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Mivart, St. George Jackson

Lessons in Elementary
Anatomy

OLD CLASS
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LESSONS

IN

ELEMENTARY ANATOMY.

L E S S O N S

i

IN

ELEMENTARY ANATOMY.

BY

ST. GEORGE MIVART, F.R.S., ETC.,

LECTURER ON COMPARATIVE ANATOMY AT ST. MARY'S HOSPITAL,
AUTHOR OF ''THE GENESIS OF SPECIES."

Jfbnbon :
MACMILLAN AND CO.

AND NEW YORK.
1889.

7 he Right of Translation and Reproduction is Reserved.

RICHARD CLAY AND SONS, LIMITFD,

LONDON AND BUNGAY.

First Edition (Pott 3vo), 1873.
w Edition (Foolscap 8vo), 1877.
Reprinted, 1879, xSSs, 1889.

SEEN BY
-PRESERVATION

SERVICES

ATE

PREFACE.

THE following " Lessons in Elementary Anatomy" are in-
tended in the first place for teachers and for earnest students
of both sexes, not already acquainted with human anatomy.

I have endeavoured, secondly, by certain additions and by
the mode of treatment, to fit them for students in medicine
and generally for those acquainted with human anatomy, but
desirous of learning its more significant relations to the
structures of other animals.

My hope is that this little volume may thus serve as a
handbook of Human Morphology.

Man has been selected as the type, because his structure
has been the most studied and is the most intimately known,
as also because our own frame is naturally the most interest-
ing to ourselves. But this book has no pretension to be a
" Comparative Anatomy." It does not profess to give a com-
plete account of the anatomy of any group of animals. It
contains but a selection of facts intended to illustrate the
variations which nature shows in that type of structure to
which man's body belongs.

So far as I am aware, this endeavour is the first of its
special kind, and I have felt much difficulty as to the facts to
be selected, fearing on the one hand to overload an elemen-

vi PREFACE,

tary lesson book, and on the other to make its contents too
scanty. It would of course be easy indefinitely to add to the
details herein stated regarding the structure of the animals
referred to. Some readers, no doubt, will expect greater
detail ; and I can hardly hope, in this first essay, not to have
overlooked points it might have been desirable to bring
forward.

Others may be disposed to think that too large a portion
of the book is devoted to the consideration of the skeleton
only.

This predominance has, however, been deliberately assigned
to the osseous structures for the following reasons : — I. The
general resemblance borne by the skeleton to the external
form ; 2. The close connexion between the arrangement of
the skeleton and that of the nervous system, muscles, and
vessels ; 3. The relations borne by the skeleton . of each
animal to the actions it performs, i.e. to the mode of life and
habits of the various animals ; 4. The obvious utility of the
skeleton in classification and the interpretation of affinity ;
5. Parts of the skeleton, or casts of such, are all we possess
of a vast number of animals formerly existing in the world,
but now entirely extinct ; a good knowledge of the skeleton
must therefore be of great utility to those interested in
Palaeontology.

Moreover, it is a recognized maxim with teachers of (exclu-
sively) human anatomy that a thorough knowledge of the
bones is not only a necessary preliminary to other anato-
mical knowledge, but that the latter is acquired with com-
parative ease when the first has been well mastered. I have
deemed it advisable to act on this maxim in teaching the
anatomy generally of man and of the animals herein
referred to.

PREFACE. vii

Certain of the facts noticed in these Lessons are recent
additions to science, yet in hardly any instance has reference
been made to their discoverers. Such references have been
omitted in order not to overload a school book with notes.
Indeed, I make very little claim to originality except as
regards the special mode adopted in my treatment of the
subject. By this I mean the exposition part passu of the
facts of human anatomy with a selection of those most
interesting and important in the anatomy of animals formed
on the same type as man himself.

The originals of many of the woodcuts are from the works
of Professors Owen, Huxley, and Flower, and of Mr. Parker
and others.

Some original drawings have been made from specimens
preserved in the Museum of the Royal College of Surgeons
and of the British Museum. Some have been added from
specimens in my own collection.

I am happy here to express my obligations for the ready
kindness with which my requirements for illustration have
been supplied.

I also feel It no less a duty than a pleasure to declare how
much I am indebted to a near relative, Mr. Henry Davies
Chapman, for having kindly undertaken, amidst the pressure
of other avocations, a patient revisal of the proofs of the
present work, the publication of which, but for this timely
assistance, might have been indefinitely delayed.

7, NORTH BAN?K, REGENT'S PARK,

November 1872.

CONTENTS.

LESSON I.

A GENERAL VIEW OF THE STRUCTURE OF THE HUMAN BODY,
AND ITS RELATION^ TO OTHER ANIMAL BODIES. Pp. i — 21.

§ I. Man's body cannot be comprehended by itself.

2. Its boundaries and chemical composition.

3. Its symmetrical relations.

4. Its substantial construction.

5. Man's body a double tube.

6. Relations of the alimentary tube and other organs.

7. Developmental characters.

8 Classification of the Animal Kingdom.
9. The Vertebrata.

10. The five other sub-kingdoms, or Invertebrata.

11. Comparisons as to the outline and chemical compo-

sition of man's body.

12. Comparisons as to its main divisions.

13. Comparisons as to its symmetrical relations.

14. As to the position of the solid supports.

15. As to the alimentary organs.

16. As to the double tube and contained organs.
17- As to the heart and vascular system.

18. As to the brain, respiratory and excretory organs.

19. As to the sense organs.

20. As to development.

21. Conceivable possibilities as to man's structure.

22. Man's body formed completely on the vertebrate type.

23. Divisions of the Vertebrata.

24. Classification of the organs of the human body.

CONTENTS.

- LESSON II.

THE SKELETON IN GENERAL.— THE INTERNAL SKELETON, THE
BACKBONE, BREASTBONE, AND RIBS. Pp. 22 — 73.

§ I. The skeleton generally.

2. The exo- and endo-skeletons.

3. The endo-skeleton.

4. The joints.

5. The divisions of the endo-skeleton.

6. The backbone composed oi" vertebrae.

7. Their different categories.

8. A dorsal vertebra.

9. A cervical vertebra.

10. The axis.

1 1. The atlas.

12. The lumbar vertebrae.

13. The sacrum.

14. The coccyx.

15. The backbone as a whole.

1 6. The breastbone.

17. The ribs.

18. Development of the spinal endo-skeleton.

19. Relations with other animals as to general structure.

20. As to numbers.

21. As to categories.

22. Relation of form and condition generally.

23. As to dorsal vertebrae.

24. As to cervical vertebrae.

25. As to lumbar vertebrae.

26. As to the atlas.

27. As to the axis.

28. As to the sixth and seventh vertebrae.

29. As to the sacral vertebrae.

30. As to the coccygeal vertebrae.

31. As to the spine in general.

32. As to modes of ossification.

33. As to the thorax.

34. As to the sternum.

35. As to the ribs.

36. As to development. ;

CONTENTS. xi

LESSON III.
THE SKELETON OF THE HEAD. Pp. 74—144.

§ I. The skull of man generally.

2. The occipital bone of man.

3. His parietal.

4. His frontal.

5. His temporal.

6. His sphenoid.

7. His ethmoid.

8. His maxillary

9. His malar, nasal, and lachrymal.

10. His palatine.

11. His vomer and turbinals.

12. His lower jaw.

13. His hyoid bone.

14. The outside of man's skull.

15. The inside of his skull.

1 6. Its fossae and cavities.

17. The development of man's skull.

1 8. Relations with other animals as to the skull's general

structure.

19. As to the occipital.

20. As to the parietal.

21. As to the frontal.

22. As to the temporal.

23. As to the sphenoid.

24. As to the ethmoid.

25. As to the maxillary.

26. As to the malar.

27. As to the nasal.

28. As to the lachrymal.

29. As to the palatine.

30. As to the vomer.

31. As to the lower jaw.

32. As to the hyoid.

33. As to the connexions of the bones,

34. As to the skull externally.

35. As to the skull internally.

36. As to its fossse and cavities.

37. As to its development.

CONTENTS.

LESSON IV.
THE SKELETON OF THE UPPER LIMB. Pp. 145—176.

§ i. Primary divisions of the limb skeleton.

2. The scapula of man.

3. His clavicle.

4. His humerus.

5. His radius.

6. His ulna.

7. His carpus.

8. His metacarpus.

9. His fingers.

10. General survey of the limb in Vertebrates.

11. The scapula generally.

12. The clavicle.

13. The humerus.

14. The radius.

15. The ulna.

1 6. The hand in general.

17. The carpus.

1 8. Bones of the first row.

19. Bones of the second row.

20. The metacarpus.

21. The digits.

LESSON V.
THE SKELETON OF THE LOWER LIMB. Pp. 177—213.

§ i. Primary divisions of the limb skeleton.

2. The os innominatum of man.

3. His femur and patella.

4. His tibia.

5. His fibula.

6. His tarsus.

7. His metatarsus.

8. His toes.

9. General survey of the limb in Vertebrates.

10. The os innominatum generally.

11. The marsupial bones.

12. The femur and patella.

13. The tibia.

CONTEXTS.

§ 14. The fibula.

15. The foot in general.

1 6. The tarsus.

17. Bones of the first row.

18. Bones of the second row.

19. The metatarsus.

20. The dibits.

LESSON VI.

THE INTERNAL SKELETON GENERALLY CONSIDERED.
Pp. 214—235.

§ I. Summary of more general characters.

2. Summary of modifications of the spinal skeleton.

3. Morphology of man's cervical vertebrae.

4. Morphology of man's axis and atlas vertebrae.

t. The more general relations of man's skeleton.

. The central axial portion.

7. Epaxial parts.

8. Paraxial parts.

9. Morphology of man's rib.

10. Hypaxial parts — hypapophyses.

11. Hypaxial parts — splanchnapophyses.

12. Summary of axial, skeletal parts.

13. Modifications of the cranial skeleton.

14. Generalization of man's cranial characters.

15. Those of the lowest Vertebrates.

1 6. Cranial serial segments.

1 7. Generalization of the appendicular skeleton.

1 8. Of the thoracic limbs.

19. Their primitive position.

20. Their serial subdivisions.

21. Of the pelvic limbs.

22. Their flexure.

23. Their serial subdivisions.

24. Comparison of the leg with the arm.

25. Comparison of the tarsus with the carpus.

26. Comparison of the digits of the foot with those of

the hand.

27. Relative importance of the axial and appendicular

skeletons.

CONTENTS.

LESSON VII.

THE EXTERNAL SKELETON, THE SKIN AND ITS APPENDAGES.
Pp. 236—280.

§ i. The external skeleton generally.

2. The parts to be treated o£

3. The skin generally.

4. Its layers.

5. Their appendages. t

6. The density of the skin.

7. The epidermis.

8. The dermis.

9. The hair.

10. Feathers.

11. The nail.

12. Epidermal structures not found in man.

13. Epithelial structures not found in man.

14. Enderonic appendages.

15. Teeth, their formation in man.

1 6. Their structure in man.

17. Their eruption and succession in man.

1 8. Their number and form hi man.

19. Definitions of the different kinds of teeth.

20. Dental formulae.

21. The situations in which teeth may be developed.

22. Their possible modes of implantation.

23. Their conditions as to number.

24. Their various forms and their contiguity.

25. The incisors in general.

26. The canines in general.

27. Molars in general.

28. Premolars.

29. True molars.

30. Progressive complications in the teeth of Beasts.

31. Non-mammalian forms of teeth.

32. Dental succession in general.

33. Dental structure in general.

34. Epithelial structures which are not true teeth.

35. External tooth-like structures.

36. The scales of Fishes.

37. Other dermal hard-structures of Fishes.

38. The antlers of Deer.

CONTENTS. xv

LESSON VIII.
THE MUSCLES. Pp. 251—364.

g I. The muscles in general.

2. Origin and insertion.

3. Different kinds — as to action.

4. Different kinds — as to morphology.

5. Muscles of man's head and neck.

6. Of the back.

7. Of the -upper extremity.
8.. Of the fore-arm.

9. Of the hand.

10. Of the abdomen.

11. Of the diaphragm.

12. Of the inferior extremity.

13. Of the leg.

14. Of the foot.

15. The muscles of Vertebrates in general — of the head

and neck.

1 6. Those of the orbit in general.

17. Those of the neck.

1 8. Those of the vertebral region in front.

19. Those of the back.

20. Those of the upper extremity.

21. Those of the fore-arm.

22. Those of the hand.

23. Those of the abdominal region.

24. The diaphragm in general.

25. The muscles of the inferior extremity in general.

26. Those of the leg.

27. Those of the foot.

28. Myological peculiarities of man.

29. Comparison of myology of pectoral and pelvic limbs.

30. Generalization of vertebrate myology.

LESSON IX.
THE NERVOUS SYSTEM AND ORGANS OF SENSE. Pp. 365 — 405.

§ I. Rank of the nervous system.

2. Its primary divisions.

3. Investing membranes.

4. The brain — its upper surface.

5. Its under surface and side.

CONTENTS.

§ 6. Its structure, as shown by a vertical longitudinal
section.

7. Other sections.

8. Its development.

9. Explanatory recapitulations.

10. Relative size of man's brain.

11. The cerebral hemispheres in general.

12. The olfactory lobes and olfactory organ.

13. The third ventricle.

14. The corpora quadrigemina.

15. The cerebellum.

1 6. The medulla oblongata.

1 7. The brain as a whole,

1 8. The spinal marrow in man.

19. The spinal marrow in general.

20. The optic nerve and eye

21. The third, fourth, and sixth nerves.

22. The fifth nerve.

23. The auditory nerve and ear.

24. The seventh or facial nerve.

25. The eighth nerve.

26. The ninth cranial nerve, and recapitulation.

27. The spinal nerves.

28. The nerves of the arm.

29. The nerves of the leg.

30. The sympathetic system.

31. Electric organs.

32. Generalization of vertebrate neurology.

LESSON X.
THE CIRCULATING SYSTEM. Pp. 406—432.

§ I. Its component parts.

2. The heart in man.

3. Its development.

4. The heart generally considered.

5. The arteries in man.

6. Their development.

7. The arteries generally considered.

8. The veins in man.

9. Their development.

10. The veins generally considered.

11. The circulation generally considered.

12. The lymphatic system in man.

13. The lymphatic system generally considered.

CONTENTS.

LESSON XI.
THE ALIMENTARY SYSTEM. Pp. 433—460.

§ I. Man's general alimentary system.

2. His mouth and lips.

3. The same in Vertebrates generally.

4. His salivary glands.

5. The salivary glands of other Vertebrata.

6. The tongue in man.

7. The tongue in other Vertebrates.

8. His oesophagus and stomach.

9. These organs in Vertebrates generally.

10. His intestine.

11. The intestine of Vertebrates.

12. The pancreas of man.

13. The pancreas generally.

14. Man's liver.

15. The Vertebrate liver generally considered.

1 6. The peritoneum.

17. Development of the alimentary system.

18. General survey of the alimentary system of the

Vertebrata.

LESSON XII.
THE EXCRETORY ORGANS. Pp. 461—497.

§ I. The excretory and respiratory organs in general.

2. The lungs of man, including their development.

3. The lungs (or homologous parts) of other animals.

4. The trachea and bronchi of man.

5. The trachea and bronchi in general.

6. The larynx of man.

7. The larynx in general.

8. Aquatic respiratory organs of Vertebrates.

9. The kidneys and bladder of man — their development.

10. The urinary system generally.

11. The supra-renal capsules.

12. The spleen.

13. The thyroid gland.

14. The thymus gland.

15. Cutaneous glands, including the rr.ammary glands.

b

CONTENTS.

§ 1 6. A retrospect as to those characters which distinguish
man from other Vertebrates, and first from Fishes.

1 7. Which distinguish him from Batrachians.

1 8. Which distinguish him from Reptiles.

19. Which distinguish him from Birds.

20. Which distinguish him from Monotremes.

21. Which distinguish him from Marsupials.

22. Which distinguish him from all animals below his own

order (Primates).

23. Which distinguish him from all but the highest Apes.

24. Which distinguish him from the highest Apes.

25. Conclusion.

INDEX, pp. 499—535-

LIST OF ILLUSTRATIONS.

FIG. PAGE

1. A Diagrammatic Section of the

Human Body taken vertically
through the Median Plane . 3

2. A Poulpe Cuttle-fish (Octopus) 6

3. A Centipede, or Hundred-legs

(Scoiopendra] 6

4. An Ascidian, or Sea-squirt (As-

cidia) 7

5. A Star-fish (U raster) . ... 7

6. A Tubularian Polyp (Bimeria) 7

7. A Foraminifer (Globigerina') . 8

8. One of the lowest Protozoa

(Protom&ba] 8

9 The Lancelet (Amphioxus) . 9

10. The Flying-Lemur (Galeopithe-

cus) 10

11. A Star-fish ( Uraster} . 10

12. A Centipede, or Hundred-legs

(Scolopeiidra) 11

13. The Lancelet (Amphioxus). . 12

14. A Long-armed Ape, or Gibbon

(Hylobates) 15

1 5 . A Lemuroid of the genus Lemur j 5

16. The Aye-aye (Cheiromys) . . 15

17. A Leaping Shrew (Macrosce-

lides) 16

18. The Flying-Lemur (Galeopithe-

cus\ 16

19. The Hyrax 17

20. The Three-toed Sloth (Brady-

pus} .......... 17

21. The Great Ant eater (Myrme-

cophaga) 17

22. The Cape Ant-eater (Orycte-

ropus) 17

23. An Armadillo (Dasypiis] ... 17

24. The Duck-billed Platypus(C>r«/-

tliorhynchiis) 18

25. The Oolitic Fossil Bird (Archce-

opteryx) 18

26. The Frilled Lizard (Chlamydo-

saurus~) 18

27. An Ichthyosaurus 19

28. A Plesiosaurus 19

FIG. PAGE

29. The great North American Eft,

with per.-istent gills (Meno-
branchus~) 15

30. The Hammer-headed Shark

^(Zyg&na) 20

31. The Eagle Ray (Myliobatis) . 20

32. The Mud-fish (Lepidosireu) . 20

33. Polypterus 20

34. A Frog-fish (Chironectes) . . 20

35. The Lamprey (Petromyzori) . 21

36. The Lancelet (Amphioxus) . 21

37. Articulation of a large Spine, by

shackle-joint, with a bony
plate (placed below) of the
skin of a Siluroid Fish ... 24

38. Axial Skeleton of the Trunk,

with the ribs of the right side
removed 25

39. A Dorsal Vertebra 27

40. A Cervical Vertebra . . . .28

41. The Axis Vertebra . . . . 29

42. The Atlas Vertebra . . . .30

43. A Lumbar Vertebra . . . .31

44. Front and Back Aspects of the

Sacrum 32

45. The Coccyx 33

46. Right Side of the Thorax . . 34

47. Diagram of the Development

of the Trunk and its Skele-
ton 36

48. Axial Longitudinal Section of

the Vertebral Column of an
Elasmobranch (Raia) ... 38

49. Lateral View of four Trunk-

Vertebra? of Siren . . . .40

50. Upper Surface of Twelfth Cau-

dal Vertebra of Leopard . . 40

51. Dorsal View of Sixth, Seventh,

and Eighth Post-sacral Verte-
brae of the Axolotl . . . .41

52. Six Trunk- Vertebrae of Polyp-

terus 41

53. Seven Trunk- Vertebras of the

Potto 41

LIST OF ILLUSTRATIONS.

FIG. PAGE

54. Anterior Surface of the Lumbar

Vertebra of a Hare (Lepus
timidus) 42

55. Anterior Surface of Twelfth

Caudal Vertebra of Leopard 42

56. Diagram of Section of Shell of a

Tortoise, made transversely
to long axis of Skeleton . . 43

57. Dorsal Surface of a Shell of a

Fresh-water Tortoise (Emys) 44

58. Spinal Column of Galago . . 45

59. Front and Back View of a

Vertebra of a Rattlesnake
(Crotalus) 46

60. Side View of Twelfth and Thir-

teenth Thoracic Vertebra of
Great Ant-eater (Myrmeco-
phaga jubata) 46

61. Section of most Pre-axial Verte-

brae, and part of Skull of Silu-
roid Fish, Beigrus .... 48

62. Section through Middle Line of

united Cervical Vertebrae of
Greenland Right Whale (Ba-
l&na mysticetus) 49

63. Third Cervical Vertebra of a

nearly full-grown Echidna
(E. hystrix) 49

64. Axis and four following Cervi-

cal Vertebra of a Spider
Monkey {A teles) .... 50

65. Lumbar Vertebrae of the Great

Armadillo (Priodontes) . . 51

66. Pelvis of a Bird anchylosed to

the Lumbar Vertebras ... 52

67. Lateral, Dorsal, and Ventral

View of First Vertebra of
Amphiuma 53

68. Atlas and Axis Vertebras of a

Chelonian Reptile . . . .54

69. Caudal Vertebras of Inuus . . 59

70. Post axial Termination of the

Vertebral Column in a Salmon 59

71. Part of the Vertebral Column of

a Sole 60

72. Lateral View of the five most

Pre-axial Caudal Vertebrae of
Menobranchus 60

73. Anterior Surface of Vertebras

of Dolphin (Globiocephalus

melas) 62

74- Caudal Vertebra of a Crocodile 63

75. Sternum of the Pig (Sus scrofa) 65

76. Sternum of a Howling Monkey

(Mycetes) 66

77- Thorax of a Gallinaceous Bird . 67
7». Ribs of the Flying Lizard

(Draco volans} 69

7Q. Vertebra of Axolotl .... 70
80. Lateral View of Sixth Vertebra

of Salamandra 71

FIG. PAGE

81. Skeleton of Head and Gills of

Lamprey ......

82. Sternum of Common Mole

(Talpa europcea) . . . .

83. Side View of Man's Skull .

84. Front View of Right Half of

Man's Skull .....

85. Outer Surface of Man's Oc-

cipital Bone .....

86. Man's Sphenoid Bone seen

from above . ...

87. Man's Ethmoid Bone . . .

88. Front View of the Right Orbit

of Man .......

89. Outer View of Under Surface

of the Right Side of Man's
Skull ........

90. A View of the Upper, or Cere-

bral, Surface of Left Side of
Man's Skull ......

91. Vertical, Longitudinal Section

of Man's Skull .... 91

92. Diagram of the Formation of

the Skull, seen from above 93

93. Diagram of the Formation of

the Skull, seen laterally . 94

94. Vertical, Longitudinal Section

of the Post -axial part of the
Skull, and of the more Pre-
axial Vertebrae of the Silu-
roid Fish Bagrus .... 96

95. Vertical, Longitudinal Section

of the Skull of a Fowl . . 98

96. Side View of the Skull of an

adult male Gorilla . . 99

97. Upper Surface of the Skull of

a Frog ....... ico

98. Diagram representing a

Transverse Vertical Section
of the Skull of a Serpent . 101

99. Upper View of the Skull of .

the Tanrec (Hemicentetcs) 102

100. Side View of the Skull of a

Perch ....... 103

101. Side View of the Skull of a

Rattlesnake (Crotalus'] . . 104

102. Vertical, Longitudinal Section

of the Skull of a Perch . .105

103. Under Surface of the Skull

of the Lemur Microccbus
•minor ....... I07

104. Under Surface of the Skull

of a Frog ....... 108

105. DiagrammaticVertical, Trans-

verse Section of the Skull of
a Lizard . . . . • • • i"

106. DiagrammaticVertical, Trans-

verse Section of the Skull of
a Chelonian ..... m

107. SideView of the Skull of a Por-

cupine ( Hystrix cristate) •

S3

oo

14

LIST OF ILLUSTRATIONS.

FIG. PAGE
108. Upper View of the Skull of a
Dolphin (Delphinus globi-
ceps) 117

FIG. PAGE

132. Right Scapula and Clavicle of
Two-toed Sloth (Cholaep^^s
Hqffmanni) . . . 157

IOQ. Under Surface of a Fowl's
Skull 119

133. Shoulder-girdle of a Bird
(Diver) jcg

no. Side View of , the Skull of a
Lizard (Varanus) . . .121
in. Hyoid of a Flying Fox (Pte-

134. Bones of the Right Arm and
Shoulder of the Small Tan-
rec (Hemicentetes) . . .159

112. Hyoid of a Lizard (Lacerta) 124
1 13. Diagram of the Changes
undergone by the Hyoid in
a Frog in passing from the
Tadpole stage to the Adult

part of Sternum of a Shrew
(Sorex) j6o
136. Right Scapula and scapular
part of Clavicle of a Shrew 160
137. Front View of Left Half of

114. Left Branchial Arches of a
Perch . . 126

Lizard (Hemidactylus) . 161

115. Side View of the Cartilaginous
Skeleton of the Head of a
Shark 126
1 1 6. Upper View of the Skull of a
Dolphin (Delphinus globi-

(Zeus) 162

139. Cartilaginous Skeleton of a
Limb of Ceratodus . ' . 163
140. Right Humerus of a Mole . 164
141. Anterior Surface of Right

117. Under Surface of the Cranium
of the Great Ant-eater

(Myrmecophagn jiibata] . 130

colomys vombatus] . . . 165
142. Right Pectoral Limb of a
Giraffe . . 167

118. Side View of a Bird's Skull . 134
119. Front View of the Skull of
the Lemur oid Indris Lan-

143. Dorsal Surface of Skeleton of
Right Hand of the Tortoise
Chelydra 168

i%er ....'.... 138

1 20. A Section of the Cranium of
a full-grown African Ele-
phant 141
121. The Skull, Anterior part of

145. Bones of Manus of Chceroptis
castanotis) 171
146. Right Pectoral Limb of a
Horse 173

Spinal Column, and Bran-
chial Basket of the Lam-
prey 143
122. Side View of the Cartilaginous
Skeleton of the Head of a
Shark 144
123. Outer or Dorsal View of the
Right Scapula of Man . . 146
124 Front View of the Right
Humerus of Man . . . 147
125. Front View of Man's Right

147. Palmar View of Left Hand of
Seps tridnctyhts . . . .173
148. Hand of Bat (Pteropus) . .174
149. Right Hand of Ostrich . . 175
150. Bones of Manus of Bandicoot
(JPerameles) 176
151. i. Ungual Phalanx of a Bear ;
2. Ungual Phalanx of a
Sloth; 3. Widely bifurca-
ting Distal Phalanx of the
Toad, Hylcedactylns (or

126. Anterior (palmar) Surface of
the Skeleton of Man's

152. Outer Side of Right Os In-
nominatum of Man . . .178

127. Front View of Scapular, or
Shoulder, Girdle of the
Skate (Raia clavata) . . 153
128. Shoulder-girdle of a Bird

nominatum of Man . . .179
154. Front View of Right Femur
of Man 181
155. Posterior Surface of Upper

Man 182

girdle of young Echidna
(Echidna hystrix) . . .155
130. Right Scapula and scapular
part of Clavicle of a Shrew
(Sorex) 156
131. Scapula of a Porpoise . . .156

156. Front View of Right Tibia and
Fibula of Man . . . .183
157. Dorsum, or Upper Surface, of
Skeleton of Right Foot . 185
158. Rudimentary Pelvic Extre-
mity of Opfaodes . . . .187

LIST OF ILLUSTRATIONS.

FIG. PAGE

159. Skeleton of Rudimentary

Pelvic Limb of Lialis . . 187

160. Pelvis of the Small Tanrec

(Hemicentetes) . . . . 188

161. Right Side of Pelvis of a Bird 189

162. Side View of Bones of Pos-

terior Extremity of Green-
land Right Whale (Balcena
jnysticetus) 190

163. Right Side of Pelvis of Frog 191

164. The two Ossa Innominata of

the Angler-fish (Lophius] . 191

165. Skeleton of Rudimentary

Pelvic Limb of Boa Con-
strictor 193

166. Pelvis of Echidna .... 194

167. Cartilaginous Skeleton of a

Limb of Ceratodus . . . 195

168. Skeleton of Rudimentary

Pelvic Limb of Lialis . . 196

169. Skeleton of Rudimentary

Pelvic Limb of Boa Con-
strictor 198

170. Side View of Bones of Pos-

terior Extremity of Green-
land Right Whale (Halcena
inysticetiis) 199

171. Right Pelvic Limb of Giraffe 200

172. Leg-bones of the Diver (Co-

lymbus) 201

173. Anterior Aspect of Bones of

Right Leg of Ornitho-
rhynchus paradoxus . . 203

Rudimentary Pelvic Ex-
tremity of Ophiodcs . . . 204

Elongated Tarsus of certain
Lemuroids 204

176. Right Foot of Emeu . . . 205

177. Left Foot of a. Monitor Lizard

(Varanus) 205

178. Skeleton of Right Pelvic

Limb of Horse .... 209

179. Right Pelvic Limb of Giraffe 209
iSo. Rudimentary Pelvic Extre-
mity of Ophiodes .... 210

Bones of Right Foot of Chee-

ropus castanotis

anes of Right Pe;

(Dipus sEgyptius)
Left Foot of a Monitor Lizard

(Varanits) 213

184. Vertebrae of an Axolotl . . 216

185. Lateral View of Sixth Ver-

tebra of Salamandra . . 216

186. Atlas and Axis Vertebrae of a

Chelonian Reptile . . .217

187. Diagram of the development

of the Trunk and its Skele-
ton 218

188. Six Trunk-vertebras of the

IBI.

182. Bones of Right Pes of Jerboa
183.

FIG. PAGE

189. Part of the Vertebral Column

of a Sole 221

190. Diagram of the further de-

velopment of the Trunk as
shown in a section similar
to the last 221

191. Skeleton of the Thorax of a

Bird 222

192. Skull and Branchial Arches

of a Shark 222

193. Diagram of a transverse Ver-

tical Section of the most
developed Skeletal Seg-
ment 223

194. Skeleton of Head and Gills

of Lamprey 224

195. Diagram of the condition of

the Skeleton in the Bran-
chial Region of a Lamprey 225

196. Diagram of the condition of

the Skeleton in the Bran-
chial Region of some
Sharks 225

197. Ideal, Generalized Diagram

of an Osseous Skull . . .227

198. Transverse Section of the

Thorax of Man .... 230

199. Transverse Section of the

Pelvic Region of Man . .231

200. Skeleton of Plesiosaurus . . 234

201. Skeleton of Ichthyosaurus . 234

202. The Frilled Lizard .... 237

203. Dorsal Surface of the Cara-

pace of a Fresh-water Tor-
toise (Emys) 239

204. Ventral Surface of the Plas-

tron of a Fresh-water Tor-
toise (Emys) 240

205. Armadillo 240

206. Polypterus 241

207. Dorsal Surface of the Cara-

pace of a Fresh-water Tor-
toise (Emys) 242

208. Diagram of a Vertical Section

of both Carapace and Plas-
tron of a Tortoise . . . 242

209. Diagram of a Feather Papilla,

seen on two opposite sides . 243

210. Transverse Section of a Nail 244

211. Sloth 245

212. Head of Male or Owen's

Chameleon 245

213. The Pangolin (Manis) . . 246

214. Tail of Rattlesnake . . . . 246

215. Ornithorhynchus, or Duck-

billed Platypus .... 247

216. Mouth of a Whale . . . .248

217. Four Plates of Baleen seen

obliquely from within . . 249

218. Vertical and Horizontal Sec-

tions of a Tooth .... 250

LIST OF ILLUSTRATIONS.

FIG.
219.

222.
223.

226.

227.

228.

229.
230.
23I-

234.
235-

236,

237'

240,
241,

243.
244,
245'

PAGE

Upper and Lower Teeth of
left side of an adult Man . 251

Ant-eater . 254

Open Mouth of the American

Eft Plethodon .... 254
Pharynx of a Tench opened

from below 255

Side View of the Skull of a
Lizard (Varanus) with
Acrodont teeth .... 256
Inner Side of Lower Jaw of

Pleurodont Lizard . . . 257
Grinding Surface of the Teeth
of the Right Half of the
Lower Jaw of the Lemu-
roid Microcebus .... 258
Side View of Skull of Porcu-
pine (Hystrix cristata) . 259
Dentition of Desmodus . . 259
A Lower Incisor of Galeopi-

thecus 259

Side View of Skull of Hemi-

centetes 260

Vertical Section of a Horse's

Incisor 260

Front View of Upper Incisors
and Canines of three genera
of Slow Lemurs .... 261
Dentition of Shrew-mouse

(Sorex) 261

Skull and Tusks of the Baby-

russa (Porcus) 262

Dentition of a Sheep . . . 262
Grinding Surface of a Left

Upper Molar (Gymnura) . 264
Grinding Surface of a Left

Upper Molar (Sorex) . . 264
Grinding Surfaces of Upper
Molars of Left Side (Uro-
trichns and Galeopithe-

cus) 265

Grinding Surface of Upper

Molar of Left Side (Talpa] 265
Grinding Surfaces of Upper
Molars of Left Side (Cen-
tetes and Chrysochloris) . 266
Dentition of the Sabre-toothed

Tiger (M achairodus] . . 266
Grinding Surface of First
Right Upper Molar Tooth
of A Hums fulgens . . . 267
Grinding Surface of Left
Upper Molar (Macrosce-

lidei.} 267

Grinding Surface of Second

Upper Molar of a Camel . 268
Grinding Surface of Right

Lower Molar (Tiipaia] . . 268
Grinding Surface of Right
Lower Molar {Chrysochlo-
ris} 268

FIG. PAGE

246. Upper and Lower Jaws (seen

from behind) of an Eagle
Ray (Myliobatis) . . . 270

247. Side View of the Skull of a

Rattlesnake (Crotnlus) . . 270

248. Vertical, Longitudinal Sec-

tion of the Poison-fang of a
Serpent 27I

249. Magnified Transverse Sec-

tion of a Serpent's Poison-
fang . 271

250. Vertical Section of the Lower

Jaw of a Shark (Lamna) . 273

251. Side View of the Pre-maxilla

of a Parrot -fish (Scarns) . 273

252. Grinding Surface of Lower

Molar of Indian Elephant 274

253. One Quarter of a much en-

larged Horizontal Section
of the Tooth of a Labyrin-
thodon 275

254. The Aardvark, or Cape Ant-

eater (Orycteropits} . . .276

255. Transverse Section of a Tooth

of Orycteropus .... 276

256. Under Surface of Head of a

Saw-fish (Pristis) . . . 277

257. A Shackle-joint 278

258. Dorsal Fin of an Acanthopte-

rygian Fish 278

259. Dorsal Fin of a Malacopte-

rygian Fish 278

260. Series of Antlers of the Com-

mon Stag 279

261. Superficial Muscles of the

Head: Right Side . . .283

262. Deeper Muscles of the Right

Side of the Head. . . .284

263. The Muscles of the Eyeball . 285

264. Muscles of the Right Side of

the Tongue 286

265. Muscles of the Front and

Right Side of the Neck . 287

266. Muscles of the Right Half of

the Pharynx 288

267. Muscles of the Back . . . 290

268. Anterior Muscles of the

Trunk 292

269. Muscles of the Right Shoulder-

blade 293

270. Inner Aspect of Superficial

Muscles of Right Shoulder-
blade and Upper Arm . . 293

271. Superficial Flexor Muscles of

Right Fore-arm .... 294

272. Deeper Flexor Muscles of

Right Fore-arm .... 296

273. Superficial Extensor Muscles

of Right Fore-arm . . . 296

274. Deeper Abdominal Muscles . 298

275. The Diaphragm 299

LIST OF ILLUSTRATIONS.

FIG. PAGE

276. Deep Muscles within Lum-
bar and Pelvic Regions . 300
277. Hind View of the Muscles of
the Pel vis and Right Thigh 301
278. Anterior Muscles of the Right

FIG. PAGE

299. Flexor Muscles and Tendons
of Fore-foot of Hyrax . .331
300. Diagram of Flexor Tendons
of Hand of Nycticebus . . 332
301. Deep Flexor Muscles of

279. Muscles of Outer Side and
Front of Right Leg . . . 304
280. Superficial Flexor Muscles of

302. Radial Side of Right Arm of
Parson's Chameleon . . . 334
303. Deeper Muscles of Extensor
Aspect of Right Fore-arm

281. Deep Flexor Muscles of Right
Leg 306
282. Superficial Muscles of Right
Side of Menopoma . . . 310
283. Deeper Muscles of Right
Side of Menopoma . . .311
284. Muscles of Neck and Shoul-

of Parson's Chameleon . .335
304. Superficial Ventral Muscles
of Right Side in Menopoma 338
305. Sub-vertebral Muscles of
Right Side of Iguana . . 340
306. Muscles of External Aspect
of Leg of an Eagle (Aquila

285. Muscles of Ventral Surface . 315
286. Superficial Muscles of Right
Side and of Extensor Sur-
face of Right Pectoral
Limb of Menobranchus . 316
287. Superficial Muscles of Ex-
tensor Side of Leg and
of parts of Trunk and Tail
of Menopoma 318
288. Superficial Muscles of the
Perch 319

307. Inner View of Right Half of
the Pelvis of Hyrax . . . 342
308. Right Side of Pelvis of Hyrax,
seen in front 343
309. Deepest Muscles of Right
Thigh of Iguana .... 344
310. Deeper Muscles of Inner As-
pect of Right Pelvic Limb
of Parson's Chameleon . 345
311. Deeper Muscles of Outer
Aspect of Right Pelvic

289. Muscles of the Ventral As-

Limb of Parson's Chame-

Wing of an Eagle (Aquila,

312. Superficial Muscles of Right

290. Deeper Muscles of Outer
Side of hinder part of
Trunk and anterior part of
Tail, and of the Dorsal
(extensor) Side of Right
Pelvic Limb of Meno-

313. Deeper Muscles of Extensor
Surface of Right Leg of
Menopoma 348
314. Deeper Muscles of Flexor
Surface of Right Hind Leg
of Menopoma . . 350

315. Muscles of Left Hind Leg of

291. Diagram of Caudal Muscles

Hyrax 352

of Right Side of Tail of
Iguana 323
292. Muscles of Right Half of a
Transverse Section of the
Tail of Iguana .... 324

316. Deeper Muscles of Back of
Right Leg of Parson's Cha-
meleon 354
317. Flexor Surface of Right Leg
of Iguana 355

293. Inner Side of Right Pectoral
Limb of Parson's Chame-

318. Tendons and Muscles of Ex-
tensor Aspect of Foot of

294. Muscles of Inside of Right
Arm of Iguana .... 327
295. Muscles of Outer Side of
Fore-limb of Hyrax . . . 328
296. Muscles of Inside of Right
Arm of Iguana .... 329

319. Muscles and Tendons of Sole
of Hind Foot of Hyrax . . 358
320. Deeper Front View of Right
Leg of Parson's Chameleon 360
321. Superficial Muscles of the
Perch 363

297. Deeper Flexor Muscles of
Right Fore-arm of Meno-

322. Diagram of Caudal Muscles
of Right Side of Tail of

298. Long Flexor Muscles and
Tendons of the Hand of
Nycticebus ,, . . . 330

323. The Upper Surface of tl^e
Brain of Man . . . . ' . 366
324. The Base of the Brain . . .363

LIST OF ILLUSTRA TIONS.

326.

370

33°-

33i-

332.
333-

334-
335-
336.

337-
338.

339-
340.

342.

343-
344-

345-
346.

PAGE

Side View of the Brain and
Upper Part of the Spinal
Marrow

The Brain as seen when a
Vertical Longitudinal Sec-
tion has been made through
its middle ...... 371

Enlarged and Diagrammatic
View of a Vertical Section
carried through the Corpus
Callosum and the parts
below ........ 371

Horizontal Section of part of
the Brain ...... 373

Diagram of a Transverse
Vertical Section of the
Brain, made through the
Second, Third, and Fifth
Ventricles ...... 374

Diagram illustrating the pro-
gressive Changes that take
place during successive
stages of the Development
of the Brain ..... 376

Right Side View of Brain of
the common Lizard (La-
cert a agilis) ..... 379

Vertical Longitudinal Sec-
tions of the Nasal Cavity . 380

Membrane developed on the
Nose of the Bat Mega-
derma lyra ..... 380

Brain of the Perch (Perca
Jln-viatilis) seen from above 381

Vertical Longitudinal, Section
of the Brain of the Perch

381

Dorsal Aspect of the Brain
of a Ray or Skate (Raia
batis) . . . 382

Dorsal Aspect of Brain of a
Pigeon (Columba livia) . 383

Left Side View of Brain of
Pigeon 384

The Spinal Cord .... 385

Diagram representing the de-
velopment of the Eye in
successive stages .... 387

Front View of the Eye, with
the Eyelids 388

Right Side of the Head of
one of the Pleuronectidse . 389

Hammer-headed Shark . . 390

Diagram illustrating the ar-
rangement of the parts of
the Brain and the origin of
the Nerves 390

Diagram to illustrate the de-
velopment of the Ear in
successive stages .... 392

The Membrane of the Drum
of the Ear 395

FIG,
347.

348.

349-

350.
351-
352.

353-
354-
355-
356.

404

359-
360.

361.
362.
363-

364-

365-
366.

367-
368.

PAGE

Diagram illustrating the dif-
ferent developments in
Sauropsidans and Ichthyo-
psidans of parts which in
Mammah become the Au-
ditory Ossicles .... 396

Head of the common Long-
eared Bat (Plecotus auri-
tus) ........ 396

Nervous Supply of the
hinder part of the Right
Side of the Head of the
Shark Hexanchus grisens] 397
Infero-lateral View of Head
and Aortic Arches of Lepi-
dosiren . ..... 398

General View of the Nervous
System, viewed from be-
hind ....... 400

Diagram of the development
of the Trunk and its Skele-
ton ........

Diagram of the further de-

velopment of the Trunk . 404
The Heart, Great Vessels,

and Lungs : Front View . 407
The left Side and the Right

Side of the Heart dissected 408
Heart of Cryptobranchus —

opened on its dorsal aspect 410
Arterial System of Man . . 412
Diagram representing the
Primitive Aortic Arches of
Mammals and Sauropsi-
dans ........ 415

The Circulation in a Tad-

pole in its primitive stage . 417
The Circulation in a Tad-
pole at a more advanced
stage ........ 417

The Circulation in a young
Frog ........ 417

Main Arterial Vessels of
Cryptobranchus . . . .418

Diagram representing the
Vessels and Aortic Arches
of a Snake ...... 419

Diagram representing the
Vessels and Aortic Arches
of a Lizard ...... 419

Diagram representing the

Main Arteries of a Bird
Diagram representing the
Main Arteries of a Mam-
mal ......

Diagram representing the
early condition of the
Circulation in Man .
Infero-lateral View of Head
and Aortic Arches o f Lepi-
dosiren .......

420

420

424

LIST OF ILLUSTRATIONS.

FIG.

369.
370.

371.
372.

373-
374-

375.
376.

377-
378.

379-

380.
381.

382.

383.
384.
385.

PAGE

The Thoracic Duct . . . .431

A Section of the Mouth and
Nose, taken vertically . . 434

A Dissection of the Right
Side of the Face .... 437

Sub-maxillary Glands and
Tongue-muscles of Great
Ant-eater (Myrmecophaga
jubata) 439

Head of the Frog Phyllome-
dusa 440

Diagram of the Stomach and
Intestines of Man . . . 442

Stomach of a Sheep . . . 443

Longitudinal Section of the
Stomach of the Great Ant-
eater (Myrmecophaga ju-
bata) . . . . . . . . 444

Stomach and adjacent Viscera
of the Bat Desmodus . . 445

Viscera of the common Fowl 447

Section of the Stomach and
part of the Intestines of a
Shark (Sqiialus maximus) 448

The Pancreas, with its Duct 449

Digestive Organs of a Sword-
fish (Xiphias gladius) . .450

Stomach and Intestine of a
Whiting (Merlangus vul-

•aris) 450

;e Liver viewed from below 452

Viscera of Lizaid (Calotes) . 453

Ideal Diagram of Under Sur-
face of Liver

ifi

386. Liver of the Two-toed Sloth

(Ckctejnu) ......

387. Liver of the Dolphin (Del-

phinus) .......

388. Diagram of the development

of the Trunk and its Skele-
ton ........

389.

457

Diagram of the further de-
velopment of the Trunk . 457

FIG. PAGE

390. Diagram of a Transverse Sec-

tion of a Lizard .... 459

391. The Heart, Great Vessels,

and Lungs : Front View . 462

392. Transverse Section of the

Chest, with the Heart and
Lungs (each Lung invested
with its Pleura) in place . 463

393. Diagram of a Lobule of the

Lung of a Bird .... 465

394. Air-bladder of the Teleostean

Fish Johnitts lobatus . . 466

395. Back View of the Neck and

Thorax of a Human Sub-
ject 468

396. Syrinx of a Raven .... 470

397. Right Lung of a Goose . . 470

398. Diagram of the Larynx . . 472

399. Larynx and upper pait of

Trachea of a Rattlesnake
(Crotalus horridus) . . . 475

400. Tracheal Structure of Proteus 475

401. Skeleton of Head and Gills

of Lamprey 476

402. First Three Branchial Arches

from Left Side of a Perch . 477

403. Left Branchial Arches of a

Perch 478

404. Skull and Branchial Arches

of a Shark 478

405. Two Lamellae (or Leaflets)

from the Gills of an Osseous
Fish 479

406. The Kidneys and Ureters,

with the Aorta and Vena
Cava Inferior, and the
Renal Arteries and Veins . 480

407. Kidney of the Seal (Phoca) . 482

408. The Spleen 484

409. Section of the Skin, showing

the Sweat Glands . . .486

410. Marsupial Pouch of an Opos-

sum (Didelphyscancrivora) 489

LESSONS

ELEMENTARY ANATOMY.

LESSON I.

A GENERAL VIEW OF THE STRUCTURE OF THE HUMAN
BODY AND ITS RELATIONS TO OTHER ANIMAL BODIES.

I. No object can be understood by itself. We compre-
hend any thing the better the more we know of other things
distinct from, but related to it.

" You understand a particular kind of animated being,
when looking inwards you see how its parts constitute a
system, and again looking outwards and around, how this
system stands with regard to other types of organized
existence."1

Man is an animal, and feels — in other words, forms one of
a multitude of different kinds of organized and sentient beings,
the bodies of which have obvious, but very various, relations
with his body. It is clear, then, from the nature of the case
that man's body can only be comprehended by means of an
extensive acquaintance with the bodies of other animals.

Experience confirms this conclusion : as the exclusive
study of man's body, though sufficient for the mere art of the
surgeon, has led to quite erroneous estimates of the nature
and meaning of parts of it ; errors corrected only through

1 Essays by James Martineau ; Second Series, p. 417.
B

2 ELEMENTARY ANATOMY. [LESS.

the general science of organic forms, i.e. the science of
Morphology.1

2. The body of man has a more or less rounded outline,
and its various surfaces are curved. Moreover, as everyone
knows, it is made up of different parts and organs — hard and
solid structures (bones) being enclosed by soft and pulpy
flesh. Indeed nearly all parts of man's body contain much
water : thus even 70 per cent, of the human brain is com-
posed of that fluid.

As to chemical composition, most ingredients of the human
body (unlike the fat) contain nitrogen ; while a peculiar
organic substance termed protein"2 (formed of the gases
oxygen, hydrogen, nitrogen, and of the solid element carbon)
constitutes its basis and foundation.

3. Man's body is evidently divisible into head, trunk, and
limbs.

Certain symmetrical relations and contrasts between dif-
ferent parts of the human frame are obvious.

Thus there is a contrast between its anterior and its hinder
aspect, and this contrast extends along each limb to the ends
of the fingers and toes. The hinder aspect in all cases is
termed " dorsal," the anterior one " ventral/' and, indeed, we
familiarly speak of the back of the hand.

Again, there is a resemblance (and at the same time a con-
trast) between the right a-nd left sides, which correspond with
tolerable exactitude one to the other. This harmony, termed
bilateral symmetry, though obvious externally, does not in
man extend to the internal organs (or viscera), which are
more or less unsymmetrically disposed.

Thirdly, there is a resemblance and correspondence between
parts placed successively, as, for example, between the arm
and the leg, or between the hand and the foot ; although this
relation is less obvious than it might be, owing to the differ-
ent directions in which the knee and elbow are bent. Such
a symmetry is termed serial, and is thus externally visible ;
but it is more manifest on a deeper examination, where we
find successive parts like the ribs or the pieces of the back-
bone, which obviously resemble each other more or less, and
so are called by a common name, while as they are placed
in " series " they are excellent examples of serial symmetry.

4. As is familiar to all, man's body consists of a solid frame-

1 Morphology, from the Greek words iiop<pti, form, and Xo>°C> discourse.

2 Protein, from TrprTcroc, first; Trpcorei'ic/i/, to be the first; irptareiov, the first
place ; because it holds the first place in relation to the albuminous principles.

GENERAL VIEW,

3

work (the bony skeleton), on which are laid bundles and layers
of flesh or muscle, the whole being enclosed by skin.

An external opening, the mouth, is the beginning of a long
and convoluted alimentary tube, which varies in size in dif-
ferent parts before reaching its termination, and has annexed
to it a variety of glands, as the liver, pancreas, and salivary
glands. This long tube occupies part of a great internal
cavity in the trunk of the body, in which cavity are also
placed the heart, lungs, spleen, kidneys, and bladder, the
heart1 being situated on the ventral aspect of the cavity.

FIG i.— A DIAGRAMMATIC SECTION OF THE HUMAN Horn- TAKEN VERTI-
CALLY THROUGH THE MEDIAN PLANE.

The ventral cylinder, containing the convoluted alimentary tube, lungs, &c.f
is bounded by the thick black line.

The dorsal cylinder, bounded by oblique lines, is shown expanding above into
the brain cavity.

5. Thus man's trunk may be conceived as a sort of fleshy
cylinder, but in fact it is made up of two cylinders of very
different size and structure.

1 The various organs here enumerated by anticipation are described in sub-
sequent Lessons.

B 2

4 ELEMENTARY ANATOMY. [LESS.

The second, and much smaller cylinder, runs along the
back, and consists of the backbone, expanding above into
the skull (or brain-case). This cylinder contains the spinal
marrow, while its upper expansion contains the brain. The
trunk of the human body consists thus of two tubes, with a
solid partition between them formed of the front part of the
backbone. Neither of these cavities is prolonged into the
limbs, which are made up of solid structures (flesh, nerves,
and vessels) wrapped round bones.

6. The long alimentary tube has no communication with the
body-cavity which surrounds it, but is (with its glandular ad-
juncts) a continuous structure, except at its terminal openings.

Thus it is not the inside of the alimentary tube which is
the true body-cavity, but, on the contrary, the space which
surrounds that tube and the other viscera. The tube itself is,
as it were, but a reflexion inwards of the external surface, the
skin which lines it being continuous at the lips with the skin
of the outside of the body.

At its upper end this tube rather bends away from the
brain or upper termination of the central part of the nervous
system.

The heart, which is a hollow muscular organ, is rhythmically
contractible and propulsive, and contains red blood ; part of
which, as it circulates, undergoes on its way back a subsidiary
(portal) circulation through the liver, by means of a double
set of vessels ramifying through that organ.

The blood-vessels which arise from the heart (i.e. arteries)
become successively smaller and smaller as they pass away
from it, and end in most minute tubes (capillaries), whence the
returning vessels (veins) take origin, growing larger as they
approach the heart. The blood is thus constantly enclosed
in distinct vessels of one kind or another.

The brain and spinal marrow form the central parts of the
nervous system. Cords or threads of nervous substance (the
nerves) extend from the brain and spinal marrow into every
part of the body.

The lungs (as has been shown in "Elementary Physiology,"
Lesson IV.) respire air, but man has not any appliance by
which to extract oxygen from air as it exists mixed up in
water, whether fresh or salt.

The sense organs, except touch, are all placed in the head,
and the respiratory organs open at the same part of the body,
namely, by the nose and mouth. Three special senses are fur-
nished with pairs of organs — two eyes, two ears, two nostrilc.

I.I GENERAL VIEW. 5

The mouth is bounded by jaws which open vertically, the
nperture itself being extended transversely.

7. Such being the more significant and general characters
of adult man, certain processes and changes of growth may
be referred to by which that condition is arrived at.

A minute rounded, almost structureless mass is the earliest
condition of the body.

The first indication of the future being, which shows itself
in that rounded mass, is given by a longitudinal groove mark-
ing the place of the spinal marrow and brain.

Beneath this a similarly longitudinal, cellular rod appears,
called the notochord,1 or chorda dorsalis, marking the place
of the future front part of the backbone.

In process of time the lower jaw appears as a solid rod
coming down on each side from the head, and a series of
similar structures, called u visceral arches" make their appear-
ance on each side, also coming down from the head like the
lower jaw, and placed one after the other behind (or, if the
body is vertically placed, beneath) that jaw, and forming later
the tongue-bone, &c.

These arches are separated by temporary apertures termed
" visceral clefts."

8. The world is inhabited by a vast animal population, of
kinds so numerous and diverse that the study of them would
be a task of hopeless difficulty were they not capable of con-
venient classification.

Fortunately they can be and have been divided and
arranged, according to their resemblances in form and struc-
ture, into a series of more and more subordinate groups.
The sum total of animals is spoken of as a kingdom — the
Animal Kingdom — in contrast with and distinction from the
Vegetable and Mineral Kingdoms.

The Animal and Vegetable Kingdoms taken together con-
stitute the "organic world," and each member of it is an
''organism."

The Animal Kingdom is made up of certain great primary
groups, each of which is termed a sub-kingdom (or sometimes
a division).

Each sub-kingdom is made up of and is divisible into
certain other subordinate (yet still great) groups, each of
which is called a class.

Each class is composed of a certain number of more sub-
ordinate divisions, each of which is termed an order.

1 NCOTOC, back, and x0^/), chord.

6 ELEMENTARY ANATOMY, [LESS.

Each order consists of smaller groups, which groups bear
each the title family.

Each family is composed of still smaller divisions, termed
genera.

Each genus is made up of one, few or many species; each
species being composed of individuals differing only as re-
gards sex, and capable of reproducing other individuals
similar to themselves.

The whole of these groups are defined by peculiarities of
form and structure ; that is to say, the classification is based
upon the number and shape of parts and organs, and not by
what such parts and organs do, i.e. it is morphological and not
physiological.

9. One great primary group, i.e. one sub-kingdom (or
division) — that to wrhich we belong — includes, besides our-
selves, all beasts, birds, reptiles, frogs, toads, and efts (or
newts), and all fishes truly so called. The creatures of this
sub-kingdom agree in possessing a spine, that is a backbone
(or a cartilaginous or gelatinous representative of it). In all
the higher of these animals, including man, the backbone is
made up of a number of bony pieces termed vertebras, and on
this account the term VERTEBRATA is given to the whole
group, which is spoken of as the Vertebrate sub-kingdom.

pIG- 2.— A POUKPE CUTTLE-FISH FIG. 3. — A CENTIPEDE, OR HUNDRED-KEGS
(Octopus). (Scolopendni).

10. Another primary group, sub-kingdom, or division, in-
cludes all snails, slugs, cuttle-fishes,1 and creatures of the
oyster and scallop class. The name MOLLUSCA* is applied to
this group, and the creatures composing it are often spoken
of as the Molluscous animals, or Mollusks.

A third great primary group or sub-kingdom is termed
ANNULOSA.3 They are creatures the bodies of which are

1 Improperly called fishes ; as also are the oyster and its allies.

2 Mollusca, from inottuscns, mollis, soft. 3 Annulosa, from anmthts, ring.

GENERAL VIEW.

made up of a longitudinal series of more or less distinctly
traceable segments or rings, at least at some period of their
lives. Such creatures are all insects, crabs, lobsters, shrimps,1
scorpions, spiders, hundred-legs, earth-worms, and leeches.
This sub-division is the richest in numbers of the whole
animal kingdom ; and even one class of it, Insecta (which
comprises all insects), contains so many species as to exceed
in number all other species of animals put together.

A fourth sub-kingdom is made up of creatures less familiar
to many, namely, sea-squirts or ascidians,2 lamp-shells, and

FIG. 4. — AN ASCIDIAN, OR SEA-SQUIRT
(Ascidia).

FIG. 5. — A STAR-FISH
( U raster].

FlG. 6, — A TUBULARIAN POLY!

(Bimeria), after Allman.

minute animals living in compound aggregations, often found
on our shores, such as iheJZustra, or sea-mat. To this sub-
kingdom the name MOLLUSCOIDA 3 has been applied.

A fifth sub-kingdom is composed of animals like star-fishes,
sea-urchins, and sea-cucumbers, together with entozoa,4 or
intestinal parasites and their allies, on all of which the
common name ANNULOIDA5 has been imposed.

A sixth primary group bears the title CCELENTERATA,6 and
contains all sea-anemones, jelly-fishes, Portuguese men-of-war,

1 Crabs, lobsters, and shrimps are sometimes improperly spoken of as shell-
fishes. 2 From UO-KOJ, a wine-skin or pouch.

3 Molluscoida, from mollusca and etc>o£, form, appearance.

4 'El/Tot;, in, and ^Coov, animal. 5 Annuloida, from anmtlus and etioj.
6 Ccelenterata, from xolXa, hollow ; ei-repa, entrails.

8 ELEMENTARY ANATOMY. [LESS.

£c., and all polyps, including many compound animals which
grow up in a tree-like manner, and the minute creatures
which by their secular existence have formed not only such
parts of the earth's surface as reefs and coral islands, but
even the State of Florida itself, of which they were un-
doubtedly the first founders.

Lastly, we1 nave the sub-kingdom PROTOZOA, r containing
all the lowest forms of animal life,, placed together rather
owing to the absence in them of characters possessed by
higher groups than from positive characters which they share
in common.

Such are the Infusoria,2 the sponges,, and those wonderful
Foraminifera3 which took (and are taking at the bottom of the
Atlantic) so large a part in the formation of the chalk, and
therefore built up much of Old England itself.

FIG. 7-— A FORAMINIFER FIG. 8. — ONE OF THE LOWEST PROTOZOA

(Globigerind). (Protomoeba), after Haeckel.

In the lowest grade of the animal kingdom is a creature,
Protogenesf at once structureless and devoid of any constant
form, as its shape varies like that of Proteus himself. A mere
morsel of semi-fluid jelly, floating in the ocean, it is destitute
of any organ,, even so much as a cell, and exhibits animality
in the last degree of structureless simplicity.

The last six sub-kingdoms may very conveniently be taken
together,. and spoken of as the Inveriebrata, in contrast to the
highest sub-kingdom, from which in so many points the other
primary groups agree in differing. Thus we have the Verte-
brata on the one hand, and on the other the Invertebrata,
including the Mollusca, Annulosa, Molluscoida, Annuloida,
Ccelenterata, and Protozoa.

IT. Having made this rapid survey of the whole animal
kingdom, it will be well to consider the general characters

1 Protozoa, from TrpSrog, first ; £vr>ov, animal.

2 So called because found in infusions when left exposed to the air for a time.

3 Foramina andferc, having holes or perforations.
< flpSTOj;, first ; "iivtvOai, to be born.

I.] GENERAL VIEW. 9

of man's structure, already noted, in relation to the other
forms of life here enumerated.

In that man's body is bounded by curved lines and sur-
faces, and its structure complex, so that upon a section being
made it is seen to consist of different parts — it agrees with
those of all other animals, as even in Protogenes there are
granules. Thus it differs from inorganic substances, which
may be, as in crystals, bounded by right lines, flat surfaces,
and have a homogeneous section— a cut crystal being the
same in structure throughout. Only very rarely (as in
spathic iron and dolomite) are minerals bounded by curved
lines and surfaces.

The presence of much water is also a common character of
organic living bodies, though man may be called solid in
comparison with some animals, more than 99 per cent, of water
entering into the total composition of a jelly-fish.

As to his chemical composition, man agrees with the whole
animal kingdom, and differs from the members of the vege-
table kingdom in the less proportion of non-nitrogenous parts
which help to compose his body.

12. I n so far as man's body is furnished with a distinct head,
he agrees not only with other vertebrates

(with one exception — the lancelet, or
Amphioxus), but also with the higher

Mollusca and Annulosa. It is a cha- FlG THE LANCELET
racter, however, quite wanting in the (Ampkioxns).

lower sub-kingdoms, and' even so- well-
organized an animal as the oyster is quite destitute of any
such part.

The presence of limbs is not a universal character even in
man's own primary division, the Vertebrata, being wanting,
e.g., in serpents ; but the possession of more than four is
known only in the Annulosar where, however, the number
may be not merely six, as in insects, but prodigious, as in
the millepedes,, or thousand-legs.

13. The contrast between dorsal and, ventral structures is
one very widely shared, but is absent in- the lowest animals —
which thus remind us of that earliest condition of man before
referred to, when his body is a minute spheroidal mass.

A dorsal and ventral symmetry may be developed such as
man does not exhibit, and this is especially the case in the
region of the tail, where (as, e.g., irt fishes and amphibians)
the structures on the dorsal side of the centre of the back-
bone tend to be repeated on its ventral side.

ELEMENTAR Y ANA TO MY.

[LESS.

FIG. 10. — THE FLYING-LEMUR
( Galeopitkecus),

The continuity of the dorsal and ventral surfaces of the
limbs with the dorsal and ventral surfaces of the body, as also
the correspondence between the dorsal (and ventral) surfaces
of the two pairs of limbs, may be more plainly exhibited than
in man. Thus in many tortoises both the knee and the elbow
are rather turned outwards, than
the former forwards and the latter
backwards, as is also the case in
the Flying- Lemur (Galeopithecus)
amongst beasts.

Bilateral symmetry is common to
man and the majority of animals.
It may, however, be much less com-
plete than in him, as in the fiat
fishes (such as the sole, turbot,
flounder, &c.), where both the eyes
come to be on one side of the head ; and it may be want-
ing altogether, not only as regards the viscera, but also as
regards the external form, as is the case in many Mollusks,
e.g. the snail.

On the other hand, this kind of symmetry may be carried
to a far greater extent than it is in man, as is the case in
the Annulosa, where not only the external form, but the in-
ternal viscera also, are bilaterally symmetrical.

An antero-posterior symmetry may be developed to a cer-
tain superficial extent, as in the reptile
AmphisbenaJ- in which it is at the first
glance difficult to tell the head from the tail.
Another form of symmetry which is en-
tirely absent in man is radial symmetry.
This symmetry is exhibited by jelly-fishes
and by sea-urchins, and star-fishes in their
adult condition — parts radiating from a FIG
common centre resembling and corre-
sponding one with each other.

Serial symmetry may be much less and much more
developed than we find it to be in man. Thus, in such
creatures as the oyster it is completely absent. In birds it
is less marked than in man, the dissemblances between their
wings and legs being more obvious, and the resemblances
more hidden, than between the human upper and lower limbs.
In contrast with this we find in forms closely allied to man
the resemblance to be exaggerated — whence the name Ouad-

1 From afjKpit;, for «/*<£/, on both sides, and fluivtiv, to go.

ii. — A STAR
( U raster).

i.J GENERAL VIEW. u

riimana has inexactly been applied to the apes, the foot
having so close a superficial resemblance to the hand.
Parts which answer to each other in serial symmetry are
termed " homotypes?

An amount of serial symmetry, however, far beyond any-
thing which man presents is developed in the sub-kingdom
Annulosa, as we may see in such creatures as the lobster.
Not only is there in such animals an obvious serial repeti-
tion in similar segments and similarly formed limbs, but a
little study shows that parts superficially unlike (as the
feelers, or antennse, jaws, claws, legs, and swimmerets) are
essentially similar structures, diversely modified to meet
diverse requirements.

The maximum of serial repetition, however, is found in the
hundred-legs and thousand-legs and
other Annulosa, in which the num-
ber of body segments is at its
maximum.

14. The possession of a solid in-
ternal frame-work to which muscles FJG. 12.— A CENTIPEDE, OK
are attached is a character man HUNDRED-LEGS (Scoiopemtra).
shares with all the members of the

Vertebrate sub-kingdom ; buf quite other conditions may
obtain and indeed numerically preponderate, as in the vast
group of Annulose animals, where the hard parts are external,
and the muscles which move them are within them and
attached to their inner surfaces, as familiarly known to us
in the lobster.

15. A permanent mouth may seem to many to be an organ
necessary to every animal. This, however, is not the case,
as animals so complexly organized as the tapeworm are alto-
gether destitute of any such structure and feed by absorption
only. Even certain minute creatures which swim freely
about to seek their food may yet have no permanent mouths,
but (as, e.g., Amoeba and Protogenes) when in contact with
their food may produce a temporary perforation in the sur-
face of their own body in which they engulph their food, the
body-wall closing up again over it.

It becomes, then, hardly necessary to say that an alimen-
tary tube is not a constant structure, still less any inferior
outlet ; for many animals, e.g. the lamp- shell (Terebratuld],
though possessing an intestine, are nevertheless aproctous.1

The various organs which aid digestion disappear as we

1 From u, not, and irpuK-rof, anus.

1 2 ELEMENTAR Y ANA TOM Y. [LESS.

descend in the animal scale, but a liver is a structure which
long persists, as e.g. in the Mollusca and many Annulosa.

1 6. In that man's body consists of a double tube — the
nervous cylinder being dorsal and the heart ventral — it agrees
with the whole of the members of his sub-kingdom, but
appears to differ from that of all invertebrates, unless it be
certain Ascidians. Recent observations show that the latter
simulate in their larval condition the vertebrate structure as
regards the existence of a dorsal nervous cylinder, as also as
regards a solid partition or simulation of a notochord, which
nevertheless is not yet unequivocally manifested, outside the
Vertebrate sub-kingdom.

A prolongation of the body cavity and even of the digestive
cavity into the limbs, strange as it may appear, is far from
unknown, as it exists not only in the star-fishes, but also in
animals as highly organized as spiders.

A direct communication between the alimentary canal and
the true body-cavity is by no means uncommon in lowly orga-
nized forms ; e.g., in the sea-anemone that canal terminates
freely in the body-cavity.

In creatures in which the central part of the nervous system
is ventral— that is to say, in all the Annulosa — the anterior
part of the alimentary tube not only bends towards but
traverses the nervous centres. That bending away from
those centres which characterises it in man, characterises it
also in all vertebrate animals.

Speaking generally, the nervous centres of invertebrates are
placed in the oral region, as not only in the Annulosa and
Annuloida, but also in the Mollusca and Molluscoida, it is
present in that part, unless absent altogether.

17. The possession of a heart and of red blood is common to
all vertebrates as well as to man, with
one solitary exception : the Amphioxus
or lancelet alone having colourless
FIG. 13.— THE LANCELET blood, and a simple cylindrical vessel

A portal circulation is shared with

man by all vertebrates, even the Amphioxus, but no inverte-
brate animal is known to be furnished with a blood distribu-
tion of the kind.

Also the enclosure of the blood in vessels is a cha-
racter common to vertebrates, but in Annulose animals (e.g.
the lobster) the blood is in part contained in wide cavities
termed sinuses. In many forms also (as in the Mollusca) a

i.] GENERAL VIEW. I3

communication takes place between the interior of the circu-
lating system and the exterior of the body, so that the water
in which such creatures live is admitted within their blood
system to a greater or less extent.

1 8. A distinct brain is common to all the members of man's
sub-kingdom except the lancelet ; but both nerves and ner-
vous centres may be entirely wanting in creatures of complex
structure like the tapeworm, or of locomotive power like the
polyp, Hydra tuba,

Respiration of air by pulmonary sacs is neither universal
in man's sub-kingdom (for fishes breathe the air contained in
water by gills), nor unknown out of it. Such structures exist
in scorpions and spiders, and an air-breathing sac is found
in slugs and snails.

On the other hand, breathing organs suited for aquatic
respiration may be developed in the most varied situations ;
e.g., attached to the legs, as in the lobster, or internal with
an external opening at the hinder end of the body, as in the
sea-cucumber, Holothuria.

Kidneys, instead of being distinct structures as in man,
may be united with biliary glands and open into the intes-
tine, as in insects.

19. Sense organs may exist in quite other situations than
those in which they are placed in man. Eyes may be placed
on every joint of a long body, as in the worm-like animai,
Polyophthalwus* or along each half of a fleshy cloak enclos-
ing the body, as in Pecten. There may often be more than
two upon the head, as in Scorpio; or they may be raised on
solid stalks, as in the lobster ; or at the end of long retractile
tentacles, as in the snail.

Auditory organs may be placed in joints of the legs, as
in some insects, e.g. locusts ; or in the thoracic part of the
body, as in crickets.

Long filamentary jointed structures (the antennas of insects)
may project from the head, to minister to a sense the nature
of which is disputable.

The mouth, instead of being extended transversely, may be
rather antero-posteriorly elongated even in man's sub-king-
dom, as in the lancelet ; and there may be numerous jaws
placed on each side of it working laterally, and not vertically,
as in the lobster.

20. Development may take place without any primitive
groove and without any chorda dorsalis, and such is the case

1 From -oAuc, many'; 6'<ji0aX/uo£, an ev<*.

1 4 ELEMENTAR Y ANA TO MY. [LESS.

in the whole of the Invertebrata (as far as yet known), with
the doubtful exception of Ascidians.

Visceral clefts and arches may persist throughout life, as in
fishes ; but with respect to this, much more will be said later.

From the foregoing concise statement of the more im-
portant general characters of man's anatomy and that of
animals generally, it is evident that his frame has been con-
structed upon a certain plan which in its main characters is
common to all the members of one large group (sub-kingdom)
of animals.

This will become manifest when we proceed more into
detail and discover structures the utility of which is, to say
the least, apparently subordinate to their significance as
conforming to a general type of structure.

21. It may well be the case that the rational faculties of
man could have been united to no more suitable a body than
that Avhich he possesses. Fancy may nevertheless amuse
itself by considering possibilities of structure (as shown by
what we find in existing animals) were he not tied down to
conformity to the vertebrate type.

The fabled Briareus is suggested by the "thousand-legs"
and centipede. A natural armour, moved by a cunningly
adjusted internal mechanism, is suggested by the lobster. A
spear tipped with poison, like the wourari, is suggested by
the wasp ; and the appliances of even the most modern
warfare by the Bombardier Beetle.

Eyes multitudinous, attached to movable stalks or at bur
fingers' ends — ears in our breast, or attached to our shin-
bones — are suggested by what we know of some insects.

22. It is the fact, however, that man's body is strictly verte-
brate, and vertebrate only. It remains then to consider it
from the vertebrate point of view. His resemblances to all
animals below the Vertebrata are so general and remote,
that it would be profitless henceforth to consider and com-
pare (in going into the details of his structure) any such
distant resemblances or relationships as those presented by
invertebrate animals, of which we accordingly here take leave.

It is needful, however, to hive a clear general conception
of the animals which compose the Vertebrate sub-kingdom, to
which repeated references will henceforth be made.

23. The Vertebrata are divisible into five great classes,
which stand in different degrees of relationship one to
another: — I. MAMMALIA (Man and Beasts); II. AYES

I.I

GENERAL VIEW.

(Birds); III. REPTILIA (Reptiles); IV. BATRACHIA (Am-
phibians) ; * V. PISCES (Fishes).

Moreover, Aves and Reptilia are classed together in a
large group (or province) which bears the name SAUROPSIDA.
Similarly Batrachia and Pisces are grouped together, and to
their united mass the common name ICHTHYOPSIDA is
applied.

The class Mammalia comprises all the creatures which
suckle their young, and is made up of man together with all
beasts, and each is spoken of as a mammal. All mammals
are divisible into three great groups or sub-classes.

The first sub-class comprises man and all the more well-
known beasts. It is called MONODELPHIA, and the animals
contained within it are termed Monodelphous mammals.
These are arranged in the following orders : —
I. PRIMATES. — Man, the Apes of the Old and New
World, together with the Le-
murs. Among the Apes and
Lemurs are — the Gorilla and
Chimpanzee, the Orang, the
Gibbons, the Proboscis Mon-
key, the Barbary Ape (Inuus],
the Baboons (Cynocephalus),
the Spider Monkey s(Ateles),
the Howlers (Mycetes) ; also
Pithcria, Chrysothrix, the
Squirrel Monkey, the Mar-
morets (Hapale), and the
genera Indris, Lemur, Microcebus, Galago, Loris,
Nycticebus, Tarsius, and Cheiromys^ or the Aye-aye.

FlG. 14. — A U3NOAKMED APE,

OR GIBBON (Hylobates).

FIG. 15.— A LEMUROID OF THR
GENUS Lemur.

FIG. 16.— THE AYE-AYE
(Clieiromys}.

II. CHEIROPTERA.— The Bats, including the Flying Foxes
(Ptcropus), the common bats, the Horseshoe and

i E.g. frogs, toads, efts.

1 6 ELEMENTARY ANATOMY. [LESS.

Vampire bats (Phyllostoma and Rhinolophus\ and
the Bloodsucker (Desmodus}.

III. INSECTIVORA. — Small insect-eating beasts, such as
the Mole, the Hedgehog, the Tanrecs (Centetes and
Hemicentetes], the Golden Mole (Chrysochloris], the
Shrew-Mice (which are not at all really mice),
Sorex, and the African jumping shrews (Macros-
celides}; also the so-called Flying- Lemur (which is
not a lemur), Galeopithecus.

FIG. 17.— A LEAPING SHREW FIG. 18.— THE FLYING-LEMUR

(Macroscelides). ( Galeopithecus).

IV. RODENTIA. — Mostly rather small animals, all formed
for gnawing, such as the Hare and Rabbit, the
Agonli, the Beaver, the Porcupine (Hystrix), the
Capybara, Dolichotis, the Squirrels, the Rats, the
Australian Rat (Hydromys), the Jerboa (Dipus\ the
Rat-mole (Spalax}.

V. CARNIVORA.— Beasts of prey, as the Cats, Lions and
Tigers, the Hyeras, Civet-cats, Dogs, Weasels,
Badger, Coatimonui, Racoon, the Ailurus, and the
Bears, the Otters and Sea-otters (Enhydrd],

VI. PINNIPEDIA.— The Seals (Phocd), Walrus ( Trich<echus\

and Sea-Bears (Otaria}.

VII. CETACEA.— The Whale-bone Whales, the Sperm
Whale, the Dolphins and Porpoises, including the
Pontoporia and Platanista and the Narwhal.
VIII. SIRENIA.— The Dugong and Manatee, with the ex-
tinct Rhytina and Halitherium, ^

IX. PROBOSCIDEA.— The African and Asiatic Elephant

and the extinct Dinotherium.

X. UNGULATA. — The Hoofed beasts, divisible into two
sub-orders : —

A. PERISSODACTYI.A. — Those with the functional toes of

the hind foot of an odd number, as the Rhinoceros,
the Tapir, the Horse and its extinct allies ; and

B. ARTIODACTYLA. — Those with the functional toes of

I.]

GENERAL VIEW.

the hind foot of an even number, as the Hippo-
potamus, the Hogs, the Peccaries, the Camels and
Llamas, the Musk Deer, the Deer, the Giraffes, the
Antelopes (including the Saiga and four-horned and
prong-horned antelopes), and Oxen, Goats, and
Sheep.
XL HYRACOIDEA. — Including only the genus Hyrax, one

species of which is " the coney" of Scripture.
XII. EDENTATA. — A very strange order, containing very-
diverse forms, namely : the two- and three-toed
Sloths (Cholcepus and Bradypus), with the extinct

FIG. 19. — THE HYRAX.

FIG. 20.— THE THREE-TOED

SLOTH
(Bradypus).

FIG. 21. — THE GREAT

ANT-EATER
(Mynnecophaga).

Mylodon and Megatherium, the Ant-eaters, the
Pangolins (see Lesson VII. for a figure), the Cape
Ant-eater (Orycteropus], and the Armadillos, in-
cluding the extinct Glyptodon.

FIG. 22.— THE CAPE ANT-EATER FIG. 23.— AN ARMADILLO

(Orycterofius}. (Dasypits).

The second sub-class comprises the Marsupials or pouched
animals only. It is called DIDELPHIA, and the animals
contained within it are termed Didelphous mammals,
consists of one order only : — . .

XIII. MARSUPIALIA.— A very varying group, containing
the true Opossums (Didclphys), the Kangaroos, the
Phalanges, the W^ombat and Koala, the Dasyures,
the Tasmanian Wolf (Thylacimis), the Bandicoots
(JPerameles), and Cheer opus.
C

*8 ELEMENTARY ANATOMY. [LESS.

The third sub-class comprises two very aberrant genera
only. It is called ORNITHODELPHIA, and the animals com-
prised within it are termed Ornithodelphous mammals. It
consists of one order only : —

XIV. MONOTREMATA. — Of this order
there are but two genera —
one the Echidna, the other
the Duck-billed Platypus or
FIG. 24.— THE DUCK-BILLED Ornithorhynchus.

f*££*£h* Tv^^T £vesA vntains al! thie

Birds (or feathered Vertebrates). It
is a very uniform class, containing only three sub-classes.

The first sub-class, the CARINAT/E, comprises all living
birds except those contained in the next sub-class, together
with the extinct Dodo and the Great Auk.

The second sub-class, the RATnvE, includes the Ostrich,
Rhea, Emeu, Cassowary, Apteryx, and the extinct Dinornis
and its allies.

The third sub-class, now extinct, the SAURUR^E, is as yet
only known to have contained that bird of the Oolite, the
Archaeopteryx.

FIG. 25.— THE OOLITIC FOSSIL BIRD FIG. 26. — THE FRILLED LIZARD

(A rclueopteryx). (Chlamydosaurus).

The class Reptilia embraces all the scaly, featherless, cold-
blooded creatures, and consists of nine orders.

I. CROCODILTA. — An order containing only the Croco-
diles, Alligators, and Gavials.

II. SAURIA. — A very numerous group, containing all the
Lizards, some of which are without legs, and might
be taken for serpents : the two-armed Chirotes,
the two-legged Bipes, Lialis, the Amphisbena, the
Chameleons, Geckoes, Iguanas, Monitors, Seines
(Cyclodus, &c.), the Agamas, the flying lizard, Draco,
and the exceptional genus Sphenodon.
ill. OPHIDIA. — In which are placed the harmless Snakes

GENERAL VIEW. 19

(Coluber, &c.), the tree-snakes, the sea-snakes, and
the very poisonous rattle-snakes (Crotalus], and
Cobras, together with all other Serpents.
IV. CHELONIA. — An order containing the Land Tortoises,
the Sea Turtles, and other fresh-water Terrapins,
including the Matamata and the European Einvs.
V. ICHTHYOSAURIA. — A group made up of the extinct
Ichthyosauri of the ancient seas.

FIG. 27.— AN IcHTHYosAfRus. FIG. 28.— A PLESIOSALRUS.

VI. PLESIOSAURTA. — An order for the similarly extinct

marine reptiles, the Plesiosauri.

VII. DICYNODONTIA. — Containing the genus Dicynodon.
VIII. PTEROSAURIA.— The extinct Reptiles of the air, which
flew like our existing bats, and consisted of the
genera Pterodactylus, Rhamphorhynchus, &c.
IX. DlNOSAURlA.— An extinct order of large Reptiles, one
of which, the Iguanodon, has left its bones on the
Wealden formation of the south of England. Igua-
nodon, Compsognathus, and Megalosaurus are other
interesting forms.

The class Batrachia is made up of four well-marked
orders : —

I. ANURA. — The Frogs and Toads — a very uniform group,
some genera of which, Ceratophrys, Ephippifer,
Dactylethra, Pipa, &c. will be referred to hereafter.
II. URODELA. — Or the Efts and Newts, amongst which the
Menopoma, Menobrancli us,
the two-limbed Siren, and
the Proteus of the Austrian
caves are worthy of special FlG.29._THE GREAT NORTH

mention. AMERICAN EFT, WITH

III. OPHIOMORPHA.— This order ^SSNTGILLs(^w<;'

contains limbless Batra-

chians with very .elongated bodies, having much the

appearance of small snakes.

IV. LADYRINTHODONTA. — These creatures are entirely

extinct, and form the genera Labyrinthodon, Arche-
. gosaurus, &>c.

The class Pisces has within it all the Fishes, properly so
c 2

ELEMENTARY ANATOMY.

[LESS.

called, excluding Whales and Porpoises (which, as we have
seen, are Beasts or Mammals) on the one hand, and Shell-fish
(which are Invertebrata) on the other. This class is divisible
into the following great groups : —

I. ELASMOBRANCHII. — An order of highly-organized
cartilaginous fishes — the Sharks (as Carchariast
Cesti-acion, Spinax, the Hammer-headed Shark,
&c.), the Rays (including Raia, Myliobates, Areto-
bates, &c.), and the Chimaera.

FIG. 30. — THE HAMMER-HEADED SHARK.
(Zygaiia).

FIG. 31. -THE EAGLE RAY
(Myliobatis).

II. GANOIDEI. — An important order containing many ex-
tinct forms, and a few very varied existing ones, as
the Lepidosiren, Ceratodits, Polypterus, Lepidosteus,
the Sturgeon, &c.

FIG. 32. — THE MUD-FISH (Lepidosiren}.

FlG. 33.— POLYPTERUS.

III. TELEOSTEL— The order containing the great bulk of
Fishes, and including the more remarkable Siluroids
(as Bagrus, &c.), the File-fishes
(Batistes], the Trunk-fishes (Ostra-
cioti), the Angler (Lophius), and
Frog-fishes (Chironectes), the Eels,
Pike, Salmon, Carp, Hippocampiis,
Odontoglossum,\\\t Soles, and other
flat fishes (Pleuronectidce), the
Parrot-fish (Scants), and very many
others.

IV. MARTSPOBRANCHIL— The Lamprey and Myxine, or
the lowly-organized cartilag'nous fishes.

FIG. 34 —A FROG-FISH
(Chironectes),

L] GENERAL VIEW. 2l

V. PHARYNGOBRANCHIL— Containing only that headless,
heartless fish without red blood— the Amphioxus or
Lancelet.

FIG. 35--THE LAMPREY FIG. 36.— THE LANCELET

( Petromyzon). (A mplrioxus) .

The foregoing list has been given to render comprehensible
the references to different animals which must be so often
given in the succeeding lessons.

In those lessons the several parts and organs of man's
body will be examined and described, not only directly, but
also in the reflected light to be derived from a' knowledge of
the more remarkable conditions of .the same parts in other
animals.

24. The organs of man's body may be divided into three
classes : —

I. Organs of Investment and Support (skeletal).
II. Organs of Motion and Innervation, i.e. Muscular and

Nervous. Structures, and organs of special sense.
III. Organs of Sustentation, i.e. nutritive, circulating, re-
spiratory, and excretory structures.

This division, however, is rather physiological than ana-
tomical, so that a more convenient classification (the one to
be adopted in the succeeding chapters) will be —

I. The Skeleton, both internal (endoskeleton} and external

(exoskeletoti).
II. The Muscular Structures.

III. The Brain and Nervous System.

IV. The Organs of Sense.

V. The Heart, Arteries, and Veins.
VI. The Alimentary Tube and its appendages,
VII. The Respiratory and Vocal Structures and the Excre-
tory Organs.

ELEMENTAR Y ANA TOMY. [LESS.

LESSON II.

THE SKELETON IN GENERAL, THE INTERNAL SKELETON,
THE BACKBONE, BREASTBONE, AND RIBS.

i. THE word " SKELETON"1 is popularly taken to denote
only the bones, or at most the bone and gristle which form
the internal support of the body.

An acquaintance with other animal structures, however,
shows that this signification is far too restricted ; for parts
which are bony in man 'may be cartilaginous (i.e. of gristle)
or even merely membranous, in other animals ; and conversely,
parts sometimes quite external, which are merely fibrous in
man, may be horn or bone, or contain bones and cartilages,
in other animals.

The nature and structure of fibrous tissue,2 of cartilage, and
of bone, have been sufficiently described in the first and twelfth
lessons of the " Elementary Physiology." It may, then, here be
shortly stated that the word skeleton, in its widest and most
scientific sense, should include not only the bones and car-
tilages, but also those fibrous structures (or membranes) which
surround such bones and cartilages, and thence radiating
invest every organ of the body, and finally clothe it externally
in the form of skin.

The whole skeleton, then, may be denoted by the term
Fibro-chondr-osteal 3 apparatus.

Fibrous tissue indeed penetrates the very bones them-
selves, and supports the marrow they contain ; it separates
each muscle from its neighbour, and surrounds and lines every
tube and passage in the body ; so that if every other tissue
could be dissolved away and yet this fibrous tissue be left,

1 Derived from a-at \/\to, to dry.

2 Each kind of substance of which the body is composed is termed a /issue.
Thus we speak of fibrous tissue and of osseous tissue or bone, also nervous
tissue, &.c.

3 Because partly fibrous, partly cartilaginous, and partly osseous.

ii.] THE SPINAL SKELETON. 23

\ve should have a complete outline model, as it were, of the
entire human frame.

Portions of this fibrous tissue which connect adjacent bones
and cartilages become very strong, and constitute the " liga-
ments " of the joints of the solid skeleton.

2. The skeleton as a whole is naturally divisible into two
parts, to be separately treated of.

(a) The external, peripheral skeleton, often called the EXO-
SKELETON,1 — the skin and its appendages.

(ff) The internal, central skeleton, often termed the ENDO-

SKELETON.2

The external skeleton will be considered afterwards. First
in order is the skeleton commonly so called, i.e. the internal
skeleton.

3. The ENDOSKELETON of man is composed of numerous
bones, together with cartilages and fibrous structures.

The number and nature of the solid parts vary with age.
In the earlier stages of existence there are no bones at all,
and the process of bone-formation (or ossification] having once
begun, goes on till the period of adult maturity is completed,
and indeed, to a less extent, throughout the whole of life.

Thus it happens that parts which are membranous in the
baby or cartilaginous in the youth, become bony in the grown
man ; and a continuation of the same process tends to fuse
together more and more, bones which at their first appearance
were separate and distinct.

Indeed, besides the coalescence of distinct bones, another
fusion of bony structures occurs. This is due to the fact
that the ends, or projecting portions, of what are essentially
and ultimate-ly one bone, arise as separate ossifications, which
are termed epiphyses? Thus the ends of the long bones of the
limbs are at first separate bones from the main part (or shaft)
of each long bone, and do not become continuous with the
shaft till near man's maturity.

The hard parts of the internal skeleton being those which
as a framework support the body, form points of attachment
for the muscles which move it ; the muscles employing the
different bones like so many levers, or fulcra, as the case
may be.

4. The great ma'ority of the bones are thus intended to
move one upon another, and the contiguous surfaces of such
movable bones form THE "JOINTS."

1 From tf ID, without. - From ifv&ov, within.

3 From ewi, upon, and <pvttv, to grow.

24 ELEMENTARY ANATOMY. [LESS.

The nature and mechanism of the different kinds of joint
have been described in the Seventh Lesson of " Elementary
Physiology," as well as the different kinds of movement which
the jointed bones are capable of performing. Joints may be
(a) immovable, (£) mixed, or (c] movable.

(a) When bones are immovably joined by an interdigi-
tation of their irregularly shaped margins (like the bones of
the roof of the skull), they are said to be joined by suture;
but they may also be immovably united by a ridge, or tongue,
on one bone being received into the grooved surface of
another bone.

(ff) When the motion allowed is exceedingly slight (as
between contiguous pieces of the backbone— or vertebrae),
adjacent plain surfaces are connected together by the addi-
tion of fibrous substance of one kind or another.

(c] When the motion allowed is greater, the adjacent surfaces
of the bones are coated with smooth cartilage, and motion is
facilitated by a fluid called synovial* Sometimes a third
and separated cartilage (termed inter-articular] is placed
between the cartilaginous surfaces of the jointed bones.

The most movable joints are those in which the adjacent
bones are articulated on the principle either of a pivot (like
that between the two uppermost bones of the neck), or of a

hinge (like that of the elbow),
or a ball and socket (like that
of the shoulder).

If one convex articulating
surface be globular, it is termed
a head; if it be elongated it is
called a condyle. If either of
these is borne upon a narrow
portion of bone, this latter is
FIG. 37.— Articulation of a large called a neck. If a pulley-like
spine, by shackle-joint, with a surface is formed by such a

bony plate (placed below) of . . . ,- , J A -,

the skin of a Siluroid fish. juxtaposition of two condyles

as to leave a depression be-
tween them, such an articular surface is named a trochlea?

The anatomy of animals (or xoofomy)3 as distinguished
from the exclusive study of man's own anatomy (or an-
thropotomy*} shows us that bones may be united in ways

1 From avv, with, and d>6v, an egg. The fluid is- contained in a fibrous bag
or sac.

2 From TpoXo<;, a pulley; -rp^a, to run.

3 i-uiov, an animal, and T^fiKi*, to cut.

4 uvtfpwTrot;, a man, and rtpveiv, to cut.

II.]

THE SPIRAL SKELETON.

other than those observed in the human body. Thus some
spiny bones of Siluroid fishes have a perforation at their
base, through which passes a bony ring attached to a plate
below — a shackle-joint. This structure, however, belongs to
the external skeleton.

5. The parts of the endoskeleton may obviously be grouped
into two divisions : —

(a) The skeleton of the head and trunk, which is called
the AXIAL1 skeleton.

(£) The skeleton of the limbs, which
is called the APPENDICULAR skeleton,
the limbs being regarded as appendages
of the axial skeleton.

First with regard to the axial skele-
ton. The skeleton of the head (i.e. the
skull) is supported on the very summit
of what is familiarly known as the back-
bone, while from each side of one region
of the latter the ribs reach forwards to
or towards the breastbone.

The skull is of so complex a struc-
ture as to require separate consideration.
The skeleton of the trunk only (that
is to say, the backbone with the ribs
and breastbone) will afford material
enough for this lesson.

6. The backbone, or, as it is often
called, the spine,2 consists of a number
of small bones placed one on the top of
the other like a pile of coins.

Each of these small bones is termed a
vertebra,3 and (with certain few excep-
tions, to be noticed later) consists of a
sort of irregular ring of bone, thickest in
front, from which certain bony promi-
nences stand out in various directions.

By the superposition of their rings,

they together form a long vertical canal

(called the vertebral canal), which is

' destined to contain and protect the spinal marrow (or spinal

cord). This series of vertebrae thus constitute the smaller,

' From being the skeleton of what is, as it were, the axis of the body.
2 The word "spine" is also frequently employed to denote any slender and
more or less pointed prolongation of a bone .

/ From v£ttre, to turn, thcujgh the mobility of most vertebrae is but slight.

_. 03.— Axial skeleton
of the trunk with the
ribs of the right side
removed to show the
vertebrae more dis-
tinctly.

26 ELEMENTARY ANATOMY. [LESS.

posterior cylinder of the human trunk, spoken of in the First
Lesson.

The thickened anterior parts of the vertebras are also
placed and adjusted one upon another, and by their super-
position form a vertical solid column, namely, that spoken
of in the first lesson as the partition separating the small
dorsal cylinder from the larger ventral one.

The thickened anterior part of each vertebra is called
its " body " or " centrum." The ring of the vertebra (which
springs from the centrum on each side of its posterior surface
meeting in the middle line behind) is termed the arch and,
because it contains part of the spinal cord, the neural r
arch — the spinal cord being, with the brain, the central part of
the nervous system.

The various bony prominences of the vertebras are termed
" processes."

The vertebrae are connected by joints of the second (or
mixed) kind. Their adjacent surfaces are for the most part
nearly flat, and we find interposed and connecting them a
dense fibrous body or disc, toughest and hardest towards its
circumference, with a pulpy substance in its middle. Each
such body is termed an intervertebral substance. No syno-
vial fluid lubricates the joints between the bodies of the
vertebrae, though present between the junctions of some of
the processes.

The vertebras are also held together by strong ligaments
which pass vertically down the centra, both in front of and
behind them.

7. The VERTEBRA are divisible into five different categories.

First come those of the neck, which are termed cervical?
They are seven in number.

Secondly, those of the back, which have the ribs attached
to them, and which bear the name dorsal. Of these there
are twelve.

Thirdly, we find certain large vertebras which do not
bear ribs : these are situate below the dorsal vertebrae, and
are called lumbar. There are five of them.

All the above vertebrae are termed " true vertebras,"
because they do not become anchylosed together, but remain
connected by ligaments and by intervertebral substances only.

Below these true vertebras come those which are called
"false," and which sooner or later anchylose together to form
two bony masses.

1 From i/eupoi/, a nerve. - From cervix, the neck.

n.] THE SPIXAL SKELETON. 27

The first of these two masses, termed the sacrum, comes
immediately beneath the lumbar vertebrae, and affords attach-
ment on each side to one of the haunch, or hip, bones. Five
or six sacral vertebrae coalesce to form the sacrum.

The second and much smaller bony mass, termed the
coccyx,1 is made up of three or four small and imperfect
vertebrae, named coccygeal.

8. Before proceeding to consider more carefully the different
vertebrae, a DORSAL VERTEBRA may first be described as a
type.

*

FIG. 39.— A DORSAL VERTEBRA.

c, centrum ; s, neural spine ; d, tubercular or transverse process ; /, capitular
process, or articular surface for the head of a rib ; /', small articular surface
for part of the head of the succeeding rib ; z, upper articular process, or
prezygapophysis ; z ', lower articular process, or postzygapophysis.

From each outer angle of the posterior surface of its
centrum there springs a pier of the neural arch. Each of
these two piers is termed a. pedicle.

From the hinder end of each pedicle a flat plate of bone
projects backwards and towards the middle line, till the two
plates meet and thus complete the neural arch. Each such
plate is termed a " lamina '' or neural lamina.

At the point of junction of the laminae a single median
process runs backwards and downwards. This is the spinous
process, or neural spine?

From the junction of each lamina with its pedicle another
process, ending -bluntly, juts outwards and backwards. This
is called the transverse process, and there are two to every
.iorsal vertebra.

From the upper and outer part of each lamina a brnall
process projects upwards, with a smooth surface on it which

1 From its fancied resemblance to a cuckoo's beak— KOKKV!-, a cuckoo.

2 Sometimes neurapophysis, from teDpuir, a nerve, and u7r6<pi;<7(<;, a process.

28 ELEMENTARY ANATOMY. [LESS.

looks mainly backwards. This is called the superior articular
process? or prezygapophysis, and each dorsal vertebra has,
of course, a pair of such.

From the lower- and outer side of each lamina a small
process projects downwards, with a smooth surface on it
which looks mainly forwards. This is called the inferior
articular process, or postzygapophysis, and there are two to
every vertebra of the back.

The articular surfaces of the two inferior articular pro-
cesses are applied to the articular surfaces of the two
superior articular processes of the next vertebra below.
Ligamentous fibres bind together the margins of the apposed
articular surfaces, between which is placed a sac containing
synovial fluid.

The upper margin of each pedicle is somewhat concave, while
its lower margin is more so. In this way, when the vertebrae
are naturally articulated together, a rounded opening appears
between each pair of adjacent pedicles. These openings give
exit to spinal nerves coming out from the spinal marrow
enclosed within the neural arches.

Two other articular surfaces on each side should be noted :
one at the outer side of the posterior and outer angle of the
centrum at its junction with the pedicle, the other at the
anterior aspect of 'the end of the transverse process. The
first of these articular sources is termed " capitular? and the
second " tubercular? for reasons which will appear later.

The diameter of the centrum from side to side exceeds but
little its diameter from behind forwards.

•Fie. 40. — A CERVICAL VERTEBRA. •

c, centrum ; s, neural spine ; « /, neural lamina ; d, posterior or tubercular
transverse process, or diapophysis ; /*, anterior (or capitular) transverse pro-
cess, or parapophysis ; d' and/', "tubercles;" z, prezygapophysis.

9. Of the seven CERVICAL VERTEBRAE, the first two are
sufficiently exceptional to demand separate notice. Any

1 From Trpof, tvyov, a yoke, and uTrdf i'<nc.

IT.] THE SPINAL SKELETON. 29

one of the other cervicals, when compared with a dorsal
vertebra, presents the following characters : —

The centrum is smaller, wider in proportion to its depth,
somewhat concave from side to side on its upper surface, and
from before backwards on its under surface.

The neural canal and neural arch are wider, and the neural
spine much smaller and shorter (except in the case of the
seventh cervical vertebra), and often bifid, so that there are
two irregular processes projecting side by side.

There is no long transverse process, but a short one juts
out from between the zygapophyses (therefore in the situation
of the transverse process of a dorsal vertebra), and another
projects from the body at the root of the pedicle, just at the
place where the capitular articular surface of a dorsal vertebra
is placed, and so may be called the capitular process. These
two short processes are connected towards their ends by a
bridge of bone which extends backwards and somewhat down-
wards from the capitular process to the posterior process.

A space is thus enclosed on each side by the pedicle, the
two processes and the bridge, and it is on this account that
the cervical vertebrae are sometimes said to have perforated
transverse processes.

As these processes are superimposed like the vertebrae that
support them, these successive, small, bony rings form a sort
of bony canal running upwards on each side of the neck-part
of the backbone, and this canal serves to protect the vertebral
artery which traverses it. The free end of each transverse
process divides into two blunt prominences called " tubercles."

FIG. 41.— THE Axis VERTEBRA.

r, centrum ; s, neural spine ; d, tubercular process ; /, capitular process ; a, an-
terior articular surface for atlas ; z, postzygapophysis ; o, odontoid process ;
hyt median vertical ridge beneath centrum.

10. The second cervical vertebra is peculiar, differs from
every other joint of the backbone, and has a special name,
the AXIS.

30 ELEMENTARY ANATOMY. [LESS.

It differs from all the other vertebrae in having a large blunt
process of bone (like a peg) continued upwards from its cen-
trum. This is the odontoid* process, and it has on its front
aspect a smooth articular surface.

The front surface of the rest of its body often bears a
slightly marked median vertical prominence.

The axis also differs from all the other cervical vertebrae
in having its neural spine stouter and rather more projecting,
though still bifid at its apex. Moreover there are no pre-
zygapophyses, but instead, there is on each side a large
articular surface in front of the root of the capitular process.

ii. The first cervical vertebra is also quite peculiar, and
bears the special name "ATLAS," because it supports the
head.

FIG. 42. — THE ATLAS VERTEBRA.

s, rudiment of neural spine ; d, tubercular process ; p, capitular process ; a, ar-
ticular surface for skull ; hy, plate of bone holding the place of a centrum, and
articulating with the odontoid process of the axis vertebra.

It differs from every other vertebra in having no true centrum,
its two lateral halves being connected together in front by a
plate of bone, which articulates by its hinder surface with the
front surface of the odontoid process of the axis, while its
own front surface developes a slight median prominence.

While in the axis the neural arch is slightly deeper and the
neural spine larger than in the other cervical vertebrae, in
the atlas the neural arch is much more slender, while the
neural spine is absent, or represented by a small tubercle
only. The neural arch is either perforated or deeply notched
above, just behind the root of the transverse process, which
is longer and larger than in the other cervical vertebrae.
Zygapophyses are entirely wanting, but we find a large
articular surface developed both below and above the r6ot of
the transverse process of each side.

The two lower of these articular surfaces join those before

1 From 65ou£, a tooth, and €i3o£, form.

ii.] THE SPINAL SKELETON; 3i

mentioned as correspondingly situate on the axis vertebra.
The upper pair of surfaces, which are larger and more
cup-shaped, articulate with two prominences on the base of
the skull.

The atlas vertebra is formed to turn on the odontoid pro-
cess of the axis as on a pivot. This is further explained in
the Seventh Lesson of " Elementary Physiology."

12. Having noted the characters of vertebrae above the
typical dorsal ones, those below (i.e. the lower dorsal and
lumbar) come next.

The lower dorsal vertebrae have their centra larger than
those of the upper, while their transverse processes become
shorter, and their articular processes change their direction,
the upper zygapophyses looking obliquely inwards, the lower
ones obliquely outwards. Finally, their neural spines project
less downwards.

In the. last dorsal vertebra a small rounded prominence
arises from the posterior margin of each upper articular
process. This prominence is termed the mammillary process,
or Metapophysis.1

Another small prominence projects backwards from
between the upper articular process and the transverse pro-
cess, and is called an Anapophysis.2

FIG. 43-— A LUMBAR VERTEBRA.

c, centrum ; s, neural spine ; /, tubercular process ; z, prezygapophysis ;
z', postzygapophysis ; Jit, metapophysis ; a, anapopnysis.

The LUMBAR VERTEBR/E have their centra still more mas-
sive than the dorsal centra, and deeper in front than behind.

The neural spines are all more massive, and project directly
backwards instead of downwards.

The transverse processes are larger, and there are no tuber-
cular or capitular surfaces, and no process in the place of
the latter, as are found in the cervical vertebrae. •

i From M«T«, after, and apophysis. 2 From uv«, backwards.

ELEMENTAR Y ANA TOMY.

[LESS.

Metapophyses and Anapophyses, visible on the first lumbar
vertebra, disappear on lower ones.

13. Below the lumbar vertebrae comes a solid complex bone
before mentioned — the SACRUM, of a roughly triangular form,
with one angle downwards. Its front surface is strongly con-
cave vertically, less so transversely. It is really made up of
five vertebrae fused together, and plain traces of its original
composition remain in the fully ossified bone of the most
aged individuals.

The centra diminish in size from above downwards through
the sacral series.

The neural canal, completed as usual (i.e. by bone) above,
remains unossified and closed by membrane only at the lower
end of the sacrum, through the imperfect development of the
neural arches of the inferior sacral vertebras.

Neural spines form a median, backwardly projecting ridge
behind the sacrum, which ridge projects most above.

Transverse processes are largely developed, especially
above. By their anchylosis they form the lateral masses of
the sacrum.

On both the anterior and posterior surfaces of the sacrum
four apertures, one oeiow the other, are visible on each side.
This appearance is produced by coalescence of the sacral
transverse processes, thus : —

FIG. 44.— FRONT AND BACK ASPECTS OF THE SACRUM.

«, auricular surface ; z, prezygapophys:s at upper end of posterior surface
of sacrum.

Nerves, as before said, pass out on each side between the
pedicles of adjacent vertebrae. Now the coalescence of the
sacral transverse processes necessarily changes each such
intervertebral opening into a pair of openings, of which one is
dorsal and the other ventral.

n-] THE SPINAL SKELETON. 33

At the summit of the sacrum is a pair of articular pro-
cesses, which join the lower articular processes of the last
lumbar vertebra.

The lower end of the sacrum is devoid of similar pro-
cesses, or has them only represented by rudiments.

On each side of the upper part of the sacrum 'is a laro-e
irregular surface, which is coated with cartilage, and articu-
lates with the hip or haunch bone. This is called the
auricidar1- surface.

14. The last part of man's spine is, as has been said alreadv
the COCCYX, which consists usually of four rudimentary
vertebr£e, completely or partially united

so as to form a small conical bone.

Its uppermost part (i.e. the first
coccygeal vertebra) articulates with the
lower end of the sacrum, not only by
its centrum, but also by two little arti-
cular processes; it has besides two FIG. 45. -THE COCCYX
rudimentary transverse processes and At its end are ^

rudimentary pedicles, between which two prezygapophyses.
latter membrane alone extends to close

the neural canal. Below this the coccyx is destitute of pro-
cesses, and consists of but smaller and smaller vertebral
centra fused together.

Thus the last vertebra is the very opposite of the first (or
atlas), being all centrum, while the atlas has no centrum at
all. The coccyx usually becomes anchylosed to the sacrum
about or after the middle of life.

15. The WHOLE SERIES of vertebras are so disposed that
the backbone, when seen in profile, forms four sigmoid curves,
directed alternately forwards and backwards (see Fig. 38).
Thus in the neck it is slightly convex forwards, more
convex backwards in the dorsal region, rather strongly
convex forwards in the loins, while below this the terminal
part of the column sweeps round in a more marked curvature
concave in front, the coccyx continuing onwards the vertical
curve of the sacrum.

These gentle curves together form a line of beauty, and
give to the vertebral column a strength ten times greater
than it would have were it quite vertical.

The thickness of the front part of the backbone (formed of
the vertebral centra) increases slowly downwards to the

1 From its resemblance to the outline of t'ie external ear.
D

34

ELEMENTAR Y ANA TOMY.

[LESS.

summit of the sacrum, and then decreases very much more
suddenly.

The anterior surface is broadest at the neck, the loins, and
sacrum, and bears no median prominences.

The posterior surface bears a median series of spines, which
are longest in the last cervical vertebra and in the trunk.
They are all directed either downwards or backwards — never
upwards.

The true vertebrae, except the first two, are locked together
by articular processes and by the bodies, which latter are
united by intervertebral substances. No other articulations
exist between them.

1 6. The breastbone, or STERNUM, extends along the front

FIG. 46.— RIGHT SIDE OF THE THORAX.
i — 12, the ribs ; ms, the manubrium ; xp, the Xiphoid process.

portion of the trunk in the middle line, but its size, com-
plexity, and importance are very much less than the back-
bone's.

It receives the ends of the upper ribs, protecting the chest
in front, and sheltering the heart.

ii.] THE SPINAL SKELETON. 35

The bone is flat. Of nearly equal width for the greats-
part of its length, it broadens out above and narrows greatly
at its lower end.

The broad upper part to which the first rib is annexed is
called the manubrium or pre-sternum.1-

The narrow lower end, which projects freely and remains
cartilaginous till late in life, is called the xiphoid2 process.

17. The RIBS are long, slender, curved bones, which extend
from the spine, and some of them join the breastbone or
sternum. They are twelve in number on each side. The
seven upper ribs on each side join the sternum by cartilages,
and are termed " true ribs." The five lower ribs do not join
the sternum, and are called "false ribs." The first rib is
much stouter and shorter than the others.
. Each rib, or costa (except the last two on each side), has a
double attachment to the backbone. At its hinder end is a
rounded "head," which articulates with the capitular surface
of the dorsal vertebrae. A little distance from this there is
on the outer side a rounded articular prominence called the
" tubercle? which joins the articular surface on the anterior
side of each transverse process of the dorsal vertebrae.
Between the head and tubercle is a narrower interval called

Each rib ends at its ventral termination in an elongated
cartilage called " costal? Those costal cartilages which are
attached to the true ribs, have somewhat pointed inner ends,
and these join the sides of the sternum. Those of the false
ribs either (as those of the upper three) blend with the lower
border of the costal cartilage next above, or else end freely in
a blunt point. The backbone and breastbone, with the ribs,
form together a sort of bony cage, called the skeleton of the
thorax? which is narrow above, broaj and widely open
below, and wider at its greatest breadth than it is deep at its
greatest depth from before backwards.

This variation in its dimension from above downwards is
produced by the corresponding variation in the length of the
ribs, which increases from the first to the eighth, and then
gradually decreases.

1 8. The DEVELOPMENT of the skeleton of the trunk, or
spinal endoskeleton, is briefly as follows : —

From each side of the primitive groove, mentioned in the
First Lesson, a longitudinal fold extends up on each side

1 A handle ; maims, a hand. 2 From ?/i/>o£, a sword ; eiioc, like.

3 From 6>t«pa£, a breastplate.

D 2

3S ELEMENTARY ANATOMY. [LESS.

(called lamince dorsales), and these meeting above form a
canal (the neural canal), while beneath the primitive groove
runs the notochord, or chorda dorsalis.

Two other longitudinal folds (called lamina ventrales}
extend down — one on each side from the notochord — and
ultimately meet below. Each lamina ventralis splits longi-
tudinally (the split extending up towards the notochord), the

FiGi 47.— DIAGRAM OF THE DEVELOPMENT OF THE TRUNK AND ITS SKELETON

AS SHOWN IN A SECTION OF THE TRUNK MADE AT RIGHT ANGLES TO ITS
LONG AXIS.

Id, lamina dorsalis ; nc, the neural canal ; n, the notochord ; ex, cartilage ex-
tending dorsally and forming the foundation of the neural lamina;/^, cartilage
extending ventrally in lye, which represents the outer part of the split wall of
the ventral lamina ; Ivi, the inner part of the split wall of the ventral lamina,
forming by ven'.ral union with its fellow on the opposite side the alimentary
tube ;//, the pleuroperitoneal space between the outer and inner split walls of
the ventral laminae.

inner fold of each such split uniting with its fellow of the
opposite side to form the alimentary canal, while the two
outer folds of the split form the body wall.

Cartilage becomes deposited at intervals along each dorsal
lamina, and surrounds and encroaches on the notochord, so
that we come to have a series of cartilaginous segments
(representing the future vertebrae), the neural laminae of
which are in the dorsal folds.

Similarly, cartilages extend down in the outer part of the
split wall of the ventral laminae. These are the cartilaginous
predecessors of the ribs, which, by their fusion in the mid-
ventral line, form the sternum.

Bone is deposited in the centra (nothing of the notochord
being left but the pulpy substance in the middle of the inter-
vertebral substances), in each neural arch, in each rib, and in
successive portions of the sternum.

Besides these separate ossifications there are also the
epiphyses, which long remain distinct as bony discs, one above
and one below each centrum ; and there are also epiphyses
in the form of little bony caps to the various processes. The

ii.] THE SPINAL SKELETON. 37

transverse processes of some at least of the cervical vertebras
arise as distinct ossifications, as also do the lateral bony
pieces in the sacrum.

In the axis vertebra not only do the transverse processes
arise as separate ossifications, but primitively both the body
and the odontoid process are distinct bones, and even an
epiphysis is formed between them, as well as below the cen-
trum and at the summit of the odontoid process.

The anterior part of the ring of the atlas also arises as a
separate ossification.

19. We will now pass on to the relations existing between
OTHER ANIMALS and man with regard to the spinal skeleton.
As most animals have their bodies horizontal, confusion in
descriptions is apt to arise from parts being " anterior " in
them which in man are " superior," and irice "versa. To avoid
this ambiguity, it will be well to imagine an axis drawn at
right angles to the general direction of the backbone. Then
all parts which in man are relatively superior, and in beasts
anterior, can be termed prc-axial in all cases ; and similarly,
parts relatively inferior in man, and in beasts posterior, can
be spoken of as post-axial : such terms referring not to the
long axis of the skeleton, but to the imaginary line drawn at
right angles to it.

In that man's spine is made up of distinct and ossified
vertebras, man agrees with the vast majority of the members
of his sub-kingdom. Yet, in the class of Fishes, there are
many examples (as in the Sturgeon, Lepidosiren, and Lam-
prey) of the persistence throughout the whole of life, of the
notochord, or chorda dor satis, of the embryo. Moreover,
when th'e spine is fully ossified, and even in man's own class
(Mammalia) it may be that the greater number of the ver-
tebrae are anchylosed together into a solid bone, as in the
extinct Glyptodon.

Instead of being connected as in man, the adjacent
vertebrae may be connected only by synovial sacs, as in
Snakes, or by intervertebral substances, perforated in the
middle ; and such sacs (as in Birds), or a large part of the
primitive notochord (as in most Fishes), may persist between
each pair of bony centra.

That degree of union which exists among the different
parts of one vertebra in man, does not by any means obtain
in all cases. Thus; in the extinct Ichthyosaurus the neural

38 ELEMENTARY ANATOMY. [LESS.

arch was permanently distinct from (i.e. unanchylosed with)
the centrum, and in the Carp the transverse processes are
separate. Even the neural arches may be made up of two
separate pieces on each side, as in Elasmobranch fishes, e.g.
Raia and Spinax.

That degree of adjustment of parts which exists in each
vertebra of man is not universal. Thus, e.g., we find in the
Tortoises neural arches- so shifted as to be respectively
annexed to* two centra, and thus the intervertebral foramen
comes to be placed opposite the middle of each vertebral
body.

A similar displacement takes place in the upper parts of
the divided neural arches of the Elasmobranchs just referred
to, so that the parts are united by a zigzag suture.

c

FIG. 48. — AXIAL LONGITUDINAL §ECTION OF THE VERTEBRAL COLUMN OF AN
ELASMOBRANCH (Raia).

c, one of the centra which, being bi-concave, forms lozenge-shaped sections by its
junctions with the concave surfaces of adjacent vertebral centra; s,.a. neural
spine ; «2> one °f tne dorsal parts of a neural lamina ; nlt one of the ventral
parts of a neural lamina.

20. The NUMBER of vertebrae in man is far less than exists
in most Vertebrates, though more than in some. No Verte-
brate has much less than a third his number — even the Frogs
having ten.

On the other hand, some sharks have more than eleven
times as many vertebras as man, and some serpents more even
than a dozen times his number.

Man has the smallest number existing in his own class,
with the exception of some Bats and Monkeys.

21. The division of the vertebras into the five CATEGORIES
of man's vertebral column is common to most forms above
Fishes, but we may find the lumbar vertebras indistinguish-
able and the sacral absent ; and in Fishes we can hardly
define even a single cervical, the vertebras being reduced to
but two categories, namely, those of the trunk and those of
the tail.

ii.j THE SPINAL SKELETON. 39

The division of the vertebras into true and false is seen to
be a very arbitrary one when we extend our view, as all are
"true" in Serpents, and those which are "false" in man are
true even in some members of his own class, e.g. the
Cetaceans. On the other hand, many vertebrae which are
reckoned to be "true" in him are "false" in other animals.
Thus, in Birds the process of anchylosis invades the lumbar
and dorsal vertebrae. In Tortoises all the trunk vertebrae are
fused, and therefore "false," while in the Glyptodon none
of the vertebrae except the coccygeal can be said to be
" true " ones.

Again, vertebrae may be more thoroughly " false " than even
in man, as in the sacrum of the Rhea (or American
Ostrich), where between the hip-bones they abort, and are
represented only by a long narrow strip of bone. Distinct
vertebrae are developed both pre-axially and post-axially to
this strip. "Degradation" is a constant character of the
last vertebrae in all classes of Vertebrates.

22. As to VERTEBRAE in GENERAL, the neural arch is the
constant character of a vertebra — persisting even where (e.g.
in Lepidosireri) the bodies are not formed.

Two neural arches may correspond to one centrum, as
in some Elasmobranchs ; and merely cartilaginous neural
arches may exist, as in the Sturgeon. The arch may present
processes which are not developed in man. The two laminae
may (as on the Axolotl) fail to meet together on the dorsal
aspect.

The centrum, or body, may have its opposite surfaces
strongly convex or concave, contiguous vertebrae uniting by a
ball and socket joint, instead of being flat or nearly so, as
in man.

The ball may be post-axial in each vertebral body, a struc-
ture termed proccelous? and found e.g. in existing crocodiles ;
or the ball may be pre-axial, which condition is called opis-
thoccelous? and is more rare, but is found e.g. in the land
Salamander, and even in man's own class, as in the cervical
vertebrae of the Ruminants.

The vertebrae may have both surfaces hollow, a structure
called amphicoelous ; 3 or bi-concave, a condition found in
most Fishes, and even some Reptiles, as the Geckoes. The
osseous bodies may be reduced to mere rings encircling the

1 From vrpo, before, and KoIXog, hollow.

2 From oTTia-Oe, behind, and KoiAo^.

3 From a'jutf><, both, and KIH\O£.

ELEMENTARY ANATOMY.

[LESS.

notochord, as in some Elasmobranchs, or to mere cartila-
ginous rudiments in its sheath.

Sometimes (as in the first coccygeal vertebra of the croco-
dile) a vertebra may be bi-convex, or have a ball at each end ;
and very rarely two prominences or two hollows may exist
side by side on one surface of a centrum, as in some cervical
vertebras of Chelonians.

The articulating processes (zygapophyses) are very con-
stant structures, and are substantially as in man, except that

FIG. 49. — LATERAL VIEW OF FOUR TRUNK-VERTEBRAE OF SIREN.
c, capitular process ; t, tubercular process ; i, interzygapophysial ridge.

in fishes they cannot be said to articulate truly. A strong
interzygapophysial ridge may connect together the pre- and

post-zygapophyses of each
side of a vertebra, as in
Siren.

The transverse processes
are structures too complex
to be more than referred to
under this general heading.
The conditions exhibited by
them in man are such as
obtain generally, but by no
means universally, in Verte-
brates above fishes. Two
transverse processes may be
developed from each side of
the same vertebra and in
the same plane. This may
be seen in the posterior coc-
cygeal vertebras of Apes and
other Mammals, and at least
occasionally in some verte-
bras of Polypterus.
The spinous processes of man are less developed than in the
Vertebrata generally. They are, however, considerably more so

FIG. 50.— UPPER SURFACE OF TWELFTH
CAUDAL VERTEBRA OF LEOPARD, §.

in, metapophyses ; p, processes serially
continuous with those which support
the posterior zygapophyses in the an-
terior vertebra ; t, transverse processes ;
t', anterior transverse process.
(From Prof. Flower's '''Osteology.")

II.]

THE SPINAL SKELETON.

than in many Vertebrates, e.g. than in Bats and Birds. Their
occasionally bifid condition in man may be repeated in much
lower Vertebrates (e.g. Axolotl), and sometimes (as in Poly-
pterus] there may be two neural spines to one vertebra, one in

FIG. 51. —Dorsal view of Sixth, Seventh,
and Eighth Post Sacral Vertebrae of
the Axolotl, showing the laterally bi-
furcating neural spines, each concave
at its extremity.

(From the College of Surgeons '
Museum.)

FIG. 52.— Six TRUNK-VERTEBRA OF

POLYPTERUS.

The third and fourth vertebrae have
each two transverse processes and
four ribs on the side shown ; the
third vertebra has also two neural
spines, s, neural spine ; p, lower
ribs. The series of upper ribs is
not distinguished by any letter.
(From the College of Surgeons '
Museum, )

the front (i.e. pre-axial) of the other. Indeed, in the Conger we
have two such projections from each side of the neural arch.

In certain flat fishes they may be detached from the arches
and intercalated between them. They may expand and
simulate dermal scutes, as in the Tortoises. They may project
through the skin of the back, as in the Potto, or be produced
into long, free filamentary processes, as in the Lizards called
Basilisks.

The intervertebral foramina of man are normal, but in

FIG 53. — Seven Trunk- Vertebrae of the Potto, showing the nervous perforations
in the neural laminae.

some animals, even so nearly allied to man as the Potto,
also in the Horse, Ox, Monotremes, and others, the nerves

ELEMENTARY ANA TO MY.

[LESS.

pass out through perforations in the neural arches them-
selves, and not between the notches of contiguous arches.

There may be additional parts and processes which are
quite wanting in man, except as represented by the slight
median ridge in front of the axis vertebra.

Such are the processes (sometimes median and azygos,1
sometimes paired) which appear on the ventral aspect of the
centrum in many animals, and which are termed hypapo-
physes.2 They may exist as single processes, as in the Hare
and in poisonous Serpents, which have them developed

FIG. 54 — ANTERIOR SURFACE OF THE
LUMBAR VERTEBRA OF HARE (Lejus
timidus).

FIG. 55. — ANTERIOR SURFACE OF
TWELFTH CAUDAL VERTEBRA
OF LEOPARD.

in, metapophysis ; /, processes
serially continuous with those
which support the posterior
zygapophyses in the anterior
vertebra ; h, hypapophyses. The
process on the side of the body
between m and h is the anterior
transverse process.
(From Prof. Flower's "Osteology."}

s, spinous process ; m, metapophysis ; az,
anterior zygapophysis ; t, transverse
process ; h, hypapophysis.
(from Prof. Flower's " Osteology"}

throughout the greater part of the vertebral column. In the
harmless snake Rachiodon some of these processes extend
into the oesophagus (swallow), and becoming coated with a
toothlike substance, act as teeth. Hypapophyses may be
developed as paired processes, as in the coccygeal vertebrae
of many beasts, or they may be in the form of Y-shaped
arches, as we commonly find them beneath some or other of
the coccygeal vertebrae when these latter are large and
numerous.

23. DORSAL VERTEBRAE, if by that be meant "vertebrae
bearing ribs," are constant parts in all Vertebrates, save
those in which, like the Lancelet and Marsipobranchs, neither
vertebrae nor annexed lateral and body-encircling structures

1 Azygos, from a, not, and £"?<'?> a fellow. This term is applied to parts
which are single, as opposed to tho-e which exist in pairs.
'2 From UTTO, under, and apophysis.

I L] THE SPINAL SKELE TON. 43

become distinctly solidified. Inasmuch, however, as man's
dorsal vertebrae form a series the first of which bears ribs
which join a sternum, man agrees with all Vertebrates (ex-
cept Serpents) above the Ichthyopsida ; but he differs from
the whole of the last-named vast group, as in that group
there is either no sternum or else no ribs which join it.

In their number the dorsal vertebrae of man are a little
below the average of his class, in which the number may
be augmented to twenty, as in the Elephant, or doubled (i.e.
twenty-four) as in the Two-toed Sloth, or on the other hand
reduced to ten, as in Azara's Armadillo. Comparing the
condition existing in man with that in the Non-Mammalian
Vertebrates above Fishes, we find his number to be smaller
than that in most Reptiles, but somewhat greater than in
Birds, where, on account of the prodigiously enlarged sacrum,
but three (e.g. Ciconia alba], seven or nine, or, very rarely,
eleven vertebrae are reckoned as dorsal.

In the main proportions of the centrum (the greater
height in proportion to breadth, smaller medullary canal,
elongated spinous processes, the articular process, short
transverse processes, and considerable lateral notches), these
vertebrae in man agree with thpse of other Mammals.

Often, however, the spinous processes may be very much
more prolonged, as in the Ungulata (e.g. the Ox and the Horse),
or they may be swollen at their summits, and more or less
anchylosed together, as sometimes in the true Opossums. On
the other hand, they are sometimes almost or quite absent,
as in Bats.

FIG. 56. — DIAGRAM OF A SECTION OF SHELL OF A TORTOISE MADE TRANS-
VERSELY TO THE LONG AXIS OF THE SKELETON.

ns, neural spine ; r, rib ; ic and hp, ventral plates not belonging to the true axial
skeleton.

The most remarkable modification of dorsal vertebras is
that in Tortoises and Turtles, where the neural spines ex-
pand at their summits into wide plates which articulate by

44

ELEMENTARY ANA TOMY.

[LESS.

suture with each other and with similarly expanded ribs, to
form the " shell " or carapace. These plates are so externally
situate as to be invested only by a horny form of skin.

FIG. 57. — DORSAL SURFACE OF A SHELL OF A FKESH-WATER TORTOISE
(Emys}.

i —8, expanded neural spines ; r1 — r^, expanded ribs. (The dark lines indicate
the plates of the horny investment of the skeleton.)

The transverse processes generally articulate with the
tubercles of the ribs, while the sides of the bodies bear
the heads of the ribs. This mode of articulation, however,
is not constant even in man's own class, as in the posterior
thoracic vertebrae of the ordinary Dolphins, where there are
no surfaces for the heads of ribs, the ribs are attached to the
ends of the transverse processes only ; while in the Sperm
Whale group (Physeteridcz] the ribs are attached exclusively
to parts which answer to the capitular surfaces of man.

The notches for the spinal nerves, as has been said, are
not constant structures, but sometimes are replaced by
direct perforations of the neural laminae.

The flatness of the surfaces of the vertebral bodies in man
is a condition constant in his class, but in Birds these
surfaces are concave in one direction and convex in another.
A ball and socket or a bi-concave articulation is to be
found in yet lower forms.

That the only articular vertebral processes are the
zygapophyses, is a character man shares with most of his

THE SPINAL SKELETON.

45

class. It is possible, however, for the neural spine to send

back a pair of processes (hyperapophyses '),

as in Galago, &c., embracing the neural

spine next below, or, as in Dolphins, that

a pair of metapophyses may project pre-

axically from one spine and embrace that

of the next vertebra. These, however, do

not support articular processes, and are

rather checks than joints.

But a much more complex mode of arti-
culation is possible. Thus, in Serpents and
Iguanas we may have a median prominence
with two articular surfaces, developed from
the pre-axial surface of the neural arch, and
fitting into a corresponding concavity on the
post-axial surface of the vertebra in front.

This pre-axial wedge-shaped process is
called the zygosphene? and the "correspond-
ing post-axial excavation is termed the
zygantrum.3

The maximum of dorsal joint complica-
tion, however, is found in the last dorsal
vertebra of certain Edentates, e.g. the Great
Ant-eater. Here each postzygapophysis
develops two additional articular surfaces,
one on each side of a notch, which receives
a process from the pre-axial side of the
neural arch, which process is furnished with
two corresponding surfaces — there thus
being three articular surfaces on each side
of such vertebra, fitting into corresponding
surfaces of the vertebra adjacent in the
mode known in carpentry as " tenon and
mortice."

In so far as man's dorsal vertebrae are all
free (i.e. true vertebrae), he agrees with other
Vertebrates, except such abnormal forms as
Chelonians and the Glyptodon, and except
also Birds, in which anchylosis unites a
greater or less number of the vertebrae next
the lumbar region.

C

rl

1 From vvfp, beyond, over, and apophysis.
- From ^vfitv, a yoke, and <r<pi]t , a wedge.
3 From £vi6v, and avrpov, a cavity.

FIG. 58. — SPINAL
COLUMN OF
GALAGO.

2, postzygapophyses ;
/;, hyperapophyses.

46

ELEMENTARY ANATOMY.

[LESS.

Those small and insignificant processes which make their
appearance as mere rudiments on the last dorsal of man are
commonly much larger in other Mammals, and may be
exceedingly developed ; as, however, they attain their maxi-

FIG. 59.— FRONT AND BACK VIEW OF A VERTEBRA OF A RATTLE-SNAKE
(Crotalus).

c (in left-hand figure), concavity of pre-axial surface of centrum ; c (in right-
hand figure), convexity of post-axial surface of centrum ; s; neural spine ; hy,
hypapophysis ; 0', post-zygapophysis ; tl, tubercular process ; t2, capitular
process ; /3, peculiar extra transverse process ; za, zygantrum ; zs, zygosphene.

mum in the lumbar region, they will be better described
hereafter. They are not certainly present in Vertebrates
below Mammals. But in some Chameleons (e.g. C. Parsonii}

FIG. 60.— SIDE VIEW OF TWELFTH AND THIRTEENTH THORACIC VERTEBR/E OF
GREAT h.

m, metapophysis ; tc, facet for articulation of tubercle of rib ; cc, ditto for capitulum
of rib ; azt anterior zygapophysis ; az1, additional anterior articular facet ;
pz, posterior zygapophysis ; pz l and pz 2, additional posterior articular facets.
(From Professor Flower s "Osteology ")

a prominence is developed from each prozygapophysis, which
may be a metapophysis, and this attains a very great size in
some C.olubrine snakes. In Birds such a process exists,

ii.] THE SPINAL SKELETON'.

47

though less developed, in the posterior cervicals of the
Great Auk.

The articular surfaces which support the ribs in man are
normal in his class. Sometimes, however, each vertebra
carries but one surface— that for the head of the rib (as in
the Dolphin). The two articular surfaces may coexist at
different levels on one single process, as in the dorsal verte-
brae of the Crocodile ; or they may be in close apposition,
and, as it were, fused together, as in Serpents ; or they may
be raised on two quite distinct processes — one dorsal, the
other ventral — as in the Ichthyosaurus and in Menobranchus.

We find in some serpents peculiar processes (Fig. 59, t$)
extending ventrally and pre-axially from the base of the
inner side of the transverse processes.

The even surface of the anterior (ventral) aspect of the
dorsal vertebrae of man is very different from what we find in
some animals, as e.g. the Penguin, Cormorant, and many
serpents, where there are long hypapophyses equalling or
exceeding the neural spines in length.

24. The CERVICAL VERTEBRAE of man, in that they are
seven in number, conform to a law which is singularly con-
stant in his class, whatever the length of the neck, whether
it be extremely long, like that of the Giraffe, or like that of the
Porpoise, reduced to a minimum. Nevertheless, this law is
not absolutely universal, as there are one or two singular
exceptions amongst Mammals. Thus the Three-toed Sloth
has nine cervical vertebras, while one of the Two-toed kind
(Cholcepus Hoffmannii] and the Manatee have but six.

In Sauropsidans the number is greater, and sometimes
there are as many as twenty-five, as in the Swan. In Batra-
chians but a single vertebra can be called cervical, and
none merit the name in the class of Fishes. Nevertheless,
the first three or four vertebras next the head may, in some
fishes, present a marked difference from those vertebrae
which succeed, being much elongated and all united by
suture, as in Fistularia and JBagrus, and they may, as in the
latter fish, develop a continuous hypapophysial canal. The
second and third vertebras may form a hollow bladder-like
case of bone, as in Cobitis, or send outwards or downwards
special processes, as in the Carp.

In that the cervical vertebras of man are smaller than
those in the other regions, he agrees with many animals and
differs from many. They may be (as in Bats and in their
extinct precursors, the Pterodactyles) absolutely larger in all

ELEMENTAR Y ANA TO MY.

[LESS.

respects than any other vertebrae. They may be (as in the
Giraffe, and indeed in Ungulata generally) larger than more
post-axial ones. On the other hand, they may be excessively
reduced — mere delicate laminae of bone, as in Porpoises.
The free condition of man's cervical vertebrae is normal and

FIG. 61. — SECTION OF MOST PRE-AXIAL VERTEBRAE, AND PART OF SKULL OF

SILUROID FISH, Bagrus.
{From Professor Owen's "Archetype of the Skeleton.'1')

at, ax, z>3, 7/4, z>5, v&, and v7, centra of the seven most pre-axial vertebrae;
s, neural spine of second vertebra ; eo, ex-occipital ; bo, basi-occipital ; hy, hyp-
apophysial plate extending along on ventral side of vertebral centra. The lateral
parts of the first two vertebrae (between eo and s) are united by suture with
each other and the skull.

almost constant in his class. Not quite so, however, for in
the true Whales they usually become anchylosed together, so
as to form a sort of cervical sacrum. They may, on the
contrary, be distinguished as the only free vertebrae except
the coccygeal ones, as is the case in Tortoises ; and as in
Birds, where the long and very mobile neck has to supply the-
place of an arm in supporting a beak which rivals in delicacy
of action any hand and fingers known to us, as is manifes't
from the wonderful construction of their many kinds of nest.

That part of each cervical vertebra which is called the
body varies as to shape in the way just described in speak-
ing of the cervical vertebrae considered as whole and entire
bones.

The pre-axial concavity and post-axial convexity which the
bodies exhibit, represent the much more marked concavity
and prominence which we find in some Mammals, e.g. the
Sheep and Horse.

In the lowest Mammals (Echidna and Ornithorhynchus) the
cervical transverse processes remain as distinct more or less

THE SPINAL SKELETON.

49

Y-shaped bones ; and we find the same in the Crocodile,
where the free end of each Y-shaped bone is singularly pro-

FIG 62— SECTION THROUGH MIDDLE LINE OF UNITED CERVICAL VERTEBRA

OF GREENLAND RIGHT WHALE (Baltena mystutus).

a articular surface for occipital condyle ; e, epiphysis on posterior end of body of
'seventh cervical vertebra ; sn, foramen in arch of atlas for first spinal nerve ;
i, arch of atlas ; 2, 3, 4, 5, 6, conjoined arches of the axis and four following
vertebrae ; 7, arch of seventh vertebra.

(From Prof. Flowers "Osteology")

lono-ed in the line of the backbone— i.e. pre- and post-axially.
In many lizards and birds the posterior cervicals bear long

FIG 63 —Third Cervical Vertebra of a nearly full-grown Echicna (E. hystn.r),
the different pieces of which it is composed being slightly separated from one
another.— tin, neural arch ; c, centrum ; t, transverse process ; v, arterial
canal; ncs, neuro-central suture.

(From Prof. Flowers "Osteology")

ribs and are only counted as cervical because their ribs do
not join a sternum, which yet is attained by the ribs of other
vertebras.

50 ELEMENTARY ANATOMY. [LESS.

The canal formed by the series of perforated transverse
processes may be replaced by one excavated inside the neural
arches, as in the cervical vertebrae of the Camels and Llamas.

In some Cetaceans the external osseous boundary of the
perforated transverse process is wanting, so that there come
to be two elongated transverse processes on each side.

The length of the cervical neural spines in man, though
much greater than in many animals, is yet quite insignificant
compared with the development they attain in certain Apes
(Gorilla, Orang, Perodicticus) and in the true Opossums.
Indeed, these animals show that the cervical spines may be
the longest ones of the whole vertebral column. In the true
Opossums and in some Armadillos their apices become
anchylosed together.

The bifurcation of the neural spines is carried further
down the backbone (i.e. extends to more vertebrae) in man
than in any other mammal ; but this is not the maximum of
complication of the part, as in the Howling Monkeys
(Mycetes) we find a trifid spine. On the other hand, we
often meet with a bifurcation in the dorsal and lumbar regions
which is not present in the human skeleton.

That faintly-marked prominence which exists in man in
front of the prezygapophysis is really a rudiment of a meta-
pophysis, as is plainly shown by the skeleton of the Spider
Monkey (A teles].

FlC. 64. — AXIS AND FOUR FOLLOWING CERVICAL VERTEBRA OF A SPIDE.R

MONKEY (A teles),
in, metapophysis.

The smoothness of the anterior surface of the cervical
vertebral bodies in man is a great contrast to their condition
in some animals (as e.g. in Birds) ; for prominences (the hypa-
pophyses) on the post-cephalic vertebrae may (as in Crotalits)

ii.] THE SPINAL SKELETON. -i

equal, if they do not exceed, the neural spines in length.
Hyperapophyses may exist upon the postzygapophyses of
the anterior cervical vertebrae, as in the Dog.

25. In the preponderating size of the LUMBAR VERTEBRAE
man but exaggerates a character generally present in his
class, but this preponderance is not universal, as is shown bv
Bats. Lumbar vertebrae are generally to be distinguished in
Mammals, and in Crocodiles and certain Lizards, but not in
any Ichthyopsidan.

In Birds, lumbar vertebrae are present indeed, but disguised
and hidden by exaggeration of the sacral anchylosis.

The number in man is below the average of his class,
though some Apes have but four, the Two-toed Sloth but
three, and the Monotremes but two.

The largest number in quadrupeds is eight, or sometimes
nine, found in the Slow Lemur — which is very remarkable, as
in that beast there are also sixteen dorsal vertebrae. There
may indeed be as many as twenty-four lumbar, as in the
Dolphins, though the limits of the region are somewhat in-
determinate in those animals.

The spinous and transverse processes of the lumbar verte-
brae are shorter relatively in man than in most Mammals,
which also have them generally directed towards the head.
The lumbar transverse processes may be excessively pro-
longed, as in Cetaceans, and the last ones may articulate or
anchylose with the sacrum, as in the Horse.

FIG. 65.— LUMBAR VERTEBRA OF THE GREAT ARMADILLO (Priodonte^.
c, centrum ; s, spine ; /, capitular process ; z ', postzygapophysis ; w, meta-
pophysis; a, anapophysis ; xl, x*, x3, **, four contiguous but distinct
articular surfaces.

{From the College of Surgeons' Museum*)

The metapophyses and anapophyses attain their greatest
length in the lumbar region : thus in the Armadillos the
former processes equal the spinous processes in length, and
E 2

52 ELEMENTARY ANATOMY. [LESS.

serve to support the bony shell of those animals. In Prio-
dontes the meta'pophyses are enormous, and there are four
articular surfaces on each side of each end of a lumbar
vertebra.

In addition to the complexity of articulation described as
existing on the last dorsal vertebra of the Great Ant-eater, we
find in this animal's lumbar region an additional articular
surface en each side of each transverse process.

A long hypapophysis may be developed, as in the Hare.
Instead of being free, as in man, the lumbar vertebras may
be anchylosed together and with other parts, as in Birds, the
Chelonians, and Glyptodon.

7.S

P

FIG. 66.— PELVIS OF A BIRD ANCHYLOSED TO THE LUMBAR VERTEBRA.

</3, last free dorsal vertebra ; c, coccygeal vertebrae ; il, ilium. ( For the other
letters see Lesson V.)

26. Inasmuch as the first two vertebrae and no more are
specially modified, man agrees with all birds and beasts, and
differs from all below. The specialization may, however, be
even greater than in him, as is the case with Chelonians,
where each cervical has its own peculiarities. Thus in the
common european Terrapin we find the fourth cervical with
its centrum convex pre-axially, and concave post-axially ; the
fifth is bi-convex ; the sixth is concave pre-axially, with a
double post-axial convexity ; the seventh has a double pre-axial
concavity and a double convexity post-axially ; the eighth has
a double concavity at each end ; the ninth has a double
pre-axial convexity and a single one post-axially, and also
curiously arched post-zygapophyses.

The ATLAS of man, in having no true body, agrees with that
of all Vertebrates above the Ichthyopsida. In the highest
member of that group, the Frog, the first vertebra has the
neural arch attached to a centrum just as the other vertebrae
have, and at the same time the power of rotation on the
second vertebra is lost.

In having two articular surfaces for the skull, man's atlas
differs from that of Birds and Reptiles, but agrees with that
of Batrachians and some Fishes.

ii.] THE SPIRAL SKELETON. 53

The total absence of articular processes is a character
common to man's class, but in Birds and in some Reptiles
(e.g. the Iguana) postzygapophyses are present.

The spinous tubercle may be enlarged into a distinct
pointed process, as in some Baboons. The neural spine may
be detached from the neural arcs, as in the Crocodile and
Tunny. It may, as in the fish Ephippus, be separated from its
centrum by the intrusion of the skull wall ; the inferior tubercle
may be drawn out into a long process, as in the Hare, or be
doubled, as in the Duck-billed Platypus. Occasionally, as in

TIG. 67.— LATEKAI., DORSAL, AND VENTRAL VIEW OF FIRST VERTEBRA OF
A inpkiuina.

Amphiuma, the body of the first vertebra may send out
a process towards the head, reminding us of the odontoid
process of the axis.

The slenderness of the neural arch and transverse processes
is exceptional in man. The arch may be open medianly
above, as in the Frog. The transverse process is expanded
into a large plate in almost all beasts below Primates, but it
may be short and imperforate, as in the common Fin Whale.

The canal for the vertebral artery is generally more com-
plex (through increase of ossification) in beasts than in
man, where indeed the osseous canal is simple. Transverse
processes are also generally absent or rudimentary below
Mammals, though the Crocodiles have them very long and
rib-like.

The free condition of the atlas is not universal, as it is
anchylosed to the axis in the Dolphin, and with all the other
cervicals in the Right Whale. It may be fused in one solid
mass with the skull, as in the Sturgeon, or with a certain
number of succeeding vertebras, as in the Rays. It may be
firmly united by suture with both, as in the Ganoid fish Bagrtis
(see Fig. 61). The anterior base of the atlas may be un-
ossified, as in the Wombat, or may remain a distinct bone,
as in the Thylacine. The real nature of this part will appear
shortly.

54 ELEMENTARY ANATOMY. [LESS.

27. In its marked peculiarities the AXIS of man agrees
with that of almost all Vertebrates above the Ichthyopsida,
where it is indistinguishable. As we have seen, however, it
may, as in many Cetaceans, not remain distinct ; and even
where it does remain distinct in them, the odontoid process
is absent or very short.

In the coalescence of that process with the centrum, man
agrees with the immense majority of his class ; but in the
Duck-billed Platypus it remains distinct as an odontoid bone,
as it does also in many Reptiles (e.g. Crocodiles, Chelonians,
and Lizards), where, however, it remains closely connected
with the bodv of the axis.

FIG. 68 — ATLAS AXD Axis VERTEBRA OF A CHELOMAX REPTILE.

ky, hypapophysis of atlas : t, transverse process ; z, prezygapophysis ; z, post-
zygapophysis ; s, neural spine : by, odontoid bone ; Aj", hypapophysis of
true centrum of axis.

(from the College of Surgeons' Museum. )

The odontoid process may present a semi-cylindrical shape,
as in the Sheep.

The slightly increased size of the neural spine of man's
axis compared with those of his other cervical vertebrae, is but
a faint indication of the great predominance it attains in many
Mammals — arching forwards and backwards over three or
four vertebrae. Its apex may be trind, as in Mycetes and the
Potto. Single or double hypapophysial processes may be
developed, and the transverse process may be long and large,
as in the Monotremes, where it (as a short and wide rib)
remains for a considerable time distinct, and is attached to
two superimposed transverse processes.

In its freedom the second vertebra varies in the way already
indicated in describing the atlas.

28. The SIXTH cervical vertebra of man scarcely differs
from the "fifth, though the capitular root of the transverse pro-
cess is slightly wider. This widening is a feeble indication
of a marked and general mammalian condition, for (though
not in the highest Apes) this root is usually much enlarged,

II.] THE SPIXAL SKELETON. 55

and forms a conspicuous plate, as e.g. in the Ox and Dog ;
and even in the Dolphin, where the cervical vertebrae are
such thin plates of bone, the same root is suddenly enlarged.

In no animal but man does the spine of this vertebra ever
bifurcate.

The SEVENTH vertebra sometimes in man has its transverse
process imperforate, by the non-development of its capitular
root. This condition, abnormal in him, is normal but not
universal in the rest of his class. In other Mammals, as also
in man, a short free rib may be attached to the transverse
process of this vertebra ; and where, as in the Three-toed Sloth,
the number of vertebrae is nine, it is the eighth and ninth
vertebrae which resemble in structure the sixth and seventh of
man — thus showing that in this animal it really is the cervical
vertebrae which are increased in number, and not that the
condition has been produced by the first two dorsal ribs
being imperfectly developed.

20. The coalescence and degradation which characterize
the SACRAL VERTEBRA generally occur more or less in Verte-
brates above the Ichthyopsida, which possess fully developed
limbs.

The coalescence is generally less extensive than in man,
though sometimes (as in Birds, some Edentates, and some
Reptiles) it is much greater.

The sacrum of man is indeed a peculiar structure as regards
the coexistence of characters each of which, taken separately,
is shared by some or other members of his own class and order.
The characters of which the coexistence is peculiar to him
are : (i) The very marked sacro- vertebral angle. (2) The trans-
verse and axial concavity of the ventral surface of the sacrum.
(3) The concurrence of as many as five, or even six verte-
brae in its formation — three of them generally contributing to
form the auricular surface. (4) Its relative breadth, and the
gradual way in which it narrows post-axially without any
sudden contraction. (5) The large size of the foramina.
(6) The small development of the spinous and other processes.

This region may, however, be more exceptional and pecu-
liar than in man, as e.g. in the Rhea, where the vertebral inter-
space between the haunch bones is filled by a very narrow
continuous ossification without a trace of division into
vertebrae.

The sacrum of man may be looked at from two points of
view, and it is very difficult to determine what parts really
answer to it in many animals.

56 ELEMENTARY ANATOMY. [LESS.

Thus: (A) it may be looked at with regard to its relation to
the nerves which pass out through its foramina in front ;r or,
(B) with regard to the skeleton only, and this again from three
other points of view : (i) with regard to the skeletal ele-
ments which comprise it ; (2) with regard to its connexion
with the hip-bones, and (3) witn regard to the bony union of
more or fewer vertebrae into one solid and complex mass.

The sacrum of nervous supply (i.e. as estimated by the
destination of the nerves passing out through it) is much more
constant than the purely osteological sacrum. It never
probably embraces more than seven or less than two, perhaps
rarely less than three vertebrae.

But while in man it is the two or three pre-axial sacral
vertebrae which have distinct costal elements, and while a
similar coexistence is probably universal in his class, very
different conditions may possibly obtain when we descend
further in the scale of animal life.

Thus, in Birds the sacrum of nervous supply appears in
part to be made up of vertebrae which have no expanded
sacral ribs, while large transverse processes are attached to
the most post-axial vertebrae of the nervous sacrum.

The purely osteological sacrum is a very variable part with,
regard to all the three conditions above enumerated, varying
even in the same species with the advance of age.

Man agrees with most if not all Mammals in having the
more pre-axial part of his large sacral transverse process a
distinct costal element. In Birds, however, the vertebrae of the
sacrum which have expanded transverse processes, do not de-
velop these from distinct ossifications. In lower forms (e.g.
Crocodiles and Tailed-Batrachians) the sacral vertebrae have,
on the contrary, a distinct and unmistakable rib attached to
each transverse process.

As regards the extent of connexion between the osteologi-
cal sacrum and the hip-bones, union is more extensive in man
than in most beasts, or animals below Birds. Often in Mam-
mals, and almost always in Tailed-Batrachians, it may be con-
fined to a single vertebra. On the other hand, ten vertebra?
may be involved in this union in Mammals, and twenty in
Birds.

That part of the haunch-bone which we shall find is named .
the ilium, alone unites in Birds (Fig. 66, //) with this great
number of vertebrae ; but in man's class it only joins four

1 As to the nerves, see Lesson VIII.

n.] THE SPINAL SKELETON. 57

or five, though when that bony element which we shall find
to be called the ischium also effects a bony union, the num-
ber may be raised to ten — as in some Armadillos.

When the osteological sacrum embraces as many as
twenty (as in the Ostrich), then the lumbar vertebra? are
encroached on by the extent of the hip-bones. Coccygeal
vertebra? indeed may take an extensive share in it, as in some
Edentates and Bats, where the osteological sacrum not only
unites with the so-called ilium, but also anchyloses with the
bone which is commonly termed the ischium.

The possession of a true osteological sacrum is a character
man shares only with Vertebrates above Fishes. Very rarely,
however, as in the Turbot, there is in Fishes even a kind of
false sacrum, formed by the anchylosis of the bodies and
ventral spines of the first two coccygeal vertebra?.

Compared with his own class only, man exhibits a sacrum
which includes a number of vertebrae attained by few others,
and but rarely exceeded, though sometimes there are six in
the highest Apes. The number may reach eight, or even (as
before said) ten in certain Armadillos ; but this is the highest
number of man's class, though about the smallest number
found in the class of Birds, where, as we have seen, there
may be as many as twenty.

Apart from union with the hip-bones, coccygeal vertebrae:
become anchylosed with the true sacrum in Mammals with
the advance of age, so as to form altogether four or five sacral
vertebra\ That the development of the sacrum is not always
in proportion to that of the pelvic limbs, is proved by the
little lizard Seps, in which, in spite of the rudimentary con-
dition of the limbs, there are three sacral vertebra?. The
sacro-vertebral angle is generally replaced by almost a
straight line, and it is not nearly so marked in any Mammals
•as in man, except in some Baboons.

The concavity of its ventral surface, which is so variable in
man himself, is generally much less marked in other Mam-
mals, but sometimes it is quite as great, as in certain Baboons.

The tapering form of the sacrum of man is also exceptional,
but it exists in the highest Apes, in Bears, and some other
Mammals. Generally, however, in man's class the sacrum
contracts suddenly at its post-axial end.

The wing-like processes (the sacral ribs) make it relatively
wider than long in most Mammals.

The sacral spinous processes of man are but rudiments of
what sometimes exist, as they are very long in Carnivora and

58 ELEMENTARY ANATOMY. [LESS.

others, and sometimes unite into a strong crest even in Pri-
mates, but especially in the Rhinoceros, some Ruminants, and
Insectivora, e.g. Sorex and Myogale.

The lower end of the sacrum in man is devoid of processes,
but in most forms there is a pair of strongly marked ones,
which are most probably tubercular processes with annexed
connate or developed ribs.

Metapophyses and anapophyses are hardly to be detected
on the sacrum of man ; but they are distinctly visible in many
Mammals, even Monkeys.

The occasional open condition of the neural canal in man
is very exceptional, being repeated only in the highest Apes.

That the sacrum has a flat articular surface at one end
for the last lumbar vertebra, and at the other for the coccyx, is
the normal condition, but the vertebras composing it may, as
in Batrachians (e.g. Menopoitia and Cryptobranchus\ be con-
vex in front and concave behind. It may, however, present a
condition such that its two component vertebrae have the
conjoined surfaces of their centra flat, and the other surfaces
respectively concave, as in Crocodiles.

30. No better example of the inadequacy of the exclusive
study of man for a full comprehension of his frame can pro-
bably be given than the human os coccygis.

The anthropotomist, though he would readily perceive that it
was the rudimentary representative of a tail, would yet never
suspect to what diverse and curious structures it corresponds.

Indeed, the COCCYGEAL REGION of the vertebral column,
instead of only varying as to the size and number of its parts,
is the subject of very peculiar modifications of structure, and
of unexpected modes of ossification and development.

It may act as an extra hand ; it may be the main or exclu-
sive locomotive organ ; it may, together with the neck, contain
the only free vertebrae of the body ; or it may be still more
reduced and rudimentary than in man.

It may in part consist of a solid bone formed by the fusion
of primitively separate vertebrae, or it may be distinguished
from the rest of the vertebral column as the only portion
never made up of separate vertebrae at any time of life.

The three, four, or five coccygeal vertebras of man may be
represented by as many as forty-six in his own class — namely,
in the long-tailed Pangolin or Manis ; and in his own order
it may reach the number thirty-three, as in the pre-eminently
arboreal Spider Monkeys, which have the tail prehensile,
serving as an additional hand. It may, on the contrary, in

THE SPIRAL SKELETON.

59

his own order, be reduced to three bones, as sometimes in the
Magot (limits}.

FIG. 69.— CAUDAL VERTEBRA FIG. 70 — POST-AXIAL TERMINATION OF THE
OF Innns. VERTEBRAL COLUMN IN A SALMON.

(Front Specimens in the British Museum.)

It is in aquatic forms that the tail attains the greatest
relative bulk, and in some Sharks may contain the prodigious
number of 270 vertebrae.

It is in the Tortoises that we find the tail supported by the
only free vertebrae which are not cervical, all those of the
trunk being immovably united with the ribs and with the
dermal bony plates forming altogether the shell, or carapace.

The maximum of degradation and abortion of the coccyx
is in the Bats, where coccygeal vertebrae may be reduced to two.

The coccyx of birds generally consists of from six to eight
vertebrae, but may have ten. At its end is a so-called plough-
share-bone, consisting of two or more anchylosed vertebras.

The peculiar coccyx of the Frog never consists of distinct
vertebrae at any time of life, but is formed by the ossification
of the membrane which surrounds the notochord, to which
two small neural arches become attached.

In osseous Fishes the end of the tail is turned up and
remains persistently as a cartilaginous rudiment at the end of
the vertebral column, generally hidden and enclosed by special
bony plates.

In the higher animals provided with numerous coccygeal
vertebrae, these vertebras are often provided with processes
and articulations as complex as those of vertebrae more
anteriorly situate. Pre- and post-zygapophyses, anterior and

6o

ELEMENTARY ANATOMY.

[LESS.

posterior transverse processes, metapophyses, neural arch and
neural spine, together with hypapophysial processes or arches
(chevron bones), may be present in man's own class. In Fishes
the hypapophysial parts may be very largely developed, as,
e.g., in the Flat-fishes. In Tailed-Batrachians, the anterior

FIG. 71. — PART OF THE VERTEBRAL COLUMN OF A SOLE.
«, neural spines ; /, transverse processes ; A, hypapophyses.

coccygeal vertebras (e.g. in Menobranchus] may be furnished
with true ribs, supported by both tubercular and capitular
transverse processes, in addition to articular, neural, and
hypapophysial parts.

FIG. 72.— LATERAL VIEW OF THE FIVE MOST PRE-AXIAL CAUDAL VERTEBRA
OF MENOBRANCHUS.

/, tubercular process ; c, capitular process ; Jty, hypapophysis.

The downwardly tapering condition of the coccygeal verte-
bras which exists in man is the general condition of such
parts ; but sometimes, as in the little Armadillo Chlamy-
dophorus, the transverse processes increase in size instead of
decreasing in that direction.

".] THE SPINAL SKELETON. 61

In lower forms, e.g. Tailed-Batrachians and Fishes, the
inferior (hypapophysial) arches sometimes develop articular
processes or parts simulating such.

31. The beautiful sigmoid curvature of the VERTEBRAL
COLUMN of man (Fig. 38) is, in its perfection, absolutely pecu-
liar to him, though some of the Apes (not the highest, but the
Baboons — Cynocephali] approximate to him in this respect.
This exceptional condition of structure in man is related to
his exceptional (erect) attitude.

As exceptional a curvature, though a very different one,
may exist. This is shown "by Bats, where the hinder part
of the spine bends sharply forwards as a quadrant, bringing
the pelvis very much in front.

The gradual thickening of the spinal axis from its cranial
end downwards to the sacrum, is a condition which obtains
generally in Vertebrates, except Fishes, Bats, and those
extinct flying Saurians the Pterodactyles, in which that axis
gradually decreases in bulk tailwards.

The post-axial projection of the neural spines, especially
those of the posterior cervical and anterior dorsal vertebrae, is
considerably less in man than in most animals of his class,
though considerably greater than in some — e.g. the Hedgehog.
On the other hand, neural spines attain in many Fishes (e.g. the
Sole, Turbot, &c.) a prolongation compared with the size of
the spinal axis vastly exceeding anything to be found even
in the marine (Cetacean) members of the class to which man
belongs.

32. The mode of OSSIFICATION of the vertebrae of man
agrees with that which exists generally in his class, most of
the vertebrae ossifying from one point in the body and one
other point in each neural arch — besides from the epiphyses,
where these exist.

The line of junction of the lateral (neural) pieces with the
central piece is termed the neuro-central suture, and in most
Mammals, as in man, it is so disposed that each lateral piece
contributes to form a portion of the body. This is not, how-
ever, universally the case, as in the Whale order the suture
is placed more dorsally, so that the central ossification forms
not only all the centrum, but also more or less of each lateral
piece.

Just as in man, so in other members of his class, separate
ossifications often indicate costal elements in the cervical,
lumbar, and sacral regions.

The fact, however, of a part being ossified by the extension

ELEMEN7'AR Y ANA TO MY.

[LESS.

into it of a neighbouring ossification (when it is said to be
exogenous '), or by an independent centre (when it is said to be
autogenous2), constitutes but a very secondary and unim-

FIG. 73 —ANTERIOR SURFACE OF VHRTEBR^E OF DOLPHIN {Globiocepkalu*
melas).

A, fifth thoracic ; B, seventh thoracic ; c, eighth thoracic ; r>, first lumbar ; r, rib ;
m, metapophysis ; t, transverse process. The dotted lines indicate the posi-
tion of the neuro-central suture.

{Prom Prof. Flowers "Osteology")

portant distinction ; since neural arches (as in the tail of
the Dog) or neural spines (as in trunk vertebrae of some
Ungulates) may ossify in either mode.

In the same way, transverse processes, both capitular and
tubercular, may be formed by outgrowths of the central ossi-
fication only, or by extensions ot the lateral ossification, or
by the concurrence of both these parts, as in Plesiosauria and
some Cetacea (see Fig. 73).

The presence of epiphyses on each side of the body and at
the tips of the neural spines, transverse processes, and meta-

1 From efo>, outside, and

2 From uvi6(;, self, and •ye

t, to arise.

"•] THE SPIXAL SKELETON. 63

pophyses, is a character common to most animals of man's
class, but the centrum does not appear to have epiphyses
in the Sirenia, Monotremata, and in the animals below the
mammalian class.

In those Mammals which have chevron-bones there are,
of course, ossifications which do not exist in man.

FIG. 74.- CAUDAL VERTEBRA OF A CROCODILE.

c, centrum ; s, neural spine ; t, transverse process ; z, pre-zygapophysis ; z\ post-
zygapophysis ; hy, hypapophysis, or ''chevron-bone."'

In the lower Vertebrata the vertebral bodies may be at
first formed by superficial ring-like ossifications, as in many
Fishes ; and in some, as in the Carp, distinct lateral ossifi-
cations may exist, one on each side of the centrum.

The walls of the two concave vertebral, articular cups may
ossify, making an hour-glass-shaped ossification, to whicn
concentric or radiating lamellae may be added, as in certain
Sharks.

Cortical ossifications (i.e. of the fibrous sheath of the
notochord) may appear and coalesce with vertebrae, as in
the coccygeal vertebrae of the Frog.

Sometimes, as in Lepidostren, bony neural arches may be
formed, and more or less embrace a permanently soft and
unossified chorda dorsalis.

33. A bony case, like the THORAX of man, exists in all
Beasts and Birds, without exception. It also generally exists
in Reptiles, but is strangely modified in serpent-like Lizards,
and in Tortoises. In the former it is enormously drawn out,
and made imperfect below by the small development of a
sternum. In the latter it attains a maximum of solidity, and
enters into bony union with the dermal skeleton.

64 ELEMENTARY ANATOMY. [LESS.

A thorax is not a constant character of Vertebrates, for it
cannot be said to exist in those Batrachians which have
no ribs, neither in true Serpents nor in Fishes, both these
groups of animals being utterly destitute of a sternum.

34. The STERNUM of man represents a part constantly pre-
sent in limbed Vertebrates above Fishes, except Chelonians,
as also in some forms in which the limbs are absent. Its
human condition, however, of serving as a ventral abutment
to ribs, though general, is not constant, as not only may ribs
exist without a sternum — as in Fishes and Serpents — but a
sternum may exist without ribs, or without forming any
cartilaginous or osseous connexion with ribs, as in the class
Batrachia.

The sternum of man, considered as a whole, is neither so
broad nor so narrow as in some other forms, and its depth
from the surface inwards is much less than may obtain.

Thus it is broader in proportion to its length in most
oviparous animals (from Birds to Batrachians), also in some
Mammals, as the Whales, and even in the Siamang Gibbon,
belonging to man's own order. In most members of man's
own order, however, and in very many of his class, it
is, as in the Dog, and in some Reptiles (as the Crocodile
and Chameleon), much more narrow in proportion to its
length.

The above exception as to Chelonians not having a ster-
num may well excite surprise, for Tortoises and Turtles have
not only well-developed limbs, but it has been commonly
supposed that part of their " shell," the great ventral shield
(or plastron), is one great sternum, or at least a sternum
with dermal ossifications added. It appears, however, that
this great complex plate does not really include a sternum.

That threefold division of the sternum which exists in man
is normal in his class. In Birds and Reptiles it also exists,
though more obscured and difficult to define.

Even in Mammals, however, this threefold division is not
universal, as (e.g. in the Greenland Whale) only the manu-
brium may exist, the rest of the sternum aborting ; while
in the Dugong we have a xiphisternum (the representative
of the xiphoid process of man), together with a manubrium,
but no ossified representative of the middle part of the
sternum.

In Tailed-Batrachians and the Slow-worm (Anguis) we have
a simple sternum which cannot be said with certainty to re-
present any one of the three divisions ; while in many Frogs

II.]'

THE SPINAL SKELETON.

and Toads we have a middle and xiphoid sternum as also in
many Reptiles, and we have all three (as before said) in some
Reptiles (e.g. the Crocodile and Chameleon) and in Birds

The manubrium forms a much larger part of the sternum in
some members of man's class than it does in him, as is the case
in the Cetacea, the Monotremes, and in the Mole, where its re-
lative length about equals that of all the rest of the sternum

On the other hand, it may be remarkably small and narrow
as in the Pig and the Horse.

FIG. 75. — STERNUM OF THE PIG (Sus icrofa).

/•s, manubrium, or pre-sternum ; tits, middle part of the sternum, or meso-
sternum ; xs, xiphisternum.

(From Professor Flower's " Osteology")

Sometimes this part may develop a strong median keel
for muscular attachment, as in Bats, the Mole, and Armadillos.
This keel, however, does not answer to the keel of Birds,
which belongs to the more post-axial part of the sternum.

The " episternal granules " occasionally present in man are
replaced in some Mammals by considerable horn-like pro-
cesses, as in the Howling Monkeys (Mycetes) and Mice.

The manubrium may be remarkably small when coexisting
with a sternum hypertrophied in other parts, as in Birds.

66

ELEMENTAR Y ANA TOMY.

[LESS.

The middle part of the sternum (mesosternuni) may be
much shorter relatively than in man, as is the case in the
Sperm Whale, and it may abort, as just said, in the Dugong.
Generally, however, in Mammals it is large and more per-
manently segmented than in him, and may (as in the Orang)
show to a much later period its median division. The divi-
sion into two lateral halves (one piece on each side only)
transitorily exists in the Struthious Birds.

FIG. 76.— STERNUM OF A HOWLING MONKEY (Mycetes).
m, bones representing "episternal granules."

The segments of the mesosternum may send down pro-
cesses together forming a sort of keel, and each furnished
with two articular surfaces for the ribs, as is the case in the
Tamandua Ant-eater.

The xiphoid cartilage, or its osseous or cartilaginous repre-
sentative, may abort altogether as a distinct part, as in the
Tailed-Batrachians and the Right Whale. It maybe long and
pointed, as in the Two-toed Ant-eater, or enlarged and rounded,
as in very many species (e.g. Sorex). It may even in Mammals
be enormously produced into two elongated horns, far exceed-
ing all the rest of the sternum in size, as in the long-tailed Pan-
golin ; and a similar but more reduced form may exist in
Lizards (e.g. Iguana, Draco (Fig. 78), and still more Stellio}.

It is in Birds, however, that the xiphisternum attains its
maximum of size and importance, forming all that part of the
sternum post-axial to the attachment of the ribs. It may
consist of one sheet (as in the Qstrich and Cassowary), or be

n-] THE SPINAL SKELETON. 67

divided into a median and two lateral processes, one on each
side (as in the Apteryx) ; or into a median process and four
lateral ones— there being an internal and external xiphoid
process on each side of the median one— as in very many
birds (^.gallinaceous birds, such as the Fowl and Pheasant).
This median process it is which bears the keel, or the greater
part of the keel, in Birds.

FIG. 77.— THORAX OF A GALLINACEOUS BIRD.

ft, keel of entro-sternum ; in, middle xiphoid process ; i, intermediate xiphoid
process ; e, external xiphoid process ; r, rostrum ; c, costal process ; k, hypa-
pophysis ; a, appendage from ribs, or uncinate process.

In certain animals (e.g. the Monotremes) there is a median
ossicle in front of the manubrium, which is often called the
episternum. This really forms part of the appendicular
skeleton, being a portion of the shoulder structure. It will
therefore be noticed under that head.

35. In possessing RIBS (that is, distinct osseous or cartila-
ginous parts attached at one end to the vertebral column, and
tending to surround the body cavity) man agrees with the
immense majority of other Vertebrates. Some, however, as
the Frogs and Toads, have none, nor can any be said to exist
in some of the lowest Fishes, e.g. the Lamprey and its allies.

In the division of the ribs into two categories, the "true"
and the "false" ribs, man agrees with all animals which have
ribs at all, except Serpents, Fishes, and Chelonians ; Serpents
F ?

68 ELEMENTAR Y ANA TOMY. [LESS.

having many ribs indeed, Fishes few or many, and Che-
lonians few, but all having no sternum, so that every rib
must be reckoned to be a false rib in them — and this in spite
of their fixity in Tortoises.

In the proportion of true to false ribs man occupies an
intermediate position. Thus the number of true ribs is more
in excess in some other animals than in him, as e.g. in the
Seals, and in Birds ; yet the number of false ribs is greatly
in excess in some other animals, especially in the Whalebone
Whales, in which there may be but one pair of true ribs.

In the shape of the ribs man is normal, and their length
always exceeds their breadth or thickness. They may, how-
ever, be vastly thicker or more massive than in him, as is
the case in the Manatee, or habitually form thickenings which
but for their constancy would be deemed a diseased condition
(pathological), as in the fish Platax.

They may also greatly exceed the breadth possessed by
man's, as in the Two-toed Ant-eater, where they overlap one
another ; they may, on the contrary, be less flattened than in
him, as in the Carnivora.

As to the number of pairs of ribs, this has already been
generally indicated in speaking of the dorsal vertebras, though
in Birds we may have ribs coming from vertebras which are
generally counted as " sacral." There may be as few as five
or six pairs, as in Ampkiuma, or the number may reach 320,
as in some Pythons. In man's class there may be as many
as twenty-four pairs, as in the Two-toed Sloth, or as few as
nine, as in the Hyperoodon.

In the fact that ribs (distinct and articulated) are confined
to the dorsal region, man agrees with most Vertebrates. Such
ribs, however (more or less free and more or less long), may
exist in the cervical region, as we see in the Crocodile and in
many Reptiles ; in the so-called " sacral" region, as we see in
Birds ; and even in the caudal regions, as we see in Meno-
branchus. Of such ribs, however, enough has been said in
treating of those regions of the spine.

The function of aiding respiration is one which the ribs
possess in the higher Vertebrata, but quite other purposes
may be subserved by them in addition to, or instead of,
respiratory action. Thus ,'certain ribs, by excessive elonga-
tion, may support a flying membrane, as in the Flying Dragon,
or by their sudden erection expand the skin of the neck, as
in the Cobra.

Terrestrial locomotion may also be due to these parts, as in

II.]

THE SPIRAL SKELETON.

Snakes, which glide along by the successive application to the

ground of the edges of ventral horny plates, each plate being

attached to the ends of a pair of

ribs. There being no sternum in

Serpents, all the ribs are, as before

said, " false ; " but all the ribs may

also be false notwithstanding the

presence of a sternum, as in

Tailed-Batrachians.

The ribs may form a solid case
for the protection of all the other
parts. Thus in Tortoises the head
and limbs can be drawn into such
a case (called the carapace), which
is formed of greatly expanded ribs
joining each other, and also the
expanded neural spines before no-
ticed, by suture (Fig. 57).

In man we find the floating ribs
float by their anterior ends only,

their hinder ends articulating with FIG. 78.— RIBS OF THE FLYING
the vertebras. The very reverse
condition to this may appear to
obtain, as in the Crocodile, where
we have ventral rib-like structures
(towards the hinoler end of the ab-
domen), which are attached ventrally, but are free at their
vertebral ends, and thus float in the reverse direction. These,
however, are hardly true ribs, but are ossifications of a more
superficial region.

The presence in the ribs of a distinct "head" and "tubercle,"
as in man, is a very general but not a constant character.
Very often, however, if not always, when there is but one
articular surface for attachment to the vertebral column,
that surface represents and is equivalent to a " head " and
" tubercle," as it were, united and fused together ; though in
Monotremes the ribs are attached only to the sides of the
bodies of the vertebras.

This gradual fusion is well shown in the different vertebrae
of the Crocodile, where, as we proceed post-axially, these two
parts become more and more approximated together.

As in man, so generally, it is at the more pre-axial part of
the series of ribs that this distinction into head and tubercle
is most marked.

LIZARD (Draco volans).

sternum ; x, one of the di-
verging branches of the xiphoid
process ; t, true ribs ; ft floating
ribs.

7o ELEMENTA R Y ANA TOMY. [LESS.

In the Whalebone Whales after the first few ribs the
" heads " and " necks "entirely disappear, the more post-axial
ribs being attached by their " tubercles " only.

The peculiar proportions of the head and tubercle of the ribs
in man are not universal, but seem to be special modifica-
tions of a more primitive type, such as exists in the Ichthyo-
saurus and in some Tailed-Batrachians.
In them the rib divides at its proxi-
mal end into two diverging and equal
processes, the upper of which (answering
to the tubercle of man) articulates with
the dorsal, or tubercular, transverse pro-
FIG. 79.— VERTEBRA OF cess, while the lower (answering to the
AXOLOTL. neck and head of man's rib) articulates

s, neural spine ; d, tuber- w[fa ^g ventral, or capitular, transverse
&SSSaS£ Process. In some other Tailed-Batra-
tion of nb;/, capitular chians the proximal end of the rib bears
SS bifuSrUcSinogf * double facet, and articulates with a
rib. similarly facetted transverse process,

which thus evidently answers to an
upper and a lower transverse process united into one.

The relation borne by these articular surfaces to the neuro-
central suture is not constant. Sometimes, as in man, the
" head" articulates mainly above that suture ; sometimes, as
in Monotremes, altogether below it. In Ichthyosaurus
both surfaces are attached altogether below that junction,
while in Plesiosaurus the point of attachment rises as we
proceed backwards.

The class of Fishes shows what abnormalities are possible
with respect to the modes of attachment of the ribs, as in
Batrachus they have a more and more dorsal origin, until, at
the anterior end of the body, they are actually attached to
the neural spines !

That double attachment which exists in man between the
proximal end of the rib and two vertebras is not universal.
Thus in Birds it is only the last rib, or the last but one,
which is attached to the point of junction of two adjacent
vertebral bodies.

The greater breadth of the first rib of man is a character
frequently found in his class and sometimes much exaggerated,
as in the Great Armadillo. Often in Mammals, and in lower
forms generally, it is only of similar breadth to those post-
axial to it.
M The greater curvature in man of the first rib is a character

ii.] THE SPINAL SKELETON. 7I

he shares with some animals (e.g. Apes and Cetaceans), though
sometimes, as in the Ungulata, it (as well as the second rib)
is almost straight.

Occasionally, as in the Guinea Pig, Rhinoceros, and others,
the first rib bears a little spinous tubercle for the attachment
of the scalenus muscle.

The ribs may consist not only of two parts, as in man, but
may have a third part intercalated between each vertebral
rib and its sternal cartilage or rib, as in the Monotremes,
Crocodiles, and many Lizards.

The vertebral rib may give off (Fig. 77, a) a post-axially
projecting process (called uncinate), which may ossify as a
distinct bone, as is the case in most Birds and in the Crocodile.

The sternal ribs may be cartilaginous or they may be
completely osseous. The latter, e.g., is the case in Birds and
the Armadillos.

In shape they may differ much from man's, expanding
greatly, as is the case in the Great Armadillo and the
Monotremes. Each sternal rib may be set at a very marked
angle with its vertebral rib, as in Birds, instead of more or
less continuing its curve, as in man.

Some of the sternal ribs may pass into each other (on the
ventral aspect of the body) directly without the intervention
of a sternum, or run right into the substance of the sternum,
as is the case with the more post-axial ribs of Chameleons and
some other Lizards.

The sternal ribs may even slightly bifurcate at their ends,
as in the Tamandua.

Bony sternal ribs may have, at their dorsal ends, synovial
articulations with the vertebral ribs, and also synovial articu-
lations with the sternum at their ventral ends, as in Birds.

I

FIG. 80. — LATERAL VIEW OF SIXTH VERTEBRA OF SALAMANDRA.

/, tubercular process ; c, capitular process — the two supporting a rib which

bifurcates at its free, distal end.

The ribs may consist of single bones only, without any
division into vertebral and sternal portions, as in Fishes and
Batrachians. Ribs may also bifurcate distally, as in some of
the two last-mentioned classes (e.g. Salamandrd) ; and lastly,

72 ELEMENTARY ANATOMY. [LESS.

there may be two distinct series of ribs on each side of the
body, one series being dor'sally situate with regard to the
other. This condition is found in many Fishes, as e.g. the
Tunny and Polypterus^ and in the latter some vertebras have
four ribs on each side springing from the doubled transverse
process before noticed (Fig. 52).

36. That mode of DEVELOPMENT of the vertebral column
which we have seen to take place in man, takes place also,
broadly speaking, in all Vertebrates ; only the process is
arrested at different stages in different forms. Thus the
notochord may, as we have seen, persist, or the ossification
of the vertebras break off at various stages, leaving a great
deal or only a rudiment of the notochord persisting.

The process of consolidation and union may proceed only
so far as to leave transverse processes distinct, e.g. the Carp,
or neurapophyses in two or four pieces, and separate from the
neural spines, as before noted.

Finally, not only may vertebrae be found denser than those
of man, as the vertebras of Serpents, but coalescence may
extend to adjacent vertebras in the several ways already
described.

Our survey shows us that the backbone aloce, without the
help of any limb, may serve as an organ for creeping over
the ground or swimming through water, for climbing trees,
for crushing prey as in the Boa Constrictor, and even as a
hand to present food to the mouth as also in the Boa, or to
grasp and bring near small detached objects, as is done by
the tail of the Spider Monkey.

FIG. 8 1. — SKELETON OF HEAD AND GILLS OF LAMPREY.

&, cartilaginous basket ; n, neural laminae. (For the parts of the skull sec
Lesson III.)

An exceptional structure which probably belongs to the same
skeletal category as the ribs and sternum may here be
mentioned. This is the cartilaginous "basket" which supports
the gills in the Lamprey. It consists of arcs of cartilage

II.]

THR SPINAL SKELETON;

73

\vhich descend (the spine being horizontal) on each side from
the soft representative of the backbone, and are connected by
transverse bars extending in the direction of the spine.
The hindermost (most post-axial) ventral part of this basket
supports the heart.

FIG. 82. — STERNUM OK COMMON MOLE (Talpa enroptea).
fs, manubrium ; JUS, mesosternum ; xs, xiphisternum ; c, point of attachment of

the clavicle.
(From Professor Flower s "Osteology.")

In some Sharks there are similar cartilaginous arcs (though
much less developed) supporting the external borders of the
partitions between the gills.

74 ELEMENTARY ANATOMY. [LESS,

LESSON III.

THE SKELETON OF THE HEAD.

I. THE remaining part of the axial endoskeleton is the
skeleton of the head, familiarly known as THE SKULL.

This large rounded bony case for the brain is also the seat
of the organs of sense, and forms one coherent mass, except
the lower jaw, which in the dry skull readily falls away from
the rest.

Neglecting for the present this lower jaw — or, as it is called
in zootomy, mandible — the rest of the skull is rounded behind
and above, and more or less flattened in front, below, and
at the sides. Behind and above, it presents a pretty smooth
and even surface, crossed by those undulating, interdigitating
lines of bony union spoken of in the last Lesson as sutures.

When sections are made it is seen that the rounded portion
forms the roof and hinder boundary of the great cavity
in which is lodged the brain, and that irregular bony promi-
nences are placed below the front part of that cavity. The
skull then may be roughly divided into —

(1) The brain-case, skull proper, or Calvarium.1

(2) The skeleton of the face.

Certain conspicuous openings and prominences occur in
different regions.

The projecting part of the back of the head is termed the
occiput, and beneath it is a large hole, looking downwards,
termed the occipital foramen. On each side of the front part
of this hole is a rounded projection, and these projections,
termed occipital condyles, articulate with the cup-shaped
hollows on the upper side of the atlas vertebra (see Fig. 89).

Thus the margins of this foramen coincide with the neural
arch of the atlas vertebra, and the interior of the skull forms
the expanded summit of the vertebral neural canal \ indeed

1 From calva, the skull.

III.]

THE CRANIAL SKELETON.

75

the brain and spinal marrow are connected and become
continuous through this occipital foramen.

If the skull be turned base upwards, a strong bluntly
pointed prominence will be seen to project from each outer
margin on a line passing from right to left through the occi-
pital condyles. The prominence is called,, from its shape, the
mastoid ' process.

FIG. 83. — Side view of Man's Skull — the lower jaw being slightly removed, and
the line of ligamentous attachment of the hyoid represented by a dotted line.

a, greater wing of the sphenoid bone ; a», opening of external auditory meatus ;
bh, body of the hyoid ; c, an occipital condyle ; c ' , corniculum of hyoid ; cr,
coronoid process ; cy, condyle of the lower jaw ; f, frontal bone ; j, malar ;

/, lachrymal ; rn, mastoid process ; m.r, maxillary bone ; «, nasal bone ;
occipital bone ; p, parietal ; pt, internal pterygoid process ; s, squamous part
of the temporal bone ; st, styloid process (connected by a dotted line with

corniculum of hyoid) ; ty, greater cornu of hyoid ; z, zygomatic process of
temporal bone.

The under surface of the face (formed by the bones of the
roof of the mouth) lies at a different level from that of the
base of the skull proper. Connecting these two surface?
there are on each side a pair of vertical bony plates ter-

* From /biao-TO£, a nipple.

76 ELEMENTARY ANATOMY. [LESS.

ales, or wings, and between the two pairs are a pair of large
openings separated by a median partition and directed back-
wards. These openings are the hinder nostrils, or posterior
nares. At each side of the skull, behind the orbit, is to be
seen an arch of bone — a sort of flying buttress connecting
the skull and face together, arid termed the zygoma.1

FIG. 84. — FRONT VIEW OF RIGHT HALF OF MAN'S SKULL.

a, the greater wing of the sphenoid, which also appears in the orbit on the outer
side of the opening marked (2) ; f, frontal ; m, malar ; )tia, mastoid process ;
me, median part of the ethmoid dividing the nasal fossa vertically in the
middle line ; «, nasals ; o, lesser wing of sphenoid bounding the opening
marked (2) on the inner side ; f, parietal ; s, squamous part of temporal
bone; i, optic foramen ; 2, sphenoidal fissure ; 3, infra-orbital foramen.

When the skull is looked at in front, we see beneath the
forehead two conical sockets for the eyes, termed the orbits^
and between them the bony prominence of the nose, beneath
which is a large aperture medianly divided by a vertical
partition and forming the front nostrils, or anterior nares.

Beneath the outer and lower angle of each orbit the bony
projection of the cheek is noticeable, termed the malar2 pro-
minence ; and the skull is bounded below (the mandible being
removed) by the free border which gives attachment to the
teeth, and is termed alveolar, because the teeth are lodged in

1 From fi'»7a>/ja, a bar.

•* From mala, the cheek-bone.

in.] THE CRANIAL SKELETON. 77

special bony sockets to which the name alveoli has been
applied.

When the skull is viewed in profile the sharp bony projec-
tion of the nose is seen in front and the round prominence
of the occiput behind, while from the malar prominence the

zygoma extends backwards to above the mastoid process

enclosing a fossa (in which is placed a muscle called the
" temporal ") and having beneath its hinder end a noticeable
aperture which is the external bony opening of the ear. A
ridge also runs upwards from the malar prominence and
forms the external margin of the bony orbit.

The skull is said to be divided into certain regions. Thus
\ve have the base or basilar region, and opposite to it the
vertex, sinciput, or sincipital region ; we have the region
of the forehead or frontal region, and opposite to it that of
the back of the head or the occipital region.

At the side of the head we have posteriorly and above, the
parietal*1- region ; beneath this and within the arch of the
zygoma, the temporal region (to which is attached the tem-
poral muscle before referred to), separated from the orbital
region by the outer, hinder bony wall of the orbit.

The skull is made up of different bones of very different
sizes and shapes. When it is looked at from above, a trans-
verse zigzag line of union is seen to run across behind the
forehead. This is called the coronal suture.2

Running directly backward from this, for some distance
along the middle line of the vertex, is another suture, termed
sagittal, and it ends behind by joining a wide V-shaped
suture with the apex upwards, which is called lambdoidal. 3

Turning now to the lower jaw, this when attached to the
skull is seen to fit, by a rounded head/ into a shallow cavity
placed on each side in front of the external auditory opening,
and termed the glenoid 4 surface.

The number of bones forming the skull decreases, with
age, by anchylosis. In its mature condition the skull of man
consists of the following bones, which it will be well to notice
separately : —

2. The OCCIPITAL bone is of course that of the occiput, and
it surrounds the great occipital foramen (or foramen mag-
num}. Naturally (when the bones of the skull are separated

1 From paries, a wall.

2 Because it is somewhere near the part where a crown or garland would be
placed. 3 From its being like the Greek letter X.

* From T/\»;K»J, a socket.

78 ELEMENTARY ANATOMY. [LESS.

at their sutures) it comes away in one piece with a very large
and irregularly shaped bone, the " sphenoid," with which it is
connected by a solid bony isthmus (forming the middle of
the base of the skull), which isthmus has to be sawn across
in order to detach the occipital bone for the purpose of
anatomical study. Above the occipital foramen the occipital
bone forms an expanded plate (the squama), marked exteriorly
by transversely extended " curved lines."

FIG. 85. — OUTER SURFACE OF MAN'S OCCIPITAL BONE.

lo, basilar part or body of the bone which unites with the body of the sphenoid ;
c, one of the two condyles ; /, superior curved line ; /', inferior curved line ;
pm, one of the jugular eminences ; so, the squama, or expanded upper part
of the occipital ; i, condyloid foramen ; fin, foramen magnum.

The " condyles," before noticed, are attached to this bone,
and external to each is a slight roughened process called the
"jugular" eminence, because it borders that aperture of the
skull through which the jugular vein comes out. Behind
each condyle is a small hole, or foramen, which allows the
hypoglossal 1 nerve to pass out from the brain.

The occipital unites, as has been said, with the sphenoid in
front. Above this junction it articulates on each side with
the bone from which springs the mastoid process and zygoma,

1 For this and other nerves see Lesson VIII.

in.] THE CRANIAL SKELETON.

79

and which is called the temporal bone. Above the mastoid
it articulates on each side with one of the two great plate-
bones which roof the skull at the top and sides, and which
ire called the parietals.

In a new-born child the occipital bone consists of four
parts : (i), a median piece in front of the foramen magnum,
and which, as contributing to form the base of the skull, is
called "basilar;" (2 and 3), two "lateral" pieces, one 'on
each side of the foramen magnum, each supporting a con-
dyle, and pierced for the hypoglossal nerve ; (4), a large
median plate placed above the foramen magnum, and there-
fore called a " supra-occipital? and which shows traces of its
origin from more than one centre of ossification.

3. The PARIETAL bone is very large, and is connected
with its fellow of the opposite side by the sagittal suture, with
the occipital behind by the lambdoidal suture, anteriorly
with the frontal by the coronal suture, and below with the
temporal bone by a suture which is called squamous,
because the margins of the bones it joins are so bevelled
off that the temporal lies on the parietal like a scale.

The parietal arises from but one centre of ossification.

4. The remaining bone of the skull-roof is the FRONTAL,
which, single in the adult, is at birth divided into two parts
by a line of separation which continues onwards the median
separation between the contiguous parietals.

The anterior end of this bone is, as it were, bent sharply
backwards on each side to form two plates which roof the
bony orbits, while between these plates a space is left filled up
naturally by the bone forming the summit of the nasal cavity,
and called the ethmoid. Above the margins of each orbit are
slight transverse curved prominences, called the superciliary
and supra-orbital ridges, while each margin itself runs out into
what is named the external angular process, at each outer
inferior angle of the frontal bone, and joins the bone of the
cheek, or malar. Besides the unions just mentioned, the
frontal unites with bones to be hereafter described, namely
the sphenoid, nasals, lachrymals, and maxillaries.

5. On each side of the skull we find an exceedingly com-
plex bone called the TEMPORAL. (See Figs. 83, 89, 90, and 91.)

Part of it, as already mentioned, articulates with the
parietal by a squamous suture, and it is this part which forms
the hinder part of the zygoma and the articular " glenoid "
surface for the lower jaw.

A portion of bone which bounds the external opening of the

8o ELEMENTARY ANATOMY. [LESS.

ear below, is continued inwards as a tube having on its under
surface a rough ridge. On account of its connexion with the
drum of the ear it is called " tympanic? and forms the floor
of the passage leading into the internal ear or meatus audi-
torius externus. Between it and the glenoid surface is a
narrow slit or fissure, called the fissura Glaseri (which trans-
mits the chorda tympani nerve), while behind it hangs down
a long, very slender process, termed "styloid," posterior to
and outside the root of which is the stylo-mastoid foramen,
which transmits the facial nerve.

The rest of the bone consists of two parts, namely, (i) the
mastoid process already referred to, and (2) an irregularly
shaped piece (which on account of its hardness is called
the petrous1 bone) projecting inwards like a wedge on the base
of the skull, between the occipital and the sphenoid. In
addition to the connexions already noted, the temporal joins
the malar by means of its zygomatic process.

The petrous and mastoid portions enclose the inner and
essential parts of the ear, the internal canal of which (called
meatus auditorius interims} opens on the inner surface of the
petrous, wedgelike piece, and gives entrance to the nerve of
hearing.

Towards the apex of the wedgelike projection is seen a
large aperture which is one end of a canal, the other end of
which opens on the under surface within and in front of the
styloid process. This is the canal for the internal carotid
artery, which thus takes its way right through the petrous
portion of the temporal bone. Internal to its anterior open-
ing and at the angle formed by the junction of the petrous
part of the temporal bone with its squamous part, are two
small openings placed one above the other. These are the
apertures of two tubes (which run backwards, parallel and
apposed like the barrels of a double-barrel gun, in the sub-
stance of the bone), the lower of which is the Eustachian
tube, and conveys air from the mouth to the internal ear. The
upper tube gives passage to the small tensor tympani muscle.
A sharp ridge runs inwards and forwards from the root of
the styloid process. This ridge is termed the vaginal process.

The temporal bone arises by very distinct and significant
ossifications.

Thus we have (i) the squamous and zygomatic portions
forming one element ; (2) the tympanic portion, which is at
first a mere delicate ring of bone ; (3) the styloid process,

1 From Tre'rpof, a stcne.

in.] THE CRANIAL SKELETON-. 81

which is at birth separate from a little cylindrical piece of
bone which afterwards forms its root, and which is called
the tympano-hyal.1

Besides these three elements, three other distinct ossifica-
tions extend and coalesce to form the petrous and mastoid
portions of the temporal bone, and are distinguished by their
diverse relations to parts of the internal organ of hearing.
Continuing our enumeration, we have (4) an ossification which
gives rise to the upper part of the petrous portion (that which
is visible on the inside of the skull) and to part of the mastoid.
It forms the upper margin of what will hereafter be noticed
as the fenestra ovalis- of the internal ear, and is especially
related to the anterior vertical semicircular canal. It is called
the pro-otic.* (5) One which gives rise to the lower part of
the petrous portion (that which is visible on the base of the
skull) and forms the carotid canal. It also forms the lower
part of the fenestra ovalis, and surrounds entirely what is
termed the fenestra rotunda. It is called the opisthotic.*
(6) One which gives rise to the mastoid process, and which
is developed upon the posterior part, and what we shall here-
after know as the posterior vertical semicircular canal of the
internal ear. It is called the epiotic'.f The mastoid process
is not prominent at birth.

6. The SPHENOID 6 is a very complex bone, and has been
likened to a creature with a small body, two pairs of wings,
and two legs.

The central part, or body (which is anchylosed with the
basilar part of the occipital), has on its upper surface a
deepish pit, called \h&sella turcica or pituitary fossa, because
it receives the pituitary body of the brain. It is bounded
behind by a vertical plate, termed "clinoid,"7 from the
summit of which projects on each side a " clinoid process.

From each side of the body there projects upwards, out-
wards, and forwards a large more or less triangular plate,
called the greater a/a, or wing of the sphenoid, which also
sends a lamellar process downwards. At the root ot t
wing are three holes. The innermost and smallest— the
vidian— transmits the vidian nerve. Above and external t

' Discovered and named by Professor Flower (« Osteology/' p. 123}. Every
bone connected with the tongue-bone, or hyoid, has the term hyal as a part

itS*ThCas also been noticed in the Eighth Lesson of " Elementary Physiology."
3 np6, before and ovS, irog, the ear. , ^^

6 K&JSSSrtr, a wedge, and efcoc, like. 7 From *J* a bed.

G

82 ELEMENTARY ANATOMY. [LESS.

this is the foramen rotundum, through which passes the
second branch of the fifth nerve. Behind this is a larger
foramen (termed from its shape foramen ovale}, which gives
exit to the third branch of the fifth nerve. On each side of
the sella turcica, at its hinder part, is a groove for the carotid
artery. This groove is bounded in front and externally by a
small tapering piece of bone which is called the lingula
sphenoidalis, and which is situated between the body of the
bone and the greater ala.

f

"FIG. 86. — MAN'S SPHENOID BONE SEEN FROM ABOVE.

a, its greater wing — the lower letter a points to that downward continuation of
the great wing which is called the external pterygoid process ; bs, its body —
showing a cut surface behind, where it has been separated from the occipital
bone ; pc, the clinoid plate, bounding the pituitary fossae behind ; ps, the
anterior, or pre-sphenoidal part of the body of the bone ; o, lesser or orbital
wing ; /, internal pterygoid process ; i, optic foramen ; 2, sphenoidal fissure ; '
3, foramen rotundum ; 4, foramen ovale : 5, groove for the carotid artery.

The greater ala passes up between the squamosal and the
frontal to the parietal bone, and forms the anterior part of the
temporal fossa and the hinder, outer part of the bony orbit.

The downwardly extending plate is called the external
pterygoid T process. The internal pterygoid process is more
slender, terminating below in a hooked-Tike, or hamular, pro-
cess. The two internal pterygoid processes form what have
been fancifully called the legs of the sphenoid. Between the
internal and external pterygoid process of each side is a space
called the pterygoid fossa, which is closed behind by a palate
bone.

From the anterior part of the body the much smaller wings
called "orbital" project outwards, one on each side. The

1 From Ti-Ttpf?, a wing

in.] THE CRANIAL SKELETON. 83

base of each is perforated by the foramen, which transmits
the optic nerve ; behind the foramen projects backwards a
small "anterior clinoid process."

Each orbital wing forms the hindermost and innermost
part of the roof of the orbit.

The greater ala and the orbital wing of each side are
separated by a long but narrow space; termed the sphcnoidal
fissure. This transmits the third, fourth, and sixth nerves and
the first branch of the fifth nerve. In addition to the junc-
tions already noted, each ala unites with the malar bone of
its own side, and the body of the sphenoid is in contact with
a bone, the vomer, hereafter to be noticed.

At an early period the sphenoid bone may be said to be
made up of ten parts: (i) the bulk of the body; (2) the
anterior part of the body, or pre-sphenoidal part ; (3 and 4)
a pair of great wings and external pterygoid processes, or
two alisphenoidal parts ; (5 and 6) a pair of lesser wings, or
orbito-spherioidal parts; (7 and 8) the pair of internal ptery-
goid processes, or proper pterygoid bones ; and (9 and 10)
the lingulae sphenoidales.

7. The ETHMOID,1 or sieve-like bone, is of singular deli-
cacy of structure and complexity of
shape. It is placed between the skull
proper and the face, hanging down
between the orbits. It consists of a
transverse cribriform plate and of
three vertical portions. The cribriform
plate is so called from its sievelike
condition (being perforated with nu-
merous small holes for the nerves of
smell); it extends between the orbital FlG. 87.1MAN,S ETHMOID
plates of the frontal and the three BONE.

vertical portions. The first of these ^, Crista gain, rising verti-
three is median, and its summit, called caliy above the horizontal
crista galli, projects a little upwards S~££^52T3
into the cranial cavity, while the main the ethmoid; me, median
part is below the cribriform plate, and ethmoid,
forms the upper and front part of the

partition between the nares, whence it is termed the " median
ethmoid"

The two other parts hang down from the under surface of
the cribriform plate, and each is termed a " lateral ethmoid"
The outer surface of each of these is smooth, and appears

1 From r,0/uo£, a sieve.
G 2

84

ELEMENTAL Y ANA TOMY.

[LESS.

in the inner wall of the orbit as what is called the os planum,
which is bounded above by the frontal, behind by the sphe-
noid, in front by the lachrymal, and below by the maxilla.
The inner surface is swollen and irregular. That part of it
immediately below the cribriform plate is called the upper
spongy bone, or superior turbinate, or turbinal,1 the part
below being termed the middle turbinate.

Besides the junctions already noted, the ethmoid unites
with the sphenoid behind, and with the nasals, vomer, lachry-
mals, palatines, and lower turbinate bones (or turbinals).

8. The MAXILLARY bone supports on each side the teeth
of the upper jaw, and forms the bulk of that jaw, and con-
tributes to form the cheek, the orbit, the nasal passage, and
the palate. The two maxillary bones meet in the middle
line below the anterior nares, where each projects as a
sharp process — the anterior nasal spine. Each sends up a
prolongation (the nasal process) to the frontal, bounding the
inner side of the orbit anteriorly, and having at its hinder
side a lachrymal bone, and on its anterior side a nasal bone.
Its hinder surface exhibits a vertical groove. On the opposite
or external side the maxillary
bone sends a process outwards,
which joins the malar, and is
called the malar process. Above,
the bone exhibits a smooth hori-
zontal surface (the orbital plate),
which forms the floor of the
orbit. In front the bone has a
concavity, termed the canine
fossa, between which and the
lower margin of the orbit is a
foramen (called infra-orbital]
which transmits the second
branch of the fifth nerve.

From within the alveolar bor-
der each maxilla sends inwards
•&. palatine plate, which is joined
by the palate bone posteriorly,
but which internally meets its fellow of the opposite side,
except where the opening of the anterior palatine canal
separates them.

In the body of the bone is a large cavity called the Cave
ot Highmore, or the Antrum Highmori.

1 So called from being curved like a turbinated shell.

FIG. 88. — FRONT VIEW OF THE
RIGHT ORBIT OF MAN.

<?, greater wing of the sphenoid ;
f, frontal bone ; /, lachrymal ;
le, qs planum ; ;«, malar ; mx,
maxillary ; «, nasal ; i, optic
foramen ; 2, sphenoidal fissure ;
3, infra-orbital foramen.

in.] THE CRANIAL SKELETON. 85

Besides the articulations mentioned, the maxilla joins with
the ethmoid, the vomer, and the inferior turbinal.

At birth there may be a suture on the palatine surface of
the bone, separating off that small front part in which the
incisor teeth are afterwards implanted.

9. The MALAR bone is irregularly triangular in shape. It
forms the outer wall of the bony orbit, and connects the
zygomatic process of the squamous part of the temporal
bone with the maxilla. It joins above with the external
angular process of the frontal, and posteriorly with the great
ala of the sphenoid.

The NASALS are small bones placed side by side above the
nares, joining the frontal above, and separating the nasal
processes of the two maxillary bones one from the other.

The LACHRYMALS are small bones, one of which is placed
at the anterior part of the inner wall of each orbit, having
the frontal above, the os planum of the ethmoid behind, the
nasal process of the maxilla in front, and the orbital plate of
the same bone below. Each is marked with a vertical groove,
which, by joining the similarly directed groove (before spoken
of) on the posterior side of the maxillary nasal process, forms
a canal leading from the orbit to the nasal cavity, and termed
lachrymal because the tears pass down it.

10. The palate bones, or PALATINES, are very irregular in
shape, and wedged in between the maxilla and the pterygoid
processes of the sphenoid. Each consists of a long vertical
plate, from the bottom of which a smaller horizontal plate
projects inwards, meeting its fellow of the opposite side in the
middle line, and completing the palate behind the maxilla.
The palatine contributes to separate the nasal fossa from the
mouth, and extends up into the orbit, where it appears at the
back part of its inner wall beneath the os planum, separating
the sphenoid .from the maxilla, and helping to bound the
spheno-palatine foramen. Its outer side is grooved vertically,
the groove forming, with the help of the maxilla, the posterior
palatine canal. Its posterior surface is interposed between
the external and internal pterygoid processes cf either side,
thus completing the pterygoid fossa in front. The palatine
articulates also with the vomer and inferior turbinal.

11. The VOMER * is a single median bone extending down
from the sphenoid and median ethmoid to the upper surface
of the bony palate, thus completing the median partition
between the nostrils. Its hinder margin marks the partition

1 I.e. ploughshare, so called from its shape.

86 ELEMENTAR Y ANA TOM Y. [LESS.

spoken of already as medianly dividing the posterior nasal
openings. In the infant this bone consists of two lateral
portions.

The inferior turbinate bones, or lowest TURBINALS, extend
(one on each side) from before backwards along the nasal
fossae, attached, though but slightly, to the inner side of the
maxillary and palatine bones.

12. The only naturally separated bone of the skull in the
adult, namely the lower jawbone, or MANDIBLE, consists ot
a curved osseous band, almost of the same depth through-
out, and convex forwards. It has a smooth rounded inferior
edge, but its upper edge is festooned by unequal cavities,
forming sockets for the teeth, whence this upper border
is termed " alveolar." The whole band is termed the body
of the mandible ; a vertical line at its middle in front is
called the syinphysis? and each half of the body external to
this line is called the horizontal ramns (or branch). At its
hinder end each horizontal ramus turns suddenly upwards at
a slightly obtuse angle, and terminates above in two processes,
the front one of which is pointed and is called the " coronoid
process? while the hinder one ends in a rounded head, " the
condyle" mounted on a narrower part termed the " neck"

This nearly vertical part on each side is called the ascend-
ing ramus, and the point where its posterior margin meets
the inferior margin of the horizontal ramus is named the
"angle." (Fig. 83.)

The condyle is wider than it is long, and fits into the glenoid
cavity of the squamous part of the temporal bone. An inter-
articular fibre-cartilage (with one synovial sac above it and
one below it) is interposed between the two bones, and the
ascending ramus is also attached to the skull by strong
ligaments.

The coronoid process rises nearly as high as the condyle,
and has inserted into it the temporal muscle which adheres,
at its origin, to the side of the skull within the arch of the
zygoma.

On the inner side of the ascending ramus is a foramen,
called the inferior dental, and another, the mental foramen,
is placed, more forwards, on the outer side of the horizontal
ramus.

The symphysis is concave vertically in front, the lower
border of the mandible projecting at the symphysis to form
the chin.

1 From o-i'/i^oyUf, to grow together.

in.] THE CRANIAL SKELETON. 87

At birth the bone consists of two parts, which are separated
at the symphysis, and at first the ascending ramus slants
much backwards, but gradually rises till it is nearly vertical
in the adult.

13. Another bone, often not reckoned as part of the skull,
is the os hyoides (so named from its resemblance to the
Greek letter v), which is placed beneath the root of the
tongue.1 It consists of a " body " with a pair of processes
on each side, one large (the great cornu) and one small
(the lesser cornu, or corniculum). The body is transversely
oblong, hollowed behind, convex in front, and narrow from
before backwards. It is called the basi-hyal.

The great cornua extend backwards from the lower outer
angle of this " body ;" they are rather long and nearly straight,
and though at first distinct bones, become anchylosed to the
basi-hyal. Each is also termed a thyro-hyal?

The lesser cornua, or comiculat arise from the upper
aspect of the " body " at its junction with the greater cornua,
and each corniculum (or, as it is also called, cerato-hyalY is
attached to this " body " by a synovial sac, though sometimes
by bony union. Each corniculum is short and conical, and
united by a ligament to the styloid process of the temporal
bone.

-==44: Considering now the OUTSIDE OF THE SKULL as a
whole, we find on its base in front the alveolar margin, —
forming a graceful curve, and surrounding the bony palate
(with its palatine foramina), which extends a little further
back than the teeth, and ends in the posterior free margin
of the palatine bones.

Behind the palate are the posterior nares, on each outer
side of which is a pterygoid fossa, bounded as before de-
scribed. In the middle of the basis cranii is the basilar part
of the occipital bone, behind it the foramen magnum, con-
dyles, and condyloid foramina.

' On each side is the petrous part of the temporal bone, with
its styloid and vaginal processes and its carotid and stylo-
mastoid foramina.

Between the front end of the petrous bone and the basi-
cccipital is, in the dry skull, an opening called the foramen
lacerum anterins.

Between the hinder part of the petrous bone and the lateral

1 For its more precise relations see Lesson XII. : the Larynx.

2 From its being placed close to the thyroid cartilage of the larynx.
' KfLiut', a horn.

ELEMENTARY ANATOMY

[LESS.

part of the occipital, is an opening named the foramen
lacerum posterius, which transmits, besides the jugular vein,

FIG. 89. — OUTER VIEW OR UNDER SURFACE OK THE RIGHT SIDE OF
MAN'S SKULL.

lo, body of the occipital bone ; c, occipital condyle ; e, anterior end of Eusta-
chian tube (between e, 5, and the vacuity behind 3, is the petrous part of the
temporal bone— somewhat triangular in shape, with its apex forwards) ; g,
glenoid surface of the temporal bone ; m, mastoid process ; «, posterior nares :
pt, pterygoid fossa ; so, squama of the occipital bone ; st, styloid process ; z,
zygomatic malar bone, joining zygomatic process of temporal bone ; i, anterior
palatine foramen ; 2, posterior palatine foramen ; 3, points in front of the
foramen lacerum anterius ; 4, foramen ovale ; 5, carotid canal ; 6, stylo-mastoid
foramen ; 7, foramen lacerum posterius.

the glosso-pharyngeal, par vagum, and spinal accessory
nerves.

in.] THE CRANIAL SKELETON. 89

Between the outer side of the petrous bone and the adja-
cent margin of the ala of the sphenoid is a groove for the
reception of the Eustachian tube.

Behind the foramen magnum is the great occipital expanse.

On each side of the base of the skull we find the zygoma
(arching but little outwards), the glenoid surface, the Eternal
auditory meatus, and the mastoid process.

Looking at the side of the skull, we see a fissure not yet
noticed. This is the ptery go-maxillary, which runs up be-
tween the posterior border of the maxilla and the adjacent
pterygoid process. At its summit it meets the inner end
of another fissure, namely the spheno-maxillary, which runs
forwards and outwards between the inferior margin of the
great ala of the sphenoid and the upper part of the maxilla.

These two fissures by their junction form an angular
depression called the spheno-maxillary fossa, and into it
open the foramen rotundum, the vidian and spheno-pala-
tine foramina, and the upper end of the posterior palatine
canal.

15. In the INSIDE OF THE SKULL, as seen from above
when a horizontal section is made and its top removed, we
note the following structures. In the middle, in front, the
crista galli and cribriform plate, bounded on each side by the
orbital plates of the frontal (which are but slightly convex),
and behind by the anterior part of the sphenoid and orbital
wings, each pierced at its base by the optic foramen, and
having a sharp posterior margin marking off the hinder limit
of what is called the anterior fossa of the skull.

The middle fossa includes, in its centre, the basilar part
'of the sphenoid (with the pituitary fossa and posterior clinoid
process), and on each side, the great ala of the sphenoid
(pierced towards its root by the round and oval foramina,
and leaving the sphenoidal fissure between it and the orbital
wing), the squamous part of the temporal bone, and the an-
terior part of its petrous portion — at the inner end of which is
seen the anterior end of the carotid canal opening immedi-
ately above the foramen lacerum medius.

A ridge running forwards and inwards along the petrous
bone defines its anterior part from its posterior, and at the
same time the anterior margin of the posterior fossa of the
skull. This ridge has attached to it a membrane called
the tentorium, which divides the cerebellum from the cerebral
part of the brain. The posterior fossa includes the hinder
part of the petrous bone with its internal auditory meatus,

ELEMENTAR Y ~ ANA TOMY.

[LESS.

the foramen lacerum posterius and condyloid foramen, and, in
the middle, the foramen magnum and basi-occipital.

FIG. 90.— A VIEW OF THE UPPER, OR CEREBRAL, SURFACE OF LEFT SIDE OF
MAN'S SKULL.

a, greater wing of the sphenoid ; bo, base of the occipital ; c, .cribriform plate ;
f, orbital plate of fruntal ; g, crista galli ; o, lesser or orbital wing of the sphe-
noid ; p, pituitary fossa ; pa, parietal ; so, squama of occipital : sq, squarnous
part of temporal bone ; 3, foramen lacerum anterius ; 4, foramen ovale ; 6,
foramen lacerum posterius ; 7, meatus auditorius internus — in the petrous part
of the temporal boae.

The removed cap of the skull is smooth within, showing
sundry slight depressions, and amongst them a longitudinal
median groove, to which is attached the membrane called the
jalx, which extends back from the crista galli and dips in
between the two upper halves of the brain.

in.] THE CRANIAL SKELETON. 9t

When the skull is divided vertically and in the direction
of the sagittal suture, we may note the vast size of the brain
cavity in proportion to the face ; also the horizontal con-
dition of the cribriform plate and foramen magnum, and the
advanced position of the latter approaching the middle line
from behind forwards.

The basilar parts of the occipital and sphenoid bones are
seen to become rapidly thicker as \ve go forwards ; they form

FIG. 91. — VERTICAL, LONGITUDINAL SECTION OF MAN'S SKULL.

a, greater wing of the sphenoid ; an, meatus auditorius interims ; bo, body of the
occipital bone ; bs, body of the sphenoid ; c, condyle ; c ', crista galli ; cy, con-
dyloid foramen ;_/", frontal ; me, median ethmoid ; mx, palatine plate of the
maxillary ; n, nasal ; o, squama of the occipital bone ; /, parietal ; //, palatine
bone ; pt, internal pterygoid process ; s, frontal sinus ; sq, squamous part of
temporal bone (beneath it is the petrous part of that bone, with the opening
an) ; t, lowest turbinal bone ; v, vomer. The straight line passing upwards
and forwards from the hinder end of the body of the occipital bone, represents
the basi-cranial axis. The line passing downwards to the front of the jaw,
represents the basi-facial axis.

the true axis of the skull, and a line drawn from the anterior
margin of the foramen magnum to the front end of the
middle part of the upper (or cerebral) surface of the sphenoid
is called the basi-cranial axis. A line drawn from the same
point of the sphenoid plate to the front part of the alveolar
margin of the maxilla is the basi-facial axis, anjfl the two
axes in man form an angle which varies from 90° to 120°.
The basi-cranial axis forms with the foramen magnum a

92 ELEMENTAR Y ANA 7V M I : [LESS.

very obtuse angle, while with the cribriform plate it forms an
obtuse one, open downwards and forwards.

The extreme length of the cranial cavity is always more
than 2] times that of the basi-cranial axis, while it may be
nearly 2f times the length of the latter.

The half of the lower jaw forms an arc joining the skull
above directly at the glenoid surface.

The half of the hyoid bone forms a much smaller arc
behind the former, and joined to the skull indirectly, namely
by the ligament which suspends it by the corniculum from
the styloid process.

When the skull is divided vertically through the external
auditory meati, i.e. transversely, or in the direction of the
coronal suture, we see that the basilar part of the occipital
forms as it were a centre.

The anterior part of the section shows the great cranial
arch rising above this centre and closed in front, while below
it is the arch of the lower jaw, and further forward the arch
of the upper jaw, enclosing the double tube of the nostrils
which extends from the anterior to the posterior nares.

The posterior part of the section shows us the hinder part
of the great cranial arch rising above the centre and closed
behind, while below it is the arch of the hyoid and its liga-
ments, reaching up to the styloid processes.

16. As to the CAVITIES OF THE SKULL : the orbits in man
are pyramidal cavities completely encircled by bone, and
each so separated off from the temporal fossa behind it,
by the malar and alisphenoid, that the elongated spheno-
maxillary fissure is the only opening left.

At the back are the optic and round foramina, and between
them the sphenoidal fissure, the vidian foramen being hidden
from view.

Within the anterior margin on the inner wall of each orbit
is the lachrymal foramen.

The two orbits are separated from each other in part by the
cranial cavity (above the cribriform plate), and in part by the
nasal cavity (below the cribriform plate).

The nasal fosses, extending backwards above the palate
from the anterior to the posterior nares, and enclosed be-
tween the maxillae, are separated from each other by the
median, ethmoid, and vomer, and in front of these by carti-
lage. The three turbinals project inwards from the outer
wall of each fossa, and beneath the lowest the inferior ter-
mination of the lachrymal canal opens.

in.] THE CRAXIAL SKELETON 93

In the substance of the frontal bone, just above the nasals
are, almost always, certain cavities filled with air called the
frontal sinuses. These communicate with the nasal fossa
below, through the middle turbinals.

The body of the sphenoid and the maxillae also contain
large air-holding cavities, termed the sphenoidal and mav-
illary sinuses, and opening respectively beneath the upper
and middle turbinals into the nasal fossse.

17. In DEVELOPMENT the first appearance of the future
skull is indicated by the expansion of the anterior end of
the primitive groove before spoken of.

FIG 92. — DIAGRAM OF THE FORMATION OF THE SKULL, SEEN FROM ABOVE.

BO, the plate of cartilage representing the future body of the occipital bone ; N,
the anterior termination of the notochord ; an, the cartilaginous auditory
capsule containing the internal ear ; p, the space afterwards becoming the
pituitary fossa, and now enclosed on its two sides by two cartilaginous rods —
the trabecitl<z cranii, which meet in front of it at(i) to form the ethmo-
vomerine plate from which the median (ME) and lateral (LE) ethmoids arise ; 2,
the second cartilaginous rod. or arch, forming the maxillary arch; 3, the
third arch, forming the mandibular arch (or lower jaw) ; 4, the fourth arch,
forming the hyoidean arch.

This expansion becomes subdivided by two lateral con-
tractions (one in front of the other, on each side), so that
three rounded cavities are produced, one behind, one above,
and one in front of the anterior termination of the noto-
chord—the primitive skull being sharply bent down just
in front of the anterior termination of the notochord.

In the walls of these rounded expansions, or vesicles, no
quadrate thickenings occur similar to those which are de-

94 ELEMENTARY ANATOMY. [LESS.

veloped (one in front of the other) on each side of the chorda
dorsalis, and which are the precursors of the vertebrae.

A solid, flattened mass surrounds the anterior termination
of the chorda dorsalis, and forms the cartilaginous foundation
and precursor of the basilar part of the occipital bone, and
may be called the basi-cranial plate.

Continuous with this on each side is a rounded mass of
cartilage which is the precursor of the petrous parts of the
temporal bone and of the lateral parts of the exoccipital ; and
the latter cartilages, growing up to meet together above,
enclose the foramen magnum with a cartilaginous ring.

From the front of the basi-cranial plate two cartilaginous
rods, called trabeculce cranii?- extend forwards and down-
wards. These at first diverge, and then converge and meet,
thus leaving a space in which the pituitary fossa comes to be
placed.

ati

FIG. 93. — DIAGRAM OF THE FORMATION OF THE SKULL, SEEN LATERALLY.
N, the anterior termination of the notochord in the cartilaginous occipital mass ;
EO, a lateral upward extension of that mass, forming the foundation of the
future lateral part of the occipital bone ; att, the auditory capsule ; a and o. the
cartilaginous beginnings of the future " greater" and "orbital" wings of the
sphenoid ; i, one of the trabeculie cranii running forwards to expand in the
ethmo-vomerine plate or foundation of the future median (ME) and lateral (LE)
ethmoids ; 2, the second (maxillary) arch running forwards to abut against the
ethmo-vomerine cartilage ; 3, the mandibular arth ; 4, the hyoidean arch.

This prolongation forwards, after sending up on each side
two cartilaginous representatives of the sphenoidal wings,
forms, as has been indicated, a median plate (termed Ethmo-
vomerine), which sends downwards three other plates to form
the median and lateral ethmoids.

The rest of the walls and roof of the skull are completed
by membrane only.

Besides the trabeculas, other cartilaginous rods extend"

1 From trabecula, the diminutive of trabes, a beam or rafter.

in.] THE CRANIAL SKELETON. 95

downwards from the basi-cranial plate, or rather from the
lateral cartilage contiguous with it.

Thus a second rod, external to the trabecula, on each side
passes forwards (almost parallel with the trabecula adjacent
to it) and fuses with the Ethmo-vomerine plate.

A third rod descends and fuses with its fellow of the op-
posite side, so forming the groundwork of the lower jaw,
which is thus laid in what is often called the first visceral
arch, but which is really the third.

The next, or fourth cartilaginous rod, meets with its fellow
below only by means of the interposition of soft structures,
and lays the foundation of the styloid processes and corni-
cula of the os hyoides, which thus are contained in what is
really ihefourt/i visceral arch, though often called the second.

The fifth visceral arch develops on each side, at its ven-
tral part, the precursor of the cornu and body of the hyoid
bone.

Ossification occurs, as has been stated, in more than one
point of most of the bones which are reckoned as single bones
in the adult man. Thus it occurs in the lateral and superior
parts of the occipital as well as in the basilar part ; in the
wings and inner pterygoid processes of the sphenoid, as well
as in those two parts of its body which may be distinguished
as the basi-sphenoid and the pre-sphenoid — the latter sup-
porting the orbital wings. In the temporal bone, as has been
pointed out, many very distinct ossifications occur.

The ossification of the ethmoid and of all the turbinals
and vomer takes place in, around, and from the ethmo-
vomerine plate and the cartilages of the trabeculae, or first
visceral arches.

The palatine bones, internal pterygoid processes, and
maxillary bones, are ossifications connected with the second
visceral arches.

The mandible — which arises from one point of ossification
on each side — invests the ventral end of the cartilage (called
Meckel's) of the third visceral arch.

1 8. Turning now to OTHER VERTEBRATES, we find that
in the possession of a cranium man agrees with all except
the Lancelet. This animal can hardly be said to have a brain
at all, so slight is the enlargement of the anterior end of
its spinal marrow : consequently its brain-case is, as might
be expected, similarly imperfect, and consists merely of the

o6

ELEMENTA K Y ANA TO MY.

[LESS.

membranous investment of this terminal part of the spinaJ
marrow.

In other Vertebrates a definite and distinct brain, en-
closed in a definite and distinct brain-case of solid tissue
(cartilaginous or osseous), with jaws and hyoidean appendages,
is almost a constant character.

In that the skull is sharply and distinctly differentiated off
from the spinal skeleton, man agrees with the vast majority
of Vertebrates, and with all Vertebrates without exception
above Fishes. It is possible, however, for the cartilaginous
representatives of vertebrae to coalesce into one mass with
the cartilaginous skull (as in the Sturgeon), or even when the
skeleton is osseous (as in the Siluroid fish Bagrns, where
these bones are suturally united). Indeed, in such cases, the
transition from spine to cranium is so gradual that it is easy
to mistake part of the vertebral column for part of the skull.

FIG. 94. — VERTICAL, LONGITUDINAL SECTION OF THE POST-AXIAL PART OF THE
SKULL, AND OF THE MORE PRE AXIAL VERTEBRA OF THE SILUROID FISH
Bagnis. (After OIVCH.)

at, body of first vertebra ; ax, body of second vertebra ; -;3 — z>7, bodies of the
next five vertebrae, each line going to the middle of a biconcave centrum ; bo,
basilar part of the occipital bone ; co, exoccipital ; 5, spinous process of the
second vertebra. Directly above ^ is the post-axially projecting supra-occi-
pital. Hy, the hypapophysial canal running beneath the first five vertebrae.

The almost completely osseous condition of the skull of
man is one common to him and to his class. In the Sauro-
psida the skull is often eked out, as it were, by considerable
tracts of cartilage or membrane, and in the Ichthyopsida
the cartilaginous portion is always more considerable, and
may constitute the greater part or the actual whole of the
solid brain-case and annexed structures.

The shape of the skull will be spoken of afterwards, but

in.] THE CRANIAL SKELETON. 97

here it may be stated that the division of it adopted in human
anatomy, into cranium and face, is one which is natural. By
the former we shall understand the brain-case proper, and no
more. By the face we shall understand not only the bones
usually included in that category in anthropotomy, but the
ethmoid and parts of the sphenoid also, namely the internal
pterygoid processes, which, as we have seen, arise in man
about the second visceral arch.

The number of bones of which the skull is composed in
man when adult is much less than in many animals ; on the
other hand, it is more than in many, where, as in the class of
Birds, the process of anchylosis is more rapid and extensive.

Certain small bones of the ear, called auditory ossicles,
are, in works on human anatomy, included in the description
of the internal ear. For this reason the full notice of these
ossicles will here also be similarly deferred ; though from the
important part they are said to play in many lower, and all
the lowest forms, and their relations to hyoidean structures,
they must be somewhat noticed even in describing the true
skeleton considered as the framewyork of the body.

19. The OCCIPITAL bone of man represents some of the
most constant ossifications of the solid cranium. The con-
dition of union its parts present in him is the one normal in
his class, though the union of its elements is often longer
delayed in some Mammals than in him.

On the other hand, the occipital bone (or parts of it) may
anchylose with more than it anchyloses with in man, as is
the case in the Sauropsida, where, except in the Chelonians,
two portions of the petrous bone (the epiotic and opisthotic)
become intimately united with parts of the occipital.

In the lower forms (or Ichthyopsida), where the skull is
ossified, either the main parts of the human occipital are
represented by distinct bones, or only a portion of them are
so represented.

Thebasilar process (basi-ocdpitaT) is a constant ossification
in all except Batrachians and some Fishes, and when y
in the latter (as the Cod. Perch, Pike, £c.), remains a distinct
bone throughout life. It may, however, as in Batrachians
and in the Lepidosiren. be represented merely by cartilage ;
and this in spite of other portions of the occipital being
ossified. The basi-occipital may give origin to a median
descending process like a hypapophysis, and may indeed (as
in the Carp) send one down so far as to penetrate the watt
of the alimentary canal and serve in mastication.

H

98 ELEMENTAR Y ANA TOMY. [LESS.

The hinder end of the basi-occipital has a more important
function in the Sauropsida than in man's class, as it develops
a convex projecting head or condyle, which articulates with
the vertebral column. In most Fishes it is concave, its con-
cavity being applied to the concavity of the body of the first
vertebra in the same way that all the bi-concave vertebrae arc
united together.

FIG. 95. — VERTICAL, LONGITUDINAL SECTION OF THE SKULL OF A FOWL.
{After Parker.}

a, angular bone of mandible ; as, alisphenoid ; az, articular bone of mandible :
bo, basi-occipital ; d, dentary bone of mandible ; f, frontal ; me, median
ethmoid ; os, orbito-sphenoid ; /, parietal ; /', pro-otic ; pf, pituitary fossa ;
px, pre-maxilla ; sa, surangular bone of the mandible ; so, supra-occipital ;
sp, splenial bone of the mandible ; sg, squamous part of the temporal bone,
or squamosal ; v, vomer.

The lateral parts (exoccipitals] are constantly ossified where-
ever the skull is ossified at all ; and their position with
regard to the spinal marrow is constant. They always
transmit, either as in man by a notch, or by a foramen, the
eighth pair of nerves, and also the hypoglossal nerve where it
exists, but this latter is wanting in Fishes.

In the fact that the occipital condyles are mainly formed
by the lateral parts (exoccipitals), man agrees with his own
class. They may, however, be entirely formed by the ex-
occipitals, as in Batrachians ; or these bones may more or
less help to form one single median convex articular condyle,
as in the Sauropsida.

The peculiarities as to the position of the foramen magnum
will be spoken of in considering the skull as a whole.

The Squama of man, or supra-occipital, is of a relative
size greatly in excess of that which exists in most forms, but
still it may attain a yet greater importance than in him. This
is the case, for example, in the Cetacea and in the Elephant,
where its relative as well as absolute size is enormous.

THE CRANIAL SKELETON.

Again, it may be divided into two parts, its upper portion
being reckoned as a distinct bone (interparietal} as, e.g., very
often in Rodents. A still more divided condition of the supra'-
occipital may obtain, as in the Ganoid fish Lepidosteus.

On the other hand, as in the Frogs and Toads, the supra-
occipital may be absent altogether, the lateral portions, or
exoccipitals, meeting as well above as below the foramen
magnum.

The faintly marked superior curved lines of the human
occiput are but feeble representations of the great bony pro-
jections which the occipital bone may develop. Thus, even
in one of the forms nearest to man/ — the Gorilla — there maybe
an enormous lambdoidal ridge. In Ruminants, again, this
ridge may be largely de-
veloped, and have bony ex-
tensions (the horns) reaching
out from it, as in the Ox.

The jugular process of man
may be developed to a much
greater extent, bearing the
name of par-occipital or para-
mastoid process, as e.g. in the
Babirussa and Capybara. It
may help to form the tym-
panic cavity, as in Birds, or be
completely absent, as in the
Ichthyopsida.

A singular relationship
seems often to exist between
an aquatic habit and defect-
ive development of the basilar

part of the occipital bone. Thus this part is altogether absent
in Batrachians, it is often imperfectly ossified in Seals, and
seems to be rudimentary in some of the Cetacea.

In the last-named animals, as also in very many I
the supra-occipital is brought into direct connexion with the
frontal— a condition very different from that of man.

20. Whereas the occipital bone of man is the representative
of four distinct bones in lower animals, his PARIETAL bone,
on the contrary, is in its normal condition, as it arises always
from a single ossification. Indeed, not only is it never mon
complex than in him, but in many animals (e.g. the MOJ
tremes, Serpents, and the Salmon) the two panetals anchylo:
at a very early period into a single, median bone.

II 2

FIG. 96.— SIDE VIEW OF THE SKULL
OF AN ADULT MALE GORILLA.

o, supra-orbital ridge ; s, sagittal ridge
(a lofty plate as indicated by the
shading) ; /, lambdoidal ridge — the
last is foreshortened as it projects
laterally.

100

ELEMENTAR Y

[LESS.

Generally, as in man, the two parietals meet, but, as has
been said in treating of the occipital, they may be encroached
upon, and depressed to the side of the skull (as in the Cetacea),
by the union of the last-named bone with the frontal.

The great size of the parietals of man is very exceptional,
and has direct relation to the immense development of his
brain. On the other hand, they may be in great part mere
bars, as in many Lizards.

The parietal may give off a lamellar expansion helping to
roof over the temporal fossa — as in the Turtle and the curious
African Rodent Lophiomys.

The exclusion of the parietal from any junction with the
sphenoid by that of the frontal bone with the temporal, which
occasionally occurs in man, is very common in Apes. On
the contrary, it may extend to join not only the greater but
also the less, or orbital, wing of the sphenoid.

The parietal may be one with the frontal, forming a fronto-
parietal bone, as in the Frog and Lepidosiren,

FIG 97.—- UPPER SURFACE OF THE SKULL OF A FROG. {After Parker.}

c, os en ceinture, or girdle-bone ; eo, exoccipital ; /", frontal part of fronto-
parietal bone ; mx, maxillary bone ; n, nasal ; op, opisthotic ; p, parietal
part of fronto-parietal bone ; f»n, pre-maxilla ; po, pro-otic ; pi, pterygoid ;
.7, quadrato-jugal ; ^7, squamosal ; sus, suspensorium of lower jaw.

From within the parietal an ossified falx may extend into
the cranial cavity, as in the Ornithorhynchus, while the junc-
tion of the parietals may be extended upwards into a large
sagittal crest, as in many Carnivora, and even in the
Gorilla.

in.] THE CRANIAL SKELETON, 101

21. The development attained by the FRONTAL bone in the
human subject is very greatly above the average of man's
class, and bears relation to the vast development of his brain
Sometimes, on the contrary, as in the Cetacea, the orbital
part may be enormously developed outwards on each side.

The primitive double condition in which, as we have seen
this bone exists in man, very often persists in adult life in
other Mammals. It may do so in Apes, though sometimes in
that order (e.g. Pithecid] not only is it united, but it even
develops a median ridge, continuing fonvards the sagittal one.

In many Reptiles and Fishes, however, this bone is single,
as in the Gecko and the Cod.

Each half of the frontal bone may meet below as well as
above, so as to form a complete bony ring, as in the Python.

The external angular process of the
frontal may rarely (as e.g. in the Horse)
join not the malar, but the zygomatic
process of the temporal bone.

In the majority of the members of
man's class this process joins neither FIG. QS.-DIAGRA.M REPRE-

Of those bones, but merely forms a SENTING A TRANSVERSE

freely projecting post-orbital process. SSS^cSS^S

Sometimes it is completely absent, f frontalj m its fdlow

as is the case in several forms, e.g. Of the other side both

the TanrCCS. above and below in the

On the other hand, in the Sauro- l^f^STSt
ps.cla, a distinct bone (either tempo- cuia crami which persist
rally as in Birds, or permanently as in "SttckSatt
Reptiles) extends downwards from the ba<,e of the skull,
postero-external part of the frontal.

This either ends freely, as in most Birds; or it contributes to
form a sort of upper zygoma, as in some Parrots and Lizards ;
or, as in Python, passes downwards to abut against the single
zygomatic arch. It is called the post-frontal.
' A bone exists in the skull of osseous Fishes which has
often been called the " post-frontal," but which has no rela-
tion to that bone of Reptiles, being really an ossification of the
ear capsule, and therefore the representative of part of the
petrous bone of man.

The superciliary ridges, which in some races of men are
much marked, may attain a far greater size, being at their
maximum in one of the highest Apes, viz. the Gorilla.

The two sides of the frontal may unite behind the cribri-
form plate, as is the case in the commonest Monkeys.

102

ELEMENTAR Y ANA TOMY.

LESS.

The frontals may develop great bony processes, which are
the bony cores supporting the corneous sheaths of hollow-
horned Ruminants, as e.g. in the Goats. They may also
periodically develop branched pro-
cesses, " antlers," as in Deer.

These will be more conveniently
considered in the Seventh Lesson.

22. The TEMPORAL bone of man
is the representative not only of a
number of distinct bones in lower
animals, but of bones of very differ-
ent natures both as to origin and
function.

What answers to the squamous
portion in man, is called the " squa-
mosal" in lower animals.

In man it is of greater relative
size, and takes a larger share in the
formation of the inner cranial wall
than is the case in most of his
class, though, strange to say, it
becomes again relatively larger in
one of the very lowest of Mammals,
i.e. the Echidna.

Below the Mammalia it becomes
excluded from all share whatever
in bounding the cranial cavity, and
may be a mere bar contributing to
form the bony scaffolding of the
skull, as in Lizards or as in bony
Fishes. A portion of it may descend
from the cranium altogether, and

FIG 99. — Upper view of the

;ull o"
centetas; showing the ab- become a mere part of ^ giU-cover

Skull of the Tanrec, Hem

sence of a zygomatic arch on

each side. flap, the pre-operculum.

The function of suspending the

lower jaw is one peculiar to this element of the skull in
Mammals, while in all Vertebrates below Mammals the
squamosal has no part in such an office.

Amongst his own class, man presents a medium develop-
ment of the glenoid surface, which may be much more con-
cave than in him (as in Carnivora), or much less so (as in
Ruminants).

Its antero-posterior concavity is thus most marked in the
hard-gripping Badger, where the anterior and posterior bony

in.] THE CRANIAL SKELETON. 1O3

margins of the glenoid surface are so prolonged that the
lower jaw cannot be removed, even from the dry skull with-
out fracture of one of those osseous processes.

FIG. loo.— SIDE VIEW OF THE SKULL OF A PERCH. (After Citvier.)
i, the frontal ; 2, the pre-frontal ; 4, the sphenotic ; 7, parietal ; 8, supra-occipital ;
9, exiotic; ir, pro-otic ; 12, pterotic ; 17, pre-maxilla ; 18, maxilla; 19,
first sub-orbital bone, or lachrymal ; 19', chain of posterior sub-orbitals ; 20,
nasal ; 21, one of a chain of post-temporal ossicles ; 23, hyo-mandibular ; 24,
ecto-pterygoid ; 26, quadrate ; 27, meta-pterygoid ; 28, operculum ; 30, pre-
operculum ; 31, symplectic ; 32, sub-operculum ; 33, inter-opcrculum ; 34,
dentary ; 35, articular ; 36, angular ; 42, urohyal ; 46, post-temporal, or bone
connecting scapular arch with skull.

The projecting (zygomatic) portion of the squamous element
is constantly present in Mammals, though it may end freely,
as in Centetes- and Sorex, or join the frontal instead of the
malar, as in the Horse.

It also projects freely downwards in most Birds, but
it may (as in some Parrots) articulate with a post-frontal
element.

In Reptiles also it may project forward, and form a sort of
upper zygoma by articulating with the post-frontal, as in some
Lizards (e.g. Sphenodon, Cyclodm\ or it may be articulated
with the cranium at one end only, as in Python — the other
end projecting backwards and slightly outwards, to give ad-
ditional mobility to the lower jaw.

104 ELEMENTARY ANATOMY. [LESS.

It may develop, as in Fishes, a post-orbital process of its
own.

Its junction with the malar is not found anywhere out 01
man's class.

The squamosal of some Birds (as the Ostrich) may send
down a process, the representative of which is more con-
spicuous in the Frog, and becomes separated off from the
superior portion in the Eft. It is this lower portion which ib
the pre-operculum of Fishes.

FIG. ioi.— SIDE VIEW OF THE SKULL OF A RATTLESNAKE (Crotalns).

a, articular bone of lower jaw; bo, basi-occipital ; </, dentary;_/", frontal ;_/",
pre-frontal ; me, median ethmoid ; inx, maxilla ; o, pro-otic ; /, parietal ; pa,
para-sphenoid ; pt, pterygoid ; px, pre-maxilla ; git, quadrate ; qs, squamosal.

The petrous and mastoid elements (petro-mastoid) of the
temporal bone require a more lengthened notice.

In the first place, it may be observed that the distinct-
ness of these united elements is shown in many Mammals
where the petro-mastoid bone remains unanchylosed and
separate from both the squamosal and tympanic elements
of the temporal bone. This is the case, e.g., in the Pig. It
may be united with the tympanic element, but not with the
squamosal, as in the Hare and the fully adult Porpoise,
being in the latter only united to the rest of the skull by
ligamentous attachment.

Still, in all man's class, what we have seen to be the con-
stituent parts of the petrous and mastoid elements always
cohere into a single mass before they unite with other cranial
elements, while such a complete primitive union never takes
place in any Vertebrate not a Mammal.

The very prominent mastoid process of man is peculiar to
him, as, though in many other Mammals it is more or less
developed, it is generally rivalled or surpassed in them by
the elongated process of the occipital bone before mentioned.

Even in the highest Apes the degradation of the mastoid

in.] THE CRANIAL SKELETON. 105

process is remarkable, and bears relation to the absence of
an erect posture of the body — a posture which distinguishes
man from the other members of his order.

Air-cells which exist, even in man, in the mastoid, extend
into the substance of the squamous element in the Gorilla,
and sometimes, as in Macroscelides and Pedetes, the mastoidal
air cavities are enormous, causing great projections of the
skull.

A large vaginal process is peculiar to man, that part being
represented but slightly even in the Gorilla.

The carotid canal is far from being a constant character of
the temporal bone, even in Mammals. Often, as e.g. in the
Cat, the carotid artery may pass through the foramen lacerum
posterius, merely grooving very slightly the petrous bone ; or
much more rarely, as in the Opossum, it may perforate the
sphenoid bone.

In most Mammals, except the highest Apes, there is a deep
pit on the inner surface of the petrous bone, as in the Hare:
this is to receive a certain part of the brain, termed the floc-
cular process of the cerebellum.

The stylo-mastoid foramen is a constant aperture, the
seventh nerve passing out through such an opening in the
petrous element wherever this is ossified in vertebrate animals.

FIG 102 —VERTICAL, LONGITUDINAL SECTION OF THE SKULL OF A PERCH.

(After Cuvier.)
i frontal, ; 2, pre frontal (or lateral ethmoid) ; 3, median ethmoid ; 4, sphenitic :

5, bisi occipital ; 6, para-sphenoid ; 7, parietal ; 8, supra-occipital ; 9, epiotic ;

10, exoccipital ; 11, pro-otic ; 12, pterotic ; 14, ahsphenoid; 13, pre-sphenoid ;

1 6, vomer.

But not only the seventh nerve, but the third portion of the
fifth also, may perforate the same bone, as is the case in
Serpents, in Batrachians, and in many Fishes (e.g. the Pike) ;
or it may only notch it, as in Crocodiles and Birds ; or it
may, as in man, pass altogether in front of it.

106 ELEMENTARY ANATOMY. [LESS.

The three elements (pro-otic, epiotic, and opisthotic) which,
as we have seen, coalesce to form the petro-mastoid part 01
the temporal bone of man, may be differently proportioned
and conditioned from what they are in him.

The Pro-otic is the largest and most important element ol
the three in Vertebrates below Mammals.

It may meet with its fellow of the opposite side below, and
thus form part of the inside floor of the skull, as is the case
in many Fishes, e.g. the Pike.

The Opisthotic constantly anchyloses with the lateral part
of the occipital before it unites with the pro-otic in all Verte-
brates below Mammals. In many forms, e.g. the Cod, it
never unites with the pro-otic at all.

The Epiotic constantly anchyloses, in all Vertebrates below
Mammals, with the squamous portion of the occipital bone
before it unites with the pro-otic and opisthotic elements.

In Fishes and in Chelonians it preserves its distinctness
from the occipital, though in Chelonians it coalesces with the
opisthotic.

These three bony barriers protecting the internal ear may
be conveniently spoken of as the periotic mass.

This mass may have added to it a part which, in some
Mammals, appears as a lamelliform expansion, as in the Mole
and still more in the Echidna, where it constitutes a con-
siderable part of the cranial wall between the occipital, the
squamosal, and the parietal bones.

In Fishes, e.g. the Cod and Pike, it appears as a bone pro-
jecting at the postero-external angle of the roof of the skull.
It is called the pterotic? It may also, in Fishes, have added
to it a large and distinct ossification, the sphenotic? which
has been called by mistake the post-frontal, and which takes
part in suspending the lower jaw.

The tympanic element of the temporal bone of man may,
even in forms so little removed as are the American Apes, be
reduced to the ring-like condition which it has in the human
infant. On the other hand, in many Mammals, e.g. in the
Dog and especially Macroscelides, it forms a large inflated
structure termed a bulla. In oviparous Vertebrates it is not
represented except by the frame of the tympanic membrane.

The styloid element may be more conveniently treated of
under the head of hyoidean structures. It is sufficient to say

1 n-rf piif , a wing.

2 So called because adjoining the alisphenoid,- by its discoverer, Mr. W. K.
Parker, F.R.S., who also discovered and named the " pterotic."

THE CRANIAL SKELETON.

107

here that it is only found very elongated and anchylosed to
the skull in man, though an anchylosed but less elongated
one is sometimes found in a species of Baboon.

103. — Under Surface of the Skull of the Lemur Microcebns minor, showing
the inflated auditory bullae (on each side in front of the foramen magnumj, and
al»o the defects of ossification in the bony palate.

The tympano-hyal will also be noticed with the hyoidean
structures. Only in Mammals, but in them constantly, does
it form a process of the skull. Its common form, as in the
Dog, is that of a small cylindrical truncated process, between
the tympanic bulla and the paroccipital process. In man it
is obscured by anchylosis with the styloid process, of which it
forms the root.

23. The SPHENOID, like the temporal bone of man, is a
highly complex one, as is made evident by what we find in
other animals.

The body of the sphenoid is a less constant structure as a
distinct bone than might be supposed. On the other hand, that
close union between it and the basi-occipital, which in adult
man is constant, is rarely found elsewhere. Even the body of
the sphenoid itself, in Mammals, is generally formed of two

! oS ELEMENTA R Y ANA TOM Y. [LESS.

distinct bones, the posterior of which is termed in zootomy
the basi-sphenoid, while the anterior ossification (in front of
the pituitary fossa) bears the name of pre-sphenoid.

The basi-sphenoid is a point of very great morphological
importance, marking as it does the anterior termination of
the chorda dorsalis, which never advances further forwards
than the hinder margin of the sella turcica.

Now, there may be no bony representative of the basi-
sphenoid at all — although more or less of the rest of the skull be
ossified— as is the case in Lepidosiren and the Batrachia ; or
it may be represented by a mere rudiment — -a little Y-shaped
bone, only forming part of the front of the pituitary fossa, as in
the Pike. Thus it need form no part of the inside floor of the
skull, nor yet any of the basis cranii, although the last-named
part be well ossified, as it is in osseous Fishes and Batrachians.
In the Ichthyopsida, in fact, only the median bony investment

FIG. 104. — UNDER SURFACE OF THE SKULL OF A FROG. (After Parker.)
c, girdle- bone ; eo, exoccipital ; mx, maxilla; par, parasphenoid ; pm. pre-
maxillri : po, pro-otic ; pt, pterygoid ; q, quadrato-jugal ; sns, suspense- ium of
lower jaw, the lower end of which represents the quadrate bone ; i>, vomer ;
i, optic foramen ; 2, foramen ovale ; 3, condyloid foramen.

of the basis cranii is a special membranous ossification, termed
the para-sphenoid, which extends, both backwards and for-
wards, far beyond the limits of the basi-sphenoidal region.
This "membrane" bone is also large and conspicuous in
Snakes (which have the body of the sphenoid in a cartilagi-
nous condition), but it seems to be representated in man, if
at all, only by the " lingulae sphenoidales."

in.] THE CRANIAL SKELETON. IO9

The basi-sphenoid itself, on the other hand, may be hyper-
trophied, sending out a long rostrum in front and lateral
processes, as is the case in Birds ; and in man's own class it
may develop descending and diverging processes, as in the
Hedgehog, Centetes, and the Porpoise. In the first two we
find a hemispherical depression on the under surface of the
sphenoid body, reminding us of the sella turcica on its
cranial surface.

The pre-sphenoid attains not only more distinctness, but a
much greater length, in Mammals generally than in man. In
all lower forms, however, it is more or less rudimentary or
absent : absent, e.g., in Batrachians ; rudimentary in Birds
and some Fishes, e.g. the Carp and Salmon.

The basi-sphenoid may be directly perforated by the in-
ternal carotid artery, as is the case in Marsupials ; or the two
carotid canals may unite in it, as in Birds.

The posterior boundary of the sella turcica, with its clinoid
processes, is more prominent in man than in almost any other
animal, and the depression of the sella is very marked in
him. It may be quite indistinct, as in Marsupials and
Batrachians.

The sella may, on the contrary, be a deep and sudden de-
pression without any prominent margins directed upwards, as
in many Fishes, e.g. the Pike.

A singular and unexpected function may be performed by
the cartilaginous body of the sphenoid, as in the Pike and
in very many other Fishes, where it forms part of the roof of
a large conical excavation of the basis cranii, in which ex-
cavation the muscles of the eyeball take their origin.

The greater wings of the sphenoid bear in zootomy the
name alisphenoid. They form a part of the cranial side-wall
which is very generally present in an osseous condition, though
not so in Chelonians or Batrachians. Alisphenoids are in-
variably developed in all the members of man's class (Mam-
malia), and also in Birds and Crocodiles. Usually they take
a relatively greater share in the formation of the cranium
than in man, whose skull-roof bones are so enormously ex-
panded. This is notably the case in Marsupials and some
Insectivora, where they extend far back and form the anterior
part of the auditory bullae, and in the Kangaroo even touch
the paroccipital process.

The orbital plate of this bone is not developed in Mammals
below man's own order, but its homologue is developed in
some Birds, e.g. Accipiter and Strixj and it is possible that

1 10 ELEMENTAR Y ANA TOM Y. [LESS.

it may also be represented by the sphenotic, which in bony
Fishes unites with the pterotic to furnish the point of suspen-
sion for the lower jaw.

The so-called external pterygoid process of man is really
but an outgrowth of the alisphenoid, and must be considered
with it. This part is absent in all animals below Birds, and
in Birds where it exists, e.g. in the Finches (Fringilla), it is
represented by but a single or double ridge.

In Mammals generally, however (except the Echidna), it is
present, and more or less as in man, though mostly it is
larger and less deep vertically.

The external carotid artery may pierce the root of this part
(as in the Dog), forming thus a special bony channel called
the alisphenoid canal. The third branch of the fifth nerve
may pass more anteriorly with regard to this bone than in
man, as is the case in the Sheep. On the other hand, it gene-
rally passes out altogether behind it. A vidian canal is often
much more conspicuous than in him, e.g. in the lower Apes.

A distinct foramen rotundum is often present and often
absent. In the latter case, the second branch of the fifth
nerve passes out through the sphenoidal fissure, as e.g. in the
Hare, Squirrel, and Stag.

Each of the lesser wings of the sphenoid is termed in
zootomy an orbito-sphenoid, and in some forms, e.g. in Rumi-
nants, the proportion they bear to the alisphenoid is the
reverse of that which obtains in man, so that the application
to them generally of the name they bear in anthropotomy,
"lesser-wings," would be manifestly out of place. These
bones are constantly present in man's class, but, unlike the
alisphenoid, are often absent in the class of Birds, though
present in many kinds (e.g. Accipiter and Tinamus). They
are mere rudiments in most Reptiles — often altogether absent
— though they maybe developed in Lizards. In Batrachians
they may be well developed, or coalesce (as in Frogs and
Toads) with the ethmoid in a way to be described in treating
of that bone. In Fishes they are generally absent, but may be
well developed, as in the Carp, where however they form one
bone with the pre-sphenoid.

Occasionally, as in the Hare, they may be so disposed as to
constitute a median, interorbital septum, the two optic fora-
mina having become merged one in the other.

The optic foramen may be excessively minute, as in some
Insectivora, and there may be a foramen passing from orbit
to orbit beneath it, as in Macroscelides.

in.] THE CRANIAL SKELETON. ni

The internal pterygoid processes of man represent very im-
portant and constant parts of the cranium, which exist in all
classes down to and including bony Fishes.

The share which they take in man in bordering and bound-
ing the posterior nares is by no means their normal office in
Vertebrates generally. In Birds and in all lower Vertebrates
(except the Crocodiles) they have no connexion with these
apertures, but are quite posterior to them, serving to connect
the hinder part of the palatine with the point of suspension ot
the lower jaw, and, except in Fishes, have also a connexion
with the sphenoidal region of the basis cranii.

Sometimes, as in Serpents, these bones may be very
movable.

In certain forms, t.e. in the Crocodiles, Ant-eaters (see
Fig. 117), and in the Echidna, these bones may develop
horizontal plates, which form the posterior part of the bony
palate. So that, in these animals, the posterior nares are
bounded by the pterygoids, both laterally and inferiorly.
The pterygoid may be swollen and bullate, as in the Mole
and in some Sloths.

The internal (but not the external) pterygoid processes
really belong, not to the cranial bones proper, but to those of
the face.

In Lizards, a peculiar dismemberment of the pterygoid,

Frc. 105.— Diagrammatic Vertical, Fro. 106. — Diagrammatic Vertical,

Transverse Section of the Skull of Transverse Section of the Skull of

a Lizard, showing the columellcz a Chelonian, showing the meeting on

ascending from the pterygoid bones each side of upward processes of the

to the parietals. pterygoids with downward processes

/, parietal ; //, pterygoid bone ; pt ', of the parietals.

columella, or dismemberment of p, parietal ; pt, pterygoid ; s, basi-

pterygoid ; s, basi-sphenoid, diverg- sphenoid,
ing processes of which join the two
pterygoids.

called the columella, may ascend and join the parietal. In
Chelonians a corresponding process of the pterygoid may
ascend and meet a corresponding downwardly directed pro-
cess of the parietal.

24. The ETHMOID is another complex aggregation of ele-
ments which are distinct in lower animals. In man's class,

1 1 2 ELEMENTAR Y ANA TO MY. [LESS.

however, it remains, for the most part, pretty much as it is
in him.

The os planum, in that it is large and conspicuous and
situated on the inner wall of the orbit, presents conditions
which man shares with the Apes, but which are very rare in
other forms. In some Cats, however, it appears in the orbital
between the lachrymal, frontal, and palatine bones.

The part corresponding to the os planum of man exists
within, and hidden by, the maxillary plate in other mammals ;
but it may be represented by a cartilage or cartilages, as in
birds.

The lateral masses of the ethmoid appear in the form
of distinct bones (pre-frontals] in Crocodiles, Lizards, and
osseous Fishes. They may, as in the Chameleon, extend on
to the maxilla, so shutting out the nasals from the anterior
nares ; and in some Chameleons they may be prolonged so
as to help to form two great bony horns projecting forwards
from the muzzle.

The median ethmoid is constantly present in a cartilaginous
or osseous condition as part of the internasal septum. Even
in fishes it is generally more or less ossified. It is possible
that it may appear on the external surface of the skull in
Mammals, as in the Seal Monachus. It does so in Fishes
(e.g. Carp and Tench), and at least in some Birds.

A peculiar condition of the parts may exist, such as is found
in the Frog, where the ethmoid forms (or is part of) a bone
which has been likened to a dice-box with a vertical parti-
tion at one end, and has been named by Cuvier os en ceinture,
or girdle-bone. It consists probably of the lesser wings of
the sphenoid united to the median and parts of the lateral
ethmoid.

The ethmoidal cells of the lateral ethmoid may attain a
much greater size and complexity than in man, as we see in
the Dog and very many Mammals. On the other hand, these
parts may utterly and entirely abort, as in the Porpoises.

A cribriform plate is common to, and generally large in
man's class ; it may be wanting, as in the Porpoise, or enor-
mous, as in the Echidna.

The crista galli is more denned in man than generally
in Mammals, but it may be very large, as in some Seals and
Ungulates.

In certain Seals again, as in Cystopkora, and in the Tapir,
the median ethmoid may extend forwards beyond the anterior
end of the nasals.

in.] THE CRANIAL SKELETON. 113

The lower turbinals may be noticed next after the ethmoid,
being of cognate nature.

The simplicity of their structure in man would hardly lead
us to anticipate the size and complexity which they may
attain in some animals, e.g. in the Badger and the Sheep'.
They may, on the contrary, abort altogether, as is the case
in the probably smell-less Porpoises. In the Elephant they
are but rudimentary.

In Fishes these bones are quite absent, and in Batrachians
are represented by a mere cartilaginous rudiment.

In Reptiles they are simple, and quite, or almost entirely,
cartilaginous, though with a slight bony outgrowth in the
Crocodile. But in Birds they may be represented by two or
three insignificant ossifications.

25. As to the MAXILLARY bone, we will consider first the
whole of it except that small portion in which the incisor
teeth are implanted ; such whole being the bone called " the
maxillary bone/' or "maxilla," in other vertebrate animals
generally.

In that it presents an external facial part, an internal
nasal part, an inferior palatine part, and a superior orbital
part, the maxillary bone of man agrees with that of almost
all Mammals.

In lower forms, except the Crocodilia, the maxilla is much
smaller, and it may be a mere filiform rudiment, as in Silu-
roids, or abort altogether, as in the Siren and the Myxinoids.

It may, on the contrary, be represented by several dis-
tinct and separate bones placed in a series along the jaw, as
is the case in the bony Pike (Lepidosteus).

Very often its length may greatly exceed its height, as in
the Great Ant-eater and in Cetaceans.

In that the bone bears teeth, we have in man a character
which is by no means universal in his class, as e.g. in the
Ant-eaters, Whalebone Whales, and the Echidna, the maxilla,
like every other bone of the skull, is edentulous. The same
is the case in Birds and Tortoises, but in many Fishes (as e.g.
the Cod) the maxilla may be edentulous, while nevertheless
other bones of the face bear teeth.

The facial surface of the bone is occasionally much swollen
out, as in the Baboons. Sometimes, as in the Paca, this
surface is rough and pitted, while the bone is excavated by
a large fossa which opens on the inner surface. Again, the
facial surface may be very imperfectly ossified and may pre-
sent a reticulated structure, as in the Hares.

I

ii4 ELEMENTARY ANATOMY. [LESS.

The infra-orbital foramen may be multifold, as in most
Apes, or may be enlarged into an enormous aperture, trans-
mitting part of the masseter muscle, as is the case in the Por-
cupine and some other Rodents. This great opening may
exist, and yet the true infra-orbital canal be denned by a bony
lamella, as in the genus Lagostomus.

The palatine plate of the maxilla exists in all Mammals
and in Crocodiles, yet even in Mammals it may occasionally
be excessively reduced, as in the Hare. In the lower classes
it is wanting.

JKK

pm'

FIG. 107. — SIDE VIEW OF THE SKULL OF A PORCUPINE (Hystrix crisiata).
a, angle of mandible ; c, occipital condyle ; cr, coronoid process of mandible ; cy,
condyle of mandible ; f, frontal , z, incisor teeth ; j, ascending branch of
maxilla enclosing the enormous infra-orbital foramen, the course of the
masseter muscle through which is indicated by an arrow ; in, molar teeth ;
7/?_r, maxilla ; n, nasal ; pin, premolar teeth ; pm', paramastoid process ; px,
premaxilla ; t. tympanic bone ; z, zygomatic arch— the part formed by the
malar.

The maxilla may acquire an enormous size, and overlap
and almost entirely conceal the frontals, as in Cetaceans.

Sometimes, as in Chiromys, the maxilla is shut out from
articulating with the nasal bone by the extension upwards
to the frontal of that separate element of the human
maxillary bone which is next to be noticed. The latter
element may, sometimes, be separated by an interval from
the part corresponding to the rest of the human maxilla, — as
in the Three-toed Sloth.

Occasionally (as in some specimens of Macacus nemes-
trinus, and in the Gavial) the maxillary bone may join its
fellow of the opposite side above the nasals, thus separating
the latter from the frontals.

Occasionally, as in some Chameleons, the maxilla may
project freely forwards as a great bony horn at the front part
of the face.

in.] THE CRANIAL SKELETON. 115

The second element of the human maxillary bone — namely,
that in which the incisor teeth are implanted— is termed i'n
zootomy the pre-maxilla. Its existence in man, even at
birth, is obscured (except on the surface of the palate) by
anchylosis, and masked by the extension over it of a delicate
plate, or lamina, of the first and far larger portion of the
maxillary bone. This lamina is wanting in all other animals,
and even in the Apes the maxillo-premaxillary suture is for a
long time or permanently very evident on the face.

A pre-maxilla is almost a constant element in an osseous
skull; nevertheless, in some Bats and Shrews (e.g. Crocidura)
it seems to abort. It may attain a vast size, as in Birds,
where it forms the greater part of the upper half of the beak,
and reduces the part representing the other element of the
human maxillary to insignificance. Generally double in Ba-
trachians, apparently always so in Fishes, a single median
ossification may nevertheless, as in Serpents, represent the
pre-maxillae of both right and left sides conjoined.

In man's class the pre-maxilla varies greatly in size in dir-
ferent animals, and this independently of the development
both of the muzzle and of the teeth ; for the Ant-eater and the
Whale are both edentulous, and both have an enormously pro-
duced muzzle, yet, while in the former the pre-maxilla is ex-
tremely small, in the latter it is very largely developed. A
nasal spine is very rare, but may exist below man, as in
Pedetes and the Walrus.

Generally the development of the pre-maxilla is related to
that of the incisor teeth, which are defined by the fact of their
being implanted in it, though when they are very large, as in
Rodents, their roots may extend backwards into the parts
which represent the first-described element of the maxillary
bone of man.

In some Bats (e.g. Vespertilio noctula], and the Ornitho-
rhynchus, we find the pre-maxilla separated by an interval
from its fellow of the opposite side. On the contrary, these
may be united not only below but also above the anterior
nares, as in the Gavial and Echidna. Again, they may be
united in the middle line, but altogether separated from the
first-described element of the human maxillary bone, as in the
Three-toed Sloth and in Serpents.

In this latter case we have normallv existing that occasional
abnormal arrest of development in man, which we call
" hare-lip."

26. The MALAR bone is almost at its maximum of relative
I 2

1 1 6 ELEMENTAR Y ANA TO MY. [LESS.

development in man, and only in Mammals and the Crocodile
does it approximate to the condition it attains in him. It is
a less constant bone than the maxillary, as it is absent in
some Mammals, e.g. Centetes and Mams, also in Batrachians,
Serpents, and generally in Fishes.

It may be merely a delicate spiculum of bone, helping to
form the zygoma, as is the case in Birds.

In none but man and Apes does the malar develop the
orbital plate, and generally in Mammals it does not even
meet the frontal outside the orbit ; and when the orbit is
encircled by bone, the malar may be separated from the
frontal by the intervention of the zygomatic process of the
temporal bone, as in the Horse.

Processes may be developed which do not exist in man, as
is the case in the Sloths, where there is both an ascending
and a descending process, but no process to form a junction
with the zygomatic portion of the temporal bone.

There may be a considerable perforation in the malar, as
in some Lemurs and Insectivora.

Sometimes, as in the Porpoise, the malar may be double—
the zygomatic portion being a separate ossification from its
front part.

27. The NASAL bones are more constant elements of the
bony skull than are the malar bones, as, except in most
Chelonians, they seem to be constantly developed. There
may be a pair of them, as in man (and this is the general
rule), or there may be but a single median ossification, as is
the case in Varanian Lizards. Even in man's class (Mammalia)
they may be represented by a single bone through their early
anchylosis, as is the case in Centetes, Spalax, and the Orang.

The very extremes of development of these bones are also
to be found in the same class, as in the last-mentioned form
(the Orang) they all but abort, and in the Porpoises they form
small rounded masses, each lying in a concavity on the
frontal bone, and not at all roofing over the nasal passages.
On the other hand, in the Porcupine they are of enormous
size, in fact the largest of the cranial bones.

In the Porpoises the two nasals may cease to follow the
general rule among Mammals, of joining each other. In
Fishes they may lie wide apart. They may be shut out from
bounding any part of the anterior nares, as in the Chameleon,
where the pre-frontal extends to the maxilla, as before
mentioned.

28. The LACHRYMALS may be altogether absent, or may

THE CRANIAL SKELETON.

117

have a different function from that they have in man ; or
having the same function as in him, they may be considerably
increased in size and importance.

They may be absent as distinct bones even in man's class
• — especially in forms which pass a large part or the whole of
their lives in water, and where the secretion of tears is super-
fluous.

Thus they are absent by anchylosis with the malar in the
Dolphins, and are wanting altogether, unless early anchylosed
with the maxillary or malar, in the Seals and Pangolins.
On the contrary, though very small, they are present in the
Elephant and Sirenia, but in an imperforate condition.

JflX-

FIG. 108. — UPPER VIEW OF THE SKULL OF A DOLPHIN {Delphinns globiceps).
(After Cuvier.)

c, occipital condyles ; e, median ethmoid in nasal fossa ; f, frontal overlapped by
mx, maxilla ; «, nasal ; /, parietal, driven down quite to the side of the skull;
f»i, pre-maxilla (here enormous) ; so, supra-occipital.

They are present and of good size in many Fishes (e.g. Pris*
tipoina\ where each lachrymal constitutes the first of a chain
of suborbital scalelike bones, which extend beneath the orbit
from before backwards. In Fishes, of course, there is no
lachrymal foramen.

These bones appear to be absent altogether in Batrachians,
and sometimes in Birds, though present, and sometimes large,
in Reptiles (e.g. Chelonians).

In that the lachrymal is confined to the orbit, man differs
-from most of his own class, except the Apes ; even in animals
so high up in the scale as Lemurs it not only extends on to
the cheek, but the lachrymal foramen is placed there.

ii8 ELEMENTARY ANATOMY. [LESS.

Often it is of great size, as in the Hare, Ant-eaters, and
Armadillos, or, as in the Deer, not only largely developed, both
in the orbit and on the cheek, but also presenting a peculiar
fossa destined to receive and shelter a special glandular
structure.

This bone may join the malar, as in the Squirrel and the
Hog. Its junction with an os planum is a very exceptional
condition, though found in Apes as in man.

It may join the palatine bone in the orbit, as e.g. in the
Rhinoceros.

It may even complete the sub-orbital foramen superiorly,
as in Dolichotis.

The lachrymal may develop a small process, as in the
Hare, or even a large osseous bulla, as in the Hippopotamus
and most Ruminants, notably in the Giraffe.

29. The PALATINE bones of man are important and con-
stant elements of the vertebrate skull, being not only repre-
sented by ossified tracts in every osseous cranium, but being
also clearly represented by cartilage in skulls which never
become divided into separate bony elements.

The condition, however, which each palatine presents in
man is a very exceptional one when we compare it with that
prevailing in Vertebrates generally, and its form and propor-
tions are exceptional even amongst Mammals, its vertical
extent in him so greatly exceeding its antero-posterior dimen-
sion. Already, in Apes, its length is greater in proportion to
its height than in man. This elongation may be enormously
increased, as in the Great Ant-eater — though the prolongation
of the muzzle does not necessarily carry with it a similar
increase in length of the palatine, as we see in the Dolphin,
Globicephalus, where it is comparatively short.

That the posterior margin of the palate bones should form
the antero-inferior border of the posterior nares is a character
which man shares with most of his class, and with no other.
In some Mammals, however (as we have seen), it is the ptery-
goids which perform this function, as in the only Sauro-
psidans (Crocodilia) having a palate with a solid bony roof
like man's.

It is the rule, however, that the anterior margin of the palate
bones forms the postero-inferior margin of the posterior nares.
as we find to be the case in Birds, non-crocodilian Reptiles,
and Batrachians,

This difference of position in the palate bones is owing to
the fact that the horizontal, or palatine, plate, and the greater

in.] THE CRANIAL SKELETON. 119

part of the perpendicular plate, are parts which have no bony
representatives in non-mammalian Vertebrates, with the ex-
ception of the Crocodiles. Only that part of each palate
bone which connects the body of the sphenoid with the
vomer and upper-maxillary bone (i.e. the sphenoidal and
orbital processes) is represented by the palatine bones of such
non-mammalian Vertebrates.

FIG. 109.— UNDER SURFACE OF A FOWL'S SKULL. (After Parker.}

/'.•>, basi -occipital ; en, points just in front of the anterior opening of the Eusta-
chian tubes ; J, malar ; mx, maxillary bone ; p, palatine bone ; pf, post-orbital
process ; //, pterygoid ; px, pre-maxilla ; q, quadrate bone ; qj, quadrato-
jugal ; so, supra-occipital ; v, vomer.

In almost all those Fishes which have no osseous skull the
palate bones are represented by the anterior part of that
cartilaginous bridge, or flying buttress, which proceeds from
within the front of the mouth backwards and outwards to-
wards the point of suspension of the lower jaw, and which in
Sharks supports teeth and is called the upper jaw.

Sometimes the horizontal plate has large defects of ossifica-
tion, as in many Marsupials and the Hedgehog.

Often in Mammals the palatine may directly join the frontal
in the orbit, as in the Hog, Lemur, and Pteropus. It may
join the lachrymal, as in the Dog. It may extend in the orbit
between the lesser wing of the sphenoid and maxillary, and

120 ELEMENTARY ANATOMY. [LESS.

between the frontal and the lachrymal, as is the case in
Dolichotis. It may or it may not take a share in the forma-
tion of the pterygoid fossa. It appears even to form part of
the margin of the optic foramen in the Echidna.

30. The VOMER again is a bone of remarkable constancy.
It is much less concealed by other bones in Vertebrates
generally than in man, and may appear not only in the palate
(where it is indeed normally visible), but also externally on
the surface of the skull.

In the fact that in the adult condition it is a median,
azygos bone, the vomer of man agrees with that of all Mam-
mals, where it is mostly large. In Birds it may be large, as
in the Ostriches, or nearly absent, as in the Pigeons. It is
almost always single in them, but may be double, as in the
Woodpeckers. In Reptiles it is generally double, but may
be single, as in the Chelonians. In Batrachians it is in-
variably large and double. In Fishes it is large and single in
nearly all, but may be double, as in Lepidosteus and Sudis.

In Mammals the shape of this bone, as might be expected,
varies generally with that of the face. Thus it is extremely
elongated in the Dolphins.

In all above Fishes it contributes to form the partition
between the nasal passages, and (except where the facial
bones develop palatal plates, as in Mammals and Croco-
diles) borders internally their posterior openings.

31. The inferior maxillary bone, or MANDIBLE, of man is a
very characteristic bone, though substantially agreeing with/
that of other Mammals.

It bears, however, a double relation to parts we find in-
lower animals. For, while inasmuch as it forms the whole
lower jaw it of course agrees with, and answers to, the whole
lower jaw of each bird, reptile, and fish ; yet in development
and essential nature, it corresponds with a certain portion
only of the lower jaw of each of these animals.

Thus it is possible for the part answering to the whole
lower jaw of man (i.e. the bone called "dentary") not to
articulate directly with the cranium, but to be connected with
it by a whole series of intermediate parts, as is the case in
all Vertebrates below Mammals, and especially in osseous
Fishes.

We may find, as in the Sauropsida, an actual lower jaw
consisting of several distinct bones (dentary, angular, sur-
angular, coronoid, splenial, and articular) suspended from the
skull by a single bone— the os quadatrum ; — or we may find,

in.] THE CRANIAL SKELETON, 121

as in osseous Fishes, the actual lower jaw, consisting of a
dentary and other bones, suspended from the side of the
skull by the intervention of more than one bone.

In the last-named group the lower jaw is suspended from
elements of the ear capsule (viz. the sphenotic, pterotic, and
pro-otic) by a bone called the Hyomandibnlar, and by other
bones the lowest of which is termed the Quadrate, with which
the uppermost part of the lower jaw articulates. The bones
from the hyomandibular to the quadrate (inclusive), or the
cartilaginous parts which in some forms may represent these,
are collectively termed the suspejisorium.

FIG. no — SIDE VIEW OF THE SKULL OF A LIZARD {Varanus).

a, articular bone of mandible ; c, coronoid bone of mandible ; d, dentary ; _/",
frontal; f, pre frontal ; f'\ post-frontal; /, lachrymal; ;;/, malar; ntx,
maxilla; «, nasal ; o, pro-otic; /, parietal ; pt, pterygoid ; pt ', columella, or
dismemberment of pterygoid ; pt" y os transversum ; pjc, pre maxilla ; q, quad-
rate bone ; *y, squamosal.

§A lower jaw, however, may be entirely and completely
absent, as is the case in the Lamprey.
In forms in which the skull is not osseous (as the Sharks)
the mandible is represented by cartilage.

Wherever below Mammals the skull is ossified, the lower
jaw consists of a bone representing the lower jaw of man and
Mammals, together with three or four other bones forming with
it the actual ramus on each side ; and, in addition, there is a
distinct part by which this complex ramus articulates with
the suspending bone or bones which sustain it.

This articular part, with the suspending bone (called the
" quadrate " in Birds and Reptiles) or bones (of which there
may be several, as in Fishes), all taken together, answers to
parts which are not commonly reckoned as portions of the
skeleton in man, namely to parts of the internal ear, i.e. to

122 ELEMENTARY ANATOMY. [LESS.

certain of the auditory ossicles, as we shall see more distinctly
when we come to treat of the organs of sense.

Confining ourselves to man's own class, his mandible
appears to be well developed, but the form and proportion
of its parts may be very different from what we see in him.

Thus there may be, as in the Great Ant-eater and Ceta-
ceans, no representative of the ascending ramus ; or it may
be very low, as in most Rodents, e.g. the Porcupine.

The coronoid process may be much developed, rising
greatly above the condyle, affording attachment to the volu-
minous temporal muscle, as in the Dog ; or it may be low
or rudimentary, as in many Rodents.

A considerable process, termed the angular process, may be
developed at the point of junction of the posterior borders of
the vertical ramus with the inferior margin of the horizontal
one, as in the Dog. This process may be distinctly bent in-
wards, as in the Opossums and almost all Marsupials.

The condyle is always either more or less eo'nvex or
flattish (thus differing from the surface offered by the
articular part of the lower jaw in animals below Mammals, in
which it is always more or less concave), but its longer
diameter may be antero-posterior, as in some Rodents, or
still more decidedly transverse than in man, as in carnivorous
animals, where the movement of the jaw is vertical and not
to and fro, — whether from before backwards, as in Rats,
Rabbits, &c., or from side to side, as in Ruminants.

Mostly in Mammals the lower jaw continues throughout
life to be made up of two bones articulating at the symphysis
by suture — as in the human infant at birth.

The symphysis generally inclines from above downwards
and backwards, and only in one Ape (the Siamang Gibbon)
is there a chin as in man.

The symphysis may be exceedingly narrow, as in the
Ant-eater and Porpoise. It may be very elongated but hori-
zontal, as in the Cachalot. The two rami may be each nearly
straight, or each may be strongly curved outwards, as in the
Whalebone Whales.

The symphysis may be narrow and grooved above so as
to give it the appearance of a spout, as in the Elephant, or
it may be extraordinarily produced downwards, as in the
Dugong.

The entrance of the dental foramen may be exceedingly
capacious and funnel-shaped, as is the case in the Dolphin.

The mandible may be directly connected with the neural

in.] THE CRANIAL SKELETON. 123

spines of the anterior (most pre-axial) vertebrae by a very
strong ligament which prevents the mouth from being widely
opened. This is the case in the Eft Desmognathus.

32. That very subordinate bone of the human skeleton, the
OS HYOIDES, or tongue-bone, is but a feeble rudiment of
skeletal structures of great size and functional importance
in the lower Vertebrates. Even less than the temporal bone
is it capable of revealing its true nature when studied in
man alone.

Small, however, and subordinate as is the os hyoides in
him, it may yet be more rudimentary still. Thus osseous
parts may be entirely absent, and only represented by two
delicate cartilages, as is the case in Serpents.

Throughout man's class we find a substantially similar con-
dition to that which exists in him. That is, we find a body
and a pair of cornua, and almost always a pair of cornicula,
but the proportions of these parts one to another, and their
degree of segmentation, vary.

riG. in. — Hyoid of a Flying Fox (Pteropus), showing the much greater length

of the cornicula than of the cornua.

I, body of the hyoid ; sh, corniculum divided into three segments -stylo-hyal,
epi-hyal, and cerato-hyal ; th, the cornua of the os hyoides, or thyro-hyal.
(From Flowers "Osteology.")

Thus the cornicula may abort altogether, as in some Apes.
>r they may be large, and represented by three distinct ossi-
ications, named respectively (from above downwards) stylo-
hyal, epi-hyal, and cerato-hyal, as is the case in the Flying Fox
and in the Dog. These cornicula are normally connected with
that process of the under surface of the petrous portion of the
temporal bone which has been named the tympano-hyal.
The lowermost of these three pieces may send out a process
and meet its fellow of the opposite side in front of the body
of the bone, as is the case in the Hyrax.

The cornua are more constant in the degree of their
development in Mammals. They may be of large size, as
in the Thylacine, but never present the segmented con-
dition we so often find existing in the cornicula. They are
perhaps at about their maximum of relative size among
Mammals, in the Horse.

124

ELEMENTAL Y ANA TOMY.

[LESS.

The body of the hyoid may be in quite a rudimentary con-
dition, as in the Sheep, or swollen and inflated to an enor-
mous relative size, as in the Howling Monkey. It may
develop in front a long, median, projecting process, termed
a glosso-hyal, as in the Horse, which in man is only repre-
sented by the vertical ridge on the anterior convex surface ot
the body of the os hyoides.

When we descend below man's class we may find (e.g. in
Birds) that the cornicula more or less abort, while the cornua
are very long and slender. A glosso-hyal may not only
extend forwards from the basi-hyal, but another azygos
median part (the uro-hyal) may extend backwards from the
basi-hyal.

A most unexpected condition may exist, as we see by the
Woodpeckers, in which both the elongated cornua curve over
the back part of the cranium, and are together inserted just
above and behind the right nostril !

In Reptiles we may (as in the Crocodiles) find a car-
tilaginous body together with one pair
of cartilaginous cornua, and these not
joining the skull. But generally both
cornua and cornicula are developed, and
may be large and complex, as in the true
Lizards, and the glosso-hyal may be
enormous, as in the Chameleon. When,
however, we descend to the class Batra-
chia we begin to perceive the full signi-
ficance of the hyoidean cornua, and this
by means of the transformation under-
gone by the Frog in its passage from
its larval (and fish-like) state as a tad-
pole to its adult condition.

In the fully-developed state the os
hyoides of the Frog consists of a body
with a pair of cornua and a pair of corni-
cula. But the process of development
shows that the pair of cornua are the last
rudiments and relics of those cartilagi-
nous arches which exist on each side of
the neck in the larva and support the gills.

These cartilaginous gill-arches of the tadpole evidently*
answer to the great cartilaginous branchial (or gill) arches r
of the Sharks, and to the bony branchial arches of the osseous

1 For further details concerning these arches see Lesson XII.

FIG. 1^2 — HYOID OF A

LIZARD -Lacerta.

(After Cztvier.)

M, body of the hyoid :
cl, corniculum ; c2,
cornua ; gh, glosso-
hyal ; ?/, uro-hyal.

XII.]

THE CRANIAL SKELETON.

I25

Fishes. These branchial arches extend on each side of the
throat upwards towards the spine-, and support the gills on
their inner sides. Other cartilaginous arches which were
spoken of in the Second Lesson as existing in the Lamprey
and some Sharks, may support the outer sides of the gills.
The branchial arches become successively smaller posteriorly,
or as we recede from the head. Thus we see what numerous
large and important parts of the lowest Vertebrates are rudi-
mentarily represented by the human hyoidean cornua.

FIG. 113. — Diagram of the Changes undergone by the Hyoid in a Frog in passing
from the Tadpole stage to the adult condition.

( Constructed from Parker s Memoir).

Upperjiiost left-hand figure, the youngest condition ; Imvest right-hand figin-e,
the adult.

h, the hyoidean arch, ultimately the corniculum ; b1 — b4, the four branchial
arches which become gradually atrophied, the cornua (or thyro-hyal), th being
their representatrve in the adult ; b , another branchial rudiment ; M, the
body of the hyoid.

The cornicula represent only the so-called hyoidean arch
— namely, that arch in Fishes which comes behind the lower
jaw and in front of the branchial arches.

We have seen that in man's own class this arch may con-
sist of several distinct bones, that is to say, of a tynipano-
hyal, a stylo-hyal, an epi-hyal, and a cerato-hyal, though in
man himself the epi-hyal is only represented by ligament.
It is, therefore, less surprising that in the lowest vertebrate
class this arch should be large and complex with bony

126

ELEMENTAL Y ANA TOMY.

[LESS.

appendages (termed branchiostegal rays} diverging from the
large cerato-hyals.

The body of the hyoid is small in Fishes, and excessively

FIG. 114. — LEFT BRANCHIAL ARCHES OF PERCH. (After Cnvier.)

i, glosso-hyal; 2, 3, and 4, basi-branchials ; 5, hypo-branchials ; 6, cerato-bran-
chials ; 7, epi-branchials ; 8, styliform pharyngo-branchial ; 9, pharyngo-bran-
chials ; 6"", inferior pharyngeal bone ; 9' and 9", superior pharyngeal bones ;
5, 6, 7, and 8, first branchial arch ; 5', 6', 7', and 9, second branchial arch ; 5",
6", 7", and g', third branchial arch ; 5", 6'", and 7'", fourth branchial arch ;
6"", fifth branchial arch.

so when compared with the enormous increase in size and
complexity of the cornua and cornicula.

FIG. 115. — SIDE VIEW OF THE CARTILAGINOUS SKELETON OF THE HEAD OF
A SHARK.

This shows the successive arches except the first pair, or irabeculce cranii,

which form the base of the skull in front of the pituitary fossa.
pq, pterygo-palatine, or second arch ; w, mandibular, or third arch ; h, hyoidean,
or fourth arch (the corniculum, stylo-hyoid ligament, styloid process, &c., of

sixth, seventh, eighth, and

man). From behind it the branchiostegal rays are seen extending backward
6£ to 65, the branchial arches forming the fifth,
ninth arches of the skull.

( From the College of Surgeons' Museum. )

A glosso-hyal and a uro-hyal, however, may exist, as we
see in the Cod.

in.] THE CRANIAL SKELETON. 127

33. Those CONNEXIONS OF THE BONES of the skull one
with another which take place in man are not all constant
in Vertebrates generally, as we have already seen. Certain
unions, however, are absolutely constant and invariable, as
that of the basi-occipital and basi-sphenoid — the pre-sphenoid
and basi-sphenoid — the parietal and occipital — the maxillary
and jugal, when the last-mentioned bone is present.

Several exceptional connexions have been already given.

In the skull of many Vertebrates vacuities often exist where
bone is present in man — tracts osseous in him being repre-
sented by membrane only. An example of such defect is seen
in that region of the skull of Lizards (e.g. Iguana) which cor-
responds with the wings of the sphenoid of the human skull.

The transitory fontanelle1 of man is permanent in some
animals, as e.g. certain Sharks, where the cranium is to a
large extent roofed by membrane instead of by bone or
cartilage.

The excessively dentated condition of certain sutures in
man is exceptional, nevertheless not unparalleled. We may
sometimes (e.g. in the Gorilla) find sutures even more
complex.

The persistence of the sutures in man is less than in
many animals, and also greater than in many. Thus we may
find, as in Fishes and Reptiles, a variety of bones distinct
which in him are united. We may, on the other hand, as in
Birds, find a number of bones united which in him are
distinct.

One suture, however, which, as has been mentioned, almost
constantly persists in other forms than man, is not repre-
sented in him (except on the palate), even at birth. This is
the one between the maxilla and the pre-maxilla. Again,
the intimate union which exists in him between the basi-
sphenoid and the pre-sphenoid is very far from persisting
even in his own class.

On the other hand, that distinctness which always obtains
in him between the petrous part of the temporal bone and
the occipital portion of the skull, is very early lost in the
Sauropsida.

The skull may present a much less compact mass than in
man s class.

Thus in Birds the elongated facial bones which go to form

1 The fontanelle is a space on the crown of the head, which, in the new-born
infant, is only closed by fibrous structures, the parietals and frontals not having
yet joined.

128 ELEMENTARY ANATOMY. [LESS.

the upper beak, being thin and elastic, are more or less mov-
able on the rest of the skull, and in the Parrots even by a
joint. In Lizards the anterior part of the skull is also more or
less movable on the posterior part. In Fishes we meet with
an extreme mobility of the jaws (the mandible being sus-
pended by a chain of bones), as also in Serpents, in which
not only is each side of the lower jaw separately movable
and united at the symphysis by a very elastic ligament, but
each part of the upper jaw can also be advanced singly ; and
thus, by successively advancing one tooth-bearing part of
the jaw after another, these animals rather drag themselves
over their prey than swallow it.

34. The general conformation of the skull shows that
almost always the proportion borne by the jaws to the cranium
is greater than in man ; and often, as in the Stork, the Whale,
the Gavial, or the Sword-fish, it is the facial part which is
enormously predominant. Thus the skull may be extraordi-
narily elongated as compared with that of man, and tapering
anteriorly, or it may be much broader in front than behind,
as in the Hammer-headed Shark. It may also be very elon-
gated but cylindrical, as in Centetes. It may be strangely
flattened, as in the Matamata Tortoise (Chelys), or it may be
singularly compressed from side to side, and high, as in the
fish Argeriosus.

Considering now the EXTERNAL SURFACE of the skull, the
superior region of man's is very exceptional in its extent, its
smoothness, and its rotundity. Generally in man's own class
a prominent sagittal ridge runs from in front backwards in the
line of the sagittal suture. This may be enormous, as in some
Seals and Carnivora, and even in the very Anthropoid Gorilla.
One of the most exceptional conditions which this region
may present is that exhibited by the Sperm Whale, or Cacha-
lot, where the cranium forms above, a great semicircular basin
for holding the spermaceti. In this and certain other animals
of the same order there is a want of symmetry in the skull
when looked at from above ; the two nostrils and pre-maxillas
being more or less unequally developed. This asymmetry is
carried much further in some of the true Fishes (namely, the
Pluronectidce, e.g. the Sole, Turbot, Flounder, &c.), where the
anterior part of the skull is extraordinarily twisted so as to
allow both the eyes to come to be on one side of the head.

Generally when the upper surface of the skull is looked at,
the anterior nares are more or less inconspicuous, and placed
in front. In certain animals, however, as the Elephant, the

in.] THE CRANIAL SKELETON. 129

Sirenia, and the Cetacea, they look upwards, and open quite
on the superior aspect of the skull. The same may be said
of those animals with a short proboscis, the Tapirs and the
Saiga Antelope.

The occiput may slope so forward that much more of it
may be seen (when the skull is viewed from above) than in
man, as is the case, e.g., in the Cape Mole (Chrysochloris\
the Elephant, and the Porpoise. It may, on the contrary,
be hidden by the projection of a large lambdoidal crest, as
in the Gorilla and Hyaena.

FIG. 1 1 5. — UPPER VIEV/'O? THE SKULL OF A DOLPHIN (Defy/units
{After Ciivier )

f, occipital condyles ; e, median ethmoid in nasal fossae ',_f, frontal, overlapped by
tux, maxilla : n, nasal ; p, parietal, driven down quite to the side of the skull ;
/;//, pre-maxilla (here enormous) ; so, supra-occipital.

It is possible that this region may be in large part mem-
branous, as in some Rays.

On the contrary, great bony productions may exist, as in
Ruminants ; either permanent bony cores sheathed with horn
as in the Ox, Goat, &c., or else bony developments (antlers)
which are annual in their growth and decay.

There may be four bony cores, as in the existing little four-
horned Antelope and in the great extinct Sivatherium.

The roof of the cranium may falsely appear to be large and
smooth, as in the Turtle and in the Rodent Lophiomys. In
them the real skull is disguised by the outgrowth of bony
lamellae, which, meeting together, arch over the temporal fossae,
and make the skull look capacious when it is not really so.

The inferior region is very rarely divisible into the three
K

j 30

ELEMENTAR Y ANA TO MY.

[LESS.

FIG. 117. — Under Surface of the Cranium
of the Great Ant-eater (Myrmecophaga
jubata), ^. SO, supra-occipital ; BO, basi-
occipital ; ExO, exoccipital ; 7>, tym-
panic ; Pt, pterygoid ; Sy, squarnosal ;
AS, ali- sphenoid ; OS, orbito-sphenpid ;
M, malar ; L, lachrymal ; PI, palatine ;
MX, maxilla ; PMx, pre-maxilla.
{From Flower's "Osteology")

parts of which it is made
up in man, the anterior
margin of the occipital
foramen forming, in the
immense majority, part
of the posterior boundary
of the inferior region.

( i ) The anterior part ot
the basis cranii of man is
in him very exceptionally
short, both compared
with the middle or gut-
tural part, and compared
with its own width. Its
relative length varies of
course with the prolonga-
tion of the muzzle. Only
in Mammals and Croco-
diles can it be defined,
as in man, by the bony
palate — formed as in him
by special developments
of the palatine and su-
perior maxillary bones.
Sometimes, as we have
seen, this part may be
augmented by the ptery-
goid bones also taking a
share in this structure,
as in the Great Ant-eater,
the Crocodiles, and Ce-
taceans.

It is possible, how-
ever, as in the Hare, for
the bony palate to be
very little developed, or,
as in the Hedgehog, to
be only imperfectly ossi-
fied. The form and pro-
portion of its component
bones afford in Birds im-
portant characters for the
classification of different
groups.

in.] THE CRANIAL SKELETON. 131

Essentially palatal structures, namely the pterygoid bones,
in forms below the mammalian class, generally connect the
palatine bones with the quadrate bone which suspends the
lower jaw. The bony palate may be enriched by the addition
of a bone not known in Mammals (the os transvermm], as is
the case in Reptiles ; or of two extra bones (the ecto-pterygoid
and the ento-pterygoid) ; besides a third peculiar ossification
(the meta-pterygoid), as in bony Fishes.

(2) The middle, or guttural part, is a noteworthy one, both
on account of the physiological importance of the structures
which modify its composition, and also on account of the
value which its various modifications possess for the purposes
of zoological classification.

Its condition in man is exceptional, both as regards the
large proportion it bears to the anterior part of the basis
cranii, and also as regards its small elongation antero-pos-
teriorly as compared with its breadth.

The variations presented as regards the mastoid and sty-
loid processes, the carotid foramina, alisphenoidal canals (for
the external carotid arteries), &c., have been already noticed
in speaking of the separate cranial bones, and need not here
be repeated.

Sometimes, as in the Crocodile and Great Ant-eater, this
guttural part of the basis cranii is nearly concealed by the
immense extension of the palate. At other times, as in the
Horse, it is much exposed by the smallness of the backward
prolongation of the bony palate.

The pterygoid fossae are found only in man's class, and by
no means always in it. Generally, as in the Dog, the pterygoid
bones are present, but the descending external pterygoid
process is absent ; so that the pterygoid fossae want seemingly
their outer walls.

The pterygoids may be swollen out into bullate expansions,
as in the Mole and Sloths.

Very often, especially in the smaller Mammals, the part
answering more or less to the petrous part of the temporal
and to the meatus auditorius externus may be, as it were,
blown up into vesicular air-containing prominences, termed
auditory bulla?.

The Eustachian tubes may unite to open into the mouth
by a median foramen, as in Birds, or may be utterly absent,
as in Fishes.

(3) The posterior part of the inferior region of man's skull
is very exceptionally developed, owing to the advanced situa-

K 2

I32 ELEMENTARY ANATOMY. [LESS.

tion of the foramen magnum. Nevertheless, its maximum
of development in Mammals is not found in him, but in the
little American Ape Chrysothrix.

In the great majority of instances the occiput is not visible
when the skull is looked at from beneath, or a projecting
lambdoidal ridge is seen in the place of the lambdoidal
suture. Occasionally, however (as in the Woodcock), the
occipital surface is largely visible, the foramen magnum
being situated far forwards.

A peculiar character may exist in the occiput, as can be
seen in the Indian Elephant, where there is a deep and sharp
double depression with a median, vertical ridge. This de-
pression curiously resembles that in which the cribriform
plate is placed in so many Mammals, the median ridge
reminding one of the crista galli. This occipital fossa is for
the reception of a strong ligament, which helps to sustain the
very weighty skull.

An anterior condyloid foramen may be entirely absent, as
in Fishes, in which class there is no distinct hypoglossal
nerve.

Great depending para-mastoid (or par-occipital) processes
may replace the mastoids, as in the Horse and the Capybara.

The anterior region of the skull of adult man presents an
appearance but very rarely approached by that of any brute.
Nevertheless, certain of the American Monkeys (e.g. Pithecia
and Nyctipithecus) present a close general resemblance,
which is also to be plainly seen in the young Chimpanzee,
and still better in the young Orang Utan.

Generally speaking, owing to the prolongation of the
muzzle, the skull is so much foreshortened when viewed in
front that its actual shape can be very little seen. The same
apparent distortion also occurs in extremely depressed or
compressed skulls.

Although the rounded frontal region of man is all but
peculiar to him, his superciliary projections are but rudiments
of what may be developed even in closely allied forms, as
we see in the Gorilla, the superciliary ridges of which are
enormous. Very generally the orbital fossae are placed so
laterally that, unlike those of man, they are very little seen
when the skull is looked at in front. On the other hand, they
may approximate more closely than in him, as in many
Monkeys. As has been said in describing the superior
maxillary bone, the infra-orbital foramen may be replaced by
a great aperture, or by a number of small apertures. The

in.] THE CRANIAL SKELETON. 133

bony cheek may, in man's own class, offer defects of ossifica-
tion, as in the Hare, or enormous prominences enclosing a
chamber, as in the Paca, or great swollen tuberosities, as in
the Mandrill.

The anterior nares may be so high up as to approach the
summit of the skull, as we see in Cetacea. They may
present a very large aperture, as in the Tapir. They may be
widely separated one from the other in the middle line, as is
the case in mosj animals below Mammals, but not in all, as
we see in Chelonians and Crocodiles, which have a median,
single nasal opening, as in man's own class.

As regards the lateral regions of the skull of man : —

(1) The temporal part may be roofed over and hidden from
view by plate-like processes extending out from the adjacent
bones, and which, meeting, enclose the temporal fossa and
muscle, giving the skull a fictitious appearance of great ca-
pacity. This is the case in the Turtle, the African Rodent
Lophiomys, and in the Frog Pelobates.

(2) The mastoid part can hardly with propriety be so
called in lower forms, where the mastoid process becomes
much smaller or aborts altogether.

The meatus auditorius externus may in the adults of very
high animals (e.g. the American Apes) be replaced by a wide,
nearly circular opening, as in the human skull at birth. The
same meatus may be directed much upwards and more or
less backwards, as in the Hare. No such part exists in the
skulls of Fishes.

(3) The zygomatic part may in man's own class present
very considerable differences from the structure which exists
in him, and more considerable still in lower forms.

Thus a zygomatic arch may be wanting, as in Centetes, the
Ant-eaters, and Manis. Both the anterior and posterior parts
of that arch may be well developed, and nevertheless may-
fail to effect a junction, as is the case in the Sloths and their
extinct allies ; or a junction may be formed by the help of a
process of the frontal, as in the Horse.

In forms below Mammalia (as e.g. in Birds, the Crocodile,
£c ) we often find a zygoma formed by the help of a bone
termed the qiiadrctto-jugal, which connects the malar in front
of it with that bone which supports the lower jaw, and which
is termed the quadrate. Besides this zygomatic arch a second
and superior zygoma may exist (as in most Lizards and in
some Birds, e.g. the Macaw " Calyptorhynchus "), formed by
the union of the squamous or zygomatic element of the tern-

1 34 ELEMENTAR Y ANA TOM Y. [LESS.

poral bone with a bone termed the post-frontal, and which
more or less occupies the place of the post-frontal process of
the frontal bone of Mammals.

A fundamentally different structure may obtain, as in Fishes,
where we have, as a rule, no malar ; and where the more con-
spicuous representative of the temporal bone (exclusive of
the representatives of the petrous portion) is the pre-operculum,
— which may perhaps be said to replace a zygoma, extending
down as it does to the quadrate bone which suspends the
lower jaw. The connexion of the quadrate bone, however,
with the maxillary bone is only effected by means of soft
structures, which must alone, therefore, represent the inferior
zygoma of the Sauropsida. The bones which connect the
quadrate with the upper jaw have relation not to the zygoma,
but to the palate.

Pf,

i 97

FIG. 118.— SIDE VIEW OF A BIRD'S SKULL. (After Parker.)

«7, surangular bone of mandible : ar, articular bone ; d, dentary ;f, frontal ; /,
malar ; /, lachrymal ; me, median ethmoid ; mx, maxillary bone ; /, parietal ;
pf, post-frontal process ; pt, pterygoid bone ; px, pre-maxilla ; g, quadrate
bone ; qj, quadrato-jugal ; sg, squamosal; v, vomer.

Returning to man's own class, we find that the lateral region
is generally much more open than in him. The spheno-maxil-
lary fissure, for example, is defined by the projection outwards
of the alisphenoid. Generally this projection is wanting ;
therefore the orbit opens widely into the temporal fossa.
This fissure may, however, be more closed up than it is even
in man, as we see in certain Apes, and notably in the Howling
Monkeys.

The pterygo-maxillary fissure may also become as it
were more or less opened out, and the spheno -maxillary fossa

in.] THE CRANIAL SKELETON. 135

be plainly visible, instead of being hidden, as it is in man.
The five foramina of that fossa, viz. the rotundum, vidian,
pterygo-palatine, posterior palatine, and spheno-palatine, are
generally present in the Mammalian class, but with the open-
ing out of the fossa become more or less, and in different
degrees, separated from each other as compared with their
common juxtaposition in man. The spheno-palatine and
posterior palatine foramina may together be represented by a
single small opening, as in the Ornithorhynchus.

35. Before considering the INTERNAL SURFACE of the
cranium as treated of in Anthropotomy, it may be well to
note the relations and conditions presented by a vertical
longitudinal section of the entire skull, which are exceedingly
significant and instructive.

The basi-cranial axis of man forms an angle which approxi-
mates to a right angle with the basi-facial axis.

In Birds the angle may be as marked as in man, and the
human condition may be even much surpassed, as in the Wood-
cock, where the facial part is so extremely bent down that its
axis forms a very acute angle with the basi-cranial axis.

Now, in all the lowest Vertebrates these two axes are in one
straight line, as in Fishes, Batrachians, and most Reptiles ;
and even in most Mammals the angle formed by them is
an exceedingly open one, approximating to 180°.

The importance,, however, of this distinction is not really
so great as at first appears, for there are great differences
with regard to it between animals which are very nearly
allied. Thus the adult Chacma Baboon differs from his ally
the Mandrill in this respect almost as much as man differs
from the Gorilla ; and while the Deer has the two axes almost
on a line, in the Sheep and Ox they form a very marked angle.

The shortness of the basi-cranial axis in man when com-
pared with the extreme length of the true brain cavity, is a
much more distinctive feature, as in all lower forms this axis is
very much longer. Thus, in the Sheep, the basi-cranial axis is
as long as the entire cerebral cavity, and in the lowest Verte-
brates (where the cerebral hemispheres form but a small part
of the brain) it very greatly exceeds it.

Similarly the angle formed by it with the plane of the occi-
pital foramen, which is so very open in man, contracts in lower
Vertebrates till it becomes a right angle ; and the same may
be said as to the olfactory angle, or that formed with the
basi-cranial axis by the plane of the cribriform plate, or
its morphological equivalent.

136 ELEMENTARY ANATOMY. [LESS.

In this way the peculiarly expanded condition of the
cerebral chamber of man may be appreciated. Taking the
basi-cranial axis as a fixed line for comparison with other
animals, we see that in him (Fig. 91) the cerebral chamber
is of great vertical extent, at the same time that its anterior
portion is so expanded as to open out the olfactory angle
from 90° to much beyond 180°, and to similarly open out the
occipital angle — circumstances in which man widely differs
from even the highest members of his class and even of his
order.

In the fact that the inside of the arch of the skull is marked
by depressions corresponding with the cerebral convolutions,1
man agrees with those members of his class which possess
such convolutions. For in that class the cranium closely
invests the brain, so that a cast of its cavity well exhibits the
general features of the cerebral surface. This character,
however, is by no means universal in the Vertebrates, for the
cerebral cavity does not contract with the lessening pro-
portions of the cranial nervous centres, there being (e.g. in
Fishes) a large quantity of soft fatty substance interposed
between those centres and the cranial walls.

The cranial cavity in man overhangs the orbits, but does
not descend between them. This is a condition which
obtains very often, but by no means universally ; for that
cavity may be not only prolonged between the orbits, but
considerably beyond them. We find this in Serpents, in
Batrachians, and in many Fishes (e.g. the Carp family), while
in Birds, Lizards, Crocodiles, and Chelonians the cranial
cavity suddenly contracts, and there is an interorbital septum
only.

The middle of the dome of the skull may be produced in-
wards as a median, longitudinal, bony plate by ossification of
the falx. This is the case e.g. in the Ornithorhynchus and
in the Sea Lion.

An ossified tentorium may exist, as in some Spider
Monkeys, in the Racoon, and others.

The base of the interior of the skull may present those
differences already noticed in describing the several cranial
bones. In man's class it is divisible into the same three
fossae as in him. This division, however, is not similarly
marked in lower forms.

(i) The anterior fossa is relatively much less extensive in
man than it is in most animals. Even in the Apes the

1 For these see Lesson VIII.

in.] THE CRANIAL SKELETON. 137

portion immediately above the cribriform plate forms a
more distinct chamber than exists in man. As we de-
scend through the mammalian class we often find it much
prolonged and of a large relative size, as in the Sheep, Pig,
and others, especially Marsupials, e.g. theThylacine. In some
forms, however, e.g. the Dolphins, the olfactory fossa is quite
wanting. Great difference in this respect may exist in nearly
allied forms — e.g. in the Ornithorhynchus and Echidna, in the
first of which the cribriform plate is very small and bird-like,
while in the second it is enormously large.

(2) The middle fossa is relatively larger in man than it
is in very many lower forms, but not in all, as we see by the
Dolphins. The foramina vary, as already noticed iii de-
scribing the several cranial bones. Very often the foramen
rotundum and sphenoidal fissure may be blended in a single
opening, as in the Squirrel ; or the optic foramen may form
but one aperture with the sphenoidal fissure, as in the Stag
and Opossum ; or the two optic foramina may be united into
a single median foramen, as in the Hare.

The foramen ovale may be one with the foramen lacerum
anterius, as in the Horse.

The optic foramina and sphenoidal fissures may together
be represented, on the inside of the skull, by a single opening,
as in the Swan ; and sometimes the optic foramen, sphenoidal
fissure, and foramen rotundum may be included in a common
aperture, as in the Booby.

The sella turcica may be as sharply limited in other forms
as in man. On the other hand, the pituitary fossa may be
altogether unmarked, as in Batrachians.

This fossa may dip down into a large canal running for-
wards and excavated in the basis cranii, as in many Fishes,
e.g. the Pike. This singular cavity has the cartilaginous floor
of the skull for its roof, while the para-sphenoid bone encloses
it below.

(3) The posterior fossa may be much more sharply defined
than in man, as when a lamella of bone (consisting of an ossified
tentorium) is attached to the projecting border of the petrous
part of the temporal bone. The proportion borne by this
fossa to the middle one varies with the size and develop-
ment of the cerebellum which it shelters. Only in man
and a few Apes (notably the Squirrel Monkey, Chrysothrix)
can this fossa be said to form any considerable part of
the floor of the skull. The internal auditory foramen in
all man's class and In Birds is placed as in him, and there

1 38 ELEMENT A RY ANA TO MY. [LESS.

is generally (as notably, e.g., in the Hare and Mole) also a
fossa for that process of the brain called the flocculus of the
cerebellum.

In some Reptiles, however (as, e.g., the Turtle), the bony
investment of the internal ear is incomplete on its cranial
side ; and in Fishes it is even widely open, forming a large
chamber communicating with the general cranial cavity, and
termed the "otocrane."

36. That degree of completeness of THE ORBITS which
exists in man — serving for the protection of the eyeball by
extensions of the cranial bones — is a very exceptional condi-
tion. Only in him and in the higher members of his order
— that is, the Monkeys — do we find such an enclosure ; but
in some of them it may be more complete than it is in him,
by the junction of the greater wing of the sphenoid with the
upper maxillary bone, so that the spheno-maxillary fissure is
reduced to a short and rounded aperture, or even (as in the
Howling Monkeys) all but or quite obliterated.

The relative size of the orbits may be much greater than in
man, as e.g. in Indris, in the Night- Ape (Nyctipitkecus\ or
in the Tarsier. On the other hand, the orbits may be rela-
tively smaller than in man, as in the Whales.

Fir,. TTQ. — Front Viev,* of the Skull of the Lemuroid Indris Laniger; showing
the large size of the orbits, which are also shown to open widely behind into
the temporal fossae.

They may be much more widely separated from each
other in proportion to their size and the size of the skull, as
in the Dog and most Mammals. On the other hand, they
may be much more approximated, as in the Tarsier and in
the Squirrel Monkey (Chrysothrix\ where they are in part
separated by membrane only. In a great number of animals,

ii i. J THE CRANIAL SKELETON. 139

as Birds and many Reptiles, they are only divided from each
other by a thin interorbital septum, made up of bone or carti-
lage or membrane. They may, on the contrary, be so widely
separated (as in the Hammer-headed Shark) that the cranium
is much broader between them than it is anywhere else.

Although it is peculiar to man's order to have the orbit
enclosed as in him, yet there are other creatures which have
the orbit protected by a bony rim, as is the case in Ruminants
(e.g. the Sheep), in the Crocodiles and Turtles, some Lizards,
and some Frogs. This enclosure is effected by the junction
of the malar with the true frontal bone (in Mammals, except
in the Horse, where the zygomatic process of the tem-
poral bone intervenes) or with a post-frontal bone. In many
fishes, however, the orbit is bounded inferiorly by a chain of
skinbones (dermal ossicles), the suborbital bones, which seem
to be serial repetitions of the lachrymal ; and in some
Birds (e.g. the Woodcock and the Macaw, Calyptorhyncus]
there is an analogous formation, and the orbits are completely
encircled by bone.

In the immense majority of man's class, however, the orbit
is not even encircled by bone, and its separation from the
temporal fossa is not in many even marked by a post-orbital
process of the frontal. The lachrymal foramen (which exists
in most terrestrial forms) need not open within the orbit, but
may be, as in Lemurs, upon the cheek.

The orbits may be continued backwards (as in many osseous
Fishes, e.g. the Pike) into a prolonged conical canal situate
beneath the cerebral cavity, and protected inferiorly by the
para-sphenoid.

In the possession of nasal fosscz limited and defined by
osseous structures man agrees with the whole of the Vertebrate,
above Fishes, except the very lowest of the Batrachians.

In the possession of two ruch fossae separated by a wide
or narrow septum, and separated from the mouth by an
osseous plate, so that they open posteriorly only into the
pharynx,1 man agrees with all the members of his class, and
with 'the Crocodiles also.

The sheltering of spongy bones (or turbinals) is a character
which the nasal fossae possess in almost all Mammals, though
such parts may be entirely wanting, as in the Dolphins.
These spongy bones may be represented only by cartilagi-
nous structures, as we find in the classes Reptilia and
Batrachia,

1 For the pharynx see Lesson XI.

I4o ELEMENTARY ANATOMY. [LESS.

The floor of these fossae may, instead of forming with the
basi-cranial axis an angle opening downwards (as in man,
the Hare, and Sheep), be parallel with it (as in the Dog), or
form an obtuse angle opening upwards, as in the Elephant,
or even a slightly acute angle, as in the Dolphins.

The nares are exceptionally high in proportion to their
length in man. Their length may be enormous, as in the
Great Ant-eater and Crocodile, where pterygoid plates follow
behind the palatine bones and so prolong the bony palate.

The nares, on the contrary, are in most Vertebrates
much shorter than in Mammals ; for there are no palatal
plates to prolong the fossae backwards, and their posterior
border is formed by the palate bones. Thus the posterior
nares in such animals (e.g. Birds, Lizards, Frogs) answer
rather to the middle portion of the human nasal fossae.

The bones which form the anterior and posterior boun-
daries of the nasal passage have been already described, as
also the asymmetrical form of the anterior nares in the
Cetacea.

The median division of the fossae, or septum narium, need
not be partly osseous and partly cartilaginous, as it is in man.
It may be quite unossified, as in Chelonians and Serpents, or
it may be ossified to the ends of the nasals, as in certain
extinct species of Rhinoceros and in some Dolphins and
Seals (e.g. the species Leonina), and in one species of Tapir,
where ossification advances even in front of the nasals. The
septum may be ossified continuously with the lesser wings of
the sphenoid, as in the Frog, where it forms the middle part
of the os en ceinture.

As to \hefrontal, sphenoidal, and maxillary sinuses, it is a
general character of air-breathing Vertebrates to have some
or other part of the cranial bones furnished with cavities
containing air. In this respect, therefore, man is no excep-
tion to the rule, and indeed he occupies an intermediate
position, as cranial air-cells may be more restricted or much
more developed than they are in him, and this not only as
regards the relative size of the air-cavities, but also as regards
the number of cranial bones so inflated.

The frontal sinuses (which are not constant in man, being
absent at least in some Australian skulls) may be much less
or more developed than in him in members of his own order,
e.g. in different Apes. In hollow-horned Ruminants they may
extend into the substance of the horns, or backwards into the
parietals and supra-occipital. The latter condition exists in

III.]

THE CRANIAL SKELETON.

141

the Hog, but attains its maximum of development in the
Elephant, where air-cavities extend even into the nasal bones ;
and the vertical section of the area of the cranial sinuses
exceeds, in the adult, that of the cranial cavity itself.

BE-

FIG 120. — A section of the Cranium of a full-grown African Elephant, taken to
the left of a middle line, and including the vomer (Vo), and the mesethmoid
(ME) : an, anterior, and/«, posterior narial aperture, fz.

This section shows the enormous thickness of the skull wall, and the prodigious
development of air-cells in the frontal above and in front of the cerebral cavity,
and above and behind the anterior nares, an.

(From Flower's " Osteology.")

In Birds also they may be well developed, while, on the
contrary, an extraordinarily dense projection of bone may
take place from the frontals, as in the Cassowary. Frontal
sinuses may be entirely wanting, as in many Mammals and
Reptiles, and as in the Frog, and this though other cranial
elements have large air-cavities, as in the Crocodile.

The sphenoidal sinuses may be much less developed than
in man, as is the case in common Monkeys and many Mam-
mals, e.g. the Sheep and Manatee. They may, however, be
very greatly developed and extend into the median plate of
the ethmoid, as in the Elephant. Similarly, in oviparous

142 ELEMENTARY ANATOMY. [LESS.

Vertebrates, they may be largely developed, as in many-
Birds, e.g. the Ostrich ; or absent, as in Serpents, e.g. the
Python.

The maxillary sinus in man is also in a medium state of
development. In very many forms the maxillary bone is
solid ; though, in the Elephant, not only the maxilla has air-
cells, but the pre-maxilla also. In the New World Rodent,
the Paca, the maxillary bone contains a large cavity which
communicates with that of the mouth even in the living
animal. In the Hare the external surface of the bone is but
imperfectly ossified.

As has been said, other bones may become inflated with
air which are not so in man. This, as we have seen, is the
case with the median plate of the ethmoid, with the nasals,
and with the pre-maxilla in the Elephant, and with the parie-
tals and supra-occipitals in the Hog. The pterygoids may
become adapted to form air-cavities, as in the Dolphins, the
Mole, and some Sloths, and in old Gavials. The greater
wings of the sphenoid may be similarly dilated, as in some
Insectivora (e.g. Centetes] and Marsupials (e.g. Hypsiprymmis).

The mastoidal cells of man are very commonly replaced
by large inflations of the tympanic or inferior petrous portions
of the temporal bone. The postero-external portion of the
skull may be very largely inflated in this way, as in Macro-
scelides, forming a great mastoidal bulla ; and even the angular
part of the lower jaw may be inflated with air, its cells being
placed in communication with those of the tympanic region
by a special tube, as in the Crocodile.

The lachrymal bone may also be inflated and form an
orbital bulla, as in almost all Ruminants, especially the Giraffe.

The upper jawbones may be extraordinarily expanded and
filled with delicate osseous air-holding cells, as in the beak of
the Toucan.

The process of DEVELOPMENT of the human skull, which has
been before noticed, is of very high zootomical interest, as
its transitory stages present very interesting resemblances to
the permanent cranial structures of very different animals.

Inasmuch as we find in the first indication of the embryo
an indication of the spinal system which is to be, but none of
the skull, we are reminded of the headless condition of that
lowest of Vertebrates, the Amphioxus or Lancelet.

In that early cartilaginous condition of the cranium in
which we have a cartilaginous mass enclosing the anterior
termination of the notochord in the middle, and an auditory

III.]

THE CRANIAL SKELETON.

capsule on each side of it, we are reminded of the permanent
condition of the skull in the Lamprey.

In that the trabeculae cranii first diverge and then con-
verge, meet, and so enclose what becomes the pituitary space,
we find a temporary condition of which large traces remain
even in adult Ophidians, where the cartilaginous trabeculae
persist as two rods, one on each side of the para-sphenoid.

FIG. i2i.— THE SKULL, ANTERIOR PART OF SPINAL COLUMN, AND BRAN-
CHIAL BASKET OF THE LAMPREY.

(From Miiller and Owen.}

-lit, auditory capsule ; b, cartilaginous basket, connected above with the side cl
the vertebral column, with seven complete and descending arches united by
transverse bands (between which the gill-openings are seen) and sheltering the
heart and pericardium at the part where the letter b is placed ; e, ethmo-
vomerine cartilage ; h, rudiment of the hyoid ; «, neural arches ; P, palato-
quadrate (or pterygo-palatine) arch, the hinder pier of which represents the
suspensorium, though there is no lower jaw.

Before the development of the third visceral arch we have
the permanent condition of the Lamprey, which is always
destitute of a mandible ; and when, in man, the visceral arches
successively arise, we have transitorily represented the piscine
condition, where the solid axes of seven or more such arches
form the mandible, the hyoidean arch, and the successive
branchial or gill-bearing arches.

In the development of the palatal, or second visceral arch,
there is sketched .out a condition permanent in Sharks, where
the lower jaws bite against a cartilaginous pterygo-palatine
arcade which takes the place of an as yet undeveloped bony
upper jaw. This condition is essentially similar to the struc-
ture of the Sturgeon, where a comparatively minute pair ot
jaws (mandibular and pterygo-palatine respectively) are
suspended at the end of a disproportionately large suspen-
sorial structure.

In that stage of the human skull which precedes ossification
we have a reminder of the exclusively cartilaginous structure
of certain Fishes.

In the distinct ossific origin of the elements of the petrous

1 44 ELEMENTAR Y ANA TOM Y. [LESS.

and mastoidal portions of the temporal bone we have a
transitory representation of the permanent conditions of the
same parts in the osseous Fishes.

In the distinct osseous origins of the wings of the sphenoid,
of the basi-occipital and basi-sphenoid, and of the lateral
parts of the occipital bone, there is exhibited a resemblance
to the permanent condition of those parts as they exist in
many animals, as has been already noticed.

FIG. 122. — SIDE VIEW OF THE CARTILAGINOUS SKELETON OF THE HEAD OF
A SHARK

This shows the successive arches except the first pair, or trabeculte cranii, which
form the base of the skull in front of the pituitary fossa.

pg, pterygo-palatine, or second arch ; m, mandibular, or third arch ; h, hyoidean,
or fourth arch (the corniculum, stylo-hyoid ligament, styloid process, &c , ot
man) From behind it the branchiostegal rays are seen extending backwards,
61 to 65, the branchial arches forming the fifth, sixth, seventh, eighth, and
ninth arches of the skull.

The same remark applies to the other parts which, at first
distinct, ultimately coalesce, such as the portions of the
ethmoid, the upper maxillary bones, the pterygoid processes,
and the squamous element of the temporal bone.

Finally, that exceptional anchylosis which occasionally
takes place in aged skulls recalls to us that union of the
cranial elements which in some Vertebrates, as in Birds, is so
much more complete than is normally the case with the bones
constituting the human cranium.

The consideration of the relations existing between Meckel's
cartilage and the summit of the hyoidean arch in man with
the suspensorial and mandibular structures of lower Verte-
brates, must be deferred until the internal ear is treated of,
and we come to examine the essential nature of its auditory
ossicles.

iv.] SKELE TON OF UPPER LIMB. 1 45

LESSON IV.

THE SKELETON OF THE UPPER LIMB.

1. THE bones of man's upper limb are divisible into three
categories : A. Those of the shoulder ; B. Those of the arm ;
and C. Those of the hand.

A. Those of the shoulder are the blade-bone, called the
scapula, and the collar-bone, called the clavicle*

B. Those of the arm are subdivisible into (a] the upper
arm, and (b} the fore-arm.

(a] In the upper arm there is but a single bone, called the
Jnnuenis.

(//) In the fore-arm there are two long bones placed side
by side, and called the radius and the ulna.

C. Those of the hand are divisible into the bones of the
wrist (or the carpus'2}, those of the middle, solid part of the
hand, called the metacarpus? and those of the fingers (or
digits), which are called phalanges*

2. The SCAPULA is a flat, triangular bone, with three borders
and two surfaces. One of these surfaces is applied against
the ribs, and is concave. It is called the subscapular fossa.
The shortest of its three borders is uppermost.

The other (dorsal or outer) surface is divided obliquely
into two unequal parts by a prominent ridge, called the
"spine," on which account the part above the ridge is termed
the supra-spinous fossa, and the part below it the infra-
spincus fossa.

This spine becomes gradually more prominent from the
vertebral border of the scapula, while at its outer end it
expands into a large freely projecting process termed the

1 davis, a key. 2 From Kapirnc. the wrist.

3 From fiera, after, and Kaprr<$£. 4 *«Aa>f, anything set in array.

146 ELEMENTARY ANATOMY. [LESS.

acromion* which is flattened in an opposite direction from
that in which the scapular spine is flattened.

The superior and shortest border of the scapula exhibits
a deep notch, which is converted into a foramen by means
of a ligament. In front of this notch rises a strongly pro-
jecting curved process, called from its beak-like shape the
coracoid.2

FIG. 123. — OUTER OR DORSAL VIEW OF THE RIGHT SCAPULA OF MAN.

a1, superior .ingle ; a2, inferior angle : ac, acromion ; ax, axillary border ; c,
coracoid ; g, margin of glenoid surface ; is, infra-spinous fossa ; «, neck and
supra-scapular notch, in superior border ; s, spine ; sst supra-spinous fossa ; v,
vertebral margin.

The hinder border is the longest. It is called the vertebral
border, because it is nearest to the backbone.

The third border (called the axillary border) ascends
obliquely from the lower end of the vertebral border to a
rounded, concave, shallow, articular surface, called the
glenoid 3 cayity (into which the head of the upper-arm bone
is received), and which is overhung within and in front by
the coracoid process on its internal side, while the acromion
overhangs it externally and behind. The part which - sup-
ports the glenoid surface is termed the neck,

The superior and vertebral borders meet in a sharp superior
angle, while at the junction of the axillary and vertebral
borders is a flattened space for the insertion of a muscle
called the teres major.

The coracoid and acromion arise from distinct centres of

1 From aKpoc, a summit, and a'>/uo£, the shoulder.

2 From Kopuf, a crow, and efoof, form.

3 From i\t]vr], a superficial cavity.

IV.]

SKELETON OF UPPER LIMB.

ossification The coracoid ossification contributes to form
the glenoid cavity.

3- The CLAVICLE is a long cylindrical bone with a slightly
sigmoid curvature, placed transversely on each side of the
neck and connecting the acromion with the manubrium of
the sternum. Its outer end, in childhood, bears a cartilage
termed the meso-scapular cartilage (which ultimately ossifies),
and is connected with the acromion by a synovial joint. The
inner end has a distinct centre of ossification (as an epiphysis)
and unites with the sternum by
a joint in which is interposed a
fibro-cartilage (the omosternum}
having a synovial membrane on
each side of it. The clavicle is
connected with the coracoid by
ligament only. . "

4. The HUMERUS (os humeri}
is the largest and longest bone
of the upper limb, and extends
from the shoulder to the elbow-
joint. It is imperfectly cylindri-
cal, with an expansion at each
end. We may consider it in the
position in which it is placed
when the arm is dependent and
the palm turned forwards.

The cylindrical part (or shaft)
has its anterior surface marked
above by a longitudinal depres-
sion, termed the bicipital groove,
because it lodges the tendon of
a muscle called the Biceps.
Below and external to this is a
roughened elevated tract for the
insertion of the deltoid muscle.

The lower part of the shaft
has its anterior surface sepa-
rated from the posterior surface
by two lines (or ridges), one on
each side, which become well marked as they approach Q
lower end of the bone. The outer of these two ridges is
termed the supinator, or external condyloid, ridge (for reasons
which will appear), while the inner one is named the i
condyloid, or pronator ridge.

L 2

FIG. 124. — FRONT VIEW of THE
RIGHT HUMERUS OF MAN.

b, bicipital groove ; cf, coronoid
fossa ; ec, external condyle ; gt,
great, or radial tuberosity ; //,
head of the humerus : ic, internal
condyle ; lh, capitellum ; //,
lesser or ulnar tuberosity; /,
trochlea.

1 48 ELEMENTAL Y ANA TOM Y. [LESS.

The hinder surface of the shaft presents an oblique groove
(called musculo-spiral), passing from above downwards.

The upper end of the humerus shows a large, rounded head,
covered, when fresh, with cartilage and articulated to the

flenoid surface of the scapula by a synovial joint, while a
brous bag (or capsular ligament) invests the whole articu-
lation.

The head is placed, not on the middle of the summit, but
on its inner and hinder aspect, so that its axis does not coin-
cide with that of the shaft.

A little below and on the outer side of the head are two
blunt prominences. One of these, termed the greater (or
radial) tuberosity, is on the outer side of the summit of the
bicipital groove. The other is called the lesser (or ulnar)
tuberosity, and is placed on the inner side of the bicipital
groove.

The lower end of the humerus expands considerably,
having a lateral prominence, termed a condyle, on each side,
but the internal condyle projects further inwards than does
the external condyle outwards.

Between these projections is placed the lower articular
surface of the humerus for the bones of the fore-arm.

This articular surface is irregularly concave and convex.
At its outer part is a rounded prominence, called the capitellum,
which joins the outer bone of the fore-arm or radius. Internal
to this is a pulley-like surface (the trochlea), which joins the
inner bone of the fore-arm or ulna. There is a deep cavity
in front of the humerus immediately above the trochlea.
This is called the coronoid fossa, because it receives the
coronoid process of the ulna.

There is another fossa, also above the trochlea, but on the
hinder surface of the humerus. This is called the olecranal
fossa, from the part of the ulna which it receives when the
arm is straightened. Sometimes a perforation connects
together these two fossae

The ends and processes of the humerus ossify separately
as epiphyses, and coalesce at about the twentieth year.

5. The RADIUS is also a long cylindrical bone, expanded
more or less at each end and flattened in front, i.e. when the
arm is dependent and the palm turned forwards.

Towards its upper end the bone, just above a roughened
prominence — the " tuberosity" — is narrowed into what is
called the neck, from which rises the head, concave above
and articulating by a synovial joint with the capitellum

IV.]

SKELETOX OF UPPER LIMB.

149

of the humerus, while by a similar joint its margin plays
into a concavity on the adjacent surface of the ulna.

At its lower end the radius becomes much broadened out,
and its posterior surface is grooved for the passage of tendons.
Its outer side is prolonged into what is called the styloid
process. The lower end of the bone articulates with the wrist
by a concave surface mainly supporting the hand, which is
carried round with the radius in pronation and supination.

These motions have been explained in the Seventh Lesson
of " Physiology/' and are pro-
duced by a rotation of the radius
on the capitellum.

When the arm and hand hang
down, the palm being directed
forwards, the position is that of
supination, and the bones of the
fore-arm are situate side by side.

When the arm and hand hang
downwards, but the back of the
hand is turned forwards, the po-
sition is that of pronation, and
the radius crosses over the ulna.

When we rest on the hands
and knees, with the palms to
the ground, the fore-arms are in
pronation.

6. The ULNA is larger than
the radius, and while the latter
is broader below than above, the
reverse condition obtains in the
ulna. The shaft is flattened in
front, with a sharp outer (or
radial) margin, to which an inter-
osseous membrane is attached
which connects the ulna with
the shaft of the radius.

Its upper end presents a deep
concavity for articulation (by a
hinge joint) with the trochlea of

the humerus. This fossa is called, from its shape, the great
sigmoid cavity? and is divided unequally by a vertical ridge
which extends between the two processes which bound the
fossa above and below respectively.

1 From 2 and c*3og.

FIG. 125. — FRONT-VIEW OF MAN'S
RIGHT RADIUS AND ULNA.

1. The Radius: /*, the head; /,
tubercle ; st, styloid process.

2. The Ulna: c, coronoid pro-
cess ; gs, greater sigmpid cavity ;
Is, lesser sigmoid cavity ; o, ole-
cranon ; st, styioid process.

ELEMENTAR Y ANA TOMY.

[LESS.

The lower process is called the coronoid,1 and is received
into the corresponding fossa on the front of the humerus.

The higher and much larger process is termed the ole-
cranon? and fits into the olecranal cavity on the back of
the humerus.

The olecranon forms the prominence of the elbow, and
terminates in a rough tuberosity.

On the outer side of the coronoid process is a small articular
surface, called the lesser sigmoid cavity, for the border of the
head of the radius, which turns upon it.

The lower end of the ulna has two eminences. The ex-
ternal or radial one, called the head, is much the larger, and
presents two articular surfaces. One of these is nearly
circular, and articulates with the wrist ; the other, narrow and
convex, articulates with a concavity on the adjacent surface
of the radius.

FIG. 126.— ANTERIOR (PALMAR) SURFACE OF THE SKELETON OF MAN'S HAND.

c, cuneiforme ; /, lunare ; m, magnum : »/1, metacarpal of thumb ; tii3 — m$, meta-
carpals of the four fingers ; p, pisiforme ; P1, first phalanx of the thumb and
four fingers — i.e. of the five "digits ;" P2, second phalanx of the five digits;
P5, third, or ungual phalanx ; sc, scaphoides ; t, trapezium ; tz, trapezoides ;
71, unciforme.

The internal eminence is called the sty loid process, and does
not directly articulate with the wrist.

1 Kopcoi/n, the top of a curve.

2 From uAeo], elbow, and Kpdvov, head. -

iv. SKELETON OF UPPER LIMB. 151

7. The CARPUS consists of eight small bones arranged in
two transverse series.

The bones of the upper, or proximal row, are : (i) the
scaplwides x (or scaphoid bone) ; (2) the lunare (or semi-lunar
bone) ; (3) the cuneiforme (or wedge-shaped bone) ; and (4) the
pisifonne (or pea-shaped bone).

The first two together form an upper convex surface which
fits into the distal articular cup of the radius.

The pisiforme stands out freely, and is rather a supple-
mentary ossification of a tendon (a kind of extra ossification
often occurring in different places) than a true bone of the
wrist. It is a small bone.

The bones of the lower, or distal row, are : (i) the trapezium ;
(2) the trapezoides ; (3) the magnum; (4) the unciforme.

These bones together form an undulating upper articular
surface, there being a concavity on the radial side to receive
a prominence of the scaphoid, and in the middle a strong
convexity fitting into the cup formed by the distal sufraces
of the three radial (or outer) carpals of the proximal row.

Distally, the second row of carpals presents varied surfaces
for the reception of the proximal ends of the bones of the
middle, solid, part of the hand (the metacarpus), which are
called metacarpals.

The magnum is the largest bone of the distal series, while
the unciforme articulates with and supports two metacarpals,
namely, the fourth and fifth.

The trapezium presents a saddle-shaped surface to the first
metacarpal, being concave in one direction and convex in
another.

8. The METACARPALS are five elongated bones, each with a
rounded head and a base moulded to suit the surface of the
adjoining part of the carpus.

The first metacarpal (that of the thumb) is shorter than the
others, and differs from them by its mode of ossification, its
epiphysis being situate only at its proximal end, while in
each of the other metacarpals there is an epiphysis at the
distal end only.

The proximal surface of the first metacarpal is deeply
concave, to suit the saddle-shaped surface of the trapezium —
its support.

9. The thumb and four FINGERS are called "digits "in
zootomy, each having a further distinguishing name.

Thus the first digit, or thumb, is termed \hzpollex.

1 From <TKd<j>r,, a boat.

152 ELEMENTARY ANATOMY. [LESS.

The second is the index.

The third is the " middle digit."

The fourth, the " ring digit."

The fifth the " little digit."

Each digit consists of three rather elongated bones, termed
phalanges, except the pollex, which has but two.

Each phalanx (like the metacarpals) ossifies by an epiphysis,
which is situated at its proximal end.

In each digit the phalanges become successively shorter
and smaller, the third phalanx (or in the pollex the second)
being very much smaller than the preceding one, but each
being a little expanded at its apex to support the nail.

10. Extending one's view to OTHER ANIMALS, it may be
remarked that man, inasmuch as he possesses limb-bones, re-
sembles the great majority of Vertebrates. Still, a vertebrate
animal may exist without limbs, as we see not only in the
Lancelet, but also in the Lamprey, and even in most Serpents.

In that man has a pair of upper (or thoracic) and lower
(or pelvic) extremities, he again agrees with most of his sub-
kingdom. Still, there are many species which only possess a
thoracic pair fully developed, as Cetaceans ; or only one pair
at all, as the Siren.

In the construction of the skeleton of the arm and hand,
man follows a rule which is universal in so far as the arm-
bones are attached to and suspended from a scapula which
forms (together with the clavicle when this exists) the root-
portion of the limb. For though the root portion may be
present without its arm-bones or distal appendages (as in
Anguis and others), yet the distal parts are. never present
when the limb-root is entirely absent.

Man agrees with the vast majority of Vertebrates in that
this limb-root consists of solid parts (scapula and clavicle)
destitute of any direct union with the spine. The limb-root,
however, may form a solid girdle, articulated above with
the spinous element of the vertebral column, which element
alone interrupts the continuity of the solid zone. This
is the case, e.g., in Raia clavata. The upper ends of the
girdle may not only meet, but overlap, though remaining
detached from the spine. This is the case, e.g., in the Toad
Dactylethra. The shoulder-girdle may be completed superiorly
by being attached to the head through special, interposed
bones — the supra-clavicle and post-temporal. This is the
case in most osseous fishes, e.g. Perch and Cod.

iv.] SKELETON OF UPPER LIMB. 153

The bones of the superior extremity of man are of medium
development as to numbers, for they may be more numerous
(though rarely much so), or less numerous, since we may
select a series of forms in which the number gradually
diminishes to zero.

FIG. 127. — FRONT VIEW OF SCAPULAR, OR SHOULDER, GIRDLE OF THE SKATE —

Raia clavata. (After Parker.)
This figure shows how in this animal the shoulder girdle abuts against each side

of the vertebral column.

c, coracoid element ; ec, epicoracoid element ; s, scapular element ; ss, supra-
scapular; v, vertebral column cut across vertically and transversely, and
showing the canal for the spinal marrow in its midst.

ii. The SCAPULA of man agrees in the essentials of its
composition with that of every species of his class except the
Monotremes. It agrees, that is, in having the coracoid pro-
cess annexed to it as a mere process ending freely, and not,
as in the Monotremes and in most lower Vertebrates, where
the coracoid is a distinct and largely developed bone, ex-
tending down to the sternum.

FIG. 128.— SHOULDER GIRDLE OF A BIRD (DIVER). (After Parker.)

c, right coracoid (its lower end abuts against the sternum — here removed) :
Cf, the clavicles (merrythought) ; sc, the right scapula — the rounded glenoid
surface is indicated in the scapula just where it joins the coracoid.

Man's scapula, apart from this process, is, as we have seen,
flat and triangular — a shape which, though common, is by
no means universal in the Vertebrata.

Thus, e.g., in Birds we find the scapula to consist of a long,
narrow, more or less sabre-shaped bone, though not quite
always so, as it becomes considerably broadened out in the
Penguin.

154 ELEMENTARY A NATO AT Y. [LESS

Even in man's own class the scapula may become much
narrowed, as in the Dog; or extremely so, as in the Shrew,
and "still more so in the Mole.

The scapula is entirely osseous in the adult in man, who in
this respect agrees with most Mammals and with Birds,
but in the majority of lower Vertebrates above Fishes, and in
the Ungulata amongst Mammals, the part answering to the
posterior border of man's scapula remains permanently, or
for a very long time, cartilaginous. In harmony with this
condition, we find that the base of the scapula in man long
remains a separate epiphysis. This part may be quite
distinct, as is the case in the Toad and some Fishes, e.g. the
Sturgeon and Raia clavata, where it bears the name of
supra-scapula.

In the fact that the scapula is the great bone of the
shoulder, man agrees with the rest of his class ; but its size
may be equalled or surpassed by the part answering to the
coracoid process, as in many Birds and Reptiles, or it may
be reduced to relative insignificance by the much greater
development of the clavicle, a1? in most Fishes.

The scapula (or rather the vertebral portion of it, or supra-
scapula), instead of being, as in man, widely separated from its
fellow of the opposite side, may be separated from it only by
the cartilaginous representative of the spinous processes of
the vertebrae, as in Raia clavata; or the two scapulas may
overlap the one the other, as in the African toad Dacty-
lethra. In the last-mentioned animal the supra-scapula is
many times larger than all the rest of the bone. Com-
paring the other members of man's class with man, we find
that the sub-scapular fossa may be situated (if we define it
by the attachment of the subscapularis muscle) not on the
inside, as in him, but on the outside of the blade, as is the
case in the Echidna.

The spine of the scapula is a structure constant in man's
class, but it may be very little developed, as in the Mole ; or
it may be easily overlooked, inasmuch as it forms the actual
anterior (in man the upper} border of the scapula in the
Monotremes. In these Monotremes its direction is so
changed that it lies on one and the same plane with the
blade of the scapula ; the supra-spinatus portion of the blade
being next the ribs, and the infra-spin atus fossa and sub-
scapular fossa together forming its actual outer surface, the
axillary margin (which ordinarily separates those two latter
fossae) aborting. The spine may be in close juxtaposition to

SKELETON OF UPPER LIMB.

155

the anterior border, as in the Dolphin. There may be a
second spine behind the normal one, as is the case in the
Armadillos.

An acromion process is the ordinary Mammalian termi-
nation to the scapular spine, but this may be utterly wanting,
as in the Hyrax and the Giraffe. It may not only be large,
but give off a distinct post-axially directed process, termed
the metacromion, as in the Hare, Elephant, and Shrew, the
acromion in the latter animal appearing to bifurcate.

•Ff

FIG. 129 — SIDE VIEW OF RIGHT SHOULDER GIRDLE OF YOUNG ECHIDNA
(Echidna hystrix}.

!>s, supra -scapular epiphysis ; ssf, sub-scapular fossa ; pf, post-scapular fossa ; cb,
coracoid border ; gbt glenoid border ; s, spine ; a, acrcmion ; ess, coraco-
scapular suture ; gc, glenoid cavity ; c, coracoid ; ec, epicoracoid ; cl, clavicle ;
ic, inter-clavicle ; ps, pre -sternum, or manubrium.

(From Flowers "Osteology."}

The acromion may join the coracoid process, and thus form
a bony loop, as in the Two-toed Sloth and in Birds — the bony
connexion answering to the ligament which connects the
processes in man.

A distinct acromion process may be developed where
there is no clavicle, as is the case in the Dolphin. It may be
very long and present an articular surface for the humerus,
as is sometimes the case in the Armadillos.

The articulation which takes place between the acromion

156 ELEMENTARY ANATOMY. [LESS.

and the clavicle is constant in mammals where the latter bone
is developed, except in the Mole and Three-toed Sloth. In
the Mole, however, there is a strong ligamentous connexion
between these parts, and in the Three-toed Sloth the sepa-
ration is a secondary condition, owing to the gradual atrophy
of the acromion which was primitively connected with the
clavicle.

The supra-spinatus fossa may be about equal to the infra-
spinatus one, as in the Dog and Shrew, or larger than it, as
in the Lion and in Sloths. It may, on the contrary, be little
more than a groove, as in the Dolphin, or it may (and this is
very exceptional) be large and situate entirely on the inner
(or body) surface of the blade, as in the Echidna.

FIG. 130.— RIGHT SCAPULA AND FIG. 131.— SCAPULA OF A PORPOISE.

If^-Slrfl (If^SeT * " — *" <™"; '• SlM°id
a, acromion ; c, coracoid ; clt clavicle ;
ma, metacromion ; mss, meso-sca-
pular segment.

The portion for the origin of the teres major muscle may
be greatly produced, as in the Armadillos and even in
Baboons.

The superior border of the scapula may be very much
longer than the base, as in Ungulates, and enormously so in
the Mole. It may, on the contrary, be relatively shorter even
£han in man, as in the Chimpanzee. It may be very convex,
as in the Mandrill Baboon ; and, most strange of all, it may
form what is apparently the posterior margin of the scapula,
as in the Echidna.

The supra-scapular notch may be converted into a foramen,
as even in one of man's order (e.g. in Mycetes), and in the Two-
toed Sloth. The notch, however, may be entirely absent, as
in the Deer and many others.

The base may be much the shortest of the three borders,
as in the Dog and Ungulates, and especially in the Mole. It

iv.] SKELETON OF UPPER LIMB. 157

may, however, be very much elongated, as in the Chim-
panzee and Dolphin.

The axillary border is, of course, drawn out where the sca-
pula is long and narrow. The most singular situation of this
border is found in the Echidna, where it appears as a slight
ridge traversing the outside of the blade of the scapula.

The postero-superior angle of the scapula may be rounded
off, as in the Dog and many others. It may, on the other
hand, be very prominent, as in the Dolphin. The inferior
angle may also be either sharp or rounded.

FIG. 132. — RIGHT- SCAPULA AND CLAVICLE OF TWO-TOED SLOTH (C/iolarj>us
Hoffmanni).

<T/J pre-scapular fossa ; pf, post-scapular fossa ; gc, glenoid cavity ; a, acromion ;
c, coracoid ; csf, coraco-scapular foramen ; cl, clavicle.

(Frojn Flower's " Osteology")

The neck of the scapula is always the narrowest part of
that bone in man's class, but when we descend we may find
it to be the widest part, as in some Fishes, e.g. Raia clavata.

Passing now to the second part of the scapula, in man called
the coracoid process, we shall find that, rudimentary as is
this part in him compared with its condition in lower forms,
it is nevertheless not at its minimum, for it may be, as in
Ungulates, e.g. the Deer, quite rudimentary. On the other
hand, it may be relatively larger than in man, as in the Two-

1 5 8 ELEMENTAR Y ANA TOM Y. [LESS.

toed Sloth, where it joins the acromion. It may be not only
long, but also forked, as in the little Pipistrelle Bat. It may
also join the clavicle, as in the Three-toed Sloth and Mole.

As has been said, this part may even in man's class (viz. in
Monotremes) be a large distinct bone connecting the scapula
with the sternum, and having an additional flat bone placed
in front of the inner end of the coracoid, called the epi-
coracoid, and a distinct rudiment of the epicoracoid may be
found in a higher Mammalian form, e.g. in Sorex.

The coracoid shares with the scapula the office of forming
the glenoid surface for the humerus, and it may become fused
with the clavicle, as in the Mole.

The coracoid may not only be a large bone rivalling or
exceeding the scapula, as in Birds, but there may be complex
structures divisible in zootomy into coracoid and epicoracoid,
as before said, and also in addition a part termed pre-cora-
coid, which, though essentially related to the coracoid, will yet
be more conveniently spoken of in treating of the clavicle.

FIG. 133. — SHOULDER GIRDLE OF A BIRD (DIVER). (After Parker.)

c, coracoid (its lower end abuts against the sternurti — here removed) ; cl, the
clavicles (merrythought) ; sc, the scapula— the rounded glenoid surface is
indicated in the scapula just where it joins the coracoid.

These coracoid elements may take the form of a large car-
tilaginous sheet passing down from the glenoid surface to the
middle line of the breast, as in Efts ; or may appear as two
bones so passing down on each side, one in front of the
other, as in the Frogs ; or as a large sheet of bone and carti-
lage often more or less perforated, as in many Lizards.

Instead of a single glenoid surface (as we find in all Ver-
tebrates above Fishes which have pectoral limbs), we find
what may possibly be several distinct glenoid surfaces, as
e.g. three in Raia clavata.

Where the coracoids are in the form of large lamellae, they
may overlap one the other, as in Batrachians, e.g. Salaman-
dra and the Frog.

The coracoid and scapula may form one cartilaginous
whole, while the supra-scapula remains distinct, as in Raia

iv.] SKELETON OF UPPER LIMB. 159

clavata. They may form one osseous whole in Birds (e.g.
the StruthionidcE or Ratita>}, continuing on in one main
direction. They may, on the contrary, as in all carinate, or
ordinary Birds, be so placed that the coracoid forms with the
scapula an acute angle open backwards.

To the parts which represent the scapula and coracoid in
osseous Fishes, the names of ulna and radius have sometimes
been respectively applied. The coracoid may attain a pro-
digious size, as e.g. in the Opah fish (Lampris).

FIG. 134. — BONES OF THE RIGHT ARM AND SHOULDER OF THE SMALL
TANREC — Hemicentetes.

This view shows the elongated scapula with blunt metacrowion and very small
coracoid; also the largely-developed clavicle attached to the end of the
acromion and projecting freely— the humerus with the prominent deltoid
ridge (or crest) and the radius applied closely in front of the ulna, which
latter bone has a well-developed ilecranon.

12. The apparent simplicity of the CLAVICLE in man would
hardly allow of a correct d priori conjecture as to the

i6o

ELEMENTARY ANATOMY.

[LESS.

complexity of the parts which may represent, or most nearly
correspond with it in the lower, and especially the lowest,
Vertebrates.

In fact, however, the clavicle of man is made up of four
parts, as has been noted. Thus we have —

(1) The body of the bone.

(2) The acromial end of the clavicle, remaining cartilagi-
nous in the young state, called the meso-scapular segment.

(3) The sternal epiphysis of the clavicle, called the pre-
coracoid.

(4) The inter-articular fibro-cartilage interposed between
the clavicle and the sternum, called the omosternum.

asff"

FIG 135.— INNER PART OF CLAVICLE

AND PART OF STERNUM OF A SHREW

— Sorex. (After Parker. )

cl, sternal part of clavicle ; ec, ep'i-
coracoid ; pc, pre-coracoid ; ost, omo-
sternum.

FIG. 136.— RIGHT SCAPULA AND
SCAPULAR PART OF CLAVICLE OF A
SHREW — Sorejc. (After Parker.)

a, acromion ; c, cpracoid ; cl, clavicle ;
ma, metacromion ; mss, meso-sca-
pular segment.

Now, inasmuch as the clavicle of man consists of only
one conspicuous element, is separated from its fellow clavicle
by the sternum, and connected externally with the acromion,
it has the general characters of the bone in his class. It
may, however, be entirely absent, as in all Cetacea and
Ungulata, in many Carnivora and Rodents.

It may, on the contrary, be very short and rudimentary,
and suspended by long ligaments both to the scapula and
sternum, as in the Guinea-pig and Rabbit.

It may be separate from its fellow cf the opposite side and
from the sternum, as in the Cassowary and Emeu.

It may — though this is very rare — have ultimately coalesced
with the coracoid, so as to form a complex single bone of
double nature, as in the so-called clavicle of the Mole, which
helps to form the articulation of the humerus.

iv.] SKELETON OF UPPER LIMB. ' 161

The clavicles may be fused together in the middle line,
as in the merrythought of Birds.

The meso-scapular segment never appears to become very
large, but the pre-coracoid part becomes very considerable in
the Ostrich, where a foramen indicates the line of demarcation
between it and the true coracoid, and it is large in many
Lizards, e.g. the Monitors. In Chelonians the pre-coracoid is
a large bone descending from the glenoidal region down-
wards and inwards towards the ventral shield of the cara-
pace. It has been spoken of as a true clavicle, as also the
anterior of the two bars which, in the Frogs and Toads, pass
inwards from the scapula, but which seems to be really a pre-
coracoid.

The last element, the omosternum, becomes amongst Mam-
mals very conspicuous in certain Shrews and Mice ; also in
certain tailless Batrachians, e.g. Pseudis and Pipa. It may
be that this element is the same as that next to be noticed,
and which otherwise has no representative in man. or in any
but the lowest Mammals.

The element in question is the inter-clavicle, which is
enormous in the Monotremes, and forms the bulk of that large
T-shaped bone which prolongs as it were the manubrium ot

FIG. 137.— FRONT VIEW OF LEFT HALF OF SHOULDER-GIRDLE OF A GECKO
'LiZA.RD—Hemidcictylus. (After Parker.)

f, curacoid ; cl, clavicle ; i, inter-clavicle ; me, meso-coracoid ; pc, pre-coracoid ;
j, scapula ; ss, supra-scapula ; st, sternum.

the sternum, and which bears on its diverging arms the small
splint-like clavicles. The same element is more or less
similar in shape in many Lizards, e.g. Iguana and Monitor.
It may be cruciform, as in Cyclodus, or a simple forwardly
directed ossicle, as in the Crocodile, or a median expanded
lamella of bone or cartilage, as in Anguis and Chelonians.

1 62 ELEMENTAR Y ANA TOM V. [LESS.

It may be small and serve to connect the clavicles, as in
Birds, where it forms the middle of the merrythought. It
may be very large and bifold, as in many Fishes, e.g. Cottus
and the Sturgeon.

The true clavicle, more or less cylindrical or at least slender
in Mammals and Birds, may become expanded in Lizards
(e.g. Hemidactylus, Cydodus, and especially Trachydosaurus].

In Chelonians also the clavicles are greatly expanded and
Form the two foremost bones of the ventral part of the
carapace, the median one immediately behind them being
the inter-clavicle.

•1

Fir,. 138.— SCAPULAR ARCH OF A FISH— Zens. (After Parker.)

/>4, the fourth or lowest of the four brachials which together may represent the
humerus, and to which the fin rays are attached ; c, coracoid : cl, clavicle ; pc,
pre-coracoid ; //, post-temporal, which connects the scapular arch with the
skull ; si, supra-clavicle— the bar of bone unmarked, which descends back-
wards, is the post-clavicle.

The great size of the clavicle here and in Trachydosaurus
prepares us for the still vaster development of this part in
bony Fishes, where the clavicles become enormous, and may
not only be provided with a distinct inter-clavicle, but also
each with a distinct portion above — the supra-clavicle (as in
the Dory, Zeus, the Sturgeon and others), and besides this
with a posterior element, a post-clavicle, as in the Dory,
Perch, and Cod.

Thus the clavicle of man, instead of being the simple struc-

SKELETON OF UPPER LIMB.

163

ture which it seemingly is, really represents some elements
which properly belong to the coracoid, and other elements
which may greatly increase both in size and complexiiy
in other animals. At the same time its inconstancy is
such that it may utterly abort, while the scapula and even
the coracoid element are largely developed.

13. That important bone of the human skeleton, the
HUMERUS, is constantly present in Vertebrates above Fishes,
wherever there is an upper limb at all, although differing
in size and shape. It never, however,
seems to be present where there is no
representative of the hand — in this
respect, as we shall see, differing from
the thighbone in the relation of the
latter to the foot.

In the lowest Vertebrates, i.e. in all
Fishes, it is difficult to say what cer-
tainly corresponds with the humerus
of man, but very probably the several
bones or cartilages which articulate
with the coracoid and scapula (at the
several glenoid surfaces before de-
scribed) may be such representatives.

In this case it may be said (i) either
that several (two to five) bones or carti-
lages together represent man's humerus,
or (2) that each of these is in fact a rudi-
mentary humerus, so that a fish has
thus several humeri on each side. It
is possible, however, that this bone (or
perhaps the next limb segment — radius
and ulna) may be represented by a
single cartilage— as in Ceratodus,

Leaving, however, these members of „

- The large upper piece articu-

FIG

39.— CARTILAGINOUS
SKELETON OF A LIMB OF
Ceratodus. (After Giin-
ther. )

the lowest Vertebrate class, w^e shall jates with the "limb root.

find that higher forms show the several

parts of man's humerus to be capable of different degrees of

development, yet that on the whole great variations are

rare.

As being the largest bone of the arm the humerus of man
follows the general rule, but it may be much exceeded in size
by a bone of the fore-arm, as in the Bat and Eagle, while
its length may be quite insignificant compared with that
of the entire limb, as in the Dolphin. Its length may, hovv-
M 2

e°'h

164 ELEMENTARY ANATOMY, [LESS.

ever, exceed that of all the rest of the limb put together, as
in the Apteryx. It may also exceed the length of the whole
body, as in the Pelican ; while a few Birds, e.g. the Martins,
have it remarkably short.

In its being cylindrical in shape man's humerus is normal,
but it may be almost as broad as long, as in the Mole and
some Cetacea. The head of the hu-
merus is generally less spheroidal than
in man, with high projecting processes
(the tuberosities), as in the Carnivora,
e.g. the Dog. It may have the form of a
transversely extended articular ridge, as
in Birds.

The shaft of the bone may be twisted
like the letter S, as in the Tortoises, but
FIG. 140.— RIGHT Hu- that twist of the shaft which we find in
man is peculiar to him and to the high-
esl: APes> though there is something like

condyle; t\ capitel- it in Birds.

lum. The greater (radial) and lesser (ulnar)

tuberosities are very constant structures,
one or both appearing down to the lowest Batrachians.

They may project much more than in man (as e.g., amongst
many others, in the Dog and Sheep), or the two maybe fused
into one, thus obliterating altogether the bicipital groove, as
is the case in the Cetacea ; or they may project much and
so sharply as to make that groove a very deep one, as in the
Turtle.

The so-called " lesser " tuberosity may be as large as the
"greater" one, or even come to exceed it in size, as in the
Two-toed Sloth, the Bat Pteropus, and the Lizard Uromastix.
Beneath the lesser tuberosity a deep cavity may exist, as in
Birds : this is to allow air to enter the air-cavity within the
bone, many bones in many Birds being thus filled with air
instead of marrow.

The rough surface for the deltoid is in man's humerus but
a faint indication of what may in other forms, e.g. the Seal,
Mole, Beaver, &c., be a very prominent ridge.

The lower end of the bone may be either more expanded
relatively than in man, or less so. Thus, e.g., the condyles
may be very greatly produced, as in the Mole, Armadillos,
and Echidna, or they may be quite rudimentary, as in the
Deer and Hare.

Very often a foramen may exist above the internal con-

iv.] SKELETON OF UPPER LIMB. 165

dyle, as e.g. in the Wombat. This serves to transmit the
median nerve and brachial artery, which are thus protected
by bone in a way found only by a very rare exception indeed,
if ever, in man. There may be a notch or a foramen above
the external condyle, as in some Lizards, e.g. Psammosa&rus.
The transverse extent of the inferior articular surfaces of
the humerus of man is greater than in very many forms, on
account of the articular surface for the radius coming to be
in front of, instead of at the side of, that for the ulna. We
see this very distinctly, e.g -., in the Dog.

FIG. 141.— ANTERIOR SURFACE OF RIGHT HUMER
vojubatns).

h, head ; kg, bicipital groove : t, great or radial tuberosity ; f, small or ulnar
tuberosity ; dr, deltoid ridge ; sr, supinator ridge ; cf, supra-condylar foramen ;
ec, external condyle ; ic, internal condyle ; ar, articular surface for ratlius ;
au, articular surface for ulna.

(From Flower's " Osteology")

The fossae for the coronoid process and olecranon, which
sometimes communicate by a perforation in man's humerus,
may do so normally and constantly, as e.g. in the Hare.

Rarely (as in some Tailed- Batrachians) a dense ligament
may connect the head of the humerus with the glenoid cavity,
as we shall see that the head of the thighbone is normally
connected with the cavity which receives it.

166 ELEMENTARY ANATOMY. [LESS.

14. The RADIUS is a bone constantly present and distinctly
represented, wherever an arm exists, in all Vertebrates
above Fishes. In Fishes its exact representative cannot be
determined. The ossicles or cartilages, however, which may
be distally annexed, to the representatives of the humerus,
probably as a whole represent both the radius and the ulna.

In the constancy of its development the radius shows its
generally greater importance as the main bone of the fore-
arm, when compared with the ulna, which latter may more
or less completely abort.

In Birds, however, it is subordinate in development to the
ulna, which is the main bone of the fore-arm in them, e.g.
the Eagle.

In its elongated figure the radius of man agrees with the
same bone as generally developed, but it may be shortened
and flattened even in some Birds, e.g. the Penguin, and very
much more so in Cetacea, e.g. the Dolphin, and still more
so in the extinct Ichthyosauria.

Instead of being free as in man, the radius may anchylose
at each end with the corresponding extremities of the ulna,
as is the case with the Sirenia.

It may be the solitary apparent representative of the bones
of the fore-arm, which are completely fused together, as in
the Frog and Camel. It may be all but the only bone of the
fore-arm, through the small development of the ulna, as is
the case in Bats and Ruminants.

That crossed position of the radius with relation to the
ulna which is called pronation in man, is the constant and
only position of the bone in many, as e.g. the Dog, Elephant,
and hoofed beasts generally. Pronation and supination,
however, are not confined to man. They exist sometimes
very distinctly, as e.g. in the Apes and Sloths.

No motion of the kind is possible in many forms in which
the radius does not cross the ulna, as in Bats and Birds,
where such a flexibility of the limb would be fatal to flight.
Pro- and supi-nation are also impossible in the Cetacea,
where there is no movable elbow-joint at all.

But the limbs may permanently retain a position which
indeed is primitive and temporary in man ; that is to say,
there may be no crossing of the bones of the fore-arm, and
yet the whole dorsum (or extensor surface) of the limb may be
turned outwards somewhat in the position in which a man puts
his arms when, resting on his two palms, he stoops to drink
from a pool between them. Even thus the primitive position

IV.]

SKELETON OF UPPER LIMB.

167

cannot be quite assumed by the adult human being, though
it is the permanent condition of some Reptiles, especially
the Chelonians.

The head of the radius is often much larger relatively
than in man, as e.g. in the Dog and Ruminants.

FIG. 142. — RIGHT PECTORAL LIMB OF A GIRAFFE.

CM, scaphoides ; rf3, proximal phalanx of third digit : d*, proximal phalanx of
fourth digit ; g, magnum ; gt, great tuberosity of the humerus ; /i, shaft of the
humerus ; lit, lunare ; «&*, united metatarsals of third and fourth digits ; <?,
olecranon ; pi} pisiforme ; r, radius : sc, cuneiforme ; ««, unciforme.

15. As with the radius, so with the ULNA, we can only
employ Vertebrates above Fishes for comparison.

In the proportion it bears to the radius, man's ulna agrees
on the whole with the relation obtaining in the majority of
forms.

It may, however, be larger and more important than the
radius, as is the case in Birds, e.g. the Eagle. On the con-
trary, it may be very much smaller and more or less abortive,
as in Ruminants and Bats. That the proportionate size of
this bone has no relation to flight is shown by the just-
mentioned fact, that it is the larger bone in Birds and the
smaller one in Bats.

168 ELEMENTARY ANATOMY. [LESS.

The olecranon process of man is larger than in many
forms ; thus e.g. it is relatively larger than in Birds. It is,
however, much larger relatively than in man in many Mam-
mals, even e.g. in Baboons, and still more in Ungulates, the
Monotremes, and the Mole. -There may be a detached sesa-
moid ossicle at the end of the olecranon, reminding the
observer of the knee-pan, or patella, of the leg. This is the
case in some Bats.

The ulna's articular surface for the humerus may merely
complete that offered by the radius, the two together forming
a single concavity for the reception of the humerus. This is
the case, e.g., in Ruminants.

The styloid process may be much more prolonged than in
man : we find it so in the Gibbons. The distal part of the
\ilna may, on the contrary, abort altogether, as in the Bats.
It generally, however, articulates with the carpus directly, as
the radius does.

16. Inasmuch as THE HAND of man is made up of the
carpus, metacarpus, and phalanges, it agrees with the corre-
sponding segment in all Vertebrates above Fishes ; where, if
any element of the arm is present, the hand is present
likewise.

17. Inasmuch as the CARPUS of man consists of a few
relatively small bones, it agrees with that of all other Verte-

FIG. 143.— DORSAL SURFACE OF SKELETON OF RIGHT HAND OF THE TORTOISE
Chelydra. (After Gegenbaur.)

c, cuneiforme ; in, intermedian (or centrale) ; /, lunare ; m1 — ?«5, metacarpals ;
r, radius; s, scaphoides; u, ulna; 1—5, the five distal carpals, namely—
i, trapezium ; 2, trapezoides ; 3, magnum ; 4 and 5, divided unciforme.

brates above Fishes, except that in some Tailed-Batrachians
and Cetaceans the parts are more or less permanently car-
tilaginous. The number of carpal bones, however, may be
increased to ten, as in Chelonians, or it may be reduced to
two, as in Birds.

iv.] SKELETON OF UPPER LIMB. 169

Very rarely, as in the Crocodile, the two proximal bones
may be so much longer than the others as to take on some-
what the character of "long bones," and to constitute by
themselves another limb segment.

1 8. The BONES OF THE FIRST ROW of the carpus, except
the pisiforme, may be represented by one single bone, as in
Pteropus.

" Inasmuch as the scaphoides articulates with the radius, it
has a character which is constant The distinctness which it
possesses in man is by no means universal. Thus the sca-
phoid coalesces with the lunare in the Carnivora and many
other Mammals, and also probably in the Crocodiles. It
unites with the cuneiforme in addition in Pteropus. It may
coalesce with the trapezium, as in the Three-toed Sloth. It may
become a considerably elongated bone, as in the Crocodile.

On the outer (radial) side of the scaphoid we often find a
small ossification of a tendon, or sesamoid ossicle, corre-
sponding with that sesamoid ossicle of the ulnar side, which is
counted as a carpal, and called the Pisiforme.

This radial sesamoid ossicle is found even in Apes, but it
attains its maximum in the Mole, where it strengthens and
broadens the hand for digging. It is found even in some
Reptiles, as e.g. in Emys europea.

An extra bone which exists in many Vertebrates, but not in
man (and which goes by the name of os centrale, or interme-
dium}, is most probably a dismemberment of the scaphoid.
It is present and distinct in the Apes, except the very highest,
and many other forms, including most Reptiles and Batra-
chians. The form of the scaphoid in Emys europea seems to
show that the centrale is a dismemberment of the scaphoid,
as indeed does its position in the Orang.

This conclusion is indicated by the occasional ossification
of the scaphoid from two centres, in the class Mammalia.

The centrale may form a very large and conspicuous part
of the carpus, to the abortion of any representative of the
trapezium. This, e.g., is the case in the Crocodile ; and if
the centrale be a dismemberment of the scaphoid, then, con-
sidering the length and size^of the undoubted scaphoid or
scapho-lunar bone in the Crocodile, the equivalent of man's
scaphoid forms alone the larger half of the carpus in that
reptile. Again, the centrale may form a singularly con-
spicuous part, as in the Chameleon, where it is surrounded
by the more distal bones of the carpus, which have re-
spectively coalesced with their adjacent metacarpals.

1 70 ELEMENTAR Y ANA TOMY. [LESS.

As has been already said, the semi-lunar bone may coalesce
with the scaphoid in many animals, e.g. the Dog. It may,
on the contrary, unite with the cuneiforme, as in the Sala-
mander and Triton, and probably in Birds. It seems also to
be generally absent as a distinct bone in Reptiles other than
Chelonians. Thus its distinctness in man is a rather ex-
ceptional character.

The separate and well-developed condition of the cunei-
forme in man is one which characterizes it generally, it being
one of the constant carpal bones ; the only noteworthy devia-
tions are that, as just said, it may coalesce with the lunare, or
even with the scaphoid also, as in Pteropus ; or that it may
be-very considerably increased in length, as in the Crocodile.
It may be relatively larger than in man, as in the Turtle ;
or smaller, as in the Mole.

The inconstancy of the pisiform* is a consequence of its
being really no true carpal, but only an accessory sesamoid,
like the radial ossicle spoken of in noticing the scaphoid.
Thus it is often absent, as in many Cetacea, the Sirenia.,
Birds, many Reptiles, and all Batrachians ; while it is very"
small in Bats, Seals, and others. It may be much larger and
longer relatively than in man, as e.g. in the Carnivora.

19. The BONES OF THE SECOND ROW are by no means so
constant in number or development as are those of the first

•<s».

FIG 144. — Left Hand of Chameleon, showing the opposition between thetwoulnar
and the three radial digits.

tnl—m$, the five complex bones formed of the union of each metacarpal with the
corresponding distal carpal bone ; r, radius ; n, ulna ; i, ulnar proximal carpal
bone ; 2, radial proximal carpal bone ; 3, intermedium or centra'e.

row. They may coalesce with the metacarpals, as is the case
in the Chameleon.

The importance and size of the trapezium in the human
carpus, owing to the relation it bears to the development of
man's thumb, are very different from what we see in some
members of man's class, and even order.

IV.]

SKELETON OF UPPER LIMB.

171

The saddle-shaped surface for articulation with the first
metacarpal is not so well developed in any other form as it is
in man.

The trapezium may be quite rudimentary, as in CJi<zropus,

FIG. 145. — BONES OF MANUS OF Chcerofitis castanotis.

c, cuneiforme ; /, lunare ; m, magnum; R, radius; s, scaphoides; id, trape-
zoides ; tin, trapezium ; U, ulna, it, uncifonne ; //., ///., and IV., second,
third, and fourth digits.

(From Flower's " Osteology"}

or altogether wanting, as in the Horse, Sheep, Pig, Dolphin,
Salamander, &c.

As to Birds, no distinct trapezium is distinguishable ; and
the same is the case with Crocodiles, but a trapezium exists
in many Lizards. As has been said, it may, as in the Three-
teed Sloth, coalesce with the scaphoides.

The trapezoides is a more constant bone than is the pre-
ceding one, as it seems to exist in all Mammals which have
a carpus, though its existence is not to be made out in Birds,
or clearly so in Crocodiles. It may be relatively smaller or

1 72 ELEMENT A RY ANA TO MY. [LESS.

larger than it is in man, and it may, as in the Three-toed
Sloth, coalesce with the os magnum.

The os magnum may be much smaller relatively than in
man (as e.g. in the Bear and Hare) ; or relatively larger (as
in the Hyrax) ; or it may seem to abort altogether, as in
Birds. Compared with the bones of the second row only, it
may be, as in the Horse, a more predominant bone than it is
in man.

The undivided state in which the unciform bone exists in
man is universal in his class.

It may, however, be represented by two distinct bones
corresponding with and supporting the fourth and fifth meta-
carpals, as in Chelonia, Chelydra, and Salamandra. There
may be no bone whatever capable of identification with it, as
in Birds. It may be much smaller or larger relatively than
it is in man.

An additional ossicle not found in man may be present in
the ligament connecting the trapezium and unciform bones.
This is the case in the Potto (Perodicticus).

20. The distinctness and development which the META-
CARPUS or middle segment of the hand attains in man are
characters which are normal. The somewhat opposed posi-
tion of the first metacarpal in him is only found in a few
Mammals besides — in Monkeys and Lemurs.

The metacarpals, however, may fuse with the distal carpals
— the trapezium with the first metacarpal, as in the Three-
toed Sloth, or all five with the corresponding carpals, as in
the Chameleon.

A more complete opposition may obtain, however, than that
which exists between the first and the other metacarpals in
man ; as is shown by the Chameleon, in which the three radial
metacarpals are as strongly as possible opposed to the two
ulnar ones.

In the number of these bones and their sub-equality of
development man agrees with many Vertebrates above
Fishes. Nevertheless, the number may be much reduced,
and the proportions of the several bones may vary in differ-
ent modes.

Thus there may be but a single metacarpal (the third), with
rudiments of two others, as in the Horse ; or there may be but
a single bone, which consists of the third and fourth fused
together, as in the Sheep, Deer, &c.

Again there may be but two, the second and third, with
another rudimentary metacarpal (which answers to man's

IV.]

SKELETON OF UPPER LIMB.

173

fourth), as in Chceropus ; or the same two with a rudiment
of the first metacarpal also, as in Cholcepns.

We may have the second and third metacarpals well de-

FIG. 146. — RIGHT PECTORAL LIMB OF HORSE.

t, cuneiforme ; k, humerus ; In, lunare ; ;«3, metacarpal of the third digit — the
only one fully developed ; w4, rudimentary fourth metacarpal ; ing, magnum ;
pi, pisiforme ; pl, proximal phalanx; /2, middle phalanx; /3, third or
ungual phalanx ; i, sesamoid ; nu, unciforme.

veloped, with a rudiment also of the first, all three being
fused together into a single bone — as is the case in Birds.

There may be but three sub-equally
developed, and these may be the second, LVi

third, and fourth, as in Proteus and 4j?i

Rhinoceros ; or they may be the first, u JU

second, and third, as in Seps tridactylits.
The three may be anchylosed together
at their proximal ends, as in the Three- FJG. 147. __ PALMAR

loed Sloth. VIEW OF LEFT HAND

The metacarpals may decrease in size OF SEPS TR1DACTYLUS-
from the first to the fifth, as in Seals ; or (After Furbringer.}
increase from the first to the fifth, as in There is h,e.re but a T'

- ,, mite rudiment of the

the Manatee. 4th digit. Thepollex,

They may be singularly unequal, the index, and third digit
third being by far the thickest and ex- are wel1
tremely short, as in the Great Armadillo ; or the third being
far the slenderest and extremely long, as in the Aye-aye.

174

ELEMENTAR Y ANA TO MY.

[LESS.

The first may disappear or be rudimentary, as happens in
very many forms ; or the second digit alone may be very
reduced, as in the Potto.

The first may be short and the four others exceedingly
elongated and slender, as in the Bats ;
or the first three may be short and the
fourth enormous, as in the Pterodactyles.
The whole five metacarpals may be
extremely short and stunted, as in the
Mole, and still more so in the Land Tor-
toises and in the Ichthyosaurus.

The number five is never increased
(except by monstrosity) in any known
Vertebrate.

21. The number of DIGITS which may
be developed has been indicated in
treating of the metacarpus. Thus there
may be but a single digit, as in the
Horse; two, as in Ruminants, and in
Chaeropus. There may be three, as in
the Rhinoceros, Proteus, and Seps
(second, third, and fourth, or first,
second, and third) ; or, as is very often
the case (e.g. Pig, Dog, &c.), there may
be four.

The digits are never certainly more
than five (except by monstrosity), al-
though in the Ichthyosaurus extra mar-
ginal bones give the appearance of more.
The filamentary bones which terminate
or fringe the fins of Fishes are not digits
at all, but are dermal ossifications called
" fin rays," which will be spoken of with
the rest of the external skeleton.

When a digit is wanting, it is generally
the pollex, as in Spider Monkeys, but it
may be the fifth, as in Pterodactyles, or
the fourth and fifth, as in Birds.

The thumb (pollex) may be more or
less opposable, as in most Monkeys and
Lemurs ; or two digits may be opposed to three, as in the
Chameleon.

The second digit may be greatly reduced, as in the Potto ;
or the third may be disproportionately slender, as in the Aye-

FIG. 148. — HAND OF
BAT (Pteropns).

m * — in 4, metacarpals of
the four fingers ; p,
pollex, with a very
short metacarpal, sc,
scaphoides.

iv.] SKELETON OF UPPER LIMB. 175

Aye ; or thick, as in the Great Armadillo. The digits may be
enormously long, as in the Bats ; or short, as in the Land
Tortoises. They may be very imperfectly developed, as in
Birds.

They may be so united by dense tissue as to be quite
incapable of separate motion, as in the Cetaceans. The

S
FIG. 149. — RIGHT HAND OF OSTRICH.

f ', radial carpal ossicle ; c2, ulnar carpal ossicle ; d"2, proximal phalanx of the
index digit which has three phalanges ; o?3, phalanx of third digit ; /, ulna ;
in 2 and in 3, metacarpals of second and third digits anchylosed together and
with that of the pollex ; /, proximal phalanx of pollex ; r, radius.

bones of the fingers or phalanges of man are the same in
number as in other Mammals with the exception of the
Cetacea. In distinctness they also agree with most, but it
is possible for the proximal row of phalanges to become
anchylosed to the metacarpals, as is the case in the Three-
toed Sloth.

The phalanges, instead of decreasing in length, distad,1 as in
man, may so increase — as in the three ulnar digits of Dasypus
villosus. A terminal phalanx of a digit may far exceed in
length its two proximal phalanges, as is the case in the
middle finger of Priodontes, and in the three middle digits of
Perameles.

The number of phalanges may be much greater than in
man, e.g. as many as fourteen, in the third digit of Glo-
biocephalus. Often in Reptiles the number of phalanges
increases from two in the pollex to five in the fourth digit, as
in the Monitor. The abortive hand of Birds at its best has but

1 As we proceed from above downwards to the fingers' ends.

1 76

ELEMENTARY ANATOMY.

[LESS.

three digits, with two phalanges to the pollex, three to the
index, and one or two to the third digit.

The terminal phalanges may bifurcate slightly, as in Pera-
meles and in the Mole, or widely, as in some Toads and Frogs.

H

gj.

FIG. 151.

1. Ungual Phalanx of a Bear, show-
ing the enlargement at the ventral
side of its proximal end, d.

2. Ungual phalanx of a Sloth, show-
ing the enlargement, d, on the
dorsal side of its proximal end.

3. Widely bifurcating distal phalanx
of the Toad, nyladactylui (or
Kaloula).

FIG. 150. — BONES OF MANUS OF
BANDICOOT (Peratneles).

c, cuneiforme ; /, lunare ; in, mag-
num ; R, radius ; s, scaphoides ;
td, trapezoides ; /;;/, trapezium ;
£/,ulna ; u, unciforme : /. — K, the
digits ; /, pollex ; I/', little finger.

(From Flower's "Osteology."}

They may develop a large fold of bone to support the claw,
as in the Cats, where the inferior part of their proximal end
is much enlarged, while it may be the upper part of the same1
which is enlarged, as in some Edentates.

SKELETON OF LOWER LIMB. 177

LESSON V,

THE SKELETON OF THE LOWER LIMB..

1. THE skeleton of the lower limbs, like that of the upper,
is divisible into three categories : A, that of the hip ; B, that
of the leg ; and C, that of the foot.

A. The skeleton of the hip, or the haunch-bone, is called
the os innominatum^ and there is one such on each side in
the adult man.

B. The skeleton of the leg is subdivisible into —

(a) That of the thigh, which consists but of one bone, called
\hefemur (os femoris}.

(b) That of the lower part of the leg, which consists of two
bones placed side by side. The larger of these is called the
tibia ; the other, much more slender and placed on the outer
side of the leg, is called \\\Q fibula, or peroneal2 bone of the leg.

C. The skeleton of the foot is subdivisible into three parts :
(a) that of the ankle, the tarsus ; 3 (b) that of the middle
part of the foot, the metatarsus ; and (c) that of the toes, or
digits — composed of the phalanges.

2. The OS INNOMINATUM is a very large bone, meeting
with its fellow of the other side in the mid-ventral line of the
body, and being strongly attached to the sacrum behind ; thus
forming, with the intervention of the last-named bone, a solid
bony girdle, supporting the trunk above, and being itself im-
pored on the limbs below-- the head of the thigh-bone fitting
into a socket on the outer side of the os innominatum.

Each os innominatum is made up originally of three dis-
tinct bones, which become united when youth is merging into
manhood. These three bones are the ilium, the ischium,
and the pubis.

1 From its not bearing any special resemblance to any one object,

2 So called bec?use it clasps the larger bone of the leg, Trepoi/j, a clasp.

3 From Tapa-og, a crate.

N

1 78 ELEMENTARY ANATOMY. [LESS.

The innominate bone thus consists of three parts, (i) A
widely expanded upper part joins the sacrum and extends
down to the socket for the thigh. This is the ilium.1

(2) From the thigh-socket a bar of bone runs forwards and
inwards. This is the pubis.2

(3) Another, stouter, piece of bone curves first downwards
from the thigh-socket, and then inwards and then upwards
till it meets the pubis. This is the ischium.3

FIG. 152. — OUTER SIDE OF RIGHT Os INNOMINATUM OF MAN.
<7, acetabulum ; at, anterior inferior spinous process of the ilium ; as, anterior
superior spinous process of the ilium ; c, crest of the ilium ; ip, ilio-pectineal
eminence ; o, obturator foramen ; /, pubis — its horizontal ramus ; pi, posterior
inferior spinous process ; ps, posterior superior spinous process ; s, spine of the
ischium ; t, tuberosity of the ischium.

The ilium has a wide outer surface (marked by two curved
lines), the upper border of which is termed the " crest" and is
convex and arched. From the front end of the crest the
anterior border descends sharply to the pubis, a blunt promi-
nence (called the ilio-pectineal eminence) marking the point
of junction. A sharp prominence (termed the anterior supe-
rior spinous process] projects from the anterior border of the
ilium at its summit, and another — the anterior inferior spinous
process — projects from it a little above the thigh-socket. From
the hinder end of the crest of the ilium descends its posterior
border, the summit of which is marked by the posterior
superior spinous process, separated by a small notch from a

1 So called from its relation to the ilia, entrails.

2 la reference to its superficial exoskeleton — i.e. the hair.

3 Named from the Greek ««TXJ'U, hips.

v.] SKELETON OP LOWER LIMB. 179

strongly marked prominence called the posterior inferior
spinous process, beneath which the border is deeply excavated
and concave.

The inner surface of the ilium is concave, forming the iliac
fossa, and at its hinder part is a rough irregular space for
articulation with the sacrum. The ilium forms about the
upper third of the socket for the thigh-bone.

sy

FIG. 153. — INNER SIDE OF RIGHT Os INXO.MINATUM OF MAN.
at, anterior inferior spinous process ; as, anterior superior spinous process ; an,
auricular surface ; c, crest ; i, ischium ; il, iliac fossa ; p, pubis— its horizontal
ramus ; pi, posterior inferior spinous process ; ps, posterior superior spinous
process ; s, spine of the ischium ; sy, part of the pubis which abuts against its
fellow of the opposite side to form the pubic symphysis.

£$•, or pubic bone, forms the inner part of the thigh-
socket, joining the ilium above, and at its junction con-
tributing to form the ilio-pectineal eminence. It thence pro-
ceeds horizontally inwards (as a band of bone flattened from
without inwards, called the horizontal ramus) till it meets with
its fellow of the opposite side, when it turns sharply down-
wards. The junction of the two pubes is termed the sym-
physis, and the part of each pubis next the symphysis is
sometimes called the body / thence the pubis runs outwards
and downwards (as a flattened band, similar to the horizontal
ramus, with which it forms an acute angle) till it meets the
ascending ramus of the ischium.

The ischium forms the outer and lower part of the thigh-
socket, and indeed of the whole t)s innominatum. The body
of the ischium forms about two-fifths of the socket for the
thigh, which cavity is situated on its outer side. The body is
broad, and sends from its posterior outer margin a large sharp

N 2

1 80 ELEMENTAL Y ANA TOM Y. [LESS.

process called the spine of the ischium. Below this, and below
the socket, the bone contracts and then expands again, the
expansion having a rough prominent surface, which is called
the tuberosity of the ischium ; and it is the two tuberosities (of
the two ossa innominata) which support the body when in a
sitting posture. Just below the tuberosity, the ischium sends
forth a flat band of bone (the ascending ramus), which, curv-
ing forwards and upwards, meets the descending bony band
of the pubis spoken of above.

The socket for the thigh-bone (which has been so often
referred to) is called the acetabulum* or cotyloid* cavity. It
has a prominent rim, except at the inner and lower part
where the rim is interrupted by a notch (the cotyloid notch).
There is no perforation in the acetabulum, but its surface just
within the notch is depressed, the depression affording attach-
ment to the very strong ligamentum teres (or round ligament)
which goes from it to the head of the thigh-bone.

Enclosed by the ilium, ischium, and pubis, there is in each
os innominatum a vacant, oval space called the obturator^
foramen, one such being placed on each side of the pubic
symphysis.

The deep concavity, in the posterior border, between the
posterior inferior spinous process of the ilium and the spine
of the ischium, is called the greater ischiatic notch; the
smaller concavity, between the spine of the ischium and the
tuberosity of that bone, is called the lesser ischiatic notch.

The two ossa innominata, together with the sacrum, form
what is called the pelvis, or basin-shaped cavity which sup-
ports the viscera.

The internal surface of each os innominatum is divided
into two parts by a prominent line running upwards and
backwards from the upper part o'f the pubis to the sacrum.

The width from side to side of the pelvis is but rarely ex-
ceeded by its depth from behind forwards, but exceeds the,
greatest vertical extent of the ossa innominata.

A strong ligament connects the tuberosity of the ischium
with the sacrum, the coccyx, and the posterior margin of the
ilium. This is called the great sacro-sciatic ligament. Another
ligament goes from the sacrum and coccyx to the spine of
the ischium. This is termed the small sacro-sciatic ligament.

1 From its resemblance to an ancient vinegar cup.

2 From KOTtiXr), a cup.

3 Because if surrounds the obturator membrane which closes up part of the
pelvic cavity.

SKELETON- OF LOWER LIMB.

181

~-ltr

3. The FEMUR is the longest bone of man's skeleton, and,
like the humerus, is more or less cylindrical, with a rounded
head to fit into the acetabulum above,
and with an expansion below with
two articular surfaces.

The shaft is slightly arched for-
wards, is smooth in front but with
an elongated prominence behind,
termed the linea aspera, which is
most marked about half-way up the
bone.

At the upper end of the shaft are
two conspicuous projections. The ex-
ternal one of these (projecting from
the outer margin of the bone, which
it continues upwards), is called the
great, or per one al r trochanter. The
internal projection, which is smaller,
more conical, and rounded, stands out
from the inner and hinder side of the
bone, and is called the lesser, or tibial
trochanter.

Between the two trochanters, on
the hinder side of the femur, a bony
prominence extends, which is termed
the posterior inter-trochanteric ridge ;
and a less marked line, the anterior
intcr-trochanteric ridge, also connects
the two trochanters on the front sur-
face of the femur.

On the inner and hinder side of the
great trochanter is a pit, termed the
trochanteric fossa.

From the inter-trochanteric ridges
a narrower rounded portion of bone
projects inwards, forming an obtuse
angle with the shaft. This is called
the neck of the femur. It ends in a
rounded head (forming a large part
of a sphere) which fits into the ace-
tabulum.

The femur is connected with the os innominatum by the
strong ligamentum teres before mentioned, the attachment of

1 Because situate on the same iside as the peroneal bone of the leg.

i h*

FIG. 154. — FRONT VIEW OF
RIGHT FEMUR OF MAN.

cc, internal condyle , e tu,
external tuberosity ; g tr,
great trochanter ; 'h, head ;
zV, external condyle ; itu,
internal tuberosity ; Itr,
lesser trochanter; n, neck
of the femur.

1 82 ELEMENTARY ANATOMY. [LESS.

which to the femur is indicated by a pit on the head of that
bone. It is also attached by a bag-like (or capsular} liga-
ment, which, extending from the innominate bone, is inserted
into the inter-trochariteric lines.

It is the neck of the femur which is so often broken by
old persons, through alteration, not only in the texture, but
also in the shape of the bone : for with age the neck comes to
form with the shaft a less and less open angle, and the bone
is thus less and less adapted to resist vertical pressure.

Itr

FIG. 155. — POSTERIOR SURFACE OF UPPER PART OF RIGHT FEMUR OF MAN.

ir, intertrochanteric ridge ; g tr, great trochanter ; / tr, lesser trochanter ; n,
neck ; /, pit in the head of the femur for the ligamentiim feres.

Fracture of the neck of the bone is called a fracture within
the capsule, because the part broken is within the capsular
ligament. Such a fracture can never be adjusted, the leg
being drawn up by the muscles and shortened, producing
incurable lameness for the rest of life.

On the outer side of the hinder part of the femur, a little
below the great trochanter, is a more or less marked vertical
ridge, which serves for the insertion of the gluteus maximus
muscle.

At the lower end of the femur are two prominences named
condyles (see Fig. 154), separated behind by a median de-
pression.

The external condyle is the larger, and more forwardly pro-
jecting ; its articulating surface is also broader and ascends
higher on the front of the bone. On its outer surface is a pit
for the tendon of the popliteus muscle, immediately above
which is a projection named the external tuberosity.

The internal condyle is longer, and descends lower down
than the external one. On its inner side is a projection called
the internal tuberosity.

The articular surfaces of the femur meet in front, and form

v.]

SKELETON OF LOWER LIMB.

183

etu-

one for the knee-pan. Posteriorly they diverge, leaving
between them a space called the inter-condyloid fossa. The
femur does not articulate with the fibula.

The knee-pan, or PATELLA, is a small bone somewhat tri-
angular, yet rounded in outline, con-
vex in front and with two articular
surfaces (to fit to the condyles of the
femur) behind.

It is attached above by its broad
upper margin to the tendon of the
front muscle of the thigh/ Below, a
ligament goes from its pointed lower
end to the upper part of the shin-bone.

4. The TIBIA, or shin-bone, is, like
the femur, an elongated bone, more
so than any other in the human body
except the femur. It transmits the
whole weight of the body to the foot.

Its upper end is very wide, and
presents two concave articular sur-
faces (condyles) — which receive the
two condyles of the femur — and be-
tween them an eminence (the spine),
behind which is a pit giving insertion
to one end of one of the crucial
ligaments which connect the femur
with the tibia. These ligaments pass,
one from the pit just mentioned to
the outer side of the inner condyle of
the femur, while the other goes from
the front of the spine of the tibia to
the inner side of the outer condyle of
the femur. Two inter-articular carti-
lages, called semilunar, are also
interposed between the cartilaginous
articular surfaces of the femur and
those of the tibia.

Two other ligaments may be noted.
One, the internal lateral ligament,

goes from the internal tuberosity of the femur to the inner
surface of the tibia ; and the other, the external lateral
ligament, goes from the outer tuberosity of the femur to the
fibula.

The shaft of the tibia is triangular in section, being pro-

FIG. 156. — FRONT VIEW OF
RIGHT TIBIA AND FIBULA
OF MAN.

c, crest of the tibia ; em, ex
ternal malleolus ; e tu, ex
ternal tuberosity ;f, fibula
/z, head of the fibula ; im
internal malleolus ; itu, in
ternal tuberosity ; s, spine
of the tibia ; t, tubercle.

184 ELEMENTARY ANATOMY. [LESS.

duced into a sharp crest in front, on the internal side of
which crest the bone is convex, and concave on its outer side.
At the upper end of the front of the shaft is a prominence
called the tuberosity, or tubercle.

The lower end of the bone is much smaller than the
upper. Its lower border has a single groove behind for the
tendons of the tibialis posticus and flexor longus digitorum
muscles. Its outer surface is concave for the reception of the
fibula. Its inner margin is produced downwards into a strongly
marked triangular process, called the internal malleolus.
This forms the bony projection on the inside of the ankle,
and articulates with the inner side of the tarsus. Another
articular surface, concave and quadrilateral, is situated on
the under-surface of the lower end of the tibia, and articulates
with the summit of the tarsus. The hinder margin of this
articular surface descends below its anterior border.

5. The FIBULA is the slenderest bone, in proportion to its
length, in the body, and extends on the outer side of the leg
from near the knee down to the ankle.

Its upper extremity is slightly enlarged into what is called
the head, which articulates with the outer side of the head of
the tibia, and gives insertion to the external lateral ligament.
It does not mount upwards so high as does the tibia.

The shaft of the bone is irregularly triangular in section.
Its lower end is expanded into what is called the external
malleolus, which forms the bony projection on the outer side
of the ankle and articulates with the outer side of the tarsus.

This malleolus projects downwards considerably further
than does the internal malleolus. On its inner side it articu-
lates with the tibia.

Thus we have in man a horizontal articular surface for the
tarsus, formed by the lower end of the tibia, and two other
articular surfaces, at right angles with it, formed by the sur-
faces of the malleoli.

6. The TARSUS consists of seven bones (none of which
can be called "long bones"), namely, the astragalus, calca-
neum, cuboides, naviculare, and three cuneiform bones. All
these are so firmly connected by ligamentous fibres which en-
velop them, that very little mobility is possible, though there
may be a slight rotation of the distal tarsal bones upon the
proximal ones, that is, upon the astragalus and calcaneum.

The movement of the foot on the leg, however, takes place
entirely by the hinge-like joint by which the tarsus articu-
lates with the bones of the leg.

v.]

SKELETON OF LOWER LIMB.

185

The astragalus x receives the weight of the trunk from the
tibia, and is a short irregularly shaped bone, with a " body,
neck, and head."

In its natural position, when the foot is on the ground, the
upper surface of the body of the astragalus is nearly hori-
zontal for articulation with the under surface of the shaft of
the tibia. Two other articular surfaces, almost at right angles
with the former, join the two malleoli respectively. The pos-

FIG. 157. — DORSUM, OK UPPER SURFACE, OF SKELETON OF RIGHT FOOT.
a, astragalus ; c1, ento-cuneiforme ; cz, meso-cuneiforme ; c3,'ecto-cuneiforme ;
ca, calcaneum ; co, cuboides ; h, distal phalanx of hallux ; m T, metatarsal of
nallux ; m 2 — m 5, metatarsals of the four outer toes ; «, naviculare.

terior surface of the body is grooved for the tendon of the
flexor longus pollicis muscle. The anterior part of the bone
is prolonged forwards as its neck, ending in a rounded, con-
vex, articular . surface (the head), which fits into the hinder
surface of the naviculare.

1 'Acr-pa-yaAof, a die.

186 ELEMENTARY ANATOMY. [LESS.

The calcaneum (or os calcis) is the bone of the heel, and
forms the posterior part of the arch of the foot, of which
the astragalus forms the keystone. The os calcis projects
much downwards posteriorly, but not inwards, and is thick
and rounded at its hinder end (called its tuberosity), into which
is inserted the tendo A chillis of the muscles of the calf. The
calcaneum articulates with the astragalus above and with the
cuboides in front.

The naviculare (or scaphoid of the foot) is much wider
than long. Behind, its surface is concave for the reception of
the head of the astragalus. In front it presents three surfaces
for articulation with the three cuneiform bones. Only the
innermost of these surfaces is convex, and that but very
slightly.

Its inner margin sends down an obtuse process, called its
tuberosity.

Of the three cuneiform bones, the innermost, the ento-
cuneiformej is the largest. Narrow above and broad below,
it presents an elongated articular surface, which is nearly flat,
for the metatarsal of the great toe. The meso-cuneiforme'2
is the smallest bone of the tarsus. It does not reach so far
forwards as do its neighbours. It agrees with the ecto-
cuneiforute^ in presenting a nearly flat articular surface for the
metatarsal which joins it.

The cuboides, placed on the outer side of the tarsus, articu-
lates with the os calcis behind, and with both the fourth and
fifth metatarsals in front. Its inferior surface is traversed by
a deep groove (for the tendon of the peroneus longus muscle),
behind which is a prominence for the attachment of a liga-
ment.

7. The METATARSUS consists of five elongated bones, of
which the first or innermost is much the thickest and the
shortest. The metatarsals have long shafts, which, except that
of the first, are slender, and have enlarged bases and rounded
heads.

The bases, or tarsal ends, of the four outer metatarsals
have quadrangular articular surfaces, which are almost flat,
and are as if bevelled off, so that the axis of each such
metatarsal is not perpendicular to its proximal articular
surface. Thus these metatarsals come to be directed more
inwardly than would otherwise be the case.

The rounded heads of the metatarsals articulate with the
hinder concavities of the proximal phalanges.

1 'EI/TO£, inward. 2 From Mf°"°£> middle. 3 'EKTO£, without.

v.] SKELETON OF LOWER LIMB. 187

The first metatarsal has its proximal, concave, articular
surface at right angles with the axis of its shaft.

The second metatarsal is the longest.

The fifth metatarsal has its base greatly enlarged, with a
considerable prominence, or " tuberosity," projecting from
the outer side of its hinder end.

8. The PHALANGES are three in number in each digit,
except the first, or great toe (hallux), which has but two.
These two, however, are much larger than those of the other
toes.

Often the second and third phalanges of the fifth digit (or
little toe) become anchylosed together.

The second phalanges are much shorter than the first, and
the third phalanges are slightly shorter than the second.

Each last phalanx has its end modified to support a nail,
much as we saw in the last phalanges of the hand.

The toes being so much shorter than the fingers, the
phalanges are of course also much shorter.

9. Comparing now the relations presented by OTHER
ANIMALS, we find that man follows a rule which is universal
in having the leg-bones attached to and suspended from a
pelvis (well developed or rudimentary), which may be looked
upon as the root-portion of the limb. This root part may,
however, be present while the distal part (leg and foot) is
more or less atrophied, but the distal parts are never present
without a rudiment of the limb-root.

The bones of the inferior extremity of man are of full

FIG. 158.— RUDIMENTARY PELVIC FIG. 159.— SKELETON OF RUDI-

EXTREMITY OF OphiodeS. MENTARY PELVIC LlMB OF LiclitS.

(After Fiirbringer.} (After F'urbringer. )

f, fibula ; tt tibia. f, femur ; z7, ilium ; pi, pubo-ischium ;

t, tibia.

average development, for though in a few animals these bones
may be a little more numerous, in a far greater number of in-
stances the difference from man consists in more or less defect

iS3

ELEMENTARY ANATOMY.

LESS,

down to complete abortion. A pelvic pair of limbs may be
developed without any thoracic ones, as in Bipes, Lialis, and
Ophiodes, and rudiments of the pelvic limbs may be the only
ones present, as in Python.

10. The INNOMINATE BONE of man is one of the most
distinctive of his skeleton, distinguishable at a glance from
that of every other animal, widely differing even from that
of the Gorilla, which, however) much exceeds it in absolute
size.

This large complex ossification, consisting as it does in man
of three primitive elements, presents three distinct bones in
lower animals — the ilium, ischium, and pubis — which, as in
man, meet to form the acetabulum.

The fusion of these elements into this one bone is a
character which man shares not only with his own class, but
also with Birds. In Reptiles, however, we find three per-
manently distinct bones, whether or not they exactly corre-
spond with the three elements of the pelvis of man.

The fusion of the two ossa innominata in a dorsal sym-
physis is a condition which sometimes occurs— as in the
Ostrich. In that his ossa innomi-
nata are solidly attached to the
vertebral column, man agrees with
all Vertebrates above Fishes, with
the exception of Cetaceans and
some Lizards. In Fishes, however,
such a union is invariably absent,
and the ossa innominata are repre-
sented in them by ventral hard
parts only.

The junction of the two ossa in-
nominata at a ventral symphysis is
a less constant character. Not only
is this junction entirely absent in
the class of Birds, with two excep-
tions (the Ostrich and the Rhea),
but in many Mammals (e.g. many
Bats, and Insectivora).

The ventral union of the ossa
innominata with a simultaneous de-
tachment from the vertebral column exists in' Fishes, but
in no other Vertebrates, unless in some Reptiles with a rudi-
mentary pelvic structure.

A detachment both from the vertebral column dorsally and

FIG. 160. — Pelvis of the small
Tanrec (Hemicentcte s),
showing the very elongated
ilia and the widely open
pubic symphysis.

v.] SKELETON OF LOWER LIMB. 189

from its fellow of the opposite side ventrally, is a condition
which may occur, as e.g. in the very imperfectly developed os
innominatum of Cetaceans and Sirenia, and certain Reptiles,
e.g. the Boa Constrictor.

In that the os innominatum joins the backbone by one
attachment only (namely, that of the ilium), man agrees with
the great majority of Vertebrates. But even in some of his
own class (as in the Armadillos, some other Edentates, and
some Bats) a 'second, ischiatic, bony attachment may be
formed, answering to what would result from an ossification
of the great sacro-sciatic ligaTnent in us.

As has been said, the form of man's os innominatum is
absolutely peculiar. Still he shares the normal characters
of his class and of Vertebrates generally, in that the inferior
bony elements on each side are rather short and mainly

FIG. 161.— RIGHT SIDE OF PELVIS OF A BIRD.

a, acetabulum ; c, caudal vertebrae ; dl—d5, three dorsal vertebrae ; z7, ilium :
to, great foramen caused by the post-axial ujiion of the ilium and ischu. m ;
is, ischium ; o, very elongated obturator foramen ; /, pubis.

directed ventrally. These elements may, however, be very
much elongated and mainly directed post-axially (i.e. back-
wards, if the body is placed horizontally), as in Birds. The
ventral elements may be single, as in Batrachians, and if
double, as in man, they may apparently consist of parts which
do not correspond with the two elements existing in him and
other Mammals : such a diversity of structure seems to exist
in Reptiles.

In so far as the ilium of man is a broad flat bone, it differs
from that of Mammals generally, and only agrees with certain
exceptional forms, such as the Elephant, Sloth, and Gorilla,

The extent of the ilium in the line of the backbone may be
very much greater than in man, as is the case in Birds, where
it is prolonged both pre- and post-axially to a very considerable
extent, thus connecting in one whole many vertebra?. It is
probably the' pre-axial part of the bird's ilium which corre-
sponds with that of man and of Mammals, while its post-
axial part seems to correspond with the ilium of Reptiles.

igo ELEMENTARY ANATOMY. [LESS.

The ilium may be a three-sided columnar bone, as in the
Kangaroo and many Rodents. The posterior part of the
ilium may become anchylosed with the ischium, as is the case
in Birds.

Wherever there is an acetabulum it is in part formed by
the ilium.

FIG. 162. — SIDE VIEW OF BONES OF POSTERIOR EXTREMITY OF GREENLAND
RIGHT WHALE (Balcenci mysticetus).

i, ischium \f, femur; /, accessory ossicle, probably representing the tibia.
(From Eschricht and Reiuhardt.}

The ilium may be altogether absent while the ischium is
present, as probably in the Cetacea. It is never present
without any other pelvic element, except in the Amphisbenian
group of Reptiles.

The prominence of the inferior anterior spinous process
in man is exceptional, yet it is exceeded in proportion in
some of the Lemuroidea.

In Marsupial Mammals and Monotremes we find two
distinct bones articulated, one on each side of the pre-axial
margin of the pubes. They are called "Marsupial bones"
and are further noticed below, § n.

The ilio-pectineal eminence is rudimentary in man com-
pared with that existing in some other animals even of his
own class. Thus in certain Bats it is a very elongated spine
projecting upwards from the brim of the pelvis, and it is a
very prominent process in the Kangaroo, and sometimes in
Marsupials arises from an independent ossific centre. In
Reptiles we find a pair of separate bones, usually called
the pubes, and meeting generally in a ventral symphysis.
They do not, however, so meet in all Reptiles, e.g. the
Crocodiles and the Snake Stenostoma. These so-called

v. ] SKELE TON OF L 0 WER LIMB. 1 9 1

pubes are at their maximum of relative size in the Tortoise,
where each develops a large process ending freely, like the ilio-
pectineal eminences or marsupial bones of Mammals.

In Tailed-Batrachians the ilia are represented by rib-like
bones which articulate each with one or at most with two

FIG. 163. — RIGHT SIDE OF PELVIS OF FROG.

//, ilium ; is, ischium ; /, pubis. The three bones meet at the upper margin of
the acetabulum.

vertebrae. In the Frogs and Toads the ilia are very peculiar,
being extremely elongated, and meeting together posteriorly
above the acetabula in an iliac symphysis. In spite of the
superficial resemblance between the limbs of man and the
Frog, the pelvic structures are thus singularly different.

FIG. 164. — The two Ossa Innominata of the Angler-fish (Lophhcs}, showing the
ascending processes which simulate ilia. The fin-rays are attached to the
outer-ventral margin of each os innominatum.

It is not probable that any solid representative of the ilium
exists in Fishes, but in the Angler (Lophius) the os innomi-
natum sends up a process simulating somewhat the ilium, as
does the innominate cartilage in the Chimaera.

The ilium of an animal may closely resemble its scapula
in shape, as in the Tortoise and Chameleon.

The so-called pubis of Reptiles may answer to the ilio-
pectineal eminences, or possibly to the marsupial bones,1 of
Mammals. A small bone attached to the front of the pubis

1 For these bones see below, p. 194.

1 92 ELEMENTAR Y A NA TO MY. [LESS.

of the Ostrich may possibly represent the mammalian mar-
supial bone.

In that man's pubis is a plainly distinct pelvic element,
man agrees with all of his class except those which have
an imperfectly developed innominate bone.

In all Reptiles this bone appears (if the view above stated
as to the ilio-pectineal eminence is correct) to be fused
with the ischium. If this be so, then the obturator foramen
has no existence in Reptilia except transitorily (as in the
young Lizard) ; while that foramen which resembles and
has been described as the obturator foramen in Reptiles
really corresponds with the space between the brim of
the pelvis and a line drawn from the marsupial bone, or
else from the ilio-pectineal eminence, to the pubic symphysis.
This false obturator foramen may be called the cordiform
foramen.

As has been already said, in some Insectivora and Bats
the pubis does not meet its fellow of the opposite side in a
ventral symphysis. In the Mole the pubis has so little
extent that the pelvic viscera pass outside and in front of
the pelvis.

The pubes in Birds are very long, and bent post-axially.
They never meet in a ventral symphysis except in the Ostrich.

As the ischium in Mammals is the more constant and
larger of the two ventral pelvic bones, it may be considered
rather itself to have absorbed than to have been absorbed by
the pubis, in those lower forms in which these two elements
do not seem to be differentiated.

The ischium of man is small compared with that of
Mammals generally ; its proportional development is closely
approached, however, in the slender Loris.

The prominent development of the spine of the ischium
is absolutely peculiar to man.

The tuberosity of the ischium in the human species is very
small and inconspicuous compared with its condition in
most Mammals. Even in the very highest Apes it is much
larger than in man, and in the Gibbons and other monkeys
of the old world it is not only very large, but everted and
flattened with a rough surface for the attachment of a
thickened skin, or callosity. It is largely everted in Dogs and
Ungulates. In all the Edentates, except the Cape Ant-eater,
the ischium anchyloses with the vertebral column, and the
same union occurs in some Bats.

In the Cetacea the pelvis is represented by what is pro-

v. ] SKELE TON OF LO IVER LIMB. 193

bably a pair of ischia. These are long and slender bones
detached from each other as well as from the vertebral
column.

This ischium may be elongated, produced backwards (i.e.
post-axially) and downwards, and separated from its fellow in
the middle line ventrally, as in all Birds except the Rhea,
in which latter these bones bend upwards and meet at their
distal ends.

The ischium of Birds generally anchyloses more or less
with the posterior part of the very elongated ilium.

In Reptiles the ischio-pubic bone generally meets its fellow
in a ventral symphysis. It may do so when the other ventral
elements do not so meet. Such is the case, e.g., in the Snake
Stenostojna. On the contrary, it may fail so to meet its
fellow, although the other ventral elements effect a junction.
We find this condition, e.g., in the Lizard Seps. Often, as
e.g. in the Boa, the bone may be represented by a mere
cartilaginous rudiment.

'•'-,

FIG. 165. — SKELETON OF RUDIMENTARY PELVIC LIMB OF BOA CONSTRICTOR.
(After Fiirbringer.)

lr, rudimentary femur, at the end of which is (t) a minute, triangular, and hook-like
tibia; i, so-called pubis- possibly an enormous ilio-pectineal eminence: /,
rudimentary ilium ; p, ischium or pubo-ischium.

A tuberosity of the ischium generally exists in Lizards ; this
does not, however, anchylose with the vertebral column, but
is connected by a strong ligament with the hinder end of the
ilium, which ligament answers to the great sacro-sciatic liga-
ment of man.

In Tailed-Batrachians the ischio-pubic bone or cartilage is
a large lamelliform expansion with an elongated symphysis.
It may form one single cartilaginous undivided plate, as in
Proteus. In Frogs and Toads the ischia are small, lamelli-
form, and so closely applied and anchylosed together as to
be, as it were, all symphysis.

In Fishes the ossa innominata have already been noticed,
and they consist probably of ischio-pubic bones or cartilages
only. We here, however, often meet with an anomaly of
connexion not found in any higher class. Thus we find the
innominate bones in many cases directly connected with the

O

194- EL EMENTAR Y ANA TO MY. [LESS.

pectoral girdle. In some Fishes, as e.g. the Angler (Lophius),
the ossa innominata are articulated directly with the hinder
border of the clavicles, while in other Fishes they very often
are but little removed from them. Fishes in which the
hinder limbs are placed far forwards are called thoracic
(as the Perch), and when still more so, jugular (as the
Cod).

Rarely, as e.g. in the Opah Fish (Lampris), the os innomi-
natum joins the coracoid, which in this species is enormously
enlarged.

FIG. 166.— PELVIS OF ECHIDNA.
z7, ilium ; w, marsupial bone ; /, pubis ; s, sacrum.

ii. Certain bones called MARSUPIAL BONES, of which no
ossified representatives exist in man, may be attached to the
pelvis. Thus, in him the internal tendon of each external
oblique muscle is neither ossified nor chondrified. In all Mar-
supials, however (except the Thylacine, or Tasmanian Wolf)
and in the Monotremes, these tendons are largely ossified,
the ossifications being movably articulated with the brim of
the pelvis. Such ossifications constitute the marsupial bones.
In the Tasmanian Wolf these parts are represented by carti-
lages, but no such structures have been detected in other
Mammals, except that there is a slight chondrification of
the same part in the Dog. In the Chameleon the brim of
the pelvis supports small bony nodules, and in the Ostrich a
small bone is attached to the front of the pubis. Possibly
<as before said) the so-called pubic bones of Reptiles may
be marsupial bones, if they do not rather correspond to
ilio-pectineal eminences.

Another possible ossification which has no representative

SKELETON OF LOWER LIMB.

195

in man is the os cloaca:. It is an azygos median structure
which extends backwards behind the ischio-pubic symphysis.
as e.g. in the Lizard Psauimosaurns.

Similarly a median azygos structure (pointed or forked)
may be developed from the front of the ischio-pubic sym-
physis, as in Menobranchus and Salamandra.

The acetabuhun of man is very well developed as compared
with that of other animals. In its formation by the three
pelvic bones it follows the universal mammalian rule. In that
its cup is completely ossified it also
resembles all Mammals except the
lowest (i.e. the Monotremes), which
agree with Birds in having the ace-
tabula perforated.

In Reptiles generally three separate
ossifications also concur to form the
acetabulum. In Crocodiles, however,
the so-called pubis does not concur
in its formation.

12. The supremacy in size of man's
FEMUR over the other parts of his
skeleton is not shared by the femur of
most other Vertebrates, and this im-
portant bone seems rarely, if ever, to
have any representative whatever in
the skeleton of Fishes. Nevertheless
a single cartilage (as in Ceratodus]
which articulates with the limb root
may be the representative either of
the thigh or leg bones.

Confining ourselves therefore, for
purposes of comparison, to Mammals,
Sauropsida, and Batrachians, we find
the femur under a certain aspect more
constantly present than the humerus.
For although it is often absent when
the humerus is present (as in forms like Siren, which have
pectoral limbs but no pelvic ones), yet it is sometimes present
in a more or less rudimentary condition when no representa-
tive of the foot coexists with it.

Such is the case, e.g., in some Whales (as the Greenland

Whale) amongst Mammals, and certain Snakes, e.g. Boa, and

certain Lizards, e.g. Lialis, amongst the Reptiles. In absolute

length the femur of man exceeds that of almost all other

O 2

FIG. 167. — CARTILAGINOUS
SKELETON OF A LIMB OF
Ceratodus. (After Giin-
ther.)

The large upper piece articu-
lates with the limb root.

196 EL EMENTA RY ANA TOM K [LESS.

animals, only the largest beasts forming an exception in this
respect.

As the longest bone of the leg (i.e. in the proportion in which
it exceeds the length of the tibia) the femur of man is dis-
tinguished from that of all Birds, and from that of almost all
other Mammals except of those Cetaceans which have a rudi-
mentary femur and a still more rudimentary tibia. Yet oc-
casionally (as e.g. in the Great Ant-eater
and certain Apes) the femur notably
exceeds the tibia in length.

In many Reptiles and Tailed-Batra-
chians, however, the femur exceeds the
tibia as much as or more than in man,
and that not only in forms like Boa,
where both bones are, though in differ-
Fir,. ^.-SKELETON OF ent degrees, rudimentary, but also where
RUDIMENTARY PELVIC both are fairly developed.
LIMB OF Liaiis. For all that the several parts of the

(After Furbringer.^ femur may exhibit different degrees of
/, femur ; z'/, ilium ; pi, development in different animals, yet on
puborischium ; t, tibia. the wnple it is a substantially constant
bone as to its form and structure ; more

so even than is the case with the humerus, as the femur
never attains the great relative length which the humerus
attains in the Bats, nor is it ever reduced to the shortness
and thickness which that part presents in the Mole.

In the proportion which it bears to the hind limb as a
whole, the femur of man is exceptionally developed, though
not quite so much so as in many Reptiles and Tailed-Batra-
chians. Its proportion, however, may become almost insig-
nificant, even in Mammals, as in the Seals. It is in these
aquatic Carnivora, and in the extinct Ichthyosaurus, that the
-femur is relatively at its shortest.

It is a short bone (when compared with the leg and foot)
in the Ruminants and Horse family.

The curvature which the shaft presents in man may be
exaggerated, as in Tortoises, while the bone may almost
become straight, as in the Lemurs, Carnivora, Bats, &c.

The development of its neck is a character which the
femur of man by no means shares with that of all Vertebrates ;
on the contrary, the neck of the bone is most exceptionally
developed in him. In the majority of cases (as e.g. in Birds)
there can hardly be said to be any neck, and in many forms,
e.g. the Rhinoceros, there is none whatever.

v.] SKELETON OF LOWER LIMB. 197

The head of the femur is almost always rounded ; rarely
(as e.g. in the Crocodile) it is transversely extended, some-
what like that of the humerus in Birds.

The greater (peroneal) and lesser (tibial) trochanters are
very constant structures, one or both appearing in a more or
less developed condition down to the lowest Batrachians.

The great trochanter may be more prominent than in man.
This is the case, e.g., in Ungulates. It may, on the contrary,
be comparatively insignificant, as in the Great Ant-eater and
Elephant ; or absent, as in the Lizard Gramniatophora.

The lesser trochanter may be about as salient as the
greater one, as in the Ornithorhynchus ; or much more so, as
in Uromastix, Lciocephalus, and Cyclodus; it may be all
but absent, as in the Elephant, or quite so, as in Birds.

The two trochanters may be equally developed, one on each
side of a very short neck, as in Bats.

The two trochanters may be fused into one, as in Testudo.

In addition to the two trochanters, the slight ridge which
serves in man for the insertion of the gluteus maximus
muscle may be drawn out into a great prominence termed
a "third trochanter." This is the case, e.g., in the Horse,
Rhinoceros, Hare, and Armadillos.

This third trochanter may be represented by a prominent
ridge running along the whole outer side of the shaft, as in
the Great Ant-eater.

The head of the femur, instead of being directed inwards,
may project forwards over the exterior surface of the bone,
as in Tcstndo and the Bats.

The pit for the ligamentum teres, though present in Birds,
may be quite absent in members of man's own class, e.g. in
Seals, Elephants, Sloths, and others. This depression, appa-
rently so important, may be present or absent in different
individuals of the same species, as in the Orang-Outan and
Gorilla.

The lower end of the femur may be more, or less, expanded
relatively than in man, and this both transversely and antero-
posteriorly.

Thus the latter dimension is greatly in excess in the Rumi-
nants ; the transverse dimension in the Seals and Ornitho-
ihynchus.

Instead of the inner condyle descending the more, it may
be the outer one that does so, as is the case in Birds.

The depression in front between the condyles — " rotnlar
surface" — (serving in man to lodge the patella) may be

198 ELEMENTARY ANATOMY. , [LESS.

wanting, as in Testtido, or all but wanting, as in the Wombat.
It may be very narrow, as in Pteropus. It may be much
marked, as in the Ruminants.

The pit for the origin of the popliteus muscle may be
much deeper, and coexist with a similar pit in the external
condyle (for the origin of the flexor longus digitorum muscle),
which condition, together with the narrowness of the rotular
surface, may give the lower end of the femur a peculiar aspect,
as in Pteropus.

The external condyle may present a marked groove sub-
dividing it. This is the case in Birds, where this groove
serves to receive the head of the fibula.

Instead of the concavity which exists in man at the pos-
tero-inferior part of the shaft (increased through the back-
ward projecting of the condyles), this part may be nearly flat,
as in Birds.

Neither tuberosity is ever perforated like the internal con-
dyle of the humerus in some Mammals.

The femur may be only a rudiment even in some Mammals,

FIG. 169.— SKELETON OF RUDIMENTARY PELVIC LIMB OF BOA CONSTRICTOR.

(After Filrbringcr.)
f, rudimentary femur, at the end of which is(/) a minute, triangular, and hook like

tibia ; i, so-called pubis — possibly an enormous ilio-pectineal eminence ; /,

rudimentary ilium ; p, ischium, or pubo-ischium.

as e.g. some fin Whales ; and the same may be the case in
some Reptiles, as e.g. Lialis Burtonii, Boa, and Stenostoma.

The PATELLA may be wanting altogether in man's own
class, as in the Wombat. It may be very small, as in the Bats
and Seals. It may be very narrow in proportion to its length,
as in the Agouti ; or extraordinarily large and elongated, as
in the Grebe; or represented by two super-imposed ossifica-
tions, as in the Ostrich. Every trace of it may be wanting,
as in the Frogs and Tortoises. It may be irregular in shape,
as in the Bustard and Ostrich.

13. That important bone of man, the TIBIA, attains a yet
greater relative size in very many Vertebrates than it does in
him. Like the femur, however, it is not universally present
in every class, as it has no distinct representative in Fishes.

As compared with its fellow leg- bone (the fibula), the tibia

v.] SKELETON OF LOWER LIMB. 199

shows a predominance of size, like that of the radius in the
arm over the ulna, and this to a yet greater degree. Thus
while, like the radius, it never aborts though its fellow may
do so, it never in existing animals even becomes the subordi-
nate bone of the two, as is the case in the radius compared
with the ulna in Birds. Yet in length it may be exceeded by
the fibula, as e.g. in the Ornithorhynchus ; and a certain slight
subordination appears to have existed in the extinct Reptiles
Ichthyosaurus and Plesiosaurus. Moreover, the two bones
are developed equally in certain existing Reptiles with rudi-
mentary limbs, e.g. Seps and Ophiodes, and in Batrachians
also.

In its elongated figure the tibia of man agrees with the
same bone as generally developed, and it never becomes in
any existing species so relatively short and thick above as
does the radius in Cetacea. Such is the case only in the
extinct Plesiosaurus and Ichthyosaurus.

The relation which it bears to the femur is less constant
than that which the radius bears to the humerus. We have
seen that where in Vertebrates above Fishes the humerus is

FIG. 170. — SIDE VIEW OK BONES OF POSTERIOR EXTREMITY OF GREENLAND

RIGHT WHALE (Batana mysticctits .

i, ischium ;./, femur ; t, accessory ossicle, probably representing the tibia.
(From Eschricht and Reinfuirdt.)

represented by a bone or cartilage, the radius is also developed.
But in Megaptera longimana and Balcunoptera musculns we
have a rudimentary representative of the femur, but none
whatever of the tibia ; while in Balcena mysticetus and in Boa
constrictor there is a tolerably large ossicle representing the
femur, but only a minute rudiment representing the tibia.

200 ELEMENTARY ANATOMY. [LESS.

Instead of being free as in man, the tibia may anchylose at
each end with the corresponding extremities of the fibula,
as is the case in the Armadillos and often in the Seals.

Very often it anchyloses with the fibula below only, as in
the Rabbit and in some Birds, e.g. Adjutant and Ostrich (and
as in one member of man's own order, Tarsius) ; or above
only, as, at least sometimes, in the Cape Ant-eater.

There may be an apparently single representative of the
two bones of the leg which are completely fused together, ar;
in the Frog.

FIG. 171.— RIGHT PELVIC LIMB OF GIRAFFE.

n, astragalus ; c, calcaneum ; at, cuboides ; d^>, proximal phalanx of third digit ;
</4, proximal phalanx of fourth digit ;/", femur ;_/', rudiments of fibula (the
line is not continued far enough — the rudimentary fibula is a small ossicle
reposing on the upper surface of the calcaneum, as shown in the figure ; :
7//3+4, metatarsals of digits 3 and 4 united into one "cannon-bone";
J>a, patella ; t, tibia.

The tibia may be the only long bone of the leg, through
the small development of the fibula, as is the case in Rumi-
nants and in the Horse tribe.

The space which exists in man between the tibia and the
fibula may be exceedingly reduced, as is the case, e.g., in Birds"

SKELETON OF LOWER LIMB.

and in some Mammals, e.g. the Cats. It may, however, be
very wide, as in the Sloths and Wombat and Cape Ant-
eater.

This bone in man is peculiarly shaped in relation to his
erect posture.

Thus, comparing man's tibia with the same bone in other
members of his own order (Primates), we find that it is longer
as compared with the spine than in any other genus except
Hy I abates and Tarsius, and longer as compared with the
radius than in any except Hapalc and Tarsius.

On the contrary, its length as compared with the femur
is less than in any other Primate.

The tubercle of the tibia is probably at its maximum of
distinctness in man as compared with the rest of his class,
and the articular surfaces for the
condyles of the femur occupy a
maximum proportion of the upper
surface of the tibia.

The sharpness of its crest in man
exceeds that of any other Primate,
and the descent of the posterior
border of the articular surface for the
astragalus below the anterior margin
of that surface is peculiar to him.

The tibia may be very much
curved, e.g. in the Ornithorhynchus,
yet it may be straight and exces-
sively long, as in many Birds.

The crest may project very promi-
nently and sharply at the upper end
of the bone, as e.g. in Ruminants, the
Kangaroo, and Hare.

The tubercle of the tibia may be
enormously produced upwards into a
long pointed process, as in certain
Birds, e.g. the Grebe and Divers.

in some forms nearly allied to man,
as the Orang, the articular surface of
the malleolus forms an obtuse angle
with the inferior surface of the tibia.

The tibialis posticus groove may be much deeper than in
man, the portion of bone separating it from that for the flexor
longus pollicis pedis having thus the appearance of a promi-
nent process. Such is the case in Nycticebus.

FIG. 172.— LEG-BONES OF
THE DIVER (Colytnbns).

I, fibula ;f, femur ; t, tibia,
with p, its enormously pro-
duced tabercle.

202 ELEMENTARY ANATOMY, [LESS.

Distinct malleoli may be wanting, and are so in Vertebrates
below Mammals. The lower end of the tibia of all adult
Birds is very different from that of the other classes. This,
however, is due to its being made up of the proximal part
of the tarsal element, on which account it cannot here be
compared with the lower end of the tibia of man and
Mammals. Nevertheless, exceptional forms (like the Ostrich)
show us that the true tibia of Birds is destitute of malleoli.

The tibia never assumes that crossed position in relation
to the fibula which the radius assumes in relation to the ulna,
and which is termed pronation. Nevertheless, a modified
action may take place in certain Marsupials, viz. the Phalan-
gers and Wombat.

Crucial ligaments and inter-articular cartilages may be
wanting, as in Tailed-Batrachians, though present in Birds
and Saurians.

14. From what has been already said it is clear that the
FIBULA of man can only be illustrated by bones of Mammals,
Sauropsidans, and Batrachians.

The fibula of man in its subordination to the tibia, occu-
pies a medium position, as has been noticed in describing
that bone.

It may be relatively more reduced in size than in man, as
is the case in Birds and in Ruminants ; or it may be com-
pletely absent when the tibia is rudimentarily represented,
as is the case in Bal&na mysticetus and Boa constrictor.

The conditions as to its anchylosis with the tibia have
already been mentioned.

In its reduced state the fibula may be quite styliform, as in
Birds ; or it may be developed inferiorly, but atrophied at its
upper end, as in Bats.

It may be represented only by a small ossification in the
place of the external malleolus, as in the Ox, and with this
there may exist (though widely separated from it) a little
styliform rudiment of the upper end of the fibula, as in the
Elk.

The fibula may be much bowed outwards, as in the Cha-
meleon and the Bat Molossus, but it is generally nearly
straight, or quite so, as in Birds.

The upper end of the bone may join the femur, as in
Marsupials and Birds, and this end may be produced
into a large process like the olecranon of the ulna (as in
Cook's Phalanger), to which even a sesamoid bone may be
annexed.

SKELETON OF LOWER LIMB.

20:

This process may attain a very great size, as e.g. in the
Ornithorhynchus and Echidna.

In man alone does the external malleolus descend greatly
below the internal malleolus. The lower end of the fibula
may be very much enlarged, as in the Hippopotamus. - Its
lower end may develop a conical process, which, turning in-
wards, may fit into a depression
on the outer side of the articular
surface of the astragalus, as in
the Sloth.

15. Inasmuch as the FOOT of
man is made up of the tarsus,
metatarsus, and phalanges, it
agrees with the same part in
Mammals and Batrachians.

In Birds, however, the proxi-
mal part of the tarsus is an-
chylosed with, and in Reptiles
more or less firmly united with,
the tibia, so that the visible foot
of Birds corresponds but with
the greater portion and not the
whole of the foot of man.

The foot, in one aspect, is less
constant than the hand, as ele-
ments of the leg (as in Balcena
and Bod) may be present while
there is no rudiment whatever
of the foot.

1 6. In that the TARSUS of man
contains certain small and dis-
tinct bones, it agrees with the
same part in all Vertebrates
above Fishes, except Birds (in
which the tarsus coalesces with

other portions of the skeleton), and except also certain
Tailed-Batrachians, in which the constituent parts of the
tarsus remain more or less permanently cartilaginous.

The number of ossicles, or cartilages, may be as many as
nine, as in the Salamander ; or may be reduced to three, as in
Proteus, Bufo bifurcatus, and Lacerta agilisj or perhaps to
two, in Ophiodes striatus.

We have seen that part of the carpus of man may be
represented by more elongated bones, as in the Crocodile.

FIG. 173 — ANTERIOR ASPECT OF
BONES OF RIGHT LEG OF Orui-
tliorkynchus paradoxns.
/, femur ; t, tibia ; f, fibula ;

/, patella.
{From Flcnver's "Osteology.")

234

ELEMENTAR Y ANA TOM \ r.

[LESS.

This variation may, however, be carried out to a much greater
decree, and in two different ways, as regards the tarsus.

FIG. 174 — RUDIMENTARY PELVIC EXTREMITY OF Ophiodes.
/.fibula; t, tibia. (After Fiirbrin%er.)

For, first, the os calcis and naviculare may be so extra-
ordinarily produced as to become completely long bones —
adding a segment to the limb — as in Tarsius, and, in a less
degree, in Galago and Cheirogaleus.

FIG. 175.— ELONGATED TARSUS OF CERTAIN LEMUROIDS.

Left-hand figure, Tarsus of Cheirogaleus; right-hand figure, Tarsus of Tarsius.
A, calcaneum ; £, cuboides ; C, naviculare.

Secondly, the os calcis and astragalus may be similarly
elongated, as in the Frogs.

SKELETON OF LOWER LIMB.

I/. The BONES OF THE PROXIMAL PART OF THE TARSUS

are always the largest and most important.

The astragalus and os cakis, and probably also the
ncruicularg) may be represented by a single bone, as in
many Lizards, and they may intimately fuse at an early age
with the distal end of the tibia, as in almost all Birds.

In this latter case these bones unite very early into one,
which remains long distinct from the tibia, only in the
Ostrich, Rhea, and Emeu ; and for some time after hatching
jn the Dorking Fowl.

FIG. 176. — RIGHT FOOT OF EMEU.

, astragalus; d 2 — d*y second, third,
and fourth digits : m, metatarsals
anchylosed together except at their
distal ends ; t, tibia ; 1 2, distal tarsal
element.

FIG. 177.— LEFT FOOT OF A MONITOR
LIZARD (Varamis}.

f, fibula ; tn T — in 5, the five metatarsals,
in T being that of the hallux ; /, tibia ;
i, astragalo-calcaneum ; 2, cuboides;
3, ecto-cuneiforme.

In Lizards this compound bone is extended transversely,
but very little backwards. It articulates with both the tibia
and fibula above, and has an irregular surface below for the
reception of the more distal tarsal bones.

206 ELEMENTARY ANATOMY. [LESS.

In Birds it is also transversely and but little antero-pos-
teriorly extended, while it sends up a process which is applied
to the front of the tibia (Fig. 176, a). It may be perforated
by one or two canals for extensor tendons of muscles.

Thus no projection corresponding with the tuberosity of
the os calcis exists in this compound bone.

Inasmuch as the astragalus of man articulates with the
tibia, it has a character which is constant. A distinctness
like that which it possesses in him is not only, as we have
seen, far from universal, but its distinctness is less than that
of its serial homologue in the hand ; for not only may the
astragalus anchylose with other tarsal elements, but with the
long bone of the limb also, as in Birds.

The astragalus may be represented by two bones, as in
the Salamander and other Tailed-Batrachians, or it may
anchylose with the naviculare, as in the Crocodile.

It may bear a larger proportion to the other tarsal bones
than it does in man, as is the case in the Seals. It may
articulate widely with the cuboid bone, as in Ruminants.

One or even two extra ossicles maybe attached to thetibial
side of the foot, as in Cercolabes. An extra ossicle is
annexed to the astragalus in the male Ornithorhynchus and
Echidna.

The astragalus may project much beyond the os calcis, as
in the Two-toed Ant-eater.

In the Sloths the astragalus has a deep cup-shaped cavity
on its outer side to receive the process of the fibula, as before
mentioned. That of the Ornithorhynchus has a cup for a
process of the tibia.

The largest bone of the human tarsus, the calcaneum,
may have its relative size to the other tarsal bones yet further
increased, as in Tarsius, where it attains one-third the length
of the spine from atlas to sacrum inclusively taken. It may,
on the contrary, be much diminished, as in the true Seals,
or still more so, as in Birds. Where it is distinctly ossified
in Tailed-Batrachians and Reptiles, it develops no tuberosity,
except in the Crocodiles, where that process is still small. In
Birds this bone seems very early to be absorbed into the
astragalus.

It never seems to anchylose with any other tarsal element,
unless it also anchyloses with the astragalus, as in Birds and
in many Reptiles, e.g. Lacerta agilis.

The tuberosity may be very much twisted in man's own
order, e.g. Perodicticus and Lens. It may be all but absent,

v . ] SKELE TON OF L 0 WER LIMB. 20 7

as in the Seals. It may be, on the contrary, enormously pro-
duced, as in the Horse.

It may have appended to it an elongated ossification which
in parts enters upon the tendo Achillis, as in Bats, and this
may be of great breadth as well as length, as in Noctilio
leporinus.

The end of the os calcis is broad, bifid, and incurved in
the Ornithorhynckus and Echidna.

In that man's ankle-joint is situated between the leg-bones
and the tarsus, it agrees with the same part not only in the
whole of his own class, but also in Batrachians. It may be,
however, that the joint by which the foot moves upon the leg
is not so situated. This is the case in all Birds, where motion
takes place not between the tarsus and the tibia, but between
the proximal and the distal parts of the tarsus, the ankle-joint
being in them an inter-tarsal one, with the proximal part of
the tarsus anchylosed to the tibia, and its distal part to the
metatarsus.

A similar joint exists in Crocodiles, though the proxi-
mal part of the tarsus is firmly attached to the leg-bones
but by fibrous tissue, and not by anchylosis.

Much more mobility than obtains in man may exist even
in Mammals, between the proximal and distal parts of the
tarsus, as in the Orang, and especially in Galago.

The leg, instead of being set on the foot vertically, as in
man, may be applied obliquely, as e.g. in the Orang and Potto.

There was, doubtless, in the Ichthyosaurus a limitation of
motion between the bones of the hind limb, similar to that
which we find in the existing Cetacea between the bones of
the fore limbs.

The naviculare, or scaphoid, may anchylose with one of
the distal row of tarsal bones, as in the Ox and Deer, where
it unites with the cuboid.

Instead of being situate as in man, it may be central and
distinct, as in Salamandra and other Tailed-Batrachians, and
as in Chelydra and Chameleo. It may be very short and
very wide transversely, as in the Horse.

Its tuberosity may be much produced, as in Hylobates. The
articular surfaces for the cuneiforme may be remarkably
convex, as in Loris.

The naviculare may be greatly produced, as is the case in
Galago and Tarsius.

18. The BONES OF THE SECOND ROW are far less con-
stant and never so large and conspicuous as are those of the

203 ELEMENTAR Y ANA TOMY. [LESS.

first row. They may coalesce with the metatarsals, as is the
case in Birds, the Chameleon, and in Bradypus. Almost
always short, these bones may yet, as in the Insectivore
Rkynchocyon, be lengthened somewhat, while the proximal
bones are not so.

The ento-cuneiforme presents characters which differ inte-
restingly from man's, in species which are closely allied to
him. Thus the articular surface for the first metatarsal,
instead of being flat, as in him, becomes convex even in
the Gorilla, and completely saddle-shaped in the Lemurs,
as also in the prehensile-footed Marsupials, e.g. the Pha-
langers.

A strong tubercle may project from the middle of the
inferior margin of the tibial surface, as in Lemur.

The ento-cuneiforme is much the largest of the three
cuneiform bones in the Seals, but it may be quite wanting, as
in the Ox and Sheep.

It may coalesce with the meso-cuneiforme bone, as in the
Horse and in Hyla palmata, or with the ento-cuneiforme also,
as in the Alligator Indus.

The meso-cuneiforme, instead of being as in man, may be
relatively very much smaller than the other cuneiforms, as
in the Armadillos called Encoubert and Cabassou, but it is
never very much larger.

It may anchylose with the second metatarsal, as in the
Chameleon and Bradypus.

As has been said, it may coalesce with one or both of the
other cuneiforms in certain Reptiles.

The ecto-cuneiforme may enormously preponderate over
the other cuneiforms, as in the Horse. It may, on the con-
trary, be decidedly smaller than the ento-cuneiforme, as in
the Seals.

It may coalesce with the third metatarsal, as in Birds, the
Chameleon, and Bradypus ; with both the other cuneiforms,
as in Alligator Indus j or with the meso-cuneiforme only, as
in Rana escnlenta. It maybe the only distinct representative
of the cuneiforms, as in Bnfo bifurcatus.

This and the meso-cuneiforme may be the largest bones of
the tarsus, as in Pygopus lepidop:is.

The single condition in which the cnboides exists in man
is universal in his class, unless sometimes in the Ornitho-
rhynchus, where it is said to be represented by two bones, as
is certainly the case in some Batrachians, e.g. in Salamandra
and the Axolotl.

SKELETON OF LOWER LIMB.

209

It may, however, coalesce with the naviculare, as in the Ox
and Deer.

It may unite with the fourth and fifth metatarsals, as in
the Chameleo and Bradypus.

19. The distinctness of the METATARSUS and the develop-
ment which this segment of the limb attains in man are

FIG. 178.— SKELETON OF RIGHT PEL-
VIC LIMB OF HORSE.

a, astragalus : c, calcaneum ; cu, cu-
boides ; ec, ecto-cuneiforme ; f, fe-
. mur ; gt, great trpchanter ; m^t meta-
tarsal of third digit ; m*, rudimentary
fourth metatarsal ; n, naviculare ; pat
patella ; /S/2, and/3, first, second,
and third phalanges of the third and
only digit ; s, sesanioid ; t, tibia ;
t 3, third trochanter.

lie. 179. — RIGHT PELVIC LIMB .OF
GIRAFFE.

a, astragalus ; c, calcaneum ; cu, cu-
boides ; d$, proximal phalanx of
third digit ; d*, proximal phalanx of
fourth digit ;/", femur ; /"', rudiment
of fibula (the line is not continued
far enough — the rudimentary fibula
is a small ossicle reposing on the
upper surface of the calcaneum, as
shown in the figure); #z3*4, meta- -
tarsals of digits 3 and 4 united into
one "cannon-bone"; pa, patella;
t, tibia.

characters which are normal in man's class, and more or
less so in that of Reptiles. The metatarsus may be of much
greater relative length than in man, as is the case in the
Ungulata.

p

210

ELEMENTAR Y ANA TO MY.

[LESS.

FIG. 180.— RUDIMENTARY PELVIC
EXTREMITY OF

_f, fibula ; t, tibia.
(After Fnrbrin^er.')

It may be that the metatarsals coalesce with the distal part
of the tarsus, as in Birds, the
Chameleon, and Bradypus.

Metatarsals may coexist each
with only one if any phalanx, as
in Ophiodes. The first metatar-
sals may widely diverge from the
line of the others, as in non-
human Primates, and in some
Marsupials, e.g. Phalangista.

A more complete divergence
or opposition, however, may
exist, as in most Birds ; or as in the Chameleon, where the
two tibial metatarsals are
opposed to the three peroneal
ones ; or as in Parrots, where
the first and fourth are op-
posed to the second and
third.

In the number of these
bones and their sub-equality
of development man agrees
with a great number of Verte-
brates above Fishes. Never-
theless, the number may be
much reduced, and the pro-
portions of the several bones
may vary in different modes.
Thus there may be but a
single metatarsal, the third,
with rudiments of the second
and fourth, as in the Horse ;
or but a single large one, the
fourth, with the second, third,
and fifth metatarsals very
small, as in Chceropus.

There may be but a single
bone, which consists of the
third and fourth fused to-
gether, as in the Sheep, Deer,
£c., and in the Ostrich ; or of
second, third, and fourth fused
together, as in the Jerboa and
the Emeu ; or of these and the first also, as in many Birds.

FIG. 181. — BONES OF RIGHT FOOT OF
Chaeropus castanotis (nat. size).

a, astragalus ; c, calcaneum ; cb, cu -
boides ; c *, ecto-cuneiforme ; «, na-
viculare ; II. III. IV. and ^., second,
third, fourth, and fifth digits.

(From Flower s " Osteology. ")

SKELETON OF LOWER LIMB.

211

In such cases a separation of the lower end of the bone
into articular condyles for the different digits indicates the
composite nature of the bone.

There may be but four metatarsals well developed, as in
the Dog ; or but three, as in Rhinoceros ; or two, as in the
Hog and Proteus ; or but one, as
has been mentioned, in the Horse
and Chan'opus.

They may be anchylosed to-
gether at their proximal ends,
as in the Three-toed Sloth.

The metatarsals never seem
to decrease in size from the first
to the fifth, but often, as in man,
from the second to the fourth.
They may increase in size from
the first to the fifth, as in the
Great Ant-eater and the Orni-
thorhynchus.

The two central ones may
greatly exceed the lateral ones,
as in the Hog ; or the first and
fifth may greatly exceed in size
the three central ones, as in the
Seal.

The second metatarsal is
never exceptionally reduced,
while the other four all remain
well developed.

The metatarsals are never
enormously elongated like the
metacarpals of Bats.

All may be extremely short
and stunted, as in the Land Tor-
toises and Ichthyosaurus.

The number five is never
increased (except by monstrosity) in any known Verte-
brates.

The vertical line of bilateral symmetry in the foot may
pass (as in the Ox and Sheep), so as to have the third meta-
tarsal on one side of it and the fourth metatarsal on the other;
or it may (as in the Horse and Rhinoceros) pass through the
middle of the third metatarsal.

The latter symmetry may prevail where there are four

P 2

FIG. 182.— BONES OF RIGHT PES
OF JERBOA (Dipus /Egyptius}.

a, astragalus; c, calcaneum ; cb,
cuboides ; c'2, meso cuneiforme ;
c 3, ecto-cuneiforme ; //. ///.
and 7K, second, third, and
fourth digits.

(From Flowers "Osteology")

2 1 2 ELEMENTAR Y ANA TOMY. [LESS.

digits, as in the Tapir ; and the former symmetry may prevail
where there are but three digits, as in the Peccary.

20. The BONES OF THE TOES. These may be entirely
wanting for all that there are metatarsals, as perhaps in
Ophoides. The number of toes (digits) which may be de-
veloped has been indicated in treating of the metatarsus.

Thus there may be but a single digit, as in the Horse, and
a single developed one, as in Chceropus.

There may be but two, as in the Ox and Sheep, Ostrich
and Proteus; three, as in the Rhinoceros, Jerboa, and Rhea ;
four, as in the Hare, Dog, and most Birds.

When one digit is wanting; it may be the fifth, as in Birds,
or the hallux, as in the Hare.

The third and fourth digits may be the only functional ones,
as in the Ostrich ; but the third may abort, leaving only the
fourth, as in Choeropus ; or the fourth, leaving only the third,
as in the Horse. The fourth and fifth may be the only
functional ones, as in the Kangaroo. The first and fifth
may be much larger than the others, as in the Seals.

The first (hallux) may be more or less opposable, as in
Monkeys, Lemurs, Opossums, and Phalangers. Other oppo-
sitions of the digits may exist, as already noticed in speaking
of the metatarsals.

The digits may be excessively stunted, as in the Land
Tortoises, but they are never so enormously produced as are
the digits of the hands of Bats. They may, however, be
very much larger with relation to the tarsus than is the case
with man, as e.g. in the Orang.

The bones of the toes in man equal in number those
developed in other Mammals, except in the Orang, where the
second phalanx of the hallux may abort altogether.

In their distinctness these bones also agree with those of
most Mammals, but it is possible for the proximal row of
phalanges to become anchylosed to the metatarsals, as is
the case in the Three-toed Sloth.

In that his phalanges decrease in length distad, man
follows the rule of his class generally. But the second
phalanges may be much larger than the proximal ones, as
in the Two-toed Sloth.

The penultimate phalanx may be considerably larger than
the more proximal ones of the same digit, as in the fourth
toe of Birds, e.g. the Eagle.

The number of phalanges may be different from that in
man. They may be much more numerous, as in the ex-

v. ] SKEL E TON OF LO VfER LIMB. 2 1 3

tinct Ichthyosaurus and Plesiosaurus, or the numbers of the
phalanges as we proceed from the first to the fifth digit
may be 2, 3, 4, 5, 4, as in Lizards, or i, 2, 3, 3, 2, as in Sala-
mandra, or 2, 2, 3, 4, 3, as in the Frog. In Birds (where the
fifth digit is never developed) the numbers of the phalanges
of the four digits, proceeding from the hallux, are mostly 2, 3,
4, 5 ; but they may be 2, 3, 3, 3, as in the Swifts, or 2, 3, 4, 3,
as in the Goatsuckers. It is by the number of their pha-
langes (4 and 5) that the two digits of the Ostrich are known
to answer to the fourth and fifth digits of other Sauropsidans
(e.g. Lizards) which have all five digits developed.

FIG. 183. -LEFT FOOT OF A MONITOR LIZARD (Varanus).

f, fibula; ;«* — mS, the five metatarsals, m * being that of the hallux: t, tibia ;
i, astragalo-calcaneum ; 2, cuboides ; 3, ecto-cuneiforme.

The terminal phalanges may bifurcate, as in the short-tailed
Pangolin, or develop a fold of bone to support the claw, as
in Cats and Edentates, e.g. the Sloths.

2 1 4 ELEMENTAR Y ANA TO MY. [LESS.

LESSON VI.

THE INTERNAL SKELETON GENERALLY CONSIDERED,

I. HAVING now reviewed the parts composing the internal
(bony and cartilaginous) skeleton of man, and seen the more
remarkable differences which corresponding parts may pre-
sent (whether by excess or defect) in other animals, we are
in a position to survey the more general relations of the
ossified or chondrified skeleton in general, and that of man
in particular, and to summarize as follows : —

The human endo-skeleton, with respect to the number and
development of its elements, is a very complete one, except
as regards the coccygeal and hyoidean parts of it. The former
of these aborts in him as in few other Vertebrates ; the latter
is less exceptionally defective.

In contrast to this completeness in man, whole skeletal
regions may be quite or all but absent in some other forms,
as in Whales and Porpoises, Eels and Serpents. In Serpents,
indeed, not only are limbs generally quite wanting, but the
hyoidean region aborts much more than it does in man.

Man's endo-skeleton is highly organized with regard to the
mutual relation and adaptation of its parts, though, except as
to the opposability of the thumb to the fingers, it is not more
perfect in this respect than is that of many beasts.

With regard to the number of separate bones of which it is
composed, when adult, man's skeleton occupies an inter-
mediate position ; as, though in many Vertebrates (especially
Fishes), the actual number is greater, yet some Vertebrates
(as Frogs, Tortoises, and most Birds) have a smaller number.

Thus, while more of the bones of the skull, as also of the
sacral region, become fused together in him than in most
forms, yet a smaller number of such bones escape anchylosis
in the class of Birds than in man.

As to the extent of persistent cartilage in the adult condi-

vi. ] GENERAL VIE IV OF INTERNAL SKELE TON. 2 1 5

tion, man shares, speaking broadly, the characters of his class.
Ossification is carried further in the class of Birds, but much
less far in Batrachians and P'ishes. In some Fishes, indeed
(both of the highest and lowest forms), the entire skeleton
remains throughout life persistently cartilaginous, while in
the lowest form of all Vertebrates (the Amphioxus or Lancelet)
it is mainly represented by fibrous membrane only.

2. Reviewing the form and development of the spine in
man, we may note certain significant facts and generaliza-
tions : —

(1) The backbone exhibits to us a good example of serial
symmetry. The successive vertebras are evidently serial re-
petitions of parts in some sense the same, i.e. are serial
homologues, or homotypes.

(2) We find that modifications may be produced by the
suppression in some vertebrae of parts existing in others, as
e.g. of the neural arch in the coccygeal vertebrae.

(3) We find that modifications may be produced by the
coalescence of parts by anchylosis, e.g. the anchylosis of the
sacral vertebrae to form the sacrum.

(4) Parts bony in one portion of the spine may be repre-
sented by membrane only in another, as we see in the neural
canal of the sacrum closed in part by membrane only.

(5) A vertebra with annexed parts (two ribs and the inter-
vening piece of the sternum) may completely encircle the
body cavity. This suggests the question whether there may
not be membranous representatives of ribs similarly enclosing
the body cavity, annexed" to paits of the spine where there
appear to be no bony ribs, as e.g. in man's lumbar and
cervical regions.

(6) The transverse processes of some at least of the cervical
vertebrae arise by separate centres. This suggests the ques-
tion as to whether their nature may not be essentially dif-
ferent from that of the transverse processes of the dorsal
.vertebrae.

(7) We have seen that a vertebra may include (besides a
centrum and neural arch with its processes) double transverse
processes, vertebral and sternal ribs, and a sternal segment ;
the whole forming an external or (parietal) ventral arch, while
beneath the centrum may be developed a second, deeper,
more internal hypapophysial arch.

(8) The varying conditions presented by the two vertebrae
next the skull in different animals above Fishes, suggest the
question whether we can reduce to a common type that

2l6

ELEMENTAR Y ANA TOMY.

[LESS.

exceptional structure, the odontoid process of the axis verte-
bra of man.

3. First, as to the question just suggested regarding man's
cervical vertebrae.

It is well known to anthropotomists that the ventral
(anterior) root of the transverse process of the seventh cer-
vical vertebra (if not also of vertebrae nearer the head) ossi-
fies separately.

At the same time the dorsal (posterior) root of the same
transverse process plainly answers to the whole of the
so-called transverse process of a dorsal
vertebra, namely, to that part which
articulates with the tubercle of the rib.
As we have seen, this cervical trans-
verse process may be, in the lowest
Mammals and in Crocodiles, a distinct,
more or less Y-shaped bone.

Now, just such a condition of the
proximal end of a rib is, as we have seen,
well exemplified in many Batrachians
(e.g. Menopoma and Menobranchus], in
which a dorsal (tubercular) and a ventral
(capitular) transverse process articulate
with a Y-shaped rib, one branch being applied to each process.
Thus a Y-shaped bone attached to a cervical vertebra may
be interpreted in two ways : (i) as a small rib which has united
with it parts of both the " tubercular " and the " capitular "
processes of the vertebra to which it is annexed ; or (2) as
a rib with a " tubercle " so largely developed as to equal the
"head and neck" in size.

Plainly, then, the "perforated" transverse processes of
man's cervical vertebrae consist, in part, of rudimentary ribs.

FIG. 184. — Vertebras of
an Axolotl, showing
the proximal bifurca-
tion of the rib to meet
the superimposed par-
axial processes ; d, tu-
bercular process ; p,
capitular process ; st
spinous process.

Frc. 185. -LATERAL VIEW OF SIXTH VERTEBRA OF SALAMANDRA.

This figure shows the rib bifurcating not only proximally to meet the super-imposed

paraxial processes, / and c (diapophysis and parapophysis), but also distally.

It was noted that the distal ends of the cervical transverse
processes of man diverge as two small processes, termed

vi .] GENERAL VIE W OF INTERNAL SKELE TON. 2 1 7

" tubercles." Now, if each transverse process represents a rib,
we have here a slightly bifurcating rib. But this, as we have
seen, is a condition which plainly obtains in certain Batra-
chians, where the rib not only bifurcates proximally, but also
distally.

4. Secondly, as to the question above suggested respecting
the " odontoid process " in man.

It has been seen how in many animals we have a distinct
" odontoid " bone — instead of an odontoid process — interposed
between the axis and the atlas ; but we have nowhere observed
a fully developed centrum of the atlas co-existing with such
an odontoid bone.

This fact indicates, what is no doubt the case, that the
" odontoid process " is the true centrum of the atlas, united,
not with the rest of its own vertebra, but xvith the centrum of
the axis.

What, then, is the nature of that transverse bar of bone
belonging to the atlas, and passing, in man, in front of and
articulating with the odontoid process ? It is probably hypa-
pophysial in its nature, as wedge-like hypapophysial ossicles
are often developed between the adjacent margins of verte-
brae on their ventral aspect, as e.g. beneath the lumbar ver-
tebras of the Mole. It may, howWer^ be an ossification of
part of an intervertebral body.

FIG. i06.— ATLAS AND Axis VERTEBRAE OF A CHELOXIAN REPTILE.

hy, hypapophysis of atlas ; t, transverse process ; z, prezygapophysis ; z , post- '
zygapophysis ; s, neural spine ; hy', odontoid bone ; hy", hypapophysis of
true centrum of axis.

{From the College of Surgeons' Mriseiim. )

Thus harmony and unity become manifested by means of
a general study of anatomy, which would escape us did we
investigate the human structure alone.

5. In considering the most general relations of the human
skeleton it will be convenient to imagine the backbone
placed horizontally, with the limbs descending at right angles
from it, such being the position of the backbone in the great
majority of Vertebrates.

2 1 8 ELEMENTAR Y ANA TO MY. [LESS.

The fundamental facts of development (noticed in the Second
Lesson) must also be borne in mind : how the dorsal laminae
ascend and form the neural canal, and how the ventral
laminae descend to form the trunk. Also, how each of these
ventral laminae splits longitudinally on each side into an outer
plate, forming the body-wall (bones, muscles, nerves, &c.),
and an inner plate, forming the alimentary canal and its ap-
pendages— the split laminae being united respectively at their
ventral ends.

FIG. 187. — Diagram of the development of the Trunk and Its Skeleton, as shown
in a section made at right angles to the trunk's long axis, nc, neural canal ;
ex, epaxial cartilages ascending to surround it ; pxr paraxial cartilages de-
scending in the plate, or layer (Ive), external to ppt the pleuro-peritoneal cavity ;
Ivi, internal plate of the split ventral lamina.

Between these outer and inner plates is a space (to be
treated of in the Eleventh Lesson) called the pleuro-peritoneal
cavity, which thus separates the external tube of the trunk
from the alimentary tube internal to it.

Not only the alimentary tube, but also the heart and the
roots of the great vessels which proceed from it, are, as we
shall hereafter see, placed within the inner wall of this
pleuro-peritoneal cavity.

6. The central axis of the skeleton is evidently the noto-
chord with the structures immediately investing it, together
with those which generally— by ossification— replace or en-
croach upon it later in the development of the individual.

In one single form, the Lancelet, and in that only, the noto-
chord extends forwards to the front end of the body, and
much beyond the spinal marrow, the anterior end of which
is the only representative of the brain. In all other forms
the notochord stops short behind the pituitary fossa or the
part representing it.

Nevertheless, median parts in the same axial line with the
notochord may be formed, as the pre-sphenoid, which is as it
were a supplemental piece of the axis added on later to the
primitive termination of the skeletal central axis.

vi. ] GENERAL VIE IV OF INTERNAL SKELETON. 219

Generally the axis of the skeleton (i.e. the backbone) con-
sists of a number of segments (vertebras) which are serially
homologous one with another.

7. From this axis we have seen corresponding arches (carti-
laginous or osseous) to arise and enclose the spinal marrow,
which is the central part of the nervous system of the trunk.
They also are serial homologues (homotypes) one of another ;
and such arches, as they extend above the axis, have been
called epaxial ' arches. In man such arches are wanting (as
bony structures) in part of the sacral and in the coccygeal
regions ; yet we have seen how numerous and complete they
may be in those regions in other animals.

8. We have seen also that a number of arcs may extend
out from the central axis on each side, and that these may
descend and meet in the middle line below, so as to form
a series of large ventral arches enclosing the body cavity.
They also are homotypes one of another ; and such arches,
as they extend from the sides of the backbone, have been
called par axial'2 arches. In man such arches are complete
only in the thorax, where the lateral arcs, each composed of
a rib and cartilage, are medianly united by the help of the
sternum.

It is evident, however, that these arcs may be much more
extensively developed in regions where they are wanting in
man, as e.g. in the cervical vertebras of the Crocodile, and in
the anterior coccygeal vertebrae of some Chelonians and of
Menobranchus.

9. Each paraxial arc, however, has been seen very gene-
rally to have two attachments to the backbone — one above,
the other below, i.e. one more dorsal than the other.

In man we have the transverse process and tubercle of the
rib placed dorsally ; and the surface for the head of the rib,
the head itself and the neck, more ventrally. In other cases,
e.g. Menobranchus^ we find a distinct dorsal (or tubercular)
process, and a more ventral (or capitular) process, giving
attachments respectively to the diverging branches of a
Y-shaped rib.

Sometimes we have seen the ribs bifurcate distally as
well as proximally, as in Salamandra ; and sometimes, as in
certain Fishes, e.g. the Tunny and Polypterus, there are two
series of ribs on each side, one above the other.

We may thus distinguish two series of paraxial parts
on each side, one made up of tubercular processes (or

1 'ETTI, upon (the skeletal axis). 2 Flapa, beside (the axis).

220 ELEMENTARY ANATOMY, [LESS.

diapophyses T) and ribs, and the other made up of capitular
processes (or parapophyses 2) and ribs.

FIG. 188. — Six TRUNK-VERTEBRAE OF THE FISH Polypterus.

p, series of inferior ribs, from the roots of which the seffes of superior ribs (s)
diverges and extends outwards and upwards.

In man, as in most Vertebrates, the superimposed pairs of
these two series of parts are completely united, except at their
root, but a wider examination shows their probable essential
duplicity, and makes visible relations and a significance in
the transverse process of his thoracic and cervical vertebrae,
which no study of anthropotomy, however patient and minute,
could of itself reveal.

10. Still less would it, from such study, be possible to divine
the nature of that hardly noticeable ridge which extends
along the middle of the body of his axis vertebra on its
ventral aspect ; yet that ridge is really a rudiment of a system
of parts hardly less conspicuous and important in the verte-
brate skeleton than the two series already noticed.

It may be remembered, however, that in some Mammals
(e.{r. the Ornithorhynchus) a median spinous process projects
downwards from beneath the centrum of the cervical verte-
bras ; as also the great development of such processes (hypa-
pophyses) in poisonous Serpents, and their extension through
the greater part of the whole vertebral column.

We have also seen how such median structures are directly
in series with and answer to processes descending in pairs,
or to forked processes, which start from a common bony
stalk ; also that arches (chevron bones) of similar nature may
attain a very large size, as in the tails of Whales and Por-
poises.

Finally, we have seen that a still more important and con-
spicuous part may be played by the same skeletal elements,
as in some Fishes (e.g. the Sole), where elongated arches and

1 From <3<a, through. a riapu, beside.

vi.] GENERAL VIEW OF INTERNAL SKELETON. 221

processes of this kind descend from the vertebral centra and
constitute a large proportion of the whole axial skeleton.

FIG. 189. — PART OF THE VERTEBRAL COLUMN OF A SOLE.

ii, the summit of one of the epaxial arches ; h, the apex of one of the hypaxial
arches ; p, one of the paraxial elements.

These elements are developed beneath the skeletal axis (the
centra), and therefore in the line of tissue by which are sus-
pended the internal plates of the primitive ventral laminae.
They have been therefore called hypaxial. l

FIG. 190. — DIAGRAM OF THE FURTHER DEVELOPMENT OF THE TRUNK AS

SHOWN IN A SECTION SIMILAR TO THE LAST.

a, alimentary canal supported by a mesentery 2 formed of the dorsal portion of the
inner parts of the split wall of the embryonic ventral laminae ; e, epaxial arch ;
/i, hypaxial arch descending in the median line in the root of the inner part
of the split wall of the ventral laminae ; /, rib, bifurcating proximally and
abutting ventrally against the sternum, which thus completes the paraxial
arch ; m, peritoneum, bounding on all sides//, the pleuro- peritoneal space.

Hypaxial processes may also be developed beneath ver-
tebrae to which complete paraxial arches are annexed, as e.g.
in the thoracic region of many Birds.

ii. Are there yet other elements of this hypaxial system
present in man's skeleton ?

1 From I»TTO, under (the axial skeleton).

2 For the explanation of a "mesentery" see Lesson XI.

222

ELEMENTARY ANA TO MY.

[LESS.

We have seen that the branchial arches of Fishes form a
series of arcs beneath the head. Moreover they grow smaller
and more contracted from before backwards, i.e. post-axially.

FIG 191.— Skeleton of the Thorax of a Bird, showing the hypaxial processes, h,
descending, which are furnished with complete paraxial arches.
(For parts of sternum see Lesson II.)

These arches are of the same essential nature as are the
hyoidean arch, the mandible, the palatine arch, and the trabe-

FIG. 192. — SKULL AND BRANCHIAL ARCHES OF A SHARK.

bj — b$, branchial arches ; k, hyoidean arch ; m, mandible;/?, palato-quadrate arch.
(From the College of Surgeons' Museum.)

culae cranii, for (as we shall hereafter see) the relations of the
nerves and blood-vessels which skirt them are similar.

In Fishes, the heart and great blood-vessels are outside
the branchial arches, and therefore (as these vessels indicate
the line of the pleuro-peritoneal division of the ventral laminae)

vi.] GENERAL VIEW OF INTERNAL SKELETON. 223

such arches belong to the hypaxial category of hard parts.
Nevertheless, as they are placed beneath the anterior end of
the alimentary tube, they evidently do not exactly answer
to those hypaxial elements of the coccygeal vertebrae, the
hypapophyses— for these, in Crocodiles and others, are placed
above the posterior continuation of the intestinal tube. At the
same time they cannot answer to ribs and sternum (i.e.
cannot be paraxial parts), for such parts must be outside the
line of the pleuro-peritoneal cavity.

Thus it appears that man's upper and lower jaws, and also
his hyoidean apparatus, not only belong, as we have seen, to
a group of skeletal parts, which become much more developed
in Fishes, but that this whole group forms one special division
of a skeletal category (the hypaxial), the parts of which may
be termed spldnchnapophysis?

FIG 193.— DIAGRAM OF A TRANSVERSE VERTICAL SECTION OF THE MOST
DEVELOPED SKELETAL SEGMENT, ACCORDING TO THE CONCEPTION PUT
FORTH IN THIS CHAPTER.

From above the centrum the epaxial parts, e (neural arches and neural spine),
ascend. From each side of the centrum the paraxial system, /, proceeds out-
wards and downwards to coalesce with the sternum below.

/, tubercular process ; tr, tubercular part of the rib ; tr ', its continuation outwards
towards the surface of the body ; c ', capitular process ; cr, capitular part of
the rib ; vr, vertebral rib ; s-r, sternal rib ; j, sternum ; a, part of the hypaxial
system related to the great vessels (hypapophysis) ; b, part of the same related
to the alimentary tube (splanchnapophyses) ; c, part related to the heart.

12. The backbone of man, then, is a partial realization of
a complex axial skeleton, as thus : —

(1) A central axis, terminating anteriorly behind the pitui-
tary fossa, and posteriorly at the end of the spine itself, seg-
mented antero-posteriorly (i.e. divided into the bodies of the
vertebrae), the segments having relation to the nerves coming
out from the spinal marrow— central parts.

(2) A superior cylinder, also segmented (the neural arches),
generally developing articular processes, and sometimes others
besides — epaxial parts.

1 From c-7rXa7Xva' entrails, and u7ro$u<7(£, because they are related (laterally
or inferiorly) to the alimentary tube.

224 ELEMENTARY ANATOMY. [LESS.

(3) An inferior cylinder, external to the pleuro-peritoneal
cavity, and segmented (ribs, &c.) — par axial parts. These
may be subdivided into two series : —

(a) Tubercular processes (diapophyses) and upper ribs.

(b} Capitular processes (parapophyses\ lower ribs, sternal
ribs, and sternum.

These two series generally, as in man, coalesce, and the
component parts may have various relations of position
to the body and neural arch from which they spring.

(4) An inferior cylinder, internal to the pleuro-peritoneal
cavity, or directly above the origin of the internal walls of
that cavity — hypaxial parts. These may be subdivided into
three possible series, two of which are known to be actually
developed as hard parts :—

(a) Parts above the alimentary cavity or its prolongation,
and in relation to the great blood-vessel immediately below
the central axis (hypapophyses).

(b) Parts bounding externally the alimentary canal
(Splanchnapophyses).

(c) Parts bounding externally the heart or great vessels,
but of coarse internal to the pleuro-peritoneal cavity.

Hypapophyses are most largely developed in Cetaceans
and Fishes, such as the Sole.

Splanchnapophyses are only formed in the region of the
head and immediately behind it, and form the trabeculae,
the jaws, and the hyoidean and branchial arches.

Sometimes, as in the Lamprey, Splanchnapophyses may
be absent as hard parts, but in the region where they would

FIG. 194. — SKELETON OF HEAD AND GILLS OF LAMPREY.

<5, hinder part of the external (paraxial) cartilaginous skeleton of the gills ; an,
auditory capsule ; h, hyoid ; «, neural arches ; /, palato-quadrate arch.

be developed, if at all, we find a system of paraxial cartilages,
bounding the gill chambers externally.1

1 See Lesson XII.

vi.] GENERAL VIEW OF INTERNAL SKELETON. 225

Sometimes, as in the Sharks, not only are there solid
splanchnapophyses, but there are at the same time external

FIG. 195.— DIAGRAM OF THE CONDITION OF THE SKELETON IN THE BRANCHIAL
REGION OF A LAMPREY (transverse vertical section).

w, neural canal; b, alimentary canal, only bounded by b ', which is a membra-
nous representative of splanchnapophysial parts ; v, the ascending vessels ;
/, the paraxial system (external cartilaginous skeleton of the gills), or branchial

paraxial cartilages (like those of the Lamprey) coexisting
with the splanchnapophysial hard parts of the branchial
region.

FIG. 196. — DIAGRAM OF THE CONDITION OF THE SKELETON IN THE BRANCHIAL
REGION OF SOME SHARKS (transverse vertical section).

«, neural canal ; b, alimentary canal, surrounded by solid visceral hypaxial
parts (splanchnapophyses) ; v, the aortic vessels, extending up outside the
branchial arches and inside the paraxial system (/), here represented by
Certain external branchial cartilages.

The general summary of the endo-skeleton here given
refers, of course, to the skeleton in its most developed con-
dition, and expresses the greatest complexities exhibited to
us amongst the whole series of vertebrate animals. But,
as the most perfect skeleton is at one time an embryonic
structure devoid of both bone and cartilage, so in the
lowest of Vertebrates the skeleton is (as we have seen) in
a soft, membranous condition. In lieu of the complex dif-
ferentiation of higher forms, we find in Amphioxus only
sheets of membrane, or lamellae, placed more or less at right
angles to the very long axis of the body and proceeding out-
wards from the notochord to the skin.

The whole series of such membranous body-girdles may
Q

226

ELEMENTAR Y ANA TOMY.

[LESS,

be considered as the precursor of the axial system, and the
parts of such lamellae as foreshadowing the future carti-
laginous and bony complexities . which come ultimately to
occupy parts of the areas of such lamellae. Such com-
plexities are the most complete expression known to us of
the axial skeleton, as the membranous lamellae are its most
imperfect and undifferentiated form.

The parts of the axial skeleton may be tabulated as
follows : —

Central

Bodies of verte-
brae (or noto- '
chord).

Epax

/"Neural spines.

u. .

VNeural arches .

Prozygapophyses.

Postzygapophyses-

Metapophyses.

Anapophyses.

Hyperapophyses.

Zygantrum.

Zygosphene.

Paraxial .

Hypaxial

Trabeculae.
Mandible.

Cornicula and hyoid.
Cornua and hyoid.
Branchial arches.

/"Diapophyses — upper ribs.

' jParapophyses— lower ribs
V and sternum.

Hypapophyses (either sin-
gle or forked, or as de-
tached chevron bones).

Splanchnapophyses

Ventral boundary of the
heart-sac, never ossified
or chondrified.

13. We may now specially consider the anterior end of the
axial skeleton, reviewing the structure of man's skull in the
light afforded by the study of other animals.

That division which was made at starting between the
skeleton of the face and of the brain-case now appears to
have been both true and significant.

All the face and both jaws are, we have seen, ossifications
around the anterior Splanchnapophyses, and are but of small
size compared with the same parts as developed even in
some members of man's own class (e.g. the Whale). More-
over, we have seen that such parts in him are but mere rudi-
ments of what may be developed in other animals, as is made
manifest in Fishes, with their largely developed branchial
skeleton and complex suspensorial apparatus for the jaws.

vi.] GENERAL VIE W OF INTERNAL SKELE TON. 227

14. The cranial characters presented by man may be
indicated in the following generalized manner : —

The skull may be said to consist of a central axis (formed
by the basi-occipital and basi-sphenoid), to which ascending
and descending arches are annexed, and in which certain
structures are intercalated.

We have the occipital arch, and in front of this a second
arch formed by the great alae of the sphenoid and the parietals,

FIG. 197. — IDEAL, GENERALIZED DIAGRAM OF AN OSSEOUS SKULL.

a, ali-sphenoid ; ar, articulare ; bh, basi-hyal ; bo, basi-occipital ; bs, basi-sphe-
noid ; cb, cerato-branchial ; ch, cerato-hyal ; cpt, ecto-pterygoid ; d, dentary ;
eb, epi-branchial ; eh, epi-hyal ; eo, ex-occipital ; ep, epiotic ; ept, ento-ptery-
goid ;f, frontal ;fo, fenestra ovalis ;f2, fenestra rotunda ; g, quadrato-jugal ;
gh, glosso-hyal ; fib, hypo-branchial ; Ic, lachrymal ; le, lateral-ethmoid ; nt,
maxilla ; ma, malar ; me, median-ethmoid ; mpt, meta-pterygoid ; «, nasal : op,
opisthotic ; os, orbito-sphenoid ; p, parietal ; pa, para-sphenoid; pb, pharyngo-

• branchial ;pf, post-frontal ;//, palatine \pm, pre-maxilla \ps, pre-sphenoid ://,
pterygoid ; ptc, pterotic; px, hyo-mandibular ; q, quadratum ; sh, stylo-hyal ; so,
supra-occipital; sph, sphenotic; sf1, squamosal ; sq 2, pre-operculum ; t, ostrans-
versum ; th, tympano-hyal ; v, vomer ; 21, upper zygoma; 2a, lower zygoma.

and, again in front, a third arch formed by the orbital alae and
the frontal.

Into the median gap bounded by the arch of the frontal,
the olfactory organ (the ethmoid) is, as it were, thrust.

Into the gap left on each side between the lateral occipital
and the great ala of the sphenoid, the auditory organ (the
temporal bone) is thrust.

Similarly, the much smaller lateral gap left between the
great ala and the orbital wing of the sphenoid is related to
the organ of sight, which, though not ossified in man, like
Q 2

228 ELEMENTARY ANATOMY. [LESS.

the olfactory and auditory organs, is protected by bony ex-
pansions (the bony orbit) round it.

Beneath the basis cranii we have (i) the great cornua
of the hyoid, which send up no connecting ligaments to it,
but which through the basi-hyal are connected, by the lesser
cornua, with the styloid processes. (2) In front of this
hyoidean arch we have the mandibular arch, and (3), again
in front of this, the arch of the upper jaw, ending posteriorly
in the pterygoid bones and amalgamated in front with the
osseous covering of the nostrils (the nasals) and -with the
outer protection of the orbits (the malars), which latter send
back a bony arch (the zygoma) to the bony envelope of the
auditory organ.

15. If we descend greatly in the Vertebrate scale — as, for
example, to an osseous Fish — we find the same generalized de-
scription will apply, while the cornua and the cornicula of the
hyoid are more solidly represented, and similar serial homo-
logues are developed in succession behind them. A lateral
zygoma (like that of man) is wanting in the Fish, but interme-
diate forms (e.g. the Crocodiles and Sphenodori] have shown
us that there may be two lateral bony arches extending back-
wards, one above and one below the orbit, and separate one
from the other. A striking difference from man may be pre-
sented by the ossification around the internal ear in Fishes,
\rhere, instead of being in one bony piece, hardly visible but
at the base of the skull, it may be in five distinct pieces, visible
at the back and the roof of the skull, and forming a very large
part of its side wall. Many other differences also exist, the
more important of which have been noted in Lesson III.

As has been said more in detail in that Lesson, the
bones of the face, including the jaws and hyoidean and
branchial arches, are all ossifications in and about the carti-
laginous arcs of the several visceral arches, or splanchnapo-
physes.

1 6. Since the facial parts may be reckoned to be splanchna-
pophysial, and therefore, as we have seen, more or less related
to the hypapophyses of the trunk (because hypaxial in their
nature), it remains for us to consider what are the most general
relations of the cranial (as distinguished from facial) parts
of man and of other Vertebrates — to what category of spinal
axial parts may they be said to appertain ?

As the side walls of the cranium are developed in the
laminae dorsales, and in part invest the notochord, they
must be reckoned to be essentially epaxial parts ; but are

vi . ] GENERAL VIE W OF INTERN A L SKELE TON. 229

they so in the sense that each of the successive cranial arches
(each cranial segment) answers to the centrum neurapophyses
and neural spine of a vertebral arch (or spinal segment) — i.e.
are they modified vertebrae ? To this it must be replied that
in development the parts which transitorily or permanently
represent in cartilage the bony brain-case of man are never
serially segmented, and thus differ fundamentally from the
cartilaginous predecessors of the bony vertebrae. Neverthe-
less, it cannot be denied that there is a singular and striking
reminiscence of vertebras in the three arches of the bony
skull. Certainly, if the essence of vertebrae consists in being a
series of bony rings fitted together and enclosing the nervous
centres, then it must be asserted that the skull is in part
composed of three bony vertebrae. Moreover the condition,
before described, of Bagrus (Fig. 60) shows how undoubted
vertebrae may become expanded, like the bony arches form-
ing the cranial walls. In their mode of development, how-
ever, these cranial segments certainly do not agree with true
vertebrae, though they have this singular secondary and in-
duced resemblance to such skeletal parts.

It may be objected, however, that the number of the
splanchnapophysial arches does not correspond with that of
the cranial ones. . To this it may be rejoined, either (i) that,
as is very probably the case, more numerous primitive cranial
segments have coalesced or ceased to be developed, though
their hypaxial members still persisting, point to their former
existence ; or (2) that though the paraxial and hypapophysial
arches correspond in number with the vertebral segments
of their respective regions, yet that the splanchnapophysial
arches, belonging to a category by themselves, may really
answer to the existing epaxial arches, and this as follows: —

The trabeculae to the first arch ;

The palatine arch to the sphenoidal arch ;

The mandible to the occipital arch ;

The hyoid and cornua to the atlas ;

The hyoid and cornicula to the axis ; and

The succeeding splanchnapophysial arches to the several
succeeding cervical vertebrae or their representatives in
lower animals. On the other hand, it may be that these
arches correspond with aborted vertebrae, all the centra of
which are, in existing animals, represented only by the basi-
occipital and basi-sphenoid.

17. We may now review man's limb-bones (or appendi-
cular skeleton) in the most generalized way.

230 ELEMENTARY ANATOMY. [LESS.

In the first place, it appears that the appendicular appa-
ratus is, in the developed skeleton, no mere portion of the
axial skeleton, but is (in all forms as yet known) a distinct
system of parts appended to and more or less closely and
variously connected with the axial system.

1 8. The upper limbs in man are suspended, as we have
seen, from an incomplete bony girdle attached to the backbone
on its dorsal aspect, by soft parts only ; but on the ventral
aspect abutting against the median portion of the paraxial
system, i.e. against the sternum— doing this, nevertheless,

FIG. 198. — Transverse Section of the Thorax of Man, showing the relation borne
by the appendicular skeleton (shoulder-girdle) to the axial skeleton : the latter
is represented by the black parts of the figure.

n, neural canal ; s, neural spine ; tc, thoracic cavity ; s, sternum ; c, clavicle ;
sc, scapula (cut through) ; A, head of the humerus.

only with the clavicles. We have seen, however, that man
has but an imperfect shoulder-girdle compared with what is
possible, for in some animals this part joins the sternum by
great coracoids, to which pre-coracoid bones are appended, as
in Echidna; and in others, as Raia, it abuts against the neural
axial canal, thus becoming a really complete shoulder-girdle.

The humerus we have found to be a bone constantly single
in all Vertebrates above Fishes — at the least. But the relations
of size of its tuberosities may be reversed, and the so-called
lesser, i.e. the ulnar tuberosity, may be the larger one.

The elbow-joint is directed backwards ; but when the
rudimentary limb first appears, the arm is so placed that
the joint would be directed outwards. Later, the elbow be-
comes rotated backwards.

When this rotation is effected the palm of the hand would
be directed forwards (i.e. pre-axially), but that by the move-
ment of pronation it becomes directed backwards (i.e. post-,
axially) or downwards — as when we rest the palm of the hand
on a table.

19. In the primitive, embryonic position, the back of the
humerus, the olecranon, and the back (or as it is called, from
its muscular relations,1 the extensor surface) of the hand are

1 See Lesson VIII.

'!.] GENERAL VIEW OF INTERNAL SKELETON. 231

all directed outwards, the thumb being turned forwards (pre-
axially), and the little finger of course at the opposite side of
the hand. The arm being placed in this position, and a line
drawn from the limb root to the tip of the middle finger,
all that is in front (man being supposed to be in the hori-
zontal attitude of a quadruped) of such a line is called
pre-axial, all that is behind it post-axial, directions corre-
sponding with those already indicated by the same term
with regard to the backbone.

20. The skeleton of the fore-arm and hand is divisible into
a. tri- and a bi-digital series, placed side by side.

Thus there is, first, the radius ; the scaphoides and lunare ;
the trapezium, the trapezoides, and the magnum ; the first,
second, and third metacarpals ; and the annexed digits —
forming the tri-digital series.

We have, secondly, the ulna ; the cuneiforme ; the fourth
and fifth metacarpals ; and the corresponding digits — form-
ing the bi-digital series.

Such being some of the leadirg points in the skeletal struc-
ture of the pectoral or thoracic limbs, what now are the
resemblances to them exhibited by the pelvic limbs, and
what the differences?

21. The pelvic limbs in man are suspended, as we have
seen, from a complete bony girdle firmly attached to the
backbone on the dorsal aspect, its two sides meeting together
uninterruptedly (at the pubic symphysis) on the ventral aspect.

FIG. 199. — Transverse Section of the Pelvic Region of Man, showing the relation
borne by the appendicular skeleton (ossa innominata) to the axial skeleton :
the latter is represented by the black parts of the figure.

«, neural canal ; s, neural spine ; ac, abdominal cavity ; /, pubis ; syt symphysis
of the pubes ; il, ilium ; f, head of the femur.

Here, then, we have a great difference between the limb-
girdles. This however disappears when man's pelvic girdle is
compared with the pectoral girdle of the Ray (R. clavata),
which is similar to the human pelvis in its relations to the
axial system ; while in most Fishes the pelvic girdle is com-
plete below only, but not at all above, thus resembling the
pectoral girdle of man.

Instead of a union on the ventral aspect by the intervention

232 ELEMENTARY ANATOMY. [LESS.

of one bone only, as in the pectoral arch, we have the con-
currence of two (the pubis and ischium), separated from each
other by an interspace — the obturator foramen.

We have seen, however, that both a coracoid and a pre-
coracoid may exist on the ventral aspect of the pectoral girdle,
so that this difference also disappears on a more extended
survey. Such a survey nevertheless reveals some other differ-
ences, as nothing in the pectoral girdle clearly corresponds
with the marsupial bones, large ilio-pectineal processes, and
os cloacae, all of these being parts which are occasionally
developed in the pelvic girdle of different animals.

The femur is constantly a single bone in all Vertebrates.
In man it differs from the humerus in that the radial (or
pre-axial) tuberosity is the larger of the two, while in the femur
the tibial (or pre-axial) trochanter is the smaller of the two.
But this difference disappears when we extend our view, as
the relative size of the trochanters varies in different forms,
as is the case with the tuberosities.

22. The knee-joint is directed forwards, and thus markedly
differs from the elbow-joint. When, however, the rudi-
mentary pelvic limb first appears, the leg is so placed that
the knee-joint is directed outwards, thus agreeing with the
primitive position of the thoracic limbs. Later, the knee
becomes rotated forwards.

In this latter position there is no necessity for any pronation
of the leg-bones to enable the sole of the foot to be applied to
the ground, and the absence of this necessity constitutes a
difference between the arm and the leg. We have seen, how-
ever, that a sort of rudimentary pro- and supi-nation becomes
possible in some Marsupials ; and in some other animals (as
the Flying Lemur, and especially the Tortoises) the position
of both the pectoral and pelvic limbs is similar— through
the elbow, knee, and the extensor surfaces being all directed
outwards in both limbs.

In Bats the thigh is turned backwards, so that the knee
bends backwards like an elbow ; and here, were it necessary
to apply the sole to the ground with the digits forwards, a
pronation of the leg-bones would be required.

23. The skeleton of the leg, like that of the arm, is divisible
into a tri- and bi-digital series, placed side by side.

Thus there is, first, the tibia ; the astragalus and naviculare ;
the three cuneiform bones ; the first, second, and third meta-
tarsals ; and the corresponding digits— forming the tri-digital
series.

VI.] GENERAL VIEW OF INTERNAL SKELETON. 233

We have, secondly, the fibula ; the calcaneum ; the cuboid ;
the fourth and fifth metatarsals ; and the annexed digits —
forming the bi-digital series.

24. In man, however, the ulna takes part in the limb joint,
while the fibula does not. As we have found, however, this
difference may disappear, for in some animals the fibula does
articulate with the femur.

Again, in man the ulna has a large proximal process — the
olecranon— while his fibula has nothing of the kind. An
olecranon-like fibular structure may, however, be developed,
as we have seen, in the Ornithorhynchus.

In man and in most animals there is a patella in the leg,
but no analogous ossicle at the elbow-joint Sometimes, how-
ever (as in the Wombat), there is a distinct ossicle above the
olecranon on the extensor side of the elbow-joint.

25. Again, the leg in man does not articulate with the tarsus
in the same manner as the arm does with the carpus — the
ulna, unlike the fibula, not entering directly into such union.
But the ulna may articulate with the carpus directly, even in
man's own order.

The scaphoides and lunare are often together represented
by a single bone which seems to answer to the astragalus,
especially since the latter may be represented by two bones,
as in the Salamander.

The os calcis is furnished with a great tuberosity of which
there is no representative in the carpus, but then this pro-
cess is not constant, as it is entirely wanting in Lizards.

The naviculare seems to have no representative in the
human carpus, but even in most Apes there is an extra carpal
— the os intermedium, or centrale.

The cuboides and unciforme of man may each be repre-
sented by two bones in other animals, so that their cor-
respondence in unity is confirmed by a correspondence in
duplicity.

The trapezium of man differs from his ento-cuneiforme in
that it has a saddle-shaped surface for the pollex ; but in
Lemur the latter bone has a surface of that shape for the
hallux.

26. The first digit is opposable in man's hand, but not in
man's foot.

In Cheiromys and many Marsupials it is opposable in the
foot, and not in the hand.

In man the digits of the hand are longer than those of the
foot, but in Macroscelides those of the foot are the longer.

234 ELEMENTARY ANATOMY. [LESS.

The second digit of the foot never aborts (the other digits
being well developed), as we have seen to be the case with
the second digit of the hand in the Potto.

Certain resemblances occur which might not be expected.
Thus when, as in Birds, the distal part of the tarsus
anchyloses with the metatarsus, the distal part of the carpus
also anchyloses with the metacarpus, and this in spite of the
greatly different use of the parts in the two limbs respectively.

But the greatest degree of resemblance between the pectoral
and pelvic limbs is shown in the existing Tortoises, and in
the extinct Ichthyosauria and Plesiosauria, where we find a
concomitant shortening of the long limb bones, and multi-
plication of phalanges.

FIG. 200. — SKELETON OF FIG. 201. — SKELETON OF

PLESIOSAURUS. ICHTHYOSAURUS.

Certain discrepancies, however, should be noted. Thus the
pelvic member is never elongated or concentrated to such
excess, as is the pectoral member in the Bats and the Moles.
Again, we may have, as in Chameleons, three pre-axial digits
opposed to two post-axial ones in the hand, and two pre-axial
digits opposed to three post-axial ones in the foot.

Though in rare instances present alone, yet, when both
are present, the pectoral limbs never show so persistent and
considerable an inferiority of development in air-breathing
animals as do the pelvic limbs in Fishes.

On the contrary, there is never a highly developed pelvic
girdle without a rudiment of a pelvic limb ; but we may, as
we have seen in Anguis, have a well-developed pectoral
girdle without any rudiment of a pectoral limb.

Again, we may have (as in Lialis) leg-bones without a
foot (fig. 1 68), but we never meet with arm-bones without a
hand.

27. It is obvious that the importance of the axial skeleton
— related as it is to the brain, the spinal marrow, and the
nerves which pass out from these — is far greater than that of
the appendicular skeleton.

Accordingly we have found that the latter may be entirely
absent (as in the Lamprey, the Ophiomorpha, and many
Serpents), but that the former is constantly present in man's
sub-kingdom.

vi.] GENERAL VIEW OF INTERNAL SKELETON. 235

The axial skeleton alone may, indeed, as in Serpents, serve
the purposes of the appendicular skeleton, and become an
instrument not only for climbing and swimming, but for
leaping, grasping, and crushing.

We have found that both categories are always present in
the two highest classes (Mammals and Birds). In the Ichthy-
opsida we have seen that the predominance of the axial
skeleton may in some (as the Lamprey) be at its maximum,
and yet that in others the appendic- lar one may be greatly
developed while the axial one is extremely reduced (as in the
Frogs).

It is the class of Birds which shows the greatest constancy
in not only the existence but in the importance both of size
and function of the appendicular skeleton. In them the
anterior part of the axial skeleton (i.e. the cervical region
and skull) is often modified by its great length and mobility
to act as an elongated prehensile limb. This function is also
performed by the posterior end of the axial skeleton in some
Reptiles (e.g. the Chameleon), and even in some beasts, of
man's own order (e.g. the Spider Monkeys), the tails of which
(as has been before said) are so prehensile as to literally serve
the purpose of a fifth hand.

236 ELEMENTAR Y ANA TOM Y. [LESS.

LESSON VII.

THE EXTERNAL SKELETON, THE SKIN AND ITS
APPENDAGES.

1. THE second category of skeletal parts remains to be
considered, namely, those which together constitute the

EXTERNAL SKELETON.

As has been said when the description of the skeleton was
begun, fibrous tissue pervades the whole of the human frame,
bounding and supporting all its organs.

With certain exceptions shortly to be noticed, it is the
skin (taking this word in its wide sense) alone of all the fibrous
structures which, in other animals than man, develops tissue
of a dense and solid nature — horny or bony.

2. Under the head of " external skeleton," or exo-skeleton,
will be considered the skin and its appendages, that is to
say, the skin, whether external or internal, together with
structures developed from or in it.

Such structures in man are the hair, nails, and teeth, but
we shall find that many and diverse exo-skeletal parts may
exist which have no direct counterparts in the human frame.

3. The SKIN of man invests his body pretty closely.
Nevertheless the roots of the fingers and toes (especially of
the three middle toes) are held together by folds of skin,
and in some cases these folds extend far along, binding the
digits together, and causing the person so affected to be
what is called " web-fingered " or " web-toed." Such a con-
dition is constant with regard to two of the toes in an animal
so nearly resembling man in structure as the Siamang
Gibbon, and is familiar to us in Ducks and Geese.

Extensions of the skin far greater than this may, how-
ever, take place. Thus, in the so-called " Flying Squirrels"
the skin of the sides, between the arms and the legs, is
much expanded, serving for a parachute. A skin parachute,

VIL] THE EXTERNAL SKELETON. 237

supported by the elongated free and movable ribs before
noticed, is found in the little Lizards called " Flying Dragons,"
and a singular fold round the neck exists in the Frilled
Lizard. A pouch beneath the throat and long filamentary
(merely cutaneous) processes on the back exist in some
other Lizards, as in adult male
Iguanas. In the Seals a fold of
skin connects together the hind
legs and the tail ; but the maxi-
mum of skin expansion is found
in Bats, as we may see in the

Common BatS Of this Country, FIG. 2oa.-THE FRILLED LIZARD.

where not only are the legs and

tail bound together by a wide fold of skin, but this is continued
on to and between the extraordinarily elongated fingers, to
form the relatively enormous wings.

Folds of skin hang freely in some animals, as e.g. the
dewlap of cattle ; and peculiar folds are developed in the
Rhinoceros, the thickness and denseness of the skin render-
ing such folds necessary to allow of free movement of the
body and limbs.

The integument may be much more distensible than in
man, as is the case, especially in those Fishes (e.g. Diodon)
which blow themselves out with air and then float belly
upwards.

4. The skin of man, as of all other Vertebrates, consists
of two LAYERS : an external layer, devoid of nerves and
blood-vessels (and consequently of feeling), and a deeper
layer, supplied with both, and highly sensitive. The external
layer is termed the epidermis? the deeper layer is called the
dermis. At the lips the external layer visibly changes in
-texture, and inside the lips and mouth it becomes soft and
moist, and is termed mucous* membrane. This, however, is
a mere modified continuation of the external skin, and it
lines the whole of the internal passages which communicate
with the exterior. The superficial layer of the skin so
reflected inwards is termed epithelium? which is thus but
a modified epidermis, and the common term ECTERON4 is
applied to both structures, as the name ENDERON 5 is ap-
plied to the] deeper or dermal layer (i.e. the dermis) where-
ever situate.

1 From fTtl and de'pya, skin. 2 From /U?KO£, M^fa, anY slimy substance.

3 From ewi and #u\Xu>, to grow. 4 From t«, out of, and <5fpo£, skin.
5 From ei-, within, and <3e'po£.

238 ELEMENTARY ANATOMY. [LESS.

The minute structure and more important characters of
the dermis, epidermis, and epithelium have been described
in the First and Twelfth Lessons of " Elementary Physiology."

5. As the skin (or integument) is thus divisible into two
parts, so also the parts annexed to it are similarly divisible
according as they have their place of origin in the substance
of the ecteron or in that of the enderon.

In the first case they are termed ecteronic, and may be
called epidermal or epithelial structures according as they
arise in the external surface of the body or in the internal
passages. In the second case they are called enderonic or
dermal structures.

Thus our hair and nails are epidermal parts of the exo-
skeleton, because they are modifications of the external layer
of the skin.

On the contrary, our teeth are dermal structures, because
they are developed from the deeper layer or enderon.

We will consider now more carefully the skin itself before
proceeding to treat of its APPENDAGES.

6. In the soft nature of his skin man agrees with the great
majority of warm-blooded Vertebrates (i.e. of Beasts and
Birds), though exceptions are to be met with even in his own
class.

On the other hand, though the vast majority of cold-
blooded Vertebrates (e.g. Reptiles and Fishes) have in one or
^both layers of the skin solid and dense structures, yet almost
all Batrachians (Frogs, Toads, and Efts) agree with man in
having an entirely soft and flexible integument.

In order to estimate the condition which man presents,
it will be well to consider what the examination of other
creatures shows us to be amongst the possibilities of skin-
structure.

7. First with regard to the EPIDERMIS. This, as we know,
is shed in man in minute fragments constantly removed by
friction and ablution, and constantly replaced. Only under
abnormal conditions and after certain diseases does it come
away in large and continuous patches.

The case is very different in some of the lower animals.
Thus the Snakes cast off the entire epidermal investment of
the body — even that of the eyes — at once, and this process is
repeated at intervals.

The little Efts, so common in our pools, also shed the
entire epidermis at once. Separating first at the lips, the skin
is pushed back over the head by the action of the fore-limbs ;

VII.]

THE EXTERNAL SKELETON.

239

the arms are then drawn out — completely inverting the ecte-
ronic investment of each separate finger. It is then pushed
back over the loins, and the legs are withdrawn, and also the
feet and toes, the skin being inverted just as a glove is turned
inside out. Finally the tail is pulled out, and then the whole
structure being rolled up in a mass is swallowed at a gulp.
It is easy, with a little patience, to shake out one of these
skin- casts in water, so as to produce a complete and as it
were shadowy image of the little creature that bore it.

The epidermis is never converted into bone, but is often
thickened and converted into horn, an approach to which
we may see in man in the labourer's hand, in the sole of the
foot, and in those unwelcome deposits on the toes — corns.
" Horn," indeed, is but a thickened form of the very same
material as that of which the minute particles we shed from
the outer surface of our skin is made, and which yield the
substance " gelatine " when boiled. Certain local thickenings

FIG. 203.— DORSAL SURFACE OF THE CARAPACE OF A FRESH-WATER

TORTOISE (Ewys).

i— 8,"expanded neural spines ; r1—^, expanded ribs ; ««, first median (or nuchal)
plate ; py, last median (or pygal) plate ; in, marginal scutes. The dark lines
indicate the limits of the plates of the horny epidermal tortoise-shell ; the thin
sutures indicate the lines of junction of the bony scutes.

may exist in animals, not abnormal like those above referred
to in man, but constant in each species. Such thickenings
are termed callosities, and may exist on the inner side of
the legs, as in the Horse, or on the breast, as in the Camel,

240

ELEMENT A RY ANA TOM Y.

[LESS.

or be so placed as to resist the friction produced by sitting on
rough branches, as in the commoner Monkeys of Africa and
India.

A familiar and very valuable modification of the epidermic
skeleton is known to us under the name of " tortoise-shell,1

FIG. 204. — VENTRAL SURFACE OF THE PLASTRON OF A FRESH-WATEK
TORTOISE (£mys).

The bony scutes are nine in number, ic, inter-clavicular scute ; c, clavicular
scute ; hy, hyo-sternal scute ; ftp- hypo-sternal scute ; xp, xiphi-sternal scute.

The horny epidermal scales are twelve in number, as indicated by the dark lines ;
one such traverses each xiphi-sternal and hypo-sternal near its middle.

which coats externally the rigid and solid bony armour of a
certain kind of Turtle. An essentially similar though com-
mercially valueless structure also invests the armour of almost
all kinds of Tortoises and Turtles, and consists of plates
disposed in regular series upon the back and on the belly.

8. The true DERMIS often becomes ossified, constituting an
exo-skeleton of the most unequivocal kind.

An example of such a condition is
to be found even in man's own class,
Mammalia, namely, in the Arma-
dillos. These creatures possess a very
complete armour, formed of small,
many-sided, bony plates (termed
scutes), with their margins adjusted
together, aggregated in masses differently in different kinds.
There is generally one mass, or shield, on the head, one
on the shoulders, one on the loins, with narrow bands of

FIG. 205. — ARMADILLO.

vii.] THE EXTERNAL SKELETON. 241

scutes (to facilitate motion) interposed in the mid-body
region. In one form, however (£hlamydophorus\ bony scutes
are confined to the hinder region of the body, where, as
has been before mentioned, they coalesce with the pelvis.
In an extinct creature of the Armadillo kind (the Glyptodon}
the armour was even more complete, as there were no move-
able bands, but the body was invested, from the neck to the
root of the tail, with one solid case or carapace.

In the Armadillos a horny epidermal skeleton is so ad-
justed to the bony case that the former is divisible into
small plates or scales corresponding with the several bony
scutes.

A similar co-ordinate development of epidermal scales and
dermal scutes is found in some Reptiles, as in certain Lizards
(Cydodus), where the whole body is so doubly invested and
protected, as it is also in the back of the Crocodile.

A solid investment of osseous plates may exist in Fishes, as'
in the bony Pike Lepidosteus and in Polypterus, but these
plates will be spoken of under the
head of dermal appendages, when
fishes' scales are under consideration.

Certain Frogs (e.g. Ephippifer and
Ceratophrys} develop some dorsal en-
deronic bony plates, which become.

connected with the underlying backbone, presenting an
appearance which reminds us of that extraordinary develop-
ment of the skeleton which we find in Tortoises.

As in the Armadillos we find bony scutes of the exo-
skeleton underlying horny epidermal scales, so we find
beneath the tortoise-shell of Chelonians such endo-skeletal
scutes together with large bony plates of the endo-skeleton ;
only, instead of the bony and horny structures being con-
formable one to the other as in the Armadillos, neither the
number nor the outline of the bony plates of Chelonians
corresponds with the number or outline of their superincum-
bent horny scales (Figs. 204 and 207).

Moreover in Chelonians, as noticed in describing the axial
skeleton, the median plates of the dorsal shield (or carapace)
form one with parts of the backbone, and the lateral plates
form one with the subjacent ribs. Besides these dorsal plates,
larger ventral scutes cover the under surface of the body,
forming what is called the plastron ; and in the Box-Tortoises
the ends of this plastron are movable and (the head and limbs
being drawn in) can be applied to the ends of the carapace,

R

242

ELEMENTAR Y ANA TO MY.

[LESS.

so that the whole creature becomes enclosed at will within
its dense and strong exo-skeleton.

FIG. 207.— DORSAL SURFACE OF THE CARAPACE OF A FRESH-WATER TORTOISE
(Emys).

i—8, expanded neural spines : rl— r8, expanded ribs ; nn, first median (or nuchal)
plate ; py, last median (or pygal) plate ; ;#, marginal scutes. The dark lines
indicate the limits of the plates of the horny epidermal tortoise-shell , the thin
sutures indicate the lines of junction of the bony scutes.

9. In the fact that the surface of the body has a soft in-
vestment which is but very partially provided even with HAIR,

TC

FIG 208. — DIAGRAM OF A VERTICAL SECTION OF BOTH CARAPACE AND
PLASTRON OF A TORTOISE, MADE TRANSVERSELY TO THE LONG AXIS OF
THE SKELETON.

c, vertebral centrum ; ns, neural spine which expands above into a median dorsal
scute ; r, rib which forms one mass with a lateral scute and terminates at a
marginal plate ; ic, inter-clavicular scute ; hy, hyo-sternal scute.

man occupies a most exceptional position amongst Mammals.
Indeed, a copious supply of hair or feathers or scales is a

vii.] THE EXTERNAL SKELETON. 243

general characteristic of Vertebrates ; and even such aquatic
beasts as are destitute of hair (the Whales and Porpoises)
are yet endowed with a fatty layer beneath the skin which is
wanting in us. In Batrachians, however, we find a naked-
ness of skin greater even than in man.

In that man is provided with hairy epidermal appendages
he agrees with all the members of his class except the
Whales and Porpoises ; but in the small amount and the
distribution of the hairy investment he stands alone. In
the forms nearest to him in structure, the Apes, hair is
always abundant on the back, though sometimes more or
less deficient on the ventral surface — the very reverse con-
dition to that of man, in whom the back is always naked.

Long hair on the head, as also whiskers and beard, are
characters variable in man and not peculiar to him, as some
Apes (e.g. Pithecia Satanas] have a luxuriant beard.

The structure of hair, and how it is formed in a small bag
(the hair sac) by the deposition of horny matter upon a little
prominence (or papilla) of the dermis, which prominence rises
from the bottom of the bag, have been described at length in
the Twelfth Lesson of " Elementary Physiology."

The difference in structure between the hairs of the differ-
ent parts of the body (as the beard, eyelashes, eyebrows, £c.)
in man is but trifling. The contrast between the mane and
tail of a Horse and the rest of his coat is far greater ; as also
between the long whiskers or feelers of many animals (as the
Cat) and the rest of their fur. But the maximum of develop-
ment (as it exists in man's own class) is shown in such
creatures as the Hedgehog and the Porcupine, where hairs
become dense and solid spines.

lo. Such structures as hairs are peculiar to warm-blooded
Vertebrates, but the warmest blooded class (that is, Birds) pre-

FIG. 209.— DIAGRAM OF A FEATHER PAPILLA, SEEN ON TWO OPPOSITE SIDES.

i. — Side on which is placed the deep groove in which the "shaft" is deposited
and from which the secondary grooves diverge at right angles to it.

2. — The opposite side, showing the median tract where the encircling grooves
vanish.

sents a peculiar kind of greatly enlarged and complex hair —
called FEATHERS — found nowhere else in the animal kingdom.

R 2

244 ELEMENTARY ANATOMY. [LESS.

A feather is formed by means of the peculiar structure of
the dermal papilla which gives rise to it. That papilla
(instead of being smooth, like the papilla of a hair) has on
one side a deep vertical groove, broadest at the base and
vanishing towards the apex of the papilla. Other less deep
grooves go from each side of this vertical groove at right
angles to it, and at very short distances from one another.
They extend all but round the papilla, vanishing at the
middle of the opposite side to that which bears the vertical
groove. Grooves smaller still and much shorter are given
off again at right angles to the second set of grooves, parallel
therefore as far as they go to the main and vertical groove.

Now, as horny matter is deposited on the papilla, it be-
comes thickest where the grooves are deepest, and of course
thinnest where there are no grooves at all, i.e. in the inter-
spaces of the grooves. With the progress of growth, this
whole horny investment splits up along these interspaces
of thinnest deposit. The part which was in the main ver-
tical groove is thickest of all, and becomes the shaft of the
feather, the parts in the secondary grooves become the
" barbs," and the still smaller portions at right angles to the
latter the " barbules." When these last are long and hang
freely, they form the sort of structure we see in an ostrich
feather. Occasionally, as in the Cassowary, a feather will
have two shafts ; this is due to the papilla having borne a
vertical groove on each side.

ii. The only form of epidermal appendage, besides hair,
which is found in man is the NAIL.

The structure of this organ is also explained in the Twelfth
Lesson of " Elementary Physiology." It is not formed in a

c

FIG. 210. — TRANSVERSE SECTION OF A NAIL.

rt, small lateral folds of the integument ; b, nail ; c, bed of the nail, with its
ridges.

bag (like a hair is), but only in a fold of skin (the root of the
nail), where horny matter is deposited upon a number of
minute, parallel, raised ridges of the deep layer — or dermis.

vi i. J THE EXTERNAL SKELETON. 245

The human nails differ in shape from those of almost every
other animal, in that they so little tend to surround or enclose
the ends of either the fingers or toes.

The nail at its maximum of development quite surrounds
and encloses the last joint of the digit which bears it, and is
then called a hoof, as we may see in the Horse or Ox.

It may be produced into a sharp point, when it is called a
claw, as in the familiar case of the Cat, and in Birds.

The nails may, on the other hand, be much reduced in
size, and not nearly extend to the end of the digits which
support them, as in the Sea Bear. They may be altogether
wanting in man's own class, as in the Porpoise, or obtain a
prodigious relative size, so that the body can be suspended
by them, in progression, as in the Sloth. The little Bats of

F,r -> Curvru FlG. 212.— HEAD OF MALE OF

0. 2II.-SLOTH. ,

our own country hang, indeed, by hook-like claws when at
rest ; either by the claws of the toes or the two thumb-claws.

The nail of one digit may differ in form from all the others,
as in that of the second toe of Lemurs and of the Hyrax.

The nail makes its appearance in its greatest simplicity in
certain Toads and one of the Efts, where it is merely a slight
thickening of the epidermis at the ends of the digits.

12. ECTERONIC APPENDAGES not found in man make their
appearance in other animals. Thus, in the Rhinoceros we
meet with a horn (or even two — one in front of the other),
entirely destitute of a bony core, and growing like a great
blunt nail from the dorsum of the muzzle, long dermal papillae
extending into it and answering to the dermal ridges beneath
the human nail.

No less than three long horns are developed in Owen's
Chameleon — one from the nose, and a symmetrical pair from
the front of the head.

Other horns which do possess bony cores are developed
from the head in pairs in the so-called hollow-horned Rumi-
nants, i.e. the Oxen, Antelopes, Goats, and Sheep ; and only
in one anomalous form, the Prongbock (Antilocapra\ are

246

ELEMENTAR Y ANA TO MY.

[LESS.

these horny structures shed at intervals ; in the rest they
persist throughout life. Normally there is never more than
one pair amongst existing Ruminants, with the exception of
Antelope quadricornis, which has two pairs. Such horns
may be straight, or curved, or spirally twisted, but they are
never branched, with the single exception of the Prong-
horned Antelope.

FIG 213. — THE PANGOLIN (Manis).

Less familiar, but not really more remarkable, is the struc-
ture developed in the scaly Manis or Pangolin.

Here the entire body is covered and protected by strong,
sharp-edged, overlapping horny plates, each of which is
comparable with a nail.

FIG. 214. — TAIL OF RATTLESNAKE.

The overlapping scales of Serpents are horny investments
of processes of the dermis, but the scales of Fishes are of
different nature, being formed in the dermis itself.

vii.] THE EXTERNAL SKELETON. 247

Curiously modified thickenings of the epidermis, which
take the form of rings, may surround the ends of the tail, as
in the Rattlesnake, These being loosely attached, produce a
singular sound, a sort of "hissing" rattle, when the tail is
vibrated by the excited animal

Nail-like structures may also be developed from the side of
the hand, as in certain Birds (e.g. Palainedea], and in one of
the lowest members of man's own class (the Duck-billed
Platypus) a hollow horny spur grows
upon each ankle.

The epidermis of the outside of
the muzzle and jaws may also be
converted into horn, as in the beak FlG. ^.-ORNITHORHYNCUS,

of Birds and in that of the Turtle. OK DUCK-BIU.ED PLATYPUS.

As a remarkable exception, the same

thing may take place in man's own class : this we see by the
Duck-billed Platypus, which really has a horny beak very like
that of a duck.

13. These being the principal modifications which investiga-
tion shows us to be possible with regard to the epidermis and
its appendages, yet other peculiarities may be present in parts
belonging to the other ecteronic division, the EPITHELIUM.

To begin with the mouth, its epithelial lining investing the
gums becomes greatly thickened and hardened in persons
who have lost their teeth, and who are so unfortunate, or so
unwise, as to have failed to replace them by artificial ones.

In certain beasts, as the Cow and the Sheep, the front part
of the upper jaw is always devoid of teeth, and a horny epi-
thelial pad is formed there against which the teeth of the
front of the lower jaw bite.

A much more developed structure, though essentially simi-
lar, is met with in the Dugong— a creature superficially like a
Porpoise, but really very different. ' In this creature the front
of each jaw is furnished with a dense horny plate, formed
(like the horn of the Rhinoceros) of a deposit of horny
matter around long processes of the deeper skin layer — the
deimis. Horny substances in the place of teeth are also
developed inside the mouth of the Duck-billed Platypus,
and there are horny teeth in the mouth of the Lamprey.

The maximum of development of this kind of structure is,
however, found in the Whalebone Whales.

The upper jaw in these creatures is furnished with very nu-
merous horny plates (termed baleeii), which hang down from
the palate along each side of the mouth. They thus form

ELEMENTAL Y ANA TOMY.

[LESS.

t\vo longitudinal series, each plate of which is placed trans-
versely to the long axis of the body, and all are very close
together. On depressing the lower lip the free outer edges
of these plates come into view. Their inner edges are pro-
vided with numerous coarse, hair-like processes, consisting

FIG. 216.— MOUTH OF A WHALE.

•

of some of the constituent fibres of the horny plates — which,
as it were, fray out, and the mouth is thus lined, except below,
with a network of countless fibres formed by the inner edges
of the two series of plates. This network acts as a sort of
sieve. When the whale feeds, it takes into its mouth a great
gulp of water, and drives it out again through the intervals
of the horny plates ; the fluid thus traverses the sieve of
horny fibres, which retain the minute creatures on which
these marine monsters subsist.

In man a few hairs grow within the nostril. In the Rabbit
hairs grow on the inside of the cheek.

YII.]

THE EXTERNAL SKELETON.

249

The epithelial lining of the stomach may take on a dense
horny structure, as in the gizzards of Birds, but this will be
again noticed under the head of Alimentary Organs.

14. We come now to enderonic
appendages. As has been said, that
part of the dermis which underlies
the epidermis is devoid of hard
structures in man, who possesses
them in the sub-epithelial enderon
only. Such structures are the
TEETH. Each tooth consists of a
" crown," which is visible, and of a
"fang" or " fangs/' which are buried
in the gum.

15. The mode of formation of the
teeth has been described in the
Twelfth Lesson of "Physiology:"
how the teeth first arise as little
processes (or papillae) of the dermis,
which appear at the bottom of a
groove running along each side
of the jaw ; how the walls of the
groove grow together, between and
over each of the papillae, and thus
enclose the papillae in what are
called the dental sacs.

Each such sac is a pouch of the
dermis, enclosing a "pinched off"
bit of the epidermis.

The papilla, assuming the form of
the future tooth, becomes hardened
by a deposit within it of calcareous
salts, the central part of the papilla
remaining soft (as the pulp) but
diminishing with the growth of the
tooth, till, when the tooth is full
grown, there is but a minute aper-
ture at the bottom of each root
to give entrance to very delicate
vessels and nerves.

16. The STRUCTURE of each tooth, how it consists of three
substances, " dentine, enamel, and cement," and the nature of
each of these, have also been described in the " Elementary
Physiology."

FIG 217. — FOUR PLATES OF
BALEEN SEEN OBLIQUELY
FROM WITHIN.

250

ELEMENTAR Y ANA TO MY.

[LESS.

Dentine forms the bulk of the tooth ; the dense enamel
coats the crown ; the cement invests the fang.

The dentine is traversed by exceedingly minute tubes
which radiate into it from the pulp cavity. The enamel is
the hardest structure in the human body, and almost en-
tirely a mineral, containing but two per cent, of animal
substance. It is made up of minute fibres, with their ends
applied to the surface of the dentine of the tooth. The ce-
ment is more like bone ; it may take a much greater share
in the formation of the tooth than is assigned to it in the
teeth of man.

FlG. 2l8. — A, VERTICAL, B, HORIZONTAL SECTION OF A TOOTH.

n ; b, pulp cavity ; c, cement of
Magnified about three diameters.

rr, enamel of the crown; b, pulp cavity; c, cement of the fangs; d, dentine,
lifted i "

17. As all know, teeth are cut. The meaning of this is
that, as the tooth develops, it rises out of its sac, the parts
superficial to its apex being absorbed. As its crown rises
its fang is developed.

The teeth appear successively in two sets. First the milk-
teeth come into place, and afterwards the second or permanent
set of teeth.

Each permanent tooth is formed in a little sac, which
at first is but a prolongation of the sac of that milk-tooth
which it is destined to succeed.

The development of the second tooth is accompanied by

vii.] THE EXTERNAL SKELETON. 251

absorption of the fang of its predecessor. Replacement is
not the effect of mechanical pressure, but the two actions
(development and absorption) proceed harmoniously, the now
fangless milk-tooth easily falling out when its successor is
ready to take its place, unless through some abnormality
of growth the aid of the dentist has become necessary.

Before mentioning the order of succession, the teeth them-
selves must be shortly described.

1 8. The TEETH OF MAN, when adult, should be thirty-two
in number.

As the two sides of each jaw are alike, it will be suffi'
cient to notice the eight teeth above and eight below of
each side.

The fangs or roots of all teeth are firmly fitted into corre-.
spondingly shaped cavities in the bones of the jaws, which
cavities are termed alveoli, and
this mode of union of parts (like a
nail driven into any substance) is
termed gontphosis?

The front tooth of each lateral
half of the upper jaw has a chisel-
shaped crown with a horizontal
cutting edge. It has a single, long,
tapering fang.

The second tooth is like the first, FlG 210._UppER AND LowEK

and these two, on account of their TEETH OF LEFT SIDE OF AN

cutting shape, are called incisors ; ADULT MAN.

but we Shall See that there is another ', incisors ; c, canines ; /;«, pre-

reason why they belong to a special lrs ; '"' m<

category.

The third tooth above is more pointed, more conical, and
has a longer though still single fang. It is called the eye-
tooth, or canine.

The fourth tooth above has a flatter and broader (from
within outwards) crown, and bears two pointed tubercles (or
cusps), one internal, the other external. Its fang is flattened
and vertically grooved, showing a tendency to division, while
at its end it is in general actually divided and has two
apertures, one in each division.

The fifth upper tooth is like that last described, and the
two, from the number of their tubercles, are called bicuspid,
and from their more flattened crowns (better adapted for
grinding) they are also called molars. The fifth differs from

1 From f6/ji(poc, a nail.

252 ELEMENTARY ANATOMY. [LESS.

the fourth, however, in having its fang often cleft for a con-
siderable distance from its end.

The sixth upper tooth is the largest of the whole series.
It has a flattened grinding surface, with four cusps, and an
oblique ridge connecting the front inner cusp with the hind
outer one. The fangs are three in number, two being placed
on the outer side, and one on the inner.

The seventh upper tooth is quite like the sixth.

The eighth upper (or wisdom) tooth is less large, though
essentially similar. The two inner cusps of its crown are
blended together, and its fangs are generally united into a
single, irregular, conical mass.

The three teeth last described are all termed (for a reason
which will shortly appear) true molars. In the lower jaw
the first two teeth are similiar in shape to the first two teeth
of the upper jaw, whence they are also called incisors.
They have also each a single fang.

The third lower tooth is pointed and conical, and has
a single root like the third tooth of the upper jaw. It there-
fore bears a similar name, and the lower canine should have
its apex within and slightly in front of the crown of the upper
canine.

The fourth and fifth teeth of the lower jaw are called bi-
cuspid molars, like the fourth and fifth teeth of the upper
one. Sometimes, however, the fourth has only a single
cusp, and it is more canine-like than the one answering to
it above.

The sixth and seventh teeth of the lower jaw are called
true molars. Each bears five cusps, three on the outer side
of each crown and two on the inner. The fangs are two to
each, but each fang is vertically grooved.

The eighth lower tooth, or lower wisdom tooth, is also a
"true molar," but differs from the two last described in
having, generally, its fangs blended together, and in having
its crown smaller than the others and more rounded.

The human- milk-teeth are twenty in number : two inci-
sors, one canine, and two molars, on each side of each jaw.

They resemble the permanent teeth, but the last molar,
both above and below, does not resemble the fifth tooth of
the permanent dentition (and which is its vertical successor),
but it resembles the first true molar in each case, though it
has nothing to do with the formation of this tooth, of which
it is, as it were, the prototype.

The details of the succession of the teeth belong rather to

vii.j THE EXTERNAL SKELETON. 253

Physiology, but it should here be noted that not only do the
permanent canine teeth come into place before the wisdom
teeth, but also even before the second molar. Moreover, the
last milk molar is shed before the epiphyses of the long bones
are united to their shafts, and before the bones of the limb
girdles have coalesced.

All the teeth of the permanent set are thus provided with
temporary or deciduous predecessors, except the last three
molars of each jaw. It is on account of this absence of
vertical predecessors that the three hindmost teeth on each
side of each jaw are called "true molars." In extending our
view to other animals we shall see that true molars must be
defined to be "teeth situated behind the hindmost tooth
having a vertical predecessor."

19. The upper incisors are implanted in what we have seen
to be a distinct bone (the premaxilla) from that- in which the
other teeth of man's upper jaw are implanted, while the
canine is the foremost tooth implanted in the true maxillary
bone. In surveying these parts in other animals we shall
see that the DEFINITION of an upper incisor is " a tooth im-
planted in the premaxilla ; " of an upper canine, " the fore-
most tooth of the maxilla, provided it be not at a considerable
distance from the anterior end of that bone." The lower
canine must be defined as " the tooth which bites in front
of the upper canine," and the lower incisors as " teeth placed
in front of or on a line with the lower canine, or, if this is
absent, teeth corresponding with the upper incisors."

The bicuspid molars of man (not having always two
cusps in other animals) are, in zootomy, termed premolars,
because they are placed in front of the true molars. An
extended view reveals facts which compel us to give to
premolars generally the following somewhat cumbrous defi-
nition : " teeth behind the place of the canines and in front
of the true molars, or, if the latter are absent, teeth behind
the place of the canines and having vertical predecessors, or
in front of molar teeth which have such predecessors."

20. Such being the dentition (i.e. tooth-furniture) of man, it
may be conveniently expressed by the following SYMBOLS : —

If, C ^, P M |, M f , for the permanent dentition. I f
means " two incisors, above and below, on each side of the
jaws ;" C \ means similarly one canine in each case ; P M |
means " two premolars on each side of each jaw ; " and M f
means "three true molars, both above and below, on each
side." Similarly the symbols D I f, D C \, DM f, for the

254

ELEMENTAR Y ANA TOMY.

[LESS.

milk dentition, refer in the same manner to the deciduous

incisors, canines, and molars respectively.

It need hardly be added that each tooth attains its full

development within a limited time, after which it grows no

more, and (with very rare exceptions) no third development

ever replaces the fall of a tooth of the permanent dentition.
An acquaintance with human structure only, would give

the student very little idea of the possibilities of development

in the matter of " teeth."

As to SITUATION, implantation, number, form, and use, and

also as to succession and structure, the greatest diversities

are to be found.

21. Man agrees with the whole of his class in that he is

only furnished with teeth upon the margins of the jaws.

Some members of his class, however, are as completely
toothless as are Birds — e.g. the Echid-
na, Pangolins, and Ant-eaters.

In Reptiles we first become ac-
quainted with the fact that true teeth
may be developed not only from the
margins of the jaws, but also from the
palate, as we find to be the case in
the Iguana and in Serpents, some of
the teeth of which latter, as will shortly
be explained, present very remarkable

peculiarities. When we descend to the Batrachians we some-

FIG. 220. — ANT-EATER.

FIG. 221.— OPEN MOUTH OF THE AMERICAN EFT PLETHODON,

Showing the numerous para-sphenoidal teeth at the extreme back of the roof of
the mouth, together with a row of palatine teeth placed behind each posterior
nasal opening in the anterior part of the palate.

times find teeth in two series not only in the upper jaw, but
also two series in the lower (as in Proteus and Meno-

vii.] THE EXTERNAL SKELETON, 255

branchus], and even (as in Pleikodori) teeth upon the under
surface of the back part of the skull.

Fishes teach us that teeth may be developed in yet other
situations, for in some of those animals (e.g. the Salmon and
Qdontoglossum), there are teeth upon the tongue ; and in
most Fishes teeth are developed at the extreme back of the
mouth, on the bones of those arches (branchial arches)
which represent permanently what have been spoken of in
the First Lesson as the transitory posterior visceral arches of
the early stages of human development. The branchial
arches of Fishes which support the gills, and are placed on
each side beneath the back of the head, sometimes (as in
the Perch), develop tooth-like bodies on their inner surfaces,
and the hinder of these lateral arches terminate (Fig. 114)
in bones called pharyngeal,1 which most frequently support
teeth (sometimes of very complex structure, as in Scarus],
termed from their situation pharyngeal teeth. Moreover,
the exactly reverse conditions to those which obtain in
man may be met with, as in the Carp and Tench, where the

FIG. 222.— PHARYNX OF A TENCH OPENED FROM BELOW, AND THE TWO ROWS

OF PHARYNGEAL TEETH DIVARICATED. (After OlVtn.)

b, basi-occipital tooth ; ph, pharyngeal teeth ; o, oesophagus.

margins of the jaws are as free from teeth as is man's throat,
while the posterior aperture of the mouth is bounded by
teeth, partly pharyngeal, and in part attached to a prolonga-
tion downwards of the hindmost bone of the base of the
skull !

We shall see that tooth-like tissue may be developed in still
more anomalous situations, but as some of the structures
referred to cannot be called teeth, and others can only doubt-
fully be so called, notice of them may be postponed.

22. As to IMPLANTATION, the changes which take place in

1 From being placed in the "pharynx." For this see Lesson XI.

2 5 6 RLE ME NT A RY ANA TOM Y. [LESS.

the process of development of human teeth are interestingly
illustrated by permanent conditions in other animals.

Thus we may have, as in Sharks, an open groove along
each jaw, in which groove dermal papillae appear and undergo
calcification directly without their becoming enclosed in sacs
at all.

We may have, as in the Pike, an enclosure of each papilla
in a sac, but no development of bone round it, the teeth
being attached to the jaw by ligament.

We may have teeth which become anchylosed to the summit
of the jaw, there being no bony wall (or alveolus) developed
on either the inner or the outer side of the teeth, as in certain
Lizards (e.g. Psammosaurus\ termed Acrodont.1

FIG. 223. —SIDE VIEW OF THE SKULL OF A LIZARD (Varanus}, WITH

ACROPONT TEETH.

a, articular bone of mandible ; c, coronoid bone of mandible ; d, dentary ; _/",
frontal; _/", pre-frontal ; f", post-frontal; /, lachrymal; m, malar; ;«_r,
maxilla ; «, nasal , o, pro-otic; p, parietal ; pt, pterygoid ; pt , columella, or
dismemberment of pterygoid ; pt" , os transversum ; px, pre-maxilla ; g, quad-
rate bone ; sq, squamosal.

We may find a development of a bony alveolar plate on
one side (the outer), to which the teeth may become attached
by actual bony growth (anchylosis), as in the Iguanian
Lizards. Such a form of attachment is termed pleurodontA
We may find two alveolar plates of bone, but no transverse
bony partitions, as in Ichthyosaurus.

We may find both alveolar plates together with transverse
partitions forming distinct alveoli, which nevertheless are
incompletely divided one from another at the hinder part of
the mouth, as in many of the Dolphin tribe ; and finally, we

1 From uVpo£ , sharp, and oSoiig, a tooth,
a From ir\evp6v, a side, and odcnc;.

VII.]

THE EXTERNAL SKELETON.

257

may meet with alveoli thoroughly complete, like those of
man, as in most members of his class.

These complete alveoli, however, may be in some respects
different from those of man. They are so where teeth grow

FIG. 224. — INNER SIDE OF LOWER JAW OF PLEURODONT LIZARD,
showing the teeth attached to the inner surface of its side.

from permanent pulps throughout the whole of life — like the
tusks of the Elephant and the teeth of many other beasts
(e.g. the cutting teeth of the Squirrel). In such cases, of
course, the deeper part of the alveolus is quite wide instead
of being attenuated as in us.

23. The NUMBER of teeth in man is interesting as being
not very far from that which is typical of the great bulk of
the class to which he belongs. It is identical with that exist-
ing in the whole of the Apes which inhabit the old world, and
those of the new world only differ from him by the presence
of one more pre-molar or by the absence of a molar on each
side of each jaw.

In man's own class the number of teeth developed may be
very great, as in the Dolphins, where the greatest number
is reached in Pontoporia, namely 220.

The large Armadillo (Priodon] may have as many as
ninety. They may be reduced to two, as in the Narwhal.

If we pass out of man's class we may find teeth many or
few, as in Reptiles ; but amongst Fishes we meet with every
extreme, from a single pointed tooth on the roof of the
mouth, as in Myxine, or two above and two below (flat and
crushing), as in Ceratodus, up to such a multitude that to
count them would be a task both useless and difficult, as in
Murcena, the Pike, or Osteoglossum.

24. The FORMS presented by the" teeth of man agree more
or less closely with what we find in many members of his
class, but have no relation, or only the most general and
distant one, to the teeth of cold-blooded Vertebrates.

Although the shape of the teeth is nearly the same in all
men, nevertheless the wisdom teeth of those races which are

S

258 ELEMENTARY ANATOMY. [LESS.

reputed lowest are larger and more equal to the teeth next
in front of them than is the case with Europeans.

When we descend to the creatures nearest to man in
bodily structure (the Apes of the old world), though we find
the number of teeth identical with that in him, yet a striking
difference is produced by the large size, especially in the
males, of the canines, which are true tusks for defence or for
attack. The last molar, or wisdom tooth, is also generally
larger relatively than in man, and in some forms is consider-
ably the largest molar of the lower jaw.

The large size of the canines causes a separation between
the lower canine and the first lower pre-molar, and between
the upper canine and the outer incisor, in order to provide
space for their apices to pass. These interspaces are each
called a diastema,1 and are wanting in man, where the teeth
are all normally close and contiguous. This contiguity and
absence of any diastema is a character which man shares
only with the little Lemur Tarsins, and with a certain extinct
hoofed quadruped, the Anoplotherium.

Most Mammals have teeth of definite kinds — incisors,
canines, or molars. This is not the case, however, with all,
as, for example, the Dolphins have teeth which are all
nearly alike.

Below the class of Mammals, only rarely in certain Lizards
(e.g. the Agamas) do teeth simulate canines with small teeth
between them in the front of the mouth simulating incisors.

25. The INCISORS of man are closely resembled by those
of the Apes, but in some Apes of the new world (Pithecia)
the lower incisors, instead of being nearly vertical, are long,
slender, approximated together, and inclined strongly forwards

FIG. 225 — GRINDING SURFACE OF THE TEETH OF THE RIGHT HALF OF THE
LOWER JAW OF THE LEMOROID Microcebus, showing the close apposition
of the canine to the two elongated incisors, which are almost horizontal in
position.

as well as upwards — a condition still more decided in the
Lemuroids. The most singular form of the Lemuroid
group (the Aye-aye — Cheiromys] has but two incisors above
and two below. These, however, are very large, and grow
from permanent pulps during the whole of life, from deep

1 From itac-TfjM', to separate.

VII.]

THE EXTERNAL SKELETON.

259

roots just like those of the Squirrel or Rat. Such teeth,
specially adapted for gnawing, as we so often know to our
cost as regards the Rat, are denser on the front surface than
elsewhere, so that the action of gnawing, as it wears away
more quickly the softer part behind, keeps a constantly sharp
chisel-shaped edge in front. Animals which have teeth thus
formed are apt to suffer fatally from the loss of one, as, there
being then nothing to wear away its natural opponent of the
opposite iaw, the latter continues to grow and complete that

FIG. 226.— SIDE VIEW OF THE SKULL OF A PORCUPINE (Hystrix crisiata).

(TYPICAL RODENT DENTITION.)

a, angle of mandible ; c, occipital condyle ; cr, coronoid process of mandible ; cy,
condyle of mandible ; /, frontal ; z, incisor teeth ; j, ascending branch of
maxilla enclosing the enormous infra-orbital foramen, the course of the
masseter muscle through which is indicated by an arrow ; in, molar teeth ;
tnx, maxilla ; n, nasal ; pm, premolar teeth ; pm, paramastoid process ; px,
premaxilla; ^, tympanic bone ; z, zygomatic arch — the part formed by the malar.

circle of which its axis (from root to apex) describes a seg-
ment. Rabbits and Hares are not unfrequently found dead
from such accidental deformity.
A pair of strong but pointed upper incisors are found in

FIG. 227. — DENTITION o?

DESMODUS.
i, incisors ; c, canines.

FIG. 228. — A LOWER INCI«OR OF
GALEOPITHFCUS, showing its
comb-like form.

the blood-sucking Bat Desmodus, and to these pointed in-
cisors notched incisors are opposed below. In another Bat
s 2

260

ELEMENTARY ANATOMY.

[LESS.

such notches are more marked, but these attain their maxi-
mum of development in the lower jaw of the Flying Lemur
(Galeopithecus], where each incisor has the appearance of a
comb, being notched by parallel notches down to the very
base of the crown. (Fig. 228).

Rarely, as in certain Insectivorous Beasts (e.g. Hemi-
centetes), the upper incisor may bear more than one cusp.

FIG. 229. — SIDE \riE\v OF SKULL OF HEMICENTETES.

An excavated incisor of a different kind is familiar to us
in the Horse, where each incisor has a deep median depres-
sion, the " mark," which has a form such as would be pro-
duced by the sudden inflection of the surface of the tooth so
as to form a deep pit. This " mark "
continues to be visible till the tooth
has worn down by use beyond the
point to which the inflection extends.
The dark colour of the " mark " is
due merely to the accumulation ot
fragments of food and foreign bodies
within the pit.

When the canine teeth are large
the incisors are generally small, as
we see in the Dog and Cat, where
there are three above and three
below on each side of each jaw.
This is the typical number of Mam-
malian incisors, but they may be as
many as f on each side, as in the
American Opossums.

Incisors may, on the contrary, be

altogether wanting though other teeth are present, as in
the Armadillos, except one kind. They may be quite want-
ing in the upper jaw but present in the lower, even in man's
own order, e.g. Lepilemur.

FIG. 230. — VERTICAL SEC-
TION OF A HORSE'S IN-
CISOR, showing the depth
of the vertical fold forming
the " mark" m.

p, the pulp cavity.
(After Rousseau.}

VIL] THE EXTERNAL SKELETON. 261

The same is the case in some Mammals of other orders,
as in the Ox, Deer, and Sheep ; as also in the extinct Ele-
phant-like creature Dinotherium, which had only two in-
cisors, but these extended downwards from the front end
of the lower jaw.

Incisors may be present in the form of enormous tusks in
the upper jaw but wanting altogether in the lower, as in the
Elephant. They may similarly be present in the upper jaw
only, but exhibit a flat grinding surface flush with the gum,
as in the Walrus.

The upper incisors may be separated by an interval from
their fellows of the opposite side, as in Loris.

FIG. 231. — Fr.oNT VIEW OF UPPER INCISORS AND CANINES OF THREE GENERA
OF SLOW LEMURS (natural size).

i, Loris; 2, Nycticebus ; 3, Perodicticus.

The front lower incisor may be enormous, and represent,
by its notched outline, several incisors fused into one. More-
over with age the teeth may become anchylosed to the jaw.

m'

FIG. 232.— DENTITION OF SHREW-MOUSE (Sorex).

i upper incisors ; i', notched lower incisor ; c, upper canine ; c', lower canine ;
pm, upper pre-molars ; pm ', lower pre-molar ; m, upper molars: m', lower
molars.

These peculiarities are exhibited by the Shrew-Mice, which,
as before remarked, are not " mice " at all, but closely allied
to the Mole and Hedgehog.

Generally having but a single fang, whether with or without
a permanent pulp, an incisor tooth may yet have a double
fang, as is the case in the Flying Lemur and in Petrodroimts.

26. The CANINE TEETH of man, as their name implies, find
in the Dog (and other flesh-eating beasts) an enlarged repre-
sentative, as also in the Apes. Such tusks, however, are far

262

ELEMENTAR Y ANA TO MY.

[LESS.

exceeded by what we find in certain of the Hog tribe, e.g. in
the Babyrussa (Porcus), where the upper canines first mount
vertically and then curve over backwards and downwards,
whence its native name, which signifies Deer-Hog.

Undoubted canines attain their
maximum in the upper jaw of the
Walrus, which develops a pair of enor-
mous descending tusks growing from
permanent pulps, and which are said
to aid the animal in its locomotion
amongst the ice.

The longest tooth developed in the
whole animal kingdom is the tusk of the
Narwhal. It may be doubted, indeed,
whether this tooth represents a canine or a molar, yet, as it is
embedded entirely in the maxilla, it cannot be an incisor.
In the female Narwhal these teeth remain undeveloped and
in the bone. In the male the tooth of one side is generally
developed, but sometimes both are so. The pulp cavity
extends nearly the whole extent of the enormous tooth,
which is said to attain a length of ten feet. Though straight,
its surface has a spirally-twisted appearance, and formerly
was sometimes exhibited as the horn of the Unicorn.

Upper canines may be present though upper incisors are
wanting, as in the case of the Musk Deer and Muntjac.
Lower canines may be closely approximated to and shaped

FIG. 233.— SKUI.I. AND

TUSKS OF THE BABYRUSSA

(Porcus).

FIG. 234. — DENTITION OP A SHEEP. (TYPICAL RUMINANT DENTITION.)

mx, maxilla ; px, pre-maxilln, which is edentulous, there being no upper in-
cisors ; i1, z'2, z3, three lower incisors of left side ; c, lower canine ; pm, pre-
molars ; m, molars.

like the incisors adjacent to and between them, as in the
Lemurs and in the Ox and Sheep tribes.

Lower canines may be altogether wanting, though both in-
cisors and molars are present in each jaw, as is the case in

vii.] THE EXTERNAL SKELETON. 263

all Rodents, i.e. in all Rats. Squirrels, Hares, Marmots, and
Porcupines.

Canines may grow from a root essentially similar to that
of man's canine, or from a double fang, as in Galeopithecus
and the Mole. On the other hand, as has been said, they
may grow from permanent pulps.

Very rarely, e.g. in the Tanrec (Centetes), the points of the
lower canines are received into corresponding pits on the under
surface of the upper jaw.

27. The MOLAR TEETH of man present a medium character
when compared with those of the other members of his class.
Often we find molar teeth relatively larger, broader, more
complex, and more suited for grinding hard or tough vege-
table substances than in him.

We see, on the contrary, that they may often become
relatively smaller, narrower, and more trenchant, so as to
serve better for cutting and dividing flesh.

The maximum both of size and complexity is attained by
the grinders of the Asiatic Elephant, where the worn surface
presents a great number of narrow transverse ridges, the nature
of which will be explained under the head of Structure.

The greatest simplicity of form is seen in the Walrus,
where each molar is perfectly simple and flat ; and in the
blood-sucking Bat Desmodus, where each molar forms a
single wedge-shaped blade.

The total number of molars reaches its maximum in the
existing creation in the little Marsupial Myrmecobius, where
they are thirty-four (f ) in number. The smallest number is
met with in the Australian Rat Hydromys, where we find |.

28. The distinction between pre-molars and true molars
which exists in man, exists also in the great majority ot
animals belonging to his class.

The number of PRE-MOLARS is often more numerous than
in him, there being three even in the American Apes, and four
in the Dog.

In form the pre-molars are generally, as in man, smaller and
less complex than are the true molars ; but in some beasts, as
for example in the Horse, there is no difference in this respect.

The first pre-molars soon present a striking difference from
those of man. Thus, even in the old-world Apes, the upper
one has its external cusp more prolonged, and the lower one
has its front edge elongated and blade-like. These teeth may
assume the shape of canines, as in Hemicentetes and in the
Camel.

26 1 ELEMENTARY ANATOMY. [LESS.

29. The TRUE MOLARS are very rarely more numerous than
in man, who has the typical number of the great (Monodel-
phous) division of his class. In the Marsupials (Didelphous
Mammals), however, there are typically four above and four
below.

They may (even where pre-molars are present) be quite
wanting in the upper jaw, while there is but one on each side
(and that very small) of the lower jaw, as in the Cats.

30. The form of the human true molars, both above and
below, will readily serve to explain the more general modifi-
cations present in man's class.

The peculiar form of the upper molar — namely, four cusps,
one at each angle, with the before described oblique con-

d

FIG. 235. — GRINDING SURFACE OF A LEFT UPPER MOLAR.
a, antero-external cusp ; b, antero-internal cusp ; c, postero-external cusp ; d,

postero-internal cusp.

The oblique ridge is seen passing from the postero-external cusp to the antero-
internal one.

necting ridge — reappears not only in some of the Apes, but in

other beasts, as e.g. in the Hedgehog and its ally, Gymnura.

A " band " of dental substance (termed the cinguluni) may

surround the tooth, and even in man's own order (Primates)

30REX

FIG. 236. — GRINDING SURFACE OF A LEFT UPPER MOLAR.

a and b, anterior cusps ; c, postero-external cusp ; i, 2, 3, and 4, the four acces-
sory cusps of the external cingulum.

may develop small accessory cusps which project downwards
external to the two outer of the four principal cusps.

By further development the external cusps of the band may

THE EXTERNAL SKELETON,

265

equal in vertical extent the four normal cusps, as in the
Shrew-mice (Sorex).

A prominence may also be developed from the internal
part of the band. When this, together with all the other pro-
minences, is sharp-pointed (as in the Flying Lemur and the
Mole Urotrichus), it produces a maximum of complexity of
this special kind.

UROTRICHUS

GALEOPITHtCUa

FIG. 237. — GRINDING SURFACES OF UPPER MOLARS OF LEFT SIDE.

a, b, c, and d, principal cusps ; i, 2, 3, and 4, accessory cusps of external

cingulum.
The prominence of the internal cingulum appears below and between b and d.

Ridges may be developed to connect the two external
normal cusps with the adjacent cusps of the band, thus form-
ing two triangular prisms placed side by side, and each with
a flat side turned outwards and an angle inwards ; while some-
times but a single prominence may represent the coalesced
external normal pair of cusps, all of the cusps being drawn
out into sharp points suitable for cracking the hard coats
of insects, and constituting the typical insectivorous type of
molar as seen in the Mole and Bat, and also in the In-
sectivorous Marsupials, Pcrameles.

FIG. 238. — GRINDING SURFACE OF UPPER MOLAR OF LEFT SIDE.
a, b, and c, principal cusps ; i, 2, 3, and 4, cusps of cingulum.

A singular modification may be presented by the squeezing
together, as it were, from behind forwards of the tooth till it

266

ELEMENTARY ANATOMY.

[LESS.

forms but a single prism, and is therefore like half of one of
the teeth last described. Such a condition exists in Ceutetes^
Hernicentetes, and especially in Chrysochloris.

eHRYSOCHLORO

FIG. 239.— GRINDING SURFACES OF UPPER MOLARS OF LEFT SIDE.
a, b, and c, remnants of principal cusps.

Another kind of modification of the teeth is that by which
the typically carnivorous molar is arrived at. This is best
exemplified by the last pre-molar, which in the Dogs, Cats,
and their allies has been called the "sectorial" or " carnassiai "
tooth of the upper jaw.

FIG. 240.— DENTITION OF THE SABRE-TOOTHED TIGER (MacJiairodns).
(TYPICAL CARNIVOROUS DENTITION.)

Here (in the Cats) it consists almost entirely of three sharp,
strong, unequal cusps placed one behind the other on the outer
margin of the tooth, and connected together by trenchant
ridges, while inside the foremost cusp is a small, short,
and blunt accessory one. From a study of Marsupial teeth
it appears that the three outer cusps answer to the cusps of
the cingulum blended with the two outer principal cusps of
man, while the rudimentary internal cusp is the representative

VIL] THE EXTERNAL SKELETON, 267

of the front, inner cusp of man — the hind inner one having
disappeared.

In the true molars of the Dog this last cusp reappears, and
in addition we find a large prominence of the internal part
of the cingulum. In the Badger this latter structure is very
much developed, extending in a marked manner along the

FIG. 241.— GRINDING SURFACE OF FIRST RIGHT UPPER MOLAR TOOTH OF
A Hums fulgens.

i, 2, 3, and 4, cusps of the external cingulum ; ic, internal cingulum ; a, b, c, and
d, the four principal cusps.

whole inner margin of the tooth. In Ailurus we have a
good example of the maximum of complexity of the carni-
vorous type of molar. We find in the molar of this
animal four principal cusps, with three cusps belonging to
the external cingulum, and two belonging to the internal
cingulum.

Returning now to the type of structure exhibited by man's
upper molar, we may follow through another series of ani-
mals yet a new chain of modifications, resulting in a very
different kind of complication.

First, one transverse ridge may connect the two posterior

MACROxCELIDES
ft

FIG. 242. — GRINDING SURFACE OF LEFT UPPER MOLAR, showing the transverse
ridges (convex forwards) which connect together the anterior and posterior
pairs of principal cusps respectively ; a, b, c, and d, the four principal cusps.

cusps, and another may similarly unite the two anterior cusps.
We see this in the Kangaroo and Macroscelides.

Next, a ridge may run along the external margin of the
tooth (probably the cingulum) and connect together the two

268 ELEMENTARY ANATOMY, [LESS.

outer ends of these two transverse ridges. We find such a
structure in the Tapir.

In the Rhinoceros, Horse, and the Ruminants, the essential
structure of the Tapir's tooth persists, but is modified by
greater and greater obliquity of the transverse ridges and by
the development of supplementary processes running more
or less at right angles to the transverse ridges.

FIG. 243.— GRINDING SURFACE OK SECOND UPPER MOLAR OF A CAMEL,
showing the double crescentic folds which have their convexities turned inwards.

In the Ruminants the transverse ridges are so much in-
clined backwards and inwards, that they come to be almost
parallel with the external wall, thus forming the well-known
double crescents with a deep excavation between them seen
in the molars o f Sheep.

• In the Horse this excavation is filled up with " cement,"
and the pattern is complicated by the development of acces-
sory processes from the convex, or inner side of the trans-
verse ridges.

MRY.OCHLORW

FIG. 244.— GRINDING SURFACE FIG. 245. — GRINDING SURFACE
OF RIGHT LOWER MOLAR. OF RIGHT LOWER MOLAR.

Tn the lower jaw an analogous series of modifications has
similar results. In the insectivorous type these modifications
result in a pair of triangular prisms (produced by the con-
nection by ridges of the five cusps answering to the five cusps
developed in the lower molar of man) ending in sharp points,
as in the Mole ; or in a single prism, as in the Golden Mole,
Chrysochloris. The prisms are reversed in position as com-

VIL] THE EXTERNAL SKELETON. 269

pared with those of the upper jaw. In the carnivorous type
modification results in a " sectorial " tooth (here, i.e. in the
lower jaw, a true molar), which may, as in the Badger, have,
in addition to man's five cusps, an anterior one and three
small posterior ones ; or only the extra one in front, as in
the Dog ; or finally, as in the Cat, this tooth may attain
its typical perfection. It does so by becoming, as it were, a
cutting blade, consisting of but two sharp cusps connected
by trenchant ridges, and biting against those of the upper
sectorial tooth like one of the blades of a pair of scissors
against the other. The posterior cusp seems to answer to
the front outer cusp of man, and the anterior cusp to the
extra anterior one of the Dog.

In the type of dentition culminating in the Horse, we start
again from the transverse ridges of the Tapir ; we find double
crescents, as in the upper jaw, but with the direction of their
convexities reversed, in the Ox and Sheep tribe ; while in the
Horse we find a similar reversal, and the extra processes
springing from the concave aspect of the crescents.

Other and different complexities of form, as in the Ele-
phant, will come more conveniently under the head of
" Structure."

31. Below Mammals we meet with great varieties of form.
Thus, in certain Fishes (e.g. the Chetodons) the teeth are like
slender bristles. In the Efts the slender denticles terminate
in two points, and in three in the Fish Platax.

In Lizards the teeth sometimes have serrated edges, as
in the Iguana; sometimes they are rounded, blunt, and
crushing.

In Fishes we may meet with every variety of shape, and
sometimes, amongst the Sharks and Rays, a very great
variety in the same mouth.

Teeth are sometimes excessively sharp and pointed, as in
Lamna and Odontaspis ; sometimes they are furnished with
singular processes, as in Goniadiis.

Sometimes, as in the Australian Shark Cestracion, the
teeth in the front of the mouth are sharp and pointed, while
as we pass backwards they become flattened till they form a
sort of pavement to the jaws.

It is the Rays, however, which present us with the most
wonderful pavement. In some of these Fishes (e.g. in
Myliobatis) the teeth are placed in close contiguity, like the
pieces of a mosaic, and, wrhat is most remarkable, long and
narrow teeth are placed in the middle line so as to cross

270

ELEMENTARY ANATOMY.

[LESS.

the mandibular symphysis, or line of junction of the two
jaws.

FIG. 246. — UPPER AND LOWER JAWS (SEEN FROM BEHIND) OF AN EAGLE RAY
(Afy/u£afis)).ah<ywva% the elongated median dental plates and the hexagonal
lateral plates.

One of the most singular modifications in the form of a
tooth is presented by the poison-fangs of Serpents.

It is a common thing for a tooth to exhibit a vertical groove :
we see it even in the canines of Apes ; and in some extinct
forms (e.g. Ichthyosaurus] the teeth were furnished with a
number of such grooves.

In poisonous Serpents, however—^, the Rattlesnake — one
large tooth on each side of the upper jaw has an exceedingly
deep, vertical, anterior groove, the margins of which groove
bend over till they meet and thus form a canal which opens

FIG. 247.— SIDE VIEW OF THE SKULL OF A RATTLESNAKE (Crotalus), showing
the large poison-fang implanted in the maxilla — in front of the letters mx.

a, articular hone of lower jaw ; bo, basi-occipital ; d, dentary; f, frontal ;f,
pre-frontal ; me, median ethmoid ; mx, maxilla ; 0, pro-otic ; /, parietal ;' pa,
para-sphenoid ; //, pterygoid ; px, pre-maxilla ; qn, quadrate ; qs, squamosal.

widely above, but by a very small aperture below. It is down
this channel that the poison is poured, the tube leading from
the poison-gland opening into the upper part of the canal.

vii.] THE EXTERNAL SKELETON. 271

32. The SUCCESSION OF THE TEETH which we meet with
in man is characteristic of most animals of his class, but
not all. In many, as in the Guinea-pig, the so-called milk-

FIG. 248.— VERTICAL, LONGITUDINAL SECTION OF THE POISON-FANG OF A
SERPENT. {After Owen.. }

gt deep groove ; o, its lower termination, which affords exit to the poison ;
p, pulp-cavity.

teeth are shed even before birth. On the other hand, they
may be retained for a relatively longer period than they are

FIG 249.— MAGNIFIED TRANSVERSE SECTION OF A SERPENT'S POISON-FANG.
(After Owen. )

Z, groove round which the substance of the tooth (containing /, the pulp-cavity)
is bent ; j, the point where the sides of the tooth meet and convert the
"groove" into what is practically a central cavity.

in man. Thus, in the Ungulates they persist till the adult
form is reached, and, at least in some, till after the bony
elements of the limb-girdles have completely coalesced.

Sometimes teeth are formed which are not destined to
cut the gum, and are re-absorbed without ever becoming
visible. This is the case with the upper incisor teeth of
Ruminants. In the Whalebone Whales, before the develop-
ment of baleen, minute teeth are developed in the dental
groove, which teeth are ultimately absorbed while the- groove
itself becomes obliterated.

In the Marsupial Mammals but a single tooth is provided
with a vertical predecessor. This tooth is the one which
would be the fourth pre-molar were the normal number de-
veloped, and it thus serves to define the last of the pre-molars.

272 ELEMENTARY ANATOMY. [LESS.

We see by this, that there may be teeth with no vertical pre-
decessors in front of others which have such predecessors.

Milk-teeth may be entirely absent in some Mammals, as is
the case in the Porpoises and Dolphins and most Edentates.

The canine teeth, as in the highest Apes, may appear after
the true molars are in place. Generally the last deciduous
molar resembles, not its vertical successor, but the first true
molar, as has been stated with regard to man.

A mode of succession may exist in man's class which
renders it difficult to define the essential nature of the anterior
molars. Such is the case in the Elephant, where six teeth
are successively developed, the hindmost ones being much
more complex than the anterior ones. Each rotates into its
position in such a way that one portion of it is worn before
the last part is in place, and ultimately the whole of the jaw
is occupied by a single tooth. The Elephant has, however,
undoubtedly two upper deciduous incisors on each side, and
three molars ought in all probability to be reckoned as
deciduous ones on each side of each jaw.

Below Mammals we may find quite other conditions of
replacement and succession ; but though of course there is
never a "milk" set, yet even in some Fishes there is a
vertical succession like that occurring in Mammals. This,
for example, is the case in the teeth of the front of the mouth
of the Fish Sargus — which teeth, moreover, bear a singular
resemblance to the incisors of man.

In the Crocodiles, as the teeth wear out or become lost,
they are replaced by others, formed on the inner side of
those which they are destined to succeed. Each new tooth
causes, by its development, an absorption of the inner wall
of an old tooth, and, entering at this aperture, it becomes
enclosed within the central cavity of the latter, so that when
the old tooth is removed the new one is found rising up
in its place. This process appears to go on indefinitely
through the whole of life in these creatures.

A far more abundant supply of new teeth and ready re-
placement of old ones are found in the Sharks. Whole rows
of teeth, getting ready for use, lie folded back one behind the
other all round the jaws. As the old teeth are lost, those
immediately behind go forward, become erect, and take the
vacant places.

The most singular succession of all is found in the Parrot
Fishes (Scams). Parrot Fishes browse upon those truly
sensitive plants the arborescent polyps, and their jaws are

vii.] THE EXTERNAL SKELETON, 273

singularly dense and hard, well suited for breaking up their
stony prey. The jaws of the fish are shaped like a parrot's
beak (whence its name) ; but it is a beak which singularly
and interestingly differs in structure from that of a bird.

FIG. 250. — VERTICAL SECTION OF THE LOWER JAW OF A SHARK (Lamna),
showing the uppermost erect tooth with the others below in various stages,
each ready to come successively into place when its predecessor is removed.
(After Owen.)

A bird's beak is, as we have seen, a modification of the
epidermis. This fish-beak, however, is a truly enderonic
structure, and calcareous, not horny. It is, in fact, formed
of an immense number of small elongated teeth, which,
closely packed side by side, are attached by their proximal
ends to the surface of both the upper and lower beak-shaped
jaws. As these jaws with the annexed denticles are worn
away by use at their margins, both are replaced by a com-
mon down-growth of bone and teeth in the upper jaw, and by
a common upgrowth of bone and teeth in the lower one.

FIG. 251.— Sit>E VIEW OF THE PRE-MAXILLA OF A PARROT-FISH (Sc<irus\
showing the closely apposed denticles which encrust it. (After Owen.)

33. The STRUCTURE of man's teeth supplies us with a
key by which we may understand that of Vertebrates gene-
rally ; nor is there any real increase of complexity as to the
number of the constituent materials, though the dentine may

T

274 ELEMENTARY ANATOMY. [LESS.

be of various degrees of vascularity.1 On the other hand,
the structure of the teeth may be much simpler than in
man in his own class, as, e.g., in the Sloths and Armadillos,
where the teeth are formed of dentine and cement only,
being destitute of enamel.

The best example of great complexity of structure of a
Mammalian tooth is that exhibited by one of the molars of
the Indian Elephant.

Such a tooth consists of a number of narrow transverse
plates of dentine, each plate being capped with enamel, and
the interspaces between the plates being filled up with a
quantity of cement, as if this material had been poured round
and between the plates, and had there solidified. As the tooth
wears, it assumes the transversely ridged appearance before
noticed, which is an effect of the different densities of the
component tissues.

Thus the enamel, being harder than either the dentine or
the cement, stands up a little along each front and hind

FIG. 252. — GRINDING SURFACE OF LOWER MOLAR OF INDIAN ELEPHANT.

(After Omen.)

d, d, two of the vertical plates of "dentine" (each surrounded by "enamel"),
which are connected together by the "cement."

margin of each transverse plate ; and in this way, proceeding
from either end of the tooth along its grinding surface, we
successively meet with layers thus arranged : — Cement,
enamel, dentine, enamel, cement, enamel, dentine, enamel,
cement, &c.

1 7.1?. may be more or less permeated by canals for nutritive fluid, which are
larger than the dentinal tubes existing in man.

THE EXTERNAL SKELETON.

A similar but less extreme complexity of structure cha-
racterizes the last molar of the largest 'animal of the Rat
order, namely, the so-called River-hog of the La Plata —
Hydrochcerus.

Foldings of the dentine, bounded by enamel and with
cement filling the valleys and interspaces, produce such com-
plex patterns as we find in the Horse and Sheep already
described, and also in the Porcupine and Beaver.

Molar teeth may grow (like those of man) from roots which
soon become calcified, so that no more growth can take place ;
and this is the more common condition of the Mammalian
molars.

They may have very long roots capable of a prolonged but
still limited increase, as in the Horse.

They may spring from persistent roots growing during the
whole of life, as in the Porcupine.

The pulp-cavity may be curiously disposed or divided.
Thus in poisonous Serpents it extends round the greater part
of the poison canal, which, it need hardly be said, is really
outside the tooth. It may be divided transversely, as in the
incisor of the Horse (Fig. 230), where one branch ascends in
front of the depression (or " mark "), and the other branch
ascends behind it. It may
be divided antero- pos-
teriorly, as in notched in-
cisors, and especially in the
comb-like ones of the Fly-
ing Lemur, where (Fig.
228) a branch of the pulp-
cavity ascends each pro-
cess of the "comb."

But the most remark-
able form of the pulp-
cavity is that which ex-
isted in those extinct Ba-
trachians the Labyrintho-
dons. In those creatures,
numerous vertical grooves
on the surface penetrate
with many inflections
deeply into the substance

of the teeth, and similar narrow processes of the pulp-
cavity interdigitate, also with many inflections, between the
inwardly extending grooves. With this structure a transverse
T 2

253.— ONE QTARTER OF A MUCH
ENLARGED HORIZONTAL SECTION OF
THE TOOTH OF A LABYRINTHODON.

276 ELEMENTARY ANATOMY. [LESS.

section of the tooth presents such a complex series of radiat-
ing contorted lines as to have obtained for the animals their
name, and for the kind of tooth the epithet Labyrinthic.

A third kind of complex tooth is presented by one Mammal
only, though certain Fishes present a more or less similar
structure. The animal referred to
is the Cape Ant-eater (Orycteropus\
which possesses the only really com-
pound teeth found amongst Beasts.
Each tooth is cylindrical in shape,
and apparently simple, but when
cut transversely exhibits a number
FIG. 254.-THE AARPVARK, of minute apertures, as does a cut
OR CAPE ANT-EATER. cane. Each of these apertures is the

(prycteropus). ,orifice of a pulp-cavity cut across,

and from each of these cavities

minute dentinal tubuli radiate in every direction, so that
the tooth is really made up of a number of very elongated
and slender denticles anchylosed together into one solid
mass.

FIG. 255. — TRANSVERSE SECTION OF A TOOTH OF Orycteropus, showing the
numerous denticles, each with its pulp-cavity.

True teeth do not co-exist with a horny beak in any
known Mammal. They did so, however, in some of those
extinct flying Reptiles the Pterosauria, and also the extinct
Reptiles Dicynodon had a tooth which grew from a perma-
nent pulp on each side of the head, though tlie jaws seem to
have been furnished with a horny beak.

34. Enderonic calcifications which can hardly be called
teeth may occur further back in the alimentary canal than
anything we have yet met with. In a little African Serpent,
Rachiodon^ certain bony processes which depend from the
ventral surface of the backbone penetrate the gullet and are
tipped with a kind of enamel. These cesophageal * teeth per-

1 (Esophagus is the name of the passage which leads from the "back of the
mouth (or pharynx) to the stomach.

VII.]

THE EXTERNAL SKELETON.

277

form a peculiar function. The animal lives on eggs, but is
devoid of lips, so that if it broke the eggs with its mouth
their contents would be lost. It has then but rudimentary
teeth in the ordinary place, but swallowing the eggs whole it
fractures them with these cesophageal teeth, and thus loses
none of the nutritive substance.

35. Structures which are quite like teeth — and indeed much
resemble those of Orycteropus — project from either side of
the very elongated rostrum which extends from the front of
the head of the Saw-fish. These, then,

are teeth quite external in position —
enderonic dermal calcifications.

This, however, is not the only in-
stance in which tooth-like structures
appear on the external surface of the
body. The Sharks and Rays, for ex-
ample, have dermal calcifications
(springing from a bony base) which
consist of a substance exceedingly
resembling dentine, and moreover
coated with a sort of enamel. These
may be quite small and thickly dis-
tributed all over the body. A skin so
furnished is called shagreen. They
may however be larger, fewer, and
placed far apart, and as it were en-
graved with elegant patterns on the
exposed surface, often forming power-
fully defensive spines, as in some
Sharks.

Other Fishes, as the Bony Pikes
{Lepidosteus)^ have a close - fitting
armour of solid, enamelled, bony scutes,
which join together by means of a peg
and socket articulation.

Fishes more familiar to us, but belonging to the same
Ganoid group, e.g. the Sturgeon, are also furnished with bony
scutes arranged in rows along the body.

The spines of some Teleostei present us with a peculiar kind
of articulation — a shackle-joint (referred to in Lesson II.),
the base of a spine forming a ring which passes through
another ring developed from an ossicle supporting it (fig. 257).

36. The SCALES OF ORDINARY FISHES (as the Perch) are
hard structures embedded in the deep layer, or dermis, and

FIG. 256. — UNDER SUR-
FACKOF HEAD OF A SAW-
FISH (Pristis), showing
the large lateral teeth on
the prolonged rostrum.

278

ELEMENTARY ANATOMY.

[LESS.

so are quite unlike the scales of Reptiles. Indeed, the
" scales" of Fishes should rather be termed "scutes."

They have been divided into two groups or kinds — those
in which the free margin is smooth and which are termed

FIG. 257. — A SHACKLE-JOINT.

Articulation of a large spine with a bony plate (placed below) of the skin of a
Siluroid Fish.

Cycloid* and those in which the free margin is toothed and
which are named Ctenoid?

37. Besides scales, spines, and plates, Fishes have OTHER
DERMAL STRUCTURES, bony or gristly, constantly present
within the dermis. One kind consists of filamentary pro-
cesses, which may be either horny or calcareous, and which

FIG. 258. — DORSAL FIN OF AN ACAN-
THOPTERYGIAN FISH, showing the
firm, spiny fin-rays, f, supported on
the inter-spinous bones, i.

FIG. 259. — DORSAL FIN OF A MALA-
COPTERYGIAN FISH, showing the soft
and sub-divided fin-rays, f, sup-
ported on the inter-spinous bones, i.

support the skin of the fins, whether those of the back, belly,
and tail, or those of the limbs. Such structures are termed
fin-rays. Another kind consists of the parts (bony or gristlv)
which support the fin-rays, and which are termed the "i?iter-
spinous" bones or cartilages. These may be seen in the
common Sole in the form of small bones extending along
each margin of the body beyond the ends of the neura-
pophysial and hypapophysial processes which respectively
project in opposite directions from the centre of the backbone.

1 From KI'IK\O£, a circle, and ei'5<>r, form.

2 From KTCC£, a comb, and eido£.

VII.]

THE EXTERNAL SKELETON.

279

38. Lastly may be noticed certain exceptional though not
unfamiliar structures which come perhaps more conveniently
under the head of the exo-skeleton than elsewhere — namely,
the BONY HORNS OF UNGULATES. In the Oxen, Goats, and
their allies, horns exist on the head as bony cores persisting
throughout life, and supporting the hollow horns before
noticed under the head of " Epidermal Structures." In the
Giraffe we meet with three bony prominences which arise as
distinct ossifications, and only later anchylose with the skull.
These are the pair of short " horns " and the median pro-
minence in front of them. They are without doubt exo-
skeletal structures. In Deer, however, we meet with bony
antlers which are shed annually and are destitute of any
horny covering. These may exist in both sexes, as in the
Reindeer, but generally in the males only. They arise as

FIG. 260. — SERIES OF ANTI.ERS OF THE COMMON STAG, showing (from No. i to
No. 8) the gradual increase (with age) of size and complexity in the antlers
developed.

No. i, the antlers which fall in the second year ; 6, antler of a young "stag of
ten ;" 7 and 8, antlers of seven years old and upwards.

soft, highly vascular prominences, and when full grown
become hardened by calcareous deposit In some months
the investing skin dries up and is rubbed away, and the horn
itself falls off after the breeding season, leaving a stump,
whence it shoots again in the following year.

Antlers, as a rule, are branched — more so as the individual
is older till maturity be attained.

280 ELEMENTARY ANATOMY. [LESS.

Some Deer have enormous antlers, weighing as much as
seventy pounds, and are formed at the rate of one pound a
day.

Great as must be the strain on the system from such a
demand, it must yet be exceeded by the effects on Birds of
the production of an entire new plumage when moulting.

The antlers, like the bony cores of the hollow-horned rumi-
nants, are rather outgrowths from the skull than skin struc-
tures. Yet in the Giraffe we find short bony horns formed
from ossifications independent of the skull, with which they
unite at a later period only.

Such are the principal structures which may be described
under the head of exo-skeleton. Other appendages of the
skin which are not skeletal, but excretory (as the milk
glands, scent glands), will be noticed in the Twelfth Lesson
as coming within the group of "excretory structures."

VIIL] THE MUSCLES. 281

LESSON VIII.

THE MUSCLES.

1. The MUSCLES of man are his "flesh," and it is the
muscles of cattle which are eaten as " the lean " of " meat."

These muscles are fleshy masses of different sizes and
shapes, separated from each other by membranes termed
aponenroses. Aponeuroses are included amongst those
fibrous and soft parts of the skeleton (referred to in Lesson
II.) which extend outwards from the bones of the endo-
skeleton to the skin, or exo-skeleton.

The nature of muscular tissue has already been sufficiently
described in the " Elementary Physiology," Lesson XII.
§ 15 ; the action of muscles in Lesson VII. § 4 ; their fixed
points, §§ 5 and 6; the kinds of movement they give rise
to, § 17; and their modes of attachment in § 19.

2. That end of a muscle which is nearest to the central
axis of the whole body, or to the root, or else to the axis of
the limb of which it forms part, is generally called its ORIGIN,
and its proximal end. The opposite extremity is generally
called its INSERTION, and its distal end.

Muscles are very often inserted into bones by means of
tendons, and then frequently, when such muscles are strong,
part of the bone extends out, as it were, a little way into the
substance of the tendons. Hence arise many such tuberosi-
ties, spinous processes, &c., as we have already made ac-
quaintance with. All the processes of the backbone are so
connected with tendons of muscles.

3. Muscles acting on bony levers produce definite MO-
TIONS, in consequence of which certain epithets are applied
to such muscles.

Thus, when two bones are united by a hinge-joint, muscles
which by their contraction tend to make the angle formed by

282 ELEMENTARY ANATOMY. [LESS.

such bones acute are termed flexors. Those, on the contrary,
which tend to open out such an angle are termed extensors.

Some muscles attached to a long bone which is relatively
fixed at one end, tend to make it describe the superficies of a
cone, or a movement of circumduction. Such muscles are
termed rotators.

Some muscles move a bone away from a given axis, and
are therefore termed abductors. Others tend to bring it
towards such an axis, and such are called adductors. The
epithets "protractors" "retractors" "elevators" and " de-
pressors" (terms which require no explanation), are also some-
times made use of.

There cannot, however, be any rational classification of
muscles according to the functions they execute, because
such functions often vary in different animals with regard to
the very same muscle.

4. A sound CLASSIFICATION of muscles must be morpho-
logical, and may be made to follow that classification of parts
which has been already given with respect to the skeleton, or
may be constructed independently. An independent general
consideration of the muscular system, however (whether ac-
cording to its simplest or most complex condition), will come
most fitly at the end of this lesson.

Arranging the muscles (in the first place) according to the
skeleton, we have —

(a) Muscles of the exo-skeleton, and

(&} Muscles of the endo-skeleton.

To this it will be convenient to add a third category,
namely —

(c] Muscles of the viscera.

The exo-skeletal system of muscles may consist of smooth
or of striped fibres.1

Such are the small muscles which go from the deep layer
of the skin to the hair-sacs, and by their contraction make
the hair " stand on end." These muscles become large and
important in Birds, and are in them striped instead of un-
striped as in Man.

Other muscles, to be hereafter noted, belong to this cate-
gory, such as the Platysma Myoides, and certain muscles
of the face of man.

The endo-skeletal system is naturally divisible, like the
skeleton itself, into an axial and appendicular portion. These

1 For an account of this difference of structure in muscular fibres, see Lesson
XII. of " Elementary Physiology/' § 15.

VIIL] THE MUSCLES. 283

general considerations, however, will be more profitable after
a review of the muscles as they exist in man, and of the
more interesting and significant deviations from his structure
which may be found in other animals.

The viscera-skeletal system of muscles consists of muscular
fibres placed on the walls of the alimentary canal, and in a
variety of tubes and organs (such as the heart, bladder, &c.),
to be hereafter noticed in describing such parts.

5. It may be useful and convenient in this book to adopt
the order usually followed in describing man's anatomy. The
MUSCLES OF THE HEAD AND NECK will therefore come
first.

FIG. 261. — SUPERFICIAL MUSCLES OF THE HEAD: RIGHT SIDE.

i, anterior part of occipito-frontalis ; i', its posterior portion ; 2, orbicularis palpe-
brarum ; 3, levator labii superioris et alae nasi ; 4, levator labii superions ;
5, zygomaticus minor ; 6, zygomaticus major ; 7, depressor anguli oris ; 8,
platysma myoides ; 9, masseter ; 10, orbicularis oris; n, anterior auricular;
12, attollens auriculam, or superior auricular; 13, retrahentes auriculam ; 14,
buccinator; 15, trapezius ; 16, sterno-mastoid ; 17, splenius ; 18, transversalis
nasi ; 19, levator menti.

Occipito-frontalis is the name applied to a thin flat muscle,
divided into two fleshy parts, or bellies. One of these is
placed in the occiput and another over the orbits, and the two
are connected by a wide aponeurosis which covers the top of
the skull and passes immediately beneath the skin.

Three little muscles, termed respectively the attollens

284 ELEMENTARY ANATOMY. [LESS.

auriculam, the retrahentes auriculam, and the zygomato-
auricularis, arise from above, behind, and in front of the ear,
to the external part of which they are attached. In rare
cases a man is able to move his ear by the contraction of
these muscles.

The orbicularis palpebrarum is a muscle which surrounds
the eye beneath the skin, and is not attached to any bone
except at the inner margin of the orbit. By its contraction it
closes the eyelids.

A little muscle, the levator palpebrtz, takes origin deep in the
orbit (above the optic foramen), and is inserted into the upper
eyelid, which it raises, No analogous muscle depresses the
lower eyelid.

Other muscles of man which are connected with the lips
or nose are :— I. Pyramidalis nasi. 2. Levator labii supe-
rioris alceque nasi. 3. Compressor nan's. 4. Depressor
alee nasi. 5. Levator proprius alee nasi. 6. Levator labii
superioris (which takes origin from the maxilla and malar).
7. Levator anguli oris (arising below the infra-orbital fora-
men). 8. Zygomaticus minor (going from the malar to join
No. 6). 9. Zygomaticus major (going from the malar to the
angle of the mouth). 10. Depressor anguli oris (springing
from the mandible), n. Depressor labii inferioris (placed
near the front of the lower jaw.

FIG. 262.— DEEPER MUSCLES OF THE RIGHT SILE OF THE HEAD.
i, temporal ; 2, corrugator supercilii ; 3, transversalis nasi ; 4, depressor alse nasi ;
t;, levator anguli oris ; 6, buccinator, traversed towards its hinder part by the
duct of the parotid gland ; 7, depressor labii inferioris ; 8, levator menti; 9,
masseter, cut short near its insertion ; 10, external lateral ligament.

The buccinator is a thin flat muscle extending between the
alveolar margins of the jaws on each side.

VIII.]

THE MUSCLES,

285

The orbicularis oris is a muscle surrounding the aperture
of the mouth.

The masseter passes from the malar down to the angle of
the lower jaw.

The temporalis occupies the side of the skull within the
zygoma, and is inserted into the coronoid process of the
mandible.

^}\Q pterygoideus interims passes from the pterygoid fossa
to the inner surface of the mandible just above its angle.

The pterygoideus externus arises from the ali-sphenoid
(including the part called " external pterygoid process "), and
is inserted into the neck of the condyle of the lower jaw and
into the inter-articular fibre-cartilage.

Inside the bony orbit, we have four slender, long, straight
muscles (or recti}, and two oblique muscles, all inserted into
the sclerotic, or outer coat of the globe of the eye.

InfR.

C.h.

FIG. 263 — THH MUSCLES OF THE EYEBALL, viewed from above and from the
outer side.

S.R., the superior rectus ; Inf.R. the inferior rectus ; E.R., the external rectus ;
fn.R., the internal rectus ; S.Ob., the superior oblique; Inf. Ob., the inferior
oblique : Ch., the chiasma of the optic nerves (II. ) ; ///., the third nerve,
which supplies all the muscles except the superior oblique and the external

The four recti all arise at the bottom of the orbit, about the
optic foramen, and are respectively inserted into the eyeball
above, within, below, and without, whence they are termed
superior, interims, inferior, and externus.

The obliquus superior (a slender muscle, like each of the
recti) also arises near the optic foramen. At the inner margin

286 ELEMENTARY ANATOMY. [LESS.

of the orbit it passes through a fibro-cartilaginous ring or
pulley, which changes the direction of the tendon, as, after
traversing it, the tendon returns backwards to be inserted
between the upper and external recti muscles.

The obliquus inferior has no pulley, and is the only short
muscle in the orbit. It springs from the orbital plate of the
maxilla near the lachrymal groove, and, passing backwards
between the floor of the orbit and the globe of the eye, is
inserted into the postero-external aspect of the latter.

The platysma myoides is a thin muscle placed imme-
diately beneath the skin of the neck, and extending from the
mandible downwards to the chest and shoulders.

The sterno-cleido mastoid is a long stout muscular strap,
double at its lower end and arising partly from the clavicle
and partly from the sternum, and inserted into the mastoid
process.

The digastric is a muscle with two fleshy bellies, with a
median tendon. Arising from the mastoid, it is inserted
inside the mandible close to the symphysis. The median
tendon is connected with the os hyoides.

FIG. 264. — MUSCLES OF THE RIGHT SIDE OF THE TONGUE.

i, stylo-glossus ; 2, stylo-hyoicl ; 3, stylo-pharyngeus ; 4, hyo-glossus ; 5, genio-
hyoid ; 6, genio-glossus ; 7, lingualis.

The stylo-hyoid, stylo-glossus, and stylo-pharyngeus are three
slender muscles all springing from the styloid process, and
inserted, the first into the corniculum of the hyoid, the second
into the base of the tongue, and the third into the thyroid
cartilage of the larynx.1

The mylo-hyoidis a flat muscle, and passes from inside the
mandible to the body of the hyoid. It unites with its fellow

1 For a description of the larynx see Lesson XII.

viii.] THE MUSCLES. 287

of the opposite side (in front in the middle line) and the
two together form the muscular floor of the mouth.

The genio-hyoid is narrow, and goes from the hyoid to the
mandible inside the symphysis.

The hyoglossus is a flat muscle, passing from the cornua
of the hyoid upwards to the side of the tongue.

The genio-hyoglossus is a flat, triangular fasciculus, arising
inside the symphysis of the mandible, and inserted in a
radiating manner from beneath the front of the tongue back-
wards to the body of the hyoid.

FIG. 265. — MUSCLES OF THE FRONT AND RIGHT SIDE OF THE NECK.

i, anterior belly of digastric ; 2, its posterior belly ; 3, mylo-hyoid ; 4, stylo-hyoid ;
5, stylo-glossus ; 6, stylo-pharyngeus ; 7, sterno-hyoid ; 8, omo-hyoid ; 9,
thyro-hyoid; 10, sterno-thyroid ; ir, anterior scalenus ; 12, middle scalenus —
the posterior scalenus is seen immediately behind it arising from the second
rib ; 13, levator anguli scapulae.

The sterno-hyoid muscle is a long band which springs from
within the sternum or clavicle, and goes to the basi-hyoid.

The sterno-thyroid (broader and shorter than the pre-
ceding) springs from within the sternum and goes to the
thyroid cartilage of the larynx.

The thyro-hyoid appears like a continuation of the last-
noticed muscle, and goes from the thyroid cartilage to the
great cornua.

288 ELEMENTARY ANATOMY. [LESS.

The omo-hyoid is a long digastric muscle which takes
origin from the hyoid and is inserted into the upper margin
of the scapula.

The anterior scalenus lies deep at the side of the neck.
It springs from the parapophyses of the cervical vertebrae
(third to sixth), and is inserted into the first rib.

The middle scalenus springs from the diapophyses of the
cervical vertebrae, and also goes to the first rib.

The posterior scalenus arises from the diapophyses of the
last two or three cervical vertebrae, and is inserted into the
second rib.

The rcctns capitis anticus major arises from the parapo~
physes of the (third to sixth) cervical vertebrae, and is in-
serted into the basi-occipital.

The rectus capitis anticus minor springs from the side of
the atlas, and also goes to the basi-occipital.

The rectus lateralis is a short muscle interposed between
the transverse process of the atlas and the jugular process of
the occipital bone.

The longus colli is attached to the front of the spine, con-
necting the centra and transverse processes of the vertebrae
from the atlas down to the third dorsal.

FIG. 266.— MUSCLES OF THE RIGHT HALF OF THE PHARYNX, seen from behind.

4, sterno-thyroid cut near its insertion and raised by a hook ; 2, median raphe,
where the pharyngeal constrictor muscles of the right and left sides meet
together behind ; 3, stylo-pharyngeus ; 4, superior constrictor of the pharynx ;
5, middle Constrictor ; 6, inferior constrictor; 7, buccinator; 8, Cut end of the
Stylo-glossus ; 9, cut end of the hyoglossus ; 10, genio-hyoid.

The constrictors of the pharynx are muscles which enclose
the alimentary canal in the region of the throat : they are
three in number (inferior, middle, and superior}, and spring

viii.] THE MUSCLES. 289

from the sides of the larynx, from the cornua and cornicula
of the hyoid, from the lower jaw and pterygoids, and meet
together in the middle line behind the pharynx, where, at
their summit, they are attached to the basi-occipital.

The soft palate is formed with the help of five pairs of
small muscles : — (i) the levator palati, descending from the
petrous bone to meet its fellow of the opposite side, and also
(2) the closely applied pair (miscalled azygos uvula) which
descend vertically from the palate; (3) the circumfleocus palati,
going from the pterygoid to the palate ; (4) the palato-glossus,
descending from the uvula outwards to the wall of the throat ;
and (5) \hzpalato-pharyngeuSy arching downwards and back-
wards from the uvula so as to leave a gap between it and the
palato-glossus.

6. The MUSCLES OF THE BACK are arranged in successive
layers. Beginning with the most superficial of these, we find
a large sheet of muscle called the trapezius. This arises
from the occiput, the dorsal spinous processes, and the
ligamentum nuchae,1 and is inserted into the spine of the
scapula, the acrdmion, and the outer third of the clavicle.

The latissimus dorsi is a very large muscular sheet which
arises from the spines of the sacral, lumbar, and six lowest
dorsal vertebras, and also from the ilium and some ribs. It
converges to a narrow fasciculus, which is inserted, by a
tendon, into the bicipital groove of the humerus.

The rhomboideus goes from the spines of the lower cervi-
cal and upper dorsal vertebrae to the vertebral border of the
scapula.

The levator anguli scapula arises from the diapophyses
of the first three or four cervical vertebrae, and goes to the
postero-superior angle of the scapula.

The serratus posticus superior is a flat thin muscle which
springs by aponeurosis from the spinous process of the two
or three upper dorsal vertebrae and from the ligamentum
nuchae, and is inserted by fleshy digitations into the second,
third, and fourth ribs.

The serratus posticus inferior similarly arises from the
spines of the last two dorsal and three upper lumbar vertebrae,
and is inserted (also by fleshy digitations) into the last four
ribs.

1 This structure consists of a band of tendinous fibres extending backwards
from the cervical spinous processes, so as to form a partition between the neck-
muscles of the two sides. It is attached above to the occiput, below to the
Spine of the seventh cervical vertebra.

U

290

ELEMENTARY ANATOMY.

[LESS.

The splenius is placed obliquely in the neck, extending
from the spines of dorsal and cervical vertebrae to the trans-
verse processes of the upper cervical vertebras and to the
mastoid process : the latter insertion defines the splenius
capitis ; the former the splenius colli.

Erector spines. Under this title is included a very large
and complex muscular mass occupying the groove which
exists on each side of the dorsum of the skeleton, between

FIG. 267. — MUSCLES OF THE BACK.

On the left side the superficial muscles are shown. On the right side not only
are these removed, but the serratus posticus inferior and abdominal muscles
also, and the vertebral aponeurosis is cut short (below 12) to show the deepest
muscles of the back.

' i, trapezius ; 2, latissimus dorsi ; 3, infra-spinatus and teres ; 4, deltoid — raised
on the right side to show the infra-spinatus, (5) teres major, and (6) teres
minor ; 7, sterno-mastoid ; 8, splenius ; 9, levator anguli scapulae ; iq, rhom-
boideus ; n, external oblique; 12, vertebral aponeurosis (lying in the same
plane with the serrati postici) ; 13, spinalis dorsi; 14, longissimus dorsi ; 15,
sacro-lumbalis.

the vertebral spinous processes and the most backwardly
projecting parts of the ribs. In anthropotomy it is divided
into a number of parts which here it will not be necessary to

viii.] THE MUSCLES. 291

describe. Its main division will suffice, and this is twofold —
one part being nearer to, the other further from, the vertebral
spines ; and each extending from a common origin in the
sacral region upwards to the neck and head, where the parts
assume distinct designations : —

Sacro-lumbalis. This name designates that part of the
erector spinae which is the more externally placed and attached
to the ribs. Its uppermost continuation (which goes to the
transverse processes of three or four cervical vertebrae) is
called the cermcalis ascendens, or sometimes desccndens.

Longissimus dor si is the term applied to the inner part of
the erector spinae ; it is attached to the transverse pro-
cesses, the metapophyses, and the ribs within their angles.
Its summit (going to the transverse processes of four or five
cervical vertebras) is called the tr answer satis cervicis.

Other minor subdivisions of the erector spinae bear the
names spinalis, semi- spinalis, imdtifidiis spines, rotatores
spines, and interspinales, the details of which will be found
in ordinary works on Anthropotomy.

The complexus is a thick muscle going obliquely to the
occiput from the diapophyses of the three uppermost dorsal
and four lowermost cervical vertebras. A small muscle pass-
ing from the spine of the axis to the occiput is called the
rectus capitis posticus major, while the rectus capitis posticiis
minor (inserted below the last) springs from the neural arch
of the atlas. The obliqui capitis pass respectively, the inferior
from the spine of the axis to the transverse processes of the
atlas — the superior from the latter to behind the mastoid
processes.

Inter-transversales connect the transverse processes of ad-
jacent vertebrae.

7. OF MUSCLES OF THE UPPER EXTREMITY WC have in

front a large pectoralis major, the fibres of which, arising
from the clavicle, sternum, and ribs, converge to be inserted
into the bicipital groove of the humerus. We have also a
pectoralis minor, which goes from the third, fourth, and fifth
ribs to the coracoid process.

The subclavius is a small muscle placed as its name im-
plies, and extending from the cartilage of the first rib to the
under surface of the clavicle.

A muscle called the serrahis magnus is really but an in-
ferior portion of the levator anguli scapulae before described.
It arises by pointed digitations from eight ribs, and is inserted
into the base (or vertebral border) of the scapula.
U 2

292

ELEMENTAR Y ANA TO MY.

[LESS.

The deltoid is triangular in outline, and covers over the
shoulder-joint. Springing from the clavicle and the spine of
the scapula, it is inserted into the rough prominence on the
outer side of the shaft of the humerus.

Supra-spinatus. This name is given to the muscle which
occupies the supra-spinous fossa of the scapula. It is in-
serted into the greater tuberosity of the humerus.

—0

FIG. 268.— ANTERIOR MUSCLES OF THE TRUNK — the pectoralis major of the right
side and the left external oblique being removed.

i, pectoralis major; 2, pectoralis minor; 3, subclavius ; 4, serratus magnus ; 5,
internal intercostals ; 6, external oblique ; 7, internal oblique ; 8, linea alba.

The infra-spinatus, also named from its origin, is also
inserted into the same tuberosity.

The teres minor is a small muscle inserted like the two
preceding, and arising from the axillary border of the scapula.
The teres major goes from the inferior angle of the scapula
to the lesser tuberosity, which also gives insertion to the large
subscapularis muscle arising from the fossa of the scapula on
its inner surface.
: The coraco-brachialis, small and inconspicuous, springs

VIII.]

THE MUSCLES.

293

from the coracoid process, and is inserted on the inner side
of the humerus.

FIG. 269.— MUSCLES OF THE RIGHT SHOULDER-BLADE, viewed from behind.
i, supra-spinatus ; 2, infra-spinatus ; 3, teres minor ; 4, teres major ; 5, latissi-

mus dorsi near its insertion ; 6, scapular head of triceps ; 7, external humeral

head of triceps.

The biceps is the well-known muscle used in flexing the
arm. It arises by two heads : one a long tendon from the

7\

FIG. 270. — INNER ASPECT OF SUPERFICIAL MUSCLES OF RIGHT SHOULDER-
BLADE AND UPPER ARM.

i, subscapularis ; 2, teres major ; 3, scapular part of triceps ; 4, internal humeral
part of triceps-, ; 5, biceps ; 6, coracoid head and tendon of biceps, on the inner
side of which is a small muscle, the coraco-brachialis ; 7, humeral head and
tendon of biceps : 8, deltoid ; 9, cut end of pectoralis major, supported by a
hook, and shown to be folded on itself; 10, brachialis anticus.

29< ELEMRNTAR Y ANA TOMY. [LESS.

margin of the glenoid cavity; the other, shorter, from the
coracoid process. The muscle formed by the union of these
heads is inserted into the tubercle of the radius.

Brachialis anticus. This term is applied to a muscle
placed beneath the biceps, springing from the front of the
humerus and inserted into the coronoid process of the ulna.

The triceps is the largest muscle of the arm, and is inserted
into the olecranon. It arises by three heads : one (long)
from the lower border of the glenoid cavity, one (external]
from the humerus below the great tuberosity, one (internal
or short] from the inner surface of the humerus.

FIG. 271.— SUPERFICIAL FLEXOR MUSCLES OF RIGHT FORE-ARM,

i, biceps; 2, brachialis anticus ; 3, triceps; 4, pronator teres ; 5, flexor carpi
radialis ; 6, palmaris longus ; 7, flexor carpi ulnaris ; 8, supinator longus ; 9,
extensor carpi radialis longior et brevior ; 10, flexor sublimis digitorum ; n,
abductor pollicis ; 12, opponens pollicis J 13, palmaris brevis.

8. The MUSCLES OF THE FORE-ARM consist of pronators
and supinators, flexors and extensors.

Pronator teres. A muscle thus named rotates the fore-arm
in the way described in- the lesson on the bones of the arm
under the name "pronation." It arises from the inner condyle

THE MUSCLES. 295

of the humerus and from the coronoid process of the ulna,
and proceeds obliquely across to the outer side of the radius.

T.\\t flexor carpi radialis arises from the inner condyle and
is inserted by a tendon into the second metacarpal.

The palmaris longits also springs from the inner condyle,
and ends in a fibrous expansion in the palm of the hand.

The flexor carpi ulnaris arises partly from the same con-
dyle, partly from the olecranon (the ulnar nerve passing
between these origins). It is inserted by tendon into the
pisiform bone and the fifth metacarpal.

"£\& flexor sublimis digitorum is (as its name implies) the
superficial bender of the fingers. It takes origin from the
inner condyle, the coronoid process of the ulna, and part of
the front surface of the radius. It divides near the wrist into
four tendons, which go respectively to the second phalanx of
each of the four digits. Each tendon splits (before it is
inserted) to allow a tendon of the deep flexor tendon to pass
through it — whence the superficial flexor is also called the
perforates*

The flexor profundus digitorum or perforans arises from
the ulna and from the membrane connecting that bone with
the radius. Above the wrist it gives rise to four tendons
which are respectively inserted into the disf1 phalanges of
the four fingers, each tendon passing through trie split before
mentioned as existing in each tendon of the perforated flexor.

The lumbricales are small worm-like muscles (whence their
name) which arise, in the hand, from the deep flexor
tendons on their radial side, and are inserted into the same
side of the respective four fingers.

Flexor longus pollicis is the name of a muscle which —
arising from the fore part of the radius and being inserted
by a long tendon into the last phalanx of the pollex — bends
the thumb.

Pronator quaaratus. A short muscle thus named extends
across from the radius to the ulna towards their distal ends.

Supinator longus. A muscle which antagonises the pro-
nators, springs from above the external condyle of the
humerus and is inserted into the outer border of the distal
end of the radius.

The extensores carpi radialis longior and brevier are two
muscles which arise, one over the other, from above the
external condyle of the humerus, and end each in a tendon ;
the first being inserted into the second metacarpal, and the
second tendon into the middle metacarpal.

296

ELEMENTAR Y ANA TOMY.

[LESS.

The anconeus is a very small triangular muscle which goes
from the outer condyle of the humerus to the radial aspect of
the olecranon.

The extensor communis digitorum stretches the fingers.
Springing from the fibrous membrane which invests its fleshy
mass, and from the outer condyle, it divides into four tendons,

FIG. 272.— DEEPER FLEXOR MUSCLES
OF RIGHT FORE-ARM.

i, extensor carpi radialis brevior; 2,
supinator brevis ; 3, flexor profundus
digitorum ; 4, one of the lumbricales;
5, flexor longus pollicis ; 6, pronator
quadratus; 7, flexor brevis pollicis;
8, opponens pollicis ; 9, adductor
pollicis ; 10, origin of the adductor
minimi digid ; n, opponens digiti
minimi.

FIG. 273. — SUTERFICIAL EXTENSOR
MUSCLES OF RIGHT FORE-ARM.

i, supinator longus ; 2, extensor carpi
radialis longior ; 3, extensor carpi
radialis brevior ; 4, extensor ossis
metacarpi pollicis ; 5, extensor primi
internodii pollicis ; 6, extensor se-
cundi internodii pollicis ; 7, extensor
communis digitorum ; 8, extensor pro-
priusdigiti minimi ; 9, extensor carpi
ulnaris ; 10, anconeus ; n, brachialis
anticus ; 12, triceps; 13, flexor carpi
ulnaris.

which are respectively inserted into the second and last
phalanges of each of the four fingers. A more or less sepa-
rate part, sending an additional tendon to the fifth digit,
is reckoned as a distinct muscle and called the extensor
minimi digiti.

viu.] THE MUSCLES. 297

The extensor carpi ulnaris springs from the external con-
dyle and from the ulna, and ends in a tendon going to the
fifth metacarpal.

Extensor ossis metacarpi pollicis. This great stretcher of
the thumb arises from both the ulna and radius (on their
hinder aspect), and is inserted by a long tendon into the first
metacarpal.

The extensor primi internodii pollicis is a small muscle
which springs from the membrane between the radius and
the ulna, and is inserted into the proximal phalanx of the
thumb, as the extensor secundi internodii (springing from
the back of the ulna) is inserted into its distal phalanx.

The extensor indicis is a narrow muscle which takes origin
from the middle of the ulna behind, and is inserted into the
posterior surface of the second and third phalanges of the
index.

Supinator brevis. A deep muscle thus named comes from
the outer condyle and upper part of the ulna, and is inserted
into the radius wrapping it round somewhat from behind.

9. The MUSCLES OF THE HAND are numerous, but small.
The thumb (which has no perforated flexor) is provided with
a flexor brevis going from the carpus to the proximal pha-
lanx ; also an abductor from the trapezium to the proximal
phalanx, and an adductor (placed in the fold of skin between
the thumb and index digit), going to the same phalanx from
the middle metacarpal. Besides these there is an opponens,
which goes from the trapezium to the outer border of the
first metacarpal.

The little finger has also an opponens, going from the
unciforme to the fifth metacarpal ; an abductor, from the pisi-
forme to the proximal phalanx ; and a flexor brevis, from the
unciforme to the same phalanx.

Small muscles called interossei arise from the sides of the
metacarpals and go to the sides of the proximal phalanges.
When the back of the hand (the other muscles being dissected
off) is looked at, four (dorsal] interossei are seen ; one going
to each side of the middle digit, one to the radial side of the
index, and one to the ulnar side of the ring digit. When the
palm of the hand is looked at, three (palmar] interossei are
seen : one going to the ulnar side of the index digit, and two
to the radial side of the fourth and fifth digits respectively.

10. The ABDOMINAL REGION of the body is invested by
three great sheets of muscle and membrane. The first of
these, the external oblique (Fig. 268, 6), springs from outside

298

ELEMENTAR Y ANA TOMY.

[LESS.

the eight or nine lower ribs, and its fibres pass downwards
and inwards (towards the mid-ventral line), being inserted
by muscle and membrane into the brim of the pelvis, part
dividing into what are called the "external" and "internal"
tendons of the muscle. Above, this muscle is connected with
the pectoralis major.

The deeper abdominal muscle, the internal oblique, is re-
presented by membrane only in the mid-ventral region. It
passes from the ilium and adjacent structures, up towards

FIG. 274. — DEEPER ABDOMINAL MUSCLES— the external oblique being removed
from the left side of the body, and the internal oblique and part of the rectus
also, from its right side.

i, the internal oblique ; its outer tendon (2) is cut and reflected from the outside
of the rectus to show its deeper tendon (3), which passes within the rectus
except towards the pubis ; 4, transversalis ; 5, its fascia ; 6, sheath of the
rectus — near the pubis, the conjoined aponeuroses of the abdominal muscles
pass in front of that muscle ; 7, pyramidalis ; 8, rectus of left side, showing
the tendinous intervals, or linece transverse.

the cartilages of the ribs, its fibres mostly proceeding in the
reverse direction to those of the muscle last described.

The deepest of the abdominal muscles, the transversalis,
springs from the ilium and lower ribs, and its fibres, proceed-
ing horizontally, end in an aponeurosis, which meets its fellow
in the mid-ventral line. The abdominal nerves extend round
the body between this muscle and the internal oblique.

Rectus abdominis. This is a long muscle which, springing
from the pubis, ascends to the cartilages of the fifth, sixth,
and seventh ribs. The rectus is separated from its fellow of

VIII.]

THE MUSCLES.

299

the other side only by a narrow interval which is occupied
by a tendinous cord — the linea alba.

The fibres of the rectus are interrupted at intervals by
transverse tendinous intersections.

A small pyramidalis muscle arises on each side of the
pelvis, and extends from the pubis to the linea alba.

Quadratus lumborum. This is a mass of muscle situate
close to the vertebral column, and extending upwards from
the ilium to the last rib.

Layers of fibres between adjacent ribs are called the ex-
ternal and internal intercostal muscles. The former extend
from the tubercles of the ribs to their cartilages. The latter
extend from the sternum to the angles of the ribs. The
intercostal nerves and vessels are interposed between them.

The levatores costarum are small groups of fibres passing
obliquely downwards from the transverse processes to the
respective ribs at their proximal parts.

Triangularis sterni is the name given to a layer of muscle
which diverges upwards to the cartilages of the ribs from the
deep surface of the lower part of the sternum.

1 1. The DIAPHRAGM is a very important muscle for respira-

VCJ

-OB

FIG. 275.— THE DIAPHRAGM, viewed from the lower or abdominal side.

V.C.I., the vena cava inferior ; CE, the oesophagus ; Ao, the aorta ; Th. D., the
thoracic duct, cut where they pass through the diaphragm, the broad white
tendinous middle of which is easily distinguished from the radiating muscular
fibres which pass down to the ribs and into the pillars in front of the vertebra;.

300 ELEMENTARY ANATOMY. [LESS.

tion, as explained in the Fourth Lesson of " Elementary
Physiology." It is a partly fibrous, partly muscular partition
between the thorax and abdomen, perforated for the passage
of certain organs— namely, the oesophagus, or swallow, and
two great blood-vessels named aorta and vena cava. The
diaphragm is strongly convex upwards and concave down-
wards, and is attached to the ensiform cartilage and several
ribs, to the centra of the lumbar vertebras, and to fibrous
structure binding down the quadratus lumborum and other
muscles. Muscular towards its circumference, the diaphragm
has a tendinous central portion.

FIG. 276. — DEEP MUSCLES WITHIN THE LUMBAR AND PELVIC REGIONS.

i, psoas parvus; 2, psoas ma^nus ; 3, quadratus lumborum; 4, inter-trans-
versarii ; 5, iliacus ; 6, obturator externus ; 7, pyriformis.

12. The MUSCLES OF THE INFERIOR EXTREMITY, though
mainly taking origin from the pelvis and leg-bones, yet
partly arise from the loins. Thus \hepsoas magnus springs
from the centra of the lumbar and last dorsal vertebrae, and
from the transverse processes of the former. Passing out
over the brim of the pelvis, it is inserted into the lesser
trochanter of the femur.

The iliacus occupies the iliac fossa of the pelvis, whence it
descends and joins the psoas magrius.

T\\Q. psoas parvus springs from the bodies of the last dorsal
and first lumbar vertebrae, and is inserted into the ilio-pecti-
neal eminence.

The glutens maximus is a very large muscular mass which
arises from the posterior part of the crest of the ilium, the

VIII.] THE MUSCLES. 301

posterior part of the sacrum, posterior sacro-sciatic ligament,
and coccyx. It is inserted into a rough line below the great
trochanter.

The glutens medius springs from outside the ilium, and is
inserted into the great trochanter.

FIG. 277.— HIND VIEW OF THE MUSCLES OF THE PELVIS AND RIGHT THIGH—
the gluteus maximus and semi-tendinosus being cut and removed.

i, origin of the gluteus maximus ; i', its insertion ; 2, great sacro-sciatic liga-
ment ; 3, gluteus medius ; 4, pyriformis ; 5, tendon of obturator internns ; 6,
gemellus inferior (immediately below this, without a number, is the quadratus
femoris) ; 7, origin of the semi-tendinosus ; 7', its insertion ; 8, semi-mem-
branosus; o, biceps femoris ; 10, adductor ; n, gracilis ; 12, 12, heads of the
gastrocnemius ; 13, vastus externus.

The glutens minimus has a similar origin, but deeper, and
a similar insertion.

The pyriformis arises from the front of the sacrum, and,
passing out of the pelvis by the sacro-sciatic notch, is inserted
into the great trochanter.

ELEMENTARY ANATOMY.

[LESS.

Muscles named obturator internns and obturator externus
spring respectively from the inner and outer surfaces of the
obturator membrane and ischium, and are inserted into the
trochanteric fossa. Two little muscles (gemelli) arising re-
spectively from the spine and tuberosity of the ischium, join
the tendon of the internal obturator above and below.

The quadratus femoris passes from the tuberosity of the
ischium to the great trochanter and to the surface of the
femur immediately below it.

FIG. 278.— ANTERIOR MUSCLES OF THE RIGHT THIGH.

i, psoas magnus; 2, iliacus ; 3, tensor vaginae femoris; 4, gluteus medius : st
sartorius ; 6, rectus femoris ; 7, vastus externus ; 8, vastus internus ; 9, points
to the junction of the extensor muscles near their insertion into the patella ;
10, aponeurosis of the knee ; n, pectineus ; 12, adductor ; 13, gracilis.

A muscle called the tensor vagina femoris passes obliquely
from the anterior, superior spinous process of the ilium to
the membrane which binds down the muscles of the thigh
on the outside.

VIIL] THE MUSCLES. 303

The sartorius is a long flat ribbon-like muscle, passing
obliquely down from the front margin of the ilium to the side
of the tibia just below the tuberosity.

The great extensor of the leg, the quadriceps, consists of
four parts — (i) the rectus femoris, passing down from the
anterior, inferior spinous process and the brim of the aceta-
bulum ; (2) the vastus externus, and (3) the vastus intermts,
fleshy masses attached respectively to the outer and inner
sides of the shaft of the femur ; and (4) the crureus, con-
sisting of fibres springing from the front of the thigh-bone.
The whole are inserted, by a tendon attached to the patella,
into the tuberosity of the tibia.

Gracilis. A muscle thus named, flat and thin, springs
from the pubis (close to its symphysis), and is inserted by a
tendon into the tibia beside the tuberosity.

The pectineus passes from the ilio-pectineal line to the
femur below the lesser trochanter.

The adductores longus, brews, and magnus, pass down-
wards and outwards from the pubis to the femur, and are
respectively inserted into the middle third of the linea
aspera, into below the lesser trechanter, and into the whole
length of the linea aspera down to the inner condyle.

Three muscles,. called the ham-string muscles, are — (i) the
biceps femoris, which springs both from the fernur and (by
tendon) from the tuberosity of the ischium, and is inserted
into the head of the fibula ; (2) the semi-tendinosus, which
arises from the ischium in common with the last, and is
inserted inside the tibia, below its tuberosity ; (3) the semi-
membranosus, which springs from the tuberosity of the
ischium (in front of the origin of the biceps], and is inserted
triply, (a] into the tibia behind its inner tuberosity, (b) under
the internal lateral ligament at the side of the inner tubero-
sity, (c) into the external condyle of the femur.

13. The MUSCLES OF THE LEG consist in front of seven
muscles.

The tibialis anticus extends along the outer side of the tibia
downwards from its outer tuberosity, and ends below in a
tendon which is inserted into the ento-cuneiforme and first
metatarsal.

The extensor proprius hallucis arises from the fibula and
the interosseous membrane connecting that bone with the
tibia. Its tendon is inserted into the second phalanx of the
great toe.

The extensor longus digit or urn pedis arises from the fibula

304

ELEMENTAR Y ANA TOM Y.

[LESS.

and interosseous membrane and outer tuberosity of the tibia.
Below, it ends in four tendons going respectively to the second
and third phalanges of the four outer (peroneal) digits.

The peroneus tertius is placed on the front of the fibula's
lower third, and its tendon is inserted into the dorsuin of the
fifth metatarsal.

The extensor brevis digitorum pedis springs from the dorsal
surface of the calcaneum and its annexed ligaments, and

FIG. 279.— MUSCLES OF OUTER SIDE AND FRONT OF RIGHT LEG.

i, external lateral ligament ; 2, tibialis anticus ; 3, extensor hallucis ; 4, extensor
longus digitorum pedis ; 5, peroneus tertius ; 6, gastrocnemius ; 7, peroneus
longus ; 7', its tendon ; 8, peroneus brevis ; 8', its tendon ; 9, annular ligament ;
10, extensor brevis pedis ; n, abductor minimi digiti pedis.

ends in four tendons, the most internal of which is inserted
into the first phalanx of the hallux. The other three become
respectively united to the long extensor tendons of the three
next digits.

VIII.]

THE MUSCLES.

305

A remarkable muscle, the peroneus longus, arises from
the outer, upper two-thirds of the fibula and from the ex-
ternal tuberosity of the tibia. It ends in a tendon which
passes behind the external malleolus, and then obliquely
across the sole of the foot to the first metatarsal.

The peroneus brevis springs from the outer, lower half of
the fibula, and ends in a tendon which, also passing behind

FIG. 280. — SUPERFICIAL FLEXOR MUSCLES OF RIGHT LEG.

i, tendon of semi-membranosus : 2, 2, heads of gastrocnemius ; 3, plantaris : 4,
soleus ; 5, great tendon of gastrocnemius, continuous below with (6) the tendo
Achillis ; 7. peroneus longus ; 8, peroneus brevis ; 9, flexor longus digitorum
pedis ; 10, tibialis posticus.

the external malleolus, is inserted into the base of the fifth
metatarsal.

Behind the leg we have seven muscles.

The gastrocnemius (forming the bulk of the calf of the leg)
consists of two fleshy heads, arising each by a thick tendon
from above each of the condyles of the femur — one external,
one internal. They unite and send down the very strong

x

306

ELEMENT AR Y ANA TO MY.

[LESS.

tendo Achillis to be inserted into the tuberosity of the cal-
caneum.

The soleus lies beneath the gastrocnemius, and arises
from behind the upper part of the fibula and tibia, while
below it joins the tendo Achillis.

The plantaris springs from the femur above the external
condyle, and gives rise to a very long tendon which goes to
the calcaneum beside the tendo Achillis.

FIG. 281. — DEEP FLEXOR MUSCLES OF RIGHT LEG.

i, popliteus ; 2, tendon of semi-membranosus ; 3, external lateral ligament of the
knee joint ; 4, cut upper extremity of soleus ; 5, flexor longus digitorum pedis;
6, flexor longus hallucis ; 7, tendon of tibialis posticus ; 8, peroneus longus ;
9, peroneus brevis ; 10. accessorius ; u, abductor hallucis, cut short ; 12, flexor
brevis hallucis ; 13, abductor digiti minimi, cut short ; 14, flexor brevis minimi
digiti.

The popliteus is a short oblique muscle which takes origin
by a thick tendon from a pit outside the external condyle,
and is inserted behind the tibia above the oblique line.

THE MUSCLES. 307

A muscle bends the toes, called \h& flexor longus digitorum
pedis, arising behind the tibia below the popliteus. It ends
in a tendon which passes behind the internal malleolus and
beneath the calcaneal arch, and then divides into four ten-
dons—one for each of the four outer digits at their distal
phalanx, each perforating in its passage a tendon of the
flexor brevis digitorum.

The long flexor is connected with a small muscle called
flexor accessorius, which passes to the tendon of the flexor
longus digitorum from the calcaneum.

The flexor longus pollicis pedis springs from the posterior
surface of the fibula and the interosseous membrane. It
ends in a tendon which passes behind the internal malleolus,
grooving the tibia, astragalus, and calcaneum. In the sole
it gives off a tendinous slip which joins the tendon of the
flexor longus digitorum, and then ends by being inserted into
the distal phalanx of the hallux.

The tibialis posticus arises from the hinder surface of the
tibia (below the popliteus) and from the interosseous mem-
brane. It ends in a tendon which first passes beneath the
internal malleolus along a special groove, and then beneath
the calcaneum, to be inserted into the tuberosity of the
naviculare and the first metatarsal.

14. The MUSCLES OF THE FOOT, besides the flexor acces-
sorius already noticed, consist of the following : —

The abductor pollicis pedis, which arises from the inner
side of the calcaneum, and is inserted into the inner border
of the first phalanx of the hallux.

^^ flexor brevis digitorum (or perforatus) arises from
the great tuberosity of the calcaneum and from membrane,
and ends in four tendons corresponding with the four smaller
toes. Each tendon is inserted into the second phalanx of a
digit, but splits opposite the proximal phalanx of the same
digit in order to allow a tendon of the long or perforating
flexor to pass through.

The abductor digiti minimi springs from the outer border
and under surface of the calcaneum, and ends in a tendon
inserted into the proximal phalanx of the fifth digit.

The lumbricales, like those of the hand, arise from the
tendons of the perforating flexor, and are respectively inserted
into the base of the first phalanges of the four outer toes.

The flexor brevis pollicis pedis springs from the cuboides
and ecto-cuneiforme, and is inserted into the inner and outer
borders of the first phalanx of the hallux.
X 2

308 ELEMENTARY ANATOMY. [LESS.

The abductor pollicis pedis takes origin from the cuboides
and third and fourth metatarsals. Passing obliquely, it is
inserted conjointly with the external insertion of the flexor
brevis pollicis.

The transversus pedis is a narrow band stretching from
the distal ends of the metatarsals and blending with the
insertion of the adductor pollicis into the first phalanx of the
hallux.

The interosseous muscles are like those of the hand, except
that it is the second digit, not the third, which has two dorsal
interossei. This condition results simply from the fact that
the origin (from the metatarsal) of the fibular interosseus of
the second digit is placed on the dorsal side of the tibial
interosseus of the middle digit.

Such is the norm il condition of man's muscles, but these
structures are liable to considerable individual variation.

15. On turning to other Vertebrate animals in order to
estimate the peculiarity of man's muscular structure, we find
that, as regards the MUSCLES OF THE HEAD AND NECK,
the occipito-frontalis truly belongs to a distinct category of
" skin -muscles," whereof the platysma myoides also forms a
part. This dermal group of muscles is very feebly repre-
sented in man compared with what we find in brutes, e.g.
the Horse, where it is termed the panniculus carnosus, and
by its contractions produces those twitchings of the skin
which must be familiar to most readers. It is most de-
veloped in such forms as the Porpoise (where it envelops the
whole body from the occiput to the tail end), the Echidna,
and the Hedgehog. In the last-named animal it is so com-
plex that it may be divided into nine pairs of muscles, one
pair being the " occipito-frontalis." When all these muscles
contract, the animal becomes " rolled up," the limbs be-
coming, as it were, enclosed in a muscular bag. The panni-
culus is commonly inserted into the arm and leg, and part
of it may, as in the Echidna, be applied round the mammary
gland, which it serves to compress.

Muscles such as those which exist in man's face may be
wanting altogether, as e.g. in the Tortoises, but some of them
may, as we shall see, be much more developed in certain
animals than they are in him.

Thus we may have his superior auricular represented by
two muscles, and his anterior auricular and his posterior
auricular by four, together with two or three extra muscles,
as in the Horse.

VIIL] THE MUSCLES. 309

Palpebral muscles may be wanting, as in Serpents, and the
orbicularis palpebraruni may be atrophied, as in \\ hales, or
replaced by a complete sphincter, as in Tetraodon.

The muscles of the nasal region, so important for expres-
sion, do not in most animals attain the distinctness they do
in man. Yet they may be distinct where little expression is
to be detected, e.g, in the Great Ant-eater. They may all
abort, as in the Crocodile, or they may receive certain addi-
tions, as in the Pig, where two muscles arise, one on each
side, from the zygoma and maxillary bone, and unite together
above the end of the snout, which they elevate ; while two
other muscles (which depress the snout) take origin, one on
each side, from the zygoma, and are inserted into the median
septum. In the Mole there are even four on each side, all
arising above the ear and passing forwards between the tem-
poral and masseter muscles, to be inserted into the extremity
of the muzzle.

The most exceptional modification of the nasal and labial
muscles is, however, found to exist in the Elephant, where
they form its remarkable trunk. For this purpose two
muscles (elevators) take origin, one on each side, from pro-
cesses above the nasals. Another pair (depressors) spring
from the pre-maxillas, while a third pair (lateral, longitudinal
muscles) take their origin from the frontal and maxillary bone
on each side. Besides these there are intrinsic muscles of
the proboscis, the fibres of which radiate from the nasal pas-
sages to the inner surface of the skin, and tend to keep
the former open.

Another peculiar condition is that existing in Cetacea, which
will be noticed in treating of the nose as a sense organ.
Here, however, it may be mentioned that in the Porpoise a
muscular layer spreads forwards from the frontal bone over
the posterior nasal structures, and another layer spreads back-
wards from the maxillary bone over the anterior nasal struc-
tures. It is by the contraction of these muscles that the nasal
passage is opened while the nasal sacs are compressed and
their contents ejected.

The masseter may attain a relative size and complexity
which are very much greater (especially when compared with
the simultaneous condition of the temporal) than in man.
This great development is well seen in certain Rodents, e.g.
Lagostonms and the Agouti, where the masseter is divided
into three portions, and traverses the singularly enlarged
infra-orbital foramen spoken of in describing the skeleton.

3io

ELEMENTAR Y ANA TOMY.

[LESS.

This muscle, even in Mammals, may be blended with the
temporal, as is the case in the Two-toed Ant-eater.

The temporal muscle of man is but very poorly developed
compared with what we find in many other forms, such as the
Tiger. It may, on the contrary, be less developed relatively
than in man, as in the Hare. It may be divided into three
or four portions, as in the Fowl and Goose.

FIG. 282.— SUPERFICIAL MUSCLES OF RIGHT SIDE OF MENOPOMA.

A A, adductor arcuum ; B, biceps; CA, constrictor arcuum ; CF, constrictor
faucium ; D, deltoid ; Dl, digastric ; EL, extensor longus ; ExO, external
oblique; LA, levator arcuum; LD, latissimus dorsi ; M, masseter; MH1,
anterior pai. of mylo-hyoid ; MH'2, posterior part of mylo-hyoid; S, sub-
clavius ; SL, supinator longus ; T, trapezius ; T, triceps ; U, ulnaris.

The pterygoid muscles of man are essentially similar to
the same parts in the whole of his class ; but these muscles
may be indistinguishably united into one, as in Menopoma,
or even with the temporal, as in Menobranchus (Fig. 286).
They may be very large, as in venomous Serpents.

1 6. The ORBITAL MUSCLES of man present a condition
which is normal, these parts exhibiting a remarkable con-
stancy in vertebrate animals.

Such parts, however, may be entirely wanting even in

VIII.]

THE MUSCLES.

Mammals, e.g. Talpa and Spalax; and in Lepidosiren, the
Lamprey, and Lancelet amongst Fishes.

On the contrary, muscles may be developed which do
not exist in man at all.

Thus in most Mammals (e.g. the Horse) a conical funnel-
shaped muscular mass may spring from around the optic
foramen, and, passing within the recti, attach itself to the
sclerotic.

FIG. 283. — DEEPER MUSCLES OF RIGHT SIDE OF MENOPOMA (the mylo-hyoids
and trapezius being removed or cut short).

AA, adductor arcuum ; CA, constrictor arcuum ; CF, constrictor faucium ; CHE,
cerato-hyoideus externus ; CHI, cerato-hyoideus interus ; D, deltoid ; Z>' and
1) 2, digastric; ExO, external oblique; G ff, genio-hyoideus; InO, internal
oblique ; LAS, levator anguli scapulae ; LD, latissimus dorsi ; M, masseter ;
S, subclavius ; SM, serratus magnus ; T, trapezius.

This mass may divide itself into two portions, as in the
Rhinoceros ; three, as in the Frog ; or into four, as in the
Porpoise. In the last case we have thus four supplementary
recti muscles within the four normal ones.

It may be that the superior oblique muscle does not pass
through a pulley. It does not do so in Vertebrates below
Mammals, where it arises at the front part, not the back of
the orbit.

The two oblique muscles may thus arise, one above the
other, from the inner angle of the orbit, as in the Frog and
in Fishes.

The muscles of the eye may take origin in part from the
basis cranii and in part from the fronto-parietal, as in the Frog ;
or they may spring from within a bony canal situated beneath
the basis cranii, as in many bony Fishes, e.g. the Carp.

312 ELEMENTARY ANATOMY. [LESS.

The eye muscles may attain a prodigious length, as in the
Hammer-headed Shark, where they arise from the basis
cranii and extend the whole length of the prolonged lateral
processes which support the eyeballs at their ends.

There may be a distinct depressor of the lower eyelid, and
in addition to this, other muscles may be developed in con-
nexion with the third eyelid, which is of large size in so many
animals, notably in Birds.

The third eyelid may be furnished with a muscle which,
arising from the temporal side of the orbit, passes through
a muscular and ligamentous loop, and is inserted into the
third eyelid's inferior margin.

This muscle may be, as in the Frog, furnished with a tendon
which forms' a loop over the conical muscular mass of the
eyeball, so that when that muscle swells by the retraction of the
eyes the loop necessarily contracts, and thus moves the eyelid.

It may be, as in the Crocodile, that the muscle of the third
eyelid takes origin from the upper and inner part of the eye-
ball, and, passing downwards round the conical muscle and
optic nerve, reaches the lower angle of the third eyelid.

Finally, as is the case in Birds, it may spring from the
lower, nasal side of the eyeball and end in a tendon which
proceeds to its insertion as in the Crocodile, except that
it passes through a pulley formed by the tendinous sheath of
a second muscle (the quadratics nictitantis) which arises from
the sclerotic at its upper and back part, and ends in forming
the sheath aforesaid. As in Birds there is no conical muscle,
this quadrate one is probably its representative.

Another muscle may also exist, as in the Frog, forming a
sort of fleshy sheet on which the eyeball rests, and which
protrudes the eyeball by its contraction.

I/. As to the MUSCLES OF THE NECK.

The sterno-cleido-mastoid of man really represents what
are two muscles in many other animals, viz. a sterno-mastoid
and a cleido-mastoid. Nevertheless it may be a single
muscle even in Reptiles, as in the Iguana.

The sterno-mastoid may be wanting altogether, as in
Birds and Batrachians.

The cleido-mastoid may also be wanting, and it may, as in
the Horse (by suppression of the clavicle and uninterrupted
union with the deltoid or pectoralis), extend directly from the
skull to the humerus as a cephalo-humeral, or even to the
ulna, as in Hyrax.

In cold-blooded Vertebrates this muscle maybe attached to

VIII.]

THE MUSCLES.

313

the fronto-parietal or to the suspensorium, and It may, even
in Mammals, be inserted above into the mandible, as in
the Horse.

The digastric of man is closely resembled only by the same
muscle in his own order. In other Mammals, e.g. the Dog, it
has but a single belly ; and in lower Vertebrates the muscle
which commonly receives this name has a very different
position. Thus in Birds and Reptiles it descends from the

Tif CUfa C.lfi. J

FIG. 284.
No. i. — MUSCLES OF NECK AND SHOULDER OF Iguana, the trapezius and

deltoid being cut short.

B, biceps; 'BA, brachialis anticus ; CM, cerato-mandibular ; CM a, complexus
major; CMi, complexus minor; Z?1 and D2, two parts of deltoid; DM,
digastric; EH, epicoraco-humeral, or sub-clavius ; JS, infra-spinatus ; LC,
levator claviculse ; OH, omo-hyoid ; P, pectoralis ; SCM, sterno-cleido-
mastoid ; SMg, serratus magnus; Tl, external long head of triceps; T3,
external humeral head of triceps ; Tz, trapezius ; x, part of complexus.

No. 2. — DEEPER MUSCLES.

CA, cervicalis ascendens ; CMa, complexus major; CMi, complexus minor;
DM, depressor mandibulae ; RAM, rectus capitis anticus major ; RPM, rectus
capitis posticus major ; Sc, scalenus ; SCAf, sterno-cleido-mastoid ; x, part of
complexus.

hinder part of the cranium to the posterior end of the man-
dible, and in some Birds is divided into three portions.

The stylo-hyoid of man is a muscle constant in his class,
but of variable size. It may be of extraordinary length, as in
the Great Ant-eater, and it may be, as in the Horse, re-
latively shorter than in man, the bony extent of the anterior

3 1 4 ELEMENTAR Y ANA TO MY. [LESS.

cornua being so much greater than in the human structure.
It may be attached above to the par-occipital process, as in
the Horse, or to the posterior part of the lower jaw, as in
some Birds, e.g. the Fieldfare.

The stylo-glossus and stylo-pharyngeus present few dif-
ferences in Mammals, except that the former may take origin
from the paramastoid process (as in Hyrax), or low down on
the anterior cornu, as in Ruminants.

The mylo-hyoid even in Mammals may be quite discon-
nected with the hyoid, and it may be exceedingly elongated
and divided into several antero-posteriorly successive parts,
as in the Great Ant-eater. The hindmost part may, even
in man's class, take origin from the sides of the occiput, as
in the Echidna. It may be very large, as in Menopoma
(Fig. 282).

The genio-hyoids are very constant, existing down to
Fishes. They maybe inserted into the cornua (not the body)
of the hyoid, as in Birds and Fishes, or into fascia bounding
the body of the hyoid beneath, as in Menopoma, or into the
uro-hyal, as in Menobranchus.

The hyo-glossus of man, arising as it does from three parts,
might be expected to present (as is the case) variations in
other animals in accordance with the varying development
of its three points of origin, namely, the body, and the lesser
and greater cornua respectively of the os-hyoides.

By a yet further modification the hyo-glossus may be de-
tached from the hyoid and blended with a sterno-hyoid also
detached from the hyoid, so that we have an enormously long
muscle entering into the substance of the tongue, but taking
origin as far back as the xiphoid cartilage. Such is the case
in the Great Ant-eater, where the hyo-glossi are reinforced
by small muscles springing from the anterior cornua. Both
lateral and median muscles exist in most Birds, and lateral
muscles (i.e. from the cornua to the tongue) exist in Reptiles
and the Frog, and even in some Fishes, all but tongueless
as are the last-named animals.

The genio-glossus may take origin from the sides of the
mandibular rami instead of from the symphysis, as in Ser-
pents, or it may have two origins (one from the symphysis and
one from the side of the mandible), as in the Great Ant-eater.
This muscle may be wanting altogether, as in Fishes, and
even amongst Birds — while nevertheless it exists not only in
Reptiles but also in Batrachians (e.g. the Frog, Salamandra,
and Menobranchus).

THE MUSCLES.

315

Other muscles, not present in man, may exist where com-
plex branchial arches replace his rudimentary thyro-hyals or

FIG. 285.— MUSCLES OF VENTRAL SURFACE.

On the right side, superficial muscles; on the left side, deeper muscles, the
mylo-hyoidei, pectoralis, and external oblique being removed. Also superficial
flexor muscles of right pectoral limb of Meuobranchus.

B, biceps; CB1 and CJ32, coraco-brachialis ; CHE, cerato-hyoideus externus ;
EO external oblique ; FL, flexor longus ; GH, genio-hyoid ; MH and
7J///2, mylo-hyoideus ; OH, omo-hyoid ; P, f\ and P2, pectoralis; R,
rectus ; 3", subclavius ; SH, sterno-hyoid ; SL, supinator longus ; T, triceps.

3i6

ELEMENTARY ANATOMY.

[LESS.

cornua. Thus we may have— I. Muscles connecting the
hyoidean and branchial arches (e.g. the cerato-hyoideus ex-
ternus and interims). 2. Muscles connecting the branchial
arches of each side (e.g. the constrictores arcuum of Meno-
branchus. 3. Muscles suspending the branchial arches to the
parts above them — as the levatores arcuum of Menobranchus.
The conditions of man's sterno-hyoid are very generally
present, but the muscle may be wanting, as in Chelonians, or

FIG. 286.— SUPERFICIAL MUSCLES OF RIGHT SIDE AND OF EXTENSOR SURFACE
OF RIGHT PECTORAL LIMB OF MENOBRANCHUS.

AB, adductor branchiarum ; B, biceps ; CP, constrictor pharyn-gis; CHE, cerato-
hyoideus externus ; D, deltoid ; Di, first part of digastric ; EB, extensor
brevis ; EL, extensor longus; ExOt external oblique; LA, levatores
arcuum; LA1, first part of the same; LD, latissimus dorsi ; M, masseter ;
MH2, mylo-hyoideus posterior ; OH, omo-hyoid ; S, subclavius ; SL I and
SL2, supinator longus; T, temporalis ; Tz, trapezius ; T2, triceps; U,
ulnaris.

arise as far back as the xiphoid, as in the Ant-eaters. It
may unite with its fellow to form a thick azygos muscle, as
in the Dolphin, or arise from the anterior ribs and be inserted
into the mandible as well as into the cornua, as in Serpents.
It may also form part of a great muscular mass passing un-
interruptedly from the pelvis to the hyoid, as in Menobran-
chus, and thus we see that it enters into the composition of
that part of each great lateral muscle which in Fishes is
inserted into the median portion of the hyoidean arch.

A separate sterno-thyroid and a distinct thyro-hyoid are
structures peculiar to man's class. The former blends with the

VIIL] THE MUSCLES. 317

sterno-hyoid even in the Platypus. It may, as in the Great
Ant-eater, take origin as far back as the eighth bone of the
sternum.

The omo-hyoid may be wanting even in Mammals, as e.g.
in the Dog. We find it, however, in Reptiles and Batrachians,
though absent in Birds. It may arise from the clavicle (as
Iguana), from the pre-coracoid (as Menobranchus], or be
bent at almost a right angle, looping round the sterno-
mastoid (as in the Chameleon).

1 8. In the VERTEBRAL REGION there may be three scaleni
muscles, as in man, or but one. They may vary also as to
the number of ribs from which they take origin, and may
reach even to the basi-occipital (as in the Agouti), or to the
mastoid process (as in the Dolphin). They may be plainly
but a continuation forwards of the levatores cost arum, as in
Birds.

They may be feebly developed, as in Reptiles, extending as
in Iguana from the first four cervical vertebras, or from the
atlas, to the first cervical rib, as in Iguana and Chameleo.
Finally, the scaleni may be indistinguishably blended with
the dorsal muscular mass, as in Batrachians and Fishes.

The rectus capitis anticus major may attain a much greater
development than in man, extending down to the sixth dorsal
vertebra.

The longus colli may arise as far back as the seventh
dorsal vertebra, as in the Agouti.

We may have in Chelonians (e.g. Emys] a very elongated
muscle extending from even the hindmost thoracic vertebras
and going to the basi-occipital, and beneath this a series of
little muscles (extending each from one vertebra to the next
but one in front) connecting together the cervical vertebras
and the anterior dorsal ones.

Again, we may have a simple muscular mass answering
apparently to both longus coitus and rectus anticus. Thus
in the Chameleon we have such a muscle arising from the
first eight or nine vertebras, and going to the basi-occipital.
The origin may be much more extensive in Serpents (where
the hypapophyses afford points of origin), and in certain
Batrachians (e.g. Menopoma and Menobranchus) a corre-
sponding muscle stretches on each side from beneath the
basis cranii throughout the whole trunk, and, diminishing
backwards, ends (or rather arises) in the sub-vertebral part
of the pelvic region.

The rectus lateralis is really but the highest of the inter-

ELEMENTAR Y ANA TOMY.

[LESS.

transfer sales. It is a constant muscle in man's class, varying
in size with the dimension of the atlantic transverse process,
and therefore being large in the Carnivora.

The pharyngeal muscles of man are structures which are
exceptional amongst Vertebrates, as they are developed in
the highest class alone.

In Birds, Reptiles, Batrachians, and Fishes there are no
proper constrictors of the pharynx, but only fibres which are
quite homologous with those of the oesophagus.

FIG. 287. — SUPERFICIAL MUSCLES OF EXTENSOR SIDE OF LEG AND OF FARTS

OF TRUNK AND TAIL OF MENOPOMA.
ES, erector spinae — directly continued into dorsal half of tail ; ELD, extensor

longus digitorum pedis ; FC, femoro-caudal ; GMx, probably rectus femoris ;

/, muscle resembling iliacus ; ILC, ilio-caudal ; IP, il'o-peroneal ; RF, part

of great extensor of thigh ; SM and ST, muscles like the semi-membranosus

and semi-tendinosus.

These fibres may, however, form a well-developed pha-
ryngeal sphincter, as in Fishes, and serve for moving those
" throat-jaws," the pharyngeal bones, which exist in so many
of the lowest Vertebrate class.

Much variety in form and in the details of attachment may,
however, exist in the Mammalian pharyngeal constrictors,
and we may find a greater degree of complexity than in man.

viii.] THE MUSCLES. 319

The muscles belonging to man's palatal region are special
Mammalian muscles, and present in the class generally the
same disposition as in him. The pendulous palate becomes
in the Cetacea a muscular canal prolonging the posterior
nares to the elongated larynx which it embraces.

19. The MUSCLES OF THE BACK of man present characters
as exceptional, when compared with those of Vertebrates
generally, as does his axial skeleton. The non-development
of a tail and the large size of the upper extremities are occa-
sions in him of muscular conditions which differ greatly from
those presented by many other forms.

Thus the first and second layers may be entirely wanting,
and the other muscles may be represented (as in Menopoma
and Menobranchus) by one great mass, running from the head
to the end of the tail on each side of the vertebral neura-
pophyses ; and this again may be, as in Fishes (e.g. the Perch),
divided by a number of aponeuroses more or less at right

-15

FIG. 288.— SUPERFICIAL MUSCLES OF THE PERCH. The fin-rays of all the fins are
cut short off.

i, great lateral muscle, showing the numerous more or less vertical tendinous
intersections slightly inflected forwards and backwards ; 2, small superficial
muscles inserted into the fin-rays of the dorsal and ventral fins ; 4, slender
longitudinal muscle lunning (in the interval of the summits of the two great
lateral muscles) between the dorsal and caudal fins ; 5, similar muscle on the
ventral margin, which also appears between the anal and ventral fins ; 6, small
radiating muscles of the caudal fin ; 7, part of the great lateral muscle inserted
into the skull ; 8 and 9, elevators of the operculum ; 10, elevator of the palato-
quadrate arch ; it and 12, muscular mass which by its contraction closes th(
jaws; 13, superficial muscles of the pectoral fin; 14 and 15, muscles of the
ventral fin.

angles to the backbone, so that the dorsal muscular mass
comes to consist not of segments extended in the line of the
skeletal axis, but of segments extending almost at right angles
to that axis.

The muscles of the back may be much less developed, re-
latively, than in man, as is the case in Birds ; or they may be
all but absent, as in Chelonians. They may, on the contrary,

320 ELEMENTARY ANATOMY. [LESS.

be excessive in mass, as in most Fishes, or in complexity, as
in Serpents.

The trapezius is a very constant muscle, but may be much
more restricted or more extended in its origin than is the
case in man. It may also be divided into two portions, as
notably in the Mole, where the two origins are very wide
apart : (i) the occiput, and (2) the first two lumbar ver-
tebrae. It may be very small, as in Menobranchus (Fig. 286) ;
or may unite with the latissimus dorsi, as in Anguis fragilis;
or with part of the deltoid, so as to go directly to the humerus,
as in some Mammals without clavicles.

In Bats a long slender segment of this muscle may pass
along the upper margin of the wing membrane from the
occiput to the distal phalanx of the pollex.

In the Flying Squirrel Pteromys a similar muscular band
goes to the rudimentary pollex, but it springs from the zy-
goma, and is therefore rather a modification of the platysma
myoides than of the trapezius ; as it is also in Galeopithecus.

739

FIG. 289.— MUSCLES OF THE VENTRAL ASPECT OF THE BREAST AND LEFT
WING OF AN EAGLE (Aquilajucosti).

(After A. Milne- Edwards.}

i, pectoralis major, sending out a slip, 2 (as the tensor petagii longus) to the first
metacarpal ; 3, tensor petagii brevis ; 4, biceps ; 5, triceps ; 6, brachialis
anticus ; 7, pronator brevis ; 8, pronator longus; 9, flexor carpi ulnaris ; 10,
extensor metacarpi radialis longus ; n, extensor carpi radialis ; 12, abductor
pollicis ; 13, points just above a long tendon of the flexor profundus ; 14, flexor
brevis digitorum.

In Birds an analogous and similarly slender muscle goes
to the pollex or to a sesamoid at its base, but this muscle
is often an offshoot from the pectoralis major, though it may
contain fibres from the deltoid or from the biceps — showing
in what diverse ways a similar want may be supplied.

The ligamentum nuchce of man is but a rudiment of that
vast band, or sheet, of fibres which in many animals (e.g. the

viii.] THE MUSCLES. . ^,

Horse) extends from the spines of the dorsal vertebrae to the
occiput, sending down a lamellar expansion to the spines of
the cervical vertebras. In the Giraffe it extends back even to
the sacrum.

This ligament may become ossified, as in the Mole.

The latissimus dorsi is another nearly constant muscle,
though of varying extent. It may, as in many Apes, send a
slip on to the olecranon, or even, as in the Echidna, to the
flexor carpi ulnaris with which it blends. It may be divided
into two parts, as is the case in the Echidna. It may arise
within the ribs, as in Chelonians, e.g. Emys. It may be
very small, as in Menopoma (Fig. 282). Finally, it may com-
pletely unite with the trapezius, as in Anguis fragilis, or it
may be altogether wanting.

The rhomboidei may be more divided than in man, as in
the Mole ; or single, as in the Hawk ; or absent, as in the
Apteryx and apparently in lower forms. A rkomboideus
capitis, which sometimes exists in man, is often present in
lower forms, as e.g. in Lemur and Nycticebus.

Levator anguli scapula. This is essentially and morpho-
logically the anterior part of that great muscle by which, in
quadrupeds, the trunk is slung between the summits of the
scapulas — the greater part of which goes by the name of the
serratus magnus — rather than a really distinct muscle.

There is a muscle commonly existing in Mammals, but
which is developed only by rare exception in man. This
(the levator claviculcz) extends from the atlas to the scapula
or to the clavicle ; it is well seen in Apes. It is a muscle of
considerable constancy, as it is found of a very large relative
size in Reptiles, e.g. Iguana (Fig. 284). It may arise from
the occipital region, as in Chameleo.

Another muscle, not found in man, but developed in some
Mammals (e.g. the Horse and Hyrax), is termed the sterno-
scapular. It extends from the sternum over the scapulo-
humeral articulation to the superior vertebral angle of the
scapula.

The serrati postici superior and inferior are both repre-
sented in many Mammals by one single continuous muscle,
which seems to attain- its maximum of development in the
Hyrax. Only the inferior serratus posticiis may be present,
as in the Three-toed Sloth, while sometimes (as in the Bats)
it is the superior which is exclusively, or all but exclusively,
developed.

The splenius capitis is a muscle the possession of which

Y

ELEMENTARY ANA TO MY,

[LESS.

man shares with his class, but which may have no distinct
representative in non-mammalian forms which are higher
than Batrachians, e.g. in the Iguana.

The splenius colli is present only in a few Mammals.

The erector spines presents in man a degree of differentia-
tion not generally found in animals below his class. Thus in
the Iguana and Chameleon it is but divisible into the longi-
tudinal parts answering respectively to the longissimus aorsi

FIG. 290.— DEEPER MUSCLES OF OUTER SIDE OF HINDER PART OF TRUNK AND
ANTERIOR PART OF TAIL, AND OF THE DORSAL (EXTENSOR) SlDE OF RlGHT
PELVIC LIMB OF Menobranchus — the gluteus maximus, rectus femoris, and
extensor longus digltorum being cut and reflected.

EH, extensor hallucis ; ELD, extensor longus digitorum ; ExO, external
oblique ; PC, femoro-caiidal ; G, gracilis ; GMd, gluteus medius ; GMi,

fluteus minimus ; GMx and R F, great extensors of thigh ; /, iliacus (?);
1C, ilio caudal ; IP, iiio-peroneal ; S, sartorius ; SJlf, semi-membranosus ;
ST, semi-tendinosus ; TA and TA I, tibialis anticus.

and sacro lumbalis, and continuing, with the intervention of
certain neck muscles, from the cranium to the end of the
dorsum of the tail. But a greater simplicity still may exist,
as in Tailed-Batrachians (e.g. Menopoma and Menobranchus),
where, without the intervention of any such neck muscles, a
simple, or more or less tendinously intersected muscular mass
extends from the skull directly to the end of the dorsum of
the tail. This dorsal muscle mav be reduced to a mere rudi-

viii.] THE MUSCLES. 323

ment, as in Emys^ where it runs between the transverse and
neural processes and the carapace.

The cervicalis ascendens. This anterior continuation of the
sacro-lumbalis is of great constancy, appearing even in
Reptiles, e.g. Iguana and Chameleo.

Transversalis cervicis. This muscle, which is the anterior
prolongation of the longissimus dorsi, is less constant, as in
at least some Reptiles, e.g. Iguana and Chameleo (Fig. 284), it
does not seem to have any distinct existence.

The complexus is a muscle of great constancy, as it is
found in Reptiles, e.g. Iguana and Chameleo (Fig. 284), while
even in Batrachians and 'Fishes it must be considered as
included in that part of the dorsal extensor mass which
adjoins the head.

The rectus capitis posticiis major is relatively much smaller in
man than in many Mammals, compared with the rectus capitis
posticus minor; while man's obliqui capitis are also relatively
smaller than in very many. Thus in the Horse the posterior
oblique hasten times the bulk of the more normally developed
rectiis posticus minor.

A whole series of muscles may be developed which in man
are entirely absent. These are the numerous muscles which
move the tail, and which may obtain a vast bulk, as in the
Cetacea and in Fishes.

To describe these muscles in detail would rather come
within the scope of a treatise on the Comparative Anatomy of

i

4 3

FIG. 291.— DIAGRAM OF CAUDAL MUSCLES OF RIGHT SIDE OF TAIL OF Iguana,
showing how the ventral mass resembles the dorsal part, and how the ten-
dinous intersections of the muscular fibres are drawn out into cones.
N, neural spine ; H, hypapophysial spire : z, zygapophysis ; t, transverse process ;
i, dorsal series of cones ; 2, upper lateral series of cones ; 3, lower series of
cones ; 4, ventral series of cones.

animals than within that of the present work. Here, however,
it may be stated that the enormous coccyx of the Porpoise is
provided not only with dorsal muscles which continue on
backwards the erector spinas (with its main divisions) from

Y 2

324 ELEMENTARY ANATOMY. [LESS.

the occiput to the tail end, but also possesses a ventral
muscular mass (extending forwards as far as the middle of
the thorax), which mass is divisible from above downwards
into two antero-posteriorly extended masses — together con-
stituting, as it were, a ventral (and here sub-vertebral) re-
flection of the erector spinse. The same appearance occurs
in some Reptiles and in Tailed-Batrachians, where the ventral
muscles of the tail .repeat below, the dorsal masses above.
But these Batrachian caudal muscles are not sub-vertebral —
not the continuation backwards of sub-vertebral ones of the
trunk, but direct continuations backwards of the abdominal
muscles, as is also the case in most Fishes. Muscles of the
tail (even in man's own order) may be very extensive, and

FIG. 292. —MUSCLES OF RIGHT HALF OF A TRANSVERSE SECTION OF THE
TAIL OF Iguana, showing the separation of the caudal muscular cones from
the vertebrae by the intrusion above of a supra -caudal mass from the trunk,
and by the intrusion below of the femoro-caudal.

A , dorsal half of caudal cones ; B, ventral half of caudal cones ; SC, supra-caudal ;
FC, femoro-caudal.

caudal muscles may have attachments such as are indicated
by their names — pu'bococcygeus, ilio-coccygcus, sacro-coccygeits,
and ischio-coccygeus respectively.

Powerful muscles and complex arrangements of tendons
are especially developed in forms which, like the Spider-
Monkey, are capable of suspending the entire body by the
grasping action of the end of the tail.

20. The MUSCLES OF THE UPPER EXTREMITY, as might

be expected, often disappear in those forms in which an upper
extremity is wanting. Just, however, as we found in the
skeleton that we might have bones of the shoulder girdle
without any of those of the arm, so we may have certain of
the muscles in question attached to that shoulder girdle
though the actual extremity be wanting. Such is the case
in sorm Reptiles, e.g. in Angnis fragilis. The muscles may
be greatly reduced in size where there is little variety of
motion, as in Birds and Cetaceans. No profitable compari-

VIII.]

THE MUSCLES.

325

son can be instituted between the limb-muscles of man and
of Fishes. Very simple muscular fasciculi represent in Fishes
the complex structures of higher vertebrates.

The pectoralis major is a nearly constant muscle, but one
which may vary greatly as to its relative size to other
muscles its degree of subdivision, and the details of its

326 ELEMENTARY ANATOMY. [LESS.

origin. Thus in many Birds it is the absolutely largest
muscle, and equals the weight of all the other muscles of
the body put together. In the last-named class it may send
a slip to the pollex, as in the Eagle (see Fig. 289, 2).

Pectoralis minor. The smaller pectoral is a much less con-
stant muscle than the large one, being very frequently absent.
Even in animals closely allied to man (e.g. many Apes) it is
inserted into the capsular ligament of the humerus instead of
into the coracoid process. It may form one with the pecto-
ralis major, as in Birds.

The sub-clavius is also an inconstant muscle. It may take
on an enormous development and be singularly modified, as in
Birds, where it arises beneath the pectoralis, and is so inserted
as by its action to antagonize that muscle ; for it sends a
tendon between the clavicle and coracoid, and the scapula
(the margin of the interspace through which it passes serving
as a pulley), by which the direction of its force is changed,
so that it serves to elevate instead of to depress the humerus.

Serratus mag nits. This, which really is one muscle with the
levator anguli scapulae, may be much more extensive or much
more restricted than in the human subject. In Quadrupeds
(e.g. the Horse) the serrati of the two sides serve to sling the
trunk from the scapulae, or summits of the columnar fore-
limbs. It may consist of several detached parts, as in the
Chameleon, or be exceedingly small, as in Menopoma
(Fig. 283).

The deltoid is a nearly constant muscle in Vertebrates above
Fishes, but may be very small, as in the Horse, or very large,
as in the Bat, or it may be divided into several parts.

The supra-spinatus of man is normal as compared with
that of other animals of his class ; but, by a strange excep-
tion, it may be placed only on the inner (or body) side of
the scapula, as in the Echidna.

The infra-spinatus\ which is also normal in man, may (as
in the Echidna) be placed at the most anterior part of the
outer surface of the scapula.

The teres minor may coalesce with the last-noticed muscle,
as in the Two-toed Ant-eater. The minor may be larger
than the major, as in the Horse.

The teres major is normal in man, but it may attain a
very much greater relative size, as in the Mole.

The subscapularis is generally in Mammals much as it is in
the human subject. It may be considerably smaller, however
(as in Cetaceans) ; and by a singular exception it may (as in the

vin.] THE MUSCLES. 327

Echidna) exclusively arise from the external surface of the
scapula.

The coraco-brachialis of man does not normally exhibit
the complexity of structure which it may exhibit in some
other Mammals. Thus, in addition to the part usually
developed in man (namely, that descending to about the
middle of the shaft of the humerus), we may have a shorter
part inserted above the tendon of the teres major and con-
nected with the capsular ligament (as in the Bonnet Monkey
and many other species), and a third part descending right
down to the internal condyloid ridge of the humerus, as in
the Echidna, in Lemur, Iguana (Fig. 296), and others.

FIG. 294.— MUSCLES OF INSIDE OF RIGHT ARM OF Iguana (seen in front), the
pectoralis and deltoid being cut short and reflected.

B, biceps; EA, brachialis anticus ; CJS1 and C2?3, coraco-brachialis; Z*1 and
D2, deltoid; EH, muscles perhaps answering to the subclavius; IS, infra-
spinatus ; P, pectoralis ; SCM, stern o-cleido-mastoid ; T1^, triceps.

The biceps as it exists in man is a fair exponent of its
normal condition, at least in his class. This muscle, however,
may arise from but a single head, which may take origin
from the scapula only, as in the Pig, or from the coracoid
only, as in the Echidna and the Iguana. Its insertion may
take place both into the ulna and radius, as in the Pig, and the
two tendons of insertion may divide, allowing the brachialis
anticus to pass between them, as in the Chameleon. This
muscle may arise even from the sternum, as in the Frog.

Brachialis anticus. This is rather short in man. It may
be divided into two parts, as in the Agouti. It may be more
or less confounded with the biceps, as in Iguana, Menopoma,
and Menobranchus.

328 ELEMENTARY ANATOMY. [LESS.

Triceps. The great extensor of the arm in man, in spite of
its size and complexity, is small and simple compared with
conditions which may obtain. Thus it may (as in Hyrax)
have four heads, and in addition a fasciculus going from the
surface of the infra-spinatus to the olecranon, and called
the dorso-epitrochlear (Fig. 295, Zte.) It may be very powerful

FIG. 295. — MUSCLES OF OUTER SIDE OF FORE-LIMB OF HYRAX.

m, serratus magnus ; Re, rhomboideus capitis ; Ssfi, supra-spinatus ; Isp,
infra-spinatus ; D, deltoid ; Tmaj, teres major : De, dorso-epitrochlear ;
jT1 — 4, triceps ; Ba, brachialis anticus ; SI, supinator longus ; Eld, extensor
longus digitorum ; Emd, extensor minimi digiti.

and take origin largely from the scapula, as in the Pig and
Echidna, or it may take origin from the coracoid also, as in
the Iguana. It may be quite rudimentary, as in the Porpoise.
21. The MUSCLES OF THE FORE-ARM in man attain almost
their maximum of complexity. As might be expected, they
become greatly reduced in animals the hands of which have
little mobility (as Birds and Cetaceans) or have a reduced
number of digits. In Birds the actions of the pronators and
supinators are modified and limited to opening and shutting
the wing, i.e. to ad- and ab-duction.

THE MUSCLES. 329

Pronator teres. This is a nearly constant muscle, being
present even in Menopoma and Menobranchus (Fig. 297). Its
size and importance are often relatively greater than in man.
It may, on the contrary, be quite absent, as in the Hedgehog
and the Horse.

FIG. 296.— MUSCLES OF INSIDE OF RIGHT ARM OF IGUANA.
B, biceps ; C, sternal margin of coracoid bone ; CB x and CB 2, two parts of
coraco-brachialis ; CC, cpsto-coracoid ; FR, flexor carpi radialis ; FL7, flexor
carpi ulnaris ; Z.Z?, latissimus dorsi ; 6° 2, subscapularis ; T1, T2, and T 4, parts
of triceps ; /, tendon from latissimus dorsi to triceps.

Flexor carpi radialis. This is normal in man, but its
insertion may vary in other animals. It may arise from the
ulna only (and not from the humerus), as in Birds.

FIG. 297.— DEEPER FLEXOR MUSCLES OF RIGHT FORE-ARM OF Mfnopoma, the

flexor longus being cut and reflected.

B, biceps; FB, flexor brevis; FL, flexor longus; SL, supinator longus; PT,
pronator teres.

The palmaris longus is often absent (as e.g. in the Hedge-
hog, in Ruminants, the Horse, &c.), or blends with the flexor
digitorum, as in the Echidna, or with the flexor radialis. Its

33°

ELEMENTAR Y ANA TOMY.

[LESS.

palmar fascia may contain a fibre-cartilaginous disc, as in
Hyrax.

The flexor carpi ulnaris of man is normal. It may be
greatly more complex and divided into four portions, as in
the Two-toed Ant-eater, where the pisiform bone is so large.

P.t

F.l.p

FIG. 298. — LONG FLEXOR MUSCLES AND TENDONS OF THE HAND OF

NYCTICEBUS.

Pt, pronator teres ; Fs, flexor sublimis digitorum : Fp, flexor profundus digitorum ;
Flp, flexor longus pollicis.

Flexor sublimis digitorum. This muscle in man presents
a degree of distinctness which is by no means constant. It

VIII.]

THE MUSCLES.

may be united with the flexor profundus in one mass, as in
the Kangaroo and Echidna. It may also be confined to
the hand, and therefore be a short muscle, as in the Iguana
and Chameleon. It is small in Birds.

That symmetrical bifurcation and definite arrangement of
the perforated tendons which obtains in man is by no means

F.C.V

F.sJ

-F.-p d

FIG. 299.— FLEXOR MUSCLES AND TENDONS OF FORE-FOOT OF HYRAX.

Plt palmaris longus ; Feu, flexor carpi ulnaris ; Fsd, flexor sublimis digitorum ;
Ffdy flexor profundis digitorum ; Flp, flexor longus pollicis ; Pf, palmar
fascia ; Fbm, flexor brevis manus ; L, lumbricales.

constant. Thus it is absent in Birds ; and in lower Vertebrates
(e.g. Iguana) this muscle can hardly be said to be inserted by
definite tendons. Even in man's own order we may see by
the Nycticebinae how the index digit may fail to have a true
perforated tendon, while the imperfect condition of the flexor
sublimis may be supplemented (as in Hyrax) by an extra

332

ELEMENTARY ANATOMY.

[LESS.

muscle, a peculiar flexor brews manns which takes origin
from the palmar fascia.

The flexor profundus digitorum in man possesses an ex-
ceptional distinctness and subdivision. As has been said, it
may be intimately united with the siiblimis, as it may also be
(even in Monkeys) with the flexor longus pollicis. When dis-
tinct from the latter, it may yet send a tendon to the thumb,
as mNycticebus. It may end in but one, or at most two ten-
dons, as in Birds. In the complete separation of this muscle
from the one next mentioned, man differs from all the Apes.

Flexor longus pollicis. This muscle is very commonly
completely united with that last described, as e.g. in Echidna,

FIG. 300.— Di. GXAM OF FLEXOR TENDONS OF HAND OF NYCTICEBUS.

The numbers indicate the digits (from the pollex to the minimus) to which the

tendons go respectively.

F Jp, flexor longus pollicis ; F /, flexor profundus digitorum ; Fs, flexor sublimis
digitorum.

Dasypus, and even in the Apes. The two united deep flexor
muscles (profundus and longus pollicis) may fail to send any
tendon at all to the two or three ulnar digits, as is the case
in Bats. When the two deep flexor muscles are distinct,
the longus pollicis may send tendons to all the digits, uniting
variously with those of the flexor profundus, as in Nycticebus,
Lori's, and Chameleo. It may send no tendon to the pollex
in a form closely allied to man, i.e. in the Orang.

Lumbricales. These may be altogether absent (as in Birds,

viii. 1 THE MUSCLES. 333

the Hedgehog, and Pig), or there may be but one, as in
Pteropus. The thumb, on the contrary, may have its own
lumbricalis, as in Dasypus Sexcinctiis^ and there may be
eight in the hand, as in Galeopithecus.

The pronator quadratiis may be much more elongated
than in man, as in the Dog and Cat. It may, however, be
completely wanting, as in the Flying Fox and in the Horse.
An accessory pronator may be developed (as in the Iguana
and Chameleon), arising from the internal condyle and radial
border of the ulna, and being inserted into the lower part of
the radius between the insertions of the pronator teres and
pronator quadratus.

FIG 301. — DEEP FLEXOR MUSCLES OF FORE-ARM OF Iguana, the more superficial

ones being cut and reflected.
B, biceps ; FCR, flexor carpi radialis ; FCU, flexor carpi ulnaris ; FPD, flexor

profundus digitorum ; PA, pronator accessorius ; PQ, pronator quadratus;

PT, pronator teres ; SA, supinator accessorius; SL, supinator longus.

Supinator longns. This is a very inconstant muscle, as
might be expected from its action, which is related to the
exceptional mobility of the fore-arm and hand of man. Thus
it is totally absent in many animals, e.g. the Horse. It may,
on the contrary, attain a vastly greater relative size than in
man, as in Bradyp^ls, where it takes origin from the lower
three quarters of the humerus, and is separable into two
parts ; it is large and double in some Reptiles, e.g. the Iguana
and Chameleon (Figs. 302 and 303).

The extensor carpi radialis longior is exceptionally distinct
in man, for in most Mammals it is more or altogether united
with the extensor carpi radialis brevior.

334

ELEMENTARY AM A TOMY.

[LESS.

Anconeus. This muscle, which in man seems to be but a
small part of the triceps, may be a very large and very dis-
tinct muscle, as in Dasypus and Phoca.

Extensor communis digitorum. This is exceptionally dis-
tinct in man, being often (as e.g. already in Nycticebus]
blended with one or more other extensors. It may be so
diminished and short as to extend only from the carpus to the
digits, as e.g. in Igtiana and Chameleo.

FIG. 302.— RADIAL SIDE OF RIGHT ARM OF PARSON'S CHAMELEON.
A3, adductor digiti tertii; A*, adductor digit! quarti ; B, biceps ; B r, B2, B3, ex-
tensores phalangorum ; E3, E4, E$, extensores metacarporum ; ERL, ex-
tensor radialis longior ; FR, flexor radialis ; MPt extensor metacarpi pollicis ;
PT, pronator teres ; SL, supinator longus.

Extensor minimi digiti. This extensor, which may be
absent, may also be present where we might hardly expect
to find it. Thus it may be present in forms in which the
digitus minimus is entirely absent, e.g. the Horse. This fact
is less remarkable, however, when it is recollected that the

VIII.]

THE MUSCLES.

335

muscle's special destination to the fifth digit is a human but
not a Mammalian character. Very often, even in man's own
order, this muscle may send tendons to the third and fourth
digits also

The extensor carpi itlnaris, normal in man, may be much
increased in size, as e.g. in the Two-toed Ant-eater. It may
be diminished — not arising from the humerus — as in some
Birds. It may, as in Iguana, be united in one with the
flexor carpi ulnaris.

FIG. 303. — DEEPER MUSCLES OF EXTENSOR ASPECT OF RIGHT FORE-ARM OF

PARSON'S CHAMELEON, the extensores radiales longior and brevior being cut

and reflected.
B, biceps ; E* — E^, extensores metacarporum : ERB, extensor radialis brevior ;

ERL, extensor radialis longior: EU, extensor ulnaris; FU, flexor ulnaris;

MP, extensor ossis metacarpi pollicis : PQ, pronator quadratus ; SL, supi-

nator longus ; T, triceps.

Extensor ossis metacarpi pollicis. This muscle of man ex-
emplifies a very constant condition, since it exists in animals
in which the pollex is entirely absent, as e.g. in the Horse.

336 ELEMENTARY ANATOMY. [LESS.

The muscle may be double and very voluminous, as e.g. in the
Chameleon. Even in very near allies of man (the Anthropoid
Apes) it ends in two tendons, one going to the trapezium, the
other to the metacarpal of the thumb.

The extensor primi internodii pollicis appears to be exclu-
sively human.

The extensor secundi internodii pollicis is often wanting.
It may coalesce with the extensor indicis, as in the Dog and
Rabbit.

Extensor indicis. This muscle may be absent as well as
that last described, as e.g. in Hyrax. It may send tendons to
other muscles besides the index, viz. to the third, fourth, or
fifth digits, as in the Lemuroidea.

Supinator brevis. This may even in Mammals be entirely
absent, as in the Horse. There may however be an acces-
sory supinator, as in the Iguana.

22. The MUSCLES OF THE HAND of man of course possess
an especial character in harmony with the special perfection
of that organ in him. Its muscles, with the exception of the
interossei, can hardly be compared with any profit with the
muscles of creatures below the rank of Mammals. For
though sometimes (as e.g. in Chameleo) we may meet with a
so-calledy&?.r0r brevis pollicis or fiexor brevis minimi digiti,
it is difficult to assert that these are really homologues of the
muscles so named in man. Nevertheless, though the muscu-
lar condition of the human hand is special, yet its essential
type is that common to the class to which man belongs, and
especially like that of his own order, Primates, the members
of which possess all the manual muscles of man, only more
or less different in form and proportion. It may be, how-
ever, that these muscles are wanting altogether, as in the
Horse and Whale, but they are generally present even where
they might not be expected (at least all), as e.g. in the Dog.

Opponens pollicis. This muscle in man attains its maxi-
mum degree of relative size. It is not only present, though
small, in the Primates generally, but it is present in forms
quite destitute of an opposable thumb, as e.g. in the Dog.

The adductor pollicis may be inserted into the index
through atrophy of the pollex, as e.g. in the Dog.

Palm.iris brevis. This muscle is not peculiar to man. It
not only exists in his order, as e.g. in Lemur, but is found
even in Marsupials, e.g. the Tasmanian Devil. In the
Echidna it has been said to take origin from the ulna.

Opponens digiti minimi. This muscle exists not only in

vni.] THE MUSCLES,

337

man and his order, but even in such forms as the Do«- and
the Bat.

Interossei. These muscles are very generally present,
existing even in the cold-blooded Vertebrates, and their
essential nature is that of flexores breves. Even in man half
of each pair of interossei acts as an extensor, being inserted
into the dorsum of the third phalanx ; while half of each pair
acts as a flexor, being inserted into the palmar side of the
first phalanx. Indeed, it is by a modification of what are
essentially interossei that some of the small special muscles
of the pollex and little finger are constructed, as the abductor
pollicis and digiti minimi.

The distinction between " palmar " and "dorsal " interossei
is really unimportant, referring only to the mode of their
origin from the metacarpals.

23. In the ABDOMINAL REGION, the body-wall of man is
composed of muscular layers such as normally exist in other
Vertebrates above Fishes. The muscles ma'y, however, be
severally more developed or less developed, or more complex
or less complex, thao they are in him.

On entering the class of Fishes we lose the superimposed
lamellse of differently directed muscular fibres of which the far
greater portion of the abdominal muscles in the higher forms
consist. In their place we have exclusively antero-posteriorly
directed fibres, and it is as if the recrus muscle had increased
vastly and entirely at the expense of the completely aborted
oblique muscles. That this is so, seems to be demonstrated
by those Batrachians which begin life with so many and close
resemblances to Fishes, which subsequently they lose. Thus
in the great persistent larva, the Axolotl, we find no truly
oblique abdominal muscles, but only as it were a hyper-
trophied rectus ; while in the rarely attained adult condition
(in which it closely resembles the genus Amblystoma] we
meet with the normal muscular abdominal structure of super-
imposed oblique lamellae.

Sometimes the number of these lamellae is greater than in
man : thus the obliqmis externus may consist of three dis-
tinct layers, as e.g. in the Iguana.

The obliquus internus of man is of moderate development.
It may be less developed than in him, as e.g. in the common
Chameleon. On the other hand it may be much larger,
relatively, as in Iguana, where it lines the whole of the
thorax ; or it may be, as in Menopoma and Menobranchus,
the largest muscle of the body, being continued on forwards

z

33^

ELEMENTAR Y ANA TOMY.

[LESS.

and backwards so as to extend from the hyoid to the distal
end of the tail.

Transversalis. This third abdominal muscle as it exists
in man is normal, but its aponeurotic part may be much

FIG. 304. — SUPERFICIAL VENTRAL MUSCLES OF RIGHT SIDE IN MENOTOMA.

ExO, external oblique ; FC , femoro-caudal ; G, gracilis ; /, iliacus ; 1C, ischio-
caudal; IIC, ilio-caudal ; SM. semi-membranosus ; ST, semi-tendinosus ; TA,
tibialis anticus.

greater than in him, as e.g. in Iguana, where its fascia is
continued on, even into the neck, within the nerves of the
brachial plexus, which pass external to it as the abdominal
nerves pass between it and the internal oblique.

vin.] THE MUSCLES.

339

Rectus abdominis. The greatest relative size of this
muscle is exemplified in the class of Fishes, where it extends
in the mid-abdomen from the tail to the pectoral arch, and
thence, forwards, to the mandibular symphysis. A complica-
tion of division may exist, as we find in the Salamander,
where there is a superficial rectus lying, on each side, imme-
diately upon a deeper one.

Even in man's own class this muscle may be very much
more developed than in him, as in the Slow Lemur, the Arma-
dillo, and Ornithorhynchus, where it goes to the first rib. The
linece transversce may be absent, as in the Hedgehog, the
Dolphin, and the Hyrax ; or they may be seven in number, as
in the Racoon ; or they may be replaced by regular abdominal
ribs which subdivide the rectus into a longitudinal series of
successive segments, as in the Chameleon.

The pelvic origin of the muscle may be wanting, as in the
Cetacea, where it arises (by a long and thin aponeurosis)
between the dorsal and ventral muscles of the tail, from the
ventral side of the transverse processes of some of the mid-
coccygeal vertebrae.

A slip from this muscle may be sent to the humerus, as in
some Armadillos and insectivorous Bats.

Pyramidalis. This may be more largely developed than in
man, as in the Iguana and in Marsupials and Monotremes,
where it arises from the marsupial bones. It becomes enor-
mous in the Ornithorhynchus.

The quadratus himborum is a nearly constant muscle ; it
may be distinctly developed in Reptiles, and is large in the
Iguana.

The development of the intercostal muscles is of course
governed by the size and number of the ribs. Thus they
may be more or less developed than in man, or they may be
completely absent.

24. The diaphragm. In the possession of a complete
partition, or diaphragm, man agrees with all the members
of his own class, but differs from all those of every other
class, though in some of the latter it may form an incomplete
partition, at the least allowing the apex of the heart to pass into
the abdominal cavity, as in the struthious Birds. In man's own
class this muscle may vary as to the extent of the central
tendon and as to the points of origin and insertion. Thus
in the Manatee (which has so many ribs) the obliquity of
the diaphragm is so extreme that the thorax extends back-
wards above the whole length of the abdominal viscera. Very

Z 2

34°

ELEMENTAR Y ANA TOMY.

[LESS.

rarely the diaphragm may contain a sesamoid bone, as in
the Camel. There may be no tendinous centre, this being
absent in the Porpoise.

In Reptiles (e.g. Iguana) a muscle, the retrahentes costarum,
(which appears to have no representa-
tive in man), arises by muscular fibres
from the sides of the bodies of the
trunk vertebras, and is inserted by
aponeurosis into the inside of the
seventh and eighth cervical ribs, and
into the seven following ribs. In
Tailed-Batrachians (e.g. Menopoma)
this muscle is very fleshy at its an-
terior end, and is carried forward
beneath the basis cranii.

25. Of the MUSCLES OF THE IN-
FERIOR EXTREMITY. Thz psoas mag-
nus may be very much larger relatively
than in man (thus it is exceedingly
large in the Rabbit and Agouti), or it
may be (as in Birds and the common
Seal) entirely wanting. It has been
supposed that the great muscular mass
which in Cetaceans (e.g. the Porpoise)
and the Seals extends forward beneath
the trunk part of the spine from be-
neath its caudal part, is a psoas.
.'';W< ilaS This is not the case, however — it is

a sacro-coccygeus extraordinarily pro-
longed forwards.

lliacits. This muscle may be want-
ing, as in the Whales and Seals ; or
relatively enormous, as in the Bats,
where it is inserted separately from
the psoas, and below the latter. The
iliacus (or else the psoas) may extend
its origin up to the last two dorsal
vertebras, as in Nycticebus.

FlG. 305. SUBVERTEBRAL

MUSCLES OF RIGHT SIDE
OF IGUANA.

QL, quadratus lumborum ;
RC, retrahentes costarum.

The psoas parvus may be altogether
anting, as in Cetaceans and Bir

wanting, as in Cetaceans and Birds.
It may be as large as the psoas mag-
nus, as in the Pig, or ten times larger, as in the Kangaroo.

A muscle may exist which extends from the coccygeal region
of the backbone to the femur, but which has no certain

viii.] THE MUSCLES. 341

representative in man. Such a muscle is the femora-caudal
of Reptiles, Birds, and Tailed-Batrachians. This (e.g. in the
Iguana and Chameleon) arises beneath the caudal vertebrae,
and, though mainly inserted into the femur, sends on a deli-
cate tendon which, passing down, is inserted into the articular
cartilage between the femur and tibia.

FIG. 306. — MUSCLES OF EXTERNAL ASPECT OF LEG OF AN EAGLE
(A quilafucosa),

i, sartorius ; 2, tensor vaginae femoris (?); 3, biceps; 4, semi-membranosus : 5,
levator coccygis ; 6, tibialis anticus ; 7, gastrocnemius.

(After A. Milne-Edwards.}

Glutens maximus. This muscle is of very exceptional size
in man, directly related as it is to his erect attitude. Never-
theless, it may be yet greater relatively in some quadrupeds
than it is in him, as e.g. in the Echidna, where it is double,
and where part passes from the sacral and coccygeal vertebras
downwards to the ankle, and represents that part of the
muscle which in man is inserted into the fascia lata, while
another portion with a similar origin is inserted into the
femur. The muscle exists in Birds and in Reptiles. In the
Chameleon (Fig. 311) it passes from the caudal vertebras to
the tendinous arch going from the posterior margin of the
ilium to the tuberosity of the so-called ischium. This muscle
may be inserted into the whole length of the femur, as in
the Seal.

The gluteus medius is very often much thicker and larger
than the gluteus maximus. This is the case, e.g., in the Horse,
where it is twelve times as big as the maximus. It may arise
not only from the ilium but from the sacral and even from the
lumbar vertebral spines, as in the Echidna. The muscle ap-
pears to be almost a constant one, as it exists, well-developed,

342

ELEMENTARY ANATOMY.

[LESS.

in Birds ; and a muscle seeming to represent it, passes from
the outside of the ilium to the femur in Reptiles and Batra-
chians.

The gluteus minimus is, when distinct, almost if not quite
always smaller than the medius, with which it may be more
or less completely blended.

The pyriformis may also be confounded with the gluteus
medius, as is the case in the Horse.

Obturator internus. This may be wanting, as in the
Ornithorhynchus and Echidna. In the Three-toed Sloth
and Ant-eater it becomes a second obturator externus smaller
than the real one, having quitted its normal place.

FIG. 307.— INNER VIEW OF RIGHT HALF OF THE PELVIS OF HYRAX.

Ot, obturator internus : Oter, obturator tertius ; PC, pubo-coccygeus ; C, coccy-

geus; Gi, gemellus inferior; Am, adductor magnus.

The gemelli may be wanting altogether, as in the Orni-
thorhynchus and Echidna. The gemellus inferior may be
almost as much developed as the obturator ; such, e.g., is the
case in the Camel. There may be but a single fleshy strip,
as in the Apteryx.

The quadratus femoris is an almost constant muscle,
though varying as to size, shape, and direction.

viii.] THE MUSCLES. 343

The obturator externus is also a constant muscle both as
to existence and position, being found even in the Frog. A
peculiar sort of additional external obturator (but with an
anomalous internal origin) may exist, as in the Hyrax, where
a third obturator springs from the inner surface of the ischium,
close to its junction with the pubes, and which, passing
through the obturator foramen, is inserted into the trochan-
teric fossa in common with the obturator externus (Fig. 308).

O.frr

FIG. 308.— RIGHT SIDE OF PELVIS OF HYRAX, seen in front.

/, iliacus ; Pin, psoas magnus ; P, pectineus ; Oter, obturator tertius ; Oe, obtu-
rator externus (cut and reflected) : Qf, qu^dratus femoris.

Tensor vagina femoris. This may be altogether wanting,
as in the true Opossums. It may, on the contrary, be very
largely developed, as in the Seals (where it arises from the
panniculus carnosus and external oblique) and in the Horse.
It may be more or less blended with the gluteus maximus,
as in Agouti.

Sartoritis. This muscle is generally present in Mammals,
though it may be altogether wanting, as in Bats. Its origin
and insertion may both differ considerably from what we find
to exist in man. Thus, in the Agouti it arises from the
ilio-pectineal eminence and the pubic symphysis. It may
have two heads (one on each side of the tendon of the
psoas magnus), as in the Horse. It may be confounded
above with the tendon of the long extensor of the thigh, as
in Ruminants. It may arise, as in the Three-toed Sloth,
from the lower part of the aponeurosis of the external
oblique, and then divide into two parts— one of these being
inserted into the femur, the other again subdividing and

344 EL E MEN 'TAR Y ANA TOMY. [LESS.

going to the inside of the tibia above the insertion of the
gracilis.

A muscle exists in Reptiles (e.g. the Iguana and Chameleon)
which may answer to this. It arises from the front pelvic
tendinous arch, or from the brim of the pelvis, and is inserted
into the peroneal side of the head of the tibia (Iguana), or,
bifurcating, sends one branch to the tibia and the other to
the inter-articular cartilage(Chameleon). (Figs. 309 and 310,6".

FIG. 309. —DEEPEST MUSCLES OF RIGHT THIGH OF Iguana, the more super-
ficial ones being removed.

A, adductor ; BF, biceps femoris ; C, crureus ; FC, femoro-caudal ; Gol, gas-
trocnemius internus ; IP, ilio-peroneal ; OE, obturatorexternus ; OI, obturator
internus ; PC 1 — 3, muscles which more or less resemble the pectineus ; Pf,
probably the gluteus maximus ; R F, part of the great extensor of the thigh ;
S, tibial adductor ; SM and ST, muscles resembling the semi-membranosus
and semi-tendinosus respectively ; VI, vastus internus ; J', tendon descending
from the tendon of the femoro-caudal to the inter-articular cartilage of the
knee-joint.

Quadriceps extensor cruris. The large muscular mass
thus named in man, has by no means in him attained its
maximum of size and complexity. Even in man's order,
e.g. Lemur, the portion called crureus, instead of being but
a mere imperfectly differentiated part of the vastus internus,
is a large and very distinct muscle; while in a nearly allied
form, Tarsius, the vastus externus. is divided into two parts.

VIII.]

THE MUSCLES.

345

and the crureus into even three, making with the rectus
femoris a sevenfold extensor muscle.

The tendon of a muscle which seems to answer to the
rectus femoris may end by uniting with the plantaris, as in
the Alligator and in Birds, in which the plantaris is the
perforated flexor of the toes, as it is also in the Rabbit.

FIG. 310. — DEEPER MUSCLES OF INNER ASPECT OF RIGHT PELVIC LIMB OF
PARSON'S CHAMELEON.

A, adductor; B, biceps; El and E2, extensores metatarsorum ; EL, extensor
longus digitorum ; f1 and F2, rectus femoris ; FD *, flexor longus digitorum ;
G, gracilis ; GE, gastrocnemius externus ; 67", gastrocnemius internus ; /,
iliacus ; IP,, ilio-peroneal ; .5", tibial adductor; ST, semi-tendinosus ; TA,
tibialis anticus; V1, vastus intemus.

The vastus internus may be almost absent, as in the Three-
toed Sloth, and the rectus may be but imperfectly differen-
tiated from the deeper part of the extensor, as is the case in
Bats. The rectus may, on the contrary, be very large and
consist of two muscles with distinct origins, as in the Alligator,
Iguana, Menopoma, and Menobranchus. The vasti and cru-
reus may be absent, as in the two last-named genera.

The gracilis in man is an exceptionally narrow and weak

346

ELEMENTAR Y ANA TO MY.

[LESS.

muscle, but its insertion may (as in the Three-toed Sloth)
occupy almost the whole length of the tibia. This muscle
may be intimately blended with an adductor, as in the Pig,
or more or less with the sartorius, as in the Coati. It may
have a special ridge on the tibia for its insertion, as in
Pteropus.

FIG. 311. — DEEPER MUSCLES OF OUTER ASPECT OF RIGHT PELVIC LIMB OF
PARSON'S CHAMELEON ; the ilio peroneal cut and reflected.

A, adductor; Z>, biceps ; Z>', gluteus primus ; D2, gluteus secundus ; Z?3, glutens
tertius ; EL, extensor longus digitorum ; F~ and F^, rectus femoris ; FC,
femoro-caudal ; FD1, flexor longus digitorum ; FD2, flexor tertius digitorum ;
G, gracilis ; GE, gastrocnemius externus ; IP, ilio-peroneal ; P, peroneus ;
S, tibial adductor : S M , semi-membranosus ; VE ', vastus externus ; Ar, gluteus
maximus ; y, tendon of femoro-caudal.

The pectineus and adductors of man may exist, in other
animals, as muscular masses of very different size and some-
times in different divisions from what they exist in him. The
adductors may be extraordinarily small and feeble, as in the
Seal.

THE MUSCLE.

347

Biceps femoris. The relative size of this muscle in man
is much inferior to its possible development, and in that it

FIG. 312. — SUPERFICIAL MUSCLES OF RIGHT LEG OF IGUANA.

BFt muscle like the biceps ; EB1-^, extensor brevis digitorum ; ELD, extensor
longus digitorum ; FC, femoro-caudal ; G, gracilis ; GMx, muscle like the
rectus femoris ; Go E, gastrocnemius externus ; IP, ilio-peroneal ; Pl and P2,
peronei muscles ; P/t muscle resembling in some respects the glutens maxinaus ;
SM* and SMZ, semi-membranosus ; TA, tibialis anticus ; VEx, vastus ex-
ternus ; x, caudal muscle.

has in him a separate head, taking origin from the femur, it
is exceptional. Sometimes (as e.g. in the Agouti) this muscle

343

ELEMENTARY ANATOMY.

[LESS.

combines with the tensor vaginae femoris and the gluteus
maximus to form an almost continuous muscular sheet, extend-
ing as to its origin from the crest of the ilium to the caudal
vertebrae and ischium, and, as to its insertion, from the patella
to the ankle, thus contributing to form a most powerful flexor
of the limb.

This muscle may be entirely wanting, as in the Bats (ac-
cording to Meckel). We may, on the contrary, find a com-
plexity of muscular structure on the peroneal aspect of the
pelvic limb, by far exceeding anything met with in the class
to which man belongs.

G-.Mx

VHV

FIG. 313.— DEEPER MUSCLES OF EXTENSOR SURFACE OF RIGHT LEG OF
MENOPOMA.

B, biceps; EB, extensor brevis ; EH, extensor hallucis ; ELD, extensor longus
digitorum ; FC, femoro-caudal ; GMd and GMi, muscles like the lesser glutei ;
GMx and RF, great extensors of the thigh ; 7, muscle resembling the iliacus ;
IIC, ilio-caudal ; IP, ilio-peroneal ; SM and ST, muscles like the semi-
membranosus and semi-tendinosus respectively ; TA, tibialis anticus.

Thus in some Reptiles and Batrachians we find four dis-
tinct muscles which, if not exactly answering to the biceps,
may most fitly be noticed in relation with it.

Thus (i) we have a muscle (sometimes called ilio-peroneal}
extending from the outer side of the ilium downwards to be
inserted by a strong tendon outside the upper part of the

VIIL] THE MUSCLES.

349

fibula, or, as in the Chameleon, by a fan-like expansion into
the outer side of the fibula. This muscle is very generally
developed, as it exists even in Menobranchns, where it seems
to represent the long head of the biceps femoris of man.

(2) We have sometimes (e.g. in Urodeles) a muscle
springing from the shaft of the femur, just below the inser-
tion of the femoro-caudal, and itself inserted into the fibula.
It seems to answer to the short head of the human biceps
femoris, and if so it is interesting to note at what a remote
distance from man we find a striking analogy to human
structure, which yet seems absent in the Sauropsida (Fie
313, B\

(3) We have the large and very remarkable muscle (the
femoro-caudal, before described) arising from the caudal
vertebrae, and inserted by a very strong tendon into the great
trochanter, but giving off a delicate tendon passing down
into the popliteal space to the inter-articular cartilage between
the femur and the tibia.

(4) Finally, we .have in some Reptiles (e.g. the Iguana) a
muscle arising from the tendinous arch, which passes from
the so-called ilium to the so-called spine of the pubis, and
inserted by a tendon (passing between the tibia and fibula)
into the front aspect of the upper part of the tibia, or passing
down to a plantar ossicle, as in the Chameleon (Figs. 309,
312, and 317, BF\

By a still greater complication this muscle may be doubled,
as in the Crocodile and Alligator ; one part having a twofold
insertion into the front of the tibia and the plantaris muscle,
the other portion having a twofold insertion into the head of
the fibula and the external gastrocnemius.

Semi-tendinosus. This is exceptionally slender in man.
Even in man's own order it may have a second head of origin
from the coccygeal vertebrae, as in the Aye-aye ; and often in
other Mammals (e.g. the Horse) it is very large. Its insertion,
even in Apes, is lower than in man and Bats. In the Dog and
Cat it is attached to the middle of the tibia, while in the Bear
it is inserted still lower. This muscle may partly end in a
tendon becoming confluent with that of the internal gastro-
cnemius, as in Birds. A muscle which may be the semi-
tendinosus, but which otherwise has no representative in man,
springs from the tendinous arch referred to in speaking of the
biceps, and is inserted into the upper part of the tibia by a
tendon common to it and to the gracilis in the Iguana, or
above it into the inter-articular cartilage in the Chameleon.

ELEMENTARY ANATOMY.

[LESS.

The semi-membranosus of man is small compared with that
of some other animals (e.g. of the Horse and Ruminants), where
it is enormous ; the rump-steak of the butcher not consisting,
as often supposed, and sometimes taught, of the gluteus maxi-
mus, but of the semi-tendinosus and semi-membranosus.

Sometimes (as e.g. in the Kangaroo) this muscle is more
or less completely blended with the semi-tendinosus. On the
other hand it may, as in Hyrax, not only be enormous, but
also arise by two heads (one from the ischium, the other from
the caudal vertebras), and have an insertion into the condyle
of the femur as well as into the tibia.

This muscle may, as in the Iguana, consist of two parts ; one
attached to the back of the leg, embracing the inner head of
the gastrocnemius — some fibres passing beneath the internal
lateral ligament ; the other inserted, in common with the
sartorius, into the peroneal aspect of the tibia (Fig. 317).

FIG. 314. — DEEPER MUSCLES OF FLEXOR SURFACE OF RIGHT HIND LEG OF

MENOPOMA.

A, adductor ; B, biceps ; FC, femoro-caudal ; FD, flexor digitorum ; G, muscle
in position more or less like the gracilis- it is cut and reflected ; /, muscle like
an iliacus ; 1C, ischio-caudal ; IIC, ilio-caudal ; IP, ilio peroneal ; SM and
ST. muscles like the semi-membranosus and semi-tendinosus respectively ;
TA, tibialis anticus.

It may, together with the preceding muscle, present what
appears to be an anomalous condition, as in the Tailed-Batra-
chians (e.g. Menopoind]^}\^.\Q. a muscle (Fig. 314, SM} takes
origin from beneath the caudal vertebrae and blends with a

THE MUSCLES.

351

second muscle (Fig. 314, ST), which, springing from the
ischium, passes downwards and ends in a fascia outside the
lower part of the flexor longus digitorum.

The semi-tendinosus and semi-membranosus may, as in the
Seal, be represented by a muscle arising from the anterior
coccygeal vertebras and inserted into the tibia, some tendinous
fibres going to the plantar surface of the hallux.

26. Of the MUSCLES OF THE LEG. The tibialis anticus,
even in Anthropoid Apes, may have the part going to the
hallux so distinct as to be reckoned a distinct muscle —
sometimes called the abductor longus hallucis. It may be
unquestionably double, as in the Echidna. It may have a
double origin and a single insertion, as in the Agouti. It may
be inserted into the second metatarsal, as in Hyrax ; and
may be altogether wanting, as in the Pig. It is inserted
into the tarso-metatarsal bone in Birds, and is situate quite
on the inner aspect of the leg in Chameleo (Fig. 310). It
exists down to the Urodeles, being apparently double even
in Menobranchus. It may arise from the femur, as in the
Frog.

Extensor proprius hallucis. This muscle may be altogether
absent, as in the Hare and Rabbit. It may even in man's
order (e.g. in Lemur) take origin from the tibia as well as
from the fibula. The tendon of the muscle may be inserted
into the second digit instead of into the hallux, which is the
case in the Echidna. Often this muscle is blended with the
extensor longus digitorum pedis. A muscle may exist in
Reptiles (e.g. in Chameleo) arising from the lower two-thirds
of the front of the fibula and inserted into the dorsum of the
second metatarsal ; and even in Urodeles (e.g. Menopoma
and Menobranchus) a small muscle arises from the lower
part of the fibula and goes to the hallux, or, in the absence of
this, to the second digit.

The extensor longus digitorum pedis may spring from the
femur, as in the Pig, Hare, Hyrax, and Horse. Apart from
diminution in the number of the tendons resulting from the
atrophy of certain digits, the subdivision and distribution of
the ultimate tendons may vary even in the Primates. It may
end in two tendons only, going respectively to the second
and third metatarsal bones (as in the Iguana), or it may be
inserted exclusively into the third, as in Chamczleo Parsonii.

The extensor brevis digitorum pedis is subject to great varia-
tions in extent and arrangement in different animals. It may
be altogether wanting, as in the Hare and Rabbit. It may

352

ELEMENTARY ANATOMY.

[LESS.

be reduced to a minimum, as in the Horse ; or be split up
into three portions, as in the Iguana ; or into seven small
muscles all arising from about the central tarsal ossicle or
the end of the fibula, and going to the five metatarsals, as in
ChamcEleo Parsonii — with other almost endless variations in
different forms.

FIG. 315. — MUSCLES OF LEFT HIND LEG OF HYRAX.

Ta, tibialis anticus ; Eld, extensor longus digitorum (the origin of this muscle
ought to have been carried up to the femur); PI, peroneus longus (this muscle
ought not to have been made to arise from the femur); Pb, peroneus brevis;
S, soleus ; G, gastrocnemius ; P, plantaris.

The peronei muscles may be much more largely developed
than in man. Thus in the Hare four such muscles, not in-
cluding the peroneus longus, send tendons to the second,

VIIL] THE MUSCLES.

353

third, fourth, and fifth digits respectively. They are muscles,
however, which are largely developed only in the Mammalian
class.

The Peroneus tertius is, amongst Primates, exclusively
human. Sometimes (e.g. in some individual Guinea-pigs) the
tendon of the peroneus longus will, pass down in front of
the malleolus, and so simulate a peroneus tertius. It is
said to be present in the Wombat.

Peroneus longus. This may be altogether wanting, as in
the Horse, and apparently in all below Mammals. Its
tendon may, as in Hyrax, pass outside the malleolus instead
of behind it. The muscle may take origin in part from the
femur (as in the Ox and Opossum), and be inserted into the
naviculare or second metatarsal.

Peroneus brevis. This may be altogether absent in man's
class, as in the Agouti. It may be reinforced by peronei
muscles going to the fourth and fifth digits (and termed
peronei quarli et quinti digiti}, as in Lemur. These have
exceedingly slend€r tendons.

In the Rabbit, a muscle which springs from the front of
the tibia and passes behind the internal malleolus, going to
the extensor tendon of the second digit, has been called the
tibialis secundi digiti. This does not exist in man.

The gastrocnemius is generally a double muscle, but there
may be only a single head and belly, as in the Echidna. The
Muscle may be very slender, and quite insignificant in size

hen compared with the flexor longus digitorum, as is the
case in Lori's. The muscle may be divided into two lateral
portions, and become connected with quite other muscles,
as is the case in the Iguana and Chameleon. Thus, in the
Iguana the external head (which, contrary to the condition in
most Mammals, is larger than the internal) ends below in a
membrane which forms, as it were, perforated tendons for the
digits. This head may arise, as in the Chameleon, by a tendon
from the inter-articular cartilage.

The internal head of the gastrocnemius of the Iguana is
closely connected with the insertion of the semi -membra -
nosus, and receives a tendon from the biceps. The internal
head may arise from the tibia only, as is the case in Parson's
Chameleon.

This muscle (Fig. 314) may be absent or included in the

semi-tendinosus (as in Menopoma), which in the sole becomes

superficial to the flexor digitorum. The tendo Achillis,

instead of being strongly inserted into the calcaneum, may

A A

354

RLE ME NT A R Y ANA TOM Y.

[LESS.

in many forms, e.g. Hyrax, pass behind and beneath it into
the plantar fascia.

The soleus, even in Nycticebus, has lost its tibial attach-
ment, is entirely muscular, and blends with the gastro-
cnemius. It may (as in the Agouti) arise from the tibia only ;
it may be inserted into the astragalus, as in the Ornitho-
rhynchus ; or it may be wanting, as in the Pig, Hyaena, Seal,
ancLothers.

FIG 316.— DEEPER MUSCLES OF BACK OF RIGHT LEG OF PARSON'S CHAMELEON

Plantaris. This muscle may be altogether absent, as in
the Wombat. It may however be present as a large belly,
and arise from the outer condyle of the femur, as in the Pig
and Rabbit. It may also, as in the same animals, end in an
expansion which runs along the sole and becomes the per-
forated tendons of the digits. This muscle may be con-
nected even with the pelvis by the intervention of the rectus
femoris, the tendon of which is continued on into it, not only
in Birds but also in the Alligator. It may be intimately
connected with the outer head of the gastrocnemius, and fleshy
bellies may replace the perforated tendons, as in the Iguana.

The popliteus may arise from the head of the fibula, even
in man's own class, e.g. in the Echidna, where it extends far

v»i-] THE MUSCLES. 355

down the leg, and the same origin exists in the Iguana

FIG. 317.— FLEXOR SURFACE OF RIGHT LEG OF Iguana, the superficial

muscles being cut and reflected.

AH, abductor hallucis ; AQ, abductor ossis metatarsi quinti ; BF, biceps femoris ;
FA L and FA 2, flexor accessorius ; FLD, flexor longus digitorum ; /<'J/,
flexor minimi digiti ; GcE, gastrocnemius externus ; Gol, gastrocnemius
internus ; IP, ilio-peroneal ; L and L 2, lumbricales ; Pl, peroneus ; PL A,
plantaris ; Pp, popliteus ; S, tibial adductor ; SM1 and SM'2, semi-membra-
nosus ; ST, semi-tendinosus ; TA, tibialis anticus ; TP, tibialis posticus ;
y, tendon of femoro-cauda].

A A 2

356 ELEMENTARY ANATOMY. [LESS.

and in Birds. It may extend almost the whole length of the
fibula, as in Phalangista. It may be entirely wanting, as
in Bats.

Besides the muscles which in man connect together the
fibula and tibia, two others may exist. One of these, the
rotator fibula, is developed in the Lemuroidea. It extends
from the back surface of the tibia to the front of the fibula,
the fibres passing obliquely downwards and outwards. It
lies beneath the popliteus, and its anterior surface is covered
by the peroneus longus.

Another muscle, the fibres of which go in the opposite
direction, exists in the Wombat and some other allied
forms. It passes downwards from the fibula to the tibia in
the place of the interosseous membrane. It is largely deve-
loped in the Iguana, Chameleon, and Menopoma, and has
been called peroneo-tibial (Fig. 320, PT}.

The flexor longus digitorum pedis may take origin not
only from the leg, but also from the femur, as in Nycticebus
and Pteropus ; and it may have mainly a fibular origin, as in
the Armadillo and Cape Ant-eater. Even in man's own order
(e.g. in Lemur) it may present the singular character of
origin from the front of the leg, ascending between the
rotator fibulae (before mentioned) above and across the
interosseous membrane, so as to be in contact with the pos-
terior margin of the tibialis anticus. It may be very much
smaller than the flexor longus hallucis, as in the Agouti and
Hyrax, and especially in the Virginian Opossum. It may, on
the contrary, be very much larger indeed than the other, and
have a double origin from the femur, thus indeed forming
two muscles, as in Chamaeleo Parsonii (Fig. 316). The gene-
rally slight connexion which exists between the tendons of
the two long flexors of man is, as it were, a remnant of a
far closer connexion existing in other forms, as (in the ex-
treme) in the Horse and Tapir, where they unite completely
into one tendon, which then again divides, in the latter
animal, to form the perforating tendons of the digits.

The flexor longus pollicis pedis seu hallucis may thus
entirely blend with the last-noticed muscle as regards its
tendon. On the contrary, as in Cyclothurus, it may be more
completely separated from it than in man. It may be entirely
absent, or it may be very large as in the Three-toed Sloth.
It may be present but send no tendon to the hallux, as in the
Orang, in which it springs from the outer condyle. It may
appear on the front of the leg, as in Chamceleo Parsonii. It is

VIII.]

THE MUSCLES,

357

still distinguishable, even in Tailed-Batrachians, as in Mcno-
pojna and Menobranchus.

The tibialis posticus may be entirely absent, even in man's
class, as in the Rabbit and Tapir. It may be very stron^
and inserted into the astragalus, as in the Echidna, or run
on to the ento-cuneiforme, as in Lemur. The muscle may
be very greatly developed, as in the Beaver and Wombat. It
is constant, as not only in Reptiles (e.g. Iguana and
Chameleo], but even in the Frog it exists (inserted into the
astragalus), though it does not seem distinct in Tailed-
Batrachians.

FIG 318. — TENDONS AND MUSCLES OF EXTENSOR ASPECT OF FOOT OF EAr;i K
(A quilafnc osa).

i, tibialis anticus ; 2 and ?,peronei ; 4, tendon of extensor longus digitorum pedis ;
5 and 6, extensor hallucis ; 7 and 8, tendons going to third and fourth digits
respectively.

(After A. Milne- Edwards.}

27. The MUSCLES OF THE FOOT of man possess of course,
like its skeleton, special characters in harmony with the
peculiar function of that organ as the sole support and agent
of progression of an erect and relatively large and ponderous
body. These muscles, like those of the hand, can for the
most part be profitably compared only with those of man's

353

ELEMENTARY ANATOMY.

[LESS.

own class, but even in that they may be reduced to a mini-
mum, as in the Horse. The foot may be largely developed,
with four elongated and prehensile digits, and yet have very
little muscular tissue, as in Birds. Some leg muscles may be
present, and yet there may be no foot-muscles, as is the case
in Lialis Burtonii.

The abductor pollicis pcdis seu hallucis is often absent, as
in the Horse ; yet it exists in both Reptiles and Batrachians,
as, e.g., in the Chameleon and the Frog.

F.l.d

FIG. 319. — MUSCLES AND TENDONS OF SOLE OF HIND FOOT OF HYRAX.

Tack, tendo Achillis; Flh, tendon of flexor longus hallucis; FM, tendon of flexor
longus digitorum ; Fbd, flexor btevis digitorum, with one of its perforated
tendons cut through and the whole muscle drawn to the one side to expose the
deep flexor tendons; A, accessorius ; L, lumbncales.

Flexor brevis digitorum. This may be absent, and then
is often replaced "by the plantaris, as, e.g., in the Pig and
Rabbit. It may arise exclusively from the surface of the deep
flexor tendon, as in Nycticebus, and in no member of man's
order but man himself does it arise from the os calcis only.

vi n.J THE MUSCLES. 359

The abductor digiti minimi may be absent, as in many
forms, e.g. the Horse; or it may be very large and aided, as in
Lemur, by another muscle (which is generally absent in man)
called abductor ossis metatarsi quinti, and which, arising
from the calcaneum, is inserted into the fifth metatarsal.

Flexor accessnrius (Fig. 319). This may be altogether
wanting, not only in such forms as the Horse, but even in
members of man's order, e.g. Lemur. It may be inserted by-
muscular fibre into the perforating flexor tendons, or it may
furnish most of the long flexor tendons, as in Hapale. It
is a more constant muscle than might be expected, as it is
to be found in the Iguana. It may be enormous, with three
fleshy bellies, as in the Three-toed Sloth.

Liimbricales (Fig. 317). These muscles may be quite
absent, as in the Hedgehog, Seal, and Three-toed Sloth, and
in Birds. They may be represented by tendons only, as in
the Horse. They may be only two in number, as in the
Agouti and Hyrax ; or they may be as many as six or seven
in number, as in Bats. They are more constant structures
than might have been expected, as they are found in Reptiles,
e.g. in the Iguana and Chameleon, and in the Frog, though
they do not seem to be developed in Tailed- Batrachians.

Flexor brevis pollicis pedis. As need hardly be said, this
muscle may be entirely absent. It may, however, reappear
when wanted, low down in the scale, e.g. in Chamceleo
Parsonii and the Frog.

The adductor pollicis pedis may perhaps be represented
in the Frog by a large muscle taking origin between the
elongated tarsal bones ; but it is inserted into the naviculare
and accessory tarsal ossicle.

Transi'ersus pedis. This may be larger relatively than in
man, as in the Apes. It may be blended with the muscle last
noticed, as in Lemur, and it may, as in many forms (e.g.
the Horse) be absent altogether. Muscular fibres may be
inserted into the metatarsal of the hallux, thus forming an
opponens hallucis, as in the Orang ; and a similar structure
may be still further developed in a singularly low form,
i.e. the Frog, where an opponens muscle is supplied to each
of the four inner digits, and this in addition to transversi
muscles, which extend between the first and second, second
and third, and third and fifth digits respectively.

A flexor brevis digiti minimi pedis may be present, as in
Apes, or it may be absent, as in many forms. It exists in
the Iguana (Fig. 317) and Chameleon. In addition to this

ELEMENTARY ANATOMY.

[LESS.

an abductor minimi digiti pedis may exist in man's order, e.g.
in Lemur, and also in the Frog, where it is largely developed.
Interossei. The interossei of the human foot are peculiar,
as in all Apes (even in the Gorilla) they resemble in arrange-
ment the interossei of the hand, owing to the arising of the
nbular interosseus of the second digit from the middle meta-

FIG. 320. — DEEPER FRONT VIEW OF RIGHT LEG OF PARSON'S CHAMELEON.

B^-B^>, extensores phalangorum ; E1 and E2, E9, extensores metatarsorum ; EL,
extensor longus digitorum ; Fff, flexor hallucis; /)I,peroneus; PP, popliteus ;
FT, peroueo-tibial ; TA, tibialis anticus.

tarsals on the dorsal side of the tibial interosseus of the middle
digit. They are nearly constant muscles, and are largely
developed even in Batrachians, as in the Frog, which animal
possesses indeed a singularly rich myological furniture of the
foot. In the Bat there are two interossei to each toe. They
may consist, as in the Horse, of two small muscles, one
being placed between the styliform and the large metacarpal
on each side.

28. Thus, as might have been expected, man's muscles
follow the type exhibited by his class and order, still pre-

viii.] THE MUSCLES. 361

seating normally certain special peculiarities, though such
differences are not absolutely constant, owing to individual
variation. Thus he is peculiar in the following points : He
has an extensor primi internodii pollids and a peronens ter-
tius. He has the flexor longus pollids disconnected from
the flexor proj cundus digitorum. His soleus arises both from
the tibia and the fibula, and his flexor brevis digitorum
springs entirely from the calcaneum. Moreover, the pero-
neal interosseus muscle of the second toe arises on the
dorsal side of the origin of the tibial interosseus of the
middle toe.

29. In comparing the myology of the pectoral and pelvic
limbs of man, we find that owing to the diverse flexure of the
two limbs, the extensors are placed forwards in the lower
limb, backwards in the upper one. The flexors of the upper
limb easily bend the hand upon the arm, but those of the
lower cannot bend the foot upon the leg ; at the most they
straighten it — a motion called " extension," but which is really
an imperfect " flexion."

The serial homology of the appendicular muscles can only
be understood by imagining the limbs in their primitive
position, with the extensors outwards, the flexors inwards.
Then we have the supra- and infra-spinatus and the iliacus,
the extensor carpi radialis and tibialis anticus, all pre-axial ;
the sub-scapularis and glutei, the peronei and the extensor
ulnaris, all post-axial.

The muscles inserted into the post-axial tuberosity of the
humerus lie in man on the inner side of the thoracic girdle
(sub-scapular surface), those inserted into the post-axial tro-
chanter of the femur lie on the outer side of the pelvic girdle
(gluteal surface). Their positions may, however, correspond
unmistakably, as in the Echidna.

Muscles inserted into the pre-axial trochanter arise within
the ribs. No muscles so arising (except in Chelonians) go to
the pre-axial tuberosity.

In man there are no common flexors or extensors taking
origin in the hand in the upper limb, and none such springing
from the femur in the lower one ; but we have seen that both
these conditions may exist in other animals.

In the arm, the long flexors of the thumb and digits arise
on the same side of the limb as that to which they are
distributed.

In the leg, they arise from the opposite side to that of their
distribution, their tendons crossing each other.

362 ELEMENTARY ANATOMY. [LESS.

In the arm, the extensor muscles cross each other; in the
leg they do not.

The triceps is the great extensor of the arm, the quad-
riceps of the leg.

The peroneus longiis and flexor accessorius are leg muscles
which resemble nothing in the arm of any animal. An
interlacing, like that which takes place between the flexor
tendons of man's foot, is absent in his hand, but is present
in the hand of some animals, e.g. Nycticebus.

An opponens present in the pollex is wanting in the hallux
in man, but the hallux of the Orang is furnished with an
opponens.

30. The muscular system is that in which the plastic power
which co-adapts structure and function is pre-eminently con-
spicuous, as is well shown in the Frog's foot and the wing-
edge muscle of Bats and Birds. Thus homologies become
difficult to determine, being disguised by such an abundance
of adaptive modifications.

Though there is a general correspondence between the
development of the skeleton and of the muscles which clothe
it, yet sometimes skeletal parts may be greatly increased in
size, while at the same time there is a simultaneous decrease
in the relative development of the muscles annexed ,*as in the
hand of Bats and the thorax of Chelonians.

The endo-skeletal muscles may be divided into (i) axial,
and (2) appendicular.

The axial muscles, like the skeleton (as we saw in' the
Sixth Lesson), may be subdivided into three groups : (i) ep-
axial, (2), paraxial, and (3), hypaxial. They have a primitive
relation to vertebral segments, but this relationship is lost,
and the segments coalesce antero posteriorly, in non -gill-
bearing Vertebrates.

The epaxial group includes the inner part of the erector
spinae and its continuations, attaining perhaps its maximum
of development in the Flat Fishes, e.g. the Sole, and its
minimum in Fishes like Ostracion and in the Tortoises.

The paraxial group includes the outer part of the erector
spina? and its continuations, also the scaleni, levatores
costarum, intercostals, abdominal muscles, rectus, and outer
lower tail muscles of Tailed-Batrachians and at least many
Fishes. This group is at its maximum of differentiation in
Serpents.

The hypaxial group includes the recti antici, longus colli,
sub-vertebral muscles of Birds, Serpents, and Tailed-Batra-

viii.] THE MUSCLES. 363

chians, also the psoas and femoro-caudal and the muscular
masses investing the chevron bones of Cetaceans, and the
lower caudal muscles of some Fishes, e.g. the Sole.

12

FIG. 321. — SUPERFICIAL MUSCLES OF THE PERCH.
The fin-rays of all the fins are cut short off.

i, great lateral muscle, showing the numerous vertical tendinous intersections
slightly but variously inflected ; 2, small superficial muscles inserted into the
fin-rays of the dorsal and ventral fins ; 4, slender longitudinal muscle running
(in the interval of the summits of the two great lateral muscles) between the
dorsal and caudal fins; 5, similar muscle on the ventral margin, which also
appears between the anal and ventral fins ; 6, small radiating muscles of the
caudal fin ; 7, part of the great lateral muscle inserted into the skull ; 8 and 9,
elevators of the operculum ; 10, elevator of the palato quadrate arch ; n and
12, muscular mass which by its contraction closes the jaws ; 13, superficial
muscles of the pectoral fin ; 14 and 15, muscles of the ventral fin.

The muscles which invest that special division of the
hypaxial skeleton, the splanchnapophyses, also constitute a
group by themselves, connecting together the hyo-branchial
arches and the jaws, the stylo-hyoid, constrictors of the
pharynx, buccinator, £c.

The appendicular muscles may be divided into those of the
limb-girdles and those of the appended limb.

They may be at a maximum of size in relation to the axial
system, but simple and without any special differentiations,
as in the Rays. They may be at their maximum of dif-
ferentiation, though less in relative or even in absolute size,
as in the highest Mammals.

This differentiation begins to be indicated directly weascend
from the class of Fishes, as we have seen that even in the
Tailed-Batrachians definite flexors, extensors, pro- and su-
pinators already appear ; and these distinctions, once esta-
blished, persist' up to man himself, though with increasing
complications. Special complications, especially of the
muscles of the pelvic limb, have been found by us to be
developed in Reptiles, such as we do not find in man's
own class.

364 ELEMENTARY ANATOMY. [LESS.

Considered independently of the bony skeleton, the muscu-
lar system may, as its simplest expression, be conceived as a
fleshy, antero-posteriorly extended envelope of the body, cut
up, at regular intervals, into a series of successive segments,
by means of transverse aponeurotic membranes extending
outwards from the body axis to the skin.

From this primitive condition the muscles of the back may
be conceived as arising by means of increasing obliquity,

4 3

FIG. 322. — DIAGRAM o? CAUDAL MUSCLES OF RIGHT SIDE OF TAIL OF Iguana,
showing the obliquity of the aponeurotic intersections of the muscular
portions which are themselves drawn out into cones yet preserving a
numerical relation to the supporting vertebrae.

JV, neural spine : //, hypapophysial spine ; z, zygapophysis ; t, transverse pro-
cess ; i, dorsal series of cones ; 2, upper lateral series of cones ; 3, lower series
of cones ; 4, ventral series of cones.

conical prolongation, and partial detachment (from muscle)
of the aponeuroses, together with condensation of their pro-
duced ends till the latter become firm tendons, directed more
or less obliquely forwards — the muscular fibres, in the mean-
while, taking slightly different directions at different depths.

The muscles of the abdomen may be conceived as arising
through atrophy of the transverse aponeuroses (of which the
linece transverse of the rectus are the last remains) and
differentiation of the muscular mass into superimposed
sheets of differently directed fibres.

The muscles of the limbs may be conceived * as arising as
conical sheaths of muscular fibres investing protruding limb-
rudiments, and becoming divided and annexed to successive
limb-segments as such limb-rudiments become developed
and segmented — finally assuming the form of a median and
two lateral groups of muscles both on the extensor and flexor
surfaces of each limb.

1 As has been suggested by Professor Humphrey, F.R.S.

THE NERVOUS SYSTEM. 365

LESSON IX.
THE NERVOUS SYSTEM AND ORGANS OF SENSE.

1. THE NERVOUS SYSTEM may perhaps be considered the
primary and most important of all the systems of parts of
which the body is composed, because it dominates and
directs, as it were, the actions of the other parts. Moreover,
sometimes at least, it serves as a criterion in settling dis-
puted homologies of structures which belong to other systems.
Thus, the question as to what bone in one animal answers to
what bone in another animal is often determined, as in the
case of some cranial bones, by the several relations of such
bones to a certain nerve ; and the same kind of test may
not improbably serve to determine many muscular homo-
logies also.

2. The PRIMARY STRUCTURES of which the nervous system
is composed (i.e. nerve-fibres and ganglionic corpuscles] have
been described in the " Elementary Physiology," Lesson
XII. "§§ 1 6 and 19, and the nervous system as a whole has
also been sketched in Lesson XL of the same work.
Therein have been duly set forth its main component parts
— the brain and spinal marrow (or cerebro-spinal axis), to-
gether with the membranes which invest them— as also the
nerves issuing from such parts, including those which are
spoken of as the sympathetic system.

3. Here we must recapitulate so far as to state that the
solid structures (skull and neural vertebral canal) which pro-
tect the cerebro-spinal axis are lined by a dense membrane —
the dura mater y while the cerebro-spinal axis itself is closely
invested by a delicate membrane — the pia mater. Inter-
posed between the two is a double very delicate epithelial
layer (called the arachnoid}, forming a shut sac (as the peri-
toneum forms a shut sac) and containing the arachnoid
fluid.

366

ELEMENTAR Y ANA TOM Y.

[LESS.

The cerebro-spinal axis encloses a cavity (of very different
size and shape in different parts) which is lined by another
very delicate epithelial layer called the ependema.

4. The BRAIN fills up the whole cranial cavity, fitting into
all those depressions which we have found to exist on the
floor of that cavity.

On removing the upper part of the skull and the dura
mater, the surface of the brain is seen as a convex mass
covered with numerous meandering, contorted prominences
(convolutions or gyri), separated by corresponding depres-
sions (fissures or suld\ The whole mass is sharply divided
by a very deep fissure running from before backwards, and
dividing the visible part of the brain into two lateral halves,

FIG. 323.— THE UPPER SURFACE OF THE BRAIN OF MAN, showing the deep
longitudinal fissure dividing the two hemispheres, with their numerous and
unsymmetrical convolutions.

termed hemisplicres, and the whole convoluted mass is called
the cerebrum. Thus the cerebral hemispheres of man extend
so far forwards, outwards, and backwards that no other part
of the cerebro-spinal axis is visible when the brain is viewed
from above The pia mater so closely invests this mass that
it passes down not only into the great median longitudinal
fissure, but into all the sulci of the cerebrum. The dura
mater passes into the longitudinal fissure only, where it forms
the falx, which, as we have found in some a.iimals (e.g. the
Ornithorhynchus), becomes ossified.

Upon pushing apart the two cerebral hemispheres, these
are seen to be connected by a large transverse band (called

ix.] THE NERVOUS SYSTEM. 367

the corpus callosum} which extends much nearer to the an-
terior than to the posterior end of the longitudinal fissure.
In front of the corpus callosum is seen nothing but the
anterior fossa of the cranial cavity ; but behind the corpus
callosum (after removing that fold of the dura mater, the
tentorium— so often ossified in brutes — which extends in from
behind, below the cerebrum) we find the upper surface of
another part of the cerebro-spinal axis, called the cerebellum,
which is marked with numerous transverse, close, narrow
grooves. To remove the entire brain from the skull it is
necessary to cut through that part of the cerebro-spinal axis
where the brain (at the foramen magnum) becomes con-
tinuous with the spinal marrow.

5. Having done this, and inverted the organ, a variety of
parts come into view, its INFERIOR SURFACE being very
irregular and complex as compared with its superior surface.

Proceeding from behind forwards, we find that the part in
front of the section which we have just made is narrow and
cylindrical. This is the medulla oblongata. It is marked by
a median groove, on each side of which is what is called
the anterior pyramid, and outside each such pyramid is a
rounded, oblong prominence, termed the olivary body ; and
external to and behind each of these is a band named the
restiform tract. The cut surface of the medulla exhibits that
double-crescentic arrangement of grey tissue described in the
"Elementary Physiology," Lesson XI. § 5.

On each side of the medulla oblongata is seen a large con-
vex mass of tissue marked with many curved, transverse,
narrow grooves. This is the cerebellum . and its two lateral
parts meet together behind the medulla and form what is
called the inferior vermis. This latter is the under part of
that median portion of the cerebellum which we saw by
divaricating the hinder parts of the cerebral hemispheres—
and which is called the superior vermis (Fig. 328, sv). The
median part of the cerebellum is small compared with its
two great lateral lobes.

The cerebellum lies in that fossa of the cranial cavity
which we have seen to be bounded in front by the petrous
part of the temporal bones, and behind by the line of attach-
ment of the tentorium to the occipital bone.

On each side of the anterior part of the under surface of
the cerebellum is a small process, or lobe, called \heflocculus.
It does not occupy any special fossa in the temporal bone.

Continuing on in the middle line, we find in front of the

368

ELEMENTAL Y ANA TO MY.

[LESS.

medulla oblongata, a convex eminence formed of transverse
fibres running across from one lateral lobe of the cerebellum

FIG. 324. — THE BASE OF THE BRAIN.

A , frontal lobe ; B, temporal lobe of the cerebral hemispheres ; CC, corpus
callosum ; Cb, cerebellum ; M, medulla oblongata ; P, the pituitary body ;
/. the olfactory nerve ; //. the optic nerve ; ///. IV. VI. the nerves of the
muscles of the eye ; V. the trigeminal nerve ; VII. the portio dura ; VIII. the
auditory nerve ; IX. the glosso-pharyngeal ; X. the pneumogastric ; XI . the
spinal accessory ; XII. the hypoglossal, or motor nerve of the tongue. The
number VI. is placed upon the pons Varolii. The crura cerebri are the
broad bundles of fibres which lie between the third and the fourth nerves on
each side. Between the crura cerebri and behind the pituitary body are placed
the rounded corpora inammillaria. S, sylvian fissure.

to the other, somewhat like a bridge, and thence called fat pons

Varolii. It lies upon the basilar surface of the occipital bone.

Emerging from the front of the pons are two masses of

longitudinal fibres (called the crura cerebri} which diverge

T x. ] THE NER VO US S YSTEM. 369

as they advance, and are crossed superficially by two an-
teriorly converging round cords, the optic tracts (which unite
to form the optic nerves), and thus a lozenge-shaped space
is enclosed. In the hinder part of this space are two small
rounded bodies placed side by side, called the corpora
mammillaria. In front of these is a slight prominence
termed the tuber cinereum, from the middle of which pro-
jects a conical process, the infundibulum; at the end of the
infundibulum is a small oval reddish mass called the pituitary
body, which is received into the pituitary fossa (or sella
turcica) of the sphenoid bone.

In front and beside these small median parts are those
voluminous masses the cerebral hemispheres, which thus
form the larger part of even the under surface of the brain.

The great longitudinal fissure is seen in the middle line in
front, and another considerable lateral fissure (called the
Sylvian fissure) separates obliquely (Fig. 325) the anterior (or
frontal] lobe from the one behind (or temporal lobe) of the
same hemisphere. This Sylvian fissure receives (when the
brain is in place) the hinder edge of the orbital wing of the
sphenoid, W7hile the frontal lobe lies upon the orbital plate ot
the frontal bone, and the temporal lobe lies in that cranial
fossa which is bounded in front by the orbital wing of the sphe-
noid and behind by the petrous part of the temporal bone.

In a groove on the under surface of each frontal lobe is a
body, shaped something like a life-preserver, with an oblong
head and a long stalk. This is the olfactory lobe, the so-
called " olfactory nerve."

Upon turning back the optic tracts— at their union in what
is called the optic commissure — a delicate layer is seen to
connect them with the anterior end of the corpus callosum.
This delicate layer is called the lamina cinerea, or lamina
terminalis.

When the brain is viewed in profile we see the convoluted
surface of one of the cerebral hemispheres with the deep
Sylvian fissure running backwards and slightly upwards from
its inferior margin, and separating the temporal lobe from
the frontal one. When this fissure is opened out, a triangular
convoluted prominence is exposed, called the Island of Reil.
Below and behind the cerebrum we see the cerebellum with
the pons Varolii in front of it, beneath which the medulla runs
down to merge into the spinal cord (Fig. 325).

To obtain a more complete knowledge of the structure of
the brain, certain definite sections must be made.
B B

370 ELEMENTARY ANATOMY. [LESS.

6. Thus, if the whole organ be VERTICALLY BISECTED in
the line of the longitudinal fissure, we find as follows : —
The inner surface of the cerebral hemisphere in view is

FIG. 325. — SIDE VIEW OF THE BRAIN AND UPPER PART OF THE SPINAL MARROW
in place, the parts which cover the cerebro-spinal centres being removed.

a, front part of atlas vertebra applied to the odontoid process (o) behind it ; b, body
of third cervical vertebra ; c, cerebrum— the long continuous groove imme-
diately above the convolution tO'which the letter c points, is the Sylvianfissure,
while the convolution itself forms part of the temporal lobe of the cerebrum ;
cB, cerebellum : m, medulla oblongata ; p, pons Varolii ; s, arch of skull cut
through ; s', spinous process of axis vertebra.

very much convoluted, and the cerebrum may be seen to
extend beyond the olfactory lobe in front and beyond the
cerebellum behind.

Beneath the middle of the cerebrum we come to the cut
surface of the corpus callosum, the front part of which
bends sharply backwards and downwards, forming what is
called the knee (gemi). Beneath the bent-back extremity of
the corpus callosum is the cut edge of the lamina cinerea (or
terminalis). At the upper part of this lamina we find the
cut surface of a transversely-extending white cord, called the
anterior commissure, and immediately behind the lamina we
find another cord, part of what is called the fornioc. This
latter structure extends, not transversely, but at first upwards
and forwards, afterwards curving backwards it passes to the
hinder part of the corpus callosum. Filling up the space
between the corpus callosum and fornix is a delicate membrane
called the septum lucidum.

Below the fornix we have evidently cut into a cavity ex-

IX.]

THE NER VO US S YS TEM.

371

tending down into the infundibulum and bounded in front
by the lamina terminalis. This cavity is called the thira

FIG. 326. — THE BRAIN AS SEEN WHEN A VERTICAL LONGITUDINAL SECTION-
HAS BEEN MADE THROUGH ITS MIDDLE.

Av, arbor vitae of the cerebellum ; c, cerebrum : cc, corpus callosum ; ^.corpora
quadrigemina ;_/", fornix (between the fornix and the corpus callosum is the
septum lucidum) ; m, medulla oblongata ; ma, corpus mammillare : on, optic
nerve ; pi, pineal gland ; pt, pituitary body ; pv, pons Varolii ; s, soft, ot
middle commissure.

ventricle. A small aperture (the foramen of Monro) opens
immediately behind the anterior part of the fornix, and a

FIG. 327. — ENLARGED AND DIAGRAMMATIC VIEW OF A VERTICAL SECTION
CARRIED THROUGH THE CORPUS CALLOSUM AND THE PARTS BELOW.

etc, anterior commissure ; cc, corpus callosum ; cbl, cerebellum ; cm, corpus
mammillare ; y^ fornix \_fnt, foramen of Monro ; /, infundibulum Ip, locus;
perforatus medius ; mo, medulla oblongata ; na, nates ; on, optic nerve ; pc,
posterior commissure ; pv, pons Varolii ; pi, pineal gland ; pt, pituitary body ;
s, soft, or middle commissure ; si, septum lucidum: t, lamina terminalis ; te,
testes ; v, velum interpositum (between it and the fornix is a space enclosed by
the folding over of the cerebrum upon the roof of the third ventricle) ; 3, upper,
and 3', lower part of third ventricle ; 4, fourth ventricle — between them is the
iter a tertio ad qitartnm ventriculuw.
B B 2

372 ELEMENTARY ANATOMY. [LESS.

little behind this aperture is the cut edge of a bundle of
transverse fibres which form what is called the soft (or middle)
commissure. The third ventricle is bounded above by a
delicate membrane, the velum interpositum, which thickens
behind and forms a small prominence which projects back-
wards and is called the pineal gland— reminding us of the
pituitary body below. The third ventricle is bounded inferiorly
by the corpora mammillaria and crura cerebri (the cut sur-
faces of which are visible in Fig. 327 just above the pons
Varolii), and by the infundibulum, into which it extends.

The cavity just described, the third ventricle, is not shut in
at its hinder end below, but continues on as a very narrow
passage (the iter a tertio ad quartum ventriculum), bounded
in front by the crura cerebri and behind by a layer of nervous
matter continuous with the pineal gland, and exhibiting the
cut surface of a small transverse cord (the posterior commis-
sure), and also two prominences in section — part of the
corpora quadrigemina. A little lower down, this passage
expands into a second cavity (the fourth ventricle), bounded
in front by the medulla oblongata and behind by the cere-
bellum above, and below the cerebellum by an exceedingly
delicate layer of nervous tissue.

The cerebellum in section shows singular radiating tree-
like ramifications of nervous substance (grey and white), due
to infoldings of the surface of the organ, and called the arbor
vita.

Thus the extension backwards of the corpus callosum
and cerebrum altogether overlaps a certain portion of the
brain, namely, the pineal gland and parts adjacent. When
these are exposed by a special section the corpora quadri-
gemina are seen to consist of two pairs of small prominences
(but little different in size) placed side by side immediately
behind the pineal gland. The anterior pair are called the
nates, the posterior pair the testes. They are solid structures.

7. OTHER SECTIONS (Figs. 328 and 329) are necessary to
make clear other matters. Thus, the foramen of Monro is
the entrance to a cavity which is placed in the cerebral hemi-
sphere of the same side, these two cavities constituting the
first and second (or two lateral} ventricles.

The so-called foramen of Monro is, in fact, a Y-shaped
passage. It is single below, where it communicates with the
third ventricle, but divides above into two branches, one to
each lateral ventricle.

Each lateral ventricle is tri-radiate and said to have three

ix.] THE NERVOUS SYSTEM. 373

cornua. The anterior cornu passes into the frontal lobe.
The posterior cornu passes into the hinder or occipital lobe.
The third, or descending cornu, passes into the temporal lobe.
Certain sulci on the surface of the cerebrum extend so deeply
as to produce eminences on the inner surface of the lateral

FIG. 328.— HORIZONTAL SECTION OF PART OF THE BRAIN, the cerebrum and
velum interpositum being removed, the fornix and septum iucidum being cut
through, and the third and fifth ventricles and the upper surface of the cere-
bellum being exposed.

ac, anterior commissure ; cc, corpus callosum ; cb, cerebellum ; r/, crura of fornix :
n, nates ; op, optic thalamus ; pc, posterior commissure ; //, pineal gland ;
j, middle, or soft commissure ; st, corpus striatum ; sv, superior vermis ;
t, testes ; 4, fourth nerve ; 5, fifth ventricle- on each side of it is a lamina of
the septum Iucidum cut through.

ventricles. One such insignificant structure in the posterior
cornu is spoken of as the hippocampus minor j another in the
descending cornu has been termed the hippocampus major.

Careful inspection shows that the septum Iucidum is really
double, enclosing a very narrow space — the fifth ventricle —
the laminae of the septum Iucidum passing downwards from
ihe corpus callosum to the fornix.

This fornix is made up of two white cords closely approxi-
mated anteriorly and diverging widely behind. Each springs
from one of the corpora mammillaria, and the two cords
(crura) ascend (side by side) behind the anterior commissure,
and with a branch of the foramen of Monro on the outer side
of each. They then curve backwards, diverging, but at the
same time united by a delicate membrane called the lyra.
They become connected with the corpus callosum, and then
pass into each descending cornu of the lateral ventricles.

374 ELEMENTARY ANATOMY. [LESS.

Two rounded bodies (the optic thalami} are placed one on
each side of the first described cavity (the third ventricle],
and are connected by the soft and posterior commissures.
Two other rounded bodies (the corpora striata) are placed one
in each cerebral hemisphere between the anterior and descend-
ing cornua. They are connected by the anterior commissure.

FIG. 329.— DIAGRAM OF A TRANSVERSE VERTICAL SECTION OF THE BRAIN,
MADE THROUGH THE SECOND, THIRD, AND FlFTH VENTRICLES.

f, cerebrum ; c', its temporal lobe : cc, corpus callosum ; cm, corpora mammillaria;
_/", fornix ; fm, foramen of Monro ; op, one of the two optic thalami ; pt, the
pituitary body ; s, middle, or soft commissure ; st, one of the two corpora
striata ; v, velum interpositum ; x, space enclosed between the velum and the
fornix ; y, fissure of Sylvius ; 2, lateral ventricles ; 2', the ascending cornu of
a lateral ventricle; 2' , its descending cornu ; 3 and 3', the third ventricle ; 5,
the fifth ventricle.

8. The DEVELOPMENT of this complex organ is as follows : —
At first there are three hollow vesicles placed one in front of
the other, their three cavities (which open one into another)
being expansions of the anterior end of the primitive groove
«ind subsequent canal of the embryonic cerebro-spinal axis.
These three vesicles are called respectively, (i) the hind-
brain, (2) the mid-brain, and (3) the fore-brain (Fig. 330).

The superior surface of the fore-brain becomes the velum
interpositum, and from its hinder part the pineal gland
arises, while the infundibulum and pituitary body appear at
its inferior surface. Its cavity is therefore what afterwards
becomes the third ventricle.

The mid-brain becomes the corpora quadrigemina above
and the crura cerebri below, while its greatly reduced cavity
is ultimately the iter a tertio ad quartum ventriculum.

ix.] THE NERVOUS SYSTEM. 375

The hind-brain sends out an outgrowth above, which is the
cerebellum. Its upper wall becomes excessively thin, a mere
delicate layer of epithelium, which roofs its cavity — the fourth
ventricle.

The anterior end of the first vesicle (or fore-brain) becomes
the lamina terminalis. On each side of it another vesicle
grows out, which is one of the cerebral hemispheres, and the
aperture of communication is the future foramen of Munro.

From the anterior part of the floor of each cerebral hemi-
sphere yet another vesicle buds forth, which is the future
olfactory lobe (or nerve), the cavity of which becomes ob-
literated in the adult.

The three original hollow vesicles and the olfactory lobes
remain small, but the cerebral hemispheres grow out of all
proportion to the other parts. They also become united
together by an outgrowth of transverse connecting fibres (the
corpus callosum), which outgrowth, by this mode of develop-
ment, comes to enclose what was originally the deepest part
of the great longitudinal fissure. The space thus enclosed is,
of course, bounded on each side by part of the inner wall of
one of the cerebral hemispheres. These parts of the inner
cerebral walls become however excessively thin, and the two
parts together form the septum lucidum, while the space
enclosed between them becomes the fifth ventricle. Thus
the fifth ventricle is quite different in its nature from all the
other ventricles of the brain, it being taken in as it were
from outside space, while all the others are either remnants of
the primitive embryonic dorsal groove and canal, or (as the
lateral and primitive olfactory ventricles) outgrowths irom
and extensions of such.

9. We may now better understand the nature of some ot
the parts before noticed.

The fornix is the median part of what was originally the
back of the hemispheres. It (together with the lyra which
joins the two diverging and posterior portions of the fornix),
really forms part of the outer wall or bag of the cerebrum,
enclosing the lateral ventricles — each half of the fornix
belonging to one of the hemispheres. As these grow back-
wards, the fornix looks more and more downwards, following
the course of the developing " temporal lobe."

Beneath the fornix is the roof of the third ventricle, i.e.
the velum interpositum, and the space between the upper sur-
face of this velum and the under surface of the closely applied
lyra is morphologically the outside of the brain, though in

376

ELEMENTAR Y ANA TOMY.

[LESS.

fact it is in the middle of the complex whole of the adult
structures.

c.

Pt

FIG. 330. — DIAGRAM ILLUSTRATING THE PROGRESSIVE CHANGES THAT TAK.S
PLACE DURING SUCCESSIVE STAGES OF THE DEVELOPMENT OV THE BRAIN.

i. The brain in its very early condition, when it consists of three hollow vesicles,
the cavity of which is continuous with the wide cavity (ti) of the primitive
spinal marrow (m). The brain substance forms an envelope of nearly equal
thickness throughout.

a. Here the first vesicle or fore-brain has developed the pineal gland (//) above

ix.] THE NERVOUS SYSTEM. 377

and the pituitary body (pt~) below. The wall at the anterior end of the first
vesicle (or fore-brain) is the lamina terminalis (/).

3. This figure shows the cerebrum (cr) budding from the first vesicle, its anterior
part (o) being prolonged as the olfactory lobe (the so-called olfactory nerve),
the cavity of the cerebrum (or incipient lateral ventricle) communicating with
that of the olfactory lobe in front and with that of the first cerebral vesicle (third
ventricle) behind. The latter communication takes place through the foramen
of Monro. The walls of the three primitive vesicles are becoming of unequal
thickness, and the cavity (b) of the middle vesicle (iter a tertio ad quartum
ventriculiim) is becoming reduced in relative size.

4. The cerebrum is here enlarged, and the inequality in thickness of the wall of
the primitive vesicles is increased. The thickened upper part of the wall of
the cerebrum is the fornix (./).

5. This figure shows the cerebrum still more enlarged, and with a tri-radiate
cavity (/, i, 2, 3). The fornix has now come to look slightly downwards ;
dotted lines indicate the downward extension of its anterior part, into the
corpora mammillaria.

6. Here the cerebrum is still more enlarged and backwardly extended. The
fornix is shown bordering the descending cornu and extending into the
temporal lobe (tl) of the cerebrum, which lobe is destined to descend (when
the brain is fully developed) so much more that it comes to advance forwards,
as in Fig. 325. The fornix borders the margin of the very thin outer wall of
the descending cornu, which when torn forms the fissure of Bichat. The
bending back of the cerebrum has now almost enclosed (between the fornix
and the velum) the space (x] which in Fig. 4 is widely open, making what is
morphologically called the outside of the brain come practically to be in its
very centre.

a, fore-brain ; b, mid-brain ; c, hind-brain ; cb, cerebellum ; cr, cerebrum ; d,
cavity of the medulla ; f, fornix ; /, lateral ventricle ; m, medulla oblongata ;
ma, corpora mammillaria ; o, olfactory lobe ; /, pons Varolii ; //, pineal gland :
//, pituitary body ; <?, corpora quadrigemina ; r, crura cerebri ; f, lamina
terminalis; //, temporal lobe of the cerebrum ; x, space enclosed by the
extension backwards of the cerebrum ; i, anterior cornu of lateral ventricle ;
2, its middle or descending cornu , 3, its posterior cornu.

The velum consists only of the ependyma, the pia mater,
and the arachnoid. Its margins are very vascular, and bear
the name of the choroid plexuses. The vascularity continues
in that part of the ependyma which passes through the
foramen of Munro into the lateral ventricles, but of course
the pia mater and arachnoid do not pass through that fora-
men, as they never get inside the ventricles at all, but are
reflected back on the under surface of the fornix. Thus the
" choroid plexuses " of the lateral ventricles are (like those ot
the third) merely portions of the ependyma, which happen
to be very vascular, and not intrusions from without.

Each cerebral hemisphere is a bag with walls of very un-
equal thickness. Thus, part of the inner wall running along
the descending cornu of the lateral ventricle is reduced to
the ependyma (with the pia mater and arachnoid), and
readily tears (forming the fissure of Bichat), and this rupture
having been mistaken for a natural opening, each lateral
ventricle has been supposed to communicate with the exterior
close to the crus cerebri. Each corpus striatum is an out-

378 ELEMENTAR Y ANA TOM Y. [LESS.

growth from the middle of the base of its hemisphere, and
forms the axis around which the whole hemisphere is de-
veloped. The " Island of Reil" lies in the outer surface of
each corpus striatum.

The optic thalami are thickenings in the outer walls of the
third ventricle.

The corpora mammillaria are the anterior inferior ends of
the fornix, being the roots of what are called its " anterior
pillars."

The roof of the fourth ventricle is formed of the ependyma
alone, the pia mater and arachnoid being reflected over the
postero-inferior surface of the cerebellum.

The " temporal lobe " of the cerebrum is developed early ;
the " occipital lobe " is a subsequent outgrowth from the
hinder part of the hemisphere.

At first the cerebral hemispheres are smooth, the various
convolutions arising successively as development proceeds.

The corpora quadrigemina are at first represented by but
a single hollow prominence on each side.

10. A survey of the brain of Vertebrates generally, shows
us that this organ in man attains a very notable degree ot
SIZE and complexity. Yet the convolutions of the cerebrum
may be still more numerous than in him, as we see in the
Whales ; and the absolute size of the organ in the same
animals exceeds that of man very considerably.

It might be supposed that the mass of the brain in man,
as compared with the weight of his body, is at a maximum ;
but it is not so, for even in some small Birds the proportional
weight of the brain is more than twice as great as in man.

Nevertheless, considering man's actual bulk, the relative
size of his brain is very large, for, speaking generally, the
larger the body the less the relative size of the brain ; so that
we may safely assert that no animal with kistiulk of body has
a brain nearly so large relatively as man has.

11. The CEREBRAL HEMISPHERES in man, in that they are
excessively convoluted, agree with those of the largest ani-
mals of man's own class, but in the smaller members of even
his own order (e.g. some American Monkeys) they may be
almost smooth, as is the case in all below Mammals. They
may be broader relatively than in man, as in Cetaceans, and
in a less degree in Seals. They may be more truncated
anteriorly (as in Ruminants), or more pointed (as in the
Rabbit).

They may, by rare exception, project back beyond the

ix.j THE NERVOUS SYSTEM. 379

cerebellum more than in man, as in the Saimiri, or they
may fail to cover that organ even in an Anthropoid Ape, i.e.
in the Siamang Gibbon. Generally it is widely uncovered,
and even in Mammals (e.g. in the Insectivorous Bats) the
cerebrum may leave the pineal gland and corpora quadri-
gemina uncovered also, as generally is the case in forms
below Mammals.

The presence of lateral ventricles is characteristic of all
Vertebrates above Fishes, though the possession of tri-radiate
lateral ventricles is a character almost peculiar to Man and
Apes — as only in the Seals besides is there a small posterior
cornu. Thus the posterior cornu appears, late in zoological
order as in chronological order, in man himself. Next to the
occipital lobe, the temporal one dwindles as we proceed
from man, the Sylvian fissure gradually opening outwards
till (as e.g. in the Rabbit) there is but a faint indication
of it. The cerebral 'hemispheres may be solid, as in Tele-
ostean Fishes, e.g. the Perch.

That transverse commissure, the corpus callosum, may be
wanting, as in all below Mammals, and where it is absent
no fifth ventricle is, of course, enclosed. Pari passu with the
diminution of the corpus callosum we find generally in man's
class an increase in the relative size of the anterior commis-
sure, but below man's class the latter remains small in spite
of the absence of the former. Sometimes, however (as in
Cetacea), with only a fairly developed corpus callosum, the
anterior commissure may be almost obsolete.

.3 2

G'

FIG. 331. — RIGHT SIDE VIEW OF BRAIN OF THE COMMON LIZARD

{Lacerta agilis).

i, olfactory lobe ; 2, cerebral hemispheres ; 3, pineal gland ; 4, one of the optic
lobes ; 5, cerebellum ; 6, pituitary body ; 7, spinal marrow.

12. The OLFACTORY LOBES of man are mere rudimentary
structures compared with their condition in many animals, as
e.g. in the Rabbit, and very often the ventricular cavity which
is but transitorily present in man, is permanent. They may
be sessile prominences, close to the hemispheres, as in the
Eels, or placed at the end of large diverging peduncles, as
in the Rays (Fig. 336, i). They may considerably exceed the
cerebral hemispheres in size, as in the Lamprey.

ELEMENTARY ANATOMY.

[LESS.

The true OLFACTORY NERVES are filaments which pass from
the lobes to the inner surface of the olfactory organ. In man
and Mammals they pass through the foramina of the cribri-
form plate to the mucous membrane, investing the spongy
bones (or lateral ethmoid and turbinals) as described in
Lesson VIII. § 13 of the "Elementary Physiology."

Pa,

FIG. 332.— VERTICAL LONGITUDINAL SECTIONS OF THE NASAL CAVITY.

The left-hand figure represents the outer wall of the right nasal cavity ; the right-
hand figure the left side of the middle partition or septum of the nose, which
forms the right wall of the left nasal cavity.

/, the olfactory lobe and its branches ; V, branches of the fifth nerve ; Pa, the
palate which separates the nasal cavity from that of the mouth; ST, .the
superior turbinal bone; MT, the middle turbinal; IT, the inferior turbinal.
The letter / is placed in the cerebral cavity. The partition on which the
olfactory lobe rests, and through which the filaments of the olfactory nerves
pass, is the cribriform plate.

An essentially similar arrangement to that in man exists in
all Vertebrates above Fishes, except in those destitute of an
olfactory organ, as the Cetacea. The place of opening of
the posterior nares within the mouth
varies not only as before noticed in de-
scribing the skull, but the aperture may
be placed half-way down the throat, as
in Myrmecophaga. The singular elon-
gation of the nose in the Elephant has
also been adverted to in the Lesson on
the Muscles. Singular leaf-like expan-
FTG.333._MEMBRANEDE- sions of membrane may be developed
VELOPED ON THE NOSE from the external skin of the nose, as
orTHBBAT-Sftffc&rwa in the Horse-shoe Bats (Rhinolophus
and Megaderma, especially the latter
genus) and Vampires (Phyllostomd) ;

and an extra median ossicle may be developed in the snout,
as e.g. in the Mole,,

IX.]

THE NERVOUS SYSTEM.

The anterior bony nares may be continued on by a single
passage having a single opening on the surface (as in the
Porpoise), the channel being also connected with a complex
appendage of sacs.

Each nostril may still have two apertures, and yet both of
these may open on the external surface, as in Fishes. Finally,
the nasal organ may be absolutely single and median, as in
the Marsipobranchs, ending below in a blind termination, as
in the Lamprey, or opening into the pharynx, as in the
Myxine.

13. The envelope of the THIRD VENTRICLE of the brain
is a most constant and morphologically important structure,
small and subordinate as it appears in adult man. We have
seen, however, that the fore-brain is relatively large at first,
even in him, and it so remains in all the members of the
lowest class of Vertebrates.

In Fishes indeed this part attains a great relative size, and
by some anatomists it is believed to combine with part of

FIG. 334.— BRAIN OF T IE PERCH
(Ptrt*JltanatiJts)SE&n FROM ABOVE.

i, one of the olfactory lobes ; 2, one
of the cerebral hemispheres ; 3, the
pineal gland ; 4, one of the hollow
vesicles commonly called " optic
lobes " ; 5, the posterior median
prominence commonly termed the
cerebellum, but by some deemed to
be a special development of the
"mid-brain."

FIG. 335.— VERTICAL LONGITUDINAL
SECTION OF THE BRAIN OF THE
PERCH.

i, an olfactory lobe ; 2, one of the cere
bral hemispheres ; 3, pineal gland

4, the so-called "optic lobes," show
ing the large cavity they contain

5, the median structure commonly
termed the cerebellum ; 6, the pitui
tary body ; 7, one of the lobi in

Jeriores.

the mid-brain to form a large pair of hollow vesicles in
proximity to the cerebral hemispheres, and to have various
complexities of structure within its cavity. This segment
of the brain is well marked out by the pineal gland abo've
and the pituitary body below.

382 ELEMENTARY ANATOMY. [LESS.

The corpora mammillaria may be single, as in the Rabbit,
or absent, as in Sauropsida. A pair of inferior prominences
may exist below this region of the third ventricle, called lobi
infer lores (Fig. 335, 7), which may, but more probably do not,
answer to the corpora mammillaria.

14. The corpora quadrigemina in man are again but feeble
rudiments compared with their possible relative development
as shown by the brains of other animals. The nates may be
smaller than the testes (as in the Hedgehog), or larger (as in
the Rabbit). In that this mid-brain region in man bears
these four prominences, it agrees with the same part in all
Mammals, but among Sauropsidans we find instead, two large
rounded hollow spheres (called the optic lobes), placed in
Reptiles immediately behind the hemispheres, but in Birds
depressed to the side of the brain, below the level of the
cerebellum (Fig. 338, 4).

It is, however, in Fishes that the mid-brain region attains
its maximum relative size. This region is considered by
most writers to form the optic lobes, but it has been asserted

FIG. 336.— DORSAL ASPECT OF THE BRAIN OF A RAY OR SKATE (Raia latis].

i, one of the two olfactory lobes ; 2, the conjoined cerebral hemispheres; 3, the
pineal gland : 4, one of the so-called "optic lobes" ; 5, the median structure,
commonly called the "cerebellum" ; 6, one of the corpora restiformia.

to be yet more developed, and to include a part which has
generally been regarded (and in all probability rightly so) as
representing the cerebellum of higher animals. Thus in the
Rays there is a great complex mass folded in numerous

ix.] THE NERVOUS SYSTEM. 383

convolutions (commonly reckoned as the cerebellum) and ex-
tending in part into the cavity of the segment of the brain
in front of it. In many Teleostei (e.g. the Conger) the cor-
responding structure may consist partly of a fold extending
into the cavity of the more anteriorly situate cranial vesicle,
partly of a great smooth median prominence behind it.

1 5. The CEREBELLUM of man, like his cerebrum, greatly ex-
ceeds the normal development of the part in Vertebrates
generally, thus differing from the intermediate brain seg-
ments which, as we have seen, are in him below the average
relative development of the same parts in Vertebrates.

As we descend from man we find an increase of the
median portion of the cerebellum (the vermis) with a de-
crease of its lateral lobes, while the flocculus on each side
becomes prominent, and is (as we have seen) received in a
special fossa on the surface of the petrous bone.

FIG. 337. — DORSAL ASPECT OF BRAIN OF A PIGEON (Columba livia).

2, one of the cerebral hemispheres ; 3, pineal gland ; 4, one of the optic lobes
(here lateral and depressed) ; 5, cerebellum.

Complex folds, forming an arbor vita, are common to
man's class, to Birds, and to the Crocodiles, but are wanting
in lower forms.

The cerebellum, even in the highest Ichthyopsida — the
Frogs and Toads— is reduced to little more than a transverse
band ; and it may be that it is hardly larger in Fishes, if,
as has been asserted, it forms but the lower part of that great
convex mass which has been usually described as the cere-
bellum, and which in the Elasmobranchs is so large and
convoluted, and is large but smooth in the Teleostei. If,
however, as is most probably the case, the convex mass is the
cerebellum, then this organ, after dwindling in size in Batra-
chians, once more regains its importance as we descend to
the lowest forms.

Transverse fibres connecting the two lobes of the cerebel-
lum on the ventral side of the medulla are wanting in Birds,

384 ELEMENTARY ANATOMY. [LESS.

and in all below. In other words, a pons Varolii is a struc-
ture peculiar to man's own class.

1 6. The MEDULLA OBLONGATA of man is normal, but less
complex than in much lower forms.

Even in some members of man's own order (e.g. the
American Apes) certain additional structures (called corpora
trapezoidea) separate the upper ends of the pyramids from
the pons Varolii.

The side walls of the fourth ventricle may be remarkably
contorted (as in Rays), forming what is called corpora resti-
formia (Fig. 336, 6).

The little extension backward, or the rudimentary condition
of the cerebellum, sometimes causes the fourth ventricle to
come plainly into view, as we see in the Frog and the Lam-
prey. The fourth ventricle may be relatively enormous, as in
Hexanckus.

17. Thus it seems that man exaggerates those characters
which distinguish Mammals from lower Vertebrates ; i.e. in
him the cerebrum and cerebellum are advanced to a maxi-
mum of relative size and complexity, while the parts which
represent those primitive segments, the fore-brain and mid-
brain, show an extreme simplicity and relative inferiority of
size. Man's brain is an example of one of three types of
structure found in the Vertebrate sub-kingdom.

FIG. 338. — LEFT SIDE VIEW OF BRAIN OF PIGEON (Colutnba li-via.~)

i, olfactory lobe ; 2, cerebral hemispheres : 3, pineal gland ; 4, one of the optic
lobes (here lateral and depressed) ; 5, cerebellum ; 6, pituitary body ; 8, optic
nerve.

The two other types are (i) the Sauropsidan brain and (2)
the Piscine brain. In the first we meet with hollow hemi-
spheres, large optic lobes (superior, or lateral and depressed)
no lobi inferiores, no enlarged roof to the third ventricle, and
no fold of brain-substance extending into a cavity beneath the
so-called optic lobes, while often a well-developed cerebellum
exhibits the arbor vitas. In the second type we meet with

IX.]

THE NERVOUS SYSTEM.

385

solid hemispheres, often with lobi inferiores (Fig. 335, 7), an
enlarged roof to the third ventricle, and a pair of large hollow
optic lobes, often with a fold of brain-substance running for-
ward into their cavity, while what is commonly reckoned as the
cerebellum is more or less developed, but without an arbor vita?.

In the lowest forms we find instead of, as in man, a series
of segments enclosed by an enormous expansion of what
were primitively terminal bodies, merely a number of seg-
ments plainly arranged in a linear series and undisguised
by the excessive development of any one constituent part.

1 8. The SPINAL MARROW in man has been described in the
" Elementary Physiology " (Lesson XI. § 4) — how the cylindri-
cal nervous mass is divided by two vertical median fissures

FIG. 339. — THE SPINAL CORD.

A, Front View of a portion of the Cord. On the right side, the anterior roots
of spinal nerves, A R, are entire ; on the left side they are cut, to show the
posterior roots, PR.

B, A Transverse Section of the Cord : A, the anterior fissure ; P, the posterior
fissure ; G, the central canal ; C, the grey matter ; W, the white matter ;
AR, the anterior root ; PR, the posterior root ; Gn, the ganglion ; and T, the
trunk, of a spinal nerve.

(one before and the other behind) into two lateral halves, each
of which is again subdivided by the two vertical series of
spinal nerve-roots (one series being made up of the anterior
roots, the other of the posterior ones) into three subordinate
and less-defined vertical segments.

The spinal marrow extends (Fig. 35 i)from the foramen mag-
num nearly to the second lumbar vertebra, being continuous
above with the medulla oblongata, and so occupies about
the upper two-thirds of the neural canal. Below this region
the canal is occupied by a bundle formed of the elongated
roots of those spinal nerves which pass out at the lower lum-
bar and sacral foramina : this bundle is called the cauda
equina. In the earlier stages of existence there is no such
bundle, the spinal marrow then occupying the whole length
of the neural canal. A relic of this early condition is seen
C C

336 ELEMENTARY ANATOMY. [LESS.

in what is called the nervus impar or central ligament, which
is a delicate filament passing down in the middle of the cauda
equina to the bottom of the sacrum or to the coccyx. It is
composed almost entirely of the pia mater which originally
enveloped the primitively co-extended spinal marrow.

Two enlargements are found in the spinal marrow : one
(called the cervical) at about from the third cervical ver-
tebra to the first dorsal ; the other (called the lumbar) at
about the last lumbar vertebras. These do not exist at first :
they are related to the nerves of the limbs.

A minute modification of tissue, the canalis centralis, con-
tinues on downwards, from the fourth ventricle of the brain,
along the middle of the spinal marrow. In the earliest
stages of life this is a very conspicuous longitudinal cavity,
being in fact the canal formed by the elevation and closing
over of the walls of the embryonic primitive groove.

19. In that the spinal marrow of man is medianly grooved
both on its ventral and on its dorsal surface, it follows the
rule of the Vertebrate sub-kingdom ; and in that it is con-
tinuous with the medulla oblongata, it agrees with all
Vertebrates except the Lancelet.

As to the extension of the spinal marrow in the neural
canal, man's embryonic condition agrees with that which is
permanent in lower forms such as Fishes. In that very class,
however, e.g. in Diodon, the spinal marrow may be much
more shortened, and the cauda equina very much longer
relatively than in man, while in his own class (as e.g. in the
Hedgehog) these characters may be more marked than they
are in him, and a conspicuous cauda equina is found in Frogs
and Tortoises.

The posterior end of the spinal marrow may present a
slight enlargement, as e.g. in the Cod.

The canalis centralis is much more conspicuous in lower
forms, and in them persists plainly throughout life as a distinct
longitudinal cavity. A singular enlargement of this canal
may take place towards the lower end of the spinal marrow,
as in Birds, where a sort of inferior repetition of the fourth
ventricle (called the sinus rhomboidalis] exists in the situation
of the lumbar spinal enlargement.

The cervical enlargement may alone exist, as in Cetaceans ;
while, on the contrary, the cervical and lumbar enlargements
may be both so far more marked than in man that the
intervening part of the spinal marrow is reduced to a very
slender condition, as is the case in the Tortoises.

IX.] THE NERVOUS SYSTEM. 387

20. The two cords which have been spoken of as the
optic tracts arise, one on each side, from the optic thalami,
and run forwards obliquely across the under surface of the
brain, to join together immediately in front of the infundi-
bulum, whence they again diverge as the OPTIC NERVES. At
the point of junction the two tracts partially exchange
their fibres as follows : — The outer fibres of each tract con-
tinue on to the optic nerve and eye of the same side. The
inner fibres cross over to the optic nerve and eye of the
opposite side. This decussation of fibres is called the optic
commissure or chiasma. Beyond the chiasma each optic
nerve passes through the corresponding optic foramen, in-
vested in a sheath of the dura mater, and surrounded by the
recti muscles. After piercing the outer coats of the eyeball,
it expands within that globe into what is called the retina.

Posteriorly the optic nerves become connected with the
corpora quadrigemina, or optic lobes, but this connexion
does not exist at first.

The structure of the EYE has been so amply described in
the Ninth Lesson of the " Elementary Physiology" that here
it is only necessary to notice its development and its more
important relations with the conditions presented by the eye
in Vertebrates generally.

FIG. 340. — DIAGRAM REPRESENTING THE DEVELOPMENT OF THE EYE IN
SUCCESSIVE STAGES, FROM FlG. I TO FlG. 3.

;/, outgrowth from fore-brain becoming cup-shaped, applied to the back of the
vitreous humour and forming the reti)ia; i, the involution of the integument
becoming posteriorly the lens (/) and anteriorly the aqueous humour ; v, the
lateral ingrowth which intrudes between the l:ns and nervous outgrowth
and becomes the vitreous humour ; op, the optic nerve ~, cc, the incipient
skin-folds which become the eyelids ; they are connected by the conjunctiva.

The eye is formed by the junction of an outgrowth from
the brain with an ingrowth from the skin.

The outgrowth is from the fore-brainj and is in the form of
a hollow process containing a prolongation of the primitive
ventricular cavity.

This process becomes cup-shaped, and embraces the back
of the part formed by the ingrowth of the skin,
c C 2

388

ELEMENTAR Y ANA TOMY.

[LESS.

- -L.G.

The ingrowth becomes pinched off, its hinder part forming
the crystalline lens, its anterior part the aqueous humour.

A third process intrudes inwards from one side, between
these two growths, and forms the vitreous humour.

The connective tissue around the whole structure becomes
condensed, as the sclerotic.

The external skin develops folds which increase and
become the eyelids, and these are lined by a membrane re-
flected over the eyeball and called the conjunctiva.

At first the optic nerves are separated, not forming a
chiasma.

At the outer angle of the orbit is the lachrymal (or tear-
secreting) gland, the tears passing down a canal which
traverses the lachrymal bone — as before noticed — into the
nares.

In the possession of eyes man agrees with the immense
majority of his sub-kingdom ; nevertheless, these parts
may be quite rudimentary and
covered by the external hairy
skin, as in the Mole. They
may even, as in Myxine, merely
consist of a minute lens in
contact with the end of the
optic nerve, which is coated with
pigment.

The eye may be relatively
much larger than in man, as e.g.
in Tarsius, and in many Birds
and Fishes.

The sclerotic may be more or
less ossified, as in Birds, Lizards,

and many Fishes, but it is never so in man's own class.
The orbital muscles have been already described.
Part of the lateral process, which forms the vitreous
humour, may persist in part in its more primitive condition
as a distinct vascular membrane, covered with pigment,
extending from near the entrance of the optic nerve to the
lens. Such is the case in Birds and many lower forms, where
it is called \he pecten, or sometimes the marsupium.

Lachrymal glands may be entirely absent, as e.g. in
aquatic forms — Fishes and Cetaceans.

Eyelids may be absolutely^ wanting, as in most osseous
Fishes ; or they may be apparently so, as in Serpents, where
they really exist in a transparent condition and quite with-

FIG. 341. — FRONT VIEW OF THE
EYE, WITH THE EYELIDS.

Lachrymal gland,/, G; andlachry-
mal duct, LD.

IX.]

'THE NERVOUS SYSTEM.

out division (into upper and lower), so that the primitive
folds have, as it were, coalesced, entirely shutting off the
conjunctival chamber from the exterior, except by means
of the communication effected with the nares through the
lachrymal canal.

A third eyelid (called the nictilating membrane) often
exists, as e.g. in Birds, attached to the inner side of the front
of the orbit. It is moved in various ways, as already noted
in describing the muscles of the eye. A minute rudiment of
this structure exists in man.

The form of the eyeball may be much less spherical than
in man. Thus it may be much flattened anteriorly, as in
Fishes ; or, on the contrary, much elongated, i.e. anteriorly
produced, as in Birds, e.g.- the Owls.

The optic nerves may, after development, entirely or all
but entirely abort, as in the Mole ; but this atrophy is very
exceptional.

On the other hand, that primitive condition of the optic
nerves in which the fibres do not decussate may persist
throughout life, as in the osseous Fishes ; nevertheless, the
nerves themselves cross (each one going to the eye of the
side of the head opposite to
that of its own origin), though
they do not form a chiasma.

Unlike the nasal organ, the
optic structure is never single
and median except by mon-
strosity.

There may even be the
appearance of two superim-
posed eyes on each side of
the head. This remarkable
structure occurs in the Fish
Anableps, and is produced
by the presence of a hori-
zontal opaque tract in the
middle of the cornea together
with a double perforation of
the iris.

Both eyes may come in the

adult to be placed on one side of the head, as in the Flat
Fishes, such as the Sole and Turbot ; or both eyes may be
closely approximated on the upper surface of the head, as
in the' Fish thence termed the Star-gazer ( Uranoscopus].

FIG. 342.— RIGHT SIDE OF THE HEAD
OF ONE OF THE PLEURONECTID^E.

390

ELEMENTARY ANATOMY.

[LESS.

Finally, each eyeball may be supported at the end of a
long outwardly projecting pedicle, as in the. Shark which on
this account is called " Hammer-headed."

21. The so-called olfactory
and optic nerves are thus not
really nerves, but prolonga-
tions and outgrowths of the
very brain itself; the other
so-called cranial nerves (ex-
cept a part of one, which part goes to the internal ear) are
properly thus designated.

The THIRD AND FOURTH NERVES (Fig. 324) arise from the
mid-brain, and go respectively— the first to all the orbital
muscles except the upper oblique and the outer rectus ; the
second, to the upper oblique orbital muscle. Both these
nerves traverse the spheno-orbital fissure.

FIG. 343. — HAMMER-HEADED SHARK.

FIG. 344. — DIAGRAM ILLUSTRATING THE ARRANGEMENT OF THE PARTS OF
THE BRAIN AND THE ORIGIN OF THE NERVES.

//, the cerebral hemispheres ; CS, corpus striatum ; T/i, optic thalamus ; P,
pineal gland ; Ft, pituitary body ; CQ, corpora quadrigemina ; Cb, cere-
bellum ; M, medulla oblongata ; /. — XII., the pairs of cerebral nerves ; Sp l
and Sp 2, the first and second pairs of spinal nerves.

The SIXTH NERVE arises from the base of the brain just
in front of the medulla oblongata, and goes through the
same fissure to the outer rectus muscle of the orbit.

ix.] THE NERVOUS SYSTEM. 391

These three nerves present a singular constancy (both as
to origin and distribution) in Vertebrates generally,"but where
there are extra muscles of the orbit, such as have been
already described in the Eighth Lesson, these muscles are
supplied by the sixth pair of nerves.

It may be, however, that the whole of these nerves are
quite blended with one division (the ophthalmic) of the fifth
nerve, as e.g. in the Lepidosiren ; or the sixth nerve alone
may form one with the fifth, as in the Bull-frog and others ;
or the third and fourth nerves may unite to form a com-
mon trunk, -as in the Lamprey, the external and inferior
rectus, together with the inferior oblique, being furnished
with nerves by the first (ophthalmic) branch of the fifth
nerve. Finally, the whole of these three nerves may abort,
as in the Myxine.

22. The FIFTH NERVE, a very large and important one,
passes forth from the side of the mid-brain, and, after swell-
ing out into what is called the Gasserian ganglion, divides
into three nerves, called respectively the ophthalmic, the
superior maxillary, and the inferior maxillary.

The ophthalmic nerve passes through the spheno-orbital
fissure. It subdivides into various branches, of which we may
note — (i), the nasal branch, which skirts the ethmoid, and
(2), the lachrymal branch, which passes along the outer side
of the orbit to the lachrymal gland.

The superior maxillary nerve passes through the foramen
rotundum and infra-orbital foramen, and goes to the nose,
eyelid, upper lip, and teeth of the upper jaw.

The inferior maxillary nerve passes out through the
foramen ovale, and goes to the tongue, salivary glands, and
adjacent parts, and, traversing the canal of the mandible,
supplies the teeth of the lower jaw with nerve filaments.

The tongue, although an organ of special sense, will be
more conveniently described amongst the other alimentary
structures in the Eleventh Lesson.

A remarkable constancy exists as to the fifth nerve in
Vertebrates, except that in some lower forms it blends, as
has been said, with the sixth nerve or with all the orbital
nerves, and, as we shall find, also more or less with the
seventh. The points of exit from the cranium may differ as
to details rven in man's own class, as has been indicated in
describing the foramina of the skull in the Lesson on that
part of the skeleton.

Comparing the essential characters of this nerve and the

392 ELEMENTARY ANATOMY. [LESS.

distribution of its branches in man, with its condition in the
lowest and in embryonic forms, it appears that the ophthal-
mic nerve is the one which skirts, by its branches, externally
the trabecula cranii of its own side, and internally the
palato-quadrate arch ; and similarly that the upper and lower
maxillary branches may be considered as two branches of
one whole, which divides to skirt the palato-quadrate arch
inferiorly (or posteriorly) with one branch, and the mandi-
bular arch superiorly (or anteriorly) with the other.

23. The next nerve, as ordinarily described in human
anatomy, is a part of the seventh, which is said to be divided
into a portio mollis and a portio dura. In this book the latter
nerve (the portio dura) will be spoken of exclusively as the
seventh nerve, and the portio mollis, or AUDITORY NERVE,
may now be considered.

This portio mollis is not, like the so-called optic and the
olfactory nerves, a cerebral outgrowth, but still it is a peculiar
nervous formation applied exclusively to minister to a special
sense, namely that of hearing.

The EAR of man has been described with great care in the
" Elementary Physiology," Lesson VIII. \\ 15 — 30,50 that
here it will be only necessary to notice the development of
the parts of the human auditory organ.

The ear, like the eye, is formed by an involution of the
skin, but this is not supplemented by an outgrowth of the

4

)e) e

jfigr.3. fig.&.

FIG. 345. — DIAGRAM TO ILLUSTRATE THE DEVELOPMENT OF THE EAR IN
SUCCESSIVE STAGES FROM FlG. I TO FlG. 4.

/', involution of integument forming a sac which afterwards becomes the mem-
branous labyrinth ; c, inferior process of the sac (/) which detaches itself and
becomes the cochlea ; /, upper part of sac which forms the semicircular canals ;
n, auditory nerve ; /"*, fenestra pvalis ; fj ', fenestra rotunda ; sf, stapes, or
columella auris ; 3 and 4, summits of third and fourth (or mandibular and
hyoidean) arches, against the upper part of which the stapes abuts, being an
outgrowth from the region of the fenestra ovalis,

brain, so that it is only the outer part of the eye which is
parallel in development to the ear.

The outer margin of the involution contracts, and so forms
a closed sac placed beside the hind-brain, and above the end
of that visceral cleft which separates the mandibular and
hyoidean arches.

ix. ] THE NER VO US S YS TEM.

393

The closed sac sends out four processes, three of which
become the three semicircular canals, while the fourth de-
taches itself, coils round, and becomes the cochlea. In the
meantime tissue on the inner side of this "labyrinth" changes
into the true auditory nerve, and thus places that structure
in direct communication with the brain.

This merely membranous labyrinth is afterwards enclosed
in dense bone — as before mentioned in describing the petrous
part of the temporal bone — the bony investment leaving two
apertures (termed respectively fti&fenestra ovalis and the
fcnestra rotunda) besides those minute foramina (at the
bottom of the meatus auditorius internus) through which
the filaments of the auditory nerve enter.

The visceral cleft meanwhile becomes differentiated into
(i) an outermost part (the meatus auditorius externus) in-
vested beneath by the tympanic bone, and closed within by
the tympanic membrane or drum of the ear ; (2), a median
part (the tympanic cavity) bounded externally by the drum of
the ear, and traversed by the auditory ossicles, the malleus,
incus, and stapes j (3), an innermost part (the Eustachian
tube)— a straight, simple canal — opening internally at the
side of the roof of the pharynx by a rather wide aperture.

The upper ends of the mandibular and hyoidean arches
become differentiated into the malleus and the incus respec-
tively, the stapes being, as it were, an outgrowth going from
the fenestra ovalis to the upper part of the hyoidean arch.

From the posterior margin of the hyoidean visceral arch a
membrane grows out which becomes the external ear, the
concha or pinna, \vhich presents various parts, amongst the
smaller yet more noteworthy of which are the soft depending
portion, or lobule, and the little conical prominence (called
the tragus) which projects backwards over the external
opening of the ear.

Such being the condition and development of the ear in
man, it remains to estimate its peculiarity and the nature of
some of its component parts by a brief survey of the more
remarkable conditions which the organ presents in other
Vertebrates.

In that he possesses an internal ear, he agrees with all
Vertebrates except the anomalous Lancelet, nor (with this
exception) does the organ of hearing ever become atrophied
in the way which we have seen such atrophy to occur occa-
sionally with the organ of sight.

A labyrinth composed of three semicircular canals is also

394 ELEMENTARY. ANATOMY. [LESS.

almost universal, the only exceptions being the Lampreys,
which have but two canals, and the Myxine, which has but
one — the whole organ in it consisting of but one circular
canal.

A cochlea is present in all Mammals and Sauropsida, but
only in the former is it spirally coiled, and not in all of
them, it bein ,*• but slightly twisted in Monotremes as in Sauro-
psidans. In man's own division, the Monodelphous Mammals,
the cochlea may be less coiled than in him, namely only one
and a half times (e.g. the Hedgehog) ; or more so than in
him, as in the Paca, which has it coiled five times.

The MEMBRANOUS LABYRINTH may, as in Fishes, be en-
closed by hard structures (bone or cartilage) in such a way
.that no fenestrae are left unsolidified, but at the same time
the bony chamber (or otocrane) may be widely open inter-
nally, as e.g. in the Carp, Cod, &c.

The opening of the primitive involution of the integument
to form the ear may persist throughout life, as in the Rays,
where it opens on the top of the head by a valvular aperture.
The external auditory meatus may be quite absent, as in
Fishes and Tailed-Batrachians, and the tympanic membrane
may appear on the surface of the cranium (though covered
with a layer of skin), as in many Frogs and Lizards.

The internal part of the primitive cleft (i.e. the Eustachian
tube) may be absent, as in Fishes ; or the two tubes may
unite into a single and median aperture, as in Birds and
the Toad Pipa; or they may open (as in the Crocodiles) by
three apertures — one median and two lateral ones — each
lateral Eustachian tube forming a singularly complex and
contorted canal. They may have narrow openings into the
pharynx, as in the higher Vertebrates, or wider ones, as in
Frogs.

The auditory ossicles may be very different from those of
man in form and relative size. Thus their relations have
been asserted to be as follows : —

In the malleus of man the processus gracilis creeps down,
as it were, to the Glasserian fissure, but it remains much
smaller than the manubrium. As we descend in the animal
scale we find these proportions reversed, till in the Echidna
the very large malleus has an enormous processus gracilis,
which descends in close contiguity to the lower jaw. In the
Sauropsida the enormous malleus becomes segmented, one
portion constituting the os quadrature, and the other forming
the os articulare of the mandible.

ix.] THE NERVOUS SYSTEM. 395

In osseous Fishes a yet further segmentation occurs, as we
find in addition a third bone, called the meta-pterygoid.

Tnc.

FIG. 346. — THE MEMBRANE OF THE DRUM OF THE EAR, seen from the inner
fide, with the small bones of the ear ; and the walls of the tympanum, with
the air-cells in the mastoid part of the temporal bone.

MCt mastoid cells ; Mall, malleus ; Inc, incus ; St, stapes ; a b, lines drawn
through the horizontal axis on which the malleus and incus turn.

The incus becomes relatively smaller as we descend to the
Sauropsida, and the stapes appears as a little straight ossicle
(the columella auris] coming to the incus from the fenestra
ovalis as usual. In Fishes, however, where there is no fenestra,
there is no such ossicle, and the representative of the incus
(i.e. the highest part of the hyoidean visceral arch) is a very
large bone termed the hyo-mandibular.

Thus, if this interpretation be correct, it is plain that our
comprehension of man's auditory ossicles would be very im-
perfect if studied only in man himself.

The three little auditory bones, the malleus, the incus,
and the stapes, instead of being all similar in nature as in
function, are singularly different.

The malleus is, as it were, the upper part of the lower jaw,
separated, reduced in size, and taken into the ear through the
Glasserian fissure, and applied to the assistance of a special
sense.

The incus is the extreme summit of the anterior cornu
of the os hyoides, separated and also applied to a similar
purpose.

The stapes is quite different in nature, being a small por-
tion of the cranial wall which has grown out, become

396

ELEMENTAR Y ANA TO MY.

[LESS.

separated, and secondarily connected with the upper part of
the hyoidean visceral arch,

•-A

FIG. 347. — DIAGRAM ILLUSTRATING THE DIFFERENT DEVELOPMENTS IN SAURO-
PSIDANS AND ICHTHYOPSIDANS OF PARTS WHICH IN MAMMALS BECOME THE
AUDITOKY OSSICLES.

(After Huxley.)

No. i, the parts in Man ; No. 2, the parts in the Lizard Sphenodon ; No. 3, the
parts in the Cod.

a, malleus, or quadratum ; a', the segment of it called os articulare ; a", the
segment of it called meta-pterygoid ; 3, incus — in the Lizard Sphenodon that
part of the continuous cartilage which answers to man's incus — in the Cod,
the hyo-mandibular ; c, the stapes — columella auris in Sphenodon ; d, the
dentary piece of the lower jaw ; s, stylo-hyoid, or, in Sphenodon, that part of
the continuous cartilage which answers to it ; s , the stapedius muscle ; s",
the stylo-hyoid muscle; bh, the basi-hyal, or body of the hyoid : h, the
corniculum of the hyoid— in the Cod, called cerato-hyal ; y, symplectic.

The external ear, or pinna, may be entirely wanting, as in
the Whales and in all below the Crocodiles, in which latter
animals it is represented by a slight fold of skin.

On the other hand, its proportions may greatly exceed
those of man, and, in the little Bat Plecotiis, may equal
in length the entire trunk. Moreover,
the tragus may be (as in the Insectivo-
rous Bats) so largely developed as to
look like a second pointed ear standing
up inside the normal one.

A lobule is almost peculiar to man,
though a rudiment of it is found in the
Gorilla,

24. The portio dura of the SEVENTH
NERVE (i\\Q facial] arises from the pos-
terior division of the hind-brain, appear-
ing at the posterior margin of the
pons Varolii, 'It enters the internal

auditory meatus, and, piercing the petrous part of the tem-
poral bone, bifurcates, and one part comes out at the stylo-
mastoid foramen, This part is distributed to the ear-scalp and

FIG. 348.— HEAD OF THE
COMMON LONG-EARED
BAT (Plecotusauritus).

t, the tragus of each ear.

IX.]

THE NERVOUS SYSTEM.

397

the muscles of the mouth, nose, and eyelids, and to the skin
of the neck ; it also sends a long and slender branch to the stylo-
hyoid muscle. The other part, called the chorda tympani,
comes out at the inner side of the Glasserian fissure, skirts
the processus gracilis of the malleus, and runs along within
the mandible to the sub-maxillary ganglion, in close juxtapo-
sition with a branch of the third division of the fifth nerve.

These relations are constant, so that the seventh nerve
divides into two branches, which respectively go to the anterior
and posterior boundaries of that visceral cleft which divides
the mandibular and hyoidean arches. In some of the lower
Vertebrates the fifth and seventh nerves are much blended,
and the two may, as in the Frog, be completely united at the
large ganglion at the root of the former.

25. The EIGHTH NERVE is a very complex structure, and
consists of at least three nerves united together, and all
arising from the medulla oblongata and passing out by the
jugular foramen.

The first of these, called the glosso-pharyngeal, supplies

FIG. 349.— NERVOUS SUPPLY OF THE HINDER PART OF THE RIGHT SIDE OF

THE HEAD OF THE SHARK Hexanckus gnseus.

(After Haeckel.)

/, palato- quadrate arch ; ht proximal part of the hyoidean arch ; &1 — 36, six
branchial arches; 1—5, proximal parts of the branchial arches; m, spinal
marrow ;f, facial nerve ; t^, inferior maxillary (or third) branch of fifth nerve ;
g, glosso-pharyngeal ; tn, mandibular division of facial nerve ; hy, hyoidean
division of the glosso-pharyngeal ; vg, nervus vagus ; /, nervus lateralis ;
sp, spinal nerves.

398

ELEMENTARY ANATOMY.

[LESS.

the mucous membrane of the tongue and pharynx and seme
of the muscles of those parts. Its essential nature is revealed
by lower forms, where (as e.g. in the Shark Hexanchus] it
bifurcates (Fig. 349, £", hy, and £2), and sends one branch to the
posterior margin of the hyoidean arch, and another along
the anterior margin of the first branchial arch. This fact
may explain its pharyngeal distribution in man.

The second, called the pneumo-gastric, or nervus vagtis,
is the longest of all the cranial nerves, as it supplies not
only the organs of the voice and of respiration, but also the

FIG. 350. — INFERO-LATERAL VIEW OF HEAD AND AORTIC ARCHES OF

LEPIDOSIKEN.

a, oesophagus ; b, anterior end of bulbus aortse ; c, common roots of the first
aortic arches ; d, third aortic arch; e, first aortic arch \f, dorsal union of the
first three aortic arches ; g~, aorta ; //, cceliac artery ; z, exit of the fifth nerve ;
k, part of operculum ; /, exit of the nervus vagus from the skull ; m, branches
to oesophagus ; n, nerve going to the rectus abdominis ; o, nervus lateralis ;
/, _first and hypertrophied rib : g, posterior part of skull ; r, segmented neural
spines ; s, chorda dorsalis ; /, mandible ; ?», quadrate.
(After Hyrtl.)

heart and the stomach. It sends back two branches to the
larynx, which are called " re-current," and the relations of
which to the arterial trunks are different on the two sides
of the body. The essential nature of this nerve is revealed
by the lowest Vertebrates, where (as in Fishes) we find it
made up of a great trunk, arising by many rootlets from the

ix.] THE NERVOUS SYSTEM. 399

medulla, and giving off a branch to border the opposite sides
of the successive branchial apertures, and then continuing on
to the alimentary canal. It also, in Fishes, gives off a special
nerve, called the nervus lateralis (Fig. 349, /, and Fig. 350, o\
to the outer skin of the lateral body-wall, immediately be-
neath what is called the " lateral line." By very rare ex-
ception the two pneumo-gastric nerves may unite and run
along the intestine to its extreme end.

The third part of the eighth nerve (named the spinal
accessory) supplies the trapezius and sterno-mastoid muscles.
It may be altogether absent, as is the case in Serpents, and
in the whole of the Ichthyopsida.

26. The NINTH NERVE is called the hypoglossal. It
arises by several roots from the medulla oblongata, and then
passes out through the anterior condyloid foramen, and is
distributed to the muscles of the tongue, the os hyoides, and
the larynx. In Fishes this nerve is usually called the "first
spinal ;" and in fact the essential nature of the hypoglossal
nerve is rather spinal than cerebral, being often closely con-
nected with what is commonly reckoned the first spinal,
even in Vertebrates above Fishes.

Thus we see that the so-called cranial nerves belong to two
categories, (i) those of special sense, and (2) those which
border the primitive visceral clefts and send off filaments to
other structures.

The fifth, seventh, and eighth nerves belong to the second
category ; the third, fourth, and sixth nerves may be regarded
as derived from the fifth.

The eighth nerve is a most complex one, the glosso-
pharyngeal portion alone being made up of an undetermined
number of cranial nerves related to those visceral clefts and
arches which become obliterated in all Vertebrates above the
Ichthyopsida.

27. 'The SPINAL NERVES arise in pairs from opposite sides
of the spinal marrow. They are related in number to the
divisions of the axial skeleton, or vertebrae, and (as has been
said in describing that skeleton) they pass out of the neural
canal either in the intervals between the neural arches, or by
direct perforations of those arches.

Each nerve arises by two roots — one anterior (or ventral),
the other posterior (or dorsal). The posterior, or dorsal,
root has a ganglionic enlargement (Fig. 339, B, Gii).

After leaving the neural canal each nerve divides into two
conspicuous branches — one dorsal, the other ventral ; but

400

ELEMENTAR Y ANA TOMY.
..1

[LESS.

FIG. 351. — GENERAL VIEW OF THE NERVOUS SYSTEM, viewed from behind.

i, cerebrum ; 2, cerebellum ; 3, cervical part of spinal marrow ; 4, facial nerve ;
5, brachial plexus ; 6, median nerve ; 7, a cutaneous nerve between which and
the median nerve is the ulnar nerve — the radial (or musculo-spiral) nerve is
seen descending the outer sides of the other fore-arm ; 8, intercostal nerves ;
9, lumbar plexus ; 10, sacral plexus ; n, great sciatic nerve dividing into (12)
the peroneal nerve — a principal branch of which is the anterior tibial nerve
and (13) the popliteal or posterior tibial nerve.

IX. ] THE NER VO US S YSTEM.

401

besides this each gives off a minute filament (or a pair) to
what is called the sympathetic system.

Of these two series of conspicuous branches, it is the
ventral one which constitutes the nerves of the limbs. In
the part of the body intervening between the pectoral and
pelvic limbs, the ventral branches pass, in the thoracic
region, between the ribs, as intercostal nerves ; and in the
abdominal region they run along between the internal oblique
and the transversalis muscles.

It may be, by rare exception (as in the Ganoid Fishes), that
the dorsal and ventral nerves, instead of being the bifurcating
branches from a common root, are distinct nerves, each
arising by its own root.

28. The NERVES OF THE ARM of man result from the inter-
mixture, in what is called the brachial plexus, of the ventral
branches of the four lowest cervical and the first dorsal
nerves.

Issuing from the plexus, the most noteworthy nerves are
the ulnar and median, which supply the pronator muscles
and the flexors of the digits, and the musciilo-spiral nerve,
which supplies the supinator muscles and the extensors of
the digits. The last-mentioned nerve comes round the back
of the humerus to pass along towards the radial side of the
front of the fore-arm. The median nerve, passing down the
inner side of the upper arm, crosses to the front of the elbow
and descends along the middle of the fore-arm. The ulnar
nerve passes down between the olecranon and inner condyle
of the humerus.

The position and number of those spinal nerves which
supply the limbs may be very different from what we find in
man. Thus, in Birds (which often have so many cervical
vertebrae) the limb nerves are more remote from the head,
while in Batrachians they are closer to it, and the brachial
plexus may be formed but by two.

Nevertheless a general resemblance exists with regard to
the nerves of the arm in all Vertebrates above Fishes, ex-
cepting, of course, those animals in which the pectoral limbs
are absent or rudimentary.

In Fishes, however, we find very different conditions,
(i) We may have, as in many osseous Fishes, but the first two
pairs of spinal nerves for the supply of the pectoral fin ; or
(2), as in the Rays, we may have an enormous number of
spinal nerves (much more than half those of the entire body),
which, though collected and connected in different bundles,
D D

402 ELEMENTARY ANATOMY. [LESS.

do not form a definite interlacement like the brachial plexus
of man and the higher Vertebrates.

29. The NERVES OF THE LEG of man result from the inter-
mixture, in what is called the lumbar and sacral plexuses, of
the ventral branches of the four lowest lumbar nerves and of
the four highest sacral nerves, five of these (the lowest lumbar
and four sacral) contributing to form the sacral plexus.

Issuing from the lumbar plexus is the crural nerve, which
goes to the front of the thigh and to the pectineus and
sartorius muscles ; while from the sacral plexus issues the
largest nerve in man's body — the great sciatic, which divides
into the anterior tibial, supplying the extensors of the foot,
and the posterior tibial, supplying its flexors and thus ap-
parently answering to both the median and ulnar nerves of
the arm.

The crural nerve passes out in front of the pelvis, but the
sciatic passes out behind it, between the great trochanter and
the tuberosity of the ischium. Its flexor branch (the pos-
terior tibial) passes on behind the knee-joint and under the
internal malleolus, while its extensor branch runs between the
gastrocnemius and biceps muscles round the head of the
fibula, and descends in front of that bone.

The lumbar plexus exists in almost all Vertebrates above
Fishes, but it may be formed of only two nerves, as in Meno-
poma and the Crocodile, and it may be more separated from
the last nerve of the sacral plexus than in man, as is the
case in Birds.

The sacral plexus, similarly constant, may be formed by
but three nerves, as in Menopoma, or but two, as in Proteus;
or it may, on the contrary, as is the case in Birds, be formed
by the concurrence of as many as six spinal nerves. As many
as four or five of these issue from foramina of the sacrum pre-
axial to those sacral vertebrae which are furnished with ex-
panded transverse processes, or sacral ribs (see Less. 1 1. p. 56).

In Lizards also the sacral plexus is mainly formed by
nerves issuing from vertebrae pre-axial to those which articu-
late with the iliac bones^two out of the three nerves which
combine to form the sciatic nerve being thus conditioned. If
therefore we take the nerves as our standard of comparison,
the so-called sacrum of Lizards does not exactly answer to
that of man and Mammals generally, but is relatively a
somewhat more post-axial structure.

A general agreement is again shown with regard to the
nerves of the leg in all Vertebrates with developed hind

ix.] THE NERVOUS SYSTEM. 403

limbs, above Fishes. It may be, however, as e.g. in Meao-
poma, that the posterior tibial is divided into two nerves,
thus making the correspondence between the nerves of the
pectoral and pelvic limbs more unmistakable than it is in
man, in whom but a single leg-nerve (the posterior tibial)
answers to both the median and ulnar of the arm.

In Fishes we find great variety as to the nerve supply of
the hinder members (ventral fins). Thus, small branches
from the ventral nerves of the fourth pair of spinal nerves
may be distributed to the ventral fins, as is the case in
thoracic and jugular Fishes ; or from the seventh and eighth
spinal nerves, as in the Carp ; or finally, as in the Sharks and
Rays, the ventral fins may be supplied by more posterior
spinal nerves, and by as many as six of them.

In man the nerves for the extensor muscles pass out post-
axially as regards the scapula, pre-axially as regards the
pelvis ; but both the corresponding set of nerves may pass
out post-axially, as e.g. in Menopoma.

30. The SYMPATHETIC SYSTEM is made up of an immense
number of small nerves and ganglia closely connected with
the arteries and with the viscera, and proceeding from two
longitudinal gangliated cords which extend upwards and
downwards one on each side of the ventral aspect of the ske-
letal axis from the pre-sphenoid to the coccyx. The visceral
nerves in passing to the various organs they supply, traverse
those folds of membrane (the mesenteries) which, as we
shall see, suspend the viscera from the backbone.

In the head, filaments of this system communicate with all
the true cranial nerves (i.e. with all but the so-called " optic "
and " olfactory " nerves), and below the head the successive
ganglia unite with the corresponding spinal nerves by the
filaments which, as before mentioned, pass from the latter to
the sympathetic.

Thus, in fact, the sympathetic system may be but a series of
internal branches of the spinal nerves of each side of the body.
In this case each spinal nerve must be considered as dividing
into three branches. One of these branches follows the line
of the ascending dorsal lamina of the embryo — as a dorsal
nerve. Another of these follows the line of the outer plate
of the bifurcating ventral lamina of the embryo — as an
abdominal nerve. The third branch — viz. the filament to
the sympathetic and its continuation — follows the line of the
internal plate of the bifurcating ventral lamina of the embryo.
If, then, this view is correct, the sympathetic system essen-
D D 2

404

ELEMENTAR Y ANA TOMY.

[LESS.

tially consists of all those branches of the cerebro-spinal
system which originally pass down to the viscera in the
inner plate of each bifurcating visceral lamina of the embryo,
and which are represented in the adult by branches similarly
extending into the mesentery,1 and by their serial homologues.

FIG. 352. — DIAGRAM OF THE DE-
VELOPMENT OF THE TRUNK AND
ITS SKELETON, as shown in a section
made at right angles to the trunk's
long axis.

iic, neural canal ; ex, epaxial cartilages
ascending to surround it ; px, par-
axial cartilages descending in the
plate, or layer {Ive), external to pp,
the pleuro-peritoneal cavity ; lvit in-
ternal plate of the split ventral
lamina.

FIG. 353.— DIAGRAM OF THE FURTHER
DEVELOPMENT OF THE TRUNK, as
shown in a section similar to the last.

a, alimentary canal supported by a me-
sentery formed of the dorsal portion
of the inner parts of the split wall of
the embryonic ventral laminae ; e,
epaxial arch ; k, hypaxial arch de-
scending in the median line in the
root of the inner part of the split wall
of the ventral laminae ; /, rib, bi-
furcating proximally and abutting
ventrally against the sternum, which
thus completes the paraxial arch ; in,
peritoneum, bounding on all sides //,
the pleuro-peritcn ;al space.

Moreover, these branches are connected together on each side
(near their origins) by commissural nerve-fibres, and it is
these two linear series of commissures (enlarged into ganglia
at their successive points of junction) which constitute the
two longitudinal gangliated cords before spoken of.

It is the presence of these commissural cords which makes
so marked a contrast between the sympathetic system and the
other branches of the spinal nerves, which in man exhibit no
signs of such continuous longitudinal union. But an extended
survey shows us that these latter (the undoubted spinal nerves)
may also be connected together by similar axially extended
commissural cords, for such do exist in the class of Pushes.

The sympathetic nerves of the viscera present three great
complications, termed (i) the cardiac plexus, (2) the solar
plexus, and (3) the hypogastric plexus : these are placed respec-
tively above the heart, behind the stomach, and in the pelvis.

1 See Lesson XI., p. 458.

ix.] THE NERVOUS SYSTEM, 405

In the existence and main characters of his sympathetic
system man agrees with the members of the Vertebrate sub-
kingdom generally ; nevertheless, the sympathetic may be
absent, as is alleged to be the case in the Marsipobranchs,
and its place may be supplied (as in the Myxine) by an ex-
tension of the pneumogastric.

31. The contraction of muscular fibre in man is said to be
accompanied by more or less electrical disturbance. This
leads us to observe that certain organs may exist for storing up
electricity so as by its discharge to administer severe shocks
to creatures in the vicinity of animals possessing and making
use of such structures. These ELECTRIC ORGANS are met with
only in the class of Fishes, and are constructed of membranous
chambers enclosing cellular plates, while special nerves end-
ing in minute ramifications are distributed upon one and the
same side of each of the plates. The arrangement of these
plates may vary, as also the position of the organs and the
source of their nervous supply. Thus, in the Torpedo there
are two such organs, one on each side, near the head ; while
in the Electric Eel there are four, two on each side of the
trunk and tail. In the Torpedo the nervous supply comes
from the medulla oblongata, while in the Electric Eel it is
furnished through the ventral branches of the spinal nerves.
In the Torpedo the cellular plates are placed horizontally, in
the Electric Eel vertically.

32. The most GENERALIZED CONCEPTION at present at-
tainable of the nervous system of Vertebrates, and therefore
of man, may perhaps be expressed as follows : —

There is a cylindrical cerebro-spinal axis with a median
cavity ending anteriorly at a lamina terminalis, from each side
of which lamina a secondary prolongation is developed. Be-
sides nerves of special sense and of parts surrounding such
special sense organs, the axis gives off a series of bifurcating
branches which skirt each side the cranial arches (splanchna-
pophyses), from the trabecula to the last branchial inclusive.

Behind these bifurcating branches, there is given off a
series of spinal nerves, and each of these nerves splits into
three branches : (i), dorsal ; (2), abdominal ; (3), sympathetic.

Certain of the abdominal branches unite to supply limb
nerves when limbs are developed. The abdominal sympa-
thetic branches, constantly united by commissural filaments,
pass down from the spine along the mesentery, and are dis-
tributed to the viscera.

406 ELEMENTARY ANATOMY. [LESS.

LESSON X.

THE CIRCULATING SYSTEM.

1. The CIRCULATING SYSTEM comprises the various chan-
nels or vessels by which the nutritive fluid of the body — the
blood — is conveyed to and from every part of the organism.
These vessels are of various and very different sizes.

The largest and most complex part of the circulating
system is the heart, which may be considered as the central
portion, all the other channels being subsidiary to it. These
latter may be divided into three categories : (A), the vessels
taking blood from the heart — which vessels are called
arteries; (B), the vessels taking blood towards the heart —
which are the veins ; and (C), the minute tubes (capillaries}
which convey the blood to the tissues, and intervene between
and connect the ends of the arteries and veins- — being dis-
tinguished from both those kinds of vessels by the absence
of muscular fibres in their walls.

In addition to these vessels, which with the heart constitute
what may be called the true circulating system, there are yet
other vessels, lymphatics and lacteals, which convey fluid
from almost all parts of the body into the veins — to which
they thus form as it were a supplementary addition.

The fluids these vessels convey into the veins are (i) the
colourless portions of the blood which have exuded from the
capillaries, and (2) nutritive juices from the walls of the ali-
mentary canal.

All these parts have been so fully described — not only as
regards their function, but also as regards their structure — in
Lesson II. §§ I — n of "Elementary Physiology," as to
render unnecessary much which must otherwise have been
here detailed.

2. The HEART in man, its form, cavities, apertures, valves,
&c., have all been described and figured in the " Elementary

THE CIRCULATING SYSTEM.

407

Physiology," Lesson II. §§ 8, 9, and 10. Nevertheless, it may
be well here to recapitulate certain leading facts.

The heart is enclosed in a shut sac— the pericardium — one
of those closed membranous bags called " serous " from the
serous fluid they contain, the largest of which is the " peri-
toneum." Not only the heart itself, but also the roots of the
great vessels which spring from it, are invested by the peri-
cardium.

'JW ,&

FIG. 354.— THE HEART, GREAT VESSELS, AND LUNGS. FRONT VIEW.

R V, right ventricle ; LV, left ventricle; RA, right auricle; LA, left auricle;
Ao, aorta; PA, pulmonary artery ; PVt pulmonary veins; RL, right lung;
LL, left lung ; VS, vena cava superior; SC, subclavian vessels ; C, carotids ;
R and LJV, right and left jugular veins ; VI, vena cava inferior ; T, trachea ;
B, bronchi. All the great vessels but those of the lungs are cut.

The heart is placed in the thorax between the lungs and
entirely above the diaphragm. Of strong muscular structure,
it is divided by a complete partition into two halves, a right
and a left, and each half is subdivided, by an incomplete
partition, into a smaller cavity or auricle, and a larger cavity
or ventricle. The auricles alone give admission to blood
into the heart ; the ventricles alone expel blood from it.

The openings of the auricles into the ventricles are guarded
by membranous valves which prevent regurgitation.

The valve which guards the entrance into the right ven-
tricle is called tricuspid, and consists of three flaps attached

4o8

ELEMENTAR Y ANA TOMY.

[LESS.

by cords (chordce tendinecz), as described in the " Elementary
Physiology," Lesson II. § 10.

The left auriculo-ventricular opening is guarded by two
flaps, forming what is called the mitral valve, from a fancied
resemblance to a bishop's mitre.

The right auricle has on its left wall an oval depression
called the fossa ovalis, and above and below this depression
it receives blood from two large veins termed respectively the
vena cava superior and inferior. Extending upwards from
the margin of the opening of the last-named vessel to the
fossa ovalis is a rudimentary fold of membrane termed the
Eustachian valve. No other valve guards the entrance
from the venae cavae into the auricle.

FIG. 355.— I. THE LEFT SIDE, AND II. THE RIGHT SIDE OF THE HEAKT
DISSECTED.

I. LA, the left auricle ; PV, the four pulmonary veins ; cd, a style passed through
the auriculo-ventricular aperture ; MV, the mitral valve; ah, a style passed
through the left ventricle into the aorta ; RA, RV, parts of the right side ol
the heart ; PA, pulmonary artery.

II. RA, the right auricle ; VCS, superior vena cava ; VCI, inferior vena cava,
the styles./*?, cd, being passed through them into the auricle ; ab, style passed
through the auriculo-ventricular aperture; TV, tricuspid valve; RV, right
ventricle ; SL, semi-lunar valves at the base of PA, the pulmonary artery,
through which the style gh is passed ; LA, LV, auricle and ventricle of the
left side of the heart.

The right ventricle, besides the opening between it and the
right auricle, has, at its upper part, another orifice ; namely,

x.] THE CIRCULATING SYSTEM. 409

that of the pulmonary artery (so called because it conveys
blood to the lungs), which is guarded by three membranous
folds, termed the semilunar "valves.

The left auricle has no less than four orifices ; namely,
those of the four pulmonary veins. Their openings are not
guarded by any valves.

The left ventricle, much thicker than any other chamber
of the heart, has, besides the opening between it and the
left auricle, one large aperture guarded by three crescentic
flaps (the semilunar valves of the aorta), which valves re-
semble in structure those of the pulmonary artery.

3. At its first embryonic appearance the heart is merely a
tube. In the DEVELOPMENT of the heart this tube becomes
bent upon itself and divided into two chambers. The pre-
axial chamber (nearest the head) becomes subdivided into
the ventricles ; the post-axial one (which alone receives blood
from the body) becomes the auricles — which later grow to be
pre-axial to the ventricles.

The further subdivision of each chamber into a right and
left segment is accomplished by the ingrowth of two septal
projections, which gradually become complete partitions,
though the partition between the auricles is not complete at
birth, an aperture existing then in that place which subse-
quently becomes the fossa ovalis.

The septum between the ventricles arises in such a manner
as to divide the chamber giving origin to the pulmonary
artery from the one whence springs that great primary artery,
the aorta.

4. Turning now to survey the heart as it exists in Verte-
brate animals generally, we find that different creatures exhibit
permanently conditions which are but transitory in man.

In so far as the heart of man consists of four distinct cavities
it agrees with that of all other animals not only of his own
class, but also of the class of Birds together with the Croco-
dilian group.

It may be that the ventricles are but imperfectly divided,
as is the case in all Reptiles except Crocodiles, in which
latter they are completely separated.

The auricles themselves may also communicate perma-
nently, as in some Chelonians ; while, on the other hand, that
trace of primitive division, the fossa ovalis, may be more com-
pletely obliterated than in man, as is the case in the Kangaroo.

Where (as in Batrachians) the heart has but a single ven-
tricle, the root of the aorta is dilated into a bulbus aort&,

4 1 o ELEMENTAR Y ANA TO MY. [LESS

or bulbils arteriosus, which may be rhythmically contractile,
as in Elasmobranchs, or not so, as in Teleosteans. Its en-
trance has valves variously conditioned in different animals.

The heart may consist of but two cavities, one auricle and
one ventricle, as in Fishes. This reduction is, however, ac-
companied by a dilatation of the root of the aorta into a
bulbus arteriosus, and of the termination of the venous chan-
nels at the heart into a sinus venosiis.

Finally, the heart may consist of but a simple tube, as in
the Lancelet, so often referred to.

FIG. 356. — HEART OF CRYPTOBRANCHUS — OPENED ON ITS DORSAL ASPECT.

(After Hyrtl.)

n, ventricle ; b, auricle ; c, vena cava ; d, right innominate vein ; e, coronary veins
from the heart opening into the right innominate vein ;_/", left innominate vein ;
g, five fleshy, semi-lunar valves at the root of the bulbus aortse ; /z, three fleshy
seiui-hmar valves placed at the entrance of the right subdivision of the bulb ;
Ji ' i a prominence below the left subdivision of the bulb ; z, membranous semi-
lunar valve at the root of the left subdivision of the bulb.

The envelope of the heart, the pericardium, may have its
cavity continuous with that of the peritoneum, as in the
Myxinoid and Elasmobranch Fishes.

The right ventricle may, as in all Mammals and Birds,
give rise to the pulmonary artery only, or, as in Crocodiles, to
an aortic arch also.

The valve separating that ventricle from the right auricle
may, as in Birds, be muscular in structure, instead of mem-
branous as in man.

In forms such as Frogs and most Reptiles (in which pul-
monary arteries co-exist with a single or an imperfectly
divided ventricle), special arrangements of valves cause the
venous blood to be propelled into the pulmonary arteries, and
mainly arterial blood into the aortic arches.

x. ] THE CIRCULA TING SYSTEM. 4 1 1

The heart may show marked signs even externally of the
division into a right and left side, as in the Dugong, where
its apex is deeply notched.

The heart may be more elongated than in man, as in Birds ;
or shorter and broader, as in Chelonians.

5. As has been said, two ARTERIES in man leave the heart,
one proceeding from the right ventricle, the other from the
left. These two channels ultimately end in distinct sets ot
capillaries, and thus there are two categories of arterial
channels.

The great artery proceeding from the right side of the
heart is termed pulmonary, and conveys the as yet unaerated
blood for purification. It soon bifurcates into a right and a
left branch, and these branches ramify in the substance of
the right and left lungs respectively.

The arterial trunk proceeding from the left side of the
heart is the largest of all, and is called the great aorta.
It ultimately ends in capillaries distributed over the whole
body, and constitutes the generally diffused (or systemic)
arterial system. The aorta arises from the upper and back
part of the left ventricle, whence it ascends forwards and to
the right, and then curves backwards and towards the left,
forming what is called the " arch of the aorta" It curves
over the left bronchus, passing obliquely from the sternum to
the spine. It then continues on in a nearly straight, vertical
line, descending along the front of the vertebral column
(rather on its left side) to the fourth lumbar vertebra, where
it divides into the two common (or unsubdivided) iliac
arteries — to be noticed shortly.

The aorta gives off from the convexity of its arch four
great arteries, two going one to each side of the head, the
two others to the two arms. Normally, however, the two
vessels, going respectively to the right arm and right side of
the head, are undivided for a short space, forming a large
trunk called the innominate artery.

The two arteries for the head are each called " common
carotid" and each bifurcates in the upper part of the neck
into two branches, called respectively the external and the
internal carotid.

The external carotid, besides physiologically important
branches to the face and the sides of the head, sends one
called the thyroid to the larynx, one called the lingual to the
tip of the tongue, and one, the posterior auricular, which as-
cends (close to the styloid process, and passing through the

ELEMENTAR Y ANA TOMY.

[LESS.

9—

Fid. 357. — ARTERIAL SYSTEM OF MAN.

root of aorta ; 2, its arch ; 3, left common carotid artery ; 3', right common
carotid ; 4, left subclavian ; 5, left vertebral ; 5', right vertebral ; 6, temporal ;
7, axillary ; 8, radial ; 9, ulnar (between the radial and ulnar arteries tl e
interosseous artery may be seen); 10, descending aorta ; n, renal artery ; TZ,
external iliac ; 13, femoral ; 14, anterior tibial ; 15, peroneal ; 16, posterior
tibial.

x.] THE CIRCULATING SYSTEM. 413

stylo-mastoid foramen) to the tympanum. The external
carotid then continues on, assuming the name of internal
maxillary, and enters the spheno-maxillary fossa.

It gives off a number of branches, and amongst them a small
one called the tympanic artery, which ascends through the
fissura Glasseri to the tympanum, and there unites (or, as it
is termed, anastomoses] with the posterior auricular ; also the
vidian, which passes back through the root of the pterygoid,
and some branches to muscles. It then ends by dividing
into the descending palatine and the nasal arteries. Of these
two, the former descends the posterior palatine canal along
with the palatine nerve, runs along the palate and enters the
anterior palatine foramen where it anastomoses with the nasal
artery. The nasal artery enters the nose through the spheno-
palatine foramen (in company with the nasal nerve), sends
twigs to the ethmoid, and, skirting the nasal septum, descends
the anterior palatine canal to anastomose with the descending
palatine as just mentioned.

The internal carotid transverses the petrous part of the
temporal bone (as already noticed in the Lesson on the Skull),
and, ascending beside the basi-sphenoid, anastomoses with its
fellow of the opposite side at the pituitary fossa. While
ascending the carotid canal of the petrous bone it gives off
a small branch which anastomoses with the tympanic, vidian,
and posterior auricular arteries. It terminates as the oph-
thalmic artery, which, entering the orbit by the optic foramen,
skirts the inner wall of the orbit and distributes small branches
in various directions.

The artery of each pectoral limb is termed the subclavian,
and springs on the left direct from the aortic arch, but on the
right from the innominate artery.

Each subclavian gives off an artery termed "vertebral,
which ascends through the perforations of the cervical trans-
verse processes, and, entering the skull through the foramen
magnum, unites with its fellow to form the basilar artery,
which latter runs along the upper surface of the basi- occipital,
gives off branches to the brain, divides, and anastomoses on
each side with the internal carotid.

The subclavian gives off certain other branches, and then
passes out of the trunk at the arm-pit as the axillary artery.
It descends the arm on its inner side, between the biceps
and the triceps muscles, and is then called brachial. At the
elbow it sinks between the pronator teres and supinator
longus, and bifurcates into the radial and ulnar arteries.

4i4 ELEMENTARY ANATOMY. [LESS.

The ulnar gives off the interosseous artery from the inter-
space between the radius and ulna, and then passes along
the inner side of the fore-arm to the hand, while the radial
traverses the front of the fore-arm obliquely to the outer
border of the wrist. These two arteries anastomose by a
pair of palmar arches (one deeper than the other) which
pass transversely between the ulnar and radial arteries. Of
course, a variety of less important branches are given off
at intervals, from the axillary artery and its subdivisions,
along the whole extent from the axilla to the palm.

The great descending aorta gives off many small branches
to the air-tubes, the oesophagus, and the spaces between the
ribs, the last being called intercostals. After passing through
the diaphragm, the aorta gives off several important branches
to the viscera in the abdomen. Such are (i) the cosliac axis,
which divides into a branch to the stomach, one to the spleen,
and one to the liver — called hepatic; (2), the superior and
inferior mesenteric arteries, which pass to the intestines by
means of those folds of membrane (mesenteries), in which,
as we shall see, the alimentary canal is slung ; (3), the renal
arteries, short and large, which pass, one on each side, to the
two kidneys respectively ; (4), the lumbar arteries, which
repeat in the abdomen the intercostals of the thorax ; and
lastly, the middle sacral, which is a small median vessel
running in front of the middle of the sacrum to the coccyx.

The common iliac arteries into which, as has been said,
the abdominal aorta divides, after a short course themselves
subdivide, each into an internal and external iliac artery.

The internal iliac is short, and distributes branches to the
viscera and muscles of the pelvis, and also to muscles of the
back. One small branch, called the superior vesical, passes
to the side of the bladder, a fibrous cord connecting it with
the back of the umbilicus or navel.

The external iliac passes out into the thigh, over the brim
of the pelvis, and takes the name of femoral. It descends
the middle of the thigh, between the vastus internus and
adductor muscles, then dips into the popliteal space, beneath
the gastrocnemius, and divides there into the anterior and
posterior tibial arteries.

The posterior tibial passes down, as its name implies (i.e.
behind the leg), and goes to the sole between the internal
malleolus and the os calcis. It gives off, almost at its origin, .
a long branch, called the peroneal artery, which runs down
behind the outer side of the leg.

x.] THE CIRCULATING SYSTEM. 415

The anterior tibial, having passed to the front of the inter-
osseous ligament, extends down the front of the leg obliquely
to the ankle, and then dips between the first and second
metatarsals and anastomoses with the posterior tibial in a
plantar arch, like the palmar arch before noticed. Many
smaller branches are, of course, given off at intervals.

6. In their DEVELOPMENT the arteries exhibit some in-
teresting phenomena.

The root of the aorta is, at a very early embryonic period,
dilated into a bulb, and from it spring five vessels on each
side (successively, however, as never more than three on each
side exist at the same time), which arch round and meet
together beneath the spinal axis to form the dorsal aorta.

FIG. 358. — DIAGRAM REPRESENTING THE PRIMITIVE AORTIC ARCHES OF
MAMMALS AND SAUROPSIDANS.

(After H. Rathke.}

a, common trunk, or root, of the aorta ; b, b, the two branches into which it
divides, and which give off the successive arches i, 2, 3, 4, and 5, which end
in c, c, two vessels which again unite to form d, the descending, or dorsal,
aorta.

The fourth arch on the left side persists, grows, and be-
comes the arch of the great aorta.

The third arch becomes the common carotid and part of
the internal carotid arteries.

The t\vo more pre-axially situate arches may not impro-
bably become ultimately the tympanic and stylo-mastoid
arteries.

The fifth arch gives rise to the pulmonary arteries ; a com-
munication between it and the great aorta, persisting for a
considerable time, is called the ductus arteriosus (Fig. 367, o).

The descending dorsal aorta is at first double, but its two
parts soon coalesce to form a single vessel. It extends

4 1 6 ELEMENTAR Y ANA TO MY. [LESS.

posteriorly into a relatively large middle sacral artery, and
gives off two considerable superior vesical (here called hypo-
gastric) arteries, which go to the umbilicus and much exceed
in size the primitive external iliac arteries.

7. The significance of these changes will appear from a
consideration of the general condition of the arteries in the
Vertebrate sub-kingdom.

A simple vesicular heart (e.g. in Amphioxus] may be con-
tinued on forwards (i.e. pre-axially) into a median artery,
whence on each side diverge very many pairs of arteries,
which ascend dorsally in contiguity with semi-cartilaginous
arches, subservient to aquatic respiration. In this case the
first arch on each side may continue uninterruptedly upwards
till it meets its fellow, the two uniting above to form the
anterior end of a long subaxial dorsal aorta. The ascending
arches behind the first do not reach the aorta, but taper as
they ascend till they terminate dorsally in a point, while each
has a contractile dilatation at its base. Meanwhile the
blood is collected by separate vessels (called veins) which
spring from each branchial arch, and, growing larger as
they ascend, pour their contents into the aorta.

This is a condition found in the Lancelet alone amongst
the Vertebrata. In no other member of that sub-kingdom
can aortic arches by any calculation, or at any period of life,
be made to exceed eleven on each side.

In the Shark Heptanchus there are probably seven distinct
branchial arches on each side.

From the Lepidosiren and Ceratodus we find there may be
five branchial arches on each side ; or there may be but four,
as in the Perch.

In Fishes the arteries run on the outer side of the branchial
arches (noticed in the Lesson on the Skull), and give off
minute twigs to membranous structures termed gills (which
will be described in the Twelfth Lesson). The blood is col-
lected in the gills and conveyed to corresponding ascending
vessels (called branchial veins) by minute twigs,1 from which
such ascending vessels take origin. The branchial arteries
springing from the aortic bulb are not directly continuous, or
connected by considerable branches, with the vessels joining
the dorsal aorta — or branchial veins.

We may find, however, as in the Frog (at that age of its
tadpole condition when the external gills begin to atrophy)
that three branchial arteries from the bulb may co-exist

1 See page 479, Fig. 405.

THE CIRCULATING SYSTEM.

with three corresponding vessels going to the dorsal aorta,
on each side — direct communications taking place between

FIG. 359. — THE CIRCULATION OF A TADPOLE in its primitive stage, when nearly
all the blood is distributed to the gills ; the pulmonary arteries being quite
rudimentary, and the vessel (or ductus Botalli) connecting together the bran-
chial artery and vein at the root of each gill, being minute.

a, bulbus aortae ; ba, branchial arteries; brl,br3, and br^>, the three gills (or
branchiae of each side); bv, the branchial veins which bring back the blood
from the gills— the hindmost pair of branchial veins on each side unite to form
an aortic arch (aa^, which again unites with its fellow of the opposite side to
form da, the descending (or dorsal) aorta. The branchial veins of the foremost
gills gives rise to the carotid arteries, cc. o, artery going to the orbit ; fa,
pulmonary artery :. i, 2, 3, anastomosing branches connecting together the
adjacent branchial arteries and veins.

neighbouring arteries and veins (by what is called a ductus
Botalli\ in spite of each artery and. vein minutely dividing
in the gill beyond such points of communication.

b,-3

FIG. 360.— THE CIRCULATION IN A TADPOLE

AT A MORE ADVANCED STAGE, when the

gills have begun to be absorbed, the pulmo-
nary arteries to increase, as also the con-
necting branches (at the root of the gills)
between the branchial arteries and branchial
veins.

The letters refer to the same parts as
>n Fig. 359.

FIG. 361.— THE CIRCULATION
IN A YOUNG FROG. Here the
gills have been absorbed, and
the blood passes directly from
the heart to the head, the
dorsal aorta, the lungs, and
the skin.

The letters refer to the same
parts as in Fig. 359.

Again, we may find, as in the adult Frog, three aortic arches
on each side, whereof the first is the common carotid, the
E E

4i8

ELEMENTAR Y ANA TOMY.

[LESS.

second meets its fellow of the opposite side above to form
the dorsal aorta, while the third sends one branch forwards
to the skin and another backwards to the lung. Here the
aortic arches are not broken up by any interposed minute
ramifications.

Again, as in Cryptobranchus, we may have two arches on
each side, all meeting to form the dorsal aorta, and each
hinder one giving off a branch to the lung. This condition

FIG. 362.— MAIN ARTERIAL VESSELS OF CRYPTOBKANCHUS.

(After Hyrtl.)

a, atlas vertebra ; b, bulbus arteriosus ; c, c, arteries going to the mouth ; d, d,
anterior, and e, e, posterior aortic arches meeting at e ', the two conjoined arches
further uniting at d'; f,f, pulmonary arteries ; g, external maxillary artery ;
h, internal carotid ; i, vertebral ; k, left subclavian ; /, right subclavian ; ;;/,
spinal artery.

reminds us of that early stage in man (before noticed) when
the ductus arteriosus connects the pulmonary artery with the
aorta ; only in Cryptobranchus, we find such a connexion per-
sisting on both sides of the body, while in man the right
great aortic arch has aborted.

We may also have, as in the Crocodile, two aortic arches
— given off respectively from the right and left ventricles —
uniting in the dorsal aorta ; or finally, as in man's class and

THE CIRCULATING SYSTEM.

419

in Birds, we may have a primitively double aortic arch spring-
ing from the left ventricle only. Of this primitively double arch
it may be the left half only (Fig. 366), which is developed, as
in Mammals, or the right half only (Fig. 365), as in Birds.

When there are two aortic arches, one from each ven-
tricle, these two arches may open into each other by a small
foramen just outside the heart, as in Crocodiles.

Thus we see that man's earliest condition is most re-
sembled by Fishes, which, however, may have a greater
number of arches than are ever developed in him, and,
moreover, these arches may all persist simultaneously. Also
a variety of other conditions, transitory in man, may be per-
manently retained by animals of different kinds.

FIG. 363. — DIAGRAM REPRESENTING
THE VESSELS AND AORTIC ARCHES
OF A SNAKE, and the changes which
the primitive condition (Fig. 358) has
undergone. In this and the three
following figures the parts left blank
are those which abort.

(After H. Ratkke.)

a, a, internal carotids ; b, b} external
carotids ; c, c, common carotids ;
</, </, d, right main aortic arch ; e,
vertebral artery ; f,f,f, left aortic
arch : g, commencement of the de-
scending aorta ; /;, /i, pulmonary
artery ; i, remnant of a primitive
aortic arch — or ductus Botalli — here
a remnant of the right first aortic
arch, No. 5 of Fig. 358.

FIG. 364.— DIAGRAM REPRESENTING
THE VESSELS AND AORTIC ARCHES
OF A LIZARD, with the changes in-
duced on the primitive condition.
(After H. Rat /ike.)

a, a, internal carotids ; b, b, external
carotids ; c, c, common carotids :
d, d, anastomosis between the in-
ternal carotids and the secondary
aortic arches ; e, e, right main aoit'.c
arch ; f^f, the subc avian arteries
(which give off the vertebral, here not
r< presented) ; g, commencement of
the great dorsal aorta ; //, h, left main
aortic arch ; i, i, /', pulmonary arte-
ries ; k, k, rudiments of the first
(right and left) aortic arches, —
Nos. 5, 5, of Fig. 358.

The great arteries of the head and pectoral limbs may
diverge from the aortic arch in different combinations in
man's own class.

E E 2

420

ELEMENTAL Y ANA TOM F.

[LESS.

Thus they may all arise from the aorta in common as one
great trunk, subsequently dividing, as in the Ox ; or the left
carotid, subclavian, and vertebral arteries may all arise sepa-
rately from the aorta, as in the Dugong ; or both common
carotids may take origin in one trunk with the right sub-
clavian, as in the Lion ; or there may be two innominate
arteries, each dividing into subclavian and carotid, as in
the Hedgehog.

FIG. 365. — DIAGRAM REPRESENTING
THE'MAIN ARTERIES OF A BIRD
(FOWL), with the changes induced
on the primitive condition.

(After H. Rathke.)

a, a, internal carotids ; b, b, external
carotids ; c, g, common carotids ; d,
root of main aortic arch (here right);
e, arch of the same ; /, right sub-
clavian (which arises from the ana-
stomosis of the first two right primi-
tive aortic arches) \g, commencement
of the descending aorta ; /«, //, left
subclavian ; /, z, t, pulmonary arte-
ries ; k, right, and /, left, rudiments
of the primitive aortic arches,—
Nos. 5, 5, of Fig 358.

FIG. 366. — DIAGRAM REPRESENTING
THEMAIN ARTERIESOFA MAMMAL,
with the changes induced in the
primitive condition.

(After H. Rathke. )

a, b, c, carotids, as before ; d, root of
main aortic arch (here left) ; c, arch
of the same ; f, commencement of
descending aorta ; g, left vertebral
artery ; h, left subclavian ; /, right
subclavian ; k, right vertebral artery;
/, continuation of right subclavian ;
m, pulmonary artery ; «, remnant of
left primitive aortic arch < No. 5 of
Fig. 358), the ductus arteriosns or
ductus Botalli.

The two common carotids may ascend in close juxta-
position, as in Birds, and one of them may be much reduced
in size, or even abort.

The vertebral artery, instead of passing through the cer-
vical transverse processes, may perforate the neural lamina?,
as in the Llamas.

The internal carotid may break up (inside the skull) into a
network of small arteries (called a rcte mirabile), as e.g. in
the Ox.

x.] THE CIRCULATING SYSTEM. 421

Very different proportions may exist between the external
and internal carotids, compared with what exists in man ;
and the course taken by each may vary in ways which
characterize different groups of Mammals respectively.

The brachial artery may also break up into a number of
small branches running side by side, as in the Sloths and
Slow Lemurs.

The femoral arteries of the same animals are also simi-
larly subdivided, and the same condition obtains in some
other animals, e.g. the Echidna.

Great convoluted retia mirabilia may also be formed by
the intercostal arteries, as we see in the Cetacea, e.g. the
Porpoise.

A small rete mirabile (in what is called — as we shall see in
Lesson XII. — a pseudobranchia) may be developed from the
first (or hyoidean) aortic arch, as e.g. in Lepidosiren and
osseous Fishes.

The intercostal arteries may be less numerous than the
intercostal spaces, as in many Fishes.

The artery of the pectoral limb may be given off from the
dorsal aorta, almost immediately after its formation, as in
Fishes.

The dorsal aorta may dilate beneath each vertebral cen-
trum of the abdomen, as in the Carp. It may give off many
small branches to the kidneys, as in Fishes.

The internal iliac arteries may be given off distinctly from
the external, as in the Kangaroo ; and, as in the same animal,
the middle sacral artery may be continued on of large size.
The internal iliacs may be larger than the external, as in Birds.

The inferior mesenteric artery may abort in man's own class,
as e.g. in the Kangaroo ; and the two cceliac arteries may
ramify in a sort of rete mirabile, as in the Porbeagle Shark.

8. The structure of the VEINS, their coats, valves, and the
primary facts as to their conditions, have been noted in the
first two Lessons of " Elementary Physiology," but the re-
capitulation of certain points is here necessary in order to
avoid obscurity.

The veins, like the arteries, may be divided into two very
unequal categories. The first of these comprises all those
which aid in bringing back blood from all parts of the body
to the right side of the heart : this consists then of the
systemic veins. The second category includes only those
veins which bring back blood from the lungs to the left side
of the heart (the left auricle) — the pulmonary veins.

422 ELEMENTARY ANATOMY. [LESS.

The systemic arteries (excluding retia mirabilia and gill
structures from consideration) never, after dividing, reunite in
a second aggregation.

The same is not the case with the veins, for certain of
them, on their way back to the heart, break up into a minute
network in the liver, whence they reunite and emerge in a
large trunk, which then unites with the rest of the systemic
venous system, and enters the heart. This secondary distri-
bution of blood in the liver (the primary distribution there,
being that of arterial blood by the hepatic artery) is what
is called the portal circulation. The veins which diverge and
become smaller in the liver — conveying venous blood into it
— are called portal veins. The veins which collect them-
selves, unite and so become larger in the liver— conveying
venous blood out of it — are called hepatic veins.

The blood from the brain and from within the cranium
is collected on each side into the internal jugular vein,
which passes out of the skull at the foramen lacerum pos-
terius, and, descending the neck, joins the subclavian vein
(of the same side of the body), which is the one bringing
back the blood from the arm.

The blood from the outside of the head, from the muscles,
teeth, &c., is collected on each side by the external jugular,
which descends the neck and also opens into the subclavian.

A great trunk, the innominate, is thus formed (by the
union of the two jugulars and the subclavian) on each side
of the body, and the two innominate veins joining together
form a yet greater trunk, called the vena cava superior, which
opens, as has been already mentioned, into the right auricle.

The veins of the legs collect themselves together into a
great vein, called the external iliac, which passes in (from
the limb to the abdomen) over the front brim of the pelvis,
and is joined by the internal iliac, bringing blood from the
pelvic viscera.

This junction forms what is called the common iliac vein,
there being, of course, one for each side of the body.

The two common iliacs unite and form one large and long
ascending trunk, called the vena cava inferior, which perforates
the diaphragm, and pours its blood also into the right auricle.

On its way this trunk receives blood from a middle sacral
vein (corresponding with the similarly-named artery) ; from
the kidneys (by short, wide renal veins) ; it also receives blood
from certain other parts ; and, finally, it receives blood from
the hepatic veins, of which more must be said.

x.] THE CIRCULATING SYSTEM. 423

The veins from certain viscera, namely, the spleen, the
mesentery, the intestines, and the stomach, finally unite into
a single trunk — the portal vein, already mentioned. This
enters the liver, and there breaks up and ramifies side by side
with the ramifications of the hepatic artery, which latter brings
arterial blood to that organ. This double supply of blood
(one arterial, the other venous) is antagonized by but a simple
set of efferent vessels, the hepatic veins. These, as before
said, collect themselves together in the liver, meet and en-
large, and finally open obliquely into the vena cava inferior
— a semilunar fold being visible at the lower border of the
orifice of each vein.

There remains one more venous structure which may be
noted, namely, what is called the azygos vein — an absurd
designation, as there are really two such veins, though that
on the right side is much the larger.

The right azygos communicates with the vena cava soon
after its own origin, and ascends on the right side of the
vertebral column, receiving venous branches called lumbar
veins and intercostals. It originates below in the lumbar
veins and terminates above in the vena cava superior.

The left azygos is similar, except in size and in that it
opens above into the left innominate vein.

The two azygos veins communicate by a transverse branch
passing behind the oesophagus, and it is here that the left
vena azygos is said (in works on human anatomy only) to
terminate — the part above this junction, and intermediate
between it and the innominate vein, being spoken of in
Anthropotomy as the left superior intercostal vein.

9. In their DEVELOPMENT the veins of man undergo re-
markable modifications.

The first veins to appear are a pair which come from the in-
testine and ventral region to the heart, and lay the foundation
of the portal and hepatic veins. These primitive veins are
called ompJialo-meseraic ; they unite and dilate into a venous
chamber (called sinus venosus] before entering the heart.

Two other venous trunks appear on each side, beneath the
primitive skeletal axis, and each sends down a vein (the
ductus Cuvieri} which opens also into the sinus venosus.

The part of each trunk which runs backwards from the
head to the ductus Cuvieri is called the anterior cardinal
vein. The part of each trunk which runs forwards from the
hind part of the body to the ductus Cuvieri is called the
posterior cardinal vein.

424

ELEMENTARY ANATOMY.

[LESS.

Another vein, called the umbilical, comes from the anterior
abdominal wall and from other parts, and joins the omphalo-

FIG. 367.— DIAGRAM REPRESENTING THE EARLY CONDITION OF THE

ClRCULATIOM IN MAN.

The course of the blood is indicated by arrows.

{After Quain and Sharpey. )

s,s, the aortic arch and descending aorta ; i,i, hypogastric or umbilical arteries,
afterwards forming the trunk of the internal iliacs, arising from the common
iliacs ; a, the same arteries ascending to the navel ; u, umbilical vein ; ci,
ductus venosus going direct to the inferior vena cava ; ^, vena portae, returning
blood from digestive organs ; /z, hepatic veins ; c, vena cava inferior ; c', vena
cava superior; r, right auricle; v' , right ventricle; /, left auricle; v, left
ventricle ; p, pulmonary artery ; o, ductus arteriosus.

x.] THE CIRCULATING SYSTEM. 425

meseraic veins, but also sends a branch directly to the sinus
venosus.

Then the combined omphalo-meseraic and umbilical veins
break up into the portal circulation— the branch direct from
the latter to the sinus remaining however for a time as the
dnctus venosus. The part of the omphalo-meseraic vein
near the heart which persists undivided thus, becomes the
hepatic vein.

In the meantime the vena cava inferior arises as a large
median vein (superficial to the aorta), receiving accessions
from the pelvic limbs and from the kidneys. It intrudes, as
it were, upon the hepatic veins, and gives its name to the
vein directly entering the heart, into which the hepatic vein
is described as opening in the adult.

After a time the posterior cardinal veins become discon-
tinuous with the anterior ones, and grow into and become the
azygos veins.

The anterior cardinal veins become the jugular and inno-
minate veins. The left ductus Cuvieri aborts, and the left
anterior cardinal vein proceeds to join the right ductus Cuvieri ;
the united trunk is thus transformed into the vena cava
superior.

While the sinus venosus becomes indistinguishably united
with the right auricle, the ductus venosus becomes ob-
literated, so that all the blood from the stomach and
intestines passes into the portal circulation on its way to the
heart. In the meantime the umbilical vein (which is, as it
were, the root of the portal and primitive hepatic veins) in
part aborts, becoming mere fibrous cord ; in part, however,
it persists, namely as the small internal iliac vein.

Concomitantly the vena cava inferior greatly increases in
relative size, as also do its roots — the external iliacs. No veins
are, on their way to the heart, re-distributed in the kidneys in
the same way that the portal vein is in the liver.

10. Turning now to the general condition of the venous
system, we find that the main conditions existing in adult
man are those of his class, but that there may be certain
variations as to the union of the larger trunks, and also as
regards the presence of venous retia mirabilia — similar to
those already noticed with respect to the arterial portion of
the circulating system.

These retia seem to attain their maximum in the abdo-
minal region of Cetaceans, e.g. the Porpoise. The two
azygos veins may be much more equal in size than in man,

426 ELEMENTARY ANATOMY. [LESS.

as in the Monotremes. Instead of a single superior cava
there may be two, the blood from the right and left sides of
the head and pectoral limbs being gathered by two entirely
distinct sets of vessels, each set ending respectively in a right
and in a left vena cava, the two venae cavas each opening by a
distinct aperture into the right auricle. This is the case in
very many Mammals, e.g. in the Rabbit. The middle sacral
vein of course increases in importance with the increase of
the coccygeal region — being thus very large in the Cetacea.

Below man's class, and that of Birds, the blood from the
caudal region and the pelvic limbs may enter the kidneys and
be therein re-distributed by ramifying branches, similar to
the re-distribution of the blood by the portal circulation in
the liver. This is the case, e.g., in Batrachians. Here, how-
ever, part of the blood from these sources is carried on, by
abdominal veins, directly to the liver. But these veins may
go directly to the vena cava inferior, as in Birds.

The great veins, before entering the heart, may dilate into a
rhythmically contractile sinus venosus, as in most Batrachians
and Reptiles.

The blood of the body may be brought back by cardinal
veins and hepatic veins exclusively, as is the case in Fishes.
These cardinal veins consist, on each side of the body, of an
anterior one receding from the head and a posterior one
advancing fom the tail — the anterior and posterior cardinal
vein of each side uniting to form a venous trunk (the ductus
Cuvieri) which descends from the point at which these join,
to the sinus venosus of the heart ; thus exactly reproducing
the primitive condition of man's venous system.

The portal vein itself may be rhythmically contractile, as
in Myxinevcs\di A mphioxus ; or the caudal vein may possess
a pair of small contractile vesicles, as in the Eel. The root
veins of the limbs may be contractile, as in many Batra-
chians, or veins so remote from the centre of the circula-
tion as those which traverse the wing membranes of Bats
may be similarly contractile.

Finally, as in Amphioxus, we may find many veins to be
possessed of this property.

The veins may be destitute of valves, even in man's own
class, as e.g. in the Cetacea.

n. We see, then, that not only structurally, but also
physiologically, the circulating system, even in man's own
sub-kingdom, may present very important divergences from
the conditions we find in him.

x.] THE CIRCULATING SYSTEM. 427

Thus the blood, instead of being propelled in a double
circuit as in man, may, as in Fishes and young Batrachians,
make but a single great circuit, not returning to the heart till
the whole round has been completed.

In this case the heart propels venous, unaerated blood
only, which, quitting that organ by the bulbus aortae, passes
to the gills, where it undergoes aeration, not by decomposition
of the water and extraction of its oxygen, but by the recep-
tion of that gas from the particles of air mechanically mixed
up with the water which the creature inhabits. Having been
thus oxygenated, the blood passes to the great dorsal de-
scending aorta, and is thence distributed over the body.

Again, more or less blood may return to the heart before
being distributed to the body generally, and thus there may
be two circulations, as in man, and in all air-breathing
Vertebrates.

In many animals which possess this double circulation,
both venous and arterial blood may be more or less mixed up
in the heart itself, and thus an impure fluid may be propelled
by the aortic arches. This condition exists in all Batrachians
and Reptiles, except the Crocodiles, though (owing to com-
plex conditions with regard to the valves of the chambers ot
the heart and of the aorta) the mixture is much less com-
plete than might be supposed, the blood from the lungs being
almost entirely forced into that aortic arch which distributes
its contents to the anterior region of the body. This is the
case even in so low an animal as the common Frog.

The two states of blood may be as strictly divided between
the two sides of the heart as in man, and yet a certain im-
purity in the circulation may exist. This is so in Crocodiles,
where the two aortic arches, coming respectively from the
venous and arterial sides of the heart, communicate.

That subordinate sub-division of the larger (or systemic)
circulation which is called the portal system may, as we have
seen, receive blood from more extensive sources than in man ;
and it may be, as we have also seen, not the" only secondary
circulation of the kind — for another like it may at the same
time exist in each kidney, as is notably the case in
Batrachians.

Rhythmical contractility, instead of being confined to
the heart, as in man, may be widely distributed, as in the
Lancelet ; and this is especially the case writh regard to the
proximal ends of the main arteries and veins, which may be
dilated respectively (as we have seen) into a bulbiis artcriosits

428

ELEMENTARY ANATOMY.

[LKSS.

(Fig's. 356 and 362) and a sinus venosus, forming as it were
two supplementary cavities to the heart. Even in man's own
class, parts so remote from the heart as the veins adjacent
to the ringers may become rhythmically contractile under
special circumstances, as we have seen with regard to the
Bat's wing.

The connexion between the systemic and pulmonary
circulation takes place in all higher Vertebrates, as in man,
i.e. only in the heart — its confusion in lower forms has just
been mentioned.

The connexion between the blood carried to the gills and
that which finds its way to the dorsal aorta may, as in most
Fishes (e.g. the Perch), take place only by the capillaries of

FIG. 368.— INFERO-LATERAL VIEW OF HEAD AND AORTIC ARCHES
OF LEPIDOSIRHN.

(After Hyrtl.)

a, oesophagus ; b, anterior end of bulbus aortse ; c, common roots of the first aortic
arches ; d, third aortic arch ; e, first aortic arch ;f, dorsal union of the three
first aortic arches ; g, aorta; k, caeliac artery; z, exit of the fifth nerve ; k,
part of operculum ; /, exit of the nervus vagus from the skull ; m, branches to
oesophagus ; n, nerve going to the rectus abdominis ; <?, nervus lateralis ; p,
first and hypertrophied rib ; q, posterior part of skull ; r, segmented neural
spines; s, chorda dorsalis ; t, mandible; n, quadrate.

the gills.1 But, on the contrary, the vessels taking the
blood from the heart to the gills may be connected by

1 For details of the circulation in the gills see p. 479, Fig. 405.

x.] THE CIRCULATING SYSTEM. 429

anastomosing branches with those which take the blood from
the gills to the aorta. This we- have seen to be the case in
the Tadpole at a certain stage of its development. Indeed,
the primitive condition in Fishes is that of a complete con-
tinuity of each arch from the heart to the dorsal aorta, and
it is only as embryonic development proceeds, that each arch
becomes broken up into a network of capillaries. Examples
are not wanting of the persistence of this primitive condition
throughout life in some of the arches, as e.g. in Monopterus
and Lepidosiren (Fig. 368).

Thus we see that two different and divergent modes of
respiratory circulation may be developed from the same
starting-point : the primitive series of aortic arches in the
one case sending out posteriorly extending branches for a
lung-circulation; in the other case, themselves bieaking up
to form a gill-circulation.

A third mode of respiratoiy circulation, that by the skin,
may supplement the others — as in Batrachians, where a
large artery is given off from the heart to the cutis. As we
shall see in Lesson XII., both pulmonary and gill respiration
may co-exist, as in certain Tailed- Batrachians.

In man the heart is placed at a considerable distance from
the cornua of the os hyoides, but in Fishes in close proximity
to their enlarged representatives— the branchial arches.

At first, however, even in him, these parts are adjoined,
and it is the subsequent displacement of the heart which
causes certain diverging and obscuring structural conditions.

Thus the great aortic arch of Mammals is the remnant of
the vascular arches going to the fourth embryonic visceral
skeletal1 arch, i.e. to the third behind the mandibular skeletal
arch. Yet the thyroid artery is placed much in front of
(i.e. preaxial to) the great aorta, though from the distribution
of the thyroid artery it probably corresponds with an artery
going to the fifth visceral skeletal arch, i.e. the third branchial
arch of Fishes, and perhaps to the fourth and fifth also.

A similar explanation may be given of the fact noticed in
the last lesson— the bending back of a nerve to the larynx
called the recurrent laryngeal. This nerve originally passed
behind the fourth aortic arch (one side of which persists as
the great arch of the aorta), without any marked curvature. In
the adult this nerve descends a long distance and then returns
upwards at a sharp angle, passing on the left side round the
arch of the aorta, and on the right side round the subclavian.

For a description of these visceral skeletal arches see pages 95 and 143.

430 ELEMENTARY ANATOMY. [LESS.

It has become, as it were, pulled out by the gradual dis-
placement downwards of the heart and its arches from what
was their primitive position. Its two ends in the meantime
retaining their primitive connexions, the whole nerve becomes
sharply bent, or " recurrent."

12. The supplementary part of the circulating organs
which goes by the name of the LYMPHATIC SYSTEM has
been already described in the second chapter of Professor
Huxley's work so often referred to, the " Elementary Physio-
logy," '§§ 5 and 6.

It will be well, however, here to recapitulate certain lead-
ing facts.

The lymphatic system consists of two sets of vessels (dis-
tinguished by their place of origin) termed lacteals and
lymphatics. Both are connected with certain rounded
structures termed LYMPHATIC GLANDS.

Each gland consists essentially of a network of finely
divided lymphatic vessels, on and amongst which capillary
blood-vessels ramify, the whole being compacted together and
surrounded by fibrous tissue.

The central part of the lymphatic system consists of a
vertical canal, which ascends in front of the vertebral column
and is called the thoracic duct. At its lower end (at the
junction of the lumbar and dorsal regions) it is dilated into
what is called the receptaculum chyli.

Into this duct all the lymphatics and lacteals ultimately
empty themselves, except those of the right arm and right
side of the head, which empty themselves into a small
vessel called the right lymphatic duct.

Both these ducts open into the corresponding innominate
veins.

Lymphatic vessels are provided with valves like man's
veins, and exist in all parts of the body ; but in the brain
they take the form of investing sheaths for the blood-vessels,
which run enclosed in lymphatics as a gas-pipe might run
inside a drain-pipe.

The lymphatic vessels have proper walls, but they originate
in mere channels, left, as it were, between the other tissues,
and thus whatever is cast loose must find its way into the
lymphatics.

The lacteals are the lymphatics of the alimentary canal,
and pass through numerous lymphatic glands which are
placed in the membranes (mesenteries) which attach that
canal to the spine.

THE CIRCULATING SYSTEM,

431

The lacteals end in the lower part of the thoracic duct.

Lymphatic glands are scattered in various parts of the
body, but those most readily observed in man are the glands
in the arm-pit, the groin, and the sides of the neck.

I

FIG. 369.— THE THORACIC DUCT.

The Thoracic Duct occupies the middle of the figure. It lies upon the spinal
column, at the sides of which are seen portions of the ribs. At the bottom of
the' figure the psoas muscles appear.

a, the receptacle of the chyle ; />, the trunk of the thoracic duct, opening at c into
the junction of the left jugular (/) and subclavian (g) veins as they unite into
the left innominate vein ; e. the right innominate vein formed by the union of
the left jugular and subclavian veins ; d, lymphatic glands placed in the lumbar
and intercostal regions ; h, /i, the cut oesophagus. Two veins are seen running
alongside the lower part of the thoracic duct, and, just above its middle,one (the
left) crosses under the duct and joins the other. These are the azygos veins.

No part of the lymphatic system of man is rhythmically
contractile.

13. In surveying this system by the light furnished by the
anatomy of other Vertebrates, we find that its condition may

432 ELEMENTARY ANATOMY. [LESS.

be both more complex and that it may be the seat of more
activity.

The right lymphatic duct may be so developed that there
may properly be said to be two thoracic ducts, side by side,
as in Birds.

The thoracic duct, even in man's own class, may be double,
and may bifurcate at a higher or lower situation.

Again, the receptaculum may be in the form of a plexus,
as in the Kangaroo.

The lymphatics of the right side of the head and neck
may open directly into the jugular vein, into which vein the
thoracic ducts also empty themselves, as in Birds ; and in
the same class the lymphatics about the kidney open also into
the renal and sacral veins. The thoracic duct may unite
with the azygos vein, as, at least sometimes, in the Hog.

The lymphatics may open directly into the coccygeal vein,
as in Fishes.

Lymphatic glands may be absent, as in Reptiles below the
Crocodiles. They may be few, and confined to the region of
the neck, as in Birds.

The lymphatics generally may take on an exaggerated
form of that condition which they have in the human brain ;
that is, they may generally appear as large reservoirs
(sinuses) surrounding the true blood-vessels. Such is the
case in the lower Vertebrata, especially in Batrachians, where
also they may form great sinuses between the skin and the
flesh, or between the muscles.

The lymphatics may be devoid of valves (which exist only
at their junction with the veins), as in the lower classes of
the Vertebrate sub-kingdom ; or the valves may be few in
number, as in Birds.

The walls of the lymphatics, in certain localities, may
become muscular and rhythmically contractile. Such pulsatile
structures are called lymphatic hearts. There may be four
of these structures, as in the Frog, where two such organs
pump the contained fluid into small veins communicating
with the subclavian veins at the shoulder, while two others,
placed at the coccyx, send their contents into the crural vein.

Two dilated lymphatic structures, answering to the hinder
lymphatic hearts of the Frog, may exist, as in some Reptiles,
and also in Birds, e.%. the Goose, Ostrich, and others. In
these classes, however, they are not rhythmically contrac-
tile pulsating structures, though even in Birds they contain
striated muscular fibres.

xi .] THE A L I MEN TARY S YSTEM. 433

LESSON XL

THE ALIMENTARY SYSTEM.

1. THE ALIMENTARY SYSTEM of man has been in great
part described in the Sixth Lesson of " Elementary Phy-
siology," §§ 13 — 22. Here, however, a certain amount of
recapitulation seems necessary for clearness.

This system begins, as all know, at the mouth, which is
furnished with lips and a tongue, and which opens behind
into the swallow (or pharynx), which, by means of the gullet
(or oesophagus), leads down into the stomach, from which a
long and very tortuous canal (the intestine) continues onwards
to the termination of the alimentary tube or cavity.

The alimentary tube, from the lips downwards, has
various fluids poured into it in different parts of its course,
and these fluids are secreted (i.e. extracted from the blood)
by certain organs termed glands.

Thus spittle is poured into the mouth by " salivary
glands." " Gastric glands " supply their secretion, the gastric
juice, to the stomach. A second set of spittle glands, the
pancreas, pour the fluid they form into the intestine ; and
that vast organ, the liver, also pours into the alimentary canal
its special formation, the bile. As has been already said,
peculiar lymphatic vessels — the lacteals — collect nutritive
fluid from the alimentary canal and convey it into the blood.

All the alimentary organs below the diaphragm — namely the
stomach, intestines, liver, and pancreas — are invested by a
fold of delicate serous membrane, which also lines the inner
wall of the whole abdominal cavity, thus forming a very large
sac, folded in an exceedingly complex manner and contain-
ing a serous fluid. This complex serous sac, by which the
viscera are attached (as in a sling) to the front wall of the
vertebral column, is called the peritoneum.

2. The MOUTH of man has been described in § 13 of the

F F

434

ELEMENTAR Y ANA TOMY.

[LESS.

Sixth Lesson of " Elementary Physiology," and its bony
framework in the Third Lesson of the present course. It
is bounded externally by fleshy and movable lips ; while be-
hind, a transverse fold of skin and muscle (called the soft

FIG. 370. — A SECTION OF THE MOUTH AND NOSE, taken vertically a little to the
left of the middle line.

a, the vertebral column ; b, the gullet : f, the windpipe ; d, the thyroid cartilage
of the larynx ; e, the epiglottis ; f. the uvula ; g, the opening of the left
Eustachian tuhe ; k, the opening of the left lachrymal duct ; /", the hyoid bone ;
k, the tongue ; /, the hard palate ; /«, «, the base of the skull ; o, p, g, the
superior, middle, and inferior turbinal bones. The letters g,f, e, are placed
in the pharynx.

palate, or velutri) hangs down, from the middle of which a
prolongation called the uvula depends. Behind this trans-
versely extended curtain is situate the posterior aperture of
the nostrils, which thus open, not into the mouth proper, but
into the pharynx.

The Eustachian tubes also open into the pharynx above.

XL] THE ALIMENTARY SYSTEM. 435

while the aperture of the windpipe is situated below — behind
the tongue (Fig. 370, g).

The teeth have been already noticed in the Seventh Lesson
of this course.

On each side, the mouth is bounded by a fleshy cheek,
only slightly distensible.

3. In reviewing the mouth as it exists in Vertebrates gene-
rally, we find that it may be entirely destitute of lips, as in
Birds and Reptiles. These structures are not, however, con-
fined to man's class, as they exist in some Fishes, e.g. the
Carp and Dory. Nevertheless, lips are mainly mammalian
structures, and may attain a much greater development than
in man. Thus, in the Right-Whales the lower lip is an enor-
mous structure, rising up on each side and overlapping the
slit-like fissures which separate the numerous baleen plates
before described.

The lips may be much more extensible than in man, as in
even so nearly an allied form as the Orang. The upper lip
may unite with the nose to form an elongated proboscis, as
in the Elephant. It may be medianly divided by a vertical
separation, as in the Rabbit, the Cat, or the Camel ; and
each lip on each side may send a process inwards, behind
the incisors, as in the Rat. Lips, by rare exceptions, may
be absent even in man's own class, as e.g. in the Ornitho-
rhynchus, and they are scarcely developed in the Dolphins.
An exceptional condition is seen in the Sturgeon, where an
exceedingly small mouth opens on the under surface of the
head, its lips being protrusible less by their own structure
than by the singularly elongated and relatively large sus-
pensorial apparatus before noticed.

In the Marsipobranchs we find a great circular lip, destined
for suction and supported by complex special cartilages ; and
finally, in the Lancelet we meet with an altogether exceptional
structure, namely, a mouth in the form of a vertical fissure,
and provided on each side with a series of long, slender,
jointed and ciliated1 tentacles.

Sensitive tentacles, numerous and of small size, may
border the lip, as in the Lamprey ; or the lip may send out
six or eight long tentacles, as in the Myxinoids. Higher
Fishes may — as in the Mullets and Siluroids — have fleshy
and sensitive labial barbs, or cirri.

A soft palate is a structure peculiar to man's own class, with

i Ciliated structures are such a* bear cilia, or minute filaments which keep up
an incessant waving motion. (See " Elementary Physiology," Lesson VII- § 3.)
F F 2

436 ELEMENTARY ANATOMY. [LESS.

the single exception of the Crocodiles, in which a transverse
fold, or soft palate, hangs down in front of the posterior nares.
A distinct uvula is only found in certain members of man's
own order. The soft palate, however, may attain a greater
development than it does in man, as e.g. in the Cetacea,
where it is changed into a muscular canal, which prolongs
the posterior nares, downwards and backwards. We may
find, as in the Camel, a second and very long transverse pro-
cess hanging down from the palate, just in front of the true
velum. It ordinarily hangs down the throat, but in males at
the rutting season is protruded from the mouth in a singular
and conspicuous manner.

The soft palate may extend eight inches beyond the hard
palate, and indeed half-way down the neck, as in the Ant-
eater.

The hard palate, instead of only having very slight trans-
verse prominences, as in man, may have them produced into
strongly projecting ridges, as in the Pig, or into transverse
rows of conical horny spines, as in the Echidna, or into great
depending and dentated ridges, as in the Giraffe — a greater
extension of a similar structure constitutes the baleen-bearing
ridges of the Whalebone Whales.

The situation of the opening of the posterior nares has
already been indicated in the Lesson on the Skull. The
Eustachian tubes and teeth have also been already noticed.

The cheeks may be distensible, so as to form pockets, or
" cheek-pouch js," as in the Ornithorhynchus. some Rodents,
and even in man's own order, as e.g. in the Baboons and the
smaller and commoner Monkeys of Africa and Asia.

That median opening of the windpipe which exists in man,
exists also in all air-breathing Vertebrates — even those which,
like Mcnobranckus, have at the same time permanent gills.
No such structure exists, however, in Fishes,1 although in
the Lamprey we meet with something analogous, as in that
animal a canal conveying water to the gills opens at the
back of the mouth, on the ventral aspect of the opening of the
gullet. In ths higher Fishes, instead of one such opening,
several on each side serve (as we shall see in the Twelfth
Lesson) to convey water from the alimentary tract to the
respiratory organs.

4. The spittle, or SALIVARY, GLANDS of man are three in
number :— (i) The parotid glands, one of which lies on each

1 As to the ductus pneumaticus of the swim-bladder, see Lesson XI T 6 i
p. 465.

•XL] THE ALIMENTARY SYSTEM. 437

side, in front of the ear, behind the ramus of the lower jaw,
and in front of the mastoid process — resting on the styloid
process and muscles. It gives off a tube, or duct, which runs
forward outside the masseter muscle, and then turns inwards,
piercing the buccinator muscle and cheek, so as to open
into the mouth opposite the second upper premolar. (2) The
sub-maxillary glands are next in size, and one on each side is
placed within the lower part of the mandible and above the
digastric muscle. Its duct runs forward and opens (close
to its fellow of the opposite side) beside the fold of skin
which attaches the under surface of the tongue to the flooi cf

Fie .371. — A DISSECTION OF THE RIGHT SIDE OF THE FACE.
a, the sublingual ; b, the submaxillary glands, with their ducts opening beside the
tongue in the Hoor of the mouth at d ; c, the parotid gland and its duct, which
opens on the siaa of the cheek at e.

the mouth. (3^ The sub-lingual glands are still smaller, and
are placed in the floor of the mouth, between the tongue and
the gum of the tower jaw. They open by numerous minute
ducts.

Besides these considerable structures, the mucous mem-
brane which lines the mouth is beset with minute buccal
glands.

5. On extending our view over man's sub-kingdom, we see
that salivary glands may be entirely absent, as is the case in
most Fishes, in Crocodiles, and in the Cetacea. Only in man's
class do we find definite glands of all the three kinds above
described, though very generally salivary glandular structures

438 ELEMENTA RY ANA TOM Y. [LESS.

exist in the tongue and in the inside of the skin investing
the jaws, as in many Reptiles, — these latter structures
answering to our buccal glands, as do also the salivary glands
of harmless Serpents. Poisonous Serpents however are pro-
vided with an extra glandular structure, placed beneath and
behind the orbit. This gland it is which secretes the venom,
and its ducts convey the poisonous fluid to the base of
the deeply-grooved poison fang described in the Seventh
Lesson. By a very rare and remarkable exception, the
poison gland may (as in Callophis intestinalis) attain enor-
mous proportions, extending backwards as far as the heart,
being lodged in the general cavity of the body.

In the class of Birds we may find sub-maxillary glands
occupying the whole of the anterior part of the space included
by the rami of the lower jaw ; or, as in the Woodpecker, a
single gland extending from between the angles of the man-
dible to its symphysis, and furnished with a distinct duct.

In man's own class, both the number and relative size of
the silivary glands may differ from what we find in him.
Thus there may be, as in the Dog, an extra structure, called
the zygomatic gland, placed in the floor of the orbit, behind
the anterior root of the zygoma (its duct opening opposite
the last true molar), and also another, the second, or accessory
sub-in:ixillary gland, smaller, and placed beneath the true
sub-maxillary, its long duct opening close to the aperture of
the true sub-maxillary of the same side.

The parotid also, as in the same animal, may be some-
what smaller in size than the sub-maxillary, but this dispro-
portion is insignificant in comparison with that produced by
the enormous development which the sub-maxillary glands
sometimes acquire, as in the Ant-eaters, where these glands
meet together and unite on the chest, superficially to the
sternum. The sub-maxillary ducts may each be connected
with a dilated vesicle, or salivary bladder, as in the Arma-
dillos; or they may branch out and break up, opening by
many minute orifices on the floor of the mouth, as in the
Echidna ; or each may remain single, but take a very tortuous
course, as in the Ornithorhynchus. Parotid glands may be
absent (the other salivary glands being present) in man's own
class, as in the Monotremes.

6. Man's TONGUE is a muscular body connected with the
os hyoides in the way already noticed in the Eighth Lesson.
Its under surface is bound down by a fold of mucous mem-
brane, called the fr&num, which proceeds from the middle

XI.]

THE ALIMENTARY SYSTEM.

439

line downwards, and then dividing, passes outwards to the
gum on each side of the lower jaw.

Both on the right and left of this fraenum is a little papilla,
on which opens the duct of the sub-maxillary gland of the
same side.

FlG. 372. — SUBMAXII.LARY GLANDS AND TONGUE-MUSCLES OF GREAT

ANT-EATER (kiynttKofkagk jubata).

a. main body of the confluent submaxillary (here subcervical and subpectoral)
salivary glands ; c, dilated portion of duct (or salivary reservoir) surrounded by
muscle : ght genio-hyoideus ; my, mylo-hyoideus ; s, prominence of shoulcfer-
joint ; sm, sterno-maxillary muscle.

(After Owen.}

On the upper surface, or dorsum, of the tongue, are three
kinds of small prominences, or papillae. Towards the front

440 ELEMENTARY ANATOMY. [LESS.

end they are mostly long and pointed, and are called conical
and filiform papillae.

Scattered over the middle of the tongue are very red
papillae, ca\\Q&fungiform, because each is narrower at its
root than at its upper part.

The third kind are the circumvallate papillae— from eight to
fifteen in number — arranged at the back of the tongue so as to
form the letter V, with the point of the V directed towards
the throat. Each of these is shaped like an inverted cone, of
which the apex is attached to the bottom of a cup-shaped
cavity, so that the papilla is surrounded by a circular furrow.
Man's tongue contains no osseous or cartilaginous struc-
ture. Its shape, degree of mobility, and extensibility are too
familiar to require notice.

7. The tongue in Vertebrates generally presents a great
variety as to form and function, relative size, and denseness
of structure.

It may be completely absent, as <?.£-. in the Siluroids, where
even the glosso-hyal bone is absent. It may, as in most
Fishes, be almost destitute of muscular tissue, and very
slightly mobile, merely investing a glosso-hyal bone, and often
being furnished with teeth.

The tongue may be apparently absent in Batrachians, as in
Pipa; or even in Reptiles, as in the Crocodile. It may be
long, pointed, and coated with a horny
sheath, with recurved processes towards
the apex, as in the Woodpecker. It
may be fixed in front and free behind —
being protruded by eversion — as in the
Frog. It may be very extensible,
thickened and somewhat cup-shaped
at the end, as in the Chameleon. It
may be exceedingly mobile and ex-
tensible, with its apex deeply cleft, as

in Serpents.

In man's own class the tongue may
terioriy. likewise only form the floor of the

mouth, as in the Dolphin. It may, as

in the Dog and Mole, have on its under surface a longitudinal
fusiform, rather dense body, attached to the rest by cellular
tissue, and called the worm, or lytta. The coniral papillae
may be horny, and shaped like small claws, as in the Cat.
Fungiform papillae may be absent, as in the Horse and
Manatee. There may be but two circumvallate papillae, as

G. 373.— HEAD OF THE

FKOG Phyllomedusa

XL] THE A LIMENTAR Y S YS TEM. 44 1

in the Rabbit and Proteles ; or but one, as in the Rat and
Pig. They may be disposed in two parallel lines, as in the
Sheep ; or altogether absent, as in the Manatee. They may
be, as in the Orang, arranged in the same way that they are
in Man ; or they may form the letter Y or T, as in the
Chimpanzee. There may be a large horny papilla on each
side, as in Manatee and Ornithorhynchus ; or there may be
horny plates on the tongue, as in the Java Porcupine.

The tongue may be extraordinarily smooth, but with little
mobility and flexibility, as in the Elephant ; or small, nar-
row, and tied down, as in the Manatee. It may have a bi-
furcating apex, as in the Seal. It may be enormous, yet
attached all round nearly to the very tip, and without
papillae, as in the Whalebone Whale.

The tongue may be exceedingly long, and furnished all
round, except at the tip, with backwardly pointing spines, as
in the Tamandua.

This organ attains its greatest relative length amongst
Mammals in Mcinis, where its muscles extend backwards,
taking origin in the very elongated xiphoid process of the
sternum. There is also a sterno-glossal muscle in the Great
Ant-eater and in the Echidna.

There may be a considerable cartilaginous lamelliform
process extending forwards beneath the tongue, taking
origin from its under surface further back, and having the
appearance of a second small tongue beneath the true one.
Such a structure is found in Lemurs. It is independent of
the papillae for the sub-maxillary ducts, which papillae are at
the same time conspicuous.

These latter may unite to form a little bifid body beneath
the tongue, as in the Gibbons.

The papillas on which the sub-maxillary ducts open may
be more elongated than in man : such is the case even in the
Chimpanzee.

8. The (ESOPHAGUS, or gullet, of man is a nearly straight
membranous and muscular tube, leading from the phaiynx
to the stomach.

It consists externally of longitudinal and also of circular
muscular fibres. Within this muscular coat there is cellular
tissue, and this again is lined with mucous membrane.

The STOMACH is formed of similar materials, and has been
sufficiently described in the Sixth Lesson of " Elementary
Physiology," § 18. It is a simple, somewhat pear-shaped
bag, curved, so that its upper surface is concave. The gullet

442

ELEMENTAR Y ANA TOMY.

[LESS.

opens near the wide left end, or fundus of the stomach,
which part is called its cardiac part. The opposite end, or
pylorus, leads into the intestine — the muscular fibres project-
ing, at the point of junction, so as to form a sort of valve.

,'L

«rr-f

FIG. 374. — DIAGRAM OF THE ST.OMACH AND INTESTINES OF MAN.
a, vermiform appendix ; ac, ascending colon ; c, ctecum ; c', cardiac end of
stomach ; d, duodenum ; dc, descending colon ; k, rectum ; li, large intestine
(extending from c to k); a?, oasophagus ; py, pyloric end of stomach ; s,
stomach ; si, end of convoluted small intestines (which begin at d) ; tc, trans-
verse colon.

9. On extending our view over Vertebrates generally, we
see that the oesophagus may be very short and wide, as in
most Fishes ; also that it may be exceedingly distensible, as
in Serpents.

It may be furnished with long, hard, conical papillae,
directed backwards, as in devonians.

It may have a special sac-like dilatation attached towards
its lower part, as in most Birds (Fig. 378, cp], where this por-
tion is called the crop, which may be double, as in Pigeons.

XL] THE ALIMENTARY SYSTEM. 443

Nothing like a crop exists in man's class, with the single
exception of the common Dormouse, which has the lower
end of the oesophagus enlarged into a glandular dilatation.

The oesophagus may be much more muscular than in
man; or it may be rather valvular at its lower end, as in
the Dugong, and still more so as in the Porpoise.

The stomach is sometimes indistinguishable from the
oesophagus, with which it is directly continuous, without any
marked constriction, as in most Fishes. It may form one
continuous canal with the oesophagus, even in Birds, e.g. the
Cormorant ; and indeed in Birds (Fig. 378, pr\ generally the
first or cardiac part of the stomach (called the proventriculus]
seems to resemble more a dilatation of the lower end of the
oesophagus — like that of the Dormouse — than a stomach
proper.

It may attain to a very much greater complexity than it
attains in man, as we see by the Sheep.

The various exaggerated forms which the stomach assumes
may be arranged under two heads : (i) an elongation, (2) a
differentiation, with distinct correlated chambers.

The first condition may exist even in man's own order, as
in the long-tailed Monkeys of India, the Semnopitheci,
which have the pyloric part of the stomach exceedingly
elongated and also sacculated, i.e. puckered up into a succes-
sive series of bags. This condition is carried still further in
the Kangaroo, where the cardiac end is also exceedingly
prolonged.

The second form of stomach is slightly exemplified in the
Pig, where the cardiac fundus is dilated into a little pouch,

FIG. 375. — STOMACH OF A SHEEP, cut open to show the various lining of the

different parts.

ce, oesophagus ; r, rumen or paunch ; rt, reticulum or honeycomb ; ps, psaherium
or manyplies ; a, abpmasum or rennet : d, duodenum.

while two parallel folds lead from the oesophagus to the
pylorus. In the Sheep, however, we find the cardiac end

414

ELEMENTAR Y ANA TOMY.

[LESS.

dilated into an enormous paunch, while close to the oeso-
phagus is a small chamber, called the reticulum (on account
of the net-like appearance of the free margins of the honey-
comb-shaped folds of its lining membrane). The rest of
the stomach is divided into a small chamber, the psalterium,
and a larger terminal portion, the abomasum. Two folds of
membrane lead from the lower end of the oesophagus to the
psalterium, and convey into it the food which descends after
that second mastication (called rumination} by which the
hastily swallowed grass, regurgitated from the paunch, under-
goes the requisite degree of comminution.

Another complication of stomach is produced by an enor-
mous increase of the muscular coat of the pylorus. A
stomach so thickened is called a gizzard, and is found in

FIG. 376. — LONGITUDINAL SECTION OF THE STOMACH OF THE GREAT
ANT- EATER (Myrmecophaga jubata).

ce, oesophagus ; c, cardiac division of the stomach ; in, thickened muscular walls
(or " gizzard ') of pyloric portion of stomach ; py, orifice of pyloric division ot
stomach.

(After Owen.)

most Birds, especially in those that feed on grain, as the
common Fowl. A gizzard may, however, be developed in
man's own class, as e.g. in the Great Ant-eater.

Yet another form of complication is exemplified amongst
Mammals by the Dugong, which animal has two long caecal
appendages attached to its stomach. Many caecal appen-
dages may coexist, as in Fishes, but these open into the

XL] THE ALIMENTARY SYSTEM. 445

commencement of the intestine, and not into the stomach
proper (Figs. 381 and 382, p}.

Another and an exceedingly exceptional condition of the
stomach may exist, as e.g. in the blood-sucking Bat Des-
modus. Here we have the cardiac end produced into an
enormously prolonged pouch, while the pyloric part is re-
duced to a rudiment — the highly nutritious food (blood)
requiring very little digestion, but needing a large chamber
for its speedy reception.

FIG. 377. — STOMACH AND ADJACENT VISCERA OF THE BAT Desmodiis.

(After Huxley.)

ae, oesophagus ; en, cardiac part of the stomach enormously elongated to cd, the
cardiac caecum ; py, short pyloric part of the stomach ; /, liver ; s, spleen.

Instead of being prolonged, the stomach may be very
much shorter than in man, and indeed its depth may exceed
its length, as is the case in the Ornithorhynchus and some
Insectivora, e.g. Rhynchocyon. It may also be globular, as
in the Fish Monnyrus.

Special glandular structures may exist which have no
representatives in man. Thus, as in the Rodent Lopliiomys,
there may be a glandular offshoot from the stomach — near
the pylorus. Again, there may be (as in the Wombat and
Beaver) a glandular mass Avithin the stomach, situated be-
tween the cesophageal and pyloric apertures. Finally, there
may be (as in the Dugong) a complex gland within the
cardiac fundus, formed by a membrane which is spirally
arranged below, but radiating above.

446 ELEMENTARY ANATOMY. [LESS.

10. The INTESTINES of man have been described in the
Sixth Lesson of " Elementary Physiology," §§21 — 23. It may
be here mentioned that the long convoluted tube immediately
proceeding from the pyloric end of the stomach is called the
small intestine. This terminates by a definite opening (de-
fended by a valve) into a much wider and sacculated tube,
called the large intestine, or colon (Fig. 374, ac, tc, and dc).
Near the point of junction, the end of the colon projects
blindly in what is called the c&cuin, which latter has at-
tached to it, near its end, a very narrow hollow process,
called the vermiform appendix: (Fig. 374, a). The colon
ascends in the abdominal cavity, passes transversely, and
then descends to terminate in the rectum. In its transverse
coarse the colon passes in close proximity to the first part
of the small intestine, called the duodenum.

The intestines, like the stomach, are formed of muscular
fibres with a mucous lining ; and this lining is, in the small
intestine, drawn out into very numerous folds (called valvulce
conniventes}, placed transversely to the course of the bowel
and in close proximity, thus vastly increasing the amount of
surface in contact with the food. No such folds exist inside
the large intestine.

11. The study of Vertebrates generally shows us that the
alimentary canal may be much more prolonged relatively,
and may be more complex than it is in man, as also that it
may be relatively much shorter and very much simpler than
in him.

In man the intestines are six or seven times the length of
the body, but in his own class they may be as little as three
times that length, or even less — as in Bats and Shrews ;
while they may be as much as twenty-seven times — as in the
Sheep.

Passing beyond man's class, we find that the intestines
may but little exceed the length of the. body, as in many
Lizards (Fig. 384) and Serpents, and may even fall short of
it, as in some Fishes.

In that his intestine is divisible into "large" and "small,"
man agrees with the great majority of members of his sub-
kingdom. Nevertheless, all distinctions between these parts
may be wanting, so that the whole intestine forms one
simple canal, as e.g. in the Carp, and still more strikingly in
the Lamprey. Even in man's own class there may be no
distinction in size between the large and small intestines, as
in the Shrews— and there is hardly any in the Porpoise.

XI.]

THE ALIMENTARY SYSTEM.

447

The proportion as to length borne by the small intestine to
the large is generally in Mammals less than in man, in whom
it is as five to one ; but the large intestine may be very
short (not more than a tenth the length of the body), as in
most Birds ; it may be, on the contrary, actually the longer
portion of the intestine, as in the Ostrich.

The presence of a csecum is not quite constant in man's
class, and this structure is never found in Fishes, though it is
often present in Reptiles, and generally in Birds. In Fishes,

FIG. 378. — VISCERA OF THE COMMON FOWL.

ce, oesophagus ; cp, crop ; pr, proventriculus ; g; gizzard ; /, liver ; gb, gall-bladder ;
p, pancreas ; d, loop of the duodenum enclosing the pancreas: si, small intes-
tine ; //, large intestine ; e, caeca ; o, oviduct ; u, ureter. — The cloaca is cut open
and some feathers are represented attached to its margin.

indeed, there are often many cascal appendages to the
intestine, but these will be noticed below in describing the
Pancreas.

In man's class the caecum often presents an inverse degree
of size and complexity compared with the stomach. It may
be enormous, as in the Indris, the Hare, the Galeopithecus,
the Koala, and the Horse. It may be very simple and short,

4+8 RLE ME N'T A RY A KA TOM Y. [LESS.

as in the Opossum and others. It may be wanting altogether,
as in the Hedgehog, Weasels, Porpoise, and others.

A vermiform appendix is very rarely found except in
man. It exists, however, in the highest Apes and in the
Wombat ; while in the Monotremes there is a small worm-like
cae um which suggests the belief that this appendix in the
Wombat is but an abruptly atrophied condition of the free
end of the caecum — a belief strengthened by the condition
found amongst Lemuroids, which have a very long caecum,
drawn out into an elongated conical termination.

The caecum may bifurcate, as in the Manatee ; or there
may be two small caeca, as in the Two-toed Ant-eater
(Cyclothorus\ or two larger ones, as in the Armadillo
(Dasypus sexcinctus) ; or, finally, there may be — as in the
Hyrax— three caeca, one at the usual situation, and two side
by side projecting from the colon. A double caecum is a very
rare condition in man's class, but it is the. rule in the class
of Birds (Fig. 378, e).

The large intestine, instead of having a form and arrange-
ment as in man, may have its various regions elongated and

FIG. 379. — SECTION OF THS STOMACH AND PART OF THE INTESTINES OF A
SHARK (Squaliis maximus).

ce, oesophagus ; c, cardiac part of the stomach ; py, its pyloric part ; s, the
spleen ; d, the duodenum ; />, a band containing six hepatic ducts ; cli, a
dilatation in which these six ducts terminate ; z, the intestine, provided with a
spiral valve.

convoluted, or the whole greatly augmented in length and
reduced in diameter, and coiled in a peculiar and character-
istic manner, as e.g. in the Sheep.

Valvulae conniventes, absent even in the species most allied
to man. reappear in an exaggerated form in the small intes-

XI.J

THE ALliMEN TA R \ ' 6 Ys 'l 'EM.

449

tine of the lowest member of his class — the Ornitho-
rhynchus. Folds of membrane may be so developed as to
form a spiral valve within the intestine, as in Sharks.

12. The PANCREAS of man is a long, soft, narrow, flattened
gland (larger at one end than the other), which lies embraced
by a curve of the duodenum. Its excretory duct traverses its
length and enters the duodenum a little below the pylorus,

V.C.T.

Ao.

FIG. 380.— THE PANCRBAS with its duct (PD\ together with the spleen

and the splenic artery (SpA). Below this artery is seen the splenic vein
running to help to form the vena porta:

Ao, the aorta ; D, a pillar of the diaphragm ; PD, the pancreatic duct exposed
by dissection in the substance of the pancreas ; Dm, the duodenum ; £D, the
biliary duct opening into the pancreatic duct at x ; y, the intestinal vessels.

receiving on its road the bile-duct (to be noticed below), so
that the two open together into the intestine. The length of
tha gland is from six to eight inches.

13. The pancreas (or sweetbread) of other Mammals may
be more developed and complex than in man, as in Bears,
and may have two ducts — as generally in Dogs. It may pre-
sent a beautiful arborescent structure, as in the Hedgehog
and Flying Fox. It may be in the form of three long lobes
meeting together, as in the Pig.

The duct may enter the intestine at a much greater dis-
tance from the pylorus than in man (as e.g. in the Beaver and
Rabbit), and quite distinctly from the bile-duct.

In Birds the pancreas appears as a narrow elongated
gland lodged in the fold of the duodenum, and generally bent
upon itself like the gut it adjoins. It has usually two ducts

G G

ELEMENTARY ANATOMY,

[LESS.

entering the intestine in advance of the entrance of the biliary
secretion.

An essential similarity exists in the pancreas, not only of
Reptiles, but also of Batrachians ; and yet in Fishes this
organ appears to be replaced by quite another structure. In
most bony Fishes there are several, or many, crecal pouches
attached to the commencement of the alimentary canal.
These may be but two in number, as in the Turbot ; or there

FIG 381. — DIGESTIVE ORGANS OF A
SWORD-FISH (Xiphias giadiiis).

/, liver; c, cardiac part of the stomach ;

FIG. 382. — STOMACH AND INTESTINE
OF A WHITING (Merlangus vulgar is).

(After Hyde S alter.)

t^fS^vK^J^SK *> -sophagus ; c, cardiac end of the

massed into a body like the conglome
rate pancreas of Mammals ; i, intes
tine

stomach ; py, pylorus ; p, numerous
pyloric caeca ; /, intestine.

may be but a single tube, as in Polypterns ; or fifty, as in the
Pilchard ; or about 120, as in the Whiting. They may be all
distinct, or they may be agglomerated together into a sort
of solid gland (showing a certain resemblance to the pancreas
of higher animals), as in the Sword-fish. The pancreas may
be altogether wanting, as in the Lancelet.

14. The LIVER of man, the largest gland in his body, has
been noticed in the Fifth Lesson of " Elementary Physiology,"

XL] THE ALIMENTARY SYSTEM. 451

It is placed rather to the right side of the body, imme-
diately beneath the diaphragm and above the stomach, and
lies within the cartilages of the ribs. The aorta, vena cava,
and the crura of the diaphragm are interposed between it
and the bodies of the vertebrae, whence it extends to the front
of the abdominal cavity and to its right and left sides.

It is a solid organ, of a dull reddish-brown colour, smooth
and convex above, concave and uneven below. It is divisible
into certain parts (or lobes), which are defined partly by
grooves and notches, partly by ligaments and blood-vessels.

In the Tenth Lesson of the present course was described
how blood is conveyed to the liver from the viscera by the
portal vein, and from the liver to the adjacent vena cava
by the hepatic veins, while the nutritive blood from the
aorta is distributed to the liver by the hepatic artery, itself a
branch of the cceliac axis. It was also noted how in an early
stage of development a stream of blood is conveyed by a
temporary vessel, the umbilical vein, which in part joins the
vena porta, in part sends small branches into the liver, and
in part directly unites with the vena cava by a temporaiy
canal called the ductus venosus.

Now the liver, when viewed above, is seen to be divisible
into two unequal parts, one right and the other left, by means
of a membranous ligament (called the broad or falciform
ligament} which descends to it from the adjacent surface of
the diaphragm and consists of two folds of peritoneum, as
will be hereafter explained. This ligament is attached to the
liver in a line running from the posterior margin of that organ
to its anterior one, and the part of the liver on the left of
the ligament is much smaller than that on its right.

Viewing the liver on its under surface (Fig. 383), there may
be seen a deep groove opposite to and corresponding with the
attachment of the broad ligament (called the longitudinal
fissure], which lodges a fibrous cord (called the round liga-
menf). The anterior part of this cord (which passes backwards
to the liver from the navel) is the remnant of the primitive
umbilical vein, while the posterior part is similarly a relic of
the ductus venosus. On this account the anterior part of the
longitudinal fissure is called the umbilical fissure, while its pos-
terior part is named \h& fissure of the ductus venosus (Fig. 385).

This longitudinal fissure then divides the liver into two

unequal lobes on its under surface, and the larger of these

lobes is again subdivided by other fissures. Thus a small

prominent lobe (called Spigelian] is placed at the hinder

G G 2

45 2 ELEMENTAR Y A iVA TOM Y. [LESS.

border of the liver, on the right-hand side of the fissure of the
ductus venosus. It is bounded behind and on its own right
side by a short and deep fissure (or rather fossa) called the
fissure of the vena cava, because that large vein runs along it.
In front the Spigelian lobe is bounded by the transverse or
portal fissure , which crosses the under surface of the left half
of the right lobe of the liver, and runs, almost at right angles,
into the longitudinal fissure. It is into this fissure that the
portal vein, the hepatic artery, and the great nerves enter, and it
is from it that the bile-duct proceeds to convey away the biliary
secretion. The portal fissure runs to the right, beyond the
limits of the Spigelian lobe. That part of the substance of
the liver which is situate behind this outer part of the portal
fissure is called the caudate lobe (Fig. 385, c], and is a sort of

FIG. 383. — THE LIVER VIEWED FROM REI.OW.

a, vena cava ; b, vena portae ; c, the ductus communis choledochus ; d, hepatic
artery ; /, gall-bladder.

ridge which proceeds from the base of the Spigelian lobe to
the under surface of the great right lobe, and is in part limited
behind by the vena cava. That part of the right lobe which
is in front of the portal, or transverse, fissure is marked by a
depression in which lies a pear-shaped bag, called the gall-
bladder, which has its blind end (or fundus) forwards. The
anterior end of this depression often notches the anterior
margin of the great right lobe of the liver (Fig. 385, </).

The bile, or hepatic, duct descends from the portal fissure,
in front of the vena porta, and meets the duct of the gall-
bladder— termed the cystic duct — at an acute angle. The
common duct formed by the union of these two is called
the ductus communis choledochus, and this passes into the
duodenum side by side with the pancreatic duct, the two
opening into the intestine by a common orifice.

XI.]

THE ALIMENTARY SYSTEM.

453

15. In that man possesses a liver, he agrees, as has been
mentioned in the First Lesson, with all the other members of
his sub-kingdom ; and in that he possesses a solid liver he
agrees also with all, excepting only the Lancelet, in which

FIG. 384. — VISCERA OF LIZARD (Calotes].

(After Salverda.)

la, lung ; //, liver ; g, gall-bladder ; s, stomach ; p, pancreas ; i, intestine :
r, rectum ; e, bladder.

animal this organ is a mere cascuin-like, saccular diverticulum
(or offshoot) of the intestine, with its apex turned forwards.

The liver may attain a much greater complexity, as regards
the number of its lobes, than we find in man, but in the
majority of Vertebrates (in all, that is, below his own class)

454

ELEMENTARY ANATOMY,

[LESS.

it is almost always very much more simple. Thus, in Fishes
the liver consists generally of one undivided mass, or of two
lobes, as in the Cod ; or three, as in the Carp and Rays— very
rarely of more, as in the Tunny.

In Reptiles the liver is single, as in the Chameleon and
Serpents, or consists of two lobes, as in the Crocodile.

In Birds there are also two lobes, to which sometimes (as
e.<r. in the Swan) there is added a small intermediate lobe
at the back, which has been deemed to answer to man's Spi-
gelian lobe.

It is in man's own class, however, that the varieties
greatest both in number and interest present themselves.

FIG. 385.— IDEAL DIAGRAM OF UNDER SURFACE OF LIVER, the front margin
being turned upwards.

(After Flower.)

c caudate lobe • cf cystic notch ; dv, remnant of ductus venosus ; g, gall-bladder ;
Ic left central lobs ; //, left lateral lobe ; llf, left lateral fissure ; p, portal
fissure ; re, right central lobe ; rl, right lateral lobe ; rlf, right lateral nssure ;
s, Spigelian loba ; it, remnant of umbilical vein ; vct vena cava. 1 he arrow
points to the vena cava.

The study of them has led to the perception that the most
definite and typical structure of the liver is as follows :— (i), A
Spigelian and (2) caudate lobe, each defined as in man ;
(3 and 4), two divisions of that part of the liver which lies on
the left side of the broad ligament, and which are named
respectively the "lateral left lobe" and the "central left
lobe;" (5), the lobe which supports the gall-bladder, and
which is called the cystic, or " central right lobe ; " (6), the
extreme right part of the great right lobe, often separated
from the central right lobe by a fissure, and named the
*' lateral right lobe,"

XL] THE ALIMENTARY SYSTEM. 455

Further subdivision is rare, though it may exist, as e.g. in
the Rodent Capromys, which has a liver consisting of many
very small lobules ; and in the Camel, which has numerous
small superficial lobules on that organ. In the Seals also
there are many secondary fissures.

The left lateral lobe may be very little developed, as in
Semnopithecus. The same may be the case with regard to
the left central, as in the Noctule Bat.

The right lateral lobe may be excessively small, as in the
Hare. The caudate lobe may be absent, and the Spigelian
quite rudimentary, as in the Wombat.

FIG. 386.— LIVER OF THE TWO-TOED SLOTH (Choicest] seen from beneath, its
front margin being turned upwards.

(After Flower.)

c, caudate lobe ; g, gall-bladder ; Ic, left central lobe ; re, right central lobe ;
rl, right lateral lobe ; s, s, enormous Spigelian lobe.

The caudate lobe may attain a great size, as in the
American Ape Pitheda (where it is as large as any other
lobe of the liver), and in the Hedgehog. The Spigelian lobe
may take on an excessive relative development, as in the little
deer Tragulus, and above all in Cholaspus.

The liver may be even more simple than in man, as in
the Dolphins, where it consists of two lobes only, and is very
small. It may, as in the Hippopotamus, have no fissures
whatever visible, the representative of the umbilical vein
running deep and enclosed in the substance of the liver.

456 ELEMENTARY ANATOMY. [LESS.

In possessing a gall-bladder man resembles the great
majority of Vertebrates, yet it may be absent in the highest
and the lowest classes. Thus in Fishes it is wanting in
a few species, as e.g. in the Lamprey and Pristis. In
Birds it is wanting in most Parrots and Cuckoos, as well
as in the Pigeons. Amongst Mammals it is absent in the
Cetacea, the Sloths, the Elephant, the Camel, the Hyrax,
Horse, Tapir, and Rhinoceros. The presence or absence of

FIG. 387.— LIVER OF THE DOLPHIN (Delphinus) seen from beneath, its front
margin being turned upwards.

(After Flower)

lie, united left lateral and left ventral lobes ; rcl, united right central and right
lateral lobes ; i>c, vena cava.

this organ, however, cannot be of very great importance, as
it is absent or present sometimes in the same species ; and
even two gall-bladders have been found coexisting in an indi-
vidual Giraffe. The gall-bladder may be placed exceptionally
on the left side, as in the Thylacine. It may be, as it were,
inverted, perforating part of the liver and appearing on the
upper surface, as in Lemuroids, e.g. Galago.

Where a gall-bladder is wanting, the bile-duct may — as in
the Elephant — be dilated at its entrance into the duodenum.

The colour of the liver may differ strikingly from that which
we find in man. This is especially the case in Fishes, where
it may be bright red, as in Holoccntrum Orientate ; or yellow,
as in Atherina presbyter ; or green, as in the Lamprey.

The liver may also be much less dense in consistency than
in man — as in Fishes generally ; and in aquatic Mammals,
such as the Cetacea, Seals, and Otter, it is said to be softer
than in other kinds of the same class,

XL]

THE ALIMENTARY SYSTEM.

457

1 6. The PERITONEUM is, as was mentioned at the begin-
ning of this lesson, a serous membrane lining the cavity of
the abdomen, and reflected, from its posterior wall, over the
viscera which the abdomen contains, and indeed more or
less completely embracing them, but nevertheless really
retaining them external to its proper cavity, as it is a com-
pletely closed sac.

To understand fully this complex structure it will be well
to revert to what was said regarding embryonic development.

It will be remembered that the laminae ventrales split, each
lamina thus forming an outer and an inner lamella ; that the
two outer lamellae meet ventrally and form the abdominal
wall of the body ; and that the two inner lamellae also meet
ventraliy and form the alimentary canal— the space included
between the two pairs of lamellae (i.e. between the outer sur-
face of the alimentary canal and the inner surface of the
body-wall) constituting the pleuro-peritoneal cavity.

Now, the whole of the surface of this cavity becomes modi-
fied to form a continuous serous membrane, and this mem-

FIG. 388. — DIAGRAM OF THE DEVE-
LOPMENT OF THE TRUNK AND ITS
SKELETON, as shown in a section
made at right angles to the trunk's
long axis.

nc, neural canal ; ex, epaxial cartilages
ascending to surround it ; px, par-
axial cartilages descending in the
plate, or layer (I've), external to //,
the pieuro-peritoneal cavity; Ivi, in-
ternal plate of the split ventral
lamina.

FIG. 389. — DIAGRAM OF THE FURTHER
DEVELOPMENT OF THE TRUNK, as
shown in a section similar to the last.

a, alimentary canal supported by a me-
sentery 2 formed of the dorsal portion
of the inner parts of the split wall of
the embryonic ventral laminae : e,
epaxial arch ; //, hypaxial arch de-
scending in the median line in the
root of the inner part of the split wall
of the ventral laminae ; J>, rib, bi-
furcating proximally and abutting
ventrally against the sternum, which
thus completes the paraxial arch ; HI,
peritoneum, bounding on all sides pi,
the pleuro-peritoneal space.

brane is the peritoneum. But the root part of the inner pair
of lamellae — i.e. that part which intervenes between the
alimentary canal and the axial skeleton — diminishes and

458 ELEMENTARY ANATOMY. [LESS.

ultimately disappears with the exception of the serous mem-
brane coating it, and thus, the two serous coats of its two
sides meeting together, the alimentary canal comes to be
slung by means of them from the skeletal axis in a peritoneal
fold, or, as it is called, mesentery. In man and in allied
animals, however, the alimentary canal is very tortuous and
convoluted, and has annexed to it many complex accessory
structures. Thus the lining peritoneal membrane, passing
from one digestive organ to another and wrapping them
round in various degrees and with various adhesions, comes
to form a wonderfully complex structure.

In man, beginning from the under surface of the dia-
phragm, we find a fold of peritoneum constituting the falci-
form ligament, before described, attaching the liver to the
diaphragm. The peritoneum then descends, coating the
abdominal aorta and inferior vena cava. It also descends,
and coats the liver. From the under surface of the liver it
again descends to the stomach, in a double fold of membrane
called the gastro-hepatic amentum. It next encloses the
stomach and also the spleen. It also invests the intestines
except the greater part of the rectum, but it coats the anterior
surface of that gut as well as the upper and inner surface of
the bladder. From between the stomach and the transverse
colon, a great, free, apron-like flap of peritoneum, called the
great amentum, hangs down loosely in front of the bowels.

This great complex bag, the peritoneum, exists in all Ver-
tebrates, but in lower forms is greatly simplified in conformity
with the simple arrangement of the viscera (Fig. 390). In
Fishes its cavity sometimes communicates with the exterior
by two apertures placed near the external termination of the
alimentary canal, as e.g. in the Lamprey, Eel, Salmon, and
others. It may communicate by a single opening placed
further forwards, as in the Lancelet. It may communicate
with the pericardium, e.g. in Myxine, the Sturgeon, and
Sharks, as was indicated in describing the diaphragm.

It may, as in most Reptiles, and in Batrachians and Birds,
line uninterruptedly the thoracic and abdominal cavity,
forming one pleuro-peritoneal sac ; thus differing from man
(and Mammals), in whom, as we shall see in the next Lesson,
the thorax has its own proper serous sac, that muscular par-
tition, the diaphragm, dividing the two cavities in Mammals.
The peritoneum may be delicate and transparent, as in man.
It is so in his class generally, and in Birds. It may, how-
ever, be black, as is sometimes the case in Reptiles and

XL] THE ALIMENTARY SYSTEM. 459

Fishes. It may have a silvery metallic lustre, as often in the
last-named class.

It may, as in Birds, form great cells which communicate
with the lungs, and thence become inflated with air.

The peritoneum may be incomplete, being reduced, as it
were by local atrophy, to shreds and patches, as in many
cartilaginous Fishes, e.g. the Sturgeon.

Instead of an omentum passing post-axially as in Mam-
mals, two such structures may extend pre-axially (i.e. towards
the head) from the oelvic region, as in many Lizards.

FIG. 390.— DIAGRAM OF A TKANSVERSE SECTION OF A LIZARD, showing the
stomach, spleen, lesser omentum, and falciform hepatic ligaments, all in the.r
typical or median position.

(After Pittard.)

ns, neural spine ; c, neural canal ; p, outer surface of body ; /', peritoneum lining
the body-cavity and investing the viscera ; a, the aorta ; s, the spleen ; g, the
stomach ; /t, the gall-duct ; ft the falciform ligament of the liver ; rt the pleuro-
peritoneal cavity.

The whole intestine (i.e. both the great and small intes-
tines) may be suspended by one continuous mesentery, even
in man's own class, as in the Shrew and the Elephant.

17. In the DEVELOPMENT of the alimentary system the
first notable modification is the splitting of the laminae ven-
trales, as already mentioned. When -by the ventral union of
the inner laminae the alimentary canal is formed, this canal
is at first a straight tube closed at both ends, and extending
along the ventral aspect of the axial skeleton.

After a time the tube, towards the middle of the body, bends
away from this axis in a sharp ventral curve, while that part
of it on the pre-axial side (side next the head) of the curve
dilates and becomes the stomach. The part on the post-
axial side of the curve becomes the transverse colon, while
the intervening loop becomes greatly lengthened and exces-
sively convoluted to form the small intestine and ascending
colon, a little bud-like offshoot laying the foundation of the
caecum. As we have seen, this proximity of the transverse

4Go ELEMENTARY ANATOMY.

colon to the stomach and duodenum, thus early initiated,
persists with great constancy. Each of the two ends of the
alimentary canal becomes perforated by means of a depres-
sion which appears on its surface, and which deepens till it
opens into the nascent alimentary canal.

The large intestine is at first of less capacity than the
small, and the vermiform appendix is at first as wide as the
caecum.

Immediately below the dilatation for the stomach a very
small offshoot grows out from the alimentary canal, and
around this a s:>ft mass of tissue is developed — the future
liver. T.he transitions which take place with regard to the
blood-vessels in connexion with this part have been already
described in Lesson X. The part of the alimentary canal
which is pre-axial to the stomach becomes, of course, the
(esophagus. It also gives off diverticula, but as these (after-
wards the lungs) are not directly related to the alimentary
system, they will be noticed in the succeeding and last Lesson.

1 8. Thus a certain rough and general approximation to
the earlier conditions of the digestive system found in man
manifestly persists in lower Vertebrata ; in some Fishes the
alimentary canal being, as we have seen, of nearly uniform
width throughout its course, without even a dilatation to form
a distinct stomach. The liver in its earliest condition recalls its
permanent form in Amphioxus. As we ascend through the
Vertebrate series, we find in the highest class a greater com-
plication of definite, distinct, and mutually related parts,
although the ascent is by no means regular. Not in man do
we find the most complex stomach, but in the Sheep. Not
in him is the caecum at its maximum, but in the Indris and
some others before mentioned. Valvulae conniventes, indeed,
are a marked character of the small intestine of man, but
they are yet more marked in the Ornithorhynchus. The liver
may be much more complex than in him, but it may also be
more simple even in his own class. The tongue may be
much longer and more mobile ; it may also be much shorter
and less mobile, or may abort altogether. Salivary glands
may be completely absent ; they may, on the contrary, attain
a size and complexity to which those of man are far from at-
taining. The alimentary system, then, hardly agrees with the
nervous system in presenting marked and readily appreciable
characters, by which man's organization exhibits an evident
and unmistakable superiority, though a certain superiority
probably exists in the reciprocal co-ordination of its parts,

xi I. J 1 'HE EXCKJ:. '1 'OR Y ORGA.\ 'S. 46 1

LESSON XII.

THE EXCRETORY ORGANS.

i. IN the First Lesson of " Elementary Physiology," § 23,
while explaining the nature of the excretory process and its
most general conditions, it was stated that the EXCRETORY
ORGANS are three in number, namely : (i), the skin ; (2), the
lungs ; and (3), the kidneys. The description of the skin and
its various appendages has formed the subject of our Seventh
Lesson. Nevertheless, the consideration of its glandular
structure was purposely deferred to the Twelfth Lesson, and
may be here considered, with the lungs and kidneys together
with adjoined and adjacent structures not yet treated of.

The lungs, however, are importers of oxygen (for the
aeration of the blood) as well as excretory organs ; it is not,
then, surprising that the external skin may assume that func-
tion also, as in fact we found (when considering the circulating
system) to be the case in Batrachians.

The function of importing oxygen into the blood is per-
formed in many animals by a set of organs of which no repre-
sentative exists in man, and which, therefore, are not referred
to in the Lessons of " Elementary Physiology," though they
must occupy no inconsiderable portion of our concluding
Lesson of " Elementary Anatomy." The organs in question
(mentioned in our First and Tenth Lessons) are the gills, or
branchia. These are delicate processes of skin, richly supplied
with blood and capable of absorbing oxygen, not by the
decomposition of the water in which they float, but by the
absorption of oxygen from the particles of air which are mixed
up with and dissolved in that water. Such structures, as might
be expected, are only found in animals which live in or
frequent water, whether fresh or salt, though not all animals
which frequent water have gills.

Thus, in being destitute of branchiae, man agrees not only
with the whole of his class (including, of course, the Whales

462

ELEMENTARY ANATOMY,

[LESS,

and Porpoises), but with the Saurop'sida also ; while in pos-
sessing lungs he agrees with all Vertebrates, except Fishes,
which with the exception of the Mud-fish (Lepidosiren] are
destitute of true lungs. First, then, may be considered the
lungs as they exist in man and Vertebrates generally. After
that will naturally follow the consideration of gills, or branchiae,
parts which in function answer to the lungs of man, though
they have no resemblance in structure or mode of development.

R. JYK;

FIG. 391.— THE HEART, GREAT VESSELS, AND LUNGS. FRONT VIEW.

R Bright ventricle; LV, left ventricle: RA, right auricle; LA, left auricle;
Ao, aorta r PA, pulmonary artery; PV, pulmonary veins; RL, right lung;
LL, left lung ; vSi vena cava superior; SC, subclavian vessels ; C, carotids;
R and LJV, right and left jugularveins ; VI, vena cava inferior ; T, trachea ;
B, bronchi. All the great vessels but those of the lungs are cut.

2. The LUNGS of man have been shortly described in
the Fourth Lesson of " Elementary Physiology." They are
two in number, one placed on each side of the heart, and
(with it and the blood-vessels, air-passages, and oesophagus)
fill up the entire cavity of the thorax. The lungs are
attached, by their roots, to the two branches of the windpipe
(hereafter to be described), and to the great vessels proceed-
ing to and fro between the lungs and the heart.

From this attachment each lung hangs down freely sus-
pended in a short serous sac — the pleura — which closely
invests it. This is the proper serous sac of the thorax.

Xlr.j THE EXCRETORY ORGANS. 463

The two pleurae line the right and left halves of the thorax,
and are reflected over the two lungs at their roots respectively.
In this way the two adjacent (inner) sides of the two pleura
traverse the thorax from behind forwards. They are not,
however, in contact, but separated by two interspaces termed
inediastina.

The anterior mediastinum contains the heart in its pericar-
dium, as described in our Tenth Lesson.

The posterior mediastinum contains the oesophagus, the
aorta, the vena azygos, and the thoracic duct, together with
the pneumogastric nerves.

FIG. 392.— TRANSVERSE SECTION OF THE CHEST, WITH THE HEART AND
LUNGS (EACH LUNG INVESTED WITH ITS PLEURA) IN PLACE.

DV, dorsal vertebra, or joint of the backbone ; Ao, Ao, aorta, the top of its arch
being cut away in this section; SC, superior vena cava ; PA, pulmonary
artery, divided into a branch for each lung ; LP, RP, left and right pulmonary
veins ; Br, bronchi ; RL, LL, right and left lungs; CE, oesophagus.

Each lung is conical in shape, and has a broad, concave
"base, which rests upon the diaphragm. The inner surface of
each lung is turned towards the anterior mediastinum, and is
adapted to the convex pericardium.

The right lung is shorter and wider than the left, and is
divided by two notches into three portions or lobes. The left
lung has only a single notch and two lobes.

Beneath the serous coat, each lung has a layer of cellular
membrane, mixed with much elastic tissue, which passes in
"between the minute air-tubes and air-cells, as described in
§ 8 of the Fourth Lesson of " Elementary Physiology."

In development the lungs first make their appearance as

464 ELEMENTARY ANATOMY. [LESS.

two little bulgings (or sacs) from the ventral side of the
cesophageal part of the alimentary canal. These little sacs
afterwards elongate, and ultimately come to hang by a single
and common supporting tube.

At first simple in structure, they gradually acquire the
complicated condition which subsequently exists.

3. In the free suspension of the lungs in the thoracic
cavity man agrees with all the other members of his class,
but they may be fixed by cellular tissue to the dorsal side of
that cavity, as in Birds and Chelonians.

Similarly their enclosure in two pleurae is an exclusively
Mammalian character. The lungs may, as in Batrachians
and Saurians, hang into the general pleuro-peritoneal cavity,
being completely invested (except at their roots) by the pleuro-
peritoneal membrane ; or they may lie on the dorsal side of
that cavity, as in Birds and Chelonians, being coated by the
pleuro-peritoneum on their ventral aspect only.

Instead of being confined to the neighbourhood of the
heart, as in man and his class, the lungs may extend to
nearly the most post-axial part of the abdominal cavity, as in
the Amphiuma and Siren.

The lungs may each be single and undivided, as in Birds
and Cetaceans ; or there may be as many as five lobes in
the right lung (as in the Hamster and Marmot), and three in
the left— or even six in the right and five in the left (as in the
common Porcupine). Sometimes there is an azygos lobe
proceeding from the right lung, and placed between the
heart and the diaphragm, as in Ornithorhynchus. This
may exist when the lungs are otherwise undivided, as in the
Elephant.

The right lung may be twice as large as the left, even in
man's class, as in the Musk Deer and Porcupine.

The lungs may be nearly equal in size, as in Frogs ; they
may, on the other hand, be still more unsymmetrically deve-
loped than in the Musk Deer. This is the case in Serpents
and Ophiomorpha ; and one lung may be quite rudimentary,
as in the common Ring Snake ; or absent altogether, as
in at least some kinds of Viper. The right lung may be
much smaller than the left, as in the snake-like Batrachian
Gym n oph ion a.

As regards the minute structure of the lungs, man agrees
with the whole of his class. The substance of these organs,
however, may consist, as in Birds, of fine tubes (the walls
of which are minutely sacculated), given off at right angles

XII.]

THE EXCRETORY ORGANS.

465

from other tubes, which again spring at right angles from the
bronchi or primary divisions of the windpipe.

The lungs may be cellular throughout their extent, while
yet the bronchi do not give off branches within them, as in
Chelonia and Crocodilia.

They may be cellular only near their root, the more post-
axial part of the lung being a simple membranous air-bag, as
in Serpents.

Part of the arterial blood, carried by the pulmonary artery,
instead of going to the lung may be conveyed by small
branches to the oesophagus, as in Menopoma, Amphiuma,
and Siren.

Part of the venous blood of the
lungs, instead of returning direct to
the heart, may enter the veins of the
trunk, as in Proteus.

When there is an air-sac which does
not both receive blood directly from
and return it directly to the heart —
/.<?., when there is no true pulmonary
circulation — such an air-sac (whether
single or double) is termed a swim-
bladder, or air-bladder, and a struc-
ture of the kind is found in most
Teleostean and in all Ganoid Fishes.

A swim-bladder, however, may
closely approximate to a lung, as in
Ceratodus, where, though blood is
not brought to that bladder directly,
as in Lepidosiren, yet blood is sent pIG.
directly to the heart by a pulmonary
vein which opens into the atrium of
the heart, or chamber representing
the (as yet undifferentiated) auricles.

The swim-bladder may present a great variety of conditions.

Thus, it may be double and connected with the ventral part
of the cesophageal portion of the alimentary canal by a short
tube, the ductus pneumaticus, as in Polypterus j or single and
connected more with the side of the same part, as in Cera-
todus and Erythrinus. It may be connected with the dorsal
part of the cesophagus, as in Lepidosteus and the Carp ; or
with the cardiac part of the stomach, as in the Herring.

The ductus pneumaticus may be long, narrow, and bent, as
in the Carp ; or short, straight, and wide, as in Lepidosteus.
H H

393. — DIAGRAM OF A
LOBULE OF THE LUNG OF A
BIRD, GREATLY MAGNIFIED.

(After Thomas Williams.}

466

ELEMENTAR Y ANA TOMY.

[LESS.

It may abort altogether in the adult (the swim-bladder thus
becoming quite separate from the alimentary tube), as in the
Cod, Perch, and very many others.

In shape the swimming-bladder may bifurcate anteriorly
as in Ludo-perca, or posteriorly as in Acanthurusj or it
may be constricted towards its middle, as in the Carp ;
or it may send out two blind processes' on each side,
as in Corvina; or a multitude on each side, as in Johnius.
Finally, the swim-bladder may give out processes from
each side, each process bifurcating dorsally and ventrally,
and each dorsal and ventral bifurca-
tion again dividing and anastomosing
with processes of the opposite side,
the whole complex structure being
invested by folds of the peritoneum.
This maximum of complexity is ex-
hibited by Callichthys.

It may be connected with the in-
ternal ear, as in the Carp (Cyprinus)
and Loach (Cobitis), by the interven-
tion of small special ossicles analo-
gous to, but not homologous with, the
auditory ossicles of man. In the
Loach the bladder seems chiefly
related to some auditory function, as
it only extends to the third vertebra.

The cavity of the swim-bladder
may be simple, as is usually the case ;
it may be divided by septa, as in
Bagrus ; it may, finally, be so sub-
divided into cells as to be like the lung
of a Reptile, as is the case in Amia.
Retia mirabilia may exist in the swim-bladder, as in the Cod.
Every representative of a lung may be absent, as in the
Sharks, Rays, Pleuronectidce, Marsipobranchii, and Ajnplii-
oxus, in all of which there is no swim-bladder.

The mechanism of aerial, pulmonic respiration, which exists
in man, exists also in all Mammals — the diaphragm being
their main agent in filling and emptying the lungs.

The lungs, however, may be filled and emptied by alternate
movements of the sternum towards and away from the verte-
bral column. This is the case in Birds (Fig. 76), where such
movements are aided by the synovial articulations between
the sternal and vertebral ribs.

FIG. 394. — AIR-BLADDER OF
THE TELEOSTEAN FISH,
Johnius lobatus.

xn. J THE EXCRETORY ORGAXS. 467

Analogous motions of the abdominal muscles and ribs
alternately dilate and contract the body-cavity, and so fill
and empty the lungs — in Saurians and Serpents.

In Chelonians, where the ribs are immovably fixed, and the
ventral side of the body is covered with a solid exo-skeleton
(the plastron), inhalation is effected by forcing air down the
windpipe by an action analogous to swallowing. The mouth
being filled with air, the posterior nares and all possible
exits are closed, except that leading to the lungs ; and down
that exit air is forced by a contraction of the muscles of the
throat. Exhalation is effected by means of muscular con-
tractions at the most post-axial part of the abdominal cavity.

In Batrachians (which are devoid of ribs, or have but very
short ones) the respiratory movements are similarly effected,
air being swallowed by contractions of the muscles of the
throat, and expelled by those of the abdominal muscles.
Thus to suffocate a Frog it is sufficient to keep its mouth
open.

4. The lungs of. man communicate with the mouth and so
with the external air, by means of a single channel, the wind-
pipe or TRACHEA ; which divides at its lower end into two
branches, termed BRONCHI, one bronchus going to each lung.

The trachea is a straight, permanently open tube, com-
mencing above at the larynx (shortly to be described), which
is, as it were, its expanded upper end. It descends, in the
middle line, in front of the oesophagus, to opposite the third
dorsal vertebra, where it is crossed in front by the arch of the
aorta, and bifurcates, dividing into the right and left bronchus.

The trachea is formed of membrane strengthened by a
series of from sixteen to twenty horizontal cartilaginous rings,
which are not however complete behind, so that the hinder
wall of the tube, being entirely membranous, is flattened.
The tube is lined with mucous membrane, and its wall con-
tains muscular fibres and cellular tissue, with glands, vessels,
and nerves.

The bronchi have the same structure as the trachea, except
that the cartilaginous rings are shorter and narrower. There
are from six to eight in the right bronchus ; from nine to
twelve in the left.

Within the lung the bronchi divide and subdivide, like the
branches, branchlets, and twigs of a tree. These successively
smaller and smaller tubes are kept distended by successively
smaller and more delicate cartilages, which are no longer in
the form of rings incomplete behind, but are irregularly-shaped
H H 2

468

JLLEMENTAR Y ANA TOA1Y.

[LESS.

pieces of various sizes. The ultimate twigs are entirely mem-
branous. The mucous lining of the tubes lines the ultimate
air-cells themselves.

FIG. 395.— BACK VIEW OF THE NECK AND THORAX OF A HUMAN SUBJECT

from which the vertebral column and whole posterior wall of the Chest are

supposed to be removed.
M, mouth; Gl, glottis; Tr, trachea; LL, left lung; RL, right lung; Br,

bronchus; PA, pulmonary artery; PV, pulmonary veins; Ao, aorta; Dt

diaphragm ; ff, heart ; VCI, vena cava inferior.

5. In that he has a trachea, man agrees with all Mam-
mals and Sauropsidans, and with the Ophiomorpha, Meno-
fioma, and Siren, amongst Batrachians. A trachea may,
however, be entirely wanting, the lungs springing immediately
from the larynx, as in the common Frog and Toad. It may
be present, but short and wholly membranous, as in
Salamandra.

It may be much shorter relatively than in man in his own
class (as e.g. in Whales), or it may be much longer, as in
Ruminants. In Birds, however, it attains its maximum of
relative length.

In so far as the trachea of man is a straight tube, it agrees
with that of all other members of his class, except the Three-

xii.] THE EXCRETORY ORGANS. 469.

toed Sloth (Bradypus\ in which it is bent abruptly on itself in
a single fold ; and with Reptiles, except some Crocodiles and
Chelonians in which it is similarly bent It may be still
more bent, even coiled (as in many Birds), and the coils may
lie beneath the skin, external to the pectoral muscles, as in
Anas senii-pahnata, or sheltered in an excavation in the
keel of the sternum, as in the common Crane and male wild
Swan.

In that there are two bronchi and no more, man agrees
with the great majority of Vertebrates that possess a trachea.
One bronchus, however, may abort with its appended lung (as
in many Serpents), or there may be a third bronchus, as in
Ruminants, the Hog, and Cetaceans.

The rings of the trachea may be ossified, as in most Birds.
They may be as few as three, as in the Dugong ; or as mary
as no, as in the Camel ; or even 300, as in the Flamingo and
the Boa. They may completely encircle the tube, as in Birds
generally, and in the Horse (though in most Mammals they
are incomplete behind, especially in Rodents). Some of
the rings of the trachea may be incomplete in front, as in the
Emeu.

The trachea may increase in size downwards, as in the
Turkey ; or it may present a more sudden enlargement before
bifurcating to form the bronchi, as in the Merganser ; or two
such enlargements, as in the Goosander. It may be divided
by a septum extending from above downwards, as in the
Penguin and Sphargis.

A special structure may be developed (as in most Birds)
at the junction of the trachea and bronchi. This is the syrinx,
and is the organ of song in singing birds. It is also called
the lower larynx, and is quite a different part from the true
or upper larynx, shortly to be described.

The syrinx is generally formed by the coalescence or modi-,
fied shape of the lower rings of the trachea and the upper
ones of the bronchi, the latter being incomplete internally, so
that the sides of the bronchi which look towards each other
are at their upper part merely membranous, forming the
membrana tympaniformis. Internally the syrinx is generally
divided by a bar of bone, from the upper margin of which a
delicate membrane ascends into the trachea, ending in a free
concave margin, whence it is termed the membrana semi-
litnaris. This highly vibratile membrane, together with two
elastic folds of mucous membrane, placed one on each outer
side of the commencement of each bronchus, are the special

470

ELEMENTAR Y ANA TOMY.

[LESS.

FIG. 396. — SYRINX OF

A RAVEN.
a, b, and c, three bony

structures.

agents of song. Their action is modified by special muscles.

Generally there are two pairs of muscles passing from the

clavicles or sternum to the trachea ; and in addition to these
may be five or six pairs of muscles pass-
ing down from the trachea to the bron-
chial rings. These additional muscles are
present in singing birds, but also in many
birds that do not sing, as e.g. the Raven.

There may be no membrana semi-
lunaris, and only three pairs of additional
muscles, in birds highly gifted as to their
powers of emitting special sounds. Such
is the case in the Parrots, where, however,
the lateral elastic folds of membrane are
well developed.

A syrinx may be formed by the trachea
only (without the intervention of the
bronchi), as in Thanmophilus and Opetio-

rhynchus, where the post-axial part of the trachea has delicate

walls, and is flattened dorso-ventrally with six or seven deli-
cate segments of rings, the rings being

interrupted laterally. The additional

muscles here pass from the part of the

trachea above (pre-axial to) the syrinx

to the tracheal ring beyond it.

A syrinx may be formed in each

bronchus (without the intervention of

the trachea), as in Steatornis, where

more than ten rings in each bronchus

may be counted before reaching the

syrinx, and where a pair of muscles

passes to each bronchus from the

trachea.

Bronchi may be absent together with

the trachea, as in the common Frog

and Toad. They may be absent though

a trachea is present, as in Siren. They

may open at once into the lung, without

ramifying, as in Ophidians. They may

traverse the lung, soon losing their car-
tilaginous rings, and having apertures

in each side leading into the large pouch-like air-cells of the

lungs, as in the Crocodile. They may similarly enter the lungs

and lose their rings, but give off secondary branches at right

FIG. 397. — RIGHT LUNG OF

A GOOSE.
{After Owen.)
a, bronchus ; l>, b, openings
into air-sacs. In the two
bronchi which are cut open
are seen the apertures of
their primary branches.

xii.] THE EXCRETORY ORGANS. 471

angles, these again tertiary ones in a similar way, as in Birds
(Fig. 393). Not only, however, may the bronchi be thus
arranged (instead of dividing like the branches and twigs of a
tree, as in man and Mammals), but they may open at the
surface of the lungs into large air-sacs, as in Birds.

In Reptiles (amongst the Chameleons and Geckos) the
lung may be drawn out, towards its post-axial end, into
narrow prolongations which penetrate between the viscera.
In Birds, however, there may be nine well-defined air-sacs,
or greatly enlarged prolongations of the membrane of the
bronchi. Two of these take origin respectively from the end
of each main bronchus, and are the posterior, or abdominal,
air-sacs. Four others are the pair of anterior and the pair
of posterior thoracic air-sacs. They lie in the thorax on the
ventral surface of the lung, and spring from primary branches
of the bronchi. The seventh and eighth air-sacs are the cervical
ones, and lie outside the thorax ; the ninth air-sac — the inter-
clai'iciilar — is formed by the coalescence of what was at first
a pair of sacs.

Very generally some of these air-sacs are prolonged into or
communicate with the air-cavities of the bones. This is es-
pecially the case with the interclavicular, the cervical, and the
abdominal air-sacs, but never with the thoracic ones.

6. The LARYNX of man has been already noticed in the
Seventh Lesson of" Elementary Physiology," §§ 21-25.

The Larynx is the expanded upper part of the trachea sus-
tained by cartilages, more or less movable, of modified
forms and special names, opening at the back of the floor of
the mouth in front of the entrance to the oesophagus, and
behind the tongue.

The largest piece entering into the composition of the
larynx is the thyroid cartilage? which produces that promi-
nence in the middle of the front of the throat, popularly
known as Adam's apple. It is formed of two plates, united
along the middle line in front, at an acute angle, but widely
open behind. The hinder margins of these two plates are
vertical and prolonged into a process both above and below.
Each of the two upper processes is connected by a ligament
with the tip of the corresponding great cornu of the hyoid
bone, the body of which bone lies over the front of the thyroid
cartilage. The hyoid is connected with the thyroid by the
thyro-hyoid membrane, and is situate at the root of the tongue,
giving origin to the muscles forming that gustatory organ.

1 From 0t<peor, a shield, and ei<5o£.

472

ELEMENTARY ANATOMY.

[LESS.

Each of the two lower processes of the posterior margins ot
the thyroid articulates with the side of the cartilage next to
be described.

This latter, the cricoid1- cartilage, forms a complete ring,
deepest behind (where the thyroid is open), placed beneath
the thyroid cartilage, and forming the uppermost ring of the
trachea, with both of which parts it is connected by mem-
brane.

The arytenoid2 cartilages are two in number, placed side
by side, at a little distance from each other, on the posterior

FIG. 398.— DIAGRAM OF THE LARYNX, the thyroid cartilage being supposed to be
transparent, and allowing the right ar.\ tenoid cartilage (A r), vocal ligament ( I'),
and thyro -arytenoid muscle ( Th A ), the upper part of the cricoid cartilage (Cr),
and the attachment of the epiglottis (Ep) to be seen. C th, the right crico-
thyroid muscle ; Tr, the trachea ; Hy, the hyoid bone.

and highest part of the cricoid cartilage. Each arytenoid
cartilage is pyramidal in form, and at the apex of each is
placed an additional and minute cartilage, called that of
SantorinL

The epiglottis* is a median, azygos cartilage, shaped
somewhat like a leaf, placed in front of the upper opening
of the larynx within the thyroid cartilage and the cornua of
the hyoid. It ends in a narrow termination below, where it is
attached by ligament to the depression at the front part of the
inner surface of the thyroid cartilage.

1 From KpiKog, a ring, and eidog.

2 From upvTiitvn, a sort of pitcher, and e?5of."

3 From en-/, upon, and -yXw-rT/g, the aperture of the windpipe.

Xii. j THE EXCRETORY ORGAN'S. 473

Finally, there are two more minute cartilages, called those
of Wrisberg, each placed in the fold of mucous membrane
proceeding, on each side, from the epiglottis to the top of the
arytenoid cartilage.

The true vocal cords are two bands of elastic tissue, one of
which proceeds on each side from the middle of the thyroid
to the base of the arytenoid cartilage.

Thefa/se vocal cords are two folds of mucous membrane
which similarly connect the thyroid and arytenoid cartilages.

Both kinds of vocal cords have their free edges turned in-
wards, and between them is the glottis (or upper opening of
the windpipe), the exact form and size of which is regulated
by delicate muscles which move the parts of the larynx one
on the other— especially the arytenoid cartilages on the cricoid
— as explained in the " Elementary Physiology."

Between the true and false vocal cords there is (on each
side) a depression termed a ventricle of the larynx, and a
small prolongation of this upwards on the inside of the
thyroid is called a laryngeal poucli.

7. In so far as man has a larynx at all he agrees with all
Vertebrates above Fishes, and in its general composition
man's larynx agrees with that of other members of his class.
Amongst Mammals, however, the laryngeal cartilages may
be more or less ossified, as commonly in the Slow Lemurs.
The larynx may be very much larger relatively than in man,
as in the Howling Monkeys (Mycetes\ where the thyroid
cartilage may be three times the size of its human repre-
sentative, while the os hyoides is almost gigantic, and exca-
vated in such a way as to form a kind of thin bony bladder ;
its excavation being an enormous exaggeration of the slight
concavity on the hinder surface of the human hyoid. The
lateral plates and lamella of the thyroid may meet together in
the middle line behind (i.e. dorsally), as in the Ornithorhyn-
chus. In contrast with this, the cricoid may be incomplete in
front (i.e. ventrally), as in the Porpoise.

The arytenoid cartilages may be exceedingly prolonged
upwards and united in the middle line, as in the last-men-
tioned animal, where they become enclosed together with the
epiglottis in a sheath of mucous membrane, the whole forming
a conical projection which is received into the posterior
nares and embraced by the muscular soft palate. In this
way the Porpoise can breathe securely while the mouth is full
of water, or while food is passing to the cesophagus on either
side of the dorsally prolonged larynx.

474 ELEMENTARY ANATOMY. [LESS.

The cartilages of Santorini may be confluent in the middle
line, as in the Hedgehog and Pteropus.

The cuneiform cartilages (of Wrisberg) may be more de-
veloped than in man, as in the Bear and Dog.

An extra, interarticular^ cartilage may be developed be-
tween the bases of the arytenoids and the cricoid, as in the
Hedgehog.

Vocal cords may be wanting, as in the Porpoise, or the
upper cords alone may be obsolete, as in the Sloths and
Armadillos. A median air-sac may be developed between
the cricoid cartilage and the first ring of the trachea, as in
A teles.

The ventricles of the larynx may be greatly dilated and
prolonged upwards so as to come into contact above, and at
the same time there may be a pair of extra sacculi opening
between the arytenoid cartilages and the glottis, while with
these may coexist a median sac, filling an enormously ex-
panded os hyoides. Such is the case in the Howling
Monkeys (Mycetes).

A median air-sac may be developed from the thyro-hyoid
membrane beneath the epiglottis, extending over the neck
and to the armpits, as in some Semnopitheci and Cyno-
cephali.

There may be, as in the Siamang Gibbon, a globular air-
sac communicating with the la.rynx by two apertures in the
thyro-hyoid membrane.

The ventricles of the larynx may be distended into
enormous air-sacs, stretching over the chest, reaching to
the armpits, and sometimes opening one into the other in
the middle line of the body, as in the adult Gorilla,
Chimpanzee, and Orang.

When we descend below man's class we see that the larynx
may be much more, or but little more, imperfect in structure
than it is in any Mammal.

Thus, in Birds we find thyroid, cricoid, and arytenoid
structures, bony or cartilaginous. There may also be in some
cases, as e.g. in the Swan, an epiglottis, but this is very rare.
More often an epiglottis-like process of the thyroid may be
developed. The cricoid may be represented by three pieces.
Vocal cords are always wanting. The thyroid has often
transversely extended fissures, or defects of solidification or
ossification, probably related to the formation of this structure
by the coalescence of primitively distinct rings or arcs.
Passing below Birds we find that both the thyroid and

THE EXCRETORY ORGANS.

475

AND TPPER PART
OF TRACHEA OF

dus). Front (i.e.
ventral) aspect.

(After He ule.)
, epiglottis ; f and
g, muscles of la-
rynx.

cricoid cartilages may be represented by a single circular
cartilage with arytenoid cartilages annexed, as in the Croco-
dile. This circular cartilage may present defects of solidi-
fication like those just spoken of in the thyroid of Birds, as
is the case in many Lizards. An essentially
similar structure may be greatly prolonged,
as in many Serpents (e.g. Crotalus and Hydro-
phis'], where we find two elongated lateral
bands connected by numerous transverse
bars which are separated from each other
by membranous interspaces. Arytenoid
FIG - — HRYNX cartu<a&es may be distinct or may be mere
processes.

The simplest form of larynx seems to be
that of Proteus, where there are only two
slender elongated cartilages (the anterior
ends of which appear to represent the aryte-
noids) placed one on each side of the slit-
like glottis, which opens in the middle of the
ventral wall of the pharynx.

A median air-sac may protrude anteriorly
from the front of the larynx
between the first ring of the
trachea and the conjoined thy-
ro-cricoid cartilage. Such is
the case in the Chameleon.

8. As has been said, respi-
ration may be effected by
means of the air contained in
water — i.e. by AQUATIC RESPI-
RATION. For this purpose the
animals which so respire do
not ordinarily take water into
aquatic lungs as the air-breath-
ing Vertebrates take air ; but
blood is copiously brought to
a surface specially exposed to a
flow of water almost constantly
maintained by one process or
another.

It may be that this flow is
effected by the action of vibratile cilia1 propelling the water
through numerous perforations in a greatly enlarged pharynx,

1 For a description of cilia see " Elementary Physiology," Lesson VII. § 3-

FIG. 400. — TKACHBAL STRUCTURE
OF Proteiis, opened from behind.

A, arytenoid part of each of the two
cartilages ; T, its tracheal part ; />',
branchial arch ; M, muscle going
from the branchial arch to the
larynx.

476 ELEMENTARY ANATOMY. [LESS.

as is the case in the Lancelet. This, however, is a solitary
exception. In all other cases the water is mechanically
propelled by muscular contractions, and so made to pass over
delicate filaments or sheets (lamellae) of membrane attached
to a greater or less number of the visceral arches.

We may have (as in Myxine and in Bdellostoma] the gills
in the form of a folded lining to six or seven pouches placed
in a linear series on each side of the body, each pouch com-
municating with the interior of the oesophagus by an aperture,
and thence receiving water. Each sac may open on the
surface of the body by a separate aperture (as in Bdellostoma
and in the Lamprey), or each sac may open into a tube
running along each side of the body external to the sacs, and
terminating by an aperture placed far back on the ventral
surface of the body (as in My.viue}. In the latter case the
water coming from the sacs passes out at one aperture on each
side of the body.

The sacs may open internally, not into the oesophagus but
into a median canal placed ventrally to the oesophagus (as in
the Lamprey). This canal ends blindly at its post-axial end,
but pre-axially opens into the mouth by a valvular aperture.

These gill-sacs are not supported by solid visceral
(branchial) arches internally, but may be, as in the Lamprey,
protected externally by a cartilaginous framework or basket,

FIG. 401. — SKELETON OF HEAD AND GILLS OF LAMPREY.

hinder part of the external (paraxial) cartilaginous skeleton of the gills ; ant
auditory capsule ; A, hyoid ; ;/, neural arches ; /, palato-quadrate arch,

which, as we saw in Lesson VI., is a paraxial, skeletal
structure.

The several gill-sacs are separated from each other by
partitions which are not solid, cartilaginous structures.

The gills may be supported internally by solid (osseous or
cartilaginous) " branchial arches," which, as we have seen in
treating of the skeleton, are those visceral arches which suc-
ceed the hyoidean and mandibular arches post-axially.

XIL] THE EXCRETORY ORGAXS. 477

The branchial arches of osseous Fishes are made up of
parts to which special names have been applied. They are
attached to a median ventral series of pieces termed bast-
branchials. The lower piece of each lateral arch is called

FIG. 402. — FIRST THRE^: BRANCHIAL ARCHES FROM THE LEFT SIDE OF A PERCH.
On the outer (convex) side of each branchial arch the series of closely-set gill
filaments (or leaflets or lamellae) are seen to be attached. On the inner (con-
cave) side of the first branch! il arch are the series of elongated processes
(supporting minute denticles) which help to prevent particles of food, or other
foreign bodies, passing from the mouth to the giil chamber.

a hypo-branchial', to this succeeds a cerato-branchia.1, then
an epi-branchial) and finally, at the summit, a pharyngo-
branchial. These solid, supporting parts are not constantly
or equally developed in all the branchial arches, as is shown
by the annexed woodcut of these arches as they exist in the
Perch (Fig. 403).

The partitions between the gills may extend from this
solid internal support, outwards to the skin — as in the Sharks
and Rays. In such case each gill-chamber opens separately
on the side of the body.

The partitions may, however, extend but a very little way
from such solid internal support, outwards to the skin, while
the vascular gill-membrane remains elongated, and conse-
quently hangs freely from the outer side of each branchial
arch. This latter condition is that which obtains in ordinary
osseous Fishes, e.g. Perch, Carp, Cod, &c Here we find but
one large common chamber in which the filamentary gills
float, but this chamber is protected by the extension back-
wards of a fold of skin (the operculuni) supported internally
by the opercular bones ; and thus there comes to be in
ordinary Fishes but a single large gill-opening on each side
behind the head.

ELEVEN TAR Y ANA TOMY.

[LESS.

The gill-chamber is further protected by a membranous
fold which lies within the opercular flap. This fold is the
branchiostegal membrane, and is supported by the bmti-

FIG. 403. — LEFT BRANCHIAL ARCHES OF PERCH. (After Cuvier.)

i, glosso-hyal ; 2, 3, and 4, basi-branchials ; 5, hypo-branchials ; 6, cerato-bran-
chials ; 7. epi-branchials ; 8, styliform pharyngo-branchial ; q, pharyngobran-
chials ; 6 , inferior pharyngeal bone ; g and 9", superior pnaryngeal bones ;
5, 6, 7, and 8, first branchial arch ; 5', 6', 7', and 9, second branchial arch ; 5",
6", 7", and 9', third branchial arch ; 5", 6'", and 7'", fourth branchial arch ;
6'"', fifth branchial arch (inferior pharyngeal bone).

cJiiostegal rays, which (like the membrane itself) are attached
to the post-axial side of the hyoidean arch.

The respiratory surfaces of the gills are supplied with
water by the mouth, which continually takes in fresh supplies,

FIG. 404. — SKULL AND BRANCHIAL ARCHES OF A SHARK.

b1— 35, branchial arches ; h, hyoidean arch; m, mandible ;pq, palato-quadrate arch.

(From the College of Surgeons Museum)

such supplies passing out, in the osseous Fishes, from the
common opening behind the operculum ; and, in the Elasmo-
branchs, from each separate aperture of the successive gill-
chambers.

XII.]

THE EXCRETORY ORGANS.

479

In the Tenth Lesson has been already described the mode
in which the blood is brought to the gills from the heart, and
from the gills to the general circulation, as also the changes
which, in Batrachians, accompany the disappearance of the
gills during the developmental metamorphosis.

The blood is carried in osseous Fishes (e.g. the Perch)
along the convexity of each branchial arch both to and from
the gill-filaments, the margins of which are skirted by
arterial and venous branches, capillary vessels being inter-
posed between them.

FIG. 405.— Two LAMELL.-E (OR LEAFLETS) FROM THE GILLS OF AN OSSEOUS FISH,
showing the course of the respiratory circulation.

s, cut surface of one of the branchial arches. On its upper side is seen a concavity
which is produced by the section of the groove which runs along the convex
and exterior (here upper) side of each branchial arch, bn, branchial arttry in
section, giving oft" the gill-arteries (go) to the adjacent sides of the gill-leaflets,
whence the blood is distributed in the leaflets : gv, the gill-veins which run
along the outer side of the gill-leaflets, collecting the blood from them by
minute veins and pouring it into bv, the branchial vein, which runs down the
groove of the branchial arch and has the branchial artery superficial and
exterior to it.

Gills which are at first conspicuous but mostly dfsappear
ultimately, are termed external branchice. Such are absent in
almost all adult Fishes, though often present in the young con-
dition, e.g. in young Sharks. In Batrachians, such as the Tad-
pole, they also disappear and give place to internal gills ; but
in some forms, e.g. Axolotl and Menobranchus, they persist
throughout the whole of life as long plume-like appendages
placed on each side of the neck.

48o

ELEMENTARY ANATOMY.

[LESS.

Special respiratory structures may be added, as e.g. in the
climbing Perch (Anabas}, where the summits of the branchial
arches — or epipharyngeal bones — become enlarged and
curiously contorted to support an extension of vascular
mucous membrane. Again, in Saccobranchus and Amphi-
pnous, we find, by a very remarkable exception, a long
lung-like sac (with a highly vascular internal surface)
placed on each side of the body, and communicating with
the mouth by an aperture placed between the first branchial
arch and the hyoid. These organs receive blood from the
aortic vessels coming from the heart, and transmit it to the
dorsal aorta.

There may be six or seven branchial sacs, as in the Sharks
Hexanchus and Heptanchus. On the contrary, not only may
the fifth branchial arch be devoid of a gill, as in all the Teleostei,
but even the fourth gill may disappear, and indeed only the
second gill may be left, as in Amphipnous.

Sometimes, as in Lepidosteus and the Sharks, the hyoidean
arch also supports a gill.

fuzz

FIG. 406.

The kidneys (A') ; ureters (Ur) ; with the aorta (Ao\ and vena cava inferior (VCI}\
and the renal arteries and veins. Bl is the bladder, the top of which is cut
off so as to show the openings of the ureters (i, i) and that of the urethra (2).

9. The general appearance, position, structure, and func-
tion of the KIDNEYS in man have been already noticed in

xii.] THE EXCRETORY ORGANS. 48i

the Fifth Lesson of " Elementary Physiology," § 6. Here it
may be added that the true kidneys are not the primitive
urinary organs, but that the first- formed structures of this
kind are what are called the Woolffian bodies — or primordial
kidneys. These Woolffian bodies are formed one on each
side of the line of attachment of the alimentary canal to the
spine. They appear very early, each as a series of trans-
versely extended tubuli, and on the outer side of each is a
duct which extends post-axially and enters that primitive
chamber at the hind end of the body (the cloaca) into which
the termination of the alimentary canal also opens.

The kidneys arise behind the Woolffian bodies, and inde-'
pendently of them ; and the ducts which pass from the kidneys
(the ureters] also terminate, independently of the termination of
the Woolffian ducts, in the same primitive chamber common
to the alimentary and urinary systems.

The Woolffian bodies are gradually absorbed, and disap-
pear as the kidneys become developed. The latter organs
are at first smooth and oval, but soon become divided, each
into about fifteen lobes. These subsequently coalesce, but
even at birth the kidney shows signs on its surface of its
previous lobulated condition.

10. In that man possesses distinct urinary or RENAL
ORGANS, he agrees with all Vertebrates, with the single
exception of the Lancelet, in which such parts have not
been yet certainly determined.

In that Woolffian bodies are formed, man agrees with all
other Vertebrates with the exception just referred to.

In that Woolffian bodies are subsequently replaced by true
kidneys, man agrees with all Mammals and all Sauropsi-
dans ; but it may be that Woolffian bodies persist, and by
themselves alone constitute the renal organs through the
whole of life, in Ichthyopsidans.

The renal organ may exist as a very elongated body made
up of a series of bodies analogous to Malpighian corpuscles,1
connected at short intervals, as in the Myxinoids.

The urinary gland may extend on each side from the head
to the opposite end of the abdominal cavity, as in the Stur-
geon, and the ureters may join together before their termi-
nation, as in the same last-menti-oned animal.

The two urinary glands may blend together behind the
pharynx, as in many osseous Fishes ; or at their posterior

1 For a description of these corpuscles see the Fifth Lesson of " Elementary
Physiology," § 9, Fig. 27.

I I

482 ELEMENTARY ANATOMY. [LESS.

end, as in Proteus ; or for their entire length, as in the
Spoonbill.

Their surface may be marked by convolutions like that of
the human cerebrum, as in Sharks and Chelonians.

The opening of the ureters may be placed behind the pos-
terior termination of the alimentary canal. This is the case
in osseous Fishes, and consequently a true bladder must be
wanting in them. Each ureter may, however, dilate into a
large bladder-like structure, as in Amia^ or there may be a
single, median vesicle. It is possible for several distinct
urinary ducts to open into this vesicle, as in the Stickleback.
Every sort of bladder-like structure may be absent, as in
Cobitis, and in all Serpents and Birds. A true bladder may,
however, be developed in Ichthyopsidans, as in the Batra-
chia, where it is placed in front of the termination of the
alimentary tube and of that common chamber (the cloaca) into
which that tube opens, as well as the bladder or rena! ducts.

The right renal organ may be much longer and placed
more forward than the left, as in Serpents.

The ureters may open, not into the bladder, but into the
cloaca, as is the case in the Monotremes, or Ornitkodclphia,
and in Reptiles.

These ducts may terminate (in the cloaca) behind the
alimentary canal, or may come rather to the side, and in
the OrnitJiodelphia rather towards the front of the cloacal
chamber.

These circumstances may serve to explain the difference
between the position of the alimentary and urinary outlets in

man's class, and the situation
of those apertures in osseous
Fishes where the alimentary
outlet is anterior. The modi-
fication by which the urinary
outlet comes to be anterior does
not result from any change
in the position of the termi-
FIG. 407.— KIDNEY OF THE SEAL nation of the alimentary tube,
condSon. g US lobulated butin the gradual production
forwards, on each side of it, ot

the ureters, till they come in non-Ornithodelphous Mammals
to end (through the intervention of the bladder and urethra)
in a canal opening altogether in front of the rectal aperture.

The kidneys may be more symmetrical in position than
in man. This is the case in most Birds, where they are

XIL] THE EXCRETORY ORGAXS. 483

imbedded in the depressions of the under surface of the
sacrum, which is so expanded in the entire class Aves.

A condition of the kidneys analogous to that which at an
early period exists in man, may not only persist throughout life
in other animals, but may be much more complete, as in the
Seals and Cetacea, where the kidneys are so divided into small
lobes as to resemble a bunch of grapes. As many as 200
lobes have been counted in the Dolphin's kidney.

11. Two small glandular bodies, of unknown function,
called SUPRA-RENAL CAPSULES, are placed one on the
summit of each kidney. Each capsule is a flattened, tri-
angular body, and shaped something like a cocked hat. It
is formed of cellular tissue, often mixed with much fat, and
provided with a fibrous coat which sends processes into the
interior of the gland, these processes accompanying blood-
vessels and nerves, which are numerous.

These organs exist in all the members of man's class, and
in a general way resemble his in position and form. They
are relatively largest in Rodents, as in the Coypu and Por-
cupine, where they are cylindrical in form.

They are relatively smallest in the Cetacea amongst Mam-
mals, where, as also in Seals, they exhibit a lobulated exterior
like that of the kidney itself.

In Birds these organs are relatively smaller, being in the
Goose only about the size of a pea. They also vary more
in shape in Birds than in man's class, and sometimes become
confluent. They are usually, in Birds, placed on the inner
side of the kidneys.

The supra-renal capsules may be in the form of a single, elon-
gated, narrow, lobulated body, situate behind the renal organ,
as mostly in Sharks ; or may appear as a yellow streak on the
ventral aspect of the urinary gland, as in the Frog and Toad.

Each supra-renal capsule may be divided into a greater or
less number of lobules, as in some Urodeles, the Sturgeon,
and many Fishes.

12. The SPLEEN of man has been noticed in the Fifth
Lesson of " Elementary Physiology," § 28. It is a ductless
body, of irregular and variable shape, richly supplied with
blood-vessels, and lying beneath the diaphragm at the car-
diac end of the stomach.

In the possession of a spleen man agrees with all other
Vertebrata, with the exception of the Lancelet, and possibly
also with the exception of the Marsipobranchii, Lepidosiren^
and Ceratodus.

ELEMENTAR Y ANA TOMY.

[LESS.

This organ may be relatively much larger than in man,
and consist of two lobes, as in the Ornithorhynchus ; it
may consist of three lobes, as in the Echidna. Occasionally in
Rodents a small detached accessory spleen may be developed,
and there are constantly accessory spleens in the Sturgeon,
the Dolphin, and Nanvha'.

v.c.r.

Ao.

Z>m.

FIG. 408. -THE SPLEEN (S//.) with the splenic artery (SpA\ Below this latter
is seen the splenic vein running to help to form the vena portce (VP).

Ao, the aorta ; Z>, a pillar of the diaphragm : PD, the pancreatic duct exposed by
dissection in the substance of the pancreas ; Dm, duodenum ; BD, the biliary
duct opening into the pancreatic duct at x ; y, the intestinal vessels.

13. The THYROID GLAND of man is a soft, reddish, and,
very vascular body, embracing the trachea in front, and
ascending to the larynx. It has no duct, and is of a more
or less semilunar form, with two lateral lobes, united by an
isthmus. It is covered by the sterno-hyoid, sterno-thyroid,
and omo-hyoid muscles.

In that man develops a thyroid gland he appears to agree
with all Vertebrates except the Lancelet.

This body may consist of two completely divided lateral
halves,, placed each on one side of the trachea and larynx, as
in Birds, Batrachians, Monitors, the Llama, the Otter, the
Mole, and others, and as even in the Orang. It may consist
of one undivided body, as in Cetaceans.

It may be represented (as in Birds) by small rounded or
elongated bodies, very vascular, placed beside the trachea,
above the syrinx, and closely connected with the carotid or

xii.] THE EXCRETORY ORGANS. 485

vertebral artery, or both. It may lie between the diverging
carotids, as in Python and Chelonia, or on the carotids, close
to the basi-branchials, as in the Frog. It is thus generally
connected with the primitive arteries to which the aorta
gives rise.

14. The THYMUS GLAND of man is but a temporary struc-
ture, which disappears in the adult, and is at its maximum of
size at about the end of the second year. It is then long and
narrow, and placed partly in the chest and partly in the neck
(between the sternum and the great vessels), and having the
appearance of a ductless gland. It is irregular in shape,
with a considerable internal cavity, but it is more or less com-
pletely divided into two elongated lateral lobes, which taper
upwards. At birth it measures about two inches in length.

In that man develops a thymus gland he agrees with air-
breathing Vertebrates generally.

It appears to be wanting in Proteus and Siren, and to be
developed in the Tadpole of the Frog only with the develop-
ment of the lungs, disappearing again in the adult, and being
transformed into fat. It is often, as in the Frog, a double
gland — one on each side. In the Chick the thymus soon
aborts, but is present, when the animal is a week old, as two
hollow tubes placed one on each side of the neck.

The thymus may be broad and flat, covering the thyroid
sternally, as in Iguana. It may send up, on each side, a pro-
cess within the angle of the mandible, and may so form a
large mass beneath the skull, as in the Calf.

15. The CUTANEOUS GLANDS of the human body are
insignificant in size, with the exception of that special agglo-
meration of them which constitutes the MAMMARY GLAND,
or breast.

They are of two kinds —sebaceous glands and sudoriferous
or sweat glands.

(1) The sebaceous glands (noticed in Lesson V. § 32 of
the "Elementary Physiology") are each a cluster of small
secreting tubes placed in the dermis, and discharging their
fatty secretion, by a small duct, usually into the sheath or
follicle of one of the hairs.

(2) The sudoriferous glands (noticed in Lesson V. §16
of the " Elementary Physiology ") consist each of a fine
secreting tube, coiled up into a ball, placed beneath the
dermis, in the subcutaneous tissue, and pouring out its con-
tents by a delicate convoluted tube opening by a pore on the
surface of the epidermis.

486 ELEMENTARY ANATOMY. [LESS.

They are placed in different degrees of proximity on dif-
ferent parts of the body; and it is said that there may be
400 or 600 in a square inch of the skin of the back, or even
2,800 in a square inch of the palm of the hand.

In size they may be about ^ of an inch in diameter, but
they may also attain to one-sixth of an inch in the axilla, or
armpit.

In man there are no great special aggregations of cutaneous
glands in certain regions, but we find many and various such
aggregations in species of his own class.

Thus there may be an aggregation of such glands open-
ing into an inverted fold of skin in front of the eye, as in

FIG. 409. — SECTION OF THE SKIN, SHOWING THE SWEAT GLANDS.

a, the epidermis ; b, its deeper layer, the rete Malpighii; e, d, the dermis, or
true skin ; /, fat cells ; g, the coiled end of a sweat gland ; h, its duct ; i, its
opening on the surface of the epidermis.

many Ruminants, e.g. the Indian Antelope and the Deer,
where the gland opens externally in a fissure near the front
angle of the eye, and is lodged in the lachrymal fossa before
referred to in Lesson III. § 28, p. 118.

A similar structure may be placed in the occiput, as in the
Camel, or behind the ear, as in the Chamois.

There may be a large gland in the temporal region open-
ing between the eye and the ear, as in the Elephant.

There may be a series of glandular structures on each

Xii.] THE EXCRETORY ORGANS. 487

flank, as in the Shrews ; or there may be a glandular sac
opening near the armpit, as in the Bat Cheirojiielcs.

There may be a gland in the sacral region of the back,
opening by a median orifice like a dorsal navel, as in the
Peccari.

There may be a gland in each groin, as in the Corinne
Antelope, or placed more medianly and post-axially, as in
the Musk Deer, where the sac may be three inches broad.

Scent-glands may open at or near the post-axial termina-
tion of the intestine, as in many Carnivora, e.g. the Skunk
and Hyaena. In the higher division of man's order (the
Apes) there are no such glandular structures, but in the
Lemuroids (e.g. Cheirotnys] there may be a shallow pit-like
gland on each side of the end of the alimentary tube.

There may be a scent-gland in the tail, as in the Desman
and the Fox, or near the arm, as in certain Bats (Einballonura
and Saccopteryx), where there is a glandular sac in each
wing-membrane.

A glandular structure may open behind the foot, as in the
Rhinoceros, or in front of it, between the toes, as in the
Sheep.

We may find (as in the male Ornithorhynchus and
Echidna) a large gland placed in the leg, and furnished
with a long duct which passes to the heel and there traverses
a perforated spur like the poison-fang of a Serpent, though it
does not seem to poison, or even to be used for defence.

In descending below man's class to Birds, we find a
peculiar cutaneous structure, the " uropygial gland" consist-
ing of two parts conjoined, and in the Swan measuring an
inch and a half in length. It is placed upon the more post-
axial caudal vertebras and ploughshare bone, and opens on
the skin, where it discharges a greasy fluid to lubricate the
feathers.

Another glandular structure is present in Birds, the Bursa
Fabricii. This is a conical cavity which opens into the post-
axial region of the cloaca. It is placed between the ureters,
on the ventral aspect of the sacrum.

In Reptiles we may find other structures. Thus there may
be, as in the Crocodile, a musky gland inside the mandible ;
or beneath it, as in the Indian Tortoise. There may be a
glandular fossa opening into the dorsal aspect of the cloaca,
as in the Terrapins ; or a pair of elongated sacs opening
beside the post-axial termination of the intestine, as in the
common Snake ; or a pair of glandular depressions of the

488 ELEMENTARY ANATOMY. [LESS.

skin placed one on each side between the eye and the nose,
as in Cro talus.

There may be a series of glands in each thigh, with a
row of conspicuous openings, called femoral pores, on its
inner surface, as in very many Lizards (Lacerta, Monitor,
&c.), or in the armpit, as in Iguana, or in front of the cloaca!
opening, as in Hysteropus.

We may find (e.g. in the Chameleon) cutaneous structures
termed chromatophores, which are little sacs containing
pigment of various colours, and each with an aperture which,
when open, allows the colour contained to appear, and when
closed conceals it. It is by the various contractions of these
sacs that the Chameleon effects those changes of colour for
which it is celebrated.

It is in the next lower class, Batrachia, that we find the
cutaneous glands carried relatively to their maximum of
development.

They may be aggregated in a mass behind the eye and
above the tympanum on each side, forming the so-called
" parotoid " glands, as in the common Toad.

There may be a similar structure on the arms, as in Pelo-
bates, or on the upper side of the leg, as in Bnfo Calamita.
The whole skin of the back may be of this nature, as in
Kalophrynus, or these glands may be localised in two longi-
tudinal series, as in Salamandra, where they extend from
the head to the end of the tail. Their secretion maybe more
or less acrid, as in the last-named genus and in the Toad.

It is not certain that true cutaneous glands, homologous
with those of higher Vertebrates, exist in the class of Fishes.
This is remarkable, seeing the very great development they
attain in the Batrachian class of Ichthyopsidans.

Nevertheless, a copious mucus exists on the skin in Fishes,
and notably in the Eel. This escapes from the deeper
structures through minute orifices, but is by some naturalists
considered to be rather itself a modified epidermis than a
true cutaneous secretion.

In most Fishes there is a complex system of special
canals, the nature of which has been commonly deemed
excretory, but is now considered to be rather sensory in
function. These canals are usually disposed symmetrically,
and are filled with a clear gelatinous substance. They con-
stitute the " lateral line," the passage of which modifies and
marks the scales it traverses, and is thus useful in zoological
classification — the lateral line forming a more or less con-

xii.] THE EXCRETORY ORGANS. 489

spicuous mark running antero-posteriorly along each side of
the body and tail of most Fishes.

That special modification of the cutaneous glands called
the MAMMARY GLAND, or breast, is peculiar to man's class,
which from this circumstance alone bears the name of
Mammalia.

These glands may be devoid of a nipple, as is the case in
the Ornithorhynchus and Echidna, or the nipples may be
very long, as in Marsupials. There may be as many as
twenty-two glands, as sometimes in
Centetesj or ten, as in the Hedgehog
and domestic Sow.

There is never one nipple only,
though very rarely their number
may be odd, as in some Opossums.

The glands may open into a little
depression, or sac, formed during
their functional activity, as in the
Echidna. FlG 4I0._MARSUPiAL POUCH

I hey may be placed inside a OF AN OPOSSUM (Didetykys
permanent cutaneous pouch, as in cancrivora\ cut open to the

\, . , eleven nipples within— one of

Marsupials. these eleven teats being me

In that group there may be four dian in position,
nipples, as in the Kangaroo ; or

eight arranged in a circle, as in Phascopale penicillata; or
four on each side and one in the middle, as in Didelphys
dorsigera ; or six on each side and one in the middle, as in
the Virginian Opossum.

These glands may be placed nearer the middle line of the
back than that of the belly, as in the aquatic Coypu Rat ;
or near the armpit, as in Pteropus.

There may be two pectoral mammae in animals remote
from man's order, as in the Elephant, Sloths, and Sirenia.

The Sirenia from this circumstance, together with their
rounded heads and fish-like tail, probably gave rise to the
belief in the existence of Mermaids.

There may be but two mammary glands, each opening in
a depression and placed quite at the hinder end of the belly,
as in Cetaceans.

In Ruminants we have posteriorly situate glands with
teats forming an " udder."

In man's own order we find, in the Ape, but two pectoral
mammae ; but amongst the Lemuroids there may be only a
pair of ventral (inguinal) glands, as in Chciromys j or a pair

490 ELEMENTARY ANATOMY. [LESS.

of inguinal and also a pair of pectoral ones, as in Tarsius ;
or two pairs of pectoral mammary glands, as in Galago.

Each teat is traversed by a single efferent canal in Rumi-
nants, Pigs, and Cetaceans ; by two in Horses and Apes ;
by five or six in some Rodents and Carnivora ; and by more
in the Elephant, Sirenia, Marsupials, and higher Primates.

As has been said, mammary glands are confined to man's
class : the only faint adumbration of such organs, outside his
class, is to be found in Pigeons, where the crop secretes a
milky fluid (during the breeding season) which mixes with
the food taken into that receptacle — the mixture serving as
food for the young. It has also been asserted that glands
lining the pouch of the Fish Hippocampus secrete a nutritious
fluid useful to its progeny.

1 6. Having now completed our elementary investigation
and exposition of the various organs and parts which make
up man's body, and having noted the more important dif-
ferences which the corresponding structures may present in
other Vertebrate animals, it may be well shortly to re-
capitulate some of the leading distinctions in a different
sequence and arrangement, in order to bring out more
clearly not only the peculiarities, but also the affinities
evidenced by various anatomical relations between the body
of man and those of other Vertebrates.

In the first place MAN differs from the entire class of
FISHES in the following points :—

(1) He has a skeleton the appendicular parts of which

are divided into upper-arm, fore-arm and hand, and
thigh, leg, and foot, respectively.

(2) His hyoid is a small structure with one pair of cornua

instead of several branchial arches.

(3) His skull is formed with a large basi-sphenoid but no

para-sphenoid ; with a large squamosal confluent
with a " petrous bone ;" and with a mandible
formed of two united pieces directly suspended
from the squamosal.

(4) His auditory ossicles are minute, and take no part in

suspending the mandible.

(5) His ribs, articulated dorsally by head and tubercle, are

connected on the ventral side with a sternum.

(6) His vertebrae have at first terminal epiphyses.

(7) He has a pelvis formed of two ilia, two ischia, and two

pubes united dorsally to a sacrum.

i.] RECAPITULATION. 491

(8) His coccygeal region is rudimentary.

(9) His skin is furnished with hair.

(10) The muscles of his limbs are numerous and complex.

(11) His cerebrum is excessively large, with a corpus cal-

losum, and his corpora quadrigemina are very small.

(12) He has distinct hypoglossal nerves, which perforate the

occipital.

(13) His olfactory nerves traverse a cribriform plate.

(14) His ear has a spiral cochlea, a tympanic membrane,

and an Eustachian tube.

(15) His posterior nares open far back within the mouth.

(16) His tongue is large and fleshy.

(17) He never has gills at any time of life.

(18) He breathes by lungs from his birth.

(19) His heart has two auricles and two ventricles.

(20) All the blood of his body passes through the lungs.

(21) There is no communication, in the adult, between the

veins and arteries, save by the capillaries.

(22) He has but one aortic arch.

(23) He is furnished with a larynx.

(24) His alimentary canal neither terminates in a cloaca nor

anteriorly to the urinary outlet.

(25) He has a complete diaphragm.

(26) His kidneys replace transitory Woolffian bodies.

(27) He has no fin rays.

(28) His blood-corpuscles are not nucleated.

(29) He is provided with salivary glands.

17. Man is distinguished from all BATRACHIANS in that —

(1) His skull is formed with a large basi-sphenoid but no

para-sphenoid, with a large squamosal confluent with
a " petrous bone," and a mandible formed of two
united pieces directly suspended from the squamosal.

(2) His skull has a well-developed basi-occipital.

(3) His auditory ossicles are minute, and take no part in

suspending the mandible.

(4) His ribs join a sternum.

(5) His vertebrae at first have terminal epiphyses.

(6) His skin is furnished with hair.

(7) His cerebrum is excessively large, with a corpus cal-

losum,and his corpora quadrigemina are very small.

(8) His olfactory nerves traverse a cribriform plate.

(9) His ear has a spiral cochlea.

(10) His posterior nares open far back within the mouth.

492 ELEMENTARY ANATOMY. [LESS.

(n) He never has gills at any time of life.

(12) His heart has two ventricles.

(13) All the blood of his body passes through the lungs.

(14) There is no communication, in the adult, between the

veins and arteries, save by the capillaries.

(15) He has but one aortic arch.

(16) His alimentary canal does not terminate in a cloaca.

(17) He has a complete diaphragm.

(18) His kidneys replace transitory Woolffian bodies.

(19) His blood-corpuscles are not nucleated.

(20) He is provided with true salivary glands.

1 8. Man is distinguished from REPTILES in that —

(1) His skull has a " petrous bone " and a mandible formed

of two united pieces directly suspended from the
squamosal.

(2) His auditory ossicles are minute, and take no part in

suspending the mandible.

(3) His vertebras at first have terminal epiphyses.

(4) His skin is furnished with hair.

(5) His cerebrum is excessively large, with a corpus cal-

losum, and his corpora quadrigcmina are very small

(6) His olfactory nerves traverse a cribriform plate.

(7) His ear has a spiral cochlea.

(8) All the blood of his body passes through the lungs.

(9) There is no communication, in the adult, between the

veins and arteries, save by the capillaries.
(10) He has but one aortic arch,
(n) His alimentary canal does not terminate in a cloaca.

(12) He has a complete diaphragm.

(13) The whole tarsus moves freely on the tibia, and there

is no intertarsal joint.

Man also differs from all Reptiles except the Crocodilia in
that—

(14) His blood-corpuscles are not nucleated.

(15) His heart is provided with two completely distinct

ventricles.

(16) His posterior nares open far back within the mouth.

19. Man is distinguished from BIRDS in that —

(i) His skull has a "petrous bone " and a mandible formed
of two united pieces directly suspended from the
squamosal.

II. 1 RECAPITULATION. 493

(2) His auditory ossicles are minute, and take no part in

suspending the mandible.

(3) His vertebras at first have terminal epiphyses.

(4) His skin is furnished with hair, and is devoid of

feathers.

(5) His cerebrum is excessively large, and with # corpus

callosum, and his corpora quadrigemina are very
small and not placed laterally and depressed.

(6) His olfactory nerves traverse a cribriform plate.

(7) His ear has a complex spiral cochlea.

(8) His solitary aortic arch arches over the left bronchus.

(9) No air-cells communicate with the lungs.

(10) He has no syrinx, but a large and complex larynx.

(n) His lungs are freely suspended in the thoracic cavity.

(12) His alimentary canal does not terminate in a cloaca.

(13) His ureters open into the bladder.

(14) He has a complete diaphragm.

(15) His posterior nares open far back within the mouth.

(16) His coracoids are small processes.

(17) His ulna is larger than his radius.

(18) His hand has five digits and nine carpal bones.

(19) His pelvis unites with the sacrum only, and not with

lumbar and dorsal vertebrae, and has its acetabula
imperforate.

(20) His fibula is free at its lower end.

(21) His tarsus does not unite partly with the tibia and partly

with the metatarsus, and form an intertarsal joint.

(22) He has five digits to his foot.

(23) His coccyx does not terminate in a ploughshare bone.

(24) He is furnished with teeth.

(25) His blood-corpuscles are not nucleated.

20. Man differs from the MONOTREMES in that —

(1) His vertebras at first have terminal epiphyses.

(2) His cerebrum has a very large corpus callosum and

small anterior commissure.

(3) His ear has a complex spiral cochlea.

(4) His alimentary canal does not terminate in a cloaca.

(5) His ureters open into the bladder.

(6) His coracoids are small processes, and he has no epi-

coracoids or large interclavicle.

(7) His acetabula are imperforate.

(8) He has no marsupial bones.

(9) His fibula has no upper olecranon-like process.

494 ELEMENTARY ANATOMY. [LESS.

^10) He has definite calcareous teeth.

(11) The mammary glands are provided with nipples.

21. Man differs from all MARSUPIALS in that—

(1) His cerebrum has a very large corpus callosum and a

small anterior commissure.

(2) He has no marsupial bones.

(3) The angle of his mandible is not inflected.

(4) His internal carotid perforates the petrous bone, anc

not the sphenoid.

22. Man is distinguished from all MAMMALS below his own

order in that —

(1) His anterior extremities are provided with thumbs.

(2) His orbits are separated off from the temporal fossae by

bony lamellae.

(3) His dental formula is I f , C *, P M f , M \.

23. Man differs from all MEMBERS OF HIS ORDER excep
the three highest genera, the Orang (Simla), the Gorilla anc
Chimpanzee (Troglodytes), and the Gibbons (Hylobates)
in that —

(1) His sternum is of considerable breadth.

(2) His metapophyses and anapophyses are very little

developed.

(3) His cerebrum is richly convoluted.

(4) His caecum has a vermiform appendix.

(5) His hallux is not formed for grasping, but for support-

ing his body in an erect posture.

24. Man differs from even the HIGHEST APES in —

(1) The position of his body being erect.

(2) The curvature of his spine and the form of his pelvis

being consequently peculiar.

(3) That his thumb reaches to the middle of the proximal

phalanx of the index.

(4) His femur being longer absolutely, its shaft more an-

gular, and its linea asperatmore projecting.

(5) The absolute length of his tibia and the sharpness of

the crest of that bone.

(6) The descent of the posterior border of the distal arti-

cular surface of the tibia below its anterior border.

(7) The much greater descent of the peroneal than of the

tibial malleolus.

MIL] RECAPITULATION. 495

(8) The shortness of the foot compared with the length

of the pelvic limb minus the foot, and compared
with that of the tibia.

(9) The great breadth of the lowest part of the tuberosity

of the os calcis.
(10) The flattened surface, for the hallux, of the ento-cunei-

form bone.
(i i) The fact of the first or second digit being the longest

one of the foot.

(12) The absolute size of the hallux, and especially of its

second phalanx.

(13) The very slight outward direction of the great toe

(which is not prehensile) and the great proportion
borne by it to the longest digit.

(14) The small proportion borne by the four outer digits of

the foot to the whole foot and to the metatarsal
bones.

(15) The successive decrease in length of the tarsus, meta-

tarsus, and digits.

(16) That the cervical spines, above the seventh, are short

and usually bifurcate.

(17) The occipital condyles being more anteriorly situate

on the basis cranii.

(18) That the cranio-facial angle varies from 90° to 120°.

(19) The cerebral cavity being more than T.\ times the

length of the basi-cranial axis.

(20) That the superciliary ridges are little developed.

(21) That the maxillo-premaxillary suture is not visible on

the face of the skull, even at birth.

(22) That he has a nasal spine.

(23) The distance between the zygomata, where widest, ex-

ceeding but little the greatest transverse diameter of
the bony brain-case.

(24) That there is a large vaginal ridge to the petrous bone,

and a long styloid process.

(25) That his jaws are relatively small.

(26) That hair is very little developed on the surface of the

body, and is deficient on the back, though ordinarily-
abundant on the head.

(27) That there is an extensor primi internodii pollicis

muscle, and also a peroneus tertius.

(28) The flexor pollicis longus and the flexor longus digi-

torum perforans being completely separate.

(29) That the solcus has a tibia] as well as a fibular origin.

496 ELEMENTAR Y ANA TOMY. [LESS.

(30) That all four heads of the flexor brcvis digit orum

pedis arise from the os calcis.

(31) That the fibular interosseous muscle of the second toe

of the foot arises from the middle metatarsal on the
dorsal side of the tibial interosseous muscle of the
middle toe.

(32) The absolute size of the brain.

(33) The greater complexity and less symmetrical disposi-

tion of its convolutions.

(34) The smallness of the canines and the absence of an

interspace between them and the adjoining teeth.

(35) That the permanent canine is cut before the second

true molar teeth.

25. A perusal of the list of characters given in the nine
preceding paragraphs must manifest to the beginner in
anatomy how small and insignificant are the characters
which separate man's structure from that of other members
of his class, compared with those which distinguish him from
Birds and other yet inferior groups.

Viewed from the anatomical standpoint, man is but one
species of the order Primates ; and he even differs far less
from the higher Apes than do these latter from the inferior
forms of the order.

This work being purely anatomical, it is only needful here
to remind the reader — of what common sense teaches us —
that to estimate any object as a whole, its powers of action
no less than its structure must be taken into consideration.

The structure of the highest plants is more complex than
is that of the lowest animals ; but for all that, powers are pos-
sessed by jelly-fishes of which oaks and cedars are devoid.

The self-conscious intelligence of man establishes between
him and all other animals a distinction far wider than the
mere superiority of his brain, in mass and complexity, or any
other physical difference, would indicate.

All, however, who admit the idea of man's moral responsi-
bility are logically compelled to go much further, and to con-
fess that in this respect he is separated from the rest of the
visible creation by an abyss so vast that no chasm separating
the other kingdoms of nature from one another can be com-
pared with it.

Evident, then, as it is from the teaching of anatomy that
the various parts of the human body have a classificatory
value indicating the zoological position of the whole struc-

xii.] CONCLUDING REMARKS. 497

ture, it is no less evident from other considerations, that to
allow mere anatomy to warp our judgment as to the
TOTALITY OF MAN'S NATURE would be a serious mistake.
To estimate correctly an existence of which mind forms a
part, recourse must be had to Philosophy, and especially
to Psychology. Unlike physical science, Philosophy is not
restricted to the interpretation of existences belonging to one
sphere only, but seeks to investigate all orders of truth and
every kind of existence which is capable of apprehension by
the mind of man.

K K

INDEX.

Each animal, the zoological position of which has not been given in the First
Lesson, has the title oj 'the group to which it belongs placed (between brackets)
after its name.

Abdominal cavity, 433.

muscles, 297, 298, 337.

veins, 426.

Abductor hallucis, or pollicis pedis, 305,
307, 308, 355, 358, 359.

magnus muscle, 342.

metatarsi quinti, 355, 359.

minimi digiti muscle, 297, 337, 359.

minimi digiti pedis muscle, 304,
306, 307.

muscles, 282.

poliicis muscle, 294, 297, 320, 337.

pollicis pedis, see Abductor hallucis
Abomasum, 443, 444.
Absorption of teeth, 251.
Acanthopterygian fin, 278.
Acanthurus (a Teleostean Fish), swim-
bladder of, 466.
Accessorius muscle, 306.
Accipiter (a Carinate Bird), skull of,

109, no.

Acetabulum, 178, 180, 189, 195.
Acrodont teeth, 256.
Acrpmion, 146, 155, 156, 757, 170.
Actions of muscles, 361.
Adductor arcuum muscle, 310, 311.

branchiarum muscle, 316.

digiti tertii muscle, 334.

digiti quarti muscle, 334.

minimi digiti muscle, 296.

muscles, 282.

muscles of thigh, 301—303, 344—
346. 350.

pollicis muscle, 296, 297, 336.
Adjutant (a Carinate Bird), 200.
Aetobatis, 20.

African Jumping Shrews, 16.
Agamas, 18.

Agouti, 16.

limb-bones of, 198.

muscles of, 309, 317, 327, 340, 343,

35i» 353. 354. 356.
Ailurus, 16.

teeth of, 267.
Air-sacs, 470, 471.
Ala, of spenoid, 76, 81, 90, 227.
Alimentary system, 433.

tube, or canal, 4, 221. 223.
Alisphenoid, 98, 109, 130, 227.

canal, no.
Alligato-s, 18.

limb-bones of, 208.

muscles of, 345, 349, 354.
Alveolar border, 76.

plates, 256.
Alveoli, 77, 251, 257.
Amblystoma (a Urodele Batrachian),

muscles of, 337.
American Apes, skull of, 132, 133.

E^t, Great, 19.

Monkeys, brain of, 378, 384.
Amia (a Ganoid Fish), swim-bladder
of, 466.

ureters of, 482.
Amoeba, n.

Amphicoelous vertebrae, 39.
Amphioxus, g, 12,21, 142, 215, 225.

arteries of, 416.

breathing organs of, 466.

circulation of, 426.

liver of, 460.

Amphipnnis (a Teleostean Fish). 480.
Amphisbena, 10, 18.

limb-bones of, 190.
Amphiuma (a Urodele Batrachian),

lungs of, 464, 465.

spine of, 53, 68.
Anabas a Teleostean Fish), gills of, 480.

K K 2

500

INDEX.

Anableps (a Teleostean Fish), eye of,

389-

Anal glands, 487.
Anapophysis, 31, 226.
Anas (Goose), trachea of, 469.
Anatomy of man as a whole, 496.
Anconeus muscle, 296, 334.
Angle, basi-facial, 91, 135, 136.

occipital, 92, 135, 136

of mandible, 86, 114.

olfactory, 92, 135, 136.
Angler, 20.

limb-bones of, 191, 194.
Angles of scapula, 146.
Anguis (a legless Lizard), spine of,
64.

limb-bones of, 161, 234.

muscles of, 320, 321, 324.
Angular bone, 98, 103, 120.

process, 79.
Animal electricity, 405.

kingdom, 5.
Ankle-joint, 207.
Annular ligament, 304.
Annuloida, 7, 12.
Annulosa, 6, 9, n, 12.
Anoplotherium, teeth of, 258.
Ant-eater, 17.

glands of, 437, 439.

intestine of, 448.

limb-bones of, 196, 197, 211.

mouth of, 254, 436.

muscles of, 316, 326, 330, 335, 342.

skull of, in, 113, 115, 118, 122,
13°. 13I» J33. J4o.

spine of, 45, 52, 66, 68.

stomach of, 444.

tongue of, 441.
Ant-eater, Cape, teeth of, 276.

Two-toed, 206.
Antelope, 17.

cutaneous glands of, 486, 487

external skeleton of, 245.
Antelope quadricornis, 246.
Antennae, 13.
Anterior auricular muscle, 283, 308.

clinoid process, 83.

commissure, 370, 371, 373, 379.

cornu, 373.

fossa of the skull, 89, 136.

inferior spinous process, 178, 179,
190

nares, 76, 133.

nasal spine, 84.

palatine canal. 84, 88.

scalenus muscle, 287, 288.

superior spinous process, 178, 179.

tibial nerve, 400,402,412,414, 415.
Antero-posterior symmetry, 10.
Anthropoid Apes, brain of, 379.

muscles of, 336.
Anthropotomy, 24.

Antilocapra, external skeleton of, 245.
Antlers of Deer, 279, 280.
Antrum Highmori, 84.
Anura, 19.

Aorta, 299, 398, 407, 409, 411, 412,
415—421, 424, 427—429, 449, 459, 463.
468, 480, 484.
Aortic arches, 398, 411, 412, 415, 416,

418—420, 428, 429.
Apes, 15.

brain of, 379, 384.

external skeleton of, 243, 264.

intestine of, 448.

limb-bones of, 164, 166, 169.

liver of, 455.

mammary glands of, 489, 490.

muscles of, 321, 326, 332, 336, 349,
359, 360.

skull of, 100, 101, 104, 106, no,
112, 114 — 118, 123, 131,134, 136,
137, 140.

spine of, 40, 50, 57, 58, 71.

teeth of, 258, 261, 263, 270, 272.

their differences from man, 494.
Aponeuroses, 281.
Appendages of skin, 236.
Appendicular muscles, 362.
Appendicuar skeleton, 25.

compared with axial, 234.

generalized, 229.
Apteryx, 18.

limb-bones of, 164.

muscles of, 321, 342.

spine of, 67.

Aquatic respiration, 461, 475.
Aqueous humour, 387.
Aquila, muscles of,~32o, 341, 357.
Arachnoid fluid, 364.

membrane, 364.
Arbor vitae, 371, 372, 383, 385.
Arch, neural, 26.
Arch of aorta, 398, 411, 412, 415, 416,

418—420, 428, 429.
Archseopteryx, 18.
Archegosaurus, 19.
Arches, cranial, 5, 95, 227.

visceral, 5.
Argeriosus (a Teleostean Fish), skull

of, 128.

Arm and leg compared, 232.
Arm, muscles of, 327, 328, 330, 333 —
335-

nerves of, 401.
Armadillo, 17, 240, 241.

glands of, 437.

larynx of, 474.

limb-bones of, 155, 156, 164* 173,
175, 189, 197, 200, 208.

muscles of, 339, 356.

skull of, 118.

spine of, 43, 50, 51, 57, 60, 65,
70, 71

INDEX.

5°'

Armadillo, teeth of 260, 274.
Arm-bones, 145.
Armpit glands, 488.
Arterial blood, 427.

system, 412.

Arteries, 406, 411 — 414, 416.
Artery (carotid), groove for, 82.

pulmonary, 468.
Articular bone, 98, 103, 104, 120, 121,

134, 227.
Articular process, inferior, 28.

superior, 28.
Articulare, 396.
Artiodactyla, 16.

Arytenoid cartilage, 472, 473, 475.
Ascending colon, 442.

cornu, 374.

ramus, 86, 114.

ramus of ischium, 179, 180.
Ascidians, 7, 12.
Astragalo-calcaneum, 205, 213.
Astragalus, 184, 185, 200, 204, 205, 206,

209, 210, 211.

Asymmetry of eyes, 389.
Ateles, 15.

larynx of, 474.

spine of, 50.

Atherina (a Teleostean Fish), 456.
Atlas vertebra, 30, 52, 217.
Attachment of teeth, 256.
Attolens auriculam muscle, 283, 284.
Auditory capsules, 93, 94.

meatus, 75, So.

nerve, 368, 392, 396.

organ, 392.

ossicles, 122, 393 — 395.
Auk, Great, 18.

spine of, 47.

Auricles, 407 — 410, 424, 462.
Auricular muscles, 308.

surface, 179.
Australian Rat, 16.
Austrian caves, 19.
Aves, 14, 15, 18.
Axial muscles, 362.
Axial skeleton, 25.

compared with appendicular, 234.
Axillary artery. 412, 413.

border of scapula, 146.
Axis vertebra, 29, 54.
Axolotl (a Urodcle Batrachian), gills
of, 479.

limb-bones of, 208.

muscles of, 337.

spine of, 39. 41, 70, 216.
Aye-aye, 15.

limb-bones of, 173 — 175.

muscles of, 349.

teeth of, 258.

Azygos uvulae muscle, 289.
Azygosvein, 423, 431.

B.

Baboons, limb-bones of, 156, 168.

mouth of, 436.

skull of, 107, 113, 135.

spine of, 53, 57, 61.
Babyrussa, skull of, 99.

teeth of, 262.

Back, muscles of, 289, 290, 319.
Backbone, 25, 215.

curves of, 33.
Badger, 16.

skull of, 102, 113.

teeth of, 267, 269.
Bagrus, 20.

skull of, 96.

spine of, 47, 48, 53.

swim-bladder of, 466.
Balsena (Whale), limb-bones of, 190,
199, 202, 203.

spine of, 49.
Balaenoptera, 199.
Baleen, 247, 249.
Balistes, 20.

Ball and socket joints, 24.
Band of a tooth, 264.
Bandicoots, 17.

limb-bones of, 176.
Barbary Ape, 15.
Barbs, feathers of, 244.
Barbules, 244.

Basi-branchials, 126, 477, 478.
Basi cranial axis, 91, 135, 136.

plate, 94.

Basi-facial, 91, 135, 136.
Basi-hyal, 87, 227, 396.
Basi-occipital, 97, 104, 119, 130, 227.
Basi-occipital tooth, 255.
Basi-sphenoid, 108, in, 227.
Basilar artery, 413.

part of occipitalj 78, 79.

region, 77.
Basilisk, spine of, 41.
Basket of Lamprey, 72, 143, 224, 476.
tat, 15.

brain of, 379.

circulation of, 426.

cutaneous glands of, 487.

ear of, 396.

exo-skeleton of, 245.

intestine of, 446.

limb-bones of, 163, 164, 166 — 168,
170, 174, 175, 188, 190, 192, 196

— 198, 2O2, 2O7, 211, 212, 232.

muscles of, 320, 321, 332, 337, 339,
340. 343. 345, 348> 349. 356, 359,
362.

nasal organs of, 380.

skin of, 237.

skull of, 115.

spine of, 38, 47, 51, 57, 59, 61, 65.

stomach of, 445.

502

INDEX.

Bat, teeth of, 265.
Batrachia, 15, 18.
Batrachians, brain of, 383.

circulation of, 426, 427, 429.

cutaneous glands of, 488.

ear of, 394.

exo skeleton of, 243.

gills of, 479.

heart of, 409.

limb-bones of, 158, 161, 164, 165,
168 — 170, 189, 199, 207.

lymphatics of, 432.

muscles of, 312, 314, 317, 318, 319,
322, 323, 337, 359, 360.

nerves of, 401.

pancreas of, 450.

peritoneum of, 458.

respiration of, 467.

skin of, 238.

skull of, 97, 99, 105, 108—110, 113,
115—118, 120, 124, 135— 137, 139.

spine of, 47, 52, 56, 58, 60, 61, 64,
66, 69-71.

supra-renal capsules of, 483.

teeth of, 275.

their differences from man, 491.

thyroid gland of, 484.

tongue of, 440.
Batrachus (a Teleostean Fish), spine

of, 70.

Bats, Blood-sucking, 16, 259.
Bat's wing, circulation of, 428.
Bdellostoma, gills of, 476.
Beak, 247.

Beaks of Fishes, 273.
Bear, 16.

larynx of, 474.

limb-bones of, 172, 176.

muscles of, 349.

spine of, 57.
Beard, 243.
Beasts, skin of, 238.

spine of, 63.
Beaver, 16.

limb-bones of, 164

muscles of, 357.

pancreas of, 449.

stomach of, 445.

teeth of, 275.

Biceps muscle, 147, 293, 294, 309, 313,
315, 316, 320, 325, 327, 329, 333

f —335-

lemons muscle, 301, 303, 304, 341,
344—346» 347. 348, 350, 354.
35 ^

Bicipital groove, 147, 164, 165.
Bi-convex vertebrae, 40.
Bicuspids, 253.
Bilateral symmetry, 2.
Bile duct, 449, 451.
Bimeria, 7.
Bipes, 1 88.

Birds, alimentary canal of, 442, 447, 448.

brain of, 378, 382, 383.

bronchi of, 471.

circulation of, 419, 420, 426.

cutaneous glands of, 487.

ear of, 394.

exo-skeleton of, 245.

eye of, 388, 389.

eyelids of, 312.

glands of, 438.

heart of, 409 — 411.

larynx of, 475.

limb-bones of, 153, 155, 158, 159,
161, 162, 164, 166 — 168, 170 — 175,
188 — 190, 192, 193, 195 — 198, 200

2O3, 2O(5 — 2IO, 212, 213.

liver of, 454, 456.

lungs of, 464, 465, 471.

lymphatics of, 432.

mouth of, 435.

muscles of, 312-314, 317— 319,324,

326, 328, 329, 331, 332, 335, 341,

342. 345, 349> 351, 356, 358> 359.

362.

nerves of, 401, 402.
pancreas of, 449.
peritoneum of, 458, 459.
respiration of, 466.
skin of, 238.
skull of, 98, 99, 101, 103, 105, 108

— 112, 113, 115, 117, 1 1 8, 120,

121, 124, 127, 130, 131, 133—137.

139, 140, 141, 144.

spinal marrow of, 386.

spine of, 37, 39, 46, 48, 50— 53,
56, 57. 59, 63—66, 68, 70, 71.

stomach of, 443, 444.

supra-renal capsules of, 483.

their differences from man, 492.

thorax of, 222.

thyroid gland of, 484.

trachea of, 468, 469.

urinary organs of, 482.
Bladder. 453, 480, 482.
Blood, circulation of, 427.
Blood-sucking Bats, 16, 259.
Boa Constrictor, limb-bones of, 189,

193, 195, 196, 198, 199, 202, 203.

spine of, 72.
Body of a vertebra, 26, 226.

of hyoid, 75, 87, 124, 126.

of ischium, 179.

of pubis, 179.

of sphenoid, 82, 91.
Body-cavity, 4.
Bombardier Beetle, 14.
Bones, 22.

of toes, 212.

Bonnet Monkey, muscles of, 327.
Bony horns of Ungulates, 278.
Bony Pike (a Ganoid Fish), exo-skele-
ton of, 241. 277.

INDEX.

5°3

Bony scutes, 239.

Booby (a Carinate Bird), skull of, 137.
Box Tortoises, exo-skeleton of, 241.
Brachial artery, 413, 421.

plexus, 400, 401.
Brachialis anticus muscle, 293, 294,

296, 313, 320, 324, 327, 328.
Bracmals, 162.
Bradypus, 17.

limb-bones of, 208 — 210.

muscles of, 333.

trachea of, 469.
Brain, 4.

as a whole, 384.

base of, 368.

development of, 374, 376.

inferior surface of, 367, 368.

lymphatics of, 432.

membranes of, 365.

of man, 366.

sections of, 371—374-

size of, 378.

upper surface of, 366.
Branches of spinal nerve, 399, 403.
Branchiae, 461.

Branchial arches, 124. — 126, 222, 225,
226, 255, 397, 429, 476—478, 480.

arteries, 416, 417, 421, 423, 479.

veins, 416, 417, 479.
Branching of antlers, 278.
Branchiostegal rays, 126, 478.
Breast, 489.
Breastbone, 34.

Bronchi, 407, 463, 467, 469, 470.
Bufo Calamita, cutaneous glands of,

488.

Bufo (Toad), limb-bones of, 203, 208.
Buccal glands, 437.
Buccinator muscle, 283, 284, 288.
Bulbus aortae, 398, 410, 417, 428.

arteriosus, 418, 427.
Bull Frog, nerves of, 391.
Bulla, 106. _
Bursa fabricii, 487.
Bustard, 198.

Cabasson (an Armadillo), 208.

Cachalot, skull of, 122, 128.

Caeca, 447.

Caecum, 442, 446 — 448.

Calcaneum, 184-186, 200, 204, 206,
209 — 211, 213.

Calf, thymus gland of, 485.

Callichthys (a Teleostean Fish), swim-
bladder of, 466.

Callophis (a Serpent), glands of, 438.

Callosities, 239.

of Camels, 239.
of Horse, 239.

Callosities of Monkeys, 240.
Calotes (a Lizard), viscera of, 453.
Calvarium, 74.
Calyptorhynchus (a Carinate Bird),

skull of, 133, 139.
Camels, 17.

bronchi of, 469.

callosities of, 239.

cutaneous glands of, 486.

limb- bones of, 166.

liver of, 455, 456.

mouth of, 435, 436.

muscles of. 340, 342.

spine of, 50.

teeth of, 263, 268.
Canal is centralis, 386.
Canine fossa, 84.
Canines, 251, 253, 261.
Cannon-bone, 200.

Cantharis (a Teleostean Fish), swim-
bladder of, 466.
Cape Ant-eater, 17.

limb-bones of, 192, 200, 201.

muscles of, 356.

teeth of, 276.
Cape Mole, skull of, 129.
Capillaries, 406.

Capitellum of humerus, 147, 148, 164.
Capitular process, 28, 216, 223, 224.
Capromys (a Rodent), liver of, 455.
Capsular ligament of hip-joint, 182.

of humerus, 148.
Capsules, supra-renal, 483.
Capybara, 16.

skull of, 99, 132.
Carapace, 44, 239.

exo-skeleton of, 241, 242.
Carcharias, 20.
Cardiac caecum, 445.

end of stomach, 442, 444, 445, 448,
450.

plexus, 403.

Cardinal veins, 423, 425, 426.
Carinatae, 18.
Carnassial teeth, 266.
Carnivora, 16.

cutaneous glands of, 487.

limb-bones of, 160, 169, 170, 196.

mammary glands of, 490.

muscles of, 318.

skull of, 100, 102, 128.

spine of, 57, 68.
Carnivorous dentition, 266.
Carotid artery, 415, 417 — 421.

canal, 80, 88, 105.
Carp, 20.

alimentary canal of, 446.

circulation of, 421.

ear of, 394.

gills of, 477.

liver of, 454.

mouth of, 435.

504 INDEX.

Carp, muscles of, 311.

nerves of, 402.

skull of, 109, no, 112, 136.

spine of, 38, 47, 63, 72.

swim-bladder of, 465, 466.

teeth of, 255.
Carpal bones, 175.

extra, 172.
Carpus, 145, 151, 168.

compared with tarsus, 233.

distal bones of, 170.

proximal bones of, 169.
Cartilages, costal, 35.
Cartilaginous arcs of Sharks, 73, 144.

basket of Lamprey, 72, 143, 224.
Cassowary, 18.

limb-bones of, 160.

skull of, 141.

spine of, 66.
Casting of skin, 238.
Categories of vertebrae, 26.
Cat, exo-skeleton of, 245.

limb-bones of, 176, 201, 213.

mouth of, 435.

muscles of, 333.

skull of, 112.

teeth of, 260, 264, 266, 269.

tongue of, 440.
Cattle, dewlap of, 237.
Cauda equina, 385, 386.
Caudal muscles, 323.

fin-muscles, 363.

vertebrae, 59, 60, 189.
Caudate lobe of liver, 452, 454, 455.
Cavities of skull, 92.
Cement, 249, 250, 274.
Centetes, 16.

mammary glands of, 489.

skull of, 103, 109, 116, 128, 133,
142.

teeth of, 266.
Centipede, 1 1.
Central ligament, 386

parts, 223.
skeleton, 23.
Centrale, 168—170.
Centres, nervous, 4.
Centrum of a vertebra, 26, 215.
Cephalo-humeral muscle, 312.
Cerato-branchials, 126, 227, 477, 478.
Ceratodus, 20, 257.
arteries of, 416.
excretory organs of, 483.
limb-bones of, 163, 195.
swim-bladder of, 465.
Cerato-hyal, 87, 123, 126, 227, 396
Cerato-hyoideus muscle. 311, 315 316.
Cerato-mandibular muscle, 313
Ceratophrys, 19.

exo-skeleton of, 241.
Cercolabes (a Rodent), limb-bones of,
206.

Cerebellum, 367, 368, 371-3.73. 377.

379, 382-385, 390, 400.
Cerebral hemispheres, 378, 382 — 384,

39°-

nerves, 390.

Cerebrum, 370, 371, 374, 377—400.
Cervical enlargement, 386.

vertebra, 28.

vertebrae, 26, 47, 216.
Cervicalis ascendens muscle, 291. .-(13,

323-

Cestracion, 20, 269.
Cetacea, 16.

bronchi of, 469.

circulation of, 421, 425, 426.

liver of, 456.

lungs of, 464.

mammary glands of, 489, 490.

muscles of, 309, 319, 323, 324, 326,

328, 339. 34°. 363-
urinary organs of, 483.
Cetaceans, brain of, 378—380, 386, 388.
limb-bones of, 152, 160, 164, 166,
168, 170, 175, 1 88 — 190, 192, 196,
199, 207.

mouth of, 436, 437.
skull of, 98 — 101, 113, 114, 122, 129,

I3Q» !33. MO-
spine of, 39, 50, 51, 54, 62, 65, 71,

224.

thyroid gland of, 484.
Chacma Baboon, 135.
Chalk, 8.
Chameleons, 18.

changes of colour, 487.
cutaneous glands of, 487.
exo-skeleton of, 245.
limb-bones of, 169, 170, 172, 174,

191, 194, 207 — 210, 23 \.
liver of, 454.
lungs of, 471.

muscles of, 317, 321—323, 325—
327. 331— 337, 339. 341- 344. 346,
349. 351— 354. 356—362.
spine of, 46, 64, 65, 71, u?, 114,

116, 124.
tongue of, 440.

Chamois, cutaneous glands of, 4?6.
Cheek, 435, 436.

pouches, 436.
Cheirogaleus (a Lemuroid Primate),

limb-bones of, 204.
Cheiromeles (a Rat), cutaneous glands

of, 487.
Cheiromys, 15.

cutaneous glands of, 487.
mammary glands of, 489.
skull of, 115, 233.
teeth of, 258.
Cheiroptera, 15.
Chelonia, 19.

thyroid gland of, 485.

INDEX.

505

Chelonians, alimentary canal of, 442.

exo-skeleton of, 241.

heart of, 409, 411.

limb-bones of, 161, 162, 167, 168,
170, 172.

lungs of, 464, 465.

muscles of, 316, 317, 319, 321, 361,
362.

respiration of, 467.

skull of, 106, 109, nr, 116, 117,
120, 133, 136, 140.

spine of, 40, 52, 54, 64, 67, 68, 217,
219.

trachea of, 469,

urinary organs of, 482.
Chelydra (a Chelonian), 168, 172, 207.
Chelys(a Chelonian), skull of, 128.
Chemical composition of man's body,

2, 9.
Chetodon (a Teleostean Fish), teeth

of, 269.

Chevron bones, 60, 220, 226
Chiasma of optic nerves, 285, 387, 389.
Chick, thymus gland of, 485.
Chimaera, 20.

limb-bones of, 191.
Chimpanzee, 15.

larynx of, 474.

limb-bones of, 156, 157.

skull of, 132.

tongue of, 441.
Chin, 86.
Chironectes, 20
Chirotes, 18.

Chlamydophorus (an Armadillo), exo-
skeleton of, 241.

spine of, 60.
Chlamydosaurus, 18.
Chceropus, 17.

limb-bones cf, 171, 173, 174, 210

— 212.
Choloepus, 17.

limb-bones of, 173.

liver of, 455.

spine of, 47.
Chorda dorsalis, 5, 36, 37.

tympani, 397.

tympani nerve, 80.
Chordse tendineae, 408.
Choroid plexus, 377.
Chromatophores, 487.
Chrysochloris, 16.

skull of, 129.

teeth of, 266, 268, 269.
Chrysothrix, 15.

skull of, 132, 137, 138.
Ciconia (a Carinate Bird), spine of, 43.
Cingulum, 264, 267.
Circulating system, 406
Circulation of blood, 427.

in gills, 479.

in infant, 424.

Circulation in liver, 451.

portal, 4, 12.
Circumduction, 282.
Circumflexus palati, 289.
Circumvallate papillae, 440, 441.
Cirri, 435.
Civet Cats, 16.
Class, 5.
Classification, 5.

of Man, 496.

of muscles, 282.
Clavicle, 145, 147, 153, 155—157. i59~

162, 230.

Clavicular scutes, 240.
Claws, 245.
Clefts, visceral, 5.
Climbing Perch, gills of, 480.
Clinoid plate, 82.

processes, 81, 83, 109.
Cloaca, 447, 481.
Cloacae, os, 195.
Coati, muscles of, 346.
Coatimondi, 16.
Cobitis (a Teleostean Fish), spine of,

swim-bladder of, 466.

urinary organs of, 482.
C -bras, 19.

spine of, 68.
Coccygeal region, 58.

vein, 432.

Coccygeus muscle, 342.
Coccyx, 33, 180.
Cochlea, 392, 393, 395.
Cod, brain of, 386.

ear of, 395, 396.

gills of, 477.

limb-bones of, 152, 162, 194.

liver of, 454.

skull of, 101, 106, 113, 126.

swim-bladder of, 466.
Coelenterata, 7.
Coeliacaxis, 451.

axis artery, 398, 414, 421, 428.
Collar-bone, see Clavicle.
Colon, 442, 446, 459.
Coluber, 19.

Colubrine Snakes, spine of, 46.
Columella, in, 121.

auris, 392, 395, 396.
Colymbus, the Diver (a Carinate Bird),

2OI.

Comb-like teeth, 275.

Common carotid artery, 411,412.

iliac artery, 414.
Comparison between limb-muscles, 361.

of axial and appendicular skele-
tons, 234.^

of carpus with tarsus, 233.

of digits of hand and foot, 233.

of fingers with toes, 233.

of leg with arm, 233.

5o6

INDEX.

Complexus muscle, 291, 313, 323.
Compound teeth, 276.
Compressor naris. muscle, 284.
Compsognathus, 19.
Concha, 393.
Condyle of a bone, 24.

of lower jaw, 75, 86, 114.
Condyles of femur, 181, 182.

of humerus, 147, 148, 164.

of skull, 74—76, 78, 88, 91, 98,
114, 117, 129.

of tibia, 183.
Condyloid foramen, 78, 108, 132.

ridges of humerus, 147.
Conger Eel, brain of, 383.

spine of, 41.
Conical papillae, 440.
Conjunctiva, 387, 388.
Connexion of skull-bones, 127.
Constrictor arcuum muscle, 310, 311,
316.

faucium muscle, 310, 311.

pharyngis, 316.
Constrictors of pharynx, 288.
Contractility of veins, 426.
Convolutions of brain, 366, 370, 378.
Cook's Phalanger, limb-bones of, 202.
Coraco-brachialis muscle, 292, 293, 315,

324» 327. 329-
Coracoid, 146, 153, 155—158, 160 — 162,

194.

Coraco-scapular foramen, 157.
Cord, spinal, 25.
Cordifonn foramen, 192.
Corinne Antelope, cutaneous glands of,

487.
Cormorant, spine of, 47.

stomach of, 443.
Corniculum of hyoid, 73, 87, 123 — 125,

225, 220, 396.

Corns, 239.

Cornu of hyoid, 75, 87, 123, 226, 229.
Cornua of ventricles, 377, 379.
Coronal section, 92.

suture, 77.
Coronary veins, 410.
Coronoid, 75, 86, 114, 120, 121, 122.

fossa of humerus, 147, 148.

process of ulna, 149, 150, 165.
Corpora mammillaria, 368, 369, 371,

374, 377. 378, 382.
quadngemina, 371, 372, 377, 378,

382, 390.

restiformia, 382, 384.
trapezoidea, 384.
Corpus callosum, 367, 368, 371, 373 —

375, 379-
striatum, 373, 374, 390.

Corrugator supercilii muscle, 284.
Corvina (a Teleostean Fish), swim-
bladder of, 466.
Costa of rib, 35.

Costal cartilages, 35.

Costo-coracoid ligament, 325, 329.

Cottus (a Teleostean Fish), 162.

Cotyloid cavity, 180.

Cow, external skeleton of, 247.

Coypu Rat, mammary glands of, 489.

Crabs, 7.

Crane,, trachea of, 469.

Cranial arches, 5, 95, 227.

cavity, length of, 92, 135.

characters generalized, 228.
Crest of ilium, 178, 179.

of tibia, 183, 184, 201.
Cribriform plate, 83, 90, 101, 112.
Crickets, 13.

Cricoid cartilage, 471, 474, 475.
Crista galli, 83, 90, 91, 112.
Crocidura (a Shrew), skull of, 115.
Crocodiles, 18.

brain of, 383.

bronchi of, 470.

circulation of, 418, 427.

cutaneous glands of, 487.

ear of, 396.

exo-skeleton of, 241.

heart of, 409, 410.

larynx of, 475.

limb-bones of, 161, 169, 170, 171,
190, 195, 197, 204, 206, 207.

liver of, 454.

lungs of, 465.

lymphatics of, 432.

mouth of, 436, 437.

muscles of, 309, 312, 349.

nerves of, 402.

skull of, 104, 105, 109, in — 114,
161, 118—120,124, 130, 131, 133,
*36, 139—141.

spine of, 39, 47, 49, 51, 53, 54, 56,
58, 63—65, 68, 69, 71, 215, 219.

teeth of, 269.

tongue of, 440.

trachea of, 469.
Crop, 442, 443, 447, 490.

of Pigeon, 490.
Crotalus, 19.

cutaneous glands of, 487.

larynx of, 475.

skull of, 104.

spine of, 46, 50.
Crown of tooth, 249, 250.
Crucial ligaments, 183, 202.
Crura cerebri, 368, 377.
Crura of fornix, 373.
Crural nerve, 402.

vein, 432.

Crureus muscle, 303, 344.
Cryptobranchus (a Urodele Batra-
chian), circulation of, 418.

spine of, 58.
Crystalline lens, 388.
Ctenoid scales, 278.

INDEX.

507

Cuboides, 184 — 186, 200, 204, 205, 208,

2IO, 211, 213.

Cuneiform bones of foot, 184 — 186, 209.

cartilages, 474.
Cuneiforme of hand, 150, 151, 157, 167,

168, 170, 171, 173, 176.
Curvature of backbone, 33.
Curved lines of occiput, 76, 78.
Cutaneous glands, 485.

nerve, 400.

Cutting of teeth, 250, 251.
Cuttle Fishes, 6.
Cyclodus, 18.

exo-skeleton of, 241.

limb-bones of, 161, 162, 197.

skull of, 103.
Cycloid scales, 278.
Cyclothurus (an Ant-eater), alimentary
canal of, 448.

muscles of, 356.
Cylinders of body, 3.
Cynocephalus, 15.

larynx of, 474.

spine of, 61.

Cyprinus (Carp), swim-bladder of, 466.
Cystic duct, 452.

fissure, 454.
Cystophora (a Seal), skull of, 112.

D.

Dactylethra, 19.

limb-bones of, 152, 754.
Dasypus, 17.

alimentary canal of, 448.

limb-bones of, 175.

muscles of, 332 — 334.
Dasyures, 17.
Deep flexors of arm, 296.

of leg, 306.

Deep muscles of head, 284.
Deer, 17.

antlers of, 279, ?8o.

cutaneous glands of, 486, 487.

horns of, 282.

limb-bones of, 156, 157, 164, 172,
207, 209, 210.

skull of, 102, 118, 135.

teeth of, 261.
Deer, Musk, 17.
Definitions of teeth, 253.
Delphinus, 129.

Deltoid muscle, 290, 291, 293, 310, 311,
313, 316, 326—328.

ridge, 165.
Density of skin, 238.
Dental formula, 253.

sacs, 249

structure, 273.
Dentary bone, 98, 103, 104, 120, 121,

134, 227.
Denticles, 276,

Dentine, 249, 250, 274.
Dentition of Man, 251.

typical, 259, 262, 266.
Depressor ala; nasi muscle, 284.

anguli oris muscle, 283, 284.

labii inferioris muscle, 284.

mandibulae muscle, 313.
Depressors (muscles), 282.
Dermal appendages, 236.

structures, 238.
Dermis, 237, 240, 486.
Descending aorta, 412, 414.

colon, 442.

cornu, 373.

palatine artery, 413.
Desman, cutaneous glands of, 487.
Desmodus (a Bat), 16.

stomach of, 445.

teeth of, 259, 263.
Desmognathus ^a Urodele Batrachian),

skull of, 123.
Development of alimentary system,

459-

of antlers, 279.

of arteries, 415.

of brain, 374, 376.

of dorsal muscles, 364.

of ear, 392.

of eye, 387.

of heart, 409

of lungs, 463.

of nerves, 404.

of peritoneum, 457.

of skull, 93, 142.

of spinal skeleton, 35, 72, 218, 221.

of teeth, 250, 254.

of veins, 423.

of vertebral column, 35.
Dewlap, 237.
Diaphragm, 299, 339, 468.
Diapophyses, 216, 219, 224, 226.
Diastema, 258.
Dicynodon, 19.

teeth of, 276.
Dicynodontia, 19.
Didelphia, 17.
Didelphous Mammals, 17

teeth of, 264.
Didelphys, mammary glands of, 489.

pouch of, 489.
Digastric muscle, 283, 286, 287, 310,

311, 313, 316.
Digits, 152, 174.

of foot and hand compared, 233.
Dinornis, 18.
Dinotherium, 16, 261.
Diodon (a Teleostean Fish), 237.

spinal marrow of, 386.
Dipus, 16.
Distal carpals, 170.

phalanx of hallux, 185.

tarsals, 184, 207.

5o8 INDEX.

Diver, limb-bones of, 201.
Divisions of animal kingdom, 5.
Dodo, 18.
Dog, glands of, 437.

larynx of, 474.

limb-bones of, 154, 156, 157, 164 —
167, 170, 174, 192, 194, 211, 212.

muscles of, 313, 317, 333, 336,
337, 349-

pancreas of, 449.

skull of, 106, 107, no, 112, 119,

122, 123, 131, 138.

spine of, 51, 55, 62, 64.
teeth of, 260, 263, 267, 269.
tongue of, 440.
Dolichotis, 16.

skull of, 118, 120.
Dolphins, 16.

exo-skeleton of, 256, 257.

kidney of, 483.

limb-bones of, 155 — 157, 163, 166,

171.

liver of, 455, 456.
mouth of, 435.
muscles of, 316, 317, 339.
skull of, 117, 118, 120, 122, 129,

J37, J39, I4°, J42-
spine of, 44, 45, 47, 53, 55, 62.
spleen of, 484.
teeth of, 258, 272.
tongue of, 440.

Dorking Fowl, limb-bones of, 205.
Dormouse, alimentary canal of, 443.
Dorsal fin, 278.

muscles of, 363.

Dorsal glands, 487, 488.

laminae, 36, 218.

vertebra, 27, 42.

vertebrae, 26, 42, 52, 59, 60, 189.
Dorso-epitrochlear muscle, 328.
Dory 162.

mouth of, 435.
Double eye, 389.
Draco, 18.

spine of, 66, 69.
Dragon, Flying, spine of, 68.
Drum of ear, 393, 395.
Duck-billed Platypus, 18, 247.

spine of, 53, 54.
Ducks, web of, 236.
Duct of liver, 452.
of pancreas, 449.
of parotid gland, 284.
Ductus arteriosus, 415, 420, 424.
Botalli, 417, 419, 420.
communis choledochus, 452.
Cuvieri, 423, 425.
pneumaticus, 465.
venosus, 424, 425, 451, 452, 454
Dugong, 16.

alimentary canal of, 443.
bronchi of, 469.

Dugong, circulation of, 420.

exo-skeleton of, 247.

heart of, 411.

skull of, 122.

spine of, 64.

stomach of, 444, 445.
Duodenum, 442, 443, 446 449 484.
Dura mater, 365, 366.

E.

Eagle, limb-bones of, 163, 166, 167,212.

muscles of, 320, 326, 341, 357.
Ear, 392.

development of, 392.

drum of, 393.

external, 396.
Earthworms, 7.
Echidna, 18.

circulation of, 421.

cutaneous glands of, 487.

ear of, 394.

glands of, 437.

limb-bones of, 164, 194, 154 — 157,
203—207, 230.

mammary glands of, 489.

mouth of, 436.

muscles of, 308, 314, 321, 326—

.328, 331, 332, 336, 341, 342, 351,

353, 357. 36i.

skull of, 102, loo, i

120, 137.

spine of, 48, 49.

spleen of, 484.

teeth of, 254.

tongue of, 441.
Ecteron, 237, 238.
Ecto-cune. forme, 185, 186, 205, 208,

209, 211, 213.

Ecto-pterygoid, 103, 131, 227.
Edentata, 17.
Edentates, limb-bones of, 176, 213.

spine of, 45, 57,

teeth of, 272.
Eels, 20.

brain of, 378.

circulation of, 426.

mucus of, 488.

peritoneum of, 458.
Efts, 19.

exo-skeleton of, 245.

limb-bones of, 158.

skin of, 238.

skull of, 104, 123.

teeth of, 269.
Eighth nerve, 397, 399.
Klasmobranchii, 20.
Elasmobranchs, brain of, 383.

heart of, 410.

respiration of, 478.

10—113, 115,

INDEX.

5°9

Elasmobranchs, spine of, 38 — 40.
Elbow-joint, 232.
Electric Eel, nerves of, 405.
Electric organs, 405.
Elephant, 16.

cutaneous glands of, 486.

limb-bones of, 155, 166, 189, 197.

liver of, 456.

lungs of, 464.

mammary glands of, 489, 490.

mouth of, 435.

muscles of, 309.

nasal organs of, 380.

peritoneum of, 459.

skull of, 98, 113, 117, 122, 128, 129,
132, 140 — 142.

spine of, 43.

teeth of, 261, 263, 269, 274.

tongue of, 441.
Elevators (muscles), 282.
Elk, limb-bones of, 202.
Emballonura (a Bat), cutaneous glands

of, 487.

Embryonic heart, 409.
Emeu, 18.

limb-bones of, 160, 205, 210.

trachea of, 469.
Emys, 19.

limb-bones of, 169.

muscles of, 317, 321, 323.

shell of, 239, 240.
Enamel, 249, 250, 274.
Kncoubert an Armadillo), 208.
Enderon, 237, 238.
Enderonic calcifications, 276.
Kudo-skeletal muscles, 282.
Endo-skeleton, 23, 214, 236.
Enhydra, 16.

Ento-cuneiforme, 185, 186, 208, 210.
Ento-pterygoid, 131, 227.
Entozoa, 7.
Epaxial arches, 219, 221.

cartilages, 218.

muscles, 362.

parts, 223, 226.
Ependema, 366.
Ephippifer, 19.

exo-skeleton of, 241.
Ephippus (a Teleostean Fish), spine

of, 53.

Epibranchials, 126, 227, 477, 478.
Epicoraco-humeral muscle, 313.
Epicoracoid, 153, 155, 160.
Epidermal appendages, 244.
Epidermis, 237, 238, 486.
Epiglottis, 434, 470, 474.
Epihyal, 123, 227.
Epiotic, 81, 103, 106, 227.
Epiphyses, 23.
Episternal granules, 66.
Epithelial tooth-like structures, 276.
Epithelium, 237, 238, 247.

Erector spinas muscles, 290, 318, 322.
Erythrinus (a Teleostean Fish), swim-
bladder of, 465.
Ethmoid, 76, 79, 83, 91, 93, 94, 104,

in, 117, 129,134.
Ethmo-vomenne plate, 93, 94, 143.
Eustachian tube, 80, 88, 89, 119, 131,

393. 394, 434—436.
valve, 401.

Excretory organs, 461.
Exoccipital, 98, 100, 108, 130, 227.
Exo-skeletal muscles, 282.

parts, 236.

Exo-skeleton, 23, 214, 236.
Expanded neural spines, 239, 242.

ribs, 239, 242.
Extension, 361.
Extensor brevis muscle, 316.

brevis digitorum pedis muscle,

304,318, 347, 348, 351.
carpi radialis muscle, 294 — 296,

32°, 333-

carpi ulnaris muscle, 296, 297, 335.
communis digitorum muscle, 296,

indicis muscle, 297, 336.

longus muscle, 310, 316, 322, 328.

longus digitorum pedis muscle,

303—305, 346—348, 35i, 352,

357,.36p.. .

minimi digiti muscle, 296, 334.
muscles of fore-arm, 296.
ossis metacarpi pollicis muscle, 296,

297, 325, 334, 335-
pnmi internodii polhcis muscle,

.296, 297, 336, 361.
proprius digiti minimi muscle, 296,

328.
proprius hallucis muscle, 303, 305,

322,348, 35L352, 357-
radialis muscle, 294—296, 320, 333

secundi internodii pollicis muscle.
296, 336.

ulnaris muscle, 335.
Extensores metacarporum muscles,
334, 335-

metatarsorum muscles, 345, 360.

phalangorum muscles, 334, 360.
Extensors (muscles), 282.

of thigh, 322, 348.
External angular process, 79.

branchiae, 479.

carotid artery, 411, 413.

carpal ossicle, 172.

condyle of femur, 181, 182, 198.

condyle of humerus, 164, 165.

ear, 396.

iliac, 412.

lateral ligament of knee-joint, 183.

lateral ligaments, 284, 304, 306.

malleolus, 183, 184, 203.

INDEX.

External oblique muscle, 290, 292, 297,
299, 310, 311, 315, 3i6, 322, 337,

tendon of, 194.

rectus muscle, 285.

skeleton, 23, 236.

surface of skull, 128.

tooth-like structures, 277.

tuberosity of femur, 181, 182.

tuberosity of tibia, 183.
Eye, 387, 388.
Eyeball, muscles of, 285.

shape of, 389.
Eyebrows, 243.
Eyelashes, 243.
Eyelids, 387-389-
Eye-muscles, nerves of, 390.
Eye-tooth, 251.

F.

Face, skeleton of, 74.

Facial nerve, 80, 396, 397, 400.

Falciform ligament, 451, 459.

False vertebrae, 26.

Falx, 90, 100, 136, 366.

Family, 6.

Fangs of Serpents, 270, 271.

of teeth, 249—251.
Feathers, 243, 244.
Feeding of Whales, 248.
Feelers of Cat, 243.
Femoral artery, 412—421.

glands, 488.

pores, 488.
Femoro-caudal muscle, 318, 322, 338,

341. 344, 346—348-
Femur, 177, 181, 187, 190, 193, 195,

196, 198, 199 — 201, 203, 209, 231.
Fenestra ovalis, 81, 227, 392, 393.

rotunda, 81, 227, 392, 393.
Fibrochondrosteal apparatus, 22.
Fibrous tissue, 22.
Fibula, 177, 183, 184, 187, 201 — 203,

209, 210, 213.
Fieldfare, muscles of, 314.
Fifth digit, 152.

nerve, 82, 105, no, 391, 397-399-
428

ventricle, 373, 374.
Filamentary appendages, 237.
File-fishes, 20.
Fin, dorsal, 278.
Fin-muscles, 319, 363.
Fin-rays, 174, 278.
Fin-Whale, spine of, 53.
Finches, skull of, no.
Fingers, bones of, 145, 151.
First rib, 70.
Fishes, 15, 19.

alimentary canal of, 442, 446. 447,
460.

Fishes, arteries of, 416.

beaks of, 273.

brain of, 379, 382, 383.

breathing organs of, 462.

caeca of, 450.

circulation of, 419,421, 426 — 429.

ear of, 394.

eyes of, 388, 389.

heart of, 410.

limb-bones of, 162, 163, i65, 168,
174, 188, 193, 194.

liver of, 454, 456.

lymphatics of, 432.

mouth of, 435, 437.

mucus of, 488.

muscles of, 314, 316—320, 323—
325. 337. 339- S62, 363-

nasal organs of, 380, 381.

nerves of, 398.

peritoneum of, 458, 459.

scales of, 246, 277.

skin of, 238.

skull of, 97—99, 101, 104, 106, no
— 113, 115 — 117, 119, 120, 126 —
128, 131 — 136, 138, 139.

spine of, 37, 38, 47, 60, 61, 64, 67,
68, 70 — 72.

stomach of, 443, 444.

supra-renal capsules of, 483.

swim-bladder of, 465.

their differences from man, 490.

tongue of, 440.

urinary organs of, 481, 482.
Fishes, osseous, spine of, 59.

Parrot, teeth of, 272.
FissuraGlasseri. 80,413.
Fissures of liver, 452, 454.
Fistularia (aTeleostean Fish), spine of,

Flat Fishes, eyes of, 389.
muscles of, 362.
spine of, 41.
Flesh, 281.
Flexion, 361.
Flexor accessorius muscle, 307, 355,

358, 359, 362.

brevis digitorum muscle, 320, 329.
brevis digitorum pedis muscle,

307, 358, 361.

brevis hallucis muscle, 306—308,
. 359-

brevis manus muscle, 331, 332.
brevis minimi digiti muscle, 297,

336.
brevis minimi digiti pedis muscle,

306, 359.
brevis pollicis muscle, 296, 297,

325, 336.
carpi radians muscle, 294, 295,

329. 333- .
carpi ulnans muscle, 294 — 296,

320, 321, 329—331.

INDEX.

Flexor digitorum pedis muscle, 350.
hallucis muscle, 360.
longus digitorum muscle, 356, 358.
longus digitorum, groove for, 184,
201.

longus digitorum pedis muscle,
305-307, 345, 346, 354, 355-

longus hallucis muscle, 306, 307,
356, 358.

longus muscle, 315, 329.

longus pollicis muscle, 295, 296,
325, 33o—332» 361-

longus pollicis pedis, groove for,
185..

minimi digiti muscle, 355

muscles of arm, 294, 296.

perfo rans muscle, 295.

pollicis pedis, see Flexor hallucis.

profundus muscle, 295, 296. 320,
330-333- 361-

radians muscle, 325, 334.

sublimis muscle, 294, 295, 330—332.

tendons, 332.

tertius digitorum pedis muscle,
346,354-

ulnans muscle, 325,335
Flexores breves muscles, 337.
Flexors (muscles), 282.
Flexure of limbs, 232.
Floccular process, 105, 138.
Flocculus of cerebellum, 367, 383.
Flounder, skull of, 128.
Flustra, 7.

Flying Dragon, spine of, 68, 69
Flying Fox, 15.

muscles of. 333.

pancreas of, 449.

skull of, 123.
Flying Lemur, to, 16, 260.

limb-bones of, 232

teeth of, 261, 265, 275.
Flying Lizard, 69
Flying Squirrels, 236.

muscles of, 320.
Folds of peritoneum, 458.

of skin, 237.
Fontanelle, 127.

Foot, 177, 200, 203—205, 209 — 211,
213.

digits of, compared vvith those of
hand, 233.

muscles of, 307, 357, 358.
Foramen, anterior palatine, 88.

condyloid, 78, 90, 108, 132.

cordiform, 192.

inferior dental, 86.

infra-orbital, 76, 84, 114.

lachrymal, 92.

lacerum anterius, 87, 88.

lacerum posterius, 88, 90.

magnum, 78, 90.

mental, 86.

Foramen, occipital, 74, 90.

optic, 76, 82, 108.

ovale, 82, 88, 90, 108, 137.

posterior palatine, 88.

rotundum, 82, no, 137.

spheno-palatine, 85.

stylo-mastoid, 80, 88, 105.

vidian, 81.

Foramen of Monro, 371, 372, 374.
Foraminifera, 8.
Fore-arm bones, 145.

muscles of, 294.
Fore-brain, 374, 377.
Formation of eye, 387.

of feathers, 243, 244.

of nail, 244.

of teeth, 249
Forms of teeth, 257.
Formula, dental, 253.
Fornix, 370, 371, 373—375, 377.
Fossa ovalis, 408.
Four-horned Antelope, 246.
Fourth digit, 152.

nerve, 373, 390, 399.

ventricle, 371, 372, 378, 384.
Fowl, limb-bones of, 205.

muscles of, 310.

skull of, 98.

spine of, 67.

stomach of, 444.

viscera of, 44".

Fox, cutareous glands of, 487.
Fracture of femur, 182.
Fraenum, 438, 439.
Freshwater Terrapins, 19.
Freshwater Tortoise, skull of. 44, 239,

240.

Frilled Lizard, 18, 237.
Fringilla (Sparrow), skull of, no.
Frog-fishes, 20.
Frogs, 19

arteries of, 416.

brain of, 383, 384.

circulation of, 417, 427.

ear of 394.

gills of, 479.

heart of, 410.

limb-bones of. 158, 161, 166, 176,
191, 193, 198, 200, 204, 205, 213.

lungs of, 462.

lymphatics of, 432.

muscles of, 311, 312, 314, 327, 343,
358—360, 362.

nerves of, 397, 401-403, 405.

respiration of, 467, 470.

skull of, 99, loo, 104, 108, no,
112, 124, 133, 139—141.

spinal marrow of, 386.

spine of, 38, 52, 53, 59. 63, 65, 67.

thymus gland of, 485.

thyroid gland of, 485.

tongue of, 440.

512

INDEX.

Frogs, trachea of, 468 .
Frontal bone, 75, 76, 79, 91, 98, 100,
lor, 103, 104, 114, 121, 129, 134,
227.

obe of cerebrum, 368.
region, 77.

sinus, 91, 93, 140, 141.
Pronto-parietal, 100.
Fungiform papillae, 440.

G.

Galago, 15.

limb-bones of, 204, 207.

liver of, 456.

mammary glands of, 490.

spine of, 45.
Galeopithecus, 10, 16.

alimentary canal of, 447.

muscles of, 320, 333.

teeth of, 259, 260, 263, 265.
Gall bladder, 447, 451, 452-455i 466-

duct, 459.

Gallinaceous Birds, spine of, 67.
Ganglia o_f nerves, 399.

of spinal nerve, 385.

sympathetic, 403.
Ganoid Fishes, nerves of, 401.

swim-bladder of, 465

spine of, 47, 48, 53

skull of, 96, 99.
Ganoidei, 20.
Gasserian ganglion, 391.
Gastric glands, 433.
Gastrocnemius muscle, 301, 304, 305,

341, 344—347. 350, 352-355-
Gastro-hepatic omentum, 458.
Ga vials, 18.

skull of, 114, 115, 128, 142.
Geckoes, 18.

limb-bones of, 161.

lungs of, 471.

skull of, 101.

spine of, 39.
Geese, web of, 236.
Gelatine, 239.

Gemelli muscles, 301, 302, 342.
Generalised appendicular skeleton, 229.

cranial characters, 228.

conception of nervous system, 404.
Genio-glossus muscle, 286.
Genio-hyoglossus muscle, 287.
Genio-hyoid muscle, 286—288, 311,

3i5, 439-

Genu of corpus callosum, 370.
Genus, 6.
Gibbon, 15.

limb-bones of, 192.

skull of, 122.

spine of, 64.

tongue of, 441.

Gibbon (Siamang), 236.
Gill arches, 124, 476.

artery, 479.

veins, 479.
Gills, 13, 416, 436, 461, 476, 477.479-

circulation in, 479.

skeleton of, 72.
Giraffe, 17.

horns of, 279, 280.

limb-bones of, 155, 167, 200, 209.

liver of, 456.

mouth of, 436.

muscles of, 321.

skull of, 118, 142.

spine of, 47, 48.
Girdle-bone, 100, 108.
Gizzard, 249, 444, 447.
Glands, anal, 487.

cutaneous, 485.

dorsal, 487.

femoral, 488

gastric, 433.

inguinal, 487.

lachrymal, 486.

lymphatic, 430, 431.

mammary, 485.

occipital, 486.

of armpit, 488.

of back, 488.

of scent, 487.

of stomach, 445.

of thigh, 488.

parotid, 488.

sebaceous, 485.

sudoriferous, 485.

sweat, 486.

temporal, 486.

uropygial, 487.

Glasserian fissure, 394, 395, 397.
Glenoid surface of skull, 79, 88.

of scapula, 146, 155-157-
Globigenna, 8.

Globiocephalus (a Cetacean), spine of,
62

limb-bones of, 175.

skull of, n 8.

GlossD-hyal, 124, 227,440.
Glosso-pharyngeal nerve, 88, 368, 397,

399-

Glottis, 468.
Glutei, 348.

Gluteus maximus, 300, 301, 341, 344,
346.

medms muscle, 301, 302, 322, 341.

minimus muscle, 301, 322, 342.

primus, 346.

secundus, 346.

tertius, 346.
Glyptodon, 17.

exp-skeleton of, 241.

spine of, 37,39 52.
Goats, 17.

INDEX.

513

Goats, exo-skeleton of, 245.

horns of, 279.

skull of, 102. 129.

Goat-sucker (a Carinate Bird.'*, limb-
bones of, 213.
Golden Mole, 16.

teeth of, 268.
Gomphosis, 251.

Goniadus (a Shark), teeth of, 269.
Goose, lungs of, 470.

lymphatics of, 432.

muscles of, 310.
Gorilla, 15.

auditory organ of, 396.

larynx of, 474.

limb-bones of, 188, 189, 197, 208.

muscles of, 360.

skull of, 99 — 101, 105, 127 — 129,
i32. '35-

spine of, 50.
Gracilis muscle, 301—303, 322, 338, 345

Grammatophora (a Lizard), 197.
Great Ant-eater, 17.

limb-bones of, 196, 197, 211.

muscles of, 309, 313, 314, 317.

skull of, 113, 118, 122, 130, 131,140.

spine of, 45, 52.
Great aorta, 411.
Great Armadillo, limb-bonesof, 173.175.

spine of, 51, 70.
Great Auk, 18.

spine of, 47.
Great lateral muscle, 363.

lateral muscle of fishes, 319.

omentum, 458.

sacro-sciatic ligament, 180, 189,193.

sciat c nerve, 400.

trochanter, 181, 182, 197, 209.
Greater cornu of hyoid, 75, 87.

ischiatic notch, 180.

sigmoid cavity, 149.

tuberosity, 148, 164, 165, 167.

wing of sphenoid, 75, 76, 82, 83,

90, 94, 109.

Grebe (Duck), 198, 201.
Greenland Whale, 190, i»=-

spine of, 64.
Grinding teeth, 251.
Groove for carotid artery, 82.
Grooves in tibia, 184.

of feather papilla, 243, 244.
Growth of antlers, 280.
Guinea-pig, limb-bones of, 160.

muscles of, 353.

spine of, 71.
Gullet, 434, 441.
Gums, 247.
Gymnophiona 'an Ophiomorphous Ba-

trachian), lungs of, 464.
Gymnura(an Insectivora), teeth of, 264.
Gyri, 366.

H.

Hair, 236, 238, 242.
Halitherium, 16.
Hallux, 187, 205, 212, 213.
Hammer-headed Shark, 20.

brain of, 390.

muscles of, 312.

skull of, 128, 139.

Hamster (a Rodent), lungs of, 464.
Hamular processes, 82.
Hand, bones of, 145.

digits of, compared with those of
foot, 233.

muscles of, 336.

skeleton of, 168.
Hapale, 15.

limb-bones of, 201.

muscles of, 350.
Hard palate, 434, 436
Hare. 16.

alimentary canal of, 447.

limb-bones of, 155, 164, 165, 172,

197, 2OI, 2IO, 212.

muscles of, 310, 351, 352.

skull of, 104, 105, no, 113, 114,
118, 130, 133, 137, 138, 140, 142.

spine of, 42, 52, 53.

tseth of, 259, 263.
Harelip, 115.
Hawk, muscles of, 321.
Head, muscles of, 336.

skeleton of, 74.
Head and neck, muscles of, 283,284,

297» 308.
Head of a bone, 24.

of femur, 181, 197.

of fibula, 183, 184.

of humerus, 148, 164, 165.

of Lamprey, 72.

of radius, 148, 149, 167*

of a rib, 35, 69, 216.

of ulna, 150.

Heart, 4, 406—408, 427, 429, 462, 463,
468.

development of, 409.
Hearts, lymphatic, 432.
Hedgehog, 16.

alimentary canal of, 448.

brain of. 382.

circulation of, 420.

ear of, 394.

exo-skeleton of, 243.

larynx of, 474.

liver of, 455.

mammary glands of, 489.

muscles of, 308, 329, 333, 339, 359.

pancreas of, 449.

skull of, 109, 119, 130.

spinal marrow of, 386.

spine of, 61.

teeth of, 261, 264,
L L

5'4

INDEX.

Hemicentetes, 16.

limb-bones of, 188.

skull of, 102.

teeth of, 260, e63, 266
Hemidactylus (a Saurian), limb-bones

of, 161, 162.

Hemispheres, cerebral, 366.
Hepatic artery, 414, 423, 451.

duct, 448, 452,

veins, 422 — 426.
Heptanchus (a Shark), arteries of, 416.

branchial arches of, 480.
Herring, swim-bladder of, 465.
Hexanchus (a Shark), brain of, 384.

branchial arches of, 480.

nerves of, 397, 398.
Highest Apes, their differences from

man, 494.

Hind-brain, 374, 375, 377.
Hinge-joint, 24.
Hip, 177.
Hippocampus, 20.

major, 373.

minor, 373.

pouch of, 490.
Hippopotamus, 17.

limb-bones of, 203.

liver of, 455.

skull of, 118.
Hog, 17.

bronchi of, 469.

limb-bones of, 211.

lymphatics of, 432.

skull of, 118, 119, 141, 142.
Hog-tribe, teeth of, 262.
Hollow-horned Ruminants, 245.
Holocentrum (a Teleostean Fish), liver

of, 456.

Holothuria, 13.
Homologues, serial, n, 215.
Homotypes, n, 215.
Honeycomb, of Sheep's stomach, 443,

Hoofed beasts, 16.
Hoofs, 245
Horizontal ramus, 86.

ramus of pubis, 178, 179.
Horn, 239.

of Rhinoceros, 245.
Horns, bony, of Ungulates, 279.
Horns of Oxen, 245.
Horny epidermal scales, 240.
Horny teeth, 247.
Horse, 16.

alimentary canal of, 447.

bronchi of, 469.

callosities of, 239.

exo-skeleton of, 245.

limb-bones of, 196, 197, 200, 207 —

2OQ, 211, 212.

liver of, 456.

mammary glands of, 490.

Horse, muscles of, 308, 311—314, 321,
323. 326> 329. 333. 334, 33°. 34^
343- 349—353, 356, 358—360.

skull of, 101, 103, no, 116, 123,
124, 131, 132, 137, 130, 171— 174.

spine of, 40, 43, 48, 51, 65.

teeth of, 267, 269, 275.

tongue of, 440.
Horseshoe Bats, 15.
Howlers, 15.
Howling Monkeys, larynx of, 473, 474.

skull of, 124, 134, 138.

spine of, 50, 65, 66.
Humerus, 145, 162—164, I73> 23°-
Hundred-legs, 7, n.
Hyaena, 16.
Hydra tuba, 13.
Hydrochcerus (the Capybara), teeth

of, 275.
Hydromys, 16.

teeth of, 263.
Hydrophis (a Serpent), larynx of, 475.

cutaneous glands of, 487.

muscles of, 354.

skull of, 129.
Hyla (a Tree- Frog), 208.
Hylaedactylus (an Anourous Batra-

chian), limb-bones of, 176.
Hylobates, 15 ; limb-bones of, 201, 207.
Hyo-glossus muscle, 287, 288, 314.
Hyoid, body of, 75, 123.

bone, 434, 471.

corniculum of, 75, 123.

great cornu of, 75, 123.

muscles of, 286.
Hyoidean arch, 93, 94, 125, 397.

nerve. 397.
Hyo-mandibular, 103, 121, 227, 395*

396.

Hyo sternal scute, 240.
Hypapophyses, 42, 217, 220, 223, 224,

226.

Hypapophysial arch, 215.
Hypapophysis of atlas, 217.

of axis, 217.
Hypaxial arch, 221.

muscles, 362.

parts, 221, 224, 226.
Hyperapophyses, 45, 51, 226.
Hyperoodon (a Cetacean), spine of, 68.
Hypo-branchials, 126, 227, 477, 478.
Hypogastric arteries, 424.

plexus, 404.
Hypoglossal nerve, 78, 98, 132, 368,

399-

Hyposternal scute, 240.
Hypsiprymnus (a Marsupial), skull of,

142.
Hysteropus fa Saurian), cutaneous

glands of, 488.
Hyracoidea, 17.
Hyrax, 17.

1XDEX.

515

Hyrax, alimentary canal, of 448.

exo-skeleton of, 245.

limb-bones of, 155, 172.

liver of, 456.

muscles of, 312, 314, 321, 328, 330,
33i, 336, 339. 342. 343, 350—354,
356, 358.

skull of, 123.
Hystrix, 16.

skull of, 114.

teeth of, 259.

Ichthyopsida, 15.

brain of, 383. .

nerves of, 339.

skull of, 96, 97, 108.

urinary organs of, 481.
Ic'ithyosauria, 19.
I ;hthyosaurus, 19.

limb-bones of, 166, 174, 196, 139,
207, 211, 213, 234.

spine of, 37, 47, 70.

teeth of, 270.
Iguanas, 18.

limb-bones of, 161.

muscles of, 312, 317, 321 — 324, 327
—329, 33i, 333-341, 344, 345-
, 347-350, 353-359, 364-

skua of, 127.

spine of, 53, 66.

teeth of, 254, 256, 269.

thymus gland of, 485.
Iguanodon, 19.
Iliac artery, 414, 421, 424.

fossa, 179.

symphysis, 191.
. veins, 422, 425.
Iliacus muscle, 300, 302, 318, 322, 338,

34°. 343. 345, 35o.

Iho-caudal muscle, 318, 322, 338, '348,
...350.

Iho-coccygeus, 324.
Ilio-pectineal eminence, 178, 190, 193.
Ilio-peroneal muscle, 318, 322, 344 —

350, 354- 355-
Ilium, 177—180, 187, 189, 191, 193, 194,

196, 198, 231.
Immovable joints, 24.
Implantation of teeth, 256.
Incisor of Horse, 260.

teeth 1 14.
Incisors, 251, 253, 258.

growth of, 259.
Incus, 393, 395, 396.
Index, 152
Indian Antelope, cutaneous g'ands of,

486.

Indian Tortoise, cutaneous glands of,
487.

Indris, 15.

alimentary canal of, 447.

caecum of, 460.

skull of, 138.

Infant, circulation of, 424.
Inferior articulating process, 28.

constrictor of pharynx, 288.

dental foramen, 86.

extremity, muscles of, 300, 340.

maxillary bone, 74, 120.

maxillary nerve, 391, 397.

oblique muscle of eye, 285.

rectus muscle, 285.

region of skull, 129.

surface of brain, 367.

vermis, 367.

Infra-orbital foramen, 76, 84, 114.
Infra-spinatus muscle, 290, 292, 293,

312, 326, 328.

Infra-spinous fossa, 145, 146.
Infundibulum, 369, 371.
Infusoria, 8.
Inguinal glands, 487
Innominate arteries, 411.

bone, 178, 188.

veins, 410, 422, 431.
Innominatum, os, 177 — 179.
Insecta, 7.
Insectivora, 16.

limb bones of, 188, 192.

skull of, 1 1 6, 142.

spine of, 58.
Insects, 7, q.

Insertion of muscles, 281,
Inside of the skull, 89.
Integument, 238.
Intelligence of man, 496.
Interarticular cartilage, 24.

cartilages of larynx, 473.
Interclavicle, 155, 161.
Interclavicular scute, 240, 242.
Intercondyloid fossa of femur, 183.
Intercostal arteries, 414, 421.

muscles, 239, 292, 299.

nerves, 400.

veins, 423.

Interior of skull, 135, 136.
Intermedium, 168-170.
Internal carotid, 411, 413.

cingulum, 267.

condyle of femur, 182.

condyle of humerus, 165.

iliac artery, 414.

lateral ligament of knee-joint, 183.

malleolus, 183, 184, 201.

maxillary artery, 413.

oblique muscle, vyt, 298, 311, 337.

pterygoid process, 75, in.

rectus muscle, 285.

skeleton, 23, 214.

tuberosity of femur, 181, 182.

tuberosity of tibia, 183.
L L 2

Si6

INDEX.

nteroperculum, 103.

nterossei (muscles), 297, 337, 360, 361.

nterosseous artery, 412, 414.

nterparietal, 99.

uterspinales (muscles), 291.
Interspinous bones, 278.
Intertransversales (muscles), 291, 300,

31?-

Inter-trochanteric ridges, 181, 182.
Jntervertebral foramina, 41.
Intestinal parasites, 7.
Intestine, 433, 442, 446—448, 450, 453,

460.
Inuus. 15.

spine of, 59.
Invertebrata, 8, 20.
Ischiatic notches, 180.
Ischio-caudal, 338, 350.
Tschio-coccygeus, 324.
Ischio-pubic bone, 187, 193.
Lschium, 177 — 180, 189, 190 — 193, 198,

199.

Island of Reil, 367, 378.
Iter a tertio ad quartum ventriculum,

37L 372.

Jaw, lower, 74, 120, 121.
Jelly Fishes, 7, 10.
Jerboa, 16.

limb-bones of, 210, 212.
Johnius (a Teleostean Fish), swim-
bladder of, 466.
Joints, 23.

shackle, 278.
Jugular eminence, 78.

Fishes, 194.

foramen, 397.

vein, 87, 422, 431.

K.

Krilophrynus (an Anourous Batra-

chian), cutaneous glands of, 488.
Kangaroo, circulation of, 421.

heart of, 409.

limb-bones of, 190, 201, 212.

lymphatics of, 432.

mammary glands of, 489.

muscles of, 331, 340, 350.

skull of. 109.

stomach of, 443-

teeth of, 267, 463
Kidneys, 3, 13, 461, 480.

circulation in the, 427.
Kingdoms of Nature, 5.
Knee-joint, 183, 232.
Knee-pan, 183.
Koala, 17.

alimentary canal of, 447.

Labial barbs, 435.
Labyrinth of ear, 393.
Labyrinthic teeth, 276.
Labyrinthodonta, 19.
Labyrinthodonts, teeth of, 275.
Lacerta (a Lizard), glands of skin of,
488.

limb-bones of, 203, 206.
Lachrymal, 75, 85, 116, 121, 130, 134,
227.

duct, 388, 434.

foramen, 92.

gland, 388, 486.

nerve, 391.
Lacteals, 406, 430.
Lagostomus (a Rodent), 114.

muscles of, 309.
Lambdoidal suture, 77.
Lamellae of gills, 479.
Lamina cinerea, 369.

of a vertebra, 27.

terminalis. 369, 371, 375, 377.
Lamina? dorsales, 36.

ventrales, 36.

Lamna (a Shark), teeth of, 369, 273.
Lamprey, 20, 21.

alimentary canal of, 446.

basket of, 476.

brain of, 379, 384.

cartilaginous basket of, 71, 143, 224.

ear of, 394.

head of, 72, 121, 125, 143, 224.

liver of, 456.

mouth of, 435.

nasal organ of, 38 1<

nerves of, 391.

other skeletal parts of, 152, 225.

peritoneum of, 458.

respiration of, 476.

spine of, 37, 67, 72.

teeth of, 247.

Lampris (Opah Fish), 159, 194.
Lampshells, 7, u.
Lancelet, 9, 12, 21, 215, 218.

anterior end of, 95, 142.

excretory organs of, 481, 483.

g'ands of, 450.

has no ear, 393.

heart of, 410.

liver of, 453.

mouth of, 435.

other skeletal parts of, 152.

peritoneum of, 458.

respiration of, 476.

spinal marrow of, 386.

spine of, 42.
Land Tortoises, 19.

limb-bones of, 174, 775, 211, 212.
Large intestine, 442, 446-448, 460.
Laryngeal pouches, 473, 474.

INDEX.

Larynx, 434, 471, 472.
Lateral ethmoid, 83, 93, 94, in, 134,
227.

ligaments of knee-joint, 183.

line, 488.

part of occipital, 79.

ventricles, 372, 374, 375, 377.
Latissimus dorsi muscle, 289, 290, 293,

310, 311, 316, 320, 321, 325, 329.
Layers of skin, 237.
Leaping Shrew, 16.
Leeches, 7.
Left auricle, 407 — 409.

lunt?, 467.

ventricle, 407—4-9.
Leg, 177.

muscles of, 303, 304, 351, 352, 355,

360.

Leg and arm compared, 232.
Leiocephalus (a Saurian), 197.
Lemur, 15.

exo-skeleton of, 245.

limb-bones of, 172, 174, 196, 208,

212.

muscles of, 321, 327, 336, 344, 351,

353, 357. 359. 360-

skull of, 107, 116, 117, 119.

tongue of, 441.
Lemur, Slow, spine of, 51.
Lemuroide a (asub-order of Primates),

muscles of, 336, 356.
Lemuroids, 15.

alimentary canal of, 44.8.

cutaneous glands of, 487.

limb-bones of, 190.

liver of, 456.

mammary glands of, 489.
Length of cranial cavity, 92.

of intestine, 446.
Lens, 387, 388.
Leopard, spine of, 42.
Lepidosiren, 20.

arteries of, 416.

breathing organs of, 462.

circulation in, 421, 428, 429.

excretory organs of, 483.

lungs of, 465.

muscles of, 311.

nerves of, 391, 398.

skull of, 97, 100, 108.

spine of, 37, 39, 63.
Lepidosteus, 20.

exo-skeleton of, 241, 277.

gills of, 480.

skull of, 99, 113, 120.

swim-bladder of, 465.
Lepilemur (a Lemuroid Primate),

teeth of, 260.
Lesser ischiatic notch, 180.

sigmoid cavity, 149, 150.

trochanter, 181, 182, 197.

tuberosity 148, 164.

Lesser wing of sphenoid, 76, 94.
Levator anguli oris muscle, 284.

anguli scapuke muscle, 289, 290,
3"> 321-

clavicular muscle, 313, 321, 325.

coccygis muscle, 341.

labii superioris alseque nasi muscle,
283, 284.

labii superioris muscle, 283, 284.

menti muscle, 283, 284.

palpebrse muscle, 284.

proprius alse nasi muscle, 284.
Levatores arcuum muscle, 310, 316.

costarum muscles, 299, 317.
Lialis (a Saurian), 18

limb-bones of, 187, 188, 196, 198,
234

muscles of, 358.
Ligaments of humerus, 165.

of jaw, 284.

of liver, 451, 452.
Ligamentum nuchar, 320.

teres, 180, 181, 197.
Limb-muscles compared, 361.
Limb-nerves, 401.
Limbs, 2, 9.

pelvic, 231.

primitive position of, 330, 232.

serial subdivisions of, 231, 232.

thoracic, 230.

upper, skeleton of, 145.
Linea aspera, 181.

alba, 292, 299.

Linea; transversae, 298, 339, 364.
Lingual artery, 411.
Lingualis muscle, 286.
Lingula sphenoidalis, 82, 108.
Lining of stomach, 249.
Lion, 16.

circulation in, 420.

limb-bones of, 156.

Sea (or Sea-Bear), skull of, 136.
Lips, 433—435-
Little digit, 152.

Liver, 445, 447, 450, 451, 454—456, 460.
Lizard, Flying, 18, 69.

Frilled, 18, 237.
Lizards, alimentary canal of, 446.

brain of, 379.

circulation in, 419.

cutaneous glands of, 488.

ear of, 394.

exo-skeleton of, 256.

eye of, 388.

larynx of, 475.

limb-bones of, 161, 162, 164, '165,
i?1. I93/2Q5, 213.

nerves of, 402.

peritoneum of, 459.

skin of, 237.

skull of, zoo — 103. no, in, 121,
124, 128, 133, 136.

sis

INDEX.

Lizards, spine of, 54, 63, 66, 71.

teeth of, 269.

viscera of, 453.

(Acrodont), teeth of, 256.

(Pleurodont).teethr of, 256, 257.
Llamas, 17.

circulation in, 420.

spine of, 50.

thyroid gland of, 484.
Loach (a Teleostean Fish), swim-
bladder of, 466.
Lobes of cerebrum, 379.

of kidney, 483.

of liver, 451, 452, 454—456.

of lung, 464.
Lobi inferiores, 381
Lobsters, 7, 12.
Lobule, 393, 396.
Lobules of lung, 465.
Locus perforatus, 371.
Locusts, 13.
Long-armed Ape, is?.
Long-eared Bat, 396.
Longissimus dorsi muscle, 290, 3-22
Longitudinal fissure of cerebrum, 366.

of liver, 452.

section of brain, 370.
Longus colli muscle, 288, 317.
Lophiomys (a Rodent), skull of, 100,
129, 133-

stomach of, 445.
Lophius, 20.

_limb-bones of, igr, 194.
Loris, 15.

limb-bones of, 192, 195, 206, 207.

muscles of, 332, 353.

teeth of, 261.
Lower jaw, 74, 75, 121.

limbs, 177.

ribs, 41, 224, 226.

zygoma, 227.
Lucio-perca (a Teleostean Fish),.

swim-bladder of, 466.
Lumbar arteries, 414.

enlargement of, 386.

plexus, 400, 402.

region, muscles of, 300.

veins, 423.

vertebra, 31, 51.

vertebrae, 26.
Lumbricales muscles, 295, 296, 307, 331,

332. 355. 358, 359

Lunare, 150, 151, 167, 171, 173, 176.
Lungs, 453, 461—465, 467—470.
Lymphatic duct, 430, 432.

glands, 430, 431.

hearts, 432.

system, 430.

Lymphatics, 406, 430, 432.
T-ya, 373, 375.
Lytta, 440.

M.

Macacus, skull of, 114.
Macaw,, skull of, 133, 139.
Macroscelides, 16.

limb-bones of, 233.

skull of, 105, 106, no, 142.

teeth of, 267.
Magnum, os, 150, 151, 167, 168, 171 —

,,173' I?6'- r
Magot, spine of, 59.

Maiacopterygian fin, 278.

Malar, 75— 77,85,115, 119, 121, 130. 227.

Malar process of maxillary, 84.

Malleoli, 183, 184, 202.

Malleus, 393— 396.

Malpighian corpuscles, 481.

Mammalia, 14, 15, 116

origin of name, 489.
Mammals, arteries of, 415, 429.
brain of, 384.
circulation of, 420.
ear of, 394.
heart of, 410.
kidneys of, 481.
muscles of, 363.
nerves of, 402.
peritoneum of, 458.
respiratory actions of, 466.
skull of, 102, 104, 109, no, 114, 116,

118, 120, 130, 135, 141.
snpra-renal capsules of, 483.
their differences from man, 493.
Mammary gland, 485, 489.
Man, brain of, 366.
dentition of, 251.

his difference from all other Pri-
mates, 494

from Batrachians, 491.
from Birds, 492.
from Fishes, 490.
from Marsupials, 494.
from Monotremes, 493.
from other Mammals, 494.
from other Vertebrates, 490.
from Reptiles, 492.
from the highest Apes, 494.
from the lower Apes, 494.
Manatee, 16.

alimentary canal of, 448.
limb-bones of, 173.
muscles of, 339.
skull of, 141.
spine of, 47, 68.
tongue of, 441.

Mandible, 74, 86, 120, 226, 229.
Mandibular arch, 93, 94.
gland, 487.
nerve, 397
Mandrill, limb-bones of, 156.

skull of, 132, 135.
Mane, 243.

INDEX.

519

Manis, exo-skeleton of, 246.

skull of, 116, 133.

spine of, 58.

tongue of, 441.

Man's anatomy generally considered,
496.

moral responsibility, 496.

myology, peculiarities of, 361.

nature in its totality, 497.

position in nature, 496.
Manubrium, 34, 35, 65, 155.
Manyplies of Sheep's stomach, 443.
Marginal scutes, 239, 242.
Mark of Horse's tooth, 260.
Marmoset, 15.

Marmot (a Rodent), teeth of, 263.
Marrow, spinal, 25.
Marsipobranchii, 20.

breathing of, 466.

excretory organs of, 483.
Marsipobranchs, mouth of, 435.

nasal organs of, 381.

nerves of, 405.

spine of, 42.
Marsupial bones, 190, 194.

pouch, 489.
Marsupialia, 17.

limb-bones of, 190, 194, 202, 208.
Marsupials, 17.

mammary glands of, 489, 490.

muscles of, 336, 339.

skull of, 109, 119, 122, 137, 142.

teeth of, 264, 266, 271.

their differences from man, 494.
Marsupium of eye, 388.
Martins, limb-bones of, 164.
Masseter muscle, 114, 283 — 285, 309 —

311, 316.

Mastoid, 75, 76, 88, 104, 133.
Matamata Tortoise, 19.

skull of, 128.
Maxillary arch, 94.

artery, 418.

bone, or maxilla, 75, 84, 100, 103,
104, 108, 113, 114, 117, 119, 121,
_ 129, 130, 134, 227.

sinuses, 93, 140, 142.
Meat, 281.
Meatus auditorius internus, 80, 90.

externus, 80, 393, 394.
Meckel's cartilage, 95, 144.
Median nerve, 400, 401.

part of ethmoid, 76, 83, 91, 93, 94,

98, 104, in, 117, 129, 134, 227.
Mediastina, 463.
Medulla oblongata, 367, 368, 370, 371,

376. 377) 384, 39°-
Megaderma (a Bat), nasal organs of,

380.

Megalosaurus, 79.
Megaptera (a Cetacean), 199.
Megatherium, 17.

Membrana semilunaris, 464.

tympanoformis, 469.
Membranes of brain, 365.
Membranous labyrinth, 394.
Menobranchus, 19, 216, 219.

gills of, 479-

limb-bones of, 195.

mouth of, 436.

muscles of, 310, 314 — 317, 319,

320, 322, 327, 329, 337, 345, 349,
351, 357-

spine ot, 47, 60.
teeth of, 254.
Menopoma, 19, 216.
lungs of, 465.
muscles of, 310, 311, 314, 317—319,

321, 322, 326, 327, 329, 337, 338,
340, 345, 348, 350, 35i, 353, 356,
357-

nerves of, 402, 403.

spine of, 58.

trachea of, 468.
Mental foramen, 86.
Merganser (a Carinate Bird), trachea

of, 469.
Merlangus (a Teleostean Fish), caeca

of, 450.

Mermaids, 489.
Mesenteric arteries, 414, 421.
Mesentery, 221, 458.
Meso-coracoid, 161.
Meso-cuneiforme, 185, 186,208, 211.
Meso-scapular segment, 156, 160,

161.

Mesosternum, 66.
Metacarpals, 150, 151, 168, 173.
Metacarpus, 145, 172.
Metacromion, 155, 156, 159, 160.
Metapophyses, cervical, 50.
Metapophysis, 31, 226.
Meta-pterygoid, 103, 131, 227, 395, 396.
Metatarsals, 167, 185, 200, 205, 209,

2I3-

Metatarsus, 177, 186, 209.
Mice, 16.

limb-bones of, 161.

spine of, 65.
Microcebus, 15.

skull of, 107.

teeth of, 258.
Mid-brain, 373, 377.
Middle commissure, 371 — 373. 374.

digit, 125.

fossa of skull, 89, 137.

sacral nerve, 422.
Milk-teeth, 250, 252, 272.
Millepedes, 9.
Mitral valve, 407.
Mixed joints, 24.
Molar teeth, 114.
Molars, 251, 263, 264.
Mole, 16.

520

INDEX.

Mole, eye of, 388.

limb-bones of, 154, 156, 158, 160,
164, 168 — 170, 174, 176.

muscles of, 309, 320, 321, 326.

skull of, 106, in, 131, 138, 142.

spine of, 65, 73, 217.

teeth of, 261, 263, 265, 268.

thyroid gland of, 484.

tongue of, 440.
Mollusca, 6, 9, 12.
Molluscoida, 7, 12.
Molossus (a Bat), limb-bones of, 202.
Monachus (a Seal), skull of, 112.
Monitors, 18.

cutaneous glands of, 488.

limb-bones of, 161, 175, 205, 213.

thyroid gland of, 484.
Monkeys, callosities of, 240.

limb-bones of, 173, 174, 212.

mouth of, 436.

muscles of, 332.

skull of, 101, 138, 141.

spine of, 38, 58.

stomach of, 443.
Monkeys, American, skull of, 132

Howling, skull of, 124, 134, 138.
spine of, 50, 65, 66.

Spider, skull of, 136.
spine of, 50, 58, 72.

Squirrel, skull of, 137, 138.
Monodelphia, 15.
Monodelphous Mammals, ear of, 394.

teeth of, 264.

Monopterus (a Teleostean Fish), cir-
culation of, 429.
Monotremata, 18.
Monotremes, alimentary canal of, 448.

circulation of, 426.

ear of, 394.

glands of, 438.

limb-bones of, 154, 158, 161, 168,
190, 194. 195.

muscles of, 339.

skull of, 99

spine of, 41, 51, 54, 63, 65, 67, 69
—71-.

their difference from man, 493.
Mormyrus (a Teleostean Fish),stomach

of, 445.

Motions of muscles, 281.
Mouth, 433—435-

of Whale, 248.
Movaole joints, 24.
Mucous membrane, 237.
Mucus of skin, 488.
Mud-fish (Lepidosiren\ 20.

breathing organs of, 462.
Mullets, mouth of, 435.
Multifidus spine muscle, 291.
Muntjac, teeth of, 262.
Muraena (a sort of Eel), teeth of,

257.

Muscles, 281.

classification of, 282.

of abdomen, 297, 298, 337.

of arm, 327, 328, 330, 333—335.

of back, 289, 290, 319.

of eyeball, 285.

of foot, 307, 357, 358.

of fore-arm, 294.

of hand, 297, 336.

of head and neck, 283, 284, 308.

of hyoid, 286.

of inferior extremity, 300, 340.

of leg, 303, 304, 351, 352, 354, 355,
360.

of lumbar region, 300.

of nasal region, 309.

of orbit, 310.

of palate, 289.

of pelvic region, 300.

of shoulder, 293.

of tail, 323, 324, 364.

of thigh, 301, 302, 344.

of tongue, 286.

of trunk, 292.

of upper arm, 293, 324.

of upper extremity, 291.

of vertebral region, 317.

of viscera, 282, 283.

serial homology of, 361.
Muscular cones, 323, 324, 364.

tissue, 281.

Musculo-spiral groove, 148.
Musculo-spiral nerve, 400, 401.
Musk Deer, 17.

cutaneous glands of, 487.

lungs of, 464.

teeth of, 262.
Mycetes, 15.

larynx of, 473, 474.

limb-bones of, 156

spine of, 50, 54, 65, 66.
Myliobatis, 20.

teeth of, 269, 270.
Mylodon, 17.

Mylo-hyoid muscle, 310,314—316,459.
Myogale (an Insectivore), spine of, 58.
Myology, general conceptions of, 364
Myrmecobius (a Marsupial), teeth of.

263.
Myrmecophaga (an Ant-eater), 17.

glands ot, 439.

nasal organs of, 380.

skull of, 130.

spine of, 46

stomach of, 444.
Myxine, 20.

circulation of, 426.

ear of, 394.
eye of, 388.

gills of, 476.

nasal organs of, 381.

nerves of, 405.

SNDEX.

521

Myxine, peritoneum of, 458.

teeth of, 257.
Myxinoids, heart of, 410.

mouth of, 435.

skull of, 113.

urinary organs of, 481.

N.

Nails, 236, 238.

formation of, 244.
Nakedness of skin, 243.
Nares, anterior, 76.

posterior, 76, 88.
Narwhal, 16.

spleen of, 484.

teeth of, 257, 262.
Nasal artery, 413.

bone, 75, 76, 85, 91, 100, 103, 114,
116, 117, 121, 227.

cavity, 380.

fossae, 92, 139.

process, 84.

region, muscles of, 309.

spine, 84.

vein, 391.
Nates, 371-373.
Nature of man as a whole, 497.
Naviculare, 184—186, 204, 205, 207,

209, 210.
Neck, muscles of, 233, 308.

of a bone, 24.

of femur, 181, 182, 196.

of mandible, 86.

of radius, 148.

of rib, 35, 70, 216.

of scapula, 146.
Nerve, auditory, 392.

chorda tympani, 80.

eighth, 396.

facial, 80, 396.

fifth, 82, 83, 105, no, 391.

fourth, 83, 390.

glosso-pharyngeal, 88, 397.

hypoglossal, 78, 98, 132, 399.

ninth, 399.

olfactory, 380 {See also Olfactory
Nerve).

optic, 83, 387 (See also Optic
Nerve).

par vagum, 88.

seventh, 105, 396.

sixth, 83, 390.

spinal, 399.

spinal accessory, 88.

third, 83, 390.
Nerves, development of, 404.

of the arm, 401.

of the leg, 402.

of special sense, 399.

origin of the, 390.

Nerves, roots of, 399.
Nervous centres, 4.

system, 365, 4oo, 405.
Nervus impar, 386.

laterahs, 397—399, 428.

vagus, 397, 398.
Neural arch, 26, 226.

canal, 218.

lamina, 27.

spines, 27, 217, 226, 239, 242.

spines, expanded, 239.
Newts, 19.

Nictilating membrane, 389.
Night-ape (an American Primate),

SKull of, 138.
Ninth nerve, 399.
Nipples, 489.

N octilio (3. Bat), limb-bones of, 207.
Is octule Bat, liver of, 455.
Nose, 380, 434.
Nose-leaf, 380.
Nostrils, anterior, 76.

posterior, 76.

Notochord, 5, 12, 36, 218.
Nycticebinas, muscles of, 331.
Nycticebus, 15.

limb-bones of, 201.

muscles of, 321, 330, 332, 334,^40,
354. 356, 358, 3&2-

teeth ol, 261.
Nyctipithecus(an American Ape), skull

of, 132, 138.
Nuchal plate, 238, 242.
Number of mammae, 489.

of skeletal parts, 214.

of teeth, 257.

O.

Obliquus capitis muscle, 291.

inferior muscle, 286.

superior muscle, 285.

tertius muscle, 342, 343.
Obturator foramen, 178, 180, 189.

externus muscle, 300, 302, 342, 344.

internus muscle, 301, 302, 342, 344.

tertius muscle, 342, 343.
Occipital angle, 92, 135, 136.

bone, 75, 77, 88, 91, 97. ._ .

condyle, 75, 114, 117.

foramen, 74, 77.

gland, 486.

region, 77.

Occipito-frontalis muscle, 283, 308.
Occiput, 74.
Octopus, 6.

Odontaspis (a Shark), teeth of, 269.
Odontoglossum (a Teleostean Fish), 20.

teeth of, 255.
Odontoid bone, 54, 217.

process, 30, 54, 217.
OZsophageal teeth, 276.

522

INDEX.

(Esophagus, 299, 398, 431, 433, 441—

445, 447, 448, 463.
Olecranon, 149, 150, 165, 167, 168.
Olfactory angle, 92, 135, 136.

lobe, 369, 375, 377, 379, 382, 384.

nerve, 368, 369, 380, 390.

organ, 380.
Olivary body, 367.
Omentum, 458, 459.
Omohyoid muscle, 287, 288, 313, 315 —

3X7-

Omosternum, 147, 160, 161.
Omphalo-meseraic veins, 423, 425.
Oolite, bird of the, 18.
Opah Fish (a Teleostean), 159, 194.
Opening of external auditory meatus,

Operculum, 103, 476.

muscles of, 319.
Opetiorhynchus (a Carinate Bird),

trachea of, 470.
Ophidia, 18.
Ophiodes (a Saurian), 187, 188, 199,

203, 204, 210, 212.
Ophiomorpha, 19.

lungs of, 464.

trachea of, 468.
Ophthalmic artery, 413.

nerve, 391.

Opisthoccelous vertebrae, 39.
Opisthotic, 8 1, 100, 106, 227.
Opossums, alimentary canal of, 448.

limb-bones of, 212.

mammary glands of, 489.

muscles of, 343, 353, 356.

skull of, 105, 122, 137.

spine of, 43, 50.

teeth of, 260.

Opponens digiti minimi muscle, 296,
297, 336

nallucis muscle, 359.

muscles, 362.

pollicis muscle, 294, 296, 297, 336.
Optic commissure, 369.

foramen, 76, 82, 108, no, 137.

lobes, 382 — 385.

nerve, 83, 368, 371, 384, 387, 390.

nerves, chiasma of, 285.

thalamus, 373, 374, 378, 390.

tracts, 369, 387.
Orang, 15.

larynx of, 474.

limb-bones of, 169, 197, 201, 207,
212.

mouth of, 435.

muscles of, 332, 356, 359, 362.

skull of, 1 1 6, 132.

spine of, 50, 66.

thyroid gland of, 484.

tongue of, 441.
Orbicularis oris muscle, 283, 285.

palpebrarum muscle, 283, 284, 309.

Orbital muscles, 310.

plate of frontal, 90.

plate of sphenoid, 109.

wings of sphenoid, 82, 83, 90.
Orbi to-sphenoid, 98, no, 130, 227.
Orbits, 76, 138.
Order, 5.
Organic world, 5.
Organisms, 5.
Organs of man's body, 21.

of sense, 365.
Origin of muscles, 281.
Ornithodelphia, 18.

ureters of, 482.
Ornithorhynchus, 18.

alimentary canal of, 449, 460.

brain of, 366.

cutaneous glands of, 487.

exo-skeletcn of, 247.

glands of, 438.

larynx of, 473.

limb-bones of, 197, 199, 201, 203,
206 — 208, 211, 220.

lungs of, 464.

mammafy glands of, 489.

mouth of, 435, 436.

muscles of, 339, 342, 354.

skull of, 100, 115, 136, 137.

spine of, 48.

spleen of, 484.

stomach of, 445.

tongue of, 441.
Orycteropus, 17.

teeth of, 276, 277.
Os articulare, 396.

calcis, 186, 204, 205.

cloacae, 195.

en ceinture, 100, 112.

femoris, 177.

hyoides, 87, 123, 125, 286, 429, 434,

. 471,473-

innommatum, 177 — 180.

magnum, 150, 151.

planum, 84.

quadratum, 103, 104, 108, 119, 120.'

transversum, 121, 131, 227.
Osseous Fishes, auditory organ of,
395-

exo-skeleton of, 277.

gills of, 479.

respiration of, 478.

skull of, 101, 108, in, 120, 121,
124, 139, 144, 159.

spine of, 59.
Ossification, 23.

of epidermis, 239.

of skull, 95.

of spine, 61.
Osteoglossum (a Teleostean Fish),

teeth of, 257.
Ostracion (a Teleostean Fish), 20.

muscles of, 362.

INDEX.

523

Ostrich, 1 8.

alimentary canal of, 447.
limb-bones of, 161, 175, 188, 192,

194, 198, 2OO, 2O2, 205, 2IO, 212,

213.

lymphatics of, 432.

skull of, 104, 120, 142.

spine of, 57, 66.
Otaria, 16.
Otocrane, 138.
Otter, 16.

liver of, 456.

thyroid gland of, 484.
Outside of skull, 87.
O%'iduct, 447.
Owen's Chameleon, exo-skeleton of,

245-

Owl, eye of, 389.
Ox, 17.

circulation of, 420.

exo-skeleton of, 245.

horns of, 279.

limb-bones of, 202, 207 — 209, 211,
212.

muscles of, 353.

skull of, 99, 129, 135.

spine of, 41, 43, 55.

teeth of, 261, 262, 269.
Oxygenation of blood, 427.
Oyster, 6.

Paca (a Rodent), ear of, 394.

skull of, 113, 133, 142.
Palamedea (a Carinate Bird), exo-
skeleton of, 247.
Palatal muscles, 319.
Palate, 434, 436.

soft, 289.
Palatine arch, 229.

bones, 85, 91, 118, 119, 130, 227.

canal, 84, 85, 88.

plate of maxillary, 84, 91.

teeth, 254.

Palato-glossus muscle, 289.
Palato-pharyngeus muscle, 289.
Palmaris brevis muscle, 294, 336.

longus muscle, 294, 295, 329, 331.
Palpebral muscle, 308.
Pancreas 433, 447, 449. 453. 484-
Pancreatic duct, 449, 452.
Pangolins, 17.

exo-skeleton of, 246, 254.

limb-bones of, 213.

skull of, 117.

spine of, 58, 66.

tongue of, 441.
Panniculus carnosus, 308.
Papilla of tooth, 249.
Papillae of feathers, 243, 244.

of tongue, 441.

Par vagum nerve, 88, 398.
Parachute-like stem-folds, 236.
Paramastoid, 99, 114, 132.
.Parapophyses, 216, 220, 226.
Parasites, 7.
Parasphenoid, 101, 104, 108, 227.

teeth, 254.
Paraxial arches, 219, 221.

cartilages, 218.

muscles, 362

parts, 224, 226.

processes, 216.

Parietal bone, 75, 76, 79. 90, 91, 98 —
100, 104, in, 117, 121, 129, 134,
227.

region, 77.

region, duct of, 284.
Paroccipital, 99, 107, 132,
Parotid gland, 436—438.
Parotoid glands, 488.
Parrot Fishes, 20.

teeth of. 272. 273.
Parrots, limb-bones of, 210.

liver of, 456.

skull of, 101, 103, 128.

trachea of, 470.

Patella, 183, 198, 200, 203, 209.
Paunch of Sheep's stomach, 443, 444.
Peccaries, 17.

Peccary, limb-bones of, 212.
Pecten, 13.

of eye, 388.
Pectineus muscle, 302, 303, 343, 344,

346

Pectoral fin, muscles of, 319, 363.
Pectoralis major muscle, 291 — 293, 320,

minor muscle, 291, 292, 326.

muscle, 313, 315^, 327.
Peculiarities of man's myology, 361.
Pedetes (a Rodent), skull of, 105, 115.
Pedicle of a vertebra, 27.
Pelican, limb-bones of, 164.
Pelobates (an Anourous Batrachian),
cutaneous glands of, 488.

skull of, 133.
Pelvic limbs, 231.

region, muscles of, 300.
Pelvis, 180, 191, 194.
Penguin (a Carinate Bird), limb-bones
of, 153, 166.

spine of, 47.

trachea of, 469.
Perameles, limb-bones of, 175, 176.

teeth of, 265.
Perch, brain of, 379, 381.

circulation of, 428.

gills of, 477—479-

limb-bones of, 152, 162, 194.

muscles of, 319, 363.

respiration of, 4?q

skull of, 97, 103, 104.

524

INDEX.

Perch, swim-bladder of, 466.

teeth of, 255, 265.
Perch, Climbing, 480.
Pericardium, 407, 410.
Periotic mass, 106.
Peripheral skeleton , 23.
Perissodactyla, 16.
Peritoneum, 221, 410, 433, 457—459-
Permanent teeth, 250.
Perodicticus (a Lenmroid Primate),
limb-bones of, 172, 206.

spine of, 50.

teeth of, 261.
Peroneal artery, 412, 414.

bone, 177.

nerve, 400.

trochanter, 181.

Peroneo-tibial muscle, 356, 360.
Peroneus brevis muscle, 304—306, 352,

353-
longus muscle, 304—306, 352, 353,

362.
muscle, 346, 347, 354, 355. 357.

36°.' ,- • •
quarti digiti muscle, 353.

quinti digiti muscle, 353.

tertius muscle, 304, 353, 361.
Petrodromus (an Insectivore), teeth of,

261.

Petrotnyzon, 21.
Petrous part of temporal bone, 88, 90,

104

Phalanges, 17, 145, 150, 152, 167, 173,
175—177, 187, 209.

limb-bones of, 202, 208, 212.
Phalangista (a Marsupial), 210.

muscles of, 356.
Pharyngeal bones, 478.

constrictor muscles, 288.

muscles, 318.

teeth, 255. .

Pharyngobranchials, 126, 227, 447, 448.
Pharyngobranchii, 21.
Pharynx, 433, 434, 441.
Phascogale (a Marsupial), mammary

glands of, 489

Phascolomys (a Marsupial), 165.
Pheasant, spine of, 67.
Philosophy, 497.
Phoca (a Seal), 16.

muscles of, 334, 351, 353.
.Pnyllomedusa (an Anourous Batra-

chian), tongue of, 440.
Phyllostoma, 16.

nasal organs of, 380.
Physeteridse (a group of Cetaceans),

spine of, 44
Physical Science, 497.
Pia mater, 365, 366.
Pig, limb-bones of, 171, 174.

mammary glands of, 490.

mouth of, 436.

Pig, muscles of, 309, 327, 328, 333, 340,

346>35I, 354, 358-

pancreas of, 449.

skull of, 104, 137.

spine of, 65.

stomach of, 443.

tongue of, 441-
Pigeon, alimentary canal of, 442.

brain of, 383, 384.

crop-secretion of, 490.

liver of, 456.

skull of, 1 20.
Pigeon's milk, 490.
Pike, 20.

skull of, 97, 105, 106, 108, 109, 113,

137, 139-

teeth of, 250, 257.
Pilchard, cseca of, 450.
Pillars of diaphragm, 299.
Pineal gland, 371-373, 376> 377> 38a

—384, 390.

Pinna of ear, 393, 396.
Pinnipedia, 16.
Pipa, ear of, 394.

limb-bones of, 161.

tongue of, 440.
Pipistrelle Bat, 158.
Pieces, 15.

Pisiforme, 150, 151, 167, 170, 173.
Pit for ligamentum teres, 182, 197.

for flexor longus digitorum, 198.

for popliteus, 198.
Pithecia, 15.

exo-skeleton of, 243.

liver of. 455.

skull of, 101, 132.

teeth of, 258.

Pituitary body, 368, 369, 371, 374, 377
384, 390.

fossa, 8 1, 82, 90, 94, 98, 369.
Pivot joints, 24.
Plantar fascia, 354.
Plantaris muscle, 305, 306, 352, 354,

355-

Plastron, 64, 240, 242.
Platanista, 16.
Platax (aTeleostean Fish), spine of, 68.

teeth of, 269.

Plates of baleen, 248, 249.
Platypus, 18.

muscles of, 317.

spine of, 53, 54.
Platysma myoides muscle, 282, 283,

286, 308, 320.
Plecotus (a Bat), auditory organ of.

396.

Plesiosauria, spine of, 62, 70.
Plesiosaurus, 19.

limb-bones of, 199, 213, 234.
Plethodon (a Urodele Batrachian),

teeth of, 255.
Pleura, 462.

INDEX.

525

Pieurodont Lizards, 257.

teeth of, 256, 257.
Pleuronectidae, 20.

eyes of, 389.

skull of, 128.

swim-bladder of, 466.
Pleuro-peritoneal cavity, 218, 221.
Pneumogastric nerve, 368, 398.
Poison fangs, 270, 271, 438.

glands, 438.
Poisonous Serpents, 438.

spine of, 42.

teeth of, 275.
Pollex, 151, 176.
Polyophthalmus, 13.
Polyps, 7.
Polypterus, 20.

caeca of. 450.

exo-skeleton of, 241.

spine of, 40, 41, 72, 219, 220.

swim- bladder of, 465.
Pons Varolii, 368, 370, 371, 377, 384.
Pontoporia, 16.

teeth of, 257.
Popliteal nerve, 400.
Popliteus muscle, 306, 354, 335, 360.
Porcupine, 16.

exo-skeleton of, 243.

lungs of, 464.

skull of, 114, 116, 122.

teeth of. 259, 275.

tongue of, 441-

Porcus (a Hog), teeth of, 262.
Porpoise, 16.

alimentary canal of, 446, 448.

breathing organs of, 462.

circulation of, 421, 425.

exo-skeleton of, 243, 245, 247.

larynx of, 473, 474.

limb-bones of, 156.

muscles of, 308, 309, 323, 340.

nasal organs of, 381.

skull of, 104, 109, 112, 113, 1 1 6,

122, 129.

spine of, 47, 48, 220.

stomach of, 443.

teeth of, 272.

Portal circulation, 4, 12, 422, 423,
45i.

fissure, 452, 454.

system, 427.

vein, 422, 423, 425, 426.
Porteagle Shark, circulation of, 421.
Portio dura, 368, 392.

mollis, 392.

Portuguese man-of-war, 7.
Position of mammae, 489.

of man in nature, 496.

primitive, 230, 232.
Positions of limbs, 166.
Post-axial parts, 37,
Post.clavicle, 162.

Posterior auricular artery, 411, 413.

auricular muscle, 308.

commissure, 371 — 373.

cornu, 373, 379.

fossa of skull, 89, 137.

inferior spinous process, 178, 179.

nares, 76, 88.

scalenus muscle, 287, 288.

superior spinous process, 178, 179.

tibial artery, 412, 414.

tibial nerve, 400, 402.
Post-frontal, 101, in, 121, 134, 135, 227.
Post-orbital, 104, 119.
Post-scapular fossa, 155, 157.
Post-temporal, 103, 162.
Postzygapophysis, 28, 217, 226.
Potto (a Lemuroid Primate),limb-bones
of, 174, 207.

spine of, 41, 54.
Pouch, \farsupial, 489.

of Hippocampus, 490.
Pre -axial parts, 37.
Pre-coracoid, 160 — 162.
Pre-frontal, 103, 104, 121.
Pre-maxilla, 98, 100, 103, 104, 108, 114,

117, 119, 121, 129, 130, 134, 227.
Pre-molar teeth, 114.
Pre-molar>, 251, 253.
Pre-operculum, 102, 103, 227.
Pre-scapular fossa, 157.
Pre-sphenoid, 95, 108, 109, 227.
Pre-sphenoidal part of sphenoid, 82.
Pre-sternum, 35, 155.
Pre-zygapophysis, 28, 217, 226.
Primates, muscles of, 336, 351, 353.

mammary glands of, 490.

spine of, 58.

their differences from man, 494-
Piimitive position of limbs, 230, 232.
Priodon lan Armadillo), teeth of. 257.
Priodontes (an Armadillo), limb-bones
of, 175-

spine of, 51, 52.
Pristipoma (a Teleostean Fish), skull

of, 117.
Pristis (Saw-fish), exo-skeleton of, 277.

liver of, 456.
Proboscis, 435.
Proboscis Monkey, 15.
Processus gracilis, 394.
Procoelous vertebrae, 39.
Pronation, 149, 166.
Pronator accessorius muscle, 333.

brevis muscle, 320.

longus muscle, 320.

quadratus muscle, 295, 296, 333.
335-

ridge, 147.

terts muscle, 294, 325, 329—331,

Prongbock (an Antelope), 245, 246.
Pronghorned Antelope, 246, 246. /

526

INDEX.

Pro-otic, 8 r, 98, 100,103, 104, 106, 108,

121.

Protein, 2.

Proteles (a Carnivore), tongue of, 441.
Proteus, 19.

larynx, 475-

limb-bones of, 173, 174, 193, 203,

211, 212.

nerves of, 402.

teeth of, 254.

thymus gland of, 485.

urinary organs of, 482.
Protogenes, 8.
Protomosba, 8.
Protozoa, 8, n.
Protractors (muscles), 282.
Proventriculus, 443, 447.
Proximal bones of carpus, 169.

of tarsus, 205.
Psalterium of Sheep's stomach, 443,

444*
Psammosaurus (a Lizard), 195.

limb-bones of, 165.
Pseudis (an Anourous Batrachian),

limb-bones of, 161.
Pseudo-branchia, 421.
Psoas magnus muscle, 300, 302, 340, 343.

parvus muscle, 300, 340.
Psychology, 497.
Pcerodactyles, 19.

limb-bones of, 174.

spine of, 47, 61.

Pteromys (a Rodent), muscles of, 320.
Pteropus, 15.

larynx of, 474.

limb-bones of, 164, 169, 170, 174,
198.

mammary glands of, 489.

muscles of, 333, 346, 356.

skull of, 119, 123.
Pterosauria, 19.

teeth of, 276.
Pterotic, 103, 106, 227.
Pterygoid, 75, 82, 91, 100, 104, 108,
in, 119, 121, 130, 134, 227.

fossa, 82, 88.

muscles, 285, 310.
Pterygo-maxillary fissure, 89, 134.
Pubic symphysis, 179, 180.
Pubis, 177 — 180, 189,191, 194, 198, 231.
Pubo coccygeus muscle, 324, 342.
Pubo-ischium, 187, 193, 196, 198.
Pulmonary artery, 407, 408, 410, 411,
415, 417—420, 424, 463,468.

sacs, 31, 471.

veins. 407, 408, 421, 463, 468.
Pulp cavity, 275.

of tooth, 249.
Pygal plate, 239, 242.
Pygopus (a Saurian), 208.
Pyloric caeca, 450.
Pylorus, 442, 444, 448, 450.

Pyramidalis muscle, 298, 299, 339.

nasi muscle, 284.
Pyramids of brain, 367.
Pyriformis muscle, 300, 301, 342.
Python (a Serpent), limb-bones of, 188

skull of, 101, 103, 142.

spine of, 68.

thyroid gland of, 485.

Q-

Quadrate, 103, 104, 108, 119, 120, 121,

!34> 227.

arch, muscles of, 363.
Quadrato-jugal, 100, 108, 119, 133, 134,

227.

Quadratum, 396.
Quadratus femoris muscle, 301, 302,

342-
lumborum muscle, 299, 300, 339,

340.

nictilantis muscle, 312.
Quadriceps extensor muscle, 303, 344,

R.

Rabbit, 16.

brain of, 378, 382.

circulation of, 425.

exo-skeleton of, 248.

limb-bones of, 160, 200.

mouth of, 435.

muscles of, 336, 340, 345, 351, 353,
354. 357> 358.

pancreas of, 449.

skull of, 122.

teeth of, 259.

tongue of, 441.
Rachiodon (a Serpent), 42.

teeth of, 276.
Racoon, 16.

muscles of, 339.

skull of, 136.
Radial artery, 412, 413.

carpal bone, 170, 175.

nerve, 400.

symmetry, 10.

tuberosity, 148, 164, 165.
Radius, 148, 166—168, 170, 171, 176.
Raia, 20.

limb-bones of, 152—154, 157, 158,
230.

spine of, 38.

Ramus of mandible, 86.
Rana (Frog), limb-bones of, 208.
Rat, 16.

mouth of, 435.

skull of, 122.

teeth of, 259, 263, 275.

tongue of, 441.

INDEX.

527

Ratitae, 18.

limb-bones pf, 159.
Rat-mole, 16.
Rattlesnake, larynx of, 475.

scales of, 246.

skull of, 104.

spine of, 46.

tail of, 247.

teeth of, 270.
Raven, trachea of, 470.
Rays, 20.

brain of, 379, 382, 384.

breathing organs of, 466.

ear of, 394-

exo-skeleton of, 277.

gills of, 476.

limb-bones of, 152.

liver of, 454-

muscles of, 363.

nerves of, 401.

skull of, 129.

spine of, 53.

teeth of, 269, 270.
Really compound teeth, 276.
Receptaoulum chyli, 430 — 432.
Recti muscles, 285.
Rectum, 442, 446, 453.
Rectus abdominis muscle, 298, 315,

339-
capitis anticus muscle, 288, 313,

3?7-

capitis posticus muscle, 291, 323.
femoris muscle, 302, 303, 318, 345,

346-

lateralis muscle, 288, 317.
Recurrent nerve, 398.

laryngeal nerve, 429.
Regions of the skull, 77.
Reindeer, horns of, 279.
Relation of scutes to scales, 241.
Relative importance of axial and ap-

pendicular skeletons, 234.
Renal artery, 412, 414, 480.

organs, 481.
Rennet, 443.
Reptiles, alimentary canal of, 447.

brain of, 382.

circulation of, 425, 427.

cutaneous glands of, 487.

f lands of, 438.
eart of, 410.
limb-bones of, 154, 167, 169, 170,

175, 188, 190, 191, 102, 193, 195,

196, 206.

lymphatics of, 432.
mouth of, 435.
muscles of, 313, 314, 318. 323, 324,

339— 342> 344? 348» 349. 358, 359,

363-

pancreas of, 450.
peritoneum of, 458.
skin of, 238.

Reptiles, skull of, 101, 103, 113, 117,
120, 121, 127, 131, i3~5, 139, 141.

spine of, 52, 64.

their differences from man, 492.

tongue of, 440.

trachea of, 469.

ureters of, 482.
Reptilia, 15, 18.
Respiration, 461.

aquatic, 475.
Restiform bodies, 382.
Restiform tracts, 367.
Rete Malpighii, 486.

mirabile, 420 — 422, 425, 466.
Reticulum of Sheep's stomach, 443,

444-

Retina, 387.

Retractors (muscles), 282.
Retrahentes auriculam muscle, 283,
284.

costarum muscle, 340.
Rhamphorhynchus, 19.
Rhea, 18.

limb-bones of, 183, 193, 205, 212.

spine of, 39, 55.
Rhinoceros, 16.

cutaneous glands of, 487.

horn of, 245.

limb-bones of, 173, 174, 196, 197,

211, 212.

liver of, 456.

skull of, 118, 140.

skin of, 237.

spine of, 58, 71.
Rhinolophus, 16.

nasal organs of, 380.
Rhomboideus muscle, 289, 290, 321,

328.
Rhynchocyon (an Insectivore), 208.

stomach of, 445.

Rhythmical contractility, 427, 432.
Ribs, 35, 67, 216, 217, 221, 223, 242.

expanded, 239.
Right auricle, 407, 408.

lung, 407.

ventricle, 407, 408.
Right Whale, mouth of, 435.

spine of, 53, 66.
Ring digit, 152.
River Hog, teeth of, 275.
Rodentia, 16.
Rodents, bronchi of, 469.

limb-bones of, 190.

mammary glands of, 490.

mouth of, 436.

muscles of, 3091

skull of, 99, 115, 122, 160.

spleen of, 484.

teeth of, 263.
Root of aorta, 412.
Roots of nerves, 399.

of spinal nerves, 385.

528 INDEX.

Roots of teeth, 251.
Rostrum of Saw-fish, 277.
Rotator fibuUe muscle, 356.
Rotatores spinse muscle, 291.
Rotators (muscles), 282.
Rotular surface, 197.
Round ligament, 180.

of liver, 452.
Rumen, 443

Ruminant detention, 262, 268.
Ruminants, brain of, 378.

bronchi of, 469.

cutaneous glands of, 486.

limb-bones of, 166, 167, 174, 196 —
198, 200—202, 206.

mammary glands of, 489.

muscles of, 314, 317, 329. 333, 343,
35o-

skull of, 99, 102, no, 118,122, 129,
139, 142.

spine of, 39, 58.

teeth of, 272.

trachea of. 468.

Ruminants, Hollow-horned, 245.
Rumination, 444.

S.

SaccMjranchus (a Teleostean Fish),

gills of, 480.
Saccopteryx (a Bat), cutaneous glands

of, 487-
Sacral artery, 414.

plexus, 400, 402.

vertebrae, 27.

vein, 422.

Sacro-coccygeus muscle, 324, 340.
Sacro-lumbalis muscle, 290, 291, 322.
Sacro-sciatic ligament, 180, 189, 193,

301.

Sacrum, 32, 55-57, 179, 180, 194.
Sagittal section, 91.

suture, 77.
Saiga, 17.

skull of, 129.

Saimiri (an American Ape), 379.
Salamander, limb-bones of, 170 — 172,
195, 203, 206 — 208, 213.

spine of, 39. 71.
Salamandra, cutaneous glands of, 488.

limb-bones of, 158.

muscles of, 314, 339.

spine of, 216, 219.

trachea of, 468.

Salivary glands, 433> 436—439.
Salmon, 20.

peritoneum of, 458.

skull of. 99, loo.

spine of. =59.

teeth of, 2^.
Santorini. cartilages of, 471, 474.

Sargus (a Teleostean Fish), teeth of,

272.
Sartorius muscle, 302, 303, 322, 341,

343-

Sauna, 18.
Saurians, limb-bones of, 202.

lungs of, 464.

respiration of, 467.
Sauropsida, 15, 382, 384.

arteries of, 415.

breathing organs of, 462.

ear of, 394—396.

kidneys of, 481.

muscles of, 349.

skull of, 96—98, 101, 120, 127.
Saururae, 18.
Saw-fish, scales of, 277.
Scaleni muscles, 287, 288, 312, 317.
Scalenus muscle, 71.
Scales, 240, 246.

of Fishes, 246, 277.

of Serpents, 246.
Scallop, 6.

Scaphoid of foot, 186, 207.
Scaphoides, 150, 151, 167—169, 171,

174, 176.

Scapula, 145, 146, 153, 161, 230.
Scarus (a Teleostean Fish), 20.

teeth of, 272, 273.
Scent glands, 487.
Sciatic nerve, 400, 402.
Seines, 18.
Sclerotic, 388.
Scolopendra, 6, n.
Scorpions, 7, 13.
Scutes, 240.

and scales, relation between, 241.

marginal, 239.

of plastron, 240.
Sea-anemones, 7.
Sea Bear, 16.

exo-skeleton of, 245.
Sea-cucumbers, 7.
Sea Lion, skull of, 136,
Sea-mat, 7.
Sea Otter, 16.
Sea-squirts, 7.
Sea-urchins, 7, 10.
Seals, 1 6.

brain of, 378, 379.

kidneys of. 482, 483.

200, 206 208, 211, 212.

limb-bones of, 170, 173, 196 — 198.

liver of, 455, 456.

muscles of, 340, 341, 343, 346, 354,

359-

skin of, 237.
skull of, 99, in, 112, 117, 128,

140.

spine of, 68.
tongue of, 441.
Sebaceous glands, 485.

INDEX.

529

Second row of carpals, 170.

of tarsals, 207.
Sections of brain, 371 — 374.
Sectorial tooth, 269.
Self-consciousness, 496.
Sella turcica, 81, 109, 137.
Semicircular canals, 392, 393.
Semilunar bone, 170.

cartilages, 183.

valves, 408 — 410.

Semi-membranosus muscle, 301—303,
305, 306, 318, 322, 338, 341, 344, 346
-350, 354, 355-
Semi-spinahs muscle, 291.
Semi-tendinosus muscle, 301 — 303, 318,

322, 338, 344, 348- 350, 354, 355.
Semnopithecus (Asiatic Ape), 443.

larynx of, 474.

liver of, 455.

Sense, organs of, 4, 13, 365.
Seps (a Saurian), 193, 199.

limb-bones of, 173, 174.

spine of, 57.

Septum lucidum, 370, 371, 373, 375.
Serial homologues, 215.

homology of muscles, 361.

subdivisions of limbs, 231, 232.

symmetry, 2, 10.
Serpents, alimentary canal of, 442, 446.

bronchi of, 469.

eye of, 388.

fangs of, 270, 271.

larynx of, 475.
•^ limb-bones of, 155

liver of 454.

liincrc of Ahc.

lungs of, 465.

muscles of, 308, 310, 314, 362.

nerves of, 399.

poisonous, teeth of, 275.

respiration of, 467.

scales of, 246.

skull of, 99, 101, 105, in, 115, 123,
128, 136, 140,142.

spine of, 37— 39, 42, 45, 47, 64, 67,
69, 72, 220.

teeth of, 254.

tongue of, 440.

urinary organs of, 482.
Serrati po«tici muscles, 289, 290, 321.
Serratus magnus muscle, 291, 292, 311,

313. 321, 325, 328.
Sesamoid, 209.
Sets of teeth, 250.
Seventh nerve, 105, 396, 399.

vertebra, 55.

Shackle-joints, 25, 277, 278.
Shaft of feather, 244.

of tibia, 183.
Shagreen, 277.
Shape of nails, 245.
Sharks, 20, 144, 222> 225-

alimentary canal of, 448, 449.

Sharks, arteries of, 416.

branchial arches of, 222.

circulation of, 419, 421.

exo-skrleton of, 277.

gills of, 477, 478.

have no swim-bladder, 466.

nerves of, 397, 398, 403.

peritoneum of, 458.

skull of, 119, 121, 124—128, 139,
J43-

spine of, 38, 59, 73.

teeth of, 256, 269, 273.

urinary organs of, 482.
Shedding of antlers, 279.

of skin, 238.
Sheep, alimentary canal of, 446, 448.

cutaneous g'ands of. 487.

exo-skeleton of, 245, 247.

limb- bones of, 164, 171, 172, 208,
210 — 212.

skull of, in, 130, 124, 135, 137,
139—141.

spine of, 48, 54.

stomach of, 443, 460.

teeth of, 261, 262, 268, 269, 275.

tongue of, 441.
Shell of Tortoise, 44, 64, 239.
Shin-bone, 183.
Shoulder, muscles of, 293.
Shoulder-blade, 145.
Shoulder-bones, 145.
Shoulder-girdle, 153.
Shrew Mouse, teeth of, 261.
Shrews, 16.

alimentary canal of, 446.

cutaneous glands of, 487.

limb-bones of, 154 — 160, 161, 164,
165.

peritoneum of, 459.

skull of, 115.
Shrimps, 7.
Siamang Gibbon, 236, 379.

larynx of, 474.

skull of, 122.

spine of, 64.
Side of brain, 370.
Sigmoid cavities of ulna, 149.
Siluroid Fishes, 96, 113.

mouth of, 435.

spines of, 278.

tongue of, 440.

Simplest myological conceptions, 364.
Sincipital region, 77.
Sinus, frontal, 91.

rhomboidalis, 386.

venosus, 410, 423, 426, 428.
Siren, 19.

limb-bones of, 152, 195.

lungs of, 464, 465.

skull of, 113.

spine of, 40.

thymus gland of, 485.
M M

530

INDEX.

Siren, trachea of, 468, 470.
Sirenia, 16.

limb-bones of, 166, 170, 189.

mammary glands of, 489, 490.

skull of, 117, 129.

spine of, 63.
Situation of teeth, 254.
Sivatherium, skull of, 129.
Sixth cervical vertebra, 54.

nerve, 390, 391, 399.
Size of brain, 378.
Skate, limbs of, 153.
Skeleton, 22.

external, 23, 236.

internal, 23, 214.

of face, 74.

of foot, 184.

of hand, 150.

of head, 74—144.

of lower limb, 177.

of spine, 25.

of upper limb, 145.

Skeletons, axial'andappendicular, com-
pared, 234.
Skin, 236, 238, 461.
Skull, 74—144.

Skunk, cutaneous glands of, 487.
Sloths, 17.

circulation of, 421.

larynx of, 474.

Jimb-bones of, 155, 156, 158, 164,
166, 169, 171 — 173, 175, 176, 189,
197, 201, 203, 206, 211 — 213.

liver of, 455, 456.

mammary glands of, 489.

muscles of, 342, 343, 345, 346, 356,

skull of, in, 114, 116, 13 r, 133, 142.

spine of, 43, 47, 5 1, 55, 68.

teeth of, 274.

trachea of, 469.
Slow Lemur, circulation of, 421.

larynx of, 473.

muscles of, 339.

spine of, 51.
Slow-worm (a legless Lizard), spine of

64.

Slugs, 6, 13.
Small intestine, 442, 446, 447.

sacro-sciatic ligament, 180.
Snails, 6. 13.
Snakes, 18.

cutaneous glands of, 487.

lungs of, 464.

skin of, 238.

See also Serpents.
Socket of thigh, 178.
Soft commissure, 371- -374.

pa.ate, 289, 434, 436.
Solar plexus, 404.
Soles, 20.

eye of, 389.

Soles, muscles of, 362, 363.

skull of, 128.

spine of, 60, 61, 220, 221, 224.
Soleus muscle, 305, 306, 352, 354, 361.
Sorex, 16.

limb-bones of, 156, 158, 160.

skull of, 103.

spine of, 58, 66.

teeth of, 261, 264, 265.
Sow, mammary glands of, 489.
Spalax (a Rodent), 16.

muscles of, 311.

skull of, 116.
Species, 6.
Sperm Whale, 16.

skull of, 128.

spine of, 44, 66.

Sphargis (a Turtle), trachea of, 469.
Sphenodon, 18.

ear of, 396.

skull of, 103.

Sphenoid, 75, 76, 78, 8r, 107.
Sphenoidal fissure, 76, 82, 83, no, 147.

sinuses, 93, 140, 141.

teeth, 2.54.
Spheno-maxillary fissure, 89, 134.

fossa, 89, 134.

Spheno-palatine foramen, 85.
Sphenotic, 103, 106, 110,227.
Spider Monkeys, 15.

muscles of, 324.

skull of, 136.

spine of, 50, 58, 72.
Spiders, 7, 12, 13.
Spigelian lobe, 452, 454, 455
Spinal accessory nerve, 88, 368.

cord, 25, 385.

enlargements, 386.

marrow, 4, 25, 385, 386, 400.

nerves, 385, 390, 397, 399, 401, 403.
Spinalis dorsi muscle, 290, 291.
Spinax, 20.

spine of, 38.
Spine, 25, 215.

curves of, 33,

of exo-skeleton, 243.

of ischium, 178 — 180.

of scapula, 145, 146, 155.

of tibia, 183.
Spines of Siluroids, 278.

of Teleostei, 277.
Spinous process, 27, 40.
Spiral valve, 448, 449.
Spittle glands, 433, 436.
Splanchnapophyses, 223, 224, 226.
Spleen, 445, 448, 449, 459, 483, 484.
Splenial bone, 98, uo.
Splenic artery, 449
Splenius muscle, 283, 289, 290, 322.
Sponges, 8.

Spoonbill, urinary organs of, 482.
Spurs, 247.

IXDEX.

531

Squalus, alimentary canal of, 448.
Squama of occipital bone, 78, 88, 90,

91, 98.
of temporal bone, 75, 76, 80. 90,

9L 98.
Squamosal, 98, 100, 102, 104, 121, 130,

134, 227.

bquamous suture, 79.
Squirrel Monkey, skull of, 137, 138.
Squirrels, 16.

skull of, no, 118.
teeth of, 259. 263,
Stag, antlers of, 279.

skull of, no, 137.
Stag of ten, 279.
Stapedius muscle, 396.
Stapes, 392, 393, 395, 396.
Star-fishes, 7, 10, 12.
Star-gazer (a Teleostean Fish), eye of,

389-
Steatornis (a Carinate Bird), trachea

of, 470.

Stellio (a Lizard), spine of, 66.
Stenostoma (a Snake), limb-bones of,

190, 193, 198.
Sternal ribs, 7:, 223.
Sterno-cleido-mastoid muscle, 286, 312,

Sterno-coracoid muscle, 325.
Sterno-hyoid muscle, 287, 315. 316.
Sterno-mastoid muscle, 283, 290, 327
Sterno-scapular muscle, 321.
Sterno-thyroid muscle, 287, 288, 316.
Sternum, 34, 64, 66, 161, 223, 226.
Stickleback, urinary organs of, 482.
Stomach, 441—443, 445, 447, 448, 453,
460.

lining of, 249.
Stork, skull of, 128.
Strix (Owl), skull of, 109.
Structure of electric organs, 405.

of nail, 244.

of teeth, 250, 269, 273.

of whalebone, 248.
Struthionidse, limb-bones o<", 159.
Struthious Birds, muscles of, 339.

spine of, 66.
Sturgeon, 20.

exo-skeleton of, 277.

limb-bones of, 154, 162.

mouth of, 435.

peritoneum of, 458, 459.

skull of, 96, 143.

spine of, 37, 39. 53-

spleen of, 484.

Stvlo-glossus muscle, 286—288, 314.
Styloid, 75- 80, 88, 106

process of radius, 149.

ulna, 149, 150, 168.
Ftylo-hyal, 123, 227.
Stylo hyoid bone, 396.
Stylo-hyoideus muscle, 286, 287, 313.

Stylo-mastoid foramen, 80, 88, 105.
Stylo-pharyngeus muscle, 286 — 288,

Subclavian artery, 412, 413, 418, 420.

vein, 422, 431, 432.
Subclavius muscle, 291, 292, 310, 311,

SIS, 31.5, 3i6, 326 327.
Suodivisions of limbs, serial, 231, 232.
Sub-kingdom, 5.
Sub-lingual glands, 437.
Sub-maxillary glands, 437 — 439.
Sub-operculum, 103.
Sub-orbital, 103.
Sub-scapular fossa, 145, 155.
Sub-scapularis muscle, 293, 325, 326,

329.

Succession of teeth. 252, 253, 271.
Sudis (a Teleostean Fish), skull of, 120.
Sudoriferous glands. 485.
Sulci of cerebrum, 366.
Superciliary ridges, 79.
Superficial flexor muscles of arm, 294.

flexors of leg, 305.
Superior articulating process, 28.
auricular muscle, 283, 308.
constrictor muscle of pharynx, 288.
maxillary nerve, 391.
oblique muscle of eye, 285.
rectus muscle of eye, 285.
vermis, 367, 373.
vesical artery, 414.
Supination, 149, 165, 166.
Supinator accessorius muscle, 333.
brevis muscle, 296, 297, 336.
longus muscle, 294 — 296, 310, 315

316,328,329, 333—335"
ridge, 147.

Supra-condyloid foramen, 165.
Supra-occipital, 79, 98, 103, 117, 119,

129, 130, 227.
Supra-orbital ridges, 79.
Supra-renal capsules, 483.
Supra-scapular, 153, 155, 161.

notch, 146.
Supra-spinatus muscle, 292, 293, 326,

328.

Supra-spinous fossa, 145, 146.
Surangular bone, 98, 120.
Sus, spine of, 65.
Suspensorium, 100, 108, 121.
Sutures, 24, 74, 77, 115, 126.
Swan, cutaneous glands of, 487.
larynx of, 474.
liver of, 454.
skull of, 137.
spine of, 47.
trachea of, 469.
Sweat glands, 485, 486.
Sweetbread, 449.
Swifts, limb-bones of, 213.
Swim-bladder, 465.
Swordfish, alimentary canal of, 450.

532

INDEX.

Swordfish, caeca of, 450.

skull of, 128.

Sylvian fissure, 368 — 370, 374.
Symbols of dentition, 253.
Sympathetic, 396.

system, 364, 401, 403, 404.
Symphysis, mandibular, U6, 122.

of ilia, 191.

pubis, 179.
Symmetry, antero-postenor, 10.

bilateral, 2, 10.

radial, 10.

serial, 2, 10.
Symplectic, 103, 30,6.
Synovial fluid, 24.
Syrinx, 469, 470.
Systemic veins, 421.

T.

Tadpole, 124.

circulation of, 417, 429.

thymus gland of, 485.
Tail, muscles of, 364.
Tail of Horse, 243.

of Iguana, muscles of, 323, 324.

of Rattlesnake, 246, 247.

of Spider Monkey, 72.
Tailed-Batrachians, circulation of, 417,
429

ear of, 394.

limb-bones of, 191, 193, 196, 202,
203, 206, 207.

muscles of, 324, 340, 350, 357, 359,
362.

spine of, 56, 60, 61, 64, 66, 69, 70.
Taipa, muscles of, 311.

spine of, 73.

teeth of, 265.

Tamandua Ant-eater, spine of, 66, 71.
Tanrec, 16.

limb bones of, 188.

skull of, 101, 102.

teeth of, 263.
Tapaia, teeth of, 268.
Tape-worm, n.
Tapir, 16.

limb-bones of, 212.

liver of, 456.

muscles of, 356, 357.

Skull Of, 112, 129, 13 T40.

teeth of, 268, 269.
Tarsius, 15.

eye of, 388.

limb-bones of, 200, 201, 204, 206,
207.

mammary glands of, 490.

muscles of, 344.

skull of, 138.

teeth of, 258.
Tarsus, 177, 184, 203.

Tarsus, compared with carpus, 232.

proximal bones of, 205.
Tasmanian Wolf, 17.

limb-bones o,f 194.
Teats, 490.
Teeth, 236, 238.

definition of kinds, 253.

development of, 252.

forms of, 257.

implantation of, 255, 256.

number of, 257.

situation of, 255.

structure of, 269.

succession of, 252, 253, 270.
Teleostean Fishes, swim-bladder of

465-
Teleostei, 20.

brain cf, 383.

branchial arches of, 480.

cutaneous glands of, 488.

spines of, 277.
Temporal artery, 412.

bone, 75, 79, 102.

fossa, 77.

gland, 486.

lobe of cerebrum, 368—370, 378.

muscle, 284, 285, 310, 316.

region, 77, 133.
Tench, skull of, 112.
Tendo Achillis, 186, 305, 306, 353, 358.
Tendons of flexor muscles, 332.
Tensor petagii brevis muscle, 320.

petagii longus muscle, 320.

tympani muscle, 80.

vaginae femoris muscle, 302, 341,

343-

Tentacles, 435.
Tentorium, 89, 136.
Terebratula, n.

Teres major muscle, 290, 292, 293, 326,
328.

minor muscle, 290, 292, 293, 326.
Terminal enlargement of spinal mar-
row, 386.

Terrapin, spine of, 52.
Testes, 371—373.
Testudo (a Tortoise), limb-bones of,

197, 198.
Tetraodon (a Teleostean Fish), muscles

of, 309.

Thigh, muscles of, 301, 302, 344.
Thigh-bone, 177, 180.
Thigh-glands, 488.
Thigh-socket, 178.
Third cornu, 373.

eyelid, 389.

nerve, 285, 390, 399.

trochanter, 197, 209.

ventricle, 371, 374, 375, 384.
Thoracic duct, 299, 430, 431, 463.

Fishes, 194.

limbs, 230.

INDEX.

533

Thorax, 32, 63, 67, 468.

of birds, 222.
Thousand-legs, 9, n.
Three-toed Sloth, 17.

limb-bones of, 156, 158, 169, 171

~J73» i?5> 211, 212.
muscles of, 321, 342, 343, 346, 356,

359-

spine of, 47, 55, 114, 115.
i hylacme, liver of, 456.
skull of, 123, 137.
spine of, 53.
Thylacinus, 17.

limb-bones of, 194.
Thymus gland, 485.
Thyro-hyal,87, 123.
Thyro-hyoid muscle, 287, 316.
Thyroid artery, 411, 429.

cartilage, 434, 471, 474, 475.
gland, 484.
Tibia, 183, 187, 190, 193, 196, 198, 200,

201, 203 — 205, 209, 210, 213.
Tibial adductor muscle, 344 — 346, 354,

355-

trpchanter, 181.

Tibialis anticus muscle, 303, 304, 322,
338. 34i, 345. 347. 348, 350—352.
354- 355, 357, 360-
posticus muscle, 305 — 307, 354,

355, 357-

posticus, groove for, 184, 201.

secundi digiti muscle, 353.
Tiger, 16.

muscles of, 310.
Tinamus (a Carinate Bird allied to the

Ratitse), skull of, no.
Tissue, muscular, 281.
Toads, 19,

brain of, 383.

cutaneous glands of, 488.

ear of, 394.

exo-skeleton of, 245.

limb-bones of, 161, 176, 191, 193.

respiration of, 470.

skin of, 238.

skull of, 99, no.

spinal marrow of, 386.

spine of, 65, 67.

trachea of, 468.
Toes, bones of, 212.
Tongue, 433» 434, 438, 439, 44 r-

muscles of, 286.
Tongue-bone, 87, 123.
Toothless Mammals, 254.
Tooth-like structures, dermal, 277.

epithelial, 276.
Torpedo (an Elasmobranch Fish),

nerves of, 405.
Tortoise-shell, 239, 240, 242.
Tortoises, 10.

cutaneous glands of, 487.

exo-skeleton of, 241.

Tortoises, limb-bones of, 164, 174, 175,
191, 196, 198, 212, 232, 234.

muscles of, 308, 362.

skull of, 113.

spinal marrow of, 316.

spine of, 38, 39, 41, 43, 44, 48, 59,

63, 64, 68, 69.
Tortoises, Land, 19.
Totality of man's nature, 497.
Toucan (a Carinate Bird), skull of, 142.
Trabeculae cranii, 93, 94, 101, 143, 226,

229.

Trachea, 407, 462, 467, 468, 471.
Trachydosaurus (a Lizard i, 162.
Tragulus (a Ruminant), liver of, 455.
Tragus, 393, 396.
Transversalis cervicis muscle, 323.

muscle, 298, 338.

nasi muscle, 283, 284.
Transverse bone, 121, 131, 227.

colon, 442.

fissure of liver, 452.

process, 27, 40, 215, 217.
Transversus pedis muscle, 308, 359.
Trapezium, 150, 151, 168, 170 — 172,

176. _
Trapezius muscle, 283, 289, 290, 310,

3", 3!3, 3J6.

Trapezoides, 150, 151, 168, 171, 176.
Triangularis sterni muscle, 299.
Triceps, 327— 329, 362.

muscle, 293, 294, 310, 313, 315,

316, 320, 325.
Trichschus, 16.
Tricuspid valve, 407, 408.
Trigeminal nerve, 368.
Triton (an Eft), limb-bones of, 170.
Trochanttric fossa, 181.
Trochanters, 181, 197.
Trochlea of a bone, 24.

of humerus, 147, 148.
True dermis, 240.

molars, 252, 253, 264.

skin, 486.

vertebrae, 26.
Trunk-fishes, 20.
Trunk, muscles of, 292, 296.

of Elephant, muscles of, 309.
Tube for tensor tympani muscle, 80.
Tbber cinereum, 369.
Tubercle of rib, 35, 69, 216.

of tibia, 183, 184, 201.
Tubercular process, 28, 216, 223, 224.
Tuberosities of femur, 181.

of humerus, 148, 164, 165.
Tuberosity of fifth metatarsal, 187.

of ischium, 178, 180, 193.

of radius, 148.

of tibia, 184.
Tunny (a Teleostean Fish), 219.

liver of, 454.

spine of, 53, 72.

534

INDEX.

Turbinal bones, 434.
Turbinals, 86, 113.
Turbot, caeca of, 450.

eye of, 389.

skull of," 128.

spine of, 57, 61.
Turtles, 19, 240.

limb-bones of, 170.

skull of, 100, 129, 133, 138, 139.
Two-toed Ant-eater, alimentary canal
of, 448.

limb-bones of, 206.

muscles of, 326, 330.

spine of, 66, 68.
Two-toed Sloth, 17.

limb-bones of, 155, 164.

liver of, 455.

spine of, 43, 47, 51, 68.
Tympanic, 80, 106, 114.

artery, 413.

cartilage, 434, 471, 474, 475.

membrane, 393.
Tympano-hyal, 81, 107, 227.
Tympanum, 395.
Types of brain, 384, 385.
Typical dentition, 259, 262, 266.

U.

Udder, 489.

Ulna, 149, 167, 168, 170, 176.

Ulaar artery, 412 — 414-

carpal ossicle, 170, 175.

nerve, 400, 401.

tuberosity, 148, 164, 165.
Ulnaris muscle, 310, 316.
Umbilical arteries, 424.

fissure, 452.

vein, 424, 425, 451, 452, 455.
Unc, forme, 150, 151, 167, 168, 172, 173,

176.

Uncinate process, 67, 71.
Ungual phalanges, 176.
Ungulata, 16.

limb bones or, 156, 157, 160, 192,
197, 209.

limbs of, 154.

skull of, 112

spine of, 43, 48, 62, 71 .
Ungulates, teeth of, 471.
Unicorn, 262.
Upper arm, muscles of, 293.

arm-bone, 145.

extremity, muscles of, 291.

limbs, -230.

muscles of, 324.
skeleton of, 145.

ribs, 41, 224, 226.

surface of brain, 366.

zygoma, 227.

Uranoscopus (a Teleostean Fish), eye
of, 389.

Uraster, 7, iq.
Ureter, 447, 480 — 482,
Urethra, 480.
Urinary glands, 481.

outlet, 482.

Urodeles, muscles of, 349, 351.
Urohyal, 103, 124.
Uromastix (a Lizard), limb-bones ol,

164.

Uropygial gland, 487.
Urotrichus (an Insectivore), teeth of

265.
Uvula, 434, 436.

V.

Vaginal process, 80.

Valves of heart, 407, 409, 410.

of lymphatics, 432.
Valvulae conniventes, 446, 448, 460
Vampire Bats, 16.

nasal organs of, 380.
Varanian Lizards, 116.
Varanus (a Lizard), 205, 213.

skull of, 121.

teeth of, 256.

Vastus externus muscle, 302, 303, 344,
346,347-

interims muscle, 302, 303, 305.
Veins, 406, 421.

in Bat's wing, 428.

pulmonary, 468.
Velum interpositum, 371, 372, 374,375.

of palate, 434-

terminalis, 377.
Vena azygos, 463.

cava, 299, 407, 408, 410, 422, 424,
425, 451, 452, 454, 456, 463, 468,
480.

portae, 424, 449,451.
Venous blood, 427.
Ventral fin, muscles of, 363.

laminae, 36, 218.
Ventricles of brain, 371—379, 381.

of heart, 407, 409, 410, 424, 462.

of larynx, 473, 474.
Vermiform appendix, 442, 446, 448.
Vermis of cerebellum, 367.
Vertebra, 25, 215.

a dorsal, 27.

seventh, 55.

sixth, 54.
Vertebrse, 6

cervical, 26, 47.

coccygeal, 33, 58.

dorsal, 26, 42.

false, 26.

in general, 39.

lumbar, 26, 51.

number of, 38.

ossification of, 61.

sacral, 27, 55.

JXDEX.

535

Vertebrae, true, 26.
Vertebral aponeurosis, ago.

artery, 412, 418.

canal, 25.

categories, 26.

margin of scapu'a, 146.

region, muscles of, 317.

rib, 71, 223.
Vertebrata, 6.
Vertebrates, their general character,

490-

V esical artery, 414, 419, 420.
Vespertilio (Common Bat], skull of,

115.

Vessels of liver, 451.
Vidian artery, 413.

canal, no.

nerve, 81.

Viper, lungs of, 464.
Virginian Opossum, 489.
Viscera of Fowl, 447.

of Lizard, 453.
Visceral arches, 5, 95, 143, 392.

clefts, 5, 393.

Viscero-skeletal muscles, 283.
Vitreous humour, 387.
Vocal cords, 473, 474.
Vomer, 85, 91, 98, 108, 119, 120, 134,
227.

Walrus, 16.

skull of, 115.

teeth of, 261, 265.
Wat.r, 2, 9.
Weasel, 16.

alimentary canal of, 448.
Web-fingered condition, 236.
Web-toed condition, 236.
Weight of antlers, 280.
Whalebone, 248, 249.
Whales, 16, 19.

brain of, 378.

breathing organs of, 462.

exo-skeleton of, 243, 247, 271.

limb-bones of, 190, 195, 198, 199.

mouth of, 247, 435.

muscles of, 336.

skull of, itg, 115, 122, 128, 138.

spine of, 48, 49, 53, 61, 64, 66, 68,

70, 220-

Whales; tongue of, 441.

trachea cf, 468.

whalebone of, 271. '
•Whale's mode of feeding, 248.
Whiskers, 243.
Whiting, alimentary canal of, 450.

caeca of, 450.

Whole nature of man, 497.
Windpipe, 434.
Wing movements, 328.
Wings of Bats, 237.

veins of, 428.
Wisdom tooth, 252.
Wolf, Tasmanian, 17.
Wombat, 17.

alimentary canal of, 488.

limb-bones of, 165, 198, 201, 202.

liver of, 455.

muscles of, 353, 354, 256, 357.

spine of, 53.

stomach of, 445.
Woodcock, 132, 139.
Woodpecker, skull of, 120, 124.

tongue of, 440.
Woolffian bodies, 481.
Worm of dog's tongue, 440.
Wrisberg, cartilages of, 473.

X.

Xiphias (Sword-fish), caeca of, 450.
Xiphi-sternal scute, 240.
Xiphi-sternum, 64.
Xiphoid process, 34, 35.

Z.

Zeus (a Teleostean Fish), 162.
Zootomy, 24.
Zygaena, 20.
Zygantrum, 45, 226.
Zygapophyses, 28, 40.
Zygoma, 76, 77, 114, 133.

lower, 227.

upper, 227.
Zygomatic glands, 438.

process, 75, 88, 101, 102.
Zygomaticus auricularis muscle, 284.

major muscle, 283, 284.

minor muscle, 283/285. \
Zygosphene,45, 226.

THE END.

RICHARD CLAY AND SONS, LIMITED.
LONDON AND BUNGAY.

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