8o Journal of Comparative Neurology 



the caudal end of the cerebellum, from which point it contracts 

 rapidly and passes under the base of the cerebellum as the nar- 

 row aqueduct. In the floor of the mesoccele, in its cephalic 

 portion is a well defined mesal furrow with a slight ridge on 

 either side. Passing caudad these ridges gradually sink to the 

 level of the metaccelian floor until at the caudal portion they 

 entirely disappear. The floor of the metaccele is approximately 

 flat. 



The membranous roof of the metaccele is much convoluted 

 and folded upon itself. Fig. 5 shows the dorsal appearance in 

 Chelydra and Fig. 7 shows its appearance from a mesal view in 

 the sea-turtle, Chelone midas. A more exact description will be 

 found in pages following. 



The Cranial Nerves. 



In the study of the ectal features of the brain no attempt 

 has been made to trace the peripheral course of the cranial 

 nerves. The only object has been to locate their ectal origins 

 and trace their course into the bony walls of the skull. 



I. Olfactories. — In Chelydra each olfactory nerves arises 

 from two roots, one from each angle of the cephalic margin of 

 the olfactory lobe (Fig. 3). The fibers of these roots are dis- 

 tinct for some distance. They then approach and with the 

 fibers of the opposite side are united into a common trunk 

 which extends to the nasal cavities where the nerves separate 

 and their fibers spread over the cartilaginous lining of the nasal 

 cavities. In CJielone midas the origin is by three roots from 

 each bulb, the third root springing from the lateral surface of 

 the cephalic margin midway between the larger roots. 



II. Optic Nerves. — The optic nerves have their superficial 

 origin along the lateral and cephalic margins of the pregemina. 

 Thence they extend cephalo-ventro-mesad around the base of 

 the infundibulum cephalad of which they decussate forming the 

 chiasma. From the chiasma they extend cephalad, lying near 

 together, until ventrad of the rhinencephal where they turn 

 sharply ventrad and laterad to either eye. They are sometimes 



