Chap. VII] MUSCULAR TISSUE 109 



Action of the abdominal muscles. — When these muscles con- 

 tract, they compress the abdominal viscera, and constrict the 

 cavity of the abdomen, in which action they are much assisted by 

 the descent of the diaphragm. By these means they give assist- 

 ance in parturition, defecation, micturition, and vomiting. They 

 also assist in respiration, and in various movements, such as 

 climbing, flexing the thorax upon the pelvis, rotation of the 

 trunk, etc. 



The inguinal canal. — Between the abdominal muscles, parallel 

 to, and about one-half inch above the inguinal ligament, is a tiny 

 canal, about one and one-half inches long, called the inguinal canal. 

 The internal opening of the canal is called the internal abdominal 

 ring, and is situated in the fascia of the transversalis muscle, mid- 

 way between the spine of the ilium and the crest of the pubic bone. 

 The canal ends in the external abdominal ring, which is in the tendon 

 of the external oblique muscle. This canal transmits the sper- 

 matic cord in the male, or the round ligament of the uterus in 

 the female. 



Weak places in the abdominal walls. — The internal and ex- 

 ternal abdominal rings, described above, the umbilicus, and an- 

 other ring situated just below the inguinal ligament, and called the 

 femoral ring, are considered weak places because they are so often 

 the seat of hernia. Hernia, ^ or rupture, is a protrusion of a portion 

 of the contents of a body cavity, and in this instance would mean 

 a protrusion of a portion of the intestine or mesentery through one 

 of these weak places. If it occurs in the umbilicus, it is called 

 umbilical hernia; in the inguinal rings, inguinal hernia; and in the 

 femoral ring, femoral hernia. The inguinal canal is larger in the 

 male than in the female, hence inguinal hernia is more common 

 in the male than in the female. 



MUSCLES OF THE UPPER EXTREMITIES 



A certain number of muscles situated superficially on the trunk 

 are frequently grouped with the muscles of the upper extremities, 

 as their function is to attach the upper limbs to the trunk and 

 move the shoulders and arms. Of these, the two superficial 



• If the skull is injured so that a portion of the brain protrudes, it would also be 

 correctly spoken of as hernia of the brain. Of course this is more unusual than 

 abdominal hernia. 



