SKELETON. 



615 



just as the first thoracic rib (7, 8, j%. 465.) 

 itself does ; and, in this particular, the clavi- 

 cle is like the rib. The sternal half of the cla- 

 vicle (bfig. 465.) and the sternal half of the first 

 rib (7, 8) are therefore as identical one with 

 the other as the sternal halves of any other 

 two thoracic ribs of serial order. But I see 

 that while the ribs join the dorsal vertebrae 

 behind, the clavicle joins the acromion pro- 

 cess of the scapula laterally. In this latter 

 particular the clavicle differs from the rib. 

 Now, granting this to be a well-marked spe- 

 cific difference between rib and clavicle, I still 

 maintain that there is as broad a difference ex- 

 isting between clavicles of mammals and birds; 

 and also between clavicles andcoracoid bones. 

 If change of place at one end from vertebra to 

 acromion process be enough to distinguish 

 clavicle (a, b jig. 465.) from rib (7, 8) in the 

 mammal body, so must change of place be 

 sufficient to characterise the bone named cla- 

 vicle {a fig. 466.) in the bird from the bone so 

 named in the mammal, for the former does not 

 join the sternum (f,fig- 466.), and the latter 

 does abut against that bone. And true it is 

 that the bone named coracoid (d,fig^QQ.) in 

 the bird joins the sternum (/), like a true 

 mammal clavicle, but yet is not considered 

 the clavicle, because its scapular end (e) joins 

 another process than the acromion. It ap- 

 pears, therefore, all circumstances considered, 

 that the mammal clavicle (n, b,Jig. 465.) is as 

 homologous to the rib (7, 8) in sternal re- 

 spect (<?, d) as it is to the bird's so-called cla- 

 vicle (n, fig- 466.) in scapular respect (c, b) ; 

 and at the same time it appears that the 



coracoid bone (d,fig. 466.) of the bird is as 

 similar to the mammal clavicle (a, b,fig. 465.), 

 and mammal rib (7, 8) in sternal junction, as 

 the bird's clavicle (a, Jig. 466.) is to the mam- 

 mal clavicle (, fig. 465.) in acromion junc- 

 tion. What, then, is the difference between 

 the rib, the clavicle, and coracoid bone ? It 

 is a difference of articular connection, which 

 all three bones appear to share in common, 

 a crosswise difference in articular connection, 

 which presents us with reasons equally strong 

 for naming either of these bones ribs, as well 

 as clavicles or coracoids. Viewed all three 

 as clavicles, they share the clavicular cha- 

 racter amongst them ; for that clavicular con- 

 nection which the one has not, the other has. 

 Viewed as ribs, all three, they share the costal 

 character likewise between them, and hence 

 follows the inquiry into truth ; namely, whe- 

 ther their originals be ribs, or bodies abso- 

 lutely distinct from ribs, passing through 

 metamorphosis. I believe them to be ribs, or 

 costal parts of whole costo-vertebral arche- 

 types, and that their difference depends 

 simply upon that act of the creative force 

 which in the process of development bends 

 them from the continuous line of serial costal 

 order, and renders them cleaving articularly to 

 various parts for the fitness of various special 

 skeletal fabrics. The track of the law of 

 metamorphosis which differences clavicles or 

 coracoid bones from ribs, may be easily fol- 

 lowed, if we will enlarge the view, through 

 comparison, and over a sufficient number of 

 facts. As in/g. 467. the rib (&) follows the 

 rib iy 9, in serial order through the thoracic 



Fig. 467. 



TJie cervical spine of the Crocodile, 



Showing that if in idea we continue the cervical ribs, a, b, c, d, e, f, g, h, i, over the cervix, in 

 the same way as we find the thoracic ribs, k, &c., enclosing thoracic space, we then find 8, 

 the clavicle, holding serial order with the costal continuations, 1, 2, 3, 4, 5, 6, 7, which 

 proves the costiform character of the clavicle itself. 



region, so does rib z, 9, and clavicle 8, taken 

 with the cervical rib A, succeed each other 

 in the same serial line ; and so likewise 

 in jig. 468. does rib e, the coracoid d, 

 and clavicle b, succeed each other in costal 

 order. These bodies are similar by succes- 

 sional position; and the only specific differ- 

 ence between them, upon which we hang the 

 names rib, clavicle, and coracoid bone, is this, 

 viz., that whilst all three bodies have a ster- 

 nal articulation (c,fi. 468.), the rib (e) still 

 holds connected with its proper vertebral 

 piece, while the clavicle (b), and the coracoid 



bone (d) disconnect themselves from their 

 vertebrae behind, and are taken up by the 

 acromion and coracoid processes of the sca- 

 pula.* 



In^/%-,469. we find the osseous pieces marked 

 1,2, 3, 4, 5, to be succeeded by the sternal 

 rib 6, which joins the partyj and constitutes 

 the costo-vertebral archetypal quantity of the 

 thorax. If, therefore, the serial order of the 

 osseous pieces a,b,c,d } e y continued into the 



* This fact will be more fully illustrated when 1 

 shall have to define the homological relations of the 

 scapulary members. 



* T T 3 



