138 



collateral hind-foot ivliich is to form the neiv rear 

 appui.^ 



§ 133. The ball and socket movement of the 

 digastrics, and of the internal oblique muscles of 

 the eyes, we should describe on the principle that 

 a rolling outward of the muscle, beginning at its 

 anterior part, represents the ball motion — a turning 

 inward, commencing in the rear portion, the reci- 

 procal socket motion (§ 39). The eyes remain 

 steady in the central line of advance while, with 

 movements similar to those of its diagonal eye 

 muscle, each digastrics brings the composite spine 

 into connection with the central movement. The 

 eyes thus belong fundamentally to the ophidian 

 (or snake) spine. 



The part of both digastric and eye muscles an- 

 terior to the loop rolls outward with the secondary 

 section of the anterior winding line, the part pos- 

 terior to the loop with its primary section — then, to 

 form the double twist, the rear portion rolls in- 

 wards with the primary section of the posterior 

 winding line, the front portion inward with the 

 secondary section. These correspondences take place 

 for the eye muscle during the ophidian spine action — 



* The newly grounded hind-foot should, in perfect action, come into 

 the print of the fore-foot which gives place to it, unless the spring has 

 carried all four feet forward. 



