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
28-774
The Baculum in Microtine Rodents
BY
SYDNEY ANDERSON
INTRODUCTION
Didier (1943, 1954) has described the bacula of several Old Worldmicrotines, and other rodents. Argyropulo studied (1933a, 1933b) fivespecies 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 Americanmicrotines. Hibbard and Rinker (1942, 1943) figured the baculum ofSynaptomys cooperi paludis and of Microtus ochrogastertaylori. Dearden (1958) studied the baculum in two Asiatic species ofLagurus, in six subspecies of Lagurus curtatus of NorthAmerica, and in six other species of microtines of other genera.
The baculum can be preserved easily with standard study skins, and ispotentially useful in interpreting relationships on any taxonomic level,and especially in determining the relationships of species within agenus, if used together with other structures.
The anatomical orientation of the baculum needs comment because someconfusion exists in the literature, especially concerning the use of theterms ventral and dorsal. The urethra lies on the anatomically ventralside of the penis, and of the baculum. In the center of the penis lies asingle corpus cavernosum penis, shown in cross section proximal to thebaculum in Figure 1c. Dorsally an artery, thinner walled than the ventralurethra, ends in a somewhat reticulate sinus surrounding primarily themiddle part of the baculum within the bulbous glans penis. The corpuscavernosum penis (the structure has no median septum, at least distally)terminates with the baculum and is closely knit to it. The site of thisbond is evident in the tuberosities and sculpturing of the base of thebaculum.
The part of the penis enclosing the baculum, when not erect, is foldedback as shown in Figures 1a and 1b. As a result the anatomically ventralsurface faces upwards, or at least posterodorsally. The use of the termventral in this account refers to the anatomically ventral side, that isto say to the side of the baculum facing the urethra.
The baculum in microtines consists of an elongate stalk, having alaterally, and to a lesser extent dorsoventrally, expanded base and[Pg184]an attenuate distal shaft. Usually, three digitate processes ofcartilaginous material in which additional ossifications may occur arisefrom the terminus of the shaft. The proportions and curvature of thestalk vary as do the proportions of the terminal ossifications to eachother and