ME. ST. GEOEGE MIYAET ON THE SKELETON OF THE PEIMATES. 
313 
and it is very marked in Ateles, in spite of the rudimentary condition of the pollex. On 
the other hand, it is not distinctly marked in Indris, and it is small in the Nycticebinse. 
The groove for the radial extensors I have found to be sometimes double in Macacus, 
Ateles, and some Nycticebinse. 
That for the extensor secundi internodii pollicis I have only found distinct in Man, 
the Chimpanzee, and Orang. 
The groove for the extensor communis digitorum is smaller relatively in the lower 
Simiidse than in Man and the Simiinee. It is small also in Ateles and Mycetes (thus 
differing from Hylobates), and generally in the Lemuroidea. 
Ulna. 
In absolute and relative length this bone varies almost as does the radius, being, 
however, always somewhat longer. 
It is thickest (in the shaft), in proportion to its length, in Cynocephalus, most 
slender in Hylobates and Indris. 
The bone is much curved in the Chimpanzee, less so in the Gorilla, Orang, and still 
less so in Man. It is generally more curved than in Man in the Cebinse*, but straighter 
than in him in the other Cebidse. It is sometimes very straight in Hylobates and the 
lower Simiidse ; also in Loris and Tarsius, but in the other Lemuroidea it is much as in 
Man. 
The greater sigmoid cavity is exceptionally broad, in proportion to its length, in Man, 
Troglodytes, and Simia ; in the other forms it is narrower, and turned more outwards, 
towards the radius. 
The lesser sigmoid cavity looks outwards in Man, Troglodytes, Simia, and the 
Nycticebinee. It looks more forwards in the lower Simiidee. 
The coronoid process (and surface for the insertion of the brachialis anticus ) is at its 
maximum of breadth in Man. In Troglodytes and Simia this part is already narrower 
than in him, and more excavated. In the Hylobates it is still narrower, and yet more 
so in the lower Simiidee, the Cebidse, Hapale, and the Lemuroidea, especially in some 
of the Nycticebinse. 
The olecranon is broadest in Man, Simia, and Troglodytes. In Hylobates it is still 
very like that of Man ; but in the lower Simiidse it is much longer, extending further up 
(i. e. in the direction of the bone’s length) beyond the sigmoid cavity, being at its 
maximum of development in this respect in Cynocephalus. The Cebidse, including 
Ateles, resemble in this the lower Simiidse, and the olecranon is very long in Mycetes. 
It is also long in Lemur and Galago, Tarsius, and Cheiromys, but is less so in Indris 
(Plate XII. fig. 7) and the Nycticebinee. 
There is a distinction between the anterior and inner surfaces of this bone in Man, 
Troglodytes, and Simia ; but thence, downwards through the order, there may be said 
to be but one surface answering to these two of Man and the highest Apes. 
* Its curved condition in Cebus is noticed by De Beainville, loe. cit p. 8. 
