SOCIETY OP THE UNIVERSITY OF ABERDEEN. 



77 



part of Meckel's cartilage which has been taken into the jaw. After 

 this stage, Meckel's cartilage rapidly atrophies, so that at birth it is 

 dilHcult to get any trace of it in connection with lower jaw. In a 

 seven months' foetus, horizontal sections through the symphysis do not 

 show nodular symphysial cartilages, but again they are to be seen in 

 sections of a foetal jaw at the ninth month. In a foetus at the 

 seventh month, all trace of cartilage has disappeared from the 

 coronoid process, but there is cartilage in the condyle and the rainus 

 still shows the open texture of the bone ; remains of the condylar 

 cartilage persist till birth. 



Fig. 16. Horizontal section of the left half of 

 the lower jaw of a human fcetus, 43 mm. in 

 length ( x 70). Shows ossification com- 

 mencing to extenJ into Meckel's cartilage ; 

 this takes place at a point between the 

 central and lateral incisor tooth germs. 



Fig. 17. Sagittal section through the con- 

 dylar cartilage of the lower jaw of a 

 human foetus, 95 mm. in length ( x 33). 



SUMMARY. 



From an examination of this series of developing humun lower 

 jaw we arrive at the following conclusions : 



Each half of the lower jaw is developed in membrane as a single 

 skeletal element the dentary and the so-called *i>li>ni<il element is 



