1864.] PROF. HUXLEY ON ARCTOCEBUS CALABARENSIS. 327 
In the lower jaw, also, the first and second grinders are unicuspi- 
date and premolar-like. The third has four cusps, connected in 
pairs by ridges, which are disposed obliquely from within outwards 
and forwards. The anterior external cusp is continued by a curved 
ridge on to the margin of the large anterior basal process of the tooth ; 
and the posterior external cusp is connected by an oblique curved 
ridge with the antero-internal. Thus the tooth acquires a doubly 
erescentic, Rhinocerotic pattern. 
In the next grinder, which is also quadricuspidate, the anterior 
basal prolongation is reduced, and the ridges connecting the pairs of 
cusps are transverse to the axis of the jaw. There is no oblique 
curved ridge. 
The last molar is like the preceding ; but there is a fifth cusp, and 
the ridges which connect the pairs of cusps are oblique, sloping from 
within backwards and outwards, or in the opposite direction to that 
observed in the antepenultimate tooth. 
There is, in both jaws, a much greater difference between the second 
grinder and the third, than between the third and the fourth, so that, 
except for the caution suggested by the similarity of the last premolar 
to the first molar in Galago sennaarensis, &c., one might suspect 
the third tooth to be a true molar, and consider that, in these 
animals, it is a premolar, and not a molar, which is suppressed. 
The roof of the palate of the Angwantibo exhibits altogether nine 
transverse ridges, each of which is convex forwards and concave back- 
wards. The eight anterior ones extend from a given tooth to the 
corresponding tooth of the opposite side. The first lies between the 
outer incisors, and the others between the following six grinding- 
teeth. There is a faint ridge behind the last molars, beyond which 
the soft palate continues the roof of the mouth for half an inch. In 
the interval between the first two ridges, in the middle line, there 
is a small round aperture which ends ceecally ; but in front of this and 
of the first ridge are two small crescentic apertures, the concavities 
of which are turned towards one another. Into either of these a 
style can be passed upwards, outwards, and backwards for a con- 
siderable distance. These passages are the so-called ducts of 
Stenson. 
Mr. Murray has noticed a similar structure in the palate of Ga- 
lago murinus as “‘two small orifices (as large, however, as the root 
of the superior incisors) situated in the middle space between the 
two incisors on each side, but a little behind their line. Their posi- 
tion suggests an analogy to Jacobson’s vesicles in the Horse ; and, on 
tracing their origin, we find that they lead to the nasal orifice, ex- 
panding before they reach it into a sort of sac, which appears to com- 
municate, by a narrow and short canal, with the nasal orifice, in this 
respect differing from Jacobson’s sac, which does not communicate 
directly with the exterior’ (‘‘ Supplementary Remarks on the genus 
Galago,’ Edinburgh New Philosophical Journal, new series, Jan. 
1860). Burmeister has observed them in Tarsius (Beitrage, p. 103); 
Van der Hoeven in the Potto (Ontleedkundige Onderzoek van den 
Potto van Bosman, p. 47); Hoekema Kingma in Ofolienus peli 
