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 " ]iippoca7iipns minor^' within 
the posterior cornu of the ventricle, by wiiich 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 
Prosimm and Antliropoidea. 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 Prosimim and the other Primates, They have charac- 
ters in which they resemble Insedivora, Rodentia, and 
Carnivora, but the weight of organization, or the sum of 
their characters, ally them nearest to the monkeys. They 
are therefore essentially a genei'alized or ancestral type. 
Recent 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. 
