Sphenoid bone

“ Each lesser wing is prolonged back into a tongue-like process, the anterior chnoid process, just internal to which is the optic foramen (fig. 5, 11) , and the two foramina are joined by the optic groove for the optic commissure. Behind this groove is a transverse elevation, the olivary eminence (22) , which marks the junction of the pre- and basi- sphenoid parts of the body of the sphenoid bone.
The middle cranial fossa is like an hour-glass placed transversely, as there is a central constricted, and two lateral expanded, parts. ”

“ Behind the lachrymal bone is the orbital plate of the ethmoid and in the suture between this and the frontal the anterior and posterior ethmoidal foramina are seen. Posteriorly the ethmoid articulates with the sphenoid, while at its lower and hinder part a small piece of the palate bone comes into the orbit. The outer wall of the orbit slopes backward and inward, the two opposite sides therefore converge as they run back. The malar bone, in front, and the great wing of the sphenoid, behind, form this wall. ”

“ Third Period.—There follows a slow and parallel growth of both brain and cranium. The ossification of the cranium itself reaches completion. At the age of seven the occipital is definitely solidified into a single bone and between the years of fifteen and twenty the [Pg 201] body of the sphenoid also becomes welded to the occiput. This process of synostosis begins from the interior of the cranium, and only subsequently manifests itself externally. ”

“ To illustrate the former viewpoint, I will mention a few of the formations in man which have been described as characterizing lower races, because they are found as typical developments in animals. One of these is a variation in the form of the temporal bone, which in man is ordinarily separated from the frontal bone by the sphenoid and parietal bones. It has been found that in some individuals the temporal bone encroaches upon the sphenoid and parietal, and comes into contact with the frontal bone. This formation is the prevalent one among the apes. ”

“ There are supra- and basi- as well as ex-occipital bones; the para-sphenoid is (? entirely) gone, and its place is taken by the basi- and pre-sphenoids, and the lateral walls contain fresh paired ossifications, the ali- and orbito-sphenoids-- all cartilage bones. The sphenethmoid is perhaps represented in part by the ethmoid.
As a result of the inflation of the brain-case, the squamosal, which slopes downward and outward in the frog, and overlies the cartilaginous suspensorium (quadrate cartilage) , has become a constituent of the brain-case wall, and slopes downwardly and in. ”

“ On the dorsal side of the cartilage there is a projecting ridge composed mainly of a bone known as the pterotic, sometimes erroneously [Pg 596] called the squamosal, and continued in front by the sphenotic. The pterotic, or the cartilaginous region corresponding to it, always supplies the articular surface for the hyomandibular.
In the floor of the skull, in the region of the pituitary body, there is formed a basisphenoid; while in the lateral parts of the wall of this part of the cranium, there is a bone known as the alisphenoid. ”

“ The upper jaw of Sphenodon and other Rhynchocephalia is provided with two parallel rows of teeth, one borne on the maxillae and one on the palatines, the mandibular teeth bite in a groove between these two rows. The bone of the jaws in Sphenodon is so hard that when the teeth get worn away, it can act as a substitute. In the young Sphenodon the vomers bear teeth, as they do also in Proterosaurus.
There is generally a continuous succession of teeth throughout life, the new tooth coming up below, or partly at the side of the one in use, and causing the absorption of part of its wall or base. ”

“ We can hardly regard the extraordinary air-cells which occupy the interspace of the two tables of the skull in the parietal and occipital bones of the Glossothere (Pl. XVI., fig. 3) as a difference depending merely on age.
The frontal and æthmoid bones are broken away in the present cranium. The sphenoid commences two inches in front of the foramen occipitale; the fractured state of the skull does not allow its anterior or lateral limits to be accurately defined; its body is occupied with large air-sinuses ”

“ There remain certain other membrane bones which are often found connected with the cranium. Of these, one of the largest is the parasphenoid which, in Ichthyopsids, is found underlying the basicranial axis. Prefrontals often, as in most reptiles, occur lying partly at the sides and partly in front of the frontal, and postfrontals similarly occur behind the orbit lying partly behind the frontals and partly at their sides. Lastly a squamosal bone is, as in Mammals, very commonly developed, and lies external and partly dorsal to the auditory capsules. ”

“ The opening of the fenestra ovalis is in the fresh skull occupied by the expanded end of the auditory ossicle, the columella, whose outer end articulates by a concave facet with a trifid extra-columellar cartilage which reaches the tympanic membrane. The lower process of this extra-columella passes into a cartilaginous rod which lies in a canal in the quadrate and is during life continuous with Meckel's cartilage within the articular bone of the mandible. ”

“ Hilaire and Cuvier, who agreed in thinking that ossification from a separate centre was the test of a separate bone, and that thus there were as many elementary bones in the skeleton as there were centres of ossification, Professor Owen points out that, according to this test, the human femur, which is ossified from four centres, must be regarded as four bones; while the femur in birds and reptiles, which is ossified from a single centre, must be regarded as a single bone. ”

“ The schneiderian membrane growing at the same time with great rapidity, advances through the infundibular passages of the ethmoid bone, is now in immediate contact with the decaying fibres of the diploië connecting the two tables of the frontal bone, which may not yet be absorbed, and passing through amongst these, whilst the pulsation of its vessels causes them to be removed, it gradually scoops out for itself a wedge-shaped cavity between the two tables, which we denominate the frontal sinus. ”

“ The pterotic (9) forms a sort of wing or free margin behind the epiotic and over the ear-cavity. The opisthotic (10) is a small, hard, irregular bone behind the pterotic. The exoccipital (11) forms a concave joint or condyle on each side of the basioccipital (12) , by which the vertebral column is joined to the skull. The parasphenoid (13) forms a narrow ridge of the roof of the mouth, connecting the vomer with the basioccipital. In some fishes of primitive structure (Salmo, Beryx) there is another bone, called orbitosphenoid, on the middle line above and between the eyes. ”

“ Two varieties are recognised—the spongy or cancellous, and the ivory or compact. The spongy or cancellous osteoma is really an ossified chondroma, and is met with at the ends of the long bones (Fig. 52) . From the fact that it projects from the surface of the bone it is often spoken of as an exostosis. It grows slowly, and rarely causes any discomfort unless it presses upon a nerve-trunk or upon a bursa which has developed over it. The Röntgen rays show a dark shadow corresponding to the ossified portion of the tumour, and continuous with that of the bone from which it is growing (Fig. 138) . ”

“ Beyond the lower-part of the said Fissure, toward the hinder-part of the Head, is to be seen {85}in the Os Sphenoides on each side, a Hole that doth not penetrate the Basis of the Skull, but makes a kind of Ductus, about an Hair's breadth long, which is open'd behind the Orbit on the top of the Space between the Apophysis Pterygoides, and the third Bone of the Jaw ”

“ But in the case of the true Placoids that analogy is faint indeed. Their skeletons contain true bone;—the vertebral joints of the Sharks and Rays possess each, as has been shown, an osseous nucleus, which retains, when subjected to the heat of a common fire, the complete form of the joint; and their cranial framework has its surface always covered over with hard osseous points. But though their skeletons possess thus their modicum of bone, unlike those of embryonic birds or mammals, they contain, in what is properly their cartilage, no gelatine. ”

“ The whole organ is best developed in Sphenodon, even in the adult; but whether it is still functional, and what its function is, remain unknown. The throwing of a beam of light upon this eye, by means of a lens, produces no effect. Whilst in Sphenodon the “lens” is rather dull and the efferent nerve is still present, in various lizards the “lens” is more perfect, but the nerve is degenerated. We conclude that the whole organ is now without the least visual function, whilst in various extinct groups of reptiles and Stegocephali it was fully developed. ”

“ And this may possibly be the reason why the bones of the skull, though not exposed to forces such as those which produce, in other bones, dense outer layers including less dense interiors, nevertheless repeat this general trait of bony structure. While, however, it is beyond doubt that some bones are not due to the direct influence of mechanical stress, we may, I think, conclude that mechanical stress initiates bone-formation. ”

“ The lateral aspect of the clavicle is prone to osteoporosis and is consistent with other bones containing a neural crest component (skull vault) being resistant to osteoporosis.
In conclusion, this study shows that genes associated with bone mass and mineral density are differentially expressed in functionally distinct skeletal sites. Our observations also demonstrate developmental gene expression-based “positional identity” in the adult skeleton. ”

“ Numerous membrane bones cover the chondrocranium externally. In the Dipneusti36 the chondrocranium is strengthened in the adult by numerous bones. One of the most characteristic is the great palatopterygoid bone which develops very early by the spreading of ossification backwards from the tooth bases, and whose early development probably accounts for the non-development of the palatopterygoid cartilage. ”

“ Sphenodon, on the contrary, has the quadrate bone firmly fixed to its adjacent bones at both ends, and is quite immovable. The vertebrae are biconcave like those of all early reptiles, not concavo-convex as are the vertebrae of most other living reptiles. The intercentra or hypocentra, little wedge-shaped bones [Pg 177] between the centra below, are more persistent in Sphenodon than in any other living land animals except the gecko lizards. Upon the whole the tuatera is the most old-fashioned of living reptiles, and in consequence it has nearly lost out in competition with new things. ”

“ The skull-cap may 47be now removed; for which purpose the cranium is to be sawed in a circular direction, about a finger’s breadth above the superciliary ridges, and lateral sinuses; the operation must be conducted with great care, or we shall be in danger of wounding the dura mater; the bone must be then divided by a few slight strokes with the chissel and mallet. We shall always find a strong adhesion between the inside of the cranium, and the dura mater ”

“ Further, as the transverse dimensions of the bone increase, the materials composing its convex and concave layers, becoming further from the neutral axis, become better [354] placed for resisting the strains to be borne. So that both by the increased quantity of dense matter and by its mechanically more-advantageous position, the bendings of the bone are progressively decreased. But as they are decreased, each new layer formed on the concave surface has its substance and its vessels less compressed; and the resulting growth and induration are rendered less rapid. ”

“ Glycosaminoglycan (Gag) concentrations are higher in limb bone. Osteocyte density in the limb bone was decreased in OVX animals, which is consistent with OVX-induced decreases in other non-cranial skeletal sites [26] . However, the osteocyte density in skull bone was unaffected during growth in an ovarian estrogen-depleted animal. This is consistent with differential responses of regional skull and limb osteoblasts and the pattern of bone loss induced by menopausal hormonal changes. However, we can not preclude that any decrease is partly in response to ageing [27] . ”

“ Polypterus [199] ) the chondro-cranium is complete in the ethmoidal and post-orbital regions, except where it has been partially replaced by cartilage bones, but in the inter-orbital region the continuity of the roof is interrupted by a large fontanelle, which is only closed by the investing frontal bones (Fig. 132, C) . There is also a large basi-cranial fontanelle in the sphenethmoid, closed, however, by the underlying parasphenoid. A large "occipital" bone continuously ossifies in the occipital cartilage and completely surrounds the foramen magnum.
{227}
Fig. ”

“ The third segment or ring consists of the presphenoid ventrad, of the frontals laterad and dorsad. The cranial opening of this ring is closed by the lamina cribrosa of the ethmoid.
The cranial portion of the skull therefore contains eleven separate bones: one occipital, one interparietal, two temporals, one sphenoid, two parietals, one presphenoid, two frontals, and one ethmoid.
The facial portion of the skull is much smaller than the [22] cranial, and lies craniad of the latter; it encloses the nasal cavity. ”

“ The state of the osseous system and the condition and number of the teeth, which strictly speaking are not bone, are among the surest guides in the determination of age. The signs furnished thereby may vary according to the periods of increase, maturity, and decline.
During fœtal life and even at the epoch of birth the bone centres are few. The distal end of the femur, the proximal end of the tibia, and the astragalus are ossified at birth. Points of ossification appear in successive order of development. ”