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The appendicular skeleton includes the bones of the thoracic girdle and forelimbs and the pelvic girdle and hind limbs (see Table 1).
The axial skeleton consists of the bones of the skull, vertebral column, ribs, and sternum (Fig. 3).
Bones of the Thoracic Limb
The thoracic girdle consists of paired scapulae and clavicles (Fig. 11). The scapula is large, whereas the clavicle is often reduced. The dog's clavicle (see Figs. 11, 13) is a small oval plate located cranial to the shoulder beneath the tendinous intersection in the brachiocephalicus muscle. The clavicle is one of the first bones to show a center of ossification in the fetal dog, but in the adult it is partly cartilaginous. It is frequently visible in dorsoventral radiographs of the trunk, medial to the shoulder joint.
The scapula (Figs. 4, 5), a flat, roughly triangular bone, possesses two surfaces, three borders, and three angles. The ventral angle is the distal or articular end which forms the glenoid cavity, and the constricted part that unites with the expanded blade is referred to as the neck.
The lateral surface (Fig. 4) of the scapula is divided into two nearly equal fossae by a shelf of bone, the spine of the scapula. The spine is the most prominent feature of the bone. It begins at the dorsal border as a thick, low ridge and becomes thinner and wider toward the neck. In all breeds the free border is slightly thickened, and in some it is everted caudally. The distal end is a truncated process, the acromion, where part of the deltoideus muscle arises. On a continuation of the spine proximally the ornotransversarius attaches. The remaining part of the spine provides a place for insertion of the trapezius and for origin of that part of the deltoideus that does not arise from the acromion.
The supraspinous fossa is the entire surface cranial to the spine of the scapula. The supraspinatus arises from all but the distal part of this fossa.
The infraspinous fossa, caudal to the spine, is triangular, with the apex at the neck. The infraspinatus arises from the infraspinous fossa.
The medial or costal surface has two areas. A small proximal and cranial rectangular area, the serrated face, serves as insertion for the powerful serratus ventralis muscle. The large remaining part of the costal surface is the subscapular fossa, which is nearly flat and usually presents three straight muscular lines that converge distally. The subscapularis arises from the whole subscapular fossa.
The cranial border of the scapula is thin. Near the ventral angle the border is concave as it enters into the formation of the neck. The notch thus formed is the scapular notch. The dorsal end of the cranial border thickens and, without definite demarcation at the cranial angle, is continuous with the dorsal border.
The dorsal border extends from the cranial to the caudal angles. In life it is capped by a narrow band of cartilage, but in the dried specimen the cartilage is destroyed by ordinary preparation methods. The rhomboideus attaches to this border.
just proximal to the ventral angle, the thick caudal border bears the infraglenoid tubercle, from which arise the teres minor and the long head of the triceps. The middle third of the caudal border of the scapula is broad and smooth; part of the subscapularis and long head of the triceps arise from it. Somewhat less than a third of the dorsal segment of the caudal border is thick and gives rise to the teres major.
The ventral angle forms the expanded distal end of the scapula. The adjacent constricted part, the neck, is the segment of the scapula ventral to the spine and dorsal to the expanded part of the bone that forms the glenoid cavity. Clinically, the ventral angle is by far the most important part of the scapula, since it enters into the formation of the shoulder joint. The glenoid cavity articulates with the head of the humerus. Observe the shallowness of the cavity.
The supraglenoid tubercle is an eminence at the cranial part of the glenoid cavity. The tubercle shows a slight medial inclination on which a small tubercle, the coracoid process, can be distinguished. The coracobrachialis arises from the coracoid process, while the biceps brachii arises from the supraglenoid tubercle.
Palpate the borders of the scapula, spine, acromion, and supraglenoid tubercle.
The humerus (Fig. 6) is located in the arm, or brachium. This bone enters into the formation of both the shoulder joint and elbow joint. The shoulder joint is formed by the articulation of the scapula and humerus; the elbow joint by the articulation of radius and ulna with each other and with the humerus...
|The Skeletal and Muscular Systems||6|
|The Neck, Thorax, and Thoracic Limb||119|
|The Abdomen, Pelvis, and Pelvic Limb||172|
|The Nervous System||310|