SKULL OF A HUMAN FETUS OF 40 MM. 325 



the cartilagines parasphenoidales (Voit, '09), the representatives 

 of the later hamular processes. The pterygoid laminae are 

 quite separate from the alae temporales, which appear, from this 

 viewpoint, as rhomboidal, perforated blocks. 



Lying along the caudal border of the nasal septum are seen the 

 anterior paraseptal cartilages in front, and the long thin plates 

 of the vomer behind (fig. 2); and within each nasal cavity is 

 a small mass of cartilage, lying in the middle meatus (fig. 12), 

 to which the name oariilago meatus medii has been given and whose 

 significance will be discussed with the regio ethmoidalis. 



Summing up the cartilaginous and osseous structures which 

 we find participating in the formation of the primitive skull, 

 we have to consider a main cartilaginous mass, or chondrocia- 

 nium, a number of accessory cartilages, the upper visceral arches, 

 and the membrane bones. 



The chondrocranium is a complicated mass of cartilage of 

 exceedingly irregular formation, in which a number of definite 

 areas may be recognized. Upon examination it is seen to con- 

 sist of a larger dorsal and a smaller ventral enlargement, united 

 by an isthmushke part, the body of the sphenoid. A median 

 stem, bent to enclose an angle of 115° open caudo-ventrally, 

 forms the main axis, this being made up dorsally of the flattened 

 planum basale and ventrally of the interorbital and nasal septa, 

 or, employing the terms of Kolliker, the pars chordalis and the 

 pars praechordalis respectively. These limbs are united by the 

 corpus sphenoidale, or Balkenplatte of the German authors, 

 which forms the apex of the angle. The four primary 

 regions of the chondrocranium, which Gaupp has named, from 

 behind forwards, the regio occipitalis, the regio otica, the regio 

 orbitotemporalis and the regio ethmoidalis, are all represented 

 in the median stem, in the order named, the first two being 

 found in the pars chordalis and the second two in the pars 

 praechordalis. 



Springing out from the sides of the planum we have the walls 

 of the posterior cranial fossa, while to the ventral end of the 

 axis are affixed the side parts of the ethmoidal and orbitotemporal 

 regions. 



