DISSECTION OF THE ABDOMEN. 327 



vertebrae, and clean the edges of its foramina. At its periphery, under 

 the costal cartilages, follow the asternal vessels (Plate 45). 



The Asternal Artery. This is one of the divisions of the internal 

 thoracic artery (Fig. 7, page 120). It passes from the thorax to the 

 abdomen by perforating the rim of the diaphragm about the 9th chondro- 

 costal joint. As here seen, it passes backwards at the rim of the 

 diaphragm, in the interval between it and the origin of the transversalis 

 abdominis, and terminates at the lower extremity of the 13th intercostal 

 space. It has three sets of branches, viz., (1) ascending branches, which 

 anastomose with the intercostal arteries of the spaces crossed ; (2) internal 

 branches to the diaphragm ; (3) descending branches, which run on the 

 peritoneal surface of the transversalis abdominis muscle. 



The Asternal Vein accompanies the artery. 



The Diaphragm (Plate 45) is the muscle which serves as a partition 

 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 

 downwai'ds 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 peri- 

 toneum, 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 120). From 

 this mid point the line of attachment of the rim rises on each side, the 

 fibi'es 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 separa- 

 tion the asternal arterj- 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 Ci'wa. — These are right and left. The right is the 

 largest, and arises by a strong tendon from the lumbar vertebrae, 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 pearl}^ white, and composed of glistening- 

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



