190 ELEMENTS OF MAMMALIAN ANATOMY. 
fibers, known as the internal capsule, separates the optic 
thalamus from the nucleus lenticularis, laterad of which 
is the external capsule, a group of fibers probably descend- 
ing from the cells of the cerebral cortex. The two nuclei 
of the corpus striatum are connected by fibers, and other 
fibers connect these nuclei with the cortex of the cerebrum 
and the optic thalamus. 
The Medulla Oblongata.—The medulla oblongata, or 
myelencephalon, is the stem of the true brain and extends 
from the point of origin of the first spinal nerve to the 
pons Varoliu. The cerebellum must be removed in order 
to study carefully the features of the medulla, and as it is 
cut away the student should notice just ventrad to it the 
very thin roof of the fourth ventricle. Its caudal portion, 
composed of a reflection of the pia mater lined with epi- 
thelium, takes the name of inferior medullary velum, and 
the cranial part, formed of pia and a thin layer of nervous 
matter, is called the anterior medullary velum (Fig. 95). 
The fourth ventricle (Figs. 95 and 96) is an enlargement 
of the canalis centralis of the cord. Two bands of fibers 
called clave, the three peduncles or crura of the cerebellum, 
and the posterior corpora quadrigemina form its lateral 
boundaries. Its cavity is shallow and pointed at either 
extremity. The floor, called fossa rhomboidea, is formed 
by the continuation of the gray matter of the spinal cord. 
Where the ventricle is widest a tract of fibers, the stria 
medullaris, arises from the midline and proceeds laterad 
to help form the auditory nerve. 
Laterad of the clava a larger band of fibers, the funiculus 
cuneatus, runs parallel with a more lateral lying bundle, the 
funiculus cuneatus lateralis, or funiculus of Rolando. The 
band of fibers on either side uniting the cerebellum to the 
medulla oblongata is the restiform body, or inferior peduncle 
of the cerebellum. On the ventral aspect of the medulla 
