GENERAL STRUCTURE OF THE ANIMAL BODY. 



The ventral cavity is confined mainly to the trunk of the body. 

 Its walls are formed by muscles and skin, strengthened in most 

 animals by bony arches, the ribs. Within the ventral cavity is 

 contained a musculo-membranous tube or canal known as the ali- 

 mentary or food canal, which begins at the mouth on the ventral 

 side of the head, and, after passing through the neck and trunk, ter- 

 minates at the posterior extremity of the trunk at the anus. It 

 may be divided into mouth, pharynx, esophagus, stomach, small and 

 large intestines. 



In all mammals the ventral cavity is divided by a musculo-mem- 

 branous partition into two smaller cavities, the thorax and abdomen. 

 The former contains the lungs, heart and its great blood-vessels, and 

 the anterior part of the alimentary canal, the gullet or esophagus ; 

 the latter contains the continuation of the alimentary canal that is, 

 the stomach and intestines and the glands in connection with it, the 

 liver and pancreas. In the posterior portion of the abdominal cavity 

 are found the kidneys, ureters, and bladder, and in the female the or- 

 gans of reproduction. The thoracic and abdominal cavities are each lined 

 by a thin serous membrane, known, respectively, as the pleural and 

 peritoneal membranes, which, in addition, are reflected over the sur- 

 faces of the organs contained within them. The alimentary canal 

 and the various cavities connected with it are lined throughout by a 

 mucous membrane. The surface of the body is covered by the skin. 

 This is composed of an inner portion, the derma, and an outer portion, 

 the epidermis. The former consists of fibers, blood-vessels, nerves, 

 etc. ; the latter of layers of scales or cells. Embedded within the 

 skin are numbers of glands, which exude, in the different classes of 

 animals, sweat, oily matter, etc. Projecting from the surface of the 

 skin are hairs, bristles, feathers, claws. Beneath the skin are found 

 muscles, bones, blood-vessels, nerves, etc. 



The appendicular portion of the body consists of two pairs of 

 symmetric limbs, which project from the sides of the trunk, and 

 which bear a determinate relation to the vertebral column. They 

 consist fundamentally of bones, surrounded by muscles, blood-vessels, 

 nerves and lymphatics. The limbs* though having a common plan 

 of organization, are modified in form and adapted for prehension 

 and locomotion in accordance with the needs of the animal. 



Anatomic Systems. All the organs of the body which have cer- 

 tain peculiarities of structure in common are classified by anatomists 



