294 NORMAL HISTOLOGY AND ORGANOGRAPHY. 



The corpus spongiosum is also composed of erectile 

 tissue, but is a single cylindrical body that lies below 

 and between the corpora cavernosa. Its posterior 

 extremity is much enlarged and rounded, and is 

 called the bulb. This lies in the ventral portion of 

 the root of the penis just in front of the triangular 

 ligament. Anteriorly the corpus spongiosum forms 

 the glans penis, which caps the corpora cavernosa. 

 The border of the glans is rounded and projecting 

 and is called the corona glandis, behind which is a 

 constriction of the penis, the cervix. In the whole 

 of its extent the corpus spongiosum encloses the 

 urethra. 



Structure of Corpus Spongiosum. This resembles 

 the erectile tissue of the corpora cavernosa, and like 

 the latter is distended with blood during erection, 

 but is less rigid. The venous labyrinth is a finer 

 meshwork and the trabeculae and fibrous tunic is 

 much thinner. In the glans the meshes are particu- 

 larly small and uniform. Plain muscle fibers enclose 

 the urethra and also form a part of the external coat. 



Urethra in the Male. The male urethra extends 

 from the bladder to the end of the penis, in length 

 about eight and one-half inches. Its walls are 

 in apposition, excepting during the passage of urine 

 or semen. The urethral cleft in the glans is vertical; 

 in the body of the penis it is transverse ; and through 

 the prostatic portion near the bladder it is crescentic. 

 It is lined by a mucous membrane, external to which 

 is a double layer of smooth muscle fibers, the inner 

 fibers disposed longitudinally and the outer circular. 

 For descriptive purposes the urethra is divided into 



