DORSAL VERTEB1LE. 



intervevtebral foramina, a series of rounded apertures which communicate 

 with the vertebral canal, and transmit the spinal nerves and blood- vessels. 



The foramen, or space enclosed by the vertebral ring, is bounded anteriorly 

 by the body, and posteriorly and laterally by the arch. The series of rings 

 united by ligaments constitutes the vertebral canal, in which the spinal cord 

 is contained. 



Texture. The bodies of the vertebrae are almost entirely composed of 

 spongy substance, the surface being covered with only a thin layer of compact 

 tissue. Venous canals, commencing at the larger foramina behind, traverse 

 the cancellated structure. The arch and processes contain a much smaller 

 proportion of spongy substance, being covered with compact tissue of con- 

 siderable density in some places. 



CHARACTERS PECULIAR TO GROUPS OP VERTEBR2E. 



The moveable vertebrae are divided into three groups, named from the 

 regions which they occupy, cervical, dorsal, and lumbar. 



Each of those groups is marked by distinctive characters. The central 

 vertebrae of each group differ so much in all their parts from those of 

 other groups, that any portion, such as the body, ring, or one of the pro- 

 cesses, is alone sufficient to indicate to which they belong. On the other 

 hand, the vertebrae at the extremities of each group are assimilated in their 

 characters to those of the neighbouring group. 



In the following description the characteristics of each group, as existing 

 in its central members, will first be given, and then the slighter differences 

 of other members will be stated. 



DORSAL VERTEBRAE. 



The dorsal vertebrae, twelve in number, support the ribs. They are the 

 simplest in form, and ought to be the first to engage the attention of the 

 student. Their position is between the cervical and lumbar groups, and 

 they are also of intern. ediate fcize. 



Fig. 2. THE SIXTH DORSAL VERTEBRA. 4 



A, viewed from above ; B, viewed from the 

 right side. 1, the body; 2, the pedicle; 3, the 

 lamina ; 4, vertebral ring, nearly circular ; 5, 

 spinous process ; 6, transverse process ; 7, 7', 

 superior and inferior articulating processes ; c, c', 

 superior and inferior facets on the body for the 

 articulation of the head of the rib ; c/, facet on 

 the transverse process for the articulation of the 

 tubercle of the rib. 



The body is somewhat narrower in front 

 than behind : its antero-posterior and trans- 

 verse diameters are nearly equal, and ib 

 is somewhat heart-shaped, as seen from, 

 above or below. It is specially characterized 

 by the presence, at the place where it joins 

 the arch, of depressed articular sui faces for 

 the heads of ribs. In the greater number 

 of instances, there are two costal surfaces 

 on each Bide, >. ne on the superior, the 

 other on the inferior border, so placed 

 that each completes with that of the adja- 

 cent vertebra a cavity for the head of one 



