MUSCLES 29 



tendon of the external oblique muscle is an aper- 

 ture, the inguinal canal, through which, in the male, 

 passes the spermatic cord. (Plates II. and IV.) 



2. The Internal Oblique Muscle lies immediately 

 under the external oblique, from which it must be 

 separated. It is also a thin, muscular sheet, aris- 

 ing from the lumbar fascia, the ventral margin of 

 the ilium, and the pubis. The fibres run obliquely 

 forward toward the mid-ventral line, where they 

 unite with those of the opposite side in a thin 

 aponeurosis. The more anterior fibres are in- 

 serted on the cartilages of the ribs. (Plate III.) 



3. The Rectus Abdominis Muscle is a long, narrow 

 muscle, arising from the symphysis pubis. It 

 runs forward, with its fellow of the opposite side, 

 to its insertion on the first, second, and third ribs. 

 The fibres of the rectus abdominis are intercepted 

 at intervals by transverse tendons, making it a 

 true " polygastric muscle." Posteriorly the rectus 

 abdominis muscle lies dorsal- to the aponeuroses 

 of the external and internal oblique muscles, but 

 anteriorly it lies between the aponeuroses of these 

 muscles. .(Plates III. and IV.) 



4. The Transversalis Abdominis Muscle, the most 

 internal of the abdominal muscles, is a very thin, 

 muscular sheet. It arises from the cartilages of 

 the posterior ribs, the lumbar fascia, and the ven- 

 tral margin of the ilium. Its fibres run trans- 

 versely and end in an aponeurosis beneath the rec- 

 tus abdominis. (Plate IV.) 



