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 at- 

 tachments. 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 digiti is the outermost of the peroneal 

 muscles ; it is strong and has 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 difi^ers from the arrangement 

 characterizing the Sciuromorpha and Myomorpha ^ As Aulacodus is 

 usually associated with Gapromys it might be expected that the 

 agreement in structure would be closer with that animal than with 

 the Porcupines : I mention Gapromys particularly since it is one of the 

 few genera of the Octodontidse 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. Dobson^ There is, in fact, 

 a close similarity between the Rodent which forms the subject of 

 the present communication and Gapromys ; the principal differences 

 appear to be the following : — 



(1) The Deltoid m Gapromys 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 Gapromys 

 it agrees with Erethizon ^ : the Deltoid is like that of Erethizon ; 



' "On the Homologies of the long Flexor Muscles, &c.," Journ. Anat. 1883, 

 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 Erethizon dorsatus," P. Z. S. 1882, p. 271. 



