GROUPS OF MUSCLES 325 



In the orbital cavity there are six muscles which are attached to and move the 

 eyeball and one muscle (the levator palpebroe superioris) which extends into and raises the 

 upper Ud (fig. 341). Of the muscles which move the eyeball five arise like the levator of the Ud, 

 from the back of the orbit. Four of these, the rectus muscles, are inserted respectively into the 

 superior, inferior, medial and lateral sides of the e3'eball and direct the pupil upward, 

 downward, medialward and lateralward. One, the superior oblique, sends a tendon through 

 a loop at the upper, front part of the nasal side of the orbit and thence to the upper surface 

 of the eyeball. Another muscle, the inferior oblique, arises from the nasal side of the front of 

 the lower part of the orbit and is attached to the lower part of the eyeball. The obhque 

 muscles prevent the rectus muscles from rotating the eyeball. These muscles are supphed 

 by the third, fourth and sixth cranial nerves. They are described in the section on the eye, p. 

 1067. In the middle ear are two small muscles (the tensor tympani and the stapedius) attached 

 respectively to the malleus and stapes and supphed by fifth and seventh cranial nerves. They 

 are described in the section on the ear, p. 1091. 



Mastication and swallowing. — The complex musculature used in biting, masticating and 

 swallowing food is used also in speech in conjunction with the muscles of the larynx and the hps. 

 The two movable bones of the skull concerned with these functions are the mandible and the hyoid 

 bone. The mandible articulates with the skull on each side; just in front of the external audi- 

 tory meatus. The hyoid bone is connected on each side by the stylo-hyoid ligament with the 

 styloid process of the temporal bone, which descends just behind the external auditory meatus. 

 A powerful group of muscles, the cranio -mandibular muscles (figs. 344, 345, 346, 347 cj, or 

 muscles of mastication, arise from the temporal fossa {temporal muscle), the zygomatic arch 

 (masseter muscle) and the pterygoid process {external and internal pterygoid muscles) and are 

 inserted into the coronoid process of the mandible {temporal muscle), the outer side of the 

 ramus {viasseter muscle), the inner side of the ramus {internal pterygoid), and into the condyle 

 of the jaw {external pterygoid). These muscles raise the jaw, move it forward and from side 

 to side, and are used in biting and chewing the food. They are innervated by the fifth cranial 

 (masticator) nerve. 



Another less powerful group of muscles, the suprahyoid group (fig. 348), is divisible into 

 two subdivisions, hyo -mandibular which extends in front between the hyoid bone and the 

 ramus of the jaw (anterior belly of the digastric, genio-hyoid, mylo-hyoid) and a hyo-temporal 

 group which extends between the hyoid bone and the temporal bone back of the external audi- 

 tory meatus {stylo-hyoid, posterior belly of the digastric). Two of the hyo-mandibular muscles 

 (the anterior belly of the digastric and the mylo-hyoid) are innervated by the trigeminal; the 

 genio-hyoid by the hypoglossal nerve. The two hyo-temporal muscles (posterior belly 

 of the digastric and stylo-hyoid) are innervated by the facial nerve. Morphologically 

 therefore, as indicated by this innervation, the muscles of this group are diverse. Physiolog- 

 ically they are closely united. The group, acting as a whole, elevates the hyoid bone and with 

 this the larynx and the tongue. If, however, the hyoid bone be fixed by contraction of the 

 neck muscles (infrahyoid muscles) attached to its lower border, the suprahyoid muscles act 

 as antagonists of the cranio-mandibular muscles and depress the jaw. The hyo-mandibular 

 muscles form, together with the tongue, the muscular floor of the mouth. When acting with 

 the hyo-temporal muscles they help the tongue to pass food into the pharynx. When acting 

 alone the hyo-mandibular muscles draw forward the hyoid bone and with it the base of the tongue 

 and the larynx and thus open the passage from the pharynx into the oesophagus. The two 

 hyo-temporal muscles, acting in conjunction with the middle and inferior constrictors of the 

 pharynx, draw the hyoid bone and larynx backward, as well as upward, and thus constrict the 

 pharynx while giving free passage for air from the naso-pharynx into the larynx. The chief 

 functions of the suprahyoid group are, therefore, to play a part in deglutition and respiration. 



Closely associated with the muscles of the suprahyoid group in the performance of 

 these important functions are the muscles of the tongue, the pharynx and the soft palate. 

 The bulk of the tongue (fig. 349) is made up of muscles which have their origin on each side from 

 the inner surface of the front part of the mandible {genio-glossus) , the hyoid bone {hyo-glossus 

 and chondro-glossus) and the styloid process of the temporal bone {stylo-glossus) . Muscles 

 also connect the tongue with the palate {glosso-palatinus) and with the pharynx {glosso-pharyn- 

 gens). These muscles, together with intrinsic longitudinal, transverse and perpendicular 

 fibre-bundles, enable the tongue to perform the complex activities associated with mastication 

 and swallowing and with speech. Diu-ing mastication the tongue passes the food from side to 

 side between the teeth. When the food has been masticated the tongue forms a bolus of it 

 and then this is passed into the pharynx by a sudden elevation of the dorsum of the tongue 

 produced in part by the muscles of the tongue, in part by the suprahyoid group of muscles. 

 The muscles of the tongue are described on p. 345. 



The pharynx is the dilated upper part of the ahmentary canal into which open the Eus- 

 tachian tubes, the nasal passages, the mouth and the larynx. The walls of the side and back 

 of the pharynx are composed mainly of muscular tissue. The chief muscles are three " con- 

 strictor " muscles on each side, a superior, a middle and an inferior, and an elevator and dilator, 

 the stylo-pharyngeus (fig. 894). The three constrictor muscles are attached to the median 

 raphe* which extends in front of the spinal column from the base of the occipital bone to the 

 sixth cervical vertebra. The superior constrictor muscle is attached to the pterygoid process, 

 the pterygo-mandibular ligament, the mandible and the side of the root of the tongue (fig. 343) ; 

 the middle constrictor to the hyoid bone ; and the inferior constrictor to the larynx. These muscles 

 constrict the pharyngeal orifice and thus force food into the oesophagus. The stylo-pharyngeal 

 muscle, which extends from the styloid pr6cess into the lateral wall of the pharjnix, serves to 



* The attachments to the raphe are usually spoken of as the insertions, those to the bones 

 in front as the origins of these muscles. The raphe is, however, a more lixed structure than 

 most of the structiu-es to which the constrictors are attached in front. 



