124 



THE SKELETON 



bones, are absent. Each angle of the parietal is in relation with a fontanelle. As in the adult, 

 the anterior inferior angle of the bone is prolonged downward toward the ali-sphenoid. 



The ethmoid consists of two lateral portions separated by the still cartilaginous ethmo- 

 vomerine plate. The ethmoid cells are represented by shallow depressions, and the uncinate 

 process is undeveloped. 



The sphenoidal conchas are two small triangular pieces of bone lying in the perichondrium 

 on each side of the ethmo- vomerine plate near its junction with the pre-sphenoid. (Indicated 

 by the * in fig. 145.) 



The maxUla presents the following characters: — The incisive suture is visible on the palatine 

 aspect of the bone. The alveolar border presents five sockets for teeth. The infra-orbital 



Fig. 152. — The Maxilla at Birth. 



Premaxillary portion 



Lateral view. 



Inferior view. 



Medial view. 



foramen communicates with the floor of the orbit by a deep fissure; this fissure sometimes per- 

 sists in the adult. The sinus is a shallow depression. 



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 forward as the fourth socket (that 

 for the first milk molar), where it turns outward at the mental foramen. This furrow lodges 

 the inferior alveolar nerve and artery, which enter by the large mandibular foramen. The con- 

 dyle is on a level with the upper border of the anterior extremity of the bone. 



The palate bones differ mainly from those in the adult in that the vertical and horizontal 

 plates are of the same length; thus the nasal fossae in the fcBtus 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, 



Fig. 153. — The Mandible at Birth. 



Lateral view 



Medial view 



which rests ui)on the hard palate, is l)n)!ul, and the bone presents quite a different appearance 

 from that in the adult. The nasal bones arc short and broad; the zygomatics and inferior 

 conchae are rolativoly very large; and the lacrimals are thin, frail, and delicate lamellae. 



Tlie hyoid consists of five parts. There is a median nucleus for the basi-hyal, and one on 

 each side for the greater cornua (thyrco-hyals). The lesser cornua are cartilaginous. 



(3) Remnanls of the Cartilaginous Cranium 



It has aheady been pointed out that at an early date the base of the skull and the face are 

 represented by hyaline cartilage, wliicli for the most part is replaced by bono before birth. 

 Even at birth renmants of this primitive chondral skull are abundant. In the cranium, carti- 

 laginous tracts exist between the various portions of the occipital bone, as well as at the line of 



