140 MAMMALIAN DESCENT. [Lkct. V. 



Very soon, whilst the superficial l)oue is forming by 

 transformation of the superficial cartilage, a thick, solid 

 har of l)one is formed in the front third of the Meckelian 

 rod of the embryo Hedgehog. The ujDper part of the 

 cerato-l)ranchial l)ar becomes detached after a time, but 

 not until it has 1)ecome ossified ; this ossification is 

 arrested, to form the malleus (or hammer bone) of the 

 middle ear. The huge epibranchial, or upper jaw of the 

 Shark, is represented in the Hedgehog by two tracts of 

 cartilage, one small and the other large. 



The large cartilage is the hinge part — the hinder 

 region of the upper jaAv. The fore ^^i^i't, which in the 

 Shark carries the upper teeth, is represented l^y an oval 

 segment of solid hyaline cartilage, which becomes con- 

 verted into the hamular process of the pterygoid 

 l)one ; the larger hind piece becomes the incus, or 

 anvil. The stapes is stirrup-shaped, and is, as I have 

 before stated, the pharyngo-branchial element of the 

 j)erfect hyoidean (or second arch). There is a ring, 

 partly cartilaginous and j^artly l)ony, formed round the 

 intersj^ace (cleft, or tympanic (cavity) of these two arches. 

 The inner jDart is l)ony, and forms the annulus, or osseous 

 ring for the ear-drum ; the next is a 2:)artly segmented 

 series of cartilaginous annuli or rings forming the coating 

 of the meatus externus or ear-porch, which ends in the 

 concha or 23rojecting j^art of the ear. 



The whole of this latter stru('ture is a specialisation of 

 t1io familiar " sjiii'acular rav" of the Shark — that small 



