ECOLOGY AND BIOLOGY OF THE PACIFIC WALRUS 



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depicted in Murie's plate, their length being 3 to 4 times the diameter (Fig. 107). 

 They are situated outside the muscular abdominal wall, in the blubber lateral to 

 the base of the penis, more as in the Phocidae than in the Otariidae. In the lean 

 adult male during the mating season, however, the prominence of the greatly 

 enlarged testes suggests some tendency toward scrotal arrangement (Fig. 108), as 

 in the Otariidae (Scheffer 1958). 



The penis lies in an abdominal sheath, and in the adult more than half of its 

 bulk is made up of bone, the os penis or baculum. A prominent median raphe of 

 pale, hairless skin extends from the penile orifice to the vicinity of the anus (Fig. 

 109). The orifice is about four-fifths the distance from anus to umbilicus. The 

 relative growth of the baculum and of the non-spermiogenetic testes was 

 described earlier (see Figs. 22 to 25). 



Female 



The anatomy of the reproductive tract of the female walrus has been described 

 by Cleland (1900) and Burne (1909) from dissection of two pre-adolescent 

 animals. As the tract of the adult differs somewhat from those described, a few 

 supplementary remarks are included here. 



The reproductive tract lies in the posterior third of the abdomen, ventral to the 

 colon and dorsal to the urinary bladder. In multiparous females, the anus and 

 entrance to the urogenital vestibule are surrounded by an area with slightly 

 longer hair than on the rest of the body. In the preputial depression, just outside 

 the ventral edge of the vestibular orifice, is the short, robust clitoris, the dorsal 

 frenular fold of which is continuous with two transverse folds that presumably 

 are homologous with the labia minora (Fig. 110). The urogenital vestibule is 15 

 to 20 cm long and about 6 cm in inside diameter. Near its anterior end it receives 

 the urethra, which enters the ventral wall through a prominent papilla, 2 to 

 3 cm in diameter (Fig. 111). Confluent with the papilla is the hymenial fold, 

 which separates the vestibule from the vagina. The height of this fold is about 

 1 cm. The vagina is 20 to 25 cm long and has about the same inside diameter as 

 the vestibule; the walls of both are about 2 cm thick. In its anterior half, the 

 vagina is partly divided by a median dorsal fold, which is continuous posteriad 

 with the most prominent lobe of the hymen and, anteriad, with the oral 

 prominence of the uterus. The oral prominence extends 3 to 5 cm into the 

 anterior end of the vagina, with consequent deep fornices laterally and ventrally. 

 In its posterolateral surfaces lie the separate orifices of the didelphic uterus. 

 Anterior to this, the cervices and corpora uteri are 10 to 15 cm long, and the 

 uterine horns, about 25 cm long and 4 cm in diameter, arc ventrolaterad to the 

 ovaries. The relative growth of the uterine horns and os clitoridis was described 

 earlier (see Figs. 27, 28). 



The partly septate vagina and wholly didelphic uterus, with no interluminal 

 connections between uterine cornua in the cervix or otherwise, are unique 

 among pinnipeds and may be atavistic, rather than adaptive to conditions in an 

 otherwise rather specialized mammal. In other otarioid seals, the lumina of the 

 uterine horns are interconnected in the corpus and cervix uteri and have a 

 common os externum; the phocoid seals have a common cervical canal, also with 

 a single os externum (Cleland 1900; Sleptsov 1943; Harrison et al. 1952). 



Adjacent to the end of each uterine horn and attached to it by a stout ligament 



