246 R. L. KITCHELL 



counts (Table 1). Van Buskirk (1945) estimated that there were 1034 

 myelinated fibers in the chorda tympani nerve in cats and 1696 fibers in the 

 dog. 



The range of the diameters of the myelinated fibers in the chorda tympani 

 nerve of the cat has been estimated to be 1.5 to 6//, with the majority of 

 fibers estimated to have diameters of 2 to Aft (Foley and Dubois, 1943). 

 Bruesch (1944) estimated the majority of myelinated fibers were 3/^ or less 

 in diameter. Van Buskirk (1945) estimated that myelinated fibers were 

 2-Aft in diameter. The data presented (Fig. 9 and Table 1) show that some 

 of the myelinated fibers in the chorda tympani nerves in the cat were less 

 than 2// in diameter. The largest fibers were in the 12 to lA/i diameter 

 group. Andersson, Landgren, Olsson, and Zotterman (1950) estimated 

 that in the chorda tympani nerve of dogs, the myelinated fibers were 4 to 

 6/1, in diameter. The data shown in Fig. 9 and Table 1 illustrate that some 

 of the myelinated fibers in the chorda tympani nerves in the dog were less 

 than 2 ft in diameter. The largest fibers were in the 12 to 14// diameter group. 



Sunderland and Roche (1958) studied the axon-myelin relationships in 

 peripheral nerve fibers and have concluded that considerable variation in 

 total fiber diameter, myelin thickness, axon diameter and internode length 

 occurs along individual fibers. They suggest that in a single myelinated 

 fiber the axon diameter is more constant than the total fiber diameter. The 

 results in the present study are not in conflict with their hypothesis. 

 Material prepared in a similar manner from different animals or different 

 species of animals should be subjected to meaningful analysis and com- 

 parison. 



The neural responses in the chorda tympani and glossopharyngeal nerves 

 have been studied in some of the domestic animals. Figures 11-16 illu- 

 strate the results of recent observations. EarHer observations have been 

 published (Kitchell, Strom and Zotterman, 1959 ; Gordon, Kitchell, 

 Strom, and Zotterman, 1959; Baldwin, Bell, and Kitchell, 1959). The 

 animal is prepared in the following manner. The animal is deeply anesthe- 

 tized with a barbiturate anesthetic. The mandible is exposed and resected 

 between the canine and premolar teeth. After ligating the mandibulo- 

 alveolar vessels, the mandible is removed by disarticulation at the temporo- 

 mandibular articulation. The mucous membranes of the vestibule and the 

 oral cavity are brought into apposition with mattress sutures. The arti- 

 cular disk of the temporomandibular articulation is removed and adjacent 

 blood vessels are ligated. The chorda tympani nerve is located and dis- 

 sected free from surrounding tissues. A dissecting microscope is used to 

 assist in the removal of fat and as much of the epineurium as possible with- 

 out damaging the nerve. This " desheathing " operation is relatively 

 simple on the non-fasciculated nerves as found in the dog and cat. In 

 animals possessing fasciculated chorda tympani (Figs. 6 and 7) extreme 



