470 Dynamic Theory. 



als, the cochlea is spiral. In the Whale tribes and the Hedghog, the cochlea- 

 makes one and a half turns. In the Paca ( a rodent) it makes five turns. 

 In the apes and man it makes two and a half turns. The ear of man, 



Fig. 213. -Ear bones of .4. Bat. B Shrew, Stapes or Stirrup bone of 



C Mole. D Hedgehog. ^.Marmot. /.Sloth. 



Blood vessels running through C and E. The discs at the hottom indicate the shape 



of the foot of the stirrup. ( Owen,) 



while more discriminating as to musical sounds than that of most other 

 animals, is far behind many of them in the acuteness of its perception 

 and its sensitiveness. 



The eustachian tube is 

 the remains of the first 

 gill slit in the embryo. 

 In the primitive cartilagi- 

 nous fishes, this gill slit 



remains open, and is a 

 blow-hole leading from the 

 back part of the mouth. 

 In the further develop- 

 ment of the ear in the 

 higher vertebrates, the gill 

 arches, before and behind 

 this gill slit, namely, the 

 first and second, originate 

 the parts of the middle 



FIG. 214. Stapes of Ungulate Mammals. 

 A. Hippopotamus. D. Horse. F. Rhinoceros. 



.-Hog. JS.-Tapir. ^.-Elephant. 



C'. Musk-ox- 



FIG 215. Stapes of Carnivorous Mammals. 

 A. Seal. B. Otter. a. Bear. D Dog. .E.-Tiger. (Owen.) 



and external ear. The tympanic membrane is formed by the coalescence 



of the sides of the gill opening at a certain point. Whatever is left of 



the opening, outside of the point at which this coalescence takes place, 



v\ >>xnes the meatus, or external auditory canal. Of the part left inside 



