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Show 272 MESSRS. B. C. A. WINDLE AND F. G. PARSONS ON [XoV. 3, the hind-limb in walking, one notices that the knee is extended and the ankle plantar flexed in order to lengthen the limb and so pull and push the body of the animal over the spot on which the foot is planted, while at the same time the knee is slightly flexed. It is probable that the expansions from the hamstrings effect the plantar flexion of the ankle by pulling up the calcaneal tuberosity, at the same time that they are causing slight flexion of the knee. A n interesting and, so far as we know, unaccounted for structure in the semitendinosus of Man, is the fibrous streak running across the muscular belly; this is seldom seen in the lower mammals, and we have not noticed it in any Ungulate, although we have carefully looked for it. Macalister, however, found it distinctly in the Muntjac (27). The nerve-supply of the semitendinosus is the special nerve to the hamstrings from the internal popliteal element of the great sciatic (see text-fig. 26, p. 274). Biceps {Flexor cruris lateralis).-It has already been pointed out how closely the biceps is connected with the femoro-coccygeus in the Ungulata, and how constantly the latter muscle is inserted into the side of the patella; we shall therefore describe as biceps only that part of the superficial lateral plane of muscle which is inserted below the patella. As the muscle is so inseparable from its neighbour the femoro-coccygeus (agitator caudae), it is very difficult to say whether any of its fibres really rise from the caudal vertebrae; we are, however, inclined to agree with Lesbres that in the Ungulates the biceps has only an origin from the tuber ischii (see text-fig. 24, BL). Its insertion is into the fascia of the upper half or more of the outer side of the leg, while from its lower border a strong fibrous process passes down to the calcaneal tuberosity, helping the gracilis and semitendinosus to ensheath the tendo Achillis. With the exception of relative size, there is hardly any variety in the biceps of different Ungulates ; it perhaps reaches its greatest development in the Tapir (58, 61, 62). Bicipiti accessorius {Tenuissimus).-This in most Ungulates is either suppressed or completely blended with the biceps. The only record we can find of it is that it is figured in Cuvier and Laurillard's Elephant (84), and may possibly be the deep part of the biceps of the Tapir described by Murie (XVII.). Muscles of the Internal Femoral Region. Pectineus.-This muscle is often difficult to distinguish from the adductor longus, especially as the latter may or may not be delaminated from the adductor mass. The origin is fairly constant, coming from some part of the ilio-pectineal line, while the insertion seems to range all over the shaft of the femur. In the Hippopotamus (1) Gratiolet describes three parts, pubic, symphysial, and ischial; of these the latter two are evidently adductor longus and quadratus femoris. In the Suidaa (6, 7, 11, 14) the muscle rises from the whole ilio-pectineal line and is inserted into the middle or distal part of the femur; it is comparatively small in this |