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Fig. 181.-HORIZONTAL SECTION OF THE SKULL A LITTLE BELOW THE LEVEL OF THE

INFERIOR ORBITAL MARGIN. 1, Canal for naso-lacrimal duct.

18. Mandibular fossa. 2. Middle concha.

19. Foramen spinosum. 3. Nasal septum.

20. Spine of sphenoid. 4. Middle meatus of nose.

21. Petro-squamosal fissure. 5. Naso-lacrimal duct.

22. Opening of bony canal of auditory tube. 6. Infra-orbital canal.

23. Carotid canal. 7. Opening into maxillary sinus from the middle 24. Upper opening of carotid canal (foramen meatus of the nose.

lacerum). 8. Roof of maxillary sinus.

25. Anterior opening of pterygoid canal. 9. Inferior orbital fissure.

26. Roof of pterygo-palatine fossa just above 10. Passing through pterygo-maxillary fissure spheno-palatine foramen.

into pterygo - palatine fossa and ending 27. Superior concha.

opposite opening of foramen rotundum. 28. Superior meatus of the nose. 11. Infra-temporal crest of great wing of sphenoid. 29. Placed in position of spheno - palatine 12. Zygomatic arch.

foramen. 13. Squamous part of temporal.

30. Placed in the pterygo - palatine fossa 14. Inferior surface of great wing of sphenoid.

near the upper part of the pterygo15. Cut pterygoid process.

maxillary fissure. 16. Tuberculum articulare.

31. Pterygoid canal laid open. 17. Foramen ovale.

SEXUAL DIFFERENCES IN THE SKULL.

Whilst it is a matter of difficulty, in all cases, to determine with certainty the sex of a skull, the following points of difference are usually fairly characteristic. The female skull is

, as a rule, smaller than the male. In point of cranial capacity it averages about a tenth less than the male of corresponding race. Undue stress must not be laid on these facts, since the female in bulk and stature measures on an average less than the male. It is lighter, smoother as regards the development of its muscular ridges, and possesses less prominent mastoid processes. In the frontal region, the superciliary arches are less pronounced, and this imparts a thinness and sharpness to the upper orbital margin, which is fairly characteristic, and can best be appreciated by running the finger along that edge of bone. For the same reason, the forehead appears more vertical and the projections of the frontal tuberosities more outstanding, though it is stated that the frontal and occipital regions are less capacious proportionately than in the male. The vertex in the female is said to be more flattened, and the height of the skull consequently somewhat reduced. In the male the edge of the tympanic plate is generally sharp, and divides to form the sheath of the styloid process, whilst in the female the corresponding border is described as being rounder and more tubercular.

Whilst it is true that no one of these differences is sufficiently characteristic to enable us to pronounce with certainty on the matter of sex, it is the case that, taken together, they usually justify us in arriving at a conclusion which, as a rule, may be regarded as fairly accurate. In some instances, however, it is impossible to express any definite opinion.

THE SKULL AT BIRTH.

The skull at birth is remarkable for the small size of its facial portion and the proportionately great development of its calvarial part, the former constituting only about one-eighth of the mass of the latter.

The bones of the cranial vault have not as yet the serrated edges which they exhibit at a later stage of growth, but are at present separated from each other by a narrow linear membranous interval, corresponding in position to the lines of the sutures by which they are ultimately united. At certain points, where these membranous sutures meet or intersect, there are areas, of varying outline, in which the space between the edges of the surrounding bones is formed of membrane only. This membrane corresponds to the overlying pericranium and the underlying dura mater. The larger of these membranous intervals, called fonticuli or fontanelles, are met with in correspondence with the angles of the parietal bone. Of these, two are placed medially, at either end of the sagittal suture.

The fonticulus frontalis, or anterior median fontanelle, formed by the convergence of four sutures, is the lozenge-shaped membranous interval between the rounded frontal angles of the parietal bones posteriorly and the sloping edges of the two halves of the frontal bone anteriorly, which are still separated from each other by the metopic suture. This space closes about the first half of the second year or later.

The fonticulus occipitalis, or posterior median fontanelle, at this stage is represented by a triradiate membranous interval interposed between the two parietals in front and the more or less pointed angular superior extremity of the occipital squama behind and below. The anterior limb of the triradiate area corresponds to the posterior more open part of the sagittal suture, whilst the lateral extensions slope laterally and downwards between the edges of the occipital squama and the posterior margins of the parietal bones on either side; variations in the outline of this fontanelle may be met with, owing to the persistence of the suture which separates the interparietal elements of the occipital bone into two halves. Closure of the occipital fonticulus takes place about the second month after birth.

The lateral fonticuli are situated at the sphenoidal and mastoid angles of the parietal bone. The fonticulus sphenoidalis, or antero-lateral fontanelle, corresponds to the region of the pterion, and is the irregular membranous interval between the sphenoidal angle of the parietal above, the posterior edge of the frontal anteriorly, and the margins of the great wing of the sphenoid and the pars squamosa of the temporal bone below; it closes from two to three months after birth.

The fonticulus mastoideus, or postero-lateral fontanelle, lies between the mastoid angle of the parietal superiorly and the mastoid portion of the petro-mastoid element of the temporal bone in front, the edge of the ex-occipital part of the occipital bone below, and the anterior margin of the supra-occipital element of the same bone behind. The site of this fontanelle corresponds to what is known as the asterion in the adult; it closes in from twelve months to two years after birth.

In any of these fonticuli independent ossicles of bone, called ossa suturarum, are liable to appear, and assist in the closure of the membranous area. At birth such an ossicle may appear in the fonticulus occipitalis, constituting what has been termed a pre-interparietal. And in the region of the pterion such ossicles have been described as epipteric bones; but it is doubtful if such independent ossicles have any morphological significance, and are not more readily accounted for on the assumption that they are mere irregularities in the ossification of the occluding membrane.

The sagittal fonticulus is occasionally seen in the skull at birth as a transverse fissure or angular cleft, notching the sagittal margins of the parietal bones, transversely to the line of the sagittal suture, and in correspondence with the position of the parietal foramina, the medial margins of which may, as yet, be unossified and formed merely by the membranous layer uniting the two bones. Frequently at birth all evidence of the previous existence of this fonticulus is absent.

Most striking at birth is the occurrence of outstanding bosses, tubera parietalia, on the surface of the parietal bones. These overlie the position of the primary ossific centres from which these bones are originally developed, and correspond to

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the greatest maximum width of the calvaria. They nark the position of what in the adult are known as the tubera parietalia, though, be it noted, that in the adult condition these reliefs need not necessarily correspond to the greater breadth of the head.

In like manner the sites of the centres from which the lateral portions of the frontal part of the frontal bone are developed are readily recognised by the presence of the frontal bosses, which impart to the child's forehead its bulging appearance, and correspond in later life to the position of the frontal tuberosities. As yet the two halves of the frontal part of the frontal bone are ununited, being separated by the frontal or metopic suture (sutura frontalis), which lies in direct continuation anteriorly with the line of the sagittal suture. The frontal suture is, as a rule, more or less completely fused by the sixth year.

The size of the infant's skull at birth varies considerably, and is to a large extent dependent on the bulk and development of the child. The size of the skull in female infants is absolutely smaller than in the case of male children, though not necessarily proportionately smaller, since the weight of female children at birth is on the average absolutely less than male foetuses at full term.

In viewing the skeleton of the face the observer is struck with the large proportionate size of the orbital and nasal apertures. The former are circular in outline, with sharp crisp margins. Under cover of the zygomatic process of the frontal bone the roof and lateral wall of the orbit is deeply recessed. The fossa sacci lacrimalis is oftentimes directed more towards the facial aspect than towards the orbital cavity. The superior and inferior orbital fissures are proportionately large, and the latter, in the macerated skull, forms a wide channel of communication with the fossa infratemporalis. The nasal aperture, apertura piriformis, is cordate in form, and exhibits a greater proportionate width than is met with in the adult; its inferior margin is not far beneath the level of the inferior orbital margins. The vertical depth of the maxillæ is small, and as yet the processus alveolaris is imperfectly developed, its inferior edge lying but little below the level of the inferior border of the arcus zygomaticus. Sunk in the alveolar border at this

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stage may be seen the relatively large hollows in which the dental sacs are lodged. Within the body of the maxilla the maxillary sinus is represented by a shallow groove, disposed in relation to the middle meatus of the nose. For this reason the space separating the orbital floor from the palatine surface of the bone is small, but is later increased to its adult proportions by the enlargement of the maxillary sinus and the consequent expansion of the body of the maxilla.

Viewed from the inferior surface, the hard palate is shallow, owing to the poor development of the alveolar border. The sutures between the ossa incisiva and the processus palatini of the maxillæ are readily recognisable, and the vertical height of the choanæ is seen to be relatively small, owing to the perpendicular parts of the palate bones not having reached their adult proportions.

The mandible consists of two parts united, in the median plane in front, by fibrous tissue to form the symphysis. The alveolar border is deeply grooved for the reception of the dental sacs, whilst the remaining substance of the body of the bone is but slightly developed. The foramen mentale pierces the bone about midway between its superior and inferior borders.

The ramus is proportionately wide, and forms with the body an angle which is very obtuse.

The coronoid process rises considerably above the level of the capitulum, and comes into close relationship with the crista infratemporalis.

The capitulum, which is proportionately more expanded than in the adult, occupies the somewhat laterally directed shallow mandibular fossa of the temporal bone.

On viewing the lateral aspect of the skull, the meatus acusticus externus, as such, is not seen; it is replaced by the slender annulus tympanicus, which supports the tympanic membrane. This ring of bone, incomplete above, is united by its extremities superiorly to the inferior surface and lateral aspect of the squamozygomatic part of the temporal bone. The ring itself is disposed so that it slopes downwards, forwards, and medially; as yet it fails to enter into the formation of the posterior wall of the fossa mandibularis, and only at a later stage does it grow laterally to form the floor of the external acoustic meatus. Through the ring the labyrinthic wall of the cavum tympani is seen ; exposed on this surface are the promontory, the fenestra vestibuli, and the fenestra cochleæ.

Posterior to the tympanic ring the sutura squamosomastoidea, still open, is seen separating the pars mastoidea from the squama temporalis of the temporal bone. On turning the skull over so that its inferior surface is exposed, the partes laterales of the occipital bone are seen separated in front from the pars basilaris by a suture, which runs through the occipital condyle on either side. Posteriorly an open suture, which curves backward and laterally on each side of the posterior margin of the foramen ovale, separates them from that part of the squama occipitalis which is developed in cartilage. The squama occipitalis at this stage exhibits a lateral cleft on each side, passing backwards from the fonticulus mastoideus, which serves to indicate the line of union of the parts which are developed in cartilage and membrane respectively. The latter, the superior, sometimes separate, constitutes the os interparietale.

DIFFERENCES DUE TO AGE.

At birth the face is proportionately small as compared with the cranium, constituting about one-eighth of the bulk of the latter. In the adult the face equals at least half the cranium. About the age of puberty the development and expansion of some of the airsinuses, more particularly the frontal sinus, lead to characteristic differences in form in both the head and face.

The eruption of the teeth in early life and adolescence enables us to determine the age with fair accuracy. After the completion of the permanent dentition, the wear of the teeth may assist us in hazarding an approximate estimate. The condition of the sutures, too, may guide us, synostosis of the coronal and sagittal sutures not as a rule taking place till late in life. Complete obliteration of the synchondrosis between the occipital bone and sphenoid may be regarded as an indication of maturity. In old age the skull usually becomes lighter and the cranial bones thinner. The alveolar borders of the maxillæ and mandibles become absorbed owing to the loss of the teeth.

This gives rise to a flattening of the vault of the hard palate and an alteration in the form of the mandible, whereby the mandibular angle becomes more obtuse.

THE BONES OF THE SUPERIOR EXTREMITY.

Clavicula.

The clavicle, or collar bone, one of the elements in the formation of the shoulder girdle, consists of a curved shaft, the extremities of which are enlarged. The medial end, since it articulates with the sternum, is called the sternal extremity; the lateral extremity, from its union with the acromion of the scapula, is known as the acromial end.

The extremitas sternalis (sternal end) is enlarged, and rests upon the disc

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