584: 



CHORD ATA. 



nor lungs, but have only pharyngeal and cutaneous respiration. 

 The capillary network in these parts is greatly developed and may 

 extend into the epithelium. Thus, also, it happens that in the 

 Anura the skin receives as large an artery as the lungs (fig. 616, cii). 



The skin is thin and slimy from the numerous mucous glands, 

 which not infrequently produce a poisonous secretion (so called 

 parotid gland in the ear region). The epithelium bears a thin 

 horny layer which at intervals is molted as a continuous sheet. 

 The derma in the Anura is undermined by large lymph spaces, 

 the presence of which makes the skinning of a frog such an easy 

 matter. Ossifications in the skin enormously developed in the 

 fossil Stegocephali occur but rarely (Gymnophiona) in recent 

 Amphibia. On the other hand the abundance of chromatophores is 

 noticeable, these, under the influence of the nerves, changing their 

 shape and thus producing color changes in many Amphibia. 



The heart (figs. 615, 616) has two auricles, distinctly sep- 

 arated in Anura, a right with venous blood, a left which with 



FIG. 615. 



FIG. 616. 



FIG. 615. Heart and arterial arches of salamander larva. (After Boas.) a 1 a 2 , right 

 and left auricles; an, arterial trunk; ad, dorsal aorta; as, left aortic arch; />, 

 direct connexion between afferent and efferent arteries; c, carotid; I, afferent 

 artery; p, pulmonary artery; v, ventricle; l~U, afferent arteries; l'-3\ gills. 



FIG. 616. Heart and arches of frog (diagram), a/ a,,, right and left auricles ; aa, 

 ventral aorta; ad, as, right and left aortic arches (radices aortse); c, carotid; cu, 

 cutaneus; ?, lingualis; p, pulmonary artery; ss, subclavian; v, ventricle; ve, 

 vertebralis; 1, 2, 4, persisting arches. 



pulmonary respiration receives arterial blood. There is, however, 

 but a single ventricle, and the arterial trunk is, at least externally, 

 single. The arterial arches show different relations and have 

 different fates. With branchial respiration the first three afferent 

 and efferent arteries are connected in two ways, the one by the 



