THE OSSEOUS MANDIBLE. 



27 



a canal wliicli receives the nasal passages in front, while 

 it opens, behind, into the pharynx, by what are now the 

 posterior nares. 



Two ossifications commonly appear near the proximal end 

 of Meckel's cartilage, and become bones moveably articulated 

 together. The proximal of these is the quadrate bone found 

 in most vertebrates, the malleus of mammals ; the distal is 

 the OS articular e of the lower jaw in most vertebrates, but 



Fis. 9. 



f-mx 



Fig. 9. — The head of a foetal Lamb dissected so as to show Meckel's 

 cartilage, 3/; the malleus, m; the incus, 2; the tympanic, Tv; the 

 hj'oid, H; the squamosal, Sq; pterygoid, Pt ; palatine, jo/ ; lachrymal, 

 L; premaxilla, /)m.r ; nasal sac, N; Eustachian tube, Eu. 



does not seem to be represented in mammals. The re- 

 mainder of Meckel's cartilage usually persists for a longer 

 or shorter time, but does not ossify. It becomes surrounded 

 by bone, arising from one or several centres in the adjacent 

 membrane, and the ramus of the mandible thns formed, articu- 

 lates with the squamosal bone in mammals, but in other 

 Vertebrata is immoveably united with the as articulare. 

 Hence the complete ramus of the mandible articulates 



