OSSICULA AUDITUS 



27 



iiitt) eoinmuiiieation with the internal organ of liearing woukl 

 lie honiolouuus throughout the series. He believed, therefore, 

 that the entire chain of ossicula auditus in the mammal is 

 etiual to the columella of the reptile, since their relations 

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



Fig. 1 5.— Head of a Human embryo of the fourth mouth. Dissected to show the 

 auditory ossicles, 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 

 skull, an, Tympanic ring; h.hif. basihyal element ; liy, so-called hyoid lione ; i)i, 

 incus ; md, bony mandible ; ml, malleus ; st, stapes ; t}], tympanum ; tr, trachea ; 

 1. (wA:), 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 W^iedersheim's Structure of Man.) 



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

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

 the glenoid part of the S([uamosal must be the quadrate which 

 has become ankylosed with it after the fashion of concentration 

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

 fact that occasionally the glenoid part of the S(|uamosal is a 

 separate bone^ appeared to confirm this way of loolving at the 



^ Of. the Anuadillo Peltci)hilus, p. 186. 



