ANATOMY OF BIRDS 285 



c. Myology : the Muscular System 



Muscular Tissue consists of more or fewer amoebiform animals ; 

 separate colonies of which creatures, isolated in various parts of 

 the body, compose the individual different muscles. They are en- 

 veloped in fibrous tissue, the sheets of which are called fascice, and 

 the ends of which, usually attached to bones by direct continuity with 

 the periosteal covering of the latter, form tendons and ligaments. 

 The muscle - animals belong to a genus which may be termed 

 Myarnmha, differing from other genera of the amcebiforms which 

 compose the body of a bird less in their physical character of being 

 elongated and spindle-shaped, or even filiform, than in their physio- 

 logical character of contractility. Under appropriate stimulus, as 

 the passage of a current of electricity, or the wave of biogen- 

 substance which constitutes a "nerve-impulse," Myamc&bcB shorten 

 and thicken, tending towards a state of tonic contraction which, if 

 completed and long sustained, would cause them to become encysted 

 as spherical bodies ; but extreme contraction is never long con- 

 tinued. By alternate contraction and relaxation all the motions of 

 the body in bulk are effected. The capacity of, or tendency to, con- 

 traction is called the tonicity of muscular fibre. The simultaneous 

 contraction of any colony of Myamoebm pulls upon the attachment of 

 the muscle at each of its ends ; in some cases approximating both 

 ends; oftener moving the part to which one end is attached, the 

 other being fixed. The action of a muscle is upon the simplest 

 mechanical principles, — nothing more or less than pulling upon a 

 part, as by a rope, the line of traction being exactly in the line of 

 contraction of the muscle ; though it is often ingeniously changed 

 by the passage of tendons around a corner of bone, or through a 

 loop of fibrous tissue, as if through a pulley. Such movements as 

 those of a turtle protruding its head, or a bird thrusting its beak 

 forward, where muscle seems to push, are fallacious ; when analysed, 

 the motion is invariably resolved into simple pulling. The swelling 

 up of a muscle in contracting must indeed impinge upon neighbour- 

 ing parts and shove them aside ; but that is an extrinsic result. 

 Muscles contract most powerfully under resistance to their tur- 

 gescence : what is effected by the fasciae which bind them down ; — 

 what the athlete seeks to increase by bandaging his swelling biceps. 

 There are two species of Myamceba. M. striata is the ordinary 

 striped fibre of voluntary motion, and also of some motion not 



Abridged from a, paper on the "Possibilities of Protoplasm," read before the Philo- 

 sophical Society of Washington, 6th May 1882. By Dr. EUiott Coues, etc. Washing- 

 ton, Judd and Detweiler. 8vo, 27 pp. Fifth edition. Boston, Estes and Lauriat, 

 1887. 



