THE HEAD AND NECK. 55 



THE NERVE-SUPPLY TO THE DEPRESSOR MUSCLES OF THE HYOID BONE. The 

 group you have just dissected comes from a loop called the ansa hypoglossal. 

 The expression cervico-Jiypoglossal would be a better term, as it would seem, as 

 it expresses the derivation of the two elements composing the loop. (Fig. 29.) 



The loop is formed by the descendens hypoglossi, anastomosing with two 

 communicating branches from the deep part of the cervical plexus. This loop 

 is formed on the front part of the carotid sheath. From it branches are given off 

 to the depressors of the hyoid bone. 



1 . Give the boundaries of tJiat part of the neck most frequently operated on by 

 the surgeon. 



Anteriorly, the mid- or mento-sternal line. Posteriorly, the anterior border 

 of the trapezius muscle. Superiorly, the mandible and masto-mandibular line. 

 Inferiorly, the clavicle and interclaviculaf ligament. 



2. Name the cervical triangles and indicate tlieir importance. 



The submaxillary or supra-hyoid triangle is bounded above by the mandible 

 and masto-mandibular line ; below, by the digastric and stylo-hyoid muscles ; 

 in front, by the mento-sternal line. It contains : (i) The facial vessels and their 

 sympathetic nerves ; (2) the submaxillary gland, its blood-vessels, nerves, and 

 capsule ; (3) the submental and mylo-hyoid vessels and nerves ; (4) the stylo- 

 mandibular ligament ; (5) the parotid gland and its contents ; (6) the vagus 

 nerve, internal jugular vein, internal and external carotid arteries. 



The superior carotid triangle is bounded above by the digastric ; below, by 

 the omo-hyoid ; behind, by the sterno-mastoid muscle. It contains: (i) The 

 common carotid artery ; (2) the external carotid artery ; (3) the internal jugular 

 vein ; (4) the vagus ; (5) spinal accessory, and (6) sympathetic nerves. 



3. The inferior carotid or tracheal triangle is bounded above by the omo- 

 hyoid, behind by the sterno-mastoid, in front by the mento-sternal line. It 

 contains : (i) The thyroid gland and its blood-supply ; (2) the trachea; (3) the 

 carotid sheath and contents ; (4) the inferior laryngeal nerve and inferior thyroid 

 vessels. 



The three foregoing triangles lie anterior to the sterno-mastoid muscle. The 

 two following ones lie posterior to the sterno-mastoid muscle. 



4. The occipital triangle is bounded in front by the sterno-mastoid, behind by 

 the trapezius, below by the omo-hyoid muscle. It contains: (i) The spinal 

 accessory nerve; (2) the descending branches of the cervical plexus; (3) the 

 transversalis colli vessels ; (4) a chain of lymphatic glands. 



5. The subclavian triangle is bounded in front by the sterno-mastoid, above 

 by the omo-hyoid, below by the clavicle. It contains: (i) The subclavian 

 artery and vein ; (2) the brachial plexus ; (3) the external jugular vein ; (4) the 

 nerve to the subclavian muscle. 



The student will please note that any arbitrary classification of contents is 

 impossible. Structures are found to form partial contents of several triangles. 

 The surgical triangles are to the modern surgeon about what totem poles would 

 be to the city council. 



6. Name the structures in the superficial fascia of the neck. 



(i) The platysma myoides muscle ; (2) the anterior, external, and posterior 

 jugular veins ; (3) the inframandibular branch of the seventh nerve, and (4) the 

 superficialis colli branch of the cervical plexus. 



7. Name the layers of deep cervical fascia and give the contents of each. 

 The first layer surrounds the sterno-mastoid muscle. 



