THE SKELETON 49 



In the carpus of the Mammalia there are usually two additional 

 bones developed in the tendons of the flexor muscles, one on each 

 side of the carpus, which may be called the radial and ulnar 

 sesamoid bones ; the latter, which is the more constant and generally 

 larger, is commonly known as the pisiform bone. The fourth and 

 fifth carpals of the distal row are always united into a single bone, 

 and the centrale is very often absent. As a general rule all the 

 other bones are present and distinct, though it not unfrequently 

 happens that two may have coalesced to form a single bone, or 

 one or more may be altogether suppressed. 



The following table shows the principal names in use for the 

 various carpal bones, — those in the second column being the terms 

 generally employed by English anatomists : — 



Radiale — Scaphoid = Naviculars 

 Intermedium = Lunar = Semilunare, Lunatum. 



Ulnare = Cuneiform = Triquetrum, Pyramidale. 



Centrale = Central = Intermedium (Cuvier). 



Carpale 1 = Trapezium = Multangulum majus. 



Carpale 2 = Trapezoid = Multangulum minus. 



Carpale 3 = Magnum = Capitatum. 



Carpale 4 

 Carpale 5 



Unciform = Hamatum, Uncinatum. 



The radial and ulnar sesamoids are regarded by Bardeleben l as 

 the rudiments of a prepollex and a postminimus digit ; the primitive 

 number of digits being thus supposed to have been seven. These 

 bones have been observed in all orders of mammals having five 

 complete digits. Occasionally, as in Peclctes caffer, the so-called 

 prepollex consists of two bones, of which the distal one bears a 

 distinct nail -like horny covering. In Bathyergus maritimus the 

 pisiform, or postminimus, is likewise double ; the two elements 

 being regarded by their describer as representing the carpal and 

 metacarpal of the presumed seventh digit. 



Similarly in the posterior limb the tibial sesamoid, and a fibular 

 ossification corresponding to the pisiform, are regarded as represent- 

 ing a prehallux and a postminimus. 



Metacarpus and Phalanges. — The metacarpal bones, with the 

 digits which they support, are never more than five in number, and 

 are described numerically — first, second, etc., counting from the 

 radial towards the ulnar side. The digits are also sometimes named 

 (1) the pollex, (2) index, (3) medius, (4) annularis, (5) minimus. 



scaphoid is accordingly also regarded as a second centrale. In the same com- 

 munication, Dr. Baur expresses his disbelief in the existence of remnants of a 

 prepollex and of a seventh digit in mammals and other vertebrates. (See Anat. 

 Anzeiger, vol. iv. pp. 49-52, 1889.) 



1 On the Prsepollex and Pramallux, etc., Proc. Zool. Soc. 1889, pp. 259-262. 



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