122 The Corpus Ponto-Bulbare 
out from the pons extends from a point about 5 mm. in front of the 
fifth nerve to 4 mm. in front of the seventh nerve. An interesting varia- 
tion to this general arrangement is found where fiber bundles encircle the 
trigeminal nerve or appear to come up out of the pons immediately be- 
hind it, and then take the regular course between the facial and acoustic 
nerves. Few specimens did not show this part of the ponto-bulbar body 
very plainly. 
Although no reference is made to it, an admirable picture of the 
pontine part is given by Retzius* in his Atlas, Plate IV, Fig. 1. On the 
left half of the brain (right side of figure) the eighth and seventh nerve 
roots can be seen just median to the flocculus. In front of these nerves 
a definitely corded ridge is present passing forward, median to the 
trigeminal nerve to be lost in the pons. The choroid plexus from the 
lateral recess hides the corresponding right part of the brain in the 
neighborhood of the seventh and eighth nerves, but the way in which the 
ponto-bulbar body arises from the transversely directed pons fibers, 
median to the root bundles of the fifth nerve, and then assumes a caudal 
direction, is particularly well illustrated. 
By far the most constant part of the ponto-bulbar body, appearing on 
mere gross examination of brain, is the welt-lke ridge which it forms 
ventral to the restiform body after it has passed between the facial 
and acoustic nerves. This portion is difficult to display in the whole 
brains preserved in formalin, because it necessitates removing the pia 
mater from the depression between the flocculus and the olive and, unless 
great care is used, this procedure takes with it the root bundles of the 
glosso-pharyngeal nerves. ‘The part of the ponto-bulbar body which is 
then brought into view, extends about 6 mm. caudally as a prominent 
elevation having a width of 3 mm. in all specimens which were measured. 
We find it nearly always extending so as to surround the most cephalic 
of the glosso-pharyngeal roots. In this event, the appearance is that of 
a hill-shaped eminence with the stumps of the glosso-pharyngeal nerve 
emerging from the summit. On the left side of the brain illustrated by 
Retzius, Fig. 11, Plate XX XVIII, there appears the best illustration of 
this portion of the ponto-bulbar body. Here the hypoglossal nerve roots 
may be recognized as they emerge mesial to the olive. Lateral to the 
olive is a well marked ridge with five root bundles of the glossopharyn- 
*Gustaf Retzius: Biologische Untersuchungen, Neue Folge XII, 1905. 
5 Gustaf Retzius: Das Menschenhirn, Vol. II, Stockholm, 1896. 
