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Show 1889.] ON PR.EPOLLEX AND PRAEHALLUX. 259 4. On the Prsepollex and Prsehallux, with Observations on the Carpus of Theriodesmus phylarchus. By Prof. K A R L BARDELEBEN (Jena). (Communicated by Prof. G. B. HOWES, F.Z.S., F.L.S.) [Eeceived April 30, 1889.] (Plate XXX.) In 1885 I gave the name "rudiments of praepollex and prae-hallux " to those bones on the inner side of the carpus and tarsus of the Mammalia which were hitherto either quite unknown, or had been but briefly described as radial and tibial "sesamoids." 1 have found these bones in all orders of Mammals which have five functional digits. The " rudiment of the praepollex" (shortly called "praepollex ") is present in Marsupials, Edentata, Rodents, Insectivora, Carnivora, and Monkeys. The praepollex is situated on the trapezium in Insectivora and Lemurs ; between the scaphoid and the first metacarpal in Rodents and Carnivora ; between the scaphoid and the trapezium in Monkeys. The praehallux articulates with the first cuneiforme in Marsupials, Insectivora, and some Carnivora; with the same bone, or with the navicular, in Edentata and Rodents; with both bones in other Carnivora; between the first cuneiform and the first metacarpal in Monkeys. The rudiments of the praepollex and praehallux are small, rounded, or elongated ossicles, often strikingly similar to a metacarpal or phalangeal bone. As almost all Mammals have also a supernumerary bone (formerly considered as a "sesamoid") on the outer side of the hand (pisiforme) and of the foot (tuberositas calcanei), I conclude (regarding these supernumerary elements as vestiges of reduced digits) that there are, in addition to the ordinarily recognized five digits, the rudiments of a sixth (internal) and of a seventh (external) digit, in both the hand and foot of Mammals. I have also found a supernumerary cartilage on the tibial border of the tarsus in the human embryo of the second month ; and Kehrer, a pupil of Wiedersheim, has shown (Berichte d. naturf. Gesellsch. zu Freiburg, Bd. i. Heft 4, 1886) that the Urodela have also rudiments of seven digits in embryonic stages. Consequently I was led to state, at the meeting of the German Naturalists and Physicians in Berlin (1886), that we must modify our former views on the pentadactyly of the higher vertebrates, inasmuch as we have ground for regarding certain cases of hyperdactyly (polydactyly), which are not unfrequently found in Mammals (more especially in the best-known Mammal, Man), as instances of atavism rather than of abnormality. Until this month I have neither had the time nor the requisite material for a more detailed inquiry into this important subject, nor had I seen the large collections of London and of North America. My intention to come to London has been on several |
