156 



EXTREMITY. 



with their paws, the clavicle is fully developed, 

 and extends the whole way from the scapula to 

 the sternum. Thus in the Rodentia this bone 

 is very perfect, as, for example, the Squirrel, 

 the Beaver, the Rabbit, the llat, &c. The Bat 

 affords an example of a very strong and long 

 clavicle, as also the Mole and the Hedgehog 

 among the Insectivora. 



Among the Edentata those tribes possess a 

 clavicle whose habits are fossorial, as the Ant- 

 eater, the Armadillos, and even the Gigantic 

 Megatherium, in which animal, however, the 

 clavicle presented the peculiarity of being arti- 

 culated with the first rib instead of with the 

 sternum. In the Quadrumana the clavicles are 

 strong and curved as in the human subject. 



In Birds, the bone which is analogous to 

 the clavicle presents similar variations in its 

 developement, according to the range of motion 

 required in the anterior extremity, or in other 

 words, in proportion to the extent to which the 

 powers of flight are enjoyed. Thus, in some 

 these bones are anchylosed along the mesial 

 line, and constitute the furculum ; in others 

 they are cartilaginous internally; and in others 

 they do not reach the sternum.* 



1 n women the clavicle is in general less curved 

 than in men ; the diminution in the incurvation 

 is most manifest in the external portion . Accord- 

 ing to Cruveilhier, the clavicles are often une- 

 qually developed in the same individual accord- 

 ing as one limb is more used than the other, and 

 sometimes the difference is sufficiently obvious 

 to enable one to ascertain from the relative size 

 of the clavicles, whether the individual is right 

 or left-handed. 



Structure. The clavicle contains a conside- 

 rable proportion of compact tissue in its shaft, 

 and a cylindrical medullary canal ; at the ex- 

 tremities the compact tissue greatly diminishes, 

 and is replaced by the reticular, which likewise 

 fills up the bone and obliterates the medullary 

 cavity. 



Developement. A strong argument as to the 

 great importance of this bone to the motions of 

 the shoulder, is derived from its precocious de- 

 velopement; for although the cartilaginous nidus 

 of the vertebra as well as that of the ribs appear 

 before that of the clavicle, yet the latter bone 

 begins to ossify sooner and is completed more 

 rapidly than any other bone in the body, ex- 

 cepting perhaps the lower jaw, which some- 

 times takes the precedence in the process of 

 ossification. It is remarkable too for the diver- 

 sity in its proportional size, which it presents 

 at different periods; thus, according to Meckel, 

 about the middle of the second month of 

 pregnancy, the clavicle is four times longer 

 than the humerus or femur, and it is not until 

 the fourth month that the hiimerus exceeds it 

 in length. The clavicle has but one primitive 

 point of ossification : a supplementary point is 

 developed under the form of a very thin lamella 

 at the anterior part of the sternal extremity .f 



Scapula, scupulum, omoplata, (U/AOJ, hume- 

 rus, wAaTu;, latus.) Fr. omoplate; Germ, das 

 Scludterblatt. This bone forms the posterior 



See AVES, p. 285, vol. i. 



t Cruveilhier, Anat. Dust. t. i. p. 219. 



and principal portion of the shoulder; it is 

 placed on the posterior and outer part of the 

 thorax, and occupies a space which extends from 

 the second to the seventh rib. 



The scapula is very thin in the greatest part 

 of its extent, quite papyraceous in some places. 

 It is triangular in form, and anatomists com- 

 monly describe its sides or borders, its angles, 

 and its surfaces. 



The borders, or costs, of the scapula are 

 three in number, and are named according to 

 the position they occupy or the relation 

 they bear: thus there are the superior border 

 or cervical, the posterior or vertebral, and the 

 anterior or axillary. The cervical border (also 

 called the coracoid) is the shortest, being some- 

 what less than a fourth of the length of the 

 vertebral border; it is connected posteriorly 

 with the vertebral at an angle the apex of which 

 is rounded off; it is slightly concave, and the bone 

 for some way below it is very thin, and the bor- 

 der itself is acute. Anteriorly it terminates in a 

 notch which is bounded in front by one root of the 

 coracoid process, (incisura semilunuris, lunula, 

 coracoid notch.) This notch is converted into 

 a foramen by a ligament which is often ossi- 

 fied, and thus the suprascapular nerve, which 

 is lodged in the notch, is separated from the 

 artery of the same name, which passes over 

 the ligament. The extent, therefore, of the 

 cervical border is from the posterior superior 

 angle to this notch. The levator anguli sca- 

 pulae and the omo-hyoid muscles are attached 

 to this border. 



The vertebral border, also called the base of 

 the scapula, is the longest, being in an ave- 

 rage-sized bone from seven to eight inches in 

 length ; it is sharp in its whole extent, which 

 is limited above by the posterior superior angle, 

 and below by the inferior angle. At the junc- 

 tion of the superior fourth with the remaining 

 portion there is an inclined surface, triangular 

 in form, the base confounded with the margin 

 of the bone, the apex continued to the spine. 

 This surface is smooth, and the ascending 

 fibres of the trapezius muscle glide over it. 

 To that part of this edge, which is above the 

 surface, the levator anguli scapula; is attached, 

 and below it the rhomboidei. 



The anterior or axillary border is limited 

 above by the glenoid cavity, and below by the 

 inferior angle of the scapula. It is much 

 thicker than either of the others, and its thick- 

 ness increases towards its upper extremity, 

 where, close to the glenoid cavity, there is a 

 rough surface which gives attachment to the long 

 head of the triceps muscle ; inferior to this, the 

 edge affords insertion to the teres minor muscle, 

 and still lower down to the teres major. 



The superior and posterior angle is formed 

 by the junction of the cervical and vertebral bor- 

 ders; it is a little less than a right angle, arid is 

 chiefly remarkable for affording insertion to the 

 levator anguli scapula; muscle. The inferior 

 angle, formed by the union of the axillary and 

 vertebral borders, is very acute; the bone here is 

 very thick and spongy ; part of the latissimus 

 dorsi glides over this angle, and sometimes 

 some of its fibres are inserted into it. It is 



