002 



DISSECTION OF THE NECK. 



Stylo-hyoid 

 muscle : 



insertion ; 



surrounds 

 digastric 

 tendon ; 



Twelfth 

 nerve in the 

 anterior 

 triangle : 



branches : 



one to hyoid 

 muscles 



is joined 

 with 



cervical 



nerves. 



External 

 carotid 

 artery ; 



extent ; 



course and 



direction. 



Parts super- 

 ficial to it, 



that bone and opens the mouth. If the jaw be fixed, the two 

 bellies acting together will elevate the hyoid bone. 



The STYLO-HYOID MUSCLE (fig. 224, H, p. 624) is thin and slender, 

 and lies immediately above the posterior belly of the digastric. It 

 arises from the posterior surface of the styloid process near the base, 

 and is inserted into the outer part of the body of the hyoid bone. 



The muscle has the same relations as the posterior belly of the 

 digastric ; and its fleshy fibres are usually perforated by the tendon 

 of that muscle. 



Action. This muscle elevates the hyoid bone in swallowing, and 

 with the posterior belly of the digastric, prevents the bone being 

 carried forwards by the elevators. 



The HYPOGLOSSAL NERVE (twelfth cranial) (fig. 224, 6 ), appears 

 in the anterior triangle at the lower edge of the digastric muscle, 

 where it hooks round the occipital artery ; it is then directed 

 forwards to the tongue beneath the tendon of that muscle, and 

 disappears in front under the mylo-hyoid. In this course the 

 nerve passes over the two carotids ; and near the great cornu of the 

 hyoid bone it also crosses the lingual artery. From this part arise 

 the descending branch, and a small muscular offset to the thyro- 

 hyoid. 



The descendens cervicis branch leaves the trunk of the hypoglossal 

 as it turns round the occipital artery, and descends on the front of, 

 or more frequently within, the carotid sheath to below the middle 

 of the neck, where it is joined by the communicating branches of 

 the cervical nerves so as to form a single or double loop (ansa cervicis) 

 with the concavity turned upwards. The descending branch gives 

 an offset to the anterior belly of the omo-hyoid ; and from the loop 

 branches proceed to the posterior belly of the omo-hyoid, to the 

 sterno-hyoid and sterno-thyroid muscles : sometimes another offset 

 is continued to the thorax, where it joins the phrenic and cardiac 

 nerves.* 



The EXTERNAL CAROTID ARTERY (fig. 217, d) springs from the 

 bifurcation of the common carotid opposite the thyro-hyoid mem- 

 brane, and furnishes branches to the neck, and face, and the outer 

 part of the head. 



From the place of origin it ascends in front of the mastoid 

 process, and ends just below the neck of the lower jaw in the 

 internal maxillary and superficial temporal branches. The artery 

 lies at first in front of the internal carotid, but it afterwards inclines 

 somewhat backwards and becomes superficial to that vessel. Its 

 position would be marked with sufficient accuracy by a line from 

 the front of the meatus of the ear to the cricoid cartilage. 



At first the external carotid is overlain by the sterno-mastoid, 

 and by the common coverings of the anterior triangular space, viz., 

 the skin, and the superficial and deep fasciae with the platysma. 

 But above the level of a line from the mastoid process to the hyoid 



* Both the descending and the thyro-hyoid branches of the hypoglossal are 

 composed of fibres which pass from the first and second cervical nerves into 

 the trunk of the nerve near the base of the skull. 



