MINUTE ANATOMY OF ORGAN OF JACOBSON IN GUINEA-PIG. 225 
lachrymal ducts are met with, in vertical transverse sections 
through the nasal organ, some distance in front of Jacob- 
son’s organs, as minute tubes, in the same position and of 
the same nature as described in my first memoir, as 
will be easily understood on comparing the figures 1, 2, 3, 
and 4 accompanying the present paper. Also backwards 
for a very long distance beyond the region of the organ of 
Jacobson about 10—12 mm.; the naso-lachrymal ducts 
retain the same position, viz. between the nasal furrow and 
the alveolar process of the upper maxilla. As I mentioned 
in my first paper, this duct is slightly flattened from side to 
side, and the diameter enlarges considerably posteriorly ; in 
the region of the hind extremity of the organ of Jacobson 
the diameters of the naso-lachrymal duct (5 in fig. 7) are 
these : 
Horizontal transverse diameter of the whole duct . 101mm. 
Vertical transverse diameter fh bs J . 2°81 mm. 
Horizontal transverse diameter of the lumen P . 060 mm. 
Vertical - - sie ss - apo LOL mms 
Vertical (thickness) diameter of the lower wali . . 0°7875 mm. 
Vertical (thickness) diameter of the upper wall. - 101 mm. 
Behind the region of the organ of Jacobson the naso- 
lachrymal ducts increase still more in diameter, the trans- 
verse diameter of the lumen alone amounting in the 
broadest part of the tube to 1:125 mm.; they become at 
the same time cylindrical, 7.e. less flattened from side to 
side. As regards the structure of the naso-lachrymal duct 
I have little to add to my previous description as far as that 
part is concerned, that belongs to the region of the organ of 
Jacobson. In the whole extent of the duct I find in close 
proximity to the epithelium lining the interior of the duct, 
and described minutely in my first memoir, but separated 
from it (epithelium) by a thin fibrous layer, ¢. e. the subepi- 
thelial fibrous layer, a plexus of large veins, most of these 
running a longitudinal course. The wall of these veins is 
exceedingly thin and appears to consist almost entirely of 
the endothelial membrane lining the lumen. Had I not 
seen the blood capillaries in connection with them, and had I 
not found some of them containing blood, I might easily have 
mistaken them for lymphatics. This plexus, which I will 
call the “subepithelial venous plexus,” is well seen in the 
region of the posterior extremity of the organ of Jacobson (see 
figs. 9, 10); it reaches its greatest development in the region 
behind the organ of Jacobson. In fig. 7 it is also noticed 
that the rest of the wall of the naso-lachrymal duct is made 
up of a very loose fibrous connective tissue ; the thickness of 
