386 PROF. G. ELLIOT SMITH ON THE 



thus clearly anticiiiated most of the recent work in this region, by distinguishing the 

 parieto-occipital from the calcarine sulcus and hy recognizing that the latter extends 

 backward, far beyond the calcar. 



Within recent years Cunningham * has called attention to a differentiation of the 

 calcarine sulcus into anterior and posterior elements, which are to be distinguished the 

 one from the other not only by a difference in the time and mode of development, but 

 also, in many cases, by their features in the adult human brain. The " anterior calcarine " 

 sulcus is the first to develop and becomes an extremely deep sulcus, which is wholly 

 responsible for the bulging of the calcar in the ventricle. In other words, it is the true 

 " calcarine sulcus." 



The sulcus which Cunningham calls " posterior calcarine " develops later and quite 

 independently of the anterior sulcus ; it never becomes as deep as the former ; as a rule 

 it does not share in the formation of the calcar, and in many cases it is separated from 

 the anterior or calcarine sulcus by a submerged fold of cortex. It is, to use 

 Cunningham's own words, " a secondary sulcus in every sense of the term " f. It 

 is therefore of a very different nature to the true calcarine sulcus, and, as it is convenient 

 to have a distinctive name, I shall call it " retrocalcariue," because it is placed on the 

 caudal side of the calcar. 



In his great monograph on the human brain, RetziusJ objects to Cunningham's 

 teaching and says that he " does not believe that such a fundamental difference between 

 the fore acd hinder parts of the fissure, as Cunningham sees, can be recognized. The 

 front part grows at least as often without a hinder addition and itself forms the hinder 

 part." The close of this quotation is interesting, as being practically a concession of the 

 writer's position and also by reason of its bearing upon the condition found in the Apes, 

 which Cunningham regards (erroneously, I believe) as differing essentially from that 

 found in the human brain. For a study of Comparative Anatomy makes it almndantly 

 clear that in the case of two sulci developing in the same line, it often happens that 

 the minor sulcus seems to be formed merely by a j^i'olongation of the major sulcus 

 rather than as an independent element. The posterior part was called " calcarine " only 

 because it was supposed to be part of the true calcarine sulcus ; but as this is not strictly 

 so, the distinct name " retrocalcariue " has been introduced. This has been done, not for 

 pedantic reasons, hut because a separate name becomes absolutely necessary in 

 Comparative Anatomy, \\here the luudamental distinction between the two elements 

 becomes more pronounced. 



Describing the development of the sulci in a Sheep's brain, Krueg says that, in a foetus 

 10 cm. long, two fuirows have appeared : one on tlie lateral aspect is the faintly marked 

 representative of the fossa Sylvii of the hiunan foetus, and the other is a more definitely 



* D. J. CiiuniugUam, " Contributions to tlie 8urf;ico Anatomy of the Cerebral Hemispheres," Mem. Eo\-. Irish 

 Academy, July 1SU2. 



t Op. cit. p. 49. 



- 'Das Meu.schcnhirn," Jena, 1896. 



The passage here quoted is taken from an article by Cunningham, Jourual of Anatomy and Thysiology, vol. xxxi. 

 p. 595. See also Ketzius, ' Biologischen Uutersuchungen.' 



