504 



THE REPRODUCTIVE 8Y8TEM 



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Each corpus CM vernosum is invested with a thick sheath of very dense 

 fibro-elastic tissue, the tunica albuyinea, divisible into an inner circular 

 and an outer longitudinal layer of fibers, and imperfect between the two 

 corpora cavernosa penis where it forms the pectinifbrm septum. From 

 the inner surface of this fibrous coat connective tissue septa, the trabec- 

 ulas, pass in all directions and form a reticular framework whose 



fibrous bands contain many smooth 

 muscle fibers. In the meshes of this 

 framework are characteristic broad 

 venous sinuses which possess no true 

 wall other than their endothelial 

 lining. In the flaccid condition of 

 the organ the blood sinuses are com- 

 pletely collapsed, their walls are in 

 contact, and their luniiua almost 

 obliterated, which gives them the 

 appearance of mere slits in the 

 dense connective tissue of the caver- 

 nous body. When distended by in- 

 jection, or, in the erectile condition 

 of the organ, by blood, these spaces 

 become widely dilated and form true 

 blood sinuses of broad caliber. 



The blood supply of the erectile 

 tissue is peculiar. The arteries ter- 

 minate either (1) in capillaries, (2) 

 by direct anastomosis with the ven- 

 ules, or (3) by opening directly into 

 the venous sinuses, in which case 



the minute terminal arterioles have a peculiar looped appearance 

 and were described by J. Miiller (1835) as helicine arteries. The 

 capillaries form a superficial plexus beneath the tunica albuginea, which 

 opens into a deeper plexus of broader vessels from which the venules 

 take origin. Blood following this course through the capillaries and 

 into the venules may not enter the venous sinuses a direction which 

 is assumed by the greater portion of the blood in the flaccid condition 

 of the organ. The deeper venous plexus communicates freely with 

 the venous sinuses so that the least obstruction to the usual venous 

 outflow diverts the circulation through these channels. 



The helicine arteries are confined to the corpora cavernosa penis, 



FIG. 447. HELICINE ARTERY IN SEC- 

 TION, FROM THE URETHRAL BULB OF 

 MAN. 



a, lumen of a helicine artery; b, 

 fibrous bands of the erectile tissue; c, c, 

 lumen of a venous blood space; m, open- 

 ing of the helicine artery into the blood 

 space; ms, muscular coat of the artery. 

 Hematoxylin and eosin. X 180. (Af- 

 ter Kolliker.) 



