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



posing these muscles is so thin that this small fasciculus can be seen shining through the 

 fibres. Emerging from under cover of the arched lower border of the combined muscles it 

 is inserted into the inner sesamoid bone at the base of the proximal phalanx of the annularis. 



The adductor hallucis is a delicate little muscle which springs from the base of the 

 metatarsus, close to the inner side of the conjoined origin of the adductors of the Index 

 and minimus. It is inserted into the outer side of the head of the metatarsal bone of 

 the rudimentary hallux. 



In a recent paper by Ruge, 1 upon the comparative anatomy of the deep muscles of 

 the sole of the foot, the author describes and figures in the Dasyurus hallucatus, a special 

 adductor of the medius. This muscle does not exist in the foot of the Dasyurus viverrinus, 

 and its presence in the specimen which Dr. Ruge dissected is somewhat difficult to 

 understand, seeing that it is rare for the digit which constitutes the centre for the 

 movements of adduction and abduction to be supplied with a special adductor. Ruge 

 considers it to be a link which binds this animal with the Ornithorhynchus jxtradoxus, 

 the pedal muscles of which have a very remarkable arrangement. 



Intermediate layer (fig. 6,/ 1 to/* 5 ). — Very little need be said regarding the muscles 

 which compose this layer. Each of the four outer toes is provided with a flexor brevis, 

 which is quite distinct from the dorsal interossei, and shows no tendency to fuse with 

 them, notwithstanding their close proximity, from the more or less complete obliteration 

 of the inter-metatarsal spaces. Each muscle arises from the base of the metatarsal bone 

 upon which it lies, and soon divides into two slips. These embrace the root of the 

 corresponding toe, and are inserted one into each sesamoid bone. The flexores breves 

 are very similar, therefore, to the same muscles in Thylacinus — differing only in the two 

 heads of each muscles springing in all cases by a common origin. 



In addition to the adductor hallucis, the rudimentary hallux is provided with a small 

 fleshy slip (figs. 5 and 6,fH), which arises from the scaphoid, and is inserted into the 

 inner side of the head of the metatarsal bone. The question naturally arises — What is 

 this muscle ? Is it a flexor brevis or an abductor ? It is supplied by the internal plantar 

 nerve, but this does not help us in our difficulty, seeing that both these muscles usually 

 derive their nerve fibres from this source. Ruge apparently considers it to be the 

 abductor hallucis, as he marks it in the figure of the foot of the Dasyurus hallucatus 

 (a.h.), but I think it is more likely that it represents both muscles fused into one. My 

 reason for this belief is, that in Phascogale, in which the hallux is slightly better 

 developed, the two muscles are distinct from each other although in very close proximity. 



The dorsal layer consists of — (1) the abductor ossis metatarsi minimi digiti (d 6x ), (2) 

 two abductors of the little toe (d s and d 6 '), (3) four dorsal interossei (figs 5 and 6, d 2 to d s ). 

 The abductors of the little toe are three in number, and arranged in a manner veri- 

 similar to those of the Thylacine. The muscle which is inserted into the sesamoid (d 6 ') 



1 Dr. Georg Ruge, Zur vergleiehenden Anatomie del teifen Muskeln in der Fussohle, Morpli. Jahrbuch, 1879. 



