14 DISSECTION OF THE DOG 



Canalis inguinalis. — The inguinal canal is a passage through the ab- 

 dominal wall in which lies the spermatic cord of the male or the round hgament 

 of the female. In the male, moreover, the testis descends into the scrotum by- 

 way of the canal. The canal is lined by a tubular connection between the 

 peritoneum of the abdomen and the tunica vaginalis of the scrotum. In 

 direction it is oblique ; its superficial extremity {annulus inguinalis subcutaneus) 

 being caudal and medial to its deep extremity (annulus inguinalis ahdominalis). 

 The canal should be examined on that side of the abdomen where the 

 muscles are yet intact. Introduce a probe or glass rod into the canal, and 

 clean, in the first place, the subcutaneous ring. This is, speaking generally, 

 an oval opening in the aponeurotic tendon of the external oblique muscle of 

 the abdomen. The lateral boundary of the ring is formed by the stout part 

 of the aponeurosis connected with the origin of the pectineus muscle. The 

 medial boundary is formed by the combined aponeuroses of the external 

 and internal obUque and the transverse muscles. 



The canal itself has a length of some 30 mm. and crosses the lateral border 

 of the rectus muscle obliquely. Near the subcutaneous ring, it runs along the 

 .grooved surface of the inguinal ligament (Poupart's ligament). The canal 

 may be considered as possessing a ventral and a dorsal wall. The ventral wall 

 throughout the whole of its extent is formed by the aponeurosis of the external 

 obhque, and, throughout the greater part of its extent, by the fleshy part of 

 the internal obUque muscle also. Close to the abdominal ring, some fibres of 

 the transverse muscle may assist in the formation of this wall, but more com- 

 monly the abdominal ring occurs solely in the fascia of the transverse muscle. 

 The dorsal wall, close to the subcutaneous ring, is formed for a very short 

 distance by the combined obhque and transverse aponeuroses. For the 

 greater part the wall is constituted by the fascia of the transverse muscle 

 covered internally by the peritoneum. 



In the female, the inguinal canal contains a funnel-shaped cavity continuous 

 with that of the peritoneum. Outside its serous lining there is a considerable 

 accumulation of fat. 



In intimate association with the inguinal canal are the external pudendal 

 and caudal epigastric vessels. The external pudendal artery and vein cross 

 the medial aspect of the spermatic cord at the subcutaneous ring. The caudal 

 epigastric vessels also cross the medial side of the canal, but they do so obliquely 

 and at a variable point in its length. Running for a distance parallel to the 

 inguinal canal, and in its dorsal wall, is the external spermatic nerve. 



Dissection. — Open the abdominal cavity by making an incision along the 

 whole length of the linea alba, and a transverse incision on each side 

 through the transverse muscle and the peritoneum. This having been 

 done, a fold of peritoneum will be discovered passing along the Hnea 

 alba to the urmary bladder. In this fold there is frequently a considerable 

 accumulation of fat. 



