3 900.] 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 Eeindeer com- 

 pared 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 the 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 the 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 en- 

 larged 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 supra orbitalia. This rid°-e 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 the Sheep, but also 

 in a great number of Antelopes, e. g. Antilope, Saiga, Gazella, 

 Hupicapra, Nemorhadvs (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 

 orbital ring of the Sheep or, to use BoydDawkins's words, "a decided 

 ovine affinity " (I. c. p. 7). 



As a result of his comparing the Musk-ox only with Oxen and 

 Sheep, Eiitimeyer (I. c. p. 10) writes : " Dem Schaf folgt dann auch 

 ferner in jeder Beziehung die Bildung des Thranenbeines." It is 

 chiefly the presence of a lachrymal groove which ha/3 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 



' Not to mention distant forms such as Antilocapra, Eeindeer, Camel, &c 



