OF DENISON UNIVERSITY. 



77 



terior commissure. This commissure, which is so large relatively as 

 to take the place of the corpus callosum of higher mammals, gathers 

 fibres from the entire ventral and occipital region and api>ears to con- 

 tain not only decussating fibres, but a large number of co-ordinating 

 strands. The connection with the olfactory lobes is evident and direct. 

 The pyramidal tracts cross the anterior commissure laterally and form 

 almost immediately a number of separate bundles passing directly 

 dorsad. They may be traced chiefly to the antero-dorsal cortex, 

 though smaller bundles pass caudad and a few isolated fibre tracts from 

 this tract seem to reach the ventro-lateral regions. 



Numerous small bundles decussate in the ventral part of the crural 

 region. 



The course of the fornix seems to be identical with that of the 

 rodents. 



A strong tract from the habenulae follows nearly the same course 

 already described for Arctomys, but the ganglion occupies the very 

 summit of the thalamus, while the ganglion of Meynert's fasciculus 

 occupies the median aspects of the upper part of the third ventricle. 

 The superior commissure is a very short distance cephalad and dorsad 

 from the posterior commissure and its fibres can be readily traced to the 

 ganglion habenulae. A tract passing from the testes to the cerebel- 

 lum was provisionally recognized. 



We have already intimated that the received statements regarding 

 the absence of the corpus callosum are only api)arently true. The 

 microscope reveals the presence of a commissure in the proper posi- 

 tion to receive this name. It is a small fibre bundle dorsad and ceph- 

 alad to the commissure of the hippocampus and is a true cortex 

 commissure. It is not larger relatively than the corresponding bundle 

 in the alligator or turtle and therefore does not impeach the validity of 

 the argument against the common origin of marsupials and other mam- 

 mals. Other details are reserved for an article now under way. 



Details of successive transverse sections through the thalamus and 

 corpora striata. 



(VI a-ig.) Section cephalad from the corpus callosum. 



At this level the whole dorsal and outer, as well as dorsu-median, 

 cortex is similar and the fibres of the white matter converge toward 

 the striatum. Two sets of fibres may be distinguished, the one pass- 

 ing toward the lateral aspects oi the corpora striata, the other being 



