MINUTE ANATOMY OF NASAL MUCOUS MEMBRANE. 99 
In this animal the shape of the organ of Jacobson resembles 
that of other mammals (see Jacobson and_Gratiolet) and of man, 
as described by Kolliker, being a tubular structure flattened 
from side to side, and leading in front into the ductus Steno- 
nianus, which opens into the oral cavity; but its diameter is 
much larger than that of the latter. It terminates behind in a 
cecal extremity. It is surrounded, not by the bone of the 
septum, but by hyaline cartilage. This latter is, however, alto- 
gether independent of the cartilage forming the upper part of 
the nasal septum. The cartilage surrounding the organ of 
Jacobson, or Jacobson’s cartilage, forms a more or less com- 
plete capsule around that organ. But there area great many 
places where the cartilaginous capsule is incomplete, and then 
the wall of the organ of Jacobson is in immediate contact with 
the bone, or rather its internal periosteum. This incompleteness 
affects more generally the lateral and lower than the median and} 
upper parts. In some places the cartilage is reduced to a few 
(one or two) small thin plates for the lower and median, and 
two larger plates for the upper part of the organ. The car- 
tilage always projects, for each organ, upwards as a plough-shaped 
plate, showing an outer convex and an upper concave surface. 
The connective tissue, 7.¢. the perichondrium, covering this 
latter surface is at the same time the tissue by which the convex 
lower border of the cartilaginous part of the nasal septum is 
fixed here. Between the two there are in some places clumps 
of fat-cells to be met with. 
The measurements of the thickness of the cartilage of 
Jacobson, where it is quite complete, as in the preparation 
from which fig. 1, Plate VII, is taken, are these: just at the 
middle of the organ of Jacobson, on either side, it is about 0:072 
mm., at about its lower part 0:18 mm., at the upper or plough- 
shaped part the diameter at its broadest part from side to side 
is about 0°56 mm.; the diameter of the plough-shaped project 
tion from the organ of Jacob soon the upper pointed extremity 
of the former is about 0°72 mm. ‘The greatest transverse dia- 
meter of the lower enlargement of the cartilaginous nasal 
septum of fig. 1 is about 0°67 mm. 
The description of the cartilage of Jacobson in the guinea-pig 
here given differs from that given by Gratiolet of the mammals’ 
organ in general. His description is quite applicable to the rabbit, 
as I shall show ina subsequent paper, for in this animal, “‘]’organe | 
de Jacobson est entouré de cornet cartilagineux.”! In the rabbit 
there exists a continuous broad slit along the upper part of the 
wall of the organ of Jacobson, and through this slit the wall, 
and especially its glands, form a continuity with the mucous 
1 Loc. cit., p. 21, 
