THE HEAD AND NECK. 57 



vical fascia. In front of them is the first layer of deep cervical fascia, which 

 delaminates on the side of the neck to enclose the sterno-cleido-mastoid muscle. 

 Behind these structures are the members making up a group ensheathed by the 

 third layer of deep cervical fascia. 



3. To what did you find the second layer of deep cervical fascia attached supe- 

 riorly and inferiorly ? 



Superiorly it was attached to the hyoid bone ; inferiorly to the posterior 

 part of the clavicle and manubrium. 



4. From what source do the depressors of the hyoid bone receive their nerve- 

 supply / 



From the ansa hypoglossal loop, descendens, and communicans noni. 



5 . Hoiv is the ansa liypoglossal loop formed ? 



It is formed by the union of two branches from the deep cervical plexus 

 with one branch from the hypoglossal nerve. 



6. What are these communicating nerves called ? 



The one from the hypoglossal nerve is called the descendens Jiypoglossi ; the 

 two from the cervical plexus are called the communicantes hypoglossi, and the 

 loop formed by their union is the hypoglossal loop. 



j. Have these communicating nerves any synonyms in anatomical literature ? 



Yes, in the older texts they are called the descendens noni and communi- 

 cantes noni. Under the classification of cranial nerves by Willis, there were nine 

 pairs. The hypoglossal belonged to this ninth pair, hence the expressions nervus 

 nonus, nervus descendens noni, and nervi communicantes noni. 



8. Can you think of a compound word that would be more specific, and at the 

 same time a more rational name than ansa hypoglossal ? 



Yes, the compound cervico-hypoglossal would express the anatomical parties 

 to the compound, and would harmonize with our rules for writing compound 

 words, by which such relations should always be expressed. 



9. Where did you find this loop ? 



On the sheath containing the common carotid artery, pneumogastric nerve, 

 and internal jugular vein. (Fig. 31.) 



The third layer of deep cervical fascia contains (Fig. 24) : 



1. The thyroid body its nerve-supply and vessels. 



2. The larynx and trachea, nerves and vessels. 



3. The common carotid artery, vagus and internal jugular vein. 



4. The external carotid artery and its branches in the neck. 



5. The cervical stage of the internal carotid artery. 



6. The hypoglossal nerve and its descending branch. 



7. The cervical sympathetic cord and ganglia. 



8. The arteries from the transverse aorta and their branches. 



9. The phrenic nerve and anterior scalenus muscle. 



10. The cervical plexus and its branches of origin. 



1 1 . The bracldal plexus and its sheath. 



12. The scaleni muscles anticus, medius, posticus. 



Dissection. Remove the group of muscles in the second layer of the cervical 

 fascia, and examine the structures in the following order : 



i. Thyroid Gland (Figs. 27 and 28). This derives its capsule from the con- 

 nective tissue in which it is developed. It has two lobes, connected by an isthmus. 

 Its arteries are a superior thyroid, which you will take to its origin, the external 

 carotid. This artery is attended by a vein. Note the anastomosis between the 

 5 



