OR OSSEOUS SYSTEM. 63 



ends of the bodies of the vertebrae can be traced for- 

 ward to a variable extent through those of the cranium, 

 as at both ends of the basilar portion of the occipital, 

 and of the body of the spenoid. The bones of the cranium 

 in osseous fishes are generally thin, diaphanous, elastic, 

 united by squamous sutures ; they present a large exterior 

 surface for the attachment of the powerful muscles of the 

 trunk, and they continue to grow and to preserve the 

 same proportions to the rest of the skeleton through 

 life. The interior of the large cranical cavity is filled 

 chiefly by the soft cellular tissue of the arachnoid coat, 

 the brain occupying but a small portion of the base of 

 the skull. The number of distinct osseous pieces in the 

 composition of the skull is greatest in fishes, and they 

 correspond nearly with the theory of this part of the ske- 

 leton, being composed of seven vertebrae, each consisting 

 as usual, of a body with four elements above, and four 

 elements below. The number of separate pieces diminishes 

 as we ascend through the vertebrated classes, by the early 

 and permanent anchylosis of a variable number of these 

 elements common to all forms of crania. 



The spine of the occipital bone, or the superior oc- 

 cipital (8,) is here large for muscular attachments, like 

 that of the vertebrae of the trunk ; and this ridge is often 

 continued forward over the whole skull to the nose. 

 From the horizontal position of the head on the trunk, 

 the occipitals and the frontals generally meet and force 

 the parietals (7,) to assume a lateral position, as we see 

 in the skulls of cetacea, for the same reason. The ele- 

 ments of the temporal bone are large^ detached, and 

 mostly moveable. The petrous portion is exterior to the 

 organ of hearing in the osseous fishes, and surrounds 

 that organ, imbedding it in its substance in the cartila- 

 ginous species,, as in higher classes. The principal frontal 

 bones (I,) are long and bounded before and laterally by 

 the anterior frontals (2,) and on the posterior and lateral 

 part by the posterior frontals (4,) as in other oviparous 

 vertebrata. The jugal (19,) is generally long, curved, and 

 slender, as in the blowing cetacea, and composed of a 

 series of separate pieces, which bound the inferior margin 

 of the orbit, they form the suborbital bones of Cuvier. 



