In the Black Yajurveda the prose portions of the various Samhitas form the only Brahmanas in the Katha and the Maitrayaniya schools. In the Taittiriya school they form the oldest and most important Brahmana. Here we have also the Taittiriya Brahmana as an independent work in three books. This, however, hardly differs in character from the Taittiriya Samhita, being rather a continuation. It forms a supplement concerned with a few sacrifices omitted in the Samhita, or handles, with greater fulness of detail, matters already dealt with. There is also a Taittiriya Aranyaka, which in its turn forms a supplement to the Brahmana. The last four of its ten sections constitute the two Upanishads of this school, vii.-ix. forming the Taittiriya Upanishad, and x. the Maha-Narayana Upanishad, also called the Yajniki Upanishad. Excepting these four sections, the title of Brahmana or Aranyaka does not indicate a difference of content as compared with the Samhita, but is due to late and artificial imitation of the other Vedas. The last three sections of Book III. of the Brahmana, as well as the first two books of the Aranyaka, originally belonged to the school of the Kathas, though they have not been preserved as part of the tradition of that school. The different origin of these parts is indicated by the absence of the change of y and v to iy and uv respectively, which otherwise prevails in the Taittiriya Brahmana and Aranyaka. In one of these Kathaka sections (Taitt. Br. iii. 11), by way of illustrating the significance of the particular fire called nachiketa, the story is told of a boy, Nachiketas, who, on visiting the House of Death, was granted the fulfilment of three wishes by the god of the dead. On this story is based the Kathaka Upanishad. Though the Maitrayani Samhita has no independent Brahmana, its fourth book, as consisting of explanations and supplements to the first three, is a kind of special Brahmana. Connected with this Samhita, and in the manuscripts sometimes forming its second or its fifth book, is the Maitrayana (also called Maitrayaniya and Maitri) Upanishad.