THE ANIMAL ANCESTRY OF MAN 



69 



the V and with the backbone lying between the limbs of the 

 V but connected with them only by muscles. In side view 

 the pelvis as a whole appeared hke an inverted y, with the 



Fig. 8. Musculature of upper arm and shoulder girdle of crocodile. 



(After Furbringer, Zur vergleichenden Anatomic des Brustschulter-apparates und der 

 Schulter-muskeln.) 



ihum, or inverted stem of the y directed upward and back- 

 ward. As a whole the pelvis lay between the muscle masses 

 of the abdomen and those of the tail and it gave attachment 

 to both (Romer). 



When such an animal raised itself off the ground the body 

 was slung Hke a suspension bridge between two piers, the 

 scapulae of the pectoral girdle forming the front pair of 

 piers and the iha of the pelvic girdle forming the rear pair. 



Fig. 9. Bridge-like construction of primitive tetrapod. 



(From Gregory, Proc. Amer. Pbilos. Soc.) 



Between these the ribs and backbone formed another 

 superposed jointed cantilever bridge supporting the head 

 and the viscera and acting as a movable base for the most 

 powerful muscles of the body. In general, forward progres- 

 sion under such an arrangement involves a series of alternate 

 and rhythmical extensions and flexions, rockings, bendings 

 and twistings. For instance, while the right hind limb is 



