320 Mil. J. S. BUUGETT ON THE 8TKUCTU11E 



these two lateral masses of cartilage send wings ventrally, which meet and fuse below 

 the dorsal aorta, enclosing it in a short canal which is roofed in by the notochord 

 itself (PI. XXXIII. figs. 2 & 4, s.A.br.). Anteriorly to the bifurcation of the 

 aorta, the basioccipital cartilages fuse below the notochord, sending forward a 

 median narrow plate of cartilage which underlies the tip of the notochord 

 (I'l. XXXIII. fig. 3, s. CIi.hr.). The fused auditory supra- and basioccipital regions 

 form on either side an exceedingly massive cranial wall. These walls are united 

 dorsally by a fairly solid bridge of cartilage of shortest extent antero-posteriorly in the 

 middle line (PI. XXXIII. fig. 2, s.oc.hr.). Ventrally, liowever, they are only 

 connected by the two little bridges of cartilage already mentioned — the one passing 

 underneath the dorsal aorta behind its bifurcation, the other below the tip of the 

 notochord in front of the bifurcation of the aorta. 



In front of the tip of the notochord the floor of the cranium is formed merely 

 of membrane, the bases of the lateral walls of the cranium being widely separated by 

 a very large fontanelle in the posterior region of which lies the hypophysis ^. The 

 hypophysis is not at this stage enclosed in a special pocket of the cranial wall or 

 " sella turcica," but curving backwards lies close under the hind end of the mid-brain 

 (separated from it by thin membrane) and above the dermis of the roof of the mouth. 

 In a 9 cm. specimen the glandular part of the hypophysis is much larger in proportion 

 and the membrane separating the hypophysis from the floor of the mid-brain has been 

 converted into cartilage of considerable thickness, while the special cavity so formed 

 remains in communication with the rest of the cranium by the opening for the passage 

 of the infundibulum. 



On the dorsal surface of the auditory region there extends forwards from the 

 anterior end of the fissure separating the supraoccipital region from the posterior 

 end of the auditory capsule a fairly pronounced ridge. On the lateral surface, along 

 the line of the horizontal semicircular canal, there is a very pronounced pterotic ridge 

 bearing in its middle portion the articulatory surface for the head of the hyo- 

 mandibular cartilage (PI. XXXIII, figs. I, 2, & 3, Pt.r.). The front portion of this 

 ridge gives off the sphenotic wing, which separating from the cranial wall passes 

 forwards as a horizontally flattened bar of cartilage to fuse again with the cranial wall 

 in the supraorbital region (PI. XXXIII. figs. 1 & 3, SpJi.). 



' At this stage the glandular part of the hj-pophysis is very small and flattened against the dermis of 

 the roof of the mouth ; its tubules open anteriorly into a small cavity which is in communication with the 

 mouth-cavity by a fairly wide duct, which persists until after the larva has grown to 9 cm. in length. 

 According to Bickford (Anatomische Anzeiger, Ed. x. p. 469), this duct remains permanently open in 

 Calamoichthys. The nervous portion of the hypophysis has a very wide lumen and passing backwards ends in 

 five iinger-like processes. In the 9 cm. specimen these have branched and become mingled with the tubules 

 of the glandular portion posteriorly, but do not appear to be continued into them as stated by Waldschmidt 

 (Anatomische Anzeiger, Bd. ii. p. 818). 



