266 FREDERICK TILNEY 
optic nerve and chiasm, chiasmatic process, prechiasmatic and 
supraoptic recesses of the third ventricle. The derivatives of 
the ventral evagination of the infundibular region in Mustelus 
are the inferior lobes, median post-chiasmatic groove and the 
infundibular process (including the pituitary surface, the saccus 
vasculosus and the lateral processes of the saccus). From the 
dorsal evagination arises the post-infundibular eminence. The 
mammillary region becomes the posterior lobe. 
DISCUSSION 
A review of the literature covering the diencephalon reveals 
certain difficulties imposed upon this region by terminology. 
These difficulties are especially pronounced in the basal region 
of the interbrain, which His (10) has called the hypothalamus. 
The advantage of this term in the adult human brain, as well as 
in other mammalian forms, is obvious; but it loses its precision 
when applied to many of the lower vertebrates. There is much 
to recommend the term hypencephalon (Unterhirn) suggested 
by von Kuppfer (7). This, however, refers to a somewhat 
arbitrary subdivision of the diencephalon, and von Kuppfer 
himself is not always consistent in its application, since in some 
instances he uses it as the equivalent of the hypothalamus, while 
in others he restricts it to the basal area of the interbrain, ex- 
clusive of the infundibulum. The latter element, ‘infundibulum,’ 
more perhaps than any other part in this region, has been a 
source of confusion. Johnston’s (11) objections to the use of 
the term ‘infundibulum’ seem well founded. As he points out, 
the application of this term to a relatively extensive embryologi- 
cal area and also to a much more restricted portion of the adult 
brain is almost certain to be misleading. Usage, however, has 
given it a permanency in the literature and in addition to this 
the phylogenetic significance attached to the part by some 
investigators cannot be overlooked. As already stated, Ayers 
(2) asserts that the hypophysis arose as an organ of taste and 
the infundibulum was its nerve. Boeke (19) has found in Murae- 
noids from the third day of embryonic life until the critical 
