The tissue of the corpora cavernosa clitoridis, or cavernous tissue, is erectile tissue, meaning its histological structure enables these bodies to fill with blood, increase in size and harden. This tissue is made up of a complex network of venous sinuses that appear as intercommunicating anfractuous cavities (cavernous labyrinth) and of a thick fibrous envelope, the albuginea, which was long believed, erroneously, to be inextensible. The sinusoid cavities, or sinuses of the corpora cavernosa, most often have wide-open lumina (though sometimes collapsed) that are very irregular. Their dimensions vary greatly. Their shapes are more often polyhedral or narrow and elongated rather than circular or oval. These sinuses present numerous recesses. The inter-sinus communications are clearly visible and the main characteristic of the sinuses is that they are richly anastomotic (Fig. 6.1). The wall of the sinuses is indeed a vessel wall, comprising an endothelial layer and a conjunctive axis made of collagenous bundles in which smooth muscle fibres may be seen. Specific stains (orcein) demonstrate the existence of a rich network of elastic fibres (Fig. 6.2). It should be noted that the walls of the sinuses are thin, especially if compared to the size of the vessel lumina. The endothelial cells, made apparent by the immunolabelling with an anti-factor VIII antibody, have junctions of varying tightness and rest on a basal lamina. Extensions originate from the sinus walls and float in the vessel lumina. Their role is probably to direct blood flow during filling. Most of these extensions appear as fingers that are curved to varying degrees (like a bent index finger). They may also take the shape of small mounts, pyramids, bull horns, points, hooks or clubs. There are also complete or incomplete bridges between two opposite sinus banks, the sinus septa, which contribute to making the sinus labyrinth even more complex. Numerous small vessels (arterioles or venules) are also housed in the sinus walls. These small vessels are very sinuous and their walls are often thick. The arterioles and their branches are called “helicine” due to their often helicoidal arrangement (see Chap. 10). The larger vessels are located at intersections in the inter-sinus connective tissue. Otherwise, a fair number of nerve endings are found in the sinus walls themselves and in the inter-sinus connective tissue (Fig. 7.​2).