116 
ANIMAL PATHOLOGY. 
it separates into its ultimate terminating filaments : one goes to, 
and is lost on, the lining membrane of the pharynx, probably be- 
stowing on it that kind of sensibility by means of which it is sti- 
mulated to contract on its contents. The other portion of the nerve 
passing through the foramen at the base of the superior cornu of 
the thyroid cartilage, ramifies upon the crico-arytenoidei muscles 
— posticus and lateralis, and upon the thyro-arytenoideus, all di- 
lator muscles. It also communicates with filaments from the 
superior laryngeal nerve — the constrictor nerve — thus establishing 
a useful and a necessary connexion and sympathy between these 
muscles of contrary power, and, in the general course of things, 
limiting both to a safe and salutary discharge of their respective 
functions. Finally, this right nerve expends itself on the mu- 
cous membrane of the larynx, giving it that sensibility, be it 
more or less, and differing in various portions of it, which is in- 
dispensable for the discharge of its important duties, whether 
the modulation of the voice, or the regulation of the respiratory 
function is concerned. In the substance of the dilator muscles, 
and of the mucous membrane of the larynx, it meets and freely 
anastomoses with the terminating filaments of the left recurrent 
nerve ; and they both unite in the dilatation of the larynx, and 
the communication of sensibility to that organ. 
The left Recurrent Nerve . — The great spinal organic nerve 
proceeds a little way into the chest before it gives off the left re- 
current. It is opposite to the superior margin of the anterior 
aorta that the left recurrent arises, and in commencing its retro- 
grade course it coils round the root of the posterior aorta, includ- 
ing that vessel, as it were, in a sling, as Mr. Percivall graphi- 
cally describes it. It now passes externally and posteriorly to 
the ligamentous remains of the ductus arteriosus; after which 
“ it is found between the transverse portion of the arch and the 
trachea. ” Its early branches have a different destination from 
those on the right side, being destined to form a part of the in- 
ferior (anterior) pulmonary plexus, in order to establish a con- 
nexion between the lungs and the larynx, parts so essentially 
connected with the act of respiration, and placed at a consider- 
able distance from each other. Other filaments are given from 
the left recurrent nerve to the cardiac plexus, still strengthening 
the connexion between the important and inseparable functions 
of respiration and circulation. As the left recurrent ascends the 
neck it comes more immediately into contact with the oesophagus, 
which lies on the left side of the neck, and that tube is most in- 
debted to the left recurrent nerve for its sensibility and muscular 
power, as the trachea owes most to the right recurrent. Many 
branches, however, are given to the trachea as the left recurrent 
