828 



OSSEOUS SYSTEM. (COMP. ANAT ) 



obvious; it is only necessary for the student 

 to recur to less distorted forms of the head at 

 once to recognise the reality of the resem- 

 blance. 



Should other proof indeed be wanting, the 

 manner in which all the cerebral nerves make 

 their exit from the cranium would in itself 

 offer a convincing argument. In every olher 

 part of the cerebro-spinal axis the nerves in- 

 variably are given off through passages situated 

 between contiguous vertebrae, which are called, 

 from this circumstance, par excellence, inter- 

 vertebral foramina ; nay, so sure is this guide, 

 that in those instances where the vertebral 

 pieces are confused, so as to be otherwise un- 

 distinguishable from each other, the position 

 and number of these foramina is sufficient to 

 indicate the number of vertebrae of which the 

 part of the skeleton in question originally con- 

 sisted, before the pieces composing it became 

 permanently anchylosed. Precisely in the 

 same manner the nerves derived from the 

 encephalon pass out through the interspaces 

 between the occipital and parietal vertebras, 

 or between the latter and the frontal ; and, 

 although from the great bulk of the encephalic 

 masses and the number of nerves derived 

 therefrom, the passages through which they 

 principally escape have been named foramina 

 lucera, indicating their size and irregularity; 



Fig. 438. 



Fig. 439. 



Skull of Boa Constrictor. 



they are not on that account less the repre- 

 sentatives of the intervertebral foramina pro- 

 perly so called. The mere circumstance of the 

 channels of some of these nerves being, in the 

 human subject and in other Mammifera, cir- 

 cumscribed by rings of bone and thus con- 

 verted into distinct foramina, to which special 

 names have been given by the human osteo- 



Section of skull of Boa. 



legist, militates in no degree asainst the grand 

 fact that it is between the cranial vertebras they 

 all make their exit. 



Having given the above general view of the 

 composition of the osseous skeleton, a more 

 difficult task now remains to be accomplished, 

 viz. to identify and compare with each other 

 the individual bones entering into the com- 

 position of the osseous system throughout the 

 different vertebral classes, and thus to analyse 

 the entire fabric. Various and conflicting in- 

 deed are the opinions of different writers on 

 this important subject, of whose names and 

 works an ample list will be given in the Biblio- 

 graphy affixed to the end of this article ; but 

 to enter into the argumentation of disputed 

 points would of course be impossible in our 

 prescribed limits. Suffice it to say, that the 

 views of the acute and sound-judging Cuvier 

 have been principally adhered to, and where 

 occasion has been found to dissent from his 

 opinion we have expressed our reasons for so 

 doing.* 



Bone* of the cranium. Frontals (1). These 

 bones in fishes form the roof of the orbit and 

 the anterior portion of the cranial box, having 

 in front and behind them other pairs of bones 

 forming the anterior and posterior boundaries 

 of the orbit which correspond with the ante- 

 rior and posterior frontals in Reptiles. In the 

 Frog the whole of the anterior portion of the 

 cranium is made up of a single bone, which 

 entirely surrounds it like a ring or girdle, and 

 represents the two frontal bones of Serpents 



* We must here especially acknowledge our 

 obligation to Professor Owen, who has most kindly 

 placed at our disposal the result of his researches 

 concerning the homology of the cranial hones of 

 Fishes : his opinions have been introduced in their 

 proper places. 



