PERINEUM. 



919 



PERICARDIUM. See HEART. 



PERINEUM (in Surgical Anatomy). The 

 perineum (in the general acceptation of that 

 term) is one of the names applied by anatomists 

 to the extensive region which contains the lower 

 part of the rectum intestine, together with a 

 portion of the genitourinary organs and their 

 appendages, and of which the circumference 

 corresponds in a great measure to the periphery 

 of the inferior aperture of the pelvis ; in the pre- 

 sent article, however, it is intended to describe 

 the perineum in the male subject only, as the 

 parts which it comprises in the female are no- 

 ticed in detail under other headings in this 

 work. 



The limits which we would assign to this 

 region are sufficiently precise : superiorly, or 

 towards the abdominal cavity, it extends as far 

 as the reflections of the recto-vesical layer of the 

 pelvic fascia and the great cul-de-sac of the peri- 

 toneum, including within its precincts the pros- 

 tate gland and the neck of the bladder, together 

 with a part of the inferior surface of that viscus 

 and the vesiculae seminales and vasa deferentia; 

 inferiorly, the perineum is quite superficial, 

 being covered by the integuments only ; and it 

 is circumscribed partly by the fixed boundaries 

 of the inferior aperture of the pelvis, and partly 

 by the obturator fascia, an aponeurotic expan- 

 sion which appears to line a portion of the 

 inner surface of the os innominatum, but is in 

 reality separated from the bone by the obturator 

 internus muscle and the internal pudic vessels 

 and nerve. 



In describing this complicated region it will 

 be advantageous to consider in the first place 

 the osseous and ligamentous structures which 

 circumscribe the inferior outlet of the pelvis, 

 and to notice in a general manner the course of 

 the rectum and urethra, together with so much 

 of the urinary bladder as is connected with the 

 perineum, for in the sequel it will appear that 

 the rectum and the urethra are the principal 

 elements of the region, and that almost all the 

 other parts contained in it are appendages of 

 either the one or the other, so that by the adop- 

 tion of this method a key to the anatomy of all 

 the subordinate structures will be obtained. 



The inferior aperture of the male pelvis exa- 

 mined after the removal of the soft parts (the 

 sacro-sciatic ligaments being preserved) is dia- 

 mond-shaped ; it is limited anteriorly by the 

 arch of the pubis, posteriorly by the extremity 

 of the coccyx, and laterally by the rami of the 

 pubis and ischium, the tuberosity of the ischium, 

 and the great sacro-sciatic ligament at eo.ch side 

 respectively. It presents three diameters, viz. 

 the antero-posterior, the transverse, and the 

 oblique. The first extends from the coccyx 

 posteriorly to the symphysis pubis in front; the 

 second passes transversely between the tube- 

 rosities of the ischia ; and the third stretches 

 from the point midway^between the tuber ischii 

 and the arch of the pubis, to the centre of the 

 great sacro-sciatic ligament of the opposite side. 

 In a well-formed male pelvis these three diame- 

 ters are almost equal, being each of them nearly 

 three and a-half inches in extent ; but in conse- 



quence of the mobility of the coccyx that bone 

 may be moved backwards considerably, and 

 under such circumstances the antero-posterior 

 diameter becomes increased to a corresponding 

 amount. 



This large space admits of a very natural 

 division into two triangles, one in front, the 

 other posteriorly ; the base of each respectively 

 corresponds to the line passing transversely be- 

 tween the tuberosities of the ischia, and the 

 apex of the one is formed by the arch of the 

 pubis, whilst that of the other is constituted by 

 the extremity of the coccyx. 



The anterior triangle is equilateral ; its sides 

 are formed by the rami of the ischium and 

 pubis, and are each from three inches to three 

 and a-half inches in length ; it contains the 

 urethra and the root of the penis, with their 

 appendages, and may be named the urethral 

 division of the perineum. 



The posterior triangle is bounded laterally by 

 the great sacro-sciatic ligaments, and in the re- 

 cent state by the edge of the gluteus maximus 

 muscle also. The coccyx usually protrudes 

 forwards so much that the area of the posterior 

 triangle is less than that of the anterior, not- 

 withstanding that the base of each of them is 

 represented by the same line. This posterior 

 triangle contains the anus with the inferior por- 

 tion of the rectum, &c., and is usually called 

 the anal division of the perineum. 



It should be borne in mind that the measure- 

 ments of the inferior outlet of the pelvis may 

 present considerable variations in different sub- 

 jects, and that the operator may be obliged to 

 modify the length and the direction of his inci- 

 sions in lithotomy to suit such cases. M. Du- 

 puytren, for example, in twenty-three subjects 

 which he examined, found the distance inter- 

 mediate between the tuberosities of the ischia to 

 vary from two inches to three and a-half inches; 

 and M. Velpeau, who measured forty subjects, 

 observed in one case these processes to be but 

 an inch and three quarters asunder, whilst in 

 another they were four inches apart. 



In order to perform successfully many of the 

 operations in this region the surgeon requires 

 an accurate knowledge of the axes of the pelvis, 

 and to study the modifications which these 

 imaginary lines exhibit in childhood and old 

 age as compared with adult life. In the full- 

 grown male the axis of the superior aperture of 

 the true pelvis takes a direction from the vici- 

 nity of the umbilicus downwards and back- 

 wards to the coccyx, whilst the axis of the infe- 

 rior aperture passes upwards and slightly back- 

 wards through the mid space between the 

 tuberosities of the ischia to the promontory of 

 the sacrum ; these two lines intersect each 

 other in the pelvic cavity, forming an angle 

 slightly obtuse and salient posteriorly : the axis 

 of the true pelvis (or in other words a line pass- 

 ing through the centres of the upper and lower 

 apertures respectively) is therefore a curved 

 line concentric with the curvature of the sacrum, 

 and having its concavity directed forwards and 

 downwards towards the symphysis pubis. 



During childhood the true pelvis is imper- 

 fectly developed ; it has but little depth, and its 



