OCR Text |
Show 404 MR. ST. GEORGE MIVART AND DR. J. MURIE [June 26, The pronator quadratus is very extensive, having attachments to the shaft of the radius and ulna for nearly their whole length, and not for half only as Meckel says*. But at the same time he also states that it is found in some other Rodents in the same condition in which we find it in Dasyprocta cristata. In the Guinea-pig, Hare, and Rabbit this muscle is very small, from the approximation of the bones. The extensor carpii radialis longior arises from the humerus above the external condyle; its fleshy belly extends about halfway down the forearm, and ends in a tendon which is inserted into the proximal end of the metacarpal of the index (fig. 3, E. c. r. 1. and b.). There is no difference in the Guinea-pig, Hare, and Rabbit. The extensor carpii radialis brevior arises beneath the last, and is inserted into the radial side of the metacarpal bone of the third digit (fig. 3, E. c. r. 1. and b.). The same in the Guinea-pig and Hare ; the muscular bellies in all are very closely applied. The extensor communis digitorum has origin from the external condyle, the muscle being strongly tendinous beneath. Passing downwards it divides into three separated tendons, which are respectively inserted into the second, third, and fourth digits. There is a second part, which gives rise on the ulnar side to a much more delicate tendon, which passes down beneath the tendon of the other part, and, dividing, goes to the third and fifth digits. Meckel t remarks that in the Marmot there are two extra extensor muscles which supply the third and fourth digits. In the Guinea-pig it is as in the Agouti, except that the tendons of the larger part are inserted into the third, fourth, and fifth digits; while the smaller part sends two tendons to the index and third digits respectively. In the Hare this muscle sends four tendons-namely, to the index and the three outermost digits ; that going to the fifth digit forms a muscular belly rather distinct from the rest, and which appears to represent the smaller part above described in the Agouti and Guinea-pig. The extensor carpii ulnaris springs from the external condyle and the contiguous part of the ulna ; its insertion is into the base of the fifth metacarpal bone (fig. 3, E. c. u.). Alike in the Guinea-pig and the Hare. Extensor ossis metacarpii pollicis. This is a very large and strong muscle, with an exceedingly broad tendon. It arises from the contiguous surfaces of the radius and ulna, and is inserted into the base of the metacarpal bone of the pollex (figs. 2 & 3, E. o. m.p.). In the Guinea-pig it is similar, except that its tendon (the pollex being absent) runs on to the base of the metacarpal of the index, though mainly inserted into the rudimentary trapezium. In the Hare, as in the Agouti, the tendon goes to the metacarpal bone of pollex. Both the extensor primi internodii and extensor secundi internodu pollicis are absent in the Crested Agouti and in the Guinea-pig. * Loc. cit. p. 302. t Loc. cit. p. 322. |