ANUS. 



181 



in the vicinity of the anus is very loose, and the 

 seat of nervous and vascular plexuses ; in the 

 latter the venous system predominates. 



A consideration of the functions of the rec- 

 tum and of its surrounding muscles, its re- 

 markable irritability and sensibility in health, 

 as well as its sympathies in disease, would lead 

 us to infer what dissection proves to exist, 

 namely, that this organ is largely supplied with 

 neives; numerous branches are furnished to it 

 from the sacral plexus, which is formed by the 

 union of the inferior spinal nerves, also from 

 the hypogastric plexus, which is chiefly com- 

 posed of filaments of the sympathetic. The 

 sacral plexus of spinal nerves furnishes, in 

 addition to many others, the hemorrhoidal, 

 vesical, and pudic branches; the hemorrhoidal 

 nerves are directed principally towards the in- 

 ferior part of the rectum, some ascend to the 

 colon, others descend even to the sphincter 

 ani : they divide into numerous filaments, 

 which are chiefly distributed to the muscular 

 fibres of the rectum and the adjacent muscles; 

 the vesical nerves in their course to the bladder 

 give some filaments to the rectum, and the in- 

 ferior or perinaeal division of the pudic nerves 

 also send several branches to the levator and 

 sphincter ani muscles. The hypogastric plexus 

 of nerves is composed of filaments from the 

 sacral plexus, which interlace with some from 

 the inferior mesenteric plexus, and with nume- 

 rous branches from the sacral ganglions of the 

 sympathetic nerves. This plexus supplies the 

 rectum, as also the other pelvic viscera; the 

 branches accompany the bloodvessels, and are 

 distributed principally to the mucous and sub- 

 mucous tissue. The cellular tissue, also, about 

 the coccyx, and the adjacent muscular fibres 

 receive some filaments from the coccygeal plexus 

 of the sympathetic. This supply of nerves 

 from these two very different sources, the one 

 presiding over voluntary, the other over in- 

 voluntary motion, corresponds with the well- 

 known functions of this organ, and causes its 

 muscles to be classed by the physiologist under 

 the head of mixed muscles, that is, partaking 

 of the common characters of the animal or 

 voluntary, and the organic or involuntary sys- 

 tems. Its supply of spinal nerves serves to 

 explain not only the influence which the will can 

 exert over its functions, but also the impaired 

 or altered state of its powers in case of disease 

 or injury of the brain or spinal cord ; thus irrita- 

 tion of the latter may cause morbid irritability 

 and contraction of the rectum, and, necessarily, 

 constipation of the bowels; or, again, paralysis 

 of the spinal cord from injury or compression 

 may lead to perfect atony of the sphincters, and 

 to the involuntary discharge of the contents of 

 the rectum. The general distribution of the 

 branches of the sacral and hypogastric plexuses 

 to the several pelvic viscera, and to the muscles, 

 &c. in the perinseum, associates these different 

 organs with each other, which is so necessary to 

 their functions, and with the urinary and genera- 

 tive organs, connecting more particularly the 

 muscles of the anus with the muscular coat of 

 the urinary bladder and with the parts about 



its cervix. This interlacement and subsequent 

 general distribution of these nerves serve also 

 to establish those several sympathies which are 

 found to exist in acute and chronic diseases of 

 the rectum and anus, between this intestine and 

 the other pelvic viscera. In some the uterus 

 and vagina partake of the irritation, in others 

 the urinary bladder is almost incessantly irri- 

 tated to expel its contents ; or, on the other 

 hand, when the sympathetic irritation engages 

 its cervix and the parts in its vicinity, the 

 most painful retention of urine is endured. 

 Chronic disease of this intestine is also very 

 generally attended with occasional attacks of 

 pain and irritation in different portions of the 

 alimentary canal, as also with pain in the 

 sacrum and loins, and in various other direc- 

 tions, which may in most cases be explained by 

 referring them to nervous irritation extending in 

 the course of some of the nervous communica- 

 tions which are found to exist in such num- 

 bers in the pelvis. 



The rectum, like the rest of the alimentary 

 canal, is freely supplied with blood. Its arte- 

 ries are named /Kemorrltoidal, and are derived 

 from three sources, viz., the abdominal aorta, 

 the internal iliac, and the internal pudic arte- 

 ries. The superior hasmorrhoidal is the con- 

 tinuation of the interior mesenteric, a branch of 

 the aorta ; the middle hemorrhoidal is derived 

 either from the internal iliac or from some of 

 its branches ; and the inferior or external he- 

 morrhoidal branches from the perinaeal division 

 of the pudic. The latter are destined directly 

 to the confines of the anus, and are lodged in 

 the subcutaneous adeps. The two former be- 

 long properly to the rectum, and are above the 

 levatores ani muscles. These arteries divide 

 into several small branches, which anastomose 

 together, and form a continued chain of inos- 

 culations along this intestine, somewhat similar 

 to that which is continued along the whole of 

 the alimentary tube. They form a complicated 

 vascular net-work between and within the mus- 

 cular fibres, and are largely distributed to the 

 mucous and submucous tissues. Some branches 

 of considerable size not unfrequently descend 

 so low even as the sphincter, particularly at its 

 posterior parts. These are liable to be divided 

 in operations for the cure of fistula;, and some- 

 times give rise to a haemorrhage, troublesome 

 and difficult to restrain. In such operations the 

 external haemorrhoidal arteries also are very 

 commonly opened, and bleed smartly ; they can 

 be secured, however, with much less difficulty 

 than the divided extremities of the superior or 

 middle haemorrhoida! vessels. 



The whole of the rectum, particularly its 

 lower portion, is encompassed by numerous 

 veins, which in some persons are very large 

 and plexiform. In the perinseum, also, many 

 venous plexuses are found in the subcutaneous 

 adeps. The external heemorrhoidal arteries 

 have their external venee comites, which run 

 outwardly to end in the internal pudic veins 

 (branches of the internal iliac). Some of their 

 branches ramify around the anus, and in some 

 cases form a. plexus, in which hnemorrhoid?' 



