1886.] GEOCOCCYX CALIFORNIANUS. 485 
demanded on the part of the investigator to see that the separation 
is made along the proper divisions. 
I am convinced from my studies that a greater difference is to be 
found among the various muscles of birds than we have ever ac- 
credited them with, and this fact leads me to believe that the day 
will come when these differences can be called into play in taxon- 
omy with excellent effect. Perhaps if the myology of the leg is 
examined as carefully as Prof. Garrod examined the muscles of the 
thigh in this class, fully as many interesting and valuable distinctions 
will come to light. 
The popliteus (Plate XLV. fig. 2, popl) is quite well developed in 
Geococcyz, where it is seen to arise from an oblique line on the back 
of the tibial shaft below the head of the bone, and the fibres 
converging to pass upwards and outwards are inserted by a short 
tendon into the corresponding aspect of the head of the fibular, close 
to the superior fibres of insertion of the flexor perforans digitorum 
profundus. When engaged upon my dissections of the Corvide, 
recently I ascertained that this muscle was absent at least in the 
American forms of the group. This was also the case with the two 
peculiar muscles next to be described. 
The flezor brevis hallucis (Plate XLV. fig. 2, 7.6.2) is an exceed- 
ingly interesting little muscle, and one that it has not been my good 
fortune to have seen in birds before, as I have just said, nor can I find 
at band any description of it for this class by any previous anatomist. 
It arises from the side and the lower margin of the inner aspect 
of the hypotarsus of the tarso-metatarsus, and from some of the 
shaft of this bone immediately below. The fibres converge to 
terminate in a small tendon, which, passing down the postero-inter- 
nal aspect of the shaft, goes to the inner side of the basal joint of 
the hallux, about which it winds to finally become inserted on its 
underside, at the proximal extremity of this joint, just a little beyond 
its articulation with the tarso-metatarsal trochlea. 
Thus it will be seen that this little muscle is entirely devoted to 
assist in flexing the hallux. Its mesial fibres meet those of the 
muscle next to be described, down the mid-longitudinal line of the 
shaft of the bone which gives it origin. 
Equally engaging with the last is another still smaller muscle, 
the ewtensor brevis annularis (Plate XLV. fig. 2, #.6), on the 
opposite side of the same bone. Here we find its origin is much the 
same as for the flexor brevis hallucis, coming off from the external 
aspect of the hypotarsus and the shaft below. It soon terminates in 
an extremely delicate little tendon, which, passing directly down to 
the fourth or reversed toe, becomes inserted on the supero-inner 
aspect of the basal phalanx of this digit. 
By its contraction it will act as a direct extensor of this toe, a 
requirement no doubt made necessary through the feeble manner in 
which this digit is now served by the slip which goes to it from the 
common extensor of these phalanges. 
This tendon of the short extensor gets its leverage by the fascia 
which circularly binds down all the tendons of the flexors and 
