DR. GUNTHER ON THE ANATOMY OE IIATTERIA. 
601 
surface itself does not correspond in form with the condyle of the quadrate bone, being 
much elongate in the direction of the longitudinal axis of the body, and, in fact, nearly 
four times as long as the opposite articular surface. 
When the jaws are closed, the upper condyles rest on the hindmost part of the lower 
articulary surface; but when in action, the lower jaw can be moved backwards to a con- 
siderable extent, the condyles advancing to the front part of the joint. As the upper 
condyles are concave, moving on a longitudinal convexity of the lower surface, they 
cannot escape sidewards, but press the hind part of the mandibles outwards ; this again 
would not be possible, if the mandibles were anchylosed at the symphysis ; so that their 
ligamentous junction finds now its explanation in the peculiar structure of the maxillary 
joints. When the jaws are at rest, the distance between the posterior extremities of 
the mandibles is 28 millims. ; when the lower jaw is drawn backwards, the distance is 
34 millims. It is evident that this structure is connected with the mode of feeding of 
this animal, which leads us next to a description of its dentition. 
Dentition (figs. 8-15). 
Dentition of full-grown specimens. — Hatteria is an acrodont in the strictest meaning of 
the term, the teeth being so intimately anchylosed with the cutting alveolar edge of the 
maxillary and palatine, as to appear mere prominences of these bones. The alveolar 
edges themselves are highly polished like the teeth , and perform the function of teeth when 
these are ground down to the edge in advanced age. This, however, is not the case 
with the premaxillaries, each of which is armed with a single broad smooth tooth, 
notched at the crown in individuals of middle age (fig. 9) ; this notch disappears when the 
tooth is somewhat ground down (fig. 8), and the teeth have then the appearance of the 
upper incisors of a Rodent. The teeth of the maxillary and palatine (figs. 2 & 4) are 
rather short, triangular, pointed, longitudinally compressed ; there are originally about 
eighteen in each maxillary, and eleven in each palatine. However, those of the ante- 
rior half of the maxillary appear to be soon ground down to the alveolar edge, with the 
exception of one midway between incisor and first palatine tooth, a trace of which is 
visible in the oldest example examined* *. From the level of the first palatine tooth, the 
maxillary teeth are persistent, although more worn than those of the palatine. The 
the outer of which is the M. digastricus, generally very distinctly separated into two portions ; the inner is a 
simple short supplementary muscle. In Hatteria, where the M. digastricus has only a narrow space for its 
origin, it is thin and simple, vertically ascending to the mastoid ; there is no supplementary muscle beneath it, 
but a strong fascia connecting the mandibular joint with the point of junction of exoccipital and quadrate bones, 
and covering the terminal cartilage of the stapes. 
* The examples figured by Gray and Owen had their teeth complete ; and although the one figured in the 
‘ Zoology of the Erebus and Terror’ was not only full-grown, but unusually large, it does not appear to have 
been old. The example also of which a full figure has been given by Dr. Gray has its teeth complete. I 
have well considered the question whether I had not to deal with two species (perhaps one from the northern, 
and the other from the southern island ) ; but, after a very careful examination, no characters to justify a specific 
distinction were revealed. 
