352 STRUCTURE OF THE VERTEBRATES 



present primitive stock) nocturnal eyes. The brain case is not 

 highly expanded, the cerebellar region being relatively greatest, 

 and has not grown forward over the long primitive face. The 

 teeth are almost like those of the insectivores. 



The Old World monkeys appear first in the Oligocene strata 

 of Egypt and evidently gave rise to the higher primates. They 

 soon became adapted for sitting upright in a tree; the brain 

 enlarged; the dental formula was typical for the recent group 

 (two premolars and three molars) ; and the foreleg became dis- 

 tinctly arm-like. The adaptive radiations which followed led 

 to the development of many specialized forms: (1) completely 

 arboreal types lacking thumbs, the specialization appearing 

 independently in both Africa and South America; (2) long- 

 tailed forms with short faces; (3) the baboons and mandrills 

 with long, dog-like heads and brilliant coloration, the most 

 aberrant of the primates; and (4) the genera which are more 

 like the human in structure. 



The anthropoid stem appears to have split from the ancestral 

 type in the Oligocene period. Dryopithecus, found in Europe, 

 is sufficiently generalized in its structure that it could easily 

 have been the stem from which the anthropoids and man 

 evolved. The skeleton shows that the line leading toward the 

 anthropoids and man was becoming less arboreal during early 

 Miocene times. 



A skull found in Southern Africa in recent years adds fur- 

 ther evidence to the relationships between the African anthro- 

 poids and man. This primate, Australopithecus, is evidently a 

 young, highly developed anthropoid, but an animal which has 

 more human characteristics than either the chimpanzee or the 

 gorilla. It probably lies near the common ancestral stem, but 

 with the group which eventually gave rise to man. 



The most famous human fossil known is that discovered in 

 Java by Dubois, Pithecanthropus erectus. Since its discovery in 

 1891 it has been extensively studied and shown to be definitely 

 human, of a very primitive type. The skull cap shows a cranial 

 capacity of only a few ounces less than that of the minimum 

 for the normal human, and although the brain was extremely 

 primitive it had evolved more than halfway between the upper 

 limit for the gorilla and the lower limit for the recent human. 



