TEXTURES.] ANATOMY 853 work, branch and sometimes anastomose. They resist the action of acetic acid like the yellow fibres of connective tissue; and Bonders has described a continuity between them and the elastic fibres of the connective tissue, which forms the investing perichondrium of this form of cartilage. The yellow fibro- cartilage has no tendency to ossify. The bars and plates of cartilage, except the encrusting hyaline cartilages, and the interarticular, marginal, and in vesting white fibro-cartilages, are surrounded by a fibrous membrane or perichondrium. In the adult human body cartilage is not penetrated by blood-vessels, but is nourished by the vessels which ramify in its investing perichondrium. In the foetus, however, and in the large masses of cartilage which are found in the skeletons of the cetacea and of the cartilaginous fishes, the cartilage is permeated by canals in which blood-vessels ramify. In the encrusting cartilages, the cartilage is nourished by the blood-vessels of the synovial membrane of the joint, which, in the case of the articular cartilage, form a vascular ring around its margin; and, both in it and in the forms of white fibro-cartilage that do not possess a perichondrium, by the vessels of the bone, to which these cartilages are as a rule attached. In the movable joints, after the child has begun to use its limbs, the synovial membrane is not continued over the free surface of the articular cartilage, but stops at its margin along the line of the vascular ring. In the foetus, however, it has been stated that both blood-vessels and synovial membrane are prolonged over the free surface of the articular cartilage.
- lop- In the development of hyaline cartilage the contents of
- of the embryonic cells of the part, where the cartilage is to be
age> produced, become clear, and a cell wall differentiates around the exterior of the cell. The nuclei in the cells divide and subdivide, so that a multiplication of the cells by endo genous reproduction takes place. Hyaline matrix sub stance then appears between the cells, and is concentrically arranged around them; it is believed to be formed by a special conversion of successive layers of the cell proto plasm into a substance which yields choncirine on boiling. The fibro-cartilages, both white and yellow, but especially the latter, yield but little chondrine on boiling, for the fibrous matrix of the white fibro-cartilage is a gelatine- yielding substance, like the white fibres of connective tissue, whilst the fibres of the yellow fibro-cartilage partake of the nature of elastic tissue. The fibro-cartilages, there fore, form a group which links together the connective and cartilaginous tissues. f OSSEOUS TISSUE. The osseous tissue, or Tjone, is that .which constitutes the hard framework of the skeleton. _Each bone consists of a hard, more or less dense, tough, and but slightly elastic material. The elasticity of the bones is more marked in young than in adult and aged persons. From differences in their external configuration, bones are divided into long or cylindrical, e.g., femur; short, e.g., carpal or tarsal bones; flat or plate-like, e.g., scapula; irregular bones, e.g., vertebrae. These variations in shape do not, however, involve differences either in composition or minute structure. Bone consists chemically of an earthy and an animal substance intimately blended together. The earthy matter forms about two-thirds of it, and consists chiefly of phosphate of lime, which, from its abundance in bone, is frequently called " bone earth." Carbonate of lime and a small proportion of soda and magnesia salts are also present. The hardness of bone is due to the presence of the earthy matter. The animal matter forms the remaining third, and yields gelatine on boiling; it imparts elasticity and toughness to the bone, and binds together the particles of earthy matter. Bone presents two different structural characters to the naked eye. The outer part of a bone is its hardest part, and forms a dense external shell, technically called the compact tissue. The interior of a bone is much less firm, and is made up of thin delicate plates or bars, or trabecles, which intersect each other at various angles, and form a lattice-like arrangement, technically called the spongy or cancellated tissue. The plates and bars of the spongy tissue are continuous with the inner surface of the compact tissue. In the long bones the interior of the shaft is hol lowed into a canal, named the medullary canal, the walls of which are formed by the compact tissue, and the can cellated tissue is found only at the articular ends of these bones; the thickness of the compact tissue in a long bone is always greater at the centre of the shaft than at or near the articular ends. i If the outer surface of the compact tissue of a long bone and the wall of the medullary canal be examined with a pocket lens, they will be seen to be riddled by multitudes of minute orifices, which are the mouths of minute tubular passages or canals that traverse the compact tissue. These passages are named Haversian canals, and their arrange ment may be studied by making thin sections through the compact tissue, and submitting these to microscopic examination, when they will be seen to pass longitudinally or very obliquely through its substance, so as to terminate by rounded orifices either on its outer surface, or on the inner surface, which forms the wall of the medullary canal. These canals are connected together at intervals by short transverse or oblique canals. Owing to these communica tions the dense osseous tissue is permeated by an anasto mosing network of canals, which, as they contain blood vessels, may be named vascular canals. These canals are circular in section, and vary in diameter from about ^ 7 th to -ro sffth inch. They not un frequently are dilated at the inner end, where they open into the spaces of the cancellated tissue. The compact tissue of all bones possesses a system of canals similar to those found in the long bones, but when bone occurs in the form of very thin plates the canals may be absent. In addition to the Haversian canals, irregular spaces, named Haversian sftaces by Tomes and De Morgan, may also be seen in sections through the com pact tissue. They are met with not only in young but in adult bones, and are regarded as produced by absorption of the bone in those particular localities. In thin sections through bone, more especially when the Haversian canals are transversely divided, the dense tissue or matrix of the bone which surrounds the canals is seen to be arranged in concentric rings, as if it were built up of a series of lamellce superimposed on each other. These lamellae do not at all times form complete circles, and the number which sur round a canal may vary from two or three to half a dozen; they are sometimes called the Haversian lamella?. Other lamellae lie in relation to the periosteal surface of the bone, and are called peripheral lamellae ; whilst others again are, as it were, intercalated between adjacent Haversian systems of lamellae, and are named intermediate or interstitial. It has been pointed out by Sharpey that a bone lamella, after the earthy matter has been dissolved out by the action of an acid, is made up of multitudes of fine trans parent fibres, which intersect each other and form a net work. Biit he has further shown that the lamellae are perforated by fibres, or bundles of fibres, which pass through them either perpendicularly or obliquely, so as to bolt adjacent lamella together. With a little care, the per forating fibres of Sharpey may be drawn out of the holes or sockets in which they are lodged. When thin sections through a macerated and dried bone are examined under the higher powers of the microscope, the lamellated matrix is seen to exhibit a very peculiar appearance, which is characteristic of the osseous tissue.
Between the surfaces of adjacent lamella) irregularly
