MUSCLES OF THE HEAD. 69 



larynx. In front of the larynx the muscle runs 

 forward m 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 four 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 oesophagus 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 three posterior portions 

 are very narrow slips. 



2. Muscles of the side of the head. 



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

 noticing how much more closely it is attached to the underlying 

 parts than ivas the case in the body. 



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



i. The depressor mandibulae has been already seen 

 and dissected. (See p. 67.) 



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 sup- 

 porting 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. 



iv. The masseter is a small muscle placed behind the 

 temporalis: it arises from the quadratojugal and 



