and these are the supposed derivatives of the superior, inferior, and anterior limiting sulci of the 

 Insula, respectively. Lastly, the postsylviaii sulcus is looked upon as the aboriginal of the 

 parallel or superior temporal sulcus. Next taking the gyral instead of the fissural homologies, we 

 are given to understand that in the Carnivore brain, for example, virtually the whole of the first, 

 and about the anterior half of the second arcuate gyrus, along with the ectosylvian sulci, become 

 submerged as the Insula ; while the anterior wall of the Sylvian fissure is formed from, or at the 

 expense of, parts in front of the anterior limbs of gyri arcuati primus et secundus, the convexity 

 of gyrus arcuatus tertius supplies the upper wall, and the posterior half of gyrus arcuatus secundus 

 provides a nucleus for the growth of the first temporal convolution. 



Trusting that this construction of the teachings of the comparative anatomist is correct we will 

 now view the parts in the light of my histological findings. It is satisfactory to be able to open 

 with the statement that no important discrepancies have been revealed. My chief guide to the 

 subsequent history and relation of the parts is the disposition of the area marked by cross-hatching 

 in my diagrams and called Ectosylvian Area A. 



Histologically this field is stamped by a peculiar cortical structure, a structure which I have 

 previously recognised in the transverse temporal gyri (Heschl) of the human brain, and one which 

 I associate with the surface impingement of the central auditory tract. Therefore without preamble, 

 which would consist of repetition of my previous writings, let me unburden my belief that this 

 particular tield of cortex represents that area which, in Man and the Anthropoid, I have called 

 "audito-sensory." From this, as a basis, important deductions can be drawn. To begin with, it is 

 obvious that the so-called Sylvian fissure of Carnivores, at any rate, is the equivalent of the 

 vallecula only of the human Sylvian fissure ; it is equally clear that the gyrus arcuatus primus, 

 along with the ectosylvian sulcal arc, are converted into the transverse temporal gyri, rotating 

 backwards and downwards in the process; the hinder limb of the gyrus arcuatus secundus, and the 

 sulcus postsylvius, are transformed into the gyrus and sulcus temporalis primus, respectively ; the 

 remainder of the temporal lobe grows but of the parts interposed between the sulcus postsylvius 

 and the visual area ; the anterior limb of the gyrus arcuatus secundus, along with some 

 " extrarhinic " cortex surrounding the so-called Sylvian fissure, contribute to the formation of the 

 Insula proper. 



It is thus seen that histology can be strongly urged in support of anatomical doctrines, but 

 before leaving the question I must point out that difficulties not quite insurmountable are pre- 

 sented by the arrangement of parts in the brain of the pig. In this animal, and apparently in 

 all Ungulates, the "Sylvian" fissure has the appearance of being unusually well-developed, but in 

 reality, according to Holl, it is a complex fissure, and contains the ectosylvian arc of Carnivorae, 

 along with the gyrus arcuatus primus, submerged within its walls. Does histology confirm this 

 supposition? Yes, because in Sus much of the cortex having "audito-sensory" characters lies 

 concealed within the "Sylvian" fissure, particularly its upper part, and it also does not spread 

 backwards as far as the fissure marked ectosylvius in my diagram. This leads up to another 

 question, viz., whether the ectosylvian fissure, here indicated, is not really the postsylvian. I have 

 already given reasons for thinking that the sulcus in this animal, commonly accepted as the supra- 

 sylvian, is, in all likelihood, the lateral fissure of other orders, and this being so, where is the 

 former fissure? It is unlikely that it can be wholly unrepresented, for it is said to be one of the 



*t stable of mammalian sulci; and, if present, it must lie somewhere between the lateral and 



rhinic fissures, but the only fissures in this situation are, first, two dimples lying above the level of 

 the so-called "Sylvian," and secondly, the above-mentioned ectosylvian fissure. Nevertheless, after 

 duly considering the evidence bearing on this and other investing areas, the only conclusion I can 

 arrive at is that these constituents, scattered and rudimentary as they appear to be, represent the 

 suprasylvian sulcus of other orders. 



