ON THE THEORY OF THE VERTEBRATE SKULL 56 1 



represents the mastoid, and it is most interesting to find it, in this 

 early condition, as distinct as in the Chelonian. 



The superior ossification has only to increase in size and remain 

 distinct in the same way as the mastoid of the turtle remains distinct, 

 to occupy the precise position of the '' occipital externe " of the 

 fish. But, further, it is most important to remark, that when this 

 primarily distinct bone has coalesced with the supraoccipital, it 

 stands in just the same relation to that bone, to the petrosal, to 

 the mastoid and to the semicircular canals, in the snake, as that 

 lateral element, early confluent or connate with the supraoccipital 

 in the chick, which I have termed the " os epioticum." I believe, 

 then, that this " os epioticum," distinct in the young snake, but 

 afterwards confluent with the supraoccipital, and becoming what may 

 be termed the epiotic ala of that bone in the adult, is the homologue 

 of the corresponding bone, or confluent ala of the supraoccipital, in 

 birds and reptiles, while in the fish it remains distinct, and constitutes 

 the " occipital externe." 



For the rest, the superior part of the cranial arch in the carp 

 resembles that of the bird. There are a supraoccipital, two parietals, 

 and two frontals ; the squamosal occupies the same position as in 

 the chick, and as in the latter, is, in the dry skull, visible from within, 

 in front of the petrosal. 



As in the Amphibia, both the mandibular and the hyoidean arches 

 are suspended by a pedicle or suspensorium, which is, to a certain 

 extent, common to both, and presents a complexity of structure which 

 can only be elucidated by the most careful study of development. 



In ordinary fishes, such as the carp, stickleback, &c., the proximal 

 end of the suspensorium is constituted by a single bone, Cuvier's 

 " temporal" whose cranial end abuts against the squamosal, petrosal, 

 and post-frontal bones. 



This temporal^ gives off posteriorly a process to which the 

 cornu of the hyoid arch is attached ; anteriorly and distally it 

 ends in an expanded plate, with which two bones are connected, in 

 front the tympanal, behind the symplectiqiie. The distal end of 

 the suspensor is constituted by the triangular jug-a I, whose distal and 

 narrower extremity furnishes the condyle with which the mandib'e is 

 articulated. 



The elongated styliform symplectique is received into a groove on 

 the posterior part of the inner surface of the ju^al, and extends nearly 

 to the condyle. In front, the jugal articulates with the transverse, 



^ In adopting the universally known Cuvierian appellations, I merely desire to avoid for 

 the present all theoretical suggestions. 



O O 



