ENCEPHALON OF REPTILES. 293 



IS shown in the medulla oblongata, which is indicated by a slight 

 tumefaction giving off the fifth, 3, 4, 5, 6, seventh, 7, eighth, 8, and 

 ninth pairs of cerebral nerves : the tract is bounded anteriorly 

 by the hypophysis covering the origin of the optic nerves. 

 The continuation of the basal fibres of the hemispheres, p, 

 into the rhinencephalon, E, is shown. 



In a side view, the several primary divisions of the chelonian 

 brain present the shapes and proportions shown in fig. 192, in Avhich 

 C is the epencephalon, o, the mesencephalon, p the prosence- 

 phalon ; E, the rhinencephalon. The epencephalon includes the 

 medulla oblongata, with the cerebellum. 



.-.:k 



Brain of a Turtle iCIidonc), side view. ecu. 



In the turtle ( Chelone, fig. 191) the cerebelkmi, c, is slightly 

 raised by the bristle, o, to expose the fourth ventricle, /*, in which 

 the sides of the calamus rise into ' teretial tracts.' The cere- 

 belluna is subelongate in its form, consisting of an arched layer 

 of neurine, smooth externally, of equal thickness throughout, 

 which spreads over a portion of the ventricle. The remainder 

 of that cavity is covered by a vascular plexus, derived from 

 the sides of the medulla oblongata, which forms a sort of valve, 

 and by becoming united to the margin of the cerebellum, com- 

 pletes the roof of the fourth ventricle, which is large and jjro- 

 longed very far back. The optic lobes, O, are smooth, sphe- 

 roidal bodies, on a plane inferior to the cerebellum and cere- 

 brum. Each lobe has its ventricle, c* , which communicates, as 

 shown by the bristle, m, with the fourth ventricle, and likewise 

 with the third ; the ' iter ' to which may be seen by divaricating 

 the optic lobes, covered by pia mater reflected down the intersjDace, 

 and by a very thin layer of neurine. From the third ventricle a 

 canal, or ' infundibulum,' is continued down to the hypophysis, and 

 another upward to the ' pineal ' body, which is pyriform, hollow, 

 and highly vascular : it occupies the interspace between the 

 optic, O, and cerebral lobes, p. These form the largest of the 



