608 JOHN D. KERNAN, JR. 



to describe the cranial portion of the basal plate as part of the 

 orbito-temporal region. The human material at his disposal 

 certainly permitted this interpretation. Gaupp, however, work- 

 ing on the lower vertebrates, has shown that the cranial portion 

 of the basal plate is better ascribed to the otic region. All re- 

 cent authors have adopted this view. (Voit '09, Mead '09, Mack- 

 lin '14, DeBurlet '15). 



The occipital region, (figs. 1 and 3) then consists of the occip- 

 ital part of the basal plate mesially, and the paired occipital 

 wings laterally. Cranially it joins the otic portion* of the basal 

 plate on a line with the cranial margins of the jugular foramina. 

 The cranial surfaces of the two parts are continuous and form 

 the clivus of the fully developed bone. Laterally the occipital 

 wings border on the otic capsules. A line drawn parallel to the 

 long axis of the basal plate, through the inner edges of the hypo- 

 glossal foramina, divides the mesial from the lateral parts of the 

 occipital region. 



The mesial part corresponds to the basioccipital of the human 

 adult. It shows two distinct areas, divided by a transverse 

 line through the cranial edges of the hypoglossa canals. The 

 caudal area slopes sharply to foramen magnum. At this point 

 there is a deep notch, the fore-runner of the intercondyloid notch 

 which separates the two prominent condyles. From the notch 

 there passes cranially on the cerebral surface a deep groove, the 

 caudal portion of the clivus, which in the adult supports the pons 

 Varolii. The most caudal part of this groove is in fairly close 

 relation with the odontoid process. From the apex and cranial 

 surface of the dens, a mass of blastema passes craniad which 

 encloses the notochord and completely fills the groove (fig. 5, 3) . 

 The notochord passes into the cartilage on the level of the cranial 

 edges of the hypoglossal canals and emerges ventrally and cran- 

 ially just caudal to the thin area of the basal plate. Thus a large 

 part of the basioccipital is hypochordal. 



The mass of blastema filling the clivus is the anlage of the 

 suspensory ligament of the axis. 



The ectal surface of the basioccipital (fig. 3) shows an axial 

 ridge which can be traced to the sphenoidal region. This ridge 



