447 
MR. YOUATT’S VETERINARY LECTURES, 
DELIVERED AT THE UNIVERSITY OF LONDON. 
LECTURE XVIII. 
On the Muscles, Nerves, Bloodvessels, and Lining Membrane 
of the Larynx. 
The beautiful mechanism of the larynx, which occupied our 
attention in the last lecture, is governed or worked by a somewhat 
complicated system of muscles. If in describing them I should 
vary, and that very considerably, from the account given us by 
our best veterinary anatomists, 1 must refer you to the dissections 
on the table, and particularly to a very elaborate one by my ta¬ 
lented pupil and friend Mr. Simpson, as my apology. 
Action of the Muscles of the Larynx .—The action of the mus¬ 
cles of the larynx is principally confined to the dilatation or con¬ 
traction of the openings into the trachea, whether between the 
arytenoid cartilages or the vocal ligaments, and thus adapting 
them to the varying purposes of respiration, and the formation 
and modulation of the voice. 
As, in describing the cartilages of the larynx, I commenced 
with the cricoid cartilage, placed at the base of the machine, so 
we will first consider the muscles of that cartilage. 
The Crico-arytenoideus Posticus .—The first pair of muscles 
that presents itself, is attached to the spine of the cricoid carti¬ 
lage, and to the whole of the roughened depressed surface on 
either side, and completely covers the posterior surface of the 
cartilage. 
The Posterior-Crico-aryienoid Muscles appear, when first ob¬ 
served, to consist of two pairs, with distinct origins and inser¬ 
tions, and a different direction of the fibres of each. It is, how¬ 
ever, so difficult to dissect the one from the other, that veterinary 
anatomists have agreed to consider them as one pair. If I were 
disposed, and I almost am, to separate them, I should speak first 
of the inferior portion, arising by a fleshy body from the base 
and side, and lower part of the spine, and surface of the cricoid 
cartilage on each side and the fibres taking a direction upwards; 
the muscle is inserted by a tendinous expansion into the summit 
of the tubercle at the base of the spine of the arytenoid cartilage. 
The fibres of the superior portion, arising from the upper part of 
the spine and general surface of the same cartilage, take a direc¬ 
tion upwards and obliquely outward, and are inserted by a thick 
fleshy attachment into the inner side of the same tubercle. It 
