7 COMPARATIVE MORPHOLOGY OF VERTEBRATES. 



nexion with the hyomandibular rays of the elasmobranchs. There are five 

 branchial arches, the last more or less reduced. Often they bear teeth on their 

 inner surfaces, thus acting as accessory chewing organs. 



FIG. 76. Side view of skull of mackerel (Scomber} after Allis. For letters see fig. 68. 



The chondrostei, the most shark-like of the GANOIDS, have no cranial cartilage 

 bones. They are also primitive in the great development of the rostral cartilage 

 (enormous in Polyodon), which gives the mouth its ventral position, and in the 



FIG. 77. Chondrocranium of Polypterus, after Budgett. a, afferent artery to external 

 gills; ft 1 - 4 , branchials; e, efferent artery from external gills; Ib, labial cartilage; 2, 5, 7, 

 nerve exits; other letters as in fig. 69. 



extension of the cranial cavity into the ethmoid region. They have a few bones in 

 the visceral skeleton, while there are numerous membrane bones in the roof of 

 the skull, a few of them readily homologized with those of other vertebrates. 



