Introduction to Annual Morphology. 21 



fibres may vary : those of the Skate are -&" in diameter, 

 of Man air", of Insects 4-1 " The lengths of fibres also 

 vary from \" to 2". Muscular fibres end in tendons, 

 the tendinous material being continued as a sheath on 

 the fibre for a short distance. Every muscle acts 

 from one end which is more or less fixed (origin), on 

 the other end, which is more or less movable (inser- 

 tion). Muscles may be classified, according to their 

 shapes and the direction of their fibres, into prismatic, 

 penniform, triangular, quadrilateral, sphincteric, ellips- 

 oidal and skew. 



The contraction of muscle is attended with chemical 

 change,* heat, the evolution of carbonic acid, and the 

 production of inosite, &c. In higher animals each 

 cubic inch of muscle is capable of giving out a con- 

 stant amount of work (about 100 foot pounds) in a 

 single contraction. As a rule, the work done by a 

 muscle bears a proportion to its weight, and for each 

 muscle when kept in action until complete fatigue 

 sets in, the total amount of work, multiplied by the rate 

 of work, is constant. The cessation of life in muscle 

 is shown by a continuous stiffness (rigor mortis) due 

 to the coagulation of myosin in the inter-fibrillar 

 spaces, which lasts until the insetting of further 

 chemical change, when the cell contents change to 

 syntonin. 



Nerv tissue is peculiarly animal, nothing similar 

 having been as yet detected in sensitive plants. Pro- 



lasm, when irritated, contracts, but its modifica- 



thc heart muscular fibres consist of uniting colls without (or with, Winkle r} 

 a sarcolcmma. 



Mu.-dc \vhc-i: iinphichromatic (alters the colour both of red 



ami blue litmus paper), but when inaction arid. In i i^rniortis 



