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Show •340 MR, A, H . GARROD ON THE DEEP [Apr. 20, may be inferred from the comparison of the dissections of different animals whose anatomy has been sufficiently investigated. Among birds peculiarities in the disposition of the plantar tendons has already attracted the attention of Prof. C. J. Sundevall, who, as is well known, divides the Passeres off from all other orders, and includes Upupa with them, because in them, and in them only, the tendon of the flexor longus hallucis muscle is quite independent of that of the flexor perforans digitorum; whilst in other birds the former joins the latter, so preventing the two from being quite independent in their action. All other descriptions which I have seen of special dissections have been confirmatory of this view ; and my own observations, with but a slight exception in the case of Botaurus, to be mentioned below, support Prof. Sundevall's separation off of the Passeres together with Upupa on this particular character. My dissections, however, have shown me that there is still more to be learnt from the plantar tendons, and that the large mass of birds which all agree in that the two above-mentioned deep flexors blend together, present among themselves peculiarities as important as that which so definitely characterizes the Passeres. To describe and to endeavour to show the bearing of these differences are the objects of the present paper. In birds generally, whatever the number of their toes, there are two muscles whose fleshy bellies are situated in the leg proper (that is, between the knee and the ankle), deep, and just behind the tibia. These muscles arise, one from almost the whole of the posterior surface of the tibia and from the fibula, in a bipenniform manner, and the other from the inferior surface of the horizontal femur, just behind the outer genual articular condyle. The former is termed the flexor perforans digitorum pedis, because its terminal tendons perforate those of the more superficial flexors on their way to the ungual phalanges of their respective toes; and the latter is termed the flexor longus hallucis, because there is generally a shorter muscle to the same digit. These two muscles descend to the ankle (the joint between the tibio-tarsus and the tarso-metatarsus) side by side ; they run behind it, in the fibro-cartilaginous or osseous mass which, in birds, is always found at the posterior part of the upper end of the tarso-metatarse, in two canals, deeper than any of the other flexor tendons; and in these canals there is always a definite relation between them. Sometimes the tendons are side by side; and then it is always that of the flexor longus hallucis which is the external of the two, the osseous vertical ridge, which is nearly always seen in the dry bone, separating them. Sometimes, however, one is superficial or, in other words, posterior to the other. When this is the case it is always the flexor perforans digitorum which is the deeper. In the Swifts, for instance, the flexor longus hallucis quite covers the flexor perforans digitorum ; but in most Parrots, as may be seen by the disposition of the osseous canals in the dry tarso-metatarse, that for the former muscle is external as well as superficial, only partially covering it. These relations are constant, and must be always borne in mind |