330 MUSCLES OF THE PERIXiEUM. 



Varicflcx. — lb 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-cavernosns, or erector penis muscle, embracing the eras 

 penis, arises from the inner part of the tuber isehii, behind the ex- 

 tremity of the erus penis, and from the pubic arch along the inner and 

 outer sides of the erus. From this origin the fleshy fibres are directed 

 forwards to a tendinous expansion which is spread over the lower surface 

 of the cms penis, and is inserted into the under and outer surfaces of 

 tliat body towards the fore part. 



Varicfk:^. — Houston has described (Dublin Hosp.. rueports, vol. v.). under the 

 name of e(i»ij)n:s.wiTS mire dorsaHs ju-nin, 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 

 insei-ted above the dorsal vein, by joining each other in the middle Ime. These 

 muscles, which are well developed in the dog and several other animals, are by 

 no means constant in the human subject. 



The Tjunbo-cavsrnosiis or ejaciilatcr urin^, may be considered as 

 a single muscle, consisting of two .symmetrical parts. 



The fleshy fibres of the muscle take origin beliind from the central 

 tendon of the perina3um,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 urethrte, 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 

 distinct from those contiguous to them, and have been described by Kobelt as 

 forming a separate muscle, to which he has given the name c'0))q)ir.s.sor hcmix- 

 ■plucf'nim. hiilhi. The fibres of this muscular slip are connected by a small tendon, 

 above the urethra, with the corresponding part of the opposite side. 



The deep transversiis perinaei muscle is a thin rather inconstant 

 fasciculus which, arising from the margin of the pubic arch, is directed 

 inwards and meets with its fellow of the opposite side behind the bulb, at 

 the central point of the perineum. Its fibres conceal Cowper's gland. 



The constrictor uretlirae muscle consists of a number of transverse 

 fibres extending across the arch of the pubis, some of them above and 

 others below the membranous portion of the urethra, and closely 

 embracing it. In some bodies a tendinous raphe, placed over the 

 middle of the urinary canal, separates each stratum into lateral halves. 



Ilchif'wns. — This muscle rests in contact with the deep layer of the triangular 

 ligament, which separates it from the anterior fibres of the levator ani. 



Circular fibres of Santorini (stratum internum circulare, ]\lUller). — 

 Beneath the transverse muscle just described is a series of circular in- 

 voluntary muscular fibres, entirely surrounding the membranous part 



