234 



The Depressor Nerve of the Rabbit. 



2. The size of the nerve and the number of fibres it contains vary in 

 different individuals. The left nerve is generally larger and contains more 

 fibres than the right. 



3. The depressor contains not only medium-sized myelinated fibres, but 

 also a considerable number of very fine myelinated fibres, and others which 

 are non-myelinated. It is, therefore, probably not wholly formed, as has 

 usually been supposed, of afferent fibres, for these fine myelinated and non- 

 my'elinated fibres closely resemble those belonging to the autonomic nervous 

 system and are presumably efferent.* 



The expenses of this investigation have been mainly defrayed by a 

 grant from the Earl of Moray Fund for promoting Eesearch in the 

 University of Edinburgh. 



DESCRIPTION OF PLATE. 



Fig. 4. — Section of vagus trunk just before the superior laryngeal branch is given off. 



On the left is seen the vagus ; on the right, the superior laryngeal ; between them 



the group of cells from which the afferent fibres of the depressor probably arise. 



Photograph x 75 diameters. Osmic preparation. 

 Fig. 5. — Section from the same preparation but taken a little lower down. The superior 



laryngeal is now quite separate from the vagus. The group of cells shown in fig. 4 



is still visible, and fibres of the depressor are beginning to accumulate at the side of 



the vagus. Photograph x 75 diameters. 

 Fig. 6. — Section from the same preparation still lower down. The three nerves now 



appear as entirely distinct bundles, each surrounded with its own perineurium, but 



enclosed in a common epineuriuni. On the left, the vagus ; on the right the 



superior laryngeal ; the depressor is the small bundle of fibres between them. 



Photograph x 75 diameters. 

 Fig. 7. — Section of a depressor nerve. Osmic preparation. Photograph x 400 diameters. 

 Fig. 8. — Section of the two filaments of origin of a depressor nerve, just before their 



union. Photograph x 400 diameters. (This section is not from the same animal 



as that from which fig. 7 was obtained.) 

 Fig. 9. — From a teased osmfc preparation of a depressor nerve. Photograph 



x 300 diameters. The figure shows medium-sized and fine myelinated fibres and a 



few non-myelinated fibres. 



* According, however, to S. W. Eanson (' Physiological Review,' vol. 1, p. 479) small 

 myelinated and unmyelinated fibres are included among visceral afferent fibres. This 

 statement is based on his own observations recorded in ' Journ. Comp. Neurology,' vol. 29. 

 See also the same Journal, vol. 24. (Private communication to E. S. S.) 



