47S 



CHORDATA. 



upipcr iilrinihis and a lower sacruliis, the connecting iilrinilo-safcular duct 

 being narrow in lire mammals. Both utrieiiius anj saeculus recei\e a 

 part of the macula acustica. CHitgrowths from the vesicle occur, giving 

 the whole the name of Lihyr'nith. From the utriculus arise three scmi- 

 circular ljihiIs. connected at either end with this cavity, each swollen at 

 one end to an a))ipiilla. coirtaining a special nerve termination, the crisla 

 aiiislica. These canals stanil at right angles to each other in the three 

 dimensions of space and without doubt subserve the function of equili- 



FiG. 532. Fig. 533. 



Fig. 532. — ilerabranous labyrintlis of {!) Myxiiic; {ID CIi:iii,n\i (after Rolziiis"). 

 (7,ampuU:o; c, uni,U\'ided vesicle witli cndolynipli iluct; </(\ cntlol\"mph duct; /, anlage of 

 lagena; », macula neglecta; 5, saeculus; i», sinus utriculi; l\ utriculus; i, anterior, 2, 

 posterior, 3, outer semicircular canals. Aurliton" nen'e and its branches dark. 



Fig. ^33. — Hunian ear (based on Sch\\all">eV a, incus and stapes; at\ external 

 meatus: c, cartilage; di\ endob'mph duct; /;, malleus; A'', temptc^ral bone; K', bony 

 lab\Tinth; A'a, ncr\c; 0. liase of conch; ,^, saeculus; 7', t\'mpanic membrane; /, fenestra 

 rotunda; tc, Eustachian tube; 11, utriculus. 



bration (p. it;). They are an outer horizontal, an anterior vertical 

 (nearly sagittal), and a posterior vertical (nearly trans\erse). The non- 

 ampuUar ends of the two \ erlical canals unite, a coitdition which is under- 

 stood wheir it is recalled that in cyclostomes these canals alone are present, 

 and in Myxiiic (llg. 5;,^, /) form a single canal with two ampulUc. A late 

 formation is an outgrowth from the saeculus, which appears e\eir in the 

 fishes as a small pocket, the Uit^ciui, containing a part of the macula 

 acustica; in the reptiles and birds the lagena becomes much larger, and 

 in the mammals is si)irally coiled and is known as the corhlca. A part of 

 the macula acustica of the lagena develops into a special nerve-end appa- 

 ratus, the ori^iDi of Corli. 



