616 MR. YOUATT S VETERINARY LECTURES. 
tween the appendices, the crura, as it were, striding over it, to 
defend it from pressure and from injury: you will see a kind and 
wise provision for the safe conduct of a vessel so important as this. 
Next, and in the decussation of the crura, and in the most 
muscular part of the diaphragm, where its fibres, or the fibres of 
the crura, are crossing each other above and below the aperture, 
passes the oesophagus. I am not sure that this intertwining of mus¬ 
cular fibres around the oesophagus in this place may not combine 
with the ureter-like entrance of that tube immediately afterwards 
into the stomach, to produce the difficulty of vomiting in most of 
our patients; at least I see probable danger in forcing down instead 
of extracting any foreign body firmly wedged in the oesophagus, 
lest the spasmodic constrictive action which the continued pres¬ 
ence of the body, and our efforts to dislodge it, will produce in 
the muscles of this tube, may be propagated to these neighbour¬ 
ing ones of the diaphragm, and thus an insurmountable obstacle 
raised to the effecting of our purpose. 
Lowest of all is an aperture through the tendinous expansion, 
and through which the vena cava posterior enters the thorax. 
It is sufficiently high in the tendinous expansion to be out of the 
way of pressure, and, being placed in that expansion, cannot 
w T ell be compressed so as to hinder the passage of the blood. It 
is well said, that the vein is held open by the whole tonic force 
of the diaphragm. 
The Tunics of the Diaphragm .—The thoracic or anterior face 
of the diaphragm is covered by the pleura, of which 1 shall pre¬ 
sently speak; and the posterior or abdominal face by the perito¬ 
neum, which belongs to the digestive system. 
The Arteries and, Veins .—This muscle, so important in its 
office, is plentifully supplied with bloodvessels. As the posterior 
aorta passes beneath the crura of the diaphragm, it gives out 
sometimes a single vessel which soon bifurcates; sometimes 
two branches, which speedily plunge into the appendices or 
crura, while numerous small vessels escaping from them spread 
over the central tendinous expansion. As the larger muscle of 
the diaphragm springs from the sides and the base of the chest, 
it receives many ramifications from the internal pectoral, de¬ 
rived from the anterior aorta; but more from the posterior inter- 
costals which spring from the posterior aorta. 
The veins of the diaphragm belong exclusively to the posterior 
vena cava. There are usually three on either side; but they 
may be almost referred to two chief trunks which come from the 
circumference of the diaphragm, and converge towards the centre, 
and run into the posterior cava, as it passes through the tendinous 
expansion. 
