142 LABORATORY MANUAL FOR VERTEBRATE ANATOMY 



the shoulder. Action, pulls clavicle craniad or turns head, acting singly, or 

 lowers head on neck. 



d) Clavolrapezius and clavobrachial. The long muscle on the side of the neck 

 and passing over the ventral surface of the shoulder to the forearm is sometimes 

 considered as one muscle, the cephalobrachial, or as two. In the latter case the 

 upper part is known as the clavotrapezius and extends from the skull to the clavicle. 

 It will be considered later. The lower part from the clavicle to the fore- 

 arm is the clavobrachialis. Origin, clavicle and fibers of the clavotrapezius; 

 insertion, ulna; action, flexor of the forearm. The clavicle will be found on 

 the inner surface of the muscle in the shoulder region, imbedded in the 

 muscle. 



e) Masseter. The great thick muscle covering the angle of the jaws, situated 

 in front of the submaxillary and parotid glands. It is covered by a very tough 

 shining fascia. Origin, zygomatic arch; insertion, posterior half of the lateral 

 surface of the mandible; action, elevator of the lower jaw. 



/) Temporal. Remove the skin from the side of the head up to the median 

 dorsal line. A great mass of muscle covered by a strong shining fascia will be 

 seen occupying the temporal fossa of the skull, dorsal to the ear. Origin, from the 

 side of the skull from the superior nuchal line to the zygomatic process of the 

 frontal bone, and from part of the zygomatic arch; insertion, coronoid process 

 of the mandible; action, elevator of the jaw, in common with the masseter. 



g) Digastric. The muscle lying along the medial surface of each half of the 

 mandible. It extends posteriorly internal to the submaxillary gland. Origin, 

 jugular and mastoid processes of the skull; insertion, mandible; action, depres- 

 sor of the lower jaw. 



h) Mylohyoid. The thin transverse sheet passing across between the two 

 digastrics from one half of the mandible to the other. Origin, mandible, the 

 origin concealed by the digastrics; insertion, median raphe; action, raises floor 

 of the mouth and brings hyoid forward. 



i) Geniohyoid. Cut through the median raphe of the mylohyoid. This 

 exposes a pair of long slender muscles, the geniohyoids, lying in the median line. 

 Origin, mandible near the symphysis; insertion, body of the hyoid; action, 

 draws the hyoid forward. 



j) Sternothyroid. Separate the two sternohyoids in the median line. This 

 exposes the trachea or windpipe, a tube stiffened by rings of cartilage. At the 

 top of the trachea is a chamber with cartilaginous walls, the larynx. The chief 

 cartilage of the larynx is the large shield-shaped thyroid cartilage, forming the 

 ventral walls of the larynx. Just in front of the thyroid cartilage the body of the 

 hyoid is felt as a bony bar. The sternothyroid muscles are located, one on each 

 side of the trachea, dorsal to the sternohyoids. Origin, sternum in common 

 with the sternohyoid; insertion, thyroid cartilage of the larynx; action pulls 

 the larynx posteriorly. 



