1 8 THE VERTEBRAL COLUMN. [chap. 1 



the addition of a thin disk-like epiphysis at each end, which 

 for a considerable period after it is fully ossified remains 

 adhering by a rough surface to the central or main part 

 of the body, and is easily separated from it by maceration. 

 Its coalescence with the remainder of the body, especially in 

 the thoracic region, is one of the last acts in the completion 

 of the bony skeleton, and does not take place until after all 

 the epiphyses of the limb bones are firmly united. Hence 

 it may be taken as a safe indication that the animal is 

 thoroughly adult. 



It must be noted that the epiphysis covers the whole 

 surface of the end of the body, whether ossified from the 

 centrum or the arch, and is therefore quite independent of 

 the position of the neuro-central suture. 



These terminal epiphyses to the bodies of the vertebrae 

 are peculiar to the Mammalia, but not found universally 

 throughout the class, as they are wanting in the Ornitho- 

 delphia and the Sirenia. In man, the highest apes, and also 

 in some of the Didelphia, they have less solidity and import- 

 ance than in other Mammals, being often mere thin osseous 

 rings, representing the circumferential portion only of the 

 ordinary epiphysis. 



The various processes of the vertebra have been divided 

 into those that are autogenous, or formed from separate 

 ossific centres, and exogenous., or outgrowths from either of 

 the just-mentioned primary vertebral constituents. 



There can be no doubt but that an autogenous process 

 of one vertebra of an animal may be serially represented 

 by an exogenous process in another vertebra of the same 

 animal; 1 and likewise that the corresponding processes of 



1 Even the arches of some of the caudal vertebras appear to be 

 ossified directly from the body, and not independently, as is the rule 

 with the thoracic and lumbar vertebrae. 



