THE FROG 85 



complicated, but the student should know at least the general location of 

 the following: 



Aponeurosis plantaris. 



The flattened and broadened continuation of the tendon of the 

 gastrocnemius muscle passing over the heel and spreading out on the 

 sole of the foot in a sort of triangle with the base toward the toes. 



Where this aponeurosis crosses the heel it is known as the 

 tendon of Achilles. 



Flexor digitorum I, II, III, IV, V. 



Each digit usually has a flexor, extensor, abductor, and ad- 

 ductor bearing the number of the toe to which it is attached, the great 

 toe being I. 



There are also small Interosseus muscles between the various 

 tarsal bones. 



For a detailed account of every muscle of the frog see : Ecker's 

 "The Anatomy of the Frog." (Oxford University Press.) 



REPRODUCTIVE ORGANS 



The sexes are separate in the frog. The male has a rather thick pad 

 on the underside of its thumb, larger in the spring at the breeding sea- 

 son, than at any other time of the year. The two rounded or oval sperma- 

 ries (A, Fig. 25) of a light yellow color are found at the upper end 

 of the kidneys, while branching masses of a yellow shade are usually at- 

 tached to them. The sperm, the male gamete ( ), 

 is produced in the spermaries, being carried through slender ducts, the 

 vasa efferentia, through the kidneys, emptying into the ureters. It will 

 be observed, therefore, that in the male frog the ureters serve both as 

 an exit for the excretion of the kidneys and the secretion of the sperma- 

 ries. In some species of frogs, the ureters are slightly enlarged, forming 

 a small sac just where they enter the cloaca, and these sacs are known 

 as seminal vesicles. The sperm are held there until ready to be dis- 

 charged. 



In the breeding season, if the body of a female (B, Fig. 25), be 

 opened, the ovaries are filled with eggs and seem to fill almost the en- 

 tire body-cavity. The ovaries, the female gonads ( ), 

 are placed in a position corresponding to the spermaries in the male. If 

 it is not the breeding season, the ovaries are rather small, slightly folded 

 and leaf-life, not very much larger than the spermaries, but of a dif- 

 ferent shape. The eggs break out of the ovary into the body-cavity and 

 make their way into the coiled oviduct through a small opening, passing 

 down into the thin-walled distensible uterus ( ). 

 The oviducts themselves are not directly connected with the ovaries, 

 but lie coiled next to the kidneys, the anterior end being a funnel-shaped 

 opening. The tube itself passes caudad beside the kidneys, opening 

 into the cloaca. The uterus is the rather large thin-walled chamber at 



