40 VERTEBRATE ANIMALS. 



and the posterior, by the occipital. Between the occipital, the parietal, and the sphe- 

 noidal, are interposed the temporal bones, part of which belong properly to the face. 



In the foetus, the occipital bone divides into four parts ; the sphenoidal into halves, 

 which subdivide into three pairs of lateral wings ; the temporal into three, of which 

 one serves to complete the cranium, another to close the labyrinth of the ear, and the 

 third to form the parietes of its drum, &c. These bony portions [centres of ossifica- 

 tion], which are still more numerous in the earliest period of fcetal existence, are 

 united more or less promptly, according to the species, and the bones themselves be- 

 come finally consolidated in the adult.* 



Their face is essentially formed by the two maxillary bones, between which pass the 

 nostrils, and which have the two intermaxillaries in front, and the two palate bones 

 behind ; between them descends a single lamina of the ethmoidal bone, named the 

 vomer; at the entrance of the nasal canal are the bones proper to the nose ; to its external 

 parietes adhere the inferior turbinated bones, which occupy its upper and posterior 

 portion, belonging to the ethmoidal. The jugal or cheek bone unites on each side the 

 maxillary to the temporal bone, and often to the frontal ; lastly, the lachrymal bone 

 occupies the inner angle of the orbit, and sometimes a part of the cheek. These bones 

 also present more numerous subdivisions in the embryo. 



Their tongus is always fleshy, and attached to a bone termed the hyoidal, 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 adhesion in a cavity formed by the ribs and 

 diaphragm, and lined by the pleura; their organ of voice is always at the upper end 

 of the windpipe ; a fleshy elongation, called the velum palati, establishes a direct com- 

 munication between their larynx and nostrils. 



Their residence on the surface of the earth exposing them less to the alternations of 

 heat and cold, their body has only a moderate kind of tegument, the hair or fur, and 

 even this is commonly scanty in those of hot climates. f 



The cetaceans, which live entirely in water, are the only ones that are altogether 

 deprived of it. 



The abdominal cavity is lined with a membrane called the peritonaeum ; and their 

 intestinal canal is suspended to a fold of it, termed the mesentery, which contains 

 numerous conglomate glands, in which the lacteal vessels ramify : another production 

 of the peritonaeum, named the epiploon, hangs in front of and under the intestines. 



The urine, retained for some time in the bladder, is discharged, in the two sexes, 

 with very few exceptions, by orifices in the organs of generation. 



In all mammalians, generation is essentially viviparous ; that is to say, the foetus, 

 immediately after conception, descends . [gradually] into the matrix, inclosed in its 

 envelopes, the exterior of which is named chorion, and the interior amnios ; it fixes 

 itself to the parietes of this cavity by one or more plexus of vessels, termed the 

 placenta, which establishes a communication between it and the mother, by which it 

 receives its nourishment, and probably also its oxygenation ; notwithstanding which, 



• Here it may be remarked that, descending in the series of verte- cessivcly assuming the conditions of this organ in fishes, reptiles, 



brates, the same is observable as in ascending to foetal life in the i birds, the lower and then higher groups of mammalians. — Ed. 



higher groups ; the progress of developement, in this and other re- t In some monkeys from Sierra Leone, the most torrid region in the 



spects, being arrested at different stages of advancement, according world, the hair is much elongated, but thin and coarse, as if designed 



to the class, order, and species : the brain for instance, in man, sue- ! to protect them from the solar rays. — E©. 



