tiONGL. .SV. VET. AKADEMIENS HANDLtNGAK. BAND 35. X:0 3. 31 



trajectories of pressure are better developed. Wheii the mnskox uses its horns as weapons 

 with hooking movements from below upwards and o))fiquely sideways from the animal, 

 there ean be distinguished two moments^) with regard to the acting forces and their in- 

 flnence on the horn. Firstly, \vhen the animal has lowered its head and receives a load 

 or chaTge on the distal tip of the book. In this moment the greatest breaking power 

 affects the horn in the curve, because this place is then at the end of the lever or most 

 distant from the porpendicular through the ti]> ;ilong which the pressnre works. Secondly, 

 when the head is raised to a normal position, the distal end is again vertical from having 

 beon more or less horizontal and the strain nfteets no^\• more the base, which is most 

 distant from the perpendienlar along which the pressure works. To successfullv with- 

 stand the disturbing intliiences of the breaking power of the tirst moment the curve of 

 the horn consists of solid horn.-) To counteract the second moment the horn is proxi- 

 mally very thick and strong and \ erv tirmly tixed to the skull as bas already been 

 stated above and is more fully described in the paper rpioted. The upper resp. outer 

 side is the strained side and in accordance with this the elastic element which naturally 

 is better apt to stånd the stretching force, tlie horny sheath, of that side is very strongly 

 developed as is already mentioned. The lower, resp. proxiraal, side is the pressed one. 

 Therefore the horny sheath of that side can A\'ithout danger be thin when it is In-aced 

 by a resistent bony core in -which the corapact layer of the corresponding side is thick 

 and strong. The trajectories of pressure are also more strongly developed on this side. 

 The fiattening of the proximal part of the horn, core as Avell as sheath, increases its 

 strength to endure torsion and violent breaking forces parallel to the longest axis of 

 the section of this part in the direction. When the muskliuU lowers its head in the 

 act of hooking the longitndinal axis of the proximal, compressed part of the horn 

 becomes more or less completely horizontal and the longest axis of its section ^'erticab 

 It has then a suitable position to withstand the pressure eftected by the weight charged 

 on the tip of the horn. This foi'ce or pressure works namely in a direction vertical 

 against the axis of the horn and ])arallel to the longest axis of the section throiigh the 

 proximal part of the horn. The curvature of the horn of the muskox is not so abrupt 

 as the same in the gnu. The horn of the former has therefore not been subjected to 

 such a special adaption to the likeness of a draghook as that of the latter (conf. above). 

 But, on the otliei- hand, the basal expansion and fiattening is a feature common to l^oth. 

 The resemblance in the exteriör shape of the horns in these two aniraals has not at all 

 its match with regard to the interiör structure. In Ovibos the main strength of the 

 horn lies in tlie strong development of the liorny matter and the bony core does not 

 even extend to tlie curve, hut in Cinrnorhcfii-s </iiu the core extends neai^ly through the 

 whole (n"gan and the sheath is not nnich developed. The mode of fixation to the skull 

 difters also quite essentiallv. In tiic gnu tlie horny sheath forms a cap över tlie pi-o- 



') The same or aiialogfnis nnes can also bo spöken of with regard to simihar movements of othei' animals 

 with curved horns. 



^) In conse(|ucnfe uf its great impctousncss this first moment may put tlie horn to a very great test and 

 often more than it can endnro as is proved liy the fact that the Swedish expeditions to East Greeiiland 1899 

 and rJOO found several siiecimens of Orilioa with the horns liroken at or near the eurve. 



