222 THE BIOLOGY OF THE ANIMAL 



fibres running downward and backward from 

 the dorsal surface, and the obliquus intemus, 

 with fibres running downward and forward. 



Turn the frog over, and study the muscles of 

 the dorsal surface. 



d. The depressor mandibuli, a triangular mus- 

 cle, posterior to the tympanic membrane. 



e. The latissimus dorsi, a triangular muscle pos- 

 terior to the depressor. 



f. The infra-spinatus, partly covered by the latis- 

 simus. Raise the supra -scapula, and examine 

 the muscles which attach it to the body. 



Clear away the transparent membrane or apo- 

 neurosis covering the back, and below it find 



g. The extensor dorsi communis, running from 

 the urostyle to the head. Lying under this mus- 

 cle look for short muscles connecting the trans- 

 verse processes of the vertebrae. 



h. The gluteus, arising from the outer side of the 

 posterior portion of the ilium, and running back- 

 ward. 



Make lists of all the muscles whose action would 

 cause the body to bend (1) downward, (2) upward, 

 (3) side wise; (4) would move the head upward; 

 (5) would depress the lower jaw ; (6) would move 

 the anterior limbs ; (7) would move the posterior 

 limbs. 



II. Muscles of the head. 



On the ventral surface of the head find 

 a. The mylohyoid, lying directly beneath the skin. 

 Remove the mylohyoid and find 



h. The geniohyoid, to one side of the median hne. 



