William Kitchen Parker.

The morphology of the skull online

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Harvard College






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^. T. BETTANY, M.A., B.Sc,




[A\X Righti reterved,]

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2.' 3Lf.


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A SKETCH of the history of the skull in the principal
types of vertebrates is here for the first time presented.
It has been attempted to narrate the facts by means of a
consistent terminology, amplifying what Prof Huxley has
admirably developed; but the descriptions involve as
few theoretical opinions as possible. The convenience of
students has been considered throughout; summaries of
nearly every stage, and of each Chapter from the second
to the eighth, have been careftdly drawn up. By the
help of the index the history of individual bones or tracts
can be examined comparatively.

Many points of interest have necessarily been omitted
in a work treating of anatomy especially in a develop-
mental aspect. It is not expected that the book will be
thoroughly intelligible after mere reading. The limita-
tions of space and of illustration will in some cases
account for this; but frequently the complexity of the
structures described is such that a brief description may
easily lack cleamess. The student should consult the
very much larger series of figures to be found in original
memoirs in the Philosophical Transactions and elsewhere*;

1 Fowl, PhiL Trana., 1869; Frog, 1871; Salmon, 1878; Pig, 1874;
Axolotl, 1877 (in the press); Sharks and Bays, Zool. Trans., 1877.
A memoir on the Snake is in preparation.

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but personal dissection will in many cases be required for
a full comprehension. It is hoped that the book may be
found useful as a help to practical work. The types
chosen are as accessible as any (the Newt or Salamander,
which will do as well, being substituted for the Axolotl).
The adult skull should first be mastered as far as possi-
ble; and then the earlier stages should be worked out
both by ordinary dissection, and by transverse and longi-
tudinal sections.

So far as interpretations are put forward, they are
given merely as honest endeavours, not as final judgments.
It has been our desire neither to exaggerate the value of
what is known, nor to force facts to bear more than legiti-
mate inferences. To assist many students to learn mor-
phology for themselves is far more our object than to
persuade them to accept our momentary ideas. Conse-
quently we have not discussed the views of the great
anatomists of the days before embryology had illuminated
the dark problems of animal structure. Our omission to
mention their names is due to no undervaluation of their
vast labours and the treasures they have bequeathed
to us.

One name, however, will remain ever connected with
the insight which realised the bearing on the vertebrate
skull of its developmental history. Prof; Huxley, since
delivering his Croonian lecture (Proc. Eoy. Soc. 1858),
has never rested in his eflforts to throw light upon this
subject; and he has had a very great share in the re-
searches and elucidations which have made this book
possible. His papers in various transactions and journals*,

1 Proc. Eoy. Soc. ; Proc. Zool. Soc. ; Jour. Geol. Soc. ; Decades Geol.
Suryey; Jour. Anat. and Phys.

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and his larger works*, bear the most emphatic testimony
to his labours. We express our cordial acknowledgments
to Mr F. M. Balfour, M.A., Fellow and Lecturer of
Trinity College, Cambridge, for reading many pages of
proof-sheets, and especially for his kind help in reference
to the first Chapter.

The illustrations are, with very few exceptions, repro-
ductions, mediate or immediate, of Mr Parker's original
drawings; some of them have appeared previously in other
works. They have been drawn on wood by Mr T. P.
Collings, and engraved by Mr J. D. Cooper.

In concluding our difficult task, we cannot but ask in-
dulgence for the errors or imperfections which must neces-
sarily be associated with the first production of a work on
what may be called almost a new subject.

1 Elements of Comparative Anatomy: Anatomy of VerUhrated

London, September, 1877.

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Pbblimimabt Embbtoloot ... 1


The Skulls of thb Dogfish and the Siatb 14


The Skull of thb Salmon ... 43
Appendix on the Skulls of Fishes 83

Mursenoids 83, Silnroids 84, Ganoids 84, Ceratodos 87, Lepido-
siren 88, GhimsBra 89, Elasmobranohs 89.


Thb Skull of thb Azolotl ... 91

Appendix on the SkoUs of Urodeles 129

Proteos 129, Siren 130, Menopoma 131, Menobranchns 133,
the Salamandrine Skull 134.


The Skull of the Common Frog . . .136

Appendix on the Skulls of Anura 176

Rana pipiens 176, Pseudis 176, Bufo 177, Dactylethra 177,
Pipa 181.

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The Skull op the Common Snake . . 187

Appendix on the Skulls of Reptiles 213

Chelone 213, Lizards 215, Crocodiles 217.


The Skull op the Common Fowl . . . 219
Appendix on the Skulls of Birds . 262

Struthionidse 262, schizognathsB 262, desmognathsB 263, aegi-
thognathse 264, saurognathse 265.


The Skull op the Pia .... 267

Appendix on the Skulls of Mammalia 301

The Human Skull 304


The MoRPHOLoaT op the Skull . . . 310

The Cartilaginous Skull 310; the Sense Capsules 320; the
Arches 326; the Cranial Nerves 332; plan and segmentation of
the Cartilaginous Skull 336; the Osseous Skull 343; Evolution 358.

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1. Head of embryo Dogfish, 11 lines long 15

2. Head of embryo Dogfish, 11 lines long, median longitudinal

section 17

3. Head of embryo Skate, 1\ in. long 20

4. Head of embryo Dogfish, 1| in. long 22

5. Head of embryo Dogfish, second stage ; basal view of oraninm 24

6. Head of embryo Dogfish, third stage; median longitudinal

. section . . 28

7. Skull of adult Dogfish, side view 86

8. Skull of Skate, nearly adult 40

9. Embryo Salmon, about J inch long; side view of head within

chorion 44

10. Embryo Salmon, about { inch long; upper view of head, dis-

* sected, the neural tissue having been removed ... 45

11. Embryo Salmon, about f inch long; lower view of head, with

the arches shining through 47

12. Embryo Salmon, partly hatched; median longitudinal section

of head 49

13. Embryo Salmon, not long before hatching; under view of

head, with arches seen through 50

14. Embryo Salmon, not long before hatching; lower view of

skull dissected, the branchial arches having been removed . 52

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16. Salmon Fry, second week after hatching; upper view of skull

dissected • 54

16. Salmon Fry, second week after hatching; transverse section of

head, through forebrain and eyeballs . • . . . 56

17. Salmon Fry, second week after hatching; side view of skull . 59

18. Young Salmon of the first summer, about 2 inches long; side

view of skull, excluding branchial arches .... 62

19. Adult Salmon; lateral view of chondrocranium with its ec-

tosteal bones « * • . . 69

20. Adult Salmon: median longitudinal section through skull,

after removal of jaws and arches « 70

21. Adult Salmon : side view of skull with all bones attached . 75

22. Head of Axolotl, just after hatching, side view ... 95

23. Larval Axolotl, about five lines long; upper view of skull,

dissected 99

24. Larval Axolotl, about five lines long ; transverse vertical section

of head, through eyeballs *.••♦.. 100

25. Larval Axolotl, three-quarters of an inch long; upper view of

basis cranii and lower jaw, dissected • . . • « 104

26. Young Axolotl, 2 J inches long; under view of skull, dissected,

the lower jaw and gill-arches having been removed « • 109

27. Young Axolotl, 2 J inches long; upper view of skull; lower jaw

removed ••..••.«.. Ill

28. Adult Axolotl ; under view of skull, the lower jaw and arches

being removed, and also the investing bones on the right

side 115

29. Axolotl, nearly adult; side view of skull. .... 120

30. Skull of Amblystoma, side view 124

31. Tadpole four lines long, four or five days after hatching; side

view of head 137

32. Embryo Frog, just before hatching ; side view of head, with

skin removed 133

33. Tadpole of Common Toad, one-third of an inch long ; cranial

and mandibuhu: cartilages seen from above .... 141

34. Tadpole about one inch long; view of face and cranial floor

from above, the brain having been removed . . . . 144

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no, PAOB

35. Tadpole one inch long; side view of Bknll disseoied • . 146

36. Tadpole with tail beginning to shiink; side view of sktill

without branchial arches ••••••• 150

37. Yomig Frog, -with tail just absorbed ; side Tiew of skull . , 155

38. Yonng Frog, near end of first summer; npper view of skull,

with left mandible remoTed, and the right extended outwards 158

39. Adult Frog; side yiew of auditory region, with semioiroular

canals and parts of middle ear displayed • • . . 161

40. Adult Frog; upper view of skull with investing bones and

lower jaw removed • . 163

41. Adult Frog ; median longitudinal section of skull^ lower jaw

removed ,,..,.««.. 165

42. Adult Frog; upper view of skull ••««•• 166

43. Adult Frog; under view of skull ...... 168

44. Adult (edible) Frog: under view of skull; investing bones re-

moved on right side (Huxley) ...... 169

45. Adult Frog; side view of skull, dissected 171

46. Adult Frog ; columella auris 172

47. Adidt Frog ; hyobranchial plate 173

48. Embiyo Snake, Ij iuch long; side view of head with facial

arches seen through •.....•• 190

49. EmbTyo Snake, about Ij inch long ; chondrocranium seen from

above, the braili and jaws having been removed . . .191

50. Embryo Snake, about 2) iuohes long; side view of head,

dissected • • • . 196

51. Adult Snake; side view of skull, with jaws removed , • 206

52. Adult Snake; under view of skull ,«•••• 208

53. Adult Snake; skull seen from above. . « « , , 210

54. Embryo Chick of the fourth day of incubation: head viewed

from below as an opaque object (Foster and Balfour) . . 220

55. Embryo Chick, fifth day of incubation ; view of cranial struc-

tures from above 221

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56. Embryo Chick, fifth day of incubation; head Tiewed from

below, with skeletal parts seen through .... 222

57. Embryo Chick, sixth day of incubation ; head seen from

below (Huxley) 224

58. Embryo Chick, seventh day of incubation; side view of skull. 226

59. Embryo Chick, middle of second week of incubation; under*

yiew of skull, with arches removed 232

60. Embryo Chick, end of second week of incubation ; posterior

view of cranium 235

61. Embryo Chick, end of second week of incubation; inner view

of hinder part of cranium 236

62. Embryo Chick, end of second week of incubation; upper view

of skull, the brain and parostoses being removed . . . 238

63. Chick two days old ; median longitudinal section of skull, the

brain being removed 242

64. Chick two days old ; external lateral view of skull . . 244

65. Chick two days old; under view of skull, with lower jaw re-

moved 246

66. Fowlof first winter; median longitudinal section of skull . 250
67 — 71. Views of nasal structures of Fowl of first winter . . 252

72. Fowl several years old; side view of skull .... 254

73. Fowl several years old; under view of skull with lower jaw

removed 256

74. Adult Fowl ; side view of columella auris .... 258

75. Fowl several years old : hyobranchial apparatus from above . 259

76. Embryo Fig, two-thirds of an inch long; side view of head

and neck 268

77. Embryo Pig, two-thirds of an inch long ; elements of the skull

seen'somewhalrdiagrammatically from below . . . 270

78. EmbryoFig,tw«-third8 of an inch long; palatal view . . 272

79. Embryo Fig, an inch and a third long; median longitudinal

section of head, with nasal septum removed .... 281

80. Embryo Pig, an inch and a third long; posterior view of a

section through the basal region of the skull . . . 284

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81. Embryo Pig, an ineh and a third long; side view of man-

dibular and hyoid arches 285

82. Embryo Pig, 2} inches long ; under Tiew of sknll with lower

jaw removed 287

83. Embryo Pig, 2^ inches long ; vertical section of head, showing

stmctnres between and beneath the orbits .... 290

84. Embryo Pig, six inches long; outer view of occipital and

auditory regions . 293

85. The Pig at birth ; outer view of auditory capsule, Ac. . 290

86. Auditory chain of bones ib.

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1. In the study of the morphology of the skull, it
is necessary to take into account all the forms whicb the
skull assumes, from its origin in the embryo to its adult
condition. Inasmuch as skeletal elements are apparent
in the head at a very early period of development, no
student will thoroughly apprehend their nature without
some knowledge of the processes by which the body of
a vertebrated animal is evolved trom its germ. The
following summary is intended to reiresh the memory
of those who have studied embryology practically, or
by reading special treatises, and also for the information
of others who may not have time for such study.

2. The fertilised and developing ovum of all ver-
tebrates contains a membrane called the blastodet^m or
germinal membrane, which is the rudiment of the future
animal It is produced by a process of segmentation,
varying greatly in details, affecting the whole or part ot
the primary ovum.

3. The blastoderm, at an early stage after its forma-
tion, consists of three layers of cells. The upper or ex-
ternal layer is called the epiblast; the middle layer, the
mesohlast ; and the lower or inner, the hypoblast. The
epiblast gives rise (1) to all the epidermis and epidermic
appendages of the body, (2) to the epithelial Uniag of

^^B.M. 1

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the cerebro-spinal canal a^d its derivatives, the ventricles
of the brain, (3) to the cerebro-spinal nervous centres,
and (4) to various parts of the organs of special sense.
The hypoblast is the source of the epithelium of the
alimentary canal and all the organs developed as diver-
ticula from it. From the mesoblast the remaining parts
of the body are derived, including muscles, bones, con-
nective tissue, and blood-vessels ; the generative and
urinary organs ; the dermis, and the mucous membranes
of the alimentary canal and of the organs connected

4. To produce this diversity of parts, the layers of
the blastoderm become thickened in various regions;
folds and pits arise in many situations, and form pouches,
sacs tubes, and processes ; the mesoblast especially splits
into distinct strata. At the same time the cells com-
posing the layers gradually alter their character as they
multiply, and, instead of being very much alike, become
more and more unlike, and specialised for the functions
they have to perform in the growing organism. In most
cases the blastoderm sooner or later grows round the
mass of nutritive material constituting the yelk, and
encloses it\

5. A portion of the blastoderm is directly developed
into the embryo : among the functions of the remainder
is the absorption and transmission of nutriment to the
embryo. The locality of the latter is early marked out
by the formation of a trench bounding an oval region
in the blastoderm. The part enclosed becomes thence-
forth the embryo; and the demarcation is made more
definite by the trench, as it grows, continually under-
mining the enclosed parts. As this trench extends inwards,
the embryo rides upon the rest of the blastoderm, now
called the umbilical vesicle, and its enclosed yelk. The

^ This description wiU not hold Rood for Mammals, where there is no
proper yelk ; but the main facts, independently of those due to the exist-
ence i)f the yelk, are true fur them. It is not intended to include the
development of Amphioxus in this general view. The account in § 6
Requires modification in its application to Osseous Fishes.

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head of the creature is from the first distinguishable as
being included within the earliest developed part of the
trench, at one end of the oval. Afterwards, certain mem-
branous appendages, the amnion and the allantois, arise
in the development of several classes of vertebrates : for
their description the reader is referred to general embryo-
logical works.

6. We have described the formation of a simple
longitudinally tubular embryo by gradual constriction of
a portion of the blastoderm from the remainder. Coinci-
dent with this process is another, by which a second
longitudinal tube is formed parallel with and alH)ve the
first. This arises by the growth of two parallel folds
from the upper surface of the embryo along its axis,
having a shallow longitudinal groove between them.
These medullary folds, after growing to a certain height,
arch over towards each other and coalesce, for a greater
or less distance, so as to form a tube open at both ends ;
it is the neural tube, in connection with which the
cerebro-spinal nervous system takes its rise. The an-
terior and posterior openings of the tube become closed
at a variable perioil after its formation.

7. The neural tube is necessarily lined with epiblast,
since it originates on the upper or epiblastic surface of
the embryo. When it is closed, there is an external
epiblastic surface as before, and an internal epiblast
lining the tube. Between these two strata the growing
mesoblast gradually penetrates until it has completely
separated the outer from the inner epiblastic layer. The
neural canal marks the dorsal region of the embryo ;
while the parts beneath it belong to the ventral aspect
of the body.

8. The original embryonic cavity, or space con-
stricted off by the trench as it grows inwards, is con-
verted into a double tube by a process of splitting, which
divides the mesoblast into two layers. The inner of
these layers, where it comes into relation with the
hypoblast^ forms with it a membrane called the


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splavchnopleure, or visceral wall : while the outer layer of
raesoblast with the adherent epiblast is known as the
somatopleure, or body-wall. The splanchnopleure grows
inwards on the ventral side of the embryo more rapidly
than the somatopleure ; and it early forms a very distinct
alimentary tube, shut off from the umbilical vesicle. A
space is thus left all round the digestive canal between
the somatopleure and the splanchnopleure : this is the
pleuroperitoneal cavity. The somatopleure of either side,
growing towards the middle ventral line at a slower rate,
meets its fellow eventually and coalesces with it to form
the ventral wall^

9. The main organs of the body which surround the
alimentary canal are developed, (1) as pouches or tubular -
protrusions from the wall of the digestive tube in different
situations : these tubes becoming branched, and sur-
rounded by differentiated mesoblast, gradually assume
characteristic forms, and fill up the larger portion of the
original pleuroperitoneal space, which however every-
where surrounds them; the lungs, liver, and pancreas
are good representatives of this class ; of course all these
organs contain hypoblast ; (2) as thickenings and develop-
ments of the mesoblast, independently of 4ihe hypoblast or
epiblast; such are the Wolffian bodies, kidneys, and sexual

10. A structure of great importance arises early,
along the axis of the embryo, between the neural and
the alimentary tube. One or other of the principal-
germinal layers* gives origin to a median longitudinal
string of cells, forming an axial rod beneath the floor
of the neural tube. Anteriorly this rod, called the noto-
chord, does not extend quite so far forwards as does the
neural canal. The formation of the limbs, as paired out-
growths from lateral ridges on the sides of the embryo,
must not engage our attention here.

^ The controverRy in vhicli the subject of the origin of the noto-
chord is at present involyed lenders this indecision necessary.

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11. The neural tube and the rudiments of the nervous
system in the anterior region of the body very early
manifest differentiation from the corresponding parts
behind them. The cephalip end of the tube is d Dated in
a pyriform manner: this dilatation increases in all di-
mensions, and its walls show a series of constrictions.
Ultimately, out of the fore end of the tube, three cerebral
vesicles are formed, one behind another, having their

Online LibraryWilliam Kitchen ParkerThe morphology of the skull → online text (page 1 of 31)