354 MR. J. BESWICK PERRIN ON THE 
The pterylography of both specimens was almost identical with that figured in 
Nitzsch’s work, so ably translated by the gifted Secretary of this Society’. 
Pectoralis magnus.—All the pectoral muscles are large and well developed. 
The superficial or great pectoral is the most remarkable (Pls. LXIII. & LXIV). 
Before the integuments have been removed from the thoracic region, the prominent and 
regular contour of the breast gives one the idea of highly developed pectorals. This, 
however, is not absolutely the case, the prominence of the anterior half being due to 
the large discoid crop, which is implanted upon the great pectorals (Pl. LXIII.); the 
latter are large, condensated, and quadrilateral in shape. The superior and anterior 
halves are entirely concealed by the crop, the posterior and superficial portions rising 
to a corresponding level with the crop. When the crop is removed, it is seen that the 
upper conjoined halves of both pectorals form a spherical cavity in which the crop rests 
(Pl. LXIV.). The keel of the sternum is aborted to a corresponding thickness with 
the pectorals in this situation. 
These interesting modifications are widely different, and exhibit in a more remark- 
able manner the law of cause and effect than is usually met with in birds bearing an 
extra-thoracic crop. Take for example the Common Pheasant. The sternal keel is 
‘ From Nitzsch’s Pterylography, translated from the German by Dr. Sclater, Ray Society’s pub., 1867:— 
A. 9. Amphibole. 
«The presence of an after-shaft on the contour-feathers is a pterylographic character common to all members 
of this family ; as also the occurrence of a circlet of feathers on the tip of the oil-gland, and the number of 
rectrices, which is always ten. With these characters, however, we seem to have exhausted the points of agree- 
ment of the genera belonging to the group; and their essential differences necessitate the following arrange- 
ment :— 
A. With the bands of the inferior tract narrow, and the outer branch distinct and freely divergent. 
B. With the stems of the inferior tract dilated, and no divergent outer branch. 
a. Dorsal tract dilated on all sides and sparsely feathered. 
b. Dorsal tract much contracted, especially its hinder part, which forms a very narrow serial band. 
“Here I place the genus Opisthocomus, which is anomalous in many respects. The figure of its pterylosis 
(Plate VI. figs. 12 & 13) shows that the continous plumage of the head, which is very sparse, but denser on 
the vertex, is continued upon the neck, and does not allow the formation of lateral neck-spaces. From the 
lower extremity of this neck-plumage the inferior tract commences as two broad bands, which run down close 
to the keel of the sternum, and become somewhat stronger at the outer margin, where the branch would be 
situated. At the end of the sternum these are narrowed, and pass on, gradually becoming weaker, to the anus, 
at which they terminate with a breadth of only two feathers. Both on the tract itself and on the spaces 
between its bands, true down feathers are placed, although not very closely. The same sparse condition is 
exhibited also by the lumbar tracts and the plumage of the crura and wings; but the narrow axillary tracts 
and the dorsal tract contain more closely approximated, although smaller feathers. The latter starts as a strong, 
triserial band from the midst of the plumage of the lower part of the neck, and divides between the shoulders 
into two limbs, with which the originally divergent feather rows of the biserial hinder part are united at the 
end: from the caudal pit onwards it becomes somewhat broader, and encloses the oil-gland, which is larger, 
and has a circlet of feathers at the tip, stronger than inthe preceding genera. In the wings there are nineteen 
remiges, of which ten are on the pinion ; the first four are graduated, and the fifth and sixth the longest. The 
tail has ten large rectrices.” ’ 
