MUSCLES OF THE HEAD. 



59 



and two oblique muscles rotate the eyeball about three axes, one 

 the axis of the eye, one vertical, and the third passing- from behind 

 forwards and inwards. The m. retractor pulls the eyeball into 

 the orbital cavity backwards and downwards, while the levator 

 raises it. 



There is less ag-reement about the movements of the eyelids, or 

 rather of the lower eyelid, for the upper has no independent 

 movements. Dugès (/. c.) says that the two muscles, which he con- 

 siders to be levatores pal^ntjrae hiferiores, and which, according" to 

 him, are connected with the m. retractor hiMi, draw up the lid as it 

 is being drawn backwards and downwards by the latter muscle. 

 The depression of the lid on the relaxation of the retractor and 

 projection of the eyeball is due simply to elasticity. Manz \ on the 

 contrary, has shown that the sinking of the eyeball by the con- 

 traction of the retractor must necessarily cause a rising' of the 

 nictitating membrane, as its tendons are attached to that muscle 

 and so must follow its movements. 



The depression of the lower lid occurs simultaneously with the 

 raising of the eyeball by means of the ra. levator tjulbi, through the 

 contraction of the m. depressor palpe1)rae mferloris, which proceeds 

 from that muscle ; this is easily understood, as they are but parts 

 of the same muscle. 



II. Muscles op the Face. 



11. J\l. hitermaxillaris s. dilatator narium (Fig. 54 im). 

 Dugès, intermaxillaire, n. i. — Zenker, intermaxillaris médius. 

 This small muscle lies in the space 

 between the vertical processes of the 

 two premaxillary bones, and consists of 

 obliquely-crossing fibres arising from 

 the one bone and inserted into the oppo- 

 site one. It brings together the pro- 

 cesses of the intermaxillary bones, so 

 that their upper extremities approach 

 each other. At the same time^ the 

 cartilaginous nasal coverings or wings 

 {an) diverge and the nares expand ; 

 hence we may regard this muscle as 

 corresponding to a dilatator narium. 



1 I. c, p. 4. 



Facial muscles of Rana esculenta. 

 an Cartilaginous nasal alae. 

 i' Vertical process of premaxillary 



bone. 

 Ini M. intermaxillaris. 

 Ill M. lateralis narium. 

 H Cartilaginous nose capsule. 



