526 PISCES FJSHES. 



number precisely accord with those with which the human ana- 

 tomist is familiar. We have already traced the third, fourth, 

 and sixth pairs to the muscles of the eye. The fifth issues through 

 the great ala of the sphenoid, and divides, as in man, into an oph- 

 thalmic branch (fig. 229, a), which runs through the orbit to be 

 distributed to the parts about the nose ; a superior maxillary 

 branch (|3), that supplies the parts about the upper jaw ; and an 

 inferior maxillary branch (^), destined to the lower jaw : the ge- 

 neral distribution of the nerve, as far as regards the face, is in fact 

 exactly similar to that of the same nerve in man ; but in fishes it is 

 found to give off other branches not met with in the human subject, 

 one of which (p) is destined to the operculum. Another () 

 takes a very remarkable course : it mounts up to the top of the 

 skull, joins a large branch of the eighth pair (0), and, issuing from 

 the cranium through a hole in the parietal and interparietal bones, 

 passes along the whole length of the back on each side of the 

 dorsal fin, receiving twigs from all the intercostal nerves, and sup- 

 plying the muscles of the fin and the fin-rays themselves. 



This branch is superficial until it reaches the little muscles that 

 move the fin. It has, sometimes, other branches equally superfi- 

 cial, which descend to the anterior parts of the muscles of the trunk 

 above the pectoral fins ; and others, which run as far as the anal fin, 

 where they form a longitudinal nerve similar to that of the back. 



(567.) The seventh pair of cerebral nerves (fig* 229, s, *) in 

 fishes, as in all other Vertebrata, is devoted to the organ of hearing, 

 and brings to the sensorium the impressions of sound. 



(568.) The sense of hearing in these creatures must necessarily 

 be very imperfect ; they have neither an external ear nor a tym- 

 panic cavity, and consequently are entirely destitute of a membrana 

 tympani, and of the ossicles of hearing : they have neither Eusta- 

 chian tube nor fenestra ovalis ; the labyrinth alone, and that more 

 simple in its composition than the labyrinth of the human ear, is 

 all that the anatomist meets with in this first appearance of an 

 auditory apparatus among the Vertebrate classes. 



The accompanying figure (fig. 233) represents the ear of a very 

 large fish, the Lophius piscatorius ; and the student will have little 

 difficulty in at once recognising all the parts of which it consists. 

 The soft parts of this simple ear are not enclosed in bony canals, as 

 in the human subject ; but the membranous labyrinth is lodged in 

 a wide cavity on each side of the cranium : so that little dissection 

 is necessary to expose the entire organ, which is surrounded on all 



