Following the demonstration of unmyelinated fibers in the spinal nerves and in the vagus nerve by means of the pyridinesilver technique (Ranson, '11 and '12; Chase and Ranson '14), Professor Ranson suggested the application of the same method to the study of certain of the cranial nerves, with especial reference to the presence or absence of unmyelinated fibers.
The nerves studied were the oculomotor, trochlear, trigemnal, and abducens of the dog and of man; and the glossopharyngeal, accessory, and hypoglossal nerves of the dog, the cat and the rabbit. The nerves were obtained by lifting off the skull cap and following them distally from their cerebral origin by chipping away the base of the skull about their foramina of exit. The difsected specimens were laid on glass slides and prepared by different methods. Some were stained by the pyridine-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 pyridine-silver method; others were stained by the Pal-Weigert method and the osmic acid method. All were cut and mounted serially.
The oculomotor, trochlear, and abducent nerves form a natural group formerly described as purely motor and consisting of large and small myelinated axons, but now recognized as containing 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.
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