226 THE DEVELOPMENT OF THE SKULL. [CHAP. 



from its relations to the notochord, and as such we shall 

 continue to speak of it. 



The second of the two divisions into which the parts of 

 the skull fall, consists of a series of paired rods, whose 

 proximal extremities are attached more or less closely to the 

 investing mass. All of these (with the exception of the 

 trabecule) are developed along the axes of the visceral 

 arches. 



Fig. 68. 



■C V 1 



View from above op the Investing Mass and of the Trabecule on 

 the Fourth Day of Incubation. (From Parker.) 



In order to shew this the whole of the upper portion of the head has heen 

 sliced away. The cartilaginous portions of the skull are marked with the dark 

 horizontal shading. 



cv I cerebral vesicles (sliced off), e eye. nc notochord. iv investing mass. 

 9 foramen for the exit of the ninth nerve, cl cochlea, hsc horizontal 

 semicircular canal, q quadrate. 5 notch for the passage of the fifth nerve. 

 Ig expanded anterior end of the investing mass, pts pituitary space. 

 tr trabecular. The reference line tr has accidentally been made to end a 

 little short of the cartilage. 



We shall commence by describing the r investing mass* 

 as we find it on the fourth day, and from this pass on to 

 the paired rods attached to it. 



