( 14 ) 

 LITERATURE ON THE FINDS OF TRICHECHUS HUXLEYI. 



35 1875. J. C. de Man. Beenderen van den mammouth en van het uit- 



gestorven rund, opgevischt in den omtrek van Zeeland. Arch. 

 Zeeuwsen Genootsch. der Welensch. lil 2. p. 101 — 127. 



36 1878. J. G. de Man. Een elandshoren, opgevischt in de Schelde. 



Mededeeling over eenige beenderen, in of nabij Zeeland ge- 

 vonden. Arch. Zeeuwsch Gen. III 3. p. 1—22. 



37 1879. F. Seelheim. Grondboringen in Zeeland. Verhand. Kon. Akad. 



der Wetenschappen Afd. Natuurk. Amsterdam. 



38 1880. J. G de Man. Derde Mededeeling over in de Schelde gevon- 



den beenderen. Arch. Zeeuwsch Genootsch. V. 1. p. 161 — 170. 



Anatomy. — "On the existence of cartilaginous vertebrae in the 

 development of tin' skull of birds". By Prof'. J. W. van Wijhe. 



(Communicated in the meeting of April 26, 1907). 



It is a well-known fact that at a certain stage of development the 

 notochord in all vertebrates extends forward as far as the hypo- 

 physis cerebri and backwards as far as the tip of the tail. 



Over the whole length of the trunk and also in the occipital 

 region of the head the dorsal part of the mesoderm is separated 

 into segments or somites. 



In the lower vertebrates: Selachians and Petromyzontes, the somites 

 are not restricted to the occipital region, but extend forward as far 

 as the hypophysis, i.e. equally far as the notochord. 



The greater part of the voluntary muscular system is formed from 

 the somites and in Amphioxus the segmentation of this muscular 

 system is permanent and distinct from the anterior to the posterior 

 end of the body. 



The original function of the somitic muscles of the Chordates 

 existed in my opinion 1 ) in the to and fro movement of the notochord 

 and so of the whole body during swimming. 



Tn the Craniotes this muscular system is interrupted in the region 

 of Ihe auricular organ and in my opinion the presence of the auricular 

 capsule is the cause of this. This capsule, which also encloses the 

 organ for equilibrium, needed a firmer attachment than could be 

 afforded by the connective tissue and found it in the parachordal 

 cartilage, through the stiffness of which the muscular fibres in this 

 region could no longer operate and consequently disappeared, partly 

 even in their origin. 



l ) Gf. van Wijhe "Ueber die Homologisirung des Mundes und die primitive 

 Leibesgliederung der Wirbelthiere." Petrus Camper, Vol. IV. 1906. 



