SKULL — MAMMALS 



203 



The goniale in reptiles usually fuses with the articulare, and the bone in question 

 in mammals does the same, forming part of the anterior or Folian process. 



Another view regards the ossicula auditus of all Amniotes as homologous 

 throughout, the whole columella being equivalent to the three mammalian bones. 

 That this cannot be so is shown by several facts. The columella arises posterior 



Fig. 211. Fig. 212. 



Fig. 211. — Relations of incus to otic capsule and developing squamosal in 72"'mm. 

 pig (Thyng, '06). i, incus; oc, part of otic capsule; 5, stapes; sq. squamosal; x, dense 

 stroma connecting incus and squamosal. 



Fig. 212. — Diagram of ear bones of embryo pig, the tympanic cavity opened. 

 g, goniale; /, inctis; Ij, part of lower jaw; m, malleus; mk, Meckel's cartilage; mm, 

 manubrium mallei; 5, stapes; sq, squamosal; z, zygomatic. Outlines of lower jaw and 

 zygomatic arch dotted. 



to the tympanic cavity (part of the spiracular cleft) and invades it from behind; 

 incus and malleus are prespiracular and enter the tympanum from in front. 

 The columellar parts all lie behind the chorda tympani nerve, incus and malleus 



Fig. 213. — Fuchs' ('00) explanation of homologies of Sauropsidan (A) and mam- 

 mahan ossicula auditus [B). cb, crus brevis; cl, crus longus; ec, extracolumella; i, incus; 

 m, body of malleus; mn, manubrium; pa, articular process of quadrate, q; paa, accessory 

 anterior process; pa, sq, Q, articular surface of squamosal covered in mandibular fossa 

 by cartilage; pi, internal process; ppr, preauricular part of quadrate. 



(This makes body of malleus a derivative of quadrate — is really a part of Meckelian — 

 and would require transfer of extracolumella, a postotic cartilage, to anterior side of 

 external auditory meatus, etc.). 



in front of it. There are other and less probable explanations advanced, one 

 being that mammals have descended from streptostyHc reptiles and that the 



