452 University of California Publications in Zoology [Vol. 13 



Another general character of the skeleton which may be exam- 

 ined is the volume of the bones compared with the entire volume of 

 the leg. Since greater volume may mean greater strength of the 

 entire osseo-muscular machine, we might expect to find the fossorial 

 members of the group again in the lead. But this seems not to be 

 the ease; table 1 (p. 485) indicates very little correlation between 

 habits and volume of bones. Curiously enough, the bones of the 

 jack rabbit are relatively larger than those of any of the other 

 rodents. This is probably influenced by three factors: (1) The 

 bones of the rabbits are thin-walled and therefore need to be rela- 

 tively large; (2) The greater relative length of the limb in the 

 rabbits increases the proportional volume of the bones; (3) The 

 larger and broader foot also causes the skeleton to measure larger, 

 since the whole foot was left attached to the leg skeleton when 

 volumetric measurements were made. It thus seems that so many 

 other factors besides habit of life influence the size of bones that 

 any correlation with habit which might exist is hidden or obliterated. 



The individual bones of the thoracic limb of the gopher will be 

 described briefly, and important differences between the bones of 

 this rodent and those of others of the series studied will be noted. 

 The figures representing the bones are drawn to scale and no meas- 

 urements are necessary. 



Clavicle (fig. E). — In the gopher the clavicle is well developed 

 and forms a true bony link between the sternum and the scapula. 

 The head of the clavicle is a large, hemispherical knob, the mesial 

 concave surface of which articulates with the cephalo-lateral angle 

 of the manubrium of the sternum. The inner third of the shaft is 



Fig. A. Lateral view of skeleton of left thoracic limb of tlie gopher, X 2. 



Fig. B. Mesial view of skeleton of left thoracic limb of the gopher, X 2. 



acr. — acromion in. con. — internal condyle 



car. — carpus lat. gv. — lateral groove 



cor. 1)d. — coracoid border. les. tuh. — lesser tuberosity 



cor. proc. — coracoid process met. — metacarpals 



crvt. ang. — coracovertebral angle nk. — neck 



del. tub. — deltoid tuberosity olec. — olecranon 



ex. con. — external condyle vTi- — phalanges 



/aZ.— falciform ratZ.— radius 



glen. ang. — glenoid angle scap. — scapula 



glen. Id. — glenoid border sp. — spine 



glvt. ang. — glenovertebral angle supgl. till). — supraglenoid tubercle 



gr. tub. — greater tuberosity ul. — ulna 



Ud. — head vert. bd. — vertebral border 



hum. — humerus 



