THE INTERPARIETAL BONE 



53 



each lateral mass, and one for the perpendicular plate; from the latter ossification 

 extends into the cribriform plate. At birth the perpendicular and cribriform plates 

 are entirely cartilaginous. By the time ossification is complete the ethmoid has 

 united with surrounding bones to such an extent that it cannot be separated intact 

 for study. 



Occipital crest 



Supraoccipital 



Temporal crest -^ /It 



Zygomatic process 



Supraorbital foramen 



Orbit 



Malar bone 

 Facial crest 



Infraorbital foramen — - 



I 



Coronoid process 



Nasal process of premaxilla 



Canine tooth 

 Foramen incisivum 



Fig. 30. — Skull of Horse, Dors.a.l View. 

 12, Supraorbital process; 14, parietal bone; 14', external sagittal crest; 15, frontal bone; 15', frontal 

 crest; 21, lacrimal bone; 22, nasal bone; 26, maxilla; 24, incisor teeth. (After Ellenberger-Baum, Anat. fur 

 Kiinstler.) 



The Interparietal Bone 



This bone (Os interparietale) is centrally placed between the squamous part 

 of the occipital and the parietal bones. It is usually described as a single bone, 

 although it ossifies from two chief lateral centers, and is sometimes distinctly 

 paired in skulls of young foals. 



The external surface (Facies externa) is quadrilateral and is flat and 



