30 MAMMALIA. 



the Cetacea, the Walrus, many Seals, the Mole, Ornithorynchus 

 and Pangolins. The ears are, on the contrary, in the African Ele- 

 phant, very large pendulous flaps ; they are much smaller in the 

 Asiatic species ; they are largest of all in many Cheiroptera, e. g. 

 Plecotus auritus, where they are nearly as long as the body, and the 

 tragus also is greatly developed, exhibiting manifold forms through- 

 out this order, in which the ears are very membranous. Hanging 

 ears appear to occur in the Dogs, Pigs, and Goats, only when domes- 

 ticated. In Man the cartilage of the ear consists only of one piece, 

 while in most Mammalia three can be distinguished. The concha 

 is the largest cartilage, and trumpet-shaped. Above the anterior 

 part of the convex surface of the concha lies the cartilage scuti- 

 formis, which merely serves as a surface of attachment to several 

 muscles, but does not contribute to the formation of the concha. 

 The cartilago annularis lies over the external auditory meatus in 

 the lower curve of the concha, to which it is united by ligament, 

 and completes the meatus. While in Man the muscles of the 

 external ear are only feebly developed, and that organ can be but 

 slightly moved, very numerous muscles turn the ear of the Mam- 

 malia in all directions. In the Horse there are enumerated seven- 

 teen separate muscles, of which 'the depressor, adductor, and rotator, 

 are in particular wanting in man. In many diving animals pecu- 

 liar valve-shaped projections are found, by which the external meatus 

 is closed and protected against the entrance of water ; thus, for 

 example, the narrow tortuous meatus of the Ornithorynchus has 

 a valve externally, and in the Water-shrew the antitragus can 

 close the external meatus at will. The external meatus is lined 

 with a delicate skin, and contains the secretory sacs of the cerumen, 

 which are not even wanting in the Cetacea. This last-named 

 order presents further peculiarities, which here require notice. The 

 tympanic cavity exhibits a very peculiar formation in the large 

 sinuses, which are appended to it, and penetrate partly into bony 

 cavities, which have been regarded as receptacles for large blood- 

 vessels, but are in truth auditory sinuses, which extend partly into 

 the cranial bones, and, partly enclosed by a peculiar smooth and 

 shining membrane, stretch over them. The completely membranous 

 and never cartilaginous Eustachian tube extends from a large mem- 

 branous sinus, with which the bony tympanic cavity is continuous, 

 inward and upward, to open upon the external side, very high 

 up in the bony nasal cavity. The internal lining of this tube 

 forms several crescentic valves, which can not however completely 



