22 ANATOMY OF VERTEBRATES 



second or normal part of the mylonyoideus. The fourth portion 

 at its anterior part arises from the angle of the jaw, then from 

 the base of the cranium, and afterward from a strong fascia 

 extended thence backward, between the post-cranial prolon- 

 gations of the nose and mouth ; the posterior and longest fasci- 

 culi come off more outwardly, and radiate to spread over and 

 blend with the gular fasciculi of the sternoglossi, passing out- 

 ward and downward, and then bending inward to envelope 

 that part of the hyoid apparatus. All the fibres of the fourth 

 portion terminate in a median raphe, which is less marked than 

 in the anterior portion. The fibres of the posterior division of 

 the mylohyoideus, especially those which are attached to the 

 under surface of the posteriorly prolonged nasal canal, form a 

 kind of muscular sheath for the basal part of the muscles of the 

 tongue. 



The cerato-hyoideus arises from the cerato-hyal : its fibres 

 converge and form a fasciculus which is inserted into the commis- 

 sural tendon of the genio-hyoid, and is connected with a strip 

 from the sternomaxillaris. After giving attachment to the fore- 

 going two muscles, and to the anterior constrictor of the pharynx, 

 its extremity is attached to the stylo-hyoideus muscle. 



In most mammals the hyoid arch, by the length of the ossified 

 part of the stylohyal and the extent of the ossification of the 

 ceratohyal is almost restricted to hinge-movements forward and 

 backward upon the proximal joints of the stylohyals as a fixed 

 point ; so that the basihyal with the tongue cannot be very far 

 protruded or retracted. In the Myrmecophaga jubata the usual 

 place of the stylohyal is occupied by a long and slender muscle, 

 the stylohyoideus, which arises from the petromastoid, and after a 

 course of five inches is inserted into the ceratohyal, here the first 

 bone of the hyoid arch. Supposing the stylohyoideus to contract 

 one-third of its length, it would protract the hyoid arch to the 

 same extent: in which act it combines with the geniohyoideus. 

 The retraction of the hyoid arch is provided for by the sterno- 

 thyroidic and their continuations, the thyrohyoidei. 



The geniohyoideus arises by a single tendon from the symphysis 

 of the jaw, runs back beneath the raphe of the anterior mylo- 

 hyoideus, slightly expands beneath the raphe of the middle 

 mylohyoideus, then again contracts and again expands, and at 

 about ten inches from its origin becomes diffused into fleshy 

 fibres, which gradually acquire a breadth of six lines, continue 

 back in close connection with the mylohyoideus to the commissural 

 tendon, and there expand, the lateral borders being attached 



