No. I.] DESMOGNATHUS FUSCA. 237 



plexus lies between the hemicerebrums at about the point 

 where they begin to diverge. Just caudal to the plexus is a 

 slight circular mesal elevation, the epiphysis. This, in some 

 specimens fixed in potassium bichromate, presented a white or 

 silvery appearance due to the presence of a pigment. 



There is no sharp line of demarcation between the dien- 

 cephal and mesencephal ; the latter is approximately circular 

 in outline and in some specimens a slight mesal furrow has 

 been detected ; this, however, is believed to be an artifact due 

 to the collapse of the roof rather than to represent the normal 

 convex condition usually observed. The cerebellum is not 

 visible, being entirely overlapped by the mesencephal. The 

 metaplexus is comparatively short and wide as compared with 

 other Amphibia. 



On the ventral aspect, the olfactory nerves pass off from 

 the latero-cephalic portion of the cerebrum. There is no very 

 marked indication of an olfactory lobe superficially ; a very 

 slight furrow more noticeable on the ventral aspect passing 

 obliquely latero-caudad, seems to differentiate these lobes from 

 the cerebrum proper. A small whitish area between the 

 intercerebral fissure and the chiasma indicates the position of 

 certain of the cerebral commissures. The chiasma is not 

 prominent ; it scarcely projects beyond the ectal surface, and 

 topographically its cephalic margin may serve as a good line 

 of division between the prosencephal and diencephal. The 

 infundibulum is well developed and is relatively wide at its 

 origin at the chiasma ; it grows still wider in its course toward 

 the oblongata ; its caudal margin is convex except at the 

 meson where is present an indentation caused by the intrusion 

 of the hypophysis. 



The mesencephal is almost entirely concealed by the infun- 

 dibulum. The metencephal is widest at its cephalic extremity 

 and tapers gradually into the myel. 



Meninges. 



In the Teleosts the meninges are represented by pia and 

 dura only, the former, perhaps, also including the arachnoid, 



