CLASS AMPHIBIA 



479 



at rest. They are long and powerful. The five toes are con- 

 nected by a web, making the foot an efficient swimming organ. 



The skin is smooth and loose; it contains large black pigment 

 spots and a lesser amount of green and golden pigments. The 

 skin consists, as in other vertebrates (Fig. 347), of two layers, an 

 outer epidermis and an inner dermis. It is furnished with a large 

 number of mucus glands which secrete the fluid that makes the 

 surface of the body J)s % /c 



slimy, and a smaller 

 number of poison 

 glands, which secrete 

 a whitish fluid of use 

 probably for defen- 

 sive purposes. 



General Internal 

 Anatomy. — The 

 body of the frog is 

 supported by a bony 

 skeleton, is moved 



by muscles, and 

 contains a well-de- 



FiG. 409. — Diagrammatic transverse section of 

 the body of a female frog, to show relation of peri- 

 toneum (broken line) to viscera. Ao, aorta; 

 Veloped nervOUS Ds, dorsal subcutaneous lymph space; G, intestine; 

 System. If the body- 7 ^ inferior vena cava; K, kidney; LS lateral 

 J subcutaneous lymph space; NC, spinal cord; 

 wall is slit open in n, n, nerves; Od, oviduct; Ov, ovary; S, great dorsal 



the ventral middle ly ™ ph SpaCe; , V ' ^ ertebral centrum; VS, ventral 



subcutaneous lymph space; /, 2, 3, mesenteries sus- 

 line from the pos- pending the intestine, ovaries, and oviducts. The 



tenor end of the s ^ n * s re P resente< i by a thick black line. (From 



Bourne.) 



body to the angle 



of the jaw, the organs in the body-cavity or codom will be 



exposed. 



The heart lies within the sac-like pericardium ; it is partially 

 surrounded by the three lobes of the reddish brown liver. The 

 two lungs lie one on either side near the anterior end of the ab- 

 dominal cavity. Coiled about within the body-cavity are the 

 stomach and intestine. The kidneys are flat reddish bodies 



