24 FRANKLIN PARADISE JOHNSON 



from a dissection with the aid of a magnifier. Rectal columns 

 and sinuses of difTerent sizes show themselves distinctly. At the 

 lower ends of the rectal sinuses can be seen the beginnings of the 

 anal valves. The ano-rectal line cannot be definitely located, 

 but the sinuous anal line is marked by the position of the anal 

 valves. In this specimen the bulbus analis does not seem to be 

 present as a distinct swelling. 



Longitudinal series of sections of embryos of 134 and 140 mm. 

 show the addition of numerous secondary folds. Owing, how- 

 ever, to the advantage which transverse sections give to their 

 study, a description of these folds is reserved for the succeeding 

 stage. The outer coats again deserve special attention. The 

 fibers of the muscularis mucosae are now distinctly seen, and 

 extend a short distance below the beginning of the zona colum- 

 naris. The circular muscle coat extends slightly below the infe- 

 rior Imiit of the same zone and terminates abruptly by becoming 

 slightly thickened. The longitudinal muscle fibers become fewer 

 and fewer when followed down. Some of them extend into the 

 connective tissue septae between the fibers of the external sphinc- 

 ter muscle. Above and to the outside of the external sphincter 

 are seen the fibers of the levator ani. 



In a series of transverse sections of the rectum of a well pre- 

 served embryo of 135 mm., the pars analis recti presents a condi- 

 tion which, although it contains more secondary folds, is never- 

 theless greatly similar to that of the above-described embryo of 

 65 mm. The three primary folds particularly occupj^ the same 

 position and present the same relations. The bulbus analis 

 again appears as a swelling as is shown in the graphic reconstruc- 

 tion presented in figiu-e 2, A. With respect to its diameter, it 

 is relatively shorter than in the younger stages, although it is 

 actually double the length of the swelling of the 65 mm. embryo. 

 Some idea of its form may be -obtained from the cross sections 

 shown in figure 2. In section 600 there are three main folds of the 

 mucous membrane, one ventral and two lateral. A glance at the 

 two following figures will suffice to show that these folds are con- 

 tinued downward on the swelling of the bulbus analis. In section 

 600 and abo\'e it the mucous membrane presents both glands and 



