SKULL OF A HUMAN FETUS OF 40 MM. 395 



the root of the alar process and the Balkenplatte, and dorsally 

 by the ventral basicochlear groove, which passes backward into 

 the sphenocochlear notch. 



The ventral surface of the alar process is almost completely 

 taken up with the attachment of the lateral portion of the wing. 

 The rounded outer extremity projects freely into the surround- 

 ing mesenchyme (fig. 1). 



The larger lateral portion of the temporal wing lies immediately 

 below the dorsal portion of the orbital wing, from which it is 

 separated by the superior orbital fissure, now open laterally 

 (fig. 4). It is rhomboidal in shape, the long axis being directed 

 upward, outward and slightly forward, towards the lateral 

 extremity of the ala orbitalis. The central portion of its mass is 

 perforated, from before backward, by the large foramen rotundum, 

 which transmits the second branch of the trigeminal nerve. The 

 nerve, however, by no means fills the foramen, the greater por- 

 tion of the space within it being occupied by connective tissue. 

 The foramen rotundum is found in Levi's 28 mm. stage, but not 

 in Jacoby's 30 mm. stage, the second branch of the fifth nerve 

 here occupying a groove upon the upper surface of the wing. It 

 is well shown in the illustrations of Fischer's ('03) ape skulls. 



Immediately below the foramen rotundum the dorsal surface 

 is concerned in the union with the ventral surface of the alar 

 process, the long axes of the medial and lateral portions crossing 

 at a right angle, open above. When regarded from above the 

 effect is as if the caudo-medial corner of the lateral portion had 

 been applied to the ventral surface of the medial portion in such 

 a way as to leave the lower extremities of both free. The fora- 

 men ovale is not as yet formed. 



Histologically there is to be seen at the junction of the alar 

 process and lateral portion a sheet of younger cartilage and 

 procartilage cells, which almost completely separates the two 

 portions. This is evidently the last trace of the primitive 

 separation of these parts, of which Levi, Fawcett and other 

 authors speak. In the 14 mm. stage Levi finds the temporal 

 wing represented by two procartilaginous anlagen, separated by 

 a sheet of connective tissue. 



