102 BULLETIN OF THE ESSEX INSTITUTE. 



inferior or lateral nasal canal, In, is a long, flattened out- 

 pushing and lies more externally. The walls of the cavum 

 nasale become thickened immediately and the epithelium 

 is specialized for sensory purposes. The walls of the 

 lateral nasal canal are thinner and contain no specialized 

 cells except at its external end. 



As we go farther forward, the lateral nasal canal sud- 

 denly widens laterally, still retaining its flattened condi- 

 tion, fig. 8, plate IV, and the external part becomes cut ofi" 

 from the main canal, forming a small and short blindsac. 

 The epithelium of this posterior blindsac is not thickened 

 or specialized, but is of the simple columnar type. This 

 blindsac occurs in each series of sections and is apparently 

 a constant structure. It is shown in outline in plate V 

 and fig. 7 cuts through its anterior end. 



The thickening seen to bound it internally in fig. 7 is 

 merely the oblique section of the wall of the lateral nasal 

 canal, which is here extending itself outward to connect 

 with Jacobson's organ, and has nothing to do with the 

 posterior blindsac itself. 



In front of the posterior blindsac, the walls of the lat- 

 eral portion of the lateral nasal canal become greatly 

 thickened and its epithelium in this region assumes the 

 same specialized condition as was found in the cavum 

 nasale. This lateral portion now assumes a more nearly 

 cylindrical shape and almost immediately leads away from 

 the lateral nasal canal and forms the duct for the organ 

 of Jacobson. From this duct, the organ of Jacobson ex- 

 tends forward, figs. 6, 5, 4, its anterior end being a little 

 posterior to the middle of the whole nasal apparatus, 

 plate V. It is the most external of the cavities connected 

 with the nasal organ and lies on a lower plane than the 

 rest. It is a rounded cone, viewed from below, and its 

 outer walls have a flattened cylindrical section while its 

 ulmen is broad and low. 



