THE SKELETON IN MAMMALIA. THE PES. 527 



In the INSECTIVORA the pes is almost always normal, and 

 provided with five digits. 



In the CHIROPTERA the pes is pentedactylate, and the digits 

 are terminated by long curved ungual phalanges. In some 

 genera the toes have only two phalanges. The calcaneum is 

 sometimes produced into a long slender process which helps 

 to support the membrane between the leg and the tail. 



Among the PRIMATES Man has the simplest form of pes. 

 In Man all five digits are well developed, the hallux being 

 considerably the largest. Sesamoid bones occur only under 

 the metatarso-phalangeal joint of the hallux. 



In the other Primates the internal cuneiform has a saddle- 

 shaped articulating surface for the hallux, which is obliquely 

 directed to the side of the foot and opposable to the other 

 digits. Two sesamoid bones are usually developed below 

 each metatarso-phalangeal joint, and one below the cuboid. 

 The second digit in Lemurs, and all except the hallux in 

 Ckiromys have pointed ungual phalanges ; in all other cases 

 the ungual phalanges are flat. In some of the Lemuroidea, 

 especially Tarsius, the tarsus is curiously modified by the 

 elongation of the calcaneum and navicular. 



