26 THE ANATOMY OF VEETEBRATED ANIMALS. 



relation to the lachrymal canal, is very generally developed; 

 and one or more supra-orbital and post-orbital ossifications 

 may be connected with the bony boundaries of the orbit. 



When these and the postfrontal membrane bone are 

 simultaneously developed, they form two series of bony 

 splints attached to the lateral wall of the skuU, one set 

 above and one below the orbit, which converge to the lach- 

 rymal. The upper series (lachrymal, supra.-orbital, post- 

 frontal, squamosal), terminates posteriorly over the proxi- 

 mal end of the quadrate bone, or mandibular suspensorium. 

 The lower series (lachrymal, maxillary, jugal, quadrato- 

 jugal) ends over the distal end of that bone, with 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 Ichthyosauria, Chelonia, Croco- 

 dilia, 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, the prefrontal above and externally, and the palatine 

 behind, to open into the fore part 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 communicates, laterally, 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 lachrymal bone may be de- 

 veloped in especial relation with it. 



In the higher Vertebrata, the nasal passages no longer com- 

 municate with the fore part of the cavity of the mouth ; for 

 the maxillaries and palatines, regularly, and the pterygoid 

 bones, occasionally, send processes downwards and inwards, 

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



