HEAD-FOLD TO TWELVE SOMITES 105 
parts, sutwra neurochordalis seu ventralis and sutura terminalis 
anterior.) 
The neuropore question resolves itself into this: What part 
of the sutura cerebralis anterior is to be called neuropore? As 
the suture extends from near the infundibulum to the pineal 
region at least, there is a wide range of choice. However, there 
is a point in the suture near its dorsal end where the separation 
of the ectoderm from the neural tube takes place later than 
elsewhere. This may be regarded as the equivalent of the 
neuropore. The suture is the site of formation of the lamina 
terminalis (Chap. VIII). 
Neh.T. 
DELP: 
Fic. 60. — The head of the same embryo from 
below x 30. 
a. i. p., Anterior intestinal portal. Kinde. s:, 
Endocardial septum. F. G., Fore-gut. Ht., Heart. 
N’ch. T., Termination of Notochord. op. Ves., 
Optic vesicle. p. C., Parietal cavity. Pra. ero- 
amnion. V. 0. m., Omphalo-mesenteric vein. 
It will be seen that according to this account most of the 
primary fore-brain includes no part of the original floor of the 
neural tube. 
Primary Divisions of the Neural Tube. The neural tube is the 
primordium of the brain and spinal cord. Its cavity becomes the 
ventricles of the brain and the central canal of the cord. There 
