54 A MANUAL OF ZOOLOGY 



What is the direction of the fibers? The intertransver- 

 sales are small muscles between the transverse processes 

 of the vertebrae. They lie beneath the preceding muscle. 

 The gluteus arises from the outer side of the posterior 

 two thirds of the ilium and is inserted into the trochanter 

 of the femur. What is the direction of the muscle? 



The Muscles of the Ventral gurface pf the Head — 

 The mylohyoid covers the entire ventral surface of the 

 head just under the skin. The fibers meet on the mid- 

 ventral line, and have their origin on the inner superior 

 border of the mandible. In the anterior angle of the man- 

 dible note the submentalis, a short muscle dorsal to the 

 fibers of the mylohyoid. The fibers have their insertion oh 

 the inner superior border of the mandible. On either side 

 of the mid-ventral line is a broad, thin muscle, the genio- 

 hyoid, just dorsal to the mylohyoid. Its origin is at the an- 

 terior end and on -the inner superior border of the man- 

 dible. The posterior end is divided and Inserted on tEe 

 hyoid apparatus. The sternohyoid is really a continuation 

 of the rectus abdominis. The inner fibers have their orig- 

 in on the sternum and the outer ones are continuous with 

 the rectus abdominis. It is inserted between the ends of 

 the geniohyoid. Dorsal to the mylohyoid and the genioh- 

 yoid is the hyoglossus. Its origin is on the hyoid appara- 

 tus. This muscle can be, traced to a point anterior to the 

 larynx, into the tongue, and backward to the tip of the 

 tongue. The petrohyoids are a group of four muscles with 

 their origin in the auditory capsule. Extending ventrally 

 they pass around the oesophagus, spread out in a fan 

 shape upon reaching the floor of the mouth, and are In- 

 serted upon the hyoid apparatus. Between the tympanic 

 membrane and the eye find the temporalis, whose origin 

 ,is on the dorsal surface of the head and the auditory cap^ 

 sule, and whose insertion is on the outer surface of the 

 posterior end of the mandible. What is the function of 

 this muscle? Partly under the temporalis is found the 

 pterygoideus, a slender .muscle with Its origin on the side 

 of the skull and its insertion on the mandible back of that 

 of the temporalis very near the joint. The masseter is a 

 small muscle behind the temporalis and inserted just in 

 front of the joint on the outer surface of the mandible. 



