43 
pus major, but as inserted in these forms into both second and third 
metacarpal. He also notes a single tendon only in Didelphys, where 
Meckel describes a double muscle.* Both radiai extensors are present 
in Petaurista.t 
In Echidna Mivart? describes both long and short extensors, the 
former inserted into the scapholunar, and the latter into the third 
metacarpal. Westling gives a similar account.§ 
In Ornithorhynchus Brooks|| notes substantially the same arrange- 
ment, only the long extensor is inserted into the first metacarpal, and 
the ligaments on the dorsum of the carpus. 
Coues’ nomenclature of the muscles of this region is different, but 
I do not think his view of the homologies can be upheld. 
In Chlamydophorus there is only one radial extensor, but two tendons 
are present, according to Macalister,** inserted into metacarpals of 
index and medius. Hyrtl{+ only gives the former insertion. Among 
other Edentates a like condition obtains to that noted by Macalister, 
but often only an insertion into the third metacarpal is found, e.9., 
Cyclothwrust % and Orycteropus.§$ 
Amongst the Jnsectivora the muscle is inserted into the second and 
third metacarpals in EHrinaceus Gymnura and the Talpide. In Chiyso- 
chloris it is attached to second metacarpal only. || || 
Amongst Rodentia it is almost invariably split into long and short 
extensors, inserted as usual|||/ and similarly in various Carnivora. 
The intermediate sector of the superficial extensor stratum is 
represented by the MW. extensor communis digitorum (figs. 9, 17, 
e.c.d. 1, and e.c.d. 2). This muscle is represented by two fleshy 
bellies united at their origins from the distal portion of the 
ectocondyle. Fibres of each head also arise from the septum 
between the two, and from the septa between their common 
origin and that of the extensor carpi radialis in front, and of the 
extensor carpi ulnaris behind. The two bellies become separate 
in the lower part of the forearm. Opposite the radio-carpal 
joint their tendons pass together through a strong and well- 
defined fibrous sheath to enter the dorsum of the manus. The 
more radial of the two tendons (e.c.d. 1) runs distally on the 
dorsal aspect of the metacarpal of the third digit, and is inserted 
into the ulnar of the two slight tubercles on the prominent dorsal 
projection of the base of the ungual phalanx of that digit, side by 
side with the tendinous slip from the M. extensor indicis et medii 
digiti (vide infra), which is inserted into the radial of the two 
tubercles. The second (ulnar) tendon of the extensor communis 
(e.c.d. 2) is slightly the stronger, and the transition from broad 
fleshy belly of this part of the muscle to narrow rounded tendon 
is a very abrupt one. It passes through the same fibrous sheath 
as the first-named tendon, and is inserted into the radial angle of 
. * xxxvilil., page 138. }xix., page 176. {xxxix., page 387. § IkiL., 
page 26. "tf page 9: “Tim lee: cite” xxvii} page 255. «TT xxve; 
page 38. tt} xxvii., page 256. §§xxi., page 306.  |||| xxvi., page 812. 
