IOWA ACADEMY OP SCIExNCE 139 



by two distinct roots corresponding to the arrangement of the glom- 

 eruli, but that the fibers so combine that all indications of their origin 

 are lost in the long nerve trunk. Similarly in Spelerpes it is impos- 

 sible to distinguish between the anterior and posterior groups of fibers 

 in their destination. The absence of a Jacobson's organ in Necturus 

 makes an important difference between the olfactory nerve of that form 

 and that of Spelerpes, in which there is a special branch to the struc- 

 ture in question. Were the absence of a Jacobson's organ in the Pro- 

 teidae, although information on this point is lacking for Typhlomolge, 

 to be considered a larval character, there would still remain to be ex- 

 plained the occurence of a well developed Jacobson's organ in the 

 perennibranch Siren. 



In Spelerpes and Necturus the gasserian ganglion is distinct from 

 the auditory and ventral facial ganglia, in marked contrast to the 

 condition in Amphiuma and Siren. Tracing out the three rami mandi- 

 bularis, ophthalmicus profundus and maxillaris to their l)ranches there 

 will be seen very close resemblances in the two forms. The r. md. 

 gives off first large motor branches to the temporal and masseter mus- 

 cles, then a large general cutaneous branch to the side of the head. The 

 main nerve continues along the side of the jaw giving off three to five 

 principal branches to the skin. A general cutaneous branch enters a 

 canal in the lower jaw from the dorsal side and in Spelerpes fuses with 

 a branch of the r. alveolaris VI'I; in Necturus the actual union with 

 the latter nerve was not found but the two come into very close asso- 

 ciation. A branch of motor and general cutaneous composition passes 

 ventrally through the lower jaw and is distributed to the intermandi- 

 bular muscle and the overlying skin. In neither Necturus nor Spe- 

 lerpes does there seem to be any anastomosing between this latter 

 ])rancli and the r. jugularis VII such as occurs in Amblystoma (Cog- 

 hill, 1902) and Plethodon (Norris, 1909). The r. oph. prof, in both 

 species divides into four main branches. Of these the first given off 

 runs dorsally at the inner posterior border of the eyeball. In Spe- 

 lerpes it is much larger and arises farther posteriorly. Its more pos- 

 terioi-- position in the latter form may be explained by the fact of the 

 much larger size of the eyeball. In Spelerpes the trochlear nerve 

 passes to its innervation along a twig of this dorsal branch of the r. 

 oph. prof. An almost exactly similar course seems to occur in Necturus. 

 The three terminal branches of the r. oph. prof, have almost identical 

 modes of origin and distribution in the two species. In neither form 

 was the exact nature of the ophthalmic-palatine anastomosis deter- 

 mined, owing to the nerves at this point being compressed. The ana- 



