XXI] VERTEBRAL COLUMN 547 



All Anura possess Eustachian pouches and a columella auris, 

 but all do not have a well-developed ear-drum. 



The skin is most loosely attached to the muscles underneath. 

 Large spaces containing .Jjm&tL are interposed between them. 

 These lymph spaces form a protection against the danger of 

 drying up. There are two pairs of sacs placed, one pair just 

 between the upper ends of the pectoral girdle, and another pair 

 just at the sides of the rudimentary stump of a tail, which have the 

 power of contraction and pump the surplus lymph into the veins of 

 the neighbourhood. These are called the anterior and posterior 

 pairs of lymph-hearts. 



7 



FIG. 268. A. dorsal, and B. ventral view of the cranium of a Common Frog, 

 Ratio, tempo raria, from which the membrane bones have mostly been 

 removed x 2. After Parker. 



1. Sphenethmoid. 2. Palatine. 3. Pterygoid. 4. Suspensorium. 

 5. Columella. 6. Exoccipital. 7. Ventral cartilaginous wall of 



cranium. 8. Pro-otic. 9. Anterior fontanelle. 10. Eight 



posterior fontanelle. 11. Qnadratojugal. 12. Nasal capsule, 



ii, v, vi, ix, x. Foramina for exit of cranial nerves. 



Turning now to the skeleton we observe many points of 

 difference between the frog and the Newt. The ribs in the frog 

 are indistinguishably fused with the transverse processes; in very 

 few Anura are they distinct and they are always vestigial. The 

 vertebrae differ from those of the Urodela in the entire suppression 

 of the ventral intercalary element, so that the centrum is constructed 

 out of basidorsal, interdorsal and basiventral elements, the last 

 named being vestigial. In some Anura the basiventral piece is 

 entirely absent, and in this case, since the centrum is constructed 

 entirely of dorsal elements, the notochord is found for a considerable 

 period of development lying in a groove on its under surface. This 



352 



