288 



MARSUPIALIA. 



Abdominal muscles, Phalangista milpina. 



supial bone (a), over which its strong inner 

 tendon is spread ; the external oblique becomes 

 aponeurotic at a line continued from the mar- 

 supial bone outwards, with a gentle curve, to- 

 wards the anterior extremity of the ilium ; and 

 in the opposite direction, or inwards, the car- 

 neous fibres of the external oblique terminate 

 in an aponeurosis along a line parallel with the 

 oblique outer margin of the pyramidalis; the 

 fascia continued from the latter boundary of the 

 fleshy fibres passes over, or dermad of, the so- 

 called pyramidalis, and meets its fellow at the 

 linea alba ; it is strictly analogous to the anterior 

 layer of the sheath of the rectus in ordinary Mam- 

 malia. It is seen reflected from the pyramidalis, 

 at b,jig. 112. The aponeurosis continued from 

 the external and inferior boundary of the car- 

 neous fibres divides as usual into two distinct 

 portions; one, corresponding to the internal or 

 mesial pillar of the abdominal ring, spreads its 

 glistening fibres, as above described, over the 

 dermal surface of the marsupial bone (c), to 

 which it closely adheres : the other column (d) 

 contracts as it descends obliquely inwards, 

 forms, like Poupart's ligament, the upper boun- 

 dary 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 di- 

 rections forwards and backwards, or those con- 

 cerned with the dilatation and diminution of 

 the abdominal space ; the contraction of the 

 abdominal muscles must draw the bones in- 

 wards 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 outwards to- 

 wards the ilium. 



In some Marsupials, as the Koala, the triceps 

 adductor 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 outwards. 



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 acetabulum : these car- 

 neous fibres pass inwards, and slightly upwards, 

 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. 



The fleshy fibres of the transversalis abdomi- 

 nis (f) are closely connected by dense cellular 

 tissue with those of the internal oblique ; they 

 are arranged in finer fasciculi, and have, as 

 usual, a more transverse direction ; they termi- 

 nate along the same line as those of the internal 

 oblique in an aponeurosis (g), which is con- 

 tinued along the inner or central surface of the 

 posterior rectus to the median line. The lower 

 boundary of the fleshy fibres of the transversalis 

 is parallel with the line extended transversely 

 between the anterior extremities of the ilia ; a 

 fascia, less compact than an aponeurosis, is con- 

 tinued downwards from this margin, and enve- 

 lopes the cremaster and the constituents of the 

 spermatic chord, as they pass outwards and 

 forwards beneath the lower edge of the internal 

 oblique. 



The pyramidalis (h) arises from the whole 

 inner or mesial margin of the marsupial bone, 

 from which the fibres diverge, the lower ones 

 passing transversely across the interspace of the 

 bones, and meeting at a very fine raphe, or 

 linea alba ; while those fibres from the anterior 

 ends of the marsupial bones gradually exchange 

 their transverse direction for one obliquely for- 

 wards. The breadth of each pyramidalis oppo- 

 site the upper end of the marsupial bone is 

 more than an inch, the thickness of the muscle 

 one line. 



The rectus abdominis or posterior rectus 

 (/) comes off from the pubis along the inner 

 part of the strong ligamentous union of the 

 broad base of the marsupial bone, and ex- 

 pands as it ascends until it attains the level of 

 the ensiform cartilage, when the rectus dimi- 

 nishes as it is inserted into the sternal extre- 

 mities of the ribs reaching to the manubrium 

 sterni and first rib in the Dasyures, as in the 

 cats. 



The slight indications of tendinous inter- 

 sections which were noticed in this dissection 

 were confined to the posterior or central super- 

 ficies of the muscle; the first extended only 

 half-way across from the outer margin. 



The cremaster (It), in the Phalanger and 

 Opossum, is not a fasciculus of fibres simply 

 detached from the lower margin of the internal 

 oblique or transversalis, but arises by a narrow 

 though strong aponeurosis from the ilium, 

 within and a little above the lower boundary of 

 the internal oblique, with the fibres of which 

 the course of the cremaster is not parallel ; it 

 might be considered as a part of the trans- 

 versalis, but it is separated by the fascia above 

 mentioned from the carneous part of that mus- 

 cle. Having emerged from beneath the margin 

 of the internal oblique, the cremaster escapes 



