marked groups of P a s se r e s , to which he has applied (Proc.
Zool. Soc. 1876, p. 507) the names Acromyodi and Meso-
myodi, according as the song-muscles (presently to he
described) are attached to the end or to the middle of the
incomplete rings forming the bronchial tubes. The latter
group, not being represented in the British Fauna, may be
here disregarded: the former group he separates into a
Normal and Abnormal division. This last contains no
British form, and therefore the Normal or true Passeres—
Oscines as they are termed by some——await our attention.*
So far as structure goes there can be no doubt of these
normal Passeres forming an extremely homogeneous group,
perhaps one of the most homogeneous groups of the same
extent to be found in Nature. The more important
osteological features are common to all its members, and
means whereby the comparative anatomist may distinguish
the various sections into which convenience requires its
separation must be sought in modifications to which in
several Orders of Birds—to say nothing of other Classes of
Vertebrates—he would attach but slight value. And not
only is there this great uniformity in the skeleton, but, so
far as known, the arrangement of the vocal organs is
nearly identical throughout these true Passeres, while at
the same time it is unlike that found in any other group of
Birds. The bulk of the Baven renders it of all the British
members of the Order that in which these organs can be
most advantageously studied, and the figures of them here
introduced are given of the natural size, being copied, and
the description modified, from the Author’s original memoir
(Trans. Linn. Soc. xvi. pp. 805-321, pis. 17, 18).f
* The Editor desires to express his thanks to Prof. Garrod for his valuable
assistance in modifying the following account of the vocal organs of the Raven,
so as to adapt it to the present state of knowledge. The Editor however must
at the same time say that his friend’s abnormal Passeres (the Australian genera
Mrnura and Atrichia) seem, from osteological characters, of greater significance
than those afforded by the voice-muscles, to be further removed from the true
Passeres than are many if not most of the Mesomyodi.
t The excellent description and figures of the trachea of the Rook and other
birds, given by Macgillivray (Br. B. ii. pp. 21-37, pis. x.-xii.), may also be
advantageously compared.
Tbe organ of voice in Birds generally may be regarded as
composed of four parts : (i.) the glottis or superior larynx,
(ii.) the windpipe or trachea, (iii.) the inferior larynx or
syrinx, and (iv.) the bronchial tubes or bronchi. The glottis
opens into the mouth at the root of the tongue. Fig. 1 of
the accompanying woodcuts shews (a, a, a) the principle
k
Eio. 3. I ’M- 4.
cartilage, lying upon the pharyngeal portion between the
hyoid or tongue-bones, and apparently performing the
double office of the thyroid and cricoid cartilages in
Mammals. It is thin and nearly triangular, the posterior
corners curving upwards. In the midst is the long and
narrow orifice of the windpipe, behind which the surface
is beset with papillae pointing backward, and serving in the
absence of an epiglottis, or cover of the opening, to direct