Subject: what are the white lines in cross sectional views in greys anatomy

Im looking at cross sections of anatomy.
This is one here.
http://en.wikipedia.org/wiki/Image:Gray417.png


Generally arteries, muscles are labeled.
But What the heck are all the white lines that are beteen muscles?
I figure they have to be a membrane but arent membranes to thin to see.

Specfically Im trying to figure out the name of the big "white thing" coming 
off the ulna and attached to the skin in this cross section.  How big are 
these things in reality

http://en.wikipedia.org/wiki/Image:Gray417.png

Re: what are the white lines in cross sectional views in greys anatomy