46 GENERAL ANATOMY OF THE SKELETON 



spaces become somewhat enlarged as the bones grow. The epiphyses remain separated from the 

 shaft by a narrow cartilaginous (cambium) layer for a definite time (Fig. 9). This layer ulti- 

 mately ossifies, the distinction between shaft and epiphysis is obliterated, and the bone assumes 

 its completed form and shape. The same remarks also apply to the processes of bone which are 

 separately ossified, such as the trochanters of the femur. The bones, having been formed, con- 

 tinue to grow until the body has acquired its full stature. 



The number of ossific centres varies in different bones. In most of the short bones ossification 

 commences at a single point in the centre, and proceeds toward the circumference. In the long 

 bones there is a central point of ossification for the shaft or diaphysis; and one or more for each 

 extremity, the epiphysis. That for the shaft is the first to appear. The union of the epiphvses 

 with the shaft takes place in the reverse order to that in which their ossification began, with 

 the exception of the fibula, and appears to be regulated by the direction of the nutrient arterv 

 of the bone. Thus, the nutrient arteries of the bones of the arm and forearm are directed toward 

 the elbow, and the epiphyses of the bones forming this joint become united to the shaft before 

 those at the shoulder and wrist. In the lower limb, on the other hand, the nutrient arteries 

 pass in a direction from the knee; that is, upward in the femur, downward in the tibia and fibula; 

 and in them it is observed that the upper epiphysis of the femur and the lower epiphysis of the 

 tibia and fibula become first united to the shaft. 



Where there is only one epiphysis, the nutrient artery is directed toward that end of the bone 

 where there is no additional centre, as toward the acromial end of the clavicle, toward the distal 

 end of the metacarpal bone of the thumb and great toe, and toward the proximal end of the other 

 metacarpal and metatarsal bones. 



Besides these epiphyses for the articular ends, there are others for projecting parts or processes, 

 which are formed separately from the bulk of the bone. For an account of these the reader 

 is referred to the description of the individual bones in the sequel. 



A knowledge of the exact periods when the epiphyses become joined to the shaft is often 

 of great importance in medicolegal inquiries. It also aids the surgeon in the diagnosis of 

 many of the injuries to which the joints are liable; for it not infrequently happens that on the 

 application of severe force to a joint the epiphysis becomes separated from the shaft, and such 

 an injury may be mistaken for a fracture or dislocation. 



Applied Anatomy. It has been stated above that the bones increase first in, length by ossi- 

 fication continuing to extend in the epiphyseal cartilage, which goes on growing in advance of 

 the ossifying process; and secondly in circumference by deposition of new bone from the deeper 

 layer of the periosteum. A thorough realization of these facts is essential to the student, when 

 he comes to consider the various pathological changes which affect bone. Anything which inter- 

 feres with the growth at the epiphyseal line will lead to a diminution in the length which the bone 

 should attain in adult life, and similarly anything which interferes with the growth from the 

 deeper layer of the periosteum will result in a disproportion in the thickness of the bone. Thus, 

 separation of the epiphyses, septic or tuberculous disease about the epiphyseal line, and excisions 

 involving the epiphyseal line, will result in varying amounts of shortening of the bone, as com- 

 pared with that of the opposite side; whereas separation or imperfect nutrition of the periosteum 

 results in defective growth in circumference. 



It is thus obvious that a careful study of osseous development is of the very greatest utility 

 in the proper understanding of bone disease; and, moreover, that an accurate knowledge of 

 the blood supply of a long bone has many important bearings. The outer portion of the compact 

 tissue being supplied by periosteal vessels, which reach' the bone through muscle attachments, 

 it follows that where the muscles or muscle attachments are well developed, and therefore amply 

 supplied w T ith blood, the periosteum will also be well nourished and the bones proportionately 

 well developed in girth ; this is well seen in strong, muscular men with well-marked ridges on 

 the bones. Conversely, if the muscle development be poor, the bones are correspondingly 

 thin and light, and if from any cause a limb has been paralyzed from early childhood, all of the 

 bones of that extremity are remarkable for their extreme thinness that is to say, the periosteal 

 blood supply has been insufficient to nourish that membrane, and consequently very little new 

 osseous tissue has been added to the bones from the outside. 



The best example of this condition is seen in connection with the disease known as infantile 

 paralysis, where a limb becomes paralyzed at a very early period of childhood, where the muscles 

 become flaccid and atonic, and where the blood supply is in consequence very greatly diminished. 

 In such cases, although the limb does continue to grow in length from the epiphyseal lines, its 

 length is considerably less than on the normal side, as a result of the imperfect nutrition ; but the 

 most striking feature about all the long bones of the limb is their remarkable tenuity, little or 

 no addition having been made to their diameters. 



In cases where the periosteum has been separated from the compact tissue by extensive 

 injury or inflammatory exudation, necrosis or death of the underlying portion of bone takes 

 place, due to interference with the blood supply, and the dead portion or sequestrum has to be 

 subsequently separated and cast off. 



Cases, however, occur in w r hich the inflammatory process affects the whole 01 a great portion 



