| OCR Text |
Show 708 DR. E. LONNBERG O N T H E [June 19, masseterica in an adult bull passes about a centimetre from the lower margin of the lachrymal bone and parallel with the same, but then it descends rather steeply to a tuber maxillare situated above the second true molar. This is constant in my material except in one bull, in which the tuber maxillare is situated on a vertical line drawn between the first and second true molars (fig. 3, p. 691). But there seems to be still more Aariation in this respect, because Biitimeyer (I. c. p. 11) as well as Dawkins (I. c. p. 7) assert that the tuber maxillare is to be found above " the first true molar." It is apparent from these facts that the situation of the tuber maxillare does not offer any valuable characteristic for classification. The foramen infraorbitale opens rather far back, as Biitimeyer also remarks, above the third premolar or even first true molar. This seems to be a singular feature among Cavicornia. In Sheep, Goats, and Gazelles this foramen is situated above the second premolar, and in other forms it is still more advanced. Budorcas (including Nemorhcedus &c.) agrees with Ov-tbos in this respect, as will be seen later. The mandible of Ovibos offers several points of interest. The processus coronoideus is strongly curved backwards and more pointed than is usual in other forms. It is also strikingly small, which can be expressed by comparing its length with the length of the mandible itself. The former measurement is in Ovibos about 16-17 per cent, of the latter, but in Sheep, Goats, and Gazelles about 24 per cent., in Rupicapra about 23 per cent., &c. The small Cavicornia seem as a rule to have their p>rocessus coronoideus more straight, thin, and squarish at the end. In Bos the condition resembles more that in Ovibos, w;ith the length of processus coronoideus about 18-5-20 per cent, of the mandibular length. This may, therefore, be regarded as a parallel development, the more striking as the most specialized Bos taurus has a shorter and more pointed coronoid than Bos bubalis. Tbe articular surface of the mandible of the Musk-ox is remarkable for its shape, because the longitudinal diameter is about six tenths or more of the transverse one. In other ruminants tbe transverse diameter is at least twice (sometimes nearly thrice) as long as the longitudinal one. The symphysis mandibulce (fig. 8, p. 709) is about a* long in Ovibos as in Bos (16 per cent, of the mandibular length in the former and 14-17 per cent, in the latter) ; but it is, as Bichardson rightly remarks (I.e. p. 70)," more vertical, and it forms an angle or chin." The formation of such an angle or chin at the symphysis mandibulce may be caused by the need to strengthen 'the symphysis in a vertical direction, because the opening of the canalis injramaxillaris is very wide and deeply excavated in the bone and thus weakens the bone. The great width of this canal may be due to the conditions under which the Musk-ox lives in the Arctic regions. It is not only this foramen which is comparatively large in Ovibos, but the foramina for blood-vessels are as a rule large. Biitimeyer has |
