
THE CHIMPANZEE AND ORANG UTAN. 355 
cession therefore takes place precisely as in the human jaw; but the permanent teeth 
are proportionally larger in the Chimpanzee, especially the incisors and laniaries. Hence, 
as the brain does not continue to expand after the development of the deciduous teeth, 
the increase of the skull is confined to the enlargement of the jaws, the widening of the 
zygomatic arches, the strengthening of the orbital buttresses, and the production of 
those muscular ridges which are indicative, as well of the force and development of the 
muscles immediately engaged in mastication, as of those which are inserted into tlie 
posterior part of the head to sustain the preponderating mass which now lies anterior 
to the occipital condyles. 
The amount of the changes, and the influences which have been concerned in their 
production, are shown in four views of the cranium of the young and old Chimpanzee 
subjoined to this paper (Plate LVI.) ; and the differences in other parts of the skeleton 
are given in the Table of admeasurements. ‘The bones of the young Chimpanzee, when 
the first permanent molaris is acquired, exhibit all the peculiarities of incomplete deve- 
lopment: the four elements of the occipital bone are separate ; the body of the atlas, 
like the basilar piece of the occiput, is detached from the processes which complete the 
ring ; the sacral vertebre are separated from one another and from the coccyx ; and the 
three portions of the os innominatum are at this time distinct. The coracoid bone is 
still joined by cartilage to the scapula; the epiphyses of the long bones are detached 
from the shafts, and are in part cartilaginous ; and the carpal and tarsal bones are but 
partially ossified ; the latter are especially imperfect as compared with those of the 
human subject at a corresponding period of dentition, and thus demonstrate the inferior 
importance of the lower extremities as means of support and progression in the Chim- 
panzee. 
The depth of the lower jaw being proportionally less than in the adult, the cavity of 
the thorax proportionally smaller, and the sternum in consequence less elevated, the 
distance between the latter and the chin is proportionally greater. The other differences 
in the relative magnitudes of the different parts of the skeleton have already been al- 
luded to in the description of that of the adult. 
§ 3. Osteology of the Orang Utan. 
The opportunity which the rare and interesting skeleton of the adult Chimpanzee in 
the possession of Mr. Walker has afforded of tracing the changes which the osseous 
structure of that species undergoes in its progress to the adult condition, induces me 
to review the question which I formerly brought under the notice of the Society! 
relating to the identity of the young Simia Satyrus with the great Pongo of Borneo, 
Pongo Wurmbii, Geoff., and to consider the osteological structure of the latter animal, 
here regarded as the adult Orang, with reference to its less powerful and more anthro- 
poid congener, the Chimpanzee. 
' Proceedings of the Committee of Science, part i. p. 9. 
