4 HUMAN EMBRYOLOGY AND MORPHOLOGY. 



mesial nasal processes fuse together; in their anterior inferio 

 angles are formed the premaxillae. The remainder forms th 

 septum of the nose. 



In the mesial nasal processes a laminar plate of cartilage 1 

 developed, which is continuous with, and forms part of, th 

 trabeculae cranii (Fig. 136). Part of this cartilage remains a 

 the septal cartilage of the nose (Fig. 3). From the septal carti 

 lage, just over the naso-palatine foramina, a small scroll-lik 

 or turbinate process is thrown out on each side to form a hoo< 

 for an isolated piece of olfactory epithelium — the organ of Jaeobson 

 They form the cartilages of Jacobson. The cartilages and orgai 

 are vestigial in man. In the mesial nasal processes are developed 

 also, the mesial or septal limbs of the alar cartilages of the nosi 

 (Fig. 3). 



The Vomer is developed in the membrane (perichondrium) whicl 

 covers the primitive septal cartilage. A centre of ossification ap 



trough for cartilaginous 

 i septum. 



fright plate 



left plate 



Fig. 4. — Showing the tl'Ough-shaped Vomer of the newly born. 



pears in the 3rd month at each side of the cartilage ; they fust 

 together under the palatal margin of the cartilage. Thus th( 

 vomer forms at first a shallow trough in which the cartilage oi 

 the septum appears to be implanted (Fig. 4). 



The Vertical Plate of the Ethmoid is formed by a direcl 

 ossification of the primitive cartilage of the septum. Ossificatioi 

 begins in the 4th month. The crista galli, the intra-cranial pari 

 of the septum, is formed in part by the ossification proceeding 

 into the attachment of the falx cerebri. 



Premaxillary Bones.— The two premaxillary bones form tht 

 sockets of the upper incisor teeth. In the human foetus at birtr 

 the suture between the pre-maxilla and maxilla can be seen or 

 the hard palate; it runs on each side from the naso-palatin< 

 foramen to the alveolus between the lateral incisor and canin< 

 (Fig. 9). On the facial aspect, the premaxilla fuses with the 



