128 DISSECTION OF THE DOG 



along the aboral border of the infraspinous muscle. Its origin is from the 

 distal third of the axillary border of the scapula and particularly from a rough 

 elevation close to the glenoidal margin. The insertion is to the crista tuberculi 

 majoris between the attachment of the infraspinous tendon and the origin of 

 the lateral head of the triceps. 



M. triceps brachit. — Two heads — caput longum and caput mediale — of 

 the triceps have already been examined. It will be noticed that the long head 

 is included in both the medial and lateral aspects of the arm. 



Caput laterale. — The lateral head arises from the crista tuberculi majoris 

 of the humerus under cover of the insertion of the deltoid. The main insertion 

 of the head is into the olecranon of the ulna in common with the rest of the 

 triceps. In addition there is a connection with the fascia of the forearm. 



Dissection. — Reflect the lateral head of the triceps. This will allow of an 

 examination of the lateral part of the medial head which has origin 

 close to the head of the humerus. The brachial and aconeus muscles 

 and the radial nerve are also exposed. A branch of the deep artery 

 of the arm accompanies the nerve and follows it into the forearm. 



M. brachialis. — The brachial muscle has its origin immediately medial to 

 the insertion of the teres minor and the origin of the lateral head of the triceps. 

 Running along the humerus in a spiral manner, the muscle crosses the flexor 

 aspect of the elbow- joint and ends in two tendons which join the two tendons 

 of the biceps. Thus it obtains insertion into both radius and ulna. 



M. aconjeus. — The aconeus is a small muscle lying between the olecranon 

 and the humerus. Its chief origin is from the lateral epicondyle ; but some 

 fibres come from the lateral collateral ligament of the joint. The insertion 

 of the aconeus is into the lateral face of the olecranon of the ulna. Some of 

 the fibres, moreover, are inserted into the capsule of the elbow-joint. 



N. radialis. — In the dissection of the medial aspect of the arm the radial 

 nerve was observed to pass between the long and medial heads of the triceps. 

 More of its course may now be examined. The nerve "will be found at first 

 between the two portions of the medial head of the triceps ; then between the 

 medial head and the brachial muscle ; and, lastly, between the lateral head 

 and the brachial muscle. Here the nerve divides into deep and superficial 

 branches, both of which proceed into the forearm. 



The superficial branch (ramus superficialis) of the radial nerve is subcutaneous 

 and accompanies the radial vein. The deep branch (ramus profundus) follows 

 the brachial muscle. 



Dissection. — Remove the skin from the forearm and the dorsum of the 

 manus. In the superficial fascia blood-vessels and nerves should be 

 discovered. 



