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 11G) important changes 



OC 



MC 



QJ 3B SR 



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. 



A!N", angularc. AR, articular portion of mandibular bar. BB, basi-branchial 

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

 zontal semicircular canal. EP, posterior vertical semicircular canal. ET, mcsethnioid 

 cartilage. PR, fenestra ovalis. HR, ceratohyal cartilage. MC, Meckel's cartilage. 

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

 lens. ON, outline of eyeball. PG, pterygoid. Q, quadrate cartilage. QJ. qnadrato- 

 jngal. RL, trabeeula cranii. SE, pre-sphenoidal region. SF, ali-sphenoidal region. 

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



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, lie) 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- 



