The afferent and efferent myelinated fibres of the avian cervical vagus.

The numbers and diamters of the myelinated fibres in the cervical vagus have been studied in normal birds and after midcervical and intracranial vagotomy. The mean total number of myelinated fibres was about 9066 in the right cervical vagus and 8535 in the left. In the right nerve about 4223 of these fibres were afferent and 4843 were efferent; of the afferent fibres about 520 had their cell bodies in the proximal vagal ganglion (or distal glossopharyngeal ganglion) and 3703 in the distal vagal ganglion. In the left cervical vagus, about 4132 afferent fibres had their cell bodies in the distal ganglion, and there were probably about 3883 efferent fibres. The largest fibres in the cervical vagus were usually about 7 micrometer in diameter, fibres of 3 micrometer or less comprising from 72% to 89% of the total.