248 
PROFESSOR H. G. SEELEY ON THE STRUCTURE, ORGANIZATION, 
is directed upward and outward, and abuts ag’ainst the lower border of the orbit, 
internal to the malar and the lachrymal. 
The anterior part of the jaw is formed in Dicynodonts by the maxillary and pre¬ 
maxillary bones. The pre-maxillary elements appear to be always comparatively large, 
and apparently single, though they may be as small in Theriodonts as in any Mammal 
and divided in the usual way. In some types the suture between the pre-maxillary 
and maxillary bones appears to be overlapped throughout its length by the sub-narial 
bone, but in other species this bone is only seen on the floor of the external narine. 
The apertures of the skull present nothing remarkable in the ways in which they 
are defined. The temporal vacuities may be extended transversely, or much extended 
longitudinally, and are always limited externally by a single zygomatic bar, into 
which the squamosal always enters, which may be underlapped by the maxillary in 
Dicynodonts, and is underlapped by the malar in Theriodonts. The orbit is circular or 
ovate, surrounded by the post-frontal, frontal, pre-frontal, lachrymal, and malar bones. 
The nares are usually anterior and divided, but their relative position in the head is 
influenced by the development anteriorly of the pre-maxillary bone. The nasal and 
frontal bones are double. The pre-frontal is distinct from the lachrymal. The latter 
bone is below the pre-frontal and above the maxillary ; it is always perforated by the 
lachrymal canal, and extends from the orbit to the narine, as in Ichthyosaurus. The 
post-frontal forms a transverse bar at the back of the orbit, extending from the frontal 
to the malar, wdiich rests upon the squamosal, and makes the lower border of the 
orbit. At the hinder margin of the frontal bones is the parietal, whidi shows no 
sign of median division, and contains the parietal foramen in its anterior part. 
External to it are plate-like bones, which margin the superior borders of the temporal 
fossae. They appear to be distinct from the parietal, and to overlap that bone 
anteriorly and the inter-parietal posteriorly, for the inter-parietal succeeds the parietal 
as a single median roof-bone, which may sometimes be double. But, while it is 
probable that the post-parietal plates are anteriorly separate from the parietal, there 
is no specimen which establishes the separation beyond question. 
The squamosal bone, by its varied development, greatly modifies the form of the 
skull. It always gives off* a strong laterally compressed zygomatic process, and in 
Dicynodonts is more or less extended inferiorly and vertically below that process, 
where it forms an arch into which the vertical part of the comparatively small quad¬ 
rate bone is received. This inferior process of the squamosal may become small, and 
in the Theriodont Galesaurus has no existence. The squamosal bone always forms the 
external lateral limit of the occipital area along its extent. 
