in the Fish Gallery of the Indian Museum. 2 1 



OUS skeleton characteristic of the Sharks and Rays. 

 Although there are also several modifications of these 

 two types, some of which are more or less intermediate 

 between them, it is here sufficient to consider these two 

 common types, as illustrated by the labelled skeletons 

 in Case 9 of the Cod-fish and Dog-fish. 



The skeleton of the Cod is of the well-ossified or bony 

 type, and as all the bones are named, the present des- 

 cription refers only to its general composition. 



It consists of two portions, namely : (1) the axial skele- 

 ton including the jaws, hyoid bone, branchial arches 

 proper, and ribs, and (2) the skeleton of the appendages. 



The Axial Skeleton consists of (1) the skull, or brain- 

 case, and (2) the backbone, which replaces the notochord, 

 and in which the remains of the notochord are imbedded. 



The skull includes (1) the segmented brain-case, or 

 cranium, (2) the bones that enclose the organs of the 

 special senses — nose, eye, and internal ear, (3) the bones 

 of the palate and jaws, and (4) the bones that support and 

 cover the gills or breathing-organs. Observe (1) that 

 the cranium forms much the smaller part, and that the 

 bones of the mouth and breathing-organs form much 

 the larger part, of the skull ; (2) that the bones of the 

 mouth and gill-cover are slung from the skull, on either 

 side, by a large hyomandibular ; (3) that the five pairs of 

 branchial -arches (of which only the first four bear gills) 

 are slung from the base of the skull. 



The backbone consists of a chain of rather simple 

 vertebrae, to some of which, behind the first, a pair of 

 ribs are attached. Those in front that bear ribs are 

 known as abdominal vertebra, those behind that have no- 

 ribs are known as caudal vertebra. Observe that the 

 backbone appears to end abruptly at two large plates of 

 bone of nearly equal size that support the caudal fin,, 

 forming what is known as a homocercal tail. 



