Occipito-frontalis J 



gland. It is supplied by the mylo-hyoid branch of the inferior dental 

 nerve. 



The genio-hyoid lies upon the deep side of the mylo-hyoid, pass- 

 ing from the symphysis to the front of the body of the hyoid bone. 

 Along its posterior border is the genio-hyo-glossus, in whose action 

 and nerve supply (hypoglossal) it participates. 



The occipito-irontalis may be taken as arising from the outer 

 part of the superior curved lines and from the neighbouring part of the 

 mastoid processes, and as inserted into the skin of the frontal region 

 not into frontal bone itself, or it could have no action. The two 

 fleshy parts of the muscle are separated by a very thin intervening 

 aponeurosis, which covers the vertex, and gives origin at the side of 

 the head to the attollens and attrahens aurem. The tendon spreads 

 out into loose connective tissue upon the temporal fascia (p. 8). The 

 median fibres of the anterior part of the muscle blend with the pyrami- 

 dalis nasi, and the others with the corrugator and with the orbicularis. 

 The aponeurosis is very intimately blended with the skin the student 

 may remember that in his first dissection he could not avoid removing 

 some of the aponeurosis with the skin, though he had no difficulty 

 whatever in separating the aponeurosis from the skull. 



When pus or blood is effused upon the top of the head its situa- 

 tion is certainly beneath the aponeurosis not between it and the 

 skin. A layer of loose connective tissue, the pericranium, intervenes 

 between the aponeurosis and the skull-vault, and it is over this that the 

 muscle and the scalp work. The scalp is readily torn down by accident, 

 or as one sees effected in the mortuary ; but when, during life, the 

 calvaria is thus laid bare the occurrence of necrosis is by no means 

 necessitated, as the nutrition of the outer table can be freely carried on 

 by the vessels of the diploe. When cleaned and readjusted, the scalp 

 promptly resumes its attachments and its office. 



The action of the muscle is to raise the skin of the forehead in 

 horizontal wrinkles, as in expressing surprise ; the posterior fleshy part 

 may be able to draw back the scalp, and so help the anterior part. 

 Being a muscle of expression, it is supplied by the facial nerve, through 

 its posterior auricular and temporal branches. When one facial nerve 

 is paralysed the skin on that side of the forehead is destitute of wrinkles, 

 and remains strangely expressionless when compared with the other 

 half (p. 67). 



The masseter arises from the zygomatic arch and is inserted into 

 the angle and ramus of the jaw. It is supplied by the third division of 

 the fifth nerve ; its action is to raise the lower jaw. 



Relatio7is. Between it and the integument are peripheral fibres 

 of the orbicularis palpebrarum, the zygomatici, risorius, and pla- 

 tysma ; the transverse facial artery ; Stenson's duct, and an offshoot 

 of the parotid gland (socia) ; and branches of both the divisions of 

 the facial nerve, and the facial artery and vein. On its deep surface 



