128 ON THE VERTEBRATE SKULL. 



of the palatine plates of these bones, which eventually unite with 

 the vomer, give rise to the apertures, which are ordinarily 

 called posterior nares. So that in Man, for example, there are 

 three pairs of " nares :" — the external, situated between the 

 anterior end of the internasal septum, the nasal bones, and the 

 premaxilla?, as in the lower Vertebrates ; the median, between 

 the vomer, the palatines, and the premaxillae, which correspond 

 with the posterior nares of the lower Vertebrates ; and the 

 posterior, between the vomer, internally, and the palatines 

 above, at the sides, and below, which are peculiar to the higher 

 Vertebrates. 



And, to return to the maxilla, we find that it reallv differs 

 altogether from the other pre-oral bones, and is, as it were, 

 fastened on to the outer sides of the premaxillary and palatine 

 bones, without having any primary direct connection with the 

 cranio-facial axis. 



The post-oral bones surround the buccal cavity, and form 

 two distinct arches — the mandibular and the liyoidean. Neither 

 of these arches is directly connected with the cranio-facial 

 axis, nor with the segments of the brain-case, but both are 

 suspended to different parts of the temporal bone, which is so 

 singularly intercalated between the middle and posterior of those 

 segments. 



The lower jaw or Mandible (Mn) consists of two rami, anchy- 

 losed at the symphysis, and each consisting of a single piece, the 

 condyle of which articulates with the squamosal. 



The Hyoid bone (Hy), composed ofits body and two pairs of 

 cornua, does not articulate directly with the temporal bone, 

 but ligaments connect it with the styloid processes, and these 

 last bones unite with the posterior part of the periotic capsules. 



Thus, the natural connections of the bones by no means 

 allow of the separation of the walls of the lower chambers of 

 the human skull into a series of arches springing from, and 

 corresponding with, the axial parts, as w T e found to be the case 

 with the walls of the upper chambers. 



If the temporal bone be detached, the hyoidean and man- 

 dibular arches come with it, and exhibit no connection with 

 the occipital or the parietal segments. Indeed, the latter is 



