286 



MUSCLES AND FASCIAE. 



Dissection. To expose the Eectus muscle, its sheath should be opened by a vertical in- 

 cision extending from the margin of the thorax to the pubes, the two portions should then be 

 reflected from the surface of the muscle, which is easily effected, excepting at the linese trans- 

 versae, where so close an adhesion exists, that the greatest care is requisite in separating them. 

 The outer edge of the muscle should now be raised, when the posterior layer of the sheath will 

 be seen. By dividing the muscle in the centre, and turning its lower part downwards, the point 

 where the posterior wall of the sheath terminates in a thin curved margin will be seec. 



The Rectus Abdominis is a long, flat muscle, which extends along the whole 

 length of the front of the abdomen, being separated from its fellow of the opposite 

 side by the linea alba. It is much broader above than below, and arises by two 

 tendons, the external or larger being attached to the crest of the os pubis ; the 

 internal or smaller portion, interlacing with its fellow of the opposite side, and being 

 connected with the ligaments covering the symphysis pubis. The fibres ascend 

 vertically upwards, and the muscle, becoming broader and thinner at its upper 

 part, is inserted by three portions of unequal size into the cartilages of the fifth, 

 sixth, and seventh ribs. Some fibres are occasionally connected with the costo- 

 xiphoid ligaments, and side of the ensiform cartilage. 



i 



Fig. 166. A Transverse Section of the Abdomen in the Lumbar Region. 



The Rectus muscle is traversed by a series of tendinous intersections, which 

 vary from two to five in number, and have received the name linese transverse. 

 One of these is usually situated opposite the umbilicus, and two above that point ; 

 of the latter, one corresponds to the engiform cartilage, and the other to the interval 

 between the ensiform cartilage and the umbilicus. There is occasionally one below 

 the umbilicus. These intersections pass transversely or obliquely across the muscle 

 in a zigzag course ; they rarely extend completely through its substance, sometimes 

 pass only half way across it, and are intimately adherent to the sheath in which the 

 muscle is inclosed. 



The Rectus is inclosed in a sheath (fig. 166) formed by the aponeuroses of the 

 Oblique and Transversalis muscles, which are arranged in the following manner : 

 When the aponeurosis of the Internal oblique arrives at the margin of the Rectus, 

 it divides into two lamellae, one of which passes in front of the Rectus, blending 

 with the aponeurosis of the External oblique, the other behind it, blending with 

 the aponeurosis of the Transversalis ; and these, joining again at its inner border, 

 are inserted into the linea alba. This arrangement of the fascias exists along the 

 upper three-fourths of the muscle ; at the commencement of the lower fourth, the 

 posterior wall of the sheath terminates in a thin curved margin, the concavity of 

 which looks downwards towards the pubes ; the aponeuroses of all three muscles 

 passing in front of the Rectus without any separation. The Rectus muscle, in. 



