208 MR. W. K. PARKER OX THE STRUCTURE AND 



the size of a mustard-seed, and is no larger directly after it is metamor|jliosed. I 

 mention tliese things to show how sensitive the Batrachians are to their surroundings ; 

 how much their tiansforraations are modified by the chances of theii- life ; and also, 

 how iiioditiablft these creatures are — Protean in their changeableness. 



The skull at this stage* (Plate 38, figs. 9, 10) is truly Petromi/zine, yet it has a 

 modification of the cranial structures not seen in the Lamprey ; viz. : the " orbitar 

 processes." These parts are free above ; but in the Tadpole of Bu/o vulgaris (Phil. 

 Trans., 1876; Plate 55, fig. 3, between q. and eth.) they are confluent with the 

 ethmoid, as Professor Huxley pointed out to me ; suggesting, at the same time, that 

 they might be the homologues of the anterior eras of the LamjDrey's susjiensorium : 

 we neither of us hold this view, now. 



The chondrocranium of the lan^al Biifo chiJoisis (figs. 7, 8) is almost circidar ; the 

 whole length, including the labials, is but httle greater than the breadth across the 

 subocular arches (sj)-) ; here the skull is oblong. 



The chondrification is nearly perfect, bvit the Hnes of union of the various elements 

 are all visible, being made up of younger, more elongated, and crowded, cells. From 

 the occipital condyles (oc.c.) to the internal nostrils (i.n.), the basis-cranii is of nearly 

 uniform size; it is then lessened by a notch, on each side, half the size of these passages, 

 and gains this breadth again, gradually. The hinder part is. as it were, cut away for 

 the ovoidal ear-capsules (au.) ; the interorbital part is struight-sided in the last and 

 pinched in tliis, and the fore-part is in two diverging bands, with a deep notch 

 between them. 



Behind the oi-bital space, the pedicle of the suspensorium ( s/>.) passes into the basal 

 plate ; in front, the ethmo-palatine bands run into it ; behind the ear-cajisules the 

 basal moieties curve round, to enclose the 9th and 10th nerves (IX., X.). From 

 the middle of the inter-auditory space, to the great notch in front, there is a siDindle- 

 shaped space of new cartilage, leaving the thicker, and older, marginal bands of the 

 same size as the free bands in front ; these latter ai-e curled over, in the frontal wall, 

 pointed, externally, in the last, and blunt in this. 



The basal tracts are as follows : — 



The inve.sting mass. — This reaches to the mindle of the hind skull, and is sepa- 

 i-ated by the cranial notochord (nc), which is shrinking, and is invested with a thin 

 (mesoblastic) layer of long cells, scarcely cartilaginous. The rest of the paired 

 cartilages ai-e due to the rapid growth of the trabeculte (tr.), and the free fore parts 

 are the " cornua" (c.tr.). The spindle-shaped, thin, new tract along the middle is 

 the first part of the " intertrabecula" (see fig. 8, i.tr.) ; it is very long and wide. 



A second region of this element is seen from above, in the last (fig. 7), as a short, 

 thick wall of cartilage, the rudiment of the perpendicular ethmoid (/>.e.). 



The internasal or fore part of this element is membranous at present in both 



* I have alreadj' described the earliest state cif tlic Batrachiaii chondrocranium (see j). 10) in that of 

 Bufo vulgaris!. 



