332 The Alligator and Its Allies 



small, oval mass of very fine tubules (k) , which do 

 not stain so darkly as do the Wolfrian tubules; 

 this mass is apparently the beginning of the 

 permanent kidney, the metanephros. Its tubules, 

 though their origin has not been determined, seem 

 to be entirely distinct from the tubules of the 

 Wolfrian body. 



A single vertical section through the anterior 

 part of the head of an embryo of this age has been 

 represented in Figure 236. On the right side the 

 plane of the section cut through the lens of the eye 

 (In); on the left side the section was anterior to 

 the lens. The upper (ul) and lower (//) eyelids 

 are more evident here than in the surface view. 

 Owing to the hardness of the lens, its supporting 

 structures were torn away in sectioning. The 

 vitreous humor is not represented in the figure. 

 The superior (ur) and inferior (Ir) recti muscles are 

 well shown on the right side ; they are attached to 

 the median part of a Y-shaped mass of cartilage (se) , 

 which may be termed the sphenethmoidal cartilage. 

 Between the branches of this Y-shaped cartilage the 

 anterior ends of the cerebral hemispheres (ch) 

 better called, perhaps, the olfactory lobes are 

 seen. Between the lower end of the spheneth- 

 moidal cartilage and a dorsally evaginated part of 

 the pharynx are two small openings (pn); when 

 traced forward these tubes are found to open into 

 the convoluted nasal chamber, while a short dis- 

 tance posterior to the plane of this figure they unite 



