PISCES FISHES. 



525 



of the eye have special nerves appropriated to them, and those pre- 

 cisely the same as in the highest Mammalia. The third pair of 



Fig. 232. 



nerves animates them all, except the external rectus and the superior 

 oblique ; and also sends off filaments to be distributed to the cho- 

 roid, although no ophthalmic ganglion has yet been discovered. 

 The fourth pair is exclusively appropriated to the superior oblique ; 

 and the external rectus, or abductor muscle, invariably receives its 

 supply from the sixth pair. 



(565.) To animals whose eyes are constantly washed by the 

 water in which they live any lachrymal apparatus would obviously 

 be superfluous ; and consequently, in the class before us, neither 

 lachrymal gland, nor lachrymal puncta, nor even eyelids properly so 

 called, are ever met with. 



(566.) Behind the optic lobes of a fish's brain the ganglia from 

 which the other cerebral nerves emanate become confused into one 

 mass, so that they are no longer distinguishable from each other. 

 The nerves themselves, however, are easily recognised, and, with 

 the exception of the ninth pair (the lingual or hi/poglossal nerves), 

 which are not met with in fishes, both in their distribution and 



