THE HEAD AND NECK. 73 



39. In dissection, where do you find the occipito-intercostal air/i / 

 Between the semi-spinalis colli and complexus muscles. (Fig. 40.) 



40. Define the word scalene and name the scalene muscles. 



A triangular figure of unequal sides. The scalenus anticus, medius, and pos- 

 ticus. 



41. Where are these muscles inserted ? 



The anticus is inserted into the scalene tubercle of the first rib ; the medius 

 into the first rib ; the posticus into the second rib. The two are separated by 

 the subclavian groove for the subclavian artery. 



42. Give the origin of the scalene muscles according to j, 6, j. 



The scalenus anticus arises from the anterior tubercles of the transverse pro- 

 cesses of the lower three ( j) ; the medius from the posterior tubercles of the 

 lower six (6) ; the posticus from the posterior tubercles of the lower three ( j) 

 cervical vertebrae. 



The cervical plexus, to be of technical as well as practical value to the 

 student, should be studied in the following analytical manner, by question and 

 answer, before dissection : 



1 . Why is this plexus called cervical ? 



On account of its derivation from cervical nerves, its location and major 

 distribution in the neck. 



2. Where is this plexus situated ? 



It is situated opposite the four upper cervical vertebrae. It is covered by the 

 sterno-cleido-mastoid muscle. It lies on or is supported by two muscles whose 

 origin we have just seen the scalenus medius and levator anguli scapulae. 



3. Is this plexus deeply located? 



No, it is the most superficially located of all the somatic plexuses. It 

 emerges from under the posterior border of the sterno-cleido-mastoid muscle 

 midway between the origin and insertion of this muscle, regardless of length of 

 neck, into the occipital triangle. 



4. What seems to be the predominating' function or physiological importance of 

 the cervical plexus f 



To aid primarily and secondarily in respiration, as follows : It furnishes the 

 phrenic nerve. This nerve supplies the diaphragm with motor influence ; it 

 supplies the serous membranes investing the diaphragm with sensation ; through 

 its relation to the sympathetic it reaches all the abdominal organs that contihge 

 the diaphragm. It communicates with the nerve to the subclavius muscle, and, 

 according to Hilton's law, must send articular branches to the sterno-clavicular 

 articulation. (See Hilton's law.) It communicates with the intercostals, by which 

 the ribs are moved in re'spiration. It communicates with the ansa hypoglossal 

 loop, by which the depressor muscles of the hyoid bone are innervated. 



The cervical plexus furnishes communicating branches to the formation of 

 the hypoglossal loop. The hypoglossal nerve is the motor nerve to the tongue. 

 This nerve unites, by its descendens hypoglossi, with the two communicantes 

 hypoglossi, previously referred to, and in this way harmony is established 

 between the nerve that moves the tongue and the nerve that moves the muscles 

 that depress the hyoid bone, on which the tongue rests. 



The cervical plexus sends motor nerves to the following muscles : sterno- 

 cleido-mastoid, scaleni, the trapezius, the levator anguli scapulae ; through its 

 descending cutaneous branches it supplies the skin over the insertion of these 

 muscles. These muscles all are accessory to respiration in asthma and other 

 diseased conditions requiring more than ordinary tranquil respiration. 



The cervical plexus communicates with the pneumogastric, and this nerve 

 supplies the organs of voice and respiration with motion and sensation. In fine, 

 the function of the cervical plexus very clearly is to innervate the muscles of 

 6 



