16 ELEMENTARY PHYSIOLOGY. [l. 



downwards and ventrally, and are absent between 

 the costal cartilages, here the internal inter- 

 costal muscle is seen ; carefully remove the 

 external intercostal, and so follow the internal 

 intercostal towards the vertebrae ; the fibres run 

 downwards and ventrally and near the vertebrae 

 are scanty or absent. 



10. Observe more closely the costal cartilages and 

 their connection with the ribs and sternum. 



11. The above mentioned muscles, especially the 

 thinner ones, should also be observed in the 

 dog, where they are larger. There are some 

 differences in arrangement. 

 The pectoral has an upper portion which runs 

 not to the scapula but to the humerus. 

 The serratus anticus runs from the whole length 

 of the internal border of the scapula to the 

 lower cervical vertebrae and first seven ribs. 

 The origins and insertions of the scaleni are 

 somewhat different. 



The serratus posticus is divided as in man into 

 an upper and a lower portion (s. p. superior 

 and s. p. inferior.) 



12. Cut through the costal cartilages on either side 

 close to the sternum, cut through the muscles be- 

 tween the 2nd and 3rd and the 8th and 9th ribs, 

 with bone forceps cut through the 3 8th ribs 

 dorsally and remove them. The pleural cavities 

 will be seen to be separated from one another by 

 the median parietal portions of the pleurae, 

 between these is a space, the mediastinum. 

 From the surface of the lungs a shred of a fine 



