COMPARATIVE ANATOMY 21 



5. Nasals. — The two nasals meet in the median line and 

 extend from the frontals to the nares. 



6. Premaxillaries.— These are paired bones forming with 

 the nasals the borders of the nasal opening. They form the 

 anterior portion of the upper jaw and bear on each side three 

 incisor teeth. 



7. Maxillaries. — The paired maxillary bones form the 

 remainder of the upper jaw on each side, and the anterior and 

 lateral portions of the roof of the mouth. Each bears one canine 

 tooth, three premolars, and one molar. The maxillaries extend 

 dorsally to meet the nasals and frontals and the median surface 

 of each maxillary forms a large part of the lateral wall of the 

 nasal cavity. Dorsal to the premolars the maxillary has a 

 projection, the malar process or zygomatic process for articulation 

 with the malar bone. The large hole in the maxillary is the 

 infra-orbital foramen for passage of a nerve and a blood vessel. 



8. Malars. — The malars are paired. Each extends pos- 

 teriorly from the malar process of the maxillary bone and forms 

 the major portion of the zygomatic arch. Each overlaps and 

 articulates with the zygomatic process of the temporal bone. A 

 post-orbital process extends toward and frequently unites with 

 the similar process of the frontal. 



9. Lachrymals. — These thin bony plates in the anterior 

 wall of each orbit frequently fall out in dry skulls. On the 

 anterior border of each is the opening of the lachrymal canal 

 (tear duct), which connects with the nasal cavity. 



10. Temporals. — The temporals are also paired, lying ven- 

 tral to the lateral borders of the parietals, and forming a large 

 part of the lateral wall of the cranium posterior to the orbit. 

 The temporal bone of mammals represents a fusion of a number 

 of bones which are separate in lower forms. The resulting 

 complicated structure is conveniently divided into four regions, 

 corresponding in a general way to the parts from which the 

 temporal has developed: the squamous, the mastoid, the petrous, 

 and the tympanic. 



The squamous region is the thin plate adjoining the parietal. 

 Anteriorly it gives off a long zygomatic process, which joins the 

 malar and forms the posterior portion of the zygomatic arch. 

 On the ventral surface of this process, near its base, is the 



