. Text-book of zoology for junior students. Zoology. MAMMALIA. The cavity of the aljdomen in Mammals is always sepai'ated from that of the thorax by a complete muscular partition—the diaphragm. The abdomen contains the greater part of the alimentary canal, the liver, pancreas, kidneys, and other organs. The thorax contains chiefly the heart and lungs. The is contained in a membranous sac—the pericardium—and consists of two auricles and two ven- tricles. The heart consists functionally of two sides, each having an aui'icle and a ventricle, which communicate with one another by apert
. Text-book of zoology for junior students. Zoology. MAMMALIA. The cavity of the aljdomen in Mammals is always sepai'ated from that of the thorax by a complete muscular partition—the diaphragm. The abdomen contains the greater part of the alimentary canal, the liver, pancreas, kidneys, and other organs. The thorax contains chiefly the heart and lungs. The is contained in a membranous sac—the pericardium—and consists of two auricles and two ven- tricles. The heart consists functionally of two sides, each having an aui'icle and a ventricle, which communicate with one another by apertures, so guarded by valves that the blood can pass from the auricle into the ventricle, but not, under ordinary circumstances, from the ventricle to the auricle. There is in the adult no direct communi- cation between the two sides of the heart. The course of the circula- tion is indicated in the subjoined diagram (fig. 225), and is shortly as follows : The venous lilood, which has become impure by passing- through the tissues, is returned by the gi-eat veins to the rigid auricle, from which it jmsses into the right ventricle. From here it is dri\en through .a great vessel, called the pulmonary artery, to the lungs, where it is submitted to the action of the air, and becomes arterial blood. It is then returned to the heai't by a series of vessels called the pulmonary veins, and is poured into the left auricle, from which it jiasses into the left ventricle. From the left ventricle it is propelled to all parts of the body by a great systemic vessel, wdiich is called the aorta. The lumjf of Maran)als are two in number, and differ from those of Birds in being freely suspended in memljranous liags. They are spongy and cellular throughout, and they never comnnmicate by apertures on their surface with air-sacs i>laced in ditierent parts of the body. The nervoui t^ijiUm of Mammals is chiefiy rcnuirkable for the. iy. '225.—Diagram of the cireiilatinn ill a Mammal. (The caviti
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectzoology, bookyear1885
