THE MUSCLES OF THE LOWER EXTREMITY. 193 



side of its own moiety, towards a longitudinal tendinous 

 and mid-line of its own. This tendon becomes stronger as 



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it approaches the obturator foramen, and passing through 

 this, is finally inserted into the head of the femur of 

 the corresponding side, and upon its outer surface. 



" Now in a great many birds the area from which the 

 obturator internus arises is of an oval outline, while on 

 the other hand in nearly an equal number of the class, this 

 area will be found to be a triangular figure. So it has 

 been said, that it can thus be utilized as a good charac- 

 ter, in this way, when taken in connection with others. 

 In some few birds, I understand, it is difficult to deter- 

 mine whether this area of origin is oval or triangular, 

 but as a rule no such difficulty presents itself. For my 

 own part it constitutes a difference which, I am free to 

 confess, I had as yet paid but little attention to, as for 

 several years past neither the proper material nor other 

 facilities for such investigations have been available. 

 Nor am I quite sure in my own mind as yet, how far the 

 form of the hinder portion of the pelvis may influence 

 the origin of this muscle ; and whether such birds do 

 not exist wherein a large obturator internus is demanded, 

 and where their pelves are short, in which cases the 

 muscle, to gain a firmer origin, would naturally spread out 

 posteriorly, and thus of necessity become triangular. 



" But as I say, I am not prepared to pass final judg- 

 ment on this matter, and render a personal opinion as 

 to whether much reliance can be placed upon it as a 

 useful character in determining affinities among birds. 



" Here then again is a field open to decide an important 

 point, and one easily to be understood, and not difficult 

 to render extensive records about. Those living where 

 land and water birds occur in abundance could soon 

 determine whether (or no) this character possessed any 



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