SUPERFICIAL ABDOMINAL REGION 441 



skin, they are seen to be covered by the pannicuhis carnosiis and a thick 

 layer of yellow fibrous tissue, through which their division into tendon and 

 muscle can faintly be discerned. These must be dissected off to bring into 

 view the true abdominal muscles, when the following lines of demarcation 

 will be discerned — 



1. The linea alba, which occupies the median line from the os pubis 

 to the ensiform cartilage, and consists of a tough layer of white fibrous 

 tissue, which unites the muscles of the abdomen together. At a little 

 more than a third of its length from the pubes is found a lozenge-shaped 

 space in which the tissue is almost entirely absent, and through which in 

 the foetus the umbilical vessels pass. This is the umbilicus, or navel, of 

 the adult. 



2. On the surface of the rectus are several transverse white lines — the 

 linese transversales. 



3. Near the edge of the rectus muscle commences the linea semilunax'is, 

 which marks the union of the fleshy and tendinous portion of the external 

 oblique. 



Obliquus abdominis externus is situated on the lateral parts of the 

 belly. Origin — by fleshy slips from the fourteen hindermost ribs, where 

 it indigitates with the serratus magnus and latissimus dorsi, and from 

 the fascia lumborum, reaching to the antero-superior spinous process 

 of the ilium. Insertion — tendinous into the whole length of the linea 

 alba, and by two strong divisions into the os pubis, between which is 

 formed the triangular space called the external abdominal ring. The 

 posterior of these, stretching from the ilium to the os pubis, is called 

 the crural arch, and corresponds with Poupart's Ligament in human anatomy. 

 Action — it flexes the pelvis on the thorax, and has the power of contrac- 

 tion, and, by this means, of expelling the feeces, and in the mare the 

 fcEtus ; it also serves to force up the diaphragm, and thus to aid in 

 expiration. 



Obliquus abdominis internus lies deeper than the foregoing muscle. 

 Origin — from the transverse processes of the lumbar vertebrae and antero- 

 inferior spinous process of the ilium and crural arch. Insertion — to the 

 inner surface of the cartilages of the three or four last ribs, and to the 

 ensiform cartilage ; also in close union with the tendon of the external 

 oblique to the linea alba. Action — to expel the fseces and urine, and to act 

 as above. Like the last, it is also a muscle of respiration. 



Transversalis abdominis is still deeper than the last-mentioned muscle. 

 It has its origin from the transverse processes of the lumbar vertebrae, 

 antero-inferior spine of the ilium, and symphysis pubis. Insertion — to the 

 inner surface of all the ribs, except the three last, linea alba, and ensiform 

 cartilage. Action — to assist the two muscles above, and to support the 

 burden of the viscei'a. 



Rectus abdominis is placed on each side the median line beneath the 

 viscera. Origin — from the symphysis pubis. Insertion — to the cartilages 

 of all the ribs, except the three first, linea alba, ensiform cartilage, and 

 four posterior bones of the sternum : it blends with the lateralis sterni, 

 covering the sides of the sternum. Action — to brace the middle parts of 

 the belly, and to contract the thoracic cavity. 



The parts connected with hernia formed hy the abo\e muscles are : — 



