682 CONSTRUCTION OP THE CAVITY OF 
through which is established a free communication between 
the three cavities formed by the pleurae, in such manner that 
in a horse of normal structure there exists but one pleural sac. 
When Muller saw these perforations for the first time, he 
thought that they were owing to the shaking about the car- 
cass had experienced. But minute examination, with all the 
care possible, showed him the unvarying existence of these 
perforations, and often in innumerable quantity. He found 
the separation complete only in the foetus Professor Larveul 
has described this particularly in his e Treatise of Splanch- 
nologij? Paris, 1847, a peculiarity which accounts for the 
passage of morbid effusions from one pleura to another ; at 
least, providing these apertures be not closed by false mem- 
branes, organised productions of inflammation. If my 
memory be faithful, Professor Thiernesse had already demon- 
strated these perforations in his course of descriptive anatomy 
for 1840. 
It necessarily results from this particular disposition that 
the signs with which auscultation and percussion may furnish 
us, for the detection of disease of the chest in the horse, 
equally possess something particular. If the third lobe of 
the lungs be alone attacked, and it is often so in the first 
instance in pneumonitis, neither auscultation nor percussion 
can prove of any great assistance to us for the detection of 
the disease. M. Muller has seen a case, wherein, as the result 
of a plastic inflammation, the sac of this lobe had become 
closed ; and the exudation being thereby encysted, the ani- 
mal died from the purulent resorption, without his being able 
to appreciate the slightest symptom through percussion and 
auscultation. 
The mobility of the skin, occasioned by the remarkable 
action of the subcutaneous muscles, is an opponent to the 
employment of the stethoscope, with a view of auscultating 
the diseases of the chest of the solipede. We need make no 
mention of other numerous circumstances, hindrances to 
convenient percussion and auscultation of the chest of horses, 
with the intention of detecting this disease. 
Nevertheless, M. Muller believes that, notwithstanding 
these inconveniences, auscultation and percussion of the thorax 
is capable of being of great help in discriminating between 
the different diseases of the chest. He especially insists 
upon the necessity of fixing the diagnostic of serous exudations 
within the pleural sac, since punction {paracentesis thoracis') 
may render palpable service. Of nine horses treated for 
hydrothorax he has seen five recovered. 
According to the conviction of Muller, four forms only 
