212 MUSCLES OF THE ABDOMEN. 



the umbilicus, upwards and outwards, to the outer side of the chest, as 

 high as the fifth or sixth rib ; and the third, oblique, from the umbilicus, 

 downwards and outwards, to the middle of the crest of the ilium. The 

 three flaps included by these incisions should then be dissected back in 

 the direction of the fibres of the external oblique muscle, beginning at the 

 angle of each. The integument and superficial fascia should be dissected 

 off together so as to expose the fibres of the muscle at once. 



If the external oblique muscle be dissected on both sides, a white ten- 

 dinous line w r ill be seen along the middle of the abdomen, extending from 

 the ensiform cartilage to the os pubis ; this is the linea alba. A little ex- 

 ternal to it, on each side, two curved lines will be observed extending 

 from the sides of the chest to the os pubis, and bounding the recti muscles : 

 these are the linea semilunares* Some transverse lines, linete transverste, 

 three or four in number, connect the linese semilunares with the linea 

 alba. 



The EXTERNAL OBLIQUE MUSCLE (obliquus externus abdominis descendens) 

 is the external flat muscle of the abdomen. Its name is derived from the 

 obliquity of its direction, and the descending course of its fibres. It 

 arises by fleshy digitations from the external surface of the eight inferior 

 TifrS"; the five upper digitations being received between corresponding pro- 

 cesses of the serratus magnus, and the three lower of the latissimus do r si. 

 Soon after its origin it spreads out into a broad aponeurosis, which is in- 

 serted into the outer lip of the crest of the ilium for one half its length, the 

 anterior superior spinous process of the ilium, spine of the os pubis, pecti- 

 neal line, front of the os pubis, and linea alba. 



The lower border of the aponeurosis, which is stretched between the 

 anterior superior spinous process of the ilium and the spine of the os pubis, 

 is rounded from being folded inwards, and forms Poupartfs ligament; the 

 insertion into the pectineal line is GimbernaPs ligament. 



Just above the crest of the os pubis is the external abdominal ring, a 

 triangular opening formed by the separation of the fibres of the aponeuro- 

 sis of the external oblique. It is oblique in its direction, and corresponds 

 with the course of the fibres of the aponeurosis. It is bounded below by 

 the crest of the os pubis ; on either side by the borders of the aponeurosis, 

 which are called pillars ; and above by some curved fibres (inter-colum- 

 nar), which originate from Poupart's ligament, and cross the upper angle 

 of the ring so as to give it strength. The external pillar, which is at the 

 same time inferior from the obliquity of the opening, is inserted into the 

 spine of the os pubis ; the internal or superior pillar forms an interlacement 

 with its fellow of the opposite side over the front of the symphysis pubis. 

 The external abdominal ring gives passage to the spermatic cord in the 

 male and round ligament in the female : they are both invested in their 

 passage through it by a thin fascia derived from the edges of the ring, and 

 called inter- columnar fascia, or fascia spermatica. 



The pouch of inguinal hernia, in passing through this opening, receives 

 the inter-columnar fascia, as one of its coverings. 



Relations. By its external surface with the superficial fascia and inte- 

 gument, and with the cutaneous vessels and nerves, particularly the super- 

 ficial epigastric and superficial circumflexa ilii vessels. It is generally 

 overlapped posteriorly by the latissimus dorsi. By its internal surface 

 with the internal oblique, the lower part of the eight inferior ribs and in- 

 tercostal muscles, the cremaster, the spermatic cord in the male, and the 



