46 GENERAL ANATOMICAL CHARACTERS 
instance of the chevron bones, that the intercentral capitular articu- 
lation of the ribs of mammals is a feature directly inherited 
from those extinct types by the gradual disappearance of the 
intercentra. 
Appendicular Skeleton.—The appendicular portion of the frame- 
work consists, when completely developed, of two pairs of limbs, 
anterior and posterior (Fig. 15). 
Anterior Limb.—The anterior limb is present and fully developed 
in all mammals, being composed of a shoulder girdle and three seg- 
ments belonging to the limb proper, viz. the upper arm or brachium, 
the fore-arm or antebrachium, and the hand or manus. 
Shoulder-girdle.—The shoulder or pectoral girdlein the large majority 
of mammals is in a rudimentary or rather modified condition, com- 
pared with that in which it exists in other vertebrates. In the Mono- 
tremata (Ornithorhynchus and Echidna) alone is the ventral portion, or 
coracoid, complete and articulated with the sternum below, as in the 
Sauropsida ; and in this group alone do we find an anterior ventral 
element, apparently corresponding with the precoracoid of the Anom- 
odont reptiles, although generally known as the epicoracoid. In all 
other mammals the coracoid, though ossified from a distinct centre, 
forms only a process, sometimes a scarcely distinct tubercle, projecting 
from the anterior border of the glenoid cavity of the scapula. The 
last-named cavity, which in the Monotremes is formed jointly by 
the scapula and coracoid, receives the head of the humerus, or 
arm-bone. The scapula is always well developed, and generally 
broad and flat (whence its vernacular name “blade bone”), with a 
ridge called the “spine” on its outer surface, which usually ends in 
a free curved process, the “acromion.” As the scapula affords 
attachment to many of the muscles which act upon the anterior 
limb, its form and the development of its processes are greatly 
modified according to the uses to which the member is put. Thus it 
is most reduced and simple in character in those animals whose limbs 
are mere organs of support, as the Ungulates ; and most complex 
when the limbs are also used for grasping, climbing, or digging. 
The development or absence of the clavicle or “collar-bone,” an 
accessory bar which connects the sternum with the scapula and 
steadies the shoulder-joint, has a somewhat similar relation, though 
its complete absence in the Bears shows that this is not an invariable 
rule. A complete clavicle is found in Man and all the Primates, in 
Chiroptera, all Insectivora (except Potamogale), in many Rodents, in 
most Edentates, and in all Marsupials, except Perameles. More or 
less rudimentary clavicles (generally suspended freely in the muscles) 
are found in the Cat, Dog, and most Carnivora, Myrmecophaga, and 
some Rodents. Clavicles are altogether absent in most of the Urside, 
all the Pinnipedia, Manis among Edentates, the Cetacea, Sirenia, 
Ungulates, and some Rodents. 
