51 
tensor communis, those muscular elements which Macalister has 
rightly recorded under the names of extensor secundi wmternodi pollicis 
and indicator respectively. 
As has already been mentioned (p. 44), Young states that the com- 
mon extensor is inserted into all five digits, an arrangement which 
Cunningham has pronounced to be unusual amongst marsupials. 
Macalister, on the other hand, passes over the common extensor in 
Koala as arranged “ as usual.”’ And when we look at Young’s descrip- 
tion in detail, we note that he found the two radial tendons of his 
common extensor passing beneath the annular ligament in a separate 
compartment from the others, and going to the pollex and index. Are 
these not in all probability Macalister’s extensor secundi and indicator 
together ? This explanation would largely harmonise the discrepancies 
between the statements of these two observers. 
I have verified by careful dissection the accuracy of Macalister’s 
description. I find that an extensor pollicis longus (secundi inter- 
nodii) is undoubtedly present. It is separable from the rest of the 
deep extensor stratum, except high up at its origin from the olecranon, 
where it is only partially separable from the fibres of the indicator 
muscle. The latter arises from the proximal part of the ulnar shaft 
and the aponeurosis covering it. Distal to this again, and separated 
from it by a small bare area of the ulnar shaft, is the origin of the 
extensor medili digiti proprius. Extensor pollicis longus passes 
through a special theca, and opposite the metacarpal its long and 
strong tendon is connected by a broad, flat, tendinous vinculum with 
the indicator tendon. It passes to the usual insertion. The tendons 
of the indicator and of the proper extensor of the middle finger pass 
through a common fibrous compartment beneath the dorsal carpal 
ligament. 
In his Monograph on the extensor indicis proprius, &c., Wenzel 
Gruber* states that in a specimen of Phascolarctos cinereus he found 
an extensor pollicis longus (secundi internodii pollicis), an extensor 
indicis proprius, and an extensor digiti medii proprius. The first- 
named had a special sheath in the dorsal carpal ligament, while the 
other two passed beneath that hgament in a common sheath, with that 
tendon of the common extensor of the digits going to the index. The 
arrangement here described is very similar to that I have just noted in 
Koala. But in my specimen there was no tendon of the common 
extensor going to the index at all, hence the indicator and extensor 
medii tendons were alone in their theca. 
In Dasyurust MacCormick found a small and fusiform extensor 
secundi internodii pollicis arising from the radial side of the olecranon 
and overlapping the lower part of the insertion of the anconeus 
externus, and thus corresponding In part to the origin of the extensor 
indicis et medii digiti in Notoryctes. He also found a muscular mass 
in series with the extensor secundi, and arising from the posterior 
surface of the ulnar shaft. It accompanied the extensor secundi under 
cover of the extensor communis, and divided into slips for the second, 
third, and fourth digits. It was very variable in size and connections. 
Sometimes the slip to the fourth digit was absent, and sometimes the 
indicial part was a distinct muscle. 
* lxi,, page 46. xXxxvi., pages 127-8. 
