DEVELOPMENT OF THE SKULL IN THE 15AT11ACHIA. 167 



4. The small girdle-bone. 



5. The definite prenasal w ith its lateral projections. 



6. The junction of the pedicle with the stylo-hyal. 



7. The absence of a distinct inter-stapedial. 



8. The absence of hypo-hyal lobes. 



9. The extreme delicacy and narrowness of the fronto-parietal bones ; this is repeated 

 m the other investing bones, but not to the same extent. 



44 (continued). — (B) Ac7'is Pickeriiir/ii. — Larva, 1 inch 2 lines long ; tail, f inch ; hind 

 legs, ^ inch ; same locaUty. 



The adult of this species is smaller than that of Camanolius, but its Tadpoles are 

 larger by one half; this specimen is more metamorphosed than the larva of that 

 minute Australian " Oxydactyle Frog" (see Plate 15, figs. G, 7). 



In this larva the chondrocranium (Plate 30, figs. 6, 7) is oval in outline, for the hind 

 part of the suspensorial bands and the fore part of the auditory capsides project, and 

 the quadrate condyles (q.c.) are drawn in towards the mid-line. It has gone beyond 

 the Petromyzine stage, for there are two bones, both of them axial and azygous : one 

 intrinsic, the cephalostyle or rudimentary basioccipital («.c.) ; and the other superficial, 

 the parasphenoid [pa.s.). The first vertebra (c.v^.) is drawn with the crown of its arch 

 cut away ; in it we see the ossifying neural arches, and the relatively huge notochord 

 («c.) beconung invested with a layer of bony deposit, principally on its upper surface 

 (fig. 6). This is taking place in the raesoblastic sheath, and is two-homed in front. 

 Entering the skuU, the notochord suddenly becomes very small, reaches to the same 

 transverse line as the Gasserian ganglia (V.), and ends in a rounded point, wliich is 

 twisted to the right hand. This styliform apex of the notochord is invested — most 

 above — with a deposit of bone, hke that which in the vertebral region forms rudi- 

 mentary " centra." The bony " cejihalostyle " has already been described as existing in 

 the adult. The occipital arch is fast finishing, for cartilage is breaking out, above, from 

 the inner edges of each auditory capsule, and this has converted most of the membrane 

 there into the same tissue. Also in front of the notochord there is a long inter- 

 trabecular tract of new, small-ceUed cartilage (fig. 6, inside tr.), and the orbital walls 

 ai'e beginning to grow over as a super-cranial {tcyminal) rudiment ; this is especially 

 seen in front. 



Between the narial passages (i.n.) the trabeculse have coalesced, convei'ging for tliis 

 purpose, but there is no appearance here of a distinct mesethmoidal rudiment. The 

 trabeculce break free of each other again, to end as free, crescentic, decurved horns, 

 from whose Inner edge a crest is growmg to fiU up the re-entering angle between them. 

 The nasal roofs are only beginmng to chondrify, and with the eye-balls, were removed 

 in making the dissection. The auditory capsules began to chondrify directly after 

 the trabeculae and suspensoria, and are now higlily developed ; then- canals {a.s.c, 

 h.s.c, p.s.c.) bulge largely, and the ampulla of the horizontal canal projects greatly. 



