. Outlines of zoology. iles tears. The ears open by horizontalslits, over which lies a flap ofskin; three Eustachian passages—one median and one on each side—open into the mouth behind the posterior nares. The nfistril^ alsa can be closed, and, as we have already noticed,their internal opening lies at the back of the mouth. The stomach suggests a birds gizzard, for it has strong muscularwalls, and its pyloric end is twisted upward so as to lie near the cardiacpart. The heart is four-chambered, the septum between the ventricles beingcomplete, as in Birds and Mammals. But as the dorsal aorta is
. Outlines of zoology. iles tears. The ears open by horizontalslits, over which lies a flap ofskin; three Eustachian passages—one median and one on each side—open into the mouth behind the posterior nares. The nfistril^ alsa can be closed, and, as we have already noticed,their internal opening lies at the back of the mouth. The stomach suggests a birds gizzard, for it has strong muscularwalls, and its pyloric end is twisted upward so as to lie near the cardiacpart. The heart is four-chambered, the septum between the ventricles beingcomplete, as in Birds and Mammals. But as the dorsal aorta is formedfrom the union of a left aortic arch containing venous blood, and aright aortic arch containing arterial blood, the blood which is driven tomany parts of the body is mixed blood, blood partly venous,partly arterial, with some of its red blood corpuscles carrying haemo-globin and others oxyhsemoglobin. At the roots of the two aorticarches there is a minute communication between them—the Fig. 352.—Half of the pelvicgirdle of a young crocodile. //., Ilium; ^ acetabulum; /j.,ischium ; /*., pubis or epipubis. 640 REPTILIA. Into the right auricle venous blood is brought by the two superiorvenEe cavas and by the inferior vena cava. The blood passes througha valved aperture into the right ventricle, and is driven thence—(o) bythe pulmonary artery to either lung, or {h) by the left aortic arch tothe body. From this left aortic arch, before it unites with its fellowon the right to form the dorsal aorta, is given off the great cceliacartery. The anterior viscera thus receive wholly venous blood fromthe heart. The blood driven to the lungs is purified there, and returns by pul-monary veins to the left auricle. Thence it passes through a valvedaperture into the left ventricle. Thence it is driven into the right aorticarch. From this the carotids to the head and the subclavians to thefore-limbs are given off. These parts of the body thus receive who
Size: 1663px × 1502px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1910, bookidcu3192, booksubjectzoology
