REPORT ON THE MARSUPIALIA. 63 



of his dissections, and also with a plate (PI. VII.) illustrating these. It is to be under- 

 stood, therefore, that the following observations upon these two animals proceed from him. 



Phascolarctos cinereus (Koala). 



The foot of this animal in the undissected state is figured in Plate VII. fig. 1. It 

 possesses five toes, of which the hallux is large, nailless, and placed at right angles to 

 the long axis of the foot, so as to oppose the other digits. The index and medius are 

 shorter and more slender than the other two, and are united by a common covering of 

 skin. The four outer toes are provided with large, curved, very deep and compressed 

 claws. 



On the removal of the skin and superficial fascia from the sole of the foot, the deep or 

 plantar fascia is seen to be well marked and arranged in the usual manner. The central 

 portion, however, is prolonged backwards in the form of a cartilaginous tonguedike 

 projection. This affords attachment, chiefly by its base, to most of the short muscles of 

 the hallux and minimus and bridges over the long flexor tendons, as they enter the sole. 

 This cartilaginous plate forms the functional heel. The backward projection of the 

 os calcis is situated at a higher level, and from its under surface a small muscular bundle 

 descends to the upper surface of the plantar cartilage, and acts as an elevator of the 

 heel 1 (PI. VII. fig. 2, I). 



The intrinsic muscles of the foot are strorigly developed, but whilst the trilaminar 

 disposition is very evident, the dorsal or abducting layer is not complete as regards the 

 typical number of distinct elements. 



A study of the attachments and actions of the individual muscles makes it manifest 

 that the middle line of the foot in this animal corresponds with the annularis or fourth 

 toe, and it thus differs from the Cuscus and man, in both of which the index or second 

 toe constitutes the centre for the movement of abduction and adduction, and also from 

 the majority of mammals in which the middle line passes along the medius or third 

 toe. It is interesting to note that the hand of the Koala agrees with the foot in this 

 respect. 2 



Plantar layer (PL VII. fig. 2). — This group of muscles exhibits many evidences of 

 muscular modifications, which can only be explained by a transference of the middle 

 fine of the foot from the medius to the annularis. It is composed of four muscles, viz. : — 



1. Adductor hallucis {p l ). 



2. Adductor minimi digiti Q/ 1 ). 



3. Adductor of the medius and index (p 2 and p z ). 



4. A slip for the annularis. 



1 This minute muscle is doubtless a differentiation of the subjacent flexor brevis digitorum. 

 - Dr. Young, Intrinsic Muscles of Marsupial Hand, Jour. Anat. and Phys., vol. xiv. p. 158. 



