302 ZOOLOGY. 



bling squirrels and bats, i.e., the lemurs, and comprising 

 monkeys, apes, and ending with man. In all the Primates, 

 the legs are exserted almost or quite free from the trunk, 

 with the great toe of the hind foot usually enlarged and 

 opposable to the others; nails, except in the marmosets, 

 replace claws. 



The hemispheres of the brain may in the lower forms be 

 quite smooth, but in all there is a well-developed "calca- 

 rine furrow/' giving rise to a " hippocampus minor" within 

 the posterior cornu of the ventricle, by which the posterior 

 lobe of the cerebrum is traversed (Flower). The collar- 

 bones (clavicles) are for the first time in the series well de- 

 veloped. The placenta is also different in shape from that 

 of other mammals, being round, disk, or cake-like. 



The Primates are divided into two sub-orders, i.e., the 

 ProsimicB and Anthropoidea. The former group embraces 

 the lemurs, which vary in size from that of a rabbit to a 

 large monkey. They are covered, the face as well as the 

 rest of the body, with a dense fur; walk on all-fours, usu- 

 ally have long tails, though the lori is tailless, while the 

 fore limbs are shorter than the hind limbs. The skull is 

 small, flattened and narrow in front; the brain-cavity small 

 in proportion to the rest of the skull, i.e., the face com- 

 pared with the monkeys. The cerebral hemispheres are 

 small and flattened, the frontal lobes narrow and pointed, 

 and behind they only slightly cover the cerebellum. 



By some authors the lemurs are separated from the Pri- 

 mates, the Insedivora and Cheiroptera being placed between 

 the ProsimicB and the other Primates. They have charac- 

 ters in which they resemble Insedivora, Rodentia, and 

 Camivora, but the weight of organization, or the sum of 

 their characters, ally them nearest to the monkeys. They 

 are therefore essentially a generalized or ancestral type. 

 Eecent discoveries have led to the hypothesis, that from 

 still older, more generalized types four lines of develop- 

 ment, respectively culminating in the typical Carnivores, 

 Cetaceans, lemurs, and monkeys, have taken their origin. 



