed from
the cervical, intercoflal, lumbar, facral and coc-
cygeal arteries. They enter the canal by the
holes through which the nerves pafs out of it,
'and communicate with other arteries, and with
each other, by a number of very fine anafiomofes.

The veins of the medulla fpinalis arc alfo
very numerous. Their fmall ramifications ex-
tend through the pia-mater, and empty them-
felves into two longitudinal finufes of the dura-
mater that invefts the vertebral canal ; thefe
two finufes are united by veins which have
tranfverfe communications correfponding to
each of the vertebrae. The firft of thefe com-
municating branches difeharges the blood into
the jugular foflae : the others empty themfelves
in the following manner, viz. the cervical into
the vertebral vein ; the dorfal into the inter-
cofial veins; and finally, the lumbar and facral-
into the veins of the fame name.

2. Membraiies of the Medulla Spinalis.

In the article on the envelopes of the brain, .
we obferved that the membranes of that vifeus
are prolonged into the fpinal canal, and cover
the medulla fpinalis. The whole is contained
in the olfeous canal forrtied by the vertebrse, the
number and articulations of which vary confi-

O 2 derably.

196 L. IX. Brain ofAnimalswith VERTEBRii:.

derably, as we have already Ihewn in the third
Ledture, when we deferibed the bones of the
fpinc. We then omitted the ftrudlure connected
with the paffage of the- nerves, and fliall now
proceed to notice it.

The annular part of each vertebra has a notch,
which is fituated inferiorly in the lumbar and
lowed dorfal vertebrae. It is common to both
edges of the adjacent vertebrae in the firft dor-
fal, and in the cervical. There is only a limple
hole in the odontoid or fecond cervical vertebrae.

This is the manner in which the nerves ilTuc
in the greater number of Mammalia and birds,
and even in the crocodile. Some quadrupeds,
however, as the horfe, have holes inftead of
notches. As the annular parts do not touch each
other in fiflies, they have neither holes nor
notches.

The pia-mater has a peculiar formation in the
interior of the vertebral canal ; it is prolonged
from each fide of the medulla, between the
roots of the vertebral nerves, in fuch a manner
as to make as many dcnticulations as there are
pairs ,of nerves. This duplicature of the pia-
mater has obtained the name of higamentum den~
ticiilalum : it commences about the margin of
the foramen magnum, and its dcnticulations
terminate towards the fird lumbar vertebrae; it
' is there confounded with the pia-mater, to which
it is applied. The fame difpofition prevails in
Mammalia and birds.

LEC-

C ‘97 ]

I

LECTURE TENTH.

DISTRIBUTION OF TIIF. PRINCIPAL NEUVi>
IN ANIMALS WITH VEUTEBR.E.

TThe central part of the nervous fyllem was de-
fcribed in the laft Lcdlure : we now proceed to
follow its branches in their diftribution to the
different parts of the body.

The mofl: remarkable circumftance this diftri-
bution prefents, is the fidelity with which Na-
ture follows one general plan, from which fhe
departs as little as polTible in the different fpe-
cies of animals.

This conftancy, of which we have already had
repeated proofs in thefkeleton, and the mufcles,
is ftill more remarkable in the nerves, though at
firft light it appears lefs necelfary.

Analogous parts always receive their nerves
from the fame pair in all animals, whatever be
the pofition of thofe parts, or however circui-
tous the courfe of the nerve may be in order to
arrive at them. Analogous nerves have alw^ays
a fimilar diftribution : they proceed uniformly
to the fime parts : even the fmalleft pairs, the
purpofes of which are mofl: limited, and which
might be moft eafily fupplied by adjacent nerves,
as the fourth and the fixth pairs, prefer ve their
exiftence and their proper ufes.

From

198 L. X. Distribution of the Nerves.

From this obfervation it feems reafonable to
conclude, that the nerves are not entirely fimilar
to each other, and are not like the arteries, every
where the conducflors of a fluid perfetftly the
fame ; but that there is, in the flruclure, mode
of aftion, and fecretion of each, fome peculiarity
relative to the functions and nature bf the organ
to which they are diftributed.

This is the principal confideration, which
renders the detailed comparifon of the nerves iit
the different claffes interefting to the phy-
fiologift.

' Article I.

*

Of the Olfactory Nerve, or the Firji Pair of the,

Brain.

A. In Man and other Mamniiferous Aninials.

We have pointed out the manner in which the
olfadory nerve arifes in Man, in the Mammalia,
and in the other claffes of red-blooded animals ;
-we fhall now follow' it through the cavity of the
cranium, until it enters the organ of fmell.

In man, when the olfadory nerve has reached
the inferior furface of the brain, it proceeds for-
ward above the membrana arachnoidea. It gra-
dually approaches the nerve of the oppofite fide ;

and.

Art. I. Olfactory Nerve. »99

and, when they arrive at the cribriform lamella
of the os cthmoides, the two nerves are feparated
from each other only by the tal x of the cere-
brum. In this courfe the nerve is received in a
jlijxht furrow’ of the anterior lobe. \NMien taken
out of the furrow, it appears trianinilnr. It is
terminated anteriorly by a final 1 and very foit tu-
bercle of a cincritious colour, the fibres ot which
enter the nafal fofl\e by the holes which pierce
the cribriform lamella of the os cthmoides.

Thefe nerves have nearly the fame difpmlition
in the monkey kind as in man ; but thofe arc the
only animals that prefent them diftin^d:, and in
an elongated form. In all the other families,
inftead of the w'hitifli cord which conftitutes
the olfaeftory nerve, w'e perceive only a large afh-
eoloured eminence w'hich fills the ethmoidal
fofia?. This medullary part is hollow, and com-
municates w'ith the cavity of the anterior ven-
tricle. To this fingular difpofition we muft at-
tribute the ignorance in which anatomifis have
fo long continued refipeding the olfadory nerve,
and the error which induced the antients to
conclude that thefe nerves, which they called
proceffus or carunciila mammilares, were the con-
duits which conveyed the pretended pituita of
the brain into the cavity of the noftrils.

Amongft Mammalia, the porpoifes and the
dolphins have no olfadory nerves. It is probable
that the other Cetacea likewife want them, as
they have no ethmoidal holes.

O4

B. In

200 L. X, Distribution of the Nerves.

I

B. In Bb'ds.

The olfadlory nerve of birds, after feparating
from the brain in the manner we have defcribed,
pafTes into an ofTeous canal, where it is accom-
panied by a vein, and thus reaches the cavity o,f
the nofe.

C. In Reptiles.

This nerve proceeds to the nolfrils in this
clafs nearly in the fame manner as in birds; but
it is longer. The canal which receives it is
partly offeous and partly cartilaginous. The
two canals have only one common' aperture
within the cranium. The olfadlory nerves of
reptiles are generally much more folid than thofc
of the preceding clalTes.

D. In Fijhes,

Cartilaginous fidies, as the ray and \\\tJJjarks^
have the olfadlory nerve very foft. It is in them
a bulb, which pa0’es obliquely forward towards
the nares, which are at a greater or lefs diflance
from the brain according to the fpecies;. In the
galeated Jhark or tope, the nerve which is at firft
Bender, afterwards enlarges, and forms a grofs
ganglion. In the le/fer dog-fijb (the Jqualns
itilits o( Linnxus) the nerve has much refem-
blance to that of the greater number of the

Mam-

I

Art. I. Olfactory Nerve.

201

Mammalia. It is thick, fliort, tubular, and fur-
rounded with an afh-coloured fubftance. It is
terminated by a femilunar ganglion, which is
feparated from the noftril by a membranous Icp-
turn. This fcptum contains various dcprelTions,
each of which is perforated by fcvcral holes,
which afford a paffage for the nervous ramifica-
tions into the membranes.

The fpinous fiffies have the olfactory nerves
very long and flcndcr. In thofe which have the
Ihout elongated, this nerve is received into a
cartilaginous tube. In thofe with ff.ort nofes
the nerve is furrounded by only a fine mem-
brane, which appears to be the fame as that
which contains the fat or oily humour that co-
vers the brain.

In moll: of thefc fifhes the nerve is of equal
breadth in its different parts. The genera
cyprinus and gadus, however, have it enlarged
at the nafal extremity into a round ganglion,
which refembles the cup of an acorn.

Article II.

Of the Optic Nerve, or the Second Pair of the

Brain.

In this article we fhall defcribe the courfe of
the optic nerve, merely from the point where it

fepa-

202 L. X. Distribution of the Nerves.

feparatcs from the correfpondent nerve after de-
cufTation, until it enters the globe of the eye to
form the retina. We fhall treat of its termina-
tion in the Lediire on Vifion.

In all rpd-bloodcd animals, without excep-
tion, the optic nerve arifes, as we have already
fhewn, from a particular tubercle of the brain.
After croHing the correfpondent nerve, it pro-
ceeds diretflly to the eye on the oppofite fide.

In mammiferous animals, birds and reptiles,
it is very difficult to diftinguifh thefe nerves
at their union : but in fifhes, particularly in
thofe that have an offeous fkeleton, it manifeflly
appears that thefe nerves crofs each other with-
out being confounded. They are in facfl con-
nedlcd to each other by cellular fubftance. We
obferve, and very eafily demonflrate, that the
optic nerve of the left fide proceeds to the right
eye, and vice verfa. In the cartilaginous fifhes
this deculTation is lefs apparent.

The optic nerve of large animals exhibits a
very remarkable firudture. Its neurilcma, or
the envelope furniffied to it by the pia-mater,
diVides it internally into a great number of lon-
gitudinal canals which contain the medullary
fubftance. This ftrmfturc is rendered very ap-
parent, when the medullary fubftance is dif-
folvcd by maceration, and the nerve inflated and
dried.— Sceftions of this nerve, thus prepared,
demonft rate the arrangement of the canals which
traverfe it.

Thefe

Art. II. Optic Nerve. 203

Thefe nervous filaments are, however, more
feparatc in the optic nerves of filhes, in which
they can be dernonfirated without any particular
preparation. They are commonly flat like the
other nerves, and fometimes aj)pear to be formed
by a very thin medullary lamina, which is told-
cd feveral times on itfclf, and contracted into
the figure of a cord. This is particularly the
cafe in the cod and i\\c fzvord fijb.

Article III.

Of the Ncrccs of the Thinly Fourth^ and Sixth

Fairs.

1. Of the Oculo-Mufeidar Neree^ gr the Third

Pair.

A-fter entering the dura-mater at the fide of
the pofterior clinoid procefs, each of thefe nerves
pafles in the fubftance of that membrane until
it reaches the broadefl: part of the fpheno-orbitar
fiflTure. When arrived in the orbit, the nerve
divides into two branches; one, which is fmall,
is diftributed to the mufcles called redus fupe-
rior oculi, and levator palpebrtE fuperioris. It
frequently contributes to the formation of the
ophthalmic ganglion which produces the ciliary
nerves. The other branch is fomewhat more

con-

204 L. X, Distribution of the Nerves.

confiderabic. It divides into three ramifications;
one is fent to the abdud:or oculi, another into
the recflus inferior, and the third terminates in
the obliquus major.

This brief defeription of the oculo-mufcular
nerve in man, may be applied to almofi: all red-
blooded animals. In all of them it pafles into
the orbit by a particular hole, when there is no
fpheno-orbitar fifiure, either fingly, or accom-
panied by fome of the other nerves appro-
priated to the organ of vifion, and is difiri-
buted in the fame manner. We fliall, however,

( have occafion to return to this nerve, and thofe
that follow it, when we treat more particularly
of the ?ye. We (hall merely remark here, that
in the rays and the Jharks^ in which the globe of
the eye is fupported upon a moveable peduncle,
one of the branches of the oculo-mufcular nerve
paffes acrofs that cartilaginous peduncle, by a
particular hole, in order to be diftributed in the
mufcles fituatcd below it.

2. Of the Pathetic No've, or the Fourth Pair.

Thefe nerves pierce the dura-mater behind the
preceding, and a little more towards the middle
line. They arc more (lender than the nerves
which iffue from the bafe of the cranium.
Lodged in the folds of the dura-mater, they
extend towards the fuperior orbitar fiffure, and
pafs into the orbit by the widefi part of it;

then

Art. III. Abductor Nerve.

2O5

then turning towards the roof of the orbit,
they terminate in the obliquus major.

The diftribution of this nerve is the fame in
moft of the red-bloodcd animals. \N e have had
the opportunity 'of examining.

d. OJ the Abductor Kerve, or the Sivth Pair.

The finglc trunk, or the two branches whicii
compofe this nerve within the cranium, pene-
trate the dura-mater above the point of the os
petrofum. They advance a fliort way between
its lamina, and reach the cavernous finus, where
they are united, and bathed in the blood of the
finus. The nerVe then becomes fomewhat thick-
er ; it receives or gives a number of filaments,
which communicate with the great intercostal
nerve. It afterwards proceeds into the orbit by
the fuperior fifiure, and terminates in the fub-
ftance of the abdu(5lor oculi.

We have oblerved that the fame difpofition
prevails in other red-blooded animals.

Article IV.

Of the Tri-facial Ner>v€s, or the Fifth Pair.

We have pointed out the manner in which the
nerve of the fifth pair feparates in vertebral

animals ;

/

2o6 L. X. Distribution or tub Nerves.

animals; we fhall now follow each of its
branches, in the different clafTes, commencing
with the ophthalmic branch, or that which pro-
ceeds to the eye.

I. Qf the Nerxnis Ophthdlmicw^, or Firjl Branch
of the Fif th Pair in Man, and other Mammi-
ferous Animals.

A. In Man.

t

The firfl: branch of the fifth pair comes out of
the cranium, by the fpheno-oirbitar filTurc, with
the third, fourth, And fixth pairs. It frequent-
ly detaches a very remarkable tranfverfe branch
to the fourth pair. Before it reaches the inte-
rior of the orbit, and while it is ftill covered by
the dura-matet, it divides into three branches :
one is dire<5tcd towards the nafal edge of the
btbit ; the fccond towards the arch or frontal
edge; and the third towards the temporal edge.
The fccond is the thickeft of the three.

The na/al branch is inferior and internal ; it
divides into two fmallcr ramifications.

One of thefe branches proceeds towards the
optic nerve, unites with the fmall branch of the
third pair, which is font to the lefler oblique
mufcle, and by this union produces a nervous
enlargement, called the lenticular or ophthalmic
ganglion. 'I'his ganglion ufually fends off the
ciliary nerves difpofed in two bundles. They

arc

Art. IV. Tri-facial Nerves. 207

are each compofed of fevcral filaments, which
enter the globe of the eye obliquely, where we
fliall have occafion to examine them when wc
treat of that organ.

The other branch, called the ethmoidal, alfo
frequently furnilhes one or two fmall twigs,
which unite to the bundle of the ciliary nerves,
it proceeds along the nafal edge of the orbit,
and divides near the anterior internal orbitar
hole ; one of the filaments enters that hole,
follows the canal of which it is the aperture,
re-enters the cranium below the dura- mater,
comes out again towards the anterior edge ol
the cribriform lamella, penetrates the nafal
membrane, and is loft above the fuperior Ipongy
bones, and on the fides of the vertical lamina;
Thefecond filament proceeds towards the pulley
of the obliquus major, and divides* into a great
number of fibres, fome of which are diftributed
to the fkin of the forehead, near the nafal angle
of the orbit ; others to the orbicularis palpebra-
rum; fome to the frontal mufcle, the caruncle,
and the membranes of the lachrymal canal.
Some of thefe fibrillse ufually unite to others
which come from the facial and fub-orbitar
nerves.

The fecond branch of the ophthalmic is called
the: frontal. It is lituated between the periofteum
of the roof of the orbit, and the elevator, of the
fuperior eye-lid. It is feparated almoft from its
origin into two branches ; one, which is the

6 moft

2o8 L. X. Distribution Of th£ NeUves;

moft internal, is direcHied towatds the obliqu-us

major oeuli, and unites with fome filaments

produced by the fecond branch of the divifion

of the ethmoidal branch : the other, which is

/

more external, proceeds to the outfide of the
- orbit by the fupra-orbitar hole or notch, and ex-^
pands on the forehead, giving filaments to the
Ikin, the adjoining mufcles, and the periofteumi
Lafily, the third branch of the ophthalmic
nerve is called z\\q lachrymal. It is fituated towards
the temporal or external edge of the orbit, and
proceeds towards the lachrymal gland. Before
it reaches that gland, it is divided into feveral
filaments ; one paffes through the gland, and is
loft in the tunica conjunctiva: another is diftri-
buted almoft entirely in the gland; a third, and
fometimes a fourth, after alfd going through
the gland, divides into feven or eight filaments,
feveral of which pafs into the temporal fofta
by the fpheno-maxillary filTure, and join with
other filaments from the deep feated temporal
nerve; one of thefe pierces the os-jugale, and
unites on the check with branches of the facia)
nerve.

D.- Ill other Momniferous Animals.

The ophthalmic branch in Mammalia reaches
theorl)it by the fpheno-orbitar fiffurc, or rather
foramen, which is al fo the optic foramen. It
is feparated into two other branches within the

cranium.

Art. IV. Tri-facial Nerves. 209

cranium, and paires in the fubftance of the dura
mater, with the third, fourth, and fixth pairs.
Upon reaching the interior ot the orbit, it di-
vides, as in man, into three branches.

That of the internal part of the orbit, which
Correfponds to the naful, is the largell of the
three. It is divided into five or fix fmall
branches. ' Some penetrate the frontal fmufes,
by fmall holes in the vault of the orbit, which
are very apparent in the Jfjcepy others .w hich arc
confidcrably larger enter the nafal cavity by the
internal orbitar foramen. Inclofed in an olfeous
canal, theyafeend into the cranium through the
large holes in the os cribri forme, which we have
already noticed, and then go out again by the
ethmoidal foramina, to be dillributcd to the
nafiil membrane. They may be ealily followed
in the Ruminantia. One or tw'o others go to
the levator palpebrae fuperioris mufcle. One of
thefe twigs alTiIls in forming the lenticular gan-
glion. In the dog^ two ciliary nerves arife from
this ganglion, which are afterwards divided :
three or four filaments rife from it in the calf.
Finally, one or feveral of thefe filaments termi-
nate in the obliquus inferior, and in the glan-
dula Harderi, of which we fiiall fpeak in treat-
ing of the Organ of Vifion, and the tears, Thefe
nerves are particularly remarkable in the Rumi-
nantia.

I

The middle branch of the ophthalmic nerve is
fuperior. It is fituated under the olfeous roof of
VoL. II. p the

210 L. X. Distribution of the Nerves.

the orbit, and is divided into two principal ra-
mifications i one, which is external, furnifhes
two filaments, that are loft in the re6lus fuperior
oculi and elevator of the eye-brow, anaftomof-
ing, at the fame time, with other filaments.
The internal ramification tranfmits branches to
the mufculus recftus internus, and one which is
very remarkable, and frequently a very thick
twig, pafting through the fuperciliary notch
or foramen, fpreads under the flein of the fore-
head, where it is loft in the mufcles.

The third branch of the ophthalmic nerve is
compofed of a great number of filaments,
which, though clofe to each other, are very dif-
tincft. They are almoft all loft in the lachrymal
gland.

II. 0/ the Ncrims Maxillaris Superior, or Se-
cond Branch of the Fifth Pair in Man and

other Mammiferous Animals.

\

A. In Man.

Having pafted out of the cranium through
the round foramen of the os fphcnoides, this
nerve almoft immediately furniftics a fmall
branch, which enters the orbit by the inferior
filTurc of that fofta. This branch unites with ^
another belonging to the lachrymal nerve, with
which it palTes, as wc have already fiiewn, into a

fmall canal of the os jugalc, to be diftributed on

the

2

Art. IV. Tri-facial Nerves. 211

the cheek, anaftomofing at the fume time with
the facial and fub-orbitar nerves, and fometimes
behind with the temporal filaments oi thq infe-
rior maxillary.

The maxillaris fuperior having reached the
interval between the bafe of the pterygoid pro-
cefles, and the fuperior part of the malar tubero-
fity, fends off one or two branches, which in the
latter cafe almoft immediately re-unite, and form
a ganglion or enlargement, which is fituated be-
fore the fpheno-palatine foramen. Several fila-
ments proceed from this ganglion in different
directions, and form very remarkable nerves :
they are fubjedl to variation in their number,
but feldom in their diff ribution.

Four or five filaments proceed, in the firfl
place, from the internal fide : thefe enter the
noftrils by the fpheno-palatine foramen, and
are diftributed to the olfactory membrane.

We next obferve behind the ganglion, another
fmall filament; which entering the canal at the
bafe of the pterigoid procefs, proceeds pofferi-
orly to the point of the os petrofum. This has
been named the Vidian nerve, from the author
who firfl deferibed its courfe. On leaving this
canal, the nerve forms two branches ; one of
thefe branches returns into the cranium, paffes
through a fmall hole of the os petrofum, which
joins the canal of the portio dura, and in which
it is united to the facial nerve. The other
branch of the vidian nerve enters the canal of

P 2 the

212 L. X. Distribution of the Nerves.

the carotid artery, and is united to the filaments
of the fitth pair, which join the fympatheticus
major. Sometimes this branch accompanies
the carotid artery, and only unites with the
great fympathetic nerve in the fuperior cervical
ganglion.

Laflly, the largefl branch, which appears to
be the continuation of the trunk, arifes from
the inferior part of the ganglion ; a great part
of it enters the pterygo-palatine canal, and it
is there divided into feveral filaments, which
pafs through the bone : fome arc difiributed in
the olfactory membrane, and others lofe them-
felves polteriorly in the uvul^ and the fma-11
mufcles. The trunk comes out by the pofte-
rior palatine foramen, and proceeding forward,
is divided into two or three branches on the
arch of the palate.-

Having detached the two branches which pro-
duce the fpheno-palatine ganglion, the maxil-
lary nerve proceeds towards the aperture of the
fub-orbitar canal ; but before it enters that ca-
nal, it furniflies a fmall branch, called the aU
veolar, which is frequently divided into two
others ; one enters the maxillary finus, another
proceeds to the alveoli, into which it penetrates.
It furniflies alfo a number of filaments to the
gums and mufcles of the li]is.

1 laving paired into the fub-orbitar canal, this
nerve takes the name of fub-orbitar : it detaches
a confidcrablc branch, which proceeds in the

fubfiance

Art. IV. Tri-facial Nerves.

213

fubflance of the bone, penetrates the finus, and
is diftributed to the roots ot the teeth. The
trunk iffues from the bone through the fub-or-
bitar foramen, and having reached the cheek,
all its filaments are loft in the mufcles ol the
face, a great number of them uniting with the
ramifications of the facial nerve.

13. In other Mammiferoiis Animals.

We have already obferved, that the maxillary
nerves come out of the cranium, in the greater
number of thefe animals, by the hole iituated
in the middle fofia, before the fpine of the os
petrofum.

The fingle trunk, when it arrives on the oiitfide
of the cranium, becomes confiderably enlarged,
and its fibres feem to crofs each other in fuch a
manner, that the two branches which it foon
after forms, appear to be produced by oppofite
filaments, viz. the pofterior, or fub-maxillary
branch, by the anterior filaments, and the an-
terior, or fupra-maxillary branch, by the pofte-
rior fibres. This difpofition is very remarkable
in dogs^ but is lefs confpicuous in the Rumi-
nantia.

The fupra-maxillary nerve proceeds almoft
horizontally from behind, forward. Having
reached the anterior and inferior parts of the
temporal foifa, it divides into a great number
of fafciculi. One bundle, which confifts of

P 3 four

I

214 L. X. Distribution of the Nerves,

four or five confiderable filaments, proceeds to-r
wards the fpheno-palatine foramen : this fafci-r
cuius then divides into two ; one branch is fent
into the cavity of the noftrils, and furniihes a
confiderable ramification, which is fpread out
upon the flefhy fubftance of the palate. Some-
times, as in the Ruminantia, this branch fepa-
rates from the trunk, even before it enters the
fpheno-palatine hole.

The other branch of the maxillaris fuperior,
which enters by the fpheno-palatine foramen,
pafies into the body of the os maxillare fupc-
rius, detaches ramifications to all the teeth, and
goes out by the fub-orbitar foramen ; it then
expands in the form of a goofe’s foot over the
face, and anaftomofes with the facial nerve.

But befides thefe two principal branches pro-
duced by the fuperior maxillary nerve, there
are fome other very remarkable liiaments, which
are detached almoft immediately after it leaves
the cranium. 1

The firfi; is a very fmall twig, which, after
anaflomofing with a ganglion, of which we
fliall fpeak hereafter, is fent into the body of
the temporal mufcle, through which it palfes,
affording it, at the fiime time, a number of fir-
laments ; it afterwards perforates the inferior
part of the orbit, and penetrates into the nofe.

Another, and far more remarkable filament,
arifes from the fpheno-palatine branch ; it forms
a ganglion, which is joined by feveral twigs,

and

Art. IV. Tri-facial Nerves. 215

and among others, by that which wc have juft
defcribed. A flat nerve afterwards feparates
from this ganglion, which, though much larger,
appears to be the continuation of the filament
at prefent under confideration : it paflTes into the
body of the bones, between the palatine and the
convexity of the pterygoid procefs: it furnilhes
feveral filaments, one of which is very diftin<ft,
and defcends to the floor of the noftrils.

Such is the general diftribution of the fuper-
maxillary nerve in moft mammiferous animals.
This fuccin(ft defcription, taken from the dog^
the rabbity the Jheepy and the calfy proves that
the diftribution does not differ from that which
takes place in man, except in circumftances
neceffarily refulting from the conformation of
the bones of the face.

TIL Of the ±^-erx'us Ma.vUlaris Inferior^ or
Third Branch of the Fifth Pair, in Jfan, and
other Mammiferous Animals.

A. In Man.

This is the largeft of the three branches fur-
nifhed by the tri-facial nerve ; it comes out of
the cranium, as we have already obferved, by
the oval foramen of the os fphenoides. It ap-
pears, at the bafe of the cranium, on the edge
which feparates the temporal from the guttural
folTa, on the inner fide of the external ptery-

P 4 goid

lib L. X. Distribution of the Nerves,

^oid mufcle ; it is almoft immediately divided
into two principal trunks, one fuperior, the
other inferior. The firft is fubdivided into five
branches, and the fecond into three. Thus
there are eight divifions of this nerve.

1. The firfi branch detaches fome filaments
to the articulation of the jaw, and to the tem-
poral mufcle; then, proceeding upward to the
notch between the two proceffes, dt penetrates
into the heart of the mafleter mufcle, through -
which it is diftributed.

2. and 3. The fecond branch of the firfi: trunk
palTes info the pofterior and lower part of the
temporal mufcle. The third alfo proceeds in
the fame direiftion, but a little more anteriorly ;
it frequently anaftamofes with a filament of the
lachrymal nerve, as w’e have already obferved.

4. The fourth branch palTes between the two
pterygoid mufcles, to w'hich it detaches fome
fmall filaments; it then proceeds to the outfide
of the buccinator mufcle, where it divides into
a grea,t number of filaments, fome of w’hich are
difiributed to that mufcle, and the mufcles of
the lips in general, while others unite with the
facial nerve.

The fifth branch is one of the final left ; it
is fent into the internal pterygoid mufcle, and
thofc of the velum palati.

6. The fixth branch appears to be the trunk
pf the nerve itfelf ; it therefore retains the name
pf maxi Haris iufcrioY ; it pafics between the two

pterygoid

Art. IV. Tri-facial Nerves. 2I~

pterygoid mufcles, and is dircvflcd towards the
dental canal of the lower jaw ; but before it
enters it, fome filaments are detached to the
inylo-hyoideus and digaftricus, and to the fub-
maxillary glands. In pafiing along the canal,
it diRribiitcs branches to each ot the teeth, and
ilfuing from the jaw through the toramen mcn-
tale, is loll: amongll the mufcles ot the lower
lip, analfomoling occaiionally \\ith filaments ol
the facial nerve.

y. The feventh branch is deflined for the
tongue ; it advances, with the preceding, be-
tween the pterygoid mufcles ; it there receives
a fmall filament, which is derived from the fa-
cial nerve, and which has been named chorda
iympani : it proceeds towards the tongue, and
when arrived at the origin of the If ilo-gloflTus
mufcle, above the maxillary gland, it produces
fome fibres, which are frequently united, and
form a fmall ganglion, from which fome fila-
ments that penetrate that gland are detached.
The nerve afterwards pafles between the hyo-
glofl'us and the gland fituated below the tongue.
It penetrates the body of that organ, and is dif-
tributed in its fubftance, in the mufcles which
fuftain it, and in the fkin which covers it.

8. Laftly, the eighth branch is the mofi: pof-
terior ; it frequently arifes from two roots, be-
tween which a fmall artery is tranfmitted. The
f^ngle trunk paffes behind the condyle of the
jaw, before the meatus auditorius : it is fubdi-

vided

2iS L. X. Distribution OF THE Nerve-s.

vidcd into a number of fmall filaments, many
of which unite with the facial nerve on the ex-
ternal part of the temporal mufcle. On this
account it has b’een called the Juperficial temporal
nerve.

I). In other Mammiferous Animals.

We have fliewn the difpofition of this branch
in the Mammalia, until its exit from the cra-
nium by the foramen ovale. It furnifhes, al-
mofl: immediately after its reparation, a pretty
large branch, which is direded into the parotid
and maxillary glands ; it afterwards divides into
two other branches, one internal, which lofes
itfclf by feveral fmall filaments in the body of
the mufcles, and even in the fubfiance of the
tongue; the other, which is external, affords a
number of ramifications to the pterygoid muf-
cles, and to thofe of the cheeks and lips, which
they traverfe in their progrefs towards the fl-ciii
of the face, where they unite with the filaments
of the fub-orbitar and facial nerves. The lar-
gefl filament, or the continuation of the branch
itfelf, paffes into the dental canal ; it* there fup-
j)lies the teeth, and ilfuing from the fora-
men incntale, terminates in the mufcles of the
lip, in the form of a goofe’s foot. The other
fmall fil imcnts arc diflributed nearly as in man.

Ill the ruy’the inferior maxillary nerve di-
vides into four principal portions, foon ^ftcr it

leaves

Art. IV. Tri-facial Nerves. 219

leaves the cranium. The moft pofterior, which
is the third, with refpedl to thicknefs, proceeds
backward, and below the condyle of the jaw,
where it forms two branches : one is flendcr, and
penetrates the parotid gland, where it divides
into a number of fmall filaments, which unite
with thofe of the facial nerve ; the other branch
follows the circuit of the jaw, and advances to
the front of the mouth ; it unites, as it palTes
along the cheek, with the middle branch of the
facial nerve, from which it previoufly receives
feveral anaflomofing filaments.

The next branch of the maxillaris inferior is
the molt flender of the four ; it is very long,
follows the ramus of the jaw, and is loft in the
buccinator mufcles and buccinal glands.

The third branch pafles into the dental canal,
and is there diftributed, in mammiferous ani-
mals in general, as we have already pointed out.

Finally, the fourth is the lingual branch ;
this is the thickeft and the moft anterior; it is
flat, in the form of a broad ribbon. It termi-
nates like a fan in radii, which run into the
mufcles of_^the tongue, and the parictes of the
mouth.

IV. Of the Nerve of the Fifth Pair h? Birds.

The fifth pair prefents nearly the fame diftri-
bution in birds, as in Mammalia.

The ophthalmic nerve comes out of the cra-

nium

220 L. X. Distribution of the Nerves.

/

nium by a particular foramen of the orbit on
the outfide of the optic nerve. It proceeds
fome way in the fubftance of the bone before
it reaches its furface. It is thick, and defcribes
a curvature which follows that of the arch of
the orbit. Its divilion does not commence un-
til it is beyond the fofla ; it ufually penetrates
into the body of the bones of the face above the
nafal finufes. It divides into three branches,
the fuperior, which is the fmalleft, is loft in the
pituitary membrane. The fecond branch, which
is the thickeft of the three and the longeft, is
received into an ofteous canal, pafles above the
nares, and terminates at the extremity of the
bill by a great number of filaments. The third
branch appears to be entirely loft in the fkin
which furrounds the aperture of the noftrils.

The fuperior maxillary nerve comes out by
the fame hole with the inferior, precifely above
the os quadratum. It proceeds from behind
forward to the inferior part of the orbit. Two
filaments are detached from it in its progrefs ;
one unites with the ramifications of the ophthal-
mic nerve ; the other afeends towards the in-
ternal fide into the body of the pterygoid muf-
cles. It penetrates the maxillary bones, and
lofcs itfclf on the lateral parts of the bill. Its
difttibution is very remarkable in ducks. Each
of the denticulations with which their bill is
furnifiied, appears to receive four or five fila-
ments.

The

Art. IV. Tri-facial Nerves* 221

The inferior maxillary nerve feparates from
the fuperior, and is dire<fled obliquely down-
ward. It detaches at firft fomc branches to the
pterygoid mufcles, and to the quadratus, which,
we (hall deferibe when we treat of madication:
The trunk afterwards defeends outwardly, and
when arrived at the inferior jaw, it divides into
two branches, one internal and one external ;
The internal, which is the continuation of the
trunk, penetrates the maxillary canal, and pro-
ceeds, in that manner, to the anterior extremity
of the mandible. In birds that have denti-
culations, as ducks, each procefs receives fila-
ments from this nerve. The external branch
feparates from the preceding, pafles through
the bone of the mandible, and fpreads upon its-
outfide, under the Ikin or horny fubftance w hich
covers the bill to its extremity.

V. OJ t/ie Nerve of the Jifth Pair in Reptiles.

Reptiles have the three branches of the fifth'
pair. In the fea tortoifes the ophthalmic palTes,
fome way, in the dura mater before it enters the'
orbit. It' tranfmits filaments to the mufcles of
the globe of the eye, and particularly to the two
lachrymal glands. The fuperior maxillary
branch is the largeft of the three. It is united
to the inferior branch at its origin, but when it
reaches the interior of the orbit, it feparates from
it to take another diredlion. It palTes along the

floor

\

i22 L. X* Distribution of the NerVes.

floor of the orbit, defcribing a very marked cur-
vature, the convexity of which is external. A
very great number of filaments proceed from
the concave or internal fide, which are loft in
the lachrymal gland. The trunk is afterwards
divided into tw'o branches : — one internal, which
correfponds to the fpheno-palatine and fub-or-
bitar nerve. It furnifhes filaments to the pa-
late and to the nerves ; and when arrived at the
anterior part of the orbit, it proceed,s outwardly
and fpreads upon the face. The other branch
of the principal trunk is external ; it pafTes alfo
upon the floor of the orbit, to which it gives
many filaments, and at length iffuing from the
inferior part of the orbit, it expands upon the
face, anaftomofing with the other facial nerves.

The inferior maxillary branch proceeds al-
moft vertically downward to the poftcrior part
of the orbit, before the petrous and articular
procefs of the os temporum. In its courfe to-
wards the lower jaw, it pafTes between the tem-
poral and pterygoid mufclcs, to which it fends
feveral filaments. Having arrived at the lower
jaw, before the articular furface, it enters the
oblong aperture, and divides in the fubftance of
the bone. It forms feveral branches on the in-
ner part of the jaw, which are loft in the muf-
- cles of the tongue, and on the outfide Tome
others which ramify under the Ikin.

VI. Of

Art. IV. Tri-facial Nerves.

223

VI. Of the Nerve of the Fifth Pair in Fifics.

We alfo find in fifiies the three branches of
the fifth pair, which we obferve in man.

The ophthalmic or mofl: fuperior branch arifes
in the cranium, and proceeds obliquely outward
and forward towards the poftcrior part of the
orbit, into which it penetrates. Arrived there, it
prefents fome variations in different fpecics with
refpedl to its fub-divifion. It ufually furnilhes
three principal branches as in the carp, the fal-
mon, the cod, and probably in the other fpinous
fiffies j bur in the ray, and in the faw-Jhark
(fqualus prijlis) this divifion takes place at a
greater diftance, and beyond the orbit, as we
ffiall fee in deferibing thefe branches.

The firft branch is the fmalleft and the moff; '
internal. It terminates at the margin of the
cavity of the nares. In the ray the branch
pafles out of the orbit without dividing, foon
after it detaches two filaments : one, which is
thick, crolTes above the nares, to which it de-
taches feveral filaments, and palTes on to lofe it-
felf in the lateral parts of the fnout. In the
fawfjark, the part of the ophthalmic branch
which proceeds to the nares, is not remarkable.
It confifts of fingle filaments which are detached
from the branch we are about to examine.

Thefecond branch of the ophthalmic nerve of
the internal fide in fpinous fiffies, is the moff:

con-

£24 L. X. Distrikution of the Nerves.

confideracle of the three. It divides into two
branches, one of which ramifies in the ficfhy parts
ot the upper lip, where its filaments unite ^'ith
thofe of .the maxillaris fuperior. The other is
diflributcd in the fott parts adjacent to the an-
gle of the mouth. This, at leaft, is the difpo-
lition in the falmon, and the carp. In rays the
continuation of the trunk fupplies the place of
this branch. It is direcled forward towards the
extremity of the fnout where it terminates. In
the fa%v-Jfoarkt the branch we are now tracing
proceeds above the mufcles of the bail of the eye,
and is fent fotward into a groove formed above
the fnout. It there divides at the external fide
into an infinite number of filaments, in the form
of network, the ramifications of which appear
to proceed to the teeth or hooks with which the
fnout of this filli is armed.

The third branch of the ophthalmicus proceeds
to the lateral parts of the face, and is dillributed
to the rnufclcsofthe jaw'S in fpinous fifnes. This
branch does not exifl; in the rdy^ but in the Jais:-
fhark it is very diftind:, and very l;;rgc. It pafTes
through the orbit below the two fuperior muf-
cles of the eye, furnifliing fome filaments which
fcxtend to the bulb. It is thendireded forward,
and confounded with the preceding branch.

We ought not to omit noticing here one very
remarkable peculiarity, to which wc ihall, how-
ever, return in the article on Secretion. The
' two branches of the ophthalmic nerve appear to.

(^ change

Art. IV. Tr!-facml Nerves.

225

change their nature at the place where they rc-
miirc. They afl'urnc a black colour, anJ parti-
cular confiftcncv, VVe have hatl occalion to
make the fame obfervation on this black colour
of the nerve in the /i’/'r, (fqnalns ^a!ens'\ irt
Avhich it is ftill more confpicuous, and in which
its ‘‘flillribution is highly important. In this
fpccies all the advanced part of the head, before
the m.outh, is perforated with numerous pores,
through which a gelatinous humour exudes, on
the flightelt compreflion. When the tkin is
rernovcii, wc obferve that this humour is con-
tained in certain cells, formed by a very com-
pact white fibrous fubllance. A great number
of the extremities of the nerves are didributed
to the parietes of thefe cells. We fliall re-
turn hereafter to the prefumed ufes of this
liquor. It is fuflicient at prefent to notice its
exiftence.

The fccond branch of the fifth pair of nerves,
which reprefents the maxillaris fuperior, is in-
termediate. It palTes below the optic nerwe,
towards the middle and inferior part of the cra-
nium. Having arrived below the nares, it di-
vides into two, three, or feveral branches/ fome
ot which proceed towards the angle of the
mouth, and terminate in the cirri, xvhen thefe
appendages exift ; others proceed towards the
middle part, where they are diftribiited into the
fubftance of the lips. This, at lead, is the cafe
VoL. II.

in

226 L. X. Distribution of the Nerves.

in the fpinous liflies we have had the opportu-
nity of examining.

The fazv-Jhark and the ray exhibit different
appearances. In the firfl: of thefe fiflies, the max-
illaris fuperior is divided, almoft immediately
after it leaves the cranium below the orbit, into
three principal branches. The firft, which is
diredled forward, and is very thick, paffes be-
low the mufcles of the eye, to which it tranf-
mits fome filaments. It in particular detaches
one which proceeds into the globe of the eye; it
then paffes to the inferior furface of the root of
the fnoiit, fends fome filaments to the margin of
the nares, and afterwards penetrates into the
longitudinal canal of the muzzle, which re-
ceives the ophthalmicus. The middle branch
confifts of feveral filaments, which are difiri-
buted to the mufcles of the mouth, and princi-
pally towards its angle, where they are loft in
the fkin which forms the lips. In the tbornback
(raja clavata) the difpofition is nearly the fame,
but we obferve that the filaments which in the
fazv-Jhark appear to terminate in the hooks of
the fnout, terminate in the tubercles or fpines,
with which the dillerent fpecies of rays are
armed.

. 'J he third branch of the fifth pair, or maxil-
laris inferior, prefents no peculiarity. In tli,e
olfcoLU fifhes, when it arrives towards the angle
of the jaw, it is loll in the bones which form it

by

Art. V. Facial Nerve.

527

by very fine filaments ; the number of which
varies. In the chondropterygii, this nerve is
diredled much more backward, and is diftri-
buted among the mufcles of the lower jaw.

Article V.

li

’»

1 1

'i

Of the Facial Xcrve, or Si/mpatheiicus Jlinor

of Jl iujloii'.

I

A. In Man.

We have explained the origin of this nerve,
and lliewn that it is almofl always diftincfl from
the portio mollis. Having entered the meatus
audkorius internus, it pafies into the canal
named the aquadn^l of Fallopius.

It follows the different curvatures of that ca-
nal, and receives in it the filament of the vi-
dian nerve, which we pointed out in treating of
the fpheno-palatine ganglion of the fupra-max-
illary branch. It afterwards furnifhes, in the
cavity of the tympanum, two fmall twigs to the
officula auditus ; and another more coniiderable
one, feme lines before it pafles out, through the
ftylo-maftoid foramen. This filament enters a
fmall 'ofleous canal, which conducts it into the
cavity of the tympanum. It palTes under the in-
cus on the tendon of the internal mufcle of the

O 2 malleus.

21% L. X. Distribution of the Nerves.

malleus. It goes out by a fmall hole in the bafe
of the tympanum to communicate with the lin-
gual portion of the third branch of the tri-facial
nerve, or fifth paij', to which it unites by a very
acute angle.

Having left the bafe of the cranium, the fa-
cial nerve divides into fevcral branches, which
vary in number, but which frequently amount
to fourteen or fifteen.

, The moft poflerior is called the occipital. It
proceeds behind the mafloid procefs, unites to a
fuperior cervical pair, and is afterwards divided
into two fmaller branches, one of which is loft-
on thcconcha of the ear, and the other in the fkin,
and fuperior part of the mufclcs of the neck.

The fccond branch communicates by one or
two filaments w’ith the fuperior part of the cer-
vical ganglion of the fympatheticus major. It
terminates in the mufcles which arife from the
ftyloid procefs, and on that account has been
named i\\q Jlylo-hyoidean branch.

The third branch is fent to the digaftric muf-
cle.

The trunk of the facial nerve pafles after-
wards into the parotid gland, which it croftes,
and to which it alFords a great number of fila-
ments.

The fourth branch produced by tho facial
nerve is diftributed to the anterior part of the
concha of the ear, and to the aponcurolis of the
temporal niulclc.

The

Art. V. Facial Nerve.

229

The fifth and lixth branches are difpofed of
nearly in the fame manner, and form with each
other very numerous anafiomofes. They are
called the temporal or jugal nerves.

The feventh branch very much refembles the
preceding. It unites with them and with the
adjacent branches, and proceeds to the orbicu-
laris palpebrarum mufcle, where it terminates
in a kind of plexus.

'The eighth branch is divided almoft imme-
diately after its origin into three others, which
alfo extend to the orbicularis, but terminate
in its inferior part.

The ninth branch pafies between the du^fl of
the parotid g'land and the zygomatic and maf-
feter mufcles. It proceeds towards the internal
angle of the eye, forming a large plexus on the
face, and uniting with a great number of fila-
ments of the fub-orbitar nerve.

The tenth, eleventh, twelfth, and thirteenth
branches alfo go to the face, one under the
other. They furnifii filaments to all the muf-
cles, and form a real nervous net -under the
fkin.

The fourteenth branch follows the edge of
the lower jaw. It is loft in the mufcles of the
lower lip, and unites with the nervous plexus of
the face.

Laftly, a number of filaments come from the
parotid gland, which have arifen from the di-
vifion ol the facial nerve. Some unite with the

branches

230 L, X. Distribution of the Nerves.

j

branches we have deferibed ; others are loft in
the mufculus cutancus, and in the fkin.

It follows from this defeription of the facial
nerve, that it covers the whole of the face, the
temples, the ears, and a portion of the occiput
and neck, and that it communicates with a great
number of other nerves ; this induced Winftow
to name it Jyynpatheticus minor.

B. In other Mammijerous Animals.

We find almoft all thefc branches in the other
Mammalia ; the variations depend entirely on
the different forms of the parts to which they
are diftributed, and the extent of the mufcles.
In animals, for example, that have the concha
of the ear very long, the branch which unites
with the firft cervical pair is much larger, and
may be more eafily traced on the fiirface of the
cartilages, where it accompanies the blood-
veflels. In the fame manner, we find that the
branches which proceed to the temporal mufcle,
are very large in the Sarcophaga. It may in
general be remarked, that the facial plexus is
more complicated.

As we have particularly examined this nerve
in the calf, it will not be improper in this place
to prefent a fuccineft defeription of it.

It leaves the cranium by the fiflurc at the
bafe of the maftoid procefs ; it crofl'cs the pa-
rotid gland, to the fubftance of which it tranf-

niits

231

Art. V. Facial Nerve.

mits a number of filaments. It irf particular
detaches one very remarkable branch, which, as
we have already fliewn, unites with another from
the maxillaris inferior. Upon leaving the pa-
rotid gland, the facial nerve divides into toui
branches ; two afeend before the ear, and pro-
ceed to the fuperior lateral and poflerior parts
of the face ; the other two branches arc fent to
its anterior parts. The mod inferior of thefc
branches divides, fub-divides, and anafiomofes
in cverv diredtion with the filaments of the
nerve of the chin. The fuperior receives a
large branch from the ma.xillaris inferior,
which pafTes behind the condyle of the jaw ;
thus united in a fingle trunk, thc\ form an ex-
panlion like a goofe's foot, which anafiomofes
with the fub-orbitar nerve.

This facial nerve prefents a very remarkable
peculiarity at its origin : it has two roots ; one
is the portiodura of the auditory nerve, which
enters the internal meatus, from which it efcapes
by the llirura Glafieri, or foramen fiylo-mafioi-
deum, which are in this animal the fame aper-
ture ; the fecond root appears to proceed from
a confidcrable ganglion of the pofterior part of
the par vagum. This ganglion is fituated in a
particular deprefiion of the inferior furface of
the bone of the tympanum : it alfo appears to
unite with the fympatheticus major, which af-
fumes almofi a cartilaginous conliftence. Two
or three fhort filaments concur in the formation

0^4 of

Distribution of the Nerves,

of this root ; it afterwards bccomps thicker,
and penetrates into the filTurej where it meets
the other root of the facial nerve ; it tranfmits
a filament to that root, and continues to pro-^
peed outward, before and below the ear.

In rabbits the facial nerve comes out of the
cranium immediately under the cartilage of the
ear, and the meatus auditorius externus, from
which it is feparated by only a fmall boney ridge.

C. In Birds and Reptiles,

The facial nerve exifts in birds and reptiles,
but its fizc is fmall, becaufe thefe animals have
no lips, and becaufe their mouth, as well as a
great part of their face, is covered with a hyrny
or fcaly fubfiance, in confpquence of which
thefe parts have but little motion or fenfibility.
We find, however, fomc of the branches : they
are not indeed cafily followed in diffedfion, but
their trunk always exifts.

D. In Fijhes.

The facial nerve is very confiderable in carti-
laginous fifties ; it is detached from the brain
by a ftngle trunk, very diftinift from the audi-
tory nerve, which belongs alfo to the fifth pair;
but foon after, and even in the cavity of the
cranium, it feparates into two branches, one
afccmls the cranium, and palTcs out through a

particular

Art. VI. Auditory Nerve. 233

particular hole, ami is diftributed under the
Ikin; the other, vhich is thicker, proceeds ho-
rizontally towards the cavity of the car, which
it enters alfo by a particular foramen. Arrived
in that cavity, it proceeds under the vcficle
which contains the amylaceous or calcareous
matter of the ear, where it unites with the au-
ditory portion of the fifth pair: the common
trunk afterwards penetrates the cavity of the
ear, to proceed outwardly, and to be diflributcd
in a great number of ramifications to the foft
parts which envelope the head.

Article VI.

Of the Auditory Nerce, or Portia Mollis of
the Seventh Pair.

In the Article on the Origin of the Nerves in
the different clafTes of animals, we have pointed
out the manner in which the auditory nerve
arifes from the brain. As it is very fhort, and
as it pafles into the organ almoft immediately
after its origin, we have at prefent only to de-
feribe, in the cerebral cavity, its connedlions
with the facial nerve, or portio dura.

In Man, and the other Mammalia, it pro-
ceeds, with the facial nerve, into the cavity of
fhe os temporum, which forms the meatus au-

ditorius

234 L. X. Distribution of the Nerves.

ditorius internus, and enters into the labyrinth
by feveral holes, the number and the magnitude
of which vary in different animals. In the Ar-
ticle on the Ear, we fhall point out its farther
diftribution in that organ ; it is very foft, and
M’e do not difeover fibres in it, as in all the other
nerves, the olfadtory excepted.

In birds, the two nerves have nearly the fame
connedlion. The auditory is very large, foft
and reddifh ; it is received into a deep conduit,
on the internal furface of the cranium, whence
it penetrates into the labyrinth by feveral fmall
foramina.

In reptiles, it is nearly the fame as in birds.

But in fifhes, the auditory nerve is very much
feparated from the facial ; it even approaches
fo near to the origin of the fifth pair, that it
may be regarded as a branch of it. In the car-
tilaginous fiflics, as the raysy it pafTcs into the
cavity of the ear, by a particular foramen, and
not by a number of holes, as in the other claf-
fes. In the fpinous fifhes, as the ear is free,
and even fituated in the fame cavity with the
brain, the nerve is diftributed diredlly into that
organ.

Arti-

Art. VII. Pneumo-gastric Nerve. 235

Article VII.

Of the Pneumo-gap ric Nerve, or Par Kagum,
vulgarly called the Eighth Pair.

A. In Man.

Tl he numerous filaments which compofc this
nerve, at its origin from the brain, approximate
and form a kind of comprefTcd cylinder; they
then pafs out of the cavity of the cranium by
an oblong aperture of the dura-mater, lituated
below the pofterior foramen lacerum.

Another nerve, which afeends from the canal
of the fpine, where it arifes by feveral filaments
from the fpinal marrow, comes out through the
fame hole, on which account it is named the
accejforius of the eighth pair.

Having reached the bafe of the cranium,
thefe nerves feem to receive a different deitina-
tion. The par vagum, properly fo called, is
tranfmitted to the lungs and the ftomach The
accefforius is direded towards the flioulder.

The principal trunk communicates, in the
firft place, with the hypogloffal, the great fym-
pathetic, the fuperior cervical, and the gloffo-
pharyngeal nerves.

It afterwards defeends almoft vertically on the
fore part of the neck, to the bread:, and is placed

near

236 L. X. Distribution of the Nerves.

near the carotid artery, and great fympathctic
nerve ; but in its courfe, icfurnifhes the neigh-
bouring parts with a number of branches, which
we (hall notice.

One is intended for the larynx, and is diftri-
buted to the mufcles and glands of that part;
another is detached towards the middle of the
neck, and, forming an arch internally, it afeends
towards the great hypoglolTus. Several fila-
ments are given off from the convexity of this
arch, and defeend into the bread ; they then
proceed to the pericardium, and are ramified in
its fubftance, forming the ple:xus called the
fuperior cardiac.

When arrived near the clavicles, the par va-
gum of the- left fide fends forward fome fila-
ments which unite with the plexus we have
juft mentioned. The analogous filaments on the
other fide are produced by the recurrent nerve ;
after this, the trunk proceeds inwardly, and
pafics into the thorax, between the veins and
the arteries : it pfefently divides into two large
branches; the moft external is the continuation
of the Crunk ; the internal is called nervtts rc^
curretis, bccaufe it rc-afeends, and partly re-
turns again out of the thorax.

This recurring branch turns round the arch
of the aorta on the left fide, and the fub-clavian
artery on the right.

The left recurrent nervedctaches fomc branch-
es, which, uniting with fome others, productxi

by

Art. VII. Pneumo-gastric Nerve. 237

by the great Tympathetic, form a pulvionary
plexus round the pulmonary artery and the
aorta, and having entered the pericardium,
where they form the inferior cardiac plexus, they
are diftributed to the heart. The recurrent
branches having arrived near the trachea artcria,
divide into filaments, fome of which afeend to
the larynx, and are dirtributed to the fmall mul-
cles of that organ, under the name of the la-
ryngeal nerves.

The trunk of the pneumo-gaftric, after furni th-
ing the recurrent branches, paflTcs behind the pul-
monary veifels, and detaches a number of fila-
ments which furround the bronchia, and pro-
duce a plexus, denominated the pulmonary : this
plexus receives a filament from the great fym-
pathetic nerve.

The branches of the par vagum afterwards
continue to defeend in the thorax, along the
oefophagus, to which they afiord a number of
filaments ; one nerve of the pair pafling before
the oefophagus, the other behind : in this man-
ner they both arrive in the abdomen, where they
form a confiderable plexus under the envelope
of the ftomach, produced by the peritonseum.:
they alfo furnifh fome filaments to the hepatic,
fplenic, and fojar plexufes, as \ve fhall fhew
when we treat of the great fympathctic nerve.

The trunk of the accelTorius feparates from
the par vagum, as it leaves the cranium; it is
direefted a little backward, as it defeends aloiio’
7 the

23? L. X. Distribution of the Nerves.

the neck ; it pafles along the fuperior portion of
the flcrno-maftoid mufclc, to which it gives
fome branches. It afterwards proceeds to the
trapezius mufcle, in which it terminates, after
detaching fome filaments to the twofplenii, be-
tween which it pafies.

B. In other Mammiftrous Animals. ■

This diftribution of the par vagum was found
nearly fimilar in four or five fpecies of Mam-
malia, which we examined for the purpofc of
tracing it. The calf only prefented one pecu-
liarity, which w'e have pointed out in the Arti-
cle on the Facial Nerve ; but the anaftomofes,
with the great fympathetic, the recurrent nerves,
the cardiac and pulmonary plexus, exhibited no
dift'crence, except in the number of the fila-
ments, fo far as the accuracy of the DifTedfor may
be relied on. The fpecies we diffedted were the
dogt the raccoon^ the bog, and the 'porcupine.

I

C. In Birds and Reptiles.

Wc have likcwife nothing remarkable to fiatc
refpcdling this nerve in birds and reptiles,
though wc have made preparations of it in fe-
veral fpecies. Wc obferve evidently , that it
is difiributed to the lungs, the heart, the (rfo-
phagus, and flomach, and that it forms plc>:-
ufes on thefe organs, in the fame manner as the

great

Art. VII. Pneumo-gastric Nerve. 239

great fympathetic nerve produces them round
all the arteries of the trunk. On leaving the
cranium, the par vagum forms dccuflations
with the lingual and glo[fo-pbaryngeal nerves ;
they afterwards feparate from each other : the
gloflb-pharyngeus is pofterior, the par vagum
in the middle, and the lingual anterior. The
par vagum does not always come out of the cra-
nium by a fingle hole ; it is formed of two or
three filaments, which afterwards rejoin, upon
receiving a communicating filament from the
glolTo-pharyngeus, and one farther down from
the lingual ; the nerve then augments fome-
what in diameter, and defeends into the bread.

D. In Fijhes.

The par vagum prefents a very peculiar dif-
pofition in filhes; this difference depends on the
nature of the organs of refpiration, for which
that nerve appears to be fpecially intended. As
the lungs or branchiae of fifhes are fituated im-
mediately below the cranium, it is obvious that
the courfe of the nerves muft be very fhort ;
and as the diftribution of the nerve takes
place almoft immediately after it leaves the cra-
nium, it may be faid to have no common trunk.

We fliall deferibe, in a general manner, what
is common in the difpofition of this nerve, and
afterwards point out particularities in different
fpecies.

The

240 L. X. Distribution OF the Nerves.

The branches of thepneumo-gaftric arediftri-
buted to three dillin(fi; parts : the firft, or anterior,
which are the largeft, and ufually four in num-
ber on each fide, proceed to the branchiae ; they
reprefent the par vagum of Mammalia : the fe-
cond, which arc much fmaller, and two or three
on a fide, are diftributed to the mufclcs, which
move the tongue in the bafe of the gills, and
to the furface of the oefophagus : laftly, the
third are fingle on each tide ; they form a very
thick nerve, which extends along the whole
body of the fifli, under the lateral line.

The branchial nerves out of the cranium
by one common foramen, and feparating from
each other, proceed towards each of the bran,
chise : before they arrive at them, they are di-
vided into two ; the pbfierior branch paffes into
the gutter which runs along the convexity of
the bone that fufiains the branchiae, and, in
its courfe, furnillics a confiderable number of
fmall ramifications to the pedinated laminae of
the gills.

The anterior branch is directed into the cor-
refpondent gutter in the concavity of the bone,
and is there divided in the fame manner: the
anterior branch of the firfi ramification re-
enters the cranium, and appears to be tranf-
mitted to the ear.

The middle branches of the par vagum,
which we have difiinguiflicd with refped to
their difiribution, arife fometimes from the

fame

Art. VII. Pneumo-gastric Nerve. 241

fame trunk as the lalt branchial, and afterwards
divide into two or three branches ; but more
commonly they come out of the cranium, as
an equal number of dillindl branches by one
common hole : one of thefe ramifies upon the
mufcles that move the branchiic, and thofe
which a6t on the teeth of the palate. Another,
which is much larger, proceeds along the oefo-
phagus, to which it is diilributed ; it may be
traced to the llomach. The third branch unites
with the cervical nerves which proceed to the
Ihoulder, or pcv5toral lin.

The lafl branch of the par vagum, and which
appears peculiar to fillies, is the long nerve of
I the lateral line of the body. We have con-
ftantly met with it in every one of the fillies
we ha\e examined, and its dillribution is nearly,
the fame in all. When wc trace it to its origin,
it is eafy'to difeover that it isthemofi: pofterior
branch of the nerve, which, inltead of defeend-
i ing towards the gullet, proceeds almofi: hori-
zontally backward and outward, in fuch a
manner as to become almofi: fupcrficial. It is
merely covered by the Ikin, and retained by a
loofe cellular fubftance. This nerve is nearly
- of an equal thicknefs throughout the whole of
its length, and may therefore be very readily
mifiaken for a tendon ; it does not appear to
I anafiomofe with the other nerves, or, if it unites
t with the inter-vertebral, the filaments are ex-
I cccdingly flender. When it arrives at the tail.
I VoL. II. R

I

4;

It

242 L. X. Distribution OF THE Nerves.

it terminates by very fmall radiated filaments,
which are diflributed to the rays of the fin.

This is the general diftribution of the pneumo-
gaftric nerve in fifhes. The varieties w'hich it
prefents refult from the ftrudlure of the fpecies.
Thus, in the Chondropterygii, as rays^ Jharks^
^c. this nerve is much longer, and all its ra-
mifications proceed from a fingle trunk, which,
does not divide until it reaches ’the part into
which it is diftributed. In the fame fiflies, the
two longitudinal nerves are fituated towards the
back, and nearer each other.

The other differences are not fufficiently re-
markable to merit a particular defeription.

Article VIII.

Of the GloJjh-phaj'yngeal Nerve.

w E have already deferibed the manner in which
the filaments which compofe this nerve arife
from the brain, and explained the motives
which induce modern anatomifts to confider
them as a difiind: pair. We fliall now purfue
its diflribution.

It makes its exit from the cranium, through a
hole in the dura-mater, very diflerent from that

of the eighth pair. The jugular foramen, into

which

I

' I
. $

Art. VIII. Glosso-pharyngeal Nerve. 243

which the vein of the fame nerve pafles, fepa-
rates thefe two nerves. Still enveloped by the
dura-mater, it exhibits a fmall enlargement,
from which two branches are detached : one is
diredled pofteriorly towards the meatus audito-
rius; another perforates the dura-mater, and
unites with the par vagum.

Having reached the bafe of the cranium, it
receives filaments from the facial and pneumo-
gaftric nerves ; it afterwards divides into fevera!
branches — one is partly diftributed to the muf-
cles attached to the ftyloid procefs, and termi-
nates in the tongue — another unites with the
hypogloffus major : — laftly, others are diftribut-
ed to the mufcles of the pharynx, along with
fome filaments of the great fympathetic nerve,
and form a plexus which envelopes the carotid
arteries ; but the principal deftination of this
nerve is to the tongue and the pharynx.

' Such is the defeription of this nerve in man.

I The other mammalia, birds and reptiles, prefent
I no remarkable difference. We have not indeed
j carried our refearches, with refpeeft to this par-
1 ticular part, fo far in them as in the human body.

^ \Ve have, however, obferved, that this nerve
proceeds to terminate in the tongue, after hav-
ing furnifhed filaments to the mufcles which
^ tnove it. In the Jiorky for example, it comes
out of the bafe of the cranium, by the hole fi-
i tuated below the ear, which correfponds to the
i pofterior foramen lacerum. It leaves this hole

R 2

in

244 L. X. Distribution of the Nerves.

in two filaments, which unite almoft immediate-
ly, and form a long quadrangular ganglion, from
^ which a fmall filament is fent inward to the
anterior mufcles of the neck : the fame gan-
glion detaches a fmall branch backward, which
unites with the eighth pair ; and a large branch
downward, on the front of the neck : the laft
is the continuation of the, nerve itfelf ; it de-
feends along the oefophagus, and divides into
two principal branches ; one afeends upon the
anterior part of the neck, and is diftributed to
the mufcles of the os hyoides, which include it,
in the form of cornua; the other defeends on
the lateral parietes of the oefophagus' and fur-
niflies a branch to the lingual nerve, with which
it anaftomofes ; the remainder of the nerve con-
tinues its courfe upon the oefophagus. From
this defeription it appears that the diftribution
of the glofib-pharyngeu? is nearly the fame as
in man.

The nerve which fupplies the place of the
gloffo-pharyngcal in fifiies, is plainly that branch
of the pncumo-gafiric which is detached mofl
anteriorly from the firft branchial nerve : it is
divided into a great number of filaments, which
penetrate the mufcles of the tongue, in which
thev are fubdivided. The trunk itfelf is loft in
the inferior part of the throat, before and be-
tween tlic branchiai.

Arti-

Art. IX. Hypoglossal Nerve. 245

/

Article IX.

Of the Great IliipogloJJhl Nerve, or Tu efth

Pair.

These nerves leave the cranium, as we have al-
ready fliewn, through the anterior condyloid fo-
ramen. As foon as they get on the out-
fide of the cranium, they become cylindrical,
and form communications with the par vagum,
the two fil'd: cervical pairs, and efpecially with
the great fympathetic nerve : after this they
proceed forward, and a little outward, until they
arrive behind the fterno-mafioid mufcle. At this
place they give oft' a large branch, which ac-
companies the jugular vein almoft to the middle
of the neck, where it forms an arch, and afeends
on the anterior part of the neck, and terminates
by uniting .»with fome filaments from the firft:
cervical nerves.

Some fmall branches proceed from the con-
vexity of this arch, and terminate in the muf-
cles.

About tw’o fingers breadth from this firft
branch, the hypoglolTal nerves detach another
branch, which is entirely loft in the fubftance of
the thyro-hyoideus mufcle.

Finally, the trunks pafs between the hyo-
glolTus, and mylo-hyoideus mufcles, and re-

R 3 ceive

2^6 L.X. Distribution or Tiie Nerves.

ceive fome filaments from the lingual branch of
the inferior maxillary nerve ; they at laft lofe
themfelves by minute ramifications in the fub-
ftance of the mufcles of the tongue.

In the other Mammalia this nerve prefents the
fame difpofition as in man. In the calf it is of
a bluilh colour, and may at firft fight be taken
for a vein. It retains this colour until it ar-
rives near and within the ramus of the- inferior
jaw. It is diftributed in the mufcles, and even
in the fubftance of the tongue towards its mid-
dle part.

In birds, the hypogloifus comes put of the
cranium, through the condyloid foramen, be-
hind the par vagum : it is fiender at its- origin,
paifes before the par vagum, which it crofles,
and with w'hich it partly unites. At this place
a fmall filament is detached from it, which pro-
ceeds towards the breaft, accompanying the ju-
gular vein. .

Continuing its courfe forward, the trunk
of the hypoglolTus crolTes the gloffo-pharyn-
geus : it then paifes under the cornu of the. os
hyoides, and proceeds towards the fuperior la-
rynx, where it terminates ; but it is prcvioufly
divided into two branches, the inferior of which
is fent forward and downward from the tongue,
and the fuperior upward and inward from the
tongue.

Wc have not obferved any nerve analogous to
the hypoglolTus in filhes.

Arti-

A. X. Sub-occipital y Cervical Nerves. 247

Article X.

Of the Sub-Occipital and Cervical A ervcs.

A. In Man.

T„e trunk formed by the union of the two
roots of the Jub-occipilal nerve, pierces the dura-
mater below the curvature of the vertebral ar-
tery. It runs for a Ihort way in the fubftance
of that membrane, and comes out on the edge
of the foramen magnum, behind the condyles:
it is then turned towards the notch in the arti-
cular procefs of the firfl: vertebra, where it
pafTcs below the vertebral artery. It then forms
a ganglion, from which fome filaments are
diftributed to the ftraight and oblique mufcles
of the head. The trunk afterwards turns be-
fore the tranfverfe procefs ; it communicates by
an anterior branch with the fympatheticus ma-
jor, the par vagum, and the hypoglolTus, and
by a pofterior branch with the firll cervical
pair : it then proceeds towards the triangular
interval of the fmall mufcles of the head, and is
diftributed to almoft all the mufcles which are
attached to the os occipitis by their fuperior
part.

'The firjl cervical pair arifes in the fame man-
ner as the preceding. After pafting through the

R 4 notch

■■ - I

248 L. X. Distribution of the Nerves.

notch between the firfl; and fecond vertebrae, ^
this pair forms a ganglion which fends off two
principal branches. The anterior of thefe com-
municates with the inferior branch of the fub-
occipital nerve, the fympatheticus major, the
hypogloffus, and the fucceeding cervical pair.
The pofterior branch, which is more confiderable,
detaches fome filaments which iTnite with the
pofterior branch of the fub-occipital, and with
that of the next cervical pair. The remainder
of the nerve is diflributed to the miifcles of the •
back part of the neck. One of the filaments ’
goes forward, communicates with the hypo-
gloffus, and is loft in fome of the mufcles of the
os hyoides, and in the glands of the larynx. j

The fecond cervical pair is divided, like all j
the others, into two branches : the anterior is 1
the largeft ; it communicates upwfirds and |
downwards with the two adjacent cervical pairs, I
with the fympatheticus and hypogloffus, and j
laftly, with the branch of the following cervi- ••
cal pair or pairs, which produce the diaphrag-
matic nerve ; after which it divides into feveral
branches.

One branch is fent backward into the mufcles
of the neck ; another forward and obliquely in- :
to the lateral parts of the car, where it commu- '
nicates with the facial nerve; a third proceeds
towards the afeending ramus of the jaw, and is
diflributed partly into the parotid gland, and ,
partly into the teguments of the ear; a fourth is

loff

A.X.Sub-occipital C5? Cervical Nerves. 249

lofl: in the anterior part of the neck, in the muf-
culus ciitaneus. All the other branches are
united with each other, and with the accelTIiry
nerve of the eighth pair. ])V this union they
form a plexus, which produces a great number
of filaments to the lateral parts of the neck,
fome of which communicate with the lympa-
theticus major.

With refped: to the pofierior divifion of the
trunk of this nerve, it unites w ith the adjacent
cervical nerves, and is lofi in the mufcles named
fplcnius, complexus, longillimus dorli, and
tranfivcrfalis colli.

The notch between the third and fourth ver-
tebrae of the neck afibrds a paflage for the
ibifd cervical pair. It is divided, as the others
are, into two branches.

The anterior branch feparates into two. The
firft receives a filament from the preceding pair,
and is then difiributed to the trapezius mufcle,
and the iterno-mafioideus. The fecond forms
two filaments ; one of which unites with the
following pair: it detaches alfo fome others
which join the facial nerve, and one very con-
fpicuoiis branch which conllitutes the diaphrag-
matic nerve. The other filament joins the
fourth pair, and partly unites with the great
fympathetic.

The pofierior branch is difiributed to the te-
guments and mufcles of the back of the neck.

The

250 L. X. Distribution or the Nerves.

The fourth pair of cervical nerves, on leaving
the medullary canal, divides into two branches,
in the fame manner as all the vertebral nerves.
The pollerior branch is partly loft in the muf-
cles of the back. The anterior, which is the
thickeft, communicates with the branch of the
preceding pair, which forms the diaphragmatic
nerve : it communicates likewife wdth the great
fympathetic, and is divided into three branches;
two unite with the fucceeding pair, and aflift in
forming the brachial plexus. The third pro-
ceeds towards the fhoulder, and is diftributed to
the mufclcs of the fcapula.

The fifth, the fixth, and the feventh' pairs of
cervical nerves may be confidered generally :
they all communicate with the adjacent pairs,
and with the great fympathetic. The fifth pair
tranfmits filaments to the pofterior mufcles of
the neck, and to thofe of the anterior part of
the thorax : fometimes one of its filaments con-
curs in- the formation of the diaphragmatic
nerve ; it is, at laft, fent into the brachial
plexus. The fixth is chiefly tranfmitted by two
large trunks to the brachial plexus : the firft
trunk receives that of the preceding pair, and
detaches fome filaments to the latiflimus dorfi.
The fecond likewife fends a filament to the great
pectoral mufcle. Finally, the feventh ipTix pro-
duces, in the fame manner, two large trunks for
the brachial plexus, which arc united fooner or

later

A.X. SuB-OCCIPITAL^ifCERVICALNe-RVES. 2^1

later to that of the fixth. The inferior branch
fiirnilhes two filaments to the fubclavian and
Icfler pectoral mufclcs.

' 13. In other Manmifcrous Ajumals.

The fub-occipical and cervical nerves exhibit
no remarkable difierenccs in any of the Mam-
malia. They all arife in the fame manner as in
man. The bulk and extent of the nervous fi-
laments which they produce, depend upon the
relative magnitude of the parts to which they
are refpediively difiributed. They all have the
fimic number of nerves, the three-toed jlotb ex-
pepted, which ought to have two pair more ;
fince, as we have fliewn in theThird Ledture, that
animal has nine cervical vertebra?.

C. In Birds.

The number of the cervical nerves varies
greatly in this clafs. The known extremes are
ten and twenty-three, equal to the number of
the vertebrae. Their difpofition is analagous to
that obferved in man. They are, however, re-
fpedlively much larger, and undergo many
flexures. They are loft, in a great meafure, un-
der the Ikin of the neck, where they may be very
eafily follovved. In general only the laft cervi-
cal pair contributes to the brachial plexus ;
the two laft pairs feldom concur in its forma-
tion.

6

D. In

2^2 L.‘X. Distribution or the Nerves,

D. In lleptiles.

Torioifes have eight pair of cervical nerves,
which are diftrihuted nearly in the fame manner
as in Mammalia. -The three lafl: pairs join
in forming the brachial plexus. The green li-
zard has four pair of cervical nerves, but only
the two lafl: enter into the compofition of the
plexus. In Jalamanders and frogs the ce'rvical
nerves cannot be properly diftinguifhed from
the dorfal, as thefe animals have no ribs. A
pair comes out bet-iveen the firffc and fecond ver-
tebrae, which is fent to the mufcles of the infe-
rior part of the neck, and under the fkin that
covers them. Thefe nerves alfo afford fome fi-
laments to the fhoLilder. From this diftribution
they may be regarded as real cervical nerves. In
frogs only two pairs enter into the compofition
of the plexus. In the falamander there arc dif-
lindlly four.

E. In Fijhts.

As the cervical vertebrae of fifhes cannot be
pofitively diftinguifiied from the dorfal, it is
very difficult to explain the diftribution of their
cervical nerves. There are never more than
four that merit this name, and frequently there
are none to which it can be applied. When thefe
nerves ex ifi, they are diftributed to the parts about
the throat, or rather to the pcdoral fin, over

which

A. XI. The Diaphragmatic Nerve. 253

which they are fpread, as we fliall fhew when
we defcribe the brachial nerves.

Article XI.

Of the Diaphi'agmatic Na\'e.

This nerve is produced chiefly by the fourth
pair of cervical nerves; but it alfo receives, as
we have fliewn, a conliderable branch from the
fiicceeding pair, and fometimes a (lender fila-
ment from the fixth ; befides, very common-
ly, a fmall branch, which is given oft' from the
convex fide of the arch, formed on the fore
part of the neck by the hypoglolTus.

Thus compofed, this nerve defeends before
the neck in a large trunk, to which fome fila-
ments from the two laft: cervical pairs, and the
cervical ganglion of the great fympathetic, are
united. It detaches fome fibrillse to the fcaleni
mufcles, and the thymus gland, when it exifts ;
after which it proceeds into the thorax, between
the fubclavian artery and vein. It is involved
in the middle refledtion of the pleura, pafTes an-
terior to the pulmonary vefiTels and veins in the
lateral parts of the pericardium, in order to ar-
rive at the diaphragm.

Here the nerve terminates : it is difiributed
by radiated fibres in the fubftance of the mufcle.

Some

2^4 L. X. Distribution of the Nei(vcs.

Some filaments, however, pafs to the abdominal
iurface, and communicate with the fubgaftric
plexus of the great fympathetic nerve.

The diaphragmatic nerve of the other Mam-
malia is in every refpedl fimilar to that of man.
It has not always the fame origin, but that is
alfo fubjedl to variation in man. It proceeds,
however, moft commonly, from the fourth cer-
vical and the two following pairs. It alfo re-
ceives the branch from the hypogloflal and great
fympathetic nerves. The other circumftances in
its diftribution do not merit a detail.

We have not been able to difcover the dia-
phragmatic nerve in birds. It is poffible, ho\v-
ever, that the mufcles which are attached to the
lungs, and which form fo large an aponeurofi^,
receive fome nervous filaments : w'e mufi: con-
fefs, however, that they have cfcaped our ob-
fervation.

Reptiles have no diaphragmatic nerve, unlefs
•tve regard as fuch the cervical pairs which are
lofi in the mufcles of the neck in thofe reptiles
that want ribs, as falamandcrs and frogs. In
them thefe mufcles produce the cfledl of the
diaphragm, as will appear in the Article on Re-
fpiration.

Fiflies having no lungs alfo want the dia-
phragmatic nerve. W^e find, however, lome
analogy in the probable fundion, and particu-
larly in the difiribuiion of one of the fiifi ver-
tebral pairs, which is difiributed to the muf-

cular

A. Dorsal and Lumbar Nerves. 255

cular feptum that feparates the cavity of the
branchiic from that of the abdomen. This nerve
is particularly remarkable in the ray and the
carp.

Article XII.

Of the Dorfal and Liunbar Nerves.

A. In Man.

The dorfal nerves leave the canal of the me-
dulla fplnalis through the holes which arc form-
ed by the correfponding notches of each two
contiguous vertebra;.

The firft pair comes out between the firft and
fecond dorfal vertebrae, and the laft between the
twelfth vertebra of the back and the fird of the
loins.

All thefe nerves divide into two branches
upon leaving the intervertebral holes ; the po-
fterior, which is the fmaller branch, is dillri-
buted to the mufcles and fkin of the back. The
anterior branch, which is the larger, comm.uni-
cates by one or two filaments with the great
fympathetic nerve, detaches fome ramifications
to the intercoftal mufcles, and thofe of the an-
terior part of the thorax, and abdomen, and af-
terwards palTes along the intercoftal fpaces to-
wards the fternum.

The

2^6 L. X.. Distribution of the Nerves.

The firft pair of dorfal nerves is diftinguifhed
by its contributing to the formation of the bra-
chial plexus in conjundlion with the lafl cervi-
cal pair.

The two following pairs produce fome branches
which pafs through the lateral parts of the
breafl, and proceed from within outwardly to
the teguments of the arm on the internal fide.

The twelfth pair is partly diftributed to the
mufcles of the abdomen, and under the tegu-
ments,- and partly into the mufcles called quad-
ratus lumborum longiflimus dorfi, and ferratus
pofticus inferior, and to the fkin of the but-
tocks.

The liimhar nerves vary in number. They are
ufually five, fometimes four, and feldom fix.
They are large in proportion as the vertebra
from which they proceed is more inferior. The
fifth therefore is ufually of the greatelt fize.

On leaving the intervertebral holes, they di-
vide into two branches, one anterior, the other
pofterior. The firfi: branch detaches a number
of filaments which unite with each of the lum-
bar ganglia of the great fympathetic nerve, and
with each of the preceding and following pairs:
it alfo tranfmits fome branches to the mulcics
of the abdomen, to tlie quadratus lumborum,
the iliacus, and the fn:in. The lafi ramifications
are commonly flexuous, in order that they may
follow the parts in their extenlion.

The pofierior branch is loft in the mufcles of
. the

A. XII. Dorsal and LuvtBAR Nerves. 257

the inferior part of the fpine. The number of
its ramifications vary confiderably.

The JirJl lumbar pair furniflies a fmall
branch, which is diftributed to the cremafler
mufcle, and the tefticles in men. In women
this branch goes partly to the uterus, and partly
to the external organs of generation.

The Jecond pair alfo furniflies fome filaments
which arc difpofed of in the fame manner as
thofe of the preceding : one of them is very re-
markable, and fometimes defeends to the knee.

The diftribution of the thirds fourth^ and fifth
pairs is nearly analogous.

The principal branches of each of thefe
nerves unite together, and form three very re-
markable trunks, which we fliall demonftrate
hereafter.

The firft is the anterior femoral nerve, com-
monly called the crural. ,

The fecond is the fub-pubic nerve, ufually
named the obturator.

The third, which is produced by a plexus of
the lumbar wdth the anterior facral nerves, is the
if chi at ic^

! C. In other Mammiferous AnbnalSy and in Birds.

I In thefe animals the dorfal and lumbar
I nerves are exactly fimilar to thofe of man.

\ They vary only with refpedt to their number,
an idea of which may be formed by confulting
VoL. II. S the

258 L. X. Distribution of theNerves.

the tables of the Vertebra which we gave in
the Third Ledlure.

C. In Reptiles.

\Vc fhail alfo refer to the tables which indi-
cate the number of the vertebrae in reptiles,
in order to fliew the number of the nerves
which ifTue from their foramina. The dif-
tribution of thefe nerves is the fame as in the
other animals, and to point it out would onlf
be repeating what we have already deferibed in
man.

D. In Fijhes.

In this clafs there is no di(lin6iion between
the different nerves of the vertebral column.
They are all didributed in the intercoftal fpaccs,
and prefent no peculiarity.

M.—B ■—

Article XIII.

Of the Pelvic and Caudal Nerves.

The pelvic or facral nerves come out of the
vertebral canal, by the holes which arc com-
monly called x\\e. facral y and which are ufually
five in number, fometimes more, fometimes Icfs.
'I’hc poflcrior branches which come out by the
podcrior foramina are the lead conddcrable. On

their

A. XIII. Pelvic and Caudal Nerves. 259

^their appearance without tlie holes they unite
with the adjoining branches, and are diftribiued
by a number of filaments to the (kin of the but-
tocks, and to the lateral parts of the anus. The
anterior branches are thofe which produce the
facral or pelvic nerves, properly fo called.

The firji pair proceeds within the pelvis to-
wards the ifchiatic notch. Having furnilhed
fome filaments to the inferior ganglia of the
great fympathetic nerve, it is united and con-
founded with the fucceeding facral pair. Ad-
vancing a little farther, it receives the large
trunk formed by the fourth or fifth pairs of the
loins: it^befides detaches a branch, which Ce-
parates from the ifchiatic portion, while it
pafies through the notch, and is difiributed to .
the mufculus gluteus medius.

The fecond pair gives off fome branches which
are diftributed nearly in the fame manner as the
firfi: ; but it is divided wdthin the pelvis, into
tw'o portions, the fuperior of which unites with
the trunk of the firft pair, as we have already
Ihewmi ; £\nd the fecond is confounded with the
third pair in order to form the ifchiatic nerve.
T wo filaments are detached from the pofteriorpart
of this pair, which accompany it into the notch,
but feparate from beyond it. The one is loft in the
gluteus maximus ; the other unites with a branch
of the following pair, and forms a fmall fingle
trunk, which is again difunited, to be diftri-
buted to the pofterior part of the thigh, and the

S 2 lefx

'i6o L. X. Distribution of the Nerves,

leg beneath the flt.in, and to the teguments of the
hip, the anus and the penis, or the vulva.

The third pair alfo unites, as we have ftated,
to the inferior branch of the fecond. It is
much fmaller; at firfl, it gives fomc filaments
to the great fymj3athetic nerve, and afterwards
furnilhes a great number which are diflributcd
within the pelvis on the neck of the bladder in
man, and on the lateral parts of the vagina in
women. In this place they unite with fome fi-
laments from' the great fympathetic nerve, and
form a very confiderable plexus. This pair alfo
furniflies a number of other branches, fome of
which are fent to the pollerior parts of the
thigh, and others beneath the fkin of the but-
tocks.

The fourth pair of facral nerves is difiributed
nearly in the fame manner as the preceding. It
befides detaches fome filaments to the mufcles
of the anus, and a large branch which unites
with others that come from the feiatic nerve,
thus forming a very remarkable trunk. This
trunk pafies between the two facro-fciatic liga-
ments, and afterwards divides into two branches;
one of which is loll in the mufcles of the anus,
and the obdurator internns ; the other proceeds
to the mufcles and teguments of the penis in
man, and to thofc of the vulva in females.

Lafily, the fifth pair, which is the fmallcfi: of
the whole, is difiributed nearly in the fame
manner as the fourth.

There

I

A. XIII. Pelvic AND Caudal Nerves. 261

There are no caudal or coccygeal nerves in man.

The other Mammalia, and the birds, prcfenc
no difference' worthy of notice in their pelvic
nerves. There are caudal nerves in the Mam-
malia. They iffue from the vertebral canal, by
holes which are formed in the vertebrae of the
tail. We Ihall deferibe them from the rabbit.

The firjl pair comes out between the laft piece
of the os facrum and the fird caudal vertebra.
It proceeds from the pelvis before the mufculus
ifchio-coccygcus by the ifchiatic notch. It
then divides into two branches : one is united
^ to the fciatic nerve ; the other continues to ad-
I vance between the pelvis and the tail until it

j enters a gland fituated under the fixth caudal
j pair of nerves, where this branch terminates ;

1 but, in its courfe, it unites with a number of
; nerves, and gives origin to others, thus forming
I a very remarkable plexus, which we lliall name
1 the caudal.

i The firft filament which is detached from

I

I this branch, paffes under the glutei mufcles, to
\ which it is diftributed; the branch is afterwards
1 joined on the internal lide by a fmall anaftomof-
1 ing filament, which appears to be derived from
j the fecond caudal pair, and on the external fide
; \ by three or four filaments, which form a reti,
I I cular plexus, from whence feveral branches go
J to the mufcles ; one which is very confidera-
^ I ble, paffes into the pelvis, and is loft upon the
{ penis, where it may be eafily followed, as its fize

Con^

262 L. X. Dis tribution of the Nervb

continues undiminifhed: again, thethird, fourth,
and fifth pair of caudal nerves fend filaments to
the internal fide; after which five or fix branches
are given off from the external fideof the mufcles
of the penis, and thofe which arife from the
ifchium*. Finally, the trunk of the firfi; caudal
pair is terminated in the gland we have already
mentioned.

The facral and caudal nerves are not diftindl
in reptiles and fifhes. We have pointed out the
difiribution of thofe which are fent to the pofte-
rior feet, or ventral fins. Thofe of the tail re-
femble the intercoftals, and are lofl in the muf-
cles.

— •

Article XIV.

i

Of the Brachial P/erus, and the. Nerres of the
Thoracic Alcmbcr,

9

A. In Mail.

We have deferibed the manner in which the
cervical nerves produce the brachial plexus by
their union. The nature of this nervous inter-
texture renders it very difficult to follow each of
the four pair of nerves which form it, when they
feparatc to be difiributcd to the arm.

All thefe nerves pafs into the interval in-
cluded between the fcalcni mufcles, and are

there

Art. XIV. Brachial Plexus. 263

there ufiially united to the fird: dorfal paii.
When thefe nerves fcparatc, they form three
principal fafciculi, from which all the nerves of
the arm arife.

The middle fafciculus produces the median
and ulnar nerves.

The poUerior fafciculus detaches the radial
and the axillary.

Laflly, the internal fafciculus gives origin
to the thoracic, fcapular, external and internal
cutaneous nerves.

This difpofition is, however, fo liable to va-
riations, that nothing pofitivccan be cflablilhed
refpeefling it ; but w hatever may be the origin
of the nerves we have enumerated, their num-
ber is conftantly found the fame. W'e fliall
now follow them in their difiribution.

1. Of the Median A’ erve.

This nerve is one of the largeft of the arm;
at the middle and anterior part of which it is
lituated on the internal edge of the brachial ar-
tery; it defeends in this manner, without pro-
ducing any remarkable branches, as far as the
articulation of the fore-arm; it afterw'ards pafles
between the tendon of the brachialis internus,
and the pronator teres mufclcs, to which it
tranfmits filaments, as well as to the fkin. It
produces, at this place, fome other very remarka-
ble branches ; one is loft in the radialis externus,

S 4 and

264 L. X. Distribution of the Nervesl;

and may even be followed a confiderable way
in that mufcle. The others are fent to the
palmaris longus, and to the flexor profundus ;
but the molt conflant of all is the branch called
'inter-ojjeous, which, after receiving an anafto-
mofing branch from the radial nerve, rranfmits
filaments to the flexor longus pollicis, and the
profundus mufcles ; perforates the interofleous
ligament, to which it furnifhes a filament; re-
appears on the external furface of the fore-arm,
and is lofl: in the flexor longus pollicis and pro-
nator quadratus.

The trunk of the median nerve accompanies
the flexor mufcles of the fingers, and reaches the
pfalm of the hand along with the tendons. It
^detaches fpveral branches to the mufcles, the
aponeurofis palmaris, and the fkin. Laflly, it
divides into four or five principal branches near
the digital extremity of the metacarpal bones ;
the firfl: of thefe branches is loft in the mufcles
of the thumb; the fecond divides into two
branches, which, after having given off fome
filaments to the adductor pollicis, run along the
edges of the thumb, and at its extremity re-
unite, forming an arch, from which a con-
fiderable number of filaments are detached.
The third branch alfo produces two fmaller
portions, which are fent in the fame manner
along the fides of the fore-finger, 'fhe fourth
is fimilarly diflributed to the middle finger.
Sometimes, however, it furnifhes only one of

the

Art. XIV. Braciiial Plexus. 265

the lateral filaments, that on the radial fide of
the finger having been fupplied by the third
branch. Finally, the fifth branch is difiributed
on the radial fide of the ring finger. The tour
digital ramifications tranfmit filaments to the
mufeuli lumbricales, to the Iheath of the ten-
dons, and to the teguments, which it is impof-
dible to trace, although they are exceedingly nu-
merous.

£. Oj the i'lnar Nerve.

This nerve defeends along the internal p>art of
the arm, until it approaches the elbow, where it
is received into a particular furrow of the cpi-
trochlea of the humerus. It afibrds fome fila-
ments to the olecranon, and to the mufcles in-
ferted in that part. The trunk of the nerve
crofies the origin of the flexor ulnaris piufcle,
and proceeds along the palmar furface of the
fore-arm on its ulnar margin. In its courfe to
the wrifl: it detaches feveral branches to the arti-
cular capfule of the fold of the arm, and to the
flexor mufcles of the fingers. At the annular
ligament of the carpus, or a little before it, the
trunk divides into two branches; one is named
the dorjal, and the other the palmar.

The dorfal branch fubdivides into filaments,
which, after uniting among themfelves, and with
others from the radial nerve, are loft in the fkin
pf the back of the hand.

The

266 L. X. Distribution of the Nerves,

/

The palmar branch furniflies the two lateral
branches of the little finger, and alfo that which
anafiomofes with the fifth branch of the median
nerve, at the extremity of the ring finger; it
likewife fends down fome filaments to the lum-
bricales and interrofiei inufcles.

I i

3. Of the Radial Nerve.

The radial is the thickefi: nerve of the arm.
Soon after it feparates from the plexus, we find it
fituated between the ulnar nerve and the axillary
artery ; it furniflies almoft immediately fome
filaments, which are loft in the fkin, and in the
triceps brachialis. The trunk of the nerve
paffes afterwards behind the humerus, round
which it turns to re-appear on the external fur-
face between the brachialis externus, fupinator
longus, and brachialis internus. It alfo pro-
duces, at this place, a fub-cutaneous branch,
which accompanies ‘the cephalic vein to the
wrifi, andfevcral other branches to the radial and
fupinator mufcles. The trunk of the nerve
then croffes the fupinator brevis, above the ar-
ticulation of the radius with the humerus, and
continues to proceed on the external furfacc of
the fore-arm. It gives a number of branches
to the mufcles, and then divides into two
branches, one of which, having paffed under
the annular ligament of the convexity of the
carpus, is lofi in the lkin, and the parts which

cover

Art. XIV. Brachial Plexus. 267

cover the back of the hand-: the next branch,
which is the largeft, divides into two others be-,
fore it reaches the annular ligament of the wrift.
One produces two ramifications ; the firfl: ter-
minates on the dorfal furface of the thumb, and
on that of the fore finger; the fecond is alfo
diftributed to the fore-finger, the middle, and
frequently to the ring-finger. The other rami-
fication alfo proceeds to the convexity of the
hand and the fingers, and is difiributed nearly
in the fame manner as the former. It is, how-
ever, commonly the fmaller of the two.

4. Of the Ad illary Ken'e.

This has alfo been named the articular nerve.
It is frequently only a branch of the radial co-
vered by the deltoid mufcle under which it
pafTes. It tranfmits- fome filaments to that
mufcle, and to the other mufcles near the arti-
culation of the humerus, as the teres-major, the
latiflimus dorfi, the ferratus major, and the fub-
fcapularis. One of its branches, which is the
mofl; remarkable, is loft in the articular capfule
of the humerus.

5. Of the Thoracic and Scapular Nerves.

The thoracic nerves in fome infiances arife
feparatcly from the brachial plexus. They are
difiributed chiefly to the pedtoral mufcles, and
are loft in the mammary glands, and in the fkin

of

268 L. X. Distribution of the Nerves.

of the breafl:. There is frequently a pofterior
branch which is lofl: in the fubltance of the la-
tilRmus dorfi, (or lumho-humeralis) mufcle.

The fcapular nerve paffes behind the notch in
the coracoid procefs, and gives branches to the
Tupra-fpinatiis and infra-fpiiiatus mufcles, and
to the fub-fcapularis,

6. Of the External Cutaneous, or Mufculo^
'Cutaneous Neree.

. This nerve perforates the coraco-brachialis
rnufcle. It is afterwards fituated between the
biceps and the brachialis internus, to both of
which it furnifhes numerous filaments. Having
reached the middle part of the humerus, it di-
'vides into two branches ; one fuperficial, and
the other deep fcated.

The fuperficial branch is the larger: it de-
feends with the cephalic vein above the tendon
of the biceps mufcle in front of the fold of the
fore- arm, where it divides into a number of
ramifications. Some of thefe arc partly lofi in
the fupinator longus, and in the Ikin, where
they anaftomofc with otlicr filaments from the
radial nerve. Other ramifications defeend to
the hand, and divide and fiib-dividc in the (kin.

The deep feated branch of the external cuta-
neous,nerve is alniofl entirely lofl in the brachi-
jilis internus mufcle ; one of the filaments pene-
trates, with the humeral artery, properly fo
called, into the medullary cavity of the bone.

7, Of

Art. XIV. Brachial Plexus. 269

7. Of the Internal Cutaneous Xcrve.

This nerve comes i'ometimes from the ulnar •
it proceeds along the pofterior and internal fide
of the humerus, between the fkin and the muf-
cles. When arrived at the fore-arm, it divides
into a number of branches which enter the fkin,
and may be traced as far as the hand.

B. In other Mu mini f emus Animals.

The brachial plexus is produced in the other
Mammalia by the three lafl: pair of cervical
nerves, and by the firfl: dorfal pair.

The articular nerve is exclufively formed by
the fifth cervical pair in the rabbity and only
one of its filaments enters into the compofition
of the plexus.

The thoracic nerves are detached from the
plexus, and are diftributed to the mufcles of
the axilla. We alfo find a nerve analogous to
the fcapular.

The internal and external cutaneous nerves are
not diflincfl:, but only branches of the three
principal cords which reprefent the median, ul-
nar, and radial nerves.

At the middle part of the arm the median
produces a branch which is diftributed to the
mufcles and the fkin, and may be regarded as a
mufciilo-cutaneous nerve. Having arrived before
the bend of the fore-arm, it detaches a number

of

^'jo L. X. Distribution of the Nerves.'

of filaments which pafs deeply along w'ith the
tendon of the biceps, and are diftributed to the
inufcles. The trunk continues to accompany
the mufcles of the palmar furface of the fore-
arm. It divides into two branches, which pafs
through two particular grooves in the ligaments
of the carpus, and are each diftributed to the
fingers, nearly as in man.

The ulnar nerve is the moft external and the
flendereft of the three. About the middle of
the arm it gives off a branch to the extenfor
mufcles of the elbow and to the fldn. This
branch appears to fupply the place of the exter-
nal cutaneous nerve. The trunk of the ulnar
having arrived before the articulation of the arm,
penetrates the aponeurofes of the mufcles which
are inferted in the external condyle : it paftes
along the ulna on the intcr-ofteous ligament,
gives branches to the flexor mufcles of the fin-
gers, and terminates in two very long filaments,
one of which goes to the external furface of the
paw’, where it is loft in the flvin ; the other fol-
lows the palmar furface, and is diflributed nearly
as in man.

The radial nerve is alfo the thickefl of the
three cords : it w inds round the humerus, and
furniflics ramifications to the extenfor mufcles
of the fore-arm : having reached the external
part of the arm, it glides between the biceps
and triceps mufcles, and divides into fevcral
branches; one becomes fupcrficial, and proceeds

to

Art. XIV. Brachial Plexus.

27 1

to the front of the fore-arm under the fkin ; the
others are loft in the mufclcs of the anterior
part of the fore-arm.

Laftly, the trunk, after fupplying the mufclcs,
divides into feveral filaments, which arc loft in
the fkin on the convex part of the fingers.

C. In Birds.

The brachial plexus in birds, is formed cx-
clulively by the laft cervical and the two firft
dorfal pairs. Their intermixture produces only
one fafciculus, from which all the nerves of the
arm are derived.

The firft cords detached from the plexus, are
intended for the pecftoralcs major and medius,
and the fub-clavius mufcles : they are large,
and four in number.

A branch, analogous to the articular nerve, is
afterwards diftributed to the mufcles which fur-
round the head-of the humerus and its articular
capfule.

Two large principal cords then arife, which
are fent to the wing.

One is direefted under the internal or inferior
furfaceof the wing. It firft detaches filaments
to the biceps and deltoid mufcles, then follow’-
ing the internal edge of the biceps, it arrives
at the bend of the fore-arm without affording
any remarkable branches. Having advanced
above the articulation of the fore-arm, immedi-
ately

272 L. X. Distribution of the Nerves.

ately under the Ikin, it divides into three
branches ; the external is the moft flcnder, and
is partly loft in the radial mufcles, and the fkin
which covers the pollex, or the baftard wing.
The middle branch pafles deeply under the
mufcles to which it is diftributed; one of its
filaments perforates the inter-ofleous ligament
to get to the fupcrior furface. Laftly, the third or
internal branch, proceeds, as the ulnar nerve, on
the internal condyle of the humerus, amongft the
tendons of the mufcles which are there inferted.
At this place it feparates into a number of fila-
ments : one pafles to the articular capfule of the
fore-arm with the humerus, and into the flcin
that covers the elbow ; fome proceed to the
flexor mufcles of the metacarpus. Two others,
which are more remarkable and longer, follow
the inferior margin of the wing under the fkin,
and are loft in the fkin^vhich covers the inner
furface of the digiti. This nerve appears to
fupply the place of the median, the ulnar, and
the mufculo-cutaneous.

The other principal cord of the brachial
plexus turns round the humerus to arrive at its
fupcrior furface, producing, at firft, fomc very
confpicuous filaments for the extenfors of the
ulna ; then two other alfo very reaiarkablc fila-
ments, which are diftributed in the form of a
goofe’s foot under the fkin, and the membranes
fituatcd between the humerus and the fore-arm.
Thefc branches appear analogous to the nervm
r, cutancus

Art. XlV. Brachial Plexus. 273

cutaneus interms. The trunk of the nerve con-
tinues to defcend along the humerus ; and, on
reaching the articulation with the ulna, is found
.fituated on the internal furface, but towards the
radial edge of the fore-arm : it pafles through,
the tendon of the radialis externus mufcle, and
upon arriving at the outer, or fuperior furface,
divides into two branches ; one, which is Ihort,
ik loll; under the flvin that covers the external
furface of the fore-arm; the other, which is
longer, is fituated between the two bones on the
inter-ofleous membrane. When it reaches the
articulation of the carpus, it pafles through a
particular groove, and is feen divided into three
filaments ; a fliort one for the pollex, and the
Other two for the external lide of each of the
digiti, upon which they are diftributed under
the (kin as far as the lafl joint.

.It is evident that this cord correfponds to the
radial nerve^ and that one of its branches fup-
plies the' place of the cutaneus internus. This
defeription is taken from the duck and the Jlork.
We prefume it is not different in the other
birds.

D. In Reptiles.

In the tortoife, the three lafl; pairs of cervical
nerves, and the firfl; of the dorfal, proceed to the
thoracic member, where they form a plexus in the
following manner : the fifth cervical pair paffes
VoL. II. T behind

274 L. X. Distribution op the Nerves,

behind the other four pairs, crofTes them in
their courfe, and unites with them in its paflage.
It then turns round the fcapula, which in this
animal is articulated with the firft dorfal ver-
tebra. 'We fliall return to the defeription of
this nerve. The fixth cervical pair proceeds
diredlly along the fcapula on its internal fur-
face : 'it is crolTed pofteriorly by the fifth, and
towards the lower third of the fcapula receives
the feventh cervical pair. The feventh is flen-
der, crofTed by the fifth and the firfi: dorfal pair,
and united with the fixth, in the manner we
have pointed out. The firfi dorfal pair partly
joins the feventh cervical, almofl at the point
where it comes out of the vertebral canal ; it is
then fent to the mufcles of the flioulder.

We fhall now purfue each of the cords we
have mentioned to their termination.

The large nerve produced by the fifth cervi-
cal pair, having arrived behind and near the
true articulation of the fcapula with the fpinc,
divides into three branches ; one, which is but a
filament, appears to bo diflributcd to the arti-
cular capfule ; a fecond, which is very flat, and
from the fides of which a vail: number of leflcr
branches extend to the mufcles of the fkin, ap-
pears to take the place of the mn/culo-cutaneus ;
the third branch, which accompanies the muf-
cles of the fcapula under the fkin, defeends to
the humerus, without producing any remarkable
branches. At this place, however, it fends oil*

fcvcral

I

Art. XIV. Brachial Plexus. 275

feveral ramifications to the extenfor mufcles of
the fore-arm. The trunk continues its direction
forward, expands and lofes itfelf under the fkin,
and may be followed as far as the hand : it may,
perhaps, be regarded as fupplying the place of
the ulnar nerve.

The fixth pair of cervical nerves having, as
we have fiiewn, affified in forming the brachial
plexus, palFes along the internal furface of the
fcapula ; about the lower third of that bone it
receives the feventh pair; the nerve then be-
comes thicker, but foon after divides into two
branches; one, which is slender, palles into the
groove, between the furca and the clavicle, and
then fpreads over the articular capfule of the
humerus, after furnifhing numerous filaments
to the mufcles which furround it ; this nerve
may be regarded as analogous to the articular in
rnan. The trunk of the nerve, which evidently
fupplies the place of the median^ upon reaching
the articulation of the humerus with the fcapula,
tranfmits filaments to the adjoining mufcles.
On arriving at the” palmar furface of the fore-
arm, it divides into three portions, two of
■which are on the ulnar fide, and fTnk deeply
into the mufcles ; the third, w'hich is much
larger, follows the radial fide of the fore-arm,
and at the bafe of the thumb proceeds to the
palm of the hand, and detaches filaments to
each of the fingers.

The ieventh cervical pair unites, as we have

T 2 ftated.

2‘j6 L. X. Di STRlflUTION OF THE NeRVES.

flated, to the fixth, at the pofterior part of the
Icapula, to form the median and articular nerves.
We have therefore no occafion to return to its
dcfcription. The firft dorfal pair is loft in the
mufcles of the ftioulder, and is not continued
throughout the arm.

The brachial plexus of the Hazard differs a
little from that of the tortoife ; it is formed by
two dorftil, and the two laft cervical pairs ; the
firft of the cervical furniflies only one of its
branches to the plexus ; ihe other going to the
neck.

In the frog, the nerves which are to be diftri-
buted to the arm, proceed from a very thick
cord, which comes from between the fecond
and third vertebrae : this makes the largeft nerve
in the whole body ; it is foon after joined by a
filament from the fucceeding pair, with which
it intimately unites ; this cord proceeds to-
wards the axilla — it fends off a branch, which
paffes above the fhouldcr, and is loft in the muf-
clcs of that part. The trunk continues its ,
courfe to the arm, and very foon forms two
principal branches ; and befides thefe, it alfo t
fends fome filaments to the extenfors of th.e ]
fore-arm, and the articular capfule of the head !
of the humerus. i

Of thefe two nervous cords, one is direefted j
forward upon the hunicrus, and repr-efents the ^
median nerve; it detaches fome filaments fo the I
mufcles and the Ikin. .Arrived at the fold of I

the

Art, XIV. Braciifal Plexus.

-77

the fore arm, the nerve plunges amongfl: the
mufcles, along with the tendon of the jlcriio-
radialis, which fupplics the place of the bi>'cps;
it afterwards divides into two branches, placed
one above the other : the moft llender is fituated
between the Hexor mufcles of the fingers ; the
larger upon the furrow, which indicates the
union of the two bones of the fore-arm ; thele
pafs under the ligaments of the carpus ; having
reached the palm, the luperficial branch is loll
in the (kin which covers that part, and the
deep feated is dillributed to each of the fingers,
nearly as in man. It aifo furniflies fomc fila-
ments to tfie mufcles of the hand.

The other cord reprefents the radial nerve;
it turns round the humerus, and furniflies,. in
the firft place, fome branches to the extenfor
cubiti : continuing to defeend round the hu-
merus, it arrives before the articulation with
the bone of the fore-arm, on the radial fide —
it pafies through the fubilance of the mufcles
to the external part of the fore-arm : it is after-
I wards divided ; one of the branches is loft un-
I der the tk-in, the other palTes under the back of
I the hand, and terminates on the convexity of
i the fingers. From this 'defeription it will ap-
i pear, that the nerves of the arm in frogs very
r much refcmble thofe of the wing in birds.

In the falamander the nerves of the arm are
! diftributed as in the frog, but the brachial
plexus is formed by two cervical, and two dor-

T 3 fal

278 L. X. Distribution of the NERVESt

fal pairs, if we may regard as dorfal vertebrae
thofe which fiiftain rudiments uf the ribs.

There are no brachial nerves in fcrpents.

E. In FiJJies.

The nerves of the perioral fin of fpinous
fifhes proceed from the two firfi vertebral pairs ;
thefe two nerves arife at a confiderable difiance
from each other, and traverfe the firfi mufcle
placed between the fpineand the firfi rib, whicfi
feems analogous to the fcalenus.

In the fahnon the anterior nerve approaches
the par vagum, of which it might be regarded
as a branch, were it not obfqrved that it comes
out through a particular foramen. In the carp
it is feparated by the laft branchial bone. The
fecond vertebral pair, intended for the flioulder,
is fitunted more pofieriorly, and nearer to the
midtile line of the body, behind the oefophagus.
Thefe two nerves proceed diretfily downward to
the internal lamina of the fcapula, where they
re-imite, but are not confounded. The firfi
vertebral pair then divides into two cords, from
which anafiomofing filaments are detached to
form a kind of plexus. A number of thefe fi-
laments are difiributed to the addudor mufclcs
of the fin. The cord, which is given off from
fhe firfi vertebral pair, likewife appears to ter-
minate in thefe mufclcs ; but it previoufly pro-
4uces a remarkable filament, which is difiri-
buted

7\rt. XIV. Brachial Plexus. 279

biited to the membrane that feparates the bran-
chial from the thoracic, or abdominal cavity,
which are here confounded. May not this fila-
ment be regarded as analogous to the diaphragm
matte nerve ? we are much inclined to this opi-
nion.

The two brachial nervous cords pafs throiigli
the holefituated before, and without the articu-
lation of the fin with the fliouldcr ; they unite
there, and produce an irradiation of nervous
filaments, fevcral of which are lofl in the muf-
clcs of the external furface of the Ihoulder, and
in the oblong articular capfulc which receives
the fmall carpal bones- Lallly, one of the fila-
ments extends under the fkin, which forms the
membrane of the radii of the fins.

In cartilaginous fillies, as the rays^ both the
diftribution and number of the brachial nerves
are very various. The firft twenty vertebral
pairs are received in a cartilaginous canal, be-
hind the cavity of the branchiae ; they unite
there, and form a large fingle cord, which ex-
tends towards the middle part of the fin, crofs-
ing the cartilaginous bar, on which the radii are
articulated.

This firft cord continues its diredlion forward,
along the cartilaginous bar, deferibing an arch,
the concavity of which is anterior, and gives
origin to a number of filaments, equal in num-
ber to the radii of the fin. All thefe filaments

T4

are

28o L.X. Distribution of the Nerves.

are lofl: in the mufcles, and may be followed to
thd margin of the fin.

The four or five vertebral pairs, which fuc-
ceed the firft twenty, likewife unite into a thick
cord, which is afterwards fubdivlded into feven
or eight filaments, for the middle radii of the
fin. Thefe are almoft perpendicular to the me-
dulla fpinalis.

The pairs of vertebral nerves which follow
to about the forty-fourth, unite two and two,
and form a cord, which perforates the cartila-
ginous bar of the poflerior part of the fin ; they
divide in the mufcles in the fame manner as the
preceding.

The nerves of the peiloral fin, or wing of
the rayy therefore, prefent a very Angular dif-
tribution.

Article XV.

Of the Nerves of the Abdominal Member.

A. In Man.

In deferibing the lumbar and facral nerves, we
pointed out the formation of the principal
trunks that arc difiributed to the inferior ex-
tremity : we now proceed to trace them particu-
larly.

1. Of

Art. XV. Abdominal Member. 281

1 . Of the. Subpubic, or Obturator Nerve.

This nerve arifes from the plexus of the lum-
bar pairs. , The place at which it is feparated
varies; it proceeds into the fmall pelvis, along
phe inner lide of the tendon of the ploas mul-
cle, and is directed towards the fubpubic fora-
men : it furniflies fome filaments to the internal
obturator mufcle ; it then palles through the
fubpubic foramen, and fends off fome filaments,
which go to the external obturator mufcle;
after which, it divides into two branches, one
anterior, the other poftcrior.

The firft.is loft in the peftineus, gracilis, and
cruralis mufcles ; it defeends almoft to the knee.

The pofterior branch is diftributed nearly in
the fame manner, but is more deep feated.

2. Of the Anterior Femoral, or Crural Nerve.

This cord is commonly formed by the plexus
of the four firft pairs of lumbar nerves ; it ac-
companies the femoral artery in its courfc
through the fmall groove, which the iliacus and
and pfoas mufcles leave between them, to which
it gives fome filaments. When under the in-
guinal arch, it divides into a confiderable num-
ber of branches deftined for the mufcles.

One branch is ufually fent to the reclus muf-
cle ; four or five to the triceps femoris ; fome
to the fartorius, feveral of which afterwards
proceed under the fkin. Laftly, others arc

diftri-

2S2 L, X. Distribution of the Nerves.

diftributed to the fafcia lata, the peclineus, the
gracilivS, and the femi-tendinofus.

Two longer filaments proceed under the (kin
of the thigh, on the internal fide : one, which
nearly follows the direction of the femoral ar-
tery, fpreads out at the knee 5 the other is con-
fiderably thicker; it defeends to the foot, nearly
accompanying the vena faphaena, and is called
nervHs Japheniis ; it frequently receives a branch
from the fubpubic nerve towards the middle of
the thigh ; it i§ chiefly diftributed to the (kin.

3. Of the Ifchialic, or Sciatic Nei^^e,

This is the largeft' nerve in the body; It is
ufually produced by the two laft lumbar, and
the three firft facral pairs: it ifTues from the
pelvis, between the gemini and pyriformis
mufcles, through the ifchiatic notch; it there
produces feme filaments for the obturator in-
ternus, the gemini, and quadratus femoris. In
this pofterior fituation, it defeends from the
ifchiatic tuberolity towards the trochanter.
Having reached the middle of the thigh, or
fomewhat lower, it divides into twm cords,
which continue to defeend and pafs into the
ham ; they then afTume the names of the pop-
liteus internusy or tihial nerve, and the poplilcus
exlernuSy or peroneal nerve.

In its courfc along the thigh, the ifchiatic
nerve furniftics alfo a number of final 1 branches

to

I

Art. XV. Abdominal Member. 283

to the femi-tendinofus, femi-membranofus, and
biceps, and to the adducftors of the thigh.

When in the ham, it fends filaments to the
popliteus, femi-tendinofus, biceps, and gaftro-
cnemii mufcles.

It alfo frequently produces a branch which
fometimes arifes from the'low'er part of the pe-
roneal nerve. This branch proceeds under the
mufcles of the tendo Achillis, on the lidc of the
fibula. It is difiributed to the fkin of the foot,
and is fometimes continued on the back of the
foot, as far as the extremities of the toes.

4. Of the Tihial N’en e, or Popliteus Internus.

This is the internal portion of the trunk of
the fciatic nerve, after it reaches below the
ham : the cord, which it forms, paffes under
the mufcles which compofe the calf of the leg,
to which it fends fome ramifications. It like-
)vife furnifhes fome to the popliteus mufcle, and
Its filaments accompany the tibial artery, pro-
perlydb called, or that which enters the bone ;
jt likewife detaches filaments to the tibialis pof-
ticus, flexor longus pollicis pedis, and flexor
communis digitorum pedis. The trunk, con-
tinuing to defeend, proceeds towards the inter-
nal malleolus ; it enters the groove formed be-
tween the tibia and the os calcis, along wdth
the tendons of the flexor mufcles. When ar-
rived under the foie of the foot, it is divided
jnto the internal and external plantar nerves the

firft

2^4 L. X. Distribution of the Nerves.

firft tranfmits filaments to the fmall mufcles of
the foot, as the (hort flexors, tranfverfales pedis,
and the abdudlors and addu^ors of the great
toe, and afterwards divides into four branches,
”vvhich are diftributed to the lumbricales and in-
terolTei mufcles, and to the fkin : the ramifica-
tions which go to the latter, are difpofed of
in the fame manner as the branches of the me-
dian nerve in the hand, forming alfo an arch
with the external plantar. — The external plan-
tar nerve fupplies the fifth toe, and external fide
of the fourth.

I

5. Feroncal Nerce, or PopUteiis E.vtcrifus.

The external branch of the fciatic nerve af-
fumes this name below the ham : at firfl it de-
taches fome filaments, which are extended for-
ward under the fkin of the leg and foot, and
which unite with the cutaneous ramifications of
the tibial nerve. It afterwards glides along the
fibula, and making a curve at the fuperior third
of that bone, is there divided into three branch-
es, two of which arc fupcrficial, and the other
deep fcated.

I'hc deep-feated braneh is difiributed to the
mufcles of the anterior part of the leg ; it ex-
tends under the fkin of the knee and foot, tranf-
mitting filaments to the cxicnfor brevis, and
the fuperior intcroffei mufcles.

Both the fupcrficial branches proceed under

the aponcurofis of the leg: the firft rifes from

it

Art. XV. Abdominal Member. 285

it towards its middle part, and pafies in the (kin
as far as the foot ; the fecond likewife pierces
the aponeurofis, about the middle of the leg>
and proceeds under the fkin, towards the mal-
leolus externus : when it reaches the foot. It
divides into feveral filaments, which, like the
preceding, terminate on the lateral part of each
of the toes.

B. In other Mammiferous Animals.

The lumbar and pelvic nerves, deftined for
the abdominal member, form a plexus prcvioufly
to their dillribution. In general it is the fame
as that which fakes place in man, or the differ-
ences are unimportant. The nervous cords arc
precifely alike in number, and divide in the
fame manner.

The anterior crural nerve arifes mod com-
monly before the fubpubic. In the groin it
produces an irradiation of mufcular filament! ;
one, which is very remarkable, accompanies
the vena faphtena under the fkin, and may be
traced to the foot.

The fubpubic nerve alfo palfes through the
foramen obturatorium ; it is diftributed to the
mufcles of the thiejh.

O

The fciatic nerve ;s alfo produced by the fa-
cral pairs ; it commonly receives anaftomofing
filajnents from the caudal pairs. In general, it
^ prefents

286 L. X. Distribution op the Nerves.

prefents no cfTential , difference from the fame
nerve in man.

C. In Birds.

The obturator nerve alfoarifes, in birds, from
the plexus, formed by the lumbar pairs ; it goes
through the fubpubic hole, with the tendon of
the obturator internus ; foon after it leaves the
pelvis^ it divides into a great number of bran-
ches, which terminate in the mufcles that fur-
foilnd ,the os femoris, and chiefly in thofe about
its articulation, and in the adducffor mufcles.

The femoral nerve is evidently formed by the
three laft lumbar pairs, which compofe a plexus
above the pelvis, from which the obturator
nerve proceeds. On reaching the groin, the
crural nerve feparates into three principal bran-
ches, which after\Vards divide and fub-dividc
in the difl'ercnt mufcles of the anterior and in-
ternal furface of the thigh. A conliderable
number terminate in the Ikin, on which they
may be very eafily traced.

The fciatic nerve is produced in birds, chiefly
by the four fuperior pelvic pairs ; it proceeds
towards the fciatic norch of the pelvis, behind
the copyloid cavity. Having left the pelvis, it
divides into two principal portions ; the pofle-
rior is a fafciculus, compofed of feven or eight
branches, which are loll in the glutei mufcles

and

Art. XV. Abdominal Member. iSy

ind adductors of the thigh. The other portion
is a fimple and very thick cord, which appears
to be th^ trunk 'of the nerve itfelf. It takes
the direiflion of the former, and detaches fomc
flender branches, which are diftributed to the
flexor mufcles of the leg. When arrived at the
middle and pofterior part of the thigh bone, the
trunk divides into two branches ; the larger
correfponds to the tibial nerve, and the other,
which is fmaller and nearer the bone, appears
to be the peroneal nerve.

When the tibial gets into the ham, it divides
into tMo branches : the thicker of the two fe-
parates into fix or feven filaments, defined to
the mufcles of the poflerior part of the leg, and
chiefly to the gcmelli and the folcus ; the other
branch continues to proceed behind the bone of
the leg ; having reached the heel, it enters a
groove, and pafles under the bones of the me-
tatarfus, at the digital extremity of which it
divides into four, three, or two portions, ac-
cording to the number of the bird’s toes: thefe
filaments are fent to the peroneal edge of each
of the toes.

The peroneal 7ierve, or the fecond principal
branch of the fciatic, is, as we have obferved,
neareft the bone. When it arrives under the
knee, it pafles towards the peroneal edge of the
leg, and divides into a number of filaments,
which are lofl: in the anterior part of the leg.
Two filaments, which are much thicker and

longer.

288 L. X. Distribution of the NERVEi^i

fongef, accompany the bones of the leg ; one
on the peroneal edge, the other on the tibial ;
in this manner they pafs above the articulation
of the tarfus, in two grooves, which are proper
to themfelves : they approach each other after-
wards, and are fituated in the anterior gutter of
the metatarfal bone, after which they again fe-
parate. The tibial branch pafles between the
fecond and third toe, and the peroneal between
the third and fourth, when the latter exifts ;
they proceed along the edges of the toes, and
terminate under the fkin, near the nail. This
d-6fcription is taken particularly from the Jlorky
though we have made iimilar refearches in fe-
vcral other birds ; it fliews that the nerves of
the abdominal member are nearly the fame, in
birds as in man.

B. In licptilLS.

in lizards^ihcut is only' a fmall nervous fila-
ment, which proceeds from the femoral nerve,
and fupplies the place of the [nh pubic. 7Tc
femoral nerve is itfelf formed of the two lali:
lumbar pairs, and pafles above the bones of the
pelvis, to be diflributed in the mufclcs of the
anterior part of the thigh. 1 he fctaUc nerve
is produced by the three pairs of nerves which
follow, and which alfo receive a filament from
the lali lumbar pair ; the only cord they form,
proceeds along the infide of the thigh, fub-
^ dividing

Art. XV. Abdominal Member. 289

t

dividing in the mufcles, and extending to the
toes.

The didribution of the nerves in the abdo-
minal member is nearly the fame in the
mander : there are no differences except in
the manner in which the plexus is formed. The *
femoral nerve is produced by a fingle lumbar
pair, which tranfmits a branch to the fciatic
plexus, formed by the two fuQcceding pairs.

In the frog, three pair of nerves enter into
the compofition of the femoral plexus, before
which they run the whole length of the ofTa
ilii, which are very long : M'hen arrived at the
thigh, the plexus fends off a nerve which cor-
refponds to iht anterior femoral ; itis diflributed
in radiated filaments to the fore part of the
thigh . The reft of the plexus proceeds into the
pelvis, and forms a large cord, which paffes to
the pofterior part of the thigh, and may be re-
garded as the fciatic nerve. A great number of
filaments are afterwards detached from it to the
mufcles ; about the middle and pofterior part
it divides into two branches, which pafs under
the ham, and reprefent the tw’o popliteal nerv’es,
t\\t external and internal: thefe are afterwards
diftribilted to the foot of the pofterior leg, nearly
in the fame manner as to the human foot.

E.' In Fijhes.

The ventral fin, which, in fifties, reprefents'
VoL. II. U the

•1^0 L. X. Distribution of the Nerves.

the poflerior extremity, receives nerves from
the vertebral pairs.

In the cartilaginous fifhes, as the ray, eight
or nine pairs proceed direftly outward towards
the ventral fin ; the four or five firfl: pairs unite
into one trunk, which paifes through a parti-
cular hole in the cartilage that fuftains the ra-
dii. The other pairs proceed immediately above
the radii. All thefe nerves are diftributed to
the mufcles, precifely in the fame manner as
in the pecfioral fin.

In the fpinous filhes, of which we ftiall men-
tion the genus Siliirus, the vertebral pairs,
which are diftributed to the intercoftal muf-
cles, detach filaments to the mufcles that
move the fin. Some of thefe may be diftincftly
followed to the membrane which covers the
radii.

Article XVI.

OJ the Great Sympathetic, alfo called the Great
Inttrcojlal or Trl-fplanchnic Nenx,

A. In Man.

This nerve cannot be confidcred as proceeding
immediately from the brain. It communicates
with the fifth and fixth pairs of the encephalon,
with the thirty pairs of vertebral nerves, with

Art. XVI. Great SYMPATHETtc; 291

the gloffo-pharyngeus, and with the par vagum.
At all thefe poipts of communication it exhi-
bits very remarkable enlargements.

The portion of the great fympathetic, which
is neareft the brain, appears in the carotid canal
of the os temporum, whwe it forms a plexus
round the carotid artery. We have already
pointed out the filaments which unite this nerve
to the fixth pair, and that which it appears to
receive from the fpheno-palatine ganglion of the
maxillaris fuperior, under the name of the vidian
nerve.

The nervous filaments of the carotid plexus
form, at the bafe of the cranium, a fingle trunk,
which produces an elongated enlargement of a
reddifli colour ; it extends nearly to the third
vertebra, and is called the fuperior cervical gan-
glion.

This ganglion receives filaments at its origin
from the firft and fecond cervical pairs; fome-
times from the gloflb-pharyngeus and the
pneumo-gaftric j to which, as well as to the
carotid artery, it is always joined by a very com-
padV cellular fubftance. Its figure is an oblong
oval, more pointed inferiorly.

After this enlargement, the trunk of the
nerve, which becomes more flender, defeends
along and behind the carotid artery, as far as the
inferior part of the neck, where it forms a new
ganglion, named the inferior 'cervicaL In its
courfe it receives or detaches filaments to each

U 2 of

292 L. X. Distribution of the Nerves*

I

of the cervical nerves at its_ pofterior part. It
gives off others from its anterior part to the
pharynx and the fat, the fibrils of which uniting
together, produce very delicate plexufes round
the carotid arteries ; the mufcles of the anterior
part of the neck alfo receive many filaments.
Lafily, among the other ramifications, which,
in confequence of their tenuity, cannot be rea-
dily traced, we obferve fome \\hich, uniting
with filaments from the par vagum, pafs into the
thorax, and form the inferior cardiac plexus, as
we have fliewn in deferibing the pneumo-gaftric
nerve.

The inferior cervical ganglion is flat. Its fi-
gure varies. It is oblong, triangular, or fquare
in different individuals. It is ufuallyTituated
before the tranfverfe procefs of the feventh ver-
tebra of the neck. It is fometimes wanting,
and then it is confounded with the firft thoracic
ganglion. It commonly, receives filaments fron^
the four laft cervical pairs, but feldom any from
the dorfal. It appears to produce others which,
proceeding to the internal fide, join the recur-
rent branch of the par vagum, the diaphragma-
tic nerve, and the nerves which form the fu-
perior and inferior cardiac plexufes.

The trunk of the fympathctic nerve enters the
thorax behind the vertebral artery. Having ar-
rived upon, or a little below the head of thcfirfl
rib, and fiill covered by the fub-clavial artery,*
' it experiences a new enlargement, called the

Art. XVI. Great Sympathetic. 293

fiiperior thoracic gau^Hon. A number of nervous
filaments run into this ganglion from the infe-
rior cervical pairs, among which there is always
a very remarkable one from the firft dorfal pair,
and even fometimes another from tiie fecond.
It produces three orders of branches. The firfl
Ainite with the cardiac plexus ; the fecond form
a plexus round the fub-clavial and vertebral ar-
teries; the others arc loft in the mufculi fcaleni
and longus colli.

The remaining part of the great fympathctic
nerve, in the cavity of the thorax, is fomewhat
thicker than in the neck. It is attached infe-
riorly to the pleura, and pafTes above the heads
of the ribs. In its courfe, as far as the dia-
phragm, it receives filaments from the dorfal
pairs, at acute angles ; at each of the points of
union it forms enlargements or ganglia, which
are named in numerical order. They vary both
in form and iizc.

At the fixth ganglion five or fix branches
are ufually detached from the nerve. They
proceed downward and inward towards the bo-
dies of the vertebra. They are there united, and
form a particular cord, which pafTes into the ab-
domen, through an aperture of the diaphragm, to
which mufcle it affords filaments. This cord is
' called the fplancbnic nerve.

1! Upon getting into the abdomen, the fplanch-
nic nerve becomes almoft immediately flat, and
fi forms a kind of nervous crefeent before the

! u 3

\

I

i

aorta.-

294 L. X. Distribution of the Nerves,

aorta. From its form this has been named the
femi-lunar ganglion. It is joined inferiorly to
that of the oppofite fide. It fends off a great
number of filaments. Some go to the diaphragm,
a number of others form a plexus round the
aorta, and the renal, cqeliac, and fuperior my-
fenteric arteries,

That which envelopes the cceliac artery is
particularly named the Jolar plexus. It re-
ceives a number of filaments from the par vagum.
The others, from their fituation with refpedl to
the arteries, are called the coronary Jiomachicy the
JpleniCy and the hepatic plexufes.

The trunk of the great fympathetic, which
we left in the thorax, continues to defeend to ;
the diaphragm, but it detaches, at the ninth and ;
tenth thoracic ganglion, and fometimes at the ;
lafi: but one, a filament called the X\xx\o. fplanchnic :
nerve y \Vhich unites with the great fplanchnic in ;
its pafiage through the diaphragm.

The fituation of the great fympathetic with-
in the abdomen is nearly the fame as in the j
thorax. It forms enlargements at each lumbar |
vertebra, which receive two or three filaments
from each of the lumbar pairs. It alfo fends |
filaments to the plexufes already deferibed i; |
there arc then plexufes formed round the in- j
ferior myfcntcric, fpcrmatic, and hypogafiric j
arteries, which are terrhed inferior myfenterir, j
fpermatir, and hypogafiric plexufes. I'he lafi of j
thefe tranfinils branches to all the adjoining ar- :

tcrics, ‘

Art. XVI. Great Sympathetic. 295

'teries, to the colon and recT:um, to the ureters,
the bladder, and the parts of generation.

Having reached the pelvis, the great fympa-
thetic proceeds to the os facrum. Arrived at
the caudal vertebrtE, the two trunks, which are
now very flender, unite and form the laft gan-
glion. In this courfe there are as many enlarge-
ments as there are facral nerves. It happens,
however, fometimes, that there is- no ganglion.

In this manner the great fy mpathetic nerve
terminates in man.

C. In other ]\Iammifcrous Animals.

The great fympathetic nerve of the other
Mammalia is nearly fimilar to that of man.
We fhall give a defeription of it, taken from ac-
curate diliedtions in the ivolf, the racoon^ the por-
cupinct the Jheepy and the calf.

The great fympathetic evidently unites, within
the cranium, and in the folds of the dura-mater,
with the fifth and lixth pair of nerves. This
anaftomqlis is very remarkable.

On entering the cranium through the foramen
lacerum, it is very diftindl from the par vagum,
but it adheres clofdy to the periofteum of the
temporal bone. When we ffretch the cord
which it forms, we obferve that it is dWided
into fix or feven filaments, which make together
a very 'compact net-work. Two or three lines
farther, according to the fize of the animal, all

G 4 thefe

296 .L* X. Distribution of the Nerves, '

thefe filaments approach each other, and arc
again united fo intimately, that the ganglion
which they produce appears, by its feclion, car-
tilaginous. Numerous filaments proceed from
this ganglion, feme of which ^re very Ihort,
and are fent to the nerve of the fifth pair. ,
Others, which are longer and fmaller, form a '

kind of reddifh coloured net, interlaced with '

blood yclfels. This is the net which Willis re-
garded as a little rete mirabile. It appears '
that the communication with the fixth pair |
takes place by means of this net, which enve-
lopes the nerve on every fide, and from which it
is feparated w;ith great difficulty. We have not
remarked any particular anaftomofing branch in
the calf^ or ip the ram.

In its courfe through the foramen lacerum,
the great fympathetic nerve detaches a nervous
filament which enters the cavity of the tympa-
num. It is alfo there intimately united with
the eighth pair, from which it feparates at the
bafe of the cranium to form -a thick cord.

Having advanced fomc lines from the cra-
nium, the great fympathetic fwclls into a large
reddifh ganglion of an elongated oval form.
This is the fuperier cervical gangliov. It unites
with the neighbouring nerves in the fame man-
ner in man.

yVftcr communicating, by filaments, with the
adjoining nerves, the fuperior cervical ganglion
proceeds to the anterior part of the neck, before
2 fli?

Art. XVI. Great Sympathetic. 297

the longus colli mufcle, as far as the fcvcnth
vertebra. la its couifc it receives very ncndcr
nervous filaments from all the cervical pairs.

In the front of the laft vertebra of the neck,
it forms a curve, which is dircactl from within
outward towards the firll rib, on the head of
which it unites with the firll thoracic ganglion.

Several filaments which go from the con-
vexity of this curve, proceed along the media-
ftinum to the pericardium, where they are loft.
Others form a plexus around the fubclavial ar-
tery.

The firft thoracic ganglion is of a femi-lunar
figure, more or lefs elongated according to the
fpecies. Its concavity is inward. On its co-
nical edge it receives or tranfmits four or five
filanients. The inoft fuperior pafles along the
vertebral artery, accompanies it into the canal,
and forms around it a plexus which may be fol-
lowed very high up, and which probably enters
into tne cranium with the artery. The other
filaments unite with the laft cervical, and with
the two firft dprfal pairs.

From the concavity or fuperior and internal
edge of this firft thoracic ganglion, one, two, or
three filaments are detached, which proceed
tranfverfely or obliquely downward tow'ards
the pulmonary arteries at their entrance into the
lungs ; they there unite with the par vagum, to
form the pulmonary and inferior cardiac plexnfes.

The trunk, of the great fympathetic conti-
nues

298 L. X. Distribution of the Nerves.

«

nues to defcend in the thorax as far as the dia^
phragm. In its pafTage it forms a ganglion
upon the head of each rib, which receives a
nervous filament from each of the vertebral
pairs. LafHy, it palTes through the diaphragm,
forming a fingle cord, which is the real fplancb-
nic nerve.

On entering the abdominal cavity, the
fplanchnic nerve proceeds towards the middle
line under the flomach : it is there frequently
divided into two cords, which afterwards re-
join. From this kind of nervous ring there
arifes either a principal trunk, or four or five
filaments, which uniting together near the coe-
liac artery, form a ganglion which is frequently
of a femi-lunar figure. A number of filaments
proceed from the edges of this ganglion, and
envelope the ftomachic, fplcnic, and hepatic
arteries, and fupply the place of the folar plexus;
others envelope the renal artery, round which
they alfo form a plexus.

The trunk of the great fympathetic fiill dc-
feends in the abdominal cavity, on the lateral
parts of the bodies of the vertebrae ; each of its
ganglia is nearly of an elongated quadrangular
form ; one of the fuperior angles receives the
continuation of the trunk; the other the ver-
tebral pair. I'he internal inferior angle tranf-
mits a branch to the aorta, which afiifls in form-
ing fom'c of the plexiiCes that furround each
of the arteries which rife from that vcfiel. The

other

Art. XVI. Great Sympathetic. 299

other angle produces the continuation of the
trunk.

In other rcfpecls the great fympathctic ap-
pears to be difpofed in all niammiferous ani-
mals as in man : it produces the fame plexufes,
with fome differences as to the number of fila-
ments and the fnape of the ganglia : but even
thefe circumftances are fubjeift to variation.

C. In Birds.

The great fympathetic in birds has many re-
femblanccs to that in mammalia: It enters the
cranium by the fame aperture as that through
which the par vagum and gloflb-pharyngeus
come out ; it alfo unites with the fifth and the
lixth pairs. The firft ganglion, or that which
correfponds to the fuperior cervical, is of a
lenticular form; it is fituated ^immediately be-
low the cranium, and communicates w'ith the
ninth pair, and particularly with the eighth,
with which it appears to be altogether con-
founded.

We find no trace of the great fympathetic in
the neck of birds; but within the thorax we
pbfervethat it detaches to the pulmonary plexus,
formed by the par vagum, a very thick nervous
filament, which is united to the firfl thoracic
ganglion.

Here the great fympathetic of birds begins to
alfume an appearance truly remarkable.

The

CO L.X. Distribution or the NfiaVEs.

The firfl nervous ganglion becomes a ccntrd
from which eight different diverging filaments
proceed. The firft unites to the plexus of the 1

brachial nerve ; the fecond defcends the neck j

in the vertebral canal along with the arteiw,
and at the middle of each vertebra forms a fmali
from which filaments are fent off to
each of the cervical pairs. We have found it
impoffible to follow it as far as the head, in the
coot, the (luck, the fwan, and the buzzard. The
third filament is confounded with the cardiac
plexus formed by the par vagum. The three
next filaments proceed from the internal fide
tow'ards the projection made by the bodies of
the vertebrae, and produce a particular cord, to
which we fh'all return. Laftly, the feventh
and eighth filaments ferve to unite this ganglion *
with the fuccceding one ; the one palfing below,
and the other above, fo as to form a curvature of
a lozenge-like fhape, in which the head of the
^ rib is received. - ‘ <

Each fuccceding ganglion produces, in this
manner, a nervous irradiation, compofed of five,
fix, or feven filaments ; four of which, two fu-
perior and two inferior, communicate with the :

preceding or follow'ing ganglion, byoneortwo
a nervous cord is formed, which fupplics the
place of the fplanchniC nerve: the lafl filament
unites with the dorfal pair fituated inferiorly.

• 'fhe cord which is produced by all the inter-
nal branches of the great fympathetic, and which ’

is

Art. XVI. Great Sympathetic, 30I

IS analogous to the fplanchnic nerve, accom-
panies the aorta on each fide. Having reached
the part where the coeliac artery divides into
three, it is united to nervous filaments derived,
from the thoracic ganglion, and thus forms one,
two, or three enlargements, which detach an,
'immenfc number of branches to envelope the
arteries on all fides. The ganglia here obvi-
oufly fupply the place of thofc named Icmi-lunar.
in man, and the filaments which proceed from
them anfwer to the folar plexus. There are
alfo other plexufcs formed on the renal and in-
ferior myfenteric arteries.

The trunk of thii nerve continues to follow
the bodies of the vertebrae, but the ganglia be-
come Icfs confpicuous w hen there are no longer
any ribs, and wc there perceive only a fmall
enlargement at the point where the vertebral
pair is united. But from the internal fide of
each of thefe fmall enlargements, tw’O or three
filaments are detached, and produce a plexus
on the aorta, anaftomofing with tkofe of the op-
pofite fide.

We clearly perceive the continuation of the
great fympaihetic nerve to the laft vertebra of
the taiL It is very eafily traced in jzvan.

' ^ D. In Repliles.

We have had no opportunity of dilTefling the
great fympathetic nerve of reptiles, except in

the

302 L. X. Distribution of the Nerves^

the mud-rtortoife. It is only diftin(fl in the in-
terior of the back fliell : it has a difpolition
analogous to that of the cervical ganglion. The
pneumo-gaflric nerve, however, adheres fo clofely
to it, that they cannot be feparated : w’e did not
perceive any filament on the neck which could
be regarded as the trunk of the nerve.

On the peritoneum, and on the bodies of the
Vertebrae, there appear very diftindl nervous
ganglia, which are manifeftly produced by the
great fympathetic.

The ganglia are exadly fimilar to thofe of
birds. There are two fuperior and two inferior
filaments whith pafs under the tranfverfe pro-
cefs of the vertebra that is united to the b^ick
fliell ; from the internal edge of each ganglion,
a fplanchnic nerve proceeds, which forms plex-
ufes round each of the arteries produced by the
aorta : one is alfo fent to aflift in forming the
pulmonary plexus.

This nerve may be very cafily traced to the
lateral parts of the firft vertebra of the tail.

E. In Fijhes.

We alfo find the great fympathetic nerve in
fifhes, but it is exceedingly flender : it is a fim-
ple nervous filament, lituated on each fide of
the vertebral column in the abdominal cavity.
It evidently furnillics filaments to the perito-
neum, which extend round the arteries that

arc

I

Art. XVI. Great Sympathetic. 303

are loft on the inteftines. We alfo obfervc that
there are communicating filaments for each of
the vertebral pairs, but there are no apparent
ganglia at the points where this union takes
place.

The great fympathetic nerve appears to enter
the cranium by the canal of the firft vertebra ;
it there accompanies the blood veflcls.

LEG-

C 304 3 '

LECTURE ELEVEXTH.

DESCRIPTION OF THE NERVOUS SYSTEM OF
ANIMALS WHICH HAVE NO VERTEBRAE.

An iMALs without vertebrae are not formed on
a common plan either with refped; to the nerves
or the mufcles : they prefent difparlties fo great
that we are compelled to adopt a mode of de-
fcription different from that purfued in the
three laft Lectures. It is neceffary to proceed in
the fame manner in which we have treated the
organs of motion in thefe animals. We muft
confider the nervous fyftem in their different
claffes, and in their -principal genera. As the
characters common to, each of thefe cla'ffes are
very few, what we have faid on that fubjedl, in
LeCt. I. Art. 3 and 5, and in LeCt. IX. Art. j,
will fuffice, and we now proceed to enter into
details. ♦

Article I.

Jjrui/i and Nerves of the Ccphalo-poduus ‘
MoUnfea.

Tv the eight-armed Jcpia, the euttle fij).\ the
calmars, the nervous lyflcm appears to rcfcmble

in

Art. j. NfiRVEs of tMe CephaIopoda. J05

in fome refpedls that of red blooded animals.
The brain is inclofed in a particular cavity of
the cartilage of the head, which is pierced by a
number of holes to give paifage to the nerves.

The cartilage of the head has the form of a
hollow and irregular ring ; its pofterior part is
the thickeil, and contains the brain ; its anterior
part contains the ears, and a femi-circular canal

which comrhunicates on each fide with the ca-

/

vity of the brain, and includes the medullary
Collar. The ce fop hagus pa (Tes through the cen-
tre of this cartilaginous ring, and is confequently,
as in all white blooded animals, furrounded by
the medullary cord. The lateral parts of the
tartilaginous ring have eminences which form
a kind of orbit on each fide.

The brain is divided into two diftinfl parts;
one next the cefophagus, the furface of which
is fmooth ; and the other towards the back,
which is round, and marked by longitudinal
ftriae.

The medullary collar arifes from the lateral
parts of both portions ; in the oHopus it is in
the form of a lamina; the anterior part of which
produces four large nerves, which, w'ith the four
correfponding nerves, proceed forward into the
eight feet which crown the head: we fhall re-
turn to their diftribution. Thefe laminae join
inferiorly, and thus encircle the cefophagus.

Two other principal pairs of nerves arife from
each lide, near the origin of the collar. The
' VoL. II. X firll

f

3o6' L. XL Nerves of iNVERtEfiRAL Animals.

firft is the optic pair : it extends direcT:ly into
the orbit ; after a fliort courfe it pafTes through
the fclerotic coat, and is there dilated into a
ganglion larger than the brain, and which has
the form of a kidney with its concave fide turned
towards the brain. The fubftance of this gan-
glion appears to be the fame as that of the brain ;
its convexity produces a multitude of fmall
nerves, as fine as hairs, which pafs through the
choroidcs, by an equal number of fmall holes,
to form the retina.

The fecond pair belongs to the mufcles of the
fac ; it originates a little above the preceding
pair: thefe nerves defeend obliquely; and, after
leaving the cerebral cavity, each flips between
the mufcles which fufiain the head, and is font
to the lateral part of the fac, near its fuperior
edge, between the body and the branchiae ; it
there divides into two branches, one of which
defeends diredlly towards the bottom of the fac,
and the other dilates into a roundifii ganglion,
which produces a multitude of nerves, difpofed
like radii. Tlicfc nerves arc difiributed to all
the flcfliy fibres of the fac and the fins.

The anterior and inferior part of the collar
gives origin to two pairs of nerves. The firlf
pair is the auditory nerves ; they arc very fiiort,
as they only traverfc a cartilaginous lamina to
penetrate the car, where they are difiributed. '

The fecond pair iffues from the cartilage, by |
two holes placed very near each other, and be- ■

neath

AkT. I. Nerves OF Tiin Cephalopoda. 307

Death the cars : the two nerves which compofe
it defcend within the peritoneum to the bot-
tom of the fac. When they arrive near the
heart, they form a complicated plexus, from
which all the nerves of the different vilccra
proceed.

Each foot has a nerve, which pafTes from one
extremity to another, like an axis, and is li-
tuated in a canal, which we deferibed when wc
treated of the Mufcles of the Feet. This nerve
is enlarged, at different fpaces, by numerous gan-
glia, which have the appearance of tubercles,
and from each of which ten or twelve nervous
filaments proceed : thefe filaments diverge and
perforate the mufcles of the interior of the
4 foot to which they diftribute branches; but
jthey proceed chiefly to the fuckers.

3 This defeription of the nervous fyftem is
'j taken from the Jepia o^opus. The other Cepha-
i^lopoda differ only in having a brain lefs dif-
Vtindlly divided, and prefenting lefs confpicuous

7

X 2

Arti-

3o8 L. XI. Nerves of Invertebral Animals.

Article IL

i

Brain and Nerves of the Gafieropodoiis Mollufca. j

A. In the Snail (Helix Pomatia.)

1 HE brain of the Snail is fituated upon the
oefophagus, behind an oval mafs of mufcles,
which envelopes the mouth and the pharynx,
and which we (hall defcribe in the Article on •
Maftication ; its fhape is nearly femi-lunar, with
its concave part directed pofteriorly. The an-
gles of the crefeent arc prolonged on each fide I
into a branch, by which the oefophagus is en- I
compafTed in a collar. The falivary glands, I
and the mufcle which retrads the mouth and 1
' brain, pafs likewife through this collar. I

The two cords produced by the brain unite I
below the oefophagus and the mufcle, in a large I
round ganglion, which is more than one half!
the fize of the brain. All the nerves proceed I
from one or other of thefe two malfes. J

Thofe furnifhed by the brain proceed from 1
the lateral parts of its convex fide. 1

There are, in the firft place, two nerves for 1
the flefliy part of the mouth ; next, one on each I
fide for the fmall horns; then two for each great I
horn, one of w'hich proceeds to the bafe of that I
hor;i, and imffes into its mufcular fubnancc;||

the ] I

Art. II. Nerves OF THE Gasteropoda. 309

the other goes to the eye. The latter is folded
confiderably on itfelf, when the horn is drawn
inward. There are, belides, fome other fila-
ments which extend to the bafe of the parts of
generation, and to the mufcles which move the
head.

The large inferior ganglion produces, at firft,
three great nerves, one for the penis, another
for the vifccra, and the third for the mufcles,
which draw the whole animal into its fhell : thf
inferior furfacc of this ganglion afterwards pro-
dutes two great fafciculi, which proceed back-
ward, and^ which, after palling between the two
mufcles before mentioned, are diftfibuted to
all the flelby parts of the foot.

The figure which Swammerdam gives of the
nerves of the fnail, appears to have been taken
from the fliig, rather than from the fliell fnail.

B. In the Slug (^Lbnax Rufus.)

The brain is alfo fituated behind the oefopha-
gus in this animal, but it has the form of a nar-
row ribbon lying crofs ways : it enlarges a little
at its lateral pans, each of which produce a fi-
lament to encircle the oefophagus, The gan-
glion which is formed by the union of thefi;
two filaments is larger than the brain.

Two principal trunks proceed, each on its re-
fpeiffive fide, in a firait line from this ganglion ;
th?y extend along the lower part of the body,

^ 3 throughout

310 L. XI. Nerves or Invertebral Animals.

throughout its whole length, preferving nearly
a parallel direcflion ; on the external fide they
each detach a numl^cr of filaments, which pe-
netrate into the flcfhy fubftance of the fkin.

A great number of other filaments alfo pro-
ceed immediately from the inferior ganglion to
the fkin.

Further, the inferior ganglion fends off two «
nerves on each fide, which go to the vifeera, and
take the diffribution of the arteries.

With refpecfl to the brain, properly fo called,
it furniflies, in the firfl: place, a nerve from each jj
fide, for the fiefliy mafs of the mouth ; then
two for each of the great horns, one of which
extends to the eye, and becomes the optic \
nerve. The nerves of the fmall horns arife
more outwardly.

C. /;? l/ie Aplyfia.

This is a fmall marine animal, very like the |
flugs, but refpiring through branchite, which
form a kind of tuft on the back, and which are
covered by a particular operculum.

The brain is fituated as in the fnail ; but the
branches which furround the oefophagus pro- |
ducc two ganglia, one on each fide, which arc ;
conjoined by a fmall filament. |

The brain furniflies, at its anterior part, two j
flendcr filaments, which encircle the flefliy mafs ^
of the mouth, and unite under it in a fmall f

ganglion^ f

Art. II. Nerves OF THE Gasteropod.^. 31 i

ganglion, whence the nerves of the lips are de-
tached. The brain afterwards affords nerves to
the horns and the eyes, which are, in this ani-
mal, lituated between the horns, and to the
male parts of generation. The two lateral gan-
glia tranfmit a multitude of nerves to all the
fiefliy parts of the foot and Ikin ; they alfo pro-
duce each a long cord, Mhich unites to its cor-
refponding cord on the aorta, near the part where
it rifes from the heart ; they there form a len-
ticular ganglion, from which all the nerves of
the difl'erent vifeera proceed,

D. In the Clio borealis.

This fmall animal has no foot, and can only
fwim. It refpires by two bnanchiae, in the form
of wings, fituated on the neck; but in other
refpeds it very much refembles the Hug. Its
nervous fyllem is analogous to that of the ap-
lyfia.

Its brain is formed of two roundilli lobes ; it
furniflies, immediately, nerves to the tentacula,
and gives origin to a double collar ; the ante-
rior extends, as in theaplylia, under the mouth,
to form a fmall ganglion. The poflerior has a
ganglion on each lide, which furniflies nerves
to the mufcular fkin that furrounds the body;
each of thefe produce one or two other ganglia,
>vhich fend nerves to the vifccra.

31? L.XI. Nerves OF Invertebral Animals.

E. In the Doris.

This is alfo a fmall marine animal limilar to
the flug, but it refpires by external branchis,
difppfed like ftars round the anus. The brain
is very large in proportion to the reft of the
body, and particularly in copiparifon with that
of other gafteropoda : it is contracted at its
middle part, and feems to form two united
lobes ; it is elongated tranfverfejy, and of a
fquare form. It is lituated immediately above
the origin of the oefophagus, behind the orbi-
cular mafs of mpfcles which form the parietes •
of the mouth. j

Six nerves proceed from the brain on each |
|ide ; one pair is deftined for the mufcles of the |
mouth, another for the tentacula. The third J,
is a cord, which paftes below the cufophagus,

and is loft in the mufcles of the foot, where it Ti
‘ ' ■ • , {
may be very diftindlly obferved on the lateral

parts of the internal furface. The fourth and *

the fifth arc direded above the mafs of the in- j

teftines, and proceed to the fkin of the bac^.

Taftly, the ftxth terminates iri the parts of gc- j

neration.

V ■ 1

E. In the Scyllea.

This is another marine animal fimilar to the
ftug, but which refpires by branchix, in the
form of wings ranged in pairs on the back ; it i
■ • ‘ • , • crawls ;

Art, II. Nerves OF THE Gasteropoda. J13

jcrawls on a furrow in its belly. The collar
jvhich furrounds the ocfophagus is a fimplc
cord, and does not enlarge into a ganglion, as
it proceeds downward. The brain, which is
above it, is of an oval form : it fends nerves to
the mouth, and to the horns, but there are no
optic nerves, as this animal has no eyes.

The nerves of the vifeera arife from the infe-
rior part of the collar, and thofe of the muf-
cles from its Tides.

G. In the Sea Ear (^llalyotis Tuberculaia.)

9

This animal has no ganglion above the oefo-
phagus to fupply the place of the brain. We
find merely a nervous filament, fituated tranf-
verfely above the oefophagus, behind the mouth.
Four fmall ramifications proceed from the mid-
dle and anterior part of this filament, two on
each fide, and are loll in the parietes of the
mouth.

At each extremity of the tranfverfe nervous
filament there is a very large flat ganglion, from
the circumference of which a number of nerves
are detached to the adjacent parts. Thefe w^e
final 1 deficribe. •

Three filaments pafis off on each fide ; from
the external furface of this ganglion one is
fient to the fetiform tentaculum, fituated above
the mouth, the other two proceed to the flat
tentaculum, like a buckler, placed more pofle-

7 riorly.

314 L.XI. Nerves of Invertebral Animals,

riorly, and on the fidcs. The mofl pofterior
appears to be intended for the eye. It is the
thickell ; the other feems loft in the mufcular
parts.

A very remarkable filament is detached from
the fuperior part ; it proceeds above the oefo-
phagus, and joins the correfponding one of the
other fide. There is a fmall enlargement at
the point of union, from which four nerves
proceed, two on each fide of the middle line.
The moft external is loft in the mufdles of the
tongue ; the other purfues the middle line of
thccefophagus.and is rami fiedover the inteftines.

Several fmall branches arc detached inferiorly,
and terminate in the fan-like mufcles that fuf-
tain the tongue.

Laftly, the ganglion is prolonged pofteriorly
into a thick nervous cord, fituated on the fidcs
and below the oefophagus, which becomes flat
as it proceeds backward ; it deferibes a femi-
lunar curve, fo that the two nerves of each fide
arc approximated, and finally touch each other
at the bafe of the tongue, and below the ante-
rior part of the large mufcle which attaches
the animal to its IhclI.

d'he contadl of thefe two nerves produces a
ganglion, from which two very remarkable
trunks, intended for the inicftincs, proceed ;
they may be followed to above the ftomach, and
wc can perceive that fome of their ramifications
enter the liver-

After

Art. II. Nerves OF, THE Gasteropoda. 315

After the formation of the ganglion, which
furnilhes nerves to the vifeera, the two trunks
penetrate by two different holes into the fub-
Ibince of the mufcle of the foot. Thefe two
holes are the origin of twO canals, which run
throughout the whole length of the foot, on the
fides of another middle canal, which appears
defined to diftribute the blood of the animal.

The two nerves, lodged in the lateral canal,
are dillributed by a great number of lateral
holes info the fubllance of the fleihy mufcles
of the foot, and of the Ihcil, where they may
be follow'ed with facility.

H. In the BuUmu.'i of Funds (^Ileli.v St agnails

Lin.) and in the Flanorbis Cornea (//e//>

Cornea Lin.)

In thefe animals the brain confifls of two la-
teral maffes, feparated by a cantraclion. The
recent fubjeff is remarkable for having thefe
maffes of a lively red colour. The diftribution
of the nerves differs very little from w'hat we
obferve in the common fnail.

Article IIL

Brain and Nerves of the Acephalous Mollufca.

The nervous fyflem of Acephalous Mollufca
formed on a plan far more uniform than that

3i6 L. XI. Nerves of Invertebral Animals.

of the Gafleropoda. In all the teftaceous ace-
phala, from the oyjler to the phot as ^ and the
teredoy there appears no efTential difference ; it
confifls always of two ganglia, one on the mouth,
reprefenting the brain, and another towards the
oppofite part. Thefe two ganglia are united by
two long nervous cords, which take the place
of the ufual collar, but which occupy a much
greater fpace — as the foot, when it exifts, and
the llomach and liver, always pafs in the inter-
val between them^. All the nerves arife from
the two ganglia.

A. I?i the AnocJontiteSy or Frcjh-wattr MiifdcSy

in Cockles, in the Venus, the Mactra, and the

M ya.

In thefe, and in general all the bivalves, which
have two cylindrical mufcles, one at each ex-
tremity of their valves, for the purpofe of
bringing them together ; the mouth is placed
near one of thofe mufcles, and the anus near
the other. The foot appears about the middle
of file Ihell ; and the tubes for the excrements
and refpiration, when they exift, go out at the
end of the flicll, oppofite to that in which the
mouth is fituated. The brain is placed upon
the anterior edge of the mouth ; it is oblong
tranfverfely ; it fends olf two cords anteriorly,
which go to the adjacent mufcles, and turning
towards each fide, jicnclrate the lobes of the

cloak.

Art. III. Nerves or Acephala. 317

I

cloak, pafling through the whole extent of their
edge. The brain furniflics alfo, on each fide,
fome filaments to the membranous tentacula,
which furround the mouth, and detaches, from
its pofterior edge, the two cords, analogous to
the medullary collar in other invcrtcbral ani-
mals. Thcfc cords proceed, each on its fide,
under the mufcular firatum, which envelopes
the liver and the other vifeera, and which be-
comes thicker, as it is continued to form the
foot, which is frequently confirudled for fpia-
ning.

When arrived at the pofterior mufcle which
clofes the valves, thefe cords approach each
other, and enlarge as they unite, to form the
fecond ganglion. This ganglion has the form
of two lobes. It is at leaft as large as the brain-
ganglion, and always much more eafily diftin-
guiftied. It detaches two principal nerves on
each fide, and the four together reprefent a kind
of St. Andrew’s crofs. The two anterior nerves,
as they afeend, proceed a little towards the fide
of the mouth, and, after having deferibed an
arch, penetrate into the branchiie. The other-
two pafs on the pofterior mufcle, precifely in
the fame manner as thofe of the brain on the
anterior. After detaching fome filaments, they
proceed into the cloak, the edge of which they
lollow’, until they join thofe of the brain ; they
thus form a continued circle. We do not yet
' know

3i8 L. XI. Nerves of Invertebral Animals.

know the origin of the nerves of the vifcera in
thefe animals.

The teflaceous acephala, in which the foot is
protruded by an extremity of the fhell, that al-
ways remains open, and the tubes, by the oppo-
fite extremities, that is to fay, in razor-jiJIj and
piddocksj the mouth, and consequently the brain,
is always near one extremity. The nerves,
which proceed from the br£?in, take therefore a
longer courfe before they diverge to join the
cloak. The cords of the collar, however, have
a much fliorter diftance to pafs before they
unite. There is a conliderable fpace, particu-
larly iri the razor-fifli, between the mafs of vif-
cera fituated in the bafe of the foot, and the
poflerior mufcle. The fecond ganglion is fi-
tuated in the middle of this fpace, between the
branchiae of each fide : it is round, and much
more diftincH: than in the other fpecics ; the
nerves it produces are however exadlly fimilar.

In the oyjler, which has no mufcle at the an-
terior part, the brain and mouth are fituated
under the kind of hood which the cloak forms
towards the hinge.' The nerves go direcflly into
the cloak itfelf. The ganglion is fituated on the
anterior furface of the fingle mufcle, imme-
diately behind the mafs of vifcera. The nerves
it produces are the fame as in the preceding
genera.

n. In

Art. III. Nerves of Acephala. 319

B. In the Afeidia.

Thefe fmall marine animals are enveloped in
an immoveable coriaceous, or gelatinous cafe,
which has two apertures ; one for the expulfioii
of the excrements, the other for the admilTion
of the water to the branchiae. The branchiae
arc in the form of a large fac, and are enclofed,
as well as the other vifeera, in another membra-
nous bag, of the fame form as the external cafe,
but fmaller, and completely adhering to that
cafe at the two apertures only. The inferior
ganglion is fituated on this membranous fac :
its pofition is between the two apertures, but
neareft that which correfponds to the anus ; it
produces four principal nerves ; two afeend to-
wards the fuperior, or refpiring aperture ; the
other two defeend towards that of the excre-
ments. There are fmaller nerves which are
difperfed throughout all the membr-anous fac.
We have not yet difeovered thofe produced by
the brain, nor the brain itfelf, which is doubtlefs
fituated as ufual on the mouth. The mouth is
in the bottom of the branchial fac.

C. In the Tritons (^Linnaeus tvhich inhabit the
Anatiferous and Balanite Shells. (^Lepds Lin'.)

Thefe animals approach, perhaps, nearer to
the Cruftacea, and particularly to the monoculi,

than

320 L. XI. Nerves of In vertebral Animals.

than to the Mollufca. Their nervous fyftem is
of a fort of middle kind between that of the
Mollufca and that of the Cruflacea and Infedls.

1 he brain is placed acrofs the mouth, which
is itfelf fituated in the part of the body corre-
fponding to the ligament, and at the bottom of
the (hell. It produces four nerves to the muf-
cles (ituated in that place, and to the (lomach,
and two others which embrace the osfophagus,
and proceed into that elongated portion of the
body- which bears the numerous articulated and
ciliated horny tentacula which the animal pro-
trudes from its Tiell. Thefe two filaments ap-
proach and form a ganglion, and then proceed
clofe to each other among thefe tentacula,
furnifhing a correfponding pair of nerves for
each pair of tentacula, but there are no apparent
ganglia at the origin of thefe nerves.

From what we have dated in this and the two
preceding articles, it rcfults.

That the nervous fyllein of Mollufca confids
in a brain placed on the oefophagus, and in a
variable number of a ganglia, fometimes ap-»
proximated to the brain, and fometimes dif-
perfed in the different cavities, Or placed under
the mufcular envelopes of the body ; that the
ganglia arc always connecfled to the brain and
to each other by nervous cords, which cflablifh
a general communication between thefe differ-
ent medullary maffes ; that the nerves all arife
cither from the brain or the ganglia; and finally,

that*

Art. IV. Nkrves OF Crustacea. 321

that there is no part which can be compared to
the medulla oblongata and the medulla fpina-
lis.

Article IV.

Brain and Nerves of the Cruft acca.

The Cruftacea, which, in their organs of mo-
tion, very much refemble infedls, though thofe
I of circulation and refpiration are exceedingly
1 different, have alfo a nervous fyftem fimilar to
that clafs, at leaft in the elfential parts.

In the long-tailed crayfjh, the middle part
! of the fyftem is a knotted cord, which extends
I from one extremity of the body to the other.

1 The foort-tailcd kind, commonly called crahs^
have a medullary circle in the middle of the
abdomen, from whence the nerves of the body
proceed like radii.

In thefe animals the brain is placed at the an-
terior extremity of the fnout, and confequently
at a confiderable diftance from the mouth, which
’ opens under the corfelet. On this account the
' cords which make the collar of the cefophagus
are more elongated than in other animals.

{\ VoL. II. Y A. Brain

i. > ,

322 L. XI. Nerves of In vertebral Animals.

A. .Brain of the common Cray-Fijli, {Aftacus
FluviatiVus, Fab. )

The brain of this animal forms a mafs which
is broader than long, and diftin6lly divided on
the fuperior furface into four round lobes. Each
of the middle lobes produces an optic nerve
from its fore part. This nerve proceeds direclly
into the moveable tubercle which fuftains the
eye, and is there dilated and divided into a
multitude of filaments, which form a pencil, and
unite to all the fmall tubercles of the eye.

Four other nerves arife from the inferior
furface of the brain ; thefe proceed to the
four antennae, and detach fome filaments to the
neighbouring parts. The cords which form
the collar, arife from the pofterior part of the
brain. About the middle of its length each
detaches a large nerve which extends to the
mandibles and their mufcles. Thefe cords
unite under the ftomach in an oblong gan-
glion, which furniflies nerves to the different
pairs of jaws. On leaving this part the two
cords remain near each other throughout the
whole length of the corfelct, where they form
five fucceffive ganglia, placed between the ar-
ticulatiorvs of the live pairs of feet : each foot
receives a nerve from its correfponding gan-
glion, which penetrates to the extremity of the
foot : the nerve of the forceps is the larged.
The medullary cords extend into the tail, where

they

Art. IV. Nerves of Crustacea. 323

they are fo intimately united that it is not
poflible to diftinguifh them. They form fix
ganglia, the five firfl of which produce each
two pairs of nerves ; the lafi produces tour,
which are diftributed as radii to the fcaly fins
that terminate the tail.

The hermit crab,\ (Pagurus, Fabr.) the tail of
which is not covered by articulated fcales, ap-
pears to have much fewer ganglia than the Cray-
\ fijh, W’^e have obferved only five,
j In the jquUla Fabr. there are ten ganglia with-

1 out reckoning the brain: that at the union of

J O

the two cords which form the collar, tranfmits
nerves to the two forceps, and to the three pair
of feet which immediately fucceed them, and
which in thefe animals are ranged almofl on the

(fame tranfverfe line } this ganglion is therefore
the longefl of all. Each of the three following
i pairs has a particular ganglion. There are af-
M rerwards fix ganglia in the length of the tail,
1 which difiribute their filaments to the thick,
timufcles of that part. The brain produces im-
^ mediately four trunks on each fide, viz. the
ii optic, thofe of the two antennae, and the cord
>i which forms the collar. As the antennae are
:j placed more pofteriorly than the brain, their
'1 nerves are direded backward.

1b. In the Common Crab (Cancer Mcenas, Lin.)

.. The brain of the crab refembles that of the

T 2 Cray-

324 L. XI. Nerves of Invertebral Akimals.

cray-fifh in its form and lituation ; it alfo fur-
nifhes analogous nerves, but they are directed .
more towards the fides in confequence of the
pofition of the eyes and the antennae. The me-
dullary cords which form the collar, detach each
a nerve to the mandibles, but the cords are pro-
longed much farther backward than in the cray-
filli before they unite. They jo.in only in the
middle of the thorax, at which place there is
■produced a medullary mafs of an oval ring-like
figure, which is eight times the fixe of the
brain. The nerves which proceed to the dif-
ferent parts arife from the circumference of this
ring. It furnifhes fix nerves on each fide to
the jaw's and the five feet, and there is a fingle
nerve W'hich arifes from the pofterior part, and
proceeds to the tail. This medullary ring may
"be faid to reprefent the ufual knotted cord, but
if it has any ganglia they are not vifible.

C. In the Onifeus Afcllus.

' Idle two cords which compofc the middle
part of the nervous fyfiem in this animal, do not
pcrfcdlyjoin. We candifiinguifli them through-
out the whole of their length. There are nine
ganglia, exclufive of the brain; but the two firfi
and the two lafl: are fo clofe together, that the
number may be reduced to feveir.

D. In

Art. IV. Nerves of Crustacea. 325

I). In jMonocidL

We know not the nervous fyftem of the mo~
lucca crab (Umtilus gigas. Fab. monoculiis poly-
phemiiSy Lin.) In the monoculus apus of Lin-
naeus, however, the indiftincl nature of that
fyftem, joined to fome other peculiarities of or-
ganization, would almoft induce us to clafs the
animal with the inarticulated worms. The brain
is a fmall globule, nearly tranfpircnt, lituated
under the interval of the eyes. The medullary
cord is double, and has an enlargement at each
of the numerous articulations of the body ; but
the w'hole is fo thin and tranfparent that the real
nature of the cord can fcarcely be afeertained.

Article V.

Brain and Nerves of the Lance of Infers.

A. Coleoptcra.

1. Lana of the Scarabceus naficornis.

We fhall give a particular defeription of the
nerves of this larva, becaufe their diftribution
is elTentially different from that which takes
place in the other coleoptera.

Y3

The

326 L. XI. Nerves of Lvvertebral Animals.

The brain is fituated under the great fcale
■which covers the head immediately above the
origin of the oefophagus : It confifts of two ap-
proximated lobes, which are very diftind; at the
front and back part. Four nerves arife from
the anterior part, two on each fide, which are
loft in the cirri and parietes of the mouth.

From the lateral and fomewhat pofterior parts
of the brain, there arifes a pair of nerves, which,
embracing the oefophagus, proceeds inferiorly
to form the nervous cord we ftiall prefently de-
fcribe.

Another pair departs from the inferior furface
of the brain, or that part which refts upon the
oefophagus : thefe are lirft direded forward ;
they afterwards turn inward, and proceed above
the middle and fuperior part of the oefophagus,
, in order to approach each other. When they
come in contad, they unite and form a fmall
ganglion, which produces a lingle nerve; this
nerve continuing to proceed pofteriorly, paftes
below the brain, and accompanies the a-fophagus
to the ftomach. It there enlarges again into a
ganglion, which furnifties fome fmall nerves that
are font to the flomach, and one more confider-
able, which is continued along the inteftinal
canal, and fends oft', at regular diftances, lateral
filaments, which are loft in the coats of this tube.
This nerve is analogous to that which Lyonnet
has defcribetl under the name recurrent, in the
(:aterpillar of the c0as,

2

The

Art. V. Nerves of Larv^. 327

The medulla fpinalis, which, as we have fliewn,
is formed by the pofterior pair of nerves of the
brain, is very thick at its origin : it forms a
large fufiform ganglion about 0,005 metre long,
and half a millimeter broad. Four or five con-
tradlions appear on its anterior part, but they
are fo flight that they feem only tranfverfc fur-
rows. The poflerior part of this ganglion is
fmooth.

From the lateral parts of this large ganglion,
which extends very little beyond the third ring
of the body, a great number of diverging ner-
vous filaments are produced. Thofe which arc
nearcft the head afeend a little; thofe which
fucceed them proceed almoft tranfverfely ; and
the laft are directed more and more pofieriorly :
the length of each is in proportion to i;s diftance
from the anterior part of the ganglion. The
two moft polferior filaments are therefore the
longeft.

2. Laj'va of the Stag Beetle (Lucanus cerxus.)

The nerves of this larva differ greatly from
thofe of the preceding, although the perfecT in-
feds are fo nearly allied in genera.

The brain confifts of two contiguous and aj-
moft fpherical lobes ; thefe produce four nerves
anteriorly for the antenna and the parictes of
the mouth ; two inferiorly, which firfl: proceed
forward, then turn back, pafs again under the
brain, and form the nerve known under the

^ 4 name

3^8 L. XI. Nerves of Invertebral Animals.

name of recurrent . Laflly, two pofleriorly,

which form a collar round the oefophagus, and
join underneath, to compofe the nervous cord
of the body.

This cord is formed of eight ganglia, which
extend to the ninth ring of the body. The dif-
tances between thefe ganglia are very unequal ;
they are joined by very flender and clofely ap-
proximated nervous filaments.

The firft ganglion, from the head, is very
large, and almofl fpherical ; it is followed al-
mofl immediately by the fecond, which is one
half Icfs, and which is diftinguifhed from it
only by a kind of contradlion ; the firft prol
duces four pairs of nerves on each fide ; one
afeends to the head ; the other three diverge,
and are loft in the mufcles of the abdomen, and
in thofe that move the head. The fecond gan-
glion, befides the two nerves that unite it to the
third, produces two other nerves, which arc
alfo direefted backw'ard, and loft in the mufcles
of the fourth ring.

The third ganglion, and thofe that follow as
far as the eighth, are fimilarto the fecond; with
this d iffcrencc, that they arc much more diftant
from each other, and that they produce longer
filaments, in proportion as they are fituated
more infcriorly. Laftly, the eighth and ninth
ganglia arc fo clofc together, that they feem to
form but one, with a flight contradion in the
middle. This double ganglion produces three

pairs

Art.V. Nerves or Larv.t. 3^9

pairs of nerves, which arc much elongated, and
extend to the parts near the anus.

y. Larvee of the Ccrambyx, IlydropkiluSy Cara-
' huSy and Staphyhnus.

The nerves of thefe larvx being very limilar,
it will be fuflicient to delcribe them in one
genus only. We fliall take for our example the
larva of l\\e great diver {HyJropbilus picens.)

The brain in this animal is lituated in the
head, above the origin of the oefophagus ; it is
formed of two lobes, which lie very clofe to-
gether. From its anterior part it detaches fomc
filaments to the palpi, the antennae, and the
parietes of the mouth. Its lateral parts pro-
duce two cords which furround the oefophagus,
and which arc the origin of the nervous cord
fituated inferiorly. It is probable that recur-
rent nerves alfo a rife from this inferior parr,
but we have not yet been able to difeover them.

The chief nervous cord is compofed of ten
ganglia, each of which produce three pairs of
nerves that are loft in the mufcles of the abdo-
men, and without any diftiinft appearance of
- their being diftributed to the inteftines. This
induces us to believe that' there is a recurrent
nerve.

The firft ganglion is very large ; it is pro-
longed pofteriorly into two nervous filaments,
confiderably removed from each other ; the fe-
cond is almoft fimilar j but the third is very

near

3J0 L. XI. Nerves of Invertebral Ani'mals.

near the fourth, which produces only a fingle
filament poftcriorly. AH the others, as far as
the tenth, prefent no particularity. The laft
is divided by a fcnfible contraction; from the
firfl: portion a fingle filament arifes on each fide,
and from the fccond, three pairs of nerves are
detached : thus four pairs of nerves arife from
this ganglion. The fourth pair is directed to
the rudiments of the parts of generation, which
are very diftinct in thefe larva in the lafi: pe..
riod of their growth.

4. Laj'va of the Water-beetle (Dytifeus Mar-

ginalis. )

The brain of this larva is fpherical, and confifis
of a fingle lobe, fituated in the head above the
origin of the oefophagus ; its anterior part pro-
duces fome filaments for the mouth ; and its la-
teral parts the two optic nerves : the latter are
compofed of two parts, which are very diftincfl
as to form. The firfi: portion, or that which
is next the brain, is of an oval figure, pointed
at the extremity which joins the brain: the
other extremity is rounded, and produces a
llender nerve, which goes direefily to the eye.
It is nearly of the fame thicknefs throughout
the whole of its extent; but it is enlarged at its
free extremity into a bulb, from which the ner-
vous filaments of the eye arife.

The two cords which embrace the oefophagus
are fiiort and thick} they arife from the inferior

furfacc

Art. V. Nerves of Larv^^:, 331

furface of the brain, and immediately unite be-
low the oefophagus, in a large fquare-lhaped
ganglion, which produces anteriorly the nerves
of the mandibles, and polferiorly two cords,
which pafs from the head into the corfelet.

There is a greater diftance between this firfl
ganglion of the nervous medulla and the fecond,
than between any of the others. It is more
than double that which ex ills between the two
next ganglia. The fecond ganglion is round ;
it produces two pair of nerves laterally ; the
anterior for the mufcles which adl upon the
head, the pollerior for thofe which move the
anterior feet. There are two cords pofteriorly,
which are direded into the breafl.

. The third ganglion is limilar in every refped
to the fecond ; it furniflies nerves to the inter-
mediate pair of feet.

The fourth ganglion is alfo produced by the
two cords which come from the preceding ; it
is lituated on the union of the abdomen with
the breaft ; it is more broad than long. Late-
rally it produces two pair of nerves, which run
tranfverfely parallel, and are loft in the mufcles.

The other eight ganglia are placed clofe be-
hind each other, and the fpace between them is
fo fmall, that we can fcarcely perceive the two
nervous filaments which unite them ; they alfo
decreafe in thicknefs, without diminifhing in
breadth, as they extend pofteriorly. They all
furnilh laterally a pair of very long nerves,

which

332 L. XI. Nerves of Invertebral Animals.

which float in the abdomen, and for the mofl;
part terminate in the mufcles that move the
wing«. One pair, however, proceeds to the
rudiments of the parts of generation.

B. Orihoptera and Hemiptcra.

The nerves of the larvae of orthoptera and
hemiptera prefent no fcnflble difference from
thofe we obferve in the perfeefl: infcdls. It will
be fufficient therefore to deferibe the nerves of
the latter,

C. Hymenoptercf.

t

In the larva of the faw-fiy {Tenthredo, Lin.)
which has a large head furniflied with eyes, the
brain is very broad and fnort ; it feems to form
four bulbs of equal magnitude, and nearly fphe-
rical ; the two external ferve as the bafe of the
optic nerves, which are flender, and which en-
large a little at their other extremity.

The firfl: ganglion is produced by two very
fmall nerves, which arife from the inferior fur-
face of the brain, and which, after having em-
braced the oefophagus, unite under the firfl: ring
of the body ; it furnifhes filaments to the muf-
cles of the feet, and terminates pofleriorly in
two other nerves, which, at the diflance of one
line, produce a fccond ganglion, and fo on in
fucceflion : the nervous cord is in this manner
formed of eleven ganglia, without reckoning

the

333

Art. V. Nerves of Larv.«.

the brain ; the farther the ganglia are removed
from the head, the more they diminilli in thick-
nefs ; they are all nearly of a round form.

D. Near op ter a.

'In the larva of the lion-ant (Myrmelcon Formi-
cariiis) the nervous fyffem has fome relation to
that of the larva of the dipterous infevfls, which
we lhall afterwards defcribe.

There is a brain fituated in the head ; it pro-
duces nerves analogous to thofe we have already
pointed out in the other larvae.

The nervous medulla confifts, in the firfl
place, of two ganglia, which are compofed of
two lobes, fituated clofe together ; thefe two
firft ganglia are feparatc from the others, and
contained in the part correfponding to the feet,
or in the thorax.

The remainder of the nervous medulla is en-
clofed in the abdomen ; it conlills of eight gan-
glia, placed in an exceedingly clofe fcrics, and
each formed of two lobes ; the firft is nearly
double the fize of the other feven. This fuc-
ceflion of ganglia appears to the eye like the
extremity of the tail of a rattle-fnake; thelaft is
' round ; the others are more broad than long. •
All thefe ganglia furnifh nerves to the mufcles.

It is probable that this difpofition and approxi-
mation of the ganglia have a relation to the
changes which take place in the infed at the

moment

334 L. XI. Nerves or Invertebral Animals*

moment of its metamorphofis, as its abdomen
then ^ occupies fix times the fpace it does in the
larva ftace.

In thofe larva of Neuroptera, which are near-
ly as long as the perfedl infedt, we find that the
ganglia are feparated in the ufual manner.

The larva of the ephemera has eleven ganglia,
without including the brain, ^which furniflies two
large optic nerves. There are three ganglia in
the thorax, and feven in the abdomen : the firfb
fix, reckoning all the ganglia, furnifii more
nerves than the five laft.

The larvae of the dragon-flies have a fmall
two-lobed brain, which produces optic nerves,
larger or fmaller according to the fpecies. The
genus aejhna has them the largeft. The reft of
the nervous fyftem forms a feries of ganglia of
different fizes. In the aejhnay the corfelet con-
tains fix, the two laft of which are the largeft
of all. There are feven fmall and equal gan-
glia in the abdomen.

E. Lcpidoptcra.

The nervous fyfiem of caterpillars confifts of
a feries of thirteen principal ganglia, which
furnifh filaments to all the other parts of the
body.

The ftrft of thefe thirteen ganglia is fituated
in the cavity of the head ; it lies above the
oefophagus, and fupplics the place of the brain;

it

Art. V. Nerves of Larv.^. 335

it appears formed fuperiorly by the union of
two round tubercles. Inferiorly it is concave,
and correfponds to the convexity of the oefo-
phagus.

This ganglion communicates with the refl of
the nervous cord by two thick, filaments, which
embrace the oefophagus, and which are united
below it to the anterior and lateral part of the
next ganglion ; it bcfides produces eight pairs
of nerves.

The firfl: partly unites with other filaments ;
produces fome for the oefophagus, and forms
feveral remarkable ganglia below the upper lip.
The largefl: and molt poficrior, which Lyonnet
has named the firjl frontal ganglion, is prolonged
pofteriorly into a thick recurrent nerve, which
is continued the whole length of the body, near
the back; this recurrent nerve furniflies fila-
ments to the oefophagus and its mufcles ; it pe-
netrates into the dorfal vefTel, and it afterwards
re-appears, and glides along the oefophagus as
far as the ftomach. This nerve produces, at
certain diftances, very folid filaments, which
keep the oefophagus attached to the fkin of the
back.

Bcfides the recurrent nerve we have juft no-
ticed, feveral filaments are furnifhed by the
pofterior frontal ganglion to the mufcles of the
oefophagus, and two to the fecond frontal gan~
glton : the latter alfo detaches feveral filaments
to the oefophagus, and, in particular, a very

remark-

336 L. XI. Nerves of Invertebral Animals.

remarkable one, which, by a fudden enlargement^
conftitutes the third frontal ganglion. This gan-
glion likewife affords fcveral filaments to the
oefophagus.

The fecond pair of the brain appears chiefly
intended for the antenna3, though it furniflies
feveral filaments to the neighbouring parts.

The third pair terminates particularly in the
antennas, and the mufcles which move them.

The fourth pair is proper to the eye of each
fide; it accompanies the air tube which goes to
that part, and is divided into fix branches, that
penetrate into the fix eyes, w hich, by their union,
form that of the caterpillar.

The fifth is direffed a little backward, where
it divides into two branches ; one poflerior, for
the adduffor mufcles of the jaw' ; the other an-
terior, which is loft in the membranes that cover
the frontal fcales.

The fixth and feventh pair unite to form a
ganglion, from which feveral filaments are de-
tached to the oefophagus and its mufcles.

Finally, the laft pair of the brain is entirely
lolt on an air tube.

But befides thefe nerves produced by the firfl:
nervous ganglion, feveral others are detached
from it, which we fliall briefly notice. In the
firfl place, we obferve, that it furniflies feveral
filaments to the dorfal canal: it afterwards gives
origin to a pretty long filament, which termi-
nates on the air veflcls, between the fecond and

third

Art. V. Nerves of Larv.^:. 337

third ganglion. LalRly, it produces a nervous
ring, which embraces the oefophagus inferiorly,
like a girth, and fupplics it with fcveral fila-
ments.

The fccond ganglion is intimately united with
the third, and is diftinguiflicd from it only by
a contradlion. The nerves which proceed from
the anterior part appear to be produced by the
fecond ganglion, and thofe which arife from the
pofierior part, feem to belong to the third.

Befides the two filaments which form the col-
lar round the oefophagus, and which unite the
firfi: to the fecond ganglion, the latter has four
pairs of v^ry difiindt nerves.

The moft anterior pair is fent forward to the
mouth, but in its courfe it divides into two
branches : one terminates in the tonecue and the
adjacent parts ; the other branch proceeds to
the lateral parts, where it fub-divides, to fup-
ply the mandible, the jaw, and upper lip, com-
municating, at the fiime time, with the firft
ganglion, and with the fecond frontal.

The fecond pair proceeds to the jaw, but de-
tachers a number of filaments to the mufcles of
the neighbouring parts.

The third pair is deftined for the fpinning
apparatus ; in its courfe it gives filaments to
the filk vefiels and mufcles of the head.

The fourth pair arifes near the contraction,
which indicates the union of the two ganglia,
between the head and the firfi: ring ; it is loft in

\ oL. 11. 2 the

33^ L. XI. Nerves of Invertebral Animals.

the fat, in the fkin of the neck, and in the muf-
cles inferted into the head.

The third ganglion, which, as we have ob-
ferved, is united to the fecond, produces only
three pairs of nerves : the poflerior is merely
the continuation of the nervous trunk of the
other two pairs ; the anterior is entirely lofl: in
the mufclps and the Ikin ; the intermediate pair
fupplies that part alfo; but it is diftributed
chiefly to the mufcles, which move the articu-
lations of the let;.

We have already dated, that each ganglion
communicates with that which precedes, and
that which follows it, by two filaments, that
are dilfincT: from their origin, and are the bifur-
cation of a fingle trunk. The middle of this
bifurcation, from the third to the eleventh gan-
glion, produces a fmall nerve, which Lyonnet
has named x\\t fpinal fveenum : this Angle nerve
is fituated in the middle line ; it prcfently di-
vides into two brunches, wjiich follow the
clivifions of the air tubes, and penetrate with
fomc pf them into the longitudinal veflcl.

The fourth and fifth ganglia produce the fame
number of nerves, the difiribution of which is
alfo nearly fimilar ; their anterior pair proceeds
to the mufcles, and to the fl<tin of the rings to
which it corrcTponds ; the intermediate pair
furnilhes, more particularly, filaments to the
mufcles of the leg.

The fixth ganglion, \\hich correfponds to

the

Art. V. Nervcs or Larv.®-

339

the fourth ring of the body, a!fo turnifhes two
pair of nct-ves, which are iofl in the mufcleS
and the fkin.

The nerves of the five following ganglia arc
dirtributed nearly in the fame manner.

The twelfth ganglion, and the thirteenth,
which is the termination of the nervous cord,
are very clofe to each other, though diAindf.
The dihribution of the nerves, produced by the
firll:, prefent nothing remarkable. 1 hofe fur-
nilhcd by the fecond are very long, being fent
to the laA rings, in the flcin and mufcles of
which the firH; pair is partly Iofl. The fecond
pair is only fub-divided when it has reached
the firfl ring; it there produces a plexus, from
which a number of filaments arc detached to
the great intefline. The trunk appears to end
on the parietes of the red:um towards the anus-

*

[

i F. Diptej'a.

I The nerves of the larva of the have

) fome refemblance to thofe of the larva of the
i fcarabicus uaji cor tils.

! The brain is formed of two lobes, placed clofe
i together, and almoft fpherical ; it is fituated
Ij above the oefophagus, on a level with the fecond
h ring of the body. A number of fmall nervous
E filaments arife from its anterior parr, and are
b diflributcd to the parietes of the mouth, to
h the mandibles, and to all the adjacent parts.

Z 2 Thefe

340 L. XL Nerves of Lwertebral Animals,

Thefc nerves are very diftineftj particularly thofe
vliich are removed from the middle line.

The poflerior part of thefe two lobes fends
off two thick branches, W’hich embrace the oefo-
phagLis, and form the origin of the nervous
medulla.

This nervous cord is very fhort, and its dia-
meter is one half Icfs than that of the brain ;
it confifls of eleven ganglia placed very near
each other, each of which produces one pair of
nerves.

Thefe nerves proceed direiflly backward.
Swammerdam has crroneoufly reprefented this
cord as twilled, like the tail of a fcorpion, and
producing nerves on the left fide only. It is
true, that thofe which arife from the right fide
are parallel to the cord, while thofe of the left
fide remove farther from it. The ganglia, thus
approximated, are eleven in number, and in a
flraight direeflion ; they produce long nerves,
wh'ch are loft in the mufcles.

The nerves of the cheeJc-v:orm ( mtifc.i putris
l.in.) are diflributed in a very curious manner.

The brain is firuated immediately above the
origin of the oefophagus, behind the head ; it
is very large in jiroportion to the reft of the
body ; it is rounded poflcr'iorly, and notched
anteriorly, as if it were formed of two lobes.

A pair of nerves arife from the anterior part
of rhe brain, proceed forward, and arc diflri-
huted to the mouth, and even to the parictes of

that

2

Art. V. Nerves of Larv^. 341

that cavity. It fliould be remarked, that thefe
nerves experience a very confpicuous enlarge-
ment previoufly to their diftribution.

Poderiorly the brain prefents an aperture,
v’hich affords a pafTage for the cefophagus : the
I nervous part, fituated on its fides, may be re-
garded as the cords which produce the medulla,

. and all below the oefophagus as the medulla it-

I f^lf.

I Two pairs of nerves arife from the origin of
the nervous medulla ; thefe are dirc»5led for-
ward, and principally dillributed to the vifeera,
and to fome of the mufcles of the anterior rings.

The third pair of nerves which this medulla
: .produces, is the moft remarkable; it comes
from the part which nearly correfponds to the
third ganglion; I fay nearly, becaufe in this
infetfl the ganglia are fo clofe to one another,

I that the medulla feems to form only one piece
> on the furface, of w-hich we merely perceive
twelve tranfverfe wrinkles, which indicate the
number of ganglia. This third pair extends
almofl tranfverfely. At a certain diftance from
t its feparation it fwells into a ganglion, and then
divides into feveral filaments ; thefe are the
ganglia which Swammerdam fuppofes are in-
tended for the mufcles of the wings, when they
fhall exift in the perfect infcdl.

Another pair of nerves, which go to the
paufcles of the body, arife from each of the

T-> 3 other

34^ L, XI. Nerves of Ixvertebral Animals.

other contracflions j but they require no parti-
cular rernark.

Article VI.

\

^rain and Nerves of ^Perfect Itifed/S,

A. Coleoptera.

1. In the Stag-heetle (Lucaims Cervus.)

w E find in this infedt, as in its larva, a brain
compofed of two approximated fpherical lobes,
fituated above the oefophagus ; its anterior part
produces two pair of nerves, which terminate in
, the palpi, and other parts of the mouth. There
is probably a recurrent nerve, but ouf reCcarches
have not yet difeovered it.

There are two ganglia on the lateral parts of
the brain, which are almoft as large as each of
the lobes. In their form they rcfemblc a pear,
and reft upon the brain by their bafe ; they are
prolonged tranfverfely into a large nerve on each
fide, chiefly intended for the eye. ' Before the
nerve arrives at that part, we obferve it detach
a flcndcr filament, ^vhich enters into the great
mandible; then, more externally, another fila-
picnt which enters into the cavity of the an-

tnmx ;

Art. VI. Nerves Of Insects. 343

tennjE; laftly, the nerve itfelf having reached
the eye, fwells again, into a bulb, and produces
* a number of nerves, which we flial! dcfcribc
when we treat of the Organ of Vifion.

Poflcriorly the brain produces two very long
and flender nerves, w'hich accompany the oefo-
phagus to the point where the head unites to
the thorax, immediately above the articular con-
dyle. The two nerves fituated above the oefo-
phagus, then produce a ganglion of a long oval
form, from which feveral nervous filaments arc
detached to the mufclcs that move the mandi-
bles, and thofe that a^l: on the head. This gan-
glion terminates poflcriorly in two parallel
nerves, which proceed to the middle of the
thorax, above the origin of the two pair of feet,
and there form a fecond ganglion of an hexa-
gonal figure ; this ganglion furniflies filatnents ’
to the mufcles of the feet, and likewife termi-
nates poflcriorly in two nerves, which extend'
above the union of the corfelct, with the pedtus ;
they there unite and form a third ganglion, which
is crcfcent-lhaped, with the convexity poflerior:
two other nerves proceed^from this convexity,
which almoll immediately produce another gan-
. glion of the fame, form, but fmaller. This
ganglion gives origin to five nerves : tw'o late^
ral, deflined to the mufcles of the intermediate
feet, into the coxse of which w'C obferve them
enter: poflcriorly two, which are flender, and
dillributed to the mufcles of the hind feet and

Z 4 , the

344 L* XI. Nerves of Invertebral Animals.

the wings. The fifth is fituated in the middle
^ iine ; it is alfo thicker: it fwells almofl imme-
diately into an oval fhaped ganglion, which is
divided pofleriorly into two exceedingly flendcr
filaments. Thefe filaments, which pafs into the
abdomen, form a kind of bridge in the breaff^
in which they occupy the middle line, and
leave between them the mufcles of the feet and
wings of either fide.

2. In the Scar abacus naficornis.

With refpecT: to the nerves, this infeel: differs
in the perfecl date from the defeription we have
given of its larva.

The optic nerves, which are very diftinil and
l^rge, proceed to the eye, into which we obferve
them enter by a multitude of filaments when
we make a horizontal fedlion of that ortran.

The nervous cord prefents a very confpicuous
difference. In the larva there is only a fingle
ganglion; but the perfecl: infeed has fcvcral,
which arc very di If inch

The firff is fituated above the condyle ; it
proceeds from the two poflcrior filaments of the
brain, and is dilfributed to the mufcles which
move the head on the corfelct. Its pofferior
part produces two filaments, which pafs into the
brealf, Xvhcrc they unite towards the middle
part, and form a triangular ganglion ; from the
fidcs of which three pairs of nerves arife, and are
diffiibuted to the mufcles. Its pofferior angle

detaches

Art. VI. Nerves of Insects. 345

detaches two parallel nerves, which proceed into
the breaft, where they form a third and a fourth
ganglion, fituatcd very near each other, and ap-
parently divided into two lobes by a longitudi-
nal furrow. All the other nerves of the body
depart from thofe two ganglia by an irradiation,
prccifely in the fame manner as in the larva.

* 3. In the JValer Beetles (Dytih us) and the
Ground Beetles (Carahus. )

The nervous fydem is entirely fimilar in thefe
infants. The brain is formed of two large he-
mifpheres, feparated from each other by a longi-
tudinal furrow. The anterior part produces the
nerves of the mouth, and the lateral, parts thofe
of the eyes and the antennae. The nerves of the
eyes are Ihort, and differ greatly from thofe of
the Hag beetles ; they are of a pyramidal form :
their bafe correfponds to the eye, and their apex
to the brain. Wc have not obferved any re-
current nerves.

The two filaments which produce the ner-
vous cord depart from the brain, not pofterior-
ly, but inferiorly, on the fide of the optic nerves :
they are very fhort, as they pafs immediately
under the oefophagus. They furnifh fome fila-
ments to the mufcles and the oefophagus.

The firfl ganglion they form lies under a kind
of bridge, formed of horny fubftance, which is
fituated in the middle of the head, and which
affords a point of attachment to the mufcles of

the

346 L.XI. Nerves OF Invertebral Animals.

the jaws ; it is of an elongated and quadrangular
figure, and occupies almofl: the whole fpacc
that correfponds to the condyle above which it
is placed.

It is terminated pofleriorly by two filaments
•which proceed in a parallel direction, and form
a fecond ganglion in the middle part of the cor-
felet. This ganglion furnifhes nerves to the
mufcles of the anterior feet. \Vc obferve them
enter into the cavity of the coxx.

The third ganglion appears bilobed, or form-
ed of two oval bulbs, the union of which is
marked by a longitudinal furrow. This gan-
glion is fituated longitudinally above theanterior
inferior edge of the bread. It fends filaments
to the mufcles of the intermediate feet.

The fourth ganglion is very near the pre-
ceding; it is of a roundifli form, and is difiri-
buted to the mufcles of the podcrior feet and
the wings.

The fpacc between the fifth and the fixth
ganglion is very fmall : their form is round ;
and they furnifh filaments to the mufcles that
move the abdomen on the bread.

The remainder of the medullary cord is form-
ed by a feries of five ganglia, fituated fo clofe to
one another, that they appear to the naked eye to
form only one; but with a glafs they may be
obferved very diftinedly. VVe even perceive the
two filaments produced by each to form the fuc-
cceding ganglion. The fifth picfents a tranf-

verfe

Art. VI. Nerves of Insects,

347

yerfe furrow, which fccnas to indicate the union
of two ganglia. The end of the medulla ap-
pears to float in the abdominal cavity, but
above the intcflines.

4. Ill the Great Diver ( Ujdrophilus piceus

Lin. )

The brain of this infefl:, which is fltuated in
the head, and above the origin of the mfophagus,
confifls of two fphcrical bulbs clofcly united.
The lateral parts give origin to the optic nerves
which proceed towards the eyes without chan-
ging their diameter, but which terminate there
by a triangular bulb that produces a vafl; num-
ber of filaments externally.

The anterior part of the brain detaches Tome
filaments intended for the parietes of the mouth.
Wealfo remark, at the fame place, a fmall fphe-
rical ganglion, which appears to belong to the
recurrent nerve that accompanies the oefopha-
gus.

1 wo filaments, which fhould produce the me-
dullary cord, arile inleriorly : they embrace the
tefophagus at their reparation, unite immedi-
ately below it, and again, in the cavity of the
head, to torm a fmall ganglion, w hich furnifhes
nerves lor the mufcles of the mandibles and the
palpi.

iwo nervous cords are detached from the
poflerior part of this firfl: ganglion. Almoft
ininf'.cdiatcly after their origin, they pafs under

a horny

34^ L.XI. Nerves of Invertebral Animals,

a horny arch, which is produced by the internal
for face of the ganache. We obferve that, they
re-appear pofteriorly, and proceed into thecor-p
lelet.

They form a fecond ganglion exacflly in the
middle of the corfelet ; its figure is quadrangu-
lar. The anterior and polferior angles produce
the nerves of the medulla, and the lateral thofc
intended for the mufcles of the anterior feet.

The interval included between the fecond
and third ganglion of the medulla is very great.
The third ganglion correfponds to the infertion
of the intermediate feet : it is large, and of a
round form 5 it furniflies nerves to the wings,
and to the intermediate pair of feet. Pofteriorly
it produces two cords, which, at the diftance of
about half a line, fwell and form a fourth gan-
glion, almoft as large as the preceding. This
ganglion detaches, from its inferior part, a num-
ber of filaments for the mufcles of the poflerior
feet, w liich are fpecially appropriated to fwdm-
ming. Two other very fhort cords produced
by the pofterior part of this ganglion fwell into
a fifth, w'hich isone half lefs than the former,and
which furniflies a Angle cord pofleriorly. This
cord paffes into a kind of longitudinal groove,
formed above the horny appendix, that furniflies
attachments to the mufcles of the coxae, and
which wc have deferibed in the firfl volume.

A lixth ganglion is fituatcd at the poflerior
and wide part of this appendix : at a certain

diflance,

Art. VI. Nerves of Insects. S49

diftance, and exadly above the union of the ab-
domen with the breafl, a fevcnth appears. Thcfe
tw'o ganglia produce only one pair of nerves,
which are diftributed to the mufcics.

There are only two ganglia in the abdomen ;
one correfponds to the middle part of the fe-
cond ring ; the other, which is the laft and
ninth, is fituated above the union of the fecond
fegment with the third. The laft ganglion but
one is in every refpeeft fimilar to the two pre-
ceding; but the ninth is one half larger, and
produces poftcriorly four pair of nerves, w hich
are diftributed on both fides to the parts of ge-
neration.

13. Orlhoptera.

In the Coch'oach (Blatta Americana.)

The brain of this infcdl is compofed of two
lobes, feparated by a very diftineft notch ante-
riorly. The optic nerves arifeon the fides, and
its anterior part detaches fomc filaments to the
parietes of the mouth, and to the inftruments of
manducation.

The nervous cords which form the medulla
arife from its inferior furface. They proceed
diredlly downward, and clofely embrace the
cefophagus. They afterwards proceed in a pa-
rallel direeftion, but very diftimfl from each other,
towards the corfelet. When 'they reach its micL-
dle, they form a very large ganglion, which pro-
duces

350 L.XI. Nerves of Invertedral ANiMAtSi

duces three pairs of nerves laterally, and one
pofleriorly. The firfl: lateral nerves afeend ob-
liquely towards the head, and furnifh filamants
to the mufcles that move it on the thorax, and
which acfl on the antennae and the parts of the
mouth. The others are diftribute'd to the tnuf*
clcs of the firfl: pair of feet.

The poflcrior nerves proceed in a parallel di-
redlion backward. At the middle of the pe<5l:us
they produce a ftill more connderable ganglion
than the fecond, which furnifhes laterally nerves
to the intermediate and pofterior feet, as well as
to the mufcles of the wings. It alfo fends off
two cords pofleriorly, which, by their union at
the junrflion of the abdomen and the breafl,
form a fourth ganglion, fituated on a projeefling
horny fubflance to which the mufcles of the
coxae are attached.

After this fourth ganglion there is only a fin-
'gle nerve, which has, at certain fpaces, fmall
enlargements, hive of thefe fwcllings may be
counted. Each produces a pair of nerves for
the mufcles of the rings of the abdomen : the
fifth is the largefl, and furnilhes befides two
nerves which ramify in the parts near the anus.

In the Gnat Green Grap^hopper {Gryllus Viri-
(lijjiniuy, Lin.)

The brain is fituarcd in the head above the
erfophagus: it confiPs of two lobes, which have
the form of pears, united at their bafe, and pro-
7 longed

Art. VI. Nerves OF Insects. 351

longed at the other extremity into an optic
nerve for the eye of each fide.

The anterior part alfo produces two nerves of
a pyramidal form, the bafe of which reds upon
the brain. Some filaments arife from the apex
of the pyramid, which are lofi: in the mandible,
the jaw and its galea, as well as in the upper lip.

Between thefe two anterior nerves we obferve
afmall ganglion, which is produced by the union
of the two filaments of the inferior furface of
the brain. This .is the recurrent nerve which
follows the intefiinal canal.

Pofteriorly, and a little infcriorly, we obferve
the origin of the two cords which form the ner-
vous medulla. They embrace the oefophagus,
below which they are immediately direded, and
form a ganglion.

This firfl: ganglion is proteded and covered
by a kind of horny bridge of a reddilh colour.
It furnifiies nerves to the mufclcs of the mouth,
and to thofc of the head within which, it is
inclofed. Pofteriorly it produces two long ner-
vous cords, which penetrate into the corfelet.

Phefe two cords unite about the middle of
the thorax before the appendix, which gives
attachment to the mufcles of the coxae and the
anterior pair of feet. At this union they form
a large bilobed ganglion, of an irregular qua-
drangular figure, the fides of w hich produce fe-

veral filaments for the mufcles of the anterior
feet. .

The

352 L.XI. Nerves of Inverte^ral Animals*

The pofterior part of this fecond ganglion
furniflics two filaments, which penetrate into
the breaff. The folid appendices of the coxse,
which afford infertions for the mufcles, pafs
between thefe two filaments. They form a third
ganglion, which correfponds to the middle fpace
included between the two intermediate feet.
This ganglion fends nerves to the mufcles of the
wings and the feet.

The fourth ganglion is alfo contained in the
breaft. It is fituated before and between the
poflerior pair of feet. It is produced by two
nervous cords from the preceding ganglion; and
furnifhes two pofteriorly, which are fo clofe to
each other that they appear to the naked eye to
make only one cord. This nerve is received
and contained in a kind of groove formed above
the triangular piece, which affords an attach-
ment for the mufcles of the feet.

The other ganglia, which are all fituated in
the abdomen, arc fix in number. They arc, the
lafi: excepted, of the fame fizc and form, placed
at equal diflances, and produced by two fimilar
and clofely approximated cords. Each furniflics
two pair of nerves for the mufcles of the abdo-
minal rings.

The lafi ganglion of the medulla is one half
larger than the live preceding. It is fituated
below the parrs of generation, tovhich it is
difiributed by four pair of lilaments.

In

Art. VI. Nerves of Insects.

353

In the Mole-cricket ( Acheta gryllo-talpa. )

The brain of this infeft is alfo compofcd of
two rounded lobes, which are particularly dif-
tini5l at the poftcrinr part.

We can clearly perceive the origin of the
nerves of the palpi, of the antennae, of the
fmooth eyes, and the eyes properly fo called.

In general the nerves of the principal medulla
are limilar to thofe we have dcfcribcd in the
cockroach. The two firll ganglia are produced
by two nerves. The firll, which is in the corfe-
let, fupplies the mufcles of the head, bread and
anterior feet. The fecond, which is larger, and
in the bread, gives filaments to the, mufcles of
the wings, and the intermediate and poderior
feet. It alfo fends two nerves poderiorly, which
produce the abdominal ganglion. The cord
then becomes Tingle and flat, like a ribband, and
contains only four ganglia, occurring at differ-
ent didances. Each produces two pair of fierves,
which are direded poderiorly, and didributed to
the mufcles. The fird correfponds to the mid-
dle part of the fird abdominal ring; the fecond
to the third, the third to the fifth, and the lad
to the ninth.

This lad ganglion is the mod remarkable of
all. It is of an oval lhape, and produces, from
the whole of its circumference, nerves which
are didributed to the neighbouring parts. Two,
which are longer than the others, diverge as

^ VoL. II. A A thev

0

I

354 L*X. Nerves of In vertebral Animals.

I

they proceed backward, and thus reprefent a bi-
furcation of the medullary cord. Thefe branches
furnifh filaments to the parts of generation.

$

C. Hemipteva.

In the oval JVater Scorpion (Hepa Cincrea, Lin.)

The nervous fyflem of this infecl confifts of
three ganglia.

The firfb, which fupplies the place of the
brain, is fituated in the head. It is formed of
two 'approximated lobes. Thefe lobes are py-
riform, and touch each other at their bafe.
Their fummils are direvd;ed obliquely forward
towards the eyes, in which they terminate, and
thus anfwer to the optic nerves by their an-
terior extremity. The middle and anterior part
of thefe lobes alfo produce fomc filaments for
the parts of the mouth.

Pofieriorly, the brain detaches two cordswhich
embrace the oefophagus as they pafs below it.
They unite at the origin of the breaft in a tetra..
gonal ganglion ; each of the angles of which
produces or receives feveral nerves. The ante-
terior receives the two cords w-hich come from
the brain ; the pofierior, the two which arc
the continuation of the medullary cord.

Hach lateral angle produces a fafciculus, com-
pofed of four nerves, w-hich arc directed to the
mufclcs of the brcail and anterior feet. Wc

obferve

Art. VI. Nerves OF Insects. 355

I obferve one of them enter into the cavity of the
coxa.

The two nerves produced by the pofterior
angle of the fecond ganglion proceed in a pa-
rallel diredlion backward. Having arrived in the
breaft above the horny appendix, to which the
mufcles of the coxae of the intermediate and
pofterior feet are attached, they fwell into a large
round ganglion, confiderably more voluminous
than the brain. A vail number of nerves are
detached from the edges of this ganglion, like
folar rays.

The two molt remarkable filaments are ex-
ceedingly long and flender. They extend from
the bread nearly as far as the anus : we have
obferved them to terminate by three minute
branches in the parts of generation of the male,
furnilhing, at the fame time, fome filaments to
the adjacent parts.

All the other filaments, which proceed from
this third and lad ganglion, are dedined to the
mufcles. We can very plainly didinguilh thofe
that belong to the middle and intermediate feet,
as they are fomevvhat larger than the others.

D. Lcpidoptera.

In the Zig-Zag Moth (Phalcena Difpar, Lin.)

The brain in this fpecies is almod fpherical.
We, however, perceive a longitudinal furrow on
the middle line. Its anterior jpart produces
It A A 2 k, fome

3^6 L. XI. Nerves OF In VERTEBRAL Animals.

fome exceedingly flender nerves. There are
two large optic nerves on the fides, which pro-
ceed into the concavity of the eye, where they
terminate by a bulb, which produces a great
number of filaments.

The cefophagus pafTes immediately behind the
brain, through a fniall triangular interval, the
pofferior fides of which are formed by the two
cords of the medulla. Thefe cords afterwards
unite, and proceed in the form o-f a (ingle trunk,
on the middle part of which we perceive only a
longitudinal furrow. Arrived in the corfclet
it forms a ganglion, the furface of which is red-
di(h. This ganglion produces two nerves po-
fteriorly, which leave between them an interval
that affords a paiTage for the horny appendices
to which the mufcles of the coxae are attached.
The two cords again unite behind thefe ap-
pendices in the fame cavity of the breaft, and
produce a much larger ganglion, the lateral
parts of which furnilfi nerves to the mufcles of
the wings and feet. It is prolonged pofteriorly
into a fingle cord, which again enlarges when it
arrives above the articulation of the breaft with
the abdomen into a third ganglion.

It fliould be remarked, that this large gan-
glion, which hasi the form of a heart, is the only
one, bcfides the brain, of a completely white
colour. All the others exhibit darker (liades,
and, wheu viewed by a glafs, we obfervein them
reddifh points more or lefs elongated and finu-

ous,

Art. VI. Nerves or Insects. 357

ous, that refemble the blood velTels of injected
glands.

The third ganglion is prolonged into a fingle
cord, which produces a fourth ganglion above
the firfl: ring of the abdomen. The latter, as
well as thole that fucceed it, detach on each
fide a long flender nerve which palfes un-
der the mufcular fibres, precifely in the fame
manner as the threads of the woof pafs through
the warp in cloth. Their direeflion is complete-
ly tranfverfe.

The fifth ganglion does not differ from the
preceding. It is prolonged into a fingle cord,
upon which we can ftill very difiincl:ly perceive
the longitudinal furrow. It is lituated in the
middle part of the third ring of the abdomen.

The fixth ganglion is, in every refpecfl, fimi-
lar to the preceding ; it is placed in the middle
of the fourth ring.

Finally, the feventh and laft ganglion is much
larger than thofe that precede it in the abdo-
men. It is of an o\al form, and fituated upon
the lunula that terminates the fifth abdominal
ring pofteriorly. Befides the nerves intended
for the mufcles of the fifth ring, which are de-
tached from this ganglion in two diftin^l parts,
it produces four other pairs pofteriorly. Thefe
nerves appear to be" difiributed to the parts of
generation, and to the mufcles of the laft abdo-
minal rings, which, in the female, are elongated
likp a tail to aflift in laying eggs.

A A 3

E. Neu-

358 L. XI. Nerves of Invertebral Animals,
E. N turoptcra.

, The infecfls with naked wings, that is to fay,
the Hymenoptera, Neuroptera, and Diptera,
which have frequently very large eyes,’have alfo
the optic nerves of a proportional fize. This is
particularly obfervable in the dragon flies. Their
brain is formed of two very fmall lobes ; but
their optic nerves Rre dilated into the form of
two large plates, which have the figure of a kid-
ney, and which is fpread upon all the inner fur-
face of the eye next the head, The remainder of
their medullary cord is exceedingly flendqr, and
furnifhed with twelve or thirteen fmall ganglia,
the lafl: of which is, as ufual, connedled with the

I

parts of generation,

F. IJpmenoptera.

The brain of the bee is fmall, and divided into
four lobes. It produces immediately the nerves
which are diftributed to the different parts of
the mouth, and the two large optic nerves which
are dilated and applied behind each eye as in
the dragon flies. There are afterwards feven
ganglia, three pf which arc in the corfelet, and
four in the abdomen. The nerves of the lafl
chiefly fupply the parts of generation.

G. Dipt era.

The apifonn fly [mufea tenax, Lin.) has a fmall
brain, formed of two lobes, which are fituatcd

very

Art. VI. Nerves of Insects. 359

very cJofe together, but diflinguiflied by a lon-
gitudinal furrow ; the anterior part produces a
lart’-e nerve, which is afterwards diilributed to
the antennae and the probofcis.

The optic nerves are very thick, cylindrical,
and equal in diameter to the length of the brain,
on the lateral parts of which they reft ; they
terminate at their extremity in a very large bulb,
which correfponds to the breadth of the eye.

The firft ganglion of the medulla is produced
by two cords, which come from the pofterior
part of the brain, and embrace the oefophagus
as a collar; it is very flendcr, and fituated in
the breaft ; it furnilhes a pair of filaments to
the mufclcs of the anterior feet.

The fecond and the following ganglia, in all
three in number, are united to each other merely
by a fingle cord. The laft ganglion is one half
larger than that which precedes it. Pofteriorly
it produces eight or nine filaments, which are.
intended for the parts near the anus ; the firft
of the. three is fituated in the breaft, where it
furnifties nerves for the mufclcs of the wings
and the feet ; the other two ganglia are in the
abdomen ; the laft but one is placed above the
union of the third ring with the fourth ; and
the laft on tljie interior and inferior edge of the
fifth ring.

In the hornet -fly (aflius crahronifermis) we
alfo obferve a fingle cord uniting the abdominal
ganglia, which are fix in number.

A 4

The

360 L. XL Nerves of Invertebral Animals.

The brain is fimilar to that of the Syrphus ;
but the bulbs, formed by the optic nerves, 'are
ftill broader, in proportion to the extent of the
eyes they have to invert.

H. Gvothopfera,

Tn the great Jcolopendra (fcolopendra morfitans)
the brain has a very lingular form; it is, as
ufual, compofed of two lobes, which are al- ‘
nioft fpherical ; it produces laterally the optic
nerves, which are very rtiort, and may be ob-
ferved to divide long before they reach the eye.
The filaments are four in number ; but two
nerves arife anteriorly, which are fo very thick,
that they appear a part of the brain, to which
they arc equal in diameter. Thefe nerves are
particularly intended for the antennae, into
which we obferve them enter, and in which they
may be followed, on account of their magni-
tude.

The two cords which embrace the oefophagus
proceed diredlly downward, and form a large
ganglion at the union 'of the firrt ring with the
head. The firrt ganglion produces two nerves
porteriorly, and fevcral towards the Tides. A
ganglion, prccifclyof the fame Ihape, is placed
above each of the articulations : thus there arc,
in all, twenty-four very dirtinert ganglia ; the
laft of all is fmallcrt, ncarelt the preceding, and
Teems to float in the abdomen ; each detaches
6 three

Art. VII. Nerves OF Worms. 361

three pair of nerves ; one which afccnds towards
the head, a fecond which runs tranlvcrfely ; both
thefe are diftributed to the mufclcs of the ab-
domen : the third defcends, and then proceeds
backward and upward; it furnifhes filaments to
the lateral mufcles, and to thofe of the back.

Article VII.

Brain and Nerves of JVorms,

Some genera of worms prefent a very diftindl
nervous fyftem, organized nearly like that of
the Cruftacea and infedls. In others, however,
that fyftem becomes fo obfeure, that we can
fcarcely recognize its exiftence. Thus the
clafs of worms which, in feveral of its genem,
ranks above infedts, with refpecl to the organs
of circulation, is reduced almoft to a level with
the zoophytes, when confidered with regard to
tlic organs of fenfation.

1. In the Aphrodita Aculeata.

The nervous fyftem is very diftinefin this
animal. Immediately behind the tentacula, fi-
tuated above the mouth, we obferve a laro-e

O

nervous ganglion, which is the brain ; it has
the form of a heart, the broadeft and bilobed
part of which is diredted backward. The point-
ed

362 L. Xr. Nerves of Invertebral Animals.

ed and anterior part produces two fmall fila-
ments for the tentacula ; and the lateral parts
fome other filaments, which are fiill more flen-
der for the parietes of the mouth. This gan-
glion is fituated immediately above the origin
of the oefophagus.

The two cords which arife from the brain,
and form the collar, are very long and delicate;
they gradually increafe in thicknefs, as they
approach the point of their union. Each then
produces a large filament, which we lhall call
the recurrent nerve ; thefe nerves are very dif-
tin<fl ; they are diredled forward towards the
part where the oefophagus, which is very fliort,
joins the ftomach ; they may be eafily followed
by the naked eye to the lateral parts of that
vifeus, which is very long and mufcular ; before
they reach the intefiines that follow the ftomach,
they fwcll into a ganglion, which produces a
great number of nervous fibrils.

The two nerves of the collar produce a very
large ganglion at their union ; it is bifurcated
anteriorly, and fituated immediately behind the
mouth, and above the oefophagus ; it is the an-
terior extremity of the chief nervous cord. We
do not obferve any filaments proceeding from
it. To this firft ganglion another fuccccds,
which is diftinguiftied from it by only a fmall
contraction ; the latter produces two nervou?
filaments, which go forwards into the miifclc*.
of the abdomen. A fcrics of ganglia, the fpaccs

between

2

Art. VII. Nerves of Worms. 363

between which are confiderably greater, after-
wards fucceed ; each of thefe fends off lix nerves,
three on a fide, which are loll in the mufcles.
Thefe ganglia are twelve in number.

The nervous cord which fucceeds, and which
occupies the pollerior third of the body, no
longer exhibits any apparent enlargement ; but
pairs of nerves are Hill detached at certain
I'paces. Finally, this cord may be followed to
the extremity of the body.

2. In the Leeches,

The nervous fyftem is a longitudinal cord,
compofed of twenty-three ganglia.

The firll is fituated above the oefophagus ; it
is fmall and rounded ; anteriorly it produces
two flcnder filaments, which proceed above the
difk of thelTiouth. The lateral parts furnilh a
thick pair of nerves, that form a collar round
the oefophagus, as they proceed downward, and
unite at the fecond ganglion.

This ganglion is of a triangular figure ; it
appears to be formed by the union of two tu-
bercles. Two of thefe angles are anterior and
lateral ; they receive the nerves that proceed
from the firft ganglion. The other is pollerior;
it is prolonged into a nerve rather more than
half a line long, which produces the third gan-
glion : the anterior part of the triangular gan-
glion which we deferibe, detaches two fmall

nerves

364 L. XI. Nerves of Invertebral AVtmals.

nerves that are loft on the oefophagus, around
the mouth.

The nine 'fucceeding ganglia are precifely of
the fame form, and produce each two pair of
nerves; they differ only in the greater or lefs
diftance at which they are placed with refped
to each other.

The third, as we have obferved, is very near
the fecond. The three following are at the dif-
tance of nearly a line and a half: but thofe
which fucceed, from the feventh to the twentieth,
are at the diftance of three or four lines : finally,
the three laft are very clofe together.

All thefe ganglia are fituated longitudinally
below the inteftinal canal, to which they fur-
nifh, from their fuperior furface, a number of
nervous filaments ; they produce on each fide
two nerves, which pafs into the longitudinal
and tranfverfe mufcles, in thefubftance of which
they are loft. Thefe nerves run in oppofite di-
reeftions, fo that they reprefent the figure of
an X.

The coat of thefe nerves is black, and very
folid : on this account, before the parts have
been immerfed in alcohol, the nerves appear
like a fyftcm of veffels.

3. In the Earth JEorm,

The nervous cord derives its origin from a
ganglion fituated above the oefophagus ; this

ganglion

Art. VII. Nerves of Worms. 365

ganglion is formed of two clofe, but very dif-
tinft tubercles; it produces a pair of fmall
nerves, which proceed to the parictes of the
mouth, and two large cords, which embrace the
oefophagus in the form of a collar ; thefe unite
to form the nervous cord, the origin of \^hich,
therefore, appears bifurcated. Three pair of
fmall nerves are detached at this place ; one
from the cord itfelf, and the others trom its la-
teral parts. They all proceed into the mufcles
of the mouth.

The nervous trunk is continued to the anus,
along the inferior part of the intelline ; its fizc
is not fcnfibly diminiflied, and the contradlions
are not very remarkable : there are, therefore,
no real ganglia.

A pair of nerves arifes between each of the
rings of the body ; thefe nerves pafs under the
longitudinal mufcles, and difappear between
them and the Ikin.

When the nervous cord reaches the anus, ir
terminates by forming a plexus, which is loft
on the parietes of that aperture.

4. In the Gordius Aro-iUaceus.

O

There is only a lingle nervous cord in this
animal, fimilar to that of the earth worm, but
its contradlions are (till lefs apparent.

5. In the Hef'ds and Tei'ehella.

In thefe animals we find, within the fkin o

the

366 L.XI. Nerves of Invertebral Animals,

the belly, a longitudinal cord, which may be
regarded as nervous : it has as many contrac-
tions as there are rings in the body. We have
obferved no nervous filament proceeding from
this cord.

6. In the Sea Worm, ( Lumhricus Marmus V\n.)

Which, by its external charadlers, approaches
nearer to the nereis than the lumbricus. The
nervous fyftem is the fame as in the nereides,
but the cord gradually increafes in thicknefs
towards the middle of the body, where it is
much more difiincH:.

7. In the Afearis Lumhricoides of Man and
the Horfe.

This animal appears to have two nervous
cords ; they are obfervable throughout the
whole length of the body, on the lateral parts
of the abdomen.

They unite above the oefophagus exadlly at
its origin on the mouth ; they are very fiender,
and produce no remarkable ganglion ; they are
fmaller at their origin than towards their extre-
mity, that is to fay, towards the anus ; but they
are equal, and prccifely fimilar to each other
with refpedt to their difierent parts. We at
firfl; obferve fome fmall granular points, which
enlarge in proportion as the nerve defeends.
When it has reached the middle of the body
longitudinally, it forms fquarc ganglia, at a

fliort

Art. -VII. Nerves OF Worms. 367

Ihort diftance from each other. Ladly, towards
the termination, for the length of nearly fix
lines, the nerve becomes more and more (lender,
and ends in a very fmall filament, which unites
with that of the other fide.

The details into which we have entered in
Articles IV. V. VI. and VII. of this Leaure,
evidently demonfirate that there exifis an ana-
logy in the organization of the nervous fyflem
of the three clalTes of Crufiacca, Infeas, and
Worms, no lefs firiking than that which pre-
vails in the external forms, in the dilpolition
of the mufcles, and in the fingular divifion,
into a feries of rings or fegments, which weob-
ferve in thofc animals. This analogy muft pre-
vent us from eftablifliing, between thefe three
clalTes, limits equally difiina with thofe that
fubfift between them and the Mollufca.

The uniform diftribution of nearly equal gan-
glia upon a cord, extending throughout the
whole length of the body, feems defigned to
furnifii each fegment with a brain peculiar to
itfelf. Thus we are gradually conduded to that
general diffufion of the medullary fubftance
which takes place in zoophytes.

Arti-

368 L. XI. Nerves or Invertebral Animals.

Article VIII.

0/ Animals, in 'ichich no dijlinct Nervous Syjiem.
has yet been difcovered.

w £ do not include, in this divifion, the ani-
mals of the clafs of Worms, or the Mollufca,
in which the rninutenefs or foftnefs of the parts
have not yet permitted us to trace the nervous
fyflem. Analogy will not allow us to doubt
its exiftence, when the parts, which accompany
it, uniformly exift. Thus the flukes (fajciola)
having vefTels, or liver, &c. muft alfo be fup-
pofed to have nerves, though we have hitherto
been unable to demonflrate them.

. We even doubt not the exiftence of a nervous
fyftem in fcveral inteftinal worms, particularly
thofe which have a cylindrical form, which wc
fuppofe to have a medulla nearly fimilar to that
we have defcribed in the large afcarides. It is
found in the gordius. Why fliould it not exift
in the echinorhincbus, flrongylns, &c. ?

But there are animals in which analogy will
not ferve us, and to w hich wc cannot attribute,
a nervous fyftem, unlefs we diftincftly obferve
it ; thefc arc fome inteftinal w^orms, very dif-
ferent in form from thofe we have mentioned,
and the greater part of zoophites.

We ftiall examine fome of them.

1 . Tn

Art. VIII. Animals WITHOUT Nervis. 369

1. In the Sea Stars, (AJterias,)

Thefe animals have parts Avhich may be re-
garded as very fimilar to nerves; but galvanic
experiments ought to be made on living in-
dividuals, to prove completely their nature.
Round the oefophagus we obferve a girth of a
foft whitilh fubftance, which produces ten fila-
ments, two to each of the branches, which form
the body of the fiar ; the two filaments belong-
ing to each branch having arrived at the bafe
of the ofi'eous and articulated llalk, which ferves
for the principal fupport of the animal, unite
to form a (hort cord, which extends diretflly
from the one to the other ; they afterw'ards both
continue along the ftalk to the extremity of the
branch, diminifliing always in thicknefs. At
the place where they are united, each produces
a fafciculus of filaments, which are diflributed
to the fiomach, which, in thefe animals, is li-
tuated in the midfl: of the body, between the
five branches. ,

The appearance of all thefe filaments is ra-
ther tendinous than nervous, and that circum-
llance has hitherto chiefly prevented us from
forming a decided opinion of their nature.

2. In the Holothuria.

In the Holothuria, properly fo called, among
which we do not include either the thalia, or
the holothuria pbyfalus of Linnaeus, we find

\oL. II, B n feme-

37® 1^* X'l. Nerves of Invertebral Animals,

fomething fimilar to what we have dcfcribed in
the fca flar, but the appearance of the cord is
much more nervous, and this we confider a
ftrong confirmation of our conjedtures.

The .parts of which we fpeak appear mofr
diflindlly in the fpecies of holothuria, which
have five longitudinal pairs of mufcles, as the
priapus and the penta6la. Between thetw'o muf-
cles which compofe each pair, there is extended
a white cord, flightly ferpentine, and marked by
tranfverfe rings, precifely like common nerves.
The five cords enlarge as they proceed tow'ards
the oefophagus, where it appears to us they
unite to furround that canal.

3. In the Sipunculust

Thefe are more lirhilar to the holothuria
than to any other animal, though naturalifls
have hitherto placed them next the Lumbricus;
they have only a fingle whitifh cord, but it
completely refemblcs thofc of the holothuria,
and it proceeds in the fame manner to embrace
the oefophagus by its anterior extremity.

If thefe obfervations apply to real nerves, it
will be necefiary to feparatc the echinoderfiiata
from the other zoophytes, and efiablifli them as
a diftindt clafs.

4. In the Sea Urchins (Echinus Marinus.)

We have not obferved in thefe animals any-
thing that refembles nerves, but analogy will
^ not

Art. VIII. Animals without Ne;ives. 371

i^ot permit us to fcparate them from the fea
ftars and holothuria. One fpecies of this genus
has been formerly very properly named the rc-
r,iaceoui urchin »

5. In the xlRinia and the Medujii.

Thefe animals form, in the clafs of zoophytes,
a fecond family, which approaches pretty near
to the preceding, and particularly to the genus
holothuria, with refpedl to the arrangement of
the parts ; but it is impofiible to perceive any
thing in them like nerves.

6. In the Polyps xvith Arms, (Hydra.)

With refpcdl: to thefe and the neighbouring
genera, which form, with the animals of the
coral kind, the third and the mofl: fimple fa-
mily of zoophyta, we have already had occafion
feveral times to obferve, that we difeover in
their bodies only a gelatinous and homogeneous
pulp, which exhibits no apparent organization.

All thefe animals have however very diftindt
fenfations: their fenfe of touch is very delicate;
they not only perceive the motions which agi-
tate the water in which they live, but they com-
pletely feel the degrees of heat and light. The
expanlion of the actiniae correfponds precifely
to the ferenity of the atmofphere. The hydra
perceives very dillindtly the prefence of light ;
it prafers it, and conltantly turns towards it.
The microfcopic animals appear to approach.

372 L. XI. Nerves OF Invertebral Animals.

in fomc meafure, the nature of polyps, by their
uniform and gelatinous ftrudlure. There are
fome, however, in which we obferve a more
complicated organization, and fcveral kinds of
internal vifcera ; but it w'ill be readily imagined
that we have not even thought of afcertaining
whether they poflefs a nervous fyftem.

LF.C-

( 373 )

LECTURE TWELFTH.

Of the Organ of Sight, or of the Eye.

, Article I,

General Idea of Vijion.

13v fight \vc difiinguifli the quantity, the co-
Jour, and the diredion of the luminous rays
which llrike our eye. The difference of colours
marks the limits of bodies in height and
-breadth ; and the difference in the intenfity of
light, joined to the experience acquired by the
fenfc of touch, enables us to recognize their
cavities and inequalities. Laftly, from the di-
re6Hon of the rays, we form an opinion as ,to
the line in which thefc bodies are lituated.

• We cannot obtain an immediate knowledge
of real diffance by fight only. We muff: in this
cafe alfo avail ourfelves of the experience ac-
quired from the fenfe of feeling, and judge of
the diffance of objects, according to their known
magnitude, compared with their apparent mag-
nitude and degree of illumination.

As vifion can only immediately afford ideas

B B 3 of

374

Lect. XII. Of the. Eye,

of the quantity, quality, and motions of the
rays of light, we are fubjedl to make erroneous
conclufions with refpecfl’ to th6 obje(5ts from
which thefc rays proceed. ^Thus rays rcflecfled '
by a mirror, exhibit objedls in a dire(5lion in
which they do not exifl. Rays refracfted by
glafleSj change the apparent magnitude of bo-
dies : when we‘ know not the real fize of an
objed, we are deceived with refped to its dif- .
tance, and v/ce verja: a very luminous body
appears ncareft to us, when thofe which are be-
tween us and it are in the fhade, &c. Sic.

Rays do not excite any fenfation, unlefs they
fall upon a nervoils membrane of the eye, called
the retina ; and they communicate no fenfation
conformable to the body which tranfmits them, •
unlefs they fall upon the retina precifely in the p
order in which they are detached from that bo- |
dy. To fjroduce this effed it is neceflary that |
all the rays which proceed from any one point !
of a body, iliould be colleded in one point of !
the retina, and that all the points of union thus J
formed fiould be difpofed in the fame manner
as in the body of which they form ihc'image.

This neccHity is a matter of fimple experi-
ence; for it is eafy to conceive that we are no j
better acquainted with the intimate nature of
light, than with that of all ther other fenfes, and
that wc (hall never be able to learn why thefc |
arc the conditions of the ideas it ‘procures us.

Rays which proceed from any point, nccef- ■

farily

Art. I. Of Vision.

375

farily diverge as they advance, and there-
fore cannot re-unite in another point unlefs
they are refracfted by fomc t ran fpa rent body
through which they pafs. This takes place in
the eye, in the fame manner as in the optical in-
Ihumcnt called a camera ohfeura. Ihe eye is
perforated by a hole named piiplly behind which
there is a tranfparent body of a lenticular torm
called cryjlalline, more denfc than the medium
in which the animal exills, and than the other
fluids contained in the eye. The cone ot rays
M’hich proceeds from any lOminous point to the
pupil, forms, after palFing through the cryflal-
Jinc, another cone, the apex of which falls upon
the retina. Thefe two cones have their axes
almoll in a flraight line. That which is per-
pendicular to the middle of the cryllalline pro-
ceeds direefUy to the bottom of the eye; that
which comes from above, falls inferiorly ; that
of the left proceeds to the right, and fo on
with refpevft to the others. Thus an inverted
image of the objedl is formed on the retina; but
as we judge of the fituation of each luminous
point by the rays it tranfmits, it follows that we
muft fee bodies, as we really do fee them, in
their proper polition.

If the rays were parallel, they would unite in
the point W'hich is called, in Dioptrics, the focus
of parallel rays ; but as thofe which come from a
point, the diftance of which is finite, diverge,
they unite in a point a little more removed from

B B 4 the

37^

Lect. XII. Of the Eye.

the cryflallinc than this focus ; and as thofe
which proceed from a very near point, diverge
ftill farther, they alfo unite ftill more remotely.

A particular eye therefore fees diftindtly only
objedts placed at a certain diflance. If its cryf-
talline has much refradlile power, that is to
fay, if it is very denfe and very convex ; or, if
its retina is removed from the cryftalline, it
can only diftinguifh near objedts : if its cryf-
talline is Iflat and lefs denfe, or its retina too
clofe to the cryflalline, it will only diftinguifli
diftant objedts.

This produces different extents of fight in one
man compared with another, and ftill greater
differences in the various kinds of animals.

The fame man may, with fome attention,
diftinguifh the fame ©bjedt at different diftances,
the limits of which may be aftigned with refpedt
to each individual. — Certain animals can dif-
cern objedls, the diftances of which arc extreme-
ly variable. Birds, for example, perceive their
prey from immenfe heights in the air, and ftill
retain it in view until they feize it: it muft follow
therefore, that the eye is capable of changing
the pofition of its parts, by approximating and
removing the retina with refpcdl to the cryftal-
line ; or that it is capable of augmenting its re-
fradtile power by incrcaling the convexity of
fome of its tranfparcnt parts ; or finally, that, in
viewing very near objedts, it only admits the
rays which are neareft to the axis, and which

arc

Art. I. Of Vision.

377

are confcqueiitly the lead diverging. We fhall
point out hereafter the means by which each of
thefe changes is fuppofed to take place. None
of thefe means however completely refolve the
problem. Perhaps the limits ol diftindt vifion
are much more confined than we imagine them
to be ; and it is probable that, in many cafes, it
only appears difiindl:, becaufe it is aflifted by
the recolledlion we have of the objedt.

Before the cryfialline there is ufually an hu-
mour, called aqueous f equal in denfity to pure
waters and behind it there is always another,
which is much more abundant, and a little more
denfe, named the vitreous. The aqueous is only
wanting in fome animals which live always in
water. It is fuppofed that the union of thefe
three bodies, of ditferent denfities, mud produce
the fame eftedl as the three objedtive glades in
achromatic telefcopes, that is to fay, they cor-
redl the difference of refrangibility in the rays.
Thefe rays are indeed ufually compound. The
white confid of feven fimple rays ; and as they
are not all refradled at the fame angle, the
images formed on the retina would, as in thofe
produced by common telefcopes, be bordered
by an iris, if this difpofition of the three hu-
mours did not exid.

The eye, however, fometimes fees what are
called accidental colours. When the retina is too
much fatigued by certain colours, it becomes
lefs fenfible of them. If we then behold a co-
lour

375

Lect. XII. Of the Eye.

lour which admits in its compofition that which
had fatigued the eye, the latter will ceafe to be
vifible.

Thus when w^e fix the eye on a white fpot,
and afterwards turn it towards white bodies,- we
obferve on them a dark fpot of the fame (hape
as that to which the eye was firfl: directed. If
the fpot on which the eye was fixed was black,
the eye, wherever it turns, will perceive one of a
lighter colour. If it was red, we obferye a
greenilh fpot on white bodies ; if yellow, a
bluifli j if green, a reddifh, &c. &c.

It muft not be forgotten, that the aqueous
humour has alfo, by its convexity, a great influ-
ence on the refradlion of rays, particularly in
animals which live in air. That convexity,
joined to w'hat is poffelfed by the vitreous, pro-
bably fupplies the effecl of the cryftalline in
eyes which have undergone the operation of the
catarad:, that is to fay, when the cryftalline
has been removed on account of its opacity.

A number of animals can only fee the fame
objecfl: with one eye at a time. Man alfo em-
ploys only one when he wifties to fee very dif-
tindly. In ordinary vifion, w'hcn the images
fall on the correfponding points of both retinte,
and when both eyes are nearly equal, we do not
tliftinguifti thefe feparate images, and we fee
objeds fimple: but if one eye be turned in a
different diredtion from the other, or if they be
very unequal, we fee double.

Arti-

Art. II. Number of the Eyes, &c. 379

Article II.

Of ihe Number, Mobilitif, relative Magnitude,

Pnfition and Direction of the Eyes in diff erent

Animals.

All rcd-blooded animals, without exception,
have two moveable eyes placed in the cavities
of the cranium, called orbits, and compofed of
the fame eflential parts as thole of man. None
have either more or lefs. There are merely
fomc apparent exceptions, when the eyes are
concealed by the (kin, as in the -zemni (inus ty-
phlus), or when the fame eye, having two pupils,
appears double, as in the (ilh called colitis aua-
blehs.

The fame obfervation applies to the mollujca
cephalopoda, or cuttle fijh.

The greater part of the gafteropoda have alfo
two eyes, but very fmall, and placed cither on a
level with the head, or on fome of the flelhy and
moveable tentacula. In fome they are fituated
at the bafe of thefe tentacula ; in others, at the
middle or the point, as may be learned from the
writings of naturalifts. In all this order, only
(;he genera clio, fcyllea, and lernea, want the eyes.

In the mollufca of the order acephala, no eyes
are found.

'pie eyes of infe<5ls appear to be of a different

nature

38o

Lect. XII. Of the Eye.

nature from thofe of the animals \vc have hi-
therto mentioned. They are divided into the
compound or Jhagrtnedy thefurfaceof which, w'hen
viewed by the microfeope, prefents a multitude
of tubercles ; and the Jimplcy which prefents
only one tubercle.

All the coleoptera and the butterflies have only
two compound, without any fimple eyes. Thefe
cy es are fometimes divided by a bar, and then
appear double. This takes place in the water
fleas ; it is faid that fimple eyes have been ob-
ferved in fome moths.

The orthoptera, the hemipteray the hymenopteroy
the neuropteray and the dipteruy have, with fome
exceptions, two compound eyes, and three fim-
ple, placed between the former. Among the
exceptions are the ephemerae and the phrygane<ey
which have two fimple eyes exceedingly large
in fome fpecies of the firft genus ; and the he-
mcrohii and lion-ant Sy which have only two fim-
ple eyes.

All winged infeils have compound eyes.

Among thofe that want wings fome have them
compound, as the onifci\ others have them fim-
ple, viz. the phalangiiy four ; the fpiders and
fcorpionSy fix or eight ; the julus and fcolopcndroy
a confidcrablc number ; laflly, others, as the
Icpifma and the limiilusy have them of both kinds.

Cray-fiflj havcalmofl: all their eyes compound,
and placed on moveable peduncles.

The larvae of infers, which undergo a femi-

iiieia-

Art. II. Number of Eyes, 381

S

metamorphofis, h^vc their eyes limilar to thofc
of the perfedl infecfls, but the larvae of infers
that are completely metamorphofed, always have
Ample eyes, which vary greatly as to number
in the different fpecies. The caterpillarSy for
example, have fix on each fide. The falje
terpillarsy or larvae of the Jazv fliesy have only
two : thofc of the bees, JiratyomeSy &c. have the
fame number. Several of the larvae which un-
dergo a complete metamorphofis, have no eyes
at all.

An infinite number of other obfer vat ions might
be made, refpeding the form, pofition, and di-
reclion of the eyes of infects, and of their larvae,
and on the efietfls thereby produced on their
vifion ; but as thefe circumfiances are external
appearances, we fliall leave the defeription of
them to naturalifts. — See Article XIII.

Among the articulated worms, there are fome-
times found fmall tubercles, which have been
regarded as Ample eyes, in confcquence of their
refemblance to rhofe of infers. Some leeches
have tw'o, four, fix, or eight. In fome of the
nereides we find two or four. In fome naides
only two, &c.

No parts that can be compared to eyes, have
hitherto been obferved in any zoophyte.

The eyes are always fituated in the head, ex-
cept in fome infects that have no wings, in whiefc
the head is confounded with the corfelet, that
is to fay, in the fpideVy phalangiuvty fcorpioiiy &c.

The

3*2

Lect. >C1I. Of THE Eye.

The relative magnitude of the eye varies^
■Ur'ithout any relation to the clafles, or even to
the natural genera. Large animals, however,
have, in general, the eye proportionally fmall :
this is obfervable in the Cetacea, and in the
elephant^ rhinoceros ^ and hippopotamus.

It is alfo .very fmall in the animals that live
conftantly under ground, as the moles y Jhrews^
mole-rat Sy and iou\t field-mice.

The frugivorous mammalia, that climb trees,
have in general the eye large, as the makis,
/quirrelsy dormicey Cfr.

A very large eye moft cdmmonly indicates
that the animal can fee in the dark. Bats
form no exception to this rule, becaufe it ap-j
pears that they are not direefted by their fight iri
flying, as we jfhall fhew when we treat of the
fenfe of feeling.

AlmcJfi: all fifhes’ have large eyes ; doubtlcfs
becaufe they live in a medium w'hich is more
obfeure than the atmofphere.

The cephalopodous mollufca have them very
large, particularly the on the contrary,

in fuch of thciGafteropoda as poflefs eyes, they
are fcarcely vifible.

If we examine ail the chagrined and Jmootb
eyes of infc(5ts, w-e will find that they prefent
larger ocular furfaccs to the light, than any
animal of the other claflcs, though each parti-
cular eye is very fmall.

The eyes of man .and monkics arc direded

forward.

Art. II. Number of Eyes, ^c.

3*3

forward. The tarfier {hmur tarfius Pall. -D/-
dclphis macrotarfus Gmel.) is of all the Mam-
malia that in which the eyes are fituated ncarefl:
each other.

In the other quadrupeds the eyes are always
more feparate, and fituated towards the fides.
They are direded a little downward in the
Cetacea. In birds their pofition is lateral, ex-
cept in the owlsy in which they look forwards as
in man.

In all j-eptilcs they arc on tlic Tides of the
head.

Fiflies vary greatly with refpeft to the pofi-
tion of the eyes. Some have them turned
ftraight upward, as in the par-gazer , in others
they are dircdled obliquely, as in the callyonymus
and the ray. Some have them both fituated on
the fame fide of the body, as the pleuroneHes*
In the greater number of fiflies, however, the
eyes arc placed laterally.

All animals, in which the fituation of theif
organs is perfeftly lateral, can contemplate obw
jeds only with one eye at a time.

Arti-

3»4

Lect. XII, Of the Eve.

^ 1

Article III.

/ •

Of the entire Figure of the Globe of the Eye;
of the Form and Proportion of its Chambers ;
and of the Denfty of its tranfparent Parts.

Before we proceed to confider the eye as a
dioptric inftrument, it is of importance to ac-
quire a knowledge of the circumftances which
may determine the general effeeft that organ
produces. Thefe confift in the forms, propor-
tions, and denlity of the cryftalline lens, and of
the two humours which accompany it.

A. Form.

The general form of the eye depends on the
nature of the medium, in which the animal it
belongs to exifts. It is almofl: fpherical in man,
and in the quadrupeds that live on the furface
of the earth ; that is to fay, in the loweft and
moll denfe part of the atmofpherc. The cornea
forms a flight projc(ftion.at its anterior part, bc-
caufe its convexity is the portion of a fpherc,
which is fmaller than that of the red: of the eyc;
this difference, however, is not apparent in the
porcupine, opojfutn, &c. *1 he globe is in ge-

o jierai

Art. III. Form of the Eye, ^c. 385

neral a little more convex anteriorly, than pof-
teriorly *•

In Fillies, and the Cetacea, which inhabit
the water, the flatnefs of the anterior part of the
eye is much more confiderable. Indeed, in a
great number of filhes, the eye reprefents a
femi-fphere, the plane part of which is forward,
and the convex backward. In the ray, the fu-
perior part is alfo flattened, fo that the eye ap-

* To afeertain with dill more prccifion how far the globe of
the eye approaches to, or departs from a true fphcrc, we may
form a table of the proportion of its axis to the tranfverfe
diameter, in the following manner :

&xb. Trinfvcrrt
diwtcur.

Man 1 : i

or. . . 1S7 : 136

Monkey The fame.

24 : 25

Ox 20 : 21

Horfe 24 ; 25

Whale (meafj.'-ed internally) C : 11

Porpoife (mcafured externally) 2 : 3

Owl 13 ; 12

Vulture IS ; i(J

Oftrich 4 ; 5

As fome eyes depart from the circular form, in their fection
from right to left, we might alfo form a table of the proportion
of their vertical diameter, or height, to their tranfvexfe diame-
ter, or breadth. The following are two examples ;

The height is to the breadth —

In the ox, as ^ ^ S7*38

In the ray, as 1 . 2

VoL. II. C c

pears .

386

Llct. XII. Of the Eye.

pears like a quarter of a fphere, divided by two
s:reat circles^ perpendicular to each other. Some
filhcs, particularly the Lin. form ex-

ceptions to this rule, and have alfo the cornea
very convex.

In birds, which are always more or Icfs ele-
vated in the atmofphere, the eye departs from
the fpherical form, in, a diredtion contrary to
that of fifhes. On its anterior part, which is
fometimes flat, fometimes in the form of a
truncated cone, a fhort cylinder is engrafted;
this cylinder is terminated by a cornea, which
is very convex, and fometimes completely he-
niifpherical, but which always belongs to a
much fmaller fphere than the porterior con-
vexity.

In owls, in particular, the conical part is moft
conflderable ; its axis is double that of the pof-
tcrior part ; but in the other birds, the cone is
commonly very flat. In the vulture, its axis is
one half of that of the pofterior part, or the
fegment of the fphere.

This difference in the eyes of the three claf-
fes depends on the proportional denflty of the
media the animals inhabit, compared to that of
the aqueous humour of the eye. As this hu-
mour is equal in dcnlity to water, it cannot rc-
frart rays in that medium, and would there-
fore be of no ufe to fiflics. Thus we find, ei-
ther that it docs not cxifl; at all in rhefe animals,
or that they poflefs it in a very fmall quantity.

In

Art. in. Form of the ErF.i 387

In sir which is very much rarefied, as that in
which birds fly, the retrangibility of the aqueous
humour is confiderable. It is therefore abun-
dant in them, and prefents a very convex lur-
fiice. Quadrupeds occupy a middle place be-
tween thefe two clafies, both with refped: to
the firufture of their eye, and the medium they
inhabit. The aqueous humour is entirely want-
ing in the ailtU-fiJhes.

The convexity df the cryfialline lens is in art
inverfe proportion to that of the cornea ; and
conrequenrly its thicknefs bears an inverfe ratio
( to that of the aqueous humour.

I The cryfialline of fifiics is almoft fpherical,

I and fometimes even perfectly fo ; it projeds
I through the pupil, and leaves fcarce any fpace
^ for the aqueous humour. We alfo find the
I convexity of the cryfialline very great in the
* Cetacea, and in fome quadrupeds, and birds that
1 dive frequently, as/cj/r, cormorants, &C. It is
j likewife very convex in reptiles,
j The form of the cryfialline in birds, is that
I of a flat lens. In the Mammalia it is more con-

i vex. Of all maminiferous animals, man has

1

j it moft flat. In all thefe animals it is compofed
i of two fegments of a fphere, the pofterior of
i which generally belongs to a fmaller fphere * :
j C c 2 its

I ■* The following table of the proportion of the axis to the
I diameter, affords an opportunity of comparing the convexities
of different cryftalllncs. It is founded partly on the obferva-

tion*

388

Lect. XII. Or THE Eye.

its dimenfions and proportions are not entirely
conftant in each fpecies ; it is generally more
convex in young fubje(5ls than in old.

It is obvious that this convexity of the cryf-

tions of Petit, (Memoires de I’Acadcmie des Sciences,
and partly on our own.

The axis is to the diameter —

In Man, as

the Monkey

Ox

Horfe

I^og

Hare

Otter

Porpolfc

Whale .

Owl

Parrot

Vulture

Tortoife

Frog

Salmon

Sword-fifh

Shad

pike

Barbel

Carp

Mackrcl

Whiting

Shark

Ray

Herring

Tcr.ch

Congre

1 : 2 generally

The fame

5 : 8

2 : 3

7 : 9
4 : 5
4:5
9 :

13 : 15

3 : 4
7 : 10

8 : 1 1

7 : 9
7 : 8

9 : 10

25 : c6
10 : 1 1

14 : 15
11 : 12
14 : 15
12 : 13
14 : 15
21 ; 22

The fame
10 : 1 1
7 : 8
11 : 12
9 : 10

talliiie

Art. III. Form of the Eye, &r. 389

talline is capable of fupplying the deficiency of
that of the cornea. In animals which have
the cornea convex, when the already conver-
ging rays arrive at the cryftalline, it is not necef-
fary that they fhould be greatly approximated
by that lens : the contrary is the cafe in thofe
which have the cornea flat.

B. Proportions.

To afcertain the fpace occupied by the cryf-
y talline, and the two humours, the eyes mull be
congealed, and divided in that (late by a plane
palling through their axis. This experiment is,
however, attended by the inconvenience of pro-
ducing an unequal dilatation in the difl'erent
parts of the eye ; but it enables us to difcover
that the cryllalline occupies lead fpace in the
human eye, and moll; in that of fifhes.

The portion of the axis occupied by each of
the three parts of the eye, may be reprefentcd
by the following fraelions ; the length of the
axis being confidered the unit :

Man

Dog

Ox

Sheep ...
Horse....

Owl

Herring.

Aqueous

humour.

3

s

•TT"

S

'•TT-

4-

•XT*

0

•TT*

8

•XT*

X

•• T •

iens.

VltTCOU*

humour^

4

X f

8

S

X 4

X 9

•T T

X I

X z

X 6

X 8

■4 1

X X

I

t 1

C c 3

It

I

I

39P Lect. XII. Of the Eve.

It would be alfo interefting to learn the pro-
portion of the total fpace occupied by each of
thefe tranfparent parts. Among the mammi-
ferous animals, the eye of man has the vitreous
humour moft abundant j it is twenty times
greater than the aqueous : in the ox, it is ten
tirqes ; and in the Iheep, nirje times greater.

C. Denjity .

If the following table, given by Monro, of
the fpecific gravity of the different tranfparent
parts of the eye in the ox and the codht correcfl,
we may conclude that the differences with re-
fpedito denfity between the mammalia and fi(he»
arc not confiderable. Diftilled water is here
fuppofed a thpufapd,

0

SFECiriC GRAVITY.

Of the aqqeous humour

Of the vitreous humour

In the Ox.
.1016...

In the

1000

1013

Of the whole crystalline

IIU...,

1165

Of its external part

1070...,

ii-m

Of it? nucleus

1160.,.,

It fliould be remarked,

however.

that the

powxr of refraefion is greater than the dcnlity
injJicatcs, in confequence of the partly inflam-
mable nature of the humours of the eye. It i^
alfo poffible that thefe humours contain more
inflammable parts in feme fpecie^ than in others,
and that their refrangibility cannot, therefore,
jjcprccifcly in the ratio of their denfity.

Art. III. Form of the Eve, c?r. 391

D. Confiflencc.

The crydalline is hardeft in thofe animals in
which it is mod conve^x. The human cryflalline
is one of the fofreft : that of the other mam-
rniferous animals and birds may be eafily bruifed ;
its middle part is, however, hard. In filbes,
that part forms a nucleus, which cannot be di-
vided without fome difficulty. The cryflalline
is alfo very hard in the aittle-fijlj : its induration
increafes with age in all animals.

The external and foftefl parts of the cryflal-
line are alfo the leall denle; it is probable that
this difpolition prevents that refiedlion of the
rays which would in a certain degree take
place, were they fuddcnly tranfmitted through
three different media ; this happens in the paf-
fage of the rays, through the objedlive glaffes
of the achromatic telefcope ; and the milky
cloud which refults from thefe repeated reflec-
tions, is one of the principal defeats of this
in liniment.

d'he aqueous humour, which is very fluid in
warm-blooded animals, is vifeous and filamen-
tous in fifhes.

The confiftence of the vitreous humour is in
general iimilar to that of the white of an egg :
as it is contained in cells, it has the appearance
of a body which is circumferibed, and not
fluid. This has induced a great number of ana-
tpmi(ls to name it the vitreous body.

C c 4

The

392

Lect. XII. Of the Eye.

The preceding data are not fufficient to ena-
ble us to calculate the effedl of the eye accu-
rately. It is alfo neceffary that we fhould know 1
the exacfl length of the radii of the fpheres, to |
which the anterior and poflerior curvatures of |
the cornea and cryftalline belong in each ani- ;
mal ; and likewife the length of the axis of the |
aqueous, cryftalline, and vitreous humours.
Laftly, the refra(ftile power of thefe three tranf- .
parent bodies compared with that of diftilled
water.

We might then determine the focus of paral-
lel rays, and the diftance at which the animal
can eafily diftinguifti objects. By’ adding to
thefe principal points the obfervations we ftiall
prefently make refpefting the means pollefled
by the different clafles of animals, for changing
the figure of their eye, we would afeertain the
'limits of their vifual faculty. i

But the dimenfions I require arc very imper-
feftly known to us : the following is, however,
a table of them, drawn up from the writings of
Petit, Monro, and my own obfervations : —

)

<

I

i

i

I

Man I

!

!

Art. III. Form of the Eye, 393

G 2 i
< ^ <
o: 3 ’

2

O o'?,

SI

fc =

*« 353
a o3

Ip

I4

O

o

Mnn

0,017

0,016

0,014

0,025

0,012

0,012

0,021

Doc

Ox

Khp(*p

T'forsp

Rahhir

0,014

0,016

0,012

0,014

008

0,010

0,014

0,014

009

0,016

004

0,009

Pnrjmisp, 1,5...'....

^'nrkpv

Dorn (^wl

Salmon, 0,.5

Pike, 0,65

E

3

X

2 3

X o

< 3

c*

«n -3

K <3
< tr

o

u

■5

o

z t

*3

o

0,003 ;00,045 0,014-

0,005

0,006

0,004.

0,009

0,008*0,008

0,OJ4!o,017

0,010|0,012

0,11610,019

0,011

0,012!

0,005

0,012

(M),045j

0,008;

We are almod entirely ignorant of the rcfrac-
tile power of the three humours. To calculate
that of the cryftalline, the curvatures of which
are well known, it is necelfary to meafure at
what diftance it colleds the parallel rays. Ac-
cording to Monro, in the cryftalline of an or,
the radius of the anterior curvature of which
was of an inch, and that of the pofterior
the focus was behind the pofterior furface;
and in the cryftalline of a cod-jijh, where the ra-
dii of the curvatures were 44, and ^ and a half,
the focus was only ^ when in the air, and ^ in
water : but he does not ftate the thicknefs of the
cryftallines, nor explain what meafure he ufed.

Arti-

V

394

Lect. XII. Of tul Eye.

Article IV.

Of the Firji Coat of the Eye, or the Sclerotica,

T. HE Sclerotic covers the whole globe of the
eye, the anterior part excepted, where it leaves
a large vacancy, which is filled up by the cornea.

The fclerotic determines the fliape of the eye;
itrtherefore can be really foft and flexible only
in animals that have the eye nearly globular,
that is to fay, in men and quadrupeds, becaufc
their fclcrotica affumes of itfelf that fhape, in
confequcnce of the nearly uniform refiftancc
made by the fluids contained in the eye to the
prefTure of its coats : but in all animals that
have the eye more removed from a fpherical
form, as the Cetacea, fiflies, and birds, that
membrane is fupported by hard acceifary parts,
or by a greater folidity of texture, and a more
confiderabic thicknefs.

In man, and in rnoft mammalia, the fclero-
tica is a whitifh opaque membrane, fomewhat
foft, moderately thick, and prefenting, at firft
fight, no apparent organization. It is refolvcd,
however, by maceration, into a cellular tex-
ture, compofed of filaments interwoven in every
diredion. 'J his flrudurc may be difeovered
without preparation in the eye of Cetacea, and
particularly in that of the whale: in this ani-

inai

Art. IV, Of the. Sclerotica. 395

mal the lateral parts of the fclerotica are nearly
an inch thick, and its bottom nearly an inch
and a half ; the lateral parts are very hard. On
cutting into them, we obfervc that their fub-
flance confifts of fibres which have a tendinous
appearance, and which form a kind of net-work,
the mefhes of which contain another fubfiance
of a fungous nature, browner and more flexible
than thefe fibres : the pofterior part is much
fofter, becaufc the melhes are there larger, and
partly filled by an oily fubfiance ; thefe two
fubfianccs, the foft and the hard, are feparated
in a very abrupt manner, and do not run grar
dually into each other.

The optic nerve paffes through the pofterior
portion of the fclcrotic, by a canal an inch and
a half long, the parietes of which are formed
by the dura-mater ; and it is very vilible that
the white fibres which form the bale of the
fderotic, are fuccelfively detached from the ex-
ternal furface of the dura-mater, of which they
appear to be an expanfion. This feems to de-
cide the queftion, whether the fclerotica be a

t

continuation of the dura-mater, in favour pf
the ancients. The queftion is, however, very
difficult of folution in other animals, in which
thefe two membranes touch only by a very thin
portion. The fderotic of the porpoife is only
two or three lines thick, but it prefents the fame
ftruefiure as that of the ivhalc. In the true
quadrupeds, this membrane difiep in nothing

eifential

39^

Lect. XII. Or THE Eve.

cfiTential from that man ; in both it is gcnc-
lally thickefl: at the anterior part, which is oc-
cafioned by the tendons of the mufcles of the
eye being inferted there.

In ih^feal the fclerotic is thick anteriorly,
and ftill more pofteriorly, but the middle zone
is thin and flexible.

The fclerotic of birds is thin, flexible, and
rather elaftic pofteriorly ; it has a bluifti and
brilliant appearance, but we perceive in it no
diftindl fibres; ic does not receive the optic
nerve by a fimple hole, but by a canal, which
paffes obliquely through its fubftance ; its an-
terior part is divided into two laminae, the in-
terval of which receives a circle of fmall thin
hard oblong bones, which lie over each other
like< tiles, and which give to the anterior part
of the edge a great degree of firmnefs, and a
fixed form. Thefe ofTicula are almoft flat in the
greater number of birds, in which they form
only an annular difk of little convexity; they
are llightly arched and concave externally in the
horyied oivl, in which they form a fhort tube, in
the ftiape of a truncated cone. They are ufually
twenty in number.

The torloije has, at the anterior part of the
fclerotic, the fame ofleous laminae as birds ;
thefe laminae are enclofed in that membrane,
without being continued into its fubflance, and
niay be eafily feparated from it.

There arc fimihir lamina:. in the fclerotic of

the

4

Art. IV. Of the Sclerotica. 397

the camelioHy and in that of feveral other lizards ;
but they do not form the anterior dilk; they
merely furround the lateral part.

In fiflies the fclerotic is cartilaginous, homo-
geneous, femi-tranfparent, elaflic, and fufti-
ciently folid to prcfcrve its form of itfelf, though
very thin in fome fpecies. In the ray it fwells pof-
teriorly into a tubercle, by which the eye is join-
ed to a particular ftalk, of which we fliall fpeak
hereafter. The fclerotic of the Jlurgeon is thicker ,
than the cavity of the eye ; it reprefents a kimi
of cartilaginous fphere, a part of which con- .
tains a fmall cavity, covered by the other mem-
branes.

The fahnon has the fclerotica, of the thick-
nefs of a line pofleriorly, and of an almoll bony
hardnefs before. This induration of the ante-
rior portion is obferved in a number of other
fpecies.

The fclerotic of the fepU is fingular. ‘Pof-
teriorly it is much removed from the globe of
the eye. The large ganglion of the optic nerve
and feveral other glandular parts are lituated
between them. The fclerotica, therefore, forms
porteriorly a truncated cone, the pointed part
of which is diredled to the bottom of the or-
bit ; to this portion the mufcles are attached :
the anterior part nearly Ihuts the globe of the
eye ; it is very foft and vifeous ; it is eafily fe-
parated, and prefents a coarfe felt-like texture,
which becomes firmer in fpirits of wine. In

2 fome

Lect. XII. Of the JEye;

398

fome fpecies it has a metallic brilliancy. As
there is no cornea, the fclerotic is wanting op-
pofite to the cryltalline; but the hole is not
fufiicicntly large to admit a view of the iris,
without difTeition.

In all animals, the fclerotic is double: a very
thin, and ufually blackifh membrane, clofely
adheres to its internal furface, and is believed
to be a prolongation of the pia-mater. In the
lion we have been able to follow it with eafe un-
der the cornea, where it becomes firm and tranf-
parent, and from which it may be detached
with facility.

The fclerotica not only affords infertions for
the firaight and oblique mufcics of the eye, but
alfo for thofe of the third eye-lid in birds, and
and in a number of reptiles. In all the clafTcs
it iranfmits, through holes which perforate it,
the optic nerve, the ciliary nerves, and the in-
ternal veflels of the eve.

From its flexibility in man and quadrupeds,
it is believed that the mufcles comprefs it, and
that the humours being thus pufhed forward,
fwcll the cornea, and render the eye capable of
diflinguifliing very near objects. It cannor,
however, have this ufc in animals, in which it
is wholly or partly inflexible, as in the Cetacea,
birds and filhes: yet their powers of diftinefl:
vifion arc, in a number of fpecics, at Icafi greater
than thofe of man.

Arti-

Art. V. Cornea and Conjunctiva. 399

Article V.

Of the trail fparcnt Cornea, and of the Coh-
junBiva.

The cornea is that tranfparent part which feenis
encafed in the vacancy left by the fclcrotic at
the fore-part of the eye. We have ftated, in
Article HI. its varieties with rcfpctft to con-»
ve.\ity: it alfo prefents fome differences in its
iliapc.

It is not always completely circular : in man,
and other mammalia, it is more broad than long,
and contracted a little towards the fide of the
nofe.

Its tranfvcrfe diameter or breadth is, to its
height.

In the ox, as ----- o-r : 23.

In all animals the cornea is compofed of thin
tranfparent lamime, glewed together by com-
pact: cellular matter, and forming, by their union,
a plate which is thicker in the middle than to-
wards the edges. This part is, therefore, of
itfelf calculated to produce a convergency of
the luminous rays ; its laminae are eafily fepa-
rated by the fcalpel, efpecially after 'a little ma-
ceration.

According to the experiments of Home, the
cornea becomes more convex w'hen we examine
7 near

400

Lect. XII. Of the Eye.

near objedls, and more plain when w’C look at
thofe that are diftant : in the firft cafe it ap-
proximates more powerfully the moft diverging
ravs.

Some have attributed this effeft to the con-
travflion of the ciliary proceffes, others to that
of the iris. It is more probable that it is pro-
duced by the llraight mufclesof the eye ; but it
is not fufficient to explain diftindtnefs of vifion
at very different diftances.

The corner is the only part to which we find
an analogy in the eyes of infecfls ; it even appears
in them to fupply the place of the cryftalline.
It is entirely hard and fcaly.

The cornea w-as long fuppofed to be a conti-
nuation of the fclerotic, but is now acknow-
ledged to be a particular membrane. It is not,
however, always attached to the fcicrotic, fim-
ply ^y cellular fubftance : the edges of the two
membranes fometimes penetrate reciprocally
into each other.. This is particularly obfervablc
in the Tvbalc. The fibres of the fclerotic in that
animal, pafs into the fubffance of the cornea in
the form of very delicate white lines, but pretty
long and confpicuous. Thefe lines arc alfo
cafily diflinguifhed in the rhinoceros.

The line of feparation of thefe two mem-
branes is fometimes Itraight, as in the ivhalr,
rhinocerosy &c. ; at other times it forms a kind of
bevel or Hope, and the cornea Hides under the
edge of the fcicrotic. This is the cafe in many

Art. V. Cornea and Conjunctiva. 401

the ox, &c. in fome other animals the edge of
the fclerotic is double, and embraces that of
the cornea in the manner of a forceps. T\\thare
affords an inftance of this kind of connecHon.

The feparation of the cornea from the fclero-
tic, may in particular be diftindUy obferved in
the tope (fqualus galeus.) Thefc membranes
form a dope or bevel, but in fuch a manner
that it is the fclerotic which becomes thin be-
hind the cornea, and not the latter as is com-
monly the cafe. The fclcrotica is white, the
cornea yellowiffi, and there is befides, between
the two, a compadl but very confpicuous cellu-
lar texture. This fubftance appears to be a pro-
dudlion of the conjundtiva, which penetrates the
I eye, to unite with the ciliary ligament and the
i iris.

i The Jepia have no cornea, and the anterior
! ' aperture of the fclerotic is not filled up. The
i cryftalline projedls acrofs it, and thei;e is no
aqueous humour. We find, however, under their
conjundtiva, a particular membrane which is
dry, fine, and tranfparent ; it envelopes the
Iclerotica itfelf, and the anterior part fupplies
the place of the cornea.

i:\\tconjunaiva is that part of the fkin which,
after being refledted, to line the internal furface
of the eye-lid, where it alfumes a liner texture,
and receives more numerous veffels, folds back
again in the contrary diredtion, and, becoming
ffill finer, covers the anterior part of the eye.
VoL. II, D D Tr

V

402

Lect. XII. Of the Eye.

It adheres very clofely to the cornea, from
which it cannot be feparated, except by mace-
ration. The part of the conjuncfliva which
covers the cornea, is tranfparent ; that which-
fpreads over the' fclerotic, is what we call the
W'hite of the eye, and is, in fad:, of that colour
when its blood-velTels are not diftended, or
rendered'too vilible by inflammation.

This defeription, taken from man, applies to
all animals which have eye-lids, with the ex-
ception of the colour of the part analogous to
the white of the eye, which fometimes varies ;
but in the fpecies which have no eye-lids, as in
the greater number of fifhes, the fkin palTes di-
redly before the eye without forming any fold :
fometimes it even does not adhere very clofely
to the eye. This is particularly obfervable in
the eeU which may be fkinned without pro-
ducing any hole in the fituation of the eye, the
fkin only exhibits at that place a round tranf-
parent fpot. It is the fame cafe in the ferpents
and cuttU-jiJh.

In the irunk-fiJ/j {ojlracion) the conjundiva is
fo fimilar to the refl: of the fltin, that \\c obferve
lines upon it which form the fame compart-
ments as on the body of the fifit.

Among the mamm.Tlia wc find a kind of raf
in which the fkin is not even tranfparent over
the eye, but is there covered with hairs, as on
the reft of the body. The eye, which is fcarcely
the fizc of a poppy-feed, is pcrfedly ufclefs.

Art. VI. Of the Choroides. 403

This rat is the zemni [mus Typblus.) An eel [inu-
rena cceciliay) and the myxine {gajlfobrancbus
cxcus.) are blind in the fame manner, in confc-
quence of the opacity of the conjundtiva.

Article VI.

Of the Second Coat of the Eye, or the Choroides
and its Appendages.

*

A. In Man.

I The choroides lines all the fclerotica interiorly,
in the concavity of which it is formed. In the
greater part of their extent, thefe two mem-
branes are only attached by a very loofe cellular
fubftance, but they are connedted by nerves and
veffels which perforate the fclerotic to proceed
to the choroides, or to pafs through it. Their
anterior part, that which is next the cornea, is
more intimately united by a circle of a cotton-
like cellular fubftance moiftened by a whitilh •
mucus. This is called the ciliary ligament. It
i is thicker and more compadl anteriorly : it be-
comes thinner and difappears pofteriorly. At
the furface oppolite to this ligament, that is to
3 Tay, on the concave furface and around the an-
i terior edge of the choroides, we obferve its in-
ft ternal lamina forming very fine folds, difpofed

D D 2 in

404 Lect. XII. Of the Eye.

in radii ; they have feme refemblance to the diik
of a radiated flower, and arc named altogether
corpus ciliare. The projedting laminae which
relulc from thefe folds, have their anterior ex-
tremity a little turned towards the axis of the
eye as they retreat from the cornea. Thus all
the extremities of thefe laminae intercept a cir-
cular fpace, which is precifely the pofition of
the cryftalline. It even appears that thefe ex-
tremities, which are called ciliary proceJJeSy arc
attached to the front of all the more acute bor-
der of the capfule of the cryfialline, and contri-
bute’to render it fixed. The laminae which
compofe the corpus ciliare, make hollow im-
preflions on the anterior furface of the vitreous
humour which occupies all that part of the eye
fituated behind them.

After having produced, by thefe internal pro-
jcdling folds or laminae, the beautiful wreath
which we have jufl: deferibed, the choroides
proceeds to form an annular veil, placed between
the cornea and the cryflallinc, which is called
the uvea : it is perforated in its middle by a hole
named the pupily and its anterior furface covers
another membrane, which is alfo annular, and
which is vifiblc through the cornea. This
membrane is the,/r/j, which we fliall deferibe
in the next article.

That part of the fecond tunic which is fitu-
ated before the cryflalline, is almofl plain in
man. It fometimes has a degree of convexity in

other

: Art. VI. Of the Choroides. 405

\ other animals, but always lefs than the reft of
ij the coat, which has precifcly the fame curva-
j turc as the fclerotica.

i The firft chamber of the eye is fituated be-
I tween this flat part of the fecond tunic, and the
greateft convexity of the cornea. The aqueous
I humour fills this chamber,
j The fubftance of the choroides is very thin
j and delicate; good injections fliew that it is aU
I moft entirely compofed of a triple vafcular tex-
ture. Its arteries form, in the firft place, the
external part : the greater number pafs through
the fclerotic, very near the optic nerve, and are
diftributed over the whole choroides, w here they
divide at very acute angles : they are named the
y/Jor^ ciliary arteries^ to diftinguilh them from
two trunks which almoft reach the iris without
dividing, and which are named the long ciliary
arteries. 'I'he internal texture is formed by the
extremities of the fame arteries, which having
pierced the choroides, form on its internal fur-
face a net-w'ork fo uniform and fo fine, that
the reticular interftices cannot be diftinguifhed
except by a very ftrong magnifying glafs. The
third texture is intermediate ; it is formed by
the veins, the courfe of which is very Angular.
They reprefent irregular arches, which meet at
certain points, and form a kind of circle. Thefe
are the veifels which we fee moft diftincftly
without injedion.

1 he internal furface of the choroides is lined,

D D 3 in

4o6 Lect. XII. Of the Eye.

in man, by a dark-coloured, or even perfeclly
black mucus, which may be removed or walhed
off with the finger or a pencil. It ferves to
prevent the rays, reflected by the internal pa-
rietes of the eye, from difturbing vifion, which
is efieffed by diredt rays. For the fame reafon
all dioptric inftruments are blackened inter-
nally. -When this pigment is removed, we
can fee by a magnifying glafs a flight villofity.
The internal lamina of the choroides feems of
a more folid texture than the reft of its body,
and is particularly named membrana Ruyfchiana.

The ciliary proceffes and the uvea have the
fame veffels, the fame villous furface, and the
fame black varnilh as the reft of the choroides.
The ciliary proceffes even leave a remarkable
impreflion of this varnilh on the anterior part
of the vitreous body, when they are feparated
from it. This cannot be done by the reft of the
membrane, on account of the pofition of the
retina.

I

B. In other Animals.

The choroides exifts in the eyes of all animal^
which are known to us. It is always vafcular,
and at leaft partly covered on its concave furfacc
by a particular mucous fubftance ; it varies with
refpeff to the ciliary proceffes, the colour and
texture of its pofterior part, the feparation more
or lefs cafy of the membrana Ruyfchiana, and
the difpofition of its blood-vcffels.

I. Of

Art. VI. Of THE ChOROIDES. 4O7

1. Of the Cilia?'!/ Pi'occffes.

The mammalia and birds have all the ciliary
procelTcs : we find them alfo in fome reptiles,
and even in the cuttle~jijh, but they are wanting
in almoft all filhes.

In man, each of the lamince of the ciliary
proccfTes reprefents a long irregular triangle ;
the fide by which the lamina joins the rcfi ot
the choroides, is convex; another, which touches
the vitreous body, is concave ; and the third,
which is next the iris, is much flrorter than the
other two. The angle which touches the cap-
fule is rounded, all the three edges are llightly
denticulated. This denticulation is much more
apparent, and even changes into a real fringe in
the large animals, as the ox, the borfe, and the
rhinoceros. It is alfo fimilar in the "jubale, in
which the angle that retains the capfulc, is pro-
longed more into a point than in the preceding
fpecies. In the Sarcophaga, particularly in the
lion, the fide which forms the bafe of the la-
minjE, is fliorter in proportion to the other fides
than in the preceding animals, fo that the op-
pofite angle projeefts mofi: : we perceive no den-
ticulation on its edges. In all thefe fpecies, one
lamina out of two or three, is fliorter than the
others ; but in this refped; a regular order is not
obferved.

In birds the ciliary procefles projecfl little ;
they are almofl: merely ferrated ftriae, a little

D © 4 undo-

Lict. XII. Of thx Eye.

408

undulating. There are, however, differences
in the fpecies.

In the horn-owl they are fine, compact and nu-
merous. In the ojlrich they arc larger and more
loofe, but in all birds their extremity adheres
very firmly to the.capfulc of the cryftalline.

In the tortoife the ciliary proceffes project fo
very little, that we could fcarcely recognize
them, were it not for the elegant impreflion
they leave on the vitreous body; but in the
crocodile thefe procefles are very beautiful, and
very confpicuous ,• they are each terminated by,
a nearly right angle. I have obferved thefe pro-
celfes in the, form of elongated threads, but few
in number, in a large foreign Iree-frog ,• they are
alfo fuch, tjiough not difHndl, in the load. I
have not obferved them in the comrxion lizardsy
nor in the ferpenls.

There is a very confpicuous body and ciliary
proceifes in the fqualus galeiis : the laminae pro-
ject almoft as much as in birds, and, after form-
ing a fhort point, which joins the capfule of the
cryltalline, they are continued with the firiae of
the uvea. I have not been able to perceive the
fame firuclure in the lay^ but it is certain that
there is nothing fimilar in the ofTcous fifhes;
their uvea paffes on, without interruption, with
the membrana Ruyfehiana, and forms with it an
uniform tunic, no part of w’hich projetih in-
wardly.

The ufe of the ciliary proceffes, in retaining

Art. VI. Of the Choroides. 409

the eryftalline, is no where fo diftin<5lly fcen as
in the eye of cuttle-fijhes zndi pulps : their ciliary
procelTes form a large zone or diaphragm, in the
aperture of which the cryftalline is truly encafcd.
A deep circular furrow paflTcs completely around
the cryftalline, and divides it into two unequal
hemifpheres. The ciliary procefles penetrate
into this furrow, where they are fo firmly fixed,
that they cannot be removed without being torn.
The procefs is not formed of projecting lamina;,
but of a continued membrane, the two furfaces
of which are marked by a circle, confiding
of a vart number of very fine radiated ftriae,
which prefent a very agreeable fpe.dacle to the
eye,

2. Of the JSIemhrana Ruijfchiana.

This membrane can fcarcely be diftinguiflieJ
from the choroides in man, monkies, [mall qua-
drupeds, and birds s but in the large quadrupeds,
although we cannot feparate it without injuring
both membranes, it is didinguiflied by its finer,
more compact, and feemingly homogeneous
texture. • The fc<5lion of the choroides prefents
to the microfeope only the open mouths of the
fmall vefiels which compofc it. That of the
Ruyfehiana is folid, and refembles the fedfion of
- a fimple membrane j for example, of the epi-
dermis. This is particularly obfervable in the
eye of the zvbale, where the apertures of the vef-

fels

410

Lect. XII. Of THE Eye.

fels are vifible to the naked eye, and where the
three layers are ealily difeovered.

The lateral and anterior parts of the Ruyf-
chiana are, as we have obferved, covered with a
mucous pigment, more or lefs dark ; it is of a
purple red colour in the. calmary which, with the
other fepi£y form probably the only exception
to this rule. Some birds have it of a deep-
brown red. This varnifh is fometimes wanting
in certain fpecies, in confequence of a difeafe
w'hich alfo whitens their hair : the white rabbitSy
white negroeSy and white mice, form examples of
this variety : their Ruyfehiana is then tranfpa-
rent, and all the parts of the choroides would
be of a white colour, if it were not for the nu-
merous vefTels diftributed in that membrane,
which give it a lively red appearance.

3. Of the Tapetum.

The bottom of the Ruyfehiana is frequently
covered with a very flight coat of this pigment,
through which wc can perceive its colour, which
varies remarkably in dift'erent fpecies. Man
and tnonkies have it brown or blackifli. Hares,
rabbits, and hogs, of a chocolate brown colour ;
but the Sarcophaga, the Ruminantia, the Pa-
chydermata, the Solipeda, and the Cetacea have
lively and brilliant colours in this part. The
ox has it of a beautiful green, changing into
azure blue. The horje, the goat, the buffalo, tlic

Art. VI. Of THE CuoRoiDES. 411

(}ag, of a filver blue, changing ro violet. The
Jbeep, of a pale yellow green, fometimcs blueiih.
The lion, the cat, the bear, and the dolphin, have
it of a pale golden yellow. The dog, the zvolj,
and the badger, of a pure white, bordcrcil with
blue. This coloured part of the Ruyfehiana is
named the tapetum : it does not occupy all the
bottom of the eye, but merely one lide, that
which the optic nerve does not pertorate.

It is dillicult to account for the life ol this
brilliant fpot in a place fo lurle vilible. Monro,
and others before him, have fuppoR\l that the
tapetum of the ox is green, in order to reprefent
to him, more llrongly, the colour of his natural
food ; but this explanation does not apply to the
other fpecies.

Birds and filhes have no tapetum; their Ruyf-
ehiana is uniformly blackifli, and covered every
where by mucous fublhance ; there is even much
more on its bottom than any where elfe in fillies.
The ray forms an apparent exception to this
rule ; there is at the bottom of its eye a beauti-
ful filver colour, produced by the tranfparency
of the Ruyfehiana, which allows the colour of
the choroides to be feen through it.

4. Of the Choroid Gland of Fijhes.

The Ruyfehiana and choroides of fifhes form
two membranes, w'hich are very diftindt, and
eafily feparated. The Ruyfehiana is black, and
corapofed of an interlacement of innumerable

veflels.

Lect. XII. Of the Eye.

413

veflcls. The choroides is cither white, filvery,
or gold coloured ; it is very thin, and little vaf-
cular.

Between thefe two membranes there is a body
which fome have named a gland, others a mufclc,
, and which deferves to be deferibed : it is ufually
of a lively red colour; its fubftance is foft, and
rather glandular than mufcular ; at leaft we dif-
tinguifh no fibres in it, though the blood-vef-
fels form deep and almoft parallel lines on its
furface; its form is ufually that of a thin cylin-
der, formed like a ring round the optic nerve :
the ring, however, is not complete; a fegment
of a certain length being always wanting. Some-
times, as in perca labrax, it confifts of two
pieces, one on each fide of the optic nerve : at
other times it is not quite circular, but prefents
an ii regular curvature ; this takes place in the
^ Jahnon, in iht moon-fiJ?j ( tetraodon-molaj and in
the cod. But in carps, and mo ft other fifties, its
figure is nearly circular.

Thofe who are of opinion that the eye changes
its figure according to the diftanCes of the ob-
jects that arc viewed, Tuppofe that the body we
have deferibed is a mufclc, intended to produce
that effeeft, by contracting the choroides ; but it
w'ould appear, that the numerous veftels which
pafs through it, ought to make us rather regard
it as a gland, deftined to fecrete fome of the hu-
mours of the eye. Thefe vcfttls are w'hite, fine,
much twifted, and appear to pafs through rhe

Ruyf-

Art. VI. Or the Choroides. 413

Ruyfchiana ; they may be fecn very diftindlly
in the moon-fijh^ and the labrax* In the cod they
are exceedingly large ; they anaftomofc together,
and are all covered by a white and opaque mucus.

Haller defcribed thefe veffels as a third or
intermediate lamina of the choroides, which he
named the vaj'cular : the glandular body itfelf
receives a number of velTels and nerves, which
are branches of the ophthalmic nerve, the trunk
of which proceeds for lome time in a fheath,
which is common to it and the optic nerve ; its
own flieath opening into that of the latter, as a
fmall vein into a larger one.

This gland does not exift in the Chondropte-
rygiij as the rays and Jharksy the eye of which
approaches nearer to that of the Mammalia, as
we have already fliewn, with refpe^fl to the ta-
peturn and ciliary procefles. The choroides of
thefe two genera conlifts, as ufual, of a triple
texture of vell'els, which hasfome thickncfsand
confiftency. The Ruyfchiana is very thin and
tranfparent ; between the two there is a layer
of 111 very matter.

The fepi^y which have feveral glandular bo-
dies between their fclerotica and their choroides,
have none between the latter and the Ruyfchi-
ana ; the reparation of thefe two membranes is
even fometimes difficult : the choroides is more
thick, foft, and vafcular ; the Ruyfchiana is
thin and dry ; there is no tapetum ; all the eye
is lined internally by a deep purple varnifh.

2 Arti-

t-«Ecf. XII. Of the Eye.

414

Article Vlf.

Of the Iris and Pupil, and of their Motions.

w E have already lliewn, in the preceding Ar-
ticle, that the uvea, "or that prodinflion of the
choroides which forms an annular veil or dia-
phragm before the cryflalline, is covered on its
anterior furface by a particular fubflance named
the iris.

A. Strud,ure of the Iris.

The iris is a half-fibrous, half-fpungy body,
tmited in the moft intimate manner to the uvea,
from which it cannot be Separated without a
great deal of trouble, and in the largefl: animals.
It is thickefi: and mofi; loofe at its greatefl: cir-
cumference, towards the ciliary ligament, where
it feems to terminate ; it is there mofi: eafily fe-
parated ; but towards the edges of the pupil it
becomes gradually thinner, and cannot be dif-
tinguifiied from the uvea.

When the long ciliary arteries arrive at the
great circumference of the iris, they are bifur-
cated, and form a circle around it : the arteries
tvhich belong to the iris, proceed from this cir-
cle ; they arc numerous ami radiated, and anaf-
tomofe together to form afecond fmaller circle.

It receives a great number of fmall ramifica-
tions

415

Art. VII. Iris and Pupil.

tions from the ciliary nerves, which, after hav-
ing perforated the fclerotica, and pafTed round
the choroides longitudinally, like ribbons, but
without penetrating it, are loft in the iris.

The ftrix, which we remark on the iris of
man, are diftinguiflicd by their colour, rather
than by their elevations ; they refemble little
rays of light, which converge as they proceed
towards the pupil : on the edge of this hole
there is a circle, which is narrower and deeper
than the external circle : thefe lines, which are
ftraight when the iris is dilated, and the pupil
contra(ftcd, are curved when the contrary difpo-
fttion takes place.

It is well known that the total colour of the
iris varies in different men, from blue to yellow,
and to deep orange. Some domeftic animals
alfo prefent varieties in the colour of their eyes,
as horfes, dogs, dec.; but wild animals have,
generally, a fixed colour for each fpecies.

In the Mammalia this colour is frequently a
deep chocolate or brown ; they have fewer co-
loured ftrite than man. In thofe in which the
pupil is not round, we frequently obferve un-
equal folds, which are occaftoned by the motions
of the iris.

Birds have the iris generally of a fmooth fur-
face, and a dark colour ; it varies, however,
greatly in different fpecies, and is frequently
very lively, as bright yellow, bright red, fky
blue, &c, ; its texture appears, by the micro-

, fcope,

N

Lect. XII., O? THE Eye.

416

fcope, to confifl of mefhes, formed by the de-
cuffation of' a multitude of very fine fibres.
The membrane of the uvea is fo fine in birds,
that -w hen the varnifh is wiped off, it is com-
pletely tranfparent, and the iris appears of the
fame colour on both fides.

In fifhes, on the cdntrary, the iris is fo fine a
membrane, that we fee the uvea through it,
which, by its golden and filvery brilliancy,
Ihews at firft fight that it is a continuation of
the choroides, which is of the nature we have
already ftated.

The iris of reptiles refembles that of fiflies in
its golden colours, but the veffels are more vifi-
' ble ; they form a beautiful net-work on the iris
of the crocodile.

B. Fibres of the Uvea.

The pofierior furface of the uvea prcfcnts
fome compadl ftrite, which arc continued with
the ciliary proceflcs ; thefe ftriae, though little
apparent in man, are of a confiderablc lize in
the large Ruminantia, particularly in the ox,
which has them more confpicuous than the hor/e,
though the eye of the former is fmaller ; they
are ftill larger in the zvbalc.

The rhinoceros has them alfo very large, and
extended almofl to the edge of the pupil. Jn
other genera they leave a fmooth fpace towards
that edge. In general, thefe firiae do not ap-
pear

Art. VII. I^us and Pupil.

417

jpear either in birds or fiflies ; we obferve, how-
ever, veftiges of them in the eyes of the large
JJjarkSi as the tope^ u'hite Jhark, &c.

Thefe fibres were long regarded as mufcular ;
they are now underflood to be fimple folds ot
the membrane.

C. klfotions of the Iris.

The ufe of the iris is to guard againfl the ad-
miliion of too many rays from one point into
the eye, and to prevent too great intenfity ot
light from producing a painful fenfation in the
retina. For this purpofe, when the objects we
look at are very luminous, the iris dilates, and
the pupil is contracted ; but when thefe objects
are obfeure, the contrary motion takes place. As
the cone of rays has its ape.x at the luminous
point, and its bafe at the pupil, that bafe is
confequently larger, in proportion as the rays
it contains are lefs approximated ; but the abfo-
lute quantity of the rays remains nearly the fame,
iinlcfs the differences in the intenfity of light
be very confiderable.

The motion of the iris is ufually involuntary ;
it depends merely on the rays which flrike the
retina. Light falling on the iris itfelf, caufes no
motion; that membrane is not irritable, and as
it has no immediate connexion with the retina,
the caufc of their fympathy can only be fought
for in the brain : when one eye receives the
VoL. II. E E light.

41 8 Lect. XII. Or THE Et£.

light, it alone contra(fls : in flecp the pupil is i
diminiflied, and the iris dilated. In fome cafes ;
great attention to the examination of certain
objecfls, or a fudden fright, produce motions in
the iris, independent of any change in the in-
tenfity of light.

1 he motion of the iris is, however, completely'
voluntary in fome animals. The has long

been known to poffefs this power; it is entirely
wanting, or at leaft fcarcely exifts, in fifnes.

When we regard an objech very clofely, our
pupil is contra(fted ; firfl, becaufe. the light
tranfmitted by near objects is more abundant : .
fecondly, becaufe that contraction admits into
the eye only the leaft diverging rays, and ex-
cludes a part of thofe which would prove too
numerous to be united on the retina.

Hunter has, however, proved, that this con- ,
tradtion of the pupil is not fufficient to explain |
the facility with which the fame eye fees diftant !
and near objedts, and that recourfe muft be had i
to another theory, though Haller and Sabbatier '
admit of no other means of refolving the pro-
blem.

D. I'lgurt of the Pupil.

The form of the pupil varies in different *
fpccics ; when it is dilated, it is generally round ; j
it alfo remains round when contraded, in man,
monkics, a number of Sarcophaga, and in the
birds ; but it approaches a vertical line in the

cat

4

\

Art; VII. Iris and Pupil, 419

cat genus, forming different lozenges, always
more narrow, according as the light is more in-
tenfe. In the ox^ and the other Ruminantia, it
is tranfverfely oblong, and in its greateft con-
tradion, becomes a tranfverfe line. In the bor/e
it is alfo tranfverfely oblong, and its fuperior
edge forms a convexity, which has fivefeftoons,

I thicker than the reft of the margin. In the
I whale it is alfo tranfverfely oblong. In the dol-
phin it approaches to the figure of a heart.

The crocodile has the pupil fimilar to that ot
the cat. It is rhomboidal in frogs.

The tortoife» the camelion, and common lizards
have it round. The|-^r/:o has it rhomboidal.

The rizjexhibits a very remarkable peculiarity ;
the fuperior edge of its pupil is prolonged into
feveral narrow ftripcs, difpofed in radii, aqd rc-
prefenting together a palm leaf ; thefe ftireds,
or ftripes, are gilded externally, and black in-
ternally, In their ordinary ftate they are folded
between the fuperior edge of the pupil and the
vitreous humours : but when we prefs the fupe-
rior part of the eye with the finger, they unfold
themfeives, and cover the pupil like a window-
blind. It is probable that in life they clofe
the pupil in this manner, either at the pleafure
of the animal, or in confequence of the aiftion
of intenfe light. The torpedo can completely
fhut its pupil by means of this veil. No other
fifties, not even the Jbarky pofTcfs any thing fi-
milar to this conformation.

E E 2

In

420 Lect. XII. Of the Eye.

In the cuttle-fijh, the'pupil is in the form of a
kidney.

E. Membrana Pupillaris.

\

In the human foetus, before the feventh month,
the pupil is clofed by a very fine membrane
contiguous to the uvea, from which it receives
its veflels ; it is torn, and afterwards completely
difappears, fo that no veffcige of it is found in
the new-born infant. This merhbrane is ob-
ferved in the foetuses of other mammalia ; but
it is pretended that it does not exift in birds.

Article VIII.

Of the Entry of the Optic Nerve into the Eye,
and of the Origin, Nature, and Limits of the
Retina.

A. Of the Entry of the Optic Na'vc,

In Ledure IX. we dcmonfiratcd the origin of
the optic nerve ; and in Lcifiurc X. we followed
it ct) its entrance into the eye ; it is ncccflary
that we fiiould now deferibe the manner in
which it penetrates that organ, and produces
the retina. . >

1. In

Art. VIII. Of the Retina.

421

1. In Jllammiferous Animals.

When the optic nerve of mammalia reaches
the fclerotica, it begins to decrcafe in diameter ;
in pairing through that tunic, it forms a trun-
cated cone, which varies in length, according
to the thicknefs of the fclerotic. When it ar-
rives at the choroidcs, it palfes through it by a
round hole, which is filled with a fmall mem-
brane, full of minute foramina. The medul-
lary fubifance, tranfmitted through the long
canals which compofe the optic nerve, feems to
flow through thefe fmall holes, in order to be
intimately mixed, and to form that nervous
expanlion which lines all the concavity of the
choroides, and is named the retina.

This point of the optic nerve forms fometimes
a flight projevflion within the eye. In the bare
and the rabbity inftead of a fmall round and cri-
briform dilk, the extremity of the nerve pro-
jeifls within the eye, and forms a kind of oval
cupola, which is flightly concave in the middle,
and from the edges of which the retina arifes.

In the greater part of mammalia we obferve
whitifh fibres around this point, which are
fomewhat more opaque than the reft of the re-
tina, and are difpofed in radii.

In the hare and the rabbit thefe fibres make
two long pencils, one to the right, the other to
the lelt : their finenefs, and their pure white
colour, enliven the brown ground of the cho-

E E 3 roides.

422

Lect. XII, Of the Eye.

roides, which appears through the reft of the
retina, thus affording a pleafing appearance to
the eye.

In man we obferve, near -the entry of the
nerve, and almoft at the point which correfponds
to the axis of the eye, a fmall fold of the re-
tina, which forms a flight convexity when the
more external membranes are removed. In the
midft of this fold there is a tranfparent point,
which, at firft fight, appears like a hole ; the
edges of this point are tinged with yellow, in
adults, but not in the new-born infant. This
peculiarity of the human eye, which had efcaped
the obfervation of all anatomifts before Soem-
mering, is found in no other animals except in
inonkies. We have obferved it in the cynocepha-
lus, in the white-nofed guenon, &c. &c. In the
firft, the tranfparent part is confiderably larger
than in man, and of an oval form ; there is
fometimes a yellow fpot at its fide.

The inaki, which of all mammalia approaches
neareft the monkies, has only a flight fold, with-
out any fpot or tranfparent point. The other '
fpccies have nothing fimilar.

r

2. In hird.f.

In birds, when the optic nerve has arrived at
the fclerotica, it is continued obliquely in a long
conic cauda, which paffes into a fhcath of the
fame fliapc, formed in the fubftance of that
membrane, and dircdled downward, and ob-
liquely

ARt. VIII. Of the Retina.

423

liquely forward. The lamina of this flieath,
which is in contact with the eye, is cleft through-
out its whole length, by a narrow' line, which
allows a palTage for the fubftance of the nerve.
This fiffure alfo exifts in the corrcfponding part
of the choroides, and is even longer there, be-
caufe the point of the nerve preferves its obli-
quity, after it penetrates the fclerotic. In con-
fequence of this difpofition, the optic nerve
does not form a round dilk within the eye, as
in the mammalia, but a round, narrow, and
very white line, the two edges and two extre-
mpics of which produce the retina.

But there is a Bill more remarkable peculiar.r
ity; it confills in a folded membrane, fufpended
the whole length of this w hite line, which fom»
have named marfupinm nigrumt and others the
pe^cn of the eye of birds.

This membrane appears to be of the fame
nature as the choroides, though it nowhere ad-
heres to it ; it is very fine, very vafcular, and
covered with the black pigment ; its veflels
come from a particular branch of the ophthal-
mic artery, diftinA from the two which belong
to the choroides ; they defc^nd along the folds
of the black membrane, and form tufts, which
are very agreeable to the eye when injedled.

This membrane penetrates direAly into the
interior of the vitreous body, and appears like a
wedge funk into it ; it is fituated in a vertical
plane, diredled obliquely forward : the angle

.E E 4 neareft

Lect. XII. Of the Eye.

424

nearefl: the cornea, in the fpecies in which it is
very broad, and the whole of its anterior edge
in thofe in which it is very narrow, comes very
near the inferior edge of the capfulc of the cryf- ;
talline ; in fome fpecies it is applied fo clofely j
to the capfule, that it is difficult to determine j
whether it is not attached to it. Such is the \
cafe in the vulture, the Jlork, and the turkey, ac-
cording to Petit, &c. But there are other birds :
in which it remains at fome diftance, and ap- /
pears attached to fome of the numerous laminae
which divide the vitreous body into cells.

In the Jlork, the heron, and the turkey, this
membrane is broader in the diredlion parallel
to the cauda of the optic nerve, than in the con-
trary diredlion. In the ojirich, the caffoveary,
and the horn-owl it has oppofite dimenfions. It
is folded like a ruffle in the diredtion perpen-
dicular to the cauda of the optic nerve ; the
folds are rounded in moft fpecies. In the
ojlrich and the caffozvary they are comprelfcd,
fharp-edged, and fo high in the diredlion per-
pendicular to the plane of the membrane, that
at firfi fight it has the appearance of a conical
purfe, rather than that of a fingle membrane.

It was from thefc two fpecies that the firfi aca-
demicians of Paris, who difeovered it, named
it the black purfe. The folds vary as to number :
there arc fixteen in thtjlork, ten or twelve in
the duck and the vulture, fifteen in the ojlrich,.
and feven in \.\\c great horn--owl.

It

Art. VIII. Of the Retina. . 415

It is difficult to form an opinion of the real
ufe of this membrane. From its pofition, a
part .of the rays tranfmitted by objects fituated
Jaterally with refpedt to the bird, may fall upon
it. Petit conjeftured that it ablorbed thefe
rays, and prevented them from injuring thedif-
timit: vilion of objetfts fituated anteriorly: others
have fuppofed, and this opinion has lately been
repeated by Home, that it pofTcfTes a mufcular
power, and that its ufe is to approximate the
cryflalline to the retina, when the bird -wifiics
to fliorten its axis of vifion, in order to obtain
a better view of difiant objedls. VV'c however
do not obferve any flelhy fibre in 'it, and the ex-
periments, which prove that it contracls after'
death, are not entirely conclulive. Belidcs, as
it is attached to the cryftalline laterally, it could
only move it obliquely. Haller confiders it as
a fimple fupport of the veflels intended for
the capfule of the cryftalline.

3. In Reptiles and Fijliea.

In all reptiles the optic nerve palTes through
the membranes of the eye diredly, and by a
round hole, as in quadrupeds ; it forms inter-
nally a fmall tubercle, from the edges of which
the retina proceeds.

It is fimilar in a great number- of fifhes, as
in the ray, in which the tubercle is papillated,
in the Jhark, all the carps, and a number of
others. The radiating fibres, which arife from

6 the

426

Lect. XII. Of THE Eye.

the edges of this difk, are even more apparent
in this clafs than in moft quadrupeds ; but there
is a certain number of fifhes, in which the for-
mation of the retina refembles, in fome refpe^ts,
that which takes place in birds.

I cannot yet name all the genera in which this
arrangement may be found. I have obferved it
in fahnoH and trouts^ mherringSy mackrel, perches,
the cod, the zeus faber, and in the moon-fijh ; it
probably exifts in a number of others. It is
formed thus : the optic nerve really perforates
the membranes through a round hole, but after
having traverfed the Ruyfehiana, it forms two
long white caudae, which follow the contour of
that membrane; thefe caudte, though parallel,
are not contiguous ; a producTiion of the Ruyf-
ehiana pafTes between them, in order to pene-
trate into the vitreous body. The retina is pro-
duced from the oppofite edges of thefe caudae
of the nerve, in the fame manner as it arifes in
birds, from the fingle white line. The produc-
% tion of the Ruyfehiana has a triangular curvi-
linear form, and Haller has compared it to a
bell ; it is black, vafcular like the reft of the
membrane, and attached, by its extremity, to
one fide of the capfule of the cryftalline, pre-
cifely in the fame manner as the pcdlen of the
eye of birds. It alfo appears to furnifti blood-
veflTeh to that capfule.

4. In

Art. VIII. Of the Retina.

427

4. In the Sepiie.

In cuttle-fijhes, after the numerous optic fila-
ments have perforated the choroides, they are
confounded in a lingle membrane^ which is the
retina.

B, Of the Retina.

This membrane has, perhaps, the leaf! con-
fillency of any in the animal body ; it is femi-
tranfparent, foft, and liable to tear by its own
weight ; but it becomes a little harder, and
more opaque, in fpirits of wine; it is merely
applied to the choroides, without adhering to
any part of it.

In all animals that hare ciliary procefTes, it
terminates around, and at the root of thefepro-
ceiTes, where it is diftincUy interfedied. In
birds it even forms a kind of roll or burr at that
part.

It may be fuppofed that it is more intimately
attached to the anterior furface of the vitreous
body, and that it is this adhefion which occa-
lions it to break at that place, on railing that
body. The imprelTion which the ciliary pro-
cefles leave on the fame furface, favours this,
opinion, and fome have gone fo far as to be-
lieve that the retina even covers the anterior
part of the cryftalline: they doubtlefs fuppofe
that this portion of the retina remains adherent
in the furrows which thefe procelTes produce

on

« X

Lect. XII. Of the Eye.

42 S

on the vitreous humour, and that It is covered
by the pigment which is left there.

But, in animals which have no ciliary procef-
fes, the retina terminates fuddenly towards the
commencement of the tivea, and nothing pre-
vents us from obferving that the anterior fur-
face of the vitreous body retains no portion of
it.

The internal furface of the retina. is inter-
fe(5led by numerous velfels which come from
the central artery of the optic nerve ; thefe vef-
fels produce more confiltency in the internal
lamina, than in the external, which is merely
pulpy. In fifhes, in particular, it is eafy to
diftinguifh, and even to feparate, thefe two
laminae ; the internal, whicb is named the
arachnoids prefents very delicate, but very con-
fpicuous fibres.

The retina is the moft fenfible part of the
whole animal body, fince light, which affeds
no other organ, caufes there great pain when
it is too intenfc ; this is not afionifiiing, for,
independent of the completely nervous nature
of that membrane, the parts, which are frtuated
before it, do not tend to diminifh the impref-
fion of light, as the integuments which cover
other nerves blunt their fenfations ; but, on the
contrary, increafe the efted of the luminous
rays, by colIed:ing them into a fmallcr fpace.

Arti-

Art. IX. Transparent Parts. ' 429

Article IX.

V

Of the Nature of the Tranfparent Parts of the
Eye, of their proper Membranes,

A. Of the Vitreous Humour.

T HIS humour, which occupies thegreateft part
of rhc eye, is inclofed in its proper membrane,
which is itfelf inclofed in the retina, but with-
out adhering any-where to the latter membrane,
unlefs, perhaps, by fome veflels. '

The membrane of the vitreous body, which is
alfo named hyaloides, is very fine, and com.^
pletely tranfparent. Spirit of wine does not
render it opaque ; its anterior furface is divided
into two laminae, which clofely adhere to the
capfule of the cryflalline. Between thefe mem-
branes air may be introduced, which exhibits a
circular canal with unequal inflations, called
the bulltilar canal of Petit.

The interior of the vitreous body is divided
into a vaft number of cells, by fepta, of the -
fame nature as the external membrane, w'hich
are extended in every diredlion : in confequence
of this difpolition, the membrana hyaloidea
cannot be emptied when perforated, as the
vitreous humour will not flow at once from all
thefe cells.

The vitreous humour is of an albuminous na-
ture.

43»

Lect. XII. Of tHE Eve<

ture, like the white of an egg; when it has rc-
itiained long in fpirits of wine, it fometimes be-
comes completely concrete. We preferve the
vitreous humour of birds indurated in this man-
ner ; at other times the vitreous humour diflolvCs
in alcohol, and only its almoft empty mem-
branes remain. We know not the caufc of this
difference.

When hardened by alcohol, or by freezing,
the vitreous humour is eafily divided into a mul-
titude of lenticular laminae, which probably re-
ceive that form from the cells in which the hu-
mour is contained.

Thefe obfervations are common to all the ani-
mals whofe eyes we have deferibed.

B. Of the Cryfialline.

The cryfialline lens isinclofed, without being
attached, in a membranous capfule, which is
foft and tranfparent, and flrongly fixed in a de-
prefTion of the anterior furface of the vitreous
body ; this capfule appears to be a fiinple cell ;
its anterior half is harder than the other ; it re-
tains its tranfparency even more flrongly than
the cryfialline.

The lens is harder in its centre than on its
fuiface; it is indurated, and becomes opaque
by boiling, and by alcohol ; but the central
part ftill retains fome tranfparency, and affumes
only a yellow colour.

In

. Art. iX. Transparent Parts. 43*

In the large animals, the cryftalline, thus pre-
pared, is divided into an infinite number of la-
minae, which are all inclofed within each other;
the moil: internal are the mofl: difficult of repa-
ration.

Thefe lamina: are themfelves divided into ex-
tremely fine radiated fibres, which proceed from
two centres, fituated at the two' extremities of
the axis, in the fame manner as the meridians
extend from the two poles of a geographical
globe.

This firuvfiure is very apparent in the ox, the
zvbale, &c.

Sometimes the cryftalline divides rather in
the dire(ftion of the fibres, than in that ot the
laminae ; it then forms feeftors or quarters of
the lens ; this takes place in the mammalia and
birds, but lefs fo in fifties. •

The cryftalline of the fepi<e divides eafily
into two hemifpheres, the limits of which are
marked externally by a deep furrow ; each hc-
mifphere confifts alfo of a number. of concen-
tric caps, compofed of radiated fibres.

Thefe fibres, which cxift in all cryftallines,
have been, by fome anatomifts, regarded as
mufcular, and capable of varying the convexity
of that lens, according to the diftance of the
objedts the animal wiflies to behold ; but thofe
eyes, from which the cryftalline has been re-
moved, have not the limits of diftind: vifion
more confined than others.

Between

432

Lect. XII. Of TriE Eye.

Between the cryftalline and its capfulc, wc
generally find a fmall quantity of a particular
fluid.

In man, and the other mammalia, that cap-
fule is nouriflied by an artery which comes
from the optic nerve ; this artery pafles through
the vitreous humour, which it alfo fupplies by
fome branches, and forms, on the pofierior fur-
face of ^ the capfule, a very complicated net,
the branches of which extend to its anterior
furface.

In birds it receives its veflels from the folded
membrane, commonly called the pe^en : th6fe
veflels arife themfelves from the central artery
of the optic nerve.

We believe that the cryftalline lens itfelf re-
ceives fome branches ; certain anatomifts have
fuppofed that it is nourifhed by abforption.

C. Of the Aqueous Humour.

This is a limpid fluid, Amply diffufed in all
that part of the eye which is before the cryf-
tallinc ; the greatefl: quantity is fituated before
the iris; the quantity behind that membrane has
been the fubjedb of much difpute ; it is certain,
however, that it is very fmall: it is fuppofed
that the aqueous humour in man is fomcvvhat
lighter than diflillcd water, that is, as 975 : tooo.
It emits no fmcll ; its tafle is flightly faltilh ; it
is not rendered opaque by alcohol; it exhales

through

i

i

/ •

j

ii

(

f

I

Art. X. Muscles of the Eye. 433

through the pores of the cornea, and its lofs
renders that membrane Hat after death. Thefc
circumHances are common to all vertebral ani-
mals.

I

Article X,

Of the SafpCnJhn of the Globe oj' the and
of it f! Mufcles.

In all red-blooded animals, the eye is fituatcd in
a cavity of the face called the orbit, the form
and Hrut5turc of which have been defcribetl in
different Articles of L.ecffure VIII. The eye,
being capable of various degrees of motion, is
fupported in different w’ays.

The orbit is mofl; commonly conical or ob-
long, and a fpace is, therefore, left pofteriorly,
unoccupied by the globe of the eye.

In all warm-blooded animals, this fpace is
filled wdth fat ; it forms a kind of cufliion, on
which the globe reffs and moves without being
injured : the ffnking of the eye in the orbit of
old people, is occafioned by the diminution of
• this fat.

The orbit of birds being proportionally lefs
deep than that of mammalia, the fat behind
their eye is fmaller in quantity ; on which ac-

^OL. II. F r count.

434

Lect. XII. Of the Eye.

• count, there is but little motion perceived in ,
the eye of birds.

Ihe rays :m(\Jbarks have a particular difpofi-
tion ; their eye is joined to the extremity of a
cartilaginous (talk, which is itfelf articulated in
the bottom of the orbit. In this manner, the
mufcles aft on a long lever, and have therefore
great power in moving the eye.

In other fifhes the eye repofes on a mafs, more
or lefs extenlive, of gelatinous matter, contained
in a loofe cellular texture : this trembling ^;laftic
mafs affords the eye a point of fupport in all its
motions.

Tht fepiic having a conical fclerotic attached
to the bottom of the orbit, it is not between it
.and the orbit, but between it and the choroides,
that the glandular bodies, which ferve to fup-
port the globe, are fituated. The part fixed to
the edges -of the optic hole, is pointed ; it pre-
. ferves, therefore, fome degree of mobility.

The mufcles of the eye, in man, arc fix in
number : four are ftraight ; thefe arc attached to
the borders of the optic foramen, and inferred |
into the anterior part of the globe of the eye, !
as far as the edge of the cornea, where they in-
creafe the thicknefs of the fclerotic.

The other two arc oblique. The obliquus Ju-
perior, or irochlearis, arifes alfo from the bottom*
of the orbit ; it fends its tendon into a cartila-
ginous pulley, fituated near the vault of that

cavity.

Art. X. Muscles of the Eye. 435

cavity, and proceeds upward, backward, and
outward, to its infertion on the fclcrotic, under
the retflus externus, or abdurtor. The ol>!iqiius
inferior arifes from the internal part ot the or-
bit, and palTes under the eye, into which it is
inferred, on the external lidc.

Monkics have the fame mufcles as man ; but
the other mammalia have at leall one more.

This is called the fufpcnforyy or choanoid mu/clr^
that is to fay, in the form of a tunnel. Jn the
Ruminantia and the horfc it really forms a
tunnel, or elongated.cone, the point of which ia
attached at the optic foramen, and the exteik.L<l
part is inferted in the whole of the interval be-
tween the four flraight mufcles, a little pofterior
to their infertion. Several fpecies, as mod of
the Sarcophaga and Cetacea, have this mufcle
divided into four, fo that they have eight muf-
culi reefti.

In the rhinoceros it is only divided into two.

I'he oblique mufcles prefent no variety in
inammiferous animals.

Birds and fiflies have, in all, only dx mufcles ;
four draight, which arife, as in man, from'the
edges of the optic foramen ; and two oblique,
both of which come trom the anterior parietes
ot. the orbit : they are attached very near each
other ; and one is inferted above, and the other
bclow^ the globe of the eye; but the fuperior
docs not pafs through a pulley, as in the mam-
malia.

F F -2

In

436 Lect. XII. Of THE Eye.

In birds, all thcfe mufcles are attached to the
foft part of the fclerotic, and we cannot follow
their tendons to its ofleouspart, without lacerat-
ing them ; they are, in proportion, much fhorter
than in the other clalTes.

In the tortoife we find the fix common muf-
clcs difpofed like thofe of fifhes, and befides,
four fmall ones, which clofely embrace the optic
nerve, and fpread over the convex portion of
the fclerotic, after being interrupted* by the
mufcle of the third eye-lid, of which we lhall
fpeak hereafter.

The difpofition is precifely fimilar in the cro-
codile.

In frogs and toads there is a great tunnel-like
mufcle, which embraces the optic nerve, and is
divided into three portions; its inferior fibres
advance more towards the edge of the eye than
its fuperior. There is only a fingle ftraight
mufcle on the inferior part, and confequently
only one depreffor. There is one very fliort
oblique mufcle, which is attached to the ante-
rior part of the orbit, and inferted diredly into
the adjoining part of the globe. The mufcle
of the third eye-lid is fo clofe to the inferior
part of the choanoides, that it becomes ftretch-
cd when the latter fwells ; this accounts for the
elevation of the third cyc-lid, when the eye
is lowered, as we fhall foon explain more
fully.

The eye of the cuitlc-jifj has only two fmall

6 mufclcs»

Art. XI. Of the Eye-lids.

437

mufclcs, one fuperior, and one anterior ; the
head being fiippofed upward.

Article XI.

Oj‘ the Eye-lids and their Motions.

The eye lids are membranous veils, formed by
the folds of the fkin ; they cover trhe eye in a
ftate of repofe, and cleanfc its furface by their
motions ; by fuddenly clofing, they prevent the
entrance of fmall bodies which might irritate
the eye, and even, in certain cafes, alTift: vifion,
by diminifliing the too great influx of luminous
rays.

/

A. In Man.

Man has only two eye-lids, the commilTure
of which is tranfverfe ; their fubflance is com-
pofed of mufcles, and a compact cellular tex-
ture, which fome have regarded as a ligament.
The furface next the eye is very fine, and con-
tains numerous veflels j the external furface is
fimilar to the refl: of the fkin ; the edge of each
is ftrengthened by a cartilage, called tarfiis^
which extends from one end of the commiffure
to the other ; it is rounded, and produces, wdth
the oppofite a conduit, on the fide next

F F 3 * the

-<.38 Lect. XII. Or THE Eye.

the eye, by which the tears flow towards th$
nole ; thelc edges of the eye- lids arc, befides^
iurnifhcd with a row of hairs, called cilia^ or
eye-laJJjcs.

1 he eyc-lids of man have only two mufcles,
the orL’icularis palpebrarum,' w'YAch clofcs them,
and the levator palpebra Jiiperiorh, which raifes
the upper eye-lid ; the inferior is lowered by its
own elaflicity. The orbicularis furrounds the
eye-lid with concentric and circular fibres,
which are attached to the internal or nafal angle,
where there Are fome other fibres which have a
tranfverfe direction.

The levator pal pebriC fuperioris arifes from the
bottom of the orbit, above the mufeuli reefli,
and fpreads in the fubflance of the fuperior eye-
lid.

In the internal angle of the eye-lids there, is a
fmall fold, in the form of a crefeent, which is
only apparent when the eye is turned from the
fide of the nofe. This is a rudiment of the
third eye-lid, which is developed in other ani-
mals.

B. I}i other Mammifcroan Ammais.

Monkics do not difler from man, in rcfpcvfl to
the cyc-lids.

In the quadrupeds, the third cye-li'd becomes
* more and more, confiderable, though it has no
proper rnyfclc, and cannot completely cover the

cyej

Art. XI. Of the Eye-lids.

439

eye; it is ufually femi-Iimar, as we obferve it
in the Ruminantia, the Edentata, and the Pa-
chydermata.

The rhinoceros has it thick and flefliy. In the
bare its loofe edge is convex. It is the fame in
rats, agoutis t &c.

In almoll all fpecies we remark a row of
pores, which doubtlefs afford a palfage for fome
un(5luous humour; a part of its body is fre-
quently occupied by a cartilaginous lamina ; this
part is named unguis by hippotomiffs. The hare
has it triangular, and very large.

In fome mammalia, bclides the ordinary
nnifcles of the two eye-lids, we obferve two
ffrata of ffbrcs, which proceed from the pani-
culus carnofus, one of which ferves to deprefs
the inferior eye-lid, and the other to raife the
fuperior.

The Cetacea have their eye-lids fo much
thickened by the oily fat fituated between the
two laminae, that they are almoft immoveable ;
they have no cilia, nor any veftige of the third
eye- lid.

C. Ifi Birds.

Birds have three eye-lids. The two common
eye-lids have the commilTure horizontal ; the
third eye-lid is vertical, and fituated in the na-
fal angle ot the eye ; it can cover that organ en-
tirely like a curtain. The two firff: contain, be- '
tween their external fkin and the internal, or

F J 4 con-

440

Lect. XII. Of the Eye.

conjuncfliva, a ligamentous mentbrane, wiiidi
is continued into the orbit, and lines the whole-
of that cavity. It is particularly the inferior
eye-lid which covers the eye by elevation ; it is
larger than the fuperior, and much thicker ; its
internal furface prefents an oval plate, almoll
cartilaginous, and perfeetly fmooth. The or-
bicularis palpebrarum pafl'es under this plate,
but in the fuperior , eye-lid it immediately
touches the edge. The levator palpcbrte fupe-
rioris is only inferted towards the external angle;
its origin is at the roof of the orbit : the infe-
rior eye-lid has a particular deprelfor, which
arifes from the bottom of the orbit ; there is no
cartilage at the edge of thefe eye-lids, and only
a fmall number of birds have cilia ; indeed,
thefe are rather feathers, with fhort barbs, than
real cilia ; thefe feathers are remarkable in the
horn-bill.

Very few birds have the fuperior eye- lids ca-
pable of being deprclTed, as much as the in-
ferior can be raifed. Among others, in which,
however, this may be obferved, are the czvls
and the goal-fuckers.

Idle third eye-lid, or mcmlraua niFlitans, has
a certain degree of iranfparcncy ; for birds
fometimes look at objeds through it ; and by it
the eagle is enabled to look at the fun. It con-
tains no mufcle internally; am! this renders the
fingular apparatus which moves it ncccllary.

Two mufeles have their fixed attachments in

the

Art. XI. Of the Ete-lids.

441

the globe of the eye, at the poflerior part ot
the Iclerotlcaj one, called mufculiis quadra/us
falpebrce icrticf, is fixed towards the upper and
back part of the eye ; its fibres defeend towards*
the optic nerve, and terminate in a tendon ol a
lingular nature ; it is no where inferted, but
fgrms a cylindrical canal, which bends a little
round the optic nerve, crolling the ilireilion ot
the fibres of the mufeie. 1 he fecond nuifclc,
called pyuvnidaliSi is lixed towards the lide and
policrior part of the globe, which is next tlic
nofe a little inferiorly ; its libres are collciflcd into
a tendon, which forms a long cord, and which
palfes through the canal of the preceding muf-
clc, as if it were the neck of a pulley : having
thus deferibed more than a fcmi-circle, it pro-
ceeds in a cellular fiieath of the fclerotic, below
the eye, to the inferior part of the free edge of
t:he third eye-lid, into which it is inferted.

It will be eafily underhood,- that the united
aiftion of thefe two mulcles mufl: pull very for-
cibly this tendinous cord, and thus draw* the
third eye-lid over the eye; it returns into the
angle of the two other eye-lids by its own
elarticity.

D. lii Reptiles.

Reptiles vary Angularly with refpecfl; to the
number and difpoution of their eye-lids : fer^
pents have none : crocodiles and tortoijes have
three, and the third is vertical, as in birds ;

there

442

Lect. XII. Of the Eye.

there arc alfo three in frogs ^ but the third is ho-
rizontal like the other two.

The horizontal eyc-lids of crocodiles and tor-
ioifes clofe exa<f1:ly ; they have each an enlarge-
ment at their edge, but no cilia ; their third
eyc-lidds fcmi-tranfparen't ; it moves from be-
hind forwards, and may cover the whole eye ; it
has only one inufcle, which is analogous to the
pyramidalis of birds ; it is fixed in the fame
manner to the poflerior part of the globe in-
feriorly. After having turned round the optic
nerve, it re-pafies under the eye, to fend its
tendon to that eye-lid ; but there are neither
the mufculusquadratus,norits fheath,as in birds.

In the other lizards there are alfo very re-
markable varieties.

The common lizards have, for eye- lids, a
kind of circular veil, extended before the orbit,
and joerforated by a horizontal filTure, which is
capable of being clofed by a fphindler mufcle,
and opened by a levator and dcprelfor ; its in-
ferior part has a fmooth round cartilaginous
difk, as in birds ; there is, befides, a fmall in-
ternal eye-lid, but it has no proper mufcle; it
is entirely wanting in the camelion, in which
animal alfo the flit of the eye-lids is fo fmall,
that the. pupil can fcarcely be obferved through
it. gecko has no moveable cye-Iid ; its eye

is protected by a flight margin of the Ikin, as
in ferpents. A fimllar difpolition appears to
prevail in i\\q feink.

In

Art/XI. Of the Eve-lids.

443

In frogs and toads the fuperior eye-lid is only
a proje-flion of the fkin, and almoft immove-
able; the inferior is more moveable, and has a
fvv'oln edge; but the third, which moves from
below upward, is moll: employed by thele ani-
mals; it is very tranfparent ; it has one mufcle
lituated tranfverfely, behind the globe, which
forms a thin tendon on each liJe of the eye, to
be inferted into the free edge of the third eye-
lid.

The fill atnanders have only two eye-lids, which
are horizontal, flelhy, and little moveable ; it
appears that they may entirely cover the eye.

E. In Fillies.

In mofl fifltes there is no moveable eye-lid ;
in fomc, as we have already obferved, the ilcin
pafl'es before the eye, without even producing
a fold. Others have only flight projeeftions,
which form a kind of eye-brows, rather than eye-
lids. Mofl oiTeous filhes have, at each angle
of the orbit, a vertical and immoveable veil,
which co'vers only a fmall part of it. This may
be eafily obferved in the filmon, niackrel, &c.

The moon-fJ/j {Tetraodon Mola ) exhibits a pe-
culiarity, which we have obferved in no other
animal ; its eye may be entirely covered with
an eye-lid, perforated circularly, and which
may be clol^d by means of a real fphincter.

Five

444-' Lect. Xll. Of the Eye.

Five mufcles, difpofed in radii, and attached
to the bottom of the orbit, dilate the aperture,

F. In Mollufca.

>

The Jepi^ and other' mollufca, which have
not the eyes at the extremity of their tentacula,

' have no eye-lid ; the fl^in covers the eye, as in
ferpents and eels : but the Jlugs, the /nails,
have an organization, which is far more com-
plicated, and much better calculated for the
protection of their eye.

This organ is fituated at the extremity of a
flefhy tube, called a horn, or tentaculum, which
may be drawn completely within the head, and
protruded by a motion fimilar to the evolution
of the finger of a glove. In Vol. I. page 433,
w^c deferibed the mufcles that draw' the fnail
into its (hell. At the external edge of each of
rhefc mufcles, .the particular mufcle of the eye
is attached ; this mufcle penetrates to the infide
of the horn, to the extremity of which it is
fixed ; when it contrails, therefore, but fiill
more when afiified by the contraction of the
great mufcle of the body, it draws the extre-
mity of the horn inwardly, in a manner which
refcmbics the turning in of a fiorking. The
annular fibres, which encircle the horn through-
owt the whole of its length, unfold the internal
part by fuccefTivc contractions, and thus bring

back

Art. XII. Glands of the Eye. 44^

back the eye to its external pofition. In the
naked Inail, the rctradors of the eyes are limply
attached to the flefliy mafs which forms the
foot. In the inferior horns, or tcntacula, which
have no eyes, the mcchanifrn is alfo the fame.

Article XII.

Of the Glands that fin'roiuid the Eye.

A. In Man.

In animals that live in air, the anterior furface
of the eye would foon become dry, and be ren-
dered foul, by dull, were it not conflantly
bathed by a limpid fluid. — It would alfo be fre-
quently injured by infedis, and a multitude of
other fmall bodies, were not uncluous fubftanccs
depofited on the edges of the eye- lids, and be-
tween the cilia: thefe purpofes are accomplifhed
by the glands, with which the eye is furrounded,
and which, in man, conlifl: of three kinds — the
glandnla lachrymalisy glanJuhc Meihomiiy and ca-
runcula lachrymalis.

The lachrymal gland is fituated towards the
upper part of the orbit, above the fuperior eye-
lid, a little towards the temple ; it appears to-
be compofed of w-hitilh grains, and formed of
two fmall lobes. It has fix or feven very fmall

canals.

446

Lect. XII. Of the Eyg.

canals, which defcend in the fubflarice of the
eye-lid, and open on its internal lurfacc, a little
above the cartilage which forms its margin.

The fluid, called tears, continually exudes
through thefe minute apertures ; it is dilfufed
over the front of the eye ; and when the eye-
lids clofe, they prefs a part of it into the fmall
triangular canal, which is formed by their edges
and the globe, towards their internal or nafal
angle.

T\\q glanduke Metbomii iecrcie fatty matter,
which anoints the edges of the eye-lids, and
prevents the tears from wetting, or pafling over
them; thefe glands are fituated in the fubftance
of both eye-lids, at their edges ; they are com-
pofed of fmall follicles, ranged in vertical and
parallel lines; their number exceeds thirty in
the upper eye-lid, and twenty in the lower ;
their apertures are fmall round holes, which ap-
pear along the edge of each eye-lid.

When the lachrymal fluid reaches the nafal

V

angle of the eye, it is abforbed by two fmall
pores, called puneJa lachrymalia, w'hich arc con-
tained in two eminences lituated at that extre-
mity of. the eye-lids. Each pore leads into a
fmall canal, and both canals into the lachrymal
flic, which opens into the nofc by the duA we
already deferibed in page of this volume.

The cavunciila lachrymalis is fituated in the in-
ternal, or nafal, angle of the cyc-lids, and is ap-
parent without dilTctflion ; it is a fmall, round,

rcddifli

Art. XII. Glands of the Eve. 447

reduilh mafs, compofed of fcven dirtindl folli-
cles, which produce a thick whirilh humour.
The life of this humour appears, in particular,
to be the proteclion of the lachrymal pores, by
arrefting light lubllanccs which might be in-
troduced into them.

1). In other Mammjf crons Animals.

Qiiadrupeds have, in general, the fame gland.s
as man, and fcvcral of them have one more.

Ihe lachrymal gland-, properly fo called, is
fub-divided into two or three bodies in the
J^uminantia. Some feparate grains have each a
ven' Oiort excretory duct.

In the hare and the rahhil the lachrymal gland
is very large; it extends above and below the
eye, and occupies the interval between the cra-
nium and the pioccfs, which, in thefe animals,
fuftains the eye-brow'; it pafTes behind the eye,
links under the zygomatic arch, comes out from
the. orbit, on the fide of the nofe, and termi-
nates there by a'confidcrable enlargement; it
appears to me to have only a lingle excretory
canal, which perforates the upper eye-lid to-
wards the pofterior angle.

The gland peculiar to certain fpecies of qua-
drupeds, and which is wanting in man, is named
glandula Harderi, though it was feenand deferib-
ed by more ancient anatomills ; it is always fi-
tuated in the internal or nafal angle, and fecretes

a thick

44S

Lect. XII. Of the Eye.

a thick whitidi humour, which is poured out by
an orifice under the rudiment of the third eye-
lid. In tbe Ruminantia it is oblong, and of a
pretty hard confirtency. In the hare it appears
to be formed of two parts, merely United by
cellular fubftance, and each fub-divided into a
great number ot lobes; the fuperior part, which
is the lead:, is whitidi i the inferior, which is
much larger, is reddilh. It is large and double
in the zvater-rat.

It alfo cxids in the Sarcophaga, in the elephant y
in the hogy in which it is oval, in the (loihsy &c.

The caruncle exids' in the Ruminantia, as
well as in man ; but in them it is formed of a
greater number of follicles.

I have not been able to perceive it in the
harCy nor in feveral other Rodentia.

There arc alfo differences in the manner in
which the tears flow'.

The Ruminantia have the lachrymal points
and, dudts as in man. Some genera of that or-
der are rendered remarkable, by the receptacles
for the tcarSy ov f off at lachrymales thefe are fmall
cavities in the cheek, one below each eye, near
its nafal angle, and communicating with that
angle by a fmall furrow. They arc found in
deeCy and in antelopes.

I’he bog has two lachrymal points* Wc alfo
find them in the Jloths and ant-eaters.

In bares, rabbits, and doubtlcfs in all the ge-
nera allied to thefe, there are no lachrymal

points,

Art. XII. Glands of the Eye. 449

points, but a crcfcent-fiiaped filTurc under the
inferior edge of the third eye-lid, which leads
into a fingle lachrymal du^. The edges of that
filfiirc are furnilhed with cartilages. There is
a fniall fcmi-lunar valve in the canal, which
prevents the fluid from ieturnii\g to the eye.

The Cetacea, like moCl: animals that livccon^
ffantly in water, have neither gland nor lachry-
mal points. We merely obferve, under the
upper cyc-lid, lome lacunx, from which a
thick mucilaginous humour flows.

C. In Bird'!.

We find, in birds, the lachrymal gland, and
that of Harderus. There is no caruncula. The
Hardcrian gland is much larger than the other,
ufually of an oblong form, and ot a flefli co-
lour ; it is fituated between the levator and ad-
ductor mufcles, or fometimes, as in the turkey^
between the adduTorand theobliquus inferior :
it produces a fingle excretory duct, which palTes
through the fubftance of the third eye-lid, and
opens on its internal furface. This gland fur-
nilhes a thick yellow humour. The lachrymal
gland of birds is ufually very fmall, almoft
round, very red, and fituated at the pofterior
angle ; it difeharges itfelf by two or three fmall
but confpicuous canals, precifely at the angle
of the two horizontal eye-lids.

Birds of the duck and other fwimming

VoL. II, G g ' and

45*3 Lect. XII. Of the Eye.

and wading birds, have a glandular, hard, and
granulated body, which occupies all the fupe-
rior part of the orbit, and turns backward, to
follow the curvature of the eye. In the tufted
duck (anas fuligula) it is fo broad that it touches
the correfpondent body, above the cranium :
this body appears to fupply the place of the
lachrymal gland ; but I have not yet difeovered
its excretory canal.

All birds have two holes, for the paffage of
the tears, placed in the interior angle between
the two firfl palpebrjE and the third : they are
broad, but have no cartilaginous border, being
foft like the refl of the furrounding fkin ; they
lead almoft immediately into the nafal fac, fi-
tuated at the bafe of the nofe.

D. In Reptiles.

Reptiles vary as much with refpect to their
lachrymal glands, as to their eye-lids.

The fea tortoifes have a very confiderable
gland at the pofterior angle; it is rcddifli, gra-
nulated, divided into lobes, and extends under
the arch which covers the temple.

In the frejh water tortoifes we find two fmall
blackifli glands, which alfo cxift in toads and
frogs ; but 1 have not yet accurately obferved
their excretory ducts.

Serpents, like fillies, have no gland in the eye.

Arti-

Art. XIII. Eye of Insects.

45 1

Article XIII.

Of the Eije of Infects and Cruftacea.

W HAT we have to fay in this article, will relate
chiefly to compound eyes ; the fimple eyes arc too
fmall for difledion.

The ftruelure of the eye of infects is fo very
different from that of other animals, even the
mollufca, that it wou-ld be difficult to believe it
an organ ot light, had not experiments, pur-
pofely made, demonffrated its ufe. If we cut
out, or cover with opaque mattet, the eyes of
the dragon-fivy it will ftrike againfl walls in its
flight. If we cover the compound eyes of the
wafpy it afeends perpendicularly in the air,
until it completely difappears ; if we cover its
Ample eyes alfo, it will not attempt to fly, but
will remain perfectly immoveable.

The furface of a compound eye, when viewed
by the microfeope, exhibits an innumerable
multitude of hexagonal facets, flightly convex,
and feparated from one another by fmall fur-
rows, w hich frequently contain fine hairs, more
or Icfs long.

Thefe facets form altogether a hard and elaf-
tic membrane, w^hich, when freed of the fub-
ftances that adhere to it pofteriorly, is very
tranfparent.

G G 2

Each

45^

. LecJt. XII. Of the Eye.

Each of thcfe fmall furfaces may be confidercd
cither as a cornea, or a cryftalline ; for it is
convex externally, and concave internally, but
thicker in the middle than at the edges; it is
alfo the only tranfparent part in this fingular
eye.

Immediately behind this tranfparent mem-
brane there is an opaque fubfiance, which va-
ries greatly as to colour in the different fpecies,
and which fometimes forms, even in the fame
eye, fpots or bands of different colours. Its
confiflence is the fame as that of the pigment of
the choroides ; it entirely covers the poflerior
part of the tranfparent facets, without leaving
any aperture for the paffage of the light.

Behind this pigment we find fome very fliort
white filaments, in the form of hexagonal
prifms, fituated clofe to each other, like the
flones of a pavement, and precifely equal in
number to the facets of the cornea; each pene-
trates into the hollow part of one of thefe fa-
cets, and is only feparated from it by the pig-
ment mentioned above. If thefe filaments arc
nervous, as in my opinion they appear to be,
we may confider each as the retina of the fur-
face, behind which it is placed : but it will al-
ways remain to be explained, how the light can
ad on this retina, through a coat of opaque
pigment.

This multitude of filaments, perpendicular
to the cornea, have behind them a membrane

which

Art. XIII. Eye of Insects.

453

which ferves them all as a bafe, and which is
confequcntly nearly parallel to the cornea : this
membrane is very fine, and of a blackilh co-
lour, which is not caufed by a pigment, but
extends to its mofl: intimate texture ; we obferve
in it very fine whitifli lines, which are tracheae,
and which produce ftill finer branches, that pe-
netrate between the hexagonal filaments, as far
as the cornea. By analogy, we may name this
membrane the cboroides,

A thin expanlion of the optic nerve is applied
to the pofterior part of the choroides. This is a
real nervous.membrane, perfectly fimilar to the
retina of red-blooded animals; it appears that
the white filaments, which form the particular
retinae of the dilferent ocular furfaces, are pro-
duftions of this general retina, which perfo-
rates the membrane I have named choroides, by
a multitude of fmall and almoft imperceptible
holes.

To obtain a diftind view of all thefe parts,
it IS necelfary to cut oft' the head of an infeft
that has the eyes large, and difletft it pofteriorly :
each part will then be removed in an order the
reverfe of that in which I have deferibed them.

In the Cray fiJheSy in general, the eye is lituated
on a moveable tubercle. The extremity, which
is rounded on every fide, and fometimes elon-
gated into a cone, when viewed by a glafs, pre-
fents the fame furfaces as the eyes of infedts.
When we cut this tubercle longitudinally, we

G G 3 obferve

454

Lect. XII* Of the Eye.

obfcrve that the optic nerve pafles through it
in a cylindrical canal, M'hich occupies the place
of its axis. Arrived at the centre of the con«
vexity of the eye, it forms a fmall button^ which '
detaches very fine filaments in every diredlionr
at a certain diftance thefe filaments meet the
choroides, which is nearly concentrical with
the cornea, and covers the fpherical brufh of
the extremity of the nerve, like a hood. All
the diftance between the choroides and the cor-
nea is occupied, as in infeefts, by white filaments,
clofely arranged in a perpendicular dire(5lion to
each other, and which have the exl;remity next
the cornea alfo coated with a black pigment.

Thefe filaments perforate the choroides, and
are continuations of thofe produced by the bur-
ton, which terminates the optic nerve.

A

EEC-

( 455 )

LECTURE THIRTEENTH.

Of the Organ of IIeaking, ou, Of the

Eau.

Article 1.

Of Sound, and Hearing in genera!.

Sound is the fenfation we experience, when
certain bodies, called foiiorons, vibrate, and
communicate their tremulous motion to the
atmofpherc around us, or to any other body in
contadl with our car. The ear, being affected
by this motion, tranfmits the imprelTion it re-
ceives to the brain. In this manner we exercife
the fenl'e of hearing.

The qualities which belong to found, may be
diftingui filed into different kinds, independent
of each other, viz.

I. Force, which depends upon the extent of
the vibrations of the body from which the
found proceeds. The greater the vibrations, the
JJronger is ih& found : the extent of the vibra-
tions is determined by the degree of impulfe
which produces them.

G G 4 2. TojiCj

r

^456 Lect. XIIT. Ok the Ear.

2. TonCj which depends upon the velocity of
the vibrations. The vibrations made by a fo-
norous body in a given timCj produce a tone
which is high or acute in proportion as thefc
vibrations are more numerous, and lozv or grave
in proportion as they are lefs numerous. The
laws of this velocity, and the circumflances
which determine it, are well known. All things
equal it is in the inver(e_ ratio of the length,
and the direct ratio of the tendon, whether that
tendon be the effecd: of external agency, or of
the particular nature of the fonorous body itfelf.

3. It,efonancey which arifes out of the inti-
mate cbmpodtion of the fonorous' body : in it
we didinguifh different tones, as the cleaVy the
Jofty the duH, the crackling. See. Sec. with the
Jaws of which we arc not yet acquainted.

4. Simple modulations of voice y the different
kinds of which are expreifed by the letters
called vowels, a, e, /, 0, ?/, ai, oUy cUy Sec. We
are cornpletely ignorant of the real nature of
ihefe modifications of found, though we arc
pretty well acquaintcil with the motions which
man and other animals give to their vocal or-
gans in producing them.

5. Articulations, the different kinds of which
arc expreffeti by the confonants, /', r, d, dec.
We know' as little of them, as we do of the
vorvcl founds, 'fhc imitations of cither of thefc
modifications of found, which we produce by
our indruments, arc, therefore, very imperfed-.

6 • The

Art. I. Sound and Hearing. 457

The human ear can diftinguifh all thcfc dif-
ferent qualities with relation to one found: this
diftiiuftion is made with wonderful accuracy, by
]‘)erfons who fiequently exertife that faculty, and
particularly bv profcluonal nuilicians. The
(Uher mammalia exhibit proofs that they are
capable of diftinguiihing the qualities of found
widch relate to fpeech, that is to fay, JiKiple t'--
cal DicdulrJiQHs and articul^lioKs ; lor we may ob-
fci ve daily, that they remember the found and
fignification of feveral words. Some are llrongly
ail'eded by certain founds. > Acute tones prO-
du:'C a painful fenfation in and wealfo ob-
ferve that thefe animals are terrified by violent
noifes : they therefore diflinguilh thefe two pro-
perties. Birds have a feeling, no lefs exquifite,
of voice, tone, ariiailaiio-: , and even refonance,
fince they learn to fing with great corrc(5lnefs,
and, when their vocal organs permit them, can
completely counterfeit the human fpccch, with
all the modifications pracufed by the individuals
they imitate.

As to cold-blooded animals, it is well known
that feveral of them call each other by certain
founds, and that others, which are incapable of
producing founds, can at leaf! underhand them,
as carps, which appear when the noife of a bell
indicates to them that they are to be fed, &c.
&c. : but we know not what qualities of found
they diftinguifh, and how far, in this refpedl,
the delicacy of their fenfe of hearing extends.

Lect. XIII. Of the Ear.

45 S

We arc flill more ignorant rcfpccfling the
flate of this fehfe in the white-blooded animals.
It is evident, however, that feveral of them
are not deftiturc of the faculty of hearing.

It would be of importance to determine the
limits within w’hich the car of each animal per-
ceives each of the qualities of found- Thus,
v/ith rcfpc(ft to force, founds, which are fo weak
as to be loft to the human car, are diftinftly
heard by certain animals. Other anim.als alfo
may, perhaps, endure founds which would
deafen us. With regard to tones, fome are too
grave, and others too acute for the human car.
Muficians have even fixed the limits of thefc
rones at two numbers of vibrations, which arc
to each other in the ratio of r : 1024: perhaps
thefe limits arc not the fame in all animals.
There are great differences between the indivi-
duals of the human fpecies, w'ith refpcift to the
faculty of cl iftingui filing two very proximate
tones. The difference is, perhaps, ftill greater
between one animal and another. .

With regard to modulation rxnd arliculation, the
people of one. country diftinguifli, in their pro-
nunciation, certain letters, between w-hich thofc
of another perceive no difference. The fame
obfervation applies to the other qualities!

It alfo appears, that an ear of fimilar ftruc-
rurc is not equally perfeft; with refpeeft to all
the different qualities of found: one car may
be found to poffefs great delicacy of hearing,

as

Art. I. Sound and Hearing. 459

as to the wcakefl; founds, and yet be altogether
incapable of diferiminating between diHerent
tones ; on the contrary, a very fine mulical ear
may be deaf t® other low founds : if fuch differ-
ences are obferved between one man and another,
we may rcafonably conclude that they exift in
a far greater degree in the various kinds of ani-
mals.

It is evident that there mufi: take place in the
car, at the moment of hearing, fome change
Avhich correfponds to each of the qualities ot
found V C difiinguilli ; but tar from being ac-
quainted with its nature, we are even Rill ig-
norant of the reqiiilitcs, on the exillence of
which, general bearing, or the fnnple perception of
found, depends.

This confideration fuggefis to us the advan-
tages that may be derived from Comparative
Anatomy. It is natural to fuppofe that the
parts, which are conftantly found in all animals
that hear, are thofe abfolutelv neceffiirv to the
mere perception of found in general ; and that
thofe parts muff have a more particular relation
to certain qualities of found, which a^e found
more developed in the animals that perceive
more perfedlly thefc qualities.

But this is the point which prefents the chief
difficulty, bccaufe it is almoft impoffible for us
to af(?ertain the kind and degree of the percep-
tions of other animals.

As to the parts effential to hearing, the exa-
mination

460 Lect. XIII. Of THE Ear.

mination \vc are about to make, of the orocans
of that fenfe, in all the animals in which it has
been difeovered, will Ihew that the only part
conhantly exiding is a gelatinous pulp, which
is covered by a fine and elaftic membrane, and
in which the lad ramifications of the auditory
nerve are I oft : this pulp fills the labyrinth in
all fpecies from man to the cuttie-fifh. The
organs of hearing of thofe animals which are
placed below the cuttle-fiih in the fcale of being,
are not yet known, though feveral of them af-
ford manifeft proofs of poftefftng that fenfe.

It is then almoft demonftrated, that the feat
of hearing reftdes in this pulp, or rather in the
nervous filaments that float or are diftributed
in it. We may form a very natural idea of the
connexion of this fubftance with the external
movements which are the caufe of found: this
quivering gclly will receive, with facility, the
concuftions tranfmitted to it by the vibration of
fonorous bodies, and communicate them to the
nervous filaments. Thus far may the motion
of found be traced ; but the procefs, w'hich is
afterwards nccciraiy to produce jierccption,
efcapes the anatomirt as well as the metaphy-
fician.

The other parts, which are not found in all
cars, can only be regarded as accefTory fub-
ftanccs, calculated each in a particular manner
to augment or to modify the fenfation. Very
plaufiblc conjeeftures may be made with refpe<fl

to

Art. I. Sol’N’d and Hearing. 461

to the efVecl of fome of thofe parts. It appears
evident, for cxamj^le, that the external ear,
which is fo large in fome quadrupeds, ferves to
increafe found, in the fame manner as the trunj-
pets iifcd by perfons who are deaf : it is very
prohal)le that the large cavities with ofTcoiis
parietes which furround the labyrinth in a num-
ber of animals, produce a limilar eH'et^l by the
refonance of their (olid and elaflic vaults. It
is fiippofed that the thin and tenfe membrane
of the tympanum, by means of the olTicula at-
tached to it, tranfniits the vibrations of the ex-
ternal air with confiderable force to the laby-
rinth. It is alfo fuppofed that the will pro-
duces, through the medium of the mufcles
which av.‘l on the olTicula, that degree of tcnfion
in this membrane, which is prccifely neceflary
to bring it in unilbn w ith the founds, to which
we are inclined to pay particular attention.

It has been conjeclured, that the fpirai and
decreafing lamina which divides the cochlea
of qua^drupeds into two fcaloe, is compofed of
ollcous fibres; aiid, as thefe fibres mufi: diminifh
in length from the bafe to the point of that
organ, that each is fitted to receive concuflions
from a particular kind of tone. Formerly, the
fame faculty was aferibed to the ofleous rings
w’hich compofe the femi-circular canals, and
w hich were believed to diminifh gradually from
the tw-o extremities of each canal to its middle.

The Euftachian tube has been regarded by

fome

4^2 Lect. XIII. Of the Ear.

fome as a fupplementary palTage for the founds
which do not reach the ear by the meatus ex-
ternus ; others have fuppofed, that it ferves as a
canal to carry off the fuperfluous humours from
the cavity of the tympanum, &c.

The inveftigations, to which we are about to
proceed, may perhaps throw fome light upon
thefe interefting queftions.

Article II.

Of the diff'erent Forms of the JMemhrane which
contains the Auditory Pulp^ or of the Meni-
hranous Labyrinth.

The membrane which inclofes the auditory
pulp is tranfparent, fine, and peculiarly elaftic:
with refpefl to its form, it may be regarded as
felf fufiained, as it preferves its fliape, indepen-
dent of the afiifiancc of the pai:ts which lur-
round it. It, is, however, finer and weaker in
the animals in which it is clofely encircled by
the bones, and particularly in man, and the
other mammalia. In young animals it is more
thick, more humid, and more cafily feparated
from the bones, than in the old.

A. In

Art. II. Membranous Labyrinth. 463

A. hi Cray-jijh.

The membrane in thefc animals fcarcclir
merits the name of labyrinth ; it rclembles a
fmall puiTe, enclofed in a fcaly cyliiulc’r, open
at both ends. The extremity by \\hich this
fmall cylinder joins the bafe of the antenna, at-
fords a palfage for the nerves into the piirfe-
The oppolite extremity is clofed by an elaflic
rnembrane, which may be named tympanum^ or,
with more propriety, fcncjlrd ovalis.

'I'hc air, or water, in which the animal live^',
a<5ls immcdiatclv on this membrane: the ex-

4

ternal appearance of this part is readily difeo-
vered, by looking at the inferior furfacc of the
bafe of the large antenmu.

Fabricius and Scarpa have deferibed it in de-
tail.

B. In the Sepiic,

The ear is almofl; as fimple as in cray-fijb %
but it is entirely concealed in the body of the
annular cartilage, which ferves as the bafe of
the great tentacula, or feet of thefe animals.

The membrane of the labyrinth is alfo a fim-
ple purfe, of an oval or roundilh form. In the
common cuitle-fijh (fcpui offichiulis) it has inter-
nally feveral conical eminences, difpofed in an
irregular manner : thefe eminences are wanting
in the other fpecies. in the pulp which fills
^ the

464 Lect. XIII. Of the Ear.

the membrane, there is a fmall body fufpended,
^vhich is oITeous _ in the cuHlc-fJJj, properly fo
called, and limilar to flarch in the oeJopus.

In the fepia o^icinaliSy it refembles a foiall
valve of a concha.

>

C. In Fijhes that have free Branchice,

The membranous labyrinth begins to afiume
a more complicated form. It is uniformly com-
pofed of three femi-circular canals, the dimen-
lions of which vary, but which all communi-
cate with a fac, more or lefs divided bv con-
tradiions. Befidcs the common pulp, this fac
contains one, two, or three fmall bones, ac-
cording to the fpecies. ' In the olTeous fifties
thefe bones are as hard as ftone. They are always
fufpended in the midfl; of the pulp, by a great
number of nervous fibrillte. .Each of the three
femi-circular canals has an enlargement, in the
form of a bubble, near the place where it pe-
netrates the fac, and two are united at one of
their extremities : in confequence of this junc-
tion, the canals communicate with the fac, by
five apertures only, inftead of fix which would
have exifted had the union not taken place.

All the circumftanccs we have pointed out
'rcfpe<5ling thefe three canals, alfo exift in the
fuperior clalTes ; the whole apparatus is fituatcd
in the fides of the cavity of the cranium, and

fixed

Art. II. Membranous Labyrinth. 465

fixed there by a cellular tilluc, conlifling of
velFcls and ofTeous or cartilaginous inuna.

J'ifhcs dinVr from each other in the torm and
proportion of the parts of the labyrinth, and
in thofc of the petrous olhcula it contains.

One of the three canals is directed obliquely
forward and outward, in a plane which is nearly
vertical ; another is dirctflcd backward and out-
ward, alfo in a vertical plane-, the third is al-
nioft horizontal, and external to the other two ;
the two extremities, which join, and open into
the fac by one aperture, are the jiollcrior extre-
mity of the lirll:, and the anterior of the fecond
canal : their other two extremities, and the two
belonging to the third canal, enter feparately.

The enlargement of the two tirll canals takes
place near the extremities, which do not unite.
In the third, it is at the anterior termination.

There arc fome obvious differences in the pro-
portional length of the canals to the dimenfions
of the lac ; but in general they arc fliortcr in
the offeous than in the cartilaginous filhes.

The mocn-jijhy the frog-fyh, and the /hirgeon,
have them very long and flender. In the ofleous
li flies, the pike and the timny have them longer
than the carpSy eels, falmoHy &c.

The file prefents more varieties than the femi-
circular canals.

In the moQn-fiJh it is a fimple cone, the point
of which is directed towards the brain, and the
VoL. II,

466

Lect. XIII. Of the Eak.

bafe enlarged, to receive the three canals. In
thcJiurgeoUi it is a broad, flat, and vertical difk,
which is fituated on the lateral and internal pa-
rictes of the cranium, and which alfo imme-
diately receives the three canals. In the/ro^-
fi/hy it is alfo a Ample fac. It appears, therefore,
that an undivided fac is a general charafter of
all the cartilaginous fifhes with free branchiae ;
but in mofl; of tlic other fiflies, the part which
receives the canals, and which we fhall name the
finusy is feparated by a contradion from the other
parr, which we fhall more particularly- call the
Jac.

The finus is ufually flender, and elongated
from before backward : the fac is oval, and is
fo fituated on the bafe of the cranium as to be
frequently found very near that of the other
car ; fometimes it lies in a dcpreflion of the bafe
of the cranium.

The pike has a fmalThollovv appendix, which
is conneefted with the poflerior part of the finus,
by a very fmall canal, and fixed, by its other
extremity, to the cranium, near the edge of the
occipital foramen ; this appendix may be re-
garded as a third divifion of the fac, and has
only, as yet, been obferved in this fifh.

In the moon-fijijy the fac contains no officula;
but, inficad of them, we find fame lumps, the
fubflance of which is more of a mucous than
of a cretaceous nature. In the jlurgeon there is

only

Art. II. Membranous Labyrinth. 467

only a fingle triangular ofliciilum, the hard nu-
cleus of which is partly furrounded by creta-
ceous matter.

In the ofleous fKlies, and c\en in fomc of the
cartilaginous kind, as ihe frog-H/hy there arc al-
ways three oflicula : two of thefe are in the fac,
viz. the largell, and a fmall one behind it ; the
third is alio very fmall, and is fituated in the
common linus of the canals.

The form of the bones, and their mode of
adhelion to the fiic, deferve to be noticed, parti-
cularly with rcfpccl to the larged.

It is commonly oblong from before backward,
lituated obliquely in the fac, convex on its in-
ternal furface, and concave on its external.

The internal furface is fmooth, but marked
with a furrow, which varies according to the
fpecies. The external furface has fome afperi-
tics. The fuperior margin is ufually denticu-
lated in a more confpicuous manner than the
inferior, and the anterior extremity has fre-
quently fome tubercles or projecTiions ; there
are two of rhefe in the olTiculum of the fikey
the mackrelj and the herritig ; three on that of
the carp, which has the middle one in the form
of a flyle. In the cody and other i\\troacby
the labrusy &c. the anterior extremity is rounded,
and has no points.

The proportional fize of this bone varies con-
fderably ; it is fmall in the eely the jlar-ga%er ^
the pleiirone&es, the doryi and the pike. Of a

H H 2 middling

468

Lect. XIII. Of the Ear.

middling fize in the herring ; and large in the
genus gadiiSy (particularly in the cody) in the
and a number of the thoracici.

Its general form is Oval in the cody and mofl
of the gadi } it is almoff round, with an inward
angle in the genus cyprimiSy as the carpy the
breaniy the tenchy the roachy and alfo in the genus
Jilurus: In the pike, the' falmoyiy and other /row/r,
and in x.\\z-jhirgeony &c. it is irregularly trian-
gular.

The furrow on the internal furface of the
bone appears to form, with an internal produc-
tion of the membrane of the fac, a fniaJI ca-
nal, which pafles through a part of the interior
of the fame fac : this furrow is commonly lon-
gitudinal ; fometimes it is fliaped like a horfe-
flioe ; it is almofl: circular in the carp. In the
cody its place is fupplied by an elevated ridge.

Some tranfverfe ftriae are almoft always ob-
ferved to extend from the furrow to the edge ;
they are intended to lodge the numerous ner-
vous filaments which fuipend the bone : thefe
ftriae arc more particularly confpicuous in the
carps y which have them radiatcil.

The denticulations on the edge of the bone
arc r?carly equal all round in the cod, and in the
carp, but the former has them blunt, and the
latter pointed ; they are found on one fide only
in fal mo tiy trouts, and perches. The congre

ccl has only three, which arc on the fuperior
niargin, &c.

The

Art. II. Membranous Labyrinth. 469

The fecond ofTicuIum of the internal ear of
filhes is ufually fituated behind the large bone,
but a little more outwardly j it is molt com-
monly of a femi. lunar form, the concave part
being turned forward ; it is of a particular lhape
in the carp, limilar to the head ot a Ipcar ; its
lize varies, but it is always much fmalLr than,
the fu ll.

The third ofliculum, we have already obferved,
is within the linus ; forneiimes it is fo near the
largcft of the bones, that it can fcarccly be dif-
tinguilhcd at firlt fight. In the genera gaJus,
fcombir, it is triangular ; in the trigla, len-
ticular. The pike has it rounded, and unequal.
It is proportionally larger in the carp^ than in
the other genera, and its furface is fcabrous,
and the edge ferrated.

CalTerius, who firlt deferibed the organ of
hearing in fifiies, conlidered thefe bones as ana-
logous to the malleus, incus, 6cc. of quadrupeds.

It has fince been conjectured, and Camper,
in particular, has Ihewn, that fubfiances thus
fufpended, in a tremulous gelly, which is cal-
culated to be put in motion by the llightelt ex-
ternal vibrations, may communicate the con-
culHons to the numerous filaments of the audi-
tory nerve, to which they are connedted.

A feptum is formed within the fac, by means
ol its internal membranes, united, with thefe'
ofiicula, and their nervous fibres : this firucture
induces us to conlider the facs as analogous to

H H j the

470

Lect. XIII. Of the Ear.

the organ, with two apartments, which is, in
man, called, from its form, the cochlea.

D; In Fijhes that have Jix'ed Branchice,

We find the fame parts as in the other fpc-
cies, but they are differently difpofed. The fi-
tuation of the fac is nearly horizontal, and its
figure is triangular. The angle which is
neareft the brain, is prolonged in a canal
which penetrates the cranium, and extends to
the external fkin, where it is clofed by only a
thin membrane: this fmall membrane may be
diftinguilhed without diffedlion, becaufe it
forms a fmall external depreflion near the nucha ;
it is, perhaps, analogous to the feneftra ovalis
in animals, of a more elevated order, and per-
forms alfo the fundlions of the tympanum.

The fecond angle of the fac is pofterior ; it
is round or oval, and contains the largefl of the
cretaceous fubftances. The third angle is di-
rected forward and outward, and the two fmall
cretaceous bodies are fituated near it.

There arc three fcmi-circular canals, each of
which has a bullular enlargement, or ampulla,
as in the other fiflies : one is anterior, and di-
rected obliquely forward and outward : the fe-
cond is external, and horizontal : the third is
poficrior, and fituated in a plane, which is al-
mofi: vertical, and directed backward and out-
ward. Thofe extremities of the three canals,

which

Art. II. Membranous Labyrinth. '47 1

which have no ampulla, communicate with the
internal angle of the fac ; the firft and the third
near the feneflra rotunda, and the fecond a little
lower. As to their other extremities, the firft
and the fecond unite, and communicate, by a
common canal, with the external angle of the
fac ; the ampullaceous extremity of the third
enters the fac feparately, very near the place
M’hence its other extremity arifes.

The whole of this organ is, as ufual, filled
with a gelatinous pulp. The folid parts con-
tained in the file do not refemblc thofe of the
olfeous fifties, w'ith refpeeft to their confiftcncc.
They are not harder than moiftened ftarch, and
may be bruifed by the fingers : the largeft of
thefe fubftances is rounded on one fide, and
comprefled and retfli- linear on the other; th^
two fmaller are nearly oval.- • •

All thefe obfervations are common to the rays
and fjarks. The fpecies of thefe two genera
dill'er from each other only in the proportion
of the canals and the fac ;• but the variations
thus produced are very unimportant.

t

' E. In Reptiles,

The membranous labyrinth in this clafs is, in
general, compofed, as in the fifties, of three ca-
nals and a fac : but there are fome fpecies which
have an additional part.

In t\\^ falamanders, whofe ear, like that of

H H 4 fifties,

472

Lect. XIII. Of the Ear.

fifhes, confifl-s of the labyrinth only. The three
canals are fituated above the fac ; they arc de-
prefTed fuperiorly, and form together a triangle
which is al molt equilateral ; each has its am-
pulla, and the fac contains a body of the con-
liflcnce of flarch, as in the rays and JJjdrks.

^ Frogs and toads differ very Uom falaman-
ders, with refpe6l to the membranous labyrinth;
they have the fame parts in the fame pofition,
and their fac alfo contains one amvlaceous fub-
Ifance : their three canals form nearly a com-
plete circle, by thdir jundlion with the fac.

Crocodiles and lizards have alfo three canals,
but they are larger, and each approaches nearer
Jo a perfedf circular form : the fac is fituated
proportionally more within the head; its mem-
branous parietes are furniflied wdth fevefal blood-
veffels, which arc particularly confpicuous in
the crocodile. The folid parrs it contains' are
three in number, and they are fmaller, and evcii'
fofter than thofe of the Chondropterygious filli-
es. Lallly, their labyrinth is rendered remark-
able, by having an additional part to thofe we
have already deferibed : this is the lirll: velligc
of the cochlea ; it is a produdion of the lac,
in the form of a cone flightly arched ; it is di-
rcfled, under the cranium, towards the middle
line, and is divided into two compartments, or
rather canals, by a double cartilaginous'feptum :
one apartment communicates with the fac ; the
other, which is a continuation of the lirll, re-
9 fleiiled

Art. II. Membranous Labyrinth. 473

flefted on itfelfi terminates at a very fmall hole,
which is doled by a membrane that feparates
it from the cavity of the tympanum.

This organ is precifcly limilar to that which
is found in all birds. Comparetti was the firlt
who deferibed it in lizards. It is very large in
the crocodile, and may be eafily prepared Irom
young fubjecls.

It is more difhcult to find this part in the ca-
mclion, and the marlled -lizard. A velligc ot it
may be obferved in ferpents . The produc-
tion which may be compared to this trumpet,
or rudiment of the cochlea in the tortnje, is
very limilar to the part wc named the fac,
flriclly lb called, in filhfes ; and this rcfemblance
conlilts not only in its form, but in the fmall
amylaceous fubliances it contains ; this feems
to leave no doubt of the analogy between the
fac and the cochlea in man, or of that between
the part we called the finus, and the veftibule.
VVe mull, therefore, judge of the perfection of
the labyrinths of thefe dilferent ears, by the de-
gree in which the cochlea is developed.

’Tortoifes and Jerpents have the femi-circular
canals, like the other reptiles. In the tortoife
they are proportionally very fliort.

The zvarm-blocd ayiimals have the labyrinth
always clofely enveloped by bones j and in ail
the fpecies, it is compofedof three femi-circular
canals, each of which has an ampulla j of a
finus common to thefe canals, called the vedi-

bule ;

474

Lect. XIII. Of the Ear.

bule ; and of an organ, with two canals or
fcala?, called cochlea, but which is not really
fpiral, except in the Mammalia.

F. In Birds.

The part correfponding to the cochlea in
birds, we have already obfervec^, refembles that
of the crocodile ; it is conical, llightly arched,
obtufe at the point, and fituated obliquely from
before backward, and from without inward, un-
der the inferior part of the cranium. The fcp-
tum, which feparates it into two fcalae, is com-
pofed of two narrow cartilaginous laminae,
united by a thin membrane throughout the
whole of their length, and (lightly twided on
themfelves ; they adhere weakly to the parietes
of the cochlea. The pofterior fcala is fhorter,
and communicates with the cavity of the tym-
panum by the fenefira rotunda, which is clofed
by a, membrane. The anterior and longer fcala
penetrates into the veftibule, and is not clofed.

The veftibule is fmall, and almoft round. The
femi-circular canals are difpofed in the follow-
ing manner : the largeff is vertical, and dircdlcd
obliquely from behind forward, and from within
outward : the fecond is horizontal, and dircdicd
outward : the third is vertical, crofles the fe-
cond, and takes a courfe which is the oppofite
of that of the firfl.

In the Paffercs the firft canal is fmalleft, and

fituated

Art. II. Membranous Labyrinth. 475

lituared farther back with rcfpedl to the other
two, than in other birds. The other differ-
ences are not important : they appear, however,
more confiderable in the birds of prey, parti-
cularly the no(5Iurnal kind ; and in the Pafleres,
than in the Gallinae and the Palmipedes.

In the cajfozvary and the ojiricb the cochlea
approaches more to a vertical pofition ; and of
all birds, the ojlrich has the fmalleft cochlea, in
proportion to the other parts. The goofc is the
fpecies in which it proceeds mofl: diredlly to-
wards the middle line.

G. In Mammalia.

The labyrinth of the mammalia does not
differ from that of other animals, except that
the cochlea is really formed w’ith feveral fpiral
turns round a conical axis, and may, therefore,
with propriety, be compared to the llieil of a
fnail.

The three canals are almoff: equal in vian ;
they do not crofs each other ; the horizontal is
rather the fmalleft ; the anterior, or vertical
canal, and the pofterior, are united at one of
their extremities; each of the three has a fmall
ampulla; the veftibule is a little rounded ; the
cochlea isfituated forwards, and a little inward ;
the plane of its bafe is almoft vertical, and di-
reefted obliquely from behind forward, and from

8 without

476

Lect. XIII. Of THE EaP..

■without inward. The breadth of the bafe docs
not exceed that of the horizontal canal.

The fpiral part forms two turns and a half;
it diminiflies rapidly, lo that the cochlea ap-
proaches, upon the whole, to a globular form.
As the axis is oblique, one fcala is anterior and
external, and the other internal and poflerior.
The internal, which is neareft the bafe of the
cochlea, is a little longer than the other, and
turns back, to terminate in the fenellra rotunda,
which communicates with the barrel, or cavity
of the tympanum. The external, which is
nearer the apex, extends to the veftibulum,
which is itfelf connetfled with the cavity of the
tympanum by the fenellra ovalis. The relative
proportions of the parts of the labyrinth vary
confiderably in the different fpecies.

In balSy properly fo called, but more par-
ticularly in ihchorfe-Jhoe hat^ the cochlea greatly
exceeds the ferni-circular canals in magnitude :
the breadth of the cochlea in the horJe-JJjoe bat
is four times greater than the circumference of
one of the canals, and the diameter of its cavity
is ten times longer than theirs.

This difproportion is much lefs confiderable
in the ternale bat.

In mofl of the Sarcophaga, and in the hog^
elephant y and horfe, the cochlea is alfo larger, in
proportion to the canals, than in man. But in
the mole it is fmaller. 'I'he hare has it alfo pro-

* portionally

'Art. II. Membranous Labyrinth. 477

portionally fmallcr than man. Its projioition
in the Ruminantia is nearly the fume as in man.
In all thcfc animals it has the fliape ot thofe
Iliclls which conchyologifls call turbinated,
that is, of a round or globular cone. The
number of the turns is as in man, two and a
half.

T\\c guinea pi?, the ru/’/u/, and x.\\c. pornipiury
have a turriculated cochlea, with three turns
and a half; thcfc arc the only examples 1 know
of this number. The r.it has, like the

other quadrupeds, only two and a half.

The cochlea is very large in the Cetacea, and
all its parts are well developed ; but the fpiral
part remains nearly in the fame plane, without
rifing upon its axis ; it makes, befides, only a
turn and a half. The femi-circular canals are
fofmall, that Camper long denied their exig-
ence. They are, however, in other refpeds,
fmilar to thofe of the rell of the mammalia,
and I have made a very perfccl dilTeiflion of
them in the foetus of the zvbale.

The proportion between the two fcalae of the
cochlea is not the fam.e in all mammalia ; that
which goes to the tympanum is fomewhat larger
than the other in man, the dog, the jloth, the ele-
phant, z\\QhorJe, the dolphin, bee. The differ-
ence is very remarkable in the hat. The fcalai
are nearly equal in the hippopotamus and the hog.
That which communicates with the veffibulum
is the largeft in the calf, the goat, the foeep, the

bare.

478

Lect. XIII. Of the Ear.

barCy the rat, the guinea pig, the cat, &c. But
even in thefe animals, the part of the 'fcala of
the tympanum, which is very near the feneffra
rotunda, widens and becomes broader than the
other.

In mammiferous animals in general, the la-
byrinth, confidered as a whole, is much fmaller,
in proportion to the reft of the head, than in
birds. It contains no folid parts in thefe two-
claffes ; we obferve only fome white parts,
which proceed from the expanfion of the extre-
mities of the nervous filaments, in the gelati-
nous pulp which fills it. Of thefe we ftiall
fpeak hereafter.

f

Article III.

Of the Manner in wh'ch the JMembranoun La-
byrinth is contained in the Bones, or of the
OJfeous Labyrinth.

The membranous labyrinth of vertebral ani-
mals is more completely contained in the bones>
and more clofcly embraced by them, in pro-
portion as thofe animals arc more perfeeft, and
poftefs ears, with which the external element
freely communicates.

A. In

Art. III. Osseous Labyrinth. 479

A. In Fijhes that have free Branchue,

The labynnth is conrained in the fame cavity
as the brain : the parietes of the cranium afford
only fome deprelTions for receiving it, and it is
retained in ihefe hollows by veffels and cellular
fubftance. Only a part of the femi-circular
canals is lituated in pulleys, or fliort offeous
canals.

In the tnoofy-jijl the large lateral dcpreflion of
the cranium, which contains the ear, is divided
by only two fmall cartilaginous columns, one
of which is horizontal, and furnifhes a pulley
to the poflerior femi-circular canal : the other
is vertical, and affords one to the horizontal
canal ; but as the interval between thefe columns
and the parietes of the cranium is ten times
greater than the diameter of the canals, they
are fufpended in that fpace by veffels and cel-
lular fubftance. The anterior vertical canal has
even no column of this kind, and there is no
deprelfion for the fac in the bafe of the cranium.

The cartilaginous columns become broader
in the frog-fiJ7jy and approach more to the
parietes of the cranium. In the offeous fifties
they are ftill farther enlarged, and there is con-
ftantly a certain portion of all the femi-circular
canals contained in others, which are formed of
bone. The pofterior and horizontal canals are
always more enclofed than the anterior ; the

latter

Lect. XIII. Of the Ear.

480

latter has only a fmall ofTcous pillar in the eel^
tne pikcy the roachy and the mackrcl. It has
merely a furrow' in the dory, and fome of the
jiigularcs. It has an ofleoiis canal, w'hich is a
little longer, in the cod and the carp : the other
two are almoft funk in the bones. In the Jalmon
and the carp the fac is commonly 'lituated in a
depreilion at the biafe of the cranium. In pro-
portion as the fac is farther removed from the
finus or veftibule,' the fofla, which receives it,
becomes deeper. This may be obferved in the
cody but particularly in the carpTund the herringy
which have the fac clofely enveloped in an
ofleous antrum, that has no outlet, except one
for the narrow canal, which joins the fac to the
finus. ' '

In all the olTeous fiflies, the finus, and the
extremities of the canals, are at liberty in the
cavity of the cranium, and the nerves have not
to pafs through bones in order to reach them/

In t\\Q. jlurgeotiy the ear begins to feparate from
the cavity which contains the brain.. The three
canals are placed in cartilages, throughout rhe^
whole of their length : the cartilaginous canals,
which receive them, arc fomewhat larger than
they arc;- the fac, to which they arc joined, is
clofely applied to the fide of the cranium ; and
between ir and the cavity for the brain, there is
a very thick membrane, connected by fevcral
ligamentous productions, and perforated by fc-
vcral holes for the palTagc of the nerves.

13. In

Art. III. Osseous Labyrinth. 481

#

B. In the C/iomIropt6ri/gu,

Or fidies that have fixed branchiir, as the
‘/ays and the jhavksy the whole of the mem-
branous labyrinth is cnclofcd in a particular
cavity, formed in the fubflance ot the cra-
nium ; this cavity is iituated on the lide ilnd
pofierior [xul of that which contains the brain,
with which it docs not communicate, <ixcept by
the holes that alTord pallages for the nerVes.

This cavity feems moulded upon the mem-
branous labyrinth itfelf; it is compofed, in the
fame manner, of three canals, and of another,
with which they join. But all thefe parts are
confiderably larger than thofe they contain, and
the latter do not adhere to the parietes of thefe
cavities, but are fufpended in them by vcfiels,
herves, and cellular fubllance. In confequence
of the iize of the external labyrinth, the ter-
mination of the membranous femi-circular
canals are fituated within the cavity which
contains the fac of the amylaceous bodies. The
holes, through which the nerves pafs, Corre-
fpond with this cavity on the internal fide ; ex-
ternally it communicates with the hole called
leneltra ovalis, which is clofed only by a mem-
brane, and by the Ikin which pafies above it.

I I

VoL. II.

C. In

482

Lect. XIII. Of the Ear.

C. In Reptiles.

The olTcous labyrinth of reptiles refembles
that of the Chondropterygii, that is to fay, it
envelopes the whole of the membranous laby-
rinth, but in a manner more or lefs clofely.

In the tortoife, the feptum which feparates
the veftibule froni the cranium, is not ofTified ;
it remains partly. membranous.

In the crocodile, and other lizards, the ofleous
labyrinth clofely embraces the membranous, or
completely covers it by a thin and hard lamina.

D. In Birds and Mammalia.

The membranous labyrinth in thefe clafles
is fo completely, and fo clofely encafed by the
bones, that its nature has long been mifunder-
ftood. It has moft commonly been regarded
as the internal periofleum of the cavities in
which it is contained. When obferved in a dry
flate, and flirivelled up into hard filaments in
thefe cavities, it has been deferibed under the
name of the nervous zones of the femi-circular
canals, or the membranous feptum of the vef-
tibulum.

Scarpa and Comparetti have, however, af-
figncd to this part its proper importance. In-
deed, when wc examine it in young and recent
fubjc(fts, wc find that it does not dilfcr from

Art. III. Osseous Labyrinth. 4S3

the analogous membrane in fiflies : that it is
really the eflential part of the labyrinth, and
that the olTeous cavities ferve only as its cafe.

Tiie oireous labyrinth of birds is formed by a
thin and hard honey plate, fo exa<ftly fitted to
the membriiious labyrinth, that \vc can even
diftinguifli in it the ampulla of the femi-circular
canals : as it is fituated in the fubfiance ot the
temporal and occipital bones, the two tables of
which are feparated by only a very open diploe,
which is eafily removed, it may, v. iihout much
trouble, be laid bare, fo as to a fiord a view of
all the parts.

Some of thefc parts, particularly two of the
femi-circular canals, are even viiiblc within
the cranium, without any preparation. The
auditory cells, of which we fiiall fpeak here-
after, and which form vacant fpaces around and
avithin the intervals of the labyrinth, render its
preparation ftill more eafy.

In mammalia, the labyrinth is ufually enve-
loped by the fubfiance of the pars' petrofa of
the os temporum, which is fo denfe in the adult
animal, that the two parts cannot be distin-
guiflied. The cavities which compofe the la-
byrinth, appear to be hollowed out in that pe-
trous fubfiance, in the fame manner as quarries,
or mines, are formed in rocks.

It is only in the foetus that the ofieous laby-
rinth can be difengaged from the fubfiance
w'hich envelopes it, and which has not then

I I 2 acquired

4§4

Lect. Xill. Of the EaR.

acquired the fame degree of hardnefs as the la-
minae, of which it is formed.

There arc, however, fome fpecies, and they
are of the number of thofe which hear befl:,
that have not the petrous fubftance around the
thin lamina of their offeous labvrinth.

In ihcmole, forcxample, thethree femi-circular
canals are difengaged, and vifible on the inte-
rior of the cranium, without any preparation.
The cochlea is enveloped by cellular ftrueflure,
almofl as lax as that of birds.

The enormous cochlea of hats is vifible, with-
out any preparation, under the bafe of the cra-
nium, where it forms a confiderable projeeflion,
fimilar to that made by the cavity of the tym-
panum, in a number of fpecies : their femi-
circular canals may be obferved within the
cranium, in the fame manner as thofe of the
mole.

In the hare-lipped bat {vefpertilio LepoyinusJ
the cochlea projeds within the cranium.

In i\\Q guinea pig (cavia cabayaj and in the
cabiai (cavia xapybara,) it projeds into the tym-
panum, under the two feneilriE, in the form of
a nipple. It has the fame appearance in the
marmot te the porcupine : and is more or Icfs

fimilar in all the Rodentia. It alfo projeds a
little within the tympanum in the elephant.

The Cetacea arc the animals which have the
fubfiance of the pars petrofa hardcfl.

Trom the deferiplion we have given of the

111 cm-

Art. III. Osseous Labyrinth. 485

membranous labyrinth, it will be eafily per-
ceived, that the ofleous vcftibulc niuft have five
holes for the extremities of the femi-circular
canals ; one for the fcala of the cochlea, which
communicates with it ; and one communicat-
ing with the cavity of the- tympanum, which is
the feneftra oval is.

We fliall not fiop to deferibe the differences
which occur in the fize, fhape, and relative po-
lition of ihefe feven holes.

The olfeous cochlea turns round a conical
axis; it may be compared to the fufee of a
watch; the proportions of its height and bafe
vary according to the fpecies. The fe(flion of
each turn of the olfeous cochlea is not round ;
there is, on each tide of the axis, a fharp ridge,
which is the fcclion of the olfeous part of the
fpiral lamina that divides all thefc turns into
two fcaliC,

In man, only that portion of the lamina
which touches the axis is olfeous ; the other
part is entirely membranous. The fame ftruc-
ture, however, does not prevail in all mam-
miferous animals. Inih^ dolphin there is only
one very narrow filfure, which divides the la-
mina, throughout its whole length, into two
parts ; that which touches the axis being three
times larger than the other. The filfure only is
completed by a membrane in the frelli Hate.

In the dolphin alfo, the olfeous part of this
Icptum, which to'uches the axis, has, under its

1 I 3 f?afe,

486

Lect. XIII. O F THE Ear.

bafe^ and in the fcala that joins the tympanum,
a imall canal, following the fame curvature
•from one extremity ot the cochlea to the other;
the tranfverfe feclion of this canal is round, and
its parietes are very flcnder; it might be re-
garded as forming a third fcala in the cochlea,
but it is probable that it ferves to envelope a
vefTel or a nerve; befides, its diameter dimi-
nifnes in the oppofite diredlion of that of the
fcalte,' and it is largeft towards the apex of the
cochlea. In the Ruminantia we alfo obferve a
fimilar canal, but proportionally much fmaller.

We have fufficiently defcribed the external
form of the os petrofum of quadrupeds, in Ar-'
tides 111. and IV. of Le6ture VIII. That of
• the Cetacea dcferves to be confidercd feparately ;
it is not articulated with the bones-of the cra-
nium, but is fufpended by ligaments under a
cavity, or vault, which is (ituated on each fide
of the bafe^ of the cranium, and principally
formed by the os occipitis.

The os petrofum may itfelf be confidcred as
formed of two portions foldered together, viz.
the cavity of the tympanum, which wc fhall
deferibe at the end of the next Article ; and
the petrous part, properly fo called, which
contains the labyrinth.

Thc'fupcrior furfacc of this fecond portion
has, towards its internal edge, a femi-circular
eminence, which correfponds to a hole in the
bafe of the cranium, and where wc obferve a
8 deprefiion.

Art. III. Osseous Labyrinth. 4S7

deprcfTion, which is the internal meatus aiidi-
torius. The cochlea is fuuated in this eminence.
The external portion ot the os petrofum is con-
fiderably larger than the eminence we have juft
pointed out ; it partly forms an arch above the
cavity of the tympanum ; it is oblong in the
dolphins. In the cachalots it is coarfely rounded,
and prolonged backward into a fcabrous procefs.
The Limanlin has it deeply bilobated.

We fliall now briefly notice the aqn^rduHs.
Thefe arc two canals, which form a communi-
cation between the labyrinth and the interior
of the cranium, different from that which affords
a paffage for the nerves ; one goes to the vefti-
bulum, near the common orifice of the two
united femi-circular canals ; its orifice, on the
fide of the cranium; is triangular, and fituated
above and behind the meatus auditorius internus :
the other arifes from the cochlea, at the fcala
tympani, very near the feneftra rotunda, and
opens into the cranium, under the inferior edge
of the os petrofum, and below the internal
meatus : thefe aquteduefts are found in all the
mammalia. They are very large in the dolphin^
particularly that of the tympanum.

In fome other mammiferous animals, as the
elephant and the horje^ the laft du(5l forms only
a narrow fiffure on the ftde of the cranium. I
have not fufficiently examined them in the other
fpecies of this clafs.

I14

Accord-

488

Lect. Xiir. Of the Ear.

According to Comparetti, two analogou?
canals are found in birds, but their ufe appear5
to us flill doubtful.

Article IV.

Oj the Cavities Jituated between the Labyrinth
and the extei'nal Element ^ or, Of the Cavity of
the Tympanum, and its Appendages.

Im the fijhes with free hranchice, whether carti-
laginous or boney, the labyrinth has no com-
munication externally : all the parts of the ear
are, inclqfcd within the cranium, and covered
by the bones.

In the fiJhes with fixed hranchiu’, or the
Chondropterygii, the labyrinth communicates
by a fmall canal, with an aperture fituated be-
hind the head, and clofed by a membrane and
the fkin : there is nothing befides this between
the ear and the furrounding element.

Among the reptiles, the falamandcr has the
labyrinth completely enclofed within the cra-
nium, and deprived of all 'external communi-
cation, as in the (iflics that have free branchiae:
but the other genera of the fame order have all
a fenedra, called oval, fupi)orting an on'eous
plate, analogous to the bone, called dapes in
• ' . man.

Art. IV, Cavity of the Tympanum.

man. The lizard genus has another aperture,
but which is clofed only by a membrane, and
which receives the name of fenejlra rolunda.
Thefe tw’o apertures cxirt in all birds, and in all
quadrupeds, as has already been (liewn.

The cavity, which is fituatcd anteriorly, and
which is more or lefs complicated in diUcrcnt
animals, is called the barrel ^ of cavity of the
tympanum ; it communicates with the mouth by
a canal, or by a fimple wide aperture, called
the Eujlachian tube : another aperture affords a
communication with the external element ; it
is fometimes fliut by a thin membrane, at other
times covered with a thick, or even fcaly fkin ;
thefe parts arc called membrana tympani.

The offcous plate, which covers the feneflra
ovalis, is connedled by a handle-like produc'tion
of a fingle piece, or by a chain of olTicula, ar-
ticulated with each other, and with the mem-
brane of the tympanum, and may therefore
communicate the imprellions received by the
latter, to the interior of the veftibulum.

The cavity of the tympanum forms the fub-
jed of defeription in the prefent Article.

A. In Reptiles.

The barrel, or cavity of the tympanum, cannot
be faid to cxift in ferpents : the ftalk of the plate
is furrounded by the flefh, and its extremity

touches^

490

Lect. XIII. Of the Ear.

I

touches the fkin, near the articulation of the
lovvcr jaw.

In toads and frogSy the whole of its poflcrior
part is membranous ; it communicates imme-
diately, with the back of the mouth, by a large
hole, which may be feen on opening the mouth
of the animal. It is very fmall, and almoft
entirely membranous in the pipa, in which the
labyrinth is connedled with the feneftra ovalis
by only a very long canal.

It is alfo membranous pofleriorly and infe-
riorly in the common lizards y and in the ca-
melion ; it communicates with the bottom of the
palate by a fhort wide canal.

V The barrel of the crocodile may be divided
'into two parts : one external, which is very
wide, and clofcd on the outlide by the mem-
brane of the tympanum, and the fkin, but en-
tirely furrounded by the bones ; and one inter-
nal, which is feparated from the former by a
contradlion, and which communicates with the
two feneflra, and with fome cavities analogous
to the mafloid cells of man, but much larger:
one of thefe cavities is placed between the femi-
circular canals, and the other is direc^Icd back-
ward and outward; the barrel is lituated towards
the fuperior part of the cranium.

The cavity of the tympanum in the tortoije
is placed more laterally; it is not fo wide ex-
ternally; and the contradion, which feparates

the

Art. IV. Cavity of the Tympanum. 491

the external part from the internal, is lefs con-
fpicuous, becaufe the proje^Tion, which it forms,
is rounded, and not acute, as in the crocodile.
The internal portion is prolonged backward, in
the form of a large round cell : in the bottom
of the cavity, oppofitc to the membrane of the
tympanum, there is a narrow canal, in which
the odiculum is funk, and which communicates
with the fenchra ovalis. The Euflachian tube
is a canal of a moderate length, which proceeds
downward, and a little backward, and termi-
nates in the palate, behind and within the arti-
culation of the jaw.

1). In Birds!

The cavity of the tympanum is alfo very wide
on the outer part, in birds : its pofterior and
inferior parictes are formed by a proje(51;ion of
the os occipitis : the anterior is, in a great
meafure, completed by a bone peculiar to birds,
called os qiudratum. We fliall deferibe this
bone when we treat of the articulation of the
lower jaw.

It communicates with three large cavities,
which are more or lefs prolonged into the fub-
ftance of the bones of the cranium, and which
particularly charadlerize the organ of hearing
in birds. Thefe cavities, being inclofed by
thin and claftic ofleous lamina, are doubtlefs
very fonorous, and confiderably augment the

eftecl

492 Lect. XIII. Of the Ear;

effecfl of found, with refpecft to the labyrinth,
Avhich they furround on all fides. In the owl
genus, particularly in the zvhite otvl (Jlrix Jiam-
. viea)^ they are more cxtenfive than in any other
birds ; the firft opens into the fuperior part of
the tympanum, and extends through the whole
breadth of the occiput, as far as the correfpond-
ing cavity of the oppofite ear, with which it
unites above the foramen magnum ; the fecond
enters the barrel at its pofterior and inferior
part ; this cavity extends only between the femi-
circular canals, and is the fmalleft of the three;
the third communicates w’ith the anterior part
of the barrel of the tympanum, above the
Euflachian tube : it paffes above that tube, and
extends through the breadth of the bafe of the
cranium ; it unites with the cavity of the other
fide, under the part which contains the pituitary
gland : thus the barrels of the tympana, in the
white owly communicate by two different chan-
nels: the third cavity furrounds the part ana-
logous to the cochlea.

This vaft extent of cells, attached to the
barrel of the tympanum, is found in the zvbite
ozvl only. In the other comffion and horned ozvls,
the cavities are a little contradlcd, and they di-
mini Ih more and more down to the caffowary and
the ojhich, which, of all birds, have them the
fmalleft. The goat- fucker^ a nodurnal bird, to
which a quick fenfc of hearing is nccclfary, has
them very large. Diurnal birds of prey, and

Art. IV. Cavity. OF THE Tympanum. 493

the Gallinje, have the firft cavity, and the third,
in the form of a narrow conical tube, without
any communication from the one fide of the
head to the other : the fecond, or that between
the femi-circular canals, is larger in the diurnal
birds of prey than in the owls, becaufe they
extend outward, behind the pofierior edge of
the barrel ; thefe cavities are generally fmall in
the An feres and Grallte. They appear to be en-
tirely wanting in feveral fpecics of parrots^ in
which the internal fubfiance of the bones of the
cranium is uniformly a very loofe diploe : their
tympanum, however, has a more confiderable
concavity pofieriorly, than that of other birds.

The Euftachian tube is completely olTeous in
birds ; it is a conical canal, which commences
at the anterior and inferior part of the tympa-
num, by a large aperture, and which paffes
under the third cavity, deferibed above, from
which it is feparated by only a thin lamina ; it
proceeds obliquely inward, contrauling gra-
dually, and terminates in a fn;ail aperture very
near the middle line, and confequently alfo very
near the tube of the other fide ; thefe two aper-
tures open into the palate behind the internal
nares.

The two feneftra, by which the labvrinth of
birds communicates with the cavity of the tym-
panum, are fituated one above the other, in a
depreflion oppofite to the membrana tympani ;
an olTeous bar feparates them. The fenefiia

7 called

+94

Lect. XIII. Of the Ear*.

called ovaliSi or that which communicates with
the veftibulum, is above the feneflra named
rotunda^ which communicates with the cochlea;
but they are both of an oval fhape ; the fenehra
rotunda is the largeft, and frequently exceeds
the fize of the other conliderably.

C. In Mammalia.

The cavity of the tympanum, in mammife-
rous animals, prefents very remarkable differ-
ences, as to dimenfions, form, ftrufture, and
internal arrangement.

In man this cavity forms almofl a hemifphere,
and the membrane may be regarded as its great
circle ; it neither projedls without nor below
the cranium ; its parietes are very unequal ; that
w’hich is oppofite to the membrane of the tym-
panum, has an angular elevation, which afeends
obliquely from before backward, and which is
named the. promontory. The fenejlra ovalis is
above it : the longeft diameter of this fcneflra is
tranfverfc, and almoft double the fmallcr ; it is
cxadly oppofite to the membrane of the tym-
panum : the fenejlra rotunda is below the pro-
montory ; it is diredlcd a little downward and
backward ; they arc both a little funk. There
are fome flight excavations in tlic barrel of the
tympanum, which might be compared to the
cells of birds, but could only be regarded as
very minute veftiges of them ; they are not

fimilar

Art. IV. Cavity of the Tympanum. 495

fimilar in all individuals ; there is one above
and before the oval fenefira, and another behind
the round ; the latter communicates in adults
\vith the cells, which are formed, at a certain
age, within the maftoid procefs of the temporal
bone. The Eudachian tube begins at the an-
terior and inferior part of the barrel, by a hole
which is nearly round ; it firft forms an ofTeous
canal, which is dire(ded downward and inward,
towards the point of the os petrofum, where it
is narrowed ; it is contiriued from this place as
a cartilaginous canal, which is enlarged, as it
advances, and terminates in the back of the
mouth, near the internal pterygoid procefs, and
confequently near the podcrior orifice of the
nares of the fame dde, by a wide aperture, like
the end of a trumpet, the edge of which forms
a proje(5ling burr, or roll. .

1. 'External Form of the Cavity of the Tym-
panum in Mammalia.

Amongd apeSy lh(t guenons and the maggots have
not the os petrofum more prominent under the
cranium than we obferve it in man, and the bar-
rel, or cavity of thetympanum, remains concealed
within it : the madoid procefs becomes very
fmall, or is almod obliterated ; but the madoid
cells extend farther into the red of the temporal
bone.

In the other mammiferous animals, beginning
with thQfapajouSy the barrel increafes confider-

ablv

4

4p6 Lect. XIII. Of thf Ear.

ably in fize, and forms a large protuberance
under the cranium.

This protuberance is oval; and its great axis
is longitudinal in the fupnjous, badgers^ civelSt
and tnartins.

It is a little rounded, and its great axis is di-
red:ed obliquely inward, in dogs, cats, and coatis*

It is almofl: round in hares and beavers.

It is femi-fpherical in ternate^ bats and pan-^
golins.

It is-more or lefs angular in the Ruminantia,
the cabiai, the Jloth, the hippopotamus, the ele-
phant, and the rhinoceros.

It is plain in the mole, and touches that of the
other fide, which , makes the cranium appear
fmooth infcriorly.

In the ant-eaters, the floor of the noflrils
being continued between the two barrels, their
projecflion, under the cranium, cannot be ob-
ferved.

In the bear there is no protuberance.

In the ^^7^' there is a long projeeflion, like a
fac or a club, which is niofl: contraefled at the
part joining the cranium.

In mofl: of the digitated mammalia there is
no mafloid procefs, except a flight protube-
rance arifing from this projeifiing part of the
barrel, or the barrel itfclf fupplies the place of
that procefs : but in the cabiai, the guinea-pig,
hogs, the Ruminantia, and horfes', there is, be-
hind the tympanum, a long procefs, which an-

fwers

Art. IV. CxYiTir of the Tympanum. 497

fvvers to the mafloid. It belongs, however, to
the occipitai bone.

In moH: of the Sarcophaga and Rodentia, the
parietes which form this projection are thin,
hard, and leave a large vacancy between them.
In bogs, on the contrary, the whole of the in-
terior is compact and cellular.

In the Carnivora and the Rodentia, the fur-
rounding lamina which cnclofes the cavity of
the tympanum, is distinguilhed from the re(t
of the os petrofum by a future, and is not united
to it mifil thefe animals reach an advanced age.

In cats and civets it is itfelf fubdivided into
two parts by another future : the poflerior por-
tion has much refemblance to a cochlea, and,
except the difference in thicknefs, is perfeffly
reprefented by the barrel of the vcbale.

£. Intcnml Divifion of the Cavity of the Tym-
paaam, and ^^aJioid Ctlis.

The oval frame which fupports the membrane
cf the tympanum, is almort parallel to the op-
■pofite fide of the cavity ; it correfponds nearly
to the middle of that lide in the monkey.

the deg, the badger, zvcajles, Rodentia, Runii-
nantia, &r. In all thefe animals, the promon-
tory correlponds to the middle or pofferior part
of the tympanum ; but a fpace always remains
bet ween it and that membrane ; and the parts
of the barrel fituated before and behind the pro-
montory, arc not fepaiated in a marked manner.
VoL. 11. K K In

49^ Lect. XlII. Of the Ear.’

In the cat and civet genera, however, there
is an ofTeous procefs, which extends from the
poftcrior and inferior edge of the frame of the
membrana tympani, to the promontory, and
M'hich, being prolonged obliquely, divides the
barrel into two unequal parts that communicate
together only by a hole. The anterior and ex-
ternal cavity is the barrel of the tympanum,
properly fo called, and contains the oflicula and
the feneftra ovalis. I'he other part, which is
much larger, contains the fenefira rotunda. In
the lion, this fenedra correfponds precifcly to
the line of feparation, and is fituated at the hok
by which the two parts communicate. The
poderior part may be regarded as analogous to
the large cells of birds, and it appears to be
given only to animals that arc remarkable for a
quick fenfe of hearing.

In a number of Sarcophaga, and even in thofe
1 have named, there is another odeous ridge,
but not fo broad as th<e former, and tranfverfe ;
it appears to ferve merely as a fupport to the
frame of the membrana tympani. The horfe
has a number of fimilar pieces.

In the fapajous and the ant-eaters, the cavity
has alfo an additional cell formed by an odeous
feparation ; but this cell is fituated before the
cavity of the tympanum, properly fo called, or
that part to which the membrana tympani be-
■longs. Thc77o/I> has a £cll at tiic bafe of the
zygomatic arch.

'1’1)C

Art, IV. Cavity of the Tympanum, 499

The barrel or cavity of the tympanum in the
elephant, has no feptum ; but its Tides are fiir-
nilhcd with a great number of prominent la-
minae, which crofs each other in every direc-
tion, and produce a multitude of irregular cells
and rinuTes. Wc find the vefUges of limilar
cells in the irregularities and deprclTions of the
barrel in feveral Rodentia, particularly the ca~
hiai, the guinea pig, the marmotte, and the por-
cupine.

In the hippopotamus, the baird, properly To
called, is extremely Tmall ; but it communi-
cates by a hole with another cavity, divided in-
ternally into a great number of irregular cells,
analogous to thofe of the lion, civet, &c.

In the feal, and the morfe, file cavity of the
tympanum is very large, rounded on every Tide,
and undivided.

•. Form and Froporlions of the Feue ftra Oralis,
and Fenejira Rotunda.

We have already Ihewn, that the fencllra
rotunda, which communicates with one of the
Tcalre of the cochlea, is only clofed by a mem-
brane. As it is always direfted backward, we
may fuppofe that it is chiefly defined to receive
^he founds produced by the refonnance of the
pofterior chamber of the barrel, which we have
juft deferibed, and which is To diftindt in noc-
turnal animals, the cat, th^e lion, &c. Scarpa

K K 2 confiders

500

Lect. XIII. 'Of THE Ear.

confiders this membrane of the feneftra rotunda
as a fecond membrana tympani.

In Man, the fhape of thcfe two feneftrze is
conformable to the names which are given to
them, though they are not perfectly regular.
The oval feneftra is a little larger than the round.

In the other animals the variations are focon-
liderable, both with rcfpecft to figure and di-
menlions, that the terms, oval and round, are
no longer applicable: we fliall fubftitute in their
Head, the iinmz^fenejlra vejlihularisy 2inA fenejlra
cocblearh.

Monkies have them fimilar to thofe of man.

In batSy the fenefira cochlearis is the largeft.

Both feneftrae are oval in the mole : a bar ex-
tends from one edge of the feneftra veflibularii
to the other, and palTcs between the legs of the
flapcs. This occafioned the mifiake of Derham,
who believed that the flapes of the mole had no
plate, but that oftc of its legs refied on the fc-
nefira ovalis, and the other on the fenefira ro-
tunda. The fame flrucflurc is found in fevcral
other mammiferous animals. In the marmottey
the ofieous bar, which pafTcs between the legs
of the fiapes, is fo thick, that when the latter
bone is removed, there appears to be two fc-
nellra^ vcftibiilarcs : this bar is always hollow,,
and affords a paffage for fomc veffcls.

In the Sarcophaga, tlic fcnefha cochlearis i%
commonly the largcll » it is nearly double the

fize

Art. IV. Cavity of the Tympanum. 501

lize of the other In cats and civets. The ermine
has them almofl: equal. In the opojfum, the fe«-
neflra veftibularis is round ; the cochlearis is
irregular and fmaller.

In the beaver and the marmottey the latter ii
triangular. In the hare it has the form of a
fmall, and almoft perpendicular filTure. The
vcftihularis is round, and much larger.

The guinea pig has them nearly equal, both
dire(5led upward, and feparated only by a thin
bar.

They are both oval, and nearly equal in the
Edentata.

In the Ruminantiathe cochlearis is thelargeff.
The calf has it nearly double the fizc of the
other. It is alfo twice as large, and fuuated
very near the other in the hog. It is three times
larger than the veftibular hole in the hippopota-
mils. In the elephanty on the contrary, it is
very fmall, irregular, and concealed behind an
elevation of the promontory.

The cochlear feneftra is largefl in the Solipeda
and the Cetacea.

4. Eiijlachian Tube.

TheofTeous part of this tube prefents few dif-
ferences that are remarkable in quadrupeds.
That part is (horter in the Sarcophaga than in
man. In cats and civets it is rather a narrow
fiffure, than a canal : it might be reprefented
as a vamnt fpace in the future, which unites

^ ^-3 the

502

Lect. XIII. Of the Ear.

the bone of the barrel to what fliould be fIri<5U)r
called the pars petrofa.

The otter, the badger, and the zvcazle, &c.
have a firnple hole, feparated from the rell; of
the cavity of the tympanum by a projedling lon-
gitudinal ridge. In the bare, the origin of the
tube within the barrel is a triangular foramen.
In the cahiat it commences by a half-formed
canal, which becomes complete in piercing
the point of the os petrofum.

In the elephant it is a long ahd wide canal,
■which begins under the membrana tympani, and
terminates at the point of the os petrofum; its
parietes are fmooth, and have no cells.

We have not yet fufficiently examined the
cartilaginous part of the tube in quadrupeds to
enable us to deferibe it.

In the horje, the.lower end of the cartilagi-
nous tube opens into a large membranous fac,
fituated at one fide of the back of the mouth ;
this fac, on fome occafions,- is filled v»4th pus,
and then produces a dangerous prclfure on the
pharynx.

1). Parikiilar Defeription of the Barrel, or
Caviti) of the Tpmpamim, in Cetacea.

The cavity of the tympanum in the Cctacca
deferves to be deferibed fcparatcly ; it is formed
by an olfcous lamina, which has the appearance
of being rolled upon iCfclf, and which, with

refpedt

Art. IV-* Cavity of the Tvmpanum. 50J

rcfped to its figure, may be compared to the
flidl, called oiiila^ except that the thick fide,
infccad of containing a fpiral cavity, is entirely
i'obd : this thick part is internal ; it is more
than two inches thick in the cachalot its edge
is blunt and rounded ; the oppofitc lide is
thinner, and its edge is irregular ; the membrane
of the tympanum is lituated between two ol its
procelfes ; this barrel adheres to the os petrofum
by its poJflcrior extremity, and by a procefs of
the anterior part of its thin edge. In the t/o/-
"phinsy the anterior procefs of the barrel alfo
afeends to the os petrofnm ; but in the cachalots
it does not reach that part. The anterior ex-
tremity of the cavity is entirely open, and there
the membranous tube commences ; this tube
afeends along the pterygoid procefS) and perfo-
rating the os maxillare, terminates at the fupe-
rior part of the nofe. This pofition of the ori-
fice, as well as the fizc of the tube, muft render

it more ufel'ul than the meatus externus to the

%

Cetacea, in diflinguifliing founds. In treating
of the fenfe of fmelling, we fhall fhew that, by
a ftruclure not lefs lingular, the Euftachian tube
alfo conveys the odoriferous emanations to the
place vhcre that feiife refides.

The aperture by which this tube communi-
cates with the nofe, is furnifhed with a' valve,
which does not permit the water to enter when
the animal ejefts at by the blow holes.

K K 4

Arti-

i04

Lect. XIII. Op THE EaP.

Article V.

Of the Membrane of the Tympanum, and its
OJfcous Frame. /

The membrane, which clofes the external aper-
ture of the barrel, and which immediately re-
ceives the vibrations of the air, and tranfmits
the imprcflions to the internal ear, is called
Irana tympanic or fometimes limply tympanum,

1. Suhfance of the Membrana Tympani.

Animals which want the barrel of the tym-
panum, as fifhes, falamanders, bzc. have no
membrana tympani. That membrane is alfo
wanting in feveral reptiles that have a barrel, as
the camelion : the fkin pafles over the external
aperture of their ear, without undergoing any
change, cither in its thicknefs or its Urudurc,
and the cxiflcncc of the organ of hearing can
only be afeertained by difTccIion. On removing
the fkin, and fome portions of the mufcles, we
find, in fome fpecies, and particularly in the
Jloiv worm (anguis fragiUs) a kind of membra-
nous expanfion.

In the tortoife, the large external aperture of
the barrel is clofed liy a very thick cartilaginous
plate, which is itfelf covered by a fcaly fkin,
perfcillly fimilar to that of the rcfl of the head.

Z In

A. V. Membrane of the Tympanum, &c. 505

In frogs toadSy the membrana tympani is
on a level wkh. the head, and the Ikin that
covers it becoming finer, it is rendered percep-
tible by an oval fpoc, which is fmoother than
the reft of the head, and ufually of a particular
colour.

In common lizards, the membrana tympani is al-
fo level with the head, but very thin, fmooth, and
tranfparent, for at that part the fkin becomes as
fmooth and fine as on the cornea of the eye.

In the crocodile, it is of the fame nature, but
more funk into the head, and covered by two
flefliy lips, which fupply the place of the ex-
ternal car.

All warm-blooded animals, birds. Cetacea, and
quadrupeds, have, like man, the membrana tym-
pani thin, tranfparent, dry, elaftic, more or lefs
funk into the head, and preceded by a canal, to
which, in fome of thefe animals, is fuperadded
the concha, or external ear.

Notwithftanding its fine texture, the mem-
brana tympani is at lead divided into three la-
mina : one, which is proper to it; one internal,
which is the continuation of the internal mem-
brane ot the barrel, and which is itfelf derived
from that of the mouth ; and one external,
which is a produiftion of the fkin.

2. Surface and DireBion of the Membrana
Tympani.

The membrane of in an, and all other mam-

miferous

Lect. XIII. Op THE Ear.

5-6

mifcrciTs animals, has a conical furface, the
point of which is directed inward, and the con-
cavity outward ; this cone is very wide, and its
apex does not correfpond to the middle of its
bafe. The mole^ however, forms an exception
to this rule, as its membrana tympani is plane.

In all birds, the difpofition is the contrary
of that of the mammalia : the apex is on the
outer part. *

In lizards, though the point projedls lefsthan
in birds, it is alfo direifted outward. It is nearly
plane in frogs and tortoifes.

The membrana tympani is on a level with the
adjacent parts of the head, and confcquently
is nearly vertical in all animals in which its fi-
tuation is fupcrficial ; but in thofc which have
it funk, its inclination, whether confidered with
relation to the head itfclf, or to the external
meatus, varies confiderahly. We fliall confidcr
it with refpccfl to the head, which mufl: be fup-
pofed upright, and the plane of the palate ho-
rizontal.

The membrane of the tympanum inclines
obliquely upward, and to one frde in the croco-
dtU : obliquely downward, backward, and la-
terally in moft birds; and even more downward,
in proportion as the bird hears weak founds
more dillindtly. In the owl it is, therefore,
very oblique. It is more vertical in thc^o^
and the parrot,

Jn quadrupeds, the manbrana tympani is

ulfo

A. V. Membrane or the Tympanum, ^c. 507

alfo more oblique, with refpcd: to the external
canal, and inclined niore downward, in propor-
tion as the animal hears better. The mole, which
has the fenfe of hearing very delicate, notwith-
fianding the want of the concha, has the mem-
brane almofb parallel to the bafe of the cranium,
and anfwering as a floor to the barrel of the
tympanum : this difpolition doubtlcfs takes

place, in order that the membrane may be ren-
dered more cxtenlive. Another rule may,
therefore, be deduced from obfervation, name-
ly, that the larger the niembrana lympani, all
other circumlfanccs being equal, the more acute
is the fenfe of hearing.

In otf^'rs, zvciizels, and badgers., the membrane
of the tympanum is almoft as oblique as in the
mole. Jt is alfo very oblique in the -haitgolin.

It is nearly vertical, and diredled forward, in
man, apes, dogs, cats, civets, and coatis.

It is almofl: vertical, and turned diredlly to-
avards the lide, in hares, caliais, marmott et, and
the greater number of Ruminantia.

S. Frame, of the JMembrane of the Tympanum.

The membrana tympani is attached to an
olfeous circle, which is called its frame. This
frame forms the extremity of the meatus audi-
torius externus, next the barrel, and is that por-
tion of it which’ firR oRifies ; it is nearly round,
and makes only a flight projedlion inward, be-
fore which there is a furrow in man. In a great

number

5o8 .

Lect. XIII. Or THE Ear.

number of mammalia, it forms a projecfliou
M’ithin the barrel, which rcprefents a narrow"
plate, circularly or elliptically twilled, one of
the edges of which is attached to the external
part of the barrel, and the other is unconnected.
This free edge is more or Icfs fliarp and wide,
according to the fpecies ; it is frequently fuf-
tainedby fome prominent fpines, which proceed
from different parts of the barrel, and join it
perpendicularly. We have already noticed them
in the laft article.

This projecting frame is not perfectly com-
plete. A fegment, which, according to the
fpecies, is a greater or lefs portion of its cir-
cumference, is almoft conftantly wanting to-
wards the upper part. The guinea-pig.^ the paca^
the fealy and the ant-eatery arc the only animals
in which I have obferved it entire. In the lat-
ter, however, it projeCts fo little, that it is diffi-
cult to diftinguifli w'herc it terminates.

It wants almoft the whole of its upper quar-
ter, in the caty the dogy the rabbity and the rat.
The part wanting is rather propqrtionally
fmaller in the Ruminantia and the Solipeda.
The elephant wants all the upper half.

• The figure of the frame i^ commonly an oval,
with the great axis defeending obliquely for-
ward, and the anterior arch Icfs convex than
the poftcrior. 'fhis oval is more oblong in the
Sarcophaga than in herbivorous quadrupeds,
it approaches a circular form, and has its Tides

almoft

A. V. Mkmbrakb of the Tympanum* 509

almoft equal in the guinea-pig and the paca :
next to them the rabbit has it moft regular.

and*the ani-eater have italmoft circular.
It is pcrfedly round in the mole.

In the Cetacea, the membrane of the tympanum,
properly fo called, has no frame ; but the bar-
rel has three procefles, which produce irregular
liotches in the aperture, and give it the figure
of three unequal lobes.

In birds the frame of the membrana tympa-
ni is not fo well defined as in quadrupeds,
and docs not proje(fl within the barrel. In fomc
fpccies, as ihte while oui, it is complete: others,
and frequently very nearly allied fpecics, as the
great-horned owl, have it interrupted at its an-
terior part, and the membrane is attached to
the fquare bone for the articulation of the lower
mandible, a procefs of which, as w'C have al-
ready obferved, always forms a part of the an-
terior parietes of the barrel, or cavity of the
tympanum.

The figure ot the frame of birds is alfo an
oblique oval, the great axis of which defeends
obliquely forward ; but it ufually approaches
more to the round form than in quadrupeds.

The direction of the great axis is lefs forward
in feveral pafieres ; but all thefe differences are
of little importance.

In reptiles, the frame is not marked by any
prominent edge ; it is interrupted pofterigrly'..
Its great axis is vertical in the iorloijc and the

commoa

510

Lect. XIII. Of the Ear.

common lizardsy and its anterior arch is more
convex. In the crocodile it is a regular oval, the
great axis of which is diredted oblii^ucly back-
ward.

Article VI.

*

Of the OJficula which efahUfi a Communicaticm
between the Membrana Tympani and the Fe-
neftra Ovalis, and of their Mufcles.

I. Of the Bone.<>.

A LL the animals which have a real fenC'ftra
veftibularis, have it clofcd by an olTeous plate of
the fame fliape. This plate communicates by a
pedicle or ftalk with the membrana tympani^
or, when that membrane does not exift, with the
Ikin, or parts near it. The ftalt is fometimes
fimple, and forms, with the plate, only one and.
the fame ofTiculum ; fometimes the communi-
cation is maintained by two or four little bones
of very different figures. This chain of oflicula
is moft complicated in the Mammalia, and
with them we fliall commtnce our defcripcion.

A. Jn Mammiferous Animuls.

All the Mammalia have four oflicula, which
arc named Malleus, Incus, Os Lcnticulare, and
Stapes.

The

Art. VI. The Ossicula. 511

The malleus is always formed of an elongated
handle, which is thin and pointed, and whicK
^adheres to the meinbrana tympani, in the di-
redlion of a line extending from the fuperior
edge of that membrane to the apex of its cone ;
and of a head which makes an angle with the
4iandle, and extends backwards and a little up-
wards within the cavity of the tympanum. .

The joins the l^ad of the malleus by an
arricLilar furface. Its oppolite part is divided into
two points'; one proceeds dircdtly backward ;
the other (iefeends in a direction nearly parallel
to the handle of the malleus, but a little moie
backward and inward. The extremity of this
fecond procefs articulates with the ojjkulum Icis-
ticulayey which is the fmallefl bone in the body
of mammiferous animals, and by it with the
Jlapes. The latter takes its name from its figure,
w'hich is that of a Itirrup. It forms almoll a
right angle with the branch of the incus which
lupporis it, and proceed ing^direcily inward, ap-
plies its oval plate or bafe to the feneftra ovalis.
Each of thefe bones varies in its fize, figure,’
' and pofition in the difrerent fpccies. Wc lhall
examine fome of thefe varieties.

1. The Malleus.

In man, the handle of the malleus, or hammer,
is nightly comprefied, and bent a little, in fuch
a manner that its point is directed obliquely
forward ; the head is a- little fliorter than the

« handle.

✓

LecT. XIII. Or THE EaT^'

handle, and forms with it an angle of 120 de-
grees ; it is terminated by an oval mafs, rounded
at the end, the pofterlor fide of which prefents to
the incus an articular furface, compofed of four
fmall planes. At the angle, formed by the head
and the handle, there is a fmall fpine direefted
upward, which is called the Jhort procejs of the
malleus. The neck, or portion of the head,
which is a little contracted, has anteriorly a
flcnder procefs, which is prolonged like a ftile,
and which is named proceJJ'us gracilis: behind
and above the neck there is alfo a fmall lamina
projecting obliquely.

The malleus of the docs not differ

from that of man, except in having, the head a
little more pointed.

In the fapajou the head is one half fhorterthan
the handle. The articularTurface occupies the
whole of the pofterior part. The proccfi'us
gracilis is continued in a plate, which extends
along the whole of the anterior edge. It is very
confpicuous in the guenons ; but in them the head
is alfo in a right line with the handle, and foims
a projection forward. It is not diflinguilhcd
from the handle in the fimia beelztbul, except
by its fudden enlargement.

In dogs and cats^ the handle has the figure of
a long pyramid with three Tides, the narroweft
of which adheres to the membrana tympani.
The angle, which the head forms with it, is as
large as in man ; the neck flcndcr, and turni;

forward ;

Art. VI. The Ossicula.

513

forward ; but the procefius gracilis, or anterior

apophyfis, .which is very long, is extended intd

a thin plate, and occupies the whole of the angle

included between the head and the handle.

«

The fhort procefs is very prominent : there is
another apophyfis at the internal furface of the
neck, which fupplies the place of the fmall
fpine in man.

The other Sarcophaga prefent no differences,
except in the length of the proceffes. The an-
terior, for example, is longefl: and narrowed in
the badger y and fhorteft and broadeft in l\\t otter.

It is very broad in the mole, and gives to the
malleus a figure nearly rhomboidal.

In the Rodentia, the handle is comprefied
like the blade of a knife, and adheres to the
membrane of the tympanum by one of its edges.
The neck makes an obtufe angle with the handle,
which bears, as ufual, the fiiort procefs. The
head, after receiving the incus on its pofterior
furface, has its thick portion fituated in the
oppofite diredion, that is to fay, forward. This
maffy portion is oval in the cabiai and the
guinea pig, and pointed in the rabbit and the rat.
The handle of the Jloths refembles that of the
Rodentia; the head is like that of the human
malleus. In the ant-eater it differs from the
form it has in the jloths, in the neck only, which,
is thinner.; and in the pangolin, in having the
fame part very fhort.

In all thefe animals, reckoning from the Ro-
dentia, the fmall internal apophyfis, or poftc-

VoL. II. L h rior

514

Lect. XIII. Or THE Ear.

rior procefs of the neck, is almoft obliterated.
It is, however, found very diftincfl in the hog
and the Ruminantia, which have the malleus
very fimilar to that of the Sarcophaga.

The feal has the handle comprefled ; and the
neck fliort, with fcarce any anterior procefs ;
the head is flightly flattened, and circular from
before backward.

There is no handle in the d^phin ; but the
membrana tympani has the form of an elongated
tunnel', and its point is fixed at the bafe of the
neck, .which feems obliquely truncated. The
anterior procefs is long and arched. The arti-
cular furfaces for the incus arc not diredted en-
tirely backward, but partly upward, on account
of the pofition of the labyrinth above the barrel.
The malleus of the whale is, in every rcfpedl,
fimilar to that of the dolphiny but double its
fize.

2. The Incus,

Or anvil, exhibits fewer difTercnces than the
malleus. In all the mammalia thefe two bones
are articulated by a very clofe ginglymus, com-
pofed at leafl:' of two furfaces, and mofl: com-
monly of four, in fuch a manner that each
bone has a convexity crofled by a concavity.
The principal variation in the incus of different
fpccies, occurs in the relative length and thick-
nefs of the two proceffes.

In man, the fuperior procefs, which is attached
to the bone of the barrel by a ligament, is Ihorter
and thicker than the inferior, which is articu-
lated

Art. VI. The Ossicula. 515

lated to the ftapes, through the medium of the
os lenticulare ; the latter is arched in fuch a
manner that its convexity is direcfled outward *
they form nearly a right angle at their jundtiOn.
The fame difpofition takes place in the orang
outang.

In the the fiiperiot* procefs becomes

more flendcr. It is almoft as long as the other
in the fapajoiis. In monkies^ in general, the ar^
ticular dcprelTion becomes deeper.

The two procefTes are flender, and nearly
equal, in the cat. The dog has them like thofe
of man. Weafeh^ otters^ and fealsy have the fu-
perior very fhort. The incus of the mole is
lingular ; its inferior, or ftapedian procefs, is
very (hort and fmall ; the other is very large,
oblong, and hollowed pofteriorly like a fpoon.
Perhaps it ferves to lodge a mufcle.

Hares and rats have the flapedian procefs very
long, and the other fcarce vifible. They are
more equal in the cabiais.

They are nearly equal, and make an obtufc
angle, in the Jloths.

The fuperior is mofi: flender in the Jheepi

They are both directed upward in ihedolphirti

3. The O/Jiculum Lenticulare^

Or orhicularey notwithftanding its fmall nefs,
varies as to form in different fpecies, but the
alterations it undergoes are too minute to be
dwelt on here.

L L 2

4. The

516 Lect. XIII. Of THE Ear.,

4. The Stapes.

1 his ofliculum differs, in fcveral fpecies, in
the reparation and curvature of its branches, in
the extent of the vacancy between them, and in
the figure of its bafis or pjate.

In moity for example, the branches are arched,
and the bafis or plate is femi-oval.

In the fapajou, the branches are nearly firaight,
and the bafis forms a narrow ellipfis.

No animal has the branches more arched, and
proportionally more feparate than the mr>le, in
which the bafis has the figure of an elongated
and narrow ellipfis.

In all animals, the pofterior branch is thicker
than the anterior. Inftead of the two branches,
the Cetacea have a folid body, compreffed coni-
cally, and perforated by only a very fmall fo-
ramen. In the lamautin, part of the fiapes
reprefents a twilled cylinder; on one fide there
is an oblique groove, and the foramen has
the appearance of the punffure of a pin. The
furface, attached to the fenefira ovalis, is ex-
ceedingly convex.

JI. In Birds.

Ilirds have only one officulum, compofed of
two branches, which form an elbow : the firfi:
is attached to the membrana rympani, from its
inferior and pofierior edge, to the apex of the
projc(fling cone, which that membrane forms
externally ; its direction is, therefore, almofl

6

Art. VI. The Ossicula.

5^7

the contrary of that of the malleus, to which
this branch correfponds. At its union with the
fccond part of the bone, there are two cartila-
ginous procefles, the poflerior ot which joins
a third branch, which runs back to the firll part
of the bone. In this manner, a triangle, nearly
right angled, is formed, the three Tides of which
arc attached to the iricmbrancof the tympanum.
I’he other part of the olTiculum makes an acute
angle with this firh: branch, and then paflcs di-
reclly into the barrel, in the form of a flender
ollcous flalk; it there expands a little, and fome-
times is divided into two or more final 1 odeous
hlaments, after which it terminates in an oval
or triangular plate, which, like the bafis of the
llapcs in mammalia, clofes the veftibular fencllra.
'I'here is no difference among birds wdth refpedt
to this officulum, except in its fize, and the fliape
of the plate. The fmall branches, which ad-
here to the membrana tympani, vary, it is true,
in their relative inclination and magnitude, but
in a manner too unimportant to merit notice.

C. In Reptiles.

The fro^_ and the toad have two ofTicula in the
ear ; one fupplies the place of the malleus, and
the incus : it is attached to the membrana tym-
pani by a flender branch which forms an acute
angle with the part that pafles into the barrel ;
that part has the fliape of a club ; its internal
extremity is the thicked, and articulates by a
double furface to the fecond ofiiculum, which

L L 3 corre-

5iS Lect. XIII. Of the Ear.

correfponds to the flapes: the latter has a femi-
elliptic form, and is applied to the feneftra ovalis
by its plane furface ; both thefe bodies, which
are ofTeous in other animals, arc cartilaginous
in the frog and toad.

,Li zards and tortoifes refemble birds, in having
a fingle ofliculum w’ith a thin hard ftalk, and
an oval or triangular plate. It is attached to
the membrane of the tympanum in the lizards^
and particularly in the crocodile^ by a cartila-
ginous branch ; but in the tortoifes its outward
extremity is direcUy implanted in the cartila-
ginous mafs, which correfponds to the mem-
brana tympani itfelf.

In the crocodile, the plate is an elongated el-
lipfis, the great axis of which is fituated longi-
tudinally.

In the tortoife, the bone is enlarged in the form
of a trumpet, and is applied to the feneftra by
a regularly oval and concave furface.

Serpents have an ofticulum, but no membrana
tympani ; its external extremity touches the
bone that fupports the lower jaw ; it is furround-
ed by the flefh, and is applied to the feneftra by
a concave plate, the edges of which arc irre-
gular.

In the camclion, the plate alfo rcfembles the
w'idc end of a trumpet ; its ftalk becomes car-
tilaginous, and is loft in the flefh.

I'he feneftra vcftibularis of falamanders is
clofcd only by a fmall cartilaginous operculum,
which has no ftalk, and is concealed by the flefh.

II. Of

5^9

4

»

Art. VI. TheOssicula.

II. Of the ^luscLV.s.

\

In man and other mammiferous animals the
oflicula have four imifcles; three to the malleus,
and one to the flapes.

The incus has no mufcle : its head is attached
to the poherior furtace ot the head of the mal-
leus, and the extremity of its fuperior procefs is
fixed to the temporal bone in the upper and
pofterior part ol the bottom *of the barrel of the
tympanum. It fhares in all the motions of the
malleus, which makes it acb like a balance upon
its fixed point.

The mufcles of the malleus are,

I. The Ttnfor Tympam, or Internus Mallei.

This mufcle arifes from the cartilaginous part
of the Kulfachian tube, and runs in a half formed
canal fituated in the os petrofum, upon the of-
feous part of that tube. Soon after it enters the
barrel, it reaches an eminence lituated before
the feneftra ovalis, which has been likened to the
fpout of an ewer. Its tendon turns upon this
eminence. It is then directed outward, and in-
fected into the internal furface of the manubrium
mallei under the proceflus gracilis- It pulls
the malleus completely inward, and ftretches
the membrane of the tympanum : by the motion
which the malleus communicates to the incus,
the fuperior leg of which remains fixed, its in-
ferior leg mull: deferibe an arch from without

L L 4 inward.

520 ‘ Lect. XIII. Of the Ear.

inward, and prefs the flapes into the fencftra
ovalis.

The Exterjuis Mallei,

Proceeds parallel to the preceding mufcle, but
more outwardly. It is inferted into the flender
procefs of the malleus, which is itfelf lodged in
a fmall canal formed above the fuperior edge of
the frame of the membrana tympani. This
mufcle is fo delicate that its real nature can
fcarcely be afccrtained. When it ads, it muft
draw the malleus forward, and thereby flretch
the poflerior half of the membrana tympani,
and communicate a balance-like motion to the
incus. In this movement the head of the incus
is lowered, the extremity of its inferior procefs
is direded backward, and a tremulous fliock is
given to the ftapes in the feneftra ovalis.

I

3. The Laxator Tympani.

This mufcle arifes from the arch of the meatus
externus, near the membrana tympani, pafTes
through the notch of the frame of that mem-
brane, and is inferted into the fmall oblique
procefs, on the neck of the malleus : it pulls that
boneoutward,and thereby relaxcsthe tympanum.
In confeqiience of the motion communicated to
the incus, it muft, at the fame time, draw the
ftapes a little from the fencftra ovalis.

The fingle mufcle of the ftapes, or —

\

The Stapedius,

Lies within the cavity of aprojedion fituatcd

behind

Art. VI. The Ossicula.

521

behind the feneftra ovalis, near the pofterior edge
oF the barrel, which is called the pyramidal emt-
nence. Its tendon comes forth from the cavity,
and proceeds diredlly to the pofterior part of the
ffapes, which it pulls backward, railing at the
fame time its anterior part a little.

We have not examined thefe mufcles in a great
number of mammalia ; but we have feen mod
of them, and particularly the Ifapedius, and
tenfor tympani, in feveral Ipccies, in which they
have prefented few varieties.

The malleus of the dolphin appears to have no
mufcle, but there is evidently one to the llapcs,
which is attached very far up, and not in the
middle of one of the branches, as in man.

The prelTure of the Hlapcs oil the feneftra ova-
lis mull have a double effect: it firft agitates
the whole interior of the labyrinth : — fecondly,
it comprelfes the gelatinous fiibftance which the
labyrinth contains, and forces it through the
cochlea, on the membrane of the feneftra ro-
tunda, which will thereby be rendered more
tenfe.

The fecond effeft muft, in particular, depend
upon a fixed prefTure produced by the adlion
of the mufcles : thefe are doubclefs contracted,
when we wifn to liften wdth great attention.

As to the fimple concuflion, or ftiock, it may
be caufed merely by the agitation communi-
cated to the membrana tympani by the vibra-

tiotis

522

Lect. XIII. Of the Ear.

tions of the air: this is, probably, one of the
immediate caufes of hearing. Animals that
have no m'ufcles to their officula, are only fuf-
ceptible of this kind of impreflion : >it would
be intcrefting to difeover whether they are ca-
pable of paying more or lefs attention to founds.

Birds have a fmall mufcle behind the ear, on
the occiput ; it penetrates into the barrel by a
hole, and is inferted into the hypotheneufe of
the fmall right-angled triangle, formed on the
inembrana tympani by the three branches of the
ofiiculum ; this mufcle ftretches the membrane,
by drawing its conical apex more outward. Two
filaments, which appear 'to be tendinous, op-
pofe the adbion of this mufcle, and prevent it
from becoming too great : one filament, which
is very long, arifes from the anterior procefs of
the cartilage attached to the tympanum, and is
fixed in the cell fituated above the Euftachian
tube; the other afeends, and is inferted into
the column which feparates the entrance of
that cell from the one above the labyrinth.

Wc are not fuHiciently acquainted with the
mufcles of the internal ear of reptiles ; and the
deferiptions of Comparetti do not pofTefs that
clearnefs which might enable us to fupply the
want of our own obfervations.

It appears’ that ferpeuts, camel ions, ZLud fala-
manders, arc entirely deftitute of thofe mufcles,
and that they arc very indiftind in tortoi/es.

Arti-

Art. VII. External Meatus.

£23

Article VII.

Of the J feu tux Auditorius E.iter)i\ix, of the
Concha, ainl of the Mnfeks oj the K.vternai
Ear.

The reptiles have no external meatus auditorius.
In the crocodile only we find Tome appearance of
that part, becaufe the fkin forms a kind of lip,
or operculum, above the membrana tympani ;
and the latter is entirely concealed, except whbn
this covering is removed. This is, doubtlefs,
the part which Herodotus regarded as the ex-
ternal ear of the crocodile^ and to which, he
fays, the Egyptians attached rings.

The external meatus of birds is very fhort ;
the orifice is commonly only a fimple hole, level
with the head, and furrounded with feathers of
a particular ftrudlure ; they are tine and eladic,
and their radii, or beards, are fimple, fmall,
elaflic, feparate from each other, and allow the
air to pafs between them. Thefe feathers arc
placed with much regularity about the aperture
which they cover. In fome birds they are elon-
gated, and affume various forms, as in the buj-
tard, the tufted-necked humming bird (Trochilus
ornatus), a fpecies of bird of Paradife^ (Paradijea
aurea,) &c.

In the ozvh, the external orifice of the ear is
fituated in the bottom of a large cavity, hol-
lowed

524

Lect. XIII, Of the Ear.

lowed out on each fide of the head, and lined
by a naked (kin, the folds of which form fepta,
which divide it like the human concha; this
Cavity would, indeed, refcmble the external ear
of man, were it projecting, and capable of mo-
tion.

The fine feathers which cover the cavity, form
the circles that give to the phyfiognomy of
thofe birds its (ingular character. The while
07f/'has a membranous operculum, of a fquare^
form, at the anterior edge of the cavity.

VVe (liall now examine the external ear in
man, and other mammiferous animals.

1. The external OJj'eous \lealus.

The external meatus is olfeous at its inner
part, or that next the tympanum. The tubular
portion of the cartilage of the external ear is
attached by membranes and ligaments to this
bony part ; it fometimes forms only a (ingle
piece with the concha, and fometimes is fepa-
rate from it.

The Cetacea are the only mammalia that have
no oifeous meatus : their external meatus is a
very (lender cartilaginous canal, which com-
mences at the furface of the (kin, where, in the
dolphin, it would fcarcely admit a pin ; it takes-
a ferpentine diredion, as it pafles through the
lard, under the (kin, to reach the membrana
tympani.

In all the other families there is an oficous

. ' canal,

Art. \H. External Meatus. 525

canal, of greater or lefs length; at lead in adult?,
for it is longer iy olfifying than nioft of the
other bony parts of the ear. The frame of the
inembrana tympani only is ofllfied in infancy,
and preferves its fizc, while the rell of the tem-
poral bone continues to incrcafc.

In man, the external. ofTeous meatus is fliort,
ftraight, and dirc(flcd almoft horizontally in-
ward, and a little forward ; its fcction is an
oval, the great axis of which defeends from be-
fore backward ; its diameter remains nearly the
fame throughout its whole length.

It is, proportionally, a little longer and nar-
rower in the guenons, and ftill more fo in the
Barbary ape ; it defeends a little in thefe Qiecies,
hut is not direclied fo far forward as in man ; it is
very fliort and circular in the Japajous and the
bats.

The Sarcophaga, in general, have it like
man, nearly horizontal. In dogs, cats, and the
badger, it proceeds diredly inward, and does not
incline either forward or backward.

It is directed a little forward in the coati.

In the otter, the pole-cat, and, in general, in
the genus muftela, it is directed backward.

The external canal of the mole is very Angular ;
it is flat in the vertical direction, but enlarges
in the horizontal ; and the great circular mem-
brana tympani ferves for its roof, in the fame
manner as it forms the floor of the barrel.

This canal is directed very much downward

526

Lect. XIII. Of the Ear.

in the Rodentia, particularly in the hares. It
alfo proceeds forward in this genus, and in the
marmottc.

Its diredfion is inward and downward in the
heaver.

The porcupine has it turned backward.

In the cabiaisy and the agoutis^ it is fliort, and
runs flraight inward ; under its inferior edge
there is a hole, which penetrates into the cavity
of the tympanum, and, in fome fpecies, unites
with the meatus by a fiflure.'

The Jlothsy pangolins^ and ant-eaterSy have the
external meatus very fliort, wide, and circular.

In the elephant it is large and long, and is
diredled a very liule downward and backward.

It defeends at an angle of 45 degrees in the
rhinoceros and the hippopotamus y but is neither
diredled forward nor backward. In the bahi-
roujfa it has the fame inclination, but is direcfled
a little forward. In the common hog it defeends
ftill more, and alfo inclines forward. All thefe
animals have it very long and very narrow.

It is fliorter in the horfcy in which it defeends
Icfs abruptly, and is inclined a little backward.

Laftly, in the Ruminantiait proceeds direcftly
inward, with a flight inclination upward.

II. The external Cartilaginous Meatus, and the

Concha.

The Cetacea excepted, there arc very few

mammi-

Art. VII. External Meatus. , 527

mammiferous animals which have not, at the
orifice of the external meatus, that kind of car-
tilaginous expanfion, like the end of a trumpet,
which is called the concha.

Thofe which want it are, in the Sarcophaga,
the molcy and fome Jhrezvs. In the Rodentia,
the zewniy and fome mole rats. In the Eden-
tata, the pangolins. And in the amphibious
mammalia, the morjcy and feveral fpccics of
/cals. .

We obferve great varieties in the concha, or
external ear of different animals : thefe varia-
tions relate to its fize, pofition, figure, and in-
ternal eminences, to the compofition of its tube,
and, finally, to its mufcles.

a. Hizi .

The animals which are remarkable for the
fize of the ear, are almofi all timid or notfiur-
nal, and therefore require a delicate fenfe of
hearing, as the feeble Ruminantia, the gazelles
and deeVy the afsy hareSy and fome fmall Roden-
tia, but particularly the bats.

In the lafi: genus, there are feveral fpecies
which have the ear as large as the whole of the
head ; and one fpecies, the eared bat (vefpertilio
aiiritusy) has it as large as the body.

The African elephant is diftinguifhed by a
large, flat, open ear, fituated clofe to the body,
and therefore not well calculated to anfwer the

purpofe

Lect, XIII. Of the Ear.

52S

piirprofe of an acouftic trumpet. The ear of the
Indian elephant is limilar, but much fmaller.

b. Direclion.

Naturalifis have remarked, that the aperture
of the concha is mod frequently diredled for-
Afard in the animals that hunt for their food, and
backward in thofe that are their prey; but this
pofition depends upon the neceflicy of the mo-
ment, and not upon any peculiar ftrudlure of
he organ. All animals which have ears of a
certain length, may vary their diredlion at plea-
fure, except, perhaps, the vejpertilio fpajma^
which has the two great ears united by their in-
ternal edges, and confequently very little move-
able.

Ears with the fuperior part of the concha
pendent, are a mark of flavery. TIogSy Jheepy
goatSy and bogSy have them always thus in fome
of their domeftic varieties. - The elephant has
alfo a pendulous ear, but unlike the preceding
animals, it is the pofterior and inferior part of
the ear that hangs down.

c. Figure.

The concha of the human car has the fliape of
half an oval, more contraefted infcrioily, and
terminated by a lobe which is filled with fat.
The anterior edge adheres to the reft of the fkin,
and is almoft rcrtil inear, with the exception of

. , the

Art. VII. External Meatus. 529

the eminences, of which we fhall fpeak pre-
fently : the fuperior and pofterior edges are tree,
and direded outward.

In the orangs and fapajous, the lobe dimi-
nilhes, and the free part becomes more confider-
able, but remains round. In the guenons and
macaqueSy it is pointed a little fuperiorly. In
the Jlriatcd monkey (Simia jacebus), it is even
grooved polieriorly by a linuofity. The form
of the car varies in the other genera, without
a'ny dired: relation to the orders to which they
belong. In general it becomes more elliptical
as it incrcafes in fize ; it belongs to ordinary Na-
tural Hillory to deferibe thofe fmall variations
of lhape, which are entirely external. It is fuf-
ficient, therefore, to refer our readers to plates
which reprefent quadrupeds.

d. Eminences.

The eminences of the human car are, r. The
fold of its fuperior and pofterior edge, called
helix : it turns inward, below its anterior part,
and is terminated above and behind the external
meatus. 2. The (harp elevation, which is al-
mofl: parallel to the helix pofteriorly, and which
afterwards crofles the ear obliquely, named
antihelix. 3. The eminence, fituatcd before the
meatus, and denominated tragus. 4. That w hich
is fituated behind the meatus, which terminates
the antihelix inferiorly, and which is called
antitragus.

, VoL. II. M M

The

530

Lect. XIII, Of the Ear.

The fold which forms the helix diminifhes
in apesy difappears in the fapajous, the ftriated
inovkeyy and in all other animals ; they have all a
fharp edge to the ear. The antihelix becomes
flat, and is replaced by a tranfverfe eminence
lituated very low' down.

The tragusy which ftill exifts in the dog, is
reduced in the hares, horfes, &c. to a flight pro-
jedlion of the fuperior edge of the concha on
the inferior.

In the bats, the tragus is particularly deve-
loped, and alTumes very remarkable forms.

In the eared bat, it is fo large that a double
concha has been afcribed to that animal : it is
forked in the vejp. Jpafina ; notched in the v. Ic-
porinus, and the v. crenatus ; oval, round, point-
ed, &c. in the other fpecies. It may fcrve to
prevent the too violent irruption of air into the
ear while the animal flies. The antitragus of
bats is generally round ; it is fomctjjries pro-
longed forward, beyond the tragus, to the angle
of the mouth. It is found of that form in the
v. moloffus.

In fome Jhrews the antitragus ferves as an
operculum to the ear. It clofes it exadly in the
aquatic Jhrew of Daubenton.

e. Compofition.

The external ear of man confifls of a Angle
piece: the concha becomes tubular, and pre-
lerves that form until it reaches the ofTcous

meatus.

Art. VII. External Meatus. 5Ji

meatus, to which it is intimately united: wc
obferve only one fiirure or irregular incifion.

In animals which have the ears rather long,
and very moveable, the tube of the ear is di-
vided into two parts, one of which is conncdled
with the concha ; the other forms a particular
tubular cartilage, attached to the ofTcous meatus
by a ligament, and has, like the portion united
to the concha, a longitudinal filTurc. In con-
fequence of this divifion, the tube may be
fhortened and elongated, as well as dilated and
narrowed.

Thefe animals have, befides, a third cartilage,
fituated above the tube of the ear ; it is flat, and
forms no part of the concavity, but merely
ferves as a point of attachment for fome mufcles.

This cartilage is triangular in the horje ; lu-
nated in the jheep ; pointed pofteriorly, and bi-
lobed anteriorly, in the rabbit \ and rhomboidal
in the dog. We fliall call it the jeutum.

III. The ]\IUSCLES.

A. In Man.

The number and fize of the mufcles of the
external ear, depend upon its degree of mobility ;
their fliapes and proportions on the pofition of
that organ, which, in its turn, is influenced by
that of the exterior orifice of the olTeous meatus.

This orifice is always fituated clofe behind the
articulation of the lower jaw ; it is, therefore,

,M M 2 farther

Lect. XIII. Or THE Ear.

532

farther back, and nearer the occiput, in pro-
portion to the length of the jaws, compared
with that of the cranium. It is alfo more elevated
with refpe(5l to the whole head, in proportion
as theafcending branches of the lower jaw are
higher, and the cranium more flat. Thus de-
fcending from man, we find that its fituation
becomes progreflively more upward and back-
ward, and that the two ears approach more and
more towards each other, until we come to the
Solipeda, in which the approximation is greateft.

The mufcles which aeft on the human ear are
reducible to three which arife from different
parts of the head, and five which proceed from
one point of the concha to another.

The three firfl: are —

1. The Superior Auris.

This is a thin radiated mufcle ; it covers a
part of the temple, and is inferred into the fu-
perior portion of the convexity of the concha,

2. The Anterior Anris,

Which is fmall, and not very diflinefl: from
the preceding ; it acifes near the zygomatic arch,
and terminates in the anterior part of the convex
fide of tlie concha.

3. The Pojlerior Auris.

'I’his is a fmall mufcle, diviJed into fome

flips

Art. VII. External Meatus. 533

Hips which arife from the' occiput, and are in-
ferted behind the concha.

The five mufcles of the concha are —

1 . The Major Helicis.

It arifes above the tragus, and is loft on the
anterior edge of the helix.

2. The Minor Helicis y

Which is extended over that part of the helix
which runs acrofs the concha.

3. The Tragicus.

%

The fibres of this mufcle arc extended tranf-
verfely over the tragus.

4. The Ajititragicus,

It arifes from the antitragus, and is loft cn
the internal edge of the antihelix.

5. The Tranfverfus Auris.

This mufcle extends acrofs that hollow fold,
on the back of the ear, w^hich correfponds to
the projedlion made by the antihelix upon the
concave furface.

Thefe mufcles have no apparent ufe in moft
men. Some of them have, however, been ob-
ferved to produce a flight motion of the ear.

B. In Quadrupeds.

The mufcles of the ears of quadrupeds are,

M M 3 in

534

Lect. XIII. Of THE Ear.

in general, very numerous ; they may be divided
into four clalTes ; i. Thofe which arife from the
head, and are inferted in the feutum : 2. Thofe
which have alfo their origin in the head, and
are inferted in the concha, or its tube : 3. Thofe
which proceed from the feutum to the concha ;
4. Thofe which extend from one part of the
concha to another.

Thefe mufcles move the ear in every direc-
tion, or turn it on its axis in fuch a manner
that the fuperior furface is fometimes placed
forward, fometimes backward, and the inferior
in the oppofite d;red;ions. We fhall deferibe
thefe mufcles in the borfet the fljeep, the rabbity
and the dog.

‘a. Mufcles which proceed from the Head to the

Kicutum.

1. The Vertko-Scutalisy

Arifes in the dog^ from the middle line, along
the whole of the upper furface of the head ; and
in the horfct from the fuperior edge of the tem-
poral folTa : it is inferted into the fuperior edge
of the feutum. In the foeep it is reduced to a
band, which comes from above and behind the
orbit ; and in the harcy to a ftill narrower flip,
arifing from the occipital creft merely : this is
the communis of Lafofle, and the fronto-auricu-
laris of Girard j it raifes both cars, and draws
their convex furfaccs towards each other.

7 ?. The

Art. VII. External Meatus. 535

2. The Jugo-Scutalis.

This mufcle arifes in the horje from the zy-
goma, afcends backward, and is inferted into
the anterior edge of the fcutum. In the dog, it
comes from the Ikin of the cheeks, and expands
confiderably, as it proceeds upward, where it
is inferted, not only into the fcutum, but alfo
in the anterior edge of the 'preceding mufcle.
It is wanting in the bare and the Jheep. It
draws the ear forward, and a little upward.

*

3. The Cervico-Scufalis.

It comes from the cervical ligament, and is
inferted in the pollerior edge of the fcutum ; it
is peculiar to the dog and the rabbity and approxi-
mates the ears pofteriorly.

b. Mufcles which proceed from the Head to the
. Concha, or to its Tube.

4. The Vertki-Auricularis,

Arifes from the crown of the head, pafles
under the vertico-fciitalis, and expands on the
concha towards its anterior edge ; it is proper
to the horje and the Jbeep, and approximates the
conchae very confiderably while it elevates
them.

5. The Supcrcili- Auricular is]

Supplies the place of the preceding mufcle

M M 4 in

53^ Lect. XIII. Of the Ear.

in the hare 2.nd. the dogi it comes from the fu-
perciliary arch, pafTes before the margin of the
fcutum, and is attached to the concha. In the
bare it is inferted by a flender tendon. In the
dog it is united throughout almoft its whole
. length, to the anterior edge of the vertico-Scu-
talis, and is inferted by an expanfion very near,
the anterior edge of the concha.

6. The Cercici- Auricular is.

It arifes from the cervical ligament, pafles
behind the edge of the fcutum, and expands on
the concha, which it moves backward, and
draws towards that of the other lide.

7- The Occipiti- Auricular is,

Comes from the parts near the occipital crefl,
and pafles below the fcutum and the lafl: mufcle;
it is attached to the concha, which it elevates,
but does not move it backward. It is not found
in the hare.

8. The Cervici-Tubalis Prof imdus.

It arifes from the cervical ligament below
the ccrvici-auricularis ; it is inferted at the origin
of the tube of the ear, which it draws back-
ward. It is double in the borfe, and wanting in
the hare.

.0. The Occipiti- A uricularis Rotator,

Arifes from the poflcrior part of the occiput,

and

Art. VII. External Meatus. 537

and is inferred in the form of a band into the
concha, near its tube: this mufcle is found in
all long-eared animals ; it turns the ear on its
axis, by directing its concavity outward and
backward when it is ereA, and downward w'hen
it is horizontal.

10. The Parotido-AuriculariSy

Which comes from the parotid gland, and
the parts next the fkin, is inferred under the
concha, near the tragus ; it lowers the ear, and
is always found. The hare has it longer than
others.

11. The Jugo-Auricularis.

In the Jheep this mufcle is very confpicuous ;
it arifes from the anterior part of the zygoma-
tic arch, and runs backward to its infertion in
the edge of the concha, next the meatus audi-
torius. In the dog it is double ;*one portion
comes from the fkin of the cheek ; the other
from the pollerior edge of the jugo-fcutalis. In
the horfey one portion arifes from the middle of
the zygoma, and another from the pofterior edge
of the jugo-fcutalis ; it draws the ear horizon-
tally forward. It does not exift in the hare,

12. The Jugo-Auriciilaris Profundus.

This is a fmall flender mufcle, found in all the
before-mentioned animals ; it is attached to the
pofterior part of the zygomatic arch, near the

articula-

53^ Lect. XIII. Of the Ear.

articulation of the lower jaw, and extends to
the part of the concha next the tube, a little fu-
periorly : it ferves chiefly to (horten the tube
of the ear.

The horfe has two mufcles belonging to
this clafs, which are not found in the other fpe-
cies, viz.

13. The Vertlci-AuricularU Rotator.

This mufcle comes from the top of the head
near the occipital eminence j paffes under the
poflerior angle of the fcutum, and over the oc-
cipiti-auricularis ; proceeds obliquely forward,
and is expanded, like a fcarf, on the anterior
part of the concha, near its tube : it turns the
ear on its axis, diredting the concavity forward
and inw'ard when it is eredl, and upward when
it is horizontal.

14. 'T/?e Vertici-Auricularis Rrofundus,

Has a common origin with the preceding; it
feparates from it under the fcutum, and defeends
between the head and the concha; it is inferted
in that part of the latter, which is inward,
when its concavity is dircdled outward, and
which is ncarefl the tube; its ufe appears to be
to lengthen the tube of the car.

c. Mufcles which unite the Scutum to the Concha,
or to the Tube o/‘ the Ear.
a. The Juperjicialy which are attached to the
fcutum,

15. The

Art. VII. External Meatus. 539.

15. The Sctttalis Anterior^

Extends from the inferior edge, and anterior
angle of the fcutum, to the front of the concha,
which it turns on its axis, and diredls upward
and forward when horizontal. It is wanting in
the dogs that have hanging ears.

16. The Scutalls PofterioVy

Proceeds from the fame edge, and fometimes
from the fame angle, and extends backward be-
hind the concha, which it elevates. It is want-
ing in the hare.

The deep-featedy which are inferred under
the fcutum.

17. The Scutalls Rotator.

\

Thismufcle arifes under the fcutum, and pro-
ceeds in the form of a fcarf, behind the part of
the concha which is next the tube. It turns
the concavity of that part towards the earth,
and backward when it is horizontal. It is double
in the bare.

d. Miifcles which extend from one Part of the
Concha of the Ear to another.

There are no mufcles of this kind in ihejheep^
and only one in the borfey viz',

18. The Tragicus.

It is lituated on the filTure of the concha, and

produces

540

Lect. XIII. Of the Ear.

produces the croffing of the edges of that part ;
it confequently contracts the aperture of the ex-
ternal meatus ; it alfo exills in the dog and the
bare. In the latter iris accompanied by

19. The Tubo-Helicus,

Which comes from the cartilaginous tube of
the concha, and which fliortens the tube of the

car.

We find in the dog^

20. The Plicator Auris.

This mufcle is analogous to thofe of the helix
in man ; it extends along the anterior edge of
the concha, near its bafe ; it folds, and deprelTes
the fuperior part of the ear.

LafUy, the dog and the horje have, on the
back of their concha,

2 1. Some fcattered flefhy fibres which arc
analogous to the tranfverfus auris of rnan.

Article VIII.

Of the Dijiribution of the Nerves ii'ithin the

Ear.

We have defcribed the meatus audiiorius inter-
miSt in pages 46 and 56 of this volume. Its
bottom is fituated nearly oppofitc to the middle

of

A. VIII. DiSTRIBUTiaN OF THE NeRVES. 54I

of the cochlea. It is divided into two foiTne br
an ofleous ridge. The fupcrior contains a hole
for the facial nerve, and a number of fmall fo-
ramina for a branch of the auditory nerve. 1 he
fecond alfo contains fcveral foramina for the
other branches of the auditory nerve.

\Vc have deferibed the orijnn of this nerve

O

pages I 5 1 &: 177 ; and its courfc to the car, pages
233 and 234. The inferior folfa through which
the chief part of the nerve palTcs is oval. Its
great diameter is t.'^aiirverfe. Anteriorly there is
a particular deprelTion uhi> h correfponds to the
bafis of the conical axis of the cochlea. It is
perforated by a vafi nuniber of fn)all foramina,
ranged in a fpiral manner, and which extend
into the holes of that cavity. In the p«ftcrior
part of the fofla there are other clulfci-s of limilar
fmall holes, but difpofed in a circular order.
One of thefe duffers leads into the veflibulum,
and two others into the femi-circular canals.
There is a fourth group, lituated, as we have
already obferved, in the fuperior folia. Thefe
fmall foramina lead alfo into the canals.

The nerves are greatly fubdivided in per-
forating the ofleous parietes, fo that they arri\e
in the labyrinth divided to an incredible degree
of minutenefs. Thofe which enter into the
cochlea, after having followed the parietes of
its axis, penetrate, according to Scarpa, into the
fubftance of its bony feptum, and come out on
the unconneCdtd lide of that feptum.

The

542

Lect. XIII. Of the Ear.

The nerve, when enclofed in the internal au-
ditory canal, appears twifled on itfelf ; and its
filaments, when beginning to be apparent, aflumc
an oblique fpiral direction.

They foon divide into four fafciculi, one of
which correfponds to the beginning of the fu-
perior femi-circular and external canal ; one to
that of the pofterior, and the third to the middle
ol the veftibulum. The fourth, which is the
continuation of the trunk, is twilled fpirally to
purfue the feries of frnall foramina which enter
into the cochlea. Its filaments fill all the tubes
of which thefe fmall holes are the orifices, and
it is thus diflributed in this part of the laby-
rinth to terminate in the membranous part of
the feptum. Numerous anallomofcs take place
among thofe filaments along the pyramidal axis#
As to the three other fafciculi, the firll, which
is the largefl, having penetrated into the olTeous
veftibulum by one of the fmall fieves of which
we have fpoken, is divided into two fmall por-
tions, which extend to the ampulai of the two
neareft femi-circular canals.

The fecond proceeds without dividing into
the ampula of the pofterior canal. The fila-
ments of thefe two fafciculi terminate in thefe
ampulae, where they fpread out like a fan, and
form a kind of feptum. The canals receive no
nerve in any other part.

The third fafciculus is fituated between the
two preceding. It extends into the mem-
branous

A. VIII. Distribution of the Nerves. 543

branous vcftibulum, and is diftributed on its
internal furface in a net-work as foft as it is
complicated.

We fliall in this place defcribe the courfe of.
the facial nerve through the ear. We pointed
out the origin of this nerve, page 152. 1 he hole
into which it enters at the bottom of the inter-
nal meatus, is the orifice of a long canal bent
in different direcffions, and called aquarJnf/ns
Falopii. This canal perforates, in the firll place,
the pars petrofa, as it afcends outwardly. It
foon receives another fmall canal, which extends
from before backward, and which conveys a
branch of the Vidian nerve of the fifth pair," to
its union w'ith the facial, (See page 2 1 1 .) The
aquedudb afterwards proceeds fuddenly back-
■w'ard, and croffes the upper part of the barrel,
where it is partly membranous. It then be-
comes offeous, is bent, and dcTcends vertically
parallel to the pofterior part of the barrel, as far
as the ffylo-maftoid-foramen.

In page 228 and the following pages, we have
deferibed the diftribution of the facial nerve af-
ter it comes out of the laft foramen ; but while
it is pafling through the aqueduiff, it detaches,
ifl, a nerve to the tenfor tympani; 2d, one to
the mufcle of the ffapes ; and 3d, a long fila-
ment which palTes through the cavity of the
tympanum, as we have fliewm in page 227, to
unite with a branch of the inferior maxillary
nerve of the fifth pair. This filament has been

named

544

Lect. XIII. Of THE Ear.

named the chorda tympanic becaufe it is fituatcd
behind that membrane in a manner fimilar to
the cord which crofles the under head of a drum.
It feparates at an acute angle, and afeends in
a fmall canal w'hich opens into the cavity of
the tympanum, under the pyramidal eminence.
It leaves the barrel by the. fijfura Glazeri. We
have already deferibed it in page 227.

The external meatus receives nerves from the
inferior maxillary branch of the fifth pair, and
from itsfuperficial temporal branch (feep.217.)
The back of the concha, and its mufcles, derives
their nerves from the occipital branch of the
facial (fee p. 228,) and from the fecond cervical
pair (fee p. 248,) which alfo fends filaments to
the concave part of the concha ; but this part
receives, befidc, another branch of the facial
nerve (fee p. 228.)

The nerves of the internal ear of mammife-
rous animals do not differ eflentially from thofe
of man. The nerves of the external ear are
larger, and more numerous, in proportion to
the fize of the concha and its mufcles ; but
they all have the fame origin.

In birds, the deprefiion which occupies the
place of the internal meatus, is oval, and its
greatefl diameter almofl: horizontal ; it contains
five holes for the paffage of the nerves, one of
which receives the facial, and four the auditory ;
three of the latter penetrate into the ofTcous vef-
tibulum, and one into the cochlea. The three

ramifi-

A. VIII. Distribution of the Nerves. 545

ramifications of the auditory nerve, which go
to the femi-circular canals, are diftributed to
the ampullae, as in man, and the mammalia.
The ramification which goes to the cochlea ex-
tends to the uppermoll of the two cartilages
which form the feptum of that organ ; when it
has reached one half of its length, it penetrates
it, and is expanded, like a goofe’s foot, on the
apex of the cone of the cochlea. Several fila-
ments afeend in the contrary dire(5tion of the
trunk, to proceed to the bafe of the fame cone.

The facial nerve of birds receives a filament
from the par vagum, fimilar to that which we
have deferibed in the calf^ page 230 ; it crofies
the ear in an olfeous canal, and, having left the
cavity of the tympanum, is diftributed princi-
pally to the palate.

In reptiles and fifties, but particularly in the
latter, we have the opp>ortunity of obferving,
ftill better than in w'arm-blooded animals, the
Gonftancy with which the branches of the au-
ditory nerve proceed to the ampullae of the
femi-circular canals : in the reptiles, it divides
before it palfes into the oITeous labyrinth, w’hich
it enters by feveral holes. In the chondropte-
rygious fifties, it penetrates by a fingle hole,
and is not divided until it is in the labyrinth.
In the other fifties it has no feptum to perforate,
the ear being fituated within the cavity of the
cranium ; but it is detached by feveral branches
VoL. II. N N from

546

Lect. XIII. Of the Ear.

from the nerve of the fifth pair, of which it
forms a part. ^

In the rays and the JJjarks there are always t>vo
branches ; the fmallcr one detaches filaments to
the fac, near the fmall amylaceous fubftanccs,
and is afterwards divided in the two ampullte
of the anterior and horizontal canals. The
other forms an expanfion, like a goofe’s foot,
in that part of the fac which contains the largefl
amylaceous fubfiance. Thefe numerous branches
frequently anaftomofe.

The facial nerve enters the ear by a particular
foramen ; it joins a branch of the auditory,
which extends into the ampulla of the pofterior
canal ; it then feparates, to come out by a fe-
cond foramen, and is diftributed to the tegu-
ments of the head and the adjacent mufcles.

The auditory nerves of fifiies are frequently
three or four in number, and are detached fepa-
rately from ihe nerve of the fifth pair; they
extend to the ampullae, and to the fac which
contains the fiones : they expand, in particular,
on thofe ftoncs, in numerous filaments ; when
they are large, the net- work formed by the
filaments is exceedingly beautiful, as may be
obferved in the cod. The fize of the nets de-
creafe with that of the calcareous bodies.

LEG-

C 5-17 ]

LECTURE FOURTEENTEI.

Of riit SiiNSE of Touch, asd its Oiican'S.

Article I.

Of the Senfdtioun produced hy Touch or FetUhg.

The fenfc of touch feems to afford us a more
iritimate communication with external bodies
than thofe of light and hearing, becaufc there
is no intermediate fubftance between them and
ns when thefe bodies adt upon that fenfc:
though, therefore, not entirely free from error,
it is lefs capable of deceiving us than the other
fenfes, the imprelTions of which it ferves to
verify and to perfect, particularly thofe of fight.
By touch alone we obtain the idea of the three
dimenfions of bodies, and confequently of their
figures as folids. The preffure, more or Icfs
forcible, more or lefs direct, made by the dif-
ferent parts of an external body, when applied
to our fkin, enables us to recognize whether
that body be flat or round, or formed with va-
rious angles. By the equality or ineqpality of
this prelTurej and the degree of friction which

N N 2 takes

548

Lect. XIV, Of Touch.

rakes place when we move any part of our fkin
along the furface of another body, we afcertain
whether that furface is fmooth or rough. The
degrees of refiftance which bodies oppofe to the
prefTure of ours, in whole or in part, afford us
the means of determining whether they are
moveable or immoveable, hard or foft, fluid or
folid ; and the prelfure or pcrcuflion of thefe bo-
dies on us, while in motion, or tending to move,
makes us acquainted with the force wdth which
they adl, and the direction of that force.

All thefe aeflions of external bodies on our
own are purely mechanical. The fenfations
they communicate may be the effects of a che-
mical change in our nervous fyftem ; but that
change can only be produced in confequence of '
Ample prelfure being capable of forming or de-
flroying fome of the combinations which enter
into this fyflem. This fuppofition is not incon-
fiftent with analogy : we know, for example,
that the combination of fire with water, which
produces vapour, may be deflroyed by the lame
means.

But the fenfe of touch alfo procures us fenfa-
tions of another kind, which appear to be pro-
duced by one of the furrounding elements pene-
trating more intimately our bodies ; I mean the
fenfations of heat and cold. Thefe fenfations
depend on the proportion which exifls between
the 'quantity of caloric we acquire or lofe
in a given moment, and ih.'it which we ac-
quire

Art. I. The S,ensation in general. 549

quire or lofe in the preceding moment ; but they
are not in diredl relation with the abfolute heat of
bodies, nor even with the proportion between
their heat and ours.

All things in other refpec'ls equal, bodies
which have an higher degree of temperature
than our own appear to us to be warm ; thofe
which are of a lower temperature feem cold.
When, however, we have touched a very cold
body, if we come in contadl with another which
is lefs cold, the latter will appear to us warm,
though it may ftill be of a temperature much
inferior to that of our owm body. Thus cellars
and fpring w'ater appear warm in winter, be-
caufe they preferve their ordinary temperature,
while other bodies change theirs.

When we touch in fucceflion two fubflances
of different deiifity, or, to fpeak more properly,
of different capacities for caloric, that which
has the greater capacity appears to us colder,
though both may be of the fame temperature,
becaufe it abftradls more caloric from us in a
given time than the other. For this reafon
marble and metals appear always cold. Water
is colder than the air, and the air, which feems
cold before we enter into cold water, appears
warm when we leave the water, &c.

Bodies which are good condudtors of caloric,
or which tranfmit it" rapidly, for the fame rea-
fon appear cold. Thus we find that filk or wool
are warmer than linen of equal thicknefs.

N N 3

This

550 Lject. XIV. Of Touch.

This part of the fenfe of touch is liable to
many more errors fh^n th^t by which we obtain
a knowledge of the figure and confiftence of bo-
dies, becaufe our judgment ppflelTes pnore influ-
ence in the latter cafe.

The general organ of touch*refi4es in th,e (kin
which covers the whole body, or rather in the
extremities of the nerves which terminate ia
that flcin.

That organ poflefles greater or lefs fenfibility,
in proportion as the nerves diftributed upon it
are more numerous, more exppfed, and lefs in-
tercepted or covered by callous parts. The heat
of bodies, their general refiflance, and their mor
tion, are more perfedlly felt when this general
fenfibility is moft delicate.'

With lefpecfl; to the motion, the refiflanpe and
the heat of a liquid pr fluid, particularly if the
animal experiencing its adtipn is irnmerfed in it,
the degree of the fenfatipn alfp depends on the
extent of the furface which the fcpfible body
prefepps tp the fluid ; but fopierhing more is
needfary for recognizing the forms of folids,
particularly thofe that arc fmall. In this cafe a
very fenfible fkin mult be extended over fcveral
fmall, d ividebi and moveable parts, capable of
embracing the folid, by their different furfaccs
feeling its flighteft inequalities, and fracing its
moft minute parts.

Thus the total perfedlion of the fenfe of touch
(Icpends on the quality of the fkin, the number

Art. I. The Sensation in general. 551

of its nerves, the extent of its furf.ice, its free-
dom from iafenfible parts, and the number,
flexibility, and delicacy of the appendices by_
which the animal can examine bodies.

As touch is the inoft important of all the
fenfeSj its degrees of perfection have a prodi-
gious influence on the nature of different ani-
mals. From the inveftigation we are about to
make, it will be found, that, of all vertebral
animals, man has this fenfe moft pcrfcdl. But
among the invcrtebral animals the fenfe of touch
improves in proportion as the others degene-
rate; and thofe which have no other fenfe,
pofTefs it fo exquifitely that fomc of them feem
even to feel the light.

Independently of the fenfations of w’hich we
have fpoken, and which have a direcl: relation
to the qualities of external bodies, we experi-
ence others in the Ikin, particularly in the
places where it is thinneft, and abounds moft in
nerves. Thefe feelings are occafloned by the
irritation w'hich the motions, rather than the
qualities or nature of bodies, produce upon the
nerves, and belong more to the order of internal
than external fenfations: thefe are ticklings,
prickings, and itchings.

Laflly, the fkin performs a different fundlion
from that of touch, which confifls in tranfpira-
tion and abforption ; that is to fay, in the exha-
lation of a part of the elements of our fluids,

N N 4 and

552

Lect. XIV, Of Touch.

and in the inhalation of a part of the fluids
which furround us.

1 his fecond kind of function does not belong
to fenfation. We ihall therefore confider it in
another place.

Article II,

^ I

Of the Skin and its Organization.

X^HE whole furface of the animal body is co-.
vered by an organ of a particular nature, named
Jkin. It is a membrane applied to all the fuper-
ficies which terminates the body, and its thick-
nefs varies according to the fpecies of animals,
and the different parts which it covers.

The organization of the fkin appears to be
effentially the fame in all the clalfes of verte-
bral animals. The external differences which it
prefents are more or Icfs conneded with the
developcmcnt of certain fuperadded parts, as we
fhall explain in the fcquel. The flrudure of the
fkin cannot, however, be eflablifhed in fo ge-
neral a manner in the aniinals that have ho ver-
tebrae, though it will be feen that its parts have
forne analogy to thofe found in red-blooded
^njmals.

The fkin of 5II the animals that have vertex

brap

r

Art. II. The Skin.

5-53

hrx is compofed of four layers, more or lefs
diftind:, but which the anatomift: feparatcs, and
may eafily demonftrate. The lowcft is called
dsnnisy cutisy corium, or the true The next

is called corpus papillarCy tcln matnmillarisy or the
villous Surface. The third, corpus reticularey or
rete mucojum. Laftly, the fourth, or moft exter-
nal, has been denominated epidermiSy or cuticle.

We do not eafily diftinguifii all thefe parts in
animals that have no vertebrae. Some of the
ftrata are more diftince, others lefs fo. 1 here
are alfo fomc fpecies in which we do not find
the whole of them. Thefe dilferences we (hall
point out more clearly in treating fuccelfively
of each of the layers.

1. The Cuticle.

This layer, as wc have already obferved, is the
mofl fuperficial. It is a tranfparent and infen-
lible pelli- le, which prevents the immediate
contad of the nerves of animals with the me-
dium in which they live. It is alfo continued
into all the apertures of the body, and lines
them internally to preferve them from the con-
tad of air or water. Thus we find it on the
eye, in the ears, the noftrils, the mouth, the
anus, the vulva, &c. ; but it is then deferibed
under different rK.mes, as has already appeared
when we treated of the conjunEtiva and the mem^
hrane of the tympanuniy and as we fhali (hew
hereafter in treating of the other organs.

7

The

554

Lect. XIV. Of Touch.

h

The confiftence of the epidermis varies with
the medium in which the animal is immerfed
and obliged to exift. It is dry, and as it were
horny in thofe that live in air; mucous, and
more or lefs vifeous in thofe that inhabit the
water.

In theanimals which are conllantly fubjeclto
the drying acliion of the air, the cuticle appears
varioufly folded, according to the parts of the
fkin to which it adheres. Thefe folds form
wrinkles, papillze, circles, and fpiral lines, which
correfpond to the elevations and depreflions of
the llcin, but chiefly to thofe of the rete muco-
fum, and the fcales when thefe lafl: exifl.

In general the epidermis is confiderably the
thickefl.on the parts whiqh are moft: expofed to
fri(fl:ion ; as the foie of the foot, the palm of the
hand, and all the other parts frequently ufed by
animals, either in walking or in grafping other
bodies.

In the furrows of the cuticle wc obferve the
holes througli which the hairs pafs. Thefe ap-
pear as conical elongations, or infundibula,
which *feem to have been forced outwardly by
the hairs, to which they ferve as flieaths.

In the animals which have fcales, inflead of
hairs, the epidermis envelopes thefe parts in
every diredion, and is intimately attached to

them.

In man the cuticle is generally very thin,

w ith the exception of the parts w hich cover the

folc

Art. II. The Skin.

555

foie of the foot and the palm of the hand.
Fridlion, or deficcation, either by heat or certain
chemical agents, harden it conliderably. They
change it into a kind of horn, which blunts, and
^ven totally deftroys the fenfe of touch. We
have very remarkable examples of this change
in blackfmiths and dyers, and in men who walk
bare-footed on burning fands.

The furrows of the epidermis form figures,
with feveral angles, on the back of the hand ; pa-
rallel and elongated lines on the palm and.onthe
fo!c of the foot; arches, curves, and very lin-
gular, clofe and fymmctrical fpirals under the
extremities of the toes.

7'he cuticle of the other mammalia is nearly
fimilar to that pf man. It is thin in proportion
gs th« hairs that cover it are compadl. That
which covers the wings of the bat is alfo very
thin, and has furrows which form many angles,
like thofe we obferve on the back of the human
hand.

In the porcupine it is thin, and little difiineft
from the other ftiata of the Ikin, which is gela-
tinous.

We find the epidermis deficcated, and as it
were fcaly on the prehenlilc tails of the beaver,
rats, ondatra, &c. and on the fcales which cover
the bodies ot the pangolins and armadillos.

In the elephant, the rhinoceros, and the
potamus, which have the fkin very thick and
deeply furrowed, the epidermis, which is alfo

thick.

556

Lect. XIV. Of Touch.

thick, and covered with fmall plates that fepa-
rate from it like fcales, finks into the different
furrows. The cuticle of the foie of the foot
prefents a very fingular flrufture. It is divided
externally by deep depreflions, nearly circular,
with fix or eight furfaces more or lefs regular,
each of which contain an infinite number of
fmall polygons much more irregular. This
gives to the whole furface of the flcin the ap-
pearance of fnagreen. The epidermis detached
from the animal, and examined by its internal
furface, exhibits elevated lines correfponding to
the furrows of the great polygons. It al fo pre-
fents others which are fmaller, and correfpond
to the little polygons. The refult of this dif-
pofition is a kind of net-work, in relief, of a
pretty regular defign, and refembling lace with
large points.

The Cetacea have a very fmooth epidermis,
without any remarkable fold, and always co-
vered with a mucous oily humour, which op-
pofes the maceration of the animal during its
refidence in the water.

In birds the epidermis of the body is very
thin, and formed of folds which correfpond to
the quincunces in which the feathers arc ar-
ranged. That of the feet is fmooth, fhining,
and formed of horny fcales. It covers the dif-
ferent plates which we obferve on the feet of
the gallinac and grallae, of which we lhall fpeak
in the article on Scales. It is detached at

certain

557

Art. II. The Skin.

/

certain periods of the year, chiefly in the moult-
ing feafon.

In all the animals we have mentioned, the
Cetacea excepted, the epidermis comes off in
fmall pellucid fcales, which give to the furface
of their (kin a mcally appearance. In fome
mammalia the cuticle is renewed at certain pe-
riods of the year, at the fame time that they
change their hair. In others it takes place more
infenfibly, and at all times as in man.

The epidermis of iortoifes is not very diflincfl,
except on the neck and limbs. It is analogous
to that of the falamanderSt w hich we- fliall de-
feribe prefently. That w’hich covers the fcales
of the back-fliell and of the breaft-plate is ex-
tremely thin. It is detached in tranfparent
laminte, the figure of w hich is exad:Iy the fame
as of the horny plates.

In the jalamanders and frogs, the epidermis is
a mucous membrane, which covers the whole
body, and which falls oft' in large pieces at fe-
veral periods of the year.

The cuticle of lizards and ferpents covers and
entirely envelopes the fcales. It is detached in
a fingle piece like a flieath, at a certain period of
the year : we obferve, in thefe kind of exuvise,
even the portion of a fphere, which covered the
tranfparent cornea.

In fifties, the epidermis, which cov rs all the
body, the fins, and other appendices, appears
always in a foft ftate; it fometimes feems alim-
‘ pie

Legt< XlV, Of Touch*

55S

pie mucous fubftance enveloping every part Of
the animal's body. It is this mucous epidermis
which renders it in general fo difficult to feize
the body of a fifli. It is alfo detached in large,
pieces at certain periods of the year.

We Ihall fee, in the fequel, when we treat of
the internal tunics of the organs, intO/which
the air, the water, or the aliments penetrate,
that the prolongation of the cuticle which lines
their internal furface, alfo becomes mucous^
and that it has a confiderable refemblance to the
external epidermis of fifhes.

VV'e alfo find an epidermis in animals that
have no vertebrae. Thofe which live in water
have it commonly mucous, and of a very dif-
ferent thicknefs in the feveral fpecies. ,

In the Cephalapoda it is nearly the fame as
in fillies.

In the naked Gafleropoda it very much rc-
fembles that of the falamanders and frogs.

In the Teftacea in general we find an epider-
mis on the furface of the fliells. In the land
kind, as the /nails, it is a dry pellicle, very cafi-
ly detached, when the flicll is, after the death
of the animal, expofed to the aclion of the at-
mofphere, or plunged into boiling water. In
the anodontites, the mufcles, and other bivalves,
w-e obferve a fimilar epidermis, which envelopes
the fliell externally. This epidermis is always
wanting on the furface of the projecting parts,
on which the animal draws its flicll along tbo

land,

,• Art. II. The Skin.

559

fand, becaufe it is there worn oft. In fome fpe-
cies of fhells, the epidermis is thick and villous,
and on this account it has been fea-cloib.

This is very remarkable in leveral fpecics ot the
crenus area ot Linnicus ; and to cxprels this pc-
culiarity he has called one ot them ptlo/a.

In all the Teftacea, the epidermis which en-
velopes the flicll is continued to produce the
pellicle which covers the animal ; and it expe-
riences the fame change as that which is pro-
longed within the body of vertebral animals.
It is,thin and mucous on all the parts which arc
not expofed to the aiftion of the ambient Huid.
In the I'pccies of Gafteropoda, however, w hole
ihcll is concealed under the fkin, and does not
ferve for a defence, the epidermis does not
change its nature. We have examples ot this in
Tome fpccies of aplyfia and /nAVtZ, as well as in
the animal which produces the ihell, called by
I.innaeus, helix balyotoidea. {L.\\.v\\.Ji^aret .) *

In the Cruftacea and the infects, w hether in
the larva, nympha, or perfect ftate, there is a
real epidermis. This Ikin, however, when once
dry and indurated, is not fufceptible of extenfion,
fo as to accommodate itfelf to the grow th of the
animal. In proportion therefore as the infedt
increafes in fize, and at fixed periods in each fpe-
cies, but W'ith refpedl to which the atmofphere
appears to have confiderable influence, t^>e ani-
rrial quits its’ epidermis, by drawing itfelf as it
were out of a cafe. This is called the moulting

period.

560

Lect. XIV. Of Tot/CH.

period, in effeefling which the infect frequently
employs feveral days, and which is fometimes
mortal to it. The greater part of the caterpil-
lars, of butterflies, and of bombices, change the
fkin feven times before they pafs into the chry-
falis ftate. The bombyx-caja quits in this man-
ner the fkin ten times. We intend to dw'ell
more particularly on the fubjeeft of moulting iii
the Article on Metamorphofis, in the Ledure
on Generation.

There is a very diftind cuticle in worms. It
is eafily feparated from the fldn in the earth-
zvorms, which have been immerfed for a few
hours in fpirits of wine, or macerated fome days
in water; it is a pretty folid pellicle, which may
be removed in a Angle piece. In the worm
called fipunculus JaccatuSy this epidermis is even
entirely feparated from the body, which is un-
conneded and floating within it, as if it were
cnclofed in a fack. The leeches^ and fome other
worms, have the cuticle mucous, like that of the
gafleropodous mollufca.

It is very difiicult to afeertain the nature of
the epidermis in Zoophites, or even to difeover
whether it cxifts in fome of them. T\\q fea-Jlars,
the urchinSy and the ablinice appear to polfcfs
it.

The medHfa are covered with a pellicle, but
fo thin and tranfparent that it cannot be fup-
pofed to confifl: of flrata. The other Zoophites,

^ the polyps y 6ic. have a mucous lurfacc, the

foftncf?

I

Art. II. The Sicin*. • 56X

foftnefs of which prevents us from diftlnguifh-
iog any membrane.

The Rete miicofum^

Is fituated, as we have already dated, imme-
diately between the epidermis and the villous
furface of the fkin. It is not membranous, but
forms rather a mucous layer, the colour of
which varies, in different kinds of animals, and
fometimes even in different parts of their fur-
face. The colour of an animal’s fkin depends
on that of this mucous fubflance, for in all thofe
which have the fkin coloured, if we remove the
epidermis, it is found almofl pellucid, and the .
cutis is alfo free from colour.

It appears that the influence of the folar rays
determines, to a certain degree, the colour of the
human fkin ; it is white in temperate countries,
becomes more and more dark in warm regions,
and, finally, becomes black in the burning cli-
mates of Africa and Afia. May not the caufe
of thefe varieties be referred to the different
degrees of light w’hich colours living bodies, by-
removing their oxygen, and developing the
carbon and hydrogen which they contain ? We
find, indeed, that men who are expofed to the
rays of the fun grow tawny, while thofe who
inhabit fubterraneous places undergo a change
fimilar to the etiolation of plants, and become
exceedingly white.

"VoL. II. ' O o

The

562

Lect. XIV, Of Tough.

^ The colour of the mucous fubflance varies
greatly in mammiferous animals. It appears to
determine, as will be feen hereafter, that of the
nails and hairs. It is even frequently found
coloured in the cavities of organs, into which it
is prolonged, as on the palate, the tongue,' the
ear, the conjuneflive and nafal membranes of
apes, dogs, Ruminantia, and Cetacea.

The rete mucofum of the mammalia is not
often of a very vivid colour. It is however
white on the cheeks of fome mandrills-, red,
violet, and carmine on their hips and nofe. It
is of a fine lilvery white colour on the belly of
the Cetacea.

The rete mucofum is thickefi in the lafi: fa-
mily of mammalia. In the dolphin and porpoije
it is nearly half a millimeter thick on the back
parts of the body and the head, which are of a
black colour. We cannot compare it better,
w'ith refpecfl to confiftence and colour, than to
the black produced by greafe between the nave
of a wheel and the axle-tree.

The mucous fubltancc is little difiimfl in
birds, and almort always white in all the parts
covered by the feathers ; but its colour on the
feet, ccrae, and caruncula: of the head, is fub-
jedl to variations.

On the taiTi and the toes, it is frequently
black, as in the ravens, the tiirkies, fome ducks,
fivans, bcc. ; grey, as in hens and peacocks-, blue,

as

Art. il. TiIe Skin.

563

as in the tihnonfe \ green, as in x.\\d'water-hen \
yellow, as in the eagle \ orange, as in t\\Q ftork ;
red, as 'u\l\\e fcolopax calidris^ &C.

The rete mucofum is black in the caruncle

fwans, grey in the cerae of the bill in a num-
ber of parrots^ white in the chops of the blue
ara, green in the cerae of the bill of the fpar-
rozv-hawky yellow in that of mo ft diurnal birds
of prey, red on the neck and cheeks of the king
of the vultures, &c. In general, it adheres to the
fkin ; it is even dilhcult ro feparate it by mace-
ration.

The colours of reptiles alfo depend on the
prefence of the mucous fubftance.

• In the tortoifes, for inftance, the fkin which
covers the feet and the neck, is not only dif-
ferently coloured by the rete mucofum, but the
fymmetrical fpots which we remark on the fcales
are produced by the fame fubftance. This we
difeover by dilfedlion. The thicknefs of the
fkin greatly diminifhes as it approaches the
breaft-plate and the back-lhell. It paflTes below
the fcales which cover thofe parts, and -which
are themfelves covered by the epidermis and
rete mucofum, the variegated colours of which
form the fpots which we obferve through the
tranfparent parts.

- It is the fame with refpedl to falamanders and
frogs. Their mucous fubftance varies ftill more
as to colour ; it is black, brown, grey, white,
green, and yellow, red-orange, carmine, &c.

O o 2 We

5^4

Lec T. XIV. Of Touch.

We alfo fmd a mucous fubflance under the
fcales of lizards and JerpentSy and its colours are
exceedingly various.

Of all vertebral animals, however, fifhes are
the moft remarkable for the brilliant and metal-
lic colours which their rete mucofum exhibits.
W^e find in them gold, filver, and copper, tin,
lead, and even all the tints which thefe metals
aflume in different degrees of oxydation. But
as the defeription of thefe colours is the pro-
vince of Natural Hifiory properly fo called, we
wifii merely to point out in this place that they
are produced by the mucous fubllancc which
adheres clofely to the internal furface of the
fcales, and with which it is frequently removed.

Moft mollufca have a rete mucofum below
their epidermis.

In the Cephalopoda it is moft commonly of a
blue or red colour, but it forms a very thin
layer.

That of the Gaftcropoda varies confiderably,
as we may obferve particularly in i\\tjlugs. It
is thick and vifeous, but dilfolves completely
in water.

May not the fubftanCe of the fticll itfelf be
really analogous to the rete mucofum, though
the term mucous cannot be applied to it ? I am
very much inclined to believe that this is the

cafe.

The calcareous fticll is in fad found imme-
diately under the epidermis j and when fome ot

its

Art. II. The Skin.

5^5

its parts arc removed, it is a kind of cruft
without any apparent organization, and not a
membrane. It is produced by fucceflive drata.
rinajly, it is coloured, and its fliades are infi-
nitely various.

In the Cruftacea, the mucous fubftance is al-
fo reprefented by the calcareous cruft liruated
below the epidermis. Its colour is ufually a
dark-green, but fometimes red, white, or black.
Alcohol, acids, and particularly the adlion of
fire, change the green colour to a red, which is
frequently very brilliant. I'his we obferve every
day at our tables in cray-fijby lobfiers^ &cc.

In infeefts, in the larva ftate, we obferve be-
tween the epidermis and the mufcles, a layer of
mucous matter, the colours of which vary in-
finitely in the different fpccies. In caterpillars^
and in the larva of fome Hymeiioptera, this
fubftance is moft remarkable for its colour. It
gives to their bodies the, moft beautiful aud
lively tints, the (hades and fymmetry of which
are truly admirable. White, purple, violet,
blue, green, yellow, aurora, black, &:c. &c.
are diftributed in the moft regular and ftriking
manner.

We are alfo of opinion that the mucous mat-
ter dried or mixed with the horny fubftance,
produces the colours exhibited by perfedt in-
ledls, for when the Lepidoptera are in their
chryfalid ftate, the fmall coloured fcales which
afterwards ornament the wings of the perfedb

O o 3 infed.

566

Lect. XIV. Of Touch.

infecfl:, are then found in a mucous (late, fimilar
to that which we obferve in the fkin of cater-^
pillars. The colours of are alfo the ef-
teefi: of the retc mucofum ; we find it under the
n<in; it has the appearance of fmall glandular
points, the (hades of which vary confiderably.
But in the Coleoptera, ^nd feveral other orders,
the colours of the fkin are diffufed through the
horny cruft, nearly in the fame manner as thofe
of the Cruftacca, through their calcareous
fhells.

The rete mucofum cannot be diftinguifhed,
except in a fmall number of fpecies of Zoophy-
ta ; and it is even fo thin, that we cannot fe-
parate it from the fkin, as may be obferved in
Tome fea-ftars and aflinia. It appears to be con-
founded with the calcareous fliell w'hich forms
the habitation of feveral other genera. This
may be obferved in fome fpecies of urchins and
corallines-, and in fhe Ceratophites, and a number
pf Lithophites.

3. Corpus PaplUare, or the Villous Surface of

the Skin.

Anatomifls have given this name to that part
of the fl^tn which is lituated between the cutis
and the retc mucofum. It is not membranous
like the epidermis, but is a furfacc produced
by the aggregation and approximation of a
fnultitudc of fmall tubercles of different fliapes,
^vhieh arefuppofed to be formed by the laft ex-
tremities

Art. II. The Skin. ' 567

tremities of the cutaneous nerves ; they are,
therefore, named nervous papUltc.

I'hough the figures of thefc tubercles arc
very different, their ftruiflure is nearly the fame:
it is eafily exhibited, by macerating them for
fome days in water ; we then obferve that each
tubercle confifts of a collcsfHon of fibrils, united
at their bafe, nearly in the manner of hairs in a
pencil. Sometimes the fibrils of the center are
longer than thofe of the circumference, and
then the jxipilla is of a conical figure. Some-
times they are nearly of the fame length, and
in that cafe it is flat.

The fenfe of touch relides particularly in thefe
papillae : we find them, therefore, in thegreateft
number, and moft confpicuous, on the tongue,
the lips, and the extremities of the fingers.

In man, the papilliE arc particularly re-
markable on the foies of the feet, and on the
palms of the hands ; they are fituated clofe to-
gether in a very compad; manner, and diftri-
buted in lines correfponding to thofe we ob-
ferve externally, and of which we have already
fpoken in treating of the epidermis. Thofe
under the nails produce a villous furface, the
compad fibrils of which are all direded. ob-
liquely towards the extremity of the fingers.
The fibrils of the lips are difpofed in the fame
manner, but they are flili more delicate, longer,
and cloler to each other.

It is nearly the fame in all other mammife-

O o 4

rous

568

Lect. XIV. Of Touch.

rous animals ; but the papillae are more deve-
loped, in proportion as the parts to which they
belong are employed in touch. In the mole^
the JhreWy and the hogy the nervous papillae are
very vifible on the fnout ; they form tufts, con-
fiding of very clofe fibres. We find them alfo
on the probofeis of the elephanty and we have
obferved them very diftincdly on the tail of the
Cayenne opojfum j it is probable that they exifl
in the fame manner in all prehenfile-tailcd mam-
malia. We have not obferved them on thefkiii
of the dalphin and porpoife^

Birds have no diftiiKfl papillae, except* under
the foie of the foot, and the toes ; they are very
clofe fet tubercles, arranged in parallel lines.
We eafily demondrate them on the feet of poul-
try, when the epidermis is removed by theadion
of fire. We alfo obferve them on the mem-
brane which unites the toes of the Palmipedes.

Reptiles refemble birds with refpedb to the
papillae ; we find none, except under their feet ;
they are very thick, and projeding in fevcral
fpecies of lizardSy and particularly in the came-
lion. We cannot didinguifii them in the fea-
iortoifeSy which have the feet in the form of
fins. They do not exid in JerpentSy or at lead
have not the form of papilhe.

We have obferved nothing under the fkin of
white-blooded animals, which can be regarded
as nervous papillae. In the cephalapodous
mollufca, however, we have feen fomc nervous

filaments

Art. II. The Skin,

5^9

filaments in the fmall globules, which appeared
to us glandular, and with which the fkin is co-
vered. In the other mollufca we can trace
fome nervous filaments into the fubftance of the
fkin, but wc have never obferved them to form
papillae.

4. The Cuth.

This is the name given to that part of the
fkin which is fituated moft internally. Ana-
tomifts have developed its flrudilure in a very
diftind: manner, by the means of certain pre-
parations, and particularly by maceration in
water. They have demonftrated, that it is com-
pofed of a tilFue of gelatinous fibres, which
crofs each other in every diredion, and which
are fo interwoven that the whole may be com-
pared to felt : among thefe fibres we d]fcovcr a
great number of fine ramifications of nerves,
and arterial, veinous, and lymphatic vefTels, to
which we fhall return in a particular article.

The organization of the cutis is fuch, that
the fibres, which compofe it, are capable of
elongation and extenfion in every diredion ; its
extenfibility was neceffary to give to the' fur-
faces of animals the power of refilling the phy-
fical adion of other bodies.

Manufadurers have profited by this property
of the Ikin, to prepare it in certain ways, which
fit it for different purpofes, in w'hich ftrength
and flexibility are necelTary, and in which a
great fridion is fullaincd j this conftitutes the

art

570

Lect. XIV. Of Touch.

t

nrt of the currier. The fibres arc likewife approx-
imated, or feparated, in order that the leather
may be applied to various ufes ; and this is the
foundation of- the arts ol the tanner, fkinner,
parchment-maker, morocco-maker,

In man, the cutis is from t\vo to three mil-
limeters thick in certain parts of the body, as
in the dorfal and lumber regions ; but it is only
half a millimeter on the arms and the body.
By maceration, and the procefles ufed by fldn-
ners, we obferve that the fibres, which enter
into its compofition, arc long, fine,- and very
folid ; but united in a lax manner.

In mammiferous animals, in general, the
cutis is thickeft on the dorfal, and thinneH; on
the ventral resfion..

It is much thinner in birds, than in the mam-
malia. In fome families, however, it has a
confiderable confidence, particularly in birds
of prey, and in the anferes. It is exceedingly
thin, even proportionally confidered, in feme
fpecies of titmoufe^ and the genus motacilla.

Reptiles, which have the body unfurniflicd
with fcalcs, or only partly covered by them,
have a very compadl and denfe fkin. We have
an example of this in the tortoijes, Jalamanders^
frogs and toads. In the two lad genera, in par-
ticular, the cutis is rendered remarkable, by
not adhering to the body in all its points, as in
the other animals, in which it is intimately
united with the cellular fubflance. In thole

genera,

Art. II. The Skim.

57t

genera, however, it adheres only at the edges of
the mouth, in the middle line of the body, the
arm-pits, and the groins. In all the other
parts, the body is free within the cutis, which
cnclofcs it like a fac.

The cutis of lizards and Jerpents ^ rclembles
that of filhes.

In this clafs of animals, we find a very tena-
cious cutis below the fcales; but it is intimately
attached to the mufcles, even much moreclolcly
than in the other dalFcs, and is very thick in
the Jlurgeoti, the Jharks, the rays, the eel, 6:c.
on the contrary, it is thin in filhes which have
large fcales, as the carps, i> reams, &:c.

We have not obferved a real cutis among the
invcrtebral animals, except in tlic cnltlc-fijh,
and the other Cephalapoda ; it is applied almofi:
immediately to the mufcles, by the means of a
very denfe cellular fubfiance ; it is itfelf of a
very coriaceous nature, and not eafily lacerated;
its fibres are very flender.

In the other invcrtebral animals, w^c find no
part that can be compared to the cutis. There
is, indeed, a pellicle below the fhell of the
cruftacea, but it is fine, tranfparent, and has
very little confidence. In infects in the larva
date, the fkin, which they cadoif in moulting,
is of the fame nature and the fame thicknefs as
that below it, and which is dedined to fucceed
. it. Even the envelope of chryfalides coarc-
fat(6y as thofe of the Lepidoptera and Diptera,

cannot

572

Lect, XIV. Of Touch.

cannot be regarded as cutis; it is ratlier a kind
of horny epidermis. Tinally, in the perfect
ftate, we find no part ot the teguments of in-
fc(fts that can be compared to the cutis. The
lame obfervation applies to the worms and the
Zoophites..

.Article III. - •

Ofilie Mufcles of the Skin, or the Fannicidus

Carnofus.

In the preceding Article, we have explained
the nature and the organization of the different
ffrata of the teguments. We fhall now proceed
to confider the motions of which the flein is
fufceptible, and the organs by which they are
produced.

In man, the fkin has very little motion ; the
mufcles inferted into it have, therefore, very
little force: they form three pairs ; two of thefc
mufcles arc particularly deffined to move the
fkin of the forehead and the head; the third
a<5ls on the teguments of the neck and the
cheeks.

All the fpacc comprifed between the occiput
and the fuperior part of the orbits, is occiipicd
immediately below the cutis, by a digaffric
mufclc, principally aponeurotic, and which is

named

Art. III. Panniculus Carxosus. 573

named occipIto-ft'ontaUs, The flefhy fibres arc
very fliort, and fitiKited at the two extremities
of the large aponeurofis, which forms a kind
of cap to the cranium. The anterior fibres are
attached to the fkin below the ejr'e- brows : the
poflerior are inferted into a tranivcrie line
above the occipital bone: their other extremity
pafles under the aponeurotic cap, to which they
are fixed. Thcfc mufclcs are more diflincl in
fome fubjeifls, than in others ; they raife the
eye-brows, corrugate the fkin of the forehead,
and produce tliofe tratiTverfe w’rinklcs, more or
Icfs parallel, which we obferve above the brow.

Immediately below the anterior Helby fibres
of the occipito-frontalis, and in the line which
correfponds to the eye-brow, w e find fome other
flelhy fibres, which arife from the nafal emi-
nence of the os.frontis, and arc inferted partly
into the fkin of the eye-brow, and partly into
ihe fibres of the occipito-frontalis, with which
they are covered : this fmall mufcle is called the
corriigator fupercilii (frouto-fiipercilius ;) it op-
pofes the elfedl of the occipito-frontalis, and
approximates the eye-brows, and thus corru-
gates the fkin above the root of the nofe.

Finally, the third pair of cutaneous mufcles,
(iboraco-facialis) in man, occupies all the ante-
rior part of the neck; they form a kind of
flefliy membrane, fituated immediately below
the fkin ; it originates, upon the anterior part
of the breaft, by flender and very diftant flefhy
4 fibres

574

I-.ECT. XIV. Of Tol'cfk

fibres in the cellular fubliance, which covers
the great perioral and deltoid mufcles, and ex-
tends to the lateral parts of the cheeks; it is
there partly attached to the lower jaw, and
partly to the zygoma; thefe mufcles are exceed-
ingly thin, and loolely connecfled in the inferior
part of the neck. They become thicker, in
proportion as they contract.

It is difficult to determine the action of thefe
cutaneous mufcles ; they a6t on the mouth by
their union with the mufcles of the lips; they
have alfo great influence on the expreffion of the
countenance. They produce very remarkable
wrinkles in the teguments of the neck and the
chin.

There are alfo forne mufcular fibres under the
Ikin of tjie ferotum in man, which are de-
nominated the dartos : but thefe fibres are very
flender. They vary confiderably, and, ftricflly
fpeaking, do not conflitute a mufcle : they are
dcltined to corrugate the fkin of the ferotum.

In all the other mammalia, we find thefe cuta-
neous mufcles; thofc of the head are commonly
lefs confpicuous, but that of the neck is moft
firongly marked : there is, bcfides, a particular
mufcle, which extends under all the fkin of the
belly, and even under the thighs, and is inferted
into the humerus.

Apci and do^s have an occipito-frontalis ; it
is alfo very thin, but its flefliy fibres are j)ro-
portionally longer than the human. \Vc find,

bdidcs.

Art. III. Panniculus Carnosus. 575

befides, under the fkin of the face, fome flefhy
fibres, which perform the adion by which thefc
animals wrinkle the lateral parts of the cheeks
and the nofe.

The cutaneous mufclc of the neck in apes is
conneefted to the fkin by a very compaifl cellular
fubrtance : it is prolonged over the face, and
unites with the fibres we have already mentioned.

In dogs^ we obferve only fome very flendcr
flefliy fibres on the neck.

The cutaneus of the belly alfo adheres very
clofcly to the fkin in thefc animals ; its fibres
cover the thorax and abdomen, and all unite
below the arm-pit, where they are inferted by
one or two tendons, along with that of the great
pedioral mufcle, under the head of the humerus.
This mufcle has the fame infertion in all the
mammalia ; it aflills in the motions of the arms,
and may be named denno-humeralis.

In the Quadrumana, Chcrioptera, and male
Sarcophaga, we alfo find mufcular fibres in the
fkin of the ferotum. They are even propor-
tionally more confpicuous in the bat, than in
man.

In the racoon, the dermo-humeralis islikewife
a very powerful rctra(5for of the prepuce ; it
forms a bundle of fibres, of the breadth of two
fingers, attached to the prepuce, and deferib-
ing an oval, with the bundle of the oppofite
fide : the remainder of the mufcle, which co-
vers the belly, is very thin. Anteriorly, the

6 mufcle

- 57^ Lect. XIV. Of To UC IT.

mufcle is attached to the humerus by two dif-
flips.

The cutaneus colli in the maYmotte \tvy much
refembles that 6f man : below it, however, we
find another thicker mufcle, which forms, as it
were, a lining to the firfl, but proceeds farther
up ; it extends to the lateral parts of the head,
and even to the face and the muzzle.

The dermo-humeralis occupies the whole of
the back, from the origin of the tail, to the
pofterior point of the trapezius. The part on
the belly arifes from the pubis, the groin, and
the thighs : all the fibres unite below the arm-
pit, where they form two tendons, one of which
is inferted with thofe of the latiflimus dorfi
and teres major, and the other with that of the
pc(floralis major.

There arc very few variations in the other
fpecies of mammalia. In almoft all of them
there arc feme mufcular fibres under the fkin of
the male genital parts, particularly in thofe that
eje<fl: their urine by fquirts.

We find a cutaneous mufcle even in the dol-
phin ; it arifes from the lateral parts of the body,
and terminates In the os humeri.

As the European hedge-hog prefents a very
complicated and curious organization in the
mufcles of the ikin, wc lhall here give an
abridged defeription of them.

It is neceflary, in the firfl place, to obfervr,
thai thofe mufcles, being attached to the Ikin,

change

Art. III. pANXicuLus Carxosus. 577

change their fituation with it, and that they are
therefpre fixed with refpecl to their points of
attachment only. We murt then fuppofe the ani-
mal placed in certain pofitions, in order that the
parts deferibed may be more readily found.

Let us fuppofe the hedge-hog rolled up as
in the pofition the 'animal alfumes for defence.
All the body is then enveloped under the fkin,
by an oval-lhaped fac, compofed of flelhy ami
concentric fibres.

Thefe fibres adhere clofely to the fkin, and
even to the root of the fpines which cover it,
and it is difficult to detach them with infiru-
ments. The fiefiiy purfe they form is thickeft
at the margin of its aperture, which correfponds
to the belly, at which place they form a kind
of fphindeer or mufcle with orbicular fibres.

When the body of the hedge-hog is elon-
gated, as in (landing or running, the figure of
this mufcle is completely changed. It is fitu-
ated on the animal’s back, where it forms an oval,
the middle part of which is very thin, but the
circular margin confulerably thicker, and more
elevated. Several acceffory mufcles arife from
different points of the margin.

Towards the head, or at the anterior ex-
tremity ot the oval, we obferve two pairs of ac-
' ceffory mufcles ; one has its origin in the mid-
dle line, and is inferted into the bones of the
nofe; the other, which arifes more externall 7,
appears to be confounded with the exterior or-
VoL. IK p p bicular

57^ Lect. XlV. Of Touch.

bicular fibres, and is infertcd anteriorly into the
lateral parts of the nofe and intermaxillary-
bones.

Another pair of mufcles arife from the pofle-
rior extremity of the oval. They are of a broad
pyramidal form, and are likewife continued
with the external orbicular fibres. The tendi-
nous point of each is inferted laterally near the
end of the tail.

There are alfo fome other fub-cutaneous muf-
cles, fituated towards the belly, or below the
great orbicular mufcle.

When the fkin of the belly is removed, we
readily perceive three difliiKft portions of fiefhy
fibres.

The firft is fituated under the throat, and cor-
refponds to the cutaneus colli. It comes from
the top of the brcafl under the fkin, and is in-
ferted on the lateral parts of the head, near the
ears. The portion of one fide unites to itscor-
refpondent by a middle line, which is made of
fat.

The fccond comes from the middle line of
the flernum ; it takes an oblique dirc<5lion, be-
coming thicker and narrower above the flioul-
ders, as it proceeds to join the edge of the great
orbicular mufcle.

The third ventral portion, which is flill more
flcndcr than the two former, extends over the
whole furface of the abdomen ; it arifes from
the circumference of the arms, from the lateral

parts

Art. III. Panniculus Carnosls. 579

parts of the tall, and from the tops of the
thighs : upon reaching the ribs, it divides. The
internal portion, whicii is the broader of the
tuo, pafics under the arm-pit, and is inferred
into the internal fide of the upper end of the os
humeri. The external is prolonged laterally,
and unites with the great orbicular cutaneus,
towards the neck.

Thefc are the nnifclcs of the fuperficial layer:
there are lliH fonie others, which are appen-
dices of the former, and are fituated under the
niufcles of the back.

One arifes from the head, where it is attached,
on both lidcs, to the podcrior edge of the ex-
ternal meatus auditorius. It is loft poftcriorly
in the anterior point of the orbicular nuifcle.

Another fmall bundle of ftefhy fibres arifes
from the laft: cervical procelTes, and is loll in ^
the cutaneus of the back.

Lartly, below the great orbicular mufcle, we
obferve fomc tranfverfe fibres, which form a
very thin layer. The anterior are attached to
the internal and upper part of the humerus :
the poftcrior, to the external bundle of the third
ventral portion.

Let us now confider the ufe of thefe mufcles.

The animal, when rolled up like a ball, is
enveloped by the orbicular mufcle. To pre-
ferve this pofition, it is fufficient to contracT;
the marginal fibres, which are very ftrong, and

P p 2 which.

5^0

Lect. XIV. Of Toucir.

which, in doling the purfe fo as to cover the
belly, have the effedl of a fpliiinflcr.

When the animal wilhes to return to its or-
dinary tpoflure, it unrolls itfelf thus : the middlfe
fibres of the oval contradl ; the external fibres
at firfl: relax, and leave the belly and the feet
free ; all the circular fibres then contradt to-
gether, and gather up towards the back.

By this general contradlion, the accefibry
mufcles are rendered fixed, and capable of con-
tracfling. The anterior move the head upward,
and extend it towards the back. The pofterior
raife the tail.

Thofe of the deep-feated layer elevate the
head and the neck ; the animal is then enabled
to walk.

If the approach of danger induce the hedge-
hog to roll itfelf up, the animal accomplilhes
this purpofe in the following manner:

The orbicular cu'^incus relaxes, and the muf-
clcs of the head and the neck elongate the oval ;
the deep tranfverfe fibres attached to the ex-
ternal portion of the ventral cutaneus, render
it broader.

Every thing now yields to the impulfc : the
flexors, and the cutaneus of the neck and breafl,
draw the head towards the belly ; the cutaneus,
and mufcles of the abdomen, bring the tail and
the thighs towards the head ; the flexors of the
lim?)s contradl.i the great orbicular mufclc then

defeends

Art. III. Panniculus Carnosus. 581

defccnds on the ribs, contradls obliquely, and
thus, alfuming the lhape of a purfc, retains the
animal in a globular form.

The cutaneous mufcles of armadillos (dafypus)
are not fo llrong, nor fo complicated as thofe
of the hedge-hog, though thefe animals have
alfo the faculty of rolling themfelves up.

The great dorfal cutaneus is thickeft at its
ventral margins, by which it Prongly adheres
to the fold that unites the tkin of the abdomen
with that of the back ; it is fixed to the ikin of
the groins and arm-pits : it alfo detaches fomc
nips, which arc inferted into the head and the
tail ; but its flefhy fibres are very fiender. A
certain number of fibres are font ofi'at dilferent
fpaces, and inferted into the anterior edge of
each of the ofieefus bands which cover the
animal.

The cutaneous mufcles of the belly are alfo
very fiender ; they furnifli fome fiefiiy fibres to
the penis : and the bundle which thefe fibres
form, very much refembles that which we have
obferved in the racoon ; but it is Id's thick.

The cutaneus colli exifis, but it is exceed-
ingly fmall ; it is prolonged under the fcales of
the face.

Among birds, thefe mufcles are more cou-
fpicuous in certain fpecies, particularly when
the bird has the power of moving at pleafure,
the leathers of the creft, neck, or tail, as
the boopoesj cockaioos, herons^ bee. They are

P d ' very

5S2

Lect. XIV. Of Touch.

very cafily difTeded in the. goof ey and from that
bird we fhall deferibe them.

The ventral ciitaneus arlfes from the feventh
and eighth ribs, by two flefhy digitations, like
the ferratus magnus ; it is broad and flat ; it
proceeds obliquely forward and upward towards
the fcapular articulation of the humerus, and is
inferred into the fkin, above the flioulder joint.

There are alfo fome flefhy fibres on the exter-
nal lateral part of each of the great pedtoral
iniifcles. In the fubflance of the fkin, imme-
diately above the arm-pit, thefe fibres arc con-
founded with the tendon of the pedloralis major.

Immediately above the broad flat part of the
bone of the pelvis, between the two ilei, we
obferve two fmall flcfliy layers below the fkin :
the fhort, and apparently papillated fibres of
thefe layers, acT: on the feathers of that part of
the pelvis, and erect them.

We alfo remark along the f!s.in of the neck,
fome longitudinal mufcular fibres, which move
that part ; they form two difiindl layers, par-
ticularly on the fides.

There is no cutaneous mufclc on the trunk of
frogSy becaufe the fkin docs not adhere to that
part of their body. Under the throat, liow-
cver, we find fome fibres, which arc attached
to the margin of the jaw, and inferted into the
cellular fubflance that unites the fkin to the
origin of the breafl.

Ill tortoifesy the cutancus colli is very vifiblc,

and

Art. III. Panniculus Carnosus. 583

and Teems to be formed of two parts ; it is ex-
tended from within the concavity of the lower
jaw, to the bottom of the neck, at the anterior
part of the brcaft-plate. A middle cellular
line unites it with the mufclc of the other fide;
it takes its origin from the tranfvcrfc procclTes
of the cervical vertebrne. Being fpread over
all the mufcles of the neck, it ferves as a girdle
to them ; in its lower part it is perforated by
the fterjio-mafloideus, w hich, as we have already
obferved, arifes from the lateral parts of the
breaff-plate.

On removing the Ik in of fpinous fiflies, fuch
as the carpy we find fomc mufcular libres ad-
hering intimately to it; they are divided into
two portions, by a longitudinal line, which cor-
refponds to the fituation of the vertebral co-
lumn. We here obferve impreiTtons made by
the tendons, inferted in the fkin ; they deferibe
curves, the convexity of which is towards the
tail. Thefe are the only parts that can be re-
garded as cutaneous mufcles in filhcs.

In the animals w ithout vertebrae, that have
foft bodies, almofl: all the mufcles may be con-
lidered as cutaneous ; for the greater number
are attached to that integument. But as they
are alfo employed in progrellion, we have de-
feribed them among the Organs of Motion.

Pp4

Arti-

584

Lect. XIV. Of Touch.

Article IV.

OJ the Cilands of the Skin, and the Subcutaneous
' Fat.

1. The Glands.

The furface of the fkin is fpontancoufly be-
dewed with fubltanceSj which appear defined
to preferve it from theadlion of the furrounding
elements, and which vary according to the na-
ture and habitation of different animals.

This humour is undluous in man, and other
warm-blooded animals ; it is a kind of far,
which would gradually accumulate on the fldn,
if we did not take care to remove it.

In the cold-blooded animals it is of a vifeous
or gelatinous nature, and does not diffolvc in
cold water : thefe animals have it in the greater
abujulance, in proportion as they rcfidc mere
condantly in the water, and have their bodies
Icfs completely covered with fcales. • It appears
to be a fupplcmcnt to this lull: kind of armour.
I'hfhcs that arc dcllitutc of fcales, therefore, as
rays and (harks, have a great quantity of this
fluid, compared with thofe that arc covered
with large fcales.

Among reptiles, thofe that have fcales, as
fnakrs nnd lizards, have the fkin almoll dry;
but thofe with naked fkins, as fuUimanders and

Art. IV. Glands of the Skin. 585

frogSy have the furface of the body always co-
pioufly lubricated with vifeous matter.

Toads -And falamaiiJers have even the power of
augmenting the fecretion of this liquor, and of
making it exude like a dew through the pores
of the (kin.

Among the animals that have white blood,
we iind that mod: of the mollufca produce a
glutinous liquor, which lubricates the wholeot
their (kin ; they even throw out a cor.liderable
quantity of it, when they arc in the lead danger.
This is particularly remarkable in fr.ailsy Sic.
In thofe that have a hard and fcaly fkin, how-
ever, nothing fimilar is exuded, and their ex-
cretions take place only at particular parts of
the body.

Tire lame animal does not produce the fame
kind of fubdance in all the parts of the fkin.
In man, for example, there arc three of thefe
excretions, beddes perfpiration.

A very fubtile oily matter tranfudes through
the pores of the whole fkin, and prevents, for
forne time, pure water from fpreading upon it.
This matter alfo appears upon the hair of the
head, and other parts of the. body, and at lad
gives them a grealy appearance, if they are aot
frequently cleaned.

A kind of ointment is -produced in certain
parts, and particularly at the roots of the hairs
in the arm-pits and the hams, &c.. from fmall
follicles, which are vifible to the eye : this

matter.

Leot. XIV. Of Touch.

586 '

matter, in hardening, attaches itfelf to thefkin,
and produces a fort of fcales, which are re-
moved by water and frieftion.

LafHy, there are glands, the apertures of
which are very vifible in certain places, that
furnifti a concrete ceruminous matter. This
fubflance may be compreffed in the form of
fmall worms : thefe glands arc found on the
lides of the nofe, behind the ears, under the
eye-lids, around the nipple, on the perinaeum,
and in the groin : they may alfo be obferved
fcatrered almofl every where, except, perhaps,
on the palm of the hand, and the foie of the foot.

We may include, in the laft kind, ’that thick
fetid matter, which accumulates in lumps be-
tween the glans of the penis and the prepuce,
and beneath the nymphse, and alfo that which
covers the edge of the anus.

We are unacquainted with the organs which
produce the firll kind of humour ; it is, per-
haps, a fimplc exhalation of the fat, which al-
ways exifts in a certain quantity under thefkin.

• The follicles, which produce thefccond kind
of ointment, are very fmall, and round, or ob-
long. Their excretory canals are fmall and
twihed.

The third kind of ointment is produced by
glands which arc named Jcbaccousy and which

arc fometimes compound.

The fubflances which anoint the fkin of
quadrupeds, arc fimilar to thofc which wc find

on

Ar-t. IV. Glands of the Skin. 5S7

on our own : fomc have them collected In large
cliificrs, on certain parts of the body, as for
example in the groin. The glands, or parti-
cular follicles, do not appear confpicuous in
the fkin of the Cetacea ; an oily fluid exudes
from the whole of its' furface, in fuch abundance
as to render it cvery-where fmooth and flippery.

In birds, the febaccous glands are diflicultly
feen, and fituated more deeply under the fkin.
On the rump there is a conglomerate gland of
a particular flru6lurc, from which they exprefs
an oil, which ferves to imbue their feathers.
We fliall deferibe this gland when we treat of
Excremcntal Secretions. At the fame time, we
lhall notice feveral other glands peculiar to
certain kinds of quadrupeds, as thofe which
produce mujk^ civet, caftor, &c.

The cutaneous glands arc more vifible in cold
blooded animals, than in the preceding.

The fauwianders have feveral glands ranged
along the back, which form elevations, or lumps ^
on the Ikin.

The toads have them fcattered irregularly, on
the w'hole furtace of the body; we obferve, in
particular, two which are very large, behind
their ears ; thefe glands produce an acrid hu-
mour, which is a poifon to very fmall animals.

In lizards, we obferve a very regular row of
fmall pores, which alfo yield a vifeous humour.

But the pores which tranfmit the vifeous
matter to the Ikin, and the fources which pro-
duce

Lect. XIV. Of Touch.

5SS

diice itj arc no wlicre fo eafily obfervcd as in
the rays and the Jharks.

On the fuperior and inferior furfacc of the
body, in thofe, fifhes, we find a great number of
very large pores, which are the orifices of an
equal nuniber of tranfparcnt excretory velTels.
In xhej^jarks, thefe vcfiels are as thick as the
tube of a quill; they proceed from certain cen-
ters, in fafgiculi, which are not divided into
branches ; thefe centers are more or lefs nu-
merous according to the fpecies, and the ge-
latinous humour they contain appears to be
formed wfithin them : the centers, however, do
not refemble glands ; we obferve in them only
acellular texture, filled itfelf with the fame hu-
mour, and to which a great number of nerves
arc in particular diftributed. In the ray, there
are two principal centers, fituated towards the
lides of the mouth. The tope (fqualiis galcus)
has only one in the fnout. We {hall return to
this fubjedl in the Article on Secretion.

In olfcous fifhes, the vifeous liquor chiefiy
exudes through pores fituated along the furrow,
which extends longitudinally on each fide of
the body, and is called thc^ lateral line: thefe
foramina arc the orifices of an equal number of
fmall tubes, which communicate with one large
tube fituated behind this line, throughout the
whole of its length. This great vefiel reaches
to the head, and is there divided into feveral
branches, which fpread over both jaws, and two

of

Art. IV. Glands of thk Skin. 589

\

of which unite towards the upper part of he
fnout. Xhe rays and Jharks have alfo thefe large
vifeous vclTels on the head, independent of the
numerous fmall vciTels which we have juft de-
feribed, and which are peculiar to them.

We obferve thefe veflcls, and the pores, which
are the orifices of their fmall branches on the
head, more diftincftly in the ebim^era vionjlrofu,
than in any other fifli. The pores are alfo very
vifible in the common pike (e/ox lucius)^ and the
fea pike (ejos bellone).

G. The Adipo/e Suhjlance.

A cellular web more or lefs firmly unites the
flcin to the flefh ; this membrane exifts in almoft
all animals, except frogs and toadsy in the greater
part of which the fkin adheres clofely only in
fome parts of the body, and is connedled with
the flefli of the other parts merely by veflels
and nerves.

We alfo find in birds, and principally under
their axillce, large portions of fkin, which ad-
here only in a very loofe manner to the flefh.
In confequence of this ftruClure, the air is ad-
mitted into the vacant fpace.

If we may believe Sparman, the rately or
honey-eating badger of the CapCy (vi^oerra melli~
vora, Lin.) prefents afimilar difpofition.

The fubcutaneous cellular membrane is ufually
filled with fat, the quantity and confiftence of

^ which

590

Lect. XIV. Of Touch; *

ivhich varies according to the fpecics, and the
Hate of each individual. Every one knows, that
the hog has the fat thicker, and more uniform,
than other quadrupeds, in which it is, there-
fore, called lard.

The Cetacea have Hill a thicker coat of lard
than the hog, but their fat is fo liquid, that it
runs off in the form of oil, without being ex-
preffed.

Animals, in which the fubcutaneous fat is
very abundant, have the fenlibility of the fkin
greatly diminilhed.

In the cold-blooded animals, there is, Hricftly
fpeaking, no fubcutaneous fat. Sometimes
only we find the inner furface of the fkin rnoi-
ffened like the reft of the body by an oleaccous
fluid. This we obferve, for example, in the
falmon and trouts. At other times we find fub-
ftancespf a very difterent nature. The moon^
fijhy for example, has, under the fkin, a layer
two or three fingers breadth thick, of a fat fub-
flance, apparently like lard, but which pre-
fents all the chemical characters of albumen.

The ufe of thefe difl'erent fubftanccs placed
under the fkin, appears to be to weaken the im-
preftions of blows, or other external fiiocks,
and to diminiflt their effeCl upon the flefti. But
the fat, in general, has feveral other ufes ; it
ferves to j)referve the flexibility of all the parts
between which it is interpofed, and, in parti-
cular, forms a kind of magazine of nutritive

fubflancc,

Art. V. Division of the Members. 591'

fubftance, which may be abforbed, and conveyed
again into the blood.

This is chiefly remarkable in anifnals which
exifl for a certain period, annually, without:
food : as thofe that fleep during winter, cater.^
pillars, when they pafs to the chryl'alid flate,
&c. Such animals do not fall into thefe le-
thargies, until after they have accumulated a
great quantity of fat, which is found to be cx-
haufted when they awake.

There are particular refervoirs for this fub-
ftance, which we fliall deferibe in the It^ars,
dormice^ marmot tes, caterpillars ^ &c. when we
come to the Article on Nutrition.

Article V.

Of the Fingers and Toes, and of their Structure
relative to the Senfe of Touch.

In Lectures IV, and V. wedeferibed the number,
form, and ule ot the bones and mufcles of the
members, and of their extremities, with refpedl:
to their ufe in motion; we are now about to
confider thefe parts in another point of view,
namely, with relation to the organ of touch.

The fingers are particularly intended to pro-
cure us a knowledge of the forms of bodies.
Two circumfiances tend to perfect or dimi-
3 nifli

592

Lect. XIV. Of Toucir.

nifli the faculty of touch : i. The divifion of
the hand and foot into fingers or toes, more or
lefs numerous, more or lefs long, diftimfl and
moveable. 2nd, The form of thefe fingers or
toes, and the nature of the teguments which
cover, arm, or protedb them. Thefe confider-
ations form the fubjecfl of the prefent article.

The organ of touch is more perfedt, in pro-
portion as the hand is divided into diftincl and
moveable fingers : man, therefore, polfelTes this
fenfe in a very eminent degree. MonkieSy in-
deed, have the hand organized like that of a
man ; but, as we obferved in treating of the
mufcles, Vol. I. p. 335, &c. they cannot move
the fingers feparately, as they have no proper
extenfor or fiexor mufcles : befides, their

thumb is (horter, and cannot be fo eafily op-
pofed to the other fingers. It is, however, on
this oppofition of the fingers that the faculty
of feizing the mofi: minute objeefts, and of dif-
tinguifiiing their flightefi eminences, depends.
But if the hand of moukirs be lefs pcrfecfl than
that of man in this refpeefi:, they have a more
advantageous organization of the foot, the toes
of which are longer and more moveable.

In man, and in the greater number of Qua-
drumana, the fingers are fiender, rounded, and
covered by a compa(5l fkin, on which numerous
nervous papillae are difpofed in a very regular
manner; their extremity is covered by a nail,
on the fuperior part only ; this nail is flat, or

femi-

Art, V. Division of the Members. 593

fewDi-cylindrical : only t\\t fapuiiis (fimia ro/Alia^
jaccbits, i^c. Lin.) have the extremity of the
toe inclofed in a horny and pointed nail, re-
fembling that of the Sarcophaga.

In the Chcrioptera, the fingers are not capa-
ble of grafping folid bodies, becaufe they are
all inclofed between two fine membranes. They
therefore do not pofTefs, in a high degree, that
part of the fenfe of touch which ferves to afeer-
tain the forms of bodies ; but the extenfivc fur-
face which the membranes prefent to the air, fit
them for receiving fuch delicate imprelTions of
reli fiance, motion, and temperature, that fome
authors have been induced to aferibe a fixth
fenfe to thefe animals.

Spallanzani had obferved that l^als blinded,
and afterwards fet at liberty, could, notwith-
fianding their total deprivation of fight, con-
duit their flight through fubterraneous palTages
without firiking againfi the walls ; that they
even turned exactly as the moft complicated
xvindings required ; that they difeerned the holes
in which their nefis were placed ; and that they
avoided cords, lines, and other obfiacles which
had been placed in their way.

Spallanzani then endeavoured to afeertain by
what fenfe thefe animals diredted their motion.

It was not fight, fince that organ was entirely
defiroyed ; it was not hearing, for the ears of
feveral individuals had been completely flopped ;
it was not fmell, for in others he had taken the

VoL. II. Qji- precau-

594 Lect. XIV. Of Touch.

precaution to fliut up the aperture of their
noftrils. '

He concluded therefore, that bats pofTefs a
fixth fenfe, of which we have no idea. Citizen
Jurine has made other experiments, w’hich tend
to prove that it is by the ear they guide their
flight ; but it appears to us, that the operations
to which he fubjedled the individuals he de-
prived of the pow'cr of direfling their motions
were of too fevere a nature, and that fomething
more was done than merely preventing the ani-
mals from hearing. It appears to us alfo, that
the nature of their organ of touch is fufficient
to explain all the phaenomena bats prefent.

The bones of their metacarpus, and the pha-
langes of the four fingers which fucceed the
thumb, arc excclfivcly elongated. The mem-
brane which unites them, prefents an enormous
furface to the air: the nerves which are diftri-
buted to it, arc numerous, and minutely divided ;
they form a net-work very remarkable for its
finenefs, and the number of its anafiomofes. It
is probable that, in the adlion of flight, the air,
w hen flruck by this wing or very fenfible hand,
impreffes a fenfation of heat, cold, mobility,
and rcfiflance on that organ, which indicates to
the animal the exiflcnce or abfence of obftacles
which would interrupt its progrefs. In this
manner blind men difeern, by their hands, and
even by the fkin of their faces, the proximity of
a wall, door of a houfc, or fide of a flrect, even

without

1

Art. V. Division of tii£ AIembers. ^95

\vithout the afTiftancc of touch, and merely -by
the fenfation which the dilference in the re-
finance of the air occafions.

The toes of the poflerior feet in bats^ arc fiini-
lar in their ftrudurc to thofe of the other Sar-
cophaga.

Notwithflanding the Plantigrada have the
fingers Very fliort and little moveable, and ge-
nerally five in number, the fenfation of touch
ought to be fomewhat more perfect than in the
Carnivora, becaufe the whole foie of their foot '
is free from hairs ; and as the contacT; with the
bodies which they touch is more immediate, the
fenfation mull be llrongerand better perceived.

The fnole has the hand greatly enlarged, and
all the fingers united as far as the nail.

The Pedimana come naturally after the Plan-
tigrada with refpedl to the prefumed perfeflion
of touch, as their great toe is feparate from the
other toes. This renders their pofienor foot a
kind of hand ; the toe is proportionally very
thick, elongated, moveable, entirely deprived
of the nail, and enlarged at its free extremity.

The chefnut coloured^ or true orang outang, is
the only animal, befides the Pedimana, that has
a feparate great toe without the nail.

The Carnivora walk on the extremity of their
toes, which are Ihort, and all placed in the fame
diredlicn, and are therefore much lefs favoured
as to the fenfe of touch, bur they are in general
compenfated by that of fmell. The greater

2 number

596

Lect. XIV^. Of ToucI^»

' number have the laft phalanx inclofed in a
cutting nail. In the and civet genera^ this
phalanx bendu back, and cannot be employed as
an organ of touch whilft the animal walks.

Among the Rodentia, the hares ^fquirrelsy and
ratSy which walk on the four feet, but on the
extremities of the toes, and which have the laft
phalanges only feparate from each other, have
an elongated conical nail which envelopes all
the free part of the toe. Some cavies, and the
porcupine y have almoft all the toes inclofed in
hoofs like thofe of hogs. The aye-aye y (Jciuriis
Madagafcarieiijis Lin.) is particularly remark-
able for the divifion of the toes of the fore feet.
All the phalanges are greatly elongated, parti-
cularly thofe of the middle toe, by means of
which the animal picks infecHis from under the
bark of the trees. This is alfo the only animal
amontx the Rodentia which has the great toe fe-
parate, and oppofcable to the others.

Lailly, the kangaroos SLndjerboaSy which ufe
chiefly the hind feet in progreflion, have the fore
feet divided like thofe of rats, and armed with
pointed nails; but the poflerior feet have the
toes enveloped in hoots.

The Ldcntata in general have the toes united
by the fkin as far as the nails, fomc of them
even, as the flolhs, walk only on the convexity
of the nails, which bend under the foie of the
foot, d'ho Cape ant-eater has flat and very broad
nails. Several armadillos have them almofl: in

the

Art. V. Division of the Members. 597

the form of hoofs. In all thefe animals the toes
vary from four to two, and are capable of no
motion except extcnlion and flexion. This dif-
pofition arifes from the deep pullies in the arti-
culations of the phalanges.

The elephant and the rhinoceros have all the
toes united by a thick and callous fkin. They
are only diflinefl: externally by the number ot
hoofs which are placed on the edges of the foot.

The hippopotamus, the tapir, and the hogs,
have the toes more feparared ; but they walk on
their extremities only, which are enveloped in
hoofs.

All the Ruminantia, without exception, have
only two toes, covered with hoofs of a triangular
form, on which they walk. The inferior fur-
face, which touches the ground, is the mofl: fofr,
and appears tuberculatcd. The external is con-
vex and fmooth. The third furface, or that
which is next the other toe, is a vertical plane.
The camel only differs a little in the form of the
hoof, which is fmall, more regularly triangular,
and prolonged inferiorly by a piece of horn
which inverts all the foie of the foot.

Finally, in the Solipeda there is only a fingle
toe, terminated by a fcmi-circular hoof, on
which the animal walks.

Before we conclude this article on the divifion
of the members in Mammalia, we rtiall notice
fome difpolitions relative to'motion, but which
have an influence on the fenfe of touch.

Q.0. 3

Lect. XIV. Of Touch.

59S

We ha.ve already pointed out one of thefe pe-
culiarities in the Chcrioptera. Amongthe Sar-
cophaga, the otters, the feals, the didelphis me->
mina, and one fpecics of Jfjrew ; and among the
Rodentia, the beaver, the ondatra, &c. which
f\\d«n and dive frequently, have all the feet pal-
mated, that is to fay, their toes are united by a
membrane.

Laflly, in t\\&morfe, and in the Cetacea, we do
not diftinguifli the toes which form the feet ;
they become real fins, on the edges of which we
however remark, in the morfes and lamantin, ru-
diments or veftiges of nails indicating the five
toes, which we indeed find, but concealed under
the coriaceous fl^in that clofcly envelopes them.

In birds, the thoracic member is not intended
to exercife the fenfe of touch ; it therefore k not.
divided at the extremity into fingers or appen-
dices, and is alfo almofi: entirely covered by
long and clofe feathers. The feet are the only
parts which poflefs the faculty of touch, and
in them it is very much blunted by the horny
laminae or fcales which cover the tarli and
the toes. Sometimes it is rendered Hill more
obtufe by feathers, and always by the callofi-
tics in the form of excrefcences and tumors
which cover the feet inferiorly.

Wc have already dt feribed, in Vol. I, page 41 r,
the number and diredion of the toes in dill'crent'
birds. They arc not in any fpecies covered
with hoofs, but arc merely furniflied with nails,

which

Art. V. Division of the Members. 599

which ftrengthcn them, without injuring the

fenfe of touch. »

In the fwimming or web-footed birds, as the
ducks, the anterior toes are united by a mem-
brane which extends to their extremity. Some-
times the pollcx is alfo united to the other toes
by this membrane. The birds how’ever in w hich
this takes place, are of all the anlcres thofe
which employ their feet mod: frequently in
touching and feizing fubltanccs. A fliort mem-
brane unites merely the bafe of the anterior toes
in gallinaceous birds. The two external toes
are aifo united at iheir bafe in a number of the
Grallae and the rapacious birds.

The.Paflerine birds have in general the two
external toes intimately united by their firfl: pha-
langes; and infome genera, as the king' s-jijhers,
and the bee-ealers, they are united nearly to the
extremity.

The fcaly membranes which border the toes
in fome wading birds, and their exceilive length,
as well as that of the nails in others, are alfo
obftacles to touch.

From w'hat we have (fated, this fenfe ap-
pears to be very obtufe in birds ; the fcanfores,
how^ever, particularly the parrots, are, with the
owls, thofe which polfefs it in the greateft per-
fection, and exercife it moft frequently.

The number of the fingers, and their flexibi-
lity, vary more in reptiles than in all the other
claffcs.

Q^Q-4.

Common

6oo

Lect. XIV. Of Touch.

Common lizards have in general five fingers,
of different I^gths, well calculated to embrace
objedls in every direction. Some, as the croco-
diles y h^ive them palmated, at leaf! in the pofterior
feet. Others, as the geckoy have them in veiled
inferiorly with imbricated fcales.

The camclion has them united by the fk'in, as
far as the nails in two parts which form the
forceps. The Ikin of their inferior furface is
furnifhed with very fenfible papillae. The long
lizards, called Jeps and chalcideSyhd.\t only three
very fmall toes. The falamanders and frogs have
them naked, and deflitute of nails ; they there-
fore enjoy a very delicate touch. It ought to
be ftill more exquifite in the tree-frogSy which
have the extremity of the toes enlarged into a
fpongy difk, capable of adhering with force to
bodies ; but in the tortoiJeSy which have the toes
palmated, this fenfe mufi: be Icfs perfed. Lafl-
ly, the ferpents are completely deprived of feet
and toes.

This is alfo the cafe with fifhes. Their fins
are intended for motion only, and are of no ufe
in afeertaining the forms of bodies.

What we have fiated in Ledurc Sixth, re-
fpeding the number and divifion of the feet in
animals that have no vertebrae, appears to us
fuflicient to enable the reader to form an idea
of the different degrees of perfedion ihefe parts
pofTcfs as to the fenfe of touch.

Arti-

Art, VI. Appendices.

6oi

Article VI.

Of the Appendices ’udiich fupply the Place of
the Fingers in exercijing the Aenfc oj Touch.

Besides the fingers, feveral animals have re-
ceived dirterent parts, which are fufficiently
moveable and fenfiblc to enable them to exer-
cife the laculty of touch. In the fpecies which
want fingers, or which have them enveloped in
infcnfible fubftances, thefe appendices fupply
their place.

The tails of feveral mamraiferous animals, as
the fapajottSy the opopTums^ one fpccies of por~
cnpincy feveral fpecies of ant-eaters, 6cc. are
fo organized, that they arc capable of embracing
bodies, and feizing them in the manner of a
hand. In Letflure III. we have deferibed the
form of the bones, and the difpofitioh of the
mufcles which are employed in this prehenfile
motion : the nerves are diftributed to them in
numerous ramifications ; they arife from the
termination of the medulla fpinalis, and come
out through the intercaudal foramina. Tails of
this kind are ufually deflitute of hair on that
part of their inferior furfacc which is applied
to the bodies they feize.

We find fimilar tails in fome reptiles, as the
camelion, and the whole body of ferpents, per-
form

6o2

Lect. XIV. Of Touch.

form the fame fundlion, when they twifl them-
felves round the objerts they wifli to feel or
comprefs ; this faculty is the more ufeful to
^ them,, as they are deprived of fingers, and every
other appendix fitted to procure them the fen-
fation of touch.

In the fpecies of mammalia, which have a
fmall number of fingers covered with horny
hoofs on all the parts that fupport the weight
of the body, the fcnfe of touch feems to refide
in the lips, which are the moft moveable parts.
We have an example of this in the Ruminantia
and the Solipeda : w'e fliall not here deferibe
the mufclcs of thefe parts, as that may be done
with more propriety in the Letflure on Mafti-
cation. The lips themfelves have a very pecu-
liar organization : the facial nerve, and that of
the fifth pair, terminate in them by an infinite
number of branches. Thefe, ramifications
anaflomofe, and form various plexufes, which
give to thefe parts a moft exquifite fenlibility.
We know that they procure us the moft deli-
cious of all the fenfations of touch.

In feveral animals, we find numerous and
compadl glands forming a layer below the f^in,
which is thin and covered with fine foft hairs;
amongft them are placed fomc long ftiff hairs,
called whijkersy each of which is implanted into
a papillatcd tubercle.

The whifkers, in confequcnce of their rigi-
dity, cafily communicate, to the nerves of the
o , lips.

Art. VI. Appendices.

6o^

lips, the flightcft concufTions they receive from
fiirroiinding bodies ; on this account, though
infeiifible rhcmfelves, they may be ranked among
tlie appendices which adill: the fenfe of touch.

The fuperior lip of the rbinoceros is prolonged
into a fmall procefs, which that animal employs
in feeling, grafping, tearing, &c. We are not
acquainted with its mufcles.

Hogs, moles, and Jhretvs have a long pointed
and moveable muzzle, to which the term
is in particular applied, and which they alfo
appear to employ as an organ ot touch. In the
fubllance of thisjiart, there is frequently a pe-
culiar bone, the form of which dift'ers accord-
ing to the fpecies ; it is fituated between the
intermaxillary and the nafal bones, and named
the hone of the Jnont : the mufcles of the fnout
fiall be deferibed when we treat of the fenfe of
Smell, in order that we may give, in one view,
every thing relative to the nofe of animals.

The probofeis of the elephant, that of the
tapir, which is lefs elongated, and the fnout of
the mujk jhreu:, or dej'man, lhall alfo be deferibed
in the fiime Leiflure ; but as they are employed
by chefe animals in the manner of real hands,
we notice them here as appendices of the organ
of touch.

The crefts, or flefliy parts on the heads of
feveral birds, particularly in the Gallinaceous
family, as cocks, turkics, &c. are perhaps alfo
ufed as an organ of touch : thefe parts are def-

titute

6^4 '

Lect. XIV. Of Touch.

titute of feathers ; they arc foft and flaccid ; and
the nerves they receive, though few in number,
muft convey to the animal the impreflions o^
external bodies.

In animals which have no members with move-
able fingers calculated to feel bodies, as fifhes,
the appendices are more numerous, larger, and
more varied. Different names have been given
to thefe prolongations of the fkin ; thofe which
arc placed about the mouth, or on the lip, are
called cirri: thofe which proceed from the upper
part, or fides of the head, are named tentacuJa.
When they proceed from lateral parts of the
body, they retain the name of fingers.

The cirri are ufually foft ; they receive fila-
ments from the fifth pair of nerves. There is
only one in the cod, and other fpecies of the
gcrwi^ gadus \ two in the Jiirmulets, &c. ; four,
which are very fliort, in the carp ; four in the
barbel ; fix or eight in the genus cobitis, and in
fevcral fpecies of Jilurus, in which the cirri of
the upper jaw arc frequently very long. The
frog-fijh, the gadus , tan, and others, have a
great number round the lips.

The ientaciila arc organized like the cirri. In
feveral fpecies of the genus lophins, thefe ap-
pendices arc fufceptible of motion, and can be
bent in diflercnt directions at the will of the
animal. It is even pretended that they arc ufed
as a bait for catching fmall filh. In the fpecies
called bijlrlo, the anterior tcntacula divides like

Art. VI. Appendices.

605

a Y, the branches of which terminate in a flefhy
mafs. The others are very long and conical.
Several fpecies of Blennius and ScorpcEHJ, have
them above the eyes.

The lateral appendices of the body, which
ichthyologirts name finijers, have an ofleous
jointed Halk, which is funilar to that of the
radii of the peiftoral fin, from which thefe
fingers do not difier except in being free and
moveable. They are chiefiy remarked in the
trigla^ and in the polynemus.

There are (till more varieties in the appendices
of w hitc-bloodetl animals.

We lhall omit here the arms of the Cephala-
poda, which we have already deferibed among
the organs of motion.

We fnall alfo pafs over the ficfhy horns of the
Gafleropoda, as wc have deferibed thole of the
fnuil in the Ledure on the Eye. Thofe of the
other genera do not dilfer, except that they are
incapable of that kind of motion by which
they are retraded, and protruded like the finger
of a glove. Their inufcular fibres only become
rigid or relaxed.

Several fpecies have fimilar appendices around
the cloak. Such are the limpets, the genus ha-
lyotis, &c. Among the Accphala, the greater
part are provided with thefe appendices, and
fome have them in great numbers. In the fpe-
cies which have the cloak completely open,
they are placed around it, and particularly to-
wards

6o6

1-ECT. XIV. Of Touch.

U'ards the anus : this may be obferved in oyjlerif
vtufcles, anodontiteSy &c. In thofe in which
the cloak opens by a tube only, the appendices
are attached to the circumference of its orifice*
Such are the genus venuSy cardiutUy The

tube itfelf furniflies thefe animals with an excel-
lent inftrument of touch. The flefliy and ci-
liated arms of the genera lingula and tcrchra^
tula are equally proper for this employment {
but thofe of the anatifa are very inferior, in
conrequence of their horny fubftance.

We alfo find cirri infeyeral fpecies of worms ;
they fometimes appear to be formed of different
articulations, like the antennae, of infects. We
have obferved nerves proceeding into thofe of
the aphrodita and nereis. There arc none in the
lutnbricus and the leechy but they are fupplied in
the latter by the two difks which terminate
their bodies.

The antennas of infedls appear to be princi-
pally employed in the fenfe of touch ; we have
deferibed the nerves that proceed to them. En-
tomologifls have deferibed their forms, which
are very numerous, and have even made them
the foundation of characflers for the genera. It
would, therefore, be fuperfluous to deferibe
them here.

Some larvtu have rctradilc tentacula, refem-
bling thofe of fnails.

In thofe of feveral fpecies of butterfiieSy as
the podaliriusy macbao»y and apollo, a finglc branch

is

Art. VII. Insensible Parts. 607

is protruded between the occiput and the body,
which is bifurcated at its extremity like the letter
Y ; this appendix appears rather an inftrumenc
of defence againft the puncture ot the ichneu-
vionSy than an organ of touch : it is moiftened
by a bitter and odorous liquor.

In x.\\t fork-taili'd bomhyx (vinula), the retrac-
tile appendices, refembling thofe of fnails, arc
fituated above the anus, at the extremity of two
fidhy proedfes.

The arms, the tufts, and the flowers of fe-
veral zoophytes ; the innumerable tcntacula of
t\\G fca urebinSy and aitinuey and the com-

plicated branches of the inednj.'ey are alfo ex-
cellent organs of touch ; but thofe are fufliciently
deferibed by Naturalills.

Article VII.

OJ the Infenfihk Parts zchlch cover the Organs
of Touch, and protect them a gauijl too ft rang
Impi'ejJions.

The epidermis defends the fkin, and prevents
the contact of external bodies from becoming
painful ; but it would not, under all circum-
ftances, be fufficient for this purpofe. Nature
has, therefore, armed it with various parts, com-

pofed

Lect. XIV. Of Touch,

60S

pofed of the lame materials as itfelf, but differ-
ing as to form and thicknefs, which ferve to
reinforce it ; thefe arc hairs^ feathers^ fcalcSt
nails y and horns.

1 . Of Hairs.

Hairs are filaments of a horny fubflance*
which are particularly intended to cover the
fl\in of mammiferous animals ; one of their ex-
tremities is implanted in the cutis, and is even ,
frequently rooted in the carnofus ; this

extremity is enlarged into a bulb, more or lefs
thick, which is inclofedin a membranous fheath,
and which contains fometimes a fmall drop of
blood. This cell is larger in proportion as the
hair is young; if it be pun6lured at this time,
the blood flows from it, and it becomes foft and
flaccid.

All the part of each hair which is without
the flein, is called thc^^j^// ,• it is a very elon- *
gated cone, the free extremity of which forms
the apex ; the hairs grow from their bafe, and
are therefore finer in young animals than in old:
for the fame reafon, they feem to augment in
number when cut, though, in fa(ff, they increafe
only in diameter.

When the hairs rife out of the fkin, they carry
with them a fmall portion of the epidermis,
which forms a kind of flieath at their bafe; this
is gradually detached under the appearance of
tranfparcnt and farinaceous fcalcs.

’ Some

Art. VII. Insensible Parts. 6o^

Some animals have, at their birth, the haii
of fome parts of their bodies more or lels de-
veloped. In other parts no hair appears until
a certain period of life.

As the hairs of the huioan body are very
flender, it is diliicult to examine their flru^lure ;
but the brifUes of hogSt and the whifleers of cats^
and other Sarcophaga, may be very well em-
ployed in this kind of inquiry.

When we examine with the microfeope the
brirtle of vi zvild Ifoar, we obferve that it is ca-
nulated throughout the whole ol its length, by
about twenty furrows, formed by an equal
number of filaments, the union of which con-
fiitutes thcfurfacc of the hair : in the middle of
the brifile there arc two canals, which contain
an humour called the medulla. The filaments
of the hair feparate by deficcation, the feparation
commencing at the point, as may be obferved
in the brifiles of brulhes : the cavities are then
empty, and we obferve in them only fome la-
minae \\hich crofs each other in difterent di-
rections.

The hairs of the elk, the mufk, the bedge-hog,
the tenrec, porcupine, &c. are not altogether li-
milar ; their furface is covered with a horny
lamina, the thicknefs of which varies, and on
which we obferve fome furrows : internally they
contain a white fpongy fubftance, which appears
at firft fight fimilar to the pith of the elder tree
(fambucus) .

VoL. II. R R

The

6io

I-ECT. XIV. Of Touch.

The colour of the hair fcems partly to depend
on that of the rete mucofum j for, as wc have
obferved in animals which have the fur of dif-
ferent colours, the various fpots feen upon the
hair indicate others below them in the fkin.

Even in the human fpecies there are very
flriking relations of this kind. Negroes, in
general, have the hair black. Perfons who have
red hair have almoft always the fkin freckled,
or covered with reddifh fpots : thofe whofe hairs
are black have commonly a dark complexion.

The colour of the hairs exifls in their horny
fubftance, and not in their medulla, which is
commonly white. This is particularly evident
in the quills of the porcupine : the colours are
infinitely various, and fome hairs arc coloured
differently in feveral parts of their length : the
works of Naturalifts may be confulted on this
fubjecT:.

The fliape of the hairs is moft frequently
round, as thofe of the head, the mane, &c.
They arc flat on the tail of bippopotiimus, and
on the body of the great anl-eater. They arc,
as it were, crimped in feveral fpccies of the
Ruminantia, and more particularly in the miijk
(mofehus mofebiferus).

Their furface prefents fpiral channels in the
mules. They arc fine, long, and filky in fomc
varieties goals, cats, &c. Thejj' appear crifped
and frizzled in the ratns. 'fhey arc fiilf and
elevated in the bogs, the Ledge bogs, the porcu..

pines.

- 6ii

Art. VII. Inscnsible Parts.

pines, &c. From their greit thickhefs in the twd
iaft animals, they have obtairletl the name of
/pines.

The climkte has great influence on the nature
of the hair, in domei\ic arlimals : in cold re-
gions they become long and rigid, as wc obferve
in the Siberian dog, the Iceland ram, 6cc. In
the climate of Spain and Syria, they become
tufted, fine and lilky, as we find them in the
Spanijh jheep, in the Maltefe dogs, and in the
goats, cats, and rabbits of Angora. In very
warm countries they become thin, of are alto- .
gether wanting, as in the dogs of Guinea, vul-
garly called Turkijb dogs, and in the African and
Indian Jbeep*

Difl'ercnt names are given to all the varieties
which the hairs prefent on different parts of the
body. Hence the appellations — hair, eye-lafhes,
ivhijbers, beard, 6cc;

All mammiferous animals, the Cetacea ex-
cepted, have a certain quantity of hair. We
fliall briefly indicate its difpofitibn in the dif-
ferent families. ’

Man has the whole body covered with fcat-
tered hairs, though, in fome parts, they are fo
fine that they cannot eafily be perceived; thofe
of the head and the bfeard are the longeft ; thofe
of the axillae and the pubis are next iri length ;
thofe of the interior of the nofe and this ears,
the eye-laflies, and the hair of the eye-brows^ are
fiill Ihorter j thofe of the other parts of the

R R 2 body

6i2

Lect. XIV. Of Touch.

body rank laft in point of length ; there arc
more on the breall and on the belly, than on the
back, which is contrary to the difpofition in
other animals. The palm of the hand and the
foie of the foot never have any.

In apes, properly fo called, the hair of the
head is not, in general, longer than that on the
other parts of the body: the hairs which cover
the fore-arm point upwards to the elbow, in-
flead of being direefted towards the hand, as
may be feen in the orang outang, and fome other
fpecies. This is one of the circumflances in
which thefe animals refemble man. In a great
number of Quadrumana the buttocks are callous,
and entirely deflitute of hairs.

Among the Cheiroptera, which have the hair
fliort, line and villous, we obferve that the flying
lemurs have fome on the lateral membrane of
the rail, and on the ears. The vejpertilio lafi-
urus Lin. has alfo fome on the membrane of
the tail. The other fpecies have only a few
fcattered hairs on the membranes of the wings,
on the nofe, and on the ears.

The hedge-bogs have the fpines, of which we
have fpoken, placed only upon the back and
the head : the members, and inferior furface of
the body, are covered with flilf brill les. In
this refpeeft the /rwreer* refemble the hedge-hoi s.
Some fpecies have the bridles and the f])incs
intermixed.

In moles andfl.re'xs the hair is fo fljort, fine

Art. Vn. Insensible Parts. 613

and clofe, chat their fkin is as fofc to the touch
as velvet.

In the Carnivora the hair varies confiderably.
In the fpecies which are covered with a Hnc
fur, as the zvcafels^ fables, ermines, martins,
there are two kinds of hair; one clofe to the
fkin, which is very fine, thick-fet, and inter-
mixed ; the other, which is longer and (lifter,
and which alone appears on the furfacc; thefe
are the two kinds of hair which conftitute fine
furs.

Nearly the fame thing takes place in the fine
haired Rodentia. In the porcupines, the fpines
on the head, neck and belly, arc more flender,
fliort and flexible, than thofe of the back : on
the tail there are about a dozen, which refemble
tubes of quills, truncated at their free extre-
mity; they are fiftular ; their other extremity is
filled up, and is flender and very flexible ; thefc
tubes refound when the animal moves its fkin ;
and it even appears that the urine can be conveyed
into them in order to be thrown to a diftance.

No family prefents more vdriety with refpecl;
to the hairs than the Edentata.

In great ant-eater (myrmecophaga jubata)
the hair is broad and flat, and has a longitudinal
furrow on both furfaces, fo that each hair re-
iembles a dried blade of grafs. The two-toed
ant-eaters are, on the contrary, covered with
very fine wool : feveral have hard and cutting
fcales, placed one above the other like the tiles

R R 3 of

6h Lect. XIV. Of Tou^h.

of a roof, in the manner of the pangolins (mains
Lin.) ; others are covered with prickles, as the
Jpinois ant-eater (echiidna). The armadillo genu^
(daJypiiSy) have, befides the fcales or offeous
bands which cover their back and head in re-
gular compartments, fomeTcattered hairs, which
are fliort and rigid like thofe of the elephant:
thefe hairs, however, fall off as the animal ad-
vances in age.

Of all the Pachydermata, the hogs have the
greateft quantity of hairs, which, in them, are
called brifiles ; they are fcattered, and frequently
bifid at their free extremity. There are very
few in the other genera,

Wc have already noticed the nature of the
hair of the elk and the mnjk. The ox^ cin-

iclopeSy zndgirafe have, in general, fhort hair.
Camels have it very fine and very fofc, particu-
larly the camelus vicunna : all have callofities,
•which are defiitute of hairs on the knees and on
the breaft. The hair of goats is long and fine,
and they have the chin furnifhed with -a pointed
beard. Sheep have the hair long, and diftin-
guiflied by a crifped or frizzled appearance, and
to it the term wool is applied.

Solipeda have the hair in general fliort, like
the Ruminantia ; that of the neck and tail,
•v’.hich is much the longeft, is more particularly
called crines.

'The amphibious mammalia have fliorr, rigid^
and yery clofe hair.

Wc

Art. VII. Insensible Parts. 615

We have already obferved that the Cetacea
have no hair.

The chemical analyfis of the hair of all thefe
animals, whatever form it affumes, whether that
of wool, briftles^Jpines^ qnillSy /calcs ^ 6cc. afiords
nearly the fame refults : when fubjecled to the
a(5tion of fire, and in open veffels, it fules or
liquifies at firfl by fwclling up; it afterwards
emits a white flame, and refolves into a black
carbon, the incineration of which is very difli-
cult.

Hair, on diflillation, yields a rcddifli liquor,
which contains prufliat of ammoniac, and an-
other fait of an ammoniacal bafis, combined
with a particular animal acid, which Bcrthollct
has named zoonate of ammoniac ; the charcoal,
which remains at the bottom of the flill, is
light: it contains carbon and the phofphat
of lime.

The hair docs not completely diflTolve in boil-
ing water, but there is feparated from it a mu-
cilaginous matter, which is its medulla ; it is
completely foluble in cauflic alkalis, and in
fome acids.

2. Of Ftathers.

Feathers arc proper to birds, as hairs are to
mammalia, and fcales to reptiles and fiflies.

Before we deferibe the forms and numerous
varieties which feathers prefent, it is right to
notice their flrii»5ture. To give a diflincfl idea

R K 4 of

6i6

Lect. XIV. Of Touch.

of this part of the fubjcdt, we lhall point out
the manner in which they grow.

At the time the young hire! leaves the cgg>
and for fome days after, it is covered more or
lefs w i?h hairs, except on the region of the belly.
Thefe hairs, which vary in colour and thick-
nefs, come out of the fkin in fafciculi, each
compofed of tenor twelve hairs; they are im-
planted in a bulb or follicle, which appears to
contain the rudiment or flieath of the feather :
after a few days the feather appears externally,
in the form of a blackifh tube ; we then obferve
that the common fafciculus of the hairs is at-
tached to the end of this tube, and that it even
penetrates into the interior of the fheath.

In proportion as the feather grows, and is
developed, the hair falls off. In fome families,
as the birds of prey, it adheres for a long time
to the extremity of the feather, in the form of
a kind of down.

It is only at this period that we obferve hairs
on the bodies of birds ; for when the feathers
arc renewed in the moulting feafon, there is
then no appearance of them.

We have already obferved, that the flieath of
the feather becomes apparent fome days after
the bird is hatched : the quills, or great feathers
of the wings and the tail, appear firfl ; the down
manifefls itfelf next, and laflly, the fmall fea-
thers of the body.

The fheath is a tube, clofed all parts, ex-
cept

Art. VII. Insensible Parts. 617

cept at thecxtremitVj which is fixed in the fkin;
we obferve there a fmall hole, or umbilicus,
by which the blood vefTels pafs into the cavity
of the tube ; when the feather is plucked out,
therefore, a flight hemorrage takes place.

On leaving the fkin, the flieath fplits, in
confequence of being dried in the air, and
the expanflve force of the contained parts. A
longitudinal laceration takes place, and the
extremity of thtjhaft of the feather comes out:
in proportion as the fliaft grows, the fhcath be-
comes more torn, and its dcficcated tunics are
detached in the form of thin pellucid fcales.

If about this period the tube be opened lon-
gitudinally, it will be found that it is formed of
numerous and cylindrical ftrata of a horny and
tranfparent fubftance, and that it contains a cy-
linder of gelatinous matter, into which the blood-
vefflels penetrate.

'The external extremity of this gelatinous
cylinder is conical, and harder than the other
parts ; it is covered by a layer of black matter,
which is the firfl; rudiment of the barbs of the
feather.

The growth of this gelatinous cylinder takes
place longitudinally ; the conical part, which '
forms its apex, comes out of the Iheath, and
brings with it the ftratum of black matter,
which fplits in drying, and forms the hrfl- barbs,
Ihe fliaft of the feather elongates and hardens ;
the firfl: cone has fcarcely made its exit from the

fhcath

6i8

Lect. XIV, Op Touch.

flieath when a fetond is formed, which comes
out in Its turn, developing new barbs, and
making an addition to the length of the fliaft,
v.nich grows always at its bafe: at laft the fliaft,
with the w'hole of its vane, is protruded from
the flreath, which becomes deficcated internally :
we then obferve only membranous cones inferted
into each other, firnilar to thofe which, by their
development, protrude the barbs externally, and
which form what is called the heart of the
feather.

When the growth of the feather is completed,
the tubular portion becomes folid, and is epn-
tinued with the fliaft, the germ of which it
formerly contained ; it is a cylinder which
joins force and elaflicity to fpecific levity. The
dry and yeficular matter we obferve within it, is
the reflduum, or veftige of the large flefliy canal
which exifted in a lefs advanced age; it is a
fort of cavernous body, formed of feveral fmall
cups or cells fucceeding each ocher ; thefe cells
are more elongated, in proportion as they ap-
proach the fliaft ; they then become fimilar to
fmall tunnels, which are of diflerent lengths
according to the fpecics, and arc incafed into
each other. The laft of the cells is divided into
two; one paffes without the line in the longi-
tudinal furrow which appears at that part ; the
Other penetrates even into the interior of the
fliaft.

The fliaft cf uic feather is the conti nation of

' ■ ■ ■ phe

Art. VII. Insensible Parts. 619

the tube. It is a cone more or lefs ’^ngated,
convex on one Turfacc, and flat and furj' -^ed on
the ocher. The barbs are attached to its ' des.
All the fupcrficies of fbatt is covered by
horny matter, 'vhich feems to proceco ii 'n the
tube. Internally, it is filled up by .1 \\ h te and
very light fpongy iubilance, liiTu.ar i.) tn.it
which we find in the quills ol tne poicuninr.

The barbs are fn’.all laoTina* ot a horns nature,
planted into the fitlcs ot the ihuft. 1 hey arc
applied to each other throtigliout rhcir vv-liolt
length, like the lcavc.s of a book. Sometime's
they arc applied very cloiely, as in the leathers
of the or the/:c.;;;; fometinu s in a more

loofe manner, as in the rump feainers of fh-a/eti-
cock.

The beards are themfelvcs fliafts, from the
edges of which an inhnitc number of hairs pro-
ceed. Thcfe hairs are fornetimes loofe, and de-
tached from each other, fornetimes compound
and fub-divided, but mort frequently fo fine
and fo compacl that they can only be perceived
with a magnifying glals. By means of thefe
hairs or harbiilic^ the barbs of the feather are fo
intimately attached to each other as to prevent
the paflage of the air.

Such is the g-^ leral organization of the fea-
thers. We fliall now conlidcr the varieties
which they prefent.

All birds change their feathers, at leaft once
^ year. The old feather is pufhed off by a new

one,

I

^20 Lect. XIV. Ok Touch.

one, which obfl:ru(fi:s the vefTels defined to the
nourifhment of the former. All the feathers do
not fall olF at once. The moulting in general
takes place about the period of laying.

Different names are given to the feathers, ac-
cording to the regions which they occupy. They
are difpofed in quincunces on the body. There
are never any on the lateral lines of the neck
and of the breaff, nor on the umbilical re-
gion. The term quills has been given to the
feathers of the wings and tail. Thofe which
are implanted in the humerus have been called
Jecondary. Their number varies confiderably ;
but there are conftantly ten attached to the me-
tacarpus, and the fingers, which are called pri^
mary quills.

We fhall {fate fomc examples of the principal
varieties of the feathers, independent' of their
colours, which are fo brilliant and fo numerous
that we could not find language to deferibe
them.

All the feathers of the caffaivary may be called
harblejs. The wing quills of that bird arc only
five in number, and refemble the prickles of the
porcupine. The other feathers qf the body have
two fiiafts from one tube, and their barbs arc
detached, long, and deflitute of barbules. They
refemble crines.

The feathers that form the crefi: of the pea-
cock have no barbules in their middle and in-
ferior part. Thofe which form the creff of the

balearic

Art. VII. Insensible Parts.

62t

lalearic crane (ardea pavoninay) arc twilled fpi-
rally on themfelves, and their barbs are only
fine hairs. The creft of the lillle e^ret {ardea
garzetla,) is alfo compofed of fiinilar feathers.
In the male turkey there is a tuft of hairs at the
bafe of the neck, which may be regarded as
barblefs feathers, &c.

fliall give the name of loofe feathers to
thofe which, though they have the barbules very
confpicuous, and frequently very long, are fo
far feparate that they cannot be attachcvl to each
other. Such are the hypochondriac feathers of
the bird of paradife, thofe of the rump of the
peacocky of the thighs of the jabirit, and the
lalearic crane \ thofe of the body in tcucanSy and
thofe which furround the ears in o'lvlSy &c.

The term floating feathers may be very well
applied to thofe of which the barbs, though
provided with barbules, are fet wide, and are
flexible, as in the feathers of the tail of the
oflrich.

Thenodlurnal birds of prey have foft feathers,
the barbs of which are covered with a long and
fllky down. On this account we fcarcely hear
the flapping of their wings when they fly. Fea-
thers of this kind may be called dozvny.

■ Other birds have the feathers of the body fur-
niflied with barbs, which are fo fine and glofiy
that we may term them filken. Such are thofe
ol the bulljinchy of the purple-throated flycatcher
{mufctcapa ruhricollisy) of x.'ti&'tanagra fepticolor^

thofe

Lac'p. XIV. Of Tou'cii.

thofe of the head of the rrd-heaJed mar.akin, and
ot the momot {rainphajios momota).

We fhall name thofe fatin feathers which have
cloic-fet barbs, bearing long, fine, and filky
barbiilcs, difpofed on the furface in fuch a man*
ner as to imitate fatin. Such are the rump fea-
thers of the ^oldeu'thrujh, thofe of the tail of the
and thole of the neck of the common duck.

Vv"e fhall apply the term metallic to the fea-
thers which have barbs of brilliant colours, re-
fembling the lufire of polillied metals. 'We
have examples of this kind in the feathers of the
humming-bird, of the jacamar, of the curucui, of
peacock, of the paradifea aurea, &c. This
brilliancy is occafioned by the breadth of the
barbs, and the fmooth furface they prefent to
the eye.

We fliall defignate by the word gcmmaceous,
all the little feathers which have the barbs that
terminate the fiiaft, coloured by imbricated femi-
circles like the fcalcs of a fifii. Of this kind
arc the head and throat feathers of the ruby^
necked humming-bird (trochilus mo/chit us), and
thofe of the head and belly of the ameibyjline
humming-bird. They exceed in lufire the pre-
ceding kind of feathers, and refemble precious
flones. 'rhccfi'ccT: is produced by the extreme den-
iity of their barbs, and the j)olilh of their furfaces.

L.afily, we fiiall make but one order of the
common feathers, fuch as belong to cocks, pigeons,
rollers, ravens, c\:c«

7

All

Art* VII. Insensible Parts. 623

All birds have feathers on fome parts of their
body. Several fpecies have them even upon
their roes, as ozvls, and fome varieties ot cocks
and pigeoHSm Others are deprivcil ot them in
certain parts of the body, as vultures and turktes
on the head, the ojlritb and the wading birds on
the thighs. Some even want them on the wings,
as the manchols.

Chemical experiments on the compofition of
the feathers, prove that they have a very great
analogy to hair. The tame retulcs are obtained
from both by the fame procefles. Feathers how-
ever contain kTs mucilaginous matter.

3. Of Horns.

*

There arc prolongations of horny fubftance
which grow upon the head of certain fpecies of
mammalia, efpecially the Ruminantia. They
allb appear on feveral other parts of animals.

We have already deferibed tlje development
of the antlers or deciduous horns, in Ledb. II .
Art. 2, when we treated of Ofteogeny. We
lhall now notice the horns which are formed
upon procefles of bone, and which grow at their
root or bafe, and have a great refemblance to
the integuments.

In the third month of conception, while the
foetus of the cow is ftill enclofed in the mem-
brane, the cartilaginous os frontis prefents no
mark of the horns which it is afterwards to bear,.

Towards-

624

Lect. XIV. Of Tovcii.

Towards the feventh month, it is in part ofTifiedi
and prefents in its two portions the fmail tu^
bercle which appears to be produced by the ele-
vation of the offeous lamina. Thefe bony tu-
mours foon after appear externally. They raifc
the fkin, which becomes callous at that part, in
proportion as the tumour grows. It becomes
at laft horny as it elongates, and it forms a kind
of flieath which covers externally the procefs of
the frontal bone. Between this fheath there are
numerous branches, of blood vefTels which ferve
to nourifh the olTeous part.

The horns therefore are only folid, hard,
elaftic, and infenlible flieaths, which protecfl the
offeous prolongation of the frontal bone. Thefe
flieaths are generally of a conical figure, and
broadefl: at the bafe, the extremity from which
they grow. Their curvatures vary with the
fpecies, and have been deferibed by naturaliflsi
They alfb prefent different channels or tranfverfe
furrows, which depend on the age of the animal,
and which denote the number of years it has
lived in a very certain manner according to the
fpecies.

The texture of the horns appears to be much
the fame in the goat, Jheep, antelope, and ox.
They confifl of fibres of a fubflance analogous
to hair, which appear agglutinated in a very folid
manner.' In the two firfl genera thefe fibres
arc fliort, and covered by fupcrincumbcnt layers

like

Art. VII. In SENSIBLE Parts.

625

like tiles. In the two laft they are longer, more
compaifl, and form elongated horns incafed in
each other.

The horns of the Rhinoceros appear to differ
fomewhat Irom thofe of the Ruminantia. 1 hey
have no olfeous part, and are not liruated on the
os frontis, but on the lines ot the nole. They
are formed however of the fame fubltance, and
we even obferve more diffiniffly in the horn of
this animal the fibres analogous to hairs. 'I'lic
bafe of the horn, indeed, prel'cnts externally an
infinite number of rigid hairs, which leem to
feparate from the tnafs, and which render that
part rough to the touch, like a brufli. When
fawed tranlverfely, and examined with a glafs,
we perceive a multitude of pores that feem to
indicate the intervals refulting from the union
of the agglutinated hairs. When divided
length-ways, numerous longitudinal and parallel
furrows alfo demonflrate the fame ftrutffure.
This kind of horn is attached by the Ikin only.
TKofe of the Rhinoceros bicornis appear al-
w'ays in a degree moveable. When fixed, as in
the unicornis^ there is a thick mucus inter-
pofed between its bafe and the bone on which
it is fituated.

The colour of the horns depends, like that of
the hairs, on the mucous fubftance. Their che-
mical analyfis affords fimilar refults. Heat
foftens, and even fufes them. It is the agent

VoL, II. S s employed

626 Lect. XIV. Op Touch.

employed in manufa(5luring them into different
articles.

From this examination of the horns, it ap-
pears that they differ cfTentially from the olfeous
prolongations called antlers of deer. The lat-
ter increafe at the extremity. They are covered
with (kin during their growth. They fall off,
and are reproduced at a certain period of the
year. The others grow at the bafe, are not co-
vered by the fkin, and are permanent.

We find feveral other Forny parts in animals.
Such are the protuberances of the head in
hillst x\\Q guinea-fowl, tht CaJfowary\ &c. Thefe
are laminae of horny fubftance which inveft the
olfeous finufes, of which we have already fpoken,
and which we fliall deferibe hereafter, in
treating of the organs to which they belong. In
the fame manner we fhall poffpone our account
of the horn which covers the jaws of birds and
feveral reptiles, the fpines of the wdngs, and the
spurs. The external defeription of thefe parts
is Indeed more the province of the natural hiflo-
rian, than of the anatomift.

' A.-()f Nails.

This name is given to the horny prolongations
which arm and protc<fl the extremities of the
fingers or toes in mammalia, birds, and rep-
tiles. Their number is in general equal to that
of the fingers and toes, 'i’heii form, as we have

already

Art. VII. Insensible Parts. 627

already obferved in the article on thedivifion of
the extremities, appears to depend on that of
the laft phalanx. They are to thefe phalanges
what the hollow horns are to the procelfes of the
os frontis which they cover.

The nails feem incafed in a duplicature of the
fkin. The part covered by the Ikin is called
the root. They grow by that part precifely in
the manner of hairs, but the oppofite extremity
wears by the friiftion of the ground, and by
other ufes to which animals apply their nails.
We obferve, therefore, that they grow exceed-
ingly long in animals that are confined, and
have few opportunities of motion.

No part of the nail is fenfible, except that
which adheres to the fkin. The free extremity
may be cut, or broken, without occafioning any
pain.

The colour depends upon that of the rete
mucofum, as we have already remarked.

The human nails appear in the third month of
conception ; the development takes place nearly
in the fame manner as in the common horns,
which w? have already deferibed. At firfl: they
appear like a kind of cartilage, which gradually
acquires a proper confiftency. Almofi: all ani-
mals have at their birth the nails in fome degree
formed.

The nails of man, and the greater part of un-
guiculatcd animals, appear to be formed of ex-
tremely thin ftrata placed one upon another. The

S s 2 anterior

628

Lect. XIV. Of To UCH.

anterior laminse are larger than thofe of the In-
ferior furface ; ^ therefore we do not perceive
externally the kind of imbrication which takes
place ; but in difeafes, or upon a tranfverfc
fedlion of the nail, after it has been completely
dried, this flru(5lure becomes manifeft. Fre-
quently we obferve on the fuperficies of the nail,
fome ftriae, or very fine longitudinal and paral-
lel lines, which appear to refult from the man-
ner in which this part is moulded upon the la-
minae it covers.

The nails feem intended to protcdl the extre-
mities of the fingers and toes. They are, in ge-
neral, wanting in thofe animals which do not
employ thefe parts either in walking or grafp-
ing. We have examples of this circumllance
in bats^ in the wings of birds, with the ex-
ception of fome fpecies of the palamedea^ tringOy
charadriiiSy and parra ; in the fins of fevcral tor-
toijes ; and in the claws of fome other aquatic
reptiles, as ftogs^ falamanders, &c. ; laftly, in
the members or fins of fifhes.

Birds have commonly nails on the toes only.
They are ftrong, and refemble thofe of the Sar-
cophagaand birds of prey. They are flat in the
web-footed, flendcr pointed, and very much
elongated on the pofterior toe of larks and
iids {parra Tin.)

I'he nail is ferrated on one of its fidcs in the
middle toe of the goat-fuckers {caprimulgns Lin.)
and of the herons.

There

Art. VII. Insensible Parts. 629

There is a fupernumerary nail, or olTeouspro-
ccfs, which forms a kind of horn on the tarfus
of the greater number of gallinae. It is called
the Jpnr. The Iris peacock { Pavo bicalcaratns)
has two. They become very long in the cock»
A curious experiment has been performed when
pullets are made capons, by cutting off this
I'pur, and fixing it in the place of the comb. It
takes root there, and grows to a confiderable
fize.

The nails prefent no particularity in reptiles.

The chemical analyfis of the nails affords
nearly the fame refult as that of the hairs and
feathers, parts with which they have much rela-
tion, both in their mode of growth, and in their
ftruefture.

Hoofs differ from nails in the following cir-
cumftances. They envelope the phalanx infe-
riorly as well as fuperiorly. They are neither
pointed nor cutting at the extremity, and both
furfaces meet to form a round and blunt edge.

Their interior is rendered remarkable by deep
and regular furrows, w’hich receive projecting
laminre, and which are not obfervable in nails.
Thefe furrows are particularly remarkable in
the elephant and rhinoceros. They are alfo very
ftrongly marked in the horfe^ but lefs confpicu^
ous in the Ruminantia. •

Between the nails and the foft parts of the
phalanx, there is always a layer of mucous mat-
ter j and in the inferior part of the hoof, there is a

S s 3 foft

6^0

Lect. XIV. Oe Touch.

foft fubftance abounding in nerves, which give
a degree of fenlibility to that part.

5. Of Scales.

Thefe are laminae, or fmall plates, of a fub-
ftance which is either horny or olTeous, and
which cover certain parts of the body of ver-
tebral apimals.

Scales have a great refemblance to hairs,
feathers, horns, and nails, in the manner of
their development, in their ufe, and in their
chemical analyfis.

They might generally be confidcred as very
flat horns, as hairs are very flender horns.

Almoft all reptiles, and the greater number
of fifhes, are entirely covered with fcales : we
obferve them only on fome parts of the body
in a very few fpecics of mammalia; and in
birds, they are mod commonly found on the
feet alone.

The term fcales is here applied to very differ-
ent fubflances ; it being ufual to include, under
this denomination, all the parts we are about to
deferibe in a general manner, in the fourclalfes
of red-blooded animals.

The fcales of the pangolin, and long~lailed
manis, arc a kind of flat nails, of a horny fub-
flancc; they are thick; their anterior t-hird,
which is bevelled and fharp-edged, is free, but
they adhere to the fkin by their other portion.
Their external furfacc is channelled longitudi-
nally.

Art. VII. Insensible Parts. 631

nally, particularly in the long-tailed inaniSy in
which they ufually terminate in three points;
they are furrowed tranfverfely on the fide next
the Ikin, and appear to be formed ot imbricated
laminae.

In the armadillos^ the fcales are fmall com-
partments of a calcareous fubftance, covered
with thick, fmooth, varnifli-like epidermis.

The fcales which cover the tail of the beavert
are limilar to thofe of the feet of birds.

Thofc on the tails of rats and opo/fums, and
feveral other prehenfilc tailed animals, arc of
the fame kind.

The fcales of the feet of birds confift of thin
laminae, of a horny fub (lance.

The fcales which cover the wings of manebotSt
are only very (liort feathers, the barbs of which
are united to the epidermis.

Among the reptiles the fcales vary greatly,
according to the genera. In tortoifes they are
plates of a horny fubftance, which are very hard
and denfe in the greater number. But in the
tejhido coridcca, and feveral others, they are foft
and flexible : fometimes thefe fcales are imbri-
cated, as in the ha'is)kes-hill turtle ; and then
they are fmooth, or channelled longitudinally :
at other times they form compartments of dif-
ferent figures ; in the latter cafe they are more
or lefs convex, and furrounded with furrows,
or concentric channels, in the midfl; of which

S s 4 are

632

Lect. XIV. Of Touch.

are points, which arc either fcabrous, elevated,
or blunt, as in the fpecies named geometrical
grcecay &c.

In the crocodile the fcales are olTeous, and
diPpofed in bands, as in the armadillos ; they are
imbricated like thofc of fifhes, and are marked
by a longitudinal ridge, or elevated line.

In the greater number of lizards and ferpents,
the fcales are only fmall plates, or compartments
of the Ikin, between < which the epidermis is
continued and moulded. The frinks and Jlow-
Tjorm have real fcales, which lie upon each other
like tiles, in the manner of the fcales of fiflies.

In the clafs of ‘fifhes, all the folid parts with
which the body is covered are called fcales ;
but the flrudture and ufe of thefe infenfible parts
render it neceffary that we fhould confider them
more in derail.

We name fcUles thofe thin horny plates
which are imbricated like ancient coats of mail,
and ufually crefeent-fhaped at their unconnedled
edge, as in carpy pike, &:c. Thefe plates mofl
commonly prefent longitudinal lines, which are
rough to the touch : their'extcrnal third is co-
loured by the rete mucofum. Thofe above the
lateral line have ufually a furrow on the furface
next the body ; fometimes they are perforated
by an oblique hole, through which a membra-
nous canal palfes ; thefe fcales are covered with
fcabrous points in the hhjles. They arc finely
jerratfd op their edges in the /ole (pleuronetles

/olcd}^

Art. VII. Insensible Parts. 633

folea). They are very fmall in eeh, in which
we cannot perceive them until the llvin is dried.
But they grow to the length of feven centime-
ters in the great fcaled bream ; in this fifli,
in particular, the flru^flure of the fcales may be
calily obferved. Belides the longitudinal, or
rather radiated lines of which we have fpoken,
w’C perceive concentric ftrite, which feem to in-
dicate that the fcales grow in every direction, by
the addition of new layers m the manner of
horns and nails.

We may name the plates of calcareous’ mat-
ter which are contained in the Ikin, ojfeous
ejciitcheons. In the trunk- fijh (cjhacion), &c;
they are fmall compartments of a regular figure,
and difpofed like mofiiic work. In the jlurgeon^
thefe plates are of different forms, hollowed
I externally by numerous holes, and bear a lon-
gitudinal ridge. In the turbot (pleuronsbles ma-
the fcutcheons are fmall, and in the form
of lozenges. In the ejjox offeus the plates are
rhomboidal, and covered with a compadl and
gloffy epidermis.

In the ibornback the fpines are curvated
points, of a tranfparent offeous fubftance ; the
bafe of the fpine is white, opaque, and hollow
internally; it exhibits the print of the mufcular
fibres, into which it is implanted.

Thefe fpines are nearly* fimilar in feveral
fpecies of diodon^ and other genera ; but* they
|:iave not a round and hollow bafe, as in the ray.

- In

^34

Lect. XIV. Of Touch.

In the piked dog-jijb (fqualus acanlhias Lin.)
the fcales or prolongations which fupply their
place are fmall briftly laminae; they are flat,
bent, figured like myrtle-leaves, and have a
longitudinal ridge in their middle.

In other fpecics of the fame genus, as the
great dog-jijh ; in the genus ibeulhis, the remora,
&c. the fkin is covered with fmall tubercles,
which are extremely hard, very clofe, rough to
the touch, and which cannot properly be called
fcales.

The fcales are covered in fifhes, as well as in

' I

all the other clafTes, by the epidermis,^ which
varies in thicknefs and foftnefs according to
the fpecies. It is the .epidermis only which is
caft: hy ferpents : the fcales below it continue to
adhere to the Ikin ; it appears that the hairs,
horns and nails are alfo formed under the epi-
dermis, which is always found on thefc parts,
unlefs it has been dcficcated, and worn off by
fridion.

All the in fen fible parts are deftituteof nerves
and vclTels, except when they include cavities
that contain them, as is the cafe with feathers,
the fpines of the ray, &c.

They grow like the epidermis, by the addi-
tion of new layers, which tranfude from the
(kin, and become united to the laminse that
have been already formed.

G. Of

/

Art. VII. Insensible Parts. 635

6. Of the Infenjible Parts in the Animals with-
out Vertebrae.

Little remains to be faid on thefe parts, lincc
the fkin of the greater number of invertebral
animals is hard and infenl'iblc, as has been al-
ready dcfcribed.

In Le(5lure II. Article “2. we have explained
the manner in which the fliell is developed.
Wehavealfo, in the Article on the Skin, in
the prefent Ledurc, made fome obfervations on
the colour of the calcareous rtiell of the Mol-
liifea and the Cruftacea.

The horny fubftance which ferves both for
bone and fkin to the greater number of perfedt
infedls, has alfo been defcribed.

The hairs or fpines appear to be a continu-
ation of the epidermis, for they are call off w'ith
it in moulting ; and others are reproduced,
w hich are longer than the preceding.

The fcales of the wings and of the body in
the Lepidoptcra, and fome other orders of in-
fers, are fmall horny plates, differently co-
loured, implanted in the fkin, and covering it
like tiles upon a houfe.

The plumes of the pterophorust of fome but-
terflies, and of the tailed hefperia^ are only pro-
longations or flircds of the wings furnifhed
with long hairs on the fides.

A -number of animals of the clafs vermes have
the body furniflied with bundles of hairs, which

arc

)

6j6

Lect. XIV. Of Touch.

are fometimes ftiff and retracflile, and ferve for
feet, as we have pointed out in the genera nereis,
ierebilla, lumhricusy &"c. In the aphrodita there
are, befides thefe briftl^s employed in progref-
iion, an infinite number of other hairs, which
are long, flexible, and of a changeable fea-green
colour ; there is alfo a tomentous felt-like fub-
flance covering the branchiae, through which
the water is ftrained.

We refer to Ledure VI. Article 8. for the
infenfible parts of Zoophytes.

/

LEG.

[ 637 ]

LECTURE FIFTEENTH.

Of the Organs of Smell and Taste.

Taste and Smell have a more immediate re-
lation to Touch, than Seeing and Hearing; they
feem indeed only more exalted modilications of
the fenfe of Feeling, by which we are enabled to
perceive the difi'erences of the more minute par-
ticles of bodies when they aredifTolved in liquids,
or in the atmofphere ; their organs are clFentially
the fame as that employed in ordinary touch, and
differ from it only by a greater development of
the nerves, and a finer and fofter texture in the
other parts. The organs of which we ha\T to
treat are, indeed, real prolongations of the
fkin, formed of all its different layers: we
therefore find the epidermis, the rete mucofum,
the villous furface, the true (kin, and the cel-
lular fubftance. The tongue of certain animals
is even furnifhed with infcnfible teguments, as
fcales, fpincs, teeth, &c.

We ftiall now deferibe the Organs of Smell
and Tafte, in the manner we have examined
^ the other fenfes ; that is, both as to their effential
parts, and with refpee'e to thofe that ferve only
to augment or diminiffi the force and extent of
the fenfations.

SEC-

63S Lect. XV. § I. Of Smell.

SECTION FIRST.

Of the Organs of Smell.

Article I.

Of the Senfc, and its Oi'gans in general.

Of all the fubftances which adl on our fenfes,
thofe which produce the fenfation of Smell arc
leaft underftood, though their impreiTions on
the animal body are, perhaps, of the moft power-
ful'and extenfive kind.

We know, in general, that this fenfation is
caufed by volatile particles diflblved or floating
in the atmofphcre, and conveyed by the air
into the nofe, where they are diftufed.

Some bodies are always odorous, becaufc, the
whole or a part of their fubftance being vola-
tile, it conftantly exhales. Others become
odorous under certain circumflanccs : for ex-
ample, when a volatile principle, which has
been retained by itsaflinity with other fubflanccs,
is extricated by the addition of fome new body ;
as the fairs which contain ammoniac^ after a more
powerful alkali has difengaged it: or when there

Art. I. The Sensation in general. 639

is united to them an external body, capable of
forming a volatile compo.'ition, as muriatic acid
is changed into oxygenated muriatie acid^ by the
accelljon of new oxygen : or, ladly, when a
fubflance, which deprived the body into which
it had entered, of its volatility, is diflodged;
as nitric acid, when it is changed into nitrous, by
the lofs of a part of its oxygen. It is, doubt-
Icfs, in one or other of thefc ways that the pre-
fcnce or abfcnce of heat, light, or luimidity,
may render certain bodies odorous ; thus fomc
flowers poflefs tliat quality only during the
night, clay acquires it when it is moiflened, &c.

Odours appear, tliercfore, to be propagated
in the air, in the fame manner as one fluid dif-
fufes itfelf, and mixes with another ; their mo-
tion is not dirciil like th.at of light; it is not
rapid, and is neither fufceptiblc of rcfra<flion
nor reflection ; it refemblcs that of the matter
of heat, w ith this diflerence only, that the fub-
Itances through which the air cannot pafs, are
alfo impermeable to odours.

Odours may combine with different bodies
by alfmity, and arc frequently deflroyed by the
fame means ; they alfo adhere in preference to
certain bodies, according to the nature of each.
Some are rnofl eafily retained in fpirits, others
in oils, &C.

Thefe phaenomena, ir will be perceived, feem
to prove that each fmell is occafioned by a par-
ticular fubflance floating in the atmofphere.

There

640

Lect. XV. § I. Of Smeei,.

There are others, however, which appear to in-
dicate that odour is not always produced in this
manner.’

Several bodies yield a flrong fmell fora great
length of time, without fufiaining any fenfible
lofs of fubflancc. Such, for example, is mufk.
Some odours are experienced when no evapo-
ration can be obferved, as the fmell which
arifes from the fridlion of copper, that produced
by the fufion of a great number of bodies, and
even by the melting of common ice. In other
cafes, real evaporations produce no fenfible
odour ; this may be remarked on the difengage-
ment of feveral gazes, and even on the ordmary
evaporation of water. Perhaps thefe phaeno-
mena only prove that the force of the fenfation
is not proportional to the quantity of the fub-
llance by which it is excited, but that it de-
pends on the nature and degree of the alfinity
of that fubftance with the nervous fluid. 'I'he
adion of the greater part of odorous fubflances
on the nervous fyflem, is rendered manifcfl: by
a number of other effects befides the fenfation
of fmell ; fome produce faintings, others gid-
dinefs, or even convulfions. Some, on the con-
trary, ferve to remove thefe diforders: indeed
the greater part of medicaments act in general
rather by their volatile and odorous parts, than
by their other principles ; and afford new proofs
of the influence cxercifed in the animal eco-
nomy by the gazeous and impalpable iubfianccs,

the

the greater part of which are doubtlcfs Hill un-*
known to Us.

VVe know not whether odours have a peculiar
vehicle, bcfides the matter of heat which is
common to them all in their quality of vapours
or'claftic fluids.

We are ignorant of the circumilances which
render them agreeable or difagreeable to us ;
and we can as little explain why fmells, which
arc difgufting to us, fcem to be pleafing to cer-.
tain animals, which teflify alfo an indilference
for thofe that are delicious to man. Though
the human fpccies, and other animals, arc in
general fond of the odour of thofe fubflances
which ferve for their particular food, that odour
is difpleafing when they arc fed ; on the con-
trary, they fometimes are fond, to a degree of
madnefs, of the odour of fubllances which arc
of no ufe to them, as cats are of vepeta. See.
Odours that are conftantly difagreeable, proceed
in general from fubftances which may prove
injutious. Venomous plants, corruj t flefh,
and poifonous metals, have almoft always a dif-
agreeablc fmell.

Whatever may be the anfwers given to thefe
queftions, the organ of Smell, in all the animals
in which it has been obferved to cxift, is a very
fine expanfion of the fkin, abounding in velTels
and nerves moiftened by a quantity of mucous
matter, and afled on by air or water impreg-
natcd'with odorous fubliances ; for it appears*

\ oj.. 1 1, T X rhuj;

^42 Lect. XV. § I. Of Smell.

^hat a fifli fmells in water in the fame manner
as other animals in air: thus odorous fubftances,
thrown into water to ferve as bait,’ attrad; fifhes
from a very confiderablc diflance, in the fame
manner as they would attrad quadrupeds or
birds through the medium of the atmofphere.
We know not whether fubftances, which are
infoluble, indiffufible, and inodorous in the air,
but which diffblve in water, as for example
fait, ad in the latter medium on the organ of
fmell of fifhes.

In all'the red-blooded animals, which refpire
by lungs, the organs of fmell are fo fituated, in
the paffage of the air, as to be impreffed by it
at the moment of infpiration. In fifhes, they
are fimply at the end of the muzzle, and mufi:
receive impreflions from the water when the
fifii fwims forward.

We are not fufficiently acquainted wfith the
nature of the olfadory membrane, nor with that
of the nerves difiributed to it, to enable us to
form an opinion refpeding the degree and the
kind of fenfations they procure to different
animals. It may, however, be at firfi fight
prefumed, that, all things in other relpcds being
equal, the animals in which the olfadory mem-
brane is mofi extenfive, enjoy the fenfation of
fmell mofi exquifitcly, and experience confirms
this conjedurc. It would he curious to learn,
why the animals which polfcfs the fenfe of fmell
in the highdl degree, arc prccifely thofe which

feed

Art. II. Nasal Cavity.

!

i

4

/

1

(

«

I

1

i

i

r

c

I

^43 ,

feed on the moft fetid fubflances, as we obferve
in dogs which eat carrion. Perhaps the Sarco-
phaga have, of all animals, the fineft fmell, as
it is neceflary they fhould be able to trace their
prey from a great diftance.

Ill treating of the organs of Smell, we fliall
have to examine the llrudure and extent of the
pituitary orolfavftory membrane, the lize and
number of the nerves dillributed to it, and the
means by which it receives the odorous exhala-
tions. Thefe fliall form the fubjcdls of the
following articles.

Article II.

Of the Form and Magnitude of the Xafal
Cavity. .

This fubjecl is included in feveral of the Ar-
ticles of Ledfure VIII: we fhall therefore

content ourfclves by referring —

For the conipofition of the nafal fofllc, to
pages 6o, &c. of this volume.

' The external aperture, pages 82, &c.

Their fize and their vertical fec^ion, pages lo.
See.

- Their tranfverfe fedlion, and their diredlion,
to pages 82, &c.

T T 2

We

f

\

644 ' Lect. XV. 5 T. Of Smell.

We fhall merely add here, that, in fome fiflics,
the nafal foflae are not formed in the muzzle,
but, on the contrary, fuftained upon pedicles,
and elevated like drinking-glafTes. Of this
number is the frog-fiJJj.

Article III.

/

Of the Shiufes which incrcapi the Kxtent of the
Nafal Cavity.

It is not proved that the fenfe of Smell refides
in thcfe finufes ; the membrane which covers
them is thinner than that of t^e refl: of thenofe;
and it does not appear to receive any ramifica-
tions of the olfadory nerve ; no ufe is attri-
buted to them, except that of fecreting an
aqueous humour calculated for lubricating die
interior of the nofe. It is certain, however,
that the animals which have the moft perfedt
frncll, have thefc finufes the longcfi ; perhaps
they are intended as refervoirs for a great quan-
tity of air impregnated with odorous particles,
in order that it may adl more forcibly on the
olfadlory membrane.

Thcfe finures hardly cxifi in young animals,
and arc not fully developed until puberty.

'i'hcy arc found only in man and quadrupc(rs;

they

Art. III. The Sinuses. 645

they communicate with the cavity of the nofc
by contra6led apertures. ^

7'here are three finufes, which are named,
from the parts they occupy, the frontal^ the
fphcnoidal, and the maxilhuy.

A. In Man.

The frontal finujcs open into the upper part
of the vault of the nofc ; they extend about
an incli in height, and a little more in breadth
on each tide above the cre-brows ; they are fc-
parated from each other by a vertical feptum.

'fhe Sphenoidal finufes open into the poftcrior
and interior part of the nafal vault ; they oc-
cupy all the interior of the os fphenoides, under
the anterior and middle part of the fella turcica;
they are alfo feparated by a vertical feptum.

The maxillary finufes y or antra Higbmorianay
fill the whole body of the fuperior maxillary
bones ; they open into the fides of the nafal
cavity, near its bottom.

B. In othc)' Mamm/ferous Animals.

i

1. The Frontal Sinufes.

Thcfe are very fmall in monkies. They are •
even entirely wanting in the greater number of
maggots and guenons. But they are conliderably
extenfive in fome of x.\\&fapajous.

Anjpng the, Sarcophaga, dogSy zvolfsy foxes,

T T 3

646

b

Lect. XV. § I. Of S?4ell.

tzt. have them mofl confiderable ; they occupy
the whole extent of the os frontis, fill the in,
terior of the two pofi-orbitar procefies, and dc'
feend on each fide in the pofterior wall of the
orbit. They are fomewhat lefs extenfive in the
iear towards the fidcs, and in the cat pofie- •
riorly. The finufes of the coati refemble thofc
of the cat. Thofe of the civet occupy only the
pofierior part of the frontal bone. There are |
none in the badger, in bats, nor in the greater i
number of zvcafels. The excavations of the •
pofi-orbitar procefies, it is true, exift in thofe :
animals, but they are only prolongations of the '
nafal cavity, communicating freely w'ith it, and
not by a narrow aperture. i

With refpefl to the Rodentia, thefe finufes ■
are wanting in rats, the marmot, the agouti, the 1
Jquirrel, the beaver, and the hare. But they are
very large in the porcupine, and penetrate even
into the fubfiance of the nafal bones.

The fame difference occurs among the Eden-
tata. The ant-eater and the pangolin have no
frontal finufes. The armadillo has them of a
moderate fize. But in the Jloth they arc very
large, and in the adult animal extend nearly to
the occiput.

The Ruminanlia exhibit varieties equally
firiking. l^hcjlag appears to have no frontal j
finufes. The ex', the and the. Av;>, have

them of an enormous fize, and extending into

the fubfiance of the offcous procefies which fill ]

the

1'

' Art. III. The Sinuses, 647

the horns. Thofc of antelopes occupy the thick-
ncTs of the os frontis, but the ofTcous part of
the horns is folid. The camel has alfo nu-
merous finufes, which are very much divided,
but they do not extend further back than the
^ frontal bone.

j Of .all animals, the elephant has the largert

j frontal finufes. It is their maghitude which

I gives to his cranium the extraordinary thicknefs

which difiinguilhes it from all others, 'fhey

(extend through the whole fubfiance of the pa-
rietal and temporal bones, and even the arti-
cular condyles of the os occipitis. Numerous
and fingular laminae divide them into cells, all
of which communicate with each other.

The frontal finufes of bogs are equally exten-
five, though lefs elevated. They proceed to
the occiput, and are only feparated from each
other by fome ofieous laminze, which are placed
in a longitudinal or flightly oblique diredion,
and which do not entirely intercept communi-
cation. There are four rows in the bahiroiiffa^
i and feven or eight in the eommon hog. The htp-
, popotamuSy and the rhinocerosy want the frontal
finufes.

The frontal finufes of the occupy a great
part of the os frontis. They do not open im-
mediately into the nofe, but communicate, by a
very large aperture on each fide, with the pof-
terior maxillary finus ; for this animal has two.

T T

4

2. The

64S Lect. XV. § I. Of Smell.

C. The ]][axillai:y S'niufe-'i.

The relations of thefe finufes do not cor-
refpond to thofe we have pointed out in the
frontal. They are rather proportionally fmaller
in the Quadrumana than in man. They are
reduced almoft.to nothing in the Sarcophaga,
the greater part of the Rodentia and Edentata,
and, in general, in all animals in* which the max-
illary bone does not form a floor under the or-
bits. Thefe finufes cxifl however, and are even
very confiderable in the porcupine ; but in the
greater part of the other unguiculated mamma-
•lia, even when the maxillary bone is hollow, the
cavity forms a part of that of the nofe, and can-
not be called a fihus, as it has no contracted
aperture.

Hogs have no finus that can properly be called
maxillary, but they have one in the bafe of the
os malae, which is particularly extenfive in the
Ethiopian hog. The hippopotamus has a final 1 one
in the fame place.

The maxillary finufes of the Ruminaiitia arc
very large, and open into the nofe by a narrow
fiflurc behind the inferior fpongy hones.

The horfe has two, the poflenor is the largefl.
It opens laterally towards the back and upper
part of the nofe by a triangular hole. Us pa-
rieres form a large projevflion within the nofe,
uhioh feparates the portion of the narcs, oc-
cupied by the ethmoidal foramina, from that in

^ which

Art. hi. The Sinuses. 649

which the two great turbinated bones are fitu-
ated. The anterior maxillary linu* opens into
the bottom of this lall part.

The interior of the olTa maxillaria of the
phant is, like that of the bones of his IkuU, di-
vided into a multitude of very large cells, all of
which communicate together, and one opens by

a hole into the bde of the nofc,

/

3. The Sphenoidal Simifes.

Thefe linufes are fmall in proportion as the
fella turcica is flat.

Monkeys and makis have them fmaller than
man. The Sarcophaga have them alfo fmaller,
and of a more elongated form. The otter, the
feal, and the pole-cat, want them entirely. It
alfo appears, that there are none in the other
unguiculated Mammalia, nor in the Ruminantia.
The hog and the hippopotamus have them, but
they are very fmall. In the elephant they are
enormous, and occupy even a part of the ptery-
goid procelfes. They are not divided into fmall
cells, like the other finufes of that animal.

In the hor/et each opens into the pollerior
maxillary finus of the fame fide.

I have not found finufcs of any kind in the
bones of the Cetacea.

The cavities of the bones of the cranium in
birds, conimunicate with their ears, and not
with their nofe. The large vacuities in the

beaks

650 Lect. XV. § I. Of Smell.

beaks of the hornbills and toucans^ communicate
indeed with their nares/ which in thefc birds
are very fmall ; but it appears, in the frefli ftate,
that the pituitary membrane clofes this commu-
nication, and that it does not penetrate into
thefe vacancies which are every-where traverfed
by ofleous filaments.

Reptiles and fiflies have nothing that can be
compared to finufes.

Article IV.

Of the ProjcRing Lamhm which vicreafe the
Internal Surfaces of the Nafal Cavity.

Besides the ufeof thefe laminse in multiplying
the internal furfaces of the nofe, and thereby
augmenting the extent of the pituitary mem-
brane, and the intenfity of the fenfation of
fmell, they alfo form conduits which are joined
to the apertures of the diflcrent finufes.

A. In JAiw,

Thefe laminae arc of three kinds, viz. the
of a tiirbinata ittferiovut formed by paiticiilar
bones ; the turbinata fuperiora, which are pro-
dudfions of the os cthmoidcs; and its anfratlno^

fities.

The

Art. IV. Projecting Lamin.^:. 651

The inferior turbi^iated hones h^ve the form of
a thin lamina, which adheres by one of its edges
to a ridge of the maxillary bone, and is (lightly
twilled in fuch a manner that the free edge
points downward. Its convex furfacc is fupe-
rior and internal. We obferve that it is marked
by fome oblique furrows. The aperture of the
maxillary finus is above it poflcriorly. The
conduit formed by its concavity, proceeds di-
rcidly from the anterior to the poderior nares.

The os etbtnoides is formed of three laminae
perpendicular to each other, and of feveral in-
termediate laminic. The cr'ihrifonn lamella^
which completes the cranium between the roofs
of the two orbits, and the two ojfa plana^ each
of which forms a confidcrable part of the inter-
nal parietes of the orbits, are the three external
laminae. We have already deferibed them. See
pages 20, 36, 48, and 61, of this volume.

Between the two o[fa plana there is a finglc
vertical lamina, w hich, continued with the vomer ^
divides the cavity of the nofe into tw’o parts.
In the interval which it leaves on each fide,
there are fome irregular lamellae w’hich adhere
to the os cribriforme, and the os planum of the
fame fide only, but not to the middle feptum.
rhefc irregular lamellae form communicating
cells which we have named anfra^uofiliesy and
which may alfo be called ethmoidal finufes. This
colle^flion of cells is clofed, on the fide of the
feptum, by a vertical and fulcated lamina. The

interval

652

Lect. XV. §1. Of Smell.

interval which remains between thefe two la-
minae, leads dircdly to the fphenoidal finus of
that fide.

The inferior part of the lamina, which is op-
pofed to the feptum, is prolonged obliquely, and
extends a little pofteriorly, where it forms a fold,
the concavity of which is direded downward ;
and the anterior part is continued with a fiiort
canal, which afeending obliquely, and pene-
trating the ethmoidal anfradluofities, leads into
the frontal finus of the fame fide. This refleded
lamina is the faperior os turbinatnm.

The two turbinated bones have a more fpongy
llruclure than the other olTcous laminae; and we
obferve, particularly in the fuperior pair, that
■they contain a multitude offmall holes.

B. I71 othei' ^lammifcrous Animals.

1. Of the OJJ'a Turbiuata Infa'iora.

We have fhewn that thefe bones form only a
fimple lamina in man. V/e fiiall now deferibe
their different degrees of complication in other
animals.

They arc fimilar to thofe of man in the vion-
kics of the old continent, but in fapajons they
begin to refcmble in flrucflure thofe of the Pa-
chydermata and Ruminantia ; in all which ani-
mals the lamina is only fimple at its bafe, and
j5 bifurcated at a fmall difiance. I he two la-
mmx which aiifc from it, arc twified fpirally

00

Art. IV. Projecting Lamin.’e. 653

on themfelvcs. They incline from the fiJc of
the maxillary bone, and make two turns, or two
and a half, according to the fpecies.

The kind of horn or concha produced by
this fpiral turning, is clqfed poderiorly in a
point. We know that it contains two canals,
one above, the other below the principal lami-
na. The inferior leads, as in man, into the
poflerior nares. In the Ruminantia, the filfure
which leads to the maxillary linns, is found in
the hollow of the fuperior canal. In the hogs,
this canal is continued pbtlcriorly by a long
furrow, at the extremity of wliich there is a
conduit which goes into the linws in the bafe
of the os mala:.

In hogs, the lamina; of tiic ofTu turbinnta are
folid, but in the Ruminantia they are perforated
by numerous foramina, more or lefs large.
Thefe foramina are fmall in JJjccp. They be-
come very large and numerous in deer \ and in
the great Ruminantia, as co'xs, large antelopes.
See. their fizc is lb confiderable tha-t they leave
between them only ofieous filaments, and the
bone rcfernbles lace.

The interior of thefe bones is divided by fe-
veral vertical partitions, which are perforated
like the red of the fepta.

In the hippopotamus, the two turbinated bones
are flattened horizontally, but in other animals
vertically. This is occafioned by the form of

the

654 " Lect. XV. §1. Or Smell.

the head. The foramina are very fine, and iri-
numerable.

The inferior fpongy bones are lefs regular in
the Solipeda. The horizontal lamina, inflead
of bifurcating folds at firfl downward, then
bends upward, and is attached behind to the
maxillary bone. It afcends pofieriorly to co-
ver the foramen of the inferior maxillary fmus,
and even to penetrate into it. Lafily, it pro-
duces, towards its middle, two or three oblique
laminae, which are attached to the anterior edge
of this hole.

In the ant-eaters y the ■pangolins y the ory^eroptis^
the armadilhSy and even in the three-toed Jloth,
the inferior turbinated bones nearly refemble
thofe of the Ruminantia. But in the tivo-toed
ant-eatery they reprefent two prifmatic boxes
clofcd on all parts, the interior of which is di-
vided by fome vertical laminae. We find two"
fimilar boxes in the makiSy but no internal di-
vilions.

Among the Rodentia, the rat has the turbi-
nated bones fimilar to thofe of the Ruminantia;
but the offa turbinata of the other genera of
that order, may be divided into two kinds: the
firfl arc formed like thofe of the Sarcophaga ;
the others, which arc met with only in the por-
atpines, the marmotiesy and a few other fpecies,
confifl of a double lamina attached longitudi-
nally, the two parts of which, feparate from each
n Other,

Art. IV. Projecting Lamin.5. 655

other, afcend by a fplral convolution, and re-
prefent a portion of the flicll called turbo ^

The other Rodentia, as the hares^ rabbits,
J.jiiirrels, heavers, rats, and the greater number
of the Sarcophaga, as dogs, bears, badgers, feals,
the domejlic cat, &c. have a very complicated
Rru(5liire in the inferior turbinated bones. The
lamina by which they arc fixed is bifurcated.
Each branch is again divided ; the lafi lamina
form, by their parallel fituation, a number ol
fmall canals through which the air pafies, and
which arc covered by the pituitary membrane.

I'he number of thefc lamina.' is very variable.
The /cu/j and the otters are the fpccies that have
moll: of them. The dogs and bears rank next.
Of all the Rodentia, the beavers have them moll
numerous, and the hares the leaf! fo.

The diredion of the canals is inofl: flraight in
the Sarcophaga, and mod curved in the Ro-
dentia.

When there are few laminae, the lad are fpi-
jally rolled as in the animals w hich have only
two.

Some Sarcophaga have the inferior turbinated
bones as fimple as the animals fird mentioned.
The lion, for example, has only a bifurcation and
’ iiod like the Ruminantia. The

Civets and geuett.es have a limple rolled bone
without holes.

pierced with many holes ; the

6^6 . Lect. XV. § I. Of SmelI.

2. Oj the OJf 'a Turhinata Superiora, and of the
Idthmoidal Celia.

The ethtnoidal cells, in a number of animals*
are very difHnd: from the fuperior turbinated
bone. The paft of the nafal cavity which con-
tains them, is fometimes feparated from the reft
by a particular feptum. In hogs^ this feptum is
formed inferiorly by a lamina w'hich belongs to
the palatine bones, and anteriorly by a pro-
jeeftion of the olTa maxillaria, which goes to the
feptum of the nares, and only permits the air to -
pafs by a narrow palFage above it.

In the horfey this projedlion docs not extend to
the feptum. it produces, however, a very evi-
dent feparation, and leaves behind it a lateral
deprclTion, w’hich is occupied by the ethmoidal
cells. The fame aifpofition prevails in the Car-'
nivora, but neither in the Ruminantia nor the
Rodentia, in which the dcprcfTion is incon-
fidcrablc.

To form an idea of the ethmoidal cells in the
greater number of animals, it is ncccflary to
imagine a great number of hollow' pedicles, all
connc<Jled to the os cribriformc. J hey extend
forward and outward, and, in proportion as they
advance, thofe which arc ncarell unite. Vefi-
cles arife from them, which increafe in fizc in
proportion as they become Id's numerous. They
are all hollow', and there are an infinite number
ef conduits or ways between them, all of w hich

com mu-

Art. IV. Projecting Laminj*;. ($57

t

communicate with each other. Such is their
fVrudlure in the Edentata, the Riiminantia, the
Solipeda, the Pachydermata, and the Sarco-
phaga. The latter of thcfe orders have them
the mofl: numerous. The Rodentia have very
few. The porcupine^ for example, has only
three or four on each fide. Some genera, as the
hare, have irregular cells, like thofe of man.
Thofe of the quadrumana are limilar.

T\\g fnperior turbinated bone is reprefented in
the Ruminantia, the Pachydermata, and the
Solipeda, by one of the cells, which is larger,
and in particular much longer than the others,
tind which extends to the inferior turbinated
bone, which it covers in the manner of a roof.
In the hog, it diminiflies towards the lower part,
and ends in a lamina, which is joined to the os
nail under its external edge. This edge, there- •
fore, appears to be*bent inwards to cover the
inferior turbinated bone. The fuperior turbi-
natum becomes thin much higher up in the
Sarcophagaj fo that the hollow part of the cell,
of which we fpeak, is not longer than in the
other animals.

C. In Birds,

The external fide of each noflril is occupied
by three kinds of lamince. The inferior turbi-
nated bone is only a fold connedled on one part
to the alae of the nofe, and on the other to the
feptum. The middle or largeft lamina, the fif-

VoL. II. u furc

/

Lect. XV. § I. Of Smell.

fure of which Scarpa compares to that of a cu^
curbite, adheres by its bottom to the ofleous
part of the feptum. It folds two and a half
times on itfelf. The fuperior lamina, which has
fome refemblance to a bell, adheres to the fron-
tal bone and to the os unguis. It contains two
apartments, each of which is prolonged into a
hollow tube. The moll internal tube extends
to the orbit, and the external terminates in a
blind cavity behind the middle lamina. Thefe
three laminae divide the nafal cavity into three
paflages. They vary in their magnitude and in-
flexions, according to the fpecies. Scarpa, from
whom w'e borrow this defeription, alTures us that
the middle makes only one turn and a half in the
Gallinae and the Pafferes, and that the fuperior
is in the fame birds very fmall. It increafes a
little in the is more confiderable in birds
of prey, and is ftill larger in the Anferes. Fi-«
nally, in the Grallae it alone occupies two thirds
of the cavity, while the middle lamina is very
flender, making only a turn and a half, and the
inferior is only an indiflind: fold.

Thefe turbinata are in general .cartilaginous.
Harwood fays, they arc membranous in the ;
cajfowary and the aibatrojs. To me they ap- \

pear ofleous in the hornbill and the toucan^ \

\

. I

D. In Reptiles.

Reptiles havealfo different projeefling lamina:

within

Art. IV. Projecting LAMii^iE. 6^9

within their nofe; but they are produced by
the folds of the internal membrane, and are not
fuftained byoffeous parts. Thttortoife has three
laminae, which divide the nafal cavity into fe-
veral foffae. The middle one correfponds to
the external aperture of the noftrils ; between
it and the ne\t, there is an oblique canal which
leads to the poflerior nares. We find only fome
tubercles in frogs and other fmall fpecies. It
does not appear that any refearches have been
made refpediing thefe parts in the crocodile.

K. In FijJics.

The internal laminae of the nares in filbes are
alfo entirely membranous ; but they ate more
numerous and more regularly difpofed than in
the other clafles. In the Chondrppterygii, the
rays and Jharks have them placed parallel to each
other on both lides of 3 large lamina, which
extends from one end of the folTa to the other.
Each conlift of a femi-lunar fold of the pituitary
membrane, and has other fmaller laminte litu-
ated on both its fides, in the fame manner as it
is placed with refpecT: to the great middle
lamina.

In the other fifhes, whether cartilaginous or
olTeous, the laminae proceed like radii from an
elevated and round tubercle. They have a very
elegant appearance in the JlurgeoHy where each is
divided into more flender lamina?, as the branch

U u 2 of

66o

Lect. XV. § I. Of Smell.

of a tree into fmaller ramifications. In fome
fpecies, and particularly in the carpy the middle
tubercle is, fomewhat oval, and this renders the
difpofition of the lamina? more like that which
prevails in the Chondropterygii.

'' Article V.

)

‘ Of the Pituitary Membrane.

T HIS membrane is a continuation of the ex-
ternal fkin ; it unites in the back of the mouth
with that produdion of the fame tegument,
which, after inyefting the lips and all the interior
of the mouth, covers the oefophagus and the
reft of the intedines.

It takes the name of pituitary membrane in
all the interior of the nofe, on its feptum, its
parietes, its laminte, and even in its finufes. It
is attached to the periodeum of all thefe parts
by a compact cellular fubdance, and is itfelf
every-where covered by the epidermis.

In the finufes it is exceedingly thin, fimilar
to a common membrane, and its vdfds can
fcarcely be obferved; but in the red of the nofc
it is more thick and foft, particularly at the
inferior and podcrior part of the feptum. Its
fubdance is pulpy or fungous. We obferve in
it a fpongy texture, rendered Icfs conipad in

fmall

Art. V. Pituitary Membrane. 66i

fmall fpots, which reprefent the mefties of a net.
Its fuperficies is of a beautiful red colour, and it
is only by examining it very clofely that we per-
ceive that colour to refult from innumerable
ramifications of fmall blood-veflels. We dirtin-
guifli them better, however, near their trunks,
particularly at the pofterior part of the fcptum,
or when they are diftended by infiammacion or
injedlions.

The furface of this membrane has a great
quantity of fmall pores, from which a mucous
humour perpetually exudes. It is fuppofed that
thefe are the orifices of an equal number of mi-
nute follicles concealed in the fubftance of the
membrane. Many of thefe follicles have even
been obferved to exift in fonie parts, and to
have common excretory canals. They were dif-
covered by Stenon in the nares of the flieep.
Ruifeh, and after him Haller, perceived feveral
to communicate with one common finus, parti-
cularly towards the anterior part of the feptum.

There have been obferved in feveral quadru-
peds, as the cozv and the Jheep^ fome parallel
white lines between them. I have feen fome of
them tranfverfe or oblique on the feptum, and
longitudinal on the inferior turbinated bones
of the Jheep.

A vifeous humour confiantly exudes from all
parts of the pituitary membrane. In inflamma-
tions produced by colds, this at firft becomes
more abundant and fluid, and a; laft turns thick,

' u 3 yellow.

Lsct. XV. § I. Op Smell.

j^cllow, and difagreeable to the fmell. The fi-
nufcs produce a more limpid fluid, which feems
intended to dilute the other.

Except the Cetacea, of which we fliall fpeak
feparately, the mammalia exhibit little differ-
ence in the ftrudlure of the pituitary membrane.

In birds, it is, according to Scarpa, very thin
on the fuperior turbinatum. The velfels form
a beautiful net-work on its furface, and a mul-
titude of pores produce mucous matter in great
abundance, particularly on the middle turbina-
tum, where the membrane is alfo more thick
and villous.

In reptiles it is every where furnifhed with re-^
ticular ramifications of blackifh vcfiels. We
alfo find thefe black veffels in fome fifhes, and
particularly in ihcpikei but in the greater num^
ber of fpecies they are red. We obferve be-
tween them fome fmall papillje, that fecrcte a
thick mucilage, which appears to be more abun-
dant in fifhes, particularly in the rays and the
Jbarks, than in the other claffes.

Article VI.

oj the ’Nerves which arc di(lrihutcd to the
ternal Parts of the Nqfc.

T HESE nerves come from the firft and the fifth
pairs.

4

I. rhe

Art. VI. Nerves of the Nose. 663

I. The OlfaBory Nerve.

We have already defcribed the origin of the
firft pair in man, page 148 ; in quadrupeds,
page 164; in birds, page 168 ; in reptiles, page
170 ; and in fifhes, pages 172 and 1760! this
volume.

We have defcribed all the portion of the nerve
between its origin and its entry into the nafal
cavity, by one or feveral foramina, in Lecflurc X,
Article i. ; it remains for us now to treat of its
pafTage through the cranium, and its diltribu-
tion in the interior of the nofe.

A. In Mammiferous Animals,

1. The Cribriform Lamella.

The mammalia are the only animals that have
a cribriform lamella to the ethmoid bone, and
we muft, even in them, except the Cetacea,
w'hich have neither an olfa^Hiory nerve, nor holes
for its palTage. All the other animals have only
a fimple hole, or a fimple canal.

The polition, and the concavity of the cri-
briform lamella, have been defcribed in Lec-
ture VIII. Article 3. §B: it now' remains for
us to fpeak of its lize, its figure, and its fora-
mina.

In man it has the form of an elongated re6I-

U u 4 3.ngle,

664 Lect. XV. § I. Op Smell.

angle, and we reckon in it about 40 fimple fo-
ramina. In monkies it is proportionally much
narrower, and its foramina are lefs numerous.

In the other quadrupeds, the cribriform la-
. mella is fliaped like a heart, or it is oval ; it is
placed at the bottom of a fofla, which a con-
tradlion, more or lefs confpicuous, feparates
from the reft of the cranium, and is perforated
by a great number of holes of different fizes,
collected in groups ; thefe groups leave be-
tween them vacant fpaces, difpofed like the
fmall and great branches of a tree, fo that the
whole lamella exhibits the appearance of very
fine lace.

The number and figure of thefe clufters of
foramina are not fubjed: to conftant laws ; but,
judging by the animals in which the fenfe of
fmell is known to exift, that fenfation feems to
be in proportion to the number of the holes.

They are large and numerous in the elephant,
the hippopota7nus, the hog, and ftill more fo in the
hind, or jhnale Jlag. The Sarcophaga have them
more numerous than all other animals. The
hog, the Jloeep, and the ant-eater have, on each
fide of the crifta galli, a range of holes which
are larger than the others. We alfo find thefe
holes, but lefs confpicuous, in fomc other fpe-
cies. The Rodentia appear, in general, to have
fewer holes than the other orders. The camel
has the lamella fmall, and the perforated fpaces

Art. VI. Nerves of the Nose, 665

larger than in the other Ruminantia. The
Edentata have the lamella large, and furnilhcd
with many holes.

2. The Olfactory Nerve.

This nerve — whether it arife from the hemi-
fpherc,as in man, and in moukies — or whether the
pia-mater unites it in fuch a manner to the ca-
runcula rnammillaris as to appear to form but
one body with it, which takes place in the other
quadrupeds, — always dilates, by its extremity,
to cover the cribriform lamella, and to pene-
trate through it by as many filaments as that
lamella has holes.

Thefe filaments are difiributed to the part of
the pituitary membrane which covers the an-
fradluofitics and turbinata of the os ethmoides,
and to the intermediate feptum of the nares :
they are fo very foft that it is difficult to trace
them. We obferve, however, fome principal
branches fpreading over the feptum. There
are, in particular, two in the peep, which are
very beautiful. Several authors believe that
this nerve does not extend to the inferior tur-
' binated bones. Though w'e have not made
particular refearches on this f bjeefi, the com-
plication of thefe bones in the animals which
have the moft acute fenfe of fmell, would pre-
yent us from adopting the fame opinion.

B* h

666

Lect. XV. § I. Or Smeli.

Ij. Birds.

%

The olfaflory nerve in birds arifcs only from
the anterior extremity of the hcmifphere, which
has been compared to the caruncula mammil-
laris of quadrupeds ; it pafTes through a canal,
the length and diameter of which varies accord-
ing to the fpecies, but which is not fubdivided.
On reaching the root of the nofe, the nerve di-
vides like a hair pencil into a multitude of fi-
brillce, which expand in the pituitary membrane
of the feptum, and the fuperior turbinata.
Scarpa is of opinion that they extend no farther,
and fuppofes that the middle and inferior tur-
binata receive nerves only from the fifth pair,
and arc not organs of fmell. The only ufe he
attributes to them is that of breaking the force
of the air, which thefe animals refpire in a
greater quantity than others, and thus prevent-
ing its fliock from injuring the fuperior turbi-
nata.

He ftates, that his experiments on living
birds have convinced him, that fmell is firongefl
in the fpecies which have the fuperior turbinata
and olfactory nerves the largcfi:. The follow-
ing is the order in which he places birds with
relation to the faculty of fmell, commencing
by thofe in which that fenfe is mofi delicate —
the GralLcy the Palmipedes^ the AccipityeSy the
PiceCy the PajJcYeSy the Q ad Una:.

C. In

Art. VI. Nerves or THE Nose. 667

C. In Reptiles.

The olfacflory nerve in this clafs dilTcrs little
from that of birds, as to its origin and its courfe j
it differs ftill lefs in its diftribution, fince it alio
divides, according to Scarpa, upon the feptum,
and the fuperior turbinatum, without proceeding
farther.

• D. In Fifhes.

V

M^hcn the olfadfory nerve arrives behind the
folded membrane which forms the naris, it is
dilated to be applied to the whole of its internal
and convex furface. Sometimes, before it ex-
pands, it fwells into a real ganglion. This may be
feen in the carp ; at other times, its expanfion
takes place without any previous enlargement ;
it is thin, and may be compared to the j-etina,
but we obferve more diftindlly the nervous fibres,
of which it is compofed. In rays and Jharks
there is a trunk under the principal fold of the
pituitary membrane, and branches in the lateral
' folds ; thefe branches produce fmall filaments,
which penetrate into the fubftance of the mem-
hrarte, where they are regularly diftributed. »

II. The Nerve of the Fifth Pair.

In all vertebral animfils, the interior of the

nofc

668

Lect. XV. § I. Of S.MfLL.

nofe leceivcs a ramification of the ophthalmic
branch of the fitch pair, as we have fhevvn,
page 206 of this volume, in man ; page 209, in
the other mammalia ; page 220, in birds ; page 222,
in reptiles; and page 223, in fiflies. This rami-
fication is called the nafal neyve.

'Y\\t fphem -palatine ganglion of the fuperior
maxillary nerve furnifhes, befides, in man and
the other mammalia, feveral filaments to the
pofierior nares. See pages 210 and 211.

The maxillary finus receives fome ramifica-
tions from the fame branch ; and the frontal
finus, fome from the frontal branch of the oph-
thalmic nerve.

In birds, the firfl nafal branch of the ophthal-
mic arifes at the place where the nerve enters
the bill ; it is (lender, and extends the whole
length of the fuperior edge of the feptum ; the
ophthalmic afterwards produces a fccond and
larjzer branch, which divides 1 into three or four
ramifications, that extend to the middle and in-
ferior turbinata. A third branch is difiributed
to the external parts of the margin of the nares.

The diftribution of the fifth pair in the nofe
of reptiles, is not correifily known to us.

In.fifbes, the nafal branch of the ophthalmic
is fometimes as large as the olfacflory nerve itfelf.
As thefe two nerves proceed a confiderable way
in a parallel (ituation in carps, the p;cnus gaiius,
the pikct ^c. fome old anatomills (Collins

among

Art. VII. Cartilages of the Nose. 669

among others) believed that thefe animals had
two olfactory nerves on each fide : this error has
been copied by feveral more recent writers.

The nafal nerve appears to us, to be princi-
pally diftributed towards the external edges of
the pituitary membrane.

Article VII.

Of the CartUagex 'irhlch cover the Jperiure of
the y()J/rilx, ami their Mafele^i.

W E have deferibed, in page 82 of this volume,
the aperture of the nafal folfa, as it exills in the
fkeleton, when the foft parts have been removed.
In the frelh ftate that aperture is furnifhed with
feveral cartilages, which more or Icfs prolong
the nafal cavity anteriorly, and which can en-
large or contra^fl its entrance by their motions.

A. In Man.

t

I. The Cartilages.

The intermediate feptum of the nofirils be-
comes cartilaginous at its anterior and inferior
part, and is prolonged to the point of the nofe ;
its anterior edge is refleefted upon the part which
is immediately under the ofia nali, in two tri-
angular

670 Lect. XV. § i. Of S.vfEii.

angular laminse, which extend to the fide of the
nofe, and increafe the planes formed by its
proper bones*

The interval which remains on each fide be-
tween thefe triangular laminae and the feptum,
is occupied by an obloUg tranfverfe cartilage,
refledled in two plates, between which is the
Vacant fpace that leads into each noftril ; one of
thefe folds is placed againfl: the fuperior edge of
the feptum, the other occupies the fubftance of
the aia, for fuch is the name given to the infe-
rior part of each of the fides of the nofe. The
ala alfo contains, towards its root, one, two, or
even three fmall irregular cartilages, which are
fometimes membranous ; all thefe parts are con—
neficd by a fat cellular fubftancc, and covered
by the Ikin.

II. The Mufcles.

Several mufcles adl on thefe cartilages, and
contribute, with the two lips, to give to the
human countenance thofe various expreffions
which charadlcrizc it:

"i. The Pyramidalis Nnji. *

This miifcle is a produtflion of the occipito-
frontalis, which defeends between the eye-
brows, and covers the fides of the nofe j it is
terminated by an aponeurolis, which is common
to it with the mufcle wc have next to notice.

3. Tbf

Art. VII. Cartilages OF THE Nose. 671

C. The Triinf^'er falls, or ComprcJJ'or A aris^

Arifes below the internal angle of the orbit,
and extends along the fide of the nofe, to unite
with its correfpondent on the back of that part.

3. The Levator Labii Super lor is Alceque A af.

This mufcle defeends from the internal dngle
of the orbit towards the lip, and, in pafling,
furniflies feveral fibres to the ala of the nofe,

4. The DcpreJJ'or A he Nafi,

Comes from the part of the maxillary bone
which contains the dentes incifores, and extends
dircdlly upward to the inferior edge of the alat
nafi.

5. The N a falls.

This mufcle has its origin in the inferior part
of the feptiim, and proceeds downward and la-
terally, to be confounded with the orbicularis of
the lips.

The a(5Hon of each of thefe mufcles may be
very eafily comprehended.

B. In other Mammifer'ous Animals.

The cartilages of the nofe and their mufcles
vary confiderably in the mammalia, as well as
the greater number of other external parts.

The cartilages of the nofe of monkies do not
differ from thofe of man, but in their extreme

fmallnefs ;

Lect. XV. § I. Of Smel£.

6y2

finallners ; they appear to have no mufcles, ex*-»
cept an expanfion of longitudinal fibres, which
uniformly covers the ‘whole face, and which
feems to be a continuation of the Panniculua
Carnofus ; this at lead we have obferved to be
the cafe in the macaques.

In the Sarcophaga, in which the nofe is not
prolonged beyond the mouth, as, for example,
the dogi the cartilages are alfo limilar to thofe
of man. The cartilage of the feptum produces
two alee which prolong the bones of the nofe,
and the edges of the noflrils are furnifhed with
two iilfle(5led cartilages : there are no didindt
mufcles, except the levator communis ala naji^ la-^
bique JuferioriSj which covers the whole cheek'j
almod in the fame manner as the expanfion we
have defcribed in the monkey ; and the defreffcr
ala nafi, which is very fmall.

In the Sarcophaga, w'hich have projeciing
and moveable fnouts, as the bcarSy and particu-
larly the coatis and the moles, the cartilages form
a complete tube, which is articulated to the
odcous narcs.

In the bear, the cartilaginous feptum is rc-
fledlcd inferiorly, as well as fiiperiorly ; the fu-
perior alac bend downwards, the inferior up-
wards ; they meet on the Tides, where they are
united by cellular fubfiances, and complete the
external parictes of each nodril. The edge of
each ala continues afterwarils to bend inward,
and forms a kind of concha, which makes an

addition

Art. VII. Cartilages of the Nose. 673

addition to the inferior os turbinatum, and
which is covered, like it, bv a prolongation of
the pituitary membrane.

This cartilaginous tube is moveable, in every
direction, on the end of the olfeous fnout : its
mufcles are particularly remarkable in the mole;
there are four on each fide, all attached above
the ear, and extending between the temporal
and the malTeter mufcles ; they terminate by an
equal number of tendons, which are placed
round the nafal tube, like ropes round a mart 4
the moft deep-feated of thefe mufcles produces
the fuperior tendon, which unites with its cor-
refpondent, and a large aponeurofis, which
covers all the upper part of the nofe. The two
next mufcles proceed to the fide of the nofe,
the one a little higher, the other a little lower :
the fourth, which is the moft externaf, unites
with the correfponding mufcle under the nofc,
as the firft does above it; thefe tendons are in-
ferred into the fungous plate which terminates
the fnout, and cover the extremity of the car-
tilages : a fmall mufcle alfo arifes from the al-
veolar edge of the inter-maxillary bone, and
deprefies the fnout. The end of the feptum is
oflified.

The fnout of the hog is, in a great meafure,
fimilar to that of the mole ; its cartilages are
only proportionally fhorter ; their extremity is
alfo ofiified on the end of the feptum ; this ani-
mal has likewife four mufcles to the nofe, but

VoL. II. X they

674 Lect. XV. § I. Of Smell.

they are fliorter, and differently lituated ; the
iuperior arifcs from the os lachrymale before
the eye; its tendon extends to the fnout, but
does not come near enough to the correfpondent
mufcles to unite M'ith it : two other mufcles
are fituated under the preceding ; they arife
from the os maxillare before the zygoma, and
partly unite, but their tendons proceed fepa-
rately, the one to the fide, the other towards the
lower part of the fnout : the fourth, which is
very fmall, proceeds obliquely from the nafal
bone, towards the infertion of the preceding
mufcle, and paffes under the tendons of the two
fjrfi.

'■ The fnout and its longitudinal mufcles are
enveloped in the hog, as in the mole, by annular
fibres, which are a continuation of the orbicu-
laris of the lips.

In the Solipeda and the Ruminantia, w'hich
have the offeous nares very open, dire<5lcd ob-
liquely upward, and formed by a large notch
on each fide of the point of the proper bones
of the nofe ; a great portion of the foft part of
the nares is 'membranous, and, in particular,
bears the name of mjlrtls ; the edge of their
aperture only enclofes a cartilage in the horfe :
this cartilage, called fcvii-lunar by Hippoto-
mifis, is analogous to the inferior cartilage of
man, and is alfo formed of two branches ; one
alrnofi parallel to the feptum, which is long and
narrow ; the other, which is fituated in the cx*

ternal

Art. VII. Cartilages of the Nose. 675

rernal ala of the nofe, is fhort, and almoft: of a
fquarefonn: all the rdl of the external ala is
only a fold of the fkin, \\ hich forms at firfl a
blind cavity, the convexity of which is vifiMe
externally, and which is named falfe nans.
A long and narrow hflureof the internal pirictes
leads into the /rwe nan's: a principal mufcle
dilates the falfe naris. It is the py7\n;i!(>a':s
Hippotomilis, and arifes from the maxillary
bone, near the origin of the zygomatic arch, by
a narrow tendon ; its flelliy part dilates, and is
loll on the convexity of the falfe naris, and in
the orbicularis labiorum : another mufcle placed
af)ove the former, and ariling from the os
maxillare, near the notch of the ollcous nares, pe-
netrates into the fold lituated between the bone
and the falfe naris, and is inferred into a carti-
laginous production of the inferior os turbina-
tum.

The femi-lunar cartilage is approximated to
thefeptum, and the noftnl is dilated by a mufcle
common to both nares, which is named Iran/-
verjalis by Bourgelot; its fibres are parallel to
the orbicularis of the lips, from which no re-
paration d i It ingui flies them. Superiorly there
are fome fibres which arife from the nafal bone,
and are inferred on the fuperior convexity of
the talfe naris ; they form the mufculus hrezis of
Bou rgelot.

The mufculus vjaxillaris of the fame author
arifes from all the anterior part of the forehead,

N X 2 proceeds

6;6 'Lect. XV. §1. Of Smell.

proceeds obliquely to one fide, and downward,
and is bifurcated ; the external branch pafles
over the pyramidalis, and extends to the com-
miflure of the lips; the internal pafies under the
pyramidalis, and intermixes with it, to be in-
ferted in the external convexity of the falfe
naris. Finally, the levator labii fuperioris may
alfo be confidered as a mufcle of the noftril, on
which it acfls powerfully ; it is a long mufcle,
which arifes from the lachrymal bone ; it pro-
duces a ftrong tendon, which unites with that
of the correfpondent mufcle on the extremity
of the offa nafi, and forms with it an aponeu-
rofis, which is inferted into the fuperior lip.

The mufcles of the nofe of the Ruminantia
are much lefs complicated ; their cartilages con-
fift only of a duplicature of the feptum, which
is continued into the external ala of the nofe by
a pointed and arched production : the noftrils
are not fo far feparate, and are directed more
forward than in the horfe.

There are two mufcles on each fide, which
arife from the inferior part of the os maxillarc,
above the anterior molares ; the fuperior divides
into two tendons, one of which proceeds to the
fuperior edge, and the other to the pofierior
angle of the nofiril; the inferior divides into
three other portions, which all go to its inferior
edge: there is alfo a depreflbr ; it is fituated
anteriorly.

We Iball terminate this dffeription of the car-
tilages

Art. VII. Cartilaqts OF THE Nose. 677

tilages of the nofe, and their mufcles, in mam-
iiialia. by that of the probofcis of the elephant.

The following defeription is th« fubftance of
that which was given by the Academicians of
Paris :

The probofcis of the elephant is a very elon-
gated cone, broadefl at the root. Its interior
is hollow, and divided into a double tube, co-
vered with a ftrong tendinous membrane, and
perforated by a number of fmall holes, \\hich
are the orifices of an equal number of mucous
cryptae, and from which a liquid flows in great
abundance. Thefe tubes afeend to the ofl'eous
nares; but a little before they arrive there, they
are twice infledled, and their commtmication
with the nares is clofcd by a cartilaginous and
elaftic valve, which the animal can open at plea-
fure, and which falls down by its own clafticity
when the mufcles ceafe to acfl upon it.

All the interval between the membranous
tubes which arc in the axis of the probofcis, and
the external fkin, is occupied by a very thick
flefliy layer, compofed of two kinds of fibres.
Thofe of the firfl: kind extend from the mem-
brane of the tubes, to a tendinous membrane
fituated under the external fkin, in fuch a man-
ner that they appear tranfverfe upon a longi-
tudinal feclion of the proboftis, and that in a
tranfverfe feclion they reprefent the radii of a
circle. They approximate the external fkin and
the membrane of the tubes, and, by comprefllng

X X 3 the

678 Lect. XV. § I. Of Smell.

the intermediate layer, produce the elongation
of the probofcis, without narrowing the tubes, in
the manner of annular fibres ; a mode of acflion
which is very remarkable. The other fibres of
the probofcis are longitudinal : they form a
number of fhoit and arched fafciculi ; the two
extremities of which are attached to the mem-
brane of the tubes, and the middle or convexity
of which adheres to the external membrane.
There are fome of theie fafciculi all along and
around the probofcis. The effect they produce
is to fhorten it wholly, or in any particular part,
as the animal pleafes.

It will be eafily conceived, that thefe partial
elongations and contraeftions, on either fide, enable
the elephant to give to his probofcis any ima-
ginable flexure; but that which is mofl difficult
of explanation, is the manner in which he con-
veys to his mouth the water which he has taken
into his trunk. As there are no annular fibres,
he cannot comprefs th.e tubes, and he has no
other means of impelling it forward but by re-
• fpi ration ; but how can this be done at the mo-
ment of fwallovving ? Perhaps the end of the
probofcis is conveyed beyond the opening of the ,
larynx.

We have diffetflcd only the foetus of nn ele-
phant, which has however enabled us to add
fomc fadls to the preceding defeription. All
the finall longitudinal fafciculi belong to four
large mufclcs, which arc almofl confounded in

Art. VII. Cartilages OF THE Nose. 679

the probofcis, but are fufbciently at

their fuperior attachment. The two anterior
are connccfled, by the whole of their breadth, to
the frontal bone above the olTH nafi ; the two
lateral adhere to the maxillary bones, under and
before the eye. The pofterior, or inferior fur-
face of the probofcis, is furniflied with fibres
which feem to be continued with thofe of the
orbicularis of the lips. I'hey arc directed from
above downward, and from within outward ; lo
that thofe on one lidc form a figure like an A,
with thofe of the other.

All rhefe mufcles are fupplied by a very large
branch of the fub-orbitar nerve, which pene-
trates, on each fide, between the lateral and in-
ferior mufcles, and ramifies through the whole
probofcis.

The probofcis of the tapir^ which we have
alfo difleified in a foetus, refemblcs in fome re-
fpeds that of the elephant, though it is much
{hotter. It is alfo compofed of two mem-
I branous tubes, furnilhed with a number of mu-
I cous lacunte, and enclofed in a flefhy mafs en-
^ veloped by the Ihin. The longitudinal fibres
i are divided only into two fafciculi, which arife
i below the eye. The tranfveffe fibres extend, as
i in the elephant, from the membrane of the
: tubes, to that which is under the fkin ; but the

tapir has, befides, a mufcle fimilar to the le-
vator labii fuperioris of the horfe. It arifes in
^ the fame manner from the parts adjacent to the

X X 4 eye.

6So

Lect. XV» § I. Of Smell.

eye, and unites in a common tendon with its
correfpondent mufeie above the noftrils. The
occipito-frontalis alfo furnifhes a tendon which
is inferted at the bafe of the probofeis, and ele-
vates it,

C. I/i Birds.

The external nares of birds have neither
moveable cartilages nor mufcles. Their aper-
ture is merely contradled by produdiions more
or lefs confiderable, of the fkin which covers
the bill. The forms and pofitions of that aper-
ture have been deferibed by naturalifts. It is
lituated laterally in the greater number of birds.
Some have it at, or even on, the bafe of the bill.
The toucans afford an example of the latter cafe.
It is fometimes broad, fometimes narrow. In
the hcronSy for example, it is a filFure into which
a pin could with difficulty penetrate. In the
/ea-fivallQWSi the two nares correfpond to an
aperture of the feptum, fo that we can fee
throuGfh them acrofs the bill. The Gallinae
have the nares partly covered by a flefhy plate.
The ravens have them clofed by a fafciculus of
ffilf feathers directed forward,, &c.

T). In Reptiles,

The external nares of reptiles areufually fur-
rifhed with only fome fiefhy ffrata, which di-
late or contradl their entrance. This is ob-

fervablo

Art. VII. Cartilages OP THE Nose. 6Si

fervable in the greater number of lizards, which
differ from each other only as to the pofition of
their external nares. They are clofefl: to each
other in the crocodiles. The tupinambis, the
Jiellions, and the camelions, have them more re-
moved, and fituated more laterally. In the fa-
lainanders they are exceedingly fmall. In frogs^
M'e obferve a fmall tube, the motion of which is
very apparent, becaufe it is extremely ufcful in
rclpiration, as will hereafter be fliewn. The
torloifes have alfo two very fmall approximated
nortrils. In the matamata, and one or two other
fpccies, they are fituated at the end of a fhort
cartilaginous probofeis.

Serpetits have fmall lateral nares, which are
capable of only a flight extenfion. The rattle~
J'nake has below and behind each naris a blind
hole, pretty deep, the ufe of which is not known,
but it gives the animal the appearance of having
four noftrils.

E. In Fijhes.

In "filhes the entry of the foffa, which forms
each naris, is narrower than the foffa itfelf.
The membrane which furrounds it, is, in a
number of offeous fifhes, and particularly in the
carp, capable of forming a fhort tube, at the
will of the animal ; but when the fifh is drawn
from the w’ater, this tube difappears.

The greater number of offeous fifhes have the
nafal aperture divided into two parts by a mem-
branous

682 Lect. XV. § I. Of Smell.

branous bar, and this gives them the appear-
ance'of having four nares. The two holes on
each fide are fometimes equal and fometimes
unequal. They are infinitely various in fize and
in pofition, but thefe external differences have
been deferibed by Ichthyologiffs.

In the Chondropterygiij the nares communi-
cate by a groove with the angles of the mouth.
A part of their aperture is commonly covered
by a lobe oT the fkin, and the mufcular fibres
which open them, are attached to the bones of
the jaws. They appear to be contracted by a
fphincter. It is difficult to obferve either di-
fiincftly.

Article VIII.

Of the Nares and the Spiracles of Cetacea.

Xhe nares of the Cetacea merit a particular de-
feription, on acc«\int of their great difference
from thofe of the other Mammalia.

The Cetacea can refpire only in air; but they
cannot receive it by the mouth, which is more
or lefs funk in the water, and could not have
taken it in by the nares, if their aperture had
been fituated at the end of the muzzle; for this
reafon their nofirils open on the fummit of the
head, which thefe animals can calily elevate

above

Art. VIII. Nares of the Cetacea. 683

above the furfacc of the water. They form,
therefore, their only means of refpiration. They
ferve befides to difeharge the water, which they
Avould be obliged to fwallow every time that
they open their mouth, if they had not the
means of ejec^^ting it through their nares, by a
mecitanifm which we Ihall prefently deferibe.

The common pituitary membrane would
doubtlcfs have been irritated by this conftant
and violent paflage of fait water, as wc may
eafily conceive, from the difagrceablc fenfation
wc feel when a few drops of the liquor wc drink
enters our nofe. On this account the nares of
the Cetacea arc lined by a thin dry fkin, which
has neither cryptae nor mucous follicles, and
which does not appear fitted to exercife the
fenfe of fmell. There are no linufes in the fur-
rounding bones, nor any internal projecting la-
minse. The os ethmoides is not even perforated
by any hole, which indeed is not neceffary, as
the olfaefory nerve does not exilf. (See pages
165 and 199.} It is not, however, certain that
thefe animals have no fmell ; but if that fenfe
exilt, it muft relide in a cavity we are about to
deferibe.

We have fliewn in page 503. that the Eufia-
chian tube afeends towards the nares. The part
of this canal which is next the car, has, at its
internal furfacc, a pretty large hole, which leads
into a -large vacant fpace fituated deepl)'' be-
tween the ear, the eye, and the cranium, main-

3 tained

6S4 Lect. XV. § I. Of Smell.

tained by a very compad cellular fubftancc, and
prolonged in different membranous linufes which
are attached to the bones. This fac, and thefefi-
nufes, are lined internally by a blackiih, mucous^
and very tender membrane. It communicates
with the frontal finufes, by a canal which afcends
before the orbit. Thofc finufes have no imme-
diate communication with the nares, properly
fo called. We find in this fac, as well as in the
nares, nerves proceeding only from the fifth
pair. Hunter flates, that he had obferved fome-
thing fimilar in two fpecies of whale, but he did
not fuppofe that the organ of fmcll w'as to be
feen in the dolphin and the porpoijcy from which
we have taken this defcription.

The following is the mechanifm by which the
Cetacea ejedl the water in thofe fpouts by which
they are rccognifed from a diftance at fea, and
which have procured to feveral fpecies the name
of blowers.

If we trace the oefophagus upwards, wc find
that, when oppofite to the larynx, it feems to
divide into two conduits, one of which is con-
tinued into the mouth, and the other alcends
into the nofe. The latter is furrounded with
glands and fiefhy fibres, which form feveral
mufcles ; fome, which are longitudinal, arc
attached to the margin of the pofierior orifice
of the offeous narcs, and defeend along that con-
duit to the pharynx and to its fidcs : the others

arc annular, and fctni to be a continuation of the

proper

Art. VIII. Nar£s of the Cetacea. 685

proper mufcle of the pharynx. As the larynx
rifes in this conduit in the manner of an obelilk
or pyramid, its annular fibres may clofe it by
iheir contradlions.

All this part is provided with mucous folli-
cles, which pour out their liquor by very con-
fpicuous foramina. When arrived at the vo-
mer, the internal membrane of the conduir,
which becomes that of the olTeous nares, ac-
quires the even and dry texture which v.e have
already deferibed. The two ofTcous nares arc
clofed at their fuperior or external orifice, by a
flefliy valve in the form of two femi-circles.
Thfs valve is attached to the anterior edge of
the orifice, and clofes it by the means of a very
ftrong mufcle lituated upon tlie intermaxillary
bones. In order to open it, an extraneous force
muft be applied from below. When this valve
is clofed, it intercepts all communication be-
tween the nares and the cavities lituated above
it.

Thefe cavities are two large membranous
facs, formed by a black and mucous Ikin ;
they are full of rtigse when empty, but: when
full afilime an oval form. In the porfoife^
each is of the fize of a drinking-glafs. Thefe
two facs are lituated under the fkin, before the
nares. They are both continued into an inter-
mediate cavity placed upon the nares, which
opens externally by a narrow filTure, in the form
of an arch. Some very fiiong flelhy fibres form

686

Lect. XV. § I. Or Smell.

an expanfion which covers all the upper part
ot this apparatus. They arifc in radii from the
circumference of the cranium, and unite upon
two facs, which they appear capable of com-
prefling very powerfully.

Let us now fuppofe, that one of the Cetacea"
contains in its mouth a quantity of water which
it wifhes to ejed; : the animal moves the

tongue and the jaws, as in thp adion of fwallow-
ing, and doling the pharynx, forces the fluid
to afcend in the conduit and the narcs, w here
its motion is fo much accelerated by the annu-
lar fibres, that the valve is raifed, and the two
facs above it diflended. When the water is in
the facs, it mav remain there until the animal is
inclined to ejed it. Fgr this purpofe, the valve
is clofed, to prevent the water from defeending
into the nares, and the facs are flrongly com-
prelTed by the mufcular expanfions w-hich cover
them. The fluid is then thrown out through
the narrow crefcent-fliaped aperture, and rifes
to a height correfponding to the force of the
prelTure.

It is faid that zvhalcs c]Qd: water to the height
of 40 feet.

Art*-

A. IX. Smell of Inverteeral Animals. 6^7

Article IX.

Of the Organs of Smell in Animals that hare no

I 'ertebrec.

w E do not find th? nofc, properly fo called,
nor even any organ which appears evidently ap-
propriated to fmell in in vertebral animals, and
yet almofi: all of them Rliord very ftrihing proofs
that they polTels this fenfe.

Infedls difeover their food at a difiance. But-
terflies feck their females, even when inclofed
in boxes, and as they arc liable to be deceived
by refemblances of odour, it is evident that
thefe infeds are guided in many circumfiances
by the fenfe of fmell. Thus the fejh-fy (mufea
vomitoria) lays its eggs on plants that have a
foetid fmell, imagining that it places them on
corrupted flefli, and the larva; which are thus
produced perilli for want of their neceflary food.

As the organ of fmell, in all animals which
refpire air, is fituated at the entrance of the or-
gans of refpiration, the moft probable conjec.-
ture that has been propofed refpeding its feat
in infeds, is that of Bafter, fince revived by
feveral naturalifis, who placed it in the mouths
of the tracheae or air tubes. In addition to the
reafons hitherto fiated in fupport of this opi-
nion, w'e may obferve, that the internal mem-
brane of the tracheae appears very well calcu-
lated

6SS Lect. XV. § I. Of Smeli,*

lated to perform this office, being foft and
moiffened, and that the mfedls in which the
tracheae enlarge, and form numerous or confi-
derable veficles, are thofe which feem to pof-
fefs the moft perfedt fenfe of fmell. Such are
all the fcarabtei^ the jiies^ the hees^ &c.

The antenna, which other anatomifls have
fuppofed to be the feat of fmell in infeefts, do
not appear to us to polTcfs any of the conditions
requifite for that organ.

The mollufca, which refpire air, may alfo
pofTefs the fenfation of fmell at the entrance of
their pulmonary velfels ; but it is not neceffary
to fearch for a particular organ of this fenfe in
them, as their whole fkin appears to refemble a
pituitary membrane. It is every where foft,
fungous, and is always moiftened by a great
quantity of mucous matter. Finally, it is fup-
plied with numerous nerves, which animate
every point of its furface.

The worms and foft zoophites, and all the
polyps, are probably in the fame fituation. It
cannot be doubted but that thefe animals enjoy
the fenfe of fmell. It is chiefly by it that they
difeover their food, particularly the fpecies that
have no eyes. Ariftotle remarked, that certain
herbs, which have a (Irong odour, were avoided
by cuttle-fiJJjes ■a^nd the obtopus.

SEC-

[ 689 3

SECTION SECOND.

Of tiik Organs of Taste.

Article 1.

Of the Senfation of Tajle.

Having treated fo fully of the four preceding
Senfes, little remains to be faid refpedling that
of Tafte, which is the leaft removed from the
ordinary fenfe of Touch.

The organs of thefe two fenfes are, indeed, fo
much alike, that they may ferve for the mutual
explanation of each other. Recourfe may be
had to the, organ of Tafte, in order to ‘obtain an
idea of parts which are not fufficiently deve-
loped for our obfervation in that of Touch.

The organ of Talle is particularly cha-
radlerized by its fpongy texture, which enables
it to imbibe liquids. The tongue can only
tafte fubftances which are liquid, or are fufeep-
tible of fluidity when diflblved in the faliva.
Infoluble bodies are taftelefs. The moft fapid
even make no impreflion oil the tongue, when it
is dry in confequence of fleknefs, or when the
VoL, II. Y y ' faliva.

r

690 Lect. XV. § II. Of Taste.

faliva, confumed by previous maftication, has
not had time to be renewed.

Nature has provided plentifully againft this
want, by a condant moHture.

In all animals which do not live in water,
numerous glands pour an abundance of fluids
into the mouth, as we fliall fee when we treat
of Maflication. The total abfence of faliva,
and perfect drynefs of the tongue, is one of the
mofl: painful fenfations that can be experienced.

The tafle of bodies feems to be greater in
proportion as they are more foluble : falts pof-
fefs it in the higheft degree; but it will be eafily
conceived, that it is impolTible to account for
the different kinds of favours attached to each
tody, and that the explications, founded on the
figures attributed to their elementary particles,
cannot now be admitted. The change which
takes place on the nerve, is doubtlefs the effecT
of the reciprocal adlion exercifed betw-ecn the
principle of each tafle, and the nervous fluid ;
but the. nature of that aeflion is ftill unknown!
to us, and of its conne(flion with the image
which refults from it, we mufl neceffarily be
always ignorant.

The fenfe of tafle in any animal is more per-
fe(fl — ifl, in proportion as the nerves, which
proceed to the tongue, are more confiderable :
2d, as the teguments of that part arc more
capable of being penetrated by fapid fubflanccs;
3d, as the tongue itfelf is more flexible, and
8 can

Art. II. Substance of the Tongue. 691

can be applied to a greater fuperficics, and em-
brace more clofely the fubdance which the ani-
mal wiflies to taftc.

In the following Articles we (hall confider the
Organs of this Senfe, under thefe three points
of view.

Article II.

*

Of the Suhjlance of the 7'ofiguc, oj' its Form,
and of its Mobility.

I^iiE tongue is at the fame time an organ of
taflc, of deglutition, and of fpeech ; but as the
parts which ferve to move it, contribute more
to the two lafl: fuiuflions than to the firfl, we
fhall not notice them at prefent. In the Article
on Deglutition, we fliall deferibe the os hyoides,
its ligaments, and its mufcles, as well as the
mufcles of the tongue, and the motions of
which that organ is fufceptible. We fhall, in
this place, only explain the nature of its fub-
flance, and the degree of its general mobility, in
fo far as it polTelTes an influence on the perfec-
tion of tafte.

In all mammiferous animals without excep-
tion, the tongue is flefhy and flexible in all its
parts, attached by its root only to the os hyoides,

Y y 2 and

692 Lect. XV. § II. Of Taste.

and by a portion of its bafe to the lower jaw ; it
differs only as to the length and extenfibility of
its free part or point. The extremes in this re-
lpe(5l are the ant-eatery which can elongate the
tongue exceedingly, and the Cetacea, which
have it attached by almofi; the whole of its in-
ferior furface.

'The other fpecies prefent no material differ-
ence from man, with regard to thefe circum-
flances.

In birdsy the tongue is always fupported by a
bone, which paffes through its axis, and is ar-
ticulated to the os hyoides ; it is confequently
very little flexible : the point only of the bone,
which becomes in a degree cartilaginous, is ca-
pable of flexion. The fliape of this bone corre-
fponds to the external figure of the tongue, being
covered only by fome mufcles, and by the te-
guments which are thin. In the zvood-peckerSy
and the zvry-necksy it is confiderably fhorter than
the fkin of the tongue. When their tongue is
elongated, therefore, the os hyoides, and its
cornua, extend forward, and penetrate into this
furplus of the fkin, which is thereby extended,
and the tongue puflied forward, as we fliall fliew
hereafter.

Reptiles vary greatly with refped: to the
tongue, as well as in many other circumftances.
The tongue of toads and frogs is entirely flefhy,
attached to the lower jaw, and, in a flatc of i c-
pofe, inflefled in the mouth.

In

Art. II. Su BSTANCE OF THE ToNGUE. 693

In faJamanderSy it is attached as far as the
point, which is not moveable, and the whole
tongue is only free on its lateral parts. Crocodiles
have it attached as clofe to the edges as its point,
and authors long fuppofed that this animal had
no tongue. It is entirely flefliy in both thefc
genera.

The flelUons and the iguanas have a flefhy
tongue, which polTefTes nearly the fame mobility
as that of the mammalia. The Jcinks and geckos
differ only in having the tongue notched at the
extremity, and in that refpe<fl it refembles the
tongue of jlow-worms y to which, in general, the
Jcinks are very much allied.

In common lizardsy the tupinamhis, or monitory
&:c. the tongue is fingularly extenfile ; it ter-
minates in two long flexible points, though
femi-cartilaginous ; it completely refembles that
of ferpents, if Me except the Jlozv-zvorms and the
amphijhenay which cannot elongate their tongue,
but which have it flat, and only forked at the
extremity.

The camelion has a cylindrical tongue, which
may be conliderably elongated by a mechanifm
analogous to that which takes place in wood-
peckers.

In fome fijhesy as the Chondropterygii, there
is no tongue at all ; the lower part of the gullet
is fmooth, and has no elevation.

In other fi/heSy as the greater number of thofe
that have free branchite, the tongue is formed

Y'Y 3 only

694 Lect. XV. § II. Of Taste.

only by the protuberance , of the middle bone,
to which thofe that fupport the branchijE are
articulated ; that bone has no mufclesj except
thofe which elevate or deprefs it in deglutition
and refpiration ; none of its parts are capable
of flexion ; it is covered only by a more or lefs
thick fkin, and is frequently furnifhed- with
teeth, which are either fharp, or in the manner
of a pavement, and which render the furface
almoft infenfible.

The jyren refembles, in this refpect, the fiflies
that have free branchiae.

The fepite^ the fnails^ and the greater part of
the gajleropodous mollujcay have a cartilaginous
tongue, the very fingular ftrudlure of which we
fhall explain hereafter ; it has no motions, ex-
cept fuch as are connedled with deglutition ; its
anterior part is fixed below the mouth, and it
is incapable of embracing ftpid bodies.

The acephalous mollujca do not appear to have
any tongue; perhaps they exercife the fenfc of
tafte by thofe tentacula, fo fimilar to papillae,
with which their cloaks are furnilhed, at the
parts where the water, which is the vehicle of
their aliments, enters.

There is no tongue, properly fpeaking, in
ivorms, though fome have given that name to
the probofeis of the tbala([emay the echinorbinenSf
&c. T\\q zoophiles have alfo no tongue ; but
the tentacula, which furround their mouth, are
frequently fo fine, and of fo delicate a fubflancc,

as

Art. II. Substance of the Tongue. 695

as to be very well calculated for the feat of taflc.
Befides, why may not the whole fkm of the
polype be fufficiently fenfible to difcern faline
fubftances dilTolved in water, fincc it is ca-
pable of feeling the light which palfes through
it ?

The numerous clafs of i'lfefls prcfents great
varieties with regard to the organs of talle.

The coleopiera, and the oriboptera, have the
part which has been named, perhaps without
much analogy, the inferior lip horny at its bafe,
and terminated at its point by a membranous
expanfion, which is, in particular, named the
tongue: the form of this tongue is infinitely
various in the diiTcrent genera, as may be feen
by confulting the works of late Entomologifts.
7'hc pharynx opens at the bafe of the tongue.

The hymenoptera^ and fome neuroptera^ have
the tongue fituated at the fame place ; but it is
concave, and perforated for the pharynx infe-
riorly, and is frequently prolonged into a pro-
bofeis, which fometimes furpaTes the length of
the whole body; this probofeis alfo preferves
the name of tongue ; it is membranous, but w'e
obferve that its fubhance is foft and fungous,
and that it is very well fitted for receiving the
impreflions of tafte. Accordingly we remark
that the infec^ls, in which it is moft developed,
arc the moft diftinguiftied for the choice of their
aliments. The hes afford an example of the
truth of this obfervation.

Y V4

All

bg6

\

Lect. XV. § II. Of Taste.

All the diptera with a flefliy probofeis, as the
the tabanusy &c. feem alfo to have an ex-
cellent organ of tafte : the two lips of their
probofeis, independent of their foft fubftance/
and the delicacy of their teguments, have the
faculty of embracing feveral points of fapid
bodies.

Th.^ lepidoptera^ or butterflies y have a' tubular
tongue? it confifts of two pieces, cxadly joined,
' and very often of a confiderablc length, and
may be capable of diftinguifhing very accurately
the nature of the liquor it fucks up, if the whole
of the canal be fenfible to that fort of impref-
fion. The fame obfervation may be applied to
the fucker of the ryngota, or bemipteray and that
of the dipterdy wdiich have not a flelhy tongue,
as the aftlusy the JlomaxySy the culeXy &c. We
cannot, however, judge of the perfeeflion of
each of thefc inftruments, merely by their pro-
portional extent. It would be necelTary to take
info the account the degree of their particular
fenfibility, which cannot be cllimated in organs
fo minute.

The cirriy the palpiy or autennul^y are fila-
ments more frequently articulated, and attached
to certain parts of the mouths of infcdls, and
which thefe animals conllantly move, for the
purpofc of touching their food while they cat.
Some authors have fuppofed them to be appro-
priated to the fenfe of tafic, fomc to that of
fmell, and, finally, others believe them to be

limple

Art. III. Teou MENTS OF THE ToNGUE. 697

fimple organs of touch ; difterent as thefe opi-
nions may be, it is not impoflible that thefe
organs may not perform at once two or feveral
functions. It is obvious, however, that this is
a fubje^ upon which we never can arrive at
certainty. We fliall defcribe thefe Palpi along
with the red of the organs of Manducation in
infedls.

Article III.

Of the Tcgiunents of the Tongue.

A. In Man.

The mufcles which form the internal fabric of
the tongue, are furrounded by a conliderable
quantity of cellular fubftance, and. covered by
a thick membrane, which is the continuation of
that which lines the interior of the mouth, and
confequently of the external fkin of the body.

The particular charadlers tof this membrane
on the tongue, are the thicknefs and foftnefs of
the part analogous to the epidermis, but, above
all, the extraordinary development of the pa-
pillae, which, though eflentially of the fame
nature as thofe of the external fkin, are much
larger, more clofe, and afford a more complete
view of their intimate ftrudlure.

All

698 Lect. XV. § TI. Of Taste.

All the fupcrior fiirface of the tongue, from
the point to nearly its root, is covered with pa-
pillae, called, on account of their figure, co-
nical i they are clofe, like the brililes of a brufh ;
on the middle of the tongue, and towards its
point, they are (harp and elevated, and their
extremity is divided into feveral filaments ; to-
wards the fides they become gradually fliorter,
and are reduced to fimple blunt tubercles.

Among thefe papillae others arc difiributed,
which are larger, but much lefs numerous ; thefe
are called fungiform papillae j they are placed on
a fmall pedicle, anfl- terminate in a large round
head ; there are more of them towards the end
of the tongue, than in any other part.

Laftly, towards the bafe of the tongue there
are about ten femi-fpherical tubercles, each
■furroLindcd with a circular fold or bur^;, and on
that account called papilla in a calyx, or inciipped
papilla s they are difpofed in two lines, which
reprefent a V with the point turned towards the
throat.

The fpace fituated between the point of this
V and the epiglottis, has no papillae, but the
membrane is rendered unequal by glands which
•are below it ; and we obferve that the greater
part of its eminences arc perforated by holes,
through which fluids, prepared by thefs glands,
pafs into the mouth ; the inferior furfacc of the
tongue has alfo no papillae, and its Ikin does

not difler from that of the rcfl of the mouth.

'I’he

Art, III. Teguments of the Tongue. 699

The part analogous to the retc mucofum is fo
thin on the human tongue, that we can fcarccly
recognize its exirtence; but it is very thick on
that of quadrupeds, where the papillae, which
pafs through it, render it completely reticular.

B. In other Mamniifcrous Animals.

The tongue of the other mammalia jircfents
the fame kind of papilhe as that of man : the
difference confifts merely in the form of the co-
nical papillae, and of the fubflance with which
they arc fometimes armed, in the fize and abun-
dance of the fungiform papillae, in the number
of the incupped papillae, and the figure which
their arrangement reprefents.

In the guenons t we obferve no difference from
the human tongue, except that the papillae with
a calyx are lefs numerous. The Cbinefe monkey

has feven difpofed in this manner The

macaque has four fituated thus * . . * ; the cyno-
cepbalus and the mandrill have only three, which
are ranged triangularly • . • We alfo find only
three in the fapajoiis, which are farther difiin-
guilhed by the little prominence of their conical
papillae.

Several hats have the conical papillae elonga-
ted, and almofi: rcfembling hairs ; thefe are par-
ticularly obfervable towards the pofterior part
of the tongue : fome of them are alfo found on

the

700

Lect. XV. § II. Of Taste.

the fides of the mouth. Thcfe papillae are as
hard as horn in fome fpecies, as the ternate hat^
in which the papillae of the extremity of the
tongue have each feveral points ; there are only
three papillse with cups on the tongue of thefe
animals, and they are very clofe together.

The cat genus has the teguments of the tongue
of a very particular nature : all the edges lof
that organ are furniflied with fmall foft conical
and with fungiform papillae, limilar to thofe of
the greater number of animals; but all the
middle part is covered by othfer papillae, which
may be divided into two kinds; fome are round-
ed, and, when a little macerated, reprefent faf-
ciculi of filaments, which feem to be the lafi:
extremities of the gufiatory nerves: the others
arc conical, pointed, and each covered with a
horny cafe, terminating in a point, which is
infleded backward ; thefe cafes render this
tongue fo extremely rough, that it tears ofi' the
fkin by licking; they may be eafily plucked
out, and have then the appearance of lb many
fmall claws. The filamentous papillae and the
horny points are placed alternately in quincun-
ecs, fo that there areas many of one kind as of
the other. There arc no fungiform papillae in
all this fpace: I believe they arc replaced by
the fafcicular, as the conical arc by thofe with
the horny cafes. The poficrior part of the
tongue afiiimcs the nature of the ordinary te-
guments : the papillae with cups arc propor-
tionally

Art. III. Teguments of the Tongue. 701

tionally fmallcr than thofc of the other genera,
and difpofed in two lines, which approach po-
fteriorly. In the common cat we fomctimcs ob-
ferve on the back part ot thcfidesof the tongue,
fome fungiform papillne dependent from very
long pedicles. Civets have a tongue fimilar to
that of cats.

The opojjums have alfo, at the middle and an-
terior part, horny cafes, or fcalcs infle(flcd
backward, but they terminate in wedges, or in
rounded edges ; the point of their tongue is
denticulated like a fringe; there arc only three
incupped papillae. The pbaLingers have the
tongue foft, like the other Sarcophaga. DogSy
bears, zveafeis, /cals, &c. all of which fcarcely
differ from man in this organ, and differ frorr
each other only as to the number of the papilh
with cups.

There are five of thefe papillas in the martin,
ten in the racoon, two large and fome very fmall
ones in the badger. I have only been able to
reckon four very fmall ones in a large dog; there
are only three, which are very large, in the hyana.
All the fpace fituated between the incupped pa-
pillae and the epiglottis^ is furnifhed with large
conical papillae, which are very acute, and more
clofe together

One of the moft ffngular tongues among the
Rodentia, is that of \.\\t porcupine : on its ffdes,
and towards the extremity, it has fome 'large
fcales, with two or three points terminated like

wedges.

702

Lect. XV. § II. Of Taste;

wedges. The refl of the furface refembles that
of the tongues of the other mammalia; there
are only two large papillae with cups. The
other Rodentia do not differ from man, except
in having fewer of thofe papillae.

The long-nofed Edentata, as the ant-eaters^
armadillos, orydleropus, all have the tongue long,
narrow pointed, and fingularly fmooth ; in the
two latter, the conic papillae are not diftinclly
feen, except with a magnifying glafs ; and in
the ant-eaters, properly Jo called, none are per-
ceptible. There are but three papillae with cups
in the orydJeropus, and only two in the armadil^
los.

The Jloths have the tongue round at the point.
The conic and fungiform papillae little deve-
loped, and only two incupped papillae.

The tongues of the Pachydermata have the
papillae little evident.

In the Ruminantia, the conic papillse, which
cover the anterior half of the tongue, are nu-
merous, clofe and fine ; each terminated by a
horny but flexible filament, which is bent
backward. Thcfe filaments can only be diffin-
guiflied by a glafs in JJjecp, gazelles, &ic. But
in the camel genus they arc long, and render the
tongue foft to the touch like velvet. The pof-
terior part of the tongue of thcfe Ruminantia
is covered with thick tubercles, which 'fome-
times rcfemblc fliort cones, and fometimes arc
femi-fphcrical, and which become fmaller to-
wards

Art. III. Teguments of the Tongue. 703

wards the fides. The papillae with cups are
ranged .on the lides of this pofterior part ; they
are pretty numerous, and cannot be cafily dif-
tinguilhed from the fungiform, which arc equally
large in this part. The camel, however, mufl
be excepted, which has the incupped papillae
very large, and concave on their furface.

In the horfe, the conical papillae arc very
fmall and compadl: ; the fungiform arc only
found on the fides of the tongue ; there arc only
three incupped papilhc, the furface of which
prefents a multitude of irregular tubercles. The
fpace fituated pofleriorly refemblcs the corre-
fponding part of the human tongue.

There is no diftincl: conical papillae obferved,
even with a glafs, either on the tongue of the
dolphin or porpoife: that organ is, in thefe animals,
covered, as it were, with fmall pimples, which
are molt numerous at its pofterior half : we ob-
ferve at its- bafe four iifliires, difpofed nearly as
the papilla with cups ufually are ; the edges of
its point are divided into fmall, narrow, and
obtufe flireds.

C. In Birds.

The tongue of birds has papillae of different
forms : fome are fiefhy, blunt and roundeef;
others are covered by horny cafes, which are
fometimes conical, fometimes cylindrical ;
others again are offeous and cartilaginous. The

latter

7^4 Lect. XV. § TI. Of Taste.

latter kind is almofl: always found at the poftc-
rior part of the tongue. They arc direcfted back-
ward, and feem rather intended to aflift degluti-
tion, by preventing the return of the food, than
to exercife the fenfe of tafte.

Vultures have the tongue rounded anteriorly,
and horny at its external third. All its furface
is fmooth, except the edges, which areferrated,
and raifed as if it were to form a canal. Each
denticulation is invefted by a cartilaginous cafe
direded backward.

The tongue of falcons is thicker, entirely
fmooth on the edge, and notched on both its
extremities.

The nodurnal birds of prey have the tongue
flefliy, and furniflied pofteriorly with foft conic
papillae direded towards the throat.

In parrots the tongue is very thick, flefhy,
and rounded anteriorly. We obferve on it fome
papillae, which are really fungiform, particu-
larly at the pofterior part.

That of toucans is narrow, and furnifhed on
each fide with long and clofe horny bridles,
which give it the appearance of a feather.

The woodpeckers and zvrynecks have the tongue
formed of two parts ; one is anterior, protrac-
tile,-and fmooth. It is pointed anteriorly, and
covered with a horny fiicath, and furniflied on
its edges with four or five ftilf fpincs direded
backward, which renders it a kind of harpoon
or barbed arrow. The other part of the tongue

is

Art. III. Teg UMENTS OF tHE ToNGUE. 7O5

is loofe, and ferves as a fheath to the os hyoides
and its cornua, when the tongue is elongated.
Its furface is covered with fmall fpines directed
backward. Each of thefe fpines appears to be
implanted in the centre of a flefhy tubercle.
The aperture of the glottis is contained in the
loofe part of the tongue.

The Galling have the tongue pointed, carti-
laginous, and in the form of the head of an ar-
row. Its furface is fmooth and without any
kind of papillae, except upon the poftcrior part.

‘There are alfo no papilla; on the tongue of
the ojlricht which is crefcent-fliaped, broad, and
fo fliort that feveral authors have fuppofed
it did not exift. Its bafe is a fold of the fkip,
which fupplies the place of the points in other
birds.

The_;<ryr, the Jiares, and a great number of
paflerine birds, have the tongue fimilar to that
of the gallinaceous family; but in feveral genera
the point is more or lefs cleft, divided into fe-
veral fmall bridles, or appears lacerated. Na-
turalifts have founded the characters of fome
of their genera of birds on the differences of the
tongue, and may be confulted as to its forms.
We alfo obferve a flight furrow, which extends
throughout the whole length of its middle part.

The duck genus, in which the tongue is flefhy,
fiat, and broad, prefents a number of varieties
as to the difpolition of the papillce.

In fzvan there is a deep furrow formed in
VoL. II. Z z . the

7o6 Lect. XV. § II. Of Taste.

'the middle of the tongue. The furface of the
anterior part is covered by a thick layer of flifF
and compact hairs diredled towards the fides.
Farther back, and towards the middle part along
the furrow, there are three rows of plates or of-
feous laminae, the bafe of which is thick, and
the lharp edge free and turned backward. More
pofteriorly, there are fome conic papillae in the
form of fhort fliff hairs, which are alfo diredled
backward Two other lateral furrows feparate
the hairs from another range of olTeous lamina,
limilar to thofe ^of the middle part, but aug-
'menting in breadth in proportion as they ap-
proach the bafe of the tongue.

The edges of the tongue are befides furnifiied
-with long fliff parallel bridles, fituatcd very
clofe to each other, and refembling the teeth i
of a comb. |

Towards the poderior third the tongue lecms ^
divided by a condderable tubercle, the furface j
of which is rugous, but has no papillae. Be- .
hind this tubercle the furface is covered with i
thick, long, and flefliy papillae, directed back- \
ward. Deep furrows, in the form of an italic ,v, 1

feparate them from each other. !

The furface of the tongue of the other fpccies , i
of ducks varies confidcrably. The Brenl ^oofe I
has alfo two ranges of odcous laminae. In the 1
wjgcon (anas penelopr) there are none, except
on the edges of the poderior third. Almod all
the fpccies have the villi dilf, and directed to-

Art. III. Teguments OF THE Tongue. 707

wards the (ides. In the velvet duck, (anas fujca,}
they extend confiderably beyond the edges of
the tongue.

In the eider duck, (anas moll{(fnna,) the point
of the tongue has a fmall, round, flat, and
horny appendix. The anterior villi arc fliorter,
and the poflerior furface is almoft fmooth.

In the , the tongue, which is a more or

lefs elongated triangle, or in the torni ot an ar-
row, is generally fmooth and flat.

In the bujlard, the fliapc of the tongue ap-
proaches that of the grallae. It di tiers, how-
ever, in having its edges turniflied with long
horny llitf papillae, the two laft of which are
very broad, fltarp, and as it were olfeous.

D. In Reptiles.

The tongue of the tortoife is furniflied fuperi-
orly with long, foft, clofe, conic papillae, which
give it the appearance of velvet.

In the crocodile they are very fhort, and re-
prefent rather flight rugae than papillae. They
form, on the contrary, a very diftindlly villous
furface in the iguanas and the jlellions. The
tongue of the ca}nelion is furniflied with deep,
clofe, and very regular tranfverfe rugae; in the
lizards, with extcnfile and forked tongues; and
in the Jerpents, that organ is Angularly fmooth,
and, as it were, horny towards its points.

The Jalamanders have, like the iguanas, a Ane

Z z 2 villous

7o8 Lect. XV. § II. Of Taste.

villous furface to the tongue ; but in the fyogs
and toads, the furface is perfeclly fmooth to the
eye, and always mucous.

No reptile has two kinds of papillae, nor glands
with a calyx.

E. In Fijhes.

The fkin which is applied to the bones that
fuftain the tongue of fifhes, refembles that of
the reft of the mouth, and does not prefent to
the eye more developed papillae. The only dif-
ferences that can be remarked, belong to the
teeth, with which the tongue is armed in certain
fpecies, and which we fhall defcribe-when treat-
ing of Maftication.

We alfo referve the defcription of the Tongue,
or the organs which replace it, in white-blooded
animals, until we come to the fame Article.

Article IV,

Of the Hijlrilmtion of the Nerves in th'e Tongue.

The fcnfe of tafle di Hers from thofe of fight,
bearing, and fmell, and refembles that of touch,
in having no one pair of nerves entirely appro-
priated to its fundtions, The tongue receives
, branches

Art. IV. Nerves of the Tongue. 709

branches from three different pairs in warm-
blooded animals, and two only fo far as we have
obferved in fifhes, but they are not all employed
in this fenfiition. Thofe which come from the
hypogloffus major, and from the glojfo pharyngens;
appear to be diftributcd only to the mufclesand
the glands, as wc have fliewn in pages 243
and 246 ; at lead we are not certain that the fi-
laments of the glolfo-pharyngeus, which go to
the inciipped papillae, arc appropriated to the
fenfc of tafte, as we are Hill ignorant whether
thefe papillx enjoy that fenfation ; and the fila-
ments of the fame nerve, which foine fuppofc
they have traced to other papillx, appear very
inconfiderable.

The tri-facial ncn'c, or the fifth pair, which
is diftributed to all the organs of fenfe, appear^i
alone to receive the imprellions of taffe, by the
lingual branch of themaxillaris inferior, deferibed
in page 217 ; for this is the only nerve which is

ft ibu ed to the teguments, in which it is evi-
dent the fenfation relides ; and it is alfo the only
nerve, the ligature feclion or compreftion of
which annihilates tafte.

Such at lead: is the opinion now adopted by
phyfiologifts. It feems to us, however, that
the anaftomofes of the fifth and ninth pairs are
fo numerous throughout the whole extent of the
tongue, that it is difficult to fay which has the
greater fhare in the filaments which go to the
papillae. The fungiform papillae receive all of

7 thefe

710 Lect. XV. § II. Of Taste.

thefe filaments, which are fufficiently large to
be traced by the naked eye ; and this circum-
Ilance, joined to the hardnefs of the conical pa-
pillae in certain animals, induces us to believe
that the principal feat of tafte is in the fungi-
form papillae.

The filaments which proceed to the papillae
below the point of the tongue, are more eafily
followed than thofe diftributed to the fuperior
furface, becaufe the principal branches pafs
along the inferior part. The filaments which
go to the upper furface foon difappear, by their
tenuity in the fubftance of the flefh through
which they are forced to pafs. They afcend, in
a parallel and perpendicular diredlion, to the
furface, where they terminate.

The difiribution of the nerves of the tongue
prefent no eflential difference in the three other
claffes of vertebral animals.

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