and protect the painted work. Sash fasteners are fixed at the meeting
rails of double hung sashes to prevent the window being opened
from the outside and serve also to clip the two sashes tightly together.
They should be of a pattern to resist the attack of a knife
inserted between the rails. Sash lifts and pulls of brass or bronze
are fitted to large sashes. Ornamental casement stays and fasteners
in many different metals are made in numerous designs and styles.
Fanlight openers for single lights, or geared for a number of sashes,
may be designed to suit positions difficult of access.
The following are the principal books of reference on this subject: J. Gwilt, Encyclopaedia of Architecture; Sutcliffe, Modern House Construction; Rivington, Notes on Building Construction (3 vols.); H. Adams, Building Construction; C. F. Mitchell, Building Construction; Robinson, Carpentry and Joinery; J. P. Allen, Practical Building Construction; J. Newlands, Carpenter and Joiner’s Assistant; Bury, Ecclesiastical Woodwork; T. Tredgold and Young, Joinery; Peter Nicholson, Carpenter and Joiner’s Assistant. (J. Bt.)
JOINT (through Fr. from Lat. junctum, jungere, to join), that
which joins two parts together or the place where two parts are
joined. (See Joinery; Joints.) In law, the word is used
adjectivally as a term applied to obligations, estates, &c.,
implying that the rights in question relate to the aggregate of
the parties joined. Obligations to which several are parties
may be several, i.e. enforceable against each independently of
the others, or joint, i.e. enforceable only against all of them
taken together, or joint and several, i.e. enforceable against each
or all at the option of the claimant (see Guarantee). So an
interest or estate given to two or more persons for their joint
lives continues only so long as all the lives are in existence.
Joint-tenants are co-owners who take together at the same time,
by the same title, and without any difference in the quality or
extent of their respective interests; and when one of the joint-tenants
dies his share, instead of going to his own heirs, lapses
to his co-tenants by survivorship. This estate is therefore to
be carefully distinguished from tenancy in common, when the
co-tenants have each a separate interest which on death passes
to the heirs and not to the surviving tenants. When several
take an estate together any words or facts implying severance
will prevent the tenancy from being construed as joint.
JOINTS, in anatomy. The study of joints, or articulations,
is known as Arthrology (Gr. ἄρθρον), and naturally begins with
the definition of a joint. Anatomically the term is used for any
connexion between two or more adjacent parts of the skeleton,
whether they be bone or cartilage. Joints may be immovable,
like those of the skull, or movable, like the knee.
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Fig. 1.—Vertical |
Fig. 2.—Vertical section |
Immovable joints, or synarthroses, are usually adaptations to growth rather than mobility, and are always between bones. When growth ceases the bones often unite, and the joint is then obliterated by a process known as synostosis, though whether the union of the bones is the cause or the effect of the stoppage of growth is obscure. Immovable joints never have a cavity between the two bones; there is simply a layer of the substance in which the bone has been laid down, and this remains unaltered. If the bone is being deposited in cartilage a layer of cartilage intervenes, and the joint is called synchondrosis (fig. 1), but if in membrane a thin layer of fibrous tissue persists, and the joint is then known as a suture (fig. 2). Good examples of synchondroses are the epiphysial lines which separate the epiphyses from the shafts of developing long bones, or the occipito-sphenoid synchondrosis in the base of the skull. Examples of sutures are plentiful in the vault of the skull, and are given special names, such as sutura dentata, s. serrata, s. squamosa, according to the plan of their outline. There are two kinds of fibrous synarthroses, which differ from sutures in that they do not synostose. One of these is a schindylesis, in which a thin plate of one bone is received into a slot in another, as in the joint between the sphenoid and vomer. The other is a peg and socket joint, or gomphosis, found where the fangs of the teeth fit into the alveoli or tooth sockets in the jaws.
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| Fig. 3.—Vertical section through an amphiarthrodial joint. b, b, the two bones; c, c, the plate of cartilage on the articular surface of each bone; Fc, the intermediate fibro-cartilage; l, l, the external ligaments. |
Movable joints, or diarthroses, are divided into those in which there is much and little movement. When there is little movement the term half-joint or amphiarthrosis is used. The simplest kind of amphiarthrosis is that in which two bones are connected by bundles of fibrous tissue which pass at right angles from the one to the other; such a joint only differs from a suture in the fact that the intervening fibrous tissue is more plentiful and is organized into definite bundles, to which the name of interosseous ligaments is given, and also that it does not synostose when growth stops. A joint of this kind is called a syndesmosis, though probably the distinction is a very arbitrary one, and depends upon the amount of movement which is brought about by the muscles on the two bones. As an instance of this the inferior tibio-fibular joint of mammals may be cited. In man this is an excellent example of a syndesmosis, and there is only a slight play between the two bones. In the mouse there is no movement, and the two bones form a synchondrosis between them which speedily becomes a synostosis, while in many Marsupials there is free mobility between the tibia and fibula, and a definite synovial cavity is established. The other variety of amphiarthrosis or half-joint is the symphysis, which differs from the syndesmosis in having both bony surfaces lined with cartilage and between the two cartilages a layer of fibro-cartilage, the centre of which often softens and forms a small synovial cavity. Examples of this are the symphysis pubis, the mesosternal joint, and the joints between the bodies of the vertebrae (fig. 3).
The true diarthroses are joints in which there is either fairly free or very free movement. The opposing surfaces of the bones are lined with articular cartilage, which is the unossified remnant of the cartilaginous model in which they are formed and is called the cartilage of encrustment (fig. 4, c). Between the two cartilages is the joint cavity, while surrounding the joint is the capsule (fig. 4, l), which is formed chiefly by the superficial layers of the original periosteum or perichondrium, but it may be strengthened externally by surrounding fibrous structures, such as the tendons of muscles, which become modified and acquire fresh attachments for the purpose. It may be said generally that the greater the intermittent strain on any part of the capsule the more it responds by increasing in thickness. Lining the interior of the capsule, and all other parts of the joint cavity except where the articular cartilage is present, is the synovial membrane (fig. 4, dotted line); this is a layer of endothelial cells which secrete the synovial fluid to lubricate the interior of the joint by means of a small percentage of mucin, albumin and fatty matter which it contains.
 Fig. 4.—Vertical section |
 Fig. 5.—Vertical section |
A compound diarthrodial joint is one in which the joint cavity is divided partly or wholly into two by a meniscus or interarticular fibro-cartilage (fig. 5, Fc).
The shape of the joint cavity varies greatly, and the different divisions of movable joints depend upon it. It is often assumed that the structure of a joint determines its movement, but there is something to be said for the view that the movements to which a joint is
