2 6 Journal of Comparative Neurology. 



dicular sections allow of the best differentiation. In either case 

 the bundle collects into a circular tract which passes without 

 branching through the cephalic division of the hypoaria and 

 then divides into a vast number of small circular bundles. The 

 arrangement is interesting and can best be understood from fig- 

 ures 1-4, Plate IV. Fig. i shows the passage of the bundle 

 into the base of the hypoarium where the fibres diverge in arches 

 much as the fingers might close about an apple, except that each 

 finger is represented by a series of bundles in the meridianal 

 plane passing toward the surface. In this region the fibres make 

 connection with the peculiar bifurcate cells of the hypoaria. 

 This takes place in the cortical part of the hypoarium and the 

 fibres which arise from the other limb of the cells pass dorsad, 

 enter the medullary portion, and effect combinations with several 

 other systems. The nature of the combinations is well illus 

 trated on Plate IX and will be discussed under the head of the 

 hypoaria. Suffice at present to say that there is direct connec- 

 tion with the cerebellum and indirect connection with the dorsal 

 tract. Immediately caudad of the margin of the hypoaria is the 

 pons region with the commissura ansulata and decussatio teg- 

 menti. There can therefore be no doubt that the hypoaria be- 

 long in the region of the pes pedunculi and the outer or cortical 

 portion may be regarded as a cellular modification of the crusta 

 while the medullary cellular region contains the homologue of 

 the tegmentum with the nigra and ruber. The specific homo- 

 logue of the ruber is apparently found in the nucleus rotundus, 

 Fritsch. 



3. The dorsal peduncle. The fibres which collect from the 

 occipital and temporal lobes or, in general, from the caudal and 

 caudo- lateral portions of the axial lobes form a stronger bundle 

 than the ventral peduncle and pass with the latter into the thala- 

 mus; but instead of curving ventro-laterad after passing the chiasm 

 they continue caudad until in the vicinity of the nidulus ruber 

 and nidulus subthalamicus, into both of which they send a strong 

 contingent by a sudden lateral flexture. Some of the fibres 

 seem to continue into the ventro-lateral fascicle of the medulla 

 and these may be derived from the ventral bundle, but of this it 

 is at present impossible to be sure. In any case it is but a small 



