THE CHIMPANZEES AND ORANGS. 5 



wards and a little inwards, disappearing between the insertions of the latissimus dorsi and 

 pectoralis major about one-fourth down the bone. The shaft of the humerus, at first 

 cylindrical, shows a full elliptical section at the middle third of the bone, below which it 

 becomes more compressed through the outward extension of the supercondyloid ridges. 

 The ridge for the insertion of the pectoralis major (g) does not reach so low down propor- 

 tionally as in Man, but is more produced in the old male Gorilla. That [t) for the 

 latissimus dorsi and teres major forms a continuous rough ridge-like tract on the inner 

 or ulnar side of the upper third of the shaft ; beyond this the inner border of the shaft 

 descends as an obtuse ridge, becoming gradually sharper and more produced (a') to the 

 internal condyloid prominence. The outer part of the humeral shaft, in its upper third, 

 is smooth and rounded : near its middle third it shows a rough ridge for the attachment 

 of the external head of the triceps, below which the termination of the musculo-spirai 

 groove sweeps into the front view of the bone. At the fore part of the shaft, at and 

 below the middle of the bone, is the rough ridge-like tract for the insertion of the deltoid, 

 which must- operate with greater force on this long humerus by being implanted lower 

 down the bone than in Man. Below this ridge the fore part of the humerus is smooth, 

 and expands to the supracondyloid prominences : it is convex transversely at its middle 

 part, and concave between this and the supinator ridge, which is slightly bent forward. 

 Immediately above the distal articular surface are two depressions divided by a ridge 

 continued to the prominence between the radial and ulnar articulations ; the outer or 

 radial depression is the smaller and shallower ; the inner or ulnar one is larger : it 

 answers to the ' coronoid fossa ' in Man, but becomes a foramen (m) in full-grown Gorillas, 

 by absorption of the thin plate of bone dividing it from the anconeal fossa behind. Tlie 

 ectocondyloid prominence (fc, I) is more marked than in Man : the entocondyloid one (o) is 

 more produced, is angular, and compressed. The back part of the humerus shows, as 

 in Man, the musculo-spirai tract dividing the ridges for the external and internal heads 

 of the ' triceps extensor.' 



The configuration of the lower articular surface is closely similar to that in Man ; the 

 whole surface extends a little further below the condyloid prominences than in Man, 

 allowing to that extent a more free sweep of the fore-arm in flexion and extension, and 

 adding power to the leverage of the tendons inserted into the antibrachial bones. The 

 anconeal fossa (fig. 3, r) is more steeply, as well as deeply, excavated, and is of a sub- 

 triangular shape — besides becoming perforated, apparently as a rule, in the full-grown 

 male Gorilla. 



The humerus of the Chimpanzee (PL III. fig. 5) being more nearly the length of 

 that of Man (fig. 8), shows at once the greater proportional thickness of the bone, with a 

 smaller proportional articular head. I have not observed an instance of absorption of 

 the bone in any Chimpanzee between the anconeal and coronoid depressions. The ulnar 

 border of the ulnar trochlea {q, figs. 5 & 6) is more produced than in the Gorilla or in 

 Man. In other respects the humerus of the Chimpanzee closely resembles that of the 



