Medicine

The sternum, (os pectoris: xiphoides ; French : le sternum) is situated in the median line, at the fore part of the thorax: it is flat and narrow, but not of equal width in its entire extent, being broad at its upper part, then narrowed somewhat, after which it widens a little; finally it becomes compressed and narrow where it joins the ensiform cartilage. Its direction is oblique from above downwards and forwards; and the inclination forwards, together with the curve backward in the dorsal part of the vertebral column, causes a considerable increase in the anteroposterior diameter of the thorax. We have to consider successively its surfaces, extremities, and borders.

The true vertebra are divided into three sets, named from the regions they occupy, cervical, dorsal, lumbar. They present, 1. certain general characters by which they may at once be distinguished from bones of any other class; 2. those of each region (cervical, dorsal, lumbar,) exhibit peculiar characters by which they are severally distinguished ; 3. certain vertebras present special or individual characters.

The sacrum, much the largest piece of the vertebral column, is placed, when the body is in the erect position, at the superior and posterior part of the pelvis, beneath the last lumbar vertebra, above the coccyx, and between the ossa innominata, between which it is inserted, in some measure like a keystone into an arch. 

The vertebral column (columna vertebralis, rachis, spina,) is situated along the median line, at the posterior part of the trunk, the length of which it determines.

The cervical vertebrae (french: vertèbres cervicales) are seven in number; they are smaller than those in the other regions, which results from the size of the body and processes being less than that of the corresponding parts in the dorsal and lumbar classes. The vertebral foramen is of a triangular form, and larger proportionally than in the other classes. 

The first dorsal vertebra is marked at each side by a complete articular surface for the first rib, and on its inferior border by a slight excavation, which receives half the head of the second : the upper articular processes are oblique, and the spinous more nearly horizontal than those below it. 

These bones of the coccyx (French: coccyx), when united together, which is usually the case in advanced life, are supposed to resemble a cuckoo's bill and are therefore called coccygeal. Most commonly there are four of them, sometimes but three; in a few instances five have been found. They diminish gradually in size from above downwards, which gives them, when taken together, a pyramidal form. As they are placed in a continuous line with the inferior third of the sacrum, they form a slightly concave surface anteriorly, a convex one posteriorly.

Amongst the lumbar vertebrae, the fifth only is distinguishable by any peculiarity deserving of notice, its body being thicker anteriorly than posteriorly, and its transverse process short, thick, and rounded. 

 

The vertebrae, or separate pieces of which the column is made up, are so named from their mobility (vertere, to turn). They are divided into true and false ; the former term being applied to those which remain separate in the adult, and retain their mobility; the latter to such as become united into one mass (viz. the sacrum), or degenerate as it were, and lose all the ordinary characters of vertebrae (viz. the coccyx). 

We include under this heading of appendices: 1° the aponeuroses, which cover the muscles or even envelop them entirely

Anatomic description of the Atlas, the Axis and the Prominent vertebra, the first second and cervical vartebra.

Muscle in humans has an average density of 1055.

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