134 J. B. JOHNSTON, 
The fibres are very fine and appear in GOLGI and haematoxylin 
sections to be non-medullated. 
d) Tracts of the Hypothalamus. 
1) Tractus lobo-cerebellaris et bulbaris rectus. — 
This tract arises from the lateral surface of the lobus, runs dorso- 
caudad through the cephalic part of the nucleus ruber until it gains 
a position on the dorsal surface of that nucleus, then turns caudad. 
The tract consists of fine smooth, and coarse varicose fibres. The 
fibres are mingled with those of the tractus tecto-lobaris in their 
course through the nucleus ruber, so that the two tracts can be 
distinguished only by finding one impregnated in one series and the 
other in another series. Dorsal to the nucleus ruber, however, the 
present tract lies ental to the tractus tecto-lobaris. Caudal to the 
nucleus ruber the tract gradually assumes a more ventral position. 
At the cephalic border of the bridge between the mid brain and 
cerebellum a small part of the fine fibres turn into the cerebellum. 
A little farther on the greater part of the coarse fibres enter the 
cerebellum. The remainder of the tract passes immediately ventral 
to the secondary vagus nucleus and continues into the medulla. 
Here it is broken up into smaller bundles which gradually grow 
smaller and disappear at about the level of the VIII nerve. The 
fibres of this tract are throughout their course non-medullated. The 
fibres are closely packed and in GoLGI sections show no sign of 
osmic blackening as do the other tracts from the lobus. 
2) Tractus lobo-cerebellaris et bulbaris cruciatus. 
— Immediately behind the optic tract and ental to the tractus tecto- 
lobaris is a large tract of fibres which comes from the lobus in- 
ferior by way of the postoptic decussation. This is the largest tract 
from the hypothalamus to the hind brain. It consists of medium- 
sized medullated fibres which fill a large part of the space between 
the nucleus ruber and the central grey matter. As the tract ap- 
proaches the medulla it is in two parts, one of which bounds dor- 
Sally the direct tract just described, while the other runs nearer 
the central cavity. Three bundles are given off from this tract to 
the cerebellum. The first traverses the cephalic part of the bridge 
to the cerebellum behind the first bundle of the direct tract above 
mentioned, the second turns upward and inward close over the 
cephalic surface of the secondary vagus nucleus, and the third, 
crossing ventral to the secondary vagus commissures, enters the 
