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 popliieus (Plate XLV. fig. 2, popl) is quite well developed in 

 Geococa/x, 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 Corvidce, 

 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 flexor brevis hallucis (Plate XLV. fig. 2,f.b,K) 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 hand 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 Une of the 

 shaft of the bone which gives it origin. 



Equally engaging with the last is another still smaller muscle, 

 the extensor brevis annularis (Plate XLV. fig. 2, JE.b), 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 



