164 STRUCTURE AND CLASSIFICATION OF BIRDS 



without the numerous subdivisions so often observable in 

 the same muscle in the (hypothetically) higher birds. Nor 

 is there the patagial fan, the junction between the tendons 

 of the longus and the brevis, a character, again, so frequent 

 among the larger birds. The complications in this case 

 seem to be much more likely an effect of specialisation than 

 that the simple conditions observable in the picarian and 

 other allied birds should be due to a process of degenera- 

 tion. 



The simplicity and relative shortness of the gut is a 

 matter, which is perhaps of importance in this connection. 

 The average relative length of the gut is much less on the 

 whole in the Pico-Passerines than in any other group. There 

 are, of course, some startling exceptions, but the general 

 statement holds. As to the caeca, it must be confessed that 

 they are as a rule small or absent. But the Coraciidse and 

 the Todida? are exceptions. The fact that both lobes of the 

 liver are frequently in this group of birds enclosed in separate 

 compartments, separated from the subomental space, seems 

 to me to be a vestige of a condition such as that which is 

 found in the crocodile. On the other hand certain of the 

 organs of the body show great variety and specialisation ; 

 particularly is this the case with the syrinx ; but to find 

 most of the organs of the body in a primitive condition, 

 while others are greatly specialised, is precisely what is so 

 often found in what are believed to be archaic types. 



There can be no doubt that the Archesopteryx, far 

 though it may have diverged from the ancestral stock, has 

 retained more of the reptile than any other form known to 

 us. One or two of the characters are shared by that large 

 assemblage of birds which has been termed the Ano- 

 malogonatae. 



In the first place the structure of the foot of fheArchceo- 

 ptenjx is that found in passerine birds. That the primitive 

 bird was arboreal seems likely, and it is not surprising to 

 find that this mode of life has led to various specialisations 

 in the foot, such as we find in the hornbills, &c. The 



