THE HEAD AND NECK. 



35 



The dilator naris posterior arises from the superior maxillary bone, from 

 the nasal notch, and is inserted into the skin of the margin of the nostril, well 

 back. These two dilator muscles antagonize the compressor nariinu. Remove 

 the skin from the forehead, and expose the anterior belly of the occipito-frontalis. 

 We are at present concerned only with the insertion of this muscle. Its anterior 

 fibres are continued on to the nose as the pyramidalis nasi ; its middle and outer 

 blend with the outer portion of the orbicularis palpebrarum. 



The muscles of facial expression, those which you have just dissected, 

 are called dermal muscles, on account of their insertion, being of such a nature 

 as to move the skin, in a most unique manner. These muscles are innervated by 

 the facial or seventh cranial nerve. (Fig. 16.) They are in the superficial fascia 

 in fact, they occupy the fascia to such a degree that some good authors speak of 

 the absence of facial superficial fascia. By their action they confer on the human 

 face facial expression in its broadest sense. 



Is not the facial nerve more than an ordinary motor nerve ? In other words, 



FIG. 15. SCHEME OF FACIAL NERVE COMMUNICATING WITH THE FIFTH CRANIAL NERVE. 



is not this nerve eligible to promotion from the rank and file of ordinary motor 

 nerves to a place among those nerves which are designated special sense nerves ? 

 For the sake of arousing your interest in the difficult dissection of this nerve, 

 you will pardon a digression for the purpose of answering the above questions. 



A slight blow on the ligamentum patellae produces reflex extension of the 

 leg on the thigh. The steps were (i) conduction of pain, by a sensory nerve, to 

 a cortical motor area, and (2) an almost simultaneous contraction of the extensor 

 quadriceps femoris ; (3) a record of the blow was recorded as memory. A com- 

 plete moto-sensory cycle was the result. The nerve that conveyed the sensation 

 of pain to the brain is called a nerve of common sensation ; the one that produced 

 motion in the extensor muscles is called a motor nerve. 



The retina responds to light, the auditory nerve to sound, the olfactory, to 

 odors. Each nerve records its experience in the brain. Now, see what the 

 facial nerve does ! It produces motion of a reflex character, as do ordinary 

 motor nerves. It is the only nerve by which vision, audition, olfaction, and 



