THE SKELETON OF THE VERTEBRATE HEAD. 103 



geal arches, the cartilages of the larynx, trachea, bronchial 

 tubes, and lungs, are all primarily developed in immediate 

 relation to the cephalic portion of the alimentary tube. 



It is remarkable that those who refer the branchial and 

 pharyngeal arches to a splanehno-skeleton have not adduced 

 the external position of the haemal axis to these arches as an 

 argument in support of their opinion. On this ground, how- 

 ever, the hyoidean, and, I believe, the mandibular arch also, 

 as internal to the first, or to the first and second aortic arches, 

 would be also thrown into the system of the splanehno-skeleton. 

 Carus has accordingly done so in the case of the hyoidean 

 arch ; but Professor Owen, overlooking the fundamental em- 

 bryological relations which indissolubly connect all these 

 arches as serially homologous, holds the hyoidean to be a 

 " strong, bony, persistent arch of the true endo-skeleton ; " 

 while, on grounds which appear to me altogether secondary, 

 he refers the branchial and pharyngeal to the splanehno- 

 skeleton, and thus relieves himself of the onus of determining 

 their " homologies." From the view I have been led to take 

 of this subject, I am under the necessity of considering these 

 arches as true haemal arches, and as certainly referable to the 

 endo-skeleton as the mandibular arch itself. I also, for the 

 same reason, conceive that the complete morphology of the 

 skeleton of the head includes the homologies of the cartilages 

 of the larynx, trachea, and lungs. 



The cartilages and bones developed in the actinal fibrous 

 laminse are most important elements in the sclerome. In the 

 head they are variously modified and arranged, not only for 

 the protection of organs, but also as a system of props to afford 

 additional security to the fundamental parts of the skeleton. 

 In the trunk they are chiefly subservient to the myome. They 

 thus exhibit their highest development in the framework of 

 the limbs, for the entire constitution of which they alone, I 

 believe, supply the elements. 



