recently came across this on Google Books. it's the complete text of Lloyd's From Latin to Spanish
, a monument of Romance lingustic geekery. it starts out with a general theoretical description of sound change and the various processes which shape it. it then goes on to give a thorough explanation of the history and evolution of phonolgy, morphology, syntax and lexicon from Old through Classical to Late Latin. and from there describes the development of Castilian during the reconquest, and subsequent developments in the Spanish language. the first half of the book is useful for anyone interested in the development of Romance from Latin, and comparisons are drawn from Portugese, Catalan, Occitan, etc. throughout.