240 GEO. H. BISHOP 
the course of these fibers indicates that they do not comprise 
a distinct third layer, but that they consist of a modification or 
distortion in the arrangement of certain bundles of the inner or 
circular layer in this region, and that this rearrangement is the 
method by which the otherwise simple musculature of the gland’s 
base is adapted to an involved and complicated manner of 
functioning. The change, during development, in the relation- 
ships of the gland to the vas deferens and seminal vesicle on the 
one hand and to the ejaculatory duct on the other gives a clue 
to the origin of this ‘third layer.’ 
Recalling that the vas deferens grows posteriorly from the 
testis sheath as a J- and finally a U-shaped fundament, one arm 
of which forms the mucous gland, the musculature may be de- 
seribed more carefully. It consists of a relatively heavy circular 
layer of fibers which is not distinctly separable into fascicles, 
lying next to the glandular epithelium, and a relatively thin 
longitudinal layer collected into distinct fascicles, between which 
a connective-tissue network allows for distention of the organ 
(pl. 2, figs. 5 and 5b). There are about thirty-five of these 
fascicles in a cross-section of the vesicle; in the gland they are 
not so distinct and the fibers are arranged in a less specific man- 
ner. Both layers are thinner over the narrow portions of the 
vas deferens adjoining either end of the seminal vesicle, and both 
taper off over the distal portion of the gland into a very thin and 
elastic connective-tissue membrane. 
It is at the base of the gland, where the musculature is heaviest 
and whence originate the three bundles of fibers comprising the 
inmost muscle layer of the gland, that the ejaculatory duct 
becomes adjoined to the mesodermal portion of the sexual ap- 
paratus. Only in the light of the significance of this junction 
can the elaborate conformation of this musculature be adequately 
interpreted. 
We may picture at the bend of the U-shaped gland-vesicle 
fundament one branch of the ejaculatory duct penetrating this 
muscle mass to reach the lumen of its respective gland. At this 
place the wall of the gland protrudes to meet the duct. This 
protruded portion becomes the basal end of the gland (text. 
