SUPERFICIAL MUSCLES OF URETHRA. 395 



are lost on the front of the triangular ligament. The anterior fibres, which 

 are the longest and best marked, are inserted into the penis on its outer 

 aspect before the erector ; and, according to Kobelt, 1 they send a tendinous 

 expansion over the dorsal vessels of the penis. Whilst the middle or in- 

 tervening fibres turn round the urethra, surrounding it for two inches, and 

 join its fellow by a tendon. 



The ejaculator muscle covers the bulb and the urethra for three inches 

 in front of the triangular ligament. 2 If the muscle be cut through on the 

 right side, and turned off the urethra, the junction with its fellow above 

 that tube will be apparent. 



Action. The two halves, acting as one muscle, can diminish the urethra, 

 and eject forcibly its contents. During the flow of fluid in micturition the 

 fibres are relaxed, but they come into use at the end of the process, when 

 the passage has to be cleared. The action is involuntary in the emission 

 of the semen. 



The TRANSVERSALS PERiN^Ei (fig. 130, ) is a small thin muscle, which 

 lies across the perinasum opposite the base of the triangular ligament. 

 Arisi ng from the inner surface of the pubic arch near the ischial tuberosity, 

 it is inserted into the central point of the perinaaum with the muscle of the 

 opposite side, and with the sphincter ani and the ejaculator urinae. Be- 

 hind this muscle the superficial fascia bends down to join the triangular 

 ligament. 



Sometimes there is a second small fleshy slip, anterior to the transver- 

 salis, which has been named transversals alter ; this throws itself into the 

 ejaculator muscle. 



Action. From the direction of the fibres the muscle will draw back- 

 wards the central point of the perinaeum, and help to fix it, preparatory to 

 the contraction of the ejaculator. 



The three muscles above described, when separated from each other by 

 the dissection, limit a triangular space, of which the ejaculator urinze 

 forms the inner boundary, the erector penis the outer side, and the trans- 

 versalis perinjei muscle the base. In the area of this interval is the trian- 

 gular ligament of the urethra, with the superficial perinaeal vessels and 

 nerves. Should the knife enter the posterior part of this space during the 

 deeper incisions in the lateral operation of lithotomy, it will divide the 

 transverse muscle and artery, and probably the superficial perinasal vessels 

 and nerves. 



Dissection (fig. 131). For the display of the triangular ligament, the 

 muscles and the crus penis, which are superficial to it, are to be detached 

 in the following way : On the left side the ejaculator urinae is to be re- 

 moved completely from the front of the ligament, and the erector muscle 

 from the crus of the penis. Next, the crus penis is to be detached from 

 the bone ; but this must be done with care so as not to cut the triangular 

 ligament, nor to injure, near the pubes, the terminal branches of the pudic 

 arterv and nerve to the penis. 



On the right side the dissector should trace out beneath the transversalis 



1 Die M'annlichen und Weiblichen Wollust-Organe, von G. L. Kobelt, 1844. 



2 Some of the deeper fibres which immediately surround the bulb, have been 

 described as a separate stratum by Kobelt. These are separated from the super- 

 ficial layer by thin areolar tissue, and join the corresponding part of the other 

 muscle by a small tendon above the urethra. The name compressor hemisphcerium 

 bulbi has been proposed for it by that anatomist. 



