THE REPTILE-LIKE BIRD. 22% 
Mammals, are still scarcely distinguishable from those of 
Tortoises and other Reptiles. The cleavage of the yoll is 
partial in the case of Birds and Reptiles, in Mammals it is 
total. The red blood-cells of the former possess a kernel, 
those of the latter do not. The hair of Mammals develops 
in closed follicles in the skin, but the feathers of birds and 
also the scales of reptiles develop in hillocks on the skin. 
The lower jaw of the latter is much more complicated than 
that of Mammals; the latter do not possess the quadrate 
bone of the former. Whereas in Mammals (as in the case of 
Amphibia) the connection between the skull and the first 
neck vertebra is formed by two knobbed joints, or condyles, 
in Birds and Reptiles these have become united into a single 
condyle. The two last classes may therefore justly be united 
into one group as Monocondylia, and contrasted to Mammals, 
or Dicondylia. 
The deviation of Birds from Reptiles, in any case, first 
took place in the mesolithic epoch, and this moreover 
probably during the Trias. The oldest fossil remains of 
birds are found in the upper Jura (Archeopteryx). But 
there existed, even in the Trias period, different Saurians 
(Anomodonta) which in many respects seem to form the 
transition from the Tocosauria to the primary ancestors of 
Birds, the hypothetical Tocornithes. Probably these Tocor- 
nithes were scarcely distinguishable from other beaked 
lizards in the system, and were closely related to the 
kangaroo-like Compsognathus from the Jura of Solenhofen. 
Huxley classes the latter with the Dinosauria, and believes 
them to be the nearest relations to the Tocornithes. 
The great majority of Birds—in spite of all the variety in 
the colouring of their beautiful feathery dress, and in the 
