NOTOCHORD AND VERTEBRAL COLUMN. 



559 



The fate of the notochord is in important respects different 

 from that in Birds. It is first constricted in the centre of the 

 vertebra (figs. 320 E and 321) and disappears there shortly after 

 the ossification ; while in the intervertebral regions it remains 

 relatively unconstricted (figs. 320 E, 321 and 322 c) and after 



FIG. 372. LONGITUDINAL SECTION THROUGH THE INTERVERTEBRAL LIGAMENT 

 AND ADJACENT PARTS OF TWO VERTEBRA FROM THE THORACIC REGION OF AN 



ADVANCED EMBRYO OF A SHEEP. (From Kolliker.) 



la. ligamentum longitudinale anterius ; lp. ligamentum long, posterius ; K. liga- 

 mentum intervertebrale ; k, k'. epiphysis of vertebra ; w. and w'. anterior and 

 posterior vertebrae ; c. intervertebral dilatation of notochord ; c'. and c". vertebral 

 dilatation of notochord. 



undergoing certain histological changes remains througJi life as 

 part of the nucleus pulposus in the axis of the invertebral ligaments^. 

 There is also a slight swelling of the notochord near the two 

 extremities of each vertebra (fig. 322 c' and c"}. In the per- 

 sistent vertebral constriction of the notochord Mammals retain 

 a more primitive and piscine mode of formation of the vertebral 

 column than the majority either of the Reptilia or Amphibia. 



1 This view was first put forward by Lushka, and his surmises have been con- 

 firmed by Kolliker and other embryologists. Leboucq (No. 424) however holds that 

 the cells of the notochord in the intervertebral regions fuse with those of the 

 adjoining tissue ; and Dursy and others deny that the nucleus pulposus is derived 

 from the notochord. 



