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Show 524 MR. F. E. BEDDARD ON THE BRAIN AND [June 14, The Tibialis posticus is covered by the Flexor tibialis; it becomes tendinous halfway down the leg. The Tibialis anticus appears to be quite normal in size and attachments. So, too, the Extensor digitorum longus and the Extensor hallucis (which is inserted on to the second digit, the first being absent). There are four Peroneal muscles ; that supplying the fifth digit is very slender, both muscle and tendon, and is inserted on to the last phalanx. The Peroneus quarti diqiti is the outermost of the peroneal muscles ; it is strong and lias an insertion corresponding to the last muscle upon the fourth digit. The Peroneus brevis is inserted on to the outermost metatarsal. The Peroneus longus is the most superficial of the peroneals in origin; its tendon crosses the sole of the foot, as has often been described in Rodents. The musculature of this Rodent is clearly more like that of the Hystricine genera than other forms; the arrangement of the long flexor tendons of the foot conform to the type met with in the Porcupines, Chinchillas, &c, and differs from the arrangement characterizing the Sciuromorpha and Myomorpha\ As Aulacodus is usually associated with Capromys it might be expected that the agreement in structure would be closer with that animal than with the Porcupines : I mention Capromys particularly since it is one of the few genera of the Octodontidae of which the muscular anatomy has been described; its anatomy has lately formed the subject of an article in these ' Proceedings' by Dr. G. E. Dobson2. There is, in fact, a close similarity between the Rodent which forms the subject of the present communication and Capromys; the principal differences appear to be the following:- (1) The Deltoid in Capromys arises partly from the spine of the scapula. (2) The Latissimus dorsi has a double insertion, one part being connected with the Pectoralis. (3) There is no tendon (?) connecting the Flexor profundus digitorum with the Flexor sublimis. (4) The Gluteeus medius is inserted by two thick tendons on to the great trochanter. (5) The Gluteeus minimus is " a narrow long muscle"; its insertion is between the two tendons of the last. (6) The Obturator internus is absent. (7) The Semimembranosus has only one part. In some of these points where Aulacodus differs from Capromys it agrees with Erethizon 3: the Deltoid is like that of Erethizon ; 1 " On the Homologies of the long Flexor Muscles, &c," Journ. Anat. p. 142. 2 "On the Myology and Visceral Anatomy of Capromys melanurus, with a Description of the Species," P.Z. S. 1884, p. 233. 3 Mivart, "Notes on the Anatomy of Erethizondorsatus," P. Z. S. 1882, p. 271. |