in.] THE CRANIAL SKELETON. 95 



downwards from the basi-cranial plate, or rather from the 

 lateral cartilage contiguous with it. 



Thus a second rod, external to the trabecula, on each side 

 passes forwards (almost parallel with the trabecula adjacent 

 to it) and fuses with the Ethmo-vomerine plate. 



A third rod descends and fuses with its fellow of the op- 

 posite side, so forming the groundwork of the lower jaw, 

 which is thus laid in what is often called the first visceral 

 arch, but which is really the third. 



The next, or fourth cartilaginous rod, meets with its fellow 

 below only by means of the interposition of soft structures, 

 and lays the foundation of the styloid processes and corni- 

 cula of the os hyoides, which thus are contained in what is 

 really ihefourt/i visceral arch, though often called the second. 



The fifth visceral arch develops on each side, at its ven- 

 tral part, the precursor of the cornu and body of the hyoid 

 bone. 



Ossification occurs, as has been stated, in more than one 

 point of most of the bones which are reckoned as single bones 

 in the adult man. Thus it occurs in the lateral and superior 

 parts of the occipital as well as in the basilar part ; in the 

 wings and inner pterygoid processes of the sphenoid, as well 

 as in those two parts of its body which may be distinguished 

 as the basi-sphenoid and the pre-sphenoid the latter sup- 

 porting the orbital wings. In the temporal bone, as has been 

 pointed out, many very distinct ossifications occur. 



The ossification of the ethmoid and of all the turbinals 

 and vomer takes place in, around, and from the ethmo- 

 vomerine plate and the cartilages of the trabeculae, or first 

 visceral arches. 



The palatine bones, internal pterygoid processes, and 

 maxillary bones, are ossifications connected with the second 

 visceral arches. 



The mandible which arises from one point of ossification 

 on each side invests the ventral end of the cartilage (called 

 Meckel's) of the third visceral arch. 



1 8. Turning now to OTHER VERTEBRATES, we find that 

 in the possession of a cranium man agrees with all except 

 the Lancelet. This animal can hardly be said to have a brain 

 at all, so slight is the enlargement of the anterior end of 

 its spinal marrow : consequently its brain-case is, as might 

 be expected, similarly imperfect, and consists merely of the 



