126 J. B. JOHNSTON, 
tracts to be described immediately. The ectal portion contains a large 
part of the fibres of the middle zone together with the most of the 
fibres of the superficial zone. This large bundle divides at once, 
at the lateral border of the tectum, into two main tracts, the tractus 
tecto-bulbaris and tractus tecto-lobaris. Two important facts are to 
be noticed about the division of this common tract: the fibres of 
the tractus tecto-lobaris are much finer than those of the tractus 
tecto-bulbaris, and some of the fine fibres arise by division of the 
fibres of the common tract at the point of separation of the two 
tracts. The division of numerous fibres is clearly seen in my pre- 
parations, so that many of the fibres of the tractus tecto-lobaris are 
to be considered as collaterals from those of the tractus tecto- 
bulbaris. The fact that all the fibres of the former tract are fine 
suggests the possibility that all of them have arisen by division of | 
fibres running in the middle zone of the tectum. 
Describing now the further course of the tractus tecto-bulbaris, 
it is a large tract of medium sized fibres which are not heavily 
medullated. It is made up of fibres from all parts of the tectum in- 
cluding the torus semicircularis Halleri (Fig. F, a), the fibres from the 
cephalic part of the tectum occupying at first the cephalic and then 
the ventral part of the bundle as it traverses the wall of the mid 
brain and turns caudad along the ventro-lateral surface of the medulla. 
As it descends from tectum to medulla the tract bends around the 
cephalic surface of the secondary vagus nucleus and in the medulla 
it runs latero-ventral to the secondary vagus tract. The tract is 
quite superficial in position and is easily followed back along the 
medulla. The fibres are relatively straight and are varicose. At 
intervals the fibres give off collaterals which enter the ventro-lateral 
columns and occasional fibres turn inward to end in those columns. 
Owing to this loss of fibres the tract grows smaller as it proceeds 
and is lost at about the level of the last roots of the vagus. 
As the large common tract divides at the lateral border of the 
tectum as above described, a considerable number of its fibres do 
not join either the tract to the lobus or that to the medulla, but 
run directly ventrad and decussate in the superficial, ventral portion 
of the commissura ansulata. These fibres join the corresponding 
tracts of the opposite side, constituting crossed tracts both to the 
lobus and to the medulla. The crossed tract to the medulla joins 
the direct tract soon after crossing in the commissure. Both 
the direct and crossed tracts are shown in Pl. 13, but the 
