[6] For the definition of the word _hoofed_, see p. 37.
This is the cause why the border to which it is fixed is so slightly noticeable under the skin in these animals; indeed, in the upper part, the bone and cartilage are not distinguishable in the contour of the corresponding region of the back; being applied to the lateral surfaces of the spinous processes, the prominence formed by the extremities of which is directly continuous with the plane of the scapula (Fig. 16).
[Illustration: FIG. 12.--LEFT SCAPULA OF THE HUMAN BEING, POSTERIOR SURFACE, PLACED IN THE POSITION WHICH IT WOULD OCCUPY IN THE SKELETON OF A QUADRUPED.
1, Cervical border; 2, spinal border; 3, axillary border; 4, supraspinous fossa; 5, subspinous fossa; 6, scapular spine; 7, glenoid cavity; 8, coracoid process; 9, acromion process.]
[Illustration: FIG. 13.--LEFT SCAPULA OF A HORSE: EXTERNAL SURFACE.
1, Cervical border; 2, spinal border--the scapula here represented, being from a hoofed animal, has a cartilage of extension attached to its spinal border; 3, axillary border; 4, supraspinous fossa; 5, subspinous fossa; 6, spine of the scapula; 7, glenoid cavity; 8, coracoid process. The scapula of the horse has no acromion process, but it is easy, if we compare the human scapula, to judge of the position which this process would occupy if it were present.]
In quadrupeds whose scapula, on the contrary, is wanting in the cartilage of prolongation (in the _clawed_,[7] such as the cat and dog), the superior border of the scapula is visible, especially when the animal is resting on its fore-limbs, particularly when it crouches; at such a time the skin is markedly raised by that border; and the spinous processes of the vertebræ, beyond which it projects, occupy the bottom of a fossa (Fig. 15). The internal surface of the scapula is turned towards the ribs; it is known, as in man (in whom this surface is anterior), as the subscapular fossa.
[7] For the definition of this word, see p. 37.
[Illustration: FIG. 14.--VERTICAL AND TRANSVERSE SECTION, AT THE SITE OF THE SHOULDERS, OF THE THORAX OF THE HORSE (DIAGRAMMATIC FIGURE).
1, Outline of the thorax at the level of the third dorsal vertebra; 2, 2, scapula; 3, spinal border of the scapula; 4, cartilage of prolongation; 5, contour of the skin.]