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Show 266 MR. F. G. PARSONS ON T E E [Mar. 20, seems to be developed in the palmar fascia. In Octodon and Myopotamus it rises only from the inner side of the olecranon process, while in Castor it comes from both the olecranon and internal condyle. In Ccelogenys and Xerus the muscle was formed by some of the internal and superficial fibres of the flexor sublimis digitorum : this arrangement corresponds to what Mivart and Murie found in Dasyprocta, though in the specimen of this animal which I dissected the muscle was absent. In Myopotamus the insertion was into the radial and ulnar palmar cartilages. The muscle was not seen in Chinchilla or Sciurus. In Spermophilus the tendon was broad and fascia-like in its whole length. Apparently this muscle is liable to great individual variation in Bodents as in Man. Flexor Sublimis Digitorum.-This muscle rises from the internal condyle in common with part of the flexor profundus; it divides into slips for the middle phalanges of the 2nd, 3rd, 4th, and usually the 5th digits, which slips are perforated for the passage of the profundus tendons. Just before the perforation there is usually a strong fibrous loop, which passes under the profundus tendon and comes into contact with the sesamoid bones in front of the metacarpo-phalangeal joints ; this is very well marked in Ccelogenys. In the Octodontidae and Dasyproctidae there are only three tendons for the 2nd, 3rd, and 4th digits. This is also the case in Castor. Mivart and Murie ' found a slip to the 5th digit in the Agouti on one side but not on the other. In Ccelogenys I met with a more interesting arrangement still; in it the tendinous loop representing the perforated portion of the tendon was present in tbe 5th digit on one side, but was entirely unconnected with the flexor sublimis, which sent no slip to this digit. Possibly the explanation of these facts may be that the Dasyproctidae show a stage in the gradual suppression of the slip to the 5th digit, a process which is complete in the Octodontidae. In Castor the muscle has an extra origin from the olecranon. Flexor Carpi Ulnaris.-This muscle usually rises, as in Man, from the inner side of the olecranon process, from the internal condyle, and, by aponeurosis, from the upper part of the posterior border of the ulna. It is inserted into the pisiform bone. In the Octodontidae and Dasyproctidae the condylar origin is wanting, as it is also in Castor and Spermophilus. Flexor Profundus Digitorum.-This muscle, which includes both flexor profundus digitorum and flexor longus pollicis of human anatomy, rises usually by four heads; two of these come from the internal condyle, one from the flexor surface of the ulna, and the last from the flexor surface of the radius. The muscle usually divides into four tendons for the outer digits, and often gives off a small tendon at right angles to the rest for the pollex. The tendons perforate the flexor sublimis and are inserted into the terminal phalanges of the digits. 1 P. Z. S. 1866, p. 383. |
