Charles R. Bardeen BW és) 
nearly to the urachus. Anteriorly it is continued into a similar mass 
extending down from the region of the suprarenal gland. 
In company with the visceral branch from the 4th sacral nerve there 
arises a nerve which extends out into a differentiating mass of tissue 
which probably represents the levator ani muscle. There is no good evi- 
dence to show that this muscle arises from the myotomes. The coccygeal 
musculature which lies dorsal and lateral to the levator ani seems, how- 
ever, evidently to arise from the ventral tips of the caudal myotomes. 
Into it extend nerves from the 4th and 5th sacral and possibly from the 
caudal nerve. This, as also in embryo CIX, is relatively at this stage 
very large. 
In embryo XXII, length 20 mm. (Plate X, Fig. 2) conditions similar 
to those just described may be found. The direction in which the sec- 
tions are cut makes a reconstruction of the region somewhat imperfect. 
The results have been controlled by study of another somewhat older 
embryo, CXLV, length 33 mm. The plexus is of a more anterior type 
than that of 144. The dorsal nerve of the penis and perineal nerves ap- 
parently arise largely from the 2d sacral nerve and the 4th sacral nerve 
seems not to enter into the pudic plexus. The perineal musculature is 
undergoing specific differentiation, but no attempt has been made to de- 
termine definitely the boundaries of the various muscles. The levator 
ani muscle is well differentiated. The visceral plexus is even more exten- 
sive than in the preceding stage. 
For comparison of embryonic conditions with the distribution of the 
pudic nerves in the adult male, the well-known illustration of Hirschfeld 
and Léveillé may be used. It is to be noted that previous to the out- 
growth of the pudic nerves the cloaca and urachus occupy a more distal 
position relative to the spinal column (Fig. CIX) than they do at the 
period when these nerves are developed (Plate X, Figs. 1 and 2). Later, 
the external genitalia shift again distally. 
The paths taken by the growing nerves are fairly direct. That of the 
dorsal nerve of the penis is most so. The perineal nerves bend more in a 
distal direction. The nerve of the levator ani muscle takes a course at 
right angles to the path of the main trunk from which it arises. It may 
readily be seen that the most anterior root fibres of the pudendal nerve 
enter the dorsal nerve of the penis, the most posterior the hemorrhoidal 
nerve. Cutaneous branches also arise from the caudal nerve. 
According to Popowsky, 99, at a period when the cloaca is still present 
a sheet of muscle forms a sphincter around its opening. Later, when the 
rectal becomes separated from the urogenital portion of the cloaca the 
sphincter is divided, the posterior portion becoming the sphincter ani 
