Vertebral Column 1 1 



time connecting the bodies strongly together, so that very little movement is possible 

 between adjacent bones, although considerable power of motion of the column as a 

 whole results from the presence of a number of segments. Each disc consists of a 

 peripheral annulus fibrosus of fibrous tissue more or less concentrically arranged, 

 surrounding a softer and more elastic nucleus pulposus. The disc is fastened to layers 

 of hyaline cartilage which cover the upper and lower surfaces of the vertebral bodies : 

 the hyaline cartilage ossifies in part as an epiphysis to the body, so that these surfaces 

 of the body present an epiphysial plate in the shape of an incomplete ring (Fig. 5). 



In the foregoing general account of a vertebra the terms " arch " and " body " 

 have been used in their ordinary descriptive sense. It is necessary, however, to say 

 that the term " centrum " is frequently used in the same sense as " body," but that it 

 does not mean quite the same, being really a more strictly accurate term for nearly 

 the whole of the " body." To understand the difference it is necessary to go a little 

 way into the development of a vertebra. The bone is laid down in cartilage which 

 afterwards ossifies, and looking at it in its early stages it can be appreciated at once 

 that there are two main parts in it the " centrum " 

 and the " neural arch " (in two pieces). But when 

 the fusion occurs the distinction is not so evident, 

 yet it can be understood if it is remembered that 

 the rib is only carried by the neural arch and does 

 not articulate with the centrum. This being so, 

 the junction of the two parts the neuro-central 

 suture, as it is termed must lie in front of the 

 articulation with the head of the rib, and yet the 



part that carries this head belongs in a varying FIG- . A dorsal vertebra from a new- 



, ., , . .. ,, , , ,, . , born child. N.N. are the two 



degree to the descriptive body, as will be seen halves of the neural arch, joining 



when dealing with the several vertebrae. the centrum, c at the neuro- 



_. ,. ,? , ., , , ,, central suture A. C. Observe that 



The difference between the values ot the terms the rib only articulates with A. 



is not great from the point of view of description, ^ inctuoSi"* i^hT "des^ri tive 



but in the interests of accuracy it should be borne in body." 



mind, and the word " centrum " ought only to be 



used when the morphological entity which lies between the neuro-central sutures is 

 definitely meant ; on the other hand, the word " body " is conveniently applied to 

 the whole mass that lies in front of the free pedicles. 



Regions of the Column. 



The vertebral column is divided into regions in which the vertebrae show 

 characteristic modifications. The most nearly typical region is that which carries the 

 movable ribs, and is called dorsal : the dorsal vertebra: are twelve in number. 



Above this, in the neck and supporting the skull, are seven cervical vertebrae, 

 while between the dorsal region and the pelvis are five lumbar segments. Below these 

 are five sacral vertebrae, fused together to form the sacrum and firmly fixed between 

 the bony side-walls of the pelvis, and the sacrum rapidly tapers below to give place 

 to the degenerated coccyx : the coccygeal vertebrae are usually four in number. The 

 presacral segments are often termed the " true vertebras," the sacrum and coccyx 

 being then called " false vertebrae." The column can thus be analysed as follows : 

 7 Cervical V.j 



12 Dorsal V. [24 presacral V. + 5 sacral V. -f 4 coccygeal V. = 33 V. 

 5 Lumbar V. ) 



Of the presacral vertebrae, the dorsal form less than half, the lumbar less than a third, and the 

 cervical a fifth or more in the recent column. 



