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, 
ox foramen magnum , on each side of which are rounded 
prominences, called condyles , by which the skull articulates 
with the first cervical vertebra. 2. Th o 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—th operiotic, 
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 
Pig. 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. 
