38 OSTEOLOGY. 



have exceedingly thin coats; and when the bony structure is divided, thej 

 remain patulous, and do not contract in the canals in which they are. contained. 

 Hence the constant occurrence of purulent absorption after amputation, in those 

 cases where the stump becomes inflamed, and the cancellous tissue is infiltrated 

 and bathed in pus. 



Lymphatic vessels have been traced, by Cruikshank, into the substance of bone, 

 but Kolliker doubts their existence. Nerves are distributed freely to the perios- 

 teum, and accompany the nutritious arteries into the interior of the bone. They 

 are said, by Kolliker, to be most numerous in the articular extremities of the 

 long bones, in the vertebrae, and the larger flat bones. 



Periosteum. The bones are covered by a tough fibrous membrane, the periosteum, 

 which adheres to their surface in nearly every part, excepting at their cartilaginous 

 extremities, and where strong tendons are attached. ,It is highly vascular; and, 

 from it, numerous vessels pass into minute orifices which cover the entire surface 

 of the bone. It consists of two layers closely united together; the outer one 

 formed chiefly of connective tissue, and occasionally a few fat-cells ; the inner one, 

 of elastic fibres of the finer kind, which form dense elastic membranous networks, 

 superimposed in several layers (Kolliker). In young bones, this membrane is 

 thick, very vascular, intimately connected at either end of the bone with the 

 epiphysal cartilage ; but less closely connected with the shaft, from which it is 

 separated by a layer of soft blastema, in which ossification proceeds on the exterior 

 of the young bone. Later in life, the periosteum is thinner, less vascular, and 

 more closely connected with the adjacent bone, this adhesion growing stronger as 

 age advances. The periosteum serves as a nidus for the ramification of the vessels 

 previous to their distribution in the bone ; hence the liability of bone to exfolia- 

 tion or necrosis, when, from injury, it is denuded of this membrane. 



Marrow. The medullary canal of adult long bones, the cavities of the cancellous 

 tissue, and the larger Haversian canals, are filled with a substance called marrow, 

 and lined by a highly vascular areolar tissue, the medullary membrane, or internal 

 periosteum. It is by means of the vessels which ramify through this membrane, 

 that the nourishment of the medulla and contiguous osseous tissue is effected. 



The marrow differs in composition at different periods of life, and in different 

 bones. In young bones, it is a transparent reddish fluid, of tenacious consistence, 

 free from fat; and contains numerous minute roundish polynucleated cells. In 

 the shafts of adult long bones, the marrow is of a yellow color, and contains, in 

 100 parts, 96.0 fat, 1.0 areolar tissue and vessels, and 3.0 of fluid with extractive 

 matters ; whilst, in the flat and short bones, in the articular ends of the long bones, 

 in the bodies of the vertebras, the base of the cranium, and in the sternum and 

 ribs, it is of a red color, and contains, in 100 parts, 75.0 water, and 25.0 solid 

 matter, consisting of albumen, fibrin, extractive matter, salts, and a mere trace of 

 fat. It consists of fat-cells with a large quantity of fluid, containing numerous 

 polynucleated cells, similar to those found in fcetal marrow. 



Development of Bone. From the peculiar uses to which bone is applied in 

 forming a hard skeleton or framework for the softer materials of the body, and in 

 inclosing and protecting some of the more important vital organs, we find its 

 development takes place at a very early period. Hence, the parts that appear 

 soonest in the embryo are the vertebral column and the skull, the great central 

 column, to which the other parts of the skeleton are appended. At an early period 

 of embryonic life, the parts destined to become bone consist of a congeries of cells, 

 connected together by an amorphous blastema which constitutes the simplest form 

 of cartilage. This temporary cartilage, as it is termed, is an exact miniature of 

 the bone which, in due course, is to take its place ; and as the process of ossification 

 is slow, and not completed until adult life, it increases in bulk by an interstitial 

 development of new cells. The next step in this process is the ossification of the 

 intercellular substance, and of the cells composing the cartilage. Ossification 

 commences in the interior of the cartilage at certain points, called points or centres 

 of ossification, from which it extends into the surrounding substance. This mode 



