156 Cincinnati Society of Natural History. 



From opening of fourth ventricle to prominence of first spinal 

 nerve, and between the several cervical nerves, each, 5 mm. 

 Height of medulla at sixth nerve, 5.5 mm. 

 Height of medulla and cerebellum, 10 mm. 



GENERAL RESULTS. 



r. The existence of very distinct types of cell-structure in the 

 cerebrum; these being related to the sensory and motor tracts 

 respectively. 



2. A diversity in axial direction between the motor and sensory 

 cells, and the probability that the connection between them is from 

 the acute end of the one to the blunt end of the other. 



3. The existence of a well-developed callosum and anterior com- 

 missure, as well as a less distinct fornix commissure in the alligator. 



4. The anterior commissure a true commissure of the axial lobes. 



5. The direct course of the taenia thalami, from the ventro- 

 posterior region of the hemispheres to the region of the superior 

 commissure. 



6. The absence of direct fibres from the optic tracts to the cere- 

 brum. 



7. The well-developed superior commissure. 



8. The structure of colliculi and corpus posterius and their con- 

 nection. 



9. The structure of the tuber cinereum. 



10. The different axial position of sensory and motor cells in the 

 medulla. 



11. The connection between the several nuclei of motor nerves 

 of the eye-ball with the optic lobes and structure of the latter. 



12. Peripheral course of the cerebral nerves. 



13. The relation between the roots of the twelfth and eleventh 

 nerves. 



EXPLANATION OF PLATES. 



Plate VII 



Figs. 1-3. — Superficial views of the brain of a young alligator, 

 as seen from the side, from below, and from above. The 

 numerals indicate the pairs of cranial nerves. 



Fig. 4. — Diagram of the ventral distribution of the cranial nerves. 



Fig. 5. —Diagram of the cranial nerves, as seen when the skull and 

 atlas are partially removed from the lateral aspects of the head. 



