348 NERVOUS SYSTEM. 
increase has affected principally the surface. of the roof, so that 
as the cerebellum has grown it has been thrown into many 
folds, the exact form of which varies in different specimens. 
The cerebellum has at the same time increased in size and has 
thus extended laterad as well as caudad and craniad. It thus 
touches the cerebrum in front (separated from it by the ten- 
torium) and aids it in concealing the midbrain and ‘tween-brain 
in dorsal view, while caudad in the same view it conceals the 
greater part of the medulla. The connections of the cerebellum 
with adjacent parts of the brain are also overhung and con- 
cealed. 
The whole surface of the cerebellum is thrown up into 
numerous folds or gyri, separated from one another by deep 
fissures or Sulci, which appear at first to render the surface 
wholly irregular. The entire mass is, however, divisible into 
a central portion, which from its resemblance to a segmented 
worm is called the vermis (7) (its cranial part is the superior 
vermis, and its caudal part the inferior vermis), and into lateral 
portions, the hemispheres (4). The vermis (7) occupies a 
median longitudinal position, and its gyri and sulci are in the 
main transverse. It is not directly connected with adjacent 
parts, and its ventral surface extends farther caudad and craniad 
than that of the hemispheres. The ventral part of the superior 
vermis is fitted against the posterior corpora quadrigemina. 
The hemispheres (£) may again be subdivided into groups 
of gyri which have received special names. One of these, the 
so-called appendicular lobe, fits into the appendicular fossa of 
the petrous bone. 
The cerebellum is connected to the adjacent parts by three 
tracts of fibres, sometimes known as crura cerebelli. The tract 
connecting it with the medulla oblongata is the corpus resti- 
forme; that connecting it with the pons is the brachium 
pontis (Fig. 141, 7); these have been described. A third 
tract passes craniad to the corpora quadrigemina (Fig. 141, 
and g); this is the brachium conjunctivum (Fig. 141, 2). 
The cerebellum is composed of white and gray matter, the 
latter on the surface (Fig. 143, ///). The folds of its surface 
present thus a contrivance for increasing the amount of gray 
