Clark, Comparative Anaiomy of the hisida. 8i 



skunk (Fig. 20). In each the width of the Sylvian fissure is 

 practically the same throughout its length and at the bottom as 

 near the surface. The study of many transections of the Sylvian 

 region confirms the statement that there is no marked widening 

 of the Sylvian fissure at any point ; there is absolutely no sign 

 of a circuminsular fissure and consequently no evidence of an 

 ectal area homologous with the insula. Recourse was then had 

 to the Weigert method with the result that it has been demon- 

 strated in each that a cellular area had been separated from the 

 cortex entad of the Sylvian fissure by a thin lamina of myelinic 

 fibres. This area is similarly situated to the claustrum of the 

 dog and in the skunk at least the fibers appear to arise from 

 the area dorsad of the Sylvian and pass to some area ventrad or 

 vice versa. In the cat, however, this lamina appears to connect 

 the area ventrad of the Sylvian fissure with the central mass of 

 myelinic fibers rather than with the area dorsad of the Sylvian. 

 The origin of these fibers does not effect the question as to 

 whether or not this is really a claustrum for, while it is known 

 that fibers from the uncus and subfrontal gyri pass entad of the 

 insula and assist in the demarcation of a claustrum in the human 

 brain, it is not known but what fibers having a different origin 

 also take part. Certain it is that if these myelinic fibers (which 

 appear to be of the association type in the dog and skunk) were 

 not there this area would remain a part of the cortex as has 

 been shown is sometimes the case in the human brain. The 

 fibers which make up this lamina are much fewer than in the 

 dog and the number is still less in the skunk than in the cat. 

 Some twelve days after I had thus independently reached the 

 conclusion that this area was homologous with the claustrum, my 

 attention was called by Professor Wilder to an article by 

 Graeme M. Hammond, in 1881 (26)- This article contains fig- 

 ures showing that the author had noticed the area in the cat, 

 sketched it though imperfectly and named it the claustrum. In 

 1889, Spitzka (56, 173) also figured this area in the cat but did 

 not name it. The writer was unable to recognize a claustrum 

 in (Weigert) transections of the brain of the mink. This animal 

 has no Sylvian fissure. 



