A MANUAL OF ZOOLOGY 53 



MUSCULAR SYSTEM— Muscles of the Ventral Body 

 Wall — Remove the skin of the ventral surface of the body 

 and find a long muscle extending from the pubis to the 

 sternum, rectus abdominis. It is divided on the median 

 line by the linea alba, and transversely into several divis- 

 ions. How many?. The pectoralis Is a fan shaped muscle 

 having its origin along the entire length of the body ta 

 the pubis. It may be considered in at least two parts, 

 the thoracic and the^abdominal, from the points of origin. 

 Trace it to the insertion on the deltoid ridge of the humer- 

 us. Just in front and partly covered by the pectoralis iS 

 the sterno-radialis. This is a triangular shaped muscle 

 with its origin on the sternum and its insertion after 

 ending in a very long tendon, is on the radio-ulna. The 

 external oblique arises on the surface of the ilium and 

 the aponeurosis of the back and spreading out in a thin 

 sheet, ends in an aponeurosis ventral to the rectus ab- 

 dominis. Its insertion is in the linea alba. What is the 

 direction of the fibers? The internal oblique lies under 

 the external oblique. It has its origin on the vertebrae 

 and the ilium and is inserted on the sternum and the linea 

 alba. 



The Muscles of the Back — The depressor mandibuli 

 is a triangular muscle posterior and partly covered by the 

 tympanic membrane. Its origin is on the suprascapula 

 and the fascia of the mid-dorsal line, and it is inserted 

 into the angle of the jaw. The contraction of this muscle 

 would do what? The cucullaris is a small muscle arising 

 from tfie middle line of the exoccipital and inserted into 

 the dorsal border of the suprascapula. What is its direc- 

 tion? The infra-spinatus isa large triangular muscle over- 

 lapped an^teriorly partly by the next muscle. Its origin 

 is on the suprascapula and its insertion is on the deltoid, 

 ridge of the humerus in common with the latissimus dor- 

 si. The latissimus dorsi is a triangular shaped muscle 

 posterior to the depressor mandibulae. It has its origin 

 in the dorsal fascia and is inserted on the deltoid ridge 

 with the infraspinatus. The extensor dorsi communis is 

 the large dprsal mass of muscles. It arises from the uro- 

 style and is inserted into the ilium, transverse processes 

 nf the vertebrae, and into the Dosterior end of the skull. 



