176 



ANUS. 



more superficial of these ; we shall distinguish 

 these muscles by the names of sphincter ani 

 cutaneus vel ellipticus, and sphincter ani pro- 

 Jundus vel orbicularis. 



Sphincter ani cutaneus (<r(piyyu, constringo,) 

 coccygeo-anal, sphincter externus, constrictor 

 ani) is the first muscle which meets the eye of 

 the anatomist in the dissection of this region. 

 It may be exposed by dividing the integuments 

 from the coccyx to near the back part of the 

 anus, and thence extending an incision on each 

 side, and about half an inch distant from the 

 edge of this opening to its forepart, whence it 

 should be continued indefinitely along the me- 

 dian line of the perinseum ; the integument 

 should then be carefully dissected off from either 

 side of this elliptical incision. 



The muscle thus exposed is thin arid flat, of 

 an elongated and elliptical form, and cleft in the 

 centre to embrace the opening of the anus ; it 

 arises posteriorly fleshy and cellular from the 

 point of the coccyx, and from a tense fibrous 

 or cellular tissue, called the recto-coccygaal liga- 

 ment, which extends from the coccyx to the 

 back part of the anus, where it divides and is 

 lost in the cellular tissue on either side. From 

 this origin the fibres of the sphincter collect 

 into a rounded fasciculus, which proceeds for- 

 wards and downwards, increasing in size, and at 

 the back of the anus divides into two bands 

 which pass one on either side of this opening, 

 each spreading out till it is an inch or even 

 more in breadth ; again converging in front of 

 the anus, these bands unite into a fasciculus, 

 which in the male is very long and passes for- 

 wards and upwards between the skin and the 

 acceletatores urinaa muscles, to be partly in- 

 serted into the median line of the superficial 

 fascia of the perineum, and partly confounded 

 and interlaced with the transversi perinaei, and 

 with the muscles which cover the bulb of the 

 urethra; through the medium of these last 

 it is even attached to the common cellulo- 

 tendinous central point of the perinaeum, be- 

 tween the rectum and the bulb, whereby it 

 is enabled to act on this part of the urinary 

 canal. This anterior insertion is very variable 

 in different persons ; in some it stops abruptly 

 at ihe bulb, while in others it continues to run 

 forwards between the skin and the acceleratores 

 as far as the dartos, in which it terminates. In 

 the female this anterior fasciculus is much 

 shorter, and ends in the sphincter or con- 

 strictor vaginae ; in the male its attachment to 

 the muscles of the bulb is often deficient, so 

 that in the course of the dissection, when the 

 superficial fascia has been removed, this ex- 

 tremity of the muscle will be found detached 

 and its insertion isolated. The entire of the 

 inferior surface of this muscle is in contact with 

 the integuments, its superior surface is related 

 to the levatores ani, acceleratores urinae, and 

 transversi perinaei muscles ; in front of the 

 anus it is confounded with the two latter, and 

 immediately behind it with the formerly named 

 muscles ; its external border is of uncertain ex- 

 tent, and is imbedded in adeps, while its inter- 

 nal edge is in close relation with the delicate 

 inflected anal skin, being separated only by a 



fine cellular tissue. This muscle is composed 

 entirely of fleshy fibres, occasionally intersected 

 by cellular and imperfect tendinous bands; 

 these fibres are placed in concentric arches, 

 those of opposite sides unite at acute angles, 

 and sometimes interlace before and behind the 

 anus ; the fasciculi are frequently separated by 

 considerable intervals, so that they appear like 

 different muscles ; some of the internal fibres 

 assume a circular arrangement ; in the female 

 this muscle is shorter, broader, and more 

 rounded, particularly in front. In structure 

 and appearance this muscle presents great 

 diversity ; in some it is red, strong, and large, 

 in others, so pale and weak as to be difficult of 

 perfect demonstration ; it is also probable that 

 during life great differences exist as to its 

 power of contraction. 



The use of this muscle is obviously to close 

 the anus, the skin of which it throws into small 

 rugae ; hence when the sphincter is paralysed, 

 there is incontinence of the contents of the rec- 

 tum ; the most internal fibres will tend to close 

 the opening more perfectly than the external or 

 elliptical, which will reduce it rather to a cleft 

 or fissure ; this muscle can also raise the anus 

 somewhat, and at the same time draw back and 

 compress the bulb of the urethra; it will also 

 express the secretion from the anal glands and 

 follicles. The sphincter ani may be properly 

 said to belong to the class of mixed muscles, 

 both as relates to its structure and function ; as 

 to the former, its paleness, scattered fibres, 

 connection with the commencement of the mu- 

 cous surface, and absence of true tendon ally it 

 to the muscular system of organic life ; while on 

 the other hand the parallel direction of its fas- 

 ciculi, and the arrangement of many of the 

 latter in the surrounding adeps, assimilate it to 

 the muscles of voluntary motion. In its functions 

 also it appears to border on the province of each 

 division of the muscular system; thus without 

 the efforts of the will, or even without any in- 

 ternal cognizance, it continues in a state of al- 

 most permanent contraction, and as uncon- 

 sciously relaxes when the functions of the part 

 impress upon its sensibility the necessity of so 

 doing ; while on the other hand the will can 

 exert a considerable control over its powers, 

 and can cause it to contract with considerable 

 and continued energy, as well as throw it into 

 a state of atony and relaxation. Although this 

 muscle belongs to the same class with the other 

 sphincters, the orbiculares oris and palpebra- 

 rum, yet it manifests a considerable difference in 

 its vitality. The natural and, therefore, the usual 

 condition of these other sphincters is relaxation ; 

 hence the mouth continues open, and partly 

 from the same cause too, the eyelids are apart ; 

 whereas the natural condition of the sphincter 

 ani when at rest is contraction, and hence the 

 anal opening is always closed, although the 

 muscle is still capable of contracting with con- 

 siderably more energy when any of the contents 

 of the rectum suddenly approach the orifice, 

 or when any irritation exists in its vicinity. 



The Sphincter ani internus vel orbicularis 

 (Sphincter intestinale, Winsl.) is of much less 

 extent than the former, and is situated more 



