78 y\H. W. K, PARKER ON THE STRUCTURE AND 



This new cartilage (co.) lies inside the nerve, as it forks to join the glosso- pharyngeal 

 (VII., IX.), and to supply the region of the first cleft, fore and aft. 



This rudimentary columella appears as a solid bud of cartilage abutting against the 

 fore edge of the large, almost circular, stapes (6';.). 



A section of these parts (Plate 11, fig. 9, St., co.) shows that, according to the rule in 

 the Batrachia, the dorsal end of this cartilage is wedged in between the antero-superior 

 margin of the stapes and the auditory capsule ; it is already constricted into two 

 regions; the massive " inter-stapedial " part (a distinct segment generally, but not in 

 Pseudis (see Plate 10, fig. 4, m.fit.), is already marked oti' from the main rod (Plate 11, 

 fio-. 9, CO.). Below the stapes (Plate 11, fig. 8,f.ti/.) the tympanic floor, once so large 

 as a down-growth of the actual skull-base, is now a mere thickening of the bulbous 

 vestibular region. 



The prsemaxiUaries (Plate 12, fig. 1, px.) have been added to the bony plates, and 

 they fit against a small inner (anterior) cartilage (u.l.); a crescentic valve to the nostril 

 is also found outside this ; the large primary upper labials have been removed ; they 

 were ready to be absorbed. 



If the metamorphosis of this skull stayed here, we should have much to contemplate 

 that is both striking and instructive ; this stage, however, is scarcely mid- way to the 

 actual end of this changing skull. 



17 (continued). — (D) Fourth larva of Psendis, rapidly acquiring the Frog-form, but 

 with a tail still 3 inches long and 7 lines wide. 



In this species the tail co-exists for a long while after many of the chai-acters of the 

 adult skull have appeared (Plate 12, figs. 2-7). At first sight this larva appeared to 

 be not very different from the last, but it had lost the contracted suctorial mouth, and 

 had gained the characteristic open gape of an adult Frog. 



This had been done by the rapid enlargement of some parts, and the rapid lessening 

 of others — an interstitial change which . appears the more marvellous the more it is 

 contemplated. 



In the broad basioccipital region the notochord (Plate 12, figs. 2, 3, nc) still persists 

 as a small thread ; and a three-rayed tract of cartilage has escaped the ex-occipital 

 growths (e.o.) ; the lateral extensions of cartilage are the occipital condyles (oc.c), 

 which are large and wide apart. 



The cranial cavity has become still wider than iu the last ; it lessens gently u]) to 

 the ethmoidal region. 



The parietals are now fairly distinct from the frontals {p-,/.), and the hinder part of 

 the " tegmen " has no uncovered cartUage, the confluent ex-occipitals having the 

 narrow part of the subquadrate parietals lying on their fore margin. 



These hinder bones send out a temporal angle behind the widest part of the frontals, 

 and then the latter bones continue this down-turned edge (orbital plate) up to their 

 narrow apex (fig. 4, /'.). 



