298 AN INTRODUCTION TO ZOOLOGY 



other small apertures in both the palatine and maxilla in its neigh- 

 bourhood. A short way up the inner part of this main lateral 

 plate is given off a horizontal lamina which passes inwards, coming 

 in contact with the pre-sphenoid for a short distance and running 

 forward along the vomer for some way. This lamina forms the 

 dorso-lateral wall of the narial passage and separates it from the 

 orbit. More ventrally the main lateral plate gives off another 

 horizontal extension, the palatal process, which passes inwards and 

 forwards to the level of the fourth pre-molar, to join with its fellow 

 in the middle line and form, not only the ventral wall of the narial 

 passage, but also the posterior portion of the hard bony roof of the 

 mouth. The posterior nares therefore come to be bounded by the 

 palatine bones save for a small part on their dorsal side which is 

 filled in by the vomer. 



The maxillae are two large bones forming the major portion of 

 the lateral walls of the nasal capsules. The main mass or body of 

 the maxilla, termed the alveolar portion of the maxilla, completes 

 the ant ero- ventral wall of the orbit. Right in the front corner 

 it is perforated by the hinder opening of the infra-orbital canal, 

 through which the infra-orbital branch of the trigeminal nerve passes 

 to be distributed to the upper lip and vibrissae. It makes its exit 

 by the well-marked infra-orbital foramen just in front of and below 

 the orbit. From the body of the maxilla a frontal wing passes 

 upwards helping to form the roof of the nasal chamber and touching 

 the pre-maxillae, the nasal, the frontal and lachrymal bones. The 

 body also gives off a palatine lamella which joins with its fellow 

 in the mid- ventral line, constituting a large part of the hard palate. 

 At its hinder edge this plate of bone joins the palatine in a curved 

 suture running in a postero-lateral direction, and about half-way along 

 this suture occurs the posterior palatine foramen which, as already 

 noted, transmits the palatine nerves and arteries. The front end 

 of the palatine plate touches the pre-maxillae and forms the posterior 

 walls of the anterior palatine foramina. The junction of the body 

 of the maxilla and the palatine plate is termed the alveolar border, 

 since in it lie the alveoli of the canine, premolar and molar teeth. 

 From the postero-lateral border of the body of the maxilla a* 

 short pointed zygomatic process runs backwards, taking part in the 

 formation of the zygomatic arch. 



The pre-maxillse are the most anterior of the bones of the skull, 

 completing the front portion of the upper jaw, and they bear the 

 alveoli of the incisor teeth. They are joined laterally to the maxillae 

 and in the middle line with one another, thus forming the lower and 

 side borders of the anterior nares. Postero-dorsally each sends off 

 a long narrow tongue, the nasal process, which lies between the nasal 



