Translation 2783

CETACEA •
CHAI.UR 1
GEMUAL ChALACURISTICS OF T:112; Ohnli
16 2
Cetacea are a group of mammals from one metre to 35 metres
in length*, which have.been adapted during thp process of evalution
* The length referred to here is the zoological length, from .
the tin of the upper jaw to tue bifurcation of the flukes.
•
to an aquatiç mode of life, mostly in a marine environment. That has
resulted in remarkable changes in a number of organs, and is strongly
expressed in the shape of the body, which in most cetaceans is very
stream-lined and torpedo-like . The tail section is laterally comlior;zontal
pressed and terminates in caudal fins (flukes). There is usually.no —
A
external sign of a cervical constriction, hair Covering, external
ear pinna, and hind limbs are all absent.
The thoracic flippers fulfil
thé • function of depth-control gear; the dorsal fin may perhaps -
increase the whales' stability while swimming.
The skin is thin, smooth, and covered externally with mucous
secretions, which aid the whales' movement tnrough the water.
Tnere
is a layer of fat under the skin, permeated by a•dense network of •
collagen fibres. That layer encompasses the entire body of the whale
and protects it from mechanical injury and loss of heat, and also
reduces the animal's specifiu Weight.
The eyes are small, •and protected from water - action by fatty
secretions from a special (liarderian) gland. There are no lacrimal
glands. The external nasal orifice (blowhole) in toothed whales is
unpaired and placed far back
whale s .
lying, at the vertex of the head.; baleen
have paired nasal orifices lying side by side, placed less
far back -- at the base of the frontal rei4on of tue head. Water is
prevented from passing into the respiratory pas-agesby a system of -
muscles in the nasal canal, •which is lecated underneath tne skull.
The larynx is so constructed that the respiratory passages and the
uullet are isolated from each other, making it possible for the animal
to'swallow food in the water The lungs are lare and elastic, are •
elongated in shape, and lie in the horizontal plane of 'the body.
the musculature in the alveolar sacs of the lungs . is very strongly
developed, preventing air from being ,
dives
squeezed out whun the animal
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