168 Prof. A. Macalister on the Myology of 



forms a powerful " tie-beam " between the ischium and femur, on 

 which hitter is a special tubercle for its reception ; it is smaller 

 in the Opossum and Phalanger, and thus seems to be specially 

 developed in those marsupials with disproportional length of 

 the fore and hind limbs. 



The iliacus iuteruus, a large muscle, arises in the Wombat 

 and Sarcophilus from the entire iliac fossa and anterior margin 

 of the ilium ; it is inserted into the ridge below the lesser 

 trochanter. There is no ilio-capsular in either of these mar- 

 supials ; it is closely attached to the psoas, as is the case also 

 in the Macrojnis Bennettii. Separation is more readily effected 

 in the Macrojjus giganteus and Opossum, but not so freely in 

 the phalanger or Perameles. 



The psoas parvus in the Wombat is a weak muscle, but has 

 a strong tendon ; its origin extends over four vertebrse. It 

 is rather stronger in SarcopJiilus^ but reaches its greatest 

 development in the leaping kangaroos, being more than six 

 times as large as the psoas magnus in the Giant Kangaroo, and 

 twice as large as the psoadiliacus in the Wallaby ; it is only 

 one-third as large in the Phalanger, and still smaller in the 

 Opossum. Thus the disproportion is only associated with 

 leaping, and not with the marsupial tj'pe of muscles. 



The psoas magnus in the Wombat arises from all the lumbar 

 and from the last dorsal vertebrae, and is inserted along with 

 the iliacus. In Sarcophilus its origin extends a vertebra 

 higher ; in the Giant Kangaroo it is attached to the lower two 

 or three lumbar vertebrae, as is also the case in Macropus 

 Bennettii and Perameles lagotis. 



The coccygeus is small and distinct in both the Wombat 

 and Sarcophilus^ and is larger in Macropus giganteus and the 

 Wallaby. 



The rectus femoris is a distinct muscle, as usual, with a 

 single marginal origin from the anterior inferior spine of 

 the ilium, in Sarcophilus, Wombat, Macropus giganteus and 

 Bennettii, Phalangista vulpina, and Virginian Opossum. Pro- 

 fessor Owen, however, describes this muscle in Perameles 

 lagotis as having two origins which are very distinct from 

 each other. 



The vastus externus is large in the Wombat, and is with 

 difficulty separated from the vastus internus ; it is even less 

 distinct in the Sarcophilus, but in the Giant Kangaroo it is 

 readily separable. In the Macropus Bennettii its origin receives 

 an accessory fasciculus from the fascial insertion of the glu- 

 teus maximus and tensor vaginae femoris. 



Tiie vastus internus in all is smaller than the externus, and 

 can be separated even from the cruraeus in Macropus Ben- 



