A, Caudal. N, Sciatic nerve.
B, Iliac portion of caud-ilio-femoralis. Is.fm, Ischio-femoralis.
X, Caud-ilio-flexorius. Is.fl, Ischio-fibularis.
Y, "Accessory" portion of the same. Sart, Sartorius.
Pif, Pubischio-femoralis.]
To return to these thigh muscles. The most primitive combination,
ambiens and _A B X Y_, is the most common; next follows that of _A X
Y_, meaning the reduction of _B_, i.e. the iliac portion of the
_caud-ilio-femoralis_; _A B X_ and _B X Y_ are less common; _A X_ and
_X Y_ are rare and occur only in smaller groups, as in subfamilies or
genera; _B X_ occurs only in _Podiceps_. But the greatest reduction,
with only _A_ remaining, is characteristic of such a heterogeneous
assembly as Accipitres, Cypselidae. Trochilidae, Striges and Fregata.
This fact alone is sufficient proof that these conditions, or rather
reductions, have been acquired independently of the various groups. _A
B Y_, _A Y_, _A B_, _X Y_ and _B_ do not occur at all, some of them
for obvious reasons. Occasionally there is an instructive progressive
evolution expressed in these formula; for instance _Phaethon_, in
various other respects the lowest of the Steganopodes, has _A X Y_,
_Sula_ and _Phalacrocorax_ have _A X_, _Fregata_, the most specialized
of these birds, has arrived at the reduced formula _A_. Further, the
combinations _B X Y_ and _A X Y_ cannot be derived from each other,
but both directly from _A B X Y_ in two different directions. Keeping
this in mind, we may fairly conclude that the flamingo with _B X Y_
points to an ancestral condition _A B X Y_, which is still represented
by _Platalea_ and _Ibis_, whilst the other storks proper have taken a
different line, leading to _A X Y_.
LITERATURE.--Well nigh complete lists of the enormous myological
literature are contained in Fuerbringer's _Untersuchungen zur
Morphologie und Systematik der Voegel_, and in Gadow's vol. _Voegel_ of
Bronn's _Klassen und Ordnungen des Tierreichs_. Only a few papers and
works can be mentioned here, with the remark that few authors have
paid attention to the all-important innervation of the muscles. A.
Carlsson, _Beitraege zur Kenntniss der Anatomieder Schiwmmvoegel_; K.
Svensk, _Vet. Ak. Handlinger. J.G._ No. 3 (1884); A. Alix, _Essai sur
l'appareil locomoteur des oiseaux_ (Paris, 1874); H. Gadow, _Zur
vergl. Anat. der Muskulatur des Beckens und der hinteren Gliedmasse
der Ratiten_,4 deg. (Jena, 1880); A.H. Garrod, "On Certain Muscles of the
Thigh of Birds and on their value in Classification," _P.Z.S._, 1873,
pp. 624-644; 1874, pp. 111-123. Other papers by Garrod, 1875,
pp. 339-348 (deep planter tendons); 1876, pp. 506-519 (wing-muscles of
Passeres), &c.; J.G. de Man, _Vergelijkende myologische en
neurologische Studien over Amphibien en Voegels_ (Leiden, 1873),
(_Corvidae_); A. Milne-Edwards, _Recherches anatomiques et
paleontologiques pour servir a l'histoire des oiseaux fossiles de la
France_ (Paris, 1867-1868), tom. i. pls. ix.-x. (_Aquila_ and
_Gallus_); R. Owen, article "Aves," Todds' _Cydopaed. of Anat. and
Phys._ i. (London, 1835); "On the Anatomy of the Southern _Apteryx_,"
_Trans. Zool. Soc._, iii., 1849; A. Quennerstedt, "Studier i foglarnas
anatomi," _Lunds Univers. Aarsk._, ix., 1872 (hind-limb of swimming
birds); G. Rolleston, "On the Homologies of Certain Muscles connected
with the Shoulder-joint," _Trans. Linn. Soc._, xxvi., 1868; R.W.
Shufeldt, _The Myology of the Raven_ (London, 1891); M. Watson,
"Report on the Anatomy of the _Spheniscidae_," _Challenger Reports_,
1883.