_Fol. 1, blank._ _Fol. 2^a_: INCIPIT EPISTOLA ISIDORI IVNIORIS HISPALENSIS EPISCOPI AD BRAVLIONEM CESARAVGVSTANVM EPISCOPVM. [Three other letters to the same and two replies; tabula generalis.] _Fol. 3^b, col. 2_: INCIPIVNT CAPITVLA PRIMI LIBRI. INCIPIT LIBER PRIMVS ETHIMOLOGIARVM ISIDORI HISPALENSIS EPISCOPI. DE DISCIPLINA ET ARTE. _Fol. 27^b, col. 1_: INCIPIVNT CAPITVLA LIBRI QVARTI. _Fol. 27^b, col. 2_: PREFACIO. [D]Omino et filio syseputo ysidor_us_..... INCIPIT LIBER YSIDORI DE RERVM NATVRA AD SISEPVTVM REGEM. _Fol. 37^a, col. 2_: INCIPIVNT CAPITVLA LIBRI QVARTI. INCIPIT LIBER QVARTVS DE MEDICINA. _Fol. 142^a_, COLOPHON: EXPLICIT LIBER ETHIMOLOGIARVM ISIDORI HISPALENSIS EPISCOPI. Folio. Quires [1-13^{10}, 14^{12}], 142 leaves, the first blank, 2 columns, 51 lines to the column, without signatures, catchwords, pagination, printer's name, place or date. Gothic lower-case type, roman capitals. Book and chapter headings printed wholly in majuscules. Large woodcut diagrams. Three-to nine-line spaces left for chapter and book initials, also spaces for occasional Greek words (mostly left unsupplied) and for small diagrams. Two pinholes, which in Mentelin's use point to a date not later than 1473. Hain *9270. Brit. Mus. 15th cent., I, p. 57 (IC. 586). Burger pl. 170. On the first page large illuminated initial with floral border ornament, and similar initials at the head of the several books. Chapter initials supplied in red or blue; initial-strokes in red throughout the volume. Blank first leaf wanting. Incorporated with the present edition of the Etymologiae by way of supplement, though not named in the table of contents, is an earlier treatise of Isidore's entitled _De natura rerum_, written at the request of Sisebut, king of the Visigoths, 612-621, and dedicated to him. It contains the sum of the physical philosophy of his time, and, being largely astronomical, is sometimes found in the MSS. under the title _Liber de astronomia_. In order to bring it into immediate connection with the corresponding section of the Etymologiae, it is placed immediately after the third book (devoted to the _quadrivium_, the last division of which is astronomy) and given irregularly the heading "Liber quartus," the regular _Liber quartus (De medicina)_ beginning twenty pages later. Two of the 48 chapters of which it is composed are wanting here, but by the subdivision of other chapters the number is raised to 58. Zainer of Augsburg, the printer of the first edition of the Etymologiae, dated 19 November, 1472, followed it the next month with an edition of _De responsione mundi et astrorum ordinatione ad Sesibutum regem_, which is the work in question under another title. Printed with the same type and the same number of lines to the page, it was in effect treated as a supplement to the Etymologiae.