50 MR. W. K. PARKER ON THE STRUCTURE AND 
the nostrils with a rounded rim, and a small valvular process ; they open laterally. 
The premaxillaries (pa.) can be seen in this view, on their outer edge, without any 
ascending or facial plate, looking no larger than the Ist maxillary tooth. 
The maxillaries (ma.) are small relatively to the skull, generally, and they have 
their infraorbital foramen (V®, see fig. 1) rather inferior than lateral; there is a small 
hole in front of the main passage ; the bone generally is curiously ribbed and wrinkled. 
Over it we see the edge of the nasal (n.), and under the contiguous parts of the 
nasal, frontal, and maxillary, the smallish, thick, perforated lacrymal (/.) comes in to 
form the foremost part of the orbital margin ; the canal (/.c.) opens on its edge. The 
jugal (j.) has as well-formed an orbital margin as the frontal, above, and they with 
the lacrymal make a rim about the eye-socket for all but its hinder fourth. Even 
there the postorbital process of each bone is thick and tends to cover in this part ; 
we shall see that this nascent perfection of the orbital rim is only temporary (see 
Plate 9, fig. 3), so that the early skull, only, can be said to look towards that of 
a Lemur; here, it is evident, we find signs of degeneracy, or retreat, from the more 
normal Mammalian type of skull. That the great peculiarity of the jugal bone is not 
something new in the existing, dwarfed Bradypodide is evident, for in this species 
2, 
this early stage shows its great peculiarities best ; they are softened down after- 
wards. * 
Below the neat orbital rim of the jugal, the bone is obliquely attached to the 
maxillary ; thence it is free, and ends in a postorbital, a zygomatic, and an infrajugal 
process ; together, these processes give a great depth to the bone ; behind the middle 
and lower snags we see the coronoid process of the mandible. 
Over the orbit the frontal rises—until at the vertex it is very high—as the roof of 
avery large skull cavity. The orbital plate of the frontal is large, but is imperfect 
below at present. The parietal (p.) is larger than would seem from the upper view, for 
it runs well down behind the auditory capsule, between it and the supraoccipital. 
The lower margin forms a sinuous line over the inside of the huge, open temporal 
fossa, and only at its middle, most projecting part does it reach the top of the 
squamosal (sg.). Besides the fontanelle at the vertex (fo.) there is another on 
each side, where the frontals and parietals diverge behind the orbits. This is, at 
present, several times as large as the upper open space, and as far as superficial bones 
are concerned, it reaches from that divergence above, and the junction of the 
squamosal and parietal behind, forwards, to the bottom of the orbit in front. In 
its fore half it exposes the large orbitosphenoid (0.s.), and in its hinder half the 
long band of cartilage (s.a.c.), which runs on to join the top of the auditory capsule, 
* If this figure of the skull of the early embryo of the Unau be compared with Reruarp’s splendid 
plates of Calodon (Copenhagen, 1878), and Gryptotherium (Copenhagen, 1879), it will be seen how 
remarkably the jugals correspond. In the latter (plate 1) there is the appearance of a small hole 
above and in front of the infraorbital foramen, which evidently corresponds with what I have figured 
in the embryo of the Unau; this small hole is also to be seen in the half-grown Ai. 
