74 



COMPARATIVE MORPHOLOGY OF VERTEBRATES. 



stapes (fig. 82). In the anurans there is no connection of quadrate 

 with stapes, but there is a slender rod, the columella, extending from 

 the tympanic membrane to the stapes. This columella arises behind 

 the tympanic cavity but with growth is included in it, so that in the 

 adult it appears to run directly through it. In the sauropsida the 

 relations are much as in the anura, but when ossification sets in, the 

 columella may form several elements. In development the columella 

 in these forms is directly connected with the hyoid arch. 



In the mammals there is 

 a chain of three bones to carry 

 the sound waves across the 

 tympanic cavity. In the 

 fenestra vestibuli is the stapes, 

 which connects with an incus 

 and lastly comes the malleus, 

 which has two long processes, 

 a manubrium which is in- 

 serted in the tympanic mem- 

 brane, and a processus an- 

 terior (Folian process) which 

 extends into the petrotym- 

 panic (Glaserian) fissure 

 of the temporal bone. That 



these parts are not to be com- 



FiG.yi.-Diagramofearbonesof embryo pig, P ared tO the Columella of the 



the tympanic cavity laid open, g, goniale; i, sauropsida and anura is 

 incus; lj, lower jaw; m, malleus; mk, Meckel's , . , , 



cartilage; mm, manubrium of malleus; s, stapes; shown by the tact that they 



s ?) squamosal; z, zygomatic : The outlines of the mva( J e t h e tympanic Cavity 

 zygomanc arch and the hind end of the jaw are 



dotted. from in front and that they 



are in front of the chorda 

 tympani nerve, the columella of the non-mammals lying behind it. 



The homologies of these parts seem clear. In development the 

 malleus is the posterior end of Meckel's cartilage, being in the position of 

 the articulare of lower groups. It articulates with the incus, which in 

 turn at first articulates with the wall of the otic capsule, as well as with 

 the stapes, and thus corresponds with the quadrate. The stapes is 

 apparently the same throughout the whole of the tetrapoda. It is to be 

 noted that many paleontologists deny the homologies recognized here, 

 think that in the mammals the quadrate has been lost in the glenoid 



