OCR Text |
Show 432 DR. C. I. FORSYTH MAJOR ON [Apr. 18, as well as in the metacarpo- and metatarso-phalangeal articulations. Among the Rodents, I have for the present come upon dorsal ossicles-apart from the one on the first digit-in Lagomys, viz., on the metacarpo-phalangeal articulation of the second, third, and fourth digits, and in Spalax. In the manus of the latter, dorsal ossicles are present on the proximal interphalangeal articulations of the 2nd-5th fingers ; in the pes, on the interphalangeal articulation of the first, and on the proximal interphalangeal articulations of the four other toes. As regards Edentates, it has been stated that " a sesamoid bone is developed on the dorsal side of the metacarpal-phalangeal articulations" of Oryeteropus1. In the skeletons of the Cape Anteater available to me, all traces of these had been carefully made to disappear. From the above fragmentary evidence it can be argued that careful research will show these dorsal " sesamoids " to be a not uncommon occurrence ; it will then be time to investigate them more closely. They too may have been originally intercalated between the phalanges, and would point towards a more remote condition than does the interphalangeal dorsal ossicle of the thumb. As to the opinion that their function is to facilitate the sliding of the tendons over osseous protuberances, and to enlarge the angle of insertion of the tendons, I may be allowed to refer to what Pfitzner has said on the subject2. II. The pisiform of Ctenomys is composed of two bones (figs. 1 & 2), as found by von Bardeleben in Bathyergus maritimus3, and moreover the distal one has, in one species (fig. 2), a horny sheath, comparable to the nail-like structure-found by O. Thomas and described by von Bardeleben4-on the so-called prsepollex of Pedetes; and to a somewhat similar one stated by Prof. Howes to overlie the enlarged "prsehallux" of Cercolabes5. The two discoveries of von Bardeleben6-by the way, the two bones of Pedetes were described by Meckel in 1825-are among his chief arguments in support of his assumption of a sixth and seventh finger; accordingly, the proximal bone of the pisiform of Bathyergus was considered "as in all probability the carpal, and 1 Flower: ' A n Introduction to the Osteology of the Mammalia,' 3rd ed., p. 309 (1885). 2 "Erlautern wir dies an dem Beispiel der Sesama dorsalia. Wenn irgend Jemand, so hiitten alsdann die ' Greifhander ' solche noting, die Affen und der Mensch ; warum finden wir sie aber statt dessen bei den Caniden, bei denen das betreffende Gelenk fast immer in Ueberstreckung bleibt ? Warum nicht eher bei den Feliden, die in diesem Gelenk schon viel energischer beugen ?" (Morph. Arb. i. p. 610, 1892).-Besides, these dorsal ossicles of CanidiE are only loosely connected with the extensor tendons ("an die Streeksehnen nur locker ange-heftet") (id. ib. p. 604). See also ib. pp. 567-571, 609-612. 3 P. Z. S. 1889, p. 260, pl. xxx. fig. 3. 4 Id. ib. 5 L. c.; Bardeleben, I. c. p. 260, footnote. 6 K. v. Bardeleben: '• Hand und Fuss. Beferat erstattet auf der 8. Vers. d. Anat. Ges. in Strassburg" (Verh. d. Anat. Ges. viii. p. 283, 1894). |