THE ANATOMY OF THE WEDDELL SEAL. 



135 



11. The relatively simple character of the mesencephalon. 



12. The small size of those parts of the cerebellar hemispheres which in man 

 would constitute their main bulk ; and the large size of those objects in relation to 

 the vallecula, which in man would be relatively small. 



13. The reduction in the posterior margin of the pons Varolii, which thereby 

 permits the bulbar root of the 5th cranial nerve to emerge directly from the side of 

 the medulla oblongata. 



LITERATURE. 



MURIE, Trans. ZooL Soc. Land., vol. viii., 1874. 



WIEDERSHEIM and PARKER, Comparative Anatomy of Vertebrates, 3rd ed., 1907, p. 224. 



CUNNINGHAM, Text-Bonk of Anatomy, edited by Cunningham, 3rd ed., p. 512. 



Sir WM. TURNER, Challenger Reports, vol. xxvi., Zoology : Report on Seals (" Brain of Elephant Seal and 



of Walrus," p. 89 et seg., plates viii., ix., x.). In connection with this Report a very full bibliography 



is provided. 



DESCRIPTION OF PLATE. 



Fig. 1. The left cerebral hemisphere, natural 

 size. 



F. Sy. Fissure of Sylvius. 



F. Ro. Fissure of Rolando. 

 S. P-c. Pre-central sulcus. 

 S. Or. Sulcus cruciatus. 



S. I-p. Intra-panetal sulcus. 

 /. R. Island of Reil. 



Fig. 2. Mesial surface of the right cerebral hemi- 

 sphere. 



S. Cr. Sulcus cruciatus. 



F. Ro. Fissure of Rolando. 



/. P-o. Internal parieto-occipital fissure. 



Op. C. Optic commissure. 



G. C. Corpus callosum. 

 Hy. C. Pituitary body. 



P. Var. Pons Yarolii. 

 Pin. Pineal body. 



Fig. 3. Basal surface of cerebral hemisphere. 

 Rli. f. Rhinal fissure. 



F. Sy. Fissure of Sylvius. 

 S. Col. Sulcus colateralis. 



C. f. Calcarine fissure. 

 P. o. Parieto-occipital fissure. 

 S. D. Sulcus dentatus. 

 0. T. Olfactory tract. 

 Op. N. Optic nerve. 

 Hy. C. Pituitary body. 

 Cr. C. Crus cerebri. 



Is. Isthmus. 

 Gun. Cuneus. 



G. L. Gyrus lingualis. 



Fig. 4. Vertical transverse section through the 

 posterior horn of the lateral ventricle of 

 the right hemisphere, viewed from behind. 

 C. f. Calcarine fissure. 

 V. Lateral ventricle. 



(ROY. soc. EDIX. TRASS., VOL. XLVHI., 847.) 



