COLD-BLOODED VERTEBRATA 



379 



micus profundus) — passes below them. The first of these 

 nerves corresponds to the two ophthalmics which are con- 

 spicuous in the dogfish — the ophthalmic branch of the 

 seventh cranial nerve and the 

 (superficial) ophthalmic branch 

 of the fifth — closely united. 

 The deep ophthalmic, which 

 is represented in the dogfish 

 by an inconspicuous twig of 

 the fifth nerve, sends branches 

 to the eyeball and runs on to 

 the snout. Although it appears 

 to arise from the fifth, it is 

 really the dorsal root of the 

 nerve whose ventral root is 

 the third (p. 75). The oph- 

 thalmic nerve of the frog is 

 a deep ophthalmic, though the 

 superficial ophthalmic, which 



does not appear as such, is F^- 271. -Transverse sections 

 . F r . .. . ' . through gill arches or a 



perhaps united with it. The 

 ophthalmic of a mammal 

 -divides not far from its origin 

 into a nasal branch, which 

 represents the deep nerve, and 

 a frontal, which may be the 

 superficial nerve. The oph- 

 thalmic branch of the seventh 

 nerve (together with the 

 buccal and external mandibular 

 branches of the same nerve 

 and the lateral line branch of 

 the vagus, which also supply 

 neuromast organs) is lost, with 

 the neuromast organs which 

 it supplies, in the adults of 

 animals higher than fishes. 

 Branches of the lateral line system extend on to the 

 pectoral fins of the skate, and are connected with the 

 exterior by rather long tubules (Fig. 268). The anterior 

 vertebrae are fused into a continuous mass. This, and 



25 



ugh gil 

 dogfish (on the right) and 

 a cod (on the left), showing 

 how Elasmobranchii and 

 Teleostomi differ in respect 

 of these organs. — From 

 Sedgwick, after R. Hert- 

 wig. 



Afferent branchial "artery ; &, 

 branchial arch of skeleton ; bP- 

 and bl 1 , gill lamellae ; /;, skin of 

 the side of the body between the 

 openings of two gill clefts in the 

 shark ; r, cartilaginous gill-ray 

 supporting the septum between 

 two gill pouches in the same ; 

 v, efferent branchial arteries, 

 double in the shark, single in the 

 cod ; z, small tooth-like tubercle 

 (in some Teleosteans elongated as 

 a "gill raker"), one of a double 

 row on the branchial arch of the 

 cod. 



