MAMMALIA. 33 
nasi; to its external parietes adhere the inferior turbinated bones, the 
superior ones which occupy its upper and posterior portion belonging to 
the os ethmoides. The jugal or cheek bone unites the maxillary to the 
temporal bone on each side, and frequently to the os frontis; finally, the 
os unguis, and pars plana of the ethmoid bone occupy the internal angle 
of the orbit, and sometimes a part of the cheek. In the embryo state 
these bones also are much more subdivided. 
Their tongue is always fleshy, connected with a bone called the hyoides, 
which is composed of several pieces, and suspended from the cranium by 
ligaments. 
Their lungs, two in number, divided into lobes, and composed of an 
infinitude of cells, are always inclosed, without any adhesion, in a cavity 
formed by-the ribs and diaphragm and lined by the pleura; the organ of 
‘voice is always at the 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 tegument, the hair, is but mo- 
derately 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 cavity is lined with a membrane called the peritoneum, 
and the intestinal canal is suspended to a fold of 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 under 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 gene- 
ration. 
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 amnios ; 
it fixes itself to the parietes of this cavity by one plexus or more of ves- 
sels 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. 
VOL. I. D 
