514 H. H. SWINNBRTON. 



orbital) baud, and forwards and inwards from the ear-sac " 

 (Parker, 73, p. 136). 



The trabeculge, now made up wholly of hyaline cartilage, 

 have fused with one another anteriorly to form a broad 

 ethmoid plate, which corresponds to Parker's " subnasal 

 lamina" and McMurrich's " rostral plate " (83, p. 625). The 

 bi-ain, Avhich in previous stages extended considerably beyond 

 this region (figs. 56 and 57, h.f.), has now relatively retired, 

 so that the prosencephalon lies upon this plate. From its 

 lateral borders arise two large processes (fig. 7, e. p. c), which 

 by reason of their position and ultimate fate may be con- 

 veniently termed the parethmoid cornua, and the line 

 joining their posterior margins may be regarded as the 

 posterior boundary of the ethmoid plate. This can then be 

 described as rectangular. For reasons which will appear later 

 it will be useful to apply the name pre-ethmoid cornua 

 (e. pr.) to the anterior angles. Behind the ethmoid plate 

 the trabecules are united for a short distance, and are then 

 separated by a narrow slit, which widens gradually to form 

 the pituitary fossa (fig. 2, p^. /•)• 



The first trace of a cranial root has appeared in the form of 

 a transverse bar {ep. c), consisting of a pair of chondrifica- 

 ticns which in older specimens are connected by pro-cartilage. 

 It lies in the dorsal fissure which separates the fore and mid- 

 brains (fig. 58, h. f. and b. m.). Immediately in front of it 

 lies the epiphysis ; consequently it is to be regarded as the 

 homologue of the epiphysial bar described by Pollard (95, 

 p. 414) in the Siluroids, and by vSagemehl in the Characinida? 

 (85, p. 41) and Cyprinidie (91, p. 511). 



Stage III. — Apart from the absence of ossifications the 

 chondrocranium has now assumed practically the adult condi- 

 tion. The intra-cranial notochord has undergone no further 

 change beyond a slight increase in absolute length. The 

 interparachordal fossa has been cari-ied some distance in front 

 of the notochord ; and the parachordals themselves have 

 united across the intervening space and across the ends of 

 the notochord {r. p., dotted outline fig. 3) in such a way that 



