SECTION III 



THE AETICULATTONS 



Revised for the Fifth Edition 

 By FREDERIC WOOD JONES, D.Sc, M.B., B.S.(Lond.), M.R.C.S.,L.R.C.P. 



HEAD OF THE DEPARTMENT OP ANATOMY AND LECTURER IN THE LONDON SCHOOL OP MEDICINE POR WOMEN. 



THE CONSTITUENTS OF AN ARTICULATION 



THE section devoted to the Articulations or Joints deals with the union of the 

 various and dissimilar parts of the human skeleton. The following struc- 

 tures enter into the formation of joints. 

 Bones constitute the basis of most joints. The long bones articulate by their 

 ends, the flat by their edges, and the short at various parts on their surfaces. The 

 articular ends are usually expanded, and are composed of cancellous tissue, sur- 

 rounded by a dense and strong shell of compact tissue. 



This shell has no Haversian canals (the vessels of the cancellous tissue turn back and do 

 not perforate it), or large lacunae, and no canaliculi, and is thus well adapted to bear pressure. 

 This "osteoid" layer may represent in part calcified cartilage rather than true bone. 



The cartilage which covers the articular ends of the bones is called articular, 

 and is of the hyaline variety. It is firmly implanted on the bone by one surface, 

 while the other is smooth, pohshed, and free, thus reducing friction to a minimum, ,' 

 while its slight elasticity tends to break jars. It ends abruptly at the edge of the 

 articulation, and is thickest over the areas of greatest pressure. 



Another form of cartilage, the white fibrous, is also found in joints: — 



(i) As interarticular cartilage in diarthrodial joints — viz., in the knee, mandibular, 

 sterno-clavicular, radio-carpal, and occasionally in the acroraio-clavicular joint. It is interposed 

 between the ends of the bones, partially or completely dividing the synovial cavity into two. •, 

 It serves to adjust dissimilar bony surfaces, adding to the security of, while it increases the ' 

 extent of motion at, the joint; it also acts as a buffer to break shocks. 



(ii) As circumferential or marginal fibro-cartilages, which serve to deepen the sockets 

 for the reception of the heads of bones — e.g., the glenoid ligaments of the shoulder and hip. 

 Another form of marginal plate is seen in the accessory volar ligaments of the fingers 

 and toes, which deepen the articulations of the phalanges and add to their secui'ity. 



(iii) As connecting fibro-cartilage. The more pliant and elastic is the more cellular form, 

 and is found in the intervertebral discs; while the less yielding and more fibrous form is seen in 

 the sacro-iliac and pubic articulations, where there is little or no movement. ^ 



The ligaments which bind the bones together are strong bands of white fibrous \ 

 tissue, forming a more or less perfect capsule [capsula articularis], round the articu- \ 

 lation. They are pliant but inextensile, varying in shape, strength, and thick- 

 ness according to the kind of articulation into which they enter. They are closely 

 connected with the periosteum of the bones they unite. In some cases — as the 

 ligamenta flava which unite parts not in contact — they are formed of yellow 

 elastic tissue. 



The synovial membrane [stratum synoviale] lines the interior of the fibrous 

 ligaments, thus excluding them, as well as the cushions or pads of fatty tissue 

 situate within and the tendons which perforate the fibrous capsule, from the 

 articular cavity. It is a thin, delicate membrane, frequently forming folds and 

 fringes which project into the cavity of the joint; or, as in the knee, stretches across 

 the cavity, forming a so-called synovial ligament. In these folds are often found 

 pads of fatty tissue, which fill up interstices, and form soft cushions between the 

 contiguous bones. The amount of fat that is normally present within a joint 

 varies greatly. It is an old observation that although there is always fat in the hip- 



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