38 ELEMENTARY BIOLOGY. [CHAP. 



fibres pass transversely across the floor of the 

 mouth. It is subdivided into a larger fasciculus 

 which supports the floor of the mouth, and a 

 smaller ribbon-shaped one which passes back on 

 either side to the angle of the lower jaw. 



S. The external oblique; underlying and external to 

 y3; forming an investment for the body wall 

 laterally. Its fibres run obliquely upwards and 

 forwards. 



e. The internal oblique ; seen on removing a portion 

 of S. Its fibres pass obliquely downwards and 

 backwards. 



£. The transversalis ; seen on removing a portion of 

 e. It forms the inner layer of the muscular 

 constituent of the body-wall; its fibres run 

 transversely, so as to encircle the trunk ventro- 

 laterally. 



2. Raise the tissues of the body-wall with a pair of 

 forceps and carefully divide them a little to the right 

 of the median line, so as to open the underlying body- 

 cavity without injuring its contents; prolong the 

 incision from the pelvis to the posterior end of the 

 breast-bone. Make a transverse incision close to the 

 pelvis and throw back the flap on each side : on the 

 under side of the left flap will be seen the anterior ab- 

 dominal vein (cf. i c. a). 



Seize the posterior border of the sternum with a 

 pair of forceps and raise it up; then, with a strong pair 

 of scissors, cut through the hard parts a little to one 

 side of the middle line, being very careful not to 

 injure the organs beneath them. Raise each half of 



