230 ME. W. K. PAKKEK ON THE STRUCTUEE AND DEVELOPMENT 



The palatine is a small ossicle, placed unconformably to the rest of the bar, at its 

 extreme fore end, and in its transverse position answers to the ethmo-palatine bone of 

 Ambhjstoma and the Batrachia. 



In the Salmon there is much that is in conformity with what is found in the Rays, 

 but greatly modified. The palato-quadrate arcade (" Salmon's Skull," plate 6. fig 2) is 

 let down, so that the top, or otic process, is halfway down the hyomandibular bone ; 

 and this process is occupied by a square ossification, the metapterygoid, between which 

 and the base of the inverted triangle of bone below (the quadrate) there is a wide tract 

 of cartilage. This tract mounts up in front, and passes into a rounded boss, the arrested 

 pedicle. Then, further forwards, the cartilage is reduced to a very narrow tract ; and 

 this wedge of cartilage, between the mesopterygoid above and the pterj'goid below, 

 shows how far the pterygoid cartilaginous jirocess grew from the front of the quadrate 

 region of the suspensorium. That tract answers to the fore part of the upper jaw of a 

 Selachian. 



But the rest of the bar, where the cartilage breaks away from between the two 

 plates of bone {jyg, m.pg), is attached by a short pedicle to the ethmoid, and then grows 

 forwards as a massive prsepalatine rod, with a swollen boss for the head of the maxillary. 

 All this part is formed out of the originally distinct ethmo-palatine rod (ibid. pi. 2. 

 figs. 6, 7,2}p-g). 



Curious and instructive it is to find that at first, as in the Skate and Urodele, this 

 distinct praeoral pleural arch is thick above and grows backwards to a point. 



By the middle of the second week after hatching, the fry of the Salmon shows a pree- 

 palatine spur, which becomes so large in the adult, and which is so well seen in the 

 separated ethmo-palatine of Ilufo vulgaris. 



The hyostylic skull of the Salmon is easily seen to be a further specialization of what 

 is so remarkable in the skull of the Skate — although in the details of the segmenta- 

 tion of the top of the hyoid arch there is some difference, the hyomandibular being an 

 independent nucleus in the Skate, and arising in the Salmon by longitudinal splittuig 

 of the primary bar (" Salmon's Skull," plate 2. fig. 3, h.m, ch). 



In the Skate (PL XLI. fig. 4, i.h.l) the posterior division of the hyoid is attached 

 above to the postero-superior angle of the hyomandibular by an iuterhyal ligament. 



This state of things is seen in Salmon embryos just before hatching (ibid. pi. 2. 

 figs. 6, 7, h.m, ch, third stage) ; but in the adult (ibid. pi. G. fig. 2) the hinder moiety 

 {e]).h, ch) is suspended from the synchondrosis between the long hyomandibular and 

 the short symplectic, exactly opposite the quadrato-metapterygoid synchondrosis. 



There this kind of specialization, the hyostylic, is carried to its uttermost degree, 

 and the articulation of the two main hyoidean moieties is but little above that of the 

 mandible and its pier ; yet the whole is but an exaggeration of what is seen in the 

 Skate. 



The structure just described may be found in by far the greater number of Tele- 



