Complex sentence: There are two types of regular Latin adjectives: first and second declension and third declension, so called because their forms are similar, if not identical to, first and second declension and third declension nouns, respectively.
Split into simpler sentences: There are two types of regular Latin adjectives: first-and second-declension and third-declension. They are so-called because their forms are similar or identical to first-and second-declension and third-declension nouns, respectively.