AND AVES OF NORTH AMERICA. 



SYNOPSIS OF THE PRIMARY TYPES EMBRACED IN THIS ESSAY. 



The Classes Aves, Reptilia, and Batrachia are those over which the present review 

 extends. The classes of veretebrata not included are : the Dipnoi, Pisces, Elasmobranchi, 

 Dermopteri, and Leptocardii and the Mammalia. 



The Aves, Reptilia, and Batrachia are characterized and distinguished from all the 

 other classes as follows : the points wherein they differ from each other are italicized. 



BATRACHIA. 



Axial element of the brain chamber a single membrane bone, the parasphenoid ; occipital 



condyles two, on the exoccipitals. 

 Mandible compound, supported by quadratum. 

 A distinct coracoid bone. 

 Limbs when present ambulatory, attached anteriorly to a scapular arch which is free from 



the cranium. 

 Xervous System. Cerebral hemispheres larger than optic lobes, not covering the optic 



thalami, and with the lateral ventricle on their inner side. 

 Fornix and arbor vita? none; medxdla oblongata straight ; olfactory lobes terminal, sessile. 

 Circulatory System. Heart with two and three chambers. 

 Three or more aorta bows; aorta with two roots from a ductus communis and bidbus 



arteriosus. 



REPTILIA. 



Axis of brain case, the basi-occipital and sphenoid elements developed in the primordial 



cartilage, the first with exoccipitals bearing one condyle. 

 Mandible compound, supported by quadratum. 

 Coracoid bone distinct. 



Limbs the anterior attached to a scapular arch which is free from cranium. 

 Metatarsals and metacarpals distinct; carpals and second row of tarsals also distinct; 



usually the first row of tarsals also. 

 Pubis not in contact with iscliia distally. 



