ANATOMY SPECIAL ANATOMY OF THE HUMAN BODY Man, zoologically speaking, belongs to the Mammalian class of the Vertebrate sub-kingdom, i.e., his young are brought forth alive, and nourished during infancy on milk secreted in mammary or milk-forming glands. In common with all vertebrate organisms, lie possesses a spine or vertebral column and a skull, in which are contained the brain and the spinal marrow, and on the ventral surface of the spinal column are situated the several subdivisions of the alimentary canal.

But man possesses certain special or distinctive anatomical characters. The most noticeable, as seen on an external inspection of his body, is his erect position. He is, indeed, the only living creature that can walk or stand erect, i.e., with the axis of the spine vertical ; with the hip and knee joints capable of beim-, fully extended, so that the leg is brought into line with the thigh ; with the foot so planted on the ground that it rests on the heel behind and on the roots of the toes in front ; with the upper limbs so arranged as to act, not as instruments of progression, but of prehension ; and with the head so balanced on the top of the spine that the face and eyes look directly to the front. His bones, joints, and muscles are constructed and arranged so as to enable him to preserve the erect attitude without fatigue. In other vertebrate the axis of the spine is oblique or horizontal, the hip and knee joints are permaresponding to the human upper extremities, are, in the form of legs, wings, or fins, instruments of progression, and the head is articulated with the spine at or near the hinder end of the skull. Owing to the oblique or horizontal attitude of the body in the vertebrate generally, and its erect describing the relative position of different parts are not used in the same sense by the human and comparative anatomist. Thus, parts which are superior, or above other parts, in the human body, are anterior, or in front, in other vertebrate ; and parts which are posterior, or behind other parts in man, are superior to them in other vertebrate. To obviate the confusion which must necessarily arise when comparing the human body with that of other vertebrates, certain descriptive terms have been recommended which. may be employed whether the position, of the body be erect or non-erect. Thus,. the aspect of parts directed towards the region where the atlas or first vertebra is situated is atlantal, that directed towards the sacrum is sacral, that towards the back is dorsal, that towards the front is ventral or hcental. Quite recently atlantal, and post-axial to sacral.

The body may be considered as divided by an imaginary plane, the mesial plane, into two lateral and similar halves, a right and left, so that it exhibits a bilateral symmetry; and the constituent parts are described as being external or internal to each other, according to their relative position to this plane. For descriptive purposes, also, we may subdivide the body into AXIAL and APpENDICULAR portions. The AXIAL part is the stock or stem of the body, and consists of the Head, I the Neck, and the Trunk. The trunk is again subdivided into the chest or Thorax, and the belly or Abdomen; and the abdomen is again subdivided into the abdo men proper and the Pelvis. The axial part contains the organs essential to the preservation of life. In the head is lodged the brain, from which the spinal marrow is prolonged down the spinal canal. At the sides of the head are the ears, and opening on to the face are the eyes, nostrils, and mouth. Prolonged down the neck are the gullet and windpipe, with the latter of which is associated the oraan of voice. Within the chest lie the heart, lungs, and gullet; and in the abdomen are contained the stomach, intestine, liver, spleen, pancreas, kidneys, and other organs concerned in the urinary and generative functions. The APPENDICULAR part forms the limbs, which do not contain organs essential to life. In man the limbs are called Upper and Lower - the former are instruments of prehension, the latter of progression. The subdivisions of the body are not homogeneous in structure, but are built up of several systems of organs, each system being characterised not only by peculiarities in form, appearance, and structure, but by possessing special functions and uses. Thus the hones collectively form the Osseous system; the joints the Articulatory system; the muscles, which move the bones at the joints, the Muscular system; and these several systems collectively constitute the organs of Locomotion. The blood and lymph vessels form the Vascular system ; the brain, spinal marrow, and nerves, the Nervous system, with which is intimately associated the organs of Sense; the lungs and windpipe, the Respiratory system; the alimentary canal, with the glands opening into it, the Digestive system; the kidneys, bladder, and urethra, the Urinary system ; the testicles, spermatic duets, and penis in the male, with the ovaries, uterus, and clitoris in the female, the Generative or Reproductive system; the skin, with the hair and nails, the Tegumentary system. These various systems are so arranged with reference to each other as to form an organic whole.

The organs of locomotion consist of the muscles or active organs, and the bones and joints or passive organs. The anatomy of the bones will first attract our attention.