UPON THE SERIES OF PREIITSTORTC CRANIA. 0)69 



the centre of the parietal eminence and parallel to the line of tlie 

 lambdoid suture, and behind by that line itself, may, with the zone 

 of brain which has been shown to underlie it, be taken as eminently 

 distinctive, according- to its lesser or g-reater width, of the brachy- 

 eephalic and dolicho-cephalic types of skull respectively. 



As some difference is found in the statements of different writers 

 as to the constancy, if not of the relations held by the supra- 

 marginal lobule to the parietal tuberosity, still of those of the 

 parieto-occipital fissure to the lambdoid suture, it is well to say 

 here that I have examined these relations as existing- between the 

 skull and the brain while in sitn, and have measured the width of 

 the zone in question in many brains removed from the skull. The 

 ordinary width of this zone in the brains of the almost exclusively 

 dolicho-cephalic population of this part of England is from 1*5" to 

 2" ; in such a skull, with a breadth-length index of "76, having 

 ascertained by boring that the centre of the supra-marginal lobule 

 corresponded to the centre of the parietal eminence, I found that 

 the distance from the former spot to the line of the parieto-occipital 



slon or excavation but by upheaval of cerebral substance, and tWs upheaval is less 

 marked in the higher than in the lower SimiadiE, and in Hominidaj is usually entirely 

 absent. As Gratiolet summed the matter up in his Memoire sur les plis Cert^braux 

 de I'homme et des Primatfes, 1854, p. 97, ' Le lobe occipital atteint le maximum de sou 

 developpement dans les Cynocephales. Beaucoup moins developpt^ dans les Macaques 

 il diminue de plus en plus en passant des Guenons aux Semnopitheques, et de ceux-ci 

 aux Gibbons et aux Orangs-Ajoutons qu'il atteint son minimum dans I'espece 

 humaine.' 



As variability in a structure or organ is justly considered to be some sort of an 

 indication that it is tending towards becoming rudimentary, the variability of the 

 occipital portions of the skiUl and of the bi-ain attains some significance. Of this 

 variability I have already spoken, p. 649 stipra. Since writing as above, a human 

 brain has been added to the series in the University Museum (No. 950 g and h"), 

 the occipital lobes in which are remarkable for the extreme scantiness of their 

 fissures and convolutions, the very reverse, extreme complexity, to wit, and sinuosity, 

 being usually found in this part of the human brain, at least in Europeans, and being 

 very ordinarily stated to be characteristic of it. See for example Cruveilhier's Anatomie 

 Descriptive, iii. 2. p. 454, ed. 4; Pansch, Abhandl. Naturwiss. Verein. Hamburg, Altona, 

 1876, p. 25; and Gi-atiolet's words applied to this lobe, 'Ses plis, d'une extreme irregu- 

 lariti?, semblent devoir echapper a toute description' (Me'moire, 1854, p. 61"). 



Taking all these considerations together, that namely of the inferiority of the 

 hydraulic character of the vascular supply of the occipital lobes, that of their histolo- 

 gical inferiority, that of their lesser amenability to disease, a privilege which we do 

 not find to be enjoyed by organs of great functional importance, and that finally of 

 their gi-eat variability, and coupling them with a comparison of the homologous lobes 

 in the Simiadaj, I am inclined to consider the occipital lobes proper of the human 

 brain as being semi-rudimentary structures. A parallel case appears to me to be 

 furnished by the history of the fourth (the azygos or post-caval) lobe of the right lung 

 in the Primates. This small lobe retains its independent vascular and bronchial 

 supply till we reach the higher Anthropomorpha ; it is lost in them and in us. 



