14 



parts depend for support and protection. The 

 brief summary of its parts and work that follows 

 here has been adapted from Wilcox and Smith. 



The Skeleton. — This consists of a backbone, 

 skull, shoulder girdle, pelvic girdle, and two pairs 

 of appendages. The backbone may be conven- 

 iently divided into regions, each comprising a cer- 

 tain number of vertebrae. The cervical vertebrae 

 include those from the skull from the first rib. In 

 all mammals except the sloth and sea cow the num- 

 ber of cervical vertebrae is seven, being long or 

 short, according as the neck of the animal is rela- 

 tively long or short. The first and second cervical 

 vertebras, known as the atlas and axis, are especially 

 modified so as to allow free turning movements of 

 the head. 



The next region includes the dorsal or thoracic 

 vertebras, which are characterized by having ribs 

 movably articulated with them. The number is 13 

 in the cat, dog, ox, sheep, and goat; 14 in the 

 hog; 18 or 19 in the horse and ass, and six or seven 

 in domestic poultry. In mammals they are so 

 joined together as to permit motion in several direc- 

 tions, but in poultry the dorsal vertebrae are more 

 rigidly articulated, those next to the sacrum often 

 being grown together with the sacrum. The 

 spines are high and much flattened in all ungulates, 

 long and slender in dogs and cats. They slope back- 

 ward, forming strong points of attachment for the 

 back muscles. Several ribs, varying in number in 

 different animals, meet and become articulated with 

 the breast bone or sternum. The sternum consists 

 of seven to nine articulated segments in our domes- 

 tic mammals, while in fowls the sternum is one 

 thin high bone furnished with a keel of varying 

 depth. The lumbar vertebrae lie between the dorsal 



