174 



AN-US. 



distinct stomach exists, and where the retained 

 matter obviously undergoes certain changes, 

 the one orifice serves the two-fold purpose 

 of admission to the food, as well as of exit to 

 its residuum. Even in some of the echino- 

 dermata, as the asteriae, in which the digestive 

 apparatus is more developed, the central cavity 

 becoming more complex, the latter is still but 

 a cul de sac, which can be protruded at the 

 mouth, the only orifice it presents. In other 

 species, however, of this class, the anus ap- 

 pears ; thus in the English echinus, where the 

 masticating apparatus is so remarkable, this 

 opening exists on the surface of the animal, 

 opposite to the mouth.* 



Jn the sipunculi the anus opens near the 

 mouth, and in the holothuriae near the respira- 

 tory organ .f 



In the several families of the articulata, viz. 

 insecta, Crustacea, and vermes, the anus exists, 

 and is always found at that end of the animal 

 opposite to the mouth, and most generally on 

 its inferior surface. 



In the mollusca it is also present, but it 

 holds situations singularly differing in the 

 different orders and genera of this class ; thus 

 in the cephalopoda, as the cuttle-fish, the 

 rectum opens into a sort of cloaca, which is 

 situated . before the neck, and which also re- 

 ceives the semen and ova, as well as the 

 secretion from the ink-bag. In the gastero- 

 poda, as the slug, it is generally found near 

 the pulmonary cavity. In the patella or 

 limpet, however, it opens on the head, and 

 in the doris on the back, surrounded by a 

 delicate fringe, a sort of branchial tuft. In 

 most of the acephala, except the oyster, the 

 rectum extends along the back of the animal, 

 beneath the hinge, and above the respiratory 

 organs ; it then passes through the heart, and 

 opens above the posterior muscle of the shells, 

 into the cavity of the maulle, or between its 

 edges, the anal opening presenting the appear- 

 ance of a fleshy disc or sphincter. 



Among fishes the anus varies, in the osseous 

 and cartilaginous divisions of this class ; in the 

 former it usually presents the appearance of 

 a round opening leading into a longitudinal 

 groove ; it is placed in front of the anal fin, and 

 of the urinary and genital aperture, contrary 

 to what occurs in all other vertebral animals. 

 In the cartilaginous fish, as the ray and shark, 

 this groove is deeper, and has the appearance 

 of a true cloaca, through which are discharged, 

 as in the sepiae and in birds, not only the alvine, 

 but also the urinal and seminal excretions. 



In reptiles the anus serves as the opening 

 of a cloaca, or common receptacle of the re- 

 siduum of the food, as well as of the urine, 

 semen, or ova ; in the batrachia, as the frog, 

 it is situated at the end of the back, and there- 

 fore above the body of the animal. In the 

 chelonia, as the tortoise, it is under the tail. 

 In the sauria and ophidia it is a transverse cleft, 

 but in the salamander it is a longitudinal fissure 

 with two prominent lips. 



* Home's Lect. on Comp. Anat. vol. ii. p. 76. 

 f Cuvier's Comp. Anat. t. iv. p. 143. 



In birds the rectum expands above the anus 

 into the cloaca, which also receives the ter- 

 minations of the ureters, the ends of the vasa 

 deferent! a, and the penis (when the latter 

 exists) ; also the openings of the oviducts, and 

 of the bursa Fabricii. In all the mammalia 

 the rectum terminates in a distinct anal open- 

 ing, which is placed at the posterior or in- 

 ferior extremity of the trunk, directly under 

 the origin of the tail, and usually in a direc- 

 tion opposite to the mouth, and in all it is 

 placed behind, and not, as in fish, before the 

 urinary and sexual orifice ; in some few of the 

 quadrumana, as the mandril, it is directed 

 upwards. In almost all mammalia it is a dis- 

 tinct orifice, giving passage to the faeces only ; 

 in the beaver and sloth, however, the rectum 

 and urethra have a common termination. The 

 monotrematous animals also, such as the 

 echidni and ornithorhynci, form a complete ex- 

 ception to this statement; in these singular 

 and anomalous creatures a single opening gives 

 exit to the faecal and urinary secretions, and 

 also subserves sexual purposes. (See INTES- 

 TINAL CANAL.) 



ANUS (in human anatomy). In the present 

 article we propose to examine not merely the 

 structures which immediately bound this open- 

 ing in man, in their normal and healthy state, as 

 well as in their abnormal and diseased condi- 

 tions, but we shall also examine the parts which 

 enclose and surround it, and which can exert an 

 influence, direct or indirect, on its functions ; 

 that is, we shall consider the anatomy, normal 

 and abnormal, of the parts contained in the 

 Anal Region. 



The Anal Region is synonymous with the 

 posterior portion of the perinaeum ; its triangular 

 area is denoted by the following outlines : the 

 apex, which is posterior and superior, is marked 

 by the extremity of the os coccygis ; its base, 

 which is before and below the latter, is defined 

 by an imaginary line extending transversely 

 from one tuber ischii to the other, and each 

 side is denoted by a line drawn from the last 

 named process to the point of the coccyx : 

 these lateral boundaries correspond to the mar- 

 gins of the glutaei maximi muscles, which over- 

 lap the inferior or the great sacro-sciatic liga- 

 ments; the base or the transverse line before 

 mentioned, separates the anal from the anterior 

 perineal or urethral region : in the adult male 

 this line will be found to be about three inches, 

 or nearly three inches and a quarter in length ; 

 in the female it is about half an inch longer, 

 and more certainly so if the individual ex- 

 amined have borne children ; great variety, how- 

 ever, has been found to exist in this measure- 

 ment, the extremes of which may be stated at 

 two and four inches. In children under twelve 

 years of age this transverse diameter of the 

 perinaeum is considerably less, in consequence 

 of the extreme narrowness of the pelvis prior to 

 puberty. 



The anal region contains the lower portion 

 of the intestinum rectum, several muscles, and 

 fasciae, some nerves and vessels of importance, 

 and an abundance of adipose substance. The 



