BY R. BROOM. 
573 
differing considerably from the normal mammalian type. In the 
middle line is a well developed papilla, supported as I have else- 
where* shown by a development of the prenasal cartilage. A 
section through the middle of the papilla shows on either side a 
wide Stenson's duct, which at its upper part is roofed over and 
protected at the sides by the anterior developments of Stenson's 
and Jacobson's cartilages. Above this is found the curved 
cartilage of the nasal floor. 
A short distance behind this plane, in a manner similar to that 
figured by Herzfeldf in the Lemur, the cartilage of the nasal 
floor becomes divided into an inner and an outer part, as does also 
the arched cartilaginous roof of Stenson's duct. The two inner 
parts unite to form Jacobson's cartilage proper; and the outer to 
form the hinder part of Stenson's cartilage. This is the condition 
shown in fig. 1. At the inner side of the upper part of Stenson's 
duct it is found receiving the duct of Jacobson. 
Almost immediately behind this Stenson's duct is found opening 
into the nasal cavity (fig. 2). Here Jacobson's duct is small, and 
lined with squamous epithelium. On this plane there is no 
ossification in the neighbourhood of the septum, but a very short 
distance beyond brings us to a plane cutting the anterior part 
of the prevomer (fig. 3, P.vo.). In a recent paper read before 
this Society J I called attention to this remarkable bone in 
discussing the homologies of the palatine process of the pre- 
maxiilary. It is well illustrated in figs. 4 and 5 — the former 
representing an anterior section; the latter a section near its 
posterior part. 
On approaching the region of the prevomer, Jacobson's Organ 
gradually becomes greatly developed, attaining its maximum near 
the posterior part of the prevomer. In this region the cartilage 
of Jacobson forms an almost complete tube, only open slightly on 
* Proc. Linn. Soc. N.S.W. 2nd Ser. Vol. x. pt. 4, 1895. 
t L.c. 
X Proc. Linn. Soc. N.S.W. 2nd Ser. Vol. x. pt. 3, 1895. 
