144 COMPARATIVE ZOOLOGY. 



from the fact that the bones remain separate in the for- 

 mer 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 bones 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 parietal. 3. The 

 frontal. These three form the main walls of the brain. 

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

 occipital, and consisting of six pieces. 5. The temporal, 

 in which is situated the ear. In Man this is one bone; 

 but in most animals there are three or more \\\Q periotie, 

 tympanic, and squamosal. 6. The malar, or " cheek-bone," 

 which sends back a process to meet one from the squamo- 

 sal, forming the zygomatic arch. 7. The nasal, or roof of 



FIG. lit. Sknll of the Horse: 1, premaxillary bone; 2, upper incisors; 3, upper 

 canines; 4, 'superior maxillary ; 5, infrnorbital 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; IT, oc- 

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

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

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

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



