56 
into two. Entering the palm these are inserted one into the 
base of the metacarpal of the pollex, and the other into the base 
of the metacarpal of the index (fig. 15). 
Considerable variety prevails among Marsupials with respect to the 
mode of insertion of this muscle. Thus in Thylacinus* it is inserted 
partly into the trapezium and partly into the metacarpal of the pollex ; 
in Phascogale* into the trapezium alone; in Cuscus* the tendon splits, 
and the slips are inserted into the palmar aspects of the bases of the 
metacarpals of the index and medius respectively. In Dasywrus+ its 
tendon occupies a special compartment in the outer part of the anterior 
annular ligament, and is inserted partly into the palmar aspect of the 
trapezium and partly into the bases of the second and third metacarpal 
bones. In Chironectes{ it is inserted into the radial side of the base 
of the metacarpal of the medius only, and in Phascolarctos$ also the 
insertion is so limited. In Phascolomys, Phalangista, Didelphys, and 
Perameles the muscle passes from the entocondyle to the third meta- 
carpal,|| but in Sarcophilus|| a slip in addition is attached to the trape- 
zium. In Myrmecobius{ it is attached to the carpus only (scaphoid 
trapezium and hg. carpi volare). It is inserted into the bases of the 
second and third metacarpals in Petawrista.** 
In Ornithorhynchus the muscle is relatively very large, and is deep 
palmo-dorsally ; the pronator radii teres les embedded in its ulno- 
palmar aspect. Its origin is from the entocondyle at its tip, but ex- 
tending deeply on its distal aspect to the very edge of the humero- 
radial articulation. Part of the muscle arises from the neck of the 
radius. 
Just above the carpus the broad fleshy belly narrows with great 
abruptness, and a single rounded tendon results which is wholly in- 
serted into the radial sesamoid bone, and has no connection except by 
means of carpal ligaments with the metacarpal bones. This radial 
sesamoid is situated on the palmar aspect of the radio-carpal joint and 
scapho-lunar bone, and is united to the latter by ligament. 
In Echidna the muscle is not relatively quite as large as in Ornitho- 
rhynchus, but it has substantially the same origin and relations in the 
forearm (I could not make certain that any of its fibres actually took 
origin from the radius in the specimen I examined for this purpose). 
In the lower part of the forearm it does not contract in width so 
markedly as does the corresponding muscle in Ornithorhynchus, but a 
stout tendon (derived from the tendinous investment of the muscles) 
appears along its palmar border. The deeper part of the muscle is 
continued, partly fleshy and partly tendinous, into the carpus. Here 
it encounters the radial sesamoid bone into which it is inserted, and 
this bone is in turn connected by strong ligamentous fibres with the 
large scapho-lunar bone in front of which it is placed. The more super- 
ficial tendon of the palmar border of the muscle as it enters the hand 
flattens out and passes in front of the sesamoid. Westling says it is 
connected with the first and second metacarpals. I find, however, that 
such a connection is at most quite indirect through the palmar carpo- 
metacarpal ligaments with which the tendinous fibres are connected. 
* iv., page 17. + xxxvi., page 130. {ft liii., page 9. § lxxil., page 230. 
xxix., page 162. ‘[ xxvi., page 822. ** xix., page 176. 
