OF THE SKULL IN THE AMPHIBIA TJRODELA. 169 



plate, the vomer (») ; the rest thin out into a small row of denticles, only attached to 

 bone in front. The bone whose fore end carries these hinder teeth is the pterygopalatine 

 (p.pg) ; it commenced as a palatine, carrying its own share of the teeth, but threw out 

 a pterygoid spur, which the teeth did not follow in its diverging course. The teeth 

 will approach still nearer to the mid line, and the non-dentigerous plate will become 

 segmented from the rest, and bend outwards to the zygoma. 



The relation of the cartilaginous to the bony parts will be still better seen by reference 

 to the figures of sections, which were made from an embryo somewhat more advanced. 



The first transversely vertical section (fig. 4) was made just in front of the internasal 

 plate (iu.c) ; it shows the thickness of that plate, and the position of the nasal roofs (ol) 

 and trabecular cornua (c.tr). These latter make a floor quite similar to the roof; the 

 roof itself has already been grafted on to the internasal plate. Where the union is 

 taking place there the nasal processes of the premaxillaries (n.px) are seen in section, 

 whilst below, the vomer and its teeth (o) are seen beneath the trabecular nasal floor. 



The second section (fig. 5) shows the same bones and cartilages as the first, but at the 

 hinder margin of the internasal plate (iu.c). The olfactory nerves (1) find their way to 

 the nasal sacs between the upper and lower cartilages (ol, c.tr), and the middle space is 

 continuous with the cranial cavity. 



The third section (PL XV. fig. 1) was made directly through the eyeballs (<?), through 

 the middle of the brain (lettered c 2 by mistake). 



The trabecular (tr) have become strongly crested, and the crest at this part is orbito- 

 sphenoidal; the floor is finished by the gently bulging parasphenoid (pa.s), and the roof 

 is filling in from the edges by the frontals (f). 



On the palate, one third the way from the skull to the face, the pterygoid spur (pg) 

 has been severed. The rest of the skeleton here to be seen is below the mouth. The 

 outermost of these bars is the mandible (mk), a ad its ovoidal section shows the articulare 

 on the inside and the dentary on the outside (ar,d). 



Next to these come the ceratohyals (c.luj) ; they have an ovoidal outline, but the 

 narrow end is below, whilst in the mandible it is above. The ceratobranchials are severed 

 close behind the first basibranchial, so that the fore end of the second is cut through 

 (b.br-) ; the lesser second ceratobranchials lie in a higher plane than the larger first pair 

 (c.br 1 , c.br' 2 ). 



The fourth section is a little oblique (PL XV. fig. 2) ; it is behind the eye, and catches 

 the mid brain (c 2 ) and backwardly turned lower part of the fore brain ; the top of the 

 infundibulum (inf) is seen in it, but not its connexion with the pituitary body. 



On one side the fore face of the ear-sac (an) is laid bare, but not on the other ; on this 

 latter side the pedicle of the suspensorium (jpd) is seen to ascend over the orbito-nasal 

 nerve (5 1 ), and to be coalesced with the alisphenoidal crest of the trabecula (tr) ; there 

 is no union besides this ascending process to the skull wall. The quadrate cartilage is 

 in relation with the articular end of the mandible (q, ar) ; from its upper edge the otic 

 process (ot.p) is seen to rise. 



On the other side the ascending process is cut through, and the Casserian ganglion 

 is exposed; it is seen between the trabecula (//') and auditory sac (cm). The para- 



