250 DETAILED SYNTHESIS. 



FlG. 180. 



Fig. 180, a plan of ribs, 

 to show direction of inter- 

 costals and how they cross. 



521. THE RECTUS ABDOMINALIS (straight of the ab- 

 domen) extends from the front lower part of the chest 

 down in front of the abdomen to the pelvis. It is divid- 

 ed by tendons into the upper, middle, and lower parts ; 

 for if the fleshy part had been continuous, its contrac- 

 tions would have produced inconvenience on account of 

 the prominence its central part would have exhibited. 

 (26, Fig. 1, PI. 20.) 



522. THE USE or THE RECTUS is to depress the 

 chest, and when moderately distended it can act with 

 greatest advantage; hence, a person can speak or use 

 the expiratory organs with greatest ease after eating a 

 reasonable quantity of food, if not to soon. 



523. THE SIDES OF THE ABDOMEN ARE WALLED by 

 three layers of Muscles, the external and internal oblique, 

 and the transverse. They are fleshy on the sides, and 

 form a dense sinewy aponeurosis over the centre of the 

 abdomen. The rectus passes down through this about 

 two thirds its length, and then passing between the fibres 

 of the transverse, extends behind them and those of the 

 oblique to the pelvis. (15, Fig. 2, PL 21.) 



524. THE USE OF THE THREE LAYERS is to draw 

 down the ribs and compress the organs of the abdomen, 

 and thus doubly assist in expelling the air in common 

 with the rectus. 



525. THE LUMBAR QUADRATUS is a stout muscle that 

 extends from the upper edge or crest of the hip to the 

 lowest rib, and assists in depressing the chest. (Fig. 181.) 



Describe Fig. 180. 521. Describe . 622. What is -? 528. How are -? 

 624. What Is ? 525. Describe . 



