10 
MAMMAL GALLERIES. 
number of ring-shaped bones placed end to end, so as to form a 
long tube for the reception of the spinal cord. The vertebrae 
are divided into live groups (fig. 1), viz. : — the cervical (cr), or 
those of the neck, almost invariably seven in number ; the 
dorsal [d), those of the back, to which the ribs are attached ; 
the lumbar (/), or loin, vertebrae ; the sacral (s), or those to 
wdiich the hip-bones are fixed ; and the caudal {cd), or those 
of the tail, ranging from 3 (in some Bats) to 47 (in the 
Insectivore Microgale longicaudata, the longest-tailed Mammal 
known). 
The ribs are curved rods of bone, from 9 to 24 pairs in 
number, attached to the sides of the dorsal vertebrae, and passing- 
round the body ; the greater part of them join the breast-bone, 
or sternum^ in front, wdiile the remainder, known as the floating 
or false ribs, have their ends free. 
Passing to the limb-skeleton, the first for notice is the 
shoulder-girdle, which in Mammals consists generally of two 
separate bones — the clavicle or collar-bone, often absent or 
imperfectly developed, and the scapula (sc) or shoulder-blade, 
to which is firmly united a small projection of bone, the 
coracoid {cr), representing a third bone, completely separate in 
Birds, Reptiles, and also in the Monotremes or Egg-laying- 
Mammals. 
The scapula i^ a more or less flattened triangular bone placed 
outside the ribs, but not attached to them by bone, wuth its 
narrow end directed towards the ventral side of the body. At 
this narrow end there is a hollow^ socket, into w’hich the head of 
the upper arm- bone fits. Along the middle of the scapula on 
its outer surface runs a long prominent ridge, terminating 
below in a prolonged process (acromion.), to the tip of which the 
collar-bone, when present, is attached ; the other end of this 
bone is united to the upper part of the breast-bone. 
The humerus (h), or upper arm-bone, is the powerful bone 
placed between the shoulder and elbow, articulating- above with 
the scapula by a ball-and-socket joint and below with the 
radius (r) and ulna (u), the bones of the fore-arm, by a simple 
hinge-joint allowing motion in one direction only. 
The two bones of the fore-arni are joined below to the w-rist- 
