INTRODUCTION. 19 



or as it is prosecuted largely with the microscope, microscopic 

 anatomy. 



Human anatomy is that department of anatomic science which 

 has for its object the investigation of the construction of the human 

 body. 



GENERAL STRUCTURE OF THE ANIMAL BODY. 



The body of every animal, from fish to man, may be divided 

 into 



1 . An axial portion, consisting of the head, neck, and trunk ; and 



2. An appendicular portion, consisting of the anterior and posterior 



limbs or extremities. 



The axial portion of all mammals, to which class man zoologi- 

 cally belongs, as well as of all birds, reptiles, amphibians, and fish, 

 is characterized by the presence of a bony, segmented axis, which 

 extends in a longitudinal direction from before backward, and which 

 is known as the vertebral column or backbone. In virtue of the 

 existence of this column all the classes of animals just mentioned 

 form one great division of the animal kingdom, the Vertebrata. 



Each segment, or vertebra, of this axis consists of 



1. A solid portion, known as the body or centrum, and 



2. A bony arch arising from the dorsal aspect. and surmounted by 



a spine-like process. 



At the anterior extremity of the body of the animal the vertebrae 

 are variously modified and expanded, and, with the addition of new 

 elements, form the skull; at the posterior extremity they rapidly 

 diminish in size, and terminate in man in a short, tail-like process. 

 In many animals, however, the vertebral column extends for a 

 considerable distance beyond the trunk into the tail. The vertebral 

 column may be regarded as the foundation element in the plan of 

 organization of all the higher animals and the center around which 

 the rest of the body is developed and arranged with a certain degree 

 of conformity. In all vertebrate animals the bodies of the segments 

 of the vertebral column form a partition which serves to divide 

 the trunk of the body into two cavities viz., the dorsal and the 

 ventral. (See Fig. i.) 



The dorsal cavity is found not only in the trunk, but also in 

 the head. Its walls are formed partly by the arches which arise 

 from the posterior or dorsal surface of the vertebras and partly by 

 the bones of the skull. If a longitudinal section be made through 

 the center of the vertebral column, and including the head, the 

 dorsal cavity will be observed running through its entire extent. 

 Though for the most part it is quite narrow, at the anterior ex- 



