Humphrey, Brain of the Snapping Turtle. 115 



Fig. 13. Here the dorsal column is partly divided forming a sulcus at a. 

 The lateral sulcus is shallow while the paramesal sulcus is deepened by the rais- 

 ing of the posterior longitudinal fasciculus into the metaccele. 



Fig. 14. Sections of the caudal portions of the 8th nerve. The dorsal 

 column has become more compact while the region of the lateral column has 

 become massive. The lateral sulcus is almost obliterated while the paramesal 

 sulcus deepened. The mesal furrow has deepened and the mesal lophius is re- 

 duced to a very small ridge. 



Fig. ij. A section through the origin of the 5th nerve. Shows a reduc- 

 tion in the region of the dorsal column, but an increase in the region of the lat- 

 eral column with a projection of that region where the nerve enters, also two 

 nidi are shown at a and b. 



Fig. 16. A sagittal section through the brain of a small turtle showing the 

 formation of the metaplexus and the caudal pocket of the metatela. 



Fig. 77. A section through a single fold of the metatela of an adult turtle. 

 Shows the blending of the two layers of the pia and numerous blood vessels 

 piercing it. In this the endyma is indicated by a heavy line while the blood 

 vessels are seen as vacant spaces. 



Fig. 18. A transection through the caudal part of the cerebellum of an 

 embryo. Shows the formaton of the metaplexus and the relation of the tubes of 

 the endolymphatic sac to the cerebellum. 



Fig. ig. A transection through the region of the metencephal of an em- 

 bryo, caudad of the cerebellum. Shows the metatela and and the relation of 

 the endolymphatic sacs and blood sinuses. 



Fig. 20. Part of a sagittal section through the cerebellum of an adult 

 turtle, to show the general histological structure. 



Fig. 21. A transection of the mesencephal in the region of the origin of 

 oculo-motor nerve. Details not filled in. Shows origin of oculo-motor nerve, 

 commissures of the mesencephal, inter-optic nidus and main nerve tracts. 



Fig. 22. A similar section at the origin of the trochlearis, showing also 

 the inter-optic and post-geminal nidi. 



Fig. 2j. Section through the decussation of the trochlearis and showing 

 the post-geminal nidi. 



Fig. 24. A section of the inter-optic nidus to show the peculiar open 

 space about it. 



Fig. 23. Part of a section of the tectum showing its structure. The lay- 

 ers are indicated as shown by Nakagawa and Van Gehuchten. 



Fig. 26. Two cells from the mesencephalic nidus of the trigeminus. 



Fig. 27. .Part of a frontal section of an embryo brain at the level of the 

 supracommissure. Shows the relations of the various parts of the diaccelian 

 roof. 



Fig. 28. Section of the same farther ventrad. Shows relation of the dor- 

 sal sac to the diencephal and opening of the paraphysis into the diaccele. 



