64 VERTEBRATE ANCESTORS OF MAN ? 



Monotreme, by the partitioning off of the cloaca into 

 rectum and urogenital sinus, by development of 

 a nipple to the lacteal gland, and by the partial retro- 

 gression of the clavicle. 



The most ancient of the marsupials lived in the 

 Jurassic period of the Mesolithic time — perhaps 

 already in the Triassic period ; and, during the Chalk 

 period, Placental Mammals began to be evolved 

 from them. 



The immediate stem-form of true apes and 

 through them of Man also comprised Prosimice or 

 half-apes, which originated probably in the beginning 

 of the Caenolithic or Tertiary time, from unknown 

 Marsupials related to the marsupial or Kangaroo 

 Rats, by the formation of a placental connection 

 between the mother and foetus, by the loss of the 

 marsupium or pouch, and the marsupial bones 

 supporting it, and by the greater development of the 

 corpus callasum of the brain. These our half-ape 

 ancestors probably possessed only a remote external 

 resemblance to the now existing short-footed half 

 apes, such as the lemur. 



Of the true apes which were evolved from the half 

 apes, the Catarhine or thin-nosed tribe of the old 

 world alone possesses a near blood relationship to 

 man. Our extinct ancient forefathers of this group 

 probably resembled the nosed ape of the present day, 

 though still covered with hair, and possessing a 

 long tail. They made their appearance about the 

 Eocaene period of the Tertiary time. 



