TIIK SKULL. 591 



as compared with the adjacent parts of the skull, and finally 

 ossifies to form the malleus bone of the ear. The processus 

 gracilis of the malleus is the primitive continuation into Meckel's 

 cartilage. 



The malleus and incus are at first embedded in the connec- 

 tive tissue adjoining the tympanic cavity (hyomandibular cleft, 

 vide p. 528) ; and externally to them a bone known as the 

 tympanic bone becomes developed so that they become placed 

 between the tympanic bone and the periotic capsule. In late 

 fcetal life they become transported completely within the tym- 

 panic cavity, though covered by a reflection of the tympanic 

 mucous membrane. 



The dorsal end of the part of the hyoid separated from the 

 incus becomes ossified as the tympano-hyal, and is anchylosed 

 with the adjacent parts of the periotic capsule. The middle part 

 of the bar just outside the skull forms the stylo-hyal (styloid 

 process in Man) which is attached by ligament to the anterior 

 cornu of the hyoid (cerato-hyal). 



While the account of the formation of the malleus, incus, and stapes 

 just given is that usually accepted in this country, a somewhat different 

 view of the development of these parts has as a rule been adopted in 

 Germany. Reichert (No. 461) held that both the malleus and the incus 

 were derived from the mandibular bar ; and this view has been confirmed 

 by Giinther, Kolliker and other observers, and has recently been adopted 

 by Salensky (No. 462) after a careful research especially directed towards 

 this point. Reichert also held that the stapes was derived from the hyoid 

 bar ; but, though his observations on this point have been very widely 

 accepted, they have not met with such universal recognition as his views 

 on the origin of the malleus and incus. Salensky has recently arrived 

 at a view, which is in accord with that of Parker, in so far as the indepen- 

 dence of the stapes of both the hyoid and mandibular arches is concerned. 

 Salensky however holds that it is formed from a mass of mesoblast 

 surrounding the artery of the mandibular arch, and that the form of the 

 stapes is due to its perforation by the mandibular artery. A product of 

 this artery permanently perforates the stapes in a few Mammalia, though 

 in the majority it atrophies. 



In view of the different accounts of the origin of the incus the exact 

 nature of this bone must still be considered as an open question, but 

 should Reichert's view be confirmed the identification of the incus with 

 the columella of the Amphibia and Sauropsida must be abandoned. 



