a correct System of Muscular Homologies. 321 
animals already noticed as instances of a greater degree of 
complexity than usual—the Hyrax, Nycticebus, &c.; and in 
all these we merely see approximation to the true type, in va- 
rious degrees of distinctness. The long muscles in Hyrax are 
probably displaced dorsal interossei, and the short inter- 
phalangeal muscles of Nycticebus may belong to the same 
e: 
Whe last class of muscles in the manus which are specially 
devoted to produce the movements of the digits is that of the 
dorsal interossei. These we usually find to be bicipital; and 
accepting this appearance as an evidence of the coalescence of 
two muscle-germs, we can easily allocate these muscles to their 
respective places. As extension is a much simpler act than 
flexion, the latter being liable to endless modifications in 
grasping, &c., so extensor muscles are much less disposed to 
vary than flexors. Taking, again, the hand of man as an ex- 
ample, we find the radial dorsal muscle of the pollex present 
as the abductor pollicis exterior of Sémmerring. The ulnar 
dorsal muscle constitutes the polliceal origin of the first dorsal 
interosseus, whose thumb insertion is obsolete. For the index 
- finger the radial dorsal muscle is developed as the first dorsal 
interosseus ; this muscle in Macacus nemestrinus has no polli- 
ceal; but it is bicipital in Sima and in the hyena and dog. 
The ulnar dorsal muscle constitutes the outer head of the se- 
cond interosseus. For the middle finger the dorsal radial 
muscle forms the medial head of the second dorsal interosseus, 
and the ulnar makes the corresponding head of the third dorsal 
of the human hand. In the ring-finger the radial muscle is 
modified into the annular origin of the third dorsal interosseus, 
and the ulnar constitutes the annular origin of the fourth. For 
the little finger the radial muscle forms the ulnar head of the 
fourth dorsal interosseus, and the ulnar forms the opponens 
minimi digiti. 
The pes exhibits an equally regular series. For the hallux 
the dorsal tibial muscle is developed as the second head of the 
abductor pollicis, and the dorsal fibular as the inner head of 
the first dorsal interosseus. The second toe has its tibial muscle 
in the form of the outer head of the first external interosseus, 
and its fibular as the inner head of the second dorsal: this 
muscle differs from its fellow in the manus in being inserted 
into the second instead of the third finger. For the third toe 
the tibial muscle constitutes part of the second dorsal inter- 
osseus, and the fibular that part of the third which is attached 
to the third metatarsal bone. Similarly the two dorsal muscles 
for the fourth toe constitute respectively parts of the third and 
fourth external interossei. For the little toe the tibial muscle 
