THE MUSCLES AND SKIN. 



21 



ous purposes in the body, some of them are broad and flat, others short 

 and thick, and, lastly, others long and comparatively slender. 



THE JOINTS. 



The places where the bones meet, and 

 are joined together by membranes passing 

 from one bone to another, are commonly 

 known as the joints. the connecting mem- 

 branes being named the ligaments, from 

 ligo, I tie. The different kinds of joints will 

 be hereafter studied in the Physiological 

 part of this work, in the section on the 

 Movements of Man and Animals. In most 

 of them, the ends of the bones are beauti- 

 fully fitted together, and covered with a 

 thinnish layer of gristle or cartilage, a 

 tough, elastic substance, smooth on the 

 free surface, and, moreover, moistened 

 with a viscid fluid, improperly termed 

 joint-oil, but named synovia, from its re- 

 semblance to the white of egg (<ro\>, sun, 

 and oov, oon, an egg), which is contained 

 in the cavities of the joints, and runs out 

 when these are opened by dividing the 

 ligaments. The interior of the joints, ex- 

 cepting only the cartilages which cover 

 the bones, is lined by a thin membrane, 

 called a synovial membrane. These facts 

 are illustrated in the annexed drawing of 

 a section of the right knee-joint, Fig. 3, 

 to the separate description of which refer- 

 ence should now be made. 



Fig. 3. 



Fig. 3. Vertical section through the 

 middle of the right knee-joint. It shows 

 the cancellated or spongy texture of the 

 lower end of the femur, 1, and upper end 

 of the tibia, 2; also the thin layer of carti- 

 lage covering the ends of those bones. 3 

 is a part of the fibula. 4 is the cavity of 

 the joint, made more apparent by separa- 

 tion of its naturally apposed surfaces, and 

 lined by the synovial membrane. 5, sec. 

 tion of the knee-pan, also covered, next 

 the joint, with cartilage. 6, a mass of fat, 

 filling up intermediate space. 7, a sepa- 

 rate synovial membrane, called a syno- 

 vial bursa. 8, one of the ligaments, pecu- 

 liar to the knee-joint, called the crucial 

 ligaments. (Bourgery.) 



THE FLESH OR MUSCLES. 



Covering up the bones generally, and attached to their surfaces at 

 certain definite places, is the soft, red, fleshy, portion, or muscular 

 substance of the body. This consists, not of one homogeneous envi- 

 roning mass, but of a great number (about 400) of distinct fleshy 

 masses of various forms and sizes, which are called the muscles, Figs. 

 4 and 5. 



On consulting these figures, it will be seen that on the shape and 

 disposition of the muscles, mainly depend the particular contours of 

 the human body. The muscles will again be noticed, in the Section 

 on the Movements of Man and Animals. In the meantime, it will be 

 observed that they are arranged in layers, some deeper than others, 

 and lying next to the bones, as seen in the left half of the trunk in 

 Fig. 4, and some more superficial, as shown on the right side of the 

 trunk. It will be noticed that, on the trunk, the muscles are generally 



