49 
further obliquely on to the apparent palmar (but still morpho- 
logically dorsal) aspect of the carpus to reach the base of the 
metacarpal bone of the pollex, into which alone it is inserted. 
In Cuscus Cunningham found this muscle partly subdivided, one slip 
being inserted into the trapezium. He regards this as corresponding 
to the separation in the human subject of an extensor primi internodii 
pollicis. In Thylacinus the subdivision was complete, while the condi- 
tion in Phascogale resembled that in Cuscus.* A like condition is noted 
both by Young} in Koala, and by Macalister also in that animal, as 
well as in the Wombat and Tasmanian devil and others.¢ The charac- 
ters of the muscle in Koala are rather striking. It has the usual radio- 
ulno-interosseous origin. Halfway along the forearm its radial border 
developes a tendon which almost immediately separates from the rest 
of the muscle. This tendon is of even width and much slenderer than 
the broad flat tendon of the rest of the muscle, which begins just above 
the wrist. Both tendons pass through a special fibrous theca at the 
wrist, crossing the supinator longus and radial extensors of the carpus. 
The long slender tendon is inserted into the radial border of the meta- 
carpal of the pollex, and lies close to but unconnected with the abduc- 
tor brevis pollicis. The thick, strong tendon of the rest of the muscle 
is inserted into the trapezium. 
Extensor profundus in Petaurista taguanoides§ consists of extensor 
secundi internodii pollicis and extensor medii digiti, the latter con- 
nected also with the second and fourth digits. 
In Dasywrvs|; MacCormick found only the pollicial attachment. So 
also Sidebotham in Chironectes.1 In Myrmecobius it is attached only to 
the trapezium.** 
According to Carlsson (quoted by Leche) ,** the insertion in Didelphys 
is into the first metacarpal and into the “ preepollex.”’ 
In LEchidna++ Mivart describes it as a delicate muscle, interosseo- 
ulnar in origin, pollicial only in insertion. It is closely associated with 
the common extensor, according to Westling.+{ 
Brooks found practically the same condition in Ormithorhynchus.§§ 
In Chlamydophorus the muscle is very large, ulnar in origin, and 
inserted into the metacarpal of the pollex. It is very much the same 
in Tatusia and Dasypus, but in Cyclothwus it is “ humeral in origin, 
and is inserted into the ossicle, which is the rudiment of the first 
metacarpal, or “of trapezium and others,’’? according to Humphry. 
In Orycteropus it is inserted into the trapezium only, and into this 
bone and partly into the first metacarpal in Myrmecophaga. || || 
Dobson does not mention the muscle in Gymnwra,71 and according 
to Leche it occurs in all except this Insectivore. 
Leche quotes from Carlsson to the effect that in Castor and Rhizomys 
besides the usual insertion (into the pollicial metacarpal) there is a 
tendinous slip to the praepollex, and in Cercolabes the latter is the only 
insertion.*** 
M. extensor indicis et medi digits proprius (figs. 9, 11, 12, and 
*iv., page 15. + Ilxxii., page 229. } xxviii., page 431, and xxix., page 
164. §xix., page 176. ||xxxvi., page 126. (liii., page 10. ** xxvi., page 
817. tt xxxix., page 387. +t} lxil., page 28. §§i., page 9. |||| xxvii., page 
258, amd xxii., page 48. UI viii. *** xxvi., page 818. 
D 
