| OCR Text |
Show 480 DR. R. W. SHUFELDT ON [Nov. 16, After we have cut away the tibialis anticus, we find another, and only one other, muscle occupying the anterior aspect of the tibia. This is the extensor lonyus digitorum. The extensor longus digitorum (Plate XLV. fig. 1, e.l.d) arises from the anterior aspect of the in-half of the tibial shaft as high up as the tibialis anticus muscle, which covers it; it also arises from a tense fascia which comes off from the lower free edge of the pro-cnemial crest of the tibia; and finally from a longitudinal line extending obliquely down the front of the shaft of the tibia to its lower third. This obliquity finally brings the tendon in which the extensor longus digitorum terminates to the middle line. Just above the condyles of the tibia, it here passes through the little bony bridge ; emerging from which it crosses the ankle-joint in front, then passes down the anterior aspect of the tarso-metatarsus bone, overlying the short extensor. At the upper end of this last-named bone, and over the ankle-joint, this tendon is firmly bound down by a fibrous fascia. In some birds we know a special bony span exists for it on the upper part of the tarso-metatarsus, as in certain Owls. When the tendon of this muscle arrives at the anterior aspect of the trochleae of the distal end of the tarso-metatarsus, it expands and bifurcates. The tendinous expansion becomes more or less attached to the underlying tissues, while each bifurcation passes one over the second, and the other over the third toe, for their entire lengths, to become inserted into the upper points of their ungual phalanges. Now from the side of the tendon that goes to the third toe another slip is differentiated off in a very peculiar manner, owing to the reversion of the toe in question. For it not only passes over the top length for insertion of this fourth digit, as in the case of the others, but its slip also splits off to make a separate insertion at the extremity of the basal phalanx of the third digit. I have had the opportunity of dissecting three feet, with the view of studying this point, and I find it to obtain in all of them. The extensor brevis digitorum (Plate X L V . fig. 1, e.b.d). This is muscle I find that, in common with many other authors, I have described in m y MSS. as the extensor hallucis brevis, from the fact that its tendon goes to the hallux alone. But here, so extraordinary is its development, that no such term would be either adequate or appropriate. Even here the short extensor of the hallux has a certain amount of individualization, though it is not fully differentiated from the other part of this extensor brevis. It, however, is not attached more than halfway down the anterior aspect of the shaft of the tarso-metatarsus, at which point it terminates in a delicate threadlike tendon ; this passes directly over the upper border of the accessory metatarsal, and along the top of the basal joint of the hallux, to become inserted in the usual manner in the base of the claw-joint. Now the remainder of the extensor brevis digitorum is attached down the shaft of the tarso-metatarsus, as far as the distal trochleae ; the outer portion of it developing a tendon about halfway down, which is concealed by the carneous fibres which overlie it. |
