DISSECTION OF THE ABDOMEN. 293 



form cartilage, where it turns round the 9th costal cartilage behind its 

 tip. It runs backwards along the middle of the superior face of the 

 rectus, giving off lateral branches, and terminating aboiit midway 

 between the sternum and pubis in branches which anastomose with 

 those of the posterior abdominal artery. It is accompanied by a 

 satellite vein. 



The Transversalis Abdominis (Plate 40). This muscle consists 

 of a fleshy band at its origin, and of an aponeurotic tendon over 

 the abdominal floor. In both of these the direction of the fibres is 

 transversely downwards and inwards towards the linea alba. It arisen 

 by its fleshy portion from the lower extremities or cartilages of the 

 asternal ribs (last ten), meeting here the origin of the diaphragm ; and 

 from the transverse processes of the lumbar vertebrse. It is inserted 

 by the inner edge of the aponeurotic tendon into the ensiform cartilage 

 and the linea alba. The posterior edge of the tendon is thin and ill- 

 defined. The inner surfixce of the entire muscle is related to the 

 parietal peritoneum, there being interposed, however, a very thin layer 

 of connective-tissue representing the fascia transversalis of man. Slender 

 branches from the intercostal or asternal vessels run on the peritoneal 

 surface of the muscle. 



Action. — Similar to that of the oblique muscles. 



Directions. — The abdominal cavity will be exposed by the removal of 

 the transverse muscle and its peritoneal lining. If only one side of the 

 abdominal wall has been dissected, the other side may now be used for 

 the better display of things not satisfactorily made out in the first; and 

 particularly, a portion of the abdominal wall in front of Poupart's liga- 

 ment should be turned back in its entire thickness, so as to expose its 

 peritoneal aspect and the internal abdominal ring. 



The Internal Abdominal Ring (Plate 44) is the abdominal opening 

 of the inguinal canal. As seen from the abdominal side, its posterior 

 or outer edge is prominent, and corresponds to the edge of the mviscular 

 part of the internal oblique ; while the opposite boundary of the ring is 

 flattened over the sublumbar muscles covered by the continuation of 

 Poupart's ligament. 



The student can now see the direct continuity between the peritoneum 

 and the tunica vaginalis, the latter membrane passing directly into the 

 inguinal canal, and forming a well-defined edge on the posterior and 

 outer side of the entrance. It is by this opening that a portion of 

 intestine or mesentery sometimes passes into the inguinal canal, or 

 onwards into the scrotum, constituting an inguinal or scrotal hernia. 



The Prepubic Artery (Plate 44). This vessel arises from the femoral 

 artery at the brim of the pubis, forming a short common trunk with the 

 deep femoral branch. It crosses to the edge of the internal oblique, and 

 divides into the external pudic and posterior abdominal arteries. The 



