886 DR. C. F, SONNTAG ON THE CLASSIFICATION 



The flexor longus digitorum includes flexor longus hallucis, and 

 arises from tibia and fibula. Superficial and deep tendons are 

 present, and the latter pierce the former, as in the manus. 



The popliteus occupies practically the whole interosseous space. 



The intrinsic muscles of the pes have already been fully 

 described (2). and the mid line in Phascolarctos has been moved, 

 as in the case of the manus, with resulting modifications in 

 structure. 



Summary of Myologiccd Features. 



1. In all animals described in this paper there are traces of 

 adherence to the primitive lamination which characterises the 

 development of mammalian muscles in general. In Fhalanger, 

 PseiulochirtfjS, and Phascolomys we observe : — 1. Inseparability of 

 the prevertebral muscles ; 2. Undivided state of the rhomboideus ; 

 3. Fusion of the trapezius with the pectoral fascia and clavicular 

 deltoid ; 4. Biceps flexor cruris has only one head of origin ; 5. 

 Separate character of the hamstrings ; 6. Degrees of sepaiution 

 of levator scapulae and seri-atus magnus. In Phascolarctos the 

 following additional ones are present : — 7. Platysma continuous 

 with muscles of orbit, auricle, and mouth ; 8. Sterno-hyoid pro- 

 longed to mandible ; 9. Styloid muscles a single sheet ; 10. 

 Digastric and mylo-hyoid fused ; 11. Hyoglossus transverse and 

 not attached to hyoid ; 12. Omo-hyoid passes into tongue; 13. 

 Internal oblique has tendinous intersections ; 14. Quadratus 

 lumboi-um absent ; 15. Supinator longus very long ; 16. Pronator 

 quadratus small ; 17. Coraco-brachialis double; 18. No extensor 

 secundi internodii pollicis ; 19. Origin of gluteus maximus ; 

 20. No soleus ; 21. Tibialis posticus double; 22. Characters of 

 peronei ; 23. Intrinsic muscles of manus and pes. 



2. Many of the myological features are similar in all these 

 animals, in many other Mai*supials, and in animals belonging to 

 the other Mammalian orders. 



3. Most of the characters not included in the above groups are 

 adaptations to suit modes of life. 



4. In the small group of characters — omo-trachelian and 

 deltoid — not included in the three preceding groups, the Koala 

 and Wombat differ from the Phalansrers. 



Classification. 



All zoologists have separated Phascolomys from the Phalan- 

 geridfe, so the work of the systematist is limited to fixing the 

 proper position for Phascolarctos. To do so it is necessary to 

 examine all characters, both external and internal. The large 

 assemblage of data so obtained must then be reduced by excluding 

 characters of little or no value for pui'poses of classification. In 

 the first place, one must remove those which are var-ying degrees 

 of persistence of primitive conditions which were once present in 

 their common ancestor. Secondly, structures which are similar as 



