THE SKULL THE CKANIUM 



313 



it binds together the mesethmoid and the two lateral ethmoid* by their 

 posterior ends. The greatest length equals the length of the anterior 

 border of the lateral ethmoid, and is twice as great as the greatest 

 width, which is slightly greater above than below. Its long axis in a 

 median line (Fig. 241), drawn between the upper and lower borders, 

 is not vertical to the lower surface of the whole ethmoid, but is so 

 directed that from below the cribriform plate slopes obliquely upward 

 and forward. On both sides of the median line it is symmetrical. It 

 is not flat, but bent sharply across the middle in such manner that, 

 while the lower half is directed from the middle downward and back- 

 ward, the upper half is directed upward and backward. The cribri- 

 form plate is extremely thin ; it consists only of posterior and anterior 

 surfaces enclosed within upper, lower, and lateral borders. 



The posterior surface (Fig. 243) enters into the formation of the 



FIG. 243. 



Upper Part of Left Lateral Ethmoid, container! 

 in Frontal >/'/<.>. 



Notch for Median Plates of Frontals. 



Foramina for Olfactory Fibres. 



Left Lateral Ethmoid, with Maxillary. 



Lower Part of Left Lateral Ethmoid, contained 

 in Sphenoidal Sinus. 



f Limit of Cribriform Plate. 

 The G-ibriform Plate. 



Edge of Cribriform Plate, ivith Orbital Plate 

 of Frontal. 



With Palatine. 



Posterior End of Vomer, with Presphenoid. 

 THE ETHMOID BONE, CRANIAL ASPECT. 



anterior wall of the cranial cavity. Its dimensions and directions 

 have been just given ; it is slightly concave transversely, especially 

 above. It is split above in the middle line, and the split extends 

 down through the superior third and receives the joined median 

 plates of the frontals. The surface, therefore, appears to separate 

 above into two diverging horns ; the tip of each horn is rounded 

 and overhung by the posterior ends of the two upper scrolls. Below 

 this split the median line is depressed for a distance representing 

 approximately its middle third. In the furrow are two parallel rows 

 of well-marked foramina, separated by a straight bar, which repre- 



