THE SKULL. 



329 



In front of the notochord, the parachordals are continued for- 

 wards as a pair of short and rather slender rods, the trabeculse 

 cranii : these lie at the sides of the pituitary body, and unite in 

 front of this to form the ethmoidal plate, which underlies and 

 supports the fore-brain. 



By the eighth day (Figs. 131 and 116) important changes 



EH 



SL 



oc 



FIG. 131. The skull of a Chick Embryo at the end of the eighth day of incu- 

 bation ; seen from the right side. The head and eye are represented in 

 outline, x 10. 



AN", ansrulare. AR, articular ]>ortion of mainlibular bar. BB, basi-branchial 

 cartilage. BK, cerato-branchial cartilage. CL, columella. EH, external or hori- 

 zontal semicircular canal. EP, posterior vertical semicircular canal; ET, rnescthruoid 

 cartilage. 3PR, fenestra ovalis. HR, ceratohyal cartilage. MC, Meokel's cartilage. 

 OC, occipital condyle. OK, slit-like aperture of olfactory capsule. OL, outline of 

 lens. ON", outline of eyeball. PG, pterj-goid. Q,, quadrate cartilage. Q,J", quadrato- 

 jugul. RL, trabecula cranii. SE, pre-'sphenoidal region. SF, ali-sphenoidal region. 

 SL, supra-occipital region. SR. supra-angular. 



have occurred in the skull, mainly associated with the growth 

 forwards of the beak. 



At the hinder end of the skull the two parachordal cartilages 

 (Fig. 116, EC) have united, above and below the notochord, to form 

 the basilar plate ; and the sides of the basilar plate, including the 

 auditory capsules which are fused with them, have grown up- 



