' J|
■ ;i
i i l :
: l t
[ a \ \
bounded before anil beliind by two sliarp lines which oiler tlicmsclvcs to the ovbilal and temporal fossæ ;
. the superciliary ridge is assisted by the squamose orbitar process of tlio median frontals anil throws
itself forwards and downwards to meet the orbitar process of tlic intermaxillaries. The descending
temporal artmdarprocess is rounded, tliick and grooved.
Connexion. Behind by an exceedingly strong articulation to the temporals, above with the
anterior edge of the parietals, before by squamose suture with tlic median frontals and intcrmaxillaries
and posteriorly and below with the jugals by harmonía.
T he J ugular Bones. / . These, like the maxillaries, arc triangular but they are not so long.
Their base has upon its inner body the concavity for the posterior and inferior portion of the eye. They
are rounded externally and terminate in a temporal spinous apophysis behind.
Connexion. Above and behind with the posterior frontals, below n ith the temporals and before
with the maxillaries.
The T emporal Bones, g. The temporalia are long, curved and slender. They may be divided
into an outer convex surface, an upper and inner concave one, an internal irregtdar smface and a
petrous portion situated at the base of the cranium. Tlic outer convex and inner concave surfaces are
separated by a sharp ridge, in continuation of that of the posterior fronlals, whicli completes the inferior
boundaiy of the temporal fossæ.
Connexion. They join the mastoides behind, within the tympani, above tlie parietals and before
the posterior frontals and jugals by serrated suture.
T he Mastoides. h. Tliesc somi-globulav Imnes compose with tlic temporals the external articular
base of the head. They are convex without and above, slightly llaltencd within and hollowed around
the large tubercle whicli reposes upon the coronoid bone of the inferior jaw.
Connexion. Above and anteriorly by serration to the temporals and within to the ossa tympani and
external occipitals.
The T vmpanal Bones, i. The tympanals arc the smallest bones of the cranium. They arc flat
and have synarthrodial edges and a semi-lunated surface.
Connexio7i. Tiicso bones articulate by suture witli the temporals, mastoides and external occipitals.
T he P arietalia. j . Commencing at the posterior extremity of thc mcdian frontals, the parietal
bones extend themselves far backwards to form the roof of tlic skull and tlic superior boundary of tlic
temporal fossæ. Wo observe upon their outer cojiue.T surface many depressions; witliin tliey are
irregularly concave.
Connexion. ■ Tliey arc articulated before witli the incdian and posterior frontals, beliind and below to
the temporals and at thoir base with the superior and external occipitals.
T he Superior Occipital Bone. k. This bone is large and has f«i ea-ZerndiJ and rtjjosierior eoiiuea.-
surface, an upper articular serrated bàrder, an inferior semidunar edge, two inferior arlictdar surfaces
and two lateral one's.
Co7inexio7i. Aljove tliey join the parietal bones by serration, below and witliout the lateral occipitals
and laterally the external occipitals.
The Inferior Occipital Bone. I. The inferior occipital bone, which is much smaller than the
preceding one, closes the base of tlic skull. It has « posterior and an anterior concave body, two
articular cavities for llic lateral occipitals and an upper and under surface. The aiiterior concave
portion receives the body of the sphenoid. The upper surface is smooth and concave in its middle from
side to side to support the medulla oblongata and its accompanying vessels.
Connexion. Superiorly with the lateral occipitals, posteriorly and below with tlic atlas and before
with llie sphenoid.
The L ateral Occipitals. hi. The lateral occipitals are thick at their median portion and
squamose at Iheir edges. They have two articular ends, an internal semi-lunar edge for the great
foramen and un anterior one sharpened and thin. Posteriorly they arc convex from witliin to without,
and before internally concave.
Connexion. Above they join the superior occipital, below the inferior, without the external occipitals
and behind the bony arch of the atlas by cartilaginous symphysis.
45
T he E xternal Occipitals. 7i. Tliese bones are more squamose than the last and have a posterior
rounded terminatioti, an anterior serrated edge, an irregular region internally and an external and
inferior flattened one.
Connexion. Beliind witli tlie mastoidean bones, without and before to the superior and two lateral
occipitals, above witli the parietalia and anteriorly with tlio tympani.
T he Sphenoid Bone. o. Tliis azygous bone offers an inferior sharp ridge, an internal flattened
surface posteriorly, an anterior spinous apophysis, two flat and considerably deep sides and a posteiior
articular base. Its inferior sharp ridge commences immediately in front of the median part of the
inferior occipital bone and advancing forwards is inserted between tlie pterygoidcans at tlie commencement
of tlieir synarthrodial junction. Its internal flattened surface supported tlic brain, tlie quantity of
wliich is proved to liave been extremely scant by its circumscribed proportions. Its articular base is
pyramidal and has its long diameter from above to below.
Connexion. Posteriorly with tlie inferior occipital and before with the pterygoideaii bones.
T he P terygoid Bones, p. The pterygoideans have a posterior thin body wliicli gradually widens
as it advances forwards until it meets without the palatals, and within, a t the anterior part of the iiinder
thiixl of the upper jaw and cranium, each otlier. Immediately after this conjunction they converge and
end finally in a spinous apophysis at tho middle of the anterior third of the head. Their upper portion
divides the orbits and nasal foramina by a spine; they arc slightly convex at their widest inferior
surface.
Co7inc.TtoH. Behind to the sphenoid bone, before with one another and the palatals.
The P alatals, q. The palatal liones are mucli wider than tlic pterygoids. They commence
beliind the jugals and passing forwai-ds occupy nearly the entire part of tlie anterior roof of (he mouth.
They are very thin.
Connexion. Posteriorly to the jugals and pterygoid liones, anteriorly to one anotiiei-, the maxillaries
and intcr-raaxillaries.
THE INFERIOR JAW.
T he Dental Bones, r. Tiie dental bones of both jaws of the Plesiosaurus are remarkable for
their anterior rostranalal form. Those of the lower jaw compose all that superior portion of it which
has relation to the tectii, the alveolar cavities for wiiich diminisli in size and depth from before to behind
until they disappear at their posterior sharpened and squamose commencement. The dental bones are
further distinguished by an elevated ridge which beginning at their hinder spinous apophysis advances
onwards and inwards until it meets its fellow, to wliich it isTinited by an immoveable articulation. Upon
its fore part arc two grooves with a direction from before to behind. The dentals are concave superiorly,
licneath convex and they have a great number of foramina upon tiieir upper and under surfaces.
Connexion. Behind and externally their spinous process is most firmly wedged between tlie anterior
portion of tlie angular and operculary bones, below their surface is opposed throughout lo those of the
opercularies, beliind and above tlicy are overlapped by tlic sur-angulars and anteriorly they unite with
one another by synarthrosis.
T he Operculary Bones, s. Tlic opercular bones arc ilattened from within to without. They
are thickest and strongest at the posterior part of the duck-billed snout and arc rounded within,
Anteriorly they sweil into a ¿ni-g-e luhercular form which at length ends in a point; posteriorly they
diminish in the same manner as the dental bones. Numerous foramina are found upon their «nZcnoí-
tuberculated portion.
Connexion. They form the inferior body of tho jaw situated licncath the orbits without, at which
rcgion they support the posterior process of the dental bones and the anterior part of tho anguiars.
Within they are in juxta-position with the angulars and sur-angulars, before with one another by
synartlirodial suture and behind with the inferior parts of tlie angulars and sur-angulars.
T he Angular Bones. I. Beneath and behind the temporal fossæ and in front of the articular
bones are placed the angulars,—two bones that have a considerable e.rienia? swr/nce and an internal
spinous process.
Connexion. Without, within and inferiorly the angular bones have connexion with the operculary
nnd dental bones, within and behind with the sur-angulars and articulars.
'to--'"' miiÉgniMiii iimn s