14 MORPHOLOGY OF THE VERTEBRATA. 



SKULL 



Is composed of cartilage without any trace of sutures, and devoid 

 of membrane bone; it articulates with vertebral column by a 

 median facet. The. maxillae and premaxillse are absent. Teeth 

 «,re developed in the mucous membrane, which covers palato- 

 quadrate and mandible. It is on account of this that these 

 cartilages are so well developed. The anterior end of right and 

 left palato quadrate are connected by ligaments. 



The sympletie is represented by a process of the hyomandi- 

 bular. 



Cartilaginous filaments pass outwards from the branchial 

 and hyoidean arches, and support the walls of the branchial 

 ■sacs. 



Mandibular arch consists of two pieces, the upper one, the 

 palato quadrate, which is articulated to the base of the skull. 



The most anterior part of skull — ethmoidial region — on the; 

 inferior surface of which is a nasal pit on each side. The cephalic 

 cartilage is prolonged forwards between the nasal pits into a 

 rostrum. The succeeding portion of the skull forms the orbits, 

 which is bridged over in front and behind by cartilage. Follow- 

 ing behind the orbital portion is the labyrinthic portion, which 

 encloses the labyrinth or essential organs of hearing. This is 

 continuous behind with the occipital segment. In the middle, 

 line, between the labyrinthic segment and occipital, is a deep 

 depression, at bottom of which are two foramina. 



BRANCHIAL SKELETON 



Supports that part of the alimentary canal which subserves 

 respiration. It is made up of complicated cartilaginous rods, 

 which superiorly are connected with the spinal column by the 

 pharyngo-branchial rods, and ventrally are united with one 

 another by single pieces — the copulse. 



The hyoid arch has the same arrangement as the branchial 

 arches. 



SHOULDER GIRDLE 



Is seen in its simplest form. It is composed of a piece pf cartilage, 

 which forms an arch on either side, being united to its fellow 

 along the ventral median line, and placed just behind the last 

 branchial cleft. The muscles which move the pectoral fins are 

 attached to it. It &gfitib&&il^(ti^os$t>®k-ull. 



