LIUAMEXTS AND ML'SCLES OF THE HORSE. 39 



Xote. — The internal intercostal muscles diifer from the ex- 

 ternal set in being continued down to occupy the spaces 

 between the costal cartilages, while in the extreme upper 

 part of the intercostal spaces, they are either absent or 

 thin and aponeurotic. This inter-cartilaginous portion is 

 insi^iratory. 



4. Levatokes Costarum. 



Origin.— Yrom the transverse processes of the dorsal vertebrae. 

 Insertion. — To the outer surfaces of the ribs, posterior to origin. 

 Action. — To draw the ribs forward and assist in inspiration. 



5. Triangularis 8terni. 



Origin.— Yvom the borders of the upper surface of the sternum, 

 extending from opposite to the 2nd costal cartilage, to the 

 ensiform cartilage. 



Insertion. — To the costal cartilages, 2nd to 8th inclusive. 



Action. — To assist in expiration, 



G. Lateralis Sterxi. 



Origin. — Outer surface of 1st rib above its cartilage. 

 Insertion. — To the side <jf the sternum, some of its fibres also 



sometimes to the 3rd and 4th costal cartilages. 

 Action. — It has a feeble inspiratory action, with the 1st rib as 



the tixed point. 



ABDOMI^TAL liEGION. 



1. External OhUqne (obliquus abdominis externusj. 



2. Internal Oblique (obliquus abdominis internus). 



3. Great StraigJd (rectus abdominis). 



4 Transverse (transversalis abdominis). 

 ^). Retractor Costae. 



Abdominal Tunic. 



This is an expansion of yellow elastic tissue spread over the ex- 

 ternal oblique muscles of the abdomen. 



