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Show 1891.] DOLICHOTIS PATAGONICA. 241 condyle of the humerus, one of them (the more superficial) being much larger than the other. The two remaining heads arise respectively from the radius and ulna. The Extensor metacarpi radialis is a large muscle, the largest of the extensors ; its tendon is inserted on to outer side of metacarpal of 3rd digit, having previously given off a slip to the head of the first metacarpal (i. e. that of 2nd digit). The Extensor communis digitorum arises not only from the external condyle of the humerus, but also by a few fibres from the ulna; its tendon splits at the wrist into four tendons supplying the four digits. The Extensor minimi digiti is the smallest of the three upper extensors ; it arises from extensor condyle and from ulna ; it supplies 4th and 5th digits. The Extensor carpi ulnaris calls for no special remark; it is as in the Agouti. These are all the extensors of the manus of Dolichotis. MUSCLES OF THE HIND LIMB. The Gracilis consists of two distinct parts as in other Rodents. One part of the gracilis is sometimes spoken of as sartorius; the muscle is inserted on to fascia covering leg from knee to ankle-joint ; it also appears to have a tendinous connection with both the semimembranosus and semitendinosus. The Semitendinosus is a strong and fleshy muscle ; it arises from the spines of the sacral vertebrae and from the tuberosity of the ischium; it is inserted by a moderately broad flat tendon, which becomes thicker at its insertion to outside of cnemial crest of tibia. The Biceps has two origins-(1) from sacral vertebrse in front of the semitendinosus and continuous with it; (2) from tuberosity of ischium, also in front of semitendinosus. It is inserted by a continuous broad sheet of muscle on to fascia covering leg. The Tibialis anticus arises by two heads-(1) by a long tendon from the femur which passes beneath the patello-tibial ligament; (2) by a fleshy head from tibia and fibula. The two parts are blended a short way down and inserted by a strong tendon on to inner side of inner metacarpal. The Extensor communis arises by a long tendon from the femur ; its tendon of insertion passes under two annular ligaments, one at ankle-joint through which the tendon of the tibialis anticus also passes, and another near the proximal end of the metacarpal; just before passing through the second annular ligament the tendon splits into two ; each of these again splits into two ; the two outer of the four tendons supply the two outer digits ; the two inner ones both go to the middle digit. The Extensor hallucis is a slender muscle arising from the tibia and fibula ; its tendon does not pass through the lower annular ligament; it supplies the second digit. The Extensor brevis is a small flat triangular muscle, two tendons arise together from the muscle and supply the two inner digits. PROC. ZOOL. Soc-1891, No. XVI. 16 |
