9o8 HUMAN ANATOMY. 



Additional communications are made with the vesico-prostatic (vesico- vaginal) 

 plexus and the internal pudic vein, and also with the internal circumflex branch of 

 the deep femoral and with the sciatic. 



7. The Middle Hemorrhoidal Vein. — The middle hemorrhoidal vein (v. 

 haemorrhoidalis media) has its origin in the hemorrhoidal plexus of the rectum, and 

 after receiving tributaries from the seminal vesicles, the prostate gland, and the urinary 

 bladder in the male and from the vagina in the female, opens into the internal iliac 

 or one of its tributaries. It is a comparatively large vein, and of importance in that 

 it forms through its connection with the hemorrhoidal plexus a communication 

 between the portal and inferior caval systems of veins. 



The hemorrhoidal plexus (plexus haemonhoidalis) which surrounds the rectum 

 is composed of two venous net-works, one of which, the intcryial hemorrhoidal p/exus, 

 lies in the submucosa of the rectum, while the other, \.\\eextc7'tial hemorrhoidal plexus, 

 rests upon its outer surface. The internal plexus is characterized in the adult, in that 

 portion of it which lies just above the anal opening, by the occurrence of round or 

 elongated bunches (glomera haeraorrhoidalia) formed by a number of small veins coiled 

 together into a mass resembling somewhat a Malpighian glomerulus. Upon the veins 

 which form the glomera, or upon those extending between adjacent glomera, ampullar 

 dilatations occur which have been regarded both as the cause and as the result of the 

 glomera formation. Be that as it may, the internal hemorrhoidal plexus presents in 

 the adult, slightly above the anus, a distinct band characterized by the occurrence 

 of glomera and dilatations, and forming what is termed the annulus haemorrhoidalis. 



The internal plexus opens partly at the anal orifice into the branches of the 

 inferior hemorrhoidal veins and partly, by branches which traverse the muscular coats 

 of the rectum, into the external plexus. This has three sets of efferent veins : 

 (i) the inferior hemorrhoidals, which open into the internal pudic ; (2) the middle 

 hemorrhoidals, which pass to the internal iliac or one of its branches ; and (3) the 

 superior hemorrhoidal, which leads to the inferior mesenteric and so to the portal 

 vein. The external plexus also communicates with the vesico-prostatic plexus in 

 the male and the vaginal plexus in the female. 



8. The Uterine Vein. — The uterine vein (v. uterina) arises opposite the 

 external os uteri from the plexus utero-vaginalis. It is at first a double vein, its two 

 trunks accompanying the uterine artery, and where that vessel crosses the ureter one 

 of the trunks passes with the artery in front of the duct and the other behind it. 

 The two trunks then usually unite to a single vein, which passes into the internal 

 iliac, frequently receiving the vesical veins or the obturator. 



The utero-vaginal plexus is formed by the veins which return the blood from 

 the uterus and vagina. The veins in the substance of the uterus are exceedingly 

 thin-walled, appearing as clefts in sections, and form a more or less distinct layer 

 (stratum vasculare) in the muscular wall of the organ. From this vessels pass to 

 both the anterior and posterior surfaces of the organ and follow a course which is 

 outward and more or less downward towards the lateral borders, where, between the 

 two layers, of the broad ligament, they form a rich plexus, the uterine plexus, the 

 vessels of which converge towards the origin of the uterine vein, opposite the external 

 OS uteri. The vaginal veins form a rich plexus in the walls of the vagina, the 

 emissaries from which are directed laterally and more or less upward, forming along 

 the lateral walls of the organ a rich vaginal plexus whose stems also converge to 

 the uterine vein at the level of the external os uteri. These two plexuses, the uterine 

 and vaginal, are continuous at the level of the external os uteri and form together 

 the extensive plexus utero-vaginalis. 



At the fundus of the uterus this plexus makes abundant connections with 

 the pampiniform plexus of the ovarian veins and with the funicular veins which 

 accompany the ligamentum teres. Lower down, throughout its uterine portion, it 

 receives affluents from the plexus of veins which occurs between the layers of the broad 

 ligament, and the lower part of its vaginal portion makes connections anteriorly 

 with the vesico- vaginal plexus and posteriorly with the external hemorrhoidal plexus. 



9. The Vesical Veins. — The vesical veins (vv. vesicales) vary somewhat in 

 number, but together represent a vessel of considerable size. They arise at the sides 

 of the bladder from a well-marked plexus which occupies in the male the groove 



