220 THE MYOLOGY OF THE EAVEN. 



one I have last described seems to correspond to this 

 writer's extensor pollicis brevis, but his description is 

 not very definite. 



I dissected four pairs of feet of this species, and 

 the dissection is by no means an easy one, before I 

 was satisfied that the facts in regard to these short 

 extensors of the toes are as I have given them above. 

 They were the same in all, and in all the extensor 

 brevis digitorum of Owen was absent. 



Professor Mivart, in his Elementary Anatomy, does not 

 mention the short extensor of the hallux as occurring 

 in birds, and this eminent biologist calls this muscle 

 the extensor proprius liallucis. 



In certain birds with zygodactyle feet, as in Geococcyx 

 for instance, the morphology of the extensor liallucis 

 brevis is quite different, and when treating the myology 

 of G. californianus it led me to consider the present 

 muscle as only a part of the extensor brevis digitorum 

 in that form, and I said in effect that the extensor brevis 

 digitorum is a muscle that may be taken as an ampli- 

 fication of the muscle I have described in the Eaveri as 

 the extensor hallucis brevis. 



But even here in Geococcyx the short extensor of the 

 hallux has a certain amount of individualization, though 



o 



it is not fully differentiated from the other part of this 

 extensor brevis (Fig. 64 bis). It, however, is not at- 

 tached more than half-way down the anterior aspect of 

 the shaft of the tarso-metatarsus, at which point it 

 terminates in a delicate thread-like tendon ; this passes 

 directly over the upper border of the accessory meta- 

 tarsal, and along the top of the basal joint of the hallux, 

 to become inserted in the usual manner in the base 

 of the claw -joint. Now the remainder of the extensor 

 brevis digitorum is attached down the shaft of the tarso- 

 metatarsus, as far as the distal trochlese ; the outer 



