114 



STUDIES IN ADVANCED PHYSIOLOGY. 



arm lies the muscle 



Fig. 57. SHOWING THE 



SUPERFICIAL MUSCLES 

 OF THE RIGHT ARM, 

 FROM BEFORE. 



1, l', pectoralis major; 

 2, 2', deltoid; 3, 3', 3", 

 biceps; 4, 4', brachialis 

 auticus; 5, 5', triceps. 

 Numbers from 6-17 refer 

 to muscles and tendons of 

 fore-arm and hand. 



which serves to extend the arm, which 

 ends in three tendons at the shoulder, 

 and is called the triceps. Then again 

 there are muscles which have a tendon 

 in the middle, thus dividing the muscle 

 into two portions. Such a muscle is 

 called a digastric muscle, that is, has 

 two bellies. Sometimes even more than 

 two occur, when the muscle is called a 

 polygastric muscle. Instances of such 

 polygastric muscles are found in the 

 anterior abdominal wall. Closer exam- 

 ination of a typical muscle will show 

 it divided up into bundles separated 

 from each other by intervening con- 

 nective tissue. On a cross section of 

 a muscle these bundles would appear 

 as irregular areas, and are familiar to 

 every one in the characteristic appear- 

 ance of a piece of lean beefsteak. This 

 connective tissue not only extends 

 through the muscle, dividing it up into 

 bundles which are called fasciculi, but 

 envelopes the entire muscle. It serves 

 to carry the nerves and blood-vessels 

 through the muscle, and is called the 

 perimysium. 



HISTOLOGY OF VOLUNTARY FIBRES. 



Fibrillation. For a more detailed study the microscope 

 must be called to aid, and it is then seen that the fasciculi 

 are divided into still smaller bundles, and that the smaller 

 bundles are finally composed of the ultimate fibres. These 

 muscle fibres all run in the same direction, which accounts 

 for the splitting observed on any piece of boiled beef. If 



