Joints of the Spine. 



157 



209. Intervertebral disc, fibrocartilago intervertebralis, 



cut through, horizontally. 



Magnification 3 : 2. 



Each fibrocartilago inter vertebral is consists of a firmer external portion, 

 annulus fibrosus, and a softer centre, nucleus pulposus. 



The annulus fibrosus is composed of concentric layers of connective tissue 

 fibres which are arranged like the leaves of an onion; inside each layer the fibre 

 bundles cross one another in network-like fashion (see Fig. 208); in the depth the 

 connective tissue layers are less sharply separated from one another and alternate with 

 layers of very soft fibrocartilage. 



The nucleus pulposus consists essentially of a very soft mass of fibrocartilage 

 with irregular connective tissue bands and contains the remains of the embryonic 

 chorda dorsalis; it is separated but not sharply from its surroundings and lies nearer 

 the posterior circumference of the intervertebral disc (see Fig. 210). In the uninjured 

 spinal column its constituents are under high pressure so that on cutting through the 

 dies they project markedly. 



