MAMMALIA. 639 



in the Cetacea the pterygoid bones remain detached; in the Ro- 

 dentia the occipital is divided into a superior and inferior portion ; 

 but, in the latter, the two frontal and the two parietal become con- 

 solidated into one bone. 



In Man the bones of the cranium become much less numerous, 

 inasmuch as all the elements of the occipital, of the temporal, of the 

 frontal, the intermaxillary, and the maxillary, composing the upper 

 jaw, and the two halves of the lower jaw, respectively coalesce ; and 

 the skull consists of but one-and-twenty bones, seven in the cra- 

 nium, and fourteen in the face. 



Even this number is not the smallest ; for in some Monkeys the 

 nasal bones unite and become consolidated into one piece. 



(720.) Having thus enumerated the different osseous pieces 

 forming the crania of all classes of vertebrate animals, we must next 

 consider them in another point of view, namely, as being continua- 

 tions of the spinal chain of bones, or real vertebrae modified in form 

 and proportions in conformity with the increased volume of the 

 nervous masses they are destined to enclose. We must, however, 

 premise that it is by no means our intention to adopt unreservedly 

 the theoretical opinions of those Continental writers who find verte- 

 bral elements in the bones of the face, and even in the nasal carti- 

 lages ; still, without overstraining the facts, it is easy to demonstrate 

 very satisfactorily, that the cranial pieces that immediately enclose 

 the cerebral masses are strictly vertebrae, and present the same 

 essential structure as those of the spinal region. 



That this is the case in the skull of a Reptile, no one, indeed, 

 who examines the subject, can hesitate to admit ; but even in the 

 Mammiferous cranium, where, from the enormous proportionate 

 size of the encephalon, the cranium is most distorted, it is not diffi- 

 cult to perceive the relationship. 



The cranial vertebrae are three in number, the occipital, the 

 parietal, and the frontal : these are exhibited in the subjoined 

 diagram, after Carus, representing those of the Sheep. 



The occipital vertebra (Jig. 296, A) has for its body thebasilar 

 portion ; the arches bound the foramen magnum laterally ; and 

 above, the spinous process, flattened out and expanded in proportion 

 to the size of those lobes of the brain and cerebellum which it de- 

 fends, forms the posterior portion of the skull. 



The body of the second or parietal vertebra (B) is the body 

 of the sphenoid; that is, more properly speaking, the poste- 

 rior sphenoid bone, whose large alse, curving upwards, meet the 



