OF THE SKULL IN THE UKODELOUS AMPHIBIA. 
579 
perfectly distinct from each other and from the frontals. Each bone has a raised line, 
or low crest, outside its middle, the shelving part outside the ridge being part of the 
temporal fossa. 
The coronal suture between the parietals and frontals is sinuous, and projects forwards 
in the middle. The abrupt coronal junction of the parietals and frontals is a great 
advance upon the perennibranchiate type of skull, where the parietals run under the 
frontals up to the prefrontals. 
The frontals are quite distinct from each other ; they become deficient at the middle, 
in front, but are very large behind. 
Each bone has a median elevation, like that on the parietals; but outside the ridge 
the bone is grooved and multiperforate ; outside this groove there is a strong and well- 
formed superorbital ridge, which makes a good crescent with the bone in front. 
The parietals (fig. 6,^?.) run into the wail of the cranial cavity, and are not mere 
roof-bones ; the frontals (f.) do this still more perfectly ; they have a good orbital plate. 
Part of the roof and the front part of the orbital edge is formed by the external 
prefrontals. These ( e.eth .) are strong bony wedges, thrust in between the frontals and 
nasals ( n .) ; they reach the open fontanelle, inwards. 
The nasals (figs. 4, 6, n.) are irregularly lobate shells of bone; they cover the nasal 
capsules, which are here as wide apart as in the Selachians ; they are fairly fixed on 
between the prefrontal behind, the maxillaries externally, and the premaxillaries in 
front. 
The latter bones [jpx.) close in the cranio-facial box ; in front they remain separate, 
have very short nasal processes, between which and their body there is a foramen ; and 
they have a large, well-developed palatine plate (fig. 5). Each bone projects so as to 
leave an emargination in the front of the face ; together, they largely help to form the 
elegant semielliptical wpjper jaw, which is dentigerous up to the commencement of the 
zygoma. 
Each bone, externally, forms the antero-inferior third of the outer narial opening 
(fig. 6, e.n.), to which it gives a thickened rim ; this opening has a triradiate series of 
sutures, the two hinder of which separate the maxillary from the premaxillary below 
and the nasal above, the other is between the nasal and premaxillary. 
The maxillary now (figs. 4-6, mx.) is a large, well-grown bone ; it has a high, outer 
facial plate, a considerable palatine plate (fig. 5), and its dentary edge runs for half 
the extent of the bone, which ends behind in a large, arcuate, zygomatic process. 
In this, perhaps the smallest of adult Vertebrate skulls, I can discern no septo- 
maxillary, although it is very common in the Caducibranchs. • 
The next bones to be described are the vomers (fig. 5, v.) ; but I must first remark 
upon the large opening ( m.n.c .) at the mid line between these bones and the palatine 
plates of the premaxillaries. 
In the Salmon (“ Salmon’s Skull,” plates 7 & 8, m.n.c) there is a median nasal canal ; 
and this evidently Petromyzine structure is very constant in the Caducibranchs ; it is 
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