THE SKELETON. 63 



seventh, and eighth vertebrae the chevron bones unite 

 ventrally in the middle line, forming an arch. The last 

 ten caudal vertebrae are scarcely more than cylinders of 

 bone representing the bodies of the vertebrae. 



The number of vertebrae in the different species of 

 mammals varies widely. As a rule, there are seven 

 elements in the cervical region. The sea cow (Manatus) 

 has only six cervical vertebrae, while the three-toed sloth 

 has nine. The number of thoracico-lumbar varies from 

 sixteen in the orang to thirty-six in the cetacean Del- 

 phinus. The elements composing the sacrum likewise 

 vary from one in the ape, Cercopithecus, to nine in some 

 of the Edentata. The human sacrum is composed of 

 from four to six vertebrae. The same is true of the 

 gorilla, chimpanzee, and orang. The caudal vertebrae 

 vary greatly in number in the different forms. In the 

 adult human there are present only four or five vertebrae, 

 which form a single bone, the coccyx, while in the embryo 

 eight segments make up the caudal region. Ossification 

 takes place, however, in only five or six segments. 



THE STERNUM. 



The sternum of the cat is composed of eight pieces, 

 called sternebrae, which lie in the median line on the 

 ventral side of the chest (Fig. 21). The sternum serves 

 for the attachment of the cartilaginous portions of nine 

 pairs of ribs. The first sternebra (Fig. 28), which ends 

 cephalad in a laterally compressed pointed process, is the 

 manubrium. The six succeeding sternebrae form the body 

 or gladiolus ; the caudal piece is called the ensiform or 

 xiphoid process. It is terminated by a flat piece of carti- 

 lage. The cartilaginous portion of the first rib articulates 

 with the manubrium near its middle. The ribs from the 



