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THE VERTEBRATE SKELETON.
THE VERTEBRATE SKELETON.
London : C.J. CLAY AND SONS, CAMBRIDGE UNIVERSITY PRESS WAREHOUSE, AVE MARIA LANE, AND H.K. LEWIS, 136, GOWER STREET, W.C. Glasgow: 50, WELLINGTON STREET. Leipzig: F.A. BROCKHAUS. New York: THE MACMILLAN COMPANY. Bombay and Calcutta: MACMILLAN AND CO., Ltd. [ All Rights reserved. ] THE VERTEBRATE SKELETON By SIDNEY H. REYNOLDS, M.A., TRINITY COLLEGE, CAMBRIDGE; LECTURER AND DEMONSTRATOR IN GEOLOGY AND ZOOLOGY AT UNIVERSITY COLLEGE, BRISTOL. Cambridge: AT THE UNIVERSITY PRESS. 1897 Cambridge : PR
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PREFACE.
PREFACE.
In the following pages the term skeleton is used in its widest sense, so as to include exoskeletal or tegumentary structures, as well as endoskeletal structures. It was thought advisable to include some account of the skeleton of the lowest Chordata—animals which are not strictly vertebrates, but it seemed undesirable to alter the title of the book in consequence. The plan adopted in the treatment of each group has been to give first an account of the general skeletal characters of the group in
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CHAPTER I. INTRODUCTORY ACCOUNT OF THE SKELETON IN GENERAL.
CHAPTER I. INTRODUCTORY ACCOUNT OF THE SKELETON IN GENERAL.
By the term skeleton is meant the hard structures whose function is to support or to protect the softer tissues of the animal body. The skeleton is divisible into A. The Exoskeleton , which is external; B. The Endoskeleton , which is as a rule internal; though in some cases, e.g. the antlers of deer, endoskeletal structures become, as development proceeds, external. In Invertebrates the hard, supporting structures of the body are mainly exoskeletal , in Vertebrates they are mainly endoskeletal ;
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CHAPTER II. CLASSIFICATION.
CHAPTER II. CLASSIFICATION.
The following classification includes only the forms mentioned in the succeeding pages . The relative value of some of the terms employed in classification is not identical throughout the book. This remark applies specially to the term group , which is a convenient one, owing to its not having such a hard and fast zoological meaning as has the term family , for instance. The term group is applied in this book to divisions of the animal kingdom of very different classificatory importance. PHYLUM
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CHAPTER III. SKELETON OF HEMICHORDATA, UROCHORDATA, AND CEPHALOCHORDATA.
CHAPTER III. SKELETON OF HEMICHORDATA, UROCHORDATA, AND CEPHALOCHORDATA.
SUBPHYLUM A. HEMICHORDATA. The subphylum includes three genera, Balanoglossus [19] , Cephalodiscus and Rhabdopleura ; and perhaps a fourth, Phoronis . The skeletal structures found in Balanoglossus [20] are all endoskeletal. They include: (1) The notochord . This arises as a diverticulum from the alimentary canal which grows forwards into the proboscis and extends beyond the front end of the central nervous system. It is hypoblastic in origin and arises in the same way as does the notochord of A
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CHAPTER IV. SUBPHYLUM D. VERTEBRATA.
CHAPTER IV. SUBPHYLUM D. VERTEBRATA.
The animals included in this great group all possess an internal axial skeleton forming the vertebral column or back-bone; and a dorsal spinal cord. The vertebral column is developed from the skeletogenous layer, which surrounds the spinal cord together with the notochord and its sheath; and in the great majority of cases the notochord becomes more or less modified and reduced in the adult. In some cases the notochord remains unmodified and the skeletogenous layer surrounding it is not segmented
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CHAPTER V. (II.) GNATHOSTOMATA.
CHAPTER V. (II.) GNATHOSTOMATA.
The mouth is supported by definite jaws. ICHTHYOPSIDA. The epiblastic exoskeleton is generally unimportant, the mesoblastic exoskeleton is usually well developed. The notochord with its membranous sheath (1) may remain unmodified, or (2) may be replaced by bone or cartilage derived from the skeletogenous layer, or (3) may be calcified to a varying extent. The first vertebra is not homologous throughout the whole series and so is not strictly comparable to the atlas of Sauropsids and Mammals. The
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CHAPTER VI. THE SKELETON OF THE DOGFISH[34].
CHAPTER VI. THE SKELETON OF THE DOGFISH[34].
Scyllium canicula. I. EXOSKELETON. The exoskeleton of the dogfish is mainly composed of placoid scales, each of which consists of a little bony base imbedded in the skin, bearing a small backwardly-directed spine formed of dentine capped with enamel. The scales are larger on the dorsal than on the ventral surface, and on the jaws they are specially large and regularly arranged in rows, there forming the teeth. The margins of the jaws or lips are without scales. A second exoskeletal structure is
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CHAPTER VII. THE SKELETON OF THE CODFISH.[35] (Gadus morrhua.)
CHAPTER VII. THE SKELETON OF THE CODFISH.[35] (Gadus morrhua.)
I. EXOSKELETON. The exoskeleton includes (1) Scales. These are of the type known as cycloid and consist of flat rounded plates composed of concentrically arranged laminae of calcified matter, with the posterior margin entire. The anterior end of each scale is imbedded in the skin and is overlapped by the preceding scales. (2) The teeth . These are small, pointed, calcified structures arranged in large groups on the premaxillae, mandible, vomer, and superior and inferior pharyngeal bones. (3) The
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CHAPTER VIII. GENERAL ACCOUNT OF THE SKELETON IN FISHES[39].
CHAPTER VIII. GENERAL ACCOUNT OF THE SKELETON IN FISHES[39].
EXOSKELETON. The most primitive type of exoskeleton is that found in Elasmobranchs and formed of placoid scales; these are tooth-like structures consisting of dentine and bone capped with enamel, and have been already described (p. 4). In most Elasmobranchs they are small and their distribution is fairly uniform, but in the Thornback skate, Raia clavata , they have the form of larger, more scattered spines. In adult Holocephali and in Polyodon and Torpedo there is no exoskeleton, in young Holoce
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CHAPTER IX. CLASS II. AMPHIBIA[50].
CHAPTER IX. CLASS II. AMPHIBIA[50].
Amphibia differ markedly from Pisces in the fact that in the more abundant and familiar forms the skin is naked, and that when the integument is prolonged into median fins they are devoid of fin-rays. The notochord may persist, but bony vertebral centra are always developed. These are sometimes biconcave, sometimes procoelous, sometimes opisthocoelous. There is only one sacral vertebra, except in rare cases. The cartilaginous cranium persists to a considerable extent but is more or less replaced
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CHAPTER X. THE SKELETON OF THE NEWT (Molge cristata).
CHAPTER X. THE SKELETON OF THE NEWT (Molge cristata).
I. EXOSKELETON. The skin of the Newt is quite devoid of any exoskeletal structures. The only exoskeletal structures that the animal possesses are the teeth, and these are most conveniently described with the endoskeleton. II. ENDOSKELETON. The endoskeleton of the Newt, though ossified to a considerable extent, is more cartilaginous than is that of the frog. It is divisible into an axial portion including the vertebral column, skull, ribs, and sternum, and an appendicular portion including the sk
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CHAPTER XI. THE SKELETON OF THE FROG[55] (Rana temporaria).
CHAPTER XI. THE SKELETON OF THE FROG[55] (Rana temporaria).
I. EXOSKELETON. The skin of the frog is smooth and quite devoid of scales or other exoskeletal structures. The only exoskeletal structures met with in the frog are:— 1. The teeth , which are most conveniently described with the endoskeleton. 2. The horny covering of the calcar or prehallux (see p. 167). II. ENDOSKELETON. The endoskeleton of the adult frog consists partly of cartilage, partly of bone and each of these types of tissue occurs in two forms. The cartilage may be hyaline, as in the om
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CHAPTER XII. GENERAL ACCOUNT OF THE SKELETON IN AMPHIBIA.
CHAPTER XII. GENERAL ACCOUNT OF THE SKELETON IN AMPHIBIA.
EXOSKELETON. The exoskeleton, at any rate in most living forms, is very slightly developed in Amphibia. The only representatives of the epidermal exoskeleton are (1) the minute horny beaks found coating the premaxillae and dentaries in Siren and the tadpoles of most Anura, (2) the nails borne by the first three digits of the pes in Xenopus and by the Japanese Salamander Onychodactylus , (3) the horny covering of the calcar or prehallux of frogs. The Urodela and nearly all the Anura, which form t
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CHAPTER XIII. SAUROPSIDA.
CHAPTER XIII. SAUROPSIDA.
This great group includes the Reptiles and Birds and forms the second of the three into which the Gnathostomata may be divided. There is nearly always a strongly-developed epiblastic exoskeleton which has the form of scales or feathers, and in some cases a dermal exoskeleton is also well developed. In living forms the notochord never persists, being replaced by vertebrae, but in some extinct forms the centra are notochordal. The vertebral centra are ossified, and only in exceptionally rare cases
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CHAPTER XIV. THE SKELETON OF THE GREEN TURTLE. (Chelone midas.)
CHAPTER XIV. THE SKELETON OF THE GREEN TURTLE. (Chelone midas.)
The most striking feature as regards the skeleton of the Turtle is that the trunk is enveloped in a bony box, the dorsal portion of which is called the carapace , while the ventral portion is the plastron . I. EXOSKELETON. a. The epidermal exoskeleton in the Green Turtle as in all other Chelonia except Dermochelys , Trionyx and their allies is strongly developed, its most important part consisting of a series of horny shields which cover over the bony plates of the carapace and plastron but do n
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CHAPTER XV. THE SKELETON OF THE CROCODILE.
CHAPTER XV. THE SKELETON OF THE CROCODILE.
The species chosen for description is C. palustris , a form occurring throughout the Oriental region, but the description would apply almost equally well to any of the other species of the genus Crocodilus , and with comparatively unimportant modifications to any of the living Crocodilia. I. EXOSKELETON. The exoskeleton of the Crocodile is strongly developed and includes elements of both epidermal and dermal origin. a. The epidermal exoskeleton is formed of a number of horny scales or plates of
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CHAPTER XVI. GENERAL ACCOUNT OF THE SKELETON IN REPTILES.
CHAPTER XVI. GENERAL ACCOUNT OF THE SKELETON IN REPTILES.
EXOSKELETON. The exoskeleton both epidermal and dermal is exceedingly well developed in reptiles. Epidermal Exoskeleton. This generally has the form of overlapping horny scales which invest outgrowths of the dermis, and are found covering the whole body in most Rhynchocephalia, Ophidia, and Lacertilia, and many Crocodilia. In the Ophidia the ventral surface of the tail is commonly covered by a double row of broad scales, while the ventral surface of the precaudal part of the body is covered by a
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CHAPTER XVII. CLASS. AVES[94].
CHAPTER XVII. CLASS. AVES[94].
Birds form a large and extremely homogeneous class of the vertebrata, and are readily distinguished from all other animals by the possession of an epidermal exoskeleton having the form of feathers. Feathers differ from hairs in the fact that they grow from papillae formed of both the horny and the Malpighian layer of the epidermis, which papillae at first project from the surface, and only subsequently become imbedded in pits of the dermis. A dermal exoskeleton does not occur in birds. The endos
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CHAPTER XVIII. THE SKELETON OF THE WILD DUCK (Anas boschas).
CHAPTER XVIII. THE SKELETON OF THE WILD DUCK (Anas boschas).
I. EXOSKELETON. The exoskeleton of the Duck and indeed of all birds is entirely epidermal in origin. Its most important part consists of feathers , but it includes also the following horny structures:— ( a ) scales , which cover the toes and tarso-metatarsus; ( b ) claws , which are attached to the distal phalanges of the toes and of the pollex; ( c ) the wide beak , which sheaths both upper and lower jaws, and whose edges are raised into lamellae, which act as strainers. Feathers. A well develo
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CHAPTER XIX. GENERAL ACCOUNT OF THE SKELETON IN BIRDS.
CHAPTER XIX. GENERAL ACCOUNT OF THE SKELETON IN BIRDS.
EXOSKELETON. The epidermal exoskeleton of birds is very greatly developed, feathers constituting its most important part. Three kinds of feathers are found, viz. ( a ) pennae including quills and coverts, ( b ) down feathers or plumulae , and ( c ) filoplumes which are rudimentary feathers. The structure of the different kinds of feathers is described on pp. 303-306. Sometimes a fourth class of feathers, the semiplumae , is recognised. They have the stems of pennae, and the downy barbs and barbu
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CHAPTER XX. CLASS MAMMALIA.
CHAPTER XX. CLASS MAMMALIA.
The skeleton of the members of this class, the highest of the vertebrata, has the following characteristics:— Some part of the integument at some period of life is always provided with hairs; these are epidermal structures arising from short papillae of the Malpighian layer of the epidermis, which at once grow inwards and become imbedded in pits of the dermis. Sometimes scales or spines occur, and epidermal exoskeletal structures in the form of hoofs, nails, claws and horns are also characterist
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CHAPTER XXI. THE SKELETON OF THE DOG[139] (Canis familiaris).
CHAPTER XXI. THE SKELETON OF THE DOG[139] (Canis familiaris).
I. EXOSKELETON. The exoskeleton of the dog includes three sets of structures: 1. hairs, 2. claws, 3. teeth. Hairs and claws are epidermal exoskeletal structures, while teeth are partly of dermal, and partly of epidermal origin. 1. Hairs are delicate epidermal structures which grow imbedded in little pits or follicles in the dermis. Specially large hairs forming the vibrissae or whiskers grow attached to the upper lip. 2. Claws are horny epidermal sheaths, one of which fits on to the pointed dist
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CHAPTER XXII. GENERAL ACCOUNT OF THE SKELETON IN MAMMALIA.
CHAPTER XXII. GENERAL ACCOUNT OF THE SKELETON IN MAMMALIA.
THE EXOSKELETON AND VERTEBRAL COLUMN. Epidermal Exoskeleton . Hair , which forms the characteristic Mammalian exoskeleton, varies much in different animals, and in different parts of the same animal. A large proportion of mammals have the surface fairly uniformly covered with hair of one kind only. In some forms however there are two kinds of hair, a longer and stiffer kind alone appearing on the surface, and a shorter and softer kind forming the under fur. In most mammals hairs of a special cha
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CHAPTER XXIII. GENERAL ACCOUNT OF THE SKELETON IN MAMMALIA (continued).
CHAPTER XXIII. GENERAL ACCOUNT OF THE SKELETON IN MAMMALIA (continued).
THE SKULL AND APPENDICULAR SKELETON. The Skull. Monotremata. In both genera the cranium is thin-walled, has a fairly large cavity, and is very smooth and rounded externally. The sutures between many of the bones early become obliterated in a manner comparable to that in birds, and the facial portion of the skull is much prolonged. In Echidna the face is drawn out into a gradually tapering rostrum, formed mainly by the premaxillae, maxillae and nasals. The zygomatic arch is very weak, and the pal
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LIST OF AUTHORS REFERRED TO.
LIST OF AUTHORS REFERRED TO.
Every reference is to the page: words in italics are names of genera or species; figures in italics indicate that the reference relates to systematic position; figures in thick type refer to an illustration; f. = and in following page or pages; n. = note. Cambridge: Printed by J. and C.F. Clay, at the University Press....
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CAMBRIDGE BIOLOGICAL SERIES.
CAMBRIDGE BIOLOGICAL SERIES.
General Editor, A.E. Shipley , M.A., F.R.S., Fellow and Tutor of Christ's College. A Text-Book of Zoogeography. By Frank E. Beddard , M.A., F.R.S., Prosector of the Zoological Society of London. With 5 Maps. Crown 8vo. 6 s. The Elements of Botany. By Francis Darwin , M.A., M.B., F.R.S., Fellow of Christ's College. With 94 Illustrations. Crown 8vo. Second Edition. 4 s. 6 d. Journal of Education. A noteworthy addition to our botanical literature. Practical Physiology of Plants. By Francis Darwin ,
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