Humphrey, Brain of the Snapping Tut tie. 83 



leave the skull or the most cephalic may be very small or en- 

 tirely absent. The most common form is shown in the figure. 

 In this three roots are found of nearly the same size, which do 

 not unite until they have passed almost through the cranial wall. 

 They then unite and join the common trunk of the 10th and 

 nth nerves. 



The arrangement of the nerves in Chelone midas and Chrys- 

 emys picta is very similar. It differs greatly from that shown 

 by Osborn (63) and Fischer (25) in the Amphibia, and also 

 in some respects from that shown by Herrick (37) in the alliga- 

 tor and Owen (64) in the Python. 



Metencephal. 



The LopJiii and Sulci of the Metencephal. — In her paper on 

 the brain of Diemyctylus Mrs. Gage (30) calls attention to the 

 existence of furrows and ridges on the ental surface of the dif- 

 ferent parts of the brain, pointing out their number in the met- 

 encephal, and their apparent definite positions and relations. 

 To these furrows and ridges she applies the name of sulci and 

 lophii. 



In the turtle these ental lophii and sulci in the metencephal 

 are very noticeable. They are of two kinds the first, or pri- 

 mary, those involving a large portion of the wall of the meten- 

 cephal, giving the general contour to the transections of that 

 region, and the secondary, those that involve only the endyma 

 and the subjacent thin layer of neuroglia. In the present discus- 

 sion the primary only are considered. It is also noticed by the 

 same author, that the position of the nidi of the metencephal 

 has an apparent relation to the position of the sulci. 



Observation of the internal structure of the metencephal 

 has led to the belief that the sulci and nidi have no mutual 

 relation, but that in the process of development the force that 

 formed the sulcus at the same time determined the position of 

 the nidus. 



A transection of the caudal part of the oblongata (Fig. 8) 

 shows a structure similar to that of the spinal cord. The H- 

 shaped form of the cinerea persists. The alba, consisting al- 



