. Chordate morphology. Morphology (Animals); Chordata. which the heart contraction is initiated. Another modifica- tion of the heart tissue is the "skeleton" found at the bases of the main vessels from the heart. In different species this may be fibrous, partly cartilaginous, or ossified. Reptiles The heart of the reptile is basically three-chambered but retains a bit of the sinus venosus. This heart diffisrs from the mammal in that three vessels exit from it: two systemic trunks, the right bearing both carotids, and a pulmonary trunk. In Tupmamhis (Figure 11-2) the two atria are com
. Chordate morphology. Morphology (Animals); Chordata. which the heart contraction is initiated. Another modifica- tion of the heart tissue is the "skeleton" found at the bases of the main vessels from the heart. In different species this may be fibrous, partly cartilaginous, or ossified. Reptiles The heart of the reptile is basically three-chambered but retains a bit of the sinus venosus. This heart diffisrs from the mammal in that three vessels exit from it: two systemic trunks, the right bearing both carotids, and a pulmonary trunk. In Tupmamhis (Figure 11-2) the two atria are com- pletely separated; they enter the ventricle to either side of a valvular apparatus from which a large knob-like process ex- tends out on the left side. This process is hollowed below and rounded above and can be pressed upward to cover the openings into the two systemic vessels. The opening of the pulmonary trunk lies in a pocket separated from the systemic portals by a muscular flap. The mechanism of operation is assumed to be as follows: blood from the right atrium enters the ventricles. This is oxygen-poor blood. This blood is directed into the cavum pulmonale by the process of the atrioventricular valve. The blood from the left atrium, which is oxygen rich, enters the main part of the ventricular chamber, swelling it outward. With contraction of the ventricle the first blood to leave is that from the right atrium, which is directed into the cavum pulmonale by the atrioventricular valve blocking the exit into the systemic openings. As the pressure in the ventricle increases, the muscular flap separating the systemic and pulmonary chambers is pushed outward closing the pul- monary exit. The atrioventricular valve is now pulled to the left exposing the systemic exits which receive the oxygenated blood. Thus there appears to be a functional mechanism for separation of the blood in this lizard. The heart of the alligator is more complex than that of the lizard or the turtle (F
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