MORPHOLOGY OF TI5LR0STEAN HEAD SKELETON. 547 



head of Anchenaspis and Silurus show that his figures give 

 such an idea. The individuals he dealt with were as far 

 advanced in respect to ossification as the stage we are now 

 considering, and accordingly were unreliable for proving the 

 presence or absence of a primarily independent cartilage in 

 this region. If such an element existed, Ave should naturally 

 expect to find it in such lowly forms as Amia and Lepidosteus; 

 but my observations on the larva of the former, and Parker's 

 on the development of the latter, show that it is not forth- 

 coming. Whatever may be the significance of the small, 

 separate choudrification described by Stohr, it is certain that, 

 as far as present knowledge goes, no part of the cartilaginous 

 upper jaw of Teleosts is primarily of independent origin, but 

 that at least as far as the connection with the ethmoid it is a 

 direct extension of the quadrate. 



Standing out from each side, but quite separate from the 

 anterior end of the dentary, is a small rod of cartilage (figs. 9, 

 10, 28, 29, L), which lies wholly within the lower labial fold 

 (/./.). Brooks (83, p. 179) describes a similar '^ rod-like 

 body ^' in the haddock, and homologises it with "the lower 

 labial cartilage in Elasmobranchs." There can be no doubt 

 that it is the same element that is present in Gasterosteus. 

 The cartihige forming it in the latter is not so hyaline as that 

 in the rest of the skull, but histologically it agrees closely 

 with that found in the tentacular skeleton of the Siluroids. 

 Though it lacks a basal plate, its basal portion is more 

 strongly developed (cp. figs. 28, 29, I.), and the whole bears a 

 close resemblance in position to the mental tentacle of 

 Silurus, and is pi'obably homologous with that. This rod of 

 cartilage is probably of more frequent occurrence among 

 Teleosts than is usually supposed, for it is present in Perca. 



Among the membrane bones, the pterygoids and suborbitals 

 have now appeared, and thus the full total of ossifications 

 present in the adult is made up. 



The pterygoid bone (fig. 13, j^y. en.) as looked at from 

 inside is triradiate; its antero-dorsal ray is proximal ly tubu- 

 lar, completely enclosing the delicate palatine cartilage, and 



