ME. ST. GEOEGE MIVAET ON" THE SKELETON OE THE PEIMATES. 
307 
being only about one-twentieth of its length (Plate XII. fig. 3). It is also narrow in 
proportion to its length in Hylobates and Simia. 
It is very broad relatively in Troglodytes, the Cynopithecinse, Lemur, Perodicticus, 
Arctocebus, Tarsius, and Cheiromys, where its thickness near the middle is about equal 
to one-tenth of its length. 
The amount of expansion of the acromial end is liable to considerable individual varia- 
tion, but it appears to be greatest in Man, the Simiinae, and Ateles ; on the other hand, 
it is remarkably small in the Nycticebinse. 
The expansion of the sternal end is subject to even greater variation. In Simia, My- 
cetes, the lower Cebidae, and Lemuroidea it often exceeds the acromial end in breadth. 
A sigmoid vertical (in Man horizontal) curvature is not generally well marked ; it is 
most so in Man, and next perhaps in Ateles, some other Cebidae, and the Nycticebinae. 
The sternal vertical (in Man horizontal) curvature, concave backwards, is so extended 
in some forms as almost to obliterate the acromial curve. This is the case in many 
Lemuroidea and, sometimes at least, in Hylobates. On the other hand, the sternal cur- 
vature is much less than in Man, even in Troglodytes and Simia, and in the lowest Si- 
miidae it disappears, as also in Indris. 
The acromial vertical (in Man horizontal) curvature, concave forwards, is more con- 
stant, only disappearing in those forms, above referred to, in which the sternal curvature 
is so extensive. It is very strongly marked in the Nycticebime and in the Indrisinae, 
but in no other Lemuroidea. 
The antero-posterior (in Man vertical) curvature is generally slight ; most marked 
perhaps sometimes in Ateles. It is this curvature which gives a sigmoid appearance to 
the clavicle in Lemur and Cheiromys. 
The tubercle and ridge for the attachment of the coraco-clavicular ligament are gene- 
rally at the margin of the bone, or nearer to it than in Man. 
Very commonly there is no distinct process or ridge other than the superior (in Man 
posterior) margin of a subclavicular fossa, as is the case in the lower Simiidse. There is, 
however, a marked tubercle in Troglodytes, and a large process in Simia and in Ateles 
and Logothrix. It is faintly marked in Mycetes and Indris. 
The acromial end of the bone has its anterior (in Man superior) surface almost always 
more or less convex, but there is a marked concavity there in Hylobates. 
The posterior (in Man under) surface of the acromial end is convex and roughened in 
Man *, and more or less so in the Simiinae ; in all the others, except the Nycticebinae, it 
is concave, and in the lower Simiidse this concavity becomes a very deep fossa. In all 
the Simiidse other than the Simiinae this part is close to the acromial end of the bone, 
but in the Simiinse the clavicle is more prolonged outwards, and most so in the Sia- 
mang. In Man, however, this prolongation is carried still further. 
Rarely, as in Simia, there is a very prominent deltoidal ridge. Sometimes a distinct 
* In a skeleton of a male African negro (No. 5372 in the Museum of the College of Surgeons) there is a 
distinct, though small, subacromial fossa. This is wanting in all the Boschismen. 
MDCCCLXVII. 2 U 
