880 Dil. C. F. SONNTAG ON THE MYOLOGY 



modified in a.ccordance with habits. He has also shown that the 

 Koala is very different from the others, his conclnsions being as 

 follows: — "The digits form two groups, of which one, including 

 the thumb and index finger, is opposable to the other, this latter 

 comprising the three remaining digits. The index digit, in point 

 of fact, constitutes a second thumb ; and, in comformity with its 

 unusual freedom of action, its special muscles are well developed. 

 Moreover, as the result of the arrangement of the digits into two 

 groups, the middle line of the hand no longer passes through the 

 tliii'd digit, but along the fourth. The muscles of the hand are 

 correspondingly modified, and hence, so far as regards their 

 insertions, the arrangement is very diflferent to what is ordinarily 

 found." 



Muscles of the Posterior Extr equities. 



Gluteus Maximus : — In Phascolarctos it has no origin from the 

 iliac crest, but springs from the sacral and caudal vertebrae. The 

 coarse fibres sweep over the great trochanter, thereby producing 

 a rounded prominence-, and are inserted into a considerable length 

 of the femoral shaft. The fibres are continuous postero-mesially 

 with the lateralis caicdce. In Fhascolomys a broad, long agitator 

 caudse shuts oS" the gluteus maximus from the sacral and caudal 

 vertebral spines, and a strong intermuscular septum, which gives 

 origin to some of the fibres of both muscles, intervenes between 

 them. The gluteus maximus also arises, as in all Marsupialia 

 except the Koala, from the iliac crests posteriorly, and from the 

 lumbar fascia. The whole muscle appears flattened, and it is 

 inserted into the back part of the great trochanter. Cunningham 

 (2) describes how the gluteus maximus is divided into three parts 

 in Phalangista maculata^ but thei'e is no obvious separation into 

 distinct parts in my specimen of Phalanger orientalis. There it 

 is a long fan-shaped sheet composed of gluteus maximus, tensor 

 fasciaB femoris, and agitator caudal. It extends from the lumbar 

 fascia anteriorly backwai-ds along the iliac crest and spines of the 

 sacral and anterior four caudal vertebrae. The part of the sheet 

 representing the agitator caudse has much coarser fibres than the 

 other parts. The insertion of the sheet does not differ in any 

 essential point from that in Phalangista Qnaculata, already 

 described by Cunningham. In Pseudochirus the conditions 

 resemble those in Phalanger, but the fibres of the agitator caudle 

 are not so coarse, or so separate from the other parts of the 

 muscle. 



Glibteus Mediics : — In all forms it is large, and frequently 

 exceeds the maximus in size. In Phascolarctos it arises from the 

 iliac crest, the gluteal surface of the ilium, and the sacral spines. 

 It is inserted into the great trochanter. The fibres are in parts 

 fused with the subjacent gluteus minimus, but there is no 

 lamination as described by Young (14). In Phascolomys it is 

 difficult to separate the medius and mimimus. In Phalanger and 

 Pseudochirus the medius and minimus, are separate. The Gluteus 



