EXTERNAL CHARACTERS. 9 



d. On each side of the mouth cavity, behind 

 the elevation caused by the mass of muscles 

 passing down to the lower jaw, is the small 

 opening of a Eustachian tube. It will be found 

 more easily later (177, b). 



5. The Limbs. 



a. Note the manner in which the limbs, when 

 not in use, are packed away between the 

 projecting edges of carapace and plastron, in 

 hollows at the sides of the neck and pelvis. 



b. "Yh^ fore limbs are flattened, clumsy, and pad- 

 dle-like. When extended they curve back 

 over the front edges of the bridges which unite 

 carapace and plastron. The division into bra- 

 ehium, antebrachium, and manus is not obvious 

 to the eye, but may readily be felt. The limb 

 ends in five digits, connected by a web, and 

 each armed with a large claw. 



c. The hind limbs show more plainly the division 

 mto femur, cms, andfes. Each terminates in 

 five digits united by a web, and possessing 

 claws, except the fifth. 



d. Seizing the pelvic region between finger and 

 thumb, note that it has a considerable range of 

 lateral sway. This movement takes place at 

 the articulation between the last dorsal and 

 the first sacral vertebra, and to some extent 

 compensates for the rigidity of the whole dor- 

 sal region of the animal. 



6. The tail, short, conical, and pointed ; usually bent 

 to one side, so as to be protected by the overlapping 

 edge of the carapace. 



