The enlargement of adventitious bursae over the head of the first metatarsal in hallux valgus; over the tarsus, metatarsus, and digits in the different forms of club-foot; over the angular projection in Pott’s disease of the spine; over the end of the bone in amputation stumps, and over hard tumours such as chondroma and osteoma, are described elsewhere.

CHAPTER XX

DISEASES OF BONE

Anatomy and physiology—­Regeneration of bone—­Transplantation of bone. 
    DISEASES OF BONE—­Definition of terms—­Pyogenic diseases: 
    Acute osteomyelitis and periostitis; Chronic and relapsing
    osteomyelitis; Abscess of bone—­Tuberculous disease—­Syphilitic
    disease—­Hydatids; Rickets; Osteomalacia—­Ostitis deformans of
    Paget—­Osteomyelitis fibrosa—­Affections of bones in diseases of
    the nervous system—­Fragilitas ossium—­Tumours and cysts of bone.

#Surgical Anatomy.#—­During the period of growth, a long bone such as the tibia consists of a shaft or diaphysis, and two extremities or epiphyses.  So long as growth continues there intervenes between the shaft and each of the epiphyses a disc of actively growing cartilage—­the epiphysial cartilage; and at the junction of this cartilage with the shaft is a zone of young, vascular, spongy bone known as the metaphysis or epiphysial junction.  The shaft is a cylinder of compact bone enclosing the medullary canal, which is filled with yellow marrow.  The extremities, which include the ossifying junctions, consist of spongy bone, the spaces of which are filled with red marrow.  The articular aspect of the epiphysis is invested with a thick layer of hyaline cartilage, known as the articular cartilage, which would appear to be mainly nourished from the synovia.

The external investment—­the periosteum—­is thick and vascular during the period of growth, but becomes thin and less vascular when the skeleton has attained maturity.  Except where muscles are attached it is easily separated from the bone; at the extremities it is intimately connected with the epiphysial cartilage and with the epiphysis, and at the margin of the latter it becomes continuous with the capsule of the adjacent joint.  It consists of two layers, an outer fibrous and an inner cellular layer; the cells, which are called osteoblasts, are continuous with those lining the Haversian canals and the medullary cavity.

The arrangement of the blood vessels determines to some extent the incidence of disease in bone.  The nutrient artery, after entering the medullary canal through a special foramen in the cortex, bifurcates, and one main division runs towards each of the extremities, and terminates at the ossifying junction in a series of capillary loops projected against the epiphysial cartilage.  This arrangement favours the lodgment