22 A Guide to the Zoological Collections 



The form and composition of the individual vertebras 

 can be learnt from the labelled specimens of abdominal 

 and caudal vertebrae mounted alongside the skeleton. 

 Each of these consists of an hour-glass-shaped body or 

 centrum, hollowed at both ends. From the dorsal sur- 

 face of the body two neural plates arch up and meet 

 above the spinal cord (which they encircle), to form a 

 neural spine. 



From the ventral surface, also, of the body of the 

 caudal vertebra a pair of haemal plates, almost exactly 

 like the neural plates, descend and meet to form a 

 haemal spine : in the haemal arch, or space between the 

 haemal plates, the main artery of the body runs. 



In the case of the abdominal vertebra the haemal 

 arch is replaced by a pair of ribs. 



Besides the neural and haemal processes and spines 

 there are articular facets by means of which (i) the 

 neural processes of the different vertebras are articu- 

 lated together, and (2) the ribs, when present, are arti- 

 culated with the vertebra that carries them. 



The Appendicular Skeleton relates to the paired fins. 

 The pectoral fins are suspended from the head by means 

 of a very complicated shoulder-girdle, from which the 

 fin-rays radiate without the intervention of any bones 

 corresponding to an arm. The ventral fin-rays are 

 attached in the same way to a pair of simple pubic 

 bones. 



[The rays of the unpaired fins are loosely connected 

 with the neural or haemal spines of the vertebras by a 

 series of interspinous bones.] 



The skeleton of the Dog-fish represents the cartila- 

 ginous type. 



