60 MR. W. K. PARKER ON THE STRUCTURE AND 
able flange or crest to the thick lower edge of this “internal angular process.” The 
incus (z.) and the stapes (sf.) are much alike in both species; the latter is seen 
edgewise in this, and flat in the other. There is a definite cartilaginous nucleuas—the 
interhyal (7.hy.), in the beginning of the tendon of the stapedius muscle (st.m.).* 
Skull of young Unau (Cholopus Hoffmanni), 8 inches long.—Third Stage. 
Taking such materials as come to hand, I now get a third stage in a very young 
Unau of the species that has only six cervical vertebrae. In interpreting the adult 
skull of this type, this stage alone is of great importance, the ankylosis of that massive 
skull being so intense.t 
A lower view (Plate 9, fig. 1) of this strongly built skull, already very solid, 
shows, in front, a very small tract of the snout, with its lateral openings (a/.n., e.n.). 
Behind it, the two wings of bone, meeting in front at a very obtuse angle, 
are the edentulous dentary regions of the premaxillaries (px.); they are quite 
inferior (see fig. 8) in position. They slightly overlap the maxillaries (m.), and close 
to the mid-line send backwards a small styloid palatine process; between the two 
there is a rounded notch, and this forms the front border of the anterior palatine 
foramen, with the aperture of JAcopson’s organ (j.0.) seen in it; each maxillary is 
cut away, as it were, obliquely, to form the hind margin of this space ; the two 
foramina open into each other, behind. 
The whole of the bony palate, solid from side to side in the first three-fifths, and 
then strongly enclosed, right and left, but exposing a spatulate tract of the endocranial 
base, is a most remarkable architectural growth. The huge first tooth—a doubtful 
“canine ”—is fixed in a large swelling socket; thus this part of the face and palate is 
greatly widened. There is then a rounded interspace, large enough for another tooth 
equal to those that follow ; there are four of these, the second is the largest, and the 
Jast the smallest of the series. These curious mammillate teeth, resembling the 
degenerate teeth of the Walrus, but devoid of enamel, make their outer alveolar wall 
sinuous; it draws in, backwards. The alveolar ‘ flange” in the hard palate is one- 
third wider than the submesial part of each bony plate; the ragged groove, right and 
left, is nearly straight, and the two are almost parallel. 
The zygomatic process of the maxillary, opposite the second tooth, projects further 
outwards than the socket of the first, an oblique suture with few “teeth” is seen 
running backwards and inwards, between this process and the jugal bone (j.). The 
palatines (pa.) scarcely form a tenth part of the hard palate; they run in, behind 
* If these two mandibles, belonging to such closely related types, be compared with those of the 
Dasypodide, already described, and with that of the lesser Ant-eater (Plate 10), and of its huge relative 
the Ant-bear, then the most easy passage is seen from type to type; during growth, the mandibles of 
the two sorts of Sloth approximate very considerably (see Plate 9, figs. 5, 8, and 9). 
+ I owe this specimen, and many others, to my lamented friend, Mr. W. A. Forbes. 
