THE RABBIT 



431 



^a». 



a horizontal partition, which separates an upper olfactory chamber from 

 a lower narial passage (p. 438). The outer sides and floor of the nasal 

 cavities are formed by the palatines, maxillae, and premaxillse presently 

 to be mentioned. The surface of the cavities is increased by three pairs 

 of thin and much-folded plates of cartilage bone known as the turbinate 

 which project into them from their walls. In the upper jaw there may 

 be recognised the same two series of bones as in the frog, the bones 

 being membrane bones. The pterygoids are two vertical plates of bone 

 attached to the lower side of the cranium at the junction of the basi- 

 sphenoid with the alisphenoid bones. 

 The palatine bones are a larger pair, 

 which consist each of a vertical por- 

 tion, attached above to the ventral 

 side of the presphenoid and behind 

 to the pterygoid, and a horizontal 

 portion which meets its fellow in the 

 median plane in the roof of the mouth 

 (p. 437). There is no quadrate bone. 

 The premaxillcB (ossa inciswd) are a 

 pair of bones which form the front of 

 the upper jaw and lodge the upper 

 pair of large gnawing teeth. It has 

 a nasal process, which passes back- 

 wards beside the nasal bone, and a 

 palatine process, which, like that of 

 the palatine bone, forms part of the 

 floor of the nasal passages. The 

 maxilla are two large irregular bones 

 which lie behind the premaxillae in 

 the facial region. The main part of 

 each bears the upper grinding teeth. 

 From this arises a palatine process, 

 like those of the premaxillae and pala- 

 tine bones, which it connects so as 

 to form a floor to the narial passages, 

 and a zygomatic process, which passes 

 outwards and backwards to form the 

 front part of the zygomatic arch. 

 The zygomatic processes of the maxilla 

 and squamosal are joined by a bar of 



bone known as the jugal or malar bone or zygoma. The lacrymah 

 are a pair of small bones which form part of the front walls of the 

 orbits, lying between the frontals and maxillse. 



The lower jaw is composed of membrane bone and 

 represents the dentaries of the frog, Meckel's cartilage, 

 which is present during development, being absent in the 

 adult. The jaw articulates, not with a quadrate but with 

 the squamosal bone (see p. 386 and Fig. 316). The hyoid 

 bone, lying in the floor of the hinder part of the mouth, 



FIG. 315. — A dorsal view of a 

 rabbit's skull. — From Thom- 

 son. 



S.O.-, Top of supraoccipital ; _ IJt., in- 

 terparietal ; T. , tympanic; Pa.^ 

 parietal ; Sg., squamosal ; Fr., 

 frontal ; /., jugal ; Na., nasal ; 

 Pmx., premaxilla. 



