Premolars compressed, pointed; and the molars with quadrate tuberculated crowns.
Owing to this joint the whole upper beak can be moved up and down with extra facility, according to the shoving forwards or backwards of the palato-pterygo-quadrate apparatus which moves sledge - like upon the cranial basis.
The maxillaries are connected with the distal anterior corner of the quadrate by the thin, splint-like jugal and quadratojugal.
The quadrate is invariably a conspicuous bone and movably articulating with the cranium and by a special process with the pterygoid.
A membranous, or ossified, tube which rises from a pneumatic foramen in the os articulare, on the median side of the articulation, and passes upwards between the quadrate and lateral occipital bone, opening into the cavity of the middle ear.
The quadrate muscle adjusts the motion, and prevents pressure upon the optic nerve; during the state of relaxation of both muscles the nictitans withdraws through its own elasticity.
In many owls the right and left ears are asymmetrical, and this asymmetry affects the whole of the temporal region, all the bones which surround the outer and middle ear, notably the squamosal and the quadrate, so that the skull becomes lopsided, one ear being turned obliquely down, the other upwards.
Quadrate bone with single proximal knob.
A diagnosis covering all the Ratitae (struthio, rhea, casuarius, dromaeus, apteryx and the allied fossils dinornis and aepyornis) would be as follows - (i) terrestrial birds without keel to the sternum, absolutely flightless; (ii) quadrate bone with a single proximal articulating knob; (iii) coracoid and scapula fused together and forming an open angle; (iv) normally without a pygostyle; (v) with an incisura ischiadica; (vi) rhamphotheca compound; (vii) without apteria or bare spaces in the plumage; (viii) with a complete copulatory organ, moved by skeletal muscles.
Continuous series, with massive, quadrate, transversely ridged or complex crowns--the posterior premolars usually resembling the molars in structure.
The other upper premolars and molars all formed on the same plan and of nearly the same size, with four roots and quadrate crowns, rather wider transversely than from before backwards, each having four columns, connected by a pair of transverse ridges, anterior and posterior.
The quadrate is indirectly articulated with the skull, first by the horizontal, movable squamosal, secondly by the columella auris.
Of scaly reptiles with movable quadrate bones; with a transverse vent, near the posterior lateral corners of which open the eversible, paired copulatory organs.
G, prefrontal; M, maxilla; J, poison-fang; Tr, transpalatine; Pt, pterygoid; p, palatine; Q, quadrate; Sq, squamosal; Pm, premaxilla; T.a, articular; Pe and Di, muscles.
No ectopterygoid pterygoid not extending to quadrate; no supratemporal or squamosal; prefrontal forming a suture with nasal; coronoid present; vestiges of pelvis present.
Squamosal large, suspending the quadrate: Boidae.
Maxillary horizontal; pterygoid reaching quadrate or mandible.
Maxillary horizontal; pterygoid not reaching quadrate or mandible: Amblycephalidae.
Maxillary vertically erectile, perpendicularly to ectoptery goid, and reaching quadrate or mandible: Viperidae.
The quadrate bones are short and stand rather vertically.
The squamosals form part of the cranial wall, being firmly wedged in between the quadrate, prootic and occipital bones.
The quadrate is carried by the horizontally-elongated squamosal, which rests loosely upon the skull.
The quadrate is short and thick, and is carried by the broad and short squamosal, which lies flat against the skull, reminding in this respect of Ilysia.
The first and second molars have quadrate crowns, with four principal obtuse conical cusps, around which numerous accessory cusps are clustered.
To the left of the gall bladder is the quadrate lobe, which is in contact with the pylorus of the stomach.
To the left of this is the left lobe of the liver, separated from the quadrate lobe by the umbilical fissure in which lies the round ligament of the liver, the remains of the umbilical vein of the foetus.
The posterior boundary of the quadrate lobe is the transverse fissure, which is little more than an inch long and more than half an inch wide.
When these have united the Spigelian lobe re of ductus venosus mental tuberosity ageal groove End of right suprarenal vein Suprarenal impression R; ght end of caudate lobe Uncovered area of right lobe Renal impression Attachment of right lateral ligament Fissu Portal fissure Umbilical fissure Quadrate lobe Portal vein Gall bladder Duodenal impression 0 Oesoph Cohc impressio; From A.
In tracing the lobulation of man's liver back to this generalized type, it is evident at once that his quadrate lobe does not correspond to any one generalized lobe, but is merely that part of the right central which lies between the gall bladder and the umbilical fissure.
The under jaws are hinged on to the quadrate bones, which extend obliquely backwards, and are immovably wedged in between the squamosal and the lateral occipital wings.
The articulation of the mandible to the quadrate-bone is such as to allow of a very considerable amount of lateral play, and, by a particular arrangement of the muscles which move the former, it comes to pass that so soon as the bird opens its mouth the point of the mandible is brought immediately opposite to that of the maxilla (which itself is movable vertically), instead of crossing or overlapping it - the usual position when the mouth is closed.
The last premolar and the molars have quadrate crowns, provided with two strong transverse ridges, or with four obtuse cusps.
Molars with quadrate crowns and a blunt conical cusp at each corner, the last notably smaller than the rest, sometimes rudimentary or absent.
From both birds and reptiles the class is distinguished, so far at any rate as existing forms are concerned, by the following features: the absence of a nucleus in the red corpuscles of the blood, which are nearly always circular in outline; the free suspension of the lungs in a thoracic cavity, separated from the abdominal cavity by a muscular partition, or diaphragm, which is the chief agent in inflating the lungs in respiration; the aorta, or main artery, forming but a single arch after leaving the heart, which curves over the left terminal division of the windpipe, or bronchus; the presence of more or fewer hairs on the skin and the absence of feathers; the greater development of the bridge, or commissure, connecting the two halves of the brain, which usually forms a complete corpus callosum, or displays an unusually large size of its anterior portion; the presence of a fully developed larynx at the upper end of the trachea or windpipe, accompanied by the absence of a syrinx, or expansion, near the lower end of the same; the circumstance that each half of the lower jaw (except perhaps at a very early stage of development) consists of a single piece articulating posteriorly with the squamosal element of the skull without the intervention of a separate quadrate bone; the absence of prefrontal bones in the skull; the presence of a pair of lateral knobs, or condyles (in place of a single median one), on the occipital aspect of the skull for articulation with the first vertebra; and, lastly, the very obvious character of the female being provided with milk-glands, by the secretion of which the young (produced, except in the very lowest group, alive and not by means of externally hatched eggs) are nourished for some time after birth.
An osteological question which has been much discussed is the fate of the reptilian quadrate bone in the mammalian skull.
Thyng, who has carefully reviewed all the other theories, the balance of evidence tends to show that the quadrate has been taken up into the inner ear, where it is represented among the auditory ossicles by the incus.
The fate of the reptilian quadrate bone (which is reduced to very small dimensions in the Anomodontia) has been referred to in an earlier section of the present article, where some mention has also been made of the disappearance in mammals of the hinder elements of the reptilian lower jaw, so as to leave the single bone (dentary) of each half of this part of the skeleton in mammals.