240 
(p) 
(q) 
(r) 
(s) 
Se 
ANATOMY OF THE RABBIT. 
and the internal jugular vein. It gives off the n. laryngeus 
superior to the larynx, the latter passing to the dorsal side 
of the common carotid artery. 
The ramus descendens of the twelfth cranial or hypo- 
glossal nerve crosses the root of the vagus from a lateral 
to a medial position. It passes backward on the ventral 
surface of the artery, and is chiefly distinguishable by its 
branches to the sternohyoideus and related muscles. 
The cervical portion of the sympathetic trunk lies on the 
dorsal surface of the common carotid, and is slightly medial 
in relation to the vagus. 
The ramus cardiacus of the vagus (n. depressor) lies on the 
dorsal surface of the common carotid on the medial side of 
the sympathetic trunk. It arises at the level of the posterior 
margin of the thyreoid cartilage. 
Occurring inthe rabbit as a separate nerve, the depressor is 
important experimentally. Stimulation of the proximal end in the 
living animal produces fall of blood pressure and retardation of the heart 
beat. The former is due toa reflex action on the bloodvessels (cf. p. 62), 
while the latter depends upon reflex stimulation of the vagus, since 
slowing of the heart does not take place if the vagi are also divided. 
The third and fourth cervical nerves may be traced 
from their origin in the intervertebral foramina to the 
musculature of the neck. They encircle the basioclavicularis 
muscle, under cover of the sternomastoideus and 
cleidomastoideus. 
Dissection of the muscles of mastication and related structures 
of the mandible. 
(a) 
(b) 
The masseter muscle. Origin: The entire surface of the 
zygomatic arch; tendinous from its anterior angle (spina 
masseterica). Insertion: Lateral surface of the angle of the 
mandible (1, a). 
The orbital structures should be freed from the zygomatic arch by 
passing a knife along its dorsal margin. The zygomatic arch may then 
be divided anteriorly and posteriorly and removed, together with the 
whole insertion of the masseter muscle. 
The temporalis is a slender, somewhat triangular muscle 
arising from the reduced temporal fossa (sulcus temporalis) 
of the skull and inserted by a long stout tendon on the 
