CHAPTER IV. 
the center of motion, whereby they are able to move a greater weight. 
Near this procefs is another called coracoides, from whofe extremity,with 
like advantage, arife two mufcles of the arm; this procefs with the former, 
and a flat ligament between them both, hinder the os humeri from being 
diflocated upwards. The fide oppofite to the focket is called the bafis of 
the fcapula, and the lower edge cofta inferior from its figure, which is 
thick, and like a rib to the fcapula; but its upper edge being very thin, is 
improperly fo called in the human fceleton, though not fo in many qua¬ 
drupeds : At the fore part of this edge, clofe to the coracoid procefs, is a 
femicircular nitch for the paflage of blood veflels, which nitch is joined 
at top with a ligament, and fometimes with bone. 
Os humeri: (Tab. xxiii.) Its upper end or head, where it is joined to the 
fcapula, is fomewhat flat and much larger than the fockct which receives 
it. At the upper part are two procefles for the infertions of mufcles of the 
arm; between thefe procefles is a long chanel, in which lies a tendon of 
the biceps cubiti. At the lower end are two confiderable procefles, both 
formed to give origins to mufcles of the wrift and fingers, and the flex¬ 
ors of thefe joints being much more confiderable than the extenfors, the 
inner procefs from which the flexors arife is therefore much larger than 
the outer, from which the extenfors take their origin: Between thefe pro¬ 
cefles is the joint. That part to which the upper end of the radius is fixed 
is fitted not only for the motion of the elbow, but alfo for the rotatory 
motion of the radius; the reft of this joint is made of portions of une¬ 
qual, but concentrick, circles; which inequality feems defigned to pre¬ 
vent the ulna from dillocating fideways, which fo fmall a joint with fo 
much motion would be very fubjeft: to: Of a like ufe is the little finus 
on the forepart of the humerus, and the large one behind; thefirft of 
which receives a procefs of the ulna when the arm is bent, and the other, 
the olecranon of the ulna, when the arm is extended. 
Ulna: (Tab. xxiv.) At the upper end it has one large procefs called o- 
lecranon, and a fmall procefs on the forepart; (fee the laft paragraph.) On 
one fide between thefe is alfo a fmall cavity, which receives the upper 
end of the radius for its rotatory motion; and down the fide of this bone, 
next the radius, is a fharp edge, from which the ligament arifes, which 
connedts thefe bones together. At the lower end, is a procefs, called fty- 
liformis, and a round head, which is received into the radius for the 
• . 
rotatory motion of the cubit. 
Radius: (Tab. xxiii.) Its upper end is received into the ulna, and joined 
to the humerus, in a manner chiefly fitted for its rotatory motion, for the 
