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By the contraction of the muscles of the thorax the thoracic cavity is enlarged, and as a result air is sucked in in exactly the same way that it is sucked into a pair of bellows when expanded. Then the contraction of another set of muscles decreases the size of the thoracic cavity, and the air is squeezed out again. The action is just as truly mechanical as is that of the blacksmith's bellows.
#Thoracic Aneurysm.# All varieties of aneurysm occur in the aorta, the fusiform being the most common, although a sacculated aneurysm frequently springs from a fusiform dilatation. The clinical features depend chiefly on the direction in which the aneurysm enlarges, and are not always well marked even when the sac is of considerable size.
The principal of these valves is that, which presides over the insertion of the thoracic duct, into the subclavian vein; many have believed this also to perform the office of a valve, both to admit the chyle into the vein, and to preclude the blood from entering the duct; but in my opinion it is scarcely sufficient for this purpose." Haller, Elem. Phys. t. vii. p. 226.
When the thoracic muscles, including the diaphragm, are thrown into spasm, the patient experiences a distressing sensation as if he were gripped in a vice, and has extreme difficulty in getting breath. Between the attacks the limbs are kept rigidly extended. The clonic spasms may be so severe as to rupture muscles or even to fracture one of the long bones.
To this bag is fastened another pipe or tube the thoracic duct which follows the line of the spine; and up this tube the small bodies travel till they come to the neck and a spot where two veins meet. A door in one opens, and the transformation is complete.
No mutationist has yet produced by breeding experiments a caterpillar without the three pairs of thoracic legs and yet developing into a moth that had normal three pairs. Morgan, with all his mutations of the adult Drosophila, says nothing of mutants possessing legs.
The mechanics of respiration manifest through the elastic movements of the lungs, and the activities of the sides and bottom of the thoracic cavity in which the lungs are contained. It is bounded by the spinal column, the ribs with their cartilages, the breastbone, and below by the diaphragm. It is generally spoken of as "the chest."
Unless the laceration is extremely small, protrusion of the stomach or some other viscera into the thoracic cavity will almost invariably result, constituting the condition known as internal or diaphragmatic hernia. Pare relates the case of a Captain who was shot through the fleshy portion of the diaphragm, and though the wound was apparently healed, the patient complained of a colicky pain.
An aneurysm may prove fatal by exerting pressure on important structures, by causing syncope, by rupture, or from the occurrence of suppuration. Pressure symptoms are usually most serious from aneurysms situated in the neck, thorax, or skull. Sudden fatal syncope is not infrequent in cases of aneurysm of the thoracic aorta.
In the thoracic form, the symptoms are bloody discharge from the nostrils, salivation, rapid, difficult breathing and swelling in the region of the throat. Local or skin lesions may occur in conjunction with, or independent of, the above forms of disease. These are carbuncles one or two inches in diameter that are hot and tender at first, but later become gangrenous, diffused swellings.
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