Page:The American Cyclopædia (1879) Volume I.djvu/820

 784 ARTICULATION is formed, called the acetabulum, exactly shaped for the reception of this hemispherical head of the thigh bone, and this socket if lined with a thin layer of dense, elastic, and polished car- Fio. 2. A section of the hip joint taken through the acetabu- lum and the middle of the head and neck of the thigh bone. L. T. Ligamentum teres, or round ligament. tilage, so that in the joint two polished surfaces meet together and allow free movement, with the least possible amount of friction ; but to lessen the effect of friction, and facilitate the movements of these surfaces one upon the other, a delicate membrane surrounds the ex- ternal borders of the articular cartilages, and secretes a viscid fluid which lubricates the sur- faces, preventing actual contact and destruc- tive friction of the cartilaginous tissues. This lubricating fluid is technically called synovia, and the secreting membrane the synovial sac or synovial membrane. To prevent the dislo- cation of the joint, a strong rope of fibrous tis- sue, very similar in structure to that part of an oyster which cannot easily be removed from the shell, connects the top of the ball with the bottom of the socket, in a somewhat loose but very strongly attached manner. This is termed the round ligament ; it is very short and very strong. The outer surfaces of the ball and socket (not in the socket, but outside) are connected by means of a strong ligamentous band of fibrous tissue, loosely connecting the hei^d of the thigh bone with the pelvic bones, on the outer riin of the socket, but strongly at- tached to the bones them- selves, which it binds to- gether firmly, while per- FIQ. 8. Diagram of a mitting a considerable free- longitudinal section of dom of motion or rotation an articulation. A. ,1. , T ii_ Bones. B. Articular m "16 joint. In Other cartilage, c. Pertoste- joints of the movable class mbne E - *^* the outer ligaments are not always continuous and cir- cular bands as in this case, but take the form of distinct fibrous ropes, strongly attached to the ARTILLERY bones, and forming strong, flexible bands, as strips of leather nailed to the body and the lid of a box serve as ligaments where there are no hinges. Thin, dense, elastic layers of carti- lage cap the articular edges and surfaces of bones in the great majority of joints ; strong, fibrous, and flexible ligaments connect the bones externally ; and, where the joints are very movable, synovial membranes surround the articulating surfaces, and the synovia which they secrete lubricates the surfaces exposed to contact, friction, and mobility. ARTIGAS, Jose, a South American general, born at Montevideo, in Uruguay, in 1755, died in Paraguay in 1851 (not, as often stated, about 1826). The son of a wealthy landed proprietor, he led for a time an adventurous life as a gau- cho, and then served as captain in the light cav- alry of the provinces, but on account of some difficulty with the governor passed in 1811 into the service of the junta of Buenos Ayres, then in insurrection against Spain. At the head of a band of gauchos, he defeated the Spaniards in several encounters, and vigor- ously supported the republican army which be- sieged the Portuguese troops from Brazil who then occupied Montevideo. Passionate and scheming, he soon acted independently, and finally detached his men from the besieging army ; whereupon Posadas, director of the junta, outlawed him and set a price upon his head. But the gauchos flocked to his standard, and Artigas, having defeated the troops sent against him, obliged his enemies to cede to him the whole of Uruguay (1814). He next com- pelled the Portuguese to abandon their attempt to regain possession of Montevideo, which had surrendered. He now acted as dictator in his native country, and made a vigorous but un- successful attempt against Buenos Ayres (1815). After various contests he was twice defeated, in 1819 and 1820, and compelled to flee to Par- aguay, where Dr. Francia, the dictator, ban- ished him to Candelaria. Here the former gaucho chief devoted himself to husbandry, and to the care of the sick and needy, and at- tained a patriarchal age. ARTILLERY, the cannon employed in war, and the troops organized to use them. The Chinese as early as A. D. 969, under the em- peror Tai-tsu, tied rockets to their arrows to propel them to greater distances, as well as for incendiary purposes. During the first half of the 13th century all the resources of their mil- itary art became known to the Arabs through the Mongol conquerors of China. The idea of the application of gunpowder to projectiles, though said to have been accidentally sug- gested to Berthold Schwarz about 1830, is probably due to the Moors or Arabs of north- ern Africa, who had artillery at Cordova as early as 1280. The Spaniards learned its use from them, Ferdinand IV. of Castile taking Gibraltar with cannon in 1309, and guns being employed soon after at the sieges of Baza, Martos, and Alicante.. A knowledge of artil-