THE SKULL 281 



bones, lying in the anterior portion of the 

 nasal cavities, in front of the ethmo-turbinals. 



iv. The naso-turbinals are a pair of thin laminae of 

 bone, folded to form pouches, and fused with 

 the inner surfaces of the nasal bones. 



V. The vomers are a pair of slender blade-like bones, 

 fused with each other along their ventral 

 margins, and embracing the lower edge of 

 the mes-ethmoid cartilage. Behind they are 

 expanded laterally, and connected with the 

 ethmo-turbinals. 



1). Bones in relation with the optic capsnles. 



The lacrymals are a pair of small lamellar bones 

 forming part of the anterior walls of the orbits, 

 and loosely wedged in between the frontals 

 and maxillae. Each is notched at its outer 

 border for the passage of the lacrymal duct, 

 which is supported by a process of the bone 

 extending forwards into the nose. 



The lacrymals correspond to the most 

 anterior of a series of small bones, placed 

 round the borders of the orbits in bony fishes. 



c. Bones in relation with the auditory capsules (cf. 

 fig. 60, p. 312). 



i. The periotics are the bones which replace the 

 cartilaginous capsules enclosing the organs of 

 hearing in the embryo. Each ossifies from 

 three centres ; but the several bones — pro-otie, 

 epiotic, opisthotic — early unite to form an 

 irregular mass, which fits loosely into the 

 side-wall of the cranium, between the occi- 

 pita segment and the squamosal, and which 

 readily falls out from the dried skull. 



In each periotic there may be distinguished 

 a dense petrous portion, enclosing the essential 

 part of the organ of hearing; and a porous 

 mastoid portion, which forms its outer and 



