Notes upon the Brain of the Alligator. 135 



The thickened posterolateral border of the ventricle is termed the 

 obex, while outside of this is the clava or dorsal column. It is 

 remarkable that a decided asymmetry is not rare in the medulla ; 

 thus, in the specimen figured, the roots of the left cranial nerves 

 are much further forward than on the right side. 



The oculo-motor nerves spring from a well-defined trigonum 

 interpedunculare, and in other respects the brain does not corre- 

 spond with the figures of Rueckhard. The transition between the 

 medulla and the cervical portion of the cord is very gradual, so that 

 the demarkation must remain vague. 



7. The cranial nerves. Considerable pains has been taken to 

 determine the peripheral course of the cranial nerves, but some 

 details, especially with relation to the accessory and sympathetic 

 fibres, remain obscure. The intervertebral expansions of the cord 

 make it easy to identify the position of the roots in that region. 

 The dorsal protuberance corresponding to the position of the sen- 

 sory root of the first cervical makes the absence of that root the 

 more conspicuous. The spinal accessory -with a strand of the 

 vagus apparently supplies the place of the dorsal roots of 

 both the first spinal and the hypoglossal, as indicated beyond, 

 though perhaps theoretical considerations may make it more 

 probable that it is the part representing the posterior fibres of 

 the vagus which has suffered this modification. This branch 

 emerges with the tenth proper from the jugular foramen, but its 

 deeper course is through an osseus path distinct from that of the 

 vagus. The accessory fibres unite with this portion of the tenth, 

 and, though the common trunk is appressed upon the ganglion 

 vagi, no evidence of actual interblending was observed. This 

 trunk gives off a branch supplying the cervical muscles soon after 

 leaving the foramen ; the larger portion, however, continues for- 

 ward, continuing externally with the vagus and glossopharyngeal, 

 to form a loop with its fellow of the opposite side below the root 

 of the tongue, giving off various branches in its course. Centrally 

 the accessory seems to extend backward as far as the dorsal root of 

 the second spinal (see Plate VII, Figs. 4-5). 



The remaining roots of the vagus unite to form a ganglion vagi 

 of considerable size. Not only does this ganglion contain the 

 fibres of the hypoglossal and glossopharyngeal, but it is perforated 

 by the posterior branch of the eighth nerve. The relations strongly 

 remind one of the condition observed by Ahlborn in Petromyzon. 



