SKULL OF A 43-MM. HUMAN FETUS. 



89 



The condensed mesenchyme enveloping the 

 maxilla was modeled and is shown in figures 30 

 and 41. Its outlines are smooth and conform 

 closely to those of the bone within. Its boundaries 

 are somewhat indefinite in places. There are 

 continuations with the mesenchyme of the maxilla 

 of the opposite side in two places, viz, through 

 an extension of the frontal processes over the 

 bridge of the nose and through a connection be- 

 tween the anterior extremities of the alveolar 

 processes of the two bones, which occurs just 

 below the paraseptal cartilages. There is, too, 

 a caudolateral connection from an extension of 

 the zygomatic process to the mesenchyme of the 

 zygomatic bone. The interior of the mass shows 

 a lessening in density, where the fibers for the 

 superior alveolar nerves traverse it. Seen from 

 within in figure 41, we note that the anterior end 

 of the alveolar process and (behind this) the 

 palatine process are forming a floor for the inferior 

 meatus, which, however, is complete only in front. 

 Caudally, it will be observed, the mesenchyme of 

 the maxilla comes into close contact with that 

 of the palate bone, which, as yet, shows a very 

 poorly developed palatine process. 



A comparison of the maxilla of No. 886 with 

 that of la shows at once that in the latter there 

 have been noteworthy developments. Not only 

 has the body become larger but the processes all 

 show progress, the zygomatic reaching out to 

 join that of the zygomatic bone, the alveolar pro- 

 jecting farther downward, and the palatine, with 

 extension much farther toward the midline, being 

 the most noteworthy. In the Bert wig model 

 these growth features are still more evident, 

 there being here almost a complete closure of the 

 infraorbital foramen and an upward extension 

 of the bone forming the medial boundary of the 

 groove for the infraorbital nerve around the 

 adjoining ectethmoidal cartilage. 



PALATE. 



The palate bone of No. 886 is represented 

 by a thin plate of irregular outline bent into 

 an inward concavity, situated between the maxilla 

 and medial pterygoid plate (fig. 26). Although 

 showing slight roughenings, the plate is remarkably 

 smooth in comparison with the adjoining inner 

 surface of the maxilla. In its medial concavity 

 rests the mucous membrane of the lateral 

 wall of the nose, as seen in figure 38. Though 

 there is none of the elongation and little of the 

 specialization of the adult condition, yet already 

 many of the parts of the mature bone may be 

 recognized. The main portion of the bone — a 



plate lying almost vertically — represents the pars 

 perpendicularis. The inward concavity— seen in 

 dorsoventral, but not in caudocranial planes — is 

 found only in its caudal two-thirds and is due to 

 the incurling of the upper and lower borders. 

 The plate is pierced by two small foramina, 

 carrying twigs from the palatine nerves, as shown 

 in figure 26. It is continuous below with the 

 horizontal part, behind with the pyramidal proc- 

 ess, above with the sphenoidal and orbital proc- 

 esses, and in front with the maxillary process, all 

 of which are as yet very rudimentary. The 

 lateral surface (fig. 28), affording a less favorable 

 view of these extensions, presents a shallow fur- 

 row, the pterygopalatine sulcus, deepening above 

 to form the sphenopalatine notch. In it appear 

 the orifices for the exit of the aforementioned two 

 nerve-twigs. Though the middle of this surface 

 shows an outward convexity in the coronal 

 plane, corresponding to the concavity upon the 

 medial surface, it also shows a marked outward 

 concavity in the horizontal plane, due to the 

 lateral projection of the caudal extremity — the 

 representative of the pyramidal process. 



The representative of the horizontal part, or 

 palatine process, forms no angle with the perpen- 

 dicular plate; on the contrary, there is simply a 

 bending in toward the midline of the lower edge of 

 the bone, especially marked in its caudal portion, 

 shown by figure 29, giving a view of the bone from 

 below. The cranial end of this part of the bone is 

 separated from the palatine process of the maxilla 

 by a distinct space (fig. 29). 



The representative of the pyramidal process is 

 the most lateral part as well as the most posterior 

 part of the bone. It is separated from the hori- 

 zontal part by an indentation and projects back- 

 ward to the level of the most anterior edge of the 

 medial pterygoid plate, but lies some distance 

 lateral to this (fig. 29). It includes three spic- 

 ules, of which the middle, terminating in a 

 flattened point, is much the longer and is separated 

 from those above and below by marked notches. 



The upper border of the bone shows a sharp 

 inbending opposite the nerve trunks descending 

 from the sphenopalatine ganglion. This, the 

 representative of the future sphenopalatine notch, 

 marks the upper end of the pterygopalatine sulcus 

 and separates the rudimentary orbital and sphe- 

 noidal parts. The former, overlaid by a small 

 branch from the sphenopalatine ganglion, is seen 

 in figure 27 from above and figure 26 from within. 

 It is, as yet, only a roughened projecting edge, 

 curving outward and forward from the spheno- 

 palatine notch. The sphenoidal process, equally 



