Outlines of comparative physiology touching the structure and development of the races of animals, living and extinct : for the use of schools and colleges . which is separated from the other contents of the lowerarch of the vertebral column by a fleshy partition, called thediaphragm (fig. 180), passing across the cavity of the body,and arching into the chest. The only access to this apartmentfrom without is by the glottis through the trachea (fig. 235, t).§ 386*. The mechanism of respiration by lungs may becompared to the action of a bellows. The cavity of the chestis enlarged by raising the
Outlines of comparative physiology touching the structure and development of the races of animals, living and extinct : for the use of schools and colleges . which is separated from the other contents of the lowerarch of the vertebral column by a fleshy partition, called thediaphragm (fig. 180), passing across the cavity of the body,and arching into the chest. The only access to this apartmentfrom without is by the glottis through the trachea (fig. 235, t).§ 386*. The mechanism of respiration by lungs may becompared to the action of a bellows. The cavity of the chestis enlarged by raising the ribs, the arches of which naturallyslope somewhat downward, but more especially by the con-traction of the diaphragm, whereby its intrusion into the chestis diminished. This enlargement causes the air to rush inthrough the trachea, distending the lungs so as to fill the ad- Q Fig. 235.—LUNGS, HEAUT, and principal blood-vessels of MAN. a r, right auricle : v r, right ventricle ; v I, leftventricle ; a, aorta ; v c, vena cava ; a c, carotidarteries ; vj, jugular veins ; a s, subclavian ar-tery ; v s, subclavian veins ; t, trachea. 226 BESPIEATION. t. Fig. 236.—Lung of the water newt (Triton cristatus) : ditional space. When the dia-phragm is again relaxed, and theribs are allowed to subside, thecavity is again diminished, andthe air expelled. These move-ments are termed-inspiration andexpiration. The spongy pulmo-nary substance being thus dis-tended with air, the blood sentfrom the heart is brought into suchcontact with it as to allow the re-quisite interchange to take place.[§ 387. The minute anatomyof the lungs, in vertebrate ani-mals, exhibits many interestingvarieties. The structure is sim-plest in the naked amphibia,where it is but little more com-plex than in the snails.* In thewater-newt, for instance, thelungs present themselves as apair Of simple elongated sacs vein. rf* «X* & *%Iw&. «^;C*/CV^B^^i^*.l •W*%\f &ivV-*-
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Keywords: ., bookcentury1800, bookdecade1870, booksubjectzoology, bookyear1870
