Clark, Comparative Anatomy of the Insula. 6g 



the negro brain, it would appear that the insula is relatively 

 shorter than in the European brain." 



The completion of the circuminsular fissure on the ventral 

 side is usually not accomplished until about the time of birth. 

 Prior to this completion of the circuminsular, which is prob- 

 ably influenced to a considerable extent by the cephalic growth 

 of the tip of the temporal lobe, the insula is continuous with 

 the ventral surface of the cerebrum through the Sylvian fossa. 

 It was probably this condition to which in 1885 Meynert (39, 4) 

 called attention as follows: "the island of Reil is connected 

 with a protuberance (the olfactory lobe) situated on the lower 

 aspect of the frontal portion of the fore brain." It will be 

 seen (Figs, i and 2) that the lateral root of the olfactory tract 

 extends into the Sylvian fossa (that portion of the Sylvian fis- 

 sure which does not close up). It is not believed, however, 

 that the fibres of this tract extend over any portion of the in- 

 sula, but on the contrary that they preserve approximately the 

 same relation to the insula as in the sheep (Fig. 34), the skunk 

 (Fig. 20), the cat (Fig. 19) and the mink, in each of which it is 

 to be noted that the fibres do not pass dorsad of the bottom of 

 the rhinal fissure, thus sharply demarcating the insula from the 

 olfactory lobe. 



THE ADULT HUMAN INSULA. 



Usually the adult human insula is entirely concealed within 

 the Sylvian fissure and can be seen only by divaricating the 

 lips of the fissure or after cutting them entirely away. Broca 

 (4, 651) says that it is not normally exposed after the second 

 year. This occlusion is a condition found so far as known in 

 all primates and in many of the imprimates. In all brains pos- 

 'sessing an insula, the cortex bends in from the lateral surface 

 and passes without interruption under the fissures and over the 

 surface of the insula completely covering it whether convoluted 

 or not. In all brains observed by the writer, the gyres of the 

 operculums are interdigitated with those of the insula. 



In 1889 Wilder ((jg, Prop. CXLI) wrote of this area in 

 man, "the insula is a part of the cortex, which, at one period 



