The content of this paper is summarized as follows:
1. The so-called acute intonation of Proto-Lithuanian was a broken intonation which owed its origin to the loss of IE laryngeal and was characterized not only by a glottal stricture but also by a sudden rising of voice and a rather strong breath pressure.
2. Leskien's Law operated only in the accented final syllables of broken intonation. Thus the shortening of the accented final syllables of broken intonation was a regular phonetic change, but that of the unaccented long final syllables was an analogical change influenced by the preceding type of shortening.
3. De Saussure's Law is the advancement of accent from the circumflected or short syllables to the immediately following syllables which got a broken intonation owing to the loss of IE laryngeal and thus showed a rather strong breath pressure.
4. Hirt's Law is the retraction of accent from the final syllables to the preceding syllables which also got a broken intonation owing to the loss of IE laryngeal and showed a rather strong breath pressure.