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Show 1882.] DR. GADOW ON THE ANATOMY OF PTEROCLES. 317 margin of the postacetabular ilium and from the lateral plane of distal half of this bone. Its tendon passes through the tendinous loop near the poplitea, and is inserted into the neck of the fibula. Its nerves come from the ischiadic plexus. M. caudce ilio-flexorius (m. semitendinosus). See fig. 1. This ribbon-shaped muscle arises from the lateral processes of some of the first caudal vertebra? and from the outer plane of the spina ilio-cau-dalis. The so-called accessory part of this muscle is well developed ; it descends from the outer and lower surface of about the distal third of the femur • and its fibres join those of the long or main part nearly at right angles. The line of junction is indicated by an oblique tendinous raphe. The two combined parts are inserted, first into the neck of the tibia by a strong tendon; secondly, a small tendon, looking like the continuation of the raphe, descends superficially to the back of the leg and joins the caput femorale internum m. gastrocnemii. Nerve-supply, together with the next muscle, from the ischiadic plexus. The m. ischio-jiexorius (m. semimembranosus) is feebly developed, and loses its independence by becoming blended with the m. cauda? ilio-flexorius, which completely covers it externally. It arises from a small part of the middle line of the lateral margin of the ischium. The m. caudce ilio-femoralis consists of two chief parts. The most lateral one, or long head (long head of femoro-caudalis), is a very narrow, slender, muscular ribbon, which arises from the proc. lat. of the last caudal vertebra?, and is inserted by a narrow thin tendon into the latero-posterior plane of the end of the proximal third of the femur. Towards its insertion the fleshy part of this long head is to a great extent blended with the more proximal or greater part: the latter (accessory femoro-caudal) arises from part of the membrane of the foramen oblongum, and from the outer plane of the hindmost or distal part of the ischium, whilst only a few fibres arise from the adjacent part of the ilium. The nerve which supplies these two muscles comes from the ischiadic plexus, and passes externally over the m. ischio-femoralis. I must mention here a peculiar little muscular slip which I have not often observed in birds. It arises (see fig. 1) as a small fleshy flat slip from the outer aspect of that region where the pubis and ischium approach each other ; it is then partly covered by the long head ; its thin tendon unites with that of the long head. It was present also on the other side, and was supplied by the same nerve-branch together with the two large heads. The presence of this little muscular slip is an instance of the great variation to which this group of the m. caudae ilio-femoralis is subject. The m. ischio-femoralis (m. obturator externus) arises with fleshy fibres from the dorsal, distal, and ventral margins of the foramen oblongum ; its strong tendon is inserted into the outer plane of the femur, just distad from the insertion of the m. obturator. It receives its nerve from the ischadic plexus. The m. obturator arises from that part of the inner plane of the ischium which bounds the foramen obturatum and also from the |