332 DE. G. ELLIOT SMITH ON 



only because the rhinal fissure has vanished, but also because the " calcarine fissure " 

 appears to branch backward and upward into two other sulci, the posterior calcarine (in 

 Man) and the parieto-occipital respectively. But, as Cunningham remarks *, these latter 

 fissures are of v^astly less morphological importance. 



In many of the Carnivora we see the beginning of that backward extension of the 

 occipital pole of the hemisphere wbich produces the occipital " lobe " of the Primates, and 

 as a result of tliis growth the "calcarine limb" of the splenial sulcus (or in other words 

 the a element) becomes acutely bent on the " culloso-marg'mal limb " or a" element 

 of the splenial sulcus. It is not difiicult to understand that the continuation of 

 such a process results in the separation of the calcarine from the less important and 

 more unstable calloso-marginal element in the Primates. In this manner we wovJd 

 have produced the extensive calcarine sulcus which Cunningham describes f in the 

 Anthropoid Apes. 



[Since the above was written I have met Avith the following interesting remarks, which 

 lend considerable support to the thesis I have independently put forward. In discussing 

 the question " whether we are justified in saying that quadrupeds have a far less 

 developed occipital lobe than the Primates," Professor Moriz Benedikt says % : — 



" The first argument for this view is that the quadrupedal classes of animals have no 

 occipital fissure. This statement appears to me to be contrary to the real condition. 

 The stem of the fork-shaped occipital fissure (the combined calcarine and parieto-occipital) 

 of Man is characterized as an arc with its convexity directed towards the posterior j)ole, 

 and it surrounds that part of the gyrus fornicatus which limits the splenium corporis 

 callosi. When we search after this fissure in a great number of gyrencephalic animals, 

 we find it, but only in connection with the fissura calloso-marginalis. 



" It may be remarked that in certain anomalous human brains the fissura calloso- 

 marginalis does not come to an end, as in typical cases, by being curved upwards, so as 

 to form the posterior limit of the paracentral gyrus of Betz. It is continued towards the 

 posterior part, forms a limit between the prsecuneal gyrus and the corresponding part of 

 the gyrus fornicatus, and unites with the stem of the fork-shaped fissure in such a manner 

 that this stem becomes the most posterior part of the calloso-marginal fissure." 



This is most important and valuable corroborative evidence ; for what Benedikt calls 

 "the stem of the fork-shaped fissure" is the same sulcus which Cunningham caUs 

 " anterior calcarine " and which I have already regarded as the caudal extremity of the 

 splenial sulcus. Speaking of Benedikt's earlier expression of this view §, Professor 

 Cunningham says, " Upon his further statement that the calcarine fissure is also developed 

 in brains below the Primates we are not in a position at present to oifer an opinion " || . 



* Cunningham, op. cit., Cunningham Memoirs, p. 41. 

 t Cunningham Memoirs, oj}. cit. 



+ Moriz Benedikt, " Some Points on the iSurface-Anatomy of the Brain, " Journal of Anatomy and Physiology, 

 sxv. p. 211. 



§ Moriz Benedikt, •' Der Hinterhaupts-Lappen der Saugethiere," Centralbl. f. d. med. Wissensch., 1877, No. 10. 

 II D. J. Cunningham, " Complete Fissures of the Human Cerebrum," Journal of Anatomy and Physiology, vol. xxiv. 

 p. 343. 



