This section is from the book "A Manual Of British Vertebrate Animals", by Leonard Jenyns. Also available from Amazon: A Manual Of British Vertebrate Animals.
Bill strong, thick, convex above, compressed at the sides, with the tomia sharp and cutting; upper mandible slightly bending towards the tip; lower one nearly straight: nostrils basal, oval, generally concealed by setaceous feathers directed forwards: wings acuminated ; first quill much shorter than the second and third; fourth longest.
(1. Corvus). Tail moderate, rounded. (2. Pica). Tail long, cuneiform.
Bill rather short, strong, compressed, clothed at the base with feathers directed forwards; both mandibles inclining equally towards the tip, the upper one slightly emarginated : crown feathers long, and capable of erection : wings rounded; fifth and sixth quills longest: tail moderate, square, or slightly rounded.
Bill long, and straight; upper mandible rounded, and longer than the lower one; both of them terminating in a slightly obtuse and depressed point: nostrils basal, round, covered by reflected feathers: wings rather acuminated; first quill shorter than the second and third ; fourth longest : tail rounded.
Bill various: feet short; adapted for climbing; toes four, two each way, or three in front and one behind.
* Bill straight, robust: feet zygodactyly.
(PICIDAE).
Bill robust, long, straight, angular, compressed, cuneated at the tip: tongue long and extensile, lumbriciform, the tip barbed: nostrils concealed by reflected bristly feathers : wings with the first quill very short; fourth and fifth longest: feet robust: tail feathers stiff, and pointed at the extremity.
Bill short, straight, somewhat conical, depressed, rounded above, the tip sharp and pointed; tongue long and extensile, lumbriciform : nostrils naked, partly closed by a membrane: wings moderate; first quill a little shorter than the second, which is longest: tail feathers soft and flexible.
** Bill generally slender : feet anisodactyle.
(CERTHIID.AE).
Bill moderate, slender, arcuate, compressed, angulated above, sharp-pointed : tongue short: nostrils naked, partly covered by an arched membrane: wings with the first quill very short; fourth longest: hind toe strong, and longer than the others: tail feathers stiff and pointed at the extremity, deflected.
Bill slender, slightly compressed, a little arcuate: nostrils basal, oval, partly covered by an arched naked membrane : wings short, and rounded ; first quill very short; second shorter than the third ; fourth and fifth equal and longest: tail short, rounded, carried erect.
Bill long and slender, arcuate, compressed, convex above, sharp-pointed: nostrils oval, open: crown furnished with a crest: wings rather long; the first quill very short; fourth and fifth longest: claws short, and not much hooked: tail square at the extremity.
Bill moderate, rather strong, straight, compressed; both mandibles equally inclining to the tip which is somewhat cuneated: nostrils oval, open, covered by setaceous feathers directed forwards: wings rather short; third and fourth quills longest: hind toe strong, and lengthened: tail short, nearly even.
*** Bill more or less curved: feet zygodactyle.
(CUCULIDAE).
Bill as long as the head, rather compressed, moderately curved, and a little hooked at the tip: gape wide: nostrils round, surrounded by a naked and prominent membrane: wings long, acuminated: first quill short; third longest; tarsi short, feathered a little below the knee: outer hind toe partly reversible: tail long, more or less cuneated.
Bill strong, arched, the culmen convex, triangular at the base, compressed at the sides and tip: nostrils basal, longitudinally cleft in a membrane: orbits naked: wings short, and concave: tarsi very long: tail long, and cuneated.
Bill broad at the base; gape wide: wings long: feet short, and weak.
* Bill strong, more or less elongated.
(MEROPIDAE).
Bill moderate, robust, higher than broad, compressed, straight; upper mandible bending at the tip: nostrils basal, linear, pierced diagonally, half closed by a plumose membrane: toes three before and one behind, entirely divided: wings long, and acuminated; first quill shorter than the second, which is longest.
Bill longer than the head, triangular at the base, slightly curved, carinated above, sharp-pointed: nostrils basal, oval, open: toes three before and one behind; the outer toe connected with the middle one as far as the second joint, the middle with the inner one as far as the first: wings long, and pointed; first quill very short, the second longest.
(HALCYONIDAE).
Bill very long, straight, quadrangular, thick and pointed: nostrils basal, pierced obliquely, linear, almost closed by a naked membrane: toes three before and one behind; the outer toe connected with the middle one as far as the second joint, the middle with the inner one as far as the first: wings moderate; the second and third quills equal and longest: tail short.
** Bill short and weak: gape extremely large.
(HIRUNDlNIDAE).
Bill short, and much depressed; upper mandible carinated, deflected at the tip; gape extending nearly to the eyes: toes three before and one behind; the outer toe connected with the middle one as far as the first joint: wings very long; first quill longest: tail forked.
Bill very short, triangular, depressed at the base; the upper mandible deflected at the tip; gape extending to the posterior angle of the eye: toes divided to their origin; all directed forwards: wings extremely long; first quill a little shorter than the second: tail forked.
(CAPRIMULGIDAE )
Bill very short, rather curved, broad and depressed at the base; the upper mandible defleeted at the tip, furnished at the basal edge with strong vibrissae directed forwards; gape extending beyond the eyes: anterior toes connected by a membrane as far as the first joint; hind toe reversible: wings long; first quill shorter than the second, which is longest: tail rounded, or forked.
§ ii. Feet not formed for grasping.
 
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