1514 THE STORY OF THE UNIVERSE 



anterior extremity commences in a shoulder-blade, 

 that is not articulated, but simply suspended in the 

 flesh, often resting on the sternum by means of an 

 intermediate bone, called a clavicle. This ex- 

 tremity is continued by an arm, a forearm, and a 

 hand, the latter being composed of two ranges of 

 small bones called the carpus, of another range called 

 the metacarpus, and of the fingers, each of which 

 consists of two or three bones, termed phalanges. 



With the exception of the cetacea, the first part 

 of the posterior extremity in all animals of this class 

 is fixed to the spine, forming a girdle or pelvis, 

 which, in youth, consists of three pairs of bones, the 

 ilium which is attached to the spine, the pubis which 

 forms the anterior part of the girdle, and the 

 ischium, the posterior. At the point of union of 

 these three bones is situated the cavity with which the 

 thigh is articulated, to which, in its turn, is attached 

 the leg, formed of two bones, the tibia and fibula; 

 this extremity is terminated by parts similar to those 

 of the hand, i. e., by a tarsus, metatarsus, and toes. 



The head of the mammalia is always, articulated 

 by two condyles, with the atlas, the first vertebra of 

 the neck. 



The brain is always composed of two hemispheres, 

 united by a medullary layer, called the corpus 

 callosum, containing the ventricles, and enveloping 

 four pairs of tubercles, named the corpora striata, 

 or striated bodies, the thalami nervorum opticorum, 

 or beds of the optic nerves, and the nates and testes. 

 Between the optic beds is a third ventricle, which 

 communicates with a fourth under the cerebellum, 



