136 SKELETON. 



cribriform plate called so from its numerous perforations. This 

 is divided, longitudinally, above and below, by a vertical pro- 

 cess ; and from the under surface on each side, is suspended the 

 cellular portion. 



The vertical process on the superior face of the cribriform 

 plate is the crista galli, which extends sometimes from the back 

 to the front of this plate, and is thickest in the middle. The com- 

 mencement of the great falx arises from it, and occasionally it 

 contains a cell or sinus opening into the nose. Between the front 

 of the crista galli and ihe os frontis, is the foramen ccecum, al- 

 ready described. On either side of the crista galli the cribriform 

 plate is depressed into a gutter for holding the bulb of the olfac- 

 tory nerve, and is perforated with many holes for transmitting 

 its ramifications. The most anterior foramen on each side is 

 oval, and transmits to the nose the internal nasal nerve, after it 

 has got into the cranium through the anterior internal orbitar 

 foramen. The margins of the cribriform plate show many im- 

 perfect cells, which are completed by joining their congeners 

 in the margins of the orbitar processes of the os frontis. 



The vertical process below the cribriform plate is called 

 nasal lamella. It generally divides the nostrils equally, but is 

 occasionally inclined to one side. It joins below, to the vomer 

 and the cartilaginous septum of the nose; in front is in contact 

 with the nasal spine of the frontal bone and with the nasal 

 bones; and behind, with the azygous process of the sphenoid. 



Each cellular portion of the ethmoid forms, by its exterior, a 

 part of the orbit of the eye, which surface is called os planum. 

 The internal or nasal face forms part of the nostril. The fore 

 part of this face is flat, but, posteriorly, in its middle, is a deep 

 sulcus, called the superior mealus of the nose. The upper tur- 

 binated bone, a small scroll, constitutes the upper margin of 

 this meatus. The inferior internal margin of the cellular por- 

 tion of the ethmoid, is formed by another scroll of bone, run- 

 ning its whole length. This is the middle turbinated bone. 

 Moreover, from the inferior margin of the cellular portion, one 

 or more laminae, of an irregular form, project so as to diminish 

 the opening into the upper maxillary sinus. 



