EXTERNAL FEATURES 219 



of the two eyes at rest overlap in front only about 27° or less. On the 

 other hand, they also overlap behind. The rabbit is one of the few 

 mammals in which vision is not solely binocular, 



(/) The external ear (auricula) and its canal, the external 

 acoustic meatus (meatus acusticus externus), leading to 

 the tympanic membrane. 



{g) Points on the head skeleton, to be identified by feeHng 

 through the skin; zygomatic arch, supraorbital process, 

 external occipital protuberance, angle of the mandible, 

 symphysis of the mandible, and the hyoid l^ne. 



3. In the trunk: 



(a) The division into thorax, abdomen, and back or dorsum. 



(b) The inclusion with the trunk of the proximal portions of 

 the limbs. The angle formed by the anterior limb with the 

 trunk represents in part the axillary fossa (fossa axillaris). 

 The depression is much less evident than in man on account 

 of the different positions of its enclosing folds formed by the 

 pectorales and latissimus dorsi muscles. A corresponding 

 inguinal furrow separates the posterior limb from the 

 abdomen and pelvis. 



(c) The anal aperture (anus), and on either side of it the 

 inguinal spaces, deep hairless depressions in which the 

 ducts of the inguinal glands open. 



(d) In the male: the urinogenital aperture at the extremity of 

 the penis ; the latter enclosed by a fold of integument, the 

 prepuce (praeputium); the scrotal sacs (scrotum), lateral 

 sacs of the integument lodging the testes. 



(e) In the female: the urinogenital aperture, enclosed by folds 

 of the integument, forming the vulva. The clitoris, the 

 homologue of the penis, is a small, rod-like structure con- 

 tained in its ventral w^all. The mammary nipples (papillae 

 mammarum), eight (to ten) in number, on the ventral 

 surface of the breast and abdomen. 



(/) The following skeletal points: on the axial skeleton, the 

 manubrium sterni, xiphoid process, costal arch, spinous 

 processes of thoracic and lumbar vertebrae; on the pectoral 

 girdle, the acromion, clavicle, and respective borders and 



