THE CEAjSIAL NERVES AND LATERAL SENSE ORGANS OF FISHES. 145 



Now to endeavour to show that the facial nerves of fishes and mammals resemble each 

 other in every minute detail would be to prove far too much. Differences are to be 

 expected, and they certainly exist. The most striking difference is in the existence of a 

 large somatic motor component in the mammalian facial. Assuming that the facial 

 muscles of mammals cannot be derived from visceral arch muscles, upon which I am 

 not competent to offer an opinion, we must regard tliis component as a special develop- 

 ment and characteristic of tlie higher vertebrates. The difficulty re the motor character 

 of the great superficial petrosal has already been alluded to, and a still farther difficulty 

 with regard to this nerve lies in Lenbossek's contention that its fibres are not connected 

 with the cells of the geniculate ganglion. The chorda tympani too, and with it neces- 

 sarily the nervus intermedins, is supjjosed to be partly motor. The absence of a visceral 

 motor ganglion corresponding to tlie post-branchial ganglion of the fish is noteworthy, 

 but it is perhaps represented by the degenerate ganglion described by Gaskell. This is 

 indeed what we should expect, in view of the reduced condition of tl\e hyoid arch and 

 its muscles. 



We thus see that even if the facial nerve of mammals does not correspond detail for 

 detail with the same nerve in lower vertebrates, which is indeed not to be expected or 

 desired, there is yet a sufficient general resemblance between the two to show that they 

 are genetically related. The mammalian facial, in short, bears in its present-day structure 

 undoubted evidence of its descent from the branchial facial nerve of a fish. 



K. Morphology of Jacobson's Anastomosis. 



The morphology of Jacobson's anastomosis, of which I have a new explanation to 

 offer, may be treated of here in connection with the trigemino-facial ganglionic complex, 

 with which I have described it. This anastomosis is essentially a connection between 

 the facial and glossopharyngeal nerves, and, as I shall show, is perfectly homologous in 

 the highest as well as in the lowest vertebrates, and is further a branch of the glosso- 

 pharyngeus which accompanies a branch of the fa(nal. 



Jacobson's anastomosis was first identified in the lower vertebrates by Stannius * in 

 1842 (198). He found it in " Gadiis callarUis " { = G. inorrhua) and described it under 

 the name of the " H. anterior s. gustatorlus.'" The correct explanation of the nerve, that 

 it is in the first place a branch of the Xlth and not of the Vllth nerve, and in the 

 second the joalatine or visceral branch of the IXth, may be deduced even from Stannius's 

 description and figures. Bonsdorff (1S46, 30) confuses Jacobson's anastomosis with 

 the sympathetic, but Jackson and Clarke (1876, 106) correctly consider it to be the 

 pharyngeal division of the glossopharyngeus. Van AVijhe (1882, 222) describes it in 

 Acipenser (p. 237) in almost the same condition as it is in the Cod and Amia, i. e. as 

 connecting the glossopharyngeus with the palatine division of tlie facial. An important 

 and interesting difference, however, is that it jmsses further forwards still and becomes 



* In his later work (1840, 199) he describes the palatinus facialis as being oocasionall}' reinforced by the palatinus 

 glossopharyngei. 



