HEAD AND NECK OF THE HORSE 



153 



In the foal the cavity is very largely encroached upon by developing 

 teeth. In the young adult the lower part of the sinus contains the long, 



Ethmoid (labyrinth).. \= fc — 



Infraorbital canal. 

 Communication between sinuses. 



Maxillary sinus (posterior part) 



Maxillary sinus (anterior part). — ., 



Facial vessels. 



M. zygomaticus. 



M. nasolabialis. 



■= Concho-frontal sinus. 



N. infraorbitalis. 



___^_^>(_ / M. levator labu superions 



"^ '^ J oroDrius. 



Fig. 67. — Dorsal aspect of the concho-frontal and maxillary paranasal sinuses. 



embedded part of the cheek-teeth (covered by a thin layer of bone), 

 which become gradually shorter as age advances and the embedded part 

 of the teeth is extruded to compensate wear of the crown. 



