326 CHARLES CLIFFORD MACKLIN 



If the structures lateral to the ventral limb of this stem be 

 removed, we have an object which roughly resembles a dipper 

 or saucepan, the curved handle being made up of the ventral 

 part of the stem, while the bowl, perforated below and at the sides, 

 is formed ventrally by the planum basale, and laterally and 

 dorsally by the walls of the posterior cranial fossa, the median 

 lip being situated at the tectum posterius. 



The chondrocranium is, at this stage, a continuous morpho- 

 logical unit, but there is histological evidence going to show that 

 certain of its parts were primarily separate. 



In addition to the chondrocranium proper a number of acces- 

 sory cartilages, which have no direct connection with it and 

 which have already been mentioned, also occur. They will be 

 discussed in connection with the regions to which they refer, and 

 are as follows: 



Cartilage cranii posterior Regio otica 



Cartilago cranii lateralis Regio otica 



Cartilago supracochlearis Regio otica 



Cartilago parasphenoidalis Regio orbitotemporalis 



Cartilago paraethmoidalis Regio ethmoidalis 



Cartilago paranasalis Regio ethmoidalis 



Cartilago meatus medii Regio ethmoidalis 



Of the recorded human embryonic skulls that of Levi ('00) 

 for the 28 mm. stage most closely resembles my specimen, but 

 is somewhat younger. The next nearest stage, represented in 

 the Ziegler model of Hertwig's 80 mm. embryo, is somewhat 

 older. 



The principal change which has occurred in the interval be- 

 tween the 28 and 40 mm. stages appears to be the development 

 of the anterior cranial fossa. In the Levi specimen this is rel- 

 atively narrower and deeper than in mine, thus indicating an 

 adaptation of this region to the increasing size of the anterior 

 part of the brain. Levi notes that this part of the skull has 

 made more rapid development than any other in the interval 

 between the 17 mm. and 28 mm. stages, and in the latter it is 

 evidently still making rapid progress. When my model is com- 

 pared with that of Hertwig, however, it is seen that in the period 



