1, Trapezius, cervical portion; 2, trapezius, dorsal portion; 3, outline of the scapula; 4, spine of the scapula; 5, latissimus dorsi; 6, small posterior serratus; 7, prominence caused by the costiform processes of the lumbar vertebræ; 8, serratus magnus; 9, external oblique; 10, pectoralis major (sterno-humeral); 11, mastoido-humeralis; 12, atlas; 13, atlas; 14, parotid gland; 15, sterno-mastoid muscle; 16, infrahyoid muscles; 17, omo-trachelian or acromio-trachelian muscle; 18, deltoid; 19, brachialis anticus; 20, triceps, long head; 21, triceps, external head; 22, olecranon; 23, radialis (anterior extensor of the metacarpus); 24, anterior iliac spine; 25, gluteus maximus; 26, gluteus medius; 27, biceps cruris; 28, semitendinosus; 29, gastrocnemius; 30, tensor of the fascia lata; 31, fascia lata covering the triceps of the thigh; 32, patella; 33, ischio-coccygeal muscle; 34, superior ischio-coccygeal; 35, lateral ischio-coccygeal; 36, inferior ischio-coccygeal.] The aponeurosis by which the great dorsal arises from the vertebral column covers, as in man, the muscles which occupy the grooves situated on each side of the spinous processes--the spinal muscles or common muscular mass, if we regard them as a whole (Fig. 70, 7); the sacro-lumbar and the long dorsal muscles covering the transverse spinal, if we consider them as distinct. It would be superfluous to enter here into a detailed examination of these muscles. If they are but little developed the spinous processes become prominent under the skin; if they are more so they may by their thickness project beyond the level of these processes, and these latter thus come to lie in a groove more or less marked, which, on account of the division which is determined by its presence, has caused the regions which it occupies to be designated by the names _double back_ and _double loins_. The muscles are extensors of the vertebral column. Under the aponeurosis of the great dorsal muscle there is found in man another muscle, the serratus posticus inferior, which, on account of being deeply placed and its slight thickness, offers nothing of interest in connection with the study of external form. It arises from the spinous processes of the three last dorsal vertebræ and those of the three first lumbar; it then passes upwards and outwards, and divides into four digitations, to be inserted into the inferior borders of the four last ribs. We repeat that it is covered by the great dorsal muscle. In the pig, ox, and horse, which have this latter muscle less developed in its posterior portion, the same small serratus muscle, known as the _posterior serratus_, is visible in the superficial layer of muscles (Fig. 69, 6; Fig. 70, 6). The number of its digitations is more or less considerable according to the species examined.