398 



branchs; that in the Tetrapoda this chain, in conformity with, and in 

 adaptation to, or perhaps caused by, the flattened down and broadered- 

 out configuration of the suspensorial region of the skull, has been bent 



Fig. 1. Evolution of the auditory ossicles. 



at an angle, the apex of which abuts against the tympanic membrane. 

 The part of the chain between tympanum and auditory capsule has 

 acted as a conductor of sound, ever since it was relieved of its pri- 

 mary, i. e suspensorial function. It is immaterial from a general 

 point of view, if this chain consists of only two pieces (columella and 

 extracolumella in Sauropsida) or if it forms three or four jointed pieces 

 as in Anura and Mammalia. I consider the extracolumella as homo- 

 logous with the malleus and incus. The string of connective tissue, 

 often cartilaginous, from the proc. internus of the extracolumella to 

 the articulare (discovered by Peters, dissected and figured by myself, 

 verified by Versluys, in various adult Lacertilia and Birds, very con- 

 spicuous and entirely cartilaginous in young Crocodiles fide Peters, 

 Parker, Gadow, Kingsley) I homologize with the cartilaginous 

 continuation of Meckel's cartilage into the malleus of foetal and young 

 Mammals. I have explained the existence of this connexion as a homo- 

 logue of the hyomandibular-mandibular ligament of hyostylic Elasmo- 

 branchs. Versluys, p. 386, makes the very pertinent remark: „Sollte 

 es durch spätere Untersuchungen bestätigt werden, daß bei den Sauro- 

 psiden das intracolumellare Stapes-Extracolumella-Gelenk, wie dies vom 

 Stapes-Incus-Gelenke der Säugetiere bekannt ist, lateralwärts von 

 der embryonalen Verbindung der Columella auris mit dem Zungenbein- 

 bogen liegt, dann scheint mir die Homologie der Gehörknöchelchen 



