TUB LOWER VERTBBKATA. 



147 



looseness of the skin. Evidently in such sinuses the lymph- 

 pressure must be extremely low, and so, in order to force 

 the lymph into the veins, there are two. pairs of muscular 

 pumping organs the lymph-hearts. The anterior pair lies 

 between the third and fourth vertebrae and pumps lymph into 

 the subscapular veins ; the posterior ones lie on either side of 

 the urostyle (see 10) and pump it into the femoral veins. 



10. The Skeleton can be recognized as consisting of the 

 same general parts as the rabbit's skull and vertebral 

 column, limb-girdles and limbs. The skull will repay a 

 fuller treatment and will be dealt 

 with in chapter xiv. The vertebral 

 column consists of far fewer ver- 

 tebrae than the rabbit's, only nine 

 in fact, the last one being followed 

 by an unsegmented bony rod, the 

 urostyle. Obviously we cannot 

 divide such a column into cervical, 

 thoracic, etc., regions ; in fact, 

 with the exception of the first and 

 two last, all the vertebrae are 

 practically identical. Each con- 

 sists of a centrum, neural arch, 

 anterior and posterior zygapophyses 

 and transverse processes. The 

 centrum is deeply concave at its 

 front end, and has at its posterior 

 end a protuberance to fit into the 

 anterior concavity of the next one 

 behind ; such a centrum is said to 

 be procoBlous. 



The first vertebra or atlas has no 

 anterior zygapophyses, no trans- 

 verse processes, an ill-defined cen- 

 trum. It articulates by very small posterior zygapophyses 

 with the second vertebra. This is not an axis vertebra 

 the frog cannot rotate its head as the rabbit can and has 

 no important pecularities. The eighth has its centrum 

 concave at both ends (amphiccelous). The ninth has a 



Fig. 72. VERTEBRAL COLUMN 

 AND PELVIC GIRDLE OF FROG. 



Dorsal view. (After Howes.) 



