376 



THE EXTERIOR OF THE HORSE. 



about being made. This done, the operator places the instrument in such a 

 position that the branch of the compass to which the half-circle is fastened is 

 perfectly tangent to the plumb-line. Then he gently moves the other branch 

 until it has the direction of the osseous segment the inclination of which he 

 desires to obtain. Having again proved the correct position of the apparatus, 

 he reads upon the half-circle the value of the angle contained between the two 

 branches, and deducts 90 degrees from this angle to obtain the desired inclina- 

 tion. 



If, on the contrary, we simply desire to measure an articular angle, the 

 plumb-line is needless. It is unfastened from the sliding cylinder, and the two 



FIG. 137. Use of the arthrogoniometer for 

 measuring the articular angles. 



FIG. 138. Arthrogoniometer for measuring 

 the articular angles. 



arms of the arthrogoniometer are placed in the prolongation of the two axes 

 of movement whose separation we desire to determine. For the metacarpo- and 

 metatarso-phalangal angles an ordinary compass is used, which is afterwards 

 applied upon an appropriate protractor in order to obtain the angle contained. 

 Although, in reality, the metacarpus and the metatarsus are not absolutely ver- 



