REPORT ON THE MARSUPIALIA. 85 



Intermediate layer. — The flexores breves, with the exception of those belonging to 

 the marginal digits, are poorly developed. They can readily be distinguished from the 

 dorsal interossei by their occupying a more plantar plane, and by their being altogether 

 invisible from the dorsal aspect of the foot. The flexor brevis minimi digiti (figs. 5 and G, 

 Pf and/ 5 ?) has a powerful fibular head, which takes origin from the under surface of 

 the cuboid, and a delicate tibial head which springs from the base of the fifth metatarsal 

 bone. 



The three succeeding short flexors (fig. 6,/ 2 ,/ 3 ,/ 4 ) are one-headed muscles — each 

 consisting of a delicate slip inserted upon the tibial side of the base of the annularis, 

 medius, and index, respectively. In the left foot from which fig. 6 was taken, the 

 flexor brevis annularis (f 4 ) was two-headed. The flexor brevis hallucis (f l ) is 

 also merely represented by a tibial head, but this is strongly marked, and has a more 

 proximal origin than its neighbours. It springs from the inner side of the ento-cunei- 

 form bone. 



Dorsal layer (figs. 5 and 6). — The muscles composing this layer are arranged (as 

 in the case of the human foot) so as to abduct the toes from a line drawn through the 

 index. They are — 



1. The abductor hallucis (d 1 ). 



2. The abductor minimi digiti (d 6 ). 



3. The abductor ossis metatarsi minimi digiti (a.o.). 



4. The dorsal interossei (d 2 to d 5 ). 



The abductor hallucis has a wide origin from a cartilaginous process attached to the 

 inner margin of the sole, and also from the plantar fascia. It is inserted into the inner 

 sesamoid bone at the root of the hallux. 



The abductor ossis metatarsi minimi digiti has the usual attachments. The abductor 

 minimi digiti is a narrow muscle arising from the outer side of the tuber of the os calcis, 

 and soon ending in a long slender tendon which is inserted into the outer sesamoid bone 

 at the base of the minimus. 



The dorsal interossei (fig. 6, d 2 to d 5 ) are four in number, one occupying each inter- 

 metatarsal space but not reaching forwards to the dorsum of the foot. They are powerful 

 single-headed prismatic muscles, and are inserted so as to abduct the toes with reference 

 to a line drawn through the index. The first and second dorsal interossei are, therefore, 

 appropriated by this digit — one being inserted upon either side of the base of its first 

 phalanx. The third is inserted upon the outer side of the base of the proximal phalanx of 

 the medius, and the fourth upon the outer side of the base of the corresponding phalanx 

 of the annularis. 



There is, therefore, a very apparent want of correspondence in the arrangement of the 

 adductors and abductors in Tamandua — the former acting towards the annularis, and the 



