RAMUS MANDIBULARIS VII. 155 



truncus hyomandibularis are given off to the operculum 

 through the r. opercularis superficialis and the r. hyoideus. 

 Goronowitsch states ('96) that these cutaneous fibres are 

 not present in Ganoids, though from the descriptions and 

 figures of Allis ('97) it is probable that they are present in 

 Amia. Goronowitsch accounts for their presence in tele- 

 osts on the supposition that the suspensory apparatus has 

 been pushed forward into the territory innervated by the 

 trigeminus. This supposition may be correct, and yet 

 the prime motive for the entrance of fibres from the Gas- 

 serian ganglion into the truncus hyomandibularis is to be 

 sought rather in the backward growth from the hyoid 

 arch of the opercular apparatus. The way in which these 

 fibres enter the hyomandibularis, as well as their periph- 

 eral distribution, go to show that they have been ceno- 

 genetically carried back by the growth of the operculum. 

 The cutaneous twigs from the trigeminus which overlie 

 the opercular canal and the preopercular bone (the infra- 

 orbital branch io. 2) have apparently also been involved 

 in this backward movement. The skin overlying the 

 cephalic end of the preopercular bone is not, however, 

 innervated from these hyomandibular fibres, but from 

 recurrent twigs from the r. mandibularis V, viz., from 

 the anastomosing branch V- VII. i. We have as yet no 

 definite knowledge of any case where the skin of the facial 

 region is innervated from the facial roots. The general 

 cutaneous fibres which Strong describes as joining the 

 truncus hyomandibularis of the tadpole from the gangli- 

 onic complex of the IX and X nerves and distributing 

 with the r. hyoideus and the r. mandibularis externus are 

 most puzzling, especially in view of the fact that the oper- 

 culum of the tadpole is known to grow back over the gills 

 very much as in the fishes. 



