THE SKULL. 311 



expanded laterally, and connected with the 

 ethmo-turbinals. 



b. Bones in relation with the optic capsules. 



The lacrimals are a pair of small lamellar bones 

 forming part of the anterior walls of the orbits, 

 and loosely wedged in between the frontals 

 and the maxillae. Each is notched at its outer 

 border for the passage of the lacrymal duct : 

 this is supported by a process of the bone 

 which extends forwards into the nose. 



The lacrymals correspond to the most 

 anterior of a series of small bones bordering 

 the orbits in bony fishes. 



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



fig. 66, p. 382). 



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-otic, 

 epiotic, opisthotic early unite to form an 

 irregular mass, which fits loosely into the 

 side-wall of the cranium, between the occi- 

 pital 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 

 posterior part, and is produced downwards 

 into the mastoid process, lying immediately 

 in front of the par-occipital process of the 

 ex-occipital bone. 



On the inner surface of each periotic, as 

 seen in a bisected skull, there are two depres- 

 sions. Of these the upper and larger one, 

 the floccular fossa, lodges the floccular lobe of 



