THE CONNECTIVE TISSUES AND THE SKELETAL SYSTEM. 



187 



rounds the cephalic end of the notochord, extends from there into the nasal 

 region and also extends around the sides and dorsal part of the neural tube 

 (brain). Unlike the anlage of the vertebral column, the anlage of the skull 

 shows no distinct division into primitive segments. The only indications of a 

 segmental character are referred to in a succeeding paragraph (small print, 

 p. 189). 



The next step in the development of the skull is the appearance of cartilage 

 in certain regions of the embryonic connective tissue. On account of the com- 

 plicated arrangement of the cartilage in the human skull, it is best to consider 



Palatoquadrate 



Palatoquadrate 

 Meckel's cartilage 



Palatoquadrate 

 Hypophysis 



Nasal fossa 

 Preorbital process 



Roof of skull 

 Marginal bar 



Prechordal plate 

 Prootic incisure 

 Jugular foramen 



} Foramina (VII Nerve) 



Notochord 

 >Otic (auditory) capsule 



Synotic tectum 



FIG. 172. Primordial cranium of Salmo salar (salmon) embryo of 25 mm. Dorsal view. Gaupp. 

 Compare with Fig. 171 and note further elaboration of parts surrounding the sense organs. 



first its more simple arrangement in the lower Vertebrates. In these there ap- 

 pear in the embryonic connective tissue around the cephalic end of the notochord 

 two bilaterally symmetrical pieces of cartilage, which extend as far as the 

 hypophysis. Then two other bilaterally symmetrical pieces appear, extending 

 from the hypophysis to the nasal region. Subsequently all these pieces fuse 

 into a single mass which extends from the cephalic end of the vertebral column 

 to the tip of the nose, enclosing the end of the notochord and, to a certain ex- 

 tent, the ear, eye and olfactory apparatus. There is left, however, an opening 

 for the hypophysis. From this mass of cartilage, chondrification extends into 

 the embryonic connective tissue along the sides and roof of the cranial 



