2 THE FROG 



more familiar pipiens. Excellent descriptions and illustra- 

 tions are to be found in Miss Dickerson's Frog Book. 



The following characters of the frog are peculiarly 

 amphibian. The skin is glandular and without an exo- 

 skeleton. The skull is autostylic and its articulation with 

 the vertebral column is by means of paired condyles on the 

 exoccipitals. The basioccipital and supraoccipitals are lack- 

 ing as well as the basisphenoid. The squamosals and para- 

 sphenoid are well-developed. The kidney is a mesonephros 

 and there is present an urinary bladder. The male 

 mesonephric duct functions as a ureter and gonoduct. In 

 the female the mesonephric duct carries only excretory 

 products, and an extra tube, the oviduct, is present to trans- 

 port the products of the gonads. The heart has two auri- 

 cles and one ventricle. Three aortic arches persist. The 

 cardinal veins have been largely supplanted by a postcaval 

 vein. Both a renoportal and an hepatoportal system are 

 present. There is a comprehensive lymphatic system. The 

 red blood corpuscles are large and oval with a prominent 

 nucleus. The brain possesses a small cerebellum. Ten 

 cranial nerves are found. The olfactory sacs communicate 

 with the mouth by means of posterior nares. There is no 

 outer ear. The tympanic membrane is attached to a 

 columella which extends across the middle ear to join a 

 cartilage which has been considered the stapes, lying in 

 the fenestra ovalis. 



Gaupp's revision of Ecker and Wiedersheim's Die An- 

 atomie des Frosches remains the most comprehensive 

 memoir on the anatomy of the frog. The Biology of the 

 Frog by Holmes is a convenient compendium with especial 

 regard to R. pipiens. 



The student must bear in mind that the frog is not a 

 good example of the generalized amphibian type. Necturus, 

 one of the tailed amphibia (see Adams, L. A., Necturus, a 



