THE SKELETON 



423 



notochord, and rapidly spread in all directions, but particularly 

 towards the surface, leaving cartilaginous ends (Fig. 241). The 

 notochord is gradually reduced and exhibits two constrictions 



Fig. 240. — The first cervical vertebrae of a young 

 embryo of Haliplana fuliginosa. (After Schauins- 

 land.) 

 s.n.b. 1,2, First and second subnotochordal bars. 



R. 3, 4, 5, 6, Ribs of the third, fourth, fifth, and sixth 



cervical vertebrae. 



and three enlargements within each centrum. The main en- 

 largement occupies the center and the two smaller swellings the 

 cartilaginous ends, the constriction occurring at the junction of 

 the ossified areas and cartilaginous ends (Fig. 241). 







J 



Fig. 241. — Section through the body of a cer- 

 vical vertebra of a chick embryo of about 12 

 days. (After Schwarck.) 

 1, Endochondral ossification. 2, Articular 

 cartilages. 3, Notochord. 4, Loosening of cells 

 of the intervertebral disc, forming a synovial 

 cavity. 5, Periosteum. 6, Ligamentum sus- 

 pensorium surrounding the notochord. 



