56 THE VOYAGE OF H.M.S. CHALLENGER. 



which has precisely the same connections as in the two preceding animals ; (2) the 

 abductor minimi digiti, which in this case is single ; (3) four dorsal interossei, which are 

 arranged similarly to the corresponding muscles in Dasyurus; (4) the abductor hallucis, 

 which arises from the base of the first metatarsal bone, and is inserted into the outer side 

 of the base of the proximal phalanx. It lies in close contact with the flexor brevis 

 hallucis, but is easfly separable from it. 



Cuscns maculata (PI. V. fig. 1, and PI. VI. figs. 5, 6). 



The foot of this animal in the undissected state is seen in Plate Y. fisr. 1. The hallux 

 is a broad powerful digit placed at right angles to the long axis of the foot, so as to 

 oppose the other toes. It is not furnished with a claw, and is curved somewhat 

 towards the sole. The index and medius are poorly developed, and are enveloped in a 

 common integumental covering as far down as the second phalangeal joints. Inde- 

 pendent movement of these digits, therefore, is rendered impossible. Of the four outer 

 toes the annularis is much the largest. In every respect this foot is admirably adapted for 

 grasping the boughs of the trees in which the animal passes its existence. 



The position of the hallux, so far apart from the other toes, somewhat disconcerts the 



typical arrrangement of the muscles in so far as this digit is concerned. Still, sufficient 



indications remain to justify the conclusion that its three muscles, viz., the abductor, flexor 



brevis, and adductor belong one to each of the three layers that are here laid down as typical. 



The plantar layer (fig. 5 p l to p 5 ) consists of three muscles, viz. : — 



1. Adductor hallucis (p l ). 2. Adductor minimi digiti (p 5 ). 



3. Adductor annularis (p*). 



The adducting muscles of both manus and pes of all animals show a strong tendency 

 to place themselves obliquely or even at right angles to the digit upon which they 

 operate. In this manner they obtain a more powerful adducting influence. In the feet 

 of the Thylacine, Dasyurus, and Phascogale we have seen these muscles seek the middle 

 line for their origin, and from this they radiate towards their insertions. In PhascogoJi 

 they all lie upon the same plane, but in Thylacinus and Dasyurus the adductors of the 

 index and minimus in pressing inwards, have thrust the adductor of the annularis 

 upwards, and have thus come to coalesce and lie superficial to it (vide Pl. VI. fig. 1, and 

 Pl. XL fig. 5). Again, in the human foot we see the transversus pedis placing itself at 

 right angles, and the adductor hallucis obliquely in relation to the great toe. But still 

 more striking examples are to be observed in the hand and more especially in the foot of 

 the Cuscus. In the hand the adductors arise from a median fibrous raphe placed over 

 the middle metacarpal bone. In the foot, adduction is effected towards a line drawn 

 through the index, and the raphe is placed over the metatarsal bone which belongs to 

 this digit (fig. 5, r.). 



