8o Journal of Comparative Neurology. 



shows that the fissure crossing this area is not a part of the 

 circuminsular but an independent fissure, probably the transin- 

 sular as previously stated. The small area cephalad undoubt- 

 edly represents a preinsula. Owing to the normally simple 

 character of this area in the dog, these individual differences 

 are very striking. 



A transection of the cerebrum of a dog is shown in Fig. 

 1 8. The insula appears as it normally exists concealed by the 

 overlapping portions of the temporal and parietal lobes. The 

 myelinic fibers of the olfactory tract readily distinguish the 

 rhinal fissure and it will be noted that they do not extend be- 

 yond the bottom of this fissure. A band of myelinic fibers 

 extending apparently from the dorsal overlapping area of the pari- 

 etal lobe, passes through the insular cortex cutting off the ental 

 layers which constitute an area probably homologous with the 

 claustrum. The study of sections caudad of this one shows 

 that this band of fibers ventrad of the insula bends around into 

 the temporal lobe. It would thus appear that a part of them at 

 least might be association fibers. Fibers also given off from 

 this band are distributed through the claustrum. Myelinic 

 fibers are also found in the ectal dense layer of cortex of the 

 insula and they extend for the most part parallel with the sur- 

 face. 



The insula receives its blood-supply directly from minute 

 branches of the medicerebral artery, which pass in from the sur- 

 face and which are seen in longisection in Fig. i8. The writer 

 has been unable in most cases to determine the origin of ves- 

 sels found in the claustrum as they were seen only in transec- 

 tion. A few however have been found which passed directly 

 across the area as in the case of the one represented in the dor- 

 sal end of the claustrunL These would seem to indicate that 

 a part of the supply might be received directly from the surface 

 arteries. In the vicinity of the fiber tracts, arteries, in general, 

 seem to follow the direction of the length of the fibers and not 

 to cross them. 



As previously stated, no macroscopic area appears at the bot- 

 tom of the Sylvian fissure of either the cat (see Fig. 19) or the 



