NEUROLOGY 297 



brain. At this point the pia mater and the ependyma, or the lining 

 cells of the ventricular membrane, form the major part of the wall. 



The domestic fowl does not have the hippocampus. 



The wall of the middle ventricle consists of an outer white layer, 

 which is arranged similarly to that of the corpus striatum. The 

 ventral rim of the wall is formed by a spiral band which consists 

 of fine medxiUated fibers, in which are imbedded a few cells. 



The processus cerebri mammillares are also called the tubercula 

 olfactoria. From these structures extend forward the olfactory 

 nerves, the posterior roots of which may be traced to the walls of 

 the lateral ventricles. 



The structure of the processus cerebri mammillaris is made up of 

 five layers as follows: 



An outer layer, which consists of colorless olfactory fibers extend- 

 ing in all directions. 



A granular groimd substance layer, in which are imbedded a few 

 cells. 



A thicker granular layer, on the inner edge of which are twenty 

 large pyramidal cells with processes pointing outward. 



A layer of closely packed cells, in which are fine meduUated nerve 

 fibers. These cells are about 5 millimeters in diameter. 



An innermost layer of ependymal cells. 



Near the hemisphere the peripheral nerve fibers and nerve cells 

 disappear, leaving only the ground substance of the processus to aid 

 in the formation of the hemisphere. 



There is a long bundle of fibers on the lower surface of the hemi- 

 sphere, which blends with the substance of the olfactory fibers. 



The peduncles of the cerebrum (Fig. 62, No. 21) are the sUghtly 

 diverging columns of nerve tissue, which form the anterior continua- 

 tion of the medulla oblongata and disappear under the optic tracts 

 and the chiasm. 



THE SYMPATHETIC NERVOUS SYSTEM 



The sympathetic nervous system commences anteriorly at the 

 large superior cervical nerve ganglion. This ganghon, anteriorly, 

 brings into communication the glosso-pharyngeal, the pneumo- 

 gastric, or vagus, and the sympathetic system. 



The following nerve trunks emerge from the superior cervical 

 nerve ganghon: a large trunk fusing with the vagus and directed 



