THE UROGENITAL SYSTEM. ' 259 



2. Cremasteric fascia (subcutaneous fascia). 



3. The levator scroti muscle (subcutaneous muscle-layer) 

 (Fig. ii3,y). 



4. Tunica vaginalis communis (transversalis fascia). 



5. Tunica vaginalis propria (peritoneum). 



The tunica vaginalis communis is inseparably united with 

 the parietal layer of the tunica vaginalis propria. Where the 

 spermatic cord passes from the abdominal wall to the scrotum 

 it is covered by integument and cremasteric fascia on its ventral 

 surface only, but is entirely surrounded by the tunica vaginalis 

 propria and tunica vaginalis communis. The canal by which 

 the spermatic cord passes through the body wall is known as 

 the inguinal canal. The end by which it opens into the 

 abdominal cavity is the internal inguinal ring, and the oppo- 

 site end is called the external inguinal ring. 



The internal inguinal ring is merely the point of connec- 

 tion between the proximal tubular portion of the tunica 

 vaginalis propria and the abdominal cavity. It is circular, and 

 is situated close against the lateral side of the lateral ligament 

 of the bladder at its middle. 



The external inguinal ring is an oval opening in the apo- 

 neurosis of insertion of the external oblique muscle. The apo- 

 neurosis of this muscle ends caudally in a free border along the 

 cranial edge of the pubis, from the ilium to the pubic tubercle. 

 The external ring is just craniad of the end of this aponeurosis. 



The inguinal canal between these rings lies along the 

 lateral border of the rectus muscle. It is one to one and a 

 half centimeters long. Its medial wall rests on the rectus 

 muscle ; its dorsal wall on the fat contained within the lateral 

 ligament of the bladder. The lateral and ventral walls lie on 

 the transversus muscle proximally, on the internal oblique near 

 the distal end. The wall itself is composed of tunica vaginalis 

 propria and communis. As it passes within the caudal border 

 of the internal oblique muscle it receives some aponeurotic 

 fibres from it. A thin aponeurosis is also continued from the 

 border of the external ring onto the tunica vaginalis propria. 



The testes (Fig. no) are the organs which produce the 

 spermatozoa. They lie one in each compartment of the scrotal 



