VI 



FORM AND FUNCTION 



169 



There is connected with this subject another strange 

 phenomenon. In many birds a thin muscle, called 

 Ambicns, arises from the Pelvis just under the thigh- 

 joint and passes forward on the inner side of the leg 

 to the knee, before reaching which it becomes a tendon : 

 it curves round the knee in a little tendinous tunnel 

 occupied by itself alone, then doubles back on the 

 outside of the leg and passes into one of the muscles 

 which bend the toes as described above. It is very 

 characteristic of birds that a muscle should, by means 



A 



Fig. 45. — Leg of chicken, the side next the hody. 

 a, ambiens muscle ; k, knee-joint. 



of a long tendon, do its work at such a distance : but, 

 curiously, it is not found in by any means all the 

 perching birds. And, besides, this the same muscle is 

 to be found in crocodiles. 1 This must not, how- 

 ever, be taken to prove any very close relationship with 

 birds. The fact that it is found in two families of birds 

 may help to prove that they are closely allied, but such 

 evidence is less dependable when we are dealing, not 



1 Refer to Appa?-eil Locomoteur des Oiseaux (M. Edmond 

 Mix), p. 443. 



