External Features. 177 



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

 inguinal spaces, hairless depressions, on 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 contained in its ventral wall. The 

 mammary nipples (papillae mammarum) , eight (to ten) in 

 number on the ventral surface of the breast and abdomen. 



(f) 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 

 angles of the scapula; on the pelvic girdle, the iliac crest, 

 pubic symphysis, and ischial tuberosity. 



4. In the anterior limb: 



(a) The division of the free portion into three segments, the 

 arm (brachium), forearm (antibrachium) , and hand 

 (manus) . 



(b) The position of the elbow (cubitus) in comparison with the 

 knee. 



(c) The five digits, designated from the medial side as: first 

 (d. primus), or pollex, second (d. secundus), or index, 

 third or middle (d. tertius s. medius), fourth (d. quartus), 

 and fifth (d. quintus s. minimus). 



5. In the posterior limb: 



(a) The division into three segments, the thigh (femur), leg 

 (crus), and foot (pes). 



(b) The knee (genu), and the popliteal fossa of its posterior 

 surface, the latter not well defined. The projection of the 

 heel (calx) , and the angle formed by the foot with the leg. 



(c) The four digits (dd„ secundus-quintus) . The vestigial first 

 digit, or hallux, is not distinguishable externally. 



