12 HUMAN EMBRYOLOGY AND MORPHOLOGY. 



nerves lie between the palate bone and superior maxilla. These 

 are canals formed between different elements. The mfra-orbitat 

 nerve at first passes forwards in a groove on the orbital aspect of 

 the superior maxilla, but in the later months of foetal life, 

 upgrowths from the malar and nasal centres of ossification of the 

 maxilla meet over the nerve and convert the groove into a canal. 



The foramen rotundum and foramen ovale are at first notches 

 on the edge of the great wing of the sphenoid, but in the course 

 of foetal growth the notches are converted into foramina. Hence 

 wherever a nerve foramen or canal is found one may conclude 

 that it marks the junction of two elements, originally distinct, or 

 is originally a groove or notch on the edge of the bone (Bland 

 ■Sutton). The malar nerves issue between the two centres of 

 ■ossification of the malar. The two malar centres may fail to 

 unite; the bone is then divided by a suture passing from the 

 orbit to the temporal fossa. It occurs rather more frequently 

 in Japanese and Mongolian skulls, hence the name of Os 

 Japonicum. 



Palatal Rugae. — In all classes of mammals the mucous mem- 

 brane on the hard palate is ridged transversely ; three or four 

 of these tranverse ridges are seen on each side of the palate of 

 the newly born child ; they tend to disappear in the adult. Food 

 is triturated between them and the rough papillae on the palatal 

 -aspect of the tongue. Their disappearance in man is probably 

 due to the soft nature of his food. 



The Antrum of Highmore. — It will be seen from figure 7 

 that the maxillary process is at first a thin plate, lying between 

 the orbit and mouth, containing the tooth buds. It rests on the 

 outer aspect and covers the cartilaginous basis of the lateral nasal 

 process which forms the outer wall of the nasal cavity (Fig. 7). 

 About the third month of foetal life the mucous membrane in the 

 middle meatus begins to bud outwards, presses before it and 

 bursts through the lateral nasal plate of cartilage and begins tc 

 distend the maxillary process. At birth the antrum is only a 

 shallow recess on the outer wall of the middle meatus. It 

 'Continues to grow until the 25th year, and is the only one ol 

 the air sinuses developed from the nasal cavity, which is present 

 at the time of birth. In the years of adolescence the antrun 

 reaches out until it inflates the maxillary part of the malar anc 



