The cranial cavity is very small, the orbit confluent with the temporal fossa, and the zygomatic arch massive.
In Ornithorhynchus the zygomatic arch is much stouter than in Echidna.
As yet there is no clear evidence that reduction of the zygomatic arch is of adaptive value.
The orbit is not encircled by bone, but there is a strong process from the frontal, which nearly meets the zygomatic arch.
The zygomatic arch is slender, and postorbital processes are not generally well developed.
The zygomatic arch is complete, but the jugal is short and only forms the middle of it.
Processes from the jugal and frontal in living forms never meet and enclose the orbit, but the zygomatic arch is always complete.
The zygomatic arch is occasionally fractured by a direct blow.
The zygomatic arch is usually slender or incomplete, and the coronoid process and angle of the mandible are commonly prominent.
The zygomatic arch is incomplete, and the jugal (fig. 91, 5) is curiously forked, but in a manner differing in the two genera.
zygomatic arch n.
The arch formed by the temporal process of the zygomatic bone and the zygomatic process of the temporal bone. Also called zygoma.