48o 



FISHES. 



vertebral column develops from the mesodermic sheath of 

 the endodermic notochord. 



The skull is a cartilaginous case, with a spacious cavity 

 for the brain, a large posterior aperture or foramen magnum 

 through which the spinal cord passes, a large ear capsule on 

 each side posteriorly, a similar nose capsule on each side 

 anteriorly, a long snout or rostrum projecting in front, two 

 incomplete regions or fontanelles on the roof. Compared 

 with the skull of a cod or of a higher Vertebrate, that of a 

 skate is simple ; it is not ossified, nor divided into distinct 

 regions, nor has it anything corresponding to the investing 

 membrane bones, which in higher animals are added to 

 the original foundations of the skull, nor do the visceral 

 arches in the skate take part in forming the skull, which 



Fig. 155. — .Side view of skate's skull. (After W. K. 

 Parker.) 



/', First labial cartilage; n.c, nasal capsule; a.o., ant-orbital; 

 Ji./'t.g., palato-pterygo-quadraLe ; lil.c, Meckel's cartilage; h.jii.^ 

 hyo-mandibular ; ejt-., epi-hyal: c.h.y cerato-h^-al ; kJi., hypo-byal ; 

 jL.l)r. 1-5, hypo-branchial; c.^?-. ,cerato-branchial ; ^.^7-.,epi-branchial ; 

 p,br\, first pre-branchial ; i.h., inter-hyal ; ni.pt., meta-pterj-goid ; 

 2j 5i 7. foramina of these ner\'es. 



arises, as usual (see p. 427), from parachordals, trabeculfe, 

 sense capsules, &c. 



The visceral arches are primitively supports for the wall of 

 the anterior part of the food canal, but at least two of them 

 are much modified alike in position and function. 



The upper jaw of the skate is a strong transverse bar, 

 formed from the union of two palato-pterygo-quadrate 

 cartilages. The lower jaw is a similar bar formed from 

 the union of two Meckel's cartilages. 



