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Show 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 hallucis joins the common flexor tendon a little further down just before its trifurcation. Lnter-osseif ovm a thick mass covering sole of foot. There is only one Lumbricalis arising from flexor tendon of outer digit. The myology of the Guinea-pig is to a considerable extent described by Messrs. Murie and Mivart in their memoir upon the Agouti1; it presents a number of differences from Dolichotis, of which the following are the principal:- (1) There is no second part to the brachialis anticus, arising from the humerus 2. (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 footnote). 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 known at greater length. Brain. As there is no description known to m e of the brain of this Rodent and no figures, I endeavour to supplement this deficiency. The brain (see fig. 4, p. 243) measures 59 m m . in length (to the end of the cerebellum) and 41 m m . 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 brain of Codogenys 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. 2 I think that the muscle which I figure (woodcut, fig. 3, x) must correspond to the one so named in the Agouti, though its insertion is quite different in Bolichotis. |