MUSCLES OF TRUNK. . 460 
yi. The rectus abdominis: runs longitudinally along 
the midventral wall, the muscles of the two sides 
being separated from one another in the middle 
line by the linea alba, a longitudinal band of 
connective tissue, immediately dorsad of which 
lies the anterior abdominal vein. Each rectus 
muscle is divided into bellies by five transverse 
tendinous intersections. 
The muscle arises from the pubes, runs forward 
and is inserted into the dorsal surface of the 
sternum and coracoid. 
/ ii, The pectoralis: a large fan-shaped muscle consist- 
ing of a thoracic portion, which arises from 
the whole length of the ventral surface of the 
sternum: and an abdominal portion arising from 
the aponeurosis along the outer side of the 
rectus abdominis almost as far back as the 
pubes. From this extensive origin the fibres 
converge to the deltoid ridge of the humerus into 
which they are inserted, the line of insertion 
extending down almost to the elbow. 
, iii, The obliquus externus: a thin sheet of muscle 
which arises from the aponeurosis of the back, a 
short distance on either side of the vertebral 
column, and covers the whole of the side of the 
body, the fibres running obliquely downwards 
and backwards to end in an aponeurosis which 
passes dorsad of the rectus abdominis to be 
inserted into the linea alba. 
iv. The obliquus internus: lies beneath the obliquus 
externus, which must be removed in order to 
see it. It arises from the transverse processes of 
the vertebre from the fourth backwards, and 
from the ilium. The fibres run downwards and 
forwards, and are inserted in front into the 
coracoid and sternum: some of the fibres surround 
and are inserted into the cesophagus and peri- 
cardium. The hinder two-thirds of the muscle 
pass dorsad of the tendon of the obliquus 
externusand are inserted like it into thelinea alba. 
