180 THE REPRODUCTIVE SYSTEM. 



cavernosum is also enveloped by a dense fibrous sheath of 

 its own, lying just within the common sheath J the septum 

 ( u pectiniform ") thus formed between the two corpora is, how- 

 ever, incomplete and interrupted. From these sheaths fibrous 

 trabeculse are given off which traverse the interior of the 

 corpora in all directions, branching and anastomosing so as 

 to divide them into a spongy system of spaces or sinuses com- 

 municating freely with one another. The fibrous trabeculce con- 

 tain some involuntary muscle and elastic tissue, and convey 

 vessels and nerves. The sinuses formed by the septa are lined 

 with endothelium, and into them open the bloodvessels, so 

 that they form a system of cavernous spaces or vascular 

 sinuses, through which the blood flows, from the arteries and 

 into the veins (Fig. 69). This arrangement constitutes erectile 

 tissue. When the venous outflow is cut off by muscular action 

 blood accumulates in the sinuses, causing the penis to become 

 turgid and erect. 



The corpus spongiosum is a compartment filled with erectile 

 tissue and containing the urethra. Its posterior end, slightly 

 expanded, forms the bulb ; its anterior end, the glans penis. It 

 is enveloped in a firm fibro-elastic sheath containing a small 

 amount of involuntary muscle. From the sheath fibro-elastic 

 trabeculge, containing occasional non-striated muscle, traverse 

 the corpus and divide it into vascular sinuses, forming erectile 

 tissue like that of the corpora cavernosa. Along the axis of 

 the corpus spongiosum passes the urethra (more fully de- 

 scribed above) surrounded by the erectile tissue, which merges 

 into the submucous tissue of the urethra. The urethra is 

 lined with columnar epithelium and into it open numerous 

 mucous urethral glands (the " glands of Littre), which are 

 scattered about in the erectile tissue of the corpus spongiosum. 



The glans penis is an expansion of the anterior extremity 

 of the corpus spongiosum, covered by closely adherent mucous 

 membrane. The mucous membrane, continuous with that 

 of the urethra, is lined with stratified squamous epithelium, 

 resting upon a tunica propria, the surface of which is studded 

 with papilla3 containing numerous special sensory nerve-ter- 

 minals. At the corona and base of the glans the mucous 

 membrane contains abundant sebaceous glands, the glandulm 

 odoriferce or glands of Tyson, unassociated with hairs, the 



