The Vertebrate Skeleton

Name: The Vertebrate Skeleton
Author: Reynolds, Sidney H. (Sidney Hugh)

Reynolds, Sidney H. (Sidney Hugh)

Skeleton

The membrane bones of the upper jaw include first the _premaxillae_, a
small bone meeting its fellow in the middle line, and forming the
extreme anterior end of the upper jaw. It gives off on its dorsal
surface a backwardly-projecting process. It is connected behind with
the _maxillae_ (figs. 24 and 26, 10), a long flattened bone which forms
the greater part of the margin of the upper jaw, and gives off near
its anterior end a short process which projects upwards and meets the
nasal.

[Illustration FIG. 26. A, LATERAL VIEW OF THE SKULL, B, POSTERIOR VIEW
OF THE CRANIUM OF A COMMON FROG (_Rana temporaria_) × 2 (after
PARKER).

    1. sphenethmoid.
    2. fronto-parietal.
    3. pterygoid.
    4. squamosal.
    5. tympanic membrane.
    6. exoccipital.
    7. parasphenoid.
    8. pro-otic.
    9. quadratojugal.
    10. maxillae.
    11. nasal.
    12. premaxillae.
    13. anterior nares.
    14. mento-meckelian.
    15. dentary.
    16. angulo-splenial.
    17. basilingual plate.
    19. quadrate.
    20. columella.
    21. occipital condyle.
    22. anterior cornu of the hyoid (cerato-hyal).
    23. foramen magnum.

    II. IX. X. foramina for the exit of cranial nerves.]

Both maxillae and premaxillae are grooved ventrally, and bear, attached
to the outer more prominent margin of the groove, a row of minute
conical teeth. These teeth are =pleurodont=, that is, are ankylosed by
their bases and outer sides to the margin of the jaw. Each tooth is a
hollow cone, the basal part of which is formed of bone, the apical
part of dentine, capped by a very weak development of enamel.

The posterior end of the maxillae is overlapped by a small bone, the
_quadratojugal_ (figs. 24 and 26, 9), whose posterior end forms part
of the articular surface for the lower jaw. Just behind the
quadratojugal there is a small unossified area which lies at the angle
of the mouth, and is connected by a narrow bar of cartilage with the
cranium; this forms the =quadrate= (figs. 24 and 26, 19). A
backwardly-directed outgrowth from the cartilaginous bar more or less
completely surrounds the tympanic membrane, forming the tympanic ring.
When followed back the maxillae and quadratojugal diverge further and
further from the cranium, till the angle of the mouth comes to be
separated from the foramen magnum by a space nearly double the width
of the cranium. This space is bridged over to a considerable extent by
two triradiate bones, the _pterygoid_ and _squamosal_.

Public-domain text, read in full here on John Shaqi.

Opening the text

The Vertebrate SkeletonReynolds, Sidney H. (Sidney Hugh)

Science

The Vertebrate Skeleton

Reynolds, Sidney H. (Sidney Hugh)

Skeleton

The membrane bones of the upper jaw include first the _premaxillae_, a
small bone meeting its fellow in the middle line, and forming the
extreme anterior end of the upper jaw. It gives off on its dorsal
surface a backwardly-projecting process. It is connected behind with
the _maxillae_ (figs. 24 and 26, 10), a long flattened bone which forms
the greater part of the margin of the upper jaw, and gives off near
its anterior end a short process which projects upwards and meets the
nasal.

[Illustration FIG. 26. A, LATERAL VIEW OF THE SKULL, B, POSTERIOR VIEW
OF THE CRANIUM OF A COMMON FROG (_Rana temporaria_) × 2 (after
PARKER).

    1. sphenethmoid.
    2. fronto-parietal.
    3. pterygoid.
    4. squamosal.
    5. tympanic membrane.
    6. exoccipital.
    7. parasphenoid.
    8. pro-otic.
    9. quadratojugal.
    10. maxillae.
    11. nasal.
    12. premaxillae.
    13. anterior nares.
    14. mento-meckelian.
    15. dentary.
    16. angulo-splenial.
    17. basilingual plate.
    19. quadrate.
    20. columella.
    21. occipital condyle.
    22. anterior cornu of the hyoid (cerato-hyal).
    23. foramen magnum.

    II. IX. X. foramina for the exit of cranial nerves.]

Both maxillae and premaxillae are grooved ventrally, and bear, attached
to the outer more prominent margin of the groove, a row of minute
conical teeth. These teeth are =pleurodont=, that is, are ankylosed by
their bases and outer sides to the margin of the jaw. Each tooth is a
hollow cone, the basal part of which is formed of bone, the apical
part of dentine, capped by a very weak development of enamel.

The posterior end of the maxillae is overlapped by a small bone, the
_quadratojugal_ (figs. 24 and 26, 9), whose posterior end forms part
of the articular surface for the lower jaw. Just behind the
quadratojugal there is a small unossified area which lies at the angle
of the mouth, and is connected by a narrow bar of cartilage with the
cranium; this forms the =quadrate= (figs. 24 and 26, 19). A
backwardly-directed outgrowth from the cartilaginous bar more or less
completely surrounds the tympanic membrane, forming the tympanic ring.
When followed back the maxillae and quadratojugal diverge further and
further from the cranium, till the angle of the mouth comes to be
separated from the foramen magnum by a space nearly double the width
of the cranium. This space is bridged over to a considerable extent by
two triradiate bones, the _pterygoid_ and _squamosal_.

Public-domain text, read in full here on John Shaqi.

The Vertebrate Skeleton

The Vertebrate Skeleton

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