STRUCTURE OF THE CRANIAL NERVES 547 



The unmyelinated fibers seen in connection with the Ilird 

 and Vlth nerves nowhere showed the characteristic arrange- 

 ment of the unmyehnated fibers seen in the spinal nerves and the 

 vagus. In the Ilird nerve the unmyelinated fibers remained 

 grouped in the nerve sheath and did not enter its substance. 

 More distally they separated from the nerve completely. The 

 unmyelinated fibers which joined the Vlth nerve and entered 

 into intimate association with the myehnated fibers were not 

 uniformly distributed throughout the nerv^e substance, but re- 

 mained at the periphery, definitely grouped in two or three of 

 the fasicles of the nerve. In no sections did these unmyelinated 

 fibers from the sympathetic system appear evenly and uniformly 

 distributed throughout the nerve substance as do tlie unmye- 

 linated fibers in the spinal nerves and the vagus. 



THE THICKMIXAL XKRVE 



The intracranial portion of the trigeminal nerve of the dog 

 and the cat, and of one human specimen was studied. Pyridine- 

 silver sections showed large and small myelinated fibers, and in 

 addition small munbers of unmyelinated fibers, appearing in 

 hygest numbers in two fasicles of the sensory portion of the 

 nerve. No sj-mpathetic fibers were seen joining the nerve within 

 the cranium. In osmic acid preparations of the Vth nerve of 

 the dog the large myelinated fibers measured 12 to 16 micra in 

 diameter, the small 3 to 6 micra. In the cat the small fibers 

 measured 4 to 7 micra, the large 12 to 16 micra, with occasional 

 fibers 18 micra in diameter. 



Till': GLOSSOPIIAUYXGEAL, ACCESSORY AND HYPOGLOSSAL NERVES 



The glossopharyngeal nerve is usually described as a mixed 

 nerve, and is recognized, according to Herrick's classification, as 

 containing both general and special v'sceral efferent fibers, and 

 general and special visceral sensory fibers, as well as somatic 

 fibers with sensory function. The accessory and hj^Doglossal 

 nerves are pure motor nerves, the former containing general and 

 special visceral fibers, the latter special somatic fibers. 



