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. Author manuscript; available in PMC: 2017 Jan 1.
Published in final edited form as: Anat Rec (Hoboken). 2015 Nov 28;299(1):25–41. doi: 10.1002/ar.23283

Figure 6.

Figure 6

S20 (A–C) and S21 (D–F) heart specimens. A, during these stages the formation of primary branches (1, 2) of the main coronary arteries occurs, but the development of the tunica media is still limited to the proximal portion of the left, main coronary artery (LCA). B, a higher magnification of A, the limitation of VSMC recruitment to more distal region of the artery (asterisk) can be seen. Note that distally the VSMCs are only on the artery’s epicardial side. C and D, at this stage epicardial veins and venules (CV) are more common; in the atrioventricular groove (*) they are adjacent to coronary arteries (CA). Development of the tunica media is limited to the largest veins at this stage. E, the left anterior descending coronary artery (CA) is undergoing development of its tunica media in the apical atrioventricular groove during the S21 stage. This is the site where the blood island was noted in Figure 4C. F, a nerve (N) and blood islands (BI) (aluminum cochineal stain), are seen near the aortic root (Ao). Magnification bar = 100 μm.