On the Trapezium of the Horse. 1 7 



examples it is at the lowest part of the trapezoid ; this latter 

 position occurring, naturally, in those instances where the 

 trapezium articulates with the metacarpal bone. Fig. 2 

 contains outline sketches of different trapezia illustrating 

 this point. 



At first sight the variation in level of the trapezium 

 appears of no moment. But the fact is of some interest 

 when taken in conjunction with the circumstance that the 

 trapezium in some modern allies of the horse {Ta^pirus 

 indicus, for example) extends from the scaphoid to the 

 metacarpus, thus articulating with three bones — scaphoid, 

 trapezoid, and second metacarpal. It would have been 

 particularly interesting to find a specimen in which the 

 trapezium actually articulated with the scaphoid in addition 

 to the trapezoid. But, though trapezium and scaphoid 

 closely approximated each other in one or two instances, 

 no definite articulation could be demonstrated. It is not 

 unreasonable to expect that, if a larger number of animals 

 be examined, such an articulation may be found. 



Bearing in mind that two bones have been described as 

 occurring in the position of the trapezium, great care was 

 exercised in order that such a circumstance, if present, 

 should not be overlooked. In no instance, however, was 

 more than one small bone found. It seemed possible that 

 one of the two bones which are mentioned by the older 

 writers (Percivall, for instance^) might have been a sesamoid 

 developed in connection with one or other of the two 

 tendons inserted in the region of the median side of the 

 carpus. But no such sesamoid bone was found. It was 

 concluded, therefore, that the occurrence of two small bones 

 at the inner (median) side of the carpus is rare. 



A minor question suggested itself during these observa- 

 tions. Is it possible that the trapezium has disappeared by 

 fusion with the trapezoid, rather than by a gradual reduc- 

 tion in size terminating in extinction ? This mode of loss 

 of identity would bring the trapezium into line with the 

 OS centrale, which, as is now generally accepted, has 



^Percivall (2), p. 54. (Trapezium) "Not invariably present: in some 

 instances two are found." 



VOL. XVI. 



