vbnewline, vbcrlf
You can make use of vba constants incorporated as as string and constant and string.
"my dog" & vbnewline & "has fleas"
There are other combo's also
VBA help/constant/misc contstants:
The following constants are defined in the Visual Basic for Applications type library and can be used anywhere in your code in place of the actual values:
Constant Equivalent Description
vbCrLf Chr(13) + Chr(10) Carriage return–linefeed combination
vbCr Chr(13) Carriage return character
vbLf Chr(10) Linefeed character
vbNewLine Chr(13) + Chr(10) or, on the Macintosh, Chr(13) Platform-specific new line character; whichever is appropriate for current platform
I don't know of any within the string itself.