68 PROCEEDINGS OF THE ANATOMICAL AND ANTHROPOLOGICAL 



cartilage opposite the lateral incisor tooth begins to be surrounded 

 above and below by bone developed in the perichondrium, the upper 

 lamella now forming a distinct inner alveolar margin (Fig. 7). The 

 cells of the cartilage in. contact with the bone are enlarged and 

 vacuolated, but so far there is no actual ossification of the cartilage. 



In a foetus 43 mm. in /ein/t/t ossification in membrane has now 

 extended so that the form of the adult jaw can readily be recog- 

 nised. The two halves of membrane bone extend forward so as 

 to nearly meet in the middle line. The bone no longer forms a 

 simple lamella but shows a lattice-like structure. The inner alveolar 

 margin at the incisor teeth is formed by a lamella which has grown 

 over in the perichondrium above Meckel's cartilage (Fig. 8). The 

 mental foramen is still relatively very much elon- 

 gated, with the mental nerve closely applied to its 

 posterior margin. The mesial wall of the dental 

 gutter now arches over Meckel's cartilage. The 

 Fi 7 -corona? sec- coronoid process and angle of the jaw are both 

 tion of the lower jaw thickened, this thickening being made up of lat- 



of a human foetus, 36 



mm. in length ( x ?). tico-like membrane bone. There is no trace of 



D., lateral incisor 



tooth germ ; j.,mem- cartilage at the coronoid process, but its apex is 



brane bone of jaw ; . 



M.C., Meckel's carti- surrounded by condensed mesodermic tissue. Ihe 

 ramus of the jaw is continued backwards and up- 

 wards as a somewhat thin lamella to the condyle which is represented 

 by condensed mesodermic tissue without any trace of bone or cartilage. 

 As to Meckel's cartilage its anterior extremity shows commenc- 

 ing ossification. This is taking place at a point opposite the interval 

 between the mesial and lateral incisor tooth germs, where the 

 cartilage is in close relation with the membrane bone. At this 

 point the cartilage cells are much enlarged, many are vacuolated, 

 others show two nuclei and the cells next the bone are broken down, 

 their nuclei lying free among the osteoblastic tissue which passes in 

 from the closely applied membrane bone (Fig. 1*5). These stages are 

 preparatory to the actual ossification of the cartilage. The relation 

 nt nerves to Meckel's cartilage in the region of the ascending ramus 



