180 ON THE STRUCTURE OF THE SKULL. 



and are not represented at all in the Fish. Hence, in the latter, 

 we- might expect to find only mandibular and hyoidean branches 

 of the portio dura corresponding with the chorda tympani on 

 the one hand, and the stylo-hyoidean and digastric branches, on 

 the other, in Man. And this is really the case. For the portio 

 dura of the Pike, which leaves the skull by a special foramen in 

 the pro-otic bone, traverses the hyoruandibular bone, and then 

 divides into two branches, one of which runs backwards to the 

 hyoidean arch ; while the other, directed forwards and down- 

 wards, passes to the inner side of the quadrate bone, and over 

 its articulation with the articulare to the inner surface of the 

 lower jaw, along which it runs to the extremity of the ramus. 

 This last branch is obviously the representative of the chorda, 

 tympani, and its relations to the quadrate and articular bones 

 are, it will be observed, very similar to those which the corre- 

 sponding nerve has to the incus and malleus in Man. 



Holding fast, then, by this determination of the homologies 

 of the articulare and quadratum, what is the nature of the other 

 bones entering into the palato-quadrate arch ? 



The metapterygoid may perhaps answer to the os orbiculare. 

 The manner of its connection with the quadrate (incus) suggests 

 this view, for which, however, I cannot pretend to offer any 

 positive proof. 



That the other three bones answer in a general way to the 

 pterygopalatine bones of Man is certain. The pterygoid of 

 Man, it is true, is in no way connected with the incus, while both 

 bones EcpA and JEpt. are united with the quadratum. But this 

 is in reality no difficulty, for we shall find that, in the higher 

 oviparous Vertebrata, the os quadratum is very generally con- 

 nected with a bone which is universally admitted to correspond 

 with the pterygoid of Man. 



Again, both the palatine and the pterygoid bones of Man 

 are articulated with the base of the skull, while the palato- 

 pterygoid arch of the Fish is not directly connected with any 

 of the basi-cranial bones ; but, in many of the higher Vertebrata, 

 the ptery go-palatine arch is almost as free of the base of the 

 skull as in the Fish. 



No doubt, then, the palato-pterygoid bones of the Fish, 



