THE ORGAN OF JACOBSON IN THE RABBIT, 551 
forming the support of the lateral wall of the nasal furrow, will 
be spoken of as the lower limb ; the second, z.e. the one forming 
the support of the front part of the lower concha, as the upper 
limb; and the third, z.e. the one extending outwards and upwards, 
as the lateral limb. In a section anterior to fig. 1, the lower limb, 
shown in fig. 1, is not present yet, but outside it is a small car- 
tilage plate coming off from the lateral limb and extending a short 
way downwards. Where the other limbs join the lower limb, this 
latter has its thickest diameter. The upper and lateral limbs 
increase also in thickness towards their upper margin. 
As regards the structure of these different parts, the same dis- 
tinction can be drawn as in the septal cartilage, viz. the upper 
portions of both the upper and lateral limbs stam much less in 
logwood, and the cartilage cells are relatively fewer than in the 
lower parts. 
In a preparation in front of the one of which fig. 1, is a repre- 
sentation, the three limbs of the above cartilage form one conti- 
nuous whole; but in the preparation shown in fig. 1 there is 
already a discontinuity noticed, at any rate on one side, between 
the upper and lower limb, as well as between the latter and the 
lateral limb. Going a little further back, e.g. fig. 1, we notice 
not only a permanent discontinuity between the two last-named 
limbs, but we perceive that the upper limb of the cartilage 
becomes greatly reduced in height, being now represented only 
by its upper less stained portion, soon to disappear altogether, and 
to be replaced by the rudiments of spongy bone, forming now the 
support of the plicated lower concha. While this happens with 
the upper limb, also the lower limb undergoes considerable 
changes, viz. it increases in height and thickness, and its lower 
_ Inargin, while greatly expanding in breadth, curves downwards 
and inwards, in the manner of a trough or hook, but so that the 
nasal furrow is now forming the lining of its (i.e. the trough’s) 
concavity. In fig. 2 this so changed lower limb is accurately 
delineated. 
It is here seen that the trough consists of an inner or median 
labium, terminating close to the lower margin of the septal car- 
tilage with a pointed extremity and an outer or lateral labium 
continuous with the lower limb of the cartilage above mentioned. 
From the convex surface of the trough a short cartilage extends 
downwards into the upper maxillary bone. This cartilage is not 
well seen in fig. 2, but is observed well in sections taken between 
the parts of figs. 1 and 2. Ina part of which fig. 2 is a repre- 
sentation it is just disappearing. 
As will be shown soon below, this trough-shaped cartilage is 
the front end of the cartilage that forms the support of the organ 
or tube of Jacobson, and it is known as Jacobson’s cartilage. 
