CH. XXXVI.] 



THE URETHRA. 



537 



The bladder is well provided with blood- and lymph-vessels, and 

 with nerves. The latter are both medullated and non-medullated 

 fibres, and consist of branches from the sacral plexus and hypo- 

 gastric plexus. Ganglion cells are found, here and there, on the 

 course of the nerve-fibres. 



The Urethra. This occupies the centre of the corpus 

 spongiosum in the male. As it passes through the prostate it 

 is lined by transitional, but elsewhere by columnar epithelium, 

 except near the orifice, where it is stratified like the epidermis 

 with which it becomes continuous. The female urethra has 

 stratified epithelium throughout. The epithelium rests on a 



fig. 425. Section of a small portion of the prostate, a, gland duct cut across obliquely ; 

 b, gland structure ; e, proetatic calculus. (Cadiat.) 



vascular corium, and this is covered by submucous tissue con- 

 taining an inner longitudinal and an outer circular muscular 

 layer. Outside this a plexus of veins passes insensibly into the 

 surrounding erectile tissue. 



Into the urethra open a number of oblique recesses or lacunae, 

 a number of small mucous glands (glands of Littre), two com- 

 pound racemose glands (Cowper's glands), the glands of the 

 prostate, and the vas deferens. The prostate, which surrounds the 

 commencement of the male urethra, is a muscular and glandular 

 mass. Its glands are tubular and lined by columnar epithelium. 



THE FUNCTIONS OF THE KIDNEYS. 



The main function of the kidneys is to separate the urine from 

 the blood. The true secreting part of the kidney is the glandular 

 epithelium that lines the convoluted portions of the tubules ; 



