140 



HISTOLOGY 



are therefore entirely motor. Still others have no ventral roots, but re- 

 ceive motor fibers through lateral roots. The fibers in the lateral roots are 

 like motor fibers of the ventral roots in that they arise from cells within 

 the central nervous system, but their processes emerge from the lateral 

 wall of the brain instead of the ventral wall. They come out immediately 

 below the entering sensory fibers of the dorsal roots. 



Beginning at the anterior end of the brain and proceeding toward 

 the spinal cord, the cerebral nerves occur in the following order: olfactory, 

 optic, oculomotor, trochlear, trigeminal, abducent, facial, acoustic, glosso- 

 pharyngeal, vagus, accessory and hypoglossal. 



FIG. 130. THE CEREBRAL NERVES OF A IZ-MM. PIG. 



Olfactory (not shown). Optic (fibers in the stalk of the eye, the lens of which is marked L). Oculomotor 

 (Oc.). Trochlear (Tr.). Trigeminal, semilunar ganglion (s.-l.); ophthalmic (oph.), maxillary 

 (va..) and mandibular (md.) branches. Abducent (Ab.). Facial, geniculate ganglion (g.); large 

 superficial petrosal (1. s. p.). chorda tympani (ch. ty.), and facial (fa.) branches. Acoustic (A.), supply- 

 ing the otocyst (Ot.). Glossopharyngeal, superior (s.) and petrosal (p.) ganglia; tympanic (t.), lingual 

 (1. r.) and pharyngeal (ph. r.) branches. Vagus, jugular (j.) and nodose (n.) ganglia; auric- 

 ular (au.) and laryngeal branches, rec. being the recurrent nerve; the main stem proceeds to the abdo- 

 men. Accessory, internal ramus joining the vagus, and external ramus (ex.). Hypoglossal (Hy.). 

 Froriep's rudimentary hypoglossal ganglion (F.) sometimes sends fibers to the hypoglossal nerve, c.i, 

 c.2, c.3, cervical nerves. 



It is desirable to use the names of these nerves rather than the numbers 

 often applied to them. The names are descriptive, but the numbers are 

 arbitrary and were very variously employed in the older anatomical works. 

 Unlike the spinal nerves, the cerebral nerves are not a series of similar 

 structures. Moreover the recent demonstration of the Nervus terminalis 

 in mammals indicates that the numbering may need further revision. 



In embryos measuring about 10 mm., the cerebral nerves are all present 

 and show their primary branches. Except the olfactory nerve, they are 



