Cervical R'ths In Man. 91 



<;ressi(iii. The impulses that accomplish this j^veal rhaiiirc ctcli into 

 the mammalian neck its very fixed characters. 



Tlie neck of the crocodile bears fourteen cervical iil)-stumps, made 

 up of seven pairs; -the first and second pairs are lon'j l)ecause the 

 pectoral girdle only caught their tii)s in its span of the ventral and 

 lateral aspects of the ne<;k; The r.cck of V<trainis l)cars less rib tissue 

 than tlie (.rocodile, and this difYeience expresses the greater move- 

 ment of the neck that the Varan iis exercises in comparison with the 

 crocodile. 



According to the activity of the neck movements, the denudation 

 of the cervical ribs that occurs as the pectoral girdle ])asses down tlie 

 neck, is more or less complete. The stiffness of ribs in the neck 

 pre^'ents free neck movement. The cervical ribs stiffen the neck, 

 therefore those impulses that set up active neck movements in asso- 

 ciation with liml) progression are destructive to cervical ribs. 



Copacoid Bones. 



These bones maintain the fore-limljs on the lateral aspects of th;* 

 body in positions that are favourable for swimming and for flight, 

 therefore they occur in Hinphibiaus, reptiles and birds. As the body 

 was lifted for mainmalian quadrupedal progression, the lateral position 

 of the fore-limbs gave place to the ventral position, and the space 

 occupied by the coracoid bones became needed, and was later occui)ied 

 by the limbs. In the impulses that established raised quadrupedal 

 progression, destructive hostility to the coracoid bones existed and 

 the coracoids are now to be seen as vestiges on the uuniimalian 

 scapula. 



Vestiges are often referred to as being capable of development, and 

 in this connection it may be pointed out that the Hying-fox. fox-bat 

 of Pteropus, a mauunal that has acquired the ability to make sus- 

 tained flight, has not redevel()])ed its coracoids. 



The coracoid bones of birds and rei)tiles cross the sternal ends of 

 the first ribs, and to avoid collision of bone with bone, the sternal 

 ends of the ribs are fibrous. In this connection it is to be noted that 

 Keen, in the American Journal of Medical Science, shows a plate of a 

 human cervical rib that had a very definite fibrous end. The signi- 

 ficance of Sibson's fascia remains to be ex))lained : a careful investiga- 

 tion of this structure is likely to establish l^etwccn cervical rib 

 develoj)ment and Sibson's fascia a close relationship, for it seems 

 probable that this fascia is the forerunner of a cervical rib. 



The. tiluDUs nature of the sternal ends of the first ril>s in reptiles 

 and birds lends a yielding character to the junction of neck and 

 chest, whereas the bony first ribs of mammals give a rigidity to the 



