THE ORGANS OP THE INTERMEDIATE LAYER OR MESENCHYME. 597 



whereas the shorter portions lying in the soft intervertebral discs 

 continue to enlarge (fig. 325 cA). Thus the chorda now acquires the 

 appearance of a string of beads, since thickened spheroidal portions 

 are joined to one another by small connecting thread-like portions. 

 Subsequently it entirely disappears in the bodies of the vertebrae, 

 especially when the latter begin to ossify (fig. 326) ; the intervertebral 

 portion (li) alone persists, although indistinctly limited from the 



Fig. 326. Longitudinal [sagittal] section through the intervertebral ligament and the adjacent 

 parts of two vertebrae from the thoracic region of an advanced embryo Sheep, after KOLLIKER. 



la, Ligament longitudinale anterius ; Ip, lig. long, poaterius ; li, lig. intervertebrale ; k, K , car- 

 tilaginous caps (epiphyses) of the vertebrae ; w and to', anterior and posterior vertebrae ; 

 c, intervertebral, c' and c", vertebral enlargements of the chorda. 



surrounding tissue, and produces by the proliferation of its cells the 

 gelatinous core of the intervertebral disc. 



Soon after the appearance of the bodies of the vertebrae the funda- 

 ments of the corresponding arches are observable. According to 

 FRORIEP'S account, there arise small, independent pieces of cartilage 

 in the membrane enveloping the spinal cord, in the immediate 

 vicinity of the bodies of the vertebrae, with which they soon fuse. 

 Their growth is rather slow. During the eighth week they still 

 appear in Man as short processes from the bodies of the vertebrae, 

 so that the spinal cord is still covered dorsally by the membranous 

 skeleton. In the third month they grow into contact with each 

 other at the dorsum ; however, it is only in the following month 



