. Elements of the comparative anatomy of vertebrates. Anatomy, Comparative. 296 COMPARATIVE ANATOMY of surface for muscular attachment without any considerable in- crease in weight. Everything, in fact, combines to establish an organ of flight with a large wing-surface and an increased strength of the muscles. Mammals.—As in Reptiles, the blood-vessels are of funda- mental importance in determining the structure of the bronchial system. The pulmonary artery crosses the main bronchus formed by the bifurcation of the trachea at its anterior end, and this point may be taken as dividing the latera
. Elements of the comparative anatomy of vertebrates. Anatomy, Comparative. 296 COMPARATIVE ANATOMY of surface for muscular attachment without any considerable in- crease in weight. Everything, in fact, combines to establish an organ of flight with a large wing-surface and an increased strength of the muscles. Mammals.—As in Reptiles, the blood-vessels are of funda- mental importance in determining the structure of the bronchial system. The pulmonary artery crosses the main bronchus formed by the bifurcation of the trachea at its anterior end, and this point may be taken as dividing the lateral bronchi into two systems—an an- terior eparterial and a posterior hy- parterial. The hyparterial series is always well developed, and consists of a double row of lateral bronchi, be- tween the roots of which the pul- monary artery passes backwards dorsally, while the corresponding vein runs along the median side of the main bronchus (Fig. 239). The epar- terial system, on the other hand, gradually becomes of much less im- portance and in certain cases is re- presented only by a single external lateral bronchus on either side (Fig. 239); and, as a rule, even the left of these disappears, only the right re- maining, and even this is not always retained. The eparterial bronchus, whether developed on one or on both sides, may arise from the trachea instead of from the main bronchus. In by far the greater number of Mammals, then, the left eparterial bronchus has disappeared, while the right is .retained; and as, therefore, the anterior lobe of the right lung belongs to the eparterial and 1 hat of the left lung to the first hyparterial bronchus, these lobes are evidently not homologous, the middle right lobe corresponding much more nearly to the anterior lobe of the left side. There is thus a want of symmetry between the right and left sides, the right lung usually retaining one more element than the left (Fig. 240a). The so-called accessory fourth lobe does not correspond to a
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectanatomycomparative
