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Show 680 MR. F. G. PARSONS ON THE [Nov. 20, the sole, lying beneath the head of the astragalus instead of projecting from the inner side of the foot as in the Tree-Porcupines. There are three cuneiforms and a cuboid. The two phalanges of the hallux are distinct, as they are in Hystrix and Erethizon; in Sphingurus they are fused together. THE MUSCULAR SYSTEM. The muscles of Atherura were found to resemble very closely those of Hystrix, described in the "Myology of the Sciuromorphine and Hystricomorphine Bodents."l In that paper I stated that I had only noticed two definite muscular characteristics of the Hystricidae as a family :- 1. The latissimus dorsi at its insertion wraps round the low^er border of the teres major. 2. The scalenus anticus is absent. Both of these points are noticeable in Atherura. The points of difference suggested between the Tree- and the Ground-Porcupines were much more numerous, and I have carefully tested them on Atherura : - 1. The digastric agrees with Hystrix in only having a slight constriction between the two bellies, in this constriction a thin layer of tendinous fibres is found on the surface. It differs from Sphingurus in not having a strong tendinous slip from the posterior belly to the hyoid bone. 2. The omo-hyoid is absent, agreeing Avith Hystrix, in which it is either absent or rudimentary, and differing from the Tree- Porcupines, in Avhich it is a large muscle. 3. The levator claviculae rises from the basioccipital bone as in Hystrix. In the Tree-Porcupines it comes from the atlas. 4. The sterno-scapularis rises from the first part of the bony sternum, not the leaf-shaped cartilage. A few fibres go to the outer part of the bony clavicle, the rest are continued as the claviculo-scapularis, Avhich runs to the spine of the scapula but only covers the outer part of the supraspinatus. This arrangement corresponds Avith that found in Hystrix, in Avhich the two parts of the sterno-scapularis are continuous, in Sphingurus they are practically separate. 5. The biceps cubiti has only the long head as in Hystrix. In the Tree-Porcupines both heads are present. 6. The coraco-brachialis is inserted from just below the insertion of the latissimus dorsi to just above the internal condyle by one continuous attachment. The musculo-cutaneous nerve passes through the muscle, i. e. a few fibres AA'hich are inserted lowest pass superficial to it. If we regard the musculo-cutaneous nerve as the separation between the second and third heads of the coraco-brachialis, both these heads are present in Atherura, and 1 P. Z. S. 1894, p. 251. |