45 
fifth only, and sometimes (Sarcophilus, Bennett’s, and Giant Kangaroo*) 
into the third, fourth, and fifth digits. 
In Koala I found the muscle with usual origin passing through a 
special theca, its tendon splitting into two, which pass on a deeper 
plane than extensor communis. The ulnar of the two tendons gees 
to minimus, the more radial is joined by a fibrous expansion from the 
tendon of the extensor medii proprius, and then passes to the annularis. 
The muscle is present both in Ornithorhynchus and Echidna.t 
For conflicting opinions regarding the homology of this muscle see 
infra (page 47). 
The ulnar sector of the superficial stratum of the extensor mass 
is represented by the M. extensor carpi ulnaris. (Dr. Brooks 
holds that the M. anconeus quartus is likewise a part of this 
sector, but I have preferred to describe it along with the extensor 
mass of the brachium.) 
M. extensor carpi ulnaris (figs. 9, 17. e.c.u.) (“ulnaris ex- 
ternus”) arises by a narrow pointed origin from the lower 
part of the ectocondyle between the preceding muscle and the 
anconeus externus, with whose distal border it is in close appo- 
sition. Fibres of the muscle also arise from the intermuscular 
septa between it and adjacent muscles. It broadens out as it 
descends in the forearm, narrowing again towards the wrist into 
a moderately strong tendon. This passes beneath a fibrous arch, 
which binds it down to the back of the lower end of the ulna 
and ulno-carpal ligament, but immediately distal to this it turns 
abruptly inwards (vide fig. 17), winding almost under cover of the 
base of the great claw of the fourth digit to reach the dorsum of 
the diminutive fifth digit, to be inserted into the rudimentary 
metacarpal bone of the latter. 
Among the Marsupials this muscle is sometimes split into two. 
Thus Cunningham found two distinct factors in Phascogale and in a 
specimen of Thylacinus,¢ while in Dasywrus$ MacCormick found two 
quite distinct tendons of insertion. In Sarcophilus|| Macalister also 
describes a second element which he identifies as ulnaris quinti, and 
which corresponds, according to MacCormick, to one of the tendons he 
found in Dasyurus. 
The muscle is sometimes merely ectocondylar and fascial in origin 
(Sarcophilus, Didelphys, Phalangista, Dasywrus), but in others an ulnar 
origin is also present (Phascolomys Macropus, Peramelis, Phascolarctos){. 
In Phascolarctos I found it ectocondylar and fascial only, its tendon 
passing through a special theca behind lower end of ulna, and then 
winding round wrist to palmar aspect of fifth metacarpal, into which 
it is inserted close beside tendon of flexor carpi ulnaris, to which it 
is in this animal functionally accessory. 
The usual insertion in this order is into the base of the fifth metacar- 
* xxix., page 164. +t i., page 10, and fig. 6; lxil., page 27. +t iv., page 
15. §xxxvi., page 126. || xxx., page 19. 4] xxix., page 164; xxxvi., page 
126; and lxxii., page 229. 
