40 



MAMMALIAN DESCENT. 



[Lect. II,' 



process equivalent to amputation. It is done, however, 

 not by a chirurgeon, for it is cut out without hands. 



Indeed, this is a kind of horticultural process, for the 

 hinder third of the proper original lower jaw is slowly 

 pinched off, and that hinder piece and its growing 

 pier or quadrate cartilage are more than half starved, 

 whilst the front two-thirds of the mandible are forced, so 

 to speak, as if grown in a hot-bed. The starved pier or 

 quadrate becomes the little incus or anvil bone of the 



'trhn 



Fig. 5. — Auditory Oiain of Bones from the Middle Ear of a New-bom Pig (Sus 

 scrofa), magnified 5 diameters, ml, malleus (hammer) ; pgr, processus gracilis 

 of malleus ; ml, manubrium (handle) of malleus ; spm, short process of malleus ; 

 i, incus (anvil) ; sci, short process (crus) of incus ; loi, long process of incus ; 

 st, stapes (stirrup) ; stm, stapedius muscle ; ihy, interhyal. 



ear-drum, whUe the hind part of the lower jaw itself, the 

 mandible, also starved, becomes the malleus, or hammer ; 

 and these two ossicles are now, for the first time, added 

 to the structures that convey the vibrations of air from 

 the ear-drum to the labyrinth. All at once, when we 

 look at the forcing process, whereby that which was 

 superficial and secondary becomes the arch of the lower 

 jaw, we see that something has been brought in for 



