THE EVIDENCE OF THE SKELETON 



121 



primitive cartilaginous cranium is always composed of the following 

 parts : — 



1. A pair of cartilaginous plates on each side of the cephalic 

 section of the notochord known as the parachordals (pa.ch., Fig. 49 ; 

 iv., Fig. 48). These plates, together with the notochord (ch.) enclosed 

 between them, form a floor for the hind and mid-braiu. 



<S^--Ctr 



-au 



Fig. 48. — Embryo Pig, two-thirds of an 

 inch long (from Parker), Elements 

 of Skull seen from below. 



ch., notochord; iv., parachordals; au., 

 auditory capsule ; py., pituitary body ; tr., 

 trabecula; ctr., trabecular cornu ; pn., 

 pre-nasal cartilage ; ppg., palato-pterygoid 

 tract; mn., mandibular arch; th.h., first 

 branchial arch ; VII.-XIL, cranial nerves. 



Fig. 49. — -Head of Embryo Dog-fish 

 (from Parker), Basal View of Cranium 



FROM ABOVE. 



ul., olfactory sacs; au., auditory capsule; 

 py., pituitary body; pa.ch., parachordal 

 cartilage; tr., trabecula; inf., infundi- 

 bulum ; pt.s., pituitary space ; c, eye. 



2. A pair of bars forming the floor for the fore-brain, known as 

 the trabecular (tr). These bars are continued forward from the para- 

 chordals. They meet posteriorly and embrace the front end of the 

 notochord, and after separating for some distance bend in again in 

 such a way as to enclose a space — the pituitary space (pt.s.). In 



