782 THE AMERICAN NATURALIST. [Vou. XXXIV. 
and the ratite birds from dinosaurs. This was supported by 
Wiedersheim ('86). 
As a result of his own detailed review and comparison, 
Fürbringer in his great monograph upon birds (88, p. 1624) 
concludes that the direct descent of birds from any known type 
of Dinosauria is excluded; that the birds are monophyletic ; 
that the resemblances between dinosaurs and birds are all 
“convergence-analogies”’ and * parallels" due to relationship 
of the “middle grade"; more definitely (88, p. 1630), he regards 
Dinosauria, Crocodilia, and Lacertilia in the order named as 
the nearest relatives of birds, and believes that the stem of the 
birds is to be sought in a common sauropsidan ancestor lying 
between the Dinosauria, the Crocodilia, and the Lacertilia ; that 
this stem, as Marsh had already supposed, is to be found in 
the last division of the Paleozoic, namely, the Permian; here 
occurred the first differentiation of fine sauropsidan scales into 
feathers. 
The problem thus presents itself now in three forms: (1) are 
birds directly descended from primitive dinosaurs? (2) have 
birds and dinosaurs originated from a common stock? (3) are 
the remarkable resemblances between these two groups entirely 
due to parallelism or homoplasy ? 
Before discussing this triple problem we may continue with 
the subject of the resemblances and differences, or positive and 
negative evidence. 
III. ADDITIONAL Avian RESEMBLANCES IN BIPEDAL 
DINOSAURS. 
Cervical Vertebral Formula. — Fürbringer (88) observes that 
the cervical + cervico-dorsal vertebrae of birds vary from ten to 
eleven (Archzeopteryx) to twenty to twenty-five in the larger, 
long-necked forms, indicating that the number of vertebra is 
distinctively an adaptive character. More in detail, we may 
give the avian formule as follows: 
