224 ELEMENTARY ANATOMY. [LESS. 



(3) An inferior cylinder, external to the pleuro-peritoneal 

 cavity, and segmented (ribs, &c.) par axial parts. These 

 may be subdivided into two series : 



(a) Tubercular processes (diapophyses) and upper ribs. 



(b} Capitular processes (parapophyses\ lower ribs, sternal 

 ribs, and sternum. 



These two series generally, as in man, coalesce, and the 

 component parts may have various relations of position 

 to the body and neural arch from which they spring. 



(4) An inferior cylinder, internal to the pleuro-peritoneal 

 cavity, or directly above the origin of the internal walls of 

 that cavity hypaxial parts. These may be subdivided into 

 three possible series, two of which are known to be actually 

 developed as hard parts : 



(a) Parts above the alimentary cavity or its prolongation, 

 and in relation to the great blood-vessel immediately below 

 the central axis (hypapophyses). 



(b) Parts bounding externally the alimentary canal 

 (Splanchnapophyses). 



(c) Parts bounding externally the heart or great vessels, 

 but of coarse internal to the pleuro-peritoneal cavity. 



Hypapophyses are most largely developed in Cetaceans 

 and Fishes, such as the Sole. 



Splanchnapophyses are only formed in the region of the 

 head and immediately behind it, and form the trabeculae, 

 the jaws, and the hyoidean and branchial arches. 



Sometimes, as in the Lamprey, Splanchnapophyses may 

 be absent as hard parts, but in the region where they would 



FIG. 194. SKELETON OF HEAD AND GILLS OF LAMPREY. 



<5, hinder part of the external (paraxial) cartilaginous skeleton of the gills ; an, 

 auditory capsule ; h, hyoid ; , neural arches ; /, palato-quadrate arch. 



be developed, if at all, we find a system of paraxial cartilages, 

 bounding the gill chambers externally. 1 



1 See Lesson XII. 



