Blank verse being in its origin only heroic verse without rhyme,[154] we may refer for its general rhythmical structure to what we have said on this metre. The rhythmical licences of this and the other iambic metres discussed in §§ 82-8 are common also to blank verse. But in addition to these, blank verse has several other deviations from the normal rhymed five-foot iambic verse, the emancipation from rhyme having had the effect of producing greater variability of metrical structure. It is for this reason it has been thought advisable to treat heroic verse and blank verse in separate chapters. At first, it is true, the two metres are very similar in character, especially in Surrey; with the further and independent development of blank verse, however, they diverge more and more. § =162.= In conformity with Surrey's practice in his heroic verse, which, as we have seen, usually had masculine rhymes, his blank verse has also as a rule masculine endings, and is thus distinguished not only from Chaucer's heroic verse, which frequently had feminine endings, but from the blank verse of later poets like Shakespeare and some of his contemporaries. As to the principal kinds of the caesura after the second and third foot there is no material difference between Surrey's blank verse and the heroic verse of the same period (cf. §§ 154, 157). The Epic caesura occurs occasionally after the second foot, e.g.: _Líke to the ádder | with vénomous hérbes féd._ p. 131; but apparently not after the third, although it does not seem to have been avoided on principle, as we often find lyric caesuras in this place, and even after the fourth foot: _His tále with ús | did púrchase crédit; || sóme Trápt by decéit; | some fórced bý his téars._ p. 120. The run-on line (or enjambement) is already pretty frequently used by Surrey (35 times in the first 250 lines), and this is one of the chief distinctions between blank verse and heroic verse. In most instances the use of run-on lines is deliberately adopted with a view to artistic effect. The same may be said of the frequent inversion of rhythm. On the other hand, it seldom happens that the flow of the metre is interrupted by level stress, missing thesis, or the use of a disyllabic thesis at the beginning or in the interior of the verse.[155] As to the peculiarities of the word-stress and the metrical treatment of syllables in Surrey, the respective sections of the introductory remarks should be consulted. Apart then from the metrical licences, of which it admits in common with heroic verse, the most important peculiarities of Surrey's blank verse are the masculine endings, which are almost exclusively used, and the frequent use of run-on lines. Cf. the opening lines of the fourth book of his _Aeneid_: