240 



COMPARATIVE ANATOMY 



The trigeminal, facial, glossopharyngeal, and vagus nerves are 

 usually described as branchial or branch iomeric nerves, i.e. they are 

 primarily related to gill-clefts. A typical branchial nerve has a 

 ganglion near its origin from the brain and divides into (1) a 

 dorsal (somatic sensory) branch to the skin, (2) a palatine (visceral 

 sensory) branch to the oral mucous membrane, and (3) a branch 

 associated with the epibranchial ganglion (p. 236) which bifurcates 



IV 



G.L.IX.X.XI 



FIG. 181. PERIPHERAL NERVES OF A HUMAN EMBRYO OF 4 WEEKS (6'99 MM. 

 IN LENGTH), RECONSTRUCTED FROM SECTIONS. (After G. S. Streeter. ) 



1, 2, 3, mamlilmlar, hyoid, and 1st branchial ridges; ///, oculomotor; IV, 

 trochlear ; l n , T 7 ' 2 , V s , the three main branches of the trigeminal ; Fniot, 

 motor portion of trigeminal ; (JV, ganglion of trigeminal ; VII, facial ; VIII, 

 auditory ganglion ; IX, glossopharyngeal with the petrosal ganglion 

 (Gy.petr) ; A', vagus with the ganglion nodosum ((Jg.nod) and the anterior 

 (superior) laryngeal nerve (Lar.siit))) ; G. L, ganglion ic ridge of the IXth, Xth, 

 and Xlth nerves ; XII, hypoglossal. The abducent (VI) is not visible. 



over the corresponding branchial cleft into a prebranchial (visceral 

 sensory) and a, postbranchial (visceral motor) nerve. 



Trigeminal Nerve. This is one of the largest of the cerebral 

 nerves. It arises from the ventro-lateral region of the anterior 

 part of the medulla oblongata (pons Varolii of Mammals) by a large 

 sensory and a smaller (ventral) motor root, has a large primarily 



