CRANIAL NERVES OF CAECILIANS 519 



4- Small nerves arising from the Gasserian ganglion 



Besides the two main trunks from the Gasserian gangUon there 

 are a few small nerves that require mention. One of these arises 

 from the lateral border of the ganglion nearly dorsal to the exit 

 of the ramus mandibularis. It is somatic sensory and, after 

 dividing within the outer cranial wall, its two branches run an- 

 teriorly, pass around the anterior border of the external expansion 

 of the pterygoquadrate bone, and go out through foramina in the 

 postfrontal bone, the larger ventral branch sending twigs an- 

 teriorly and posteriorly to the skin in the region of the angle 

 of the mouth, the smaller dorsal division going anteriorly (figs. 

 25-23, 7nd.2). In other amphibians (Amphimna, Siren) a 

 somatic sensory branch of the ramus mandibularis has a similar 

 distribution. 



At about the same level with the preceding nerve, but arising 

 from the dorsal side of the ganglion, a second sensory nerve 

 (figs. 23-20, 44, Vd) passes immediately dorsally between the 

 ventral border of the parietal bone and the dorsal trabecular 

 bone, then through a canal in the parietal. It divides in the 

 canal and, on emerging from the skull, is distributed to the skin 

 in the dorsolateral region. This is a nerve which in amphibians 

 generally is referred to by writers as 'dorsal fifth.' 



Directly dorsal to the exit of the ramus itiaxillaris a small 

 nerve passes anteriorly and slightly dorsally which merits special 

 consideration. As will be noticed later, the facial nerve con- 

 tributes a dorsal component {VII lid.) to the fifth nerve, which 

 can be traced from the brain through the root of the seventh 

 nerve (fig. 28) into what appears to be a distinct ganglionic mass 

 on the posterior dorsal border of the Gasserian ganglion (figs. 

 27, 44, gild.). From this small mass of ganglion cells a nerve 

 strand (os) passes anteriorly into the Gasserian ganglion proper. 

 This is sharply differentiated by its much darker color from the 

 fiber tracts of the trigeminus (figs. 26-23). After leaving the 

 Gasserian ganglion it runs anteriorly, dorsal to the ramus max- 

 illaris, in the space between the temporal and masseter muscles, 

 taking a position at the lateral edge of the orbitosphenoid region 



