MAMMALIA. 275 



The facial part of the skull consists of the olfactory capsules 

 and jaws with associated parts. The olfactory capsules are 

 separated from the cranial cavity by the cribriform plate, from 

 which a vertical partition, bony behind (lamina perpendicular is), 

 cartilaginous in front (septum nasi), extends forwards and separates 

 the two capsules. This partition, together with the cribriform 

 plate, constitutes the mesethmoid, and its lower edge rests in a 

 deep furrow on the upper surface of the elongated vomer. 



The posterior wall of each capsule is partly formed by the small lachrymal, 

 which also makes up part of the anterior orbital wall. Its outer side is 

 deeply notched to transmit the lachrymal duct. The capsule is partly 

 roofed in behind by the frontal, but mainly by an elongated flat 'nasal, 

 which, with the premaxilla, largely bounds the external naris. The cap- 

 sular side-wall and floor are principally formed by the premaxilla and 

 maxilla. The nasal cavity contains the ethmo-turbinal behind and above, 

 a bone made up of thin lamellae disposed in a complex manner, which is 

 fused with the cribriform plate, and a similarly constructed but more 

 delicate maxillo-turbinal in front. From the nasal bone a delicate curved 

 fold, the naso-turbinal projects into the cavity. 



The margin of the upper jaw is formed by premaxillce and 

 maxillae. With the latter a zygomatic arch, running along the 

 lower side of the orbit, is connected externally, while internally 

 they come into relation with palatine and pterygoid bones. 



The premaxillce contain sockets for the upper incisor teeth. Each sends 

 an elongated nasal process upwards and backwards along the outer edge of 

 the nasal, a delicate palatine process backwards along the roof of the mouth, 

 and a stout maxillary process backwards and outwards to unite with the 

 maxilla. This is a large, extremely irregular bone that forms the jaw- 

 margin with the premaxilla, a little way behind which bone it dilates to 

 contain the sockets of the grinding teeth, and projects into the front part 

 of the orbit. The maxilla also forms a large part of the side-wall of the 

 nasal capsule, and in this region is very loose in texture. From its external 

 side, above the grinding teeth, a stout zygomatic process projects, which is 

 connected by the laterally flattened jugal with the zygomatic process of the 

 squamosal to make up the zygomatic arch, a bony bar forming the lower 

 boundary of the orbit. A small, horizontal palatine process runs from the 

 inner side of the maxilla, and unites with its fellow in the middle line to 

 form the front part of the bony palate, a transverse bridge of bone between 

 the first four grinding teeth of opposite sides. The inner surface of the 

 maxilla behind this is covered by the palatine, a thin vertical plate uniting 

 above with the orbital process of the pre-sphenoid. The bony palate is 

 completed behind by the horizontal palatine process of this bone which 

 unites with its fellow. The posterior nasal chamber is bounded laterally 

 by the palatines, which are united behind with the downward processes of 

 the ali-sphenoids, and with the pterygoids. Each pterygoid is a small 

 plate, behind, and in the same plane as the palatine. It is produced 

 below into a curved hamular process, and connected above with the junction, 

 between basi- and ali-sphenoids. 



