INTERNAL STRUCTURE OF THE PONS VAROLIL. 463 
very far from being complete. When a transverse section through the upper part of the 
pons is compared with one close to its lower border, it becomes at once apparent that the 
_ numerous scattered bundles of longitudinal fibres which enter the ventral part of the pons 
from above, if brought together into one tract, would form a strand very much larger than 
the two pyramids which leave its lower aspect and enter the medulla. It is clear, there- 
fore, that many of the longitudinal fibres which pass into the pons from above do not pass 
out from it below into the medulla. What becomes of these fibres that are thus absorbed in 
the pons? It is known that the pyramidal bundles suffer a small loss by the fibres which 
nucleus 
7——0O 
Substantia 
_-gelatinosa 
Rolandi 
»~ mH 2 © 
5 H 5 
S = — 3 = 
re (>) = oe = in 
LE EGY ay © a 6 os FB ) 
Ss 2 : s 9 eS & a 
eS 5 oS a pe ye 
Ae Dp v Pet ks) BS) IS) H 
2 ess = Ss Ss n S 
Este awa payee Oe one 
EN ay cag a) ES Mes We SNE 
es ~ & # Bont Fe Ons Restiform body 
Dia Boas Hae eaigigea at siore 
ACR Ss St oe & PHS ere 
=_ js = = 
w 5 mn Se 
= = = 
= ae poe & 50% 
oO in ons 
= L Sis 
AG 5 3 
A & Ae 
Spinal root of 
fifth nerve Vestibular 
y— nerve (VIII.) 
OO 
Substantia gela- ; 
tinosa Rolandi ——__»\ AN 
Facial nerve ——__. 
Spinal root of 
— fifth nerve 
Facial nucleus ~——Facial nucleus 
; 
Superior olive 
: 
| Central teg- 
mental tract 
Fillet 
. ER 
N 
\ 
ee , 
Middle peduncle of 
| cerebellum 
. Transverse fibres of pons 
. 
F Fic. 344. SECTION THROUGH THE LOWER PART OF THE HUMAN PONS VAROLII IMMEDIATELY ABOVE 
f THE MEDULLA. 
- . 
_ they send to the nuclei of origin of the efferent nerves which arise within the pons (viz. the 
~ motor root of the fifth, the sixth, and seventh nerve nuclei) ; but this loss is, comparatively 
speaking, trifling. It is clear, therefore, that other longitudinal bundles enter the pons 
| from above than those which form the pyramidal tracts. These bundles occupy a lateral 
| and dorsal position in the ventral part of the pons, and may be termed the cortico-pontine 
fibres, seeing that they are supposed to come from the cerebral cortex and end in fine 
_ ramifications around the cells of the nucleus pontis. 
. The transverse fibres are of two kinds, viz.: (1) those which arise in the cortex of the 
— cerebellum ; and (2) those which take origin in the nucleus pontis. The former are the 
axons of certain of the cells of the cortex of the cerebellum (cells of Purkinje). They come 
_ chiefly from the lateral hemisphere, but also to some extent from the central lobe of the cere- 
bellum, and enter the pons by the middle peduncle. They end in fine ramifications around 
the cells of the nucleus pontis, some on the same side as the peduncle through which they 
reach the pons, but the majority in the gray matter of the opposite side. 
The transverse fibres which arise in the pons take origin as axons of the cells of the 
nucleus pontis. Crossing the mesial plane, they enter the middle peduncle of the opposite 
side, and thus reach the cerebellar cortex, where they end in ramifications round certain 
of the cortical cells. The middle peduncle thus contains both efferent and afferent cere- 
bellar fibres, and no fibres pass continuously through the pons from one middle peduncle 
