DEVELOPMENT OF THE NOSE. 97 



processes ; between the two processes (lateral nasal and maxillary) the lachrymal 

 groove passes from the eye to the nose (figs. Ill, 112). The maxillary processes 

 also abut in front against the outwardly curving ends of the processus globulares, 

 which together form as just mentioned, an intermaxillary process, and the three 

 eventually coalesce to form the upper boundary of the mouth, which is thus shut 

 off from the anterior orifice of the nasal fossse (fig. 113). But further back the 



Fig. 115. OUTLINE OF A TRANSVERSE VERTICAL SECTION THROUGH THE NOSE AND UPPER JAWS OP A 



SHEEP'S EMBRYO WITH OPEN PALATE. (From Kolliker.) 



The lower jaw and tongue are removed ; m, the mouth ; d, dental germs ; p, the palate plates 

 approaching each other in the middle ; /, the nasal fossae ; c, nasal cartilage ; s, septal cartilage ; j, the 

 two organs of Jacobson with their cartilages internally. 



olfactory depressions, which are now developed into cleft-like cavities, and are in- 

 creasing in complexity by the development of the projections which are to form the 

 turbinate bones, are still freely in communication with the buccal cavity, and it is 

 only by the growth of the palatine processes of the maxillae (fig. 115,^) and their 

 coalescence in the middle line with one another, and with the lower part of the nasal 

 septum, that the nasal cavities are cut off from the mouth and from one another, 

 and now only open posteriorly into the upper part of the pharynx by the posterior 

 nares (cJwanw). 



The median or septal part of the external nose, with its columella below, is 

 formed, as above stated, of the coalesced mesial nasal processes, the alas nasi being 

 developed from the lateral nasal processes. The septum is at first broad and de- 

 pressed, so that the nostrils are widely separated from one another (fig. 114), a con- 

 dition which remains to a certain extent permanent amongst some' of the dark races 

 of mankind. 



From the above description ifc will be seen that the olfactory organs are at first altogether 

 distinct from the mouth, that they subsequently pass backwards, as grooves, deepening into 

 distinct clefts, along the roof of the moubh and forming in fact the upper part of the embryonic 

 buccal cavity, and that finally they are again gradually separated from that cavity by the 

 growth of a horizontal septum to form at first the hard and afterwards the soft palate. 



The median union of the palate begins in front about the eighth week and reaches the 

 back pare and is completed about the tenth week. Imperfect coalescence of these parts pro- 

 duces the malformations of hare-lip and cleft palate in their various degrees. Usually, how- 

 ever, in man the coalescence is completed at a comparatively early period of foetal life, 

 although a vestige of the original separation may be found in front at the junction of the 

 maxillary processes with the coalesced globular processes (intermaxillary), as the naso-palatine 

 canal or incisor foramen, which is occupied by connective tissue, blood-vessels, and a branch 

 of the fifth nerve. In many mammals, however, an actual communication remains through- 

 out life between the nostrils and mouth in this situation. 



The organ of Jacobson is early visible on either side of the nasal septum at its lower part 

 in the form of a narrow tube, oval in section, running horizontally in the substance of the 

 septum and opening anteriorly near the upper orifice of the naso-palatine canal. When the 

 cartilage of the septum becomes formed, a special curved plate of cartilage is seen partially 

 enclosing this organ ; but both the organ itself and the cartilage are less conspicuous in man 

 than in most mammals. According to Gegenbaur the rudiment which has been described in 

 VOL. i. H 



