144 
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 periotic, 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 
Fig. 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. 
