MAMMALIA. Al 
upper extremity of the trachea; a fleshy curtain, called the 
velum palati, establishes a direct communication between their 
larynx and nasal canal. 
Their residence on the surface of the earth rendering them 
less’ exposed to the alternations of cold and heat, their tegu- 
ment, the hair, is but moderately thick, and in such as inhabit 
warm climates, even that is rare. 
The Cetacea, which live exclusively in water, are the only 
ones that are altogether deprived of it. 
The abdominal cayity is lined with a membrane called the 
peritoneum, and the intestinal canal is suspended to a fold or 
it called the mesentery, which contains numerous conglobate 
glands in which the lacteals ramify: another production of 
the peritoneum, styled the epiploon, hangs in front of and un- 
der the intestines. 
‘The urine which is retained for a time in the bladder finds 
an exit in both sexes, with very few exceptions, by orifices 
in the organs of generation. 
In all the Mammalia, generation is essentially viviparous; 
that is, the foetus, directly after conception, descends into the 
uterus enveloped in its membranes, the exterior of which is 
called chorion and the interior amntos; it fixes itself to the 
parietes of this cavity by one plexus, or more of vessels called 
the placenta, which establishes a communication between it 
and the mother, by which it receives its nourishment, and most 
probably its oxygenation, notwithstanding which, the foetus 
of the Mammalia, at an early period, has a vesicle analogous 
to that which contains the yolk in the Ovipara, receiving in 
like manner vessels from the mesentery. It has also another 
external bladder named the allantoid, which communicates 
with the urinary one by a canal called the wrachus. 
Conception always requires an effectual coitus, in which the 
semen masculinum is thrown into the uterus of the female. 
The young are nourished for some time after birth by a 
fluid (milk) peculiar to animals of this class, which is pro- 
duced by the mamme at the time of parturition, and continues 
to be so as long as is necessary. It is from the mamme that 
Vou. I.—F 28 . 
