380 J. B. JOHNSTON 



We have fairly clear and complete evidence as to the location 

 of the neuroporic recess in mammals. In a previous communi- 

 cation ('09 b) the writer identified as this recess a pit located in 

 the pig of 15 mm. and larger just above the anterior commissure. 

 Figure 39 of that paper may be consulted in this connection.. 

 The development of the pig has since been carefully reviewed 

 and the writer is convinced of the correctness of this view. The 

 pit in question is the embryonic representative of the recessus 

 triangularis of Schwalbe and lies over the anterior commissure 

 and between the fornix columns. In a later communication ('10c) 

 were given median sections of rabbit and cat embryos showing 

 the same recess between the anterior and the pallial commissures. 

 Sheep embryos show the same relations. Figures 8 and 24 show 

 the neuroporic recess and lamina supraneuroporica in a human 

 embryo of 37 mm., for the opportunity to study which I am 

 indebted to Dr. G. Carl Huber. 



Neumayer ('99) figures early stages of rabbit and sheep em- 

 bryos in which he clearly identifies the neuroporic recess (under 

 the name of lobus olfactorius impar) and shows that it comes 

 to lie between the anterior and pallial commissures. Several of 

 his figures are reproduced in Ziehen's article on the morphogene- 

 sis of the central nervous system of mammals in Hertwig's Hand- 

 buch. The pit which the writer identified as neuroporic recess 

 in cat embryos was figured by Martin ('93) who showed that 

 the so-called lamina terminalis grows thinner in later stages at 

 the location of this pit. It is well known that the recessus 

 triangularis (rec. inferior of Elliot Smith) exists in this same 

 position in adult monotremes, marsupials and many mammals. 

 Werkman ('13) in his recent work on the development of the 

 commissures in lower mammals shows the neuroporic recess in 

 embryos of the mole and the bat (figs. 5, 8, 13, 15, 17, 18, c.ep.). 



It is proposed that hereafter the name recessus neuroporicus 

 be adopted for this pit in the brains of all vertebrates, instead 

 of recessus triangularis (Schwalbe) or recessus inferior (Elliot 

 Smith). The recessus neuroporicus may be defined as a pit ex- 

 isting in the embryos or adults of all vertebrates in the topo- 

 graphic rostral wall of the third ventricle, marking the point at 

 which the dorsal seam of closure of the neural tube last separated 



