1900.] STRUCTURE OF THE MUSK-OX. 687 



Sect. 1. — The Development oe the Horns oe the Musk-ox. 



The peculiar shape, structure, and position of the horns of the 

 Musk-ox make them more interesting objects for an investigation 

 than the greater number of horns of other Cavicornia. The 

 material on which this essay is based has been brought home by the 

 Swedish Expedition to East Greenland in 1899, under the direc- 

 tion of Professor A. G. Nathorst, and consists of a skull of a young 

 calf and several skulls of adult bulls and cows. Unfortunately 

 no intermediate stages are represented by young or half-grown 

 animals, because no such animals were seen, Professor Nathorst 

 informs me. This gap is to some degree filled by Sir John 

 Richardson's description and fine figure of the skull with the 

 horn-cores of a yearling or "16 months old " bull '. With the aid 

 of this description and figure, and above all by the extremely 

 interesting markings of growth and structure which were made 

 visible by preparing longitudinal sections of a horn of an old bull, 

 I think that I shall be able to present a fairly exact sketch 

 of the development of the horns of the Musk-ox. In preparing 

 this I have had the valuable assistance of my friend G. Svenander, 

 Cand. Phil., who has made the accompanying drawings of horns 

 in three different stages of development, and to whom I therefore 

 beg to express my best thanks. 



The origin of the horn-cores is conspicuous in the young summer 

 calf as a slight prominence on the lateral surface of the frontal 

 bone, about 1 cm. from the upper surface of that bone and about 

 as far from the fronto- parietal suture, but 8| cm. from the 

 posterior mai'gin of the orbit. 



The development of the horn must be slow during the first 

 winter, because, as Mr. II. Lydekker informs me, the calves which 

 were brought to Tromso by a Norwegian vessel, and subsequently 

 sold to the Duke of Bedford, had not auy horns even in December. 



In the second summer the growth must be rather rapid, as the 

 horn-cores of a 16 months old bull according to Richardson's 

 figure (I.e.) measure about 11 or 12 cm. The author mentioned 

 describes them in the following way : — " The horn-cores have a 

 purely lateral origin, and do not rise at all above the facial line, 

 but, springing from an almost cylindrical root immediately behind 

 the orbits, stand out laterally with a moderate inclination basilad 

 and antiniad, their axis forming with the mesial plane of the 

 cranium an angle of 62°. These cores are moreover, in themselves, 

 concave on their facial or coronal aspect, by which they receive a 

 uniform upward curve in the direction of their length, in addition 

 to their general direction of outwards, basilad, and forwards. 

 The tips of the cores in this yearling extend further from the sides 

 of the skull laterally than any part of the massy core or its sheath 

 in the four-year-old animal." With the help of this description, 

 and assuming that the horns of an adult animal have not been 



1 Zoology of the ' Herald, ' p. (57, pi. iv. 



45* 



