OSSEOUS SYSTEM. (Coup. AN AT.) 



Fig. 434. 



10 10 



Skull of the Perch ( Perca ftuviatilis), after Ctivier. 



an association of several osseous pieces, certain 

 elements of a vertebra may be modified in 

 position and proportions so as to perform the 

 ordinary functions of others which may be 

 atrophied or absent : thus in Fishes the inferior 

 transverse processes are gradually bent down- 

 wards until in the dorsal region their extremities 

 meet and perform the functions of the haema- 

 pophyses. 



From the vertebral elements named above 

 every possible variety is presented by these bones 

 throughout all the races of animals possessing 

 them. The body alone (fig. 433, d) may be de- 

 veloped without the addition of any of the other 

 parts, as in the terminal bones of a Mammal's 



825 



tail or of the human os cocct/gis, or the neura- 

 pophyses may exist without an ossified body, as 

 in some cartilaginous Fishes. The vertebrae of 

 the human skeleton present body, neurapophy- 

 ses, neural spine, and transverse processes, as do 

 the rib-bearing vertebrae of the Fish. The 

 caudal vertebrae of the Fish, in order to give the 

 great vertical expansion required in this region 

 of their skeleton, have the centre, the neura- 

 pophyses, and neural spine as well as the 

 haemapophyses and haemal spine to the ex- 

 clusion of the transverse, while in the earlier 

 caudal vertebrae of the tail of the Crocodile 

 (Jig. 433, g^all the elements enumerated exist 

 in a medium state of developement. 



From these data, therefore, the osteologist 

 is enabled to explain the composition of any 

 vertebra that may be offered to his inspection ; 

 nevertheless there are numerous apparent ex- 

 ceptions which are well calculated to puzzle the 

 student, met with, especially in the vertebrae of 

 Serpents or of the neck of some Birds, where the 

 processes are so complicated by the bifurcation of 

 their extremities, or by foramina passing through 

 their roots, or the great size of the articulating 

 processes, or lastly, by the exuberant deposition 

 of osseous matter in particular parts of the 

 bone, that the greatest possible distortion may 

 easily be produced without at all violating the 

 prescribed laws in accordance with which the 

 osseous system is organized. Not unfrequently 

 indeed stunted ribs, or even derivations from 

 the exoskeleton, may become consolidated with 

 the proper vertebral elements in such a manner 

 as not to be readily distinguishable from them, 

 producing additional complications which are 

 sometimes very embarrassing. 



Skull. The osseous framework of the head 

 appended to the anterior termination of the 

 spinal column is by far the most complex part 

 of the skeleton, being composed of very nume- 

 rous bones connected together by suture or 

 otherwise, but differing marvellously in their 



Fig. 435. 



is 



Base of skull and vpcrcular bunts of Perch. 



