272 FREDERICK TILNEY 
having no contact with this gland. The ventral surface because 
of its relations may be called the pituitary surface, the dorsal 
one because of its participation in the formation of the saccus 
vasculosus, the saccular surface. These two surfaces are pres- 
ent in the bird; but in the cat, although the dorsal surface of 
the infundibular process is much thinner than its ventral surface, 
there is no other evidence of the tendency toward saccus for- 
mation. As development proceeds in the selachian, the pituitary 
surface maintains its primitive relations unchanged while the 
saccular surface becomes more extensive and in Mustelus at the 
period of 20 em. shows the first evidence of a rich vascularization 
and the tendency of its thin wall to be thrown into numerous 
convolutions typical of the .saccus vasculosus. The pituitary 
and saccular surfaces extend laterad for a considerable distance, 
their size being reduced as they extend farther away from 
the median line so that they ultimately form two long tapering 
outgrowths, one at either extremity of the infundibular process, 
called the lateral processes. Similar outgrowths are observed 
-in the development of the bird, and while no definitely correspond- 
ing structure is found in the cat, the lateral extremities of the 
infundibular process are much extended in a manmer which 
seems to be reminiscent of the lateral processes in the bird and 
selachian. In the bird, as already shown, the dorsal surface 
of the infundibular process is convoluted but non-vascular; its 
walls are thick. All of the morphological evidence concerning 
it tends to show that this surface is the strict homologue of the 
saccular surface in the selachian, and that, whereas in the fish 
it proceeds to form the saccus vasculosus, the saccus formation 
in the bird is aborted, although the sauropsid still retains evi- 
dence of the tendency toward the formation of this structure. 
Furthermore, the late stages of embryonic life in the bird corre- 
spond in many details to the saccus formation as it appears in 
this region of the selachian. 
In the mammal, as illustrated by the cat and other Felidae, 
there is nothing which suggests the saccus formation in any part 
of the infundibular process further than the very thin dorsal 
surface which is emphasized, in the early stages, by the rapid 
