CHAPTER XIX. 

 THE SKULL. 



Three distinct sets of elements may enter into the composition 

 of the skull. These are (1) the cranium proper, composed of true 

 endoskeletal elements oi'iginally formed in cartilage, to which are 

 usually added exoskeletal osseous elements, formed in the manner 

 already described p. 447, 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 departments of verte- 

 brate 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 enibryological 

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

 inaugurated by Huxley in his Croonian lecture in 18.58, 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 ver- 

 tebra ; 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 of very interesting memoirs have been 

 published on the subject by Parker, which together constitute a most 

 striking contribution to our knowledge of the ontogeny of the skull 

 in a series of types ; and in Germany Gegenbaur's monograph on the 

 cephalic skeleton of Elasmobranchii has greatly promoted a scien- 

 tific appreciation of the nature of the skull. 



In the present chapter only the most important features in the 

 development of the skull will be touched on. 



B. E. II. 30 



