DEVELOPMENT OF THE SKULL IN THI-: BATRACIirA. 199 



toucliing all these points of the hind skull would form part of a very large circle, and 

 this arc would be sub-equal to that formed by the cheek and jaw bones, right and left. 



The muzzle is very wide, but its arc would forn\ part of a circle only half the size of 

 the one just supposed. 



A semi-circle hnishinof the lateral outline would make the form into an ovoid. 



A rather narrow tract of cartilage divides the right and left bony masses of the 

 hind skull, but the prootic is confluent with the ex-occipital {au., e.o.). This common 

 bony mass reaches beyond the horizontal canal, externally, and in front runs up to the 

 optic fenesti-a (II.), enclosing the foramen ovale (V.). Most of the cartilaginous 

 teo-men tympani {t.ty.) is covered by the large ear-shaped temporal plate of the 

 squamosal (sq.) ; its rounded hind part, however, is naked. 



The epiotic eminences {ej'-) are wide, they are not covered by the roof bones, but 

 much of the anterior, and the ampulla of the horizontal, canal, are covered, for the post- 

 orbital process is broad, and unites by suture with the squamosal. Tlie endocranium 

 in the oi-bital region is much overlapped by the roof slal^s ; it is of nearly equal breadth 

 before and behind, and is gently narrowed behind the middle. 



The girdle-bone (eth.) takes up three-fifths of this territory, and does not finish its 

 own wings ; but it sends forwards a short median and a pair of lateral bony growths 

 under the nasal region (fig. 2, eth., s.n.l.) ; its margins are sinuous. The unossified 

 wings of the ethmoid are segmented from the ascending process of the palatine 

 cartilage (fig. 3, e.pa.) ; they are very solid, and in front are continuous with the broad 

 subnasal laminae (fig. 2, s.n.l). These laminae end in front in dilated horns; the inner 

 cornua, or pro-rhinals [p.rh.), are conical, and turn inwards. The snout is transverse, 

 gently emarginate, and moderately broad ; from its angles a nairowish band of cartilage 

 runs backwards on each side, these are confluent, behind, with the wings of the 

 ethmoid: they are the arrested nasal roofs {n.r.); between them and the widened 

 top of the septum [s.n.) there is a large crescentic fontanelle (or fenestra). 



The first and second labials {u.l^.u.l'~.) are well developed; the second nostril-valve 

 is very large and solid. The palato-suspensorials are so modified as to form the 

 type of a sub-group — the Biifonine, as distinguished from the Ranine. Primarily, as I 

 have shown in a former paper (" Batrachia," Part II., Plate 54, p. 607), the development 

 of these parts takes place as in Jiana, but their metamorphosis is much modified. The 

 bony plates here use up much of the cartilage, which remains as an ethmo-palatine 

 (fig. 3, e.^>a.) jointed oS" from the ethmoid above and free below, exactly, now, like that 

 of a Skate or a Salamander. The pterygoid cartilage also (fig. 3, pg.) is now, as in 

 those types, quite free from the ethmo-palatine, and is, what we find in Selachians, in 

 young Teleosteans, and in Urodeles — merely a symplectic process of the suspensorium 

 of the lower jaw. 



The palatine bone, also {pu-), is composed of two parts : the normal ect osteal plate, 

 and a sub-distinct knife-hke crest, which is very sharp and steep ; the old remnant, 

 undoubtedly, of a dentigerous plate, like the palatine bone of a Urodele. 



