116 PHYSIOLOGICAL SERIES. 



C. 117. The right half of a portion of the trunk of a Python 

 (Python sebce) seen from within ; to show the internal 

 rib-muscles. 



Dorsal to the origin of the abdominal muscles, there 

 are two costal retractors ; of these two the internal (M. 

 costo-vertebralis superior) is the most strongly developed. 

 Its fasciculi arise from the hypapophyses of the vertebrae, 

 and passing forward over 6 ribs are inserted in the seventh. 

 The last three ribs in this specimen have been stripped, 

 leaving only the costo-vertebralis inferior at their base ; 

 this is a small muscle for the protraction of the ribs. 

 O.C. 63 L. 



C. 118. Ventral body-wall and ends of the ribs of a Python 

 (P. sebce) seen from above, showing the abdominal and lower 

 intemal costal muscles. 



The abdominal muscle (composed of two sheets inti- 

 mately connected together) arises from the middle of each 

 rib and passes diagonally across the body direct to the 

 ventral middle line, where it is inserted in a strong apo- 

 neurosis. It tends to flatten the body during locomotion. 

 The left half of this muscle has been retained, the right cut 

 away, to show the ventral shield muscles and the cutaneus 

 internus passing forward from the ribs to the skin. Two 

 internal costal retractor muscles are shown on the right 

 side, the one (retrahens costarum brevis) takes a longi- 

 tudinal course between the points of the ribs ; the other 

 (retrahens costarum longus) arises beneath the origin of 

 the abdominal muscle and is inserted on the 5th rib in front, 

 6 mm. from the point. 0. C. 63 K. 



C. 119. Transverse section through the body of a Python (Python 

 seb#), showing the position and double nature of the 

 abdominal muscle-sheet. O.C. 63 N. 



C. 120. A portion of the ventral body-wall of a Python (P. seba) 

 seen from, above, showing the ventral shield muscles. The 

 most conspicuous cf these are the interscutales majores. 

 They take their origin from the middle of the anterior edge 

 of the ventral shields and pass outwards and backwards to 



