EXPLANATIONS OF FIGURES. 



All drawings were made by Mr. James F. Didusch according to geometric projection. With 

 the exception of figure 7, which was made from a profile reconstruction, all figures were drawn from 

 the original plaster-of-paris models made from human fetus No. 886 of the collection of the Carnegie 

 Laboratory of Embryology. The number of the model from which each figure was drawn is given, 

 together with the magnification. 



Fiq. 1. Chondroeranium from above with frontal and 

 parietal bones on right side. The densest 

 part of the frontal bone is inclosed by a 

 dotted line. The basal plate is not quite 

 horizontal, the cranial end being a little the 

 closer to the eye of the observer. Model 1. 

 X6.25. 



Fig. 2. Chrondrocranium from below with cartilaginous 

 branchial arch skeleton extirpated. Frontal 

 and parietal bones are shown on right side. 

 The basal plate is not quite horizontal, the 

 caudal end being a little the closer to the 

 eye of the observer. The view is directly 

 into the anterior nares. Model 1. X6.25. 



Fig. 3. Skull from front, showing membrane bones on 

 right side. Face is seen in frank view. 

 The cervical vertebra and cartilaginous 

 branchial arch skeleton are also seen. 

 Model 1. X6.25. 



Fig. 4. Skull from back, giving a frank view of the 

 foramen occipitale magnum. The cervical 

 vertebrae are seen, their arches being as yet 

 unclosed dorsally. Note the alinement of 

 the hemiarch tips with the dorsal foraminal 

 prominences, representing the extremities 

 of the hemiarches of the occipital vertebra. 

 The right half of the interparietal bone is 

 seen. Model 1. X6.25. 



Fio. 5. Skull from right side, showing membrane bones. 

 The cervical vertebras and cartilaginous 

 branchial arch skeleton are included. Only 

 the right half of the skull is shown. Model 

 1. X6.25. 



Fig. 6. Left half of chondroeranium, cervical vertebrae, 

 and cartilaginous branchial arch skeleton 

 as seen from left side. Model 1. X6.25. 



Fiq. 7. Profiles of external form of head, brain and up- 

 perend of spinal cord, and skull, in their nor- 

 mal relation to one another, as seen from 

 the right side. Drawn from a profile 

 reconstruction. X 1.9. 



Fig. 8. Condensed mesenchyme enveloping the vomer, 

 seen from front, side, and above. The 

 anterior extremities of the vomer are indi- 

 cated. The gutter in the center is for the 

 lower edge of the nasal septum. There is 

 a slight amount of lateral curvature. The 

 cut edges of the mesenchyme are indicated. 

 Model 22. X12.5. 



Fig. 9. Two halves of the vomer from the same point of 

 view as that of figure 8. They are very 

 slender spicules of bone lying along the 

 lower border of the nasal septum. Model 

 21. X12.5. 



Fig. 10. Median stem of skull as seen from right side. 

 It consists of the basal plate behind and 

 the interorbital and nasal septa in front, 

 forming an obtuse angle at the body of the 



sphenoid. The adjoining exoccipital car- 

 tilage is shown in part. Junctions with 

 cartilage lying laterally are shown. Model 

 4. X12.5. 



Fig. 11. Right half of basal plate and parts of upper two 

 cervical vertebrae, sectioned in the mid- 

 sagittal plane. The cut surface is seen 

 in frank view. Shows the preossification 

 center for the basioccipital, the notochord, 

 the pharyngeal bursa with a little of the 

 epithelium of the roof of the pharynx, the 

 temporal wing, dorsum sells and a portion of 

 the exoccipital. Model 8. X12.5. 



Fig. 12. Left cartilage of Jacobson from left side with 

 neighboring septum. Models 2 and 25. 

 X12.5. 



Fig. 13. Cartilages of Jacobson from below in relation to 

 nasal septum. Models 2 and 25. X12.5. 



Fig. 14. Right half of occipital cartilage and parietal 

 plate from in front and within, with the 

 ascending process and right half of inter- 

 parietal bone in its mesenchyme. Con- 

 nections with adjoining cartilages are 

 shown. Model 24. X6.25. 



Fig. 15. Interior of right otic capsule from within and 

 above. The inner wall of the capsule* has 

 been cut away to show the lateral wall of 

 the cavity. Figure 21 shows this cavity 

 modeled as a solid. The superior and 

 posterior semicircular canals are shown, 

 with the entrances to the lateral canal. A 

 good view is afforded of the spiral septum 

 in the wall of the cochlear space. The 

 membrane filling in the vestibular window 

 is indicated. Other features are the 

 medial end of the tuba auditiva with its 

 entrance into the pharynx, the alar pro- 

 cess of the temporal wing of the sphenoid, 

 the alicochlear commissure, the internal 

 carotid artery, and views of the fifth and 

 seventh cranial nerves. Model 14. Xl0. 



Fig. 16. Right otic capsule and associated structures 

 seen from right side, front, and a little 

 below. The suprafacial commissure has 

 been removed. The facial nerve is shown 

 in its relation to the otic capsule and 

 styloid process, with its off-shoots, the 

 chorda tympani and the great superficial 

 petrosal nerves, the latter arising from 

 the geniculate ganglion. The tip of the 

 long cms of the incus appears in relation 

 to the chorda tympani. A prominent 

 object is the tympanic cavity fundament, 

 of which the lateral surface is shown, pre- 

 senting an impression at the site of the 

 future tympanic membrane. The auditory 

 tube is shown in its full extent. The im- 

 mense semilunar ganglion with its root and 



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