ON THE NOTOCHORD 



245 



earthy or ossific material to distribute to distant developing 

 chordal textures, whereby they can undergo the common 

 process of growth, then so active everywhere throughout 

 the embryonic organism ; we, therefore, would regard it, 

 as a vascular mechanism, or vehicle, whose function a 

 temporary one ceases with the arrival of the more 

 advanced fcetal condition, when the necessity for its 



FIG. 104. SECTIONS OF THE VERTEBRAL COLUMN OF A HUMAN FCETUS 

 OF EIGHT WEEKS. (From Kolliker.) 



A, transverse longitudinal section of several vertebrae, i, i, chorda dorsalis, its 



remains thicker opposite the intervertebral discs ; 2, is placed on one of the bodies 

 of the permanent vertebrae ; 3, on one of the intervertebral discs. 



B, transverse horizontal section through a part of one dorsal vertebra, i, remains of 



the chorda dorsalis in the middle of the body ; 2, arch of the vertebra ; 3, head 

 of a rib. 



existence no longer continues ; and this latter stage 

 would seem to be reached when the ossification of the 

 various units of the vertebral column has been effected 

 to that extent, which yields a stable, protection and 

 support to the developing brain and spinal cord, and 

 which then allows its future nutritional economy to be 

 developed, on the ordinary lines of growth, to the stage, 

 of self-supporting efficiency and organic independence. 



If this be so, and we regard it as developmentally 

 reasonable, and suitable, in the circumstances, we should 



