XECT. II.] BONES FORMING THE EAR-CHAIN. 43 



glenoidal cavity or cartilaginous facet ; there is no hinge 

 nothing is joined to it. 1 But in the mammal the 

 large superficial cartilaginous tract, after serving as the 

 matrix out of which most of the lower jaw is formed, 

 becomes segmented into three parts at the hinge ; the 

 lower part is the condyle, or head of the joint, the upper 

 the glenodial facet, or shallow cup, attached to the 

 temporal bone, and the intermediate part the meniscus, 

 a, sort of pad, the interarticular fibro-cartilage. 



I could not find, in my young specimen of the Duck- 

 bill, splints on the large rough malleus corresponding to 

 the "angulare" and " supra-angulare," two bones that 

 strengthen the upper or articular portion of the jaw in 

 birds and reptiles. But I find the " angulare " in several 

 kinds of mammals, and in the Koala, a kind of Marsupial, 

 both of these well-known splints of the compound jaw 

 of the ovipara are found as small separate pieces. 



After long years of labour and much vacillation of 

 mind on the matter, I am now quite satisfied that the 

 stapes, or little stirrup-bone of the ear-drum, is the 

 uppermost element of the second, or hyoid arch. 



Those who have studied human anatomy know that 

 the three little bones which are fastened as a chain across 

 the inside of the cavity of the ear-drum or " middle ear," 

 are called malleus (hammer), incus (anvil), and stapes 

 (stirrup). The latter bone, by its base, stops up a small 



1 The reader who is not familiar with the skull, is referred to my figures of those 

 of the Fowl and the Pig in the Philosophical Transactions of the Royal Society, 

 1869, plate Ixxxvii. ; and ibid., 1874, plates xxxiv.-xxxvii. 



