312 



MAMMALIAN ANATOMY 



front to the posterior half of the lower edges of the inner, or median, 

 surfaces of the nasal bones. 



The short anterior border makes an obtuse angle with the superior 

 border, being directed downward and forward ; it then turns down- 

 ward and backward so as to pass to the inferior border without forming 

 a distinct angle. To the anterior border is attached the posterior end 

 of the cartilaginous nasal septum. 



The inferior border is for the most part straight, and truncate or 

 rounder behind, leaving a small triangle between the mesethmoid, the 

 vomer, and the presphenoid, which in the natural state is filled by a 

 triangular, vertical plate of cartilage. In front, the inferior border 



FIG. 242. 



Mesethmoid or Perpendicular Plate 

 of Ethmoid. 



With Maxillary. 

 Mesethmoid, with Cartilaginous Nasal Septum. 



Part of Left Lateral Ethmoid entering opening 



into Fruntal >'ms. 

 Upper Part, contained in Nasal Cavity. 



.Left Lateral Ethmoid, with Fruitful. 



Lower Part of Left Lateral Ethmoid, near 

 Maxillo-turbinal. 



Vomer. 



THE ETHMOID BONE, ANTERIOR ASPECT. 



becomes the anterior border. The anterior and inferior borders are 

 subject to considerable variation, dependent on the degree of extension 

 backward of the cartilaginous septum. 



The inferior border is split into two edges by a longitudinal fissure ; 

 the edges articulate with the ridges on each side of the median groove 

 on the upper surface of the vomer, leaving a channel between the 

 mesethmoid and the vomer which is filled with cartilage. 



THE CRIBRIFORM PLATE. 



The cribriform plate of the ethmoid is a thin quadrilateral plate 

 situated in the middle line at the upper back part of the bone, where 







