200 Royal Irish Academy. 



Dr. Cunningham dissents from several of his predecessors as to a 

 sexual difference in the position of the fissure of Rolando, which they 

 regarded as indicating a greater relative mass of brain-matter in the 

 frontal lobe in the male than in the female. This difference Dr. 

 Cunningham has not observed ; if there be any, he thinks it is in 

 favour of the female frontal lobe. In the Rolandic angle, too, in 

 which the apes differ from man, some writers find a sexual human 

 difference, which Dr. Cunningham, as well as Eberstaller, denies. 

 The only variation he recognises is that in brachycephalic heads the 

 angle opens out, and in dolicocephalic heads becomes more acute. 

 The length of the Eolandic fissure is substantially the same in the two 

 sexes, but is much greater in the anthropoids than in man. Curiously, 

 in the chimpanzee and orang the upper end of the Eolandic fissure is 

 further back than in man, which indicates a greater relative antero- 

 posterior length of the upper part of the frontal lobe in the anthro- 

 poids ; but the lower part is much shorter than in man. In the lower 

 apes of the old world the fissure of Eolando is, throughout its course 

 further forward than in the human hemisphere. 



Coming now to the intraparietal furrow of Turner, Dr. Cunningham 

 observes that it is rather a system of sulci than a single sulcus. It 

 consists of three portions : the sulcus postcentralis, divided into a 

 superior and an inferior portion ; the ramus horizontalis, and the 

 ramus occipitalis. As to the process of its evolution and the typical 

 arrangement of its parts, there has been considerable difference of 

 opinion among anatomists. From a study of the brain in the foetal 

 condition and in the apes. Dr. Cunningham arrives at the conclusion 

 that the ramus horizontalis and the inferior sulcus postcentralis are 

 originally continuous, whilst the superior sulcus is a superadded 

 element. In the human brain is found every possible form of com- 

 bination of the segments of the sulcus distinct from the ramus occipi- 

 talis ; but there is a general tendency towards a union of the two 

 originally separate postcentral elements of the sulcus, and a divorce 

 from the lower of these of the ramus horizontalis. The intraparietal 



centres. The lower part associated with the arm centres appears first, because the 

 upper limbs in their development are always in advance of the lower limbs. In 

 the embryo the buds which constitute the earliest form of the upper limbs have 

 been pushed out before the corresponding hinder limb buds have made their 

 appearance." 



