680 
CONSTRUCTION OF THE CAVITY OF 
which are very numerous in regard to it, that the results 
obtainable from auscultation and percussion of the chest in 
cases of disease in it, have proved, if not nil , at least very 
problematical. It has appeared to him, as well as to other 
veterinarians, impossible to hit upon any diagnostic product 
of auscultation, which could unfold his doubts, or even estab- 
lish a false diagnosis. In cases such as the last he has often 
found jpost-mortem pathological productions for which he had 
made no sort of calculation whatever. 
The construction of the thoracic cavity of the horse differs 
much from that of any other animal. Whilst in man, the ox, 
&c., the true ribs constitute, in a great measure, the parietes 
of the thorax, in the horse the parietes formed by the true 
ribs envelope only the smallest portion of the lungs. In its 
anterior part, the thorax is so narrow that from a level with 
the sixth rib, it contains only, over and above the great 
vessels belonging to the trachea and heart, a tongue of lung- 
on each side, about one tenth of the thickness of the organ. 
And the direction of the diaphragm is such that its inferior 
border is attached on a level with the 7th and 8th ribs, while 
the superior reaches as far back as the 18th. In consequence 
of which it happens that the front part of the lungs lie over 
the abdominal viscera. Especially is it worthy of remark 
that the lungs are placed within on the same region in point 
of function as the stomach and the liver. Here also has the 
thorax its greatest extent of capacity. From this it follows 
that percussion must most often lead to error, since the gases 
generated in the stomach and large guts surrounding it, im- 
pede the discovery of impermeability of substance of lung, or 
even of positive exudation. 
At the anterior parts of the thorax, the thickness and 
fleshiness of the shoulders obstruct the recognition of morbid 
processes going on in the fore-part of the lung, a circum - 
stance the more to be regretted since this part in the horse, 
as in man, is the oftenest found diseased. Add to this the 
presence of the trachea, the aorta and the anterior vena cava, 
and it must be evident, according to the simple law of 
acoustics, that it is impossible to detect, with any positive 
accuracy, the slightest symptom. 
The principal circumstai ^ces which, according to Muller, 
hinder the appreciation of morbid changes in the lungs, 
through auscultation, are, on the one side, the structure of the 
lung and the dimensions of the pulmonary air cells, and on 
the other side the existence of a third lobe of lung which 
produces, in the centre of the thorax, modifications existing in 
no other animal. 
