128 BRAIN AND BODY OF FISH 



gustatory mechanism in man ; here the anterior part of the tongue 

 is supphed by the chorda tympani, which represents the branch of the 

 facial nerve passing along the inner surface of the mandible in fish 

 and the taste-buds have a true gustatory function. 



The anatomy of fish and its nomenclature is very much obscured 

 by the fact that the detailed knowledge of human anatomy supphes 

 the terms which are used in describing simpler, but similar, structures 

 in a lower vertebrate, such as a fish. We propose to approach our 

 problem in the reverse direction and follow the simple nervous 

 structure of a fish upwards to the higher vertebrates. If we take 

 the facial lobe of a carp, a typical teleostean fish, we note that the 

 facial lobe hes anteriorly to the vagals, and can be looked upon as a 

 forward extension of the latter, although in this fish the bilobed 

 character of the facial is lost. It receives all the gustatory fibres 

 by the Vllth or facial nerve from the lips, tongue, barbels and body. 

 This nerve, the Vllth, or as it is called by T. H. Huxley, the portio 

 dura, has been described by this great anatomist, in the pike. 

 " The portio dura of the pike, which leaves the skull by a special 

 foramen in the pro-otic bone, traverses the hyomandibular bone 

 and then divides into two branches, one of which runs backwards 

 to the hyoidean arch, while the other is directed forwards and 

 dowTiwards and passes to the inner surface of the lower jaw, along 

 which it runs to the extremity of the ramus." This last branch is 

 represented in Man by the chorda tympani. But, as has already 

 been stated, the facial muscles so important and largely developed 

 in man are not represented at all in fish. Hence, in the latter we 

 might expect to find, only mandibular, and hyoidean branches of 

 the portio dura corresponding with the chorda tympani on the one 

 hand, and the stylo-hyoidean and digastric branches on the other 

 in man. And this is really the case, as the following pages will show. 



The facial nerve in man at once raises the picture of a lop-sided 

 face, due to Bell's paralysis, which is caused by disease affecting this 

 nerve. Sir Charles Bell, the first nem-ologist, insists that this 

 nerve is the respiratory nerve of the face and points out its diminished 

 importance in fish as being due to the absence of facial muscles in 

 these animals. The correctness of this assumption is borne out by 

 the study of the facial lobe in Teleosts, which we have seen is an 

 anterior extension of the vagal lobe. Huxley helps us to under- 

 stand the change in the function of tliis nerve. He points out that 

 the portio dura of the seventh nerve in man perforates the petrous 

 bone, and after skirting the inner wall of the tympanum leaves the 

 skull by the stylo-mastoid foramen. Before it does so it gives off a 

 recurrent branch, the chorda tympani, which takes a very singular 



