CHAPTER XIX. 



PHYSIOLOGY OF THE CRANIAL NERVES. 



THE Cranial nerves are commonly enumerated as nine pairs; but 

 the number is in reality twelve pairs, the seventh nerve consisting as it 

 does, of two nerves, and the eighth of three. All arise (superficial ori- 

 gin) from the base of the encephalon, in a double series which extends 

 from the under surface of the anterior cerebral lobes to the lower end 

 of the medulla oblongata. Traced into the substance of the brain and 

 medulla, the roots of the nerves are found to take origin from various 



&-VVV 



Fio. 365. Fourth ventricle, with the medulla oblongata and the corpora quadrigemina. The 

 roman numbers indicate superficial origins of the cranial nerves, while the other numbers indicate 

 their deep origins, or the position of their central nuclei. 8, 8', 8", 8'", auditory nuclei nerves; t, 

 funiculus teres; A, B, corpora quadrigemina; c g, corpus geniculatum; p, c, pedunculus cerebri; m, 

 c, p, middle cerebellar peduncle; s, c, p, superior cerebellar peduncle; t, c, p, inferior cerebellar pe- 

 duncle; I, c, locus caeruleus; e, , eminentia teres; a, c, ala cinerea; a, n, accessory nucleus; o, obex; 

 c, clava; /, c, funiculus cuneatus; /, gr, funiculus gracilis. 



masses of gray matter, which are all connected one with another, and 

 with the cerebral hemispheres. 



The roots of the olfactory and of the optic nerves have been already 

 mentioned. The third and fourth nerves arise from gray matter be- 

 neath the corpora quadrigemina; and the roots of origin of the remainder 

 of the cranial nerves can be traced to gray matter in the medulla oblon- 



