120 PHYSIOLOGICAL SERIES. 



The optic lobes are rounded, of moderate size and sharply 

 defined. They lie upon the dorsal surface of the brain in 

 the di-pre--ion between the cerebrum and cerebellum and 

 are separated mesially by a sharp furrow. The cerebellum 

 i- a largo hollow hemispherical protuberance hanging like 

 a hood over the anterior end of the rhomboid fossa. Its 

 walls are relatively thin. The fourth ventricle (rhomboid 

 fossa) is spacious ; it is covered by a membranous roof, the 

 lateral parts of which are extensively pleated and highly 

 vascular (this vascular membrane has been removed and 

 mounted on the left). In the floor of the fourth ventricle 

 lie a pair of well marked fasciculi longitudinales. 



Stieda, Zeits. wiss. Zool., Bd. xxv. 1875, p. 361. 



D. 141. The brain of a Turtle (Chelone mydas) isolated and >ecn 

 from the left side. The olfactory peduncle is continuous 

 posteriorly upon the ventral surface with a rounded hemi- 

 spherical boss, known as the tuberculum olfactorium, which 

 extends backwards at the base of the brain almost to the 

 optic chia>ma, and includes also part of the lateral and mesial 

 walls of the hemisphere. The hemisphere is relatively very 

 deep dorso-vent rally, and is thus in striking contrast to that 

 of Testudo or the Ophidia. The dorsal parts of the hemi- 

 spheres extend back nearly to the optic lobes, but laterally 

 leave a considerable area of the thalamencephalon, covered 

 by the optic tracts, exposed. The inftindibulum is very 

 prominent. The ventral curvature of the medulla oblongata 

 is well seen. 0. C. 1312 D. 



D.142. The brain of a Turtle (Chelone mydas). The dura mater 

 has IM-I-II removed from the left side, and the vessels of the 

 pia mater minutely injected. iThe partial removal of the dura 

 shows how loosely it envelopes the brain and at the same t ime 

 displays the form and disposition of the cerebral organs. A 

 white bristle has been inserted into the infundibulum, and 

 a Mark hri.-tle into the ruptured distal extremity of the 

 epiphysis. The sac-like membranous roof of the medulla 

 N -li..\vii, \vitb n brittle placed beneath its non-vascular 

 median pan. llack llnvad ha> been tied round the Uth, 



