62 ’ (HE MUSCULAR SYSTEM OF THE FROG. 
2. Muscles of Back. 
Pin out the frog on its belly: remove the skin, and clean the - 
muscles un order. 
i. The depressor mandibuli: a Hivoaid triangular 
muscle which arises from the fascia covering the 
dorsal surface of the suprascapula: the fibres run 
downwards behind the tympanic membrane, and 
converge to be inserted into the angle of the 
lower jaw. The muscle by its contraction opens 
the mouth. 
iii The cucullaris: a small oblong muscle which, 
arising from the exoccipital near the middle line, 
runs backwards and outwards, and is inserted 
into the dorsal border of the suprascapula. 
“iil. The latissimus dorsi: a triangular muscle lying 
behind the depressor mandibuli: it arises from 
the fascia dorsalis just behind the shoulder girdle, 
its origin being partly covered by the obliquus 
externus. ‘The fibres run forwards and outwards, 
converging to be inserted by a long tendon into 
the deltoid ridge of the humerus. 
_ Dassect away the depressor mandibuli and latissimus dorsi 
from their origins, and turn them down. 
iv. The infraspinatus arises from the dorsal surface of 
the suprascapula, partly overlapped by the 
latissimus dorsi: it runs outwards to be inserted 
into the deltoid ridge of the humerus; its 
action is to elevate the arm. 
Lift up the suprascapula and note the muscles attaching it to 
the body, viz. : 
v. The retrahens scapule, behind. 
vi. The levator anguli scapula, in front. 
Remove the suprascapula on one side; and clean the median 
longitudinal muscles of the back. 
vii. The extensor dorsi communis: a longitudinal mass 
of muscle arising from the urostyle, and running 
forwards and slightly outwards: it is inserted 
‘into the illum, into the transverse processes of 
