SUPRAHYOID MUSCULATURE 



343 



divided into two fasciculi, a condition normal in many mammals. A special fasciculus may 

 arise from the temporo-mandibular articulation or from the zygomatic (malar) bone. Its 

 deepest fibres may be fused with the temporal muscle. The two fasciculi of the external 

 pterygoid may be distinct, as in the horse. It has been seen fused with the temporal and with 

 the digastric muscle. The internal pterygoid may send a fasciculus to the masseter. It may 

 give origin to the stylo-glossus. Inconstant fasciculi (accessory pterygoids) extending from the 

 body of the sphenoid to the pterygoid process represent perhaps remnants of the muscles which 

 act on the movable pterygoids possessed by many inferior vertebrates. 



3. SUPRAHYOID MUSCULATURE 



(Fig. 348) 



From the hyoid bone there extend to the base of the skull on each side four 

 muscles which form a fairly well-defined group. They are situated external to 



Fig. 348. — Anterior and Lateral Cervical Muscles. 



Stylo-glossus 

 Hyo-glossus 



Mylo-hyoid 



Anterior belly of 

 digastric 



Raphe of mylo- 

 hyoid 



Thyreo 



Inferior constrictor 

 Anterior belly of omo- 

 hyoid 



Sterno-hyoid 

 Sterno- 



Stylo-hyoid 



.Posterior belly of 

 digastric 



Splenius capitis 

 Sterno-mastoid 

 Levator scapulae 



Scalenus medius 

 Tranezius 



Scalenus posterior 



Posterior belly of 

 omo-hyoid 



^f..,.^v-^v^^^^^^^^T^T''fli 



the musculature of the tongue and pharynx. They elevate the hyoid bone and 

 larynx and depress the mandible. The most superficial of the group is the 

 slender, fusiform stylo-hyoid, which arises from the styloid process of the temporal 

 bone and is inserted into the body of the hyoid. Immediately behind this is the 

 flattened posterior belly of the digastric, which extends from its origin in the 

 mastoid notch to a tendon that runs between two divisions of the tendon of the 

 stylo-hyoid and is attached to the hyoid bone by an aponeurotic process. From 

 the digastric tendon the flat, triangular anterior belly is continued to the back 

 of the ventral portion of the inferior margin of the mandible. Internal to this 

 anterior belly the thin, quadrangular mylo-hyoid arises from the inner surface of 

 the bodv of the mandible and is inserted into a median raphe extending from the 

 mandible to the hvoid. Still more internally the triangular genio-hyoid extends 

 from the hyoid to' the mental spine of the mandible. The last two muscles form 

 the muscular floor of the mouth. The motor innervation of the posterior belly 



