548 



ZOOLOGY 



SECT. 



The skull is elongated, 

 narrow in front, broader 

 and depressed behind. 

 The nasal cavities are 

 very large, especially in 

 the Porcupines, with air 

 sinuses in the upper 

 part. In some the optic 

 foramina fuse into one. 

 An interparietal is often 

 present. Paroccipital 

 processes are developed. 

 The orbit and the tem- 

 poral fossa are always 

 continuous. The nasal 

 bones are large, and the 

 nasal aj^ertures are ter- 

 minal or nearly so. The 

 premaxillse are always 

 very large. A remark- 

 able feature of the skull 

 is the presence in many 

 of a large opening cor- 

 responding to the infra- 

 orbital foramen. The 

 middle joart of the 

 zygoma is formed by the 

 jugal; the latter often 

 helps to bound the 

 glenoid cavity, as in the 

 Marsupials. The jDalate 

 is short, and the anterior 

 palatiiae foramina large. 

 The periotic and tym- 

 panic may become anky- 

 losed together, but not 

 to the neighbouring 

 bones. The coronoid 

 process of the mandible 

 is sometimes rudiment- 

 ary or absent ; the angle 

 is often produced into a 

 process. 



The scapula of the 

 Rodentia is generally 

 long and narrow. The 

 spine sometimes has a 



