LOOOMOTIOlSr. 



The entire locomotor system of tissues is derived from, the 

 embryonic mesoblast. These include the muscles, bones, carti- 

 lage, and connective and fibrous tissues ; and the tissues that 

 make up the vascular system or the motor apparatus for the 

 circulation of the blood. Locomotion in the mammal is effected 

 by the movement of certain bony levers, while the equilibrium 



of the body is maintained. 

 The whole series of levers is 

 bound together by muscles, 

 tendons, ligaments, etc., and 

 play over one another at cer- 

 tain points where they are in- 

 vested with cartilage, and 

 kept moist by a secretion from 

 the cells covering the syno- 

 vial membranes that form the 

 inner linings of joints. 



Cartilage, a very low form 

 of tissue destitute of blood- 

 vessels, and hence badly re- 

 paired when lost by injury 

 or disease, forms a series of 

 smooth surfaces admirably 

 adapted for joints, and espe- 

 cially fitted to act as a series 

 of elastic buffers, and thus 

 prevent shocks. Bone, though 

 brittle in the dried state, possesses, when alive, a favorable de- 

 gree of elasticity, while sufficiently rigid. Provision is made 

 by its vascular periosteum and central marrow (in the case of 

 the long bones), as well as by the blood-supply derived from 

 the nutrient artery and its ramifications throughout the osseous 



