MALE PERINEUM 349 



Around the anus they anastomose with the corresponding 

 arteries of the opposite side, and with branches from the 

 middle and superior haemorrhoidal arteries. They likewise 

 send a few twigs round the distal border of the glutaeus 

 maximus, in company with the perforating cutaneous nerve, 

 to supply the skin in the distal part of the buttock. 



Inferior Haemorrhoidal Nerve. This nerve accompanies 

 the vessels of the same name. It may proceed directly from 

 the sacral plexus, but more frequently it is a branch of the 

 pudendal nerve. It perforates the medial wall of Alcock's 

 canal, enters the ischio-rectal fossa, and then it breaks up 

 into muscular, cutaneous, and communicating branches. The 

 muscular twigs supply the external sphincter ani : the cutaneous 

 offsets are given to the skin which surrounds the anus, while 

 the communicating filaments pass forwards to join the long 

 perineal branch of the posterior cutaneous nerve of the thigh 

 and the scrotal nerves. 



Perineal Branch of Fourth Sacral Nerve. This small 

 nerve enters the ischio-rectal fossa by piercing the coccygeus 

 muscle at the side of the coccyx. It is distributed to 

 the skin between the anus and coccyx, and to the external 

 sphincter ani muscle. 



The perineal artery and the perineal nerve will be found 

 in the anterior angle of the fossa close to the lateral wall. 



Ano-coccygeal Body. An indefinite mass of muscular and 

 fibrous tissue which lies between the tip of the coccyx and 

 the anus receives the name of ano-coccygeal body. It is best 

 seen in sections through the pelvis, and it requires notice on 

 account of the support which it gives to the lower part of 

 the rectum and the anal canal. The muscular tissue which 

 enters into its constitution belongs to the levator ani and 

 the external and internal sphincter muscles (Symington). 



UROGENITAL TRIANGLE. 



The superficial fascia in this locality has already been 

 studied. The following is a list of the structures which still 

 require to be examined : 



1. The posterior scrotal vessels and nerves. 



2. The long perineal branch of the posterior cutaneous nerve of the thigh. 



3. The root of the penis. {The bulb and the crura. 



