DEVELOPMENT OF THE SKULL IN THE UKOUELES. 203 



B. Tlie Endocranium. 



The chondrosteous endocranium is consideiably altered ; and the basal region is largely 

 losing its cartilage and becoming membranous again, as in the first stage (figs. 1 & 7). 



The foramen magnum (/. m) is supero-posterior, the occipital condyles [oc. c) postero- 

 inferior ; they also look obliquely inwards, and are pedunculate, with an interspace twice 

 their own breadth for the " odontoid rudiment.'" 



There is a broad superoccipital tract of cartilage (oc. r) above, and a smaller tract 

 below ; but the ossified sheath of the notochord {est) is now coalescing with the upper 

 face of the parasphenoid, and most of the parachordals and parachordal ends of the 

 trabeculge have been absorbed (fig. 7, tr, iv). This is quite like what we see in the 

 adult Proteus and Me)iohranchus. 



On each side the bulbous auditory capsules and the narrow occipital moieties are 

 well ossified from the condyles up to the "sphenotic" projections {sp.o). 



Below (fig. 7, vb, st), the floor of the vestibule has in front of the fenestra ovalis an 

 imperfect ring of cartilage, and the large, oval, outturned stapes is also unossified. 



The sphenethmoids {sp.e) have not spread much further fore and aft ; but they form 

 stronger walls to the interorbital region. 



The trabecular comua [c. tr), the enlarged nasal roofs {no), and the ethmo-palatine 

 appendages {ej). a) are now all coalesced together, exactly as in Sieboldia and Menopoma 

 (Pis. XXXVI. , XXXVII.). The notch between the comua is larger ; and the intertra- 

 becular bridge (i.n. c) is slightly smaller ; and these parts are much more hidden by the 

 superficial bones, both above and below. 



A tongue of cartilage has grown from the papilla on the suspensorium ; this is the 

 pterygoid foregrowth (e.pg) : it has even now become less by yielding its substance to 

 its bony pterygoid floor {iJff), but is not cut oS as a distinct " epipterygoid," as in 

 Sieboldia and Menopoma (Pis. XXXVI., XXXVIL). 



The quadrate bony centre {g) is larger ; the rest of the visceral centres are but little 

 altered since the larva was possessed of gills (PI. XL. figs. 3-5). 



c. Comparison of the Skull in the Cryptobranchiate Stages of Triton cristatus vxith 



that of other Vrodeles. 



I have already referred to the conformity of this semitransformed skull with that of 

 the great Cryptobranchiate species, viz. Sieboldia and Menopoma : these three skulls 

 agree marvellously, on the whole ; but the epipterygoid is never cut 03", even in the 

 adult (PI. XLI. figs. 1, 4, & 6, pg). 



But we catch in this stage of Triton just that condition of the palatine after it has 

 thrown off" its new pterygoid limb, ready to become ankylosed to the vomer, from which 

 it was once segmented as a tooth-carrying plate. The epihyal elements, however, are 

 entirely suppressed in this kind, as they are in the majority of the Caducibranchs ; the 

 stapes also never ossifies in this type. 



VOL. XI.— PART Yi. No. 5. — January, 1882. 2 1 



