THE ETHMOID BOXE. 43 



The anterior margin of the crista galli is vertical and broad, usually pre- 

 senting a groove, which completes the foramen caecum of the frontal bone. 

 Below the level of the cribriform lamella, the anterior margin of the central 

 plate articulates with the nasal process of the frontal and with the nasal bones. 

 The inferior margin articulates in front, and sometimes even in its whole 

 extent, with the septal cartilage of the nose ; and in its posterior half, in the 

 adult, is more or less completely joined by osseous union on one or both 

 sides to the two plates or alae of the vomer. The posterior margin is very 

 thin, and is united to the sphenoidal crest of the sphenoid. This plate 

 presents a number of grooves and minute canals leading from the foramina 

 of the cribriform lamella, for the transmission of the olfactory nerves. 



The LATERAL MASSES enclose a number of spaces of irregular form, the 

 ethmoidal cells, which in the recent state are lined with prolongations of the 

 mucous membrane of the nose. On the external aspect of each lateral mass 

 is a thin, smooth lamina, of a quadrilateral form, the orbital plate or os 

 planum, which closes in the ethmoidal cells, and forms a considerable part of 

 the inner wall of the orbit. The orbital plate articulates iu front with the 

 lachrymal, behind with the sphenoid, above with the frontal, and below with 

 the orbital surfaces of the superior maxillary and palate boues. In front of the 

 orbital plats the lateral mass extends forwards, under cover of the lachrymal 

 bone ; and from this part descends the uncinate or cuneiform process, a long 

 thin lamella which curves downwards, outwards, and backwards, forming 

 part of the inner wall of the maxillary antrum, and articulating at its 

 extremity with the inferior turbinated bone. (See fig. 50.) 



The internal aspect of each lateral mass forms part of the external wall of 

 the nasal fossa, and consists of a thin, uneven, osseous plate, connected above 

 with the cribriform lamella, and exhibiting a number of canals and grooves 

 for branches of the olfactory nerve. It is divided at its back part by a channel, 

 directed upwards and forwards from its posterior margin to about its middle. 

 This is called the superior meatus of the nose, and communicates with the 

 posterior ethmoidal cells. The short margin which overhangs this channel 

 constitutes the superior turbinated process or spongy bone. Below this is a 

 slightly folded margin of much greater extent, and free in front, the inferior 

 turbinated process or middle spongy bone, which overhangs the middle meatus 

 of the nose. From the front of the middle meatus a passage, the infundi- 

 buhim, is prolonged upwards and forwards through the anterior ethmoidal 

 cells, and opens into the frontal sinus. (See also tig. 54.) 



In the separate ethmoid bone the cells are open posteriorly and superiorly, 

 but when the bone is in connection with the rest of the cranium these cells 

 are closed, above by the frontal bone, and behind by the sphenoidal spongy 

 bones. In the superior margin are two grooves, which complete with the 

 frontal bone the internal orbital foramina. 



The CRIBRIFORM LA.MELLA corresponds in size to the incisura ethmoidalis of 

 the frontal bone which it occupies. At the sides of the crista it is depressed 

 into two grooves which lodge the olfactory bulbs ; and it is pierced by 

 numerous foramina, for transmission of the filaments of the olfactory nerves. 

 The foramina, which lie along the middle of each groove, are simple perfora- 

 tions ; the internal and external sets are longer, and are the orifices of 

 small canals which subdivide as they descend on the central plate and 

 lateral masses. At the anterior extremity is a small fissure at each side of 

 the crista galli, close to its base, and externally to this a foramen, connected 

 usually by a slight groove with the anterior internal orbital foramen, which 

 transmits the nasal branch of the ophthalmic nerve. 



