190 MR. ST. G. MIVAET ON THE SKELETON OF THE PRIMATES. 



small and less marked than in Man. The surface which joins the unciforme (PI. XLII. 

 fig. 1 1 «) is strongly concavo-convex, and thus differs much from that in Man, and more 

 resembles the corresponding surface in Troglodytes. 



Pisiforme. (Plate XLII. figs. 12-14.) 

 The pisiforme of the Orang is much smaller, both absolutely and relatively, than 

 that of the Gorilla, and rather so than that of the Chimpanzee. It is always shorter 

 than in the last-named form, but yet, sometimes at least, differs from the pisiforme of 

 Man in being rather longer than broad. Its palmar surface (PI. XLII. fig. 13) is slightly 

 concave, and the bone projects downwards and ulnad near the unciforme process. 



Trapezium. (Plate XLII. figs. 15-20.) 



A striking difference exists between this bone in the Orang and the homologous one 

 of the Gorilla, inasmuch as the two large tuberous processes which exist in the latter 

 form' are here Avanting. It differs in the same way, though to a less degree, from the 

 Chimpanzee's ; and even as compared with Man's, the tubercle and groove of its palmar 

 aspect are somewhat less marked (PL XLII. fig. 17). 



The saddle-shaped surface for the metacarpal of the poUex is always (as also in 

 Troglodytes) much inferior in relative size to that of Man ; indeed, even in absolute 

 size, it is much inferior to his. There seems, however, to be considerable variation as 

 to the development of this part, as sometimes (PI. XLII. figs. 15 & 17, a) there is a very 

 distinct, though small, saddle (the surface being strongly concavo-convex), while in 

 other instances (PI. XLII. figs. 16 & 18, «) both concavity and convexity are very slight. 

 This variation is not confined to the Orang, but exists also in Troglodytes^. 



The surface for articulation with the metacarpal of the index (PI. XLII. fig. 17 5) is 

 generally very close to that for the metacarpal of the poUex — a circumstance in which 

 the Orang differs from Troglodytes, and resembles Man. The surface for the index 

 looks more palmad than in Man or Troglodytes, but, as in them, it is continuous with 

 the articular sm-faces for the trapezoides and scaphoides. The distal pair of these three 

 surfaces form a more marked angle with each other than in Man and Troglodytes; 

 while the proximal pair (for trapezoides and scaphoides) generally meet together at a 

 rather more open angle than in those genera. A sesamoid ^ bone is interposed between 

 the trapezium and the scaphoides on the radial side of those bones. 



' Owen, Trans. Zool. Soc. vol. v. p. 10. 



- The saddle is unusually little marked in the skeleton of a Gorilla, No. 5779 A, in the Museum of the Eoyal 

 College of Surgeons ; and in the detached and articulated manus of a Chimpanzee, No. 744, in the same collec- 

 tion, it is ahsolutely wanting. Professor Huxley has noticed the absence of a saddle-shaped surface in this 

 species. See 'Medical Times,' 186-t, vol. i. p. 42S. 



= Figured hy Prof. Vrolik in Todd's Cyclopaedia of Anat. and Phys. vol. iv. p. 204, fig. 124 )'. Mr. W. H. 

 Flower also informs me he observed its existence in the wiist of an adult male Orang in the Leyden Museum. 



