44 ANATOMY OF THE RAT 



Triceps BracMi Muscle. This muscle has three heads — 

 the caput longum, caput laterale, and caput mediale. 



Caput longum. This head lies on the dorsal side of the 

 upper arm. Origin, the anterior third of the axillary- 

 margin of the scapula. Insertion, the olecranon. 



Caput laterale. This head lies on the lateral surface of 

 the upper arm. Origin, the larger tubercle of the humerus. 

 Insertion, the olecranon. 



Caput mediale. It lies along the dorsal surface of the 

 humerus. It is wedge-shaped, being pointed at the anterior 

 end, but greatly increasing in size posteriorly. Origin, the 

 dorsal and dorsolateral surfaces of the humerus through- 

 out practically the whole ventral surface of the muscle. 

 The pointed anterior end of the muscle reaches nearly to 

 the head of the humerus. Insertion, the olecranon. The 

 caput mediale is not seen superficially, but is found when 

 the caput laterale and caput longum are removed. 



SUPERFICIAL MUSCLES OF THE TRUNK 



External Oblique Muscle. This is a very extensive thin 

 muscle situated laterally and ventrally on the thorax and 

 abdomen. Anterior origin : it is attached along the side of 

 the thorax by a muscular slip to each rib from the fourth 

 to the twelfth. Posterior origin, the lumbodorsal fascia. 

 The anterior slips interdigitate with the posterior slips of the 

 serratus anterior. Insertion : (1) it fastens to a fascia on the 

 ventral surface of the thorax and abdomen; (2) is attached 

 along the whole length of the inguinal ligament (a white, 

 stout, slender ligament extending along the angle between 

 the inner surfaces of the hip and body, from the symphysis 

 pubis to the crest of the ilium) ; (3) a broad branch of the 

 muscle extends back to the symphysis pubis. Carefully ex- 

 pose all parts of the origins and insertions and determine 

 the muscle 's probable action by an inspection of its relations. 



