GLIRES 



483 



f*t.¥>.s- 



Fig. 375. — The bones of the hard palate and upper permanent teeth of man. 



a.p.f., Anterior palatine foramen, or incisive foramen ; c, canine tooth ; i., incisor teeth ; m., molar teeth ; 

 m.p.s., suture b-tween maxillary and palatine bones ; p.p./., posterior palatine foramen ; pm., pre- 

 molar teeth ; s.n.p., posterior nasal spine. 



GLIRES 



The second cohort of the placental mammals, called Glires, is 

 coterminous with the old order Rodentia. They retain a number 

 of primitive features, such as a small brain, five fingers and toes 

 and plantigrade gait, and separate radius and ulna. Their chief 

 adaptive features are the development of the teeth and jaws for 

 gnawing, and an extreme fecundity, which is achieved partly 

 by large litters and many of them in a year, and partly by an early 

 sexual maturity. The result is that they can and do increase 

 rapidly in numbers, but that the population becomes too large 

 to be maintained and is drastically reduced by disease or other 

 means. The result is cyclical fluctuation in abundance, the period 

 being fairly constant for each species. Both in numbers of species 

 and numbers of individuals the Glires exceed all other mammals. 

 Fortunately they are always small. They were long kept together 

 in a single order, but it is now considered that the two obvious 

 subdivisions have only a superficial resemblance and they are 

 therefore termed Orders, the Lagomorpha and the Rodentia in 

 the strict sense. Even the placing of these in a single cohort 

 is more a matter of convenience than of reason ; both orders 

 are certainly well isolated from all other mammals. 



