EEPORT ON THE MARSUPIALIA. 115 



( 



ITylobates leuciscus. J consists of J second) 



Chimpanzee. 1 ) Plantar layer I united in first, but separate in the 



} 



1. Adductor hallucis (two heads 

 united in first, but separ; 

 second). 



2. Adductor minimi digiti. 



Orang. | Plantar layer J 1. Adductor hallucis (two heads united in first. 

 Gorilla. ) consists of ( but separated in second). 



From this table it will be observed that, whilst in the majority of the animals 

 quoted, the plantar layer is complete, a diminution in the number of its elements can 

 be traced through the Hapale and the Chimpanzee and Hylobates until we come to the 

 Orang and Gorilla in which there is merely the adductor hallucis. But the Orang seems 

 to stand intermediate between the Gorilla, in which not a vestige of the absent muscles 

 is to be found, and the other apes in which they are present. Euge has shown in his 

 important article upon the " deep muscles of the foot," 2 that in this animal the place of 

 the lost adductors of the second, fourth, and fifth toes is taken by tough strands of 

 connective tissue, and that the nature of these is borne out not only by the deep division 

 of the external plantar nerve lying subjacent to them, but also by the presence in 

 connection with them of weakly developed muscular fibres. The regressive changes, 

 therefore, by which these muscles have disappeared are very clearly indicated in the 

 foot of the Orang. 



Intermediate layer. — In the Quadrumana we never find a complete layer of flexores 

 breves, i.e., a two-headed muscle provided for each toe. The flexor brevis hallucis and 

 the flexor brevis minimi digiti generally retain their two slips, but the flexor brevis 

 annularis and the flexor brevis indicis are often represented by a single head, whilst the 

 flexor brevis medii seems in the great majority of cases to be absent. 



According to Bischoff the Gorilla, 3 the Chimpanzee, the Hylobates, the Cynocephahis, 



1 Since writing the above I have had the opportunity of examining the foot of a young Chimpanzee. The 

 adductors were three in number, viz. : (1) adductor hallucis, (2) adductor minimi digiti, and (3) adductor annularis. The 

 adductor hallucis was represented by an oblique and a transverse part, both of which were very strongly marked, and in 

 close apposition to each other, but yet quite separable. A very interesting point in connection with the adductor 

 obliquus hallucis was that it was supplied by twigs from both plantar nerves ; the internal plantar nerve sent a branch into 

 its superficial surface, whilst the terminal filaments of the deep division of the external plantar nerve sank into its deep 

 surface. Nor could it be said that this double nerve supply was due to its having amalgamated with the outer head of 

 the flexor brevis hallucis, because this muscle was present, although greatly reduced in size from being pressed deeply 

 into the sole by the largely developed adductor. The adductor minimi digiti was well marked, and arose from a 

 central raphe common to it and the transverse adductor of the hallux. The adductor annularis was exceedingly feeble, 

 and took origin from the deep surface of the raphe which separated the adductors of the great and little toes ; further, 

 it was partially coalesced with the subjacent interossei, and could not be raised without lacerating muscular fibres. 



"- Loc. cit., p. 650. 



3 Duvernoy and Maealister both describe the flexor brevis hallucis in the Gorilla as consisting of an inner head 

 alone. Bischotf, however, points out that the former has regarded the true outer head as corresponding to the inter- 

 osseus primus volaris in the hand, whilst the latter has, in all probability, looked upon it as an opponens, a muscle of >vhkh 

 Bischotf could find no trace. 



