THE SKELETON 35 



plates of the palatine, maxilla, and premaxilla form the floor 

 of the nasal cavity and as well, the hard palate or roof of the 

 mouth. The interior of the nasal cavity is occupied by the 

 ethmoid. A portion of the ethmoid sometimes forms j)art of 

 the inner wall of the orbit back of the lachrymal bone and is 

 known as the os planum. 



The auditory capsule is enclosed in the temporal bone. The 

 temporal bone is formed by the fusion of the squam^ous, petrous, 

 and tympanic bones, which form, respectively, the squamous, 

 petrous, and tympanic portions of the bone. 



The optic capsule is the largest and most conspicuous of 

 the sense capsules. With exception of the malar all bones 

 connected with it have already been noted. 



It is thus seen that each of the three posterior cranial rings 

 is related to an important sense organ. The olfactory organ is 

 anterior to the frontal segment, the organ of sight lies between 

 the frontal and parietal, and the organ of hearing, between the 

 parietal and occipital segments. 



These anatomical relations kept in mind will serve to orient 

 the several features of the complex bony skeleton of the head. 

 We shall now examine the skull from its several aspects. 



As seen from the dorsal aspect (Fig. 17) the general outline 

 of the skull is oval. It presents a median somewhat ])ear- 

 shaped portion and the lateral expanded zygomatic arches. The 

 surface is smooth and unevenly convex in both directions. The 

 anterior half is flattened and triangular in shape. I'he pos- 

 terior half is very convex and circular. The antero-posterior 

 midline is marked by the sagittal suture, which divides the 

 surface into two symmetrical halves. The sagittal suture is 

 crossed transversely midway back by the fronto-parietal or 

 coronal suture. The postero-lateral angles of the anterior moiety 

 is projected outward and downward as the fronto-postorhital 

 processes. These approach similar projections from below and 

 form the posterior bony rim of the orbits. The orbit of the 

 cat is not entirely closed behind, differing in that respect from 



