494 



DISSECTION OF THE THOKAX. 



relations. 



To see the 

 inter- 

 vertebral 

 substance. 



Inter- 

 vertebral 

 discs : 



form and 



connec- 

 tions ; 



FIG. 180. INTERVERTEBRAL SUB- 

 STANCE IN THE LUMBAR REGION 

 WITH ITS LAMIN.E DISPLAYED. 



a. Superficial, and b, deeper 

 layer, the fibres in the two taking 

 different directions. 



pedicle. The hinder surface of the ligament is in contact with the 



dura mater ; and between the band and the centre of the bodies are 



intervals where large veins issue from the bones. The fibres are 



arranged as in the anterior liga- 

 ment ; and they are more closely 

 united with the intervertebral sub- 

 stance than with the bone. 



Dissection. To see the inter- 

 vertebral discs, the anterior and 

 posterior common ligaments must 

 be taken awa} r ; and to show their 

 structure, one disc should be cut 

 through horizontally (fig. 182), 

 while another is to be divided 

 vertically by sawing through the 

 bodies of two vertebrae (fig. 181). 

 The intervertebral substances or 

 discs (fig. 180) are placed between 

 the bodies of the vertebrae, with 

 the exception of the atlas and axis. 

 Each disc is a flattened or slightly 

 biconvex plate (fig. 181), which 



is firmly united to the adjacent surfaces of two bodies ; and its form 



and size are determined by the bones between which it lies. It is 



connected in front and 



behind with the an- 

 terior and posterior 



common ligaments ; and 



on the sides, in the 



dorsal region, with the 



stellate and interarticu- 



lar ligaments of the 



ribs. 



In the sections that 



have been made the 



intervertebral substance 



is seen to consist of 



two different parts, 



an external, firm and 



laminar, and an in- 

 ternal, soft and pulpy 



(fig. 181). 

 outer part of The outer laminar 



Lmni- P art ( fi g- 182 ' a ) f rmS 

 more than half of the 



disc. The laminae are 



disposed concentrically, but do not form complete rings ; and they 

 are attached by their edges to the bodies of the vertebrae (fig. 18 1, a). 

 They are composed for the most part of white fibro-cartilage ; but 

 the superficial ones consist of fibrous tissue. The fibres are parallel 



structure ; 



FIG. 181. VERTICAL SECTION OP THE INTER- 

 VERTEBRAL SUBSTANCE. 



a. Peripheral laminar part. 



b. Central pulpy part. 



