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The Depressor Nerve of the Rabbit. 

 By B. B. Sakkar. 



(Communicated by Sir E. Sharpey Schafer, F.R.S. Eeceived October 31, 1921.) 

 (From the Department of Physiology, Edinburgh University.) 

 [Plate 4.] 



Since the discovery of the depressor nerve,* much work has been done in 

 connexion with its important influence on the regulation of blood-pressure, 

 but (so far as I am aware) no attempt has been made to determine its 

 histological structure. 



Origin and Course of the Depressor. 



Cyont gives the following description of the origin of the nerve. The depressor nerve 

 in the animals worked upon usually begins with two branches at the point of departure 

 of the superior laryngeal nerve from the vagus, one from each of the two nerves. The 

 nerve soon after its origin passes towards the cervical sympathetic, in company with 

 which it descends the neck towards the inferior cervical ganglion. With this ganglion 

 it is often connected by fine branches : it then turns inward past the subclavian artery, 

 and loses itself at the base of the heart, to which it passes from behind between the 

 pulmonary artery and the aorta. Just before entering the heart tissue the two 

 depressors lie close to one another. 



This is stated by Cyou to represent the course of the nerve in rabbits, cats, and horses, 

 and probably in other mammals in which the cervical sympathetic runs separately from 

 the vagus. 



My own observations have been made upon rabbits. I have not been 

 able to substantiate the statement that a separate depressor is present 

 in the cat, and I have had no opportunity of investigating the subject in 

 horses. 



Besides making a number of sporadic observations on animals killed for 

 different purposes, I have examined the depressor systematically on both 

 sides in seven rabbits. I find that it varies greatly in its mode of origin, 

 which is usually, as stated by Ludwig and Cyon, from two branches, one 

 from the vagus, the other from the superior laryngeal (fig. 1). But in some 

 cases it was a single nerve throughout (fig. 2), while in others the two 

 branches of origin ran separately for a greater or less distance, and even to 

 their destination (fig. 3). j When single the nerve was generally found to 



* Ludwig and Cyon, Arbeit, physiol. Anstalt, Leipzig, 1866. 

 t ' Methodik d. physiol. Experimente,' 1876. 



| Figs. 1, 2, and 3, are merely diagrams, and are not intended to represent the actual 

 size, distance apart, or length of the nerves. 



