division and rearrangement of the parts of the primitive 

 muscle sheets, there have resulted, without doubt, muscles 

 which represent functional parallelisms, i.e. analogs. Where 

 homologies begin or end must be arbitarily decided in each 

 case. 



Table 14-3 serves to show the homologies of the muscles 

 discussed in the several groups, and in additional groups, 

 and also indicates the nature of muscle synonymies, i.e. a 

 listing of the names applied by different authors to a muscle 

 of a particular organism or to the same muscle in different 

 animals. For example, the pars scapularis of the deltoid is 

 called the dorsalis scapulae in the Urodele, while in the 

 bird the term dorsalis scapulae has been applied to the teres 

 major. Synonymies are a usual feature of comparative 

 studies since through time more accurate and thorough 

 studies have lead to refinements of knowledge. Each step in 

 this process has been marked by changes in nomenclature. 

 The process is still going on. 



General observations on muscles 



On the basis of the eye muscles, the agnath is distinct 

 from the gnathostome, if one assumes that the lamprey is 

 representative. The weight of evidence supports such an as- 

 sumption and there is no reason why one should suspect 

 that the lamprey's eye musculature is anything but unmodi- 

 fied. The several groups of tetrapods show similar and per- 

 haps parallel variations in their eye musculature. 



Demonstration of a common pattern of tetrapod limb 

 mu.sculature has the value of focusing attention on the 

 many adaptational changes observed in the several groups. 

 One can observe muscles in every stage of multiplication, 

 change of relationship, or loss. This variation suggests that 

 musculature is of limited value in terms of broad phy- 

 logenies either because of the difficulties of analyzing the 

 many details of structure involved in such a complex system 

 or the ready response of this system to adaptive modification. 



SKELETAL MUSCULATURE 



441 



