48 ELEMENTS OF MAMMALIAN ANATOMY. 
groove. The groove becomes fainter distally and finally 
disappears entirely. The chevron bones are the paired 
ossicles projecting ventrad from the cranial ends of the 
bodies of the vertebre, from the second or third to the 
thirteenth vertebra. In the sixth, seventh, and eighth ver- 
tebre the chevron bones unite ventrally in the middle line, 
forming an arch. The last ten caudal vertebrze are scarcely 
more than cylinders of bone representing the bodies of the 
vertebree. 
The number of vertebre in the different species of mam- 
mals varies widely. As a rule, there are seven elements in 
the cervical region. The sea cow (Manatus) has only six 
cervical vertebrze, while the three-toed sloth has nine. The 
number of thoracico-lumbar varies from sixteen in the 
orang to thirty-six in the cetacean Delphinus. The ele- 
ments 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 vertebre. 
The same is true of the gorilla, chimpanzee, and orang. 
The caudal vertebra 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 sternebre, which lie in the median line on the ven- 
tral 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 craniad 
in a laterally compressed pointed process, is the manu- 
brium. The six succeeding sternebree form the body or 
