The structure and life of birds

Preface

The aim of this book is an ambitious one. It attempts to give good evidence of the development of birds from reptilian ancestors, to show what modifications in their anatomy have accompanied their advance to a more vigorous Hfe, and, after explaining, as far as possible, their physiology, to make clear the main principles of their noble accomplishment, flight, the visible proof and expression of their high vitality. After this it deals, principally, with the subjects of colour and song, instinct and reason, migration, and the principles of classification, and, lastly, gives some hints as to the best methods of studying birds. The field is a wide one, but this is not in every way a drawback. Specialisation has its evils as well as its advantages. Many of our best ornithologists write admirably of the life and habits of birds, but leave out of sight their anatomy and physiology. Thus they separate things which in nature are mutually dependent. The anatomists and physiologists, on their side, limit themselves sternly to their , own departments. Their works,.

X PREFACE

too, are often over-elaborate for those to whom ornithology is not the main business of life. Many people, however devoted to the subject, have not . the time for the proper study of Dr. Gadow's great work, which, moreover, being written in German, is a sealed book to numbers of English readers. For the study of bird anatomy they are often thrown back upon the good but insufficient treatises written for the use of medical students. Natural History books, describing the lives of birds, are many, and, not . a few of them, first-rate, though, curiously, there was not, to my knowledge, any English book in which a general review of the known facts and of the problems of migration had been successfully undertaken, till the appearance of the second volume of Professor Newton's Dictionary of Birds, containing a very able article on the subject. There are several books in English treating of flight. Of these Professor Marey's Animal Alechanisni seems to me the best. But some of his most instructive experiments have been made since its publication, and an account of them is to be found only in his later and larger work, Le Vol des Oiseaiix. It has been my wish to bring the work of the anatomist and physiologist into connection with that of the student of flight and that of the outdoor naturalist. With this object I have made some investigations and observations which, I believe, may lay claim to originality, and I have consulted the best English, French, and German books upon ornithology, as well as a number

PREFACE xi

of papers to be found in the Proceedings and Transactions of learned societies. Wherever it has been possible, I have verified what I have learnt from books by the methods explained in the concluding chapter. Discussions with mathematicians, in particular with Mr. T. J. Bowlker and Mr. R. C. Gilson, to whom my most cordial thanks are due, have greatly helped me in dealing with the difficult problems of flight. Mr. A. H. Macpherson has very kindly put at my service the results of some of his observations on the song and on the migration of birds. I have also to thank Mr. F. E. Beddard, without whose encouragement I should not have begun this work. In important cases I have mentioned in footnotes the source to which I am indebted for facts or theories, and at the end of each chapter I have given a list of some of the best books and papers on the subject treated of Those of my readers who wish to proceed to a more special study of any of the different branches of ornithology will, I hope, find these references an assistance.

On many parts of the subject I have delivered lectures to the Hailevbury Natural Science Society. In this book I have followed much the same lines, in the hope that it may prove useful to lovers of birds here and elsewhere. Technical terms, except such as are unavoidable, I have dispensed with, and, as far as possible, I have explained difficulties, never, intentionally, wrapped them in the obscurity of big words. There is only one species of ornithologists with whom xii PREFACE

I have no sympathy — the species represented by a boy famous in fiction, whose fondness for birds always led him. to throw stones at them. It includes many varieties and sub-varieties, but all its representatives are either random slaughterers or cold-blooded exterminators. I would urge my readers to oppose them by joining the Society for the Protection of Birds}

The illustrations are, nearly all of them, by Mr. Prendergast Parker, who has taken great pains to make them accurate and really illustrative. Professor Howes has very kindly watched their progress and in a good many cases provided the specimens from which they were drawn. I am much indebted to him for this great assistance. Dr. Hans Gadow, Mr. W. B. Hardy, Mr. Gilson, and Mr. Macpherson have been very kind in reading proof-sheets, and I wish most warmly to thank them for the great service they have thus rendered me.

1 For particulars about the Society address the Horir Secretary, Mrs. F. E. Lemon Hillcrest, Redhill, Surrey.

CHAPTER I. Introductory

CHAPTER n The Skeleton of Bird and Reptile .

The fore limb — The breastbone and the bones that meet at the shoulder joint — The ribs — The hind limb — The skull • — The vertebral column.

CHAPTER in.

Evidence of Relationship to Reptiles 29

CHAPTER IV.

Connecting Links • 41

CHAPTER V.

The Process of Change from a Reptile to a Bird .... 53

CONTENTS

CHAPTER VI.

PAGE .

Form and functiox 60

Digestive apparatus — The heart and circulation — The valves of the heart^The blood — Breathing apparatus and pneumatic bones — The process of breathing — Lungs of lower vertebrate animals — Regulation of temperature — Problems connected with the hollow bones of birds — -The kidneys — The nerves — The brain — -The eye — The ear — The organ of voice — Muscles and tendons — Bones — Ligaments — Feathers, their structure and development — Varieties of contour feathers — Feather tracts — Moulting — Change of colour without moulting — Spurs — The beak— The foot — Perching — Swimming.

CHAPTER Vn.

The wings as levers, the air as fulcrum — Horizontal flight — The bird in motion, support given by the air — The general shape of the bird — Passive machinery — Active machinery — The spreading of the wing — Active and passive machinery (summary) — Weight of the breast muscles — Movements of the wing partly due to the action of the air — The tail — Rate of stroke — Phases of the stroke — Figures described by the different parts of the wing — The bird's trajectory — • Long distance flight — Upward flight — Horizontal and gliding flight — Flight in troops — Wind and flight — Rising with the help of the wind — Soaring — Steering — Stopping, use of the bastard wing — Force exerted in flight — Proportion of wing area to weight in large and small birds — Velocity — A note on flying machines — Conclusion.

CHAPTER VHL The Bird Within THE Egg 275

CHAPTER IX, Youth, Maturity and Age 286

CONTENTS

CHAPTER X.

PAGE

Bird Topulation 294

CHAPTER XI.

Colour, Song and Allied Phenomena 297

Nature of colours — Objective colours — Subjective colours — Variety of colours in the same bird — Protective coloration. — Sexual coloration, song, antics, combats — Theories to explain these phenomena — Summary

CHAPTER XH.

Coloration of Eggs 321

CPIAPTER XIH.

Instinct and Reason ■ . . . . 327

Song — Nest-building — The cuckoo instinct — Piracy — The death-feigning instinct— Origin of instincts.

CHAPTER XIV.

Migration 347

The distances covered — The east and west migration — The return route — Return to the same spot — The time occupied in migration — The beam wind theory— Wings shaped for long flight— From far south to far north— The height at which migrants fly— Order of departure— Partial migrants —The nesting-places of migrants — The cause of migration — How migrants find their way — E.xceptional migrations — Stray wanderers — A note on geographical distribution.

xvi CONTENTS

CHArXER XV.

PAGE'

Classification 379

CHAPTER XVI.

The History of the Ostrich 391

CHAPTER XVH.

Outdoor and Indoor Ornithology 304

INDEX 407

LIST OF ILLUSTRATIONS

FIG. PAGE

Gulls on the Wing Frontispiece

1. Skeleton of Hatteria Lizard 7

2. Skeleton of Fowl 8

3. Tibia and Fibula of Fowl 9

4. Hand of {a) Lizard, {b) Chick 10

5. {a) Sternum of Iguana, (<^) Coracoid, Scapula, and

Clavicle of Fowl 13

6. Hind Foot of Hatteria Lizard 17

7. (a) Two Vertebra of Snake, (/;) Two Neck-Verte-

BRiE OF Eagle 23

8. Pelvis of {a) Lizard, {b) Bird 27

9. Skull of Rhea viewed from below 32

10. Side View of Skull of Rhea 33

11. Part of Vertebral Column of Rabbit; showing

Epiphyses - 33

12. Coracoid of Rhea with Rudimentary Precoracoid 34

13. Head of Arch^opteryx 35

14. Wing of Arch^opteryx 35

15. Tail of Arch/eopteryx . 36

16. Vertebra of Hatteria Lizard 38

17. (i) Pterodactyl, (2) Wing of Pterodactyl .... 44, 45

18. Pterodactyl restored 47

19. Dinosaur Si

b xviii LIST OF ILLUSTRATIONS

FIG PAGE

20. Diagram illustrating Circulation of Blood .... 70

21. (a) Bird's Heart, {l>) Human Heart, opened to show

Valves 73

22. (a) and (d) Red and White Corpuscles of Man, (c)

AND {d) Red Corpuscles of Humming Bird and Ostrich, {e) Amceb.^ 75

23. Air-sacks — Diagram 80

24. Section of (a) Femur of Ostrich, (i) of Skull of

Carinate Bird 82

25 Diaphragm of Duck 85

26. Diagram illustrating Process of Breathing .... 87

28. Humerus of {o) Skua, (3) Hornbill, {c) Eagle .... 11 1

29. Two Cubes 113

30. Brain of Bird 118

31. Eye of (a) Man, {d) Typical Bird, (c) Owl 122

32. Section of Retina of Bird 125

33. {a) Human Ear, (6) Ear of Owl, (c) of Thrush . . . 132

34. Syrinx of Raven 137

35. Convolutions of Crane's Trachea 140

36. Striated and Unstriated Muscle 142

37. {a) Feather carrying Nestling Down-feather, (d)

Nestling "Down" of Thrush, (c) of Pigeon, (d) Thread Feather 145

38. Contour Feathers, (a) Plumelike, {d) Flight-Feather 147

39. Barbules and Barbicels to illustrate interlock-

ing ijl8

40. Cassowary's Feather 150

41. Illustration of Development of Feather 151

42. Beak of (i) Falcon, (2) Duck 162

43. Foot of (i) Woodpecker, (2) Grebe . . . . • .... 165

44. Flexor Tendons of Toes of (a) Fowl, (d) Passerine

Bird 167

LIST OF ILLUSTRATIONS xix

FIG. PAGE

45. Ambiens Muscle 169

46. Diagram illustrating the Velocity of the Wing's

Descent . '. 177

47. Diagram illustrating Combined Action of Wings . iSo

48. Parallelogram of Forces 181

49. Boat sailing at an Angle to the Wind— Diagram . 182

50. Diagram illustrating the Action of the Air upon

the \Ving 1S3

51. Diagram explanatory of the Amount of Support

afforded by the Air to a Bird in MotiOxN . . . 187

52. Birds Gliding : (a) Tern with Wings partly flexed ;

id) Gull with Wings outstretched 191

53. A Paper Toy illustrative of Gliding Flight . ,. . 192

54. Wing, showing Elastic Ligaments and the Muscle

that rotates the Secondary Feathers 199

55. Primary Wing-feather of Heron, showing Narrow

Outer Web 203

56. Humerus, showing Attachment of Important Flight-

muscles 204

57. Gulls Fly'ing, showing various Positions of Wing 218

59. Gulls Flying 219

60. Figure described by Tip of Crow's Wing 221

61. Gull Flying — to illustrate the Question of Tra-

jectory 224

62. Breastbone of (a) Frigate Bird, {d) Duck 225

63. Flight in Troops ■ 230

64. Diagram to illustrate Flight at Right Angles to

the Wind ^ 241

65. Pigeons Flying — to show the Use of the Bastard

Wing 254

66. An Egg and its Contents 277

67. Embryo Chick, Sixty-eight Hours Old ....... 2S0

XX LIST OF ILLUSTRATIONS

FIG. PAGE

68. {a) Transverse Section through Embryo during

Third Day, (d) Diagram of the Circulation of THE Yolk-sack 281

69. Hyoid Bone of Crow 282

70. Diagrams of Aortic Arches (a) on Third Day, {6) on

Fifth or Sixth Day 283

71. Diagram showing Aortic Arches in {a) Lizard, {i>)

Bird, (<r) Man 284

72. Wing of Hoatzin {a) Young, (/') Mature 289

73. Cone characteristic of the Structure of Blue

Feathers 299

74. Snipe's Tail-feather 309

75. Sternum of Ostrich 383

76. Spinal Feather Tracts of Snipe and Blackbird . . 384

77. Albatrosses on Nest 399

THE

STRUCTURE AND LIFE OF BIRDS

CHAPTER I

INTRODUCTORY

A BIRD seems to have more life in him than any other Hving creature. A Swift will outpace the fastest racehorse. Migratory birds arrive unexhausted after a flight of hundreds of miles. An Ostrich will leave behind the horseman who pursues him. The Penguin swims as if water were the native element of birds. And this vitality shows itself in many other ways, notably in the brilliant colours of the plumage, as in the Bird of Paradise or the Peacock. Sometimes, as in the Argus Pheasant, there is great richness of colouring without any gaudiness. Even when there is neither brilliancy nor richness of hue, but the plumage is of the very soberest, there is often such a brightness about the eye and the general air of our birds that their plainness passes unnoticed. Their leading characteristic is not their dull colouring but their grace and sprightliness. Not even the most dazzHng and ethereal of Humming-birds surpasses the Wheatear in beauty. High spirits are anothersign of vitaHty in most if not in all birds. The Thrush will sing by the hour together for pure jollity. With our English birds this is the common way of giving expression to hilarity. Some foreign species hold most elaborate dances, and in all lands the fights among the cock birds in spring are signs of exuberant life. To find food and meet the actual needs of the day seems easy enough, so that there is a large surplus of energy to devote to pleasure or rivalry.

There is nothing in nature more wonderful than the instincts of birds — for the present we must use this much-debated word without explanation — nothing, perhaps, that presents more interesting problems. Take, for instance, the migratory instinct. The Swallow travels to the south of Africa to spend the winter and returns in spring to build her nest, often in the very chimney where she reared her brood the previous year.

The nests are in many ways interesting, from their beauty, from their wonderful variety — birds belonging to the same family often building quite differently — and from the fact that young birds have to build their first nest without any instruction. Take again the extraordinary instinct of the Cuckoo, and the still more extraordinary instinct of her infant progeny. Then, too, there is the death-feigning and wound-feigning instinct. All these, however much they may be studied, can never lose their interest

I INTRODUCTORY 3

The bodies and brains of birds are suited to their full and varied life. Their circulation is rapid, their temperature higher than that of mammals, their lungs, though small, are probably the most efficient in the animal kingdom, their bones and their muscles have been adapted for purposes of flight, running, or swimming, they have brains that are, comparatively speaking, highly developed.

And yet the bird is a near relation of the lizard. He is descended, unless nearly all our great authorities are at fault, though not from any existing reptile, yet from ancestors that were definitely reptilian. And yet how enormous is the difference between these descendants from the same stock ! For the two lines must meet if we trace them upward far enough.

A lizard is limited to earth, and even there his gait is an undignified shuffle. True, he slips with unsurpassed nimbleness into his hiding-place on a hot day when the sun has warmed his sluggish blood. But though he be the fastest of lizards, many a bird of no great size is a better runner, and could, without having recourse to the magic of wings, easily distance him in a race of more than a few yards. His forehead is low, hardly rising above his nose, showing, if other evidence were wanting, that his intellect is feeble. Indeed, in this respect, he is hardly above the boa-constrictor who mistakes his blanket for a rabbit and swallows it. His blood is cold, and when the thermometer sinks a little below the freezing-point he torpifies. In the winter he merely exists, while the bird lives. He eats but little and digests slowly — ■ a sign of the sluggishness of his whole life. Both.

B 2 in body and in brain he presents a striking contrast to the bird. But the evidence of anatomy is irresistible. From hzard-hke ancestors the bird is descended. A reptilian fore limb has been modified and adapted for flight, two of the five fingers having disappeared during the process, and one of the remaining three having shrunk almost to a mere rudiment. The breast bone has attained wonderful dimensions for the attachment of the muscles of flight. The hind leg has been much strengthened so as to make the quadruped a biped and keep the wings from dragging in the mire. The back has been stiffened, since an approach to rigidity is required for flight, and, perhaps still more, for the nearly horizontal carriage of the body in walking. A long neck, snakelike but more supple than a snake, brings the ground within easy reach of the longest-legged of the race. The scales have become feathers. The part of the brain in which the higher faculties reside has grown, so that the forehead rises high. The eye has become large and has acquired a wonderful keenness of sight. The three-chambered reptile's heart has become a four-chambered heart, and untold advantages have thereby been gained. The lungs have not been enlarged, but their effectiveness has been many times multiplied. In many cases the heavy bones have become hollow and are filled with air. The teeth are gone, but a gizzard or muscular stomach, better placed and equally efiicient, has taken over their work. The gastric juices are stronger and equal to dealing with hearty and frequently recurring meals. All this — better heart, better lungs, better digestive

I INTRODUCTORY 5

apparatus — means higher temperature, comparative superiority to external conditions, greater vitality, and greater enjoyment of life. And the changes from first to last have not been additions of new organs, but adaptations of existing materials.

The differences between a bird and a reptile are so striking, they lie so much on the surface, that we are in danger of seeing the differences only and passing over the resemblances, some of which are obscure and require a minute knowledge of anatomy. But there is no reason why the pedigree should be taken on trust. Much of the evidence that enables us to trace it is easily intelligible.

After trying to make clear the development of the bird from reptile ancestors, I shall go on to describe (i) his structure in more detail and the work done by the different organs, (2) what cannot be dissociated from his structure, his life and habits.

Chapter II The Skeletons Of Bird And Reptile

Tlie Fore Limb

I WILL now put the skeletons of a bird and of a lizard side by side and compare them. Everywhere there are striking contrasts, but since the power of flight is the prominent characteristic of birds, or of most of them, the fore limb shall be the startingpoint. At the outset it will be necessary to learn the names of the bones that compose it, taking them first in the lizard, since there they are more easily made out. The first bone is the Humerus, or upper-arm bone (HU, fig. i). Then follow two which lie side by side, one slender and one stout. The former of these is the Radius (R), and is described as being praeaxial in position — i.e., in front of the axis, the axis of any part of a limb being an imaginary central line drawn through it lengthwise ; the other is the Ulna (U), and is postaxial or behind the axis. These terms, praeaxial and postaxial, should be thoroughly understood, because, in all the transformations which they

CH. II SKELETONS OF BIRD AND REPTILE

J3 2 s

6," • - . „

IJ. „ o!

•-"^ 3

in " p<

.fiS-

J"

e

u

K

V c o J3

o s

a

bO

a.

?J

o

a

a

TS

rt a u

■s

a*

a

i2

<y

1-*

.a

o

CI. S

<u i-i rt ^ rt

*-*

TS

P.

o

ii.

..

-g

■a

oj

C

u

>r

rf

c 3 s

P.

M

rt u:

rt

C a

THE STRUCTURE AND LIFE OF BIRDS chap.

Fig. 2. — Skeleton of Fowl (after Marshall and Hurst). A, acetabulum ; at, atlas vertebra ; ax, axis vertebra ; cl, clavicle ; cm, carpo-metacarpus ; co, coracoid ; CR, cervical rib ; n i, 2, 3, 4, digits ; dh, dorsal rib; FE, femur; hu, humenis ; HV, hyoid bone that supports the tongue; IL, ilium ; IS, ischium; K, keel of sternum ; MC, i, 2, 3, metacarpals; mt, first metatarsal; PB, pubis ; py, pygostyle ; r, radius ; rc, radial carpal ; sc, scapula ; sp, spine ; sr, sternal piece of rib; tm, tarso-metatarsus ; tt, tibio-tarsus ; u, ulna; uc, ulnar carpal ; up, uncinate processes.

undergo, bones remain, relatively to each other, in the same position. Hence it often happens that to observe carefully the position of a bone is the best way to discover what bone it is. The wrist now follows, consisting of two rows of bones called Carpals (C, fig. 4a), with a central one (CE) wedged in between the two, after these the five Metacarpals, the bones of the hand (MC).

Next to them come the finger bones, each division being called a Phalanx (D i, 2, 3, 4, S)- The thumb has two' phalanges, the second digit three, the third four, the fourth five, and the fifth three. And at the end of each digit is a claw. Apart from its being featherless, nothing less suited for flying can be imagined.

If we turn now to the bird we shall find that the Humerus (HU, fig. 2) has broadened, especially at the nearer end, and is covered with great

protuberances, good evidence that powerful muscles spring from it and are attached to it. Till we come to the fingers, there will be a striking increase in the length of the various bones. A bird's wing would be an outrageously long leg for a lizard of equal weight and bulk. When the long radius and ulna are extended, the elbow-joint allows of no turning motion. As is essential for flight, they are held stiff whatever

Fig. 3. — Tibia and Fibula of

Fowl.

F, fibula ; T, tibia.

lo THE STRUCTURE AND LIFE OF BIRDS CHAP.

strain is put upon them. The Radius is a very slender bone, the Ulna much thicker, with small but well-marked projections at the points where the great feathers grow. Of the nearer row of carpal bones there are only two (RC and UC), whereas there are three found in the lizard ; in the bird the small intermediate one has disappeared, and also the central bone

Fig. 4.— Hand of (a) Hatteria Lizard ; {b) Chick, ci, near row of carpals ; C2, farther row of carpals ; CE, central bones — there are often two ; D i, 2, 3, 4, 5, digits ; MC, metacarpals ; P, pisiform bone, originally a tendon ; R, radius ; u, ulna.

beyond it. Of the more distant row there is not a sign in the mature bird, but, if we examine the skeleton of an embryo, it may be made out. In a young chick there are still two free bones to represent it (C 2, fig. 4). In the adult these have been fused with the Metacarpals beyond. The tendency to fusion, or, as it is technically called, ankylosis, is found in many parts of

II SKELETONS OF BIRD AND REPTILE ii

the bird's skeleton, and may be regarded as a most marked characteristic. The bone formed by the fusion of the farther row of carpals with the metacarpals forms a broad slab on which rest many of the most powerful feathers of the wing. Its compound nature is described by its name of Carpo-metacarpus, or wrist-hand bone (CM fig. 2). Of the five metacarpals only three remain, and these three are fused together at their bases. Farther on they separate and can be easily distinguished. The first is only a slight projection from which the thumb ^ springs, the second is long, strong, and nearly straight, the third after describing a curve fuses again with the second at its farther end. The very short thumb consists of two phalanges only, the last being very small. It frequently has attached to it a claw suggestive of reptilian ancestry. The second and third digits are far away at the ends of their long metacarpals, attached firmly one to the other so that neither can move separately. The second is formed of three phalanges, of which the first is broad and plate-like, the last very minute ; the third digit is insignificant, with only a single phalanx. In digits I and II the final phalanx is often missing. The two united fingers have some slight 'power of movement, which many birds turn to account ; but in no part of the hand is there what can in any ordinary sense be called a joint. The wrist-joint, also, has much changed its character. It allows the hand to move freely towards the place where the fifth digit (or

1 I am taking it for granted for the Dresent that this digit corresponds to our thumb. See p. 42.

" little finger ") should be. The up-and-down movement that the lizard has, and that we have in our wrists, has almost disappeared : when the wing is extended, it does not exist at all ; when it is flexed, some movement of the kind becomes possible. The fusion of one row of carpal bones with the metacarpals has no doubt helped towards this rigidity which is so important to the wing. At the shoulder-joint there is always the utmost free play,

A bird's bones combine in a most remarkable way lightness and strength. It is popularly supposed that all birds, or at any rate those which fly much, have all their chief bones hollow and marrowless. This is, however, a fallacy ; some of the best flyers — e.g., the Swallow — having even the Humerus solid. But whether pneumatic or not, the bones are always fine in the grain and strong.

The chief results of the changes that the fore limb has undergone may now be summed up. ( i ) It is of most remarkable length. (2) It is at one time rigid, at another flexible, according as rigidity or flexibility is required. Contrast with a bird's hand a lizard's with its waggly fingers. And how neatly and comfortably the wing folds, when it is to be put to rest upon the body, in the form of a 2- (s) There are broad surfaces of bone to support the feathers. (4) Strength is combined with lightness. (5) The loss of two metacarpal bones and two fingers has been a gain, since the present hand formed of three united metacarpals and two united fingers (I am disregarding the insignificant " thumb ") is more efficient for purposes of flight than a hand with five fingers could well be.

The Breastbone and the Bones that meet at the shoulder-joint.

A powerful wing would be of no use without powerful machinery for moving it, and a lizard with a bird's wings would be no more able to fly than any

Fig. 5. — {a) Sternum of Iguana, with interdavicle, coracoid, precoracoid, and clavicle.

CL, clavicle ; co, coracoid ; icl, interdavicle ; pco, precoracoid ; st, sternum ; (V) Coracoid, scapula, and clavicle of fowl. CO, coracoid ; sc, scapula ; cl, clavicle.

ordinary lizard. In the bird's skeleton the enormous breastbone suggests a great deal. They must be strong muscles which have so strong and big a bone to which to attach themselves. No two things can be more unlike than the breastbones of the bird and the lizard, and the same may be said of the associated bones. In the lizard the whole apparatus is flat and weak. Its chief component, the Sternum (ST, fig. 5 a) or breastbone, is a level expanse with ribs attached to its margin. Down the middle may be seen running a thicker and stronger bone, which throws out a branch on either side, so that the whole makes something of a X shape. This bone is called the Inter-, clavicle (ICL), and it will be seen that the Clavicles (CL) or collar-bones converge upon it.. This interclavicle was formerly thought to correspond to the keel, the high, projecting ridge upon a bird's breast. But this is not the case, for the interclavicle is a membrane bone — i.e., a hardened ossified membrane — while the keel of a bird's breastbone originates from cartilage or gristle. There is also a bone called the Coracoid (CO) running from the shoulder-joint to the fore part of the sternum, and this bone in the lizard divides into two, the fore part being called the Precoracoid (PCO). Both parts are thin and weak. At the shoulder-joint the Coracoid and Clavicle are met by another bone, the Scapula (SC) or shoulder-blade,, which with the Coracoid forms the socket. The Scapula is a thin expanse of bone approaching close to the back-bone, to which it is attached by muscles. The upper part, the Supra-scapula, consists of gristle or cartilage not completely ossified. In the bird all this has been metamorphosed, though the materials are in the main the same. There is the sternum with a high ridge added which ossifies — i.e., becomes bone — from a different centre. In the young bird the keel is at first mere gristle, which at a certain point begins to ossify, and the process continues till the bone of the keel meets and joins the bone of the sternum proper.