DISSECTION OF THE NECK. 65 
ures in man), but occasionally the posterior ends are 
connected by a slender band or isthmus passing across 
the trachea. 
7. The Mylo-hyoid Muscle lies anterior to the hyoid 
bone, between the rami of the mandible. It is a 
thin muscular sheet which arises from the hyoid bone 
on each side, and is inserted along the inner side of 
the mandible; it meets its fellow in the mid-line and 
forms the floor of the mouth. 
8. The Digastric Muscle is the thick muscle cover- 
ing the angle and part of the body of the mandible. 
It arises from the occipital bone of the skull, and is 
inserted into the mandible, serving to depress the 
jaw. In the dog it is not truly a digastric muscle, 
though a tendinous line may be observed running 
across its belly somewhat posterior to the middle. 
9. The Vago-sympathetic Nerve. The combined 
trunk of the vagus and sympathetic nerves lies along 
the trachea on each side, in the same sheath with the 
carotid artery and internal jugular vein. Expose it 
on the left side at the middle of the neck, and dis- 
sect it anteriorly. To expose its origin from the 
skull, cut the digastric muscle at its mandibular inser- 
tion and reflect it backward. When the parts are a 
little more dissected it will be well to remove this 
muscle entirely, taking care not to cut the hypoglossal 
nerve. 
10. The Superior Laryngeal Nerve is a_ branch of 
the vagus; it arises far forward, somewhat beyond the 
anterior end of the larynx. At its origin from the 
vagus there is an enlargement of that nerve known as 
the eanglion or the tunk of the vacus. Trace the 
superior laryngeal to the larynx, which it enters and 
supplies with sensory fibres, giving also motor fibres to 
