25 



March 8, 1836. 

 William Yarrell, Esq., in the Chair, 



Mr. Ogilby read a paper, entitled " Observations on the oppos- 

 able power of the Thumb in certain Mammals, considered as a zoolo- 

 gical character : and on the Natūrai Affinities which subsist between 

 the Bimana, Ouadmmana, and Pedimana." 



In the summer of 1829 it occurredto Mr. Ogilby to observe that 

 two li\'ing individuals of Mycetes Seniculus did not use the extre- 

 mities of their anterior limbs for the purpose of holding objects be- 

 tween the fingers and thumb, as is common among the Cįuadnnnana ; 

 and he ascertained also, on closer exaniination, that the thumb, as 

 it has generally been considered, was not in these animals opposable 

 to the other fingers, but originated in the šame line -nith them. 

 Struck with the apparent singularity of the fact, he \vas induced to 

 pay particular attention to all the other animals, referred bj' zoolo- 

 gists to the Quadi-UTnanous family. to which he had access ; and the 

 continued observation of more than six years has assured him that 

 the non-opposable character of the inner finger of the anterior ex- 

 tremities, which he first observed in the specimens referred to, is 

 not confined to the genus Mycetes, but extends throughout the 

 whole of the genera of the South American Monkeys, individuals of 

 all of which have now been seen by him in the livdng statė. In 

 none of them, conseąuently, does a true thumb exist on the ante- 

 rior limbs : and as a further conseąuence it follows, that the whole 

 of them have hitherto been incorrectly referred to the Quadnimana 

 by zoologists generally. There is a solitaiy exception among de- 

 scriptive ^vriters from this mode of viewing the subject, D'Azara 

 (as Mr. Ogilby has very recently become aware) having spoken of 

 the anterior extremities of some of the species observed by him as 

 having five fingers originating on the šame line witli each other : 

 but the statements of that original observer appear, in this respect, 

 either to have been unnoticed by other authors or to have been 

 passed by as undesen-ing of attention, so entirely Tvere they at va- 

 riance with the preconceived notions of all. 



Of the eight natūrai genera which include all the knoMTi Monkeys 

 of the Westem Hemisphere, one, Ateles, is entirely destitute of a 

 thumb, or has that member existing only in a rudimentary form be- 

 neath the skin. In five others, Mycetes, Lagothrix, Aottts, Pitkeda, 

 and HapaJe, the anterior thumbs (using the ordinary expression for 

 them) are placed absolutely on the šame line with the other fingers, 

 are of the šame form ■vvith them, act invariably in the šame direc- 

 tion, and are totaJly incapable of being opposed to them. In the tvvo 

 remaining genera, Cebus and CaUithrix, the extremities of tlie an- 

 terior hmbs have a greater extemal resemblance to the hands of Man 

 and of the Monkeys of the 01d World : the intemal finger is placed 



No. XXXIX. — Proceedi.vrs of the Zoological Suciety. 



