52 
In Sarcophilus* Macalister describes an “ extensor indicis” giving 
ships to second, third, and fourth digits, in addition to an extensor 
secundi internodii pollicis, as in Dasywrus. The author views this 
series of slips as forming a third group of extensors of the digits. His 
second group, or extensor secundus digitorum, is constituted by the 
homologue of the human extensor minimi digiti, which in Sarcophilus 
arises with the extensor communis, and supplies tendons to the third, 
fourth and fifth digits.+ 
In Wombat,* extensor pollicis longus is present, but the extensor 
indicis is absent, and the extensor secundus digitorum supplies only the 
fourth and fifth digits. 
It is at least difficult to reconcile this overlapping of the series of 
slips from Macalister’s extensores secundus and tertius respectively, 
with Brooks’s view{ that the extensor minimi digiti is simply a dis- 
placed element of the extensor brevis series of slips which form 
originally an extensor profundus in the forearm. 
In Chironectes§ an extensor secundi internodii pollicis is present, 
giving slips to both pollex and index, and a like condition obtains in 
Murmecobius|\. 
In Ormthorhynchus Dr. Brooks, following Meckel,{ has described an 
“extensor indicis et pollicis,’ giving tendons to pollex, index, and 
medius. Itis large, ulnar in origin (extending up to and upon olec- 
ranon), and it is subcutaneous for a large part of its extent. This 
muscle is plainly the one noted by Coues** under the name of “ flexor’’ 
(extensor) carpi ulnaris, though the insertion given by him is inexplic- 
able tome. I have already alluded (p. 46) to the confusion introduced 
by Coues’ unfortunate statements. I have made dissections which fully 
corroborate Dr. Brooks’ description in almost every detail. Coues’ 
description of this region must, therefore, be put aside as erroneous. 
In Echidna neither Mivart++ nor Westling~ has described any deep 
extensor, save the extensor ossis metacarpi pollicis. Indeed, Mivart 
expressly states that neither extensor secundi internodii pollicis nor 
extensor indicis are present. I have already (p. 47) referred to the 
presence of such a muscle in dissections I have made of the forearm of 
Echidna. It is quite a large muscle, arising from the proximal half of 
the dorsal aspect of the shaft of the ulna and from the base of the 
olecranon. Its origin upon the shaft of the ulna is parallel with that 
of the extensor ossis metacarpi, which indeed is slightly overlapped by 
it. It is largely covered at its origin by the origin of the extensor 
carpi ulnaris, and under cover of this the upper pointed end of its 
erigin touches the insertion of the anconeus externus. Below, the 
muscle passes beneath the extensor communis, which position it occu- 
pies for the rest of its course, hence in Westling’s figure it does not 
come into view. On the dorsum of the hand its tendon flattens out 
beneath the expansion of the common tendon which it joins, but fibres 
of it may be traced to all the four outer digits. 
Thus the condition in Echidna is essentially the same as that in 
Ornithorhynchus. Itis probable that the muscle just described is repre- 
sented in Westling’s account by the deep head of the extensor communis 
*xxix., page 164. { Cf., also iv., page 17. fi., page 14. § liii., page 10. 
|| xxvi., page 818. {1 i., page 10, and fig. 6; lxii., page 27. ** iii., page 
Od, (ep oxix. “PP ixii. 
