The brain of Acipenser. 85 
central canal becomes the IV ventricle and the bundles of fine fibres 
at either side are easily traced forward into continuity with the 
structure which is recognized as the lobus vagi of GORONOWITSCH 
and others. The commissure, which bounds the IV ventricle caudally 
is the commissura infima Halleri, the cells in this commissure and 
at the sides of it constitute the nucleus of the commissure of CAJAL, 
and the bundle continuing caudally from the commissure is the 
cervical bundle of CagaL (96). These structures are all recognizable 
in sagittal sections, the cells of the nucleus and the cervical bundle 
being especially distinct in a series of sagittal sections stained by 
methylene blue and acid fuchsin. I havé studied the same structures 
in two series of GOLGI sections, one frontal and one sagittal, the 
only series in which they were impregnated. From the sagittal 
sections I have taken three photographs (Phots. 29, 30, 31) which 
show the lobus vagi connected with the commissure by a considerable 
number of impregnated fibres, and show also one or two cells of 
the nucleus and a few fibres of the cervical bundle. Following the 
lobus vagi forward it increases gradually in size and forms a large 
projection into the IV ventricle. It is largest at about the level of 
the glossopharyngeus. In front of this point there appear an in- 
creasing number of medullated fibres arranged in bundles and cut 
across in frontal sections. The number of cells decreases and at 
the level of the VIII the lobe consists almost entirely of medullated 
fibres. Finally these bundles turn laterad and, piercing the wall of 
the medulla, form the sensory root of the facialis proper (Phots. 8—13). 
At the caudal end of the medulla the lobus vagi is the most dorsal 
structure, but farther cephalad it is overtopped and pushed mesad 
by the greatly developed acusticum. 
Ending of sensory roots in lobus vagi. — The dorsal 
roots of the vagus are numerous and as they enter the medulla 
each rootlet divides into several bundles. These enter the dorso- 
lateral angle of the lobe and their fibres break up into end-branches 
chiefly in the dorsal and mesial portions (Phot. 8). The fibres 
usually divide by an equal Y-branching, and sometimes the branches 
- diverge, one running cephalad, the other caudad. More often the 
two branches continue in a nearly parallel course and end not far 
apart. Although the end-branching of the individual fibres is not 
especially profuse, they enter in large bundles and their branches 
form a dense mass of nerve twigs. 
