The: Bones of the Skull. 95 



14. THE ZYGOMATIC BONE. 



The zygomatic bone (os zygomaticum) is a separate element only in 

 very young animals. In the adult it is fused anteriorly with the zygo- 

 matic process of the maxilla, the position of the original suture being 

 roughly identifiable as the point where the free horizontal portion of 

 the zygomatic arch arises from the transverse zygomatic process. It 

 forms an almost sagittal plate of bone bridging the orbit and serving for 

 the attachment of the masseter muscle of the mandible. Its dorsal 

 margin forms posteriorly a smooth, horizontal articulation with the 

 zygomatic process of the squamosal, the end of the bone projecting con- 

 siderably behind the articulation. 



15. THE NASAL BONE. 



The nasal bone (os nasale) is a thin, elongated bone forming the roof 

 of the nasal fossa, and, in conjunction with its fellow of the opposite side, 

 the dorsal boundary of the piriform aperture. It is loosely articulated 

 with the maxilla and with the bone of the opposite side by smooth 

 (harmonic) sutures. The medial margin is supported by the dorsal edge 

 of the nasal septum. The internal surface bears the nasoturbinal scroll. 



16. THE VOMER. 



The vomer is the median, somewhat sickle-shaped, vertical plate of 

 bone separating the ventral portions of the nasal fossae. It is visible 

 from the palatal surface through the incisive foramina, but its extent is 

 best shown in the divided skull. It forms a support for the ventral 

 border of the nasal septum, and its posterior portion bears a shelf-like 

 projection, the ala vomeris, which assists in the support of the ethmo- 

 turbinal. 



17. THE LACRIMAL BONE. 



The lacrimal bone (os lacrimale) is a small element lying in the anterior 

 wall of the orbit. It is loosely articulated with the surrounding bones, 

 and in the dried skull is frequently missing unless care has been taken 

 to keep it in place. It consists of a basal portion, somewhat rectangular 

 on its orbital surface, and of two processes, namely, the subcutaneous 

 process and the hamulus lacrimalis. The subcutaneous process is the 

 prominent hook-like projecting laterad beyond the orbital rim. 

 The hamulus lacrimalis is a small process, directed toward the nasal 

 cavity. It bears a groove which, in association with a corresponding 

 groove of the maxillary bone, forms the first portion of the nasolacrimal 

 canal. 



18. THE PALATINE BONE. 



The palatine bone (os palatinum) forms the posterior portion of the 

 palatine bridge and the major portion of the lateral wall of the naso- 

 pharynx. It consists of two portions — horizontal, and perpendicu- 

 lar. The horizontal portion (pars horizontalis) is that lying in the plane 



