Figure 3
Sagittal sections of the developing heart of Scyliorhinus canicula immunolabeled with A4.1025 antibody and counterstained with hematoxylin. (a) Stage 26. The heart consists of four A4.1025-positive segments: sinus venosus (SV), atrium (A), ventricle (V) and conus arteriosus (C). The inset (a′) shows the endocardium and the monolayered myocardium separated by the cardiac jelly (arrowhead). (b) Stage 28. The ventricular myocardium, which is thicker than the rest of the myocardium, has up to three densely arranged myocyte layers (b′). (c) Stage 29. Small spaces (asterisk) appear in the middle zone of the ventricular myocardium. (d) Stage 30. The cardiac jelly has disappeared. The intramyocardial spaces become larger, forming cavities (asterisks) in the ventricular wall, which are delimited by radial myocardial fascicles or trabecular ridges (arrows). The cavities are coated by endocardium, as shown in the inset (d′). (e) Stage 31. Two myocardial layers, inner and outer, separated by conspicuous cavities (asterisk), are distinguishable in the ventricle. (f). Stage 32. The cavities are wider, and the ventricular wall is thicker. (g) Stage 33. The myocardial trabeculae of the ventricle become more complex, forming a meshwork. (h) Stage 34. A4.1025 labelling decreases in both the ventricle and conus. The trabecular meshwork resembles that of the adult. The developing trabeculae are lined by endocardium and anchored to the prospective compact layer (h′). B, bulbus arteriosus; PC, pericardial cavity. Scale bars: 100 µm (a–h) and 50 µm (a′, b′, d′, h′).
