552 
ME. W. K. PAEKEE ON THE STETJCTTJEE AND DEVELOPMENT 
appear in an ascending survey of the Urodeles ; the new pair are the maxillaries (mx.). 
These are small dentigerous styles applied to the outer side of the trabecular cornua and 
nasal roof-plates: in Menobranchus there is sometimes one of these bones (Huxley, 
op. cit. p. 190); in Proteus they are absent (Plate 28). 
The premaxillaries, frontals, parietals, and squamosals are fast growing into their 
typical size and. shape (figs. 6 & 7 ,px.,f.,p., sq.), and the parasphenoid (fig. 7 , pa.s.) is 
now notched in front and subalate behind ; it reaches to the basilar belt of cartilage (iv.). 
But the pterygo-palatines (p-pg-) are most modified; the dentigerous part is now a 
small territory compared to the long, flat pterygoid wing, which is very narrow in front 
and gently widens to its oblique end beneath the suspensorium. 
This narrow neck between the toothed and toothless regions of the bone is becoming 
ready for dislocation in the next stage. The only bone that can be as yet called endo- 
skeletal is the notochordal “ cap.” 
The free postoral arches need not take our attention for some time to come. 
Sixth Stage. Young Axolotls 2\ inches long. 
Every moderate increase of size in these “fry ” of the Axolotl is attended with some 
important and instructive morphological change. 
If the metamorphosis of this type was studied for its own sake, irrelatively to the 
structure and development of the skull in other Yertebrata, it would be fraught with 
great interest. 
But the details of each stage are full of instruction ; and when these are compared 
and commented on, stage by stage, we seem to be acquiring the very grammar of this 
difficult language, so as to be in a position to decipher these most ancient hieroglyphics. 
This stage is perhaps the one which presents us with the greatest number of suggestive 
conditions in its changed and still changing elements, and nearly every thing one sees 
here tends to send the mind hither and thither, throughout the length and breadth of 
the kingdom of the Yertebrata. 
The occipital condyles are still more elegantly finished than in the last stage, and the 
basicranial lips have now united beneath the notochord (Plate 24. fig. 2, iv.). The 
edges of the ascending part of the arch are united now as much, relatively, as they will be 
(fig. 2, s.o.). The trabecular half of the notochord (figs. 2 & 4, nc .) is an alate centrum , 
whose jagged bony edges are growing into the substance of the symmetrical cartilages, 
right and left. This is a “ prae-basioccipital ” bone ; it is not followed by a posterior 
joint like itself, the rest of the notochord and its investing mass remaining soft. In one 
important respect this type lies on the level of the “ Dipnoi,” for it has a pair of small 
exoccipital bones (figs. 2 & 4, e.o.) ; these are formed as rings round the 9th and 1 0th 
nerves (9, 10)*. 
* These bones are very small in Ceratoclus forsteri (see Huxley, Proc. Zool. Soc. Jan. 4, 1876, p. 38) as 
compared with those of Lepidosiren ; in the cranium proper these are the only bones that can he called intrinsic 
in those types and in this larva. 
