y6 ELEMENTS OF MAMMALIAN ANATOMY 



ligameniinn teres holding the femur in place. The junction of 

 the pubis with its fellow is known as the symphysis. The 

 cranial portion of the bone lying on either side of this is called 

 the body, the caudal part taking the name of ramus. The latter 

 forms part of the boundary of the obturator foramen and meets 

 the ramus of the ischium. This foramen gives passage to the 

 obturator nerve and vessels. 



In the Sirenia, which have no pelvic limbs, the innominate 

 bones are rudimentary. In the Cetacea these bones are also 

 rudimentary, which fact indicates that the ancestors of these 

 forms possessed functional hind-limbs. 



The femur, or thigh-bone, may be recognized by its spherical 

 head with a pit for the attachment of the ligamentum teres 

 which aids in holding the head in the acetabulum. 



The greater trochanter projects from the proximal end of the 

 bone to a level with the head. On this process are inserted the 

 pyriformis, gluteus medius, and gluteus minimus muscles, all 

 of which originate on the innominate bone. The lesser tro- 

 chanter is the small projection on the caudal aspect of the proxi- 

 mal portion of the bone (Fig. 41). The intertrochanteric ridge 

 or posterior intertrochanteric Une extends between the two 

 trochanters, and lying between this line and the neck is the 

 digital fossa. The external and internal condyles are the articu- 

 latory processes on the distal end of the bone. The blunt 

 projections at their roots are the external and internal tuberosi- 

 ties. The intercondyloid notch forms the depression on the 

 caudal aspect between the condyles. On the cranial aspect is 

 the trochlear surface for articulation with the patella. Two 

 small sesamoid bones, the fabellae, are present on the caudal 

 aspect of the condyles, but they are usually removed in prepar- 

 ing the skeleton. The linea aspera is the slightly roughened line 

 beginning on the caudal side, distal to the middle and extending 

 proximally a short distance, where it bifurcates. 



The form of the femur varies but little among mammals 

 having functional posterior limbs. No living Sirenia have any 



