Notes upon the Brain of the Alligator. 137 



be traced superficially dorsally to the eminentia acustica, protrud- 

 ing into the ventricle. It soon divides into two diverging trunks, 

 the posterior of which, as already seen, perforates the vagus 

 ganglion ; the anterior was not traced. Beneath the anterior eighth, 

 somewhat ventrad and candad to the main trunk, is the simple 

 seventh root. It passes cephalad parallel to the anterior portion of 

 the fifth, behind the orbit, to the facial region. 



The sixth nerve, situated almost directly ventrad of the eighth, 

 consists of two separate fibre clusters, the anterior one containing 

 three, the posterior two fibres. Its course is the usual one. 



The fifth nerve preserves the usual relations, its sensory and motor 

 strands entering at once the gasserian ganglion, from which 

 emerges the common trnnk. The division into a superior and 

 inferior branch takes place at once, the inferior division giving off 

 a small branch to the masseteric region, then passing to the infe- 

 rior maxillary, where it divides, the larger branch perfora- 

 ting the inferior maxillary and supplying its alveoli, the smaller 

 being distributed to the adjacent muscular insertions. The upper 

 branch gives off branches to the eye-ball and passes behind the 

 latter to the facial region, where it subdivides. No special descrip- 

 tion of the peripheral distribution of the third and fourth nerves is 

 necessary, as their course seems to correspond closely with that of 

 other vertebrates. The chief hiatus left by Rabl-Rueckhard has 

 thus been filled. 



II. — Histology and Description of Sections. 



1. The commissures of the cerebrum. Three sets of fibres com- 

 mingle at the level of the anterior commissure (a). The uppermost 

 or c alios sal band \s well displayed in a transverse section in front of 

 the chiasm (Plate VIII., Fig. 9), as a strongly arched, compact 

 group of apparently commissural fibres dipping downward from 

 the lower inner margin of the median portion of the mantle, form- 

 ing a sharp upper curvature to ascend to the corresponding portion 

 of the mantle of the opposite hemisphere. Its fibres radiate in all 

 directions, especially anteriorly, and apparently pass chiefly to the 

 ventrical wall of the mantle, but their exact relation to the fibres 

 next to be described must be left for the present undecided. 

 (b) A loop crosses from one hemisphere to the other beneath 

 the callosum, which is thought to represent the rudiment of 

 the fornix. In close connection with this is a fibre tract which 

 lies approximately parallel to the median fissure, and pursues an 



