62 MUSCLES OF THE THORAX. 



band and reflect the cut ends ; the remaining divisions 

 of the pectoralis will be fully exposed. The fibres 

 arise along the whole length of the sternum, pass 

 obliquely forward and outward to be inserted into the 

 head and upper part of the shaft of the humerus, and 

 partly also into the fascia covering the biceps muscle 

 of the arm. 



Ciit across the pectoralis muscle and reflect the cut 

 ends. 



2. The Sternalis Muscle is a small fan-shaped mus- 

 cle lying lateral to the anterior end of the sternum. 

 The muscular fibres arise at the level of the cartilagi- 

 nous portion of the 2d and 3d ribs from a strong 

 fascia ; they pass obliquely forward and outward to be 

 inserted into the ist rib. 



3. The Scaleni Muscles arise from the transverse 

 processes of the last four cervical vertebrae, and are 

 inserted into the ribs. In the dog four scaleni may 

 be distinguished lying close to one another : 



a. The Scalenus Primus lies nearest to the ven- 

 tral mid-line ; it arises from the transverse processes 

 of the 5th and 6th cervical vertebrae, and is inserted 

 into the ist rib where the bony and cartilaginous por- 

 tions meet. 



b. The Scalenus Secundus is much longer; it 

 arises from the transverse processes of the 4th and 5th 

 cervical vertebrae by two tendons, and is inserted into 

 the bony ribs from the 3d to the 7th. 



c. The Scalenus Tertius lies dorsal to the ante- 

 rior end of the secundus ; it arises in common with it, 

 but is inserted into the bony portion of the ist rib to 

 the outer side of the insertion of the primus. 



d. The Scalenus Quartus is a very small muscle 

 inserted into the ist rib between the primus and 



