Normally occurring intraluminal projections in the arterial system of the mouse

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Abstract
The arterial system of 27 ICR/Albino mice was studied by: (1) examining 8 μ thick serial histological sections, (2) observing under the dissecting microscope the interior of arterial segments split longitudinally, (3) making reconstruction models, 100 times magnified from serial sections and (4) applying various histological and histochemical stains to determine morphological details. Almost regularly at each point of origin of an arterial branch, a structure forming a specific anatomical entity was observed and referred to as an intraluminal projection. A typical projection consists: (1) of an elevation or cushion located at the proximal edge of the orifice, (2) of two collateral ridges running distally at the sides of the orifice and becoming gradually thinner and taller, and (3) of a union of collateral ridges into a semilunar, flap‐like, movable structure guarding the distal edge of the orifice. Imperfectly developed intraluminal projections were occasionally encountered at the origin of large arteries from the abdominal aorta. Histologically a projection is entirely luminal to the internal elastic membrane, has an endothelial covering of thickened endothelial cells and consists of a stroma containing polygonal elongated cells which have oval nuclei and resemble smooth muscle fibers. They are surrounded by a network of elastic and reticular fibers. The intraluminal projections may regulate the volume and pressure of blood entering the branch by sphincteric and valvular mechanisms.