No. 3.] MUSCLES AND NERVES IN AMIA CALVA. 593 
In 12 mm. and 14 mm. specimens the median fold in the 
base of the infundibulum is not yet formed, but there is already 
a slight thickening of the tissue, indicating its position. The 
hypophysis has much the appearance that it has at 50 mm., but 
there is less evidence of glandular formation. The vein vo 
lies entirely behind the organ, instead of behind it and along 
the posterior portion of its lateral edge, as at 50 mm., and is, 
as at that age, directly continuous with it. The base of the 
brain, above the vein, is formed of a single layer of cells, as is 
also the saccus vasculosus, which is, as in Acipenser (No. 69), a 
simple sack-like prolongation arising from the lower posterior 
limit of the base of the infundibulum and running directly back- 
ward, its hind edge being wedged under the front end of the 
medulla. It is narrow in front, widens considerably as it extends 
backward, and contains a large central cavity, but gives at this 
age no indication whatever of a glandular structure or of associa- 
tion with such a structure. Immediately dorsal to it there is 
another posterior prolongation of the infundibular cavity which 
turns upward in front of the front end of the medulla and ends 
there blindly. It is the saccus dorsalis infundibuli of von 
Kupffer in Acipenser (No. 69, p. 19), and from it arise laterally 
the cavities of the lobi inferiores, as in Acipenser. 
In the adult (Fig. 64, Pl. XX XVIII) there is a true lobus 
infundibulum, not shown by Goronowitsch (No. 50) in his 
figures, and there is also a large and long saccus vasculosus (sv) 
not shown by him, the part called by him the saccus being the 
lobus infundibulum or part of that structure. The lobus infun- 
dibulum lies between and below the lobi inferiores (/), the 
hypoaria of Gage (No. 40, p. 281), and its posterior portion is 
trilobate in outline. The median of the three lobes contains 
the posterior prolongation of the infundibular cavity, described 
above, and the two lateral lobes contain each a slight lateral 
prolongation of that cavity. 
In the base of the median lobus there is a median slit-like 
opening which leads directly into the anterior end of the 
saccus vasculosus, which is here formed of a single layer 
of cells lined externally by a large venous sinus of a semi- 
circular or horse-shoe shape. At the hind end of the slit 
