63 
site sides of the proximal phalanx of the pollex, the radial inser- 
tion being in close relation to the insertion of the abductor. 
Along with this may be described the VW. flexor brevis indicis, 
represented by one small fleshy belly taking origin from the 
palmar aspect of the third metacarpal and inserted into the 
palmar aspect or perhaps the ulnar border of the base of the 
proximal phalanx of the index. 
I know of no other instance amongst the Marsupials where modifi- 
cation by suppression of the intrinsic musculature of the hand has gone 
on to such an extent as in Notoryctes. And with regard to Marsupials 
generally, Young has remarked* that in no other class of mammals has 
the common mammalian “type’”’ of this musculature been so con- 
stantly adhered to as in the Marswpialia. The case of Notoryctes is 
therefore the more noteworthy. There can be little doubt that the 
extreme degree of structural modification here exhibited is simply the 
result of a very marked specialisation from functional requirements. 
A study of the skeleton of the hand will amply confirm this conclusion. + 
Further, be it noted, that the structural modification of this group of 
muscles is wholly in the way of suppression, and that in so far as 
intrinsic muscles are present their homologies are quite easily inter- 
preted. There is no representative whatever of the palmar layer 
of “adductores’? The only representative of the dorsal layer of 
*“‘ abductores’’ is the abductor-pollicis; while the intermediate layer of 
“flexores”’ is represented by three bellies, viz., both bellies of the 
flexor brevis pollicis and the ulnar belly of the flexor brevis indicis. 
In view of the anomalous reduction in the musculature of the region 
under notice, it is unnecessary to institute any systematic comparison 
with other forms, and it will suffice to take note of the condition as 
regards the muscles of the hand in a few animals in which we might 
expect similar, or at least parallel, modifications. 
As already stated, the condition in Notoryctes is quite unique 
amongst marsupials. And although the Echidna is a powerful digger 
and burrower, a glance at its skeleton is sufficient to discourage one 
from expecting any very marked myological resemblance to the hand 
of Notoryctes. It is, however, the case that in Hchidna we have an 
instance of considerable reduction from the type. The muscles 
present (apart from the lumbricals), with one exception, belong to the 
dorsal layer of abductores. These latter are—Abductor pollicis (Flexor 
brevis pollicis of Fewkes{), and five interosseous muscles. The re- 
maining muscle is reckoned by Mivart$ as a sixth interosseous, but 
Westling takes it to be equivalent both to a flexor brevis and an 
opponens pollicis.t It arises from the tendon of the flexor carpi 
radialis, and is inserted, according to Westling, into the proximal 
phalanx and metacarpal cf the pollex on its radial aspect. 
In Chlamydophorus|| Macalister found a slender cylindrical abductor 
pollicis, an opponens pollicis, and a muscle which he regarded as con- 
joint flexor brevis and abductor pollicis. He further states that these 
polliceal muscles are absent in Cyclothurus, Bradypus, and Cholepus,| 
* xxxv., pages 158-9. t+ liv., Pl. viii. {xii., page 28. § xxxix., page 
389. || xxvii., page 253. 
