90 



THE SKELETON. 



Masseter muscle at its lower part. Of the four processes, the frontal is thick 

 and serrated, and articulates with the external angular process of the frontal 

 bone. To its orbital margin is attached the external tarsal ligament. The 

 orbital process is a thick and strong plate, Avhich projects backward from 

 the orbital margin of the bone. Its supero-internal surface, smooth and 

 concave, forms, by its junction with the orbital surface of the superior max- 

 illary bone and with the great wing of the sphenoid, part of the floor and 



Bristles passed 



through temporo- 



malar canals. 



With frontal. 



FIG. 55. -Left malar bone. Outer surface. 



PIG. 56. Left malar bone. Inner surface. 



outer wall of the orbit. Itsinfero-external surface, smooth and convex, forms 

 part of the zygomatic and temporal fossae. Its anterior margin is smooth and 

 rounded, forming part of the circumference of the orbit. Its superior margin, 

 rough and directed horizontally, articulates with the frontal bone behind the 

 external angular process. Its posterior margin is rough, and serrated for articu- 

 lation with the sphenoid ; internally it is also serrated for articulation with the 

 orbital surface of the superior maxillary. At the angle of junction of the sphe- 

 noidal and maxillary portions a short, rounded, non-articular margin is generally 

 seen ; this forms the anterior boundary of the spheno-maxillary fissure : occasion- 

 ally, no such non-articular margin exists, the fissure being completed by the direct 

 junction of the maxillary and sphenoid bones or by the interposition of a small 

 Wormian bone in the angular interval between them. On the upper surface of 

 the orbital process are seen the orifices of one or two temporo-malar canals ; one 

 of these usually opens on the posterior surface, the other (occasionally two) on 

 the facial surface : they transmit filaments (temporo-malar) of the orbital branch 

 of the superior maxillary nerve. The maxillary process is a rough, triangular 

 surface which articulates with the superior maxillary bone. The zygomatic pro- 

 cess, long, narrow, and serrated, articulates with the zygomatic process of the 

 temporal bone. Of the four borders, the antero-superior or orbital is smooth, 

 arched, and forms a considerable part of the circumference of the orbit. The 

 antero-inferior or maxillary border is rough, and bevelled at the expense of its 

 inner table, to articulate with the superior maxillary bone ; affording attachment 

 by its margin to the Levator labii superioris proprius, just at its point of junction 

 with the superior maxillary. The poster o-superior or temporal border, curved like 

 an italic letter/, is continuous above with the commencement of the temporal 

 ridge ; below, with the upper border of the zygomatic arch : it affords attachment 

 to the temporal fascia. The postero-inferior or zygomatic border is continuous 

 with the lower border of the zygomatic arch, affording attachment by its rough 

 edge to the Masseter muscle. 



Development. The malar bone ossifies generally from three centres, which 

 appear about the eighth week one for the zygomatic and two for the orbital 

 portion and fuse about the fifth month of foetal life. The bone is sometimes, 



