NERVE TISSUE. 83 
Describe the sarcolemma. 
It is a thin, structureless membrane, so delicate that it cannot be 
seen unless it is separated from the muscle substance by artificial means. 
What is the appearance of unstriped or involuntary muscle tissue ? 
It is made up of spindle-shaped cells interlacing or running in 
bundles. These cells may appear to have faint longitudinal striations. 
They have only one nucleus and that is in the centre of the cell sub- 
stance. The cell is enclosed in an exceedingly delicate sheath resem-* 
bling the sarcolemma of voluntary muscle. 
What is the peculiarity of heart muscle ? 
It is an involuntary muscle, but its fibres are striated transversely. 
Describe the cells of heart muscle. 
They are quadrangular in shape, and often branched at one extremity. 
They are joincd end to end in forming the fibres of the muscle. These 
fibres divide and freely anastomose by means of the branching pro- 
cesses of the cells. ‘The cells are striated transversely and longitu- 
dinally, though the transverse strise are not as distinct as in voluntary 
muscle. The cells seem to have no sarcolemma or investing membrane. 
NERVE TISSUE. 
Name the structural elements of nerve tissue. 
Nerve fibres and nerve cells. 
How many kinds of nerve fibres are there and what are they called ? 
Two; medullated and non-medullated fibres. 
To what nerve systems do they each belong ? 
The medullated fibres to the cerebro-spinal and the non-medullated 
fibres to the sympathetic nervous system. 
Of what elements is a medullated nerve fibre composed ? 
Asis cylinder, medullary sheath, and neurilemma or sheath of 
Schwann. 
Describe the axis cylinder. 
It is a cylindrical structure, delicately striated longitudinally, and 
runs through the axis of the nerve fibre. It is supposed to be the 
path taken by nerve impulse, and that the other sheaths are for its 
protection. It seems to be a continuous process from the nerve cell 
to the nerve ending. 
3—H.P.B. 
