"I want the file from line 19" -- What does this mean? Is there a file name on line 19? (Sorry but I can't open files on this device to look myself.) Either way you can specify how much of the file you want to read by using offsets or range specification.
rowoffset = 18;
coloffset = 0;
file = csvread(filename,rowoffset,coloffset,[19 0 19 end]);
I'm not sure if end will technically work there for the column range definition, and I'm also fairly sure that you don't want to specify a row offset and start at range 19 (pretty sure that will put you at row 37), but using it as an example of how you can do things.
If you are trying to read some data other than a numeric value you can use a similar range definition in xlsread, as csvread only interprets numeric data.