MUSCULAR SYSTEM OF MAMMALIA. 



9 



Abdominal muscles, Phakmgista vulpina. 



with the anterior layer of the sheath of the rectus in ordi- 

 nary Mammalia. It is seen reflected from the pyramidalis, 

 at b, fig. 4. The aponeurosis continued from the external and 

 inferior boundary of the 

 carneous fibres divides as 

 usual into two distinct por- 

 tions. One, a, correspond- 

 ing to the internal or 

 mesial pillar of the abdo- 

 minal ring, spreads its 

 glistening fibres, as above 

 described, over the dermal 

 surface of the marsupial 

 bone, c, to which it closely 

 adheres : the other co- 

 lumn, d, contracts as it 

 descends obliquely in- 

 ward, forms, like ' Pou- 

 part's ligament,' the upper 

 boundary of the space 

 through which the psoas and iliacus muscles and femoral vessels 

 and nerves escape from the pelvis, and is finally inserted, thick 

 and strong, into the outer end of the base of the marsupial bone. 



This bone is so connected with the pubis that its movements 

 are almost limited to directions forward and backward, or those 

 concerned with the dilatation and diminution of the abdominal 

 space; the contraction of the abdominal muscles must draw the 

 bones inward so as to compress the contents of the abdomen, and 

 so far as the connections of the bone permit, which is to a very 

 trifling degree, the external oblique may draw it outward toward 

 the ilium. In some Marsupials, as the Koala, the triceps adduc- 

 tor femoris sends a slip of fibres to the external angle of the 

 base of the marsupial bone, and would more directly tend to bend 

 that bone outward. 



The upper or anterior fibres of the internal oblique have the 

 usual origin ; the lower ones, e, arise fleshy from the outer and 

 anterior spine of the ilium, and for an inch along an aponeurotic 

 chord extended from that process to the upper part of the aceta- 

 bulum : these carneous fibres pass inward and slightly upward, 

 and terminate close to the outer margin of the rectus, where they 

 adhere very strongly to the transversalis, but give off a separate 

 sheet of thin aponeurosis which is lost in the cellular sheath of 

 the posterior rectus. 



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