1889.] ON PR^POLLEX AND PRiEHALLTJX. 



259 



4. On the PrcepoUex and Pr^liallux, with Observations on the 

 Carpus of Theriodesmus phylarchus. By Prof. Karl 

 Bardeleben (Jena). (Communicated by Prof. G. B. 

 Howes, F.Z.S., P.L.S.) 



[Received April 30, 1889.] 

 (Plate XXX.) 



In 1885 I gave the name "rudiments of prsepollex and prfe- 

 hallux " to those bones on the inner side of the carpus and tarsus of 

 the Mammaha which were hitherto either quite unknown, or had 

 been but biiefly 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 prsepollex" (shortly called " prae- 

 poUex") is present in' Marsupials, Edentata, Rodents, Insectivora, 

 Carnivora, and Monkeys. The prsepollex is situated on the trape- 

 zium in Insectivora and Lemurs ; between the scaphoid and the 

 first metacarpal in Rodents and Carnivora ; between the scaphoid 

 and the trapezium in Monkeys. The pr?ehallux 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 prae- 

 j)ollex and prEehallux are small, rounded, or elongated ossicles, often 

 strikingly similar to a metacarjjal or phalangeal bone. As almost 

 all Mammals have also a su|)ernumerary bone (formerly considered 

 as a "sesamoid") on the outer side of the hand (pisiforme) and of 

 the foot (tuberositas calcanei), I conclude (regarding these super- 

 numerary 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, 188G) that the JJrodela 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 

 ))entadactyly 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 

 abnormahty. 



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 



