HEAD AND NECK OF THE HORSE 129 



of the atlas, and are inserted into the basilar part of the occipital 

 bone. 



M. RECTUS CAPITIS LATERALIS. — The lateral straight muscle is also 

 small and fleshy, and runs between the wing of the atlas and the 

 jugular process of the occipital bone. 



N. CERVICALIS PRIMUS. — The ventral branch of the first cervical 

 nerve pierces the alar foramen of the atlas to gain the fossa atlantis, and 

 will now be observed to emerge from the interval between the lateral 

 straight and the caudal oblique muscles. Its division into two branches 

 has already been remarked. 



Dissection. — Detach the origin of the stylo-glossal muscle from the 

 hyoid bone. Remove the jugulo-hyoid muscle, and cut through the 

 cartilaginous connection between the hyoid and temporal bones. Then 

 clean the occipital artery and the last few cerebral nerves at their exit 

 from the cranium. 



N. GLOSSOPHARYNGEUS : N. VAGUS : N. ACCESSORIUS : N. HYPO- 

 GLOSSUS. — The first three of these nerves leave the cranium together 

 by the jugular foramen. For a certain distance the tenth and eleventh 

 nerves are enclosed in a common fibrous sheath, after which they 

 diverge at an acute angle. 



On the glosso-pharyngeal nerve, immediately at its exit, there is an 

 elongated, greyish ^^e^i^osaP gfa-n^/ion (ganglion petrosum). The small 

 tympanic nerve (n. tympanicus) leaves the ganglion, and at once turns 

 upwards between the tympanic and petrous parts of the temporal bone 

 to gain the interior of the tympanum. Fine filaments also connect the 

 ganglion with the jugular ganglion of the vagus and the cranial cervical 

 ganglion of the sympathetic. Two other branches of the glosso- 

 pharyngeal nerve should be sought. One of these crosses the surface of 

 the diverticulum of the Eustachian tube, gives twigs to the pharyngeal 

 plexus, and assists in the formation of the carotid plexus. The other 

 branch is small, and terminates in the stylo-pharyngeal muscle. 



The hypoglossal nerve leaves the cranium by the hypoglossal fora- 

 men, runs for a short distance between the diverticulum of the auditory 

 tube and the capsule of the atlanto-occipital joint, and then traverses 

 the angle of divergence of the vagus and accessory nerves. 



Ganglion cervicale craniale. — The fusiform, greyish cranial 

 cervical ganglion of the sympathetic nervous system, lies on the 

 dorsal posterior part of the diverticulum of the Eustachian tube close 



1 Petrosus [L.], rocky, stony (the ganglion is named from the bone with which 

 it is associated). 

 9 



