REPORT ON THE MARSTJPIALIA. 75 



adducting slip occasionally found in connection with the medius in the foot of the 

 Ornithorhynchus. Certainly its presence is equally unaccountable. 



Intermediate layer. — Only three muscles of this layer are present, viz. — 



1. Flexor brevis hallucis (/'). 2. Flexor brevis indie is (/'-). 



3. Flexor brevis minimi digiti (f 5 )- 



The flexor brevis hallucis although very minute, is yet complete in so far that it 

 possesses two heads. These arise by a common origin from the fibrous structures 

 on the plantar surface of the middle cuneiform bone. Diverging from each other they are 

 inserted into the sides of the second phalanx of the hallux. 



The flexor brevis indicis has also two heads, but the tibial head alone is fleshy. It is 

 composed of a collection of very short muscular fibres, which arise from the under surface 

 of the middle cuneiform bone, and are inserted into the inner and plantar aspect of the 

 first phalanx of the index. The fibular head is represented by a short fibrous cord which 

 lies along the outer side of the head. 



The flexor brevis minimi digiti is the best developed muscle of the. intrinsic group. 

 It is represented by the outer head alone. This springs from the anterior aspect of the 

 projecting tuber of the os calcis and is inserted into the outer side of the second phalanx 

 of the minimus. It is covered by the outermost belly of the flexor brevis digitorum with 

 which it is partially united. 



Dorsal layer. — Only two muscles belonging to this group are found, viz. — 



1. The abductor hallucis (d 1 ) 



2. The second dorsal interosseus (d 3 ). 



The abductor hallucis, which is very rudimentary, arises from the fascia at root of the 

 hallux and is inserted by a minute thread-like tendon into the tibial aspect of the ungual 

 phalanx of this digit. 



The second dorsal interosseus muscle is also very small. It lies in the second inter- 

 metatarsal space, but can only be detected from the plantar aspect, of the foot. Tapering 

 towards its distal extremity, it terminates in a tendon which splits into two portions, a 

 very delicate hair-like part for the tibial side of the second phalanx of the medius and a 

 much stronger part for the fibular side of the second phalanx of the index. Whilst there- 

 fore the main action of this muscle must be regarded as that of an abductor of the 

 index, opposing in this respect the adductor indicis, it nevertheless possesses through 

 its minute insertion into the medius an approximating influence upon the index 

 and medius. 



In the pes of the Echidna there is no clue as to what has become of the absent 

 intrinsic muscles. It is probable that they are lost by suppression. A strange feature 



