THE SENSE ORGANS 145 
| 
wl 
\ 
fap 
\vy 
an $ sal 
SoS i 
~-- 
ae ee an —— 
TLL ELL OO TET IPD de 
Cj). FA 
Fic. 89.—A-D, Various STAGES OF DEVELOPMENT OF [THE SO-CALLED] JACOBSON’S ORGAN 
OF THE URODELIA, illustrated by a series of transverse sections. fF, transverse 
section through the nose and Jacobson’s organ of Lacerta agilis ; G, the same of 
a placental Mammal; H, the same of Ornithorhynchus, after Symington ; I, diagram- 
matic side view of G. 
In A the organ commences medially and basally ; in D the lateral position is attained ; 
E, the Gymnophione, in which separation from the principal cavity is effected ; na., 
nasal cavity ; jc., Jacobson’s organ ; ¢,7., Jacobson’s cartilage ; g.m., inter-maxillary 
gland ; g.n., nasal gland ; n.0., olfactory nerve; n.¢., trigeminal nerve; d.n., nasal 
duct ; mx., upper jaw; sp., septum nasi; 0.d., dumb-bell-shaped bone, forming a 
support for Jacobson’s organ. 
cavity (ye., Fig. 88, G, H, 1). In most Mammals this becomes 
constricted off and secondarily connected with the buccal cavity. 
A lateral displacement does not take place, and the organ remains 
between the floor of the nasal cavity and the roof of the mouth, 
1.€. 1n 1ts original position. It is always lined with a pronounced 
sensory epithelium, innervated by the ventral fasciculus of the 
olfactory nerve (n.0., Fig. I). 
Recent investigation has proved, without doubt, that vestiges 
of a Jacobson’s organ are to be found in adult human beings. 
Before considering these in detail, however, certain structures 
which attracted the attention of the earlier investigators need 
to be dealt with. 
Huscke’s “plough-share cartilage” in Man was formerly 
regarded as the vestige of the two cartilaginous tubes lying near 
the base of the nasal septum, which in many lower Mammals 
envelop the organ of Jacobson. This is incorrect, since, as 
Spurgat has shown, the same cartilages are found in the human 
organs of Jacobson as in those of the lower Mammalia, but in a 
much reduced condition. These organs, together with the Sten- 
son’s canals, open into the buccal cavity through the ductus 
L 
