The spine (vertebral column) consists of thirty-three superimposed bones termed vertebrae. Of these the upper twenty-four remain separate throughout life and form three groups. The first seven are called cervical, the succeeding twelve thoracic (dorsal), and the last five lumbar. In adult life the last nine vertebras ankylose to form two composite bones named the sacrum and the coccyx. The sacrum is formed by the fusion of five vertebrae from the twenty-fifth to the twenty-ninth inclusive; the four terminal are vestigial, and form the coccyx. In order to gain a general notion of the characters of a vertebra, it is desirable to select a bone from the middle of the thoracic series.
We have seen, that after bringing together all the fragments the Hippocratic writers have transmitted to us, relative to the structure of the human body, it would be impossible to compose from them a regular or complete treatise on anatomy ; for, with the exception of the skeleton, they possessed very limited and imperfect notions of any organic apparatus. They confounded, under a common name, the
The superior or descending vena cava carries to the heart the blood returned from the head and neck and upper extremities through the right and left innominate veins, and from the walls of the thorax, either directly through the greater azygos vein, or indirectly through the innominate veins.
The frontal bone, (os frontis, coroaale,) situated at the anterior part of the skull, and upper part of the face, is divisible into two parts (frontal and orbital), differing in size and position: of these, one extends upwards towards the vertex, forming three-fourths of the extent of the bone; the other, inferior and horizontal in its direction, forms the roof of the orbits. To place the bone in its natural position, hold it so that the orbital plates shall look downwards, and the smooth convex surface forwards.
The sleep is structured in cycles. The number and length of the cycles vary by age and individuals but on average for an adult the cycle lasts 90 minutes and about 4-6 cycles occur per night. Each cycle is divided into two parts: the non REM (non-rapid eye movement) and the REM (rapid eye movement) sleep. Dr. Michel Jouvet discovered the phase called "REM sleep." In the late 1950s, he made experiments on cats and noted a phase of rapid cortical activity identical to the waking phase. In 1962, Jouvet presented the necessary arguments to validate his theory on sleep, theory that states two dependent states of different structures and mechanisms.
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