THE SKELETON. 



485 



divided into distinct regions, nor has it anything corre- 

 sponding 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 arises, as usual (see p. 431), from para- 

 chordals, trabecule, sense capsules, etc. 



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 in connection with the 

 jaws. 



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



Fig. 204. — Side view of skate's skull. 

 — After W. K. Parker. 



P., First labial cartilage; n.c, nasal capsule; a.o. , antorbital ; 

 p.pt.q., palato-pterygo-quadrate; M.c, Meckel's cartilage; 

 k.m., hyo-mandibular; e./t., epi-hyat ; c.h., cerato-hyal ; h.h. y 

 hypohyal ; A.^n 1 - 5 , hypobranchials ; c.br., cerate-branchial ; 

 e.br., epibranchial ; p-br*., first prebranchial ; i.h., inter-hyal ; 

 fn.pt., meta-pterygold ; 2, 5, 7, foramina of exit of the corre- 

 sponding nerves. 



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. 



From the ear capsule to the articulation of upper and 

 lower jaw there extends on each side a club-shaped cartilage, 

 which connects the jaws with the skull, known as the 

 hyo-mandibular or suspensorium. It is the upper half of 

 the second arch. Attached to it is a slender four-jointed 

 rod — the lower half of the hyoid arch. 



Then follow five branchial arches, each primarily four- 

 jointed, forming the framework of the gill-bearing region. 



