Boros István (szerk.): A Magyar Természettudományi Múzeum évkönyve 3. (Budapest 1953)
Éhik, Gy.: The occurrence of the Root-vole (Microtus oeconomus Pall.) at the Kisbalaton
On the base of above figures the condylobasal length of the various crania may be expressed in values of frequency as : 26,3<26, 6—28<30 mm. The average is 27,63 mm measured on 35 skulls. Against this the values of frequency of 58 germán oeconomus, given by Zimmermann (5, p. 178), are : 23,1 <24,1 —26,5< 29 mm, the average being 25,5 mm. It is evident at once that the Kisbalaton (and Somorja) specimens have larger skulls than the germán ones, which, regarding- their isolation, is not to be wondered at. Zimmermann, irt his work, gives also the mandibular length of the german oeconomus. I have measured this length with Duerst's method (1, p. 332) from the condylion mediale to the infradentale (cm —id). The mandibular length of 35 adult Kisbalaton oeconomus are : 15,5 mm 16 mm 16,5 mm 17,0 mm 17,5 mm 15,9 16|4 16^9 VIA 117,9 4 sp. s 11 6 8 6 The minimum value was 15,6 mm, the maximum 17,9 mm, or, expressed in a formula: 15,6^16,0—17,4-=17,9 mm, Those of the german oeconomus (Zimmermann^ data): —-=14,5—15,5-= 17,5 mm. These results perfectly correspond with the figures of the condylobasal length, that is, the mandibula is relatively longer, too. The result is the same if the mean value (16,66 mm) of the mandibular length is compared with the mean value of the german animals (15,6'mm). Zimmerman n's work serves also to compare the cranial and corporal lengths of the animals with those of the german specimens. The average cranial and corporal length of these latter is 112,8 mm, as against the, smaller 109,9 mm of the Kisbalaton specimens. Therefore M. oeconomus mehelyi is a geographic subspecies with a smaller body but a bigger head than even M. oeconomus slimmingi. The absolute caudal length of the Kisbalaton oeconomus — with the young animals together! — varies between 40—60 mms, giving lower figures than the german specimens, where the same figures are : 30—61 mms. I have already observed during my investigations that the specimens with the biggest skulls are males. I have therefore calculated the mean figures of the craniometric data of all developed males (sen., ad., s. ad) and females. My measurements ended with the interesting result that the males are bigger than the females (see data at end of Table). In comparison I have also added the figures of the type specimen of M. oeconomus mehelyi, belonging to the Somorja population which correspond to the values of the Kisbalaton animals in all essentials. To rightly interpret the tabular data I find it necessary to give my methods of measuring. I have measured the condylobasal length of the skull from the aboral point of the condylus to the external inguinal point of its part wedged between the intermaxillar incisors. Zygomatic breadth = the greatest breadth between the zygomatic arches (O g n e v, vol. VI. p. 404. fig. 195, no. 7.). Interorbital constriction = measured at the narrowest point (O g n e v, I.e. fig. 195. no. 8.). Breadth of the brain-case = the longitude measured between the external points of the auditorae bullae (1. c. fig. 195. no. 13.). The length of the brain-case = the distance between the posterior orbital angle of the frontale and the aboral point of the crania media occipitalis (1. c. fig. 195. no. 11.). Diastema — measured from the interior labial edge of the incisor's root to the furthest oral point of the
