232 FREDERICK TILNEY 
sponding to the short, broad infundibular stem, the infundib- 
ular canal (12) is not well defined, although it may be recognized 
as a slight constriction occurring dorsad at the area of transition 
between the saccus vasculosus and the post-infundibular emi- 
nence and ventrad in the region in which the pituitary surface 
of the infundibular process passes into the median post-chias- 
matic groove (23). The post-chiasmatic recess (33) corresponds 
in its subdivisions to the post-chiasmatic eminence, there being 
two large lateral diverticula extending into the inferior lobes in 
connection with a median canal which communicates cephalad 
with the suprachiasmatic portion of the third ventricle and 
caudad with the recess of the infundibular process. Cephalad 
to the post-chiasmatic eminence the ventricular floor is elevated 
above the chiasm to form the chiasmatic process (2) which 
passes across the floor as a prominent transverse ridge. The 
dorso-cephalic surface of this ridge becomes rapidly depressed 
as it proceeds cephalad, and in the mid-sagittal plane becomes 
the caudal boundary of the prechiasmatic recess (38). 
Traced laterad this recess leads into a small tubular canal 
which extends for some distance above the optic nerve, the 
supraoptic recess (42). In the selachian the lamina terminalis 
(20) occupies a nearly horizontal plane, extending with a slight 
dorsocephalic inclination from the prechiasmatic recess to the 
corpus striatum. 
EMBRYOLOGICAL ANALYSIS OF THE DIENCEPHALIC FLOOR IN THE 
CAT, CHICK AND DOG-FISH 
The following analysis of the floor of the interbrain is based 
upon some recent work of Prof. H. von W. Schulte (12), in which 
the writer collaborated.! It is shown in this study that the fore- 
brain in the cat consists of two primitive elements, the optic 
vesicles and the mammillary region. The latter persists with 
but little alteration until a relatively late period. The primi- 
' In connection with this work it gives me pleasure to express my-indebtedness 
to Professor Schulte for, although it was my privilege to collaborate with him 
in the study of the early development of the brain in the domestic cat, the new 
ontogenetic interpretation resulting from this investigation originated with him. 
