OF DENISON UNIVERSITY. 



67 



to coincide with the i)hysiological re-iuircnicnts of the organ. The 

 great simphcity of these cells in Arctomys adapts it for their study. 

 We incline to accept Beevor's suggestion in ])art, /. r, that the ascend- 

 ing processes of Purkinje's cells turn at ri-ht an-lcs and connect with 

 fibres leading to the brain 



7'/ie MesencepJialon. 



We preface our own observations with Stieda's account of the 

 corpora f[uadrigemina in the rabbit, which is as follows : 



"The peduncular region has the following nuclei. Above the 

 united pyramid tracts and lower longitudinal bundles is a cell group 

 on either side, each of which consists of two j)arts. The under (ven- 

 tral) portion is the larger and contains many small cells (.012- 16 mm ) 

 in a granular ground mass ; the ui)per, smaller jjortion has large angu- 

 lar cells of .14 mm. diameter. This nucleus may be called Nucleus 

 peduncidaris. On the lower margin of the central gray, thus near the 

 floor of the aqueduct, is the oculomotor nucleus of either side. It 

 consists of cells of moderate size (.04 mm.) and angular form. Be- 

 tween the two nuclei and near the floor of the ventricle are numl>ers 

 of small triangular or fusiform cells. The fibres from the oculomotor 

 nucleus are very numerous and pass through the nucleus peduncularis 

 and between the bundles of the anterior columns to their roots.'' 



" The central gray of the jjosterior corpora (piadrigemina is lim- 

 ited by fibre tracts. Laterally the nucleus of the trochlearis is mingled 

 with these fibres. [The author's figures are here derived from the dog, 

 and we are left in doubt as to the condition in the rabbit, though he 

 ex])licitly states in a foot-note elsewhere that he introduces references 

 to drawings of other brains that are described only where they are 

 similar.] The nerve fibres of the corpora (juadrigemina are j)artiy 

 transverse, which decussate in small bundles above the aipieduct, and 

 ])artly oblique bundles." 



•'The central part of the nates is, like the other gray matter, com- 

 posed of small nerve cells scattered in a granulate mass, but the super- 

 ficial portion exhibits di.stinct interstratification of a white zone |)arallcl 

 to the surface. With high powers an outer zone devoid of cells, may 

 be seen ; below this a zone of granulated substance with s<attere(l 

 small cells, then a layer of numerous transversely cut bundles of hbres 

 separated by gray substance, containing stellate nerve .ells (.005-.012 

 mm.) with well-develojjed processes." 



