228 DR. E. KLEIN. 
cartilage of the concha and to the upper maxilla is the same 
as in the adult animal. The epithelium lining it is stratified 
epithelium composed of a deep layer of columnar cells, and 
inside these are a good many layers of polyhedral cells. 
In the front part the lumen of the duct is not at all dis- 
tinct; in the posterior portion of the duct the lumen becomes 
very conspicuous, and the epithelium resembles, in all 
respects, stratified pavement epithelium, the superficial cells 
being, however, not much flattened. 
I measured the thickness of the epithelium lining the 
naso-lachrymal duct in this embryo, and I find it to be about 
0:068 mm., the lumen of the duct being 0 22—0:03 mm. In 
a part behind the region of the organ of Jacobson the thick- 
ness of the epithelium is smaller, being 0°056, while the 
lumen is 0°12 mm. 
For the sake of completeness I append here a few points 
concerning the structure of the Stenonian ducts, which, as 
is well known, pass closely side by side, and in the median. 
line, from the nasal to the oral cavity. 
In the adult guinea-pig the nasal extremity of each of 
these ducts is an oblong cleft lined with a continuation of 
the mucous membrane of the lower nasal furrow ; the epithe- 
lium is ciliated columnar epithelium, and underneath this 
is a membrane very vascular and infiltrated with lymph- 
corpuscles. There are no secreting glands, mucous or other, 
visible in this part, and the mucous membrane is in. imme- 
diate contact with the bone of the palate. 
As the ducts approach the oral cavity, but while still in 
the bone of the palate, they become much smaller, but in a 
transverse section are still cleft-like, and lined with strati- 
fied pavement epithelium, whose superficial cells are poly- 
hedral. Having passed the bone and approaching the oral 
cavity, the ducts become still smaller, they remain cleft- 
like, and are lined with stratified pavement epithelium, whose 
superficial cells are as much flattened as those of the palatine 
mucous membrane. The mucosa underneath the epithelium 
of the ducts is dense fibrous tissue, and there are indications 
of minute papilla. There is now already to be seen a trace 
of the Stenonian cartilage in the periphery of the wall of 
the ducts. 
Still nearer towards the oral cavity, while the ducts enlarge 
in diameter, and while their shape becomes more cylindrical, 
the above rudiment of the cartilage forms now for each duct a 
curved plate, semicircular in transverse section, whose con- 
cave surface embraces the outer part of the wall of the duct. 
