2 6 
MONOTREMATA. 
of a bright-brown hue on the upper parts of the body, and whitish 
on the under parts. When from two to four inches in length 
only, the beak is proportionately much shorter than in the adult 
(being shorter than the head), and the body is destitute of hair. 
Skull of the Ornitkorhynchus. 
The skull of the Ornithorhynchus is much elongated, and has 
the facial portion remarkably produced and depressed, and, owing 
to the divergence of the superior maxillary and intermaxillary 
bones, Is expanded in front. A striglit line lying lengthways on 
the mesial portion of the upper surface of the skull, would touch 
very nearly at every part, from near the occiput to the anterior 
boundary of the facial bones. The temporal fossae are narrow, 
and the orbits are of moderate size ; the zygomatic arch is deep 
and moderately long, niul sends up a post-orbital process; the 
zygoma appears to be formed entirely of meeting processes of the 
squamous portion of the temporal bone and superior maxillary. 
Professor Owen could find no malar bone either in the skull of 
a young Ornithorhynchus, or in that of an immature Echidna. 
The glenoid cavity for the lower jaw is concave in the transverse 
direction, and slightly convex from before backwards, and has no 
posterior descending process. The frontal bones are very small, 
and the parictals large. The sutures of the cranial hones soon be¬ 
come obliterated, and in this respect, as well as in their thinness 
and density, remind us of the skull of a bird. The nasal bones are 
large, and much extended in the longitudinal direction. The supe¬ 
rior maxillaries arc greatly expanded immediately under the ante¬ 
rior root of the zygoma, to give support to the large horny molar 
teeth, and arc continued forwards, on the outer side of the 
intermaxillaries, to within a short distance of their apices. The 
intermaxillary bones are rather narrow, depressed, widely separated, 
