454 HISTORY OF THE HUMAN BODY 



front and one behind the slit, are known respectively as rami 

 prce- and post-trematici. In this connection it is interesting to 

 see that the spiracular opening, which probably represents the 

 gill-slit next in order anteriorly to the regular series, is simi- 

 larly included between the internal mandibular (chorda tym- 

 pani) and the hyo -mandibular of the Facialis, which thus be- 

 come, respectively, the prce- and post-trematic branches of that 

 nerve. It is even possible in like manner to consider the maxil- 

 lary and mandibular branches of the Trigeminus as similarly 

 related to the mouth opening, resting upon the probability of 

 the identification of the mouth with an original gill-slit anterior 

 to the spiraculum. We have thus a character of great value 

 in the resolution of the cranial nerves into their original meta- 

 meric elements, one which will be considered later in the treat- 

 ment of this difficult and unsolved problem. 



Of these five branchial nerves, the Glosso-pharyngeus, as 

 the most anterior and consequently the most modified (earliest 

 absorbed by the cranium) possesses additional branches not 

 represented in the others, and these have run forward and 

 supply parts anterior to it. One of these is a communicating 

 branch between this nerve and the Facialis and passes from its 

 ganglion (ganglion petrosum) to that of the Facialis (ganglion 

 geniculare) . This nerve possesses no special name in lower 

 forms, other than the generic ramus communicans, but in the 

 higher forms it becomes the tympanic (nerve of Jacobson), 

 and forms an intimate means of communication between these 

 nerves and the Trigeminus. Below this is the palatine, lying 

 near the Facialis branch of the same name, and developing a 

 few connections with it. A small lingual branch is present in 

 the Dipnoi. 



There remains but one further element to be considered, 

 but this is an extensive one, the ramus intestinalis Vagi. This 

 appears in primitive forms as a separate element, with its 

 own ganglion, but in all other cases it arises with the rest of 

 the Vagus and its ganglion becomes lost in the general mass, 

 the ganglion jugulare. This is the branch which, even more 

 than the lateralis, has earned for the nerve to which it belongs 



