The deep plantar tendons passerine; palate aegithognathous.
The above two characters in combination suffice to separate a passerine bird from all others.
The deep plantar tendons are the muscles which run down the leg of a bird and move the toes. There are several types or forms of these muscles. The late Professor Garrod thus writes about them : -
" In birds generally, whatever the number of their toes, there are two muscles whose fleshy bellies are situated in the leg proper (that is, between the knee and the ankle), deep, and just behind the tibia. These muscles arise, one from almost the whole of the posterior surface of the tibia and from the fibula, in a bipenniform manner, and the other from the inferior surface of the horizontal femur just behind the outer genual articular condyle. The former is termed the flexor perforans digitorum pedis, because its terminal tendons perforate those of the more superficial flexors on their way to the ungual phalanges of their respective toes; and the latter is termed the flexor longus hallucis, because there is generally a shorter muscle to the same digit.
" These two muscles descend to the ankle (the joint between the tibio-tarsus and the tarso-metatarsus) side by side; they run behind it, in the fibro-cartilaginous or osseous mass which, in birds, is always found at the posterior part of the upper end of the tarso-metatarse, in two canals, deeper than any of the other flexor tendons; and in these canals there is always a definite relation between them. Sometimes the tendons are side by side ; and then it is always that of the flexor longus hallucis which is the external of the two, the osseous vertical ridge, which is nearly always seen in the dry bone, separating them. Sometimes, however, one is superficial or, in other words, posterior to the other. When this is the case, it is always the flexor perforans digitorum which is the deeper. In the Swifts, for instance, the flexor longus hallucis quite covers the flexor perforans digitorum ; but in most Parrots, as may be seen by the disposition of the osseous canals in the dry tarso-metatarse, that for the former muscle is external as well as superficial, only partially covering it.
" These relations are constant, and must be always borne in mind in all attempts to identify the muscles. Prom these it can be inferred, as is verified by dissection, that the tendon of the flexor longus hallucis crosses its companion superficially on its way from the ankle to its insertion in the hallux.
" Just before, or just at the commencement of, the sole of the bird's foot (near the joint between the metatarsus and the phalanges) these two tendons generally split up to supply the toes."
The manner in which these tendons serve the toes and their relation to each other, when combined with other characters, are of the greatest service in diagnosing the various orders of birds.
The deep plantar tendons are said to be passerine when the flexor perforans digitorum serves the three front toes and the flexor longus hallucis serves the hind toe, both tendons being perfectly disconnected in such a manner that the hind toe is separately movable from the front toes. This formation is shown in the accompanying sketch : -
The determination of the character of the deep plantar tendons in a freshly-killed bird is very easy. In a dried state the tarsus and toes must be macerated in water until soft, when the tendons can be dissected without difficulty.
The palate of a bird is termed aegithognathous when the vomer is broad and blunt and disconnected from the maxillo-palatines, which are separated from each other by a considerable interval. The principal bones in the palate of a bird are shown in the accompanying sketch of the skull of a Raven, which has the palate aegithognathous.
The determination of a passerine bird, as before stated, rests on the association together of the above two characters.
The order Passeres contains about half the total number of living birds, or somewhat more than 6000 species. Of these nearly 1000, or one sixth of the number, are found within the limits of the Indian Empire, either as residents or as seasonal visitors.
The primary division of the Passeres into two large groups is based on the mode of attachment of the muscles of the syrinx, and may be thus expressed : -
Birds in which the intrinsic muscles of the syrinx are fixed to the ends of the bronchial semi- rings ………………….Acromyodi.
Birds in which the intrinsic muscles of the syrinx are fixed to the middle of the bronchial semi-rings ………………….Mesomyodi.
The Acromyodi have the muscles of the syrinx complex and consisting of numerous pairs. The Mesomyodi have the muscles simple, consisting in many cases of only one pair, consisting in many cases of only one pair.
All the Passeres of the Old World belong to the Acromyodian group with the exception of three small families, viz. the Philepittidae from Madagascar, the Xenicidae from New Zealand, and the Pittidae from India, the Oriental, Aethiopian, and Australian regions. The Eurylamidae, frequently associated with these Mesomyodian Passeres, I propose to elevate to the rank of an Order.
It follows from the above that all the Indian Passeres, with the exception of the Pittidae, belong to the Acromyodian group.
The Mesomyodi may therefore be dismissed from further consideration with the remark that they are divided into two groups: the Oligomyodae, with the lower end of the trachea unmodified; and the Tracheophonae, with the lower end of the trachea modified to form an organ of voice. The Pittidae fall into the first group, as do also the Philepittidae and Xenicidae. The remainder of the Oligomyodae; and the whole of the Tracheophonae occur only in the New World.
No success has attended the efforts of anatomists to subdivide the Acromyodi into two or more groups by internal characters, and no two naturalists agree in the arrangement and extent of the families of this difficult group. In drawing up the annexed scheme of the families that occur in India I have endeavoured to avail myself of those characters which appear to be constant and easy of examination.
A very useful character to be employed in determining the position of a bird is the number of primaries in the wing ; but before this can be used with absolute precision, it is necessary to eliminate by other characters those families some of the members of which possess nine primaries and others ten. Such families are the Dicaeidae and Alaudidae.
The Dicaeidae without a single exception, possess serrations on the margins of both mandibles for about a third of their Length from the tip. These serrations are seldom visible without a lens and a white background, but with these aids they are plainly discernible.
The Alaudidae differ from all the other Acromyodi in having the hinder part of the tarsus scutellated or divided transversely into shields or scales. The ordinary bilaminated (longitudinally) and smooth condition of the hind tarsus is shown in fig. 5, p. 18, the tarsus of a Crow ; the tarsus of a Lark will be figured in its proper place.
Having eliminated these two families, all the other Acromyodi may be divided into two groups, the one possessing nine primaries and the other ten. There is some difficulty in counting the number of primaries, or quill-feathers attached to the manus, in the wing of a bird; but this can be overcome by the student bearing in mind that, in the Acromyodi, there are ten primaries when the first is rudimentary or notably small and nine when the first is fully formed and reaches nearly, if not quite, to the tip of the wing.
The nine-primaried Passeres of India form three families which are well differentiated.
The ten-primaried Passeres constitute a large assemblage of birds. The Nectariniidae may be divided off by the tubular tongue and the Ploceidae by the position of the nostrils ; but the remaining birds form a group which is so homogeneous that it seems impossible to divide them into families by structural characters.
Under these circumstances my attention was drawn to the characteristic plumage of the nestling, and I have found the use of this character highly satisfactory. In the magnificent collection of birds now contained in the British Museum young birds and nestlings are sufficiently represented to render a classification on this basis feasible. The young of some species, however, are wanting in the collection, and these species may not in every case have been relegated to their proper families, but such birds are few.
The nestling plumage of the ten-primaried Passeres seems to be of five types. In the first the nestling resembles the adult female; in the second the nestling resembles the adult female, but is more brightly coloured and generally suffused with yellow ; in the third the nestling is cross-barred; in the fourth it is streaked, and in the fifth and last mottled or squamated .
Before it is possible, therefore, to make use of the annexed scheme of the classification of the families of the Passeres and to place a bird in its proper family, a knowledge of the plumage of the nest ling is necessary. This is nob so difficult as might at first sight appear. A series of a dozen skins of a species will generally contain a specimen which will furnish some hint as to the plumage of the immature bird. If, in such a series, all the specimens be absolutely alike, sex for sex, then it may be inferred that the young bird resembles the adult. If, on the other hand, one specimen differs from the others in possessing characteristic marks, such as bars, streaks, or mottlings, or in being more brightly coloured than the others, whilst preserving the same pattern of colour, a conclusion may be drawn from such a circumstance sufficient to allow of the species being placed in its appropriate place. It is to be hoped that the student in India when collecting specimens will recognize the importance of securing young birds and thus work out for himself the position and affinities of every species he meets with.
* Mr. Seebohm, in the fifth volume of the British Museum Catalogue, made use of the character of the plumage in the nestling to separate the Sylviinae from the Turdina, but restricted the application of this character to the more typical genera.
Scheme of Indian Passerine Families,
a. (Acromyodi.) The intrinsic muscles of the syrinx fixed to the ends of the bronchial semi-rings.
a1. The edges of both the mandibles perfectly smooth, except for the presence of a single notch in many species.
a2. The hinder part of the tarsus longitudinally bilaminated, the laminae entire and smooth.
a3. Wing with ten primaries; the first notably small.
a4. Tongue non-tubular.
a5. Nostrils always clear of the line of the forehead; the space between the nostril and the edge of the mandible less than the space between the nostril and culmen.
a6. Plumage of the nestling resembling that of the adult female, but paler.
a7. Nostrils completely hidden by feathers and bristles ………………….Corvidae, vol. i.
b7. Nostrils bare or merely overhung by a few hairs or plumelets.
a8. Rictal bristles always present.
a9. With 12 rectrices.
a10. Inner and hind toe equal …………………Crateropodidae, vol. i.
b10. Inner and hind toe very unequal ………………….Sittidae, vol. i.
b9. With 10 rectrices. ………………….Dicruridae, vol. i.
b8. Rictal bristles absent. ………………….Certhiidae, vol. i.
c7. Each nostril covered by a single stiff feather ………………….Regulidae, vol. i.
b6. Plumage of the nestling re¬sembling that of the adult female but brighter ………………….Sylviidae, vol. i.
c8. Plumage of the nestling cross-barred ………………….Laniidae. vol. i.
d6. Plumage of the nestling streaked.
d7. With rictal bristles.
c8. First primary quite half the Length of second ………………….Oriolidae, vol. i.
d8. First primary much less than half the Length of second ……………Eulabetidae, vol. i.
e7. Without rictal bristles ………………….Sturnidae, vol. i.
e6. Plumage of the nestling mot¬tled or squamated.
f7. Nostrils more or less covered by hairs ………………….Muscicapidae, vol. ii.
g7. Nostrils not covered by any hairs ………………….Turdidae, vol. ii.
b5. Nostrils pierced partly within the line of the forehead; the space between the nostril and the edge of the mandible greater than the space between the nostril and the culmen ………………….Ploceidae, vol. ii.
b4. Tongue tubular …………………. Nectariniidae, vol. ii.
b3. Wing with nine primaries, first and second nearly equal,
c4. Bill flat, broad, and notched; the longest secondaries reaching to the middle of the wing ………………….Hirundinidae, vol. ii.
d4. Bill conical, pointed, and entire; the longest secondaries reaching to a point midway between the middle of the wing and the tip ………………….Fringillidae, vol. ii.
e4. Bill long, slender, and notched; the longest secondaries reaching nearly, or quite, to the tip of the wing ………………….Motacillidae, vol. ii.
b2. The hinder part of the tarsus trans-versely scutellated ……………….Alaudidae, vol. ii.
b1. Both mandibles finely and evenly serrated on the terminal third of their edges ………………….Dicaeidae, vol. ii.
b. (Mesomyodi.) The intrinsic muscles of the syrinx fixed at or near the middle of the
bronchial semi-rings ………………….Pittidae, vol. ii.