XIIl] 



OF SHEEP AND GOATS 



623 



of the horn; but, in the general distribution of the curves, it is 

 in complete accordance with theory. Similar anticlastic curves 

 are well seen in many antelopes; but they are conspicuous by 

 their absence in the cylindrical horns of oxen. 



The better to illustrate this phenomenon, the nature of which 

 is indeed obvious enough from a superficial examination of the 

 horn, I made a plaster cast of one of the horny rings in a horn of 

 Ovis Animon, so as to get an accurate pattern of its sinuous edge : 

 and then, filling the mould up with wet clay, I modelled an anti- 

 clastic surface, such as to correspond as nearly as possible with 

 the sinuous outline*. Finally, after making a plaster cast of this 

 sectional surface, I drew its contour-lines (as shewn in Fig. 322), 

 with the help of a simple form of spherometer. It will be seen 

 that in great part this diagram is precisely similar to St Venant's 



^-^ 



Fk. 321. 



Fig. 322. 



diagram of the cross-section of a twisted triangular prism; and 

 this is especially the case in the neighbourhood of the sharp angle 

 of our prismatic section. That in parts the diagram is somewhat 

 asymmetrical is not to be wondered at: and (apart from inac- 

 curacies due to the somewhat rough means by which it was made) 

 this asymmetry can be sufficiently accounted for by anisotropy 

 of the material, by inequalities in thickness of different parts of 

 the horny sheath, and especially (I think) by unequal distributions 

 of rigidity due to the presence of the smaller corrugations of the 



* This is not difficult to do, with considerable accuracy, if the clay be kept 

 well wetted, or semi-fluid, and the smoothing be done with a large wet brush. 



