1916] Holliger: Anatomical Adaptations in the Pocket Gopher 481 



nearly corresponds to the human supinator. Its action doubtless 

 gives the slight supination of the manus which has been noted in 

 the gopher (Merriam, 1895, p. 17; Stephens, 1906, p. 142). 



42. Prmiator quadratus (pron. quad., pi. 39) is a thin layer of 

 fibers arising on the mesial surface of the distal third of the ulna, 

 and inserted on the mesial surface of the distal third of the radius. 

 It furnishes the chief pronating force in the gopher and antag- 

 onizes the action of the supinator. 



Grouping of Muscles According to Function 



In considering the functions of muscles it is convenient to 

 study together those which have a similar action. We have, there- 

 fore, divided the muscles of the thoracic limb of the gopher and of 

 the other rodent forms into eight functional groups, and in the 

 following volumetric work the volumes of all the muscles of the 

 group are used in comparisons, rather than the volumes of the 

 individual muscles. 



The principal movements which the scapula is capable of per- 

 forming may be divided into two classes: (1) Rotary movements 

 around a center located in the flat part of the bone and perpendicu- 

 lar to its surface; (2) Gliding movements of the bone as a whole 

 over the thoracic wall. The muscles attached to the clavicle may 

 be considered as assisting in one or another of these movements. 

 We shall not attempt a further analysis of these movements, or 

 the separation of the shoulder muscles into sub-groups ; the following 

 considerations make it inadvisable to do this : ( 1 ) These movements 

 are very complex and the same muscle often participates in both of 

 the above classes of movements; (2) The variations in origins and 

 insertions found in the different forms make homologous muscles 

 uncomparable in their action. All of the muscles which move the 

 shoulder girdle are therefore grouped together, as follows, the 

 numerals referring to the numbers of the muscles in the descriptive 

 list (pp. 463 to 481) : 



Group 1. Muscles which move the shoulder girdle : 



2 Trapezius 



3 Rhomboideus capitalis 



4 Rhomboideus minor 



5 Rhomboideus major 



7 Sternomastoideus 



8 Cleidomastoideus 



9 Bascioclavicularis 



