OF MICROPTERUS CINEREUS. 497 
suture being visible anteriorly, as well as to the exoccipitals ; but they are still ununited 
to the supraoccipital and frontals. In adolescent and adult specimens they present, in 
common with the squamosal, a well-marked fossa for the attachment of the temporal 
muscle. 
The sguamosals furnish a part of the postorbital process. They are readily separable 
from all the other bones in the young birds, and in adolescent individuals are still 
anchylosed to the frontals, and only partially so to the alisphenoids. 
The periotics are readily separable from the surrounding bones in the young (un- 
fledged) birds, but are fully anchylosed to them in the adolescent (flying) specimens, 
In general form, as may be seen from the figure (fig. 21), they do not differ materially 
from those of the young of the domestic Fowl, as figured by Professor Huxley in his 
Croonian Lecture “On the Theory of the Vertebrate Skull” and “Elementary Atlas 
of Comparative Osteology,” 
The guadrate bones are proportionally thinner and with deeper hollows than in some 
other species of Ducks, such as the Muscovy; and their orbital processes are much 
larger, more angular, and more sharply pointed than in that bird. The fossa for arti- 
culation with the posterior extremity of the quadrato-jugal is comparatively shallow. 
The pterygoids possess the same general form as the corresponding bones in the 
Muscovy, but are longer, and have the various ridges and depressions more strongly 
indicated. 
The zygomatic arch is feeble, if the size and strength of the other bones of the skull 
be taken into consideration. Its three elements, the quadratojugal, jugal, and jugal 
process of maxillary, appear to remain distinct throughout life. 
The frontals, as usual, are very large. In the youngest specimens they are, like the 
other cranial bones, readily separable from those which surround them; and even in. 
flying birds they are distinct from the parietals, squamosals, and ethmoid, and only 
slightly anchylosed to the alisphenoids and posterior portion of the interorbital septum. 
Eyen in the youngest specimens they present extensive, well-marked glandular impres- 
sions, which in adult individuals are separated by an elevated mesial ridge, so that the 
middle line of this region of the cranium is higher instead of lower than the lateral 
portions, as is the case in most Anatide, with the exception of the Swans. 
The nasals, lachrymals, intermaxillary, maxillaries, and palatines are unanchylosed, 
both in the unfledged and flying birds; and even in the oldest specimens examined by 
me the lachrymals are only very partially anchylosed to the nasals, thus differing from 
those of the Mallard and most other Ducks, in which they are entirely, or almost 
entirely, anchylosed in adult birds, ‘They send backwards from their upper margins, 
immediately behind the articulation with the nasals, a strong, rather rugged process, 
which is either absent or very feebly developed in the other species of Anatide 
examined by me. ‘The space intervening between the postorbital process and the 
descending (or anteorbital) process of the lachrymal is much wider than in some other 
