Part 7

The floor of the cerebral cavity is bounded caudad by the prominent dorsum sellæ (Fig. 42, _f_; Fig. 43, _g_), just craniad of which is the rounded depression known as the sella turcica (Fig. 42, _g_; Fig. 43, _h_), for lodgment of the hypophysis. A number of foramina pierce the floor of the cavity in this region. Just ventrad of the cranial tip of the petrous portion of the temporal is the small =foramen lacerum= (medius). Craniad and laterad of this is a row of four foramina: the caudal one is the foramen ovale (Fig. 42, _i_); then come in order the foramen rotundum (_j_), the orbital fissure (_k_), and the optic foramen (Fig. 42, _l_; Fig. 43, _k_). The two optic foramina are connected by the shallow transverse =chiasmatic groove= (Fig. 42, _m_), for the optic chiasma. Another small foramen continues caudad from a groove on the floor of the orbital fissure; this opens on the ventral surface of the sphenoid, between the wing and the body of the bone. The groove and foramen constitute the =pterygoid canal=, which transmits a nerve,--the =nerve of the pterygoid canal=, or Vidian nerve.

The cranial cavity narrows at its cranial end to form the small =olfactory= fossa (Fig. 43, _III_) which lodges the olfactory bulbs. This is bounded by the frontals and the lamina cribrosa (Fig. 42, _o_) of the ethmoid; caudad it opens directly into the cerebral fossa. Numerous openings through the lamina cribrosa for the olfactory fibres connect the olfactory fossa with the nasal cavity. The roof of the fossa is marked by a prominent median crest from the united edges of the frontals.

The =nasal= cavity is almost completely filled by the ethmoid and vomer and the conchæ nasales. Its roof is formed by the nasal bones and portions of the frontals; its sides by the frontals, lachrymals, maxillaries, premaxillaries, and palatine bones; its floor by the horizontal plates of the palatines, maxillaries, and premaxillaries.

[Illustration: FIG. 43.--SKULL, MEDIAN LONGITUDINAL SECTION, SHOWING THE CAVITIES.

_I_, cerebellar fossa; _II_, cerebral fossa; _III_, olfactory fossa. 1, occipital bone; 2, interparietal; 3, 3′, parietal; 4, temporal (4, squamous portion; 4′, petrous portion; 4″, tympanic portion); 5, sphenoid; 6, presphenoid; 7, palatine; 8, frontal; 9, maxillary; 10, premaxillary; 11, ethmoid; 12, nasal; 13, incisor teeth; 14, canine; 15, 16, 17, premolars; 18, molar. _a_, condyloid canal; _b_, hypoglossal canal; _c_, jugular foramen; _d_, internal auditory meatus; _e_, appendicular fossa; _f_, tentorium; _g_, dorsum sellæ; _h_, sella turcica; _i_, hamular process; _j_, pterygoid process of sphenoid; _k_, optic foramen; _l_, presphenoid sinus; _m_, _m′_, frontal sinus; _n_, lamina perpendicularis of the ethmoid (broken at cranial edge).]

The nasal cavity opens craniad by the large =nares= (Fig. 39, _j_; Fig. 42, _r_), which are bounded by the premaxillary and nasal bones. In the natural condition this opening is divided by a median cartilage which is continuous with the lamina perpendicularis (Fig. 43, _n_) of the ethmoid, thus forming a partition which divides the nasal cavity into two separate halves. From the floor of the cranial part of the cavity rises a ridge formed of the nasal crests of the maxillaries and premaxillaries, and the cranial portion of the vomer. Farther caudad the vomer spreads out in a horizontal plane and separates from the floor of the cavity, so that the nasal cavity is thereby divided by a horizontal

## partition into dorsal and ventral portions. The ventral portion is

small, forming the inferior meatus of the nose; it ends caudally at the =choanæ= (posterior nares, Fig. 41, _o_) which lead into the nasopharynx. That portion of the nasal cavity lying dorsad of the vomer is almost completely filled by the ethmoid and the conchæ nasales, superior and inferior. It is bounded caudally by the lamina cribrosa of the ethmoid (Fig. 42, _o_). The nasal cavity communicates with the cranial cavity by the foramina for the olfactory fibres in the lamina cribrosa; with the nasopharynx by the choanæ; with the exterior of the body by the nares; with the mouth-cavity by the foramina incisiva or anterior palatine foramina (Fig. 42, _s_); with the orbit by the sphenopalatine foramen and the nasolachrymal canal. It communicates directly also with the frontal sinuses (Fig. 43, _m_, _m′_), the sphenoidal sinuses (Fig. 43, _l_), and with the cells of the labyrinths of the ethmoid.

JOINTS AND LIGAMENTS OF THE SKULL.

=Sutures of the Skull.=--The bones of the skull join each other by means of immovable articulations known as sutures. These sutures are designated by combining the names of the bones between which they are situated: as, =sphenofrontal= suture (=sutura sphenofrontalis=), between the sphenoid and frontal; =nasomaxillary= suture (=sutura nasomaxillaris=), between the nasal and maxillary bones. When a suture joins the two corresponding bones of opposite sides the prefix =inter= is used, as the =intermaxillary= suture (=sutura intermaxillaris=) between the maxillaries. The sutures bounding the parietals have, however, received special names not derived in this manner. The suture caudad of the parietals, separating them from the occipital and interparietal, is known as the =lambdoidal= suture; that between the two parietals is the =sagittal= suture; that separating the parietals and squamous portions of the temporals is the =squamous= suture; that between the parietals and frontals is the =coronal= suture. The suture separating the two frontals also is known as the =frontal= suture, in place of interfrontal.

=Articulations of the Mandible.=--In man the two halves of the mandible are united craniad, so as to form a single bone. In the cat the two halves are separate, but articulate closely at the =symphysis menti= by a thin interarticular cartilage.

The articulation of the mandible at the mandibular fossa of the temporal is covered with a close =articular capsule=. The mandibular fossa is lined with cartilage. A slender ligament passes from the angular process of the mandible caudad to the external auditory meatus, being attached to the latter about 8 millimeters from its medial end. This is the =stylomandibular ligament=.

V. BONES OF THE THORACIC EXTREMITIES.

=Scapula= (Figs. 44 and 45).--The scapula may be described as a flat triangular bone with one angle rounded. It lies beneath the muscles on the lateral face of the thorax near its cranial end. From its lateral surface there projects a flat ridge (Fig. 44, _g_), the =spine= of the scapula. The ventral end of the ridge is free as a curved process, the =acromion= process (Fig. 44, _j_).

[Illustration: FIG. 44.--SCAPULA, LATERAL SURFACE.

FIG. 45.--SCAPULA, MEDIAL SURFACE.

_I_, fossa supraspinata; _II_, fossa infraspinata; _III_, fossa subscapularis; _IV_, fossa for teres major. _a_, vertebral border; _b_, coracoid border; _c_, glenoid border; _d_, glenoid angle and fossa; _e_, coracovertebral angle; _f_, glenovertebral angle; _g_, spine; _h_, tuberosity of the spine; _i_, metacromion; _j_, acromion; _k_, supraglenoidal tubercle; _l_, incisura scapulæ; _m_, coracoid process; _n_, groove indicating portion of spine; _o_, _o′_, ridges for attachment of muscle-fibres.]

The ventral angle of the scapula (_d_), the =glenoid= angle (lateral angle of human anatomy), is much heavier than the others and bears a concave, pear-shaped articular facet, the =glenoid fossa=, for articulation with the humerus. The border with which this angle is more nearly continuous may be called the =glenoid= border (_c_) (axillary border of human anatomy).

Near the narrower cranial end of the glenoid fossa is a small curved projection of the bone, the =coracoid= process (Fig. 45, _m_). The border upon which it lies is the =coracoid border= (_b_) (superior border of human anatomy). The third border is turned toward the vertebral column and is the =vertebral border= (_a_).

The angle between the glenoid and vertebral borders is the =glenovertebral= angle (_f_) (inferior angle of human anatomy), and that between the coracoid and vertebral borders the =coracovertebral= angle (_e_) (medial angle of human anatomy).

The medial or costal surface (Fig. 45) is smooth and nearly flat. A shallow furrow (_n_) marks the position of the spine of the scapula. Between the furrow and the coracoid border are two oblique parallel ridges (_o_ and _o′_) for the insertion of muscle-fibres. Near the glenoid border is a well-marked ridge separating the subscapular fossa (_III_), comprising the greater part of the medial surface of the scapula, from the fossa in which the teres major muscle has origin (_IV_). The surface presents several nutrient foramina usually directed toward the glenoid angle.

The lateral surface (dorsal surface of human anatomy) (Fig. 44) is divided by the spine (_g_) into two portions. The portion of the scapula craniad of the spine and the cranial surface of the spine bound the =supraspinous= fossa (=fossa supraspinata=) (_I_), while the surface caudad of the spine and the caudal portion of the spine bound the =infraspinous= fossa (=fossa infraspinata=) (_II_).

The spine (_g_) begins as a triangular elevated area in the middle of the vertebral margin and runs toward the glenoid angle. It rises gradually for about two-fifths of its length and then the margin becomes broader and the spine remains of the same height to its glenoid end. There is a rough thickening, the =tuberosity= (_h_) of the spine, situated on its free border about midway between the tip of the acromion and the vertebral end of the spine. The spine is inclined toward the glenoid margin so as to form an angle of about 60 degrees with the caudal half of the lateral surface.

At the base of the acromion process (_j_) the margin of the spine presents a flat triangular projection, the =metacromion= (_i_), directed toward the glenoid border.

The acromion (_j_) continues in the direction of the spine. It is thicker than the spine, smooth and rounded on both its surfaces and both its borders, and its apex is connected by fibrous tissue to the clavicle.

The coracoid border (_b_) presents a slight rounded notch, the =incisura scapulæ= or suprascapular notch (_l_), just dorsad of the glenoid angle, and at its ventral end bears the coracoid process (_m_) which is directed ventromediad.

The glenoid angle (_d_) is the only one requiring special mention. Between the root of the coracoid process and the glenoid cavity it presents a tubercle, the =supraglenoidal= or bicipital tubercle (_k_), for the tendon of origin of the biceps muscle. The glenoid angle is separated by a contracted neck from the rest of the bone. Between this angle and the inner margin of the acromion there is left a deep notch, the =great scapular notch=.

[Illustration: FIG. 46.--CLAVICLE.

_a_, medial end; _b_, lateral end.]

=Clavicle.= =Clavicula= (Fig. 46).--The clavicle in the cat is greatly reduced. It is a slender curved rod of bone imbedded in the muscles of the shoulder and connected by fibrous tissue to the apex of the acromion process. The lateral end (_b_) is slightly enlarged.

=Humerus= (Figs. 47 and 48).--The humerus forms the support of the upper arm and articulates by its proximal end with the scapula at the glenoid cavity, and by its distal end with the radius and ulna, the bones of the lower arm. It is a nearly cylindrical bone with enlarged ends, and is so curved that its dorsal and ventral borders are hooked at the opposite ends so that it has the form of an Italic _f_.

The proximal end of the bone bears on its dorsomedial portion a thickening, the =head= of the humerus (_a_), which bears a smooth ovoid articular facet by which the bone articulates with the glenoid cavity of the scapula. The head is not separated from the body by a distinct anatomical =neck= as in the human humerus.

[Illustration: FIG. 47.--HUMERUS, VENTRAL SIDE.

FIG. 48.--HUMERUS, MEDIAL SIDE.

_a_, head; _b_, greater tuberosity; _c_, lesser tuberosity; _d_, bicipital groove; _e_, pectoral ridge; _f_, deltoid ridge; _g_, rough area for insertion of latissimus dorsi and teres major; _h_, nutrient foramen; _i_, capitulum; _j_, trochlea; _l_, coronoid fossa; _m_, radial fossa; _n_, medial epicondyle; _o_, lateral epicondyle; _q_, supracondyloid foramen.]

Along the lateral border of the proximal end of the shaft is a high rough ridge semicircular in side view, the =great tuberosity= (_b_). It gives attachment to muscles and is marked on its dorsal border by a deep depression for the tendon of the infraspinatus muscle. On the medial margin of the proximal end closely associated with the head is a smaller elevation, the =lesser tuberosity= (_c_), also for muscular attachment.

Between the greater and lesser tuberosities on the ventral surface is seen a broad groove, the =sulcus intertubercularis= or =bicipital groove= (_d_), which passes distad onto the surface of the shaft. In the natural state it is converted into a canal by overlying tendons and lodges the tendon of the biceps muscle.

The shaft is nearly cylindrical at its middle, but its dorsoventral diameter is slightly greater than its mediolateral diameter. Its proximal end is flattened mediolaterad, while its distal end is flattened dorsoventrad.

From the ventral margin of the greater tuberosity a ridge, the =pectoral= ridge (_e_), is continued onto the surface of the shaft, and from the dorsal margin another ridge, the =deltoid= ridge (_f_), passes distad and ventrad so as to meet the pectoral ridge near the middle of the ventral surface of the bone. On the medial margin of the bone near the junction of the first and second fourths is a roughened area (_g_) for the attachment of the tendons of the latissimus dorsi and teres major muscles, and on the same surface near the junction of the second and last thirds is a nutrient foramen (_h_).

The distal end of the bone presents a smooth saddle-shaped articular surface, which, in well-marked bones, is divided, when seen from the ventral surface, by a slight nearly median ridge into two unequal portions, lateral and medial (_i_ and _j_). The lateral half is rounded and is called the =capitulum= (_i_). It is broader ventrad than dorsad, and is not continued onto the dorsal surface of the bone. It is for articulation with the proximal end of the radius.

The medial half of the surface, the =trochlea= (_j_), is concave and passes directly into the capitular surface laterad, but is limited mediad by a sharp ridge. It is continued onto the dorsal surface of the bone, where it is limited also laterad by a ridge. It articulates with the semilunar notch of the ulna.

Proximad of the trochlea the dorsal surface presents a deep fossa, the =olecranon fossa=, which receives the olecranon of the ulna when the arm is straightened. On the ventral surface (Fig. 47) are two shallower fossæ separated by a longitudinal ridge. The one over the trochlea receives the coronoid process of the ulna when the arm is bent, and is called thence the =coronoid fossa= (_l_). The one over the capitulum, the =radial fossa= (_m_), receives a triangular facet on the proximal end of the radius at the same time. Between the radial and coronoid fossæ on one side and the olecranon fossa on the other is only a thin plate of bone. On the medial surface of the distal end is a considerable roughened elevation, the =medial epicondyle= (_n_) (epitrochlea). It gives origin to flexor muscles and to the ulnar collateral ligaments of the elbow-joint. Opposite the medial epicondyle over the capitulum is the =lateral epicondyle= (_o_) for the origin of extensor muscles of the forearm and of the radial collateral ligaments of the elbow-joint. From the lateral epicondyle a ridge, the lateral =supracondyloid ridge= (_p_), continues proximad, curving onto the dorsal surface of the bone and ending about opposite the junction of the deltoid and pectoral ridges.

Proximad of the medial epicondyle the bone is pierced near its medial margin by an oblique oval foramen, the =supracondyloid foramen= (_q_).

=Radius= (_I_, Figs. 49 and 50).--In the usual position the radius lies with its proximal end on the lateral side of the arm, articulating with the capitulum of the humerus. The proximal end is thus laterad of the proximal end of the ulna. Its distal end, however, lies on the medial side of the distal end of the ulna, so that the radius in the natural position crosses ventrad of the ulna.

The radius is a curved bone slightly flattened dorsoventrally, with enlarged ends. It may be described as consisting of a shaft and of a proximal and a distal end. Its proximal end presents on the ventral surface a tuberosity, the =bicipital tuberosity= (_c_), for the insertion of the tendon of the biceps muscle. Proximad of this the bone is contracted to form a =neck= (_b_) which is surmounted by a =head= (_a_). The head has on its proximal surface a depressed oval facet by which it articulates with the capitulum, and on its ulnar border a long narrow facet, the =articular circumference= (_d_), for articulation with the radial notch of the ulna; also a triangular facet (_e_), which fits into the radial fossa of the humerus.

The shaft is convex dorsad and concave ventrad. The distal end is somewhat pyramidal. From its medial or radial side a wedge-shaped process, the =styloid= process (_f_), extends distad. The distal surface of the end together with the lateral surface of the styloid process form a concave articular cavity (_g_) which fits against the scapholunar bone.

[Illustration: FIG. 49.--RADIUS AND ULNA, DORSOLATERAL VIEW.

FIG. 50.--RADIUS AND ULNA, VENTROMEDIAL VIEW.

_I_, radius; _II_, ulna. _a_, head of radius; _b_, neck; _c_, bicipital tuberosity; _d_, articular circumference; _e_, facet for radial fossa of humerus; _f_, styloid process of radius; _g_, facet for articulation of scapholunar bone; _h_, semilunar (or great sigmoid) notch of ulna; _i_, coronoid process; _j_, olecranon; _k_, area for insertion of brachialis and clavobrachial muscles; _l_, rough area for attachment of interosseous membrane; _m_, styloid process of ulna.]

The dorsal surface of the distal end is marked by longitudinal grooves for tendons, and its lateral or ulnar surface bears a concave facet for articulation with the ulna.

=Ulna= (_II_, Figs. 49 and 50).--The ulna is a long slender bone, flattened mediolaterad. It is enlarged at its proximal end and becomes gradually smaller toward the distal end.

The proximal end is marked ventrally by a deep excavation, the =semilunar notch=, or =great sigmoid cavity= (_h_). By the saddle-shaped articular surface of the semilunar notch it articulates with the trochlea. This articular surface is divided into two parts by a transverse non-articular area. The distal boundary of the semilunar notch is a blunt process, the =coronoid= process (_i_), which bears on its lateral surface a concave facet, the =radial notch=, for the head of the radius.

The portion of the bone proximad of the semilunar notch is called the =olecranon= (_j_). It fits into the olecranon fossa of the humerus when the arm is straightened, and is rough at its end for the insertion of tendons.

The body of the ulna becomes triangular distad. The distal end is slightly larger than the shaft just proximad of it, and bears on its radioventral side a hemispherical head for articulation with the radius. Distad of the head the bone continues as the flattened =styloid= process (_m_), which projects distad from its dorsolateral side and is smooth on the medial side of its apex, for articulation with the cuneiform bone of the wrist.

=Carpus= (Fig. 51).--The carpus (wrist) consists of seven bones arranged in two rows, three in the proximal row and four in the distal row. Beginning on the medial side of the hand (thumb or radial side), the first bone in the proximal row is the =scapholunar= (_a_) (equal to the scaphoid or navicular and lunar of the human hand). It articulates with the radius. The next is the =cuneiform= (_b_), articulating with the styloid process of the ulna, and the next, which is attached to the cuneiform and projects freely ventrad, is the =pisiform= (_c_).

In the distal row the bone on the radial side is the =trapezium= (_d_); the next is the trapezoid (_e_), the next the os magnum (_f_), and the last the unciform (_g_). The distal row articulates with the metacarpals or bones of the palm of the hand (1-5).

In the kitten the scapholunar is represented by three bones, the =scaphoid= or navicular, on the radial side, the =lunare=, between the scaphoid and the cuneiform, and a =centrale=, which lies distad of the other two.

_Scapholunar Bone._ _Os scapholunaris_ (Fig. 51, _a_).--The scapholunar is a quadrangular bone with the ventroradial angle produced into a blunt process. Its proximal surface is smooth and articulates with the distal end of the radius. The distal end is marked by oblique ridges and articulates with the unciform, os magnum, trapezoid, and trapezium. The ulnar surface articulates with the cuneiform, and the dorsal surface of the ventroradial process with the radial sesamoid.

_Cuneiform Bone._ (_Os triquetrum BNA_) (Fig. 51, _b_).--The cuneiform bone has the form of a flattened pyramid. Its base articulates with the unciform, its proximoulnar surface with the pisiform except at its dorsal margin, where it articulates with the styloid process of the ulna. On its proximoradial surface is a smooth facet for articulation with the scapholunar.

_Pisiform Bone._ _Os pisiforme_ (Fig. 51, _c_).--The pisiform bone is about twice as long as broad, with enlarged ends. Its dorsal end articulates with the cuneiform, and on its proximal surface, separated from the above by a smooth ridge, is a smooth facet for articulation with the styloid process of the ulna.

[Illustration: FIG. 51.--CARPUS, METACARPUS, AND PHALANGES, DORSAL SURFACE.

_a_, scapholunar bone; _b_, cuneiform; _c_, pisiform; _d_, trapezium; _e_, trapezoid; _f_, os magnum; _g_, unciform; _h_, radial sesamoid; _i_, proximal phalanges; _j_, second phalanges; _k_, distal phalanges; 1, 2, 3, 4, 5, metacarpals in order from the radial side.]

_Unciform Bone._ (_Os hamatum BNA_) (Fig. 51, _g_).--The unciform is a wedge-shaped bone with the apex of the wedge directed proximad, and smooth for articulation with the scapholunar. By a part of its ulnar surface it articulates with the cuneiform, and by its radial surface with the os magnum. Its distal end articulates with the fourth and fifth metacarpals.

_Os magnum._ (_Os capitatum BNA_) (Fig. 51, _f_).--The os magnum may be described as an oblong plate bearing on its proximal surface a semicircular ridge which crosses it diagonally. The proximal end of the bone articulates with the scapholunar. Its distal end articulates with the third metacarpal except near its ventroulnar angle, where it articulates with the fourth metacarpal. Its ulnar surface articulates with the unciform. Its radial border articulates with the trapezoid, the third metacarpal, and, by two facets, with the second metacarpal.

_Trapezoid._ (_Os multangulum minus BNA._) (Fig. 51, _e_).--The trapezoid is somewhat wedge-shaped, with the apex of the wedge pointing ventrad. Its proximal side articulates with the scapholunar, its distal side with the second metacarpal, its ulnar side with the os magnum, and its radial side with the trapezium.

_Trapezium._ (_Os multangulum majus BNA._) (Fig. 51, _d_).--The trapezium has the form of a triangular prism curved into a semicircle. The convex face looks proximad and articulates by its ventral half with the scapholunar. The ulnar surface articulates with the second metacarpal dorsally, and ventrally with the trapezoid. Its radial surface articulates with the first metacarpal.

=Bones of the Hand or Manus= (Fig. 51, 1-5).--The _Metacarpals_. _Metacarpus._--The metacarpals are the five bones of the palm of the hand; they are numbered from one to five, beginning with the thumb. They are cylindrical elongated bones with enlarged ends. The distal end is called the head, and the proximal end the base. Each head bears a hemispherical articular facet which is marked over its ventral half by a prominent smooth ridge. The surface dorsad of the ridge articulates with the proximal head of a phalanx. The ridge and the surface at its sides are for a pair of sesamoid bones.

The first metacarpal (1) is the shortest. Its head is oblique, and it articulates by the ulnar half of its proximal surface with the trapezium (_d_); by the radial half with the radial sesamoid (_h_).