Every Veda has four parts:
1) It’s core – the “saṁhita” part
It’s explanatory appendixices:
2) explanations – the “brāhmaṇa” parts
3) essentializations – the “āraṇyaka” parts
4) philosophy – the “upaniṣad” parts
Each saṁhita has branches (śakha), and each branch is supposed to have a brāhmaṇa, āraṇyaka, and upaniṣad. Over time many have been lost or blended. Taittiriya Āraṇyaka, for example, presents the essentials of the “Taittiriya” branch of Kṛṣṇa Yajurveda. [Yajurveda has two “trunks” – Kṛṣṇa (black) and Śukla (white).]
Purāṇas (pañcama veda, the fifth veda) don’t have the same structure, because their original intention is to be narrated – so their language is flexible and elaboration can be worked into the text itself as new iterations of purāṇas are recorded, as they are told by new narrators. So separate appendices on Purāṇa are not needed.