Clark, The hmda of the Pig. g 



The plane of the insula is perpendicular to the lateral as- 

 pect of the brain, as is the case in the sheep and calf. This 

 position of the plane, as well as the location of the insula in the 

 Sylvian fossa, is probably due to the undeveloped state of the 

 frontal lobes and the unusual development of the olfactory crus. 

 For in the horse, whose frontal lobes are more highly developed 

 and whose crus is much smaller, the insula stands at an angle of 

 about 45° to the lateral surface and the larger part of the insula 

 is located in the Sylvian fissure. Moreover in one brain (pig) 

 (No. 4) this plane makes an angle of not more than 6o°-65° with 

 the lateral aspect. This being the case in but one brain, it 

 naturally suggests an individual peculiarity. 



The area which represents the insula in the pig is quite large 

 and generally well defined except at its junction with the tem- 

 poral lobe. In but three instances was there any distinct line 

 ot demarcation. In one of these the depression was slight, 

 about like the average fissure upon the insular area and might 

 have been caused by pressure of an artery. In the second 

 insula this depression was at least twice as deep as the first and 

 easily recognizable as a true fissure. In still another, Fig. 7, 

 this depression reached a depth of nearly four mm. completely 

 separating the insular area from the temporal lobe. In the last 

 mentioned brain the fissure in question was visible upon the 

 lateral aspect of the brain while in the two preceding it was not. 



The cephalic boundary of the insula is unusually sharply 

 defined by the circuminsular fissure in pigs of one year and 

 over, as shown in Figs. 6, 7, 8, 9 and 10, while in those of 

 6-10 months the insula is so narrow cephalad that it may grad- 

 uate insensibly into the frontal lobe without the formation of a 

 fissure. This is shown in Fig. 5. The area becomes suddenly 

 much thicker dorso-ventrally near the temporal lobe. Upon 

 this area one fissure (t. Fig. 5) at least, appears to be constant. 

 It seems to originate upon the lateral surface of the insula 

 nearly opposite the mouth of the Sylvian fissure. It sometimes 

 extends scarcely to the dorsal surface while in others (those of 

 one year and over) it may extend dorso-caudally almost across 

 the insular area as in Figs, 6, 8 and 10. 



