14 OSTEOLOGY. 



tables, and the spongy tissue between, the diploe' ; the tables 

 also in some facial bones may be widely separated, with air 

 cavities between them. 



Irregular hones include all which are classed with the fore- 

 going. They are found in the vertebral column, in the skull, 

 and also in the limbs. They usually possess many angles and 

 indentations, with surfaces for articulation aud tendinous 

 attachment, and consist of a thin, dense, external case of 

 compact bone enclosing cancellated tissue. In proportion to 

 their size they present a much larger extent of articular 

 surface and greater mechanical strength than any other class. 



SURFACES OF BONES. 



No bone is strictly geometrical in form, although, to a casual 

 observer, some may appear so. The chief irregularities consist of 

 certain eminences and depressions, a knowledge of which is one 

 of the first requisites in the study of osteology. Eminences and 

 depressions Qxe articular or non-articular ; the former are clothed 

 with cartilage, and assist in the formation of joints. 



Non-articular eminences exist extensively on the external 

 surfaces of most bones, and receive the attachments of tendons 

 and ligaments. They are of various shapes, sizes, and densities, 

 and frequently named from their real or supposed resemblance to 

 some known object. 



The term process or apophysis, may be generally applied to 

 prominent- elevations, but processes so called are not necessarily 

 non-articular, and certain other terms are, rather arbitrarily, 

 applied. A spine is an elevation which tends to become pointed ; 

 a tubercle is a small blunt projection, which, if more developed, 

 would be called a tuberosity, while the name trochanter is 

 applied to the largest and most prominent of these A crest or 

 ridge implies a roughened line or border. 



Non-articular depressions may serve as channels of trans- 

 mission, passing completely through a bone or part of a bone, 

 and may bear either of the names foramen, canal, aqueduct, or 

 w.eatus, the first name being the most used ; or they may be 

 blind cavities in the surface of jhe bone, and if roughened for 

 the attachment of tendons or ligaments, the term fossa is some- 

 times applied to them. The terms notch and fissure indicate 

 depressions or grooves, which transmit various structures, and the 

 approximation of two notches in contiguous bones . sometimes 

 forms a foramen. When we find a depression leading to two or 

 more foramina it may be termed an hiatus. 



