WEST OF ENGLAND VETERINARY MEDICAL ASSOCIATION. 807 
inferior laryngeal or left recurrent; it originates from tlie pneumo- 
gastric or fifth pair of cranial nerves. It may be well to remark here 
that, in almost all instances in the animal organism, we find that where 
there are two organs destined to perform the same function on either side 
of the body, they are precisely alike in form, arrangement, and distribu¬ 
tion ; but to this rule we have a remarkable exception in the inferior 
laryngeal nerves. Firstly, to trace the course of that on the right side. 
It leaves the parent trunk or pneumogastric just as the latter enters the 
thorax, that is between the two first ribs (here a large plexus is formed 
by the pneumogastric and sympathetic nerves). The right recurrent now 
turns upward and winds in an inward direction round the trunk common 
to the anterior dorsal and posterior cervical arteries; then it passes up 
the neck very near the carotid artery, the tenth, and sympathetic nerves, 
direct to the right side of the larynx, to supply the companion muscles to 
those on the other side. 
Now, on the left side the recurrent or inferior laryngeal nerve leaves 
its parent pneumogastric opposite about the fourth dorsal vertebrae, 
then passes backward and turns round, the posterior aorta being very 
closely applied to it. In this part of its course it communicates with the 
cardiac and pulmonary plexi, and sends fibres to the heart itself, and these 
are the points to be particularly borne in mind. Having turned round 
the aorta, the nerve passes directly forward to get out of the thorax, and 
thence up the neck to the muscles on the left side of the larynx, corre¬ 
sponding to those supplied on the other by the right nerve. In its 
passage up the neck, the left recurrent has relatively the same position 
with the carotid artery as has that on the right side. 
Now that we are posted in the anatomy of these parts, we ask ourselves 
how it is that the muscular atrophy is brought about, and the reason of 
the left side being always atfected in preference to the right. The differ¬ 
ence in the course of these two nerves must necessarily answer this latter 
question, but we should now be able to discover at what portion of its 
course this first cause produces its effect; it cannot take place at its peri¬ 
pheries, because, if so, the one side would be affected no oftener than the 
other ; therefore, whatever it may be, it must exert its influence on some 
other portion of the nerve’s course. 
We are already aware that the nerve on the left side has its own pecu¬ 
liar communication with the inferior cervical ganglion, with the lungs 
through the pulmonic plexi, and with the heart by sending branches to 
it, at the same time winding close around the posterior aorta. Therefore 
we conclude, and probably rightly so too, that in consequence of one of 
these connections it is that the left nerve becomes diseased, and this we 
accept as an ultimate fact, leaving quite unexplained in what way or why 
this connection influences the tissue so as to produce the result we 
observe. 
To the thinking pathologist this is very unsatisfactory; but we have 
to reflect for a moment only to discover that we have arrived as close 
to the pathology of “roaring” as we have to the knowledge of the primary 
cause of many other pathological conditions, as many of our so-called 
causes are but the effects of some primary action—for instance, the atro¬ 
phied condition of the muscles of the larynx is the result of the paralysed 
nerve; this latter, again, but the effect of something else. 
On reviewing the list already enumerated, we find fright and over¬ 
exertion ; and there are, doubtless, many well authenticated cases of its 
thus supervening. Now, such as these tend somewhat to confirm the 
theory held by many, that the production of the disease is primarily due 
to an injury of a mechanical nature; if so, our suspicions are immediately 
