OP THE WOMBAT, KOALA, AND PHALANGEBS. 



869 



three dorsal and cervical vertebrpe. In Phascolomys I observed 

 similar fusion of these muscles. A single thick muscular sheet 

 extends from the third dorsal vertebra to the basi-occiput 

 (text-fig. .35). A small bundle of fibres becomes detached, and 

 I'uns to the front of the thiid cervical vertebra when it fuses with 

 the bundle from tlie opposite muscle. The main mass, in my 

 opinion, represents rectus capitis anticus major. The mesial part 

 represents longus colli, and the rectus capitis anticus minor is 

 absent. In Phalanger there is more separation between the longvis 

 colli and rectus capitis anticus major, and there is no rectus 

 capitis anticus minor. But in Pseudochirus there is considerable 



Text-figure 35. 



C.i. 



R.C.A.M 



D.I. 



L.C. 



Prevertebral muscles in 'Phascolomys mitclielU. 

 Letters in text. 



fusion. It appears, therefore, that the conditions in Phalanger 

 do not adhere so much to the primitive condition as do those in 

 Phascolarctos, Phascolomys, and Pseudochirus. 



Muscles of the Back, Thorax, and Abdomen. 



Trapezius : — In all forms the origin extends from the occiput 

 to the seventh dorsal spine, although Young (14) gave the eightli 

 spine as well in Phascolarctos. The clavicular insertion varies, 

 however. In Phascolarctos and Pseicdochirus most of the fibres go 

 to the clavicle, but some cross it and run to the clavicular deltoid, 



Proc. Zool. Soc— 1922, No. LIX. 59 



