A REPRESENTATIVE VERTEBRATE. FROG 



343 



which produce eggs and internal secretions, 

 two oviducts or Fallopian tubes about 4 

 inches long, a uterus, a vagina, and the ex- 

 ternal genitalia. The ovaries are almond- 

 shaped and weigh from 2 to 3V2 grams. They 

 contain at birth about 70,000 developing egg 

 cells, most of which later disappear. The 

 ova discharged from the ovary into the 

 coelomic cavity then enter the oviduct and 

 are carried to the uterus; here, if an egg is 

 fertilized, it remains during embryonic de- 

 velopment. 



A general account of reproduction and de- 

 velopment is contained in Chapter 34. 



Skeletal system 



The principal functions of the skeleton 

 are mechanical support, motion, and protec- 

 tion. The internal supporting framework of 



Premaxilla 

 Moxilia 

 Vomer 

 Nasal 



Phalanges— 



Metacarpals 



Carpats' 



Suprascapula y. 



Radio-ulna ^ 



Humerus 



the frog's body is an endoskeleton consisting 

 largely of cartilage and bone. Cartilage 

 (gristle) is a tissue in which the cells are 

 embedded in a matrix that they secrete; it 

 is firm, tough, and elastic (Fig. 43). Bone 

 tissue is a connective tissue impregnated 

 with mineral salts. About 58 per cent of 

 bone is calcium phosphate, 7 per cent cal- 

 cium carbonate, and 33 per cent organic 

 matter such as cells and gelatinous sub- 

 stances. The endoskeleton supports the soft 

 parts of the body, furnishes points of at- 

 tachment for the muscles, and protects 

 some of the delicate organs such as the 

 brain, spinal cord, and eyes. 



A study of the skeleton reveals an inter- 

 esting story of the relation of structure to 

 function. The ridges, lines, depressions, and 

 protuberances on a bone all have some func- 

 tional significance and are, therefore, mean- 



Sphenethmoid 

 Frontoparlefal 



Pterygoid 



Squamosal 



Proofic 



Exoccipital 



Atlas 



Phalanges 



Metatarsals 



Tarsals 



Vertebral 

 column 



Sacral 

 vertebro 



Urosryle 



Ilium 



Femur 



Tiblo-fibuta 



Calcar 



Astragalus 

 Calcaneus 



Ischium 



Figure 226. Skeleton of the frog. 



