32 Professor Owen on the [Feb. 9, 



ment of the intermaxillary bone — that part being more produced in 

 the orang-outang, giving it a less open facial angle ; it differs also in 

 the form of the orbits, which in the orang-outang are a full oval, but 

 in the gorilla square-shaped, more nearly approaching those in the 

 human species ; it differs likewise in significant modifications of the 

 base of the skull, as, for example, in tlie greater depth of the glenoid 

 cavity, which joint, instead of being defended by merely the post- 

 glenoid process in the inferior quadrumana, is now defended by a 

 ridge developed from the tympanic bone, which ridge corresponds 

 with the vaginal process in the human subject. In the conformation 

 of the grinding surface of the teeth there is also a marked difference, 

 which brings this great ape of Africa more nearly to the human 

 subject, in reference to that character, than any other known species 

 of the quadrumanous order. The characteristic of the grinding 

 surface of the molar teeth in man, as may be seen in almost all 

 varieties of the human species, is, that the four tubercles on the 

 grinding surface are united by a ridge describing a strong sigmoid 

 curvature. This is repeated in the gorilla, which also presents 

 another important approach to the human subject in the commence- 

 ment of a projection of the nasal bone. Like the chimpanzee, the 

 superior extremities are longer than the lower ones ; and the inner- 

 most digit of the foot is converted into a powerful thumb. 



Having premised this account of the mature characters of the 

 different species of orangs and chimpanzees, the lecturer next pro- 

 ceeded to contrast their structure with that of man. With regard 

 to the dentition of these anthropoid apes, the number and kinds of 

 the teeth, like those of all the quadrumana of the old world, 

 correspond with those in the human subject ; but all these apes 

 differ in the larger proportionate size of the eanine teeth, which 

 necessitates a certain break in the series, in order that the prolonged 

 points of the canine teeth may pass into their place when the mouth 

 is completely closed. In addition to the larger proportionate size of 

 the incisors and canines, the bicuspids in both jaws are implanted 

 by three distinct fangs — two external and one internal : in the 

 human species, the bicuspids are implanted by one external and one 

 internal fang : in the highest races of man these two fangs are often 

 connate ; very rarely is the external fang divided, as it constantly 

 is in all the species of the orang and the chimpanzee. 



With regard to the catarrhine, or old-world quadrumana, the 

 number of milk teeth is twenty, as in the human subject. But both 

 chimpanzees and orangs differ from man in the order of develop- 

 ment of the permanent series of teeth : the second true molar 

 comes into place before either of the bicuspids have cut the gum, 

 and the last molar is acquired before the permanent canine. We 

 may well suppose that the larger grinders are earlier required by 

 the frugivorous apes than by tlie omnivorous human race ; and 

 one condition of the earlier development of the canines and 

 bicuspids in man, may be their smaller relative size as compared 

 9^ 



