. Chordate morphology. Morphology (Animals); Chordata. right anterior cardinal vein (precava) cardiac artery from left ventricle^ carotids pulmonary arch sinus venosus right ventricular chamber. left ventricular chamber B semilunar valve arrow through foramen of Ponizza. eft atrium Figure 11-3. Dorsal view of heart and main blood vessels of the alligator. A, as seen from below, B, and details of foramen of Panizza, C. systemic blood passes through the right trunk, which leads into the carotid arches, and the right systemic arch. Embryological development The development of the rep- tile's hear
. Chordate morphology. Morphology (Animals); Chordata. right anterior cardinal vein (precava) cardiac artery from left ventricle^ carotids pulmonary arch sinus venosus right ventricular chamber. left ventricular chamber B semilunar valve arrow through foramen of Ponizza. eft atrium Figure 11-3. Dorsal view of heart and main blood vessels of the alligator. A, as seen from below, B, and details of foramen of Panizza, C. systemic blood passes through the right trunk, which leads into the carotid arches, and the right systemic arch. Embryological development The development of the rep- tile's heart is much like that of the mammal's. The heart tube is formed of bilateral components and flexed. Posteriorly the vitelline veins form a sinus venosus. Anterior to the sinus, con- strictions delimit an atrium, a ventricle, and a truncus. The flexion continues until the atrium lies dorsal to the ventricle. The atrium becomes divided by an interatrial septum into right and left chambers connected by perforations through the septum. There is no evidence of an interventricular septum (in Lacerla), but a fold arises from the ventral ven- tricular wall to separate the cavum pulmonale from the main ventricular cavity. This fold may represent a modified interventricular septum. The truncus of the reptile is subdivided into three parts rather than two. A series of folds appear which spiral around the wall of the truncus in a clockwise direction from front to rear. These folds arise at the base of the arches and ex- tend posteriorly. At the heart end, there is a large dorso- lateral fold on the left side and a smaller ventrolateral fold on the right. Smaller folds now appear dorsolaterally on the right and ventrolaterally on the left. The large left dorso- lateral fold extends gradually across the chamber and meets the opposite fold to subdivide the truncus into pulmonary and systemic channels. This septum extends the length of the truncus from the arches to the ventricle. The right dor-
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