DEVELOPMENT OP THE SKULL IN THE UEODELES. 177 



suspensorium ; but towards the front margin of the pterygoid bone {pg) an " epi- 

 pterygoid cartilage " [ep.g) is seen ; its length is equal to half the width of that bone, in 

 a groove of which it lies, and beyond which it projects towards the jugal process of the 

 maxillary, to which it is attached by a ligament. This cartilage — a mere sigmoid style 

 — had once a large base, which grew directly out of the front of the suspensorium ; 

 the pterygoid bone has used up this wide proximal part. 



That bone {ixj), which at first grew out from the palatine as an edentulous snag, 

 has become individuated and transformed into a most important part of the cranio- 

 facial building. 



It is, now, far from its original root, a huge two-leaved blade, with a sharp twisted 

 falcate handle, which handle is thoroughly ankylosed to the quadrate bone {q). 



Above (PI. XXXVI. figs. 1, 2) the inner blade is suturally joined to the sphenethmoid 

 (sp.e), and even to the parietal on the right side; below (PI. XXXVII. fig. I) it articu- 

 lates on each side with half the edge of the parasphenoid. This latter articulation is a 

 gross and dim foreshadowing of the light and elegant articulation of the pterygoid with 

 the basis cranii in Lizards and many Birds. 



Both the individuated epipterygoid cartilage {e.pg), and the bone {pg) by its outer lobe, 

 are obliquely attached to the distal part of the maxillary by an oblique ligament. 



Between the temporal process of the parietal and the ascending process of the 

 suspensorium the trigeminal nerve can be seen in the large foramen ovale, its double 

 outer part (v^ ^) passing outwards, over the cartilage, and its orbito-nasal branch (v^) 

 running beneath it ; this branch escapes again outside and above the optic nerve (ii). 

 The mandible (PI. XXXVI. figs. 2, 3) has a huge reniform condyle ; and the thick 

 upper end is largely ossified by the ectosteal articulare. The Meckelian cartilage [mk) 

 runs nearly to the end of the jaw. 



The hyoid arch is typically segmented above, but has more than the normal joints 

 below ; there is a pharyngo-hyal {p.hy) confluent with the stapes to form the columella, 

 and an epihyal {e.hy) articulated with the hind margin of the suspensorium. 



In the Frog the pharyngo-hyal, which is equivalent to the hyomandibular and 

 symplectic of fishes, forms the jointed columella ; but in that type, as in all the Anura, 

 the columella keeps distinct from the stapes, as the incus does in the Mammalia ; the 

 Urodele foreshadows the " Sauropsida " in having a compound [hyo-otic) columella. 



The stapes (PI. XXXVII. figs. 1, 2, st) is a thick, oval, ossified disk of cartilage ; and 

 its ectosteal plate runs onto the round, narrow, proximal end of the pharyngo-hyal, 

 ossifying it. The distal half is not ossified, and is dilated into a pedate mass, which on 

 the left side is confluent with the suspensorium, and on the right side is distinct and 

 is articulated with it; over this part the main trunk of the facial nerve (vii) runs. 

 Halfway down, the suspensorium is notched, sinuously. To this part the epihyal {e.ky) 

 is attached by ligamentous fibres ; it is semioval, with the attached edges sinuous ; it 



