THE FROG 13 



brevis (partly covered by the extensor cruris brevis) is attached 

 to the lateral distal side of the os cruris, while the tibialis anticus 

 longus lies between the external cruris brevis and the tibialis 

 anticus brevis on the one side and the peroneus on the other. 



Work out the origin and insertion of these muscles and add 

 them to the drawing showing the ventral superficial muscles of 

 the thigh. 



The muscles of the ankle and foot are numerous. They may be 

 grouped as flexors on the plantar side, extensors on the dorsal 

 side. 



THE ORAL CAVITY. Open the mouth and find the in- 

 ternal nares (choanae) by inserting a probe in the external naris. 

 Look in the roof of the mouth, between the choanse, for the 

 vomerine teeth. What is the shape of the tongue? How is it 

 attached? How does this differ from the condition in yourself? 

 Note where the Eustachian tube enters the mouth or, better, 

 pharynx. Look in the floor of the back part of the pharynx for 

 a longitudinal slit, the glottis, bounded by a pair of semicircular 

 elevations (caused by the arytenoid cartilages beneath the 

 lining membrane). Behind the glottis the oesophagus begins. 



Draw the floor and roof of the mouth, illustrating all of these 



points. 



VISCERAL ANATOMY. With the injected specimen lay 

 back the skin of the ventral surface as before and note, on its 

 inner surface, two branches of the great cutaneous artery and a 

 single trunk of the great cutaneous vein. Note where they enter 

 the deeper structures. 



Lay open the body cavity (peritoneal cavity or coelom) by 

 a cut a little to one side of the median line, extending from the 

 origin of the hind legs to the shoulder-girdle, which can be felt 

 through the flesh, cutting nothing but the body wall. 



Lift the wall very carefully and see the abdominal vein extend- 

 ing dorsally from the wall to the liver and running backwards in 

 the ventral body wall. Follow it posteriorly to its origin by the 

 union of two femoral veins, one coming from each hind leg. Sketch 

 these in blue on a sheet intended to show the entire venous 

 system. 



Make transverse cuts, in front and behind, through the body 

 wall and pin out the flaps, exposing the viscera. Most conspicu- 

 ous are the dark-colored liver in front and the coils of the intes- 



