178 ON THE STRUCTURE OF THE SKULL. 



riorly into the re-entering angle between the vomer and the 

 pre-maxilla and maxilla. It is usually regarded as the palatine 

 bone. 



Before attempting to discuss the homologies of these several 

 constituents of the palato-quadrate arch in the fish, it will be 

 necessary to take into account the nature and arrangement of 

 its post-oral facial bones. 



In Man, the post-oral bones are arranged in two arches — the 

 mandibular and the hyoidean ; or, more strictly speaking, since 

 the hyoidean arch is really composed of two, indicated by its 

 lesser and greater cornua, there are three post-oral arches. 



In the Pike, the lower jaw forms a mandibular arch, obviously 

 corresponding in a general way with that of Man ; behind this 

 follows a second arch, answering to the styloid processes, stylo- 

 hyoid ligaments, and cornua minora of the human hyoid, but 

 with much greater masses of bone entering into its composition ; 

 and this is succeeded by no fewer than five other arches, the four 

 anterior of which, supporting the gill filaments, are termed the 

 " branchial arches" while the last pair, which cany no branchiae, 

 and are much smaller than the others, are called the " inferior 

 pharyngeal bones" 



The symphysis of the lower jaw is formed by the ligamentous 

 union of two bones, which carry the inferior teeth of the Pike, 

 and correspond respectively w 7 ith the rami of the human man- 

 dible. But, besides these dentary bones (D, Fig. 65), each half of 

 the lower jaw of the Pike has two other constituents, which are 

 not represented in the human low r er jaw. One of these is a 

 small bone, which forms the lower part of the angular process of 

 the jaw. It is termed the os annulare, or angular piece (An, 

 Fig. 65). The other is a large triangular bone, which fits in 

 between the dentary and the angular, and is termed the articular 

 (os articular e, Ar.), because on its upper surface it bears a con- 

 cave articular fossa, into which the condyle of the quadrate bone 

 is received (Fig. 71). The cartilage which partially forms the 

 walls of this fossa is continued into a long tapering rod, which 

 lies upon the inner surface of the articular and of the dentary, 

 and terminates in a point shortly before reaching the symphysis 

 (Mch., Fig. 71). 



