( 15 ) 



The effect of tliis was also fell in (lie region in front of the 

 auricular organ, but here part of the somitic muscles remained on 

 account of a change of function. They became attached to the here 

 developing eye-ball and now served for the movement of this latter 

 and no longer for the movement of the whole body. This was 

 accompanied by far-reaching shiftings, which can still lie followed 

 in the individual development. 



The cartilaginous skeleton forms a system which appears only late 

 in the development of the vertebrates and long after the appearance 

 of the muscular system. As soon as the first cartilage may be 

 observed, the muscular system in the head lias undergone the 

 changes here indicated. In the auricular region the somitic muscles 

 have degenerated; partly they were not even indicated; in the region 

 in front of the auricular organ they have entirely changed in place 

 and shape and have entered into the service of the eye-ball. Only 



in the region behind the auricular organ — the occipital region 



the myotomes - - generally numbering three — still stand in the 

 original order, like the myotomes of the trunk. 



Head and trunk are separated in the ontogeny — although the 

 border is later somewhat shifted in a caudal direction — already 

 before the cartilaginous spinal chord appears, and I see no reason 

 for assuming that this separation should not have taken place also 

 in phytogeny before the appearance of the spinal chord. 



The segmentation of the spinal chord depends on that of the 

 muscular system. The bo l\ of a vertebra is not formed opposite the 

 middle of a myotome, but opposite the border of two successive 

 myotonies. Balfour luis given the explanation of this at first sight 

 curious phenomenon-, the first muscular fibres occupy the whole 

 length of a myotome and lie laterally of the tissue, surrounding the 

 notochord. Now it is no more than natural that the solid points of 

 attachment which in this tissue are formed for the muscular fibres, 

 namely the origin of the vertebral bodies, are formed opposite the 

 borders of two successive myotomes. 



If we now ask where the appearance of vertebral bodies in the head 

 must be expected, the answer must be that this cannot be in the 

 auricular region, since here the myotomes have disappeared at the 

 time of the appearance of the cartilage. No more can this be the 

 case in the region in front of the auricular organ, for here the 

 myotomes have entirely altered their place and have entered into 

 the service of the eye-ball. 



Only in the occipital region one would expect the appearance of 

 two or three vertebrae. Yet until recently nobody has observed them 



