_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.