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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 phe
nomena 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 relation
ship 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 1, 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.
The former contains the heart, lungs, and the anterior part of the alimentary canal, the gullet or esophagus; the latter contains the continuation of the alimentary canal, the stomach and intestines, and the organs in connection with it, the liver and pancreas. In the posterior portion of the abdominal cavity are placed the kidneys and organs of reproduction. The external surface of the entire body is covered over with the skin. The alimentary canal and the various cavities in connection with it are lined by a mucous membrane. Between the skin and mucous membrane are found bones, enveloped by muscles, blood-vessels, nerves, and lymphatics. The appendicular portions of the body contain no organs essential to life. They also consist fundamentally of bones, muscles, blood vessels, nerves, and lymphatics, covered with skin. The limbs are modified in form, and adapted for prehension and locomotion in accordance with the needs of the animal. The animal body not, therefore, a homogeneous organism, but is composed of a number of diverse parts. These structures, which have certain peculiarities of structure in common, form anatomical systems; e.g., the osseous or bony, the muscular, the nervous systems. A combination of several different structures working together for the accomplishment of a definite object constitutes a physiological apparatus; e.g., the digestive, the respiratory, and the urinary apparatus. As all vertebrate animals have the same fundamental plan of structure, and as their organs and tissues perform actions which closely resemble those of man, a general knowledge of the form, the construction, and the arrangement of the organs and tissues of different types of animal life forms an indispensable basis for the study of human physiology.
THE SKELETON.. Within the body of man and all vertebrated animals there is a highly developed framework, consisting of bones and cartilages, technically known as the skeleton (Fig. 1), the function of which is to afford support to all the softer tissues, to afford attachment for muscles, and to protect many delicate organs from injury. In addition to the bony skeleton there is a secondary framework, composed for the most part of fibrous or connective tissue, which ramifies everywhere throughout the body, uniting its various parts and affording support and protection to the ultimate elements of the tissues.
The skeleton naturally divides itself in accordance with the fundamental division of the body into, I, an axial, and 2, an appendicular portion. The axial portion consists of the bones of the spine, the head,