632 PISCES. 



the elements, or ossific centres, of which the cranial bones of higher 

 animals are composed remain here permanently separated, overlapping 

 each other, so as to form squamous sutures, but never becoming fused 

 together, as the elements of the human skull invariably do at a very 

 early period. 



(1700.) No fewer than twenty-six bones enter into the composition 

 of the cranium we are now considering ; to which, as is now generally 

 allowed, the following names are applicable. 



(1701.) The frontal bones are each divided into three portions, called 

 respectively the principal frontal (l)*, the anterior frontal (2), and the 

 posterior frontal (4). 



(1702.) Between the anterior frontal bones is the ethmoid, a simple 

 vertical lamella, which is often merely a cartilaginous plate. 



(1703.) The middle of the base of the cranium is made up of two 

 bones : the basilar (fig. 312, 5), a portion of the occipital, forming the 

 body of the occipital vertebra ; and the body of the sphenoid (6), a di- 

 stinct bone, which is prolonged anteriorly into a lengthened process, 

 which serves as the base of the membranous septum between the orbits. 



(1704.) The parietal bones (7) are placed behind the posterior frontal; 

 but they do not generally touch each other, being separated by an inter- 

 posed bone called the interparietal (8). 



(1705.) The occipital bone is made up of five portions : namely, two 

 external occipitals (9), two lateral occipitals (10), and the basilar bone 

 (5), already noticed, by which the head is articulated with the first 

 vertebra of the spine. 



(1706.) Two detached bones, which represent the great or temporal 

 alee of the sphenoid, fill up the space between the body of the sphenoid 

 and the posterior frontal. 



(1707.) Two other pairs of bones, which are elements of the temporal 

 bone in Man, likewise assist in forming the cranium : these are called 

 the mastoid bones (12) and the petrous bones (13). 



(1708.) A single bone, analogous to the anterior portion of the body 

 of the human sphenoid, and which, as will be fully evident hereafter, 

 is essentially distinct from the posterior portion, bears the name of the 

 anterior sphenoid, while the orbital alee of the sphenoid are found in 

 the two bones marked 14. 



(1709.) These, therefore, together with the representative of the 

 vomer (16), complete the cranial portion of the skull; no fewer than 

 six azygos and twenty pairs of bones entering into its composition. 



(1710.) Bones composing the upper jaw. The upper jaw consists 

 of two pairs of bones, which, from the looseness of their connexion with 

 the other bones of the face, are endowed with considerable mobility. 



* In order to simplify the subject as much as possible and prevent unnecessary 

 repetition, the reader will observe that, throughout all the figures connected with the 

 osteology of the Vertebrate, corresponding bones are indicated by the same numbers. 



