TRANSVERSALIS ABDOMINIS 



409 



arcnatum externum, gives origin to a i)ai-t of the (Iia})liragui. Between the middle 

 and posterior layers is placed the erector spinte muscle. This posterior layer 

 hlends with the vertebral aponeurosis, and gives origin to the latissimus dorsi, the 

 serratus posticus inferior, and otlier muscles. 



Nerve-supply. — The anterior primary branches of the lower thoracic nerves 

 and the ilio-hypogastric and ilio-inguinal branches of tlie first nerve of the lumbar 

 plexus. The nerves as they run forward between this muscle and the obliquus 

 internus distribute filaments to its outer surface. 



Action. — The muscles of the two sides with their intervening aponeurosis form 

 a strong girth round the a])dominal viscera, and by their contraction compress most 

 powerfully the contents of the abdomen. 



Fig. 304. — Tkaxsveksalis Ahdohixis and Sheath of Rectus. 



External intercostal 



Internal intercostal 



Posterior portion of 

 sheath of rectus 



Transversalis ^° 

 abdominis 



Fold of Douglas 



Transversalis fascia and 

 internal abdominal ring 



Conjoined tendon 



Poupart's ligament 



Gimberuat's ligament 



— Serratus magnus 



Lumbar fascia 



It will thus be seen that tlie three layers of the transverse muscle in the 

 abdominal wall cross one another at various angles, one pair passing transversely 

 forwards, a second forwards and U])wards, and a third forwards and downwards. 

 The following objects are gained l)y this arrangement: (1) the wall is rendered 

 much stronger, and the proliability of a hernial protrusion of any portion of the 

 viscera between the separated fibres of the muscles is diminished; (2) contraction 

 of the wall is permitted in every direction; (o) greater approximation of the mova- 

 l)le boundaries of the abdominal wall is* obtained by means of the obliquity of the 

 muscles which effect this movement. For example, two parallel bones can have 

 the distance between them diminished only by one half, supposing that the mus- 

 cular fibres producing this movement run ])er]>endicularly from one lione to the other; 

 but if the fibres cross one another obliquely, like those of the external and internal 



