CHAP. XIII.] 



DOUBLE-HAND. 



331 



B 1 . Digits in two homologous groups, forming "Double-hands." 



*492. Double-hand I. Seven digits in two groups of four and three. 

 Male : left arm abnormal, having seven digits arranged in two 

 groups, the one an external group of four normal digits, and the 

 other an internal group of three digits 2 . (Fig. 91.) Described 

 from a dried specimen in Mus. of Harvard Med. School. The man 

 was a machinist and found the hand not merely very useful to him 

 in his business, but he also thought that it gave him advantages 

 in playing the piano. 



" The fore-arm consists of the normal left ulna and of a right one in 

 the place of a radius. The left one shews little that calls for comment, 

 excepting that there is a projection outward at the place of the lesser 

 sigmoid cavity to join a corresponding projection from the other ulna. 

 The upper surface of this projection articulates with the humerus. At 

 the lower end the styloid process is less prominent than usual, and the 

 head rather broad. The right or extra ulna is put on hind side before, 

 that is, the back of the olecranon projects forward over the front and 

 outer aspect of the humerus. If the reader will place his right fore-arm 

 on the outer side of the left one he will see that it is necessarv for the 



I 



; ■ 

 : . . 



. i* ho 



■ '• 



II 



Fig. 91. I. The left band of No. 492 from the dorsal surface. 

 II. The humerus and two bones of the fore-arm at the elbow of the same c 

 0, olecranon. O 2 , the secondary " olecranon ". I, the inner condyle of the 

 humerus. I 2 , the second or external " inner condyle." 



(After Dwight.) 



ulna to be thus inverted if the thumbs are to toucli and the palms 

 to be continuous. This olecranon is thinner, flatter, and longer than 

 normal. The coronoid process is rudimentary. From the side of this 

 process and from the shaft just behind it arises the projection already 



1 Every case known to me is given. 



2 This is the case reported by Jackson, to Bost. Soc. of Med. hup.. 1852. 



