70 



COMPARATIVE ANATOMY 



The quadrate, which serves as a support (suspensormm) for the 

 jaws, either remains separated from the skull by an articulation— 

 that is, is only united to it by connective-tissue — or it forms one 

 mass with it. 



The hyoid — which has always close relations with the man- 

 dibular arch,, and may also take part in its suspensorial apparatus i 



Tig. 53. — Diagrammatic! Figdke of an Embryoxic Elasmobeakch Skull, 

 showing the relations of the viscebal arches. 



iV, nasal capsule ; A , eye ; 0, auditory capsule ; Tr, trabecula ; Q and PQ, 

 quadrate and palatopterygoid, which are bound to the trabecula by ligaments 

 at t ; Jf , Meckel's cartilage ; L, labial cartilages ; H, hyomandibular ; K, 

 hyoid arch ; a to e, branchial arches, between which the gill-clefts {I-to V) are 

 seen ; i9, spiracle ; C, notochord ; 6, vertebriE, br, brain ; lip.c, spinal cord. 



— becomes divided, as do the true branchial arches, into a number 

 of segments, the upper of which in many Fishes is distinguished as 

 the hyomandibular (Fig. 53), from which a sympkclic may be 

 differentiated distally. In the mid- ventral line there is a basi-hyal 

 connecting the arch of either side, and embedded in the tongue 

 (entoglossal or glossohyal). 



c. The Bones of the Skull. 



It is usual and convenient to distinguish in the entire skeleton 

 between the bones which are formed in connection with cartilage, 

 and eventually replace it to a greater or less extent (^cartilage 



■■ It appears to be probable that the hyomandibular and hyoid proper are 

 separate in origin : possibly also the xjiiracidar cartilage (p. 75), often looked 

 upon as representing fused mandibular rays, represents the remains of an entire 

 arch ; and Dohrn maintains that Meckel's cartilage and the palatoquadi-ate each 

 represents a distinct arch. 



