PRENTISS: POLYDACTYLISM IN MAN AND DOMESTIC ANIMALS. 293 



Bauniuller ('92) figures the manus of a roebuck (Cervus caprea) 

 which was composed of five digits. The abnormality was found on both 

 fore feet. Baumiiller regards the extra digit as a pollex, and attributes 

 its presence to reversion. 



Bateson ('94) remarks with reference to polydactylism in the sheep 

 and ox, that the extra digits are in all cases formed by duplication or 

 variation. As to the development of digits ir and v he asserts that 

 " there is no such case." 



In the ox, a number of cases of polydactylism have been observed 

 and described. They may be divided into two groups : (1) manus or 

 pes of three digits, all of nearly equal size, and borne on a single meta- 

 carpal bone (Bateson, '94, Figs. 114, 115, p. 375). In these cases the 

 presence of both accessory hoofs (rudiments of ii and v) in their 

 normal positions makes it certain that the vestiges of digits ii or v have 

 not developed, but that either in or iv has become duplicated. Four 

 cases are described by Bateson, and it is stated by Goodman ('68) that 

 the abnormality was common and frequently inherited in a herd of Eng- 

 lish cattle. (2) Manus of four digits, ii and v both being developed ; 

 the accessory hoofs are located at the distal extremities of the extra 

 digits ; each supernumerary digit is composed of a distinct metacarpal 

 element, and digit ii has in addition two small phalanges. Boas ('90) 

 describes two cases, and considers them good instances of reversionary 

 polydactylism. 



B. Observations. 



Two cases of polydactylism in the manus of the ox have come under 

 ray observation. Both specimens had been disarticulated at the 

 carpo-metacarpal joint, and the carpal bones were thus unfortunately 

 lost ; they were right and left fore feet and probably belonged to one 

 animal. Both are abnormally wide at the distal end of the cannon 

 bone ; in each the hoof of the radial side is very broad and incompletely 

 divided into two parts (Fig. W, p. 294, and Plate 21, Fig. 29). The 

 accessory hoof of the ulnar side of the manus is normal in position, but 

 that of the radial side is absent in both cases. 



In the left manus (Fig. 29) the skeletal parts are well formed. The 

 metacarpus is of normal length, and is distinctly divided into three 

 elements, each of which bears an articular head for a corresponding digit. 

 These three elements represent three metacarpal bones, and we may 

 designate them as ii, in, and iv. in is larger than either of the 

 others; its distal articular surface is unsymmetrical, as the trochlear ridge 



