THE UROGENITAL SYSTEM. 259 
2. Cremasteric fascia (subcutaneous fascia). 
3. The levator scroti muscle (subcutaneous muscle-layer) 
(Fig. 113, 7). 
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. 110) are the organs which produce the 
spermatozoa. They lie one in each compartment of the scrotal 
