MUSCLES OF THE HEAD 59 



iv. The hyoglossus arises on either side from the 

 posterior bony horn of the hyoid : the two muscles 

 converge and meet each other in front of the 

 larynx. In front of the larynx the muscle runs 

 forward in the middle line as a stout band nearly 

 to the chin : it then enters the tongue, and runs 

 along it backwards to the tip. 



V. The petrohyoid muscles are a set of five muscular 

 bands which arise close together from the outer 

 surface of the auditory capsule, and diverging in 

 a fan-like manner, pass round the floor of the 

 pharynx and cesophagus to be inserted in front 

 into the median ventral line of the pharynx, and 

 behind into the side of the hyoid. The first or 

 most anterior band is a wide thin sheet of mus- 

 cular tissue, while the four posterior portions 

 are very narrow slips. 



2. Muscles of the side of the head. 



Remove the skin carefvMy from the side of the head and jaws, 

 noticing how much more closely it is attached to the underlying 

 parts than was the case in the body. 



a. Depressors of the lower jaw ; opening the mouth. 



i. The depressor mandibulse has been already seen 

 and dissected. (See p. 57.) 



b. Elevators of the lower jaw ; shutting the mouth. 



These lie in the space between the auditory capsule 



and the eye. 



ii. The temporalis arises from the upper surface of 

 the auditory capsule, and passes outwards and 

 downwards between the pterygoid and maxillary 

 bones, and in front of the cartilaginous ring 

 supporting the tympanic membrane, from which 

 some of its fibres arise : it is inserted into the 

 coronoid process of the lower jaw. 

 iii. The pterygoideus is a slender muscle placed just in 

 front of the temporalis and partly covered by it : 

 it arises from the side wall of the skull, and is 

 inserted into the mandible further back than the 

 temporalis, and very close to the joint. 



