525

17

in the Garfowl. The mandible retains as instructive marks of its primitive composit-
tion in the Penguin as in the Garfowl, and enables one to see that in the former the
surangular is relatively longer, the dentary shorter, but with its lower prong more pro-
duced posteriorly ; the angular is more produced behind the articular ; the rostral part
of the dentary corresponds in shape with the same part of the premaxillary, and differs
in the same degree from that of the Garfowl. 1.

The sternum, perhaps the most characteristic of natural affinity of any single bone in
the bird's skeleton, exemplifies the essential distinction of the two species, which are
alike adaptively modified for marine existence, with abrogation of the power of flight.

In the Penguin the sternum is destitute of episternal process, and has two posterior
notches, equalling in depth half the length of the entire bone. The front and lower
borders of the keel are straight. The coracoid grooves meet at the mid line, and their
posterior wall is developed into a broad triangular process, with an obtuse apex, the
outer angle of the base of which answers to the costal process of the sternum in Alca
impennis. The costal part of the lateral border is relatively shorter in the Penguin, and
affords articulation to only six haemapophyses. The lateral margins behind the costal
portion converge to the posterior part of the sternum, the middle part of which between
the lateral styles narrows to a point where the keel ends.

The coracoids in Aptenodytes are conspicuous for their great length and strength, for
their columnar-like convexity transversely on the outer or fore surface, and their
flattened hinder or inner surface, which is concave transversely at its lower third. In
Aptenodytes antarcticus the length of the coracoid is four-fifths that of the sternum ;
in Alca impennis it is less than two-fifths. The inner lamelliform process from the
scapular end is more produced in Aptenodytes, and is notched in Eudyptes, instead of
being perforated ; the outer lamelliform process from the sternal end is much less pro-
duced. The scapula in Aptenodytes is remarkable for its unusual breadth as compared
with that of other birds; it is nearly twice as long as the humerus, whereas in Alca
impennis it is shorter than the humerus.

The clavicles in the Penguin are also of unusual breadth towards their upper end,
and converge to their medial union at a more acute angle than in Alca impennis. The
humerus, besides being relatively shorter in the Penguin, is broader and more compressed,
less expanded at both ends, but especially proximally.

1 In Sula the basioccipital is impressed by a pair of large and deep circular pits for the insertion of strong
musculi recti capitis antici : these pits are bounded externally by strong ridges descending and diverging from
the sides of the occipital condyle to the hypapophysial tuberosities. From the outside of the base of each
tuberosity a buttress flies upward and outward to the paroccipital, circumscribing the space in which lie the
carotid and pneumogastric foramina. The pretympanic fossa between the alisphenoid and mastoid rises vert-
cally for more than half an inch; its inferior subcircular opening or entry is 4 lines in diameter. There are no
pterapophyses. The coalesced palatines present a narrow, oblong, flattened surface below ; and from the mid line
of the posterior part descends a triangular crest of bone, between the pterygoid articulations. The palatal
nostril is single, medial, 2 lines wide by 8 lines long.
C