OSSICULA AUDITUS 



27 



into communication with the internal orcjan of hearing woukl 

 he 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 

 aif the same to the tympanum on the one liand and to 



Fig. 15. — Head of a Human embryo of the fourth month. Dissected to show the 

 auditory ossides, tympanic ring, and Meckel's cartilage, with the hyoid and thyroid 

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

 skul]. an. Tympanic ring ; b.hy, basihyal element ; %, so-called hyoid bone ; in, 

 incus ; ind, bony mandible ; ml, malleus ; st, stapes ; <jj, tympanum ; tr, trachea ; 

 T. {ink), hrst skeletal (mandibular) arch (Meckel's cartilage) ; II. second skeletal 

 (hyoid) arch ; HE. third (hrst branchial) arch ; IV. V. fourth and fifth arches 

 (thyroid cartilage). (From Wiedersheim's SInictnrc nf 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^ appeared to confirm this way of looking at the 



^ Cf. the Armadillo Peltephilus, ]>. 186. 



