MORPHOLOGY OF THE SKULL 



95 



TIr' maxilla preseuts the fullDwinc: characters : — The maxillo-premaxillary suture i.s visible 

 on the palatine aspect of the bone. The alveolar border presents five sockets for teeth. The 

 infraorbital foramen communicates with the floor of the orbit by a deep fissure ; this fissure 

 sometimes persists in the adult. The antrum is a shallow ^Toove. 



The mandible at birth consists of two halves united by fibrous tissue in the line of the future 

 symphysis. Each half is a bony trough lodging teeth. The trough is divided by thin osseous 

 partitions into five compartments : of these, the fifth is the largest, and is often subdivided by a 

 ridge of bone. The floor is traversed by a furrow as far foi^ward as the fourth socket (that for 

 the finst milk molar), where it turns outwards at the mental foramen. This furrow lodges the 

 mandibular (inferior dental) ueiTe and artery, which enter by the large mandibular foramen. The 

 comlyle is on a level with the mental extremity of the bone. 



Fig. 106. — The Maxilla at Birth. 



premaxillary portion 



Outer view. 



Inferior view. 



Inner view. 



The palate bones diff'er mainly from the adult bone in that the vertical and horizontal plates 

 are of the same length ; thus the nasal fossae in the foetus are as wide as they are high, whereas 

 in the adult the height of each nasal fossa greatly exceeds the width. 



Concerning the remaining bones little need be said. The vomer is a delicate trough of bone 

 for the reception of the inferior border of the ethmo-vomerine plate ; its inferior border, that 

 which rests upon the palate, is broad, and the bone presents quite a different appearance from 

 the adult vomer. The nasal bones are short but broad ; the malar and inferior turbinals are 

 relatively very large ; and the lachrymals are thin, frail, and delicate lamell;«. 



The hyoid con.sists of its usual five parts. There is a median nucleus for the basi-hyal, and 

 one on each side for the greater cornua (thyro-hyals). The lesser cornua are cartilaginous. 



Fig. 1»»7.— Thk ^NlAxniBLfi at Birth. 



OUTER VIEW 



INNER VIEW 



Remnants of the cartilaginous cranium. — It has already been pointed out that at an early 

 date the base of the skull and the face are represented by liyaline cartilage, whitJi for the most 

 part is replaced by bone before birth. Even at birth remnants of this primitive chondral skull 

 are abundant. In the cranium, cartilaginous tracts exi.st between the various i)ortions of the 

 occipital bone, as well as 'at the line of junction of the occipital with the i)etrosal ami sphenoid. 

 The dorsum ephippii is entirely cartilaginous at birth, and the la.^t portion of this cartilage 

 disappears with the ankj'losis of the basi-uceipital and basi-s|)henoid about the twenty-fifth year. 

 A similar strip of cartilage lying between the jugular proce.ss and the jugular .surface of the 

 petrosal persists until late in life. A strij) of cartilage unites the ali-si)henoids with the linffulas, 

 and for at least a year after birth this cartilage is continuous with that which throughout life 



