KONGL. SV. VET. AKADEMIENS HANDLtNGAR. BAND 35. N:0 3. 9 



tentli of the lengtli of this organ measured as abo^•e but of course considerablv less of 

 the spiral axis. The trajisverse ribs strengthen the horny sheaths against torsion and 

 coiTugation. The liorns of Strepsiceroft are a good deal divergent and must consequently 

 be resistant also against a bending force applied sideways. The screw shape of the horn 

 is then also nseful, becanse the ridges follow the spiral of the horns and consequently 

 strengthen them against violence from all sides. The length of the horns and their di- 

 vergence is favourable when two kudu bulls are fencing, because a skilful fighter can then 

 wound its adversary on the sides of its neck and shonlders without moving the whole 

 body forward, Avhich would simultaneously exposé his own flank. 



It has been said above that the horns of Sfreps/ceros can be regarded as a further 

 specialisation in the saiue direction of developraent as that which has taken place in Trcu/c- 

 la-phus. The spiral rotation has been increased so that the liorn is not only twisted 

 ronnd its own axis, but has l)een laid m an open spiral. The cause of the twisting was 

 supposed to stånd in correlation with tlie development of longitudinal ]"ibs. Such an 

 assnmption is corroborated by the disposition of the horny material in the sheath of the 

 kudu. On a transverse section of such a horn it can lie seen that on the basallv, and 

 consequently originally, lateral side the sheath is considerably thinner than on the origi- 

 nallv median side. About 27 cm. from the base of the horn measurinor 79 cm. in lenoth 

 this is expressed as follows. (^n the oi-iginally lateral side the tliickness of the sheath 

 is near the great anterior ridge 4 nmi. and on the middle of the same side between tlie 

 anterior ridge and the latero-posterior thickening, which corresponds to a ridge, about 

 4' 2 mm. On the originally median side the thickness of the sheath is 5 nnn. near tlie 

 rib, and towards the middle of the same side about 7 to 8 mm. This might be explained 

 in the following way. For the development of the ridges the material is consumed in a 

 larger degree and consequently the adjoining parts of the sheath and the portion between 

 two ridges which are situated near eacli other must become thinner. Such an arrange- 

 raent can also take place without danger because the ridges brace the sheath sutficiently. 

 ()n a distance from the ridges the horny material can be evenly deposed without disturb- 

 ing influences and accordingiy the growth be quicker. This again results in a spiral 

 curving of the horn, because the place of maximum-growth is not situated directly oppo- 

 site the place of minimum growth, but the shortest distance between these two places is 

 less than half the periphery. A line laid through the points where the growth takes 

 or has taken place most slowly onght to be the shortest and run all the time on the 

 inner conca^-e side of the spiral. The proxiraal end of this line lies on the lateral side 

 of the horn. The line through the point of quickest growth runs on the convex peri- 

 pherical side of the spiral and has its proximal end on the median side of the horn. 

 In a horn of Strepsiceroa with a straight axial length of 90 cm. the difference betwee]] 

 these two lines is not less than 30 cm. This relation may, to a certain extent, serve as 

 an index to the difference in growth on the lateral and median sides. On the outer 

 structure of the horn as well, the different rapiditv of growth may be recognized, naniel)^ 

 on the transverse ribs of the median side. Anteriorly and on the median side these ribs 

 are quite transversal and often showing a convex upper outline at the most peripherical 

 part of the spiral (where the growth is most rapid). Posteriorly, however, they make a 



K. St. Vet. Aknd. Handl. Baud 35. N;o 3. 2 



