38 Journal of Comparative Neurology. 



near (a) Fig. 3, Plate IV, not much ventrad of the commissural 

 portion. It may be presumed that its fibres ultimately reach the 

 nidulus ruber (rotundus) and it would then simply signify a 

 curious deviation from the com. horizontalis with the fibres of 

 which these correspond. There are about 30 very large and 

 well-medullated- fibres. 



In the study of the commissures the composition diagrams 

 formed by drawing the superposed outlines of two transverse sec- 

 tions separated by a small interval and filling in the details on 

 one side from one section, on the other side from the 

 other, prove very useful. Thus Fig. i, Plate XII, has 

 on the left side details from a section immediately cau- 

 dad of the chiasm, while the right side is some dis- 

 tance caudad at the junction of the hypophysis. The out- 

 lines of the second section are distinguished by shading. On 

 the left side a portion of the cuneus and hii)pocampal lobe of 

 the hemisphere remain, on the right, the temporal lobe has be- 

 come distinct and the mesaxial lobe has nearly disajjpeared. 

 On the left the dorsal peduncle is just entering the thalamus. 

 The commissura transversa is cut in the middle and a small por- 

 tion of the inferior commissure is seen. The tuber still retains 

 the fibres which unite with the latter {Tr. till), ad Com. v.) adja- 

 cent to which is the nidulus tuberis dorsalis. On the right side 

 the two peduncles are distinct and separated by a small cell clue- 

 ter, the transverse commissure is seen adjacent to the optic tracts 

 ascending with the latter, but perfectly distinguishable b)' reason 

 of its smaller fibres. The geniculatum is* also well-developed 

 in this region and the tract, tuber, ad com. ventr. is passing 

 from the tuber to join the commissura ventralis on the ventro- 

 mesal aspect of the geniculatum. 



In Fig. 2, we have two sections from regions still farther 

 caudad, similarly composed. On the left side the commissura 

 horizontalis is in section and immediately ventrad lies the dorsal 

 tuber commissure, both of which turn caudad, the former to the 

 nidulus ruber. The commissura minor, which in Fig. i was in 

 section, is now on its way dorsad and on the right side has 

 nearly reached its s])ecific terminus in the interval between the 

 dorsal and ventral optic tracts. On the right side the vent, ped- 



