STRUCTURE OF BONE. 



lous in their internal structure. Upon the exterior of the bone are 

 processes and rough surfaces for the attachment of muscles, and 

 foramina for the transmission of vessels and nerves, and the attach- 

 ment of ligaments. The character of long bones is, therefore, their 

 general type of structure and their divisibility into a central portion 

 and extremities, and not so much .their length ; for there are some 

 long bones as the second phalanges of the toes which are less 

 than a quarter of an inch in length, and are almost equal, and in 

 some instances, exceed in breadth their longitudinal axis. The long 

 bones are, the clavicle, humerus, radius and ulna, femur, tibia, and 

 fibula, metacarpal bones, metatarsal, phalanges and ribs. 



Short* bones are such as have no predominance of length or 

 breadth, but are irregularly cuboid in form : they are spongy in in- 

 ternal texture, and invested by a thin crust of condensed osseous tissue. 

 The short bones are, the vertebrae, coccyx, carpal and tarsal bones, 

 patellae, and sesamoid bones. 



Flat bones are composed of two layers of dense bone with an inter- 

 mediate cellular structure, and are divisible into surfaces, borders, 

 angles, and processes. They are adapted to enclose cavities ; have 

 processes upon their surface for the attachment o muscles ; and are 

 perforated by foramina, for the passage of nutrient vessels to their 

 cells, and for the transmission of vessels and nerves. They articulate 

 with long bones by means of smooth surfaces plated with cartilage, 

 and with each other either by cartilaginous substance, as at the 

 symphysis pubis ; or by suture, as in the bones of the skull. The 

 two condensed layers of the bones of the skull are named tables ; 

 and the intermediate cellular structure diploe. The flat bones are 

 the occipital, parietal, frontal, nasal, lachrymal, vomer, sternum, 

 scapulae, and ossa innominata. 



Irregular bones are those which are not distinctly referrible to 

 either of the above heads ; but present a mixed character, being 

 partly short and partly flat in their conformation. The bones of this 

 class are, the temporal, sphenoid, ethmoid, superior maxillary, in- 

 ferior maxillary, palate, inferior turbinated bones, os hyoides, and 

 sacrum. 



Structure. In structure, bone is composed of lamellae, which are 

 concentric in long, and parallel in flat bones. Between the lamella? 

 are situated numerous small longitudinal canals and minute oval 

 corpuscules. The longitudinal canals (canals of Havers) contain me- 

 dullary substance and vessels, and communicate with each other, 

 and with the medullary canal or cells. Each longitudinal canal is 

 surrounded by a series of concentric lamellae, and between these 

 lamellae, as well as between the lamellae which constitute the great 

 medullary canal of the bone, the oval corpuscules are situated. In 

 the extremities of long, in short, and in flat bones, the cells repre- 

 sent the Haversian canals, and are each surrounded by concentric 



* Wilson's classes of short and irregular bones are usually included in the title ossa 

 Cfassa or thick bones. G, 



