80 SKELETON. 



Of these there are four oblique or articulating processes, which 

 articulate with the corresponding ones of the bones, above and 

 below; two transverse processes, which project, one on either 

 side, from between the oblique processes; and one spinous pro- 

 cess, which is placed on the middle of the bone behind. The 

 two oblique, and the transverse process on each side, come from 

 a common base or root that arises from the lateral posterior part 

 of the body, and present collectively a very irregular appear- 

 ance. Their faces and inclinations are much modified in the 

 several vertebrae. The spinous process is also much modified 

 in regard to size, shape, and inclination. 



The body and processes form the periphery of the foramen 

 for the spinal marrow, and, by their thickness and strength, 

 afford an excellent protection to the latter. This spinal fora- 

 men is of a triangular shape, presenting its base in front and its 

 apex behind. It is considerably larger than the spinal marrow 

 of the part, including its vessels, membranes, and the nerves 

 that proceed from it; in this respect the foramen differs very 

 materially from the cavity of the cranium, which is exactly 

 filled by the brain. 



At the upper part of the spinal foramen of a vertebra, between 

 the body and the upper articulating, or oblique process, is a 

 groove. There is another groove between the lower oblique 

 process and the body. These grooves, by the approximation of 

 the contiguous vertebrae, are converted into perfect holes, called 

 inter-vertebral foramina, and are for the transmission of the 

 spinal nerves and blood vessels. 



The bodies of the vertebrae are extremely light and spongy, 

 being formed principally of the cellular matter of bone, and are 

 covered, with the exception of their upper and lower surfaces, 

 with a very thin lamella of compact substance. The processes, 

 for the most part, have a thick and compact structure, enabling 

 them to sustain conveniently the weight of the body and the ac- 

 tion of the different muscles, as applied to them. 



Of the Cervical Vertebra, generally. 



The cervical vertebrae differ among themselves, but are dis- 

 tinguished by certain common properties from the other bones, 



