COLUMBIA LIBRARIES OFFSfTE HEALTH SCIENCES STANDARD HX00016250 ^rff »rt liTi fin r^T, -. ' : n, r . ' . RECAP ^''tife; r [E^lQjTjjrijDrriJiJlrinJfpjgfru^ i 1 1 1 1 1 i i 1 I i THE LIBRARIES COLUMBIA UNIVERSITY I 1 1 1 1 1 1 1 1 i ETrin3rruTJrRnJiruiJFrui3[rin]nT^ Digitized by the Internet Archive in 2010 with funding from Open Knowledge Commons (for the Medical Heritage Library project) http://www.archive.org/details/textbookofanatom02cunn f TEXT-BOOK OF ANATOMY. NUNQUAM ALIUD NATURA, ALIUD SAPIENTIA DIGIT THE ORGANS OF SENSE AND THE INTEGUMENT. By EOBEIiT HOWDEN. THE NOSE. The nose constitutes the peripheral part of the organ of smell (organon olfactus), since to the upper portion of its mucous lining the branches of the olfactory nerve are distributed. It consists of an external portion, the outer nose, which projects from the face, and of an internal part, or cavum nasi, which is divided by a vertical septum into right and left cavities or fossae. The outer nose, or nasus exteruus, forms a more or less triangular pyramid, of which the iipper angle is termed the root (radix nasi), and is usually separated i'rom the glabella by a depression, while its base (basis nasi), directed downwards, is per- forated by the apertures of the nostrils (anterior nares). Its free angle is named the point (apex nasi), and the anterior border, joining root and point, is termed the dorsum nasi ; the upper part of the dorsum is supported by the nasal bones, and is named the bridge. The lateral aspects of the nose are continuous with the eyelids above and witli the cheeks below, forming with the latter a varying angle. Each lateral surface ends inferiorly in a moltile and expanded pnrtion, the ala nasi, which forms the outer boundary of the anterior nares, and is limited above by a furrow, the alar sulcus. The skin covering the nose is thin and movable over the root, but thick and adherent over the point and alse, where it contains numerous large sebaceous glands. The arteiial supply of tlie outer nose is derived from tlie facial aud oplithalmic arteries, and its veins drain themselves into the facial and oplithalmic trunks. Its principal lymphatic vessels follow the course of the facial vein and 02)en into the submaxillary lymphatic glands. From the root of the nose one or two vessels curve backwards above the orbit to reach the u]iper parotid glands, while a third gronp runs below the orbit to the lower parotid glands. The facial nerve supplies its muscles, while the sensory nerves for the skin are the infratrochlear and nasal bi'anches of the ophthalmic nerve and the infraorlntal branch of the superior maxillary nerve. The nose presents great variety as to its si/e and shape, and certain well-defined types, sucli as aquiline, Grecian, etc., are described. The relation which its breadth, measured across the alae, bears to its lengtli, measured from root to point, is termed the nasal index, and is exiwessed thus : greatest breadth x 100 greatest length. In white races this index is below 70 (leptorhines) ; in yellow races, between 78 and 8o (mesorliines) ; aii;e CartilaKC of septum Sesamoid cartilage Lower lateral cartilage Crus laterale Crus medial o 720 THE OEGANS OF SENSE. ) cartilaa Lower edge of -cartilage of ■ieptum _ _/ ratty tissue of ala nasi Fig. 552. — Cartilages of Nose from Below. The nasal fossa above and behind the vestibule is divided into two parts, viz. an upper or olfactory, and a lower or respiratory region. The olfactory part, or regio olfactoria, is a narrow, slit-like cavity, and comprises the region of the superior turbinated bone, together with a correspond- ing portion of the septum. The respiratory- part, or regio respiratoria, is expanded, and includes the lower and remaining parts of the fossa. Inner Wall or Septum Nasi (Eig. 549). — Where the bony septum is deficient, below and in front, the gap is filled by the septal cartilage. Until the seventh year the nasal septum lies, as a rule, in the mesial plane, but after this age is very often deflected to one or other side — more frequently to the right — the deflection being usually greatest along the line of junction of the vomer and mesethmoid. Deflec- tion of the septum is more common in European than in non-European skulls — occurring in about 53 per cent of the former and in about 28 per cent of the latter (Zuckerkandl, Anatomie der Nasenhohh, 1892). Associated with, or apart from, this deviation, lateral crests or spurs of bone are found, in about 20 per cent of skulls, projecting from the septum into one or other nasal fossa. In the floor of the fossa, close to the lower edge of the septal cartilage and immediately over the incisive foramen, a slight depression, the recessus naso-palatinus, may be seen. It is directed downwards and forwards, and indicates the position of the communication which originally existed between the nasal and buccal cavities. In the septum, a little above and in front of this depres- sion, is a minute orifice, not always rec ognisable, from which a blind pouch ex- tends upwards and Ijack wards for a distance of from 2 to 9 mm. This is the rudi- mentary organ of Jacobson foiga- non vomero- nasale) and is supported by the vomerine carti- lage. In many of ^^^^- ^^3. — Coronal Section through Nasal Foss/e ; Anterior Half of Section the lower animals ^''^''™ ™°'' ^'''"^°- this organ is well developed (Fig. 554), and prubaljly plays a part in the sense of smell, Ijeing lined by epithelium similar to that in the olfactory part of the nose and supplied by brandies of the olfactory nerve. Outer Wall ri'"ig.455). — Above the superior turbinated bone is a narrow recess, the recessus spheno-ethmoidalis, into the posterior pai t of which the sphenoidal air-sinus opens. The superior meatus (meatus nasi superior) is a short oblique fissure, directed downwards and backwards under CDver of the superior turbinated bone ; into its antero-superior portion the posterior ethmoidal cells open by one or more orifices. Inferior turbinated bone NASAL FOSS^. 721 The narrow slit-like interval between the nasal septum and the inner aspect of the middle turbinated bone is named the olfactory cleft or sulcus. The middle meatus (meatus nasi medius), situated below and to the outer side of the middle turbinated bone, is a roomy passage, and is continued forwards into a slightly depressed area termed the atrium meatus nasi, which lies immediately above the vestibule. The atrium is limited above and in front by a low ridge, the agger nasi, the representa- tive of the naso-turbinal found in many animals. On raising or removing the middle turbinated bone a rounded elevation, bulla ethmoidalis, caused by the middle ethmoidal air-cells, is seen. This varies in size and is directed downwards and forwards, whilst opening either on it or above it are the orifices of the middle ethmoidal cells. Curv- ing upwards and forwards, below and in front of the bulla ethmoidalis, is a deep, narrow groove, the hiatus semilunaris, into which the anterior ethmoidal cells and the antrum of Highmore open. The opening from the antrum (ostium maxillare) is situated near the lower and back part of the hiatus, and is placed near the OrS'iiis ot Jacobson Fig. 554. — Section through Nose of Kitten, showing position of Jacobson's organ. Frontal air-sinus. Bristle passed from it into infundibulinii Opening of middle ethmoidal cells Openings of posterior ethmoidal cells Recessus spheno-ethmoidalis sphenoidal air-sinns Cut edge of inferior lurbinaled bone Bristle passed into opening of nasal duct Fig. 555.- -View of the Outer Wall of the Nose— the Turbinated Hones having been removed. 1. Vestibule. 2. Opening of antrum of Highmore. 3. Hiatus semiUiiiaris. 4. Bulla ethmoidalis. 5. Agger nasi. li. Opening of anterior ethmoidal cells ". Cut edge of superior turbinated bone. 8. Cut edge of middle turbinated bone. 0. Pharyngeal orifice of Eustachian tube. roof of the antral cavity. A second opening (ostium accessorium) is not infrequently seen in the middle meatus above the posterior part of the inferior turbinated bone. The middle meatus extends upwards and forwards, and, becoming narrowed, is continued into the infundibulum or channel leading into the frontnl air-sinus. The inferior meatus (mtalus n;isi inferior) lies below the iuierior turbinated bone, 50 722 THE OEGANS OF SENSE. ^ Epithelium 2_ Duct of one of Bosnian's -lands Fig. 556. — Section through the Olfactory Mucous Membrane. under cover of the anterior part of which is found the slit-like orifice of the nasal duct (see p. 741). Mucous Membrane (membrana mucosa nasi). — The Schneiderian or nasal mucous membrane is thick, highly vascular, and firmly bound to the sub- jacent periosteum and perichondrium. It is continu^ous, through thechoanee, with the mucous lining of the naso- pharynx ; through the nasal duct and lachrymal canals, with the conjunc- tiva ; and, through the apertures lead- ing into the air- sinuses, with the delicate lining of these cavities. Throughout the respiratory region it is covered by columnar, ciliated epithelium, interspersed amongst which are goblet or mucin cells, whilst between the bases of the columnar cells smaller pyramidal cells are interpolated. It contains a freely anastomosing venous plexus, which in some parts, e.g. over the inferior turbinated bones, forms a kind of cavernous tissue (plexus cavernosus concharum). Many acinous glands, secreting a watery fluid, are embedded in it, and are especially large and numerous in the posterior half of the nasal fossae, while in children it con- tains a considerable amount of adenoid tissue. In the olfactory region the mucous mem- brane is yellowish in colour, more delicate, and covered by non-ciliated columnar epithelium (Figs. 556, 557). Em- bedded in it are numerous tubular and often branched glands, the glands of Bowman (gl. olfactorite) ; these are lined by polygonal cells and open by fine ducts on its free surface. The epithelium covering the olfactory region consists of: (1) supporting cells, (2) olfactory cells, and (3) basal cells. 1. Supporting Cells. — The outer part of these cells is columnar in shape and contains fine granules of yellow pigment, whilst the deeper portion is attenuated and frequently branched. They contain elliptical or oval nuclei, which are situated Olfactory hairs Supporting cells Olfactory hairs Body of "cell A B Fig. 557. — Olfactory and supporting Cells. M. Sehultze C Human (v. Brunn). -Xucleus .Central process A. Frog B. Human THE EYE. 723 at the deep ends of the columnar parts of the cells, and form what is termed the zone of oval nuclei. 2. Olfactory Cells. — Thej are spindle-shaped and lie between the deeper, attenuated parts of the supporting cells ; their nuclei are circular and form the zone of round nuclei. Each cell gives off a peripheral and a central process, the former of which is rod-like and ends on a level with the free extremities of the supporting cells, where it is surmounted by a pencil of short filaments, termed the olfactory hairs. A fine membrane, the membrana limitans externa, covers in miny animals the free surface of the epithelium, and is pierced by the olfactory hairs and by the ducts of Bowman's glands. The central process is a ^ ery delicate varicose filament, whicli passes inwards and is continuous with a fibril of the olfactory nerve. Each of these nerve fibrils probably retains its independence from its point of origin in an olfactory cell to its termination in the olfactory bulb, in the glomerular layer of which it forms a free arborisation. 3. Basal Cells. — These cells are branched, and lie on a basement membrane between the deep extremities of the supporting and olfactory cells. Olfactory Nerves. — These nerves arise from the under aspect of the olfactory bulb and are transmitted through the foramina in the cribriform plate of the ethmoid bone. They are at first lodged in the bony canals or grooves situated on the inner and outer walls of the olfactory area, and, reaching the deep surface of the mucous membrane, are continued into the central processes of the olfactory cells. The olfactory nerves possess no medullary sheath. The fifth cranial nerve supplies branches of ordinary sensation to the nasal mucous membrane as follows : The septum is chiefly supplied by the naso-palatine nerve, but its posterior part receives .some filaments from Meckel's ganglion and the Vidian nerve, and its anterior portion from the nasal branch of tlie ophthalmic. The outer wall is supplied — (1) by the upper nasal branches of the Vidian nerve and ISIeckel's ganglion ; (2) by the lower nasal branches derived from the anterior palatine ; and in front by (3) the outer division of the nasal branch of the ophthalmic. The floor and anterior part of the inferior meatus are supj)lied by a nasal In'anch of the anterior sujjerior dental nerve. Blood-vessels. — Arteries. — The chief artery of the nose is the spheno-jaalatine branch of the internal maxillary artery. This reaches the nasal cavity through the spheno-j)alatine foramen, and divides into — («) posterior nasal, which ramifies over the turbinated bones and sends branches to the antrum and to the frontal and ethmoidal cells ; and (6) naso-palatine, the artery of the septum. Twigs are given to the upper j^ortion of the cavity by the anterior and posterior ethmoidal arteries, while its posterior part receives some small branches from the descending palatine vessel. The nostrils are suj^jjlied by the lateral nasal branch of the facial, and by the septal artery of the superior coronary. The antrum is partly suj^plied by the infraorbital artery, whilst tlie siihenoidal sinus gets its chief supply from the j^terygo-jialatine A'essel. The veins form a dense plexus almost resembling cavernous tissue in structure. This condition is well seen in the respiratorj- region, and esjiecially so over the middle and inferior turl)inated bones and on the lower part of tlie septum. The venous blood is carried in three chief directions, viz. forwards into the facial vein, backivards into the sj^heno-^^alatine vein, and upicards into the ethmoidal veins. The ethmoidal veins communicate with the ophthalmic veins and the veins of the dura mater ; further, an ethmoidal A'cin passes uj:) through the cribriform j^late of the ethmoid, and either oj^ens into the venous plexus of the olfactorj' bulb or directly into one of the veins of the orbital part of the frontal lobe of the brain. The lymphatics form an irregular net- work in tlie superficial part of the mucous membrane, and can be injected from the subdural or subarachnoid space. The larger vessels are directed backwards towards the choanaj, and are collected into two trunks, of which the larger passes to a lymphatic gland in front of the axis vertebra, and the smaller to one or tM'o glands situated near the great cornu of the hyoid bone. The development of the nose is described in the section wliich deals with " General Embryology " (p. 38). THE EYE. The eyeball or globe of the eye (bulbus oculi) constitutes the chief part of the organ of sight (organon visus) ; but, associated with its description, certain accessory structures, such as the eyelids and the lachrymal apparatus, fall to be considered. 50 a 724 THE OEGANS OF SENSE. THE EYEBALL. Situated in the anterior part of the orbital cavity, the eyeball is protected in front by the eyelids and by their mucous lining, the conjunctiva, and is pierced behind by the optic nerve, or nerve of sight, which spreads out to form its innermost tunic, the retina. The tendons of the ocular muscles are attached to its outer surface a short distance in front of its equator, while its posterior two-thirds are Caual of Schlemm' Suspensory ligament- Lerii Cornea Anterior chamber Iris ^^§5^^ Posterior chamber ivj^^^^^feiJSv^ Ciliary process Canal of Petit Vitreou: Optic axis Fovea centralis Lamina cribrosa sclerfe i — Arteria centralis retinae Optic nerve Fig. 558. — Diagram of a Horizontal Section through left Eyeball and Optic Nerve (four times enlarged). enveloped by a loose membrane, termed the capsule of Tenon, or fascia bulbi, which separates it from the surrounding orbital fat. The eyeball is not quite spherical, being composed of the segments of two spheres, viz. an anterior, transparent, corneal segment, possessing a radius of 7 or 8 mm., and a posterior, opaque, scleral segment, with a radius of about 12 mm. (Fig. 558). The anterior or corneal segment, in consequence of its shorter radius, projects as a dome in front of the scleral portion, the union of the two parts being indicated externally by a slight groove, the sulcus sclerse. The central points of the anterior and posterior curvatures of the eyeball constitute respectively its anterior and posterior poles, while a straight line joining the two poles is termed its sagittal axis (axis optica). The axes of the two eyeballs are almost parallel, diverging only sliglitly in front ; but the axes of the optic nerves converge behind, and, if prolonged backwards, would meet in the region of the dorsum sellre of the sphenoid. An imaginary line encircling the globe midway between its two poles is named its equator, and meridional lines (meridiani) may be drawn from pole to pole at right angles to the equator. Its sagittal and transverse diameters are nearly equal — about 24 mm.; its vertical diameter is about 23'5 mm. All three diameters are rather less in the female than in the male, but the size of the eyeball is fairly constant in the same sex. What are popularly described as large eyes owe their apparent increase in size to a greater prominence of the globe and to a wider fissure between the eyelids. SCLEEA. 725 At birth the eyeball is uearl}^ «pherical and has a diameter of about 17 "5 mm. By the age of puberty this has increased to 20 or 21 mm., after which it rapidly reaches its adult size. The eyeball (Fig. 558) consists of three concentric tunics or coats, contained within which are three transparent refracting media. The three tunics are : (1) an outer fibrous coat, the sclero-cornea, consisting of an opaque posterior part, the sclera, and a transparent anterior portion, the cornea; (2) an intermediate vascular, pigmented, and partly muscular tunic, the tunica vasculosa oculi, com- prising from behind forward the chorioid, the ciliary body, and the iris ; (3) an internal nervous tunic, the retina. The three refracting media are named, from before backwards, the ac[ueous humour, the crystalline lens, and the vitreous body, SCLERA. The sclera, sclerotic coat, or white of the eye, is a firm, opaque membrane, which forms something like the posterior five-sixths of the outer tunic. Thickest posteriorly (about 1 mm.), it thins at the equator to 0'4 mm.-0'5 mm., and again increases to O'G mm. near the sulcus scleroe. In the child it is thinner than in the adult, and presents a bluish appearance, caused by the pigment of the chorioid shinmg through it, while in old age it assumes a yellowish tinge. Its outer surface is covered by a layer of endothelium and is in contact with the capsule of Tenon — a lympli space, the suprascleral lymphatic space, only intervening. In front of the equator it is roughened by the attachment of the tendons of the ocular muscles, while its anterior part is covered by mucous membrane, the conjunctiva. Its deep surface presents a brownish colour, and is loosely attached to the chorioid, except at the optic entrance and in the neighbourhood of the sulcus sclerse. It is pierced behind by the optic nerve, the entrance for which is funnel-shaped, wide behind and narrow in front, and is situated 1 mm. below and 3 mm. to the nasal side of the posterior pole of the eyeball. The fil^rous sheath of the nerve blends with the outer part of the sclera, while the nerve bundles pass through a series of orifices ; this perforated portion is named the lamina cribrosa sclerse. Around the entrance of the optic nerve are some fifteen or twenty small apertures for the passage of the ciliary nerves and short ciliary arteries. The two long posterior ciliary arteries pierce it, one on either side, some little distance from the optic entrance ; while a little behind the equator are four openings, two above and two below, for the exit of veins, called venae vorticosae. Near the sulcus scleras it is perforated by the anterior ciliary arteries. Its inner surface is lined Ijy flattened endothelial cells ; and between it and the chorioid is an extensive lymph space, the spatium perichorioideale, which is traversed by the ciliary nerves and arteries just mentioned, and by an irregular meshvvork of fine, pigmented, connective tissue, the lamina fusca, which loosely attaches the sclera to the chorioid. At the corneo-scleral junction the fibrous tissue of the sclera passes continuously into that of the cornea, and in the deeper part of this junction there is a circular canal, the sinus venosus sclent?, or canal of Schlemm, which connnuuicates externally with the scleral \-eins, and internally, through numerous small openings, with the anterior chamber of the eyeball. The sclera consists of bundles of white fibrous tissue, together with some fine elastic fibres, the bundles forming equatorial and meridional layers, which inter- lace with each other. Numerous spaces containing connective tissue cells and migratory cells exist between the fibres. Pigmented cells are plentiful in the lamina fusca, and a few are also found in the tissue of the sclera, near the optic entrance and in the region of the corneo-scleral junctit)n. The sclera receives its blood-supply from the short posterior ciliary and anterior ciliary arteries, while its veins open into the vense vorticoste and anterior ciliary veins. The cell spaces play the part of lymphatics, and communicate with the perichorioidal and supra- scleral lymph spaces. Its nerves are deri^'ed from the ciliary nerves, which, after losing their medullary sheath, pass between the fibrous bundles ; their exact mode of ending is not accurately known. 726 THE OEGANS OF SENSE. COENEA. The cornea forms the anterior sixth of the outer tunic and is transparent, in order to admit hght into the interior of the eyeball ; its index of refraction is from 1 -33 to 1-35. Its anterior surface (facies anterior) is covered by a stratified epithelium, continuous with that which lines the conjunctiva ; its posterior surface (facies posterior) is dkected towards the anterior chamber of the eyeball and is in contact with the aqueous humour. Its degree of curvature varies in different individuals ; it is always greater in youth than in old age, and is, as a rule, slightly greater in the vertical than in the horizontal plane. It diminishes also from its centre to its periphery, and is less on the nasal than on the temporal side of the anterior pole. The anterior surface of the cornea is almost, but not quite, circular, measuring 11 mm. vertically ■, Isti'atified ^. epithelium 3^ y Anterior ' elastic lamina and 11-9 mm. transversely, while its posterior surface is circular and has a diameter of 13 mm, Its periphery is overlapped by the tissue of the sclera as the glass of a watch is overlapped by the metal rim, with, however, this essential difference, that the tissue of the cornea is directly continuous with that of the sclera. The cornea consists, from before backwards, of the follow- ing strata, viz, (Eig. 559) : — 1. A layer of stratified epi- thelium. 2. An anterior elastic lamina. 3. The substantia propria. 4. A posterior elastic lamina. 5. A layer of endothelium. 1. The layer of stratified epi- thelium (epithelium cornese) is continuous with that which covers the free surface of the conjunctiva and consists of six or eight strata of nucleated cells. Deepest of all is a single layer of perpendicularly arranged columnar cells, the flattened and often-expanded bases of which rest on the anterior elastic lamina, while their opposite ends are rounded and contain the nuclei. Superficial to this layer are three or four strata of nucleated, polygonal cells, the majority of which exhibit finger-like processes which join with the corresponding processes of neighbouring cells. The more superficial layers assume the form of nucleated squames. The entire thickness of this stratified epithelium is about 45 ^ at the centre and about 80 /x at the periphery of the cornea. 2. The anterior elastic lamina (lamina elastica anterior, Bowmani) is from 19-20 // thick, and may be regarded merely as a differentiation of the outer part of the substantia propria from which it is with difficulty separated. It is not stained yellow by picrocarmine, thus differing from true elastic tissue, and its degree of development varies in different animals. 3. The substantia propria presents, in a fresh condition, a homogeneous appear- ance ; but, with the assistance of reagents, it is seen to consist of modified con- nective tissue, with some few elastic fibres. An amorphous interstitial substance biads the fibres into bundles, and, in turn, cements the bundles into lamellae, which are directly continuous with the fibrous tissue of the sclera. The fibres of any one lamella cross those of adjacent lamellse almost at right angles, while the superimposed lamellee are joined by sutural fibres and by amorphous substance. Between the lamellse are found the cell spaces or lacunae of the cornea — irregu- Posterior elastic lamina Endothelium Fig. 559. — Vertical Section of Cornea (magnified). VASCULAK AND PIOMENTED TUNIC OF THE EYE. 727 larly stellate in shape, and communicating freely with each other by means of fine canaliculi. The corneal cells or corpuscles are contained in these lacunae, without, however, completely filling them, tlie remainder of the cavities being occupied by lymph. These cells are nucleated, flattened, and star-like, and their branched pro- cesses join those of neighljouring cells in the canaliculi. Migratory or lymph cells are also found in cell spaces. Ill old age a grayish opaque rhig, l.". Id 2 iniu. iu breadth, is frequently seen near the peri- phery of the cornea ; it is termed the arcus senilis, Jiiid resuUs from a deposit of fat granules in tlie lamellae and corneal corjjuscles. 4. The posterior elastic lamina (lamina elastica posterior, Demoursi, Descemeti) is a clear, structureless meml)rane, covering the posterior aspect of the substantia propria and possessing a thickness of 6-8 /j. at the centre and 10-12 /y. at the peri- phery of the cornea. Less firmly attached than the anterior elastic lamina, it may be stripped off, when it will be found to roll up with its attached surface inwards. Between the ages of twenty and thirty small wart-like projections appear on its deep surface, near its periphery, and these increase in size and number as years ad\-ance, so that in old age the membrane may attain a thickness of 20 /x. Towards the peri})hery of the cornea the lamina divides into three sets of filires — anterior, middle, and posterior. The anterior fibres pass behind the canal of Schlemm into the sclera, the middle give attachment to the ciliary muscle, while the posterior are continued as radiating and anastomosing fibres into the substance of the iris, and constitute the ligamentum pectinatum iridis, A number of irregular spaces, the spaces of Fontana, or spatia anguli iridis, exist between the fibres of this pectinate ligament. Better developed in the horse and ox than iu man, these spaces are lined by a prolongation of the corneal endothelium, and communicate internally with the anterior chamber and the lymph spaces of the iris, and externall}' with the canal of Schlemm. 5. The layer of endothelium (endothelium camera anterioris) consists of a single stratum of nucleated, flattened, polygonal cells, which present a fibrillar structure and are continued as a lining to the spaces of Fontana ; this layer of endothelium is also reflected ou to the anterior surface of the iris. Vascular and Nervous Supply of the Cornea. — In the foetus tlie cornea is traversed, almost as far as its centre, by capillaries ; lint in the adult it is devoid of blood-vessels, excejjt near its margin. The capillaries of the conjunctiva and sclera pass into this marginal area for a distance of about 1 mm., where they terminate in loops. All the remainder of the cornea is nourished by tlie lymph which circulates in its cell spaces and canaliculi. The nerves of the cornea, discovered by Schlemm, are derived from the ciliary nerves. Around its periphery they form a plexus, the plexus annularis, from which fibres pass into the cornea, where, after "a distance of 1 or 2 mm., they lose their medullary sheaths and ramify in the substantia projjria, forming what is termed the fundamental or stroma plexus. Perforating fibres (fibr;e perforantes) extend from this plexus through the anterior elastic lamina and form a sub- epithelial plexus, from which fine filaments ramify between the epithelial cells as far as the super- ficial layers. From the an- nular and stroma jjlexuses fibrils pass to the substantia propria and come into close relation with the corneal corpuscles. Jleiubrane of Brucli Lamina VASCULAR MENTED AND PIG- TUNIC. The middle, vascular, and pigmented tunic (tunica vasculosa oculi) comprises, from behind forwards, the chorioid, the ciliary body, and the iris (Kig. 558). The chorioid (chorioidea) intervenes between the sclera and the retina, reaching as far forwards as the ora serrata of the latter (p. 731). Dark brown or black in colour, it is pierced posteriorly by the optic nerve, and is here firmly attached 50/' Fio. 560. -VEnrrcAL Section of Chorioid and Inxeu Part OF SCLEHA. 728 THE ORGANS OF SENSE. Cornea Canal of Schlemm. _Circulus arteriosus major Conjunctival vessels Recurrent artery of cliorioid Anterior ciliary vessels to the sclera. Thicker behind than in front, its outer surface is flocculent and is connected to the sclera by the ciliar j vessels and nerves, and by the loose lamina fusca. Its inner surface is smooth and adheres to the outermost or pigmented layer of the retina. The chorioid consists of blood-vessels and branched pigment cells embedded in a loose connective tissue, and presents from without inwards three layers, viz. : {a) the lamina suprachorioidea ; (&) the proper tissue of the chorioid ; and (c) a thin transparent membrane, the lamina basalis or membrane of Bruch (Eig. 560). 1. The lamina supra-chorioidea resembles the lamina fusca of the sclera, and consists of a series of fine non- vascular lamellee, each containing a delicate network of elastic fibres, amongst which are stellate, pigmented cells, together with amoeboid cells. The spaces between the laminae are lined with endothelium, and to- gether form the spatium perichorio- ideale, already referred to (p. 725). The proper tissue of the chorioid consists of blood-vessels and numerous pigmented cells, supported by connective tissue and elastic fibres, together with some smooth muscular fibres. Its outer part contains the larger blood - vessels, and is named the lamina vasculosa, while its inner portion is composed of a network of fine capillaries, and is termed the lamina choriocapillaris ; these two laminae are joined by a thin inter- mediate stratum. The arteries of the chorioid are derived from the short posterior ciliary vessels, which pierce the sclera around the optic entrance and form a wide -meshed plexus in the lamina vasculosa. Their circular muscular coat is well developed, and longitudinal muscular fibres are also present in the larger branches. The veins, destitute of muscular tissue, are super- ficial to the arteries; they are surrounded by peri -vascular lymphatic sheaths and converge to form whorls, which open into the venae vorticosse. In the tissue between the blood-vessels are numerous stellate, flattened, and pigmented cells. The lamina chorio-capillaris, or membrane of Ruysch, is composed essentially of small capillaries, whicli form an exceedingly close network, embedded in a finely granular or almost homogeneous tissue. The intermediate stratum between the malina vasculosa and lamina chorio-capillaris consists of a network of delicate -Suprascleral vessels Vena vorticosa ■Long posterior ciliary artery Short posterior ciliary artery ^ Outer and Onner vessels of optic sheath Optic nerve Central artery and vein of retina 561.— Diagram of the Circulation in the Eye (Leber). VASCULAR AND PIGMENTED TUNIC OF THE EYE. ^29 Cornea. Anterior chamber Canal of Schlemm Spaces ot Fontana Conjunctiva Pars iridica retina; Ciliary process ganientum pectinatuni iridis Circular fibres of ciliary muscle Radial fibres of ciliary muscle elastic fibres and contains almost no pigment cells ; it is lined next the lamina chorio-capillaris by a continuous layer of endothelium. The lamina basalis, or membrane of Bruch, is transparent and nearly structure- less. Its outer surface presents a trelHs-like network of fibres which unite it to the membrane of Euysch, while its inner surface is smooth and is in contact with the pigmented layer of the retina. Tapetum. — In many animals a brilliant iridescent appearance is seen on tlie postero-external part of the cliorioid to whicli the name tapetum is applied. Absent in man, it may be dne, as in the horse, to a markedly fibrous condition of tlie .-tratum intermedium (tapetum iibrosum), or as in tlie seal, to the presence of some five or six layers of flattened iridescent cells lying imme- diately outside the hiiuina chorio-capillaris (tapetum cellulosxim). The ciliary body (corpus ciliare) connects the chorioid to the circumference of the iris (Fig. 562), and presents the following three zones, viz. : (a) the orbiculus ciharis, (b) the ciliary processes, and (c) the ciliary muscle. The orbiculus ciliaris forms a zone of about 4 mm. in width im- mediately adjoining the chorioid, and exhibits numerous radially- arranged ridges. The ciliary processes (processus ciliares), about seventy in number, form a circle of radial thicken- ings, each of a somewhat triangular shape. The base of the triangle is di- rected forwards towards tlie equator of the lens, while the apex is con- tinuous behind with some three or four ridges of the orbiculus ciliaris. They vary in size, the largest having a length of 2-5 mm. The structure of the orbiculus ciliaris and ciliary processes is similar to that of the chorioid, but the capillaries are larger and more tortuous, fjq, se-^.— Section through Ciliary KEiiioN OF Eyeball. and there is no lamina chorio-capillaris. The deep aspect of the ciliary processes is covered by two strata of columnar epithelium, the anterior layer of which is pigmented ; these two strata form a direct continuation forwards of the retina and constitute the pars ciliaris retinae. This epithelium is invaginated to form more or less tubular glands, which may take a share in tlie secretion of the aqueous humour. The ciliary muscle (m. ciliaris) is triangular on antero- posterior section, and consists of two sets of fibres — radial and circular (Fig. 562). The radial fibres (fibra3 meridionales, Briickei) spring from the corneo-scleral junction behind the canal of Schlemm and from the ligamentum pectinatuni iridis, and radiate back- wards, to be attached to the ciliary processes and orbiculus ciliaris. When they contract the chorioid is drawn forwards and the lens becomes more convex, owing to the relaxation of its suspensory ligament (see p. 736). The circular fibres (fibrre PenchorioiJal lympli space Zonule of Zinn Retina 730 THE OEGANS OF SEKSE. circulares, Mlilleri) form a triangular zone behind the ligamentum pectinatum iridis, close to the periphery of the iris, and also extend backwards under the radial fibres. Considerable individual differences are found as to the degree of develop- ment of these two portions of the ciliary muscle. The radial fibres are always more numerous than the circular fibres, the latter being absent or rudimentary in myopic eyes, but well developed, as a rule, in hypermetropic eyes. The iris forms a contractile diaphragm in front of the lens, and is pierced a little to the nasal side of its centre by an almost circular aperture, the pupil (pupilla), which, during- life, is continually varying in size in order to regulate the amount of light admitted into the interior of the globe. It divides the space between the cornea and lens into two parts, which are filled by the aqueous humour, and named respectively the anterior and posterior chambers of the eyeball. Its peripheral border, or margo ciliarls, is directly continuous with the ciliary body, and, through the medium of the ligamentum pectinatum iridis, with the posterior elastic lamina of the cornea. Its free edge, or margo pupillarls, forms the circumference of the pupil, and rests upon, but is not attached to the anterior surface of the capsule of the lens. The distinctive colour of the eye, in different individuals, depends on the arrangement of the pigment in the iris ; in the blue eye this is hmited to the posterior surface of the iris, but in the brown or black eye it is also scattered throughout its stroma. In the albino the pigment is entirely absent, and the red appearance of the eye in such a case is pro- duced by the network of blood-vessels in the iris. The pupil is closed, during the greater part of foetal life, by a thin transparent vascular membrane, the membrana pupillarls, continuous with the pupillary margin of the iris. Its vessels, derived partly from the vessels of the iris and partly from those of the capsule of the lens, converge towards the middle of the membrane, near which they form loops so as to leave the central part non-vascular. About the seventh month the vessels begin to be obliterated from the centre towards the circumference, and this is followed by a thinning and absorption of the membrane, which becomes perforated by the aperture of the pupil. This perforation gradually enlarges, and at birth the memlDrane has entirely disappeared, although in exceptional cases it persists. On the anterior surface (facies anterior) of the iris is a layer of flattened endothelium, placed on a basement membrane, and continuous with that which lines the spaces of Fontana and covers the back of the cornea. Depressions or crypts are here and there seen in which the endothelium and basement membrane are ab- sent, and are, by some, re- garded as stomata, throuQ-h which the lymphatics of the iris communicate with the cavity of the anterior cham- ber. Its posterior surface (facies posterior) is covered by a basement membrane, on which are placed two layers of columnar, pigmented epi- thelium, continuous with the pars ciliaris retinae and termed the pars iridica retinae. The proper tissue of the iris, or stroma iridis, consists of delicate connective tissue and elastic fibres, with pigmented cells, blood-vessels, nerves, and non-striped muscle. The blood-vessels of the iris (Fig. 563) are derived from the long and anterior Anterior ciliary arteries 4\ \ I 1113 of choi-ioid Aperture of /pupil (.'irculus Miajor Fig. Anterior ciliary arteries 563. — Blood-vessels of Iris and Axtehiok Part of Chorioid, viewed from the front (Aruold). THE KETINA. 731 ciliary arteries. The long ciliary arteries, two iu number, pierce the sclera on the inner and outer side of the optic nerve respectively, and extend forwards between the solera and chorioid towards the ciliary margin of the ii'is. Here each divides into an upper and a lower branch, and the resulting four Ijranches anastomose in the form of a circle, termed the circulus arteriosus major. This circle is joined by a varying number of anterior ciliary arteries derived from the lachrymal and muscular branches of the ophthalmic artery, and, after supplying the ciliary muscle, sends converging branches inwards towards the aperture of the pupil, around which a second circle, the circulus arteriosus minor, is formed. The veins proceed towards its ciliary margin, and eonnuunicati;; with the veins of the ciliarv processes and with the canal of Schlenmi. The convergence of the blood-vessels towards the aperture of the pupil gives to the anterior surface of the iris a striated appearance. The non-striped muscular fibres are arranged in two sets : (a) circular, (b) radial. The circular fibres form a baud around the pupillary aperture, by the contraction of which its size is lessened, and hence it is termed the m. sphincter pupillae. The radial fibres extend outwards from the sphincter to the ciliary margin and cunstitute the m. dilatator pupillse. Many anatomists regard the radial fibres, in man and most mammals, as being elastic and not muscular. In animals, where the radial fibres are muscular, the degree of their development varies considerably ; they are feebly marked in the rabbit, but well developed in the bird, and still more so in the otter. The nerves of the chorioid and iris are derived from the long and short ciliary nerves. The former, two or three in number, are branches of the nasal nerve ; the latter, varying from eight to fourteen, are derived from the ciliary ganglion. Piercing the sclera around the optic entrance the nerves traverse the perichorioidal lymph space, where they form a plexus, rich in nerve-cells, from which filaments are supplied to the blood-vessels of the chorioid. In front of the ciliary muscle a second plexus, also rich in nerve-cells, is formed, which supplies the muscle itself, and sends filaments into the iris as far as its pupillary margin, for the supply of its muscular fibres and blood-vessels. The sphincter pupilhe is supplied by the third cranial nerve, whilst filaments from the sympathetic are distributed to the dilatator pupillte. THE RETINA. The retina, or nervous tunic of the eyeball, is a soft, delicate membrane, in which the fibres of the optic nerve are spread out. It consists of two strata, viz. : (a) an outer, pigmented layer (stratum pigmenti), attached to the chorioid ; and (b) an inner nervous lamina, the retina proper, in contact with the hyaloid membrane of the vitreous body, but only attached to it at the optic entrance and in the region of the ciliary processes. Expanding irom the entrance of the optic nerve the retina appears to end, a short distance liehind the ciliary body, iu a wa\y border, the ora serrata. Here its nervous elements cease and the membrane becomes suddenly thinned, but a delicate continuation of it is prolonged over the posterior aspect of the ciliary body and iris. This continuation consists of the stratum pig- menti, together with a layer of columnar epithelium, and constitutes tlie pars ciliaris retinae and pars iridica retinae already rel'erred to (pp. 729 and 730). The portion behind the ora serrata is termed the " physiological retina," or pars optica retinae, and its thickness gradually diminishes from 0"4 mm., near the optic entrance, to 0"1 mm. at the ora serrata. Viewed from the front it presents, at the posterior pole of the eyeball, and therefore directly in the axis of the globe, a small yellowish spot, the macula lutea. Somewhat oval in shape, the greatest or transverse diameter of the macula measures from 2-3 mm. ; its central part is depressed and named the fovea centralis. About 3 mm. to the nasal side of the posterior pole and about 1 mm. below its level is a whitish, circular disc, the optic disc, or poms opticus, which corresponds with the entrance of the optic nerve and has a diameter of about I'o mm. The circumference uf the optic disc is slightly raised and is named the colliculus nervi optici, while its depressed central portion is termed the optic cup, or excavatio papilUv nervi optici. The optic disc consists merely of nerve- 732 THE OEGANS OF SENSE. I Stratum t pigmeuti fibres, the other layers of the retina being absent, and constitutes the " blind spot " of physiologists. The nervous layer of the retina is transparent during life, but becomes opaque and of a grayish colour soon after death. If an animal be kept in the dark before the removal of its eyeball, the retina presents a purple tinge, due to the presence of a colouring matter uamed rhodopsin or visual purple, which, however, becomes rapidly bleached on exposure to sunhght. This colouring matter is absent from the macula lutea, and also over a narrow zone, 3-4 mm. in width, near the ora serrata. Structure of the Retina (Figs. 564, 565, 566). — The nervous elements of the retina are supported by non-nervous or sustentacular fibres, and are arranged in seven layers, to which must be added the stratum pigmenti. Our conception of the minute structure of the retina, as of all nervous tissues, has of late years been greatly advanced by the discoveries of Ramon y Cajal, on whose observa- tions the following description is based (Fig. 565) : — ■ The layers from within outwards, i.e. from vitreous body to chorioid, are : 1. Layer of nerve-fibres (stratum opticum). 2. Layer of nerve-cells (ganglionic layer). Inner molecular or inner plexiform layer. Inner nuclear layer or layer of inner granules. Outer molecular or outer plexiform layer. Outer nuclear layer or layer of outer granules. Layer of rods and cones (bacillary layer). Layer of pigmented epithelium (stratum pigmenti). 1. Layer of nerve-fibres or stratum opticum. — The fibres of this stratum are nearly all centripetal, and are mostly continuations of the non-medullated axons of the cells, in the ganglionic layer. Some, however, are centrifugal and end in branched clubbed extremities in the inner molecular or inner nuclear layers. 2. Ganglionic or nerve-cell layer. — The cells of this stratum vary in size, are oval or pyriform in shape, and form a single layer, except at the macula lutea, where several strata are present. Each cell contains a large micleus, and gives off, from its inner aspect, an axon which is continued as a fibre of the nerve-fibi'e layer. From the outer surface of each cell numerous dendrites arise, which form arborisations in the inner molecular layer. The cells may be divided intounistratified, multistratified, and dift'use, according as their dendrites ramify in one or in several strata of the inner molecular layer, or extend throughout nearly its whole thickness. 3. Inner molecular orinner plexiform layer. — This is chiefly constituted by the interlacement of the dendritic arborisations of the cells of the gan- glionic layer with those of the inner nuclear layer, and has been divided by Ramon y Cajal into five strata. It sometimes contains horizontal cells or spongioblasts, whose branched processes ramify in it. 4. Inner nuclear layer or layer of inner granules. — This is the most complicated of the retinal strata, and consists of numerous cells which may be divided into three groups, viz. : (a) bipolar cells, (h) horizontal cells, and (c) spongioblasts, or amacrine cells. (a) The bipolar cells, by far the most numerous are fusiform and nucleated, and each gives oft' an external and an internal process. The internal processes terminate in flattened tufts at different levels in the inner molecular layer, while the external produce an abundant ramification in the external zone of the outer molecular layer. These bipolar cells are divided into rod bipolars, cone bipolars, and giant bipolars. The rod bipolars end peripherally in vertical arborisations around the button-like ends or spherules of the rod fibres, and, centrally, in branched extremities _ stratum ^£ [ opticum jMeiiibrana limitans interna Fkj. 564. — Diagrammatic Section op the Human Retina (rnoilitiud from Schultze). THE EETIXA. Y33 which mostly become applied to the cells of the ganglionic layer. The cone bipolars end peripherally in flattened arborisations in the outer molecular layer in contact with Fig. 565. — Perpendicular Sections of Mammalian Retina (Cajal). A, Layer of rods and cones ; B, Outer nuclear layer ; C, Outer molecular layer ; D, luuer nuclear layer ; E, Inner molecular layer ; F, Ganglionic layer ; G, Stratum Opticum ; r, rods ; c, cones, r.(/, rod granules ; eg, cone granules ; r.b, rod bipolars ; c.b, cone bipolars ; c.r, contact of rod bipolars vrith the spherules of the rod fibres; c.c, contact of cone bipolars with the branches of the cone fibres; ar, internal arborisation of cone bipolars ; ar', internal arborisation of rod bipolars ; c.n, centrifugal nen-e fibre; h, horizontal cells; s.s, stratified spongioblasts; d.s, diffuse spongioblasts; s.g, stratitied ganglion cell ; M, Sustentacular fibre of Miiller. the ramifications of the foot-plates of the cone fibres, and, centrally, ramify in some one of the five strata of the inner molecular layer. The giant bipolars form, peripherally, an extensive horizontally arranged arborisation in the outer mole- cular layer ; centrally, they ramify in one or other of the strata of the inner molecular layer. (b) The horizontal cells are of two varieties : (1) small, flattened, star-like cells, lying immediately below the outer molecular layer, and sending a tuft of dendrites outwards towards the bases of the cone fibres, while their axons are directed horizontally for a variable distance ; (2) large, in-egular cells, lying internal to the above and ending in finger-like ramifications in the outer molecular layer. Their axons run horizontally for some distance, and end in extensive varicose arborisations under the spherules of the rod fibres. (c) The spongioblasts are situated in the innei-most part of the inner granular layer and have not yet been shown to possess axons. Their dendrites ramify in the inner molecular layei', it may be in one stratum (stratified spongioblasts) or in several strata (diftuse spongioblasts). 5. Outer molecular or outer plexiform layer — This is constituted by the interlacement of the dendrites of the bipolar and horizontal cells, just described, with the spherules of the rod fibres and the ramifications of the foot- plates of the cone fibres. It is divided into two strata : (a) externa/, indicating the contact of the rod bipolars with the spherules of the rod fibres ; (b) internal, the line of contact between the cone bipolars and the branches of the cone fibres. 6. Outer nuclear layer or layer of outer granules.— This is made up of clear granules somewhat resembling those of the inner nuclear layer, and are divisible into two kinds : (a) cone granules, (b) rod granules. The cone granules are the larger, and each contains an oval nucleus ; they lie immediately inside the outer limiting membi'ane, through which they are continuous with the cones of the next layer. Each is prolonged internally as a straight fibre, which, on reaching the outer mole- cular layer, expands to form a foot-plate, from which several horizontal fibrils are given off. The rod granules are far more numerous than the cone oranules, and each contains a small oval nucleus, which is transversely striated. V, A cone and two rod.s from the human retina (modified fi'om Max Schultze) ; B, Outer part of rod separated into discs. 734 THE OEGANS OF SENSE. Fig. 568. — Section through outer Layers of Eetina (semi-diagram- matic). Their outer processes are continuous, through the outer limiting membrane, with the rods of the next layer, while their inner processes pass into the outer molecular layer and end in free, unhranched spherules amongst the arborisations of the rod bipolars. 7. Layer of rods and cones. — This consists of two sets of structures, viz. rods and cones. Except at the macula lutea the rods are far more numerous than the cones and assume the form of elongated cylinders, while the cones are shorter than the rods and taper externally to fine points. Each rod and cone consists of two segments — inner and outer. The inner segment of the rod only slightly exceeds in diameter its outer segment, whereas the inner segment of the cone greatly exceeds its outer part. The inner segments of both rods and cones have an affinity for staining reagents, and consist of a basal homogeneous portion and an outer longitudinally striated part, the proportion of the latter to the former being greater in the cones than in the rods. The outer seg- ments have not the same affinity for ^'epithei7um™fTu° reagents, but tend to break trans- MAN Retina (viewed versely into numerous discs (Fig. 566, from the surface). B). The colouring matter, rhodopsin, already referred to, is found only in the outer segments of the rods, the terminal parts of which extend into the layer of pigmented epithelium. 8. Layer of pigmented epithelium (stratum pigmenti).- — This consists of a single stratum of cells which, on surface view, are hexagonal (Fig. 567), their outer flattened surfaces being firmly attached to the chorioid. When seen in profile the outer part of each cell contains a large oval nucleus and is devoid of pigment, while the inner portion is filled with pigment and extends as a series of thread-like processes amongst the outer segments of the rods and cones. When the eye is kept in the dark the pigment accumulates near the outer part of the cell, but when exposed to light it streams in between the rods and cones (Fig. 568). It will be seen from the foregoing description that there is no direct continuity between the nervous elements which form the different layers of the retina. In the inner molecular layer there is merely an interlacement between the dendrites of the ganglionic layer and the arborisations of the cells of the inner granular layer, and a similar inter- lacement in the outer molecular layer between the rod and cone elements and the processes of the outer granules. Sustentacular fibres of the retina (fibrse Mlilleri). — These support the nervous structures and extend from within outwards through the thickness of the retina as far as the bases of the rods and cones (Fig. 565, M). They begin at the inner surface of the nerve-fibre layer in single or forked expanded bases, by the apposition of which a delicate membrane, the membrana limitans interna, is formed. In the ganglionic layer they give off' a few lateral branches, and, on passing through the inner nuclear layer, supply lateral ramifications amongst the inner granules for their support ; in this part of each fibre there is seen an oval nucleus. In the outer nuclear layer they break up into a network of fibrils which surround the rod and cone fibres, and end externally at the bases of the rods and cones in a delicate membrane, the membrana limitans externa. Structure of the macula lutea and fovea centralis. — The yellow colour of the macula is due to the presence of pigment in the inner layers of the retina. At the circumference of the macula the nerve-fibre layer is greatly thinned and the rods are few in number ; the ganglionic layer, on the other hand, is thickened and may contain from seven to nine strata of cells, while the outer granular layer is also thicker and its bipolar cells have an oblique direction. At the fovea centralis the retina is much thinned, since here its nerve-fibre and ganglionic layers are absent and its other strata greatly attenuated. The stratum pigmenti, on the other hand, is thicker and its pigmentation more pronounced. The cone nuclei are situated some distance internal to the outer limiting membrane, and thus the thin inner and outer granular layers are in apposition. There are no rods, and the cones, closely crowded together, are narrower and their outer segments more elongated than elsewhere, so that the line of their bases, indicated by the membrana limitans externa, presents a convexity directed forwards. The fovea centralis and macula lutea are spoken of by the physiologist as the "region of distinct vision." EEFEACTING MEDIA OF THE EYEBALL. 735 Structure of the ora serrata.— Here the nervous layers of the retina suddenly cease ; the layer of rods and cones first failing, to be immediately followed by the disappear- ance of the other nervous strata. In front of the ora serrata the retina is prolonged over the ciliary processes in the form of two layers of cells : (a) an inner layer of columnai^epitheliura, and (b) an outer, consisting of the stratum pigmenti, the two forming the pars ciliaris retinae. The same two layers are prolonged over the back of the iris, where both are pigmented and form the pars iridica retinte. Vessels of the retina (Fig. 569).— The retina is sui)plied by the arteria centralis retinae, a branch of the opiithalmic artery, which pierces the sheath of the ojjtic nerve about three-(iuarters of an inch behind the eyeball, and makes its ajjpearancc in the centre of the optic disc. Here it divides into an upper and a lower branch, and each of these again bifur- cates into an internal or nasal, and an external or temporal, branch. The resulting four branches ramify towards the peripliery of the retina, and are named the superior and inferior temporal and the superior and inferior nasal arteries. The temporal arteries pass outwards above and below the macula lutea, to which they give small branches • Upjier nasal brancli Optic disc Lower nasal branch Upper temporal branch Upper and lower macular arteries Macula lutea Lower temporal branch Fig. 569. — Blood-vessels of the Retina. these do not, however, extend as far as the fovea centralis, which is devoid of blood-vessels. The macula also receives two small arteries (superior and inferior macular) directly from the porus opticus. The larger vessels run in the nerve-fibre layer near the membrana limitans interna and form two capillary networks — an inner, in the nerve-fibre layer, and an outer, in the inner nuclear layer. The inner network arises directly from the arteries and sends numerous small branches to the outer network, from which the veins take origin. The vessels do not penetrate deeper than the inner granular layer, nor do the arteries anastomose except through the capillary plexuses. The veins follow the course of the arteries ; they have no muscular coats, but consist merely of a layer of endothelial cells, outside which is a perivascular lymphatic sheath, surrounded by delicate retiform tissue. EEFKACTING MEDIA OF THE EYEBALL. The vitreous body (corpus vitreum) is a transparent, jelly-like substance situated between the crystalline lens and the retina, and occupying the posterior Ibnr-lii'ths of the glolje (Fig. 558). In front it presents a deep concavity, the fossa patellaris, for the reception of the posterior convexity of tlie lens. It is enclosed within a thin transparent membrane, the membrana hyaloidea, which is in contact with the membrana limitans interna of the retina and adherent to it at the optic entrance. The portion of the membrana hyaloidea in front of the ora serrata is thickened and strengthened by radial fibres, and is termed the zonule of Zinn, or zonula ciliaris. Situated Ijehind the ciliary body the zonula is radially folded and presents a series of alternating furrow^s and elevations. The ciliary processes are received into, and are firmly adherent to, the furrows, with the result that, if removed, some of their pigment remains attached to the zonula. The elevations of the zonula are not attached to the interciliary depressions, but are separated by a series of lymph spaces (recessus camene posterioris) ; these may be regarded as diverticula of the 736 THE OEGANS OF SENSE. Fig. 570. — C'axal (w Petit distended AND VIEWED FROM THE Froxt (eulargecl). posterior chamber with which they communicate. As the zonula approaches the equator of the lens it splits into two chief layers, viz. : (a) a thin posterior lamina, which covers that portion of the membrana hyaloidea which lines the fossa patellaris; and (b) a thicker anterior layer, termed the suspensory ligament of the lens (Fie-.' 558), which blends \vith the front of the lens capsule a short distance from its equator. Scattered fibres of this ligament are also attached to the equator itself and to the regions immediately anterior and posterior to it. By this suspensory ligament the lens is retained in position, and its convexity varies inversely with the degree of tension of the ligament. The radial fibres of the ciliary muscle, by pulling forward the ciliary processes and the attached zonule of Zinn, relax the ligament, and thus allow the lens to become more convex. Behind the suspensory ligament a sacculated lymph space surrounds the equator of the lens ; it is named the canal of Petit, and may easily be inflated on introducing a fine blow-pipe through the suspensory ligament (Fig. 570). In the foetus a blood-vessel, termed the arteria hyaloidea, is continued from the arteria centralis retinae forwards through the vitreous body for the supply of the capsule of the lens. Its position, in the adult, is represented by a lymph channel, termed the canalis hyaloideus of Stilling (Fig. 558), the presence of which may be de- monstrated by shaking up the vitreous body in a solution of picrocarmine, when some of the pig- ment may be seen to extend along the canal (Anderson Stuart). When the vitreous body is treated by a weak solution of chromic acid it presents a series of concentric, peripherally arranged strise, together with numerous radial strise converging towards its centre. Between these the more fluid part lies, and it frequently contains vacuolated amceboid cells scattered through it. The vitreous body consists of 98-4 per cent of water, having in solution about 1-4 per cent of sodium chloride and traces of extractives and albumen. The crystalline lens (lens crystallina) lies in front of the vitreous body and behind the iris, and is a biconvex, transparent body (Fig. 558). It is enclosed in a thin, transparent, homogeneous capsule, the capsule of the lens (capsula lentis). The central points of its anterior and posterior surfaces are termed respectively its anterior and posterior poles, a hne joining which is known as its axis (axis lentis) ; its peripheral circumference is named the actuator (tequator lentis). Its axiai measurement is 4 mm., and its transverse diameter from 9-10 mm. Its anterior surface (facies anterior lentis) is less curved than the posterior, and its central part corresponds with the aperture of the pupil and is directed towards the anterior chamber. Around the aperture of the pupil the pupillary margin of the iris rests upon the lens, but its peri- pheral part is separated from it by the aqueous humour of the posterior chamber. Its posterior surface (facies posterior lentis), more convex than the anterior, occupies the fossa patellaris of the vitreous body. The relations of its equator to the suspensory ligament and the canal of Petit have already been referred to. The superficial ijart of the lens possesses a refractive index of about 1-4, and its central part or nucleus one of about 1-45. The curvatures of its surfaces, especially that of the anterior, are constantly varying during life for the purpose of focusing rays from near or distant objects on the retina. The lens substance (substantia lentis) consists of a soft outer part, the substantia corticalis, easily crushed between the finger and thumb, and of a dense central part. NucIpus lentis Fig. .571. — Lens hardened in Formalin and dissected to show its concentric laminae (enlarged). EEFEACTING MEDIA OF THE EYEBALL. 737 Fi( — DiAGRA^nrATic Reprksen'tation of the Radii Lextis ok the Fcetal Lens. A, Seen from the frout ; B, From beliiud. the nucleus lentis. Faint lines (radii lentis) radiate from its anterior and posterior poles towards its equator. In the fcetiis they are three in number, and form with each other angles of 120" (Fig. 572). From the anterior pole one ray ascends vertically and the other two diverge downwards, while from the posterior pole one ray descends vertically and the other two diverge upwards. In the adult the rays may be increased to six or more. They represent the free edges of a corresponding- number of septa which dip into the substance of the lens, and along which the extremities of the different groups of lens fibres come into contact, and are attached by a clear, amorphous substance. The lens, when hardened, exhibits a series of concentrically arranged laminae (Fig. 571), superimposed like the coats of an onion and attached to each other by a clear, amorphous substance. Each lamina is split along the radiating lines, and consists of a series of hexagonal, riband-like fibres, the fibrte lentis, which are adherent to each other by their margins ; those of the deeper laminas are smaller and serrated, but non-nucleated ; while those of the superficial coats are larger and nucleated, but non-serrated. The fibres extend in a curved manner from the rays on the anterior surface to the rays on the posterior surface, but no fibre extends from pole to pole. Fibres which start at or near one pole end at or near the equator on the opposite surface, and vice versa, wdiile the intervening fibres take up intermediate positions. Between the substantia lentis and the anterior part of the capsule there is a layer of nucleated columnar epithelial cells, the epithelium lentis. On being traced towards the equator its cells become gradually elongated and transformed into lens fibres, which, when fully formed, lose all trace of their nuclei, except in the more superficial laiuino3. Ea,ch lens fibre represents, therefore, a greatly elongated columnar cell (Fig. 573). In the foetus the lens is soft, of a pinkish colour, and nearly spherical ; while in old age it becomes more flattened than in the adult, and, losing its transparency, assumes a yellowish tint. Chambers of the Eye and Aqueous Humour (Fig. 558). — As already stated (p. 730), the space between the cornea and the lens is divided by the iris into two unequal parts, viz. the anterior chamber in front and the posterior chamber behind. These are filled by the aqueous humour, and, in the adult, communicate freely through the aperture of the pupil, but in the tVetus are separated from each other by the pupillary membrane. The anterior chamber (camera oculi anterior) is bounded in front by the cornea, behind by the iris and lens, whilst peripherally it communicates with the spaces of Fontana. The posterior chamber (camera oculi posterior) is triangular Equator of the Lens. ^^^ section, and is bounded in front by the iris, behind by Showing the gradual trail- the circumferential part of the lens and its suspensory liga- iit^^e'if tiiM'l^''omer ^^^^^^^ ^ ^^^^ ^'^^^^ o^' ^^^^ triangle, situated externally, corresponds BabiK-hiii). with the thick, anterior extremities of the ciliary processes. It communicates with the recessus camera?, posterior and canal of Petit. The aqueous humour has a refractive index of about 1-336, and consists of about 98 per cent of water, with 1-4 per cent of sodium chloride and traces of albumen. 51 Fui. .o7o. Section thkough the 738 THE OEQANS OF SENSE. EYELIDS. The eyelids or palpebrae are two movable cutaneous curtains situated in front of the eyeball, and named, from their position, upper and lower. The upper is the larger and more movable, being provided with a special elevator muscle, the m. levator palpebrse superioris. The interval between the lids is termed the palpebral fissure (rima palpebrarum), and measures transversely about 30 mm., but varies considerably in different individuals and in different races. When the eye is open the fissure is elliptical in shape, but when closed it assumes the form of a transverse slit, which lies on a level with the lower margin of the cornea. The two lids meet at the extremities of the fissure, and form the outer and inner angles, or canthi. Their free margins are flattened and are surmounted by eyelashes from the external Conjunctn a — ^ Y^^=^i Meibomian gland in tarsal plate' Muscle of Riolan Tendon of levator palpebrse Orbicularis palpebraram Eyelashes Fig. 574. — Vertical Section through Upper Eyelid. canthus to a point about 5 mm. from the inner canthus — a point indicated by a small papilla, the papilla lacrimalis. Internal to this papilla the margins are rounded and destitute of eyelashes, and form the upper and lower boundaries of a triangular space, termed the lacus lacrimalis, which is occupied by a small pale-red body, the caruncula lacrimalis. This caruncula consists of a minute island of modified skin, and contains sweat glands, sebaceous glands, and fine hairs. Posteriorly the lids are lined by a mucous membrane, the conjunctiva, and are in contact with the eyeball, except near the inner canthus, where, Ijetween the eyeball and the caruncula lacrimalis, there intervenes a vertical fold of conjunctiva, the plica semilunaris conjunctivse. This, which in many animals contains a plate of cartilage, is tlie representative of the membrana nictitans, or third eyelid of birds, etc. In each lid there exists a framework of condensed fibrous tissue, which gives consistence and shape to the lid, and is termed the tarsal plate or tarsus. In front of the tarsus are the fibres of the orbicularis palpebrarum muscle and the EYELIDS. 739 integument, while embedded in its posterior surface, and covered Ly the conjunctiva, are numerous modified sebaceous glands named the tarsal or Meibomian glands. The superior tarsal plate (tarsus superior) is larger than the inferior and of a half oval shape, with its greatest vertical diameter measuring about 10 or 11 mm. Its upper margin is thin and convex, and is continuous with the tendon of the levator palpebrse superioris muscle, while its lower edge is thick and straight. The inferior tarsal plate (tarsus inferior) is a thin, narrow strip, with a nearly uniform vertical diameter of about 5 mm. The extremities of the two plates are continuous with the external and internal tarsal ligaments. Tlie external tarsal ligament is a narrow band attached to the malar Ijone ; it divides, at the outer canthus, into upper and lower pieces which are fixed to the margins of the respective tarsal plates. The internal tarsal ligament is a strong band attached to the nasal process of the superior maxillary bone directly in front of the lachrymal groove ; it divides at the inner canthus into two slips, one for either tarsal plate. The eyelids are further strengthened by meml»ranous expansions, termed the superior and inferior palpebral ligaments, which extend into them from the margin of the orbit. The superior ligament is continuous, along the upper margin of the orbit, with the pericranium and with the periosteal lining of the orbit, and blends below with the tendon of the levator palpebrpe superioris. The inferior ligament is prolonged from the under edge of the inferior tarsal plate to the lower margin of the orljit, where it is continuous with the periosteum of the face and orbital floor. Externally the two palpebral ligaments fuse to form the external tarsal ligament, while internally they become thinned, and, separating from the internal tarsal ligament, are attached to the lachrymal bone behind the lachrymal sac. These two palpebral ligaments form a kind of septum or diaphragm, the septum orbitale, between the superficial and deep structures of the eyelids; this septum is perforated by the vessels and nerves, which extend from the orbital cavity to the face or scalp. The skin covering the lids is thin and delicate, and is continuous, at their margins, with their conjunctival lining. It contains numerous small sweat glands and fine hairs, the latter being provided with sebaceous follicles. Branched pigment cells are present in the cutis, and pigment also exists in the deep layers of the epidermis. The subcutaneous tissue is loose and devoid of fat, and in it are found the fil)res of the orbicularis palpebrarum muscle — a small separate bundle of which, termed the muscle of Riolan, occupies the margin of the lids behind the eyelashes. The Meibomian glands, or glandula3 tarsales, are elongated sebaceous glands with numerous lateral offshoots ; they are embedded in the tarsal plates and filled with cubical epithelium. There are from twenty-five to thirty in the upper lid, and from twenty to twenty-five in the lower ; they open by small ducts, about 1 mm. in length, along the lid margins behind the eyelashes ; the ducts are lined by stratified epithelium placed on a basement memltrane. Between the eyelashes and the muscle of Eiolan are two or three rows of modified sweat glands, termed the glands of Moll ; the l)locking of a duct of one of these glands frequently gives rise to a stye. H. Miiller described a layer of non-striped muscle in each lid : in the iipper extending from the tendon of the levator palpebrse superioris to the upper tarsal plate, and in the lower connecting the inferior tarsal plate with the inferior oblique muscle. The tendon of the levator palpebral superioris divides into three parts — an anterior, passing between the bundles of the orbicularis to the deep surface of the skin ; a middle, attached to the superior tarsal plate ; and a posterior, to the fornix conjunctivie : there is no corresponding nuiscle in the lower lid. The eyelashes are curved, silky hairs which project from the free margins of the lids ; in the upper lid they arc longer and more numerous than in the lower, and are curved upwards, while those of the lower lid are bent downwards. Conjunctiva. — Tliis is the name appUed to the mucous membrane which lines the back of tlie lids (tunica conjunctiva palpebrarum), and is continued on to the front of the eyel)all (tunica conjunctiva bulbi). The line along which it is reflected from the lids on to the globe of the eye is termed the fornix conjunctivae. The palpebral portion adheres intimately to the tarsal plate and presents numerous papilliE. It is covered by a layer of columnar epithelial cells, beneath the bases 51a 740 THE OEGANS OF SENSE. of which are small flattened cells. Near the fornix a number of acino-tubular glands, much more plentiful in the upper than in the lower hd, open on its free surface. The conjunctiva bulbi is thinner than that lining the lids, and is loosely attached to the sclera by submucous tissue. The plica semilunaris conjunctivse has already been referred to (p. 738). On the cornea the conjunctiva is represented merely by the stratified epithelium already described (p. 726). Vessels and Nerves. — Tlie chief arteries of the eyelids are the superior and inferior palpe- bral branches of the ophthalmic, which pierce the septum orbitale above and below the internal tarsal ligament, and run tortuously outwards in the corresponding lid near its free margin. On reaching the region of the outer canthus they anastomose with each other and with twigs from the lachrymal, superficial temjjoral, and transverse facial arteries, and in this way an arch is formed in each lid (upper and lower tarsal arches). Secondary smaller arches are found, one above the primary arch in the upper lid, and another below that of the lower lid, while the upper lid also receives branches from the supraorbital and frontal arteries. The veins are arranged in two sets : (a) subconjunctival or retrotarsal, opening into the muscular tributaries of the ophthalmic vein, and (b) pretarsal, into the angular and superficial tempoi-al veins. The lymphatics, like the veins, form pre- and retrotarsal networks, which communicate with each other through the tarsal plates. The lymph is chiefly drained into the j)e.rauricular and parotid lymphatic glands, but partly, by vessels which accompany the facial vein, into the submaxillary lymphatic glands. The sensory nerves of the eyelids are supplied by the fifth cranial nerve — the upper lid chiefly by the supraorbital and supratrochlear branches of the ophthalmic ; the lower, by the infraorbital branch of the superior maxillary. The region of the outer canthus receives some filaments from the lachrymal nerve, that of the inner from the infratrochlear. These sensory nerves form a marginal plexus behind the orbicularis palpebrarum muscle. The levator palpebrse muscle is supplied by the third cranial nerve and the non-striped fibres of the lids by the sympathetic. LACHEYMAL APPAEATUS. The lachrymal apparatus (apparatus lacrimalis) consists of : (1) the lachrymal gland, which secretes the tears ; (2) the lachrymal canals, by which they are drained from the front of the globe ; and (3) the lachrymal sac and nasal duct, which convey them into the nasal cavity. The lachrymal gland is a flattened, oval body situated in the upper and outer part of the orbital cavity, and consists of two portions — orbital and palpebral — imperfectly separated from each other by the expansion of the tendon of the levator palpebrae superioris muscle. The orbital portion, or glandula lacrimalis superior, is firm and much larger than the palpebral part ; it measures transversely about 20 mm., and sagittally from 12-14 mm. It occupies the fossa lacrimalis on the inner aspect of the external angular process of the frontal bone, and is fixed by fibrous bands to its periosteum, while its inferior surface is in contact with the levator palpebrse superioris and external recti muscles which intervene between it and the globe of the eye. The smaller, palpebral portion, or glandula lacrimalis inferior, consists of small, loosely aggregated lobules. It lies below and in front of the orbital portion, and projects into the posterior part of the upper eyelid, where its deep surface is in contact with the conjunctiva. The ducts which drain the orbital portion are from three to five in number ; they pass between the lobules of the palpebral portion, and open at the upper and outer part of the fornix conjunctivae. The ducts of the palpebral portion number from three to nine ; some of them join those from the orbital part, while others open separately at the fornix conjunctivae. The lachrymal gland has a structure similar to that of the parotid, and is supplied by the sympathetic and lachrymal nerves and by the lachrymal artery, while its veins are drained into the ophthalmic vein. The lachrymal canals (ductus lacrimales) commence by minute orifices, termed the puncta lacrimalia, at the apices of the papillae lacrimales already referred to (p. 738). The upper canal is the smaller of the two, and at first ascends for a short distance, and then runs inwards and slightly downwards ; the lower descends for a short distance and then runs horizontally inwards. At the angle where they change their direction each is dilated into an ampulla (ampulla ductus lacrimalis). They occupy the margins of the lids, where these bound the lacus lacrimalis, and the two canals open close together into the outer and fore-part of the lachrymal sac, a little below its middle ; sometimes they open separately into a pouch-like dilatation of the sac, termed the sinus of Maier. Each canal is lined by a DEVELOPMENT OF THE EYE. 741 stratified epithelium placed on a tunica projDria, outside which is a layer of striped muscular fibres derived from the tensor tarsi muscle. These muscular fibres are arranged somewhat spirally around the canals, but at the bases of the ]japilke they are circular in direction and form a species of sphincter. On contraction they serve to empty the contents of the lachrymal canals into the lachrymal sac. The lachrymal sac and nasal duct together form the passage by which the tears are conveyed from the lachrymal canals to tlie nose. The lachrymal sac (saccus lacrimalis) is the upper expanded part of the passage, and measures from 12-15 mm. in length, about 7 mm. antero-posteriorly, and from 4-5 mm. transversely. It lies in the groove formed by the lachrymal bone and nasal process of the superior maxilla, and ends above in a rounded, blind extremity or fundus, while it narrows below into the nasal duct. Here a fold of mucous membrane, named the valve of Beraud, together with a laterally directed pouch, the sinus of Arlt, are sometimes present. Near its superior extremity it is crossed in front by the internal tarsal ligament, from the upper and lower edges of which the orbicularis palpebrarum takes origin, while behind it is the tensor tarsi muscle, or muscle of Horner. The nasal duct (ductus naso-lacrimalis) averages about 18 mm. in length, and has a diameter of from 3-4 mm. Eather narrower near its middle than at its upper and lower extremities, it is directed downwards and slightly backwards, and opens into the inferior meatus of the nose at the junction of its anterior with its posterior three-fourths, i.e. a distance of 30-35 mm. from the posterior lioundary of the nostril. Its lower orifice is somewhat variable in form and position, and is occasionally duplicated. It is frequently guarded by a fold of mucous membrane, termed the valve or plica lacrimalis of Hasner. Through this orifice the mucous lining of the duct is continuous with that of the nose. The mucous membrane of the duct is thrown into inconstant folds, several of which have been described as valves. Its epithelium is columnar and in part ciliated ; opening into the lower part of the duct are numerous glands similar to those in the nasal mucous membrane. The nerves of the lachrymal canals and sac are derived from the infratrochlear In-anch of the nasal ; their arteries from the inferior palpebral and nasal. The veins of the nasal duct are large and numerous, forming a sort of erectile tissue similar to that in the nose. Development of the Eye. The retina and optic nerveare developed from a hollow outgrowth of the fore-brain, termed the optic vesicle (see pp. 478 and 595). This extends towards the side of the head, and its Lens rudiment Optic cup Optic stalk I Outer layer of optic cup Inner layer of optic cup ens I Optic stalk Chorioiilal lissure Lens Fig. .57o. — Sectioxs through Pohtions of the Heads of Fcetal Rabbits, to illustrate the counexion of the optic cup witli tlie foi-e-braiu, and the invagination of the ectoderm to form the lens. connexion with the brain is gradually elongated to form the optic stalk. The ectoderm overlyino- tlie optic vesicle becomes thickened, invaginated, and finallv ciit off as a hollow '517) 742 THE OEGANS OF SENSE. island of cells, which is developed into the lens and is named the lens vesicle. This lens rudiment indents the outer and lower part of the optic vesicle, which now assumes the form of a cup (optic cup), lined by two layei's of cells continuous with each other at the margin of the cup. The inner of these strata, thicker than the outer, is named the retinal layer, and becomes differentiated into the nervous and supporting elements of the retina ; while the outer, named the pigmentary layer, forms its pigmented epithelium. The edge of the optic cup extends in front of the equator of the lens, and bounds the future aperture of the pupil. In front of the lens, and also opposite its equator, the retinal layer is thin, and represented only by a sti'atum of columnar cells which becomes closely applied to the pigmentary layer, the two forming the pars ciliaris and pars iridica retinee. The in- dentation of the optic cup extends as a groove for some distance along the postero-inferior aspect of the optic stalk, forming what is termed the chorioidal fissure (Fig. 576). Through this fissui'e the mesoderm passes inwards between the lens and the retina to form the vitreous body, while the arteria centralis retinae also becomes enclosed in it and so gains its future position in the centre of the optic nerve. The arteria centralis is prolonged forwards from the porus opticus through the vitreous body, as a cone of branches, as far as the back of the lens. B}' the fifth or sixth month all these branches have disappeared except one, the arteria hyaloidea, which persists until the last month of fcetal life, when it also atrophies, leaving only the canalis hyaloideus to indicate its position. The lens rudiment, at first in contact with the ectoderm, from which it is derived, soon becomes separated from it by mesoderm, and then consists of a rounded vesicle lined by epithelium. The epithelium which lines the anterior part of the vesicle remains as a single layer of cells — the anterior lens epithelium of the adult. The cells lining the posterior part of the vesicle become elongated into lens fibres, and by the forward growth of these the cavity of the vesicle is obliterated. This elongation into lens fibres is greatest at the centre of the lens, while near the equator the fibres are shorter, and here the gradual transition between the anterior epithelium and -Optic Cup and Lens viewed the lens fibres is seen (Fig. 573). The lens becomes FROM Behind and Below, to show enveloped in a vascular tunic, which receives its vessels So"s™„fthe"rt'rS ceSL"'! f"- "- -t" A centralis reti„«. and from the vessels tina; (from model by Ziegler). 01 the iris. Ihe front part of this tunic forms the membrana pupillaris, and this, like the rest of the tunic, disappears before birth. The hollow stalk of the optic cup becomes solid by the thickening of its walls and the obliteration of its cavity, and, acquiring nerve-fibres, becomes the optic nerve. These nerve- fibres are mostly centripetal, and are derived from the nerve-cells of the retina : but a few are centrifugal and have their origin in the brain. The further development of the retina resembles, in certain respects, that of the spinal cord. Cameron states ("The Development of the Eetina in Amphibia," Journ. Anat. and Physiol., London, vol. xxxix.) that in the early stages of the development of the inner or retinal layer of the optic cup all the structures, described by His as being present in tlie spinal cord of the iuiman embryo, are to be found, viz. (a) spongiolilasts, (6) germinal cells, and {c) neuroblasts. The spongioblasts undergo ramification and form a network or myelospongium, and also give rise to the inner and outer limiting membranes ; the latter is next the original cavity of the optic vesicle, and therefore corresponds to the inner limiting membrane of the spinal cord. The spongioblasts also form tlie groundwork of the inner and outer molecular layers into which the processes of the neurol:>lasts grow and arborise. The germinal cells are always situated beneatli the external limiting membrane, and by their division give rise to the neuroblasts. The first-formed neuroblasts are larger tlian those of succeeding generations, and are found in the site of the future ganglionic layer. The germinal cells in the middle of the convexity of the retinal cuj) cease to divide at an early stage of development, and become dire(;tly transformed into the rod and cone cells from which the rods and cones develop as processes ; lience tliese structures appear first over the middle of the convexity of tlie I'etma, and gradually extend towards tlie margin of the retinal cup. The nuclei of the retinal neuroblasts undergo a progressive diminution in size — in some cases to one-fourtli of that of their earlier stages. Cameron, after a careful study of the neuro- blasts, not only in the retina, ]jut in the wall of the cereljral vesicle and spinal cord, is of opinion that the neuroblastic nuclei are destitute of a proto])lasmic investment, and that what has l.ieen described as a zone of " clear protoplasm " surrounding these nuclei during the process of karyo- kinesis is simply the achromatic nuclear substance set free Ijy the disappearance of the nuclear niemljrane ; and, furtlier, that the i)rocesses whicli grow out from the neuroljlasts in reality issue from the substance of the nuclei and thus cause tlie gradual diminution in size of the latter. " The processes of the retinal 'ganglion -cells ' and of the cells of the inner nuclear layer first show THE EXTEENAL EAE. 743 tliemselves as protrusions of tlie nuclear contents, while the rods and cones are at first also protrusions of the nuclei of tlie external nuclear layer. The rod and cone elements, when they first api^ear, do so as perfectly clear sjjherical globules consisting of nothing more than nuclear achromalin. The axis-cylinders of tlie o])tii' nerve arise as processes of the nuclei in the ganglionic layer, and the great difficulty which is experienced in staining the indi\idual fibres of the retinal nerve-fibre layer is due to the fact that they are composed of the achromatic nuclear substance of the ganglionic nuclei. The origin of the axis-cylinders from these nuclei supports the contention of those who insist on the fact that the axis-cylinder process of a nerve- ceU can be traced right into the nucleus of that cell." The molecular layers make their apj^earance as jalexuses of myelospongium. The internal molecular layer is fii'st develoijed at the centi-e of the retinal cup, and gi'adually extends towards the cup margin, and into it the processes from the nuclei on either side grow and ramify. The rod and cone filn'cs, and the outer processes of the internal nuclear layer, grow into and arborise within the external molecular layer. The most interesting points with reference to the development of the nuclear layers are, (1) the extrusion of the various processes from the nuclei as already described, and (2) the free manner in which these nuclei multiply by direct division during the metamorphosis. It is interesting to note that the retinal nuclei are formed during the early stages by mitotic or indirect division of the germinal cells, while later they appear capable of multiplying by amitotic or direct division only. The first evidences of the rods and cones are in the form of clear, absolutely achromatic globules, which lie between the nuclei of the external nuclear layer and the outer limiting membrane. Whenever these are protruded beyond this membrane they grow with great rapidity, and exert an influence on the retinal pigment cells, causing them to protrude their processes, the pigment of which they seem to digest and absorb, since they now stain deeply with iron-alum-hasmatoxylin. This gives us a clue to the mode by which the rhodopsin function of the rods in the adult is conducted, for these structures actually owe their growth and development to the ingestion of pigment from the pigment-cell processes. The condensed mesoderQi suiTounding the optic cup becomes the sclera and chorioid. In the portion of the mesoderai which lies in front of the lens a cleft-like fissure appears, and divides it into a thick anterior and a thin posterior layer. The former becomes the substantia propria of the cornea ; the latter, the stroma of the iris and anterior part of the vascular tunic of the lens. The fissure represents the future anterior chambei", and its lining cells form the layer of endothelium on the back of the cornea and front of the iris. The eyelids arise as two integumentary folds above and below the cornea, each being covered on both its surfaces by the ectoderm. By the third month the folds meet and unite with each other at their edges, the eyelids being only pei'manently opened shortly before birth ; in many animals they are not opened until after birth. The ectoderm forms the epithelium of the conjunctiva and the stratified epithelium of the cornea. It is also invaginated at the lid margins to form the hair follicles and the lining cells of the Meibomian glands and glands of Moll, and, at the fornix conjunctiva;, to form the lining of the alveoli and ducts of the lachrymal gland. The nasal duct, lachrymal sac, and canals represent the remains of the fuiTow which extends from the inner angle of the eye to the nasal cavity between the superior maxillary and lateral nasal processes (p. 40). It is at first filled by a solid rod of cells, which becomes liollowed out to form the duct and canals. THE EAR. The ear or organ of hearing (organon auditus, Fig. 577) consists of three portions — external, middle, and internal — the last constituting its essential part, as within it are distributed the peripheral terminations of the auditory nerve. EXTEENAL EAE. The external ear ^ includes — {a) the pinna or auricula, attached to and pro- jecting from the side of the head; and {h) the passage or external auditory meatus (meatus acusticus externus), leading inwards from the most depressed part of the pinna as far as the tympanic membrane or outer wall of the middle ear. The Pinna. The pinna or auricula (Fig. 578) presents two surfaces, outer and inner, the latter forming an angle (cephalo-auricular angle) of about 30°, with the side of the ^ Although it is usual to speak ol' the e.xteriial, middle, and internal ear, it would be more coiTCct to use the terms external, middle, and iuteiual portions of tlie ear. 51c 744 THE OEGANS OF SENSE. Tympanic ca^ it\ , w itli cliam of Obbicles Semicircular canal UtnclP I Ductus endolymphaticus Saccule Cochlea ■I'inna Eustachian tub Membrana tynipani Eecessus External auditory meatus Fig. 577. — Diagrammatic View of the Organ of Hearing. head. The outer surface is irreg-ularly concave, but presents several well-marked elevations and depressions. The deepest of the depressions is situated near its middle, and is named the concha (concha auri- culse). It is divided by an almost transverse ridge, the crus helicis, into an upper, smaller, and a lower, larger por- tion : the former is termed the cymba con- chse ; the latter, which leads into the meatus, the cavum conchse. An- teriorly, the crus helicis is continuous with the margin of the pinna or helix, which is folded over, in the greater part of its extent,like the rim of ahat,andisdirectedat first upwards, and then backwards and down- wards, to become gradu- ally lost a little below the middle of the pinna. Near the point where the helix begins to turn down- wards a small tubercle, the tuberculum superius (Darwini), is often seen ; it will be again referred to. In front of the descending part of the helix is a second elevation, the antihelix. Single below, it divides superiorly into two limbs, termed the crura antihelicis, between which is a triangular depression, the fossa of the antihelix, or fossa triangularis. The elongated furrow between the lv|i helix and antihelix is named the crus antihelicis superior-^^™^ fossa of the helix or scapha. The concavity of the concha is over- lapped in front by a tongue-like process, the tragus, and behind by a triangular projection, the anti- tragus ; the notch, directed down- wards and forwards between these two processes, is named the incisura intertragica. The tragus really consists of two tubercles, the upper of which constitutes the tuberculum supratragicum of His, and is separated from the helix by a groove, the sulcus auris anterior. The lobule (lobulus auriculee) is situated below the incisura intertragica, and is the most dependent part of the pinna. The inner or cranial surface is also irregular, and presents elevations corre- sponding to the depressions on its outer surface, e.g. eminentia conchse, eminentia triangularis, etc. The pinna is usually smaller and more finely modelled in the female than in the male, but presents gi'eat variations in size and shape in different individuals. In the newly-born child its length is about one-tliird of that of the adult, while it increases slightly in length and breadth in old age. The relation of the width to tlie heiglit is termed the auricular index, and is expressed as follows : — width of pinna X 100^ ^^^.^^j^^ .^^^^_ length 01 pinna Fossa triangularis- Crus antihelicis inferior- Cymba conchaj- Tragus Incisura intertrasica- Fig. 578.- -ViEW OF Outer Surface of Left Pinna (half natural size). THE PINNA. 745 M. helicis major Spina helicis ^ M. lielicis minor M. tragicii — -. Fissure of t Santorini_H^ Isthmus eartila — ^ einis auris Incisuia tenninalis auris M. antitragicus -Fissura antitragohelicina Cauda helicis Fig. 579. — Outer Surface of Cartilage of Pixxa (oue-lialf natural size). This index is less in white than in dark races. The cephalo-auricular angle may be practically absent, as in those cases where the skin of the head passes directly on to tlie outer surface of the pinna, or it may be increased to nearly a right angle, so that the outer surface of the pinna looks directly forwards. Tlie tuberculum superius, the significance of which was recognised by Darwin, is a somewhat triangular prominein-e whicli jirojects forwards when the helix is well rolled over, but backwards and upwards wlien the incurving of the helix has been arrested. More frequently present in men than in women, it is of developmental interest since it has been sho'viai to be well marked at the sixth month of foetal life, the entire pinna, at this stage, resembling in appearance that of tlie adult macaque. The lobule may be small and sessile or considerably elongated ; it may adhere to the skin of the cheek {i.e. webbed), or may tend to bifurcate at its lower extremity. Structure of the Pinna. — The greater part of the pinna consists of a lamella of yellow fibro-cartiluge, the cartilage auriculae ; the cartilage is, however, absent from the lobule, which is composed of fat and connective tissue. When laid bare, the cartilaginous lamella (Figs. 579, 580) presents, in an exaggerated condition, all the inequalities of the pinna, and is seen to be prolonged inwards, to form a considerable portion of the external auditory meatus. The cartilage of the helix projects an- teriorly as a conical eminence, the spina helicis, whilst its inferior ex- tremity extends downwards as a tail-like process, the cauda helicis, which is separated from the lower part of the antitragus by a fissure, termed the fissura antitragohelicina. The cartilage of the pinna is con- tinuous with that of the meatus by a narrow isthmus (isthmus cartila- ginis auris) measuring from 8-9 mm. in breadth. This isthmus corresponds externally with the deepest part of the incisura intertragica, and internally it forms the outer boundary of a deep fissure, the incisura terminalis auris, which separates the cartilage of the meatus from that of the concha. The upper edge of the tragus fits into an angle below the crus helicis. If the incisura terminalis auris, together with the isthmus and the incisura intertragica, be taken as representing the boundary between the cartilage of the pinna and that of the meatus, it follows that the tragus really forms a part of the meatal cartilage. On the cranial aspect of the cartilage (Fig. 580) the eminences produced by the concha and fossa triangularis are separated by a transverse furrow, the sulcus anti- helicis transversus, corresponding with the crus antihelicis inferior; further, the eminentiaconchaiiscrossed horizontally by a groove, the sulcus cruris helicis, and almost vertically by a slight ridge, the ponticulus : the latter indicates the attachment of the M. auricularis pos- terior. In addition to the fissures dcscrilted, others, termed the fissures of Santorini, are found, usually one in the tragus and one or more in the cartilage of the meatus. Ligaments of the Pinna. — The cartilage of the pinna is attached to the skull by two fibrous bands which form its extrinsic ligaments, viz. : an anterior, stretching from the zygoma to the spina helicis and tragus ; and a j^osUrior, passing from the eminentia conchae and upper wall of the meatus to the mastoid M. transversus Ponticulus Cauda helicis J[. obliquus Sulcus antihelicis transversus Siiina helicis Cartilage of tragus Incisura terminalis auris Cartilage of meatus FiC! 580. — Inner Surface of Cartilage of Pinna (oue-liall' natural size). 746 THE OEGANS OF SENSE. process. Small ligamentous bands pass between individual parts of the pinna, and form what are termed its intrinsic ligaments. Muscles of the Pinna (Figs. 579, 580). — The muscles of the pinna are divided into two groups, extrinsic and intrinsic. The extrinsic muscles pass from the pinna to the skull or scalp, and are described in the section on Myology. The intrinsic muscles, on the other hand, are confined to the pinna and are six in number, four on its outer and two on its cranial aspect. (a) On the outer surface (Fig. 579) — 1. M. helicis major, passes upwards from the spina helicis along the ascending part of the helix. 2. M. helicis minor, covers the crus helicis. 3. M. tragicus, quadrangular in shape, consists of fibres running vertically over the greater part of the tragus. Some of its fibres are prolonged upwards to the spina helicis and constitute the m. pyramidalis. 4. M. antitragicus, covers the antitragus and passes obliquely upwards and backwards as far as the antihelix and cauda helicis. (5) On the cranial surface (Fig. 580) — 1. M. transversus auriculae, consists of scattered fibres, which stretch from the eminentia conchae to the convexity of the helix. 2. M. obliquus auriculae (Tod), comprises a few fasciculi, which run obliquely or vertically across the furrow corre- sponding with the crus antihelicis inferior. A small muscle, the stylo-auricularis, sometimes extends from the root of the styloid process to the cartilage of the meatus. Skin of the Pinna. — The skin covering the pinna is thin and smooth, and is prolonged inwards, in the form of a tube, as a lining to the external auditory meatus. It adheres firmly, on the outer surface of the pinna, to the subjacent perichondrium. Hairs are well developed on the tragus and antitragus, and also in the incisura intertragica, forming the barbula Mrci, which guard the entrance to the concha. Soft downy hairs are found over the greater part of the pinna and point towards Darwin's tubercle. Sebaceous glands, present on both surfaces of the pinna, are most numerous in the concha and fossa triangularis. Sweat glands are found on both surfaces, but are much more numerous on the cranial aspect. Vessels of the Pinna. — The arteries for tlie pinna are derived — (a) from the snjserficial tem- poral, which sends two or three branches to the outer sm^face ; and (6) from the j)osterior auricnlar, whicli gives three or four branches to the cranial surface. From the latter two sets of twigs are prolonged to the onter surface, one turning round the free margin of the helix, and the other passing through small fissures in the cartilage. The veins from tlie outer surface open into the superficial temporal vein ; those from the cranial surface chiefly join the posterior auricular vein, but some communicate with the mastoid emissary vein. The lymphatics take three directions, viz. : (a) forwards to the parotid lymphatic glands, and especially to tlie jjreauricular gland in front of the tragus ; (b) downwards to the lymphatic glands which accompany the external jugular vein, and to the glands under the sternomastoid ; and (c) backwards to the mastoid lymphatic glands. Nerves of the Pinna. — The muscles of the pinna are supplied by the seventh cranial nerve. The skin receives its sensory nerves from — (a) the great auricular, which supplies nearly the whole of the cranial surface, and sends filaments in company with the branches of the posterior aiuicular artery to the outer surface ; (6) the auriculo-temj)oral, which suj)plies the tragus and ascending part of the helix ; (c) the small occipital, which sends a branch to the uf)per part of the cranial surface. External Auditory Meatus. The external auditory meatus (meatus acusticus externus) (Figs. 580, 581) is the jjassage leading inwards from the concha as far as the membrana tympani. Its average length, measured from the bottom of the concha, is about one inch (24 mm.), but, if measured from the level of the tragus, nearly one inch and a half (35 mm.) On account of the obliquity of the membrana tympani its anterior and inferior walls are longer than the posterior and superior. The tube consists of two parts, viz. : (a) an external fibro-cartilaginous portion, the pars cartilaginea, having a length of about 8 mm. ; and (&) an internal osseous portion, the pars ossea, uieasuring about 16 mm., and formed by a portion of the temporal bone. The entire meatus forms a somewhat S-shaped bend (Fig. 582), and may be divided into EXTERNAL AUDITORY MEATUS. "47 (1) pars externa, directed inwards, forwards, and slightly mm. ; (2) pars media, inclining inwards and backwards for Pars osspa of external aiuUtoiy im-alu Recessns epityiiipaiiicus Malleus Cochlea Cavuiii tyMipaui Meinbraiia tympani Internal carotid artery three portions, viz. upwards for about about 5 mm. ; (3; pars interna, the longest of the three, passing forwards, in- wards, and slightly downwards. On transverse section the canal is seen to be elliptical, its greatest diameter having an inclina- tion down wards and backwards. Widest at its outer ex- tremity, it becomes somewhat narrower at the inner end of the pars cartila- ginea ; once more expanding in the outer part of the pars ossea, it is again constricted near the inner end of the latter, where its narrowest part, or isthmus, is found at a distance of aljout 19 mm. from the bottom of the concha. The inner extremity of the meatus is nearly circular and is closed by the membrana tympani. Cms antihelicis inferior Cymba concha; Cms helicis Pars cartila;,'iin.-a of external auditory meatus Cavuni conchaj I^ower boundary of incisura intertragica Fig. 581. -Vertical Traxsvehse Section of Ri<;ht Ear : Anterior Half OF Hection, viewed from Ijeliiml (natural size). Bezokl gives the diameters of the meatus as fohows : — At the commencement of the pars cartihiginea. At the end ,, ,, ,, . . . At the comnKnicemeut of the pars ossea At the end ,, m ,, ... Greatest. 9-08 mm. 7 '79 mm. 8*67 mm. 8 'IS mm. Least. 6 "54 mm. 5-99 mm. 6*07 mm. 4-60 mm. Condyle of , jaw- Parotid Ldaml Biiny part of Eustiichian tube Internal eanjtid artery Membrana tympani First turn of I'ljchlea Cavnm tympani Mastoid air-cells The lumen of the pars cartilaginea is influenced by the mo\emeiits of the lower jaw, being increased when tlie jaw is depressed. This can be easily verified by inserting a finger into the meatus, and then al- ternately opening and shutting the mouth. The condyle of the jaw lies in front of the pars ossea, while be- tween the jaw and the pars cartilaginea there intervenes a portion of the parotid, gland. Be- low the meatus is the retro-mandibular part of the parotid gland. Behind the pars ossea, and separated from it bya thin plate of bone, are the mastoid air- cells. Structure of the Meatus. — The cartilage of the meatus, directly continuous with that of the pinna, is folded on itself to form a groove, opening upwards and backwards, the margins of which are connected l)y fibrous tissue. The inner end of the cartilage is firmly fixed to the outer margin of the bony meatus, whilst its outer extremity is continuous with the cartilage of the tragus (vide p. 745). A couple of Antihelix Lateral sinus Fig. 582.— HouizoNTAL Section through Right Ear Section seen from lielow (natural size UrrKR Half ok 748 THE OKGANS OF SENSE. fissures, the fissures of Santorini, exist in the anterior portion of the cartilage of the meatus, and are filled by fibrous tissue. In the outer part of the meatus the cartilage forms about three-fourths of its circumference ; but, on passing inwards, the propor- tion of cartilage to fibrous tissue diminishes, with the result that near the inner end of the pars cartilaginea the cartilage forms merely a part of the anterior and lower boundaries of the canal. The osseous portion (pars ossea) of the meatus is described on p. 117 ; but it raay be well to state here that in the newly-born child it is rejjresented only by an incomplete ring of bone, the annulus tympanicus, together with a small portion of the squamous temporal, which articulates with, and bridges over the interval between, the extremities of the ring superiorly. In the concavity of the annulus is a well-defined groove, the sulcus tympanicus, in which the circumference of the membrana tymjjani is fixed. On the inner aspect of the anterior part of the aimulus, a little below its free extremity, a groove, the sulcus malleolaris, is directed clo-^vnwards and forwards. It transmits the processus gracilis and anterior ligament of the malleus, the tymjjanic artei'y and the chorda tymjoani nerve. It is limited above by a well-marked ridge, the crista spinarum of Henle, which ends in front and behind in a spinous process (spina tympanica anterior and posterior). Below the sulcus malleolaris there is a second, less prominent lidge, the crista tympanica of Gruber, which subsequently unites with a process of the tegmen tym^jani, and so shuts off the canalis musculo-tubarius from the Glaserian fissure. A fibrous plate, the tympanic fibrous plate (Symington), intervenes l^etween the annulus tympanicus and the inner end of the cartilage of the meatus, and into this plate the bony ring extends. The bony outgrowth does not, however, proceed uniformly throughout its circum- ference, l)ut occurs most raj)idly in the anterior and posterior parts of the ring. These outgrowths fuse about the end of the second year of life, so as to surround a foramen in the floor of the meatus (foramen of Huschke), which is usually closed by the fifth year, but persists until adult life in some 19 j^er cent of skulls (Biirkner). The lumen of the meatus in tlie newly -born child is extremely small : its outer part is funnel- shaped ; its inner a mere slit, bounded below by the tympanic fibrous plate and above by the obliquely -placed membrana tympani. The skin which envelopes the pinna lines the entire meatus, and covers also the outer surface of the tympanic membrane. It is thick in the pars cartilaginea, and contains fine hairs and sebaceous glands, the latter extending inwards for some distance along the postero-superior wall of the pars ossea. The sweat glands are enlarged and of a brownish colour ; chey constitute the glandulse ceruminosse and secrete the ear wax or cerumen. Vascular and Nervous Supply of the Meatus. — The meatus receives its blood-supply from the posterior auricular and superficial temjaoral arteries, and also from the deep auricular branch of tlie internal maxillary artery, the last distributing some minute branches to the membrana tympani. The veins open into tlie external jugular and internal maxillary veins, and also into the pterygoid plexus, while the lymphatics have a similar mode of termination to those of the ])inna. Sensory nerves are sujiplied to the meatus by the auriculo-temporal brancli of tlie fifth and by the auiicular branch of the vagus. MIDDLE EAE OE TYMPANIC CAVITY. The tympanic cavity (cavum tympani) is a small air chamber in the temporal bone, which intervenes between the membrana tympani and the outer wall of the internal ear or labyrinth (Figs. 581, 582). Lined by mucous membrane, it contains a chain of ossicles (ossicula auditus) which reaches from its outer to its inner wall, and by means of which the vibrations of the membrana tympani are transmitted across the cavity to the internal ear. Attaclied to the ossicles are several ligaments, together with a pair of small muscles, while certain nerves are either distributed to the cavity or pass through it. The tympanic cavity consists of two portions : (1) The tympanum proper, or atrium, lying immediately to the inner aspect of the membrana tympani ; and (2) tlie recessus epitympanicus, lying above the level of the membrane and containing the greater part of the incus and the upper half of the malleus. Including this recess, the vertical and antero-posterior diameters of the tympanic cavity are rather more thafi half an inch (15 mm.) The distance between its outer and inner walls is about 6 mm. above and 4 mm. below, while at its central part, owing to the bulging of the two walls towards the cavity, it measures only from H- to 2 mm. MIDDLE EAK OK TYMPANIC CAVITY, 749 The tympanic cavity presents for examination a roof, a floor, and four walls, viz. anterior, posterior, external, and internal. The roof (Fig. 5S3) (paries tegmentalis) is formed by a thin plate of l)one, the tegmen tympani,'"constituting a portion of the upper surface of the petrous-temporal. It extends backwards so as to cover in the mastoid antrum, and forwards, to form Antrum niastoideutn Recessus epitympanicu:- Prominentia canalis facialis Fenest Canal for tensor tyn Processus coclilearifo Promontory with grooves for tympanic plexus Osseous part of Eustachian tube Brisble introduced into the foramen for Jacobson's nerve Pyianiid Sinus tympani JIastoid air-cells Fossula rotunda Course of canalis facialis Fig. 583. — Section through Left Temporal Bone, showing inner wall of tympanic canty, etc. the roof of the canal for the tensor tympani muscle. It separates the tympanum and antrum from the cranial cavity, and may contain a few air-cells, whilst occasion- ally it is partly deficient. In the child its outer edge corresponds with the petro- squamous suture. The floor (fundus tympani sen paries jugularis) is narrower than the roof, and consists of a thin plate of bone which separates the cavity from the fossa jugularis ; anteriorly, it extends upwards and becomes continuous with the posterior wall of the carotid canal. The inner orifice for Jacobson's nerve, or tympanic Itranch of the glosso- pharyn- geal, is seen near the junction of the floor with the inner wall. The posterior wall (paries mas- toidea) presents, from above down- wards : (1) A rounded or triangu- lar opening, which extends backwards from the recessus epitympanicus and leads into the mastoid antrum (Fig. 583); the latter "■" - '^*^%^^'.?i*if^ ^'C' willbeagaiureferred Fig. 584.— Left Membran\ Tympani and Recessus Epitympanicus, ^^e^ved to (\) 752) ('2) A ^''°"' within. The head and neck of the malleus have been removed to Vr- _ r \-'J show the membrana flaccida and the tynipano-malleolar folds, x 3. depression, the fossa incudis (Fig. 584), which lodges the extremity of the short process of the incus ; this fossa is situated in the postero-inferinr part of the recessus epitympanicus. (3) A minute conical bony projection, the pyramid or eminentia pyramidalis (Fig. 583), the summit of which is perl'orated by a round aperture for the passage of the tendon of the stapedius muscle. 1'his aperture is continued downwards and backwards as a canal in front of the Fallopian aqueduct, and frequently opens, by a minute orifice, on the Meniliraua Haccida (Shrapnell) Anterior and posterior tynipano-malleolar folds Tenilon of tensor tympani muscle (cut) Manubrium mallei Membrana tensa Sulcus tympanicus 750 THE OEGANS OF SENSE. base of the skull in front of the stylo-mastoid foramen. It communicates with the EaUopian aqueduct by one or two small foramina, through which the vessels and nerve pass to reach the stapedius muscle. A minute spicule of bone often extends from the pyramid to the promontory on the inner wall of the tympanum. (4) A small aperture, the apertura tjonpanica canaliculi chordae (Fig. 584), which is situated immediately internal to the posterior edge of the membrana tympani, nearly on a level with the upper end of the manubrium mallei, and transmits the chorda tympani nerve. (5) A rounded eminence, the prominentia styloidea, is sometimes seen below the last ; it is caused by the upward and forward prolongation of the styloid process. The anterior wall (paries carotica) is narrowed in its transverse diameter by the approximation of the outer and inner boundaries of the cavity, and in its vertical diameter by the descent of the roof and ascent of the carotid canal. It presents (Fig. 583) two parallel canals, one above the other, separated by a thin lamella of bone, the processus cocMeariformis (septum canalis musculo-tubarii). These run forwards on the outer wall of the carotid canal and open in the angle between the petrous and squamous parts of the temporal bone. The higher and smaller of the two is termed the canal for the tensor tympani muscle (semicanalis m. tensoris tympani), and lies immediately below the tegmen tympani. It has a diameter of about 2 mm., and extends on to the inner wall of the tympanic cavity above the anterior part of the fenestra ovalis. The lower and larger canal gradu- ally increases in size from before backwards, and forms the bony part of the Eustachian tube (semicanalis tubse auditivse). It opens on the anterior wall of the tympanic cavity opposite the orifice leading into the mastoid antrum. Below the orifice of the Eustachian tube the anterior part of the tympanic cavity is separated from the ascending portion of the carotid canal by a thin plate of bone in which there are sometimes gaps or deficiencies. It is perforated by a small canal, the carotico-tympanic canal, which transmits the small, deep petrosal nerve from the sympathetic plexus of the carotid artery to the tympanic plexus. The Eustachian tube is described on p. 753. The outer wall (paries membranacea) is formed almost entirely by the mem- brana tympani (Fig. 584), which closes the inner extremity of the external auditory meatus, and is fixed throughout the greater part of its circumference in a groove, the sulcus tympanicus. The bony ring containing this sulcus is deficient superiorly where it exhibits a distinct notch, the notch of Rivinus. On a level with the upper edge of the membrane, and in front of the ring of bone in which it is fixed, is the inner end of the G-laserian fissure, or remnant of the fissura petro-tympanica. This transmits the tympanic branch of the internal maxillary artery, and lodges the processus gracilis and anterior ligament of the malleus. Close to the inner extremity of the fissure is the canal of Huguier, or iter chordae anterius through which the chorda tympani nerve leaves the tympanum. Membrana Tympani. — This is an elliptical disc, its greatest diameter, 9 to 10 mm., being directed from above and behind, downwards and forwards, whilst its least diameter is from 8 to 9 mm. Its antero-inferior portion inclines markedly inwards, and thus the membrane is placed very obliquely, forming an angle of about 55" with the lower and anterior walls of the external auditory meatus ; its antero-inferior part is, therefore, most distant from the outer orifice of the meatus. The membrane is said to be more oblique in cretins and deaf mutes, and more per- pendicular in musicians. The circumference of that portion of the membrane which is fixed in the sulcus tympanicus is consideraljly thickened, and is named the annulus fibro-cartilagineus. It is prolonged i'rom the anterior and posterior extremities of the notch of Kivinus to the short process of the malleus in the form of two ligamentous bands, the anterior and posterior malleolar folds or ligaments (plica malleolaris anterior et posterior). The small triangular portion of the membrane (Fig. 584) situated above these folds is thin and lax, and constitutes the pars flaccida or membrane of Shrapnell; the main portion of the membrane is, on the other hand, tightly stretched and termed the pars tensa. A small orifice, sometimes seen in the pars flaccida, is probably either a pathological condition or has been artificially pro- duced during manipulation. The handle of the malleus is firmly fixed to the inner MIDDLE EAE OE TYMPANIC CAVITY. 751 surface of the membrana tympani and draws its central portion inwards, rendering its outer aspect concave. The deepest part of this concavity corresponds with the lower extremity of the handle of the malleus, and is named the umbo membranse tympanse or navel. The membrane tympani consists of three layers : (1) external, integumentary (stratum cutaneum) ; (2) middle, fibrous (membrana propria) ; (3) internal, mucous (stratum mucosumj. The external layer (stratum cutaneum) is continuous with the integumentary lining of the meatus, and consists of a thin layer of cutis covered by epidermis. The cutis is thickest near the circumference ; the epidermis, on the other hand, is thickest near the centre of the membrane. The middle layer (membrana propria) consists of two sets of filjres : (a) external or radial (stratum radiatum), situated immediately under the integument, and radiating from the handle of the malleus to the annulus fibro-cartilagineus ; (b) internal or circular (stratum circulare), the fibres of which- are numerous near the circumference, but scattered and few in number near the centre of the membrane (Fig. 584). Both radial and circular fibres are absent from the pars flaccida, which is constituted merely by the apposition of the cutaneous and mucous layers. Gruber pointed out that, in addition to the radial and circidar fibres, there exists, next the stratum mucosum, a series of dendritic or branched fibres, which are best developed in the posterior part of the membrane. The internal layer (stratum mucosum) is continuous with the general mucous lining of the tympanum. It is thicker over the upper part of the membrane than near its centre, and is covered by pavement epithelium. Otoscopic Examination of the Tympanic Membrane (Fig. 585).— The membraue, in the living, is of a " pearl-giay " colour, but may jirescnt a reddish or yellowish tinge, depending ujjon the condition of its mucous lining and on the condition of the cutaneous lining of the meatus ; the posterior segment is usually clearer than the anterior. At the antero- superior part, close to its periphery, a whitish point appears as if pro- jecting towards the meatus ; this is Jrcminana flaccida the short process of the malleus. Anterior tympano' ^.i-"- 1 111 J malleolar foW Passing doAATiwards and backwards from this point to the umbo is a ridge caused by the handle of the malleus, the lower extremity of which appears rounded. Two ridges, corresponding with the tym- pano-malleolar folds, extend from the sliort process of the malleus, one forwards and upwai'ds, the other backwards and upwards. Behind, and near the lower extremity of the handle of tlu' malleus, is a reddish or yellowish spot, due to tlie promontory of the inner tympanic wall shining through membrane be very transparent, the long process of the incus may be visible behind the upper part of the handle of tlie malleus, and reaching downwards as far as its middle. From the lower end of the handle of the malleus, the "cone of light" or "luminous triangle" extends do\vn- wards and forwards, its apex being directed towards the handle ; this triangle varies in size in different people. A line prolonging the handle downwards divides the membrane into two parts, wliile another, drawn at right angles to this through the umbo, will subdivide it into four quad- rants, viz. postero-superior, postero-infericr, antero-superior, and antero-inferior ; this subdivision is useful in enabling the otologist to localise and descrilie accurately the seat of lesions in the membrane. Vascular and Nervous Supply of the Membrana Tympani. — The arteries are arranged in two sets, one on the cutaneous and another on the mucous surface. These anastomose by means of small branches which pierce the membrane, especially near its ]>eriphery. The first set is chiefly derived from the cieep auricular branch of the internal maxillary, whilst those on the mucous surface are small and proceed from the tymiianic branch of the internal maxillary, and from the stylo-mast oid liranch of the posterior auricular. The veins from the cutaneous surface open into the external jugular; those from the inner surface partly into the venous plexus on the Eustachian tube, and partly into the latei'al sinus and veins of the dura mater. The outer surface of the membrane receives its nerves from the auriculo-temporal branch of the fifth and from the auricular branch of the vagus ; the inner surface, from the nerve of Jacobson (tympanic branch of the glosso -pharyngeal). The lymphatics, like the blood-vessels, are arranged in two Handle of malleus- Antero-snperior- quadi-ant Antero-inferior quadrant Posterior tympano- nialleular fold Short process of malleus Long process of incus Postero-superior quadrant Postero-infericr quadrant Cone of light Fig. 585. -Left Tympanic Membrane (as viewed froni the external auditory meatus). x -3. If the 752 THE OEGANS OF SENSE. sets, cutaneous and mucous, wliich, liowever, communicate freely witli eacli other. Kessel has described as lymphatics the spaces between the branches of Gruber's dendritic fibres. The inner wall of the tympanic cavity (paries labyrinthica) is formed by the outer surface of the internal ear or labyrinth (Fig. 583). It presents — (1) a rounded eminence, the promontory (promontorium), which is caused by the first coil of the cochlea, and is grooved for the tympanic plexus of nerves. (2) An oval or some- what reniform opening, the fenestra ovalis seu vestibuli, which is situated above and behind the promontory, with its long axis directed from before backwards. It measures 3 mm. in length and Ih mm. from above downwards, and lies at the bottom of a funnel-shaped recess, the fossula fenestrae vestibuli. In the macerated bone it leads into the vestibule of the labyrinth, but is closed in the recent state by the foot of the stapes, surrounded by its ligamentum annulare. (3) An elevation, the prominentia canalis facialis, which is situated above the fenestra ovalis, in the recessus epitympanicus. This indicates the position of the upper part of the aqueduct of Fallopius, which contains the facial nerve and is continued backwards and downwards behind the tympanic cavity, to end at the stylo - mastoid foramen. (4) The processus cochleariformis, or septum canalis musculo-tubarii ; this process extends backwards, above the anterior end of the fenestra ovaUs, where it makes a sharp outward curve, and forms a pulley over which the tendon of the tensor tympani muscle plays. (5) A funnel-shaped recess, the fossula fenestras coclilese, which is situated behind and below the promontory, and almost hidden by its overhanging edge. It leads forwards, upwards, and inwards to an irregularly oval opening, termed the fenestra rotunda seu cocMeae, which in the macerated bone communicates with the cochlea, but in the recent state is closed by a membrane, the membrana tympani secundaria. This membrane appears angularly bent along a line joining its antero-inferior two-thirds with the postero-superior third. It consists of three layers: (a) external, continuous with the mucous lining of the tympanum and containing a network of capillaries; (b) middle, or substantia XDropria, the fibres of which radiate chiefly towards the periphery of the membrane — some branched, dendritic fibres are also present ; (c) internal, continuous with the epithelial linmg of the labyrinth. (6) Between the fenestra ovalis above and the fossula rotunda below is a small circular depression, the sinus tympani, which is perforated by one or two minute foramina for blood-vessels, and indicates the position of the ampuUated extremity of the posterior semicircular canal. Mastoid Anteum and Mastoid Aie-cells. The mastoid antrum (antrum mastoideum seu tympanicum) is seen in the tem- poral bone at birth as a cavity, having a vertical measurement of 7-9 mm. and a transverse of 9-11 mm., and is nearly as large in the newly-born child as in the adult. Koofed in by the tegnien tympani, its floor and inner wall are formed by the petro-mastoid, while externally it is closed by the junction of the thin outer part of the squama with the pars mastoidea. It communicates with the epitympanic recess by a triangular or rounded opening, on the inner wall of which, immediately above and behind the canalis facialis, is a smooth, convex area of bone indicating the position of the ampullated extremities of the superior and external semicircular canals. At birth its outer wall has a thickness of only 1-2 mm., but by the ninth year this has increased to about 10 mm. Coincident with the growth of the mastoid process the mastoid air-cells are developed downwards and backwards as diverticula I'rom the antrum, and present the greatest possible variations in different skulls. They may be large, comparatively lew in number, and involve the whole process, in which case the compact bone which surrounds them is extremely thin, and the innermost cells are only separated by a transparent lamella from the lateral sinus — a lamella which, in some instances, is partly deficient. In other cases the cells may be small and numerous, only invading a portion of the process, the remainder consisting of diploetic tissue. No definite conclusion can be come to as to their condition by external percussion or examination. A solid process is occasionally seen. The air-cells are not limited to the mastoid process, but extend forwards over the roof of the meatus, upwards towards the squama, and inwards towards the EUSTACHIAX TUBE. 753 temporo-occipital suture, whilst in a few cases they are seen to invade the pars jugularis of the occipital bone. They, together with the antrum, are lined by thin mucous membrane continuous with tliat of the tympanic cavity ; the deep surface of the mucous membrane is firmly fixed to the periosteum, while its free surface is covered by a layer of flattened, non-ciliated epithelium. Fascia salpingo. Mucous glands Eustachian Tube. The Eustachian tube (tuba auditiva Eustachii) leads from the tympanic cavity to the naso-pharynx, and transmits air to the former, in order that the pressure on the inner and outer surfaces of the membrana tympaui may be equalised ; it may also serve to convey mucous secretion away from the tympanic cavity. Its outer extremity, the ostium tympanicuin tubse auditivse (Fig. 583), opens into the anterior part of the tympanic cavity below the canal for the tensor tympani muscle. Directed downwards and inwards, the tube ends ou the upper part of the naso- pharynx by a wide orifice, the ostium pharyngeum tubae auditivse (Fig. 555). It measures about an inch and a half (36 mm.) in length, and forms with the horizontal plane an angle of 30° to 40°, with the sagittal plane an angle of about 45", and with the bony part of the external meatus one of 135° to 140°. It consists of two portions : (a) an antero-internal, fibro-cartilaginous part, the pars cartilaginea tubse auditivse, having a length of about one inch ; and (b) a postero-external, osseous part, the pars ossea tubse auditivse, measuring half an inch in length. The two portions are not in the same plane, the cartilaginous part inclining downwards a little more than the osseous portion, and forming with P^'^ryngea it a wide angle. Its lumen is widest at the ostium pharyngeum, narrowest at the junction of the bony and cartilaginous portions, forming here the isthmus, and again expanding towards the tympanic cavity ; hence it presents, on longitudinal section, somewhat the appearance of an hour-glass. The pars ossea occupies the angle between the squamous and petrous parts of ihe temporal bone, and is separated by the processus cochleariformis from the canal containing the tensor tympani muscle, whilst immediately to its inner side is the carotid canal. The pars cartilaginea con- sists partly of cartilage and partly of fibrous membrane. The cartilage (cartilago tubai auditivaj) presents the form of an elongated triangular plate, of which the apex is firmly attached to the inner end of the pars ossea, while the base is free, and forms a projection on the u])per and posterior aspects of the pharyngeal orifice. The upper edge of this cartilaginous plate is bent outwards in the form of a hook, and so produces a i'urrow open below and externally, the furrow being converted into a complete canal by the fibrous part of the tube. On transverse section (Fig. 586) the cartilage presents two laminae continuous with each other superiorly : (a) lamina medialis, broad and thick ; and (&) lamina lateralis, thin and hook-shaped. At the ostium pharyngeum the lamina medialis forms the entire inner wall of the tube, but it gradually diminishes in breadth on approaching the isthmus tubse. Fissures are often seen in the cai*tilage ; sometimes it is completely separated into several pieces, or accessory islands may be observed in the roof, floor, or membranous part. The upper and inner aspects of the cartilage are firmly fixed to the base of the skull, where it lies in a groove, the sulcus tubae auditivse, situated between the great wing of the sphenoid and the petrous-temporal. Extending forwards on to the 52 Fig. .586. — Traxsverse Section of the Cahtilaginocs Part of the Eustachian Tdbe. 754 THE OEGANS OF SENSE. root of the pterygoid process this sulcus ends at a projection, the processus tubarius, on the middle of the internal pterygoid plate. The tensor palati muscle lies to the outer side of the tube and receives some fibres of origin from its lamina lateralis; these fibres constitute the dilator tubse muscle of Eiidinger. To the inner side of the cartilage are found the levator palati and the mucous membrane of the pharynx. The membranous part (lamina membranacea) consists of a strong fibrous membrane, stretching between the two edges of the cartilage, and so com- pleting the under and outer parts of the canal. Thin above, it becomes thickened below- and forms the fascia salpingo -pharyngea of Troltsch, which gives origin to some of the fibres of the tensor palati muscle. Between this fascia and the mucous lining of the tube is a layer of adipose tissue. The pharyngeal orifice of the Eustachian tube (ostium pharyngeum tubie), tri- angular or oval in shape, is situated on the lateral wall of the naso-pharynx, the centre of the opening being on a level with the posterior end of the inferior tur- binated bone. It is bounded above and behind by a pad or cushion produced by the inner end of the cartilage, which here abuts against the mucous membrane. The posterior part of this cushion is very prominent and forms the anterior boundary of the fossa of Rosenmiiller. Prolonged downwards from it is an elevation of the mucous membrane, termed the plica salpingo-pbaryngea, which covers the small salpingo-pharyngeus muscle. From the upper part of the cushion an indis- tinct fold, the plica salpingo-palatina, extends to the palate. The mucous hning of the tube is continuous behind with that of the tympanic cavity, and in front with that of the naso-pharynx. It is thin in the pars ossea, contains few, if any, mucous glands, and is firmly fixed to the bony wall ; whilst in the pars cartilaginea it is loose and thrown into longitudinal folds. Numerous mucous glands open into the tube near its pharyngeal orifice, and here also there exists a considerable amount of adenoid tissue, which constitutes the " tube-tonsil " of Gerlach. This adenoid tissue is continuous with that of the naso-pharynx, and, like it, is especially well developed in children. The lumen of the tube is lined with ciliated columnar epithelium. The tube is opened, during deglutition, by the dilator tubee and salpingo- pharyngeus muscles. The former springs superiorly from the cartilaginous hook of the tube, and blends inferiorly with the tensor palati. When the dilator tubse contracts, the cartilaginous hook and membranous part of the tube are drawn out- wards and forwards. Some anatomists are inclined to the view that the entire tensor palati acts chiefly as a dilator of the tube, and Eiidinger has named it the abductor tubse. The salpingo-pharyngeus muscle draws downwards and back- wards the inner cartilaginous plate, increasing the angle between it and the outer plate. Some difference of opmion exists as to the precise action of the levator palati ; probably it assists in opening the tube. The Eustacliian tube receives its blood-supply from the ascending pharyngeal artery and from tlie middle meningeal and Vidian branches of the internal maxillary artery. Its veins form a network which opens into tlie pterygoid venous plexus. The sensory nerves of the tube are derived from the tympanic plexus and from the pharjaigeal branches of the second division of the fiftli cranial nerve. The tube of the child differs considerably from that of the adult ; its lumen is relatively wider, its direction more horizontal, and its pars ossea relatively shorter. Kunkel states that its j)haryiigeal orifice is below the level of the hard palate in the fcetus ; at birth it is on the same level as the palate, whilst at the fourth year it is 3 to 4 mm., and in the adult 10 mm., above it. The pharyngeal orifice forms a narrow fissure, and its cartilage projects less towards the middle line. Tympanic Ossicles. Tlie tympanic ossicles (ossicula auditus) form an articulated column connect- ing the outer with the inner wall of the tympatiic cavity, and are named, from without inwards, the mallevis or hammer, the incus or anvil, and the stapes or stirrup. The first is attached to the inner surface of the membrana tympani ; the last is fixed within the circumference of the oval fenestra. The malleus (Fig. 587, B, D), the largest of the three ossicles, has a length of 8 to 9 mm., and consists of a head (capitulum mallei), a neck (collum mallei), and a TYMPANIC OSSICLES. 700 handle (manubrium mallei), together with two processes, Adz. : {a) processus longus seu anterior, (b) processus brevis seu lateralis. The head and neck are situated in the epitympanic recess ; the processus brevis and manubrium are fixed to the inner surface of the membrana tympani ; whilst the processus longus is directed forwards towards the Glaserian fissure, to w^hich, in the adult, it is connected by ligamentous A SB C 15 D E Fig. 587. — Tympanic Ossicles ok Left Ear (enlarged about three times). A, lucus, seen from the front ; B, Malleus, viewed from behind ; C, Incus, and D, Malleus, seen from inner aspect ; E, Stapes. T. Body of incus, with articular 7. Processus brevis. 14. Facet for incus surface for bead of malleus. S. Manubrium. 15. Manubrium. 1) Processus lonsus. 9. Body. Iti. Head. 3. Processus lentioularis. 10. Short process. 17. Xeck. 4. Articular surface for incus. 11. Lonsc process. IS. Crus anterius. y. Head. 12. Processus longus. 11'. Crus posterius. U. Xeek. 13. Head. 20. Foot-plate. fibres. The head, somewhat rounded, is smooth and convex above and in front, and presents, on its posterior aspect, a facet for articulation with the body of the incus. This facet is directed obliquely downwards and inwards, and reaches slio-htlv on to its mesial surface. More or less elliptical in form, it is constricted near the niiddle so as to resemble, somewhat, the figure 8 ; an oblique ridge, corresponding with the constriction, divides the facet into two parts — an upper and larger, dii'ected back- Recessus epitympanicus Body nf incus Short process of incus- Ligament of incus Chorda tympanijierve ■ Pyramid, with tendon of stapedius nuiscle issuing from it Superior ligament of malleus Head of malleus Foot of stape: Anterior ligament of malleus Handle of malleus Tensor tymi>ani muscle Processus cochleariformis Osseous part of ustachian tube '^<'' '^ ^^^i^ -i Fig. 58?. — Left :\[kmbuan-a Tymi'am and Chain of Tymtanic Ossicles (seen from inner aspect), x 3. wards, and a lower and lesser, directed inwards. Opposite the lower part of the constriction the inferior edge of the facet is very prominent, and is continued up- wards into the oblique ridge just referred to ; it forms a tooth-like process, the spur or cog-tooth of the malleus. On the back of the head, below this spur, is an oblique crest, the crista mallei, to wdiich is attached the external ligament of the malleus. The neck is tlie slightly constricted portion immediately below the head. Flattened from before backwards, its outer surface is directed towards the membrana fiaccida, 756 THE OEGANS OF SENSE. whilst its inner is crossed by the chorda tympani nerve. The handle is directed downwards, inwards, and backwards from the neck, forming with the long axis of the head an angle, opening inwards, of 126° to 150°. Its upper part is flattened from before backwards, but towards the lower end it is twisted on itself, so that its surfaces look outwards and inwards ; moreover, the lower end is slightly curved, the concavity being directed forwards and outwards. It is fixed, along its entire length, to the membrana propria of the tympanic membrane by its periosteum and by a layer of cartilage (Gruber). This latter intervenes between the handle and the membrane, and must be regarded as a residue of that stage of development when the entire malleus was cartilaginous. On the inner aspect of the handle, near its upper extremity, a slight projection for the attachment of the tendon of the tensor tympani muscle may be seen. The long process is a slender spicule springing from the fore-part of the neck and directed forwards towards the Glaserian fissure. In the foetus it constitutes the longest process of the malleus and is directly continuous with Meckel's cartilage. In the adult it usually assumes the form of a small pro- jection, since its anterior part is represented merely by fibrous tissue. The short process may be looked upon as the upper extremity of the handle projected out- wards ; it is fixed to the upper part of the membrana tympani by the cartilaginous layer already referred to, and to the extremities of the notch of Eivinus by the anterior and posterior malleolar folds. The incus (Fig. 587, A, C) is best likened to a bicuspid tooth with widely divergent fangs. It consists of a body (corpus incudis), a long process (crus longum), and a short process (crus breve) ; the two processes form with each other an angle of 90° to 100°. The body and short process are situated in the epitympanic recess. The body presents a more or less saddle-shaped surface for articvilation with the head of the malleus. This surface is directed forwards, and its lower part is hollowed out for the accommodation of the cog-tooth of the malleus. In front of this hollow it is prominent and spur-like. The short process is thick, triangular in shape, and projects horizontally backwards ; its conical extremity, covered with cartilage, articulates with the fossa incudis in the postero-inferior part of the epitympanic recess. The long process projects, almost perpendicularly, downwards from the body into the tympanic cavity, where it lies parallel with, but 1^ mm. behind and internal to, the handle of the malleus. Its lower end is bent inwards and narrowed to form a short neck, on the inner extremity of which is a small knob of bone, the processus lenticularis, for articulation with the head of the stapes. Until the sixth month of foetal life this process exists as a separate ossicle, termed the OS orbiculare. The stapes (Fig. 587, E) presents a head (capitulum stapedis), a neck (coUum stapedis), two crura (crus anterius et posterius), and a base or foot-plate (basis stapedis). The head, directed outwards, is concave externally for articulation with the processus lenticularis of the incus. The neck is the slightly constricted part immediately internal to the head, and from it the two crura spring; the tendon of the stapedius muscle is inserted into the posterior aspect of the neck. The anterior crus is shorter and less curved than the posterior. Diverging from each other, the crura are directed inwards and are attached — one near the anterior, the other near the posterior end of the foot-plate. The foot-plate almost completely fills the oval fenestra, and, like it, is somewhat oval or reniforni, its anterior end being the more pointed. In the recent condition a membrane fills the arch formed by the crura and the foot-plate, the crura being grooved for its reception. In the child the crura of the stapes are less curved than in the adult, and the opening bounded by them and the foot-plate is nearly triangular. Articulations of the Tympanic Ossicles. — The joint between the head of the malleus and the body of the incus (articulatio incudomalleolaris) is diarthrodial, and may be described as one of reciprocal reception. It is surrounded by a capsular ligament, from the inner surface of which a wedge-shaped meniscus projects into the joint cavity and incompletely divides it. The articulation of the processus lenti- cularis and the capitulum stapedis (articulatio incudostapedia) is of the nature of an enarthrosis and is surrounded Ijy a capsular ligament. An interarticular carti- lage has been described as occurring in this joint, while some observers deny the TYMPANIC OSSICLES. 757 presence of a synovial cavity and regard the articulation as a syndesmosis, the articular surfaces being held together merely hj fibrous tissue. Ligaments binding the Ossicles to the Walls of the Tympanic Cavity (lig. ossiculorum auditus). — The malleus is attached to the walls of tlie tympanum by three ligaments (Fig. 588), viz. anterior, superior, and external. The anterior liga- ment (lig. mallei anterius) consists of two portions : (a) the band of Meckel, which is attached to the base of the processus longus, and passes forwards through the Glaserian fissure to reach the spine of the sphenoid ; it represents the remnant of a portion of Meckel's cartilage, and was formerly described as the laxator tympani muscle ; (b) a firm bundle of fibres, the Ii[/. mallei anterius of HdmhoUz, which extends from the spina tympanica posterior at the anterior boundary of the notch of Piivinus to the anterior aspect of the malleus, above the base of the processus longus. The superior ligament (lig. mallei superius) extends, almost vertically, from the head of the malleus to the roof of the epitympanic recess. The external ligament (lig. mallei laterale) is short and fan-shaped ; its fibres converge from the posterior half of the notch of Piivinus to the crista mallei. The posterior part of this ligament is strong and constitutes the ligamentum mallei posticum of Helm- holtz. It forms, together with the ligamentum mallei anterius, the axis around which the malleus rotates, and the two constitute what Helmholtz has termed the " axis-ligament " of the malleus. The posterior extremity of the crus breve of the incus is tipped with cartilage and fixed by means of a Hgameut, the ligamentum incudis posterius (Fig. 588), to the fossa incudis. Some observers describe this as a diarthrodial joint. A superior ligament, the ligamentum incudis superius, is sometimes present, but consists mainly of a fold of mucous membrane. The vestibular surface and the circumference of the foot of the stapes are covered by hyaline cartilage, and a similar layer lines the opening of the fenestra ovalis ; that encircling the base of the stapes is joined to that which lines the fenestra by a dense ring of elastic fibres, named the ligamentum annulare baseos stapedis. The posterior fibres of this annular hgament are thicker and shorter than the anterior, and thus the anterior end of the foot- plate is free to make greater excursions, during the movements of the Ijone, than the posterior. Development of the Tympanic Ossicles. — It is generally maintained that the malleus and incus are developed from the upper end of Meckel's cartilage, and that the stapes ai'ises fi'om the mesoblast in the region of the fenestra ovalis where it is developed around a small artery, the stapedial artery, which atrophies in man, but persists in many nummials. On the other hand, Gadow (Fhil. Trans., London, vol. clxxix.) says "the whole system of the one to four elements of the middle ear, which have all the same function, is to be looked upon as one organ, of one common origin, viz. a modification of the hyo- mandibula, the proximal paramere of the second visceral arch."' Muscles of the Tympanic Cavity. — These are two in number, viz. m. tensor tympani and m. stapedius. The m. tensor tympani is the larger, and takes origin from the roof of the carti- laginous part of the Eustachian tube and from the adjacent part of the great wing of the sphenoid. It also receives some fibres from the bony canal in which it lies, and ends in a tendon which bends outwards, nearly at a right angle to the belly of the muscle, round the pulley-like, posterior extremity of the processus cochleariformis. Passing across the cavity of the tympanum this tendon is inserted into the inner edge and anterior surface of the manubrium mallei, near its upper end. AVhen the muscle contracts it draws inwards the handle of the malleus, and so renders tense the membrana tympani ; it probably also slightly rotates the malleus around its long axis. It receives its nerve from the motor division of the fifth cranial nerve through the otic ganglion. The m. stapedius arises within the pyramid, and from the canal which prolongs the hollow of the pyramid downwards. Its tendon emerges from the apex of the pyramid and is inserted into the posterior surface of the neck of the stapes. On contraction it draws back the head of the stapes, and so tilts the anterior end of the foot-plate outwards towards the tympanic cavity and the posterior end inwards 758 THE OEGANS OF SENSE. towards the labyrinth, thus rendering tense the ligamentum annulare — the outward movement of the anterior end of the foot-plate being greater than the inward move- ment of its posterior end. The muscle is supplied by the facial nerve. Movements of the Tympanic Ossicles. — The manubrium mallei follows all the movements of the membraua tympani, while the malleus and incus move together around an axis extending forwards through the short process of the incus and the anterior ligament of the malleus. When the membraua tympani moves inwards it carries with it the handle of the malleus, and the incus, moving inwards at the same time, forces the foot of the stapes towards the labyrinth. This inward movement is communicated to the fluid (perilymph) in the labyrinth, and causes an outward bulging of the secondary tympanic membrane, which closes the fenestra rotunda. These movements are reversed when the membraua tympani is relaxed, unless the outward movement of the membrane be excessive. In such a condition the incus does not follow the full outward movement of the malleus, but merely glides on this bone at the incudo-malleolar joint, and thus the forcible dragging of the foot of the stapes out of the fenestra ovalis is prevented. The cog-tooth arrangement, already described, on the head of the malleus and body of the incus, caiises the incudo-malleolar joint to become locked during the inward movements of the handle of the malleus, the joint becoming unlocked during its outward movements. Mucous Lining of the Tympanic Cavity (tunica mucosa tympanica). — This is continuous, through the Eustachian tube, with that of the naso-pharynx ; it also extends backwards and lines the mastoid antrum and air-cells. Thin, transparent, and closely united with the subjacent periosteum, it covers the inner aspect of the membrana tympani and is reflected over the ossicles and their ligaments. It also supplies sheaths for the tendons of the tensor tympani and stapedius muscles, and forms the following mucous folds, viz. : (a) one from the roof of the epitympanic recess to the head of the malleus and body of the incus ; (b) one enveloping the chorda tympani nerve and long process of the incus ; (c) two extending from the short process of the malleus — one to the anterior, the other to the posterior margin of the notch of Eivinus. A recess, the pouch of Prussak, is situated between the membrana flaccida and the neck of the malleus. Communicating behind with the tympanic cavity, this pouch may serve as a reservoir to confine pus or other fluid, since its opening into the tympanum is above the level of its floor, a condition analogous to the opening from tlie antrum of Highmore into the nasal cavity. The fold of mucous membrane which extends downwards to envelop the chorda tympani nerve gives rise to two pouches, one in front of, and the other behind, the handle of the malleus ; these are named the anterior and posterior recesses of Troltsch. The epithelium which lines the mucous membrane is flattened over the membrana tympani, promontory, and ossicles, but ciliated and columnar over the greater portion of the rest of the cavity. The chorda tympani branch of the facial nerve passes from behind, upwards, and forwards through the tympanic cavity. Its course is described on p. 687. Vessels and Nerves of tlie Tympanic Cavity. — The arteries which supply the tympanic cavity are : (1) The tympanic artery, a branch of internal maxillary, which reaches the cavity by way of the Glaserian fissure. (2) Tlie stylo-mastoid branch of posterior auricular, which passes through the stylo-mastoid foramen and aqueduct of Fallopius ; it supplies Ijranches to the mastoid antrum and air-cells, to the stapedius nuiscle, to the floor and inner wall of the tympanic cavity, and forms an anastomotic circle, around the membrana tympani, with the tympanic artery. (3) The middle meningeal artery sends a branch to the tensor tympani muscle, and, after entering the skull, gives off its petrosal artery, which is conducted to the tympanum along the hiatus Fallopii ; some twigs from the posterior division of the middle meningeal reach the antrum and epitympanic recess through the petro-squamous fissure. (4) The internal carotid artery, in its passage through the canal in the temporal bone, gives oft' one or two tympanic twigs, while (5) a branch from the ascending pharyngeal accompanies the nerve of Jacobson. The veins drain tlieir contents into the pterygoid plexus, the middle meningeal vein, and superior petrosal sinus. The nerves wliich supply the muscles of the tympanic cavity have already been referred to (pp. 757, 758;. The mucous memljrane receives its nerves from the tymj^anic plexus, which is described on p. 690. Early Condition of Tympanic Cavity.— During the greater part of intrauterine existence the tympanic cavity is almost completely filled by a soft, reddish, jelly-like embryonic tissue. The narrow, slit-like space is lined by epithelium, which is ciliated over the promontory, but squamous elsewhere. Towards the end of fcetal life the gelatinous tissue becomes thinned and the cavity correspondingly enlarged. At birth it is filled with fluid which l^ecomes absorbed., coincident with the passage of air from the naso-pharynx through the Eustachian tube. OSSEOUS LABYEINTH. 759 INTEENAL EAR The innermost, and, at the same time, the essential part of the organ of hearing is situated in the substance of the petrous-temporal Ijone, and consists of two sets of structures, viz. : (1) a series of cavities hollowed out of the bone and constituting the bony labyrinth Tlaliyrinthus osseus) ; these cavities are continuous with each Superior semicircular can;il Ampulla of superior semicircular canal Caiialis facial! Recessus ellipticus Crista vestibuli Recessus .splufricus Cochloa Fenestra rotunda Fenestra ovalis Ampulla of posterior senijl circular canal | Ampulla of external semi- circvilar canal I External semicircular canal Fig. .589. — Left Bony Labykinth (viewed from the miter aspect). Posterior semi- circular canal Crus commune Scala tym}iani Lamina spiralis ossta Scala vestibuli Opening of aqueductus cochlese Oijening of crus comnnine Fenestra rotunda i Opening of aqueduclus vestibu Rece.ssus coclilearis Fic. 590. -Intrhior of Left Bony L.^byuinth (viewed from outer aspect). other, and are named from before Ijackwards the cochlea, vestibule, and semicircular canals (Figs. 589, 590) ; (2) a complex arrangement of membranous channels (Fig. 592), situated within, but not nearly tilling, the bony labyrinth and forming the membranous labyrinth (labyrinthus mcmbranaceus). These channels are named the ductus cochlearis, utricle, saccule, and membranous semicircular canals ; the utricle and saccule are lodged within the bony vestiluile. OSSEOUS LABYEINTH. Vestibule. — The vestibule forms the central portion of the osseous labyrinth, and communicates behind with the semicircular canals and in front with the cochlea. It is somewhat ovoid in shape, its long axis being directed forwards and outwards. It measures about 6 mm. antero-posteriorly, 4-5 mm. from roof to floor, and about 3 mm. from without inwards. Its outer wall is directed towards the tympanic cavity, and in it is seen the fenestra ovalis, wdiicli, in the recent state, is closed by the foot of the stapes. Its inner wall corresponds with the bottom of the internal auditory meatus, and presents, at its antero-inferior part, a roimded depression, the recessus sphsericus, which lodges the saccule. This recess is perforated by some twelve or fifteen small foramina, which constitute the macula cribrosa media, and transmit the filaments of the auditory nerve for the supply of the saccule. The recessus sphtericus is limited above and behind by an ol)lique ridge, tlie crista vestibuli, the anterior extremity of which is triangular in shape and named the pyramid (pyramis vestibuli). Posteriorly this crista divides into two limbs, between which is a small depression, the recessus cochlearis of Eeichert, perforated by some eight small fora- mina, which give passage to the nervous filaments for the supply of the posterior extremity of the ductus cochlearis. Above and behind the crista vestilmli, in tlie roof and inner wall of the vestibule, is an oval depression, tlie recessus ellipticus, which lodges the utricle. The pyramid and adjacent part of the recessus elliiiticus are perforated by some 25-30 small apertures, wliich constitute tlie macula cribrosa superior seu major. The foramina in the pyramid transmit the nerves to the utricle ; those in the recessus, the nerves to the ampullary ends of the superior and external semicircular canals. Behind and below the recessus ellipticus is a furrow, gradually deepening to form a canal, the aqueductus vestibuli, which passes backwards through tlie petrous bone, and opens, as a .slii-liko fi.s.surc. about midway between the internal auditorv meatus and the ejroove lor the lateral sinus. This 760 THE OEGANS OF SENSE. aqueduct measures 8-10 mm. in length, and gives passage to the ductus endo- Ijmphaticus and a small vein. The posterior part of the vestibule receives the five rounded apertures of the bony semicircular canals ; its anterior part leads, by an elhptical opening, into the scala vestibuli of the cochlea. This opening is bounded inferiorly by a thin osseous lamella, the lamina spiralis ossea, which springs from the floor of the vestibule immediately to the outer side of the recessus sphsericus, and forms, in the cochlea, the bony part of the septum between the scala tympani below and the scala vestibuli above. Erom the anterior part of the floor of the vestibule a narrow cleft, the fissura vestibuli, extends forwards into the bony canal of the cochlea. It is bounded internally by the lamina spiralis ossea just referred to, and externally by a second, smaller lamina, the lamina spiralis secundaria, which projects inwards from the outer wall of the cochlea. These two lamina are continuous with each other around the posterior extremity of the fissure. Semicircular Canals (canales semicirculares ossei). — The semicircular canals (Eigs. 589, 590), three in number, are situated above and behind the vestibule. They are distinguished from each other by their position, and are named superior, posterior, and external. They open into the vestibule by five apertures, since the inner extremity of the superior and the upper extremity of the posterior join to form a common canal or cms commune. Differing slightly in length, each forms about two-thirds of a circle, one extremity of which is dilated and termed the ampulla (ampulla ossea). Somewhat compressed laterally, their greatest internal diameter is from 1 to 1-5 mm., whilst the diameter of the ampulla is about 2 mm. The superior semicircular canal (canalis semicircularis superior), 15-20 mm. in length, is vertical and placed transversely to the long axis of the petrous bone. Its convexity is directed upwards, and its position is indicated on the anterior sur- face of the petrous-temporal by an eminence. Its ampuUated end (ampulla ossea superior) is anterior and external, and opens into the vestibule immediately above that of the external canal. Its opposite extremity joins the non-ampuUated end of the posterior canal to form the crus commune, which is about 4 mm. in length, and opens into the upper and inner part of the vestibule. The posterior semicircular canal (canalis semicircularis posterior) is the longest of the three and measures from 18-22 mm. Its ampullary end (ampulla ossea posterior) is placed inferiorly, and opens into the lower and back part of the vestibule, where may be seen some six or eight small apertures, forming the macula cribrosa inferior, for the trans- mission of the nerves to this ampulla. Its upper extremity ends in the crus commune. The external canal (canalis semicircularis lateralis) is the shortest. It measures from 12 to 15 mm., and arches nearly horizontally outwards. Of its two extremities the external is ampullated (ampulla ossea lateralis), and opens into the vestibule immediately above the fenestra ovalis and in close relationship to the ampullary end of the superior canal. Although, the three canals are generally regarded as oi^ening into the vestibule by five orifices, some observers incline to the view that the ainpnllary ends of the suiaerior and external canals form a common orifice, and that, consequently, there are onlj'- four openings for the three canals. Crum Brown {Jo urn. Anat. and Physiol.^ London, vol. viii.) pointed out "that the exterior canal of one ear is very nearly in the same plane as that of the other ; while the sujserior canal of one ear is nearly parallel to the posterior canal of the other." Cochlea.^ — When freed from its surroundings the cochlea assumes the form of a short cone (Fig. 591); the central part of its base (basis cochleae) corresponds with the bottom of the internal auditory meatus, whilst its apex or cupola is directed forwards and outwards, and comes into close relation with the canal for the tensor tympani muscle. It measures about 9 mm. across the base and about 5 mm. from base to apex, and consists of a spirally arranged tube, which forms from 2\ to 2 1 coils around a central pillar termed the modiolus. The length of the tube is from 28 to 30 mm., and its diameter, near the base of the cochlea, 2 mm. Its coils are distinguished by the terms basal, central, and apical ; the first, or basal coil, gives rise to the promontory on the inner wall of the tympanum. ^ 111 the following description the cochlea is supposed to l)e placed on its base. OSSEOUS LABYKINTH. 761 The modiolus is about 3 mm. in height, and diminishes rapidly in diameter from base to apex, while its tapered extremity fails to reach the cupola by a distance of 1 mm. Its base (Ijasis modioli) corresponds with the area cochleae on the fundus of the internal auditory meatus, and exhibits the tractus spiralis foraminosus, which transmits the nerves for the basal and central coils of the cochlea and the foramen centrale, which gives passage to the nerves for the apical coil. The foramina of tlie tr ictus spiralis foraminosus traverse the modiolus, at first parallel to its long axis, but, after a varying distance, they bend outwards to reach the attached edge of the lamina spiralis ossea, where they Ijecome expanded and form by their apposition a spiral canal, the canalis spiralis modioli of Rosenthal, which lodges the ganglion of Corti, or ganglion spirale cochleae. From this spiral canal numerous small foramina, for the transmission of vessels and nerves, pass outwards to the free edge of the lamina spiralis. The lamina spiralis ossea, a thin, fiat shelf of bone, winds round the modiolus like the tliread of a screw, and, projecting about half-way into the cochiear tulie, incompletely divides it into two passages, of which the upper is named the scala vestibuli ; the lower, the scala tympani. The lamina spiralis ossea commences at the floor of the vestibule, near the fenestra rotunda, and ends close to the apex of the c(jchlea in a sickle-shaped process, the hamulus, whicli assists to form an Cupola Hamulus Section tlirough promontory- Lamina spiralis ossea secundaria' Fissura vestibuli Lamina spiralis ossea Recessus cochlearis of vestibule Fig. 591. Canalis centralis Canalis sjiiralis modioli Modiolus Scala ve.stibuli Lamina spiralis ossea Scala tympani Tractus spiralis foraminosus Internal auditory meatus -Section' of BoNt Cochlea. aperture named the helicotrema. In the basil coil the upper surface of the spiral lamina forms almost a right angle with the modiolus, but the angle l)ecomes more and more acute on ascending the tube. In the lower half of the liasil coil a second smaller bony plate, the lamina spiralis secundaria, projects inwards from the outer wall of the cochlea towards the lamina spiralis ossea, without, however, reaching it. If viewed from the vestibule the slit-like fissura vestibuli, already referred to (p. 760), is seen between the two osseous spiral laminae. A membrane, the mem- brana basilaris, stretches from the free edge of the lamina spiralis ossea to the outer wall of the cochlea, and completes the septum between the scala vestibuli and scala tympani, but the two scalas communicate with each other through the opening of the helicotrema at the apex of the cochlea. The scala tympani begins at the fenestra rotunda, through which, in the macerated bone, it communicates with the tympanic cavity ; in the recent condition the fenestra is closed by the secondary tympanic membrane (vidle p. 752). At the commencement of the scala tympani a crest, termed the crista semilunaris, stretches from the attached margin of the lamina spiralis ossea towards tlic m'ifice of the fenestra rotunda. Close to tliis crest is seen the inner orifice of the aqueductus cochleae, a caual measuring from 10 to 12 mm. in length, and opening on the under aspect of the petrous bone internal to the fossa jugularis. Through it there is established a communication between the scala tympani and the subarachnoid space, and through it, also, a small vein passes to join the inferior petrosal sinus. The scala vestibuli, the higher of the two passages, begins in the vestibule ; its diameter in the basal coil is less than that of the scala tym]iani, but in the upper coils it exceeds that of the latter. Internal Auditory Meatus. — It is convenient, at this stage, to study the 762 THE OEGANS OF SENSE. fundus of the internal auditory meatus, which has been referred to as forming the inner wall of the vestibule and the bas3 of the modiolus. It is divided by a trans- verse ridge, the crista transversa, into two parts — an upper or fossula superior and a lower or fossula inferior. The anterior part of the fossula superior is termed the area facialis and exhibits a single large opening, the commencement of the aque- duct of Fallopius, for the transmission of the facial nerve. Its posterior part is named the area vestibularis superior, and is perforated by the nerves for utricle and ampullas of the superior and external semicircular canals. The anterior part of the fossula inferior is termed the area cochleae, and consists of the canalis centralis and the surrounding tractus spiralis foraminosus, for the passage of the nerves to the cochlea. Behind the area coohlese, and separated from it by a ridge, is the area vestibularis inferior, which transmits the nerves to the saccule, whilst at the posterior part of the fossula inferior is seen a single foramen, the foramen singulare, which gives passage to the nerves for the ampulla of the posterior semicircular canal. MEMBKANOUS LABYEINTH. The membranous labyrinth (labyrinthus membranaceus) assumes, more or less closely (Fig. 592), the form of the bony labyrinth in which it is situated, but does not nearly fill it. It contains a fluid termed endolympb, while the interval between it and the bony labyrinth is named the perilymphatic space, and is occupied by a fluid termed perilymph. The perilymphatic space in the vestibule measures about 3 mm. from without inwards, and about 3 '5 mm. from before backwards. It is continuous behind with the Recessus utriculi ■i i, j.- „ , r j-I, perilymphatic space of the semicircular canals, and opens in front into the scala vestibuli. At the apex of the cochlea it is continuous through the helicotrema with the scala tympani, which is shut off from the tympanum by the secondary tympanic membrane. It is also prolonged into the aqueduetus cochleae, at the extremity of which it communicates with the subarachnoid space. The membranous semicircular canals and the membranous canal of the cochlea follow the course of their bony tubes and lie along the inner aspect of their outer walls. The bony vestibule, on the other hand, contains two chief membranous structures, the utricle and saccule. The former receives the extremities of the membranous semicircular canals, whilst the latter communicates with the membranous canal of the cochlea. Moreover, the cavities of the utricle and saccule are indirectly connected, and thus all parts of the membranous labyrinth communicate with each other, and the contained endolymph is free to move from one portion to another. The vestibule, also, contains the ductus endolymphaticus and the com- mencement of the ductus cochlearis. The utricle (utriculus), the larger of the two sacs (Fig. 592), occupies the postero-superior portion of the bony vestibule. Its highest part, or recessus utriculi, lies in the recessus ellipticus and receives the ampullae of the superior and external membranous semicircular canals. Its central part receives on its lateral aspect the non-ainpullated end of the external canal, and is prolonged upwards and backwards as tlie sinus superior, into which the crus commune of the superior and posterior membranous canals open. Tlie ampulla of the. posterior membranous canal opens into its lower and inner part, or sinus inferior. The floor and anterior wall of the recessus utriculi are thickened to form tlie macula acustica utriculi, to which are distributed the utricular fibres of the auditory nerve. Whitish in colour, and of an oval or nearly rhombic shape, this macula measures 3 mm. in length and 2*3 mm. in its greatest breadth. Saccule Ductus cochlearis Ductus reuniens Ductus endolymphaticus Ampulla of posterior canal Saccus endolymphaticus Fig. 592 Ampulla of superior semicircular canal Ampulla of external canal Sinus superior Ductus utriculosaccularis Sinus inferior -Diagrammatic Representation of the Different Parts on the Membranous Labyrinth. MEMBRANOUS LABYRINTH. V63 The saccule (sacculus) occupies tlie recessus spluerieus, in the lower and fore-part of the vestibule (Fig. 590). Smaller than the utricle, it is of an oval shape and measures 3 mm. in its longest, and about 2 mm. in its shortest diameter. It presents anteriorly an oval, whitish thickening, the macula acustica sacculi. This has a breadth of about 1"5 mm., and to it are distributed the saccular fibres of the auditory nerve. The superior extremity of the saccule is directed upwards and backwards, and forms the sinus utricularis sacculi, which abuts against, but does not fuse with, the wall of the utricle. From the lower part of the saccule a short canal, the ductus reuniens of Hensen, opens into the ductus cochlearis, a short distance in front of its vestibular or blind extremity. A second small channel, the ductus endol3miphaticus, is continued irom the posterior part of the saccide, and, passing between the utricle and the inner wall of the ^•estibule, is joined by a small canal, the ductus utriculosaccularis, which arises from the inner aspect of the utricle. It then enters and traverses the aqueductus vestibuli and ends, under the dura mater on the posterior surface of the petrous bone, in a dilated blind extremity, termed the recessus Cotugnii, or saccus endolymphaticus ; this, according to Riidinger, is perforated by minute foramina, through which the endolymph may pass into the meningeal lymphatics. The vesti])ule also contains the blind extremity (ceecum vestibulare) of the ductus cochlearis, which lies immediately below the saccule in the recessus cochlearis of Reichert ; from here it passes forwards into tlie spiral tube of the cochlea. The walls of the utricle and saccule are composed of connective tissue which blends, along their attached surfaces, with the periosteal lining of the vestibule. It is modified internally to form a homogeneous membrana propria, which is covered by a layer of pavement epithelium and is thickened at the maculae acustica-. Towards the periphery of the macuhe the epithelium is cubical, while on them it is columnar. The structure of the maculae in the utricle and saccule is practically the same ; two kinds of cells are found, viz. (a) supporting cells, and (h) hair cells. The supporting cells are some- what fusiform, each con- taining, near its middle, a nucleus. Their branched, deep extremi- ties are attached to the membrana propria ; their free ends lie between the hair cells and form a thin inner limiting cuticle. The hair cells are flask- shaped and do not reach the membrana propria, but end in rounded ex- tremities which he be- tween the supporting cells. Each contains, at its deepest part, a large nucleus, the rest of the cell being granular and pigmented. From the free end of each there projects a stiff, hair-like process, which, on the application of reagents, sphts into several finer filaments. The nerve-fibres pierce the membrana propria, and end in arliorisations around tln> deep extremities of the hair cells. A collection of small, rhombic crystals of carbonate of hme, termed otoconia, adheres to each of the maculaj. Wall of bony canal Lumen of mem brauous canal Fig. 593. -Tkansveuse Section of Human Semicircdlar Canal (Riidinger). 764 THE OEGANS OF SENSE. The membranous semicircular canals (ductus semicirculares) are elliptical on transverse section (Fig. 593), and are attached to the greater circumference of the bony tubes. The peripheral portion of the ellipse is fixed to the periosteal lining of the bony canal, whilst the opposite part is free, except that it is connected by irregular bands, the ligamenta labyrintlii canaliculorum, which pass through the peri- lymphatic space to the bony wall. Like the bony canals, each of the membranous canals is dilated at one extremity into an ampulla (ampulla membranacea), which is especially developed towards the concave aspect of the tube. While the mem- branous ampullsB nearly fill the corresponding portions of the bony tubes, the cahbre of the remaining parts of the membranous canals is only equal to about one-fourth of that of the osseous canals. Each membranous canal consists of three layers, viz. : (a) an outer fibrous stratum which contains blood-vessels, together with some pigment, and fixes the tube to the bony wall ; (6) an intermediate, transparent tunica propria, presenting a number of papilliform elevations which project towards the lumen. The fibrous layer and tunica propria are thinnest along the attached surface of the tube, and in this region also the papilliform elevations are absent ; (c) an internal epithelial layer, composed of pavement cells. In the ampullae the tunica propria is much thickened, and projects into the cavity as a transverse elevation, termed the septum transversum, which, when seen from above, is somewhat fiddle-shaped; its most prominent part is covered by auditory epithelium forming the crista acustica, at each end of which is a half-moon-shaped border of small columnar cells, the planum semilunatum. The cells covering the crista acustica consist of supporting cells and hair cells, and are similar in their arrangement to those in the maculse of the utricle and saccule. The hairs of the hair cells are, however, considerably longer, and project as far as the middle of the ampullary lumen. In fresh specimens they appear to end free, but in hardened preparations are seen to terminate in a soft, clear, dome-like structure, the cupola terminalis, which is striated, the striee converg- ing towards its concavity. The nerves form arborisations around the bases of the hair cells. The membranous cochlea (ductus cochlearis or scala media) commences in the SCALA VESTIBULI Reissner's membrane Membrana tectoria Sulcus spiralis iuternus Limbus laminae spiralis Coclilcar nerve libres iniiei' liair cell Outer hair cells Heiubrana basilaris / SCALA TYMPANI / Fig. 594. — Section across the Ductus Cochlearis (Retzius). recessus cochlearis of the vestibule by a blind extremity (crecum vestibulare), close to which it receives the ductus reuniens of Hensen (vide p. 763). It forms a spirally arranged canal inside the bony cochlea, and ends at the apex of the latter in a second blind extremity, the lagena, or caecum cupulare, which is fixed to the cupola and partly bounds the helicotrema. As already stated (vide p. 761), the mem- brana basilaris extends from the free edge of the lamina spiralis ossea to the outer MEMBEANOUS LABYEINTH. 765 Outer attaclmient of Reissncr's membrane wall of the cochlea. A second, more delicate membrane, the membrane of Eeissner, or memhrana, vestibularis, stretches from the thickened periosteum covering the upper surface of the lamina spiralis ossea to the outer cochlear wall, some little distance above the external attachment of the membrana basilaris. A canal is thus enclosed between the underlying scala tympani and the overlying scala vestibuli, and con- stitutes the membranoiis cochlea or ductus cochlearis. Triangular on transverse section, it possesses a roof, an outer wall, and a Hoor, and is lined throughout with epithelium and filled with endolymph. On its floor the epithelium is greatly modified, and here are found the endings of the cochlear division of the auditory nerve. The roof or vestibular wall of the ductus cochlearis is formed by the mem- brane of Eeissner, which consists of a delicate, nearly homogeneous membrane, covered on its two surfaces by a layer of epithelium. Its entire thickness is about 3 //. The outer wall of the ductus cochlearis (Fig. 595) consists of the periosteal lining of the bony cochlea, which, liowever, is much thickened and greatly modified to form what is termed the ligamentum spirale cochleae. Occupying the whole outer wall, this ligament projects inwards interiorly as a triangular prominence, the crista basilaris, to wliicli the outer edge of the membrana basilaris is attached. The fibres of the membrane radiate into the lio-ameut in the form of a series of bundles analogous to the ligamentum pecfcinatum iridis. In the upper part of the ligamentum spirale the periosteum is of a reddish yellow colour, and contains, immediately under its epithelial lining, numerous small blood-vessels and capillary loops, forming the stria vascularis. The lower limit of this stria is bounded by a prominence, the prominentia spiralis, in which is seen a vessel, tlie vas prominens, and between this prominence and the crista basilaris is a concavity, the sulcus spiralis externus. The height of the outer wall diminishes towards the apex of the cochlea. • The floor or tympanal wall of the ductus cochlearis is formed by the peri- osteum covering that portion of the lamina spiralis ossea which is situated to the outer side of Eeissner's memljrane, and by the membrana basilaris, which stretches from the free edge of the lamina spiralis ossea to the crista basilaris. On the inner part of the membrana basilaris the complicated structure termed the organ of Corti is situated. The lamina spiralis ossea consists of two plates of bone, between which are placed the canals for the branches of the cochlear nerve. On the upper plate the periosteum is thickened and modified to form the limbus laminse spiralis, the outer extrenuty of which forms a C- shaped concavity, the sulcus spiralis internus. The portions of the lim])us wliich project outwards, above and below this concavity, are termed respectively the labium vestibulare and labium tsrmpanicum. The latter is perforated by some 4000 small apertures, the foramina nervosa, or habenula perforata, for the transmission of the cochlear nerves. Externally it becomes continuous with the Fig. .595. — Transverse Section through Octer Wall of Ductus Cochlearis (Schwalbe). 766 THE OEGANS OF SENSE. membrana basilaris. The upper surface of the labium vestibulare presents a number of furrows crossing each other nearly at right angles, and intersecting a series of elevations which, at the free margin of the labium, form a row of tooth-like structures, some 7000 in number, the auditory teeth of Huschke. Covering the limbus is a layer of apparently squamous epithelium ; the deeper protoplasmic portions of the cells, however, with their contained nuclei, fill up the intervals between the elevations and auditory teeth. This layer of epithelium is continuous with that covering the under surface of Eeissner's membrane and with that which lines the sulcus spiralis internus. Membrana Basilaris. — The inner part of this membrane is thin, and supports the organ of Corti ; it is named the zona arcuata, and reaches as far as the foot- plate of the outer rod of Corti. Its outer part, extending from the foot-plate of the outer rod of Corti to the crista basilaris, is thicker and distinctly striated, and is termed the zona pectinata. The substantia propria of the membrane is almost homogeneous, but exhibits, in its deeper part, numerous fibres. These fibres are most distinct in the zona pectinata, and number, according to Retzius, about 24,000. Covering the under surface of the membrana basilaris is a layer of con- nective tissue, which contains, in its inner part, small blood-vessels, one of which, larger than the rest, lies below the tunnel of Corti and is named the vas spirale. The width of the membrana basilaris increases from 210 /x in the basil coil to 360 /x in the apical coil. Organ of Corti (Fig- 596). — Placed upon the inner portion of the membrana basilaris, the organ of Corti consists of an epithelial eminence which extends along the entire length of the ductus cochlearis, and comprises the following structures, viz. : (1) Corti's rods or pillars, (2) hair cells (inner and outer), (3) supporting cells of Deiters, (4) the cells of Hensen and Claudius, (5) the lamina reticularis, and (6) a cuticular membrane, the membrana tectoria. The rods of Corti form two rows, inner and outer, of stiff, pillar-like structures, and each rod presents a base or foot-plate, an intermediate elongated portion, and an upper end or head. The bases of the two rows are planted on the membrana basilaris some little distance apart. The intermediate portions incline towards each other and the heads Outer rod of Corti Inner rod of Corti Inner hair cell Hensen's stripe Membrana tectoria Sulcus spiralis Limbus lamina; internus spiralis Outer hair cells Cells of Hensen Membrana basilaris Cells of Cliudius CQ Space of Nuel Tunnel of Oorti Fig. 596. — Transverse Section of Corti's Organ from the Central Coil of Cochlea (Retzius). come into contact, so that, between the two rows above and the membrana basilaris below, there is enclosed a triangular tunnel, the tunnel of Corti ; this tunnel increases both in height and width on passing towards the apex of the cochlea. The inner rods number nearly 6000, and the head of each resembles somewhat the upper end of the ulna, pre- senting a deep concavity, externally, for the reception of a corresponding convexity on the head of the outer rod. The part of the head which overhangs this concavity is prolonged outwai-ds, under the name of the head-plate, and overlaps the head of the outer rod. The expanded bases of the inner rods are situated on the innermost portion of the membrana basilaris, immediately to the outer side of the foramina nervosa of the labium tymjjanicum. The intermediate parts of the inner rods are sinuously curved, and form, with the MEMBEANOUS LABYKINTH. 767 membrana loasilaris, an angle of about Q0\ The outer rods number about 4000, and are longer than the inner, especially in the upper part of the cochlea. They are more inclined towards the membrana basilaris, and form with it an angle of about 40\ The head of each is convex internally, to fit the concavity on the head of the inner rod, and is prolonged outwards as a plate, tlie phalangeal process, which becomes connected with the lamina reticvilaris. In the head is an oval body which has an affinity for certain reagents. The main part of each i-od consists of a nearly homogeneous material, which is finely striated. At the bases of the rods, on the side next the tunnel, is a nucleated mass of protoplasm which reaches as far as the heads of the rods, and covers also the greater part of the tunnel floor. This may be regarded as the undifferentiated part of the cell from ■which the rod was developed. Slit-like intervals, for the transmission of nerves, exist between the intermediate portions of adjacent rods. Hair Cells. — These, like Corti's rods, form two sets, inner and outer. The former consists of a single row l^'ing immediately internal to the inner rods- — the latter of three, oi", it may be, four rows placed to the outer side of the external rods. The inner hair cells are about 3500 in number, and have a greater diameter than the inner rods, and so each is suppoi'ted by more than one rod. Somewhat oval in shape, their free extremities are surmounted by about twenty fine hair-like processes, arranged in the form of a crescent, with its concavity directed inwai'ds. The deep end of the cell is rounded, and contains a large nucleus. It reaches only about half-way down the rod, and in contact with it are the arborisations of the nerve terminations. To the inner side of this row of hair cells are two or three rows of elongated columnar cells, which act as supporting cells, and are continuous with the low columnar cells lining the sulcus spiralis intei'nus. The outer hair cells number about 12,000, and form three rows in the basal coil and four rows in the upper two coils, although in the higher coils the rows are not so regularly arranged. Their rounded free extremities support some twenty hairlets arranged in the form of a crescent, opening inwards. Their deep extremities reach about half-way to the membi'ana basilaris, and are in contact with the nerve arborisations. Alternating with the rows of the outer hair cells are the rows of Deiters' supporting cells, the lower extremities of which are expanded on the membrana basilaris, whilst their upper ends are tapered ; tiie nucleus is placed near the middle of each cell, and, in addition, each cell contains a bright, thread-like structure called the supporting fibre. This fibre is attached by a club-shaped liase to the membrana basilaris, and expands, at the free end of the cell, to form a phalangeal process of the membrana reticularis. The cells of Hensen, or outer supporting cells, consist of about half a dozen rows, immediately outside Deiters' cells, and form a well-marked elevation on the floor of the ductus cochlearis. Their deep extremities are narrow and attached to the membrana basilaris, while their free ends ai'e expanded ; each cell contains a distinct nucleus and some pigment gi-anules. The columnar cells, situated externally to the cells of Hensen, cover the outer part of the zona pectinata, and are named the cells of Claudius. A space, the space of Nuel, exists between the outer rods of Corti and the neighbouring row of hair cells. It connuunicates internally with Corti's tunnel, and extends outwards between tlie outer hair cells as fai- as Henscn's cells. The lamina reticularis is a thin cuticular sti-ucture which lies over Corti's organ, and extends from the heads of the outer rods as far as Hensen's cells, where it ends in a row of quadrilateral areas which form its outer border. ( )n looking at it from above it is seen to consist of two or three x'ows of structures, named phalanges, which are elongated cuticular plates resembling in shape the digital phalanges. The innermost row is formed by the phalangeal processes of the heads of the outer row of Corti's rods ; the succeeding row, or rows, represent tlie expanded upper ends of Deiters' supporting cells. The number of rows of phalanges, therefore, varies with the number of rows of outer hair cells and the alternating cells of Deiters. The phalanges separate the free ends of the hair cells from each other, since these are seen to occupy tlie somewhat circular apertures between their constricted middle portions. The membrana tectoria (Fig. 596) is an elastic membrane overlying the sulcus spiralis internus and the orgiui of (.-orti. Attached, by its inner end, to the linibus laminiX* spiralis, near the lower edge of Reissner's membrane, it reaches outwards as far as the outer row of hair cells. Its inner portion is thin and overlies the auditory teeth of Huschke. Its outer part is, at first, much thickened, but becomes attenuated near its external border, which, accoi'ding to Retzius, is attached to the outer row of Deiters' cells. Its lower edge presents a firm, homogeneous border, and opposite the inner row of hair cells contains a clear, spirally arranged band, named Hensen's stripe. Probably the membrana tectoria acts as a damper comparable to the otoconia in the utricle and saccule. ^68 THE ORGANS OF SENSE. Auditory Nerve (Fig. 597). — The auditory nerve consists of two main parts, the ramus vestibularis and the ramus cochlearis ; as the former traverses the internal auditory meatus it presents a gangiiform swelling, the ganglion of Scarpa. The Sinus superior Ampulla of external canal Ampulla of superior canal Macula acustica iitriculi Macula acustica sacculi Ramus vestibularis Nei\us facialis Ramus cochleaus Superior semicircular canal External semicircular canal Posterior semicircular canal Ligamentum spirale Membrana basilar is Branches of ramus coch- learis to Gorti's organ Branch of ramus cochlearis to ampulla of posterior canal Ampulla of posterior canal Sinus inferior Ductus endolymphatious Spiral fibres Ganglion spirale Nerve-tibres which pass out between the two layers of the lamina spiralis ossea Ductus reuniens Fig. 597. — Membranous Labyrinth of a Five Months'^Fcetus, viewed from its postero-mesial asi^ect (Retzius). ramus vestibularis divides into three branches, the filaments of which pass through the foramina in the area vestibularis superior, and are distributed to the macula acustica utriculi and the ampullae of the superior and external semicircular canals. The ramus cochlearis gives off a branch to the macula acustica sacculi and another to the ampulla of the posterior semicircular canal. The former exhibits a gangii- form swelling beyond which its filaments pass through the foramina in the area vestibularis inferior ; the latter is trans- mitted through the foramen singulare, and in this part of its course the nerve possesses two gangiiform enlargements. The remainder of the ramus cochlearis is distributed to the hair cells of Corti's organ, the branches for the basal and middle coils entering the foramina in the tractus spiralis foraminosus, those for the apical coil passing up through the canalis centralis of the modiolus. Extending upwards, in the bony canals of the modiolus, the nerve-fibres radiate outwards between the lamellae of the lamina spiralis ossea. Contained in the spiral canal of the modiolus, near the attached margin of the lamina, is a ganglion which winds spirally round the modiolus, and is named the ganglion spirale or ganglion of Corti (Fig. 598). It consists of bipolar nerve-cells, and each nerve fibre, probably, has its continuity interrupted by one of these cells. Beyond the ganglion spirale the nerve-fibres extend outwards, at first in bundles, and then in a more or less continuous sheet, from the outer edge of which they are again collected into bundles, which pass through the foramina nervosa of the labium tympanicum. Beyond this they appear as naked axis -cylinders, and, turning in a spiral manner (inner or first spiral fasciculus), send fibrillse towards the Fio. .598. — Part of Cochlear Nerve, highly magnified (Henle). DEVELOPMENT OF LABYEINTH. 769 inner row of hair cells. Other fibrils pass outwards between the inner rods and form a second spiral fasciculus in Corti's tunnel, from which fibrils extend outwards across the tunnel, and, passing between the outer rods, enter Nuel's space. They form a spiral fasciculus on the inner aspect of each row of Deiters' cells, and from these fasciculi tibrillte. pass towards the bases of the outer hair cells. Scliwalbe divides tlie auditory nerve into three portions, vi/. : (1) ramus utriculo-ampullaris, corresponding witii the ramus vestibularis already described ; (2) ramus sacculo-ampullaris, lur the saccule and posterior ampulla ; and (3) ramus cochlearis, for the ductus cochlearis. Vessels of the Internal Ear. — Tlie auditory artery, a Ijranch of the basilar, enters the internal auditory meatus and divides into vestibular and cochlear branches. The vestibular branch sup- jjlies the soft tissues in tlie vestibule and semicircular canals, each canal receiving two arteries, which, starting from opposite extremities of the canal, anastomose on the summit of the arch. The cochlear branch divides into numerous twigs, which enter the foramina in the tractus spiralis foraminosus, and run outwards in the lamina spiralis ossea to reach the soft sti-nctures ; the largest of these arteries runs in the canalis centralis. The stylo-mastoid artery also supplies some minute branches to the cochlea. Siebenmann describes the auditory artery as dividing into three branches, viz. : (1) anterior vestibular, (2) cochlear proper, and (3) vestibulo-cochlear. The veins from the cochlea and vestibule unite at the bottom of the meatus with the veins from the semiidrcular canals to form the internal auditory vein, which may either open into the posterior part of the inferior jjetrosal sinus or into the lateral sinus. Small veins also pass through the aqueductus cochleae and aqueductus vestibuli, the former opening into the inferior petrosal sinus or into the internal jugular vein, the latter into the sujjerior petrosal sinus. /Auditory pit Development of Labyrinth. The epithelial lining of the labyrinth is derived from an invagination of the cephalic ectoderm, termed the auditory pit, which appears opposite the hind brain immediately above the first visceral cleft. The mouth of the pit is closed by the growing- together of its margins, and it then assumes the form of a hollow vesicle, the otic |^^^ vesicle, lined by ^JI'Mv->? Fi( otic vesicle Rudiment of ductus coclilearib -Sections through the Region of the Hind Brain ok i'lETAi. (to iUustrate the development of the labyriuthiue epithelium). epithelium ; the vesicle sinks into the subjacent mesoderm, and is met by the auditory nerve growing out from the neural crest. The vesi- cle soon becomes pear-shaped ; its upper tapering part is named the recessus laby - rintM, and forms the future ductus endolymphaticus. About the fifth week, the lower part of the vesicle is prolonged forwards as a tubular elongation, the futui'c ductus cochlearis. This is at first straight, but soon becomes curved on itself, so that at the twelfth week all three coils are ditl'ercntiatcd. From the upper part of the vesicle the semicircular canals are developed, and appear as hollow, disc-like evaginations, the central parts of the two walls of which coalesce and disappear, leaving only tlie peripheral rings or canals. The three canals are free about the beginning of the second month, and are developed in the following order, viz. : superior, posterior, and external. The intermediate part of the otic vesicle reiiresents the vestibule, and is divided by a constriction into an anterior part, the saccule, communi- cating with the ductus cochlearis, and a posterior portion, the utricle, receiving the ex- tremities of the semicircular canals. The constriction extends for some distance into 53 III A the ectoderm is invaginated to form the auditory pit ; in B the auditory pit is closed and detached from the ectoderm, forming the otic vesicle ; while C sliows a further stage in the development of the vesicle. " 770 THE OEGANS OF SENSE. Recessus labyrinth] the ductus endolymphaticus, and thus the utricle and saccule are only indirectly connected by a Y-shaped tube. Another constriction makes its appearance between the saccule and the ductus cochlearis near its commencement, and forms the canalis reunions of Hensen. The epithelial lining is at first columnar, but becomes cubical throughout the whole labyrinth, except opposite the terminations of the auditory nerve, where it forms the columnar epi- thelium of the maculge of the utricle and saccule, of the cristas ampullge, and of the organ of Corti. On the floor of the ductus cochlearis two ridges appear, of which the inner forms the limbus laminfe spiralis, whilst the cells of the outer become modified to form the rods of Corti, the hair cells, and the supporting cells of Deiters and Hensen. The mesoderm surrounding the otic vesicle is differentiated into : (1) a fibrous layer, the wall of the membranous labyrinth ; (2) a cartilaginous external capsule, the future petrous bone ; and (3) an intervening layer of gelatinous tissue, which is ultimately absorbed to form the peri- lymphatic space between the bony and membranous labyrinths. Cochlear part Saccule A, Left lab3'rintli of a human embryo of about four weeks ; B, Left Lab3'riuth of a human embryo of about five weeks (from W. His, jun. ) OEUANS OF TASTE. The peripheral organs of the sense of taste (organon gustus) consist of groups of modified epithelial cells, termed the taste buds, which are found on certain parts of the tongue and its immediate neighbourhood. Taste buds are present in large numbers - around the circumference of the papillfe vallatse, while some are also found on their opposing walls (Fig. 601). They I 'i \^\ ,:i ^'''% J -6 ■■m-m'f'm^imv>m B A A, Section through a papilla vallata of human tongue. 1. Papilla. 2. Vallum 3. Taste buds. 4. PapillK'. 5. Taste buds. il. Duct of serous gland. Fig. 601. B, Section through a part of the papilla foliata of a rabbit. are very numerous over the fimljrite linguse, which correspond with the papillse foliatse of the tongue of the rabbit, and are also found over the posterior part and sides of the tongue, either on the papillae fungiformes or throughout the stratified epithelium. They exist, also, on the buccal surface of the soft palate and on the posterior aspect of the epiglottis. OEGANS OF TASTE. 771 Structure of Taste Buds (Fig. 602). — They are oval or flask - shaped, and occupy nests in the stratified epithelium of the regions mentioned. The deep extremity of each is somewhat expanded and rests upon the corium ; the free end is perforated by a minute pore, termed the gustatory pore. They consist of modified epithelial cells, which are grouped under the two varieties of— (a) supporting cells, Gustatory hairs SupiK)rting ymmM •'«« - ftS/|%9' Fk;. 602. A, Three-quarter surface view of taste bud from the papilla foliata.of a rabbit (highly magnitied). B, Vertical .section of taste bud from the papilla foliata of a ralibit (highly magnitied). and (6) gustatory cells (Fig. 603). The supporting cells are elongated, nucleated spindles, and are mostly arranged like cask staves to form the outer envelope of the bud. Some are, however, found in the interior of the bud, amongst the gustatory cells. The latter occupy the centre of the bud, and present a nucleated cell-body, which is prolonged into a peripheral and a central process. The peripheral process is rod-like and almost hyaline, and terminates at the gustatory pore in a hair- like filament, gustatory hair. The central process passes inwards towards the deep extremity of the bud, where it ends free, eitlier in a single varicose filament or by becoming bifurcated or branched. Nerves of Taste. — The nerve which supplies the taste buds over the anterior part of the tongue is probably the chorda tympani, which, although a branch of the facial nerve, is generally regarded as being continuous with the pars intermedia of Wrisberg ; that for the posterior part is the glosso- pharyngeal. The internal laryngeal branch of the vagus nerve supplies the epiglottis, together with a small area of the tongue immediately in front of it. The nerve fi])rils, having lost their medullary slieaths, ramify partly between the gustatory cells and partly amongst the cells of the bud capsule. It was formerly thought that the nerve-fibrils were directly continuous with the central ends of the gustatory cells, but this view is no longer entertained. The ducts of Ebner's glands open into the bottom of the valleys surrounding the papillffi vallate, and the serous-like secretion of these glands probably washes the free hair-like extremities of the gustatory cells, and so renders them ready to be stimulated by successive substances. It should be added that there is a close association between the senses of smell and taste. This can be best appreciated by considering the defective taste perceptions resulting from inflammatory conditions of the nasal mucous membrane, or the common practice of holding the nose in order to minimise the taste of nauseous drugs. Fiti. 603. -Isolated Cells from Taste Bud OF Rabbit (Eugclmaun). Supporting cells. h, Gustatory cells. 772 THE SKIN OR INTEGUMENT. THE SKIN OR INTEGUMENT. OEGANS OF TOUCH. Duct of sweat gland' Papillae of ^ corium ' Sebaceous glands Erector muscle I The Skin. The skin (integumentum commune) covers the body, and is continuous, at the orifices on its surface, with the mucous lining of its alimentary and other canals. It contains the peripheral terminations of the sensory nerves, and serves as an organ of protection to the deeper tissues. It is the chief factor in the regulation of the body temperature, and by means of the sweat and sebaceous glands, which open on its free surface, constitutes an important excretory structure. Its superficial layers are modified to form appendages in the shape of hairs and nails. The superficial area of the skin averages about one and a half square metres, whilst its thickness varies from 0'5 to 4 mm., beincT greatest on the palms of the hands and soles of the feet, and on the back of the neck and shoulders, and least on the eyelids and penis. It is very elastic and resistant, and its colour, determined partly by its own pigment and partly by that of the blood, is deeper on exposed parts and in the regions of the geni- tals, axillpe, and mammary areolae, than elsewhere, colour also varies with race and age, the different races of the world being roughly classified, according to the colour of their skin, into the three groups of white, yellow, and black. Pinkish in colour in childhood, the skin assumes a yellowish tinge in old age, while in certain diseases {e.g. icterus and melasma Addisonii) it undergoes marked alteration. The surface of the skin is perforated by the hair follicles and by the ducts of the sweat and sebaceous glands, and on the palms, soles, and flexor aspect of the digits it presents numerous permanent ridges (cristse cutis) which correspond with rows of underlying papilke. Over the terminal phalanges these ridges form distinctive patterns, which are retained from youth to old age, and are utilised for purposes of identification. Folds of the skin (retinacula cutis) are seen in the neighbourhood of the joints, and it can be thrown into wrinkles by the contraction of the sub- cutaneous muscles, where these exist. Over the greater part of the body it is freely Oblique section throug a Pacinian corpuscle Fig. 604. Papilla of hair -Vertical Section of the Skin (schematic). The STRUCTURE OF THE SKIK 773 movable ; but on the scalp and outer surface of the pinna, as well as on the palms and soles, it is bound down to the subjacent tissues. The skin consists of two strata, viz. : a deep, termed the dermis or corium, and a superficial, named the epidermis (Fig. 604). The corium gives elasticity and sensibility to the skin, and consists essentially of a felted interlacement of connective tissue and elastic fibres. In its deeper part, or stratum reticulare, the fibrous bundles are coarse and form an open network, in the meshes of which are vessels, ner^■es, pellets of fat, hair follicles, and glands. This reticular stratum passes, as a rule, without any line of demarcation, hito the panniculus adiposus or subcutaneous fatty tissue, but in some parts it rests upon a layer of striped or unstriped muscular fibres — the latter in the case of the scrotum. In the superficial layer, or stratum papillare, of the corium, the connective tissue- bundles are finer and form a close network. Projecting from its free surface are numerous finger -like, single, or branched elevations, termed papillae (Fig. 605), the free ends of which are received into corresponding depres- sions on the under sur- face of the epidermis. These papilke vary in size, being small on the eyelids, but large on the palms and soles, where they may attain a length of 225 II; and produce the permanent cvirved ridges already alluded to. Each ridge usually contains two rows of papilke, between which the ducts of the sweat glands pass to reach the surface. The papilke consist of fine connective tissue and mil l^^s.:f. ."Stratum luciduiii Stratum jrianulosum Stratum ''erminativum Fig. 605. Blood-vessels and nerves -Veutical Section of Epidermis and Papillae ok Cokium (liighly magnitieil). elastic fibres, mostly arranged parallel to the long axis of the papilla. The majority contain capillary loops, but some the terminations of nerves. The superficial surface of the corium is covered by a thin, homogeneous basement membrane. The epidermis covers the corium ; it is non-vascular and consists of stratified epithelium. Its superficial layers are modified to form the stratum comeum, or homy- layer of the skin, which may be separated by maceration or blistering from the deejier, softer portion, or stratum mucosum (Malpighi). The epidermis consists from witljin outwards of tlie following five strata (Fig. G0~>) : — 1. The basilar layer, or stratum germinativum, which comprises a single stratum of nucleated colunmar cells planted by denticulated extremities on the basement membrane of the corium. 2. The stratum mucosum, which consists of six or eight layers of polygonal, nucleated "prickle" or " finger" cells, the processes of which join those of adjacent cells. Between the cells of this layer are minute channels, in which leucocytes or pigment granules may be seen. The cells of the stratum mucosum are charac- terised by the presence of numerous epidermic fibrils, which are coloured violet by hsematoxylin and red by carmine. These fibrils are unaffected by boiling, but swell up under the action of acids and alkalies, and form the filaments of union 53 a 774 THE SKIN OE INTEGUMENT. between adjacent cells. On account of their presence, L. Eanvier (Com^Jt. rend., Paris, Jan. 1899, tome cxxviii.) has named this layer the stratum filamentosum. The dark colour of the negro's skin is caused by the presence of numerous pigment granules in the deeper layers of this stratum ; the pigment — of which melctnin forms an important constituent — is absent from the more superficial layers of the epidermis. 3. The stratum granulosum, which comprises two or three layers of horizontally arranged, flattened cells, scattered around the nuclei of which are elliptical or spherical granules of eleidin, a substance staining deeply with carmine, and probably representing an intermediate stage between the protoplasm of the deeper cells and the keratin of the superficial layers. 4. The stratum lucidum, which is an apparently homogeneous layer, but is in reality made up of several strata of flattened or irregular squames, some of which may contain eleidin granules. 5. The stratum corneum, which comprises several layers of flattened non- nucleated squames, the more superficial of which are from time to time removed by friction, and may be seen partly detached on the surface. Eanvier named these partly detached squames the stratum disjunctum. The deeper cells contain granules of a fatty material which has the consistency and plasticity of beeswax, and stains with osraic acid. The peripheral parts of the cells consist of keratin, a highly resistant substance which is unaffected by mineral acids, and is indigestible in pepsin-hydrochloric acid. Macleod {Proceedings of the Anatomical Society of Great Britain and Ireland, May, 1902) found that after digestion of the stratum corneum in the latter fluid the cells "presented the appearance of a fine network, like a honeycomb, the contents of which had completely gone. The periphery of the cell alone resisted the action of the pepsin and had become keratinised." L. Eanvier {op. cit.) has pointed out that the stratum lucidum is really double, and has named the deeper of its two layers tlie stratum intermedium ; this he describes as consisting of two or three layers of clear cells with atroj)hied nuclei, while in the cell-walls the epidermic fibrils " are rolled w]) like the threads of a cocoon." Eegeneration of the epidermis is generally regarded as taking place by cell j^roliferation in the stratum germinativum, tlie young cells gradually passing tlirough the polyhedral and granular stages, and ultimately becoming the horny squames of the stratum corneum. Professor Thomson of Oxford considers that, although this view meets all the requirements in white i-aces, a difhculty is met witli if it is applied to coloured races, where most pigment is found in the deeper cells of the stratum mucosum, while the suiJerficial layers are free from colour. If the deeper cells advance to the surface, it is only reasonable to suppose that they would carry their pigment with them. This theory, therefore, necessitates a satisfactory explanation of the disappearance of the jaigment from the suiierficial layers. He suggests that possibly the growth of tlie epidermis is analogous to the growth of the cork cambium of j^lants, the stratum mucosum corresponding to the green cells, and the stratum corneum to the corky laj^er of the cambium. If such be the case — and he insists that there is much evidence in supjiort of it — the deeper cells would advance inwards towards the corium, and the superficial cells would grow outwards towards the surface. Under this view the active layers would be the stratum granulosum and stratum lucidum, and by it many of the difficulties would be explained, including tlie mysterious dis- apjiearance of the pigment from the superficial laj^ers ; it would also aft'ord a reasonable explanation of how it happens that, in old age, a negro's hair becomes white, while his skin retains its blackness. Vessels and Nerves of the Skin. — The arteries form a plexus in the sub- cutaneous tissue from which branches extend into the corium, where they supply the hair follicles and glands, and form a second plexus vinder the papilhe, to which small loops are given. The veins and lymphatics commence in the papilhe, and, after forming a su])papillary plexus, open into their respective subcutaneous vessels. The nerves of the skin vary in number in different parts of the body, being extremely numerous where the sense of touch is acute, e.g. on the palmar aspect of the terminal phalanges, while in the skin of the back, where the sensibility is less, they are fewer in number. Tliey form a plexus in the corium, and either terminate amongst the cells of the epidermis, or in special end organs named tactile corpuscles. Those ending in the epidermis form a rich subepithelial plexus, from which delicate fibrils pass between the cells of the rete mucosum, where they become beaded, and end in rounded swellings on flattened discs — the tactile discs of Eanvier. APPENDAGES OF THE SKIX. 775 The special end organs are of three chief varieties (Fig. 606) : (a) Corpuscula bulboidea (Krausii), fouml on the Hps, glans peuis, etc., and consisting of a connective tissue capsule enclosing a core of elongated and polygonal cells, amongst which the axis-cylinder of the nerve fibril becomes branched and its ramifications end in clubbed extremities, (h) Corpuscula lamellosa (Vateri and Pacini). These are small, oval bodies, with a long diameter of 2 to 3 mm., and are found in the subcutaneous tissue attached to the nerve trunks. They are very numerous on the digital nerves, but are present in many other situations, e.g. in the mesentery. Each possesses a sheath, consisting of a number of concentrically arranged connective tissue lamelLe, covered by endotlielium continuous with the perineurium. The central part of each corpuscle consists of a soft, almost homogeneous core. The nerve-fibre passes along the centre of the stalk of the corpuscle, and, reaching the core, loses its medullar}- sheath, whilst its axis- cylinder passes into tlie core and becomes branched near its distal extremity, the branches ending in bulbous enlargements, (c) Corpuscula tactus (Meis- sneri). These are very numerous on the flexor aspect of the hands and feet, and especially so in the skin over the terminal phalanges; but they also exist in other parts of the body. They occupy certain of thepapilltBof thecorium, and are oval in shape, their long diameter in the hand being from 110/x to IGO/j.. They consist of a connective tissue capsule, which sends imperfect septa into the interior of the corpuscle. One or two nerve-fibres perforate the capsule, either directly or after taking a spiral course around it ; and losing, as a general rule, their medullary sheath, their axis-cylinders break up into fibrils, which end in gloluilar or discoid enlargements. Ruffiiii lias descriljed a siiecial variety of terminal corpuscle in the Iiunian finger. They are termed Ruffini's endings, and are situated either at the junction of tlie corium and subcutaneous tissue, or are emlif(l(U'd in tlie latter. Of an oval sliape, they consist of a coimective capsule witliin Avliicli tlie axis-i yliiider divides into varicose filaments, and these terminate in small knohs. Fig. 606. — Tactile Corpuscles. A, End bulb (Krause). B, Corpuscle of Pacini \ , cl n ■ \ ,,' ri 1 f Ar ■ ■ (alter Kanvier). C, Corpuscle of Meissner / ^ 1 ArPENDAGES OF THE SkIN. The appendages of the skin comprise the nails, the hairs, the sebaceous, and the sudoriparous or sweat glands. Nails. — The nails or ungues (Figs. 607, 608) are epidernuil structures, and, in man, represent the hoofs and claws of the lower animals. The root of the nail, or radix unguis, is liidden from view and embedded in a fold of skin ; the body (corpus unguis), or uncovered part, rests on the corium and ends in a free edge (^margo liber). The greater part of the lateral margins is overlapped by a diqtlicature of skin, termed the nail-wall or vallum unguis. The nails are pink in colour, with the exception of a small semilunar area near the root, which is more opaque than the rest, and is named the lunula. The lunuhe diminish in size from the thumb towards tlie little finger, while the thickness of the nail diminishes towards its root and lateral margins. The corium under tbe nail is iiighly vascular and sensitive, and presents, especially under the anterior part of tlie body, numerous longitudin- ally arranged papillae The part of the corium under the body is termed the nail bed; that under the root, the nail matrix. Tlie deep part of the nail consists of 776 THE SKIN OE INTEGUMENT. the stratum germinativum and stratum mucosum, while its superficial horny porbion is constituted by a greatly thickened stratum lucidum, and consists of nucleated, keratinised squames. The stratum corneum is represented by the thin cuticular fold overlapping the lunula, and termed the eponychium, while the stratum granu- losum can only be traced as far forwards as the nail root. Homy pait of nail stratum mucosuiu Xail bed Vallum Fig. 607. — Transverse Section of a Nail. Hairs. — Hairs (pili) are well developed on the scalp, pubes, and margins of the e}'ehds, in the axilla, the vestibule of the nose, and at the entrance to the concha, and also on the face of the male. Those on the genitals and face appear about puberty. Eudimentary over the greater part of the body, they are entirely absent on the flexor surfaces of the hands and feet, over the dorsal aspect of the terminal Eponychium Horny part of nail Stratum. mucosum Xail matrix Fig. 608. — Longitudinal Section through Root of Nail. phalanges, the glans penis, the inner surface of the prepuce, and inner aspect of the labia. Marked variations, individual and racial, exist as to the colour of the hair, and also as to the manner of its growth ; hence the terms straight, curly, woolly, etc. are used to designate it. Straight hairs are coarser than curly ones, and have, moreover, a circular or oval outhne on transverse section, curly hairs being flat and riband-like. The root of the hair (radix pili) is embedded in a depression of the skin, termed the hair follicle (Fig. 604) ; while the free portion is named the stem or shaft, and consists from witliout inwards of three parts, viz. cuticle, cortex, and medulla. The cuticle is formed by a layer of imbricated scales which overlap one another from below upwards. The cortex consists of longitudinally arranged fibres made up of elongated, closely applied, fusiform cells, which contain pigment and sometimes air spaces, the latter especially in white hairs. The medulla, absent from the fine hairs of the body generally and from the hairs of young children, forms a central core, which appears black by transmitted, and white by reflected light, and is composed of polyhedral nucleated cells containing pigment, fat granules, and air spaces. The hair follicle (folliculus pili) consists of an oblique or curved — the latter in APPENDAGES OF THE SKIX. 777 curly hairs — invagination of the epidermis and corium, which in the case of large hairs extends into the subcutaneous tissue (Fig. 604) ; some little distance below its orifice the ducts of the sebaceous glands open into it. The portion of the follicle derived from the corium (dermic coat) consists of a fibrous sheath of external longi- tudinal and internal circular connective tissue fibres, the latter being lined by a hyaline layer directly continuous with the basement memljrane of tlie corium. The parts of the follicle derived from the epidermis are named the inner and outer root sheaths. Below the orifices of the sebaceous gland ducts the outer root slieath is formed by the stratum germinativum and stratum mucosum, while above them all the epidermal strata contribute to it. The inner root sheath surrounds the cuticle of the hair, and consists from without inwards of — (a) Henle's layer, a single stratum of nucleated, cubical cells ; (5) Huxley's layer, a single or double layer of polyhedral nucleated cells ; and (c) a delicate cuticle, consisting of a single layer of flattened Fibrous sheatli )^ Deriveii from / Basement membrane j" the corium — -^/ Stratum germinativum ^ ()„ter root Stratum mucosum /slieath ■n'^ ^^ Heule's layer "v ^.V^'-^'^'^ TT 1 • 1 I Inner root -<^V>-<^ Hu.xley s layer L ,^^y^ V-'i ^--Cuticle I Section of hair Fig. 609.— Traxsversk Section of Hair Follicle with contained Hair (higlilj' maguitied). imbricated cells, with atrophied nuclei. The bottom of the hair follicle is indented by a vascular papilla (papilla pili), derived from the corium and capped by the bulb (bulbus pili) or expanded part of the hair root. The cells of the bulb are continuous with those of the outer root sheath, and form the diftereiit parts of the hair, as well as its inner root sheath. The vessels form capillary loops in the papilla of the hair, and send twigs into the outer layer of its fibrous sheath ; the inner and outer root sheaths and the different parts of the hair are uon- vascular. The nerves terminate in longitudinal and annular fibrils below the level of the sebaceous glands and outside the hyaline layer of the follicle. Sebaceous glands (glanduke sebaceae) exist wherever there are hairs, and their ducts open into the superficial part of the hair follicles (Fig. 604) ; the number of glands associated with each follicle varies from one to four. On the labia minora and mammary areolai they open on the surface of the skin independently of hair follicles, and in the latter situation undergo great enlargement during pregnancy. The deep extremity of each gland expands into a cluster of oval or flask-shaped alveoli, which are surrounded by a basement membrane, and filled with polyhedral cells containing oil droplets. By the breaking down of the superficial cells, their oily contents are liberated as the sehum cutaneum and discharged into the hair follicle, whilst the deeper cells undergo proliferation. The size of the gland bears 778 THE SKIN OE INTEGUMENT. no proportion to that of the hairs, since they are very large in the minute hair follicles of the fcetus and newly born child, and also in the follicles of the rudimen- tary hairs of the nose and certain parts of the face. Bundles of non-striped muscular fibre are associated with the hair follicles, and are named the mm. arrectores pilorum. Attached to the deep part of the hair follicle, and forming with it an acute angle, they pass outwards close to the sebaceous glands, to end in the papillary layer of the corium. Situated on the side of the hair towards which it slopes, they, on contraction, diminish the obliquity of the hair follicle and render the hair more erect, and, at the same time, com- press the sebaceous glands and expel their contents. The condition of "goose- skin " is caused by the contraction of these slender muscles. Tliomson suggests tliat the condition of curly liair is produced by tlie contraction of tliese small muscles. Straight hair is thick and rounded ; curly hair is flat and ribbon-like. When the erector muscle contracts, the thick rounded hair resists the tendency of the muscle to bend it, while the flat hair, not sufiiciently strong to resist the strain of the muscle, becomes bent, and. this is probably the explanation why the follicle assumes the curved form characteristic of the scalp of a bushman. The sebaceous gland lies in the concavity of the bend between the follicle and the muscle, and forms a mass of greater resistance, around which the follicle may be curved by the contraction of the muscle. The cells at the root of the hair accommodate themselves to the curved follicle, and, becoming more horny as they advance to the surface, retain the form of the follicle in which they are moulded. The sudoriparous or sweat glands (glandulEe sudoriferse) are relatively few in number on the back of the trunk, but are very plentiful on the palms and soles, where they open on the summits of the curved ridges. Each consists of an elongated tube, the deeper portion of which forms its secretory part, and is coiled in the sub- cutaneous tissue or deep part of the corium in the form of an ovoid or spherical ball, termed the glomerulus or corpus glandulse sudoriferae (Fig. 604). The superficial part of the tube, or ductus sudoriferus, extends through the corium and epidermis, and opens on the surface by a funnel-shaped orifice, the porus sudoriferus ; where the epidermis is thick the duct is spirally coiled. The glomeruli, as a rule, vary in diameter from 0"1 to 0"5 mm., but in the axillse they are much larger, and may measure from 1 to 4 mm. Each is surrounded by a capillary network and by a capsule of connective tissue, inside which is a homogeneous basement membrane. The lumen of the tube is lined by a layer of nucleated, granular, and striated, columnar, or prismatic epithelium, between the deep extremities of which and the basement membrane is a layer of non-striped muscular fibres, the long axis of which is more or less parallel with that of the tube. The excretory ducts are devoid of muscular fibres, and consist of a basement membrane lined by two or three layers of polyhedral cells, which are covered, next the lumen of the tube, by a thin cuticle. The glands of Moll (glandular ciliares), opening at the margins of the eyelids, and the glandulse ceruminosse of the external auditory meatus, are modified sudoriparous glands ; the former are, however, not coiled up to form glomeruli, while the cell protoplasm of the latter contains yellowish pigment, and their gland ducts, in the fcetus, open into hair follicles. Development of the Skin and its Appendages. Skin. — Tlie vascular and sensitive coriani is developed from the mesoderm, the cells of which, immediately underlying the ectoderm, have, by the second month of foetal life, become aggregated together and flattened parallel to the surface of the embryo. By the third month they are seen to form two layers, the superficial of which becomes the corium, and the deeper the subcutaneous tissue ; the papillte of the corium make their appearance in the fourth month. The epidermis, nails, hairs, sweat and sebaceous glands are all of ectodermal origin. The epidermis at first consists of a single layer of cells, but by the end of the second month it is duplicated, and then exhibits a superficial layer of irregular cells and a deeper layer of more or less cubical cells. By the third month three strata are seen : (a) a deep layer, consisting of a single stratum of cubical cells — the future stratum germinativum ; {h) a middle layer, comprising two or tiiree strata of irregular cells — the future stratum DEVELOPMENT OF THE SKIX AND ITS APPEXDAGES. 779 mucosuni ; and (c) an outer layer, a double stratum of large cells. This outer layer appears to be homologous with a thin membrane, termed the epitrichlum, first described as covering the embryo of the sloth and overlying its hairs, but since shown to be present in birds and mammals. Over the hairy parts of the body it disappears about the sixth month ; but over the free edge and root of the nails, and on the palms and soles, it develops into several layers of cells, which, in these parts, probably persist to form the thick stratum corneum. The part which persists over the root of the nail is termed the eponychiiim, and covers the proximal part of the lunida {irkle p. 776). The stratum lucidum is differentiated from tlie cells of the epitrichium, and, where the latter is lost, possibly forms the supei-ficial layer of the epidermis as it does the horny part of the nails. Nails. — The first rudiment of the nails is seen about the beginning of the third month of embryonic life, and consists of a thickening of the epitrichium over the extremity of the digits. Owing to the growth of the palmar aspect of the digits, the nail rudiment comes to be placed dorsally, and, at its proximal edge, an ingrowth of the stratum njucosum occurs to form its root, while the future nail becomes limited behind and later- ally by a groove. The superficial cells of the stratum mucosum become keratinised to form a thick stratum lucidum, the future nail proper, over the greater part of which the epitrichium disappeai's. The latter persists in the adult as the perionyx across the root of the nail, and, until fifth month, also forms a thick mass over the extremity of the nail, and is continued into the stratum corneum over the end of the digit. The future distal edge of the nail, at this stage, is continuous with the stratum lucidum in front of it ; but this continuity is lost, and by the seventh month the nail presents a free border. The nails grow in length, and are renewed, in case of removal, by a proliferation of the cells of the stratum mucosum at the root of the nail, while an increase in their thickness takes place from the part of the same stratum which underlies the lunula. Hairs. — The hair rudiments appear about the third month of embryonic life as solid downgrowths of the stratum mucosum, which pass obliquely into the subjacent corium. The deep end of this column of cells becomes expanded to form the hair bulb, and rests on a papilla derived from the corium, the epidermis immediately overlying which becomes differentiated into the hair and its inner root sheath, while tlic peripheral cells form its outer root slieath. The surrounding corium becomes condensed to form tlie fibrous sheath of tlie hair follicle, the hyaline layer of whicli is continuous with the basement membrane covering the corium. The hair gTadually elongates, and, reaching the neck of the follicle, its extremity lies at first under the epitrichium, but becomes free on the disappearance of the latter. This takes place about the fifth month, and the first crop of hairs constitutes the laniKjo, which is well developed by the seventh month. The lanugo consists of ver}- delicate hairs, some of which are shed before, the remainder shortly after birth — the last to drop out being those of the eyelashes and scalp — and are replaced by stronger hairs. Shedding and renewal of the hairs take place during life, the renewal being, of course, absent in the case of baldness. Prior to the shedding of a hair active growth and proliferation of the cells of the hair bulb cease, and the papilla becomes atrophied, while the hair root, gradually approaching the surface, at last drops out. New hairs arise from epidermic buds, M'hich extend downwards from the follicle, and their development is identical with that of the original hairs. Sebaceous Glands. — These appear al)Out the fifth month as solid outgrowths from the sides of the hair follicles, and consist of epidermal offshoots continued from the cells of the outer root sheath. Their deep ends become enlarged and lobulated, to form the secreting part of the gland, while the narrow neck connecting this with the follicle forms its duct. The sebaceous seci'etion, together with the cast-oft' epidermal cells, is collected on the surface of the body during the last months of intrauterine life, and forms a layer of varying thickness, tei'med the vernix caseosa or smecpna embri/oniim. Sweat Glands. — These, like the hairs, arise as solid downgrowths of the stratum mucosum. They descend, however, perpendicularly, instead of obliquely, and are of a 3'cll()wish coli)ur : they appear on the palms and soles eai'ly in the fifth month, but much later over the hairy parts of the body. The downgrowths extend through the corium, and, on reaching the subcutaneous tissue, become coiled up to form the secreting part of the gland. The lumen of the gland does not open on the surface until the seventh month. THE VASCULAR SYSTEM. By Alfked H. Young and Arthur Eobinson. The vascular system consists of a series of tubular vessels, with more or less distinct walls, which run through all parts of the body. Some contain blood, others are iilled with a colourless fluid called lymph ; hence the distinction between the blood-vascular system and the lymph-vascular system. The two systems differ, not only as regards their contents, but also in their relations to the tissues amongst which they lie ; for whilst the vessels of the former system, with the possible exception of the splenic vessels, are closed, those of the latter communicate freely with intercellular spaces and serous sacs. The blood-vascular system is tubular throughout ; the tubes or vessels possess distinct walls ; they vary in size and in the structure of their walls, but all con- tain blood, which is conveyed through them to and from the tissue elements of the body. The blood is propelled along the vessels chiefly by a central propulsive organ — the heart. The outgoing vessels from the heart, along which blood is transmitted to the tissues, are termed arteries ; the vessels which return blood from the tissues to the heart are known as veins; whilst the smallest tubes — those which connect tlie arteries and veins together, constituting at once the terminations of the arteries and the commencements of the veins— are called capillaries. Blood capillaries are very small (hair-like) vessels with exceedingly thin walls, which permit of the easy passage outwards of the nutritive plasma from the blood to the tissues, and, in the opposite direction, of some of the products of tissue changes and of modified food material from the alimentary canal. Arteries and veins are simply conducting passages; structurally they diflfer from capillaries in the greater complexity of their walls. They vary greatly in size, but are always larger than capillaries. The calibres of the arteries and veins increase progressively from the periphery up to the heart, where the vessels reach their greatest size. With the increase in calibre there is a corresponding increase in the thickness and complexity of their walls. Structure of Blood Capillaries. — Capillaries measure from ^^^^j- to o-oVo of ^^ inch in diameter, and about J^- to -2V of an inch in length. Their walls are simple, and, in the smallest capillaries, consist principally of elongated elastic endo- thelial cells, with sinuous edges, pointed extremities, and oval nuclei. The cells are cemented to one another along their margins by intercellular cement, which readily stains with nitrate of silver. Here and there the cement substance appears to accu- mulate, forming minute spots indicative of the less perfect apposition of the edges of the cells. These spots, when small, form the so-called stigmata; when larger they are known as stomata. The larger capillaries are invested by a connective tissue sheath consisting of branched cells which are united together and to the endothelial cells of the capillary wall. This sheath is termed the adventitia capillaris. Capillaries are arranged in networks, the nature and character of which differ in different tissues. The small arteries which end in them are known as capillary arterioles, and the venous radicles whicli commence from them are appropriately termed capillary veins. 780 STEUCTUEE OF AETEEIES. 781 Structure of arteries and veins. — The delicate elastic endothelial rneinljrane forming the wall of the simplest capillaries extends as a continuous lining through- out the whole of the blood-vascular system. The constituent cells are fusiform, narrow, and pointed in the arteries, whilst in the veins tliey are somewhat shorter and broader. The most essential structural difference between capillaries and the arteries and veins which they unite together, is to be found in the presence, in both of the latter, of involuntary muscular fibres inter- posed between the endothelial lining '''• externa, and the outer connective tissue sheath. In small vessels, e.g. capil- lary arterioles, the muscle cells are few in number and more or less scattered. In lar^^er vessels the C 1! -*" A-^ Al Fig. 610. — Stuuctcre ok Blood-Vessels (diagiammatic). walls become stronger and thicker, ai, Capillary-with simple endothelial walls. A2 Larger capillary — with connective tissue sheath, "atlventitia capillaris." B, Capillary arteriole— showing muscle cells of middle coat, few and scattered. C. Artery — muscular elements of the tunica media forming a continuous layer. muscular fibres increase and form a continuous layer, whilst yellow elastic and ordinary white connec- tive tissue are added in varying proportions. The walls of the vessels thus become more complex, and numerous strata may be distinguished ; these, however, are for convenience regarded as forming three layers, which are known as the inner, middle, and outer coats, superadded to which is the investing common sheath. Structure of Arteries. — The walls of arteries are stronger and thicker than those of veins of corresponding §ize, the inner and middle coats being particularly rich in elastic and muscular elements. Inner coat (tunica intima). — The simple endothelial layer of the arterioles is strengthened by the addition of yellow elastic tissue, the fibres of which are arranged in such a manner as to simulate a fene- strated membrane. In arteries of medium size the ^|a elastic lamina is separated from the endothelium by a layer of connective tissue consisting of branched cells and numerous fibrils. In the larger arteries the sub-end othelial connective tissue is considerably increased, and delicate elastic fibres appear which connect it with the more externally situated fene- strated elastic layer. The middle coat (tunica media) in the capil- lary arterioles consists solely of scattered unstriped muscle fibres; the indiAidual fibres are circularly disposed, but do not entirely surround the vessel. In small arteries the muscle cells are so far increased in amount that they form a continuous though thin layer. As the arteries increase in size additional layers of muscle cells are added, and the greater thickness of the arterial wall is mainly due to this increase of the muscular elements of the middle coat. In the larger vessels delicate laminic of elastic tissue alternate with the layers of muscular fibres, and in the aorta and the carotid arteries, as well as in some of the branches of the latter, the elastic elements largely preponderate. In the first part of the aorta, in the pulmonary artery, and in the arteries of the retina, the muscular fibres are entirely replaced by elastic tissue. The external coat (tunica externa) of an artery cimsists almost entirely of fibrillated connective tissue, with connective tissue corpuscles lying in corre- sponding spaces. In all but the smallest arteries numerous elastic fibres are also present. The elastic element is specially strong near the middle coat in small and medium sized vessels, and is sometimes described as the external elastic Fig. 611. — TuANSVERSE Section THROUGH THE \VaLL OF A LaHGE Artery. A, Tunica intima. B, Tunica media. C, Tunica externa. -: > M-' 782 THE VASCULAE SYSTEM. membrane of Henle. In some arteries longitudinally arranged unstriped muscular fibres are also found in the external coat. The sheath of an artery (vagina vasis). — In addition to the three coats above described, arteries are enclosed in a sheath of the surrounding connective tissue, and are more or less connected with it bj fine strands of fibrillated connective tissue. Structure of Veins. — The walls of veins are similar in structure to those of arteries ; they are, however, thinner, so much so, that, although veins are cylindrical tubes when full of blood, they collapse when empty, and their lumina almost disappear. The structural details of the three coats vary somewhat in different veins ; in most the inner coat is marked by folds which constitute valves. Like the arteries, the veins are enclosed in connective tissue sheaths. The inner coat (tunica intima). — In the majority of the veins the inner coat includes an internal endothelial layer, a middle layer of sub-endothelial connective tissue, and an outer layer of elastic tissue. The inner coat of a vein is less brittle than the inner coat of .an artery, and is more easily peeled ojEf from the middle coat. The sub-endothelial tissue is a fine fibrillated connective tissue, less abund- ant than in the arteries, and indeed in many cases it is absent. The elastic layer consists of lamellse of elastic fibres which are arranged longitudinally, and it rarely forms a fenestrated membrane. One of the chief peculiarities of the inner coat is the presence of folds of its substance which con- stitute valves. The valves are of semilunar shape, and they are usually arranged in pairs. Their convex borders are continuous with the vessel wall, and their free borders are turned towards the heart ; '^ ' ^ whilst, therefore, they do not interfere with the free flow of blood onwards, they prevent any backward flow towards the periphery, and they help to sustain Fig. 612.— Tbansverse Section of the column of blood in all vessels in which there is an THE Wall op a Vein. upward flow. Each valve consists of a fold of the A, Tunica intima. B, Tunica media, inner Or endothelial layer, strengthened by a little C, Tunica externa. . ,. , '' ■, ^ -, ,-, i-i n , ^ connective tissue. As a general rule, the wall oi the vein is dilated above each valve into a shallow pouch or sinus ; consequently, when the veins are distended they assume a nodulated appearance. The valves are more numerous in the deep than in the superficial veins, and in the veins of children than in the veins of adults. The middle coat (tunica media) is much thinner than the corresponding coat of an artery, and it contains a smaller amount of muscular and a larger amount of ordinary connective tissue ; indeed, so much does the latter preponderate that it separates the muscular fibres into a number of bands isolated from each other by strands of connective tissue, and the muscle fibres do not form a continuous layer. In some of the veins the more internal muscular fibres do not retain the transverse direction which is usually met with both in arteries and veins ; on the contrary, they run longitudinally. This condition is met with in the branches of the mesenteric veins, in the femoral and iliac veins, and in the umbilical veins. The middle coat is absent in the thoracic part of the inferior vena cava ; it is but slightly developed in many of the larger veins, whilst in the jugular veins its muscular tissue is very small in amount. The external coat(tunicaexterna). — This coat consists of whitefibrousand elastic tissue. In many of the larger veins a considerable amount of muscular tissue is also present ; this is the case in the iliac and axillary veins, the abdominal part of the inferior vena cava, the azygos veins, and in the renal, spermatic, splenic, superior mesenteric, portal, and hepatic veins. The striped muscle fibres of the heart are pro- longed into it at the terminations of the vense cavee. The external coat is frequently thicker than the middle coat, and the two are not easily sejjarable from one another. Vascular and Nervous Supply of Arteries and Veins. — Blood-vessels. — The THE HEAET. 783 walls of the blood-vessels are supplied by numerous small arteries, called vasa vasorum, which are distributed to the outer and middle coats. They arise either from the vessels they supply or from adjacent arteries, and after a short course enter the walls of the vessels in which they end. The blood is returned by small vense vasorum. Lymphatics. — Although the cell spaces in the middle and inner coats may be regarded as the commencement of lymphatics, definite lymphatic vessels are limited to the outer coat. Nerves. — Arteries and veins are well supplied with both medullated and non- medullated nerve-fibres. The fibres form dense plexuses on the outer surfaces of the vessels, from \vliich filaments pass to the middle coat to be distributed almost entirely to its muscular fil)res. Divisions of the Blood- Vascular System. — Blood-vessels convey blood to or from the tissues of the body generally, or to and from the lungs. The former constitute the systemic vessels or general system; the latter form the pulmonary system. These two systems are connected together by the heart. The venous trunks passing to the liver form a subsidiary part of the general systemic group of vessels, which is known as the portal system. THE HEART. The heart (cor) is a hollow muscular organ, and is enclosed in a filjro-serous sac known as the pericardium. It receives blood from the veins, and propels it into and along the arteries. The cavity of the fully developed heart is completely separated into right and left halves by an obliquely placed longitudinal ^eptum, and each half is divided into an upper receiving chamber, the auricle, and a lower ejecting chamber, the ventricle. The separation of the auricle from the ventricle, liowever, is not complete. Externally a comparatively shallow constriction, runniug transversely to the long axis of the organ, indicates the distinction between the auricles and ventricles ; internally a wide aperture is left lietween the auricle and ventricle of each side. Each auriculo- ventricular aperture is provided with a valve which allows the free passage of blood from the auricle to the ventricle, but effectually prevents its return. It has ah-eady been pointed out tfiat tlie delicate walis of tfie blood fajiiilaries alfow of the free passage outwards of miti-itive plasma from the l^lood. It passes into spaces, or intercellidar channels, in wliich tlie tissue elements lie ; tlius the latter are directly bathed in Ijlood plasma. The intercellular spaces form the commencement of the lymph -vascular system. Tliey communi- cate together, and open into lymi^li -vessels which carry the used plasma back to the blood-vascular system, bnt in addition they also convey new nutritive material, the prodnct of digestive processes, from the alimentary canal. Lymph -vessels, in otlier words, convey material from the tissues. Blood-vessels convey mateiial both to and from the tissues. The removal of waste products from the blood is jirovided for by sjiecial organs, some of which are simply interposed in the course of the general circulation — e.;/. the liver, the kidneys, and the skin. Tlie lungs, however, wliei'e tlie imjiure or A'enous blood receives its main sup]ily of oxygen and gives up most of its carbonic oxicU', etc., do not lie in the course of tlie general or systemic circulation ; from them a secondary or pulmonary circulation is established, by which venous blood is conveyed from the heart to the lungs by the pulmonary artery and its branches, and, after passing through the pulmonary capillaries, is returned again to the heart as pure arterial blootl by the jiulnionary veins. The heart, anatomically a single organ, is correspondingly modified, and, as described above, it is divided by a se2)tum into a right and a left ])art. The right side receives the blood from the systemic veins, and ejects it into the jiulmonary artery ; whilst the left side receives blood from the pulmonary veins, and ejects it into the main systemic artery — the aorta. The shape of the heart is that of an irregular and somewhat flattened cone : and a base, an apex, two surfaces (inferior and antero-superior), and two l.iorders (right and left) are distinguishable. An oblique groove — the auriculo-ventricular groove (sulcus conniarius) — runs transversely to the long axis of the organ, and separates tlie upper auricular portion from the lower ventricular part. The separation of the auricular portion into right and left chambers is only marked externally at the base of the heart, 784 THE YASCULAE SYSTEM. where an indistinct interauricular groove exists. The division of the lower part into right and left ventricles is more definitely marked on the surface by anterior and inferior interventricular sulci (sulci longitudinales). The heart lies in the middle mediastinum. It is enclosed in the pericardium, and this latter accordingly intervenes between it and the neighbouring structures. It rests below on the diaphragm. Its long axis, from base to apex, runs obliquely from behind forwards, downwards, and to the left. The hase (basis cordis), formed entirely by the auricles, and almost entirely by the left auricle, is directed upwards, backwards, and to the right. It lies in front of the descending thoracic aorta, the oesophagus, and the lower right pulmonary vein, which separate it from the bodies of the sixth, seventh, and eio-hth dorsal vertebrae. On the whole the base is somewhat flattened, and is irregularly quadrilateral Ligamentum arteriosum Left pulmonary artery Vestigial fold of Marshall Left pulmonary veins Eight pulmonary artery Superior vena cava Right pulmonary veins "^1 I'lus terminalis Transverse branch of left coronary artery Left marginal artery Inli.rior vena cava Left ventricle Riaht ventricle Coronary sinus Fig. 613. — The Base and Inferior Surface of the Heart, showing the openings of the great vessels and the line of reflection of the serous pericardium. in form. It presents the orifices of the superior and inferior vense cavfe and, the four pulmonary veins. The opening of the superior vena cava is situated at the upper right angle, that of the inferior cava occupies the lower angle on the right side ; between and a little to the left of these openings are the orifices of the two right pulmonary veins, and immediately to the right of the latter is the indistinct posterior interauricular sulcus, which descends to the left of the orifice of the inferior vena cava. The openings of the two left pulmonary veins are situated near the left border of the base ; and the portion of the surface which lies between the right and left pulmonary veins forms the anterior boundary of the great oblique sinus of the pericardium. The base is limited below by the lower part of the auriculo-ventricular groove, in which the coronary sinus lies ; its upper border is in relation witli the bifur- cation of the pulmonary artery, A fold of pericardium, the vestigial fold of Marshall (ligamentum v. cavse sinistra) descends, near the left border of the base, THE HEAET. 785 from the left branch of the pidmonary artery above to the left superior pulmonary vein below ; and from the lower end of this fold, crossing obliquely Ijelow the left pulmonary vein to reach the coronary sinus, is the small oblique vein of Marshall (v. obliqua atrii sinistri [Marshalli]). Further, it is from the base that the visceral layer of the pericardium, which elsewhere completely invests the heart, is reflected, the lines of reflection corresponding with the orifices of the great vessels.^ The cqKX (apex cordis), bluntly rounded, is formed entirely by the left ventricle. It is directed downwards, forwards, and to the left, and is situated, under cover of the anterior border of the left lung and pleura, behind the fifth left intercijstal space, three and a quarter inches from the anterior mesial line. The inferior surface (facies diaphragmatica) is formed hx the ventricular part Left auricle Pulmoiiarv artery Superior vena cava Right coronary arterv ight auricular f /^ appendix Right coronary ^r\ artery jj \ Anterior ventri ^,^ , cular artery 'ij^ ^ Right marginal artery Left auriculai- appendix Tran.sverse branch of left oronary artery Interventricular branch of h'ft coronary artery Left ventricle Left marginal artery Right ventricle Fig. 614. — The Anteuo-Scfkhiuk Slkk.\(.e ok the IIeakt. of the heart. It rests upon the diaphragm, chiefly on the central tendon, but upon the left side, on a small portion of the muscular substance also, and it is divided into two areas — a smaller to the right side and a larger to the left side — by an oblique antero-posterior groove, the inferior interventricular sulcus. It is separated from the base by the posterior or inferior portion of the aurieulo-ventricular sulcus. The antero-superior surface (facies sterno-costalis) is directed upwards, for- wards, and to the left. It lies behind the body of the sternum and the inner extremities of the cartilages of the third, fourth, iifth, and sixth ribs on the right side, and a greater extent of the corresponding cartilages on the left side. This surface is separated into upper and lower sections by the anterior portion of the auriculo - ventricular groove, which runs obliquely from above down- wards, and from left to right, from the level of the third left to that of the sixth right costal cartilage. The upper section of the surftxce, which is concave, is formed ^ lu the fa?tus aiul young child the auricular portion of the heart forms uot only the ba.<;e, but also the posterior part of the inferior or diaphrasniatie surface. 54 786 THE VASCULAE SYSTEM. bj the auricles ; it is separated from the sternum by the roots of the aorta and the pulmonary artery, and is continuous laterally with the auricular appendices which, projecting forwards, embrace the great vessels. The lower section of the antero- superior surface is convex ; it is formed by the ventricular part of the heart, and is divided by an anterior interventricular sulcus into a smaller left and a larger right part. At the junction of the auricular and ventricular parts of this surface are the orifices of the pulmonary artery and the aorta, the former lying in front of the latter. The right margin of the heart consists of an upper auricular part and a lower ventricular part. The former is almost vertical; it lies behind the cartilages of the third, fourth, fifth, and sixth ribs on the right side about half an inch from the margin of the sternum ; it is in relation with the right pleura and lung, the phrenic nerve with its accompanying vessels intervening, and it is marked by a shallow groove — the sulcus terminalis — which passes from the front of the superior vena cava to the front of the inferior vena cava. The lower part of the right margin (margo acutus) is sharp, thin, and usually concave, corre- sponding with the curvature of the anterior part of the diaphragm ; it is formed by the right ventricle, and it lies almost horizontally in the angle between the diaphragm and the an- terior wall of the thorax, passing from the sixth right costal cartilage behind the lower part of the body of the sternum, or the ensiform cartilage, and behind the cartilages of the sixth and Fig. 615. — The Relation of the Heart to the Anterior Wall of the Thorax. I, II, III, IV, V, VI, the upper six costal cartilages. seventh ribs on the left side to the apex of the heart. The left margin (margo obtusus) is formed mainly by the left ventricle, and only to a small extent by the left auricle. It is thick and rounded. It lies in relation with the left pleura and lung, the phrenic nerve and its accompanying vessels intervening, and it passes from just above the third left costal cartilage, about an inch from the sternum, to the apex of the heart, descending obliquely and with a convexity to the left. THE CHAMBERS OF THE HEART. Auricles (auricula cordis). — The auricular or basal portion of the heart is culjoidal in form. Its long axis, which lies transversely, is curved, with the con- cavity of the curve forwards. It is divided into two chambers — the right and left auricles — by a septum which runs from the front backwards and to the right, 80 obliquely that the right auricle lies in front and to the right, and the left auricle behind and to the left. Each auricle is also somewhat cuboidal in form, the long axes of both being vertical, and each chaml^er possesses a well-marked ear-shaped, forward prolongation, which projects from the anterior and upper angle, and is known as the auricular appendix. The right auricle (atrium dextrum) receives, posteriorly, the superior vena cava above and the inferior vena cava below. Between these, and a little above its middle, it is crossed posteriorly by the lower right pulmonary vein. It is continuous below and in front with the right ventricle at the auriculo- ventricular aperture. Above and in front it is in relation with the ascending aorta, and from the junc- tion of tliis aspect with the right lateral boundary the right auricular appendix THE CHAMBEES OF THE HEAET. 787 is prolonged forwards. On the right side it forms the upper portion of the right margin of the heart, and is in relation with the right phrenic nerve and its accom- panying vessels, and with the right pleura and lung, the pericardium intervening. On the left the auricle is limited by the oblique septum which separates it from the left auricle. The sulcus terminalis is a shallow groove on the surface of the right auricle, which passes from the front of the superior vena cava to the front of the inferior vena cava, and indicates the junction of the primitive sinus venosus with the auricle proper. The interior of the auricle is lined with a glistening membrane, the endo- cardium; its walls are smooth, except anteriorly and in the auricular appendix wliere muscular ])undles, the musculi pectinati, i'orm a series of small vertical Vena cava superior Upper right pulmonary vein l^ower right piihiiouary vein JIu.scull ijectinati Annulus ovalis Fossa ovalis Eustachian valve Aorta Pulmonary artery Ri^ht auricular appendi-X Conns arteriosus Anterior cusp of tricuspid valve Cliordse tendine Moderator band Vena cava inl'crior Coronary (Thebesian) valve Musculi papillares Fig. 616. — The Cavities of the Richt Auricle and Right Ventkici.e of the Heart. columns. These terminate above in a crest, the crista terminalis, which corresponds in position with the sulcus terminalis externally. At the upper and Ijack part of the cavity is the opening of the superior vena cava, devoid of a valve. At the lower and back part is the orifice of the inferior vena cava, bounded in front by the rudimentary Eustachian valve ; and immedi- ately in front and to the left of the Eustachian valve, between it and the auriculo- ventricular orifice, is the opening of the coronary sinus, guarded 1)y the Thebesian valve. The auriculo-vcntricular aperture, guarded by a tricuspid valve, is known as the tricuspid orifice. It is situated in tlie inferior part of the anterior l)ouiidary, and admits three fingers. A number of small fossx, foramina Thebesii (foramina venarum minimarum), are scattered over the walls, and into some of these the venae minimi cordis open. In the septal wall is an oval depression, the fossa ovalis, ]iounded above and in front by a raised margin, the annulus ovalis (liuibus i'ossa? ovalis), which is continuous interiorly with the Eustachian valve; this fossa is the remains of an aperture, the foramen ovale, through which the two auricles communicated with each other liefore birth, and even in the adult a portion of the aperture persists at the upper part of the fossa in about one in five cases. Between the apertures of the superior and inferior venje cavse, and behind the upper part 54 a •88 THE VASCULAE SYSTEM. of the fossa ovalis, a small eminence may be distinguished, which is called the tubercle of Lower (tuberculum intervenosum) ; in the foetus it probably directs the blood from the superior vena cava to the tricuspid orifice. The Eustachian valve (valvula vense cavse inferioris) is a thin and sometimes fenestrated fold of endocardium and sub-endocardial tissue, which extends from the anterior and lower margin of the orifice of the inferior vena cava to the anterior part of the annulus ovalis. Varying very much in size, it is usually of falciform shape, its apex being attached to the annulus and its base to the margin of the inferior caval orifice. It is an important structure in the fcetus, directing the blood from the inferior vena cava through the I'oramen ovale into the left auricle. The Thebesian valve (valvula sinus coronarii) is usually a single fold of endo- cardium which is placed at the orifice of the coronary sinus ; occasionally it consists of two cusps. It is almost invariably incompetent. The left auricle (atrium sinistrum) is in relation behind with the descending thoracic aorta and the cesophagus. Below and in front it is continuous with the left ventricle. Its antero-superior surface is concave, and lies in close relation to the roots of the ascending aorta, the pulmonary artery, and the left coronary Left anterior cusp of pulmonary valve' Left posterior cus of pulmonary valv Le!t posterior cnsp of aortic valve Left coronary artery Anterior cusp of mitral valve Posterior cusp of mitral valve Left ventricle- Conns arteriosus Right anterior cusp of pulmonary valve Right coronary artery Anterior cusp of aortic valve Bight posterior cusp of 'aortic valve Anterior (infundibular) cusp of tricuspid valve Right (marginal) cusp of tricuspid valve Posterior (septal) cusp of tricuspid valve Right ventricle Fig. 617. -The Bases of the Ventricles of the Heart, sbowing the auriculo-ventricular, aortic, and puliiioiiary orifices and their valves. artery. Its right side, formed by the interauricular septum, is directed forwards and to the right. Its left side forms a very small portion of the left margin of the heart, and from its junction with the antero-superior surface the long and narrow auricular appendix is prolonged forwards round the left side of the ascending portion of the aorta and the trunk of the pulmonary artery. The four pulmonary veins enter the upper part of the posterior surface, two on each side. The interior of the left auricle is lined with endocardium, and its walls are smooth, except in the auricular appendix where musculi pectinati are present, and on the septum, in a position corresponding with the upper part of the fossa ovalis on the right side, where there are several musculo-fibrous bundles radiating for- wards and upwards. These septal bundles are separated at their bases by small semilunar depressions, in the largest of which remains of the foramen ovale may be found. Foramina Thebesii, and the apertures of vense minimi cordis, are scattered irregularly over the inner aspect, whilst in the inferior part of the anterior boundary is tlie auriculo-ventricular aperture. The latter is oval in form ; its long axis is placed obliquely from before backwards, and from left to right, and is capable of admitting two fingers. It is guarded by a valve formed of two large cusps, and is known as the mitral orifice. Ventricles. — The ventricular portion of the heart is conical and somewhat THE CHAMBEES OF THE HEAET. 789 flattened. The base, directed upwards and backwards, is partly continuous with the auricular portion and partly free. It is perforated by four orifices, the two auriculo- ventricular, the aortic, and the pulmonary. The auriculo- ventricular orifices are placed one on each side below and behind; in front and between them is the aortic orifice, whilst the orifice of the pulmonary artery is still farther forward, and slightly to the left of the aortic. In the triangle (trigona fibrosa) between the auriculo-ventricular and the aortic orifices is embedded the central fibro-cartilage, a mass of fibro-cartilaginous tissue which is the representative of the os cordis of the ox. It is continuous with the upper part of the interventricular septum, and witli fibrous rings which surround the apertures at the bases of the ventricles. The inferior surfaces and the antero-superior surfaces of the ventricles constitute respectively the greater portions of the corresponding surfaces of the heart ; the former rest upon the diaphragm, whilst the latter are directed upwards and forwards towards the sternum and the costal cartilages of the left side. The apex of the left ventricle forms the apex of the heart. The right margin, which is thin, forms the horizontal portion of the right margin of the heart ; and the left margin, wdiich is thick and rounded, forms almost the whole of the left margin of the heart. The ventricular portion of the heart is divided into right and left chambers. The interventricular septum (septum ventriculorum) is placed obliquely, with one surface directed forwards and to the right, and the other l3ackwards and to the left ; it bulges into the right ventricle, and its lower margin lies to the right of the apex of the heart, which is, there- fore, formed entirely by the left ven- tricle. The margins of the septum are indicated on the surfaces by anterior and inferior interventricular sulci. The right ventricle (ventriculus dexter) is triangular in form. Its base is directed upwards and to the right, and in the greater part of its extent it is continuous with the right auricle, with which it communicates by the auriculo - ventricular orifice ; but its left and anterior angle projects in front of the auricle, and gives origin to the pulmonary artery. Its inferior wall rests upon the diaphragm. The antero-superior wall lies behind the lower part of the left half of the sternum and the cartilages of the fourth, fifth, and sixth ribs of the left side. The left or septal wall, which is directed backwards and to the left, bulges into its interior, and on this account the transverse section of the cavity has a semilunar outline. The cavity itself is a bent tube consisting of an inferior portion or body into which the auriculo-ventricular orifice opens, and of an antero-superior part, the infundibulum or conus arteriosus, which terminates in the ])ulm(inary artery. The angle In'tween the two limbs is formed l\v a thick ledge of muscle. The right auriculo-ventricular orifice is guarded l»y a tricuspid valve (\alvula tricuspidalis). The three cusps of this valve are a right or marginal (cuspis medialis), a left or infundibular (cuspis anterior), which intervenes between the auriculo-ventricular orifice and the infundibulum, and a posterior or septal (cuspis 54 & Fig. 618. — The Kelatio.ns ok the Heart and the Auriculo -Ventricclar, Aortic, and Pulmon^vky Orifices to the Anterior Thoracic Wall. I to VII, Costal cartilages. A, Aortic orifice. Ao, Aorta. C, Clavicle. LA, Left auricle. LV, Left ventricle. M, Mitral orilice. P, Pulmonary orifice. UA, Kiirht auricle. HV, Right ventricle. SVe, Superior vena cava. T, Tricuspid orifice. 790 THE VASCULAE SYSTEM. posterior). Each cusp consists of a fold of eudocardium, strengthened by a little intermediate fibrous tissue, and the bases of the cusps are generally continuous with each other at the auriculo-ventricular orifice, where they are attached to a fibrous ring, but they may be separated by small intermediate cusps which fill the angles between the main segments. The apices of the cusps hang down into the ventricle. The margins, which are thinner than the central portions, are notched and irregular. The auricular surfaces are smooth. The ventricular surfaces are roughened, and, like the margins and apices, they give attachment to fine tendinous cords, the chordae tendinese, the opposite extremities of which are attached to muscular bundles, the musculi papillares, which project from the wall into the cavity of the ventricle. The pulmonary orifice, which lies in- front and to the left of the tricuspid orifice, is guarded by a pulmonary valve composed of three semilunar segments (valvulse semilunares a. pulmonaUs), two of which are placed anteriorly and one posteriorly. The convexity or outer border of each semilunar segment is attached to the wall of the pulmonary artery. The inner border is free, and it presents at its centre a small nodule, the corpus Arantii (nodulus valvulte semilunaris), and on each side of this body a small, thin marginal segment of semilunar form, the lunula (lunula valvules semilunaris). Each segment of the valve is formed by a layer of endo- cardium on its ventricular surface, an endothelial layer of the inner coat of the artery on its arterial surface, and an intermediate stratum of fibrous tissue. Both the attached and the free margins of the cusps are strengthened by tendinous bands, and strands of condensed fibrous tissue radiate from the outer borders to the corpora Arantii, but they do not enter the lunulse. When the valve closes the corpora Arantii are closely apposed, the lunulse of the adjacent segments of the valve are pressed together, and they project vertically upwards into the interior of the artery. The cavity of the right ventricle is lined by endocardium ; the walls are smooth in the conus arteriosus, but are rendered rugose and sponge-like in the body by the inward projection of numerous muscular bundles, the columnse cameae (trabeculse carnese). These bundles are of three kinds ; the simplest are merely columns raised in relief on the wall of the ventricle ; those of the second class are rounded bundles, free in the middle, but attached at- each end to the wall of the ventricle. One special bundle of this group, called the moderator band, is attached by one extremity to the septum, and by the other to the antero-superior wall, at the base of the anterior papillary muscle ; it tends to prevent over-distension of the cavity. The third group of columnse carnese are the musculi papillares, conical bundles continuous at their bases with the muscular wall of the ventricle, and terminating at their apices in numerous chordse tendinese which are attached to the apices, the borders, and ventricular surfaces of the cusps of the tricuspid valve. The musculi papillares of the right ventricle are — (1) a large anterior muscle, from which the chordse pass to the infundibular and marginal segments of the valve ; (2) a smaller and more irregular posterior muscle, sometimes represented by two or more segments, from which chordse pass to the marginal and septal cusps ; and (3) a group of muscular bundles, varying in size and number, which spring from the septum and are united by chordse to the infundibular and septal cusps. The walls of the right ventricle, the septal excepted, are much thinner than those of the left, but the columnse carnese of the first and second classes are coarser and less numerous in the right than in the left ventricle. The left ventricle (ventriculus sinister) is a conical chamber, and its cavity is oval in transverse section. The base is directed upwards and backwards, and in the greater part of its extent it is continuous with the corresponding auricle with which it communicates through the mitral orifice, but in front and to the right of its communication with the auricle it is continued into the ascending aorta. The mitral orifice is oval ; its long axis runs obliquely from above and to the left downwards and to the right, and it is guarded by a valve consisting of two cusps, which is known as the mitral valve (valvula bicuspidalis). The two cusps of the valve are triangular and of unequal size. The smaller of the two, placed to the left and behind, is named the marginal, and the larger, placed to the STEUCTUEE OF THE HEAET. 791 right and in front, between the mitral and aortic orifices, is known as the aortic cusp. The buses of the cusps are either continuous with each other at their attachments to the fibrous ring round the mitral orifice, or they are separated by- small intermediate cusps of irregular form and size. The apices of the cusps hang down into the cavity of the ventricle. The auricular surfaces are smooth ; the ventricular surfaces are roughened l)y the attachments of the chordcc tendineae, which are also connected with the irregular and notched margins and with the apices. The structure is the same as that of the cusps of the tricuspid ^alve, but the ventricular surface of the anterior (or aortic) cusp is relatively smooth ; therefore the blood flow into the aorta is facilitated. The aortic orifice is circular ; it lies immediately in front and to the right of the mitral orifice, from which it is separated by the anterior cusp of the mitral valve, and it is guarded by the aortic valve, formed of three semilunar segments (valvuke semilunares aortse), one of which is placed anteriorly and the other two posteriorly. The structure of these cusps and their attachments are similar to those of the cusps of the pulmonary valve. The cavity of the left ventricle is separable, like that of the right, into two portions, the body and the aortic vestibule ; the latter is a small section placed immediately below the aortic orifice, and its walls are non-contractile, consisting of fibrous and fibro-cartilaginous tissue. The cavity is lined by endocardium. The inferior wall and the apex are rendered sponge-like by numerous fine colunmte carneee of the first and second classes, whilst the upper part of the antero-superior wall and the septum are relatively smooth. There are two papillary muscles of much larger size than those met with in the right ventricle — an anterior and a posterior ; each is connected by chordte tendineae with both cusps of the mitral valve. The walls of the left ventricle, with the exception of the septum, are three times as thick as those of the right ventricle, and they are thickest in the region of the widest portion of the cavity, which is situated aljout a fourth of its length from the base. The muscular portion of the wall attains its minimum thickness at the apex, but the thinnest portion of the boundary is at the upper part of the septum, which consists entirely of fibrous tissue ; here it is occasionally deficient, and an aperture is left through whicli tlie cavities of the two ventricles communicate. The interventricular septum (septum ventriculorum) is a musculo-membrauous partition. It is placed oliliquely, one surface looking forwards and to the right, and bulging into the right ventricle, and the other backwards and to the left towards the left ventricle. Its antero-superior and inferior margins correspond respectively with the anterior and inferior portions of the interventricular sulcus, and it extends from the right of the apex to the interval between the pulmonary and aortic orifices. In the main part of its extent it is muscular (septum musculare ventriculorum), and this portion is developed from the wall of the ^Tntricular part of the heart ; but its upper and posterior portion, the pars membranacea (septum meml^ranaceum ventriculorum), which is developed i'rom the septum of the aortic bulb, is entirely fibrous, and constitutes the thinnest portion of the ventricular walls. The pars membranacea lies between the aortic vestibule on the left and the upper part of the right ventricle, as well as the lower and left part of the right auricle, on the right. Stkuctuee of the Heart. The walls of tlie Leart consist mainly of peculiar striped muscle, the myocardium, which is enclosed between the visceral layer of the pericardium, or epicardium, exlernallv, and the endocardium internally. The muscular fibres differ from those of ordinary voluntary striped muscle in several Avays : they are shorter, many of them being oblong cells with forked ex- tremities which are closely cemented to similar processes of adjacent cells ; they form a reticulum, and the nuclei lie in the centres of the cells. Moreover, in some of the lower mammals, in the yoimg child up to the end of tlie lirst year, and occasionally in the human adult also, still mure peculiar libres, the fibres of Purkinje, are found immediately beneath the sub-endocardial tissue. These are large cells which unite with each other at their extremities ; their central portions consist of granular protoplasm, in which sometimes one, but more frequently two nuclei are embedded, and the periplieral portion of each cell is transA-ersely striated. These cells, in short, present in a permanent form a condition wdiich is transitory in all other striped muscle cells. 792 THE VASCULAK SYSTEM. Tlie reticiilatiug cardiac muscle cells are grouped iu sheets and strands wliicli have a more or less characteristic and definite arrangement in different parts of the heart ; by careful dis- section, and after special methods of ijrejjaration, it is possible to recognise many layers and bundles, some of which are, however, probably artificially produced. In the auricles the muscular fasciculi fall naturally into two groups, those special to each auricle, and those common to both auricles ; the former are situated deeply under cover of the latter. The deep special fibres are — («) LoojDed fibres which pass over the auricles from before back- wards or from side to side ; their extremities are attached to the fibrous rings which surround the auriculo-ventricular orifices. (6) Annular fibres which surround (1) the extremities of the large vessels which open into the auricle, (2) the auricular appendices, and (3) the fossa ovalis. The superficial fibres, Avhich are common to both auricles, for the most part run transversely across the auricles, but a few of them turn into the interauricular septum. They are most numerous on the anterior asj^ect. In the ventricles, also, two main groups of fasciculi, a superficial and a deep, have been described, but it is in this region especially that there is doubt regarding the individuality of many of the muscular bundles which have been noted, for it appears probable that many of them are artificial products due to the method adopted by the dissector. There is no doubt that in the middle of the thickness of the ventricular walls the arrangement of the fibres is mainly circular, some surrounding one and some both ventricles. Near the surfaces the fasciculi assume an oblique direction, and it is not imjarobable that many of the bundles are arranged in figure of 8 loojas, whose upper extremities are attached to the fibrous rings round the auriculo- ventricular orifices. The superficial fibres of the ventricles are attached above to the fibrous rings at the base, and from this attachment they pass obliquely downwards to the apex, those on the anterior surface trending towards the left, and those on the inferior surface towards the right. On the inferior surface almost all the fasciculi appear to pass across the septum, but on the anterior surface the middle fasciculi dip into it, and only those near the base and apex cross from right to left. All the superficial fibres which reach the apex are coiled there into a whorl or vortex, through which they pass upwards into the substance of the left ventricle, those descending from the front and left side entering the base of the j^osterior papillary muscle, whilst those from the back and right side terminate in the anterior papillary muscle. The muscular fasciculi which enter the papillary muscles are continued, by means of the chordae tendinese, to the flaps of the mitral vah^e and so to the fibrous ring round the mitral orifice ; obviously, therefore, many of the superficial fasciculi of the ventricles form simple oblique loops which commence externally at the fibrous rings round the right and left auriculo-ventricular orifices, and terminate internally by gaining attachment to the ring round the left of these orifices (mitral). The deep fasciculi of the ventricles may be subdivided into two main groups — (1) Those common to both ventricles, and (2) those special to each ventricle. The fasciculi common to both ventricles include — {a) Fibres which commence above from the posterior sections of the fil^rous ring at the base of the right ventricle ; either directly or by means of the chordae tendineae of the posterior papillary muscle they pass obliquely downwards to the septum, traverse it, and ascend to the front of the fibrous ring at the base of the left ventricle, (b) Fibres from the anterior portions of the fibrous ring at the base of the right ventricle, which jjass obliquely downwards and assume a transverse course in the posterior wall of the left ventricle, (c) Annular fibres which encircle both ventricles. The deep special fibres of the left ventricle are («) V-shaped looj^s which commence at the fibrous ring at the base, and descend to the apex, where they turn upwards in the septum, and terminate by joining the central fibro-cartilage ; (b) fibres which descend from the base, enter the lower and front part of the septum, and, passing through it, assume an annular course in the posterior wall. The deep special fibres of the right ventricle are {a) looped fibres which pass downwards in the external wall from the fibrous rings to the apex, where they enter the septum and ascend to the central fibro-cartilage ; (6) circular fibres round the pulmonary orifice ; and (c) radiating fasci- culi from the base of the anterior papillary muscle to the front part of the pulmonary orifice. The epicardium, or visceral portion of the pericardium, consists of white connective and of elastic tissue, the latter forming a distinct reticulum in the deeper part. The surface which looks towards the pericardial cavity is covered with flat polygonal endothelial j^lates, which are partially separated liere and there by stomata through which the pericardial cavity communicates with the lymphatics of the ej^icardium. The endocardium lines the cardiac cavities and is continuous with the inner coats of the vessels which enter and leave the heart. It consists, like the epicardium, of white connective tissue and elastic fibres, but it is much thinner than the epicardium, and its elastic fibres are in some places blended into a fenestrated membrane. Its inner surface is covered with endothelial cells, and it rests externally upon the sub-endocardial tissue, in which there are Ijlood-vessels and nerves ; the endocardium itself is entirely devoid of vessels. Size of the Heart. — The heart is about five inches (125 mm.) long, three and a half inches (87 mm.)l«'oad ; its greatest depth from its antero-superior to its inferior surface is two and a half inches (62 mm.), and it is roughly estimated as being about the same size as the closed fist. The size, however, is varial^le, the volume increasing at first rapidly, and then gradually, with increasing age, from 22 cc. at birth to 155 cc. at the fifteenth year, and to 250 cc. by the twentieth year. From this period to the fiftieth year, when the maximum volume (280 cc.) is attained, the in- THE PEEICAEDIUM. 793 crease is much more gi-adual, and after fifty a sliglit decrease sets in. Tlie volume is the same in both sexes up to the period of puberty, but thereafter it pre]ionderates in the male. Weight. — The average weight of the heart in tlie male adult is 11 ounces (310 grms.), and in the female adult 9 ounces (255 grms.) ; but the weight varies greatly, always, however, in definite relation to the weight of the body, the relative proportions changing at different periods of life. Thus at birtli the heart weighs 13|- drachms (24 grms.), and its relation to the body weight is as 1 to 130, whilst in the adult tlie relative proportion is as 1 to 205. The heart is said to increase rapidly in weight up to the seventh year, then more slowly up to the age of puberty, when a second acceleration sets in ; but after the attainment of adult life the increase, which continues till the seventieth year, is very gradual. The above changes affect the whole heart, but the several parts also vary in their relation to each other at different periods of life. During foetal life the right auricle is heavier than the left ; in the first month after birth the two become equal, and at the second year the right again begins to preponderate, and it is heavier than the left during the remainder of life. In the latter part of foetal life the two ventricles are equal ; after birth the left grows more rapidly than the riglit, until, at the end of the second year, a position of stability is gained, when the right is to the left as 1 to 2, and this proportion is maintained until death. Capacity. — During life the capacity of the ventricles is probably the same, and each is capable of containing about four ounces of blood, whilst tlie auricles are a little less capacious. After death the cavity of the right ventricle appears larger than that of the left. Vascular Supply of the Heart. — Tlie walls of the heart are supplied l)y the coronary arteries (p. 800), the branches of wliich pass through the interstitial tissue to all parts of the muscular substance and to the sub-eudocardial and sub-epicardial tissues ; the endocardium and the valves are devoid of vessels. The capillaries, which are numerous, form a close-meshed network around the muscular fibres. Sometimes the valves contain a few muscular fibres, and in these cases they also receive some minute vessels. The majority of the veins of the heart end in the coronary sinus, which opens into the lower jjart of the right auricle ; some few very small veins, how- ever, open directly into the right auricle, and others are said to end in the left auricle, and in the cavities of the ventricles. Lymphatics of the Heart. — Lymphatic vessels are freely distributed throughout the whole substance of the heart, 1 mt they are most numerous in the sub-endocardial and the sub-pericardial tissues, and the vessels which lie in the latter situation communicate through stomata with the jjericardial cavity. The smaller lymphatic vessels accomiiany the blood-vessels ; ultimately they converge to two main trunks — an anterior and an inferior — which lie respectively, at their com- mencements, in the anterior and the inferior auriculo-ventricular sulci. Each is formed by one or more tributaries which collect lymph from the ventricles and auricles. The inferior trunk accompanies the right and the anterior trunk the left coronary artery. At the upper part of the heart the trunks pass backwards, at the sides of the pulmonary artery, jjierce the pericardium, and they terminate in tlie glands which lie round the bifurcation of tlie tracliea. Nerves of the Heart. — The heart receives its nerves from the sui)erficial and deep cardiac l^lexuses which lie l>eiieath the arch of the aorta, and through them it is connected with the vagus, the spinal accessory (through the vagus), and tlie sympathetic nerves. After leaving the plexuses many of the nerve-fibres enter the walls of the auricles, and anastomose together in the sub-epicardiai tissue, forming a plexus in which many ganglion cells are embedded, esjiecially near the terminations of the inferior vena cava and the j^ulmonary veins. From the sub- epicardial auricular plexus, nerve filaments, on which nerve ganglion cells have been found, pass into the substance of the auricular walls. Other fibres from the cardiac plexuses accompany the coronary arteries to the ventricles, and upon these also ganglion cells are found in the region immediately below the auriculo-ventricular sulcus. The nerve-fibres which issue from the ganglionated plexuses of the heart are non-medullated. They form fine plexuses round the muscle fibres, and they terminate either in fine fibrils on the surfaces of the muscle fibres, or in nodulated ends which lie in contact with the muscle cells. THE rEKICARDIUM. The pericardium is a tibro-serous sac vvhich surrounds the heart. It lies in the middle mediastinum, and is attached below to the diaphragm, and above and behind to the roots of the great vessels. Anteriorly and posteriorly it is in relation with adjacent structures ; laterally it is in close apposition with the pleural sacs. The fibrous pericardium is a strong fibrous sac of conical form ; its base is attached to the central tendon and to a part of the muscular substance of the diaphragm, and it is pierced by the inferior vena cava. At its apex and posteriorly it is gradually lost upon the great vessels which enter and emerge from the heart, giving sheaths to the aorta, the two branches of the pulmonary artery, the superior vena cava, the four pulmonary veins, and the ligamentum artt riosum. Its anterior surface forms the posterior boundary of the anterior mediastinum, and it gives attachment, above and below, to the superior and inferior sterno-perieardial 794 THE VASCULAE SYSTEM. lio-aments. In the greater part of its extent it is separated from the anterior wall of the thorax by the anterior margins of the lungs and pleural sacs, but it is in direct relation with the left half of the lower portion of the body of the sternum and, in many cases, with the inner ends of the cartilages of the fourth, fifth, and sixth ribs of the left side. Its posterior surface forms the anterior boundary of the posterior mediastinum ; it is in relation with the cesophagus and the descending aorta, both of which it separates from the back of the left auricle. Each lateral aspect is in close contact with the mediastinal portion of the parietal pleura, the phrenic nerve and its accompanying vessels intervening. The inner surface of the fibrous sac is lined by the serous pericardium, which is closely attached to it. Left phienic nerve Lett \ agub nei ve Aorta 'II /""AW W » Right phrenic nerA e Superior vena cava ^ _ „„^x^ vx «, a^^ .^n x .:^ r^ m/-.x^ vx >^ y^^ .^Nx.-..-^,^, m Lett pulmonaiy aitepy Pulmonary artery Superior vena cava nfWZ-ii^i:^^^^^ Left bioncliU'i LiJ 7 Loll pulmonaij ^eins in root of luntr Bight pulmon-^ ary veins' Pericardium Inferior vena cava 5^ I II ; II nionary veins Pencardium Diaphiagm Fig. 619. — PosTERioii Wall of the Pericardium after removal of the Heart, showing the relation of tlie serous pericardium to the great vessels. From a formalin preparation made by Professor Birmingham. The serous pericardium is a closed sac containing a little fluid (liquor peri- cardii). It is surrounded by the fibrous pericardium and invagiuated by the heart. It is, therefore, separable into two portions — the parietal, which lines the inner sur- face of the fibrous sac, and the visceral, which ensheaths, or partially ensheaths, the heart and the great vessels ; but the two portions are, of course, continuous with each other where the serous layer is reflected on to the great vessels as they pierce the fibrous layer. The majority of the great vessels receive only partial coverings from the visceral layer : thus the superior vena cava is covered in front and laterally ; the pulmonary veins in front, above, and below ; and the inferior vena cava, for a very short distance, in front and laterally. The aorta and the pulmonary artery are enclosed together in a complete sheath of the visceral layer ; and when the pericardial sac is opened from the front it is possible to pass the fingers behind them and in front of the auricles, from the right to the left side, through a passage called the great transverse sinus of the pericardium. The THE PULMOXAEY ARTERY. 795 spaces or pouches which intervene between the vessels which receive partial coverings from the serous pericardium are also called sinuses ; and the largest of them, which is bounded below and on the right by the inferior vena cava, and aljove and on the left by the left inferior pulmonary vein, is known as the great oblique sinus. It passes upwards and to the right behind the left auricle, and lies in front of the oesophagus and the descending thoracic aorta. A small fold of the serous pericardium, tlie vestigial fold of Marshall (liga- mentum v. cav?e sinistra), passes from the left puhnonary artery to the left superior pulmonary vein behind the left extremity of the transverse sinus. It merits special attention because it encloses the remains of the left superior vena cava, which atrophies at an early period of fcetal life. Structure. — The fibrous pericardium consists of ordinary connective tissue fibres felted togetlier into a dense, unyielding membrane. The serous pericardium is covered on its inner aspect by a layer of flat endothelial cells which rest upon a basis of mixed white and elastic fiVjres in wliicli run numerous blood-vessels, lymphatics, and nerves. THE ARTERIES. THE PULMONARY ARTERY. The pulmonary artery (a. pulmonalis) springs from the anterior and left angle of the base of the right ventricle, at the termination of the infundibulum. It is slightly larger at its commencement than the aorta, and is dilated immediately above the valves into three pouches, the sinuses of Valsalva. It runs upwards and backwards towards the concavity of the aortic arch, curving from the front round the left side of the ascending aorta to reach a plane posterior to the latter ; and it terminates, by dividing into right and left branches, opposite the sixth dorsal vertebrae. Its length is a little more than two inches. Relations. — The pulmonary artery is enclosed within the fibrous pericardium, and enveloped along with the ascending aorta in a common sheath of the visceral layer of the serous pericardium. It lies behind the inner extremity of the second left intercostal space, from which it is separated by the anterior margins nf the left lung and pleural sac. Its posterior relations are the root of the aorta, the anterior wall of the left auricle, and the first part of the left coronary artery. To the right it is in relation with the right coronary artery and the right auricular appendix, and to the left with the left coronary artery and the left auricular appendix. Immediately above its bifurcation, between it and the aortic arch, is the superficial cardiac plexus. The right branch of the pulmonary artery is longer and larger than the left. It passes to the hilum of the right lung, forming one of the constituents of its root, and, entering the lung, descends with the main bronchus to the lower extremity of the organ. Relations. — Before it enters the lung the right pulmonary artery passes behind the ascending aorta, the superior vena cava, and the upper right pulmonary vein. At first it lies below the arch of the aorta and the right bronchus, in front of the oesophagus, and above the left auricle and the lower riglit puhnonarv vein ; then it crosses in front of the right bronchus immediately below the eparterial branch, and readies the hilum of the lung. After entering the lung the artery descends, behind and to the outer side of the main bronchus and between its ventral and dorsal branches. Branches. — Before entering the hilum it gives of!" a large branch to the upper lobe which accompanies the eparterial bronchus, and in the substance of the lung it gives off numerous branches which correspond with and accom]iany the dorsal, ventral, and accessory branches of the right bronchus. The left branch of the pulmonary artery, shorter, smaller, and somewhat higher in position than the right, passes outwards and backwards from the bifurca- tion of the pulmonary stem, and runs in the root of the left lung to the hilum ; it then descends in company with the main bronchus to the lower end of the lung. 796 THE VASCULAE SYSTEM. Relations. — Before it enters the lung it is crossed in front by the upper left pulmonary vein ; hehind it, is the left bronchus and the descending aorta ; above, the aortic arch, to which it is connected by the ligamentum arteriosum, and the left recurrent Fig. 620. — The Pulmonary Arteries and Veins and their Relations. Parts of the ascending aorta and superior vena cava have been removed. 1. Aorta. 2. Superior vena cava. 3. Upper right pulmonary vein. 4. Right pulmonary artery. 5. Superior vena cava. 6. Left innominate vein. 7. Innominate artery. 8. Right innominate vein. '.). SubclaviiLs muscle. 10. Clavicle. 11. Internal mammary artery. 12. Subclavian vein. 13. Suprascapular artery. 14. Transverse cervical artery. 15. Vertebral artery. 10. Inferior thyroid artery. 17. Internal jugular vein. 18. Common carotid artery. 19. Superior thyroid artery. 20. Sterno-thyroid muscle. 21. Omo-hyoid muscle. 22. Sterno-hyoid muscle. 23. Platysma. 24. Sterno-liyoid muscle. 25. Sterno-thyroid muscle. 26. Sterno-mastoid muscle. 27. Phrenic nerve. 28. Vagus nerve. 29. Vertebral artery. 30. Inferior thyroid artery. 31. Thoracic duct. 32. Left subclavian artery. 33. Subclavius muscle. 34. 1st rib. 35. Left common carotid artery. 36. Aorta. 37. Ligamentum arteriosum. 38. Left pulmonary artery. 39. Uijper left pulmonary vein. 40. Pulmonary artery. laryngeal nerve; heloio, it is in relation with the lower left pulmonary vein. After enter- ing the lung it descends, like the right pulmonary artery, behind and on the outer side of the stem bronchus, and between its ventral and dorsal branches. Branches. — Just before passing through the hilum it gives off a branch to the upper lobe, and in the substance of the lung its branches correspond with the ventral, dorsal, and accessory branches of the bronchial tube. THE THOEACIC AORTA. 797 THE SYSTEMIC ARTERIES. THE AORTA. The aorta is the main trunk of the arterial system. It commences at the base of the left ventricle and ascends, with an inclination to the right, to the level of the second right costal cartilage ; then curving Imckwards and to the left, it reaches the left side of the lower border of the fourth dorsal vertel)ra, and finally descends through the tliorax into the abdomen, where it termiuates, on the left of the mesial plane, at the level of the fourth lumbar vertebra, by bifurcating into the two common iliac arteries. The portion of the aorta which is situated in the thorax is, for convenience, termed the thoracic aorta, and the rest of the vessel is known as the abdominal aorta. THE THORACIC AORTA. The thoracic aorta is subdivided into the ascending portion, the arch, and the descending portion. The ascending aorta (aorta ascendens) lies in the middle mediastiuum. It springs from the base of the left ventricle, behind the left margin of the sternum, opposite the lower border of the third left costal cartilage and the body of the sixth dorsal vertebra. From its origin it passes upwards, forwards, and to the right, and it terminates in the arch of the aorta, behind the right margin of the sternum, at the level of the second costal cartilage. Its length is from 2 to 2-^ inches (50 to 57 mm.), and its breadth is Ijl inches (28 mm.) In the adult it is a little narrower at its commencement than the pulmonary artery is, but in old age it enlarges and exceeds the latter vessel in size. The diameter, however, is not uniform throughout the whole length of the ascending aorta ; four distinct dilatations are present. Three of these, small and pouch-like, are known as the sinuses of Valsalva (sinus aortse). They are situated at the origin of the aorta, immediately above the semilunar cusps of the valve which guards the aperture of communication with the left ventricle ; one is anterior in position, and two are situated })Osteriorly. The fourth dilatation is formed by a diffuse bulging of the right wall, and is known as the great sinus of the aorta. Relations. — The ascending aorta is completely enclosed within the fibrous peri- cardium which blends above with the sheath of the vessel. It is enveloped, together with the stem of the pulmonary artery, in a tubular prolongation of the serous pericar- dium, and at its origin has the pidmonary artery in front, the anterior wall of the left auricle behind, and the right auricular appendix on its right side. In the upper part of its course the ascending aorta is overlai)ped by the anterior margins of the right lung and right pleural sac, whilst behind it ax'e the right auricle, the right branch of the pulmonary artery, the right bi'onclius, and the left margin of the superior vena cava. The superior vena cava lies on the right side, and partly behind the upper part of the ascending aorta, whilst the pulmonary artery is at first in front of it and then, at a higher level, on its left side. Branches. — Two l)ranches arise from the ascending aorta, viz. the riiiht and the left coronary arteries. The former springs from the anterior, and the latter from the left posterior sinus of Valsalva (p. 800). The arch of the aorta (arcus aortic; lies in the superior mediastinum behind the lower part of the manubrium sterni, and connects the ascending with the descending aorta. It commences behind the right margin of the sternum, on a level with the second costal cartilage, and extends to the lower border of the fourth dorsal vertebra. As its name implies, it forms an arch ; in this there are two curvatures, one with the convexity upwards, and the other with the convexity forwards and to the left. From its origin it runs for a short distance upwards, l)ackwards, and to the left, in front of the trachea ; then it passes backwards, round the left side of the trachea to the left side of the body of the fourth dorsal vertebra, and finally turns downwards to become continuous with the descending aorta. 798 THE VASCULAE SYSTEM. At its commencement it has the same diameter as the ascending aorta, 1^ inches (28 mm.), but after giving off three large branches, the diameter is reduced to a httle less than one inch (23 mm.) Relations. — It is overlapped in frout and on the left side by the right and left lungs and pleural sacs, but much more by the latter than the former, and in the interval between and behind the pleural sacs it is covered by the remains of the thymus gland. As it turns backwards it is crossed vertically on the left side by four nerves in the following order from before backwards : — the left phrenic, the inferior cervical cardiac branch of the left vagus, the superior ca^rdiac branch of the left sympathetic, and the trunk of the left vagus, and the left superior intercostal vein passes obliquely upwards and to the right between the vagus and phrenic nerves. Behind and to the right side of the arch are the trachea, deep cardiac plexus, the left recurrent laiyngeal nerve, the left border of the oesophagus, and the thoracic duct. Above are its thi'ee large branches — the innominate, the left common carotid, and the left subclavian arteries — and crossing in front of the roots of these is the left innominate vein. Below is the bifurcation of the pulmonary artery and the root of the left lung ; the ligamentum arteriosum, which is also below, attaches it to the commencement of the left pulmonary artery, whilst to the right of the ligament is the superficial cardiac plexus, and to its left is the left recurrent laryngeal nerve. Branches. — The three great vessels which supply the head and neck, part of the thoracic wall, and the upper extremities — viz. the innominate, the left common carotid, and the left subclavian arteries — arise from the aortic arch. The descending aorta (aorta descendens).— The thoracic portion of the de- scending aorta lies in the posterior mediastinum ; it extends from the termination of the arch, at the lower border of the left side of the fourth dorsal vertebra, to the aortic opening in the diaphragm, where, opposite the twelfth dorsal vertebra, it becomes continuous with the abdominal portion. Its length is from seven to eight inches (17'5 to 20 cm.), and its diameter diminishes from 23 mm. at its commencement to 21 mm. at its termination. Relations. — Immediately behind it is the vertebral column and the anterior common ligament. It rests also on the vena azygos minor superior and the vena azygos minor inferior, whilst from its posterior aspect the aortic intercostal branches are given off. In front it is in relation, from above downwards, with the root of the left lung, the peri- cardium which separates it from the back of the left auricle, the oesophagus with the oeso- phageal plexus of nerves, and the crura of the diaphragm which separate it from the SjDigelian lobe of the liver. On the left side are the left lung and pleura. On the right side the thoracic duct and the vena azygos major form immediate relations along its whole length. The oesophagus also lies to the right of the upper part of the descending aorta, whilst the right lung and pleura are in close relation below. Branches. — Nine pairs of aortic intercostal arteries, two left bronchial arteries, four or five oesophageal, some small pericardial, and a few posterior mediastinal branches, usually arise from the descending aorta. THE ABDOMINAL AOETA. The abdominal portion of the descending aorta lies in the epigastric and umbilical regions of the abdomen. It extends from the middle of the lower border of the last dorsal vertebra to the left side of the body of the fourth lumbar vertebra, where it bifurcates into the right and left common iliac arteries. The |)oint of division is a little below and to the left of the umbilicus, opposite a line drawn transversely across the abdomen on a level with the highest points of the iliac crests. At its commencement it is 21 mm. in diameter, but after the origin of two large branches, the coeliac axis and the superior mesenteric arteries, it diminishes considerably, and then retains a fairly uniform diameter to its termination. Relations. — Behind, it is in contact with the upper four lumbar vertebrae and THE ABDOMINAL AOETA. 799 intervening intervertebral discs, the anterior common ligament, and the left lumbar veins ; the lumbar and the middle sacral arteries spring from this aspect of the vessel. In front, and in close relation with it, there are from above downwards the following structures : the coeliac axis and solar plexus, the pancreas and splenic vein, the superior mesenteric artery, the left renal vein, the third part of the duodenum, the root of the mesentery, the aortic plexus, the inferior mesenteric artery, the peritoneum and coils of small intestine. More superficially the stomach, the transverse colon, and the great and small omenta, are in front. On the ric/ht side, in the upper part of its extent, are the thoracic duct and Hepatic veins Inferior phrenic artery Suprarenal body- Inferior vena cava Renal artery Renal vein Right ovarian vein Ovarian artery Ureter Psoas muscle Ascending colon Coninion iliac vein Common iliac artery Middle sacral artery Ileum Csecum External iliac artery External iliac vein -CEsophagus -Cms of diaphragm Inferior phrenic artery Suprarenal body Cojliac axis Suprarenal vein Superior ^mesenteric artery Renal artery Lumbar arteries Ureter Left colic artery Ovarian artery Inferior mesenteric artery —Descending colon Psoas muscle Common iliac artery Sigmoid artery Commou iliac vein Superior h»mor- rhoidal artery Iliac colon Pelvic colon External iliac /^M Artery Externa iliac vein Fallopian tube Fig. 621. — The Ahduminal Aorta and its Bkanches. reccptaculum chyli, the vena azygos major, and the right crus of the diaphragm, tbc latter separating it from the right semilunar ganglion and from the upper part of the inferior vena cava. In its lower part it is in direct relation with the inferior vena cava. On the left side, the left crus of the diaphragm with the left semilunar ganglion, and the fourth part of the duodenum, are in close relation with its upper part, whilst in the lower portion of its extent the peritoneum and some coils of the small intestine are in contact with it. Branches. — Tlic branches form two groups, visceral and parietal, and each group consists of paired and unpaired vessels, as follows : — 800 THE VASCULAE SYSTEM. Visceral, Parietal, Unpaired. Paired. Unpaired. Paired. Coeliac axis Suprarenal Superior mesen- Renal teric Inferior mesen- Spermatic or teric ovarian Middle sacral j Inferior phrenic 1 Lumbar (four pairs) 1 Common iliac i BRANCHES OF THE ASCENDING AORTA. COEONAKY AkTEPJES. The coronary arteries are two in number, a right and a left ; they are distributed almost entirely to the heart, but give also some small branches to the roots of the great vessels, and to the pericardium (Figs. 613, 614, and 617). The right coronary artery (a. coronaria dextra) springs from the anterior sinus of Valsalva. It runs forwards, between the root of the pulmonary artery and the right auricular appendix, to the auriculo- ventricular sulcus, in which it passes to the right, and then, turning round the margin of the heart, is continued to the left as far as the posterior end of the inferior interventricular sulcus, where it ends by dividing into two terminal branches. It is accompanied by branches from the cardiac plexus, and is in relation with the right coronary vein. Branches. — Of tlie two terminal branches, one, the transverse (ramus circumflexus), is of small size ; it is simply the continuation of the main trunk which runs farther to the left to anastomose with the transverse branch of the left coronary artery. The other, the interventricular (ramus descendens), is much larger than the transverse branch. It runs forwards in the inferior interventricular sulcus, sup2:)lies both ventricles, and anastomoses, at the apex of the heart, with the interventricular branch of the left coronary artery. In addition to the terminal branches small aortic and pulmonary twigs are distributed to the roots of the aorta and pulmonary artery respectively. A right auricular branch passes upwards on the anterior surface of the right auricle, between it and the ascending aorta ; one or more preventricular branches, of small size, descend on the anterior surface of the right ventricle ; a branch of larger size, the marginal artery, descends along the right margin and gives branches to both surfaces of the right ventricle. The left coronary artery (a. coronaria sinistra) arises from the left posterior sinus of Valsalva. . In its course and distribution it resembles in many respects the right coronary artery, the chief difference being that it divides much sooner into its two terminal branches ; the trunk of the artery is therefore correspondingly short. Erom its origin it runs forwards between the root of the pulmonary artery and the left auricular appendix, and, reaching the auriculo- ventricular sulcus at the upper end of the anterior interventricular groove, divides immediately into trans- verse and interventricular terminal branches. Branches. — The transverse terminal branch (ramus circumflexus) runs to the, left margin of the heart, and there turns to the inferior surface where it comes into relation with the coronary sinus ; it ends by anastomosing with the transverse Ijranch of the right coronary artery. It supplies the left auricle, the left margin of the heart, and the posterior part of the lower surface of the left ventricle. The interventricular terminal branch (ramus descendens anterior) passes down the anterior interventricular sulcus to the apex of the heart, where it anastomoses with the interventricular In-anch from the right coronary ; it supplies both ventricles, and is accom- panied by cardiac nerves and by the great cardiac vein. A left auricular branch, or Ijranches of small size, 2)ass to the wall of the left auricle, and small aortic and pulmonary branches are also given to the roots of the aorta and pulmonary artery. beanches of the arch of the aoeta. The branches which arise from the arch of the aorta supply the head and neck, the upper extremities, and part of tlie body wall. They are three in number, viz. the innominate, the left common carotid, and THE COMMON CAEOTID AETEKIES. 801 the left subclavian arteries. The innominate is a short trunlv from the termination of which the right common carotid and the right subclavian arteries spring (Figs. 620 and 624) ; thus there is at first a difference l>etween the stem vessels of opposite sides, but beyond this the subsequent course and the idtimate distribution of these vessels closely correspond. THE INNOMINATE ARTERY. The innominate artery (a. anonyma, Fig. 620) arises behind the middle of the lower part of the manubrium sterni, from the convexity of the arch of the aorta near its right or anterior extremity, and terminates opposite the right .sterno- clavicular articulation, where it divides into the right subclavian and right common carotid arteries. Course. — The trunk, whicli measures from one and a half to two inches (37 to 50 mm.) in lengtli, runs upwards, backwards, and outwards in the superior mediastinum. Relations. — Posterior. — It is in contact behind, with the trachea below and with the right pleural sac above. Anterior. — The left innominate vein crosses in front of the lower part of the artery, and above this the sterno-thyroid muscle separates it from the sterno-hyoid and the right sterno-clavicular joint. The remains of the thymus gland, which separate it from the manubrium sterni, are also in front. Lateral. — The right innominate vein and the upper part of the superior vena cava are on the right side of the artery. On its left side is the origin of the left common carotid artery, whilst at a higher level the trachea is in contact with it. Branches. — As a rule the innominate artery does not give off any branches except its two terminals, but occasionally it furnishes an additional branch, the thyroidea ima The thyroidea ima is an inconstant and slender vessel. When present it sometimes arises from the arch of the aorta, but it usually springs from the lower part of the innominate. It passes upwards in front of the trachea, through the anterior part of the superior mediastinum and the lower part of the neck, and gives off branches to the lateral lobes aiid isthmus of the thyroid body and to the trachea. THE AKTEKIES OF THE HEAD AND NECK. The vessels distributed to the head and neck 'are chiefly derived from the carotid trunks ; there are, however, in addition, other vessels which arise from the main arterial stems of the upper extremities, and it ^\i\\ be advantageous to describe tlie most important of these, viz. the vertebral arteries, with the carotid system. The smaller additional branches will be considered along with the remaining branches of the subclavian arteries. The carotid system of arteries consists on each side of a common carotid trunk, which divides into internal and external carotid arteries, from which numerous branches are given off. The internal carotid arteries are distributed almost entirely to the contents of the cranial cavity internal to the dura mater, and to tlie structures in the cavity of the orbit. The external'carotid arteries, on the other hand, supply structures of tlie head and neck more externally situated. It is to be observed, however, that the vascular supply of the brain is not wholly derived from the internal carotid vessels, but that the vertebral arteries also contribute lirgely to it. THE COMMON CAROTID ARTERIES. The right and the left common carotid arteries are of unequal length. The right common carotid commences at the bifurcation of the innominate artery, behind the right sterno-clavicular articulation ; the left arises in the superior mediastinum from the arch of the aorta, but each terminates at the level of the upper border of the thvroid cartilage ; the left arterv has thus a short intra- 55 802 THE YASCULAE SYSTEM. thoracic course, and so far its relations call for separate consideration ; whilst in the rest of its conrse it passes, like the right common carotid, upwards in the neck and has almost similar relations. Thoracic Portion of the Left Common Carotid. — The thoracic or mediastinal portion of the left common carotid artery (a. carotis communis sinistra) extends from the upper aspect of the aortic arch, a little behind and to the left of the origin of the innominate artery, to the left sterno-clavicular articulation, where the cervical portion commences. It is about one or one and a half inches in length (25 to 37 mm.), and it runs upwards and slightly outwards through the upper part of the superior mediastinum, lying farther back than the innominate artery. Relations. — Posterior. — The vessel is in contact behind and from below upwards with the trachea, the left recurrent laryngeal nerve, the oesopliagus, and the thoracic duct. Anterior. — The left innominate vein runs obliquely across the front of the artery, upon which cardiac branches from the left vagus and sympathetic descend vertically. These structures, together with the remains of the thymus gland and the anterior margins of the left lung and pleura, separate the artery from the manubrium sterni, and from the origins of the sterno-hyoid and sterno-thyroid muscles. Lateral. — The innominate artery below and the trachea above are on the right side. The left pleura, and, on a posterior plane, the left phrenic and vagus nerves and the left subclavian artery are on its left side. Cervical Portion of the Left Common Carotid Artery. — The cervical part of the left common carotid artery is about three and a half inches long ; it extends from the left sterno-clavicular articulation to the level of the upper border of the thyroid cartilage and the lower border of the third cervical vertebra, where it ends by dividing into the external and internal carotid arteries. Course. — It runs upwards, outwards, and backwards, through the muscular and the lower part of the carotid divisions of the anterior triangle of the neck. In the lower part of its extent it is separated from its fellow of the opposite side by the trachea and the oesophagus, and in the upper part by the relatively wide pharynx. Relations. — It is enclosed, together with the internal jugular vein and the vagus nerve, in a sheath of deep cervical fascia — the carotid sheath. Posterior. — The longus colli and scalenus anticus below, and the rectus capitis anticus major above, are separated fi'om the posterior surface of the artery and sheath by the prevertebral fascia and the sympathetic cord. The inferior thyroid artery crosses close behind the vessel about the level of the first ring of the trachea ; lower down the vertebral artery and the thoracic duct are posterior to it, and the vagus nerve lies behind and to its outer side. Anter'ior. — The descendens cervicis nerve descends sujjerficial to the artery, usually outside the sheath, but sometimes enclosed in it. Opposite the sixth cervical vertebra the omo-hyoid muscle and the sternomastoid branch of the superior thyi'oid artery cross the carotid artery, which is overlapped, above the omo-hyoid muscle, by the anterior border of the sterno-mastoid, and it is frequently crossed, in this part of its extent, by the superior thyroid vein. Below the omo-hyoid the artery is covered by the sterno-thyroid, the sterno- hyoid, and the sterno-mastoid muscles, and it may be overlapped by the lateral lobe of the thyroid body ; it is also crossed beneath the muscles by the middle thyroid vein, whilst occasionally a communication between the common facial and anterior jugular veins descends in front of the artery along the anterior border of the sterno-mastoid. Just above the sternum the anterior jugular vein is in front of the arterj', but separated from it by the sterno-hyoid and sterno-thyroid muscles. Lateral. — The trachea and oesophagus, with the recui'rent laryngeal nerve in the angle between them, are internal to the lower part of the artery ; the pharynx and larynx are internal to its upper part. The carotid gland lies immediately to the inner side of the termination of the artery. The internal jugular vein occupies the outer part of the cai'otid sheath, and lies not only to the outer side of the artery, but also overlaps it in fi'ont, especially in the lower pa)'t of its extent. Branches. — As a rule no branches are given off from either of the common carotid arteries except the terminal branches and some minute twigs from each to the correspond- ing carotid sheath and carotid body. THE EXTEEXAL CAEOTID AETEEY. 803 The right common carotid artery, as already stated, differs as regards origin from the left common carotid. In length and general position it corresponds with the cervical portion of the left common carotid, and its relations also are very similar. Such differences as exist may be briefly summarised as follows : — The internal jugular vein on both sides lies external to the artery ; on the left side it runs well in front of the carotid artery in the lower part of the neck, whilst on the right side the vein is separated from the outer surface of the artery at its lower end by a well-marked interval in which the vagus nerve appears. The thoracic duct does not come into relation with the right common carotid, and there is also a Anterior superlicial temporal artery Transverse facial artery Posterior superficial temporal arter>- Angular artery Superficial temporal artery Internal maxillary artery Posterior auricular artery Posterior belly of digastric nuisc" Fu!. 622. — Thk Cahotid and Subclavian Auteiues and their Branches. difference in the relations of the recurrent laryngeal nerves to the arteries on the two sides. On the left side the nerve crosses behind the mediastinal part of the left artery, and lies internal to its cervical part, whilst the corresponding nerve ou the right side passes behind the lower part of the carotid artery in the neck to reach its inner side, and the oesophagus has a less intimate relation with the right than with the left common carotid artery. THE EXTERNAL CAROTID ARTERY. The external c?, and through the mylo-hyoid muscle with the submental branch of the facial. 551) 806 THE VASCULAE SYSTEM. (3) Facial Artery. — The facial or external maxillary artery (a. maxillaris externa. Fig. 622) springs from the front of the external carotid immediately above the lingual, and termmates at the side of the nose, where it divides into lateral nasal and angular branches. Course.— It commences in the carotid triangle and passes upwards internal to the posterior belly of the digastric and the stylo-hyoid muscles. It turns over the upper border of the digastric, and runs forwards and downwards in a groove in the submaxillary gland to the anterior border of the lower margin of the ramus of the mandible, then it turns round the lower border of the body of the mandible, and is continued upwards and inwards, in the face, to its termination. Relations. — In the carotid triangle the artery is comparatively superficial, except just at its origin, which is beneath the anterior fibres of the sterno-mastoid muscle. Its deep surface rests on the middle and superior constrictor muscles which separate it from the lower part of the tonsil. As it passes into the submaxillary triangle it is crossed by the stylo-hyoid muscle and by the posterior belly of the digastric. In the submaxillary triangle it is embedded in a groove in the posterior part of the submaxillary gland, and it is separated by the gland from the more superficially situated facial vein. In the upper part of the submaxillary region the artery is just under cover of the ramus of the lower jaw. Turning round the lower border of the body of the jaw, which it grooves slightly, the artery becomes more superficial than in any other part of its course, being covered only by platysma, fascia, and skin. At this point the facial vein is close behind the artery, and lies on the surface of the masseter. On the face the artery lies between the platysma, the risorius, tlie zygomaticus major, and the levator labii siiperioris, which, with skin and fascia, are superficial to it, and the buccinator and levator anguli oris, which are deeper. The termination of the artery is in the substance of the levator labii superioris et alee nasi. The facial vein, though still posterior to the artery in the face, runs a somewhat straighter course, and is situated at some little distance from it. Branches. — Four named branches are given off in the neck, and seven in the face. In the Neck. — (a) The ascending palatine (a. palatina ascendens. Fig. 624) is a small artery which arises from the facial as it enters the submaxillary triangle. It ascends internal to the internal pterygoid and upon the superior constrictor, and, passing between the stylo-glossus and the stylo-pharyngeus muscles, I'eaches the apex of the petrous portion of the temporal bone, where it turns downwards accompanying the levator palati muscle, pierces the pharyngeal aponeurosis, and enters the soft palate. It supplies the lateral wall of the upper part of the pharynx, the soft palate, the tonsils, and the Eustachian tube, and it anastomoses with the tonsillar branch of the facial, the dorsalis linguse, the posterior palatine branch of the internal maxillary, and with the ascending pharyngeal artery which sometimes replaces it. (6) The tonsillar (ramus tonsillaris), a small artery which arises close to the ascending palatine. It passes upwards between the internal pterygoid and the stylo-glossus, pierces the superior constrictor, and terminates in the tonsil. It supplies the middle and superior constrictor muscles, and it anastomoses with the dorsalis linguse, with the ascending- palatine branch, and with the ascending pharyngeal artery. (c) The submaxillary or glandular branch is frequently represented by two or three small twigs (rami glandulares) which pass directly from the facial trunk into the substance of the submaxillary gland. {(l) The submental branch (a. submentalis) arises from the facial just as the latter vessel turns round the inferior border of the body of the jaw. It is the largest branch given off in the neck, and it runs forwards, on the outer surface of the mylo-hyoid muscle, and internal to the upper part of the submaxillary gland, to the symphysis menti, where it turns upwards round the margin of the jaw, and terminates by anastomosing with branches of the mental and inferior labial arteries. In the neck the submental artery supplies the mylo-hyoid muscle, and the submaxillary and sublingual glands, the latter by a branch which perforates the mylo-hyoid muscle. It anastomoses with the mylo- hyoid branch of the inferior dental and with the sublingual artery. In the face it supplies the structures of the lower lip, and anastomoses with the mental branch of the inferior dental, and with the inferior labial and inferior coronary branches of the facial artery. In the Face. — (e) The inferior labial branch (a. labialis inferior) arises from the front of the facial artery immediately above the lower border of the mandible. It runs forwards beneath the depressor muscles of the angle of the mouth and the BRANCHES OF THE EXTEENAL CAEOTID AETERY. 807 lower lip, supplying the; skin, muscles, and mucous membrane, and anastomoses with the mental branch of the inferior dental, with the inferior coronary, with the submental, and with its fellow of the opposite side. (/) The inferior coronary springs from the front of the facial artery, either together witli or directly above the inferior labial branch. It runs forwards beueatli the depressor anguli oris, and between the fibres of the orbicularis oris and the mucous membrane of the lip. It supplies the adjacent parts, and anastomoses with its fellow of the opposite side, and with the mental, inferior labial, and submental arteries. (V/) The superior coronary (a. labial is superior) springs from the front of the facial beneath the zygomaticus major, and runs forwards and inwards between the orbicularis oris and the mucous membrane of the upper lip to the middle line. It supplies the skin, muscles, and mucous membrane of the upper lip, and by a septal hranch the lower and front part of the septum of the nose. It anastomoses with its fellow of the opposite side, with the lateral nasal, and, on the septum nasi, with the naso-palatine branch of the spheno-palatine artery. (A) The masseteric branch, sometimes represented by several twigs, arises from the posterior aspect of the facial trunk a sliort distance above the lower margin of the jaw. It passes upwards and backwards across the masseter, and anastomoses with the transverse facial artery. (^) The buccal is au inconstant brancli which, when present, arises from the back of the facial artery above the masseteric branch, and runs upwards and backwards, across the buccinator muscle, to anastomose with the buccal branch of the internal maxillary artery. {k) The lateral nasal, one of the terminal branches of the facial artery, is usually small. It ramifies on the ala of the nose, supplying the skin, muscles, and lower lateral cartilages, and anastomosing with the angular branch, witli the nasal branch of the ophthalmic, and with branches of the spheno-palatine artery. (0 The angular (a. angularis), the other terminal branch of the facial, continues the direction of the main trunk along the side of the nose to the inner angle of the orbit. It supplies the skin and muscles of the side of the nose, and anastomoses with the lateral nasal, and with the nasal and palpebral branches of the ophthalmic artery. (4) Occipital Artery (a. occipitalis, Figs. 622, 623, and 650). — This vessel arises from the back of the external carotid artery, below the posterior belly of the digastric muscle, and terminates near the inner end of the superior curved line of the occipital bone by dividing into internal and external terminal branches. Course. — It commences in the carotid triangle and runs upwards and back- wards, parallel with and under cover of the posterior belly of the digastric, to the interval between the transverse process of the atlas and the base of the skull, where it turns backwards in a groove on the under surface of the mastoid portion of the temporal bone ; as it leaves the groove it alters its direction and runs upwards and inwards on the superior oblique muscle to the junction of the inner and middle tliirds of the superiorjcurved line of the occipital lione, where it enters the superticial fascia of the scalp. Relations. — In the first or ascending part of its course the occipital artery crosses successively the internal carotid artery, the hypoglossal nerve, the vagus nerve, the' internal jugular vein, and the spinal accessory nerve; it is covered by the lower fibres of the posterior belly of the digastric and the anterior part of the sterno-mastoid muscle, and, close to its origin, it is crossed by the hypoglossal nerve. In the second, or more horizontal part of its course, it is still under cover of the sterno-mastoid and digastric, and lies internally against the rectus capitis lateralis, which separates it from the vertebi-al artery. In the third pai-t of its coui-se it rests upon the superior oblique and conii)lexus, and is under cover of the sterno-mastoid, the splenius capitis, and the trachclo-mastoid muscles. At its termination it is crossed by the great occipital nerve ; it passes either through the trapezius or between the trapezius and the sterno-mastoid, and pierces the deep fascia of tlie neck before it enters the superficial fascia of the scalp. Branches. — ('0 Muscular branches (rami musculares) go to the surrounding muscles. The sterno-mastoid branch (a. sternucloido-mastoidea) is the most important of this group ; it springs from the commencement of the occipital, is looped downwards across the hypo- glossal nerve, and is continued downwards and backwards, below and in front of "the spinal accessory nerve, into the sterno-mastoid muscle where it anastomoses with the sterno-mastoid branch of the superior thyroid artery. (6) The meningeal are irregular branches (rami meuingei) given off fi-om the occipital 55 c 808 THE VASCULAE SYSTEM. behind the mastoid process. They enter the posterior fossa of the sknll through the anterior condyloid foramen, or through the foramen lacerum posterius ; they supply the upper part of the internal jugular vein, the lateral sinus, and the dura mater in the posterior fossa of the skull, and they anastomose with the middle meningeal and with meningeal branches of the ascending pharjaigeal artery. (c) The mastoid, a small and irregular branch (ramus mastoideus) given off from the occipital behind the mastoid process. It enters the posterior fossa of the skull through the mastoid foramen, supplies the dura mater, and anastomoses with branches of the middle meningeal artery. (d) The princeps cervicis (ramus descendens) is a large branch given off from the occipital upon the surface of the superior oblique. It passes inwax'ds to the outer border of the complexus, wdiere it divides into superficial and deep branches. The supei'ficial branch runs over the complexus, between it and the trapezius, and anastomoses with the superficial cervical artery. The deep branch runs betw^een the complexus and the under- lying semispinalis colli, and anastomoses with branches of the vertebral and profunda cervicis arteries. (e) The auricular (ramus auricularis) is an inconstant branch which, as a rule, is only given off from the occipital when the posterior auricular artery is absent. It ramifies over the mastoid process, and supplies the inner surface of the pinna. (/) The terminal branches (rami occipitales) are internal and external. They ramify in the superficial fascia of the posterior part of the scalp, anastomosing with the posterior auricular and superficial temporal arteries. They are both accompanied by branches of the great occipital nerve, and the internal branch gives off a parietal twig, which passes into the skull through the parietal foramen to supply the walls of the superior longitudinal sinus, and to anastomose with the middle meningeal artery. (5) Posterior Auricular Artery (a. auricularis posterior, Figs. 622, 623). — The posterior auricular artery springs from the back of the external carotid, im- mediately above the posterior heUy of the digastric muscle, and terminates between the mastoid process and the back of the pinna by dividing into mastoid and auricular branches. Course and Relations. — Commencing in the posterior part of the submaxil- lary triangle, it runs upwards and backwards, under cover of the posterior part of the parotid gland, to the interval between the mastoid process and the external auditory meatus. It is accompanied in the terminal part of its course by the posterior auricular branch of the facial nerve. Branches. — (a) Muscular branches are given to the sterno-mastoid, the digastric, and the styloid group of muscles. (6) Parotid branches pass to the lower and posterior part of the parotid gland. (c) A stylo-mastoid branch (a. stylomastoidea) is given off at the lower border of the external auditory meatus. It runs upwards by the side of the facial nei've, enters the stylo-mastoid foramen, and ascends, in the aqueduct of Fallopius, to the upper part of the inner Avail of the tympanum where it terminates by anastomosing with the petrosal branch of the middle meningeal artery. It supplies branches to the external auditory meatus, the mastoid cells, the vestibule, and semicircular canals, the stapedius muscle, and the tympanic cavity (a. tympanica posterior). One of the latter branches, anastomosing with the tympanic branch of the internal maxillary, forms, in young subjects, a vascular circle round the membrana tympani ; other branches anastomose with tympanic branches from the internal carotid and the ascending pharyngeal arteries, and with the auditory branch of the basilar. (d) The auricular, or anterior terminal branch (ramus auricularis), ascends beneath the retrahens aurem muscle. It gives branches to the scalp in the posterior part of the ternpoi'al region, which anastomose with the superficial temporal and occipital arteries, and to the pinna. The latter branches supply both surfaces of the pinna, piercing or turning round the margins of the cartilage to gain the outer surface, and they anasto- mose with the auricular branches of the superficial temporal artery. (e) The mastoid, or posterior terminal branch (rannis occipitalis), runs upwards and backwards along the insertion of the sterno-mastoid muscle. It supplies the sterno- mastoid, the occijjito - frontalis, and the skin, and it anastomoses with the occipital artery. (6) Ascending Pharyngeal Artery (a. pharyngea ascendens, Fig. 624). — This BEANCHES OF THE EXTERNAL CAROTID AETEEY. 809 arises from the inner surface of the lower part of the external carotid, and terminates in the wall of the pharynx and in the soft palate. Course. — Commencing in the carotid triangle, usually as the first or second branch of the external carotid, it ascends on the wall of the pharynx to the apex of the petrous portion of the temporal bone. Relations. — Internally it is iu relation with the constrictor muscles of the pharynx. Behind it arc the transverse processes of the cervical vertebrae, the sympathetic cord, and the rectus capitis anticus major. Externally it is in relation with the internal carotid artery, and it is crossed by the stylo-pharyngeus muscle, the glosso-pharyngeal nerve, and the pharyngeal branch of the vagus. Branches. — The branches of this artery ai'e very irregular and inconstant, but the following have received names : — (a) Pharyngeal Branches (rami pharyngei). — Small twigs which ramify on the walls of the pharynx and supply the middle and superior constrictor mu>:cles, the tonsil, and the lower part of the Eustachian tube. They anastomose with branches of the superior thyroid, lingual, and facial arteries. (b) Prevertebral. — Small branches distributed to tlie prevertebral nuisclcs and fascia, the deep cervical glands, and the large nerve trunks. They anastomose with tlie ascending- cervical and vertebral arteries. (c) Meningeal (a. meningea posterior), one or more small branches which enter the craniima by the anterior condyloid, the posterior lacerate, or the middle lacerate foramen, and supply the dura mater. They anastomose with branches of the middle meningeal and vertebral arteries. (d) Tympanic (a. tympanica inferior), a small artery which accompanies the tympanic branch of the glosso-pharyngeal nerve to the tympanic cavity, where it anastomoses with the other tympanic arteries. (e) Palatine. — A very variable artery which sometimes replaces the ascending palatine branch of the facial artery. When present it springs from the upper part of the ascend- ing pharyngeal artery, pierces the pharyngeal aponeurosis above the upper border of the superior constrictor muscle, and descends into the soft palate with the levator palati muscle. It supplies the mucous membrane of the snpero-lateral part of the pharyngeal wall and the tissues of the soft palate, and it anastomoses with the palatine branches of the internal maxillary, the facial, and the lingual arteries (7) Superficial Temporal Artery (a. temporalis superiicialis, Fig. 622). — This artery, one of the terminal branches of the external carotid, commences iu the upper part of the parotid gland, behind the neck of the mandible, and terminates in the scalp, from one to two inches (25 to 50 mm.) above the zygoma, by dividing into an anterior and a posterior terminal branch. Course. — The artery ascends over the posterior root of the zygoma, and passes into the superficial fascia of the temporal region. It is accompanied by the auriculo-temporal nerve and by the superficial temporal vein which usually lies posterior to it. As it crosses the zygoma it lies immediately beneath the ekin, and it may be easily compressed against the subjacent bone. Branches. — (i^O Parotid, small l)ranclies (rami parotidci) to the upper part of the parotid gland < {()) Articular, to the temporo-mandibular articulation. (c) Auricular. — Small branches (rami auriculares anteriores) to the outer sui'face of the pinna and to the external auditory meatus. They anastomose on the surface of the pinna with branches of the posterior auricular artery, and in the external meatus with branches of the internal maxillary artery. ((/) Transverse Facial (a. transversa faciei). — A branch of moderate size which rises in the substance of the parotid gland. It emerges from the upper part of the anterior border of the gland, runs forwards across the masseter, below the zygoma and above Stenson's duct, accompanied by the infra-orbital branches of the facial nerve which may lie either above or below it. It is distributed to the parotid gland, the masseter, Stenson's duct, and the skin, and it terminates iu branches which anastomose with the infra-orbital and buccal branches of the internal maxillary artery, and with the buccal and masseteric bi'anches of the facial artery. (e) Middle Temporal (a. temporalis media). — A hranch which usually springs from the superhcial temporal in the parotid gland. It crosses the zygoma, pierces the temporal 810 THE VASCULAE SYSTEM/ fascia and the temporal muscle, and terminates in the temporal fossa by anastomosing with the deep temporal branches of the internal maxillary artery. (/■) Orbital (a. zygomatioo-orbitalis). — This branch may spring directly from the superficial temporal, but it is frequently a branch of the middle temporal. It runs forwards above the zygoma between the two layers of the temporal fascia. It supplies branches to the orbicularis palebrarum, and anastomoses, through the malar bone and round the outer margin of the orbit, with the lachrymal and palpebral branches of the ophthalmic artery. ig) The anterior terminal branch (ramus frontalis) runs forwards and upwards, in a tortuous course, through the superficial fascia of the scalp towards the' frontal eminence, lying at first upon the temporal fascia, and then upon the epicranial aponeurosis. It supplies the frontalis and the orbicularis palpebrarum, and anastomoses with the lachrymal Auterior meningeal artery Anterior branch of middle meningeal artery Deep temporal arteries Infraorbital artery Middle menin- geal artery Small menin- geal artery Posterior superior dental artery Buccal artery Mental ai'tery - Submental artery Posterior branch of middle men- ingeal artery Superficial tem- poral artery Internal maxil- lary artery ^ Occipital artery Inferior dental __ artery Mylo-hyoid artery Posterior aunculai artery Stern o-mastoid muscle Levator anguli scapulae mubcle Trapezius muscle Occipital artei y External carotid artery Facial artery Lingtial artery Internal carotid aitery- Scalenus medius muscle Superior thyroid artery Common carotid artery Fig. 623.— The External Carotid, Internal Maxillary, and Meningeal Arteries. and supraorbital branches of the ophthalmic artery, with the posterior terminal branch of the superficial temporal, and with its fellow of the opposite side. (A) The posterior terminal branch (ramus parietalis), less tortuous than the anterior, runs upwards and backwards in the superficial fascia of the scalp. It anastomoses, anteriorly, with the anterior terminal branch, posteriorly with the posterior auricular and occipital arteries, and, across the middle line, with its fellow of the opposite side. It supplies the skin and fascia, and the attrahens and attollens aurem muscles. (8) Internal Maxillary Artery (a. maxillaris interna). — The internal maxillary artery coniinences in the parotid gland behind the neciv of the lower jaw, and terminates in the spheno-maxillary fossa. Course and Relations. — Although the internal maxillary artery is only a short trunk it has many important relations, in the consideration of which it is convenient to arbitrarily divide the vessel into three parts. The first part extends from the back of the neck of the mandible forwards into the zygomatic fossa as BEANCHES OF THE EXTEE]^AL CAEOTID AETEEY. 811 far as the lower border of the external pterygoid muscle. It lies between the spheno-maudibular ligament and the neck of the jaw, along with the auriculo- temporal nerve and the internal maxillary vein. The second part is in the zygo- matic fossa, and ascends upwards and forwards. It may lie superficial to, or under cover of, the lower head of the external pterygoid muscle. In the former case it is situated between the temporal and external pterygoid muscles, and in the latter between the external pterygoid muscle and the branches of the third division of the fifth nerve. The third part passes between the upper and the lower heads of the external pterygoid, tiirough the pterygo-maxiUary fissure and into the spheno-maxillary fossa. Branches. — From the first part. — («) Deep auricular (a. auricularis profunda), a small branch which rises in the parotid gland and jjasses upwards to enter the external auditory meatus. It supplies the temporo-mandibular joint, the parotid gland, and the external meatus, and anastomoses with branches of the superficial temporal and posterior auricular arteries (6) The tympanic (a. tympanica anterior), a variable and small branch which com- mences in the parotid gland. It runs upwards and backwards, traverses the Glasserian fissure, and enters the tympanum through its outer wall. In the tympanic cavitv it anastomoses with tympanic branches from the internal carotid and the ascending j)haryngeal arteries, and with the stylo-mastoid branch of the posterior auricular, forming with the latter, in young subjects, a circular anastomosis round the tj-mpanic membrane. (c) Middle Meningeal (a. meningea media). — The lai-gest liranch of the internal maxillary. It ascends between the external pterygoid muscle and the spheno-mandibular ligament, and passes between the two roots of the auriculo-temjioral nerve and through the foramen spinosum, to enter the middle fossa of the cranial cavity. Before it enters the skull it lies behind the third division of the fifth nerve, and is accompanied by two veuce comites which also pass through the foramen spinosum. In the middle cranial fossa it passes forward, and upwards for a short distance, in a groove on the great wing of the sphenoid, between the dura mater and the bone, and divides into anterior and postex'ior terminal branches. Branches.— (i.) Petrosal (ramus j^etrosus superficialis). — A small branch which arises from llie middle meningeal soon after it enters the cranium. It passes through the hiatus Fallopii and anastomoses with the stylo-mastoid branch of the posterior auricular artery ; it also sends some small branches into the tym^janic cavity (ii.) Gasserian. — Minute branches which supply the Gasserian ganglion and the roots of the fifth cranial nerve. (iii.) Tympanic (a. tympanica superior). — A small twig wliich reaches the tympanic cavity through the canal for the tensor tympani muscle, or througli the petro-squamous siUiue. (iv.) Orbital. — An anastomosing branch which occasionally arises from the anterior ternnnal branch. It passes through the foramen lacerum anterius into the orbit, and anastomoses with the lachrymal artery. (v.) Anterior terminal, the larger of the two ternnnal branches, passes upwards along the great wing of the sphenoid to the antero-inferior angle of the paiietal bone, where it is sometimes enclosed in a distinct l)ony canal ; it is continued upwards a short distance behind tlie anterior border of the parietal bone almost to the vertex of the skull, sending branches Ibrwai-ds into the anterior, and backwards towards the posterior cranial fossa. (vi.) The posterior terminal branch passes backwards from the great wing of the sphenoid to the squamous jiart of the temporal bone, beyond which it ascends to the middle of the inner surface of the parietal bone. It sends branches upwards to the vertex, and backwards towards the posterior cranial fossa. By means of its various branches the middle meningeal artery anastomoses with its fellow of the opposite side, with meningeal branches from the occipital, ascending pharyngeal, ophthalnuc, and lachrymal arteries ; also with the stylo-mastoid branch of the posterior auricidar, the small meningeal artery, with the deep temjtoral arteries through the substance of the temporal bone, and with its fellow of the opposite side. (d) A small meningeal branch (ramus meningeus accessorius) may arise either directly from the hrst part of the internal maxillary or from its middle meningeal branch. It passes upwards, on the inner side of the external pterygoid muscle, enters the middle fossa of the skull through the foramen ovale, supplies the Gasserian ganglion and the dura mater, and terminates by anastomosing with branches of the middle meningeal and internal carotid arteries. (e) The inferior dental (a. alveolaris infei-ior) is a braucli of moderate size whicli passes downwards between the splieno-mandibular ligament and the mandible to the mandibular foramen. It is accompanied by the inferior dental nerve which lies in front. 812 THE YASCULAE SYSTEM. After entering the foramen it descends in the mandibular canal, and terminates at the mental foramen by dividing into mental and incisive branches. Branches. — Before it enters the mandibular foramen it gives off two branches. (i.) The lingual, a small twig to the buccal mucous membrane which accompanies the lingual nerve, (ii.) The mylo-hyoid (ramus niylohoideus), a small branch which is given off immediately above the mandibular foramen. It pierces the spheno-mandibular ligament, and descends in the mylo-hvoid groove, in company with the mylo-hyoid nerve, to the floor of the mouth, where it anastomoses, on the superficial surface of the mylo-hyoid muscle, Avith the submental branch of the facial artery. In the mandibular canal the following branches are given off : — (i.) Molar branches to the molar teeth, (ii.) Bicuspid branches to the bicuspid teeth, (iii.) The incisive terminal branch, which sujjjslies the incisor teeth and anastomoses with its fellow of the opposite side, (iv.) The mental terminal branch (a. mentalis), which jjasses through the mental foramen, emerges beneath the dejjressor labii inferioiis, and anastomoses with its fellow of the opposite side, with the inferior coronary, the inferior laliial, and with the submental arteries. From the second 2^art. — (a) The masseteric (a. masseterica), a small branch which passes directly outwards, through the sigmoid notch, to the deep surface of the masseter muscle. It anastomoses in the substance of the muscle with branches of the transverse facial and with the masseteric branches of the facial artery. {b) Deep Temporal. — Two in number, anterior (a. temporalis profunda anterior) and posterior (a. temporalis profunda posterior). They ascend between the temporal muscle and the squamous portion of the temporal bone, siipplying the muscle and anastomosing with the temporal and lachrymal arteries, and, through the substance of the temporal bone, with the middle meningeal artery. (c) Small pterygoid branches (rami pterygoidei) supply the internal and external pterygoid muscles. (fZ) The buccal (a. buccinatoria), a long, slender branch which passes obliquely forwards and downwards with the long buccal nerve. It supplies the buccinator muscle, the skin and mucous membrane of the cheek, and anastomoses with the buccal branch of the facial artery. From the third part. — (a) A posterior superior dental branch (a. alveolaris superior posterior) descends in the zygomatic fossa, on the posterior surface of the superior maxilla, and ends in branches which supply the molar and bicuspid teeth and the mucous membrane of the antrum, they also give twigs to the gums and to the buccinator muscle. (b) Au infra-orbital branch (a. infra-orbitalis) commences in the spheno-maxillary fossa. It enters the orbit through the spheno-maxillai-y fissure, and runs forwards in the infra- orbital groove and canal to the infra-orbital foramen, through which it passes to emerge on the face beneath the levator labii superioris. Whilst in the infra-orbital groove it gives branches to the inferior rectus, the inferior oblique and the lachrymal gland. In the infra- orbital canal it gives small twigs to the incisor and canine teeth (aa. alveolares superiores anteriores) and to the antrum. In the face it sends branches upwards to the lower eyelid, to the lachrymal sac, and to the nasal process of the superior maxilla, which anastomose with branches of the ophthalmic and facial arteries ; other branches run downwards to the upper lip, where they anastomose with the superior coronary artery ; lastly, some branches run outwards into the cheek to unite with the transverse facial and the buccal arteries. (c) The posterior or descending palatine (a. palatina descendens) runs downwards through the spheno-maxillary fossa, passes through the posterior palatine canal, and reaches the mucous memln-ane of the roof of the mouth, where it runs forwards, internal to the alveolar process, to terminate in a small branch which ascends through the anterior palatine fossa and Stensen's canal and anastomoses with the spheno-palatine branch of the internal maxillary artery. As it descends it gives off several small twigs which pass, through the accessory palatine canals to supply the soft palate, and to anastomose with the ascending palatine and tonsillar branches of the facial and with the ascending pharyngeal artery. In its course forwards in the roof of the mouth it supplies the gums and the raucous membrane of the hai'd palate, and also the palate and superior maxillary bones. (d) The Vidian (a. canalis pterygoidei) is a long, slender branch which runs back- wards through the Vidian canal with the Vidian nerve. It supplies branches to the upper part of the pharynx, to the levator and tensor palati muscles, and to the Eustachian tube. One of the latter branches passes along the wall of the Eustachian tube to the tympanic cavity, where it anastomoses with the other tympanic arteries. (e) The pterygo-palatine is a small artery which runs backwards, with the pharyngeal branch of Meckel's ganglion, to the roof of the pharynx. It supplies the upper and back THE INTERNAL CAEOTID ARTEEY. 813 part of the roof of the nose, the roof of the pharynx, the sphenoidal sinus, and the lower part of the Eustachian tube, and anastomoses with the Vidian branch of the internal carotid. (/) The spheno-palatine branch (a. spheno-palatina) springs from the termination of the internal maxillary artery. It passes inwards through the spheno-palatine foramen into the nasal cavity, where it divides into many branches. One of these, the internal nasal or naso-palatine, which is sometimes looked upon as the continuation of the artery, ci'osses the back part of the roof of the nose, and descends in a groove on the vomer to the incisive foramen, where it anastomoses with the termination of the posterior palatine artery and with the septal branch of the superior coronary. The outer or external nasal branches of the spheno-jDalatine artery supply the greater part of the outer wall of the nasal fossa and the cavity of the antrum, anastomosing with branches of the infraorbital, ethmoidal, and lateral nasal arteries. Branches are also distributed to the ethmoidal cells, to the sphenoidal sinus, and to the upper j^art of the pharynx. THE INTERNAL CAROTID ARTERY. The internal carotid artery (a. carotis interna, Figs. 622, 624, and 627) com- mences at the termination of the common carotid, opposite the upper border of the Frontal artery Nasal artery Ciliary arteries Facial artery Vertebral arteries - Internal carotid artery Ascending pharyngea artery Ascending palatine artery Stylo-glossns muscle..._ Stylo-pliaryngeus niusclp Posterior auricular artery. Occipital artery. Facial artery- Lingual artery. External carotid artery^ Superior thyroid artery. Common carotid _ artery Vertebral artery Thyroid axis artery Subclavian artery _ Internal niamniaiy artery [nnoniinate artery Fui. 621.— TiiK t'AUOTU), Subclavian, and Vkutkbual Auteiues and theu{ Main Bhanches. thyroid cartilage, and terminates in the middle fossa of the skull, close to the commencement of the fissure of Sylvius, where it divides into the middle and anterior cerebral arteries. Course. — It passes through the carotid and submaxillary triangles, traverses the carotid canal of the temporal bone, crosses the upper part of tlie foramen lacerum medium, aiul runs in the outer wall of the cavernous sinus in the middle fossa of the skull. At its origin it lies behind and to the outer side of the external carotid, but as 814 THE VASCULAE SYSTEM. it ascends internal to the posterior beUy of the digastric and the stylo-hyoid it gets to the inner side of that A'esseL After entering the submaxillary triangle it ascends, in relation with, the posterior surface of the parotid gland, to the carotid canal iu the temporal bone, through which it passes to the apex of the petrous portion of the temporal bone, where it turns upwards, through the upper part of the foramen lacerum medium, into the middle cranial fossa. It then runs forwards in the outer wall of the cavernous sinus to the lower root of the small wing of the sphenoid, there it turns upwards and then backwards and outwards to its termination. Relations. — The relations of the various parts of the artery require separate cousideration. I71 the Xeck. — Posterior. — The rectus capitis auticus major, the prevertebral fascia, and the sympathetic cord, separate it from the transverse processes of the cervical vertebrae, and somewhat to its outer side are the internal jugular vein and the vagus nerve. The spinal accessory and the glosso-pharyngeal nerves are also behind and to the outer side of the artery for a short distance in the upper pai't of the neck, and they intervene between it and the internal jugular vein. Internal or deep to the internal carotid is the external carotid artery for a short distance below, and afterwards the wall of the pharynx, the ascending pharyngeal artery, the pharyngeal plexus of veins, and the external and internal laryngeal nerves. Just before it enters the temporal bone the levator palati muscle is to its inner side. External or superficial to it are the sterno-mastoid, skin, and fascia, and it is crossed beneath the sterno-mastoid from below upwards by the hypoglossal nerve, the occipital artery, and the posterior auricular artery. It is also crossed more super- ficially by the digastric and stylo-hyoid muscles, and in the upper part of its extent it is covered by the posterior part of the parotid gland. Passing obliquely across its anterior and outer surface, and sejoarating it from the external carotid artery, are the following structures, viz. : the stylo-pharyngeus, the tip of the styloid process or the stylo-glossus muscle, and the stylo-hyoid ligament, the glosso-pharyngeal nerve, the pharyngeal bi'anch of the vagus, and some sympathetic twigs. In the Carotid Canal. — The artery, as it passes upwards and inwards, is in front of and below the cochlea and the tympanum ; behind and internal to the canals for the Eustachian tube and tlie tensor tympani ; and below the Gasserian ganglion. The thin lamina of bone which separates it from the tympanum is frequently perforated, and that between it and the Gasserian ganglion is not infrequently absent. In its course through the canal it is accompanied by small veins and nerves. The veins are tributaries from the tympanum, which communicate above with the cavernous sinus and below with the internal jugular vein. The nerves are the upwai'd continuations of the sympathetic cord ; they form two plexuses — one on the outer side of the artery, the carotid plexus, and one on the inner side, the cavernous plexus. As it enters the cavity of the cranium the internal cai'otid artery pierces the external layer of the dura mater and passes between the lingula and the sixth cranial nerve externally, and the posterior petrosal pi'ocess of the body of the sphenoid internally. In the Cranial Cavity. — The artery runs forwards in the outer wall of the cavernous sinus in relation with the third, fourth, the ophthalmic division of the fifth, and the sixth cranial nerves externally, and with the endothelial wall of the sinus internally. When it reaches the lower root of the small wing of the sphenoid it turns upwards to the inner side of the anterior clinoid process, pierces the inner layer of the dura mater, and comes into close relation with the under surface of tlie optic nerve immediately behind the optic foramen. It then turns abruptly backwards beneath the optic nerve, and on the inner side of the anterior clinoid process which it frequently grooves ; inclining outwards, it runs between the second and third nerves, and beneath the anterior perforated space, to the inner end of the stem of the Sylvian fissui-e, where it turns upwards, at some distance from the outer side of the optic chiasma, and, after piercing the arachnoid, divides into its two terminal branches, the anterior and middle cerebral arteries. Branches of the Internal Carotid Artery. Branches are given off from the internal carotid in the temporal bone and in the cranium, but, as a rule, no branches are given off in the neck. In the Temporal Bone. — (1) A tympanic branch (ramus carotico-tympanicus), very small, perforates the posterior wall of tlie carotid canal, and anastomoses in the tympanum with the stylo-mastoid artery and with the tympanic branches of the internal maxillary and ascending pharyngeal arteries. BEANCHES OF THE INTERNAL CAEOTID AETEEY 815 (2) The Vidian is a small and inconstant branch -which accompanies the great deep petrosal nerve in the Vidian canal : it anastomoses with the Vidian branch of the internal maxillary arter}-. In the Cranium. — (1) Cavernous, small branches to the walls of the cavernous sinus and to the third, fourth, fifth, and sixth nerves. (2) Gasserian, minute twigs which supply the Gasserian ganglion. (3) Pituitary branches j^ass to the pituitary body. (4) Meningeal branches ramify in the dura mater of the middle cranial fossa, anasto- mosing witli the branches of tlie middle and small meningeal arteries. (5) Ophthalmic Artery (a. ophthalmica, Fig. 624). — This artery springs from the front and inner side of the internal carotid as it turns upwards on the inner side of the anterior clinoid process. It passes forwards and outwards, beneath the optic nerve and through the optic foramen into the orbital cavity. In the orl:»it it runs forwards for a short distance on the outer side of the optic nerve, and it is in relation externally with the lenticular ganglion and the external rectus muscle : turning upwards and inwards, it crosses between the optic nerve and Middle internal frontal artciy Coi-pus callosinn Sejituni kiciiiuiii Posterior internal frontal artery Parieto-occipital artery Anterior internal / frontal arterv Internal orbital arterv Anterior cerebral artery External orbital artery Middle cerebral artery Calcarine artery Temporal branches of posterior cerebi'al Temporal branch of middle cerebral Posterior cer- Crus ebral artery cerebri Fic. 62.'). — DisTRinrTioN of the Cerebral Arteries ox the Mesial, Tentorial, and Ixfekior Surfaces of the Cerebral Hemispheres. The auterior cerebral artery is coloured green, the middle cerebral artery red, and the posterior eereltral arterj' orange. the superior rectus to the inner wall of the orbit, where it turns forwards to terminate at the inner and front part of the orbital cavity by dividing into frontal and nasal l.)ranches. It is accompanied at first by the nasal nerve, and in the terminal part of its course by the infra- trochlear nerve. Branches. — TIk- l)ranchos of the oiihthabnic artery are luimerous. («) The posterior ciliary, usually six to eight in number, run forwards at the sides of tlie oiitic nerve ; they suou divide into numerous branches wliicli pieree the l)ack part of the sclerotic coat ; the majority t-erminate in the choroid coat of the eye as the short cilnirji arteries (aa. ciliares jiosteriores Ijreves), but two of larger size, the long ciliary arteries (aa. ciliares posteriores longa^), run forwards, one on each side, almost in the horizontal plane of the eyeball, between the sclerotic and the choroid coats, to the base of the iris, where they divide. The resulting l.tranchi-s anastomose together and form a circle at the outer periphery of the iris, from which secondary branches run inwards and anasto- mose together in a sccdikI cii-cle near the inner margin of the iris. (b) The central artery of the retina (a. centralis retina?) arises near to, or in common with, the preceding vessels. It pierces the inner and under side of the optic nerve, about half an inch (12 nun.) behind the sclera, and runs in its centre to the retina, where it breaks up into terminal liraiiches. ^(•1 Kecurrent (a. meiiingea anterior). — A small branch which passes backwards through the spheiuiidal iissure into the middle fossa of the cranium, where it anastomoses with the middle and small meningeal arteries, and with the meningeal branches of the internal carotid and lachrymal arteries. 816 THE VASCULAR SYSTEM. (d) The lachrymal artery (a. lacrimalis) arises from the ophthalmic on the outer side of the optic nerve. It runs forM^ards along the upper border of the external rectus to the upper and outer angle of the orbit, and in its course gives off branches to the lachrymal gland, muscular branches to the external and superior recti, j^alpebral branches to the upper eyelid and the upper and outer part of the forehead, temporal and malar branches, which accompany the temporal and malar branches of the tempore -malar nerve, to the face and the temporal fossa respectively; anterior ciliary branches (aa. ciliares anteriores), which perforate the sclera behind the corneo- scleral junction and anastomose with the posterior ciliary arteries ; and a recurrent meningeal branch, which passes backwards througli the outer part of the sphenoidal fissi;re to anastomose in the middle fossa of the skull with the middle meningeal arteiy. (e) Muscular. — These branches are usually arranged in two sets, outer and inner. The former supply the upper and outer, and the latter the lower and inner orbital muscles. They anastomose with muscular branches from the lachrymal and the supra-orbital vessels, and they give off anterior ciliary branches. (/) The supra-orbital branch (a. supra-orbitalis) is given off as the ophthalmic artery crosses above the optic nerve. It jaasses round the inner borders of the superior rectus and levator palpebrae muscles, and runs forwards between the latter and the periosteum to the supra-orbital notch, accompanying the frontal and supra-orbital nerves. Passing through the notch it reaches the scalp, and, perforating the frontalis muscle, anastomoses with the superficial, temporal, and frontal arteries. (g) Ethmoidal branches, anterior (a. ethmoidalis anterior) and posterior (a. ethmoidalis posterior), arise from the ophthalmic as it runs forwards along the inner boundary of the orbital Ascending parietal artery Ascending frontal arteries Parieto-occipital artei-y Calcarine artery. Calcarine artery Inferior external frontal artery External orbital artery Parieto-temporal artery Temporal brandies of middle cerebral Fig. 626. — Distribution of Cerebral Arteries on the Outer Surface of the Cerebrum. Anterior cerebral artery is coloured greeu, the middle cerebral red, and the posterior cerebral orange. cavity. They j^ass inwards between the superior oblique and the internal rectus. The posterior, which is much the smaller of the two, traverses the posterior ethmoidal canal, and sup^^lies tlie posterior etlimoidal cells and tlie posterior and upper part of the outer wall of the nasal cavity. Tlie anterior ethmoidal artery passes tlirough the anterior ethmoidal canal with the nasal nerve, enters the anterior fossa of the skull, and crosses the cribriform plate of the ethmoid to the nasal notch, through which it reaches the nasal cavity, where it descends with the nasal nerve in a groove on the back of tlie nasal bone, and finally passes between the upper lateral cartilage and the lower border of the nasal bone to the tip of the nose. It supplies branches to the membranes of the brain in the anterior cranial fossa as well as to the anterior ethmoidal cells, the frontal sinus, the anterior and uj^per part of the nasal mucous membrane, and the skin on the dorsum of the nose. (h) Palpebral branches (aa. pal];)el)rales), upper and lower, are given off near the termination of the ophthalmic They are distriljuted to the upper and lower eyelids, and they anastomose with tlie lachrymal, supra-orbital, and infra-orbital arteries. (i) The nasal terminal branch (a. dorsalis nasi) passes out of the orbit above the internal tarsal ligament. It pierces the pal])ebral fascia, and terminates on the side of the nose by anastomosing with the augular liraurh of the- farial artery. (k) The frontal terminal branch (a. frontalis) pierces the jialj^ebral fascia at the uj^per and inner part of the orbit, and ascends, with the suijra-trochlear nerve, in the suijerficial fascia of the anterior and mesial part of the scalp, anastomosing with its fellow of the opposite side and with the supra-orbital artery. (6) The posterior communicating artery (a. communicans posterior) rises from the internal carotid near its termination, it runs backwards below the optic tract and in BEANCHES OF THE INTEENAL CAEOTID AETEEY. 817 front of the crus cerebri, and passing above the third nerve, joins the posterior cerebral artery forming part of the circle of Willis. It gives branches to the optic tract, the crus cerebri, the interpeduncular region, and the uncinate convolution of the brain. The posterior communicating artery varies much in size ; it may be small on one or both sides, sometimes it is very large on one side ; occasionally it replaces the posterior cerebral artery, and it sometimes arises from the middle cerebral artery. (7) The anterior choroidal (a. choroidea) is a small branch, which also rises near the termination of the internal carotid ; it passes backwards and outwards, between the crus cerebri and the uncinate convolution, to the lower and front part of the choroidal fissure which it enters, and it terminates in the choroidal plexus in the descending cornu of the lateral ventricle. It supplies the optic tract, the crus cerebri, the uncinate convolution, and the posterior part of the internal capsule. (8) Anterior Cerebral Artery (a. cerebri anterior). This is the smaller of the two terminal branches of the internal carotid. It passes for\Yards and in- wards, above the optic chiasma and immediately in front of the lamina cinerea, to the commencement of the great longitndinal fissure, where it tnrns round the genu of the corpus callosum, and runs backwards to the parietal lobe of the brain. At the commencement of the great longitudinal fissure it ,is closely connected with its fellow of the opposite side by a wide but short anterior conununicating artery (a. communicans anterior), and in the remainder of its course it is closely accompanied by its fellow artery of the opposite side. Branches. — Branches of all the cerebral arteries are distributed both to the basal ganglionic masses of the brain and to the cerebral cortex ; they therefore form two dis- tinct groups — (a) central or ganglionic ; (6) cortical. The branches of the anterior cerebral include : {a) Central or ganylionic branches. — The antero-mesial arteries, a small group of vessels, constitute the central branches of the anterior cerebral artery ; they pass upwards into the base of the brain in front of the optic chiasma, and supply the rostrum of the corpus callosum, the lamina cinerea, and the septum lucidum. (6) Cortical branches. — {b^) Internal orbital, one or more small branches which supply the internal orbital convolution, the gyrus rectus, and the olfactory lobe. (J)-) Anterior internal frontal, one or more branches which are distributed to the anterior and lower part of the marginal convolution, and to the anterior portions of the superior and middle frontal convolutions. {!?) A middle internal frontal is distributed to the posterior part of the marginal convolution, and to the upper portions of the superior and ascending frontal and ascend- ing parietal convolutions. {b^) The posterior internal frontal runs backwards to the quadrate lobule. It supplies the corpus callosum, the quadrate lobe, and the upper part of the superior parietal lobule. (9) Middle Cerebral Artery (a. cerebri media). — The middle cerebral is the larger of the two terminal branches, and the more direct continuation of the internal carotid artery. It passes outwards in the fissure of Sylvius to the outer surface of the island of Eeil, which it crosses; and divides, in the posterior limiting sulcus of Eeil, into parieto-temporal and temporal terminal branches. Branches. — {a) Central or gayiglionic. — Numerous and very variable in size. These branches are given off at the base of the brain, in the region of the anterior perforated space. Two sets, known as the internal and the external striate arteries, are distinguishable. {a}) The internal striate arteries pass upwards through the two inner segments of tlie lenticular nucleus (globus pallidus) and the internal capsule to terminate in the caudate nucleus. They supply the anterior {tortious of the lenticular and caudate nuclei and of the internal capsule. (a-) The external striate arteries pass u{)wards through the outer segment (puta- men) of the lenticular nucleus, or between it and the external capsule, and they form two sets : an anterior, the lenticulo-striate, and a posterior, the lenticulo-optic ; both sets traverse the lenticular nucleus and the internal capsule, but the lenticulo-striate arteries terminate in the caudate nucleus, and the lenticulo-optic in the optic thahuuus. One of the lenticulo-sti-iate arteries, which passes in the first instance round the outer side of the lenticular nucleus, and afterwards through its substance, is larger than its companions ; it fi'equently ruptures, and is known as the artery of cerebral haemorrhage. 56 818 THE VASCULAE SYSTEM. (b) Cortical branches are given off as the middle cerebral artery passes over the surface Of the island of Eeil at the bottom of the Sylvian fissure, as follows : — (b^) The inferior external orbital runs forwards and outwards, and is distributed to the outer part of the orbital surface of the frontal lobe and to the inferior frontal con- volution. (b-) The ascending frontal branch, turns round the upper margin of the Sylvian fissure, and is distributed to the ascending frontal convolution and to the posterior jDart of the middle frontal convolution. (b^) The ascending parietal branch emerges from the Sylvian fissure and passes upwards along the posterior border of the ascending parietal convolution, supplying that convolution and the superior parietal lobule. (6-*) The temporal branch passes out of the Sylvian fissure, and turns downwards to supply the superior and middle temporal convolutions. (b^) The parieto-temporal branch continiies backwards, in the direction of the main stem, and emerges from the posterior end of the Sylvian fissure ; it supplies the inferior parietal lobule, the external occipital convolutions, and the posterior part of the temporo- sphenoidal lobe. Vertebral Artery. The vertebral artery (a. vertebralis, Eigs. 624 and 627) is the first branch given off from the subclavian trunk ; it arises from the upper and back part of the parent stem, opposite the interval between the anterior scalene and the longus colli muscles, and terminates at the lower border of the pons Varolii by uniting with its fellow of the opposite side to form the basilar artery. Course and Relations. — The vertebral artery is divisible into four parts. The first part runs upwards and backwards, between the scalenus anticus and the outer border of the longus colli, to the foramen in the transverse process of the sixth cervical vertebra. It is surrounded by a plexus of sympathetic nerve fibres, covered anteriorly by the vertebral and internal jugular veins, and crossed in front by the inferior thyroid artery. On the left side the terminal part of the thoracic duct also passes in front of it. The second part runs ujjwards through the foramina in the transverse processes of the upper six cervical vertebrae. As far as the second cervical vertebra its course is almost vertical ; as it passes through the transverse process of the axis, however, it is directed obliquely upwards and outwards to the atlas. It is surrounded by a plexus of sympathetic nerve fibres, and also by a plexus of veins. The artery lies in front of the trunks of the cervical nerves, and internal to the intertransverse muscles. The third part emerges from the foramen in the transverse process of the atlas, between the anterior primary division of the sub-occipital nerve internally and the rectus capitis lateralis exter- nally, and runs almost horizontally backwards and inwards round the outer side and back of the superior articular process of the atlas. In this course it enters the sub-occipital triangle, where it lies in the groove on the upper surface of the posterior arch of the atlas (sulcus arterise vertebralis). It is separated from the bone by the sub-occipital nerve, and is overlapped superficially by the adjacent borders of the superior and inferior oblique muscles. Finally, this part of the artery passes beneath the obhque ligament of the atlas and enters the spinal canal. The fourth part pierces the sj)inal dura mater and runs upwards into the cranial cavity. It passes between the roots of the hypoglossal nerve above and the first dentation of the hgamentum denticulatum below, pierces the arachnoid, and, gradually inclining inwards in front of the medulla, reaches the lower border of the pons Varolii, where it unites with its fellow of the opposite side to form the basilar artery. Branches. — Fnjnt the first 2jart. — As a rule there are only a few small muscular twigs from this portion of the artery. From the second part. — (1) Muscular branches which vary in number and size. They supply the deep muscles of the neck, and anastomose with the profunda cervicis, the ascending cervical, and tlie occipital arteries. (2) Spinal branches (rami spinal es) pass from the inner side of the second part of the vertebral artery through the intervertebral foramina into the spinal canal, where they give off twigs which pass along the roots of the spinal nerves to reinforce the anterior and VEETEBEAL AETEEY. 819 posterior spinal arteries ; tliey supply the bodies of the vertebrae and the intervertebral discs, and they anastomose with corresponding arteries above and below. Frovi the tkinJ jKivt. — (1 ) Muscular branches to the sub-occipital muscles. (2) Anastomotic branches wljich nnitc with the princeps cervicis branch of the occi- pital and with the profunda cervicis artery. F^rmi the fourth 'part. — (1) Meningeal (rami meningei). — One or two small branches given off before the vertebral artery pierces the dura mater. They ascend into the pos- terior fossa of the skull, whei'e they anastomose with meningeal branches of the occipital and ascending pharjMigeal arteries, and occasionally with branches of the middle meningeal artery. (2) Posterior Spinal (a. spinalis posterior). — The posterior spinal branch springs from Antftrior comiimnieating artery Olfactory tract Anterior cerebral artery Optic cliiasma Irit'iiiKlibuluiii 3rd cranial nerve - 4tli I'ranial iier\p ilth cranial nerve lOtli cranial nerve lltli cranial ni>rvt Middle cerebral artery Internal carotid artery AJiterior choroidal artery Posterior com- municating artery Posterior cerebral art«ry Superior cere- bellar artery Transverse pontine arteries Basilar artery Anterior inferior cere- bellar artery Posterior inferior cerebellar artery Vertebral artery l-.'lli iiaiiial nerve Anterior spinal art«ry Fig. 6"27. The Akteiues ok the Base ok the Brain. The Circle w Willis. the vertebral directly aftLM- it has pierced the dura niator. It runs downwards upon the side of the medulla and the spinal cord in front nf the posterior nerve roots. It is a slender artery, which is continued to the lower part dt' the cord by means of reinforce- ments from the spinal branches of the vertebral and intercostal arteries. It gives off branches to the pia mater, which for*n more or less regular anastomoses ou the inner sides of the posterior nerve roots, and it terminates below by joining the anterior spinal artery. (3) The anterior spinal branch (a. spinalis anterior) arises near the termination of the vertebral. It runs oblicpiely downwards and inwards, in front of the medulla, and unites with its fellow of the opposite side to form a single anterior spinal artery, which descends in front of the anterior fissure of the si)inal cord, and is continued as a fine vessel along the filum teriuinale. Tlie anterior spinal artery is reinforced as it descends by anastonios- 820 THE VASCULAE SYSTEM. ing twigs from the spinal branches of the vertebral, intercostal, and lumbar arteries. It gives off branches which pierce the pia mater and supjDly the cord, and it unites below with the posterior spinal arteries. (4) The posterior inferior cerebellar (a. cerebelli inferior posterior) is the largest branch of the vertebral artery. It arises a short distance below the pons and passes obliquely backwards round the medulla, at first between the roots of the hypoglossal nerve, and then between the roots of the spinal accessory and vagus nerves, into the vallecula of the cerebellum, where it divides into external and internal terminal branches. The trunk of the artery gives branches to the medulla and to the choroid plexus of the fourth ventricle. The internal terminal, or vermiform branch, runs backwards between the inferior vermiform process and the lateral lobe of the cerebellum ; it supplies principally the former structure, and anastomoses with its fellow of the opposite side. The external or hemispheric branch passes outwards on the lower surface of the hemisphere and anastomoses with the superior cerebellar artery. Basilar Artery (a. basilaris). — This artery is formed by the junction of the two vertebral arteries ; it commences at the lower border and terminates at the upper border of the pons Varolii, bifurcating at its termination into the two posterior cerebral arteries. Course and Relations. — It runs upwards in a shallow groove on the front of the pons Varolii, behind the sphenoidal section of the basi-cranial axis and between the sixth nerves. Branches. — (1) The transverse, a series of small arteries which pass round the sides of the pons, supplying it (rami ad pontem), the middle peduncles of the cerebellum, and the roots of the fifth cranial nerve. (2) The auditory (a. auditiva interna), a pair of long but slender branches which accompany the eighth cranial nerve. Each enters the corresponding internal axiditory meatus with the seventh and eighth nerves, and, passing through the lamina cribrosa, is distributed to the internal ear. (3) The anterior inferior cerebellar (a. cerebelli inferior anterior), two branches which arise, one on each side, from the middle of the basilar artery. They pass backwards on the anterior parts of the lower surfaces of the lateral lobes of the cerebellum, and anastomose with the posterior inferior cerebellar branches of the vertebral arteries. (4) The superior cerebellar (aa. cerebelli superiores) branches, two in number, arise near the termination of the basilar. Each passes outwards at the upper border of the pons, directly below the third nerve of the same side, and tui'ning round the outer side of the crus cerebri below the fourth nerve, reaches the upper surface of the cerebelhun, where it divides into an internal and an external branch. The internal branch supplies the upper surface of the vermiform process and the valve of Vieussens. The external branch is distributed over the upper surface of the lateral hemisphere, anastomosing at its margin with the inferior cerebellar arteries. (5) Posterior Cerebral Arteries (aa. cerebri posteriores, Figs. 625 and 627). — These are the two terminal branches of the basilar. They run backwards and upwards, between the crura cerebri and the uncinate convolutions and parallel to the superior cerebellar arteries, from which they are separated by the third and fourth cranial nerves. Each posterior cerebral artery is connected with the internal carotid by the posterior communicating artery ; it gives branches to the tentorial surface of the cerebrum, and is continued backwards, beneath the splenium of the corpus callosum, to the calcarine fissure, where it divides into calcarine and parieto-occipital branches, which pass to the outer surface of the occipital lobe and supply the inner and tentorial surfaces of the occipital lobe and the posterior part of its outer surface. Branches. — (A) Central or ganglionic. — This group includes (a^) A postero-mesial set of small vessels which pass on the inner side of the crus cerebri to the posterior perforated space. They supply the crus, the posterior part of the optic thalamus, the corpora albicantia, and the walls of the third ventricle. (a^) A poster o-lateral set of small vessels which pass round the outer side of the crus cerebri. They supply the corpora quadrigemina, the brachia, the pineal body, the crus, the posterior part of the optic thalamus, and the corpora geniculata. {ofi) A posterior choroidal set of small branches which pass through the upper part of THE SUBCLAVIAN AETEEIES. 821 the choroidal fissure, and, after entering the posterior part of the velum interposituni, end in the choroid plexus in the body of the lateral ventricle and the upper part of its descending cornu. (B) Cortical. — (b^) The anterior temporal, frequently a single branch of variable size, is not uncommonly replaced by several small branches. It supplies the anterior parts of the uncinate and the occipito-temporal convolutions. (6-) The posterior temporal is a larger branch than the anterior. It supplies the posterior part of the inicinate gyrus, the greater part of the occipito-temporal convolution, and the lingual lobule. (6^) The calcarine branch is the continuation of the posterior cerebial artery along the calcarine fissure. It supplies the cuneate lobe, the lingual lobule, and the posterior part of the outer surface of the occipital lobe. (6-*) The parieto - occipital branch, smaller than the calcarine, passes along the corresponding fissure to the cuneus and precuneus. Circle of Willis (Fig. 627). — The cerebral arteries of opposite sides are intimately connected together at the base of the brain by anastomosing channels. Thus the two anterior cerebral arteries are connected with one another by the anterior communicating artery, whilst the two posterior cerebrals are in continuity through the basilar artery from which they rise. There is also a free anastomosis on each side between the carotid system of cerebral arteries and the yertebral system by means of the posterior communicating arteries, which connect the internal carotid trunks and posterior cerebral arteries. The vessels referred to form the so-called circle of Willis (circulus arteriosus [Willisi]). This is situated at the base of the brain, in the region of the inter- peduncular space, and encloses the following structures : the posterior perforated space, the corpora albicantia, the tuber cinereum, the infundibulum, and the optic commissure. The " circle " is irregularly polygonal in outline, and is formed posteriorly by the termination of the basilar and by the two posterior cerebral arteries, postero-laterally by the posterior communicating arteries and the internal carotids, autero-laterally by the anterior cerebral arteries, and in front by the anterior communicating artery. It is stated that this free anastomosis equalises the flow of blood to the various parts of the cerebrum, and provides for the continuation of a regular blood-supply if one or more of the main trunks of the basal vessels should be obstructed. AETEEIES or THE UPPEE EXTEEMITY. The main arterial stem of each upper extremity passes through tlie root of the neck, traverses the axillary space, and is continued through the upper arm to the forearm. In the latter it only runs a short distance, terminating just below the bend of the elbow by bifurcating into the radial and ulnar arteries which descend through the forearm to the hand. That portion of the common trunk which lies in the root of the neck is known as the subclavian artery, the part in the axillary space is termed the axillary artery, whilst the remaining part is called the bracliial artery. THE SUBCLAVIAN ARTERIES. On the right side the subclavian artery (a. subclavia. Figs. 620 and 622) com- mences at the termination of the innominate artery behind the sterno-clavicular articulation, whilst tliat on the left side arises from the arch of the aorta behind the lower part of the manubrium sterni. The riglit artery is about three inches long (75 mm.), and it lies in the root of the neck. The left artery is about four inches (100 mm.) long, and is situated not only in the root of the neck, but also in the superior mediastinal part of the thorax. In the root of the neck each artery arches outwards across the apex of the lung and behind the anterior scalene muscle, and is divided into three parts, which Ue resiiectively to the inner side, behind, and to the outer side of the muscle. The extent to which the arch rises above the level of the clavicle varies considerably, and not uncommonly it reaches the level of the lower part of the thyroid body. 56 a 822 THE VASCULAE SYSTEM. The first parts of the subclavian arteries differ materially from each other both in extent and relations. The relations of the second and third parts are similar on both sides. The first part of the left subclavian artery springs from the arch of the aorta to the left of and behind the commencement of the left common carotid and on the left side of the trachea. It ascends, almost vertically, in the superior mediastinum to the root of the neck, where it arches upwards and outwards to the inner border of the scalenus anticus. Relations. — Posterior. — In the superior mediastinum, from below upwards, it is in relatiou behind aud on its inner side with the left margin of the oesophagus, the thoracic duct, and the left longus colH muscle, whilst the outer part of its posterior surface is covered by pleura. Anterior. — In front and to the right of the artery are the vagus, the left superior cardiac branch of the sympathetic, the left inferior cardiac branch of the vagus, the left phrenic nerve, and the left common carotid artery. It is also crossed obliquely by the left innominate vein above and by the left vagus nerve below, and it is overlapped on the left side by the left lung and pleura. Lateral. — Internally it is in relation, from below upwards, with the trachea, the left recurrent laryngeal nerve, the oesophagus, and the thoracic duct. Externally it is closely invested by the left pleura, and it ascends in a groove on the inner aspect of the left lung. As it turns outwards at the root of the neck it lies behind the terminations of the internal jugular, vertebral, and subclavian veins, the phrenic nerve, the sterno-thyroid and sterno-hyoid muscles, the anterior jugular vein, and more superficially the sterno-mastoid muscle, and the deep cervical fascia ; the thoracic duct arches obliquely over it, and it lies in front of the apex of the pleural sac. The first part of the right subclavian artery (Fig. 620) extends from the back of the right sterno-clavicular articulation to the inner border of the scalenus anticus. It is thus limited to the root of the neck. Relations. — Posterior. — Behind this part of the artery, and intervening between it and the upper two dorsal vertebrse, are the recurrent laryngeal nerve, the posterior part of the annulus Vieusseni, and the apex of the right pleural sac. Anterior. — In front it is in relation with the right vagus, the cardiac branches of the vagus and the sympathetic, the anterior portion of the annulus Vieusseni, the internal jugular and vertebral veins, and more superficially the sterno-hyoid and sterno-thyroid muscles, the anterior jugular vein, the sternal end of the clavicle, the sterno-clavicular ligaments, and the sterno- mastoid muscle. The recui'rent laryngeal nerve passes beloto it and intervenes between it and the apex of the pleural sac. The second part of the subclavian artery, on each side, extends from the inner to the outer border of the scalenus anticus, behind which it lies. Relations. — Behind and beloio it is in relation with the pleural sac. In front it is covered by the anterior scalene and the sterno-mastoid muscles. The anterior scalene separates it from the subclavian vein, which also lies at a slightly lower level, from the transverse cervical and suprascapular arteries, from the anterior jugular vein, and, on the right side, from the phrenic nerve. The third part of the subclavian artery is the most superficial portion. It extends from the outer border of the anterior scalene to the outer border of the first rib, lying partly in the clavicular portion of the posterior triangle and partly behind the clavicle and the subclavius muscle. Relations. — It rests upon the upper surface of the first rib. Immediately behind it is the lowest trunk of the brachial plexus, which separates it from the middle scalene. In f7rjnt of it and at a slightly lower level lies the subclavian vein. The external jugular vein crosses the inner part of this portion of the artery in its course to the sub- clavian vein, and just before its termination receives the transverse cervical and supra- scapular veins ; these vessels also pass superficial to the artery, which is thus covered by venous trunks ; it is also crossed vertically, behind the veins, by the nerve to the subclavius muscle. The outer section of this part of the artery lies behind the clavicle and the subclavius muscle, and it is crossed from within outwards by the suprascapular artery. BEANCHES OF THE SUBCLAVIAN AETERY. 823 which is separated from it by the layer of deep cervical fascia which binds the posterior belly of the omohyoid to the posterior border of the subclavian groove. Moi-e superficially the thii'd part of the artery is covered by the superficial layer of the deep fascia, the descending clavicular branches of the cervical nerves, the platysma, and the skin. Branches of the Subclavian Artery. (1) The vertebral artery is distributed almost entirely to the head and neck, and its chief function is to supply the posterior part of the brain. Its description has therefore been «iiven with that of the other cerebral arteries (see p. 818). (2) Thyroid Axis (truncus thyreo-cervicalis, Figs. 620 and 622). — This branch arises close to the inner border of the scalenus anticus, and directly above the origin of the internal mammary artery, from the upper and front part of the subclavian artery. After a short upward course of about two lines (4 mm.), it ends under co^■er of the internal jugular vein by divitling into three Ijranches — viz. the inferior thyroid, the transverse cervical, and the suprascapular. (A) The inferior thyroid artery (a. thyreoidea inferior, Fig. 620) ascends along the anterior border of the scalenus anticus, and turns inwards opposite the cricoid cartilage to the middle of the posterior border of the lateral lobe of the thyroid body ; it then curves inwards and downwards, and descends to the lower end of the lobe, where it divides into ascending and inferior terminal branches. Relations. — Behind it is the vertebral artery externally and the longus colli muscle internally ; the recurrent laryngeal nerve passes either in front of or behind the vessel, opposite the lower border of the thyroid body. It is covered in front by the carotid sheath, which contains the common carotid artery, the internal jngular vein, and the vagus nerve ; the middle cervical ganglion of the sympathetic lies in front of the artery as it bends inwards, and on the left side the thoracic duct also passes in front of it. Branches. — It gives ofl:" the following branches : — (a) Muscular. — Xumerous small branches pass to the scalenus anticus, the longus colli, the infra-hyoid muscles, and the inferior constrictor of the pharynx. (6) The ascending cervical branch (a. cervicalis ascendens) usually springs from the inferior thyroid near its origin, .though not iincommonly it rises separately from the thyroid axis. It ascends parallel with and internal to the phrenic nerve, in the angle between the rectus capitis anticus major and the scalenus anticus, to both of which it gives branches. It also gives off spinal branches which pass through the intervertebral foramina to the spinal canal, and it anastomoses with branches of the vertebral, occipital, ascending pharyngeal, and deep cervical ai'teries. {<•) (Esophageal (rami oesophagei) are small branches given to the walls of the oesopliagus, which anastomose with the oesophageal branches of the thoracic aorta. {d) Tracheal branches (rami tracheales) are distributed to the trachea; they anasto- mose with branches of the superior thyroid and with the bronchial arteries. (e) An inferior laryngeal branch, (a. larjnigea inferior) accompanies the recurrent laryngeal nerve to the lower part of the larynx. It enters the larynx, beneath the lower border of the inferior constrictor, gives branches to its muscles and mucous membrane, and anastomoses with the laryngeal branch of tlie superior thyroid. {/) The ascending terminal branch supplies the posterior and lower part of the thyroid body, and anastomoses with branches of the superior thyroid artery. {(/) The inferior terminal branch is distributed to the lower and inner part of the thyroid body. It anastomoses with its fellow of the opposite side and with branches of the superior thyroid artery. (B) The transverse cervical arteiy (a. transversa colli, Figs. 620 and 622) runs upwards, outwards, and backwards from the thyroid axis across the posterior triangle of the neck to the anterior border of the trapezius, where it divides into superficial cervical (ramus ascendens) and posterior scapular (ramus descendens) branches. It is very variable in size, and not infrequently the posterior scapular arises separately from tlie third part of the subclavian. Immediately after its origin, under cover of the internal jugular vein, it crosses the scalenus anticus, lying superficial to the phrenic nerve and under cover of the sterno-mastoid muscle; on the left side it is also crossed superficially by the terminal part of the thoracic duct. Passing from beneath the sterno-mastoid, it enters the 56 6 824 THE YASCULAE SYSTEM. lower part of the posterior triangle of the neck, where it lies upon the trunks of the brachial plexus, and, as it runs upwards and backwards to its termination, it passes beneath the posterior belly of the omo-hyoid. Branches. — («) Small muscular branches to the surrounding muscles. (6) The superficial cervical artery (a. cervicalis superficialis), ixsually a slender branch, passes beneath the trapeziiis ; it runs upwards over the levator anguli scapula? Le^ ator anguli scapuLe Posterioi scapular aitery Trapezuis Ouio li^0id Supiascapular artery Rliomboideus minoi Posterior scapulai artei\ Rhomboideus majoi Infrasxjinatu^ Long head of triceps Teres majoi Latissinms doisi Infraspinatus Deltoid Teres minor Circumflex nerve Posterior circumflex artery Dorsalis scapulae artery Triceps (ext. head) Superior prufunda artery Musculo-spiral nerve Triceps (ext. head) Brachialis anticus Fio. 628.— DrssECTiON of the Back of the Shoulder and Upper Arm, showing the anastomosing vessels on tlie dorsum of the scapula, and the posterior circumflex and superior profunda arteries. and upon the splenius, and anastomoses with the arteria princeps cervicis, a branch of the occipital artery, and it sends branches downwards which accompany the spinal accessory nerve and anastomose with the posterior scapular and suprascapular arteries. (c) The posterior scapular artery descends in front of the levator anguli scapulfe and the rhomboid muscles, close to the posterior border of the scapula. It runs parallel with, and a short distance away from, the nerve to the rhomboid muscles, and it sends branches into the supraspinous, the infraspinous, and the subscapular fossse, which BEANCHES OF THE SUBCLAVIAN ARTEEY. 825 anastomose with branches of the suprascapular and subscapular arteries. It also sends branches backwards through and between the rhomboid muscles, which anastomose with the supei-ficial cervical artery and with the dorsal branches of the intercostal arteries. (C) The suprascapular artery (a. trausversa scapuhe) springs from the thyroid axis, and terminates in the int'raspinous fossa of the scapula. As a rule it is smaller than the transverse cervical artery. Commencing behind the internal jugular vein, it crosses the .scalenus anticus and phrenic nerve, and is covered in front by the steruo-mastoid and the anterior jugular vein ; on the left side it lies behind the termination of the thoracic duct also. Continuino- outwards and backwards behind the clavicle, and crossiucr superficially to the third part of the subclavian artery and the cords of the brachial plexus, it reaches the suprascapular notch and passes over the suprascapular liga- ment. From this point it descends with the suprascapular nerve through the supraspinous fossa and beneath the supraspinatus muscle, and passing through the great scapular notch in front of the spino-glenoid ligament, enters the infra- spinous fossa, w^liere it anastomoses with the dorsal branch of the subscapular and with branches of the posterior scapular arteries. Branches. — (a) Muscular, to the sterno-mastoid, the subclavius, and the muscles on the dorsum of the scapula. (6) The medullary, a small branch to tlie clavicle. (c) The suprasternal, to the sternal end of the clavicle and the sterno-clavicular joint. {(I) Acromial branches, which ramify over the acromion process, anastomosing with the acromial Ijranches of the acromio-thoracic and the posterior circumflex arteries. (e) Articular, to the acromio-clavicular and shoulder-joints. (/') The subscapular, which is given off as the artery, passes over the suprascapular ligament. It passes down into the subscapular fossa, gives branches to the subscapularis, and anastomoses with the branches of the subscapular and posterior scapular arteries. (fj) Supraspinous, which ramify in the supraspinous fossa, supplying the muscle, and anastomosing with the posterior scapular. (h) Terminal branches ramify in the infraspinous fossa, and anastomose with the dorsalis scapuho and with branches of the posterior scapular artery. (3) Internal Mammary Artery (a. mammaria interna. Fig. 620). — This arises from the lower and front part of the subclavian at the inner border of the scalenus anticus and immediately below the origin of the thyroid axis. It terminates behind the inner extremity of the sixth intercostal space by dividing into the musculo-phrenic and the superior epigastric arteries. The artery passes at first downwards, forwards, and inwards, lying upon the pleura, and behind the subclavian vein, the sternal end of the clavicle, and the cartilage of the first rib : it is crossed obliquely from without inwards by the phrenic nerve, which usually passes in front of it. From the cartilage of the first rib it descends vertically, about half-an-inch from the border of the sternum, and lies in the upper part of its course in front of the pleura, and in the lower part in front of the triangularis stcrni. It is covered anteriorly by the cartilages of the upper six ribs, the intervening intercostal muscles, and the terminal portions of the intercostal nerves, and it is accompanied by two veuse comites, which unite together above and on its inner side to form a single trunk which terminates in the innominate vein. Branches. — («) The comes nervi phrenici (a. pericardiaco-phrenica), or superior phrenic artery, is a long slender branch which is given off from the upper part of the internal mammary. It accompanies the phrenic nerve through the superior and middle mediastinal spaces to the diaphragm, where it anastomoses with the inferior phrenic and musculo-phrenic arteries. In its course downwards the artery gives of\' numerous small branches to the pleura and pericardium, which anastomose with oftsets of the mediastinal and pericardial branches of the aorta and internal mammary arteries, and also with the bronchial arteries, forming the wide-meshed subpleural plexus of Turner. (6) Mediastinal branches (aa. mcdiastinales anteriores), small and numerous, pass to the areolar tissue of the anterior mediastinal space and supply the remains of the thymus gland and the sternum. 826 THE VASCULAE SYSTEM. (e) Pericardial. — These are several small branches which ramify on the anterior aspect of the pericardium. (d) The anterior intercostal (rami intercostales) are two in number in each of the upper six intercostal spaces. They pass outwards for a short distance either between the pleura or the triangularis sterni and the internal intercostal muscles ; they then pierce the internal intercostal muscles, and ramify between them and the external intercostal muscles, anastomosing with the aortic and superior intercostal arteries and their collateral branches. (e) The anterior perforating branches (rami perforantes), one in each of the upper six intercostal spaces, are small vessels which pass forwards with the intercostal nerves, piercing the internal intercostal muscle, the anterior intercostal membrane, and the pectoralis major, to terminate in the skin and subcutaneous tissue. They supply twigs to the sternum, and those in the third and fourth spaces, usually the largest of the series, give off branches to the mammary gland. (/) The musculo-phrenic (a. musculo-phrenica), or external terminal briinch of the internal mammary artery, runs downwards and outwards from the sixth intercostal space to the tenth costal cartilage. In the upper part of its course it lies upon the thoracic surface of the diaphragm, but it pierces the muscle about the level of the eighth costal cartilage, and terminates on its abdominal surface. Its branches are : — (i.) Muscular, which supply the diaphragm and anastomose with the superior and inferior phrenic arteries. (ii.) Anterior intercostal branches, two in each of the seventh, eighth, and ninth intercostal spaces ; they are distributed in the same manner as the corresponding branches of the internal mammary artery, and terminate by anastomosing with the aortic intercostals and their collateral branches. (g) The superior epigastric (a. epigastrica superior), or internal terminal branch of the internal mammary artery, descends into the anterior wall of the abdomen. It leaves the thorax, between the sternal and costal origins of the diaphragm, and enters the sheath of the rectus, lying first behind, and then in the substance of the rectus muscle. It termi- nates by anastomosing with branches of the deep epigastric artery. Its branches are : — (i.) Muscular, to the rectus, to tlie flat muscles of the abdominal wall, and to the diaphragm. (ii.) Anterior Cutaneous. — These branches pierce the rectus and the anterior portion of its sheath. They accompany the anterior terminal branches of the lower intercostal nerves, and terminate in the subcutaneous tissues and skin of the middle portion of the anterior abdominal w^all. (iii.) Ensiform, a small branch which crosses the front of the ensiform process to anastomose with its fellow of the opposite side. It supplies the adjacent muscles and skin. (iv.) Hepatic branches of small size pass backwards in the falciform ligament to the liver, where they anastomose with branches of the hepatic artery. (4) Superior Intercostal Artery (truncus costo-cervicalis, Fig. 624). — The superior intercostal artery springs from the back of the second part of the sub- clavian artery on the right side and from the first part on the left side. It runs upwards and backwards from its origin, over the apex of the pleural sac, to the neck of the first rib in front of which it descends, between the first thoracic ganglion of the sympathetic cord and the first dorsal nerve, to the first intercostal space, where it divides into two branches which are distributed to the upper two intercostal spaces. Branches. — (a) The profunda cervicis (a. cervicalis profunda). — This branch some- times arises from the subclavian artery directly ; but more commonly it springs from the superior intercostal at the upper border of the neck of the first rib. It runs backwards, like the dorsal branch of an intercostal artery, passes between the first dorsal and last cervical nerves, and between the transverse process of the last cervical vertebra and the neck of the first rib to the back of the neck, where it ascends between the complexus and the semispinalis colli muscle to terminate by anastomosing with the deep branch of the princeps cervicis artery. It also anastomoses with branches of the ascending cervical and vertebral arteries, suppUes the adjacent muscles, and sends a spinal branch, through the intervertebral foramen between the last cervical and the first dorsal vertebrae, into the spinal canal, where it anastomoses with the spinal branches of the vertebral and inter- costal arteries. (h) Terminal. ^ — The two terminal branches run oiit wards — one in the first and one in the second intercostal space. Each runs near the upper border of its space, passing at first between the pleura and the posterior intercostal membrane, and then between the THE AXILLAEY AETEEY. 827 internal and external intercostal muscles. The branches terminate by anastomosing with anterior intercostal branches of the internal mammary artery. Each gives off muscular branches to the intercostal muscles — a nutrient branch to the rib below which it lies, and a collateral branch which runs along the lower border of the space and terminates by anastomosing with an anterior intercostal branch of the internal mammary artery. THE AXILLARY ARTERY. The axillary artery (a. axillaris) lies in the axillary space. It is tlie direct continuation of the subclavian artery, and it becomes the brachial artery. The axillary artery commences at the outer border of the lirst rib, at the apex of the axillary space. It descends, with an outward inclination, along the external Brachial plexus Axillary- artery Acioiaio- thoracic artery Axillary vein Ulnar nerve Long thoracic artery JiOng subscapular nerve Subscapular artery Dorsalis scapula artery Teres major Latissinius dorsi Fig. 629. — The Axillary Artery and its Branches and Relations. wall of the space, i.e. to the inner side of the shoulder-joint and the humerus, to the lower border of the teres major, where it becomes the brachial artery. A line drawn from the middle of the clavicle to the inner border of the prominence of the coraco-brachialis and biceps muscles, when the arm is abducted until it is at right angles with the side, indicates the position and direction of the artery. The position and direction, however, and to a certain extent the relations also of the axillary artery, are moditied by changes in the position of the upper extremity. With the arm lianging by the side the axillary artery describes a curve with the concavity directed downwards and inwards, and the vein is to its inner side. When the arm is at right angles with the side, the axillary artery is almost straight, it lies closer to the outer wall of the axilla, and the vein overlaps it in front and on the inner side. When the arm is raised above the level of the 828 THE VASCULAE SYSTEM. shoulder the axillaiy arteiy is curved over the head of the humerus, and the vein lies still more in front of it. For descriptive purposes the artery is divided into three parts : the first part lies above, the second behind, and the third part below the pectoralis minor muscle. Though we have followed the usual custom in describing three parts of the axillary artery, — a division which is perhaps of practical interest in so far as it emphasises the fact that the axillary artery is surgically accessible above the pectoralis minor, — it is to be noted that the upper border of the pectoralis minor is usually exactly opposite the outer border of the first rib, at the point where the axillary artery begins. In the strict sense, therefore, no part of the artery is above the pectoralis minor. Relations of the first part. — Posterior. — The first part of the artery is enclosed, togetlier with the vein and the cords of the bracliial plexus, in a prolongation of the cervical fascia known as the axillary sheath, behind which is the upper serration of the sen-atus magnus muscle, the contents of the first intercostal space, the inner cord of the brachial plexus, the internal anterior thoracic and the posterior thoracic nerves, the latter descending vertically between the artery and the serratus magnus. Anterior. — It is covered in front by the costo-coracoid membrane, the upper part of which splits to enclose the subclavius muscle. The membrane intervenes between the artery and the cephalic vein, the branches of the external anterior thoracic nerve, the branches of the acromio- thoracic artery with their accompanying veins, and the clavicular part of the pectoralis major mi\scle, superficial to which are the deep fascia, the platysma, the descending- clavicular branches of the cervical plexus, and the superficial fascia and the skin. Behind the costo-coracoid membrane the artery is crossed by a loop of communication between the external and internal anterior thoracic nerves. Lateral. — Above and to the outer side are the outer and posterior cords of the brachial plexus and the external anterior thoracic nerve. Below and to the inner side is the axillary vein, the internal anterior thoracic nerve intervening. Relations of the second part. — Posterior. — Behind this portion of the artery is the posterior cord of the brachial plexus and a layer of fascia which separates it from the subscapularis muscle. Anterior. — In front is the pectoralis minor, and more superficially the pectoralis major, the fasciae and skin. Lateral. — To the outer side lies the outer cord of the brachial plexus. On the inner side the inner cord of the plexus lies in close relation to the artery, and intervenes between it and the axillary vein. Relations of the third part. — Posterior. — The third part of the artery rests posteriorly upon the lower border of the subscapularis, the latissimus dorsi, and the teres major. It is separated from the fibres of the subscapularis by the circumflex and musculo-spiral nerves, and from the latissimus dorsi and teres major by the musculo- spiral nerve alone. Anterior. — It is crossed in front by the inner head of the median nerve. In its upper half it lies under cover of the lower part of the pectoralis major, the fascia and skin, whilst its lower part, which is superficial, is covered by skin and fascia only. Lateral. — To the outer side lie the median and musculo-cutaneous nerves and the coraco-brachialis muscle. To the inner side is the axillary vein. The two vessels are, however, separated by two of the chief branches of the inner cord of the brachial plexus. In the angle between the vein and the artery, and somewhat in front of the latter, lies the internal cutaneous nerve ; in the angle behind is the vihiar nerve. The lesser internal cutaneous nerve lies internal to the vein, and the vense comites of the brachial artery ascend along the inner side, to terminate in the axillary vein at the lower border of the subscapularis muscle. Branches of the Axillary Arteey. (1) The superior thoracic (a. thoracahs suprema. Fig. 629), a small branch which arises from the first part of the axillary at the lower border of the sub- clavius. It runs downwards and inwards across the first intercostal space, pierces the inner part of the costo-coracoid membrane, and supplies branches to the sub- clavius, the jjectoralis major and minor, and to the serratus magnus and the inter- costal muscles ; it anastomoses with branches of the suprascapular, the internal mammary, and the acroniio-thoracic arteries. (2) The acromio-thoracic (a. thoraco-acrondalis. Fig. 629) arises near the upper border of the pectoralis minor, from the second part of the axillary artery. It is a BEAXCHES OF THE AXILLARY AETEEY. 829 very short trvmk, of considerable size, which passes forwards, pierces the costo- coracoid membrane, and terminates beneath the clavicular portion of the pectoralis major by dividing into four terminal branches — clavicular, pectoral, humeral, and acromial. (a) The clavicular branch (ramus clavicularis) is a long slender artery which runs upwards and inwards to the sterno-clavicular joint, anastomosing witli the superior thoracic, with branches of the suprascapular, and with the first perforating branch of the internal mammary artery. It supplies the adjacent muscles and the sterno-clavicular articulation. (6) The pectoral (rauuis pectoralis), or thoracic, is a large branch which descends between the two pectoral muscles, to both of which it gives branches, and it anastomoses with the intercostal and long thoracic arteries. (c) The humeral branch (ramus deltoideus) runs outwards to the groove between the pectoralis major and the deltoid, in which it descends by the side of the cephalic vein to the insertion of the deltoid. It anastomoses with the acromial branch and with the antei-ior circumflex ai-tery, and it gives branches to the pectoralis major and deltoid muscles and to the skin. [d) The acromial branch (ramus acromialis) runs upwards and outwards across the tip of the coracoid process to the acromion, where it anastomoses with the last-described branch, with the acromial branches of the suprascapular, and with the posterior circumflex arteries. It gives branches to the deltoid. (3) The long thoracic (a. thoracalis lateralis) arises from the second part of the axillary, and descends along the lower border of the pectoralis minor to anastomose with the intercostal and subscapular arteries, and with the pectoral branch of the acromio - thoracic. It supplies the adjacent muscles, and sends branches to the outer part of the mammary gland ; hence it is not infrequently called the external mammary artery. (4) The alar thoracic is only occasionally present as a distinct branch, but it is frequently represented by a number of small irregular branches, which may either arise from the axillary or from the thoracic and subscapular branches. It is distributed to the glands and areolar tissue in the axilla. (5) The subscapular artery (a. subscapularis) is the largest branch of the axillary artery. It arises from the third part of the artery, opposite the lower border of the subscapularis, along which it descends to the lower angle of the scapula and to the inner wall of the axillary space. It is accompanied by the second or long subscapular nerve ; it supplies the adjacent muscles, and it anasto- moses with the posterior scapular, the suprascapular, the long thoracic, and the lateral branches of the intercostal arteries, and gives off one named branch, the dorsahs scapulae. The dorsalis scapulae artery (a. circumflexa scapuUie) is frequently larger than the continuation of the subscapular arteiy. It arises about one and a half inches (37 mm.) from the commencement of the subscapular trunk, and passes backwards into the triangular space between the subscapularis above, the tei'es major beloM-, and the long head of the triceps externally. Turning round, and usually grooving the axillary border of the scapula, under cover of the teres minor, it enters the infraspinous fossa, where it breaks up into V)ranchcs which anastomose with branches of the posterior scapular and suprascapular arteries. Whilst it is in the triangular space the dorsal artery gives off an infrascapular branch which passes into the subscapular fossa beneath the subscapularis, and terminates by anastomosing with the bi'anches of the posterior and suprascapular arteries. It also gives off in the same situation a descending branch, which runs down- wards to the lower angle of the scapula between the teres major and minor muscles, and small branches are given to the deltoid and scapular head of triceps. (6) The posterior circumflex (a. circumflexa humeri posterior) arises from the third part of the nxillary artery and passes backw^ards, accompanied by the circum- flex nerve, through an intermuscular cleft, the so-called quadrilateral space, which is bounded by tlie teres minor and subscapularis above, the teres major below, the long head of the triceps internally, and the humerus externally. It turns round the surgical neck of the humerus under cover of the deltoid muscle, and terminates in numerous branches which supply the deltoid. As a rule it is an artery of large size, only slightly smaller than the subscapular. 8 BO THE VASCULAE SYSTEM. Branches. — (a) Muscular to the teres major and minor, the triceps heads, long and external, and the deltoid ; (6) An acromial brancli, which ascends to the acromial process, where it anastomoses with the acromial branches of the suprascapular and the acromio-thox'acic arteries ; (c) A descending branch, which runs downwards along the external head of the triceps to anastomose with the superior profunda artery ; (d) A^:^...^^ Articular to the shoulder-joint; (e) Nutrient to the head of the humerus ; (/) Terminal, which supply a large portion of the deltoid, and anastomose with the anterior circumflex and acromio-thoracic arteries. (7) The anterior circumflex artery (a. circumflexa humeri anterior) is a small branch which is given off from the third part of the axillary close to, or in common with, the posterior circumflex. It passes outwards behind the coraco-brachialis and the two heads of the biceps, round the front of the surgical neck of the humerus, and terminates by anastomosing with the posterior circum- flex. At the bicipital groove it gives a well- marked ascending bicipital branch which ascends along the long head of the biceps, supplying the sheath of the tendon, and giving branches to the shoulder-joint. It also gives muscular branches to the adjacent muscles, one of which descends along the tendon of insertion of the pectoralis major. THE BEACH I AL AETEEY. The brachial artery (a. brachialis, is the direct continuation of the axillary. It commences at the lower border of the teres major, and terminates in the ante-cubital fossa at the level of the neck of the radius, by dividing into the radial and ulnar arteries. The general course of the brachial artery is downwards and outwards, along the inner side of the arm. Its position may be in- dicated on the surface by a line drawn from the lower part of the axillary space at the junction of its anterior and middle thirds to the centre of the bend of the elbow. Bicipital fascia Supinator lonjriis Fig. 630. — The Brachial Artery and Branches. Relations. — Posterior. — Itlies successively in front of the long head of the triceps, the musculo-spiral nerve and the superior profunda artery intervening, the internal head of the triceps, the insertion of the coraco-brachialis and the brachialis anticus. Anterior. — It is overlapped in front by the inner border of the biceps, is crossed at its centre by the median nerve, and in addition is covered by deep and superficial fascia and by skin. In the ante-cubital fossa a thickened portion of the deep fascia, the semilunar or bicipital fascia, separates it fi'om the median basilic vein and the anterior branch of the internal cutaneous nerve, both of which lie in the superficial fascia. Lateral. — To the outer side it is in relation above with the median nerve, and below with the biceps. To the inner side it is in relation in the upper part of its extent with the basilic vein, the internal cutaneous, lesser internal cutaneous, and ulnar nerves, and in the lower part with the median nerve. Two venjc comites, one on each side, accompany the artei-y, and communications between these pass across the vessel. THE EADIAL AETEEY. 831 Bkanches of the Brachial Aiiteky. (1) The superior profunda (a. profunda brachii) is a large branch ^Yhich arises from the inner and back part of the brachial soon after its comniencenieut. It runs downwards and outwards, with the luusculo-spiral nerve, in the musculo- spiral groove, and divides at tlie back of the humerus into two terminal branches, the anterior and the posterior. Not infrequently this division takes place at a higher level, and the artery appears double. The anterior terminal branch accompanies the musculo-spiral nerve tlirough the external internmscular septum, and descends between the supinatur longus and the brachialis anticus to the front of the external condyle, where it anastomoses with the radial recurrent artery. The posterior ternnnal branch descends behind the external intermuscular septum, and anastomoses behind the external condyle with the posterior interosseous recurrent artery and with the anastomotic artery. Whilst they are lying at the back of the humerus one of the terminal branches gives off — (a) a slender twig, which descends in the substance of the internal head of the triceps to the back of the elbow, where it anastomoses with the anastomotic artery ; (b) a nutrient branch, whicli enters a foramen on the posteri(jr surface of the humerus ; and (c) an ascending branch, which anastomoses with the descending branch of the posterior circumflex artery. (2) Muscular branches are given to the biceps, coraco-l>rachialis, brachialis anticus, triceps, and pronator radii teres. (3) Nutrient. — A small artery which arises from the ndddle of the biachial and enters the nutrient foramen on the inner side of the shaft of the humerus. (4) The inferior profunda (a. collateralis ulnaris superior) is smaller than the superior profunda, with which it sometimes rises by a common trunk ; usually, however, it springs from the inner and back part of the middle of the brachial. It runs downwards and backwards, with the ulnar nerve, through the internal intermuscular septum, and tlien, descending more vertically, reaches the back of the internal condyle of the humerus, where it terminates by anastomosing with the posterior and anterior idnar recurrent and anastomotic arteries. (5) The anastomotic (a. collateralis ulnaris inferior) rises from the inner side of the brachial artery about two inches (50 mm.) above its termination. It runs inwards behind the median nerve and in front of the brachialis anticus, it then pierces the internal intermuscular septum, and turns outwards between the inner head of the triceps and the posterior surface of the bone to the external con- dyle. It supplies the adjacent muscles and anastomoses, in front of the internal condyle, with the anterior ulnar recurrent, behind the internal condyle with the posterior ulnar recurrent and the inferior profunda, at the middle of the back of the humerus with a branch of the superior profunda, and behind the external condyle with the posterior terminal branch of the superior profunda and the posterior inter- osseous recurrent artery. The Eadial Artery. The radial artery (a. radialis, Figs. 631, 632, and 633) is the smaller of the two terminal branches of the lirachial artery, but it is the more direct continuation of the parent trunk. It commences in the ante-cubital fossa opp(.)site the neck of the radius, and terminates in the palm of the hand, l»y anastomosing w'ith the deep branch of the ulnar artery, and thus completing the deep palnuir arch. The trunk is divisible into three parts. T\\ii first 'part lies on the front of the forearm. It runs downwards aud some- what outwards to the apex of the styloid process of the radius. The second part curves round the outer side of the wrist and across the back of the trapezium to reach the proximal end of the first interosseus space. The tJiird pa)'f passes forwards through the first interosseous space to the palm of the hand, where it joins the deep branch of the ulnar artery. Relations of the first part. — Posterior. — It passes successively in front of the following structures : the tendon of insertion of the biceps, the supinator brevis, the pronator i-adii teres, the radial portion of the He.xor sublimis digitorinn, tlic flexor longus polHcis, the pronator quadratus, and tlie anterior ligament (if the wrist-joint. Anterior. — 832 THE VASCULAE SYSTEM. Biceps Brachial artery Median nerve Museiilo-spiral iier\e Eadial recurrent^ artery Bracliialis anticus Supinator longus Supinator hrevis Radial recurrent artery Supinator brevis Flexor sublimis digitoruiff~ Radial artery Ulnar artery The artery is overlapped in the upper half by the anterior border of the supinator longus ; in the remainder of its extent it is covered only by skin and fascia. Lateral.— To the outer side is the bi'achio-radialis, or supinator longus, and the radial nerve. This latter lies quite near to the artery in its middle third. To the inner side is the pronator radii teres above and the flexor carpi radialis below. Two venee comites, one on each side, accompany the artery. Branches of the first part. — (1) The radial recurrent (a. recurrens radialis) arises in the ante-cubital fossa. It springs from the outer side of the radial in front of the supinator brevis. It runs outwards, passes between the radial and posterior interosseous nerves, and then ascends to the external con- dyle of the humerus, where it anasto- moses with the anterior terminal branch of the superior profunda. The radial recurrent supplies numerous muscular branches to the supinator longus, the supinator brevis, the extensor carpi radialis longior, and the extensor carpi radialis brevior. (2) Muscular branches (rami mus- culares) to the muscles on the radial side of the anterior aspect of the forearm. (3) The superficialis volae (ramus volaris superficialis. Fig. 631) is a slender vessel which arises a short distance above the wrist and runs downwards across the ball of the thumb. It usually pierces the super- ficial muscles of the thenar eminence, and terminates either in their sub- stance or by uniting with the ulnar artery and completing the superficial palmar arch of the hand. (4) An anterior radial carpal branch (ramus carpeus volaris) passes inwards beneath the flexor tendons and their synovial sheaths, and crosses the anterior carpal ligaments. It anasto- moses with the anterior carpal branch of the ulnar artery to form the anterior carpal arch, and it receives communi- cations from the anterior interosseous artery and from the deep palmar arch. Relations of the second part. — As it curves round the outer side and the back of the wrist, the radial artery lies upon the external lateral ligament of the intercai-pal joint and upon the back of the trapezium. It is crossed by the extensor ossis meta- carpi pollicis, the extensor brevis pollicis, and the extensor longus pol- licis ; more superficially it is covered by fascia, in which are some fila- ments of the radial nerve and the commencement of the radial vein, and by skin. Branches of the second part.— (1) Dorsales Pollicis. — Two small arteries which run along the borders of the dorsal aspect of the thumb ; they supply the skin, tendons, and joints, and anastomose with the palmar digital arteries. Radialis Flexor longus pollici: Superticiali Fig 631 THE Front of radial and — Superficial Dissection of the Forearm and Hand, showiug the ulnar arteries and the superficial palmar arch with its branches. THE EADIAL AETEEY. 833 Biceps- Radia recurrent artery Orbicular ligament Supinator longus Musoular branch of artery Radial artei-y - Pronator teres (2) Dorsalis Indicis. — A slender artery which nins downwards on the uhiar head of the first dorsal interosseous muscle and along the dorsal aspect of the radial border of the index-finger. (3) and (4) The metacarpal or first dorsal interosseous and posterior radial carpal arise bv a common trunk which crosses beneath the extensor longus poUicis. (a) The metacarpal branch (a. metacarpea dorsalis) descends on the dorsal aspect of the second dorsal interosseous muscle, and divides opposite the heads of the metacarpal bones into two digital branches which supply the adjacent sides of the index and middle fingers. (6) The posterior carpal branch (ramus carpeus dorsalis) runs inwards on the dorsal carpal ligaments, and in front of the extensor tendons, to anastomose wath the posterior carpal brancli of the ulnar artery, and to complete the dorsal carpal arch which receives tlie terminations of the anterior and posterior interosseous arteries. The dorsal carpal arch gives oft" the second and third dorsal interosseous arteries (aa. meta- carpse dorsales), which descend on the dorsal aspects of the third and fourth dorsal in- terosseous muscles as far as the heads of the metacarpal bones, where each divides into two branches (aa. digitales dorsales), for the adjacent sides of the third and fourth and the fourth and fifth fingers respectively. Each dorsal interosseous artery is con- nected with the deep palmar arch by a superior perforating branch which passes through the xip2:ier part of the correspond- ing interosseous space, and wdth a digital branch from the superficial palmar arch by an inferior perforating' branch which passes through tlie lower part of the space. Relations of the third part. — The third part of the radial artery passes forwards between the two heads of the first dorsal interosseous muscle to reach the palm, where it turns inwards beneath the upper part of the oblique adductor muscle of the thumb, and, after passing through the upper fibres of the tranverse adductor, or between the adjacent borders of the oblique and transverse adductors, it unites with the deep branch of the ulnar artery, completing the deej) palmar arch. Branches of the third part. — (1) The princeps pollicis (a. princeps poUicis) branch is given off as soon as the radial arteiy enters the palm. It runs downwards in front of tlie first metacarpal bone, between the oblique adductor and the opponens pollicis, and under cover of Fig the long flexor tendon, and divides near the lower end of the bone into collateral branches which run along the sides of the thumb and anastomose with the dorsales pollicis arteries. (2) The radialis indicis (a. volaris indicis radialis) is a branch which descends between the ulnar head of the first dorsal interosseous muscle and the transverse adductor of the thumb. It runs along the radial side of the index-finger to its tip, supplying the adjacent tissues ; not uncommonly it anastomoses with the superficial palmar arch. 57 Brachial artery Anastomotic artery Brachialis anticus Pronator teres Ulnar recurrent arterj' Flexor profundus digitoruni Ulnar' artery Anterior interosseous artery Anterior communicating artery Deep branch of ulnar artery Deep palmar arch Palmar interosseous arteries Digital artery 632. — Deep Dissection of the Front of the FoKEARM AND Hand, showiug the radial and ulnar arteries and their branches and the deep palmar arch and its branches. 834 THE VASCULAE SYSTEM. The Ulnar Aetery. The ulnar artery (a. ulnaris, Figs. 631 and 632) is the larger terminal branch, but the less direct continuation of the brachial arterj". It commences in the ante-cubital fossa, opposite the neck of the radius, and terminates in the palm of the hand, where it anastomoses with the superficialis volte to form the superficial palmar arch. Erom its origin it runs obliquely downwards and inwards, beneath the muscles arising from the internal condyle, to the junction of the upper and middle thirds of the forearm, where it comes into relation with the ulnar nerve ; it then descends vertically, on the radial side of the ulnar nerve, to the wrist, crosses in front of the main part of the annular ligament to the radial side of the pisiform bone, and enters the palm of the hand to form the main part of the superficial palmar arch. Relations. — Posterior. — From above downwards it lies in front of the lower part of the brachialis anticus, the flexor profundus digitorum, and the deep portion of the anterior annular ligament. Anterior. — In front it is crossed, in the oblique part of its course, by the pronator radii teres, the median nerve, which is separated from the artery by the deep head of the pronator, the flexor sublimis digitorum, the flexor carpi radialis, and the palmaris longus. In the middle third of the forearm it is overlapped by the anterior border of the flexor carpi ulnaris, and in the lower third it is covered by skin and fascia only. A sliort distance above the wrist the palmar cutaneous branch of the median nerve lies in front of it, and as it crosses the anterior annular ligament, it is bound down by a fascial expansion from the tendon of the flexor carpi ulnaris. Two vense comites, which frequently commimicate with one anothei', lie one on either side of the artery. Lateral. — On the radial side there is also, in its lower two-thirds, the flexor sublimis digitorum. On its tdnar side there are the flexor carpi ulnaris and the ulnar nerve. Branches. — (1) The anterior ulnar recurrent is a small branch which arises in the ante-cubital fossa, frequently in common with the posterior ulnar recurrent. It passes upwards to the front of the internal condyle, under cover of the pronator radii teres, and anastomoses with branches of the anastomotic and inferior profunda arteries. (2) The posterior ulnar recurrent branch, larger than the anterior, arises in the ante-cubital fossa, from the inner side of the ulnar artery, and ascends on the brachialis anticus, and under cover of the muscles which rise from the internal condyle to the back of that prominence, where it passes between the humeral and olecranoid heads of the flexor carpi ulnaris, and anastomoses with the inferior profunda and anastomotic arteries. It gives branches to the adjacent muscles and to the elbow-joint. (3) The common interosseous artery (a. interossea communis), a short trunk which springs from the outer and back part of the ulnar artery in the lowti- part of the ante- cubital fossa. It passes backwards towards the upper border of the interosseous membrane, and divides into anterior and posterior interosseous branches. (3a) The anterior interosseous artery (a. interossea volaris) descends in front of the interosseous membrane, between the adjacent borders of the flexor longus pollicis and the flexor profundus digitorum, to the upper border of the pronator quadratus, where it pierces the interosseous membrane, and continues its descent, first on the posterior surface of the membrane, under cover of the extensor longus pollicis and extensor indicis, and then on the radius, in the groove for the extensor communis digitorum, and it terminates on the back of the carpus in tlie posterior carpal arch. It is accompanied whilst in front of the interosseous membrane by the anterior interosseous nerve, and after it has pierced the membrane, by the posterior interosseous nerve. Branches. — («) Nutrient to the radius and ulna; Qj) Muscular to tlie adjacent muscles; (c) The anterior communicating, a slender branch which clescends behind tlie pronator quadratus and in front of tlie, interosseous memljranc. to anastomose with the anterior carpal arch ; {d) Small anastomotic branches are given oil at the back of the forearm to anastomose with the posterior interosseous artery ; (c) The comes nervi mediani (a. niediana) is a long slender branch which rises from the upper part of the artery and descends in the front of the median nerve to the pahn, whei'c it anastomoses with recurrent branches of the superficial jialmar arch. (36) The posterior interosseous trunk (a. interossea dorsalis) is usually smaller than the anterior interosseous. It passes backwards between the upper border of the inter- osseous membrane and the oblique ligament, and then between the supinator brevis and the extensor ossis metacarpi pollicis, ;ifter which it descends between the superficial and deep muscles on the back of the forearm to the wrist, where it anastomoses with the anterior interosseous artery and with the posterior carpal arch. As it crosses the THE AKTEEIAL AECHES OF THE WEIST AND HAND. 835 Tricnps — extensor ossis metacarpi poUicis it is accompanied by the posterior interosseous nerve, but in the remainder of its course it is separated from the nerve by the deep muscles. Branches. — («) A posterior interosseous recurrent ;i. iuterossea recnrrens) braiicli i.s given off as soon as the 2:)0.stci-i(H' inti;rosseouH artery has passed beneath the lower border of the siqjinator brevis. It ascends on tlie i^osterior surface of the supinator brevis, inider cover of the anconeus, to the back of the external condyle of the luimerus, where it anastomoses with the posterior terminal Iji'anch of the superior pi-ofunda and with branches of the anastomotic artery. (6) Muscular branches to 1 )oth super- ficial and deep muscles on the back of the f(n-earm. (r) Cutaneous branches to the skin ou the liaek of the forearm and the back of the wrist. (4) The anterior ulnar carpal (ramus carpcus volaris), a small branch given oti" above the an- terior annular ligament; it passes outwards beneath the flexor ten- dons and their sheaths oil the anterior surface of the carpal ligaments, and anastomoses with the anterior carpal branch of the radial to form the anterior carpal arch. (5) The posterior ulnar carpal branch, (ramus carpeus dorsalis) arises from the back of the inner side of the ulnar artery just above the pisiform bone. It passes backwards under cover of the flexor and extensor carpi ulnaris muscles to the back of the carpus, where it unites with the posterior carpal branch of the radial to form the posterior carpal arch. (G) Profunda (ramus volaris profundus). — This branch de- scends between the abductor and flexor brevis minimi digiti, and, turning outwards l)eneath the flexor brevis, theopponens minimi digiti, and the flexor tendons and their sheaths, joins the termina- tion of the radial artery to com- plete the deep palmar arch. Supinator bre\ Posterior iiitci-- osseous recurrent artery Posterior inter- osseous artery Flexor car]n ulnaris Extensor carpi ulnaris Anterior inter- osseous artery Posterior inter- osseous artery Posterior earpal arch Superior per- forating artery Dorsal inter- osseous arteries Supinator longus Extensor carjii radialis lon^ior Extensor carpi ulnaris Extensor communis igitoruni Extensor carpi radialis brevior Posterior interosseous nerve Pronator radii teres Extensor ossis metacarpi poUicis Extensor longus poUicis Extensor brevis pollieis Extensor indicis iiadial artery Dorsalis poUicis arteries Dorsalis indicis The Arterial Arches of THE Wrist and Hand. 1 A -U '"''"• ^^■^- — '^'"^ POSTElUOlt INTEUOSSEOUS AKTERY AND THE Anterior Carpal Arch second p.vut ok the Rauial auteuy, with their branches. (Fig. Go2). — The anterior carpal arch lies ou the trout of the carpus l)ehiud the llexor tendons and their synovial sheaths. It is formed by the union of the anterior carpal branches of the radial and ulnar arteries, and it receives the communicating branch from the anterior interosseous artery above and recurrent liranches from the deep palmar 836 THE VASCULAE SYSTEM. arch below. The branches of distribution which pass from it supply the ligaments and syno"vdal membranes of the wrist and of the intercarpal and carpo-metacarpal joints. Posterior or Dorsal Carpal Arch (Fig. 633). — This arch lies on the posterior carpal ligaments under cover of the extensor tendons and their sheaths. It is formed by the union of the dorsal carpal branches of the radial and ulnar arteries, and receives the terminations of the anterior and posterior interosseous arteries. Branches. — («) Articular to the adjacent articulations. (6) Dorsal interosseous, tn'o slender branches which run downAvards on the third and fourth dorsal interosseous muscles to the clefts of the fingers, where each divides into collateral branches. They communicate near their origins with the deep palmar arch by the superior perforating arteries, and near their terminations with the palmar digital vessels through the inferior perforating arteries. Their collateral terminal branches run downwards on the dorso- lateral aspects of the fingers Avhich bound the third and fourth interosseous spaces, and they anastomose with the collateral digital branches of the palmar digital arteries. Superficial Palmar Arch (arcus volaris super ficialis, Fig. 631). — This arterial arch includes the terminal portion of the ulnar artery, and is usually completed externally by the superficialis volse, or sometimes by the radialis indicis, or the princeps pollicis. It extends from the ball of the little finger to the inner border of the superficial head of the flexor brevis pollicis, and reaches as low down as a line drawn across the palm at the level of the lower border of the fully abducted thumb. It is covered by the integuments and the central portion of the palmar fascia, and, on the ulnar side of the palm, by the palmaris brevis, and it is accompanied by vense comites. It is in contact behind with the flexor brevis and opponens minimi digiti, and with the digital branches of the ulnar and median nerves, as well as with the flexor tendons and the lumbrical muscles. Branches. — Four digital arteries (aa. digitales volares communes) arise from the convexity of the arch. The innermost descends along the ulnar border of the little finger, accompanied by the internal digital branch of the ulnar nerve ; the outer three pass down- wards superficial to the digital nerves, along the nuddle of the three inner interosseous spaces towards the interdigital clefts, just above which each digital artery divides into two collateral digital arteries (aa. digitales volares propria3), which supply the contiguous sides of the fingers bounding the cleft. As the collateral digital branches descend along the sides of the fingers they lie superficial to the corresponding digital nerves, and supply branches to the joints, to the flexor tendons with their sheaths, and to the skin and subcutaneous tissues on the palmar surface ; they also send backwards dorsal branches which anastomose with the dorsal digital arteries and supply the tissues on the dorsal aspects of the second and terminal phalanges. Some of the backwardly-directed branches form a plexus in the matrix of the nail. In the pulp of the finger-tips anasto- mosing twigs join to form arches from which numerous branches are given off to the skin and subcutaneous fat. Each of the outer three digital arteries is joined immecl lately above its division by a palmar interosseous branch from the deep palmar arch and an inferior communicating- artery from a dorsal interosseous artery. The innermost digital ai'tery is joined by a branch which comes either from the inner palmar interosseous artery or from the deep palmar arch. Deep Palmar Arch (arcus volaris profundus. Fig. 632). — The deep palmar arch extends from the base of the metacarpal bone of the little finger to the upper end of the first interosseous space, and is formed by the terminal part of the radial artery, anastomosing with the deep branch of the ulnar. It is from half to three quarters of an inch (12 to 18 mm.) above the level of the superficial palmar arch, and it lies deeply in the palm, in contact with the bases of the metacarpal bones and their ligaments and on the origin of the interossei muscles ; it is under cover of the flexor tendons and their synovial sheaths. Branches. — ('t) The superior perforating (rami perforantes) ; three small arteries which pass backwards through the inner three interosseous spaces, and between the origins of the dorsal interossei muscles. They anastomose on the dorsum of the hand with the dorsal interosseous arteries. PAKIETAL BEANCHES OF DESCENDING THOEACIC AOETA. 837 (b) Small irregular recurrent branches pass upwards and unite with the anterior carpal arch. (c) The articular to the adjacent articulations. (d) The palmar interosseous arteries (aa. metacarpese volares) are three vessels which pass downwards on the interosseous muscles of the three inner spaces and under cover of the flexor tendons. They terminate by anastomosing with the palmar digital arteries just before the latter vessels divide into collateral branches. (e) The communicating, a small irregular branch which passes inwards between the flexor tendons and the short muscles of the little flnger to anastomose with the innermost palmar digital artery. BRANCHES OF THE DESCENDING THORACIC AORTA. The branches given off from the thoracic portion of the descending aorta are distributed chiefly to the walls of the thorax and to the thoracic viscera. They contribute also to the supply of the spinal cord and its membranes, and to that of the vertebral column and of the upper part of the abdominal wall. The branches, which are numerous and for the most part arranged in pairs, are as follows : — ('Intercostal. Subcostal. Diaphragmatic. I^The vas aberrans. Parietal. 4 j^v-i ^:~ Visceral. Bronchial. Oesophageal. Pericardial. Mediastinal. Pakietal Bkanches of the Descending Thoracic Aorta. 1. Intercostal Arteries (a. intercostales). — There are nine pairs of aortic intercostal arteries. They usually arise separately, though not uncommonly a pair may take origin by a common trunk from the back of the aorta, aud are distributed to the lower nine intercostal spaces, to the spinal column, to the contents of the spinal canal, and to the muscles and skin of the back. The flrst three on each side also give branches to the mammary gland. The arteries of opposite sides closely correspond, but, since the aorta in the thoracic region hes on the left side of the spinal column, the right intercostal arteries cross the front of the vertebral column, behind the oesophagus, the thoracic duct, and the vena azygos major, and are longer than the left arteries. In other respects the course of all the aortic intercostal arteries is almost identical. They run outwards and backwards on the sides of the bodies of the vertebree to the inter- costal spaces, passing behird the pleura, and being crossed, opposite the heads of the ribs, by the sympathetic cord. The lower arteries are also crossed by the splanchnic nerves, and those on the left side are in addition .crossed by the smaller azygos veins. On reaching an intercostal space each artery runs upwards, some- times behind, sometimes in front of the corresponding intercostal nerve, to the upper border of the space, along which it is continued in the subcostal groove. It lies at first between the pleura and the posterior intercostal membrane, immediately below the intercostal nerve ; it then pierces tlie intercostal membrane, and runs between it and the external intercostal muscle as far as the angle of the rib, beyond which it is continued forward between the internal and external intercostal muscles. In the subcostal groove the artery hes between the corresponding vein above and the intercostal nerve below, aud it terminates in front by anastomosing with an anterior intercostal branch of the internal mammary or of the musculo- phrenic artery. The lower two intercostal arteries on each side extend beyond their spaces to the abdominal wall, and anastomose with branches of the superior epigastric, subcostal, and lumbar arteries. Branches. — (a) Dorsal (ramus posterior). — As each artery enters its intercostal space it gives oft' a posterior or dorsal branch which passes backwards, accompanied by the posterior primary division of a spinal nerve, internal to the superior costo-transverse ligament, betweeti the necks of the ribs which bound the space, and between the adjacent transverse pi'ocesses, to the vertebral groove, where it divides into internal and external terminal branches. The internal branch (ramus cutaneus medialis) passes back- 57 « 838 THE VASCULAR SYSTEM. wards and inwards either over or through the multifidus spinse, giving branches to the muscles between which it passes and to tlie vertebral column. The external branch (ramus cutaneus lateralis) runs outwards under cover of the longissimus dorsi to the interval between it and the musculus accessorius. It terminates in the skin of the back, after giving branches to the adjacent muscles. A spinal branch (ramus spinalis) from each dorsal artery passes through the corresponding intervertebral foramen, and enters the spinal canal, to the contents and walls of Avhich it is distributed. It divides into three branches — neural, post-central, and pre-laminar. The neural hunch divides into two branches which run inwards on the roots of the spinal nerve, pierce the dura mater and arachnoid, and divide into branches some of which pass to the membranes of the cord, whilst others are continued on to reinforce the dorsal and ventral spinal arteries. The pcM-central branch divides into ascending and descending branches which, anastomosing with similar branches above and below, form a series of vertical arches on the back of the bodies of the vertebree. The arches of opposite sides are connected by short transverse anastomoses. Tlie pre-laminar branch is small, and its ascending and descending branches are distributed in a similar though less regular manner on the posterior wall of the spinal canal. {b) A collateral branch, springs from the trunk of each intercostal artery near the angle of the rib. It descends to the lower border of the intercostal space, along which it runs forwards to anastomose in front, like the intercostal artery itself, with a separate anterior intercostal branch of the internal mammary or musculo-phrenic artery. The collateral branches of the lower two intercostal arteries on each side are inconstant ; when present they are small, and terminate in the abdominal wall. (c) Muscular branches (rami musculares) to the adjacent muscles are given off both by the main trunk and its collateral branch. (cZ) A lateral cutaneous (ramus cutaneus lateralis) offset from the intercostal artery accompanies the lateral cutaneous bi'anch of the intercostal nerve. In addition to the above-named branches the first aortic intercostal on each side anastomoses with the superior intercostal, and may supply the whole or the greater part of the second intercostal space, and the first right aortic intercostal frequently gives origin to the right bronchial artery. The upper three or four aortic intercostals on each side give branches to the mammary gland which anastomose with branches of the long thoracic and internal mammary arteries. Longitudinal anastomoses between adjacent intercostal arteries and their dorsal branches sometimes exist near the necks of the ribs, or near the transverse processes. These longitudinal anastomoses are of considerable morphological interest. 2. The subcostal arteries are the last pair of parietal branches given off from the thoracic aorta. They are in series with and are very similar to the aortic intercostal arteries, but are situated below the last ribs. Each runs along the lower border of the twelfth rib in company with the last dorsal nerve. It passes beneath the liga- mentum arcuatum externum to the abdomen, and there crosses in front of the quad- ratus lumborum, and behind the kidney and the adjacent part of the colon. It next pierces the aponeurosis of origin of the transversalis abdominis, and runs between the transversalis and the internal oblique muscles, anastomosing with the lower intercostal arteries, with the lumbar arteries, and with branches of the superior epigastric artery. 3. Diaphragmatic branches (aa. phrenicte superiores) are given off from the lower part of the thoracic aorta. They are small vessels which ramify on the upper surface of the diaphragm, and anastomose with branches of the superior phrenic and musculo-phrenic arteries. 4. The vas aberrans is a variable and inconstant branch of the thoracic aorta ; it represents the dorsal roots of the fourth and fifth right aortic arches of the embryo. When present it arises from the front and right side of the upper part of tlie main trunk near the upper bronchial artery, and passes upwards and to the right behind the oesophagus ; it frequently anastomoses with the right superior intercostal artery, and it may be enlarged and form the first part of the right subclavian artery. Visceral Branches of the Descending Thoracic Aorta. 1. The bronchial branches (aa. bronchiales) of the thoracic aortfs are usually two in numljer — an upper and a lower — and both pass to the left lung. The upi^er left bronchial artery arises from the front of the main trunk opposite the fifth PAKIETAL BEANCHES OF THE ABDOMINAL AORTA. 839 dorsal vertebra; the inferior left hroncliial artery usually takes origin near the lower horder of the left bronclius. Both vessels are directed downwards and out- wards to the back of the bronclius, which they accompany, and, dividing similarly, they follow its ramifications in the lung. They not only supply the walls of the bronchial tubes and the substance of the lungs, but also give branches to the bronchial glands, the pnlmonary vessels, the pericardium, and the oesophagus. As a rule there is only one right bronchial artery, and it arises from the first right aortic intercostal artery ; but it not uncommonly arises from the upper left bronchial artery, and more rarely it springs directly from the aorta. In its course and distriljution it corr(^sponds to the bronchial arteries of the left side. 2. The oesophageal branches (aa. cesophageai) are variable; usually four or five small branches spring from the front of the aorta and pass forwards to the oesophagus, in the walls of which they ramify, anastomosing above with branches of the left bronchial and inferior thyroid arteries, and below with oesophageal branches of the coronary and phrenic arteries. 3. The pericardial branches (rami pericardiaci) consist of three or four small irregular \essels which are distributed on the surface of the pericardium. 4. Small mediastinal branches (rami mediastinales) pass to the areolar tissue and glands in the posterior mediastinal space, and to the posterior pait of the diaphragm. BRANCHES OF THE ABDOMINAL AORTA. The branches of the abdominal portion of the aorta are distributed almost entirely to the walls and contents of the abdominal cavity, but some also supply small branches to the vertebral column, and to the contents of the spinal canal, and others are prolonged into the pelvis. They are divisible into parietal and visceral groups, both of which include paired and single (unpaired) vessels. flnferior phrenic. -| Lumbar. [Conimon iliac. Single. Middle sacral. T, . . 1 I Paired. -, Lumbar. TT;r./.=^„i Parietal.- r, •,• Visceral. ^(Jonimon iliac. /'Suprarenal. Paired, j Renal. I Spermatic or ovarian. j Coeliac axis. Single. -, Superior mesenteric. [inferior mesenteric. Parietal Branches of the Abdominal Aorta. 1. The inferior phrenic arteries (aa. phrenicaj inferiores, Fig. 634) are two in number, and are of small size ; they arise, either separately or by a common trunk, from the aorta, immediately below the diaphragm on the under surface of which they are distributed. Diverging from its fellow, each artery runs upwards and outwards on the corresponding cms of the diaphragm — that on the right side passing behind the inferior vena cava, that on the left beliind tlie oeso- phagus— and just before reaching the central tendon of the diaphragm it divides into internal and external terminal branches. The internal branch of each artery runs forward and anastomoses with its fellow of the opposite side, forming an arch, convex forwards, along the front of the central tendon of the diaphragm. Ofllsets from this arch anastomose with the superior phrenic, musculo-phrenic, and internal mammary arteries. The external branch passes outwards towards the lower ribs, and anastomoses with the musculo-phrenic and lower intercostal arteries. In addition to su])plying the diaphragm each inferior phrenic artery frequently gives a superior capsular branch to the suprarenal body. of its own side, and occasion- ally small hepatic branches pass through the coronary ligament to the liver. Further, the left artery gives branches to the oesophagus which anastomose with oesophageal branches of the aorta and of the coronary artery, whilst from the artery of the right side mimite branches pass to the inferior vena cava. 2. Tlio lumbar arteries (aa. lumbales) correspond to the intercostal In-anches of the thoracic aorta. They are in series with them, their distribution is very similar, and, like the intercostals, they arise, either separately or by. common trunks, from the back of the aorta. 57b 840 THE VASCIJLAE SYSTEM. There are usually four pairs of lumbar arteries, but occasionally a fifth pair arises from or in common witli the middle sacral artery. From their origins the lumbar arteries pass backwards and outwards on the front and sides of the bodies of the upper four lumbar vertebrae to the intervals between the adjacent transverse processes, beyond which they are continued in the abdominal wall. They lie on the bodies of the corresponding lumbar vertebrae. In their back- Hepatic ^•eills Inferior plireuic artery Suprarenal body Inferior vena cava Right ovarian vein - Ovarian artery - Ureter — External iliac vein Ascending colon Common iliac vein -; Common iliac arteiy Middle sacral artery External iliac artery _ ffisopliagus Crus of diaphragm Inferior plirenic artery Suprarenal body Co3liac axis Suprarenal vein Superior — mesenteric artery Renal artery Lumbar arteries _ Ureter Left colic artery Ovaiian artery Inferior mesenteric aiteiy — Descending colon Psoas muscle _ Common iliac artery -Sigmoid artery _ Common iliac vein Superioi' luemor- rlioidal artery Pelvic colon External iliac i]-tery External iliac vein Fallopian tube Uterus Fig. 634. — The Abdominal Aorta and its Buanohes. ward course, and while still in relation with the vertebral bodies, each artery is crossed by the sympathetic cord, and then, after passing internal to and being pro- tected by the fibrous arches from which the muscle arises, it runs behind the psoas muscle and the lumbar plexus. The upper two arteries on each side also pass behind the crura of the diaphragm. Beyond tlie interval between the transverse processes of the vertebrte each artery turns outwards aud crosses the quadratus lumborum — the last usually passing in front of, and the others behind the muscle ; it then pierces the aponeurosis of origin of the trans versalis, and proceeds forwards in the lateral abdominal wall in the interval ])etween the transversalis and internal oblique COMMON ILIAC AETERIES. 841 muscles. The lumbar arteries anastomose with oue another, with the lower iuter- ■costal and subcostal arteries, and with branches of the superior and deep epigastric and of the deep circumflex iliac and ilio-lumbar arteries. Fine twigs also pass from the lumbar arteries to the extra-peritoneal fat, and anastomose with corresponding branches from the inferior phrenic and ilio-lumbar arteries, and mth small branches from the hepatic, renal, and colic arteries, to form the subperitoneal plexus of Turner. The abdominal aorta lies but little to the left of the middle line, and con- sequently the right lumjjar arteries are scarcely longer than the left. On the right side the arteries, which near their origins lie more in front of the vertebral bodies, pass behind the inferior vena cava, the upper two arteries being separated from this vessel by the right crus of the diaphragm. The upper two right arteries also pass behind the receptaculum chyli and the lower end of the large azygos vein. Branches. — Dorsal (ramus dorsalis). — Each kimbar artery gives off, opposite the interval between the vertebral transverse processes, a dorsal brancli of considerable size. It is analogous with and distributed like the corresponding branch of an aortic intercostal artery (p. 837). Muscular branches are given off, both from the main trunk and itg dorsal branch, to the adjacent muscles. 3. The middle sacral ar' •ry(a. sacralis media. Fig. 634) is a single median vessel. It is commonly regardea as a caudal aorta and as the direct continuation of the abdominal aorta. It is, however, of small size, and almost invariably arises from the back of the aorta about half-an-inch above its bifurcation. It descends in front of the two lower lumbar vertebra and of the sacrum and coccyx, and ends opposite the tip of the last-named bone by anastomosing with the lateral sacral arteries to form a loop from which branches pass to the coccygeal body. In its course it passes at first behind the lowxr part of the abdominal aorta. Opposite the fifth lumbar vertebra it is crossed by the left common iliac vein, below which it is covered by peritoneum and coils of small intestine as far as the third sacral seg- ment, and in the rest of its e. mt by the rectum. It is accompanied below by vena3 comites, wdiich, however, u e above to form a single middle sacral vein. Small parietal branches pass ^transversely outwards on each side to the last lumbar vertebra and to the sacrum. They anastomose with the lateral sacral arteries, and they usually give off small spinal offsets which enter the anterior sacral foramina. Small and irregular visceral branches pass to the rectum and anastomose with the superior and middle luemorrhoidal arteries. COMMON ILIAC ARTERIES. 4, The common iliac arteries (aa. iliacie communes. Figs. 634 and 640) are the terminal branches of the abdominal aorta. They are formed by the bifurcation of the main trunk, and commence opposite the middle of the body of the fourth lumbar vertebra a little to the left of the middle line. Each artery passes down- wards and outwards across the bodies of the fourth and fifth lumbar vertebra? and the intervening intervertebral disc, and terminates at the level of the lumbo- sacral articulation and in front of the corresponding sacro-iliac joint by dividing into the internal and external iliac arteries. The direction of each common iliac is well indicated by a line drawn from the bifurcation of the aorta to a point midway l)etween the symphysis pubes and the anterior superior spine of the ilium. The angle included between the two diverging trunks is about 60^ in the male and about 68° in the female. The right artery is, for obvious reasons, a little longer than the left ; the former is about two inches, and the latter one and three-quarter inches in length. Relations. — Anterior. — .Both artei'ies are covered anteriorly by peritoneum, and are separated by it fi'om coils of the small intestine. Conununicatiug branches between the aortic and hypogastric plexuses of the sympathetic pass in front of the arteries, each of which is also crossed anteriorly near its termination by the corresponding ureter. The left artery is in addition crossed in front by the superior h;emorrhoidal vessels. 842 THE VASCULAE SYSTEM. Posterior. — Behind the artery of each side are the bodies of the fourth and fifth lumbar vertebrse, Avith the intervertebral disc above the latter, the psoas muscle, the sympathetic cord. These relationship's, however, are much closer on the left side than on the right. The right common iliac, except at its lower end, where it is in contact with the psoas, is separated from the structures named by the terminations of the right and left common iliac veins and the commencement of the inferior vena cava. The left common iliac, which is not so separated, lies on the inner border of the psoas. Somewhat deeply placed in the areolar tissue between the psoas and the lumbar vertebrae, the obturator nerve, the lumbo-sacral cord, and the ilio-lumbar artery form posterior relations to the artery of the corresponding side. Lateral. — On both sides of each artery are coils of small intestine. The commence- ment of the inferior vena cava lies to the outer side of the upper part of the right artery, and on the inner side of this vessel are the right common iliac vein below and the left common iliac vein above. The last-named vein lies on the inner side of the left artery. The Paired Visceral Branches of the Abdominal Aorta. 1. Suprarenal or Capsular Arteries (aa. suprarenales, Fig. 634). — There are •three sets of suprarenal arteries — the superior, middle, and inferior. Of these the middle only arise from the aorta direct ; the superior spring from the inferior phrenic, and the inferior from the renal arteries. The middle suprarenal arteries are two small branches which arise, behind the pancreas, from the sides of the aorta, close to the origin of the superior mesenteric artery. They run, one on each side, outwards and upwards upon the crura of the diaphragm, and just above the renal arteries, to the suprarenal bodies to which they are distributed, and they anastomose with the superior and inferior suprarenal arteries. 2. Renal Arteries (aa. renales, Fig. 634). — The renal arteries arise, one on each side, from the aorta, about half-an-inch below the origin of the superior mesenteric artery and opposite the second lumbar vertebra. Both arteries are of large size, and the right, which is a little longer than the left, is frequently slightly lower in position. Each artery runs almost transversely outwards to the hilum of the corresponding kidney. It passes in front of the crus of the diaphragm and of the upper part of the psoas muscle. The left artery lies behind the pancreas; the right vessel passes behind the inferior vena cava, the head of the pancreas, and the second part of the duodenum. The renal vein usually lies below and in front of the artery, but near the kidney the vein not un- frequently occupies a posterior position. On reaching the hilum of the kidney each artery divides into three branches, two of which pass in front of the pelvis of the ureter, and between it and the renal vein, and the third behind the pelvis. In the renal sinus these primary branches break up into numerous secondary branches which enter the kidney substance between the pyramids. Branches. — The following branches are given off by eacli renal artery, in addition to the terminal branches : — (a) Inferior suprarenal (a. suprarenalis inferior), which passes upwards to tlie lower part of the suprarenal body. (h) Ureteral. — Small branches to the upper part of the ureter, which anastomose with branches of the spermatic or ovarian arteries. (c) Peri-renal. — Small branches to tlie fatty capsule of tlie kidney, which anastomose with the lumbar arteries. (d) Glandular offsets, either from the main trunk or from some of its branches, jiass to the renal and lumbar glands. 3. Spermatic Arteries (aa. spermaticse internse). — The spermatic arteries in the male, and the corresponding ovarian arteries (aa. ovaricse) in the female, are two long slender vessels, one on the right side and one on the left, which arise from the front of the abdominal aorta, a short distance below the origins of the renal arteries. Each spermatic artery runs downwards and outwards to the internal abdominal ring ; it then traverses the inguinal canal, and consequently takes a downward and inward course. On emerging from the canal, through the external abdominal ring, it enters the scrotum, in which it descends, almost vertically, but in a tortuous VISCEEAL BEANCHES OF THE ABDOMINAL AOETA. 843 manner, to end immediately above the testicle by dividing into testicular and epididymal branches. Relations. — In the abdominal cavity the arteries lie heliiud the peritoneum, to ■which they are closely attached, and in front of the psoas muscles. The right artery is also in front of the inferior vena cava. Each artery descends in front of the ureter, the genito-crural nerve, and the lower end of the external iliac artery of its own side, and is accompanied by two spermatic veins which unite above into a single trunk. The anterior relations differ on the two sides. The right artery lies behind, and is crossed, by the ileo- colic, the right colic, and the terminal branches of the supei-ior mesenteric artery, and by the third part of the duodenum, the termination of the ileum, and the vermiform appendix. The left artery is crossed in front by the left colic and sigmoid branches of t])e inferior mesenteric artery and by the iliac colon. At the internal abdominal ring the spermatic artery comes into relation, at its inner side, with the vas deferens. Tlie two structures run together round the outer and anterior aspects of the deep epigastric artery to the inguinal canal. In the inguinal canal the spermatic artery, along with the other constituents of the spermatic cord, is enclosed in the infundibular and cremasteric fascia;, the intercolumnar fascia being added at the external abdominal ring. In this part of its course the artery lies in front of the vas deferens, and behind the anterior part of the pampiniform plexus and the spermatic veins wliich arise from it. Branches. — («) Ureteral branches, small in size, are distributed to the middle part of the ureter, anastomosing above with branches from the renal and below with brandies from the vesical arteries. (b) Cremasteric branches, given oft' in the inguinal canal and upper part of tlie scrotum, supply tlie cremaster muscle, and anastomose with the cremasteric branch of the deep epigastric. (c) Terminal Branches. — (i.) The epididymal branch runs down^^•ards to the epididymis, which it sui^iilies. It also gives twigs to the vas aberrans, the coni vasculosi, and the tunica vaginalis, and anastomoses with the artery of the vas deferens, (ii.) The testicular branch descends on the upper and back part of the testicle, and breaks up into numerous peripheral and central Ijranches. The peripheral branches pass through the tunica alljuginea and ramify on its inner surface ; they anastomose with one another and with the central branches. The central branches pass through the mediastinum testis and along the surfaces of the septa. 3rt. The ovarian arteries (aa. ovaricse, Fig. 634) in the female closely corre- spond to the spermatic arteries in the male. They are, however, much shorter, and, instead of passing through the abdominal wall, descend into the pelvis, where they run between the layers of the broad ligament to terminate between the ovaries and the uterus by anastomosing with the uterine arteries. Relations. — In the upper part of its course the relations of each ovarian artery are like tiiose of the corresponding spermatic artery, but about the level of the anterior superior spine of the ilium each ovarian artery turns inwards, and, ci'ossing the upper part of the external iliac vessels (artery and vein), descends in the anterior border of the fossa ovarii, on the lateral wall of the pelvis, to the broad ligament, where it is placed below the Fallopian tube. Branches.— («) Ureteral, to the middle 2)art of the ureter. (Ji) Tubal, to the Fallopian tube, which anastomose with branches of the uterini'. ((■) Ligamentous, to the round ligament, as far as tlie inguinal canal. (d.) Ovarian branches, numerous, pass to tlie liiluni of the o\aiy, and thence to the substance of the organ. (e) A uterine branch is formed by the conlinuatiou of the trunk to its anastomosis with the uterine branch of the internal iliac. The UNrAiKETi ok Single Visceral Beanciies of the Aiu>ominal Aorta. 1. The cceliac artery or cceliac axis (a. coeliaca, Figs. 634 and 635) arises from the front of the abdominal aorta, immediately below the aortic orifice of the diaphragm and between its crura. It is a sliort but wide vessel which runs almost horizontally forwards for a distance of about half-an-inch, and then terminates by dividing into three large branches— the coronary or gastric, tlie hepatic, and tlie splenic. Relations. — Tiie short trunk extends from the aorta behind the lesser sac of peritoneum, by which it is separated from tiie stomach, or from the small omentum, 844 THE VASCULAR SYSTEM. in frout. It runs below the Spigelian lobe of the liver, and above the upper border of the pancreas and the splenic vein, and it is surrounded by the solar and coeliac plexuses of the sympathetic ; the right semilunar ganglion is to its right side, and the left semilunar o-ano-lion and cardiac end of the stomach are on its left side. Branches. — (a) The coronary or gastric artery (a. gastrica sinistra) is the smallest branch of the coeliac axis. It runs obliquely upwards and to the left, and reaches the smaller curvature of the stomach close to the oesophagus. It then turns sharply forwards, downwards, and to the right, and runs towards the pyloric end of the stomach to anastomose with the pyloric branch of the hepatic artery. In the first part of its course the artery lies behind the lesser sac of the peritoneum ; it then passes into the left pancreatico-gastric fold, and is continued between the layers of the small omentum. Branches.— (1.) (Esophageal (rami oesophagei).— When the artery readies the stomach a large Inferior phrenic arteries Superior pancreatico- duodenal artery / Gastro-duodenal artery Right gastro-epiploic artery Left gastro- \ epiploic artery Splenic artery 'Coronary artery Hepatic artery Pyloric artery Fig. 635. — The Cceliac Axis and its Branches. oesophageal branch is given off, which passes upwards on the cesopliagus, and gives oJB'sets to it which anastomose with cesoiDhageal branches of the thoracic aorta and with branches of the inferior phrenic, (ii.) Grastric branches are distributed to both surfaces of the stomach. They anastomose with branches of the vasa brevia of the splenic, and with branches of the gastro- epiploic arterial arch on the greater curvature of the stomach. (h) The splenic artery (a. lienalis. Fig. 635) is the largest branch of the coeliac axis. It runs a more or less tortuous course behind the stomach and the lesser sac of the peritoneum, and along the upper border of the pancreas. It lies in front of the left suprarenal capsule and the upper end of the left kidney, and passes forwards between the two layers of the lieno-renal ligament, where it divides into from five to eight terminal branches (rami lienales) which enter the hilum of the spleen and supply the splenic substance. It is accompanied by the splenic vein, which lies below it. Branches. — (i.) Pancreatic (rami pancreatici). — Numerous small branches (pancreaticse parvie) are given off to the pancreas. One large branch (pancreatica magna), occasionally present, enters the upper border of the pancreas, about the junction of its middle and left thirds, and runs from left to right in the substance of the pancreas, a little above and behind the pancreatic duct. ]3otli the small and large arteries supply the substance of the pancreas, and anastomose with one another and with branches of the pancreatico- duodenal arteries. VISCEEAL BEANCHES OF THE ABDOMINAL AOETA. 845 (ii.) The vasa brevia (aa. gastric^ breves), or short gastric branches, four or five in number, are given off either from the end of the main vessel or, more commonly, from some of its terminal branches. They pass between the layers of the gastro-splenic omentum to the left end of great curvature of the stomach, and anastomose with the oesophageal, the gastric, and the left gastro-epiploic arteries. (iii.) The left gastro-epiploic branch (a. gastro-epiploica sinistra) arises from the front of the splenic, close to its termination, and passes forwards Ijetween the layers of the gastro-splenic omentum to the left end of the great curvature of the stomach, along which it is continued, from left to right, between the layers of the gastro-colic or great omentum. It ends by anastomosing with the right gastro-epiploic artery, and it gives off numerous gastric branches to both surfaces of the stomach, which anastomose with the vasa brevia and with branches of the coronary and pyloric arteries. Long slender omental branches pass to the omentum and anastomose with branches of the colic ax'teries. (c) The hepatic artery (a. hepatica, Fig. 635) runs along the upper border of the head of the paDcreas to the right pancreatico-gastric fold of peritoneum, in which it turns forwards to the upper border of the first part of the duodenum. It then passes upwards, between tiie layers of the small omentum, in front of the portal vein and to the left of tile common bile duct, and reaches the transverse fissure of the liver, where it divides into right and left branches. Branches. — (i.) The pyloric artery (a. gastrica dextra) is a small branch which arises opposite the upper border of the first part of the duodenum. It descends to the pylorus, running between the layers of the small omentum, and then turns to the left along the smaller curvature of the stomach. It gives branches to both surfaces of the stomach, and terminates by anastomosing with the coronary artery. (ii.) The gastro-duodenal artery (a. gastro-duodenalis).^ — This branch of the hepatic ai'ises just above the upper border, descends behind, and terminates opposite the lower border of the first part of the duodenum. In its course it lies between the neck of the pancreas and the first part of the duodenum, and it is in front of the portal vein. The common bile duct is on its right side. The vessel ends by dividing into the right gastro- epiploic and the superior pancreatico-duodenal aiteries. The right gastro-epiploic artery (a. gastro-epiploica dextra) is the larger of the two terminal brandies of the gastro- duodenal ; it passes from right to left along the greater curvature of the stomach, between the layers of the gastro-colic omentum, and unites with the left gastro-epiploic branch of the splenic artery. From the arterial arch so formed branches pass ujjwards on both surfaces of the stomach, and anastomose with branches of the pyloric and coronary arteries. Other branches pass downwards to the omentum, and anastomose with branches of the colic arteries. The superior pancreatico-duodenal artery (a. pancreatico-duodenalis superior) runs a short course to the right, between the duodenum and the head of the pancreas, and divides into anterior and posterior terminal branches which descend, the former in front of and the latter behind the head of the pancreas, to anastomose with similar branches of the inferior pancreatico-duodenal artery. They supply the head of the pancreas, anastomosing in it with the pancreatic branches of the splenic artery : branches are also given to the second part of the duodenum and to the common bile duct. (iii.) Terminal branches. — The right hepatic artery (ramus dexter) passes either in front of or behind the hepatic duct and behind the cystic duct, to the right end of the transverse fissure of the liver, where it divides into two or more branches which enter the substance of the liver and accompany the branches of the portal vein and the hepatic duct. As it crosses just above tlie junction of the hepatic and cystic ducts, the right hepatic ai'tery gives off" a cystic Ijranch. The cystic arteri/ (a. cystica) runs downwards and forwards along the cystic duct to the gall-bladder, where it divides into upper and lower branches ; the upper passes downwards between the gall-bladder and the under surface of the liver, to both of which it gives offsets ; the lower branch is distributed on the under surface of the gall-bladder, between it and the peritoneum. The left hepatic artery (ramus sinister) is longer and narrower than the right. It runs to the left end of the transverse fissure, gives one or two branches to the Spigelian lobe, crosses the longitudinal fissure, and breaks up into branches which terminate in the substance of the left lobe of the liver. 2. The superior mesenteric artery (a. mesenterica superior, Figs. 634, 636, and 659) springs from the front of the aorta, about half-an-inch below the origin of the cceliac axis and opposite the first lumbar vertebra. It passes obliquely downwards and forwards, crossing in front of the left renal 846 THE VASCULAR SYSTEM. vein, the lower part of the head of the pancreas, and the third part of the duo- denum ; opposite the latter it enters the root of the mesentery, in which it continues to descend, curving oljliquely from above downwards and to the right, to the right iliac fossa, and crossing in this part of its course obliquely in front of the aorta, the lower part of the inferior vena cava, the right ureter, and the right psoas muscle. At its origin it lies behind the neck of the pancreas and the splenic vein ; where it passes in front of the duodenum it is crossed anteriorly by the transverse colon, and in the lower part of its extent it is concealed by coils of small intestine. / ^. Middle colic arterv - Inferior pancreatico duodenal artery Right colic artery Ileo-eolic artery Termination of superior niesfu- H'lJ.' teriearteiy Duodeno- ejunal flexr.re Rami intestini euuis "-^>*/->* '-js^;f'^ Fig. 636. — The Spi'euiok Mesenteric Artery and its Branches. Branches. — It gives oif numei-oufs branches whicli supply the duodeiiuiii and the pancreas in part, the whole of the small intestine below the duodenum, and the large intestine nearly as far as the splenic flexure. The branches are as follows : — (a) Rami intestini tenuis (aa. intestinales), or branches to the small intestine, varying from ten to sixteen in number; they spring from the convexity of the suj)erior mesenteric artery, and pass obliquely forwards and downwards between the layers of the mesentery, each dividing into two branches which anastomose with adjacent branches to form a series of arcades from which secondary branches are given off. This process of division and union is repeated three or four times ; thus four or five tiers of arches are VISCEEAL BEANCHES OF THE ABDOMINAL AOETA. 847 formed, from the most distal of which terminal branches are given off to the wails of the jejmium and ileum. Branches from the successive arcades are also given off to the mesenteric glands. The terminal branches anastomose together in the walls of the gut, forming a vascular network which communicates above with the inferior pancreatico- duodenal artery and below with the terminal brancli of the superior mesenteric trunk. The vascular loops and branches are accompanied by corresponding veins, lymphatics, and nerves. (b) The inferior pancreaticoduodenal artery (a. pancreatico-duodcnalis inferior). It arises eitlier from the trunk of the superior mesenteric, at the upper border of the third part of the duodenum, or from the first of the rami intestini. It runs to the right, between the head of the pancreas and the third part of the duodenum, and terminates by dividing into two branches, anterior and posterior, wliicli ascend, the former in front and the latter behind the head of the pancreas ; they supply the head of the pancreas, the second and third parts of the duodenum, and they anastomose with the similar branches of the superior pancreatico-diiodenal artery. (c) The middle colic artery (a. colica media) is a large branch which springs from the front of the superior mesenteric as it enters the root of the mesentery. It runs down- wards and forwards in the transverse mesocolon, and terminates by dividing into two branches, right and left, which anastomose respectively Avith the right and left colic arteries, forming arcades from which secondary and tertiary loops are derived, the terminal branches being distributed to the walls of the transverse colon. {(7) The right colic artery (a. colica dextra) springs from the right or concave side of the superior mesenteric, either alone or in the form of a common trunk which divides into right and ileo-colic branches. It runs to the right, behind the peritoneum on the posterior wall of the abdomen, and in front of the right psoas, the ureter, and the spermatic or ovarian vessels, towards the ascending colon, near w'hicli it divides into an ascending and a descending brancli. The former passes upwards, and anastomoses in the transverse mesocolon with the middle colic artery. The latter descends to anastomose with the ujDper branch of the ileo-colic, and from the loops thus formed branches are dis- tributed to the walls of the ascending colon and the beginning of the transverse colon. (e) The ileo-colic artery (a. ileo-colica) arises by a common trunk with the right colic, or separately from the right side of the superior mesenteric, and passes downwards and outwards, behind the peritoneum, towards the lower part of the ascending colon, where it terminates by dividing into an ascending branch which anastomoses with tlie lower branch of the right colic, and a descending branch which communicates with the colic terminal branches of the superior mesenteric trunk. (/') Terminal. — The lower end of the superior mesenteric artery divides into five branches — (i.) ileal, (ii.) appendicular, (iii.) anterior ileo-csecal, (iv.) posterior ileo-ctecal, and (v.) colic. The ileal branch (a. ilea) turns upwards and to tin- ]cit in the lowest part of the mesentery, and aiiastoincisi-s with the rami intestini. The appendicular branch, (a. appendicularis) passes behind the ttTmiiial portion of tlie ileum, and through the meso-appondix to the vermiform pro- cess, upon which it end?. The anterior ileo-csecal crosses the front of the ileo-ca'cal junction in a fold of peritoneum ; the posterior ileo-csecal crosses the ileo-ca;cal junction posteriorly, and the colic runs upwards to the ascending colon. The ileo-ctecal branches siipply the AvaUs of the caecum, and, like the colic branch, anastomose with branches of tlie ileo-colic artery. 3. The inferior mesenteric artery (a. mesenterica. inferior, Fig. 634) arises from the front and towards the left side of the aorta an inch and a half above the bifurcation ; it passes downwards and shghtly outwards, lying behind the perito- neum and on the front of the left psoas muscle, to the upper and outer border of the left common iliac artery, where it becomes the superior hemorrhoidal. Branches. — (") 'fhe left colic artery (a. colica sinistra) arises from the left side of the inferior mesenteric near its origin. It runs upwards and to the left towards the splenic flexure of the colon, where it divides into ascending and descending branches. The ascending branch crosses in front of the lower end of the left kidney, passes between the hiyers of the transverse mesocolon, and, turning inwards, terminates by joining the left branch of the middle colic artery. The descending branch passes downwards behind the peritonevun to the inner side of the descending colon to unite with the superior sigmoid artery, and from the loops thus formed brandies are distributed to the descending colon. In the whole of its course the left colic artery lies behind the peritoneum, and on the posterior abdominal wall ; it crosses in front of the left psoas and the left ureter. 848 THE VASCULAE SYSTEM. (b) The sigmoid branches (aa. sigmoidese), usually two in number, arise from the convexity of the inferior mesenteric, and pass downwards and outwards to the iliac colon. They lie behind the peritoneum, and in front of the psoas, the ureter, and the upper part of the iliacus. They terminate by dividing into branches Avhich anastomose with the left colic above and with branches of the superior haemorrhoidal beloAV, forming a series of arches from which branches are distributed to the lower part of the descending colon, the iliac colon, and the pelvic colon. (c) The superior liaemorrhoidal artery (a. hsemorrhoidalis superior) is the direct continuation of the inferior mesenteric. It enters the mesentery of the pelvic colon, crosses the front of the left common iliac artery, descends into the pelvis as far as the third piece of the sacrum, or in other words the junction between the pelvic colon and the rectum, and divides into two branches which pass downwards on the sides of the rectum. Half-way down the rectum each of the two terminal branches of the superior hsemorrhoidal artery divides into two or more branches which pass through the muscular coats and terminate in the submucous tissue, where they divide into numerous small branches which pass vertically downwards, anastomosing Avith each other, Avith offsets from the middle hsemorrhoidal branches of the internal iliac arteries, the inferior hsemorrhoidal branches of the internal pudic arteries, and Avith branches from the middle sacral artery. The superior hsemorrhoidal artery supplies the mucous membrane of the pelvic colon and the rectum and the muscular coats of the pelvic colon. THE INTERNAL ILIAC ARTERY. The internal iliac or hypogastric artery (a. hypogastrica, Eigs. 634, 637, and 640) in the fcetus is the direct continuation of the common iliac trunk. It supplies numerous branches to the pelvis, runs upwards on the anterior abdominal wall to the umbilicus, and is prolonged as the umbilical artery to the placenta. One of its pelvic branches — the sciatic — is at first the main artery of the inferior extremity, but subsequently another branch is given off which becomes the chief arterial trunk of the lower limb. This branch is the external iliac artery ; it soon equals and ultimately exceeds the internal iliac in size, and it is into these two vessels that the common iliac appears to bifurcate. When the placental circulation ceases and the umbilical cord is severed, the part of the internal iliac trunk which extends from the pelvis to the umbilicus atrophies, and is afterwards represented almost entirely by a fibrous cord, known as the obhterated hypogastric artery. It is only at its proximal end that the atrophied part remains pervious, and here it forms the commencement of the superior vesical artery ; accordingly, the permanent internal iliac artery is a com- paratively short vessel. Owing to the arrangement of some of its branches it appears to end in an anterior and a posterior division, the former of which is to be regarded as the continuation of the vessel to the obliterated hypogastric, whilst the latter is simply a common stem of origin for some of the branches. With this explanation the internal iliac artery may be described in the usual manner. It arises from the common iliac opposite the lumbo-sacral articulation, and descends into the pelvis, to terminate, as a rule, opposite the upper border of the great sciatic notch, in two divisions — anterior and posterior — from each of which branches of distribution are given off. The artery measures about one and a half inches in length, and is the inner of the two terminal branches of the common ihac artery. Relations. — Anterior. — The artery on each side is covered in front and internally by peritoneum, under which the corresponding ureter descends along the anterior border of the artery. The ilio-pelvic colon crosses from the front to the iimer side of the left artery, and the terminal part of the ileum bears the same relation to the right artery. Posterior to it are the internal iliac vein and the commencement of the common iliac vein ; behind these is the lumbo-sacral cord and the sacrum. Lateral. — On its outer side the external iliac vein separates it from the psoas muscle above, Avhilst beloAV this is the obturator nerve, embedded in a mass of fat Avhich intervenes between the internal iliac artery and the side Avail of the pelvis. On its inner side it is crossed by some of the tributaries of the internal iliac vein, and is covered by peritoneum. BKANCHES OF THE INTEEXAL ILIAC ARTEEY 849 Branches. — The internal ihac artery supphes the greater part of the pelvic wall and viscera, and its branches are also distributed to the buttock and thigh and to the external organs of generation All the branches may be given off separately from a single undivided parent External iliac vein Psoas muscle Hypogastric artery _ Deep circuintlex iliac \>^\'ffli^ artery VVVM} Superior vesical artery^-'^"^ Obturator vein Deep epigastric artery Hound ligament Obturator nerve Obturator artery Dorsal artery of clitoris Artery to corpus cavernosum Sympathetic cord Lateral sacral artery Internal iliac vein Gluteal artery ciatic artery Internal pu'lic artery Sacral plexus Fig. 637. — Thk I.ster>'.\l Ijjac ARxr.Hv and its Bkanche.s in thk Fhmale. 1. Great sacro-sciatic ligament. 2. Uterine artery. 3. Vaginal arterj'. 4. Inferior hremorrlioidal nerve. 5. Inferior hseniorrhoiilal artery. 6. Dorsal nerve of clitoris. 7. Internal pudic artery. 8. Perineal nerve. 9. Superficial perineal artery. 10. Arterv to bulb. trunk, but as a rule they arise in two groups corresponding to the two divisions in which the artery under these circumstances appears to end. Posterior division [ parietal Anterior division parietal visceral j Ilio-lumbar Lateral sacral (Gluteal j' Obturator Sciatic I Internal pudic .Superior vesical (Obhterated hypogastric) , Middle vesical lul'erior vesical Middle liii'inorrhoidal. In the fuiiuile the inferior vesical is replaced by a vaginal branch, and an additional branch, the uterine, is triven off. 58 850 THE VASCULAE SYSTEM. Branches of the Posterior Division. The posterior terminal division gives off the ilio-lumbar and lateral sacral arteries, and is continued as the gluteal artery. No visceral branches are derived from this division. 1. Ilio-lumbar Artery (a. ilio-lumbalis). — This vessel runs upwards and outwards across the brim of the pelvis to the iliac fossa. It passes in front of the sacro-iliac articulation, between the lumbo-sacral cord and the obturator nerve, and behind either the lower part of the common or the upper part of the external iliac vessels and the psoas and iliacus muscles. In the iliac fossa it anastomoses with branches of the deep circumflex iliac and obturator arteries. It also gives off offsets to the iliacus, and supplies a large nutrient branch to the ilium. A lumbar brancli (ramus lumbahs) ascends behind the psoas to the crest of the ihum. It supplies the psoas and quadratus lumborum, and anastomoses with the lumbar and deep circumflex iliac arteries ; it also gives off a spinal hranch which enters the intervertebral foramen between the fifth lumbar vertebra and the sacrum, and is distributed like the spinal branches of the lumbar and aortic intercostal arteries. 2. Lateral Sacral Arteries (aa. sacrales laterales). — There is sometimes only a single lateral sacral artery on each side ; more commonly there are two, superior and inferior. Both branches run downwards and inwards on the front of the sacrum. The inferior passes in front of the pyriformis and the sacral nerves, and descends on the outer side of the sympathetic cord to the coccyx where it terminates by anastomosing with the middle sacral. The superior branch only reaches as far as the first or the second anterior sacral foramen, and then it enters the sacral canal. It anastomoses with the lower branch and with the middle sacral artery. Transverse branches are given off by the lateral sacral arteries to the pyriformis, and to the sacral nerves. Spinal offsets are also given off, which pass through the anterior sacral foramina to the sacral canal ; they supply the membranes of the cord, the roots of the sacral nerves, and the filum terminale, and anastomose with other spinal arteries. They then pass backwards through the posterior sacral foramina, and anastomose on the back of the sacrum with branches of the gluteal and sciatic arteries. 3. Gluteal Artery (a. gluteea superior. Figs. 637 and 643). — After giving off the ilio-lumbar and lateral sacral branches, the posterior division of the internal iliac is continued as the gluteal artery. This is a large vessel which pierces the pelvic fascia, passes backwards between the lumbo-sacral cord and the first sacral nerve, and leaves the pelvis through the upper part of the great sciatic foramen. It runs above the pyriformis muscle to the buttock, immediately on reaching which it terminates, Ijetween the adjacent borders of the pyriformis and gluteus medius muscles and beneath the gluteus maximus, by dividing into superficial and deep branches. (a) The superficial brancli divides at once into numerous branches, some of which supply the gluteus maximus, whilst others pass through it, near its origin, to the overlying skin. The branches freely anastomose with branches of the sciatic, internal pudic, internal circumflex, deep circumflex iliac, and lateral sacral arteries. {h) The deep terminal brancli, accompanied by the superior gluteal nerve, runs forwards between the gluteus medius and minimus, and, after giving a nutrient branch to the ilium, subdivides into upper and lower branches. The upper hranch, running forwards along the origin of the gluteus minimus from the middle curved line of the ilium, passes beyond the anterior margins of the gluteus medius and minimus to anastomose, under cover of the tensor fasciae femoris, with the ascending branch of the external cii'cumflex artery. It also anastomoses with the circumflex iliac artery, and it supplies muscular branches to the adjacent muscles. The lotver hranch passes more directly forwards, across the gluteus minimus, towards the trochanter major, along with the branch of the superior gluteal nerve which supplies the tensor fasciae femoris. It supplies the glutei muscles, and anastomoses with the ascending branch of the external circumflex artery. Before leaving the pelvis the gluteal artery gives muscular branches to the pelvic BEANCHES OF THE INTEENAL ILIAC AETEEY. 851 diaphragm and the obturator internus, small neural branches to the roots of the sacral plexus, and nutrient branches to the hip-bone. Branches of the Anterior Division of the Internal Iliac Artery. The anterior division gives off both parietal and visceral branches, and is continued as the hypogastric artery, which for the greater part of its extent is obliterated. The parietal branches are the obturator, the pudic, and the sciatic. The visceral branches include the superior, middle and inferior vesical, and the middle htemorrhoidal arteries in the male. Similar \isceral branches are also given off in the female, but the inferior vesical is replaced by the vaginal artery, and an additional branch, the uterine artery, is also given off. Visceral Branches. 1. The superior vesical artery (a. vesicalis superior) arises from the anterior division of the internal ihac. It divides into numerous branches wliich supply the upper part of the bladder, anastomosing with the other vesical arteries, and it also gives small branches to the urachus, and often to the lower part of the ureter. It may in addition give off the middle vesical artery, and not un- frequently the long slender artery to the vas deferens arises from one of its branches. 2. Obliterated Hypogastric Artery. — Atrophy of that portion of the internal iliac artery, which extends from the side of the bladder to the umbilicus (a. umbih- calis), has already been referred to. It is complete between the imibihcus and the true origin of the superior vesical artery, but between this origin and the apparent ending of the internal iliac in its two divisions the atrophy is incomplete, and the lumen of the vessel, though greatly diminished in size, remains, and is looked upon as the first part of the superior vesical artery. Strictly speaking, the first of these two parts only constitutes the " obliterated hypogastric " (ligamentum umbilicale laterale). It is a fibrous cord which runs forwards and upwards towards the apex of the bladder, whence it ascends^ on the posterior surface of the anterior abdominal wall and on the outer side of the urachus to the umbihcus. As it passes along the wall of the pelvis it is under cover of the peritoneum, and it is crossed by the vas deferens in the male, and by the round ligament in the female. 3. The middle vesical artery is usually given off behind the superior vesical. It is distributed to the posterior surface of the bladder as low down as the base ; and to the vesicuke seminales. 4. The inferior vesical artery (a. vesicalis inferior) is a very constant branch which runs inwards upon the upper surface of the levator ani to the base of the bladder. It also gives branches to the seminal vesicles, the vas deferens, the lower part of the ureter and the prostate, and it anastomoses with its fellow of the opposite side, with the other vesical arteries, and with the middle hiemorrhoidal artery. The artery to the vas (a. deferentialis), which not unfrequently arises from the superior vesical, is a long slender vessel which runs downwards to the vas and vesicula seminales, and is then continued with the vas deferens to the testicle, where it anastomoses with the spermatic artery. It also anastomoses with the cremasteric branch of the deep epigastric artery. 5. The middle haemorrhoidal artery (a. hiemorrhoidalis media) is an irregular branch which arises either directly from the anterior division of the internal iliac or from the inferior vesical branch ; more rarely it springs from the internal pudic artery. It runs inwards, and is distributed to the muscular coats of the rectum ; it also gives branches to the prostate, the seminal vesicle, and the vas deferens, and it anastomoses with its fellow of the opposite side, with the inferior A'esical, and with the superior and inferior luemorrhoidal arteries. 6. The vaginal artery (a. vaginalis) in the female usually corresponds to the inferior vesical in the male ; in which case it arises from the anterior di^dsion of the internal iliac, either independently or in common with the uterine artery. 852 THE VASCULAE SYSTEM. Occasionally both inferior vesical and uterine vessels are present, and not un- commonly the vaginal artery is represented by several branches. The vaginal arteries run downwards and inwards on the floor of the pelvis to the sides of the vagina, and divide into numerous branches which ramify on its anterior and posterior walls. The corresponding branches of opposite sides anastomose and form anterior and posterior longitudinal vessels, the so-called azygos arteries. They also anastomose above with the cervical branches of the uterine artery, and below with the perineal branches of the internal pudic. In addition to supplying the vagina, small branches are given to the bulb of the vestibule, to the base of the bladder, and to the rectum. 7. The uterine artery (a. uterina) arises from the anterior division of the internal ihac, either separately or in common with the vaginal or middle hsemorrhoidal arteries. It runs inwards and slightly forwards, upon the upper surface of the levator ani, to the lower border of the broad ligament, between the two layers of which it passes inwards, and arches above the ureter about three- quarters of an inch from the uterus. It passes above the lateral fornix of the vao-ina to the side of the neck of the uterus, and is then directed upwards, until it almost reaches the fundus, just below which, however, it turns outwards beneath the isthmus of the Fallopian tube and anastomoses with the ovarian artery. It supphes the uterus, the upper part of the vagina, the inner part of the Fallopian tube, and gives branches to the round ligament of the uterus. It anastomoses with its fellow of the opposite side, and with the vaginal, the ovarian, and the deep epigastric arteries. Pakietal Branches of the Anterior Division of the Internal Iliac. 1. The obturator artery (a. obturatoria. Figs. 637 and 640) runs forwards and downwards along the lateral wall of the true pelvis, just below its brim, to the obturator foramen, through the upper part of which it passes. It terminates im- mediately on entering the thigh by dividing into internal and external terminal branches, which skirt round the margin of the obturator foramen beneath the obturator externus muscle. It is accompanied in the whole of its course by the obturator nerve and vein, the former being above it and the latter below. To its outer side is the pelvic fascia, which intervenes between it and the upper part of the obturator internus muscle, whilst on its inner side it is covered by peritoneum; between the peritoneum and the artery is the ureter. When the bladder is distended it also comes into close relation with the anterior part of the artery. In the female the ovarian vessels and the broad ligament are on the inner side of the obturator artery. Branches. — All the branches except the terminal are given off before the artery leaves the pelvis. They include : — (a) Muscular branches to the obtvu-ator internus, levator ani and ilio-psoas muscles. (6) A nutrient branch to the ilium, which passes beneath the ilio-psoas muscle, supplies the bone, and anastomoses with the ilio-lumbar artery, (c) A vesical branch, or branches, pass inwards to the bladder beneath the lateral false ligament, (d) A pubic branch (ramus pubicus), which ascends on the back of the pubes, and anastomoses with its fellow of the opposite side and with the pubic branch of the deep epigastric, is given off just before the artery leaves the pelvis. In its upward course it may pass either on the outer or inner side of the external iliac vein, whilst not unfrequently it runs on the inner side of the crural ring. In the latter case it is important in relation to femoral hernia ; and this importance is emphasised when, as sometimes happens, the obturator artery arises as an enlarged pubic branch of the deep epigastric artery instead of from the internal iliac, (e) Terminal. — The internal terminal branch (ramus anterior) runs forwards, and the external (ramus posterior) backwards round the margin of the obturator foramen. They lie on the obturator membrane, and under cover of the obturator externus. They anastomose together at the lower margin of the foramen, and both give off offsets which anastomose with the internal circumflex artery, and twigs of supply to the adjacent muscles. The external branch also gives an acetabular branch to the hip-joint, which passes upwards, through the cotyloid notch on the inner side of the transverse ligament, to supply the ligamentum teres and the head of the femur. BEANCHES OF THE INTEENAL ILIAC AETEEY. 853 2. Internal Pudic Artery (a. pudenda interna, Figs. 637 and 638). — The internal pudic artery arises from the anterior division of the internal iliac close to the origin of the sciatic artery, which slightly exceeds it in size. It runs down- wards and backwards in front of the pyriformis muscle and the sacral plexus, from both of which it is separated by the pelvic fascia, and on the outer side of the rectum to the lower part of the great sciatic foramen. In this course it pierces the pelvic fascia, passes between the pyriformis and coccygeus muscles, and leaves the pelvis to enter the buttock in company with the corresponding veins, the sciatic vessels and nerves, the pudic nerve, and the nerve to the obturator internus. In the buttock it lies, under cover of the gluteus maximus, on the spine of the ischium, between the pudic nerve and the nerve to the obturator internus, the former being internal to it. It next passes through the small sciatic foramen Crus ppnis Superficial perineal artery Transversus perinei muscle Internal pudic artery Inferior lueinor- rhoidal artrr\ Crus penis Dorsal artery of penis and arti?ry to corpns cavernosum Bulb of penis ( ompi-essor urethrse Artery to bulb Superficial perineal artery I'ransverse perineal artery Internal pudic artery Inferior luiemor- ilioidal artery ■ luteus maximus 6.38. — The PEiu>rEAL Distribution of the Intkknal Pudic Auteky in the Male. and enters the] perineum, in the anterior part of which it terminates by dividing into the arteryjof the corpus cavernosum and the dorsal artery of the penis. In the first part of its course in the perineum the artery lies in the outer fascial wall of the ischio-rectal fossa, where it is enclosed in the space known as Alcock's canal. This, which is situated about one and a half inches above the lower margin of the tuberosity of the ischium, contains also the pudic veins and the terminal parts of the pudic nerve, viz. the dorsal nerve of the penis which lies al)Ove tlie artery, and the perineal division which lies below the vessel. From the ischio-rectal fossa the internal pudic is continued forwards between the two layers of the triangular ligament of the urethra, and close to the ramus of the pubis. About half-an-inch below the subpubic ligament it turns somewhat abruptly forwards, pierces the anterior layer of the triangular ligament, and immediately divides into its terminal branches, viz. the artery of the corpus cavernosum and the dorsjil artery of the penis. The division sometimes takes place whilst the artery is still between the layers of the triangular ligament. Branches. — In the pelvis it gives small branches to the neighbouring muscles and to the roots of the sacral plexus. 854 THE YASCULAE SYSTEM. In the huttock. — {a) Muscular branches are given to the adjacent muscles. (6) Anastomotic branches unite with bi-anches of the gluteal, sciatic and internal circumflex arteries. In the ischio-rectal fossa. — (c) The inferior hsemorrhoidal artery (a. hsemorrhoidalis inferior) pierces the inner wall of Alcock's canal, and runs obliquely forwards and inwards. It soon divides into two or three main branches, which, sometimes arising separately, pass across the space to the anal passage. The artery anastomoses in the walls of the anal passage with its fellow of the opposite side, and with the middle and superior hsemor- rhoidal arteries ; it also anastomoses with the transverse perineal arteries, and it supplies cutaneous twigs to the region of the anus, and others which turn round the lower border of the gluteus maximus to supply the lower part of the buttock. (d) The superficial perineal artery (a. perinei) arises in the anterior part of the ischio- rectal fossa, pierces the base of the triangular ligament, and divides into long slender branches (aa. scrotales posteriores in the male, labiales posteriores in the female) which are continued forwards in the urethral triangle, beneath the superficial perineal fascia, to the scrotum. It anastomoses with its fellow of the opposite side, with the transverse perineal and the external pudic arteries, and it supplies the muscles and subcutaneous structures of the virethral triangle. (e) The transverse perineal artery is a small branch which arises either from the internal pudic or from its superficial perineal branch. It runs inwards along the base of the triangular ligament to the central point of the perineum, where it anastomoses with its fellow of the opposite side, with the superficial perineal branch, and with the inferior hsemorrhoidal arteries. It supplies the sphincter ani, the bulbo-cavernosus or sphincter vaginae, and the anterior fibres of the levator ani. In the urethral triangle. — (/) The artery to the bulb (a. bulbi urethrse), a branch which is usually of relatively large size, is given off" between the layers of the triangular ligament. It runs transversely inwards along the posterior border of the compressor urethrae, and then turning forwards a short distance from the outer side of the urethra, it pierces the anterior layer of the triangular ligament and enters the substance of the bulb. It passes onwards in the corpus spongiosum to the glans, where it anastomoses with its fellow and with the dorsal arteries of the penis. It supplies the compressor urethrse muscle, Cowper's gland, the corpus spongiosum, and the penile part of the urethra. In the female this artery supplies the bulb of the vestibule. (g) The artery of the corpus cavernosum (a. profunda penis in the male; a. pro- funda clitoridis in the female) is usually the lai'ger of the two terminal branches. Immediately after its origin it enters the cms penis, and runs forwards in the corpus cavernosum, which it supplies. (A) The dorsal artery^ of the penis (a. dorsalis penis in the male ; a. dorsalis clitoridis in the female) passes forwai'ds between the layers of the suspensory ligament, and runs along the dorsal surface of the penis with the dorsal nerve immediately to its outer side, whilst it is separated from its fellow of the opposite side by the median deep dorsal vein. It supplies the superficial tissues on the dorsal aspect of the penis, sends branches into the corpus cavernosum to anastomose with the artery to the corpus cavernosum, and its terminal branches enter tlie glans penis, where they anastomose with the arteries to the bulb. It also anastomoses with the external pudic branches of the femoral.' ' 3. Sciatic Artery (a. glutsea inferior, Eigs. 637 and 639). — The sciatic artery arises, usually distinct from the pudic artery, but sometimes in common with it, from the anterior division of the internal iliac. It descends a little behind and external to the pudic vessels, pierces the pelvic fascia, runs backwards between the first and second, or second and third sacral nerves, and passing between the pyriformis and coccygeus muscles, leaves the pelvis through the lower part of the great sciatic foramen, and enters the buttock just below the pyriformis. In the buttock it descends behind and to the inner side of the great sciatic nerve beneath the gluteus maximus, and behind the obturator internus, the two gemelli, the quadratus femoris, and upper part of the adductor magnus muscles, to the upper part of the thigh. Below the lower border of tlie gluteus maximus the artery is comparatively superficial, and having given off its largest branches, it descends as a long slender vessel with the small sciatic nerve. Branches. — In the pelvis. — Small and irregular branches supply the adjacent viscera BEANCHES OF THE INTEENAL ILIAC AETEEY. 855 Gluteus maximus -— -^J Great sciatic ligament Inttrnal pudic artery Sciatic a7'tery Comes nervi Biceps and seniitendiiiosus and muscles and the sacral nerves ; they anastomose with branches of the internal pudic and lateral sacral arteries. In the buttock. — («) Muscular branches are given off to the muscles of the buttock and to the upper partsof the hamstring muscles. They an- astomose with the pudic, internal cir- cumflex, and obtur- ator arteries. (6) The coccygeal branch arises immediately after the artery leaves the pelvis. It runs inwards, pierces the great sacro-sciatic ligament and the gluteus maximus, and ends in the soft tissues over the back of the lower part of the sacrum and of the coccyx. It gives semimembranosus several branches to the gluteus maximus, and anastomoses with branches of the gluteal and lateral sacral ai'teries. (c) An an- astomotic branch passes transversely outwards, over or under the great sciatic nerve, towards the great trochanter of the femur. It anas- tomoses with branches of the gluteal, pudic, internal and external circumflex, and the first perforating arteries, taking part in the formation of the so-called " crucial anastomosis." {d) Cutaneous branches, accompanying twigs of the small sciatic nerve, pass round the lower border of the gluteus maximus muscle to the integu- ment, (e) The comes nervi ischiatici (a. comitans n. ischiadici) is a long slender branch which runs down on the surface, or in the substance of the great sciatic nerve. It supi)lics the nerve, and anastomoses with tlie perforating arteries and with the termination of the profunda. Adductor niagnus JIuscular brancli of profunda artery Gluteus medius Gluteus miuimus Keep branch of gluteal arter>- Pyriformis Obturator iuteruus and geinelli Ascending branch of internal circumflex artery Quadratus fenioris Transverse branch of iuteiiial circumflex artery 1st perforating artery 2nd perforating artery 3rd perforating artery Termination of _ profunda artery (4th perforating) Short head of biceps head of biceps 'opliteal vein Superior external articular Gracilis Popliteal artery Superior internal articular artery Semitendinosus'^ Gastrocnemius Muscular artery Fig. 639.— The Auteiues ok the Buttock and the B.vck ok the Thigh and Knee. 856 THE VASCULAE SYSTEM. AETEEIES or THE LOWEE EXTEEMITY. The main artery of each lower Ihnb is continued from the corresponding com- mon iliac artery. It descends as a single trunk as far as the lower border of the popliteus, and ends there by dividing into the anterior and posterior tibial arteries. Distinctive names are, however, applied to different parts of the artery, correspond- ing to the several regions through w^hich it passes. Thus in the abdomen it is called the external iliac artery, in the upper two-thirds of the thigh it receives the name of the femoral artery, whilst its lower part, which is situated on the flexor aspect of the knee, is termed the popliteal artery. THE EXTERNAL ILIAC ARTERY. The external iliac artery (a. iliaca externa) extends from a point opposite the sacro-iliac joint at the level of the lumbo-sacral articulation to a point beneath Poupart's ligament, midway between the anterior superior spine of the ilium and the symphysis pubis, where it becomes the femoral artery. Its length is about three and a half inches (87 to 100 mm.), and in the adult it is usually somewhat larger than the internal iliac artery. It runs downwards, outwards, and forwards along the brim of the pelvis, rest- ing upon the iliac fascia, which separates it above from the inner border, and below from the anterior surface of the psoas muscle, and it is enclosed with its accompanying vein in a thin fascial sheath. Relations. — Anterior. — It is covered in front by peritonenm, which separates it on the left side from the pelvic colon, iliac colon, and coils of small intestine, and on the right side from the terminal portion of the ileum, and sometimes from the vermiform appendix. The ureter, descending behind the peritoneum, sometimes crosses the front of the artery near its origin, and in the female the ovarian vessels cross the upper part of the artery. Near its lower end the artery is crossed anteriorly by the genital branch of the genito- crural nerve and by the deep circumflex iliac vein. In the male this part of the artery is also crossed by the vas deferens, and in the female by the round ligament of the uterus. Several iliac lymphatic glands lie in front and at the sides of the external iliac artery, and almost invariably one of these is directly in front of its termination. Posterior. — The iliac fascia and psoas muscle lie behind the artery. Near its upper end the obturator nerve is also posterior to the vessel. Lateral. — Externally is the genito-crural nerve ; internally, and on a somewhat posterior plane, is the external iliac vein. Branches. — In addition to small branches to the psoas muscle and to the lymphatic glands, two named branches of considerable size spring from the external iliac artery, viz. the deep epigastric and the deep circumflex iliac. (1) The deep epigastric artery (a. epigastrica inferior, Figs. G37 and 640) arises immediately above Poupart's ligament from the front of the external iliac. Curving forward from its origin it lies in the extra-peritoneal fat, it turns round the lower border of the peritoneal sac, and runs upwards and inwards along the inner side of the internal abdominal ring and along the outer border of Hesselbach's triangle; it then pierces the transversalis fascia, passes over the semilunar fold of Douglas and enters the sheath of the rectus abdominis. For a short distance it ascends behind the rectus, but it soon penetrates the substance of the muscle, and breaks up into branches which anastomose with terminal offsets of the superior epigastric branch of the internal mammary artery and with the lower intercostal arteries. At the internal abdominal ring in the male the vas deferens, the spermatic vessels, and the genital branch of the genito-crural nerve book round, the front and outer side of the artery, the vas deferens turning inwards behind it ; whilst in the female the round ligament of the uterus and the genital branch of the genito-crural nerve occupy the corresponding positions. Branches. — (a) Muscular branches wliich spring mainly from the outer side of the artery supply the rectus, the pyramidalis, the transversalis, and the oblique muscles of the abdominal wall, and anastomose with branches of the deep circumflex iliac, the THE EXTEENAL ILIAC AETEEY. 857 lambar, and the lower intercostal arteries, {h) Cutaneous branches which pass from the front of the deep epigastric pierce the rectus abdominis and the front part of its sheatli, and terminate in the subcutaneous tissues of the anterior abdominal wall, where they anastomose with corresponding branches of the opposite side and with branches of the superficial epigastric artery, (c) The cremasteric branch (a. .spermatica e.Kterna in the male, a. ligamenti teretis uteri in the female) is small. It descends through the inguinal canal and anastomoses with the external pudic and superficial perineal arteries, and in the male with the spermatic artery also. In the male it accompanies the spermatic cord, supplying its coverings, including the crcmaster. Tn the female it runs with the round Psoas muscle Ureter Genito-crural nerve External cutaneous nerve Ilio-ingiiinal nerve Ilio-lunibar artery Anterior oniral nerve Iliacus muscle Psoas muscle External iliac artery Deep circumflex iliac artery External iliac vein Deep epigastric artery Round licrament Inferior vena cava Common iliac artery Left common iliac vein _ Right common iliac vein Internal iliac vein Internal iliac artery "Pelvic colon Ureter rterine artery ( ivary Utenis Fallopian tube —Obturator artery Superior vesical artery iiladder Obliterated hypo- gastric artery Urethra S\mphysi3 Fro. 6-10. — The Iliac Arteries and Veins in the Female. ligament, {d) The pubic branch (ramus pubicus) descends either on the outer or the inner side of the crural ring to anastomose with the pubic branch of the obturator artery ; it also anastomoses ■with its fellow of the opposite side. Sometimes when the obturator branch of the internal iliac artery is absent, the pubic branch of the deep epigastric artery enlarges and becomes the obturator artery, which descends to the obturator foramen either on the outer or the inner side of tiie crural ring. In the latter case the artery may be injured in the ojieration for the relief of a strangulated femoral hernia. (2) The deep circumflex iliac artery (a. circumtiexa ilium profunda, Figs. 637 and G40) springs Ivuiu the outer side of the external iliac artery, usually a little below the deep epigastric, and immediately above Poupart's ligament. It runs outwards and upwards to the anterior superior spine of the ilium. In this part of its course it lies just above the lower border of Poupart's ligament, and is enclosed in a fibrous canal formed by the union of the transversalis and iliac fascia?. A little beyond the anterior superior spine it pierces the transversalis abdominis, ami 858 THE VASCULAE SYSTEM. is continued terminate by Sartorius Tensor fascite femoris Pectineus Adductor brevis Kectus femoris backwards between the transversalis and the internal oblique, to anastomosing with branches of the iho-lumbar artery. Branches. — (a) Muscular to the upper parts of the sartorius and the tensor fasciae femoris, and to the muscles of the abdominal wall. One of the latter branches is fre- quently of consider- able size; it pierces the transversalis muscle a short dis- tance in front of the anterior superior Common femoral spine of the ilium, '^'^ ^^^ and ascends verti- cally between the transversalis and the internal oblique, an- astomosing w'ith the lumbar and epi- gastric arteries. (6) Cutaneous branches pierce the internal and external oblique muscles. They ter- minate in the skin over the crest of the ilium, and they anas- tomose with the gluteal, the super- ficial circumflex iliac and the ilio-lumbar arteries. THE FEMORAL ARTERY. Adductor longus Internal circum- flex artery Superficial femora) artery Profunda artery Anastomotic artery Sartorius Anastomotic artery Superior external articular artery Superior internal articular artery Inferior internal articular artery Anterior tibial recutrent aiteiy The femoral artery (a. f emoralis, Eigs. 641 and 642) continues the ex- ternal iliac into the thigh. It com- mences at the lower border of Poupart's ligament, and, de- scending through the upper two- thirds of the thigh, terminates at the opening in the adductor magnus. At one time it was customary to speak of the first one and a half inches, as far as the origin of the profunda branch, as the common femoral, and to say that it divided into the superficial and deep femoral branches, of which the former was the direct continuation of the common trunk. The morjDhology and development of the vessel gives no support for such terminology, and it should be discontinued. Course. — Its general direction is indicated by a line drawn from the point of Fi«. 641.— The Femoral Artery and its Branches. THE FEMOEAL AETEEY. 859 origin midway between the anterior superior spine of the ilium and the symphysis pubis to the adductor tubercle, the thigh being flexed and rotated outwards. In its upper half the femoral artery lies in Scarpa's triangle, and is comparatively superficial ; at the apex of the triangle it passes beneath the sartorius, enters Hunter's canal, and is thus more deeply placed. At its entry into Scarpa's triangle both the artery and its vein are enclosed, for a distance of one and a quarter inches, in a funnel-shaped fascial sheath formed of the fascia trans versalis in front and the iliac fascia behind. This is called the femoral sheath ; it is divided by septa, running from front to back, into three compartments, the outer of which is occupied by the femoral artery and genito- crural nerve. The middle contains the femoral vein, and the internal compartment constitutes the crural canal. Relations. — lu Scarpa's ti-iangle the femoral arteiy is covered by skin and fascia, by superficial inguinal lymphatic glands and small superficial vessels. The anterior part of the femoral slieath and the cribriform fascia are in front of the upper part of the artery, and the fascia lata is in front of the lower part. Near the apex of the tiiangle the artery is crossed by the internal cutaneous nerve, and not infrequently by a tributary of the internal saphenous vein. Behind, it is in relation, from above downwards, with the posterior part of the femoral sheath, the pubic portion of the fascia lata and the psoas, the pectineus, and the upper part of the adductor longus miiscles. The nerve to the pectineus passes between the artery and the psoas ; the femoral vein and the profunda artery and vein intervene between it and the pectineus, and the femoral vein also separates it from the adductor longus. The femoral vein which lies behind the artery in the lower part of Scarpa's triangle passes to its inner side above, but is separated from the artery by the outer septum of the femoral sheath. On the outer side of the artery is the anterior crural nerve above ; lower down the internal saphenous nerve and the nerve to the vastus internus are continued on the outer side. The crural branch of the genito-crural nerve is in front and to the outer side above, and runs for a short distance in the femoral sheath. In Hunter's canal the artery has behind it the adductor longus and the adductor magnus, whilst in front and to the outer side is the vastus internus. The femoral vein is also behind the artery, but lies to its outer side below and to its inner side above. Superficial to the artery is the fascial roof of the canal, upon which is the sub-sartorial plexus of nerves and the sartorius muscle. The internal or long saphenous nerve enters Hunter's canal with the artery, and runs first on its outer side, then in front, and lastly on its inner side. Branches. — The femoral artery gives off the following branches : — (1) Superficial branches. (a) The superficial external pudic {b) The superficial epigastric. (c) The superficial circumflex iliac. (2) Muscular. (3) The deep external pudic. (4) The profunda. (5) The anastomotica magna. (a) The superficial circumflex iliac (a. circumtiexa ilium superficialis) springs from the front of the femoral artery just below Poupart's ligament. It pierces the femoral sheath and the fascia lata, external to the saphenous opening, and runs in the superficial fascia as far as the anterior superior spine of the ilium. It supplies the outer set of inguinal glands and the skin of the groin, and it sends branches through the fascia lata which anastomose with the deep circumflex iliac and supply the upper parts of the sartorius and tensor fascia3 femoris muscles. (6) The superficial epigastric artery (a. epigastrica superficialis) arises near the preceding. It pierces the femoral sheath and the cribriform fascia, and passes upwards and inwai'ds between the superficial and deep layers of the super- ficial fascia of the abdominal wall towards the umbilicus. It supplies the inguinal glands and the integument, and anastomoses with its fellow of the opposite side, with the deep epigastric, and with the superficial circumflex iliac and superficial external pudic arteries. (c) The superficial external pudic artery (a. pudenda externa superficialis) also 860 THE VASCULAR SYSTEM. springs from the front of the femoral artery, and, after piercing the femoral sheath and the cribriform fascia, runs upwards and inwards towards the spine of the pubis, where it crosses superficial to the spermatic cord. It supplies the integument of the lower part of the abdominal wall, the root of the dorsum of the penis in the male, and the region of the mons Veneris in the female, and it anastomoses with its fellow of the opposite side, the deep external pudic, the dorsal artery of the penis, and the superficial epigastric arteries. (2) Muscular branches are distributed to the pectineus and the adductor Sartorius Tensor fascis femoris Siiperfleial cir- cumflex iliac artery Rectus femoris Psoas and iliacns Profunda artery External cir- cumflex artery Vastus externus Vastus internus Femoral artery Femoral vein Crural canal 1 Superficial ex- ternal pudic artery Deep external pudic artery Long saphenous ^-ein Adductor longus Gracilis Fig. 642. — The Femoral Vessels in Scarpa's Triangle. muscles on the inner side, and tu the sartorius and the vastus internus on the outer side. (3) The deep external pudic artery (a. pudenda externa profunda) rises from the inner side of the femoral. It runs inwards, across the front of the pectineus, and in front of or behind the adductor longus, to the inner side of the thigh ; it then pierces the deep fascia, aud terminates in the scrotum, where it anastomoses with the superficial ]ierineal and superficial external pudic arteries, and with the cremasteric brancli of the deep epigastric artery. (4) The profunda artery (a. profunda femoris, Fig. 640) is the largest branch of the femoral artery. It arises about an inch and a half below Poupart's ligament, from the outer side of tlie femoral artery. Curving backwards and inwards, it passes behind the latter vessel, and runs downwards, close to the inner aspect of THE FEMOEAL AETEEY. 861 the femur, to the lower third of the thigh, where it perforates the adductor magnus and passes to the back of the thigh. Its termination is knoNvn as the fourth perforating artery. As the profunda descends it lies in front of the iliacus, the pectineus, the adductor l>revis, and the adductor magnus. It is separated from the femoral artery by its own vein, by the femoral vein, and by the adductor longus muscle behind which it passes. Branches. — (a) Muscular branches are given Dft'frum the profunda both in Scarpa's triangle, and whilst it lies Ijetween the adductor muscles ; many of them terminate in the adductors, others pass through the adductor magnus, and terminate in the hamstrinijs, where they anastomose with the transverse branch of the internal circumflex and with the upper muscular branches of tlie po])liteal artery. (b) The external circumflex artery (a. circumtlexa femoris lateralis, Figs. 641 and 6-12) springs from the outer side of the profunda, or occasionally from the femoral artery above the origin of the profunda. It runs outwards across the front of the iliacus, and between the superficial and deep brandies of the anterior crural nerve, to the outer border of Scarpa's triangle; then, passing behind the sartorius and the rectus femoris, it terminates by dividing into three terminal branches — ^tlie ascending, the transverse, and the descend- ing. Before its termination it supplies branches to the muscles mentioned and to the upper part of the crureus. (i.) The ascending terminal branch, (ramus ascend ens) nms upwards and outwards, beliiud the rectus femoris and tlie tensor fasciie femoris, along the anterior intertrochanteric line, to the anterior borders of the gluteus medius and mininuis, between which it j^asses to anastomose with the deep branches of the gluteal artery. It supplies twigs to the neighbouring muscles, anasto- juoses with the gluteal, the deep circumflex iliac, and the transverse branch of the external circumflex arteries, and, as it ascends along the anterior intertrochanteric liiie, gives oft' a brancli which jjasses between the two limbs of the Y-shaped ligament into the hip-joint, (ii.) The transverse terminal branch, is small ; it runs outwards between the crureus and tlie rectus femoris, passes into the substance of the vastus externus, winds round the femur, and anastomoses with the ascending and descending branches, with the perforating branches of the profunda, and with the sciatic and internal circumflex arteries. (iii.) The descending terminal branch, (ramus descendens) runs downwards behind the rectus and along the anterior border of the vastus externus accomi^anied by the nerve to the latter muscle. It anastomoses with the transverse branch, with twigs of the inferior ])erforating arteries, with the anastomotic branch of the femoral, and with the superior external articular branch of the jjopliteal artery. (c) The internal circumflex artery (a. circumflexa femoris medialis, Fig. 611) springs from the inner and back part of the profunda, at the same level as the external circumflex, and runs backwards, through the floor of Scarpa's triangle, passing between the psoas and the pectineus ; crossing the upper border of the adductor brevis it is continued backwards beneath the neck of the femur, and passes between the adjacent borders of the obturator externus and the adductor brevis to the upper border of the adductor magnus, where it divides into two terminal branches, a transverse and an ascending. Branches. — (i.) An articular branch (ramus acetabuli) is given off as the artery jtasses beneath the neck of the femur. It ascends to the cotyloid notch where it anastomoses with twigs from the posterior branch of the obturator artery, and it sends branches into the cotyloid cavity and along the ligamentum teres to the head of the femur, (ii.) Muscular branches are given oft" to the neighbouring muscles. The largest of these branches usually rises inuueJiately before the ternunation of the artery, it descends on the anterior aspect of the adductor niagnu.-^ and anastomoses with the muscular branches of the 2>rofunda artery, (iii.) The ascending terminal branch (ramus i)rofundus) passes upwards and outwaids, between tlie ubturator externus and the quadrat us femoris to the digital fossa of llie i'ennu', where it anastomoses with branches of the gluteal and the sciatic arteries, (iv.) The transverse terminal branch (ramus superflciali-s) runs backwards between the lower border of the (piadratus feumris and the U2)]K'r border of the adductor magnus to the hamstring muscles. It anastomoses in front of tlie lower part of the gluteus maxinius with the sciatic and tirst perforating arteries and witli the transvei-se branch of the external circumflex, and in the substance of the lianistrings with the muscular branches of the profunda. (d) The perforating arteries (Fig. 643), including the terminal branch of the profunda, are four in number. They curve backwards and outwards round the posterior aspect of the femur, lying close to the bone, in front of well-marked tendinous arches, which interrupt the continuity of muscular attachments; their terminal branches enter the vastus oxteinius and anastomose in its substance with each other, with the descending branch of the external circumflex, witli the anastomotic, and with the superior external articular branch of the popliteal. 862 THE VASCULAR SYSTEM. Gluteus maximus The first perforating artery (a. perforans prima) pierces the insertions of the adductors brevis and magniis, and some of its branches anastomose in front of the gluteus maximus with the sciatic, with the transverse branch of the internal circumflex, and with the transverse branch of the external circumflex, forming what is kno^^al as the crucial anastomosis. The second perforating artery (a. perforans secunda) pierces the adductors brevis and magnus, and then passes be- tween the gluteus maximus and the short head of the biceps into the vastus externus. It anastomoses with its fellows above and be- low, and with the in- ternal circumflex and the upper muscular branches of the pop- liteal artery. The third (a. per- forans tertia) and fourth perforating arteries pass through the adductor magnus and the short head of the biceps into the vastus externus. Their anastomoses are simi- lar to those of the second perforating. A nutrient branch. (a. nutricia femoris) to the femur is given off either from the second or third perforating artery, usually the former ; an additional nutrient branch, may also be supplied by the first or fourth per- forating arteries. Adductor magnus ^luscular branch of profunda artery Gluteus medius Gluteus minimus Deep branch of gluteal artery Pyriformis Obturator internus and gemelli Ascending branch of internal circumflex artery Quadratus fenioris Transverse branch of internal circumflex artery Ist perforating artery 2nd perforating ' artery Gracilis Popliteal ai-terj Superior internal articular artery Semitendinobus Gastrocnemius 3rd perforating artery Termination of lu'ofunda artery (4th perforating) Short head of biceps — Tjong head of biceps Popliteal vein Superior external articular artery Gastrocnemius (5) The anas- tomotic (a. genu suprema) arises near the termina- tion of the femoral artery in the lower part of Hunter's canal, and divides almost immediately into a superficial and a deep branch ; indeed, very fre- quently the two branches arise separately from the femoral trunk. Muscular artery Fio. 643. —The ARTJiuxEs ok the Buttock and the Back ok the Thioh and Knee. (a) The super- ficial branch (ramus saphenus) passes through the lower end of Hunter's canal with tlie long sapben- ous nerve, and appears superficially on the inner side of the knee between the gracilis and the sartorius. It gives twigs to the integument of the upper and inner part ot the leo-, and it anastomoses with the inferior internal articular artery, {b) iiie aeep branch (ramus musculo -articularis) descends in the substance of the vastus internus along the anterior aspect of the tendon of the adductor magnus. It anastomoses witli THE POPLITEAL AETERY. 863 the superior internal articular artery, and it sends branches outwards, one on the surface of the femur and another along the upper Vjorder of the patella, to anastomose with the descending branch of the external circumflex, the inferior perforating artery, the superior external articular, and the anterior tibial recurrent. THE POPLITf:AL ARTERY. The popliteal artery (a. poplitea) is the direct continuation of the femoral. It commences at the upper and inner part of the popliteal space, under cover of the semimembranosus, and terminates at the lower border of the popliteus muscle, and on a level with the lower part of the tubercle of the tibia, by dividing into the anterior and the posterior tibial arteries. From its origin the artery descends, with an outward inclination, to the inter- space between the condyles of the femur, whence it is continued vertically down- wards to its termination. Relations. — Anterior. — It is in contact in front and from above downwards with the popliteal surface of the fenuir, the posterior ligament of the knee-joint, and the fascia covering the posterior surface of the popliteus. Posterior. — The artery is overlapped behind by the outer border of the semi- membranosus above ; it is crossed about its middle by the popliteal vein and the internal popliteal nerve, the vein intervening between the artery and the nerve ; whilst in the lower part of its extent it is overlapped by the adjacent borders of the two heads of the gastrocnemius, and is crossed by the nerves to the soleus and popliteus and by the plantaris muscle. Lateral. — On its outer side it is in relation above with the internal popliteal nerve and the popliteal vein, then with the outer condyle of the femur, and below with the outer liead of the gastrocnemias and with the plantaris. On the inner side it is in relation above with the semimembranosus, in the middle with the inner condyle of the femur, and below with the internal popliteal nerve, the popliteal vein, and the internal head of the gastrocnemius. Popliteal lymphatic glands are arranged irregularly around the artery. Branches. — (1) Muscular branches are given otf in two sets, upper and lower. The upper muscular branches are distributed to the lower parts of the hamstring muscles, in which they anastomose with branches of the profunda artery. The lower muscular, or sural, arteries (aa. surales) enter the upper parts of the gastro- cnemius, the plantaris, the soleus, and the popliteus muscles, and they anastomose with branches of the posterior tibial artery and the lower articular arteries. (2) The articular branches are five in number — viz. upper and lower external, upper and lower internal, and an azygos branch, (a) The superior external articular artery (a. genu superior lateralis) passes outwards above the external condyle, behind the femur and in front of the biceps tendon, into the vastus externus, where it anastomoses with tlie anastomotic, the descending branch of the external circumflex, and the lowest perforating artery ; it also sends branches downwards to anastomose with the inferior external articular and with the anterior tibial recurrent. (6) The superior internal articular artery (a. genu superior medialis) passes inwards above the internal condyle, behind the femur, and in front of the tendon of the adductor magnus, into the vastus internus. It anastomoses with branches of the anastomotic and of the superior external articular artery. (c) The inferior external articular artery (a. genu inferior lateralis; runs outwards across the popliteus muscle and in front of the plantaris and the external head of the gastrocnemius ; then turning forwards, it is joined by the inferior external articular nerve, and passes to the inner side of the external lateral ligament. It terminates by anasto- mosing with its fellow of the opposite side and with the superior external articular and anterior tibial recurrent arteries. {d) The inferior internal articular artery (a. genu inferior medialis) passes inwards below the inner tu])crosity of tlie tibia, along tlie upper border of the popliteus and in front of the internal head of the gastrocnemius, to the inner side of the knee, where it turns forwards between the bone and the internal lateral ligament, and terminates anteriorly by anastomosing with its fellow of the opposite side, witli the recun-ent branch of the anterior tibial artery, and with the superior internal articular artery. (e) Tlie azygos articular artery (a. genu media) passes directly forwards from the front 864 THE YASCULAE SYSTEM. of the popliteal artery, pierces the central part of the posterior ligament of the knee-joint, and enters the intei'condylar space. It supplies branches to the crucial ligaments and to the synovial membrane, and is accompanied by the azygos articular branch of the internal popliteal nerve, and sometimes by the genicular branch of the obturator nerve. (3) Cutaneous branches are distributed to the skin over the popliteal space. One of these, the superficial sural artery, descends in the middle line of the back of the calf along with the external saphenous nerve. Semimembranosus Semitendiuosus Superior internal . articular artery Muscular artery Inferior internal articular artery Popliteus Soleus Posterior tibial artery Nutrient artery — Posterior tibial artery Flexor loiigu diaritorui Communicating artery Calcaneau artery - Biceps Superior external - articular artery - Muscular arterj' - Popliteal artery Inferior external 'articular artery The Posterior Artery. Tibial Anterior tibial artery ^luscular artery Flexor longus lallucis -Tibialis posticus Jeroneal artery Peroneus lonaus Peroneus brevis The posterior tibial artery (a. tibialis posterior), the larger of the two terminal branches of the popliteal, commences at the lower border of the pop- liteus and terminates midw^ay between the tip of the inner malleolus and the most pro- minent part of the heel, at the lower border of the internal annular ligament. It ends by dividing into the internal and the external plantar arteries, which pass onwards to the sole of the foot. The artery runs downwards and inwards on the back of the leg between the superficial and deep layers of muscles, and covered by the deep inter- muscular fascia which inter- venes between them. Flexor longus hallucis — - Posterior peroneal artery Relations. — Anterior. — It is in contact in front, and from above downwards, with the tibialis posticus, the flexor longus digit- orum, the posterior surface of the tibia, and the posterior ligament of the ankle-joint. Posterior. — The artery is crossed about an inch and a half below its origin by the posterior tibial nerve. Elsewhere it is in contact with the intermuscular fascia, which binds down the deep layer of muscles. More super- ficially the upper half of the artery is covered by the fleshy parts of the soleus and gastro- cnemius muscles, between which is the plantaris ; the lower half of the artery is much nearer the surface, and is only covered by skin and fascia, except at its termination, where it lies beneath the internal annular ligament and the origin of the abductor hallucis. Lateral— T\\G artery is accompanied by two venae comites, one on either side. The posterior tibial nerve lies at first on the inner side of the vessel, then crosses behind it, and is continued down on its outer side. In the last part of its course the artery is separated Fig. 644. -The Popliteal and Posteeior Tibial Arteries AND THEIR BliANCHES. PLAXTAE AETEEIES. 865 from the internal malleolus by the tendons of the tibialis posticus and the flexor longus digitorum, whilst the tendon of the flexor longus hallucis lies behind and external to it. Branches. — The posterior tibial gives oft' numerous branches, the largest of which, the peroneal, forms one of the chief arteries of the leg. The branches include — (1) Two large muscular branches which are distributed to the soleus, the tibialis posticus, the flexor longus digiturum, and the flexor longus hallucis. They anastomose with the deep sural branches oi. the popliteal artery and the lower internal articular artery. (2) The medullary branch (a. nutricia tibitc), the largest of the medullary group of arteries, springs from the upper part of the posterior tibial, pierces the tibialis posticus, and enters the medullary foramen on the posterior surface of the tibia. In the interior of the bone it divides into ascending and descending branches, the former passing upwards towards the head of the bone, and the latter downwards towards the lower extremity. Before entering the tibia the medullary artery gives small muscular branches. (3) A communicating branch (ramus communicans) unites the posterior tibial to the peroneal artery about an inch above the inferior tibio-flbular articulation. It passes behind the sliaft of the tibia and in front of the flexor longus hallucis. (4) Cutaneous branches are distributed to the skin of the inner and posterior part of the leg. (5) An internal malleolar branch (a. malleolaris posterior medialis) is distributed to the internal surface of the inner malleolus, anastomosing with a corresponding branch of the anterior tibial artery. (6) The peroneal artery (a. peronsea. Fig. 644) is the largest branch of the posterior tibial. It arises about an inch below the lower border of the popliteus, curves outwards across the upper part of the tibialis posticus to the postero-internal border of the fibula, along which it descends to the lower part of the interosseous space, and it terminates about an inch above the ankle-joint by dividing into anterior and posterior terminal branches. As the peroneal artery passes outwards from its origin it lies behind the tibialis posticus, and is covered posteriorly by the deep intermuscular fascia and by the soleus. As it descends along the postero-internal border of the fibula it lies in a fibrous canal between the tibialis posticus in front and the flexor longus hallucis behind. The peroneal artery is accompanied by two veufe comites, and is crossed in front and behind by communicating branches between them. Branches. — (a) Muscular branches are distributed to the soleus, tibialis posticus, flexor lougus hallucis, and peroneal muscles. Some pass through the interosseous membrane and supply the anterior muscles of the leg. (b) A medullary branch (a. nutricia fibulas) enters the medullary foramen of the fibula. (c) A communicating branch (a. commuuieans) passes across the back of the lower end of the shaft of the tibia, abiuit an inch above the inferior tibio-fibular articulation, to anastomose with the posterior tibial artery. {d) The terminal branches are : (i.) The anterior terminal branch or anterior peroneal arterij (ramus perforans), which passes forwards between the lower border of the interosseous luembran'e and the interosseous inferior tibio-fibular ligament, and runs in front of the ankle to the dorsum of the foot, where it anastomoses with the external malleolar branch of the anterior tibial artery and with the tarsal branch of the dorsalis pedis ; it also supplies branches to the inferior tibio- fibular articulation, to the ankle-joint, and to the peroneus tertius. (ii.) The posterior terminal branch (rani us calcaneus lateralis), ov jiosterior -peroneal artery, passes downwards behind the inferior tibio-fibular articulation and external malleolus to the outer side of the heel and the foot. It supplies the ankle, the inferior tibio-fibular articulation, and the calcaneo-astragaloid joint, and anastomoses with the internal calcaneal branch of the external plantar artery, and with the tarsal and metatarsal branches of the dorsahs pedis. Plantar Akteries. (7) The internal aud external plantar arteries are the teruiinal branches of the posterior tibial artery. They arise beneath the origin of the abductor hallucis muscle, midway between the tip of the internal malleolus and the most prominent part of the inner side of the os calcis. Internal Plantar Artery (a. plantaris medialis). — This is the smaller of the two terminal brandies of the posterior tibial artery. It passes forwards along the inner side of the foot, in the interval between the abductor hallucis aud the "tiexor brevis digitorum, to the head of the first metatarsal bone, where it terminates by uniting with the plantar digital branch of the dorsalis liallucis, which is distributed to the inner side of the great toe. In its course forwards it gives branches to the adjacent muscles and articulations, and to the subjacent skin ; it also gives three 59 866 THE YASCULAE SYSTEM. digital branches wiiich anastomose at the roots of the inner three interdigital clefts, with the princeps hallucis branch of the dorsalis pedis and with the inner two digital branches from the plantar arch. Some of the cutaneous branches of the internal plantar artery anastomose, round the inner border of the foot, with the inner cutaneous branches of the dorsalis pedis artery. External Plantar Artery (a. plantaris lateralis). — This artery, the larger of the two terminal branches of the posterior tibial artery, runs forwards and outwards, first between the flexor brevis digitorum and the accessorius and then in the interval between the flexor brevis digitorum and the abductor minimi digiti, to the inner side of the base of the fifth metatarsal bone, where it Internal calcaneal *^^™^ abruptly inwards ; branch of 'external it then passes across the bases of the metatarsal bones and the origins of the interossei, and above the oblique adductor of the great toe, to the outer side of the base of the first metatarsal bone, where it terminates by anastomosing with the dorsalis pedis artery. The last part of the artery is convex forwards and forms the plantar arch, which is completed by the dorsalis pedis. Calcaneal brancli c posterior tibial arter Posterior tibial arter Internal ] a External p] Flexor longus digitorum tendon Flexor longus liallucis tendon Flexor brevis hallucis muscle plantar artery g calcaneo- cuboid ligament Flexor accessorius muscle Abductor minimi igiti muscle Arteria magna liallucis lique adductor illui-is ital arteries Branches. — Between its origin and the base of the fifth metatarsal the ex- ternal plantar arteiy gives off (a) the internal calcaneal branch, which is distributed to the skin and the sub- cutaneous tissue of the heel. (b) Muscular branches to the abductor hallucis, flexor brevis digitorum, ac- cessorius, and abductor minimi digiti. (c) Cutaneous branches to the skin of the outer side of the foot. Between the base of the fifth metatarsal bone and the first interosseous space it forms the plantar arch (arcus plantaris), and gives off (J) four digital branches (aa. metatarsse plantares) ; (e) three posterior perforating arteries (rami pcrforantes) to the dorsal interosseous arteries ; and (/) articular branches to tlio tarsal joints. The outermost digital branch runs along the outer side of the little toe, supplying the skin, joints, and the flexor tendons with their synovial sheaths. The inner three digital branches run forwards on the plantar surfaces of the interossei, the inner two lying dorsal to the oblique adductor of the great toe, and all three passing dorsal to the transverse adductor. At the bases of the interdigital clefts the three inner digital arteries divide into collateral branches (aa. digitales plantares) which run along the plantar aspect of adjacent toes, and supply skin, joints, and the flexor tendons and sheaths. Opposite the last phalanx of each toe the digital arteries anastomose. Fig. 645.— The Plantar Ahtekies and XHEm Branches. THE ANTEEIOE TIBIAL ARTEEY. 867 The posterior perforating arteries are three in number ; they pass dorsal wards through the three outer interosseous spaces, between the heads of the dorsal interosseous muscles, and terminate by uniting witli the dorsal interosseous branches of the metatarsal artery. Anterior perforating branches which communicate with the dorsal interosseous arteries are given oft' from three of the digital just before they two or arteries divide. The Siipi-rior external articular artery Anastomotic artPrv articular branches are numerous and irregular : they supply the joints and ligaments of the tarsus on its plantar aspect. The Anterior Tipsial Artery. lul'i'rior external articular artt-ry Anterior tibial recurrent arterv Anterior tilii.il Superior internal articular arterv Inferior internal articular artery Gastrocnemius Anterior tibial nerve Extensor longus disitoruni Extensor lon>;us lialhicis Anterior peroneal artery External malleolar artery Tarsal artery Digital artery Digital arterv The anterior tibial artery (a. tibialis anteriorj, the smaller of the two ter- minal divisions of the pop- liteal, commences opposite the lower border of the popliteus muscle, and ter- minates in front of the ankle, where it is continued into the dorsal artery of the foot. Course and Relations. — From its origin at the back of the leg the artery passes forwards to the front, between the two uppermost slips of the tibialis posticus and above the upper border of the interosseous mem- brane. It then descends resting, in the upper two- thirds of its course, upon the anterior surface of the in- terosseous membrane aud, subsequently, on the shaft of the tibia and the anterior ligament of the aukle-joint. In the upper tliird of the anterior compartment of the leg it lies between tlie extensor longus digitorum externally and the tibialis anticus internally ; in the middle third it is between the extensor longus hallucis and the tibialis anticus ; in the lower third the extensor longus hallucis crosses in front of the artery and reaches its inner side, and the last part of the vessel lies between the tendon of the extensor longus hallucis and the innermost tendon of the extensor longus digitorum. The anterior tibial nerve is at first well to the outer side of the artery, but it soon passes in front of the vessel, and it lies in front of the arterv in its middle 59 a pedis Cutaneous brancli Kxtensur brevis digitorunij Fig. 646. — The-; Anteuikk Tii:iai. Autkhv .\ni) us Hi(.\NCHt> 868 THE VASCULAE SYSTEM. third ; lower down the nerve is usually found on the outer side again, and at the ankle it intervenes between the artery and the innermost tendon of the extensor longus digitorum. Two venas comites, with numerous intercommunications, accompany the artery. Obviously the anterior tibial artery is, at least in its upper part, deeply placed ; moreover, its lateral muscular boundaries overlap it. In the greater part of its extent it is, however, easily accessible from the surface ; and beyond being crossed by the nerve and tendon, as already described, is only covered, in addition, by skin, fascia, and the anterior annular ligament. Branches. — Close to its origiu the artery gives off superior fibular and posterior tibial recurrent branches ; after it reaches the front of the leg it gives off anterior tibial reciirrent, muscular, cutaneous, internal malleolar, and external maUeolar branches. (1) The superior fibular branch is a small vessel which may arise separately from the anterior tibial artery, or by a common stem with the posterior tibial recurrent ; occasion- allv it springs from the lower end of the popliteal artery, or from the posterior tibial. It runs upwards and outwards behind the neck of the fibula and through the fibres of the soleus, and it terminates in branches which supply the soleus, the peroneus longus, and the skin of the upper and outer part of the leg. It anastomoses with the inferior external articular artery. (2) The posterior tibial recurrent branch (a. recurrens tibiabs posterior), also small, and not always present, runs upwards in front of the popliteus muscle to the back of the knee-joint. It aiiastomoses with the inferior articular branches of the popliteal, and gives branches to the popliteus mtiscle and the superior tibio-fibular articulation. (3) The anterior tibial recurrent branch (a. recurrens tibialis anterior) arises from the anterior tibial artery in front of the interosseous inembrane. It runs upwards and inwards, between the upper part of the tibialis anticus and the outer tuberosity of the tibia, accompanied by the recurrent articular branch of the external popliteal nerve, and after supplying the tibialis anticus and the superior tibio-fibular articulation it pierces the deep fascia of the leg ; it is comrected with the anastomoses round the knee-joint formed by the articular branches of the popliteal artery, the descending branch of the external circumflex artery, and the anastomotic artery. (•i) The muscular branches are distributed to the muscles of the front of the leg, and a few small branches also pass backwards to the deep surface of the tibialis posticus muscle. (5) The cutaneous branches supply the skin of the front of the leg. (6) The internal malleolar branch (a. malleolaris anterior medialis) arises from the lower part of the anterior tibial artery, and is smaller than its companion on the outer side. It runs inwai'ds, beneath the tibialis anticus tendon, ramifies over the internal malleolus, anastomosing with branches of the posterior tibial artery, and is distributed to the skin and to the ankle-joint. (7) The external malleolar branch (a. malleolaris anterior lateralis), more constant and larger than the internal, passes outwards beneath the extensor longus digitorum and pei'oneus tertius towards the external malleolus. It anastomoses Avith the anterior peroneal and tarsal arteries, and supplies the ankle-joint and the adjacent articulations. Dorsalis Pedis Artery (a. dorsalis pedis). — The dorsal artery of the foot is the direct continuation of the anterior tibial ; it commences opposite the front of the ankle-joint, and extends to the posterior extremity of the first interosseous space, where it passes to the plantar aspect of the foot, and, anastomosing with the termination of the external plantar artery, completes the plantar arch. It is covered superficially by skin and fascia, including the inferior part of the anterior annular ligament, and it is crossed, just before it reaches the first inter- osseous space, by the innermost tendon of the extensor brevis digitorum. It rests upon the anterior ligament of the ankle, the head of the astragalus, the astragalo- navicular ligament, tlie dorsum of the navicular bone, the dorsal naviculo- cuneiform and the inter-cuneiform ligaments between the internal and middle cuneiform bones. On its outer side is the internal terminal branch of the anterior tibial nerve, which intervenes between it and the extensor brevis digitorum and innermost tendon of the extensor longus digitorum. On its inner side it is in relation with the tendon of the extensor proprius hallucis. Two venae comites, one on each side, accompany the artery. THE ANTEEIOR TIBIAL ARTEEY. 869 Pfti'oneus brevis Extensor longus flisitorniii Anterior peronea arterj External nialleolai Anterior tibial artery Extensor longus liallucis Tibialis anticus Intenial malleolar artery Arteria dorsalis lallucis As it passes through the hase of the first interosseous space it lies between the two heads of the first dorsal interosseous muscle, and in the sole of the foot it is dorsal to the flexor brevis hallucis. Branches. — On the dorsum of the foot the dorsahs pedis artery gives off cutaneous brandies, tiie tarsal braucli, tlie metatarsal branch, and the dorsalis hallucis or first doi-sal interosseous. In the sole of the foot, and before it unites with the external plantar artery, it gives off the princeps hallucis. (1) Cutaneous branches, two or three in number, are distributed to the skin on the dorsum and inner side of che foot ; they anastomose with branches of the internal plantar artery. (2) The tarsal branch (a. tarsea lateralis) is given off opposite the head of the astragalus; it runs outwards beneath the extensor brevis digitorum, supplying that muscle and the tarsal joints, and anastomoses with branches of the anterior peroneal, metatarsal, and external plantar arteries, and with the external malleolar artery. (3) The metatarsal artery (a. arcuata) arises opposite the internal cunei- form bone. It runs out- wards on the bases of the metatarsal bones, beneath the long and short extensor tendons, supplies the ex- tensor brevis, and anasto- moses witli branches of the tarsal and external plantar arteries. It gives off tlireo dorsal interosseous arteries (aa. metatavse.e dorsales) which run down- wards on the nuiscles which occupy the three outer inter- osseous spaces to the clefts of the toes, where each divides into two collateral digital branrhes (aa. digitales dorsales) for the adjacent sides of the toes bounding the cleft to which it goes. The outer side of the little toe receives a branch from the outermost dorsal interosseous artery. Each dorsal interosseous artery gives off a 2'^osterior j^'i'^foratiiuj hninch which passes through the posterior part of the interosseous space, between the heads of the dorsal interosseous nuiscle, to anastomose with the plantar arch, and an anterior perforatin;/ branch, which descends through the anterior part of the space to anastomose with the correspouiling ))lantar digital artery. (4) The dorsalis hallucis artery (first dorsal interosseous) is contiinicd forwards from the dorsal artery of the foot, and runs on the dorsal surface of tlie first dorsal interosseous nuiscle. It ends by dividing into collateral dorsal digital brandies for the adjacent sides of the first and second toes. Before it divides it usually gives oft' a dorsal digital branch which passes beneath the tendon of the extensor hallucis to the inner side of the great toe. (5) The princeps hallucis ^plantar digital arterv) springs from the termination of 59 b Dorsal interosseous- arterii-s Fig. <347. — The Uuhsau-s Pkdis Ahtkkv and its Bhanches. 870 THE VASCULAE SYSTEM. the dorsalis pedis in the sole of the foot ; it runs forwards in the plantar part of the first interosseous space, and divides, at the interdigital cleft, into collateral digital branches for the supply of the adjacent sides of the first and second toes on their plantar aspects. Before its division it supplies a plantar digital branch to the inner side of the great toe. THE VEINS. Veins commence at the terminations of the capillaries. They converge towa.rds the heart, and unite with one another to form larger and still larger vessels, until finally seven large trunks are formed which open into the auricles of the heart. Three of these, the superior vena cava, the inferior vena cava, and the coronary sinus, belong to the systemic circulation; they contain venous blood, and open into the right auricle. The remaining four belong to thG pulmonary circulation ; they return arterialised blood from the lungs, and open into the left auricle. In addition to the systemic and pulmonary veins, there is also a third group of veins, constituting the portal system, in which blood from the abdominal part of the alimentary canal, and from the spleen and pancreas, is conveyed to the liver. The portal system is further peculiar in that it both begins and ends in capillaries. From its terminal capillaries in the liver the hepatic veins arise, and as these open into the inferior vena cava the blood of the portal system is finally poured into the general systemic circulation. The hepatic veins also receive blood supplied to the liver by the hepatic arteries. PULMONAEY VEINS. The terminal pulmonary veins (v. pulmonales, Eigs. 613 and 620), two on each side, open into the left auricle of the heart. Their tributaries arise in capillary plexuses in the walls of the pulmonary alveoli. By the union of the smaller veins larger vessels are formed which run along the anterior aspects of the bronchial tubes, and, uniting together, ultimately form a single efferent vessel in each lobe, which passes into the root of the lung. Thus there are five main pulmonary veins, but, immediately after entering the root of the lung, the vessels from the upper and middle lobes of the right lung join together, and so only four terminal pulmonary veins open into the left auricle of the heart. Neither the main stems nor their tributaries possess valves. Relations. — In the root of the lung the upper pulmonary vein on each side lies below and in front of the pulmonary artery. The lower pulmonary vein on each side is in the lowest pai't of the root, and it is placed much farther back than the upper vein. On the right side the upper pulmonary vein passes behind the superior vena cava, and the lower behind the right auricle. They both terminate in the upper and back part of the left auricle close to the interauricular septum. On the left side both upper and lower pulmonary veins cross the front of the descend- ing aorta, and they terminate in the upper and back part of the left auricle near its left border. All four pulmonary veins perforate the fibrous layer of the pericardium, and receive partial coverings of the serous layer before they enter the auricle. SYSTEMIC VEINS. The systemic veins return blood to the right auricle of the heart through the superior vena cava, the inferior vena cava, and the coronary sinus. The two first- named receive blood from the veins of the body and limbs and from most of the abdominal and pelvic viscera. The coronary sinus receives blood from the veins of the walls of the heart alone. General arrangement. — The veins of the body wall and limbs form two groups — (1) the superficial veins ; (2) the deep veins. The superficial veins, which commence in the capillaries of the skin and sub- cutaneous tissues, lie in the superficial fascia, and are very numerous. They THE SUPEEIOR VENA CAVA AND ITS TRIBUTAEIES. 871 frequently anastomose with one another, and they also communicate with the deep veins, in which, after piercing the deep fascia, they terminate. They may or may not accompany superficial arteries. The deep veins accompany arteries, and are known as vence comites. The large arteries have only one accompanying vein, but with the medium-sized and small arteries there are usually two vente comites, which freely anastomose with each other by short transverse branches of communication. Visceral veins usually accompany the arteries which supply viscera in the head, neck, thorax, and abdomen. As a rule there is only one vein with each visceral artery, and, with the exception of those which enter into the formation of the portal system, they terminate in the deep systemic veins. THE CORONARY SINUS AND THE VEINS OF THE HEART. The coronary sinus (sinus coronarius, Fig. 613) is a short, but relatively wide, venous trunk which receives the majority of the veins of the heart. It lies in the inferior portion of the auriculo- ventricular sulcus, between the left auricle and the left ventricle, and it is covered superficially by some of the muscular fibres of the auricle. It terminates in the lower and back part of the right auricle, between the orifice of the inferior vena cava on the right, and the right auriculo- ventricular orifice in front ; an imperfect valve, consisting of one or two cusps, called the valve of Thebesius, is situated at the opening of the sinus into the auricle. The apertures of all the tributaries of the coronary sinus, except that of the oljlique vein, are provided with valves, which, however, are frequently incompetent. Tributaries. — (1) The great cardiac or left coronary vein (v. cordis magna, Fig. 614) commences at the apex of the lieart. It ascends in the anterior interventricular sulcus to the auriculo-ventricular groove ; it then turns to the left, and, passing round the left margin of the heart into the postero- inferior part of the auriculo-ventricular groove, terminates in the left extremity of the coronary sinus. It receives tributaries from the walls of both ventricles and from the wall of the left avu'icle. It also receives the left maiyinal vein, which commences at the lower extremity of the left margin of the heart, along which it ascends to its termination. (2) Small cardiac or right coronary vein (v. cordis parva). — This vein is very vari- able ; as a rule it commences at tlie right margin of the heart in the auriculo-ventricular sulcus, passes to tlie left, and terminates in the coronaiy sinus near its right end. It receives tributaries from the walls of the right auricle and the right ventricle ; one from the latter, the ri(/ht marginal vein, ascends along the right margin of the heart, and sometimes opens directly into the right auricle. (3) The oblique vein of Marshall (v. obliqua atrii sinistri, Fig. 613) is a small venous channel which descends obliquely on the posterior wall of the left auricle and terminates in the coronarj' sinus. Its orifice is not provided with a valve. It is of special interest, inasmuch as it represents the left superior vena cava of some other mammals, and is developed from the left duct of Cuvier. (4) The inferior interventricular, inferior cardiac, or middle cardiac vein (v. cordis media), commences at the apex of the heart, and, passing backwards in the inferior interventricular sulcus, terminates in the right end of the coronaiy sinus. It receives tributaries from the inferior ])arts of the walls of both ventricles. Veins of the heart which do not end in the coronary sinus. — (a) The anterior cardiac veins (vv. cordis anteriores) are two or three small vessels whicli ascend on the anterior wall of the right ventricle to the auriculo-ventricular groove, where they either end separately in the right auricle or terminate in the conunencement of the small cardiac vein. (A) The vence minima' cordis. — A number of small veins which commence in the substance of the walls of the heart, and terminate directly in its cavities, principally in the auricles ; some few, however, open into the ventricles. THE SUPERIOR VENA CAVA AND ITS TRIBUTARIES. The superior vena cava (Figs. G19 and 620) returns the blood from the head and neck, the upper extremities, the thoracic wall, and a portion of the upper part 59 c 872 THE YASCULAE SYSTEM. of the posterior wall of the abdomen. It is formed, at the lower border of the first right costal cartilage, by the union of the two innominate veins, and it descends, with a slight convexity to the right, to the level of the third right costal cartilage, where it opens into the upper and back part of the right auricle. It is about three inches (7'5 cm.) long ; in the lower half of its extent it is enclosed within the fibrous layer of the pericardium, and it is covered in front and laterally by the serous layer. Relations. — It is overlapped in front by the margins of the right lung and pleural sac and by the ascending aorta. The lung and pleura intervene between it and the second and third costal cartilages, the internal intercostal muscles in the first and second intercostal spaces, and the internal mammary vessels. It is in relation behind with the right vagus nerve, the vena azygos major, the right bronchus, the right pulmonary artery, and the upper right pulmonary vein. On its left side are the commencement of the innominate artery and the ascending portion of the aorta, whilst on the right side it is in close relation with the right pleura, the phrenic nerve and comes nervi phrenici vessels intervening. Tributaries. — In addition to the two innominate veins, by the vmion of which it is formed, the superior vena cava only receives one large tributary, viz. the vena azygos major; but several small pericardial and mediastinal veins open into it. The Azygos Yeins. The vena azygos major (v. azygos, Eig. 660) commences either from the back of the inferior vena cava, at the level of the right renal vein, or as the direct upward continuation of an anastomosing channel which connects together the lumbar veins of the right side, and which is known as the right ascending lumbar vein. The great azygos vein ascends through the aortic orifice of the diaphragm, and is continued upwards through the posterior mediastinum. In the upper part of its course, it first passes behind and then arches forwards above the root of the right lung to its termination in the posterior part of the superior vena cava, immediately before the latter vessel pierces the pericardium. It frequently possesses imperfect valves. Relations. — In the abdomen it lies on the bodies of the upper lumbar vertebra3, behind the right cms of the diaphragm and the inferior vena cava, and to the right side of the thoracic duct. In the thorax it lies on the bodies of the lower eight dorsal vertebrse, the intervening discs, and the anterior common ligament, and it crosses in front of the right aortic inter- costal arteries. In the lower part of the postei'ior mediastinum it is covered in front by the right pleura and lung ; at a higher level it is overlapped by the right margin of the ceso- phagus, and immediately before its termination it is crossed by the root of the right lung. On its right side it receives the right posterior intercostal veins. On its left side it is in relation, in the greater part of its extent, with the thoracic duct and, as it arches for- wards over the root of the lung, with the right vagus nerve. About the level of the seventh dorsal vertebi'a it receives the vena azygos minor superior, whilst at the level of the eighth dorsal vertebra the vena azygos minor inferior opens into it. In addition to the left azygos veins it receives the right posterior intei-costal veins, except that from the first space but including the right superior intercostal vein, the right subcostal vein, and, through the ascending lumbar vein, the upper right lumbar veins. It also receives the right bronchial veins and some small oesophageal, pericardial, and mediastinal tributaries. The vena azygos minor superior (v. hemi-azygos accessoria) is formed by the union of the fourth, fifth, sixth, and seventh left posterior intercostal veins. It lies in the posterior mediastinum on the left sides of the bodies of the fifth, sixth, and seventh dorsal vertebrae, and crosses the spine from left to right opposite the body of the seventh dorsal vertebra, passing behind the aorta, oesophagus, and thoracic duct ; it terminates in the vena azygos major. It receives the left bronchial veins, some small posterior mediastinal veins also open into it, and it communicates with the left superior intercostal vein. The vena azygos minor inferior (v. hemi-azygos) commences in the epigastric region. At its origin it is connected either with the left ascending lumbar vein or with the left renal vein. After piercing the left crus of the diaphragm it ascends on the left sides of the THE INNOMINATE VEINS. 873 bodies of the lower dorsal vertebrae, and opposite the eighth dorsal verteVjra it turns to the right, crosses the front of the spine behind the aorta, oesophagus, and thoracic duct, and terminates in the vena azygos major. As it ascends in the posterior mediastinum it lies internal to the sympathetic cord, behind the roots of the splanchnic nerves, and superficial to the lower left intercostal arteries. Through the left ascending lumbar vein it receives blood from the upper lumbar veins of the left side ; the lower four posterior intercostal veins, the left subcostal vein, and small mediastinal tributaries also terminate in it. Not infrequently the upper and lower minor azygos veins unite, opposite the seventh or eighth dorsal vertebra, to form a common trunk which terminates in the azygos major. The bronchial veins do not quite correspond to the bronchial arteries, and they are not found on the walls of the smallest bronchi. On each side the tributaries run in front of and behind the bronchial tubes to the root of the lung, where they unite, as a rule, into two small trunks ; those of the right side open into the vena azygos major, and those of the left into the vena azygos minor superior, or into the left superior intercostal vein. On both sides they are joined by tracheal and posterior mediastinal veins. Some few small bronchial veins, including most of those from the smaller tubes, open into the pulmonary veins. Intercostal Veins. — There are two sets of intercostal veins (vv. intercostales), the anterior and the posterior. The anterior intercostal veins are tributaries of the internal mammary or of the musculo-phrenic veins, and are described with those vessels (p. 874). The posterior intercostal veins (Fig. 660) are eleven in number on each side. A single vein runs in each intercostal space ; it is situated in the subcostal groove above the corresponding artery. On the right side the posterior intercostal vein of the first space accompanies the superior intercostal artery across the front of the neck of the first rib, and terminates in the vertebral or innominate vein. The second, third, and fourth intercostal veins of the right side unite together to form a common trunk, the right superior intercostal vein (v. intercostalis suprema dextra), which terminates by joining the vena azygos major. The fifth to the eleventh posterior intercostal veins of the right side open separately in the vena azygos major. On the left side the fii'st posterior intercostal vein follows a course similar to that taken by the corresponding vein on the right side, and terminates in the left vertebral or innominate vein. The second, third, and fourth posterior intercostal veins of the left side unite to form the left superior intercostal vein (v. intercostalis suprema sinistra), which runs from behind forwards along the left and anterior aspect of the aortic arch. It passes obliquely between the left vagus and phrenic nerves, crosses the root of the left subclavian artery, and ends in the lower part of the left innominate vein. The fifth, sixth, seventh, and eighth posterior intercostal veins of the left side terminate in the vena azygos minor superior, and the ninth, tenth, and eleventh in the vena azygos minor inferior. Each posterior intercostal vein is provided with valves, both at its termination and along its course, which prevent the blood flowing towards the anterior aspect of the thoracic wall. Its tributaries are derived from the adjacent muscles and bones, and a short distance from its termination it receives a dorsal tributary which passes forwards to it between the transverse processes of the vertebra". This dorsal vessel is formed by the union of small veins which issue from the muscles of the back, from the anterior and posterior spinal plexuses which lie respectively in front of the bodies and behind the arches of the vertebra;, and by venous channels which issue through the intervertebral foramina ; the latter vessels commence in the spinal canal, where they are connected with the anterior and ])osterior spinal veins. The Inno^itnate Veins. The innominate or brachio-cephalic veins (vv. anunynK\> dextra et sinistra Figs. 619 and 6-0), two in number, right and loft, return blood from the liead and neck, the upper extremities, the upper part of the posterior wall of the thorax, the anterior wall of the thorax, and the upper part of the anterior wall of the abdomen. Each innominate vein commences behind the sternal end of the clavicle of the corresponding side, and is formed by tlie union of the internal jugular and sub- clavian veins; the two innominate veins terminate liy uniting together, at the lower border of the cartilage of the first rib on the right side, to ibrni the superior 874 THE VASCULAE SYSTEM. vena cava. To reach this point the left vein has to pass from left to right behind the manubrium sterni, and it is therefore about three times as long as the right vein. The innominate veins do not possess valves. The right innominate vein is a little more than one inch (3 cm.) in length. It descends almost vertically to the lower border of the first costal cartilage, and terminates in the superior vena cava. Relations. — It is in relation in front with the sternal end of the clavicle and the sterno-hjoid and sterno-thyroid muscles. It partly overlaps the innominate artery, which lies to its left side, and it is in front of the right vagus nerve and the posterior part of the upper end of the right pleural sac. The phrenic nerve and the accompanying vessels run along its right side, and intervene between it and the right pleural sac. Tributaries. — In addition to the veins by the union of which it is formed, the right innominate vein receives the right vertebral and internal mammary veins, and sometimes the right inferior thyroid vein and the first right posterior intercostal vein. The right lymphatic duct also opens into it. The left innominate vein passes from left to right, with a slight obliquity downwards, behind the upper part of the manubrium sterni, to the lower border of the first right costal cartilage, where it terminates in the superior vena cava. It is a little less than three inches long (6 to 7"5 cm.) Relations. — It is covered in front, in the greater part of its extent, by the sterno- hyoid and sterno-thyroid muscles, but at its right extremity it is slightly overlapped by the right pleura, and in the middle line the remains of the thymus gland intervene between it and the posterior surface of the sternum. It rests posteriorly upon the left subclavian artery, the left phrenic, and the left vagus nerves, the left superior cardiac branch of the sympathetic, the inferior cervical branch of the left vagus, the left common carotid artery, the trachea, and the innominate artery. Its lower border is in relation with the arch of the aorta, and on its upper border it receives the inferior thyroid vein of one or both sides. Tributaries. — It receives the vertebral, internal mammary, inferior thyroid, and superior intercostal veins of its own side, the first left posterior intercostal vein, and some pericardial, thymic, anterior bronchial, and anterior mediastinal veins. Sometimes the right inferior thyroid vein joins it, but usually this vessel terminates in the right innominate vein or in the commencement of the superior vena cava. The thoracic duct opens into it just at the angle of junction of the internal jugular and subclavian veins. Internal mammary veins (w. mammarise internee). — Each internal mammary artery is accompanied by vense comites ; they commence by the union of the venae comites of the superior epigastric and musculo-phrenic arteries, between the sixth costal cartilage and the triangularis sterni, and at the upper part of the thorax they fuse into a single vessel which enters the superior mediastinum and ends in the innominate vein of the same side. The tributaries of the internal mammary veins are — (a) The venae comites of the superior epigastric and musculo-phrenic arteries, which in their turn receive tributaries which correspond with the branches of the arteries they accompany, (b) Six anterior perforating veins which accompany the corresponding arteries, one lying in each of the upper six intercostal spaces, (c) Twelve anterior intercostal veins from the upper six intercostal spaces, two veins lying in each space with the corresponding branches of the internal mammary artery, (d) Small and irregular pleural, muscular, mediastinal, and sternal veins. The internal mammary veins are provided with numerous valves which prevent the blood from flowing downwards. Superior epigastric veins (w. epigastricee superiores). — The vense comites of the superior epigastric artery receive tributaries from the substance of the rectus abdominis, the sheath of the muscle, and the superjacent skin and fascia; they pass with the artery, between the sternal and costal origins of the diaphragm, and terminate in the internal maniuiary veins. Musculo-phrenic veins. — The venee comites of the musculo-phrenic artery com- mence in the abdomen, pass through the diapliragm with the artery, and terminate in the internal mammary veins. They receive as tributaries the anterior intercostal veins of the seventh, eighth, and ninth intercostal spaces, and small venules from the substance of the diaphragm. VEINS OF THE HEAD AND NECK. 875 Vertebral Veins (w. vertebrales). — These correspond ouly to tlie extra-cranial parts of the vertebral arteries. Each commences by the union of offsets from the intraspinal venous plexuses, and, issuing from the spinal canal, passes across the posterior arch of the atlas with the vertebral artery to the foramen in the transverse process of the atlas. It then descends througli the foramina in the cervical transverse processes, and breaks up into a plexus of venous channels which surround the artery. At the lower part of the neck these channels unite to form a single trunk which issues from the foramen in the transverse process of the sixth cervical vertebra, and descends, in the interval between the longus colli and scalenus auticus muscles, to terminate in the upper and back part of the innominate vein, where it possesses a uni- or bi-cuspidate valve. Relations. — In the first part of its course the vein Hes in the suboccipital triangle. The second, plexiform portion, is in the canal formed by the foramina in tlie transverse processes of the cervical vertebra}, and, with the artery which it surrounds, lies in front of the trunks of the cervical spinal nerves. The third part, in the root of the neck, is between the longus colli and scalenus anticus muscles, in front of the first part of the vertebral artery, and behind the internal jugular vein. Tributaries. — In addition to the offsets from the intraspinal venous plexuses by the union of which it is formed, each vertebral vein receives the following tributaries : — (a) Small vessels which issue from the muscles, ligaments, and bones of the deeper parts of the neck, and the lower and back part of the head, {b) Offsets from the intraspinal venous plexuses which pass out of the spinal canal by the intervertebral foramina. (c) The anterior deep cervical or anterior vertebral vein, a vessel which is formed by the union of tributaries which issue from a venous plexus which lies in front of the bodies and on the roots of the transverse processes of the cervical vertebrfe. This vessel accompanies the ascending cervical artery, and terminates in the lower part of the vertebral vein, immediately after the latter has issued from the foramen in the sixth cervical transverse process, (d) The posterior deep cervical (v. cervicalis profunda) or posterior vertebral vein ; this commences in the suboccipital triangle from a venous plexus with which the vertebral and occipital veins communicate. It descends behind the transverse processes of the cervical vertebrse in company with the profunda cervicis artery, tm-ns forwards at the root of the neck, between the transverse processes of the sixth and seventh cervical vertebrse or between the latter and the neck of the first rib, and opens into the vertebral vein. It receives blood from the muscles, ligaments, and bones of the back of the neck, {e) The posterior intercostal vein from the first intercostal space some- times opens into it. (Occasionally the venous plexus round the vertebral arter}- ends below in two terminal trunks, anterior and posterior, instead of one. In these cases the second terminal vessel lies behind the lower part of the vertebral artery, passes through the foramen in the transverse process of the seventh cervical vertebra, and turns foi-wards on the outer side of the artery to join the anterior trunk, thus forming a common terminal vein which ends in the usual manner. Inferior Thyroid Veins (vv. thyreoideoe inferiores). — Each inferior thyroid vein conmiences by the union of a series of tributaries which issue from the isthmus and the corresponding lateral lobe of the thyroid body. The two veins descend along the front of the trachea into the superior mediastinum, where the right inferior thyroid vein terminates in the junction of the two innominate veins, and the left in the upper part of tlie left innominate vein ; or the two veins unite to form a single trunk, which usually ends in the left innominate vein, but occa- sionally in the right. In their descent through the neck tlie inferior thyroid veins frequently anastomose together, and sometimes these anastomoses are so frequent and irregular that a venous plexus is formed in front of the lower cervical portion of the trachea. VEINS OF THE HEAD AND NECK. Internal jugular veins (Figs. 620 and 650).— Eacli internal jugular vein (v. jugularis interna) commences in the posterior compartment of the jugular foramen, as the direct continuation of the lateral sinus, and terminates behind tlie sternal part of the clavicle by uniting with the subclavian vein of tlie same side to form the innominate vein. 876 THE VASCULAK SYSTEM. At its commencement it is dilated, forming the bulb of the jugular vein, and in this situation it lies behind and somewhat to the outer side of the internal carotid artery and the last four cranial nerves. As it descends it accompanies first the internal and then the common carotid artery ; inclining forwards during its descent, it gradually passes from its original position, behind and to the outer side of the internal carotid artery, and Hes more completely to the outer side of the internal and common carotid arteries, and indeed somewhat overlaps the latter in front. This is more especially the case on the left side, for both internal jugular veins trend slightly towards the right as they descend ; consequently at the root of the neck the right vein is separated from the right common carotid artery by a small interval filled by areolar tissue, whilst the left vein is more directly in front of the corresponding common carotid artery. Within an inch of its lower extremity each internal jugular vein is pro- vided with a valve, which, however, is frequently incompetent. It consists of one, two, or three cusps. Relations. — The vein lies in front of tlie transverse processes of the cervical verte- brae, the rectus capitis lateralis, rectus capitis anticus major, and scalenus anticus muscles, the ascending cervical artery, which runs upwards in the interval between the attach- ments of the two latter muscles, and the phrenic nerve ; the suprascapular and the transverse cervical arteries intervene between it and the scalenus anticus. At the root of the neck the vein lies in front of the first part of the subclavian artery and the origins of the vertebral artery and the thyroid axis, and on the left side it is in front of the terminal part of the thoracic duct. On the inner side of the internal jugular vein, immediately below the skull, are the internal carotid artery and the last four cranial nerves ; in the rest of its extent it is in relation internally either with the internal or the common carotid artery, whilst to its inner side and somewhat posteriorly, between it and the large arteries, lies the vagus nerve. Each internal jugular vein is covered in the Avhole of its length by the sterno-mastoid muscle ; near its upper end it is crossed by the posterior belly of the digastric, whilst in its lower half, in addition to the sterno-mastoid, the omo-hyoid, the sterno-hyoid, and the sterno-thyroid muscles are superficial to it. Just below the transvei'se process of the atlas, and under cover of the sterno-mastoid, the vein is crossed on its outer side b^r the spinal accessory nerve and by the occipital artery ; about the middle of its course it is also crossed by the communicans cervicis nerve, and near its lower end by the anterior jugular vein ; the latter vessel, however, is separated from it by the sterno-hyoid and sterno- thyroid muscles. Superficial to the vein are numerous deep cervical lymphatic glands. Tributaries.— («) The inferior petrosal sinus, which joins it near its commencement. (/>) Pharyngeal branches from the venous plexus on the wall of the pharynx, (c) The common facial vein, which receives the facial vein and its tributaries, {d) The lingual veins (vv. linguales), small venge comites, which commence chiefly in the subliiigual and dorsalis lingua3 veins, and accompany the first and second parts of the lingual artery, (e) The ranine vein, which commences beneath the tip of the tongue, and accompanies at first the two terminal parts of the lingual artery, and afterwards the hypoglossal nerve. (/) The superior thyroid vein (v. thyreoidea superioris), which accompanies the corresponding artery, {g) The middle thyroid vein, which passes backwards from the lateral lobe of the thyroid body and crosses the middle of the outer aspect of the common carotid artery, (h) The occipital vein (v. occipitalis) occasionally terminates in the internal jugular vein. In many cases, however, it ends in the suboccipital plexus, which is drained by the vertebral and deep cervical veins (see p. 875). The common facial vein (v. facialis comnmnis) is formed by the union of the facial vein (v. facialis anterior) with the anterior division, or terminal branch, of a venous trunk which lies in substance of the parotid gland, and which is called the temporo- maxillary vein (v. facialis posterior). It accompanies the first part of the facial artery in the carotid triangle, passes between the sterno-mastoid, and terminates in the anterior border of the internal jugular vein. Just before it disappears beneath the sterno-mastoid, the common facial vein frequently gives off a large branch, which descends along the anterior boi'der of the sterno-mastoid to the suprasternal fossa, where it joins the anterior jugular vein. The facial vein (v. facialis anterior. Fig. 648) commences at the inner angle of the orbit in the angular vein, which is formed by the union of the supra-orbital and frontal EXTEENAL JUGULAE VEIN. 877 veins. It passes downwards and backwards on the face, from the inner angle of the orbit to the lower and anterior part of the masseter muscle, which it crosses, lying in the same plane as the facial artery, but following a much straighter course. After crossino- the lower border of the jaw it passes across the submaxillary triangle, superficial to the submaxillary gland, and separate from the facial artery, which here lies in a deeper plane, and it terminates a short distance below the angle of the jaw b}' uniting with tlie anterior division of the temporo-maxillary vein to form the common facial vein. The facial vein receives tributaries corx-esponding with all the branches of the facial artery, except the ascending palatine and the tonsillar, wliich have no accompanying veins, the blood from the region which they supply being returned for the most part throu^'-h the pharyngeal plexus. The facial vein also communicates with the ptervgoid plexus which surrounds the external pterygoid muscle by means of an anastomosing channel, called the deep facial vein, which passes backwards between the masseter and buccinator muscles into the zygomatic fossa. The inferior thyroid veins have already been described (see p. 875). Subclavian Veins. — The subclavian vein (v. suLclavia) of each side is the direct continuation of the main vein of the upper extremity, the axillary vein ; but through its tributary, the external jugular vein, it also receives blood both from the superficial and deep parts of the head and neck. From its commencement at the outer border of the first rib it runs inwards below and in front of the corresponding artery, from which it is separated by the lower part of the scalenus unticus nuiscle, and it terminates behind the sternal end of the clavicle, in the innominate vein of the corresponding side. As it passes inwards it forms a slight curve, the convexity of which is directed upwards. Each subclavian vein possesses a single bicuspid valve which is situated imme- diately on the distal side of the opening of the external jugular vein. Relations. — The subclavian vein is in relation in front with the posterior layer of the costo-coracoid membrane, which separates it from the subclavius muscle, and the nerve to the subclavius, and with the back of the sternal end of the clavicle, from which it is partly separated, however, by the fibres of the sterno-hyoid and sterno-tliyroid muscles. It is closel}' attached in front to the posterior surface of the costo-coracoid membrane, consequently it is expanded when the clavicle is moved forwards, a condition of affairs which constitutes a distinct danger when operations are being performed in the neighbour- hood of the vein, for in the event of the vessel being wounded, forward movement of the clavicle may cause air to be sucked into the vein with fatal results. Behind the vein, and on a higher plane, are the first and third parts of the subclavian artery, but it is separated from the second part by the scalenus anticus. To the inner side of the anterior scalene the posterior relations of the vein, in addition to the sub- clavian artery, are the upper part of the internal mammary artery, the phrenic nerve, and the cervical portion of the pleura. it rests upon the upjK-r surface of the first rib. Tributaries. — Whilst the subclavian vein is the direct continuation of the axillary vein, and receives the blood from the upper extremity, it has, as a general rule, onlv one named tributary, viz. the external jugular vein. The external jugular vein (>". jugularis externa, Fig. 648) is formed on the superficial surface of the sterno-mastoid muscle, a little below and behind the angle of the jaw, by the union of the posterior auricular vein with the posterior terminal branch of the temporo-maxillary vein. After its formation the external jugular vein descends, with a slight obliquity backwards, to the anterior part of the subclavian portion of the posterior triangle of the neck, where it pierces the deep fascia, and, after crossing in front of the third ])art of the subclavian artery, terminates in the sul)clavian vein. Whilst on tlie surface of the sterno-mastoid nuiscle it is covered by the super- ficial fascia and platysma muscle, and it lies parallel with, and slightly in front of, the great auricular nerve ; after crossing the transverse cervical nerve it reaches the ])ostorior border of the sterno-mastoid, wliere it receives a tributary called the posterior external jugular vein, whicli commences in the superficial tissues of the upper and Imck part of the neck, and runs downwards and forwards across the roof 878 THE VASCULAE SYSTEM. of the upper part of the posterior cervical triangle to its termination in the external jugular vein. As the external jugular vein pierces the deep cervical fascia in the subclavian triangle, its wall is closely attached to the margin of the opening through which it passes, and as it is crossing in front of the third part of the subclavian artery it is joined by the suprascapular, transverse cervical, and anterior jugular veins. There are usually two valves in the lower part of the vein — -one, which is generally incompetent, at its termination, and a second at a higher level Tributaries. — In addition to the posterior auricular vein and the posterior division Superficial temporal ^ em — nr Occipital ^ em Internal maxillary ^ em^ Temporo-maxillarj \ em Posterior auriculai \ em Anterior division of temxjoro-maxillarj \ em Posterior external jugulai \ em Transverse cervical ^ en Snpra-orbital vein Angular vein Lateral nasal vein Superior coronary veiu Inferior coronary vein Facial vein Inferior labial vein Anastomosis between common facial and anterior jugular veins Anterior jugular vein External jugular vein , Fig. 648. — Supehficial Veins of the Head and Neck. of the temporo-maxillary vein by which it is formed, the external jugular vein receives the posterior external jugular vein, which has already been described, the transverse cervical and suprascapular veins from the region of the shoulder, and the anterior jugular vein. Occasionally the cephalic vein also opens into it. The posterior auricular vein. (v. auricularis posterior, Fig. 648) receives tributaries from the posterior parts of the parietal and temporal regions and from the inner surface of the pinna. It is considerably larger than the posterior auricular artery, which it only accompanies in the sculp. At the base of the scalp it leaves the artery and descends in the superficial fascia, over the upper part of the sterno-mastoid, to open into the commence- ment of the external jugular vein. The posterior division of the temporo-maxillary vein (see p. 880). VEINS OF THE SCALP. 879 The transverse cervical and suprascapular veins accompany the corresponding arteries; not infrequently they open directly into the subclavian vein. The anterior jugular vein (v. jugularis anterior) commences over the anterior bell}' of the digastric muscle, and is formed by the union of small veins from the lower lip and the submental region. It descends in the superficial fascia, at a variable distance from the middle line, and perforates the superficial layer of the deep fascia just above the inner end of the clavicle. It there enters the space above the manubrium sterni, which lies between the first and second layers of the deep cervical fascia, and which is called Burns's space, where, after anastomosing with its fellow of the opposite side and receiving a communication from the facial vein, it turns outwards, between the sterno-mastoid super- ficially and the sterno-hyoid, sterno-thyroid, and scalenus anticus muscles deeply, to terminate at the outer border of the latter muscle in the external jugular vein. The Veins of the Scalp. The veins which drain the blood from the superficial parts of the scalp are the frontal, the supra-orbital, the superficial temporal, the posterior auricular, and the occipital. The blood from the deeper part of the scalp, in the region of the temporal fossa on each side, passes into the deep temporal veins, which are tributaries of the pterygoid plexus. Tlie frontal (v. frontalis) and supra-orbital veins (v. supra-orlji talis) receive Idoixl from the inner and front part of the scalp. They unite together, near the upper and inner angle of the orbit, to form the angular vein ; before the union is effected the supra-orbital vein sends a branch backwards through the supra-orbital notch into the orbital cavity, where it terminates in the ophthalmic vein, and as this branch passes through the notch it receives the frontal diploic vein (p. 881). The superficial temporal vein (v. temporalis superficialis) receives tributaries from the outer part of the frontal region, from the greater part of the super- ficial area of the temporal region, and from the anterior part of the parietal region. It passes downwards, across the posterior root of the zygoma, into the parotid gland, where it unites with the internal maxillary vein to form the temporo- maxillary trunk. The posterior auricular vein (v. auricularis posterior) drains the posterior portions of the temporal and parietal areas of the scalp. It runs downwards across the mastoid portion of the temporal bone, and terminates in the external jugular vein. The occipital vein (v. occipitalis, Eig. 648) receives tributaries from the inner and posterior part of the parietal region and from the occipital region. As a rule it pierces the occipital origin of the trapezius, and, passing deeply into the sub- occipital triangle, terminates in a plexus of veins which is drained by the vertebral and deep cervical veins. It sometimes communicates with the external jugular vein, and occasionally an offset from it accompanies the corresponding artery and ends in the internal jugular vein. It generally receives the mastoid emissary vein ; one of its tributaries receives the parietal emissary vein, and occasionally an emissary vein from the torcular Herophili opens into it. The Veins of the Okbit, the Nose, and the Pterygo-maxillary Eegion. The veins of these three regions are closely associated together ; for although the orl)ital blood is returned for the most part to the cavernous sinus by the ophthalmic vein, the latter vein is closely connected with the pterygoid plexus which lies in the pterygo-maxillary region. Veins of the Orbit. — The veins of the orbit correspond, with the exception of the frontal ^'ein, with the branches of the ophthalmic artery, and they gradually converge, as they pass backwards in the orbit, until they form two nuiiu trunks, an upper (v. ophthalmica superior) and a lower (v. ophthalmica inferior); these terminate, separately or by a single trunk, in the anterior end of the cavernous sinus, to which they pass through the foramen lacerum antorius, and between the two heads of the external rectus muscle. The superior ophthalmic vein communicates, at the internal angle of the orbit, 880 THE VASCULAR SYSTEM. with the angular vein, and the inferior ophthalmic vein communicates through the spheno-maxillary fissure with the pterygoid plexus. Veins of the Nose. — The veins of the walls of the nasal cavity end partly in the ethmoidal tributaries of the superior ophthalmic vein, partly in the septal affluent of the superior coronary and in the lateral nasal veins, both of which are tributaries of the facial vein ; but the majority of the veins of the nose, both from the septal and outer walls, join together to form a spheno-palatine vein which passes through the spheno-palatine foramen and the spheno-maxillary fossa, and terminates in the pterygoid plexus. Pterygoid Plexus and the Internal Maxillary Vein. — The pterygoid plexus (plexus pterygoideus) of veins lies in the zygomatic and pterygoid fossae. It covers the inner surface of the internal pterygoid muscle, and surrounds the external pterygoid. It receives tributaries which correspond with and accompany the branches of the internal maxillary artery — viz. spheno-palatine, ptery go-palatine, vidian, infra-orbital, posterior superior dental, posterior palatine, buccal, two or three deep temporal, pterygoid, masseteric, and inferior dental veins, and the vena comites of the middle meningeal artery. It communicates superiorly with the cavernous sinus through the foramen ovale, anteriorly with the inferior ophthalmic vein through the spheno-maxillary fissure, and between the masseter and the buccinator with the facial vein by the deep facial anastomosing branch. It also communicates posteriorly and internally, on the inner side of the internal pterygoid, with the pharyngeal plexus, and it terminates posteriorly in the internal maxillary vein. The internal maxillary vein is a short vessel which accompanies the first part of the internal maxillary artery, between the spheno-mandibular ligament and the neck of the lower jaw ; it enters the parotid gland, and terminates by uniting with the superficial temporal vein to form the temporo-maxillary trunk. Occasionally the internal maxillary vein is double. The temporo-maxillary vein (v. facialis posterior) is a short trunk which is formed in the upper part of the parotid gland, behind the neck of the jaw, by the union of the superficial temporal and internal maxillary veins. As it descends it hes superficial to the external carotid artery, and it is crossed by the cervico- and temporo-facial branches of the facial nerve. It terminates at the lower part of the parotid gland by dividing into posterior and anterior divisions. The posterior division passes backwards, perforates the deep cervical fascia, and unites on the upper part of the sterno-mastoid muscle with the posterior auricular vein to form the external jugular vein. The anterior division passes downwards and forwards into the carotid triangle, where it terminates in the common facial vein. VENOUS SINUSES AND VEINS OF THE CRANIUM AND OF ITS CONTENTS. The venous channels met with in the cranial walls and cranial cavity are : — (1) The diploic veins (vv. diploicee), which lie in the cancellous tissue between the outer and inner tables of the cranial bones. (2) The meningeal veins, which accompany the meningeal arteries in the outer layer of the dura mater. (3) The veins of the brain, which lie between the folds of pia mater and in the subarachnoid space. (4) The cranial venous sinuses, channels which are situated between the outer and inner layers of the dura mater; they receive the blood from the terminal cerebral veins. Diploic and Meningeal Veins. The diploic veins (vv. diploicse) are anastomosing spaces in the cancellous tissue of the fiat bones of the skull ; they are lined by endothelium. The number of efferent vessels which emerge from these spaces is not constant, but usually there are at least four — viz. a frontal, two temporal, anterior and posterior, and an occipital. VEINS OF THE BKAIX. 881 The frontal diploic vein (v. diploica Iroiitalis) is one of the most constant ; it drains the anterior part of the frontal bone, and, passing through a small aperture in the upper margin of the supraorbital notch, terminates in the supraorljital xem. The anterior temporal diploic vein (v. diploica temporalis anterior) drains the posterior part of the frontal bone and the anterior part of the parietal bone ; it pierces the great wing of the splienoid, and terminates either in the spheno-parietal sinus or in the anterior deep temporal vein. The posterior temporal diploic vein (v. diploica temporalis posterior) drains the posterior part of the parietal ])one ; it runs downwards to the posterior inferior angle of the parietal bone, and terminates in the lateral sinus, to which it passes either through a foramen in the inner table of the parietal bone or through the mastoid foramen. The occipital diploic vein (v. diploica occipitalis) is usually the largest of the ■\nti iKir toii'ponil diploic vein Occipital diploic FiDiit il diploic vein Fig. 649. — The Veins ov the Diplok. series ; it drains the occipital bone, and terminates either externally in the occipital vein or internally in the lateral sinus. The meningeal veins (v. meningeal) commence in two capillary plexuses, a deep and a superficial. The deep plexus is a wide-meshed network in the inner layer of the dura mater. Its efferent vessels terminate in the superficial plexus. The superficial plexus lies in the outer layer of the dura mater. It consists of numerous vessels of uniform calibre which frequently anastomose together, and terminate in two sets of efferents ; of these, one set ends in the cranial blood sinuses, and the other accompanies the meningeal arteries. The efferent meningeal veins are peculiar, inasmuch as they do not increase in size as they approach theii terminations, and they are irregular in their relations to the arteries ; as a rule the middle meningeal arteries alone possess two venje comites, the other meningeal arteries usually having only one accompanying vein. Veins of the Brain. The veins of the brain include the veins of the cerebrum, of the mid-brain, of the cerebellum, of the pons, and of the medulla oblongata. They do ni>t possess valves. GO 882 THE VASCULAE SYSTEM. Veins of the Cerebrum (w. cerebri). — The cerebral veins are arranged in two groups/ (a) the deep and (b) the superficial. The deep veins issue from the substance of the brain. The superficial veins lie upon its surface in the pia mater and the subarachnoid space. The terminal trunks of both sets pierce the arachnoid membrane and the inner layer of the dura mater, and open into the cranial venous sinuses. (a) The deep cerebral veins are the choroid veins, the veins of the corpora striata, the veins of Galen, and the inferior striate veins. Each choroid vein (v. chorioidea) is formed by the union of tributaries which issue from the choroid plexus in the descending horn of a lateral ventricle. It ascends along the lateral border of the velum interpositum, and passes forwards in the outer border of that fold of pia mater to the foramen of Monro, where it receives efferents from the choroid plexus of the third ventricle, and ends by unit- ing with the vein of the corpus striatum to form the vein of Galen. The vein of the corpus striatum, on each side, is formed by the union of tributaries which issue from the corpus striatum and from the optic thalamus. It runs for- wards between these bodies, in a groove in the floor of the lateral ventricle, and, after receiving tributaries from the walls of the anterior horn of the ventricle, including the septum lucidum, it terminates at the apex of the velum interpositum, where it joins the choroid vein to form the vein of Galen. The veins of Galen are three in number — a right and a left vein, and the vena magna Galeni. Each lateral vein of Galen commences at the apex of the velum interpositum, near the foramen of Monro, by the union of the vein of the corpus striatum with the choroid vein. The two veins run backwards between the layers of the velum, and terminate beneath the splenium of the corpus callosum by uniting to form the vena magna Galeni. The ti'ibutaries Avhich enter each vein, after its formation, are the basilar vein, the efferent veins from the choi'oid plexus of the third venti'icle, and veins from the posterior part of the corpus callosum, the pineal body, the corpora qaadrigemina, and the walls of the posterior cornu of the lateral ventricle. The vena magna Galeni (v. cerebri magna [Galeni]) passes backwards and slightly upwards from its origin, and ends in the anterior extremity of the straight sinus. In addition to the two veins of Galen, by the union of which it is formed, it receives tributaries from the posterior parts of the callosal convolutions, from the inner and tentorial surfaces of the occipital lobes of the brain, and from the upper surface of the cerebellum. An inferior striate vein descends on each side from the substance of the corpus striatum, and, after passing through the anterior perforated space, ends in the basilar vein (p. 883), which, as already stated, is a tributary of the corresponding- lateral vein of Galen. (b) The superficial cerebral veins are more numerous and of larger calibre than the cerebral arteries. They lie upon the surface of the cerebrum, they drain blood from the cerebral cortex, and they are divisible into two sets, the superior and the inferior. The superior cerebral veins (vv. cerebri superiores), twelve or more in number, lie in the pia mater and subarachnoid space on the upper and outer aspect of the cerebral hemispheres. They run inwards to the margin of the longitudinal fissure, where they receive tributaries from the inner surface of the hemispheres, and they terminate in the superior longitudinal sinus. The anterior veins of this set are small and run transversely inwards, but the posterior are large and run obliquely forwards and inwards ; they are embedded for some distance in the wall of the sinus, and their orifices are directed forwards against the blood stream. The inferior cerebral veins (vv. cerebri inferiores) He on the lower and outer aspects of the cereliral hemispheres ; they run downwards and inwards, and terminate in the sinuses which lie at the base of the skull — viz. the cavernous, the superior petrosal, and the lateral sinuses. One of these veins, the superficial Sylvian vein, runs along the posterior horizontal limb and stem of the fissure of Sylvius to the BLOOD SINUSES OF THE CEANIUM. 883 cavernous sinus ; occasionally it is united by an anastomotic loop, known as the great anastomotic vein (if Trolard, with the superior longitudinal sinus, and some- times by the posterior anastomotic vein with the lateral sinus. The anterior cerebral vein (jf each side lies in the great longitudinal fissure, and accompanies the corresponding anterior cerebral artery ; it receives tributaries from the corpus callosum and the callosal convolution. Turning downwards round the genu of the corpus callosum, it reaches the base of the brain, and terminates in the basilar vein. The deep Sylvian vein hes deeply in the fissure of Sylvius ; it anastomoses freely with the superficial Sylvian vein, receives tributaries from the island of Reil and the adjacent opercula, and terminates in the basilar vein. The basilar vein commences at the anterior perforated space ; it is formed by the union of the anterior cerebral vein with the deep Sylvian vein and with the inferior striate vein. Passing backwards round the crus cerebri, it terminates in a vein of Galen. Its tributaries are derived from the tuber cinereum, the corpus albicans, the posterior perforated space, the uncinate gyrus, the inferior cornu of the lateral ventricle, and tlie crus cerebri. Veins of the Mid-brain. — The veins of the mid-brain terminate for the most part in the veins of Galeu. Cerebellar Veins. — These veins also are divisible into two groups, the super- ficial and tlie deep. The former are quite independent of and much more numerous than the arteries. They form two sets, the superior and the inferior. The superior superficial cerebellar veins (vv. cerebelli superiores) terminate in a single median or vermian efferent vessel which is sometimes double, and in several lateral efferents. The superior vermian vein runs forwards and ends in the vena magna Galeni, and the lateral superior cerebellar veins terminate in the lateral sinuses or in the superior petrosal sinuses. The inferior superficial cerebellar veins (vv. cerebelli inferiores) also form a small vermian and numerous lateral efferents ; the former runs backwards and joins either the straight sinus or one of the lateral sinuses, and the latter end in the inferior petrosal and occipital sinuses. The deep cerebellar veins issue from the substance of the cerebellum and terminate in the superficial veins. Veins of the Pons Varolii. — The deep veins from the substance of the pons pass forwards to its anterior surface, where tliey become superficial, and, anastomosing together, form a plexus which is drained by superior and inferior efferent veins. The superior efferent veins join the basilar vein ; the inferior efferent veins either unite with the cereliellar veins, or they open into the superior petrosal sinus. Veins of the Medulla Oblongata. — Deep veins of the bulb issue from its sub- stance and end in a superficial plexus. This plexus is drained by an anterior and a posterior median vein and ]iy radicular veins. The anterior median vein is continuous below with the corresponding ^-ein of the spinal cord ; it communicates above with the plexus on the surface of the pons. The posterior median vein is continuous below with the posterior median vein of the cord, from wliich it ascends to the lower end of the fourth ventricle, where it divides into two branches which join the inferior petrosal or basilar sinuses. The radicular veins issue from the lateral parts of the plexus and run with the roots of the last four cranial nerves ; they end in the inferior petrosal and occipital sinuses. Blood Sinuses of the Ckanium. The venous sinuses of the cranium are spaces between the layers of the dura mater; they are lined by an endothelium which is continuous with the endothelium of the veins. They receive the veins of the brain, communicate frequently with the meningeal veins and with veins external to the cranium, and terminate directly or indirectly in the internal jugular vein. Some of the cranial blood sinuses are unpaired, others are paired. Unpaired Sinuses. — These are the superior longitudinal, the inferior longi- tudinal, the straight, the circular, and the basilar. G0(^ 884 THE YASCULAE SYSTEM. The superior longitudinal sinus (sinus sagittalis superior) commences in the anterior fossa of the cranium, at the crista galli, where it communicates through the foramen csecum with the veins of the nasal cavity or with the angular vein. It passes upwards, then backwards, and finally downwards in the convex margin of the falx cerebri, grooving the frontal, parietal, and upper part of the occipital bones. As it descends it passes slightly to the right side, and it ends at the level of the internal occipital protuberance by becoming the right lateral sinus. Instead Inferior loujiitudinal simis Vena magna Galeiii Straight Mn penoi petiooal sinus L'i\einous sinus Facial nerve ^ y f IJ^ Posterior aniicular *r /J I ^^^'^ artery Occipital sinu^ Sup. oblique muscle Occipital aitery - Princeps cervici') arteij Vertebral aitei\ Complexus muscle Suboccipital nei\e Sterno-mastoid muscle -Splenius capitis muscle External carotid artery J Parotid gland Stylo-hyoid muscle Hypoglossal nerve itemal carotid artery uicle (posterior belly) Trachelo- Spinal Internal Sterno-mastoid Common carotid artery mastoid muscle accessory nerve jugular vein artery Fig. 650. — Dissection of the Head and Xeck, showing the cranial blood sinuses and the upper part of the internal jugular vein. of passing to the right, it occasionally turns to the left, and ends in the left lateral sinus. In either case its termination is associated with a well-marked dilatation, the torcular Hewpltili, which marks a confluence of sinuses, and which is lodged in a depression at one side of tlie internal occipital protuberance. The torcular is connected, across the protuberance, by an anastomosing channel with a similar dilatation, which marks the junction of the straight sinus with the lateral sinus of the opposite side. Opening into the superior longitudinal sinus are the superior cerebral veins, and it communicates on each side by small openings with a series of spaces in the dura mater, the lacunae laterales, into which the Pacchionian bodies (arachnoidal villi) project. It also communicates, by emissary veins which pass through the foramen Ccecuin and through each parietal foramen (emissarium parietale), with the veins on the exterior of the cranium. Its cavity, which is triangular in transverse section, is crossed by several fibrous strands called the chordse Willisii. The inferior longitudinal sinus (sinus sagittalis inferior) lies in the posterior two-thirds of the lower free margin of the falx cerebri. It terminates posteriorly BLOOD SINUSES OF THE CEANIUM. by joining with the vena magna Galeni to form the straight sinus. It is circular in transverse section, and it receives tributaries from the falx cerebri and from the inner surface of the middle third of each cerebral hemisphere. The circular sinus (sinus circularis) is situated in the pituitary fossa, and sur- rounds the pituitary body. It is usually formed by anterior (sinus intercavernosus anterior) and posterior (sinus intercavernosus posterior) transverse channels which pass across the pituitary fossa from one cavernous sinus to the other. Olfiftou 1 nil Infi.i troclilear nen ^huiua trocliledi- nerve ^Oculo niotoi nerve Sl)lieiio parietal sinus ■Oplitlidlniie vein Antdioi clinoid piocess Troclilear nerve < )c nlo motor nei\e \biliicent nerve Cuciilir sinus Oplitlial. nerve "supiMior nuiMllary nerve Iiifi nor iixilliry nerve neinous sinus Basilar sinus Optic nrrve ( )ptic coniniissure Anterior cerebral artery MiiUlle cerebral artery Posterior coiiininni-_ eating artery Oculo-niotor nerve Posterior cere- bral artery Superior cere- bellar arterx' Troclileai nerve Abilucent nerve Trigeminal nerve Superiiir petrosal sinus l''acial nerve Pars inter- media Auditory nerve Glosso-pliaryn- geal nerve Pneumogastrie, ner\ ( Spinal accessory n( Hyi)oglos-?nl m i \ 1 ati lal siMus \i'ilebi il aitei Spinal (cml Openings of occii)ital sinuses'"^ / Superiur loiigitudinnl sinus Falx cerebri (cut) Fig. 651.— Basal Blood Sinuses hf the Ddra Matkh. The basilar sinus (plexus basilarisj.— The term l)asilar sinus is applied to a venous plexus situated in the dura mater on the basilar part of the occipital bone. It connects the posterior ends of the cavernous or the anterior ends of the inferior petrosal sinuses together, and communicates below with the anterior spinal veins. The straight sinus (sinus rectus) is formed by the union of the inferior longi- tudinal smus with the great vein of Galen. It runs downwards and backwards, along the line of attachment of the falx cerebri to the tentorium cerebelli. As a general rule it turns to the left at the internal occipital protuberance, dilates some- what, and becomes continuous with the left lateral sinus, its dilatation being united 886 THE VASCULAK SYSTEM. with the corresponding dilatation on the lower end of the superior longitudinal sinus — the torcular Herophili — by a transverse anastomosing channel. Occasion- ally the straight sinus terminates in the right lateral sinus, and in that case the superior longitudinal sinus ends in the left lateral sinus. It receives some of the superior cerebellar veins and a few tributaries from the falx cerebri. Paired Sinuses. — There are six pairs of sinuses, viz. the lateral, the occipital, the cavernous, the superior petrosal, the inferior petrosal, and the spheno-parietal. Lateral Sinuses. — Each lateral sinus (sinus transversus) commences at the internal occipital protuberance, the right usually as the continuation of the superior longitudinal, and the left as the continuation of the straight sinus. Each passes outwards in the outer border of the tentorium cerebelli and in a groove in the occipital bone. From the lateral angle of the occipital bone it passes on to the posterior inferior angle of the parietal bone, which it grooves ; then it leaves the tentorium and turns downwards on the inner surface of the mastoid portion of the temporal bone ; from the latter it passes to the upper surface of the jugular process of the occipital bone, and turns forwards and then downwards into the jugular foramen, where it becomes continuous with the internal jugular vein. Its tributaries are some of the superior and inferior cerebellar veins, a posterior diploic vein, and the superior petrosal sinus. It is connected with the veins out- side the cranium by emissary veins which pass through the mastoid and posterior condylar foramina. The occipital sinuses (sinus occipitales) lie in the attached border of the falx cerebelli and in the dura mater along the postero-lateral boundaries of the foramen magnum ; frequently they unite above and open by a single channel into the com- mencement of either the right or the left lateral sinus, but their upper extremities may remain separate, and then each communicates with the commencement of the lateral sinus of its own side. They open below into the terminal part of the corre- sponding lateral sinuses, and they communicate with the posterior spinal veins. Each occipital sinus is an anastomosing channel between the upper and lower extremities of the lateral sinus of tlie same side, and each receives a few inferior cerebellar veins. The cavernous sinuses lie at the sides of the body of the sphenoid bone. Each sinus (sinus cavernosus) commences anteriorly at the inner end of the sphenoidal fissure, where it receives the corresponding ophthalmic vein, and it terminates at the apex of the petrous portion of the temporal bone by dividing into the superior and the inferior petrosal sinuses. Its cavity, which is irregular in size and shape, is so divided by numerous fibrous strands that it assumes the appearance of cavernous tissue, and in its outer wall are embedded the internal carotid artery with its sympathetic plexuses, the third, fourth, first, and second divisions of the fifth, and the sixth cranial nerves. Its tributaries are the spheno-parietal sinus and the inferior cerebral veins, including the superficial Sylvian vein. It com- municates with the opposite cavernous sinus by means of the circular sinus ; with the pterygoid plexus in the zygomatic fossa by an emissary vein which passes either through the foramen ovale or through the foramen Vesalii ; with the internal jugular vein by small venous channels which accompany the internal carotid artery through the carotid canal, and by the inferior petrosal sinus ; with the lateral sinus by the superior petrosal sinus, and through the ophthalmic vein with the angular vein. The spheno-parietal sinuses (s. spheno-parietales) are lodged in the dura mater on the under surfaces of the small wings of the sphenoid bone close to their posterior borders. Each sinus communicates with the middle meningeal veins, receives veins from the dura mater, and terminates in the anterior part of the corresponding cavernous sinus. Superior Petrosal Sinuses. — Each superior petrosal sinus (s. petrosus superior) commences at the apex of the petrous portion of the temporal bone in the posterior end of the corresponding cavernous sinus. It runs backwards and outwards in the attached margin of the tentorium cerebelh, above the fifth cranial nerve, and grooves the uppsr border of the petrous portion of the temporal bone, at the outer extremity of which it terminates in the lateral sinus at the point where the latter is turning downwards on tlie inner surface of the mastoid portion of the temporal bone. It receives inferior cerebral, superior cerebellar, tympanic, and diploic veins. THE SPINAL A^EINS. 887 Inferior Petrosal Sinuses. — Au interior petrosal sinus (s. petrosus inferior; commences at the posterior end of each cavernous sinus ; it runs backwards, out- wards, and downwards in the posterior fossa of the cranium, in a groove along the lower margin of the petrous portion of the temporal bone and the adjacent border of the basilar portion of the occipital bone, to the anterior compartment of the jugular foramen of the same side, through which it passes. It crosses the last four cranial nerves either externally or internally, and it terminates in the internal jugular vein. Its tributaries include inferior cerebellar veins and veins from the internal ear, which pass to it through the internal auditory meatus, the aqueductus cochlea, and the aqueductus vestibuli. The Spinal Veins. The spinal veins include — ( 1 ) The extra-spinal veins. (a) The anterior spinal plexus. (0) „ posterior ,, (2) The veins of the bodies of the vertebrte. (3) The intra-spinal veins. (a) The anterior longitiidinal veins. (b) „ posterior ,, „ (4) The veins of the spinal cord. The anterior spinal plexus lies in front of the bodies of the verteltne. It consists of a number of relatively small anastomosing channels, -which communicate with the veins of the bodies of the vertebra?, and which receive tributaries from the adjacent muscles and ligaments. Its efferent vessels terminate in the cervical region in the anterior deep cervical vein, in the dorsal region in intercostal veins, in the lumbar region in the lumliar veins, and in the sacral region in the lateral sacral veins. The posterior spinal plexus consists of numerous anastomosing venous channels which lie on the laminte and round the spines and the articular and transverse processes of the vertebr.e. The plexus receives tributaries from the muscles and skin of the back, and communicates, through the ligamenta subflava, with the posterior longitudinal spinal veins in the interior of the spinal canal. Its efferent vessels pass between the transverse processes of the vertebrce, or through the sacral foramina, and terminate in the vertebral, the intercostal, the lumbar, and the lateral sacral veins respectively. Veins of the Bodies of the Vertebrae. — The cancellous tissue of the bodies of the vertebne is permeated by large venous channels which communicate anteriorly with the anterior spinal plexus. These channels terminate posteriorly in the vence basis vertebrce, wliich open into transverse anastomosing vessels which connect the anterior longitudinal spinal veins. Anterior Longitudinal Spinal Veins. — Two anterior longitudinal spinal veins collect blood from the bodies of the vertebne, from the adjacent ligaments, and from the spinal dura mater. They are plexiform vessels which extend from the foramen magnum to the coccyx, behind the bodies of the vertebnie and along the margins of the posterior common li^'ament, and they are connected together, opposite each vertebral body, by transverse anastomoses which lie between the posterior common ligament and the bodies of the vertebra) ; these transverse anastomoses are greatly dilated opposite tlie centres of the bodies where they receive the vente basis vertebrae. Each anterior longitudinal sj)inal vein comnuuiicates round the margin of the canal with the correspondiuir posterior vein, and it gives oft' efferent vessels which pass through the intervertebral foramina to terminate, according to the region in which they are placed, in the vertebral, intercostal, lumbar, or lateral sacral veins. Superiorly the anterior longitudinal spinal veins give off" large offsets, above the arch of the atlas, which form the commencement of the vertebral veins : through the foramen magnum they communicate with the basilar and with the occipital sinuses. The posterior longitudinal spinal veins are placed, one on each side, between the dura mater anteriorly and the laminie and ligamenta subflava posteriorly. They are plexiform vessels which extend along the whole length of the spinal canal. They receive tributaries from the lamin;v, ligaments, and s]iinal membranes, and from a post-spinal plexus of veins which lies between the lamin.o of the vertebr.e and the deep muscles of the luick : they anastomose with each other by transverse channels which pass across the laniina\ with the posterior spinal plexus bv vessels which pierce the lioamenta subflava, and with the 60 h 888 THE VASCULAE SYSTEM. ' anterior longitudinal veins round the margins of the canal. Their efferent vessels unite with those of the anterior longitudinal veins, and terminate with them. By means of the longitudinal spinal veins and the anastomoses between them, a venous ring is formed within the spinal canal opposite each vertebra. Commencing in front, opposite the body of the vertebra, where it receives the vena basis vertebra, it passes outwards to the anterior longitudinal spinal vein, turns backwards along the inner side of the pedicle and the inner surface of the lamina to the posterior longitudinal vein, and is completed by the anastomoses between the posterior longitudinal veins. This ring- communicates through the ligamenta subflava with the posterior spinal plexus, and through the intervertebral fbi'amina with the vertebral, with the dorsal tributaries of the intercostal or lumbar veins, or with the lateral sacral veins, according to the region in which it lies. Superiorly the posterior longitudinal spinal veins communicate with the occipital sinuses, and as these also commimicate with the anterior spinal veins, and the latter with the basilar sinus, a venous ring is completed round the foramen magnum. Veins of the Spinal Cord. — The veins of the spinal cord issue from the substance of the cord, and terminate in a plexus in the pia mater. In this plexus there are six longitudinal channels — one antero-median, along the anterior fissure, two antero-lateral, immediately behind the anterior nerve roots, two poster o-latercd, immediately behind the posterior nerve roots, and one postero-median, over the posterior septum. Eadicular efferent vessels issue from the plexus, and pass along the nerve roots to communicate with the efferent vessels from the anterior and posterior longitudinal spinal veins, and to terminate in them. The veins of the spinal cord vary very much in size, but they are largest on the lower and on the posterior portions of the cord. The postero-median and antero-median veins are continued above into the corresponding veins of the medulla oblongata. The antero-lateral and postero-lateral veins pour their blood partly into the median veins and partly into the radicular veins ; indeed, the greater part of the blood from the spinal cord is returned by the latter veins. THE VEINS OF THE UPPER EXTREMITY. The veins of each upper extremity are divisible into two sets — viz. superficial and deep. Both sets open eventually into a common terminal trunk which is known as the axillary vein. This vein is therefore the chief efferent stem of the upper extremity. It is continued as the subclavian vein to the innominate vein, and its blood, together with that of the corresponding side of the head and neck, reaches the superior vena cava. The Deep Veins of the Upper Extremity. The deep veins, with the exception of the axillary vein, are arranged in pairs which accompany the different arteries and are similarly named. So far as these veins (vense comites) are concerned it will be sufficient to state that they are pro- vided with valves, that they are situated one on either side of the artery with which they are associated, and that they are usually united together by numerous transverse anastomoses which cross in front of or behind the artery. The axillary vein, however, requires more detailed consideration. The Axillary Vein. The axillary vein (v. axillaris, Fig. 629) commences as the direct continuation of the basilic vein, opposite the lower border of the teres major. It passes upwards and inwards through the axilla, along the inner side of the corresponding artery, and terminates at the outer border of the first rib by becoming the subclavian vein. It possesses a Iticuspid valve which is usually situated opposite the lower border of the subscapularis muscle. Relations. — Its anterior relations are similar to those of the axillary artery, but, in addition, the vein is crossed in front, under cover of the clavicular part of the pectoralis THE SUPEKFIGIAL VEINS OF THE UPPER EXTEEMITY. 889 ■ Radial veins Commencement of median vein major, by the pectoral branches of the acromio-thoracic artery, and by branches of the internal anterior thoracic nerve, and it receives in front, just above the upper border of the pectoralis minor, the termination of the cephalic vein. Behind it are the muscles which form the posterior wall of the axilla, the axillary fat, and the fii'st ser- ration of the serra- tus magnus. The long thoracic nerve intervenes be- tween it and the serratus magnus, and the subscapu- lar nerves and the subscapular artery pass between it and the subscaiDularis. It is separated from the axillary artery on the outer side, in the lower part of its extent by the ulnar and internal cutaneous nerves, in the middle of its course by the inner cord of the brachial plexus, and in the upper part of the axilla, behind the costo - coracoid membrane, by the internal anterior thoracic nerve. To its inner side lie the outer set of axillary glands, and in the lower part of the axilla the lesser internal cutaneous nerve. Tributaries. — In addition to tributaries corre- sponding with the branches of tlie axillary artery, it receives the vense comites of the brachial artery, at the lower border of the subscapularis, and the cephalic vein, which joins it at the upper border of the small pectoral muscle. The Superficial Veins of the Upper Extremity. The superficial veins of tfie upper extremity commence in the superficial fascia of the palm and dorsum of the hand and of the fingers. The superficial veins of tiie palmar aspects of the fingers terminate for the most part in dorsal digital veins, ^vhich run along the dorso-lateral borders of the digits ; some, however, pass upwards into the palm and join the superficial palmar veins, which, in comparison with the superficial dorsal veins, are relatively few and small. The superficial veins of tlie palm anastomose togetlier, forming a more or less polygonal plexus from which some efferent vessels pass laterally round the borders of the palm to the dorsal plexus of the hand, whilst others ascend towards the wrist, where they end either in the median or the anterior ulnar superficial veins of the forearm. Fig. 652. — Superficial Veins ox the Dorsum of the Hand and Digits. 890 THE VASCULAE SYSTEM. Cephalic vein- \ TR 11 ft The superficial veins on the dorsal aspect of each digit form two longitudinal vessels, the dorsal digital veins (vv. digitales dorsales propriye), which ascend along the dorso-lateral borders of the digit. They receive tributaries from the palmar aspect of the digit, from the pulp of the tip, ^ 'y^ from the subungual tissues, and from the superficial tissues of the dorsum. The dorsal digital veins, which run along the adjacent borders of the second, third, and fourth interdigital clefts, unite, at the apices of the clefts, to form three dorsal interosseous or interdigital veins (vv. meta- carpse dorsales), which terminate on the dorsum of the hand in a dorsal venous arch or dorsal venous plexus ; the radial or outer vein of the index-finger ends in the same arch. The dorsal venous arch of the hand receives not only the dorsal interosseous or interdigital veins, and the radial digital vein of the index-finger, but also numerous tributaries from the superficial tissues of the dorsum of the hand, which anastomose frequently together and form a plexiform network. The arch lies opposite the lower parts of the shafts of the four inner meta- carpal bones, and terminates at its radial end in the superficial radial vein, and at its ulnar end in the posterior or dorsal ulnar vein ; the dorsal digital veins of the thumb open into the superficial radial vein, and the innermost or ulnar digital vein of the little finger ends in the posterior superficial ulnar vein. Superficial Veins of the Forearm. — There are four main superficial venous trunks in the forearm — viz. the median, the radial, and the anterior and posterior ulnar veins. The median vein (v. mediana cubiti) commences, as a rule, on the dorsal aspect of the base of the thumb by the union of a number of efferents from the dorsal plexus ; it turns round the radial border of the forearm, receives numerous tri- butaries from the radial and median portions of the palm, and ascends to the middle of the bend of the elbow, where it is joined by the deeip median vein, a large anastomosing channel which connects it with the deep veins, and immediately afterwards terminates by dividing into median cephalic and median basilic ])ranches. The median cephalic (v. mediana cephalica), or outer branch of the median vein, runs upwards and outwards in the groove between the biceps and the supinator longus muscles. It crosses the musculo-cutaneous nerve superficially, and terminates, a short distance above the external condyle, by uniting with the radial vein to form the cephalic vein. Median cephalic vein- Median basilic vein- Median vein- Deep median vein- Posterior ulnar vein- Radial veins] Anterior ulnar vein- Palmar jdexus- Fk;. il\\- 65-3. — Sdperficial Veins on the Flexor Aspect of the Upper Extremity. THE SUPEEFICIAL VEINS OF THE UPPER EXTEEMITY. 891 Bracliiali.s aiiticii luuscl Bicei Ceplialic vei Radial recurrent artery Musculo- cutaneous nerve The median basilic vein (y. laediaiia Ijasilica) is the inner branch of the median vein. Punning more transversely than the median cephalic vein, it passes upwards and inwards along the groove between the biceps and the pronator radii teres. It is crossed superficially by the anterior terminal branch of the internal cutaneous nerve ; it lies upon the bicipital lascia, which separates it from the brachial artery, and it terminates by uniting with the anterior and posterior ulnar veins to form the basilic vein. The radial vein (v. radialis) commences in the dorsal venous plexus of the hand, and, after receiving some of the dorsal digital veins of the thumb, runs up the radial border of the forearm in relation with the anterior di\dsieus directly into the inferior vena cava. Renal Veins (w. renales). — Each renal vein is formed liy the union of five or six trilnitaries which issue from tlic liilum of tlie kidney, wliere they lie in front of the corresponding arteries. 894 THE VASCULAE SYSTEM. The right renal vein is about one inch long ; it passes behind the second part of the duodenum, and terminates in the right side of the inferior vena cava. The left renal vein crosses in front of the left psoas, the left crus of the diaphragm, and the aorta immediately below the superior mesenteric artery. It lies behind the pancreas and the fourth part of the duodenum, and, running above the third part of the duodenum, terminates in the left side of the inferior vena cava. The left spermatic or ovarian vein, according to the sex, and almost invariably the left suprarenal vein, open into it. Lumbar Veins (vv. lumbales). — There are usually four lumbar veins on each side, one with each lumbar artery ; the vein with the subcostal artery is not included in this number. The lumbar veins are formed by the union of anterior and posterior trunks between the transverse processes of the vertebrse. The anterior tributaries commence in the lateral walls of the abdominal cavity, where they communicate with the superior and deep epigastric veins. The posterior tributaries issue from the muscles of the back in the lumbar region, and receive tributaries from the spinal plexuses. The main stems pass forwards on the bodies of the vertebrae ; on each side they run behind and to the inner side of the psoas muscle, whilst those of the left side also pass behind the aorta. They terminate in the posterior part of the inferior vena cava. Not uncommonly the corresponding veins of opposite sides unite together to form a single trunk which enters the back of the inferior vena cava. All the lumbar veins of each side are united together by a longitudinal anastomosing vessel, the ascending lumbar vein, which passes upwards in front of the transverse processes of the lumbar vertebrae, and usually ends above in an azygos vein, whilst below it connects the lumbar veins with the ilio-lumbar and lateral sacral veins. Spermatic Veins (vv. spermaticae). — The spermatic veins on each side issue from the testicle and epididymis and form a plexus, the pampiniform plexus. The plexus forms part of the spermatic cord, and consists of from eight to ten veins, most of which lie in front of the vas deferens ; it passes upwards in the inguinal canal, and, near the internal abdominal ring, terminates in two main trunks which ascend with the corresponding spermatic artery for some distance, receiving tributaries from the ureter, and, occasionally, on the left side from the iliac and pelvic colon ; ultimately the two veins unite together and a single terminal vein is formed. The terminal spermatic vein on the right side opens into the inferior vena cava, that on the left side into the left renal vein. The left spermatic veins are longer than the right, the left testicle being lower than the right, and the termination in the left renal vein being at a higher level than the termination of the right vein in the inferior vena cava. The spermatic veins on each side lie upon the psoas muscle and the ureter. They are covered by peritoneum, and they are crossed on the right side by the termination of the ileum and the third part of the duodenum, and on the left side by the iliac colon. They are provided with valves both in their course and at their terminations, but occasionally the valve at the oritice of the left spermatic vein is absent. The ovarian veins (vv. ovaricee), on each side, issue from the hilum on the anterior border of the ovary. They pass between the layers of the broad ligament, where they anastomose freely and form the pampiniforrn plexus, which extends outwards towards the brim of the pelvis. From the plexus two veins are formed which accompany the corresponding ovarian artery; they pass in front of the external iliac artery, and then upwards behind the peritoneum and in front of the psoas muscle and ureter. The veins of the right side, like the corresponding spermatic veins, also pass behind the termination of the ileum and the third part of the duodenum; whilst the left veins, near the brim of the pelvis, pass behind the commencement of the pelvic colon. The two veins on each side ultimately fuse together to form a single terminal vein which ends, on the right side in the inferior vena cava, and on the left side in the left renal vein. As the left ovarian veins ascend on the psoas they sometimes receive tributaries from the iliac and pelvic colon. THE ILIAC VEINS. 895 The Iliac Veins. The common iliac veins (Figs. 640 and 655), right and left, are formed by the union of the corresponding external and internal iliac veins. Each commences opposite the brim of the pelvis, immediately behind the upper part of the internal ihac artery of its own side, and both vessels pass upwards to the right side of the body of the fifth lumbar vertebra, at the upper part of which, just behind and to the outer side of the right common iliac artery, they unite together to form the inferior vena cava. The right common iliac vein (v. iliaca communis dextra) is much shorter than the left ; it passes in front of the obturator nerve and the ilio-lumbar artery, and at first behind and then somewhat to the outer side of the corresponding common iliac artery. The left common iliac vein (v. iliaca communis sinistra) is much longer than the right, and is also placed more obliquely. It passes upwards and to the right, in front of the body of the fifth lumbar vertebra, and across the middle sacral artery. For some distance it runs along the inner side of the left common iliac artery, and then passes behind the right common iliac artery. It also passes behind the mesentery of the pelvic colon and the superior haemorrhoidal artery. Tributaries. — Each common iliac vein receives the coi-responding external and internal iliac veins and the ilio-lumbar veins. The left common iliac vein receives in addition the middle sacral vein. The ilio-lumbar veins (vv. ilio-lumbales) receive tributaries from the iliac fossa, fi'om the lower parts of the spinal muscles, and from the spinal canal. There is a single vein on each side which accompanies the corresponding artery. Tt passes behind the psoas muscle and terminates in the common iliac vein. Middle Sacral Veins. — The vense comites of the middle sacral artery commence by the union of tributaries which issue from the venous plexus in front of the sacrum, through which they communicate with the lateral sacral veins and receive blood from the sacral part of the spinal canal. They unite above into a single stem (v. sacralis media), which terminates in the left common iliac vein. The internal iliac vein (v. hypogastrica. Fig. 640) is a short trunk formed by the union of tributaries which correspond to all the branches of the internal iliac artery, with the exception of the hypogastric or umbilical and the ilio-lumbar branches. It commences at the upper border of the great sciatic notch, and ascends to the brim of the pelvis, where it unites with the external iliac vein to form the common iKac vein. It lies immediately Ijehind and slightly to the inner side of the internal iliac artery, is crossed externally by the obturator nerve, and is in relation internally, on the left side with the pelvic colon, and on the right side with the lower part of the ileum. Tributaries. — The tributaries, which are numerous, are conveniently divisible into extra-pelvic and intra-pelvic groups. The extra-pelinc trihutaries are all parietal, and include the obturator, internal pudic, sciatic, and gluteal veins. Obturator Vein (v. obturatoria). — This vein is formed by the union of tributaries which issue from the hip-joint and from the nuiscles on the upper and inner part of the thigh. It enters the pelvis through the obturator foramen, runs backwards along the lateral wall lying on the pelvic fascia immediately below the corresponding artery, and, passing between the internal iliac artery on the outside and the xireter on the inside, terminates in the internal iliac vein. Sciatic Veins (vv. glutacpe inferiores). — The ventu comites of the sciatic artery com- mence in the subcutaneous tissues on the back of the thigh ; they ascend with the sciatic artery, and pass deeply into the buttock beneath the gluteus maximus, where they receive numerous tributaries from the surrounding muscles. Entering the pelvis through the great sciatic foramen, they unite into a single vessel, which terminates in the lower and anterior part of the internal iliac vein below the termination of the obturator vein. Gluteal Veins (vv. glutacic superiores). — The vena^ comites of the gluteal artery are formed by tributaries which issue from the muscles of the buttock. They accompany 896 THE VASCULAE SYSTEM. the artery through the great sciatic foramen, and terminate in the internal iliac vein ; they frequently unite together before reaching their termination. Internal Pudic Veins. — The venfe comites of the internal pudic ai'tery commence by tributaries which emerge from the corpus cavernosum of the penis (vv. profundee penis) or clitoris (vv. profundte clitoridis). They follow the course of the internal pudic artery, and usually join together into a single vessel (v. pudenda interna) which terminates in the internal iliac vein. As tributaries they receive the veins from the bulb, the superficial perineal and inferior htemorrhoidal veins (vv. hfemorrhoidales inferiores), and veins from the muscles of the buttock. The inferior haemorrhoidal veins, which commence in the substance of the external sphincter of the anus and in the walls of the anal canal, anastomose with the middle and superior ha^morrhoidal veins, and consequently connect the portal and vena caval systems together. The intra-ixlvic tributaries of the internal iliac vein are either (a) parietal or (6) visceral ; the former comprises the lateral sacral veins, the latter includes the efferent vessels from the plexuses ai'ound the several pelvic viscera. (a) Parietal : Lateral sacral veins (w. sacrales laterales) accompany the corre- sponding arteries, and terminate on each side in the inner and back part of the internal iliac vein. {h) Visceral tributaries are derived from the rectum and from the plexvises associated with the uterus, vagina, bladder, and prostate. They include the middle hsemorrhoidal, the uterine, the vaginal, and the vesical veins. The middle haemorrhoidal veins (vv. heemorrhoidales mediales) are very irregular ; sometimes they cannot be distinguished. When present they are formed by tributaries which commence in the submucous tissue of the rectum, Avhere they communicate with the superior and inferior lisemorrhoidal veins ; they pass through the muscular coat, and fuse together to form two middle haemorrhoidal veins, right and left, each of which runs outwards beneath the peritoneum, on the upper surface of the levator ani, to terminate in the internal iliac vein. In the male each middle haemorrhoidal vein receives tributaries from the seminal vesicle and vas deferens of its own side. Uterine Plexuses and Veins. — The uterine plexuses lie along the lateral borders of the uterus ; they receive tributaries, which are entirely devoid of valves, from the uterus, and they communicate above with the ovarian, and below with the vaginal plexuses. The uterine veins (vv. uterinee), usually two on each side, issue from the lower parts of the uterine plexuses above their communications with the vaginal plexuses. At first the uterine veins on each side lie in the inner part of the base of the bi'oad ligament above the lateral fornix of the vagina and the ureter ; they then pass backwards, accom- panying the corresponding artery, in a fold of peritoneum which lies between the back of the broad ligament and the recto-uterine fold ; finally they ascend in the floor of the ovarian fossa, and terminate in the internal iliac vein. Vaginal Plexuses and Vaginal Veins.— The vaginal plexuses lie at the sides of the vagina. They receive tributaries from the walls of the vagina, and communicate above with the uterine plexuses, below with the veins of the bulb, in front with the vesical plexus, and behind with the veins which issue from the middle and lower parts of the htemorrhoidal plexus. A single vaginal vein issues from the upper part of the vaginal plexus on each side ; it accompanies the corresponding arteries, and terminates in the internal iliac vein. Superior Vesical Plexus. — The superior vesical plexus of veins lies on the outer surface of the muscular coat of the bladder at the fundus and the sides. It receives tributaries from the mucous and muscular walls, and its efferent vessels terminate in the prostatico-vesical plexus in the male, and in the inferior vesical plexus in the female. Prostatico-vesical Plexus. — This plexus is distributed round the prostate and the neck (jf the Ijludder, and is enclosed between the proper fibrous capsule of the prostate and its sheath of recto-vesical fascia. In front it receives the dorsal vein of the penis, which usually terminates by two branches ; behind and above it communicates with the superior vesical plexus, and receives tributaries from the seminal vesicles and vasa deferentia. One or more efferent vessels pass from it on each side and open into the corresponding internal iliac vein. The inferior vesical plexus of the female, which represents the prostatico-vesical plexus of the male, surrounds the upper part of the urethra and the neck of the bladder. It receives the dorsal vein of the clitoris, and its efferent vessels terminate in the internal iliac vein. THE DEEP VEINS OF THE LOWER EXTREMITY. 897 Dorsal Veins of the Penis (w. dorsales penis). — There are two dorsal veins of the penis — tlie superficial and the deep. The superficial dorsal vein receives tributaries from the prepuce, and runs backwards immediately lieiieatli the skin tu the symphysis, where it divides into two branches whicli terminate in the superficial external pudic veins. The deep dorsal vein lies on the dorsum of tlie penis beneath the deep fascia. It commences in the sulcus behind the glans, by the union of numerous tributaries from the glans and the anterior parts of the corpora cavernosa, and runs backwards in the mid- dorsal line, in the sulcus between the corpora cavernosa from which it receives many additional tributaries. At the root of the penis the vein passes between the two layers of the suspensory ligament, and then between the sub-pubic ligament and the deep transverse ligament of the jierineum, thus reaching the space between the two layers of the triangular ligament, where it lies above the membranous part of the urethra, and is enclosed in some of the fibres of the compressor urethne. Passing through the posterior layer of the triangular ligament, it enters the pelvis, and terminates, usually liy two Ijranclies, in the prostatico-vesical plexus. The dorsal vein of the clitoris in the female has a similar course to that of the deep dorsal vein of the penis in the male. It terminates in the inferior vesical plexus. THE VEINS OF THE LOWER EXTREMITY. The veins of the lower extremity, like tliose of the upper extremity, are arranged in two groups, the superficial and the deep, and in the lower as in the upper limb the deep veins are associated with the arteries as vente comites, wliilst the super- ficial veins which he in the subcvitaneous tissues ultimately terminate in the deep veins. There is, therefore, a general similarity in the arrangement of the veins of the upper and the lower limbs, but there are differences in the details of the arrange- ment which are of some importance. Thus, in the upper extremity, there are two deep veins with each artery from the fingers to the root of the limb, w'here a single trunk, the axillary vein, is formed; but in the lower extremity each main artery has two vense comites only as far as the middle of the limb, where a single trunk is formed. This vessel, tlie popliteal vein, is the commencement of the main venous stem of the lower extremity ; it is continued upwards through the thigh as the femoral vein, and along the brim of the pelvis as the external iliac vein, which terminates by uniting with the internal iliac vein to form the common iliac vein. Further, the superficial veins of the upper hmb are more numerous than those of the lower limb, for in the forearm there are four main superficial veins, and in the leg two ; in the arm two main superficial veins, and in the thigh only one. In the upper limb the blood which passes through the superficial veins is poured into the efferent trunk vein at the root of the limb — that is, into the axillary vein ; but in the lower limb the blood from the superficies of the outer parts of the leg and foot passes into the commencement of the main efferent vein, the popliteal vein, at the middle of the limb — that is, in the region of the knee, whilst the blood from the superficial parts of the inner aspect of the lower limb is poured into the femoral vein near the root of the limb in the upper part of Scarpa's triangle. In addition to the above-mentioned differences in the general arrangement of the veins of the upper and the lower extremities, it must also be noted that in the upper extremity all the l)lood of the limb, both that from the shoulder-girdle region as well as that from the projecting portion of the limb, is returned to the main efferent venous trunk ; but in the lower extremity the greater part of the blood from the region of the pelvic girdle, and a considerable portion from that of the thigh, is returned by the gluteal, oliturator, sciatic, and pudic veins to the internal iliac vein, which in the adult is not the main efferent vein of tlie lower extremity. TiiK Deep Veins of the Lower Extremity. All the arteries of the lower limb except the popliteal and femoral trunks are accompanied by two vence comites. They usually lie one on each side of the artery ; they are connected with each other by transverse channels which pass in front of or behind the artery, and they are provided with numerous valves. 61 898 THE YASCULAE SYSTEM. The popliteal vein (v. poplitea, Fig. 643) is formed, at the lower border of the popliteus muscle, bj the union of the venae comites of the anterior and posterior tibial arteries. At its commencement it lies to the inner side of and somewhat superficial to the popliteal artery, and to the outer side of the internal popliteal nerve. As it ascends through the popliteal space it gradually inclines towards the outer side of the artery, and in the middle of the space it is directly behind the artery, separating the artery from the internal popliteal nerve, which is still more posterior, whilst at the upper end of the space it is to the outer side of the artery, Sartorius Tensor fascise femoris Superficial cir- cumflex iliac artery Eectus femoris Psoas and iliacus Profunda artery External cir- cumflex artery - Vastus externus Vastus internus Femoral artery . Femoral vein - Crural canal supeiticial ex- t rnal pudic iiteiy Deep external pudic artery Long saphenous vein Adductor longus Gracilis Fig. 656. — The Femoral Vessels in Scarpa's Triangle. and still between it and the internal popliteal nerve. It then passes through the adductor magnus muscle and becomes the femoral vein. The popliteal vein, which is provided with two or three bicuspid valves, is closely bound to the artery by a dense fascial sheath. Not uncommonly there are one or more additional satellite veins which anastomose with the popliteal vein, and in these cases the artery is more or less completely surrounded by venous trunks. Tributaries. — In addition to the vena) comites of the anterior and posterior tibial arteries, it receives tributaries which correspond with the branches of the popHteal artery, and it also receives one of the superficial veins of the leg, viz. the external or short saphenous vein. The femoral vein (v. femoralis) is the direct continuation of the popliteal vein. THE DEEP VEINS OF THE LOWEK EXTKE:\nTY. 899 — Superficial epigastric vein Superficial circumflex iliac vein --Superficial pu'lic vein -—Femoral vein Long saphenous vein External superficial femoral vein Internal superficial femoral vein It commences at the junction of the middle and lower thirds of the thigh, at the opening in the adductor magnus muscle. It then ascends through Hunter's canal, and through Scarpa's triangle, and terminates a little to the inner side of the middle of Poupart's ligament hy hecom- ing the external iliac vein. In Hunter's canal it lies liehind, and at first to the outer side of, the femoral artery, and upon the adductors magnus and longus which separate it from the profunda vessels. In the lower part of Scarpa's triangle it is behind and to the inner side of tlie artery, and immediately in front of the profunda vein which |. -' y separates it from the profunda artery, hut in the upper part of Scarpa's triangle it is directly on the inner side of the femoral artery. About one and a-half inches below Poupart's ligament it enters the middle compartment of the femoral sheath, through which it ascends to its termination, Ipug between the compart- ment for the femoral artery on the outer side and the crural canal on the inner side. It usually contains two bicuspid valves — one near its termination and the other just above the entrance of its profunda tri)3utary. ^ ^//^ ~ ^ /\ -^jMM Long saphenous vein Tributaries. — It receives tributaries (vente comites) which correspond with the branches of the femoral artery and the larger of the two superficial veins of the lower extremity, viz. the long saphenous vein, whicli entei'S the femoral vein where that vessel lies in the middle compartment of the femoral sheath. The external iliac vein (v. iliaca externa. Figs. 637, 640, and 655) is the upward continuation of the femoral vein. It commences on the inner side of the termination of the external iliac artery, immediately behind Poupart's ligament, and ascends along the brim of the pelvis to a point at the level of the lumbo-sacral articulation and oyjposite the sacro-iliac joint, and immediately behind the in- ternal iliac firtery, where it ends by join- ing the internal iliac vein to form the common iliac vein. It lies at iirst on the inner side of the external iliac artery, but on a somewhat posterior plane, and then directly behind the artery, whilst just before its termination it crosses the outer side of the internal iliac artery, and se])arates that vessel from the inner border of the psoas muscle. In its whole course the vein Ues anterior to the obturator nerve. It is usually provided with one biseupid valve, ]»ut some- times there are two. Its tributaries correspond to the Itranches of the external iliac artery ; thus the deep circumflex iliac (v. circumtlex ilium profunda) and deep X3 •■-^•~ "Long saphenous vein "Dorsal venous arch Fi,;. (Ja: — The Intkunal ou Loxi; Sai-hexous Vein and its Tributahies. 900 THE VASCULAE SYSTEM. epigastric (v. epigastrica inferior) veins open into it close to its origin, whilst in addition it frequently receives the pubic vein. The pubic vein forms a communication between the obturator vein and the external ihac vein. It varies in size, and may form the main termination of the obturator vein from which it arises. Commencing in the obturator foramen, it ascends at the side of the pubic branch of the deep epigastric artery, and reaches the external iliac veiu. The Superficial Veins of the Lower Extremity. The superficial veins of the lower extremity terminate in two trunks, one of which, the external or short saphenous vein, passes from the foot to the popliteal space ; whilst the other, the internal or long saphenous vein, extends from the foot to the groin. The superficial veins of the sole of the foot form a fine plexus, immediately beneath the skin, from which anterior and lateral efterents pass. The anterior eiferents terminate in a transverse arch which hes in the furrow at the roots of the toes, and the lateral efferents pass round the sides of the foot to the internal or external saphenous veins. The transverse arch also receives small plantar digital veins from the toes, and it gives off interdigital efferent branches to the dorsal venous arch. The superficial veins on the dorsal aspect of each toe unite together to form two dorsal digital veins (v. digitales pedis dorsales) which run along the borders of the dorcal surface. The dorsal digital veins of the adjacent borders of the interdigital clefts unite, at the apices of the clefts, to form four dorsal interdigital veins which terminate in the dorsal venous arch. The dorsal digital vein from the inner side of the great toe ends in the long saphenous vein, and that from the outer side of the little toe terminates in the short saphenous vein. The dorsal venous arch (arcus venosus dorsalis pedis) lies in the subcutaneous tissue, between the skin and the branches of the musculo-cutaneous nerve, opposite the lower parts of the shafts of the metatarsal bones. It ends internally by unit- ing with the inner dorsal digital vein of the great toe to form the long saphenous vein, and externally by joining the outer dorsal digital vein of the little toe to form the short saphenous vein. The dorsal venous arch receives the dorsal inter- digital veins ; interdigital efferents from the plantar transverse arch, and numerous tributaries from the dorsum of tlie foot, which anastomose freely together, forming a wide-meshed dorsal venous plexus, open into it behind. The internal or long saphenous vein (v. saphena magna) is formed by the union of the inner extremity of the dorsal venous arch with the inner dorsal digital vein of the great toe. It passes upwards in front of the internal malleolus, crosses the inner surface of the lower part of the shaft of the tibia, and ascends immediately Ijehind the internal border of that bone to the knee, where it lies just behind the iuternal condyle of the femur; continuing upwards, with an inclination forwards and outwards, it gains the upper part of Scarpa's triangle, where it perforates the cribriform fascia and the femoral sheath to reach its ter- mination in the femoral vein. In the foot and leg it is accompanied by the long saplienous nerve, and for a short distance below the knee by the superficial branch of the anastomotic artery. In the thigh, branches of the internal cutaneous nerve lie in close relation with it. It contiins from eight to twenty bicuspid valves. Tributaries. — It communicates freely through the deep fascia with tlie deep inter- muscular veins. In the foot it receives tributaries from tlie inner part of the sole and from the dorsal venous plexus. As it ascends in the leg it is joined by tributaries from the dorsum of the foot, the inner side and back of the heel, the front of the leg and the back of the calf, and it anastomoses freely with the short saphenous vein. In the thigh it receives numerous tributaries, some of which usually converge to form two superficial femoral veins. Of these, one, the external, ascends from the outer side of the knee and terminates in the internal saphenous vein about the lower part of Scarpa's triangle ; the other, the internal, receives a communication from the external saphenous vein, and ascends from the back of the thigh along its inner side to terminate in the long saphenous THE POETAL SYSTEM OF VEINS. 901 vein almost opposite the terminatiou of the external supcrhcial femoral vein. The last tributaries to enter the long saphenous vein are the superficial circumflex iliac, epigastric, and pudic veins. Tliey accompany the corresponding ai'teries, and terminate in the long saphenous vein immediately before the latter vessels perforate the cribriform fascia. The superficial circumflex iliac vein receives blood from the lower and outer part of the abdominal wall and the upper and outer part of the thigh. The supei-ficial epigastric vein drains the lower and inner part of the abdominal wall, and the superficial pudic vein receives blood from the dorsum of the penis and the scrotum in the male, and from the labium majus in the female. The external or short saphenous vein (v. saphena parva) is formed by the uuiou of the outer extremity of the dorsal venous arch with the outer dorsal digital vein of the little toe. At first it passes backwards along the outer side of the foot and below the external malleolus, lying on the external annular ligament in company with the external saphenous nerve ; then it ascends behind the external malleolus, and along the outer border of the tendo Achillis, still in company with the external saphenous nerve, to the middle of the calf, above which it is continued in the superficial fascia, accom- panied by the superficial sural artery, to the lower part of the popliteal space, where it pierces the deep fascia, and terminates in the popliteal vein. It communicates round the inner side of the leg with the internal saphenous vein, and through the deep fascia with the deep veins, and it contains from six to twelve bicuspid valves. Tributaries. — It receives tributaries from the outer side of the foot, from the outer side and back of the heel, from the back of the leg, and occasionally a descending tributai'y from the back of the thigh. Just before it pierces the popliteal fascia it gives off a small branch which ascends round the inner side of the thigh and unites with the internal superficial femoral vein. In this way a communication is established between the external and internal saphenous veins ; this communication is frequently enlarged, and not uncommonly constitutes the main continuation of the extei'nal saphenous vein. Fig. 658. — The ExTEKNAL on m; VEIX .-V^D JT.S TrIBL l.\i;ll.: THE POETAL SYSTEM. The portal system iucludes the veins which convey blood from almost the whole of the abdominal and pehic parts of the alimentary canal, and from the spleen and pancreas, to the liver. The tributaries of origin of these veins agree closely with the terminal branches of the corresponding arteries. They are single vessels, which for some distance accompany the corresponding arteries, and are similarly iiauiid. The larger or terminal veins, however, leave their associated arteries; the inferior mesenteric vein joins the splenic vein, and the latter unites with the superior mesenteric vein to form the portal vein, which passes to the liver. These veins, together with their tributaries, constitute the portal system. All the vessels of this system are devoid of vah'es. 61 taculum chyli. Some of them also conmiunicate with the thoracic duct. In addition to the posterior intercostal glands, smaller lateral intercostal glands are sometimes interposed in the courses of the deep vessels of the thoracic wall. They have, 924 THE VASCULAE SYSTEM. however, but little practical importance. When they are present they lie near the orio-ins of the lateral branches of the intercostal arteries. The internal mammary or sternal glands (lymphoglandulas sternales), which lie alono- the side of the internal mammary artery, one or two, as a rule, being placed opposite the anterior end of each intercostal space. Their afferents are derived from the deeper parts of the anterior portion of the thoracic wall, from the deep part of the front of the abdominal wall by vessels which ascend along the superior epigastric artery, from the inner portion of the mammary gland, and from the anterior part of the diaphragm and the anterior diaphragmatic glands. Some of their efferents pass to the anterior mediastinal glands, but the majority ascend to the root of the neck, where they terminate either directly in the corresponding innominate vein, or, according to the side on which they lie, they end in the thoracic duct, or the right lymphatic duct if it is present. The diaphragmatic glands are arranged in three groups — the anterior, middle, and posterior. The anterior group lies behind the ensiform process and the anterior ends of the seventh costal cartilages. It receives lymph from the anterior part of the diaphragm, and from the anterior part of the upper surface of the liver. Its efferents pass to the internal mammary glands. The middle group consists of two lateral portions which lie at the sides of the pericardium near the phrenic nerves. On the right side these glands are closely associated with the upper part of the inferior vena cava, and some of them lie on the anterior wall of that vessel internal to the fibrous sac of the pericardium. The afferents of the middle diaphragmatic glands are derived from the middle part of the diaphragm and from the upper surface of the liver. Their efferents join the posterior mediastinal glands. The posterior group has very little importance, and practically constitutes a lower section of the posterior mediastinal glands. It lies between the pillars of the diaphragm and the posterior wall of the thorax, and receives lymph from the immediately adjacent parts. Its efferents end in the higher posterior mediastinal glands. 2. Visceral Thoracic Glands. — Of these there are : — The anterior mediastinal glands (lymphoglandulse mediastinales anteriores) are embedded in the loose tissue of the anterior mediastinal region. They receive afferents from the middle part of the upper portion of the liver which ascend through the falciform ligament, from the anterior part of the diaphragm, and from the lower sternal glands. Their efferents pass upwards to the superior mediastinum, where some of them enter the superior mediastinal glands, whilst others, continuing upwards, terminate on the right side in the right lymphatic duct, and on the left side in the thoracic duct. The superior mediastinal glands (lymphoglandulse mediastinales superiores) are grouped round the innominate veins, along the upper part of the aortic arch, and in front of the thoracic portion of the trachea. They receive afferents from the heart, the pericardium, the thymus, and the anterior mediastinal glands. Their efferents terminate at the root of the neck in the right lymphatic and thoracic ducts. The middle mediastinal glands are situated round the primary bronchi and the lower end of the trachea, and they are separable into the following groups : — The bronchial glands, which lie principally on the anterior aspects of the primary bronchi and along their upper borders. They receive lymph from the lungs which has previously passed through a series of inter-bronchial or pulmonary glands, which lie in the angles of division of the bronchi in the hilum and in the substance of the lungs. Their efferents unite with the efferents of the superior mediastinal and internal mammary glands to form a common broncho-mediastinal trunk on each side. This vessel when it is present ends on the left in the thoracic duct or the innominate vein, and on the right in the right lymphatic duct or in •one of the large veins at the root of the neck. The inter-tracheo-hronchial glands, which lie between the primary bronchi and beneath the end of the trachea. They receive afferents from the heart and from DEVELOPMENT OF THE BLOOD VASCULAR SYSTEM. 925 the lower part of the trachea, and communicatiug vessels connect them with the bronchial glands. Their eiferents either join the broncho-rnediastinal trunk if it is present, or the thoracic or right lymphatic duct, or they end directly in one of the great veins at the root of the neck. Tlie posterior mediastinal glands (lymphoglandulse mediastinales posteriores) lie along the aorta and the cesophagus in the posterior mediastinum. They receive afferents from the posterior part of the pericardium, the posterior part of the diaphragm, and from the cesophagus. Their efferent vessels pass mainly to the thoracic duct, but some of the upper ones on the right side end in the right lymphatic duct, and a few join the bronchial glands. The deep Ismiphatic vessels of the thorax have been included in the description of the tributaries of the deep glands. As in the abdomen and pelvis, the main deep lymphatic vessels accompany the blood-vessels of the region. DEVELOPMENT OF THE BLOOD VASCULAR 8Y8TEJiL The Pericakdium, the Peimitive Aoet.e, and the Heart. A general account of the development of the primitive vascuh^r system and of the estabhshment of the fcetal circulation has been given iu a previous chapter (see p. 60 et seq.), and it is there pointed out that the earliest blood-vessels of the developing ovum appear in the vascular area of the yolk sac, i.e. outside the body of the embryo altogether. Almost simultaneously, however, two longitudinal vessels aj^pear in the embryo itself. They are formed in the splanchnic mesoderm of the pericardial area, and are easily distiuguishable before that area is carried downwards to form the ventral wall of the foregut during the evolution of the headfold. The two longitudinal vessels are the rudiments of the primitive heart and of the principal blood-vessels. The changes which take place in them, and which result in the formation of the fully developed heart and vessels, will be more easily understood after the development of the pericardial sac, together with the alterations it undergoes both as regards position and relations, have been carefully studied. Development of the Pericardium and the Primitive Aortae. — The pericardial area is i-ecognisable as soon as the mesoderm has extended over the embryonic area of the developing ovum. It is somewhat semilunar in shape, it lies at the extreme anterior end of the embryonic region, and it limits the bucco-pharyngeal area or membrane in front and at the sides (Figs. 17 and 18). The mesoderm of the pericardial area is continuous laterally with the general mesoderm of the embryonic area, but in those mammals in which a pro-amnion is formed it is separated in front from the extra-embryonic mesoderm by the pro-amniotic area, whilst in other mammals also it remains quite sej)arate from the extra- eml)ryonic mesoderm in front though it is more closely related to it. With the formation of the coelom the mesoderm of the pericardial area is separated into an upper or somatic and a lower or splanchnic layer, and it is in the latter that the two small tubes which constitute the first blood-vessels of the body of the embryo appear. The two tubes, or primitive aortaj, which run longitudinally and parallel to one another, apparently end at first blindly both in front and behind, but as development proceeds they extend backwards, one on each side of the bucco-pharyngeal membrane, and beneath the mesodermal somites, to the caudal region, behind which they pass on to the walls of the yolk sac to join the blood-vessels of the vascular area ; before ending they give off branches to the allantois. In the human embryo the yolk sac is relatively small and unimportant, and accordingly the branches which go to the allantois, or rather to the chorion along the body stalk, appear to form the more/lirect posterior continuations of the primitive vessels. The anterior end of each primitive trunk passes forwards to the anterior margin of the pericardial area, and is continued on to the yolk sac, where it also joins the vessels of the vascular area. During the formation and evolution of the headfold the pericardial area increases in size, its cavity enlarges, and both it and the bucco-pharyngeal area are reversed iu position (Figs. 27 and 49). Both these areas are carried forwards somewhat with the headfold, in which it is to be remembered the primitive foregut is included, but when the headfold is completely formed the pericardial area lies ventral to the foregut, and its primitive upjjer somatic surface is now its lower or anterior surface ; the original lower or splanchnic surface is superior or dorsal, whilst what was, at first, the anterior border of the pericardial 926 THE VASCULAE SYSTEM. area is converted into the posterior end of the reversed area, and it forms the anterior limit of the umbilical orifice. In brief, the relative positions of its several parts are reversed, and at this period the pericardial cavity which, like the area, is semilunar in shape, extends from side to side beneath the foregut, and its cornua are continuous at the sides of the foregut with the general body cavity of the embryo. Subsequently this con- tinuity is obliterated, and the pericai'dial cavity is separated from the pleuro-peritoneal part of the general body cavity or coelom. The mesoderm at the posterior end of the reversed pericardial region, where the somatic and splanchnic layers are continuous, i.e. just in front of the umbilicus, increases in thickness and forms a semilunar mass, the septum transversum, in which the liver and the ventral part of the diaphragm are formed. The latter extends mesially from the anterior wall of the body to the foregut, immediately in front of the gastric dilatation, whilst laterally it forms two falciform projections which encroach from without upon the portions of the coelom which lie at the sides of the foregut. Ultimately the lateral portions of the diaphragm pass inwards, and, fusing with the mesentery of the foregut, they separate the pleuro-peritoneal portion of the coelom into three parts — two anterior, one on each side of the foregut, thejAeural sacs, and a posterior, the 2^eritoneal cavity. When the pericardial region is completely reversed the two vessels developed in its splanchnic layer lie side by side in what is 1st cephalic aortic arcii iiow its dorsal wall. Posteriorly they are con- tinued through the septum transversum to the wall of the yolk sac. Anteriorly they are con- tinued, as the first cephalic aortic arches, through the mandibular arches which have developed at the sides of the bucco-pharyngeal membrane, to the dorsal wall of the gut, where they pass backwards beneath the paraxial mesoderm to the posterior end of the body, whence they are continued, in the human subject, along the body stalk to the placental portion of the chorion, giving off branches to the walls of the ali- mentary canal and yolk sac. These two primitive embryonic vessels are the primitive aortse. After the formation of the cephalic and caudal folds, each primitive aorta may be looked upon as consisting of three parts united by two arches : — an anterior ventral part, the anterior ventral aorta, situated partly in the septum transversum and partly in the dorsal wall of the pericardium and the root of the neck ; a dorsal part, the primitive dorsal aorta, which extends beneath the paraxial mesoderm from the dorsal end of the mandibular arch to the tail fold ; a posterior ventral part, the posterior ventral aorta, which passes to the yolk sac ; the anterior part of the posterior ventral aorta soon atrophies, and the remainder of the vessel is then prolonged from the posterior part of the ventral wall of the body to the placenta by a new branch. The two arches which unite the three main portions of each primitive aorta together are an anterior, the first cephalic aortic arch, which lies in the mandibular arch and passes from the anterior ventral aorta to the anterior end of the primitive dorsal aorta, and a posterior, the primary caudal aortic arch, which passes in the tail fold and at the side of the hind gut, from the primitive dorsal aorta to the posterior portion of the primitive ventral aorta. As development proceeds a series of transformations occurs in the various sections of the primitive aortse. These transformations are, with few exceptions, alike on the two sides, but the transformations which occur in one section are entirely different from those met with in the other sections ; therefore each part must, to a certain extent, be considered separately. Each anterior ventral aorta is divisible into three parts. The posterior part lies in the septum transversum. Posteriorly it forms the terminal portion of the vitelline vein, and carries the blood from the wall of the yolk sac. For a long time each vitelline vein remains separate from its fellow of the opposite side, but afterwards the two veins unite to form a common stem, which terminates at first in the posterior part of the heart, and subsequently in the liver. The anterior section of the posterior part of the anterior ventral aorta Anterior primitive ventral aorta Primitive dorsal aorta Vitelline vein Umbilical vein Branches to yolk sac Vitelline artery Posterior primitive ventral aorta Primary caudal arch Allantoic artery Placenta Fig. 665. — Diagram of the Primitive Vas- cular System before the Formation of THE Heart. DEVELOPMENT OF THE BLOOD VASCULAE SYSTEM. 927 Ceplialic aortic — arch Anterior veiiti-al aorta rriniitive (Jor.sal aorta vein Duct of Cuvier Cardinal vein Portal vein Brandies to. alimentary canal 1st cephalic aortic arch 2nd ceijlialic aortic arch 3rd cephalic aortic arch —4th cephalic aortic arch 5th cephalic aortic arch Bulbus arteriosus\ •Ventricle I A • I -Hear Auricle j Sinus venosus J Umbilical vein rapidly enlarges and unites witli its fellow of the opposite side to form the sinus venosus or posterior chamber of the primi- tive heart ; after a time this grows forwards out of the septum into the pericardium, and is absorbed into the auricular portion of the heart. The middle part of the anterior ventral aorta lies in the dorsal wall of the pericardium and projects Vertebral artery forwards into its cavity. It lies subclavian artery close to its fellow of the opposite Pnmitive jugular side, and as the two vessels rapidly enlarge their inner walls approach each other, and, fusing together, form a single median vessel which constitutes the primitive heart (the sinus venosus being excepted) in- cluding the bulbus arteriosus, the latter being afterwards developed into the roots of the pulmonary and aortic vessels. The anterior portion of the an- terior ventral aorta is embedded in the tissues at the upper or anterior part of the pericardium, that is, at the root of the neck. At first it is connected with the primitive dorsal aorta by a single cephalic aortic arch, but afterwards three, and eventually four, additional arches connect it with the anterior part of the primitive dorsal aorta. As the neck lengthens this part of the anterior ventral aorta is elongated. For the greater part of its extent it remains separate from its fellow of the opposite side, and it takes part in the formation Posterior ventral aorta Caudal aortic aroli _ Hypogastric artery Fig. 666. — Diagram op the Primitive Blood-vessels after the formation of the heart. Primary caudal arches Dorsal ^orta> 7th pair of segmental arteries Post-costal anastomoses 1st pair of segmental arteries Umbilical vein Branches to yolk sac Vitelline artery Isl cephalic aortic arch ;iid cephalic aortic arch 3rd cephalic aortic arch jth cephalic aortic arch th cephalic aortic arch iulbus arteriosus utricle Yolk sac Auricle Sinus venosus Vitelline vein Fui. 667. — DiAGKAM OF THE VKIMITIVE BLOOD-VESSELS AFTER THE FORMATION OK THE HeART. BUT REKOHE ITS SUBDIVISION BY SEPTA INTO AUBICLES AND VENTRICLES. of the great vessels of the head and neck. Posteriorly, however, it unites with its fellow of the opposite side to form the apex of the bulbus arteriosus. After the completion of 928 THE VASCULAE SYSTEM. the cephalic aortic arches the portions of the anterior ventral aorta which lie between their lower extremities are known as the ventral roots of the cephalic aortic arches. The primitive dorsal aorta may be conveniently divided into two parts. The anterior part extends from the dorsal end of the first cej)halic aortic arch to the root of the fore- limb. It remains separate from its fellow of the opposite side, and forms the dorsal roots of the cephalic aortic arches of its own side. It takes part in the formation of the great vessels of the head and neck and, on the left side, of part of the aorta of the adult. The remaining portion extends from the root of the fore-limb to the pelvic region ; it passes inwards, and unites with its fellow of the opposite side beneath the vertebral column to form the greater part of the permanent systemic aorta. The primary caudal arch connects the primitive dorsal with the posterior ventral aorta. As it passes ventrally it lies on the inner side of the Wolffian duct. After a time it is replaced by a secondary caudal arch which lies at the outer side of the Wolffian duct, and this subsequently becomes the common and internal iliac arteries and the root of the hypogastric artery, the external iliac being merely an offset from it to the hind-limb. The greater part of the primitive posterior ventral aorta disappears early, and its secondary continuation to the placenta becomes the remainder of the hypogastric artery, which passes from the internal iliac artery, by the side of the bladder and along the ventral wall of the abdomen, to the umbilicus, whence it is continued along the umbilical cord to the placenta. Having considered thus briefly the main parts of the primitive aortic vessels, and having noted, shortly, the fate of each portion in the subsequent phases of development, we may now turn to a more detailed consideration of the metamorphoses which occur in those , parts of primitive vessels, viz. the anterior ventral aortse, the cephalic aortic arches, and the anterior parts of the primitive dorsal aortse, where most striking and most complicated trans- formations result in the formation of the heart, the aorta in part, the pulmonary artery and its primary branches, the chief arterial trunks of the head and neck, and the first part of the main artery of the right upper extremity. vv. Fig. 668. — Development of the Heart. Diagram showing the changes of form and external appearances at different stages. Modified from His's models. III.B and IV. B are side views ; the other figures represent the heart as seen from the front. A, Auricle ; A.B, Aortichulb ; A.C. Auricular canal ; A.P, Auricular appendix ; L.V, Left ventricle ; O.A.C, Opening of auricular canal; P.V. A, Primitive ventral aorta ; R.V, Right ventricle ; S. V, Hinus venosus ; V, Ventricle ; V. V, Vitelline veins. inwards, their inner walls come in contact, single median tube is formed. This is the Development of the Heart, of the FIRST part of the AoRTA, AND OF THE Pulmonary Artery. Of the three parts into which each anterior ventral aorta is divisible the middle is situated in the splanchnic mesoderm of the dorsal wall of the pericardium. As development proceeds the middle parts of both anterior ventral aortee enlarge and project into the cavity of the peri- cardium, whilst at the same time they grow fuse together, and disappear, and so a simple primitive heart, which is completed in front DEVELOPMENT OF THE HEAET AND AOKTIC BULB. 929 and behind the pericardium ])y the fusion of the adjacent ends of the anterior and posterior parts of the anterior ventral aortte. The simple tubular heart, at first straight and of fairly uniform calibre, soon alters in form and in the relative position of its different parts. It becomes irregularly enlarged, and a series of four dilatations, with intervening constrictions, can be distinguished. The dilatations, from behind forwards, are as follows : — (1) the sinus venosus or saccus reuniens, (2) the auricle or atrium, (3) the ventricle, atid (4) the aortic bulb or bulbus arteriosus. The short constriction between the auricle and ventricle is known as the auricular canal, and tlie less pronounced constriction which intervenes between the ventricle and the aortic bulb is termed the fretum Halleri. In addition to this alteration in form, the tubular lieart elongates, much more so than the pericardium in which it lies, whilst at tlie same time the anterior extremity of the aortic bulb and the sinus venosus are withdrawn, from the root of the neck and the septum transversum respectively, into the pericardium. Of necessity, therefore, the single lieart is bent upon itself, and it projects more and more into the pericardium, pushing forwards the visceral layer of the serous lining of this cavity, and carrying with it a mesentery of splanchnic mesoderm which is known as the mesocardium. The bending of the heart results in the formation of a U-shaped loop, the posterior or venous limb of the loop lying to the left and below, with the body in the erect posture, the anterior or arterial limb being to the right and above, whilst the intervening stem of the loop runs from the left and below upwards, forwards, and to the right. The apex of the aortic bulb is bent a little to the left and reaches the middle line. Subsequently the auricle ascends behind the ventricle, and the ventricular opening of the auricular canal, the short communicating passage between the auricle and ventricle, is seen as a transverse slit at the upper part of the left or posterior end of the ventricle. As the ventricular chamber enlarges its upper end passes towards the middle line, and the ventricle is no longer so obliquely directed from left to right but lies more in the mesial plane. As the result of these changes of position, and the coin- cident modifications in size of the different parts, the aortic bulb is eventually placed immediately in front of the auricle, and the opening of the auricular canal is nearer the middle of the upper part of the posterior wall of the ventricular chamber. During its further growth the ventricle enlarges principally at its anterior or ventral part ; the dorsal part is not materially altered in position, and consequently the openings of the auricular canal and the aortic bulb remain relatively close together. The aviricle increases in size by lateral expansion and by forward extension of its lateral angles ; the forward extensions embrace the sides of the aortic bulb, and constitute the rudimentai-y auricular appendages. In the meantime the mesocardium disappears and the heart lies free in the pericai'dium except at its extremities. DivisiOxN[ OF THE Heart into its different Chambers, and Division of THE Aortic Bulb; Whilst the changes in form, position, and size of the different sections of the primitive heart, which have just been described, are taking place, the division of the heart cavity into its four permanent chambers, and of the aortic bulb into its aortic and pulmonary portions commences. These divisions are brought about by the growth of septa in the ventricle, auricle, and aortic bulb, and by the thickening and fusion of the middle portions of the upper and lower walls of the auricular canal. The thickenings of the walls of the auricular canal are called endocardial cusMons ; they meet and fuse together mcsially to form tlie septum intermedium by which the central portion of the canal is obliterated, whilst the lateral portions are left patent as small triangular channels which still connect the auricular and ventricular chambers. The separation of the ventricular part of the heart into right and left chambers is indicated, externally, at a very early period, by a groove, well marked in front and below, but less distinct behind where it runs upwards to the auricular canal ; whilst internally, in a corresponding position, a ventricular septum (s. inferius) grows upwards from the inferior part of tiie ventricular wall. The postcrioi- part of the upper border of this septum unites witli the lower end of the fused endocardial cusliions of the auricular canal : the anterior part of its upper border terminates a sliort distance below the orifice of the aortic bulb, where it unites witli tlie septum of the aortic bulb whicli, at a later period, descends to meet it. The division of the aortic bulb commences at its distal end between the orifices of the fourth and fifth cephalic aortic arches. It is due to the ingrowth of two endocardial 63 930 THE VASCULAE SYSTEM. thickenings which meet and fuse together from their distal to their proximal ends, forming a septum which divides the interior of the aortic bulb into two parts, and then projects downwards into the ventricular chamber till it meets and fuses with the anterior part of the upper border of the ventricular septum. The upper or distal part of the septum of the aortic "bulb commences from the dorsal wall of the cavity between the fourth and iifth cephalic ai'ches, and it is placed transversely, but its lower end lies more antero-posteriorly, therefore it twists spirally as it descends, and as a result the right part of the ventricle is thrown into continuity with the fifth cephalic aortic arches, whilst the left part of the ventricle retains continuity with the remaining cephalic aortic arches. After the septum of the aortic bulb is completed, grooves appear along its margins on the surface of the bulb ; the grooves deepen until they divide the septum and consequently the bulb into two parts ; the part in connexion with the right ventricle and the fifth aortic arch becomes the pulmonary artery, and the part in connexion with the left ventricle and the remaining arches becomes the ascending aorta. The separation of the primitive auricle into right and left portions is indicated externally by the appearance of a groove on the upper and posterior wall ; opposite this 7th segmental artery Dorsal aorta Vertebral artery Basilar artery Posterior cerebral artery Middle cerebral artery Inferior vena caval blood- stream Anterior cerebral artery Interauricular septum Fig. 669. — Development of the Heabt and the Main Arteries. Diagram of the heart, showing the formation of its septa, and of the cephalic portion of the arterial system. groove an auricular septum grows downwards in the interior of the auricle. Its lower border gradually approaches the endocardial cushion in the auricular canal, and for a time a small opening is left between the upper ends of the fused endocardial cushions and the lower edge of the septum. This is the ostium primum ; it is closed by the fusion of the septum with the endocardial cushions, but before its closure is completed an aperture appears in the upper part of the septum ; this latter aperture, the ostium secundum, becomes the foramen ovale. A second auricular septum, the septum secimidum, grows downwards to the right of the first septum ; its lower margin passes the foramen in the septum primum which is called the foramen ovale, but stops some distance from the posterior wall of the auricle, and this margin constitutes the limbus Vieussenii. The limbus Vieussenii forms the upper and anterior boundary of a depression in the auricular septum w^hich is called the fossa ovalis. The floor of the fossa is formed by the primary septum, and the foramen ovale which lies at the upper part of the fossa is closed after birth by the fusion of the primary and secondary septa. The sinus venosus, which in the early stages receives the vitelline veins from the yolk sac, the allantoic or umbilical veins from the placenta, and the ducts of Cuvier which return the blood from the Wolftian bodies and the body of the embryo, is also divided into two parts by the formation of a ledge-like projection from its posterior wall and the lower end of the septum secundum of the auricle crosses the ledge between the DIVISION OF THE HEART AND AOETIG BULB. 931 two parts and becomes continuous with the Eustachian valve along the anterior margin of the inferior vena cava. The sinus venosus lies at first below and behind the auricle, with which it communicates freely. It is gradually divided into a large right and a small left cornu, and its orifice of communication with the auricle is constricted, and ultimately it is transformed into a cleft which opens from the right end of the sinus into the back of Internal jugular vein External jugular vein Vertebral artery Subclaxian artery Subclavian vein Innominate veins Right pulmonary artery Superior vena cava Vena azygos major Right auricle Right ventricle Hepatic vein Inferior vena cava — Intercostal veins Obliterated portion of the right cardinal vein Stem foiTiied by fused vitelline veins Lumbar vein Coiiinion iliac artery External iliac artery Internal iliac arterv 1st cephalic aortic arch (obliterated) Internal carotid artery 2nd cej)halic aortic arch (obliterated) External carotid 3rd cephalic aortic arch forming part of internal carotid Vertebral artery Subclavian artery 4th cephalic aortic arch fonning arch of aorta Left superior intercostal vein Ductus arteriosus (part of tlie filth aortic arch) Pulmonary artery Vena azygos minor superior Left auricle Left ventricle Vena azygos minor inferior Ductus venosus Dorsal aorta Obliterated left cardinal vein Renal vein Umbilical vein H Placenta Allantoic arteries Fig. 670. — Diagram of the Couhse of the Fcetal CntcuLATioN. the right part of the auricular chamber ; the cleft is guarded by two lateral valve-like folds of endocardium, the right and left venous valves, which become continuous above with a transitory downward projection from the roof of the auricle, known as the septum spurium. The orifice of communication is divided into two parts as the right part of the cavity is absorbed into the auricle. The left part of the orifice becomes the opening of the coronary sinus and the right is opened out as the right part of the sinus is absorbed into the auricular cavity. In the early stages the veins of the two sides opened into the corresponding sections 932 THE VASCULAE SYSTEM. of the sinus venosus, but numerous transformations, which are described in the account of the development of the veins, occur, and finally all the veins, except the left duct of Cuvier, open into the right end of the sinus, and ultimately into the auricle as the right part of the sinus is absorbed into it ; the left part of the sinus becomes a mere appendage of the right, and is transformed into the coronary sinus which receives the blood from the walls of the adult heart. Thus, when the development of the heart is completed, all the large veins which reach the heart, with the exception of the pulmonary veins, open into the right auricle, and into that part of the chamber formed by the absorption of the right end of the sinus venosus. Indications of the primitive separation of the auricle from the sinus venosus are still recognisable in the adult, as the sulcus terminalis on the exterior, the corre- sponding crista terminalis in the interior, and the Eustachian and Thebesian valves ; the Eustachian valve is a remnant of part of the valvular fold which was situated at the right margin of the slit-like aperture of communication between the sinus venosus and the auricle, whilst the valve of Thebesius represents a fold of endocardium. The valves which guard the auriculo-ventricular orifices are downgrowths from the lower end of the auricular canal. The valves of the pulmonary and aortic apertures are preceded by four endocardial thickenings at the lower end of the aortic bulb^anterior, posterior, and two lateral. As the septum of the bulb descends it fuses with the middle parts of the lateral thickenings ; thus, when the septum of the bulb has descended below the lower orifice of the bulb, dividing it into aortic and pulmonary apertures, three endocardial thickenings are found in each aperture, one anterior and two posterior in the pulmonary aperture, and the reverse in the aortic orifice. From these thickenings the semilunar valves of the aortic and pulmonary apertures are developed, and they retain their original positions until after the sixth month of foetal life ; ultimately, however, they are twisted round, so that in the adult the pulmonary valves are placed two in front and one behind, and the aortic one in front and two behind. The Aortic Arches — Formation of the Chief Arteries. The aortic arches at the head end of the embryo connect the aortic bulb and the ventral aortse in front of the bulb with the corresponding parts of the primitive dorsal aortse. The arches, ten in number, are arranged in pairs. There are, therefore, five arches on each side, and they are distinguished from before backwards by their numerical designation. ^ The first is formed during the development of the head fold by the bending of the primitive aorta ; it lies at the side of the bucco-pharyngeal area, and subse- quently in the substance of the mandibular arch. The remaining aortic arches are formed quite difl^erently, and grow dorsally through the substance of the remaining visceral arches, as these are formed in regular succession in the side wall of the pharyn- geal portion of the foregut. The second springs directly from the anterior ventral aorta, and passes through the hyoid arch to the dorsal aorta, but the third, fourth, and fifth spring by a common trunk from the apex of the aortic bulb. Subsequently, however, and as the neck grows forwards, the anterior ventral aorta is elongated, and the third and fourth arches arise separately from it. At this later period, therefore, four vessels, two on each side, spring from the aortic bulb, viz. the two fifth arches and the two anterior ventral aortse from which the anterior four pairs of arches arise. When the septum of the aortic bulb is developed, the bulb is divided into two parts, one (the pulmonary artery) connecting the fifth arches with the right ventricle, and the other (the ascending aorta) connecting the ventral aortic stems, and thraugh them the first, second, third, and fourth pairs of arches, with the left ventricle. Each cephalic aortic arch is connected with the arch immediately behind it by a dorsal root, and in the cases of the first three arches by a ventral root also ; but the venti'al root of the fourth arch connects it with the aortic bulb. The dorsal and ventral roots of the arches are simply portions of the primitive ventral and dorsal aortas, which are so named merely for descriptive purposes. From the dorsal roots a series of segmental branches are given off, which pass dorsally, between the rudiments of the transverse processes of the cervical vertebrae, to supply the spinal cord and its membranes and the muscles and fascise of the back. The five pairs of arches do not all persist in their entirety, but remains of each are ' In some of tlie lower forms six aortic arches have beau recognised, and it is possible that what we know as the fifth in the human subject corresjjonds with the sixtli, the fifth not being formed, or jDOssessing only a very transitory and rmlimentary existence. THE BRANCHES OF THE PEIMITIVE DOESAL AOET^. 933 found even in the adult. The first and second pairs disappear almost entirely; from the ventral ends of the first arches, however, the supei-ficial temporal, the internal maxillary, the lingual and the facial artei'ies are formed ; whilst from the ventral ends of the second arches the ascending pharyngeal, posterior auricular, and occipital arteries are derived. On each side the ventral roots of the first and second arches persist as the stem of the corresponding external carotid arter}'. The internal carotid is formed by the third arch together with the dorsal I'oots of the second and first arches, and is continued forwards to the cereljrum by an outgrowth from the anterior end of the dorsal root of the first arch. The ventral root of the third arch becomes the common carotid artery. The dorsal root of the third arch disappears. On the right side the ventral root of the fourth arch forms the innominate artery, and the arch itself is converted into part of the subclavian artery, whilst the dorsal root disappears. On the left side the ventral root of the fourth arch forms the small portion of aorta which lies between the innominate and left common carotid arteries. The left fourth arch itself and its dorsal root form the arch of the aorta from the origin of the left carotid artery to the attachment of the ductus arteriosus. The ventral portion of the fifth arch on each side remains as the first part of the cor- responding pulmonary artery. The dorsal part disappears early on the right side, but on the left side it persists and remains patent up to birth as the ductus arteriosus. After birth it is obliterated and transformed into a fibrous cord. The fate of the primary caudal arches, their secondary successors, and that of the posterior ventral portions of the primitive aorta?, has already been fully considered (p. 928). The Primitive Doesal Aort^e — Formation of the Descending Aorta. Coincidently with the development of the cephalic aortic arches the anterior portions of the dorsal sections of the primitive aortfc are converted into the dorsal roots of the aortic arches. As already pointed out, certain parts of these disappear entirely, wliilst other parts are utilised in the formation of the pei'manent vessels. Behind the fifth arches the two primitive dorsal aortfie remain separate as far back as the root of the fore-limb. To this extent the right vessel disappears, whilst the left remains and forms a portion of the descending aorta. From the roots of the fore-limbs backwards to the caudal arches the dorsal aortse fuse together, beneath the vertebral column, to form the remainder of the descending aorta. The Branches of the Primitive Dorsal Aortj^. Each primitive dorsal aoi'ta gives oft' from its dorsal surface a series of somatic seg- mental arteries, from its sides aii irregular series of intermediate (visceral) branches, and from its ventral surface a group of segmental splanchnic branches to the walls of the alimentary canal, see (Figs. 677 and 678). The somatic segmental arteries divide into ventral and dorsal branches which accom- pany the posterior and anterior primary branches of the spinal nerves respectively, and the ventral branches give off lateral off'sets. The various branches of the somatic seg- mental vessels anastomose freely together. The splanchnic segmental arteries also anastomose freely together. Ultimately, from the somatic vessels and their branches and anastomoses are developed the vertebral, the basilar, and the spinal arteries : part of the right s\ibclavian artery, the whole of the left subclavian artery, and their continuations in the fore-limbs : the intercostal and lumbar arteries, and the internal mammary and deep epigastric arteries; whilst from the splanchnic segmental arteries the majority of the blood-vessels which supply the alimentary canal arc developed. The intermediate visceral arteries supply the organs derived from the inter- mediate cell mass, viz. the suprarenal capsules, the kidney, and the ovaries or testicles ; but for a full account of the transformations which the various vessels and anastomoses Tuidergo, reference must be made to the account of the morphology of the arteries. The Arteries of the Limbs. Little is known of the precise details of the development of the arteries of the limbs, but there is not much doubt that they are formed almost entirely by prolongations of or from somatic segmental arteries or their branches. The chief arterial stem of each upper extremity is represented by the subclavian, the axillary, the brachial, and the anterior interosseous arteries ; these vessels form a con- tinuous trunk which is developed, on the left side entirely and on the right side mainly, 934 THE VASCULAE SYSTEM. from the coi*responding seventh somatic segmental branch of the primitive aorta, from its ventral branch, and from the lateral offset of the latter. It is indeed the lateral offset of the ventral branch, growing outwards into the developing limb, which forms the prolongation of the stem. The root of the right stem vessel, constituted by the right subclavian artery from its origin almost as far as the point at which the right vertebral artery arises, is formed by the fourth right aortic arch ; on the left side the fourth arch takes no part in the formation of the subclavian artery. In the lower limbs the primary main arterial stem, on each side, is represented by the sciatic, the popliteal, and the peroneal arteries. The sciatic artery arises from the caudal arch, and it, together with its prolongation through the popliteal space and leg, is probably formed from a somatic segmental vessel, but to which parts of this it corresponds is not clear. The external iliac artery, prolonged into the limb as the femoral artery, is developed at a later period than the sciatic artery. It arises from the caudal aortic arch above the origin of the sciatic artery, and, like the latter trunk, is probably a modified somatic segmental vessel. The femoral artery soon after its formation unites with the primary main stem, at the upper part of the popliteal space ; the sciatic artery then atrophies and loses its connexion with the popliteal artery, and ultimately a permanent chief stem vessel is formed, which includes the external iliac, the femoral, the popliteal, and the peroneal arteries, and obviously it repi'esents the two somatic segmental vessels by which it is formed. Both in the upper and in the lower limb, branches which attain a large size are given off from the main stem artery a short distance beyond the joint between the upper and middle sections of the limb, i.e. below the elbow in the upper limb and below the knee in the lower limb, and on account of the relatively great en- largement of these branches the continuity of the original stem is obscured. Thus it is that, in the adult, the brachial artery, the direct continuation of the stem which is divided into subclavian, axillary, and brachial sections, appears to terminate by dividing into the radial and ulnar arteries, whilst originally it was continued through what, in the adult, is the upper part of the ulnar artery to the anterior interosseous artery; the posterior interosseous, the radial, and the ulnar arteries being merely branches from the main stem. Similarly, in the lower extremity the popliteal artery, which is the continuation of the original stem artery, appears to terminate in the adult by dividing into the anterior and posterior tibial arteries, both of which in reality are branches from the sides of the main stem which was continued to the foot as the peroneal artery. Lateral sinus Primitive jugular vein Internal jugular vein _ Subclavian " vein Primitive jugular vein Duct of Cuvier Cardinal vein Vitelline vein Umbilical vein —External iliac vein , Cardinal vein (internal iliac) Fig. 671. — Development of the Venous System (Diagrammatic). Stage I. — Tlie ducts of Cuvier, the vitelline veins, and the umbilical veins open directly into the heart. DEVELOPMENT OF THE VEINS. Simultaneously with the formation of the arteries by which the blood is distributed to the embryo and to the rest of the ovum, and in a similar manner, a series of vessels is developed by means of which the blood is returned to the heart. These vessels are the veins, of which there are two main groups. One group returns blood from the abdominal viscera and the annexa (the yolk-sac and allantois) ; the other group includes the vessels which return blood from the Wolffian bodies, the body wall, the head and neck, and the limbs of the embryo. The first group consists of the vitelline, allantoic, and portal DEVELOPMENT OF THE VEINS. 935 veins ; the second group includes tlie primitive jugular and the cardinal veins and the ducts of Cuvier, The ti'unks of the vitelline veins are formed by the posterior parts of the anterior primitive ventral aorta), and necessarily they open into the posterior part of the heart (sinus venosus). They collect blood from the yolk-sac, and ascend along the vitello- intestinal duct to be continued upwards along the sides of the duodenum. Three transverse anastomoses soon form between them, of which the lower and the upper are in front of and the middle is behind tlie duodenum ; thus two vascular circles are formed round that portion of the gut. Whilst the loops are being formed the liver grows rapidly, and it interrupts the direct con- nexion of the vitelline veins with the heart. When the upper vascular loop is established the two vitelline veins, which appear to be prolonged from its sides, enter the liver and bi'eak up into capillaries, from which two new vessels arise which carry the blood to the sinus venosus. The veins which carry the blood to the liver are now known as the venae advehentes ; they become the right and left divisions of the portal vein. The vessels which carry the blood to the sinus venosus are the venae reve- hentes, and they become the hepatic veins. From the inferior part of the lower venous circle the vitelline veins fuse into a common stem which receives the veins from the abdominal portion of the gut, and this, together with the left half of the lower loop, becomes the superior mesenteric vein, which passes in front of the third part of the duodenum and there receives the splenic vein. The middle anastomosis and the right half of the upper loop become the portal vein. The iipper anastomosis and the left vena advehens become the left branch of the portal vein. The right vena advehens forming the right branch, and the left half of the upper and the right half of the lower loop disappeai*. The allantoic or umbilical veins com- mence in the placenta and fuse into a single stem which traverses the umbilical cord to reach the embryo, and divides at the umbilicus into right and left divisions. The two veins tlien pass through the septum transversum, one to the right and the other to the left, and open into the sinus venosus. Lateral sinus External jugular vein Internal jugular vein Subclavian vein Transverse anastomosis Lower part of primitive jugular vein Duct of Cuvier Cardinal vein Transverse anastomosis Vena revehens Liver Vena advehens Umbilical vein Stem formed by fused ^^te^ine veins " Renal vein Transverse anastomosis External iliac vein . — Development of the (Diagrammatic). Venous System After a very short period the communica- Stage II.— The vitelline and umbilical veius terminate in tions with the sinus are obliterated, and ^lie liver and transverse auastomoses have formed , ,, . 1 • J, -11 ■ r betweeu the vitellme, cardinal, and primitive jugular both vems end m the venous capillaries of ..gj^g ^f opposite sides. the liver, the blood they convey now pass- ing to the sinus venosus by the hepatic veins. This condition also is only transitory, for the right vein soon undergoes complete atrophy and disappears, whilst the left opens into the upper loop of the vitelline veins. In the meantime, however, another channel, the ductus venosus, has been developed, which passes directly from the upper loop of the vitelline veius, or rather from the left vena advehens to the right hepatic vein, and by this channel the greater part of the placental blood passes to the heart without traversing the liver substance. Some of the ])lacental blood, however, goes to the liver by the left vena advehens. Finally the left vena revehens loses its connexion with the sinus venosus and opens into the right vena revehens. The left umbilical vein and the ductus venosus remain pervious until birth, when the placental circulation ceases. The two vessels then rapidly atrophy, and are subsequently represented by fibrous cords, of which that formed from the left umbilical vein is known as the round ligament of the liver. 936 THE VASCULAE SYSTEM. Lateral sinus Internal jugular vein ■External jugular vein •Subclavian vein Transverse anastomosis Cardinal vein -Duct of Guvier ■Transverse anastomosis Vena revehens The primitive jugular and cardinal veins, and the ducts of Cuvier, which constitute the main veins of the "Wolffian body, and of the body wall, head, neck, and limbs of the embryo, are represented in the adult by the external jugular veins, the whole of the right and part of the left innominate veins, the superior vena cava, the azygos veins, the left superior intercostal vein, part of the inferior vena cava, the right common iliac vein, a small part of the left common iliac vein, and both i-ight and left internal iliac veins. The primitive jugular vein of each side returns blood from the head and neck, and corresponding upper extremity, and it terminates below by fusing with the cardinal vein to form a coirimon trunk, the duct of Cuvier, which opens into the sinus venosus. Each cardinal vein returns blood from th e body w^all, the Wolffian body, and the lower extremity of its own side. Numerous transverse anastomoses are developed between the primitive jugular and cardinal veins of opposite sides, and of these four are specially important, one between the primitive jugular veins and thi-ee between the cardinal veins ; the former becomes the left innominate vein ; of the latter, the upper two become the transverse parts of the upper and lower smaller azygos veins, and the third forms the left common iliac vein. As these transverse channels develop further changes occur in the primitive jugular and cardinal trunks. At first" the upper extremity of the primitive jugular vein is in direct continuity with the venous sinuses of the cranium through an aper- ture, the post-condyloid foramen, in front of the external ear ; but this continuity is destroyed, and the aperture in the skull closes as soon as a new vessel, which becomes the internal jugular vein, has grown upwards from a point on the inner side of the primitive jugular trunk and has established a communication with the lateral sinus through the jugular foramen. This vessel rises behind the sterno-clavicular joint, just opposite to, or slightly below, the entrance of the subclavian vein into the outer side of the primitive jugular vein. With the exception of its upper extremity, the whole of the primitive jugular vein remains on both sides in the adult. On the right side, above the transverse anastomosis between the two primitive jugular veins which becomes the left innominate vein, it forms the external jugular vein, and that portion of the right subclavian vein which inter- venes between the external jugular and internal jugular veins, and also the right innominate vein ; below the anastomosis it forms the upper part of the superior vena cava, the lower part of the latter vessel from the entrance of the vena azygos major downwards repre- senting the right duct of Cuvier, which, though it is placed transversely in the early stages, becomes more vertical as the heart descends in the thoracic cavity. On the left side above the transverse anastomosis it forms the external jugular vein, the innermost part of the subclavian vein, and a small part of the left innominate vein ; the main part of the latter vessel being formed, as before stated, from the transverse anastomosis. The Vena advehens Umbilical vein ■Splenic vein uperior mesenteric vein itelline vein Transverse anastomosis External iliac vein Fig. 673. — Development of the Venous Systeji (Diagrammatic). Stage III. — The right umbilical vein has disapiieared, and the superior mesenteric and splenic veins have joined the fused vitelline veins. DEVELOPMENT OF THE VEINS. 937 Right innominate vein Superior vena cav Vena azvsos ma, Right hepatic vein Lett hepatic vein Right brancli of portal vein Inferior vena ca^ a Ductus venosus Left branch of portal vein Umbilical vein portion of the left primitive jugular vein which lies below the anastomosis is represented in the adult by the upper part of the left superior intercostal vein.^ The portions of the cardinal veins lying Ijclow the transverse anastomosis which becomes the left common iliac vein remain ; that on the right ^ \ forms the right internal and I >y \ ^^ — lateral sinus common iliac veins, but the ^^i^^i/ ^\ left formsonl}^ the left internal ^^ l\ iliac vein and a small part of I , , , . , • i! // 1 Internal jiignlar vein the left common iliac vein, for the transverse anastomosis commences on the left side almost opposite the point of entrance of the external iliac subclavian vein, whilst it terminates on ^'*'"' the right side at a higher level. From the left common iliac vein to the renal vein the cardinal vein of the left side disappears ; that on the right side becomes the lower part of the inferior vena cava, to which the blood passes from the left side of the ab- dominal wall by means of small transverse anastomosing channels which existed be- tween the cardinal veins, and which persist as the terminal portions of the left lumbar veins. Above the renal veins part of the right cardinal vein persists as the vena azygos major, and the left forms the upper and lower minor azygos veins and the lower part of the left superior intercostal vein. The azygos minor veins open into the azygos major by the two transverse anastomosing channels which form between the upper parts of the cardinal veins. The up[)cr i)art of the inferior vena cava is de- veloped as an outgrowth from the common trunk formed by the fusion of the ductus venosus with the risrht hepatic ,^. vein. It grows dowinvards, '^''«- 674.-Development of the Venous System (Diagi'ammatic). behind the liver and along the ^^^?'^ IV.-The left umbilical has joined the upper part of the left .,,._] - ,, ,"-, , vitelline vein ; tile ductus veuosus and the upper part ot the inlcnor rignt Siae Ot tllC VCrteoral ^.^^^^ ^^^^ j,.^^.g .,ppearea, and portious of the primitive jugular and column, to the interval be- cardinal veins have atrophied, tween the kidneys, where it divides into two brandies, of which the right anastomoses with the right cardinal vein ^ The account wliicli has been given of the primitive jugular veins is that which has been generally accejtted for many years, but in 1895 Salza's observations on the guinea-pig led him to dispute the correctness of the description, and flail's recent investigations on human embryos confirm Salza's work. From the results of the investigations of these observers it appears that the external jugular vein is a secondary vein, and the internal jugular is part of the primitive jugular which originally e.xtended forwards to the anterior end of the superior longitudinal sinus. Its connection with the sinus is soon lost, and the only intracranial remainder of the primitive vein is the cavernous sinus. Supi'aren; Renal vein Spermatic ■Spermatic vein Inferior vena cava Right common iliac veil Right external iliac Right internal iliac vein Left common iliac vein Left external iliac vein Left internal iliac vein Middle sacral vein 938 THE VASCULAE SYSTEM. at the level of the reual vein ; it receives the suprarenal vein, and it terminates in a tapering extremity which is said to become the spermatic vein of the right side. The left branch passes across the front of the aorta below the superior mesenteric artery, and unites with the left cardinal vein at the point of the entrance of the renal vein. It gives off an upper branch which becomes the left suprarenal vein, and a lower which becomes the left spermatic vein. As before pointed out, the left cardinal vein disappears between the renal vein and the left common iliac vein, whilst the right remains as the lower part of the inferior vena cava. The left division of the upper part of the inferior vena cava, which crosses the aorta below the superior mesenteric artery, remains as the inner portion of the left renal vein, which therefore receives the left spermatic and left suprarenal veins as tributaries. The Veins of the Limbs. Two sets of veins are developed in each limb, the superficial and the deep ; the former are the primary vessels, and as a rule they are quite apart from the limb arteries ; the deep veins are secondary, and they accompany the arteries of the limb. At the peripheral extremity of each limb a venous arch is developed, which is subse- quently connected with the digital veins. In the upper extremity the arch terminates on the ulnar (post-axial) side of the limb in a trunk which afterwards becomes the posterior ulnar, basilic, axillary, and subclavian veins. At a latter period additional superficial vessels are formed, and of these a median vein which drains the palm, and a radial which commences on the radial side of the dorsum of the hand, are the most important. The radial passes up the preaxial border of the limb, becomes the cephalic, and for a time terminates in the primitive jugular vein ; ^ this connexion is usually lost,^ and a new com- munication is formed with the axillary vein. The median vein ends in an anastomosing "vessel between the basilic and cephalic veins at the elbow, and through which it also communicates with the deep veins. In the lower extremity the peripheral venous arch terminates in a fibular or post-axial trunk, which remains in the adult as the external saphenous vein ; its connexion with the sciatic vein, which was its original continuation upwards, is soon lost, and a new com- munication is formed with the popliteal vein. The internal saphenous vein is a later development which appears on the pre-axial border of the limb, and terminates in the femoral vein. The deep veins appear as a series of anastomosing channels at the sides of the arteries. The Pulmonary Veins. The pulmonary veins develop simultaneously with the lungs, and at first the veins from both lungs unite to form a single trunk, which enters the left auricle posteriorly, close to the auricular septum ; subsequently the single trunk is absorbed, and two veins, one from each lung, enter the left auricle, and eventually, as the result of further absorption, two veins from each lung terminate in that cavity. The Lymphatic Vessels. — The lymph vessels commence as outgrowths from the large veins at the root of the neck and gradually extend throughout the body by a pro- cess of budding, at least this appears to be the case in the pig. The growth therefore is from the centre to the periphery, and the communications with the large serous cavities must be formed secondarily. MOKPHOLOGY OF THE VASCULAR SYSTEM. . In conformity with the general plan of the vertebrate body, the vascular system is essentially .segmental in character. This is obvious, even in the adult, in the intercostal and lumbar vessels. It is distinguishable, though less obvious, in the vessels of the head and neck and of the pelvis. The segmental arteries and veins form a series of bilaterally symmetrical vessels, each of which is united to the vessels of adjacent segments by intersegmental channels, which anastomose with one another, through the i^ortions of the segmental vessels which they connect together, and thus form longitudinal trunks. The longitudinal trunks are mainly, though not exclusively, intersegmental. From tliem the main stem vessels of the individual are formed, and from or to these latter the segmental vessels apj^ear to proceed as branches or tributaries. In the course of development the longitudinal trunks become the most im23ortant trunks in the individual, and tliey are formed before the segmental vessels make their appearance. ' See note on page 937. ^ In certain cases it remains, and then the cephalic vein crosses the front of the clavicle and terminates in the external jugular vein. MOEPHOLOGY OF THE AETERIES. 939 The Segmental Arteries and their Anastomoses. The main longitudinal trunks are the primitive aortte. The descending aorta is formed, in So.SA. 1 '^i^^AA Fig. 67.5.- -DlAGRAM OF THE CEPHALIC AORTIC ARCHES, AND OF THE SEGMENTAL AND InTERSEG.MENTAL Arteries in the Region in Front of the Umbilicus. C.A.A. I, II, III, IV, V. The cephalic aortic arches. Co. D.D. D.Sp. L.B. L.E.D. P.D.A. Po.C. Anastomosing vessel between the primitive ventral aorta and the ventral somatic anastomosis. Dorsal division of a somatic segmental artery. Dorsal splanchnic anastomosis. Lateral branch of ventral division of somatic segmental artery. Branch to lateral enteric diverticnhim. Primitive dorsal aorta. Post-costal anastomosis. Po.T. Post-transverse anastomosis. Pr.C. Pre-costal anastomosis. P.V.A. Primitive ventral aorta. So.S.A. ], 2, 3, 4, 5, 6, 7, 8. Somatic segmental arteries. Sp.S.A. Splanchnic segmental arteries. V.D. Ventral division of a somatic segmental artery. V.E.D. Branch to ventral enteric diverticulum. V.V. Vitelline vessels. V.So. Ventral somatic anastomosis. V.Sp. Ventral splanchnic anastomosis. SoSA the greater part of its extent, Ijy the fusion of the dorsal parts of the primitive aorta?, and from it the segmental arteries arise in j^airs. In a typical segment of the body of the embryo there are three seg- mental arteries on each side. One rises from the dorsal surface of the primitive dorsal aorta, i.e. from the dorsal longitudinal trunk, and runs outwards in the tissues developed from the somatic mesoderm ; it is distributed to the body wall, in- cluding the sjunal column and its contents, and is termed a somatic segmental artery. A second vessel rises from the side of the jnimitive dorsal aorta ; it is distributed to the structures developed from the intermediate cell mass, viz. the suprarenal body, the kidney, and the ovary or testicle, and it is ac- cordingly termed tlu- intermediate visceralartery. Tlie third aili-ry, which is known as the splanchnic segmental artery, sj)rings from the ventral surface of the descending aorta. It runs in the tissues de- velojied from the siilanchnic meso- derm, and supplies the wall of the alimentarv canal. Fig VEDiHy) 676. — Diagram of the Caudal Aortic Arch, and of the Segmental and Intersegmental Arteries in the Region behind the umbilicus. So.S.A. Somatic segmental arteries. Sp.S.A. Splanchnic segmental arteries. V.E.D. (Hy). Branch to a ventral enteric diverticulum. Vi.C. Visceral branch fiom the caudal arch. V.V. Vitelline vessels. Cd.A.A. Caudal aortic arch. D.Sp. Dor.sal splanchnic ana- stomosis. M.S. Middle sacral artery. Pa.C. Parietal branch from ■ caudal arch. P.D.A. Primitive dorsal aorta. P.V.A. Primitive ventral aorta. Tlie somatic segmental arteries form in the early embryo a regular series of paired vessels throughout the cervical, dorsal, lumbar, and sacral regions. It is, however, only in the doi-sal and lumbar regions that their original charactere are retained. The paired vessels pass backwards 940 THE VASCULAE SYSTEM. PrU PrN bv tlie sides of the A-eitebr£e, and divide into dorsal and ventral branches which accompany the c6rre«pondin<7 anterior and posterior primary divisions of the spinal nerves. The ventral branches run outwards between the ribs in the dorsal region, and m correspond- incT positions in the lumbar region. They are connected together, near their commencements, by a series of precostal anastomoses which pass in front of the necks of the ribs, and they are also connected to^-ether near their terminations bv ventral anastomosing channels which run m the thoracic reo-ion behind the costal cartilages, and in the lumbar region behind or m the substance of the rectifs abdominis muscle. Each ventral branch gives off a lateral offset which is distributed like the lateral cutaneous branch of a spinal nerve. The dorsal branches run backwards between the transverse processes of the vertebrae ; they are connected behind the necks of the ribs by post-costal anastomoses, and again behind the transverse processes of the vertebrae by post-transverse anastomosing channels. Moreover, each dorsal branch, as it passes by the corresponding interverte- bral foramen, gives off a spinal offset which enters the spinal canal along the corresponding nerve -root, and divides into a dorsal, a ventral, and a neural 'branch. The dorsal branches of these spinal arteries are con- nected together along the ventral surfaces of the laminae by pre-laminar anastomoses, and the ventral branches are united on the dorsal surfaces of the vertebral centra with their fellows above and below by post-central anastomoses ; they are also united with their fellow^s of the opposite side by transverse communi- cating channels. The neural branches of the spinal arteries divide similarly into dorsal and ventral branches ; the dorsal branches of each side are connected together by post- neural anastomoses, and the ventral branches unite in the middle line both with their fellows above and below and with those of the opposite side, forming a single longitudinal pre-neural trunk. In the dorsal and lumbar regions of the body the somatic segmental arteries persist and form the intercostal and lum- bar arteries. These vessels a vcuuiai ciii,c.i^ uivciui^uxLi^ spring from the dorsal aspect V.Sp." Ventral 'splanclinic ana- of the descending aorta, usually in pairs. The corresponding vessels of opposite sides, how- ever, occasionally fuse together at their origins, simultaneously with the fusion of the dorsal longitudinal trunks to form the descending aorta, and then they arise by common stems The precostal anastomoses between the ventral branches of the somatic segmental arteries are only represented in the dorsal region by the superior intercostal arteries ; m the lumbar region they disappear entirely. The anastomoses between the anterior ends of the ventral branches of the somatic segmental arteries persist as the internal mammary and deep epigastric The lateral offsets of the ventral branches are represented by the cutaneous arteries which accompany the lateral cutaneous branches of the spinal nerves. i i i The post-costal and post-transverse anastomoses usually disappear m the dorsal and lumbar regions, but the post-costal anastomoses occasionally persist in the upper dorsal region, and take part in the formation of the vertebral artery, which in such cases arises from the first or second intercostal artery. In some carnivores the post-costal longitudinal vessels persist m the upper dorsal region, and form, on each side, a trunk which is connected with the first aortic intercostal, and which supplies the five anterior intercostal spaces. The pre-laminar, the post-central, and the pre- and post-neural anastomoses persist, the two VSo Fig. 677.— Diagram showing the Arrangement and Communications OF THE Segmental and Intersegmental Arteries at an early Stage of Development. C, Coelom ; D.Sp, Dorsal splanchnic anastomosis ; In, Intestine ; I.V, Inter- mediate visceral artery ; L.B, Lateral branch of the ventral division of a somatic segmental artery ; P.C, Post-central anastomosis ; P.D.A, Primitive dorsal aorta; Po.C, Post-costal anastomosis; Po.N, Post- neural anastomosis ; Po.T, Post-transverse anastomosis ; Pr.C, Pre- costal anastomosis ; Pr.L, Pre-laminar anastomosis ; Pr.N, Pre-neural anastomosis ; So.S.A, Somatic segmental artery ; Sp.S.A, Splanchnic segmental artery ; V.E.D, Branch to a ventral enteric diverticulum - V.So, Ventral somatic anastomosis stomosis. MOKPHOLOGY OF THE AETEEIES. 9-il latter aiding in tlie furmation of the dorsal and lumbar portions of the pre- and post-spinal arteries respectively. It is in the cervical region, how- ever, that the most interesting changes occur. The first six pairs of somatic segmental arteries lose their connexions with the dorsal roots of the aortic arches, i.e., in other words, with the longitudinal anasto- mosing channels in this region. The seventh pair, however, persist in their entirety ; and from them are formed, on tlie right side, a portion of the subclavian trunk, and on the left side the whole of the subclavian stem from its commencement up to the origin of the vertebral artery. On each side the ventral branch of the seventh segmental artery forms that portion of the subclavian arterj^ which lies between the origins of the vertebral and internal mammary arteries, and also the trunk of the internal mammary artery as far as the upper border of the first costal cartilage. The remainder of the in- ternal mammary artery represents Fig. 678. — Diagram of the Segmental and Intersegmental the ventral longitudinal anastomoses Arteries at a later Period op Development than jn between the ventral branches of the Fig. 677. seventh and the following somatic q^ Ccelom ; D.A, Dorsal aorta ; D.Sp, Dorsal splanchuic anastomosis ; segmental arteries. Tlie contiuua- i>f^ Intestine ; V.E.D, Branch to ventral enteric diverticulum ; tion of the subclavian artery, beyond V.Sp, Ventral splanclniic anastomosis, the inner margin of the first rib, is the persistent and enlarged lateral oftset of the ventral branch of the seventh somatic segmental artery, which is continued outwards into the upper limb behind, or postaxial to the shoulder girdle. The tliyroid axis and the superior intercostal artery, both branches of the subclavian artery, are persistent pre-costal anastomoses, and PC PoN PrL ppn SoSA the ascending cervical artery belongs to the same series of vessels. The verte- l)i'al artery, which apj^ears as a branch of the subclavian in the adult, is mor- phologically somewhat complex. The first part rejjresents the dorsal branch of the seventh somatic segmental artery; the second part, that passing through the cervical transverse processes, con- sists of the persistent post-costal an- astomoses between the first seven seg- mental arteries ; a third part, that lying on the arch of the atlas, is the spinal branch of tlie first somatic seg- mental artery and its neural continua- tion ; whilst finally the upper part of the vertebral artery, that in the cranial cavity, appears to rej^resent a prolonga- tion of the preneural anastomoses, which still farther upwards are prob- ably represented by the basilar artery. As ah'eady stated, the post-costal an- astomoses below the seventh segmental artery occasionall}' persist, and in such cases the vertebral may lose its con- nexion with the subclavian, and spring from one or other of the dorsal branches of the upper intercostal arteries. The profunda cervicis artery is to be regaraed as a remnant of the post- transverse longitudinal anastomoses. Pr.N, Pre-neural anastomosis; P. V. A, Friniitivf ventral aorta: The origin of the seventh somatic 80.S.A, Somatic segmental artery ; V.E.D, BianL-h to a ventral segmental artery from the dorsal lougi- enteric diverticulum ; V.So, Ventral somatic auastomosis. tudinal trunk is at first some distance VSo VED Fig. 679. — Diagram showing the Arrangemknt and Com- munications OF the Segmental Arteries in the Region of the Cephalic Aortic Arches. C.A.A, Cephalic aortic arch ; In, Intestine ; L.B, Lateral branch of a somatic segmental artery ; L.E.D, Branch to a lateral enteric diverticulum ; P.C, Post-central anastomosis ; P.D.A, Primitive dorsal aorta ; Po.C, Post-costal anastomosis; Po.N, Post-neural anastomosis ; Po.T, Post-transverse anastomosis ; Pr.C, Pre-costal auastomosis ; Pr.L, Pre-laminar anastomosis ; 942 THE VASCULAR SYSTEM. behind tlie fiftli aortic arcli, but, simultaneously with the elongation of the neck and the retrac- tion of the heart into the thoracic region, it is shifted forward until it is opposite the dorsal end of the fourth aortic arch. The middle sacral artery is formed by the fusion of two vessels, each of which springs from the primitive aorta in exactly the same manner as a somatic segmental artery ; it may therefore be looked upon as consisting of fused somatic segmental vessels which have been prolonged backward for the supply of the caudal appendage. It is, however, commonly regarded as the direct continuation of the descending aorta, and consequently as being mainly intersegmental. Its mode of origin and general nature do not lend much support to the latter view. The intermediate visceral arteries supply the organs derived from the intermediate cell mass. They form a somewhat irregular series of vessels in the adult, but presumably in the primitive condition there was a pair in each segment of the body ; many of these disappear, however, and the series is only represented in the adult by the suprarenal, the renal, and the spermatic or ovarian arteries — ^possibly, also, by some of the branches of the internal iliac arteries. The splanchnic segmental arteries arise in the embryo from the ventral aspects of the primitive dorsal aortse, and are distributed to the walls of the alimentary canal. They anasto- mose with their fellows in front and behind in the dorsal wall of the gut ; those in front of the umbilicus also communicate together on the ventral wall of the gut, whilst those behind the umbilicus terminate ventrally in the posterior sections of the ventral aortse. After the fusion of the dorsal longitudinal trunks to form the descending aorta, the origins of the splanchnic arteries in each segment fuse into a common stem, or either the right or left artery altogether disajoj^ears, whilst at a later period the majority of the splanchnic segmental arteries lose their direct connexion with the descending aorta ; those which retain their connexion are the left bronchial arteries, the oesophageal branches of the aorta, the coeliac axis, and the superior and inferior mesenteric arteries, the three latter vessels greatly increasing in size. The coronary or gastric branch of the coeliac axis, as it passes from its origin to the small curvature of the stomach, represents a right splanchnic artery ; the remainder of the coronary artery and the pyloric branch of the hejoatic are remnants of the ventral anastomoses between the splanchnic arteries in front of the umbilicus. The splenic artery is a branch given off from a splanchnic artery to an organ developed in the gastric mesentery, and the hepatic is a branch from the ventral splanchnic anastomoses to the hepatic diverticulum from the wall of the duodenal portion of the fore-gut. The superior and inferior mesenteric arteries represent at their origins splanchnic branches, and in the remainder of their extent the dorsal anastomoses on the gut wall. The Aoeta, Pulmonary Artery, and other Chief Stem Vessels. The heart and the majority of the great arterial trunks of the body, including the aorta, the innominate, part of the right subclavian, the common, external, and greater parts of the internal carotids, the common and internal iliacs, and the pulmonary arteries, are all modified portions either of the primitive aortse or of the aortic arches. The developmental changes, which result in the formation of the vessels named, are described in the preceding chapter, and the morphology of these vessels is obviously the same as that of the trunks from which they are derived. It will be sufficient, therefore, to point out that the primitive aortee are to be regarded as the greatly enlarged pre-central or pre-vertebral longitudinal anastomoses between the successive segmental arteries of each side ; obviously, therefore, each primitive aorta, like the rest of the longitudinal anastomoses, consists chiefly of intersegmental elements. The origins of the segmental vessels only enter into its formation in so far as they connect the inter- segmental vessels together, and so complete the longitudinal anastomoses. The first cephalic aortic arches and the primary caudal arches are simply portions of the primitive aortae. The other aortic arches have possibly a different morphological significance, but their exact nature is not definitely settled. The second, third, fourth, and fifth cephalic aortic arches of each side are developed in the un- divided mesoderm of the head region behind the first arch. They spring from the anterior part of the primitive aorta which, after the head fold is formed, lies on the ventral aspect of the fore-gut, and they extend at the side of the pharyngeal part of the fore-gut to the dorsal aorta. Thus in some respects they resemble segmental vessels. Behind the umbilicus some of the segmental splanchnic arteries pass from the dorsal to the ventral aorta in the splanchnic mesoderm on the wall of the alimentary canal. In addition to the vessels already mentioned, there are given off from the ventral aort;je and the aortic arches a series of branches which sujjply ventral and lateral diverticula from the alimentary canal ; these are rejJ resented in the adult by the superior thyroid, the thyroidea ima, and the terminal branches of the hypogastric arteries. Iliac Arteries and their Branches. — The common iliac arteries are undoubtedly formed from the primitive aortic longitudinal vessels ; they are simply those portions of the right and left primitive aortaj respectively which lie immediately beyond or caudal to the -pev- manent descending aorta. The direct continuation of each is the primary caudal arch, which forms the origin of the superior vesical artery, and is prolonged as the hypogastric artery; these continuous channels are for the most part made up of intersegmental vessels. So also are the permanent vessels into which they are transformed. Keference has already been made to the fact that the primary caudal arch almost entirely disappears, and that a secondary caudal arch is developed in lieu of it (p. 928). The internal iliac arteries are almost entirely formed from the secondary caudal arches. The MOEPHOLOGY OF THE VEINS. 943 primary caudal arch, beyond doubt, is not a segmental vessel ; tlie secondary arch may be, but this is still unproved. The branches of the internal iliac artery which rejjresent offsets of the " caudal arch j^ortion of the primitive aortas are arranged in two groups — (1) a visceral set which supplies the walls of the hind-gut and the genital organs, and (2) a parietal set which is distributed to the body wall and to the hind -limbs. The branches distril>uted to the gut prob- ably represent the segmental splanchnic vessels given off from the dorsal longitudinal vessels ; those to the genital organs ajjjjear to correspond with the intermediate visceral branches, for they are distributed to organs derived from the intermediate cell mass. The parietal set are to be regarded as modified somatic segmental branches of the dorsal longitudinal trunks. The lateral sacral arteries wliich lielong to this group represent, in the greater parts of their extent at least, the pre-costal anastomoses. The Limb Arteries. In all probability the vessels of both the anterior and the posterior extremities are derived from several somatic segmental arteries, the majority of which, however, in the course of phylo- genetic develojjment, have atropliied. The upper limb is sui^plied in man by tlie lateral offset from the ventral branch of the seventh somatic segmental artery. It passes out into the extremity behind the shoulder girdle, courses through the upjjer arm, enters the antecubital fossa, and is continued through the forearm, in the early stages, as the anterior interosseous artery, to the deep part of the palm, where it terminates in the deep palmar arch. At a later period a median artery is given off from the parent stem, and it terminates in a superficial palmar arch ; still later the radial and ulnar branches are given oft". The latter grow rapidly, soon exceeding in size the parent stem, and they terminate in the superficial and deep palmar arches. The interosseous and median arteries decrease, and generally lose their direct connexions with the 2^3,lmar arches. The posterior interosseous artery is also a secondary branch from the jjarent stem, and the digital arteries are offsets from the palmar arterial arches. The chief arteries of the lower extremities spring directly from the caudal arches, and may be looked wpoii as being essentially segmental ; whether they represent the whole or only parts of typical somatic segmental arteries, however, is not clear. The arteries of the hind-limbs certainly show no very obvious indications of division into dorsal and ventral branches, though such indications are not entirely wanting. In their com- parative absence it is sujjposed tliat the dorsal branches have been either supjjressed or incor- porated with the common stems ; that similarly the ventral branches and their lateral offsets are indistinguishaljly fused, and that probably both are represented in a limb artery. The original stem vessel of the lower limb is the sciatic artery, which is continued down- wards behind the pelvic girdle into the poi^liteal and peroneal arteries, and so to the plantar arch. Subsequently the external iliac artery is given oft' from the caudal arch above the origin of the sciatic, and, j^assing into the limb in front of the j)elvic girdle, it becomes the femoral artery. This vessel ultimately imites with the upjier part of the j^opliteal artery, and after this communication is established the lower part of the sciatic atrojjhies and loses its connexion with the j:)opliteal, which henceforth aj^pears to be the direct continuation of the femoral trunk ; therefore, whilst tlie main artery of the upjjer limb is formed by the j^i'olongation of the lateral branch of one segmental artery, the corresponding vessel of the lower extremity is developed from representatives of two somatic segmental arteries, the external iliac and femoral trunks being the representatives of one, whilst the jjopliteal and its continuation, the jieroneal, are parts of another. The first main artery of the leg is the peroneal, which is continueil into the plantar arch ; after a time, however, the jjosterior and anterior tibial branches are given oft' from the stem, over which, as a rule, they soon jjreponderate in size, and they terminate in the plantar arch, whilst the parent trunk diminishes and loses its direct connexion with the arch. The peroneal artery corresponds in position and development witli the interosseous trunk and the anterior interosseous artery in the forearm. The posterior tibial apparently corre- sponds with the median artery ; it develops in a similar way, and lias similar relations to homologous nerves, the posterior tibial nerve representing the combined median and ulnar nerves of the upjier extremity. The anterior tibial artery represents the posterior interosseous, whilst the radial and ulnar arteries of the uj^per extremity are not represented in the lower limb. MORPHOLOGY OF THE VEINS. Two dorsal longitudinal vessels, one on each side, connect the successive segmental veins together. They do not, however, in any part of their coui-se, fuse together to form a single vessel comparable to the descending aorta. Of these dorsal longitudinal vessels, that on the right side greatly enlarges, and from it the main stem vessels wliicli rt'turu blood from the body walls, tlie liead and neck, and the liuibs, are almost entirely formed. Tlie left dorsal longitudinal vessel remains relatively small — in part.s, indeed, it altogether disajipears — and the lilood conveyed to it by the corresponding segmental veins is transmitted across the middle line to the chief functional stem by later developed and superadded transverse communicating channels, which are formed between the more primitive longitudinal anastomoses. 944 THE VASCULAE SYSTEM. Tlie primitive dorsal longitudinal anastomosing channels include on each side (1) the primi- tive jugular vein, (2) the primitive cardinal vein, and (3) the duct of Cuvier ; the last-named vessel, however, is not so much a longitudinal anastomosis as a communicating channel between the longitudinal anastomoses and the heart, for it is formed by the junction of the primitive jugular and cardinal veins, and opens into the sinus venosus of the j^i'imitive heart. From these vessels, and from the transverse communications which are established between the primitive jugular and cardinal veins of opposite sides, the chief veins of the head and neck and the body are formed ; there are in addition, however, three later-formed vessels from which some, or portions of some, of the main stem vessels of the body are evolved. These later-formed vessels are the two internal jugular veins,i and the upper part of the inferior vena cava, whilst from the latter of these portions of the renal veins, the suprarenal veins and the spermatic or ovarian veins are possibly developed as offsets ; moreover, it must not be forgotten that the veins of the extremities are, like the extremities themselves, secondary structures, and that they are developed at a later period than the veins of the trunk, with which, however, they ultimately communicate. In the light of these facts the morphology of the chief veins of the trunk and limbs may now be considered. The external jugular vein is obviously a portion of an intersegmental anastomosis, for it is part of the primitive jugular vein, which originally extended from the internal occipital jDrotuberance to- the jDOst-condyloid foramen, and thence to the duct of Cuvier. During the course of develop- ment the intracranial part of the primitive jugular, on each side, is converted into the horizontal portion of the lateral sinus and the occasionally persistent squamo -petrosal sinus ; outside the cranium the trunk of the temporo-maxillary vein, the whole of tlie external jugular vein, and that portion of the subclavian vein which intervenes between the external and internal jugular veins, are formed from the primitive jugular. On the right side the right innominate vein and the upper part of the superior vena cava are also formed from the primitive jugular vein, whilst on the left side the lower portion of the vessel becomes the upper part of the left superior intercostal vein.^ After the formation of the limbs the primitive jugular receives the pre-axial and post-axial veins of the fore-limb of the same side, which pass respectively along the radial and ulnar borders of the limb ; both join the primitive jugular vein, the former above and the latter below the clavicle.^ Subsequently, however, the pre-axial vein of the fore-limb loses its connexion with the primitive jugular vein, and opens below the clavicle into the post-axial vein, and the upper part of that vessel becomes the outer part of the subclavian vein, i.e. that portion of the sub- clavian vein which extends from the outer border of the first rib to the entrance of the external jugular vein, the remainder of the subclavian being formed by the portion of the primitive jugular vein which intervenes between the entrance of the pre-axial vein and the junction with the internal jugular vein. The internal jugular vein is a newly formed anastomosing vessel which commences from the primitive jugular vein at the root of the neck and grows upwards to the base of the skull, where it jjasses through the jugular foramen, and ascends along the inner surface of the mastoid portion of the temporal bone to join the lateral sinus, of which it becomes the sigmoid portion. It i^robably represents a dorsal splanchnic intersegmental venous anastomosis.^ The innominate vein of the left side is an enlarged transverse anastomosis between the two primitive jugular veins, and the corresponding vessel on the right side is the portion of the right primitive jugular vein which lies between the origin of the right internal jugular vein and the transverse anastomosis between the two primitive jugular veins. The superior vena cava is also formed from the primitive longitudinal anastomosis on the right side ; the upper portion, which lies above the entrance of the azygos vein, being the lower part of the right primitive jugular vein, and the lower portion, which is enclosed within the peri- cardium, is the persistent right duct of Cuvier. The only other vein formed from the jugular portion of the dorsal longitudinal anastomosis is the upper part of the left superior intercostal vein, which represents the part of the left primitive jugular vein lying below the transverse anastomosis which becomes the left innomi- nate vein ; occasionally this part of the left primitive jugular vein becomes enlarged, and forms a vertical left innominate vein which terminates in a left superior vena cava, the latter being formed from the left duct of Cuvier. This arrangement is the regular and normal condition in many mammals. The internal iliac veins, the right common iliac vein, the lower part of the inferior vena cava, the vena azygos major, and the vertical portions of the upper and lower left azygos veins, and part of the left superior intercostal vein, are all parts of the primitive cardinal veins. They represent, therefore, portions of the dorsal longitudinal intersegmental anastomoses. The internal iliac veins are the persistent lower sections of the cardinal veins, and their visceral and parietal tributaries jjrobably represent more or less modified splanchnic and somatic segmental veins. The left coinmon iliac vein may, in the lower irdvt of its extent, represent the part of the left cardinal vein immediately above the junction of the jDre-axial hind-limb vein with the latter vessel, but the greater part of it is an enlarged transverse anastomosis between the cardinal veins at the level of the pelvic brim. The; right common iliac vein, on the other hand, is the portion 1 See note on p. 937. '^ Ibid. * If the observations recorded on ]). 937 are correct, then the external jugular vein is not the primitive jugular vein but a uewly-formed vessel into which the pre-axial vein opens. MOEPHOLOGY OF THE VEINS. 945 of the right cardinal vein which lies between the entrance of the limb vein and the transverse anastomosis whicli becomes the left common iliac vein. Tlie inferior vena cava, from its com- mencement to the entrance of the renal veins, is a portion of tlie riglit cardinal vein, and the right lumbar veins which terminate in it are the somatic .segmental -s'ein.s of the right side of the lumbar region ; whilst the left luml)ar tributaries are the left lumbar segmental veins, which have Ijeen transmitted across the middle line by transverse anastomosing channels which connected the lumbar sections of the cardinal veins together. The up2:)er part of the inferior vena cava is a new anastomosing channel formed between the upper end of the right hepatic vein and the right cardinal vein. This section of the inferior vena cava grows downwards from the right hepatic vein. The right and left renal veins originally terminated in the corresponding cardinal vein.s, and are therefore probably intermediate visceral segmental veins, but that part of the left renal vein which crosses the middle line is either an enlarged transverse anastomosis between the cardinal veins, or an outgrowth from the lower end of the upper part of the inferior vena cava ; apparently the latter, for as the U2)per section of the inferior vena cava grows downwards from the right Iiepatic vein it divides into two branches, right and left, each of which joins the corresponding cardinal vein close to tlie termination of the renal vein. Before it fuses with the cardinal vein of its own side, each of the terminal branches of the upper section of the inferior vena cava gives off branches which ultimately become the suprai-enal and spermatic veins ; there can be no doubt, however, that both the suprarenal and spernuitic veins are intermediate vi.-^ceral segmental veins, and in all proliability they originally terminated in the corresponding cardinal veins, their development froin the upper section of the inferior vena cava being due to the production in the embryo of a condition which has been secondarily acquired during the development of the sj^ecies. If this is the case, it is extremely probable that the left spermatic vein represents not only an elongated intermediate visceral segmental vein, 1)ut also a portion of the left cardinal into which it opened. The vena azygos major is the persistent upjier jjortion of the left cardinal vein, a fact which is emphasised by its frequent connexion with the inferior vena cava at the level of the I'ight renal vein. The right intercostal veins which open into the vena azygos major are somatic segmental veins, the upper three or four of which have united together by pre-costal anastomoses to form a right superior intercostal vein. The vertical portions of the left azygos veins are remnants of the left primitive cardinal vein, and their transverse jiortions are enlarged transverse anastomoses comparalile to the left innominate and left common iliac veins. The left, like the right intercostal veins, are segmental somatic veins ; but whilst the right superior intercostal A'ein is formed by pre-costal anastomoses between the upper three or four dorsal somatic segmental A^eins, the left sujjerior intercostal vein (Fig. 674) represents the up2:)er part of the left cardinal vein and the i')aYt of the left primitive jugular vein below the transverse anastomosis, which becomes the left innominate vein ; moreover, the left superior intercostal vein frequently retains in the adult a connexion with the oblique vein of Marshall, which represents the left duct of Cuvier, by means of which both the left primitive jugular and the left cardinal A'eins originally communicated with the heart. Visceral Veins. — The portal vein represents j)ortions of the ventral longitudinal anastomosing vessels, being derived from the vitelline veins. The pyloric vein is a sj^lanchnic intersegmental ventral longitudinal anastomosing vein. The coronary vein is partly a ventral and partly a dorsal splanchnic intersegmental longitudinal anastomosis, and the superior and inferior mesenteric veins are dorsal sjilanchnic longitudinal intersegmental A'enous anastomoses, the splenic vein being merely a tributar\' from a lymphoid organ developed in the dorsal mesentery. The facial vein is a combination of somatic and splanchnic veins of several segments, and the internal maxillary vein is j^i'obably of similar nature. The thyroid and bronchial A-eins return blood from organs developed from diverticula from the walls of the alimentary canal; they are, thei'efore, more or less modified segmental splanchnic A-eins ; so also aitjiarently are the vesical and the middle and inferior hemorrhoidal A'eins. The cardiac veins are simjily "vasa vasorum," and they belong therefore to the sjilauchnic group of vessels, but it is imjiossible to say Avhether they are segmental or intersegmental. The coronary sinus into which they open is a portion of the sinus venosus of the heart, and therefore of an originally intersegmental vessel. The hepatic and pulmonary veins are ni-w vessels wliiih ri'tujii blood to the heart after the liver and lungs have been interposed in the vascular system. It is noteworthy that some pai'ts of the .sidandinic venous system, i.e. the portal vein and the coronary sinus, are portions of the most primitive vascular system, and that othei-s, i.e. the thyroid, bronchial, mesenteric, A^esical, and ha^morrhoidal A'eins, apjiear to belong to a someAvhat secondary group of splanchnic A"eins of combined segmental and intersegmental character ; more- over, some of the secondary group of A'eins o]>en into the primary splanchnic veins, e.g. the superior and inferior mesenteric into the poital vein ; some open into the dorsal longitudinal anastomosing veins, e.g. the A'esical and htemorrhoidal veins open into the cardinal veins, Avhich are intersegmental anastomoses ; othei's again open into an entirely neAV Aein, viz. the internal jugular,^ wliich is developed along the dorso-lateral border of the fore-gut, and which is therefore comparable to the dorsal venous splanchnic intersegmental anastomosis, Avhich in the abdominal region becomes converted, after fusion of the vessels of oi:)posite sides, into the greater parts of the superior and inferior mesenteric A'eins ; the latter, however, open into a A'eiitral longitudinal ' Se§ note on p. 937. 64 946 THE VASCULAE SYSTEM. anastomosiug A'essel, tlae portal vein, wliilst tlie former joins a dorsal longitudinal anastomosing trunk. Veins of the Limbs. — Tlie veins of the limbs, like the arteries, were probably at one time segmental in character, but we have no absolute jDroof that this was tlie case. Looked at from an embrvological standpoint, the most j)rimitive limb veins are a superficial distal arch and a post-axial trunk vein in each extremity ; at a later period digital veins are connected Avith the distal arch, and a j^re-axial trunk is formed. In the upper extremity the distal arch and its tributaries remain as the dorsal venous arch and the digital veins, and the j^ost-axial vein becomes the joosterior ulnar, the basalic and axillary veins, and also that part of the subclavian vein which lies external to the termination of the external jugular vein, tlie remainder of the subclavian vein being formed from the primitive jugular A^ein itself. The pre-axial vein of the upper extremity is represented in the adult by the radial and cephalic A^eins ; the latter A^essel originally terminated in the external jugular A^ein aboA'e the claA'icle, the union Avith the axillary portion of the post-axial A^essel being a secondary condition ; the j^riniary condition is, lioAveA^er, frequently retained in man, and is constant in many monkeys. The anastomosis between the pre-axial and post-axial veins in the region of the elboAV, and the connexion of the anastomosing channels, is l^rought about by neAvly-formed A^essels of secondary character. The distal arch in the lower extremity and the tributaries connected with it remain in the adult as the dorsal A^enous arch of the foot and the digital veins. The post-axial vein becomes the external saphenous A^ein, Avhich Avas originally continued upAvards as the sciatic vein to the internal iliac portion of the cardinal A'ein ; its connexion with the poi^liteal vein, and its more occasional connexion Avith the internal sajshenous vein, being brought about by the formation of secondary anastomoses. The pre-axial A^ein of the lower limb becomes the long saj)henous vein, which is continued upAvards to the cardinal portion of the left common iliac vein as the ujjper part of the femoral and the external iliac A^eins. The ven£e comites of the arteries in both the upper and loAver extremities are secondarily developed vessels Avhich become connected Avith the upper portions of the pre-axial venous trunks. ABNOEMALITIES OR VARIATIONS OF THE VASCULAR SYSTEM. Abnormalities are of sjjecial interest to the anatomist because ol their morphological signifi- cance, and the Avascular system is, perhaps more than any other, rich in such abnormalities, many of Avhich are of great practical importance. With the exception of those irregularities Avhich are directly due to the efi'ect of morbid conditions and external influences, all abnormalities are the result of modifications of normal develojjmental j^rocesses. The exceptions referred to are, howeA^er, very numerous ; thus disease and external influences may lead to the obliteration of vessels, a condition Avhich is invariably associated Avith the enlargement of collateral vessels, and it will be obvious that abnormalities so 25roduced may occur in almost any situation. Abnormalities Avhich are determined by, or are dependent ujDon, modifications of the usual deA'elopmental p)rocesses are of greater interest. In the human subject they are generally due eitlier to the retention of conditions Avhich normally are only transitory, or to the acquire- ment of conditions which, though not as a rule jaresent at any time in man, occur normally in other animals. There are in addition other A^ai'iations from the normal, such as the division of the axillary artery into radial and ulnar branches ; the higher or loAver division of the brachial artery ; the formation of " vasa aberrantia," e.g. of long slender vessels connecting the axillary or brachial to the radial, ulnar, or interosseous arteries ; the altered position of certain vessels, as e.g. the trans- ference of the suljclavian artery to the front of the scalenus anticus, or of the ulnar artery to the front of the siq^erficial flexor muscles ; all of Avhich, though undoubtedly due to alterations of ordinary develoijmental processes, still do not represent conditions met Avith, either temporarily or permanently, in man or in other animals. Their occurrence cannot at present be adec[uately exi>lained, and their retention is entirely dej^endent upon their utility. To the first and last of these difterent groujjs of abnormalities it is not necessary to refer i'urtlier, Avhilst with regard to the rest it Avill be suflicient to indicate those of greatest importance. They can only, however, be fully understood and explained on the basis of a comprehensive knowledge of the development and morphology of the vascular system, to the chapters on which the reader is referred. ABNOEMALITIES OF THE HEAET. The heart ]uay be transposed fj'om tlie left to the right side of the body, a condition wdiich is usually associated Avith general transposition of the viscera, and with the presence of a right instead of a left aortic arch. The external form of the heart does not as a rule vary much, but occasionally the apex is slightly bifid, a cliaracter it normally possesses at an e^rly stage of its development, and Avhich is ABNOEMALITIES OF AETEPJES. 947 retained in the adult in many cetaceans and sirenians. The internal conformation of the heart deviates from the normal much more frequently ; more particularly is this the case Avith regard to the septa which separate the riglit from the left chambers. The interauricular septum may be entirely absent, as in fishes ; it may be fenestrated and incomplete, as in some amphilnans ; or the foramen ovale may remain patent, as in amj^hiljians and reptiles. Tlie interventricular septum may be absent, as in fishes and amphibians, or incomplete, as in reptiles ; when incomplete, it is usually the " pars membranacea septi " wliicJi is deficient. ABNOEMALITIES OF AETEIIIES. Tlie pulmonary artery and the aorta may arise by a common stem, as in fishes and some amphibians, and the common stem may spring either from tlie right or the left ventricle, or from both. In these cases the aortic bulb lias remained undivided, and the normal position of the interventricular septum in relation to the lower orifice of the aortic bulb has been altered. Again, owing to malposition of the aortic septum, the pulmonary artery may .spring from the left ventricle and the aorta from the right ventricle. In some cases tlie root of the pulmonary artery is obliterated, and the blood passes to the lungs along tlie patent ductus arteriosus. Occasionally the arch of the aorta is on the right side instead of the left, a condition which is normal in birds. More rarely there are two permanent aorl ic arches, right and left, as in reptiles ; the ccsojihagus and trachea in these cases are enclosed in a vascular collar, the two arclies unite dorsally, and the beginning of the descending aorta is double. Quite independent of this condi- tion, lioweA'er, the two primitive dorsal aortas sometimes fail, either altogether or i^artially, to unite together, and the descending aorta is accordingly represented, to a corresponding extent, by two tubes. A more common, though still rare, form of double aorta is that due to the pei'sistence, in whole or in part, of the septum formed by the fused walls of the primitive dorsal aortae from which the descending aorta is developed. The length of the descending aorta is determined largely by the extent to which fusion of the two primitive aortae takes place. Accordingly, when this deviates from the normal, the termi- nation of the descending aorta is at a correspondingly higher or lower level than usual, and resulting from this the lengths of the common iliac arteiies are almost invariably proportionately modified. The bifurcation ^ of the aorta may be as low as the fifth lumljar vertebra, less frequently it is higher than usual ; it is rare, however, to find it higher than the third or second lumbar vertebra. The aorta, instead of bifurcating into two common iliac arteries, may terminate in a common iliac artery on one side and an internal iliac artery on the opposite side, the external iliac artery on the irregular side arising, at a higher level, as a branch of the aortic stem. This arrangement apjjroaches the condition met with in carnivores and many other mammals, in which the aorta bifurcates into two internal iliac arteries, the external iliacs arising from the aorta at a higher level as lateral branches ; it is due either to a more extensive fusion than usual of the primitive dorsal aortte, or to the origin of the external iliac arteries from the primitive dorsal aortte being at a higher level than is ordinarily the case ; if the condition is due to the latter cause, it may be that the external iliac arteries in carnivores, and the external iliac arteries which occasionally rise from the aorta in man, are somatic segmental arteries of a higher segment than the normal external iliac arteries of the human subject. The Branches of the Aorta. The coronary or cardiac arteries may arise by a single stem. When arising separately both may S2iring from the same sinus of Valsalva ; or again, their interventricular and transverse branches may all arise as distinct vessels from a single sinus of Valsalva. This variability is not so remarkable, seeing that the arteries in question are merely enlarged " vasa vasorum " raised to a position of special importance liy the development of the heart. The branches of the arch, of the aorta are sometimes increased and sometimes decreased in number. The highest number recorded is six, viz., riglit subclavian, right vertebral, right coniiuuu carotid, left common tvarotid, left vertebral, and left subclavian. Apparently this condition is the result of the absorption of the innominate artery and of tlie roots of the subclavian arteries, to points beyond the origins of the vertebrals, into the arch. By variations of this proces.s of absorption other combinations may be produced ; thus, instead of the roots of the subclavian arterii's Ijeing absorbed, the riglit common carotid and innominate arteries may alone be absorbed, in which case the five following branches sjiring sei)arately from the arch of the aorta: right subclavian, right external carotid, right internal t-arotid, left common carotid, and left subclavian. The trunk most commonly absorbed is the initial part of the left subclavian ; the number of branches then arising from the arch of the aorta is four, the additional vessel being the left vertebral, which arises between the left common carotid and the left subclavian. Occasifnially the usual three branches from the arch are increased to four by the formation of a new vessel, the " thyroidea inia." This may be placed between the innominate and h-ft carotid trunks, in which case it represents a jiersistent ventral visceral branch from the ventral root of the fourth left aortic arch ; in other cases the thyroidea ima sjirings from the innominate artery and ^ It is to be observed that the exact point of hifnrcatiou of tlie aorta, in relation to the vertebral oohiinii, is not cMitircly ileterniiui.'il 1)V the len^'th of the descending aorta. 64: a 948 THE VASCIILAE SYSTEM. represents a ventral visceral branch of the ventral root of tlie fourth, right arch. Very rarely the right vertebral artery arises separately, and forms a fourth branch of the arch of the aorta, the rest of the branches being normal. This condition cannot be accounted for by any modifica- tion of the ordinary developmental processes. It may possibly be due to the persistence of an irregular or unimportant anastomosis between the ventral root of an aortic arch and the seventh somatic segmental artery. Decrease in the number of branches from the arch of the aorta is most frequently due to fusion of the ventral roots of the fourth aortic arches, the result being that a stem is formed common to the right subclavian and the right and left common carotid arteries ; whilst the left suliclavian, arising separately, is the only other branch which springs from the arch of the aorta. If the fusion of the ventral roots proceeds further and includes those of the third arches, the result as regards the branches given off from the arch of the aorta is the same, viz. there is a common stem for the right subclavian and both carotids, and a separate left subclavian trunk ; but the common stem now gives off the right subclavian artery, and then continues as a single vessel for some distance before it divides into the two common carotids, of which the left crosses in front of the trachea. This arrangement is common in many quadrumana and in some other mammals. It is only very occasionally when the number of branches from the arch of the aorta is reduced to two, that these consist of a right subclavian artery and of a single stem common to the two carotids and the left subclavian arteries. In such cases, however, the right common carotid crosses m front of the trachea, and the variation is one of practical imjjortance. It does not apj)ear to exist as a normal condition in any mammal. Probably it is due to fusion of the ventral roots of tlie fourth aortic arches, with absorption of the left fourth arch and the left sub- clavian into the stem so formed, whilst the right subclavian is relatively displaced. The two common carotids may arise by a common stem, and the left subclavian arise separately from the arch of the aorta, whilst the riglit subclavian springs from the descending aorta. This arrangement probably results from the disappearance of the fourth right arch and the fusion of the ventral roots of the fourth arches of opposite sides. Sometimes two innominate arteries, right and left, replace the three usual branches of the arch of the aorta. This is the normal arrangement in bats, moles, and hedgehogs. It is obviously the result of the disajDjjearance of that ]3ortion of the arch which intervenes between the left carotid and left subclavian arteries, and the consequent fusion of these two vessels. In a similar way may be explained the rarer condition in which the three ordinary branches of the arch arise by one single stem, which divides into right and left innominate arteries. In most ruminants, in the horse and in the tapir, this arrangement is constant. It will be evident that other combinations and modifications may be met with in the branches of the arch of the aorta as the result of fusions and absorj^tion. The bronchial arteries obviously correspond to sj)lanchnic segmental arteries and their continuations to diverticula from the walls of the gut, therefore the usual origin of tlie right bronchial artery from the first riglit aortic intercostal artery must result from the persistence of an anastomosis between a sj^lanchnic segmental artery and the first part of a somatic segmental artery ; the origin of the right from the upj)er left bronchial artery, wliicli sometimes occurs, is due to the fusion of the roots of two sj)lanchnic segmental arteries. The occasional origin of a bronchial vessel from an internal mammary artery can only result from the persistence and enlargement of an anastomosis between a splanchnic segmental artery and the A'entral branch of a somatic segmental artery. The origin of a bronchial branch from a subclavian artery may have the same or a different significance on opposite sides of the body. A bronchial artery arising from the left subclavian artery corresponds with the origin of the right bronchial artery from the first aortic intercostal artery ; it is due to the persistence of an anastomosis between a sjjlanchnic segmental artery and the root of a somatic segmental artery, and tlie origin of a bronchial artery from a right subclavian artery may be due to a similar cause. It may, on the other hand, be due to the enlargement of an anastomosis between a splanchnic Ijranch of the descending aorta and a sjjlanchnic branch of the fourth right aortic arch. When, as occasionally happens, the bronchial artery arises from the inferior thyroid, it is due to the persistence and enlargement of an anastomosis between splanchnic arteries. Intercostal Arteries. — Variations of the intercostal arteries are not very common, Ijut they are significant and interesting. Corres2)onding vessels of opposite sides may arise from a common stem which has been formed by the fusion of tlie roots of two somatic segmental arteries after or simultaneously with the fusion of the j)rimitive dorsal aorta3. The number of intercostal arteries may be reduced, one artery supplying two or more intercostal sjjaces ; in these cases the roots of origin of some of tlie somatic segmental arteries in the dorsal region have disappeared, and the precostal anastomoses between tlieir ventral branches have jJersisted. Occasionally tlie numlier of the aortic intercostal arteries is increased, an additional artery being given to the second intercostal space, which is usually supplied by the suj)erior intercostal artery ; this is brought about by the persistence of the root of the tenth somatic segmental artery and the disappearance of the precostal anastomosis between the ventral branches of the ninth and tenth somatic .segmental arteries. Very rarely the first aortic intercostal artery sends a branch upwards between the necks of the ribs and the transverse processes of the upper dorsal region ; this branch supjilies tlie up2)er intercostal spaces, the superior intercostal artery being small or absent, and it terminates by liecoming the piofunda cervicis artery. It is due to the persistence of the postcostal anastomoses in the upper dorsal region, and is a repetition of a condition regularly present in some carnivores. AB^'OEMALITIES OF AETERIES. 949 There are no very important variations of the oesophageal, pericardial, and mediastinal arteriiip. Lumbar Arteries. — Variations of the lumljar arteries are very similar to those of the intercostal arteries, and they are due to similar causes. The lumbar arteries of opposite sides may arise by common stems from the back of the aorta ; and the last pair of lumbar arteries may arise in common with the middle sacral artery. Further, a lumbar artery may have its area of distrilmfion in(^r('ascd to the adjacent segment. Tlie inferior phrenic arteries are very variable ; they may arise by a common trunk either from the cceliac axis or from tlu- aorta ; they may arise separately either from the aorta or from the cocliac axis, and more commonly from the latter vessel ; or again, one may sjH-ing from the aorta or cceliac axis, and the other from the coronary, renal, or even from the superior mesenteric artery. The middle sacral artery usually springs from the back of the aorta above its bifurcation ; it may be considerably above, or more rarely it may spring directly from the bifurcation. Not infrecpiently it aris(« from the last lumbar artery or from a stem common to the two last lumbar arteries, and occasionally it arises from a common or internal iliac artery. Some- times it apparently gives off the last pair of lumbar arteries, and very occasionally an accessory, renal, or a hsemorrlioidal branch arises from it. The vessel is not always present, it may be double, entirely oi' in 2^*11'*, and it may bifurcate at its termination. The renal arteries frecpiently deviate from the normal arrangement. The arteries of opposite sides may sjiring from a common stem, or there may be two or more renal arteries on one or both sides. The accessory arteries are more common on the left than on the right side, and an accessory artery rising below the ordinary vessel is more common than one rising above it. Accessory renal arteries may be derived not only from the aorta, but also from the common or internal iliac arteries ; they ha^^e also been described as arising from the inferior jihrenic, spermatic, lumbar, or middle sacral arteries, and even from the external iliac artery. As the kidney is developed in the region of the first sacral vertebra, and afterwards ascends to its perma- nent position, it is not surprising that it occasionally receives arteries from the main stem of more than one of the segments of the liody through which it has passed, and it is usually found that the lower the position of the kidney in the abdomen the more likely it is to receive its arteries from the lower part of the aorta or from the common iliac arteries. The accessory renal arteries which spring from the inferior phrenic, the spermatic, and lumliar arteries can only be the result of the persistence and enlargement of anastomosing channels between the renaf and either another intermediate visceral, or a somatic artery. The spermatic or ovarian arteries may be double" on one or both sides ; the arteries of oppo- site sides may spring from a common trunk, or they may rise from the renal or suprarenal arteries. The right artery may jjass behind instead of in front of the inferior vena cava. The spermatic and ovarian arteries arise from the upper lumbar portion of the aorta, because the testicles and ovaries are developed in and obtain their arteiial suj^ply in that region, and the vessels are elongated as the testicles and ovaries descend to their permanent positions. The occurrence of two spermatic arteries on one side is probably an indication that the testicle was develojied in at least two segments of the body, and the origin of a spermatic artery from a renal or suprarenal artery is due to the obliteration of the root of the original vessel and the enlarge- ment of an anastomosis between the intermediate visceral arteries of adjacent segments. The cceliac axis may be absent, its branches arising separately from the aorta or from some other source. Sometimes it gives off only two branches, usually the coronary and splenic, and occasionally it gives four branches, the additional liranch lx4ng either a second coronary artery or a sej^arate gastro-duodenal artery. The hepatic artery may spring directly from the aorta or from the superior mesenteric artery, and the left liej)atic artery occasionally arises from the coronary artery. Accessory hepatic arteries are not uncommon, and they originate either from the coronary, superior mesenteric, renal, or inferior mesenteric artery. The coronary artery is occasionally double ; it may spring directly from the aorta, and it may give oil' llic hit liepatic or an accessory hepatic artery. The splenic artery may arise from "the middle colic, from the left hepatic, or from the inferior meseiileric aitery. The superior mesenteric artery may be double, and it mav supply the whole of the alimentary canal fium llie second part of the duodenum to the end of the" rectum, the infei'ior mesenteric artury being absent. In addition to its ordinary liranches it may give off a hepatic, a splenic, a pancreatic, a gastric, a gastro-ejiijdoic or a gastro-duodenal branch. Very rarely it gives off an oni]ihalo-mesenteric branch, which passes to the region of the umbilicus and becomes connected with capillary vessels in the falciform ligament of the liver. The inferior mesenteric artery may give hepatic, renal, or middle colic branches ; occasion- ally it is absent, being rejilaced by branches of the superior mesenteric, and sometimes, as in ruminants and some rodents, its left colic liranch does not anastomose with the midtlle colic artery. All these variations of the unpaired visci'ral branches of the abdominal aorta are merely due to modifications of the usual processes by which these vessels are developed. The origin of the branches which usually rise from the coeliac axis, from the trunk of the aorta is the result of the retention of a greater numlier of the splanchnic segmental arteries than usual. A double superior mesenteric arterv results from the pei-sistence of" both the riglit 64 & 950 THE VASCULAE SYSTEM. and left splanchnic vessels from whicli tlie suiDerior mesenteric artery is formed, these remaining separate instead of fusing together. All the other variations are the results of the obliteration of the usual chaiuiels, combined with the enlargement of anastomoses which exist both between the splanchnic arteries of adjacent segments and the splanchnic and intermediate visceral arteries. The Aeteries of the Head and Neck. Innomiliate Artery. — From what has already been said with reference to the branches of the arch of the aorta, it will be seen that the injiominate artery may be absent. On the other hand there may be two innominate arteries, a right and a left, each ending in corresponding common carotid and subclavian trunks, and the two A^essels may themselves arise by a common stem. The branches given off by the innominate artery may be increased in number, or the innomi- nate may only vary from the normal as regards length. As a consequence of such modifications m length, tlie origins of the right common carotid and riglit subclavian arteries may be situated at a higher or lower level than usual, whilst, in the absence of the innominate artery, both these branches may arise directly from the aorta. Common Carotid Arteries. — When tlie right common carotid artery arises separately from the arcli of the aorta, it may be the first, or much more rarely the second branch. In the former case the fourth right aortic arch has been obliterated, and the right subclavian artery springs from the descending aorta ; in the latter case either the innominate stem has been absorbed into the arch of the aorta, or the ventral root of the fourth right aortic arch has fused with part of an elongated fourth left arch. Whether arising as the first or second branch, the origin may be to the left of the mesial plane, and the trunk may pass in front of the trachea, or behind the oesophagus, before it ascends in the neck. The left common carotid artery varies as regards its origin much more frequently than the right vessel ; not uncommonly, and apparently because of the fusion of the ventral roots of the fourth aortic arches, it arises from a stem common to it and to the right common carotid and right subclavian arteries. Both common carotids may vary as regards their termination. They may divide at a higher or lower level than usual, the former more commonly than the latter ; whilst in a few exceptional cases the common carotid does not divide, but is continued directly into the internal carotid, and from this the branches usually given off by the external carotid are derived. This arrangement is jDrobably due to obliteration of the ventral roots of the first and second aortic arches, the arches persisting and being divided into the branches which generally arise from their ventral extremities. Usually the common carotids give off no branches, luit not infrequently one or more of the branches of the external carotids arise from them. The external carotid artery may be absent, or it may, in rare cases, arise directly from the arch of the aorta. The number of its branches may be diminished either by fusion of their roots or by transference to the internal or common carotid arteries. On the other hand, the number of its branches may be increased ; thus the sterno-mastoid artery, the hyoid branch usually given off liy the superior thyroid artery, or the ascending palatine branch of the facial, may arise from it. Sometimes the branches may arise in the usual Avay, but may deviate from the course generally taken ; more particularly is this the case with the internal maxillary artery, which may jaas:; either between the heads or entirely external or internal to both heads of the external pterygoid muscle. The internal carotid artery is rarely absent. Occasionally it springs from the arch of tlie aorta, and iiL its course througli the neck it may vary somewhat in length and in tortuosity. One or more of tlie branches usually derived from the external carotid artery may arise from it, and it sometimes gives off a large meningeal brancli to the posterior fossa of the skull. Its posterior communicating branch may replace the posterior ce.rel)ral artery ; on the other hand, the ujajjer jiart of the internal carotid may be absent, and the posterior communicating artery may become the middle cerebral artery. The anterior cerebral branch of the internal carotid may be absent, or I'ather it may arise from the corresponding artery of the opposite side ; or there may be three anterior cerebral arteries, the third arising from the anterior communicating artery wliich connects the two anterior cerebrals together. The oplithalmic artery, as it traverses the orbit, may j^ass either over or under tlie optic nerve. It is occasionally rejDlaced by a branch of the middle meningeal artery. The vertebral artery may have a double origin — one from the subclavian, and one from the inferior thj^roid artery or from the aorta. The riglit vertebral may arise from the common carotid or from the arch of the aorta. Occasionally it springs from the descending aorta, an arrangement associated with the persistence of the dorsal roots of the fourth and fifth right arches. The left vertelual artery not infrequently springs from the arch of the aorta, arising between the left common carotid and left subclavian arteries ; this is evidently due to the absorption of the stem of the seventh segmental artery into the aortic arch. Very exceptionally the left A'erteljral is a branch of an intei'costal artery. In its course upwards either vertebral artery may enter the ^'ertebrarterial foramen of any of tlie lower six cendcal vertebra. ABXOEMALITIES OF ARTEKIES. 951 The cases in which it does uot euter oue of the lowest of these are apparently associated witli its formation in part from the precostal instead of from the postcostal anastomosing channeli:. Tlie artery may enter the spinal canal with the second instead of with the fii'st cervical nerve, or, after leaving the foramen in tlie transverse process of the tliird vertebra, it may di\-ide into two Ijranches, one of which accompanies the second and the otlier the first cervical nerve ; the two branches unite together again in the spinal canal to form a single trunk. Sometimes, thougli rarely, it gives off superior intercostal and inferior thyroid branches. Tlie upper end of one of the vertel>rals is sometimes very small, or it may Ije entirely wanting ; in the latter case the basihir artery is formed by the direct continuation of the opposite vertebral Tlie basilar artery may Ije double in part or the whole of its extent, or its cavity may be divided by a more or less complete septum. It may terminate in one instead of two posterior cerebral arteries, the missing A^essel being supi)lied Ijy tlie enlargement of the posterior com- municating branch of the internal carotid. The Auteries of the Upper Llmb. Subclavian Arteries. — The variations, so far as regards tlie origins of tlie suljclavian arteries, have already been mentioned (p. 947). Other interesting modifications are met with in resjject of its position and branches. The subclavian artery may reach as high as oue or even one-and-a-half inches above the ass in front of oi' through the scalenus auticus instead of lieliiud it, ur the vein may accompany it Ijehind the muscle. The branches of the subclavian artery may b>e modified with reference to their points of origin; thus those of the first i)art may he furtlier in or out than usual, the suprascapular or some other branch of the thyroid a.xis may arise sejjarately from the tliird part of the artery, and not uncommonly the posterior scapular artery is a branch of this part. The abnormalities of tlie vertebral Ijranch have ah-eady been described ; those of the thyroid axis and its branches are numerous but not important. The internal mammary artery, usually a branch of the first part of the subclavian, is very ^■al•iable as regaids its origin. It may arise from the second or third parts, or from the thyroid axis, or it may spring from the aorta, or from the iiuiominate or axillary arteries. All these ^'ariations are due to obliteration of the normal origin and the opening up of anastomoses. The internal mammary artery sometimes descends in front of the cartilages of oue or more of the lower true ribs, and occasionally it gives oft' a large lateral branch (a. mammaria lateralis) which descends on the inner side of the cliest wall nearly in the mid-axillary line, a point of imi)ortance in paracentesis. A few cases have also been noticed in wliicli a Ijroiicliial artery lias arisen from the internal luammar}'. The superior intercostal branch of the suljclavian may lie absent. In any case its deep cervical branch may rise directl}- tVdm the subclavian trunk. The superior intercostal is some- times formed from a postcostal insttiad of a precostal primitive channel, and in this case it passes between the necks of the ribs and the transverse processes of the A'erteljrte instead of, as usual, in front of the necks of the ribs. The axillary artery does not xavj much as regards its origin or course. Its relations may be modified by the existence of a muscular or tendinous "axillary arch," which, passing from the latissimus dorsi to tlie pectoralis major, crosses the lower part of the artery superficially ; and ii further interesting modification is associated with an anomalous arrangement of its branches. Occasionally tlie sub-scapular, circumflex, and superior and inferior profunda arteries arise from the axillary l)y a common stem. In these cases the chief branches of the brachial plexus are gi'ouped round the common stem instead of round the main trunk, and it is suggested that the common stem in question was originally the trunk artery of the upper limb, the lower part of which has lieeu oliliterated, tlie circulation being carried on by a vas alierrans wliich anastomoses below either witli tlu; brachial artery or with one of the arteries of the forearm. It is also .said that a rudiment of this artery exists in a muscular branch wliicli pa.turator artery and to the subsequent enlargement of the anastomosing pubic branches of the oljturator and deep epigastric arteries. The course of the abnormal obturator artery is of importance. From its origin it descends into the pelvis on the inner side of the external iliac vein, and in the majority of cases on the outer side of the crural ring, but in three-tenths of the cases, and more frequently in males than in females, it descends on the inner side of the ring. The obturator artery sometimes gives off' an accessory pudic branch whicli passes along the side of the prostate, pierces the triangular ligament, and terminates by dividing into the artery of the corpus caA'ernosum and the dorsal artery of the penis. When this occurs the pudic artery is small, and it terminates in the artery to the bulb. Occasionally the accessory pudic arises from the pudic artei'v in the pelvis, or from one of the vesical arteries. The external iliac artery may ))e much smaller than usual, especially if the sciatic artery persists as the main \xssl'1 uf tlie lower limb. It may give off two deep circumflex iliac branches, a dorsal artery of tlie penis, an internal circumflex artery of the thigli, or a vas aberrans, and its deej) circumflex iliac and deep epigastric branches may arise at higher or lower levels than usual. The Arteeies of the Lower Llmb. The femoral artery is small, and ends in the profunda and circumflex branches, when the sciatic artt'r\- forms the principal vessel of the lower limb. The profunda branch, which usually arises from the outer side of the femoral trunk, about one-and-a-half inches below Pouimrt's liga- ment, may commence at a higher or a lower level, and from the back or the inner side of the femoral trunk. Absence of tlie profunda has been noted, and in these cases tlie branches usually given oft' by it spring diiectly from the femoral artery. The femoral artery may be double for a portion of its extent, or it may he joined by a vas al)er]'ans given oft" from tlie external iliac artery. In addition to its ordinary branches, it may furnish one or both of the circumflex arteries of the thigh, and sometimes it gives ofl', near the origin of the jn'ofunda, a great saphenous artery, such as exists normally in many maninials. This vessel descends through Scarjia's triangle and Hunter's canal, and accompanies the internal saphenous nerve to the inner side of tlie foot. The deep circumflex iliac, the obturator, and tlie deep epigastric arteries are occasionally given off from the femoral. The popliteal artery may exceptionally form the direct continuation of the sciatic artery. It sometimes divides at a higher or lower level than usual, and the division may be into either two or three branches ; if three terminal branches are present, they are the anterior and posterior tibial and the peroneal arteries, and if only two, either the anterior and posterior tibial, or the anterior tibial and the peroneal arteries. Occasionally the artery is double for a short portion of its course, and it has been found tu cross first behind the inner head of the gastrocnemius to the inner side of the knee, and then in front of the inner head of the gastrocnemius to regain the popliteal siiace. The number of its branches may be reduced, or they may be increased by the addition of a vas aberrans which connects it with the posterior til)ial artery. Its superficial sural branch may enlarge to form a well-marked small saphenous artery. The posterior tibial artery may be small or altogether absent, its place being taken by branches of the ])er(ineal artery ; again, it may be lunger ur shorter than usual, in conformity with the higher or lower division of the popliteal trunk. The peroneal artery is large if either the anterior or i)osterior tibial arteries are small. The anterior terminal braiich of the peroneal is almost invariably large when the anti-rior tibial artery is small ; in some cases, indeed, it replaces the whole of the dorsalis jjcdis continuation of the latter vessel ; in othei's, however, only the tarsal and metatarsal luamhes are so replaced. The peroneal sometimes arises from a stem common to it and the anlerinr tiliial artery. The anterior tibial artery may be absent, its iilace being taken by Inanches of tlie posterior tibial and peroneal arteries. It is longer than normal when the poi)liteal artery divides at a higher level than usual, and in these cases it may pass either behind or in front of the popUteus muscle. Occasionally the anterior tibial artery and its dorsiilis pedis continuation are larger than normal, and the terminal part of the dorsalis pedis takes the place, more or less completely, of the external ])lanlai' artri'v. The internal plantar artery is sunulimes very small, and it may be absent; its place is 95-4 THE VASCULAK SYSTEM. taken by brandies of tlie dorsalis pedis or external plantar arteries. Tbe external plantar artery also may be small or absent, tbe jalantar arcb being formed entirely by the dorsalis pedis. ABNOEMALITIES OF VEINS. Abnormalities or variations of veins are as frequently met with as those of arteries, and they are due to similar causes. The Superior Vena Cava. The superior vena cava may develoj) on the left side instead of the right. This peculiarity is due to the persistence of the left duct of Cuvier instead of that on the right side, and it is associated with absence of the coronary sinus, which is replaced by the lower part of the left superior vena cava. An exceptional case is recorded in which the opening of the coronary sinus into the heart was obliterated, and the cardiac veins terminated in a trunk which joassed iipwards to the left innominate vein. This trunk was obviously formed by enlargement of the left duct of Cuvier and the lower part of the left primitive jugular vein. Not very uncommonly, as the result of the jjersistence of both ducts of Cuviei', there are two superior veufe cavae, the transverse anastomosis which usually forms the left innominate vein being small or entirely absent. In these cases the left innominate vein descends m the left part of the superior mediastinum, crosses the aortic arch, is joined by the left superior intercostal vein, and becomes the left superior vena cava ; this latter vessel descends in front of the root of the left lung, and terminates in the lower and back part of the right auricle. It receives the great cardiac vein, and, turning to the laack of the heart, replaces the coronary sinus. This arrangement is normal in many mammals. Occasionally in man the left superior vena cava terminates in the left auricle, and the coronary sinus, wliich represents a part of the sinus venosus, has been seen to have a similar ending ; both these abnormal endings must be the result of malposition of the interauricular septum. The vena azygos major may be formed on the left side ; it then arches over the root of tlie left lung, and terminates in the left end of the coronary sinus. This is the normal arrangement in some mammals, and it is due to the persistence of the left cardinal vein and the left duct of Cuvier. The azygos veins may be reduced or increased in number. In the former case there may be only one azygos vein wliich receives the intercostal veins of both sides, or there may be two azygos veins, a right and a left, the left usually being divided into ujaper and lower sections Avhich are connected by a smaller intermediate portion, and united to the right vein by one or more transverse anastomoses, or it may terminate by joining either the left innominate vein or the left superior vena cava. The small intermediate section on the left side may form a sej)arate vessel, and then the number of the azygos veins is increased to four, each of the three left veins terminating in the right vein. When there is only one azygos vein the portion of the left cardinal vein, from which, usually, the vertical portions of the left azygos veins are formed, has disappeared, and the left intercostal veins open into the right azygos vein by separate transverse anastomoses, as in the case of the left lumbar veins and the inferior vena cava. On the other hand, when there is only one left azygos vein the intermediate sections of the thoracic part of the left cardinal vein and one or more of the transverse anastomoses have jjersisted, whilst, when the left azygos terminates in the left innominate vein, the transverse anastomoses have disappeared, and the lower j)art of the left primitive jugular vein has remained patent. Occasionally the vena azygos major takes the j)lace of the upper part of the inferior vena cava, and the whole of the left cardinal vein is enlarged ; in these cases the upper jjortion of the normal inferior vena cava is absent or exceptionally small. The internal jugular vein is sometimes smaller or larger than norinaL In eitlier case com- 2)ensatory changes in size occur in the lateral sinus and internal jugular vein of the opjDOsite side, or in the external and anterior jugular veins of the same side. The external jugular vein is sometimes absent, or it may be smaller than usual ; in both cases eitlier the anterior or internal jugular veins are enlarged. In some of the cases in which the external jugular vein is small it receives no communication from the temiioro-maxillary vein, but is merely the continuation of the posterior auricular vein. On the other hand, it may be enlarged, and receive the whole of the temporo-inaxillary vein. The anterior jugular vein may be absent, or it may be unusually large, especially in the lower ])art of its extent, ai)d after it has received an occasional tributary from the common' facial vein. The temporo -maxillary vein may terminate entirely in the common facial vein, or in the external or the iiitcriiul jugular vein. It may be very small, and occasionally it is absent. Variations of tlie cranial blood sinuses are not numerous. One lateral sinus may be absent or very small when, as a rule, that of the opposite side is enlarged. The inferior longi- tudinal, the occipital, or the spheno-jiarietal sinuses may be absent, and there may be an additional jjetT'o-scpiamous tributary to the lateral sinus. The petro-squaiuous sinus, when jjresent, is the remains of that portion of the 2>i'imitive lateral sinus which crossed tlie temporal bone, j^assed through the post-condyloid foramen and terminated in the primitive jugular vein. Very occasion- ally in the human adult it still pierces the skull behind the condyle of the jaw, and terminates in the temporo-maxillary viiin, and this is tlie normal arrangement in some mammals. ABNOEMALITIES OF THE LYMPHATICS. 955 The Veins of the Upper Exteemity. The superficial veins of the forearni are extremely varialjle ; any of theiii may lie al):^ent, hut most commonly it is the median or the radial vein which is wanting. The median cephalic and the cephalic veins may be small or aljsent, and on the otlier hand tlie cephalic vein may be larger than usiiaL Moreover the cephalic vein may end in the external jugular vein, its original terndnation ; or it may be connected witli the external jugular vein liy an anastomosing channel which sometimes passes over the clavicle and sometimes through tliat Ijoiie. The basilic vein is sometimes larger and sometimes smaller than usual, and it may pierce the fascia of tlie arm at a liigher or at a lower level than is customary. The vense comites of the arteries of the upper extremity generally tcrniiiiate at the lowei- liorder of the subscaj)ularis, where they join the axillary vein, Ijiit they may end above or 1>elow the position of their usual termination. The subclavian vein sometimes passes behind instead of in front of the scalenus anticus muscle, and it has 1)een seen jsassing between the clavicle and the subclavius muscle. The Inferior Vena Cava. The lower part of the inferior vena cava is sometimes absent, in which case the common iliac veins ascend, one on the right and the other on the left of the aorta, to the level of the second lum1)ar vertebra, where the left common iliac vein receives the left renal vein, and then crosses in front of or Ijehind the aorta to fuse with the right corresponding vein ; in these cases, therefore, the inferior vena cava commences at the level of the second lumbar vertebra, and it represents only the ujjper and last-formed part of the ordinary vessel; the common iliac veins, each of which receives the luml)ar veins of its own side, are exceptionally long, and they may or may not be united at the pidvic Ijriiu by a small transverse anastomosing channel. Occasionally the inferior vena cava does not terminate in the right auricle, Ijut is continuous with the vena azygos major, wdiich is much enlarged, all the inferior caval Ijlood being then carried to the superior vena cava. In these cases the hej)atic veins open directly into the right auricle w'ithout communicating with the inferior vena cava. The lower part of the inferior A'eua cava sometimes lies to the left instead of to the right of the aorta ; this condition is associated with a long right common iliac vein, which crosses ol)liquely from right to left to join the shorter left common iliac vein. After receiving the left renal vein the misi^laced inferior vena cava crosses in front of the aorta, reaching the right side at the level of the second or first lumbar vertebra. In other cases, however, the left inferior vena cava continues upwards through the left crus of the diaphragm, usurping the lA-dce of a greater or smaller jiart of the left azygos vein ; having entered the thorax, it may cross to the opposite side and terminate in the vena azygos major, or it may continue ujjwards on the same side, and after arching over the root of the left lung, descend behind the left auricle, to terminate in the right auricle in the situation of the coronary sinus. In this grouj:) of cases also the hepatic veins o]H'n separately into the right auricle. The tributaries of the inferior vena cava are also subject to variation. Additional renal, spermatic, ovarian, or suprarenal veins may be present. Two or three lumbar veins of one or both sides may unite into a common trunk which terminates in the inferior A'ena cava, and the hepatic veins may open sejjarately, or after fusing into a common truidv, into tlie right auricle near the opening of the inferior ^'ena cava. No explanation of the variations of the inferior vena cava and its tributaries is necessary, beyond the statement that they are due to persistence of portions of the cardinal veins which usually disapjjear, and to the persistence of transverse anastomoses and triljutaries which usually atrophy, or to modifications of those which ordinarily take part in the formation of the inferior vena caval system. The left common iliac vein is short and the right long when the inferior vena cava lies on the left side. The common iliac veins may be absent, the internal iliac veins uniting to form the commencement of the inferior vena cava, into wdiicli the external iliac veins open as lateral triliutaries. The Veins of the Lower Extremity. Till- long saphenous vein is not subject to much variation, but the short saphenous vein may terniiuate liy joining the long saphenous, or, after jiiercing the di-ej) fascia in the lower jiart of the thigh, it may ascend and join the sciatic vi'in or one of the trilmtaries of the profunda vein. The venae comites are generally described as terminating in the lower extremity, at the lower part of the popliteal space, but they may a.-^cend as far as ScarjKi's triangle; ;vs a matter of fact, although as a rule there is only one large popliteal and one large femoral vein, one or more small additional veins usually accompany the poi)liteal and femoral arteries. In a few cases the popliteal vein does not pierce tlie lower jKirt of the abductor magiius, but ascends behind that muscle and becomes continuous with the jirofunda vein, the femoral artery being nnacconipanied by any large vein during its passage through Hunter's canal. ABNOEMALITIES OF THE LYMPHATICS. Variations of the glands and smaller vessels of the lymphatic system are so common that tliev can hardly be regarded as abnormalities ; variations of the larger vessels, however, are 956 THE VASCULAE SYSTEM. comparatively rare. This is especially tlie case with respect to the two terminal trunks, the thoracic duct and the right lymphatic duct, the abnormalities of which are interesting and important. "When the arch of the aorta is on the right instead of on the left side, the thoracic duct usually terminates in the right innominate vein, in which case it receives the tributaries which usually open into the right lymphatic duct, whilst the corresponding area on the left side is drained by lympliatics terminating in a left lymphatic duct which opens into the commencement of the left innominate vein. A similar arrangement of the terminal lymphatic ti'unks sometimes occurs even wlien the arch of the aorta is in its normal position on the left side. In either case the thoracic duct may commence in the usual way, and after reaching the level of the fifth dorsal vertebra continue upwards on the right side, instead of crossing to the left side, of the vertebral column ; more rarely it commences on tlie left side and crosses over to the right at a higher level. In one case in which the thoracic duct opened into tlie right innominate vein, instead of the left, no trace of a lymphatic duct was discovered on the left side. Occasionally the thoracic duct commences and terminates in the usual manner, but crosses the vertebral column immediately after its origin and ascends on the left side. Not uncommonly there is no distinct receptaculum chyli, in which case the terminal lymphatic vessels of the abdomen merely imite to form a larger vessel whicli does not present any obvious dilatation, and from which the thoracic duct is continued. The terminal lymphatic trunk may 023en into the internal jugular vein previous to its junction with tlie subclavian, instead of into the commencement of the innominate vein. Occasionally the thoracic duct is double, either on the whole or in part of its extent, and sometimes it breaks up into a plexus of vessels which may reunite into a single trunk in the upper part of the thorax. Both the thoracic duct and the right lymphatic duct may before terminating divide into branches which, though sometimes reuniting on each side into a single ti'unk, not infrequently open separately into the great veins at the root of the neck. As a rule the thoracic duct joins tlae commencement of the left innominate vein, but it may end in the internal jugular, vertebral, or subclavian veins of the left side ; whilst very rarely, it opens into the vena azygos major. THE RESPIRATORY SYSTEM. THE ORGANS OF RESPIRATION AND VOICE By D. J. Cunningham. The organs of respiration are the larynx and trachea, which together cuustitute a median air-passage ; the two bronchi or branches into which the lower end of the trachea divides ; and the two lungs to which the bronchi conduct the air. In connexion with the lungs we have likewise to consider the pleural membranes — two serous sacs which line the portions of the thoracic cavity which contain the lungs, and at the same time give a thin coating to these organs. The larynx opens above into the lower, part of the pharynx, and the air which passes in and out from the air-passages likewise traverses the pharynx, the nasal fossre, and also the buccal cavity if the mouth is open. This connexion between the digestive and respiratory systems is explained by the fact that the respiratory apparatus is secondarily developed as an outgrowth from the front aspect of the priuiitive fore-gut of the embryo. In most mammals the upper aperture of the larynx opens into the part of the pharynx which lies behind the nasal chambers. In man, however, the upper opening of the larynx is placed lower down, below the communication between the mouth and pharynx, and both nasal and buccal breathing may be carried on with very nearly equal ease. THE LARYNX OR ORGAN OF VOICE. The larynx is the upper part of the air-passage, specially modified for the pro- duction of the voice. Above, it opens into the pharynx, whilst below, its cavity becomes continuous with the lumen of the trachea or windpipe. Position and Relations of the Larynx, — In the natural position of the neck, and whilst the organ is at rest, the larynx is placed in front of the bodies of the fourth, fifth, and sixth cervical vertebra?,. Its highest point, represented by the tip of the epiglottis, reaches as high as the lower border of the body of the third .cervical vertebra, whilst its lower limit, or the lower border of the cricoid cartilage Vsually corresponds to the lower border of the body of the sixth cervical vertebra. Fi\)m the vertebral column the larynx is separated, not only by the pre^■ertebral muscles and prevertebral layer of cervical fascia, but also by the posterior wall of the! pharynx — indeed tlie posterior surface of the larynx forms the lower part of the anterior wall of the pharynx, and is covered by the lining mucous membrane of that^section of the alimentary canal. TheUarynx lies below the hyoitl bone and the tongue, and in the interval between \the great vessels of the neck. It forms a more or less marked projection on the front of the neck, and in the median line it approaches very close to tlie surface, being merely covered by skin and the two layers of fascia. Laterally it is more deeply placed. Thus it is overlapped by the sterno-mastoid muscle, covered by the two strata of thin ribl)on-like muscles which are attached to the thyroid cartilage and tlie hyoid bone, and hidden to some extent by the upward prolonga- tions of the lateral lobes of the thyroid body. The position of the laniyx is intlucnoed by movements of tlio lioad and neck. Thus it is elevated when the head is thrown back, and depressed when the chin is carried 957 958 THE EESPIEATOEY SYSTEM. downwards towards the chest. Again, if the finger is placed upon it during deglutition, it will be seen that the laiyns moves to a very considerable extent. The pharyngeal muscles attached to it, and more especially the stylo-pharyngeal miiscles, are chiefly responsible for bringing about these movements. During singing, changes in the position of the larynx may also be noted, a high note being accompanied by a slight elevation, and a low note by a slight depression of the organ. The position of the larynx is not the same at all periods of development and growth. In the foetus, shortly before birth, it lies much higher up in the neck. Thus its lower border corresponds to the lower border of the fourth cervical vertebra. Its permanent position is not reached until the period of puberty is attained (Symington). This descent of the larynx has been stated to be due to the rapid and striking growth of the facial part of the skull which lies above it (Symington). It is very doubtful, however, if the facial growth has any influence in this direction. In the anthropoid ape, in which the face forms a much greater part of the skull than in man, and in which, in the transition from the infantile to the adult condition, the facial growth is even more striking than it is in man, the larynx occupies a relatively higher position in the neck. In the early stages of growth all the thoracic viscera undergo a gradual subsidence. The larynx in its descent follows these. Indeed it cannot do otherwise, seeing that the bifurcation of the trachea between infancy and puberty moves downwards more than the depth of one thoracic vertebra. General Construction of the Larynx. — The wall of the larynx is constructed upon a somewhat complicated plan. There is a frame-work composed of several cartilages. These are connected together at certain points by distinct joints and also by elastic membranes. Two elastic cords, which stretch in an antero-posterior direction from the front to the back wall of the larynx, form the ground- work of the true A^ocal cords. Numerous muscles are likewise present. These operate upon the cartilages of the larynx, and thereby not only bring about changes in the relative position of the true vocal cords, but also produce different degrees of tension of these cords. The cavity of the larynx is lined with mucous membrane, under which, in certain localities, are collected masses of mucous glands. CARTILAGES OF THE LARYNX. There are three single cartilages and three pairs of cartilages entering into the construction of the laryngeal wall. They are named as follows : — (Thyroid. (^^Tteuoid _ o-i ,-1 ) n ■ -J T)-j i-'i ; Cormcula larvngis, or the Smgle cartilages ■( Cricoid. raired cartilages < ,-. "p o \l • ■ ° F ■ -1 H' ) cartilages ot Santorini. " "^ ■ \ Cuneiform cartilages. Thyroid Cartilage (cartilage thyreoidea). — The thyroid cartilage, the largest of the laryngeal cartilages, is formed of two quadrilateral plates termed the ala, which meet in front at an angle, and become fused along the mesial plane. Behind, the ahe diverge from each other, and enclose a wide angular space which is open behind. The anterior borders of the alee are only fused in their lower parts. Above they are separated by a deep, narrow V-shaped median notch, called the incisura thyroidea. In the adult male the angle formed by the meeting of the anterior borders of the two al£e, especially in its upper part, is very projecting, and with the margins of the thyroid notch, which lies above, constitutes a marked subcutaneous prominence in the neck, which receives the name of the pomum Adami. The angle which is formed by the meeting of the two alse of the thyroid cartilage varies to some extent in different individuals of the .same sex, and shows marked differences in the two sexes and at different periods of life. In the adult male the average angle is said to be 90° : in the adult female it is 120" ; whilst in the infant the alae meet in the form of a gentle curve convex to the front. The posterior border of each ala of the thyroid cartilage is thick and rounded, and is jjrolonged beyond the superior and inferior borders in the form of two slender cylindrical processes, termed cornua. The superior cornu is longer than the inferior cornu. It is directed upwards, with a slight inclination inwards and backwards, and it ends in a rounded extremity, which is joined to the tip of the great cornu of CARTILAGES OF THE LARYXX. 959 the hyoid bone by the lateral thyro-hyoid ligament. The inferior comu is shorter As it pi'oceeds downwards it curves slightly Hyoid bone Epiglottis Cartilage triticea — Superior coriiu '}(_[_ I thyroid cartilage ; Thyroid iiotcl Pomum Adaii Crico-thyroiil membrane Inferior cornu of thyroid cartilag Cricoid cartilag Fig. 680. — The Cartilages and Ligaments of the Larynx viewed from the Front. and stouter than the superior cornu. inwards, and upon the inner face of its extremity it shows a circular flat facet, by means of which it articulates with a similar facet on the lateral aspect of the cricoid cartilage. The su'perior border of the ala is for the most part slightly convex, and in front it dips suddenly down to Ijecome continuous with the margin of the thyroid notch. Posteriorly, where it joius the superior cornu, it exhibits a shallow notch or concavity. The inferior border is to. all intents and purposes horizontal, but it is marked oif liy a projection, termed the inferior tubercle, into a short posterior part, which shows a shallow concavity in front of the inferior cornu, and a longer part wliich lies in front of the tubercle, which is also concave, but to a less degree. The externcd surface of the ala is divided into two unequal ijreas by an oblique line or ridge. This line begins above at the superior tubercle, a prominence situated im- mediately below the superior border, and a short distance in front of the root of the superior cornu. From this the oblique line proceeds downwards and forwards, to end interiorly in the inferior tubercle on the lower border of the ala. The area which lies behind the oblique line is much smaller than that which lies in front. It is covered by the inferior constrictor muscle of the pharynx. The larger anterior area is for the most part covered by the thyro-hyoid muscle. To the oblique line are attached the sterno-thyroid and thyro-hyoid muscles. The inner surface of the ala of tlie thyroid cartilage is smooth and slightly concave. Cricoid Cartilage (cartilago cricoidea). — The cricoid cartilage is shaped like a signet- ring. Behind, there is a broad, thick plate somewhat quadrilateral in form and termed the posterior lamina ; whilst in front and later- ally, the circumrerence of the ring is com- ])leted by a curved band, called the anterior arch. The lumen of the ring enclosed by these parts is circular below, but above the ring is compressed laterally, so that the lumen l)ecomes elliptical. The superior border of the posterior lamina presents a faintly-marked mediiiii notch. On either side of tliis there is an oval convex facet which looks more out- wards than upwards, and which articulates with the base of the arytenoid cartilage. The Fig. 681.— Profile View of the Cartilages posterior surface of the lamina is divided by AND Ligaments of the Larynx. an elevated median ridge into two depressed areas which give attacliment to the posterior crico-arytenoid muscles. The front part of the anterior arch of the cricoid is in the form of a narrow band, l)ut as it proceeds backwards towards the posterior Epiglottis Hyoid bone Inferior tubercle Inferior cornu of thyroid cartilage fjrico-thyroid membrane Cricoid cartilage 960 THE EESPIEATOEY SYSTEM. Hj old bone lamina its superior border rises rapidly, and in consequence the arch becomes much broader. The inferior border of the cricoid is nearly horizontal, although it frequently presents a median projection in front, and a lateral projection on either side. It is joined to the first ring of the trachea by an intervening elastic membrane. On the outer surface of the cricoid cartilage, at the place where the anterior arch joins the posterior lamina, a vertical ridge descends from the arytenoid articular facet. On this, a short distance from the lower border of the cartilao-e, a prominent circular articular facet is visible for articulation with the inferior cornu of the thyroid cartilage (Eig. 683, p. 963). The inner surface 'oi the cricoid cartilage is smooth, and is lined by mucous membrane. The narrow band-like part of the anterior arch of the cricoid cartilage lies below the lower border of the thyroid cartilage, whilst the posterior lamina is received into the interval between the posterior portions of the alae of the thyroid cartilage. Arytenoid Cartilages (cartilagines arytsenoidese). — The arytenoid cartilages are placed one on either side of the mesial plane, and rest upon the upper border of the posterior lamina of the cricoid cartilage, in the interval between the posterior portions of the alse of the thyroid cartilage. They pre- sent a somewhat pyramidal form. The pointed apex or summit of each is directed upwards, and at the same time curves backwards and inwards. It supports thecorniculumlaryngis. Of the three surfaces, one looks directly inwards towards the cor- responding surface of the opposite cartilage, from which it is separated by a narrow interval ; another looks backwards ; whilst the third is directed outwards and forwards. The internal surface, which is the smallest of the three, is triangular in outline. It is narrow, vertical, and even, and is clothed by the lining mucous membrane of the larynx. The j^osterior surface is smooth and concave from above downwards ; it lodges and gives attachment to the arytenoideus transversus muscle. The antero- external surface is the most exten- sive of the three (Fig. 683, p. 963). Its middle part is marked by a deep depression in which is lodged a mass of mucous glands. Upon this surface of the arytenoid cartilage the powerful thyro- arytenoid muscle is inserted, whilst a small tubercle a short distance above the base gives attachment to the superior thyro-arytenoid ligament — the feeble sup- porting ligament of the false vocal cord. The three surfaces of the arytenoid cartilage are separated from each other by an anterior, a posterior, and an external border. The external harder is the longest, and it pursues, as it is traced from the apex to the base, a sinuous course. Eeaching the base of the cartilage, it is pro- longed outwards and backwards in the form of a stout prominent angle or process, termed the processus muscularis. Into the front of this process is inserted the crico- arytenoideus lateralis muscle ; whilst into its posterior aspect the crico-arytenoideus posticus muscle is inserted. A small nodule of yellow elastic cartilage, called the sesamoid cartilage, is frequently found on the external border of the arytenoid cartUage, where it is held in position by the investing perichondrium. The anterior border of the arytenoid is vertical, aud at the base of the cartilage is _ Cartilago triticea Thyro-epiglottidean ligament Superior cornu of thyroid cartilage Cartilage of Santorini Arytenoid cartilage Muscular process of arytenoid cartilage Inferior cornu of thyroid cartilage Fig. 682. — Cartilages and Ligaments of Larynx, as seen from behind. JOINTS AND LIGAMENTS OF THE LAIJYNX. 9G1 prolonged horizontally forwards into a small sharp-pointed process called the processus vocalis. It receives this name because it gives attachment to the iul'erior thyrd- arytenoid ligament or sujjporting band of the true vocal cord. The base of the arytenoid cartilage presents on its under surface, and more particularly on the under surface of the processus muscularis, an elongated concave facet for articulati(^n with the upper border of the posterior lamina of the cricoid cartilage. Cartilages of Santorini (cartilagines corniculata-). — The cartilages of Santorini, or tlie cornicula laryngis, are two minute conical nodules of yellow elastic. cartilage which surmount the apices of the arytenoids, and prolong the upper curved ends of these cartilages in a backward and inward direction. Each cartilage of Santorini is enclosed within tlie posterior part of the corresponding aryteno-epiglottidean fold of mucous membrane. Cuneiform Cartilages (cartilagines cuueiformes). — The cuneiform cartilages are not invariably present. They are two minute rod-shaped pieces of yellow elastic cartilage, each of which occupies a place in the corresponding aryteno- epiglottidean fold of mucous membrane immediately in front of the arytenoid cartilage and the cartilage of Santorini. On the superficial surface of each a collection of mucous glands is present, and this tends to make the cartilage stand out in relief under the mucous membrane. Epiglottidean Cartilage (cartilago epiglottica). — The epiglottis is supported by a thin leaf- like lamina of yellow fibro-cartilage which is placed behind the root of the tongue and the body of the hyoid bone, and in front of the superior aperture of the larynx. When divested of the mucous membrane, which covers it behind and also to some extent in front, the epiglottideau cartilage is seen to present the outline of a bicycle-saddle, and to be indented by pits and pierced by numerous perforations. In the former, glands are lodged, whilst through the latter, blood-vessels and in some cases nerves pass. The broad end of the cartilage is directed upwards, and is free. Its margins are, to a large extent, enclosed within the aryteno-epiglottidean folds of mucous membrane. The anterior surface is only free in its upper part. This part is covered with mucous membrane, and looks towards the pharyngeal part of the tongue. The posterior surface is covered throughout its whole extent by the lining mucous membrane of the laryngeal cavity. The lower pointed extremity of the cartilage is carried downwards in the form of a strong fibrous band, termed the thyro-epiglottidean ligament. Ossifiication of the Cartilages of the Larynx. — The thyroid and cricoid cartilages and the greater part of the arytenoid cartihxges are composed of the liyaline variety of cartilage. The apical parts, and also the vocal processes of the arytenoid cartilages, the cartilages of Santorini, the cuneiform cartilages, and the epiglottis, are formed of yellow fibro-cartilage, and at no period of life do they exhibit any tendency towards the ossitic change. The thyroid, cricoid, and basal portions of the arytenoids, as life advances, become more or less completely transformed into bone. In males over twenty years of age, and in females over twenty-two years of age, the process will usually be found to have begun (Chievitz). It is impossible, however, by an examination of the laryngeal cartilages, to form an estimate of the age of the individual, although in old age it is usual to find the thyroid, cricoid, and the hyaline part of the arytenoid completely ossified. It wtjuld appear that the pi-ocess is somewhat slower in the female than in the male. The thyroid is the first to show the change ; then, but almost at the same time, the cricoid, and lastly, a few years later, the arytenoid. JOINTS, LIGAMENTS, AND MEMBRANES ()F TH1-: LARYNX. Crico-thyroid Joints (articulationes cricotliyrejidese). — These are diarthrodial joints, and are formed by the apposition of the circular facets on the tips of the inferior coruua of the thyroid cartilage with the elevated circular facets on the sides of the cricoid cartilage. A capsular ligament is thrown around each articula- tion, and this is lined by synovial membrane. On the posterior aspect of the joint a strengthening band is present in the capsule. The movements which take place at th ' crico-thyroid joints are of a twofold character, viz. gliding and rotatory. In the first case the thyroid facets ulide upon the cricoid surfaces in different directions. 65 962 THE EESPIRATOEY SYSTEM. The rotatory movement is one in which the thyroid cartilage rotates to a slight extent around a transverse axis which passes through the centre of the two joints. Crico- arytenoid Joints (articulationes cricoaryt^enoideai). — These also are diartlirodial articulations. In each case there is a joint cavity surrounded by a capsular ligament, which is lined by a synovial membrane. The cricoid articular surface is convex, whilst that of the arytenoid is concave ; both are elongated or elliptical in form, and they are applied to each other, so that the long axis of the one intersects or crosses that of the other at an acute angle. In no position of the joint do the two surfaces accurately coincide — a portion of the cricoid facet is always left uncovered. The capsule of the joint is strengthened behind by a band which is inserted into the inner and back part of the base of the arytenoid cartilage, and plays a somewhat important part in the mechanism of the joint ; it arrests effectually excessive forward movement of the arytenoid cartilage. The movements which take place at the crico-arytenoid joint are of a twofold kind, viz. gliding and rotatory. The ordinary position of the arytenoid during easy, quiet breathing is one in which it rests upon the outer part of the cricoid facet. By a gliding movement it can ascend upon the cricoid facet, and advance towards the median plane and its fellow of the opposite side. The gliding movements, therefore, are of such a character that the two arytenoid cartilages approach or retreat from each other and the mesial plane. In the rotatory movement the arytenoid cartilage revolves around a vertical axis. By this movement the vocal process is swung outwards or inwards, so as to open or close the rima glottidis. The joint between the arytenoid and the cartilage of Santorini may either partake of the nature of an amphiarthrosis or of a diarthrosis. The tips of the two cornicula laryngis can generally be made out to be connected to the upper border of the posterior lamina of the cricoid cartilage by a dehcate Y-shaped ligament termed the ligamentum jugale. Thyro-hyoid Membrane (membrana hyothyreoidea). — This is a broad mem- branous and somewhat elastic sheet which occupies the interval between the hyoid bone and the thyroid cartilage. It is not equally strong throughout. It presents a central thick portion and a cord-hke right and left margin, whilst in the intervals between these it is thin and weak (Figs. 680 and 681, p. 959). The central thickened part (ligamentum thyro-hyoideum medium) is largely composed of elastic fibres. Below, it is attached to the margins of the thyroid notch, whilst above, it is fixed to the posterior aspect of the upper margin of the body of the hyoid bone. The upper part, therefore, of its anterior surface is placed behind the posterior hoUowed- out surface of the body of the hyoid bone ; a synovial bursa of variable extent is placed between them, and in certain movements of the head and larynx the upper border of the thyroid cartilage slips upwards behind the hyoid bone. On either side of the strong central part, the thyro-hyoid membrane is thin and loose. It is attached below to the upper border of the thyroid cartilage, and above to the posterior aspect of the great cornu of the hyoid bone. It is pierced by the internal laryngeal nerve and the superior laryngeal vessels. The posterior border of the thyro-hyoid membrane on each side is thickened, round, and cord-like, and is chiefly composed of elastic fibres. It is termed the ligamentum thyro-hyoideum laterale, and extends from the tip of the great cornu of the hyoid bone to the extremity of the superior cornu of the thyroid cartilage. In this ligament there is usually developed a small oval cartilaginous or bony nodule wliich receives the name of the cartilago triticea. The deep surface of the lateral part of the thyro-hyoid membrane is covered by the pharyngeal mucous membrane. Behind its central part lies the epiglottis, but separated from it by a mass of adipose tissue (Fig. 686, p. 966). Crico-thyroid Membrane (memljrana cricothyreoidea). — This is a very important structure, which must be considered in three parts, viz. a central and two lateral, all of which arc directly continuous with each other, and differ only in the nature of their superior connexions. The central part of the crico-thyroid membrane is strong, tense, and elastic. It is triangular in shape, and is attached by its broad >)ase to the upper border of the anterior arch of cricoid cartilage, whilst above, it is fixed to the middle part of the lower border of the thyroid cartilage (Fig. 680, p. 959). It is pierced by minute apertures, and is crossed superficially by the crico-thyroid Cricoid cartilage JOINTS AXD LIGAMENTS OF THE LAEYNX. 963 branch of the superior laryngeal artery. The central part of the crico-tliyroid mem- brane, therefore, closes in front the interval between the cricoid and thyroid cartilages. The lateral part on each side presents very different connexions. It is not attached to the lower border of the thyroid cartilage, but slopes upwards and inwards within the thyroid ala, and thus diminishes materially the transverse width of the lower subdivision of the laryngeal cavity. Its attachments are very definite. Below, it (■# . , ., J ••ill Aiytenoul cartilage is fixed to the upper border of the cricoid I / Muscular process cartilage, immediately subjacent to the \ \_^ / y/ lining mucous membrane of the larynx ; \^ 77 ''Z ~N. vocai process above, it is directly continuous with the ^^C^/ / A^ inferior thyro-arytenoid ligament or sup- ^yL/ ^^ w\ porting band of the true vocal cord. This J^ /'/^\:^-~~.^i^^ JM_ji\md ^lottidis ligament, indeed, may be looked upon r^C JE, ^^i^^^^^/^T' as constituting the upper thickened free / x^m^I"'. ■ ' ^z'^--/ u-ament of true border of the lateral part of the crico- | ||Kk,: M^^^L^erZl^rt of crico- thyroid membrane. In front, the lateral I ^\ ^«jbi,-.>iaj^ iiiyroiieriiug the lateral part of tlie tliyro-hyoid membrane to supply the laryngeal nuieous membrane. The re- current laryngeal nerve reaches the larynx from below, and siijiplies all the intrinsic laryngeal nuiscles with the exciqiti(m of tlie crico-tliyroid. The superior laryngeal artery, a branch of the superior thyroid, accompanies the internal laryngeal nerve ; whilst the inferior laryngeal artery, which springs from the inferior thyroid, accompanies the recurrent laryngeal nerve. These two vessels ramify in the laryngeal wall and supply the mucous membrane, the glands, and muscles. Growth-Alterations and Sexual Differences in the Larynx. — A considerable amount of variation may be noticed in the size of the larynx in diflei'ent individuals. This is quite independent of stature, and explains to a great extent the diflercnce in the 972 THE EESPIRATORY SYSTEM. pitch of the Yoice which is observable in different persons. But quite apart from these individual variations, there is a marked sexual difference in the size of the larynx. The male larynx is not only absolutely but also relatively larger than the female larynx. This is noticeable in all its diameters, but more particularly in the antero-posterior diameter, and to a large extent the increase in the latter direction is produced by the strong develop- ment of the laryngeal angle or pomum Adami in the male. The great antero-posterior diameter of the male larynx necessarily implies a greater length of the vocal cords and a lower or deeper tone of the voice than in the female. In the newly-born child the larynx, in comparison with the rest of the body, is some- what large (C. L. Merker), and it continues to grow slowly and uniformly up to the sixth year of childhood. At this period there is a cessation of growth, which persists until puberty is reached, and then a stage of active growth supervenes. Up to this time the larynx in both sexes is similar in its characters, and although the growth which now occurs affects both the male and the female larynx, it is much more rapid and much more accentuated in the male than in the female. As a result of this the voice of the male breaks and assumes its deep tone. It is interesting to note that the growth activity of the larynx at puberty is intimately connected with the development of the sexual organs. In an individual who has been castrated when young the larynx attains a size which exceeds that of the female only to a very small degree, and the high pitch of the voice is retained. Appearance presented by the Interior of the Larynx when examined by the Laryngo- scope.— When the cavity of the larynx is illuminated and examined by the laryngoscopic mirror the parts which surround the superior aperture of the larynx, as well as the interior of the organ, come into view. Not only this, but when the vocal cords are widely separated it is pos- sible to inspect the interior of the trachea as low down as its bifur- cation. In such an exa- mination the arched upper border of the epi- glottis constitutes a conspicuous object, whilst, behind this, the bulging on the anterior wall of the vestilnile, formed by the cushion of the epiglottis, may constitute a feature of the picture. The middle glosso-epiglottidean ligament, with the vallecular fossa on either side of it, can also be inspected in the interval between the epiglottis and the base of the tongue. The sharjj ary- epiglottidean folds are clearly visible, and in the back jjortion of each of these can be seen the two prominent tuljercles which are formed by the enclosed cuneiform cartilage and the cartilage of Santorini. Behind these tubercles is the postei-ior wall of the pharynx, whilst to their outer side the deep sinus pyriformis may be seen. In the interior of the larynx the false and the true vocal cords are easily recognised, and the interval between the false and the true cord, or, in other words, the entrance into the laryngeal sinus, ajjpears as a dark line on the side wall of the larynx. The false vocal cords are red and fiesliy-looking ; the true vocal cords during phonation are tightly stretched and pearly white — the white colour being usually more apj^arent in the female than in the male. The outline and yellowish tinge of the jjrocessus vocali.s at its attach- ment to the true vocal cord, as well as, to a slight extent, the outline of the fore j^art of the base of tlie arytenoid cartilage, can in a successful laryngoscopic examination be made out. The true vocal cords during ordinary inspiration are seldom at rest, and witli the laryngoscope their move- ments may be studied. It should be borne in mind that the picture afforded by the laryngoscope does not give a true idea of the level at wliich the different parts lie. The cavity apj^ears greatly shortened, and its depth diminished. THE TRACHEA. The trachea or windpipe is a wide tube which is l\:ept permanently patent by A B Fig. 692. — Cavity of the Larynx, as seen by means of the laryngoscope. A. The rima glottidis closed. B. The rima glottidis widely open. 1. Rings of the trachea. 2. Processus vocalis of the arytenoid cartilage. 3. Aryteno-epiglottidean fold 4. Sinus pyriformis. 5. Laryngeal sinus. (.!. Vallecula. 7. True vocal cord. S. Cushion of epiglottis. 9. Middle glosso-epiglottidean fold. 10. Base of tongue. 11. Epiglottis. 12. False vocal cord. 1.3. Cuneiform tubercle. 14. Tubercle of Santoriui. THE TEACHEA. 973 Tliyroid cartilase ! — < 'rico-thyroiil mfinbi-ane Cru'oid caitilan Part of trachea covered by istlinms of tliyroid body " a series of cartilaginous rings embedded in its wall. These rings are deficient posteriorly, and consequently the tube is not completely cylindrical : its hinder wall is fattened. The trachea begins a])0ve at the lower Ijorder of the cricoid cartilage, and opposite the lower margin of the sixth cervical vertebra. Erom this it extends downwards through the lower part of the neck into the superior media- stinum of the thorax, in which it ends at the level of the upper Ijorder of the fifth dorsal vertebra by dividing into the right and left l^ronchus. The leno-th of the trachea in the male is from four to four and a half inches, and in the female from three and a half to four inches, but exen in the same individual it varies consider- ably in length with the movements of the head and neck. The lower end of the trachea is fixed in position. This is a necessary provi.sion to prevent dragging on the roots of the lungs during movements of the head and neck. The remainder of the tube is surrounded by a (quantity of loose areolar tissue, and possessesa considerable amount of mobility. Further, its wall is highly elastic, and thus when the head is thrown back the tube elongates through stretching, and when the chin is depressed its length is diminished bv the recoil of its wall. The trachea does not present an absolutely uni- form calibre throughout its whole length. About its middle it exhibits a slight expansion or dilatation, and from this the calibre dimin- ishes in an upward and a downward direction. Close to the bifurcation it is again slightly expanded (Braune and Stahel). These differences in the calibi'e of the tube are de- termined by the surroundings of the trachea. The upper part is narrowed through its being clasped by the thyroid body. Fui'ther, a short dis- tance above the bifurcation an impression, sometimes strongly marked, is usually seen on the left side of the trachea. This is due to the close contact of the aortic arch as it passes backwards against this part of the tube. It is evident therefore that the second slight diminution in calibre which is described by Braune and Stahel is pro- duced by the proximity of the aorta. Lejars gives the average antero- posterior dia- meter of the trachea in the living person as 11 mm., and the transverse diameter as 12 the lumen of the tube is considerablv greater. Pulmonary artery Fig. 693.— The TKACHE.i and Bronchi. The thyroid body is indicated by a dotted line and a purple tint. 5 mm. In the dead subject 974 THE EESPIEATOEY SYSTEM. Vagus nerve subclavian artery Left recurrent laryngeal nerv The trachea adheres rigorously to the median line except towards its lower end, where it deviates very sHghtly to the right. As it descends it recedes rapidly from the surface. This is due to its following the curvature of the vertebral column, from which it is separated by the oesophagus alone. Relations of the Trachea. — In the study of the rela- tions of the trachea it is con- venient to consider it in the two stages of cervical and thoracic. When the chin is held so that the face looks forwards the cervical part of the trachea measures from 2 to 2h inches in length ; but when the head is thrown back the length is consider- ably increased. In its upper part the trachea is clasped by Left subclavian aiten X (^,^CL*^^--.<: > y "" the thyroid body, the isthmus of which is applied to its anterior surface, and covers the second, third, and fourth rings, whilst on each side the lateral lobe of the same body is applied to its lateral surface, and extends down- wards as low as the fifth ring. On either side of the cervical trachea is the common carotid artery, whilst the recurrent laryngeal nerve ascends in the groove between the trachea and the oesophagus. Posteriorly the trachea is in relation to the oesophagus, which intervenes between it and the bodies of the verte- brae, and deviates somewhat to the left as it descends. In addition to the isthmus of the thyroid body two thin muscular strata, composed of the sterno-hyoid and sterno- thyroid muscles, and also the deep fascia and integument, separate the cervical trachea from the surface. In the middle line of the neck there is a narrow diamond-shaped space between the inner Fig. 694. — Transvekse Sections through the trachea aud its imme- margins of these muscles, within which the trachea is merely covered by the integu- ments and fasciai. It is important to note that in the lower part of the neck the deep cervical fascia is in two layers — viz. a strong stratum applied to the anterior surface of the sterno-hyoid and sterno-thyroid muscles, and a weaker superficial layer stretching across between the two sterno-mastoid muscles. Beneath these muscular and fascial layers the inferior thyroid veins descend on the surface of the trachea, Ep.irterial broncliu; Vairus nerve Thoracic duct IJioiicliial artery ""^.X,^ ^ ^ end az\ gos major 694. — Transvekse Sections through the trachea aud its imme- diate surroundings at the level of each of the tipper five dorsal vertebrae. THE BEONCHI. 975 and sometimes the occasional thyroidea ima artery passes upwards in front of the tube. At the upper border of the manubrium sterni the innominate artery may be seen crossing the trachea obliquely. The thoracic part of the trachea is situated in the back part of the superior mediastinum, being separated from the bodies of the vertebne by the oesophagus alone. Immediately above its bifurcation the deep cardiac plexus of nerves is placed in front and on either side of the trachea. At the level of the fourth dorsal vertebra the aortic arch is very intimately related to it. At first in front of the tube, the aortic arch passes backwards in close contact with its left side. The three great vessels which spring from tlie aortic arch are also placed in close proximity to the trachea. The innominate and left common carotid arteries, at first in front, gradually diverge as they proceed upwards and come to lie on either side of the tube — the innominate to the right, and the left common carotid to the left. In front of these vessels are the left innominate vein and the remains of the thymus body. On the right side the thoracic part of tlie trachea is in relation to the right vagus nerve, and is clothed by the right mediastinal pleura ; on the left side are the left subclavian artery and the left recurrent laryngeal nerve. Structure of the Wall of the Trachea. — The wall of the trachea and bronchi is composed uf (1) a fibro-elastic uieuibrane in which the cartilaginous rings are embedded ; (2) within this, and on the posterior aspect of the tube, a layer of muscular tissue, termed the musculus trachealis ; and (3) the lining mucous membrane. The fibro-elastic membrane is strong and dense, and, passing round the whole circum- ference of the tube, it becomes continuous superiorly with the perichondrium which invests the cricoid cartilage. Embedded in its substance are the series of cartilaginous rings. These vaiy in number from 15 to 20, and are composed of hyaline cartilage. They are horseshoe-shaped, the posterior fourth of the circumference being deficient, so that behind, each ring ends in two rounded extremities. The external surface of a tracheal ring is flat and even, and does not project much beyond the level of the membrane in wliich it is embedded ; the inner surface, however, is convex in the vertical direction, and consequently it bulges slightly into the lumen of the trachea. The intervals between the rings are somewhat narrower than the rings themselves, and neigiibouring rings frequently show a more or less complete fusion, whilst others present other irregularities, such as a tendency to bifurcate. The lowest ring is specially adapted to the tracheal bifurcation. In the middle line i)i front it inclines downwards, and from this median peak a cartilaginous strip is carried backwards in the fork between the two bronchi. The musculus trachealis is a continuous layer of involuntary muscular tissue placed in the posterior part of the wall in front of the fibro-elastic membrane. The muscular bundles are arranged transversely, and are attached to the extremities of the rings, and also to the deep surface of the rings for a short distance beyond their extremities. In the intervals between the rings the transverse muscular bundles are attached to the fibro- elastic membrane. It is evident that, by its contraction, this muscle will reduce in a marked degree the lumen of the tube. The mucous membrane is laid smoothly over the interior of the tube upon a layer of submucous areolar tissue. Lymphoid tissue enters largely into the composition of the tracheal mucous membrane, and its inner surface is lined by columnar ciliated epithelial cells. The action of the cilia exercises an important influence in producing an upward movement of the mucus which is pi'esent on the surface of the mucous membrane. Numerous longitudinal bundles of elastic tissue are present in the posterior wall of the trachea, more particularly in its lower part, between the uuicous membrane and the musculus trachealis. In connexion with the mucous membrane there is a plentiful supply of acinose mucous glands. These are placed in the submucous tissue, and also on the posterior as})cct of tiie tube on the exterior of the musculus trachealis as well as amidst its nuiscular bundles. They send tiieir ducts to the surface of the mucous membrane, where they open by trumpet-shaped mouths. THE BRONCHI. The two bronchi proceed obliquely downwards and outwards from the termina- tion of the trachea, each towards the hilum of the corresponding lung. Like the trachea they are kept permanently patent by the presence of cartilaginous rings in their walls. Tliese rings are deficient posteriorly, so that the bronchi exhibit a 97G THE EESPIRATOEY SYSTEM. flattened posterior surface in every respect similar to the trachea. The two bronchi differ from each other, not only in the relations which they present to sur- rounding structures, but also in length, in width, and in the direction which they pursue (Fig. 693, p. 973). The first collateral branch arises from the right bronchus, much nearer the trachea than in th3 case of the left bronchus. It is this which determines the length of these primary divisions of the trachea, and although there is much varia- tion in this matter, it may be said that, as a rule, the left bronchus is at least twice as long as the right bronchus. According to Henle there are from six to eight rings in the right and irom nine to twelve rings in the left bronchus. A marked difference is also noticeable in the calibre of the two tubes. The right bronchus is wider than the left in the proportion of 100 : 784 (Braune and Stahel), and this asymmetry is clearly due to the fact that the right lung is more bulky than the left. The right bronchus, as it passes towards the hilum of the right lung, takes a more vertical course than the left bronchus. It therefore lies more in the line of the trachea, and to this, as well as to its greater width, is due the greater tendency which foreign bodies exhibit, when introduced into the trachea, to drop into the right in preference to the left bronchus. The average angle which the right bronchus forms with the median plane is 24*8°, whilst the angle formed by the left bronchus with the median plane is 45-6°. The more horizontal course of the left bronchus is probably determined by the marked projection of the heart to the left side of the mesial plane (Merkel). Relations of the Bronchi. — Arching forwards over the right bronchus is the vena azygos major, whilst arching backwards over the left bronchus there is the arch of the aorta. Occupying the interval between the bronchi there is a cluster of bronchial lymphatic glands, and an irregular chain of similar glands is carried along each tube towards the hilum of the lung. On the posterior aspect of each bronchus the vagus nerve breaks up into the posterior pulmonary plexus, whilst the left bronchus, as it proceeds downwards and outwards, crosses in front of the oesophagus and the descending thoracic aorta. But perhaps the most interesting relation is that presented on each side by the corresponding pulmonary artery. On the left side the pulmonary artery crosses in front of the left bronchus above the level of its first collateral branch, and then turns round its outer side to gain its posterior aspect. All the left bronchial branches, therefore, are placed below the left pulmonary artery, and are in consequence termed hyparterial. The right pulmonary artery, on the other hand, crosses in front of the continuation of the right bronchus below its first collateral branch. This branch is therefore termed the eparterial bronchus, whilst all the others are classified as hyparterial. Structure of the Walls of the Bronchi. — The wahs of the bronchi present u structure similar to that seen in the trachea. THE THORACIC CAVITY. A central vertical partition, termed the mediastinum thoracis, which extends from the vertebral column behind to the anterior thoracic wall in front, subdivides the thoracic cavity into two large lateral chambers which contain the lungs. From the fact of each of these chambers being lined by an extensive and separate serous membrane called the pleura, they receive the name of the pleural cavities. The mediastinum or intervening partition is built up of several structures which lie in or in close proximity to the mesial plane. The more important of these are the heart, enveloped in its pericardium, the thoracic aorta, with the great vessels which spring from its arch, the pulmonary artery, and the great veins in the neighbourhood of the heart, the thymus gland or its remains, the trachea, cesopliagus, and thoracic duct, and the pneumogastric and phrenic nerves. Tiie ])leural cavities in which the two lungs lie comprise much the largest part of the thoracic cavity. Each is bounded heloto by the corresponding cupola of the diaphragm ; and as the right cupola rises to a higher level than the left, the right pleural cavity presents a smaller vertical depth than the left. In front, the wall of each pleural chamber is formed by the costal cartilages and the sternum ; THE PLEURAL MEMBRANES. 977 laterally, ])j the shafts of the ribs and the intercostal muscles as far back as the angles of the ribs ; hehind, by the portions of the ribs, with the intervening inter- costal muscles, which lie internal to the costal angles ; and internally, Ijj the bodies of the vertebrae and the mediastinal partition which completely shut off the one chamber from the other. The mediastinum is not median in position. Owing to the marked projection of the heart to the left side, and to the position of the descending thoracic aorta on the left side of the mesial plane, the left pleural cliamljer, although it is deeper than the right, is greatly reduced in width. The two pleural cavities, therefore, are very far from being symmetrical in form. Each pleural cavity is completely lined by a separate serous membrane termed the pleura. The portion of this membrane which clothes the mediastinum or intervening partition forms tlie lateral boundary of a space termed the mediastinal or interpleural space, within which the parts whicli build up the mediastinum are placed. THE TWO PLEURAL MEMBRANES. The pleura or pleural membrane of each side not only lines the corresponding pleural cavity, but at the pulmonary root it is prolonged on to the lung so as to give it a complete investment. It is customary, therefore, to recognise a visceral or investing part (pleura visceralis) and a parietal or lining part (pleura parietalis). The inner surface of the membrane {i.e. that surface which is turned towards the interior of the cavity) is coated with squamous endothelium, and presents a smooth, glistening, and polished appearance ; further, it is moistened by a small amount of serous fluid. In consequence of this the surface of the lung covered by visceral pleura can glide on the wall of the cavity, lined as it is by parietal pleura, with the least possible degree of friction. In the pathological condition known as pleurisy the surface of the membrane becomes roughened by inflammatory exudation, and the so-called " friction sounds " become evident ^vhen the ear is applied to the chest. Visceral Pleura. — The visceral pleura is very thin, and is so firmly bound down to the surface of the lung tliat it cannot be detached without laceration of the. pulmonary substance, and then only in small pieces. It dips into the fissures of the lungs, lines them down to the very bottom, and thus completely separates the dif- ferent lobes of the lungs from eacli other. The visceral pleura becomes continuous with the mediastinal part of the parietal pleura over the root of the lung, and also through the ligameutum latum jjulmonis. Parietal Pleura. — Different names are applied to the parietal pleura as it lines the different parts of the wall of the cavity in which tlie lung lies. Thus there is tlie costal pleura, the diaphragmatic pleura, the mediastinal pleura, and the cervical pleura ; but it must be borne in mind that these terms are merely used for convenience in description, and the portions of the membrane so designated are all directly continuous with each other. Tiie cervical pleura rises up into tlie root of the neck, through the superior aperture of the thoiax, and forms a douu'-shaped roof for the pleural cavity. Its summit or highest point reaches the level of the lower border of the neck of the first rib ; but owing to the great obliquity of the first costal arch, this point is placed from one to two inches above the anterior extremity of the first rib, and from a half to one and a half inches above the clavicle. The cervical dome of G6 Fig. 695. — Diagram showing Arrangkment op Pleural Saos, as seen in transverse section. 978 THE KESPIEATOEY SYSTEM. Right vagus nerve Tracliea CEsophagus Left subclavian artery Sulcus bubclavius pleiini is supported on the outer side by the scalenus anticus and scalenus medius muscles, ^Yhilst the subclavian artery arches over it, and lies in a groove on its inner and anterior aspect a short distance below its summit. At a lower level the innominate and subclavian veins also lie upon its inner and anterior aspects. The cervical cul de sac of pleura is strengthened and held in place by an aponeurotic expansion, first described by Sibson, which is spread over it, and is attached to the inner concave margin of the first rib. This fascia is derived from a small muscular slip which takes origin from the transverse pro- cess of the seventh cervical vertebra. Left ^ agus nerve The COStal Left common „i_,,„„ :: „ tl^p taiotid artery P-lcura lb Lnti Leftinno- strouffest and miiinte vein , 1 • 1 , i. e thickest part oi the parietal pleura. It lines the deep surface of the costal arches and of the intervening in- tercostal muscles. In front it reaches the back of the sternum, whilst behind it is carried forwards on the bodies of the vertebrae. It is easily detached from the parts which it covers, except as it passes from the heads of the ribs on to ■the vertebral column. Here it is somewhat tightly bound down. The diaphragm- atic pleura covers the portion of the upper surface of the diaphragm which lies to the outer side of the base of the peri- FiG. 69']. — Dissection of a Subject hardened by Formalin-injection, to show the cardium, but it relations of the two pleural sacs as viewed from the front. The anterior and doCS not dipdowil diaphragmatic lines of pleural reflection are exhibited by black dotted lines, whilst ^^ ^.j^^ bottom of the outlines of the lungs and their fissures are indicated 1 >y the blue lines. , ° the narrow in- terval between the thoracic wall and the diaphragm. In other words, a strip of the upper surface of the diaphragm adjoining its costal attachment is left uncovered. The mediastinal pleura extends backwards from the posterior surface of the anterior thoracic wall to the vertebral column, and it clothes the side of the mediastinum or partition intervening between the two pleural cavities. It is continuous with the pleura costalis of its own side, both in front and behind, along two lines which are respectively termed the anterior and posterior lines of pleural THE PLEUEAL MEMBRANES. 979 reflection: whilst below it becomes continuous with the diaphragmatic pleura of its own side at the base of the pericardium. Above the level of the root of the hmg the mediastinal pleura passes directly backwards from the sternum to the vertebral column. In this region the left mediastinal jdeura is appKed to the arch of the aorta and the phrenic and vagus nerves ; to the left innominate vein, the left superior intercostal vein, and the left common carotid and left sul jclavian arteries ; to the oesophagus and the thoracic duct. The rightmediastinal pleura, on the other hand, is applied, above the level of the root of the lung, to the upper part of the superior vena cava and right innominate vein ; to the ric{ht innominate artery ; to the vena azygos major, as it nooks forwards above the bronchus; to the vagus and phrenic nerves ; and to the right side of the trachea. Opposite the root of the lung, as well as in the region below it, the mediastinal pleura clothes the corresponding aspect of the peri- cardium, and is somewhat firmly attached to it. As the phrenic nerve passes downwards upon the pericardium it is likewise covered over by the pleura. In the region corresponding to the upper lateral aspect of the pericardium the mediastinal pleura is prolonged outwards, so as to form an invest- ment for the root of the lung, and become continuous around tbe hilum of the lung with the visceral pleura. Below the root of the lung the two layers of pleura which invest it come into apposition with each other, and are prolonged down- wards as a distinct fold, termed the ligamentum latum pulmonis. This fold stretches between the pericardium and the lower part of the inner surface of the lung, and ends below in a free border. Behind the root of the lung and the ligamentum latum pul- monis the mediastinal pleura on the right side is carried backwards to the vertebral column on the oesophagus , whilst on the left side it is carried backwards over the descending aorta, and to a small extent, in the region immediately above the diaphragm and in front of the aorta, over the lower end of the oesophagus. Lines of Pleural Reflection. — These are three in number — viz. the anterior or sternal, the posterior or vertebral, and the lower or diaphragmatic. The pleural cavities are not symmetrical. The left is longer and narrower than the right, and it thus happens that the lines of pleural reflection do not accurately correspond on the two sides of the body. Further, although the posterior line of reflection is fairly constant, the other two Fk; 697. — Lateral View ok the Rkjht Pleihai, Sac in A Subject il\.rdened by Formalin -injection. The blue lilies iiidioate the outline of the riglit lung, ami also the position of its lissures. 980 THE EESPIEATOEY SYSTEM. CEsopliagus Left subclavian arteiy V Left common carotid arterj Left superior intercostal vein Left innominate vein reflection-lines are subject to marked variations in different subjects. Consequently the following description must be regarded as merely giving the average condition. The posterior or vertebral line of pleural reflection is that along which the costal pleura is continued forwards from the vertebral column to become the mediastinal plevira. On the right side, above the root of the lung, the pleura passes from the bodies of the vertebrse on to the right side of the trachea; whilst below this level, and behind the peri- cardium, it passes from the vertebral bodies on to the cesophagus. On the left side, and above the arch of the aorta the pleura along this line of reflection is carried from the vertebral column on to the oesophagus and thoracic duct ; below that level it passes on to the descending thoracic aorta. In the upper part of the chest the right and left lines of reflection are placed well apai't from each other, and about equidistant from the mesial plane. As they are traced downwards they approach more closely to each other and deviate to the left, so that whilst the reflection on the right side takes place from the front aspect of the vertebral bodies, on the left side it takes j)lace from the left aspect of the vertebral column. This is due to the position of the descend- ing thoracic aorta. The anterior line of pleural reflection is that along which the costal pleura leaves the anterior thoracic wall to become the mediastinal pleura. The line diflers somewhat on the two sides, and in both cases shows a tendency to deviate to theleft (Fig. 696, p. 978). Behind the upper part of the manubrium sterni the two pleural sacs are separated from each other by an angular inter- val. The lines of reflection at the inlet of the thorax correspond to the sterno- clavicular joints. From these points, as they are traced downwards, they converge on the back of the manubriiun, until at last they meet a short distance above the upper end of the gladiolus. Here the two sacs come into contact with each other, and the lines of reflection coincide. From this they proceed down- 698. — Left Pleural Sac in a Subject hardeis'ed by Formalin- wards on the back of the INJECTION, opened into by the removal of the costal part of the parietal sternum with a slight de pleura. The lung has also been removed so as to display the media- „;,,+;„,-, !„ fV.Q loff^r.f +V,c Diaphragm pie stinal pleura. viation to the left of the mesial plane, until a point immediately above the level of the stei-nal attachments of tlie fourth costal cartilages is reached, and here the two sacs part company. The line of reflection of the right pleura is continued downwards in a straiglit line behind the sternum until the back of the ensiform cartilage is reached, and here the sternal reflection-line passes into the right diaphragmatic THE PLEUEAL MEMBEANES. 981 reflection-line. Opposite the sternal attachment of the fourth costal cartilage the reflection line of the left pletira deviates outwards on the back of the sternum, and is continued downwards at a variable distance from the right pleura. A small triangular area of pericardium is thus left uncovered by pleura, and therefore in direct contact with the anterior chest-wall. Leaving the sternum, the reflection-line of the left pleura descends parallel and close to the left margin of the sternum behind the fourth intercostal space, the fifth costal cartilage and the fifth intercostal space, to the back of the sixth costal cartilage. Here it turns outwards and downwards, and passes into the dia- phragmatic reflec- tion-line of the left side. From the back of the sternum the r/r\ Right subcla^ lan vessels Internal iiiamim Right inno minate vein Sterno-hyoid muscle Sterno-thyroid muscle Stei iio-mastoid muscle Thyroid body Internal jugular vein Plueiiic nerve Scalenus anticus - 'subclavian artery (left) Left \ agus nerve ^sj-'5ubcla\ian vein (left) jmmon carotid artery Left innominate vein First rib \ortic arch T;eft lolje of thymus and Left lung rj- Pulmonary fissure Pericardium Fig. 700. -Dissection of Thorax and root of the Neck from the front to show the relations OF THE Lungs, Pericardium and Thymus Gland. the lung differs considerably at different periods of life. In early childhood the lung is rosy-pink, and the darker colour and the mottling of the surface which appear later are due to the pulmonary substance, and chiefly the interstitial areolar tissue becoming impregnated more or less completely with atmospheric dust and minute particles of soot. At every breath foreign matter of this Ivind is inhaled, but onlj' a small jn'oijortion of it reaches the hing tissue. The greater part of it becomes entangled in the slimy mucus which coats the mucous memljrane of the larger air-passages, and is gradually got rid of along with the mucus through the activity of the cilia attached to the lining epithelium. By the constant upward sweep of these a current towards the j)haryiix is established. The fine dust and soot particles which reach the finer recesses of the lungs, and ultimately the interstitial issue, is partly conveyed away by the lymphatic vessels to the bronchial glands, which in consecpience become in many cases absolutely black. The colour of the lung, therefore, depends to some THE LUNGS. 985 extent ui^on the purity of the atmosphere which is inhaled, and it thus liappens that in coal- miners the surface of the hmg may be very nearly uniformly black. The foetal lung differs in a marked degree from the lung in an individual who has breathed. After respiration is fully established, the lung soon comes to occupy almost the whole space allotted to it in the pleural cavity ; in the fcetus, on the other hand, the lung is packed away at the back, and occupies a relatively much smaller amount of space in the thoracic cavity. Further, it is firm to the touch, and sinks in water. It is only when air and an increased supply of blood are introduced into the lung that it assumes the soft spongy and buoyant quahties which are characteristic of the adult lung. Form of the Lungs.— The lungs are accurately adapted to the walls of the pleural chambers in which they are placed, and in the natural state they bear on Fig. 701. — Mediastinal Surf.vces of the two Lungs of a Subject hardened by FoKMALiN-rNjECTiox. A, Right luug. B, Left lung. 1. Base. 2. Fissure. 3. Carrliac depression. 4. Groove for iiinuiiiinate vein. ."). Groove for innominate artery. 0. Apex pulmonis. 7. Groove for vena azygos major. S. Eparterial bronchus. SI. Pulmonary artery (right). 10. Fissure. 11. Groove for aorta. 12. Bronclius. 13. Pulmonary artery (left). 14. Apex pulmonis. 15. Groove for left subclavian artery. 16. Groove for left innominate vein. 17. Cardiac depression. IS. Fissure. Hi. Base. the surface impressions and elevations which are an exact counterpart of the irregularities on the walls of the cavity in which they lie. When care has been taken to harden it in situ, each lung presents an apex and a base, an inner and an outer surface, and an anterior and a posterior border. The apex pulmonis is blunt and rounded, and rises above the level of the oblique first costal arch to the full height of the cervical dome of pleura. It therefore protrudes upwards througli the thoracic inlet into the root of the neck. The sul)clavian artery arches outwards on its inner and anterior aspects a short distance below its summit, and a groove (sulcus subclavius) corresponding to the vessel is apparent upon it. At a lower level on the apex pulmonis a shallower and wider groove upon its inner and anterior aspects marks tiie position of the innomi- nate and subclavian veins. Although these vessels impress the luug they are separated, from it by the cervical pleura. The basis pulmonis preseuts a semilunar outline, being curved around the base of the perieardiuin. It is adapted to the u]»per surface of the diaphragm, and conse- quently it is deeply hollowed out. As the right cupola of the diaphragm ascends higher than the left, the basal concavity of the right lung is deeper than that of 986 THE EESPIEATOEY SYSTEM. the left lung. Laterally and behind, the base of each king is limited by a salient thin margin which descends for some distance in the narrow pleural recess (sinus phrenico-costalis) between the diaphragm and the chest wall. This basal margin of the lung extends lower down on the outer side and behind than it does in front, but it falls considerably short of the bottom of the phrenico-costal sinus of pleura. Thus, after expiration, it reaches in the mammillary line the lower border of the sixth rib; in the axillary or mid -lateral line the eighth rib; whilst behind it pro- ceeds inwards along a straight horizontal line so as to reach the vertebral column at the level of the extremity of the spine of the tenth dorsal vertebra. During respiration the thin basal margin rises and falls in the phrenico-costal sinus of the pleura, but even after the deepest breath it never reaches the lowest limit of this recess. The bases of the lungs establish important relations with certain of the viscera which occupy the costal zone of the abdominal cavity, the diaphragm alone intervening. Thus LAVIAN ARTERY nnominate: vein Fig. 702. — Outer or Costal Surfaces of the two Lungs. A, Eight lung. B, Left hmg. the base of the right lung rests upon the right lobe of the liver ; whilst the base of the left lung is in relation to the left lobe of the liver, the fiuidus of the stomach, the spleen, and in some cases to the splenic flexure of the colon. The outer surface of the lung (facies costalis pulmonis) is extensive and convex. It is accurately adapted to that part of the wall of the pleural cavity which is formed by the costal arches and the intervening intercostal muscles, and it presents markings corresponding to these. Thus the imprint of the ribs appear as shallow oblique grooves, while the intercostal spaces show as elongated intervening bulgings. The inner or mediastinal surface of the lung (facies mediastinalis pulmonis) presents a smaller area than the outer surface. It is applied to the mediastinal septum, and presents markings in accordance with the inequalities upon this (Fig. 701, p. 985). Thus it is deeply hollowed out in adaptation to the pericardium upon which it fits. This pericardial concavity comprises the greater part of the media- stinal surface, and owing to the greater projection of the heart to the left side, it is much deeper and more extensive in the left lung than in the right lung. Above and behind the pericardial hollow is the hilum of the lung. This is a wedge-shaped depressed area, within which the vessels, nerves, and lymphatics, together with the THE LUXGS. 987 Trapezius ,Supni-spinatus Clavicular part of pectoralis major' Coi'acoi Cephalic vein — j.L ^jternal part of pectoralis major" Axillary artery Brachial nerves Axillary vein Pectoralis minor' Spine of scapula Infra- spinatus Subscapularis Sen-atus mascnus Rhoniboitleus —major bronchus, enter and leave the organ. Amidst these structures also are some bronchial glands. The hilum is surrounded by the reflection of the pleura from the surface of the lung on to the pulmonary root. Behind the hilum and peri- cardial area there is ciavifi.' on each lung a narrow strip of the inner sui - face of the lung which is in relation to the lateral wall of the pos- terior mediastinum. On the right lung this part of the surface is depressed, and corre- sponds to the oeso- phagus ; on the left lung it presents a broad longitudinal groove, which is pro- duced by the contact of the lung with de- scending thoracic aorta, and also, close to the base, a small flattened area in front of this which is ap- plied to the oesophagus where it pierces the diaphragm. The portion of the inner surface of the lun« which lies alDove 'the hilum and peri- cardiac hollow is ap- plied to the lateral aspect of the superior mediastinum, and the markings are accordingly somewhat different on the two sides. On the left lung a broad deep groove, produced by the aortic arch, curves backwards over the hilum, and becomes continuous with the aortic groove on the posterior mediastinal surface. From this a narrower, deeper, and much more sharply-marked groove ascends, and turns outwards over the apex pulmonis a short distance from the summit. This is the sulcus suljclavius, and it contains the left subclavian artery when the lung is in place. In front of this a shallow wide groove, also leading up to the front aspect of the apex, corresponds to the left innominate vein. In the right lung the hilum is also circumscribed above by a curved groove, but this is narrow and more distinctly curved than the aortic groove on the left side. It lodges the vena azygos major as it turns forwards to join the superior vena cava. From the anterior end of the azygos sulcus a wide shallow groove extends upwards to the lower part of the front of the apex pulmonis. This is produced by the apposition of the lung with the vena cava superior and the right innominate vein. Close to the summit of the apex there is also, on its inner aspect, a sulcus for the upper end of the innominate artery. In addition to the hilum, it must now be evident that the inner surface of each lung presents three areas which correspond respectively with (1) the middle mediastinum (i.e. the pericardial hollow) ; (2) the posterior mediastinum : and (3) the superior mediastinum ; and that in each of these districts impressions correspond- ing to structures coutained within these portions of the interpleural space may be noticed. The posterior border of the lung is tiiick, Ioul;", and rounded. It forms the most Diaphragm Fig. 703. — S.vgittal Section thkough Left Shoui.deu and Left Lung. 988 THE EESPIEATOEY SYSTEM. bulky part of the organ, and occupies the deep hollow in the thoracic cavity which is placed on either side of the spine. Indeed the term " border " is somewhat inappropriate, as it forms in reality a somewhat extensive surface deeply impressed by the ribs, and not in Scalenus mediu Brachial ner\ cs Subclaviii-i- Subclavian artery Subclavian vein Omo-hyoi(k ^^>~' Clavicle-^^ /V^* Trapezius >ei 1 atus magnus any way marked off from the outer surface of the lung. . The anterior border of the lung is short and ex- ceedingly thin and sharp. It begins abruptly above, immediately below the groove on the apex for the innominate vein, and extends down to the base, where it becomes con- tinuous with the sharp basal border. The thin anterior part of the lung is carried forwards and inwards in front of the pericardium into the narrow pleural recess be- hind the sternum and costal cartilages (sinus costo-mediastinalis). The anterior border of the right lung fills up this recess completely, and in the upper part of the chest is only separated from the corresponding border of the left lung by the two layers of mediastinal pleura which are reflected backwards from the ster- num to the pericardium. The anterior border of the left lung, in its lower "part, shows a marked deficiency or notch (incisura cardiaca) corresponding to the apex of the heart, and where this exists the lung margin leaves a considerable portion of the pericardium uncovered, and fails to completely fill up the costo-mediastinal sinus of the pleural cavity. During respiration the anterior margin of the left lung at the incisura cardiaca advances and retreats to a small extent in this pleural sinus in front of the pericardium. Fissures and Lobes of the Lungs. — The left lung is divided into two lobes by a long deep fissure which penetrates its substance to within a short distance of the hilum. Above and below the hilum this fissure cuts right through the lung and appears upon the mediastinal or inner surface. Viewed from the outer aspect of the organ, it begins at the posterior border about two and a half inches below the summit of the apex, about the level of the vertebral end of the third rib, and is continued downwards and forwards in a somewhat spiral direction to the base of the lung, which it reaches a short distance behind its anterior end. The upper lobe of the lung (lobus superior) lies above and in front of this cleft. It is conical in form, with an oblique base, and the apex and the whole of the anterior border of the lung belong to it. The lower lobe (lobus inferior) lies below and behind the fissure. It is the more bulky of the two, and includes almost the entire base and the greater part of the thick posterior border. In the right lung there are two fissures subdividing it into three lobes. One of these fissures is very similar in its position and relations to the fissure in the left lung. It is, however, rather more vertical in its direction, and ends lielow somewhat Diaphragm (f^\ Reflection \^ 1. 1 'of pleura Fig. 704. -Sagittal Section through the Left Shoulder Lung, and Apex of the Heart. ROOT OF THE LUNG. 989 further outwards. It separates the lower lobe from the upper and middle lobes. The second cleft begins in the main fissure at the posterior border of the lung, and proceeds horizontally forwards, to end at tlie anterior border of the lung at the level of the fourth costal cartilage. The middle or intermediate lobe of the right lung is triangular or wedge-shaped in outline. Variations. — Variations in the pulmonary fissures are fairly common. Thus it sometimes happens that the middle lohe of the right hmg is imj^erfectly cut off from tlie up])er lobe. Supei-numerary fissures also are not infrequent, and in this Avay the left lung may be cut into three lobes, and the right lung into four or even more lobes. The occurrence of a lobus azygos in the right lung is a variation of some interest, seeing tliat such a lobe is constant in certain mammals. It is a small accessory lobe, jiyramidal in form, which makes its apjiearance on the lower part of the inner aspect of the right lung. In certain cases the vena azygos major is enclosed Avithin a fold (jf pleura, and is sunk so deeply in the pulmonary substance of the right lung that it marks oil a small accessory lobe. ROOT OF THE LUXG. The term root of the lung (radix pulmonis) is applied to a number of structures which enter and leave the lung at tlie hilum on its inner surface. They are held together by an investment of pleura, and constitute a pedicle which attaches the lung to the mediastinal wall of the pleural cavity. The phrenic nerve descends a short distance in front of the pulmonary root, whilst the vagus nerve breaks up into the posterior pulmonary plexus on its posterior aspect under cover of the investing pleura. The delicate anterior pulmonary plexus is placed in front of the root of the lung beneath the pleura, whilst from the lower border of the root of the lung the ligamentum latum pulmonis extends downwards. These are the relations wliich are common to the pulmonary root on both sides of the body, but there are others which are peculiar to each side. On the right side the superior vena cava lies in front of the pulmonary root, whilst the vena azygos major arches over its upper aspect. On the left side the aorta arches over the root of the lung, whilst the descending thoracic aorta passes down behind it. Constituent Parts of the Pulmonary Root. — The most important structures which enter into the formation of the pulmonary root are (1) the two pulmonary veins ; (2) the pulmonary artery ; (3) the bronchus. But in addition to these there are one or more small bronchial arteries and veins, the pulmonary nerves and the pulmonary lymphatic vessels, and some bronchial glands. Tlie pulmonary nerves come from the vagus nerve and also from the symj'athetic .system. They enter the lung and foUow the air-tubes through the organ. The bronchial arteries are small vessels which carry blood for the supply of the lung tissue. They arise from the aorta or from an intercostal artery, and vary in number from one to three for each lung. In the root of the lung they lie on the posterior asj^ect of the bronchus, and they follow the air-tubes through the organ. Part of the blood conveyed to the lung by the bronchial arteries is returned by the I^ulmonary veins ; the remainder is returned by special bronchial veins which open on the right side into the vena azygos major, and on the left side into the vena azygos minor superior. The lymphatic vessels of the lung, as they emerge from the hilum, unite into a small number of trunks, which, jjlaced behind the large pulmonary vessels, open into the bronchial glands. The bronchus in the root of the lung lies behind the great pulmonary vessels. The pulmonary artery occupies a dilferent position on the two sides in relation to the main or undivided part of the bronchus. On the right side it is placed below it, whilst on the left side it crosses the bronchus and occupies a higher level in the pulmonary root. The two pulmonary veins on both sides lie at a lower level in the root of the lung than tbe puhuonary artery and bronchus, wliilst the u})per of the two veins occu])ies a ]ilaue in I'rout of the pulmonary artery (Fig. 701, p. 985). Distribution of the Bronchial Tubes within the Lungs. — The two lungs are not symmetrical; the right huig is subdivided into three lobes, and the left lung is cleft into two lobes. The bronchi exhibit a corresponding want of symmetry. The right bronchus, as it approaches the pulmonary liiluni, gives off two branches for the upper and middle lobes of the right lung respectively, and then the main stem of the tube enters the lower lobe. The hft bronchus sendsolf a large branch to the upper lobe of the left lung, and then sinks into the lower lobe. The first branch of the right bronchus i'or the upper right pulmonary lobe leaves the main stem about one 990 THE EESPIEATOEY SYSTEM. inch from the trachea. The first brancli of the left bronchus, on the other hand, takes origin about twice that distance from the trachea. The relation of the pulmonary artery to the bronchial subdivisions is different on the two sides. On the right side it turns backwards to reach the posterior aspect of the bronchus below the first and above the second bronchial branch. On the left side the pulmonary artery turns backwards above the level of the first bronchial branch. On the right side, therefore, the first bronchial branch is placed above the pulmonary artery, and in consequence it is termed the eparterial bronchus ; all the others lie below the artery, and are termed hyparterial bronclii. On the left side there is no eparterial branch ; they are all hyparterial. When the main stem of the bronchus is followed into the inferior lobe of each lung, it is seen to travel downwards and backwards in the pulmonary substance until it reaches the thin back part of the base of the lung which lies between the diaphragm and the thoracic wall, and there it ends. As it proceeds through the inferior lobe it gives off a series of large ventral and a series of smaller dorsal branches. As a rule these are three in number in each case, and the dorsal and ventral branches do not arise opposite to each other, but alternately, one from the back, and then another, after a slight interval, from the front of the tube. The first hyparterial division on each side (i.e. the branch to the middle lobe of the right lung and the branch to the upper lobe of the left side) is generally regarded as the first member of the ventral group. It was Aeby wbo first recognised tbe existence in each, lung of a main or stem bronchus giving off a ventral and dorsal series of brancbes, and wbo drew tbe distinction between tbe eparterial and byparterial broncbial branches. A consideration of these relations led this author to concbide that the eparterial bronchus and the upper lobe of the right bmg have no morpholo- gical equivalents on the left side of the body. In other words, he was led to believe that the middle lobe of the right lung is the homologue of the upjoer lobe of the left lung. Hasse, who has also investigated the subject, endorsed this view, witli certain modifications and additions, and the hypothesis, either in its original state as jjresented by Aeby, or as subsequently modified by Hasse, has been, until lately, very generally accej^ted by anatomists. More recent research, however, has seriously affected the stability of this conclusion. Narath contends that the distinc- tion between the eparterial bronchus of the right side and the hyparterial bronchi of both sides is not one of fundamental importance, and further, that a branch which arises from the first hyparterial bronchus on the left side and turns upwards into the apex of the left lung is the direct equivalent of the eparterial bronchus of the right side. This he terms the apical bronchus, and he believes that it represents the first dorsal branch of the left stem-bronchus. Huntington, in a very convincing paper, strongly supjDorts the contention of Narath, and holds that, excejit " for purposes of topography, we should abandon the distinction between ej)arterial and hyparterial bronchi.'' With Narath he regards the eparterial bronchus as a secondary branch which has migrated in an upward direction on the main stem. Accoixling to Himtington, therefore, Aeby's proposition should be amended as follows : — Right side. Left side. Upper + middle lobe = Upper lobe. Lower + cai'diac lobe = Lower lobe. The cardiac lobe mentioned in this table is the occasional azygos lobe to which reference has already been made, and it is interesting to note that, whilst the lobe in c^uestion as a separate entity is rarely seen in tlie human lung, the bronchus wliich corresponds to it is always present in the pulmonary substance as an accessory branch, which proceeds from the main stem as it traverses the lower lobe of the right side. It receives the name of the cardiac bronchus. Structure of the Lung. The lung is constructed so that the blood which reaches it through the pulmonary artery is brought into the most intimate relation Avith the air which enters it through the trachea and bronchi. An interchange of materials between the blood and the air is thus rendered possible, and the object of respiration is attained. As a result of this inter- change the dark impure blood which flows into the lung through the pulmonary artery is rendered bright red and arterial. Lobules of the Lung. — A thin layer of subplenral connective tissues lies subjacent to the continuous coating which the lung receives from the visceral pleura. From the deep surface of this subpleural layer fine septal processes penetrate into the substance of the lung, and these, with the connective tissue which enters at the hilum upon the vessels and bronchi, constitute a supporting framework for the organ. The lung is lobular, and on the siu'face the small polygonal areas which represent the lobules are indicated by the STEUCTUEE OF THE LU:SG. 991 pigment present in the connective tissue septa which intervene between them. Although no pigment is present, the lobular character of the lung is particularly well marked in the foetus, and with a little care the surface lobules in the fcjetal lung can be separated from each other by gently tearing through the intervening connective tissue. The lobules thus isolated are pyriform or pyramidal in form. The broad bases of these lobules abut against the subpleural layer, whilst each of the deep narrow ends receives a minute division from the bronchial system of tubes. The lobules which lie more deeply in the substance of the organ are not so large, and are irregularly polygonal in form. Alveolar Ducts, Infundibula, and Air-cells. — The larger branches of the bronchi, as they traverse the lung, give otf numerous divisions which, by repeated branching, ultimately form a system of tubes which pervade the entire organ. At first the bronchial divisions come off at very acute angles, bnt as the finer ramifications are reached this character becomes much less apparent. Thei'e is no anastomosis between the bronchial branches. Within the various lobules the finer bronchioles send off further branches, which pro- ceed at right angles from them. Soon the ultimate tubes are reached. These are not cylindrical, but have their walls pouched out by numerous hemispherical diverticula. Such a bronchiole is called an alveolar duct, and the diverticula are the air-cells or alveoli. Finally the alveolar duct divides into two, three, or more tei-minal parts, which become expanded and form the club-shaped, blind terminations of the bronchial s3'stem of tubes. These cfccal endings are the infundibula, and the walls of each are thickly covered by alveoli or air-cells, all of which open into the infundibulum as into a corridor. Structure of the Bronchi. — ^When the large bronchi enter the lung they become cylindrical, and lose the flattening on the posterior aspect which is characteristic of the primary bronchi outside the lung. They possess the same coats as are present in the case of the trachea and primary bronchi, but as the tubes become smaller by repeated division, these coats become correspondingly tliinner and finer. Certain marked differences also in the manner in which the constituents of these coats are arranged become apparent. In the external fibro-cartilaginous coat the cartilage is no longer present in the form of incomplete rings, but in irregular plates or flakes deposited at various points around the wall. As the tubes diminish these cai-tilaginous deposits show a corresponding reduc- tion in size, until at last, in bronchi of 1 mm. in diameter, they disappear altogether. The glands in relation to the tubes for the most part cease to exist about the same point. The muscular or middle coat, which in the trachea and primary bronchi is confined to the back wall of the tube, forms a continuous layer of circularly-arranged bundles in the bronchi as they ramify within the lung. Spasmodic contraction of the muscular coat gives rise to the serious symptoms which accompany asthmatic atVections. The muscidar libres of the middle coat may be traced as far as the infundibula, on the walls of which they are present in considerable numbers. The mucous lining of the tubes becomes greatly thinned as it is followed into the smaller bronchioles. It contains a large number of longitudinally- arranged elastic fibres, and is disposed in longitudinal folds, so that when the tube is cut across the lumen presents a stellate appearance. The mucous membrane is lined by ciliated columnar epithelium. Structure of the Infundibula and Alveoli.— The walls of the infundibula and alveoli are exceedingly fine and delicate, but nevertheless constituents continuous with those observed in the three coats of a bronchus arc found entering into their construction. The epithelium is reduced to a single layer. Further, it is no longer columnar and ciliated, but it has become flat and pavement-like. Two kinds of epithelial cells may be recognised — (1) a few small granular polygonal cells, arranged singly or in groups of two or three ; (2) more numerous thin cells of lai'ge size, and somewhat irregular in outline. Outside the epithelium is a delicate layer of faintly-fibrillated connective tissue. This is strengthened by a network of elastic fibres which is specially well marked around the mouths of the alveoli, and is also to some extent carried over the walls of the air-cells. Muscular fibres are likewise present on the walls of the infundibula, but it is questionable if any are prolouged over the air-cells. Pulmonary Vessels. — The pidmonary artery, as it traverses the lung, divides with the bronchi, and closely accompanies these tubes. The resultant branches do not anasto- mose, and for the most part they lie above and behind the corresponding bronchi. The fine terminal divisit)ns of the artery join a dense capillary plexus which is spread over the alveoli or air-cells. This vascular network is so close that the meshes are barely wider than the capillaries which form them. In the partitions between adjacent alveoli there is only one layer of the capillary network, and thus the blood flowing through these vessels is exposed on both aspects to the action of the air in the air-cells. The radicles 992 THE EESPIEATOEY SYSTEM. of the pulmonary yeiu arise in, and carry the blood from, the pulmonary capillary plexus. Each afferent arteriole supplies the blood which flows through the capillaries spread over a number of neighbouring alveoli, and in feke manner each efferent venous radicle drains an area corresponding to several adjoining air-cells. At fii'st the veins run apart from the arteries, but after they have attained a certain size they join them and the bronchi. As a rule the pulmonary veins are placed on the lower and front aspect of the corre- sponding bronchi. Development of the Eespiratory Apparatus. The larynx, the trachea, the bronchi, and the lungs arise as an outgrowth from the ventral aspect of the foregut. The first indication of a respiratory tract occurs in the human embryo when it has attained a length of 3-2 mm., on or about the fifteenth day of development. A median longitudinal groove makes its appearance within the foregut on its ventral wall. This extends from the pharynx in front to the region of the stomach behind, and it gradually deepens as it passes backwards. The hinder or gastric end of the pulmonary groove ends iu a blind diverticulum or pocket, which freely communicates with the cavity of the foregut, and forms a hollow median protrusion on the ventral aspect of this portion of the primitive alimentary canal. The opposite end of the gi'oove is bounded by the furcula (see p. 35). Farther, it is lined with endoderm or hypoblast continuous with the endodermal lining of the foregut. Trachea and Larynx. — The pulmonary groove on the ventral aspect of the foregut becomes first partially and then completely separated from the part of the foregut which lies on its doi'sal aspect by two lateral ridges which grow inwards and finally meet. Two tubes ai-e thus formed — viz. one behind, the oesophagus, and the other in front, the trachea and larynx. At their cephalic ends a communication between the two tubes is preserved as the permanent communication between the larynx and pharynx. The cephalic end of the air-tube which is thus separated off from the foregut becomes enlarged to form the larynx, whilst the remainder is developed into the trachea. The cai'tilages of the larynx do not make their appearance until the eighth or ninth week. The thyroid cartilage is believed to be formed out of the ventral portions of the cartilages which support the 4th and 5th visceral arches of the two sides united in the median plane. The epiglottis takes form in the upper or front part of the furcula (see chapter on Embryo- logy, p. 35), whilst the aryteno-epiglottidean folds and the arytenoid cartilages ai'e developed in its lateral portions. The cricoid cartilage and the tracheal rings are formed in the mesoderm of the aii'-tube. Lungs and Bronchi. — The endodermic diverticulum, or pocket in which the gastric end of the primitive respiratory groove terminates, very early bifui'cates into two vesi- cular portions, which represent the primitive right and left bronchi and lungs. From the first the right pulmonary vesicle is slightly the larger of the two. Both elongate, and almost immediately each part undergoes a subdivision — the right into three vesicles, and the left into two vesicles — thus early indicating the three lobes of the right lung and the two lobes of the left lung. The endodermal cells form the epithelial lining of the air- passages, whilst from the mesoderm are derived the blood-vessels and the other tissues which build up the lung. The hypoblastic or endodermal subdivisions thus formed are embedded within the surrounding mesoderm. The main endodermal subdivisions continue to branch and reVjrcxnch, pushing their way into the pulmonary mesoblast, until the complete bronchial tree is formed. The method of subdivision is veiy characteristic, and from the first the various branches ai"e bulbous or flask-shaped at their extremities. These bifurcate, and although at first the two subdivisions in each case appear of eqiial importance, one grows out as the continuation of the main bronchial stem, whilst the other remains as a lateral branch. When the ramification of the endodermal tubes into the lung mesoderm is complete, the small terminal flask-shaped extremities of the various branches represent the infundibula. At first these are devoid of air-cells, but between the sixth month and the termination of gestation the alveolar diverticula make their appearance on the alveolar ducts and on the infundibula. It is thus seen that the epithelial lining of the entire system of bronchial tubes, infundibula and alveoli, is originally derived from the endodermal lining of the foregut. The other constituents which enter into the constitution of the lungs and bronchi are derived from the mesoblast. The rudiments of the lungs grow backwards on either side of the oesophagus into the fissure-like portion of the coelom which occupies the thoracic region. They push before them the epithelial lining of the latter, and thus acquire their covering of visceral pleura. By the development c)f the diaphragm and the pericardium the pleural portions of the coelom become cut oft' from the peritoneal cavity and from each other. THE DIGESTIVE SYSTEM. By Ambkose Biemingham. Under this head will be described the parts which are connected with the reception and mastication of the food, and its digestion and passage through the body. As the greater part of the digestive system is placed within the abdomen, the description of this cavity as a whole, with that of its lining membrane the peritoneum, will he included. The different parts of the digestive system may be grouped under the following heads, viz : — 1. The Alimentary Canal or Digestive Tube. 2. The Digestive Glands. 3. Accessory Parts. Alimentary Canal. — The alimentary canal, taken as a whole, measures about 30 feet in length (Fig. 705), and consists of the following parts in order: — mouth, pharynx, oesophagus, stomach, small and large intestines: The mouth is the first division of the tube. It is separated from the nasal cavities above by the palate, and opens behind into the pharynx. This latter is an expanded portion of the canal lying behind both the mouth and the nasal cavity, the former opening into it through the isthmus of the fauces, the latter through the posterior nares ; whilst lower down, immediately below the base of the tongue, the aperture of the larynx is found on its anterior wall. Opposite the lower border of the larynx, the pharynx is succeeded by the oesophagus, a long and comparatively straight portion of the digestive tube, leading through the neck and thorax to the abdomen, which it reaches by piercing the diaphragm. Immediately after entering the abdomen the tube expands into a pear-shaped dilatation, the stomach. This is followed by over 20 feet of small intestine, the junction of the two being marked by a constriction, the pylorus. The small intestine presents three more or less arbitrary divisions — namely, (a) the duodenum, a part about 10 inches in length, curved somewhat like a horse-shoe, and closely united to the posterior abdominal wall ; (b) the jejunum, which includes the upper two-fifths, and (c) the ileum, the lower three-fifths of the small intestine beyond the duodenum. The jejunum and ileum are mu\al)ly suspended from the posterior abdominal wall by the mesentery, a fan- shaped fold of the peritoneum or lining membrane of the abdominal cavity. The terminal part of the ileum opens into the side of the large intestine, a few inches (2h) from the blind commencement of the latter. There is thus formed at the beginning of the great intestine a cul-de-sac, the caecum, in connexion with which is found a small worm-shaped diverticulum, the vermiform appendix. The orifice through which tlie ileum opens into the large intestine is guarded by the ileo-csecal valve, whicli prevents any return of its contents from the large into tlie small bowel. After the caecum comes the 'ascending colon, which runs up in the right side of the abdomen. This is succeeded in order by the transverse colon crossing from right to left, the descending colon running down on the left side, the sigmoid flexure of the colon (whicli includes the iliac and greater part of the pelvic colons of tht^ text), and finally tlie rectiun, which opens on the surface at the anus. Digestive Glands. — Whilst the greater part of the alimentary canal is furnished with numerous minute glands contained entirely within its walls, 67 993 994 THE DIGESTIVE SYSTEM. there are in addition certain special accumulations of glandular tissue, namely, the liver, the pancreas, and the salivary glands, which, although developed in the Bile due- Transverse colon (cut) Hepatic Hexuie of colon -^^^^ Coniinon orifice of bile and pancreatic ducts Duodenui Pancreatic duct Splenix flexure of colon Fk;. 705. — Genkkal View ok the Dkiestive Sy.stem (diagranimatic). The traiisver.se colon lias lieen cut to .show the duodenum, but its course is indicated by dotted line.s. Tlie vermiform appendix i.s seen hanging down from the caecum. The loop of large intestine which precedes the rectum is marked "sigmoid flexure," and includes the iliac colon and the greater i)art of the jjelvic colon. ernhryo as outgrowths of its wall, lie entirely outside the tube in the adult, and are connected with it })y special ducts through which the gland-secretions pass. The largest of these, the liver, is placed in the upper and right portion of THE MOUTH. 095 the abdominal cavity, immediately beneath the diaphragm, anVl its .secretion — the bile — is conveyed into the duodenum by the bile duct. The pancreas, next in size, lies across the front of the vertebral column, with its rio-ht end or head restintr in the concavity of the duodenum, into which its secretion flows through the pancreatic duct. The salivary glands, of which there are three chief pairs — parotid, submaxillary, and sublingual — are placed about the face, and their ducts, which convey the saliva, open into the mouth. Whilst the secretion of these latter undoubtedly possesses some digestive action, and they must consequently be classed as digestive glands, nevertheless the saliva is to be looked upon as a mechanical lubricant, which facilitates swallowing and the movements of the tongue in speaking and masticating, rather than as an aid to the digestive process. Accessory Parts. — Under this heading we group the teeth, tongue, gums, palate, and tonsils. The teeth, 32 in number in the adult, are embedded in the jaws and surrounded by the gums. Tlie tongue is a muscular organ, useful alike in masticating, swallowing, speaking, and in the exercise of the sense of taste, wliich specially resides in its modified epithelium ; it occupies the greater portion of the floor of the mouth, whilst the roof of that cavity is formed by the hard palate anteriorly, and by the soft palate behind. Finally, the tonsils (Fig. 707) are two large masses of lymphoid tissue, found on the side-walls of the oral portion of the pharynx, just behind the mouth. THE MOUTH. The mouth is the expanded upper portion of the digestive tube, specially modified for the reception and mastication of the food. In it we distinguish : the aperture of the mouth placed between the lips ; the vestibule, the slit-like space which intervenes between the teeth and gums internally, and the lips and cheeks externally (Fig. 706) ; and the cavity of the mouth, which lies within the round of the dental arches, and opens behind into the pharynx through the isthmus of the fauces (Fig. 707). The aperture of the mouth (rima oris) is the upper or anterior opening of the ahmentary canal, and is bounded above and below by the corresponding lips, which, by their junction at the sides, form the angles of the mouth (commissure labiorum). In a state of rest, with the lips in apposition, the rima appears as a slightly curved line, corresponding in length to the interval between the first premolar teeth, and in level to a line drawn across just below the middle of the upper incisor crowns. The shape of the rima varies with every movement of the lips, from the resting linear form, curved like the conventional bow, to a circular or oval shape when the mouth is widely open, or the " pursed up " condition pro- duced by the contraction of the orbicularis oris. The vestibule (vestibulum oris. Fig. 706) lies immediately within the aperture of the mouth. In the normal resting condition its cavity is practically obliterated by the meeting of its walls, which reduces it to a slit-like space. It is limited on the one hand by the deep surface of the lips and cheeks, and on the other by the dental arches and gums. Its narrow roof and floor are formed respectively by the reflection of the mucous membrane, from the deep surface of the lips and cheeks to the corres})onding gum. This reflection is interrupted in the middle line by a small but prominent fold of the mucous membrane, tlie frenulum, which connects the back of each lip to the front of the gum. The upper frenulum is the better developed, and is readily brought into view by everting the lip. On the outer wall of the vestibule, opposite the crown of the middle u}>per molar, is seen, upon a variably developed eminence (Fig. 716), the small opening of Stenson's duct, which conveys the saliva from the parotid gland to the mouth. When the teeth are in contact the vestibule communicates with the cavity of the mouth, only through the small and irregular s])aces left between the opposing teeth, and posteriorly by a wider but variable aperture behind the last molars. Advantage is souietiiue.s taken of tlie presence of tlii.** aperture, wliicli lies between the wisdom teeth and the ramus of the jaw, for the introduction of liquid food in certain ca.ses — trismus, anchylosis, etc, — in whidi the mouth is rigidly closed. 996 THE DIGESTIVE SYSTEM. The anterior border of the masseter can be distinctly felt with the finger, on the outer wall of the vestibule, when the muscle is thrown into a state of contraction. Still further back, the front of the coronoid process, bearing the lower part of the insertion of the temjaoral muscle, can be easily made out. Whilst the pterygo-maxiUary ligament, which corresponds to, and is felt along with, the anterior border of the internal pterygoid, is distinguishable as a pliant ridge when the finger is carried from the front of the coronoid process inwards behind the wisdom teeth to the cavity of the mouth. In addition to Stenson's duct, the ducts of numerous small glands which are embedded in the lips and cheeks open into the vestibule. Under normal conditions, as pointed out above, the lips and cheeks lie against the teeth and gums, obliterating the cavity of the vestibule, and heljjing, with the aid of the tongue, to keep the food between the grinding sui-faces of the molar teeth during mastication. In facial palsy, however, owing to the paralysis of their muscles, the lij^s and cheeks fall away froni the dental arches, and allow the food to pass out from between the teeth and to accumulate in the vestibule. Lips (labia oris, Fig. 708). — These are the two movable folds, covered superfici- ally by skin, and on their deep surface by mucous membrane, which surround the rima oris. Laterally the two meet at the angles of the mouth, and beyond this are Palatine glands Superior linsualis 2nd molar tooth Digastric Platysma Mylo-liyoid Coronal Section through the closed Mouth. The slit-like character of the vestibule, the manner in which the tongue fills up the mouth cavity, the close ajjposition of the teeth, the relations of the roots of the upjier molars to tlie antrum of High- more, the plica sublingualis over the sublingual gland, and the position of the rauine artery should he noted. prolonged into the cheeks, with which they are continuous. The upper lip presents on its superficial surface a well-marked vertical groove, the pMltrum, bounded by two distinct ridges descending from the columella nasi (Fig. 71^); inferiorly the groove widens out, and terminates opposite a slight projection — the labial tubercle — on the free edge of the upper lip. This tubercle is particularly well developed in children, and is chiefiy responsible for the characteristic curve of the rima oris. The lower is usually longer and more movable than the upper lip. In passing from before backwards the following structures are found in the lips : — (1) The skin, which is closely beset with hairs, small and fine in the child and female, long and stout in the adult male. (2) A layer of fatty superficial fascia continuous witli the fascia of the face generally. (3) The orbicularis oris muscle, continuous at its periphery with the various muscles converging towards the mouth. A numljer of its fi})res, or those of the muscles joining it, pass through the super- ficial fascia and are attached to the skin, thus estabhshing a close connexion between the latter and the muscle. (4) The submucous tissue, which is occupied by an almost continuous layer of racemose glands — the labial glands (glandules labiales). These open into the vestibule, and their secretion is said to be mucous. (5) The mucous membrane of the mouth, covered by stratified squamous epithelium. Between the orbicularis and mucous membrane, but nearer to the THE MOUTH. 997 former, that is, in the deeper part of the submucosa, the coronary artery is found a short distance from the free margin of the Hp, running to meet its fellow of the opposite side. The free margin of the lip is covered by a dry and otherwise modified mucous membrane. It begins where the integument changes colour at the outer edge of the lip, and ends posteriorly just behind the line along which the two hps meet Avhen closed, where it passes into the ordinary moist mucous membrane of the vestibule. It presents numerous simple vascular pajjillai, and its nerves (which are derived from the infra-orbital in the upper lij), from the long buccal at the angles, and from the mental branch of the inferior dental in the hjwer lip) terminate in special end organs, hence the acute sensitiveness of this part. In the child, at birth, the margin of the lip is divided by a very pronounced groove or fissure into an outer and an inner zone, differing considerably in their apj^earance. When the tongue is pressed firmly against the back of the lips and moved about, the labial glands can be distinctly felt through the mucous membrane, giving the impression of a knobby or irregular surface. The glands, Avhich are about the size of hemp-seeds and can be readily displayed by removing the mucous memljrane, are more numerous in the lower than in the upper lip. Stoppage of their ducts, with the resulting distension of the glands, gives rise to " mucous cysts," a well-known jjathological condition. It should be remembered, in connexion with epithelioma of this part, that the lymphatics of both lips pass down to join the submaxillary lymphatic glands. Cheeks (buccie). — The cheeks resemble the Ups in structure, Ijeing formed of cor- responding layers. Superficially is the skin. Under this lies the fatty superficial fascia of the face, through which Stenson's duct runs inwards to pierce tlie buccinator ; in it also, near the end of the duct, are found four or five mucous glands, as large as hemp-seeds. These are known as the molar glands (glanduhe molares) ; their ducts pierce the cheek and open into the vestibule. Beneath this superficial fascia lies the buccinator muscle, covered by the thin bucco- pharyngeal aponeurosis. Deeper still is the submucosa, which, like that of the lips, contains numerous racemose buccal glands (glandular buccales). And finally the mucous membrane is reached (Fig. 709). An important constituent of the cheek of the infant is the sucking pad (corpus adiposum buccse), an encajjsuled mass of fat, distinct from the surrounding superficial fascia, which lies on the outer side of the buccinator, and j)asses backwards into the large recess between that nuiscle and the overlying anterior part of the masseter. This fatty mass, which is relatively more developed in the child than in the adult, strengthens the cheek, and helps it to resist the effects of atmospheric pressure during the act of sucking. In the adult the remains of the jjad can be distinctly made out under the anterior border of the masseter. Cavity of the Mouth Proper (cavum oris proprium). — This is the space situated within the dental arches. The latter, with the gums, separate it from the vestibule (Fig. 706), so that the two communicate, when the teeth are in contact, only by the irregular interdental spaces, and through tlie passages behind the wisdom teeth already referred to. Posteriorly the cavity of the mouth opens, through the isthmus of the fauces, into the pharynx (Fig. 707). Its roof is formed by the hard and the greater part of the soft palate ; whilst its floor, in the ordinary resting condition, is entirely occupied by the tongue (Fig. 709). If, however, the tip and marginal parts of the tongue l^e raised, there is exposed a limited surface to which the term " floor of the mouth " or sublingual region is more usually applied (Fig. 712). The sublingual region (Fig. 712) is covered by the oral mucous membrane which is carried across from tlie deep surface of the gum to the inferior aspect of the tongue, with the mucous membrane of which it becomes continuous. When the tip of the tongue is raised the membrane forms in the middle line a prominent fold, the frenum linguae, stretching from tlie floor of the mouth to the under surface of the tongue. On each side of the frenum, near its junction with the floor, there can be readily made out a prominent soft papilla (caruncula sublingualis), on which the opening of Wharton's duct (of the submaxillary gland) may be seen (Fig. 712). Running outwards and backwards on each side from this, and occupy- ing the greater part of the floor of the mouth, there is a well-marked ridge (plica sublingualis) due to the projection of the underlying sublingual gland, most of the ducts of which open near the crest of the ridge. 998 THE DIGESTIVE SYSTEM. When tlie moutli is closed, and resj)iration is carried on tlirougli the nose, the cavnin oris is reduced to a slit-like space, and j^i'acticallj- obliterated by the tongue coming in contact with the palate above, and with the gums and teeth laterally and in front (Fig. 706). When the mouth is slightly open and the teeth nearly in contact, the tongue becomes somewhat concave or grooved along the middle line, and leaves a channel-like space between it and the palate, while it remains in contact with the roof and gums laterally. By depressing the hyoid bone with the root of the tongue, the cavum oris can be increased to a consideral:)le size even when the teeth are in contact. Finally, by the simultaneous descent of the lower jaw and hyoid bone with the tongue, and the ascent of the soft j)alate, the ca^aty is increased to its greatest dimensions (Fig. 707). Gums (gingivae). — This term is applied to the red firm tissue, continuous with the mucous membrane of the vestibule on the one hand, and with that of the palate or floor of the mouth on the other (Fig. 706), which covers the alveolar borders of the maxilla and mandible, and surrounds the necks of the teeth. The gums are composed of dense fibrous tissue, inseparably united to the periosteum and covered by mucous membrane. They are richly supplied with blood-vessels, but sparsely with nerves, and are covered by stratified squamous epithelium. Around the neck — or more correctly the base of the crown — of each tooth, the gum forms a free overlapping collar, and at this part particularly it is closely beset with small papilla?, visible to the naked eye. In thickness it usually measures from 1 to 2 mm. THE PALATE AND ISTHMUS FAUCIUM. The palate (palatum) is the term applied to the strongly-arched structure which forms the roof of the mouth, and projects posteriorly into the pharynx as a pliant fold, imperfectly dividing that cavity into two (Figs. 708 and 710). Its anterior half or more has a foundation of bone, and separates the nasal iossse from the mouth. This part is known as the liard palate. The posterior portion, which is free from bone, separates the naso-pharynx above, from the mouth and oral pharynx below, and is known as the soft palate. The hard palate (palatum durum, Fig. 708) occupies the space within the upper dental arch, and is continuous with the gums in front and laterally, whilst behind it passes into the soft palate. It is formed by the palatal processes of the superior maxillary and palate bones (Fig. 721), covered by periosteum, and by a layer of firm mucous membrane. Beneath this mucous membrane, particularly at the sides and in front, is found a considerable quantity of dense filbrous tissue, firmly united to the periosteum on the one hand and to the mucous membrane on the other. This dense tissue forms an effective protection for the palate, and, in addition to the palatine vessels and nerves, it contains in its posterior half a large number of racemose (palatine) glands. Traversing the middle of the palate is seen a faint central ridge or raphe (Fig. 707), indicatiug its original develoj^ment from two lateral halves. Behind, this raphe is continued along the sLift palate to the base of the uvula, and in front it ends in a slight elevation, the incisive pad or papilla i:)alatina. From the anterior end of the raphe a series of transverse ridges of mucous niemljrane, about six in number, run outwards, just behind the incisor teeth ; they are known as the palatine rugse, and are composed of dense fibrous tissue. Sometimes a small jjit, which will admit the point of a ^^in, is seen on each side immediately behind the central incisor teeth, and about 2 mm. from the middle line. These pits corresjjond to the lower openings of Stenson's canals, with wliich they are occasionally continuous. The soft palate (palatum molle, or velum pendulum palati, Fig. 708) is a movajjle valve-like fold which runs obliquely downwards and backwards, like the " tongue " of a whistle, across the cavity of the pharynx almost as far as its posterior wall. Whilst it is attached to the hard palate in front, and blends witli the pharyngeal walls laterally, its posterior border is free, and between it and the posterior wall of the pharynx is left a valvular passage — the isthmus of the pharynx — through which the naRO-])harynx and the oral pharynx communicate with one another. The soft palate is composed of two layers of mucous membrane between which are contained the palatine muscles, vessels, nerves, and connective tissue, the aponeurosis of the palate, and, in addition, a very large number of racemose glands. These glands are arranged in a thick continuous layer on the inferior surface beneath the mucous membrane, and form quite one-half of the mass of the soft palate THE PALATE AND ISTHMUS FAUCIUM. 990 generally, whilst in its anterior part, where muscular filires are wanting, they constitute almost its entire thickness. Its upijer surface, which is convex, forms a continuation backwards and downwards of the floor of the nasal fosste (Fig. 708), and is covered by a pro- longation of the nasal mucous mem- Ijrane — ciliated in its upper half or more. The under surface is arched, The philtnnii Rai)liP of palate -Tonsil Anterior palatine arch Tongue ro7 -Open Mouth showin(i Palate and Tdnsils. It also .shows the two palatine arches, and the pharyngeal isthmus through which the naso-pharyux aLove com- municates with the oral portion of the pharynx below. ■07). and prolongs l)ackwards the roof of the mouth, towards the cavity of which it looks. In front the soft palate is attached to the posterior edge of the hard palate. Laterally it blends with the side wall of the pharynx along a very oblique line as it slopes down- wards and backwards (Fig. 708). Its posterior margin is thin and free : it presents in the middle line an elongated conical projection, the uvula (Fig. 707), and at each side of this a sharp con- cave edge arches outwards, and passing downwards and slightly backwards becomes continuous with a ridge on the side wall of the pharynx termed the posterior palatine arcii (posterior pillar of fauces). From the under surface of the soft palate, 7 or 8 mm. Y^^■ further forwards, and near the base of the uvula, spring another pair of ridges, the anterior palatine arches (anterior pillars of fauces), which pass downwards and slightly forward to the sides of the tongue (Fig The anterior part of the soft palate for 8 or 10 mm. (-J- inch) contains practically no muscular fibres ; it is composed of the palatine aponeiarosis, covered by an extremely thick layer of glands on the under surface and by mucous membrane on both surfaces. This anterior portion is much less movable than the rest of the soft palate, and forms a relatively horizontal continxiation backwards of the hard palate, stretching across between the two internal pterygoid plates. It is upon this portion chiefly that the tensor palati acts. The posterior and larger part contains muscular fibres in abundance, slopes strongly downwards, and is freely movable, being the portion upon which the remaining palatine muscles act. The palatine aponeurosis, which is confined to the anterior part of the soft palate, is in the form of a thin flat sheet, constituting, as it were, a kind of comiuon tendon for the palatine muscles whicli are attached to (or blended witli) its posterior margin ; whilst its anterior margin is united to the posterior edge of the palatal processes of the palate bone. With the exception of the aponeurosis of the tensor palati which passes into its lateral part, the muscles do not, as a rule, reach further forwards than to Avithin 8 or 10 mm. of the posterior edge of the hard palate. The uvula, already referred to, is a conical projection, very variable in lengtli, which is continued downwards and backwards from the middle of the soft palate. It is composed chiefly of a mass of racemose glands and connective tissue covered by mucous membrane, and containing a slender prolongation of the azygos uvuhe muscle in its upper part. The mucous membrane of tlu" i)alate, whicli is covered by stratified si|uauu)us epitlK-liuni, is firmer and iiion- closfly adlicivnt in front, near the niga-, tlian behind, near the soft jialate. Mucous glands, the orifices of which can be seen as dots witli the naked eye, are extremely abundant iu the soft ])alate, and in the ]K)sterior half of the hard palate, except near the rajilie. They are wanting in the anterior pari of the palate, where the mucous membi-ane is particularly dense. The palatine rugae (which correspond to more strongly developed ridges in cjtrnivora, etc.) are very well marked in the child at birth, although, perhaps, relatively less distinct in the foetus of five or six mouths ; iu old age they become more or less obliterated and irregular. At birth, 1000 THE DIGESTIVE SYSTEM. also, and in tlie foetus, tlie incisive pad at the anterior end of the raj)he is continued over the edge of the gum into the frenulum of the upper lij). The vessels of the palate are derived from the posterior palatine artery, which runs forwards on the hard palate close to the alveolar border, and from the ascending palatine branch, of the facial, which accompanies the levator palati to the soft palate. The nerves — all branches of Meckel's ganglion — are : the large posterior palatine, which descends through the j)osterior palatine canal and runs forward on the hard palate with the posterior palatine artery ; the naso-palatine, which jjasses down through the foramen of Scarpa and reaches the front of the hard palate ; and the small posterior and accessory posterior palatine nerves, which run through the accessory palatine canals and supply the soft palate. Fauces or Isthmus of the Fauces (isthmus faucium). — This is the aperture through which the mouth communicates with the pharynx (Fig. 707). It is bounded at the sides by the anterior palatine arches, above by the under surface of the soft palate, and below by the dorsum of the tongue ; in width it corresponds pretty closely to the cavum oris. The anterior palatine arches (arcus glosso-palatinus), often known as the anterior pillars of the fauces, are two prominent folds of mucous membrane, containing the palato-glossus muscles in their interior, which bound the isthmus of the fauces laterally (Fig. 707). Springing above from the under surface of the soft palate, a little way (about 8 mm.) in front of its free edge, and near the base of the uvula, they pass downwards and slightly forwards to join the tongue a little behind the middle of its lateral border. The posterior palatine arch is described with the pharynx (p. 1034). THE TONGUE. The tongue (lingua) is a large mobile mass composed chiefly of muscular tissue, and covered by mucous membrane, which occupies the floor of the mouth and forms the anterior wall of the oral pharynx (Fig. 708). Whilst the sense of taste resides chiefly in its modified epithelium, the tongue is also an important organ of speech, and, in addition, it assists in the mastication and deglutition of the food — functions which it is well fitted to perform, owing to its muscular structure and great mobility. In length it measures, when at rest, about three and a half inches, but both its length and width are constantly varying with every change in the condition of the organ, an increase in length being always accompanied by a diminution in width, and vice versa. In describing the tongue we distinguish the following parts : the body (corpus linguse), made up chiefly of striped muscle, and forming the mass of the organ ; the dorsum (Fig. 709), which looks towards the palate and pharynx, and is free in its whole extent; the base, the posterior wide end which is attached to the hyoid bone ; the apex or tip, the pointed and free anterior extremity ; the margin, which is free in its anterior half or more, i.e. in front of the attachment of the anterior palatine arch (Fig. 709). Finally, the unattached portion on the inferior aspect, seen when the apex is turned strongly upwards (Fig. 712), constitutes the inferior surface; whilst the attached portion, fixed by muscles and mucous membrane to the hyoid bone and mandible, is known as the root. The dorsum of the tongue (dorsum linguse), when the organ is at rest, is strongly arched from before backwards in its whole length (Fig. 708), the greatest convexity corresponding to the attachment of the anterior palatine folds. When removed from the body the tongue, unless previously hardened in situ, loses its natural shape, and appears as a flat, elongated oval structure, which gives a very erroneous idea of its true form and connexions. The dorsum is naturally divided into two areas — an anterior or oral part, which lies nearly horizontally on the floor of the mouth, and constitutes about two-thirds of the length of the whole tongue (Fig. 709 J ; and a posterior or 'pliary7igeal 'part, the remaining third of the organ, which is placed nearly vertically, and forms the anterior wall of the oral pharynx (Fig. 710). The separation between these two parts, wliich differ in appearance as well as in direction, is indicated by a distinct V-shaped groove, called the sulcus terminalis (Fig. 710), the apex of which is directed backwards, and corresponds to a blind depression on tlie surface of the tongue, the foramen caecum, whilst its diverging Hmbs pass outwards and forwards THE TONGUE. 1001 towards the attachments of the anterior palatine arches. The foramen csecum is the remains of a tubular down-growth formed early in embryonic life, in the region of the dorsum of the tongue, from which the isthmus of the thyroid gland is developed (see page 38). The posterior or pharyngeal portion of the dorsum linguae (Fig. 708), nearly vertical in direction, forms the greater portion of tbe anterior wall of tlie oral pharynx (Fig. 710). Its surface is free from evident papilhe, but is thickly studded Middle turbinated bone Middle meatus of nose Iid'erior iiieitii'i of nose Superior meatus i>{ nose Genio-glossus Genio-hyoid bplienoidal sums Infeuoi tuibinateil bone Posterior edge of nasal septum \ / Orifice of Eustacliian ^^ tube sa pliaryiigea Part of the pharyngeal tonsil Lateral recess of pharynx Levator cushioTi Salpingo- pharyngeal fold Glands in soft palate __ Anterior palatine arch Supratonsillar fossa Plica triangularis Tonsil Posterior jialatine arch Epiglottis Aryteuo- epigloltic fold Cricoid cartilage Lymphoid fullicl Uyoid bone Flu. 708.— Sagittal Skction through Mouth, Tongue, Larynx, Pharynx, and Nasal Cavity. Tlie .section was slightly oblique, aud the posterior edge of the nasal sejitnm has been preserved. The specimen is viewed slightly from below, hence the apparently low position of the inferior turbinated bone. with rounded projections, each presenting, as a rule, a little pit, visible to the naked eye, at its centre ; the great majority of these are lymphoid follicles (iblliculi tonsillares linguales, Fig. 713, C) similar to those found in the tonsils; some few are said to be mucous glands ; all are covered by a smooth mucous membrane, and they combine to give to this region a characteristic nodular appearance. The mucous membrane of this portion of the tongue is separated from the muscular substance by a submucous layer in wliich the lymphoid follicles and the mucous glands lie embedded (Fig. 708). At the sides it is continuous with that covering the tonsils and the side wall of the pharynx ; whilst behind 1002 THE DIGESTIVE SYSTEM. it is reflected on to the front of the epiglottis, forming in the middle line a prominent fold, the frenulum epiglottidis or middle glosso - epiglottic fold (plica glosso-epigiottica media, Fig. 709), at each side of which is a wide depression;, the vallecula. Two lateral glosso-epigiottic folds have beeu described, but these pass from the side of the epiglottis, not to the tongue, but upwards along the wall of the pharynx, upon which they are soon lost ; consequently the term pharyngo-epigiottic is more applicable to them. The anterior or oral portion of the dorsum lingnae, namely, the part in front of the sulcus terminalis (Fig. 709), is convex, both from before backwards and Internal jugular vein Hypoglossal nerve Spinal accessory nerve I)igastric muscle I Stylohyoid Glosso- • pharyngeal nerve Parotid gland Temporo- niaxillary vein External carotid artery Styloglossus Ascending palatine artery Internal pterygoid Epiglottis Frenulum epiglottidis Masseter Pharyngeal portion of tongue Internal carotid artery I Pneumogastric nerve 1 Sympathetic \ \ 1 Ascending pharyngeal aitery 3. \ I Odontoid piocess Fungiform papilla Buccinatoi Post-pliaryngeal lymphatic gland Superior constrictor muscle Posterior palatine arcli 'Tonsil Pharyngo-epiglottii' 'fold Anterior palatine arcli Circumvallate papillaj -Raphe of tongue Conical papilUi- Fungifoim papilli Fio. 709. — Horizontal Section through Mouth and Pharynx at the Level of the Tonsils. Till' stylopharyngeus, wliich i.s .sliowu immediately to the inner side of the e.xterual carotid artery, anil the prevertebral muscles, are not indicated by reference lines. from side to side in the resting condition of the organ (Fig. 706). It usually Y)resents also a slight median depression, along the centre of which may be seen some indication of a median raphe in the form of an irregular crease, which ends posteriorly near the foramen caecum. The mucous membrane of this portion of the dorsum is thickly covered with the prominent and numerous papillae (papillai linguales) which give the tongue its most characteristic appearance. Oh the pharyngeal part of the tongue there are also small papillary projections of the coriuiu, IjLit the ejntheliuni tills up all tlie intervals between the papillse, and, as it were, levels off the surface, so that none are visible to the eye as jji^ojections above the general level. Over tlie anterior part of the tongue, on the contrary, the pi'ojections of the corinm ai'e large and prominent, and tlie intervals between them, while they are covered, yet are not filled up, by the epithelium, so that the projections stand out distinctly and indej^endently, and in places attain a height of nearly 2 mm. above the general surface. THE TONGrE. 1003 Papillae of the Tongue (Fig. 709). — These are formed by variously-shaped projections of the corium of the mucous membrane, covered by thick caps of epithe- lium. They are of three different varieties : — 1, Conical or filiform (papillae conicae, p. filiformes) ; Internal carotid artery Forainen lacerum medium Cartilage of Eustachian tube Cavity of Eustachian tube Levator palati Inferior turbinated bone Lateral recess of pharynx 2, Fungiform ('pa[iilhe fungi- formes et p. lenti- culares) ; and o, Circumvallate (papilhc vallata^). The conicalor filiform papillae (Fig. 711) are the smallest and most numerous, forming as they do a dense crop of minute pro- jections all over the anterior two- thirds of the dorsum, and also upon the upper part of the margin and tip, of the tongue. Pos- teriorly they are arranged in divergent rows running out- wards and fur- wards from the raphe, parallel to the limbs of the sulcus terminalis. More anteriorly, the rows become nearly trans- verse, and near the tip irregular. Each papilla is composed of a conical ])rojection of the corium, beset with micro- scopic papillu' like those of the si 1 cap of stratifieil s([uainous epithe- lium. Often, however, the cap of epithelium is broken up into several long slender liair-like processes, giving rise to the variety known as fififorni paj>ilkf. The cap of epithelium is l)eing constantly shed and renewed, and an excessive or diminished rate of shedding or renewal, coupled with the presence of various fungi, gives rise to the several varieties of "tongue" found in different diseases. The conical and filiform papilhe are probably of a ])rehensible or tactile nature, and arc highly developed, and horny, in carnivora. Levator cusliion Sujierior constrictor muscle Glands in soft palate Uvula Palatopliaryngcus Circumvallate papillte Sulcus terminalis Glossopharyngeal nerve Foramen cecum Lymphoid follicle Middle constrictor muscle Epiglottis Pliaryngo-epiglottic fold Lingual artery Hyoglossus muscle Hyoid bone Superior laryngeal artery Internal laryngeal nerve Aryteno-epiglottic fold Sinus pyriformis Superior aperture of larynx Inferior constrictor muscle Toi) (if cricoid cartilage '10. — Thk Anti:kiiih Wall IK THK PhaKYNX WITH ITf- I.M BEHIND. OUIKICKS. SEKX 5kin and covered '^'^'^ specimen from which tlie drawing was made was obtained from a formaliu-liardened . ''fi • 1 1 body, by removing the posterior wall of the pliarynx while leaving the anterior by a tlUCK long ^^.^y\ undisturbed. The following points should be noted : the greatest width of the pharynx, above, at the lateral recesses ; tlie posterior nares. with the inferior turliiuated bones seen through them : tlie levator cushion : and the pharyngeal portion of the tongue. 1004 THE DIGESTIVE SYSTEM. Fungiform papilla Conical and fungiform papillte. x 30. Secondary papilte Taste-buds A circumvallate papilla, x 12. Fig. 711. — The Papilla op Tongue. The fungiform papillae (Fig. 711) are larger and redder, but less numerous than the last variety, and they are found chiefly near the tip and margins of the tongue, comparatively few being present over the dorsum generally. Each is in shape like a " puff-ball " fungus (Halhburton), papiite^'^ consisting of an enlarged rounded Conical papiite .^s^^^^ / head, attached by a somewhat narrower base. As in the case of the conical papilltTe, the corium is studded over with microscopic papillae, which are buried in the covering of squamous epithelium and do not appear on the surface. Most of the fungiform papillae, if not all, appear to be furnished with taste-buds, and they are probably intimately connected with the sense of taste. The circumvallate papillae (Fig. 711), much the largest of all the papillae of the tongue, are confined to the region immediately in front of the sulcus terminalis and foramen caecum. Usually about ten in number, they are arranged in the form of the letter V, with the apex backwards, just in front of and parallel to the sulcus ter- minalis. One or two of the papillae are usually placed at the apex of The upper illustration shows conical and fungiform papilla, the V, immediately anterior tO the the lower a circnni vallate papilla. C, Corium, and foramen CffiCUm. In appearance a E, Epithehum of the mucous membrane. The wavy . ,, ^ .,, i i dark lines represent arteries. CirCUmvallate papilla rCSCmblcS VCiy closely the impression left by press- ing the barrel of a small pen on soft wax (Fig. 710). Each is composed of a cylindrical central part (1 to 2-5 mm. wide), slightly tapering towards its base, and flattened on its crown, which projects a little above the general surface of the tongue. This is surrounded by a deep, narrow, circular trench or fossa, the outer wall of which is known as the vallum. The vallum appears in the form of an encircling collar very slightly raised above the adjacent surface (Fig. 709). As in the case of the other forms, the circumvallate papillae are made up of a central mass of corium, beset with numerous microscopic papillae on the crowns, but not on the sides, and covered over, as are the surfaces of the fossa and vallum, by stratified squamous epithelium. Into the fossae open the ducts of some small serous glands (Fig. 711). On the sides of the circumvallate papillae, as well as upon the opposed surface of the vallum, are found, in considerable numbers, the structures known as taste- buds, the special end-organs of the nerves of taste. The apex (apex linguae), and the margin (margo lateralis) of the tongue in front of the attachment of the anterior palatine arch, are free, and lie in contact with the teeth when the tongue is at rest. On the upper half or more of the margin and a,])ex, papillae are present as on the dorsum ; but on the lower part they are absent, and the surface is covered by smooth mucous membi'ane. Just in front of the anterior palatine arcli, on the margin, are usually seen about five or six distinct vertical folds, forming the folia linguse, which ai'e beset witli taste-buds, and corresjiond to a well-defined area (the papilhe foliatae) on the side of the tongue in certain animals (rabl)it, hare, etc.), in which it forms an imjjortant jaart of the organ of taste. The inferior surface (facies inferior) of the tongue, which is exposed by turning the apex of the organ u])wards, is limited in extent (Fig. 712), and is free from visible papilke, the surface being covered by a smooth mucous membrane. Running THE TONGUE. 1005 along its middle, except near the tip, is a depression, from which a fold of mucous membrane, the frenulum linguae, passes down to the floor of the mouth, and on towards the hack of the mandible, distance from it, the large ranine vein is distinctly seen through the mucous membrane. Further out still are situated two indistinct, fringed folds of mucous membrane, the plicae fimbriatae, which converge somewhat as they are followed forward towards tlie tip, near which they are lost. From the inferior surface of the tongue the mucous membrane passes across the floor of the mouth to the inner surface of the gum, with the mucous covering of which it becomes continuous. The plicae fimbriatae correspond j^retty closely to the course of the ranine arteries as they run towards the tip ; the arteries, however, are deeply 2>laced in the sub- stance of the tongue, at a distance of 3 to 6 mm. from the inferior surface. The jilicie, which are more distinct at birth and in tlie foetus, are said to correspond to the under tongue found in the lemurs. The root of the tongue (radix lingufe) is the portion of the inferior aspect which is connected by muscles and mucous membrane to the mandible and hyoid bone. It is of very consideralDle extent, and is, with the base, the most flxed part of the organ. It is also the situation at which the vessels and nerves as well as the extrinsic muscles enter. At each side of the frenulum, and a short The philtruin Layer of muscle cut to show the "land Fig. Fiemiluni liiiguse Openings of Wharton's ducts Sublingual gland riica sublingualis, with openings of ducts of sublingual land '12. — Open Mouth with Tongue raised, and the Sublingual and Apical Glands exposed. The sublingual gland of the left side has been laid bare by removing the mucous membrane ; to e.xpose the apical gland of the right side a thin layer of muscle, in addition to the mucous membrane, has been removed. A branch of the lingual nerve is seen running on the inner aspect of the gland. The ranine vein is faintly indicated on this side also. Structure of the Tongue. — The tongue is chiefly composed of striped muscular tissue, in connexion with which are found a considerable admixture of fine fat and a median septum of connective tissue occupyiug the central part of the organ. In addition, there ai'c vessels, nerves, glands, and lymphoid tissue, the whole being covered over by nuicous membrane, except at the root (Fig. 713). The muscular tissue is derived partly from the terminations of the extrinsic muscles — namely, the hyoglossus, styloglossus, genioglossus, palatoglossus, and chondroglossus ; but also largely from the intrinsic muscles — namely, the superior lingualis, inferior lingualis, the transverse, and the vertical lingual muscles. These are so arranged that they form a cortical portion, made up chiefly of longitudinal fibres — derived above from the superior lingualis and the hyoglossus, at the sides from the styloglossus, and below from the inferior lingualis. This cortex surrounds a central or medullary portion, divided into two lateral halves by the septum, and formed in great jjart by tlie ti'ansverse and vertical fibres, and also by the fibres of the geuioglossi ascending to the dorsum. The muscular fibres derived from these various sources end by being inserted into the deep surface of the nmcous membrane. The detailed description of the extrinsic and intrinsic muscles will be found on page 414. The septum is a median fibrous partition found in the medullary portion only, and easily exposed b}' separating the two geuioglossi on the under surface of the tongue. Anteriorly it usually extends to the apex ; whilst posteriorly it grows gradually narrower, and expanding transversely at the same time, it passes into a broad sheet (the hyoglossal 1006 THE DIGESTIVE SYSTEM. membraue) which is united to the upper border of the hyoid bone, and gives attachment to the posterior fibres of the genioglossus. From the sides of the septum the transverse fibres of the tongue arise. The mucous membrane ou the anterior two-thirds of the dorsum, and on the free margins, is firm and closelj' adherent to the underlying muscular substance, the fibres of which are inserted into it. On the posterior third of the dorsum, and on the inferior surface, it is neither so firm nor so closely united to the muscular substance, from which it is separated in both of these situations by a layer of submucous tissue. The mucous membrane of the tongue, like that of the rest of the mouth, is covered by stratified squamous epithelium. Glands of the Tongue. — Numerous small racemose glands are found scattered beneatli the mucous membraue of the posterior third of the tongue ; and a small collection of similar glands is present at the margin, opposite the circumvallate papillae. Small serous glands are also found embedded in the dorsum near the circumvallate papillse, into the fossae of which their ducts open (Fig. 711). The chief collections of glandular tissue in the tongue, however, are foiuid embedded in the muscle of the under surface, a little way behind the apex, on each side of the middle line (Fig. 712). They are known as the apical glands (glandulae linguales anteriores of Nuhn or Blandin). These apical glands are displayed liy removing the mucous membrane and also a layer of Transverse Vertical i^^Sf/oH^ fibres fibres " ^fTT^' \oduIes ol Epitheliui 1 1\ mphoid tisiUL I KauiUL artei} Transverse fibres Mucous _lai K inferior linsualis Septum Fig. 713. — A, Transverse, and B, Longitudinal Vertical Section through the Tongue (Krause) ; C, A Lymphoid Follicle from Back Part of Tongue (Macalister, slightly modified). muscular fibi'es (derived from the united inferior lingualis and styloglossus) about 2 mm. in thickness from the under surface of the tongue a little distance behind the aj^ex. They are oval in shape, often partly broken up by muscular fibres, and they measure from | to | in. (12 to 19 mm.) in length. They are mixed serous and mucous glands, and they open by three or four very small ducts on the inferior surface of the tongue. Vessels. — The chief artery is the lingual. This vessel jjasses forwards on each side beneath the hyoglossus muscle, and then is continued on to the apex — between the genioglossus on the inner side and the inferior lingualis externally — under the name of the ranine artery. Anteriorly it is covered by the filares of the inferior lingualis, and lies I to j inch from the surface. Near the apex the arteries of opposite sides are connected by a liranch which pierces the se^itum, but otherwise, with the exception of capillary anastomosis, they do not comnumicate. The dorsalis lingruae branch of the lingual is distributed to the pharyngeal part of the tongue, whilst some twigs of the tonsillar branch, of the facial are also distributed in the same region. The veina are : the ranine, the chief vein, wiiich lies beneath the mucous membrane at the side of the IVenuiii, and muis Ijackwards over the hyoglossus muscle with the hypoglossal nerve ; two vense comites, Mdjicli accomijany the lingual artery ; and a dorsalis linguae vein from the l)ack of the tongue. These either unite and form a common trunk, or open sejiarately into the internal jugulai' vein. Nerves. — The nerves which sujjply the tongue are : (1) The hypoglossal, the motor nerve of the tongue, which enters the genioglossus and passes up in its substance to the intrinsic muscles, in wliich it ends. (2) The lingual, a branch (jf the inferior maxillary nerve, which is accom- panied by the chorda tympani branch of the facial. The lingual, after crossing the hyoglossus muscle, breaks up and enteis the inferi(U' lingualis and genioglossus, and thus makes its way upwards to the mucous membrane of the anterior two-thirds of the tongue — the lingual itself conferring common sensation on this part, the chorda tympani probably carrying to it taste GLANDS. 1007 fibres. (3) The glossopharyngeal nerve jiasse.s forwards Ijeneath llie uppei- part of the hyoglor^siis, and sends its terniinal brunrlies to tlie mucous membrane of the jiosterior tliird of the tongiu-, supplying the circumvallate papilla?, and the ])art of tlie tongue behind these, witli both gustatory and common sensory fibres. (4) The internal laryngeal nerve also distributes a few til)res to the posterior ]>art of the l»ase of the tongue, near the epiglottis. Tlie lymphatics of tlie anterior half of the tongue pass down tlirough the fioor of tlie mouth and join the submaxillary lymphatic glands. Those from the posterioi' half run with the ranine vein across the liyoglossus muscle (whei'e they are connected with some small lingual glands) and join the deep cervical glands. GLANDS. Various organs, ditteriug widely both in structure and function, are commonly included under the general term glands. It is made to embrace: (a) tlie glands vith ducts, such as the digestive glands (liver, pancreas, salivary glands, etc.), the sweat and sebaceous glands of the skin, the testes, etc., and the small glands embedded in the walls of the digestive and respiratory tracts; (b) the so-called ductless glands (spleen, thyroid, suprarenals, etc.), which possess no ducts, but throw their secretions into the blood or lymph passing through them. We sliall here consider only the true glands — namely, those included in the first grou]) mentioned above, which are all characterised by the possession of ducts: and what follows refers to them alone. A gland may be defined as an epithelial organ which separates or elaliorates from the 1)lood some substance which is either to be discharged from the body or used further in the economy. The product of the activity of the gland is knowTi as its secretion, and the secretion is conveyed to its destination in all true glands, as explained above, by the gland duct. Every gland is primarily an outgrowth of the epithelium from the surface to which the secre- tion of the gland is to lie suljsequently conveyed. This outgrowth may remain luidivided, con- stituting a simple gland. On the other hand, it may lu-eak up into two or more branches, giving rise to a compound gland. We thus arrive at tlie two great classes of glands — simple and compound. A simple gland may remain tubular, when it is known as a simple tubular gland, of which Lieberkuhn's follicles in the wall of the small intestine and the sweat glands are examples. Or it may be dilated at its extremity, the enlargement being known as an acinus {&klpos, a grape or grape-stone) or alveolus, thus constituting a simiile acinous or alveolar gland, of which there are few examples in man (viz. some sebaceous glands), though they are numerous in the skin of the frog, etc. This gives us two varieties of simple glands — tubular and acinous or alveolar. Similarly a compound gland may remain tubular, constituting a compound tubular gland, such as the kidney, testicle, and the majority of tlie gastric glands. Or, on the other hand, the terminal branches of its ducts may be beset with ttilatations {i.e. acini or alveoli), giving rise to a compound acinous or alveolar gland, which latter, owing to a remote resemblance presented Ijy its clustering lobules to a miniature bunch of grapes, is often known as a racemose gland (racemus, a cluster). Most of the glands of the body are examples of this variety — e.g. the salivary glands, the small glands of the mouth, tongue, j^harpix, oesophagus, respiratory passages, eyelids, etc. Thus we arrive at two varieties of compound glands also — -tubular and acinous or alveolar. A compound acinous (racemose) gland is composed of a main duct which branches and re-branches more or less freely according to the size of the gland, and the terminal divisions of which end finally in specialised secreting parts, the acini or alveoli, quite distinguishable from the ducts or conducting j^arts. In true acinous glands the acini or alveoli are distinctly saccular ; in other glands, such as the pancreas, this is not the case, the acini being long and narrow. Accordingly, the term acino-tubular has been introduced and ajiplied to glands of this latter type, which is usually made to include the pancreas, the prostate, and Brunner's glands. > It should be added that the term acino-tubular is by some authors used exclusively instead of acinous for all racemose glands. There is one gland, however, which cannot be included in any of tlu' above varieties, and which must be placed in a class by itself. This is the liver. It is composed of an enormous number of small secreting lobules, between which run tlie branches of the bile-duct. The.se lobules in the mammalian liver cannot in any way be compared to acini, or to collections of acini, as their cells are not arranged around a central himen, but form a practically solid mas.-<, with minute bile cai?illaries running everywhere between them. It might in mammals, for want of a better term, be classed as a solid gland. The foregoing may be summarised in tabular form thus : — 1. Simple glands. - Duct undivided. ((() Simple tubular. —Undilated at (Mid — e.g. Lieberkiihn's follicles, sweat, and many gastric glands. (/)) Simple acinous (ah-eolai- or saccular). — Dilated at end — e.g. some sebaceous glands (rare) ' Sonii' authorities consider the glaml.s of Bniuuer to belong to the class of conipouml tubular glands ( bleiilenhain, Watiiey, Jonnesco, etc.). 1008 THE DIGESTIVE SYSTEM. II. Compound glands. — Duct divided. (fl) Compound tubular. — Branclied elongated tubes, no acini — e.g. testes, kidney, most gastric glands. (6) Compound acinous or alveolar (racemose glands), branched duct with saccular acini on terminal branches — e.g. salivary, sebaceous, and Meibomian glands ; the mucous glands of the mouth, tongue, palate, pharynx, nose, CESophagus, and resjiiratory tube, (c) Acino-tubular. — Branched duct, with elongated narrow acini on terminal branches — e.g. pancreas, Brunner's glands, prostate. III. Solid gland.— The liver. To save confusion it may be pointed out that instead of acinus the term alveolus (and also saccule and follicle) is often used, and also that the term " racemose gland " is often conveniently used instead of compound acinous gland. General Structure of Glands. — Whilst the small glands, such as those of the mouth and pharynx, are placed in the mucosa or submucosa immediately beneath the point at which their ducts open on the surface, the large glands form distinct masses, generally surrounded by special capsules, and often lie at a considerable distance from the points at which their ducts open. One of these large glands of the acinous type, such as the parotid or submaxillaiy, presents the following general arrangement. The gland is made up, as can be seen with the unaided eye, of a number of masses, often as large as peas, which are surrounded and held together by connective tissue. These are known as lobes, and to each a branch of the duct passes. The lobes are in turn made up of a number of smaller masses — lobules — each having a special branch of the lobar duct. These again are composed of smaller lobules, and so on to a varying degree. Finally, the smallest are made up of a terminal branch of the duct, with a cluster of acini or alveoli developed upon it. The acini or alveoli, the special secreting portions of the gland, are composed of a basement membrane, often fenestrated or basket-like, formed of flattened cells, on the outer side of which the blood and lymph vessels lie. The inner surface of this membrane is lined by the secreting epithelial cells, usually polygonal in shape, which almost com- pletely fill the alveolus. A small lumen, however, is left, into which the secretion of the cells is shed, whence it passes into the duct of the lobule, and thus to the main duct. The blood-vessels and lymphatics, on entering the gland, break up and run, branching as they go, in the connective tissue which conveys them to all parts of the gland. Mucous and Serous Glands. — Two distinct varieties of salivary glands ai'e found, the serous and the mucous, differing not only in the nature of their secretion, but also in the character of the epithelium lining their alveoli. In those Small duct from an alveolus Large duct Duct Crescent of Gianuzzi An alveolus with secreting cell Connective tissue Fig. 714. — Section of a Serous Gland on the left, a Mucous Gland ON THE KIGHT SIDE (Bohm and V. Davidoff). In the serous glaud tlie granular secreting cells and the ceutrally-placed nucleus ,-p. 71 ^\ ^.i, ' • iT should be noted. The relatively clear cells,, with the dark crescents of (_ S- '14) the cpithe- Gianuzzi, are distinctive in the mucous gland. lial cells are large, clear, or faintly granular, and the nucleus lies as a rule near the base of the cell. In addition, many mucous glands, but not all, have small flattened or crescentic cells, distinctly granular, which stain strongly with ordinary stains, lying between the basement membrane and the bases of the chief cells. These are the crescents or demilunes of Gianuzzi. In the acini or alveoli of serous glands, on the other hand (Fig. 714), the epithelial cells are distinctly granular, the granules staining well with ordinary stains ; the nuclei are rounded and lie near the centre of the cells, and no demilunes are present. In man the parotid and the small glands which open into the fossae of the circum- SALIVAEY GLANDS. 1009 vallate papilla; alone are serous. The submaxillary and the apical gland of the tongue are mixed, the serous alveoli being the more nimierous ; whilst the sublingual, labial, buccal, and all other glands of the mouth, tongue, and palate are said to be nutcous. Salivary Glands. This term is generally understood to include only the three large masses of glandular tissue found on each side of the face — namely, the parotid, submaxillary, and sublingual glands. But, as previously pointed out, numerous other small glands Intprnal ju^'iilar vein Hypoglossal iiervf Spinal accessory iiorvo Digastric muscle Stylohyoiilv^ i Glosso- T^» pharyngeal nerve^^ J Parotid gland-J. J Teniporo- | * maxillary vein— — L Kxternal carotid^ I artery Styloglossus- Ascending palatine Internal carotid artery Pneuniogastric nerve Sympathetic Ascendiiip I h irj i geal artery Olontoid process """I\M Internal pterygoid Epiglottis~p-i Frenulum epiglottidis ^ Masseter Pharyngeal portion, of tongue Fungiform pai ill Buccinator ,Post-pharyngeal ympliatic gland ^Snjierior constrictor muscle Posterior palatine arch Pharvngo-epiglottic Ibid ' Anterior palatine arch Raphe of tongue Conical papillaj Fungiform papilla Fid. 715. — HoKi/oNTAL Section thkough Mouth and Phauynx at the Level ok the Tonsils. The styloiiharyngeus, which is shown imnieiliately to the inner side of the external carotid artery, and the prevertebral muscles, are not indicated by reference lines. of a similar nature are found in the lips, cheeks, palate, tongue, etc. These have already been sufficiently described, and require no further mention. Parotid Gland (glandula parotis).— This, the largest of the salivary glands, is a distinctly lobulated mass of a yellowish or light reddish-brown colour, which is I'llaced in a deep recess (the parotid recess) at the side of the head, below and in front of the ear (Fig. 716). It extends up to the zygoma, down to the angle of the jaw or even to a lower level, and backwards to the sterno-mastoid muscle. Internally it lies on the styloid process, and anteriorly its facial process is continued for a variable distance over the surface of the masseter. When the gland is carefully removed without disturbing the suri'ounding parts, the recess which it occupies is seen to be a considerable space, between the ramus of the jaw in front and the sterno-mastoid muscle behind, with a floor formed of two sloping walls, an anterior and a posterior, which meet at an angle corresponding pretty ^ 68 1010 THE DIGESTIVE SYSTEM. closely to the styloid process. Thus the recess is three-sided (Fig. 715), the third side corresponding to the parotid fascia covering the gland. Into this parotid 7-ecess the greater pai-t of the parotid gland fits closely. From its anterior part, however, the variably-developed facial process is continued forward over the masseter muscle. Parotid Fascia. — The parotid recess is covered over on the one hand, and lined on the other, by fascia. The covering layer is specially known as the parotid fascia, and both it and the lining layer are derived from the deep cervical fascia, which divides below to enclose the gland. The parotid fascia proper is connected above to the zygoma ; behind, to the auditory meatus and anterior border of the sterno-mastoid ; below, it is continuous with the deep cervical fascia, and in front it passes forwards over the masseter, and blends with the fascia of that muscle. The layer of fascia beneath the gland forms a lining for the recess, and is united above to the periosteum over the auditory meatus and back part of the glenoid fossa ; internally it is connected to the styloid process ; whilst below it joins the deep cervical fascia. Taken together, the two layers form a definite capsule which completely encloses the gland. In connexion with the lower and anterior part of this capsule is developed a special flat band, the stylomandibular liga- ment, which passes downwards and out- wards from the styloid process to the angle of the jaw. It separates the anterior part of the parotid gland from the back of the internal pterygoid muscle; per- haps occasionally, also, from the upper and posterior part of the submaxillary gland. Shape and Rela- i)uctofBaithoiin(iare) tions of the Parotid Wharton's duct Gland.— Like the Duct of sublingual gland • i • i. -i. recess m which it Sublingual gland , . . i lies, the mam mass of the parotid gland is three -sided (Fig. oublingual and the deeper parts of tlie submaxillary glands. Four ducts of '-'-'-'/' iilie liliree the subliugnal gland are shown opening on the floor of the mouth over the SliriaceS being Slipei'- gland, a fifth is shown opening into the anterior end of Wharton's duct, flolal anterior and The course of Wharton's duct is shown by a dotted line. . ' ■ posterior. The superficicd surface is closely covered by the parotid fascia, and its lower part is also crossed by the highest fibres of the platysma. The anterior surface, approximately flat, lies in contact with the wide posterior surface of the in- ternal pterygoid muscle ; it is also related to the posterior border of the mandible and the masseter muscle, whilst from its superficial part the facial process is continued forwards over that muscle. The jmsterior surface lies from without inwards against (1) the anterior border of the sterno-mastoid and the auditory meatus, (2) the posterior belly of the digastric and the occipital artery, and (3) the spinal accessory nerve and carotid slieatli — the internal jugular vein within the sheath being in very close relation. The inner angle formed by the meeting of the anterior and posterior surfaces corresponds to the styloid process and the styloid muscles (Fig. 715). Above, tlie gland is limited superficially by the. zygoma; more deeply a tliin process runs up into tlie posterior part of the glenoid Stenson's duct Orifice of duct Parotid gland Masseter (cut) Mucous membrane (cut) Deep process of submaxillary gland Mylohyoid muscle (cut) Submaxillary gland Lower border of mandible Mylohyoid muscle Anterior belly of digastric Hyoid bone Fk;. 716. — The Salivary Glands and theu« Ducts Tlie greater jiortion of the body of the mandible lias been removed to expose the SALIVARY GLANDS. 1011 fossa. Tnferiorhj it usually readies a little distance lit'l(»\v a Hue ])roloDged hori- zontally l)ackwards frouj tlie angle of the jaw, Ijut its limit in this directiou is variable. Occasionally the parotid gland passes down a considerable distance below the angle of the mandible, lying here superficial to the posterior part of the submaxillary gland, from which it is separated by a thickened band of the deep cervical fascia, passing from tlie angle of the jaw to the fascia of the sterno-mastoid. At other times it does not quite reach the angle. The facial process of the gland — often of considerable size — is a flat and some- what triangular portion which runs forwards from the upper part of the gland, and overlaps the masseter muscle to a varying extent ; from its most anterior part the parotid duct emerges, and a separated portion of this process, often found lying immediately above the duct, is known as the socia parotidis (glandula parotis accessoria). Traversing the substance of the gland (Fig. 715) are found :— (1) the temporo- maxillary vein ; (2) on a deeper plane, the branches of the facial nerve passing forwards; and (3) more deeply still, the external carotid artery which lies beneatli the lower part of the gland, but is embedded in its deep surface above. Just before it emerges, the artery divides into its two terminal branches in the gland substance. The parotid or Stenson's duct (ductus parotideus) leaves the anterior border of the gland at its most prominent part (Fig. 716). It first runs forwards across the masseter, usually accompanied by the socia parotidis which lies above it, and also by branches of the facial nerve ; whilst the transverse facial artery is commonly some distance above, though its relation is variable. Having crossed the masseter, it turns abruptly round the anterior border of this muscle and runs inwards through the fat of the cheek, practically at right angles to the first part of its course, to reach the buccinator, which it pierces. Then passing for some distance (5 to 10 mm.) between the buccinator and mucous membrane, it opens into the vestibule of the mouth by a very small orifice, on a variably-developed papilla, opposite the crown of the second upper molar tooth. The course of the duct, which is fairly constant, can be marked on the side of the face by drawing a line from the lower edge of the auditory meatus to a point midway between the ala of the nose and the red of the lip ; the middle third of this line corresponds fairly accurately on the surface, to the course pursued by the duct. The gland varies in weiglit from half an ounce to an oiuice or more. Several small lolies or processes are found in connexion with it — viz. one rumung backwards between the sterno-mastoid and the digastric ; a glenoid lobe of very small size, which lies in the posterior part of the glenoid cavity ; a pharyngeal process (Fig. 715), which runs forwards and inwards between the styloid process and the external carotid artery towards the pharynx. A pterygoid extension running forwards between the two pterygoid muscles, although described, axnnot properly lie said to exist. Stenson's duct measures from li to 2^ inches (38 to 62 mm.) in length, and ^ inch (3 to 4 mm.) in diameter. The calibre of the duct is very much greater than that of its orifice, which only admits a fine bristle, and for this reason the duct may, to some extent, be looked upon as a reservoir for the saliva, as well as a duct for its conveyance. In the child it pierces the "sucking pad " on its way to the mouth. Vessels and Nerves. Tlie arteries wliirli f^upjily the gland arise from the external carotid, and from the l)ranches of this artery in relation U) the gland. The veins join the temporo-maxillary and its tributaries. The lymphatics 2>ass to both the superficial and the deep cervical glands ; there are also a few small parotid lymi^hatic glands, ■which lie on the surface of the upper and lower part of the parotid beneath the capsnla Some are said to be embedded in the substance of the parotid itself The nerves are derived {a) from the auriculo-temporal, and {h) from the sympathetic on the external carotid. The fil>res of the sympathetic are niaiidy vaso-constrictor. Those of the auriculo-temporal convey to the glaud secretory fibres from tlie glosso-pharyngeal. Submaxillary Gland. — The submaxillary gland is next in si/e to the parotid, and resembles it in its lol)ulati()n ami colour. It is placed partly in the sub- maxillary triangle and partly uiukir cover of the pcisterior part of tlie mandible near its angle (Fig. 716). In size and shape it may be compared to a small walnut willi three Hattened 1012 THE DIGESTIVE SYSTEM. sides. It is enclosed in a complete capsule derived from the deep cervical fascia : embedded in this capsule, and superficial to the gland, are found a few submaxillary lymphatic glands, which are of importance owing to their connexion with the lymphatics of the hps and of the anterior half of the tongue. Ill considering the relations of the gland, it is well to remark tliat there is in this region a three-sided space bounded externally by the inner surface of the mandible below the mylohyoid ridge, internally and above by the mylohyoid muscle running inwards and downwards, and below by the skin and fascia passing from the margin of the jaw obliquely inwards and downwards to join the side of the neck. In tliis space the gland lies with external, internal, and inferior surfaces corresponding to the walls of the space. The stcperjicial or inferior surface looks downwards and outwards ; it is covered by the deep cervical fascia and the platysma, and is crossed by the facial vein, which lies superficial to the gland, whilst the artery passes in part beneath it. The external surface rests against the inner aspect of the lower jaw (submaxillary fossa) for an inch and a half forward from the angle, to which latter it usually reaches behind. The deep or internal surface lies on the posterior part of the mylohyoid muscle, and behind this, on the hyoglossus and the posterior belly of the digastric with the stylohyoid ; for the gland is not contained within the limits of the sub- maxillary triangle inferiorly, but passes down some little distance over the digastric muscle. From the deep surface, anterior to its middle, a narrow tongue-like deep process (Fig. 716) is continued forwards beneath the mylohyoid muscle along with the duct. The posterior end of the gland, which is its most bulky portion, either abuts against, or lies very close to, the sterno-mastoid, and is often overlapped by the lower end of the parotid gland. The facial artery, on its way to the border of the mandible, lies in a groove in the upper and back part of the gland. The submaxillary or Wharton's duct leaves the deep surface of the gland about its middle, and runs forwards beneath the mylohyoid muscle with the deep process, along the upper and inner aspect of which it is placed (Figs. 716 and 712). Pursuing its course forwards beneath the floor of the mouth, on the inner side of the subungual gland, the duct crosses the hyoglossus and the genioglossus muscles, and finally opens on the floor of the mouth at the side of the frenulum linguse, where its small orifice is placed on the summit of a soft papilla (caruncula sub- lingualis) close to its fellow of the opposite side. While running forward beneath the floor of the mouth the duct, which is about two inches long (50 mm.), is crossed on its inferior aspect by the lingual nerve near the anterior border of the hyoglossus, that is opposite the 2nd molar tootli. The nerve at the time is arching from the posterior end of the mylohyoid ridge (against wliicli it lies) inwards and forwards in order to reach the under surface of the tongue, and in this course it passes beneath the duct at the point indicated. As in the case of Stenson's duct, the calibre of Wharton's duct is much greater than that of the orifice by which it opens ; for this reason it may likewise be looked upon as forming, to some extent, a reservoir for the saliva secreted by the gland. Vessels and Nerves. — The arteries come chiefly from the facial and its submental branch : the veins are similarly disposed. The nerves are derived from the submaxillary ganglion (which lies above the deep process of the gland), and are composed of fibres from the cliorda tympani, from the lingual, and from the sympathetic on the facial artery. The lymphatics pass to the submaxillary lymphatic glands. Sublingual Gland. — This is an elongated almond-shaped mass, flattened from side to side, and much wider (from above downwards) in front than behind, which lies on the floor of the mouth beneath the plica subungualis— a ridge of the mucous memljrane produced by the prominent upper border of the gland. It is usuaUy from 1^ to If inches (37 to 45 mm.) in length, whilst its bulk is about equal to that of two or three almonds. It is placed between the mandible externally, the genioglossus internally, the mylohyoid muscle below, and the mucous membrane of the mouth above (Fig. 706). Its detailed relations are as follows : — Its outer surface rests against the inner aspect of the body of the mandible above the mylohyoid ridge. Its inner surface is in contact with the genioglossus and the hyoglossus muscles, as well as with Wharton's duct, which runs forwards between the gland and the muscles. Bdoiv, it rests on the mylohyoid, and at its posterior part on the deep process of the submaxillary gland ; whilst its upper DEVELOPMEXT OF SALIVAEY GLANDS, PALATE, AXD TONGUE. 1013 prominent border is covered only by the mucous membrane of the mouth, here raised up by the gland to form the plica sublingualis (Fig. 712). The anterior portion of the gland is much deeper and more bulky than the posterior half, and it meets its fellow in the middle line beneath the frenulum lingute. The posterior extremity grows gradually more slender, and ends near the posterior part of the mylohyoid ridge, where it lies above the deep process of the submaxillary gland. Its ducts, generally known as the ducts of Rivinus (ductus sublinguales miuores), are numerous and of small size ; they leave the upper part of the gland, and, after a short course, open on a series of papillte, visible to the naked eye, which are placed along the summit of the plica sublingualis. The gland is not enclosed in a distinct capsule, thus differing from the parotid and submaxil- lary glands ; but its numerous lobules, which are smaller than those of the glands just mentioned, are held together by fine connective tissue, loosely, but still in such a manner as to make one more or less consolidated mass out of what was, in the embryo, a number of separate glands. As a rule all the ducts open separately on the summit of the plica sublingualis, and appar- ently none of them join Wharton's duct. Frequently some of those from the anterior and more bulky part of the gland are larger than the others, but the presence of a large duct running alongside of Wharton's duct, and opening with or beside it (ductus major Eivini, duct of Bartholin), is very rare, and must be considered as an exceptional condition in man, although normal in the ox, sheep, and goat. The same may also be said of ducts from the sublingual, which are described as 02)ening into the duct of Wharton. Vessels and Nerves. — Tlie arteries are derived from the sublingual branch of the lingual and from the submental branch of the facial. The nerves come from the lingual, the chorda tympani, and the sympathetic, through a branch of the submaxillary ganglion which joins the lingual, and is conveyed by it to the gland. The apical gland of the tongue (Nuhn's) is described with the tongue, p. 1006. Development of the Salivary Glands, Palate, and Tongue. The general development of the lips, mouth, palate, and tongue is described on pages 37 to 42, and reference wiF be made here only to a few special points bearing upon this matter. Several explanations of the formation of the philtrum or groove on the front of the upper lip have been put forward ; most probably it is produced by the imion of the median fronto-nasal process with the two maxillary processes (see p. 39), the floor of the groove being formed by the fronto-nasal process, and the ridges bounding the groove at the sides corresponding to the line of meeting of the fronto-nasal with the maxillary processes. The salivary glands are developed as solid outgrowths of the buccal epithelium, one each for the submaxillary (the first developed) and the parotid, several for the sublingual gland. The outgrowths are at first simple ; they subsequently divide, and finally develop alveolar enlargements on their extremities. By a separation of the lining cells, the ducts, and later on (about the 22nd week) the alveoli, become hollowed out, and present a lumen as in the adult. The development of the palate is given at page 40 ; but it should be mentioned that, in order to account for the position which the fissure in cleft palate usually occupies, viz. between the centi'al and lateral incisors, the theory has been advanced by Albrccht, that each premaxilla is made up of two separate segments, an inner (or endo-gnathion), containing the central incisor, and an outer (or meso-gnathion\ containing the lateral incisor (the rest of the maxilla constituting the exo-gnathion). Between these two segments of the premaxilla (endo- and meso-gnathion) the cleft is said to run, and not between the premaxilla and maxilla as usually held. Tongue. — The tongue is developed in the embryo, not on the floor of the primitive mouth, but upon the anterior wall of the pharynx, and in two parts, which are at fii-st distinct but soon unite. The anterior two-thirds of the organ is formed from the tuberculum impar, a single median elevation, developed on the ventral wall of the pharynx, immediately behind the first, or mandibular, visceral arch. Behind the tuberculum inipar, at first, lies a prominent elevation — the furcula, from the anterior part of which the epiglottis is formed — the two being separated by a distinct sulcus, the sinus arcuatus (see p. 37). Soon, however, the ventral exti'cmities of the second and third visceral ai'ches, growing downwards, imite across the middle line. The tuberculum is thus separated from the furcula, and the middle portion of the sinus arcuatus is divided into an anterior and a posterior part. The ventral ends of the two arches having fused, develop, after a little time, into a prominent semilunar ridge, the rudiment of the posterior 1014 THE DIGESTIVE SYSTEM. third of the tongue. This ridge embraces the back of the tuberculum impar, but it is separated from it iu part by the anterior division of the sinus arcuatus, ^'hich persists even iu the adult as the foramen creciim, with the sulcus terminalis running forwards and outwards on each side from it. Finally, the two rudiments of the tongue — the tuberculum impar and the semilunar ridge — become blended, the only indication of the original separation being the foramen caecum, the sulcus terminalis, and the different characters "svhich the mucous membrane presents on the two divisions of the organ. At the foramen caecum the downgrowth which gives rise to the isthmus of the thyroid gland takes place, and a part of the thyro-glossal duct which in the early condition connects the two may in rare cases persist in the adult in connexion with the foramen. Permaneut canine 1st permanent XJremolar 2nd permanent premolar 1st permanent molav 2nd permanent mol central incisor THE TEETH. The teeth are highly modified portions of the mucous membrane of the mouth, specially developed to perform the important function of mastication, that is, the division and trituration of the food which takes place in the mouth before the holus, as the resulting mass is called, can be swallowed. Each tooth is a calcified papilla of the mucous membrane of the Permanent lllOUth, and COnsistS incisor lil^e that membrane Permanent of tWO cMcf pOrtionS — namely, the den- tine derived from the connective tissue, and the enamel from the epithelial layer of the mucous mem- brane. The dentine constitutes the chief mass of the tooth, whilst the enamel forms a cap for the portion which projects above the gum. There is also found in the teeth another special tissue — the cemen- tum or crustapetrosa, a form of modified bone — which en- dental canal Mental fmanifn Fig. 717. — Tketh of a Child over Seven Years old (moditied from Testut). By removing the bony outer wall of the alveoli, the roots of the teeth which have been erupted, and the jjermanent teeth which are still embedded iu the mandible and maxilla, have been exposed. The milk teeth are coloured blue, the permanent teeth yellow. It will be seen that the first permanent molars have appeared, the central and lateral milk incisors have been replaced Ijy the corresponding permanent teeth in the upper jaw, but the milk canine and molars have not yet been shed. In the lower jaw the central milk incisor has CaSCS the rOOtS, thCSC been replaced by the permanent central ; the lateral has notf yet been shed, but latter bcino" formed its permanent successor is making its way up to the sui-face on its lingual side. p|-,-jpfl-,r ^.f rlpritinp In addition, the canine and two molars of the milk set persist. The position -^ . ' of the crowns of the permaneut teeth between the roots of the milk molars, Ucntme and anil the deep situation occupied by the permanent canines, should be noted, enamel but particu- Observe also the absorption of the root of the lower lateral incisor. Iprlv tbp Inttpv arp the hardest and most resistant structures in the body, and are thus specially fitted for the functions which they have to perform. Temporary and Permanent Teeth.. — The mouth of the infant at birth contains no teeth, although a number, partly developed, lie embedded in the jaws beneath the gum. Some six months later teeth begin to appear, and by the end of the second year a set, known as the milk teeth, twenty in number, has been " cut." Then follows a pause of about four years, during which no visible change takes place in the mouth, although in reality an active preparation for further develop- ment is going on beneath the gum. THE TEETH. 1015 At the end of this period, namely, about the sixth year, the next stage in the production of the adult condition begins. It consists in the eruption of four new- teeth — the first permanent molars — one on each side, above and below, behind those of the milk set. This is followed by the gradual falling out of the twenty teeth which have occupied the mouth since the second year (Fig. 717), and the sub- stitution for them of twenty new teeth, which take up, one by one, the vacancies created Ijy the dropping out of each of the milk set. finally, the adult condition is attained by the eruption of eight additional teeth — the 2nd and 3rd molars — two on each side, above and below, behind those which have already appeared. All of these — the permanent set — have appeared by the end of the twelfth or thirteenth year, except the four wisdom teeth, which are usually cut betw'een the seventeenth and twenty-tiftli year, but are often delayed until a very much later period, and occasionally never appear. The set of teeth which, as indicated above, begin to appear in the infant about the sixth month, are known as the deciduous, temporary, or milk teeth (dentes decidui), whilst those which succeed them and form the adult equipment are the permanent teeth (dentes permanentes). The milk teeth are twenty in number, and are named as follows in each jaw, beginninu' at the middle line : — central incisor, lateral incisor, canine, first molar and second molar ; or more briefly, two incisors, one canine, two molars. This is con- veniently expressed by the " dental formula " for the deciduous teeth in man, which shows the number of each class of teeth above and below on one side of the mouth, viz. : — i. #, c. \, m. f . The permanent teeth, thirty - two in number, are named in each jaw, beginning at the middle line: — central incisor, lateral incisor, canine, 1st premolar (or bicuspid), 2nd premolar (or bicuspid), 1st molar, 2nd molar, and 3rd molar or wisdom tooth (dens serotinus). The dental formula for the permanent set in man is thus : — i. n, c. \, 2^yii- i, m. %. General Form and Structure. — A tooth consists (Fig. 71S) of (1) the crown (corona dentis), the portion projecting above the gum, whicli varies in shape in the different teeth, and in all, except the incisors and canines, bears on its grinding surface a number of tubercles or cusps (tubercula coronte), varying in number from two to five in the different teeth ; (2) the neck (collum dentis), the faintly constricted part which is surrounded collar - wdse by the gum, and which connects the crown with (3) the root (radix dentis), the portion of the tooth which is embedded in the alveolus of the maxilla or the mandible. In the majority of teeth, namely, in aU except the molars, the root, as a rule, is single, or nearly so, and consists of a long, tapering, conical, or flattened piece, perfectly adapted to the alveolus in which it lies. In the molar teeth (and in some of the others occasion- ally) the root is divided into two or three tapering or flattened roots or fangs. At the apex of each root there can be made out, even with the naked eye, a minute opening (foramen apicis) througli which the vessels and nerves enter the tooth. On uiakint;- a section of a tooth (Fig. 718), it will l)e seen that the interior of 68 6 Bone I ('(Miieiit or cnist.i potrosa Alveolar periosteum or root-memlirane Fk;. 718. — Vkkticai, Skction of Casink ToitTii to illustrate its various parts, and its structure. 1016 THE DIGESTIVE SYSTEM. the body is occupied by a cavity of some size, generally called the pulp cavity (cavum dentis), owing to the fact that it is filled in the natural state by the soft and sensitive tissue known as the pulp. This pulp cavity gradually narrows below, and is prolonged into each root of the tooth as a slender tapering passage, the root canal (canalis radicis), which opens at the apical foramen already referred to. Through these root-canals, which also contain some pulp, the vessels and nerves, which enter at the apex, pass to the interior of the tooth. Short diverticula of the pulp cavity are prolonged into the bases of the cusps in the molar and premolar teeth, and in the incisors also there are similar slight pro- longations of the cavity towards the angles of the crown. The roots of the teeth are embedded in the sockets or alveoli of the jaws, to which they are accurately adapted, and firmly united (Fig.. 718) by a highly vascular layer of connective tissue — the alveolar periosteum (alveolo-dental perios- teum or root-membrane). This is attached to the wall of the alveolus on the one hand and to the root of the tooth on the other, whilst above it is continuous with the connective tissues of the gum. So accurately are the root and the alveolus adapted to each other over their whole extent, and so firmly does the periosteum bind them together, that, under normal conditions, the tooth is quite firmly fixed iii the bone, and no movement of the root within the alveolus can take place ; the vessels and nerves entering at the apex are thus secured against pressure or strain. When, however, the alveolar periosteum is inflamed it becomes swollen and exquisitely sensi- tive ; the tooth, as a result of the swelling, is pushed partly out of its socket, its crown projects above those of its neighbours, and strikes against the opposing tooth when the mouth is closed, giving rise to much pain and discomfort. The neck, although a useful term, can scarcely be recognised as a distinct constriction in the permanent teeth ; it corresponds to the line along which the gum and alveolar periosteum meet, or along which the gum is imited to tlie tooth ; but, as already pointed out, the gum does not stop at the neck, but forms a free fold which surrounds the base of the crown collar-wise for a short distance. The outline of the margin of the gum opposite the labial and lingual surfaces of the crown is usually concave, but oj)posite the proximal and distal sides of the tooth it is convex, and reaches much nearer to the edge of the crown than on the other surfaces. In the incisors and canines the pulp cavity, which is about ^ to j- tlie diameter of the tooth, passes very gradually into the root canal (Fig. 718), so that it is difficult to say where one ends and the other begins. The reverse is the case in the molars, whilst the premolars are somewhat variable in this respect. Tartar is a liard calcareous deposit from the saliva (salivary calculus), often found on the teeth near their necks. It is composed of lime salts, and its deposit is largely determined by the presence of organisms (leptothrix, etc.) in the mouth. THE PERMANENT TEETH. The permanent teeth (Figs. 719 and 724) are thirty-two in number, sixteen above and sixteen below, or eight in each half of either jaw ; and, although we can group them under four heads — incisors, canines, premolars, and molars — the individual teeth differ so much in their characters that each tooth will require a separate description. Descriptive Terms.— Before describing the permanent teeth, it is requisite that certain terms which are employed to denote the surfaces of the teeth should be defined. This is a matter of some importance, seeing that the terms inner and outer, anterior and posterior, cannot, owing to the curvature of the dental arches, be properly applied to all the teeth in the same sense. The terms given below have been adopted seeing that they are free from the danger of misconception. The part of a tooth which comes in contact with the teeth of the opposite jaw is known as the grinding or masticating surface (facies masticatoria. Fig. 721). The surface in contact with or looking towards its predecessor in the row is known as the proximal surface (fades medialis in incisors and canines, facies anterior in premolars and molars) ; the opposite surface, namely, that which looks towards its successor in the row, is known as the distal surface {fades lateralis in incisors and canines, fades posterior in molars and premolars). The surface which looks towards the tongue is the lingual surface (facies lingualis), and that looking in the opposite direction, i.e. towards the lips and cheek, the labial surface (facies labialis). The portion of a tooth which touches its neighbour in the same row is known as the contact surface (facies contactus). THE TEETH. 1017 Incisor Teeth (denies incisivi, Figs. 719 and 720). — These teeth, four in number in each jaw, are used specially for cutting the food, hence their name. The crown of each is chisel-shaped, and presents an anterior or labial surface which is convex in all directions, a posterior concave surface, and a chisel-like edge, which, when first cut, is surmounted l:)y three small tubercles separated hj two grooves. These tubercles, however, are soon worn down, and the edge becomes straight or nearly so. Owing to the fact that the upper incisors overlap those in the lower jaw, the cutting edge is worn away, or becomes bevelled, on the posterior aspect in the former, but on the anterior aspect or summit in the latter. The upper, but particularly the upper central incisors, are of large size, and slope somewhat forwards ; Srd niolai lin^molar Canine Central incisor Ist premolar f\ Lateral incisor 3rfl molar 1st premolar 2n'T Teeth of the Eight Side, The upper row shows the upper teeth, the lower row the lower teeth 3rd molar 2nd molar Inner or Lingual Aspect. The cingulum is distinct on the upper incisors and both canines, the lingual cusp on the upper lateral incisor and the upper canine. its root is also more flattened. On the labial surface of the crown, of both canines and premolars, a wide low vertical ridge (labial ridge) can generally be made out (Fig. 719) ; it is most dis- tinct on the canine and first upper premolar. Premolar or Bicuspid Teeth (dentes premolares, Figs. 719 and 720). — Eight in number, two in each jaw above and below, the premolar teeth are placed behind the canines, and in front of the molars as indi- cated by the term " premolar." The crown which, unlike that of the incisors and canines, is flattened from before backwards (proximo-distallj), is characterised by the presence of two cusps (Fig. 721), hence the term bicuspid often applied to these teeth. One of the cusps, the larger, is placed on the outer or labial, the other on the inner or lingual side. The labial and Ungual surfaces are both convex. The "root is single, but it is, as a rule, flattened from before backwards (proximo- distally) and grooved, showing in this a tendency to division, which often actually f " r1^^^ ^''^i^^^^'^%. takes place in the first upper premolar. '^ *■' '^^ '" The upper premolars are easily distin- -The Ui'J'Er Permanent Teeth, viewed guishecl by the fact that their twO CUSps from below. ^^^ large and are separated from one The cusps of the premolars and molars of the right another by a distinct autcro- posterior side (left of picture) are particularly well shown, r- /-r?- Htoin t.-i j. • iiT i The ridge from the inner anterior (proximo- ^^SUre (Fig. 721) ; whllst in the lower lingual) to the outer posterior (labio-distai) cusp premolars, on the otlicr hand, the separa- is also distinct in the first and second molars, tion between the twO CUSpS is UOt effected J he second molars show lour cusps, one of i ,• r> • j.i then, small, although three only are frecpiently "^7 ^ COntmuOUS fisSUre aS HI the Upper found. teeth, but by two dimple-like depressions separated Ijy a ridge, which joins the two cusps (Fig. 722). In the upper premolars, therefore, the two cusps are separated by a fissure, in tluj lower they are united by a ridge. The first upper ijreniolar is often slightly larger than the second ; the reverse is the case in the lower jaw. The outer or labial surface of the crown is usually somewliat larger than the Fig. 721. THE TEETH. 1019 inner or lingual surface in all premolar^. Tlie upper are distinguished from the lower bicuspids, as pointed out above, by tlie fact that in the upjjer the two cusps are separated by a groove, in the lower they are united by a ridge ; in the latter also the cro'svns are more circular (Figs. 715 and 722). It will further usually be found that the outer or labial surface of the crown is strongly sloped (bevelledj inwards, near the grinding surface, in the lower premolars. The first can usually be distinguished from the second by the fact, that, while the lingual cus2) and surface are smaller than the laljial in the first premolar, they are nearly of the same size in the second. In addition, the root of the first upper premolar is bifid or nearly so, and its labial ridge is fairly distinct, but is indistinct in the second. In the first lower premolar the lingual cusjj and surface are very small, in fact the cusp is quite rudimentary. It should, however, be added that it is often extremely difficult to identify the various bicuspids. The diff"erences may be expressed in tabular form thus : — Premolars. Boot. Cusp and Surface. Upper (have two cusps separated by a groove) '1st premolar bifid, or uea •ly so Lingual smaller than labial. .2nd ,, single Lingual nearly as large as labial. , Lower (have two cusps united by- a ridge) 1st premolar single JLingual much smaller than labial. 2nd „ j Lingual nearly as large as labial. Molar Teeth (dentes molares). — The molar teeth, als(.t known as the grinders or multicuspidati, are twelve in number — three on each side above and below — and are disliuguished as first, second, and third molars. The latter is also known as the wisdom tooth, owing to its late eruption. All the molars are characterised by the large size of the crown and the possession of three or more trihedi'al cusps on the masticating surface (Figs. 721 and 722). Thej are the largest of all the teeth, but they diminish in size from the lirst to the third, the last being, as a rule, the smallest of the three. In shape the crown is more or less quadrangular, with convex labial and lingual surfaces. The roots are either two or three in number, but frequently in the wisdom teeth they are united to a varying degree. The molars of the upper and lower jaws differ so considerably in their further details that they must be considered separately. They may be most readily dis- tinguished from one another by the fact that normally the upper molars possess three roots (Figs. 719 and 720), whilst the lower molars have two at most. The number of cusps, though not so reliable a guide as the form of the root, is also generally sufficient to distinguish them. In the upper molars there are either three or four cusps, whilst in tlie lower the number is most commonly five (see, however, page 1021). In the upper molars, the crown, viewed from the grinding surface (Fig. 721), is rhomboidal in shape (;i.e. quadrangular with the angles not right angles). The outer (labial) and the inner (lingual) surfaces are convex. The number of cusps is either four or three. On the ^first there are invariably four — two on the labial and two on the lingual side — the antero-internal (proximo-lingual) of these being connected with the postero-external (labio-distal) by an oblique ridge (Fig. 721), which is also found on the second and third molars when these bear four distinct cusps. The second upper molar has either four or three cusps in about an equal proportion of European skulls, whilst in the third the number is much more frequently three than four. The roots in the upper molars are three in number (except, occasionally, when the three roots of the wisdom tooth are confluent), two being external or labial, and the third internal or palatal (Figs. 719, 720, and 723). In the lower molars, the crown, viewed from above (Fig. 722), is somew^hat cubical. The outer and inner surfaces are convex, as in the upper molars. The Jirst, as a rule, bears five cusps, two being on the outer side, two on the inner, and the fifth behind and external, that is, between the two posterior cusps and somewhat to the outer side. The second, has usually only four cusps ; a fifth, however, is sometimes present. The third has either four or five, the former number more frequently than the latter. The roots of the lower molars are two in number, each wide, grooved, and 1020 THE DIGESTIVE SYSTEM. flattened from before backwards. One is placed anteriorly, the other posteriorly, and both are usuaUj recurved in their lower portions (Fig. 719). As in the corre- Central incisor Lateral incisor 1st premolar !nd premolar 1st molar Fig. 722. — The Lower Permanent Teeth, viewed from above. spending teeth of the upper jaw, the roots of the lower wisdom teeth are often more or less united into a single mass. The chief characters of the upper and lower molars may be summarised thus : — Molars. ' 1st Upper. 2nd Upper. 3rd Upper. Upper Cusps . 4 3 01-4 3 or 4 3 (or 1) Roots . 3 3 r 1st Lower. 2nd Lower. 3rd Lower. Lower. Cusps . 5 4 01-5 4 or 5 Roots . 2 2 2 (or 1 ) The molars diminish in size from before backwards. This remark applies particularly to the wisdom teeth, which are extremely variable in form and j^osition among civilised races. The long axis of the upper molars has a general direction downwards and outwards ; whilst that of the lower molars, which the former partly overlap, slopes upwards and inwards, with the result that the outer cusps of the lower molars lie in the groove seijarating the inner from the oviter cusps of the upper teeth (Fig. 706, p. 996). As a further result of this overlapping, the outer edge of the crown is sharj) and the inner edge rounded in the ui)per molars ; whilst the inner edge is sliarp and the outer edge rounded in the lower set. The cause of this is obvious. The outer margins of the upper molars overlap their fellows on the buccal side, whilst the inner margins of the lower molars overlap their fellows on the lingual side ; these margins, therefore, are subject to comparatively little attrition, and consequently remain sharp. The other margin of each tooth, on the other hand, strikes against the groove on the crown of the opposing tooth, and con.sequently becomes worn and round. The fissures which sei)arate the cusps on the grinding surfaces of the molar teeth are generally continued as faint grooves on the labial and lingual surfaces. Upper Molars. — The crovras, as already stated, are rhomboidal in shape, and when viewing their grinding surfaces, as in Fig. 721, if the planes of sej^aration between them be prolonged, they would strike the middle line near the back part of the hard palate ; in other words, their THE TEETH. 1021 proximal and distal surfaces are not in transverse but in oVjlique planes, sloping strongly back- wards and inwards, and converging somewhat internally. A kiKjAvk-dge of this is useful in determining the side to wliich an upper molar belongs, as is the fact that the anterior labial root is broader than the posterior (Fig. 723). As regards the nuviher of cusps (Fig. 721) : — The first ui:)per molar has four cusps in practically all skulls (99 per cent) ; occasionally, indeed, another, but very rudimentary, cusp is present on tlie lingual side of the antero-internal (proximo-lingual) cusj). The second molar has either three or four in an almost equal proportion of Europeans, but more frequently four taking the teeth of all nations together. (According to Tojiinard, four cusjjs are present in 66 per cent of all races, and in 58 \mv cent of European, Semitic, and Egyptian skulls ; according to Zuckerkandl, in 73'5 \)(iv cent of the lower races and 45'6 per cent of Euroj)eans.) The third upper molar has three cusps much more frequently than four amongst Europeans (four cus])s only in 36 per cent, although it has four cusps more frequently in certain lower races). It should be remarked that, while there are practically always four cusps in the first molar, still there is a tendency to the disappearance of the postero-internal (disto- lingual) cusp, which tendency grows more pronounced as we pass backwards to the second and third inolai's. The other cusps are practically constant. The three roots of the upjaer molars (Figs. 719, 720, and 723) are a large inner or 2)alatal, sub-cylindrical in shape, and two external or labial roots, smaller and flattened from before backwards. The palatal fang, which is placed opposite the posterior labial root, is often united to one of the others. The lower j)art of the anti'um of Highmore generally extends down between the palatal and the two laljial fangs (Fig. 706, p. 996), but the latter jaroject on its floor more frequently than the palatal root. In the wisdom tooth the three roots are frequently more or less united into a single conical jjrocess (Fig. 723). Lower Molars. — The crowns are more massive than those of the upper molars, and are elongated antero-pos- tcriorly (Fig. 722). A crucial groove separates the foiu' chief cusps from one another ; this bifurcates behind to en- close the fifth cusp, which lies slightly to the outer side of the middle of the tooth. Hhd number of cus'ps present in the lower molars is as follows : — The first has usually five cusjjs (62 per cent of all races, 61 per cent of Eurojjeans) ; the second has four cusps, as a rule (five cusps in only 24 per cent of all skulls) ; the lower wisdom tooth has four cus^js a little more frequently than five (five in 46 jjer cent of all skulls), but like the upper wisdom tooth it is extremely variable. The roots of the lower molars (Fig. 719), two in number, are flattened from before backwards, and very wide. The anterior of these has two root canals ; the i:)osterior but one (Fig. 723). The wisdom tooth has commonly two roots like its fellows; occasionally the two are united. In determining the side to which a lower molar belongs, it should be rememi)ered that the lower i)art of the root is generally curved backwards, and also that the blunter margin of the crown (see above) and tlu' fifth cusp, if pix'sont, are on the outer side. Arrangement of the Teeth in the Jaws. — The teeth are arranged in eacli jaw in a curved row — the dental arch (arcus dentalis) — of appro.xiiuately a semi-oTal form (Figs. 721 and 722). The curve formed by the upper teeth, however, is widi-r than that formed by the lower set, so that when the two are brought in contact the upper incisors and canines overlap their fellows in front, and the outer cusps of the upper premolars and molars overlap the corresponding cusps of the lower teeth (Fig. 706, p. 996). It wiU also be seen that, as a rule, the teeth in one jaw are not placed exactly opposite tlieir fellows, l)ut rather opposite the interval between two teeth, in the other jaw (Fig. 724). Tliis arrangement is bnnight about largely by the great width of the upper central incisors as compared with Fig. 723. — Horizontal Sections through bdth the Upper AND Lower Jaws to show the roots of the teeth. The sections were carried throutjh the bones a short ilistance from tlie edge of their alveoLar borders. Tlie upper tigure shows the upper teeth, tlie lower figure the lower teeth. Note the flattened roots of the lower incisors, the two root canals in the anterior root of each lower molar, and the coutiueuce of the three roots of the upper wisdom teeth. 1022 THE DIGESTIVE SYSTEM. their feUows of the lower jaw, which throws the upper canines and the succeeding teeth into a position behind (distal to) that of the same named teetli of the lower set. But as the lower molars are larger in their antero - posterior diameter than those of the upper row — and this remark applies par- ticularly to the wisdom teeth — the two dental arches terminate behind at approximately the same point. The upper dental arcli is said to fonn an elliptical, the lower a parabolic curve (Figs. 721 and 722). The line formed by the grinding surfaces of the upjjer teeth, as seen on profile view (Fig. 724), is Tisually somewhat convex, owing largely to the failure of the wisdom tooth to descend into line with tlie others. Similarly the line of the lower teeth is as a rule concave. In both jaws the crowns of the front teeth are higher (longer) than those of the molars. Period of Eruption of the Per- manent Teetli. — Although there is considerable variety in the dates at which the various permanent teeth appear above the gums, the order of eruption is practically constant in different individuals, and is as follows : — Before any of the temporary teeth are lost the first permanent molars appear behind the 2nd milk molars. Next the central milk incisors faU out, and their places are taken by the permanent teeth of the same name ; then follow the remaining teeth in the following order: Lateral incisors, 1st premolars, 2nd premolars, canines, 2nd molars, and 3rd molars. It will be observed that the eruption of the canine is delayed until the two premolars, which succeed it in the row, are cut, so that it breaks the otherwise regular order of eruption. The 1st molar is sometimes popularly known, owing to the date of its eruption, as the " six- year-old tooth," and the 2nd molar as " the twelve-year-old tooth." The dates at which the eruption usually takes place may be simply stated as follows for the lower teeth ; those of the upper jaw appear a little later : — 1st molars appear soon after the 6th year. Central incisors appear soon after the 7 th year. Fig. 724. — To show tlae relation of the upper to the lower teeth when the month is closed. The manner in which a tooth of one row usually strikes against two teeth of the opposite row, and the resulting interlocking of the teeth, is to lie noted. Lateral „ 8th 1st premolar 9th 2nd 10th Canine „ 11th 2iid molar 12 th 3rd „ from the 17th to Variations in the Number of the Teeth. — The presence of an additional tooth is by no means uncommon. It may appear in connexion with the incisor, jiremolar, or the molar groujis. Windle veiy ju'Operly draws a distinction between " suj^ernumerary " or imjaerfect additions to the dentition and "supplemental" teeth which corresj^ond in size with those with whicli they are associated. Wlien a supplemental incisor appears it has an interesting bearing ujjou the solution of the much -debated jDoint as to which incisor has disap2)eared from the primate dentition. The addition of a third 2>i'emolar may be looked uj^on as a reversion to the condition present in the New World Apes and the Lemurs. The presence of a fourtli molar has not infrequently been obseived, anct recently it has formed the subject of an instructive and sugges- tive ]ia])iT by .r. T. Wilson (Jonrn. A'liat. and Phys., vol. xxxix. part ii.). The Milk Teeth. The deciduous, temporary, or milk teeth (dentes decidui) are twenty in number, ten above and ten IjcIow, or five in each half of each jaw — namely, two incisors, one 8TEUCTUEE OF THE TEETH. 1023 Lati'ial iiici Central incisor •Jnd molar crown -2nil molar canine, and two molars. They may be distinguished from the permanent teeth by their smaller size, their well-marked and constricted necks, and, in the case of the molars, by the wide divergence of their roots (Fig. 725). Otherwise they correspond so closely to the same named teeth of the permanent set, that they require no separate description, except in the case of the molars. The first upper molar has but three cusps on its crown — two external and one internal : the first lower molar has four — , , , two external and two internal, and the crowns of both are flattened horn, side to side. The second molars of the upper jaw have four, those of the lower jaw five cusps each. In every case the second are much larger than the first molars. The cusps are sharper and are separated by deeper fissures or foss;u than those of the permanent teeth, whilst the roots of the milk molars, except for their greater di- vergence, agree with those of the permanent set. Tlie marked con.strictioii at the i^t niulai neck of the milk teeth (Fig 725) is p^^_ 72.^.-The Milk Tekth ok thk Levt Siuk. due to a gi'eat thickenuig ot tlie cap of enamel on the crown and its '^''^ masticating surfaces of the two upper molars are shown above, abrupt termination as the neck is I" the second row the upper teeth are viewe.Urmn the outer reached. The enamel, too, is much °^- l^^'.'^l «de. In the third row the lower eeth are shown , .. T xi • xi in a similar manner : and below are the masticating surtaces whiter as a rule than m the per- ^^ ^^^^ ^^^^ j^^^^^. ^^^^j,^^^ j,^ ^,^^ specimen from which the manent teeth, it should Lie added f^^^^ ^pp^j. ^^^^.^^ ^^^^ drawn the two outer or buccal cusps that the labial surface of the canines ^e^e not distinctly separated, as is often the case, and molars departs very markedly from the vertical ; it slopes strongly inwards towards the mouth cavity as it apiJroache.s tlu- grinding surface of the crown, which latter is, as a result, much reduced in Avidth. The divergenc(^ of the fangs in the milk molars allows the crowns of the permanent jiremolais to fit in between them before the milk molars are shed. Central incisor Lateral incisor •.'11.1 UK crown Structure of the Teeth. As mentioned above, the teeth are composed of three special tissues, enamel, dentine, and crusta petrosa, in addition to the pulp which occupies the tooth cavity. The chief mass of the tooth is formed of dentine, which surrounds the pulp cavity and extends from crown to root ; outside this is a covering of enamel on the crown, and a layer of crusta petrosa or cement on the root. The enamel (substantia adamantina) is the dense, white, glistening layer whicli forms a cap, thickest over the cusps, for the portion of each tooth projecting above the gum (Fig. 718). At the neck it ceases gradually, being here slightly overlapped by the crusta peti'osa. It is composed chiefly of phosphate and carbonate of lime (phosphate of calcium 89-82 per cent, carbonate of calcium 4-37 per cent, magnesium phosphate 1-34 per cent, a trace of calcium fluoi'ide, other salts -88 per cent), and has generally been considered to contain aliout 3-6 per cent of organic sulistance ; but this Tomes has recently shown to be inaccurate : " That which ha.s heretofore been set down as organic nialter is simply water combined with the lime salt*. Enamel is to be regarded as an inorganic substance comi)0.sed of lime .silts, which have been deposited in particular patterns and formed under the influence of oiganic tissues, which have tliemselves disappeared during its formation." Enamel consists of calcified microscopic prisms (prisniata adamantina), radiating from the surface of the dentine, on which their inner ends lie, to the surface of the crown, on wliich they terminate by free ends. These prisms are hexagonal in shape, solid, and of considerable length, for most of them reach from the dentine to the surface of the crown without interruption. The prisms, which are calcified themselves, are held together by the smallest jiossible amount of calcified matrix (Tomes), in old teeth the cap of enamel is 1024 THE DIGESTIVE SYSTEM. Pulp cavity often worn aAvay over the cusps, the dentine is then exposed, and is easily recognised by its yellowish colour, which contrasts strongly with the whiteness of the enamel. Whilst adjacent enamel prisms are in general parallel to one another, they do not usually take a straight, but rather a wavy course, and in alternate layers they are often inclined in opposite directions, thus giving rise to certain radial striations seen by reflected light (Schreger's lines). Certain other pigmented lines, more or less parallel to the surface, are also seen in the enamel (brown strise of Retzius). They are due to true pigmentation (Williams), and mark the lines of deposit of the enamel during its develop- ment. The enamel prisms are more or less tubular in certain animals — viz. in all marsupials except the wombat, in the hyrax, certain insectivora, and certain rodents. Nasmyth's membrane (enamel cuticle) is an extremely thin (^ij-Joo^ of an inch) cuticular layer which covers the enamel of recently-cut teeth, and is very indestructible, resisting almost all reagents. Two chief views are held as to its origin. One that it is the last formed layer of enamel, which has not yet been calcified, and therefore the final product of the enamel cells. The other that it is produced by the outer layer of cells of the enamel organ. This latter seems to be the more probable view. Dentine (substantia eburnea) is the hard and highly elastic substance, yellowish white in colour, which forms the greater part of the mass of every tooth (Fig. 726). Like the enamel it is highly calcified, but it differs from enamel in containing a very con- siderable amount of organic matter and water incorporated with its salts, which are chiefly phosphate and carbonate of lime. Fresh human dentine contains 10 per cent of water, 28 per cent of organic and 62 per cent of inorganic material. The organic matter is com- posed chiefly of collagen, and to a less extent of elastin. The organic matter consists of (1) calcium phosphate (with a trace of fluoride), (2) calcium carbonate, and (3) magnesium phosphate, the percentages present in dried dentine being 66-72, 3-36, 1-08 respectively. Dentine consists of a highly calcified organic matrix, which is itself practically structureless, although everywhere traversed by tubes — the dentinal tubes — which give to this tissue a finely striated appearance, the strise usually running in wavy lines. The dentinal tubes begin by open mouths on the wall of the pulp cavity, whence they run an undulating, and at the same time a some- what spiral course, towards the periphery of the dentine. They give off fine anastomosing branches, and occasionally divide into two. Somewhat reduced in size, they usually end in the outer part of the dentine. The tubules are generally described as being lined by special sheaths (dentinal sheaths of Neumann) which are composed of a most resistant material, and possibly are calcified. It should be mentioned that the presence of these sheaths as separate structures is doubted by some authorities, who hold that the part described as the sheath is only a modified portion of the dentinal matrix surrounding the tubules. The dentinal tubules are occupied by processes, prolonged from the outermost cells of the pulp — the odontoblasts. These processes are called after their discovcrei', Tomes' fibrils (dentinal fibrils), and they are probably sensory in function. The concentric lines of Schreger, frequently seen in the dentine, are due to bends in successive dentinal tubes taking place along regular lines parallel to the ijeriphery of the dentine. Other lines (the incremental lines of Salter), due to imi:)crfect calcification, are found arching across the substaiace of the dentine, c;liiefly in the crown. There must also Ije mentioned the interglobular spaces, intervals ](;ft in the dentine, as a result of imperfect calcification, bounded by the fully calcified surroiuiding dentine, the contour of which is in the form of a number of small projecting Bone Cement or crusta petrosa \ Alveolar periosteum or root-menibraiie Fifi. 726. — Vertical Section of Canine Tooth, to iUustrate its various parts, and its structure. DEVELOPMENT OF THE TEETH. 1025 globules of dentine. These interglobular spaces are very numerous in the outer or " granular layer" of tlie dentine, j^articularly beneath the cementum (see Fig. 726). The crusta petrosa or cementum (substantia ossea) is a layer of moditied bone which encases the whole of the tootli except its crown. Jt begins as a very thin stratum, slightly overlapping the enamel at the nock. From this it is continued, increasing in amount, towards the apex, which latter is formed entirely of this substance. It is relatively less in amount in the child, and increases during life. In places the dentine seems to pass imperceptibly into the crusta petrosa (the "granular layer" of dentine marking the jmiction of the two, see Fig. 726), and some of the dentinal tubes are continuous with the lacuntc of the cementum. Like true bone, it is laminated, it possesses lacuna?, canaliculi, and, when in large masses, it may even contain a few Haversian canals. The tooth pulp occupies the pulp cavity and the root canals of the teeth. It is composed of a number of branched connective tissue cells, the anastomosing processes of which form a fine connective tissue network, containing in its meshes a jelly-like material, in addition to numerous vessels and nerves, but no lymphatics. The most superficial of these cells form in the young tooth a continuous layer of columnar, epithelium-like cells, lying on the surface of the pulp against the dentine; they ai-e known as odontoblasts, for they are the active agents in the formation of dentine. From the outer ends of the odontoblasts processes ai'e continued into the dentinal tubes, where they have been already referred to as Tomes' fibrils. The vessels of the pulp are numerous, and form a capillary plexus immediately within the odontoblasts. The nerves form rich plexuses throughout the pulp, but their exact mode of ending is unknown. The alveolar periosteum (alveolo- dental periosteum or root-membrane) is a layer of coimective tissue free from elastic fibres, but well supplied both with blood-vessels and nerves, which fixes the root of the tooth in the alveolus, being firmly united by perforat- ing fibres of Sharpey, to the crusta petrosa on the one hand, and to the bone of the alveolus on the other. It establishes a communication between the bone of the jaw and the cementum, and above it is continuous with the tissue of the gum. Its blood comes chiefly from the arteries, which subsequently enter the apical canals for the supply of the pulp, but in part also from the vessels of the bone and those of the gum (hence the relief obtained in dental periostitis by lancing the gum). Development of the Teeth. At the beginning of this chapter a tooth was described as a calcified papilla of the mucous membrane, composed of two chief parts — ^ namely, the enamel formed by the epithelial layer, and the dentine by the connective tissue layer of the mucous membrane. The details of the process by which such a tooth is developed from the two layers of the mucous membrane are both numerous and intricate, and can be but briefly described here. In lower vertebrates (sharks, rays, etc.), teeth which correspond essentially, both in structure and development, to those of mammals, are found on the surface of the body, and are known as dermal teeth. The following outline of the development of the dermal tooth of a shark may assist in rendering the de- velopment of the human teeth more intelligible : — First, a papilla is formed from the corium or con- nective tissue layer of the skin (Fig. 727, li), which papilla is covered over by the epithelial layer. Next the superficial (connective tissue) cells of the papilla begin to form a layer of dentine on the surface of the papilla (Fig. 727, C), which it soon encases, the remains of the papilla persisting in tiie interior as the future pulp. At the same time the deepest cells of the epithelium deposit a layer of enamel, outside the dentine, over the summit of the papilla (Fig. 727, C), and subsequently the two — enamel and dentine — ^become inseparably united, thus giving rise to the substance of the tooth. At a later period the epithelium covering the summit disappears and the tooth comes to the surface ; this constitutes its eruption (Fig. 727, D). 69 A, Section of skin showing epithelium c, basement mem- brane b, and connec- tive tissue layer c. B shows the papilla of the connective tissue layer growing up coveretl by the epi- thelial layer. In C the superficial cells of the papilla z begin to deposit dentine d over the papilla, and at the same time the deepest cells of the epithelium deposit enamel (i. D shows the tooth breaking through the epithelium and reaching the surface. Fk;. 727. — DiAORAM to illustrate the Dkvki.oi'.mknt ok a Dermal Tooth IN THE Shark. In all tigures— a, enamel ; b, basement mem- brane ; c, connective tissue layer of skin ; (/, dentine ; c, epithelium ; and :, superficial cells of papilla. 1026 THE DIGESTIVE SYSTEM. I. Sliows the downgrowth of the dental lamina D.L from the surface epithelium E and the beginning of the enamel germ E.G. II. Shows the further growth of tlie enamel germ and its invagination. III. Tlie enamel germ is more invaginatey- — Foramen lacerum medium W/^^^T^ Cartilage of Eustachian tube A^ -Cavity of Eustachian tube wall is occupied by the nasal, oral, and laryngeal cavities, as well as by the base of the tongue ; and to the lateral boundaries of all these parts the sides of the tube are connected. In this way it comes to be at- tached from above downwards to the following- more or less fixed points : — (1) The Eustachian tube and internal pterygoid plate ; (2) the pterygo- maxillary liga- ment, the pos- terior end of the mylohyoid ridge on the inner as- pect of the lower jaw, and the mucous mem- brane of the mouth ; (3) the base of the tongue and the hyoid bone ; and (4) the thyroid and cricoid cartilages of the larynx. Above,it is firmly fixed by its apo- neurosis to the Fk;. 729. — The Anteriok Wall of the Pharynx with its Orifices, seen periosteum of the FROM BEHIND. basi-occlpltaland The .specimen frOni which tlie (Iniwiiig was made was obtained from a f'ormalin-hardeneil -i-jpfi.Qiio riortion body, by removing the posterior wall of the pharynx while leaving the anterior ^n ,■, ,^ ■, wall undisturbed. The following points should be noted : the greatest width of 01 the temporal the pharynx, above, at the lateral recesses ; the posterior nares, with the inferior boUCS ; and in turbinated bones seen through them ; the levator cushion ; and the pharyngeal o/J(l|j-JQp the portion of the tongue. , ' „ , , raphe oi the con- strictors is attached to the pharyngeal tubercle of the occipital bone. Below it becomes continuous with the oesophagus. Behind and at the sides, the pharynx is connected merely by loose areolar tissue to the surrounding parts. —Levator palati Inferior turbinated bone —Lateral recess of pharynx Levator cushion Superior constrictor muscle Glands in soft palate Uvula Palatopharyngeus Cireumvallate papillae Sulcus terminalis — ^Glossopharyngeal nerve Foramen Cfecum LymiJhoid follicle Middle constrictor muscle Epiglottis Pharyngo-epiglottic fold Lingual artery Hyoglossus muscle Hyoid bone Superior laryngeal artery Internal laryngeal nerve Aiyteno-epiglottic fold Sinus pyriformis Superior aperture of larynx Inferior constrictor muscle Top of cricoid cartilage THE PHAEYNX. 1031 The pharynx presents the following relations: — In front, as already descrilied, are the nasal cavities, the mouth, base of tongue, and larynx, all of which are seen on its anterior wall (Fig. 729). Beliincl, it is separated by loose areolar tissue (known as the retro-pliaryngeal space) from the prevertebral fascia and muscles, which inter- vene between it and the six upper cer^'ical vertebrse. At the sides are placed the carotid sheaths with their contents, whilst the styloid process with its muscles, and the glosso-pharyngeal nerve, running downwards and forwards, form lateral Middlfi tnrhinateil boiiR MiiVlle meatus of nose liilVriur iiwatus of iicsc Superior meatus of nose Sphenoitlal sinus Infenor turbinated bone Posterior edge of nasal septum Orifice of Eustachian tube Bursa pbaryngea Part of the pharyngeal tonsil Lateral recess of pharynx Levator cushion Salpingii- pharyngeal fold Glands in soft palate Anterior palatine arch Supratonsillar fossa ' Plica triangularis Tonsil Posterior jialatine arch Genioglossus Epiglottis Aryteno- epiglottie fold rricoiliaryngea). Another less develojied ridge, the salpingo-palatine fold (plica salpingo-palatina), passes from the anterior border of 1034 THE DIGESTIVE SYSTEM. the Eustachian orifice downwards and forwards to join the palate. In front of the latter lies an indistinct groove, the naso-pharyngeal groove, which indicates the separation of the nasal cavity from the naso-pharynx. .The levator palati muscle in descending runs parallel to the Eustachian tube, and along its lower border. As it enters the palate, it produces^ particularly when in a state of contraction, an elevation just below the Eustachian orifice, known as the levator cusMon (torus levatorius. Figs. 729 and 730), Avhich in its outer portion abuts against the lower part of the orifice, and forms its base when that opening assumes its usual triangular shape. Occasionally the Eustachian orifice is of an oval or slit-like form, Avith sloping edges, but the triangular shape described above is much more commonly found. Immediately behind each Eustachian orifice is seen the lateral recess of the pharynx (recessus pharyngeiis, fossa of Rosenmiiller), a nearly vertical, slit-like depression of considerable depth (Figs. 729 and 730), which runs outwards in the form of a flattened pouch or diverticulum. The lateral recesses project out over the uj)per margin of the superior constrictor, and beneath the petrous portion of the temiDoral bone, corresponding to the position of the sinus of Morgagni on each side. The recess is the remains of the inner or pharyngeal portion of the second visceral cleft, the lower part of which is represented in the supratonsillar fossa. Oral Pharynx (pars oralis). — This is the portion of the pharyngeal cavity which lies behind the mouth, and intervenes between the soft palate above and the superior aperture of the larynx below. Its anterior wall is occupied by the isthmus of the fauces, leading into the mouth ; and below this by the pharyngeal portion of the tongue, almost vertical in direction. Its lateral wall (Fig. 730) presents a triangular area (sinus tonsillaris), bounded in front by the anterior palatine arch, behind by the posterior palatine arch, and below by the sides of the tongue in its pharyngeal portion. This area is occupied in the greater part of its extent by the tonsil, above which is found a depression, the supratonsillar fossa (Fig. 730), which is of consider- able interest clinically. The posterior palatine arch (arcus pharyngo-palatinus, posterior pillar of Posterior thc fauccs) Is a prominent fold of palatine arch niucous membrane, containing the wuTmuf^^^ palato-pharyngeus muscle in its in- Tonsii terior, which springs above from the Anterior postcrior cdgc of the soft palate, and, palatine arch pg^ggjj^g dowuwards and shghtly back- wards, ends below on the side-wall of ■'""""' the pharynx (Fig. 730). The two posterior palatine arches form the lateral boundaries of the pharyngeal isthmus, which passage theycan modify both in size and shape by the con- traction of their contained muscles. The anterior palatine arch is de- scribed on i:)age 1000. The pharyngeal isthmus (isthmus Fig. 732.-OPEN Mouth showing Palate and Tonsils, pharyngo-nasalis) is the very oblique It also shows the two palatine arches, and the pharyngeal and SOmewhat triangular Orifice isthiuus throuKh which the naso-pharynx above coin- through which the Oral pharynx COm- municates witli the oral portion of the pharynx .^ • i i i below. municates with the naso-pharynx (Fig. 732). It differs considerably in size and shape in different individuals, being in some so small that the naso-pharynx can be explored from the mouth only with very great difficulty ; whilst in others it is of much larger dimensions (Fig. 731) and aff'ords ample space for the rhinoscopic examination of the naso-pharynx and the back part of the nasal cavities. Raphe of palate Uvula THE PHARYNX. 1035 In general it may be described as triangular in shape, the sides corre- sponding to the posterior palatine arches, and the base, which is behind, being formed by the posterior wall of the pharynx. The apex of the triangle is directed towards the soft palate, and is encroached upon, and overlapped from below by, the uvula, whicli assists in the closure of the orifice (Fig. 732). By the contraction of the palato-pharyngei muscles, which are enclosed within the palatine arches, the sides of the isthmus can be approximated, like two curtains, and its size correspondingly diminished. When, at the same time, the uvula and soft palate are elevated, and the whole pharynx in this region is narrowed by the contraction of the superior constrictor, tlie apertvu'e can be completely closed, and the oral separated from the nasal pharynx, as in the acts of swallowing and vomiting. Internal jugular vein Hypoglossal nerve Spinal accessory nerve Digastric muscle stylohyoid Glosso- pharyngeal nerve Parotid gland Teniporo- maxillary ^'''''~T~f^=^£ilffi: External carotid A — L J> •^'>Ty the oesophagus as well. Possibly this margin is so strongly developed and so prominent in order that it may bear the pressure of the liver off the gullet, whicdi otherwise might be interfered with in its dilatation during the passage of food. When the stomach is fully distended the abdominal part of tlie oesophagus almost disappears, being absorbed into the stomach in its distension. Variations. — The chief anomalies found in the oesophagus are : (1) Annular or tubular con- stri(;tions ; (2) diverticula, of which the most interesting — kno^vn as "pressure pouches" — are usually situated on the posterior wall close to its junction with the pharynx, and these some- times require surgical interference ; (3) doubling in jiart of its cour.se ; and (4) communications between the trachea and oesophagus. Structure of the CEsophagus (Fig. 738).— The a^sopliageal wall is composed of three proper coats — (1) muscular, (2) submucous, and (3) mucous. In addition, it is sur- rounded by an outer covering of areolar tissue (tunica advcntitia), by which it is loosely connected to the various structures related to it in its course. This loose covei'ing pei'mits of its free movement and of its increase in size, or of its diminution, during the act of swallowing. The muscular coat (tunica muscularis) is com- posed of two layers — an outer of longitudinal, and an inner of circular fibres. The longitudinal layer is liighly developed, and, unlike the condition usually found in the digestive tube, it is as stout as, or in places stouter than, the circular layer. Its fibres form along the greater length of the tube an even covering outside the circular layer, and below they are con- tinued into the longitudinal fibres of the stomach. Above, near the upper end of the oesophagus, the longitudinal fibres of each side, separating at the back, pass round towards the anterior aspect and form two longitudinal bands (Fig. 736), which run up on the front of the tube, and are attached by a tendinous band to the upper part of the back of the cricoid cartilage (Fig. 737). The circular muacular fibres, though not forming such a thick layer as the longitudinal fibres, are never- theless well developed. Below they are continued into both the circular and oblique fibres of the stomach. Above they pass into the lower fibres of the inferior constrictor of the pharynx. The muscular fibres are entirely of the striated variety at the upper end of the oesophagus. Soon uustripcd fibres begin to appear, increasing in number as we descend. In the lower lialf or two-thirds, only uustriped muscle is found. The longitudinal fibres for about tlic upper fifth of the tube arc entirely strij)ed ; in the second fifth striped and unstriped are mixed ; whilst in the lower throe-fifths unstripod fibres alone are present. The circular fibres are entirely striated for the first inch ; after this unstriped fibres appear ; and in the lower two-thirds, only unstriped muscle fibres are found (D. .1. Cofley). The longitudinal fibres arc often joined by slips of inistripcd muscle, or elastic fibres, which spring from various sources, including the left pleura (constant, Cunningham), the bronchi, back of trachea, pericardium, aorta, etc. These slips assist in fixing the ODSophagus to the surrounding structures in its passage through the thorax, and have been aptly compared to the tendrils of a climbing plant (Treitz). The submucous coat, composed of areolar tissue, is of very considerable thickness in 70 )li,uitil(liii;i libres divera;iiit riaclR-a Fii . 736. — Dissection to show the arrangement of the muscular tihres on tlie back of the ossophagus anil pliarvnx. Traced upwards, the lon- gitudinal uuiscular fibres of the oesophagus are seen to separate behind ; passing round to the sides, tliey form two longitudinal bands which meet in froiit above, and arc united to the cricoid cartilaLrc as sliown in the next figure. 1042 THE DIGESTIVE SYSTEM. Inferior constrictor Fit rcular fibres cesophagus 737. — The Lower Part of the Pharynx AND THE Upper Part of the (Esophagus have been slit up from behind, and the mucous membrane removed to show the muscular fibres. The two longitudinal bands are seen coming round to the front to be attached by a common tendon to the upper border of the cricoid car- tilage. See explanation of last figure. order to allow of the expansion of the tube during swallowing. It connects the mucous membrane loosely to the muscular coat, and admits of the former being thrown into folds when empty. In this coat are contained the numerous racemose mucous glands which open into the cavity of the oesophagus (Fig. 738). The mucous membrane is of a greyish pink colour, much paler than that of the pharynx, and of a firm and resistant texture. It is covered by a thick stratified, squamous epithelium, on the surface of which the open- ings of numerous glands are found. Below, its junction with the gastric mucous mem- cricoid cartuage brauo is indicated by a distinct, irregularly dentated or crenated line, which runs trans- Tendiuous band versely round the tube. In carefully preserved specimens the smooth mucous membrane of the oesophagus above this line contrasts strongly with the mammillated gastric mucous membrane below. Owing to the inelasticity of this coat, and the fact that it is but loosely connected to the muscular coat by the submucosa, it is thrown into a series of longitudinal folds when the oesophagus is empty and contracted ; hence the stellate lumen often seen in sections of the gullet. Glands. — Numerous racemose mucous glands, large enough to be distinctly seen with the naked eye, are found in the submucosa. They are pretty evenly distributed over the whole tube, and do not appear to be more numerous towards either end (Coffey). In addition to these, other glands, resembling closely those of the cardiac end of the stomach, are found in the mucous membi'ane of certain portions of the oesophagus. They are entirely confined to the mucosa, and do not extend beyond the muscularis mucosse. These glands are specially numerous at both the upper and lower ends of the tube (Coffey, Schafer). Vessels and Nerves. — Its arteries consist of numerous small brandies derived, in the neck, from the inferior thyroid, in the thorax, from the bronchial arteries and thoracic aorta, and in the abdomen, from the coronary artery of the stomach, and also from the left i^hrenic. The veins form a plexus on the exterior of the oesophagus, from which Ijranches pass, in the lower part of the tulje, to the coronary vein of the stomach, and, higher up, to the azygos, and thyroid veins. There is thus established on the lower part of the oesophagus a free communica- tion between the portal and systemic veins. The lymphatics pass to the inferior set of deej) cervical glands iii the neck, and to the joosterior mediastinal glands, many of wliich, of large size, are seen ai'ound the tube, in the thorax. Tliii nerves are derived from the recurrent laryngeal, and from the cervical symjjathetic in the ne(;k, IVom tlie pneumogastrics and sympathetic in the thorax. Development of the (Esophagus. The oesophagus is developed from the foregiit lying between the pharynx and the dilatation which represents the future stomach. At first, owing to the flexure of the head Submucosa ^\ltll mucous glands Circular muscular libies \r( olar coat Fio. 7o8. — Stim.'ctuiie of the O'^sophagOs, transverse section (after Horsley). THE ABDOMINAL CAVITY. 1043 on the trunk in the early embryo, it is relatively short, but, as the neck is developed, it gradually becomes elongated and more or less cylindrical. The superficial epithelial cells are ciliated and somewhat cylindrical between the fourth and eighth months of foetal life (Neumann) ; subsequently the adult condition is established. THE ABDOMINAL CAVITY. As the remaining parts of the digestive system he within the abdomen it will be necessary to describe that cavity as a whole, aud to refer briefly to its lining membrane — the peritoneum— before passing on to the consideration of the viscera which are contained within it. The abdomen is that portion of the cavity of the trunk which lies below the diaphragm. It is the largest of all the cavities of the body, and contains the greater part of the digestive, urinary, aud generative systems of organs, in addition to numerous vessels, nerves, and other structures. Shape. — -In general, the abdominal cavity is of a somewhat oval form, with the long axis directed vertically, and the wide end upwards. It is strongly flattened from before backwards, and is encroached upon in the middle line posteriorly by the projection forwards of the vertebral column, on each side of which it presents the appearance of a deep wide groove. Boundaries. — The cavity is limited above by the concave vault of the diaphragm, which is dome-shaped and divided into a right and a left cupola by an intervenino- depression. Into the right cupola fits the greater part of the liver ; in the left lie the stomach and spleen. On the upper surface of each cupola is placed the base of the corresponding lung, whilst between them, on the depression, rests the under surface of the heart. During expiration, the right cupola ascends almost to the level of the rio-ht nipple ; it is highest at a point about one inch internal to the nipple line, and here it reaches the upper border of the fifth rib, or even the middle of the fourth inter- costal space. On the left side it is one-half to one inch (12-25 mm.) lower, and in the middle line it crosses the inferior extremity of the gladiolus about the level of the sixth rib cartilage. Below, the cavity is limited by the pelvic floor, formed by the levatores ani, and coccygei muscles, covered on their upper surface ]jy the pelvic fascia. The anterior wall is formed by the aponeuroses of the three flat abdominal muscles, together with the two recti, which latter constitute powerful braces for the wall, on each side of the middle Kne. The lateral lualls are formed by the muscular portions of the obli(iui and transversales muscles, and below by the iliac bones with the iliacus muscles. Finally, the cavity is limited behind by the lumbar portion of the vertebral column with the psoas muscle on each side, and the quadratus lumboruni still further out. The iliac bones also enter into the formation of the lower portion of the posterior wall. The upper portion of the cavity lies under cover of the ribs, which alford con- siderable protection to this part of the abdomen, particularly at the sides and behind, in which latter position the cavity is further protected by the vertebral column. Anteriorly, on the other hand, the ribs are wanting below the sternum, and here, the abdominal wall is formed only of aponeuroses and muscles. But even at the sides and back there is a considerable zone, usually one to two inches wide (Cunningham), between the lower ribs above and the crest of the ilium below, which has no bony support except that afforded by the vertebral column. Whilst the circumference of the diaphragm is attached to the lower part of the thoracic framework in front and at the sides, and to the lumbar vertebra^ behind, the central portion of the dome, on the other hand, namely, the central tendon, is placed high up, under cover of the ribs, and in a more or less horizontal plane. As a result, the peripheral muscular part slopes almost vertically upwards from the circumference of the thoracic framework to the central tendon, and lies for a considerable distance in contact with the deep surface of the ribs ; thus the diaphragm comes to form, not only the roof of the cavitv, but it also enters into 70 a 10-i4 THE DIGESTIVE SYSTEM. the formation of the lateral, posterior, and, to a less extent, of the anterior walls ; and almost as much of the cavity of the abdomen as of the thorax lies under shelter of the ribs. Owing to the fact that the boundaries of the abdomen are formed chieflj of muscles, it follows that its walls are capable of contraction to a verj considerable extent, and the size of the cavity can consequently be altered in all directions. Its chief changes in form are due to the descent or elevation of the diaphragm, the contraction or relaxation of the anterior and lateral walls, and the raising or lowering of the pelvic floor. Within the muscles forming its walls, the abdomen is lined by an envelope of Diaphragm. Attachment of falciform ligament' Right lobe of liver- Gall-bladder V- Transverse colon l,fl?!^!!!^ Small intestine Ascending colon Anterior superior spine ~W^^ Caecum —^ Outline of liver Great omentum (cut) Transverse mesocolon with jejunum beneath it Tfenia of transverse colon External oblique muscle Internal oblique Position of umbilicus Part of iliac colon (sigmoid flexure) Small intestine SCALE IN INCHES SCALE IN CENTIMETRES Fig. 7-39. — The Abdominal Viscera in situ, as seen when the abdomen is Laid open and the great omentum removed (drawn to scale from a photograph of a male body aged 56, hardened by formalin injections). The ribs on the right side are indicated by Roman numerals ; it will be observed tliat the eighth costal cartilage articulated with the sternum on both sides. The subcostal, intertubercular, and right and left Poupart lines are drawn in black, and the mesial plane is indicated by a dotted line. The intercostal muscles and part of the diaphragm have been removed, to show the liver and stomach extending up beneath the ribs. The stomach is moiierately distended, and the intestines are particularly regular in their arrangement. fascia, which separate the muscles from the extraperitoneal connective tissue and peritoneum. This aponeurotic layer is distinguished in different localities as : — (1) the transversalis fascia on the anterior and lateral walls, lining the deep surface of the transversalis muscle and continuous above with the fascia clothing the under surface of the diaphragm ; (2) the iliac fascia on the posterior wall, covering the psoas and iliacus muscles ; (3) the anterior layer of the lumbar SUBDIVISION OF THE ABDOMINAL CAVITY. 1045 aponeurosis, also ou the posterior wall covering the front of the quadratus lumborum ; and (4) the pelvic fascia, lining the pelvis. Apertures. — Certain apertures are found in the walls of the abdomen, some of which lead to a weakening of the parietes. These are : the three openings in the diaphragm for the passage of the inferior vena cava, the cesopliagus, and the aorta respectively ; the apertures in the pelvic floor, through which the rectum, the urethra, and the vagina in the female, reach the surface ; the inguinal canal, through which the spermatic cord (or round ligament) passes, in leaving the abdominal cavity ; and lastly, the crural canal, a small passage which runs down from the abdomen along the inner side of the femoral vessels. The two latter con- stitute on each side weak points in the abdominal wall, through which a piece of intestine occasionally makes its way, giving rise to inguinal or femoral hernia respectively. Extraperitoneal or Subperitoneal Connective Tissue (tela subserosa). — Between the fascia which covers the deep surfaces of the abdominal muscles, and the peri- toneum which lines the cavity, there is found a considerable quantity of connective tissue, generally more or less loaded with fat, which is known as the extraperitoneal or subperitoneal connective tissue. This is part of an extensive fascial system which lines the whole of the body cavity, outside its various serous sacs, and is continued on the several vessels, nerves, and other structures which pass from these cavities into the limbs and neck. In the abdomen it is divisible into a parietal and a visceral portion, both com- posed of loose connective tissue. The former lines the cavity, whilst the latter passes forwards between the mesenteries and other peritoneal folds to the viscera. These two portions of the extraperitoneal tissue are perfectly continuous with one another, and contain in their whole extent avascular plexus, through which a com- munication is established between the vessels of the abdominal wall, on the one hand, and those of the contained viscera on the other. The parietal portion is thin and comparatively free from fat over the roof and anterior wall of the abdomen, and here the peritoneum is more firmly attached than where the tissue is fatty and large in amount. In the pelvis, on the other hand, the tissue is loose and fatty, and, as such, it is continued up for some inches on the anterior abdominal wall above the pubes, to permit of the ascent of the bladder during its distension, and the attendant stripping of the peritoneum oft' this portion of the anterior abdominal wall. Here also the urachus and the obliterated hypogastric arteries will be found passing up in its substance. On the posterior wall the tissue is large in amount and fatty, particularly where it surrounds the great vessels and kidneys. From this latter portion especially the visceral expansions are derived in the form of prolongations around the various branches of the aorta. These expansions are connected with the areolar coats of the blood-vessels and are conducted by them into the mesenteries and other folds of the peritoneum, and thus reach the viscera. The chief uses of this tissue are : (1) to unite the layers of the abdominal wall together ; (2) to connect the viscera to these walls and to one another in such a loose manner that their distension or relaxation may not be interfered with, which would not be the case if the connecting medium were firm or rigid ; (3) in addition, it is a storehouse of fat, forms sheaths for the vessels and nerves, and establishes, through its vascular plexus, communication between the parietal vessels and those distributed to the abdominal viscera. Subdivision of the Abdominal Cavity. The abdomen is divided naturally by the pelvic brim into two parts, the abdomen proper, and the cavity of the pelvis. The former of these is further sub- divided, artijiciaUy, into nine regions. The pelvic brim (Figs. 166 and 167, p. 221), which separates the two natural divisions of the cavity, is formed behind by the base of the sacrum, at the sides by the iliopectineal lines of the innominate bones, and in front by the pubic crests and 70?) 1046 THE DIGESTIVE SYSTEM. the symphysis pubis. In the erect position it usually makes an angle of about 55 to 60 degrees with the horizontal. The two portions of the abdominal cavity which the brim separates meet at an angle, the abdomen proper running almost SCALE IN INCHES SCALE IN CENTIMETRES Pi,; 740. — The Front of the Body, showing the subdivisions of the abdominal cavity and the position of the cliief viscera. (From a photograph of the body represented in the preceding figure. ) The viscera iu Fig. 739 have been traced in red on this figure. The photographs for these two figures and for Fig. 744 were talcen from tlie same body, under precisely similar conditions ; consequently the relations of the deeper parts to the surface are correctly obtained by superimposing the pictures as in this illustration. The liver occupies a slightly lower position than usual. vertically upwards from it, whilst the pelvic cavity slopes backwards and shghtly downwards. The pelvic cavity i« bounded in front and at the sides by the portions of the in- nominate bones below the level of the iliopectineal line. These bony walls are partly clothed, in front and laterally, by the obturator internus muscles, and internal to these by the parietal portion of the'^ pelvic fascia, as low down as the white line. The posterior THE ABDOMINAL CAVITY. 1047 wall is formed by the front of the sacrum, covered on each side by the pyriformis muscle. This wall (as represented by the pyriformis muscles) meets the lateral wall at the anterior border of the <.;reat sciatic foramen ; through this foramen the pyrifoi*mis passes out, thus closing up what would otherwise be a large aperture in the pai'ietes of the cavity. The floor is composed of the two pairs of muscles which form the pelvic diaphragm, namely, the levatores ani and coccygei — covered by the visceral layer of the pelvic fascia. These muscles pass on each side, from the lateral wall of the pelvis, down- wards and inwards towards the middle line, and present a concave upper surface towards the pelvic cavity. Subdivision of the Abdomen Proper. — Owing to the large size of the cavity, and in order to localise more correctly the position of the various organs contained within it, the abdomen proper is artilicially subdivided by two liorizontal and two vertical lines (Fig. 7-40) drawn on its anterior wall. From these lines imaginary planes are supposed to be continued backwards, wliich divide up the cavity into nine regions. Of the two horizontal lines, one is drawn around the trunk at the level of the lower border of the tenth costal cartilage ; this is known as the subcostal line, and the imaginary plane corresponding to it, as the subcostal plane. The second horizontal line is drawn at the level of the highest point of each iliac crest, visible from the front ; this point corresponds to the tubercle seen on the outer lip of the crest, about two inches behind the anterior superior spine, and can be easily located ; the line and plane are consequently known as the intertubercular line and plane respectively. The vertical lines are drawn, one on each side, perpendicularly upwards from a point on Poupart's ligament midway between the anterior superior spine and the symphysis pubis. These lines and the corresponding planes are known as the Poupart lines and planes respectively. By the two horizontal lines the abdomen is divided into tliree zones, an upper or costal, a middle or umbilical, and a lower or hypogastric zone. By the two perpendicular lines each of these is subdivided into three parts, a central and two lateral. Thus, in the upper zone, we get a hypochondriac region or hypochondrium on each side, and an epigastric region or epigastrium in the centre. Siuiilarly,, the umbilical zone is divided into right and left lumbar regions, with an umbilical region between. And the hypogastric zone has a hypogastric region or hypogastrium iu the centre, with right and left iliac regions at the sides. In addition, the portion of the abdominal wall above the pubis is known as the suprapiibic region, and that immediately above Poupart's ligaments, as the inguinal region. The three central divisions, namely, the epigastric, umbilical, and hypogastric regions, can conveniently be further subdivided by the mesial plane, passing through the middle of the body, into right and left halves. The upper horizontal, or su1)costal, plane passes behind, through the upper part of the third lumbar vertebra, or the disc between the .second and third lumbar vertebne. The intertubercular l)lane cuts through tlie nuddle or upper i)art of the fifth lumbar vertebra. The lower margin of the tenth costal cartilage frecpiently corresponds to the most dependent part of the thoracic framework. Often, however, the eleventh costal cartilage descends 4 to h inch lower. Nevertheless, the tenth cartilage is selected in drawing the subcostal plane, for two chief reasons, namely, it is visil,)le from the front as a rule, and it is comparatively fixed, whilst the eleventh, being a floating ril), is mucli more movable, is varial>le in lengtli, and more difficidt to locate. Contents of the Abdomen. — Tiie following structures are found within the abdominal cavity : — 1. The greater part of the alimentary canal, viz. stomach, small intestine, and large intestine. 2. Diijestive cilands : the liver and jiancreas. 3. Ductless (jlands: the spleen and the two suprarenal bodies. 4. Urinary a2^parati(s: the kidneys, lu'eters, bladder, and part of urethra. 5. The internal (jeneratire ortjans according to the sex. 6. Blood and lymph vessels, and lymphatic ylands. 1. The abdominal portion of tlie cerebro-spinal and sympathetic nervous systems. 8. Certain /ft'/((7 remains. 9. The 2)entoneum — the serous membrane which lines the cavity, and is reflected over most of its contained viscera. 70 (^ 1048 THE DIGESTIVE SYSTEM. THE PEEITONEUM. The arrangement of the peritoneum is so complicated, and its relations to the abdominal contents so intricate and detailed, that it will be expedient to postpone its complete description until the various organs, with their special peritoneal relations, have been separately considered. Nevertheless, it will be necessary to give here a general account of the disposition of the membrane, and to refer to the three varieties of folds which it forms in passing from organ to organ, or from these to the abdominal wall. The peritoneum (tunica serosa) is the serous sac which lines the abdominal cavity and invests most of the abdominal viscera, to a greater or less degree. Like the pleurffi, the tunica vaginalis of the testicle, and other serous sacs, its walls are composed of a thin layer of fibrous tissue, containing numerous elastic fibres, and covered over on the side turned towards the cavity of the sac by flattened endothelial cells. Like them, too, the peritoneum in the male is a completely closed bag, but in the female this is not the case, for the abdominal end of each Fallopian tube opens into the sac, whilst the other end of that tube communicates with the interior of the uterus, and thus, indirectly, with the exterior. Normally the membrane secretes only sufficient moisture to lubricate its surface, otherwise the sac is perfectly empty, and its opposing walls lie in contact, thus practically obhterating its cavity. The use of these lubricated and highly polished serous linings, found in the abdomen and certain other cavities, is to facilitate the movements of the contained viscera during any changes in size or form which they or their containing cavity may undergo. As a result of this arrangement, notwithstanding the tonic pressure of the abdominal wall on its contents, the stomach and intestines are free to move with the greatest ease and the least degree of friction, when any change takes place either in the organs themselves or in their surroundings. The peritoneum is a thin glistening membrane, which may aptly be compared to a coat of varnish applied to the inner aspect of the abdominal walls, and to the surface of the contained viscera, except where these are directly applied to the walls or to one another. It forms throughout its entire extent a continuous and distinct sheet, but it is united so intimately to the viscera, and follows the irregularities of their walls so closely, that it appears at first sight to be a superficial Small sac Foramen of Winslow, with arrow passed through it Rectum Pouch of Douglas 741.— Diagrammatic Mesial Section of Female Body, to .show the peritoneum on vertical tracing. The great sac of the peritoneum is black and is represented as being much larger than iu nature ; the small sac is very darkly layer of thcSC walls, rather than w."l^/l\ vf"""""" °" ''""^TJ' '^iT ^/ ^ ''^"*! a separate membrane. Outside line ; and a white arrow is passed through the foramen of , , •'^ . , . , Winslow from the great into the small sac. the pcntoneum lies the extra- peritoneal connective tissue — al- ready described — which connects it more or less intimately to the fascial lining of the abdominal walls and to the aljdominal viscera. If we trace the peritoneum as a continuous layer, beginning in front, we find THE PEEITONEUM. 1049 Falciform ligament Foramen of Winslow .StoHiacl Round ligament of liver Lesser omentum (cut) Portal vein that it lines the deep surface of the anterior abdominal wall, and is continued upwards to the under surface of the diaphragm (Fig. 741), the greater portion of which it covers. From the posterior part of the diaphragm it is reflected or carried forwards on to the upper surface of the Kver, and then down over the stomach, intestines, and other abdominal viscera — clothing them all — to the pelvis. In like manner, when traced laterally from the anterior wall, the membrane will be found to line the sides of the cavity, and passing back- wards to clothe the posterior abdominal wall, and the viscera lying upon it (Fig. 742, B). It should be pointed out that all the abdominal viscera are either directly fixed by con- nective tissue to the posterior abdominal- wall, or suspended by blood-vessels from it. In the former case the X)eritoneum is re - fleeted directly from the wall on to the viscera ; in the latter it runs along the blood-vessels to reach the viscera, which it clothes, and then returns to the wall on the opposite sides of the vessels, which it thus encloses in a fold. Whilst the main sac of the peritoneum lies in front of the abdominal various viscera, covering them over and dip- ping down between them, it should be mentioned that there is a special diverti- culum derived from this "great sac," which turns in behind the stomach, and covers its posterior surface ; this is known as the lesser or smaller sac, and it will be described in detail later on. The aperture through which one sac communicates with the other is termed the foramen of JVinslow. In passing from organ to organ, or from these to the abdominal wall, the peritoneum forms numerous folds, whicli are divided according to their connexions into three classes : — (a) Omenta are folds of peritoneum which pass from the stomach to other abdominal organs. They are three in number, namely : (1) The great or gastro- colic omentum, which hangs down like an apron from the great curvature of the stomach, and passes to the transverse colon, connecting this latter, very loosely. Asceiuiing colon Descending colon Fig. 742. — Diagrammatk' Tra.nsveusic Sections ok Abdomen, to show the peritoneum on transverse tracing. A, at level of foramen of W'inslow ; B, lower clown. In A note, one of the vasa brevia arteries jiassing to the stomach hetween the layers of the gastro-splenic omentum, and also the foramen of Winslow leading into the lesser sac which lies liehiud the stomach. 1050 THE DIGESTIVE SYSTEM. however, to the stomach Fuiidu: Superior or parietal surface the lesser or g astro -hepatic omentum, which extends from the lesser curvature of the stomach to the Kver ; and (3) the f^as^ro-s2?/emcome%^W7/i, which passes from the stomach to the spleen. (h) Mesenteries are folds of peri- toneum which unite portions of the intestine to the posterior abdominal wall, and convey to them their vessels and nerves. There are several mesenteries, e.g., the mesen- tery proper, which connects the jejunum and ileum to the posterior abdominal wall, the transverse meso- colon, the pelvic (or " sigmoid ") mesocolon, and occasionally others. (c) Ligaments are peritoneal folds which pass between abdominal viscera other than portions of the digestive tube, or connect them to the abdominal wall. As examples of these may be mentioned most of the ligaments of the liver, the so- called " false ligaments " of the 1 ladder, and the broad ligaments I the uterus. This term is also applied to several ■) lall folds which connect portions of 1 e intestinal tube to the parietes, but 1 ) not convey to them their vessels id nerves. The gastro -phrenic and phreno-colic ligaments are examples of these. THE STOMACH. The stomach (ventriculus) is the large dilatation found on the diges- tive tube immediately after it enters the abdomen (Figs. 743 and 744). It constitutes a receptacle in which the food accumulates after its pass- age through the oesophagus, and in it take place some of the earlier processes of digestion, resulting in the conversion of the food into. a viscid soup-like mixture, known as chyme. The chyme as it is formed is allowed to escape intermittently through the pylorus, into the small intestine, where the digestive pro- cesses are continued. Although the form of thestomach varies considerably under different conditions, in general it is of an irregularly pyriform shape, with a wide or cardiac end directed back- wards and to the left, and a narrow the duodenum. In addition to (a) its two ends, the stomach presents for examination the following parts : (&) tivo Antrum pylori Great omentum (cut) Cardia Gastro-pliremc lisament Gastro-siilenic omentum (cut) \^ Uncovered area i Superior oi parietal surface Inferior oi visceral surface Lesser omentum (cut) — Pylorus, Superior or parietal surface Great omentum (cut) Inferior or visceral surface Fi(!. 74-3. — Moderately Distended Stomach, viewed, A, from front ; B, from inner or right side ; and C, from the outer or left side. (Prom jDhotograi^hs of the stomach shown in Figs. 739 and 744. The contents of tlie stomach were carefully removed through an artificial opening, and replaced with gelatine, the stomach remain- ing in situ throughout the operation. After the jelly hardened, its exact orientation was carefully noted, and pins indicating the vertical, horizontal, and transverse planes having been inserted, the organ was removed and photographed. ) pyloric end which runs to the right to join THE STOMACH. 1051 curvatures, greater and lesser, separating (c) tv:o surfaces, superior and interior ; and {d) two orifices, the cesophageal orifice or cardia, and the pyloric orifice or pylorus (Fig. 743). Position and Form of the Stomach. — When empty, or nearly so, the stomach lies in the left hypochondrium and left part of the epigastrium, with its wide end or fundus directed backwards towards tlie diaphragm, its long axis lying almost in a horizontal plane, and its pyloric portion running to the right to join the duodenum. In this state the whole organ is narrow and attenuated, particularly the pyloric portion, which is contracted, and resembles a piece of tliick-walled small intestine. When distended, tlie organ assumes the form of an irregular pear, and both stomach AttacliMient of falciform liKaiuent' Spleen (anterior angle) Transverse mesocolon, with slouiacli resting on it Hepatic flexun Apex of vermifori append' Terminal part of ileuii CiBCum I'elvic colon (sigmoid flexure) Fn;. 744. — The AnDuMiNAi. Visckha akteu tiik IIemoval hf thk JE.U'XUiM and Ileum 'Jroiu a pliotograph of the same body as Fig. 739). The transver.se colou is much more reguhir than usual. Both the liver and ca'cum extend lower down than normal. The subdivisions of the abdominal cavity are indicated by dark lines. the cardiac and pyloric portions become full and rounded (Fig. 7-43). It still lies within the hypochondriac and epigastric regions; but in extreme distension, or in exceptional cases, it may pass down below the subcostal plane and reach into the umbilical and left luml)ar regions. As a result of the general increase in length which takes place during distension, the pylorus is moved a variable distance to the right beneath the quadrate lobe of the liver, and at the same time the long axis of the whole organ becomes much more oblique, running forwards, downwards, and to the right. Finally there is developed a special dilatation of the pyloric portion, known as the antrum pi/lori, which in extreme distension is carried so far to the right that it may even reach into the hypochondrium. In brief, it may be said that tlie stomach when empty is contracted, not collapsed ; that it assumes a narrow, attenuated shape, its cavity being practically obliterated, and its pyloric portion contracted to the size of small intestine ; and in 1052 THE DIGESTIVE SYSTEM. addition, that its long axis lies in an almost horizontal plane. With distension there comes a general enlargement of the various diameters, an elongation of the whole organ, with a consequent passage of its pyloric portion to the right beneath the liver, the development of the antrum pylori, and an inclination of its axis from behind downwards and forwards, without any rotation. Natural Form of the Stomach. — As seen in male bodies the viscera of whicli have been hardened by the intravascular injection of formalin, the empty stomach, as already stated, presents an attenuated or slender pear-shaped appearance, and is sharply bent on itself, particularly at the junction of the cardiac and pyloric portions. As a rule it is somewhat flattened from above do-^Tawards in its cardiac portion, but preserves in its whole length, more or less, an irregularly rounded or cylindrical form. Its long axis is directed, in the cardiac portion, from behind forwards and to the right with a slight inclination downwards ; then it bends almost at a right angle, and in the pyloric portion runs to the right towards the pylorus. Even in the empty condition, the cardiac portion retains, as a rule, an apjjearance of rotundity, and never assumes a comjaletely collapsed and flattened, form ; although it sometimes is very much contracted, and approaches the tubular form of the pyloric portion. The collapsed, flat-walled, and flaccid bag, often pictured as the empty stomach, does not rejjresent its true condition during life, but is rather the result of post-mortem softening, re- laxation, and pressure. The stomach, like the bladder, and like other hollow viscera with muscular walls, is not an inert bag, but an extensile living organ capable of expansion and contraction, which adapts the size of its cavity to the amount of its contents. When food enters, it expands, the expansion being proportionate to the amount of food that enters ; and when the food passes away or is absorbed, it contracts, until its cavity is reduced to little more than a stellate lumen. In the gradual passage of the stomach from the empty to the distended condition we may recognise three stages. First stage. — This commences with an enlargement of the fundus, and is followed by an expansion of the whole cardiac portion, which passes upwards and also to the left towards the diaphragm, displacing the coils of the transverse colon, which lie here when the stomach is empty. The j)yloric portion for 3 or 4 inches still remains contracted and cylindrical. In this condition the stomach is frequently found after death. Second stage. — As distension goes on the lesser curvature opens out, the pyloric portion (with the exception of its last inch) exjiands, but its junction with the cardiac portion usually remains distinct, until disten- sion is almost complete. Tliircl stage. — A further general expansion of the whole stomach takes place ; the diameters of both cardiac and pyloric portions, as well as the length of the organ, are increased ; and the great curvature presses forwards against the anterior abdominal wall in front, where the restraining influence of the ribs is absent. The pyloric end for about 1 inch (2-5 cm.) from the pylorus remains narrow (constituting the pyloric canal of Jonnesco), but to the left of this it Ijulges forward, forming the antrum pylori, which is most distinct at the great curvature. By the increase of the organ in length the antrum is carried a considerable distance to the right beneath the liver — even further than the pylorus itself — so that the terminal part of the stomach is bent backwards and to the left, in order to reach the pylorus, which latter very rarely passes more than one and a half or two inches to the right of its normal position, namely, in the empty condition, within half-an-inch (12 mm.) of the middle line. Finally, as it fills, the stomach becomes gradually more oblique, so that in the distended state the long axis of the posterior two-thirds of the organ is directed forwards, downwards, and to the right, and forms an angle of about 40" to 45" with both the horizontal and sagittal planes (Fig. 743), whilst its anterior third is stiU more oblique. There is, however (as pointed out by Jonnesco), no distinct rotation of the organ on its long axis — no turning of the great curvature more forwards, nor of the so-called anterior surface more upwards. In the change from the distended to the empty state these stages are reversed ; the whole stomach is contracted, or drawn in, from all directions towards the lesser curvature ; this latter is bent upon itself to an acute angle, and the long axis of the organ, becoming less oblique, approaches the horizontal. Although this description of the shape and direction of the stomach is at variance with the generally accepted accounts, it is based ui:>on the examination of a considerable number of specially -hardened bodies, and has been found to apply so generally, that it is advanced here as the condition most frequently found in the male immediately after death, and as, in all probability, giving a near approximation to the conditions present during life. It must, however, be admitted that, in the female, as a result of tight lacing, the stomach is often found to assume an abnormal vertical position ; but this condition is associated with displacement of other abdominal organs in the neighbourhood, and cannot be looked upon as normal. [In the present edition it has been thought right to leave the above description of the stomach as it was originally written by Professor Birmingham. Subsequent investigation has served to show the accuracy of his views in so far as the various stomach forms which he describes are con- cerned, and the shape whicli he ascribes to the empty condition of the organ, and which he was the first to describe lias been proved beyond dispute to be frequently met with in properly prepared subjects. The question, however, whicli is being at present discussed is whether this stomach-form, in which the cardiac part forms a more or less capacious sac, and the pyloric part is tubular and thick-walled, is not rather to be associated Math a jDarticular stage in the digestive act. From investigations on the cat by means of Ecintgen rays, Cannon has shown that during THE STOMACH. 1053 digestion the stomach becomes divided into a cardiac saccular reservoir in which no peristaltic movement can be detected, and a long tubular pyloric portion along which successive constriction waves are seen to be constantly ^^assing. In the latter the food is triturated and mixed with the gastric juices, and \vheu fully prepared it is squirted at irregular intervals througli the pyloric orifice into the duodenum. — Ed.] Size and Capacity of the Stomach. — Probably no organ in the body varies more in size witliiu the limits of health than the stomach. Moreovei", as its tissues change so rapidly after death, measurements made on softened and relaxed organs are not only worthless but quite misleading. Consequently it is difficult, perhaps impossible, to arrive at a correct estimate of its size and capacity. The lenr/th of the stomach in the fully distended condition is about 10 to 11 inches (25 to 27'5 cm.), and its greatest diameter not more than 4 to 4^ inches (10 to 11-2 cm.) ; whilst its capacity in the average state rarely exceeds 40 ounces, or 1 quart. The length has been estimated by different authorities at from 10 to 13.V inches (26 to 34 cm.) ; its diameter, from Z\ to 6 inches (8 to 15 cm.) ; and its caj^acity from \\ to 5 pints. The measurements of the cajaacity given by Dr. Sidney Martin are probably tlie most acciu-ate : he states tluit the capacity varies between 9 and 59 oz., with an average of from 35 to 40, or a little over a litre. The distance in a direct line from the cardiac to the pyloric orifice varies from 3 to 5 inches (7*5 to 12 "5 cm.), and that from the cardia to the summit of the fundus from 2i to 4 inches (6-2 to 10-0 cm.). As regards the weight, I have found the average of twelve wet sjjecimens freed from their omenta to be 4| oz. (135 grms.), with a maximum of 7 oz. (198'45 gi-ms.) and a minimum of 3 J oz. (99 '22 grms.). Glen denning gives the weiglit as Ah ounces. Relations and Connexions of the Stomach. — The relations will be much more readily uuderstood if we briefly consider the disposition of the portion of the abdominal cavity in which the stomach lies, a portion which has such con- stant and definite surroundings that it perhaps merits the title of "stomach chamber." Thi^ stomach chamber (Figs. 745 and 746) is a space in the upper and left portion of the abdominal cavity which is completely occupied by the stomacli when that organ is distended, but into which the transverse colon also passes, doublingup over the stomach, when tliis latter is empty. The chamber jjresents an arched I'oof, an ii'regularh^ sloping floor, and an anterior wall. The roof is formed partly l^y the visceral surface of the left lobe of the liver, and in the rest of its extent by the left cupola of the diajjhragm, which arches gradually downwards behind and on the left to meet the floor. The^oor or '■'■stomach bed " (Fig. 745) is a sloping shelf on which the under surface of the stomach rests, and by wliich it is supported. The bed is formed lu-liind by the top of the left kidney (with Its suprarenal capsule) and the gastric surface of tlie spleen ; in front of this, by the wide upper surface of the panireas ; and more anteriorly still, by the transvei-se mesocofon riuining forwards above the small intestine, from the anterior edge of the pancreas to the colon (Fig. 745), which latter completes the floor anteriorly. Finally, the anterior wall of the stomach chamber is formed liy the al)dominal wall, between the ril)S on the left and the liver on tlie right side. This chamber is completely filled by tlie stomach, when that organ is distended. When, on the otlier hand, the stomach is empty and contracted, it still rests on the floor, or stomach bed, but occupies only the lower portion of the chamber, whilst the rest of the space is tilled by the transverse colon, which turns gradually uinvards as the stomach retracts, and finally comes to lie both above and in front of that organ and innuediately beneath the diajdiragm — a' f;ict to be remembered in clinical examinations of this region. Left cupola of diapliragiu Gall-bladder Liver Fig. 745. — The Stomach Chamber Duodeniini \NU STO.MACH Bed. From the same bodj' as the preceding figure, after the stomach had been removed. 1054 THE DIGESTIVE SYSTEM. The upper (or parietal) surface of tlie stomach is more convex and more extensive than the lower. It lies, when the organ is distended, in contact with the roof and anterior wall of the stomach chamber, and thus comes into relation with the under surface of the left lobe of the liver on the right, the vault of the diaphragm on the left, and the anterior abdominal wall in front (Fig. 739). When the stomach is Fossa for Spigelian lobe Right phrenic vessel^ Vena cava Hepatic vein Hepatic artery \ Portal vein Pylorus (Esophagus Right supraienal body Coronary artery Diaphragm Left suprarenal body Splenic aiteiy / Kidney // Upper surface of pancreas Gastric surface of spleen Spermatic vein Ureter Right common iliac ■vein Right cummon iliac artery Left common iliac vein Under surface of pancreas Attachment of transverse mesocolon Duodeno- jejunal flexure Gastro-duodenal artery and neck of pancreas Superior mesen- teric artery "duodenum Ureter Colon Fig. 746.— The Viscera and Vessel'5 o^ ihe Fo'sTeriou Abdominal Wall. The stomach, liver, and most of the intestines have been removed. The peritoneum has been preserved on the right kidney, and also the fossa for the Spigelian lobe. In taking out the liver, the vena cava was leit behind. The stomach bed is well shown. (From a body hardened by chromic acid injections. ) empty, on the other hand, the transverse colon, as just explained, doubles up over it, and separates this surface from the roof of the chamber. The lower (or visceral) surface, more flattened than the upper, rests upon the stomach Ijed, and comes into relation with the following parts : — Behind, at the fundus, with the diaphragm and gastric surface of the spleen ; in front of this with THE STOMACH. IO55 the left kidney, the suprarenal, and the upper surface of the pancreas, and, more anteriorly still, with the transverse mesocolon and colon. From all of these the stomach is separated by the small sac of the peritoneum (the anterior layer of which clothes this surface), except below and to the left of the cardia, where the peritoneum is absent, over an irregularly triangular area (Fig. 743), and here the stomach lies in direct contact with the diaphragm (sometimes also with the top of the left kidney and suprarenal capsule). It should be pointed out that the under surface of the stomach is separated from the diiodeno-jejuual fk'xure and the Ijeginning of the jejumim by the transverse mesocolon only. By cutting tlii'ough this, the surgeon is enabled to Ijring the stomach and duodenum together in the operation of gastro-intestinal anastomosis. The cardiac end or fundus (fundus ventriculi) is, in the distended condition, a large rounded cul-de-sac, which projects Ijackwards and upwards ao-ainst the left cupola of the diaphragm ; opposite the (esophageal orifice it passes into the body of the stomach. Its surfaces are merely prolongations of the upper and lower surfaces of the organ, and accordingly its relations are similar. Thus the uj^per surface lies against the left cupola of tin- diaphragm (and occa.sionally the left lol)e of the liver, when this extends further than usual to the side) ; whilst the lower surface rests chiefly on the gastric surface ot the sjileen, and also on the left kidney. The highest part of the fundus reaches to the level of a point on the chest wall about halt'-au- incli (12 mm.) internal to the apex point of the heart. The narrow or pyloric end, when the stomach is empty, is contracted and cylindrical, and runs transversely to the right, lying as a rule beneath the left lobe of the liver. During distension it is carried to the right beneath the quadrate lobe, and its terminal part is there directed backwards in order to reach the duodenum. Even in this condition its last inch remains comparatively undistended. The lesser curvature (curvatura ventriculi minor) is directed towards the liver, and corresponds to the line along which the lesser omentum is attached to the stomach, Ijetween the pyloric and oesophageal orifices (Fig. 743). It is connected to the liver by the lesser omentum, between the layers of which the gastric and pyloric vessels run along the curvature. This curvature, when the stomach is empty, presents a sharp bend at the junction of the cardiac and pyloric ])ortions, but when fully distended it forms an open curve except near its jiyloric end, where it becomes convex, corresponding to the S-shaped form of this portion of the organ (see below). On viewing a distended stomach fi'om the right side (Fig. 743, B), it will be observed that the line of the lesser ciu'vature turns slightly on to the ui)2)er aspect in order to reach the cardia, which is situated rather on the upper surface than on the border of the stomach. The great curvature (curvatura ventricuH major), which is usually over three times as long as the lesser curvature, corresponds to a line drawn from the cardia over the summit of the fundus (Fig. 743), and then along the line of attachment of the great omentum as far as the pylorus. In general, it is directed to the left and forwards, but at its beginning, near the cardia, it of course looks in the opposite direction. The great curvature corresponds in the greater part of its length to the attachment of tlie great omentum ; and in close relation to it, but between tlie layers of the omentum, run the right and left gastro-epiploic vessels. Antrum Pylori.— This is a iiromincnce of the great curvature in the distended stomach, situated a short distance from the pylorus. When the stomach is distended, the pyloric portion, near its right extremity, becomes curved somewhat like tlie letter S placed horizontally. The first curve of the S is convex downwards and forwards, and this liecoming more prominent with distension, forms a projection of the great curvatui-e known as the antrum pylori. The terminal jjart of the ^' extends to the pylorus ; it is about one inch (2-5 cm.) in length, and it api)ears never to become distended to any noticeable extent. This latter is the part described by Jonnesco as the iwloric canal. The terms cardiac and pyloric portions are often employed to indicate the wider and narrower portions of the stomach respectively. The cardiac portion includes aliout two-thirds of the length of the whole oi'gan ; the pyloric ])ortion the remaining third. Except in complete dis- tension, the junction of the two is usually indicated by a slight constriction, and occasionally thei-e is a thickening of the muscular fibres (apparently those of the oblique layer), corresponding in i)art to the constriction. The oesophageal orifice or cardia is the aperture at which the gullet opens into the 1056 THE DIGESTIVE SYSTEM. stomach. It is situated at the upper end of the lesser curvature, to the right of the fundus, and nearer the upper than the lower surface of the stomach (Fig. 743, B). The cardia is very deeply placed, and lies about four inches behind the sternal end of the seventh left costal cartilage, at a point one inch from its junction with the sternum. Posteriorly it corresponds to the level of the eleventh dorsal vertebra. Owing to tlie fixation of tlie cesopliagus by its passage tlirougli tlie diaphragm, and the close connexion between tbe stomacli and tlie diaphragm, near the cardia where the peritoneum is absent, this is the most fixed part of the whole organ. The object of this immobility is evidently to maintain a clear passage for the food entering the stomach. The orifice is oval rather than round, with its long axis very oblique ; and although the presence of a A^alvular arrangement at the cardia has been advocated by several authorities, it is difficult to find satis- factory proof of its existence in hardened bodies. It seems more probable, on the whole, that no such arrangement naturally exists here. On the other hand, the muscular margins of the oesophageal opening in the diaphragm, and the circular fibres of the lower end of the oesophagus, which are j)articularly well developed, aftord, by their simultaneous contraction, an effective means of closing the oesophagus immediately above the cardia, and thus of preventing regurgita- tion of the contents of the stomach. The pyloric orifice or pylorus is the aperture through which the stomach com- municates with the duodenum. It is marked on the surface by a slight constriction, most evident at the curvatures ; and in the interior by a prominent thickening of the wall — the pyloric valve (valvula pylori) — produced by a special development of Pi'loric sphincter I.iiii'.'itiifliinl inusruKi ci at Circular muscle fibres of the rtuodenuni I Brunner s ^landb Longitudinal musculai coat (duodenum) Mucous membrane of the duodenum Duodenum Pyloric canal Longitudinal muscular coat Mucous coat Submucous coat Fig. 747. Pyloric sphincter I ] Pyloric orifice , Briinner's glands -LOKIilTUDINAL SECTION THROUGH THE PYLORIC CaNAL AND COJIMENCEMENT OF THE Duodenum in a New-born Child. (From Stiles.) the circular muscular fibres, known as the pyloric sphincter (musculus sphmcter pylori). When examined post-mortem in the ordinary way, the aperture, viewed from the duodenal side, is somewhat oval in form, and closely resembles the external OS uteri (Cunningham). When seen from the opposite side, it presents an irregular or stellate appearance, owing to the fact that the rugee of the gastric mucous memljrane are continued up to the orifice. The pylorus rests on the neck of the pancreas below and behind, and is over- lapped by the liver above and in front. Its average position can be marked on the surface of the body by the intersection of two lines; one drawn horizontally half- way between the top of the sternum and the pubic crest (Addison), the other drawn vertically a little way (i inch, 12 mm.) to the right of the middle line. During the earlier stages of gastric digestion the sphincter pylori is strongly contracted and the aperture firmly closed, but it opens intermittently to allow of the passage of properly digested portions of the food. As digestion advances the sphincter probably relaxes somewhat ; but in hardened bodies a really patent pylorus is rarely or never found, which would seem to THE STOMACH. 1057 Liver (enlarged) Tentli rib Gall- bladder Transverse colon Ascending colon Falciform ligament (cut) Pyloric end of stomach Subcostal line SCALE IN INCHES SCALE IN CENTIMETRES Fli. 48. -Abdomex of Female, SHOwixr; Displacements RESULTING FROM TiGHT LaCING. indicate that the pylonis is normally closed, or nearly so, and that its opening is an active rather than a passive condition, as in the case of the anal canal. As regards its size, the pylorus is stated to be about | inch (12-.5 mm.) in diameter, but there is no doubt that this represents neither its full size nor the calibre of the valve when at rc^st. Foreign bodies with a diameter of | to 1 inch have been known to pass through the pylorus without giving rise to trouble, even in children. On the other hand, when at rest, with an empty stomach and duodenum, the aperture, as seen in formalin-hardened Ijodies, is practically closed, and pre- sents a stellate or purse-mouth appear- ance, viewed from either aspect. In hardened bodies with distended stomach and duodenum, the aperture, which is somewhat oval, is practically closed, and from the duodenal side resembles, as Cunningham has shown, the external OS uteri. But both in the empty and the distended condition of the stomach position of the pylorus seems to be rather a tubular umbilicus narrowing, extending over at least h to 1 inch of the canal, than a sudden con- striction. When the stomach is empty the pylorus is usually placed near (i.e. within h inch, 12 mm. of) the middle line, beneath the left or sometimes the quadrate lobe of the liver, and at the level of the first lumbar vertebra, or the disc between this and the second lumbar. During distension it is j^ushed over beneath the cpiadrate lobe for a variable distance, but very rarely more than li or 2 inches to the right of the middle line ; and its orifice, instead of looking towards the right, is then The directed backwards, for, as already ex- plained, the antrum in distension is carried to the right in front of the pylorus, or even beyond it. Peritoneal Relations. — The stomach is almost completely covered by peritoneum — the anterior surface being clothed by the posterior layer of the great sac, and the posterior surface by the anterior layer of the small sac. From the lesser curvature the lesser omentum extends to the liver, whilst from the great curvature the great omentum passes down to the transverse colon. Higher up still, on the left, the continuation of the great omentum, namely, the gastro-splenic omentum, passes off (from the inferior svirface, a little below the great curvature) to the spleen. Finally, a small peri- toneal fold, known as the gastro-phrenic ligament, is found running from the stomach up to the diaphragm along the left side of the oesophagus. A small, irregnlarly triangular, area (Fig. 744), about 2 inches wide and 1.^ inches from above downwards, during moderate distension of the stomach, on the inferior surface below and to the left of the cardia, is uncovered by peritoneum, and over it the organ is in direct contact with the dia]iliragm, occasionally also with the top of the left kidney and suprarenal. From the left angle of this " uncovered area " the attachment of the great omentum (gastro-splenic part) starts ; ami at the right angle the coronary artery passes on to the stomach. In the child at birth the stomach is scarcely as large as a small hcu-cgcr, and its eapacit}' is about one ounce (28-3 granuncs). In shape it corresponds pretty closely to that of the adult, and the fundus is well developed. In the female (l''ig. 748), as a result of tight lacing, the stoniacli is often displaced in position and distorted in shape, so that instead of running obliquely forwards, down- wards, and to the riojit, it is placed nearly vertically along the left side of the vertebral column, in which direction it has a very considerable length. Its lower part bends rather suddenly, and runs upwards and to the right to join the pylorus, which is often placed quite superficiallv below the liver. As a i-esult of the displacement, tlic left extreniitv of the 71 ' liver is much enlarged, and extends on the left side to the ribs, where it was folded back on itself for over an inch. The pyloric end of the stomach and the beginning of the duodenum are quite superficial below the liver, and all the viscera are displaced downwards. (From a photo- graph of a body hardened bj' injections of formalin.) 1058 THE DIGESTIVE SYSTEM. pancreas is pushed downwards from the horizontal until it almost assiunes a vertical position. The narrowing and inversion of the lower margin of the thoracic framework at the same time constricts the stomach about its middle, and often leads to a bilocular condition. Hour-glass or Bilocular Stomach. — This is a condition of the organ, by no means rare, in wliicli the stomach is more or less completely sejjarated into two divisions — a cardiac and a ijyloric — the normal arrangement in certain rodents and other animals. As a rule the former division is the larger, but occasionally the two are nearly equal, or the pyloric portion may exceed the cardiac in size. Sometimes the condition is temi^orary, and the result of a vigorous contraction of the circular muscular fibres at the seat of constriction. In other cases it is per- manent, and may be due to cicatricial contraction after gastric ulcer, or to some other pathological condition. The condition is more frequent in the female than the male, and is rarely found in the foetus or child. Gland mouths Stkuctuee of the Stomach. The stomach wall is composed of four coats — namely, from without inwards : (1 ) peritoneal, (2) muscular, (3) submucous, and (4) mucous (Fig. 749). Peritoneal or Serous Coat (tunica serosa).^ — This coat is formed of the peritoneum, the relations of which to the stomach have already been described. It is closely attached to the subjacent muscular coat, except near the curvatures, where the con- nexion is more lax ; and it confers on the stomach its smooth and glistening appearance. Muscular Coat. — The muscular coat, which is composed of unstriped muscle, is thinnest in the fundus and body, much thicker in the pyloric portion, and very highly developed at the pylorus. It is made up of three incomplete layers — an external of longitudinal, a middle of circular, and an internal of oblique muscular fibres. The external layer (stratum longitudinale) con- sists of longitudinal fibres, continuous with those of the oesophagus, on the one hand, and those of the duodenum on the other (Fig. 750, A). They are most easily demonstrated on the lesser curvature, where they can be traced down from the right side of the oesophagus. Over the great curvature and on the two surfaces they are present as an extremely thin and irregular sheet. Towards the pylorus the longitudinal fibres grow much thicker, and also much tougher and more closely united, but they do not take any part in the foi-mation of the pyloric valve. A specially-condensed Ijand of these can be often made out both on the front and back at the antrum pylori, the form of which is said to be due to their presence. These bands are known as tlie pyloric ligaments (ligamenta pylori). The middle layer (stratum circiilare) is composed mainly of circular fibres, continuous with the more superficial of the circular fibres at the lower end of the oesophagus (Fig. 750, B). They do not commence as a series of circular bundles surroiinding the fundus, as usually described. On the contrary, they begin as a set of U-shaped bundles which loop over the lesser curvature at the right of the cardia, and pass downwards and to the left on both surfaces. Further to the right these looped fibres are succeeded by circles wliich surround the organ completely. Traced towards the narrow end of the stomach, the circular bundles grow thicker, and at the pylorus they undergo a further increase, giving rise to the pyloric sphincter which surrounds the orifice as a thick muscular ring. On the gastric side the pyloric sphincter passes gradually into the thick circular fibres of the pyloric portion of the stomach. On the opposite side it ceases abruptly, onl}' its outer part being continued into the circular fibres of the duodenum (Fig. 751). The internal layer (fibr^c obliqme) is composed of fibres which are arranged on tlie fundus and adjacent parts of the stomach, in much the same manner as those of the middle layer are on the body and pyloric portion of the organ (Fig. 750, C). Continuous above with the deeper circular fibres of the lower end of the cesopliagus, they begin as Oblique iiiusculai' fibres Circular muscular fibres Longitudinal muscular fibres Peritoneum Fig. 749. — Section THuorGH Wall (jf Stomach, Cardiac Portion (slightly modified from Stcilir). STEUCTUEE OF THE STOMACH. 1059 U-shaped bundles which loop over the stomach immediately to the left of the cardia, and run very obliquely downwards and to the right for a considerable distance on both surfaces of the organ. These looped fibres, as we pass to the left, gradually become less oblique, and finally form circles which surround the wide end of the stomach completely, even as far as the summit of the fundus. The oblique fibres can be most readily shown by removing the circular fibres on either surface below the cardia. When traced towards the right, they will be found to terminate by turning down and join ing the Hbres of the circular layer. Submucous Coat (tela submucosa). — The submucous coat is a laj^er of sti'ong but loose connective tissue, which lies between, and unites the muscular and mucous coats (Fig. 7-i9). It is more loosely attached to the former and more closely to the latter coat, and it forms a bed in which the vessels and nerves break up befoi'e entering the nuicous membrane. Mucous Coat (tunica mucosa). — If examined in the fresh state soon after death, the mucous coat is of a reddish-gray colour and of moderate consistence. When examined some time after death, the colour turns to a darker gray, and tlie whole membrane becomes softer and more pulpy. It is thicker (over 2 mm.) and firmer in the pyloric than in the cardiac portion, and is thinnest at the fundus, where it often shows signs of post- mortem digestion. When the stomach is empty all three outer coats, which ai'e extensile, contract ; whilst the inextensile mucous coat, as a result of its want of elasticity, is thrown into numerous prominent folds or ruga', which project into the interior and, as it were, occupy the cavity of tlie contracted organ. These are, in general, longitudinal in direction, with numerous cross branches, and they are largest and most numerous along the great curvature. They dis- appear when the stomach is distended. When the surface of the mucous coat is examined in a fresh stomach, it is seen to be marked out into a number of small, slightly elevated, polygonal ai'eas (arete gastricrc) by numerous linear depressions ; the mucous membrane is consecpiently said to be mammilldti'd (Fig. 752, A). These little areas, which measure from 1 to 6 mm. in diameter, are beset with numerous small pits (foveolio gastricio, about "2 nun. wide), which arc the mouths of the gastric glands, and they ai'e so closely placed that the amount of surface separating them is reduced (particularly in the pyloric portion, where the gland mouths arc widest) to a series of elevated ridges (plictv villoscc) resembling villi on section. Although the gland mouths cannot be seen with tiie naked eye, a very slight magnification is sufficient to show them clearly ; it is also })ossible to see the gland tubes leading off from the bottom of each (Fig. 7~)2, B). Fic. 750. — Thk Thuke Layers ok thk Mrsi.ri.AH Coat ok I'HE Stomach. A, Outer or lougitmliual layer ; B, MiiUlle or circular layer ; C, Internal or oblique layer, a, Longi- tudinal fibres of asophagus ; A, Superticial circular fibres of cesophagus passing into circular fibres of stomach in B ; c, Deep circular fibres of (vsopliagus passing into oblique fibres of stomach in C ; d, Oblique fibres forming rings at the fundus ; e, Submucosa. 1060 THE DIGESTIVE SYSTEM. , PVLORUS . P Blood-vessels. — The arteries of tlie stomach are all derived ultimately from the ca3liac axis. The coronary arises from this trunk direct. Having reached the lesser curvature and given off an oesoj)hageal branch, it divides into two large branches, which run, one on each side, along this curvature, and join below with two similarly disposed arteries derived from the lyyloric branch of the hej^atic. From the two arches thus formed, four or five large branches j^ass to each surface of the stomach, aiid soon pierce the muscular coat. Along the great curvature several smaller branches reach the stomach from the rigid and left gastro-epifloic arteries, which are branches respectively of the gastro- duodenal and the sjalenic, and run in the great omentum close to its attachment to the stomach. Finally, four or five vasa hrevia, branches of the splenic, are distributed to the fundus of the stomach, Fig. 751. — Diagram to show which they reach by j)assing forwards between the layers of the Formation of Pylorus. gastro-sj)lenic omentum. At first the arteries lie beneath the peri- P, Peritoneum ; L, Lougi- toneum ; very soon, howeA^er, they pierce the muscular coat, which tudinal layer of muscular they supply, and reaching the submucosa, break uj) to form a close fibres ; C, Circular layer ; network of vessels. From these arise numerous small branches, M, Mucous membrane ; V, -yyliich enter the mucous membrane and form capillary plexuses Villi. It wUl be seen that around the glands as far as the surface. the pyloric narrowmg is due ^he veins begin in the capillary plexuses around the glands ; practically entirely to a •,• ,i p ° , i • ii i j- i ■ 9 • Gradual thickenin/ of the ^^^^iting, they form a network m the submucosa, from which arise circular muscular fibres branches that jDierce the muscular coat, and finally end in the which stops abruptly at the following veins : the right gastro-epiploic, which joins the superior pyloric orifice. mesenteric ; the left gastro-einploic, and four or five veins corre- sponding to the vasa hrevia arteries, which join the splenic ; the coronary or gastric vein, which runs along the lesser curvature towards the cardia, receives an oesophageal branch, and then turns down and runs beside the coronary artery to join the portal trunk ; and the pyloric vein, corresj^onding to the same named artery, which also joins the portal. These veins contain numerous valves, which, though comj)etent to prevent the return of blood in the child, are rarely so in the adult. ru The lymphatics arise in the mucous membrane around the gastric glands ; they then join a jilexus of valved vessels in the sub- mucosa, from which the chief trunks Mammilte: pass with the blood-vessels to the curvatures, being joined on the way by the efferent vessels of a subperi- toneal lymphatic plexus. They are connected watli the sujjerior gastric glands along the lesser curvatures, tlie inferior gastric glands along the great curvature, and the sjxLenic glands, which they reach with the m t-i f vasa brevia. Finally, the eft'erent gastric glands, vessels of all these join the coeliac witii gland tubes at bottom Depression between two mammilla^ Mouth of :'astric gland ^%'^'V^^'^^H^ m%^ The nerves are derived from the two pneumogastrics and from the solar 2)lexus of the symjaathetic. The pneumogastric nerves pass down through the diaphragm with the ccsoi^hagus, tlie left lying on its front, the right on its back ; in this way they reach the upper and lower surfaces of the stomach resiDectively. yig. Here they unite with the sympathetic fibres from the cccliac plexus (an off- shoot of the solar jdexus), which jiass to the stomach with the branches of the coeliac axis. The nerve fibres, which are chiefly non-medullated, form two gangliated plexuses, those of Auerbach and Meissner, in the muscular and submucous coats resjiectively. The develoi)iuent of the stomach is described with that of the intestines on p. 1105. 752. — The Mucous Membrane of Stomach. A, Natural size ; B, Maguified 25 diameters. In A the rugte and the mammillated surface are shown. In B the gland mouths (foveolse gastricne), with the gland tubes leading off from some of them, and the ridges separating the mouths (plica; villosse) are seen. INTESTINES. As the coats of the remaining portions of the digestive tube agree in many particulars, it will be convenient to describe the general structure of the intestines STEUCTUEE OF THE IXTESTIXES. 1061 here. Subsequently, any peculiarities ol structure in particular regions will be described with the corresponding division of the tube. Structure of the Intestines. The wall of the intestines, like that of the stomach, is made up of four coats, which are named from without inwards — serous or peritoneal, muscular, submucous, and mucous (Figs. 753 and 754). 1. Serous Coat (tunica serosa). — This is formed of peritoneum, and confers ou the intestines their smooth and glossy appearance. It varies in the extent to which it clothes the different divisions of the tube, giving the duodenum, the ascending, descending, and Two iiiesenteric lymphatic glaiu Mesentery glands ^^, Lynijihatic Peutoneal coii Circular muscular fibres Lon''itudinal muscular fibres Fig. 753. — A Poktiox of S.mall I:ntestine, with Mesentery and Vessels. The peritoneal coat has been renioveil from the right half, and the two layers of the muscular coat exposeil. iliac colons, and the rectum only a partial covering; whilst it clothes the jejunum and ileum, the cfccum, the transverse and the pelvic colons completely. The detailed arrangement of this coat will be given with the description of each division of the intestinal tube. '2. Muscular Coat (tunica muscularis). — This consists of unstriped muscle arranged in two layers — an outer, in which the fibres run longitudinally, and an inner, in which they are circularly disposed. The muscular coat is thicker in the duodenum than in any other part of the small intestine, and it gradually diminishes in thickness until the end of the ileum is reached. On the other hand, in the large intestine, it is thickest in the rectum and thinner towards the beginning of the colon. The longitudinal layer (stratum longitudinale) of this coat is much thinner than the underlying circular layer. In the small intestines it forms a complete sheet, continuous all round the gut (Fig. 753), but thickest at its free margin ; whilst in the large intestine it is divided up into three longitudinal bands (Fig. 762), known as the tcenice coli, which will be more fully described in connexion with the colon. The circular layer (stratum circulare), much thicker than the longitudinal layer, is composed of bundles of muscular fibres arranu'ed circularly round the tube (Fig. 753), and forming in all parts a continuous sheet. Unlike the longitudinal fibres, those of the circular layer take part in the formation of the pyloric and ileo-c;ccal valves. 3. Submucous Coat (tela submucosa). —This is a loose but strong layer of areolar tissue connecting the muscular and mucous coats, on which chiefly depends the strength of the intestinal wall. In addition to forming a bed in which the vessels break up before entering the mucous coat, it contains the glands of Brunner in the duodenum (Fig. 754), and in both small and large intestine the bases of the solitary glands lie in it (Fig. 754). 4. Mucous Coat (tunica mucosa). — The mucous membrane constitutes the inner coat of the intestine, on which its digestive functions depend. It is everywhere composed (Fig. 754) of the following parts: — (1) A layer of striated, columnar, epithelial cells resting on (2) a basement membrane. Outside this lies (3) a layer of retiform tissue, containing a considerable number of scattered lymphoid cells. This layer is limited towards the submucosa by (4) an extremely thin sheet of unstriped muscle, the 71a 1062 THE DIGESTIVE SYSTEM. LIE8ERKUHNS GLA Submucosa Circular muscular fibres Longitudinal muscular fibres Peritoiieum Lieberkiiliii's gland ■r,r:t DUODENUM X 12 Villi Liebei-kiihn'i gland Muscularis mucosae Brunner's glands Circular muscular fibres Longitudinal muscular fibres able Peritoneum muscularis mucosa, -uliich is not visible to tlie naked eye. The mucous membrane is verv vascular, particularly in the small intestine. It is thicker in the duodenum than in the jejunum, and thicker in this latter than in the ileum. Throughout both the small and large intestines the sub- stance of the mucous membi'ane is closely beset with innumer- small (micro- scopic) tubular glands, known as the glands or follicles of Lieberkiilin (giand- uke intestinales). In shape they are minute straight tubes — like diminutive test-tubes — with their mouths opening on the sur- face, their closed ends lying in the deeper part of the mucous coat, and their cavities lined by columnar epithelium. They open on the surface between the villi of the small intestine, and are present also on the valvulfe conniventes. In the large gut their orifices are found all over the surface of the mucous membrane. Submucosa — :=]5rt=®=^=; Circular muscular fibrt- > Longitudinal muscular fibres Fig. 754.- Blood-vessels forming net- work in sub- mucosa Blood-vessel SMALL INTESTINE X 20 -Diagram to show tlie structure of the small and large iutestine aud the duodenum. Certain special developments of the mucous coat, found in particular regions of the intestinal tube, must next be considered : these are the (1) villi ; (2) valvulse conniventes ; (3) solitary glands ; and (4) agminated glands, or Peyer's patches. Villi (villi intestinales). — If the mucous membrane of any part of the small intestine be examined, it is seen to present a soft, velvety, or fleecy appearance (Fig. 755, B); this is due to the presence of an enormous number of minute pro- cesses, knoAATi as villi, which cover its surface. Villi are minute cylindrical or finger-like projections of the mucous membrane (Fig. 754), about -gV^h or ^ih of an inch (1-2 to 1-6 mm.) in height, and barely visible to the naked eye, which are closely set all over the surface of the mucous membrane of the small intestine. Beginning at the edge of the pyloric valve, they are said to be broader but shorter in the duodenum, and to grow narrower as they are followed down through the intestine to the ileo-csecal valve, at the edge of which they cease. They are found, not only on the general surface of the mucous membrane, but also upon the valvules conniventes, and, while they are not present over the solitary glands, they are found in the intervals between the individual nodules of the Peyer's patches. They are connected with the absorption of the products of digestion which takes place in the small intestine. Valvulse Conniventes (plicas circulares). — When the intestine is empty and contracted, its mucous membrane may in places be thrown into effaceable folds or rugce, which disappear on distension. But in addition to these, there are found in certain portions of the small intestine a series of large, permanent folds, which are not effaceable ; these are known as valvulte conniventes (Fig. 755). They are usually more or less crescentic in shape, and resemble a series of closely-placed shelves running transversely around the gut. They rarely form more than two- thirds of a circle ; sometimes, however, they present a circular or even a spiral arrangement, the spiral extending little more than once round the tube, as a rule. STEUCTUEE OF THE INTESTINES. 1063 Occasionally they bifurcate at one or both ends ; sometimes, too, short irregularly directed branches pass off from them. They are usually about 2 to 3 inches (5 to 7 '5 cm.) in length, and their breadth, that is their pro- jection into the cavity, may be as much as ird of an inch (8 mm.), whilst in thick- ness, as seen when cut across, they measure about -^th inch (3 mm.). They are com- posed of two layers of mucous mem- brane, placed back to back, with a little submucosa between, to bind the two together, and are covered with villi and Lie berk iihn's fflands. Their Fig. 755. — Yalvul.e Connivextes (uatural size). A, as seen in a bit of jejunum which has been filled with alcohol and hardened B, a portion of fresh intestine spread out under water. use is to increase the amount of surface available for secretion and absorption. Valvular conniventes are not found in the upper part of the duodenum. They begin at a distance varying from 1 to 2 inches (2-5 to 5 cm.) from the pylorus. At first they are small, irregular, and scattered ; but they grow gradually larger as we pass down, and when the opening of the bile-duct is reached (4 inches from the pylorus) they have become distinct and prominent. In the rest of the duodenum, and in the upper half of the jejunum, they are highly developed, being large, broad, and closely set. In the lower half of the jejunum they become gradually smaller and fewer. Passing down into the ileum, they become still smaller and more irregular, and, as a rule, they practically cease a little below the middle of the ileum. The mucous membrane covering the folds possesses villi, solitary glands, and Lieberkiihn's glands, like the mucous membrane of the general surface between the valves. Ofttai jiatclies of valvuL-ie comiiventcs, miicli reduced in size, can be traced to within a short distance of the ileo-cascal valve. According to Sappey, Luschka, and others, they usually reach to ■\vitliin two or three feet of tlie end of tlie iUaim. Solitary G-lands (noduli lymphatici solitarii). — These are minute nodules of lym- phoid tissue, opaque and of a whitish colour, found projecting on the surface of the mucous membrane throughout the whole length of both the small and large intestines. Isolated lymphoid cells are found in abundance scattered through the connec- tive tissue layer of the intestinal mucous membrane generally ; in places these cells are gathered together to form little nodules, siipported by a iramework of reti- form tissue, and surrounded by a lymphatic space which communicates below with the lymphatics of the submucosa. Such a collection of lymphoid cells constitutes a solitary gland. They are usually of a rounded or oval shape (Fig. 754), the wide end resting in the submucosa, the nodule itself piercing the muscularis mucosae, and the narrow end projecting slightly above tlie surface of the mucous membrane. In size they vary from -jfVth to j^th of an inch ("6 to 3"0 mm.), but their average bulk is about that of a small grain of sago, to which they bear some resemblance. As already mentioned, they are present throughout the small and large intestines, being particularly abundant in the vermiform appendix and caecum. In 71 ?> 1064 THE DIGESTIVE SYSTEM. Two solitaiT glands the small intestine they are found on the valvulse conniventes, as well as upon the general surface of the mucous membrane between them. Payer's Patches, or Agminated Glands (noduli lymphatici aggregati, tonsillse Peyers patch iiitestinales). — A Peyer's patch consists of a large number of lymphoid nodules grouped closely together so as to form a slightly elevated area, usually of an oblong form, on the surface of the mucous membrane (Fig. 756). In length they vary from half an inch (12 mm.) or less to three or four inches (100 mm.), and in width they commonly measure from a third to half an inch (8 to 12 mm.). Their number is variable, but in the average condition about 30 or 40 are found. They are best marked in young subjects, where they form considerable elevations above the general surface, and may be as many as 45 in number. After middle life they atrophy, and in old age, although usually to be found, they are indistinct, occasionally being marked by little more than a dark discoloration of the mucous membrane. They are invariably situated along the free surface of the intestine opposite the line of mesen- teric attachment, with their long axis corresponding to that of the bowel. Consequently, in order to display them, the tube must be slit up along its attached or mesenteric border. Peyer's patches are entirely confined to the small intestine, being largest and most numerous in the ileum, solitary gland Intermediate fonn particukrly in its lowcr part, whcrc they usually Fig. 756.— Peter's Patch and ^.ssume an oblong shape ; in the lower half of the Solitary Glands, from intestine jejunum they are small, circular, and few in number ; °Jj^^^'^ *^^° ^^^'^^ °^'^ (natural in its upper part they are rare ; and, although their presence has been noted in the lower portion of the duodenum, they may be said to be as a general rule absent from this division of the intestine. Near the lower Ijorder are seen a few small patches made up of two or three lymphatic nodules ; they are marked "intermediate form." Tlie valvulse conniventes stop at tlie margins of Peyer's patches, and are not continued across them ; but villi are found on the surface of the patches, in the intervals between the lymphoid nodules. The chief bowel lesion in tyj^hoid fever is found in Peyer's j)atches and the solitary glands. When the surface of a Peyer's patch from a child's intestine (in which these structures are particularly well develoj^ed) is carefully examined, it is seen to be made up, not of a series of separate, rounded nodules grouped together, but rather of a niunber of wavy, irregular, and branching ridges connected with one another by cross branches (Fig. 756), the whole recalling in miniature the appearance of a raised map of a very mountainous district in which the chief chains run irregular courses, and are joined to one another by connecting ridges. Small patches, intermediate in form between solitary glands and Peyer's patches, and consist- ing of two or three lymphoid nodules, are also usually present. THE SMALL INTESTINE. The small intestine is the portion of the digestive tube which is placed between the stomach and the beginning of the large intestine. It commences at the pylorus, where it is continuous with the stomach, and ends at the ileo-csecal valve by joining the large intestine. It occupies the greater j)ortion of the abdominal cavity below the hver and stomach (Fig. 740), and is found in the umbilical, hypogastric, and both lumbar regions ; also, but to a less extent, in the other regions of the abdomen, and in the pelvic cavity. In length, the small intestine usually measures over 20 feet. According to Treves, it is 22|- ft. in the male, 23 in the female, whilst Jonnesco gives the average length at 24 ft. 7 ins., or 7i metres. In form it is cylindrical, with a diameter varying from nearly two inches (47 mm.) in the duodenum to a little over an inch (27 mm.) at the end of the ileum ; there is thus a gradual diminution in its size from the pylorus to the ileo-csecal valve. • STRUCTUEE OF THE IXTESTINES. 1065 This portion of the digestive tube is divided more or less arbitrarily into three parts (Fig. 705) — namely, the duodenum, constituting the tirst eleven inches, dis- tinctly marked off from the rest by its fixation and the absence of a mesentery ; the jejunum, whicli comprises the upper two-tifths, and the ileum, the lower three-fifths of the remainder. The two latter parts pass imperceptibly into one another, and the line of division drawn l)etween them is entirely artificial ; however, if typical parts of the two — namely, the beginning of the jejunum and the end of the ileum — be selected, they differ so much in size and in the appearance presented by their lining mucous membrane, that they can be distinguished from one another without difficulty. Both the jejunum and ileum are irregularly disposed in the form of crowded loops or coils (Fig. 739) which are connected to the posterior abdominal wall by a great fan- shaped fold of peritoneum, containing their vessels and nerves, and known as the mesentery. This is of such a length that the coils are able to move about freely in the abdominal cavity, and consequently the position occupied by any portion of the tube, with the exception of the beginning of the jejunum and the ending of the ileum, can never be stated with certainty. Nevertheless, it may be said that, in general, the jejunum occupies tbe upper and left portions of the cavity below the stomach, the ileum the lower and right divisions, its terminal part almost always lying in the pelvis, just before it joins the large gut. The. small intestine is relatively longer in the cliild tlian in tlie adult ; at birth it is to the total height of the child as 7 to 1, whilst iii'the adult the proportion is as 4 to 1. Notwithstanding Treves' results, it is generally held that the small gut is relatively longer in the male than the female. It should perhaps be added that in formalin-hardened liodies the small bowel rarely measures more than 12 or 13 feet in length. Similarly its diameter is often reduced in places to i or | inch (12-5 to 18-7 mm.), although the greater part of the gut may retain its usual width : these narrow parts have apparently been fixed in a state of contraction. THE DUODENUM. The duodenum, the portion of the digestive tube which immediately succeeds the stomach, is the first part of the small intestine, and differs from the rest of that tube in having no mesentery, and also in l)eing closely fixed to the posterior al)dominal wall — conditions which are evidently associated with its relation to the bile and pancreatic ducts, both of which open into its cavity. Shape and Divisions. — The duodenum begins at the pylorus, about the level of the first lumbar vertebra, and ends, after a somewhat C-shaped course, at the left side of the first or second lumbar vertebra (Fig. 757). It is generally described as being made up of three parts, namely : — (1) The first or superior portion, which begins at the pylorus, passes backwards and to the right beneatli the liver, and ends at the neck of the gall-bladder, by turning down and joining (2) the second or descending portion. This begins at the neck of the gall-bladder, runs down behind the transverse colon (Fig. 758), and ends opposite the thml or fourth lumbar vertebra by turning to the left, and passing into (3) the third or inferior portion. This at first runs more or less transversely to the left, across the vena cava, and tben ascends, in front of the aorta, as far as the under surface of tlie pancreas, where, at the level (^f the first or second lumbar vertebra, it bends abruptly forwards, forming the duodeno-jejunal flexure (Fig. 757), and passes into the jejunum. Taking tlio wliole of the duodenum together, it forms an irregularly C-shaped curve, with the opening of the C directed upwards and to the left, and the ends reaching to within about two inches of one another. Within the concavity of tlie curve the head of the pancreas is placed. The incomplete ring which the duodenum makes does not all he in the same plane ; for, whilst its greater part is placed in a transverse-vertical plane, the middle portion bends strongly backwards, round the right side of tbe vena cava, and lies almost in a sagittal plane (Fig. 757). Position and Size. — As a rule, a little more than half of the duodeuum lies in the epigastrium, the remainder, namely, about the lower tbird of the descending 1066 THE DIGESTIVE SYSTEM. portion aud the adjoining two-thirds of the inferior or third portion, are placed in the umbilical region. With the exception of the terminal ascending portion of the third part, the whole of the duodenum lies to the right of the middle line. Its length is usually about 11 inches (27"5 cm.), its first portion being the shortest and its third portion the longest. Its diameter varies considerably, and may be Fossa for Spigelian lobe Right phrenic vessels \ Vena cava Hepatic -1 em Hepatic aiteiy Portal vein Pylorus Bile duct Right suprarenal body (Esophagus ' Coronary artery Diajihiagm Left supiaienal body Splenic aiteiy Kidney Upper suiface of pancreas Gastric surface of spleen Spermatic vein Ureter Right common iliac - vein Right common iliac artery Left common iliac vein Under surface of pancreas Attachment of transverse me'iocolon Duodeno- jejunal flexure Gabtro-duodenal artery and neck of pancreas Superior mesen- teric artery ^ Duodenum Uieter Colon Fig. 757. — Thk Visceka and Vessels on the Pusteuidr Abdominal Wall. The stomach, liver, and most of the intestines have been removed. The peritoneum has been preserved on the right kidney, and the fossa for the Spigelian lobe. In taking out the liver, the vena cava was left behind. The stomach-bed is well shown. (From a body hardened by injection of chromic acid.) stated to average about 1^ inclies when empty, but it may be as much as two inches when distended. Relations. — The first or superior portion (pars superior) begins at the pylorus opposite the first lumbar vertebra. Erorn this it runs to the right, and then backwards, beneath the liver when the stomach is empty, but directly backwards THE DUODEXUM. 1067 when it is full ; and ends at the neck of the gall-bladder by turning downwards and passing into the second part. Its length varies from about Ih to 2 inches (3-7 to 5-0 cm.), and is said to be greater when the stomach is empty than when distended. Its relations (Eigs. 757 and 758) are as follows -.—Above and in front lies the quadrate lobe of the liver, which hangs downwards and to the right over the tube. Below, it rests on the head and neck of the pancreas (the latter running up behind it for a little way). Behind it, close to the pylorus, the portal vein ascends to the liver, and the bile duct with the gastro-duodenal artery passes downwards. Further to the right, as it bends backwards, it lies against tlie right side of the vena cava. Its im-itoneal relations for about an inch from the pylorus are the same as those of the pyloric end of the stomach, that is to say, both the anterior and posterior Toji of .small sac Inferior vena cava Lesser omentum (onf) \ Right lateral ligament of liver Left lateral ligament of liver / ffisopliageal opening in diaphragm Gastro-plirenic ligament Corresponds to 'uncovered area' of stomach Gastro-splenic omentum (cut) I'lueno-colic ligament Transverse coUm cnjssiiiLj (liioJenuni / Head of pancreas Great ouientum (cut) Part of small sac Left end of ti'ansverse mesocolon plenic flexure of colon Transverse mesocolon (cut) Root of mesentei-y (cut) Fig. 758. — The Peritoneal Relations of the Duodenum, Pancreas, Si'Leen, Kidneys, etc. From a body hardened by injections of formalin. In removing tlie liver, stoniacli, and intestines the lines of the peritoneal reHexious were carefully preserved. The peritoneum is coloured l>lue. surfaces are covered, and the lesser and great omenta are attached to its upper and lower borders respectively (Fig. 758). Beyond this, however, only the anterior surface has a serous coat. The pi'iitoneal covering of the first lialf of tlie posterioi- surface is derived from a diver- ticulum of the small sac which runs to the right behind the duodenum for the distance mentioned. When the stomach is distended, the first inch of the duodenum — which is movable on account of its complete peritoneal covering — is carried to the right with the pylorus, and thus brought 1068 THE DIGESTIVE SYSTEM. into line witli tlie second or terminal half, wliicli is always directed backwards. Hence tlie whole of the first portion of the duodenum is directed backwards when the stomach is full. The second or descending portion (pars descendens) begins at the neck of the gall- bladder, passes down behind the transverse colon, and ends at the right side of the third or fourth lumbar vertebra. In length it measures 3| or 4 inches (8-7 to 10 cm.). In front, it is crossed about its middle by the beginning of the transverse colon (Fig. 758). Above the colon, it is in contact with the narrow end of the gall-bladder and below it with the coils of the small intestine. Behind, it is connected by areolar tissue to the inner part of the right kidney, with its ureter and renal vessels ; it is also related, as a rule, to the right psoas muscle below the kidney (Eig. 757). To its outer or right side lies the liver (here presenting the duodenal impression) above, and often the ascending colon below. To its inner side are the inferior vena cava and the head of the pancreas, this latter overlapping it somewhat in front. The common bile duct, after passing down behind the first portion of the duodenum, descends between the head of the pancreas and the second portion, nearly as far as its middle ; here it is joined by the pancreatic duct, and the two, piercing the wall of the duodenum obliquely, open by a common orifice on its inner aspect, about 3| to 4 inches (8-7 to 10 cm.) beyond the pylorus. Peritoneal relations. — There is no peritoneum on the posterior or deep surface of this part, whilst its superficial or anterior surface is covered, except where it is crossed by the colon (Fig. 758). When the beginning of the transverse colon is completely covered by peritoneum, and has a mesentery (a condition which often seems to be determined by a liver large in the vertical direc- tion), the whole of the anterior surface, with the excej)tion of the insignificant area between the two layers of the transverse mesocolon, is covered by the peritoneum. On the other hand, when this part of the colon has no mesentery, it lifts the peritoneum off the front of the duodenum, and leaves a considerable " uncovered area," which is united by areolar tissue to the back of the colon. The third or inferior portion (pars inferior) begins at the right side of the third or fourth lumbar vertebra. From this it first runs more or less transversely to the left across the vena cava (Fig. 757) for one or two inches, and then passes very obliquely, or even vertically, upwards in front of the aorta and left psoas muscle. Finally, having reached the lower surface of the pancreas, it bends forwards, and passes into the jejunum. Owing to the different directions which they take, we can recognise two divisions, a transverse and an ascending terminal, in this portion of the duodenum (Fig. 757). In front, it is crossed (about the junction of its two divisions) by the superior mesenteric vessels, and also by the root of the mesentery (Fig. 758). On each side of this it is covered by coils of small intestine. Behind, its horizontal portion lies on the vena cava ; its ascending portion on the aorta, the left renal vessels, and the left psoas muscle, all of which separate it from the vertebral column. Above, it is closely applied in its whole extent to the head of the pancreas. The left side of the ascending terminal ])art, which is free, lies in contact with some coils of the small intestine. Peritoneal relations. — The third portion of the duodenum is covered by peri- toneum on its anterior surface throughout, except where it is crossed by the superior mesenteric vessels and the root of the mesentery which contains them (Fig. 758). In addition, its ascending terminal portion is also clothed by this membrane on its left side; and here are usually found one or two small peritoneal pouches known as the duodenal fossse. Tlie attacliment of the root of the mesentery begins above quite close to tlie duodeno-jejunal flexure, on tlie front of the duodenum ; from this it runs down on the anterior aspect of the ascending terminal part, and finally leaves the duodenum about the union of the two divisions of its third portion. Duodenal Fossae. — In the neighbourhood of the ascending part of the third portion of the duodenum are found three well-known fosspe of the peritoneum which are of some surgical interest ; these are the superior and inferior duodenal and the paraduo- denal fossse (Fig. 7-59). Other rarer forms are occasionally present. THE DUODENUM. 1069 Transverse meso- colon AVhen the ascending terminal part of the duodenum is drawn over to the right, and the angle between its left side and the posterior abdominal wall examined, one or two triangular folds of peritoneum will generally be found crossing over this angle from the duodenum to the abdominal wall. Each fold has one edge attached to the duodenum, another to the parietal peri- Transverse colon toneum at the left of the duo- denum, whilst the third is free, and bounds the oj^ening of a small pouch which lies behind the fold. One of these, the superior' duodenal fold, is situ- ated near the termination of the duodenum, with its apex directed up and its free margin down. It sometimes contains between its two layers the termination of the inferior mesenteric vein. Behind it lies the superior duodenal fossa, the opening of which looks downwards, and will usually admit the tip of a finger (Fig. 759). The second, known as Superior duodenal fossa Inferior duodenal fossa The mesentery (cut) -Ti^.s^— ^"^^ 'ip ^ Inferior mesenteric vein '' ^^\^ Inferior mesenteric artery -The DroDENAL Fo.ss.e and Folds. Fk:. 759.- the inferior- duodeiud fold, is The transverse colon and mesocolon have been thrown up, and the placed lower down, at the side mesentery has been turned to the right and cut. The paraduodenal of the same part of the duo- ^°^^^ ^°* Landzert) is situated to the inner side of the inferior 1 1. <• 1 J • mesenteric vein, between it and the terminal part of the duodenum, denum. Its free border is it is not shown in the illustration, directed upwards, as is the mouth of the inferior duodenal fossa, which lies behind it. This latter is lai'ger and more constant than the superior duodenal fossa, and is present in 75 per cent of bodies, whilst the superior is present in 50 per cent (Jonnesco). Paraduodenal Fossa (fossa of Landzert). — This fossa, which is best seen in the infant, is placed some distance to the left of the terminal part of the duodenum. It is produced by the inferior mesenteric vein raising up a fold of peritoneum, as it runs along the outer side of the fossa, and then inwards above it (see Fig. 759, where the vein, but not the fossa, is shown). It is limited below by a sj^ecial fold (the mescntcrico-meso- colic fold). According to Moyuihan, this is the only fossa to the left of the duodenum capable of developing into the sac of a hernia ; and Avhen this occurs, the inferior mesenteric vein always lies in the anterior margin of the orifice of the sac (accompanied for some distance by the ascending branch of the left colic artery). In addition to the above, a duodeno-jejunal fossa at the front of the duodeno- jejunal flexure, and five other fossct, have — perhaps unnecessarily — been described in this region. Peritoneal Kelations of the Duodenum. — Whilst the relations of the peritoneum to the second and third portions of the duodenum are u.sually described as in the foregoing account, it should i^erhaps be iiointod out, that it is not really the front, but the right half of the circumference of the descending j^ortion which has a serous coat. Similarly, it is the lower and anterior half of the circumference of the transvci-se part of the thiitl portion wliich is clothctl l)y ])eritoneum, whilst considerably more than half of the circumference of its ascending terminal part is covered ; for the peritoneum forms a fokt running in behind this part, in addition to covering its left side and half its anterior aspect. Interior of Duodenum. — Xo valvulne conniventes are found iu the duocienum for an inch or two beyond the pylorus. Here they begin ; at first as low, scattered, and irregular folds; further down, tliev gradually become larger, more regular, and more numerous ; and by the time the middle of the descending stage is reached they have attained a considerable develop- llood-like valvula connivens Bile pa])illa Common open- iii},' of bile and pancreatic duct Frenulum Fig. 760.— Thk Bii.e Pai'ili-a in the InTERIOU ok the DrODENLM. 1070 THE DIGESTIVE SYSTEM. ment. In the lower part of the duodenum the folds are large, prominent, and closely set. On the inner aspect of the descending portion, about its middle — namely, 3^ or 4 inches (8'7 to 10 cm.) beyond the pylorus — is seen a prominent papilla, on which the bile and pancreatic ducts open by a common orifice (Fig. 760). This is known as the bile papilla (papilla duodeni ; caruncula major of Santorini). The bile papilla is placed beneatb, and protected by, a prominent, bood-like valvula con- nivens, wbicli is situated immediately above it. From its lower margin a firm ridge of the mucous membrane (the phca longitudinalis duodeni) descends for a considerable distance, and acts as a frenum, which fixes the papilla and directs its apex somewhat downwards (Fig. 760). The papilla is prominent, and nipple or dome-shaped, and at its summit is placed the small orifice, which will usi;ally admit tlie jioint of a pencil ; the whole liears a close resemblance to the nozzle of a perfume-spray. Nearlj" an inch higher wp, and invariably on the A'entral side of the bile papilla (sometimes as much as a i to | inch distant), is seen a second and smaller papilla (the caruncula minor of Santorini), at "the point of which is placed the very small orifice of the accessory pancreatic duct. This second papilla seems to be constantly present, although sometimes so small that it may easily escape detection unless carefully sought for. When well developed, it may have a hood -like valvula connivens and a little frenulum, like those of the bile papilla. Structure of the Duodenum. — The peritoneal coat, which is incomplete, has already been described in detail, in connexion Avith each division of the duodenum. The muscular coat is well developed, and is pierced by the bile and pancreatic ducts, but otherwise calls for no special description. The submucosa differs from that of the rest of the small intestine, in that it con- tains, especially in the upper half of the duodenum, the glands of Brunner (gland ulse duodenales). These are small acinotubular glands, closely resembling the pyloric glands of the stomach, which lie in the submucous coat, and send their ducts through the muscularis mucosae to open on the surface between LieberklUm's glands, or sometimes into these glands themselves (Fig. 754). They can be exposed by removing the peritoneal and muscular coats, and also some of the submucosa, when they appear as little round or flattened masses of a reddish gray colour, varying in size from J^th to -jVth of an inch in diameter (-5 to 2-0 mm.). They form an almost continuous layer as far as the opening of the bile duct ; beyond this they diminish progressively, and completely disappear near the duodeno-jejunal flexure. The mucous membrane, which is thicker in the duodenum than in any other part of the small intestine, is covered throughout with broad short villi. Its other character- istics have been already fully described. Various Forms of Duodenum. — Three diff'erent types of duodenum have been described — (1) The annular, in which the curves separating the various portions are open, and the two extremities come fairly close to one another. (2) Tlie U-shaped, in which the transverse part. of tlie third portion is very long, and the ascending portion nearly vertical ; and (3) the V-shaped duodenum, in whicli the transverse part of the third portion is very short or absent. Duodenal Pouch. — A diverticulum of the duodenum, arising from its left side just above the opening of the Ijile duct, and running into the substance of the jjancreas, is occasionally found. It is possibly connected witli one of the outgrowtlis of the duodenum from which the pancreas is developed in the embryo. Vessels and Nerves. — The duodenum receives its blood from the superior and inferior pancreatico-duodenal arteries, branches of tlie gastro-duodenal and superior mesenteric arteries respectively. Tlie blood is returned by tlie corresponding veins, the superior of which opens into the superior mesenteric, and the inferior into the beginning of the portal vein. Tlie lymphatics pass to a set of glands placed along the pancreatico-duodenal arteries, and thence to the cocliac glands. The nerves come from the solar plexus of the sympathetic. Duodeno-jejunal Flexure. — When the ascending terminal portion of the duodenum reaches the under surface of the pancreas, at a point opposite the left side of the first or second lumbar vertebra, it turns abruptly forwards, downwards, and to the left, and passes into the jejunum. This abrupt bend is known as the duodeno-jejunal flexure. Unlike the rest of the duodenum, which is subject to considerable variations in position in different individuals, the duodeno-jejunal flexure is fixed by a thin band of unstriped muscle, which is attached above to the strong connective tissue around the coeliac axis, as well as to the left crus of the diaphragm, and below joins the muscular coat of the duodenum at the flexure. This band is known as the suspensory muscle of the duodenum (inusculus sus- pensorius duodeni — Treitz). THE JEJUNUM AND ILEUM. 1071 The course taken bv the gut at the (luodeuo-jc^uual flexure is variable: the chief directions in their order of frequency are— (1) do-mn\ards, forwards, and to the h-ft ; (2) directly forwards and downwards ; (3) to tlie left, and tlien do-miwards ; (4) forwards and to the riglit (Harman). Some of the fibres of the suspensory nniscle ai'C said by Lockwood to pass into tlie mesen- tery, and he consequently caUs it "the suspensory muscle of the duodenum and mesentery proper." THE JEJUNUM AND ILEUM. The upper two-fifths, that is, ahout 8 feet of the small intestine beyond the duodenum, are known as tlie jejunum (intestinum jejunum). The succeeding three- fifths, which usually measures about 12 feet, constitute the ileum. The ileum opens into the large intestine at the junction of the csecum and ascending colon, where its orifice is guarded by the ileo-csecal valve. Both the jejunum and ileum are connected to the parietes by a large fold of Attacliment of falciform ligament' Tenth rib- Gall-bladder Hepatic flexure Third part of duodenum Apex of vermiform appendix Terminal part of ileun Ctecum-^* Spleen (anterior angle) Splenic flexure Transverse mesocolon, with stomach resting on it Terminal part of duodenum Descending colon Root of mesentery (cut) Pelvic (sigmoid) mesocolon Pelvic colon (sigmoid flexure) Bladder Fig. 761.--TFrF, Abdominal Viscera after the Removal of the Jejcnum and Ileum (from a photognij)!! of the same l)0(ly as depicted in Fig. 739). The transverse colon is much more regular than usual. Hotli tlie liver and eoecuiu extend lower down than normal. The suhdivisions of the abdominal cavity are iiiilicated liy dark lines. peritoneum — the mesentery — which conveys vessels and nerves from the posterior abdominal wall to these divisions of tlie intestine. The part of the tube to which the mesentery is connected is known as the mesenteric or attached liorder ; the opposite side is the free border. The mesentery (mesenterium) is a broad fan-shaped fold, composed of two layers of peritoneum, which connects the small intestine to the back of tlie abdomen. One border of the fold is wide and contains the intestine within it (Fig. 753). The other, known as the root of tlie mesentery (radix meseuterii), is compara- tively narrow, being only 6 or 7 inches wide, but it is much thicker than the part near the gut, for it contains between its layers a considerable amount of fatty suliperitoneal tissue, in addition to the large vascular trunks passing to 1072 THE DIGESTIVE SYSTEM. the intestiue. The root is attached to the posterior abdominal wall along an obhque line, extending approximately from the left side of the second lumbar vertebra to the right iliac fossa (Fig. 761). In this course its line of attachment passes from the duodeno-jejunal flexure down over the front of the terminal part of the duodenum, then obliquely across the aorta, the inferior vena cava, the ureter, and psoas muscle, to reach the right iliac region. The opposite border of the mesentery is frilled out to an enormous degree, so that, while the root measures but 6 or 7 inches, the free border is extended to some 20 feet, thus resembling a fan, one border of which may be twenty or thirty times as long as the other. The length of the mesentery, measured from its root to the attached edge of the intestine directly opposite, usually measures at its longest part about 6 inches (8 or 9 inches, Treves and Lockwood). Behveen the two layers of the mesentery (Fig. 753) are contained (a) the intestinal branches of the superior mesenteric vessels, accompanied by the mesenteric nerves and lymphatics ; (&) the mesenteric lymphatic glands, which vary from 40 to 150 in number ; (c) a considerable amount of fatty connective tissue, continuous with the extra-peritoneal areolar tissue ; and (d) the intestine itself. The j)eritoneuni from the right side of the mesentery j^asses out on the posterior abdominal wall to clothe the ascending colon, and, above, it is connected by a fold with the transverse meso- colon. That of the left side, similarly, passes across the parietes to the descending and iliac colons. The mesentery begins above, immediately beyond the ending of the duodenum — that is, in the angle of the duodeno-jejunal flexure — and it ends below in the angle between the ileum and ascending colon. It is very short at each end, but soon attains the average length. Its longest l^art goes to the portion of the small intestine situated between two points, one six feet, the other eleven feet from the duodenum (Treves). Whilst the root of the mesentery pursiies at its attachment an almost straight line from one end to the other, if cut across a very short distance from the posterior abdominal wall, it will here be found to form a wavy or undulating line. Further out still this condition becomes more and more marked ; and finally, if the bowel be removed by cutting through the mesentery close to its attach- ment to the intestinal wall, it will be seen that its free edge is not only undulating, but is frilled or plaited to an extreme degree. When shown in this way, it is found that the plaiting or folding is not quite indiscriminate, but that the main folds, of which there are usually six, run alter- nately to the right and left. As a rule, the first fold runs to the left from the duodeno-jejunal flexure, and goes to a coil of jejunum which lies under the transverse mesocolon, and helps to support the stomach (this coil has been already referred to, page 1053). The second fold passes to the right, the third to the left, and so on up to tlie fifth and sixth, which are usually small. From the margins of these primary folds secondary folds project in all directions, and from these again even a third series may be formed. This order is of course by no means constant, but if the intestine be removed from a hardened body in the way suggested, without disturbing the mesentery, it will be found to be arranged with more or less regularity, on some such plan as that indicated. Arrangement of Coils of Small Intestine. — Although the greatest variety is found in the disposition of the small intestine, and it is impossible to state in what regions of the abdomen the different parts of the tube will be found, still it may be said that in general the jejunum (as might be expected from the position at which it begins) is placed above and to the left, in reference to the ileum, which latter lies below and to the right. Again, the upper part of the jejunum is usually situated to the left of the duodeno-jejunal flexure, in contact with the under surface of the pancreas and transverse mesocolon ; and, similarly, the terminal part of the ileum almost always lies in the pelvis, from which it passes up over the right side of the pelvic brim to reach the ileo-ciecal orifice. Another portion of the small intestine is not uncommonly found in the pelvis ; this is the part with the longest mesentery, and lies between two points, six and eleven feet respectively from the duodenum (Treves). Differences between Jejunum and Ileum. — If the small intestine be followed down from tlie duodenum to tlie cfecum no noticeable change in appearance will be found at any one part of its course, to indicate the transition from jejunum to ileum ; for tlie one passes insensil)ly into the other. Nevertheless, a gradual change takes place, and if typical parts of the two, namely, the upper portion of the jejunum and the lower portion of the ileum, be examined, they will be found to present characteristic differences, which are set forth in the following table : — THE JEJUNUM AND ILEUM. 1073 Wider, 1| to Ij inch in diameter. Nanower, IJ to 1 inch in diameter. Wall, thicker and heavier. Wall, thinner and lighter. Redder and more vascular. Paler and less vascular. ValvuliB conniventes well develojjed. Valvulae conniventes absent or very small Peyer's jjatches, few and small. Peyer's patches, large and numerous. The villi are also said to he shorter and broader in the jejunum, more slender and filiform in the ileum (Eauber). The terminal portion of the ileum, after crossing the brim of the pelvis, runs upwards, and also slightly backwards and to the right, in close contact with the caecum, until the ileo-cttcal orifice is reached. Meckel's Diverticulum (diverticulum ilei). — This is a short wide i^rotrusion which is found springing from tlie lower j^art of the ileum in a little over 2 per cent of the bodies examined. It is usually about 2 inches long, and of the same width as the intestine from which it comes off. Most commonly it is found about 2| feet from the ileo-ciecal valve, and ojiposite the termination of the superior mesenteric artery. As a rule, it runs at right angles to the gut, and its end is free ; but occasionally it is adherent either to the abdominal wall, the adjacent viscera, or the mesentery, when it may be the cause of strangulation of the intestine. The diverticulum is due to the jaersistence of the j^roximal jjortion of the vitelline (or vitello- intestinal) duct, which connects the primitive intestine of the embryo with the yolk sac. In shajDe it may be cylindrical, conical, or cord-like, and it may present secondary diverticula near its tip. It arises most frequently from the free border of the intestine, but it sometimes comes off from the side. It runs at right angles to the gut most commonly, but it may assume any direction, and it often is provided with a mesentery. In 3302 bodies sjoecially examined with reference to its existence, it was present in 73, or 2'2 j^er cent, and it ajjpeared to be more common in the male than in the female. In 59 ou^t of the 73 cases its position w'iih reference to the end of the ileum was examined : its average distance from the ileo-cajcal valve was 32^ inches measured along the gut, the greatest distance being 12 feet, and the smallest 6 inches. In 52 specimens the average length was 2-1 inches, the longest being 5j inches, the shortest i inch. The diameter usually equals that of the intestine from which it springs ; but occasionally it is cord-like, and pervious only for a short way ; on the other hand, it may attain a diameter of 3| inches. (The foregoing results have been comi^iled from the reports of The Collective Investigation of the Anatomical Society of Great Britain and Ireland — L. J. Mitchell, Kelynack, Rogie, and Augier.) Vessels and Nerves of the Jejunum and Ileum. — The arteries for both the jejunum and ileum — the vasa intestini tenuis — come from the superior mesenteric, and are contained between the two layers of the luesentery. After breaking u]3 and forming three tiers of arches, the ter- minal branches (Fig. 753) reach the intestine, whei'e they bifurcate, gi\'ing a branch to each side of the gut. These latter run transversely round the intestines, at hrst under the peritoneal coat ; soon, however, they pierce the muscular coat and forui a plexus in the submucosa, from Avhich numerous Ijranches pass to the mucous membrane, where some form ple.xuses around the glands of Lieberkiihn, whilst others pass to tlie villi. The veins are similarly disposed, and the blood from the whole of the small intestine beyond the duodenum is returned by the superior mesenteric vein, \\-hich joins with the sjilenic to form the portal vein. The lymphatics of the suuiU intestine (known as lacteals) begin in the villi, and also ac lyui[)liatic sinuses surrounding the bases of the solitary glands ; a large plexus is formed in the submucosa, a second lietween the two layers of the muscular coat, and a third beneath the peritoneum. The vessels from all these pass up in the mesentery, being connected on the way with the numerous (from 40 to 150) mesenteric glands, and finally unite to form one, or a few, intestinal lymphatic trunks, which open into the receptaculum chyli. The nerves come froui the solar plexus, through the superior mesenteric, which latter accompanies the superior mesenteric artery between the layers of tlie mesentery, and thus reaches the iute.;tiue. Some of the fibres are derived ultimately from the right vagus. The nerve-fibres are non-medullated, and form, as in other parts of the canal, two gangliated plexuses — that of Auerbach in the muscular coat, and the plexus of Meissner in the sub- mucosa. Structure. — Tlie serous coat is complete in all parts of the jejunum and ileum. Tlie muscular coat is thicker in the jejunum, and grows gradually thinner as it is traced down along the ik'uni. The submucosa contains tiie bases of the solitary glands (Fig. 754), but otherwise calls for no special remark. The mucous coat is thicker and redder above, iu the jejunum, thinner aiul paler in the ileum. It is covered throughout by villi, which are shorter and broader in the jejunum, longer and narrower in the ileum. In its whole extent it is closelv beset with Lieberkiihu's follicles, and numerous solitary glands are 72 1074 THE DIGESTIVE SYSTEM. seeu projecting on its surface. Peyer's patches are particularly large and numerous in the ileum; they are fewer, smaller, and usually circular, in the jejunum. Finally, the mucous membrane forms valvulsje conniveutes, which are much more prominent in the jejunum ; they are smaller and fewer in the upper part of the ileum, and usually disappear a little below its middle. THE LAEGE INTESTINE. The ileum is succeeded, by the large intestine (intestinum crassum), which begins on the right side, some 2| inches below the ileo-ctecal junction, and com- prises the following parts : — 1. The caecum, a wide, short cul-de-sac, consisting of the portion of the large bowel below the ileo-caecal junction. It lies in the right iliac region, and from its inner and back part a worm-shaped outgrowth, the vermiform process, is pro- longed (Fig. 761). 2. The ascending colon extends from the caecum, up in the right side of the abdomen, to the liver : here the gut bends to the left, forming the hepatic flexure, which connects the ascending colon to the transverse colon. 3. The transverse colon is a long loop of intestine which arches across the abdominal cavity in an irregular manner. It ends at the lower extremity of the spleen, where it turns downward, forming the splenic flexure, and passes into the descending colon. 4. The descending colon runs down on the left side, from the splenic flexure to the iliac crest. 5. The iliac colon extends from the crest of the ilium to the brim of the pelvis, where it is succeeded by the pelvic colon. 6. The pelvic colon is a large loop of intestine which is usually found in the pelvis. The iliac and pelvic portions of the colon taken together are commonly described as the sigmoid flexure of the colon. 7. The rectum, the terminal part of the large bowel, succeeds the pelvic colon, and ends at the anal orifice. In its course the laree bowel is arranc^ed in an arched manner around the small intestine, which lies within the concavity of its curve (Fig. 739). In length, the great intestine is equal to about one-fifth of the whole 'intestinal Sacculations Appendices epiploicae Fig. 762. — Large Intestine. A piece of transverse colon from a child two year.s old. The three chief characteristics of the large intestine — sacculations, tseuioe, and appendices epiploicse — -are shown. canal, and usually measures between 5 and 5|- feet (180 to 195 cm.). Its breadth is greatest at the CEecum, and from this — with the exception of a dilation at the rectum — it gradually decreases to the anus. At the caecum it measures, when distended, about 3 inches (75 mm.) in diameter; beyond this it gradually diminishes, and measures only Ih inch (37 mm.) or less in the descending and iliac divisions of the colon. The large intestine, with the exception of the rectum and vermiform appendix, may be easily distinguished from the regularly cylindrical small intestine by (a) the presence of three longitudinal bands — the taeniae coll — running along its surface (Fig. 762) ; (h) by the fact that its walls are sacculated ; and (c) by the presence of numerous little peritoneal processes, known as appendices epiploicae, projecting THE LAKGE INTESTINE. 1075 from its serous coat. In addition, the larger intestine is usually wider than the small, but too much reliance cannot be placed on this character, for the jejunum is often — indeed, generally — wider than the empty and contracted descending colon. Tsenise Coll. — In the large bowel, unlike the small, the longitudinal fibres of the muscular coat do not form a complete layer, continuous all round the tube, but, on the contrary, are broken up (Fig. 762) into three bands, known as the taeniae coll. These bands, which are about -|- inch (6 mm.) wide, begin at the base of the vermiform appendix, and run along the surface of the gut at nearly equal distances from one another until the rectum is reached. Here they spread out and form a layer of longitudinal muscular fibres, which is continuous all round the tube (see p. 1087). The bands are about one-sixth shorter than the intestine to which they belong ; consequently, in order to accommodate the bowel to the length of the tienite, the gut is tucked up, giving rise to a sacculated condition (Fig. 762). Three rows of pouches or saccules are thus produced, along the length of the tube, between the tsenite. If the tosnise be dissected off, the sacculations disappear, the intestine becomes cylindrical, and at the same time about one-sixth longer. The appendices epiploicae (Fig. 762) are little processes or pouches of peritoneum, generally more or less distended with fat, except in emaciated subjects, which project from the serous coat along the whole length of the large intestine, with the exception of the rectum proper. When the interior of a piece of distended and dried large intestine is examined, its saccules appear as rounded pouches (haustra), separated by crescentic fokls (phcie semihniares coli), con-esponding to the creases on the exterior separating the saccules from one another. The position of the three taeniae on the intestines is as follows : — On the ascending, descending, and iliac colons one tsenia lies on the anterior aspect of the gut, and two behind, namely, one to the outer (postero-external), the other to the inner side (postero-internal). It is chietly along the first of these (the anterior) that the appendices epiploicfe are found. On the transverse colon their arrangement is different, but is rendered exactly similar by turning the great omentum, with the colon, up over the thorax. On the transverse colon in the natural position, the anterior taenia of the ascending and descending colons becomes the posterior (or postero- inferior, taenia libera), the postero-external becomes the anterior (or omental), and the postero- internal the superior or mesocolic. The anterior and postero-external ttenias of the iliac colon pass below on to the front of the pelvic colon and rectum. In formalin-hardened bodies portions of the large intestine, but particularly of the descending and sigmoid colons, are often found fixed in what appears to be a state of contraction, when they are reduced to a diameter of about f or if of an inch (16 to 19 mm.). Under similar con- ditions parts of the small intestine are found corresipondingly reduced. The appendices epiploicae, although generally said to be absent in the foetus, can be distinctly seen as early as the seventh month, but at this time they contain no fat. Structure of the Large Intestine. — The serous coat is complete on the vermiform appendix, caecum, transverse colon, and pelvic colon ; incomplete on the ascending, descending, and iliac divisions of the colon and on the rectum. It will be described in detail with each of these portions of the intestine. The mucous coat is of a pale, or yellowish, ash colour in the colon, hut becomes nuieh redder in the rectum. Unlike that of the small intestine, its surface is smooth, owing to the absence of villi, but it is closely studded with the orifices of numerous large Lieberkiihn's glands. Solitary glands are also numerous, particularly in the vermiform process (Fig. 767). Vessels and Nerves. — The ctecum and vermiform appendix receive their blood from the ileo-colic artery ; the ascending colon from the right colic ; and the transverse colon from the middle colic wliich lies in the transverse mesocolon. These are all branches of the superior mesenteric artery. The descending colon is supplied by the left colic, and the iliac and pelvic colons by the sigmoid arteries, branches of the inferior mesenteric. The rectum derives its blood from the three hsemorrhoidal arteries, which will be described with that division of the gut. The veins correspond to the artiaies, and join the inferior and superior mesenteric vessels, which send tlieir blood into the portal vein. The lymphatics begin in the mucous meml.)rane, and form a large plexus in the submucosa ; leaving the gut, those of the c;ecum, ascending, transverse, and upper half of the descending colon, pass to the mesocolic glands, which lie behind the ascending and descending divisions of the colon and between the layers of the transverse mesocolon. The lymjihatics from the lower half of the descending, and from the iliac and pelvic colons, join the left lympluuic trunk of the lumbar glands. Those of the rectum will be described later. 72 a 1076 THE DIGESTIVE SYSTEM. Nerves. — The nerves come from the superior mesenteric plexus, an offshoot of the solar plexus, and from the inferior mesenteric, a derivation of the aortic plexus. The arrangement is similar to that of the nerves of the small intestine. Anterior tsenia coli Upper segment of ileo-colic valve Tsenise coli Orifice of appendix THE CECUM AND APPENDIX. Caecum. — After leaving the pelvic cavity, as already described, the terminal portion of the small intestine passes upwards, backwards, and to the right, and opens, by the ileo-ciecal orifice, into the large intestine some 2| inches from its lower end. The portion of the large gut which lies below the level of this orifice is known as the csecum (caput csecum coli). In shape (Fig. 763) it is a wide, unsymmetrical, or lop-sided cul- de-sac, furnished with the taenite and sacculations usually found in the large intestine. Its lower end or fundus is directed downwards and inwards, and usually rests on the front of the right psoas muscle, close to the brim of the pelvis ; whilst the opposite end is directed upwards and out- wards, and is continued into the ascending colon. Fig. 763.-CiECUM showing Ileo-c^cal Val\-e. j^g unsymmetrical form is due to The cfecum lias been distended with air and dried, and a portion the fact that the outer and inner of its anterior wall has been removed. portions of the organ undergo an un- equal development in the child. The inner (or inner and posterior) section lags behind, whilst the outer (or outer and anterior) division grows much more rapidly, and, projecting downwards, soon comes to form the lower end or fundus of tlie caecum. As a result the original extremity of the gut, with the vermi- form process springing from it, is hidden away behind and to the inner side of the fundus. In length the distended csecum usually measures about 2| inches (60 mm.) ; whilst its breadth is usually more, and averages about 3 inches (75 mm.). Position. — It is situated, when normal, almost entirely within the right iliac region of the abdomen, immediately aljove Poupart's ligament ; but its lower end projects inwards in front of the psoas and reaches the hypogastrium (Fig. 769). On the other hand, it is sometimes found, even when quite healthy, high up in the right lumbar region (owing to the persistence of the fcetal position), or hanging over the pelvic brim and dipping into the pelvic cavity to varying extents. In the great majority of cases the csecum is completely covered by peri- toneum on aU aspects, and lies quite free in the abdominal cavity. In a small proportion, namely, about 6 or 7 per cent of bodies, the posterior surface (probably as a result of adhesions) is not completely covered, but over a greater or less portion of its extent is bound down to the posterior abdominal wall by connective tissue. Relations. — Behind, the csecum rests on the ilio-psoas muscle ; generally, too, on its ()int of intersection of the intertuliercular and Pou]>art linos. A point 1 to 1 .', inches (2-5 to 37 cm.) lower down would correspond to the orifice of the vermiform process. In bodies hardened in. situ with forniaUn, tlie valve and orifice present an entirely difierent appearance (see Fig. 764, in Avhicli three different forms of liardened valves are .•^hown), suggesting, much more closelv tluin in the dried state, the appearance of telescoping or inversion mentioned above. In tliem also the two segments of tlie valve are much thicker and shorter, but they can always be distinguished, and are found to bear the same relation to one another as in the dried condition, altliough this mav be obscured by foldings or ruga\ The aperture may be slit-like or rounded, with sloping or inhmdibuliform edges ; the frenuhi are not so prominent at tinies ; but the whole valve projects much more abruptly into the cavity of the ciecum than in the distended and dried specimen. 72 b 1078 THE DIGESTIVE SYSTEM. Structure of the Ileo-caecal Valve. — Each segment of the valve is formed of an mfoldino; of all the coats of the gut, except the peritoneum and the longitudinal muscular fibres, and consequently it consists of two layers of mucous membrane, with the sub- mucosa and the circular muscular fibres between, all of Avhich are continuous with those of the ileum on the one hand and of the large intestine on the other. The surface of each segment turned towards the small intestine is covered with villi, and conforms in the structure of its mucous membrane to that of the ileum ; whilst the mucous membrane of the opposite side resembles the mucous coat of the large bowel. MUCOUS ME.MBRAN In the dried specimen the upper segment usually projects further into the cavity of the cgecum than the lower, so that the aperture appears to be placed between the edge of the lower segment and the under surface of the upper. There is little doubt, as pointed out by Symington, that the efficiency of the ileo-caecal valve is largely due to the oblique manner in which the ileum enters or invaginates the CEecum ; this oblique passage alone, as in the case of the ureter piercing the wall of the bladder, would probably be sufficient to prevent a return of the csecal contents. In the great majority of cases, when' in position within the body, the Pjg -g5 Diagrammatic Section ileum is perfectly protected from such a return, although when THROUGH THE JUNCTION OF ILEUM the parts are remoA^ed, and then distended with fluid, this often WITH CiECUM, TO SHOW THE passes through the valve, and reaches the small intestine. Formation of the Ileo-c^cal Still, the efficiency of such a test, applied when the Valve. parts are deprived of their natural supports, cannot be relied upon. The size of the segments of the valve, as seen in the dried condition, varies considerably ; they are sometimes very imperfect ; and even the absence of both has been recorded. But here again there is danger of falling into error, through examining the parts under such artificial conditions. Development of Caecum and Appendix. — The cjecum first appears in the embryo, at about the fifth week, as a small outgrowth of the wall of the primitive gut (mid -gut), not yet difterentiated into small and large intestines. At this time the outgrowth is of the same size throughout, and is practically equal to the intestines in diameter. About the eleventh week, whilst the large and small bowels are still of the same wddth, it has increased very considerably in length (Ijeing equal to about five times the diameter of the small intestine, and thus being relatively as long as in the adult) ; but even at this early date the basal portion, for about one- fifth of its length, is quite as wide as the intestine, whilst the remaining four-fifths of the out- growth— the future appendix — is only about one-half or one-third the diameter of the gut. From this it is seen that the distal portion of the outgrowth, which subsequently becomes the vermiform process, begins to lag behind even at this early period of its development. The basal portion continues to expand Avith the gut ; the distal part grows rapidly enough in length, but otherwise enlarges very slowly, so that, tOAvards the end of foetal life, the caecum has attained a conical shape, the Avider end joining the ascending colon, the narrow end tapering gradually and jiassing into the vermiform process. This form, known as the infantile type of c£ecum, is retained for some time after birth, or even may (in 2 or 3 per cent of cases) persist throughout life. As early as the sixth or seA'enth month of foetal life the wall of the terminal portion of the small intestine adheres to the inner side of the caecum for some distance beloAV the ileo-cgecal orifice. And this connexion, which is rendered more intimate by the j^assage of two folds of peritoneum, one on the front, the other on the back, betAA^een the two jaarts, jDrofoundly modifies the subsequent groAA'th of the caecum, and determines very largely its adult form. For, Avhen the csecuiu begins to expand, the inner asj^ect is prevented, by its connexion Avith the termination of the ileum, from enlarging as freely as the rest of the wall ; in consequence of this the outer part groAvs and expands much more rapidly, producing the loj)-sided appearance already referred to, and soon comes to form the loAvest part or fundus of the caecum, and the greater jaart of its sac ; Avhilst the original apex, Avitli the vermiform appendix si^ringing from it, anchored, as it Avere, to the end of the ileum, is thrust to one side, and finally lies on the inner and posterior aspect of the ctecum, a little AA-ay beloAv, and usually posterior to, the end of the ileiuai. Tlie position of the caecum varies at different periods of foetal life. About the eleventh or twellth Aveek it lies immediately beneath the liver, and to the left of the middle line; it then gradually travels to the right, crossing the descending duodenum, and is found lying on the right side, just beneath the liver, at the fourth month. From this it descends slowly to its adult position, Avhich it usually approaches toAvards the end of foetal life, but it may not actually reach it until some time after birth. An imperfect descent gives rise to the lumbar position of the caecum, or an excess in this direction to the joelvic i^osition (referred to on p. 1076). Types of Csecum. — Three chief types of caecum may be distinguished — the fcetal type, conical in shajje and nearly symmetrical, with the lower end gradually passing into the vermiform THE C^CUM AND APPENDIX. 1079 appendix ; the infantile, in whicli the passage from the caecum to the vermiform process becomes more abrupt, tlie outer wall more prominent, and the whole sac more unsj-mmetrical ; and the lop- sided adult form, as described above, which is the condition found in 93 or 94 per cent of adults. Structure. — Nothing in the arrangement of the mucous and submucous coats calls for special notice. The t^enite or longitudinal bands of the muscular coat all spring from the base of the vermiform appendix (Fig. 766) ; the anterior runs up on the front, internal to the main prominence of the ctecum ; the postero-external runs up behind this pi'ominence ; whilst the postero-internal passes directly upwards behind the ileum (Fig. 766). The longitudinal fibres on the upper aspect of the ileum partly join the postero- internal taenia ; those on the front and back join the circular fibres of the large gut. The sei'ous coat has, in connexion with it, certain folds and fossae which are described at p. 1081. Vermiform Process or Appendix Caeci (Fig. 768). — The appendix is a worm- like tubular outgrowth which springs from the inner and back part of the ctecum about 1 to 1} inches (2'5 to 3-75 cm.) below the ileo-ctecal orifice. Prom this it generally runs in one of three chief directions, namely — (1) over the brim, into the pelvis ; (2) upwards behind the caecum ; or (3) upwards and inwards, thus pointing i/ COLIC BRANCH ILEO-COLIC ARTERY - ^ ___^ ILIAC BRANCH — , CAECAL BRANCH _ C^ 1 .,/^ 1 c \vV >; T^" /k> ^^^.^^^^ A M V\ ARTERY 0F_/ \r] APPENDIX // Fig. 766. — The Blood Supply of the C-ecum axd Vermiform Appendix. The illustration to the left gives a frout view, in that to the right the ciBcum is viewed from behind. In the latter the artery of the appendix, and three taeniae coll springing from the base of the ajijieudix, should be specially noted (modified from Jonnesco). towards the spleen ; each of which has been considered to be the normal position hy one or more observers. In the first of these situations it is quite evident as it hangs over the pelvic brim ; in order to expose it in the second, the caecum must be turned upwards ; whilst, in the tliird position, it lies behind the end of the ileum and its mesentery, and these must be raised up in order to display it. In addition to the positions just mentioned, it has been found in almost every possible situation in the abdomen which its length and the extent of its mesentery would allow it to attain. In every ease the anterior tamia of the ctecum, which is always distinct, offers the surest guide to the process, the base of which can be located with certainty by following this tamia to the back of the caecum (Fig. 766). Its size is almost as variable as its position. Taking the average of numerous measurements, its length may be given as about 3^ inches (92 mm.. Berry), and its breadth as \ inch (6 mm.. Berry). On the other hand, it has been found as long as 9 inches (230 mm.), and as short as \ inch (18 mm.). Even its absence has been recorded (Fawcett). Its lumen or cavity is variable in its development, and is found to be totally or partially occluded in at least one-fourth of all adult and old bodies examined. This is looked upon as a sign of degeneracy in the process, which is by many considered to be undergoing a gradual obliteration in the human species. It opens into the cavity of tbe caecum on its inner, or inner and posterior aspect (Fig. 763), at a point 1 to 1^ inches (2-5 to 3-8 cm.) below, and somewhat behind 1080 THE DIGESTIVE SYSTEM. the ileo-csecal orifice. These are the relative positions of the two orifices, as seen from the interior of the ceecum ; viewed from the exterior, the base of the appendix is within f inch of the lower border of the ileum. This apparent difference is due to the fact that the ileum adheres to the inner side of the caecum for a distance of nearly 1 inch before it opens into it. Sometimes the orifice of the appendix has a crescentic fold or valve (valvula processus vermiformis) placed at its upper border ; but it is probably of very little functional importance when present, for the aperture of the appendix is usually so small that its cavity is not likely to be invaded by the contents of the ceecum. The vermiform process is completely covered by peritoneum, and has a con- siderable mesentery, the meso- appendix (mesenteriolum processus vermiformis), which extends to its tip as a rule, and connects the process to the under surface of that part of the mesentery proper which goes to the lower end of the ileum. The appendix is relatively, to tlie rest of the large intestine, longer in the chilci at birth than in the adult, the proportion being about 1 to 16 or 17 at birth and 1 to 19 or 20 in the adult. (The difference is certainly not as great as stated bj^ Ribbert, who makes the proportion 1 to 10 at birth and 1 to 20 in the adult.) The process attains its greatest length and diameter during adult and middle age, and atrophies slowly after that time. It is said to be slightly longer in the male than in the female. Total occlusion of its cavity is found in 3 or 4 per cent of bodies ; it is then converted into a fibrous cord. Partial occlusion is present in 25 per cent of all cases, and in more than 50 per cent of those over 60 years old, whilst it is unknown in the child. This frequency of occlusion, the physiological atrophy which takes place after middle life, the great A'-ariations in length, and other signs of instability, have been considered to point to the retrogressive character of the appendix. A vermiform process is found only in man, the higher apes, and the wombat, although in certain rodents a somewhat similar arrangement exists. In carnivorous animals the c£ecum is very slightly developed ; in herbivorous animals (with a simple stomach) it is, as a rule, extremely large. It has been suggested that the vermiform process in man is the degenerated remains of the herbivorous caecum, which has been replaced by the carnivorous form. Another and perhaps more probable view regards the appendix as a lymphoid organ, having the same functions as Peyer's patches, and like these undergoing degeneration after middle life (Berry). In the foetus and child, as well as in the adult with the infantile type of cascum, the appendix springs from the true apex, not from the inner and posterior aspect. Foreign bodies, although reputed to find their way very easily into the appendix, are rarely found there after death. On the other hand, concretions or calculi, formed of mucus, faeces, and various salts, are often present (Berry). Structure (Fig. 767). — The serous coat is complete, and forms a perfect investment for the process. The muscular coat, unlike that of the rest of the large intestine, has a. Fig. 767. — Structure of the Vermiform Appendix. A. From a child two years old. B. From a male, age 56. It will be observed that the submucosa is almost entirely occupied by lymphoid nodules and patches. The muscularis mucosifi is very faint, and lies quite close to the bases of Lieberkiilm's glands. The longi- tudinal layer of muscular fibres forms a continuous sheet. continuous and stout layer of longitudinal fibres, which passes at tlie root of the process into the three taenia) coli (Fig. 768). The layer of circular fibres is well developed. The submucosa is almost entirely occupied by large masses of lymphoid tissue surrounded by THE CiECUM AXD APPENDIX. 1081 sinus-like lymph spaces. Owing to the large size of these lymphoid nodules, the areolar tissue of the submucosa is compressed against the inner surface of the muscular coat, and forms a well-marked fibrous ring, which sends processes at intervals between the lymphoid masses towai'ds the mucous membrane. The inner portion of this fibrous ring seems to have been generally mistaken for theniuscularis mucosae, which latter, as seen in Fig. 767, lies internal to the chief masses of lymphoid tissue, and not outside it, as figured by Testut. These lymphoid nodules, which correspond to solitary glands, have, owing to their great number, been almost completely crushed out of the mucosa (in which they chiefly lie in the intestine) into the submucosa. The mucous coat corresponds to that of the large intestine in its general characters, but the Lieberklihn's glands are fewer, and irregular in their direction ; the muscularis mucossc is thin and ill-defined ; it lies just internal to the lymphoid nodules of the sub- mucosa, and immediately outside the base of Lieberkiihn's glands. Some few lymphoid nodules lie in the mucous coat also. Blood-vessels of the Caecum and Vermiform Appendix (Fig. 766). — These parts are supplied witli Ijlood by the ileo-csecal artery. This gives oft', near the upper angle formed by the junction of the ileum with tlie small intestine — (a) an anterior ca'cal artery, which pas.ses down on the front of the ileo-cfecal junction to the csecuni, and Ijreaks ujj into numerous branches for the .supply of that part ; (b) a j)osterior cwcal artery, similarly dis])0sed on the back ; and (c) the artery of the ai^jjendix. The last-named bi'anch passes down behind the ileum (Fig. 766), then enters the mesentery of the appendix, and running along this near its free border, sends off several branches across the little mesentery to the aj^pendix, before finally ending iu it. The coui-se of the artery behind the ileum is said to render it subject to jiressure from ftecal masses in that gut, and thus to predispose to an interference with the supjily of the appendix, and morbid changes in the jn-ocess. It has also been said that the apjiendix receives a small branch from the left ovarian artery in the female — a statement which I have been unable to verify. The veins correspond to the arteries. The lymphatics pass with the vessels to join a few small glands which are found in the mesentery of the apj^endix at its base, the efferent vessels from which join the mesocolic glands behind the ascending colon. Caecal Folds and Fossae. — The peritoneum forms in the neighbourhood of the Ccecum certain fosste, of which the most interesting and important are — (a) the retro- csecal or retro-colic fossae ; (b) the ileo-csecal fossa ; and (c) the ileo-colic fossa. VERMIFORM PROCESS RETRO-CAECAL FOSSA B Fig. 768. — The Cecal Folds and Foss^. In A, the cajcum is viewed from the front ; the mesentery of the apj^endix is distinct, and is attached above to tlie under surface of the portion of the meseuter.y going to the end of the ileum. In B, the coecum is turned ujiwards to &\\o\s a retro-csecal fos-^a, which lies behiml it and the beginning of the ascending colon . The retro-colic fossae (Fig. 768, B) are only occasionally present, and are exposed by turning the ctocum and adjacent part of the ileum upwards. Two forms, external and internal, arc described ; the first lies behind the outer part of the ascending colon, immediately above the c;ecum ; the second beliind its inner part. Those fossto are specially interesting because, wlven present, they frequently lodge in the vermiform process (see Fig. 768, W), a condition which is said to favour the production of appendicitis. Ileo-caecal Fossa and Fold. — If the appendix be drawn down, and the finger run 1082 THE DIGESTIVE SYSTEM. towards the csecum, along the lower border of the terminal part of the ileum, its point will generall}^ run into a fossa situated in the angle between the ileum and caecum (Fig. 768, A), which is known as the ileo-csecal fossa. The fold which bounds the fossa in front is the ileo-cpecal fold (the " bloodless fold of Treves "). It passes from the ileum to the fi'ont of the meso-appendix, which latter forms the posterior wall of the fossa. Ileo-colic Fold and Fossa. — Similarly, if the finger be run out along the wpiper border of the ileum towards the csecuni, it will usually lodge in a smaller fossa, the ileo-colic, which is bounded in front by a small peritoneal process, the ileo-colic fold (Fig. 768, A), containing the anterior csecal artery. THE COLON. Ascending Colon (colon ascendens). — This section of the great gut begins about the level of the intertubercular plane, opposite the ileo-caecal orifice, where it is continuous with the csecum. From this it runs upwards and somewhat back- wards, with a slight concavity to the left, until it reaches the under surface of the liver, where it bends forwards and to the left, and passes into the hepatic flexure (Fig. 769). In its course it lies in the angle between the quadratus lumborum behind, and the more prominent psoas internally (Fig. 742). It is situated chiefly in the right lumbar region, but it extends slightly into the hypochondrium above ; and, although it usually begins about the level of the intertubercular line, still with a low position of the csecum it will extend further down, and may occupy a considerable part of the iliac region. Its length is about 8 inches (20 cm.), and it is wider and more prominent than the descending colon. It generally presents several minor curves or flexures, and it often has the appearance of being pushed into a space which is too short to accommodate it. Relations. — In front, it is usually in contact with the abdominal wall, but the small intestine frequently intervenes, particularly above (Fig. 739). To its inner side lie the coils of the small bowel and the psoas ; to the outer side is the lateral wall of the abdomen. Its posterior surface, which is free from peritoneum as a rule (Fig. 742), is connected by areolar tissue to the iliacus muscle as far up as the crest of the ilium, to the quadratus lumborum above this, and finally to the lower and outer part of the right kidney. In the great majority of cases only the two sides and the anterior surface are covered by peritoneum, the posterior surface being destitute of a serous coat (Fig. 742). In a small proportion of bodies, however, the ascending colon is provided with a complete peritoneal coat and a mesentery, but this latter is so short that it admits of but a slight amount of movement in the gut. Like the csecum, the ascending colon is frequently found distended with gas or fseces after death, hence in part its large size and prominence as compared with the descending colon, which is generally emj^ty. Hepatic Flexure (flexura coli dextra). — The hepatic flexure is the bent piece of the large intestine between the end of the ascending colon and the beginning of the transverse colon (Figs. 758 and 769). When the ascending colon, lying on the front of the kidney, reaches the under surface of the liver, it bends — usually acutely, sometimes obtusely — forwards and to the left, and on reaching the front of the descending duodenum, passes into the transverse colon. The flexure is placed between the descending duodenum internally and the lower thin margin of the liver, or the lateral abdominal wall, externally ; above, it corresponds to the colic impression on the liver, and behind it rests on the kidney. Its peritoneal relations are similar to those of the ascending colon. Transverse Colon (colon transversum). — This is the long and arched portion of the large intestine which lies between the hepatic and splenic flexures. It begins where the colon crosses the descending duodenum at the end of the hepatic flexure (Fig. 769). From this it runs transversely to the left, and for the first few inches is comparatively fixed, being united to the front of the descending duo- denum and the head of the pancreas either by a very short mesentery or by areolar tissue. Immediately beyond this a long meseutery is developed, which allows the THE COLON. 1083 colon to hang down in front of the small intestine, at a considerable distance from the posterior abdominal wall. Towards its left extremity the mesentery shortens again, thus bringing the gut towards the tail of the pancreas (Fig. 758), along which it runs upwards into the left hypochondrium, under cover of the stomach, as far as the lower end of the spleen, where it passes into the splenic flexure (Fig. 757). Its two ends lie in the right and left hypochondriac regions re- spectively, whilst its middle portion hangs down into the umbilical, or even the hypogastric region. Its average lengtlt is about 19 or 20 inches (47"5 to 50'0 cm.), that is more than twice the distance, in a direct line, between its two extremities. This great length is accounted for by the curved and somewhat irregular course which the bowel pursues. Relations. — The greater part of the transverse colon lies behind the great omentum, which must consequently be turned upwards in order to expose it. Above, it is in contact, from right to left (Fig. 769), with the liver and gall-bladder, the stomach, and, near its left end, with the tail of the pancreas and lower end of the spleen (Fig. 758). In front are placed the omentum and the anterior abdominal wall ; towards its termination the stomach is likewise in front. Behind, it first lies in contact with the descending duodenum and head of the pancreas ; beyond this, where it liangs down, the small intestine is placed below and behind, and it is con- nected to the posterior abdominal wall (more correctly, to the anterior border of the pancreas) by the transverse mesocolon. It is also loosely connected to the stomach by the great omentum, which is attached to its anterior surface. The transverse mesocolon and the great omentum are described with the peritoneum, p. 1097. The transverse colon is completely covered by peritoneum, with the exception of the first few inches of its posterior surface, which are often, if not usually, uncovered. The state of the peritoneal covering on the back of the first part of the transverse colon would seem to depend, in some degree, on the extent to which the liver passes dowmwards on the right side. With a small high liver no mesentery is present, and the posterior surface is devoid of peritoneum ; on the otlier hand, when the liver is enlarged in the vertical direction, it pushes the colon downwards before it, and brings the upper line of the peritoneal reflection from its back, into contact with the lower, thus giving rise to the mesentery. In the foetus of three or four months every part of the colon is supplied with a long mesentery ; subsequently this, as a ]*ule, disajapears at the beginning of the transverse colon, but it may be reproduced in the manner stated. Splenic Flexure (flexura coli sinistra). — The terminal portion of the trans- verse colon runs upwards (also backwards and to the left) until the lower end or base of the spleen is reached ; here it bends sharply, forming the splenic flexure, and runs down into the descending colon. The flexure is placed deeply in the left hypochondrium, behind the stomach, and in contact with the base of the spleen. It lies at a higher level than the hepatic flexure, and is connected to the abdominal parietes by the phreno-colic ligament, wdiich helps to maintain it in this position. Phreno-colic or Costo-colic Ligament (ligamentum phrenocoKcum, Fig. 758). — This is a triangular fold of peritoneum, with a free anterior border, which is attached internally to the splenic flexure and externally to the diaphragm opposite the eleventh rib. Owing to the fact that the base of the spleen rests upon it, the ligament has also received the name of sustentaculum lienis. The phreno-colic ligament is formed in the foclus fi'om the left margin of the great omentum (Jonnesco and Fig. 758). The peritoneal covering of tlie splenic Hexure is similar to that of the descending colon. Descending" Colon (colon descendens). — This is much narrower and loss obtrusive than the ascending colon : indeed in a large number of cases it is found firmly contracted. It begins in the left hypochondrium at the splenic flexure, passes down on the left side of the abdomen, and ends in the lumbar region, opposite the crest of the ilium, by passing into tlie iliac colon. Its course is not quite straight, for it first curves downwards and inwards along the outer side of the left kidney, and then descends almost vertically to the ihac crest (Fig. 769). 1084 THE DIGESTIVE SYSTEM. Its length is usually from 4 to 6 inches (10 to 15 cm.), and its tvidth, which is less than that of the ascending colon, about 1| inches (37 mm.). Relations. — The descending colon first hes in contact with the outer aspect of the left kidney; below this it is placed, like the colon of the opposite side, in the angle between the psoas and quadratus lumborum muscles. Behind, it rests upon the lower part of the diaphragm above, and on the quadratus lumborum below. In front (and somewhat to the outer side also, except when the bowel is distended) are placed numerous coils of small intestine, which hide the colon completely from stomach Attachment of falciform ligament' Hepatic flexure — Spleen (anterior angle) Splenic flexure Transverse mesocolon, with stomach resting on it §Mm% Terminal part of duodenum Descending; colon Apex of vermiform appendix V' Terminal part of ileum CEecum Root of mesentery (cut) Pelvic (sigmoid) mesocolon Pelvic colon (sigmoid flexure) Bladder Fig. 769. — The Abdominal Viscera after the Removal of the Jejunum and Ileum (from a photograph of the same body as depicted in Fig. 739). The transverse colon is much more regular than usual. Both the liver and CEecum extend lower down than uormal. The subdivisions of the abdominal cavity are indicated by dark lines. view, and compress it against the posterior abdominal wall. To its inner side lies the lower part of the kidney above, the psoas below. In the great majority of bodies only the front and sides of the descending colon are covered ])j peritoneum (Fig. 779) ; the posterior surface, being destitute of a serous coat, is connected to the posterior wall of the abdomen by areolar tissue. In a small proportion of cases, on the other hand, the serous coat is com- plete, and the colon is furnished with a short mesentery. Up to tlie foiu'th or fifth month of foetal life the descending colon has a complete investment of peritoneum and a long mesentery. After the fifth month the mesentery adheres to, and soon Wends with, the parietal peritoneum on the j^osterior abdominal wall, and is completely lost as a rule. The persistence of this mesentery, in a greater or less degree, explains the occasional presence of a descending mesocolon in the adult. Sigmoid Flexure and Rectum. — It was formerly customary to divide the remaining portion of the lai'ge intestine into sigmoid flexure and rectum. The former was said to begin at the crest of the ilium, to lie in the iliac fossa, and to end at the brim of the pelvis. Or, in later years, the " sigmoid colon " was described as " that part of the colon which is attached to the left iliac fossa, fr'om the iliac crest to tlie bidm of the true pelvis" (Symington). Its upper part was said to be covered by peritoneum on the anterior and lateral surfaces only, its lower part THE COLON. 1085 to form a large loop with a complete seroiLS coat and a long mesentery, whicli hung doA\Ti into the pelvic cavity when the bladder and rectum were empty, and passed up out of it when these were distended. The rectum was described as beginning at the brim of the pelvis, opposite the left sacro-iliac joint, and as ending at the anus. It was divided into three portions, of which the fii-st extended from tlie brim of tlie pelvis to the middle of the third piece of tlie sacrum, liad a complete covering of peritoneum, and was connected to tlie pelvic wall by a mesentery — the mesorectum. The second and third parts of the rectum we may pass over for the present, as they agree in general with the descrijition of the rectum given below. Treves in 1885, and Jonnesco in 1889, directed attention to the fact that no such loop as the classical sigmoid flexure, lying in the iliac fossa, was to be found in nature ; and also, that the separation of the first portion of the rectum from the sigmoid flexure — so-called — was both artificial and inaccurate. They pointed out that the " first part of tlie rectum " really belongs to the sigmoid flexure, with which it lias everything in common, and that on no grounds could it be properly assigned to the rectum. An unbiassed study of the parts concerned, particularly in bodies the viscera of which have been hardened in situ, will leave little doubt on an unprejudiced mind that the old descriptions are not only artificial but erroneous. Consequently, the admirable account of this part of the intestine, given by Jonnesuo, will be followed in its main features in descriliing the divisions of the bowel lieretofore known as the sigmoid flexure and first part of the rectum. Jonnesco, recognising that this portion of the intestine lies partly in the iliac fossa and partly in the pelvis, very approi^'iately calls the former the iliac; colon and the later the pelvic colon. The iliac colon includes the portion of the " sigmoid flexure " wliich extends from the crest of the ilium to the inner side of the psoas muscle (that is practically the brim of tlie pelvis), and is usually destitute of a mesentery. The pelvic colon embraces the remainder of the "sigmoid colon" and the first part of the rectum, both of which are attached by a continuous mesentery, and form one large loop lying in the pelvic cavity, and ending at the level of the third sacral vertebra by passing into the rectum proper. Iliac Colon (colon iliacum). — This corresponds to the portion of the " sigmoid flexure " which lies in the iliac fossa, and it has no mesentery. It is the direct continuation of the descending colon, with which it agrees in every detail, except as regards its relations. Beginning at the crest of the ilium, it passes downwards and somewhat inwards, lying in front of the iliacus muscle. A little way above Poupart's hgament it turns inwards over the psoas, and ends at the inner border of this muscle by dipping into the pelvis and becoming the pelvic colon (Fig 769). It usually measures about 5 or 6 inches (12-5 to 15 cm.) in length, but it varies consideralily in this respect. Relations. — Be- hind, it lies upon, and, as a rule, is con- nected by areolar tissue to, the front of the ilio-psoas muscle. In front, it is usually covered by coils of small intestine, which hid(ut from view; but when distended, or it occupies a position tliitu it comes into contact with Cut edge of peritoiieuiii Situation of intersigiiioid- fossa Pelvic colon turning down Pelvic mesocolon Beginning of rectum Pelvic colon Bladder- Fio. 770. — Tni: Ii.iac and I'ki.vic Coi-uns, from ii fonnaliii-lianleiieil male l>o(ly, ageil 30. The pelvic colon was unusually long ; its coui'se is shown, as well as that of the beginning of the rectum, by dotted lines. It first runs across the upper surface of bladder to the right pelvic wall, then recrosses the pelvis in a line posterior to its first crossing ; finally it returns towards the middle line, and passes into the rectum. As a rule, after crossing to the right side of the pelvis, tlie pelvic colon turns backwards and inwards to i-each the nnddlc line, where it passes into the rectum. when lower usual, direct the anterior abdom inal wall. As a rule (90 per centof bodies — Jonnesco),it is covered by peritoneum ouly 1086 THE DIGESTIVE SYSTEM. on its anterior and two lateral surfaces. Occasionally (10 per cent of cases) it is com- pletely covered, has a short mesentery (1 inch, 2 to 3 cm.), and is slightly movable. In its course it passes down over tlie iliac fossa near its middle, generally forming a curve witli its concavity directed inwards and upwards, and having readied a point 1^ or 2 inches (4 to 5 cm.) above Poupart's ligament, it turns inwards across the psoas towards the pelvic cavity. Occasionally the iliac colon occupies a lower position than usual, and runs along the deep surface of Poupart's ligament, immediately behind the anterior abdominal wall. Pelvic Colon (colon pelvinum). — This corresponds to the portion of the " sigmoid flexure " which Lies in the pelvis, together with the so-called " first part of the rectum." The pelvic colon is a large coil of intestine, which begins at the inner border of the left psoas muscle, where it is continuous with the iliac colon, and ends at the level of the third sacral vertebra by passing into the rectum proper. Between these two points it has a well-developed mesentery, and forms a large and variously-shaped coil, which usually lies in the cavity of the pelvis (93 per cent). "Whilst the loop of the pelvic colon is very irregular in form, the following may be given as perhaps its most common arrangement. Beginning at the inner margin of the left psoas, it first plunges over the brim into the pelvis, and crosses this cavity from left to right ; it next bends backwards and then returns along the posterior wall of the pelvis towards the middle Kne, where it turns down and passes into the rectimi (Figs. 769 and 770). Relations. — In its passage into the pelvis it crosses the external iliac vessels ; in running from left to right across the cavity, it rests on the bladder or uterus, according to the sex ; whilst above it lie the coils of the small intestine. It is completely covered by peritoneum, and is furnished with an extensive mesentery — the pelvic mesocolon — -which permits of considerable movement. Sometimes, when longer than usual (Fig. 770), the pelvic colon, in returning from the right side of the pelvis, crosses the middle line, going even as far as the left wall, and then turns back a second time towards the middle of the sacrum, Avhere it joins the rectum at the usual level, thus making an S-shaped curve within the pelvis. On the other hand, when the loop is short (a not infrequent occurrence), all its curves are abridged, and it fails to pass over to the right side, but runs more or less directly backwards after entering the pelvis. From what has been said it will be seen that the loojj of the pelvic colon is subject to numeroiis and considerable variations, which are chiefly dependent upon its length and that of its mesentery, and also ujjon the state of emjDtiness or distension of itself and of the other pelvic viscera. When the intestine is long the loop is more complex ; when short, more simple. When the bladder and rectum are distended, or when the ^^elvic colon itself is much distended, it is unable to find accommodation in the true pelvis, and consequently it passes up into the abdominal cavity, almost any part of the lower half of which it may occupy. But, as already stated, in the great majority of cases (92 per cent, according to Jonnesco) it is found after death lying entirely within the pelvic cavity. In length, the pelvic colon generally measures about 16 or 17 inches (40 to 42'5 cm.), but it may be as short as 5 inches (12 cm.), or as long as 35 inches (84 cm.). The pelvic mesocolon, which corresponds to both the sigmoid mesocolon and the meso- rectum, is a fan-shaj)ed fold, short at each extremity, and long in its middle ^^ortion (Figs. 769 and 770). Its root is attached along an inverted V-shaped line, one limb of which runs up close to the inner border of the left psoas, as high as the bifurcation of the common iliac artery (or often higher) ; here it bends at an acute angle, and the second limb descends over the sacral promontory and along the front of the sacrum to the middle of its third j^iece, where the mesentery ceases, and the pelvic colon passes into the rectum. Wlien the pelvic colon ascends into the abdominal cavity this mesentery is doubled uji on itself, the side which was naturally posterior becoming anterior. Intersigmoid Fossa (recessus intersigmoideus). — When the pelvic colon witli its mesentery is raised upwards, a small orifice will iisually be found beneath the mesentery, corresjaond- ing to the apex of the V-shaped attachment of its root to the posterior abdominal wall. This orifice leads into a fossa which is directed upwards, and will often admit the last joint of the little finger. It is known as the intersigmoid fossa, and is due to the imjjerfect blending of the mesentery of the descending colon of the foetus with the parietal i^eritoneum. In the foitus this mesentery is well developed, and extends from the region of the vertebral column out towards the descending colon. After a time it begins to unite with the underlying parietal peritoneum ; but in the region of the intersigmoid fossa the union is rarely perfect, hence the presence of the fossa. In the child at birth only the terminal part of the pelvic colon lies in the pelvis. This is chiefly owing to the small size of the pelvic cavity in the infant. Beginning at the end of the iliac colon, the pelvic colon generally arches upwards and to the right across the THE EECTUM. 1087 abdomen towards the right iliac fo.ssa, wliere it forms one or two coils, and then passes down over the right side of the pelvic lirini into the pelvic cavity. In cases of imjjerforate anus, it is important to remember, in connexion with the ojjeration for forming an artificial anus, that, whilst the iliac colon is found in the left iliac region, the pelvic colon (" sigmoid flexure ") usually lies on the right side, and passes over the right jtortion of the Ijrim to enter the pelvis. Structure of the Pelvic Colon. — Only tlie arrangement of the muscular coat need be referred to. As the tteiiiie of the desijemliiig colon are followed down, it will be found that the postero- external band gradually j^asses on t