I.] THE FROG. 37 



B. Preliminary, and general disposition of the viscera. 



I. Place the animal on its back and pin down high and 

 dry, inserting the pins through the limbs and point of 

 snout. Raise the ventral integument with forceps and 

 slit it up with scissors along the middle line from the 

 lower jaw to the origin of the hind limbs; pin back 

 the two flaps and note : — 



a. The skin; it is but loosely connected with the sub- 

 jacent muscular wall of the trunk, the two being 

 separated by spacious chambers {lymph cavities^ cf. 

 Sect. I. a). 



h. A large vein {great-cutaneous) on the under-surface 

 of each flap of skin. 



c. Some of the muscles of the body wall; covered by 



a thin sheath or aponeurosis, through which they 



can be seen — 



a. The rectus abdominis; running from pelvis to 



sternum along the middle line, and divided into 



a number of segments by transverse tendinous 



intersections. 



A large vein {anterior-abdominal) will be seen, 

 running along the ventral middle line, immediately 

 under cover of this. 



^. ^\\Q pectoralis ; an immense tract of tissue arising 

 from the ventral wall of the trunk externally, and 

 in front ventrally, to a. It is subdivided into a 

 series of lesser muscles which converge towards 

 the base of the fore-limb. (Note that it is 

 confluent posteriorly with a, and, in front, sub- 

 divided up by tendinous intersections.) 



y. The mylohyoid or sub-maxillaris ; a sheet of 

 muscle, tendinous in the middle line, whose 



