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Show 1 900.] STRUCTURE OF THE MUSK-OX. 705 fifth (T 2 T) anteriorly, and by the jugal to a little less than two-fifths (T 4 T) inferiorly. The length of the orbital tube is, in an old bull, between 6 and 7 cm. posteriorly and about 4| cm. anteriorly. In a cow the same measurements are about 5 and 3| cm. respectively. Already in the young calf the orbits protrude about 2\ cm. measured posteriorly.] The reason why the orbital tubes have attained such a great development is double, but easy to understand. Firstly, a look at the skull of the Beindeer compared with those of other Cervicornia, teaches us that a ruminant, living in Arctic regions, and therefore provided with a long fur, is apt to develop a tube-like prolongation of tbe orbital ring for the purpose of not getting the eyesight hindered by the long hairs. This may be certainly applied to the Musk-ox also. It may be added, further, that the situation of the horns probably would to a great extent prohibit the animal from noticing any object, except those just in front, if the eyes were not protruding. Secondly, when for the reasons mentioned the eyes have become protruding, the peculiar development and position of the horns make a strong protection for the eyes, and one well needed; for it has already been said that when a Musk-bull charges he uses his horns sideways or at least obliquely. It is thus evident that the eye easily could be damaged, as it is just in the way of attack, if it were not protected by its thick bony case. That the eye-tube is meant for protection can also at once be seen from tbe heavy structure of the bony wall, which in an adult bull, above and below, reaches a thickness of more than 2\ cm. The lower thickening is produced by the enlarged jugal, and the upper one by a stout ridge beginning on the lachrymal and extending in a median direction over the frontal to the neighbourhood of the foramina supraorbitalia. This ridge is also very useful when the bull is butting with its forehead. The orbital tubes are, however, not a new organ acquired by Ovibos, but only a development and prolongation for certain purposes of an orbital ring such as it exists not only in tbe Sheep, but also in a great number of Antelopes, e. g. Antilope, Saiga, Gazella, Bupicapra, Nemorhcedus (at least some species), &C.,1 in which the direction of the orbital brim is the same as in Ovibos, although much narrower. It is, therefore, no reason whatever to regard the orbital tubes of Ovibos as an excessive development of the orbitalring of theSheep or,to use BoydDawkins's words,-':a decided ovine affinity " (/. c. p. 7). As a result of his comparing the Musk-ox only with Oxen and Sheep, Biitimeyer (I. c. p. 10) writes : " D e m Schaf folgt dann auch ferner in jeder Beziehung die Bildung des Thranenbeines." It is chiefly the presence of a lachrymal groove which hao created such an opinion, I think ; but, as I have shown in the previous paper, the presence of an anteorbital gland is far from being an exclusively ovine character, and accordingly a lachrymal groove or pit is just as little so. The bending outward of the lachrymal bone for its 1 Not to mention distant forms such as Antilocapra, Reindeer, Camel, |
