MUSCLES OF THE HEAD. 225 



accompanied by a lateral movement, during which the extremity of the jaw 

 is carried to the opposite side. 



5. Digastricus. 



Synonyms. Bourgelat has made two distinct muscles of this the digastricus and 

 stylo-maxillaris. Girard has described it as the stylo-maxillaris. (Percivall has 

 evidently followed Bourgelat's example, and divided the muscle into digastricus and 

 stylo-maxillaris. Leyh adopts the same course.) 



Form Structure Situation Direction. Composed of two fleshy bodies 

 more or less divided by intersections, and united at their extremities by a 

 median tendon, this muscle is situated in the intermaxillary space, and 

 extends from the occiput to near the symphysis of the chin, describing a 

 curve upwards. 



Attachments. It takes its origin from the styloid process of the occipital 

 bone, by its superior fleshy body. It terminates : 1, On the curved portion 

 of the posterior border of the lower jaw by a considerable fasciculus, which 

 is detached from the superior fleshy body j 1 2, On the internal face of the 

 same bone and the straight portion of its posterior border, by aponeurotic 

 digitations which succeed the muscular fibres of the inferior fleshy body. 



Relations. The superior belly of the muscle responds, superficially, to 

 the parotid gland and the tendon of insertion of the sterno-maxillaris ; 

 deeply, to the guttural pouch, the submaxillary gland, and the larynx and 

 pharynx. The median tendon passes through the ring of the hyoideus 

 magnus. The lower belly is in contact, outwards, with the ramus of the 

 inferior maxilla ; inwards, with the mylo-hyoideus muscle. 



Action. When this muscle contracts, it acts at the same time on the 

 hyoid bone, which it raises in becoming straight, and on the lower jaw, 

 which it pulls backwards and depresses at the same time. 



C. Hyoideal "Region. 



This region includes six muscles grouped around the os hyoides, which 

 they move. Five of these are pairs : the mylo-hyoideus, genio-hyoideus, stylo- 

 hyoideus, Jcerato hyoideus, and the occipito-styloideus. The single one is the 

 transversalis hyoidei. 



Preparation. Separate the head from the trunk, and remove the muscles of the 

 cheeks on one side, with the parotid gland. 2. The branch of the inferior maxilla being 

 thus exposed, it is sawn through in two places : at first behind the last molar, then in 

 front of the first. 3. After having separated the pterygoids and the stylo-maxillaris 

 from the upper fragment or condyle, and the coronoid process, it -is torn off by pulling 

 it backwards ; then the pterygoids and the digastricus are excised. 4. The inferior fragment 

 of the jaw bearing the molar teeth is turned down by isolating the mylo-hyoideus from the 

 mucous membrane. 5. Carefully remove the tongue by separating its extrinsic muscles 

 from the genio-hyoideus, the anterior appendix of the hyoid bone, the transverse muscle, 

 and the small hyoideus. 



The dissection having been performed in this manner, the large hyoideal branch may 

 be separated from the -small, by sawing through the head longitudinally, leaving the 

 symphysis menti intact, and turning down the corresponding half to the side already 

 dissected, as well as the great hyoid branch, the pharynx, larynx, and soft palate. 



1. Mylo-hyoideus. 



Form Situation Structure. A membranous muscle situated in the 

 intermaxillary space, flattened from side to side, elongated in the direction 



1 This is the fasciculus which Bourgelat has described as a distinct muscle, and 

 named the stylo-maxillaris. 



