DEVELOPMENT OF THE SKULL IN THE BATRACHIA. 91 



The extra -branclilals {e.r.hr.^'*) are quite r.ormal, and each has its own c?rato- 

 branchial rudiment (c.hr}'*) coalesced below with it. 



The fronto-parietals (fig. l,f-p.) are small blades of bone, pointed in front, broader 

 behind, and resting on the roof-edge of the skull. 



The parasphenoid (fig. 2, pa.s.) is very noticeable ; it is JJ-shaped, and half cleft into 

 two pieces ; this character attains in this, and in its congeneric larva, to an extent not 

 seen by me in any other type of the " Ichthyopsida ;" a front notch is seen in every 

 stage of Pseudis, but it is small. 



Most of the cranial nerves (fig. 2, II., V^., V- I, VII., VII'., IX., X.) are shown 

 issuing from their foramina, as in the last kind of larva. 



19 (continued). — (B) Cystignathus ocellatus (?). — Second larva; 3j inches long; tail, 

 2^ inches ; hind legs, 1 line long. Brazils. 



In development, this Tadpole corresponds very exactly with my huge youngest larva 

 of Pseudis (Plates 1 and 2) ; the hinds legs are relatively of the same size and are at 

 the same stage. 



The chondrocranium (Plate 17, figs. 5, 6) is one-half larger than the last, and certain 

 changes have taken place in it of importance. The notochord (hc.) is shrinking, and 

 the basal plate closing in upon it ; the occipital condyles (oc.c.) are better formed, and 

 the cranial cartUage has fused more completely with the auditory capsules. A dis- 

 coidal exoccipital encloses the 9th and 10th nerve {e.o., IX., X.), and the prootic {pv.o.) 

 is beginning to creep up the front of the auditory capsule behind the foramen ovale. 



The canals of the ear (a.s.c, h.s.c, p.s.c.) are very clearly seen above; below, the 

 capsules are getting flattened sides, which lessen backwards ; in the side, under the 

 large leafy tegmen tympani {t.ty.) the fenestra ovalis has become almost vertical, and 

 a nucleus of cartilage is now to be seen in the soft plug of tissue that fills it ; this is 

 the stapes (fig. 6, St.). The tegmen tympani is elegantly angulated behind ; in front 

 it is continuous with the spiracular cartilage (sj3.o.), a large sub-falcate flap, which has 

 coalesced also now with the budding "otic process" {ot.jh). The interorbital region 

 of the skull is more perfect, but of the same shape ; the pear-shaped fontanelle (/o.) 

 is widest, now, further back, and the front tegmen is more solid, and has united with 

 the trabecular edges and hidden median cartilage to finish the ethmoidal region. 

 . The olfactory nerves (I.) are seen emerging, but the nasal roofs are still membranous, 

 and were removed in the preparation. Yet the intertrabecula is filling in the space 

 between the trabeculae up to the membranous margin of the internal nostrils (i.n.). 

 That membrane, however, has in it no spur growing from the trabecular cornu (c.t):), 

 which is narrowed further forwards than in the last stage ; for the rest, these, and the 

 upper labials {n.l'.u.V'.), are only larger. The pedicle of the palato-suspensorial arch 

 {pd.) is less transverse; the orbitar process {or. p.) is further out; the post-palatine 

 rudiment {2^t.pa.) is now fairly differentiated from the ethmoidal wing (ale.), now 



X 2 



