SKULL OF A HUMAN FETUS OF 40 MM. 321 



wide, upward-slanting, anterior root of the ala orbitalis, in front 

 of which is a broad, flattened, triangular surface. This we 

 recognize as the floor of the anterior cranial fossa. Perforating 

 it, in the area lateral to the median septum, which represents 

 the developing cribriform plate, are several foramina, the largest 

 being the paired fenestrae cribrosae. Hook-like, backwardly 

 projecting processes mark the dorso-lateral limits of the floor, 

 which ventro-laterally is widened by the orbital plate of the 

 frontal bone. 



The only portions of the osseous cranial vault yet in evidence 

 are the rudimentary frontal portion of the frontal bone and the 

 net-like parietal — these being separated by a rather wide space. 



Finally, the cranial aspect discloses to view certain accessory 

 cartilages. Above the dorsal wall of the posterior cranial fossa 

 may be seen two cartilages, lying close together, both small, 

 but the left considerably smaller than the right. They may be 

 known as the cartilagines cranii posterior es. Above each parietal 

 plate, medial to the parietal bone, is seen an isolated nodule of 

 cartilage, that on the right being larger and more elongated than 

 that on the left; these may be called the cartilagines cranii later- 

 ales. Below and in front of the cranial pole of each cochlea there 

 is a sjnall, rounded masls of cartilage, which may be termed 

 the cartilago supracocMearis. 



CARTILAGE 



Passing, next, to a consideration of the lateral aspect of the 

 primitive skull (fig. 3), we note that it is made up of two main 

 masses, dorsal (posterior) and ventral (anterior), almost sepa- 

 rated by a large gap between the otic and orbitotemporal regions. 

 The dorsal region is composed principally of cartilage, and 

 presents a fairly smooth, convex, fenestrated surface, the most 

 lateral part being formed by the rounded outer wall of the pars 

 canalicularis of the otic capsule. Behind this the flat surface is 

 seen to widen, and then quickly narrow, and to sweep backwards 

 and inwards to unite with the corresponding plate of the oppo- 

 site side in the tectum posterius. Above, the wall is heightened 



