Fig. 8. Lateral views of auditory ossicles. × 20.
A. B. taylori analogous, adult, female, No. 28104 KU, 4 kms. ENE Tlalmanalco, 2290 meters, Estado de México.
B. B. musculus pallidus, adult, male, No. 28346 KU, Cahuilotal, Sacacoyuca, 960 meters, Guerrero.
The general plan of structure of the auditory ossicles in Baiomys resembles that in Calomys, Akodon, and Thaptomys. The ossicles of Calomys and Thaptomys, in particular, closely resemble the auditory ossicles of Baiomys musculus. The short process of the incus is knoblike in Calomys and Thaptomys, and the general conformation of malleus and stapes in those two genera is nearly identical to that in B. musculus. In Akodon, the anterior and posterior crus of the stapes is more rounded than in B. musculus, resembling that in B. taylori.
Reithrodontomys differ from Baiomys in having a more elongate orbicular apophysis on the body of the malleus, an elongated short limb on the incus, and a stapes having anterior and posterior crura bowed as in mice of the genus Peromyscus.
In Ochrotomys, the orbicular apophysis of the malleus resembles the orbicular apophysis of B. musculus, but the short process of the incus is longer, resembling the short process of B. taylori. In general conformation of the malleus, incus, and stapes, Ochrotomys shows closer resemblance to B. taylori than to B. musculus.
In Holochilus the anterior crus and posterior crus of the stapes are similar to those in B. musculus, but in shape and size of malleus and incus, Holochilus differs considerably from B. musculus and B. taylori.
In Zygodontomys, size and shape of the ossicles differ greatly from those of Baiomys.
In the genus Peromyscus, only Peromyscus floridanus (subgenus Podomys) possesses a knoblike short process on the incus similar to that in B. musculus; representatives of the other subgenera examined possess an elongated short limb on the incus. The conformation of the ossicles of both Onychomys and Oryzomys appears to be more nearly like that in Peromyscus than that of Baiomys.