MR. YOUATTS VETERINARY LECTURES. 
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an irregular muscular expansion, proceeding from the inferior 
surface of the lumbar vertebrae posteriorly and superiorly, adhering 
to the ribs on either side, and extending obliquely forward and 
downward to the sternum; or, rather, it is a flattened muscle 
arising from all these points, with its fibres all converging towards 
the centre, and terminating there in an expansion of tendinous 
substance. 
Anatomy of the Diaphragm .—In the short account which I 
purpose to give of the structure of the diaphragm, I shall follow, 
as nearly as I can, the description of our best anatomist, Mr. 
Percivall. You at once perceive that the diaphragm may be 
divided into the main circular muscle, with its central tendinous 
expansion forming the lower part, and two appendices , or crura, 
as they are called, from their peculiar shape, constituting its su¬ 
perior portion. We trace the fleshy origin of the grand muscle, 
laterally and interiorly, commencing from the cartilage of the 
eighth rib anteriorly, and following pretty closely, as we proceed 
backward, the union of the posterior ribs with their cartilages; 
excepting, however, the two last. The attachment is peculiarly 
strong; it is denticulated ; it encircles the whole of the lateral 
and inferior part of the chest as far as the sternum, where it is 
connected with the ensiform cartilage. Immediately under the 
loins are the appendices of the diaphragm, commencing, on the 
right side, from the inferior surfaces of the five first lumbar verte¬ 
brae, by strong tendons which soon become muscular, and form a 
kind of pillar; and, on the left, proceeding from the two first 
lumbar vertebrae only, and from the sides rather than the bodies 
of these vertebrae, and these also unite and form a shorter pillar 
or leg. The left crus or appendix is shorter than the right, that 
it may be more out of the w ay of pressure from the left curvature 
of the stomach, which, with the spleen, lies underneath. Oppo¬ 
site to the 17th dorsal vertebra, these two pillars unile and form 
a thick mass of muscles, detached from the vertebrae, and leaving 
a kind of pouch between them and the vertebrae. They not only 
unite, but they decussate: their fibres mingle and again separate 
from each other, and then proceed onward to the central tendinous 
expansion, towards which the fibres from the circular muscle, and 
the appendices, all converge. 
The tendinous central Expansion. —We shall presently see 
that the diaphragm is the main agent, both in ordinary and ex¬ 
traordinary respiration. In its quiescent state, it presents its 
convex surface towards the thorax, and its concave one towards 
the abdomen. The anterior convexity abuts upon the lungs; the 
posterior concavity is occupied by some of the abdominal viscera. 
The effect of the action of this muscle, or the contraction of its 
