232 THE DEVELOPMENT OF THE SKULL. [CHAP. 



the alisphenoid (Fig. 70, as) and posteriorly the supraoccipitals 

 (Fig. 70, so) have approached much nearer to each other above; 

 and at the same time the thickenings to form the occipital 

 condyles have greatly increased (Fig. 70, oc). 



The quadrate (Fig. 70, q) has undergone great modifica- 

 tions. In the earlier stage it was a simple knob of cartilage, 

 but now it sends a process forwards, the orbital process, and 

 a long process backwards which articulates with both the 

 'periotic capsule' and the exoccipital (Fig. 70, eo); down- 

 wards it sends a two-headed process to articulate with the 

 extremity of Meckel's cartilage. 



The fenestra ovale and fenestra rotundum (Fig. 70, fr) 

 appear during this stage, and in the former the head of the 

 small stapes (Fig. 70, st) is placed. 



The palatine (Fig. 70, pa) and pterygoid (Fig. 70, pg) 

 bars have increased in length, the former being the longer; 

 between them and the base of the skull there has appeared 

 a mass of tissue which will eventually become the sphenoidal 

 rostrum (parasphenoid). 



The second arch is not changed much; while the parts 

 of the third arch, corresponding with the first branchial arch 

 of osseous fishes, have increased in size, but have not under- 

 gone other modifications. 



13. In the next (Parker's third) stage, which occurs 

 about the middle of the 2nd week of incubation, the pre- 

 nasal cartilage (Fig. 71, pn) has greatly increased in length 

 and lost its downward curvature, so that it is in the same 

 straight line as the septum nasi and the ethmoid; the con- 

 tinuous plate thus formed while increasing in length is at 

 the same time narrowed except just in front of the pitui- 

 tary space, where it becomes expanded on each side into an 

 ear-shaped process. 



The pituitary space is still open and admits the internal 

 carotids; behind it is another azygos slit (Fig. 71, nc) along 

 the median line, in which the notochord can be seen. This slit 

 is a new formation, and as the skull outgrows the notochord, 

 the surrounding parts will become the post-pituitary part of 

 the basisphenoid. 



The outgrowths forming the alisphenoids have largely 

 increased. When looked at from below they are almost 

 entirely concealed by the ossified hasitemporals (Fig. 71, ht), 



