REPORT ON THE MARSUPIALIA. 109 



and the inner head of the flexor brevis medii. The third muscular branch springs from 

 the fourth digital nerve and dips into the sole between those tendons of the flexor longus 

 digitorum which go to the medius and annularis. It is destined for the supply of the 

 flexor brevis medii — to both heads of which it gives filaments — and the third dorsal 

 interosseus, but it likewise communicates on the one hand with the second muscular 

 branch of the internal plantar and on the other with the terminal filament of the deep 

 division of the external plantar nerve. 



The deep division of the external plantar nerve is a very small twig, and ends in the 

 flexor brevis annularis. The abductor minimi digiti is supplied by the superficial division 

 of this nerve. 



Ccelogenys paca (the Paca). 



The foot of this rodent is pentadactylous. The hallux, however, is very rudimentary 

 and the minimus is much smaller than the three central toes, which are nearly of an equal 

 length. The plantar and intermediate layers of intrinsic pedal muscles in this animal 

 are well represented. The dorsal layer is very deficient. 



Plantar layer. — In this group there are three muscles, viz. : — 



1. Adductor hallucis. 2. Adductor indicis. 3. Adductor minimi digiti. 



They all arise by a common origin from the middle of the plantar surface of the tarsus, 

 and, separating, they radiate from each other to reach their insertions. The adductor 

 hallucis is inserted into the extensor tendon upon the outer side of the base of the hallux ; 

 the adductor indicis into the extensor tendon upon the same aspect of the base of the 

 index ; and the adductor minimi digiti into the extensor tendon upon the inner aspect of 

 the base of the first phalanx of the minimus. 



Intermediate layer.— As in the Beaver, the index, medius, and annularis have each 

 a two-headed flexor brevis. This muscle springs from the base of the corresponding 

 metatarsal, and its two heads, embracing the root of the toe with which it is connected, 

 are inserted partly into the sesamoid and partly into the extensor tendon. 



The flexor brevis minimi digiti has only a fibular head. This is a stout, fleshy belly 

 which springs from the under surface of the external cuneiform bone, and is inserted into 

 the outer sesamoid of the minimus. 



The flexor brevis hallucis is represented by a tibial head which is much smaller than 

 the preceding muscle. It arises from the under surface of the scaphoid, and is inserted 

 upon the inner side of the first phalanx of the hallux. 



Dorsal layer. — This layer is poorly developed. It has the following components : — 



1. The abductor hallucis. 



2. The second and fourth dorsal interossei. 



3. The abductor ossis metatarsi minimi digiti. 



