THE FROG 9 



Sketch these muscles on a separate sheet, leaving room 

 behind for the following muscles. 



Cut through the deltoid and portio sternalis of the pectoral 

 near the median line, exposing the coraco-brachialis brevis and 

 longus muscles, which run from the coracoid, near the sternum, to 

 near the middle of the humerus. Add these to sketch, then 

 split the sternum longitudinally, exposing the deeper muscles, as 

 follows: On either side of the median line a strong sternohyoid 

 muscle, arising in part from the coracoid and sternum, in part 

 as an anterior prolongation of the rectus abdominis, and passing 

 forward to be inserted on the hyoid between the geniohyoids. 

 The omohyoid muscle is inserted on the hyoid just lateral to the 

 sternohyoid. It runs obliquely outwards and backwards to its 

 origin on the inner surface of the scapula. Other muscles are 

 exposed by deeper dissection. Lift the sternohyoid and see the 

 thyreoid gland lying in the hinder angle of the body of the hyoid. 

 Farther back, in the angle between sterno- and omohyoid muscles, 

 is the pseudothyreoid body. Sketch these in their proper rela- 

 tions. 



Remove the skin from the dorsal surface of head and trunk, 

 noting the expanded tympanum surrounded by a ring of carti- 

 lage, the annulus tympanicus, supporting the tympanic mem- 

 brane. Note that in removing the skin the membrane is often 

 split, indicating that it is composed of more than one layer. 



A little behind the tympanum is the depressor mandibulse 

 (digastric) muscle, which extends downward from the dorsal 

 fascia to its insertion on the posterior angle of the lower jaw. 

 Separate this muscle and turn it outward, exposing its other head, 

 attached to the posterior arm of the squamosal, as well as the 

 cucularis muscle, arising from the prootic and squamosal and 

 inserted in the anterior border of the scapula, external to the 

 origin of the deltoid. The thymus gland may now be seen hi the 

 angle between the cucularis and the head of the deltoid. It 

 should be inserted in the drawing which you will make later. 



Just in front of the tympanum is the temporalis muscle, which 

 arises from the upper part of the prootic and passes under the 

 anterior arm of the squamosal and over the pterygoid bone to its 

 insertion on the coronoid process of the lower jaw. In front of 

 and partly covered by the temporalis is the pterygoideus muscle, 

 arising from the fronto-parietals and passing downwards and 



