8 MR. C. TATE REGAN ON THE 



of the anterior ridges and ends in front of the priapial r-ibs. 

 (3) The lateral ridge (Ir.), on the aproctal side from the level 

 of the end of the pulvinular appendage to the level of the priapial 

 ribs ; this ridge almost reaches the surface at the lower margin 

 of the glandular groove. The axial bone passes backwards on the 

 aproctal side of the priapial ribs and anteplem^al cartilage, and in 

 the region of the anus it becomes stouter and expands down- 

 wards ; the ctenactinium (eta.) is attached to the aproctal side 

 of this part of the axial bone. In the region of the seminal 

 papilla the axial bone extends upwards nearly to the glandular 

 groove, and behind this it contracts to form a terminal style [st.) 

 that runs backwards and ends just in front of the transverse 

 portion of the terminal coil of the vas deferens. 



Anterior infrasulcar bone {is.). — This is a laminar bone that 

 lies near the surface on the aproctal side. It is broad posteriorly 

 and tapers anteriorly ; behind it extends from the floor of the 

 glandular groove under the base of the infrasulcar papilla to out- 

 side the proximal end of the ctenactinium ; for the greater part 

 of its length its upper edge is just below the edge of the lateral 

 ridge of the axial bone ; anteriorly it lies within the inner surface 

 of the infrapulvinular groove (PI. II. B, is.) and is quite a slender 

 bone. IsTear its posterior end, where its lower edge overlaps the 

 end of the ctenactinium, it bears an inner knob to share with the 

 axial bone in supporting that appendage. 



Posterior infrasulcar bone {is.'). — A bone whose expanded 

 upper surface lies just below the floor of the glandular groove, 

 below the anterior part of the seminal papilla ; it is a solid bone 

 that extends downwards and inwards on the api-octal side of the 

 axial bone : from its upper surface it sends forwards a laminar 

 process that runs below the anterior infrasulcar bone into the 

 base of the infrasulcar prominence. 



Papillary bone (p.). — A bone that supports the seminal papilla, 

 which it enters from behind and below, and then divides into 

 three branches that expand into laminae lying just below the 

 skin, one on the inner side of the papilla and two, an upper and 

 a lower, on its outer side. Before entering the papilla the bone 

 is a slender rod that curves downwards across nearly to the 

 ctenactinium and then tapers forwards and inwai^ls, ending a 

 little in advance of the seminal papilla on the aproctal side of the 

 axial bone {cf. PI. II. A, and text-fig. 7 A, p.). 



The pulvinular appendage (pva.) is subconical, somewhat com- 

 pressed ; it is a mass of parenchymatous cartilage, but has the 

 structure of true hyaline cartilage on the inner side near the 

 base; in this region it is hollowed out for the reception of a 

 cartilaginous peg that arises from a bone in front of it (PI. II. B), 



The pulvinulus consists of fibrous connective tissue sur- 

 rounding two longitudinal bones, the inner and outer pulvinular 

 bones. 



The inner pulvinular bone (pv.') is largest posteriorly, wheie 



