vi Journal of Comparative Neurology. 



held by the parieto-occipital and calcarine fissures. These may be 

 termed the precursors of these fissures. 



19. The precursor of the parieto-occipital fissure sometimes 

 shows an unbroken continuity of existence with the parieto-occipital 

 fissure of the adult brain. In other cases it is obliterated, and its 

 place is afterwards taken by a secondary sulcus, which attains, how- 

 ever, a very great depth. 



20. In the adult brain the parieto-occipital fissure, even in its 

 complete form, does not form any eminence on the inner wall of the 

 posterior horn of the ventricle, because it does not extend downwards 

 as far as the cavity. Above its lower end the hemisphere is solid. 



21. The posterior end of the calcarine precursor is in every case 

 obliterated, and the anterior part retained. The extent of the part 

 obliterated varies considerably in different brains. 



22. The anterior preserved portion of the calcarine fissure forms 

 the " stem " of the — <-shaped fissural arrangement on this part of 

 the hemisphere, and its hinder part corresponds to the calcar avis. 



23. In the place of the hinder portion of the calcarine precur- 

 sor, which is obliterated, a secondary furrow appears. This may be 

 termed the posterior calcarine sulcus. 



24. The posterior calcarine sulcus is formed in two pieces 

 which run together, and also form the "stem." In this way the en- 

 tire length of what, in anatomical language, is called the calcarine fis- 

 sure is formed. 



25. The posterior calcarine sulcus is not a complete fissure. 



26. In the ape the entire length of the calcarine fissure is repre- 

 sented by that portion of the fissure which in man is termed the 

 "stem," and by that alone. The posterior carcanne sulcus does not 

 exist in any form in the apes. 



27. The cuneus, therefore has a different morphological value 

 in the apes and in man. In connection with this compare the 

 abnormal human hemispheres. These exhibit certain conditions which 

 approximate to those present in the apes." 



The Fossa and Fissura Sylvii. 



The sign of the Sylvian depression appears at the end of the sec- 

 ond month of development. Dr. Cunningham summarizes his inves- 

 tigations as follows: — 



"i. As growth proceeds the outline of the Sylvian fossa changes 

 considerably. At first nearly circular, it elongates in a vertical direc- 

 tion and then backward on itself and assumes a triangular outline. 



