SKULL OF A 43-MM. HUMAN FETUS. 



101 



Fia. 36. Condensed mesenchyme around right mandible 

 viewed from approximately the same 

 point as that of figure 35. It shows the 

 developing teeth of the right lower jaw. 

 The mesenchyme is connected across the 

 midline with its partner of the opposite 

 side, the cut edge being shown. Model 23. 

 X12.5. 



Fig. 37. Mucous membrane of inner wall of right nasal 

 cavity, overlying the septum; it is cut 

 away to show the right organ of Jacobson. 

 (Compare with figure 10.) Model 20. 

 X12.5. 



Fia. 38. Mucous membrane of lateral wall of right nasal 

 cavity, overlying the right ectethmoid, 

 showing folds for the developing concha;. 

 The mucous membrane fits over the struc- 

 tures seen in figure 41. The elongated 

 nasopharyngeal canal, flanked by the 

 developing palate and medial pterygoid 

 plate, is well seen. Model 18. X12.5. 



Fig. 39. Lateral aspect of right ectethmoid from the 

 front, side, and a little below, showing 

 especially the nasolacrimal duct, with the 

 nasolacrimal sac and the lacrimal ducts 

 above, and, below,the expanded end, applied 

 to but not perforating the external aspect 

 of the mucous membrane of the inferior 

 meatus. The tip of the paranasal car- 

 tilage lies just lateral to the duct and 

 the tiny shred of osseous tissue representing 

 the lacrimal bone is seen lying along the 

 posterior maxillary process. The cupular 

 process of precartilage is conspicuous in 

 the lower part of the figure. The broad 

 plate of epithelium, which represents the 

 future inferior meatus, but which has not 

 yet undergone cleavage except posteriorly, 

 is plainly shown. Model IS. X12.5. 



Fig. 40. Anterior end of right ectethmoid, with the 

 epithelial plug in the anterior naris, em- 

 braced medially by the cupular process of 

 precartilage. The terminal portion of the 

 nasolacrimal duct is shown, entering the 

 space for the inferior meatus, with a small 

 portion of the mesenchyme of the maxilla. 

 Model 19. X12.5. 



Fig. 41. Medial aspect of right ectethmoid, showing the 

 developing conch*. Precartilage is espe- 

 cially evident in the superior concha, the 

 small process of the,middle meatus, and the 

 cupular process. The other conchae are 

 edged wi th it. The mesenchyme envelopes 

 of the maxilla, the palate, and the medial 

 pterygoid plate are seen. The cartilagin- 

 ous hamular process is conspicuous, as are 

 also the developing teeth of the right side 

 of the upper jaw. (Compare figure 30.) 



Note also the tip of the nasolacrimal duct 

 in the space for the inferior meatus. 

 Model 25. X12.5. 



Fig. 42. View of right hyoid arch from without, below, 

 and behind. The connection with the 

 otic capsule is seen above and below 

 appears the lesser cornu of the hyoid 

 cartilage. The relations of the facial 

 nerve, chorda tympani, and tympanic 

 cavity are well seen, and the handle of the 

 malleus is plainly shown in a concavity 

 representing the stratum mucosum of the 

 future tympanic membrane. Model 17. 

 X12.5. 



Fig. 43 Medial aspect of left ectethmoid (compare with 

 figure 41), showing developing concha;. 

 The anterior portion of the tectum nasi has 

 been trimmed a little farther laterally than 

 on the right side, and hence the cut surface 

 is not quite the same in the two figures. 

 The cupular process is omitted. Model 3. 

 X12.5. 



Fia. 44. View of right hyoid arch from within and slightly 

 above, with its membranous connection 

 with the lesser cornu of the hyoid below 

 (as in fig. 42) and the cut edge of its con- 

 nection with otic capsule above. Fitting 

 into the curvature of its upper portion 

 is the epithelium of the developing tym- 

 panic cavity, which from this point of view 

 is almost parallel with the plane of the 

 paper. The ring-like stapes is seen and to 

 it is attached the tendon of the stapedius 

 muscle, with the muscle itself passing 

 medial to the facial nerve and to the upper 

 end of the styloid process. The handle of 

 the malleus is also seen, with the chorda 

 tympani lying just medial to it. Model 17. 

 X12.5. 



Fig. 45. Cartilages of the hyoid, thyroid, cricoid, and 

 upper end of the trachea, seen from the 

 front. On the left side of the model the 

 preeartilaginous edging of the upper three 

 cartilages is shown. Model 12. X12.5. 



Fig. 46. Right half of the same structures seen in figures 

 45 and 47, viewed from within. The 

 precartilage of the arytenoid is seen and 

 should be compared with the young cartil- 

 age of the same structure shown in figure 

 47. Model 13. X12.5. 



Fig. 47. Same structures seen in figure 45, but viewed 

 from behind. The asymmetry evident in 

 the arytenoids and in other places is duo 

 to the fact that on the left side of the model 

 the precartilage was shown, whereas on 

 the right side only the cartilage and young 

 cartilage appear. Model 12. X12.5. 



