SKULL OF A 43-MM. HUMAN FETUS. 



65 



Lewis as "occipital condyle" in his figure 6. I 

 have examined the Lewis model and agree with 

 his labeling of the occipital condyle. It would 

 .seem that Kernan has placed his direction line for 

 the occipital condyle much too near the midline 

 and that the occipital condyle is to be found at or 

 near the point designated by him as the "Processus 

 costalis et transversus, occipital vertebra." The 

 relation of the articular surface of the atlas in 

 Kernan's sections seems to favor this view. It is 

 quite obvious, too, that in his plate 3 Kernan has 

 mislabeled the hypoglossal foramen, calling it the 

 "foramen jugulare." If his labeling is correct, 

 then the "rib element, 2nd occipital vertebra" 

 passes in front of the jugular foramen — a relation- 

 ship which is evidently impossible. 



In his description and figures of the cat's 

 chondrocranium, Terry (1917) has apparently in- 

 cluded the "costal bar" of Kernan with the para- 

 condyloid process, considering the process to be 

 even more extensive than I have conceived it to be. 



SUPRAOCCIPITAL CARTILAGE. 



Behind the lamina alaris the squama occipitalis, 

 the right side of which is seen from within in 

 figure 14, becomes progressively wider to the region 

 lying between the upper extremity of the foramen 

 magnum and the anterior end of the occipito- 

 parietal commissure; after this it becomes some- 

 what narrower. Its surfaces are fairly smooth, 

 but there are certain markings which should be 

 mentioned. 



Just within the capsulo-occipital commissure is 

 the medial capsulo-occipital groove, deepened in 

 front by the posterior end of the otic capsule, 

 around which it curves. Posteriorly this groove 

 is bordered, in places rather indefinitely, by a low 

 ridge, which becomes confluent below with the 

 jugular tubercle. Just behind the capsulo- 

 occipital foramen this ridge is quite well marked. 

 The groove contains the transverse sinus which, 

 when traced from above, descends until it reaches 

 the sigmoid sulcus, where it turns sharply and runs 

 forward for a short distance before plunging down- 

 ward again into the jugular foramen. The cor- 

 responding lateral capsulo-occipital groove is 

 indefinite. 



The lateral occipital eminence (figs. 4, 5, 6) is not 

 so conspicuous as in la, nor is the cartilage of the 

 plate here so thick. Behind it the ectal surface 

 shows a wide, shallow but distinct groove, limited 

 below by the crescentic ridge, bordering the 

 U-shaped area of cartilage around the superior 

 incisure; the latter, in turn, protrudes slightly, as 

 figure 4 shows. The ends of this low ridge are 



confluent with the extremities of the crescentic 

 ridge in the region of the dorsal foraminal promi- 

 nences. Both shallow groove and low ridge are 

 represented upon the ental surface in reverse, as 

 shown in figure 14. 



The crescentic ridge or crista arcuata occipitalis 

 (figs. 2, 4, 5, 6) sweeps upward, backward, and 

 inward from the tip of the paracondyloid process 

 to end rather indefinitely in the region of the dor- 

 sal foraminal prominence. Its structure is very 

 similar to that of la. The ventrolateral end is 

 narrow, raised, and distinct, but as the ridge 

 passes backward it broadens and flattens out. 



Judging from his plate 2, Kernan has divided the 

 structure which I termed in la the crescentic ridge 

 into two parts, the dorsomedial of which he labels 

 "crescentic ridge" and the ventrolateral, "costal 

 bar, lamina alaris." I used the term "crescentic 

 ridge" (as I have done in No. 886) to apply to the 

 entire ridge, beginning at the tip of the para- 

 condyloid process and ending upon the border of 

 the foramen occipitale magnum. Kernan says 

 that this structure is the inferior nuchal line. I 

 think it will be obvious to anyone who examines 

 the models of the chondrocranium showing these 

 ridges and compares them with the mature skull, 

 that this interpretation is not correct, for, as is 

 well known, the inferior nuchal lines, although 

 arising anteriorly from the same region, viz, the 

 jugular process, yet meet dorsally upon the ex- 

 ternal occipital crest at a point some distance 

 behind the posterior margin of the foramen 

 occipitale magnum. In the models, on the con- 

 trary, the ridges do not meet, but end upon the 

 margin of the foramen, at the dorsal foraminal 

 prominences, which are situated some distance 

 anterior to the posterior limit of the primitive 

 foramen. Now, if the primitive foramen closes 

 by the approximation of the dorsal foraminal 

 prominences (which represent the tips of the 

 neural hemiarches of the occipital vertebra, as 

 described in my former paper), then these cres- 

 centic ridges will meet upon the posterior border 

 of the foramen, and not some distance behind it, 

 as do the inferior nuchal lines. If, on the other 

 hand, the dorsal foraminal prominences do not 

 fuse in the final closure of the foramen, then these 

 crescentic ridges will never meet, but will end 

 upon the foraminal margin. Thus their posterior 

 extremities can not be made to coincide with 

 those of the inferior nuchal lines. It does not 

 seem possible that in the closure of the primitive 

 foramen more of its area will be taken up than 

 that of the wide superior occipital incisure (lying 

 above and behind the dorsal foraminal promi- 

 nences), judging from my later stage and that of 



