478 B. F. KINGSBURY 
of the former. The medial plane sections in each of these series 
have been compared with the parasagittal sections and the 
general plane of the external ‘fissura rhombomesencephalica’ in- 
dicated by lines. It appears clear that the expansion and push- 
ing forward of the neural plate carries the point in question for- 
ward (and downward) (figs. 18, 19, 20). Subsequently the 
(cephalo-caudal) expansion of the primitive infundibulum and 
the increase in extent of the mesencephalic floor shifts it relatively 
backward (figs. 20, 21, 22, 23) to again advance it with the growth 
of the rhombencephalon (figs. 24, 25, 26). In comparing figures 
20 to 24, the relations of the second head somite material may 
be noted. In figure 20 the two short lines mark its cephalo- 
caudal extent as it lies paraxially. In figure 21 the neural plate 
has begun to separate from closer contact with the notochord in 
this region. In this space a dense mesenchymal growth from the 
second head somite has appeared in figures 22 and 23. From 
this somite much at least of the mesenchyme occupying the 
plica encephali ventralis is derived. 
This comparison of a close series of stages indicates that the 
point of the prospective fovea isthmi in the neural plate corre- 
sponds closely at least to the anterior end of the notochordal 
plate. It does not seem possible more closely to establish the 
correlation, due to the differences in differentiation and growth 
earlier mentioned, without resort to an extensive and supple- 
mentary series of models of the region, or experimentally. The 
point could hardly be tested experimentally in shark or chick. 
In the Amphibia, however, this would seem quite possible, 
where, it might be incidentally remarked, I have found (Gn 
Amblystoma punctatum) conformity to the developmental 
pattern of the head outlined here for shark and chick. The 
comparison instituted entirely suffices, however, to establish 
clearly the incorrectness of the His diagram (His, 92, fig. 1; ef. 
Kingsbury, ’20, fig. 4), in which the notochord extends to the 
infundibular fold and to the anterior end of the neural plate. 
The His conception of the brain plate, therefore, which the 
diagram illustrates fails of substantiation. The His term, 
‘neurochordal suture,’ however, deserves, I think, retention, but 
