84 Journal of Comparative Neurology. 



almost wholly in the Sylvian fossa, only the caudal end extend- 

 ing dorsad into the Sylvian fissure. With one exception the 

 fissures are merely broad shallow depressions which indicate a 

 tendency to divide the area into five gyres. The caudal fissure 

 probabl}' represents the transinsular and is the only one indenting 

 the lateral surface of this area. The plane of the insula is 

 nearly perpendicular to the lateral surface ; the surface is well 

 rounded and throughout its entire length lies just dorsad of the 

 olfactory tract. The insula is present also in the fallow deer 

 {Cariacus clama) and exposed on both sides. At least three 

 fourths of the insula is cephalad of the ventral end of the Syl- 

 vian fissure. The transinsular fissure is rudimentary on the 

 left side but better developed on the right. The difference in 

 the position, relative development, form, and relations of the 

 insula in the camel and deer are very great and more marked 

 than one might expect in animals so closely related. 



The area which represents the insula in the sheep (Figs. 32- 

 33) is, contrary to the rule, exposed. It is probably due .to this 

 fact that this area has not previously been treated by writers 

 on the sheep brain. Only Leuret and Owen seem to have 

 recognized it. The former states that, except in the sheep, 

 they [supplementary convolutions] are found "only in the brains 

 of man, elephant and monkeys." Owen says : "the minor in- 

 ter-Sylvian convolutions are exposed in the elephant and 

 sheep." 



This area, as has been rightly said, is exposed in the sheep 

 and' throughout its length lies just dorsad of the olfactory tract 

 in the Sylvian fossa. The rhinal fissure which separates these 

 areas is always well defined. In adults the lateral exposed sur- 

 face is usually indented by two (apparently three) fissures — the 

 most cephalic and caudal being found upon dissection to be 

 parts of the circuminsular, while the median one is the lateral 

 outcrop of what the writer considers the homologue of the 

 transinsular fissure. Other indentations are frequently noticed 

 but they are usually slight and are probably caused by pressure 

 of branches of the medicerebral artery which lie in them. Up- 

 on dissection, it becomes evident from the greater fissuration 



