1916] Holliger: Anatomical Adaptations in the Pocket Gopher 483 



Group 5. Extensors of the forearm: 



21 Triceps brachii 



22 Extensor antibrachii parvus 



23 Anconeus medialis 



24 Anconeus lateralis 



Group 6, Flexors of the forearm: 



25 Biceps brachii 



27 Brachialis 



40 Pronator teres 



Group 7. Extensors of the hand: 



29 Extensor carpi radialis brevis 



31 Extensor digitorum communis 



28 Extensor carpi radialis longus 



34 Extensor carpi ulnaris 



33 Extensor digiti quinti proprius 



30 Abductor pollicis longus 



32 Extensor pollicis et indicis 



Group 8. Flexors of the hand: 



36 Flexor carpi ulnaris 



38 Flexor digitorum profundus 



37 Flexor digitorum sublimis 



35 Palmar is longus 



39 Flexor carpi radialis 



Volumetric Measurements 



As a basis for functional comparison of similar muscles in dif- 

 ferent forms we must have an idea of the force normally exerted 

 by such muscles. It has been shown by physiological experiment 

 that the volume of a muscle is a true indicator of the work it can 

 perform. Foster (1896, p. 124) expresses this law as follows: 



If two muscles are unequal both in length and sectional area, the work 

 done will be the greater in the one which has the greater bulk, which con- 

 tains the greater number of cubic units. In speaking, therefore, of the 

 work which can be done by a muscle, we may use as a standard a cubic 

 unit of bulk, or, the specific gravity of the muscle being the same, the imit 

 of weight. 



Volume was selected rather than weight as an indicator of 

 strength, because it seemed to be better adapted for testing both 

 the bones and the muscles. 



The volumes of the various structures were determined by im- 

 mersing them in graduated glass vessels of appropriate sizes con- 

 taining water, and noting the displacement. The chief objection to 

 this method is that the amount of liquid contained in the tissues 



