40 - HAROLD SAXTON BURR 



nasal process. As is shown in figure 8 mp., this is a thin plate 

 of cartilage that lines the medial and anterior surface of the nasal 

 capsule, between the sac and the premaxilla. 



Correlated with the posterior growth of the ethmoid column 

 is a lateral chondrification of the mesenchyme overlying the 

 medial-dorsal aspect of the nasal sac. In this manner is formed 

 a roughly rectangular plate of cartilage whose lower surface is 

 concave to fit the dorsal aspect of the sac, and whose posterior 

 edge marks in a general way the anterior boundary of the orbit. 

 This is the tectum nasi (fig. 8 tc). 



The cartilages formed in the above manner almost completely 

 surround the olfactory sac, only the region about the external and 

 the internal nares is left uncovered. 



Development after operation. The first visible effect of the 

 removal of the nasal sac is a sinking in of the skin in the nasal 

 "region. Iti the case of the bilateral operations this is so marked 

 as to give a veritable 'pug dog' effect, which increases with age. 

 Figure 10, a drawing of a section through the head of a larva 

 with a unilateral operation, shows how marked this caving in is. 



A study of sections of these unilaterally operated larvae shows 

 at once that most of the capsular structures that arise in con- 

 nection with the olfactory sac are absent. The ethmoid column, 

 the tectum nasi, and the medial nasal process are all absent. 

 There is, however, a slight indication of a solum nasi. The 

 anterior trabecular plate is apparently regularly formed, though 

 thicker than is normally the case on the operated side. The 

 antorbital process is also formed, though, as a glance at figure 

 6 will show, it is atypical in form and position. 



The trabecula of the operated side is very much thickened 

 (fig. 11). In addition the ascending process of the premaxilla 

 has become connected laterally with the maxilla by a thin plate 

 of bone, bridging over the region that would have been occupied 

 by the external nares, figures 5 (bp) and 10. The formation of 

 this unusual bony connection has apparently drawn the maxilla 

 in, so that it no longer possesses the normal curvature (fig. 6). 

 The line of the lower jaw follows that of the upper perfectly. 

 There is in the lower jaw a compensating curvature to that of 



