THE EAR AND HEARING. 
167 
But it is in the Trias that evidences of the proximity of 
land become most numerous and most striking. Breccias 
and pebble beds occur on two distinct horizons in the 
Triassic series— (a) in the Bunter Conglomerate, and (b) in 
the Keuper Basement Breccia. 
(To be continued.) 
THE EAR AND HEARING. 
BY W. J. ABEL, B.A., F.R.M.S. 
( Continued from page 123.) 
In Animals partaking of the nature of two classes, the 
ear is still a constant mark of difference. The Ornithorhynehus 
and other Monotremata, for example, possess the columella 
of a bird ; whilst the whale and other Cetacea have a peculiar 
iclitliyic-mammalian ear. The whale, for example, would 
seem to hear, as it were, backwards, for the eustacliian 
tube opens into the blow-liole, and the external orifice is 
nearly closed. The petrotympanic bone acts as a true 
otolith, whilst the mammalian ossicula (small ear bones) 
and tympanic membrane are also present. When, therefore, 
the cetacean comes to the surface for air, it is able to hear 
aerial vibrations through the medium of the eustacliian 
tube, the while the otolithic ear'is immersed, and cognisant 
of aquatic sounds. 
It is in the mammalian ear that we reach the highest 
perfection. The external ear is now added (very motile 
in the lower animals, and to some extent also in certain 
men, especially savages), possessing a suite of muscles, and 
every ap*pliance for the discrimination of the faintest sounds. 
The cochlea, which we found commencing in reptiles, is 
here very complex, enabling the mammal to distinguish 
delicate shades of tone. The tympanic membrane is also 
fully exposed to aerial vibrations, whilst the columella is 
replaced by a chain of exquisite ossicles, connecting, as 
the columella does in birds and reptiles, the tympanic mem¬ 
brane with the covering of the fenestra ovalis, which com¬ 
municates with the internal ear. 
Taking the human as our type of the mammalian ear, 
we may describe it as consisting of three parts—the external, 
middle, and internal ear (or labyrinth). 
The External Ear includes the visible part called the 
Auricle or Pinna and the passage leading to the membrane of 
the drum. The auricle consists of one piece of cartilage 
having divisions scattered throughout it, and penetrating 
