THE SKELETON. 87 



bone. These sesamoid bones are frequently lost in clean- 

 ing the skeleton. 



The number of functional metatarsals in mammals 

 varies from one to five. Usually the number of meta- 

 carpals and metatarsals is the same, but in the tapir 

 there are four metacarpals and but three metatarsals. 

 All Monotremata, Carnivora, and Primates have five 

 metatarsals, but in the cats, dogs, and hyenas the first 

 metacarpal is vestigial. In early geological times all 

 mammals possessed five metatarsals, the number of 

 which in many cases has gradually diminished owing to 

 environment, as is shown in the phylogeny of the horse 



(Fig. 35)- 



The Kquidae possess but one functional metatarsal 

 and two rudimentary ones, although Orohippus, the an- 

 'cestor of the horse, had three functional metatarsals. 



The phalanges of the cat's foot are twelve in number. 

 Each metatarsal except the first supports three phalanges. 

 The proximal phalanges are the stoutest, and the distal 

 the smallest. Each distal phalanx bears a claw. 



In all five-toed mammals, such as Primates, there are 

 fourteen phalanges, each digit being composed of three, 

 except the hallux, which has two. 



PRACTICAL QUESTIONS AND SUGGESTIONS. 



1. Describe the articulations of the innominate bone. 



2. How do you distinguish the cephalic from the caudal aspect of 

 the os innominatum? 



3. Which processes derive their names from their location? 



4. Draw the lateral aspect of the os innominatum and label all fea- 

 tures. 



5. Name the four parts of the bone in order of size. 



6. What two orders of mammals have no pelvic limbs? 



7. Describe what is seen in viewing the femur from the cephalic 

 aspect. 



8. Name the processes of the femur. 



9. Draw the distal aspect of the femur. 



