90 



SKULL OF A 43-MM. HUMAN FETUS. 



rudimentary, rises upward and inward from this 

 notch and is surmounted by the caudal end of the 

 sphenopalatine ganglion. Its upper edge descends 

 upon the uppermost spicule of the pyramidal 

 process. 



The maxillary process, representing the cranial- 

 most part of the bone, is seen from within in 

 figure 26, and from above in figure 27. It is 

 flattened, its anterior edge is turned a little in- 

 ward, and its ventral border projects downward 

 toward the adjoining maxilla, giving to the pro- 

 cess a hook-like appearance. Its upper portion 

 fits into a notch upon the caudal aspect of the 

 ectethmoid, between the caudal extremities of 

 the maxillo-turbinate below and the planum 

 antorbitale above, as figure 41 shows. There is a 

 wide interval separating it from the maxilla. 

 Seen from within (fig. 26), the caudal edge of 

 the palatine process of the maxilla seems to fit 

 into the notch which the lower border of the 

 process makes with the perpendicular plate, but 

 when seen from below (fig. 29) we note that there 

 is a wide space separating the two bones. In la 

 the bone was somewhat more advanced. 



Views of the condensed mesenchyme enveloping 

 the palate bone are seen in figures 30 and 41, and 

 from these it will be noted that it is continuous 

 with that of the medial pterygoid plate. This 

 mesenchyme is shown, partially cut away, in 

 figure 28. Its relation to the nasal cavity appears 

 in figure 38. Its surfaces are somewhat more 

 smooth than those of the bone, but the out- 

 lines of the two are everywhere in general agree- 

 ment. 



The spheno-palatine ganglion is, roughly, a 

 three-sided pyramid of nerve cells with the 

 base directed downward and the apex dorso- 

 craniad. It lies in what will be the spheno- 

 palatine fossa, with the sphenoidal process of 

 the palate bone below, the processus alaris of 

 the sphenoid dorsocaudal, and the ala tempo- 

 ralis lateral. A medial projection overlaps slightly 

 the upper margin of the palate and thus encroaches 

 somewhat upon the space from which it will later 

 be excluded by the upward growth of the hori- 

 zontal plate. Communicating with the caudal 

 extremity of the base is the nerve of the pterygoid 

 canal, while the medial side shows the two spheno- 

 palatine branches from the maxillary nerve. 

 The palatine nerves emerge from the base and 

 lie in the pterygopalatine sulcus. 



MEDIAL PTERYGOID PLATE. 



The medial pterygoid plate has been described 

 with the orbito-temporal region and its mes- 

 enchymal investment has also been referred to 

 with the palate bone. 



ZYGOMATIC. 



The zygomatic bone is a rather thin plate 

 of osseous tissue stretching between the zygo- 

 matic processes of the temporal and maxilla, 

 but separated from both (figs. 3 and 5). Its 

 lower edge is seen in figure 29. It is not divided 

 into separate parts. It possesses four sharply 

 defined angles, the dorsal, caudal, ventral, 

 and cranial. Wide notches cut into the upper 

 and lower borders of the plate, giving to it an 

 S-shaped appearance. The bone lies with the 

 lateral surface looking a little downward and 

 forward, as well as outward. Many of the char- 

 acters of the adult condition will be recognized. 

 The dorsal angle, rounded and projecting upward, 

 but separated from the frontal bone by a very 

 wide space, represents the frontosphenoidal pro- 

 cess. The temporal, the longest of the processes, 

 which forms the caudal angle, is more slender and 

 is directed upward, backward, and slightly out- 

 ward. It does not overlap the zygomatic process 

 of the temporal, as in la, but rather is separated 

 by a short space from that process, as shown in 

 figure 5. Thus the zygomatic arch is incomplete. 

 Between the temporal and frontosphenoidal 

 processes is the representative of the temporal 

 border of the adult bone, a thin edge with a deep 

 upward concavity. This curvature is more 

 sharply marked than in the adult. 



The malar tubercle forms the ventral angle 

 and is the bluntest of all the processes. The edge 

 of the bone joining it with the temporal process — 

 representative of the masseteric border of the 

 adult — pursues a more or less direct course, 

 although marked by minor irregularities. The 

 remaining angle, representing the infraorbital 

 process, points cranially and a little medially and 

 is separated from the malar tubercle by a well- 

 marked incisure, directed downward, the repre- 

 sentative of the portion of the bone which will 

 later articulate with the maxilla. Between the 

 infraorbital and frontosphenoidal processes the 

 edge, representing the infraorbital border, is 

 straight, except for slight roughenings. The 

 lateral surface is fairly smooth and, in general, 

 plane, with a slight outward concavity near the 

 cranial end. The medial surface is similar and, 

 in a position corresponding to the outward con- 

 cavity, there is an inward convexity, which may be 

 the representative of the orbital process. The 

 thickest portion of the bone is in the region of the 

 malar tubercle. 



SQUAMA TEMPORALIS. 



The squamous portion of the temporal bone 

 consists of a thin narrow plate, placed just 



