296 THE RABBIT 



(ii) The periotics (around the internal ear), between the occipital segment 

 and the squamosals. Each periotic has an outer dense petrous portion 

 and an inner porous mastoid portion. 



(iii) The tympanies,* on the outer sides of the periotics. Each consists of 

 an upper funnel-like part (the bony wall of the external auditory 

 meatus), and a bulbous base, the t}rmpanic bulla, which encloses the 

 tympanic cavity containing the three ear ossicles. 



(iv) The squamosals,* connected with the auditory capsules, a pair of bony 

 plates situated in front of the periotics below the parietals and articu- 

 lating with the parietals, frontals, orbito-sphenoids, and ali-sphenoids. 

 Each sends forwards and outwards a stout zygomatic process, which 

 has ventrally the articular surface for the lower jaw and which 

 articulates with the jugal bone to form the zygomatic arch. 



The upper jaw consists of the following bones : — 



(i) The premaxillae,* a pair of bones forming the anterior part of the upper 

 jaw, articulating with each other in front and with the maxillae behind 

 and sending a long, slender nasal process backwards between the 

 nasal bone and the maxilla. The palatal processes of the premaxillae 

 on the roof of the mouth form the incomplete anterior portion of the 

 hard palate. 



(ii) The maxillae,* a pair of large irregular bones. From each a zygomatic 

 process is given off ; it is prolonged upwards as the orbital process, 

 and outwards it fuses with the jugal, forming the boundary of the orbit 

 anteriorly. The zygomatic process of the squamosal, fused to the 

 other end of the jugal, completes the zygomatic arch. The body or 

 alveolar portion of each maxilla is produced inwards ; and these parts 

 meeting together in the middle line of the roof of the mouth, thus form 

 a part of the posterior portion of the hard palate. 



(iii) The pterygoids,* a pair of thin vertical plates of bone attached to the 

 skull at the junction of the ali-sphenoids with the basi-sphenoid. 



(iv) The palatines,* a larger pair of plates, each consisting of a vertical 

 portion attached above to the ventral side of the presphenoid and 

 behind to the pterygoid, and a horizontal portion which meets its 

 fellow in the middle line in the roof of the mouth, thus forming a part 

 of the posterior portion of the hard palate. 



(v) The jugals or malars,* a pair of flattened bar-like bones. Each one is 

 connected with the zygomatic processes of the maxilla and squamosal, 

 and forms the median and longest portion of the zygomatic arch. 



Note the two incisor teeth on each premaxilla, and the three premolars and 

 three molars on each maxilla. 



The lower jaw or mandible has the following parts : — 



A pair of bones, the rami of the mandible, united in front. Each ramus 

 represents a single bone, the dentarjs and is made up of a stout horizontal 

 portion bearing a single incisor, two premolar and three molar teeth, and a 

 thinner posterior portion with a dorsal or coronoid process and a ventral 

 posterior part or angular process. The ascending portion of the ramus ends in 



