DISSECTION OF THE ABDOMEN. 337 



between the thoracic and abdominal cavities. In outline it has some 

 resemblance to the heart of playing-cards, the point being at the ensiform 

 cartilage, and the base at the spine. Its general direction is oblique 

 downwards and forwards. Its anterior or thoracic surface (Plate 22) is 

 convex, covered by pleura, and related to the bases of the lungs. Its 

 posterior surface is concave, covered for the greater part by peritoneum, 

 and related to the liver, stomach, spleen, and intestines. It consists of a 

 muscular rim, two muscular pillars or crura, and an aponeurotic centre. 



The Fleshy Rim is composed of soft muscular fibres, the lowest of 

 which are attached outwardly to the upper face of the ensiform cartilage 

 about one inch behind its junction with the sternum (Fig. 7, page 122). 

 From this mid point the line of attachment of the rim rises on each 

 side, the fibres taking origin from the cartilages of the last ten ribs, or 

 from the ribs themselves above the chondro-costal joints. On each side 

 these fibres meet, or are separated by only a narrow line from, the 

 fibres of the transversalis abdominis at their origin ; and along the line 

 of separation the asternal artery runs. The muscular fibres are all 

 directed from these points of origin inwards, where, along a denticulated 

 line, they terminate in the tendinous centre. 



The Pillars, or Crura. — These are right and left. The right is the 

 largest, and arises by a strong tendon from the lumbar vertebra), through 

 the medium of the inferior common ligament. Its muscular fibres 

 terminate in the tendinous centre, some of them diverging to the right, 

 but without joining the muscular rim, while others descend to near the 

 mid point. The left pillar has a similar origin from the left side of the 

 lumbar vertebrae, and its fibres terminate in the tendinous centre, being 

 sometimes continuous outwardly with the muscular rim. 



The Tendinous Centre is pearly white, and composed of glistening 

 fibres interlacing in various directions. By the descent of the pillars 

 into it, it is partially divided into right and left halves, or leaflets. 



Ligamenta Arcuata. — On each side of the pillars the rim of the 

 diaphragm arches with a free edge over the apices of the psoas muscles, 

 forming the so-called arcuate ligament. 



Foramina of the diaphragm : — 



The Foramen Sinistrum. — This is a slit between the fibres of the right 

 crus, formed slightly to the left of the mesial plane, and a little below 

 the spine. It transmits the ossophagus, the oesophageal continuations 

 of the vagus nerves, and the pleuro-oesophageal branch of the gastric 

 artery. 



The Foramen Dextrum. — This is the aperture by which the posterior 

 vena cava passes from the abdomen to the thorax. It is formed near 

 the middle of the tendinous centre, but a little to the right of the 

 mesial plane. The margins of the opening are closely adherent to the 

 wall of the vein, and here the phrenic sinuses empty. 



