80 ZOOLOGY. 



divided into right and left passages by a middle partition, 

 the nasal septum. Outside the skull, on its wings, is a 

 flask-like bone, the btdla tympani or tympanic, protecting 

 the middle ear, and from above this there passes an arch, 

 the cheek-bone or zygoma, to the upper jaw, forming in 

 front the bony lower protection of the cavity containing the 

 eye, the orbit. The cheek arch, nasal passage, and jaws, 

 form collectively the " facial apparatus," as distinguished 

 from the cranium, and the whole skull is sometimes re- 

 ferred to as the " cranio-facial apparatus." Two eminences 

 for articulation with the atlas vertebra, the occipital con- 

 dyles, lie one on each side of the lower boundary of the 

 foramen magnum. 



16. The Brain-case. The floor of the cranium con- 

 sists of a series of cartilage-bones, the basi-occipital, basi- 

 sphenoid, pre-sphenoid, and ethmoid, the last of which 

 sends forward a median plate, the nasal septum already 

 mentioned. Like extended wings on either side of the 

 basi-occipital are the ex-occipitals. Similarly, the ali- 

 sphenoids are wings to the basi-, and the orbito-sphenoids 

 to the pre-sphenoid. Between the ex-occipital and ali- 

 sphenoid there is wedged in a bone, the periotic, containing 

 the internal ear. Above the foramen magnum the median 

 supra-occipital bone completes what may be called the 

 occipital ring, encircling the hind-brain. A. pair of parietals 

 come above the ali-sphenoids, and a pair of frontals above 

 the orbito-sphenoids. At the side the brain-case is still 

 incomplete, and here the squamosal enters into its wall. In 

 the external view (fig. 46) the tympanic bulla hides most of 

 the periotic bone from without. 



17. Upper Jaw and Palate. The outer edge of the 

 upper jaw and the cheek arch are made up of three paired 

 bones. First comes the premaxilla, containing, in the dog, 

 the three incisors of either side. Then comes the maxilla, 

 bearing the rest of the teeth a sabre-like canine, four pre- 

 molars and two molars. The jugal (also called malar) 

 reaches over from the maxilla to meet a zygomatie process 

 of the squamosal bone, the two forming the zygomatic arch. 



