1865.] AXIAL SKELETON IN THE PRIMATES. 561 
the three is the homologue of the Human last lumbar vertebra*. In 
all the rest of the order, but one or two vertebrz articulate with the 
ilium, except sometimes in Afeles and in Indris, when three again 
share in that office. 
The Sacro-vertebral Angle.—In most Primates the sacrum and 
lumbar vertebrae appear (as far as one can judge from skeletons 
alone) to lie almost, or quite, in one line, so that the promontory is 
very slightly marked. Troglodytes presents in this respect a great 
contrast to the Human structure. In Simia the sacro-vertebral angle 
is rather more marked ; but sometimes in Cynocephalus it is so much 
so as almost to rival that of Man+. 
The same may be said of the concavity of the anterior surface of 
the sacrum, though this is subject to great individual variation. It 
is most marked in Man and the Cynocephalit ; and is more so in 
Simia§ than in Troglodytes. t 
The foramina vary greatly as to their relative size; but they ap- 
pear to be generally small in Troglodytes and Cynocephalus, and 
especially large in Man, Simia, Ateles, and Indris. 
The sacrum gradually tapers posteriorly in T’roglodytes and Simia, 
and more or less in Hylobates, also in the Nycticebine and in Indris, 
as well as in Man; but in very many forms of the order it is very 
wide at its anterior end (the transverse processes standing out like a 
pair of expanded wings), and then suddenly contracts, so that the 
transverse diameter of the third sacral vertebra is very much smaller 
than that of the first. This is especially the case in the Semnopithe- 
cine and Cynopithecine; in the Cebide generally, especially in 
A teles, the contraction is not so marked ; and in some, as also in many 
Lemuroidea, the transverse processes of the last sacral expand so as 
much more nearly to equal those of the first sacral vertebra in breadth. 
On account of these wing-like transverse processes, the breadth of 
the sacrum, in the Semnopithecine and Cynopithecine, generally 
exceeds its length. 
In Troglodytes, Simia, and Indris, and still more in the Nyctice- 
bine, the length exceeds the breadth. 
In the other genera these dimensions are generally more or less 
subequal. 
The spinous processes of the sacrum tend generally, with age, to 
run together and form a ridge. They are relatively least developed 
in Man, Simia, and Nycticebus. They are relatively larger in Loris, 
Tarsius, and Indris, attaining their maximum in Lagothriz ||. 
* Prof. Owen remarks that in a young Chimpanzee four vertebre articulate 
with the ilia. See Osteological Catalogue, vol. ii. p. 781, no. 5173. 
t See the skeleton of a Mandril (no. 4719) in the Museum of the Royal Col- 
lege of Surgeons; also Cynocephalus porcarius (no. 35d) in the British Museum. 
t It is strongly marked in Macacus speciosus (no. 1085 a in the British Mu- 
seum); and in Cynocephalus porcarius (no. 35d in the same collection) the 
transverse concavity of the sacrum is quite as great as in Man. 
§ Yet in the skeleton (nos. 43, 10, 2, 1) in the Osteological Collection of the 
British Museum the anterior surface of the sacrum is quite flat. In nos. 45, 10, 
2, 2, 3c, in the same collection the sacrum, on the other hand, is as concave an- 
tero-posteriorly and transversely as in Man. 
|| See the skeleton (no. A. 4718 @) in Museum of the Royal College of Surgeons. 
