NERVOUS SYSTEM. VERTEBRATA. 



121 



9th, 10th, Itth, and 12th cranial nerves. The forward 

 course of the accessorius roots to join the vagus are 

 particularly clearly seen. 0. C. 1312. Hunterian. 



D. 143. The brain of a Turtle (Ckelone my das) in sagittal section 

 seen from the left side. In this section the thin mesial wall 

 of the right hemisphere has been exposed showing a tract 

 of fibres radiating over the precommissural area. A similar 

 though far more strongly marked tract (tr. hippocampo- 



Fig. 81. 



PARAPHY. 

 MONRO FOR. \ DORS. SAC. 



PAR. STALK MESEN. 

 ' COMM. SUP./ COMM. 



COMM.V. ~: p-JM "-TK.RDVENT. 

 OPT. CHl! ^<&^ X CORP. PIT. 



Brain of Chelone mi/das, in sagittal section. 



mesencephalicus) is found in Birds ; it forms a direct con- 

 nection between the hippocampus and the tectum opticum. 

 The anterior commissure and psalterium can be seen close 

 together in front of and below the foramen of Monro. The 

 optic thalamus is small ; it is joined to its fellow across the 

 cavity of the third ventricle, as in the Mammalia, by a large 

 soft " commissure " in which is situated a central nucleus 

 of considerable size. The roof of the third ventricle is 

 evaginated to form a group of three successive elongated 

 outgrowths, constituting together the club-shaped promi- 

 nence seen in the previous specimen between the hinder 

 parts of the hemispheres. The foremost outgrowth is the 

 paraphysis, the intermediate and largest the dorsal sac, 

 and the most caudal the epiphysis. The specimen also 

 shows very clearly the large cavities of the optic lobes and 



