158 MORPHOLOGY OF THE ORGANS OF VERTEBRATES. 



supraoccipital. In the floor of the cranium in front of the basi- 

 occipital is a basisphenoid, and in front of this a presphenoid. 

 Still farther in front, in the region of the ethmoid plate and the 

 nasal capsules, a mesethmoid. In the trabeculae are developed 

 two bones on either side, an alisphenoid in front of the otic cap- 

 sules, and an orbitosphenoid in the neighborhood of the eye. 

 The otic capsules each ossify into three bones, a prootic in 

 front, an epiotic above, and an opisthotic behind. These bones 

 form the floor and a part of the lateral walls of the skull. Not 



pao 



FIG. 167. Base of skull of alligator {Alligator Indus'}, bo, basioccipital ; i>s, 

 basisphenoid; eo, exoccipital; et, opening of Eustachian tube; fm, foramen mag- 

 num; pao, paroccipital ; //, pterygoid; q, quadrate ; qj, quadratojugal ; so, supra- 

 occipital; sq, squamosal ; tr, transversum. 



all of them are always developed, and again two or more may 

 fuse together or with membrane bones. 



The pterygoquadrates of either side develop into a pair of 

 pterygoid and a pair of quadrate bones, while Meckel's carti- 

 lage never ossifies, or at most gives rise to an articulare on 

 either side, where the lower jaw articulates with the quadrate. 

 The other visceral arches may ossify to a greater or less extent, 

 but the names of the resulting bones are the same as those 

 given the cartilages. 



In all terrestrial vertebrates certain cartilages or bones are 

 developed in connection with the ear, and the most diverse 

 views have been advanced regarding the homologies of these 

 ossicula auditus. The following account is based upon personal 



