264 MUSCLES OF THE PERINJEUM. 



The transversus perinwi muscle arises from the inner surface of the pubic 

 arch, near the ischial tuberosity, and is directed obliquely forwards and 

 inwards to unite with the muscle of the opposite side, as well as with the 

 sphincter ani and bulbo-cavernosus at the central point of the perinseum. 

 It lies immediately in front of the line where the perinseal dips back to join 

 the subpubic fascia. It is sometimes absent, and at other times one or 

 more small muscular slips are found lying on the same plane with it, in 

 front or behind. 



The ischio-cavernosus, or erector penis muscle, embracing the crus penis, 

 arises from the inner part of the tuber ischii, behind the extremity of the 

 crus penis, and from the pubic arch along the inner and outer sides of 

 the crus. From this origin the fleshy fibres are directed forwards to a 

 tendinous expansion which is spread over the lower surface of the crus penis, 

 and is inserted into the under and outer surfaces of that body towards the 

 fore part. 



This muscle serves to compress the crus penis, with which its tendinous fibres are 

 blended, and thus it contributes to produce, or at least to maintain, the erection of 

 the penis. 



The muscles of the two sides have been described by Krause as in some cases con- 

 nected by a thin tendinous expansion, which, according to that anatomist, extends 

 along the outer side of the penis over the dorsal surface of the organ, and at the same 

 time over the vessels lying upon it (Mtiller's Archiv, 1832) : but this connection 

 between the muscles has been in vain sought for by Theile and by Kobelt (Die m'ann- 

 lichen und weiblichen Wollust-Organe, 1844). By Houston there have also been 

 described (Dublin Hosp. Reports, vol. v.), under the name of compressors venae, 

 dorsalis penis, two slips of muscle, separated from the erectores penis on each side 

 by an interval, though apparently belonging to them. They are said to arise from 

 the pubic arch, above the origin of the erector muscles and the crura of the penis, 

 and, passing upwards and forwards, are inserted above the dorsal vein, by joining each 

 other in the middle line. These muscles, which are well developed in the dog and 

 several other animals, are by no means constant in the human subject. 



The bulbo-cavernosus, accelerator urinse, or ejaculator seminis, may be con- 

 sidered as a single muscle, consisting of two symmetrical parts. 



The fleshy fibres of the muscle take origin behind from the central tendon 

 of the perinseum, and from a median tendinous raphe' interposed between 

 the two halves of the muscle. The larger number of the fibres are directed 

 round the bulb and the adjoining part of the corpus spongiosum urethrre, 

 and join above that body with those from the opposite side by a strong 

 aponeurosis. At the fore part, a portion of the muscle passes over the 

 sides of the corpus cavernosum, and is attached to that body in front of the 

 erector penis : from its insertion a tendinous offset is said to be prolonged 

 over the dorsal vessels of the penis (Kobelt). The posterior fibres, shorter 

 than the anterior, are inserted into the front of the triangular ligament. 



The fibres which invest the most prominent part of the bulb are more or less dis- 

 tinct from those contiguous to them, and have been described by Kobelt as forming a 

 separate muscle, to which he has given the name compressor hemisphcerium bulbi. 

 The fibres of this muscular slip are connected by a small tendon, above the urethra, 

 with the corresponding part of the opposite side. 



This muscle compresses the bulb and the adjoining part of the corpus spongiosum 

 of the urethra, so as to evacuate fluid lodged in the canal, as well as to increase the 

 turgescence of the glans during erection. 



The deep transversus perincei muscle is a thin rather inconstant fasciculus, 

 which, arising from the margin of the pubic arch, is directed inwards and 



