Produced by Chris Curnow, Alex Gam, Joseph Cooper and the Online Distributed Proofreading Team at http://www.pgdp.net UNIVERSITY OF KANSAS PUBLICATIONS MUSEUM OF NATURAL HISTORY Volume 12, No. 3, pp. 181-216, 49 figs. February 19, 1960 The Baculum in Microtine Rodents BY SYDNEY ANDERSON UNIVERSITY OF KANSAS LAWRENCE 1960 UNIVERSITY OF KANSAS PUBLICATIONS, MUSEUM OF NATURAL HISTORY Editors: E. Raymond Hall, Chairman, Henry S. Fitch, Robert W. Wilson Volume 12, No. 3, pp. 181-216, 49 figs. Published February 19, 1960 UNIVERSITY OF KANSAS Lawrence, Kansas PRINTED IN THE STATE PRINTING PLANT TOPEKA, KANSAS 1960 [Illustration] 28-774 The Baculum in Microtine Rodents BY SYDNEY ANDERSON INTRODUCTION Didier (1943, 1954) has described the bacula of several Old World microtines, and other rodents. Argyropulo studied (1933a, 1933b) five species of Cricetinae and _Microtus socialis_. Ognev (1950) illustrated numerous species of Eurasian microtines. Hamilton (1946) figured and described the baculum of 11 species of North American microtines. Hibbard and Rinker (1942, 1943) figured the baculum of _Synaptomys cooperi paludis_ and of _Microtus ochrogaster taylori_. Dearden (1958) studied the baculum in two Asiatic species of _Lagurus_, in six subspecies of _Lagurus curtatus_ of North America, and in six other species of microtines of other genera. The baculum can be preserved easily with standard study skins, and is potentially useful in interpreting relationships on any taxonomic level, and especially in determining the relationships of species within a genus, if used together with other structures. The anatomical orientation of the baculum needs comment because some confusion exists in the literature, especially concerning the use of the terms ventral and dorsal. The urethra lies on the anatomically ventral side of the penis, and of the baculum. In the center of the penis lies a single corpus cavernosum penis, shown in cross section proximal to the baculum in Figure 1c. Dorsally an artery, thinner walled than the ventral urethra, ends in a somewhat reticulate sinus surrounding primarily the middle part of the baculum within the bulbous glans penis. The corpus cavernosum penis (the structure has no median septum, at least distally) terminates with the baculum and is closely knit to it. The site of this bond is evident in the tuberosities and sculpturing of the base of the baculum. The part of the penis enclosing the baculum, when not erect, is folded back as shown in Figures 1a and 1b. As a result the anatomically ventral surface faces upwards, or at least posterodorsally. The use of the term ventral in this account refers to the anatomically ventral side, that is to say to the side of the baculum facing the urethra.