11 



progressive enlargement of the external scapular head of this muscle. 



Several analogous changes are observed in the m. scapulo -humeral is 

 anterior. In scincids, the muscle in the form of a single (not separated 

 into heads) mass originates from the outer side of the anterior part of the 

 coracoid, the "epicoracoid," and a small part of the scapula. In the 

 lacertids, there is a separation of the muscle into a coracoid and a slightly 

 smaller scapiilar heads. In th gekkonids, the latter is completely reduced. 

 A similar trend, evidently parallel, also occurs in the Iguanomorpha. The 

 muscle in the agamids is quite similar to that of the scincids and the la- 

 certids; it was weakly divided into two parts. In the advanced agamids 

 (Phrynocephalus ) , the scapular head of the m. scapuLo-humeralis anterior is 

 greatly reduced, although not complete, resembling the condition observed 

 in gekkonids. 



Noting the strong similarity between the Gekkota and the Scincomorpha, 

 we must also mention a number of characteristics which permit the differen- 

 tiation of the gekkonids from other lizards (within the Scincogekkonomorpha 

 division), iinite the entire group of Gekkota, and perhaps, are slightly more 

 advanced than in the Scincomorpha. Thus, in Gekkota, there is a reduction of 

 the lig. axillaris; part of the fibers of the m. dorsalis scapulae spread to 

 the inner side of the suprascapular tendon; the scapular head of the m. 

 scapulo-hi:imeralis anterior and the scapular part of the coracoid head of the 

 m. subcoracoscapularis completely disappear; there is a crossing in the m. 

 pectoralis and in the m. pubo-ischio-femoralis intemus IV (Siikhanov, 1957); 

 the inner head of the m. femoro-tibialis merges with its outer head; there is 

 a progressive reduction of the inner head of the m. gastrocnemius to its 

 complete reduction in the Caspian gecko; in several forms, merging of the m. 

 fl. tibialis intemus II and m. fl. tibialis externus is observed. Signifi- 

 cant changes occur in the eyes (Underwood, 1951» 195^), and the cranial 

 arches are reduced, etc. There is the opinion that the amphicoelous verte- 

 brae of the gekkonids are a secondary derived condition (Underwood, 195^), 

 but at the same time there are the facts, presented previously which indicate 

 the extreme primitiveness of the Gekkota. Thus, this question must remain 

 open . 



From the aforementioned data, we can clearly see that there are two 

 sharply differing types of muscle structure in the locomotor apparatus of the 

 lizards - the Scincogekkonomorpha and the Iguanomorpha. It is interesting 

 that the musculature of the pectoral girdle and forelimbs in the first group 

 is definitely primitive, but that of the pelvis and hindlimbs is more 

 advanced. In the Iguanomorpha, the relation is reversed - muscles of the 

 pelvis are more primitive, but in the pectoral girdle there are very many 

 specializations . 



We are still far from completely understanding the role of the indi- 

 vidual muscles or even their complexes in locomotion. The possibility of 

 muscles of the locomotor apparatus being included in performance of functions 

 not directly connected with locomotion (digging, displaying, etc.) makes it 

 even harder to understand their evolution. Nevertheless, it is remarkable 

 that we still have two basic classes of locomotion in lizards - crawling in 

 the scincomorpha and elevated body posture during movement in the Iguano- 

 morpha. Each type of locomotion influences all aspects of the animal (we 



