| OCR Text |
Show 19Q5.] HARES FROM SOUTHERX SWEDEN. 281 of each zygomatic arch is especially different in the two species. In L. europceus the distance from the anterior end of the deep groove for muse, masseter lateralis (portio profunda) to the anterior vertical border of the arch itself is greater than the height of the same portion of the zygomatic arch. In L. timidus the condition is quite the opposite, the height of the anterior portion of the zygomatic arch being greater than the distance from the anterior end of the groove or fossa mentioned above and the anterior border of the arch. In the hybrid the condition is intermediate, but nearer that of L. timidus. The anterior, inferior angle of the orbit in the hybrid has a structure which, singularly enough, differs from that of both parental forms. In both the latter the jugale and the lower part of the 'processus splieno-orbitalis of the maxillary project in such a way that a rather deep fossa is formed in the inferior anterior angle of the orbit between the bones mentioned and the alveolar protuberances. This fossa is, however, entirely missing in the hybrid. This depends evidently upon a different arrangement of the insertion of the muscles. In the parental forms, to judge from my material, the anterior portion of the masseter lateralis is confined to the interior surface of the zygomatic arch and its upper margin in the anterior corner of the orbit; but in the hybrid it spreads further forward on the facial area, where a tubercle and some rugosities indicate the limit of its insertion. The difference between the hybrid and the parental forms indicates accordingly an increase of a part of the masticating apparatus in the former. The very great development of the whole zygomatic arch of the same shows that other parts of the masseter as well have been enlarged to a considerable extent. The greatest height of jugal is in the hybrid 12*5 mm., while the greatest corresponding measurement for L. timidus is 10 mm., and for L. europceus only a little more than 9 mm., so far as my material goes. The fossa pterygoidea in the hybrid specimen is larger (its width being more than 8 mm.) than in either of the parental species, and its shape is intermediate: thus the musculus pterygoicleus internus has a wider area of insertion in the hybrid than in the parental forms, and the great breadth of the lamina latercdis proves the same for the m. pterygoideus externus. The sidcus temporalis of the squamosum has in the hybrid almost the same shape as in L. timidus, that is to say deeper and narrower than in L. europceus. The supraorbital processes are very strongly developed in the hybrid, but the frontal region of the skull behind the processus supraorbitcdesposteriores is very strongly constricted, not measuring-more than 13 mm. This, which is the more striking when the great size of the skull is considered, I regard as an inheritance from L. europceus ; as of ten skulls of L. timidus none is so narrow, the limits of variation being 15-19 mm. and the usual dimension 17 mm. In L. europceus the same dimension is in my material from 12 to 15 mm. |
