COMPARATIVE ZOOLOGY. 



the bones remain separate in the former case, while 

 those of the chick become united together (anchylosed) 

 in the full-grown Bird; but many bones are present 

 in the Fish which have no representatives in the Bird. 

 The skull consists of the brain - case and the face. The 

 principal parts of the skull, as shown in the Dog's, are : 

 1. The occipital bone behind, enclosing a large hole, or 

 foramen magnum, on each side of which are rounded 

 prominences, called condyles, by which the skull articulates 

 with the first cervical vertebra. 2. The two parietal bones. 

 3. The two frontal bones. These five form the main walls 

 of the skull. 4. The sphenoid, on the floor of the skull in 

 front of the occipital, and consisting of six pieces. 5. The 

 two temporal bones, in which are situated the ears. In 

 Man each temporal is a single bone ; but in most animals 

 there are three or more the periodic, tympanic, and squa- 

 mosal. 6. The molars, or " cheek-bones," each of which 

 sends back a process to meet one from the squamosal, 

 forming the zygomatic arch. 7. The two nasals, forming 



Fi. 111. Skull of the Horse: 1, premaxillary bone; 2, upper incisors; 3, upper 

 canines ; 4, superior maxillary ; 5, infraorbital foramen ; 6, superior maxillary 

 spine ; 7, nasal bones ; 8, lachrymal ; 9, orbital cavity ; 10, lachrymal fossa ; 11, 

 malar; 12, upper molars; 13, frontal; 15, zygomatic arch; 16, parietal; 17, oc- 

 cipital protuberance ; 18, occipital crest ; 19, occipital condyles ; 20, styloid proc- 

 esses ; 21, petrous bone ; 22, basilar process ; 23, condyle of inferior maxillary ; 

 24, parietal crest ; 25, inferior maxillary ; 26, lower molars ; 27, anterior maxillary 

 foramen; 28, lower canines; 29, lower incisors. 



