The brain of Acipenser. 123 
nerve fibres as in the older fish. It is certain, then, that the caudal 
portion of the hypophysis in Acipenser is penetrated by several 
tubular expansions of the ventral wall of the corpus mammillare 
which are lined with ciliated epithelium and are in every way com- 
parable with the walls of the saccus. In older fish these tubes lose 
their connection with the cavity of the corpus mammillare. 
Two sets of nerve fibres, afferent and efferent, are to be re- 
cognized in the saccus. The afferent fibres are neurites from the 
ciliated cells. I have stated that in GoLGI sections of Acipenser 
I have in a few cases seen nerve fibres arising from the bases of 
these cells and entering the nerve bundles, and that in methylene 
blue sections of Amiurus (stained intra vitam) I have found the 
same cells and fibres stained. In the latter material I have traced 
individual fibres from their cells of origin into the inferior lobes. 
In Acipenser these fibres are fine and form dense bundles which 
are very conspicuous in any histological sections (Phots. 19, 20 21). 
Those from the larger, caudal part of the saccus form paired bundles 
which enter the lateral walls of the mammillare from the caudal 
direction, while those from that part of the saccus imbedded in the 
hypophysis enter at the junction of the mammillare and lobi and 
join the former bundles in the lateral wall of the corpus mammillare. 
There are several dense bundles which run up over the lateral face 
of the cavity of the mammillare (Phot. 19), bend cephalad and run 
forward in the dorsal wall of the mammillare and ot the lobi 
(Phot. 20, 21), divide into smaller bundles and break up in end- 
branches in a nucleus occupying the extreme ventral angle of the 
thalamus (Phot. 22, cf. page 114 above). I have demonstrated the whole 
course of these fibres after entering the mammillare and their end- 
branching in GOLGI preparations. 
The efferent fibres which end freely in the epithelium of the 
saccus I have shown in Phots. 56, 58, 61, 62. These fibres come 
from the ventral wall of the lobi inferiores and are distributed to 
both parts of the saccus. The GoLGI sections from which the 
photographs are taken show these fibres only in the saccus tubes in 
the caudal part of the hypophysis, but I have followed the bundles 
without difficulty from the lobi to the body of the saccus in histo- 
logical sections. Photographs 56 and 58 show the general arrange- 
ment of these fibres. The sections are sagittal, the cavity of the 
mammillare being above and the inferior lobe being seen sligthly at 
the right. The bundle of fibres comes from the inferior lobe, following 
