348 PRACTICAL ANATOMY. 



CLASSIFICATION OF MUSCLES ACCORDING TO FUNCTION. 



( i. Extensor longus pollicis ; insertion, base of second phalanx. 

 Extensors of the pollux \ 2. Extensor brevis pollicis; insertion, base of first phalanx. 



I 3. Extensor ossis metacarpi pollicis; insertion, base of metacarpal. 



I i. Extensor carpi radialis longior ; insertion, base of second meta- 



Ex tensors of the carfius -: ,- ' j i u L r i. j 



) 2. Extensor carpi radialis brevior; insertion, baseof third metacarpal. 



v 3. Extensor carpi ulnaris; insertion, base of fifth metacarpal. 



/ i. Extensor communis digitorum ; insertion, base of second and 



extensors of t e tgt s -< 2 j xtensor m innni digiti ; insertion, with extensor communis. 

 l. 3. Extensor indicis digiti ; insertion, with extensor communis. 



Extensors of the forear,,. \ [' The triceps ; insertion, into the olecranon process of the ulna. 

 ( 2. The anconeus ; insertion into the oblique line of ulna. 



f i. Brachio-radialis ; insertion, base of styloid of radius. 



Supinator of the radius -, 2. Supinator radii brevis ; insertion, posterior and external surfaces 

 (. of radius. 



Dissection. Trace out the tendons of the three extensors of the thumb by 

 cutting through the deep digital fascia. Take each to its insertion according to 

 insertions given in the classification above. Do not cut the annular ligament. 

 See if two compartments in the annular ligament transmit the three thumb 

 extensors. 



Extensor Carpi Radialis Longior and Brevior. Locate the insertions of 

 these tendons, in the bases of the second and third metacarpal bones respectively 

 on the radial side. Trace the same upward, under the annular ligament, and 

 behind the three extensors of the thumb. (Fig. 243.) 



The extensor communis digitorum sends a tendon to each finger. The 

 tendon of the extensor communis digitorum to the index finger is joined by the 

 tendon of the extensor indicis; the tendon to the little finger, by the tendon of 

 the extensor minimi digiti. Demonstrate this on your dissection. 



The insertion of the extensor tendons is as follows (Fig. 243) : The extensor 

 tendon of each finger divides into three parts, opposite the first phalangeal articu- 

 lation (Fig. 244) ; the middle portion is inserted, just across the joint, into the 

 base of the second phalanx ; the two lateral portions pass the joint, unite on the 

 dorsum of the second phalanx, and pass to the base of the third phalanx, where 

 they are inserted. See whether this muscle and the extensor indicis occupy the 

 same compartment under the annular ligament. Now trace the extensor minimi 

 digiti through a separate compartment in the annular ligament. (Fig. 244.) 



Insertion of the extensor carpi ulnaris : Cut down on its tendon near the base 

 of the fifth metacarpal ; follow the tendon through a groove behind the styloid 

 process of the ulna, and trace it through a separate compartment in the posterior 

 annular ligament. 



Compartments of the Posterior Annular Ligament (Fig. 244). Cut 

 through the annular ligament and find the following compartments and then- 

 contents, and see whether the same are lined by synovial membrane. 



1. For extensor ossis metacarpi pollicis and extensor brevis pollicis. 



2. For extensor carpi radialis longior and brevior. 



3. For extensor longus pollicis. 



4. For extensor communis digitorum and extensor indicis. 



5. For the extensor minimi digiti. 



6. For the extensor carpi ulnaris. 



The Brachio-radialis, or Supinator Radii Longus. Supinate the radius 

 and you will find this muscle, on the radial side, inserted into the- base of the 

 styloid process of the radius. (Fig. 246.) 





