CHAPTEE III. 



TERMINOLOGY AND TOPOGRAPHY OF THE SKELETON. 



In order to readily comprehend tlie subsequent account of 

 the modifications of the skeleton iu the various sub-classes 

 and groups of Fishes, the student has to acquaint himself with 

 the terms used for the numerous bones of the fish skeleton, 

 as well as with their relative position. The skeleton of any 

 of the more common kinds of osseous fish may serve for this 

 purpose ; that of the Perch is chosen here. 



The series of bones constituting the axis of the body, and 

 destined to protect the spinal chord and some large longi- 

 tudinal blood-vessels, is called the vertebral or spinal column ; 

 the single bones are the vertehrce. The skull consists of the 

 bones surrounding the brain and organs of sense, and of a 

 number of arches suspended from it, to support the com- 

 mencement of the alimentary canal and the respiratory 

 organs. 



The vertebra (Fig. 22) consists of a body or centrum (c), 

 with a concave anterior and posterior surface, and gene- 

 rally of several processes or apophyses, as — 1. Two neura- 

 pophyses (na), which, on the dorsal side, rising upwards, form 

 the neural arch over the canal, in which the spinal chord 

 is lodged. 2. Two jjaropqpAysgs (j^a) usually projecting from 

 the lower part of the sides of the body, or two hcema- 

 pophyses (ha) which actually coalesce to form on the ventral 

 side the haemal canal for a large trunk of the vascular sys- 



