GENERAL STRUCTURE OF THE ANIMAL BODY. O 



If the organs, however, are subjected to a further analysis, they 

 can be resolved into simple structures, apparently homogeneous, to 

 which the name tissue has been given e. g., epithelial, connective, 

 muscle, and nerve tissue. When the tissues are subjected to micro- 

 scopic analysis, it is found that they are not homogeneous in struc- 

 ture, but composed of still simpler elements, termed cells and fibers. 

 The investigation of the internal structure of the organs, the physical 

 properties and structure of the tissues, as well as the structure of 

 their component elements, the cells and fibers, constitutes a depart- 

 ment of anatomic science known as HISTOLOGY, 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 and 



2. An appendicular portion. The axial portion consists of the head, 

 neck, and trunk ; the appendicular portion consists of the anterior 

 and posterior limbs or extremities. 



The axial portion of all mammals, to which class man zoologically 

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

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

 tends in a longitudinal direction from before backward, and which is 

 known as the vertebral column or backbone. In virtue of the exist- 

 ence of this column all the class 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 con- 

 siderable distance beyond the trunk into the tail. The vertebral 

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



