1905. | CLAVICLE OF DIPLODOCUS, 293 
In Chelonia the penis sometimes exhibits internally a partially 
bifid structure. 
For the purpose of this paper the penis of birds is of quite 
exceptional interest. In its origin it is not only traceable to the 
Crocodilian type, but shows a very great amount of asymmetry, and 
besides in the Ratite a distal bifurcation of the corpus fibrosum 
(text-fig. 48, p. 291). In Séruthio the distal part of the penis is 
changed into a glans-like organ, while in Rhea the corpus fibrosum 
consists of an exceedingly hard and nearly cartilaginous substance. 
A bifurcation like that observable in the problematical bone of 
Diplodocus is also frequently to be met with at the distal end of 
the mammalian os penis, which is often asymmetrical. The os penis 
of mammals always shows quite remarkable variability. For 
comparison with the bone of Diplodocus, side and hind views of 
the os penis of the European Otter (Zuéra lutra) are given (in 
text-fig. 49, p. 292), and one can see at a glance the well-rounded, 
smooth, condyle-like, distal ends, the proximal rugosities, and the 
lateral impressions for the attachment of the corpus fibrosum. In 
other mammals the corpus fibrosum is not attached laterally to the 
ossified element, but ends in a deep pit situated at the proximal 
end of the latter. 
We have therefore to consider the following propositions :— 
(1) That among the Mammalia it is the corpus fibrosum with 
which the os penis comes in close contact, forming the anterior 
prolongation into the glans penis, that the os penis ossifies from 
fibrous matter; that a corpus fibrosum is algo present among 
Reptilia, and that therefore an os penis in Dinosaurs can only 
have originated from the corpus fibrosum. 
(2) That in hea the corpus fibrosum is quite as hard as cartilage, 
and differs from this only by not possessing cartilage-cells. 
(3) That in Sauropsida a glans is frequently present. 
(4) That it is quite a common thing to find bird-like characters 
in various parts of the Dinosaurian skeleton. 
5) That among the birds the Ratites show the most primitive 
and still the best-developed male genital organ. 
(6) That the shape and variation of the problematical bone in 
Diplodocus are well in accord with its being an os penis, while 
they militate against its determination as clavicular. 
(7) Lastly, that this so-called clavicula when present is always 
found only as an unpaired organ showing the same direction of 
curvature. 
Hence I am of opinion that it is at present advisable to remove 
the subject of this paper from the shoulder-girdle and determine 
it as the ossified axis of the penis. 
Further evidence and, especially, further discoveries are naturally 
necessary before so delicate a question can be regarded as definitely 
settled; but since Hatcher's single argument against the bone in 
question being an os penis (namely, its asymmetry) breaks down 
on reference to Struthio or even to Lwtra, the balance of the 
argument is at present in favour of this newer interpretation. 
Proc. Zoou. Soc.—1905, Vou. II. No, XX. 20 
