19 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 Varolii. 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 rhomb oidea, 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 



