402 THE NASAL REGION IN EUTAENIA. 



slight prolongation forward is found (c), and which appears in sec. 

 tion in Fig. 4. A similar prolongation is found on the level of the 

 turbinal, the cartilage of which furnishes a ledge on which the duct 

 rests for a short distance, after which it is completely surrounded 

 by the lachrymal bone for a portion ot its course. As it approaches 

 the eyeball it lowers to its anterior angle, and takes a sharp turn 

 inward and upward to terminate in its gland, situated on the inner 

 surface of the eyeball, and separated from its fellow of the opposite 

 side by the basisphenoidal rostrum. 



The cartilages (Figs. 3, 4, Ic , Ic") which have been termed lachrymal 

 above, are but backward continuations of the transverse band con- 

 necting the turbinal cartilage with that of the pedicle of the Organ of 

 Jacobson. When the lachrymal duct has reached the palatine bone, 

 they apply themselves to its outer and under wall and fuse, forming 

 a plate continued behind with the blindly ending basal portion of the 

 duct. The plate behind the latter becomes flattened horizontally, and 

 terminates in front of the choana of its side. 



The sections from the embryo head reveal some important points 

 which may be summarized here. 



The roof of the mouth exhibits in the main the features of the 

 adult palate. No glandular structures are present, there being but 

 an involution of the lining membrane to form, the future upper lip 

 gland. (Fig. 5, gl.) The opening of the Organ of Jacobson is situated 

 in the groove to be found laterally from the choanal depression. 



The Organ of Jacobson has the same form as in the adult. The 

 cellular columns number about twenty in each section, while in the 

 adult the number reaches sometimes as high as sixty. But the 

 remainder of the roof, of which they are the constricted portions, is 

 much thicker, and in it 8-10 layers of cells may be counted. Neither 

 these nor those of the columns are possessed of peripheral processes, 

 •at least such are not demonstrable. Fibres arising from the inner 

 surfaces of the olfactory lobes pass down the sides of the septum, 

 'enter the outer ends of the columns, and terminate at its cells. The 

 whole roof does not exhibit, in addition to the division into columns, 

 any difference from that lining the upper nasal chamber. Its floor 

 is lined by two layers of interfitting columnar cells. 



The continuity of the cartilage of the Organ of Jacobson with that 

 ■of the nasal cavity, which only a study of many sections of the adult 

 shows, is demonstrated by oue, or at most two sections, from the 



