56 GREAT NORTHERN DIVER OR LOON.
Young in winter.. l'Iato CCCVI. figi 2.
Hill pale yellowish-green, the ridge and tip of the upper mandible
dusky. ••-• Iris- brown. . Feet du^ky, externally, pale yellowish flesh-colour
internally, webs dusky, bytiyollow. in the middle..Claws yellowish
brown. All the upper -parts, are of a uniform dark gréyish-brown,
each feather margined with lighter, the!, lower parts white,;, the sides
of the neck at the lower part whitish, streaked with dusky ; the sides
dusky, without spots.
Towards spring the eye a-ssumes- a redder tint, and the pinmage of
the upper parts gradually becomes spotted with white ; and when .the
moult is. completed about the end ! of summer, the plumage is as in the.
adult, although the tints are improved at each successive: moult for several
years.
A fine male killed, at Boston, 34 incili!» in length, with an alar extent
of 56, presents the following characters. There is a general layer
of subcutaneous adipose tissue, and tlu: skin- is very tenacious. Tin:
external aperture of the ear roundish, very small, having a diameter
of only 2 lines. The • tongue; is 2 inches 1 line in length-, fleshy, as
high as broad, slightly concave I and longitudinally grooved above, tapering
to.a horny.point. . On- the palato-'aro.O rows ot' papilla; ; the!
posterior, aperture of t i e nares is linear 2§ inches in length. The
aperture of the glottis is | an- inch long, with numerous papillae along its
.sides and behind. The pharynx is extremely , dilatable, as is .tie
cesophagu.S.i Which is 17 inches, long, passes along the right side of the
neck, together with the trachea, and when distended has an average
diameter of 2i indies, but on entering the thorax contracts to IsJ.
The structure of the (esophagus in birds may be very conveniently
examined in this species, the different layers: being remarkably developed
in it. Properly speaking, it has only two coal*.—-the outer muscular,
its external layer composed of transverse: or circular fihr.es, the
internal of equally distinct longitudinal fibres, which are not straight,
but irregularly undulate® The 'inner, or mucous eoat, when cpfl
traded falls into longitudinal plaits. The proventriculus iè 2§ inches
long, the glandules large, roundish, simple, and disposed in fc continuous
belt. Over this part, the transverse muscular fibres are remark,
ably developed. The right lobe of the liyer is ,5| inches long, the
left, lobe 5 J,. The lieart is very large, of a broadly conical form, 3
GREAT NORTHERN DIVER OR LOON. 57
inches long, 25 inches in breadth. • The stomach is three inches long,
2J in breadth, of an-elliptical form, a little compressed:; its lateral,
muscles » lines in thickness, and compose.! of strong large fasciculi ;
tlu; tendons inch in diameter; the uuti.nilar lining thick, its upper
anitlower parts marked-with strong longitudinal ridges having
numerous transverse fissures ; the grinding surfaces irregularly wrinkled,
With a deep fissure down the middle of each. The pylorus is 8 lines
in diameter when distended, awl is destitute of valve, but has a
strong promiiumt- rim. I11 the stomach were remains of fishes, and
some ^pebbles, chiefly quartz, the largest è lineéSteng. The intestine
measures'6 feet 6 inches in length,- and varies in diameter from 8
to 6 lines.' The rectum is 8§ inches long, the cloaca extremely large,
forming a. cavity about 3 inches in diameter. The caeca are I f inch
long, cylindrical, rounded at the extremity ,; one of them 7 lines, the
other 9 Sues, in diameter, ,,'•> •
The trachea; when moderately extended, measure* 13| inches in
length, inconsiderably depressed, its transverse diameter at the upper
part 9J linos, at the lower (>,j lines; the .rings cartilaginous, of moderate
breadth, uniform, with a contraction in the middle before and
behind, their number 134, the,! foi® lowest united* The bronchi are
composed of about 20 narrow 'cartilaginous half rings, The contractor
muscles sire very broad but thin, their fibres irregularly disposed in
front; they become thicker-and narrower toward- the lower part, and
are continued beyond the sterno-traeheal muscles, which come off
from the . 20th ring from the inferior larynx, to the membrane between
the last tracheal and first bronchial ring.