. The chordates. Chordata. Mammalia: Skin, Muscles. Skeleton .-)<n . TRANSVERSOSPINALIS., TRANSVERSE PROCESS, M. QUADRATUS LUMBORUM LONGISSIMUS 0ORS1. M. RHOMBOIDEUS. SERRATUS POSTERIOR. ,SCAPULA. LATISSIMUS I GLENOID MANUBRIUM STERN Fig. 458. Thoracic and lumbar muscles of man as seen in cross section. Thoracic muscles on the right, lumbar on the left. The muscle arrangement is fundamentally like that of any mammal. (After Braus. Courtesy, Neal and Rand: "Chordate Anatomy," Philadelphia, The Blakiston Company.) ventral surface of the thoracic and lumbar regions of the ve
. The chordates. Chordata. Mammalia: Skin, Muscles. Skeleton .-)<n . TRANSVERSOSPINALIS., TRANSVERSE PROCESS, M. QUADRATUS LUMBORUM LONGISSIMUS 0ORS1. M. RHOMBOIDEUS. SERRATUS POSTERIOR. ,SCAPULA. LATISSIMUS I GLENOID MANUBRIUM STERN Fig. 458. Thoracic and lumbar muscles of man as seen in cross section. Thoracic muscles on the right, lumbar on the left. The muscle arrangement is fundamentally like that of any mammal. (After Braus. Courtesy, Neal and Rand: "Chordate Anatomy," Philadelphia, The Blakiston Company.) ventral surface of the thoracic and lumbar regions of the vertebral column extend longitudinal muscles whose action opposes that of the longissimus dorsi. The shortest of the vertebral muscles extend only from one vertebra to the next, representing a single primary segment of the body. They attach either to similar or to unlike parts of the adjacent vertebrae (interspinales, intertransversarii, transverso- spinales). Longer muscles extend over distances of two or more vertebrae. NECK The vertebrate head is equipped with important sense-organs whose value to the animal is increased if their relation to external space can be altered—that is, if the animal can "look about" or "listen" in a particular direction. There is also a mouth furnished with teeth whose primary use is the grasping of food rather than the chewing of it. The advantage of possessing a neck derives from the free mobility which it gives to the head, thereby enhancing the utility of the sense organs, increasing the facility of getting food, whether plant or animal, and enabling the animal to use the teeth more effec- tively as organs of combat. The neck is well developed in birds, but it seems likely that the ability to look backward while moving forward may be of even greater value to the terrestrial mammal than to the bird, the mammals being, in general, more prone to eat one another than are the toothless birds. In most mammals the neck is well elo
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