Histology and embryology / José F. Nonidez.

  • Nonidez, José F. (José Fernandez), 1892-1947.
Date:
1941
Catalogue details

Licence: In copyright

Credit: Histology and embryology / José F. Nonidez. Source: Wellcome Collection.

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    edges of the septum secundum with the septum primum. The edge of the former becomes the limbus of the oval fossa, the septum primum the membranous portion of the fossa. This fusion closes the foramen. 2. The sinus venosus. The sinus venosus soon develops a large right and a smaller left horn. The horns receive the blood return- ing to the heart through the primitive embryonic veins (p. 132). a. The right horn. After their formation (p. 139), the superior and inferior vena cava open into the right horn. Rapid atrial growth incorporates the horn into the wall of the right atrium, and the venae cavae open directly into the latter. b. The left horn. It becomes the coronary sinus. c. Transformations of the valves. The opening of the sinus venosus into the atrium is guarded by two valves (valvulae venosae). The left valve is incorporated into the septum. The right forms the: (1) Crista terminalis, which is a continuation of its cephalic portion: and the: (2) Eustachian and Thebesian valves, which arise from the remainder of the valve. The former (valve of the inferior vena cava) is larger than the Thebesian (valve of the coronary sinus). 3. The pulmonary veins. The single pulmonary vein of the early embryo splits into right and left branches which in turn bifurcate. During the rapid growth of the atria first the single stem, then its two branches of bifurcation, are incorporated into the atrial wall, and the four branches (two for each lung) come to open directly into the atrium. 4. Origin of the aorta and pulmonary artery. They arise early in embryonic life through division of the aortic bulb (bulbus, p. 3:33). This is accomplished by two lateral ridges which meet and fuse in the midline. a. Relative position. After they are formed, the two arteries are not parallel but arranged somewhat like an X; the more ventral of the two is the pulmonary artery, the other the aorta (crossing toward the right dorsal to the pulmonary). b. Aortic and pulmonary valves. They arise from endocardial thickenings of the aortic bulb. 5. The ventricles. The ventricles are lateral outpocketings of the [ *35 ]