98 THE COMMON FROG. [chap. 



fibres of the successive muscles being differently- 

 directed. Thus we have (i) the external oblique (the 

 fibres of which pass obliquely downwards and back- 

 wards), (2) the internal oblique (the fibres of which 

 pass obliquely downwards and forwards), (3) the 

 Transversalis (with transverse fibres), and (4) the 

 Rectus abdomiiius (situated in the middle line of the 

 body, and with fibres directed antero-posteriorly). 



Fig. 6i- — Deeper Abdominal Muscles of Man — the external oblique being removed 

 from the left side of the body, and the internal oblique and part of the rectus 

 also, from its right side, i, the internal oblique ; its outer tendon (2) is cut and 

 reflected from the outside of the rectus to show its deeper tendon (3), which 

 passes within the rectus except towards the pubis ; 4, transversalis ; 5, its fascin ; 

 6, sheath of the rectus — near the pubis, the conjoined aponeuroses of the ab- 

 dominal muscles pass in front of that muscle : 7, pyramidalis ; 8, rectus of left 

 side, showing the tendinous intervals, or linea tratisversi^. 



In the frog we also meet with the vast sheets of 

 muscle with oppositely directed fibres (the external 

 and internal oblique;, and with a median, antero- 

 posteriorily directed rectus muscle. 



A very different condition exists in fishes, where 

 there is indeed a median antero-posteriorly directed 

 rectus, but where the abdomen and tail are encased 



