SUMMARY. 

 I. CHONDROCRANIUM. 



General development. — The chondrocranium of No. 886 is well developed and is 

 practically a homogeneous mass of cartilage, with but little trace of the regions of 

 earlier separation of the parts. Almost all of it is represented. 



Type of cartilage. — The cartilage is almost all of mature type. Young cartilage 

 and precartilage are found principally at the anterior end, which is undergoing the 

 most rapid development. 



Evidences of preossification change. — In all, ten centers were found where the 

 cartilage showed the change which ushers in ossification. Of these, four were paired 

 and two unpaired. In none was actual bone formed. At the peripheries of these 

 centers there was a gradual transition of the modified cartilage into the surrounding 

 normal cartilage. The areas of these centers have been carefully indicated in the 

 figures and have been described. They may be briefly recapitulated: 



In the occipital region there are: (1) a single center for the basi-occipital; (2) 

 paired centers for the exoccipitals ; (3) a single large center for the supraoccipital. 



In the orbito-temporal region there are: (1) paired centers in the temporal 

 wings; (2) paired centers in the alar processes, these being very slightly developed. 



The remaining paired centers are found one in each lower end of Meckel's 

 cartilage. 



Central stem. — The angle made by the chordal and prechordal parts of the cen- 

 tral stem is 115°, as in la. It has become narrower since the 21 mm. stage of 

 Lewis, where it was 125. 



Orbital wings. — That the outer ends of the orbital wings become depressed, 

 thus widening the angle made by the lines joining the limbus sphenoidalis with the 

 lateral extremities of the wings, following the stage of No. 886, is evident from a 

 comparison of this angle in No. 886 with the corresponding angle in the adult skull. 

 This flattening of the floor of the anterior cranial fossa is probably associated with 

 the growth of the brain. 



Comparison op Chondrocranium of No. 8S6 with that of la. 



The chondrocranium of No. 886 is considerably less developed than that of la 

 and much of the cartilage is of a younger type. The points of contrast may be 

 summarized as follows : 



(a) Parts absent from No. 886 and -present in la. 



1. Supracochlear cartilages. 



2. Superior paraseptal cartilages. 



3. Lateral cranial cartilages. 



4. Posterior cranial cartilages. 



(b) Parts present in No. 886 and absent from la. 



1. Alicochlear commissure. It was represented in 7a by a process. The carotid foramen 

 was thus closed in No. 886 and open in la. From the alicochlear commissure is 

 developed the lingula. 



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