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Show 1894.] MYOLOGY OP RODENTS. 267 In the Octodontidae there are always four tendons to the digits and one to the thumb. There are also four lumbricales. In the Hystricidae no slip is sent to the thumb in Hystrix and Sphingurus, but Mivart describes the muscle as dividing into five tendons in Erethizon dorsatus l. Fig. 3. RuOl . POL FLEX.SO FLEX.CARP R A o . Left fore foot of Sphingurus prehensilis (superficial dissection). There were three lumbricales in Hystrix and Erethizon1, four in Sphingurus. The Chinchillidae have no slip to the thumb and four lumbricales. In the Dasyproctidae there is no slip to the thumb and three lumbricales. In the Caviidae the arrangement is the same. In the Sciuromorpha there are four tendons in Sciurus, Pteromys, and Arctomys, but Xerus and Castor have five. The number of the lumbricales in Bodents seems liable to individual variation, as a rule the one on the ulnar side is larger than the rest and rises from the front of the flexor profundus before it divides. Pronator Quadratus.-This muscle is usually well marked, 1 P. Z. S. 1882, p. 271. |