ANATOMY OF THE HORSE. 27 



formed into two concavities, tlie ethmoidal sinuses ; these are 

 divided by a broad perpendicular plate, which extends upwards 

 to unite with the nasal spine; (the partition between the fron- 

 tal sinuses;) below, it is received into the groove of the vomer ; 

 while in front it sustains the cartilaginous septum of the nose, 

 the septum nasi ; altogether completing the division of the nasal 

 cavity into two chambers : the ethmoidal plate itself is com- 

 posed of two thin laminae which in old subjects become conso- 

 lidated into one. Posteriorly, on either side, the body presents 

 the optic hiatus, transversely oval, leading to the optic foramen : 

 the posterior surface is oval to form a junction with the sphe- 

 noid bone. Arising from the upper and fore part of the body is 

 a pyramidal eminence somewhat curved, called the crista galli : 

 it sustains in front the perpendicular plate, the falciform process 

 of the dura mater behind, while from its sides extend the cribri- 

 form plates — two ovoid, thin, brittle lamellae, which are received 

 between the frontal orbital plates and the floors of the frontal 

 sinuses, pierced by numerous small holes for the transmission of 

 the filaments of the olfactory nerves, and whose concave cere- 

 bral surfaces are denominated the ethmoidal fossae and are 

 occupied by the olfactory sinuses. To the outer side of either 

 fossa opens the internal orbital foramen ; from which a fissure 

 runs upward to the part of the cribriform plate connected with 

 the principal cornu of the ethmoidal cells. 



The Ethmoidal Cells, the voluminous structure protrud- 

 ing from the front of the cribriform plates, consists of a great 

 many thin, brittle, porous osseous plates, curved or rather con- 

 voluted so as to form numerous narrow, elongated, cornuform 

 sinuses, rendered separate and distinct from one another by in- 

 tervening longitudinal grooves, with which from above they all 

 in common have communication. These canals proceed, con- 

 verging a little as they advance, to terminate underneath the 

 superior turbinated bone, at the back of the nasal fossa, within 

 a space communicating with the middle meatus. The anterior- 

 most cornu or cell is conspicuously long and capacious : the 

 rest increase in dimensions according to their proximity to this 

 large one. Issuing from the front of the cells is a broad, thin, 

 funnel-like process, which unites with the superior turbinated 

 bone and forms a sharp prominent crest, serving as an imper- 

 fect septum between the frontal and maxillary sinuses. 



The Lateral Portions, alse or wings, display more convexity 

 than concavity superiorly, the reverse inferiorly : they originate 

 from the supero-lateral parts of the body ; consist of thin, flex- 

 ible plates; spread outward and upward, contributing to the 

 posterior and inyvard parts of the orbits ; and terminate in semi- 



