20 ATLAS AND TEXT-BOOK OF HUMAN ANATOMY. 



most important short bones of the human body are: the true vertebrae, the carpal bones, the 

 tarsal bones, the patella, and the sesamoid bones. 



In addition to the long, flat, and short bones there are a number which cannot be classified 

 in any of the three categories. These are designated as irregular bones ; as a rule, they repre- 

 sent transition forms between the broad and flat bones, as in the cases of the sacrum and of 

 many of the cranial bones. Among the latter there are also some — for example, the temporal 

 bone and the occipital bone — which in a portion of their extent are typical flat bones, while in 

 their remaining portions they would be regarded as belonging to the group of the short or irreg- 

 ular bones. 



All the varieties of bones may possess prominences which take the form of projections, 

 ridges, and processes of the most varied shapes. According to their size and form, they are 

 designated as tubercles, tuberosities (rough, more or less pronounced projections), spines, crests 

 (rough lines or projecting ridges), processes, condyles (also termed condyloid or articular processes), 

 epicondylcs (i. e., projections situated above the condyles), and outgrowths (apophyses). In 

 a similar manner many bones possess excavations (fovea or jossce), impressions, grooves, furrows 

 (sulci), notches (incisures), perforations (foramina), slits (hiatus), and canals. The enlarged 

 rounded ends, particularly of the long bones, are frequently called heads, while the constriction 

 situated beneath them is known as the neck. All bones possess larger or smaller fora^nina for 

 the entrance of the nourishing blood-vessels; these are known as the nutrient foramina, and 

 are particularly large in the shafts of the larger long bones, where they lead into a nutrient canal, 

 which extends into the medullary cavity. 



The bones of the human body are usually studied in the macerated condition, i. e. y after 

 their soft parts have been removed by putrefaction. The bones of the living body and of the 

 dead subject, however, consist not only of bony substance, but also of a series of soft tissues, 

 some of which partly resist putrefaction, so that the "entire bone" is composed of the following 

 constituents: (i) The actual bony tissue; (2) the periosteum; (3) the articular cartilage; (4) 

 the bone-marrow; and (5) the nutrient vessels and nerves. 



The macerated bone represents not only the bone-ash, *. e ., the calcium salts of the bone, but also contains other 

 organic constituents. The bone substance consists chemically of almost two-thirds inorganic, and of a little more than 

 one-third organic material ; the latter is chiefly gelatin or ossein, and may be demonstrated in the form of the so-called 

 bone-cartilage by extracting the calcium salts with acids. The inorganic constituents of bone are, calcium carbonate 

 (about 85.5 per cent.), calcium phosphate (about 9 per cent.), calcium fluoride (about 3.5 per cent.), and magnesium 

 phosphate (about 1 .75 per cent.), and may be demonstrated by heating the dried bone to incandescence. Both the bone 

 cartilage and the calcined bone retain the original shape of the bone from which they were obtained, the organic and the 

 inorganic constituents being intimately intermingled. 



The actual bony tissue appears in two modifications, which pass into each other, how- 

 ever, without demarcation, the compact substance and the spongy substance. The former has 

 a dense and apparently quite uniform structure, while the spongy substance consists of a fine 

 network of bony trabeculae, which at first sight seem to be without definite arrangement. 



In reality, however, the architecture of the spongy substance is by no means irregular. 

 Its parts are arranged in such a manner as to produce a firm and resistent structure with the 

 greatest possible saving in weight, and a careful examination of its trabeculae and plates will 



