442 APPLIED ANATOMY. 



with the above through the pararectal lymph-nodes while the remainder accompany 

 the middle and inferior hemorrhoidal vessels and drain the lower part of the anal 

 canal above the white line. A third group comes from the skin of the margin of the 

 anus and drains into the inguinal nodes. The pararectal (anorectal of Gerota) nodes 

 may become enlarged in cases of nonmalignant ulcer and can be felt in the region of 

 the ampulla by the finger introduced through the anus, thus leading to a mistaken 

 diagnosis of carcinoma (Fig. 447). 



Nerves. The anus is supplied by the inferior hemorrhoidal branch of the inter- 

 nal pudic nerve, which, as shown by Hilton, crosses the ischiorectal space on the outer 

 surface of the levator ani muscle and passes between the internal and external sphinc- 

 ters to emerge between them at the white line, from whence it sends filaments up on 

 the mucous membrane and down on the skin. This explains the great sensitiveness 

 of the region. It also supplies the external sphincter, hence the association of spasm 

 with pain. 



AFFECTIONS OF THE RECTUM AND ANUS. 



Examination. If the buttocks are drawn aside the mucous membrane of the 

 anus is everted and a considerable portion of the anal canal becomes visible. The 

 lower part of the columns and crypts of Morgagni and the anal valves are seen. If 

 the patient strains or bears down, the mucous membrane of the anal canal is brought 

 into view in almost its entire length. One is thus enabled to see dilated veins or 

 hemorrhoids, ulcers, fissures, foreign growths, both benign and malignant, and the 

 openings of fistulae. By means of a speculum the entire anal canal can be seen. It 

 should be introduced pointing obliquely anteriorly, and if it is desired to view the 

 interior of the rectum above after it has passed the internal sphincter it is to be 

 directed obliquely upward and backward. In digital examination the first resistance 

 encountered is that of the external sphincter; as its edge is passed a sulcus can often 

 be felt, immediately following which the internal sphincter is passed and the finger 

 enters the rectum. The sulcus is about opposite the crypts of Morgagni and is 

 formed by the interval between the contraction of the external sphincter below and 

 the internal sphincter blended with the insertion of the levator ani above. It is just 

 above Hilton's white line. 



Imperforate Anus. In an early stage of the development of the embryo the 

 cloaca is the common termination of the genito-urinary system and the intestinal 

 canal. Later the cloaca becomes divided by a septum into the urogenital sinus in 

 front and the rectum behind. A depression in the skin called the anal pit appears 

 opposite the rectum and the membrane between disappears in the fourth month. 

 This membrane is produced by the growing together of the ectoderm and entoderm, 

 the mesoderm being pushed aside. The failure of this membrane to perforate forms 

 imperforate anus. The method of development explains the various malformations 

 of these parts. The anal pit may be absent ; the membrane may not perforate ; the 

 rectum may end in a blind pouch some distance up from the anus ; or it may discharge 

 through a sinus into the bladder or vagina. 



Hemorrhoids. Hemorrhoids or piles are varicosities or dilatations of the 

 veins of the anus or anal canal. The middle hemorrhoidal veins are not enlarged 

 because they do not drain the mucous membrane, they are not inside but outside 

 the rectum. When the inferior hemorrhoidal veins are dilated they form external 

 hemorrhoids and are situated at the margin of the anus below the white line and 

 external sphincter, and they cannot be replaced in the rectum. When the superior 

 hemorrhoidal veins are dilated they form internal piles (Fig. 448). The dilatation 

 involves the superior hemorrhoidal veins from the beginning of the mucous mem- 

 brane at the white line up the entire length of the anal canal and sometimes a short 

 distance up the rectum. There is a natural tendency for external piles to be covered 

 almost wholly by skin and for internal piles to be covered solely by mucous mem- 

 brane. Inflamed internal piles can be pushed back in the rectum. If an internal 

 pile is continued down over the white line or an external pile is continued up over 

 the white line then they are called intero-external piles. Hemorrhoids consist almost 

 wholly of dilated venous sinuses. The existence of arterial hemorrhoids is now 

 denied although small arterial branches are sometimes encountered in the ordinary 



