THE NERVOUS SYSTEM. Tot 
may be seen the anterior pyramids, composed of a band of 
fibers lying on either side of the median line and apparently 
emerging from the pons. They form a section of the 
crossed pyramidal or motor tract connecting the brain with 
the cord. The olivary eminence lies just laterad of the 
pyramid. The fact that seven posterior cranial nerves 
originate from the medulla shows the importance of this 
part of the brain. The destruction of the respiratory 
centers, or vital knot, lying ventrad to the caudal end of the 
fourth ventricle causes instant death. 
The Cerebellum, or Little Brain.—The cerebellum, 
which in the cat lies caudad of the cerebrum and dorsad 
of the medulla, resembles the cerebrum in being composed 
of an outer layer of gray matter or cells and an inner 
mass of white matter made up of fibers. While within the 
cerebrum there are several important ganglia or masses of 
gray matter, in the cerebellum only one chief mass of gray 
matter, the corpus dentatum, is present in each hemisphere. 
The outer layer of gray matter, known as the cortex, is 
folded into numerous convolutions, between which are deep 
sulci (Fig. 95). The central core of white matter forms 
an arborescence known as the arbor vite. 
The cerebellum (Fig. 92) is seen to consist externally 
of two lateral portions, the cerebellar hemispheres, a median 
vernuform process and three pairs of peduncles or crura 
which are bands of fibers uniting it with other parts of the 
brain and cord (Fig. 96). The separation between the 
hemispheres and vermis or vermiform process is most 
marked on the cranial aspect. 
The peduncles are named, according to their location, 
superior, middle, and inferior. The middle peduncle, or 
brachium pontis, is a dorsal prolongation of the fibers of 
the pons Varolii (Fig. 93). In order to display the other 
peduncles a portion of the cerebellum must be cut or picked 
