The brain of Acipenser. 69 
attached to the wall of the thalamus between the base of the epi- 
physis and the superior commissure. GORONOWITSCH was of course 
in error in considering this as a dorsal diverticulum of the fore 
brain. It is the paraphysis or Zirbelpolster of later authors. 
The commissura superior and the ganglia habenulae may be 
seen in Phot. 5 in deep shadow just in front of the adhering ragged 
edge of the paraphysis, while in Phot. 6 they appear wholly isolated 
by the removal of all choroid parts of the ‘tween brain roof. In 
the latter photograph the larger size of the right ganglion is evident. 
The ridge running forward from the ganglion on either side along 
the dorsal border of the thalamus is due in part to the tractus 
olfacto-habenularis. Beneath it lies the nucleus anterior. In Phot. 3 
the ganglion habenulae occupies the caudal part of the cavity of 
the paraphysis and the nucleus anterior makes up a large part of 
the low triangular elevation seen directly ventrad to this ganglion. 
The relatively wide cavity of the thalamus leads down into the much 
more spacious cavity of the lobi inferiores, in front of which the 
floor of the ‘tween brain is formed by the optic chiasma (Phot. 3). 
The large inferior lobes are seen (on the left side only) in 
Phots. 5, 6, and 7, projectiug far out laterally beyond the thalamus. 
In Phot. 4 the lobe appears as an olive-shaped body as large as 
the tectum. In front of it is the optic nerve, and its caudal wall 
is continuous with the less expanded, but still large, corpus mammillare. 
Ventral to the inferior lobes is the hypophysis and caudal to both 
the saccus vasculosus. In median section the cavity of the inferior 
lobe appears nearly circular (Phot. 3). It is bounded by a prominent 
rounded ridge which projects inward. At its caudal border this ridge 
is notched to give communication with the cavity of the corpus 
mammillare. From the point at which this communication is effected 
the cavity of the C. mammillare extends dorsad and ventro-cephalad 
in the form of a crescent. Caudad the C. mammillare communicates 
by a wide passage with the saccus vasculosus. Several of the lateral 
subdivisions of the saccus are visible in Phot. 3, as is also the close 
relation of the caudal end of the hypophysis to the saccus and the 
C. mammillare. | 
D. The Fore Brain. 
The choroid roof of the fore brain fuses completely with the 
ventral wall of the paraphysis, so that they appear on gross examin- 
ation as a simple membrane. After this membrane is removed 
