IOO NORMAL HISTOLOGY. 



at least, exist in different parts of the fibres ; but 

 that the living fibre is made up of distinct elements, 

 having the structure which we see in the isolated or 

 partially isolated sarcous elements, although proba- 

 ble, is by no means proven, since this isolation by 

 chemical means may signify only a tendency to 

 break up in certain directions, and not a definite, pre- 

 existing separate structure. 



2. The nuclei, which in the mammalia lie upon 

 the surface of the fibres, and directly beneath the 

 sarcolemma, in the amphibia, fishes, and certain 

 birds, also embedded within the contractile sub- 

 stance, are usually large, flat, and ellipsoidal in shape, 

 contain nucleoli, and lie with their long axes coinci- 

 dent in direction with the axis of the fibres. They 

 are irregularly scattered along the fibre, and a small 

 amount of granular matter is usually seen in their 

 immediate vicinity. 



3. The sarcolemma, a delicate, structureless, mem- 

 branous sheath, is so thin, and so closely encloses 

 the contractile substance and nuclei, that we cannot 

 usually see it, unless we separate it by artificial 

 means from the underlying structures. Where the 

 muscular fibres join tendons, the sarcolemma ends in 

 the form of a pointed or rounded blind sac, to which 

 the tendon-fibres are attached. 



The muscular fibres lie closely packed together, 

 their ends lapping over on to adjacent fibres, and 

 forming bundles which are enclosed in sheaths of 



