82 
MARION HINES 
of the fourth ventricle, continuous with a deeper groove in the 
wall of the cord and of the mesencephalon. 
limitans fig. 8, (Sul. lim.). 
TABLE 2 
Other embryos consulted for this contribution 
This is the sulcus 
The part of the mesencephalon which 
NUMBER caeee COLLECTION PLANE OF SECTION THICKNESS CONDITION 
mm. bE 
163 9.0 Mall Transverse 20 Excellent 
H566 11.6 Chicago Transverse 15 Excellent 
I eA: 13.7 Chicago Transverse 10 Poor 
H398 14.5 Chicago Horizontal 25 Excellent 
719 15.0 Mall Transverse 40 Fair 
iH 5 16.0 Chicago Transverse 15 Poor 
H465 16.0 Chicago Transverse 15 Good 
317 16.0 Mall Coronal 20 Good 
406 16.0 Mall Sagittal 20 Good 
492 16.0 Mall Coronal 40 Excellent 
H516 17.0 Chicago Transverse 15 Good 
576 lino) Mall Sagittal 15 and 20 Excellent 
1390 18.0 Mall Sagittal 2, Good 
432 18.5 Mall Sagittal 20 Good 
431 19.0 Mall Sagittal 20 Good 
H202 20.2 Chicago Horizontal 25 Fair 
H 19 20.6 Chicago Transverse 20 Fair 
840 24.8 Mall Transverse 50 Good 
455 24.0 Mall Transverse 20 Good 
632 24.0 Mall Sagittal 40 Fair 
H 39 25.0 Chicago Transverse 25 Fair 
405 26.0 Mall Sagittal 40 Good 
1008 26 .4 Mall Sagittal 40 Excellent 
H 50 29.2 Chicago Transverse 25 Fair 
878 36.0 Mall Sagittal 100 Good 
H 98 38.4 Chicago Horizontal 25 Fair 
448 52.0 Mall Sagittal Good 
267 59.0 Mall Sagittal Good 
H 44 60.0 Chicago Transverse 25 Fair 
lies dorsal to this sulcus is thin and expanded. The part which 
lies ventrally foretells the future thickening of the mesencephalic 
floor. This ventricular groove passes through the diencephalon 
and seems to lose itself in the vicinity of the cavity of the optic 
