22 ANATOMY OF THE RAT 



maxillary bone. The process is attached to the vomer 

 along the median suture of the hard palate. The vomer 

 forms part of the nasal septum. The elongated maxillo- 

 turhinal hone attaches to the inner surface of the premax- 

 illary. It lies lengthwise of the nasal cavity and extends 

 upward from its line of attachment. 



Zygomatic Bone (Os Zygomaticum, Malar, Jugal) 



The zygomatic bone is a small bow-shaped element of 

 membranous origin, joining the zygomatic processes of the 

 maxillary and squamosal bones, thus completing the zygo- 

 matic arch. 



Vomer, or Ploughshare, Bone 



This fragile bone, which is membranous in origin, com- 

 prises the ventral portion of the nasal septum. It unites 

 ventrally with the premaxillary bone. It splits dorsally 

 into two longitudinal lamina, between which the cartilag- 

 inous part of the nasal septum is inserted. The posterior 

 part of the bone is without a ventral attachment. 



Nasal Bone (Os Nasale) 



The nasal bones roof the anterior nares and the nasal 

 cavity back to the frontal bones. The ventral surface is 

 concave, both the lateral and the median borders bearing 

 a flange. The median flanges of the two nasals unite to 

 form a ridge for the attachment of the nasal septum. The 

 lateral flange articulates with the frontal process of the 

 premaxillary bone. This flange is widest where the naso- 

 turhinal hone (see longitudinal section of the skull) is 

 attached to it. The line of attachment of the nasoturbinal 

 runs forward and medially from this point. The nasal 

 bone is a membrane bone. 



