SOCIETY OF THE UNIVERSITY OF ABERDEEN. 



71 



tooth, and still lower below the germ of the canine tooth which ex- 

 tends down almost to the lower border of the jaw. From the lateral 

 incisor to behind the canine tooth, Meckel's cartilage is ossifying 

 and practically enclosed by a sheath of bone. At this stage then 

 Meckel's cartilage passes from behind forwards lying at first just 

 inside the condyle, then descending it runs along below the inner 

 alveolar shelf gaining the lower border of the jaw, under the canine 

 tooth germ ; at this point it passes into the jaw, becoming ossified 

 and rising up gains the middle line just under central incisor tooth. 



IV. 



V. 



Fig. 10. Horizontal sections through the lower jaw of a human foetus, 72 mm. in length (x 6). 

 I. shows the tooth germs lying to the inner side of the membrane bone of the outer alveolar 

 wall; II. and III. show the anterior extremities of MecUel's cartilages, with membrane bone 

 to the outer side ; IV. at a still lower level shows the anterior extremities of Meckel's 

 cartilages rising up from below the canine tooth germ ; V. shows ossification extending into 

 Meckel's cartilage ; VI. Meckel's cartilage at the level of the lower border of the jaw. D. 1.- 

 D. 4., tooth germs; J., membrane bone; M.C., Meckel's cartilage ; Mn., mental nerve. 



In a foetux 80 mm. in leiujtli the main differences are in the 

 further ossification of Meckel's cartilage, and the beginning of a 

 cartilaginous nucleus at the anterior border of the coronoid process. 

 A regular bony symphysis joined by connective tissue is now well 

 developed, and behind this are the remains of the anterior extremities 

 of Meckel's cartilages. That part of Meckel's cartilage from the 

 ((Mitral incisor to the canine tooth is wholly taken into the membrane 

 bone of the lower jaw, and is largely resorbed and undergoing ossifi- 



