Mammalia: Skin, Muscles. Skeleton 



.-)<n 



. TRANSVERSOSPINALIS., 



TRANSVERSE PROCESS, 

 M. QUADRATUS 

 LUMBORUM 



LONGISSIMUS 0ORS1. 



M. RHOMBOIDEUS. 



SERRATUS POSTERIOR. 

 , SCAPULA. 



LATISSIMUS I 



GLENOID CAVITY. 



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 elongated, but there is con- 

 siderable variation in length. At one extreme is the giraffe, at the other 



