THE REPTILE GALLERY. 



GENERAL NOTES ON REPTILES. 



There is but a short step from the Class of Birds to that of 

 Reptiles. No doubt, as regards external appearance, the dissimi- 

 larity between the living animals of these two classes is sufficiently- 

 great to allow of a sharp line of demarcation being drawn between 

 them : Birds being shortly characterized as warm-blooded vertebrate 

 animals clothed with feathers, Reptiles as cold-blooded, and covered 

 with horny or bony shields, tubercles, or " scales." But there 

 are numerous and important agreements between these two classes, 

 especially in the structure of their skeleton, in their internal 

 organs, and their mode of propagation ; and their close relation- 

 ship becomes still more apparent when fossil forms are examined, 

 such as Hesperornis and Archceopteryx, of which a cast is placed in 

 Case A, in the corridor leading from the Bird- into the Reptile- 

 Gallery (see also the figure given on p. 35 of the Geological Guide). 



Reptiles are termed " cold-blooded " because the temperature of 

 their blood is raised but a few degrees above, and varies with, that 

 of the outer atmosphere, owing to the imperfect separation of the 

 divisions of their heart, which allows more or less of a mixture of 

 the arterial and venous currents of the blood. Reptiles are ovi- 

 parous or ovoviviparous ; no important change takes place after 

 exclusion from the egg ; they breathe by lungs throughout life. 

 Their skull articulates with the vertebral column by a single occi- 

 pital condyle (see fig. 1), and their lower jaw with the skull by a 

 separate bone (quadrate) (see figs. 1, 13, and 14). 



The remains of the oldest known Reptiles, those found in the 

 Permian formations, seem to belong to the Rhynchocephalian type, 



