102 Journal of Comparative Neurology. 



crad, while Fig. 2 of the same plate is a horizontal section 

 through the same region. 



In sections at one side of the me<lian line the habena ap- 

 pears as a triangular body perched ui)on the Meynert's nidulus, 

 which latter gives origin to Meynert's bundle, which here, as in 

 fishes, consists of medullated fibres and "gelatinous tracts." 

 These separate and arch laterad only to collect in the locus in- 

 terpeduncularis at which point no very distinct nitlulus occurs. 

 The tract of the post-commissure lies ventro-ce[)halad of 

 the ojjtic ventricle and is passing toward the dorsal longitudinal 

 fascicle. 



The ruber occupies a triangular space cephalo-ventrad of 

 Meynert's bundle and extends ventrad of the latter. There is a 

 distinct nidulus ventrad of the pre-commissure. h^ibres from the 

 the dorsal peduncle gather about the ruber and evidently effect 

 new combinations. There is a band ascending through the ru- 

 ber to the brachia, as in fishes. It probably originates from a 

 branch of the infra-commissure. h"ar laterad what seems to be 

 the homologue of the internal geniculate appears just caudo-me- 

 sad of the external. 



None of the sections show any tracts in the course of the 

 pre-preduncles of the cerebelluni as described for fishes. An 

 oblique series of longitudinal sections affords clear testimony to 

 the fact that the optic brachia rather than optic tracts are closely 

 associated with the geniculate and infra-commissure. 



In all well [)repared horizontal sections the region of the 

 pes corresponding to the base of the hypoaria of fishes contains 

 the same large branching "switch-cells" which we have de" 

 scribed. This region, "locus niger, " we regard as the point 

 where motor fibres of the ventral peduncles from the cerebrum 

 effect connections with the mid-peduncles of the cerebellum. 



Jlic midbrain of turtles is characterized by the grest devel- 

 opment of the ventricles and a(]ueduct, the whole structure be- 

 ing simplified and extended longitudinally. 



The grey matter of the prethalamus (/.r., region of chiasm) 

 is collected in concentric bands about the ventricle ventrally. 

 Dorsally the infra-habenaria occiii)y the triangular protuberance 



