142 



shoulder joints combine the character of both sets of 

 limbs, and the lower jaw is the substitute ground. 



§ 138. The eyes, if we trace the optic nerves 

 (which we have attempted to do further on), may 

 be considered to combine both rear and front appuis' 

 as the foot ends of the ivhole system, first for the 

 ophidian spine, and successively for all the others,, 

 as they form. For the trot they first assume their 

 relation to the ophidian spine, and then, by the ac- 

 tion of the neck, the bi-composite relation is superadded.. 

 For a variation from this gait the lower jaw, head- 

 joint, and shoulders, may first act, and then on the 

 eyes the composite spine may be brought in. 



§ 138. The pelvis and the shoulder-blades act 

 with both C C. The third S is so rigid in its com- 

 position that it is difficult to separate the movements 

 of its C G, except by their effects. At the formation 

 of the bi-composite spine the lohole third S is merged 

 in the rear G of the ophidian, as is tJie ivhole neck S 

 in its anterior G, bringing the cross-line centre of this 

 spine betiveeii the lung lobes. 



§ 139. The lower jaw is the ground of junction 

 between the composite and bi-composite spines, and 

 on it the re-actions from the real ground, as well as 

 from all the substitute grounds (§§ 81, 82, 125) 

 come in bearing. These are essentially collateral. 



