1 30 HEAD AND NECK 



and the twig which the nerve gives to the mylo-hyoid muscle. 

 Define the band of fascia which surrounds the intermediate 

 tendon of the digastric and binds it to the greater cornu of the 

 hyoid bone. Note that the tendon is embraced by the cleft 

 lower end of the stylo-hyoid muscle. Clean the posterior belly 

 of the digastric and the stylo-hyoid muscle, which descends along 

 its anterior border. Note that the posterior belly of the digastric 

 and the stylo-hyoid disappear, postero-superiorly, under cover 

 of the angle of the mandible. Clean the anterior belly of the 

 digastric, and then examine the floor or medial boundary of the 

 triangle. Immediately behind the anterior belly of the digastric 

 it is formed by the posterior fibres of the mylo-hyoid muscle ; 

 and more posteriorly and on a deeper plane it is formed by the 

 hyoglossus muscle (Figs. 51, 68). 



Clean the portion of the mylo-hyoid which is exposed and, 

 at its posterior border, immediately above the greater cornu of 

 the hyoid bone, secure the hypoglossal nerve and the lingual 

 vein ; the vein lies below the nerve. Displace the lingual vein 

 and the hypoglossal nerve upwards ; cut through the fibres 

 of the hyoglossus, immediately above and parallel with the 

 greater cornu, and display the lingual artery, which in that 

 position lies immediately above the greater cornu, parallel with 

 the lingual vein but separated from it by the hyoglossus 

 muscle. 



All the structures which have been mentioned above will be 

 met with in the dissection of other regions, when a full account 

 of them will be given. 



Turn next to the carotid triangle, so called because it 

 contains parts of the common, internal, and external carotid 

 arteries. It is bounded posteriorly by the anterior border of 

 the sterno-mastoid ; above and anteriorly by the posterior 

 belly of the digastric ; and below and anteriorly by the anterior 

 belly of the omo-hyoid. 



Dissection. Trace the anterior facial vein from the digastric 

 triangle, across the superficial surface of the posterior belly of 

 the digastric, to the posterior border of the muscle, where it 

 unites with the posterior facial vein, which is descending from 

 under cover of the lower end of the parotid gland. The trunk 

 formed by the union of the anterior and posterior facial veins 

 is the common facial vein. Trace the common facial vein 

 downwards and backwards to its union with the internal jugular 

 vein, at or under cover of the anterior border of the sterno- 

 mastoid. Remove the deep fascia and the areolar tissue, and 

 the lymph glands which lie in the angle between the posterior 

 belly of the digastric and the anterior border of the sterno- 

 mastoid, below the lower end of the parotid gland ; secure the 

 lingual vein, which passes backwards from the tip of the 

 greater cornu of the hyoid bone to join the internal jugular 

 vein ; and the hypoglossal nerve, as it crosses, at a higher 

 level, superficial to the internal and external carotid arteries. 

 As the nerve turns forwards across the large arteries it is 

 itself crossed, superficially, by the sterno-mastoid branch of 



