96 Journal of Comparative Neurology. 



Figs. 4, 6 of Vol. II.; also Plate XIII, Fig. 4, Plate XII, Fig. 

 8, Vol. I. 



Figs. I and 2, Plate VIII, of the present number illustrate 

 the relations in the black snake. Fig. 12, Plate IX, is a cross 

 section of the black snake and Figs. 4 and 5 are from cross sec- 

 tions of Eutaenia. 



A series of consecutive sections of Tropidonotus give es- 

 pecially clear distinctions between the several miduli. 

 TJie Supra-comuiissural Tract. 



The fibres of the supra-commissure, after passing through 

 the habena in an oblique cephalo-ventral course, arch laterad and 

 follow the lateral margin of the front of the thalamus to a point 

 cephalad of the optic tract and laterad of the peduncles and there 

 cross to the base of the cerebrum. The whole course of this 

 tract from the habena to the post-rhinal lobe can be followed in 

 one oblique section of Tropidonotus. (Fig. i (13), Plate VI.) 

 The path of the fibres in the cerebrum is in the fissure scpnrat- 

 ing the pyriform from the post-rhinal lobe. 



There seems to be little doubt that the fibres are derived 

 from the radix lateralis olfactorii. 



It has seemed to the writer that the coarse fibred tract 

 from the supra-commissure is not accompanied in this course by 

 the finer fibres of the commissura habenaria but it can not be 

 affirmed positively that the latter passes directly cephalad to en- 

 ter the cerebrum at a higher level than its fellow, though such 

 is the appearance. 



The DioicepJialon and MescnccpJialon. It will be convenient 

 to commence the study of these segments by an examination of 

 a series of horizontal sections of the black snake. First, how- 

 ever, a glance at the brain itself, or the sections in the plates, 

 will show that the major part of the roof is composed of two 

 ovid segments corresponding to the nates of anthropotomy. 

 Caudad of these are the buried testes or "corpora posterior." 

 The roof of the diencephalon and its lateral aspects are largely 

 embraced by the mesencephalon and, while the optic tracts 

 cross its lateral aspects in a broad band only slightly penetrating 

 the geniculata. 



