SOCIETY OF THE UNIVERSITY OF ABERDEEN. 73 



In a foetus 103 mm. in length, both condylar and coronoid car- 

 tilages are perhaps at the height of their development, while the 

 anterior ends of Meckel's cartilages are mostly resorbed. Behind the 

 symphysis all that remain of the anterior ends of Meckel's cartilages 

 are two small cartilaginous nodules ; above these and independent of 

 them is to be seen an unpaired cartilaginous nodule. That part of 

 Meckel's cartilage between the central incisor tooth and the canine 

 tooth has now become quite resorbed by osteoclasts, and invaded by 

 the surrounding bone tissue. The varying appearances seen in coronal 

 sections of the jaw of this fetus are presented in Fig. 14. In the 

 specimen there appears a strip of cartilage along the upper edge of the 

 outer alveolar margin, and in the region of the inner alveolar margin 

 there is a somewhat similar strip of cartilage inside the incisor tooth 

 germs. These pieces of cartilage are not in any way connected with 

 Meckel's cartilage, but seem to arise much in the same way as the 

 coronoid cartilage. 



In the sections the relations of the condylar cartilage can readily 

 be traced. Its anterior extremity reaches as far forward as a point 

 just behind the termination of the inner alveolar margin that is, just 

 in front of the base of the coronoid process. Traced backwards from 

 this point, the cartilage enlarges, finally terminating in the condyle. 

 At first the cartilage is covered by a thin lamella of bone on its out- 

 side, but, as traced backwards, it is covered on both aspects by the 

 periostium of the jaw. The condylar cartilage, towards its anterior 

 part, now shows regressive changes, being destroyed by giant cells, 

 and its place taken by marrow tissue, while round it young bone 

 tissue is being deposited. Posteriorly the cartilage is still uninjured, 

 and the condyle is formed by hyaline cartilage covered with peri- 

 chondrium. 



As regards the coronoid cartilage, it consists of cartilage covered 

 with a perichondrium continuous with the periostium of the bone ; 

 below the boundary between the bone and the cartilage, just behind 

 the tooth gutter, there are numerous osteoclasts and marrow tissue. 



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