660 PISCES. 



so that they are no longer distinguishable from each other. The nerves 

 themselves, however, are easily recognized, and, with the exception of the 

 ninth pair (the lingual or Tiypoglossal nerves), which are not met with 

 in fishes, both in their distribution and number precisely accord with 

 those with which the human anatomist 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 ophthalmic branch (fig. 319, 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 in- 

 ferior maxillary branch (0), destined to the lower jaw : the general 

 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 

 (ji) 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 inter- 

 costal nerves, and supplying the muscles of the fin and the fin-rays 

 themselves. 



(1818.) This branch is superficial until it reaches the little muscles 

 that move the fin. It has sometimes other branches, equally superficial, 

 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. 



(1819.) The seventh pair of cerebral nerves (fig. 319, s s), in fishes 

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

 to the sensorium the impressions of sound. 



(1820.) The sense of hearing in these creatures must necessarily be 

 very imperfect : they have neither an external ear nor a tympanic 

 cavity, and consequently are entirely destitute of a membrana tympani 

 and of the ossicles of hearing ; they have neither Eustachian tube nor 

 fenestra ovalis ; the labyrinth alone, and that more simple in its com- 

 position 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. 



(1821.) The accompanying figure (fig. 323) represents the ear of a 

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

 difficulty in at once recognizing 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 sides with the 

 same kind of oily or mucilaginous fluid which fills up the wide inter- 



