OSSICULA AUDITUS 



into communication with the internal organ of hearing would 

 be homologous throughout the series. He believed, therefore, 

 that the entire chain of ossicula auditus in the mammal is 

 equal to the columella of the reptile, since their relations 

 are the same to the tympanum on the one hand and to 



.in i. 



FIG. 15. Head of a Human embryo of the fourth mouth. Dissected to show the 

 auditory ossicles, tympanic ring, and Meckel's cartilage, with the by old and thyroid 

 apparatus. All these parts are delineated on a larger scale than the rest of the 

 skull, an, Tympanic riug ; b.hy, basihyal element ; hy, so-called hyoid bone ; in, 

 incus ; md, bony mandible ; ml, malleus ; st, stapes ; tp, tympanum ; tr, trachea ; 

 1. (ink), first skeletal (mandibular) arch (Meckel's cartilage) ; II. second skeletal 

 (hyoid) arch ; III. third (first branchial) arch ; IV. V. fourth and fifth arches 

 (thyroid cartilage). (From Wiedersheim's Structure of Man.) 



the foramen ovale on the other ; and that the lower jaw 

 articulates in the same way in both. It follows, therefore, that 

 the glenoid part of the squamosal must be the quadrate which 

 has become ankylosed with it after the fashion of concentration 

 in the mammalian skull that has already been referred to. The 

 fact that occasionally the glenoid part of the squamosal is a 

 separate bone 1 appeared to confirm this way of looking at the 



1 Cf. the Armadillo Peltephilus, p. 186. 



