Clark, Comparative Anatomy of the Instda. 79 



surface while that of the seal, panther, hyena and most primates 

 is nearly parallel to the the lateral surface. 



The insula of the Thibet bear {^Ursus tJubciiamis), Fig. 

 13, is very different in its appearance from the preceding — as 

 if, instead of the prolonged growth caudad, as in the raccoon, 

 the surrounding areas which presumably have reached a higher 

 state of development, had produced a cephalo-caudal compres- 

 sion of this area, resulting in the formation of two parallel gyres 

 separated by the transinsular fissure. Relative to the length of 

 the cerebrum, the insula in this specimen is much shorter than 

 that in the raccoon. The transinsular fissure here is deep and 

 coincides very closely both in direction and position with the 

 Sylvian. The area is sharply demarcated by the circuminsular 

 fissure except at the cephalic end w^here a slight depression 

 probably marks the cephalic boundary. The area is well 

 rounded and the plane of the insula is parallel to the lateral sur- 

 face. The insula was not wholly concealed, a small portion of 

 the caudo-ventral end of the cephalic subgyre being visible be- 

 fore dissection. The area was almost entirely within the Syl- 

 vian fissure. In 1888 Turner (5<), 566) said : "In the brain of 

 the Polar Bear, I have shown that an entire arched convolution 

 is concealed within that [Sylvian] fissure." 



This area in the dog {Canis familiaris) is situated normally 

 at the bottom of the Sylvian fissure and is entirely concealed. 

 The plane is parallel to the lateral surface or nearly so. It is a 

 well rounded, oval area somewhat triangular in form, is sharply 

 defined by the circuminsular fissure and, as stated by Huxley, 

 is usually unfissured. Figs. 14 and 15 represent an exceptional 

 condition. The insula was exposed on both sides and was sit- 

 uated almost wholly in the Sylvian fossa. The area was well 

 rounded and its outline approximately rectangular. Another 

 peculiar specimen is shown in Fig. 16. Here the insula, while 

 entirely concealed within the Sylvian fissure, was crossed by a 

 fissure which may represent the transinsular fissure and if so 

 the preinsula is the smaller. In order to determine with greater 

 certainty the nature of this fissure the area was removed and 

 sectioned. The shallowness of the fissures (Fig. 17) plainly 



