242 MR. F. E. BEDDARD ON [Apr. 7, 



The only Peroneal muscles present are the Peroneus longus and 

 the Peroneus quarti digiti ; the latter has an attachment to ankle 

 as well as to 4th digit. 



There are three long flexors. 



The Flexor communis overlies the Tibialis posticus ; their tendons 

 join at the ankle ; the tendon of the Flexor halhicis p'ms the common 

 flexor tendon a little further down just before its trifurcation. Inter- 

 osseii oxm a thick mass covering sole of foot. There is only one 

 Lumbricalis arising from flexor tendon of outer digit. 



The myology of the Guinea-pia; is to a considerable extent 

 described by Messrs. Murie and Mivart in their memoir upon the 

 Agouti^; it presents a number of differences from Dolichotis, of 

 vrhich the following are the principal : — 



(1) There is no second part to the brachialis anticus, arising from 



the humerus ^. 



(2) The Triceps has only three heads. 



(3) The Flexor sublimis has four tendons. 



(4) There are several extensor muscles of the hand not present in 

 Dolichotis. 



(5) Peroneus brevis present. 



In most of these points Dolichotis also differs from the Agouti — in 

 all except as to the second part of the Brachialis anticus (see foot- 

 note). 



On the whole in myology Dolichotis is nearer to the Agouti than 

 to the Porcupines, but it differs from both in the reduction of the 

 extensors of the manus and the peroneal muscles. 



There are at present so few Rodents of which the myology is known 

 that I do not propose to deal with the resemblances of Dolichotis to 

 such types as are kuown at greater length. 



Brain. 



As there is no description known to me of the brain of this Rodent 

 and no figures, I endeavour to supplement this deficiency. 



The brain (see fig. 4, p. 243) measures 59 mm. in length (to the 

 end of the cerebellum) and 41 mm. greatest breadth. 



The corpora quadrigemina are well exposed, as is the case with 

 most Rodents, but not in the Squirrel and Porcupines. 



The cerebral hemispheres are provided with well-marked sulci, 

 which are more numerous than in a hvnin of Ccelogenys paca of 

 about the same size. 



The relation between the size of the animal and the complexity of 

 the cerebral convolutions is not so plain in the Rodents as in some 

 other groups ; the Porcupines form the principal exception ; they 

 have all very smooth brains, as compared with other Rodents of a 

 similar size or even smaller. 



The Rhinal fissure of Dolichotis is deeper behind than in front ; 



1 P. Z. S. 1866, p. 383. 



^ I think that the muscle wliich I figure (woodcut, fig. 3, .r) must correspond 

 to the one so named in the Agouti, though its insertion is quite different in 

 Dolichofis. 



