II OSSICULA AUDITUS 27 
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 
Lig eg 
Pig 
md. 
Fie. 15.—Head of a Human embryo of the fourth month. 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; 6.hy, basihyal element ; hy, so-called hyoid bone ; in, 
incus ; md, bony mandible ; m/, malleus ; st, stapes ; ty, tympanum ; ¢7, trachea ; 
I. (mk), tirst 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’ appeared to confirm this way of looking at the 
1 Cf. the Armadillo Peltephilus, p. 186. 
