156 THE SKULL. [chap. 



development in some of the Porcupines (Hystrix), where 

 nearly all the bones of the upper part of the cranium are 

 expanded by great air sinuses formed within their walls. In 

 the Hare, and some others, the two optic foramina in the 

 orbitosphenoids are confluent ; and in consequence, in the 

 (dried skull, there is a direct aperture of communication 

 /between the orbits above the craniofacial axis. 



The supraoccipital is more or less vertical, and does 

 not extend far on to the upper surface of the cranium. 

 There is often a distinct interparietal. There are generally 

 moderately developed paroccipital processes, which in the 

 Capybara (Hydrochcerus) are of great length, curving for- 

 wards and compressed laterally. They are. also very large 

 in the Coypu [Myopotamus). 



The parietals are moderate or small. The frontals, except 

 in the Squirrels, Marmots, and Hares, have little more than 

 a rudiment of a postorbital process, and there is never any 

 marked corresponding process arising from the zygoma, so 

 that the orbit is perfectly continuous with the temporal fossa. 

 The latter is always very small. 



In a very remarkable East African genus, Lop/iiomys, a 



/broad bony lamella extends from the upper part of the 



) parietal outwards and downwards to join a similar ascending 



( plate from the malar, and so forming an arched covering 



to the temporal fossa, an arrangement unknown in any 



other mammal, but recalling that met with in the tortoises. 



The whole of the superior surface of the cranial bones of 



' this animal are covered with miliary granulations, disposed 



with perfect regularity and symmetry. 1 



The nasals are both long and wide, and generally extend 

 so far forwards as to make the anterior nares quite terminal 

 and vertical, or even with a downward inclination. In 

 1 See A. Milne-Edwards, Nouv. Archiv. du Museum, iii. 1867. 



