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Show 172 MR. F. G. PAHSONS ON T H E [Jan. 14, found is that the outer division of bis extensor carpi ulnaris is really the extensor minimi digiti, the tendon of which has lost its digital attachments and has become inserted into the base of the fourth metacarpal bone. Supinator Brevis.-The description of this muscle given in the other Rodents applies to the Myomorpha, with the exception that in the latter a sesamoid bone is usually found in the tendon. The only animals in which this bone was wanting were Bathyergus and Georychus. The relationship of the tendon of the supinator brevis to the external lateral ligament of the elbow is interesting, in some cases, as in that of Bathyergus, there is a well-marked external lateral ligament, situated behind the tendon, but in others, of which Cricetomys is an example, the tendon itself seems to form the lateral ligament, and has the orbicular ligament attached to it. Extensor Ossis Metacarpi Pollicis.-In all cases this muscle rises from both bones, and is inserted into the base of the metacarpal bone. In the Gerbille its tendon was double. In Cricetus and Cricetomys it had an extra insertion into the radial sesamoid bone or palmar cartilage. Extensor Primi lnternodii Pollicis.-In every animal examined this was absent. Extensor Secundi lnternodii Pollicis.-This muscle was only seen in Georychus, where it was well-marked, it accompanied the extensor indicis and separated on the back of the hand. This arrangement is practically the same as that already described in Castor. Extensor Indicis.-As in other Rodents the extensor indicis rises from about the middle of the back of the ulna, and is inserted only into the dorsal side of the index. In Myoxus it rises from the top of the back of the ulna close to the olecranon. In the Vole 1 dissected the tendon had acquired a secondary attachment to the prominent ridge on the back of the radius at its low7er end, while the part of the tendon between this and the index was wanting. Palmaris Brevis.-When a palmar ossicle is present, which is not so often the case as in other Rodents, the muscle is attached to it. W h e n there is no ossicle it is attached to the palmar fascia. In Microtus and Bathyergus no palmaris brevis was found. Flexor Brevis Digitorum Manus.-This muscle was found in Cricetomys, Cricetus, Georychus, and Bathyergus. In the first three it arose from the palmar ossicle, but in the last from the fascia just external to the pisiform bone. Muscles of the Thumb.-In almost all cases the abductor pollicis can be made out, and has its origin from the palmar ossicle. The flexor brevis was made out with difficulty in Myoxus, Georychus, and Bathyergus; in the two latter the thumb is provided with a pair of sesamoid bones, as in all the other fingers. Bathyergus has a prominent cartilaginous spur on the outer and inner side of the hand; these probably represent the prepollex and postminimus. |