b.  bright  bands  ;  d.  dim  bands  ;  n.  nuclei  ;  s,  s'.  sarcolemrna,  rendered  visible  as  a
minute  blister  (/)  by  absorption  of  water  and  by  the  rupture  of  the  muscle-
fibre  at .?.  (A,  from  Huxley's  Physiology.}

on,  increase  in  length  while  their  nuclei  multiply  by  fission,
each  enormously  elongated  cell  thus  containing  a  consider-
able number.
Connective-tissue. — We  will  next  examine  a  piece  of  the
delicate  web  of  connective-tissue  which  binds  the  muscles
together.
Under   the    high  power,  connective-tissue  is  seen  to  be

FRACT.  ZOOL.  I


THE    FROG


CHAP.
composed  of  a  sort  of  irregular  network  of  delicate  bundles
of  wavy  fibres  called  white  connective-tissue  fibres  (Fig.  33,  w\
which  cross  one  another  in  all  directions.  Amongst  them
are  found  single  fibres  sweeping  across  the  field  in  bold


FIG.  33. — Connective-tissue  from  between  muscles  of  frog's  leg.
c.  cells  ;  e.  elastic  fibres  ;  iv.  white  fibres  :  -all  of  which  are  imbedded  in  a  delicate
matrix,  not  specially  indicated  in  the  figure.
curves  and  called  elastic  fibres  (e) :  it  is  owing  to  their
elasticity  that  the  tissue  cannot  be  spread  out  when  wet.
Scattered  among  the  fibres  are  numerous  nucleated  cells  (c)  of
very  varied  and  often  irregular  form  :  these  are  the  connective
tissue  cells.  The  fibres,  as  well  as  the  cells,  are  imbedded
in  a  soft,  homogeneous,  ground-substance  or  matrix.
vii  CARTILAGE  115

Thus  connective-tissue  consists  partly  of  cells,  but
between  these  and  forming  the  main  substance  of  the  tissue,
is  a  matrix  or  intercellular  substance,  enclosing  fibres.  In
the  embryo  the  tissue  consists  of  closely  packed  cells,  but,  as
development  proceeds,  these  separate  from  one  another,  and
the  ground-substance  is  formed  between  them.
