JOINT LIABILITY. 269 JOINTS. share the other should have paid: and this right he can enforce by action. At common law tlie death of one joint obligor terminated his liability, and the survivor or sur- vivors continued solely liable, but this rule is now changed in most jurisdictions by statute, and the estate of the decea.sed is liable for his share. In the absence of statutes to the contrary, the discharge of one person jointly liable by opera- tion of law, as by bankruptcy, does not release the others even for the proportionate share of the bankrupt. See Coxtbact; Bond. JOINT OWNERSHIP. A general expression for the o^'ner5hip by two or more persons, in common, of one and the same piece of property. The owT.ership of any property, real or personal, may be thus shared. The expression is not of precise legal signification, but is generally em- ployed to include such various forms of common ownership as joint tenancy, tenancy in common, parcenary, and tenancy by entireties, and some- times, also, the ownersliip of property by partner- ships and unincorporated joint-stock associa- tions. These differ greatly in their characteristics and in the nature of the rights which they con- fer, but they all have the conunon characteristic that each individual ownei-'s interest is an un- divided share of the entire property affected, and not a definite part or parcel of the whole. The various forms of joint ownership are considered under their appropriate titles. See also Owi^R- SHiP: Property. JOINTS. A name given to the divisional planes which traverse rocks, separating them into irregular prismatic blocks. All consolidated strata, , whether of igneous or sedimentary character, are broken by joints, although some variations are observal)le depending upon the different rock materials. In sedimentary rocks the joints are vsually arranged in two series that intersect each other at a high angle and are approximately perpendicular to the bedding planes. Vhen the strat-a are inclined, one series in most cases trends with the dip, while the other follows the direction of the strike, thus giving rise to the classification of dip-joints and strike-joints. In igneous rocks there is .a wider range in the num- ber and direction of the joint planes. Granite and other coarse-grained rocks of igneous nature are often traversed by two sets of perpendicular joints forming columns, and by a third set inter- secting the other two and articulating the col- umns into segments. The finer crystalline masses such as basalt exhibit a great number of joints so arranged as to form complex polygonal prisms of remarkable regularity. This is well shown in the illustrations of Fingal's Cave (see St.ffa) and Giant's Causeway (q.v.). Jointing is of great assistance to quarrying operations: the rock is readily removed in blocks, which could be obtained by sawing and blasting onlywith diffi- culty. Tlie cause of joints is variously explained as the result of contraction of rocks upon cool- ing or diying, of earthquake shocks, and of com- pression strains. See Geology, JOINTS, CoiiPABATm; Anatomy of. Among invertebrate animals there are many cases of articulation which indicate the presence of joints, but they are mostly confined to that type which is characterized by the presence of jointed ap- pendages, the arthropods. Among the worms we find nothing to which the word joint can prop- erly be applied, the relation of the successive segments to each other not justifying the term. It is even open to question whether the relation- ship of the segments in the arms of erinoids and brittle-stars is such that the word joint ought to be used. The joints are generally very simple, consisting merely of the connecting of successive skeletal pieces, by strips of connective tissue or muscle. In erinoids we find a very peculiar joint, the 'syzygy,' which occurs at more or less regular intenals throughout the length of the arm, and may also occur in the stalk. A syz^gv- has been defined as a joint in which the two skeletal pieces "are closely and immovablj' fitted together, though they can be separated by alkalies." If the union is still more complete, so that alkalies will not separate the pieces, the result is called 'an- kylosis.' In sea-urchins we find excellent ex- amples of true joints, in the attachment of the spines to the test by means of ball-and-socket joints, the base of the spine being hollowed out to fit smoothly over a polished tubercle, and held in position by a band of muscular and connective tissue. Although the spines of many starfishes show considerable mobility, there is seldom any well-marked joint. The only example of joints among mollusks would seem to be in the con- nection between the eight pieces of the chiton's shell or in the hinge of a bivalve shell, but these are hardly worthy the designation. Among ar- thropods (insects, arachnoids, and crustaceans) joints abound, for not only are the antennte and feet jointed appendages, btit even the mouth-parts and the wings work upon joints. In all these eases, however, there are no skeletal ossicles, the segments being merely sections of the uniformly inclosing exoskeleton, with the muscle or con- nective tissue strands within themselves. The freedom of movement is rendered possible by the marked thinning of the exoskeleton at the joints into a delicate, flexible membrane, while muscles pass from each joint into the next one. Among vertebrates the various joints are of the same general structure and plan as in man, varying with the degree of ossification and the complexity of the organs concerned. JOINTS, DiSE.SES OF THE. Attempts have been made to classify these diseases according to the anatomical condition, as diseases of the carti- lage (chondritis) , the articular capsule {synovi- tis) , or of the bone (osteitis) ; but practically the surgeon views inflammation of the joint as a whole, and uses the term arthritis oftener than the others. Diseases of the joints are caused by cold, injuries, gout, syphilis, tubercle necrosis, or caries. 'Water on the knee' is the popular name for chronic synovitis of the knee-joint, in which there is an effusion of fluid into the svno- vial cavity. 'White swelling' is the popular name for tubercular arthritis. Dislocation may follow some joint diseases; suppuration may accom- pany some: while, in other cases, adhesions grow- ing in the joints may cause 'fibrous anlo'losis.' or stiffened joint, or, in still other cases, denuded articular ends of bones may join together forming •bony ankylosis' with permanent immovable joint. Eest is the first treatment for a diseased joint, pain being a danger signal that cdnnter-indicates use. Hot and cold effusions to the joint, alter- nately, with evaporating lotions, are useful in some cases: but domestic treatment of a joint, in ignorance of the conditions, is always hazard-
