NERVOUS SYSTEM. VEETEBBATA. 197 



From the position of the sulcus in this specimen and by 

 comparison with the brains of Dolichotis and Tamanduas, it 

 seems more likely to be a representative of the lateral (or 

 combined lateral and coronary). 



Note that the corpus callosum is rather short and plump, 

 such as is found in the more primitive Insectivora. 



0. C. 1323 E /. 



D. 241. Two casts of the cranial cavity of an American Beaver 

 (Castor canadensis). 



Family SCIUEID^E. 



D. 242. The right half of the brain of a Squirrel (Sciurus vulgarix) . 



No sulci are present in the pallium. 



The corpus callosum is long and narrow with a definite 

 genual thickening. 



The anterior quadrigeminal bodies are very large, 

 probably because an active arboreal animal needs a well- 

 developed visual apparatus. 0. C. 1323 F. 



D. 243. The brain of a Squirrel (Sciurus capistratus) . 



In spite of the large size of the anterior quadrigeminal 

 bodies, they are completely hidden by the cerebral hemi- 

 spheres. 0. C. 1323 Fa. 



D. 244. The left half of the brain of a Squirrel (Sciurus capis- 

 tratus). 



Observe the large size of the optic nerve, with which 

 the prominence of the anterior quadrigeminal bodies is 

 associated. ' O.C. 1323 FC. 



Section HYSTRICOMOBPHA. 

 Family OCTODONTIDJE. 



D. 245. The brain of a Coypu (Myocastor coypus), ( ? ). 



This brain resembles that of the Beaver but is much 

 smaller. The rhinal fissure however is well developed. 



The pallium is devoid of well-defined sulci, although there 

 is a slight furrow on the caudal surface^ possibly representing 



