60 MAMMALIA. 



spines ; in Echidna it is divided into four rounded, perforated extrem- 

 ities, beset with small tubercles. 



The Bone of the penis, which principally belongs to the glans, is 

 met with in many animals, namely, in the Apes, Cheiroptera, Car- 

 nivora (even in the Seal and Walrus), many Rodentia, and some 

 Cetacea, as in the Whales (though its existence has been disputed 

 by other writers), but not in the Pachydermata and Ruminantia. In 

 Man, to wit, in the Negro race, where the penis is very largely de- 

 veloped, there frequently occurs a small prismatic cartilage from one 

 to two lines in length, as a rudiment of this bone. The bone usually 

 arises at the end of the fibrous septum, and advances toward the 

 glans, the tendinous fibres of the septum being attached internally 

 to its periosteum. Among the Apes, where the bone of the penis is 

 often very large, it appears to be entirely wanting in the Orangs. In 

 the Fox and in the Dog-kind it is large, and hollowed out inferiorly 

 in the form of a groove ; it is very small and thin in the Cat, curved 

 in the shape of a hook anteriorly in Mustela, and bent in the form 

 of the letter S in the Rackoon ; it is terminated anteriorly by two 

 rounded bodies in the Otter, has a small but broad shovel-shaped 

 extremity in the Squirrel, and is deeply slit in the Marsupiata. This 

 bone serves obviously to increase the rigidity of the penis during the 

 act of copulation, which, as is known, is in many animals a pain- 

 ful operation. The penis has the usual muscles (m. m. ischio-caver- 

 nosi and bulbo-cavernosi), and in many animals where the penis is sit- 

 uated in the direction backward, there is found a pair of muscles often 

 thick-bellied (m. pubo-cavernosi) arising from the ,pubis, the tendons 

 of which are attached to the dorsum of the penis, and seem to 

 be instrumental, during copulation, in giving the penis an anterior 

 direction. 



The same diversity, which is observed in the Mammalia in ref- 

 erence to the form of the internal and external sexual organs, is 

 met with in the fetal envelopes, e. g. in the allantois, the umbil- 

 ical vesicle and placenta. The latter exhibits great diversities, 

 which are frequently characteristic of whole genera and families. 

 Thus, the true Carnivora, such as the Cats, Dogs, Seals, &c., 

 have a girdle or band-shaped placenta, so that the membranes 

 of the ovum are free at both of its ends or poles. On the 

 border of this annular placenta, there often appear, as in the Dog, 

 beautiful green pigmentary deposites. In the Ruminantia the pla- 

 centa is divided into a great number of distinct round or but- 

 ton-shaped cotyledons, which are distributed over the whole ovum 



