vi.] GENERAL VIEW OF INTERNAL SKELETON. 223 



such arches belong to the hypaxial category of hard parts. 

 Nevertheless, as they are placed beneath the anterior end of 

 the alimentary tube, they evidently do not exactly answer 

 to those hypaxial elements of the coccygeal vertebrae, the 

 hypapophyses for these, in Crocodiles and others, are placed 

 above the posterior continuation of the intestinal tube. At the 

 same time they cannot answer to ribs and sternum (i.e. 

 cannot be paraxial parts), for such parts must be outside the 

 line of the pleuro-peritoneal cavity. 



Thus it appears that man's upper and lower jaws, and also 

 his hyoidean apparatus, not only belong, as we have seen, to 

 a group of skeletal parts, which become much more developed 

 in Fishes, but that this whole group forms one special division 

 of a skeletal category (the hypaxial), the parts of which may 

 be termed spldnchnapophysis? 



FIG 193. DIAGRAM OF A TRANSVERSE VERTICAL SECTION OF THE MOST 

 DEVELOPED SKELETAL SEGMENT, ACCORDING TO THE CONCEPTION PUT 

 FORTH IN THIS CHAPTER. 



From above the centrum the epaxial parts, e (neural arches and neural spine), 

 ascend. From each side of the centrum the paraxial system, /, proceeds out- 

 wards and downwards to coalesce with the sternum below. 



/, tubercular process ; tr, tubercular part of the rib ; tr ', its continuation outwards 

 towards the surface of the body ; c ', capitular process ; cr, capitular part of 

 the rib ; vr, vertebral rib ; s-r, sternal rib ; j, sternum ; a, part of the hypaxial 

 system related to the great vessels (hypapophysis) ; b, part of the same related 

 to the alimentary tube (splanchnapophyses) ; c, part related to the heart. 



12. The backbone of man, then, is a partial realization of 

 a complex axial skeleton, as thus : 



(1) A central axis, terminating anteriorly behind the pitui- 

 tary fossa, and posteriorly at the end of the spine itself, seg- 

 mented antero-posteriorly (i.e. divided into the bodies of the 

 vertebrae), the segments having relation to the nerves coming 

 out from the spinal marrow central parts. 



(2) A superior cylinder, also segmented (the neural arches), 

 generally developing articular processes, and sometimes others 

 besides epaxial parts. 



1 From c-7rXa7X va ' entrails, and u7ro$u<7(, because they are related (laterally 

 or inferiorly) to the alimentary tube. 



