Cervical Ribs in M<tu. \)\) 



]iorpoise has produL-ed a much stiffer neck than tlic manatee. The 

 ankylosiTi!2r process is all-surticient for stiffening purposes. The ribs 

 that develop on the seventh vertebra of the manatee are perfect 

 sternal ribs, and they bear every evidence of being- respiratory ribs. 



The iiiipacti(»n and ankylosis of the neck bones of the porpoise has 

 carried ts head towards its lungs, and the fornuition of cervical ril)s 

 has carried the thorax of the manatee nearer the head. Marine 

 aninuds derive some advantage by the lungs being near the head, for 

 there, by l)uoyancy, they assist the nostrils to come to the surface 

 when the oxygen su])ply has been used up beneath the water. 



It appears that cervical ribs develop in manatees and dugongs in 

 association with the lungs, and that the need for the stiffening effect 

 of ribs upon the neck, as an aid to water progression, may be ignored 

 as a causative factor in the development of cervical ribs. 



Tt is difficult to ascertain the rate of speed at which these slow- 

 moving sirens travel, but as the fast-moving porpoises exhibit im- 

 pacted necks, it may be inferred that the greater the speed, the greater 

 the impaction of the neck. When the neck is ankylosed, as the result 

 of impaction, it is, for all practical purposes, reduced to a condition 

 that functionally corresponds to the neck area of fish. Under the 

 sluggish movements that are executed by the dugong, the force that is 

 set up by the action of the tail muscles, and which is resisted by the 

 water, is mainly transmitted through the bones of the spine, and it is 

 not great enough to impact the cervical vertebrae and its effect on the 

 bones is shown only by their flattened state. 



It appears from the study of mammalian neck bones that water 

 pressui'e, in the absence of quadrupedal progression on land, is a great 

 destroyer of fixed mammalian neck-type, but that even these ex- 

 tremely hostile neck impulses are insufficient to destroy mammalian 

 neck-type when use is made tm rock and ice of the fore-limbs for 

 supporting the weight of the body. 



Mammalian Quadrupedal Progression. 



All nianunals that' go on four limbs are not oquallv developed in the 

 fore and hind limbs, and there are many degrees of quadrupedalitv. 

 The most perfect quadruped is the horse ; its limbs are entirely 

 devoted to progression and supporting body weight ; therefore its neck 

 type is fixed and cervical ribs are unknown in these animals. 



Animals that have the power of standing for long periods have 

 narrow chests ; a narrow chest is a good point in a horse, and great 

 transverse measurement is the mark of an underbred or slow animal. 

 The full pectoral region that is so adiuired in soldiers has its counter- 

 part in the flying-fox. Narrowness of the cephalic end of the thorax 



