682 



THE REPRODUCTIVE ORGANS 



in remarkably firm fibrous sheaths. Two, the corpora cavernosa, are alike 

 and are firmly joined together. They receive below and between them the 

 third part, or corpus spongiosum. The urethra passes through the corpus 

 spongiosum. The enlarged extremity, or glans penis, is continuous with the 

 corpus spongiosum. Cowpcr's glands are at its base, and their ducts open 

 into the base of the urethra. 



The Prostate Gland. The prostate is situated at the neck of the 

 urinary bladder, and encloses the base of the urethra. The prostate is made 

 up of small compound tubular glands embedded in an abundance of mus- 



FIG. 491. Human Spermatozoa (after Retzius). A, Side view; B, front view. 



cular fibers and connective tissue. The glandular substance consists of 

 numerous small saccules, opening into elongated ducts, which unite into a 

 smaller number of excretory ducts. The acini of the upper part of the prostate 

 are small and hemispherical, in the middle and lower parts the tubes are 

 longer and more convoluted. The ducts, twelve to twenty in number, open 

 into the urethra. They are lined by a layer of columnar cells, beneath which 

 is a layer of small polyhedral cells. 



The muscular tissue of the prostate not only forms the chief part of the 

 stroma of the gland, but also forms a continuous layer inside the fibrous sheath, 

 as well as a layer surrounding the urethra continuous with the sphincter of 

 the bladder. 



The Seminal Fluid. The sperm cells of the testes are joined on their 

 way to the exterior by the fluids secreted by the mucous lining of the various 

 tubules and glands. Of the fluids the chief ones are the secretions of the 



