OF

HUMAN PHYSIOLOGY.

INTRODUCTION.

Definitions. If the body of any animal be dissected, it will be found to be composed of organs, such as the heart, stomach, lungs, brain, etc.; these organs again, upon a closer examination, will be found to be composed of simpler structures, known as tissues; e. g., epithelial, connective, muscular, and nervous. A description of the several organs which make up the body of any animal, their external form, their internal arrangement, their relations to each other, constitutes the science of ANIMAL ANATOMY. This may naturally be divided into--

1. Comparative Anatomy, the object of which is a comparison of the structures of two or more animals, with a view of determining their points of resemblance or dissimilarity.

2. Special Anatomy, the object of which is the investigation of the construction, form, and arrangement of the organs and tissues of any individual animal. The study of the tissues, their properties, and minute structure constitutes that branch of anatomy known as His

TOLOGY.

Human Anatomy is that department of anatomical science which has for its object the investigation of the construction of the human body. Animal Physiology is a study of the vital phenomena exhibited by the organs and tissues of which the body of any animal is composed. This may be divided into

1. Comparative Physiology, the province of which is a comparison of the vital phenomena exhibited by the various structures of two or more

animals, for the purpose of unfolding their points of resemblance and dissimilarity.

2. Special Physiology, the object of which is a study of the vital phenomena exhibited by any individual animal.

Human Physiology is that department of physiological science which has for its object the study of the vital phenomena, functions, or actions exhibited by the organs and tissues of the human body in a state of health. The functions of the human body may be arranged in three groups viz. :

1. Nutritive Functions, which have for their object the preservation of the individual, e. g., digestion, absorption, the formation and circulation of blood, respiration, calorification, secretion and excretion.

2. Animal Functions, which bring the individual into conscious relationship with the external world, e.g., sensation, motion, language, mental and moral manifestations.

3. Reproductive Functions which have for their object the preservation of the species.

General Structure of the Animal Body.-The body of every animal, from fish to man, may be divided into I, an axial, and 2, an appendicular portion. The axial portion consists of the head, neck, and trunk; the appendicular, of the anterior and posterior extremities, or limbs.

The axial portion of all mammals, to which class man zoologically belongs, as well as all birds, reptiles, batrachians, and fish, has a hard, bony, segmented axis, running from before backward, known as the back bone or vertebral column, in virtue of which all the classes just mentioned form one great division of the animal kingdom, the Vertebrata. This axis, at its anterior extremity, is variously modified and expanded to form the head. In all vertebrate animals the vertebral column forms a partition between two cavities, viz., the dorsal and the ventral. The dorsal cavity, formed by the arching of bony processes arising from the bodies of the vertebra, is narrow but elongated; anteriorly it is expanded, and forms the cavity of the head. It contains the brain and spinal cord. The ventral cavity is confined mainly to the trunk, and contains the alimentary or food canal and its appendages, as well as the heart and larger blood-vessels. The alimentary canal begins on the ventral side of the head, at the mouth, and terminates at the posterior extremity of the body.

In all mammals, the ventral cavity is subdivided by a transverse musculomembranous partition into two smaller cavities, the thorax and abdomen.