490 HISTORY OF THE HUMAN BODY 



what different from the rest and are absolutely constant. They 

 are situated in the ampullae and are in the form of ridges which 

 encircle them and project into the lumen. They are thus dis- 

 tinguished from the others as cristcz acusticcz. The remaining 

 five are evidently formed by the successive breaking up of a 

 single large area, due to the differentiation of parts of the laby- 

 rinth, and the history of this segmentation and later migration 

 is represented in the phylogenetic series (Fig. 133). Thus, in 

 the cyclostomes the acoustic region, aside from the one or two 

 semicircular canals, is represented by a single area, macula 

 acustica communis, covering the bottom of what is here a 

 simple sac (Fig. 133, a). The differentiation of utriculus and 

 sacculus gives a separate area to each, respectively, the ma- 

 cula acustica recessus utriculi and macula acustica sacculi 

 (Fig. 133, b). With the gradual development of the lagena 

 in fishes there appears an outgrowth of this latter area which 

 finally separates from its place of origin and establishes itself 

 as the auditory area for the newly developed part, under the 

 name of papilla acustica lagena. This gradual separation of 

 both lagena and its acoustic area is accompanied by a similar 

 separation of the nerve, which splits off a supply branch for 

 the new area. (Fig. 133, cf. b and c.) A small macula is 

 also formed near the utricular macula, the macula acustica neg- 

 lecta, evidently an offshoot from the latter, although no phylo- 

 genetic proof of this appears as in the former case. The fifth 

 and last of the auditory areas, not counting the cristse acus- 

 ticse of the ampullae, the papilla acustica basilaris, also be- 

 longs in the lagenar region, and appears in the higher urodeles 

 as an offshoot of the papilla lagense (Fig. 133, d). 



To put these points into the form of a phylogenetic 

 history we may take as a starting point the macula communis 

 of cyclostomes, which may be considered to hold all the later 

 elements within itself. In fishes we find a primary macula for 

 each of the two parts into which the labyrinth has become 

 divided, also a macula neglecta, which has presumably sepa- 

 rated from the one belonging to the utriculus at some point 

 below the fishes. Within the group of the selachians the 





