98 MARION HINES 
ing the medial limb of the caudate nucleus from the hypothalamus 
runs over the floor of the foramen and ends in the recessus preop- 
ticus (Rec. preop.) as described before. This sulcus is joined 
at its dorsal end by the anterior portion of the sulcus limitans. 
The hypothalamus is the same as described for H 41. Within 
its floor are found the recessus mamillaris, the infundibulum, 
its recessus, the bed of the optic chiasma and the preoptic recess. 
It is not possible to identify the sulcus upon the medial surface 
of this thalamus, comparable to the sulcus dorsalis found in the 
embryos previously described. In the epithalamus the habenula 
(Hab.), the superior commissure (Hab. com.), and the epiphysis 
(Ep. ev.) are easily identified. Immediately anterior to the 
habenula the diencephalic roof plate is non-membranous. Its 
anterior end, however, extends forward over the paraphysis in 
the form of membranous pockets, the postvelar tubules of Warren 
(P. vel. t.). These ependymal tubules (Warren, 717, fig. 18, 
pl. I, p. 125), invaded by vascular connective tissue, seem com- 
parable to the dorsal sac of amphibians and reptiles. 
The telencephalon medium joins the rostral limb of the plexus 
chorioideus ventriculi tertii at the most anterior attachment of 
the postvelar tubules (fig. 18, P. vel. ¢.). From this point in the 
telencephalic midline to the preoptic recess the region which 
shows the greatest growth in length and breadth is the massive 
portion of the lamina terminalis (fig. 18, Lam. term.). Only a 
small region immediately ventral to the angulus terminalis has 
remained thin and tenuous. The antero-posterior measure- 
ment of the area chorioidea is almost the same as that of the two 
embryos, 27.8 mm. and 36.1 mm. in length. Of this, the tela 
chorioidea telencephali medii (fig. 18, Tel. ch. tel. med.) occupies 
its anterior half and the paraphyseal arch its posterior (fig. 
18, Par. p.). The pouch itself extends over the area chorioidea 
a real evagination of midline tissue continuous with the velum 
transversum. In the series this is the only embryo which has 
the typical circular constriction of the stem of the paraphysis. 
Although the figure delineates but one sac, there are two small 
lateral pouches which open directly into the central evagination. 
These relationships are similar to the one which Warren (717 
fig. 14, p. 121) has described for a 25-mm. human embryo. 
