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Show 1886.] GEOCOCC\X 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 afford 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 m y 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 from the flexor longus hallucis, it would 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 X L V . fig. 1,/^, 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. W e also have in Geococcyx an unusually large flexor perforatus medius primus pedis (Plate XLIV. fig. 2,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* |
