MAMMALIA. S3 



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 velwn 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, 

 w^hich 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 urachus. 



Conception always requires an effectual coitus, in which the semen 

 masciilinum is throvni into the uterus of the female. 



VOL. I. U 



