250 ANATOMY OE VERTEBRATES. 



to swing freely to and fro. The posterior and anterior sphenoids 

 continue distinct bones in all Mammals during a period of life at 

 which they form one continuous Ijone in Fishes. 



The loose connections of most of the bones of the face may 

 likewise remind the homologist of their condition in the im- 

 perfectly developed skull of the embryos of higher animals ; but 

 this condition is especially subservient to the peculiar and ex- 

 tensive movements of the jaws, and of the bones connected with 

 the hyoid and branchial apparatus. 



Not any of the limbs, j^roperly so called, of Fishes, are pre- 

 hensile ; the mouth may be propelled and guided by them to the 

 food, but the act of seizing must be performed by the jaws. 

 Hence in many fishes both upper and lower maxillary bones enjoy 

 movements of jirotraction and retraction, as well as of opening 

 and shutting. The firm connections of the upper jaw, and wedged 

 fixity of the bone suspending the under jaw, which characterise 

 the higher Reptiles and Mammals, woiild be imperfections in the 

 Fish ; in which, therefore, such characters are not only absent, 

 but special developement in the opposite direction not unfre- 

 qucntly goes so far as to produce the most admirable mechanical 

 adjustments of the maxillary apparatus, compensating for the 

 absence of hands and arms, like those which have been exemplified 

 in the instance of the Epihidiis ijisidiutor.^ AVe must guard our- 

 selves, howe^'cr, fi'om inferring absolute superiority of structure 

 from apparent complexity. The lower jaw of fishes might at first 

 view seem more complex than that of man, because it consists of 

 a greater numljer of pieces, each ramus being composed of two or 

 three, and sometimes more separate bones. But, by parity of 

 reasoning, the dental system of that jaw might be regarded as 

 more complex, because it supports often three times, or ten times, 

 perhaps fifty times, the number of teeth which are found in the 

 human jaw. We here perceive, however, only an illustration of 

 the law of vegetative repetition as the character of inferior organ- 

 isms ; and we may view in the same liglit the nmltiplication of 

 pieces of which the supporting jicdicle of the jaw is composed in 

 Fishes. But the great size and the doidile glenoid or trochlear 

 articulation of that jiedicle, are developements beyond, and in 

 advance of the condition of the Ijones sujipcniing tlie lower jaw 

 in Manunals, and relate l)oth to the increase of the ca]iacity of'the 

 mouth in Fishes tor the hulgment of the great hyoid and branchial 

 ap])aratus, and to the sujiport of tlie opercula, or doors whicli open 

 and close the branchial cliamliei-s. The di\ ision i>f the lono- 



' r- ii'j, fig. 87. 



