HEADS AND TAILS. 



47 



jaws respectively, and form the arches or sup- 

 ports of the gills and tongue. 



The true skull or cranium forms the receptacle 

 for the brain, and the organs of hearing, sight 

 and smell. It is box- 

 like in form, and 

 hollow. Within its 

 central cavity lies the 

 brain. On the outside 

 of this hex we shall 

 notice two pairs of 

 projections, one pair 

 at its hinder, and one 

 at its anterior end. 

 The former are the 

 capsules which lodge 

 the organ of hearing ; 

 the latter, which have 

 a form something like 

 an inverted saucer, 

 lodge the organ of 

 smell. Between these 

 capsules for the organs 

 of hearing and smell 

 lies a cavern-like hollow for the lodgment of the 

 €ye, and is called the orbit. At the extreme 

 hinder end of the skull is a small hole from 

 which the spinal cord emerges from the brain. 

 So much for the cranium. 



We turn now to the series of arches which, as 

 we have already seen, form the supports to the 

 anterior region of the mouth and the gullet. 

 These are arranged in pairs. The first pair 

 form what we know as the jaws. They differ 



Fig. 5.— Skull of Dog-fish, showing 

 the separate cranium containing 

 the brain and organs of sight, 

 smell and hearing, and the dis- 

 tinct jaws and gill arches. S. 

 skull; Ac. auditory capsule (hear- 

 ing); Oc. olfactory capsule (smell); 

 0. orbit; J. jaws ; A. gill arches. 

 The 1st pair are for the support of 

 the jaws, attaching them to the 

 skull, the 2nd pair, represent the 

 1st pair of true gill arches, the 

 solid supports in the wall of the 

 alimentary canal, p. 20. 



