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Show 706 MR. T. M A N N E R S - S M I T H O N T H E [Dec. 4, Pectineus.-There are two pectinei, an internal and an external. The internal arises from the lesser spinous process, as it is called by Owen. The muscle is inserted into the femur just below lesser tuberosity and close to the obturator externus. It is supplied by the obturator nerve. The pectineus externus arises from the pectineal spine (greater spinous process of Owen). It is inserted into the femur halfway down the shaft. Obturator externus.-Occupies the usual situation. At first sight it appears to be divided into a superior and an inferior portion. Superior portion is more probably inferior gemellus, or, since it receives two branches from the same nerve, it may represent inferior gemellus and quadratus femoris. Its origin, too, would correspond in position to the combined origin of those muscles. The two parts of the obturator externus are easily separated at their origin, but not so at their insertion. The inferior portion is supplied by obturator nerve; the superior by tAvo fine twigs from that branch of great sciatic which supplies adductor magnus in part and semimembranosusl. Quadratus femoris is present in Echidna and appears to have a similar origin and insertion to the muscle described as superior part of obturator externus. The muscle is most probably combined quadratus femoris and gemellus inferior. Obturator internus is absent. The muscle Avhich occupies the usual situation of origin of this muscle is one of the ischio-caudal muscles. Coues describes three ischio-feinoral muscles in the region of externus, a, b, and c: a, and probably b, he considers represent obturator externus ; c he considers represents obturator internus. Hamstring Muscles. Semimembranosus.-This is a fairly large muscle arising from the tuber ischii. It is situated between the muscle representing semi-tendinosus and biceps above and the adductor group beloAv. It is inserted into the inner side of the head of the tibia. The chief nerve-supply is from the sciatic, the nerve reaching the muscle on its superior surface. There is, in addition, a very slender branch of the obturator nerve, Avhich supplies the inferior posterior portion of the muscle \ Semi-tendinosus, with Avhich biceps appears to be blended, is a large sheet Avhich arises by a narroAv tendon from the tuber ischii. The muscle spreading out is inserted by its anterior fibres into the expanded upper extremity of the fibula and into a strong tendinous band which passes from this process to patella. These portions most probably represent biceps ; the posterior part becomes thin and apneurotic and is inserted into the crest of the tibia. Coues describes this muscle entirely as biceps, looking upon semi- 1 Macalister mentions a large gemellus ('Vertebrate Morphology'). Meckel says they are both absent in Ornithorhynchus. 2 It appears to have very much the same attachment and position in Echidna (Mivart, loc. cit.). |