244 GEO. H. BISHOP 
ulatory duct (7), and at a third, the lumen of the gland swells out 
into the gland’s elbow (m). In text figure 1 these regions may 
be identified between x and y, v and z, and y and g, respectively. 
The three tracts of the inner ‘third layer’ may then be derived 
as follows (pl. 1, figs. 1 to 4, x, y, and 2, and text fig. 3, x’’—2, 
y’’—y, and 2’’—z): 
a. Fibers of the inner circular layer originating along the 
median side of the gland, from a region anterior to the opening 
of the vas deferens, and from the muscle mass in the valve 
guarding it, pass on the medial side of the gland toward its base, 
here penetrated by the ejaculatory duct (2’’—2). 
y. Fibers from the same region, but passing dorsal to the vas 
deferens, extend posteriorly around the protruding elbow of the 
gland (y’’-y). 
z. Both sets of fibers pass anteriorly on the opposite side of 
the gland’s base, between the ejaculatory duct and the gland’s 
elbow, to the region on the gland opposite to the end of the vas 
deferens (2’’-z). 
The anatomical findings suggest and bear out this derivation 
for these three muscle tracts, except that the muscles extend 
anteriorly further along the side of the gland than the mass of 
the circular fibers from which they are believed to have been 
derived. This may be considered a functional modification to 
afford that insertion of the fibers on the sides of the gland which 
would enable them to operate most effectively. 
Along these three tracts and extending for about the same 
distance, the glandular epithelium is elevated into the lumen 
of the gland in such a manner as to give its cross-section a trilobed 
shape (pl. 1, fig. 3). Qne channel so caused (between two adjac- 
ent tracts) extends distally from the expanded elbow of the gland; 
along the lateral aspect, between y and z; a second, along the 
medial side from the valve anterior to the opening of the vas 
deferens, between x and y, and a third, between x and z distal 
to the end of the ejaculatory duct and passing opposite to the 
valve, is continuous ventromedially with the basal transverse 
pocket of the gland which receives vas deferens and ejaculatory 
duct. Distally all three merge into the uniformly rounded 
bulbous sac in which the gland ends. 
