Fig. 2. Yellowfin tuna fixed at ambient pressure. (A) Transverse section through the longitudinal elements and media of the anterior bulbus. The elastin is heavily stained and shows the circumferential alignment of the elastin fibres (ef) in the media. The circumferential orientation of the elastin fibres is changed to longitudinal within the longitudinal elements. Scale bar, 100 µm. (B) Transverse section of the ventral aorta less than 1 cm anterior from the bulbus section in A. The wall of the ventral aorta is much thinner than the wall of the bulbus and has elastin lamellae (el) separated by layers of smooth muscle (sm). Collagen (co) is abundant within the adventitia. Scale bar, 100 µm. (C) Longitudinal section of the posterior bulbus. Smooth muscle occurs near the outer edge of the media, sandwiched between two layers of longitudinal elastin fibres (lf). Scale bar, 100 µm. (D) Longitudinal section of posterior bulbus. The smooth muscle layer shown in C is attached to the pocket valve (V) separating the bulbus from the ventricle. Scale bar, 1 mm. Stained with Verhoeff's elastic stain.

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