a correct System of Muscular Homologies. 315 
_ nerally exhibit an individuality of action separate from the 
others: these are the inner and the outer. For these we have 
what at first sight appear as gs special muscles often 
present; but, as Meckel remarked, these can be resolved into 
the ordinary and typical series which we have developed for 
the others, only in a position of greater specialization. 
Discarding for the present the longer digital muscles, we 
ean resolve the muscles of the pes and manus into the fol- 
lowing :— 
1. A short extensor for the fingers or toes. 
2. A short flexor for the fingers or toes. 
3. A complete series of palmar interossei. 
4. A complete series of dorsal interossei. 
The first of these muscles is developed on the dorsum of the 
human foot, and is there attached to the four inner toes; only, 
however, in the case of the great toe is its typical insertion 
into the first phalanx preserved, as in the three other digits its 
tendon is confluent with that of the long extensor. It is not 
usually inserted into the little toe; but I have once seen this 
muscle in man sending a fifth-tendon to that organ. In the 
manus of man a corresponding muscle occurs as an anomaly 
occasionally, and as such has been described by Mr. Wood 
ey Royal Soc. 1865, p. 382) and by myself (Proc. Royal 
ish Acad. April 1867) ; when present, it is often inserted, 
fleshy or tendinous, not directly into. the fingers, but into the 
extensor longus tendons. ‘This muscle is of rare occurrence in 
the normal anatomy of lower animals; to my knowledge it is 
og ea as present in the Bradypus tridactyla, according 
to Meckel; and the same writer describes a corresponding 
muscle arising from the lower end of the ulna in the two-toed 
Anteater. The comparative anatomy of this muscle in the pes 
exhibits but little variety; it is present in Ornithorhynchus, 
Hyrax, Myrmecophaga, Macropus, Arctomys, Bear, Nasua, 
Pteropus, Rhinolophus, Stenops, Macacus, Ateles, Cebus, Calli- 
thrix, Cercopithecus, Ai, Hystrix, and many other animals, in 
different degrees of perfection, but never varying to any great 
extent from its usual place. 
The second of these muscles may be looked upon as the 
antithesis of the short extensor: it is the short flexor of the 
toes and fingers. If we compare the actions of flexion and 
extension of the digits, we shall find at once that, usually, the 
latter is provided for by the great development of large and 
long muscles arising in the forearm. On account of this the 
flexor of the first phalanx is not usually needed in this its 
primary capacity ; and consequently we find it split up or mo- 
23* 
