884 DB. C. F. SONNTAG ON THE MYOLOGY 



But they are inserted into a tendo Achillis. It is therefore 

 evident that the degree of sepai^ation of the intern us and externus 

 differs in these Marsupialia. 



Soleus : — In Phascolarctos and Phalanger there is no separate 

 soleus, and the observations of Cunningham (2), Macalister (5), 

 andi Young (14) have shown that it is really contained within the 

 gastrocnemius externus, as the latter has a fibular origin. More- 

 over, the plantaris lies under cover of the inner part of 

 gastrocnemius externus, and not under the part which corresponds 

 to soleus. In Phascolomys the soleus has a small fibular head, 

 but no tibial origin. 



Plantaris : — -In Phalanger sind Phascolarctos it is well developed, 

 and it is inserted into the plantar fascia, but Young (14) observed 

 it inserting into the tendo Achillis in one Koala. In Phascolomys 

 it is absent. 



Tibialis Anticics : — In all forms it arises from the outer surface 

 of the shaft of the tibia, and the interosseous membrane ; but its 

 insertion varies. In Phascolornys, according to Macalister (18), it 

 is inserted into the entocuneiform. In my specimen two tendons 

 are given off. One goes to the entocuneiform, and the other to 

 the hallux. The latter takes the place of the extensor longus 

 hallucis, which is absent as a separate muscle in my specimen. In 

 Phalanger a,nd Phascolarctos the insertion is into the entocuneiform 

 alone. And in these genera a separate extensor hallucis arises 

 from the fibula. 



Extensor Digilorimi Longus : — Macalister (18) describes it in 

 Phascolomys as arising from the fibula and front of the tibia, and 

 running to the four toes. In my specimen (text-fig. 41) it arises 

 from the tibia, fibula, and interosseous membrane. It soon divides 

 into slender inner and stout outer portions. The former gives 

 three delicate tendons to the first, second, and third toes, but the 

 three stout tendons of the lateral portion go to the inner, dorsal, 

 and lateral parts of the inner toe. In Phascolarctos (text-fig. 41) 

 the muscle likewise consists of two parts, whereas Young (14) 

 states that in being separable into two portions the Koala differs 

 from such marsupials as have been examined. Three tendons 

 emerge. The first is slender and divides into slips for index and 

 medius. The second is of medium size and runs to annularis. 

 The third is powerful and divides into tendons to annularis and 

 minimus. In Phalanger three tendons are disposed as in 

 Phascolarctos, but the muscle itself is not divisible into two. 

 There is, therefore, a greater resemblance between these arboreal 

 forms than there is between Phascolarctos and Phascolomys. 



Peronei : — The muscles composing the groups differ considerably. 

 In Phascolarctos, as pointed out by Young (14), there are four 

 components — longus, brevis, quarti metatarsi, and quinti meta- 

 tarsi, — aiid nil are fibular in origin. In Phalanger, as in Phalan- 

 gista maculata, there are three components — longus, brevis, and 

 some muscular slips representing portions of the extensor brevis 

 digitorurn. In Phascolomys Macalister (18) described long and 



