68 EQUINE ANATOMY. 



Internal face has digital marks, and the internal parietal 

 protuberance. The borders are dirided into superior, 

 inferior and lateral, and are articular. Development : 

 three nuclei of ossification. 



Fkontal. — Division : Two faces and four borders. 

 External face divided into three parts, shows the 

 orbital process, the supra-orbital foramen, and a cavity 

 for the internal oblique muscle of the eye. Internal 

 face is also divided into two parts, superiorly has a 

 median crest and a notch for the sphenoid ; inferiorly 

 it opens in the frontal sinuses. Borders : the superior 

 articulates with the parietal, the inferior with the nasal 

 and lachrymal, the lateral has a superior notch for the 

 sphenoid, and one inferior for the orbital foramen. 

 Development : two nuclei of ossification. 



Ethmoid. — Division : Perpendicular lamina and 

 two lateral masses. Perpendicular lamina : Two 

 faces, flat ; four borders : the superior forms the crista- 

 galli process ; the inferior, continuous with the septum 

 nasi ; the anterior, with the septum of the frontal 

 sinuses ; the posterior, with that of the sphenoidal 

 sinuses. Lateral masses. — Division : Middle part, base 

 and apex. The external surface of the first is divided 

 into external and internal portions; the internal sur- 

 face forms the cavities of the volutes. Tlie base has 

 the cribriform plate and the ethmoidal fossa. The 



