Humphrey, Brain of the Snapping Turtle. 79 



well developed being in the cephalo-caudal diameter about 60 

 per cent, of the length of the cerebrum. The general shape 

 of the dorsal portion of each pregeminum is sub-hemispherical, 

 resting upon its plane surface with the convexity dorsad. The 

 two gemina are separated by a deep furrow, making the dorsal 

 wall of the mesoccele very thin along the meson. The cephalic 

 limit of the mesencephal is strongly marked on the dorsal sur- 

 face by a transverse furrow. The basal portion of the mesen- 

 cephal, upon which the hemispherical parts of the pregemina 

 rest, projects caudad beyond the pregemina. At either side of 

 this projection is a small tubercle raised slightly above the gen- 

 eral surface (Figs. I, 5, psg). These tubercles I have homolo- 

 gized with the postgemina. Between these postgemina the 

 caudal projection of the mesencephal is convex caudad, this con- 

 vex surface is furrowed on the mesal line (Fig. 1). This forms 

 two small projections that I have homologized with the ' ' inter- 

 optic lobes of Spitzka. That author first describes them in Ig- 

 uana (78) and speaks of them as "a concealed mass" in tur- 

 tles. I find these to be quite prominent in the chameleon. 

 The optic nerves have their ectal origin from the cephalic and 

 lateral aspects ol the pregemina from which origin they pass 

 ventro-cephalo-mesad in a broad band lying close about the in- 

 fundibulum, immediately cephalad of which they decussate, 

 forming the chiasma. 



Epencephal. — The cerebellum in its general shape is plate 

 like with the convexity cephalo-dorsad. Its base rests upon the 

 brain stem caudad of the mesencephal, from which attachment 

 it arches dorso-caudad (Fig. 3). To its caudal extremity is at- 

 tached the metatela. No pons can be distinguished and conse- 

 quently no sharp division between epencephal and metencephal 

 can be made. 



MentencepJial. — This segment unlike the others has a roof 

 entirely membranous. If this roof be removed we see from the 

 dorsal aspect the wide cavity of the metaccele (Fig. 1). This 

 appears as if formed by the spreading apart of the walls of the 

 dorsal furrow of the myel. From the caudal portion the cav- 

 ity widens gradually, reaching its maximum width ventrad of 



