33 6 



PRACTICAL ANATOMY. 



SECOND STAGE IN DISSECTING THE PELVIC OUTLET. 



Dissect the crura from the rami and turn them upward over the pubic bone 

 and fasten them out of your way. Cut the central cylinder the corpus spongi- 

 osum off even with the outer layer of the triangular ligament. Detach the 

 external sphincter ani and the two superficial transverse perineal muscles at the 

 central perineal point. Then your field will look like the left side of figure 233. 



The triangular ligament (Fig. 233) occupies the space under the pubes. It 

 consists of two layers, superior and inferior, also called superficial and deep tri- 

 angular ligaments, between which are found : (i) The membranous urethra (Fig. 

 232) ; (2) the duct of Cowper's gland perforating the superficial triangular 

 ligament (Fig. 233) and opening into the bulbous urethra (Fig. 232); (3) the 

 dorsal nerves and vessels of the penis perforating the suspensory ligament of the 

 penis and supplying the back of the penis (Fig. 233) ; (4) the deep transversus 

 perinjei or compressor urethra,', the muscle of Guthrie. (Fig. 234.) 



The above structures are seen on removing the inferior layer of the triangular 



Subpubic ligament with aperture for 

 dorsal vein of the penis 



DORSAL NERVE 



Anterior layer of triangular 



ligament 

 Dorsal artery of penis 



Deep triangu- 



lar ligament 



Artery of corpus 



caverttosii>n 



. I rtcry to bulb 



^/ Pudic veins 



DORSAL NERVE 



POSITION OF COWPER'S 

 GLAND 



iial pudic arterjt 



Crus penis 

 Aperture for artery of corpus 



cnrerno*" tn 



Superficial triangular ligamen 

 Isohio-eavernoBus, or erector pen 

 Aperture for artery 



to bulb 



Urethral aperture 

 Aperture for Cow- 



per'a duct 

 Position of bulb 



Apertures for super- 

 ficial perinatal 

 vessels and nerve 



Fascia of Colles, 

 turned backwards 



Posterior border of 

 permaeal ledge 

 (junction of trian- 

 gular ligaments 

 with fascia of 

 Uolles) 



FIG. 233. DIAGRAM OF THE SUPERFICIAL AND DEEP TRIANGULAR I.K;AMKNT. 



ligament. (Fig. 233.) Now study the attachments of, and the foramina in, the 

 triangular ligament and compare your work with figure 233. 



You will now dissect the iscbio-rectal fossa. You have traced the inferior 

 haemorrhoidal vessels through the fatty mass of this fossa to the rectum and anus. 

 You will now remove the fat and study the geometrical parts of this region. 



The outer wall is formed by the obturator interims muscle and the innominate 

 bone. This muscle is covered by a dense fascia of the same name. This fascia 

 splits to form a canal (Alcock's) in which are the internal pudic vessels and 

 nerve. The inner wall of the ischio-rectal fossa is formed by the levator ani and 

 coccygeus muscles. These, as you will see, embrace the rectum and give it sup- 

 port. The levator ani muscle arises from the white line. This line extends from 

 the spine of the ischium to the pubic bone. The obturator fascia de laminates at 

 the white line, and gives origin to the levator ani muscle in the split between the 

 upper and lower branches into which it divides. The apex, then, of the fossa is 

 at the white line. The boundaries, as you will now see them on your work, of 

 the inlet of the fossa are: (i) The external sphincter ani; (2) the superficial 

 transversus perinaei ; (3) the greater sacro-sciatic ligament ; (4) the glutens maxi- 

 mus muscle; (5) the tubers of the ischium. The base of the fossa is the skin 



