MALE REPRODUCTIVE ORGANS 1253 



distance of 20 to 25 mm. This area is paler in colour and free from the plication 

 that characterizes the rest of the mucous membrane; it is bounded posteriorly 

 by a transverse ridge, the plica ureterica, extending between the orifices of the 

 ureters, and toward the urethral orifice presents a median longitudinal elevation, 

 the uvula vesicce, which is apt to be especially prominent in aged persons. The 

 internal urethral orifice is normally situated at the lowest point of the bladder, at 

 the junction of the anterior and posterior surfaces. It is surrounded by a more 

 or less distinct circular elevation, the urethral annulus, and is usually on a level 

 with about the center of the symphysis pubis and from 2.0 to 2.5 cm. behind it. 



Structure. — The general characteristics of the mucous membrane of the bladder, which is 

 lined by epithehum of the transitional variety, have already been described. It rests upon a 

 loose submucous tissue, which contains numerous elastic fibres. The greater part of the thick- 

 ness of the wall is formed, however, of the muscular coat, consisting of non-striped muscle 

 tissue, the fibres of which are arranged in three more or less distinct layers. The outer layer 

 is composed mainly of longitudinal fibres, some of which are continued forward to the pubis 

 from the neck of the bladder to form the mm. pubovesicales and others backward to form the 

 mm. rectovesicales. To this outer layer the term m. detrusor urinoe has been applied, but it 

 should be noted that it does not contract independently of the circular layer. The middle 

 ayer is thicker than the outer and more uniformly developed. It consists of fibres having 

 for the most part a circular direction and is well developed over all the upper portion of the 

 bladder, but becomes thinner in the region corresponding to the trigone. It is here that the 

 inner layer is chiefly developed, consisting of fibres, which are situated partly in the submucous 

 tissue and have a general longitudinal direction throughout the region of the trigone. At 

 the neck of the bladder, however, they form a strong circular bundle, which is continued into 

 the prostatic portion of the urethra and forms what is termed the internal sphincter of the bladder. 



Vessels. — The arteries of the bladder are usually two in number, the superior and inferior 

 vesical, branches of the hypogastric artery; the fundus also receives branches from the middle 

 hsemorrhoidal and in the female twigs are also sent to it from the uterine and vaginal arteries. 

 The veins form an extensive plexus at the sides of the bladder, from which stems pass to the 

 hypogastric trunk. The lymphatics accompany the veins and communicate with the hypo- 

 gastric nodes, some of those from the fundus passing to nodes situated at the promontory of 

 the sacrum. 



Nerves. — The nerves are derived partly from the hypogastric sympathetic plexus and partly 

 from the second and third sacral nerves. The fibres from the latter constitute the nervi 

 erigentes, stimulation of which produces contraction of the general musculature and relaxation 

 of the internal sphincter. On each side of the bladder there is formed a sympathetic vesical 

 plexus, from which superior and inferior vesical nerves pass to the corresponding parts of the 

 bladder. 



Development.^— In the earlier stages of development the urogenital ducts and the digestive 

 tract open below into a common cavity, the cloaca, from the ventral portion of which a long 

 tubular outgrowth, the allantois, extends out to the placenta through the umbilical cord. 

 Later the cloaca becomes divided in the frontal plane into a ventral portion which receives the 

 urogenital ducts, and a dorsal portion, which becomes the lower end of the rectum. From 

 the upper part of the ventral portion the bladder is developed. Since the cloaca is fined by 

 endqderm the mucous membrane of the bladder is mainly derived from that embryonic layer, 

 but it is worthy of note that portions of the lower ends of the ureters are taken up into the wall 

 of the bladder, giving rise to the area of the trigone, whose mucous membrane is thus of meso- 

 dermal origin. The portion of the allantois within the body of the foetus is transformed after 

 birth into a fibrous cord, the urachus. 



The urethra will be considered later in connection with the reproductive 

 organs. 



B. THE REPRODUCTIVE ORGANS 



The reproductive organs include those of the male [organa genitaha virilia], 

 and those of the female [organa genitaha muliebria]. 



THE MALE REPRODUCTIVE ORGANS 



The reproductive organs of the male consist of (1) two testes in which the 

 spermatozoa are formed, (2) their ducts, the ductus def erentes ; enclosed through- 

 out a portion of their course in the spermatic cord; and the seminal vesicles, 

 reservoirs for the semen, connected with the ductus def erentes; (3) the penis, 

 the organ of copulation, which is traversed by the urethra; (4) the urethra, a 

 canal into which the ductus deferentes open and which also gives exit to the 

 contents of the bladder; (5) the prostate gland, a musculoglandular structure 

 surrounding the beginning of the urethra; (6) the bulb o -urethral glands which 

 open into the urethra. 



