154 PHYSIOLOGICAL SERIES. 



in order that the arrangement of the sulci on the cranial 

 surface may be compared with that of the mesial surface 

 (fig. 41).] 



The sulcus a begins immediately behind the pseudo- 

 sylvian, and pursues a course upward, i. e. mesially, to 

 terminate just in front of the caudo-mesial angle of the 

 dorsal surface. 



The sulcus ty is the deepest and most constant of the 

 radiating sulci on the mesial surface of the hemisphere. 

 It appears to spring from the hippocampal fissure at u 

 short distance behind the supracommissural exposed portion 

 of the fascia dentata. In most brains it crosses the dorsal 

 edge and joins the sulcus ft on the dorsal surface. The latter 

 pursues a course for a variable distance in front and parallel 

 to the sulcus . Its mode of termination is variable. In 

 this specimen it bends forward opposite the mid- point of 

 the sulcus a, and, after a short oblique course, ends in a 

 bifid extremity. In the other specimen (D. 191) it behaves 

 in a different manner (fig. 43, ft). In specimen I). 192 

 there is a short sulcus below ft, which may be regarded as 

 a part of the same sulcus, as the two are commonly united 

 as in specimen D. .191. 



On the dorsal surface of the hemisphere there are 

 commonly two oblique or sagittal sulci (fig. 38, 8 and e), 

 and behind them a short sulcus <y, parallel to a and ft. 

 Behind ft there are two sulci, ? and rj, and behind these 

 again two others, o and p. 



The greater part of the hemisphere is thus divided into a 

 series of slightly oblique transverse bands by the series of 

 sulci, 7, ft, a, +77, and O + /JL. The shallow sulcus TT on 

 the mesial surface (fig. 41) is placed above ami parallel to 

 the anterior part of the inppooampol fissure *. 



It is very significant that the most constant and primitive 

 sulci of the Meta- and Eutherian neopallium, such as the 

 calcarine (splenial), orbital (presylvian), and suprasylvian 

 sulci, are absent. This is one of the many manifestations 

 of the great ga \ > which separates the Monotremcs I'roin all 

 other mammals. I' resented f>y Prof. G. Elliot Smith. 



Waldeyer (Review only), Merkel and Bonnet's 



* The indicating letter ir has been omitted in the figure. 



