ON CERTAIN MUSCLES OF BIRDS. 219 
me on account of a peculiarity in the structure of the nasal bones, 
which is sufficiently special in my estimation to justify the separation 
of all those birds in which itis found into a single order by themselves. 
There are considerable myological differences amongst its families 
according to their habits, the only uniform character being the 
presence of the femoro-caudal muscle. The ambiens is absent in the 
Alcide (Alca, Uria) and some Columbe. 
The minor divisions of the orders above defined must now engage 
our attention. 
The order GALLIFORMES may be divided into three main divisions 
or cohorts—«. the Struthiones, 8. the Gallinacee, and y. the Psittact. 
a. The Struthiones are peculiar in the structure of the palate; and 
in them the sciatic nerve and artery always perforate the fibres of the 
accessory femoro-caudal in a manner not found in any other birds. 
They are divisible into four families, the first three of which have 
no oil-gland :— 
1. Struthio and Rhea, which form each the type of a separate sub- 
family. In common they have the formula B. X Y*, the ambiens 
muscle present, and long sacculated ceca coli, which in Struthio are 
situated peculiarly far from the cloaca. There is no aftershaft to the Page 121. 
-contour feathers. Struthio has two carotids, Rhea only the left. 
2. The genera Casuarius and Dromeus. They have the formula 
' AB. XY and B.XY respectively. The ambiens muscle is absent, 
the cca coli are short, and there is.a very large aftershaft to the 
contour feathers. There are two carotid arteries. 
3. Apteryz, in which there is an extra femoro-candal muscle, the 
formula otherwise being A B. X Y. The ambiens is large; the ceca 
coli are well developed ; and there is only one carotid, the left. 
4. The Orypturi, with a formula AB. XY. The ambiens muscle 
is large; the ceca coli are well developed ; and an oil-gland is present, 
well tufted. The aftershaft may or may not be present on the contour 
feathers. 
8. The Gallinacee all comprise B. XY in their formula; the 
ambiens is present in all; and except in the Musophagide there are 
always ceeca to the intestine. 
They are divisible into six families :— 
1. The Palamedeide, with formula A B. X Y, the ambiens present, 
cxeca sacculated as in Struthio and Rhea only, two carotid arteries, no 
aftershaft or a very small one, and a tufted oil-gland. = 
2. The Galline, with formula AB. X Y or B. X Y. The ambiens 
: (* In Struthio there is also, as subsequently recorded by Professor Garrod in his 
MSS., a femoro-caudal muscle of “ fair size and quite distinct from the accessorius.”” 
‘ The proper formula therefore for this genus is AB. XY. Ep.] 
