Kingsbury, Brain of Nectiitus. 163 



MesencepJial. — (Figs, i, 4, 21, 22.) The dorsal aspect is 

 slightly more convex than that of the preceding segment, from 

 which it is ill defined. No mesal furrow was found indicating a 

 pair of gemina. Upon the ventrimeson its extent is limited, 

 extending from the infundibulum to the Mittelhirngrube of 

 Burckhardt, the Isthmusgrube of His. Considerable morpho- 

 logical importance has been attached to this depression; 

 it forms a convenient landmark and will be designated here as 

 the mesencephalic pit. It seems to be much more marked in 

 Nectutiis than in other urodeles, the cinerea at the meson con- 

 sisting of but two layers of cells and reaching the ectal surface 

 of the brain. Cephalad of this have been located the region 

 of the albicantia and the corpiis interpedunciilare . The oculo- 

 motor nerves also leave the brain in this immediate neighbor- 

 hood. 



The entocinerea forms a continuous mass surrounding 

 the mesoccele. A differentiation into zones such as occurs in 

 Anura and to a less extent in certain other urodeles, is not well 

 marked in Nectiinis ; an ill defined, discontinuous stratum of 

 alba divides the entocinerea of each tectum into an ectal and 

 ental layer, and in places a third is suggested. 



Epcnccphal. — The cerebellum of Nectiinis is exceedingly 

 simple and consists, as Osborn found in Ampkmma, of a small 

 band of fibers passing from one side to the other, and ' ' con- 

 taining no cells save the simple endyma. " 



The question as to whether or not the epencephal should 

 be recognized as constituting a segment of equal value with the 

 others is a difficult one, and indeed the indication of a 

 division into segments is very obscure. Certainly, in urodeles, 

 there is nothing except the exceedingly rudimentary cerebel- 

 lum to represent that which in higher forms attains so great a 

 development ; and, viewed from the condition in urodeles 

 alone, the inclusion of cerebellum and oblongata by His under 

 a single segment, would appear justifiable. The term applied 

 by him, RJiombencepJialon, or Rhombencephal, is however 

 open to criticism since the same name had been previously 

 applied to the lumbar enlargement of birds. This is, how- 



