88 PllACTICAL HISTOLOGY [XI 



wavy course from the pulp-cavity outwards. These, 

 dividing as they go, and giving off many anastomosing 

 lateral branches, finally end either in loops or in small 

 irregular cavities, the so-called interglobular spaces, on 

 the surface of the dentine. 



In some places the dentinal tubules are cut trans- 

 versely. Here the central dark spot indicates the space 

 formerly occupied by the dentinal fibre, the ring round 

 this is the dentinal sheath. 



The Cement or Crusta Petrosa. This differs 

 little from bone, but Haversian canals are generally 

 absent. 



The canaliculi of the lacunae next to the inter- 

 globular spaces, open into these, thus bringing the 

 dentinal fibres into connection with the bone-corpuscles. 



Where the cement is massive, wavy ' contour ' lines 

 may be seen, indicating the successive deposits. 



The Enamel, consisting of striated fibres or prisms, 

 perpendicular to the surface of the dentine. 



12. Sections of lower jaw of a foetal mammal (chromic acid 

 0'2 p.c.). Stain with picrocarmine or as in 9. Note the 

 stages of the development of the teeth, and also the osteoblasts 

 and osteoclasts of the young sub-maxillary bone. 



DEMONSTRATIONS. 



1. Longitudinal section of insertion of round 

 ligament into head of femur (picric acid, hsematoxylin). 

 Note the transition from the fibrous tissue of the 

 ligament to fibro-cartilage, and from this to hyaline 

 cartilage. 



