288 General 



As it may be asked why I have not made use of the claustruui in working out the homologies 

 of this region in general, and of the Insula in particular, I would mention that I have not wholly 

 disregarded this structure. In fact, in every brain examined I have endeavoured to make a surface 

 projection drawing of the nucleus. Of course such a drawing is apt to be inexact, on account of the 

 depth at which the claustruui is placed, but on the whole I find that the anterior limb of the gyrus 

 arcuatus, and the extrarhinic cortex immediately behind " Sylvius," commonly overlie this body, and 

 this is the area of cortex, as I have mentioned, which I regard as the forerunner of the Insula. 



FRONTAL LOBE. 



In practically all the regions we have discussed some feature has been detected, either with 

 the unaided eye or with the microscope, which in being reproduced in the human organ has 

 yielded some insight to the course of events attending the phylogenetic development of the part. 

 But, in the case of the frontal lobe, if we except the orbital sulcus, not a single surface depression, 

 which we can look upon as the original of any sulcus in the human lobe, is recognisable, nor does 

 a careful collateral and comparative examination of the lobe under the microscope enable us to 

 decide, with any measure of assurance, that it is covered by a kindred type of cortex. This 

 lack of resemblance lightens our remarks on the homologies of the lobe, for the orbital sulcus is 

 alone left for consideration, and it is soon dismissed, because earlier writers appear to be correct 

 in correlating it with the sulcus orbitalis transversus of Homo. At the same time some general 

 reflections bearing on the question of cerebral ontogeny and phylogen}', and of sufficient importance 

 to commit to paper, are engendered. 



GENERAL REFLECTIONS. 



When we take account of the composition of the lower mammalian brain, and compare it with 

 that of Homo, we are immediately struck by the truth that the surface of the former is almost 

 entirely occupied by cortex dominating those simple functions, which, in the case of a lowly 

 terrestrial animal, are essential to survival, inasmuch as they provide avenues of information, 

 either for the obtainment of prey and pabulum, or for escape from oppressing foes. Of course the 

 same functions exhibit varying degrees of importance in different animals, but named in approximate 

 order of value, they are those of smell, sight, hearing, common sensation, and locomotion. It is 

 also interesting to have abundant proof of the fact, that when as a result of the mode of life it 

 adopts in the combat for existence a given animal is forced to place special reliance on some 

 particular function, then at the expense of the remainder a relatively greater extent of pallium is 

 allotted to that function. This cannot be better exemplified, although the illustration is an old 

 one, than by noting the large proportion of brain devoted to the olfactory sense, in macrosmatic 

 animals. In Man the case is widely different, for, while retaining possession of all these fields of 

 primitive cortex dominating simple functions, he has risen superior to the necessity of relying upon 

 the specialisation of one or more of these functions, or even of adopting a safe mode of life, by 

 developing cortex for the government of those high psychic processes which make him preeminent 

 among beings. 



Thanks to the, discriminating powers of the microscope, guided by the researches of workers in 

 the departments of comparative anatomy, physiology, pathology, and embryology, we are now able 

 to draw a map of the brain indicating the precise extent and distribution of most of the areas of 

 cortex governing these primitive and higher functions, respectively. And, in reference to the 

 primary and essential areas, it is extremely interesting to find that, when a type of cortex pertaining 

 to one of these senses once has its architecture established, there is a remarkable leaning towards 

 the preservation of the original structural plan, and this in spite of the specialisation or degradation 



