1886.] GEOCOCCXX CALIFORNIANUS. 483 



admirably hold the several groups of flexor tendons in place, and at 

 the same time they act as pulleys for their guidance and afl'ord 

 correct application of the force intended to flex the toes. 



The flexor longus hallucis (Plate XLIV. figs. 2, f.l.h ; Plate 

 XLV. figs. 1, 2, f.l.h) has two separate heads, the one coming off 

 from the outer side of the external condyle of the femur, and the 

 other, far more fleshy, arising from the posterior aspect of the same 

 bone between the condyles. Above this muscle is overlapped by 

 the more superficial flexors, while in turn it has beneath it the 

 flexor perforans digitorum profundus. About halfway down the 

 leg it gives way to a strong tendon, which, passing deep in the 

 tibial cartilage, crosses the ankle-joint to pass through the outer 

 canal of the osseous portion of the hypotarsus of the tarso-metatarsus. 

 Down the back of the shaft of this latter bone the tendon exhibits a 

 disposition to develop an osseous rod in its continuity, but this does 

 not actually occur in my specimen. It lies in this region just above 

 the tendon of the deep flexor, and, immediately above the sole, 

 makes a fibrous connection with it of some extent. This fibrous 

 " vinculum " is in no way oblique as it is described by Garrod for 

 many birds, but passes directly from one tendon to the other for 

 about 8 millimetres, and were it not known that it as a rule passes 

 obliquely yrom the ^e^'or longus hallucis, '\tvio\Adi be quite impossible 

 here to designate which tendon was responsible for the connection. 



In the foot the long tendon of the hallux passes in the usual way 

 to become inserted on the tubercle at the underside of the proximal 

 end of the ungual phalanx, 



As its name indicates, our next muscle, the flexor perforatus 

 indicis primus pedis (Plate XLV. fig. 1,/j), has its tendon attached 

 to the nether side of the basal phalanx of the index digit, and 

 consequently aids in bending that toe. 



Above, as a flat, long muscle, it comes off' by a thin tendon from 

 the external surface of the outer femoral condyle, arising with the 

 flexor perforatus medius secundus pedis. 



We also have in Geococcyx an unusually large flexor perforatus 

 medius primus pedis (Plate XLIV. fig. 1,f.^, which here arises by 

 two slips, an outer tendinous one, from the external condyle of the 

 femur, which has a common origin with other muscles there arising 

 and is intimately connected with the dense fascia about the front of 

 the knee-joint ; while the second slip arises from between the femoral 

 condyles, in common with other flexors that come off from that point. 

 The two heads are quite independent, but merge with each other 

 before they terminate in their common tendon at the lower third of 

 the tibial shaft. 



It passes through the tibial cartilage, overlaid by, but in close 

 company with, the far more diminutive and narrower tendon of the 

 flexor perforatus annularis primus pedis. 



"When it arrives under the basal phalanx of the median toe, the 

 outer one of the anterior pair, it bifurcates to allow the other two 

 flexor tendons to pass, while the slips thus formed become attached 

 to the sides of the shaft of this joint close to its distal head. 



32* 



