38 FREDERICK TILNEY AND LUTHER F. WARREN 



d'Erchia ('96) 109 found this structure only as a simple fold in 

 the embryo, while recently Warren ('17) 417 has identified a small 

 but solid protuberance at the anterior extremity of the inter- 

 brain roof-plate in the human embryo which he believes is the 

 anlage of the paraphysis. This, however, soon disappears, leav- 

 ing no trace of its presence, although there develops in the 

 neighborhood of its origin certain prolongations which Warren 

 has described as the diencephalic prolongations. In the adult 

 brain of other mammalian forms no paraphysis has been ob- 

 served. The velum transversum, if present at all, has been 

 observed in the early embryonic period only and then as a simple 

 fold. This statement is based on the observations of d'Erchia. 

 The dorsal sac, because of the much-altered condition in the 

 mammalian brain due to the development of the corpus callosum, 

 has become much flattened and reduced to the level of the general 

 plain of the roof-plate. It has undergone further change in the 

 fact that it has acquired a rich vascularization and become 

 definitely plexiform, giving rise to the tela chorioidea superior 

 of human anatomy. The caudalmost portion of the dorsal sac 

 immediately in front of the epiphysis is elevated and pushed 

 back over the dorsal surface of the pineal body in such a way as 

 to form a thin, roofed sac whose ventral wall lies upon the dorsal 

 surface of the epiphysis. This is the recessus suprapinealis 

 described by Reicher^ 326 in 1859. A commissura habenularis is 

 the next element in the roof-plate, and this is situated in relation 

 with the peduncle of the epiphysis. The epiphysis in mammals 

 undoubtedly represents the proximal portion of the pineal organ. 

 The epiphysis itself is a solid, more or less conical shaped body 

 connected with the roof of the brain by one or more sets of 

 so-called peduncles. As a result of the development of the 

 corpus callosum, the epiphysis has gradually been brought to 

 assume a position which brings it into relation with the superior 

 colliculi of the midbrain. Situated between the epiphyseal 

 peduncles there is a small pineal recessus. The entire epiphysis 

 is located in a position much removed from the inner surface of 

 the skull. 



