28 THE ANATOMY OF VERTEBRATED ANIMALS. 



upper series (lachrj'mal, supra-orbital, post-frontal, squamosal), 

 teriuiiiates posteriorly over the proximal end of the quadrate 

 hone, or inandibular suspensorium. The lower series (lacliry- 

 mal, maxillary, jugal, quadrato-jugal) ends over the distal end 

 of that bone, vs^ith which the quadrato-jugal is connected. 

 The two series are connected behind the orbit by the post- 

 orbital (when it exists), but more commonly by the union of 

 the jugal with the post-frontal and squamosal. The Ichthy- 

 osauria, Chelonia, Groeodilia, and some Lacertilia, exhibit 

 this double series of bones most completely. 



Each nasal passage, at first very short, passes between the 

 premaxilla below, the ethmoid and vomer on the inner side, 

 tlie prefrontal above and externally, and the palatine behind, 

 to open into the forepart of the mouth. And, before the cleft 

 between the outer posterior angle of the naso-frontal process 

 and the maxillary process is closed, this passage communi- 

 cates laterallj', with the exterior, and, posteriorly, with the 

 cavity of the orbit. When the maxillary and the naso-frontal 

 processes unite, the direct external communication ceases ; 

 but the orbito-nasal passage, or lachrymal canal, as it is 

 called, in consequence of its function of conveying away the 

 secretion of the lachrymal gland, may persist, and the lachry- 

 mal bone may be developed in especial relation with it. 



In the higher Vertebrata, the nasal passages no longer 

 communicate with the forepart of the cavity of the mouth ; 

 for the maxillaries and palatines, regularly, and the pterygoid 

 bones, occasionally, send processes downward and inward, 

 which meet in the middle line, and shut off from the mouth 

 a canal which receives the nasal passages in front, while it 

 opens, behind, into the pharynx, by what are now the poste- 

 rior 7iares. 



Two ossifications commonly appear near the proximal end 

 of Meckel's cartilage, and become bones movablj' articulated 

 together. The proximal of these is the quadrate bone found 

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

 the OS articulare of the lower jaw in most vertebrates, but 

 does not seem to be represented in mammals. The remainder 

 of Meckel's cartilage usuallj^ 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 thiis formed articulati?s with 

 the squamosal bone in mammals, but in other Vertebrata is 



