THE STRUCTURE OF THE THIRD, FOURTH, FIFTH, 



SIXTH, NINTH, ELEVENTH AND TWELFTH 



CRANIAL NERVES 



SUMNKIl L. KOCH 



From the Analomical Laboratory of the Xorthivestern University Medical School 



FIVE FIGURES 



FoUowmg the denioiistration of uiiinyeliiiatccl fibers in the 

 spinal Rentes and in the vagus nerve by means of the pyridine- 

 silver technique (Ranson, '11 and '12; Chase and Ranson '14), 

 Professor Ranson suggested the appUcation of the same method 

 to the study of certain of the cranial nerves, with especial refer- 

 ence to the presence or absence of unmyelinated fibers. 



The nerves studied were the oculomotor, trochlear, trigem'nal, 

 and abducens of the dog and of man; and the glossophaiyngeal.. 

 accessory, and hypoglossal nerves of the dog, the cat and the 

 rabbit. The nerves were obtained by Ufting off the skull cap 

 and following them distally from their cerel)ral origin by chip- 

 ping away the base of the skull about their foramina of exit. 

 The di^sccted specimens were laid on glass slides and prepared 

 by different methods. Some were stained by the p>Tidine-silver 

 method; others were placed in 50 per cent pyridine solution for 

 seven days, washed, and then treated with silver nitrate, water, 

 and pyrogallic acid as in the j^yricUne-silver method; others were 

 stained by the Pa'-Weigert method and the osmic acid method. 

 All were cut and mounted serially. 



The oculomotor, trochlear, and aixlucent nerves form a natu- 

 ral group formerly described as pureh' motor and consisting of 

 large and small myelinated axons, but now recognized as con- 

 taining somatic afferent as well as efferent fibers. The nerves 

 are described as communicating with the ophthalmic division 

 of the trigeminal nerve and with the cavernous plexus of the 

 sympathetic system. 



' Contribution no. -40. 



541 



