138 Veterinary Medicine. 



tributed ; that the left vagus nerve on the other hand proceeds 

 backward in company with the left innominate artery as far as 

 the base of the heart, where on about the level of the space be- 

 tween the sixth and seventh ribs it gives off the left recurrent 

 nerve ; that this left recurrent nerve closely applied at its point of 

 origin to tlie great parent arteries turns round the posterior aorta 

 enclosing it in a loop, and gaining the lower end of the windpipe 

 follows its course to the larynx. It will thus be understood how 

 many chest diseases may implicate the left recurrent nerve, and 

 from which the right, which extends no deeper than between the 

 two first ribs, may be completely exempt. The frequent superven- 

 tion of roaring as a sequel of chest diseases receives in this an ample 

 explanation. Its connection with pleurisy becomes especially 

 probable, as the nerve lies in contact with the surface of the 

 pleura alike in its descending and ascending course within the 

 chest. 



Finally the loop encircling the posterior aorta exposes the nerve 

 to constant stretching and shocks from the heart's action during 

 violent exertions and in excited states of the circulation generally. 

 Vaerst and Sussdorf show that the nerve is habitually flattened 

 between the posterior aorta and trachea, the effect being worst 

 when the heart's action is excited. 



It remains to notice a few instances in which dissection estab- 

 lished the connection of interference with the nerve at some part 

 of its course and the existence of roaring. 



(a.) Godine found in a roarer a tumor about the size of a 

 chicken's ^%%, pressing on the commencement of the pulmonary 

 artery. He attributed the roaring to the impaired circulation of 

 blood in the lungs by the pressure on the artery. Considering 

 that the tumor must have been precisely in the situation of the 

 left recurrent nerve at its point of origin, it becomes much more 

 probable that the symptom resulted from pressure on this nerve. 



(b.) The elder Bouley found in one case a considerable engorge- 

 ment of the group of lymphatic glands in the anterior part of the 

 chest and through the centre of which the left recurrent nerve 

 passed. 



(c.) Fergusson of Dublin dissected a roarer in which he found 

 besides some tumors of the lymphatic glands in the pelvic and 

 sub-lumbar regions, an indurated and enlarged gland about four 



