346 FISHES. 



and sometimes the tubular character of the edge is continued as in the 

 lotus, and in several of the silures, on one of its sides, into a tentaculum 

 (feeler) of greater or less size. At other times these edges do not 

 exist, as we see in the sombres, in which, moreover, the posterior orifice 

 is a vertical line. 



The nostrils of lophius, by a remarkable singularity, are supported 

 like mushrooms, each on a small stalk ; the head of this sort of mush- 

 room contains the cavity of the nostril, which opens in the usual way, 

 by two small orifices, 



In some, the posterior opening is under the lip ; this is the case in 

 some foreign congers, a coincidence sufficiently remarkable with what 

 occurs in the sirens and proteus. 



In the species in which the fossa is round the folds of the pitui- 

 tary membrane which line it, are disposed like radii of a circle round a 

 centre or short line* ; but in those in which the fossa is oblong or elonga- 

 ted, they are ranged on each side of an axis, forming very regular combs, 

 or rather representing the feathers of a quill. Their number and the 

 amount of their prominency vary much ; they can scarcely be seen in 

 the lump-fish : in the perch, for example, they are only sixteen in 

 each nostril ; in the turbot twenty-four ; in the conger or eel, they 

 are almost innumerable, on each side of a salient axis, which runs 

 along the entire length of the internal surface of the tube of the nostril. 

 The rays themselves are subdivided into small branches in the stur- 

 geon, and perhaps even in other species ; in a word, the surface of 

 this membrane is multiplied in various ways. 



This surface is furnished with numerous fine vessels, secreting an 

 abundant mucus with which their intei'vals are filled. 



The olfactory nerve, coming out from the anterior tubercles of the 

 brain, sometimes single, sometimes double, sometimes divided into 

 filaments, varying in length and size, according to the species, goes to 

 the posterior or convex surface of the nostril. It varies a good deal as 

 to its course, and as to the manner in which it arrives at its destination. 

 In certain fishes, such as the tetrodon, it is very slender ; in others, 

 as the cod, it is slender, but double or triple. In the ray and squalus, 

 it is thick and single, and sometimes so much, so as to seem but an 

 appendix of the brain ; in the tunny it is simple, also, throughout its 

 entire length. In the perch, it is divided into two in its middle, and its 

 filaments are multiplied in the neighbourhood of the nostril. In the 

 turbot and in lophius, it is divided from its origin near the brain, into 

 several filaments. In the conger and eel, it is divided almost from 

 its origin into two large trunks, which give each successively a great 

 number of branches, subdivided into smaller ramifications for all the 

 lamellae of their long nostril. 



In several genera, the olfactory nerve, as we have said, when it 

 arrives at the nasal fossa, swells to the size of a ganglion ; this we see 

 in the cod, carp, and in the cypiins generally. 



* The olfactory nerves, and the nostrils of the perch detached from the bones, 

 are shown pi. VII. fig. 2. One of the nostrils is entire and opened, to show the 

 rays : the other is cut in the middle to shew the distribution of the nerve to the 

 membrane. 



