CHAPTER XIX. 



THE SKULL. 



THREE distinct sets of elements may enter into the compo- 

 sition of the skull. These are (i) the cranium proper, composed 

 of true endoskeletal elements originally formed in cartilage, to 

 which are usually added exoskeletal osseous elements, formed 

 in the manner already described p. 542, and known in the 

 higher types as membrane bones. (2) The visceral arches formed 

 primitively as cartilaginous bars, but in the higher types largely 

 supplemented or even replaced by exoskeletal elements. (3) The 

 labial cartilages. 



These parts present themselves in the most various forms, 

 and their study constitutes one of the most important depart- 

 ments of vertebrate morphology, and one which has always 

 been a favourite subject of study with anatomists. At the end 

 of the last century and during the first half of the present 

 century the morphology of the skull was handled from the point 

 of view of the adult anatomy by Goethe, Oken, Cuvier, Owen, 

 and many other anatomists, while Duges and, nearer to our own 

 time, Rathke, laid the foundation of an embryological study of 

 its morphology. A new era in the study of the skull was 

 inaugurated by Huxley in his Croonian lecture in 1858, and in 

 his lectures on Comparative Anatomy subsequently delivered 

 before the Royal College of Surgeons. In these lectures 

 Huxley disproved the then widely accepted view that the skull 

 was composed of four vertebrae ; and laid the foundation of a 

 more satisfactory method of dealing with the homologies of its 

 constituent parts. Since then the knowledge of the development 

 of the skull has made great progress. In this country a number 



