8 



MAMMALS 



acquainted with them must refer to other works. Our notice of the other parts of 

 the skeleton must be equally brief. In the backbone or vertebral column, the first 

 vertebra, or that which articulates with the skull is known as the atlas ; following 

 which is the axis vertebra, remarkable for having the body or basal portion of the 

 atlas vertebra fixed to it, and known as the odontoid process. This separation of the 

 body of the atlas vertebra from its proper segment is constant throughout the greater 

 part of the vertebrate subkingdom. The remaining five of the cervical, or neck-verte- 

 brae, are distinguished from the dorsal, or vertebrae of the region of the chest, by the 

 absence of ribs. The ribs of most of the dorsal vertebrae articulate in the middle 

 line of the inferior aspect of the body with the breastbone, or sternum, which is 

 itself composed of several segments. The dorsal vertebrae are succeeded posteriorly 

 by a smaller number, forming the region of the loins, which have no ribs, and are 

 termed lumbars. Behind the latter there are several coalesced vertebrae forming the 

 so-called sacrum, to which the haunch-bones articulate ; and these are again suc- 

 ceeded by the tail, or caudal vertebrae, of which the number varies according to the 

 length of the tail itself. 



In the majority of Mammals the fore-limb is con- 

 nected with the trunk simply by the blade-bone, or 

 scapula, which lies on the back surface of the anterior 

 ribs ; and in front by the collar-bone, or clavicle, 

 which connects the scapula with the sternum. The 

 bones of the fore-limb are, firstly, the arm-bone or 

 humerus, which has condyles at its lower end ; and, 

 secondly, the two parallel bones of the fore-arm, of 

 which the outermost (when the palm of the hand is 

 turned forwards) is the radius, and the other the 

 ulna. The radius is always present, but in many 

 Hoofed Mammals only the upper end of the ulna 

 remains, which is fused with the radius. The radius 

 articulates below with the upper of the two transverse 

 rows of small solid bones forming the wrist or carpus ; 

 beyond these we have in man and monkeys, as well as 

 in certain other groups, five elongated bones, termed 

 metacarpals, the four outermost of which are sue- 



DIAGRAM OF THE BONES OF THE ^.^ ^ ^ **** P halan g eal b ^ of the fingers 



LEFT FORE-FOOT OF A FIVE- or dl g lts - The thumb, or first digit, which lies on 

 TOED MAMMAL (Phenacodus). tne same side as the radius, has, however, only two 

 (^ nat. size.) of these phalangeals. 



The bones marked s, i, c, t, td, m , and The hind-limb differs from the fore-limb in that 



^TS5SS; the ^-""ate, or haunch-bones, which together 

 the finger- or toe-bones. After osbom. form the pelvis, are connected by an immovable bony 



union with the sacral region of the vertebral column. 



The thigh-bone or femur, corresponding to the humerous of the arm, articulates with 

 a cavity in the innominate, termed the acetabulum. The leg has two parallel bones 

 articulating with the lower end of the thigh-bone or femur ; of which the larger, or 



