50 



THE SKELETON 



convertt'd into candi-^ ))y the frontal Ijone. The anterior canal tran^^niits the anterior 

 ethmoidal artery and nasal nerve; the posterior is for the posterior ethmoidal artery, 

 and a Immch of the nasal ner\e. 



The superior and middle turbinals project on the inner aspect of the lateral 

 mass; thev coalesce anteriorly, hut are separated posteriorly hy a space, termed the 

 superior meatus. Eawh turl»inal has an attached upper, and a free, slightly con- 

 voluted, lower honk'r. In the recent state they are covered with mucous memlirane, 

 and present numerous forannna for Ijlood-vessels, and grooves for twigs of the 

 olfactory nerves. 



On the under surface of each lateral mass, near the anterior corner of the os 

 planum, an irregular hunina of hone projects downwards and Ijackwards. This is 

 the unciform process : it articulates with the ethmoidal process of the inferior 

 turhinal, and forms a small part of the inner wall of the antrum. The anterior 

 part of the lateral mass projects forwards in front of the os planum and articulates 

 with the inner surface of the nasal process of the maxilla. 



The ethmoidal cells occupy the space betAveen the os planum and the turl)inals; 

 they are divided l)y a thin septum into an anterior and a posterior set. The cells 

 are imperfect in the ethmoid; they require the juxtaposition of other bones to make 

 them complete. Above, they are closed by the horizontal plate of the frontal, 



Fig. 60.^-The Ethmoid. (Side view.) 



/Tf- CRISTA GALLI 



ANTERIOR ETHMOIDAL GROOVE 



UNCIFORM PROCESS 



INFERIOR TURBINAL 



POSTERIOR ETHMOIDAL GROOVE 



SPHENOIDAL TURBINAL 

 MIDDLE TURBINAL 



posteriorly by the sphenoidal turhinal and the orbital process of the palate, inferiorly 

 by the maxilla, and anteriorly by the lachrymal. The anterior set communicate 

 with the frontal cells above, whilst below they open into the middle meatus of the 

 nose by a sinuous canal, the infundibulum. The posterior cells open into the 

 superior meatus, and occasionally communicate with the sphenoidal cells. 



The cells are sometimes divided into groups, according to the bone which lies in 

 innnediate juxtaposition. Those along the superior <Hlge are the fronto-ethmoidal ; 

 those beneath the lachrymal, lachrymo-ethmoidal, usually two in number. 

 Those along the lower edge are the maxillo-ethmoidal ; and ]iosteriorly there are 

 the spheno-ethmoidal, ccjmpleted l)y the sithenoidal turl)inals, and a palato- 

 ethmoidal cell. 



Articulations. — The ethmoid articulates with tin' frontal, sphenoid, two i)alate 

 l)ones, two nasals, vomer, two inferior turlnnals, the sphenoidal turbinals, two max- 

 illie, and two lachrymal bones. The posterior surface of each lateral mass comes 

 into relation with the sphenoid on each side of the crest and rostrum, and heljis 

 to close in the s|)henoi(lal simis. 



Blood-supply. — The anterior and ])osterior ethmoidal, and from the nasal 

 or s|)heno-]ialatine branch of the internal maxillary artery. 



Ossification. — Tlie ethmoid has three centres of ossitii-ation. Of these, a 

 nucleus api)ears in the fourth month of intra-uterine life in each lateral cartilage. 



