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  the 
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  vertebra  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  V 
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. 
