88 FRANKLIN PEARCE REAGAN 



the many observations supporting this view may be mentioned 

 those of Baumgarten, Broman, Huxley, Keibel, Kingsley, 

 Peters, Rabl, Reichert, Schenk, Schafer, Zittel, and Zondek; 

 closely allied to this view we have phylogenetically the hyo- 

 mandibular origin of the stapes, supported by Baraldi, Claus, 

 Gegenbaur, Hasse, R. Hertwig, Ktikenthal, and Wiedersheim, 

 and Parker. On the other hand, there are observations which 

 tend to show that the entire stapes arises from the otic capsule, 

 constituting then, a portion of the cranium and in no way re- 

 lated to the visceral skeleton. Among these observations may 

 be mentioned those of Fuchs, Kolliker, Marshall, Parker and 

 Bettany, and Wiedersheim. Minot derived the stapedial plate 

 as an independent chondrification in the fenestra ovalis. These 

 interpretations have been combined into a third ^dew according 

 to which the stapes is formed partly from the otic capsule (i.e., 

 the stapedial plate), and partly from the hyoid arch. This view 

 of the mixed origin of the stapes has been supported by Grade- 

 nigo, van Norden, and Schultze. Giinther described the stapes 

 as developing from the mandibular arch. Dreyfuss thought it 

 developed from either the first or second arch. Cope and Frazer 

 described the origin of the stapes as 'peri-arterial.' O. Hertwig 

 regards its origin as uncertain. Finally one might mention 

 the view of Siebenmann who would dismiss as immaterial the 

 possibility of a definite relation of embryonic visceral cartilage 

 and adult ear ossicles. 



One must admit with Keibel (1912, p. 281) that ''there is 

 great difficulty in tracing back a skeletal structure to the early 

 pre-chondral stages, and it carries with it the danger of sub- 

 jective interpretation." It seems desirable temporarily to set 

 aside considerations of phylogeny and attack the problem from 

 the point of view of the mechanics of development involved in a 

 single ontogeny. 



It is a well known fact that the crania of all vertebrates pass 

 through a common phase of development which may be regarded 

 as a ground-plan of vertebrate cranial formation. Surrounding 

 the anterior end of the notochord there is found a parachordal 

 cartilage, and anterior to this are located the trabeculae. In the 



