334 PRACTICAL ANATOMY. 



The lowest fibres into the triangular ligament ; (2) the middle, surround the 

 bulb ; (3) the upper ones pass out across the corpus spongiosum and are inserted 

 into the dorsum of the penis and pubic bone. Notice, also, the nerve-supply to this 

 muscle from the internal pudic. Now cut through the bulb down to the sound 

 and see (i) the bulbous part of the urethra and (2) the erectile tissue ; the latter 

 is the specific element of the bulb, and, taken with the remaining part of the 

 middle cylinder of the penis, is called the corpus spongiosum. Notice the dense 

 fibrous capsule of the bulb, derived from the outer layer of the triangular liga- 

 ment, upon which the bulb rests. See the nerves and vessels /rom the internal 

 pudics. 



Dissection of Superficial Transversus Periiuci. Trace this little muscle from 

 the tuberosity of the ischium to the central point of the perineum, it being inserted 

 between the sphincter ani and the accelerator. Notice the nerve-supply. 



Dissection of the J'e/iis. With the scissors cut through the mid-line of the 

 skin of the scrotum and under part of the penis. Now carefully remove the integu- 

 ment from the entire organ. As stated above, the penis is composed of three 

 cylinders, which converge from three different sources. These three cylinders 

 are (i) the two corpora cavernosa and (2) the urethal cylinder or corpus 

 spongiosum, which unite to form a triangular body with three compartments. 

 In transverse section. (Fig. 231.) See, now, that each cylinder has special char- 

 acteristics, (i) The central cylinder, resting on the outer layer of the triangular 

 ligament, begins in the bulb and terminates in an expansion, the glans penis, 

 which receives the conical extremities of the lateral cylinders. (Fig. 232.) (2) 

 The lateral cylinders, the corpora cavernosa, begin in blunt crura from the ischio- 

 pubic ramus, are covered by compressor muscles, erectores penis, and terminate in 

 pointed extremities in the distal expansion of the corpus spongiosum the head of 

 the penis. Observe, also, that each cylinder has common characteristics : (i) a 

 fibrous elastic envelope ; (2) erectile tissue. Lastly, see the middle cylinder 

 traversed from end to end by the urethra. Now cut down on the sound and 

 expose the urethra. (Fig. 232.) 



The urethra is the mucous canal extending from the bladder to the extremity 

 of the glans penis. In its course it pierces the prostate from base to apex, 

 the deep and superficial triangular ligaments with the intervening compressor 

 urethrse muscle, and the whole length of the corpus spongiosum. It may hence 

 be divided into three segments : (i) Prostatic ; (2) membranous (the portion lying 

 in the space between the two transverse triangular ligaments) ; and (3) spongy. 

 (Fig. 232.) 



Having completed the first stage of the dissection of the pelvic outlet, review 

 your work carefully, and see if you have found the following structures : 



1. You removed the skin, learned the boundaries of the pelvic outlet, and 

 classified the same into an anterior or perinea/ portion, and a posterior or iscliio- 

 rectal portion. 



2. You saw the deep layer of the superficial fascia, Colics' fascia, having 

 two attachments: (i) To the ischio-pubic ramus ; (2) to the triangular ligament. 



3. You located the greater sacro-sciatic ligament, cut the same, and found 

 the main trunk of the internal pudic nerve with its accompanying vessels. In 

 this locality you found two nerves given off. One of these you traced through 

 the fat in the ischio-rectal fossa, in many branches, to the corrugator cutis ani 

 and external sphincter ani muscles, and also to the skin covering these muscles ; 

 this was the inferior hicmorrlioidal nerve. The other you traced, under the name 

 of superficial perincal nerve, to (i) the accelerator, (2) the erector penis, (3) 

 the superficial transversus perinxi, and to the skin covering these muscles. 



4. Then you located the central point of the perineum, and learned the muscles 

 meeting there and their nerve-supply as follows: (i) Accelerator urina- ; (2) 



