THE SPINE. 79 



lumbar portion is convex in front, and concave behind the 

 pelvic and caudal portion is concave in front, and convex be- 

 hind. This arrangement is the result of the different degrees 

 of thickness in the bodies of the vertebrse, and especially in the 

 fibro-cartilages which unite them to each other. Wherever 

 these cartilages are thin at their anterior margin, there is a 

 concavity ; but where they are thick at the same point, there 

 is a convexity. 



There are seven vertebrae to the neck, called cervical; 

 twelve to the thorax, called dorsal; and five to the loins, 

 called lumbar. In reckoning the number of the vertebrae, the 

 one next to the occiput is always the first; and so on, succes- 

 sively, to the last. Albinus, however, has departed from this 

 rule, and counts them from below, upwards. 



General Characters of a Vertebra. 



A vertebra (verttbre) consists in a body, in seven processes 

 or extremities, and in a canal or foramen for lodging the spinal 

 marrow. 



The body of a vertebra is at its fore part ; it is somewhat cy- 

 lindroid or oval, but varies considerably from these figures ac- 

 cording to its position in the spine. The anterior part of the 

 body is convex ; but the posterior part is concave, where it con- 

 tributes to the spinal canal. The superior and inferior surfaces 

 are fiat, with the exception of a ridge of hard bone at the cir- 

 cumference, more elevated, and not so extended in some bones 

 as in others. These ridges are, in young subjects, epiphyses. 

 There are many foramina, large and small, to be seen on the 

 front and back surfaces of the bodies. They transmit arteries 

 and veins, and some of them are used for fastening the liga- 

 ments of the spine. On the posterior face of the body there 

 are two foramina larger than the others, occupied by veins 

 coming from the interior of the vertebra. These veins corre- 

 spond with the diploic sinuses in the head, and have been parti- 

 cularly described by M. Breschet, of Paris, in a thesis present- 

 ed to the School of Medicine in 1819. 



The processes are placed a.t the posterior part of the vertebra. 



