CRANIAL NERVES OF CAECILIANS 515 



ventral border of the ophthalmic are the abducens nerve and the 

 ramus palatinus VII. The ophthalmic ganglion i.s somewhat 

 lenticular concavoconvex in cross-section, the concavity toward 

 the brain (figs. 23, 24, gop.) The ramus ophthalmicus profundus 

 emerges from its extreme anterior end (figs. 22, 44, op.). 



2. The ramus mandibularis V 



As stated above, the nerve leaves the lateral ventral border of 

 the Gasserian ganglion directly opposite the entrance of the root 

 (figs. 25, 26, 7nd.), passing out through a notch in the anterior 

 border of the proximal part of the pterygdquadrate bone. Curv- 

 ing ventrally around the base of the pterygoquadrate, it passes 

 between the anterior mesial and the posterior lateral divisions of 

 the masse ter muscle (figs. 25, 26) and then enters the lower jaw 

 through a foramen in the dorsomedial border of the gonial bone. 

 Within the jaw it divides into: a) a posterior ramulus intennan- 

 dibularis which passes out through a foramen in the ventromedial 

 part of the gonial to supply the intennandibular muscle and the 

 skin overlying it (figs. 25. 44, md.5); h) a ramulus alveolaris 

 (md.^a.) that soon unites with the ramus alveolaris VII (alif.), 

 which has entered a canal in the gonial considerably farther pos- 

 teriorly (figs. 24-20, 16, 15) ; c) the main nerve, ramulus mandi- 

 •bularis externus {md.Jf), that passes anteriorly in a space between 

 the gonial and the dentary bones, soon in a canal in the dentary, 

 in which it runs as far as the symphysis. The combination of 

 the two alveolar nerves {alv. + md.^a), composed of somatic 

 and visceral sensory fibers, runs at first along the dorsal border 

 of Meckel's cartilage (figs. 23, 22) ; farther anteriorly, as the 

 gonial decreases in size, in a groove in the medial border of the 

 dentary (figs. 21, 20, 16, 15) as far as the symphysis. It and its 

 branches are distributed to the bases of the teeth of the lower 

 jaw, and presumably to the lateral epithelium of the floor of the 

 mouth. The ramulus mandibularis externus innervates the 

 skin overlying the lower jaw. In the larval stage of Ichthyophis 

 the ramulus mandibularis externus V, runs not within the mandi- 

 ble, but along its lateral border, accompanied by the ramus 

 mandibularis externus VII (r. mentalis externus). 



