334 



THE MUSCLES OF THE TRUNK. 



muscle ; it is separated from the muscle of the other side by a narrow interval, 

 which is occupied by the linea alba. It arises from the pubis by a flat tendon 

 consisting of two parts, of which the internal is much the smaller and is connected 

 with the ligaments covering the front of the pubic symphysis, becoming blended 

 with the one of the opposite side, while the external is fixed to the pnbic crest. 



Fig. 296. DEEP MUSCLES OP THE FORE 



PART OP THE TRUNK AND SHOULDER. 



(Allen Thomson.) f 



For the explanation of the references 

 in the upper part of the figure see p. 211. 



c, c, cartilages of the fifth ribs ; d, 

 ensiform process ; e, symphysis pubis ; f t 

 anterior superior iliac spine ; 12, origin 

 of the serratus magnus ; 13, 13, on the 

 right side, the rectus abdominis ; on the 

 left side, 13', 13', the divided ends of the 

 same muscle, a portion being removed ; 

 14, pyramidalis muscle, exposed on the 

 left side ; 15, on the right side, the in- 

 ternal oblique muscle ; 15', origin of its 

 lower fibres from the deep surface of 

 Poupart's ligament ; 15", conjoined ten- 

 don of the internal oblique and trans- 

 versalis ; 15, on the left side, cut edge 

 of the internal oblique, shown dia- 

 grammatically, to indicate the manner in 

 which its aponeurosis splits to form the 

 sheath of the rectus muscle ; 16, aponeu- 

 rosis of the external oblique muscle, unit- 

 ing in front with the sheath of the rectus. 



Expanding and becoming thinner 

 as it ascends, the muscle is in- 

 serted into the cartilages of three 

 ribs, the fifth, sixth, and seventh, 

 as well as usually into the bone of 

 the fifth, by three distinct slips of 

 unequal size. Some fibres also are 

 frequently found attached to the 

 ensiform process. 



The fibres of the rectus muscle 

 are interrupted by three or more 

 irregular tendinous intersections, 

 known as the inscription** ten- 

 dinece. The three which are most 

 constant are placed, one opposite 

 the umbilicus, another on a level 

 with the lower end of the ensiform 

 process, and the third intermedi- 

 ately between the first two ; and these generally run across the whole or the greater 

 part of the muscle. When one or two additional transverse lines occur, they are 

 usually incomplete ; one of them is very generally placed below the umbilicus, the 

 position of the other is variable. The intersections do not usually penetrate the 

 whole thickness of the muscle, but are confined chiefly to its anterior fibres, and 

 are firmly united to the anterior wall of the sheath of the muscle, while the posterior 

 surface of the muscle has no attachment to the sheath. 



Varieties. The rectus is sometimes joined by some fibres springing from the lower part of 

 the linea alba. The insertion of the muscle has been seen prolonged upwards to the fourth, 



