256 



MUSCLES OF THE ABDOMEN. 



The number of the points of insertion of this muscle to the vertebrae, and the 

 extent of its connection with the last rib, vary in different instances. It is sometimes 

 attached to the body or transverse process of the last dorsal vertebra. 



This muscle is placed between the middle and deepest layer of the lumbar aponeu- 

 rosis, and its inner part is covered in front by the psoas muscle. 



Fig. 201. 



10* 



Fig. 201. DIAGRAM OP A TRANSVERSE SECTION OP THE WALL OP THE ABDOMEN, TO 

 SHOW THE CONNECTIONS OP THE LUMBAR AND ABDOMINAL APONEUROSES, AND TIJE 

 SHEATH OF THE RECTUS MUSCLE. 



A, at the level of the third lumbar vertebra ; B, the fore part, at a few inches above 

 the pubes. 



a, spinous process of the third lumbar vertebra ; 5, body ; 1, section of the external 

 oblique muscle ; 2, internal oblique ; 3, transversalis ; 4, a dotted line to mark the 

 position of the fascia lining the abdomen ; 5, 5, in A, the anterior and posterior parts of 

 the sheath of the rectus, formed by the aponeurosis of the internal oblique splitting at its 

 outer edge 2' ; 6, points by two lines to the section of the rectus muscle in A and B ; 

 7, innermost layer of the lumbar aponeurosis, covering in front the quadratus lumber um, 

 and passing to the root of the transverse process ; 8, points to the section of the psoas 

 magnus and parvus muscles ; 9, the section of the erectores spinse muscles ; 9 + , the 

 middle layer of the lumbar aponeurosis passing to the extremity of the transverse process ; 

 10, 10 + , the posterior layer of the lumbar aponeurosis, connected with the latissimus 

 and serratus inferior : in A, at the sheath of the rectus, the aponeurosis of the external 

 oblique is seen to unite in front with the sheath, while that of the transversalis is seen 

 uniting with it behind : in B, the section is taken below the semilunar fold of Douglas, 

 where all the tendons pass in front of the rectus as at 5' ; the + near this, and in a 

 similar place in A, marks the middle line and the place of the union of the several 

 aponeuroses in the linea alba. 



ACTIONS. The abdominal muscles not only form a great part of the wall to enclose 

 and support the abdominal viscera, but by their contractions are capable of acting 

 successively on those viscera, on the thorax, and on the pelvis. When the pelvis and 

 thorax are fixed, the abdominal muscles constrict the cavity and compress the viscera, 

 particularly if the diaphragm be fixed or be made to descend at the same time, as 

 occurs in vomiting and in the expulsion of the foetus, the faeces, and the urine. 



