Susanna Phelps Gage . 425 



believe that at all stages of development, the hypophysis and its corre- 

 sponding fold of the brain-wall represent the morphologic cephalic end 

 of the body and of the brain. It logically follows that the cephalic end 

 is the point at wliich the dorsimesal and ventrimesal lines meet. The 

 ventrimesal line is present from the beginning as the middle line between 

 the neural plates. The dorsimesal line is that in which the original mar- 

 gins of the neural plates unite in closing the brain tube. 



To redetermine the exact location of this point of union of the two 

 lines, young specimens of both immammalia and mammals, including man 

 as far as material was available, have been examined step by step from 

 the open neural plates to the closed neural tube and until adult land- 

 marks become unmistakable. From these observations reported in 1903 '■" 

 and 1904,'° it becomes certain to me that the original margin or dorsi- 

 meson extends as far as the hypophysial fold of the brain (Figs. 3, 4). 

 This is irrespective of the exact place where the final closure of the neural 

 tube takes place. In all the higher forms examined this final closure is 

 between the eye-stalks, its adult representative being the pre-optic recess. 

 In torpedo, as Kupffer found in sharks, this point of final closure lies be- 

 tween the olfactory lobes. But even here, in earlier stages the original 

 margin of the neural plate extended as in mammals to the hypophysial 

 region. The difficulties of determining the cephalic end of the tube in 

 lamprey and other forms having an original solid neural plate are, that 

 when the cavity does form, it has seemed somewhat uncertain as to the 

 location of the front of the tube. From my observations it seems that 

 even in the lamprey the front of the tube can be placed at the hypophysis. 

 In amphibia the large size of cells and the consequent thickening produce 

 an obscurity as to the exact formation, but here again, the weight of evi- 

 dence seems to show that the original cleft between the two sides of the 

 neural plate extends to the hypophysial region. 



The human embryo here under special consideration is the most illumi- 

 nating of any specimen examined for the purpose of determining the 

 exact point at which final closure takes place, because that event is delayed 

 until the surrounding parts are so well developed that identification is 

 unmistakable. At the point recognized by Mall as the neuropore, lying 

 between the eye-stalks, a connection of brain and skin tissues exists and 

 extends through a number of sections (lOO/u. or more). In parts the 

 arrangement of cells indicates that the margins have only recently united 

 (Fig. 16). t'igs. 1-8 show the relations of the neuropore, and the extent 



=»Gage, Susanna Phelps, Science, N. S., XVII, 1903. 



■'"Gage, Susanna Phelps, Amer. Jour. Anat, IV, 1904, No. 2, p. VIII. 



