124 



ANIMAL MECHANICS. 



portion of the common tendon of the fl. dig. prof., as shown 

 in the drawing. 



If we call the cross section of the common tendon 100, we 

 find the cross sections of the thumb and four fingers, as fol- 

 lows : — 



I. Macaque {deep flexors ofjingers)* 

 Flexor dig profundus, . . . 100 



1. Thumb, 19.3 per cent. 



2. Other fingers, . . . 40.0 „ 



3. Deficiency, .... 40.7 



Total, . . .100.0 



In the hand of the Sooty Mangabey (Cercocebus fuliyinosus) 

 I obtained the following results : — 



2. Sooty Mangabay (deep flexors of finger's). 

 Flexor dig. prof . . . 100 



1. Five fingers, . . . 50.8 per cent. 



2. Deficiency, . . . 49.2 „ 



Total, . . . 100.0 



In the monkeys of the New World (Fig. 17 6.), a more 

 degraded type of thumb is found to exist; for the flexor ten- 

 don of the thumb proceeds, not from the central and upper 

 portion of the common flexor tendon of the fingers, but from 

 the side of that tendon, as shown in the drawing ; an arrange- 

 ment which reduces the thumb, as in animals lower than 

 monkeys, to a simple finger. In some of these monkeys 

 also the thumb itself becomes rudimentary, and is not fur- 

 nished with any flexor tendon whatever. The A teles, or 



