298 



BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



usually limited to the phalanges. Such conditions have beeu described 

 by Struthers ('63), Arloing ('67), and Boas ('85). 



— pJvx. 1. 



B. Observations. 



Through the kindness of Dr. Frothingham, of the Harvard Veterinary 

 School, an abnormal manus of a polydactyle colt came under my observa- 

 tion. The specimen came from Texas. Externally the hoof was almost 



completely divided into two : each 

 mt' carp. \ •' , • , , 



portion was several inches long, and 



curved away from the other. On ex- 

 amining the skeletal parts (Fig. Z), 

 they were found to be normal down to 

 tlie distal end of the first plialanx, 

 which was bifurcated and bore two 

 articular surfaces. Each of these car- 

 ried two phalanges, which resembled 

 tlie median and ungual phalanges 

 of the artiodactyle digit. The two 

 series were mirrored images of each 

 other ; each os pedis was slightly con- 

 cave on the surface facing the median 

 plane of the digit, and convex on the 



■phx. 2^ opposite side, so that the two fitted 

 together would give a phalanx of 

 nearly normal form. A navicular of 

 about half the length of the normal 



'p\x. 3* l)one articulated with the posterior 



face of eacli os pedis, thus resembling 



the condition of ruminants. 

 Fio. Z. — Anterior view of left polv- _,, . . i i i i • i i 



dactyle manus of the horse, showing dupli- This specimen had been dried be- 



cation of digit in. mVcarp., distal end of fore it waS examined, and the inner- 

 third metacarpal bone; pAx. 1, first phalanx . 1 , .4- -u^ „4.„ i:„.i i,,,f r>x- 

 of third digit; phx. 2'S 2^ duplications of nation COuld not be studied, but ex- 

 second phalanx; phx. 3", 3^, duplications aminatiou of the chief luuscle tendoiis 

 of ungual phalanx, i natural size. showed that the extensor pedis and 



flexor perforans were duplicated at their distal ends. This case is there- 

 fore simply an example of duplication of digit in. 



It has long been known that the " splint bones " of the equine manus 

 represent rudimentary metacarpals, but until recently the presence cf 

 phalangeal vestiges in the manus of the embryo has been denied. 



phx. 2° — • 



phx. 3"—" 



