NS 



SKULL OF A 43-MM. HUMAN FETUS. 



The frontal process is thin and triangular in 

 shape and lies in a hollow on the lateral aspect of 

 the ectethmoid, between the region of the lacrimal 

 bone above and the paraseptal process and adjoin- 

 ing cartilage below. With the basal plate hori- 

 zontally placed, it projects almost directly for- 

 ward and lies in a sheath of condensed mesen- 

 chyme which reaches forward around the develop- 

 ing nose to join with its neighbor of the opposite 

 side in the formation of a band or chaplet in 

 which the nasal bone will later be developed. It 

 is quite evident that the frontal process is extend- 

 ing upward in this band, the inner surface of 

 which is applied medially, near its upper ex- 

 tremity, against a portion of the ectethmoid which 

 presents, upon the inner surface, the representa- 

 tive of the agger nasi. It is clear, therefore, 

 thai the frontal process later takes to itself the 

 modeling of the cartilage here. 



The outer surface of the process shows a few 

 small foramina and at the apex the aforementioned 

 unclosed end of the incisive suture appears. Its 

 inner surface is largely occupied by the groove 

 already described, together with its borders. 

 There is a rough, spiculated area above and behind 

 the groove. Just above the upper border of the 

 process the nasolacrimal duct courses backward 

 for some distance before turning downward to its 

 termination. The lower border curves inward 

 close to the paraseptal process of the ectethmoid, 

 making of the post-transverse incisure a foramen. 



The zygomatic process is represented by a thin 

 plate of bone which ends in a dorsolateral spur 

 (fig. 29) and which is separated from the nearest 

 point of the zygomatic bone by a wide interval. 

 It projects much more directly backward than 

 in the adult. Its lateral edge is the direct ex- 

 tension of a ridge which forms the lateral side 

 of the groove for the infraorbital nerve. Its 

 anterior surface looks also somewhat upward. 

 It narrows as it descends into the depths of the 

 infraorbital groove. The posterior surface, as it 

 passes downward, turns outward, widens, and 

 goes over upon the lateral surface of the body. 

 The medial border of the plate is continuous with 

 the lateral edge of the tooth gutter (fig. 29). 

 The process shows several irregular spicules of 

 bone. 



The groove for the infraorbital nerve is formed 

 laterally by a forward extension of the lateral 

 border of the zygomatic process and medially by a 

 continuation backward of the upper border of the 

 frontal process. It is narrower in front than be- 

 hind and its floor is pierced by foramina carrying 

 the superior alveolar nerves. 



The alveolar process is as yet represented only 

 by the crescentic, irregular, roughened edges of 

 the tooth gutter (fig. 29). Beginning caudally 

 but a little in front of the extremity of the zygo- 

 matic process, it sweeps forward and inward 

 practically to the midline. The gutter is filled 

 with developing teeth (fig. 30). The outer 

 border, which separates the alveolar process from 

 the facial surface, commences caudally as the 

 medial margin of the zygomatic process. It is 

 marked near this point by a small, backwardly 

 projecting spur. Opposite this point there is a 

 much larger spur of the same character upon the 

 inner border. In front of this the two borders 

 proceed to their craniomedial end with many 

 slight but no great irregularities. The tooth 

 gutter lies in almost a perfect plane. Its two 

 borders are crossed near the middle, by an 

 imperfect bridge (the interalveolar septum between 

 the canine and the first milk molar) and in its 

 depths are seen the superior alveolar nerves. 

 The crescentic bar of tissue representing the 

 developing teeth (figs. 30, 41) extends cranio- 

 medially almost as far as the midline and caudally 

 a little beyond the bone. There are enlargements 

 representing imperfectly the individual teeth. 



The palatine process is rudimentary. It is 

 seen best in figure 29 as a shelf of irregular bone 

 fitted into the concavity formed by the inner bor- 

 der of the tooth gutter. Caudally, it comes close 

 to but does not touch, the palate bone. The 

 medial edge, of serrated appearance, is widely 

 separated from its fellow of the opposite side ami 

 forms an obtuse angle with the caudal border. 

 The lower surface, although irregular, contrives 

 to form with the laterally lying alveolar process 

 a surface which is, in general, plane (figs. 26, 29). 

 The superior surface, on the contrary, slopes up- 

 ward, especially in its cranial extremity, upon the 

 body of the bone and is honeycombed by holes. 

 It thus displays maxillary and premaxillary parts, 

 the latter being very small. Upon the os incisi- 

 vum there is, as yet, but slight trace of a palatine 

 process. 



Among other features of the mature bone which 

 are represented in this maxilla may be briefly 

 mentioned the nasal notch, which embraces the 

 anterior end of the ectethmoid and appears as a 

 sharp crescentic border running down from the 

 lower border of the frontal process to the region 

 of the future anterior nasal spine; also the infra- 

 orbital margin , passing backward and outward from 

 the upper edge of the frontal process, crossing the 

 infraorbital groove, and continuing upon the outer 

 border of the zygomatic process. 



