. Outlines of zoology. in the mesentery below the stomach lies therounded spleen. A whitish thyroid gland lies on the ventralsurface of the trachea a short distance in front of the heart. Vascular system.—The heart is completely enveloped bythe pericardium, and is three-chambered, consisting of twothin-walled auricles and a muscular ventricle. From theventral surface of the ventricle arises the conspicuoustruncus arteriosus, which is formed by the bases of theaortic arches, and exhibits a division into two parts. From40 626 REPTILIA. the more ventral part arises the left aortic arch, whichcurv
. Outlines of zoology. in the mesentery below the stomach lies therounded spleen. A whitish thyroid gland lies on the ventralsurface of the trachea a short distance in front of the heart. Vascular system.—The heart is completely enveloped bythe pericardium, and is three-chambered, consisting of twothin-walled auricles and a muscular ventricle. From theventral surface of the ventricle arises the conspicuoustruncus arteriosus, which is formed by the bases of theaortic arches, and exhibits a division into two parts. From40 626 REPTILIA. the more ventral part arises the left aortic arch, whichcurves round to the left side, first giving off a short connect-ing vessel {ductus Botallii) to the carotid arch. From theother division of the truncus arteriosus, a great arterialtrunk arises, and this gives off the right aortic arch and theright and left carotid arches. The right aortic arch sends aductus Botallii to the carotid arch of the right side, and thencurves round the heart to join the left arch, the two thus. Fig. 342.—Heart and associated vessels of a lizard.—After Nuhn. A.^ Right auricle; jugulars (/.), subclavians i^^^ and inferiorvena cava (/.) enter it. K., ventricle; tr.^ truncus arteri-osus ; I, first aortic arch giving off carotids; 2, second aorticarch;^.a:., pulmonary artery; Sea., subclavian artery ; Ao.,dorsal aorta. A.^, left auricle; pulmonary veins () enterit. In the lizard described, the left jugular is not developed. forming the dorsal aorta. The carotid arches supply the headregion with blood. From the base of the truncus arteriosus,the right and left pulmonary arteries also arise (Fig. 342). From the right aortic arch as it curves round, arise the right and leftsubclavian arteries, which carry blood to the fore-limbs. A coeliaco-raesenteric artery arises from the dorsal aorta and supplies the vessels are also given off to the genital organs, etc., and then atthe anterior end of the kidneys the aorta divides into two
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Keywords: ., bookcentury1900, bookdecade1910, bookidcu3192, booksubjectzoology
