MORPHOLOGY OF TELEOSTEAN HEAD SKELETON. 523 



as Uranoscopus warns us not to place too mncli reliance on 

 mere sculpturing. 



The intercranial notochord (PI. 30, fig. 27) has continued 

 to increase somewhat in total length, and by reason of the 

 multiplication of cells its internal structure, especially at its 

 extremity, has become denser even than in the previous stage. 

 In the same region it has become slightly attenuated, but 

 posteriorly its diameter has more than quadrupled (fig. 27). 

 Possibly in association with this increased bulk the internal 

 tissue is much looser and the vacuoles are normal. The 

 funnel-shaped expansion thus made gives to this region of 

 the basioccipital, when viewed from behind, that couically 

 concave appearance so chai-acteristic of it in many Teleosts. 



It is thus seen that at no stage in development is there any 

 sign of a reduction or suppression of the intercranial noto- 

 chord ; the real fact of the case being that during the whole 

 period of skeletogenesis the length of the notochord increases 

 only thrice, whilst that of the cranium itself increases approxi- 

 mately twenty times (cp. figs. 50 and 21, ch.). The natural 

 outcome of this disproportionate growth is the retirement of 

 the notochord or, more accurately, the advancement of the 

 skeletal elements, so that the pituitary and interparachordal 

 fossae are carried far away in front of the notochord. A 

 similar apparent retirement has been noted by Parker in 

 Lepidosteus (81/;, p. 458) and in Salmo (73, pp. 125, 102). 

 Since he gives no details, however, concerning the condition 

 in the adult, it is impossible to make any comparisons as to 

 the relative rate of growth in these fonns. 



The suture between the basioccipital and exoccipital 

 (fig. 21, oc. e.) differs from that between the other bones of 

 the chondrocranium, in being formed by the interdigitation of 

 bony lamellae. Between it and the pro-otic there still remains 

 (fig. 21) a small area of exposed cartilage. Medianly it is 

 overlapped by the forked end of the parasphenoid, for the 

 reception of which it has a deep channel formed by a down- 

 growth of the cartilage and bone on either side (PI. 30, fig. 36). 

 From the middle of the roof of this channel the basioccipital 



